Carbonate-Hosted Zn-Pb Mineralization in the Lower

Carbonate-hosted Zn-Pb mineralization in the Lower Cambrian Sekwi Formation, Mackenzie Mountains, NWT: Stratigraphic, structural, and lithologic controls, and constraints on ore fluid characteristics

Beth J. Fischer

Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (M.Sc.) in Geology

School of Graduate Studies Laurentian University Sudbury, Ontario

Published Heritage Direction du 1+1 Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-87713-5

Our file Notre reference ISBN: 978-0-494-87713-5

NOTICE: AVIS: The author has granted a non L'auteur a accorde une licence non exclusive exclusive license allowing Library and permettant a la Bibliotheque et Archives Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par I'lnternet, preter, telecommunication or on the Internet, distribuer et vendre des theses partout dans le loan, distrbute and sell theses monde, a des fins commerciales ou autres, sur worldwide, for commercial or non support microforme, papier, electronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats.

The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in this et des droits moraux qui protege cette these. Ni thesis. Neither the thesis nor la these ni des extraits substantiels de celle-ci substantial extracts from it may be ne doivent etre imprimes ou autrement printed or otherwise reproduced reproduits sans son autorisation. without the author's permission.

In compliance with the Canadian Conformement a la loi canadienne sur la Privacy Act some supporting forms protection de la vie privee, quelques may have been removed from this formulaires secondaires ont ete enleves de thesis. cette these.

While these forms may be included Bien que ces formulaires aient inclus dans in the document page count, their la pagination, il n'y aura aucun contenu removal does not represent any loss manquant. of content from the thesis. Canada

Abstract

The Sekwi Formation, a Lower Cambrian carbonate unit, is a preferred base metal sulfide host in the Mackenzie Mountains zinc district (Northwest Territories, Canada), but controls on the mineralization are poorly understood. Stratigraphic work in three mineralized areas together with petrographic, fluid inclusion and isotopic studies, demonstrate a first-order structural control (proximity to Cretaceous-Tertiary faults), a second-order lithological control (dolograinstone/rudstone and dark, mottled dolostone), and a local stratigraphic control on the distribution of mineralization. Structural relationships indicate a Late Cretaceous or Tertiary age for much of the mineralization, but some evidence implies that that there was also an earlier (Late Devonian or Early Carboniferous) mineralizing event. At least two fluids mixed to form the showings. Fluid 1 originated as Cretaceous seawater, or formation water containing dissolved Neoproterozoic evaporite rock, and had thermally equilibrated with the Sekwi Formation at 4-6 km depth by the time of mineralization. Fluid 2 originated in felsic crystalline basement, and carried the most radiogenic Sr yet recorded from the northern Canadian Cordillera. Fluid 2 scavenged metals from the sedimentary pile as it moved upward through a network of faults under pressure caused by Cretaceous-Tertiary compress ional orogeny. Fluid 2 was 250-350°C and hydrothermal when it penetrated susceptible strata of the Sekwi Formation by hydraulic fracturing and dissolution, and catalyzed thermochemical reduction of the sulfate in fluid 1. This reaction consumed local organic matter. The reduced-sulfur species then reacted with the metals brought by fluid 2, precipitating metal sulfides in the lowest susceptible units. Preferred sites of mineralization were in the hangingwall and immediate footwall of regional thrusts where steep faults intersected each other and susceptible units. This model will be a useful tool in exploration for new deposits or deposit extensions, but further work is needed to refine it.

iii Acknowledgements

My primary source of support for this thesis project was my employer, the Northwest Territories Geoscience Office, who was willing for me to take on the role of a student every summer for three years and who granted me nine months of unpaid leave in 2006-07. The NTGO is a partnership between the federal Department of Indian Affairs and Northern Development and the territorial Department of Industry, Tourism and Investment. The territorial side of the partnership funded the Sekwi Mountain project, which is the umbrella NTGO project that supported my field and analytical work, through the Strategic Investments in Northern Economic Development program. The federal manager of NTGO at the time, Carolyn Relf, and directors on the federal side granted permission for me to transform my function from that of Geoscience Information Manager to Project Geologist, despite the capacity gaps they were left to deal with The federal side of the partnership also provided funds for analyses, as well as personal financial support through the Career Development Program and the Northern Scientific Training Program. Carolyn Relf s personal support and encouragement were key to beginning the project, and when Scott Cairns took over her job while I was away at school in 2007, he continued the support seamlessly. I am particularly grateful for his patience and understanding when I developed a devastating neurological disease, and over the three years it took to obtain a diagnosis and semi-effective medication. During that time, for the most part I could not function, at either my job or my thesis project. His support has meant more to me than he probably realizes.

Many other staff at NTGO have provided support, inspiration, and encouragement. In particular, Edith Martel, who took on management of the Sekwi Mountain project, has provided a wonderful variety of assistance. It had been a quarter- century since I had used a Brunton compass; as soon as she realized how little I knew, she began to teach me, and has continued to provide advice whenever I asked, and encouragement when I didn't. Hendrik Falck reviewed an early draft, answered endless questions about how to approach things, kept reminding me of my priorities in life, and listened with compassion throughout the horrible times when the disease was ruining me. He helped my outlook more than anyone else and I cannot thank him enough for that.

iv Eagle Plains Resources Ltd. and Terralogic Exploration Inc. were a major source of support, providing helicopter time and field accommodations for parts of the 2006, 2007, and 2008 field seasons. Thanks especially to Aaron Higgs, Glen Hendrikson, and the crew at the Border Lake camp in 2008, and to Brent VanSickle for flying me around that year.

I was assisted in the field in 2007 by Ryan Pippy and Danielle Thomson, who put up with my idiosyncrasies with good humor, and in 2008 by John Law, an extraordinary source of cheer. Ryan Pippy found the TIC Ryan zone while taking a break from the pogo. Thank-you to Justin MacDonald and Chris Leslie, my fellow students on the Sekwi Mountain project in 2006, for being awesome, and to Rob MacNaughton for listening and teaching. Mike Pope led me on a tour of the Sekwi Formation, and has since been a source of knowledge and help. Stan and Helen Stevens and their family Glen, Dan, and Jessica (Mackenzie Mountains Outfitters) run the hunting lodge where we stayed in 2007; they are warm and genuine people and took exceptional care of the Sekwi Mountain project crew. A special thanks to Stan Stevens for flying me back to the Wells when I twisted my knee, and to Frank Pope for driving me around me when I got there. Harold Grinde and family at Shale Lake (Gana River Outfitters) were kind and welcoming hosts of our crew in 2007 and 2008, and the Simpson family (Ramhead Outfitters) at Godlin Lakes were likewise in 2006. The services provided by Canadian Helicopters, Sahtu Helicopters, and Fireweed Helicopters were dependable, skilled, and safe. Jane and her staff at the Mackenzie Valley Hotel in Norman Wells regularly went out of their way to make us comfortable; they are a model for exceptional service standards.

My primary supervisor, Elizabeth Turner, opened up the fascinating world of carbonate rocks for me, sharing her knowledge and enthusiasm for three years. She showed me how to measure a stratigraphic section, how to look at a carbonate rock, and by her example, how to see the relationships between rock units and structures in the field. Elizabeth supported my work financially as well, through her NSERC Discovery Grant in 2006 and 2007. Daniel Kontak, my second supervisor, taught me how to think about fluid inclusions as well as use the equipment, guided my initial thoughts on the

v analytical work, took it upon himself to walk me through use of the SEM on fluid inclusion evaporates, spent a memorable afternoon with me on the petrographic microscope discussing mineral textures, and provided a critical and detailed review of the analytical part of the first draft of this thesis, which improved the end product significantly. I thank both of my supervisors for teaching me these things, and for the time they spent with me. Also at Laurentian University, Mike Lesher and Darrel Long were unfailingly supportive and encouraging; thank you.

A large number of people, including some I barely knew, took the time to advise and encourage me in various ways. At the forefront of these are Bob Sharp of Trans Polar Geological Consultants Inc. and Sarah Gleeson of the University of Alberta; others include Jeff Packard, Glen Prior, Michel Malo, Hamish Sandeman, Brian Cousens, and Dan Marshall. I could not have continued what 1 had started without the physicians who identified my disease and addressed it, Drs. Morse and Pawluk. Finally, I would never have started this without the support of my sons Frederick and Garrett, who tolerated the change in lifestyle and actively encouraged me.

vi Dedication

To the researchers and physicians who seek to treat and cure Willis-Ekbom disease, and to professors of geoscience, Drs. George Chao, Simon Hanmer, and Giorgio Ranalli Co-Authorship statement

Although I am named as sole author of this dissertation, the paper that will be modified from Chapter 2 will be submitted for publication under the authorship of Fischer, Turner, and Kontak, to better reflect the contributions of my supervisors to the project. Elizabeth Turner conceived of the project theme, provided guidance and training in field studies and carbonate systems, and reviewed the draft manuscript. Daniel Kontak provided guidance and training in fluid inclusion studies and mineral petrography, advice on interpretation of isotopic analyses, and a critical review of the analytical part of the manuscript and the deposit model. I determined the direction of the project, managed it, and wrote the manuscript. My supervisors' knowledge, experience, and insights were invaluable, however, they never forced their views on me, they allowed me to draw my own conclusions, and any mistakes are my own.

viii Table of contents

Abstract iii

Acknowledgements iv

Dedication vii

Co-Authorship statement viii

Table of contents ix

List of tables xiii

List of figures xiv

Chapter 1. Introduction 1

Objectives 1

Format 1

Geological history of the northern Mackenzie Mountains 4

Carbonate-hosted mineralization in the Mackenzie Mountains 10

Previous studies 15

References, Chapter 1 18

Chapter 2. Controls on carbonate-hosted Zn-Pb mineralization in the Early Cambrian Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada 27

Introduction 27

Geological Framework 31

Geology of the Mackenzie Mountains 31

The Sekwi Formation host unit 33

Carbonate-hosted mineralization in the Mackenzie Mountains 36

Previous work in the AB, TIC and Palm areas 37

Terminology 39

Methods 40

ix Field and petrographic studies 40

Metallogenic compilation 40

Stratigraphic correlation 41

Fluid inclusion studies 42

Isotopic studies 44

Geological Studies: Results and Interpretation 44

Metallogenic compilation 44

Stratigraphic correlation 49

AB showings 49

TIC showings 62

Palm showings 75

Laboratory Studies: Results 80

Fluid inclusion petrography 80

Microthermometry 83

SEM-EDS analyses 95

Isotopic studies 96

Laboratory Studies: Interpretation 100

Interpretation of fluid inclusion results 100

Interpretation of isotopic analyses 103

Discussion 114

Dolomitization of the Sekwi Formation 114

Controls on mineralization 116

Evidence for at least two fluids 120

Host-unit burial history and hydrothennal vs. geothermal fluids 120

Fluid properties and sources of components 127

x Timing of mineralization 128

Models 131

Conclusions 135

References, Chapter 2 139

Appendix (1). Isotope and element analytical methods 155

Chapter 3. Concluding remarks 156

References, Chapter 3 158

Appendix A. Petrography of secondary minerals at showings in the AB, TIC, and Palm areas 160

Appendix B. Stratigraphic sections measured in the AB, TIC, and Palm areas; from NWT Special Volume 1 164

Appendix C. Geology of the AB area, parts of NTS 106C/16 and 106F/01; NWT Open File 2010-04 191

Appendix D. Use of the cycling technique for microthermometric measurements of temperatures of homogenization in fluid inclusions 260

References, Appendix D 260

Appendix E. SEM-EDS data from evaporate mounds 261

References, Appendix E 269

Appendix F. Sulfur isotope systematics 270

Introduction 270

Bacterial reduction of seawater sulfate 270

Thermochemical reduction of seawater sulfate 271

Reduced sulfur released during de-sulfurization of organic matter 272

Equilibrium fractionation vs. kinetic effects 274

References, Appendix F 276

Appendix G. List of publications and contributions generated by this project 279

xi Papers and maps 279

Abstracts 280

Appendix H. Table of abbreviations pertaining to fluid inclusion study 281

xii List of tables

Chapter 2

Table 2-1. Major characteristics of the studied showings 45

Table 2-2. Petrographic and hand specimen characteristics of sphalerite at the studied showings 46

Table 2-3. Informal members of the Sekwi Formation in the AB area 50

Table 2-4. Informal members of the Sekwi and Franklin Mountain formations in the TIC area 67

Table 2-5. Th and salinity data for FIAs 87

Table 2-6. Results of isotopic analyses on mineral samples from Sekwi Formation zinc showings 97

Appendix B

Table B-l. Locations of measured stratigraphic sections in the AB, TIC, and Palm areas 164

Appendix £

Table E-l. Correlation of areas on the SEM slide with chips of polished sections 261

Table E-2. SEM-EDS analyses of Na, Mg, CL, K and Ca for evaporate mounds from experimentally decrepitated fluid inclusions 264

Table E-3. Normalized atomic percents of cations (Na, K, Ca, Mg) and anions (CI) detected in the evaporate mounds 267 List of figures

Chapter 1

Figure 1-1. Location of the Mackenzie Mountains zinc district in the northern Canadian Cordillera 2

Figure 1-2. Regional geological context of the studied areas 5

Figure 1-3. The stratigraphic setting of the studied showings 6

Chapter 2

Figure 2-1. Location of the Mackenzie Mountains zinc district in the northern Canadian Cordillera 28

Figure 2-2. Regional geological context of the studied areas 30

Figure 2-3. The stratigraphic setting of the studied showings 32

Figure 2-4. Fence diagram of the Sekwi Formation in the northern and central Mackenzie Mountains 34

Figure 2-5. Map of AB the area 38

Figure 2-6. Textures of mineralized rocks in the AB area 55

Figure 2-7. More textures of mineralized rocks in the AB area 58

Figure 2-8. Paragenesis of mineral phases in the AB, TIC and Palm areas 60

Figure 2-9. Cemented breccias in the AB area, from a curvilinear trend that crosses the AB Fault 63

Figure 2-10. Geological setting of the TIC and Palm showings and geology of the TIC area 64

Figure 2-11. Textures of mineralized and nearby rocks at the TIC showings 70

xiv Figure 2-12. Looking east at strata hosting the Palm Main and Waterfall showings 76

Figure 2-13. Textures of mineralized rocks at the Palm showings 77

Figure 2-14. Fluid inclusions 81

Figure 2-15. Summary of microthermometric heating results 85

Figure 2-16. Histograms of Th for twelve FIAs 90

Figure 2-17. Microthermometric freezing results 91

Figure 2-18. Salinity of fluid inclusions and assemblages 94

Figure 2-19. Salinity and Th for FIAs from the Sekwi Formation zinc showings (this study) compared to the rest of the Mackenzie Mountains Zn district and to global carbonate-hosted Zn districts 96

Figure 2-20. Sulfur isotope values for sphalerite and barite from the Sekwi Formation zinc showings, grouped by showing area 98

Figure 2-21. Strontium isotope ratios for sphalerite, barite, and dolomite from the Sekwi Formation zinc showings, grouped by showing area 111

Figure 2-22. Burial history of the Sekwi Formation 121

Figure 2-23. Range of possible pressure-temperature conditions of trapping, and isochores for FIAs that yielded Th and salinity data 124

Appendix C

Map, NWT Open File 2010-04: Geology of the AB area In pocket

Appendix E

Figure E-l. Back-scattered electron images of fluid inclusion evaporate mounds 262

xv Chapter 1. Introduction

Objectives

This report describes an investigation carried out as a Masters of Science research project into the origin and nature of carbonate-hosted Zn±Pb mineralization in the Lower Cambrian Sekwi Formation of the Mackenzie Mountains zinc district, Northwest Territories, Canada (Fig. 1-1), and encompasses over 200 carbonate-hosted Zn±Pb showings, primarily in the Mackenzie Mountains, and an equal or greater number of clastic-dominated Pb-Zn ("SEDEX") showings, primarily in the Selwyn Mountains to the west. The district is remote and without infrastructure, which has left it neglected at most times and relegated to the sidelines of investment during periods of elevated base- metal prices in the 1970s and early 2000s. The main objectives of this study were

1. to determine whether the Sekwi Formation is a preferred host of mineralization, as was suggested by early exploration work;

2. to determine the controls on the localization of anomalous base metal concentrations (showings) within the Sekwi Formation; and

3. to illuminate the sources and flow paths of mineralizing fluids.

All three objectives feed into the primary objective of developing an effective exploration model for carbonate-hosted Zn±Pb deposits in the Mackenzie Mountains.

Format

The remainder of Chapter 1 provides a broad background for the rest of the report. It consists of a geological history of the Mackenzie Mountains, a description of carbonate-hosted Zn-dominated deposits and the related, carbonate-hosted Cu-dominated deposits in the district, and a summary of previous work relevant to carbonate-hosted base-metal mineralization in the Mackenzie Mountains. Chapter 2, the body of this report, is in the format of a journal paper, including references and its own Appendix.

1 Chapter 1. Introduction

Tsiigehtchio

A \Plain^\\/ I| \ Z1 i, "NJ I Fort Good Hope — , j/ si w L, uKon Y Northwest Territories

.Whrteh<

W"130°W Studied deposit area • Community • Carbonate-hosted Zn±Pb showing # City • Other Zn±Pb showing === Road

Figure 1-1. Location of the Mackenzie Mountains zinc district in the northern Canadian Cordillera. Carbonate-hosted showings include the Gayna River deposits (G) and the Prairie Creek deposits (P). Zincilead showings in the "other" class are predominantly clastic-hosted ("SEDEX"). Black box shows location of Figure 1-2. Projection is Universal Transverse Mercator (UTM), zone 9, using NAD83 datum.

Chapter 2 introduces the study in more detail, describes the methods and results, and provides a discussion and conclusions. Chapter 3 presents concluding remarks and recommendations. The report is completed by a number of appendices containing supplemental information:

• Appendix A provides detailed descriptions of the studied showings to supplement the descriptions in Chapter 2.

2 Chapter 1. Introduction

• Appendix B reproduces drafted columns for six stratigraphic sections measured in the three studied areas. These sections are reproduced from Appendix D of NWT Special Volume 1 (Martel et al., 2011).

• Appendix C is a reproduction of NWT Open File 2010-04 (Fischer et al., 2010), which consists of a map covering 38 km2 at 1:20,000 scale of the AB area, and a report summarizing the results of the mapping and observed controls on mineralization.

• Appendix D contains a brief description of the cycling technique described by Goldstein and Reynolds (1994), and used in this study to determine temperatures of homogenization for fluid inclusions in sphalerite. It supplements the microthermometry material in Chapter 2. • Appendix E presents the SEM-EDS data for a number of evaporate mounds from experimentally decrepitated fluid inclusions. These data supplement the microthermometry material in Chapter 2. • Appendix F is a discussion of sulfur isotope systematics. This isotopic system is more complex and more-easily misunderstood than the others. • Appendix G is a list of publications generated as part of this M.Sc. thesis project. • Appendix H contains a table of the abbreviations used to describe the fluid inclusion study. Pockets in the back contains a disc with a digital version of this report in Portable Document Format (PDF), and the oversized map associated with Appendix C.

Appendices B and C are re-printed with permission of the Northwest Territories Geoscience Office (NTGO). NWT Special Volume 1 is a report on the NTGO's Sekwi Mountain Project, a mapping project carried out in the central Mackenzie Mountains (National Topographic System (NTS) map sheets 105P - Sekwi Mountain, 106A - Mount Eduni, and 95M - Wrigley Lake) during parts of four field seasons (2005-2008). The Sekwi Mountain Project supported a number of thematic studies within and around the map area, including this M.Sc. project.

3 Chapter 1. Introduction

Geological history of the northern Mackenzie Mountains

This information expands on the brief description in Chapter 2 of the geological setting of the project area. The Mackenzie Mountains are part of a fold-and-thrust belt that forms the eastern edge of the northern Canadian Cordillera (Fig. 1-1). The mountains consists of unmetamorphosed to low-grade Neoproterozoic to Cretaceous sedimentary rocks and subordinate igneous rocks, deposited on the western margin of ancestral North America. The stratigraphic succession from Neoproterozoic to Cretaceous is described by Turner et al. (2011), whose work is the source of much of the information in this section; additional references are noted where appropriate.

Paleoproterozoic supracrustal rocks of the Wernecke Supergroup, exposed west of the Mackenzie Mountains in the Selwyn and Ogilvie mountains (Thorkelson et al., 2005), are believed to underlie the Mackenzie Mountains (Cook and Erdmer, 2005). The oldest rocks exposed in the Mackenzie Mountains, however, are early Neoproterozoic rocks of the Mackenzie Mountains supergroup, deposited in a rift-related, epicratonic basin (Long et al., 2008; Fig. 1-2, 1-3). The supergroup is up to 5.6 km thick and consists of a lowermost carbonate unit, a siliciclastic-dominated fluvial and deltaic succession (the Tsezotene Formation and Katherine Group), and an upper, mixed, carbonate-dominated succession (the Little Dal Group) whose early deposits were in an actively faulting shelf- and-basin environment. Upper parts of the Little Dal Group represent a variety of successive marine environments, including a restricted, evaporitic lagoon in which the Gypsum formation was deposited. Rift-related mafic sills intrude the lower part of the Mackenzie Mountains supergroup, and basalts cap it.

The late Neoproterozoic Windermere Supergroup records rifting of the supercontinent, Rodinia, and subsequent development of a passive margin on Laurentia, the ancestral North American craton (Young, 1976; Eisbacher, 1981; Ross, 1991). The earliest deposits of the Windermere Supergroup are a rift-related sedimentary succession, the Coates Lakes Group (Jefferson, 1983), which consists of red, green and tan mudstone, volcanic and carbonate conglomerate, sandstone, evaporite, and microbial dolostone, and, at the top, a thick limestone interval. Overlying the Coates Lake Group is the glaciogenic Rapitan Group, which consists of red and green diamictite and mudstone, locally with

4 Chapter 1. Introduction thick intervals of jasper-hematite iron formation (Yeo, 1978). This group records the Sturtian glaciation, the first of two globally correlated Neoproterozoic glaciations (Hoffman, 2009) represented in the Mackenzie Mountains. The Rapitan Group is overlain by the Hay Creek Group (Yeo, 1978; Turner et al., 2011), which records the second great Neoproterozoic glaciation, the Marinoan. The Hay Creek Group consists of a thick, lower interval of shale and siltstone (Twitya Formation), and an upper interval that represents a carbonate platform in the east (Keele Formation) and glaciogenic slope deposits in the west (Ice Brook Formation). It is terminated by a cap carbonate ("Teepee dolostone").

Legend Quaternary & ice Neoproterozoic Windermere Cretaceous intrusions Supergroup H9I Late Paleozoic mixed shelf •• Earty Neoproterozoic Mackenzie •• Late Paleozoic basin Mountains Supergroup (silicidattic inundation) Paleoproterozoic Wemecke Supergroup •• Earty Paleozoic Sefcvyn Basin •i Earty Paleozoic Mackenzie Platform Sekwi Formation Border Studied area of I Carbonate-hosted Fault carbonate-hosted ZntPb showing ZntPb showings UTM projection. NAD83. Zone 9N [EFiE

Northwest Territories

,-vV iTrTT:

Figure 1-2. Regional geological context of the studied areas. Geology from Gordey and Makepeace (2003) for the area south of 659N and west of 1309W; eastern strip is from Gordey et al. (2010a, b) and Roots et al. (2010), northern strip from Aitken et al. (1982).

5 Central Mackenzie Mountains 105B106A, 95M NW TECTONIC MESOZOC FORMATION AhMNIIYAFFINITY FORELANDBASN CRETACEOUS UNNAMED IGNEOUS SELWYN ™ ROCKS JURASSIC PLUTONS "0CKS TRIASSIC FANTASQUE PERMIAN FM SILICICLASTIC/ CARBONIFEROUS CARBONATE SHELF

UPPER SILICICLASTIC mfn^BASIN

MIDDLE

LOWER MACKENZIE PLATFOR SILURIAN

ORDOVCAN SELWYN BASIN

CAMBRIAN

ED ACARAN BLUEFIOWER FM

EXTENSION AND

(Martnoan Glaciation) RIFT-RELATED SUCCESSIONS CRYOGENIAN SSturtian Glaciation)

•LfTTlic VOLCANIC SUCCESSION

TONIAN ysw:* r - WUDC'RAC Kt 0 f M EPICRATONIC BASIN

Figure 1-3. The stratigraphic setting of the studied showings, reproduced from Gordey and Roots (2011). Right column shows the major tectono-stratigraphic packages. Left column shows formations (colored), groups, supergroups, and stratigraphic ages. Jagged lines show facies changes from SW (paleo-basin; left side of each column) to NE (paleo-land; right side). Vertically ruled gaps indicate local depositional hiatuses. Chapter 1. Introduction

The uppermost part of the Windermere Supergroup is an un-named group that consists of two more large-scale, shoaling-upward cycles of basal siliciclastic rocks and upper carbonate rocks (Sheepbed and Gametrail formations, Blueflower and Risky formations).

The Neoproterozoic rifting and passive-margin development recorded in the northern Canadian Cordillera by the Windermere Supergroup did not extend to the southern Canadian Cordillera until the terminal part of the Proterozoic (Colpron et al., 2002), at which time rifting and southward opening of the paleo-ocean caused uplift to the north (MacNaughton et al., 2000). The latest Precambrian to Cambrian succession in the Mackenzie Mountains records this uplift in the fluviodeltaic Backbone Ranges Formation (Gabrielse et al., 1973; MacNaughton et. al., 1997, 2008a) and the overlying and partly coeval shelf siltstone and sandstone of the Vampire Formation (Fritz, 1982). A continent-wide marine transgression followed in the Early Cambrian (Sauk I as modified by Long and Norford, 1997). This transgression is recorded in the Mackenzie Mountains by the dominantly carbonate deposition of the Sekwi Formation (Handfield, 1968). The Backbone Ranges Formation and parts of the upper Sekwi Formation comprise the earliest depositional elements of the Lower Paleozoic Mackenzie Platform.

The Mackenzie Platform was a relatively stable tectonic feature from the Cambrian until the Middle Devonian. West of the Mackenzie Platform, the Selwyn Basin was a major, deep-water, marine embayment into the western edge of North America from the Cambrian until the Middle Devonian (Gabrielse, 1967; Gordey and Anderson, 1993). Fine terrigenous sediments and minor slope carbonates were deposited in the Selwyn Basin. The eastern margin of the basin (western margin of the platform) migrated back and forth with time. Middle Cambrian basinal shale of the Hess River Formation (Cecile, 1982) directly overlies the Sekwi Formation in the western Mackenzie Mountains, but to the east, the Sekwi Formation is overlain by Middle Cambrian deep- water carbonate rocks of the Rockslide Formation, or disconformably by the Ordovician silty limestone slope strata of the Rabbitkettle Formation (Roots et al., 2010). The Middle Cambrian Hess River and Rockslide formations record the Sauk II marine transgression (Aitken, 1993) that is not evident on the contemporaneous platform. Volcanism and graben development in the basin during the Late Cambrian and the Middle Ordovician

7 Chapter 1. Introduction are attributed to incomplete rifting events, which formed the Misty Creek Embayment (Cecile et al., 1997). This paleo-embayment, around which the studied showings eventually formed, is a regional, northwest-trending (present-day direction) indentation into the Laurentian shore, on the north edge of the Selwyn Basin. A long period of uninterrupted deposition in the basin and embayment, from the Ordovician to the Early Devonian, is recorded by the Duo Lake (Cecile, 1982) and Sapper (Gordey and Anderson, 1993) formations.

The Mackenzie Platform above the Sekwi Formation consists of Ordovician to Middle Devonian platformal carbonate deposits, including those from shoal, reef, and lagoon environments (Fritz et al., 1992). Transitional facies, marking a change in character from platform to slope, have been identified at various Ordovician to Devonian stratigraphic levels. The Sekwi Formation in shoreward sections is overlain unconformably by Ordovician platformal dolostone and siltstone of the Franklin Mountain Formation and its basin-transitional facies variants (Cecile, 1982). Major regional unconformities mark three periods of regression, uplift, and erosion, and are separated by periods of marine carbonate-dominated deposition. The first of these unconformities developed in the Late Cambrian, and was followed by the Sauk III transgression and deposition of the Franklin Mountain Formation (Aitken, 1993). The second developed in the Middle Ordovician, and was followed by the Tippecanoe transgression (Sloss, 1963) and deposition of the Mount Kindle and Whittaker formations (equivalent units given different names in the northern and southern areas of exposure; Turner et al., 2011).

The third regional unconformity developed in the late Early to Late Silurian, and was followed, during the Early and early Middle Devonian, by an extended period of platformal carbonate deposition. Lateral and vertical variations in lithofacies have been used to define ten formations in the northern Mackenzie Mountains, as summarized by Turner et al. (2011). The lowest of these are the Tsetso and Camsell formations, which have a significant terrigenous content. The latter includes a brecciated, evaporitic facies. The overlying Sombre and Arnica formations are dolomitized, and their lateral, platform- edge equivalent, the Grizzly Bear Formation, is partly dolomitized. The younger Landry

8 Chapter 1. Introduction

Formation is a limestone. The Bear Rock Formation, a brecciated, evaporitic dolostone, is a peritidal, shoreward equivalent to parts of the Sombre, Arnica, and Landry formations. Finally, the youngest units of this period of deposition are the Hume and laterally equivalent Headless and Nahanni formations, which consist of argillaceous limestone overlain by locally dolomitic, skeletal limestone.

Beginning in the late Middle Devonian, tectonism and uplift north and west of the Mackenzie Mountains region (Nelson et al., 2002, 2006) coincided with a continent-wide marine transgression. The inundated Mackenzie Platform became a depocenter for fine silt and sand of the Canol and Imperial formations throughout the Late Devonian, while coeval turbidites of the Earn Group accumulated in the block-faulted and partly uplifted, former Selwyn Basin to the west (Gordey et. al., 1992).

By Early Carboniferous time, a topographically complex marine shelf had developed. Carbonate and siliciclastic strata were deposited in deep sub-basins and on intervening highs. Poorly preserved younger rocks record deep-water sandstone, chert and carbonate deposition in the Carboniferous-Permian, and deep siliceous basins later in the Permian.

Orogenesis from the mid-Jurassic to the Tertiary was related to the accretion of allochthonous terranes to the western margin of ancestral North America, although pre- Mesozoic extenstional structures indirectly influenced the geomotery of the deformation (Gordey and Roots, 2011; Gordey et al, 2011). Shortening of the sedimentary cover generated east- to northeast-verging folds and thrusts in a wide, arcuate (concave southweastward) belt. (The orogen is called the Laramide by some, but this usage is controversial; for example, Gabrielse and Yorath, 1992). Deformation in this belt was brittle and thin-skinned (Gordey and Roots, 2011; Gordey et al, 2011). A basal detachment is thought to extend beneath the entire belt within sedimentary cover, and is roughly estimated to be about 14 km deep beneath the study area (Gordey et al., 2010b).

In the study area, deformation began in the mid-Cretaceous and lasted until the Tertiary. Northeast-verging structures dominate the present-day map pattern. Restricted exposures of Early Cretaceous rocks 100 km south of the study area, in the central

9 Chapter 1. Introduction

Mackenzie Mountains, originated as eastward-transported fluvial and deltaic sediments shed by the rising orogen, and later caught up in it. Mid-Cretaceous peraluminous and metaluminous plutons in the west-central Mackenzie Mountains were emplaced shortly after deformation (Woodsworth et al., 1992). The dominant structural feature of the Mackenzie Mountains is the Plateau fault, a contractional fault that strikes southeast for over 300 km. Multiple levels of detachment are postulated for this structure (Gordey et al., 2011), including a major detachment along the Gypsum formation of the Neoproterozoic Little Dal Group. This detachment is about 9 km beneath the studied showings.

In the Mackenzie Mountains, the strike of regional contractional faults is slightly more northerly than the fold axes they cut, implying a change in the principal stress directions with time (Aitken et al., 1982). Preservaton of the panel of Cretaceous sedimentary rocks mentioned above is attributed to low-angle extensional faulting that accompanied the main deformation, possibly during a period of relaxation. Elsewhere in the northern Cordillera, a dextral strain regime was present during the Eocene, but data are lacking for the Mackenzie Mountains.

Carbonate-hosted mineralization in the Mackenzie Mountains

A review was made of available information on carbonate-hosted showings in the Mackenzie Mountains, using the NORMIN (2011) database maintained by NTGO as a starting point. The primary resource was a collection of assessment reports written by exploration companies and submitted in accordance with federal legislation to the NTGO for eventual public access. One of the key results of the review was the determination of four stratigraphic levels that are preferred hosts for carbonate-hosted Zn±Pb mineralization; this is discussed in Chapter 2. Other aspects of the review are discussed here.

A wide variety of mineralization types is present in the Mackenzie Mountains, and includes stratabound, sediment-hosted copper (Kupferschiefer type) in the Coates Lake Group; clastic-dominated Pb-Zn ("SEDEX") and barite deposits in the Ordovician- Devonian Selwyn Basin and siliciclastic rocks of the Late Devonian inundation; Chapter 1. Introduction carbonate-hosted Zn±Pb (Mississippi-Valley-type or MVT) deposits in rocks of the Little Dal Group and the Mackenzie Platform; a similar, Cu-dominated variant that is present mainly in Proterozoic hosts; iron formation in the Rapitan Group; vein-hosted base metals; emerald in non-igneous settings; and a number of commodities related to Cretaceous intrusions, including placer gold, skarn metals, pegmatite-hosted rare metals, and gem minerals (Yukon Minfile, 2005; NORMIN, 2011 and references therein; Ootes et al., 2011). By far the most common type is the carbonate-hosted Zn±Pb (Zn- dominated) type. In a restricted area of the central and northern Mackenzie Mountains between 128-132°W and 64-65°N, and 128-130°W and 63-64°N (NTS 105P, 106A, and 106B), there are 100 carbonate-hosted Zn-dominated showings recorded in the NORMIN database. This number under-represents the true number, because many single entries are for groups of showings. There are also seven carbonate-hosted showings that are dominated by Cu-sulphosalt minerals, but are otherwise very similar to the Zn-dominated type and lack evidence of the early diagenetic origin that characterizes the stratabound copper type. These are here assigned to a "carbonate-hosted, Cu-dominated" type, which cannot be confirmed as a separate mineralization type due to the paucity of descriptive data.

Recent discussions on the classification and genesis of carbonate-hosted Zn-Pb deposits are summarized by Leach et al. (2005). Deposits of this type have simple mineralogy, are stratabound and epigenetic, and occur in carbonate-dominated platformal successions. Metals and sulfur from crustal sources carried by basinal brines were deposited between 75° and 200°C. Controls are faults and fractures, dissolution collapse breccias, and lithological transitions. Topographically derived hydraulic head and thermohaline convection are both accepted as driving mechanisms of fluid flow, though seismic pumping has been proposed for a number of deposits (Muchez et al., 2005). Mixing of two fluids is a preferred stimulus for deposition of metals. There are no universally accepted criteria for distinguishing the much-discussed Irish subtype from classic MVT deposits. Irish-type fluids were somewhat higher-temperature (up to 240°C) and circulated deeply in extensional margin settings, precipitating ore minerals syn- depositionally or early during diagenesis (Wilkinson, 2003), whereas MVT fluids were, on average, lower-temperature and in most cases circulated more shallowly in foreland

11 Chapter 1. Introduction basins related to collisional orogens, precipitating ore well after or late during diagenesis. Pre-ore dissolution is a major ore control for classic MVT deposits, but is of subordinate importance in Irish-type deposits (Leach et al., 2005; Hitzman and Beaty, 1996). The Irish type and classic MVT are best regarded as sub-types of carbonate-hosted Zn-Pb deposits (Paradis et al., 2007).

Carbonate-hosted zinc-dominated showings occur in almost every carbonate unit in the Mackenzie Mountains succession, but are relatively sparse in the Windermere Supergroup and abundant in the Lower Paleozoic succession. They are are concentrated in four stratigraphic intervals: the Neoproterozoic Little Dal Group, the Early Cambrian Sekwi Formation, the Ordovician-Silurian Mount Kindle Formation, and the Middle Devonian Arnica and immediately overlying Landry formations (Chapter 2). References for this information, unless otherwise noted, are publicly available assessment reports (above). The host rocks of these showings are thoroughly dolomitized, except for those of the Landry Formation. Host rocks include types that are bioturbated, argillaceous, sandy, fenestral, intraclastic, skeletal, and oolitic. These are commonly vuggy, fractured, or brecciated. Ore minerals typically are sphalerite, its alteration products smithsonite and hydrozincite, and galena. Lead carbonates and sulfates (cerussite, angelsite) and minor amounts of copper sulfides and carbonates (chalcopyrite, tetrahedrite, chalcocite, malachite, azurite) are less common. Both void-filling and replacement textures occur in single deposits. Cements of fine- to coarse-grained ore and gangue minerals, commonly paragenetically zoned, occupy micropores, larger vugs, veins, and the matrices of crackle, mosaic and rubble floatbreccias and packbreccias (sensu Morrow, 1982) with dissolution and fitted-fabric textures. Replacements are massive, disseminated, or selective of fossil and other grains. Pyrite or marcasite is invariably present, though its abundance varies widely. Dolomite is ubiquitous, not only as coarse, void-filling cement, but also as replacement of the host limestone in a wide zone around most showings. Barite, calcite, and fluorite are common, ore-stage void-filling phases, and minor quartz may be present as a late phase.

Commodities of economic potential are zinc and lead. In most cases zinc is more abundant, but in one showing it is absent entirely. Silver is anomalous in a few of the

12 Chapter 1. Introduction deposits. Copper minerals (mainly chalcopyrite and tetrahedrite, locally chalcocite) are present in many of the showings, and are abundant in two (Dap and Toad; NTGO, 2009; Darney et al. 1976), but the potential for Cu to be an economic by-product is unknown because it was generally not assayed for. Copper is more abundant in the carbonate- hosted, Cu-dominated showing type (below). Barite varies in abundance, but is not economically significant.

The best-studied of the carbonate-hosted Zn-dominated showings are the Prairie Creek group of deposits in the southern Mackenzie Mountains (Paradis, 2007), and the Gayna River deposits in the northern Mackenzies (Turner, 2007; Wallace, 2009; Fig. 1-1). The Prairie Creek deposits consist of three distinct styles and generations of mineralization. The earliest is hosted by dolostone of the Mount Kindle Formation and is thought to have formed during the Silurian, syn-depositionally or during early diagenesis and at the same time as clastic-dominated Pb-Zn deposits in the Selwyn Basin (for example, Howard's Pass). This early mineralization type consists of stratabound, relatively high-temperature replacement of carbonate host rock by sulfide minerals. The other mineralization types are a carbonate-hosted Zn-dominated (MVT) type that consists of pyrite, sphalerite, and rare galena in breccias, veins, and vugs in grossly stratabound layers of vuggy, Early Devonian dolostone; and a vein-hosted Zn-Pb-Ag-Cu type that consists of quartz-carbonate-sulfide veins parallel to regional, north-trending faults of Late Cretaceous to Tertiary age. Most of the mineral resource exists in the stratabound and vein types, from which a combined measured and indicated, NI 43-101 -compliant resource has been calculated to be 5.84 million tonnes grading 10.71 %Zn, 9.89 %Pb, 0.326 %Cu, and 161.1 g/t Ag (Stone and Godden, 2007). No resource estimate has been made of the MVT type.

The Gayna River deposits are hosted by the Grainstone formation in the upper part of the Little Dal Group, but are structurally related to the top edges of giant microbial reefs rooted in the lower part of the group (Turner, 2007). Sphalerite with minor pyrite and galena fills veins and voids in a number of undelimited breccia zones. Historically estimated resources include 56 kilotonnes averaging 14.52% combined Zn- Pb and 1,066 kilotonnes averaging 4.51% Zn-Pb (Hewton, 1982). Only a few other

13 Chapter 1. Introduction showings have been drilled. Some of the best drill results are from the Bear-Twit deposit, which is hosted by silicified, brecciated skeletal dolostone of the Mount Kindle Formation. Bear-Twit consists of sphalerite-galena (± tetrahedrite) fracture-fill and minor breccia cement with associated dolomite, calcite, quartz, and barite. Twenty-one drill holes through the main showing intersected numerous high-grade zones, including 23 m of 15.75% Zn, 11.16% Pb, and 4.16 oz/T Ag (Bagshaw, 1974), but the mineralization was deemed too patchy to warrant further work.

The showings studied in this project are hosted by the Sekwi Formation in three areas, the AB, TIC, and Palm areas (Fig. 1 -2). The AB and TIC areas were drilled in the 1970s, but mineralized intervals were narrow (McArthur and McArthur, 1977a, b; Ronning, 1975). No other showings in the Sekwi Formation have been drilled, but some have been extensively sampled. For example, representative grab samples taken every 30 cm across 9 m of the Ice 9 showing averaged 8.20% Pb and 12.50% Zn (Brock, 1973). The Ice 9 showing consists of fracture-filling and disseminated galena and smithsonite in vuggy, orange, quartz-rich dolostone of the Sekwi Formation.

Based on publicly available descriptions, most showings of carbonate-hosted, Zn- dominated type in the Mackenzie Mountains have a clear spatial association with faults or fractures, and exhibit fracture-filling textures (e.g., Royle, 1976; Dewing et al., 2006). Some have dissolution textures that seem to have developed concurrently with mineralization. The mineralization at many showings is stratabound, but controls are not clear.

The carbonate-hosted, Cu-dominated mineralization type is primarily a copper deposit, with accessory zinc or silver. The amount of zinc varies from absent to major. The dominance of copper sulphosalts in these deposits is diagnostic. A number of the Zn- dominated showings contain copper sulphosalts, but always in trace to minor amounts (e.g., Adamson, 1974; Brock et al., 1976; Dewing et al., 2006). Mineralization in the Cu- dominated type is in quartz or quartz-calcite veins in parallel fractures in dolostone, or in dolomite-calcite cement in dolostone or limestone breccias. Mineralized zones are pervasively fractured and associated with late faulting, but are grossly concordant with bedding (e.g., Anderson et al., 1973; Cukor, 1974); in these respects, this deposit type is Chapter 1. Introduction like the carbonate-hosted Zn-dominated type. The main ore minerals are tetrahedrite, chalcopyrite, bornite, or bournonite; there are also the secondary copper minerals malachite and azurite, and rarely covellite, chalcocite, and boulangerite. In some occurrences, sphalerite, secondary zinc minerals, and galena are important. A drill hole through one such showing cut 32 m of calcite-tetrahedrite in a cemented dolostone breccia that averaged 0.9% Cu and 1.1 oz/ton Ag (RML 3 showing; Kim, 1972). The vein type of mineralization at Prairie Creek consists of tetrahedrite-tennantite in quartz-calcite veins (Paradis, 2007), and is inferred here to belong to the Cu-dominated type.

Previous studies

A limited number of academic studies have focused on Mackenzie Mountains carbonate-hosted zinc showings. Macqueen (1976) postulated a genetic link with hydrocarbons, suggesting that both metals and mature hydrocarbons were mobilized during deep-burial diagenesis of shales, and migrated laterally to carbonate traps. The deposits were interpreted to post-date hydrocarbon migration, pre-date the Cretaceous- Tertiary orogeny, and display a strong stratigraphic control due to the required presence of laterally equivalent shales containing sufficient organic matter and metals.

Dual episodes of mineralization were proposed on the basis of the minor element chemistry of sphalerite from 48 carbonate-hosted showings in the northern Canadian Cordillera (McLaren and Godwin, 1979). The samples that defined one population came from showings hosted by older rocks (Proterozoic and Early Cambrian), and the others came from showings hosted by younger rocks, thus a mineralizing event was proposed to have occurred in the Middle or Late Cambrian, and a younger event in the Late Devonian or later. Godwin et al. (1982) began with the assumption that these separate events occurred in the Cambrian and Late Devonian, and showed that the Pb isotope data for galena from numerous carbonate-hosted and clastic-dominated Pb-Zn showings in the northern Canadian Cordillera were compatible with this assumption.

Morrow (1990) and Morrow and Aulstead (1995) studied the origin of the Manetoe dolomite, a regionally extensive, vuggy, dolomitized facies of Early to Middle Devonian strata (Arnica, Landry, Headless, and Nahanni formations) that extends over Chapter 1. Introduction

'y 38,000 km in the southern Mackenzie Mountains and the subsurface east and south of the mountains. The Manetoe facies is a continuation of the better-known Presqu'ile facies at the Pine Point Zn-Pb mine. The dolomitization represented by these facies affected a vast volume of rock sometime after the Middle Devonian and prior to hydrocarbon migration into vugs of the Manetoe facies in the Carboniferous. Hydrocarbon migration was accompanied and followed by calcite and quartz cementation of the host vuggy dolostone, which in turn was followed by minor galena-sphalerite fracture fillings. There was therefore a regional mineralizing event, albeit perhaps minor, in the Mesozoic or later. Morris and Nesbitt (1998) identified six regional fluid-flow events, of which three were associated with metal deposition. They linked the Manetoe event to a major, regional carbonate-hosted metal-deposition event on the basis that the Manetoe facies was the host of MVT mineralization at Prairie Creek, however that host has since been identified as the Silurian Root River Formation (Paradis, 2007). Morris and Nesbitt also identify a late calcite±quartz veining event associated with deposition of the vein-type mineralization at Prairie Creek. This interpretation appears to remain valid. The veins occupy thrust planes and later, high-angle brittle-fault planes throughout the Mackenzie Mountains, and appear to be correlative with the carbonate-hosted, Cu-dominated deposits described above. The age of the vein event is Cretaceous-Tertiary on the basis of field relationships and hydrogen isotope values (Morris and Nesbitt, 1998).

Paradis (2007) interpreted new and previously published isotopic data from the three types of mineralization (stratabound, MVT, and vein-type) at the Prairie Creek mine in the southern Mackenzie Mountains. Data included C, O, and Sr isotope analyses for both void-filling and host-replacive dolomite and S-isotope analyses for sulfides from all three mineralization types; and Pb-isotope data for sulfides from the vein-type deposits, and for sulfides and dolomite from the MVT and stratabound deposits. Strontium-isotope ratios ranged up to 0.7285 for the vein minerals, to 0.7239 for the stratabound minerals, and only to 0.7127 for the MVT minerals. Until now, the 87Sr/86Sr values from the vein- type and stratabound mineralization were the highest published for the northern Cordillera. Both those types of mineralization, although widely separated in time, were formed from basement-derived fluids, whereas the MVT type, between the others in age, was formed from seawater-derived fluids. Lead isotopes of the stratabound and MVT Chapter 1. Introduction sulfides share a common source but, surprisingly, the vein-sulfide leads define a distinct population. Therefore, the vein-type metals derived from a source that was distinct from the source of stratabound and MVT metals.

Ore-related fluids in the northern and central Mackenzie Mountains were interpreted to have been between 88° and 236°C, with salinities of 10 to 34 wt. % NaCl equivalent (Carriere and Sangster; 1999; Gleeson, 2006; Wallace, 2009). Mixing of more than one fluid was suggested for a number of deposits (Gleeson, 2006; Wallace, 2009). A recent study of the Gayna River deposit (Wallace, 2009) detected three stages of ore deposition and used Re/Os geochronology of pyrobitumen to obtain a Cretaceous- Tertiary age for the main ore stage. Precipitated metals were extracted from the underlying shales and sulfur was generated by thermochemical reduction of sulfate from local evaporites. Fluid inclusion homogenization temperatures at Gayna average 195°C.

Studies of carbonate-hosted Zn-Pb deposits and dolomitization in the northern Rocky Mountains (Nelson et al., 2002; Paradis et al., 2006) summarized work that is relevant to the regional paleohydrology and metallogeny of the Mackenzie Mountains. Their stable isotope and fluid inclusion data expand the dataset of Qing and Mountjoy (1992), Morrow et al. (1990), and others, confirming an eastward-decreasing Devonian temperature gradient resulting from an eastward flow of fluid from the northern Cordillera into the Pine Point region and the Western Canada Sedimentary Basin.

17 Chapter 1. Introduction

References, Chapter 1

Adamson, T.J., 1974, KEG Group-Report on 1973 Field Work: unpublished Assessment Report 080318, submitted by Dynasty Explorations Limited, Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Aitken, J.D., 1991. Chapter 4, Stratigraphy; 4B. Cambrian and Lower Ordovician - Sauk sequence, in Stott, D.F. and Aitken, J.D., editors, Sedimentary Cover of the Craton in Canada: Geology of Canada, n. 5, Geological Survey of Canada, Ottawa, p. 96-124 (also published as The Geology of North America, v. D-l; Geological Society of America).

Aitken J.D. and Cook D.G., 1974. Effect of antecedent faults on "Laramide" structure, MacKenzie arc; GSC Paper 74-1, Part B, p. 259-264; Geological Survey of Canada, Ottawa, Canada.

Aitken, J.D., Cook, D.G., and Yorath, C.J., 1982, Upper Ramparts River (106G) and Sans Sault Rapids (106H) map areas, District of Mackenzie: Memoir 388, Geological Survey of Canada, Ottawa, Canada, 48 p.

Anderson, R.E., Miller, D.C., and Risby, P., 1973, Geological and Geochemical Report, TET-RAP Claims: unpublished Assessment Report 060056, submitted by Bethlehem Copper Corp. Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Bagshaw, R.G., 1974, Diamond Drilling Report - 1974, submitted by Cominco Ltd.: unpublished Assessment Report 080367, submitted by Cominco Ltd., Dept. of Indian Affairs and Northern Development, NWT Geology Division, Yellowknife (http://www.nwtgeoscience.ca)

Bellamy, J.R., 1977, Summary Diamond Drilling Report on the BEAR-TWIT Property: unpublished Assessment Report 080594, submitted by Bethlehem Copper Corp. Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Brock, J.S., 1973, Geological, Geochemical, and Prospecting Investigations on the TEE- LIN, RAK, ARN EMILY and ICE Claims Groups: unpublished Assessment Report 080339, submitted by Welcome North Mines Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Brock JS, McArthur GF, McArthur ML, 1976. Geological, Geochemical and Diamond Drilling Report on the REV Claims: unpublished Assessment Report 080488, submitted by Welcome North Mines Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

18 Chapter 1. Introduction

Carriere, J.J. and Sangster, D.F., 1999, A multidisciplinary study of carbonate-hosted zinc-lead mineralization in the Mackenzie Platform (a.k.a. Blackwater and Lac de Bois platforms), Yukon and Northwest Territories, Canada: Open File 3700, Geological Survey of Canada, Ottawa, 146 p.

Cecile, M.P., 1982, The Lower Paleozoic Misty Creek Embayment, Selwyn Basin, Yukon and Northwest Territories: Bulletin 335, Geological Survey of Canada, Ottawa, Canada, 78 p. and 1 map.

Cecile, M.P., Morrow, D.W., and Williams, G.K., 1997, Early Paleozoic (Cambrian to Early Devonian) tectonic framework, Canadian Cordillera: Bulletin of Canadian Petroleum Geology, v. 45, p. 54-74.

Colpron, M., Logan, J.M., and Mortenson, J.K., 2002, U-Pb zircon age constraint for late Neoproterozoic rifting and initiation of the lower Paeozoic passive margin of western Laurentia: Canadian Journal of Earth Sciences, v. 39, p. 133-143.

Cook, F.A. and Erdmer, P., 2005, An 1800 km cross section of the lithosphere through the northwestern North American plate: lessons from 4.0 billion years of Earth's history: Canadian Journal of Earth Sciences, v. 42, p. 1295-1311.

Cukor, V., 1974, Report on the DAY-NOON Group of Claims: unpublished Assessment Report 080343, submitted by Jomial Investments Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca).

Darney, R.J., Ikona, C.K., Yeager, D.A., 1976, Assessment Report-TOAD Mineral Claims; Dept. of Indian Affairs and Northern Development, NWT Geology Division, Yellowknife: unpublished Assessment Report 080530, submitted by Harman Management Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Dewing, K., Sharp, R.J., Ootes, L., Turner, E.C., and Gleeson, S., 2006, Geological assessment of known Zn-Pb showings, Mackenzie Mountains, Northwest Territories: GSC Current Research 2006-A4, Geological Survey of Canada, Ottawa.

Eisbacher, G.H., 1981, Sedimentary tectonics and glacial record in the Windermere Supergroup, Mackenzie Mountains, northwestern Canada: Paper 80-27, Geological Survey of Canada, Ottawa, Canada, 40 p.

Fischer, B.J., 2011, Appendix D, Detailed stratigraphic sections measured through the Sekwi Formation, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories:

19 Chapter 1. Introduction

NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 364-395.

Fischer, B.J., Atherton, C., Parker, E., and Law, J., 2010, Geology of the AB area, parts of 106C/16 and 106F/01: NWT Open File 2010-04,Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map scale 1:20,000, 1 report, 66 p.

Fritz W.H., 1982, Vampire Formation, a new upper Precambrian(?)/Lower Cambrian Formation, Mackenzie Mountains, Yukon and Northwest Territories: Paper 82-IB, Geological Survey of Canada, Ottawa, Canada, p.83-92.

Fritz, W.H., 1992, Cambrian Assemblages, in Fritz, W.H., Cecile, M.P., Norford, B.S., Morrow, D., and Geldsetzer, Chapter 7. Cambrian to Middle Devonian assemblages, in Gabrielse, H. and Yorath, C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, Canada, p. 155-184 (also published as The Geology of North America, v. G-2, Geological Society of America).

Fritz, W.H., Cecile, M.P., Norford, B.S., Morrow, D., and Geldsetzer, H.H.J., 1992, Chapter 7. Cambrian to Middle Devonian assemblages, in Gabrielse H. and Yorath C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n.4, Geological Survey of Canada, Ottawa, Canada, p. 153-218 (also published as The Geology of North America, v. G-2, Geological Society of America).

Gabrielse, H., 1967, Tectonic evolution of the northern Canadian Cordillera: Canadian Journal of Earth Sciences, v. 4, p. 271-298.

Gabrielse, H., and Yorath, C.J., 1992. Chapter 1. Introduction, in Gabrielse, H. and Yorath, C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, p. 5-11 (also published as The Geology of North America, v. G-2, Geological Society of America).

Gabrielse, H., Blusson, S.L., and Roddick, J.A., 1973, Geology of Flat River, Glacier Lake, and Wrigley Lake map-areas, District of Mackenzie and Yukon Territory: Memoir 366, Geological Survey of Canada, Ottawa, Canada, 153 p., 3 maps.

Gleeson, S., 2006, A microthermometric study of fluid inclusions in sulfides and carbonates from Gayna River and the Bear-Twit base metal prospects, Mackenzie Mountains, NWT: NWT Open Report 2006-005, Northwest Territories Geoscience Office, Yellowknife, Canada, 10 p.

Godwin, C.I., Sinclair, A.J., and Ryan, B., 1982, Lead isotope models for the genesis of carbonate-hosted Zn-Pb, shale-hosted Ba-Zn-Pb, and silver-rich deposits in the northern Canadian Cordillera: Economic Geology, v. 77, p. 82-94.

20 Chapter 1. Introduction

Goldstein, R.H. and Reynolds, T.J., 1994. Systematics of Fluid Inclusions in Diagenetic Minerals: SEPM Short Course 31, Society for Sedimentary Geology, 199 p.

Gordey, S.P. and Anderson, R.G, 1993, Evolution of the northern Cordilleran miogeocline, Nahanni map area (1051), Yukon and Northwest Territories: GSC Memoir 428, Geological Survey of Canada, Ottawa, Canada, 214 p.

Gordey, S.R and Makepeace, A.J., compilers, 2003, Yukon digital geology, version 2.0: Open File 2003-9(D), Yukon Geological Survey, Whitehorse, Canada, 1 disc.

Gordey, S.R, Geldsetzer, H.H.J., Morrow, D.W., Bamber, E.W., Henderson, C.M., Richards, B.C., McGugan, A., Gibson, D.W., and Poulton, T.P., 1992, Chapter 8. Upper Devonian to Middle Jurassic assemblages, in Gabrielse H. and Yorath C.J., editors,Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, Canada, p. 221-328 (also published as The Geology of North America, v. G-2, Geological Society of America).

Gordey, S.P., Martel, E., MacDonald, J., MacNaughton, R., Roots, C.F., and Fallas, K. (compilers), 2010. Geology of Mount Eduni, NTS 106A Northwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-09, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Gordey, S.P., Martel, E., MacDonald, J., Fallas, K., Roots, C.F., and MacNaughton, R., 2010. Geology of Mount Eduni, NTS 106A Southeast, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-12, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Handfield, R.C., 1968, Sekwi Formation, a new Lower Cambrian formation in the southern Mackenzie Mountains, District of Mackenzie (95L, 1051, 105P): Paper 68-47, Geological Survey of Canada, Ottawa, Canada, 23 p.

Hewton, R.S., 1982, Gayna River: A Proterozoic Mississippi Valley-Type lead-zinc deposit, in Hutchinson, R.W., Spence, C.D., and Franklin, J.M., editors, Precambrian Sulphide Deposits, H.S. Robinson Memorial Volume: Special Paper 25, Geological Association of Canada, p. 667-700.

Hitzman, M.W. and Beaty, D.W., 1996. The Irish Zn-Pb(-Ba) orefield, in Sangster D.F., editor, Carbonate-Hosted Lead-Zinc Deposits, 75th Anniversary Volume: Society of Economic Geologists, Special Publication No. 4, p. 112-143.

Hoffman, P.F., 2009, Pan-glacial - a third state in the climate system: Geology Today, v. 25, n. 2, p. 107-114.

21 Chapter 1. Introduction

Jefferson, C.W., 1983, The Upper Proterozoic Redstone copper belt, Mackenzie Mountains, N.W.T.: unpublished Ph.D. thesis, University of Western Ontario, London, Ontario, Canada.

Kim, B.Y., 1972, Drill Logs - RML Claims, Godlin Lakes Area: unpublished Assessment Report 060085, submitted by Arrow Inter-America and Godlin Copper, Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Leach, D.L., Sangster, D.F., Kelley, K.D., Large, R.R., Garven, G., Allen, C.R., Gutzmer, J., and Walters, S., 2005, Sediment-hosted lead-zinc deposits: a global perspective, in Hedenquist, J.W., Thompson, J.F.H, Goldfarb, R.J., and Richards, J.P., editors, Economic Geology 100th Anniversary Volume: Society of Economic Geologists, p. 561-607.

Leary, G.M. and Royle, D.Z., 1974, Geology Report on the Tap-Glug Claims, Godlin Lakes, NWT, 105P/14: unpublished Assessment Report 080365, submitted by Amax Exploration Inc., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Long, D.G.F. and Norford, B.S., 1997, Following coastlines: the paleogeography of Canada from the Late Precambrian to the Early Ordovician: Ontario Petroleum Institute, v. 32.

Long, D.G.F., Rainbird, R.H., Turner, E.C., and MacNaughton, R.B., 2008, Early Neoproterozoic strata (Sequence B) of mainland northern Canada and Victoria and Banks islands: a contribution to the Geological Atlas of the Northern Canadian Mainland Sedimentary Basin: Open File 5700, Geological Survey of Canada, Ottawa, Canada, 24 P-

MacNaughton, R.B., Narbonne, G.M., and Dalrymple, R.W., 2000, Neoproterozoic slope deposits, Mackenzie Mountains, northwestern Canada: implications for passive-margin development and Ediacaran faunal ecology: Canadian Journal of Earth Sciences, v. 37, p. 997-1020.

MacNaughton, R.B., Dalrymple, R.W., and Narbonne, G.M., 1997, Early Cambrian braid-delta deposits, Mackenzie Mountains, north-western Canada: Sedimentology, v. 44, p. 587-609.

MacNaughton, R.B., Roots, C.F., and Mattel, E., 2008, Neoproterozoic-(?)Cambrian lithostratigraphy, northeast Sekwi Mountain map area, Mackenzie Mountains, Northwest Territories: new data from measured sections: Current Research 2008-16, Geological Survey of Canada, Ottawa, 15 p.

MacQueen, 1976, Sediments, zinc and lead, Rocky Mountain belt, Canadian Cordillera: Geoscience Canada, v. 3, p. 71-81.

22 Chapter 1. Introduction

Martel, E., Turner, E.C. and Fischer, B.J., editors, 2011, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, 423 p.

McArthur, G.F. and McArthur, M.L., 1977, Geological and geochemical report on the AB-BB-DAB mineral claims (AB Project), Mackenzie Mining District, NTS 106C16, Northwest Territories, Canada, Work performed July 15 - September 2, 1976: unpublished Assessment Report 080621, submitted by Welcome North Mines Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

McArthur, G.F. and McArthur, M.L., 1977, Arctic Red Project, 1977 Final Report, Mackenzie and Backbone Ranges, NTS 106A, B, C, F, G, 105N,0, Yukon and Northwest Territories: unpublished report, Welcome North Mines Ltd., confidential property of Eagle Plains Resources Ltd. in 2008.

McLaren, G.P. and Godwin, C.I., 1979, Minor elements in sphalerite from carbonate- hosted zinc-lead deposits, Yukon Territory and adjacent District of Mackenzie, Northwest Territories, in Morin, J.A., Marchand, M., Craig, D.B., and Debicki, R.L., editors, Mineral Industry Report, 1977, Yukon Territory: Yukon Geological Survey, Whitehorse, p. 5-21.

Morris, G.A. and Nesbitt, B.E., 1998, Geology and timing of palaeohydrogeological events in the MacKenzie Mountains, Northwest Territories, Canada, in Parnell, J., editor, Dating and Duration of Fluid Flow and Fluid-Rock Interaction: Geological Society, London, Special Publications n. 144, p. 161-172.

Morrow, D.W., 1982. Descriptive field classification of sedimentary and diagenetic breccia fabrics in carbonate rocks: Bulletin of Canadian Petroleum Geology, v. 30, p. 227-229.

Morrow, D.W.and Aulstead, K.L., 1995, The Manetoe Dolomite - a Cretaceous-Tertiary or a Paleozoic event? Fluid inclusion and isotopic evidence: Bulletin of Canadian Petroleum Geology, v. 43, n. 3, p. 267-280.

Morrow, D.W., Cumming, G.L., and Aulstead, K.L., 1990, The gas-bearing Devonian Manetoe facies, Yukon and Northwest Territories: Geological Survey of Canada, Bulletin 400, 54 p.

Muchez, P., Heijlen, W., Banks, D., Blundell, D., Boni, M., and Grandia, F., 2005, Extensional tectonics and the timing and formation of basin-hosted deposits in Europe: Ore Deposit Reviews, v. 27, p. 214-267.

23 Chapter 1. Introduction

Nelson, J.L., Paradis, S., Christensen, J., and Gabites, J., 2002, Canadian Cordilleran Mississippi Valley-Type deposits: A case for Devonian-Mississippian back-arc hydothermal origin: Economic Geology, v. 97, p. 1013-1036.

Nelson, J.L., Colpron, M., Piercey, S.J., Dusel-Bacon, C., Murphy, D.C., and Roots, C.F., 2006, Paleozoic tectonic and metallogenic evolution of pericratonic terranes in Yukon, northern British Columbia, and eastern Alaska, in M. Colpron, M. and Nelson, J.L., editors, Paleozoic Evolution and Metallogeny of the Pericratonic Terranes at the Ancient Pacific Margin of North America, Canadian and Alaskan Cordillera: Special Paper 45, Geological Association of Canada, p 323-360.

NORMIN, 2011, The Northern Minerals Database, 2011/02/01: Northwest Territories Geoscience Office, Yellowknife, Canada (http://www.ntgomap.nwtgeoscience.ca)

NTGO, 2009, Northwest Territories Geoscience Office Discovers Promising New Mineral Prospect In The Mackenzie Mountains: Information Notice, Nov. 16, 2009: Northwest Territories Geoscience Office, Yellowknife, Canada (http://www.nwtgeoscience.ca/news)

Ootes, L., Fischer, B.J., Rasmussen, K.L., Borkovic, B., Long, D.G.F., and Gordey, S.P., 2011, Chapter 7. Mineral Deposits and Prospects, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 255-265.

Paradis, S., 2007, Isotope geochemistry of the Prairie Creek carbonate-hosted zinc-lead- silver deposit, southern Mackenzie Mountains, Northwest Territories, in Wright, D.F., Lemkow, D., Harris, J.R., editors, Mineral and energy resource assessment of the Greater Nahanni Ecosystem under consideration for the expansion of the Nahanni National Park Reserve, Northwest Territories: Geological Survey of Canada, Open File 5344, p. 131- 176

Paradis, S., Turner, W.A., Coniglio, M., Wilson, N., and Nelson, J., 2006, Stable and radiogenic isotopic signatures of mineralized Devonian carbonate rocks of the northern Rocky Mountains and the Western Canada Sedimentary Basin, in Hannigan, P., editor, Potential for Carbonate-hosted, Lead-zinc, Mississippi Valley-type Mineralization in Northern Alberta and Southern Northwest Territories: Geoscience Contributions, Targeted Geoscience Initiative: Bulletin 591, Geological Survey of Canada, p. 75-103.

24 Chapter 1. Introduction

Exploration Methods: Special Publication n. 5, Geological Association of Canada, Mineral Deposits Division, p. 185-203.

Ronning, P., 1975, A geological report with a drilling survey on the TIC-TIL mineral claims 16 miles WNW of Palmer Lake, mineral claim map NTS 106-B-9: unpublished Assessment Report 080499, submitted by Serem Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Roots, C.F., Martel, E., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Northwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-13, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, scale 1:100,000.

Ross, G.M., 1991, Tectonic setting of the Windermere Supergroup revisited: Geology, v. 19, p. 1125-1128.

Royle, D.Z., 1976, Welcome North Mines Limited Final 1974 Property Report: unpublished Assessment Report 061443, submitted by Welcome North Mines Limited, Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca).

Sloss, L.L., 1963, Sequences in the cratonic interior of North America: Geological Society of America Bulletin, v. 74, p. 93-114.

Thorkelson, D.J., Abbott, J.G., Mortenson, J.K., Creaser, R.A., Villeneuve, M.E., McNicoll, V.J., and Layer, P.W., 2005, Early and Middle Proterozoic evolution of Yukon, Canada: Canadian Journal of Earth Sciences, v. 42, p. 1045-1071.

Turner, E.C., 2007, Lithofacies and structural controls on Zn-Pb mineralisation at Gayna River, NWT: GAC-MAC Joint meeting 32, May 23-25,2007, Geological Association of Canada.

Turner, E.C., Roots, C.F., MacNaughton, R.B., Long, D.G.F., Fischer, B.J., Gordey, S.P., Martel, E., and Pope, M.C., 2011, Chapter 3, Stratigraphy, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 31-192.

Wallace, S.R.B., 2009, The genesis of the Gayna River carbonate-hosted Zn-Pb deposit: unpublished M.Sc. thesis, Edmonton, Canada, University of Alberta, 117 p.

Wilkinson J.J., 2003, On diagenesis, dolomitisation and mineralisation in the Irish Zn-Pb orefield: Mineralium Deposita, v. 38, p. 968-983.

25 Chapter 1. Introduction

Woodsworth, G.J., Anderson, R.G., and Armstrong, R.L., 1992, Plutonic regimes, in Gabrielse, H. and Yorath, C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, Canada, p. 493-531 (also published as The Geology of North America, v. G-2, Geological Society of America).

Yeo, G.M., 1978, Iron-formation in the Rapitan Group, Mackenzie Mountains, Yukon and Northwest Territories, in Mineral Industry Report 1975, EGS 1978-5, Economic Geology Series, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 170-175.

Young, G.M., 1976, Iron-formation and glaciogenic rocks of the Rapitan Group, Northwest Territories, Canada: Precambrian Research, v.3, n.2, p.137-158.

Yukon MINFILE, 2005, A database of mineral occurrences: Access database created 2005, downloaded October 2006, Yukon Geological Survey, Whitehorse, Canada (http://www.geology.gov.yk.ca/databases_gis.html)

26 Chapter 2. Controls on carbonate-hosted Zn-Pb mineralization in the Early Cambrian Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada

Introduction

The Mackenzie Mountains zinc district in the northern Canadian Cordillera (Fig. 2-1) encompasses over 200 carbonate-hosted Zn±Pb showings, including 30 within the Early Cambrian Sekwi Formation (NORMIN, 2011). The area is remote, with aircraft- only access and a short working season, therefore it remains poorly explored and its deposits sparsely studied.

Exploration in the 1970s led to the suggestion that the Sekwi Formation was one of a few preferred stratigraphic hosts for carbonate-hosted Zn±Pb mineralization (Dawson, 1974). The unit was therefore chosen as a focus of renewed exploration in 2004-2008. However, the Mississippi Valley-type deposit model was of questionable use because most of the carbonate-hosted showings in the Mackenzie Mountains have a spatial affinity with late faults (references in NORMIN, 2011). These observations lead to two questions that differ mainly in scale. The first is whether the Sekwi Formation is indeed a preferred host for mineralization over other units in the stratigraphic succession, and if so, why. This question is addressed briefly with a compilation of mineral showings data for a restricted area of the Mackenzie Mountains, but the data needed to answer this question properly are lacking. Bedrock maps of most of the area are based on reconnaissance work and have been outdated by newer stratigraphic studies. Since the discovery and description of most of the showings is at least as old as the original mapping, their stratigraphic hosts are, in many cases, improperly or uncertainly identified.

The second question is the nature of the controls that dictate where mineralization is located within the Sekwi Formation. This study specifically considers whether there was a structural control, as suggested by the observed spatial association with faults, whether there was a

27 6 i/1 r \ xHv /"-»I f/ ^va V \\ Fort Good Hope — I V P 'ukon \j Northwest Territories ~

[Wiglei

lahanni Butte-

.Vtfiitehorse

Studied deposit area • Community • Carbonate-hosted Zn±Pb showing # City • Other Zn±Pb showing === Road

Figure 2-1. Location of the Mackenzie Mountains zinc district in the northern Canadian Cordillera. Carbonate-hosted showings include the Gayna River deposits (G) and the Prairie Creek deposits (P). Zincllead showings in the "other" class are predomi nantly clastic-hosted (also known as "SEDEX"). Black box shows location of Figure 2-2. Projection is Universal Transverse Mercator (UTM), zone 9, using NAD83 datum. Chapter 2. Controls on mineralization in the Sekwi Formation stratigraphic control such that certain levels of the Sekwi Formation were preferentially mineralized, and whether there were lithological controls that caused specific rock types to become mineralized in preference to others. The results contributed to development of a deposit model, which will aid in the discovery of mineralization.

Previously published stratigraphic and metallogenic data from a number of government and industry reports were compiled and re-interpreted to improve understanding of stratigraphic controls. Three separate areas of the northern Mackenzie Mountains were studied in detail (Fig. 2-2). Logistical reasons contributed to the choice of areas. The three areas are spread along 130 km of strike-length, and each area encompasses three to ten Sekwi-Formation-hosted Zn±Pb showings. Some of these were discovered in the 1970s, others during 2006-2008. In the Palm area, the Main and Waterfall zones were examined; in the TIC area, the C and Ryan zones; and in the AB area, the AB Main, AB-C, Point, and Link showings. The approach in each area included detailed stratigraphy, petrography, and analytical work, but the scope and density of the work was greatest in the best-mineralized area, the AB area, where field work included property-scale mapping.

The field studies were supplemented by analyses designed to reveal the nature of the mineralizing fluids. Strontium isotopes gave indirect information on the depth at which fluids scavenged metals and Sr. Sulfur isotopes placed constraints on the sources of S and therefore the path of fluids, and carbon and oxygen isotopes shed light on the types of rocks the fluids interacted with. Fluid inclusion microthermometry supplied temperature, salinity, and density data for the mineralizing fluids. Together, these data constrained the deposit model.

29 Legend Quaternary & ice Neoproterozoic Wndermere • Cretaceous intrusions Supergroup Late Paleozoic mixed shetf 0i Early Neoproterozoic Mackenzie • Late Paleozoic basin Mountains Supergroup (siliciciastic inundation) Paleoproterozoic Wernecke Supergroup • Early Paleozoic Seiwyn Basin • Early Paleozoic Mackenzie Platform •• Sekwi Formation Border Studied area of Carbonate-hosted Fault cartonate-hosted ZrctPb showing Zn±Pb showings UTM projection, NAD83, Zone 9N

Yukon -

: Northwest Territories

Figure 2-2. Regional geological context of the studied areas. Geology from Gordey and Makepeace (2003) for the area south of 659N and west of 130^W; eastern strip is from Gordey et al. (2010a, b) and Roots et al. (2010), northern strip from Aitken et al. (1982). Chapter 2. Controls on mineralization in the Sekwi Formation

Geological Framework

Geology of the Mackenzie Mountains

The Mackenzie Mountains are part of a fold-and-thrust belt that forms the eastern edge of the northern Canadian Cordillera (Fig. 2-1). These mountains consist of early Neoproterozoic to Cretaceous sedimentary rocks, and subordinate igneous rocks (Fig. 2- 2), the bulk of which were deposited on the western margin of ancestral North America. The regional stratigraphic succession is described by Turner et al. (2011) and summarized in Figure 2-3, and as follows. Although Paleoproterozoic to Mesoproterozoic rocks of the Wernecke Supergroup (western side of Fig. 2-2; Thorkelson et al., 2005; Cook and Erdmer, 2005) may underlie the study area, the oldest exposed rocks are the early Neoproterozoic Mackenzie Mountains supergroup (MMSG). The MMSG is a mixed succession of carbonate and terrigenous clastic rocks deposited in an epicratonic basin (Long et al., 2008). The Windermere Supergroup, which overlies the MMSG, is also a mixed succession. It records continental rifting and development of a passive margin (Young, 1976; Eisbacher, 1981; Ross, 1991). This passive margin provided a stable tectonic base for the carbonate-dominated Mackenzie Platform, which endured for 150 m.y. from the latest Proterozoic until the Middle Devonian (Fritz et al., 1992). One of the earliest depositional elements of the platform was the carbonate-dominated Sekwi Formation (Handfield, 1968), host of the studied showings. This highly variable unit is described in more detail below.

West of the Mackenzie Platform, the Selwyn Basin was a major, deep-water, marine embayment that developed in Cambrian times in the western edge of North America and lasted until the Middle Devonian (Gabrielse, 1967; Gordey and Anderson, 1993). Beginning in the late Middle Devonian, tectonism and uplift to the north and west led to inundation of the platform and deposition of siliciclastic sediment across the former basin and platform (Gordey et al., 1992). Mixed siliciclastic and carbonate rocks of a Late Paleozoic shelf are preserved south of the studied showings. The entire package was uplifted and thrust northeastward (present-day directions) during Late Cretaceous to Tertiary orogeny, AGE TECTONO-STRATIGRAPHIC Zn-Pb IN PACKAGES CARBONATE UNITS NE SW MESO- Cretaceous

Permian mixed shelf

basin (siliciclastic inundation)

Selwyn Basin Silunan (SW), Mackenzie Oraovician Platform (NE) C //////

Windermere Supergroup (rift, \R«dMon«R| f passive margin)

Mackenzie Mountains supergroup (epicratonic basin) intrusive rocks # known Zn±Pb volcanic rocks showings evaporitic rocks I to (531"8 9-15 16-25 >26

Figure 2-3. The stratigraphic setting of the studied showings, left column shows the major tectono-stratigraphic packages of Fig. 2-2. Names are of units referred to in the text; all are formations except the Little Dal Group. Jagged lines show facies changes from SW (paleo- basin) to NE (paleo-land). White gaps indicate local depositional hiatuses. The right-hand column shows only the carbonate-dominated, formation-level units. The pattern indicates the number of showings hosted by that unit in a selected region of the Mackenzie Moun tains. Columns are modified from Gordey and Roots (2011). Chapter 2. Controls on mineralization in the Sekwi Formation

resulting in an arcuate, northwest-trending belt of largely unmetamorphosed rocks in northeast-verging folds and thrust slices (Gabrielse, 1992). Late Cretaceous orogenic plutons intrude the central and southern Mackenzie Mountains (Woodsworth et al., 1992).

The Sekwi Formation host unit

The Sekwi Formation is a lithologically diverse unit of limestone and dolostone with subordinate siliciclastic rock and geographically restricted volcanic rock. It forms narrow, northwest-trending belts in thrust slices along the western margin of the Mackenzie Mountains and the southeastern Selwyn Mountains (Figs. 2-1, 2-2). Fritz (1975, 1976, 1978, 1979a, b, 1981, 1992) measured 34 stratigraphic sections through the formation. The formation was described for specific areas by Gabrielse et al. (1973), Aitken et al. (1973, 1982), and Gordey and Anderson (1993). Three trilobite biozones for the Early Cambrian (Fallotaspis, Nevadella, and Bonnia-Olenellus) were established from Sekwi Formation specimens and correlated globally by Fritz (1972). The sedimentology and stratigraphy of the formation were described by Krause (1979) and Krause and Oldershaw (1978, 1979). Its lithofacies were interpreted in a sequence stratigraphic framework by Dilliard (2006) and Dilliard et al. (2010). Its carbon and oxygen chemostratigraphy was studied by Dilliard et al. (2007). A synthesis of available information on the Sekwi Formation was provided by Fischer and Pope (2011), and is summarized briefly below.

In the central Mackenzie Mountains, the Sekwi Formation is from 30 m thick in the east to over 1380 m in the west (toward the paleo-basin). It has been divided into three informal members for this study, based on its regional stratigraphy (Fig. 2-4). The Lower Carbonate member is dominated by deep-water facies and includes nodular, silty limestone, lime siltstone, shale, dark lime mudstone, thinly bedded dolostone, and local meter-scale carbonate turbidites and debrites attributed to syn-depositional faulting (Krause and Oldershaw, 1979; Dilliard et al., 2010). In shoreward sections, the Lower Carbonate member locally has a karsted upper contact. The Quartz-sandy member in the

33 Figure 2-4. Fence diagram of the Sekwi Formation in the northern and central Mackenzie Mountains. Composite sections are generalizations of previously measured stratigraphic sections (referenced on the figure). AB, TIC, and Palm sections are from this study (see text). Correlation of members is based on Fritz's (1976,1978,1979a) lithological correlations, which were guided by the assumption that the Nevadella - Bonnia-Olenellus biozone boundary remained within one lithological unit. Second-order sequence-stratigraphic units (SO, S1-S3, and S4-S6, colored fences) are from Dilliard (2006) for southern columns and have been tentatively projected to northern columns. Stratigraphic locations of ARN, TEE, Emily and Ice showings are from exploration assessment reports (Brock, 1973; Helmseadt and McGregor, 1974); ARN and TEE uncertainty is indicated by vertical bars. Simplified from Fischer and Pope (2011). Northwest Composite Hess River Fm. compiled from Fritz (1976) sections 1 & 2 and Krause (1979) Arctic Red River section

North Composite compiled from Fritz (1976) section 4, Fhtz (1979) section 31 and Krause (1979) Mountain River section transitional Rabbitkettle(?) Fm. Franklin Mountain Fm FM2 i

Cloudy(?) Fm Duo Lake(?) Fm Franklin Mountain Fm.

Sekwi Fm. Quartz arenite Thick-bedded fenestra! Mudcracked Mottled Backbone 0) Argillaceous Ranges Fm. Renalcis mounds P AB Area orange marker at base (this study) Legend ••limestone, thin to very thin bedded jfiHdolostone, (h'n to very thin bedded Sekwi Fm. Lower doiostone medium to thick bedded nodular limestone Carbonate member fiiiii I ilimstone breccia Nevadells wackestone/fioatstone Vampire Fm. Southeast packstone/njdstone Composite grainstone (compiled from dolograinstone shale or mudstone Fritz (1976) dolostone/dolorudstone. siltstone section 10 black to dark grey sandstone Krause (1979) •200 m Hess River Fm microbial boundstone/ calcareous June Lake doloboundstone dolomitic section, and oncoids quartz-rich dolostone / Dilliard (2006) oncoids in rudstone texture dolomitic sandstsone 100m section 10) ooids resistant ckslide(?) Fm skeletal recessive archeocyathans stromatolites karst fenestra) fabric xom mud cracks formation boundary chert member boundary (informal) vuggy member boundary (local, informal) & name sphalerite +/- galena correlation line & member boundary (local, informal) cemented breccia unconformity fault sequence name S6 Nevadella biozone boundary & name

Location Map130 128 W • measured stratigraphic section from previous work used to build composite section

°nnefpj stratigraphic section (measured or o composite) Sekwi Fm. Lower from this study, and Zn showing in Sekwi Fm Carbonate member • other Zn showing & ampire Fm stratigraphic g section in § Sekwi Fm compiled from Fntz (1976) section 7, Fritz (1978) section 25. Krause 300.000E 500.000E (1979) Ingta River section, and UTM z9 NAD83 South Composite Dilliard (2006) section 1 Chapter 2. Controls on mineralization in the Sekwi Formation

middle of the Sekwi Formation (Fritz 1976, 1978, 1979a) is a quartz-arenite marker unit in the west-central Mackenzie Mountains, but elsewhere is less distinctive and consists mainly of sandy dolostone with thinner intervals of dolomitic quartz arenite (Gabrielse et al., 1973; Fritz, 1981; Gordey and Anderson, 1993; this study). The Upper Carbonate member is dominated by variably dolomitized, shallow-water, subtidal to peritidal rock types, except in the northwestern Mackenzie Mountains (south of the AB area), where deeper-water lime siltstone and siltstone dominate, and in shoreward sections, where paleosols are common. Ooid, oncoid and intraclast grainstone and rudstone units are medium- to thick-bedded, and form resistant cliffs, whereas skeletal wackestone, packstone, and floatstone are thinner bedded and less resistant. Mottling, bioturbation, and terrigenous silt are common in this member.

The Sekwi Formation was deposited as a west-facing, mixed carbonate- siliciclastic ramp during the Early Cambrian marine transgression (Dilliard et al., 2010). It conformably overlies fine siliciclastic rocks of the Vampire and Backbone Ranges formations. South and west of the study area, it is overlain conformably by Middle Cambrian Hess Formation, whereas non-deposition and erosion in the study area have left younger units disconformably on top (Fig. 2-4; Fritz 1976, 1978, 1979a; Cecile, 1982; Gordey and Anderson, 1993).

A second-order sequence and six overlying third-order sequences were identified in the Sekwi Formation of the central Mackenzie Mountains by Dilliard (2006) and Dilliard et al. (2010). A thinly bedded, lithic arenite from the upper part of the Sekwi Formation was interpreted, based on 57 detrital zircon ages, to have been derived predominantly from erosion of MMSG rocks exposed along the Mackenzie arch, with an additional component derived from more-distal Mesoproterozoic sources in Labrador and the southeastern United States (Leslie, 2009).

Carbonate-hosted mineralization in the Mackenzie Mountains

A wide variety of mineralization types is present in the Mackenzie Mountains (Yukon Minfile, 2005; NORMIN, 2011 and references therein; Ootes et al., 2011), but by

36 Chapter 2. Controls on mineralization in the Sekwi Formation far the most common is the carbonate-hosted zinc-lead type, also known as Mississippi Valley type or MVT (Leach et al., 2005; Paradis et al., 2007). Showings of this type are concentrated in the northern and central Mackenzie Mountains (Fig. 2-1) and occur in almost every carbonate unit in the succession (Fig. 2-3), yet few of these showings have been drilled or studied in detail. The showings are generally enclosed by thoroughly dolomitized rocks that are vuggy, fractured, or brecciated. Ore minerals are sphalerite, smithsonite, hydrozincite, and galena. In some showings, there are subordinate carbonates and sulfates of lead, and carbonates, sulfides, and oxides of copper. Gangue minerals include ubiquitous dolomite, together with pyrite, marcasite, barite, calcite, fluorite, and quartz. Both space-filling and replacement textures are common, even in the same deposit. Most showings have an obvious spatial association with faults or fractures. At many showings, the mineralization is said to be stratabound as well, but lithologic and stratigraphic controls are not clear. Commodities of economic potential are zinc and lead; silver and copper are locally anomalous. A more detailed discussion is provided by Fischer (2011a).

A limited number of studies have directly addressed the origin of Mackenzie Mountains carbonate-hosted zinc showings (Macqueen, 1976; McLaren and Godwin, 1979; Godwin et al., 1982; Carriere and Sangster; 1999; Gleeson, 2006; Paradis, 2007; Wallace, 2009). Studies that focused primarily on fluid movement in the Mackenzie Mountains (Morrow et al., 1990; Morrow and Aulstead, 1995; Morris and Nesbitt, 1998) or on showings in the northern Rocky Mountains (Nelson et al., 2002; Paradis et al., 2006; and references therein) are also relevant.

Previous work in the AB, TIC and Palm areas

In the AB area (Figs. 2-2, 2-5), the Sekwi Formation contains three major zinc showings (AB-C, which is divided into upper and lower zones, Link 800 m to its northeast, and AB Main 3 km to its northwest), one major zinc showing in the overlying Franklin Mountain Formation (Dab), and a dozen or so subsidiary showings in both formations (including Point in the Sekwi Formation, 400 m southeast of AB-C). A channel sample at AB Main returned an average of 8.34% Zn over 5 m (Eagle Plains Legend Legend, continued Ordovician-Silurian Cloudyf?) Formation Members 2a & 2c; mottled dolostone, wackestone Ordovician-Silurian Duo Lake(?) Formation m Member 2b; ooid grainstone & dolograinstone Cambro-Ordovician Franklin Mountain Formation ijggj Member 1; vuggy dolostone Early Cambrian Sekwi Formation Proterozoic - Early Cambrian Backbone Ranges Formation Member 4; arenite, dolostone, wackestone^^^ . ., , , . Cemented breccia zone ^y Rock-matrix breccia zone Member 4g;ootd dolograinstone H Member 3; dolostone • Studied Zn±Pb showing Fault, thrust fault

HV Member 2/3/4; dolostone & limestone * Zn±Pb showing Location of photo in Fig. 8

132*20'W contours in feet ^132*16\^\ ^

Figure 2-5. Map of the AB area. Studied showings are the large, labeled stars. AB-C consists of upper and lower zones. Dab is a significant showing in Franklin Mountain Formation. Cemented breccias in dolostone of Sekwi and Franklin Mountain formations, and polymict rock-matrix breccia in the latter, describe a curvilinear trend that crosses the Cretaceous-Tertiary AB Fault. The axis of a paleo-valley in Sekwi Formation lies some where between Link and Point, where Sekwi members 3 and 4 are absent and Franklin Mountain Formation was deposited directly on member 2c. Locations of photos in Fig. 2-9 are marked a, b, c, and d. Modified from Fischer et al. (2010). Chapter 2. Controls on mineralization in the Sekwi Formation

Resources Ltd., 2009). Grab samples selected from the best mineralization along roughly 4 m of strike length at AB-C averaged 12.6% Zn (McArthur and McArthur, 1977).

The TIC C, D, and E zones were discovered in 1974 within an area of 1.8 km2. Trenches were opened 200 m south of the C zone, probably because the ground was too steep at the zone itself. Assays from the trenches were generally poor, but included an average of 0.5 % Zn and 5.4 % Pb for a 4.5-meter channel sample (Ronning, 1975). Drill holes intersected isolated, short intervals of mineralization.

The Palm showings consist of the Waterfall zone and, 350 m to the north- northwest, the Main zone. These were discovered in 1975, when a grab sample of the Waterfall zone returned an assay of 6.8 % Zn and a chip sample of the Main zone yielded 3.3 % Zn over 20 m (Yeager et al, 1976).

Terminology

The terminology of Dunham (1962), as modified by Embry and Klovan (1971), is used to describe carbonate rocks. The modifiers "argillaceous", "silty", and "sandy" refer to the presence in a carbonate rock of terrigenous mud, silt, and sand, respectively. Coarse fragmental rocks are named according to the breccia classification of Morrow (1982). "Mottled" carbonate rock is characterized by centimeter-scale, irregularly shaped but grossly equant, diffusely bordered domains defined by variations in crystal size, color, and/or mineralogy, including siliciclastic and organic content. Mottling is typically more evident on weathered surfaces. Micropores are pores that are visible with a microscope, but not easily with the unaided eye.

Showing and occurrence both refer to an anomalous concentration of an element of economic interest. The word dolostone is used for rock composed of the mineral dolomite, despite the priority of the word dolomite, because of the inherent value of a clear distinction between mineral and rock. Abbreviations used in this report and pertaining to the fluid inclusion study are summarized in Appendix H.

39 Chapter 2. Controls on mineralization in the Sekwi Formation

Methods

Field and petrographic studies

A 90-m-thick section was measured through the strata hosting the AB Main showing (Appendix B), and 38 km2 were mapped around the AB group of showings at 1:20,000 scale (Appendix C). Detailed observations were made of the AB Main, AB-C (upper and lower), Link, and Point showings (Fig. 2-5). Mineralized samples were collected for petrography, fluid inclusion studies, and isotopic analyses from all of these except Link.

In the TIC area, four stratigraphic sections were measured (Appendix B), and the C and Ryan zones were sampled. The Ryan zone, 400 m south-southwest of the C zone, is not mentioned in the report on earlier work (Ronning, 1975). Sections measured in 1975 (Ronning, 1975) were used to verify interpolations between sections measured in this study. In the Palm area, one stratigraphic section was measured through the Palm Main zone (Appendix B). The stratigraphy at both the Waterfall and Main zones was examined and mineralized rocks were sampled.

Thin sections, polished thin sections, and doubly polished thick sections of rock samples were examined with a petrographic microscope. Many thin sections were stained with a mixture of potassium ferricyanide and Alizarin red-S (as per Miller, 1988) to differentiate calcite, dolomite, and ferroan species of each. The cathodoluminescence of selected sections was examined under a petrographic microscope attached to a Nuclide Luminoscope.

Metallogenic compilation

In order to address the question of whether the Sekwi Formation is indeed a preferred host of mineralization over other units in the succession, the available database of mineral showings and publicly available references (NORMIN, 2011 and references therein) was examined for a restricted area. The regions bounded by 128° and 132°W, 64°

40 Chapter 2. Controls on mineralization in the Sekwi Formation and 65°N, and by 128° andl30°W, 63° and 64°N, were selected because of the availability of recently updated geology maps (Martel et al., 201 la). This region includes two of the studied areas (Fig. 2-2), but most of the showings documented in the database were not visited. Carbonate-hosted Zn-Pb showings were identified from the descriptive data and assigned a host formation. Although the descriptions of many showings n the NORMIN database are limited, the approximate stratigraphic level is usually well-identified, so host-unit assignments are reasonably confident.

Stratigraphic correlation

In order to determine whether mineralization was restricted to any specific stratigraphic level in the Sekwi Formation, data were acquired from all stratigraphic sections previously measured through the entire formation. Four areas were chosen to represent paleo-basinward and paleo-landward depositional positions along the nascent paleo-shelf: two in the north near the studied showings, and two in the south. The southern areas were included because of the recent sequence-stratigraphic work there (Dilliard, 2006; Dilliard et al., 2010). To highlight regional patterns, data from two to four previously measured sections in each area were compiled and re-drafted into one, generalized, composite stratigraphic column per area (Fig. 2-4). The South and Northwest composite columns represent basinward deposition and the Southeast and Northeast represent near-shore environments. The Northeast composite column is representative of the Sekwi Formation near the TIC and Palm showings. The Northwest composite column is some distance south of the AB area and therefore has a more basinal character.

For each of the studied areas, a stratigraphic column through the mineralized interval was created from data acquired during this project. The column for the Palm area is a measured section, that for the TIC area is a composite of four measured sections, and that for the AB area is derived from mapping. In addition, detailed stratigraphic columns have been published in exploration reports for four other groups of showings hosted by Sekwi Formation (Helmsteadt and McGregor, 1974). Lithofacies correlation between the detailed columns for each showing area and the composite columns created from regional data allowed each showing area to be located accurately within the three-member

41 Chapter 2. Controls on mineralization in the Sekwi Formation stratigraphic framework already developed for the Sekwi Formation (Fischer and Pope,

2011).

Correlation of depositional events is more dependable if sequence-stratigraphic boundaries are used, as opposed to lithofacies boundaries, since, in marine carbonate environments, the frequency of lateral changes in lithofacies ensures that lithofacies boundaries are generally diachronous. For this reason, the second-order stratigraphic sequences identified in the vicinity of the South and Southeast composite columns (Dilliard, 2006; Dilliard et al., 2010) were extended to the Northeast and Northwest composite columns, primarily on the basis of sedimentological data (Fig. 2-4; Krause, 1979).

Fluid inclusion studies

Samples for fluid inclusion analysis were collected from coarse-grained sphalerite and associated cement phases at the AB Main showing, the upper zone of the AB-C showing, the Point showing, the TIC C and Ryan showings, and the Palm Main showing. Thirty-seven doubly polished, 100 micron-thick sections from these samples were studied for fluid inclusion assemblages (FIAs), which are groups of co-genetic, petrographically associated inclusions (Goldstein and Reynolds, 1994).

During initial petrographic observations, fluid inclusion assemblages (FIAs) were identified and classified according to the criteria of Goldstein and Reynolds (1994). The FIAs were designated primary if they were parallel to or defined a growth zone, or were confined to the core of the host crystal, and secondary if they defined planar or curvilinear arrays that terminated at the crystal edge. FIAs were classified as pseudosecondary if they were planar or curvilinear arrays that terminated at a growth zone inside the crystal. If each end terminated in a different growth zone, or if one end terminated at the broken edge of the chip, the FIA was classified as "secondary or pseudosecondary". If a FIA was not extensive enough to define a growth zone, but defined a small plane parallel to crystal edges or growth zones, or a tight cluster unrelated to fractures, it was classified as "primary or pseudosecondary".

42 Chapter 2. Controls on mineralization in the Sekwi Formation

Following initial petrographic observations, thick sections containing suitable FIAs were removed from the glass slide and broken into chips that would fit into the microthermometry stage, which was a Linkam THMSG 600 stage attached to a petrographic microscope. A Linkam TP93 control unit attached to the stage regulated the flow of heated and cooled air across the chip to raise and lower its temperature, which was recorded by a thermocouple sensor on the stage and displayed on the control unit. Phase changes in the heated or cooled inclusions were observed through the microscope ocular. Before microthermometry sessions, the control unit was calibrated against the triple point and critical point of H2O and the critical point of CO2 using fluid inclusion standards. The machine precision was estimated at ±0.1°C by re-checking the critical point and triple point of standards during the course of the experiments. Repeatability of better than ±0.1°C was obtained from repeated measurements of the standards after calibration and before experimental runs.

Heating experiments were undertaken on 158 inclusions from 27 FIAs. From these, homogenization temperatures (Th) were determined for 86 inclusions, and minimum Th (discussed below) were obtained for a further 47 inclusions. After consistency criteria (below) were applied, Th from 34 inclusions in seven FIAs and minimum Th from 22 inclusions in 5 FIAs were deemed valid. Freezing experiments were undertaken on 49 inclusions in 18 FIAs. Of these, 33 inclusions in 18 FIAs yielded salinity data and estimates of NaCl and CaC^/MgCb content.

Four fluid-inclusion chips from the TIC area were chosen for their abundance of primary FIAs to be analyzed by SEM-EDS (scanning electron microscope - energy- dispersive spectrometer). The chips were heated until the inclusions decrepitated, creating evaporate deposits around the emptied vacuoles. The analyses provided a semi quantitative composition of the solute component of the bulk fluid inclusions on each chip, and assisted in the choice of an appropriate model composition for interpreting fluid chemistry (Appendix E).

43 Chapter 2. Controls on mineralization in the Sekwi Formation

Isotopic studies

Samples from each showing area were selected for mineral isotopic analyses. The samples were hand-crushed and mineral grains picked with the aid of a binocular microscope. Sphalerite was prepared from seven samples from the AB area, four from the TIC area, and two from the Palm area, whereas galena and pyrite were separated from one sample from the TIC area. Secondary, void-filling dolomite was obtained from one sample from each area, and barite from two samples from the AB area. Individual grains were analyzed, and so the analytical results are biased by small-scale variations in composition, and the range of compositions is under-represented (Schaefer et al., 2004). Analytical methods are described in Appendix (1). All data are expressed in the customary notations of 5 and per mil (%o) and referenced to the international standards of VSMOW for 81S0, VCDT for 534S, and VPDB for 5I3C.

Sulphur isotopic compositions (§34S) were obtained for all 13 samples of sphalerite, the galena and pyrite from TIC, and the two barite samples from AB. Oxygen isotopic compositions were obtained for the barite, and oxygen and carbon for the dolomite from each showing area. Strontium isotopes were analyzed in eight samples of sphalerite (four from the AB area, three from TIC, and one from Palm), the dolomite from each showing area, and the barite from the AB area.

Geological Studies: Results and Interpretation

Major characteristics of the showings in each area are summarized in Table 2-1. Petrographic characteristics of sphalerite at each showing are described in Table 2-2. Petrographic characteristics of other secondary minerals at each showing are described in Appendix A.

Metallogenic compilation

The results of the regional metallogenic compilation are summarized in Figure 2- 3, where the number of known Zn±Pb showings in each formation, within the restricted

44 Host Showing Host rock member1 Ore Gangue2 Style Characteristics AB Main Argillaceous, laminated to mottled, 2a Sphalerite Dolomite, barite, Dissolution Sphalerite fills cm-scale breccia voids and mm-scale peloid-skeletal-ooid-intraclast pyrite breccia cement, fractures Sphalerite fills microporosity in the dolopackstone to wackestone; microporosity matrices of oolite and debrite, and is concentrated minor intraclast dolorudstone fill, adjacent to dark, organic?-rich seams and in strata- (debrite) (replacement) parallel layers

AB-C& Ooid (-oncoid-intraclast) 2b; also 2a Sphalerite, Dolomite, barite, Dilational (& Sphalerite fills cm-scale breccia voids and mm-scale Link dolograinstone; minor silty, at AB-C (galena) pyrite/marcasite, dissolution) fractures. In grainstone, sphalerite fills inter-ooid mottled, locally laminated lower zone (quartz, calcite, breccia cement, porosity, replaces the dolomitized ooid matrix, is dolostone pyrobitumen) microporosity concentrated in mm-scale, strata-parallel layers, and fill, replacement rarely, fills vein-adjacent ooid molds. In mottled dolostone, sphalerite is concentrated in organic?- rich, anastomosing seams. AB Point Burrowed, organic?-rich dolostone 2a Sphalerite Dolomite, quartz, Void-fill Sphalerite fills cm-scale vugs, and fills mm-scale with up to 25% detrital quartz pyrobitumen, voids in 1-2 cm sandy burrows (pyrite) TICC Oncoid dolorudstone; ooid- Darkl Sphalerite, Dolomite, quartz, Dissolution Sphalerite and galena fill cm-scale voids in breccia. intraclast-(skeletal) dolograinstone; galena pyrite/marcasite, breccia cement Galena has curved crystal faces fine to medium crystalline calcite. Possible dolostone, locally with ghost barite cortical grains and laminations

TIC Ryan Intraclast dolofloatstone; ooid- Dark2 Sphalerite, Dolomite, calcite, Dissolution Sphalerite and galena fill cm-scale voids in breccia intraclast dolograinstone; packstone galena pyrite/marcasite, breccia cement and grainstone with skeletal, quartz intraclast, and cortical grains Palm Main Mottled dolomudstone grading into Mottled Sphalerite Dolomite, quartz, Dissolution Sphalerite fills cm-scale breccia voids and mm-scale peloid (-skeletal) dolograinstone pyrite breccia cement fractures Palm Fenestral dolostone Fenestral Sphalerite Dolomite, pyrite Fenestral void- Sphalerite fills mm-scale fenestral voids Waterfall fill '• • •I.ll.l.ll. I Jl 11 •I• •I I .1.1111.1 informal gangue minerals other than matrix dolomite Table 2-1. Major characteristics of the studied showings. Enclosure within brackets indicates features that are local or minor. AB Main Color and pleochroism In lOO^m section: colorless with clear yellow/orange rims Growth zoning None Isotropy In 100|im section: anisotropic grey with discontinuous blue streaks in irregular, tartan-like and lamellar patterns; and nearly colorless with anisotropic brown twin lamellae Reflectance color Light grey Twinning Lamellar or discontinuous, sub-parallel lamellar-like (rarely irregular tartan-like) patterns: twins? Habit Anhedral, very fine to very coarse Solid inclusions Occasional dolomite rhombs 30|im Fluid inclusions1 Most are very highly irregular in shape, very dark, concentrated along cleavage planes, and possibly naturally decrepitated. Some are s2|um, dark, aqueous LV with low V (~2%). Some secondary, light monophase and 2-phase inclusions are present along cleavages Cathodoluminescence Dull reddish to purplish brown. Patches of bright blue, rare moderately bright yellow patches Other Brecciated crystal fragments within larger crystals; fragments are clear with less inclusions and have twins at different orientation than surrounding crystal AB-C upper zone Color and pleochroism In 100|im section: colorless to turbid brown. Rims are locally deep yellow. In 30n: medium brown Growth zoning Delicate 0.05- 0.4 mm colloform banding in shades of grey and brown. Wider, brown or yellow growth zones are rare. Colors refer to lOOum section Isotropy in lOO^m section: anisotropic grey with discontinuous blue streaks in irregular, tartan-like and lamellar patterns; local brown to black anisotropy; locally in isotropic view. In 30i*m section: black, nearly isotropic (twin planes change color) Reflectance color Light grey Twinning Lamellar or discontinuous, sub-parallel lamellar-like, and irregular tartan-like patterns may be twins. Also chevron deformation twins Habit Anhedral, very fine to very coarse. Spherical and banded aggregates of microcrystals Solid inclusions <1 to lOOum, irregularly shaped. Few dolomite rhombs 8(im Fluid inclusions1 Most inclusions are submicroscopic. Rare 2-12nm aqueous LV inclusions with low V, rare monophase inclusions. Dark to medium, some too dark to see into. Rounded or slightly angular, mostly equant to slightly elongate. Small, isolated pseudosecondary planes entirely within single grains of late sphalerite. Secondary groups of 2-3 dozen dark, 2-10nm inclusions related to fractures. Cathodoluminescence Moderately dull reddish brown with brighter yellowish red core and very bright blue to white patches on the rims. Locally the bright blue occupies the core. Local thin rim of bright orange is caused by alteration Other Brecciated crystal fragments served as nuclei for continued crystal growth; fragments are clear with less inclusions and have twins at different orientation than surrounding crystal AB-C lower zone Color and pleochroism In 30|im unpolished section: grey with golden brown rims Isotropy In 30|im unpolished section: anisotropic grey and yellowish grey Habit Anhedral, very fine to very coarse Growth zoning, reflectance, twinning, inclusions and cathodoluminescence were not studied.

Table 2-2. Petrographic and hand-specimen characteristics of sphalerite at the studied showings (part 1 of 3). AB Point Color and pleochroism In lOOpim section: colorless with deep yellow rims, to deep orange. In 30(im section: medium-light brown Growth zoning Well-defined, deep orange bands in larger crystals in 100|im section. Some zones defined by fluid inclusions Isotropy In 100|im section: Isotropic along c-axis; anisotropic blue-grey and grey in lamellar patterns in other orientations. In 30|im section: isotropic Reflectance color Unusual greyish white with caramel internal reflections Twinning Rare lamellar twins Habit Anhedral, very fine to megacrystalline Solid inclusions Few dolomite rhombs 8|im, rare chalcopyrite blebs 5-20(i Fluid inclusions1 Type 1: Very dark to light.

Table 2-2. (continued, part 2 of 3) TIC, Fluid inclusions1 (continued) Type 2: Very rare. Light brown petroleum? inclusions with small, dark brown V (<5%), commonly flat-looking. Show evidence of necking, both prior to and after separation of a vapor phase during geological cooling. Present as pseudosecondary or secondary FIAs associated with pseudosecondary or secondary planes of very dark Type 1. Cathodoluminescence Dull brown Other Planes of dense chalcopyrite blebs ("chalcopyrite disease"); blebs are 5-20 microns and locally define growth zones or seem to emanate from fractures Palm Color and pleochroism In 100|im section: light to deep yellow, except fenestral form at the Waterfall zone is medium golden brown Growth zoning Rare colloform banding in shades of grey Isotropy In 100|im section: anisotropic grey and brown in irregular, tartan-like pattern. Fenestral form is isotropic Reflectance color Light grey, locally with amber internal reflections Twinning None visible Habit Anhedral, very fine to coarse. Spherical colloform aggregates of sub-microscopic crystals Solid inclusions Opaque, non-reflective, organic? inclusions Fluid inclusions1 Type 1: Most inclusions are submicroscopic. Rare, very dark, aqueous LV inclusions,

1 LV refers to two-phase, liquid-vapor inclusions. V refers to the apparent volume of the vapor bubble as a percentage of inclusion volume. FIA stands for fluid inclusion assemblage.

Table 2-2. (continued, part 3 of 3) Chapter 2. Controls on mineralization in the Sekwi Formation area, is indicated. The Sekwi Formation contains 26 confirmed showings, which is more than any other unit. Three other stratigraphic levels are preferentially mineralized. These are the Neoproterozoic Little Dal Group, which contains 19 known showings (most of these are in one area, and are collectively known as the Gayna River deposit); the Ordovician-Silurian Mount Kindle Formation, which hosts 14-16 showings; and the combined Arnica and Landry formations, which host 18-25 showings.

Stratigraphic correlation

The correlations that evolved from the regional stratigraphic compilation are shown in Figure 2-4. The host rocks in the Palm, TIC, and AB areas all belong to the Upper Carbonate member of the Sekwi Formation, but they were deposited during different sequences (see Methods, Stratigraphic correlation). The AB showings are near the middle of the SI-3 sequence, the Palm showings are near the top of SI-3, and the TIC showings are within S4-6. The ICE group of showings is in the Lower Carbonate member and the SO sequence. Other groups are at various levels of the Upper Carbonate member (Fig. 2-4), in sequence SI-3 and possibly S4-6. There is no clear restriction of showings to any one member or sequence, although there appears to be a preference for the Upper Carbonate over the Lower Carbonate member, and for the higher sequences (above SO).

AB showings

Geology: A generalized geology map of the AB area (Fig. 2-5) shows the locations of the studied showings. Stratigraphy and structure of the area are discussed elsewhere by Fischer et al. (2010). The oldest unit is the quartzite-dominated Backbone Ranges Formation. The overlying Sekwi Formation has been divided into informal members named 1, 2a, 2b, 2c, 3, and 4, from base to top (Table 2-3). Overlying the Sekwi Formation are the following: dolostone of the Cambro-Ordovician Franklin Mountain Formation (Norford and Macqueen, 1975), black shale and thinly bedded carbonate rock assigned to the Ordovician-Silurian Duo Lake Formation (Cecile, 1982), and thinly

49 Thick- Mineral Mbr. ness Description ization TOP 4 110- Ranges from 110 m near AB Main to 250 m thick near AB-C. Consists primarily of None 250 m very thinly to medium-bedded sandy dolostone, quartz arenite, and skeletal carbonate rocks, but contains a wide variety of subordinate rock types: ooid grainstone, intraclast rudstone, oncoid-skeletal floatstone, all of these dolomitized; silty dolostone, microbially laminated dolostone, and argillaceous limestone. Parallel laminations, current ripples, and very low-angle cross-laminations are common in quartz-rich beds. Normal grading occurs locally in skeletal beds. Horizontal burrows are common. Skeletal components are trilobites, brachiopods, ovoid clasts of microbial clots, and, in a possibly correlative interval, Salterella. A dolomitized ooid grainstone occurs near the top of member 4. Variably dolomitized

3 ~10-70 About 70 m thick in the vicinity of AB-C, where it consists of three intervals of The cross- m resistant, buff-weathering, finely crystalline, finely vuggy dolostone separated by stratified recessive intervals of dark grey, mottled dolostone. The lowest cliff-forming interval interval hosts is cross-bedded and cross-laminated, with angles between cross-strata and set traces of boundaries ranging from 5 to 20 degrees. At AB Main, the lowermost cross-bedded sphalerite at interval lies directly on member 2b, and the upper part of member 3 is missing. Rare one locality ghost allochems in the upper two cliffs are suggestive of oncoids and intraclasts. Pervasively dolomitized 2c 0-70 m 50-70 m thick near the AB-C showing but absent at the AB Main showing. Orange- A few minor weathering, burrowed and bioturbated, skeletal packstone to floatstone; zinc subordinate dark, mottled, argillaceous and silty dolostone; some microcrystalline occurrences mud(-skeletal) bioherms at the base. Skeletal components are trilobites, brachiopods, Archeocyathans, and ovoid clasts of microbial clots. Variably dolomitized 2b 0-50 m An ooid (-oncoid ± skeletal ± peloid) grainstone to packstone, and locally an oncoid Significant rudstone with a grainstone matrix, that forms a prominent, 50 m high cliff in the mineralization vicinity of the AB-C showing but thins southward, where it has a muddier matrix, (AB-C upper thins westward toward AB Main, and disappears altogether to the southwest. zone and Link) Skeletal components are trilobites, brachiopods, and ovoid clasts of microbial clots. Variably dolomitized. 2a 40 m Dark grey, argillaceous to silty, organic matter-rich, laminated to mottled limestone, Significant variably dolomitized, that contains local intervals of skeletal wackestone, and mineralization isolated lenses of ooid grainstone and oncoid-intraclast floatstone. Near AB Main, (AB Main and this member contains a 20-m interval of intraclast dolorudstone interpreted as a AB-C lower debrite, and near AB-C, a possible tempestite. Skeletal components are trilobites zone) and brachiopods 1 >5 m Buff-weathering, finely crystalline, vuggy dolostone. Local ghost laminations. Rare Very fine, zebra fabric sparsely disseminated sphalerite and galena at one locality BASE Table 2-3. Informal members of the Sekwi Formation in the AB area. For depositional environments and other stratigraphic details, see Appendix C. Mbr = member. Chapter 2. Controls on mineralization in the Sekwi Formation

51 Chapter 2. Controls on mineralization in the Sekwi Formation bedded limestone with abundant secondary black chert tentatively correlated with the Silurian Cloudy Formation (Cecile, 1982).

The bulk of the mineralization in the Sekwi Formation is hosted by members 2a and 2b (Tables 2-2, 2-3). In the laminated variant of member 2a, laminations are defined by concentrations of dark, organic? matter and sphalerite. In the mottled variant, mottles are richer in terrigenous silt, more coarsely crystalline, and lighter gray than the surrounding millimeter-scale, anastomosing seams that contain sphalerite and dark, organic? matter.

Simple, unbranched, millimetric burrows in member 2a are locally highlighted by bleached alteration halos, suggesting that burrows served as porous fluid conduits. Higher in the stratigraphic section, the same rock types as in members 2a and 2b are not mineralized. These include the dark, mottled dolostone of member 2c and a 10 m-thick ooid dolograinstone near the top of member 4.

The structural character of the AB area is dominated by faults. Strata are subhorizontal, except near the major faults where there are tight, footwall folds. Two major, east-striking, contractional faults cross the area, the AB Fault and Fault 2 (Fig. 2- 5). Regional tectonic considerations identify these faults with Late Cretaceous to Tertiary transpression (Aitken et al., 1982; McMechan et al., 1992). Fault 2 brings Backbone Ranges Formation northward, up against the Sekwi and Franklin Mountain formations. The AB Fault brings Sekwi and Franklin Mountain formations up against the Duo Lake(?) and Cloudy(?) formations. These are underlain by Franklin Mountain Formation, which is exposed in all the low-lying areas north of AB Fault, and Sekwi Formation, which is exposed in a riverbed north of the mapped area. The AB Fault and Fault 2 are continuous for over 20 km in the AB area. Most of the showings in the Franklin Mountain Formation are north of the AB Fault, whereas all of the showings in the Sekwi Formation are between the two faults. The AB Fault can be traced southeastward through stepped discontinuities as far as the Palm showings, a distance of over 130 km (Fig. 2-2).

The area between the regional reverse faults, where the Sekwi-hosted showings lie, is intensely faulted at all scales by steep to moderately dipping faults with normal,

52 Chapter 2. Controls on mineralization in the Sekwi Formation reverse, and unknown sense. In the absence of a structural study, it is assumed that most of these formed during transfer of strain between the regional faults, but at least one shallow fault with normal displacement (Fault 8, Appendix C) is better explained as a post- or mid-thrusting relaxation feature. Sub-horizontal faults represented by gouge and subtle stratal offsets are present at both the AB Main and AB-C showings, and are probably the same general age as the regional-scale thrusts. The mineralized breccia at the AB-C showing (upper zone) occupies the intersection of three steep faults or goassanous planes, one of which passes through the lower zone as well. The AB Main showing terminates upward against a small fault and lies between two larger faults. The Link and Point showings lie within 150 m of major faults.

Each informal member of Sekwi Formation is significantly thicker in the AB-C area than to the west in the AB Main area (Table 2-3), which indicates that Sekwi sediments were deposited into a topographic low in the AB-C area. This depression may have been a relict of earlier faulting. Faulting has been demonstrated to have occurred during deposition of the Lower Carbonate member in NTS 105P (Dilliard et al., 2010). Stratigraphic relations also reveal erosion or non-deposition of Sekwi Formation between the area around Link and Point, where Franklin Mountain Formation lies directly on member 2c, and southwest of Point where Franklin Mountain Formation lies on member 3 (Fig. 2-5). Up to 330 m of strata are missing that are present at AB-C. This area may have been a topographic high during deposition of members 3 and 4, or it was subsequently uplifted along a steep fault and eroded. The Franklin Mountain Formation above the Link showing is also unusually thin, suggesting that the area remained elevated above its surroundings during Franklin Mountain deposition. The concentration of mineralization near the edge of the paleo-depression is suggestive of a genetic link.

Dolomitization: A laterally extensive, pervasive, fabric-destructive dolomitization (herein called pervasive-destructive) is constrained by primary layering to members 1 and 3, which consist of coarse dolostone that retains almost no evidence of sedimentary fabric. In members 2 and 4, a laterally extensive, partial dolomitization is selective of either the grain component or the matrix (incomplete-retentive type). Member 2 is dolomitized pervasively in proximity to mineralization, but its primary fabric is retained

53 Chapter 2. Controls on mineralization in the Sekwi Formation by allochem ghosts (pervasive- retentive type). The pervasive-retentive and incomplete- retentive types of dolomite are present in two modes, replacive and void-filling. The void-filling variants do not preserve fabric but are co-genetic with the replacive types. The pervasive-retentive and incomplete-retentive types of dolomite replace allochems such as ooids, replace the calcite cement between allochems, or fill voids including matrix micropores, dissolved-grain molds, and macro-voids. Petrographic textures reveal that a microscopic porosity developed during dolomitization, and was subsequently occluded by sphalerite or dolomite.

Pervasive-retentive dolomite is mildly ferroan to non-ferroan. It replaces the matrix and grains of allochem-bearing rocks, and forms interlocking, very fine to fine anhedral crystals with curved or irregular interfaces, though local variants are planar- faced. It is characterized by a brown color that arises from abundant inter- and intracrystalline, non-reflective matter (organic matter, clay, or submicroscopic grains of sulfide minerals). Euhedra of replacive dolomite commonly penetrate solution seams; there are no examples of partly dissolved euhedra adjacent to solution seams. The void- filling variant of pervasive-retentive dolomite fills breccia voids and veins (see next section). It ranges from finely to very coarsely crystalline, is free of intracrystalline dark matter, and is colorless, although turbid with an abundance of fluid inclusions. It forms optically continuous overgrowths on replacive variants of the same type (Fig. 2-6A). The void-filling variant is commonly saddle dolomite with classic undulatory extinction, curved cleavages, and spearhead-shaped crystal terminations (Radke and Mathis, 1980). It has a duller cathodoluminescence than the bright orange of the matrix-replacive variant. Veinlets of the void-filling variant are continuous across solution seams.

Mineralization at theAB Main. AB-C. and Link showings: The AB Main showing in Sekwi member 2a (Table 2-3) is poorly exposed on a talus-covered hillside, but is at least 5 m wide and 20 m long. Mineralization consists of disseminated sphalerite, and sphalerite-cemented rubble floatbreccia with extensive dissolution of host fragments. The AB-C showing, 3 km to the east of the Main showing, consists of lower and upper zones. The lower zone of disseminated to semi-massive sphalerite is largely hosted by Sekwi member 2a, extending into member 2b. It occupies a restricted strike-length (<20 m)

54 Figure 2-6. Textures of mineralized rocks in the AB area. PPL = plane polarized light, RL = reflected light, XPL = cross-polarized light. Dol = dolomite, dst = dolostone, Sp = sphalerite. A) Limpid, coarse, void-filling dolomite and cloudy, fine to medium, replacive dolo mite, both PR-type. Individual crystals of replacive dolomite grew into the void without visible breaks, and have cloudy brown bases and clear tops (circled). Such textures suggest that host replacement and void filling were not separated widely in time and derived from the same fluid flow event. AB Main showing. Unpolished 30- pim section. PPL. B) Spheroidal, gray sphalerite (Sp) and coarse, orange dolomite (Dol) fill a void between dark gray fragments of dolograinstone (dst). AB-C showing, upper zone. Outcrop photo. Scale in millimeters. C) Delicate growth-banding in a sphalerite spheroid that nucleated on a triangular fragment of earlier, brecciated sphalerite. Just outside the field of view are cracks in the banded sphalerite that are sealed by a third phase of sphalerite. AB-C showing, upper zone. 100-|im doubly polished section. PPL. D) Same view as C, with crossed polars. Blue anisotropy in tartan and lamellar patterns in micro-brecciated sphalerite. AB-C showing, upper zone. 100-nm doubly polished section. XPL. Chapter 2. Controls on mineralization in the Sekwi Formation within a poorly exposed, vertical stratigraphic interval of about 15 m. The upper zone in member 2b is a sphaleritic cemented breccia presenting a continuum of fabrics from fitted, angular crackle breccia with dilational textures, to rubble floatbreccia with dissolution textures. The upper zone can be traced 50 m along strike, 40 m across strike, and through approximately 25 m of stratigraphic thickness, but the consistency of grade within that volume is largely unknown. The Link showing, also in member 2b, is virtually identical in style to the AB-C upper zone, except that it preserves an earlier or more distal phase of the brecciation-precipitation process, showing that fluids invaded initially along bedding planes, then later across the beds. The Link showing is exposed for about 20 m along strike and 10 m across strike.

Mineralization in the AB area can be categorized into two intergradational styles. The breccia style predominates whereas the intact-host style is subordinate, except in the lower zone at AB-C where the breccia style is absent. In the breccia style, macroscopic voids are cemented by varying proportions of marcasite/pyrite, sphalerite, dolomite, barite, quartz, and calcite. Breccias range from crackle to rubble breccias, with fragments that are angular to well-rounded. A progression of textures exists from fitted-fabric to dissolution. The cement phases are normally blocky, indicating growth in open spaces, but locally are fibrous or bladed perpendicular to cavity walls, from growth during incremental opening of the cavities. Pyrite/marcasite is the earliest significant void-filling phase. It forms decimetric veins and masses, randomly oriented blades, and cockscomb rims of twinned crystals up to 2 cm long that grew directly on the host dolostone or on a microscopic rim of intervening dolomite. Marcasite is identified solely by its habit and may have reverted to pyrite. These thick masses are absent and only thin rinds of pyrite are present where sphalerite has precipitated. Pyrite is concentrated at the edges of breccia fragments, and also lines re-brecciated fragments of older sulfides. Rarely, pyrite has a colloform habit.

Sphalerite of the breccia style of mineralization is pale yellow to yellowish green with thin red rims and is commonly emphasized on weathered surfaces by chalky white alteration. A pale gray color typifies weathered sphalerite in the upper zone at AB-C. Sphalerite in the breccias commonly forms microcrystalline spheroids and hemispheroids

56 Chapter 2. Controls on mineralization in the Sekwi Formation

(Fig. 2-6B) that have locally coalesced into bands up to 2 cm thick. Spheroids and bands are delicately growth-banded (Table 2-2; Fig. 2-6C, D).

Coarsely crystalline dolomite and barite occupy the central zones of breccia voids. Dolomite commonly shares boundaries with sphalerite crystals, and the two minerals have an overlapping paragenesis. Barite typically assumes a bladed habit in radial aggregates, but also forms fibrous rims on micropores. Macroscopic sphalerite hemispheres and microscopic dolomite rhombs nucleated on barite blades, the edges of which are deeply corroded and replaced by both sphalerite and dolomite. At AB-C, barite also fills the centers of voids lined by sphalerite, which indicates overlapping precipitation of sphalerite and barite in the AB area.

Sphalerite, marcasite, and barite have been re-brecciated and sealed by later generations of sulfide (Fig. 2-6C, D) and dolomite. Pyrobitumen is a minor vug phase in the AB-C and Point areas. Rare quartz forms colorless, translucent, euhedral prisms up to 2 cm long. Microscopic quartz growth zones locally mimic the shapes of adjacent sphalerite crystals, indicating that the quartz nucleated on the sphalerite. Sub-grain development in quartz reflects post-precipitation strain at AB Main. Coarse, white calcite is a rare phase at AB-C and was not sampled. A post-brecciation dolomite phase occupies veins that cut the mineralization at all of the showings.

The non-breccia, intact-host style of mineralization consists of disseminated to semi-massive sphalerite and pyrite. Sphalerite (Table 2-2) is fine- to coarse-grained and pale greenish yellow. In mottled dolostone of member 2a, sphalerite fills cavities between rounded grains of quartz silt and sand, and other microscopic voids, and locally has expanded outward from these centers by replacement of dolomite. In debrite, sphalerite is present preferentially in the dolostone matrix between clasts. Sphalerite in member 2b fills micropores in the inter-ooid matrix and locally replaces the matrix and dolomitized ooids (Fig. 2-7A, B).

Pyrite is abundant in the intact-host style of mineralization, in the lower zone at AB-C and the lower parts of AB Main. It fills hairline fractures, forms aggregates, and selectively replaces shell fragments. Some pyrite grains replace the host dolomite. Pyrite

57 Figure 2-7. More textures of mineralized rocks in the AB area. PPL = plane polarized light, RL = reflected light, XPL = cross-polarized light. Dol = dolomite, dst = dolostone, Sp = sphalerite. A) Sphalerite occludes micro-porosity in dolomitized rock. Note the euhedral termina tions of the dolomite in the sphalerite, indicating that the dolomite grew into voids prior to sphalerite deposition. Outlines of replaced ooids are traced by curved array of dolomite crystals (e.g., upper right). The dolomite is of the PR type. AB Main showing. Unpolished 30-nm section. PPL. B) An ooid is defined by the concave outlines of inter-ooid sphalerite grains. Precipita tion of the sphalerite probably began in a micropore of the dolomitized inter-ooid matrix (Fig. 2-7A). The sphalerite grew outward by dolomite replacement, halting at the ooid boundary but continuing with relatively straight edges in other directions. AB-C showing, lower zone. Unpolished 30-iim section. PPL. C) A 30-pim framboid made of spherical, 0.5-2 urn crystals of pyrite (yellow). The framboid is overgrown by subhedral pyrite (150 |i), which has been partially replaced by sphalerite (grey). AB-C showing, lower zone. Polished 30-nm section. RL. D) A rind of pyrobitumen (black) around the sphalerite grain (orange) has been disag gregated into straight-edged segments by intervening dolomite (white; arrows). AB Point showing. 100-pim doubly polished section. Combined RL and XPL. Chapter 2. Controls on mineralization in the Sekwi Formation grains are concentrated along stylolites, in organic?-rich domains, and adjacent to large sphalerite grains.

Some pyrite pre-dates the ore-related pyrite. Euhedral, 30-40 |im pyrite grains disseminated in the host rock locally have mottled interiors of variable reflectivity, resembling the synsedimentary or syndiagenetic "sooty" pyrite of Large et al. (2007). Tiny, disseminated pyrite grains enclose polyhedral, 30-|xm framboids composed of 0.5-2 |jm, spherical microcrystals of pyrite (Fig. 2-7C). Micron-scale pyrite grains are enclosed by crystals of matrix-replacive dolomite, whereas those that are not enclosed have been partly replaced by sphalerite. There are no micron-scale pyrite grains in the calcite marine cement that is still preserved between ooids in areas peripheral to the showings.

Mineralization at the Point and other occurrences: The Point showing (Fig. 2-5) consists of scattered mineral occurrences in members 1 and 2a. Although these unit at the Point have been patchily brecciated, the mineral occurrences are outside the breccia patches, in vugs and, in member 2a, isolated, centimetric domains that may have been burrows or molds.

A sample was taken of a 3-cm grain of dark red sphalerite that grew in a vug in member 2a silty dolostone. This grain provided isotopic and fluid inclusion data (below). A narrow rim of dolomite that lines the vug, separating the sphalerite grain from the host rock, is microscopically growth-zoned with ferroan and non-ferroan zones. The youngest of these dolomite crystals are coated with pyrobitumen, as is the sphalerite grain. The vug is occluded by coarse dolomite and quartz. This late dolomite is non-ferroan and mostly saddle dolomite, with some anhedral crystals. The pyrobitumen rind around the sphalerite grain has locally been disaggregated into straight-edged segments by intervening dolomite (Fig. 2-7D), or spalled away to lie in curved shapes between saddle dolomite crystals. The pyrobitumen is metallic, amorphous, and pleochroic. The paragenetic position of pyrobitumen between the sphalerite and the saddle dolomite (Fig. 2-8) is corroborated by the presence nearby of a set of black, pyrobitumen-filled microfractures that cut the host rock and the early dolomite, but not the saddle dolomite. The saddle dolomite was followed by coarse quartz, which contains inclusions of dolomite and has corroded the spear-tips of saddle dolomite. The quartz clearly postdates the pyrobitumen, TJ o C £ i ° Ia aa; brecciatiori & void-filliriq §. §. AB pyrite/marcasite dolomite barite galena sphalerite pyrobitumen quartz calcite

TIC pyrite/marcasite dolomite galena sphalerite pyrobitumen quartz calcite

Palm pyrite/marcasite dolomite sphalerite quartz time •

Figure 2-8. Paragenesis of mineral phases in the AB, TIC and Palm areas. Thick lines emphasize ore- mineral phases. Dashed lines indicate uncertain continuity. Overlap between lines indicates paragenetic overlap at that showing. Question mark denotes uncertain overlap relationship with one or more of the other minerals at that showing. Gray lines for the AB area are alternative interpretations - either one gray line or the other must be true. Galena at AB Point was accompanied by an unidenti fied copper mineral. Dolomite during the pre-ore phase represents dolomitization of the host rock. Not shown explicitly on the diagram is the recrystallization of dolostone at TIC, which probably happened during the brecciation phase. Chapter 2. Controls on mineralization in the Sekwi Formation because it contains growth zones defined by pyrobitumen inclusions. Calcite replaces parts of some saddle dolomite crystals, but its relationship to quartz is unknown. The sphalerite grain is altered and replaced by dolomite and quartz along microfractures and cleavages.

Near the Point sample, isolated vugs in brecciated dolostone of member 1 contain galena, pyrite, sphalerite, and trace amounts of an unidentified copper mineral. In one vug, minute crystals of sphalerite nucleated on transparent, mm-scale quartz prisms. Galena and pyrite occlude fenestra-like vugs, and galena occludes porosity in larger, dolomite-lined vugs.

Other showings in the Sekwi and Franklin Mountain formations are small occurrences of smithsonite, sphalerite, and rarely, galena and chalcopyrite, except for the Dab showing in brecciated dolostone of the Franklin Mountain Formation. The Dab showing is located north of the AB Fault, where sphalerite cements a dissolution breccia over 20 m thick and 85 m in strike-length.

Paragenesis: The paragenetic sequences at the AB showings is shown in Figure 2-8. The framboidal and early-crystalline pyrite in the AB area is enveloped by matrix dolomite crystals, is present in dolomitized ooids and matrix but absent in calcitic marine cement, and is replaced by sphalerite. These features indicate that this early generation of pyrite was introduced after sea-floor cementation, and before matrix-replacive dolomitization. Framboids have been linked to bacterial activity (Machel, 2004) which would have to have taken place no later than early diagenesis. Therefore the pyrite is early diagenetic, and the matrix-replacive dolomitization post-dates it.

The microscopic porosity that was later occluded by sphalerite and dolomite in the unbrecciated host rocks (Fig. 2-7A) developed synchronously with the matrix- replacive dolomitization, as inferred from the petrographic evidence that the micropores formed by dissolution of inter-ooid cement. Micropore development is a common feature of matrix dolomitization (Machel, 2004; Davies and Smith, 2006). These events were followed by localized brecciation and the precipitation of void-filling phases. The earliest cement phase is a non-saddle, white or gray dolomite, which was followed by

61 Chapter 2. Controls on mineralization in the Sekwi Formation overlapping precipitation of marcasite, barite, pyrobitumen, sphalerite, saddle dolomite, and quartz, in that order of first appearance. Although the mobility of pyrobitumen, even at low pressures and temperatures, in most cases prevents unequivocal determination of its relative timing, at the Point showing a fortuitous combination of textures confirm its position (above). A protracted episode of precipitation is suggested for quartz, which pre dates sphalerite (at Point, where sphalerite nucleated on quartz) and post-dates sphalerite and saddle dolomite (at AB-C, where quartz nucleated on sphalerite, and at Point, where quartz has corroded the saddle dolomite that replaced the sphalerite). An alternative explanation (Fig. 2-8) is two generations of sphalerite and one of quartz, but the paucity of quartz makes evaluation of alternatives difficult.

Trend ofbrecciation: Brecciation is common in the vicinity of the AB-C, Link, and Point showings and in the creekbed to their north (Figs. 2-5, 2-9). These all are cemented mosaic or crackle packbreccias, generally with dilational textures, whose clasts are locally themselves dissolution or dilational breccias. The cement consists of various combinations of dolomite, barite, sphalerite, and marcasite, including crack-seal dolomite alone and massive marcasite alone. The paragenetic sequence is everywhere the same as that determined for the Point and AB-C showings (Fig. 2-8), and trace amounts of sphalerite are associated with pyrobitumen wherever it occurs. Sphalerite is absent along the creekbed north of the showings, but the breccias are otherwise identical.

Those breccias describe a north-trending, curvilinear zone that crosses the AB Fault, affecting Sekwi Formation south of the fault and Franklin Mountain Formation north of it (Fig. 2-5). The affected Franklin Mountain Formation rocks are a polymict rock-matrix dolostone breccia. The origin, dimensions, and relative age of the polymict breccia are unknown, but it describes a trend on surface that is coincident with the curvilinear trend of the cemented breccias.

TIC showings

Geology: The TIC area (Fig. 2-2,2-1OA) is 3 km northeast of a regional, northeast-verging thrust fault that places Sekwi Formation over Cambro-Ordovician

62 Figure 2-9. Cemented breccias in the AB area, inferred to have a common origin based on textures and paragenesis. Photos were taken from various locations along a curvilin ear trend that crosses the AB Fault (see Figure 2-5 for locations). Brt = barite, Dol = dolomite, dst = dolostone, Mrc = marcasite, Sp = sphalerite. A) Cemented breccia in dolostone of Franklin Mountain Formation north of the AB Fault. Cement consists of a disrupted cockscomb rim of 1-cm marcasite blades, and a core of coarse white dolomite. B) A vein in dark gray, mottled dolostone of Sekwi Formation member 1, just south of the AB Fault. Concentrations of such veins create a brecciated texture. The vein consists of coarse, white dolomite, and a rim of cockscomb marcasite in 1-cm blades. Late, en echelon, dolomite-filled extension fractures cut the vein. C) Cemented breccia in oncoid-ooid dolostone at the AB-C Upper showing in Sekwi Formation member 2b. Host dolostone consists of blue-black, angular fragments. Most of the rock in this view is breccia cement, consisting of early marcasite that was fractured and subsequently cemented by sphalerite (a pinkish gray rim on the marca site) and barite (white). Sphalerite is innocuous-looking and easily over-looked. D) Crackle and mosaic cemented breccia in Sekwi Formation member 2a near the Point showing. An early phase of dolomite (not present at the other breccia locations) has comb texture. Later marcasite with cockcomb texture forms a rim of 1-cm blades on this early dolomite. The core is white barite. Figure 2-10. Geological setting of the TIC and Palm showings, and geology of the TIC area. A) Geological setting of the TIC and Palm showings. Geology from Gordey and Makepeace (2003) and Gordey et al. (2010a). B) Detailed geology of the TIC area, superimposed on a regional geology backdrop from 10A. Traces of measured stratigraphic sections are shown as black lines. Units are informal, local members of the Sekwi and Franklin Mountain formations. The locations of the D and E zones are from Ronning (1975). C) Generalized stratigraphic sections and correlation of units in the TIC area. Horizontal scale of columns represents weathering resistance. Intervals are colored by informal, local member as in 10B; gradational colors represent units that can't be separated with confidence due to heavy alteration. Gray lines and hatching show the alternative correlation without a fault present between the unmeasured section and section TIC1 (see text). Thicknesses in the unmeasured section are estimates made during a quick visit by E.C. Turner. A) TIC and Palm - Regional geological setting B)T1C - Geology and stratigraphk section locations

130 10 W 130 0W 129*50'W Legend, Fig. 10A M Mid-Late Devonian silkiclastic basin / Measured stratigraphk H Mid-Cambrian to early Mid-Devonian Selwyn Basin section (TIC area. Fig. 9B) Mackenzie platform to' Fault observed, 'i >1911 Early to early Mid-Devonian carbonate units approximate; thrust Late Silurian to Early Devonian carbonate units fault observed, 130 10W 130&W Ordovkrian-Silurian Mount Kindle Formation approximate MB Cambro-OrdovicianFranklin Mountain Fm. Legend, Fig. 106 and 10C Legend, Fig. 10B (continued) Early Cambrian Sekwi Fm. Zn-Pb {major, minor) COf Franklin Mountain Fm. Proterozoic-Cambrlan Backbone Ranges Fm. Cambro-Ordovician Franklin Mountain Fm. O Sekwi Fm. Proterozok Windermere Supergroup (transitional fades); local, informal members PCb Backbone Ranges Fm. MB FM2; dolostone breccia //*' Formation contact: observed, inferred • FM1;siltstone C)TIC - Stratigraphk correlation //'Member contact: observed, inferred Early Cambrian Sekwi Fm.; local, informal members: TIC1— Measured stratigraphk section m Laminated4; laminated dolostone IHi Storm; cross-laminated lime siltstone Quartz; quartz dolostone Dune; dolostone, dune-scale bedforms Dark3?

300m ncoids & Laminated 3? Lamin ated3? NORTH SOUTH Laminated3 Dark2? 200m Microbial? Dark**--* Microbial Microbial nmtasur section Darkl 1290m through the Czone Microbial! Microbial!

Storm Legend, Fig. 10C (continued) 245m distance between Quartz correlation (certain, uncertain,alternate) bases of sections A cemented breccia fault (probable, possible) unconformity Chapter 2. Controls on mineralization in the Sekwi Formation

Rabbitkettle Formation (Gordey and Makepeace, 2003). This fault is semi-continuous with the AB Fault in the AB area, over 100 km to the northwest. In the TIC area itself, the Sekwi Formation is overlain by a facies variant of the Franklin Mountain Formation that has a character transitional between the platformal dolostone of typical Franklin Mountain Formation and the deeper-water, slope deposits of the stratigraphically equivalent Rabbitkettle Formation. Steep, regional, ESE-striking faults with decameter to 200-m displacements are 100-200 m apart. Beds dip very gently southward.

Geological interpretation and correlation (Fig. 2-10B, C) is hampered by poor exposure, fabric-destructive alteration, subtle faulting, and lateral facies changes. Correlations were made among the three stratigraphic sections measured north of the C zone (TIC2, TIC3 and TIC5), and tentatively extended south to the obliteratively dolomitized, brecciated, and faulted section measured south of the C zone (TIC1; Appendix B).

The stratigraphic units identified in the northern sections are described in Table 2- 4. The Sekwi Formation was deposited in various inner- and back-ramp settings. A number of the described units record high-energy waves, currents, and storms affecting an unprotected shelf. Two shallowing-up cycles end respectively with the Microbial 1 and Microbial members (Fig. 2-10C). These are overlain by a deeper-water succession terminating at the top of the Sekwi Formation. Within Microbial 1 and Microbial, up to five smaller-scale, shallowing-up cycles are recorded by shallow-subtidal to intertidal facies dominated by microbial and stromatolitic doloboundstone, each terminating upward in supratidal facies with desiccation features.

The Darkl and Dark2 members (Table 2-4) are the hosts of significant mineralization. Many parts of these members have a dark gray or black color on weathered and fresh surfaces. In the Darkl member, the darkness is imparted by abundant reddish brown, non-crystalline matter, concentrated at dolomite crystal boundaries and in (im-scale zones between cleavages, but also distributed throughout the interior of dolomite crystals. At less than 50x magnification, this matter appears as dark, intracrystalline wisps. Some of it is reflective and pleochroic, and may be bituminous; it is interpreted as organic. Sparsely disseminated, very fine to microcrystalline pyrite Thick- E 1 U. Mbr ness Description TOP FM2 >15 m Dolostone conglomerate or auto-breccia; clasts are cobble-sized, subangular to angular, tabular, in packbreccia texture, locally have a preferred orientation, and consist of dolostone with subordinate siltstone and black chert; matrix is dolostone; chert clasts contain disseminated grains and aggregates of dolomite that weather to give it a porous texture and indicate the chert is of replacive origin; some clasts have fitted boundaries from penetrative dissolution and many are coated by a soft, black crust (possibly, solution seam residue) Franklin Mountain FM1 15-28 Siltstone, calcareous sandstone, dolomitic limestone, dolomudstone with phosphate granules; m exposed only as thin plates of rubble Lamin- 11-16 Light grey dolostone, parallel-laminated and microbially laminated dolostone with cm-scale ated4 m banding and local broken muddy layers, and mottled dolostone; cm-scale dykes of tan- (L4) weathering carbonate sand have penetrated along and across bedding; the top half is bleached, vuggy dolostone with parallel-laminated, non-laminated and microbially laminated cm-scale bands Dark3 8-23 m Medium grey to black, laminated dolostone, mottled (bioturbated) dolostone, minor oncoid (D3) dolofloatstone and rare oolite; thinly bedded, local millimetric rip-up clasts and thin layers disrupted by burrowing and by soft-sediment deformation, cm-scale banding of color and crystal size may reflect primary compositional layering, microbial laminations at base

Lamin- 40-50 Dolomudstone alternating with wavy-laminated dolosiltstone on a scale of millimeters, some ated3 m microbially laminated dolostone; indicators of episodic storms or high-energy events are (L3) ubiquitous in the north (layers with mud rip-up clasts, convolute bedding, mm-scale fitted synsedimentary breccias, and storm lags alternating with laminated layers), but decrease to the east, where the unit is laminated as well as banded on a cm-scale (with color and crystal-size variations that may reflect primary compositional layering); storm indicators are absent in the south, where the unit is laminated, and has dm-scale fenestral beds and a few intervals containing ghost oncoids or large ooids

Sekwi Dark2 8-35 m In the northern part of the TIC area, finely crystalline, buff weathering dolostone, upper part is (D2) fenestral; in the southeast, a dark to medium grey weathering, thinly bedded, parallel laminated to bioturbated dolostone with cm-scale banding of color and crystal size; in the south, a dark, grain-rich lithofacies containing 1-5 mm oncoids and intraclasts in packstone, wackestone, floatstone and rudstone textures, ooid dolograinstone, minor partly-micritized skeletal fragments, and local ripples; hosts the Ryan zone

Micro- 20-37 Microbially laminated dolostone and stromatolitic boundstone of columnar and hemispherical bial2 m stromatolites to 40 cm high with load structures underneath; desiccation cracks, tepee (M2) structures, mm-scale mud rip-up clasts in packstone textures, rare burrow-mottling, ghost oncoids in cm-scale domains; horizons of fenestral vugs Darkl 33-41 In the northern part of the TIC area, medium grey to black weathering archeocyathan (Dl) m doloboundstone overlain by finely to coarsely crystalline oncoid dolofloatstone/rudstone capped by oolite, minor microbially laminated dolostone; grades to southeast into dark, bioturbated dolostone and oncolite; to south into dark to light grey, mottled dolostone with minor boundstone and oncolite, possible fenestral structures and microbial laminations; the oncoids are a distinctive, spherical variety up to 4 cm in diameter, morphologically similar to those above the Palm showing; upper part of the interval has been affected by dissolution brecciation and hosts the C zone

Table 2-4. Informal members of the Sekwi and Franklin Mountain formations in the TIC area. Fm = Formation, Mbr = member. Thick- E 1 U_ Mbr ness Description Micro- 20-45 Microbially laminated dolostone and stromatolitic boundstone with columnar and biall m hemispherical stromatolites; desiccation cracks and tepee structures at one to three levels, (Ml) minor oncoids and intraclasts in floatstone and wackestone textures, trilobite resting traces, bedding plane burrows, and near the top, a stromatolitic bioherm and a 1-cm horizon of black chert Vuggy 8-29 m Intraclast dolorudstone or massive vuggy dolostone to skeletal(?) dolofloatstone with few (V) primary features preserved; some ghost laminations and fenestral fabric; abundant cemented breccia Storm 40 m Variably dolomitized lime mudstone and lime siltstone with parallel and wavy laminations,

Sekwi (S) plenty of indicators of episodic storms (millimetric mud rip-ups grading into fitted, synsedimentary breccias; storm lags; convolute bedding; starved ripples; possible lenticular bedding; alternation of bioturbated with disrupted layers), and an overall change upward from indicators of fast suspension sedimentation to intense bioturbation, perhaps related to a lessening of storm activity with time Quartz 5 m Quartz-sand-rich dolostone and dolomitic quartz sandstone; trough cross-bedding, and (Q) sinuous current ripples with mud in their troushs Dune >12 m Finely crystalline dolostone that preserves meter-scale, low-amplitude dunes suggestive of (D) wave-generated bedforms, overlain by laminated dolostone BASE 1 brackets enclose abbreviation used in Fig. 10B Table 2-4. (continued) Chapter 2, Controls on mineralization in the Sekwi Formation

(including "sooty" pyrite as in the AB area) may contribute to the dark color. Silt- to fine sand-sized, silicate (clay?) grains are ubiquitous but comprise less than 1% of the rock. Ghost oncoids that are visible in hand sample are not discernable in thin section because of their large size and the subtle difference in organic?-matter content that defines their boundaries; however, the nucleus of one oncoid is a micrite-rimmed, dolomite-replaced intraclast. The brecciated parts of the Darkl member are buff or tan, and not dark (Fig. 2- 11 A); either they lost organic? matter during brecciation and mineralization, they never had it, or the dark parts gained it. At the C zone, the Darkl member is a breccia consisting of micro-porous, replacive dolomite disrupted by larger voids that are filled with carbonate and sulfide cement. The replacive dolomite is typically a finely crystalline mosaic of anhedral grains.

The Dark2 member at the Ryan zone is rich in allochems. It includes oncoid-intraclast dolopackstone and dolorudstone, ooid dolograinstone, and dolostone with 2-5 mm ovoid, spherical and pseuodopod-shaped allochems in wacke-, pack-, float-, and rudstone textures. The nature of the lithofacies is hinted at by the preservation of densely branching microbial growths, micritized shell fragments, wavy, muddy, organic?-matter rich laminations, ooidic laminations, and a clotted (peloidal?), micritic fabric (Fig. 2- 1 IB, C).

Dolomitization: All but the lowest units at TIC are pervasively dolomitized. None of this dolomite is clearly eogenetic or syngenetic. The peritidal dolostone units (Microbial1 and 2), although well-preserved, are not finely preserved with the microcrystalline aspect typical of shallow, early dolomite, therefore either they had a limestone precursor or their dolostone precursor has been recrystallized (Mazullo, 1992). Replacive dolomite affects every unit, whereas void-filling dolomite occurs in breccias that are best-developed in specific stratigraphic layers. Dolostone that surrounds breccia bodies has coarser crystals, a homogeneous appearance without primary features, and a bleached aspect.

Replacive dolomite forms mosaics of microcrystalline to coarsely crystalline, anhedral crystals (Fig. 2-1 IB) in both brecciated and unbrecciated rock. It is distinguished microscopically from void-filling dolomite by the presence of abundant solid inclusions that give it a cloudy brown appearance, especially in the cores of crystals, Figure 2-11. Textures of mineralized and nearby rocks at the TIC showings. PPL = plane polarized light, RL = reflected light, XPL = cross-polarized light. Dol = dolomite, dst = dolostone, Gn = galena, Py = pyrite, Sp = sphalerite. A) Host rock at the TIC C zone includes this skeletal-oncoid dolorudstone. The brecciation process has preferentially dissolved the matrix between oncoids. White dashes outline a cluster of well-preserved oncoids, magnified in the white-bordered inset. Yellow dashes and magnified inset show a skeletal grain. Bars in the insets are 1 cm. B) Replacive dolomite preserves densely clotted, micritic fabric of the host rock. Micro pores are partially occluded by clearer dolomite, including void-filling saddle dolomite with curved cleavages and sweeping extinction (lower left). A thin layer of black, organic material lines the inside of the large pore (lower left). TIC C showing, 100-|im doubly polished section, PPL C) Vein filled by sphalerite with blue anisotropy, cutting a dolomitized, peloidal host rock. White arrow points at dense peloidal texture. Relict grains with circular cross-sections are visible at left (small white arrow) and bottom. Dark blebs in the sphalerite are chalcopyrite (yellow arrow). TIC Ryan showing, 100-^m doubly polished section, XPL. D) A 10-cm vug occluded by red and green sphalerite. The host rock is a finely crystalline, vuggy dolostone. TIC Ryan showing, outcrop photo. E) Galena and green sphalerite cement the dolostone fragments in a mosaic breccia. Fragment roundness betrays the influence of dissolution on the final texture. A thin, early rim of white dolomite is visible on some of the fragments. TIC C showing, outcrop photo. F) Sphalerite (medium gray, right) replaces a pyrite (yellow) cube. Both sphalerite and pyrite are replaced by galena (light gray), which also has replaced dolomite (dark, at left) along crystal boundaries. Tiny flecks of deeper yellow in the sphalerite (especially at bottom right) are chalcopyrite disease. TIC Ryan showing, 100-nm doubly polished section, RL photomosaic.

Chapter 2. Controls on mineralization in the Sekwi Formation and which preserve the clotted texture of pre-dolomite micrite (Fig. 2-11B, C). The replacive dolomite locally is re-crystallized: it contains dolomite inclusions of different optic orientation, or is substrate to small dolomite crystals that nucleated on it. It has a patchy luminescence and lacks zoning. Abundant micropores in the replacive dolomite remain open. Larger pores are partly or fully occluded by coarse dolomite and other cement phases. Void-filling dolomite is finely to very coarsely crystalline, commonly the saddle variant, and light colored, even where turbid with an abundance of fluid inclusions. As in the AB area, single crystals of replacive dolomite are overgrown by the void-filling type.

Brecciation: All mineralization at TIC is in cemented breccias, and all rock types contain at least a small amount of cemented breccia. Dissolution brecciation and void creation was most intense in the grainy floatstones and wackestones of the Vuggy, Darkl, and Dark2 members. Most cemented breccias are floatbreccias dominated by dissolution textures. Cements are typically calcite and dolomite, though some are pyrite; the latter breccias are marked by striking, rusty stains on the outcrop. Breccias in the Franklin Mountain Formation are cemented by calcite alone. The C and Ryan breccias are cemented primarily by sphalerite and galena.

A distinctive, 20 m-wide zone of two types of breccia is present 50 stratigraphic meters above the Ryan zone and 180 m east of it. This breccia zone is primarily a rock- matrix rubble floatbreccia, consisting of elongate, granule- to cobble-sized clasts of vari colored dolostone, locally with a preferred sub-horizontal orientation, supported by a vuggy dolostone matrix. Secondarily, meter-scale domains within the rock-matrix breccia are a dissolution-derived rubble packbreccia consisting of mm-scale, rounded dolostone remnants in a dolomite cement, and locally, collapsed bedding. No clasts of rock-matrix breccia occur in the cemented breccia and vice versa, and so the relative timing of the two brecciation events could not be determined. The entire breccia zone is unusual in that it appears to have developed in the Laminated3 unit, but the host unit is not firmly identified owing to intense recrystallization.

The strata-permeating fluids may have been meteoric and percolated downward. They could also have been burial solutions, perhaps hydrothermal, that moved upward Chapter 2. Controls on mineralization in the Sekwi Formation through unmapped fault conduits. There is no meteoric signature in fluid inclusions in sphalerite, but this does not preclude sphalerite mineralization of a pre-existing meteoric breccia. Conditions favorable to meteoric influence may have developed during intermittent exposure at the ends of shallowing cycles in upper Sekwi time (Microbial1 and Microbial members), or during regional exposure following sub-Upper Cambrian erosion.

Ronning (1975) inferred that TIC breccias in drill core originated by solution- collapse, but did not provide descriptions of crystal silt or detrital silt filling pores, which would have confirmed this postulation. Geopetal structures were described, which may have formed during solution collapse, and collapsed bedding is present near the rock- matrix breccia zone in section TIC1, confirming that at least some breccia originated by solution-collapse. Furthermore, geopetal structures in clast molds in the Franklin Mountain Formation show that some form of burial or diagenetic dissolution post-dated the sub-Upper Cambrian unconformity. On the basis of these observations, a burial or hydrothermal origin is inferred for the brecciating fluids, not a meteoric one.

The brecciation was probably part of the dolomitizing process: dolomitization that begins as matrix-replacive can advance to a stage of dissolution, in which remaining calcitic patches in the matrix and calcitic allochems and biochems are dissolved, created a highly permeable dolostone with vuggy porosity (Machel, 2004). The mineralizing and dolomitizing fluids are inferred here to have been one and the same on the basis of the overlapping paragenetic relationship between void-filling dolomite and sulfides, plus the optical continuity and consequent presumed co-geneticity of the matrix-replacive and void-filling dolomite types. A burial or hydrothermal fluid invaded susceptible strata, causing dolomitization, followed by dissolution and collapse resulting in brecciation, then by mineralization and re-crystallization of the host dolostone.

Mineralization: The C zone is on a steep, talus-covered hillside about 80 stratigraphic meters below the top of the Sekwi Formation. Mineralization is erratic but locally massive, and exposed in discontinuous outcrop along 300 m of strike-length within 20 vertical meters. The Ryan zone, 450 m to the southwest, is about 20 m long and

73 Chapter 2. Controls on mineralization in the Sekwi Formation appears on casual inspection to be at the same stratigraphic level as the C zone, an observation that was later refuted by our work (below).

Breccia voids at both zones range up to decimeters in scale and are cemented by varying amounts and proportions of dolomite, quartz, sphalerite, galena, pyrite, and calcite (Fig. 2-1 ID, E). Sphalerite (Table 2-2) is coarse, blood-red to deep green, and riddled with microscopic chalcopyrite disease (Fig. 2-11C, F). Euhedral prisms of quartz grow on galena cubes and are overgrown by sphalerite. Pyrite is commonly an early phase, replaced along its edges and fractures by sphalerite (Fig. 2-1IF), though elsewhere sphalerite preceded galena and pyrite. Galena in coarse crystals with curved faces is locally the dominant cement phase, and its overall abundance at TIC is about half that of sphalerite, a far larger proportion than at AB or Palm. Rare textural evidence indicates that brecciation continued after precipitation of the ore minerals. The mineral paragenesis is summarized in Figure 2-8.

Correlation of units in the mineralized area with units to the north: Despite the intense re-crystallization and brecciation around the C and Ryan zones, it was nevertheless possible at the C zone to recognize the major stratigraphic units identified in measured sections to the north (Fig. 2-10). The presence of archeocyathan doloboundstone and oncoid dolorudstone (Fig. 2-11A) in the C-zone host rock correlates it clearly with the Darkl member. This, in turn, allows correlation of the overlying, heavily brecciated, locally laminated, locally fenestral dolostone with the Microbial member. Overlying that, about 50 stratigraphic meters above Darkl, is a pale, brecciated, oncoid-bearing, locally fenestral and weakly mineralized interval that might be a pervasively altered variant of the Dark2 member. A laminated, microbially laminated, and mud-cracked unit above that is probably correlative with the Laminated3 member, and above that, a vuggy and locally fenestral, laminated, or intraclastic unit with a couple of thin, dark horizons is correlated with the Dark3 member.

The abundance and diversity of allochems and biochems in the Ryan host rock, near the TICl section (Fig. 2-10), is compatible with its being the Darkl member, but the presence of a stratigraphically lower unit that is clearly Darkl supports correlation of the Ryan host with the Dark2 member. The upper part of the TIC 1 section, east of the Ryan Chapter 2. Controls on mineralization in the Sekwi Formation zone, is much harder to correlate with units elsewhere. The interval above the Dark2 member is tentatively correlated with the Laminated3 member but is much thicker than Laminated3 elsewhere. It is a vuggy dolostone with mm- to cm-scale vugs, cm- to m- scale layers defined by the density of fenestra-like vugs, and intermittent, meter-scale domains of cemented breccia. The dolostone has a coarse, recrystallized appearance, and rare ghost oncoids and lamination are the only clearly primary features retained. This possible Laminated3-equivalent is interrupted by the rock-matrix breccia described above, which is succeeded upward by laminated, non-vuggy dolostone, and at the top of the section, a silicified, carbonate-cemented dolostone breccia.

The Darkl, Microbial, and Dark2 units may be uninterrupted between the C and Ryan zones, as shown by one interpretation in Figure 2-IOC (grey lines and hatched fill). The favored interpretation is that a fault lies between the two showings (black lines and gray fill). These alternatives are discussed below (Discussion , Controls on mineralization, TIC area). The correlation of units is the same in both interpretations.

Palm showings

Geology: The Main and Waterfall zones at Palm were previously thought to be hosted by the same unit (Yeager et al, 1975), but that has been refuted by the current study. A stratigraphic section through the Palm Main zone (Figs. 2-4,2-12; Appendix B) shows a progression upwards from a bioturbated, dolomitic lime mudstone into the Renalcis mounds member (Renalcis sp. boundstone and Salterella sp. grainstone), then into the Argillaceous member (burrowed, argillaceous to silty lime mudstone and dolostone, grading upwards into laminated dolosiltstone thinly interbedded with recessive, argillaceous dolostone). A covered interval separates this from the Mottled member, which is 24 m thick and hosts the Palm Main mineralization. The Mottled unit consists of dark gray-weathering, finely to microcrystalline, mottled dolostone to peloid (-skeletal) dolograinstone (Fig. 2-13A). Coarse, centimeter-scale domains (burrows?) contain significantly less organic? matter than finer, inter-burrow material. At the Palm Main zone, this unit has been affected by dissolution brecciation.

75 Legend Informal, local members of Sekwi Fm.: Measured stratigraphic section Q Quartz arenite; dolomitk. cross-bedded / Stratigraphic contact F Thickly bedded fenestra!; dolostone, oncoid dolorudstone; fenestra! Fault (exposed, covered) X Mud-cracked; dolomudstone, dolosiltstone; laminated. TP, mud-cracks, mm-intraclasts * Zn±Pb showing ODQ Orange dolomitk quartzite; marker unit mm Franklin Mountain and Rabbitkettle fms. M Mottled; dolostone,peloid dolograinstone; mottled s Sekwi Fm. A Argillaceous; lime mudstone, dolostone, dolosiltstone; burrowed, argillaceous R Renakis mounds; boundstone and skeletal grainstone L lime mudstone; bioturbated, dolomitk

Figure 2-12. Looking east at strata hosting the Palm Main and Waterfall showings. Inset shows a larger view. Named units are discussed in the text. B

Figure 2-13. Textures of mineralized rocks at the Palm showings. PPL = plane polarized light, RL = reflected light. Dol = dolomite, Py = pyrite, Qtz = quartz, Sp = sphalerite. A) Dissolution breccia in mottled peloid dolograinstone, cemented by sphalerite, pyrite, and dolomite. Palm Main showing, hand sample, cut surface. Scale numbered in centimeters. B) Colloform sphalerite that has been brecciated and partly replaced by dolomite (dark gray, non- reflective) and pyrite (white, reflective). Indentations in the sphalerite banding (arrow at right) originate at a 4-pim pyrite grain that inhibited subsequent sphalerite growth at that spot. Palm Main showing, 100-|im doubly polished section, RL. C) A vug in a matrix of replacive, anhedral dolomite has been occluded by sphalerite (light gray). The sphalerite is replaced along fractures (by dolomite?) and overgrown by euhedral dolomite rhombs that contain inclusions of sphalerite. (Textures are somewhat equivocal, but if the sphalerite replaced dolo mite, then sphalerite would be expected along fractures and edges of the dolomite, not isolated in the middle of dolomite crystals.) Quartz (dark gray, non-reflective, sharp outline; hexagonal, prismatic form) also replaces the sphalerite, and tiny grains of pyrite (white) overgrow the euhedral dolomite. Palm Main showing, 100-|jm doubly polished section, RL. Chapter 2. Controls on mineralization in the Sekwi Formation

Above the Mottled member is the Mudcracked member (thinly to medium- bedded, laminated, mudcracked dolomudstone, interlayered with recessive dolomitic siltstone and thin beds of intraclast wackestone to floatstone). Near the base of the Mudcracked member, an orange-weathering, dolomitic quartzite forms a distinctive marker horizon 1 m thick. Above the Mudcracked member is the Thick-bedded fenestral member, a thick interval of thickly bedded, finely crystalline dolostone with fenestral fabric, and rare intraclast dolowackestone and laminated dolomudstone. The top of the fenestral unit is a narrow interval of homogeneous, conchoidially fracturing dolostone overlain by a few meters of mottled dolostone containing a bed of large (1-2 cm), spherical oncoids similar to those in the Darkl member in the TIC area. Above the Thick- bedded fenestral member, at the top of the measured section, is the Quartz-arenite member, at least 5 m of massive to cross-bedded, dolomite-cemented, quartz arenite. The top of the Sekwi Formation is roughly 450 m above that, below light gray-weathering oncoid dolofloatstone of the Franklin Mountain Formation.

At the Waterfall zone, the same succession is present (Fig. 2-12). The lowest interval is the Mottled member, which is not mineralized even though it is stratigraphically equivalent to the host of the Main zone mineralization. Above the mottled unit is the Mudcracked member with the orange marker near its base, then the Thick-bedded fenestral member. This unit hosts the Waterfall mineralization, and is a light brownish-orange-weathering, finely to microcrystalline fenestral dolostone. A homogeneous, conchoidially fracturing dolostone overlying the fenestral host is correlative with the same interval in the Palm Main section.

The Palm area is on-trend with the extension of the AB Fault (Figs. 2-2, 2-1OA). Steep faults trend NNW and west. Two steep, south-side-down faults that trend west between the Palm Main and Waterfall zones are expressed as gullies and revealed by subtle lithological changes along apparent strike across the gullies, for example, from a mudcracked dolostone on one side to a fenestral dolostone on the other side (Fig. 2-12). The Palm Main-zone mineralization is immediately north of the larger, west-trending fault, which has about 75 m of horizontal offset. Mineralization decreases dramatically with distance north of the fault (Yeager et al, 1975), which has been traced for only 100

78 Chapter 2. Controls on mineralization in the Sekwi Formation m. It is not exposed and not known to affect any strata younger than the Sekwi Formation.

Dolomitization: The lower units at Palm include limestone and dolomitic limestone, but the bulk of the section is completely dolomitized. As at AB and TIC, there are matrix-replacive and void-filling varieties of dolomite. Matrix-replacive dolomite crystals are anhedral with curved to planar faces, but euhedral where they protrude into micropores and veins. Void-filling dolomite is both saddle-shaped and planar-faced. An early phase of orange, void-filling dolomite is ferroan; a later, white, non-ferroan dolomite envelops isolated sphalerite grains. The spearhead-shaped terminations of saddle dolomite crystals have been rounded by dissolution along solution seams.

Mineralization: At the Waterfall zone, reddish-brown sphalerite occludes millimetric fenestral porosity along a strike length of approximately 10 m. Very fine grained pyrite is disseminated in the host rock. Centimetric patches of dissolution breccia are cemented by dolomite-pyrite ±quartz, without sphalerite. Sub-millimeter polyhedra of pyrite line the edges of vugs. Euhedral quartz prisms have grown into the centers of vugs, which are sealed by white dolomite.

The Palm Main zone is a 10 m by 10 m area marked by conspicuous white efflorescence and smithsonite/hydrozincite fracture coatings. The host Mottled member is a dissolution floatbreccia and locally a mosaic breccia with dilational textures. Sphalerite (Table 2-2) seals small fractures, occludes micropores along with dolomite, and cements the breccia, along with dolomite, quartz, and minor pyrite (Fig. 2-13A). Sphalerite in breccia voids typically forms clusters of grains nucleated on the host rock, or separated from it by dolomite or pyrite. An earlier generation or an earlier phase of the same generation of sphalerite is colloform, and was replaced by early, matrix-replacive dolomite and by pyrite (Fig. 2-13B, C). Dolomite fills the centers of voids. Anhedral quartz is a minor phase in vein centers, where it surrounds euhedral dolomite crystals.

Fine-grained pyrite crystals with hexagonal and pentagonal cross-sections are disseminated throughout the matrix of the Main-zone host rock. Larger pyrite grains are concentrated near the boundaries of breccia voids and veins, in the host rock as well as

79 Chapter 2. Controls on mineralization in the Sekwi Formation the cement. Tiny grains of pyrite are coeval with colloform sphalerite, whereas larger pyrite euhedra post-date sphalerite and dolomite (Fig. 2-13B). The paragenesis is summarized in Figure 2-8.

Laboratory Studies: Results

Fluid inclusion petrography

Twenty-seven fluid inclusion assemblages (FIAs) warranting further study were identified in eight fluid-inclusion sections. Twenty-two of these assemblages were primary or pseudosecondary (20 in sphalerite, two in quartz) and five were secondary or pseudosecondary (four in sphalerite, one in quartz). Of the 178 inclusions in these 27 assemblages, 158 were subjected to microthermometry.

Fluid inclusions in sphalerite (Table 2-2) and quartz are of two main types. Most inclusions are aqueous L-V (liquid-vapor) inclusions (Type 1; Fig. 2-14A, B, C). Type 2 inclusions are secondary and may contain petroleum (Roedder, 1972), but this has not been confirmed. Type 2 inclusions are present in sphalerite at the TIC, Palm, and AB

Point showings as <2% of total inclusions. Fluid inclusions in quartz are Type 1, with rare examples of a third type consisting of monophase aqueous liquid. Only Type 1 inclusions were studied microthermometrically.

Many fluid inclusions in sphalerite were too dark to see into, especially during thermometric experiments (e.g., Fig. 2-14C). Dark inclusions commonly define secondary trails (Fig. 2-14B). Where vapor bubbles were visible in the inclusions, they occupied an estimated 5-10% of the inclusion volume, excluding some occurrences of vapor-rich inclusions that may reflect necking. These volume estimates are compatible with densities of 0.87-0.99 g/cm3 calculated from microthermometric data (below). The larger inclusions typically are negative cubic or rectangular in shape, whereas smaller ones are rounded and equant to elongate, but shapes are variable and also include flat and irregular shapes. Type-1 inclusions range from <1 to 50 |im in longest dimension. (It is not possible to discern two phases in the smallest of these, which are only inferred to be

80 Figure 2-14. Fluid inclusions. A) Typical equant, light, low-V, 2-phase, aqueous inclusions, in sphalerite from TIC C zone. B) A secondary FIA of negative-crystal-shaped, dark, 2-phase, aqueous inclusions in sphalerite from TIC Ryan zone. Inset: Large (12 |im), dark, 2-phase aqueous inclusion with negative-crystal shape, from same sample. C) An FIA (827C1-2 #4) of light and dark, multi-sized, aqueous, 2-phase inclusions. Sphalerite from TIC C zone. D) Opaque inclusions with highly irregular shapes, typical of inclusions in sphalerite from the AB Main showing. Inclusions are concentrated along cleavage planes and have been extensively modified since entrapment. Arrows indicate inclusions that may have decrepitated due to internal overpressure (note short "arms" or fractures radiating from corners). Chapter 2. Controls on mineralization in the Sekwi Formation

Type 1.) Inclusions in sphalerite that were studied with microthermometry ranged from 2 to 30 nm, with 78% <10 |im.

FlAs of all genetic types are common in sphalerite at the Point showing in the AB area and the C and Ryan showings in the TIC area. In sphalerite from the AB Main showing, swarms of small, opaque inclusions with highly irregular shapes darken the cleavage planes. Some exhibit opaque fractures radiating into the host crystal (Fig. 2- 14D), a texture reminiscent of overpressure-induced decrepitation (Sterner and Bodnar, 1989). Rare inclusions <2 fim have visible vapor bubbles. In the AB-C upper zone, most inclusions are submicroscopic, but late sphalerite contains rare, isolated pseudosecondary planes and secondary groups related to fractures. At the Palm Main showing, most inclusions are submicroscopic, though a few range up to 20 (im; primary and pseudosecondary planes were identified, but their constituent inclusions were too small for microthermometry. In primary and pseudosecondary assemblages from the Point and TIC showings, petrographic evidence is present of inclusion necking subsequent to development of a vapor phase during geological cooling (post-phase-change necking). Fluid-inclusion sections were not made from the AB-C lower zone or Palm Waterfall samples because preliminary petrographic observations advocated against the presence of useable inclusions in sphalerites.

Type 1 fluid inclusions in quartz are rounded and equant, with rare development of negative crystal shapes, and contain <10% vapor by volume. Most are <1 nm but the studied inclusions were 1-15 jim. Primary planar arrays define or lie parallel to grain margins or occupy growth zones in the cores of crystals. Some planes are identifiable as pseudosecondary, and anastomosing planes parallel to undulatory extinction directions are secondary. Most inclusions do not form identifiable FIAs. Quartz at both the AB Main and AB-C upper zone is turbid with abundant, small Type 1 inclusions. Many of the larger inclusions in quartz at the Palm and AB Main showings are highly irregular with a number of narrow arms. Evidence of inclusion necking is common in quartz at AB Main.

82 Chapter 2. Controls on mineralization in the Sekwi Formation

Microthermometry

The following terminology is used in discussing thermometric data in this study: primary or pseudosecondary FIAs were trapped during growth of the crystal and are therefore called "syn-sphalerite" or "syn-quartz" FIAs, whereas FIAs in sphalerite that were classified as "secondary or pseudosecondary" are termed "syn/post-sphalerite". Syn-sphalerite FIAs were chosen for microthermometric studies from the AB-C upper zone (1 FIA), Point (6), TIC C (5), and TIC Ryan (7) showings. Syn-quartz FIAs were chosen from the AB Main showing (2) and the AB-C upper zone (1) in the absence of useable inclusions in sphalerite. Two syn/post-sphalerite FIAs from the Point showing and one each from the TIC C and TIC Ryan showings were studied, as well as one clearly secondary (post-sphalerite) FIA from the Point showing. Most of the studied FIAs contained inclusions with a range of shapes, sizes, and darkness. This range helps ensure that any post-entrapment, natural re-equilibration processes affecting the inclusions will be revealed by a wide range of temperatures of homogenization (Th's; by contrast, same- sized inclusions would tend to re-equilibrate to the same degree, yielding Th values whose consistency might falsely suggest a lack of post-entrapment modification; Goldstein and Reynolds, 1994). Heating studies were done on all inclusions in a chosen FIA that had a sufficiently large vapor bubble, and freezing studies were then done on the largest inclusions in those FIAs. Few FIAs had more than one inclusion large enough to observe melting phase changes in.

Heating experiments: Given that most inclusions were small and dark, the cycling technique described by Goldstein and Reynolds (1994; see also Appendix D) was used to bracket the temperatures of homogenization. Using this method, the Th of most inclusions was determined to within 5° or 10°C. Heating rates were up to 50°C/min between room temperature and the highest temperature achieved in the previous run, then 5°C/min to the next incrementally higher temperature before another cooling cycle was implemented. During cooling, if the vapor bubble happened to return within the dark part of the inclusion and hence was not observed during its return, the cycle was repeated to the same maximum temperature until the bubble returned within the visible part of the inclusion (or until a small bubble bounced into view, which was taken to indicate non- Chapter 2. Controls on mineralization in the Sekwi Formation homogenization). Many of the inclusions studied were so dark that only 20% of their volume was visible. The common darkening of inclusions on heating (below) exacerbated the problem. When multiple runs failed to produce a visible bubble return, study of that particular inclusion was abandoned. Thus the time required to determine whether a bubble had homogenized within a given 10°C range often involved multiple cycles. If the upper end of the Th range of an inclusion could not be determined, the lower end was recorded as Thjncm, the minimum Th of the inclusion; this situation arose when the return of the vapor bubble was obscured or, in one FIA, because cycling was not used.

Many of the heated inclusions exhibited anomalous vapor-phase behavior, herein referred to as vapor-phase persistence: the bubble shrank to a tiny dot that bounced rapidly about the inclusion over a temperature range of 30° to 100°C before disappearing, but in many cases did not homogenize (i.e., it returned on rapid cooling as a tiny bouncing dot) even over a further range of up to 80°C. Attempts to homogenize these inclusions usually resulted in leaking, stretching, and decrepitation of the inclusion. Possible reasons for vapor-phase persistence are discussed below. For inclusions displaying this behavior, a temperature at which the bubble became tiny (Ty) and a temperature at which it finally disappeared (Td) were usually recorded. Ty were consistent among the inclusions in an FIA and represent a minimum Thinc (Thjncm). Td values varied over a large range and were not used further.

Since the Th of each inclusion is a range, the average of the minimum and maximum bracketing temperatures for each inclusion is regarded as the Th for that inclusion (Thmc; Fig. 2-15). Machine error (±0.1 °C) and reading error (±0.05°C) are negligible compared to the 5-10°C range bracketing each Thjnc (grey error bars in Fig. 2-

15). The Thjncm values are compatible with the rest of the data (Fig. 2-15) but could not be used further. Consistency of Thjnc among the inclusions in an FIA (90% within 10°C) was required to confirm a lack of post-entrapment modification; most of the studied FIAs failed this test. For those that passed, ThpiA was calculated as the average of all Thjnc for the assemblage (Table 2-5, Fig. 2-15). A ThnA value is therefore the minimum temperature at which the fluid in the assemblage was trapped. It is significant, and different from many studies (see for example, Leach et al., 1996; Baker and Seccombe,

84 syn-Sp FIAs syn/post-S P syn-Qtz AB-C AB Point TIC Ryan TICC AB Point TIC TIC AB Main AB-C upper Ryan c up. 1 300- g

{ .

•

° T . 29 74 • V • • f 4 £ a E Th (°C) ThF* • • * 1

J i g 200- 174-241l°C • * A • 2« . 12o M • (,4

'3 130-180°C • :: • H ;> 1 3C 2 t 3

f 1 > 30 t I • I 1 in 13 jb o M M »S — £1 JQ r 9 JO a t * « * • z • z ; j ; j 5 » s ** * * 5 S * C" Q « • • ^ 7 < ff < £ Q Q 2 £ d e T < i s 3 3 < s 5 u ^ A ^ 8 - S !! 8 5 £ § £ S g C y SO £ CD S CO 8 » 8 « < 3 S; K; N SO 03 3 • fig' " m ** s Assemblage data Inclusion data

• ThF1A (average of 3 or more consistent Th^) • Th|r>c (at center of range determined by cycling)

0 Th^ (average of 3 or more consistent Ty) 3# Th^ of 3 inclusions 1 loerror o Ty(seetext) I ^incm = minimum Th^ (upper end of range could not be determined)

Figure 2-15. Summary of microthermometric heating results. Each column of data represents one FIA. Th of individual inclusions (grey symbols) are provided to enable a visual evaluation of the number and quality of inclusion Th data that went into derivation of the assemblage data (bold

black symbols). Assemblage temperatures (ThF1A) and minimum assemblage temperatures (ThFIAJ are explained in the text; FIAs that provided these are named in bold font. (Names are sample

number with FIA-number suffix; Table 2-5.) The range of ThFIA for syn-sphalerite assemblages is

shaded gray, as is the range of ThFIAm. The minimum temperatures (Ty, Thjncm, ThFIAJ are compatible

with the constrained temperatures (Th.nc, ThFIA), and the overall range of ThF(Am in syn-sphalerite assemblages is about 50°C lower than the ThF1A range. Error bars for FIAs are la whereas error bars

for Thjnc show the range determined by cycling. Where more than one inclusion Th plots in the same spot, the number of inclusions is given beside the symbol. See text for details and Appendix H for a table of abbreviations. Chapter 2. Controls on mineralization in the Sekwi Formation

2004; Mernagh et al., 2004; Yang et al., 2004; Stoffell et al., 2008), that the Th used in graphs and charts is the Th of an entire assemblage, not of a single inclusion (discussed further below).

For FIAs displaying vapor-phase persistence, a minimum tfifia (ThFiAm) is given by the average Ty. A Ty consistency of 90% within 20°C was required to calculate a ThpiAm- This looser constraint is justified by the subjectivity in deciding when the bubble is "tiny", and the openness of the upper end of the Ty range. Fifteen inclusions with vapor-phase persistence homogenized after Ty was obtained, over a range from 15 to 87°C above their Ty value (for example, 827C1-2 #2b and 824A1 #4 in Fig. 2-15), whereas inclusions without vapor-phase persistence homogenized within 5°C of Ty (824A2-1 #5b).

All inclusions homogenized to the liquid phase. Twelve FIAs yielded acceptable ThpiA or ThFiAm data, including one that was moderately variable (sensu Goldstein and

Reynolds, 1994; 80% of its Thjnc within 12.5°C). The other 15 FIAs yielded inconsistent or incomplete data due to one of three factors. The first factor was post-phase-change necking, which was revealed by inconsistent Thinc (obviously-necked assemblages were excluded from microthermometric study, whereas inconsistency of Th revealed necking that was not petrographically obvious). Second, if fewer than three inclusions yielded a

Thjnc, they were deemed unrepresentative of the FIA. Failure to measure Thjnc was generally related to poor visibility in small, dark inclusions with "thick" walls (i.e., the appearance of thick walls due to trapping of light by internal reflection). However, even large inclusions sometimes darkened dramatically on heating, making it impossible to observe phase changes. This darkening was usually permanent. Finally, the following physical changes to inclusions on heating indicate a violation of the assumption that the volume and composition of the inclusions have remained constant since trapping (Roedder and Bodnar, 1997): (1) a permanent, visible increase in size of the vapor bubble at some point during the heating run, which indicated that the inclusion had stretched; and (2) decrepitation of the inclusion without homogenization.

86 Classi T^FIA ThflAm # Inclusions NaCI-MgClrH20 NaCI-CaCI2-H20 fica re Show lo la Heating in heat gave froz gave la Den £ 1 s 3 4 tion < ing Sample FIA Age ThFIA ThfiA err+ err- ThflAm ThRAm note FIA ed Th | Ty en Tm, iTrrihh S 1OS X* lo XN S loS XN sity syn-Sp AB AB-C 892A spl psy insuffi 4 2 1 4 2 2 3.76 0.05 0.66 0.06 3.61 0.05 0.70 0.06 up cient data per syn-Sp AB Point 951D 4 psy gas" 9 9 0 4 2 2 18.99 1.47 0.68 0.14 19.23 1.04 0.72 0.15 syn-Sp AB Point 951D 5 iy/psv 219.2 2.9 5.8 4.2 4 4 3 3 3 3 15.03 0.96 0.68 0.05 15.45 0.86 0.72 0.05 0.0479 syn-Sp AB Point 9S1D 7a IV necked 7 7 6 0 syn-Sp AB Point 9S1D 8a iy/psy necked 5 5 3 0 syn-Sp AB Point 951D 8b iy/ psy 142.9 12.5 8 8 0 7 0 syn-Sp AB Point 951D 10 iy necked 6 6 5 0 syn-Sp TIC Ryan 824A1 2 psy 130.0 0.0 4 4 2 4 0 syn-Sp TIC Ryan 824A1 4 iy gas? 6 2 2 2 1 1 1 16.55 0.72 16.86 0.76 syn-Sp TIC Ryan 824A1 5 ly/psy 155.3 0.6 b 5 5 0 5 1 1 1 16.88 0.71 17.19 0.75 syn-Sp TIC Ryan 824A1 7 iy 241.3 10.9 28.8 11.3 10 10 10 4 4 16.25 0.00 0.71 0.00 16.60 0.00 0.75 0.00 0.0468 syn-Sp TIC Ryan 824A2-1 1 iy necked 7 6 6 1 2 2 2 15.55 0.58 0.72 0.04 15.89 0.63 0.76 0.03 syn-Sp TIC Ryan 824A2-1 4a b ly/psy gasc 12 12 2 12 1 1 1 18.11 0.58 18.64 0.61 syn-Sp TIC Ryan 824A2-1 5b psy 174.0 0.0 2.0 2.0 169.0 0.0 5 5 3 5 4 4 4 19.46 0.96 0.77 0.09 19.50 0.90 0.80 0.09 0.0496 syn-Sp TIC C 827C1-2 1 ly/psy 131.7 5.8 4 4 2 3 syn-Sp TIC C 827C1-2 2a psy 200.4 4.9 9.6 5.4 10 10 7 1 1 1 17.89 0.57 18.48 0.60 0.0487 syn-Sp TIC C 827C1-2 2b psy 218.3 5.8 11.7 8.3 180.0 0.0 7 5 3 5 1 1 1 7.39 0.66 7.45 0.70 0.0475 syn-Sp TIC c 827C1-2 3 iy necked? 4 4 3 0

1 2 4 3 syn/p = syn/post a: Ty riot noted, b: Th(nc are minimums because cycling was not done; c: Ty range too wide (inconsistent data) ' units are wt%N units are mol/ cm

Table 2-5. Th and salinity data for FIAs. FIAs are grouped by age relative to host crystal (Sp = sphalerite, Qtz = quartz) and second arily by showing. Detailed relative-age codes are ly = primary, psy = pseudosecondary, 2y = secondary. Shaded rows mark success

ful acquisition of ThF|A; for these FIAs, densities were calculated (Fig. 2-23). ThF)A and Thf|Am are averaged from mutually consistent

component Th.nc and Ty, respectively. The number of inclusions on which various types of data are based is provided under the header inclusions. Errors of one standard deviation (la) are provided for calculated data that are based on >1 inclusion. Maxi mum errors in ThF|A (err+, err-) are provided. Salinity (S) in weight percent equivalent NaCl (wt%N) and proportion by weight of NaCl

to NaCl+MgCl2 or to NaCl+CaCl2 (XJ were calculated for individual inclusions, and averaged if there was more than one inclusion per FIA that yielded salinity data. Detailed explanations are provided in the text. Classi T^FiAm # inclusions NaCI-MgCI2-H20 NaCI-CaCI2-H20 fica Show la la Heating in heat gave froz gave lo Den 2 3 3 4 ing Sample FIA ThRA err+ err- FIA ed Th | Ty en S loS XN loXN S loS sity tion Area Age ThF|A ThpfAm Thpj^ note Tm, ITrrihf, syn-Sp TIC C 827C1-2 4 ly/psy gas/ 17 11 5 2 2 2 7.91 0.00 0.67 0.01 7.99 0.01 0.72 0.01 necked syn/p- AB Point 951D 1 2y / psy gas? 5 0 5 3 2 7.60 1.48 0.81 0.09 7.57 1.51 0.84 0.08 c-bp syn/p- AB Point 951D 2a 2y necked 7 7 2 7 7 3 5.25 1.30 0.63 0.06 5.17 1.36 0.67 0.06 Sp syn/p- AB Point 951D 6 2y / psy 150.0 0.0 3 3 2 3 0 Sp syn/p- TIC Ryan 824A1 6 2y / psy gasa 7 7 3 0 iPCn syn/p- TIC C 827C1-2 6 2y/psy 215.0 0.0 5.0 5.0 7 7 5 1 1 1 6.42 0.74 6.36 0.78 0.0477 Sp syn-Qtz AB Main AB11 qzl ly/psy necked 4 4 4 1 1 1 11.75 0.84 11.90 0.88 syn-Qtz AB Main AB11 qz2 psy 215.0 0.0 5.0 5.0 4 4 3 2 1 1 5.39 0.54 5.36 0.57 0.0474 syn-Qtz AB AB-C U 892A qzl psy necked 7 7 4 5 2 2 2.02 0.66 1.87 0.70

Table 2-5. (continued) Chapter 2. Controls on mineralization in the Sekwi Formation

ThFIA or ThFIAm data were obtained from three FIAs, two of which were syn- sphalerite, from the Point showing (in the AB area), eight FIAs, seven of which were syn- sphalerite, from the TIC C and TIC Ryan showings, and one syn-quartz FIA from the AB

Main showing (Table 2-5, Fig. 2-15, 2-16). There was no significant difference in tiifia between the two areas, nor in ThpiAm- ThpiA ranged from 174 to 241°C (in 5 FIAs), and ThFiAm from 132 to 180°C (in 6 FIAs). The only FIA that was clearly primary had the highest ThFiA value (241°C). The other ThpiA values are from FIAs classified as "primary or pseudosecondary" (one FIA), "pseudosecondary" (two FIAs), and "secondary or pseudosecondary" (one FIA), and may represent a cooling of the fluid as sphalerite was being precipitated.

Freezing experiments: The cycling method of Goldstein and Reynolds (1994) was also used to determine the last melting temperatures of ice and hydrohalite in the inclusions. Rapid undercooling of an inclusion at -50° to -60°C/min to a temperature of - 90°C or less was followed by an initial, moderately fast warming run (30°C/min) to establish ballpark melting temperatures. After a second rapid cooling, the inclusion was subjected to a number of warming and cooling runs in which warming rates were slowed near known phase changes to as little as l°C/min. The completion of melting was tested for by rapid cooling: immediate return of the solid phase indicated that melting was not complete when the rapid cooling began. The small size and darkness of the inclusions inhibited observations and made identification of phase changes difficult, thus multiple observations were made of each suspected phase change. Sometimes a phase change that could be seen and bracketed within 2 or 3 degrees during rapid warming was impossible to pinpoint more accurately during slower warming runs. It was not uncommon for a temperature to be obtained for hydrohalite melting (Tmhh), but not for ice melting (Tmj), in which case the data were not usable for salinity calculations. The Tmhh and Tmj data for each inclusion are presented in Figure 2-17.

89 Key syn-Sp • ThF1A

• ™F1Am syn/post-Sp

• ThFIA

• ThFIAm • syn-Qtz ThFiA 1 if) I I h 1 1 <180° >20QM i r < - H 1 HOi :D fr .v Th range (°C) &

Figure 2-16. Histograms of Th for twelve FIAs. ThF1Am is the minimum ThRA determined from Ty (see text). A) The data are indistinctly grouped into <180°C and 200-220°C, with a single, high-Th outlier.

B) Thf|Am is between 0° and 50°C less than the true ThF1A for an assemblage. To test the

apparent grouping, ThF|Am has been increased by 20°C. The new value would be the true

ThF1A if, in the absence of vapor-phase persistence, the inclusions would have homog enized at a temperature 20°C higher than Ty. The data still define two groups plus an outlier. The distinction between the two groups will be lost if ThF|Am is increased by >30°C. syn-Sp FIAs syn/post-S syn-Qtz AB-C AB Point TIC Ryan AB Point AB Main upper

moderately salir e

moderately

Assemblage data Inclusion data

O Tm^ofFIA + Tmto with error Mulitple indusions used to calculate Tm of FIA: ° Tmte • Tm^ofFIA 4 Tm^ with error • Tm^ J 1o error 2 2 inclusions with same Tm

Figure 2-17. Microthermometric freezing results. Each column of data represents one FIA.

Melting temperatures of hydrohalite (Tmhh) and ice (Tm,) for individual inclusions are small symbols. Where Tm for more than one inclusion plots in the same spot, the number of inclusions is given beside the symbol. For FIAs in which more than one inclusion provided data, the inclusion symbols are gray and their average (Tm of FIA) is marked by large black symbols (squares for hydrohalite and pentagons for ice). FIAs that provided these are named in bold font. (Names are sample number with FIA-number suffix; Table 2-5.) Ice melting temperatures fail into two groups, representing saline and moderately saline fluids. These are shaded gray, along with the narrow range of hydrohalite melting tem peratures. Error bars for FIAs are lo. Some error bars are angled to avoid overlap; error is represented by the length of the bar measured on the vertical scale. See text for details. Chapter 2. Controls on mineralization in the Sekwi Formation

Hydrohalite melted before ice in all inclusions. Where data from more than one inclusion were available, Tmhh and Tm, of inclusions were averaged to give Tmjce and Tmhh for FIAs with errors of la (Fig. 2-17), but these were not used in salinity calculations; instead, salinities for each inclusion were averaged to give FIA salinities (see below). Errors for Tmhh and Tmj of inclusions are the machine error of ±0.1°C plus a subjective reading error that depended on heating rate and clarity of the phase transition. An asymmetrical error was assigned when the presence of a phase was certain at one temperature, its absence probable at a higher temperature, and its absence certain at a yet- higher temperature, in which case Tm was placed midway between the phase-present and phase-probably-absent temperatures.

Complex, low-temperature behavior in studied inclusions included recrystallization, the reappearance of a crushed vapor bubble, and the melting of unknown phases. Possible melting at temperatures from -55° to -40°C in most of the studied inclusions suggests the presence of CaCh or MgCh (Davis et al., 1990). For some inclusions, the lowest-temperature events were at or above -31°C, precluding the 9+ 9+ dominance of Ca and suggesting, instead, a major component of Mg ormetastable salts of K+ or Na+ (Davis et al., 1990). On the basis of this information, two model systems were chosen to represent the studied fluids, the NaCl-MgCh-FhO system of Dubois and Marignac (1997) and the NaCl-CaCl2-H20 system of Oakes et al. (1990, 1992). The Aqso3e program of Bakker's (2003) FLUIDS package, which accepts Tmj and Tmhh as input, was used to calculate salinities and MgCh mass percentages for each inclusion using the NaG-MgC^-F^O system. Salinities are expressed in weight percent

NaCl equivalent (wt. %n). Equation 2 of Oakes et al. (1990) was used to calculate salinities of each inclusion using XN and Tm; as input, where XN is the mole fraction NaCl/(NaCl+CaCl2). The program provided by Chi and Ni (2007), based on the previously published experimental data of Yanatieva (1946, referenced in Chi and Ni,

2007) and Oakes et al. (1990, 1992), was used to calculate xN from Tmhh. The difference in salinities calculated by the two systems is well within the salinity errors, averaging 0.2 wt. %n and ranging up to 0.6 wt. %n.

92 Chapter 2. Controls on mineralization in the Sekwi Formation

Salinities and weight-percent amounts of the component salts for the two model systems are presented in Figure 2-18. Salinity for an FIA in which more than one inclusion yielded the requisite data is presented as the average of inclusion salinities; the error in this case is la in the positive and negative directions for both salinity and XN, and is typically negligible for xN- Standard deviation does not represent uncertainty well for such small sample sizes, therefore, for the NaCl-CaCh-FhO system only, the

maximum errors in salinity and xN for each inclusion were calculated using the upper and lower bounds of error on measured Tmhh and Tmj (Fig. 2-18A). These errors represent the most conservative possible estimate of uncertainty.1 Salinity data for the the NaCl-MgCl2-H20 model system are presented without error information, for clarity.

Tmj falls into two groups (Fig. 2-17), one between -11° and -17°C and the other mostly above -5°C, whereas Tmhh is fairly consistent, between -22° and -25.6°C. This pattern is reflected in the salinities (Fig. 2-18) and confirmed by the maximum-error polygons (Fig. 2-18A): the fluids comprise two groups, a saline one and a moderately saline one, both of which are dominated by NaCl with a smoothly varying 15-37 wt. % of the salinity contributed by CaCh or MgCh. Both fluids are represented in the syn-

1 Sources of error considered in the calculation of maximum errors, besides machine and reading errors, are as follows. Positive errors in salinity were calculated as the difference between salinity (S) and maximum salinity (S^). Smax was calculated using the minimum Tm,ce and either minimum or maximum

XN, whichever gave the greater salinity [from Fig. 2-2 in Oakes et al. (1990) it is evident that for Tmj > -

10°C, the maximum salinity will be derived from the minimum XN, whereas for Tm, < -10°C, Smax is associated with the maximum XN ]. Negative errors in salinity were calculated in a reciprocal way. Note that the resultant errors in salinity are not symmetric even when positive and negative errors on Tmj are equal, due to the reliance of salinity on powers of the absolute Tm„ which is always a larger number for the minimum of the Tm, range than the maximum, thus, the difference between S and Smin will always be greater than that between S and Sraax. Oakes et al. (1990) calculated a 1 a error of 0.038% from the fit of experimental data to their equation; this is an order of magnitude lower than the maximum errors calculated as above and was therefore ignored. Errors in the equation used to derive XN are not given by Chi and Ni (2007). Other potential sources of error unaccounted for are the unknown experimental errors pertaining to the hydrohalite-ice cotectic (Yanatieva, 1946, referenced in Oakes et. al., 1990) and inaccuracies in its plotting (Figure 2 of Oakes et al., 1990).

93 Chapter 2. Controls on mineralization in the Sekwi Formation sphalerite inclusions, whereas only the moderately saline fluid is represented in the syn/post-sphalerite and syn-quartz inclusions. Both fluids are present in the AB and TIC areas.

94 A H2O

Figure 2-18. Salinity of fluid inclusions and FIAs, using (A)

the NaCI-CaCI2-H20 model system of Oakes et al. (1990, 1992), and (B) the NaCI-

CaCl2 0.2 0.4 0.6 0.8 NaCI MgCI2-H20 model system of XNaCi = wt% NaCI/(NaCI+CaCl2) Dubois and Marignac (1997). Larger symbols show FIA salinities derived by averaging ABarea TIC area 2 number of data from >1 inclusion. Errors • • syn-sphalerite FIA indusions O O syn/post-sphalerite FIA averaged are shown only in A. Bars are a syn-quartz FIA j: j >1 lo for the averages; many are too small to show at this scale. Gray boxes are the maximum errors on salinity of B H2O individual inclusions, moderately explained in the text. Group saline ings of data into moderately saline and saline populations are highlighted in B.

MgCl2 0.2 0.4 0.6 0.8 NaCI XNaCi = wt% NaCI/(NaCI+MgCl2) Chapter 2. Controls on mineralization in the Sekwi Formation

SEM-EDS analyses

Qualitative SEM-EDS analyses of evaporate mounds from TIC sphalerite and galena provided 31 spectra that collectively demonstrate the presence of Na-rich and K- rich end-member fluids containing very little Mg or Ca, and a third group of fluids that contain Na, K, and variable amounts of Ca and Mg (Appendix E).

Isotopic studies

Values for sphalerite and barite 834S are shown in Figure 2-19 and Table 2-6. Barite from the AB area has high positive values typical of latest Neoproterozoic to Early Paleozoic seawater sulfate (+28.0 and +31.7%o). Sphalerite at AB and TIC has a wider range of moderately high positive values (+10.1 to +20.6%o), except for the AB Point showing which has a lower 834S of +7.4%o. At the Palm Main showing, 534S values for sphalerite are distinctly depleted compared to the standard (-2.6 and -6.0%o), suggesting a difference in the source or supply process for sulfur.

The three samples of secondary dolomite (Table 2-6) show mildly negative 8I3C values of -0.8 to -5.1%o and a narrow range of moderately heavy oxygen (+20.7 to +21.9%o). The barite 8180 values (12.8 to 13.4%o) are lighter than those of associated dolomite (Table 2-6).

Strontium isotope ratios for sphalerite and dolomite (Fig. 2-20 and Table 2-6) are all high (> 0.713). One sample of sphalerite from TIC C has a significantly higher ratio (0.730) than any other sample. The rest are scattered smoothly between a high of 0.722 and a low of 0.713. Barite ratios are lower (0.709 - 0.710).

96 50 100 ThF1A(®C) 200 250 • Mackenzie Mts. district Sekwi Fm. deposits, FIAs: includes: AB area: • syn-sphalerite, J-_J Gayna R. deposits • syn/post-sphalerite a syn-quartz "*f * * •f ColruiiSekwi Fm.Pm Honncitdeposits B • • • (this study) TIC area: O syn-sphalerite a Prairie Cr. MVT x syn-sphalerite, Th is ThflAm deposits o syn/post-sphalerite

Figure 2-19. Salinity and Th for FIAs from the Sekwi Formation zinc showings (this study) compared to the rest of the Mackenzie Mountains Zn district and to global carbonate-hosted Zn districts. Each point repre sents averaged inclusion data from one FIA. Ranges for the Mackenzie Mountains district are from the current study, studies of Gayna River (Wallace, 2009) and Prairie Creek (Fraser, 1996; MVT style of mineralization only), Carriere and Sangster (1999), and Gleeson (2006). Other districts for comparison are the Alpine and Silesia- Cracow district (Leach et al., 1996,2005), Gays River (Kontak, 1998), the Irish district (Wilkinson, 2010), Lennard Shelf (LS; Leach et al., 2005), Monarch - Kicking Horse (MK; Vandeginste et al., 2007), the Ozark and mid-continental U.S. region (Oz - Miss; Leach et al., 2005), and Pine Point (Gleeson and Turner, 2006). Ranges represent data for fluids inclusions in sphalerite. The ranges for Gays River, Oz-Miss, Irish, and LS include data from secondary inclusions. Salinity ranges repre sent the complete range of data available, whereas Th ranges for Gays River and the Alpine-Silesia district

represent only the most abundant Ths. wt%N = weight percent NaCI equivalent. B^SCOT Area Showing Sample Mineral %S ±0.3 %o AB AB Main AB15 sphalerite 44 16.6 AB AB Main AB16 sphalerite 40 16.6 AB AB-C upper 892A sphalerite 41 13.7 AB AB-C upper 945A sphalerite 46 10.4 AB AB-C upper 945E1 sphalerite 47 20.6 AB AB-C lower C10 sphalerite 46 15.2 AB Point 951D sphalerite 59 7.4 TIC C 827A1 sphalerite 56 10.1 TIC C 827C1 sphalerite 59 15.7 TIC C 827C2 sphalerite 50 14.5 TIC Ryan 824A1 sphalerite 52 11.4 Palm Palm Main 973A sphalerite 46 -2.6 Palm Palm Main 186B sphalerite 51 -6.0 TIC C 827C2 galena 21 10.3 TIC C 827C2 pyrite 69 -2.2 AB AB Main AB27 barite 16 28.0 AB AB-C Upper 892A-Bar barite 15 31.7

6"OVSMOW Area Showing Sample Mineral wt%02 ±0.3%. AB AB Main AB27 barite 30.1 13.4 AB AB-C Upper 892A barite 34.2 12.8

6'°OVSMOW 13 Area Showing Sample Mineral 6 CTOB ±0.3%. AB AB-C upper 945E1 dolomite -0.9 20.7 TIC C 827C2 dolomite -5.1 20.9 Palm Palm Main 186B dolomite -0.8 21.9

,7Sr/"Sr Area Showing Sample Mineral 10.00001 AB AB Main AB16 sphalerite 0.712612 AB AB-C Upper 892A sphalerite 0.713759 AB AB-C Upper 945A sphalerite 0.715099 AB Point 951D sphalerite 0.719941 TIC C 827A1 sphalerite 0.730199 TIC Ryan 824A1 sphalerite 0.722479 Palm Palm Main 973A sphalerite 0.717766 AB ABMain AB27-Bar barite 0.709984 AB AB-C Upper 892A-Bar barite 0.708816 AB AB-C Upper 945E1-DOI dolomite 0.71521 TIC C 827C2-DOI dolomite 0.72059 Palm Palm Main 186B-DOI dolomite 0.713113

Table 2-6. Results of isotopic analyses on mineral samples from Sekwi Formation zinc showings. sphalerite X barite |

20 u-> S to " n=10 i * n=28 10 4 1-

-10 AO ti . Gypsum Redst.R. AB TIC nPalm 'l. Fm. Fm.

Figure 2-20. Sulfur isotope values for sphalerite and barite from the Sekwi Formation zinc showings, grouped by showing area. For com parison, ranges are shown for 28 samples of gypsum from the Gypsum formation of the Neoproterozoic Little Dal Group (Turner, 2009) and 10 samples of gypsum from the Redstone River Formation (Redst. R. Fm.) of the Neoproterozoic Coates Lake Group (Strauss, 1993), both of which are possible sources of the sulfur at the show ings. An arrow marks the sphalerite sample from the AB Point show ing. Chapter 2. Controls on mineralization in the Sekwi Formation

Laboratory Studies: Interpretation

Interpretation of fluid inclusion results

The following issues raised during the heating experiments require explanation: vapor-phase persistence, darkening, and changes in volume of inclusions during heating. The tendency of a mineral to stretch around fluid inclusions is related to its hardness, cleavability, and ductility, as well as to the inclusion's shape, size, and composition (Bodnar and Bethke, 1984; Goldstein and Reynolds, 1994). Sphalerite is a moderately hard, moderately ductile mineral that requires an internal overpressure of 550 bars or more to initiate stretching in inclusions <20 (am in diameter, and at least 450 bars for inclusions of the largest size encountered in the current study (30 jam; Bodnar and Bethke, 1984). Achievement of these internal overpressures in gas-free inclusions of 6-10 wt. %N requires at least 40°C of heating above Thjnc (Bodnar and Bethke, 1984). However, small amounts of a volatile substance, such as methane, can raise the pressure inside an inclusion dramatically during heating (Hanor, 1980; Diamond, 2001, 2003). The behavior of the Sekwi Formation sphalerite inclusions on heating does not allow discrimination between a purely aqueous system and one with a small amount of dissolved gas (Diamond, 2001). Up to 0.062 mol% of CO2 or 0.0024 mol% of CH4, for example, could be dissolved in an aqueous system at lab conditions without developing a separate, volatile-rich phase (Diamond, 2003). Furthermore, a considerably greater amount of volatiles can exist in an inclusion without being detected petrographically; for example, a gas with 2.5 mol% CH4 was released by crush analyses of inclusions that visually consisted only of aqueous vapor and liquid phases (Jones and Kesler,1992). Dissolved volatiles can cause large increases in internal pressures for moderate temperature increases (for example, 530 bars over 25°C; Jones and Kesler, 1992). Small amounts of a volatile substance are therefore inferred to have caused the observed stretching, decrepitation, and vapor-phase persistence in Sekwi Formation sphalerite samples.

The phenomenon of vapor-phase persistence is probably caused by stretching that initiates just prior to final homogenization of the inclusion. The persistent size of the tiny

100 Chapter 2. Controls on mineralization in the Sekwi Formation vapor bubble with continued heating suggests that a linear relationship is maintained between inclusion-volume increase (i.e., stretching) and temperature. Bodnar and Bethke (1984) quantified similar behavior for inclusions hosted by fluorite and attributed the stretching to plastic flow by dislocation glide in the host.

Many inclusions darkened permanently on heating. The darkness of an inclusion depends on both its shape (irregular shapes increase internal reflections) and the contrast in refractive indices between the host mineral and inclusion fluid (the greater the contrast, the more light is reflected back into sphalerite at their interface; e.g., Roedder, 1984). There was no observed change in shape or composition of any of the darkened inclusions, but it is conceivable that tiny irregularities, such as microfractures, formed in the inclusion walls as a consequence of high internal pressures due to the presence of volatiles, and that these irregularities increased the amount of internal reflection.

The presence of volatiles raises the temperature at which an inclusion will

homogenize. Inclusions that homogenized normally did so within 5°C of Ty, so ThFiA >

ThFiAm+5°C. The median ThFiA is 70°C greater than the median ThFiAm, so it can be estimated also that ThpiA < ThnAm+70°C.

In a number of FIAs from the AB Point, TIC C, and TIC Ryan showings, some inclusions displayed vapor-phase persistence and others did not. Whether an inclusion displays vapor-phase persistence may be a function of its size or shape, since stretching is initiated more easily in large, irregularly shaped, and angular inclusions (Bodnar and Bethke, 1984)

The average Th (191.7°C) of all 75 inclusions from syn-sphalerite FIAs chosen for analysis in this study is 19°C less than the average syn-sphalerite ThpiA (for internally consistent FIAs; 210.6°C, Table 2-5). No assemblage with petrographically obvious necking was chosen for microthermometry, yet within-FIA inconsistency in Thinc revealed post-entrapment modifications in numerous FIAs, whose Th data were therefore rejected. This illustrates the point made by Goldstein and Reynolds (1994) that inclusion Th's can only be realistically interpreted within the context of assemblages: even though an assemblage has been identified petrographically as primary without post-entrapment

101 Chapter 2. Controls on mineralization in the Sekwi Formation modifications, consistency of the Th of inclusions within it must still be demonstrated in order to assure use of only unmodified FIAs in the final interpretation. If that had not been done in this study, a Th would have been assumed that was too low by 19°C. As a second example, if one considers only the primary subset of syn-sphalerite FIAs in this study, the average Thjnc of all inclusions is 203°C, which compares to 241°C for those from the one clearly unmodified FIA, a difference of 38°C.

Freezing of most inclusion systems leads to metastable supercooling. Solid phases will nucleate on melting, and a clathrate phase should nucleate in an inclusion containing a carbon-based volatile substance, thereby revealing the presence of the volatile substance. However, at low mole fractions of volatile substance, this phase would melt before ice (Diamond, 2001), and although it might persist metastably into the liquid water field, it would be of very low volume, hence difficult to detect in small inclusions (Diamond, 2001; also Goldstein and Reynolds, 1994 for methods of detection). Some indications of possible clathrate were observed in two FIAs, but neither of these were suspected to contain volatiles based on their heating behavior.

At least two fluids were present during mineralization at the TIC and AB Point showings (Figs. 2-17, 2-18): a moderately saline one with 2 to 8 wt. %N and a saline one with 15 to 19.5 wt. %n (and an outlier at 12 wt. %n). There is no noticeable difference in

ThFiA between the moderately saline and saline fluids, but relatively few data were acquired, and two temperature populations might easily be masked by the uncertain range separating ThFiAmin from T1ifia- If ThFiAmin is assumed to be 10 or 20 degrees less than

Thfia, a clear grouping of the data into two populations ensues (Fig. 2-16B). The minimum temperature of the mineralizing fluid (as represented by syn-sphalerite ThpiA data) ranged from 174°C to 241°C (both end values are outliers; three of the five ThFiA determinations were between 200° and 218°C). Only five syn-sphalerite FIAs provided both ThpiA and salinity data; these are not enough to show trends (Fig. 2-19). The Gayna River group of deposits, hosted by the upper part of the Little Dal Group in the northern Mackenzie Mountains, have the highest Th of the districts shown in Figure 2-19 (161-268 °C for primary inclusions in sphalerite; Wallace, 2009). Other deposits in the Mackenzie Mountains district range up to 218°C (Carriere and Sangster, 1999; Gleeson, 2006). The

102 Chapter 2. Controls on mineralization in the Sekwi Formation

Sekwi showings, like the Gayna River deposits, are at the upper end of the Mackenzie Mountains Th range, but the Gayna River deposits are significantly more saline. Globally, only the Irish district and the Gays River deposits in Nova Scotia have Th comparable to the Mackenzie Mountains district; the highest Th for every other district is <160°C.

Interpretation of isotopic analyses

Sulfur: An overview of sulfur-isotope systematics is provided in Appendix F. The sulfur species of relevance in mineralizing fluids for carbonate-hosted base metal deposits are H2S and SO42". The relative concentrations of these species can have a significant eflFect on the isotopic fractionation between them, and therefore on the isotopic composition of sulfides precipitated from the fluid (Ohmoto and Rye, 1979). If the dissolved sulfur species in the fluid are in isotopic equilibrium, the isotopic ratio of the fluid is the proportional sum of the isotopic ratios of both sulfide and sulfate species in the fluid (Appendix F). The degree of fractionation at equilibrium between S species 'S varies strongly with temperature, and the proportion of dissolved SO4 * to H2S varies with

34 34 pH,yt)2, and the activities of cationic species; the relationship of 5 Sh2s to 5 SflUjd varies with all of these factors. There are many starting conditions that lead to a lower 534S in the precipitated sulfides than in the total fluid, but strongly positive values in the precipitated sulfides have no way to arise other than from a strongly positive source (Ohmoto and Rye, 1979). Only if the fluid is reduced and dominated by H2S will the S34S

34 values of precipitated sulfides be almost identical to the total 5 SflUjd.

If the studied system was not in isotopic equilibrium, the H2S and SO42" in the fluid will be effectively non-reactive and independent of each other (Ohmoto and

34 Goldhaber, 1997), and 8 Sh:s will be dominated by kinetic effects. Potential sulfur sources for precipitated minerals can, in this case, be chosen on the basis of geological

34 constraints, and evaluated by comparing the expected 5 SH2s resulting from the kinetic effects of each process with the observed §34S of precipitated minerals. Thermochemical and bacterial reduction of seawater sulfate are both processes dominated by kinetic effects (Appendix F).

103 Chapter 2. Controls on mineralization in the Sekwi Formation

The sulfur in carbonate-hosted base metal deposits is sourced ultimately from either seawater sulfate or organically bound sulfur (Ohmoto and Goldhaber, 1997; Leach et al, 2005). The 534S of seawater sulfate has fluctuated since the Neoproterozoic between +12%o, a low reached in the Permian, and +32%o, a high at the Neoproterozoic-Cambrian boundary; modern seawater is +20%o (Faure and Mensing, 2005). Seawater during any given epoch had a 534S range of a few per mil. There is very little fractionation of S

34 34 isotopes during dissolution or precipitation of sulfate minerals (i.e., A5 Ssuirate-5 Ssoi =

+1.65 ± 0.1296o during precipitation; Faure and Mensing, 2005), and so 834S of evaporitic sulfate minerals is very close to that of their reservoir, which is contemporaneous seawater sulfate.

The 834S values of sulfur in marine organic matter, including petroleum, vary from -23 to +32%o (Anderson and Pratt, 1995; Faure and Mensing, 2005), and are age- specific, being lighter than contemporaneous seawater by 5 to 20%o (Orr, 1974). This is because the S-isotopic signature of organic matter is dominated by early-diagenetic addition of bacterially reduced, isotopically light sulfur from the surrounding sediments (Thode et al., 1960; Thode, 1981). There is little or no fractionation during migration or low-temperature maturation of oils, however, high-temperature maturation (>135°C) in the presence of evaporitic sulfate causes an increase in 834S of the oil to values that may approach those of the sulfate reservoir, due to isotopic exchange during sulfurization- desulfurization reactions (Orr, 1974). De-sulfurization itself does not cause fractionation, thus the 834S of organically derived S in sulfide minerals is similar to the 534S of the (diagenetically modified) parent organic matter.

The 534S of sphalerite and galena from TIC and AB are moderately high positive values, except for the somewhat lower AB Point sphalerite, while pyrite at TIC and sphalerite at Palm have negative values (Table 2-6; Fig. 2-20). The following possible sources of sulfur are discussed: de-sulfurization of organic matter, thermochemical reduction of seawater sulfate, and bacterial reduction of seawater sulfate (Orr, 1974; Worden et al., 1995; Ohmoto and Goldhaber, 1997).

104 Chapter 2. Controls on mineralization in the Sekwi Formation

Since organic matter has 834S that is 5 to 20%o less than contemporaneous seawater sulfate (Appendix F), which was +12 to +32%o during the Phanerozoic (above), it follows that the range of 534S of organic matter that accumulated during the

Phanerozoic is -8 to +28%o. These values are certainly compatible with an organic source for S in all three showing areas. However, there are no published studies of sulfur isotopes in organic matter from the Mackenzie Mountains, and this, combined with uncertainty about the age of mineralization, makes it difficult to evaluate organic matter as a source of S at the studied showings.

Thermochemical reduction of seawater sulfate is the most attractive process to explain the heavier 534S of sulfides in the TIC and AB areas. The source of the sulfate (seawater or evaporite deposits) is discussed separately (below). Consistently high positive 834S values can derive from thermochemical sulfate reduction (TSR) in systems effectively closed by a limited availability of SO4" (Worden et al., 1995). Closure ensures that each aliquot of dissolved sulfate is reduced as it becomes available, no matter its

S34S, so the 534Sh2s of the final product is the same as that of the source reservoir. Such a process would produce 834Sh2S with a narrow range that matches that of seawater sulfate of the same age as the evaporite. Sphalerite from AB and TIC, however, display a wide range of 834S (+7.4 to +20.6%o). Including early pyrite from TIC and sphalerite from the Palm showings widens the range even further (-6.0 to +20.6%o). This forces consideration of other processes that may have contributed S to these showings. Incomplete TSR in an open system is one such process. TSR is associated with a negative fractionation, and this will be preserved in the 834S of the reduced sulfur if the supply of SO4 was not rate- limiting and if the entire reservoir was not consumed. However, TSR is associated with a maximum fractionation of -14%o (Kiyosu and Krouse, 1990), thus to produce sphalerite with 834S of -6%o would require a source sulfate with 834S of +8%o; there are no recorded sulfate deposits with such light sulfur. The observed values could also be produced by TSR followed by equilibrium fractionation in a fluid rich in unreacted SO4; however, the conditions under which this could happen are restrictive, for instance, for a neutral fluid containing 0.01 mole total S, the molar ratio of dissolved SO4 to H2S would have to be 10 or more and the temperature of the fluid would have to remain under 240°C (Ohmoto and

105 Chapter 2. Controls on mineralization in the Sekwi Formation

Goldhaber, 1997). If the fluid was acidic, the proportion of SO4 would have to be even greater.

Bacterial sulfate reduction (BSR) is associated with a strong negative fractionation. Since BSR in a closed system can produce sulfide minerals with positive S34S (e.g., Ohmoto and Goldhaber, 1997), it should be evaluated as a possible source of all the sulfur in the studied showings. In a closed BSR system, sulfides with negative 834S would form early in the process and co-exist with later, heavier sulfides. At AB, TIC, and Palm, all the analyzed sulfides are heavier than +7%o, except for three samples whose

834S are -6.0 to -2.2%o (TIC pyrite and Palm sphalerite). The lack of strong negative values and the paucity of mildly negative ones rules out closed-system BSR as the source of heavy sulfur.

A mixture of bacteriogenic S with TSR-derived S can explain the range of observed values. For example, if BSR-derived sulfide that had a 834S value of -20%o mixed in a ratio of 20:80 with TSR-derived sulfide that had S34S of +20%o, the average 834S of the mixture would be +12%o, very close to the average +10.1%o of the measured sulfides. The bacteriogenic S is most likely second-generation, re-mobilized from sedimentary pyrite or early-diagenetic, BSR-produced sulfide minerals. First-generation BSR is unlikely to have been the source because there is no evidence that mineralization took place on or near the seafloor, and in fact spatial relations at Palm Main - where the most-negative sulfur is - and in the AB area suggest that mineralization formed during or after Cretaceous-Tertiary faulting. Microscopic, disseminated pyrite of probable sedimentary or early-diagenetic origin is common in the carbonate host rocks at TIC and AB, but is also expected to be common in most of the marine sedimentary units in the succession.

Seawater sulfate can be contained in seawater that penetrates the subsurface, or it can be captured in evaporitic rocks and subsequently dissolved by sub-surface fluids. There are a number of candidate evaporite formations in the Mackenzie Mountains that could have been the sulfate reservoir. The oldest are the early to middle Neoproterozoic Gypsum formation of the Little Dal Group, and the middle to late Neoproterozoic Redstone River Formation of the Coates Lake Group. Twenty-eight samples of anhydrite

106 Chapter 2. Controls on mineralization in the Sekwi Formation from two stratigraphic sections measured through the Gypsum formation had 534S values of+14 to +18%o (Turner, 2009). Ten samples of anhydrite and gypsum from the Redstone

River Formation had 534S of+15 to +25%o (Strauss, 1993). The Early Devonian Camsell Formation was deposited in restricted basins 50 to 200 km SE of the studied showings. The late Early Devonian Fort Norman Formation (dolostone-anhydrite) and its surface equivalent, the Bear Rock Formation (limestone breccia), are extensive on the Mackenzie platform east of the showings. Sulfur isotope data for these units are not available, but they can be expected to have §34S of+17%o or so based on global values for Early

Devonian evaporites (Faure and Mensing, 2005). There are also Middle Devonian shale- hosted barite deposits that have 834S of 23.9 to 56.5%o (Fernandes, 2011). Seawater of Late Cretaceous age had 534S values of+18 to +20%o (Faure and Mensing, 2005).

The Devonian evaporites are probably too light to have been the source of S in this study. The maximum 534S obtained from Gypsum formation (18%o) is also lower than some of the sphalerite in this study (20.6%o). The Redstone River Formation is heavy enough to have been the source reservoir but is of limited geographic extent. Late Cretaceous seawater is also heavy enough; it is considered a possible source reservoir of S in the studied showings. Of the evaporite units, the Gypsum formation is the most probable S source because of its greater geographic extent and corresponding volume, and its proximity beneath the studied showings (Aitken and Cook, 1974; Blusson, 1974; Gordey et al. 2010a). Its maximum §34S may not have been sampled, and furthermore, there is no apparent reason that heavier sulfur from the Redstone River Formation couldn't have been involved along with S from the Gypsum formation.

The sulfur in barite at AB is at least 7 to 11 %o heavier than in associated sphalerite (Fig. 2-20), and exceeds the heaviest value measured in the possible evaporite sources by 6%o. It is possible for precipitated sulfate to be heavier than its source evaporite if the sulfate is precipitated from a fluid in which evaporitic/seawater SO42" and co-existing TSR-produced H2S are undergoing isotopic equilibrium fractionation. This seems improbable in a system in which SO42" availability is rate-limiting, as postulated for the system that produced the heavier sulfides at TIC and AB (above). The heavy S in barite may also have been produced during disequilibrium reduction (e.g., TSR) in a system

107 Chapter 2. Controls on mineralization in the Sekwi Formation closed to SO4 Alternatively, a fluid containing dissolved evaporitic/seawater SO4" mixed with a fluid containing H2S from dissolved, BSR-derived pyrite, creating a SO4: H2S ratio favorable for fluid fractionation of S isotopes (above) and capable of producing

SO4 * heavier than in the original fluid (Ohmoto and Rye, 1979). A variant on the latter process is for the S042"-bearing fluid to dissolve sulfide minerals along its flow path, producing the same effect.

If different sulfide species precipitate in equilibrium, a predictable, temperature- dependent fractionation among them can be used to determine the temperature of precipitation. Fractionation increases with decreasing bond strength, therefore S34S decreases in the following order: sulfate minerals - pyrite - sphalerite - galena. Pyrite, sphalerite, and galena were separated from a sample of the TIC C zone. The sphalerite and galena were very coarse-grained, intimately intergrown, and petrographically co- genetic, whereas the pyrite was partly replaced by galena. The 834S of the pyrite is -2.2%o and much lower than 834S of sphalerite or galena (14.5 and 10.3%o, respectively), which proves its disequilibrium with those minerals (Ohmoto and Rye, 1979). Precipitation temperatures calculated from the sphalerite-galena pair assuming isotopic equilibrium yielded a temperature of only 144 ± 25°C, which is much lower than the average 209°C ThpiA obtained from fluid inclusion microthermometry for the TIC C zone. The fractionation was larger than expected, whereas disequilibrium precipitation of two minerals would typically lead to an observed fractionation that is smaller than the equilibrium fractionation. The pair are interpreted to have precipitated in equilibrium, then later re-equilibrated to the measured values.

Sulfur isotope ratios were measured in co-genetic barite and sphalerite from a sample of AB-C Upper zone. The 534S of barite and sphalerite that precipitated from an equilibrium fluid at 200°C would differ by 29.6%o (Aba-sp = 29.6%o); at 300°C, the difference would be only 20.4%o. In the AB sample, the difference is 18%o (Table 2-6). Textural relations in this sample indicate that sphalerite precipitated both before and during barite precipitation. Assuming isotopic equilibrium, using the measured Aba-sp along with experimentally determined equilibrium fractionation factors (Ohmoto and Goldhaber, 1997), the temperature of precipitation is calculated as 337°C.

108 Chapter 2. Controls on mineralization in the Sekwi Formation

The sulfur isotope data are best explained as follows. The S in sulfides was derived primarily by TSR of dissolved sulfate from either Neoproterozoic evaporites or Cretaceous seawater, and was mixed with S derived by BSR. Sphalerite from Palm and pyrite from TIC exhibit the strongest BSR influence. The S in barite was produced by fractionation within a mixed fluid containing both SO4 and H2S. The sphalerite and galena in a TIC sample were precipitated in equilibrium but later re-equilibrated, invalidating the calculated temperature of precipitation. The barite and sphalerite from an AB sample precipitated in equilibrium at 337°C. The implications of this are discussed below.

Oxveen: The average 5180 value for three samples of secondary, void-filling dolomite is +21.2%o (Table 2-6). An equation that describes the temperature-dependant fractionation of oxygen isotopes between dolomite and water (Zheng, 1999) can be used to calculate the 8180 value of the fluid from which the dolomite precipitated. The temperature of the fluid is constrained by the similarity between Sr isotope ratios of dolomite and sphalerite, which suggests the two minerals precipitated from the same fluid. Therefore, the temperature is assumed to have been between 200°C and 350°C (from microthermometry results; this range is refined below; Discussion, Fluid properites). Solving the fractionation equation of Zheng (1999) for these temperatures 10 ID and the average 8 O value of the void-filling dolomite determines the 5 O value of the 1 Q dolomite-precipitating fluid to have been between +11.1 and +16.5%o. Such 8 O values preclude a purely meteoric or seawater origin for the precipitating fluid and suggest interaction with marine sedimentary rocks, which have 8I80 values of 15-32%o (Phanerozoic examples; Faure and Mensing, 2005). If the fluid interacted with igneous or 1X terrigenous sedimentary rocks (8 O values of 0-11%o; Faure and Mensing, 2005), it would be expected to have lower 8lsO values than calculated; eg. at 200-350°C, it would equilibrate to -9.8 to +6.4%o. The calculated +11 to +17%o range of S180 values for the dolomite-precipitating fluid is compatible with a fluid that equilibrated with marine carbonate rocks at 200-350°C.

The same approach can be used to estimate the 8180 values of the barite- precipitating fluid, using the experimentally derived equation of Kusakabe and Robinson

109 Chapter 2. Controls on mineralization in the Sekwi Formation

(1977) for oxygen isotope fractionation between barite and saline water, and the average

5!80 value of+13.1%o for two barite samples. By assuming temperatures from 100° to 400°C, the 5,80 value of the barite-precipitating fluid is calculated to have been -0.6 to

+12.5%o. In this case, although barite and sphalerite precipitation alternated with time, there is little evidence that they precipitated from a single fluid, and the Sr isotope ratios 1 ft of barite suggest strongly that they did not. Furthermore, the calculated 8 O values of the barite- and dolomite-precipitating fluids are different at every temperature (the barite fluid is consistently lighter), additional evidence that the two minerals precipitated from different fluids. Since there is other evidence for the existence of two fluids during mineralization (two populations of salinity data, clustering at the ends of a range of Th data, two Sr reservoirs (below), two sources of sulfur), it can be assumed that the barite precipitated from a cooler fluid than the sphalerite and dolomite. This fluid at 150°C would have had 5180 of +3.6%o, or at 200°C, +6.6%o. These values imply a fluid that did not interact with rocks as long as the dolomite-precipitating fluid, or interacted with lower-S180 rocks, or interacted in a system with a larger fluid:rock ratio.

Carbon: The 5!3C values of secondary dolomite are mildly negative, and not as low as would be expected were the carbon derived from oxidation of organic matter during TSR. The precipitation during TSR of carbonate minerals with signatures suggestive of an inorganic marine source during TSR is not uncommon (Machel et al., 1995) and may be due to: (1) a sulfate reduction - organic matter oxidation reaction that doesn't generate bicarbonate (HCO3 ; equation 3a of Machel et al., 1995), in which case carbonate minerals are not precipitated as a result of TSR, or (2) prior saturation of the pore fluid with respect to a carbonate mineral containing inorganic marine carbon, in which case the introduction of a small amount of TSR-derived HCO3" with light C would initiate precipitation of the carbonate mineral with heavy C.

The 513C value of the dolomite-precipitating fluid can be calculated using the factors for equilibrium fractionation between dolomite and CO2 given graphically by Ohmoto and Goldhaber (1997), but this requires knowledge of the relative proportions of oxidized and reduced carbon species in solution, or an assumption that those species were not in equilibrium, an uncertain assumption above 300°C (Ohmoto and Goldhaber, 1997).

110 Chapter 2. Controls on mineralization in the Sekwi Formation

The HCO3" produced by dissolution of carbonate minerals is thought to have a very similar 813C value to that of the original mineral, regardless of whether the fractionation is controlled by equilibrium processes (Ohmoto and Goldhaber, 1997). If the same is true of precipitation as dissolution, it follows that dolomite that was dissolved and re-precipitated locally, without intervening changes in the redox state or chemistry of the fluid, would have essentially unchanged 813C values. Sekwi Formation S13C values range from -6.5 to +3.5%o (Dilliard, 2009). The 813C values of secondary dolomite at the showings fall neatly within this range, and are compatible with local derivation of the carbon.

Strontium: The measured strontium isotopic ratios (87Sr/86Sr) of sphalerite, barite and dolomite (Table 2-6, Fig. 2-21) are inferred to reflect the same ratio that was in the fluid from which these phases precipitated. This is reasonable given that Rb, from which 87Sr is produced by radioactive decay, is excluded from the structures of those minerals. 87Sr/86Sr ratios of sphalerite and dolomite from all three showings are consistently much higher than 87Sr/86Sr of seawater at any time from the Cambrian to the present (Veizer et al., 1999), and include the highest values yet published for any minerals in the northern Canadian Cordillera (0.713 to 0.730). Dolomite has similar 87Sr/86Sr values (0.713 to 0.721) and was probably sourced from the same fluid as sphalerite. These high values

on indicate that mineralizing fluids interacted with a radiogenic reservoir enriched in Sr, which also implies elevated Rb. Barite has lower Sr ratios (0.709-0.710) that are more typical of a seawater or marine carbonate-rock source. Barite is present only in the AB area, where paragenetically it was preceded and succeeded by sphalerite, and succeeded by dolomite.

Candidate Rb-87Sr reservoirs for the Sr in sphalerite and dolomite include granitoid rocks and felsic gneisses in the basement, and any siliciclastic rocks in the succession that were produced by weathering of granitoid rocks. If one invokes convective circulation, which has a downward component of flow, potential reservoirs for 87 w the elevated Sr/ Sr measured in dolomite and sphalerite include the Lower Paleozoic shales overlying the showings, as well as a number of dominantly shale units in the Proterozoic rocks underlying the showings. A 15-20 km thickness of supracrustal rocks,

111 0.730

1c 0.720 CO

maxWCSB 0.710

a) a. TJ <0 <0 AB TIC Palm

Figure 2-21. Strontium isotope ratios for sphalerite, barite, and dolomite from the Sekwi Formation zinc showings, grouped by showing area. The regional maximum 87Sr/®6Sr of leachable Sr in shales of the Western Canada Sedimentary Basin (maxWCSB) is shown for reference (Machel and Cavell, 1999). Arrows mark sphalerite data from the AB Point and TIC C showings. Chapter 2. Controls on mineralization in the Sekwi Formation tentatively correlated with parts of the Mesoproterozoic Wernecke Supergroup and the early Neoproterozoic MMSG, is deduced by seismic evidence and geological reasoning to lie beneath the fold-and-thrust belt of the northern Cordillera (Fort Simpson basin; Cook and Erdmer, 2005). Beneath this basin, at depths of more than 30 km, is the poorly understood, westward-thinning Nahanni-Fort Simpson terrane, which at least locally includes granitic rocks (Jefferson and Parish, 1989; Thorkelson et al., 2005), and the Cordilleran lithospheric mantle (Cook et al., 1999; Cook and Erdmer, 2005; Lynn et al., 2005). Although these deeply underlying units may contain possible Sr donors, the depth of circulation would have to be explained before either was invoked as a source of radiogenic Sr.

The Sr isotopic composition is not known for any of the underlying and most of the overlying possible source units. Samples of the Cambro-Ordovician Rabbitkettle Formation, which contains some silty shales but is predominantly a carbonate unit, returned 87Sr/86Sr analyses of 0.711 and 0.712 (Cousens, 2007). The mobile component of Sr (that available to be leached by passing fluids) in Devonian shales of the southern Western Canada Sedimentary Basin was determined to have a Sr isotope ratio of 0.712 (Machel and Cavell, 1999). Numerous whole-rock samples of younger age from the same basin, up to and including Pleistocene glacial till, have consistent ratios of <0.712. A few whole-rock analyses of Cambrian strata led to the presumption that, if the mobile proportion of the Cambrian rocks would be separated, it would have the same ratio as the Devonian shales (references in Machel and Cavell, 1999). On these bases, the 0.712 value was deemed a maximum 87Sr/86Sr for strata in the Western Canada Sedimentary Basin from Recent to Devonian, and potentially a maximum also for strata as old as Cambrian. The measured Sr isotope ratios of the Sekwi-hosted sphalerite and dolomite are much higher than this. Highly radiogenic Sr is characteristic of tectonic provinces dominated by older granitic and gneissic rocks (e.g., Superior Province, 0.7295, Churchill, 0.7248) whereas less-radiogenic Sr characterizes younger provinces (Grenville, 0.7151, Paleozoic, 0.7117; Faure and Mensing, 2005). The strikingly radiogenic Sr of the Sekwi mineralization (0.713 - 0.730) probably reflects a Precambrian, felsic crystalline source.

113 Chapter 2. Controls on mineralization in the Sekwi Formation

87 fiA The Sr/ Sr ratios of sphalerite and dolomite vary continuously from 0.713 to 0.722, with a high-value outlier from TIC C sphalerite at 0.730 (Fig. 2-21). The higher values, from the TIC and Point showings, indicate either a longer interaction of fluids with the radiogenic reservoir, or a different reservoir that was richer in radiogenic strontium. Passage of the TIC-Point fluids through deeper, basement faults could have caused both a longer residence time and interaction with a different source. Including those from barite, the measured 87Sr/86Sr values are spread over a range that suggests mixing of very-radiogenic and marine-carbonate end-member fluids.

Discussion

Dolomitization of the Sekwi Formation

The Sekwi Formation consists regionally of limestone, yet around each showing it is pervasively dolomitized, suggesting the possibility that dolomitization was genetically related to mineralization. In the AB area, the pervasive-destructive type of dolomitization is limited to members 1 and 3, the incomplete-retentive type has affected members 2 and 4, and the pervasive-retentive type surrounds the mineralized showings in member 2. The vertical extents and coarseness of these forms of dolomitization preclude their being primary (Machel, 2004). The lateral extents of the pervasive-destructive and incomplete- retentive types are characteristic of burial diagenesis (Machel, 2004) but not unique to it, because laterally extensive bodies of dolomite can also form from hydrothermal fluids (Davies and Smith, 2006). Oomoldic dolomite of the incomplete-retentive type in member 2 of the Sekwi Formation has the same dull cathodoluminescence and non- ferroan nature as the void-filling variant of the pervasive-retentive type at the showings. The pervasive-retentive type is genetically related to mineralization and is hydrothermal (below). Its similarity with at least some of the incomplete-retentive type supports a hydrothermal origin for the incomplete-retentive type as well.

The mineralization-related, pervasive-retentive type of dolomitization consists of replacive dolomite punctuated by micro-pores, and void-filling dolomite. The void-filling dolomite is later than the replacive, because veinlets of the former cross-cut the latter, but

114 Chapter 2. Controls on mineralization in the Sekwi Formation both are inferred from petrographic evidence to have originated from different stages of the same fluid-flow event (a common phenomenon in dolostones; Braithwaite, 1991). The evidence is that single crystals commonly change in character from replacive to void-filling where they are located at the edge of a void (Fig. 2-6A). Apparent overgrowth can also arise through replacement of a precursor void-filling phase by dolomite, but there is no evidence of replacement or a replaced mineral. In addition, it is improbable that two temporally distinct fluid events could create the observed, property- scale spatial relationship at AB, in which the extent of pervasive, replacive dolomitization contains the extent of brecciation and void-filling dolomitization (see also Davies and Smith, 2006). Petrographic textures show that micropores developed early in the replacive-dolomitization process and were occluded by void-filling dolomite later in the same process, a sequence of events that has also been described by Machel (2004) and Davies and Smith (2006).

Co-genetic, void-filling dolomite and micro-porous replacive dolomite are recognized in the TIC and Palm areas as well. In the TIC area, however, replacive dolomite has been recrystallized and the dolostone around breccia bodies has an altered appearance in outcrop. Petrographic evidence of recrystallization (discussed above) is supported by the generally patchy luminescence of the dolomite (Braithwaite, 1991) and its lack of zoning (Mazzullo, 1992).

The synchroneity of replacive dolomite with void-filling dolomite, and the independently determined synchroneity of void-filling dolomite with sphalerite at all of the showings, indicate that dolomitization, brecciation, and mineralization were overlapping parts of one fluid-flow event at each showing. The mineralizing process began with post-diagenetic dolomitization that was pervasive near the showings and selective distal to them. The dolomitization process included matrix replacement, development of inter-grain micro-porosity, and grain-selective dissolution followed by mold-filling. Dolomitization was followed by the main mineralizing event. Sphalerite occluded micro-voids and grew outward from them to replace the surrounding dolomite. At some showings, textural evidence of early events was obliterated by intense brecciation, precipitation of blocky cements in the voids, and local re-brecciation,

115 Chapter 2. Controls on mineralization in the Sekwi Formation annealing, and re-crystallization of the host dolostone (Fig. 2-8). In the AB and Palm areas, brecciation was induced by hydraulic fracturing and enhanced by later dissolution. TIC showings are dominated by extreme dissolution textures and retain no evidence of any possible initial hydraulic fracturing. Brecciation and ore-mineral precipitation were complete prior to precipitation of quartz and calcite.

Controls on mineralization

AB area: This study has highlighted three controls on mineralization in the AB area, which are structural, stratigraphic, and lithologic (Appendix C). The first-order control is structural. This control is also evident in the Palm area. Mineralization is spatially associated with fractures and faults at multiple scales, from microscopic to regional. Regional and property-scale faults, although barren, were probably active during mineralization and served as fluid conduits, whereas precipitation occurred in the microscopic and mesoscopic fractures at the propagating tips of faults. The obvious mineralization-related faulting is Cretaceous-Tertiary. A paleo-vally that may have been a fault graben (AB showings, Geology) is spatially related to a number of showings, including AB-C, Link, and Point, all of which lie close to the locus of thickening, within the thicker strata. This association raises the possibility that Cambrian faults were also fluid conduits, but does not clarify whether mineralization was Cambrian or the faults were re-activated in the Cretaceous-Tertiary.

Two second-order controls are lithological and stratigraphic. The lithological control applies clearly to all three showing areas. It is expressed in the fact that only specific rock types are mineralized. Rocks susceptible to mineralization are dark, mottled dolostone with silt-rich, porous, burrowed domains in a finer, organic?-matter rich matrix (AB-C Lower, AB Main, AB Point, Palm Main), and dolomitized grainstone to rudstone that is either organic?-rich or directly overlies organic?-rich dolostone (AB-C Upper, Link, TIC C, TIC Ryan). A subordinate susceptible rock type is fenestral dolostone that overlies organic?-rich carbonate mudstone (Palm Waterfall). The stratigraphic control is clear only in the AB area, where susceptible rocks are mineralized only where they are the lowest such rocks in the local stratigraphic succession. Being lowest, they would be

116 Chapter 2. Controls on mineralization in the Sekwi Formation the first encountered by mineralizing fluids rising along fault conduits, as has been suggested for deposits in the Irish Midlands (Hitzman and Beaty, 1996). For example, the ooid dolograinstone of member 4 is not mineralized, whereas the dolograinstone of the underlying member 2 is, and the Franklin Mountain Formation is not well mineralized where it overlies susceptible, mineralized lithofacies in the Sekwi Formation. Thus, mineralized rocks are adjacent to a fault or fracture that served as a conduit for mineralizing fluids during active tectonism, are of a type that is susceptible to mineralization, and are the lowest susceptible rocks in the local stratigraphic succession.

TIC area: In the TIC area, only one of the three controls evident at AB clearly applies. Mineralization is confined to zones of dissolution breccia, which are concentrated in susceptible rock layers. Drilling between the C and Ryan zones (Ronning, 1975) intersected 60 m of breccia with minimal sulfides at the expected level of the Darkl member. This confirms the impression given by outcrop exposures that there is a strong lithologic control on dissolution brecciation.

Near the TICl measured section and the Ryan showing, there is a vertically extensive zone of recrystallization and brecciation that is at least partly due to solution collapse. The vertical extent of this zone requires that fluids moved across stratigraphy, perhaps along a fault or fracture (Fig. 2-1OB, C). This inferred structure is located where the rock-matrix breccia is exposed on surface, parallel to known faults in the area. The thickness of the Laminated3 member in the TICl section would then be due to structural repetition. Exposure is poor and compatible with an offset of anywhere from 0 to 30 m. In the alternative interpretation, no fault is present, and solutions moved along permeable horizons and vertically along unmapped fractures.

Brecciation is stronger in the Dark and Vuggy units, which comprise rocks with grainstone/rudstone or, less commonly, fenestral textures. As at AB, rocks with these characteristics seem to have high alteration potential (the same intrinsic factors that promote burial diagenesis and are discussed by Choquette and James, 1990). However, the Vuggy unit is brecciated at section TIC2 but not at TICl; the Darkl unit is brecciated at the C zone but not in the adjacent section TICl, and is brecciated in section TIC5 but not in the adjacent section TIC3; and the Dark2 and Dark3 units are brecciated in the

117 Chapter 2. Controls on mineralization in the Sekwi Formation southern sections but not in the north. There is thus some kind of over-riding spatial control on brecciation. Furthermore, mineralization in the breccia is patchy, showing that there are also spatial controls on sulfides. The nature of these controls is unknown. There may have been a primary patchy distribution of susceptible rock types, which is captured by the "fault-absent" interpretation (Fig. 2-IOC). The "fault-present" interpretation allows for the possibility that metal sulfides precipitated only in proximity to a fault conduit. Detailed mapping is needed to detect if there are any faults near the Ryan and C zones. The D and E zones are interpreted to be within 100 m of a fault that has about 20 m of offset where it crosses a saddle east of the showings (Fig. 2-1OB).

In summary, at TIC, geological considerations (above) show that the mineralization was likely part of the same event as the dolomitization and dissolution brecciation. The brecciation and subsequent mineralization were confined to susceptible rocks, which were those of the Dark and Vuggy units, but were also subject to a primary spatial control that remains unidentified.

Palm area: Mineralization at Palm is controlled primarily by the location and perhaps the orientation of fault conduits. Although the porosity of the Fenestral member and the inherent dissolution potential of the Mottled member were important in localizing precipitation, it is clear from field observations that the primary control was fluid access along faults. A stratigraphic control is absent or subordinate in this area: the lowest susceptible unit at the Waterfall zone (the Mottled member) is not mineralized.

A steep, south-side-down fault adjacent to the Main zone bears a direct spatial relationship to intensity of mineralization, and is presumed to have conducted the mineralizing fluids. Only the north side of the fault is mineralized, even though a suitable rock, the fenestral unit, lies south of the fault. The dip of the fault is unknown. It has been demonstrated that fluids tend to rise into the hangingwall of a normal fault in response to fault-related stress fields and fluid buoyancy (Phillips, 1972; Davies and Smith, 2006). It can be shown, by application of the same principles, that the hangingwall preference holds for reverse faults as well. These principles may indicate why the north side of the fault is a preferred site for mineralization, and may account for the absence of mineralization in the Mottled unit at the Waterfall zone.

118 Chapter 2. Controls on mineralization in the Sekwi Formation

Sekwi Formation: Mineralization in the Sekwi Formation is more common in the Upper Carbonate member and in the higher stratigraphic sequences. It is proposed that this reflects the relative paucity of susceptible rock types in the Lower Carbonate member and earlier sequence, which are dominated by deep-water, fine-grained deposits.

Mackenzie Mountains: The Sekwi Formation is confirmed as a preferred host of mineralization in the overall succession, pending better data on other host formations. Three other stratigraphic levels in the Mackenzie Mountains contain a disproportionate number of carbonate-hosted showings: the Neoproterozoic Little Dal Group, the Ordovician-Silurian Mount Kindle Formation, and the Middle Devonian Arnica and Landry formations. These preferences may be a larger-scale expression of the lowest susceptible-carbonate control discussed above.

Organic matter is deemed to be of importance as a lithological control in the studied Sekwi Formation-hosted showings, but it has not been definitively identified in the host rocks (aside from pyrobitumen in vugs), and its importance in the overall succession is difficult to assess. Available descriptions do not mention organic matter, although they commonly describe the host as a black or dark dolostone (Dewing et al., 2006; references in NORMIN, 2011). There are numerous examples of dark, possibly organic-rich rock that is not mineralized, both within and outside the Sekwi Formation, so if organic matter is of importance, it is so only where the other controlling conditions were already met.

119 Chapter 2. Controls on mineralization in the Sekwi Formation

Evidence for at least two fluids

At least two fluids were present during mineralization. This is established by microthermometry for the TIC and AB Point showings, where a moderately saline fluid

(2 to 8 wt. %N) and a saline one (12-15 to 19.5 wt. %N) participated in precipitation of sphalerite. It is also suggested by the S isotope data which are best explained by the mixture of a fluid containing dissolved evaporitic SO4 or TSR-derived H2S with a fluid containing BSR-derived H2S. The involvement of two fluids left evidence of two 1 R different 5 OfiUjd values, two different Sr reservoirs (a highly radiogenic, deep one and a marine-carbonate one), and a range of temperatures that may represent the mixing of a wanner and cooler fluid. A Na-rich and a K-rich fluid, both of which were Ca- and Mg- poor, are inferred from SEM-EDS analyses of fluid inclusion evaporate mounds at TIC (Appendix E) to have mixed together, subsequently equilibrating to varying degrees with a carbonate host and acquiring correspondingly variable amounts of Ca and Mg.

Host-unit burial history and hydrothermal vs. geothermal fluids

The microthermometry data indicate that at least some of the mineralizing fluids at AB Point and TIC were hotter than the measured TIIFIA of 174-241°C. In order to identify times at which the host rock and associated geothermal fluids may have been that hot, it is necessary to know the pressure-temperature history of the host rock. If this history reveals that the mineralizing fluids were hotter than any temperature achieved by the host rock during its history, then the fluids were hydrothermal. In that case, it is necessary to identify episodes of orogeny, extension, or igneous activity during which hydrothermal flow might have occurred. In the upper parts of the crust under consideration, temperature increases with depth along a geothermal gradient that is approximately linear. Normal geotherms in the upper parts of Phanerozoic orogens are 20-30°C/km (Condie, 2005), but measured gradients in the Mackenzie Plain, east of the Mackenzie Mountains, indicate much higher Cenozoic gradients of 28-37°C/km (Feinstein et al., 1996). Modern surface heat-flow in the northern Cordillera averages 105 mW/m2 (as compared to 73 mW/m2 in the southern Cordillera). A corresponding modern

120 Chapter 2. Controls on mineralization in the Sekwi Formation geothermal gradient for the northern Cordillera is roughly calculated to be between 27°

•y and 34°C/km. Gradients of 30° and 35°C/km were therefore chosen as representative.

Figure 2-22 is a time vs. depth chart that shows isotherms for a constant geotherm of 25°C/km throughout the Paleozoic and most of the Mesozoic, and for elevated gradients beginning with the onset of the Cretaceous-Tertiary orogeny, achieving maxima of 30 and 35°C/km by the end of the Late Cretaceous. Although modern heat flow in the northern Cordillera is elevated compared to other Phanerozoic orogens, it is not known if the higher gradient began with orogeny, as implied in Figure 2-22, or at some other time. The depths of the top and bottom of the Sekwi Formation were calculated by summing the thicknesses of overlying units, at the times represented by their stratigraphic ages. Thicknesses are un-decompressed, maximum thicknesses of units currently overlying Sekwi Formation in the region between 63° to 65°N and 128° to 132°W. The Sekwi Formation in that area is up to 1000 m thick, although in the vicinity of the showings it does not exceed 800 m. Basinal units that do not overlie the Sekwi Formation near the studied showings (eg. Hess River Formation) are excluded, even though they overlie it elsewhere. Exhumation is shown beginning with the Late Cretaceous (Martel et al., 201 la) and largely completed by 50 m.y. ago. Earlier intervals of extension and Late Devonian tectonism are shown. Any uplift associated with tectonism is not represented; such omissions exaggerate burial depths. Conversely, maximum measured stratigraphic thicknesses represent minimum depositional thicknesses after unknown amounts of erosion, mechanical compaction, and dissolution. Other sources of error are introduced by the use of regional maximums of stratigraphic thickness, because the Lower to Middle

2 See, for example, Ranalli (1995) for derivation and discussion of the equation. Tz = T0 +(qo/C)z -

Az*/2C where Tz = temperature at depth z in degrees Kelvin (K), T0 = temperature at surface in K, q0= surface heat flux in W/m2, C = thermal conductivity in W/mK, and A is the radiogenic heat function. This equation is valid for an isotropic crust in steady state without heat sinks, where heat is transferred by conduction (second term) and generated by radioactivity (third term). Tz was calculated for thermal conductivities in W/mK of 4 for basalt and 3.3 for granite (Brown et al., 1992), and heat generation rates in 10"6 W/m3 of 2.8 for granite and 0.09 for tholeiitic basalt (Ranalli, 1995). Cordilleran crust can be assumed to be somewhere between these extremes.

121 orogeny, plutonism to SW tectomsm, orogeny o—— •ill Carb Pm Ter EwlvLm

EJR

150°C base

200°C

age (Ma)

Figure 2-22. Burial history of the Sekwi Formation. Dashed gray lines are isotherms. The Cambrian to Late Cretaceous isotherm is 25°C/km. Isotherms for both 30°C/km and 35°C/km are shown for the period from 100 to 0 m.y. ago; the range between them is shaded (see text). Black lines show the depths of the top and base of the Sekwi Forma tion through time. Unconformities are represented by horizontal parts of the curves. Dashed portions represent a hypothetical 500-1000m of Cretaceous foreland sedimenta tion (see text); for clarity, the path of exhumation is shown for only the maximum depth. Stratigraphic thickness data are from: Blusson (1971,1972); Fritz (1976,1978,1979a); Morrow (1991, and unpublished field notes at Geological Survey of Canada, Calgary); Gordey and Anderson (1993); and Martel et al. (2011a). Periods of tectonism (peaks are marked by hollow circles, duration is denoted by lines), orogeny (thick lines), and pluto nism (filled ellipses) are from Cecile (1982), Gordey et al. (1987), Gordey and Anderson (1993), Morrow et al. (1990), Nelson et al. (2006), and Martel et al. (2011a). The duration and cause of the Late Devonian or Early Carboniferous thermal event are not known. The timeline is from Gradstein et al. (2004). Chapter 2. Controls on mineralization in the Sekwi Formation

Paleozoic Mackenzie Platform was characterized by subregions with differential subsidence (Morrow, 1991; Cecile et al., 1997). Undocumented (later-eroded) deposition is, for the most part, not accounted for; very few strata of Late Paleozoic and Mesozoic age are preserved and their paleogeographic distribution is largely unknown. However, Cretaceous sedimentation is assumed to have occurred in the foreland of the advancing orogen (dashed lines, Fig. 2-22). The circumstances that allowed accumulation of 1300 m of Cretaceous strata in a fault-bounded block southeast of the showings were unusual (Gordey et al., 2011). Two alternative thicknesses of Cretaceous strata over the showings, of 500m and 1000m, are shown on the figure; 1000 m is probably excessive. The geothermal gradient may have increased during episodes of tectonism and orogeny other than the Cretaceous-Tertiary, and in fact a regional geothermal anomaly is known from the Late Devonian (Morrow et al., 1990, and below); these increases are not shown. Since the mineral showings under consideration are in the hanging wall of the Plateau Fault, tectonic loading during the Paleozoic and Mesozoic is assumed to have been minimal.

The top of the Sekwi Formation in the study area was buried to a maximum depth of 5.4 km, and its base to 6.5 km, prior to its exhumation during the Cretaceous-Tertiary orogeny (Fig. 2-22). Under the geothermal conditions shown, the Sekwi Formation was never buried deeply enough to reach even 200°C. If a 35°C/km gradient prevailed prior to the Cretaceous, the base of the Sekwi Formation may have reached temperatures over

200°C, but not the maximum ThFIA of 241°C determined in this study. Th represents a minimum temperature of trapping (Tt), with the difference between Th and Tt increasing with pressure of trapping (Pt) and therefore with depth; so no matter when mineralization occurred, the temperatures of the ore-forming fluids were higher than could be achieved by burial under the assumed geothermal gradients. Their temperature can be explained either by a regional geothermal anomaly that was larger and earlier than the one shown in Figure 2-22, or hydrothermal fluids.

Times of orogeny and extension that are candidates for raising the regional geothermal gradient or for stimulating migration of hydrothermal fluids are indicated in Figure 2-22. Structural and stratigraphic evidence show that extension, with localized components of compression, created the Misty Creek Embayment in the Middle to Late

123 Chapter 2. Controls on mineralization in the Sekwi Formation

Cambrian (Cecile, 1982; Gordey and Anderson, 1993). Mid-Ordovician renewal of extension, accompanied by intermittent volcanism, lasted until the Early to Middle Devonian (Cecile, 1982). A Late Devonian regional geothermal anomaly is suggested by conodont color alteration indices (CA1) of 4 to 5 (corresponding to temperatures of 190° to 480°C; Epstein et al., 1977; Rejebian et al., 1987) in the vicinity of the Palm and TIC showings, and CAI of 4 to 6 (190° to 550°C) across the Mackenzie Platform south and east of the study area for all rocks up to early Late Devonian in age, combined with much lower CAI of 2.5 to 3.5 for younger rocks of latest Devonian to Late Carboniferous age (Morrow et al., 1990; Martel et al., 201 lb). This thermal event created the Manetoe facies, an extensive vuggy dolomitization of mid-Early to early Middle Devonian strata across 38,000 km2, and was followed by maturation and migration of hydrocarbons (Morrow et al., 1990). Regional uplift occurred sometime after the Middle Devonian (Cook et al., 1999) and may have been associated with the Late Devonian thermal event. The latest event was the Cretaceous-Tertiary orogeny. These are all candidate episodes for hydrothermal or elevated-temperature geothermal flow, but larger geothermal anomalies would be required during the earlier candidate episodes, when the burial temperatures were less.

If the composition and Th of the fluid in an FIA are known, and appropriate equations of state are available, the fluid's density can be determined. Fluid densities in this study ranged from 4.7x10"2 to 5.0x10"2 mol/cm3 (Bodnar, 2003). The density and other data can be used to construct isochores in pressure-temperature (P-T) space for the fluid from each FIA (Fig. 2-23; Bodnar, 2003). Fluids trapped during mineralization are constrained to have P, T along their respective isochores. The temperature of trapping (Tt) can therefore be determined for any imagined pressure of trapping (Pt) by projecting the intersection of Pt with the isochore down to the temperature axis (for example, if FIA 824A1#7 was trapped at 1970 bars, Tt was about 370°C). Furthermore, the estimated maximum depth of burial (Fig, 2-22) constrains Pt to <1970 bar (using a pressure gradient of 303 bar/km). If a typical geothermal gradient prevailed, the P,T of any parcel of Sekwi Formation would lie on the line of that gradient at all times, and therefore Pt,Tt would be at the intersection of the gradient and the isochore. Conversely, a volume of Sekwi Formation under the influence of hydrothermal fluids would have P,T on an

124 F!A isochores syn-Sp syn/post-Sp syn-quartz

2000 , maxPt (base), Late Cret.

maxPt (top) Late Cret min Pt -V for Tt= possible Pt 337'C Mid Devonian

• range of 1000 possible trapping conditions

possible Pt Mtd Cambrian

200 v t f 300 ft 400 maxTt for coolest FIA: maxTt for hottest FIA: Temperature (C) 260-278'C Figure 2-23. Range of possible pressure-temperature conditions of trapping, shaded gray, and isochores for FIAs that yielded Th and salinity data. Isochores are labeled with FIA number followed in brackets by molar volumes in cm3/mol. The three geotherms used in Fig. 2-22 are shown as gray lines. Horizontal dashed lines are relevant pressures. Maximum pressure of trapping (maxPt) is for a lithostatic gradient of 303 bar/km and an estimated maximum depth of burial of 5.4 km for the top of the Sekwi Formation and 6.5 km for its base at the beginning of the Late Cretaceous (Fig. 2-22; see text). Estimated Pt are also shown for the cases of mineralization during the Middle Devonian and Middle Cambrian. Thick, vertical dashed lines are temperatures of trapping, determined from the intersection of Pt lines with isochores. The maxi mum possible temperature of trapping (maxTt) corresponds to the greatest depth of burial and is about 270°C for the coolest FIA and 360°C for the hottest. The diagram shows that the actual Tt of the hottest fluid studied (FIA 824A1#7) was between 241°C (ThFIA) and about 360°C (max Tt), and its pressure was between 30 bar (pressure at homogenization, Ph) and 1970 bar (max Pt). The 337°C temperature calculated for the AB area from the barite-sphalerite geothermometer corresponds to Pt>1450 bar (dashed blue lines), equivalent to a depth of >4.8 km. Programs used to calculate the isochores are from the package FLUIDS (Bakker, 2003). Bulk fluid-inclusion densities and molar volumes at homogenization were calculated using the BULK program (version 01/03), using measured ThFIA, mass% salts calculated with AqSo3e (v. 03/02) for the system H20-NaCI-MgCI2, (using data from Dubois and Marignac (1997), and the equation of state of Zhang & Frantz, 1987). Isochores in the one-component field were calculated with the ISOC program (v. 01/03), using as input the bulk fluid inclu sion molar volumes and amount-of-substance fractions at homogenization T-P that were output by the BULK program, and the same equation of state (Zhang & Frantz, 1987). Sp = sphalerite. Chapter 2. Controls on mineralization in the Sekwi Formation unknown curve whose shape would depend on the fluid's initial T and cooling characteristics, but would include a section with a steep positive slope. Without knowing the shape of the hydrotherm, its intersection with the isochore (its Pt,Tt) cannot be located. None of the isochores from our samples intersect any of the illustrated geothermal gradients at pressures below the maximum possible Pt of -2000 bars. This confirms that a hydrothermal fluid is the only reasonable source of heat for the observed temperatures and densities. The coolest fluid trapped in the five inclusions shown in

Figure 2-23 was between 174°C (the coolest TIIFIA) and 260°-268°C (maximum T at top and base of Sekwi Formation, respectively). The hottest fluid was between 241°C and 350°-370°C.

The application of a barite-sphalerite geothermometer gives a precipitation temperature of 337°C (above). The approximate Pt for a fluid with Tt of 337°C, Th of 219° to 241°C, and similar density to fluids in this study would be 1450 to 1970 bars (Fig. 2-23), corresponding to a depth of 4.8-6.5 km. The two fluid inclusions studied with Th<219°C must have had a Tt<337°C, otherwise Pt would be outside the range of possible trapping conditions (Fig. 2-23). Therefore, 337°C is near the high end of the entire range of mineralizing fluid temperatures.

Since there were two fluids, one of which was hydrothermal, it follows that the other was geothermal, and the range of measured Th is a mixing trend. The temperature of the hydrothermal fluid can be estimated from the isochore data and depth-of-burial constraints as between the extremes of 174°C and 370°C. Under the highest reasonable geothermal gradient of 35°C/km, the temperature at the base of the Sekwi Formation would have been 217°C, so that termperature is taken to be the maximum allowable temperature of the geothermal fluid. To establish the lowest allowable temperature, the lowest ThnAm is raised by 5°C, the smallest difference that might exist between ThFiAm and ThFiA (see Interpretation of fluid inclusion results). The geothermal fluid was therefore 135-217°C, and the hydrothermal fluid, which had to have been hotter, was probably 250-350°C.

126 Chapter 2. Controls on mineralization in the Sekwi Formation

Fluid properties and sources of components

Many of the studied inclusions are inferred to have contained minute quantities of dissolved volatiles. Only three FIAs containing such inclusions yielded salinity data; two of these belonged to the saline group and one to the moderately saline group. Thus, both fluids probably contained small quantities of a volatile substance such as CH4 or CO2 (Hanor, 1980; Diamond, 2003). This conclusion depends on the presence of volatiles being the cause of vapor-phase persistence, darkening, and stretching.

The properties of mineralizing fluids fluctuated with time between reducing and oxidizing. This is revealed by the overlap of sulfides and sulfate in the paragenetic sequence at AB, and the temporal alternation of ferroan and non-ferroan dolomite at AB Point and Palm Main. More-gradual, unidirectional change in the chemical composition of the fluid is shown by the change from the bright cathodoluminescence of the matrix- replacive dolomite to the dull luminescence of the void-filling dolomite. Both scales of change may have been in response to fluid mixing.

The first step in putting together the information on two fluids is to assume that the fluid with highly radiogenic Sr, which must have come from a deep source, was also the warmer, hydrothermal fluid. For the sake of argument, it is assumed to have been the saline fluid as well, but the alternate assumption (that the shallow fluid was the saline one) would not alter the model (below) that derives from these assumptions. By default, then, the marine-carbonate Sr was carried in the cooler, more-shallowly circulating fluid, which was moderately saline. Consideration of the regional stratigraphy suggests that the shallower fluid (fluid 1) carried seawater/evaporite sulfate, and the deeper fluid (fluid 2) leached base metals from the thick sedimentary pile. Either fluid may have carried the required component of bacterially reduced sulfide, but limited evidence from sulfur isotopes (the high positive fractionation of 34S into barite and the geographic gradient in 834S values of sulfide minerals) suggests that the H2S was not in the same fluid as the

SO4, therefore it was in fluid 2. Fluid 2 equilibrated with felsic crystalline rocks (based on Sr isotope data from sphalerite and dolomite) and later with marine carbonates at 250°-350°C (oxygen isotope data from dolomite and SEM data from evaporate mounds).

127 Chapter 2. Controls on mineralization in the Sekwi Formation

Fluid 1 persisted after the main mineralizing phase, since microthermometry indicates that it was involved in the precipitation of post-sphalerite quartz and the formation of secondary fluid inclusions in sphalerite..

The marine 87Sr/86Sr values in barite (0.7088-0.7100; Table 2-6) suggest that fluid 1 equilibrated with a marine carbonate rock having the same range of values (see Interpretation, above). The most obvious candidate is the host Sekwi Formation, which has a compatible 87Sr/86Sr range of 0.7085 to 0.7200 (Dilliard, 2006). To test this possibility, the 5180 of a fluid that equilibrated with Sekwi Formation can be calculated and compared with the 5180 of the barite-precipitating fluid, which is +2.5%o at 135°C or

+7.4%o at 217°C. Sekwi Formation has 5180 of+14 to +27%o (Dilliard, 2006). A fluid that equilibrated with Sekwi Formation at 135°C would have 5I80 of +0.4 to +12.6%o; at

217°C, 5lsO of +5.1 to +18.1 %o. Thus, the calculated §,80 range of the barite- precipitating fluid and the 87Sr/86Sr values of barite are compatible with fluid 1 equilibrating with Sekwi Formation at 135-217°C.

Timing of mineralization

The dolomitization and mineralization event at AB-C and AB Main post-dates the development of solution seams. At Palm, at least some chemical dissolution due to burial compaction post-dated the precipitation of ore-stage dolomite. Solution seams in carbonate rocks develop over a wide range of shallow to intermediate burial depths, with the shallowest appearance and eventual morphology dependent on the duration of burial, rock composition, temperature, and other factors (for example, Tada and Siever, 1989; Railsback, 1993a, b; Nicolaides and Wallace, 1997). The shallowest known depth of formation for solution seams in argillaceous limestone without meteoric influence is roughly 500 m (Nelson et al., 1988; Lind, 1993; Fabricius, 2000), however, meteoric waters enable formation of solution seams at shallower depths. There are no meteoric cements at Palm or AB, and no evidence of meteoric fluids in inclusions at Palm (Carriere and Sangster, 1999). Thus, the host rock in the Palm area was at least 500 m deep at some time after mineralization. This burial might have occurred at any time between about the mid-Ordovician and mid-Eocene; mineralization is constrained poorly, Chapter 2. Controls on mineralization in the Sekwi Formation to pre-mid-Eocene. Late-stage mineralizing fluids at AB may have included a meteoric component, because a syn-quartz FIA in a post-sphalerite quartz grain contained dilute fluid (2.0 ±1.1 wt%N; Fig. 2-18). Thus, the relationship of mineralization to solution seams doesn't provide useful constraints on the age of mineralization for these showings.

Constraints on age also follow from the depth of mineralization, which has been constrained for the AB-C upper zone to 4.8-6.5 km (assuming barite and sphalerite were in equilibrium; Fig. 2-23). The Sekwi Formation was buried to these depths between Late Devonian and Late Cretaceous (Fig. 2-22). A more broadly applicable constraint follows from the presence of a geothermal fluid that was 135-217°C at the depth of trapping (which follows from microthermometry and is therefore applicable to the AB Point, TIC C, and TIC Ryan showings). Under a gradient of 30-35°C/km, that depth would have been between 3.9 km and the deepest that the base of the Sekwi Formation was buried, about 6.5 km. The depth of mineralization was therefore at least 4 km, which constrains it to between Early Devonian and Late Cretaceous (Fig. 2-22).

Geological evidence in the Palm and AB areas shows the mineralization to be post-diagenetic and controlled by late faults; and in the AB area, a curvilinear zone of intermittent brecciation that is genetically associated with mineralization crosses a late reverse fault. The simplest explanation for this requires that mineralization postdate the fault. Deformation due to contractional orogeny in the AB and Palm areas began sometime during the Late Cretaceous (Gordey et al., 2011), therefore at least some mineralization is Late Cretaceous or younger. If the pyrobirumen at AB Point was emplaced during the initial migration of hydrocarbons in the Mackenzie Mountains, and not re-mobilized later, that particular showing was mineralized in the Late Devonian or Early Carboniferous (Morrow and Aulstead, 1995). Geological constraints for the age of the TIC showings are not as narrow; mineralization is post-diagenetic and therefore post- Early Ordovician. The depth-of-burial constraint (4-6.5 km) provides a narrower age constraint for TIC than does geological evidence.

Recent work on the Gayna River deposit, a Zn-Pb deposit hosted by Neoproterozoic carbonate rocks in the northern Mackenzie Mountains, tentatively supports a Cretaceous to Tertiary age for that deposit as well, based on Re/Os isotope Chapter 2. Controls on mineralization in the Sekwi Formation analyses of ore-stage pyrobitumen (Wallace, 2009), however, the genetic association of the pyrobitumen with the ore is not certain. The Prairie Creek Zn-Pb-Ag deposits in the southern Mackenzie Mountains display three clearly different ages and styles of mineralization: a syngenetic or early diagenetic replacement type in Silurian dolostone, an MVT type in an Early Devonian host, and a vein type that fills dilatant fractures parallel to regional, Cretaceous-Tertiary faults (Paradis, 2007). The 87Sr/86Sr data from these deposits form two separate populations, one from the stratabound and Cretaceous- Tertiary-vein types of mineralization (0.7142-0.7285), and the other from the MVT mineralization (<0.7127). The stratabound and vein types of mineralization have distinct lead sources (Paradis, 2007). The combined data from Sekwi-hosted showings and Prairie Creek support the existence of at least two temporally separated mineralizing events, one of which extended across the entire Mackenzie Mountains.

Chalcopyrite disease is present in sphalerite at the same showings that have the highest 87Sr/86Sr values, the TIC showings and the Point showing. Chalcopyrite disease has been attributed to the replacement of high-Fe sphalerite by a combination of chalcopyrite and low-Fe sphalerite at temperatures between 200 and 400°C (Barton and Bethke, 1987), a process that requires the presence of copper in the system. The presence or absence of chalcopyrite disease at the studied showings probably reflects the presence or absence of copper in the fluid - i.e., the fluid's composition - rather than higher versus lower fluid temperature, because limited evidence suggests equally high temperatures at showings with and without chalcopyrite disease. Although syn-sphalerite TIIFIA data were not obtainable for any of the low-87Sr, chalcopyrite-disease-free showings (Palm and AB showings except Point), a TIIFIA of 215°C was obtained for a syn-quartz (paragenetically post-sphalerite) FIA at AB Main. That Th is comparable to the TIIFIA of the high-87Sr, chalcopyrite-diseased showings (ThpiA = 174 to 241°C). Based on this evidence, Th is inferred not to have differed significantly between showings with and without chalcopyrite disease, meaning that the presence of chalcopyrite disease is explained by compositional differences between the fluids rather than their temperatures. This inference, combined with the distinctly higher 87Sr/86Sr and lower 834S at Point than at other AB showings, and the evidence (albeit inconclusive) for mineralization during

130 Chapter 2. Controls on mineralization in the Sekwi Formation hydrocarbon migration, suggests that at least two, temporally distinct mineralizing events were responsible for the observed mineralization in the AB area.

Models

Any carbonate-hosted base metal deposit requires metals, sulfur, a reductant if the sulfur is oxidized, and one or more fluids to transport these components to the site of sulfide-mineral precipitation. A driving mechanism for fluid movement is also required. The characteristics of the fluids, as determined from this study, are described above.

Sulfur may be transported in solution as sulfate or sulfide, or may be available as deposits of solid sulfate or sulfide at the site of mineralization. There is no evidence of prior sulfide or sulfate deposits at any of the studied showings, and S isotope evidence is best explained by transportation of S in solution, mostly as SO4 " in fluid 1 and the reaminder as H2S or HS~ in fluid 2.

The transportation of metals and reduced sulfur in a single fluid through carbonate rocks is improbable because of the high acidity required to stabilize the metals in solution with reduced sulfur, and the buffering effect the carbonate host rock would have on an acidic solution (e.g., Leach et al, 2005). The single-fluid reduced-sulfur model has been invoked for some deposits in the Viburnum Trend (Sverjensky, 1981; 1986), but is thought to be more plausible where most of the fluid's journey was through siliciclastic rocks and its metal load was deposited in the first carbonate rocks encountered (Leach et al., 2005). That is not a viable mechanism for the studied showings because there are unmineralized carbonate rocks underlying all of them. However, a small amount of bacteriogenic reduced sulfur did travel in the same fluid as either the metals or the sulfate.

The most abundant reductant in sedimentary basins is organic matter, which can exist as migrating hydrocarbons or at the site of deposition as trapped gas or solid organic matter. The only petroleum inclusions in sphalerite are clearly secondary, which suggests that the reductant was not a fluid. There are, however, suggestions of larger than normal amounts of organic matter at all of the showings. The host units at TIC C and Ryan, Palm

131 Chapter 2. Controls on mineralization in the Sekwi Formation

Main, AB Main, AB-C Lower, and AB Point are all dark gray to black with possible organic matter, and minor pyrobitumen is ubiquitous in the AB area.

A number of driving forces have been invoked to explain the movement of mineralizing fluids in carbonate-hosted Zn districts (Garven and Raffensperger, 1997). The tectonic fluid-expulsion (Oliver, 1986; Machel, and Cavell, 1999) and topography- driven flow (Garven and Freeze, 1984a,b; Morrow, 1998a) models both predict mineralization in the foreland of an orogen, far from the locus of uplift, yet the Sekwi deposits are adjacent to faults related to the uplift. If, as it appears, the age of the deposits is coincident with uplift of the host rocks in the Late Cretaceous or Tertiary, then models of deposit formation require a fluid-driving mechanism based on convective circulation (Garven and Raffensperger, 1997) or seismically-induced fluid fluxes (Sibson et al., 1975; Sibson, 2001).

The combined evidence discussed above requires the depositional model to comply with the following conditions. Two fluids participated in formation of the mineralization. Fluid 1 was geothermal,l 35-217°C, contained dissolved Neoproterozoic evaporites or Late Cretaceous-seawater sulfate, had a marine-Sr isotope signature, and had equilibrated with Sekwi Formation or a similar marine carbonate. For the sake of argument, it was of moderate to low salinity whereas fluid 2 was saline. Fluid 2 was hydrothermal, 250°-350°C, and carried base metals and extremely radiogenic Sr. It probably was a mixture of two precursors, a Na-rich and a K-rich fluid, and initially contained very little Ca or Mg. Either fluid 1 or fluid 2 carried some sulfur from dissolved sedimentary (BSR-derived) sulfide minerals; limited and indirect evidence from barite 834S values suggests this was fluid 2. Ideally, the model would allow for two mineralizing events in the AB area (above, Timing of mineralization).

The time of movement of the hydrothermal fluid is constrained by the depth of mineralization and regional tectonic history to the Devono-Carboniferous or Late Cretaceous, and by showing-scale geology to the Late Cretaceous. The Late Cretaceous - Early Tertiary Plateau fault is the main structural feature of the central Mackenzie Mountains. Its basal detachment is estimated to be at approximately 14 km, and a second major level of detachment along the Little Dal Group Gypsum formation is at about 7 km

132 Chapter 2. Controls on mineralization in the Sekwi Formation beneath the north-central Mackenzie Mountains in the vicinity of the Palm showings (Gordey et al., 2010a). The basal detachment is within the sedimentary pile well above the basement, which is estimated to lie below 30 km depth (Gordey et al., 2011). A structural cross-section shows the Palm area to be vertically above the locus along which the Shale Lake fault departs from the Gypsum formation detachment to cut up through overlying strata (Gordey et al., 2010b). The TIC area is clearly along-trend of the same line, 20 km northwest of Palm, and it is reasonable to assume a similar relationship in the AB area 110 km northwest of TIC (Fig. 2-2), based on regional geology (Blusson, 1974; Gordey and Makepeace, 2003).

A model is hereby proposed, in which a saline fluid 2 became hotter as it circulated through felsic crystalline basement. When compression began in the Late Cretaceous, fluid 2 moved up a network of faults and fractures, propelled by buoyancy and seismic pumping, acquiring metals and bacteriogenic sulfide from shale-dominated units in the thick pile of overlying sediments, and Ca and Mg from carbonate rocks (possibly including the host Sekwi Formation). Fluid 2 lost heat as it rose, so that it was 250-350°C when it was at 4-6 km depth. Where fluid 2 encountered carbonate lithofacies with high alteration potential (dolograinstone/rudstone or burrow-mottled dolostone), it penetrated these strata by hydraulic fracturing and dissolution, dolomitizing and locally brecciating them.

Meanwhile, fluid 1 originated either as Late Cretaceous seawater that acquired heat and salinity as it descended through bedrock to Sekwi Formation, or as formation water that rose from the level of the Little Dal Group evaporite unit, where it had dissolved the sulfate rock, to the Sekwi Formation. In either case, it contained marine Sr, was moderately saline, and equilibrated thermally with the host Sekwi Formation. If fluid 1 originated as formation water, it must have experienced a component of convective flow or (if mineralization happened after the main deformation) extreme lateral flow, in order to arrive at the Sekwi Formation, which was above the evaporite unit at all times.

Thermochemical reduction of the fluid-1 sulfate by organic matter in the Sekwi Formation was catalyzed by the BSR-derived H2S or HS" in fluid 2. Sekwi Formation pore waters became enriched in reduced sulfur, which combined with the metals brought Chapter 2. Controls on mineralization in the Sekwi Formation by fluid 2 to precipitate pyrite and ore minerals. Hydraulic fracturing and brecciation created new pathways for F^S-bearing fluid to move upward buoyantly, leading to precipitation of sulfides in overlying units that were not rich in organics, such as the oncoid-ooid grainstone at AB-C and Link (AB area). Fracturing was aided by localized structural dilation, for example, in the transfer zones between regional contractional faults.

Another model is for the dissolved sulfate to have been reduced distally and carried to the Sekwi Formation as dissolved sulfide, where it encountered fluid 2. In this scenario, fluid 1 contained dissolved sulfide, not sulfate. The fluid that carried dissolved sulfate can be called proto-fluid 1. Reduction of the dissolved S04 in proto-fluid 1 might have been initiated by an encounter with migrating hydrocarbons (in which case mineralization would be Carboniferous or later; Morrow and Aulstead, 1995), or alternatively by passage of proto-fluid 1 through rocks rich in organic matter other than the Sekwi Formation. Hydrocarbon source rocks and other non-Sekwi organic-rich strata are restricted to the Phanerozoic stratigraphically above Sekwi Formation, so if proto- fluid 1 acquired its sulfate by dissolution of Neoproterozoic evaporites, it must have moved upward through kilometers of strata from its Neoproterozoic source, and subsequently, reduced fluid 1 must have moved downward from the site(s) of reduction to Sekwi Formation. Flow in both upward and downward directions implies convective circulation, which requires a driver such as a heat differential between shallower and deeper areas. An alternative sulfate reservoir is Late Cretaceous seawater that acquired heat and salinity and was reduced as it descended through the shaley, organic matter-rich units overlying Sekwi Formation. In either case, fluid 1 descended through mostly non- reactive, siliciclastic strata until it arrived at Sekwi Formation. In this model, subsequent activity along the Plateau fault and various steep faults provided the means and route for hot fluid 2 to rise from the basement as far as Sekwi Formation, where it encountered the reduced sulfur of fluid 1. Metal-sulfide precipitation, fracturing and brecciation proceeded as in the first model.

To distinguish between evaporitic and seawater sulfate reservoirs, further data such as halogen ratios in fluid inclusions would be helpful, or mass balance calculations

134 Chapter 2. Controls on mineralization in the Sekwi Formation to determine the plausibility of a fluid evolving that contained sufficient SO4 in the time available from Late Cretaceous seawater. Modeling of fluid flow in plausible Late Cretaceous structures would provide a useful test of both of the models, and help to distinguish between the two possible sulfate reservoirs. Neither model addresses the possibility of two separate mineralizing events in the AB area, because the evidence for two events is indirect and, as yet, uncorroborated. Measurements of organic matter in the Sekwi Formation would be useful to aid in determining the site of reduction.

The Mackenzie Mountains deposits appear to be late-orogenic, like the Alpine deposits of the Silesia-Cracow district of Poland (Leach et al., 1996). The Mackenzie Mountains deposits formed in a very different environment than did the syngenetic to early-diagenetic Irish deposits (Hitzman and Beaty, 1996), despite similarly high fluid temperatures. Furthermore, the Lennard Shelf deposits of Australia, which formed almost as early in the depositional history of their host rocks as the Irish deposits (15-30 Ma; Verncombe et al., 1996), are characterized by low fluid temperatures. The temperatures of ore-forming fluids, although necessarily related to regional processes, are clearly not diagnostic of those processes, nor of the timing of mineralization with respect to them.

Conclusions

The Sekwi Formation is confirmed as a preferred host of mineralization in the Mackenzie Mountains zinc district (Fig. 2-3). Structural, stratigraphic, and lithologic features controlled the localization of mineralization within the Sekwi Formation. The first-order control in the AB and Palm areas is proximity to faults. A spatial association of mineralization with faults and fractures at multiple scales is present. Strontium isotope evidence shows that mineralizing fluids circulated through Proterozoic basement rocks, and so faults must have provided access to the overlying Sekwi Formation strata. No fault conduits have been positively identified at the TIC showings, but a fault is hypothesized (Fig. 2-1OB, C) to explain the spatially restricted distribution of mineralization.

A second-order stratigraphic control is present in the AB area. Susceptible rock types are mineralized only where they are present at the base of the local stratigraphic succession, because these were the first encountered by rising fluids. A third control is

135 Chapter 2. Controls on mineralization in the Sekwi Formation lithologic. The mineralized rocks in all three areas have increased alteration potential due to the contrast in crystal size and composition between mm- to cm-scale domains. There are only three recognized rock types that are well mineralized: dolograinstone/rudstone, in which allochems (predominantly ooids, oncoids or intraclasts) contrast with matrix; dark, mottled dolostone, in which centrimetric mottled domains with a high siliciclastic content contrast with the surrounding, finer, dark rock; and fenestral dolostone in which mm-scale fenestral vugs contrast with the surrounding, very finely crystalline rock. The host rocks are either dark with organic? matter or overlie dark, organic?-rich rocks. These three susceptible rock types are common throughout the Sekwi Formation, but are mineralized only where they occur in proximity to fluid conduits and, in the AB area, low in the local stratigraphic succession. The preference of mineralization for the Upper Carbonate member is probably a lithological rather than stratigraphic control, reflecting the relative abundance of susceptible rocks in that member.

The long (>500 m.y.) history of the host rocks cautions against any assumption that all of the showings are of the same age. The TIC and AB-Point fluids tapped a more- radiogenic Sr reservoir or spent a longer time in a radiogenic reservoir, were supplied with S that had a distinctly lower 834S, and were more Cu-rich than the fluids that deposited the other AB-area showings. The presence of two distinct fluids in a restricted geographic area such as that near AB Point and AB-C can best be explained by the development of two discrete plumbing systems at separate times, that is, by two mineralizing events. The spatial association of mineralization with late faults in the Palm and AB areas suggests a very young age for at least some of the mineralization, especially in the AB area, where a curvilinear zone of mineralized breccia crosses a Cretaceous- Tertiary fault. However, a Late Devonian or Early Carboniferous age is implied by the paragenetic relationships of sphalerite, pyrobitumen, and saddle dolomite at the AB Point showing.

The model that best explains the field observations and analytical data calls for the mixing of two fluids in Sekwi Formation host strata. Fluid 1 was geothermal, 135°- 217°C, moderately saline, and had equilibrated with marine carbonate rocks. It contained sulfate from Neoproterozoic evaporites or Cretaceous seawater. Fluid 2 originated in

136 Chapter 2. Controls on mineralization in the Sekwi Formation felsic crystalline basement. It rose up active faults under pressure during the Cretaceous- Tertiary orogeny, cooling as it rose, leaching metals and bacteriogenic sulfide from the deep sedimentary pile and acquiring Ca and Mg from carbonate strata. It was a saline, hydrothermal fluid of 250-350°C when it reached the Sekwi Formation at 4-6 km depth and moved laterally into susceptible layers by dissolution and hydraulic fracturing, causing dolomitization and local brecciation. The minor sulfide in fluid 2 catalyzed thermochemical sulfate reduction (TSR) in organic-rich strata that contained sulfate from fluid 1 in their pore waters. The sulfide, both TSR-produced and bacteriogenic, combined with the metals from fluid 2 to precipitate as metal sulfide deposits in the lowest susceptible units of the Sekwi Formation. The data from this study, in combination with existing data on highly radiogenic Sr at both Prairie Creek and Gayna River (Paradis, 2007; Wallace, 2009), suggests there was an expulsion of mineralizing fluids from great depths throughout the Mackenzie Mountains region during the Late Cretaceous or Tertiary.

In the AB area, undiscovered mineralization may be present in the subsurface north of the AB Fault, where Sekwi Formation is probably the lowest susceptible unit. Particular targets in this area are the at-depth and along-strike extensions of the curvilinear breccia zone. Mineralization should also be sought regionally, in the hanging wall and immediate footwall of the southeastern continuation of the AB thrust fault, wherever meso-scale faults cut susceptible rocks of the Sekwi Formation. In the TIC area, mineralization is expected at the intersection of the postulated fault with the Darkl unit (Fig. 2-10B). (Interestingly, the 1975 vertical drill holes were sited 300-400 m east of the projected intersection.) Along-strike extensions of the mineralized Darkl and Dark2 units that are topographically lower, and therefore less eroded, should be sought outside the immediate TIC area. Extensions of the mineralization at Palm should be sought in mottled and fenestral hosts north of the Palm Main-zone fault, on strike with the Main zone to its east.

Significant carbonate-hosted Zn±Pb deposits in the Mackenzie Mountains should be sought in the Upper Carbonate member of the Sekwi Formation. Mineralized Sekwi Formation will be heavily dolomitized in the hangingwall of regional contractional faults,

137 Chapter 2. Controls on mineralization in the Sekwi Formation and will be disrupted by a number of steep faults. Areas sandwiched between two thrust splays may be particularly conducive to steep faulting. Controlling factors known from other deposits, such as the presence of a low-permeability cap rock over susceptible units, should not be ignored even though they were not identified in this study. Any unit near the bottom of the local succession that consists of the susceptible rock types described above, especially if it is a dark, organic-rich unit or overlies an organic-rich unit, is a potential host of mineralization only if it is cut by steep faults, preferably faults that intersect each other within the susceptible unit.

138 Chapter 2. Controls on mineralization in the Sekwi Formation

References, Chapter 2

Aitken, J.D. and Cook, D.G., 1974, Geological maps showing bedrock geology of the northern parts of Mount Eduni and Bonnet Plume Lake map area, District of Mackenzie, N.W.T.: Open File 221, Geological Survey of Canada, Ottawa, Canada, 1 map at 1:250,000 scale.

Aitken, J.D., Macqueen, R.W., and Usher, J.L., 1973, Reconnaissance studies of Proterozoic and Cambrian stratigraphy, lower Mackenzie River area (Operation Norman), District of Mackenzie: Paper 73-9, Geological Survey of Canada, Ottawa, Canada, 178 p.

Anderson and Pratt, 1995, Isotopic evidence for the origin of organic sulfur and elemental sulfur in marine sediments, in Vairavamurthy, M.A. and Schoonen, M.A.A, editors, Geochemical Transformations of Sedimentary Sulfur: American Chemical Society, Washington, USA, p. 378-396.

Baker, D.E.L and Seccombe, P.K., 2004, Physical conditions of gold deposition at the McPhees deposit, Pilbara craton, western Australia: fluid inclusion and stable isotope constraints: The Canadian Mineralogist, v. 42, p. 1405-1424.

Bakker, R.J., 2003, Package FLUIDS 1. Computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties: Chemical Geology v. 194, p. 3-23.

Barton, P.B. Jr. and Bethke, P.M., Chalcopyrite disease in sphalerite: Pathology and epidemiology: American Mineralogist, v. 72, p. 451-467.

Blusson, S.L., 1971, Sekwi Mountain map area, Yukon Territory and District of Mackenzie: Paper 71-22, Geological Survey of Canada, Ottawa, Canada, 17 p.

Blusson, S.L., 1972, Geology, Sekwi Mountain, Northwest Territories and Yukon Territory: Map 1333A, Geological Survey of Canada, Ottawa, Canada, scale 1:250,000.

Blusson, S.L., 1974, Five geological maps of northern Selwyn Basin (Operation Stewart), Yukon Territory and District of Mackenzie, NWT: Open File 205, Geological Survey of Canada, Ottawa, Canada, 5 maps, scale 1:250,000.

Bodnar, R. J., 2003, Chapter 4: Introduction to aqueous-electrolyte fluid inclusions, in Samson, I., Anderson, A., and Marshall, D., editors, Fluid Inclusions: Analysis and

139 Chapter 2. Controls on mineralization in the Sekwi Formation

Interpretation: Short Course Series v. 32, Mineralogical Association of Canada, Vancouver, Canada, p. 81-100.

Bodnar, R.J. and Bethke, P.M., 1984, Systematics of stretching of fluid inclusions I: Fluorite and sphalerite at 1 atmosphere confining pressure: Economic Geology, v. 79, p. 141-161.

Braithwaite, C.J.R., 1991, Dolomites, a reivew of origins, geometry and textures: Transactions of the Royal Society of Edinburgh: Earth Sciences, v. 82, p. 99-112.

Brock, J.S., 1973, Geological, Geochemical, and Prospecting Investigations on the TEE- LJN, RAK, ARN EMILY and ICE Claims Groups: unpublished Assessment Report 080339, submitted by Welcome North Mines Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Brown, G.C., Hawkesworth, C.J., and Wilson, R.C.L., 1992, Understanding the Earth: Cambridge University Press, New York.

Cecile, M.P., 1982, The Lower Paleozoic Misty Creek Embayment, Selwyn Basin, Yukon and Northwest Territories: Bulletin 335, Geological Survey of Canada, Ottawa, Canada, 78 p. and 1 map.

Cecile, M.P., Morrow, D.W., and Williams, G.K., 1997, Early Paleozoic (Cambrian to Early Devonian) tectonic framework, Canadian Cordillera: Bulletin of Canadian Petroleum Geology, v. 45, p. 54-74.

Chi, G.X. and Ni, P., 2007, Equations for calculation of NaCl/(NaCl+CaC12) ratios and salinities from hydrohalite-melting and ice-melting termperatures in the H20-NaCl- CaC12 system: Acta Petrologica Sinica, v. 23, p. 33-37.

Choquette, P.W. and James, N.P., 1990, Limestones - The burial diagenetic environment, in Mcllreath, I.A. and Morrow, D.W., editors, Diagenesis: Geoscience Canada Reprint Series 4, p. 75-111.

140 Chapter 2. Controls on mineralization in the Sekwi Formation

Cook, F.A., van der Velden, A.J., and Hall, K.W., 1999, Frozen subduction in Canada's Northwest Territories: Lithoprobe deep lithospheric reflection profiling of the western Canadian Shield: Tectonics, v. 18, p. 1-24.

Cousens, B.L., 2006, Radiogenic isotope studies of Pb-Zn mineralization in the Howards Pass area, Selwyn Basin, in Wright, D.F., Lemkow, D., and Harris, J.R., Mineral and Energy Resource Assessment of the Greater Nahanni Ecosystem Under Consideration for the Expansion of the Nahanni National Park Reserve, Northwest Territories: Open File 5344, Geological Survey of Canada, Ottawa, Canada, p. 279-292.

Davies, G.R. and Smith, L.B. Jr., 2006, Structurally controlled hydrothermal dolomite reservoir facies: An overview: AAPG Bulletin, v. 90, n.l 1, p. 1641-1690.

Davis, D.W., Lowenstein, T.K., and Spencer R.J., 1990, Melting behavior of fluid inclusions in laboratory-grown halite crystals in the systems NaCl-H20, NaCl-KCl-H20, NaCl-MgC12-H20, and NaCl-CaC12-H20: Geochimica et Cosmochimica Acta, v. 54, p. 591-601.

Dawson, K.M., 1974, Carbonate-hosted zinc-lead deposits of the northern Canadian Cordillera, in Report of Activities Part A, April to October 1974: Paper 75-1A, Geological Survey of Canada, Ottawa, Canada, p. 239-241.

Diamond, L.W., 2001, Review of the systematics of C02-H20 fluid inclusions; Lithos, v. 55, p. 69-99.

Diamond, L.W., 2003, Chapter 5: Introduction to gas-bearing, aqueous fluid inclusions, in Samson, I., Anderson, A., and Marshall, D., editors, Fluid Inclusions: Analysis and Interpretation: Short Course Series v. 32, Mineralogical Association of Canada, Vancouver, Canada, p. 101-158.

Dilliard, K.A., 2006, Sequence stratigraphy and chemostratigraphy of the Lower Cambrian Sekwi Formation, Northwest Territories, Canada: Unpublished Ph.D. Thesis, Pullman, Washington, Washington State University, 300 p.

Dilliard, K., Pope, M.C., Coniglio, M., Hasiotis, S.M., and Lieberman, B., 2007, Stable Isotope Geochemistry of the Lower Cambrian Sekwi Formation, Northwest Territories, Canada: Implications for ocean chemistry and secular curve generation: Palaeogeography, Palaeoclimatology, and Palaeoecology, v. 256, p. 174-194.

Dilliard, K., Pope, M.C., Coniglio, M., Hasiotis, S.M., and Lieberman, B., 2010, Active synsedimentary tectonism on a mixed carbonate-siliciclastic continental margin: third- order sequence stratigraphy of a ramp to basin transition, lower Sekwi Formation, Selwyn Basin, Northwest Territories, Canada: Sedimentology, v. 57, p. 513-542.

141 Chapter 2. Controls on mineralization in the Sekwi Formation

Dubois, M. and Marignac, C., 1997, The H20-NaCl-MgC12 ternary phase diagram with special application to fluid inclusion studies: Economic Geology, v. 92, p. 114-119.

Dunham, R.J., 1962, Classification of carbonate rocks according to depositional texture: AAPG Memoir 1, American Association of Petroleum Geologists, p.l 08-121.

Eagle Plains Resources Ltd., 2009, AB (Fe, Pb, Zn) (http://www.eagleplains.com/projects/nwt/ab/documents/ABProjectSummary2009.pdf)

Eisbacher, G.H., 1981, Sedimentary tectonics and glacial record in the Windermere Supergroup, Mackenzie Mountains, northwestern Canada: Paper 80-27, Geological Survey of Canada, Ottawa, Canada, 40 p.

Embry, A.F. Ill and Klovan, J.E., 1971, A late Devonian reef tract on northeastern Banks Island, N.W.T.: Bulletin of Canadian Petroleum Geology, v.19, n.4, p.730-781.

Epstein, A.G., Epstein, J.B., and Harris, L.D., 1977, Conodont color alteration - an index to organic metamorphism: Professional Paper 995, United States Geological Survey, Washington, USA, 27 p.

Fabricius, I.L., 2000, 10. Interpretation of burial history and rebound from loading experiments and occurrence of microstylolites in mixed sediments of Caribbean sites 999 and 1001, in Leckie, R.M., Sigurdsson, H., Acton, G.D., and Draper, G., editors, Proceedings of the Ocean Drilling Program, Scientific Results, v. 165, p. 177-190, doi:10.2973/odp.proc.sr. 165.006.2000.

Faure, G. and Mensing, T.M., 2005, Isotopes, Principles and Applications, 3rd edition: John Wiley and Sons, Inc., Hoboken, NJ, USA, 897 p.

Feinstein, S., Issler, D.R., Snowdon, L.R., and Williams, G.K., 1996, Characterization of major unconformities by paleothermometric and paleobarometric methods: application to the Mackenzie Plain, Northwest Territories, Canada: Bulletin of Canadian Petroleum Geology, v. 44, p. 55-71.

Fernandes, N.A., 2011, Geology and Geochemistry of Late Devonian-Mississipian Sediment-Hosted Barite Sequences of the Selwyn Basin, NWT and Yukon, Canada: Unpublished M.Sc. Thesis, University of Alberta, Edmonton, Canada, 130 p.

Fischer, B.J., 201 la, Chapter 7.3, Carbonate-hosted Zn-Pb (± Ag, Cu, Ba) and Carbonate-hosted Cu (± Ag, Zn), in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 260-264

142 Chapter 2. Controls on mineralization in the Sekwi Formation

Fischer, B.J., 201 lb, Appendix D, Detailed stratigraphic sections measured through the Sekwi Formation, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 364-395.

Fischer, B.J., and Pope, M.C., 2011, Chapter 3.4.2, Lower Cambrian carbonate succession in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 142-149.

Fischer, B.J., Atherton, C., Parker, E., and Law, J., 2010, Geology of the AB area, parts of 106C/16 and 106F/01: NWT Open File 2010-04, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map scale 1:20,000, 1 report, 66 p.

Fritz, W.H., 1972, Lower Cambrian trilobites from the Sekwi Formation type section, Mackenzie Mountains, northwestern Canada: Bulletin 212, Geological Survey of Canada, Ottawa, Canada, 90 p.

Fritz, W.H., 1975, Broad correlations of some Lower and Middle Cambrian strata in the North American Cordillera: Paper 75-1 A, Geological Survey of Canada, Ottawa, Canada, p. 533-539.

Fritz, W.H., 1976, Ten stratigraphic sections from the lower Cambrian Sekwi Formation, Mackenzie Mountains, northwestern Canada: Paper 76-22, Geological Survey of Canada, Ottawa, Canada, 42 p.

Fritz, W.H., 1978, Fifteen stratigraphic sections from the Lower Cambrian of the Mackenzie Mountains, northwestern Canada: Paper 77-33, Geological Survey of Canada, Ottawa, Canada, 19 p.

Fritz, W.H., 1979, Cambrian stratigraphic section between South Nahanni and Broken Skull Rivers, southern Mackenzie Mountains: GSC Paper 79-IB, Geological Survey of Canada, Ottawa, Canada, p. 121-125.

Fritz, W.H., 1979, Eleven stratigraphic sections from the Lower Cambrian of the Mackenzie Mountains, Northwestern Canada: Paper 78-23, Geological Survey of Canada, Ottawa, Canada, 19 p.

Fritz, W.H., 1981, Two Cambrian stratigraphic sections, eastern Nahanni map area, Mackenzie Mountains, District of Mackenzie: Paper 81-1A, Geological Survey of Canada, Ottawa, Canada, p.145-156.

143 Chapter 2. Controls on mineralization in the Sekwi Formation

Fritz, W.H., 1992, Cambrian Assemblages, in Fritz, W.H., Cecile, M.P., Norford, B.S., Morrow, D., and Geldsetzer, H.H.J., Chapter 7. Cambrian to Middle Devonian assemblages, in Gabrielse, H. and Yorath, C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, Canada, p. 155-184 (also published as The Geology of North America, v. G-2, Geological Society of America).

Fritz, W.H., Cecile, M.P., Norford, B.S., Morrow, D., and Geldsetzer, H.H.J., 1992, Chapter 7. Cambrian to Middle Devonian assemblages, in Gabrielse H. and Yorath C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n.4, Geological Survey of Canada, Ottawa, Canada, p. 153-218 {also published as The Geology of North America, v. G-2, Geological Society of America).

Gabrielse, H., 1967, Tectonic evolution of the northern Canadian Cordillera: Canadian Journal of Earth Sciences, v. 4, p. 271-298.

Gabrielse, H., compiler, 1992, Structural styles, Part E. Foreland Belt, in Gabrielse, H. and Yorath, C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, p. 634-650 (also published as The Geology of North America, v. G-2, Geological Society of America).

Garven, G. and Freeze, R.A., 1984a, Theorectical analysis of the role of groundwater flow in the genesis of stratabound ore deposits. 1. Mathematical and numerical model: American Journal of Science, v. 284, p.1085-1124.

Garven, G. and Freeze, R.A., 1984b, Theorectical analysis of the role of groundwater flow in the genesis of stratabound ore deposits. 2. Quantitative results: American Journal of Science, v. 284, p. 1125-1174.

Garven and Raffensperger, 1997, Hydrology and geochemistry of ore genesis in sedimentary basins, in Barnes, H.L., editor, Geochemistry of Hydrothermal Ore Deposits, 3rd ed.: New York, USA, Wiley, p. 125-189.

Gleeson, S.A. and Turner, W.A., 2006, Fluid inclusion constraints on the origin of the brines responsible for Pb-Zn mineralization at Pine Point and coarse saddle dolomite formation in southern Northwest Territories: Geofluids v. 7, p. 51-68.

144 Chapter 2. Controls on mineralization in the Sekwi Formation

Goldstein, R.H. and Reynolds, T.J., 1994. Systematics of Fluid Inclusions in Diagenetic Minerals: SEPM Short Course 31, Society for Sedimentary Geology, 199 p.

Gordey, S.P. and Makepeace, A.J., compilers, 2003, Yukon digital geology, version 2.0: Open File 2003-9(D), Yukon Geological Survey, Whitehorse, Canada, 1 disc.

Gordey, S.P. and Roots, C.F., 2011, Chapter 2. Regional Setting, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 18-30.

Gordey, S.P., Abbott, J.G., Tempelman-Kluit, D.J., and Gabrielse, H., 1987, "Antler" clastics in the Canadian Cordillera: Geology, v. 15, p. 103-107

Gordey, S.P., Geldsetzer, H.H.J., Morrow, D.W., Bamber, E.W., Henderson, C.M., Richards, B.C., McGugan, A., Gibson, D.W., and Pouiton, T.P., 1992, Chapter 8. Upper Devonian to Middle Jurassic assemblages, in Gabrielse H. and Yorath C.J., editors, Geology of the Cordilleran Orogen in Canada: Geology of Canada, n. 4, Geological Survey of Canada, Ottawa, Canada, p. 221-328 (also published as The Geology of North America, v. G-2, Geological Society of America).

Gordey, S.P., Martel, E., Fallas, K., Roots, C.F., MacNaughton, R., and MacDonald, J., 2010a, Geology of Mount Eduni, NTS 106A Southwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-11, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Gordey, S.P., MacDonald, J.D., Roots, C.F., Fallas, K., and Martel, E., 2010b, Regional cross-sections, detachment levels and origin of the Plateau fault, central Mackenzie Mountains, Northwest Territories: NWT Open File 2010-18, Northwest Territories Geoscience Office, 1 sheet, scale 1:100,000.

Gordey, S.P., MacDonald, J.D., Turner, E.C. and Long, D.G.F., 2011. Chapter 5. Structural geology of the central Mackenzie Mountains; in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley

145 Chapter 2. Controls on mineralization in the Sekwi Formation

Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 215-250.

Gradstein, F.M., Ogg, J.G., Smith, A.G., Bleeker, W., and Lourens, L.J., 2004, A new geologic time scale, with special reference to Precambrian and Neogene: Episodes, v. 27, p. 83-100.

Hanor, J.S., 1980, Dissolved methane in sedimentary brines: potential effect on the PVT properties of fluid inclusions: Economic Geology, v. 75, p. 603-613.

Helmsteadt, H. and McGregor, J.A., 1974, Geological Investigation of the ICE-EMILY Claim Group, Mackenzie Mountains, NWT: Unpublished Assessment Report 080357, submitted by Geomont Exploration Company Limited, Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Hitzman, M.W. and Beaty, D.W., 1996, The Irish Zn-Pb(-Ba) orefield, in Sangster D.F., editor, Carbonate-Hosted Lead-Zinc Deposits, 75th Anniversary Volume: Society of Economic Geologists, Special Publication No. 4, p. 112-143.

Jefferson, C.W. and Parrish, R.R., 1989, Late Proterozoic stratigraphy, U-Pb zircon ages, and rift tectonics, Mackenzie Mountains, northwestern Canada: Canadian Journal of Earth Sciences, v. 26, p. 1784-1801.

Jones, H.D. and Kesle, S.E., 1992, Fluid inclusion gas chemistry in east Tennessee Mississippi Valley-type districts: Evidence for immiscibility and implications for depositional mechanisms: Geochemica et Cosmochimica Acta, v. 56, p. 137-154.

Kontak, D.J., 1998, A study of fluid inclusions in sulfide and nonsulfide mineral phases from a carbonate-hosted Zn-Pb deposit, Gays River, Nova Scotia, Canada: Economic Geology, v. 93, p. 793-817.

Krause, Schroeder-, F.F., 1979, Sedimentology and stratigraphy of a continental terrace wedge: the Lower Cambrian Sekwi and June Lake formations (Godlin River Group), Mackenzie Mountains, Northwest Territories, Canada: Unpublished Ph.D. Thesis, Calgary, Canada, University of Calgary, 253 p.

Krause, F.F., 1982, Evolution of a mixed carbonate/terrigenous platform; Lower Cambrian continental terrace wedge of Mackenzie Mountains, Northwest Territories, Canada: AAPG Bulletin, v. 66, n. 5, p. 590, abstract.

146 Chapter 2. Controls on mineralization in the Sekwi Formation

Krause, F.F. and Oldershaw, A.E., 1978, Stratigraphic and paleoenvironmental analysis of the Sekwi Formation, Mackenzie Mountains, Northwest Territories, in Laporte, P.J., Gibbins, W.A., Hurdle, E.J., Lord, C., Padgham, W.A., and Seaton, J.B., compilers, Mineral Industry Report 1975, Northwest Territories: EGS Open File 1978-5, Dept. Indian Affairs and Northern Development, NWT Geology Division, Yellowknife, Canada, p. 136-156.

Krause, F.F. and Oldershaw, A.E., 1979, Submarine carbonate breccia beds; a depositional model for two-layer, sediment gravity flows from the Sekwi Formation (Lower Cambrian), Mackenzie Mountains, Northwest Territories, Canada: Canadian Journal of Earth Sciences, v. 16, n. 1, p. 189-199.

Large, R.L., Maslennikov, V.V., Robert, F., Danyushevsky, L.V., and Chang, Z., 2007, Multistage sedimentary and metamorphic origin of pyrite and gold and in the giant Sukhoi Log deposit, Lena gold province, Russia, Economic Geology, v. 102, p. 1233- 1267.

Leach, D.L., Viets, J.G., Kozlowski, A., and Kibitlewski, S., 1996, Geology, geochemistry and genesis of the Silesia-Cracow zinc-lead district, southern Poland: Special Publication n. 4, Society of Economic Geologists, p. 144-170.

Leslie, C.D., 2009, Detrital zircon geochronology and rift-related magmatism: central Mackenzie Mountains, Northwest Territories: Unpublished M.Sc. thesis, Vancouver, Canada, University of British Columbia, 224 p.

Lind, I.L., 1993, 26. Stylolites in chalk from Leg 130, Ontong Java Plateau, in Berger, W.H., Kroenke, J.W., and Mayer, L.A., et al., Proceedings of the Ocean Drilling Program, Scientific Results, v. 130, p. 445-451, doi:10.2973/odp.proc.sr.130.006.1993.

Lynn, G.E., Cook, F.A., and Hall, K.W., 2005, Tectonic significance of potential-field anomalies in western Canada: results from the Lithoprobe SNORCLE transect: Canadian Journal of Earth Sciences, v. 42 , p. 1239-1255.

147 Chapter 2. Controls on mineralization in the Sekwi Formation

Machel, H.G., 2004, Concepts and models of dolomitization: a critical re-appraisal, in Braithwaite, C.J.R., Rizzi, G., and Darke, G., editors, The Geometery and Petrogenesis of Dolomite Hydrocarbon Reservoirs: Geological Society, London, Special Publications, 235, p.7-63.

Machel, H.G. and Cavell, P.A., 1999, Low-flux, tectonically-induced squeegee fluid flow ("hot flash") into the Rocky Mountain Foreland Basin: Bulletin of Canadian Petroleum Geology, v. 47, n. 4, p. 510-533.

Machel, H.G., Krouse, H.R., and Sassen, R., 1995, Products and distinguishing criteria of bacterial and thermochemical sulfate reduction: Applied Geochemistry, v. 10, p. 373-389.

MacQueen, 1976, Sediments, zinc and lead, Rocky Mountain belt, Canadian Cordillera: Geoscience Canada, v. 3, p. 71-81.

Martel, E., Turner, E.C. and Fischer, B.J., editors, 201 la, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, 423 p.

Martel, E., MacNaughton R.B. and Fischer, B.J., 201 lb, Chapter 6. Metamorphism and thermal maturity, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 251-254.

Mazzullo S.J., 1992, Geochemical and neomorphic alteration of dolomite: a review: Carbonates and Evaporites, v. 7, p. 21-37.

McArthur, G.F. and McArthur, M.L., 1977, Geological and geochemical report on the AB-BB-DAB mineral claims (AB Project), Mackenzie Mining District, NTS 106C16, Northwest Territories, Canada, Work performed July 15 - September 2, 1976: Unpublished Assessment Report 080621, submitted by Welcome North Mines Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

148 Chapter 2. Controls on mineralization in the Sekwi Formation

Mernagh, T.P., Heinrich, C.A., and Mikucki, E.J., 2004. Temperature gradients recorded by fluid inclusions and hydrothermal alteration at the Mount Charlotte gold deposit, Kalgoorlie, Australia: The Canadian Mineralogist, v. 42, p. 1383-1403.

Miller, J., 1988, Microscopical techniques I; Slices, slides, stains and peels, in Tucker, M., editor, Techniques in Sedimentology, Oxford, United Kingdom, Blackwell, p. 86- 107.

Morrow, D.W., 1982, Descriptive field classification of sedimentary and diagenetic breccia fabrics in carbonate rocks: Bulletin of Canadian Petroleum Geology, v. 30, p. 227-229.

Morrow, D.W., 1991, The Silurian-Devonian sequence in the northern part of the Mackenzie shelf, Northwest Territories: Geological Survey of Canada, Bulletin 413, 121 P-

Morrow, D., 1998, Regional subsurface dolomitization: Models and constraints: Geoscience Canada, v. 25, p. 57-70.

Morrow, D.W., Cumming, G.L., and Aulstead, K.L., 1990, The gas-bearing Devonian Manetoe facies, Yukon and Northwest Territories: Geological Survey of Canada, Bulletin 400, 54 p.

Nelson, C.S., Harris, G.J., and Young, H.R., 1988, Burial-dominated cementation in non tropical carbonates of the Oligocene Te Kuiti Group, New Zealand: Sedimentary Geology, v. 50, p. 233-250.

149 Chapter 2. Controls on mineralization in the Sekwi Formation

Pacific Margin of North America, Canadian and Alaskan Cordillera: Special Paper 45, Geological Association of Canada, p 323-360.

Nicolaides, S. and Wallace, M.W., Submarine cementation and subaerial exposure in Oligo-Miocene temperate carbonates, Torquay Basin, Australia: Journal of Sedimentary Research, v. 67, p. 397-410.

Norford, B.S. and Macqueen, R.W., 1975, Lower Paleozoic Franklin Mountain and Mount Kindle formations, District of Mackenzie: Their type sections and regional development: Paper 74-34, Geological Survey of Canada, Ottawa, Canada, 37 p.

NORM IN, 2011, The Northern Minerals Database, 2011/02/01: Northwest Territories Geoscience Office, Yellowknife, Canada (http://www.ntgomap.nwtgeoscience.ca)

Oakes, C.S., Bodnar, R.J., and Simonson, J.M., 1990, The system NaCl-CaC12-H20:1. The ice liquidus at 1 atm total pressure: Geochimica et Cosmochimica Acta, v. 54, p. 603-610.

Oakes, C.S., Sheets, R.W., and Bodnar, R.J., 1992, (NaCl+CaC12){aq}: Phase equilibria and volumetric properties, in Program and Abstracts, Fourth biennial Pan-American Conference on Research on Fluid Inclusions (PACROFIIV), p. 128-132.

Ohmoto, H. and Goldhaber, M.B., 1997, Chapter 11, Sulfur and carbon isotopes, in H.L. Barnes (editor), Geochemistry of Hydrothermal Ore Deposits, 3rd edition: New York, USA, John Wiley & Sons, Inc., p. 517-611.

Ohmoto, H. and Rye, 1979, Isotopes of sulfur and carbon, in Barnes, H.L., editor, Geochemistry of Hydrothermal Ore Deposits, 2nd edition, New York, USA, Wiley, p. 509-567.

Oliver, J., 1986, Fluids expelled tectonically from orogenic belts: Their role in hydrocarbon migration and other geologic phenomena: Geology, v. 14, p. 99-102.

Orr, W.L., 1974, Changes in sulfur content and isotopic ratios of sulfur during petroleum maturation - Study of Big Horn Basin Paleozoic oils: AAPG Bulletin, v. 58, p. 2295- 2318.

150 Chapter 2. Controls on mineralization in the Sekwi Formation

Paradis, S., 2007, Isotope geochemistry of the Prairie Creek carbonate-hosted zinc-lead- silver deposit, southern Mackenzie Mountains, Northwest Territories, in Wright, D.F., Lemkow, D., Harris, J.R., editors, Mineral and energy resource assessment of the Greater Nahanni Ecosystem under consideration for the expansion of the Nahanni National Park Reserve, Northwest Territories: Open File 5344, Geological Survey of Canada, Ottawa, Canada, p. 131-176.

Paradis, S., Hannigan, P., and Dewing, K., 2007, Mississippi Valley-Type lead-zinc deposits, in Goodfellow, W.D., editor, Mineral Deposits of Canada, A Synthesis of Major Deposit Types, District Metallogeny, the Evolution of Geological Provinces and Exploration Methods: Special Publication n. 5, Geological Association of Canada, Mineral Deposits Division, p. 185-203.

Phillips, W.J., 1972, Hydraulic fracturing and mineralization: Journal of the Geological Society of London, v. 128, p. 337-359.

Radke, B.M. and Mathis, R.L., 1980, On the formation and occurrence of saddle dolomite: Journal of Sedimentary Petrology, v. 50, p. 1149-1168.

Railsback, L.B., 1993a, Contrasting styles of chemical compaction in the Upper Pennsylvanian Dennis limestone in the midcontinent region, U.S.A.: Journal of Sedimentary Petrology, v. 63, p. 61-72.

Railsback, L.B., 1993b, Lithologic controls on morphology of pressure-dissolution surfaces (stylolites and dissolution seams) in Paleozoic carbonate rocks from the mideastern United States: Journal of Sedimentary Petrology, v. 63, p. 513-522.

Ranalli, G., 1995, Geology of the Earth, 2nd ed.: London, UK, Chapman and Hall, 413 p.

Rejebian, V.A., Harris, A.G., and Huebner, J.S., 1987, Conodont color and textural alteration: An index to regional metamorphism, contact metamorphism, and hydrothermal alteration: Geological Society of America Bulletin, v. 99, p. 471-479.

Roedder, E., 1972, Data of Geochemistry, Sixth Edition, Chapter JJ. Composition of fluid inclusions: Geological Survey Professional Paper 440-JJ, United States Geological Survey, Washington, USA, 164 p. and 12 plates.

151 Chapter 2. Controls on mineralization in the Sekwi Formation

Roedder, E. and Bodnar, R.J., 1997, Chapter 13: Fluid inclusion studies of hydrothermal ore deposits, in Barnes, H.L., editor, Geochemistry of Hydrothermal Ore Deposits, 3rd edition: New York, USA, John Wiley and Sons, Inc, p. 657-697.

Ronning, P., 1975, A geological report with a drilling survey on the TIC-TIL mineral claims 16 miles WNW of Palmer Lake, mineral claim map NTS 106-B-9: Unpublished Assessment Report 080499, submitted by Serem Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Ross, G.M., 1991, Tectonic setting of the Windermere Supergroup revisited: Geology, v. 19, p. 1125-1128.

Schaefer, M.O., Gutzmer, J., Beukes, N.J., grayling, L.N., 2004, Mineral chemistry of sphalerite and galena from Pb-Zn minealization hosted by the Transvaal Supergroup in Griqualand West, South Africa: South African Journal of Geology, v. 107, p. 341-354.

Sibson, R.H., 2001, Chapter 2: Seismogenic framework for hydrothermal transport and ore deposition, in Richards, J.P. and Tosdal, R.M., editors, Structural Controls on Ore Genesis: Society of Economic Geologists, Reviews in Economic Geology, v. 14, p. 25- 50.

Sibson, R.H., Moore, J.M., and Rankin, A.H., 1975, Seismic pumping - a hydrothermal fluid transport mechanism: Journal of the Geological Society, London, v. 131, p. 653- 659.

Stoffell, B., Appold, M.S., Wilkinson, J.J., McClean, N.A., and Jeffries, T.E., 2008, Geochemistry and evolution of Mississippi Valley-Type mineralizing brines from the Tri- State and northern Arkansas districts determined by LA-ICP-MS microanalysis of fluid inclusions: Economic Geology, v. 103, p. 1411-1435.

Sterner, S.M. and Bodnar, R.J., 1989. Synthetic fluid inclusions - VII. Re-equilibration of fluid inclusions in quartz during laboratory-simulated metamorphic burial and uplift: Journal of Metamorphic Geology, v. 7, p. 243-260.

Strauss, H., The sulfur isotopic record of Precambrian sulfates: new data and a critical evaluation of the existing record: Precambrian Research, v. 63, p. 225-246.

Stone D.M.R. and Godden, S.J., 2007, Technical report on the Prairie Creek Mine, Northwest Territories, Canada: Report filed by Canadian Zinc Corporation with Canadian Securities Administrators in accordance with National Instrument 43-101 (http://www.canadianzinc.com/docs/CanadianZinc43-l 01 000.pdf)

Sverjensky, D.A., 1981, The origin of a Mississippi Valley-type deposit in the Viburnum Trend, Southeast Missouri: Economic Geology, v. 76, p. 1848-1872.

152 Chapter 2. Controls on mineralization in the Sekwi Formation

Sverjensky, D.A., 1986, Genesis of Mississippi Valley-type lead-zinc deposits: Annual Review of Earth and Planetary Sciences, v. 14, p. 177-199.

Tada, R. and Siever, R., 1989, Pressure solution during diagenesis: Annual Review of Earth and Planetary Sciences, v. 17, p. 89-118.

Thode, H.G., 1981, Sulfur isotope ratios in petroleum research and exploration, Williston Basin: AAPG Bulletin, v. 65, p. 1527-1535

Thode, H.G. and Monster, J., 1963, Sulfur isotope geocehmistry of petroluem, evaporites, and ancient seas: AAPG Bulletin, v. 47, p. 2076

Thode, H.G., Harrison, A.G., and Monster, J., 1960, Sulfur isotope fractionation in early diagenesis of Recent sediments of northeast Venezuela: AAPG Bulletin, v. 44, p. 1809- 1817.

Thom, J. and Anderson, G.M., 2008, The role of thermochemical sulfate reduction in the origin of Mississippi Valley-type deposits. I. Experimental results: Geofluids, v. 8, p. 16- 26.

Turner E.C., 2009. Lithostratigraphy and stable isotope values of the early Neoproterozoic Gypsum formation (Little Dal Group), Mackenzie Mountains Supergroup), NWT. NWT Open Report 2009-002, Northwest Territories Geoscience Office, Yellowknife, Canada, 26 p.

Turner, E.C., Roots, C.F., MacNaughton, R.B., Long, D.G.F., Fischer, B.J., Gordey, S.P., Martel, E., and Pope, M.C., 2011. Chapter 3, Stratigraphy, in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 31-192.

Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, F., Carden, G.A.F., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O.G., and Strauss, H., 1999, 87Sr/86Sr, 813C and 5180 evolution of Phanerozoic seawater: Chemical Geology, v. 161, p. 59-88.

Verncombe, J.R., Chisnall, A.W., Dentith, M.C., Dorling, S.L., Rayner, M.J., and Holyland, P.W., 1996, Structural controls on Mississippi Valley-type mineralization, the southeast Lennard Shelf, western Australia: Economic Geology, Special Publication n. 4, p. 74-95.

Wallace, S.R.B., 2009, The genesis of the Gayna River carbonate-hosted Zn-Pb deposit: Unpublished M.Sc. thesis, Edmonton, Canada, University of Alberta, 117 p.

153 Chapter 2. Controls on mineralization in the Sekwi Formation

Wilkinson J.J., 2010, A review of fluid inclusion constraints on mineralization in the Irish ore field and implications for the genesis of sediment-hosted Zn-Pb deposits: Economic Geology v. 105, p. 417-442.

Worden, R.H., Smalley, P.C., and Oxtoby, N.H., 1995, Gas souring by thermochemical sulfate reduction at 140 °C: AAPG Bulletin, v. 79, p. 854-863.

Yang, X-M., Lentz, D.R., Chi, G., and Kyser, T.K., 2004, Fluid-mineral reaction in the Lake George granodiorite, New Brunswick, Canada: implications for Au-Mo-Sb mineralization: The Canadian Mineralogist, v. 42, p. 1405-1424.

Yeager, D.A., Darney, R.J., Ikona, C.K., 1976, Preliminary geologic report on the PALM mineral claims, NTS 106A: Unpublished Assessment Report 080569, submitted by Harman Management Ltd., Dept. of Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife (http://www.nwtgeoscience.ca)

Young, G.M., 1976, Iron-formation and glaciogenic rocks of the Rapitan Group, Northwest Territories, Canada: Precambrian Research, v.3, n.2, p.137-158.

Zhang, Y.G. and Frantz, J.D., 1987, Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl - KC1 - CaCl2 - H2O using synthetic fluid inclusions: Chemical Geology v. 64, p. 335-350.

154 Chapter 2. Controls on mineralization in the Sekwi Formation

Appendix (1). Isotope and element analytical methods

Stable isotopes of S, O, and C were analyzed at the Queen's Facility for Isotope Research at Queen's University in Kingston, ON using a Finnigan MAT 252 mass spectrometer (MS) with continuous-flow technology provided by a Finnigan MAT Conflo 11. The MS was coupled to a Carlo Erba NCS 2500 elemental analyzer for S analyses and a Thermo Finnigan thermal conversion elemental analyzer for C and O. Powdered barite samples were first treated with nitric acid to remove dolomite contaminants and mixed with granular V2O5 to ensure complete combustion. Carbon and oxygen isotope compositions of dolomite were measured on CO2 extracted from the powdered sample by dissolution under vacuum in 100% H3PO4.

Sulfur is reported relative to Canyon Diablo Troilite (CDT), oxygen relative to Vienna Standard Mean Ocean Water (SMOW), and carbon relative to Vienna Peedee Belemnite (PDB) standards. Values are expressed as per mil (%o) differences in isotopic

3 ratios relative to the stated standard: [(ratiosampie-ratiostandard)/ratiostandard]xl0 .The analytical precision for both 834S and 5180 values is ~0.3%o, and for 813C is ~0.1%o.

Strontium isotopes were measured at the Queen's Facility for Isotope Research with a MAT261 multicollector TIMS in static mode. Results are presented as ratios of 87Sr to 86Sr. The analytical precision for 87Sr/86Sr is ±0.00001.

A number of fluid inclusion chips were heated to force decrepitation of the fluid inclusions, then mounted on carbon strips. Qualitative scanning electron microscope (SEM) analyses of the decrepitate mounds were obtained at Laurentian University with a JEOL JSM 6400 SEM that had a light-element, energy-dispersive, X-ray emission spectrometer.

155 Chapter 3. Concluding remarks

Chapter 3. Concluding remarks

The conclusions at the end of Chapter 2 form a starting point for development of an effective exploration strategy for carbonate-hosted Zn±Pb deposits in the Mackenzie Mountains zinc district. The issue of regional controls is still outstanding: why are the Sekwi Formation and three other discrete, stratigraphic levels preferred hosts of mineralization? The question can't be resolved without clarification of the stratigraphic and structural settings of a large and representative number of showings. That clarification cannot come about without more-detailed bedrock mapping. The currently available maps are reconnaissance in scale and, with the exception of the maps produced by NTGO's Sekwi Mountain Project (Gordey et al., 201Oa, b, c and Roots et al., 2010a-f), are over 30 years old and do not incorporate more-recent stratigraphic work.

It would be of benefit to differentiate burial from hydrothermal dolomitization throughout the district, to determine the stratigraphic and lithological controls on dolomitization and what, if any, influence pre-existing burial dolomitization had on mineralization. Although dolomitization in the Sekwi Formation has been inferred to be co-genetic with mineralization (Chapter 2) and related to faulting (Chapter 2; Krause, 1979), the relationship is not so straightforward everywhere in the succession. The pervasiveness of dolomitization throughout the lateral and vertical extents of the overlying platformal Franklin Mountain Formation suggests that the dolomitization in that unit derives from diagenetic processes in the burial environment (Machel, 2004). The dolomitized Franklin Mountain Formation overlies Sekwi Formation that is generally not dolomitized except near showings; the Franklin Mountain Formation hosts relatively few showings but the Sekwi Formation hosts numerous showings. Did early dolomitization inhibit later mineralization? The Mount Kindle Formation is extensively dolomitized, yet it is one of the preferred stratigraphic hosts for mineralization. It is extensively silicified as well; does silicification bear any relationship to mineralization? Are the silicified portions of Franklin Mountain Formation, such as in the AB area, more favorable for mineralization? The Arnica and overlying Landry formations together comprise one of the preferred stratigraphic settings for carbonate-hosted Zn±Pb deposits in the district. Most showings are in either the uppermost Arnica or the lowermost

156 Chapter 3. Concluding remarks

Landry, so the contact is an important control. The Arnica Formation, like the Franklin Mountain Formation, is a pervasively dolomitized platformal carbonate unit, whereas the Landry Formation is limestone. Is the Landry Formation a preferred host compared to the Arnica Formation? Why was the Landry not dolomitized by the passage of mineralizing fluids? How did the contact exert its control?

The age of the mineralizing event or events is still unknown, but more evidence is pointing to a young age for some of the Mackenzie Mountain showings (Chapter 2) and a Devonian age for others in the Mackenzie Mountains and for showings in the northern Rocky Mountains (Chapter 2; Nelson et al., 2002; Paradis et al., 2006). Both ages of mineralization have been identified at Prairie Creek, in the MVT and vein-type deposits, and correspond to two distinct sources of lead. These two lead sources have also been recognized throughout the northern Cordilleran and Western Canada Sedimentary Basin (Paradis et al., 2006; Paradis, 2007). Careful geological observations complemented by stable and radiogenic isotopic analyses of paragenetically well-identified phases will provide important clues to the ages of carbonate-hosted deposits, as well as clarify the sources of fluids and their components. All such studies should avoid the prior assumption of a single mineralizing event.

Additional fluid inclusion work should use an infrared camera to improve visibility inside the dark, sphalerite-hosted inclusions. Bulk analyses of fluid inclusions could identify the anion component of solutes, and explain the paucity of CI in the SEM- EDS analyses of evaporate mounds (Appendix E). Halogen ratios might clarify whether fluid 1 was seawater or contained dissolved evaporite.

The deposit model proposed in Chapter 2 could be refined in many ways. Mass balance calcuations could address such questions as whether there was enough sulfate in Cretaceous seawter to provide the sulfur called for, and whether there was enough organic matter in Sekwi Formation to account for all the reduction. Total-organic-carbon measurements on rock samples would reveal the organic content of the dark units in Sekwi Formation and other potential reductant strata. Modelling of fluid flow could help establish what pathways were used and the forces driving fluid movement. These are some of the issues that should guide future research.

157 Chapter 3. Concluding remarks

References, Chapter 3

Davies, G.R. and Smith, L.B. Jr., 2006, Structurally controlled hydrothermal dolomite reservoir facies: An overview: AAPG Bulletin, v. 90, n.l 1, p. 1641-1690.

Gordey, S.P., Martel, E., Fallas, K., Roots, C.F., MacNaughton, R., and MacDonald, J., 2010a. Geology of Mount Eduni, NTS 106A Southwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-11, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Gordey, S.P., Martel, E., MacDonald, J., MacNaughton, R., Roots, C.F., and Fallas, K. (compilers), 2010b. Geology of Mount Eduni, NTS 106A Northwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-09, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Gordey, S.P., Martel, E., MacDonald, J., Fallas, K., Roots, C.F., and MacNaughton, R., 2010c. Geology of Mount Eduni, NTS 106A Southeast, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-12, Northwest Territories Geoscience Office, 1 map, scale 1:100,000.

Krause (Schroeder) F.F., 1979, Sedimentology and stratigraphy of a continental terrace wedge: the Lower Cambrian Sekwi and June Lake formations (Godlin River Group), Mackenzie Mountains, Northwest Territories, Canada: Unpublished Ph.D. Thesis, Calgary, Canada, University of Calgary, 253 p.

158 Chapter 3. Concluding remarks

Potential for Carbonate-hosted, Lead-zinc, Mississippi Valley-type Mineralization in Northern Alberta and Southern Northwest Territories: Geoscience Contributions, Targeted Geoscience Initiative: Bulletin 591, Geological Survey of Canada, p. 75-103.

Roots, C.F., Martel, E., Fallas, K., Gordey, S.P., and MacNaughton, R. (compilers), 2010. Geology of Mount Eduni, NTS 106A Northeast, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-10, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, scale 1:100,000.

Roots, C.F., Martel, E., MacNaughton, R., Fallas, K., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Northeast, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-14, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, scale 1:100,000.

Roots, C.F., Martel, E., MacNaughton, R., and Gordey, S.P. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Southwest, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-15, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, scale 1:100,000.

Roots, C.F., Martel, E., and MacNaughton, R. (compilers), 2010. Geology of Sekwi Mountain, NTS 105P Southeast, Mackenzie Mountains, Northwest Territories: NWT Open File 2010-16, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, scale 1:100,000.

Roots, C.F., Martel, E., Gordey, S.P, MacNaughton, R., and Fallas, K., 2010. Legend for the geology of Sekwi Mountain, Mount Eduni, and northwest Wrigley Lake areas (NTS 105P, 106A, and 95M NW), Mackenzie Mountains, Northwest Territories: NWT Open File 2010-19, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 sheet.

Wallace, S.R.B., 2009, The genesis of the Gayna River carbonate-hosted Zn-Pb deposit: unpublished M.Sc. thesis, Edmonton, Canada, University of Alberta, 117 p.

159 Appendix A. Petrography of secondary minerals

Appendix A. Petrography of secondary minerals at showings in the AB, TIC, and Palm areas

The following table lists the main petrographic characteristics of secondary barite, dolomite, quartz, and calcite at the AB Main, AB-C, and AB Point showings in the AB area, the C and Ryan zones in the TIC area, and the Main zone in the Palm area.

AB Main Mineral Petrography Barite Large blades rooted in clusters of small, anhedral grains. Fibers lining micro pores. Local sub-grain development along grain boundaries Dolomite Void-filling: Slightly ferroan, anhedral, very fine to coarse, some saddle, locally recrystallized Quartz Euhedral prisms. Local sub-grain development Calcite Absent Fluid Inclusions1 Barite Abundant planes of secondary or pseudosecondary inclusions, sub-micron, rarely to 2 urn, monophase or very small V Dolomite Turbid with dense, sub-micron inclusions Quartz Fluid inclusions are abundant in sub-grain cores; mostly <3 urn, up to 7 urn; 2- phase LV with 1-5% V; some monophase inclusions (a few of which are associated with inclusions that have 10-20% V, indicating post-phase-change necking). Inclusion shapes are rounded to slightly angular; equant, elongate, or very irregular: some LV inclusions with narrow arms radiating from a central core may have been decrepitated by internal overpressure. Quartz sub-grain boundaries are defined by a paucity of inclusions. Primary FIA planes parallel grain boundaries and consist of 2-3 dozen 1-2 pirn inclusions. Pseudosecondary trails do not cross sub-grain boundaries. Cathodoluminescence Barite Not studied Dolomite Matrix: Bright orange Void-filling: Moderately dull orange + growth zones of moderately bright orange Quartz Non-luminescent AB-C (Upper and Lower) Mineral Petrography Barite Fine to coarse blades with corroded edges Dolomite Matrix: Anhedral, very fine to fine, interlocking crystals, brown from intracrystalline organic matter Void-filling: Anhedral, very fine to coarse, saddle to non-saddle, slightly ferroan to non-ferroan; non-saddle is locally twinned with planar extinction (calcite?) AB-C (Upper and Lower), Mineral Petrography (continued)

160 Appendix A. Petrography of secondary minerals

Quartz Euhedral prisms; earliest growth zone defined by a paucity of inclusions Calcite Not studied Fluid Inclusions1 Barite Few, small inclusions Dolomite Dense, sub-micron inclusions Quartz One crystal studied. Initial growth zone against sphalerite substrate is inclusion-free, remainder of crystal has multiple pseudosecondary planes and dense arrays of inclusions in no clear pattern, totaling as much as ~20% of the crystal volume. Aqueous LV with low V, <1-20 nm, mostly 1-4 jim, light, wide variety of irregular shapes Calcite Not studied Cathodoluminescence Barite Non-luminescent to very dull, dark reddish purple. Marked at regular intervals (at cleavage intersections?) by triangular pits of bright, speckled, yellowish orange. Cut by fine, parallel lines (one cleavage?) of moderately bright red Dolomite Matrix and ooids: Bright orange Micritic patches in matrix and rings in ooids: Moderately bright orange Void-filling, saddle: Moderately dull orange core, surrounded by thin, bright orange zone ± moderately bright orange zone. Veinlets and micro-domains of the matrix (the latter may be filled pores) are filled with coarser, inclusion-poor dolomite that is moderately dull with streaks of moderately bright orange Void-filling, non-saddle: Very dull red-orange; edges may be zoned diffusely, alternating moderately bright and dull Quartz Dull, variably luminescent (scrappy looking), dark purple Calcite Not studied AB Point Mineral Petrography Barite Absent Dolomite Matrix: Anhedral with curved inter-crystal boundaries. Early void-filling non-saddle: Anhedral, speckled under crossed nicols, growth- zoned; earliest pulse is non-ferroan, later pulse has ferroan growth zones; latest has intercrystalline bitumen Void-filling, saddle: Spearhead-shaped crystal terminations and undulatory extinction. Non-ferroan. Crystal terminations are corroded adjacent to quartz Quartz Euhedral to subhedral crystals. Contains dolomite inclusions and corrodes saddle dolomite. Growth zones are defined by different angles of extinction and are outlined by dense fluid inclusions, locally by bitumen inclusions Calcite Coarse, twinned calcite cuts the primary marine cement (radial fibrous calcite) in veinlets and fills adjacent intra-ooid porosity. Locally calcite replaces saddle dolomite Fluid Inclusions1 Dolomite Turbid with abundant fluid inclusions AB Point, Fluid Inclusions1, continued Quartz Hexagonal core of crystal defined by zone of dense inclusions. Secondary trails

161 Appendix A. Petrography of secondary minerals

cross core and outer grain Calcite Not studied Cathodoluminescence Dolomite Matrix: moderately bright orange. Early void-filling, non-saddle: moderately bright orange with clusters of irregular, bright orange patches (alteration?). Void-filling, saddle: an initial pulse of bright orange, zoned, followed by very dull, dark purplish red (± moderately bright orange zones). Void-filling, ooidic: Non-luminescent with bright orange rims Quartz Dull, light to medium purple to purplish red Calcite Vein calcite is bright orangey red with irregular streaks of dull, purplish red concentrated near rims of veins. Primary marine cement is very dull, brownish red, and primary micritic ooids are dull, brownish red TIC (C and Ryan) Mineral Petrography Barite Absent Dolomite Matrix: Anhedral, planar to curved boundaries, micro- to finely crystalline, polymodal, turbid Void-filling: Anhedral, euhedral rhombic to saddle-shaped, very fine to megacrystalline. First-precipitated rim is limpid, later crystals are turbid with unidentified inclusions Quartz Euhedral to subhedral hexagonal prisms, fine to very coarse Calcite Anhedral to euhedral rhombs, coarse to very coarse Fluid Inclusions1 Not studied Cathodoluminescence Dolomite Matrix: Bright orange, mottled with darker patches Void-filling: Bright orange cores; thinly zoned rims alternate among non- luminescent, dull, and bright orange; latest growth is thick and non-luminescent Quartz Non-luminescent Calcite Not studied Palm Main Mineral Petrography Barite Absent Dolomite An early ferroan phase and a later, less abundant, non-ferroan phase Quartz Coarse, anhedral to euhedral hexagonal prismatic grains Calcite Absent

Palm Main, continued Fluid Inclusions1 Dolomite Almost opaque with submicroscopic inclusions, themselves opaque and not

162 Appendix A. Petrography of secondary minerals

identifiable as fluid or solid. Edges of dolomite grains are inclusion-poor Quartz Dusty with sub-micron inclusions. Some larger, opaque, wispy, multi-armed inclusions that may be decrepitated. Isolated areas of abundant aqueous LV inclusions, <1-3 |im, ~5% V, some monophase inclusions. Inclusions rarely form a definable array. Uncommon secondary, anastomosing planes parallel to very faint undulatory extinction represent healed fractures. No FIAs suitable for microthermometry Cathodoluminescence Not studied 1L = liquid phase, V = vapor phase, FIA = fluid inclusion assemblage

163 Appendix B. Stratigraphic sections

Appendix B. Stratigraphic sections measured in the AB, TIC, and Palm areas; from NWT Special Volume 1

This appendix is reproduced from NWT Special Volume 1, Appendix D (Martel et al., 2011) with the permission of the publisher, the Northwest Territories Geoscience Office. The caption of Table B-1 has been modified from the original, and the legend and section pages have been shrunk to fit inside the wider margins of this document.

Contents:

Table B-1. Locations of measured stratigraphic sections in the AB, TIC, and Palm areas

Legend for measured sections

Measured stratigraphic sections (drafted by K. Rentmeister)

Section BF06AB

Section BF06Palm

Section TIC1 (referred to as section BF07TIC1 in the original publication)

Section TIC2 (referred to as section BF07TIC2 in the original publication)

Section TIC3 (referred to as section BF07TIC3 in the original publication)

Section TIC5 (referred to as section BF07TIC5 in the original publication)

164 Appendix B. Stratigraphic sections

Described by Year whom w/ Section Thickness Section base Section top measure Section measured by thickness of Sekwi d name whom Latitude Longitude Northing Easting Latitude Longitude (m) Fm. (m) B.J. Fischer w/ 2006 BF06AB 64.9905900 -132.3000977 7211468.87 344378.98 64.9892534 -132.3002935 91.0 91.0 E.C. Turner B.J. Fischer w/ 2006 BF06Palm 64.4049377 -129.7975929 7142380.09 461554.34 64 4043152 -129 7923065 1830 157.8 EC. Turner B.J. Fischer w/ 2007 TIC1 64.5307933 -130.1711367 715668258 443808 74 64 5327400 -130.1561033 277.5 277.5 R. Pippy B.J. Fischer w/ 2007 TIC2 64.5463583 -130.1702306 7158416.13 443884.20 64.5559367 -130.1740767 360.9 316.9 D Thomson B.J. Fischer w/ 2007 TIC3 64.5475983 -130.1705417 7158554.58 443871.83 64.5511817 -130.1679567 160.0 160.0 D. Thomson B.J. Fischer w/ 2007 TIC5 64.5468383 -130.1605917 7158461 13 444347 35 64.5473367 -130.1413150 1989 1794 D. Thomson

Table B-1. Locations of measured stratigraphic sections in the AB, TIC, and Palm areas. See also Figures 2-5, 2-10, and 2-12 for locations; section BF06AB on Figure 2-5 is at the showing labeled "Main". Northing and easting are for UTM projection for zone 9N using NAD83.

165 Appendix B. Strutiuraphic sections

Legend Carbonate rocks

l r—^ limestone i ' T~ ~T dolostone • skeletal grains

® © lime mudstone dolomudstone oncoids

% calcisiltstone m dolosiltstone ° 0 ° ° ooids

dark grey to black dolomitic = cm-scale weathering limestone intradasts /calcareous dolostone dolostone ^—7-^ dolostone cemented conglomerate breccia Siliciclastic roc Carbonate rocks with dolomitic shale siliciclastic component j_' i-M argillaceousargil siltstone i ,'| limestonelime 55 quartz-sandy dolomitic 59 limestone siltstone argillaceous quartz arenite dolostone

thinly bedded silicidastic-silty arenite dolostone dolomitic quartz-sandy quartz arenite •'••i''1' dolostone

Symbols Key to page layout — argillaceous w wackestone formation i' packstone informal member — silicidastic-silty stratigraphic thickness (m) ••••= quartz-sandy 0 grainstone •• peloids 1 floatstone interval number °° ooids « rudstone B boundstone (set at base of interval) • oncoids MB microbial boundstone covered interval ^ skeletal 5 contact gradational mm-scale intradasts a contact interstratified ^ cm-scale intradasts ^ bedding strike & dip (N to top) A stromatolites -- vein = parallel laminated 0 vug wavy laminated J-'J stylolitic = microbially laminated 2t?cemented breccia - cross laminated z:, rock-matrix breccia cross bedded •** fault —cross bedded (low angle) cai calcite /v wave ripple tw chert wave dune Doi dolomite v/- load cast 1 pyrite "v mud cracks iv° pyrobitumen i burrows quartz bioturbated M silicified heavily bioturbated sp sphalerite ^ fenestral photograph (number follows) weathering profile (from left to right: y dolostone dykelets • representative rock sample recessive, semi-recessive, (number follows) semi-resistant, resistant)

166 Appendix B. Siratiyraphie sections

continued Section BF06AB(1of2)

50m-

$ R F Intraclast doloftoatstone to dotorudstone, buff weathering, pale grey, finely crystalline, massive. Clasts n AB2 8 A&< are angular. <1 mm - 30 cm. some weakly laminated, light and dark grey to greyish brown to black, some broken and enclosed in dolomite matrix, some rimmed by sphalerite. Local 1 mm quartz grains Q BF06AB28 \floating in matrix. Dolomite veinlets and coarse dolospar in vugs. Sparse, fine pyrtte.

40m—

Lower 1.4 m is same as interval 3. Upper 0.4 m is dolostone. buff weathering, pale grey, finely crystalline, massive. Dolomite-filled fractures and centimetre-scale void-fill of dolomite and barite. Siickenlines.

Intraclast dotorudstone to doloftoat stone (debrtte), medium grey weathering, medium grey, finely O AB2_3_A to B crystalline, massive. Similar to interval 2 except darker and brecciated; some burrows. Angular breccia • BF06AB27 fragments in cement of dolomite and barite. Two generations of dolomite (orange and white) infractures and voids. Sphalerite in medium red-brown, 1-2 mm grains is present in breccia cement. tra AB2_2_A to G Intraclast dotorudstone to do loBoat stone (debrtte), light grey weathering, light grey, finely crystalline. • BF06AB26 stone, light grey weathering, medium grey, finely crystalline, brecciated, thinly parted led?). Irregular, cm to dnvscaie patches of dissolution cemented breccia, consisting of grey one fragments within dolospar. Local sNckensides on parting (bedding?) surfaces consist of Q AB2J.A&B fN d dolomite with crystalline overgrowths. ~10 m downstream (south) from Leg 1 interval 15. J • BF06AB25X m Base of Leo 2. /Basalil 0.30 3 mrr is intraclast dotorudstone (debrite). pale to medium grey to buff weathering, finely /crystalline, lower contact covered. Potymict clasts of pale to medium grey, finely crystalline dolostone Leg 2 /and less common, dark grey (argillaceous?) rock. 1 mm to 7 cm maximum dimension, in highly l«g 1 -WiaWe shapes mostly tabular to ovoid. Diffusely banded with concentrated solution Mams where clasts are less dense. Oblong, sNidclastic-rich domains 1 cm long may represent burrows or clasts. iFine to coarse sphalerite concentrated hi lenses or layers <1-3 mm thick, locally in knots, preferential lin matrix as opposed to clasts. Rare coarse pyrite grains. Gully with outcrop. Upper 0.6 m is fault Igouge and dotordustone. Seams of shaiy, comminuted rock wrap around centimetre-scale, massive, Isphaleritic intraclast dotopackstone to dotorudstone. Coarse, dissemianted sphalerite. To east abutting 1Ithis is different unit, inferred fault between them; to east is sphalerite-free except immediately adjacent 'FG \lto hut Top of irdwval i» Innnf I »g 1 Dolostone to intraclast (-skeletal) doloftoat stone, medium grey weathering. light grey, finely crystalline, a AB1_12_AtoB 1thinly bedded, medium partings, solution seams. Matrix is of ooid (-intraclast) dotograinstone, clasts \ are of organic-rich, argillaceous dolostone and multi-generational intraclast-ooid dotograinstone- • BF06AB18to 19 \ dotopackstone.

Siliciclastic-silty peloid dotopackstone, orange to pale orange weathering, medium grey, finely a AB1_11_AtoE 33 7-1Q T~1 PyBrt \crystalline, weakly, thirty, parallel-laminated, also solution seams resemble laminations, thin parting. • BF06AB5to 10 \Laminations are defined by abundance of aBochems and terrigenous grains. }°o PR SpPyDolBrtOtz^- ^ Lower 0.2 m is argillaceous petoid?-intraclast-skeletal dolostone, medium grey on weathered and > fresh surfaces, very finely crystalline, with thin, planar laminations, fissile. Specks of pyrite along a AB1 _9_A Si AB1_10_A \ solution seams. From 0.2 to 0.3 m is skeletal-intraclast (-ooid-petoid) dotopackstone. cream 2^ \ weathering, light grey, finely crystalline, thickly planar-laminated with thin, solution-seam partings. • BF06A86to 9 \ tower contact sharp. Specks of pyrite concentrated in organic-rich clasts. local barite in radiating \ blades. From 0.3 to 1.8 m is dolostone, pale mange to buff weathering, medium grey, finely \ crystalline, massive. From 0.9 m to 1.8 m are abundant solution seams.

\ Dolostone, ooid-intraclast dotopackstone to dolowackestone, and intraclast dotorudstone. orange \ weathering, medium grey, finely crystalline, medium bedded with btocky, medium partings \ Intraclasts are of ooid-intradast grainstone and laminated, argillaceous dolostone. Local. \ centimetre-scale cortical grains. Millimetre-scale, mud-filled burrows in heavty brecciated rock I AB1_6_AtoG I (unclear if burrowed remnants, which float in breccia cement, are remnants of matrix or clasts). • BF06AB11 and 17,39 \ Brecciated; void-flBing cement phases are sphalerite, barite, dolomite, pyrite, minor quartz. \\ Aggregates of coarse pyrtte and centimetre-long pyrite lenses, coarsely to finely disseminated, Awhite-weathering. pale green sphalerite, coarse barite and dolomite to vugs with pyrite and quartz. \ and coarse dolomite in late veins. Gully with outcrop. iDotostone, orange weathering, medium gray, very finely crystalline, medium bedded with btocky. Cl AB1_4_A Imedium partings. Mottled, heavily bioturfcated. Argillaceous? Top 0.3 m is a covered ridge wth • BF06AB4 ' jfloat of porous, red-brown gossanous rock. uGufly. 1 Dolostone, mottled (70%). and doiosiltstone (30%), interstratified in medium beds, ochre a abi_2_a 1 weathering, medium grey, finely crystalline, thin to medium partings. DotosiKstone is faintly pi BFO6AB3 1 laminated (mm scale). Dolostone. orange weathering, medium grey, very finely crystalline, medium bedded with medium to O ABi_i_At<

thick styloBtic partings, lower contact covered. Mottled, heavily bioturfcated. Argillaceous? Base of Leg 1 Q BF06AB2 Base of section

167 Appendix 15. Ntmtigraphic sections

Section BF06AB (continued)

Top of section 91.0m

90m. Dotostone, buff weathering, orange on fractures, light grey, medium crystalline, massive, non-parallel, AB2_20_A to 8 thin to medium parting. Late dolomite veins. Top of Leg 2. Q BF06AB38

Intraclast-oncoid dolofloatstone, dark grey to orange, lumpy weathering, medium grey, finely crystalline, thinly bedded, medium parting, undulating solution seam surfaces slightly discordant to ©F bedding gives rubbly weathering appearance. Grains up to 1 cm. Allochems in vague bands. Mottled. DolQtz.—•' Coarse, white and orange dolomite ± quartz in vugs and fractures. Heavily fractured, with abundant • BF06AB36&37 slickenlines and dolomite veins in 3 zones -3 m apart. White efflorescence in lower beds. CN

Ooid-peloid dolograinstone, orange to dark grey weathering, medium grey, thin to medium (mostly a AB2J8.A medium) bedded, medium partings. • BKJ6AB35

70m. Dotostone, light grey weathering with a highly irregular weathered face, light grey, massive, medium 131 AB2J6.A partings. Possible ghost spheroidal grains up to 0.5 cm, possibly bioturbaied. • BF06AB34

CM Oolostone. light grey weathering with a highly irregular weathered face, light grey, massive, medium partings. Possibleghost spheroidal grains up to 03 ati. possibly btoturoaled. • BF06AB33 oFR; Oncoid dolofloatstone to aobwackestone grading into fenestra! dotostone, light grey to pale orange a AB2_13_A to C weathering, light grey, finely to medium crystafllne, medium bedded and parted, possible microbial \laminae and dolomite-filled, millimetric fenestral vugs. • BF06AB32 Dotostone, orange weathering, fight grey, finely crystalline, massive with medium partings, styloiites, • BF06AB31 —\1-5 mm dolospar-fitted fenestral vugs. Dotostone, orange weathering, itght grey, finely crystalline. massive witn some tnicK partings, stytowes. AB2J1_A Some dark-fiHed, fenestrae-like structures. B 6F06AB30 Dolostone, medium orange-grey weathering, medium grey, finely to medium crystalfine, local wispy, thin t» A82_10 _A to C laminations, medium btocky patting. Irregular bedding at base suggests there may be a fault in the covered interval be tow. Qossanous at top Pyrite ± dolomite in bedding-parallel stringers, vugs, and a 1 • BF06AB29 ~~\m-long pod.

continued

168 Appendix B. Siraliyraphic sections

Section BF06Palm, Leg 1

/Dolostone, dark orange-grey weathering, locally slightly argillaceous, weakly laminated, thinly —'parting. /Dotostone. yellowish grey weathering, pale grey, medium crystaine, massive with poorly developed medium partings. Unidentified skeletal fragments. /Alternating argillaceous dolostone (yellowish grey weathering, medium grey,"finely crystaline, thinly CB6BF1-26A&27A —' bedded, fissile) and mottled dolostone (yellowish grey weathering, medium grey, finely to medium \ crystalline, medium bedded, 0.5 to 1 cm mottles or burrows, some with geopetal dolospar in upper • 6BF1-26 parts, rare microscopic skeletal fragments) in 0,2 to 0.3 m conformable beds. Lower 0.4 m is semi-recessive argillaceous dolostone. yellowish grey weathering, light grey, finely crystalline, thinly parallel laminated. Upper 1.3 m is dolostone, yellowish grey weathering, light grey, 21,22 50^ —\poorty parallel laminated. Dolostone, yellowish grey weathering, light grey, poorly parallel laminated,

1 jS. \ Argillaceous dolostone, yellowish grey weathering, light grey, finely crystaine, thinly parallel • 6BF1-19 \laminated. / / / —i Dolostone to siliciclestic-silty dolostone, medium grey weathering, light grey, thickfy laminated to 06BF1-18A \ very thinly bedded. Less than 10% of the interval consists of intertayers of siNtidastic-silty • 6BFM8 \ dolostone.

Calcareous dolostone, medium grey weathering, dark grey, finely to medium crystalline, massive, heavily r—ifton lfiAtoB £3) \burrowed. Up to 50% pyrite concentrated outside burrows. '

Lime mudstone, orange-grey weathering, medium grey, thinly bedded, intertayers of yellow dolostone up to 1 cm thick, burrowed. Upper 0.4 m is argillaceous lime mudstone, medium grey weathering, medium-dark grey, platy to shaley, compositionally gradational with underlying rocks.

SilteWastic-sllty, dolomitic lime mudstone to intraclast packestone, orange-grey weathering, medium —.grey, laminated and very thinly bedded. Interfcedded muddy and silly layers and lenses. One 0.5 cm 06&fl-13AtoE \greded bed with basal lag (storm bed). Parallel, undulatory, and ripple cross-laminations. Sparse • 6BF1-13 *1 7 I 5^ \ burrowing. Local milimetrie intraclasts in thin beds. -i\ ICalcareous trilobite-SattenVa dolowackestone to dolofloatstone, siliddastic-siKy. orange-grey Weathering, medium grey, thin undulatory bedding, burrowed.Trilobites whole and fragemented Q6BF1-12A • 6BFM2AtoG —ilmore common at base of unit, burrows increase toward top.

068F1-11A / ' ^G/\^ II Argillaceous lime mudstone, orange-grey weathering, medium grey, platy. Sparse Saltorella. • 6BFM1

, IDolomitic Saitewtta (-trilobite) packstone. orange-grey to medium grey weathering, medium grey, 06BF1-10AtoB A medium bedded. Very thin lime mudstone intertayers. Allochems are preferentially dolomitized. • 6BFM0A toB \ Trilobite fragments are concentrated in layers. 1-10 cm domains are altochem-free. i Basal 0.1 m is recessive argiRaceous lime mudstone, medium grey on weathered and fresh (surfaces. Overlying 0.3 m is dolomitic SattereBa grainstone, orange-grey weathering, thinly D6BF1-8A toB I bedded, burrowed. Wave dune wavelength 30 cm. amplitude 10 cm, crest trends 070 and is Isubhorizontal. Allochems are preferentially dolomitized. Burrows are 2-5 mm wide x 1 an long. • 6BF1-8 \ Top 1.7 m is covered. Dolomitic Renafds boundstone, orangey-grey weathering, medium to dark grey, massive Renalsts blebs to 8 mm, dark grey weathering, Mack, locally with saccate structure, in rounded humps draped D6BF1-6A toH a» by 1 cm-thick layers of skeletal (trilobite?) wackestone to lime mudstone Possible millimetre-scale • 6BF1-6 to • \burrows in boundstone.

"D a> Dolomitized lime mudstone to trtobKe-Salterella skeletal packstone, medium dark grey weathering, 5 burrowed and mottled, thinly bedded. Dolostone 80%, limestone 20%. Packstone as discrete layers in 06BF1-4Ato D o k. which Salterella define planar fabric. Irregular, millimetre-scale intertayers of dolostone; more dolostone Q6BF1-4 6BF1-4-5 u.3 and mors burrows toward top. _Q

/Dolomitic lime mudstone, medium dart grey weathering, orange on fractures, medium grey, /burrowed (sub-millimetre) and mottled, thinly bedded. Dolostone 70%, limestone 30%. Dolomite • 6BF1-3 I fills allochem moulds and burrows. Peloids or very small ooids in a layer 2 cm thick. Some trilobite I fragments. White efflorescence.

/ Dolomitic lime mudstone. medium grey weathering, orange on fractures, medium grey, burrowed KS6BFI-2A I (mm to cm-scale) and mottled (cm-scale), thinly bedded/parted. Dolostone 80%, limestone 40%. / Discrete burrows in imestone are preferential dolomitized, locally have geopetal fill. Limestone •6BF12 / mottles surrounded by dolostone seams form 1-2 cm, irregular bands (disrupted bedding?).

I Dolostone, intracJast? (-skeletal) dolowackestone, and limestone, siiiciclastic-silty, orangey buff I weathering, medium grey, finely crystalline to silty, thinly interfcedded, laminated and 06BF1-1A ' cross-laminated. Laminations are resistant, orange-brown, defined by normally graded silkxlastic •6BFM silt. Burrowed. 20% 2-3 mm ovoid to elongate fragments or intra clasts and locally up to 20% Jmm-scale skeletal fragments concentrated in non-silty layers. Burrows are rich in siliciclastic silt, iTsemi-spherical to oblong, and emphasized adjacent to solution seams (resisted dissolution). Base of section

169 Appendix B. Siraligraphic sections

Section BF06Palm, Leg 1 (continued)

1(X Quartz arenlte. Orange marker unrt. Orange-brown weathering, medium grained,massive. Fractured. _ B 6^1-42*

Lower 3.3 m is dolostone, regular thick parallel laminations. Dolomite vein parallel to feu It in interval 42. Upper " 6BF1-4GA 0.2 m is argillaceous dolostone. medium grey weathering, medium grey, thinly bedded, fissile, not laminated. °

40,41

Dolostone, greenish grey to medium yellowish grey weathering, medium grey, finely crystalline, poorly to well Q 66F1-39 parallel laminated. Drapes the interval below.

Dolostone, medium yellowish grey weathering,medium grey, finely crystalline,massive, locally argillaceous. \jnterval thins laterally.

Argillaceous dolostone with mudstone partings, light qrev to oranoe weathering, medium orev. thick undulatorv DJ6BF1-36A \ laminations, platy partings, mm-scale horizontal burrows. Sparse microscopic skeletal fragments. [J6BF1-36 "O

Ooid dotograinstone, brownish grey weathering, dark grey,medium crystalline. Dolomite-veined, incipiently brecciated. Pyrite along fractures.Ootds are <1 mm. • 6BF1-34

Dolostone, orange-grey weathering, medium grey, mediumcrystalline, thickly parting. Locally burrowed, one #07 3 cm-thick layer of oncold (-skeletal) dolorudstone. Vuggy and veined with dolomite,calcite, quartz: pyritk (In 6BF1-33A DolCalQtzPy.

|Bold arrow: Base of Leg 2 is 80m SSE along strike \

continued

170 Appendix B. Straligraphic sections

Section BF06Palm, Leg 2 T continued

Dotomudstone, olive grey to brown-grey weathering, dart grey, finely crystalline, thickly paring at base. OGBF2-32AtoD medium wavy parting at top. fenestra!. MiHimetric fenestral vugs concentrated in a 40 cm-thick layer H6BF2-32-4 about 4 cm above base, sparser above but increasing toward top.

I Sittstone, rusty brown weathering, medium grey, thinly laminated, fissile to platy. Lower 0.5 m is —'covered. / Dotomudstone. olive grev to brown-grey weathering, dark grey, very finely crystalline. Rare hint of r-]6BF2-28 mottling but mostly homogenous. Dolostone, light brown weathering, medium grey, finely crystalline, thinly (to medium) bedded with OI6BF2-27A gently wavy bedding planes. Mottled with argillaceous wisps around lighter grey domains. (""16BF2-27 Dolostone, orange brown weathering, light grey, medium crystalline, regularly medium parting. Possible 06BF2-26AtoB fenestral vugs are mm-scale, are filled with coarse dolomite, and weather up. Q6BF2-26 *> ' *c /Dolosiistone as in Interval below intertoedded wfth dotomltic caldsitite as in Interval 18. / I DotoslHstone as In Interval below except without recessive Interbeds. Yellowish brown weathering^aBf 2-24A j j medium grey, irregularly laminated, thinly to medium bedded. Mudcrack teepee at base. j1Dolosiltstone with recessive interbeds of dolomkic terrigenous siltstone, yellowish brown I /weathering, medium grey, irregularly laminated, thinly to medium bedded, fissile in recessive 06BF2-23A j layers. Argillaceous veneer on bedding planes of recessive layers. Local mm-scale intradasts, soft-sediment deformation. it Dolostone, medium grey and pale brown weathering, medium grey, Ussie to massive. Alternating ( 68F2-22A "O 7 fissile dolostone with argillaceous partings, and non-partino dotostone in 20-30 cm beds. 0> //Dolostone, pale orange weathering, medium grey, poorly thickly laminated. i I6BF2-21A //Lower 0.1 m and upper 0.2 m are dolomrtic caicisittstone. 0.2 m in the middle are same as interval U '//15 except possibly fenestral. w f Lower 0.4 m and upper 0.3 m are dolosittstone, pale brown weathering, irregularly thinly U laminated. Not as argiHaceous or silicidastic as previous interval. Middle 0.2 m is same as interval "O 14 except without intracJast packstone beds. Dolosiltstone with intracJast dotopackstone beds, pale grey weathering, medium grey, finely J crystalline, weH laminated with parallel to wavy laminations. Argillaceous film on bedding (Manes. KS6BF2-14AtoD j Cm-scale, teepee-shaped, dessication cracks. Local, 3-5 cm-thick beds of intradast rip-ups • 6BF2-14 (intraclasts are up to 2 cm x 2 mm). Local siltcictastic-silty laminations. / Dolostone, dark grey and orange-brown weatherino, medium parting, intensely bioturbated. ~ 06BF2-13A Mm-scale burrows and cm-scale mottles. \MUle efflorescence. P66F2-13 • Lower 0.2 m is dolostone to intraclast dolopackstone. pale orange-brown weathering, pale grey, irregular 5 (discontinuous thick laminations. Laminations and lenses rich in siliciclastlc silt are up to 1 cm thick. , ^. —ilTop 0.6 m is calcisWstone, medium to dark grey weathering, orange on fractures, medium grey, <&F2 12 A

Mottled dolostone, olive-brown-grey weathering, medium grey, finely to medium crystalline, massive. KS66(;2-1AtoB je Rare thin layers of spheroidal, cm-scale grains (oncoids?). Peloids in upper 1 m. Dissolution breccia, SpDoiPyQtz2? cement of dolomite with minor sphalerite, pyrite, and quartz, white efflorescence and brown carbonate • 6BF2-1-1S6BF2-1-6 .Us crusts, dolomite veining, mm to cm-scale pyrite vugs. Omlih |Bold arrow: top of Leg I is 77m NNW along strike | Base of Leg 2

171 Appendix B. Ntratigraphic

Top of section Siilciclastlosilty dolostone, pale orange weathering with dark grey weathering wisps and irregular tatches of siliceous material, medium grey. JDolomitic quartz arenite to quartz-sandy dolostone, fine grained, parallel laminated, tabular Q6BF2-53A 2S""—'cross-stratified.Polo stone clasts to 2 cm tonp. • 6BF2-53 /Dolomitic quartz arenite. medium bown weathering, pale grey-brown. At 0.4 m (In a 5 cm bed) /and from 0.5 to 0.7 m are scattered tabular, lenticular, and irregularly shaped dolostone clasts (and D 6BF2-50A, 6BF2-51A, 50-52 lenses?) 1 mm to 2 cm in size; elongate clasts are parallel to bedding. From 0.4 to 0.5 m is planar and 68f2-52A \low-angle cross-stratified (possible HCS). Dolomitic quartz arenite. grey-bown weathering, pale grey, medium to fine grained, moderately well Di6BF2-49AtoC sorted, rounded quartz grains, locally dolomite-cemented, locally burrowed, massive. Some dolostone fragments <1 cm. • 6BF2-49 —'/Dolostone . pinkish brown weathering, medium grey, thinly wavy parting to massive. Sparse biack D6BF2-47A / miHimetrto sketetat? fraomems. Argillaceous partings. • 6Bf 2-47 — /Same as interval 43. //Lower 0.3 m is sWcfclastic-silty dolostone, yellowish buff to pale orange weathering, medium grey, /finely crystalline, thinly parting. Shiny grey sllty partings. Argillaceous to silicidastic-silty wisps and seams define a vague planar fabric. Millimetre burrows. Same as interval 43 except containing 1.45 terrigenous silt. Upper 1.0 m is sibcicJastiosilty dolostone, less s8ty and less fissile than below. This CB 6BF2-44A, 6BF2-45A I upper interval has intense burrow-mottling (centimetric lighter grey domains surrounded by darker toB I grey, wispy argillaceous seams); local irregular thin banding (bioturbated bedding); and spheroidal • 6BF2-44&45 U to ovoid structures (oncoids?) with concentrically zoned rims but featureless interiors (zoning is w II only visible on weathered surfaces), and are 0.5 to 4 cm diameter. Spheroids are draped by —II solution seams, and therefore were created and preferentially dolomitized prior to burial —|lcompaction. |Dolostone, finely to medium crystalline, massive, very thickly irregularly parting- Abundant solution a 6BF2-43A l|seams create knobbly parting surfaces. • 6BF2-43 |Lower 0.4 m is dolostone with mm to cm-scale dolowackestone Bed's containing miHimetric tabular 36,39 llintraclasts, yellowish grey to pale brown weathering, light grey, well parallel laminated, medium a6BF2-4t« ll parting. Upper 1.3 m is dolostone, as in interval 38, compositionally gradational with underlying lj rocks.

IDolostone as in interval 38. One 4 cm-thick layer of recessive dolomitic siltstone.

|ADolostone, cryptocrystailine, massive, homogeneous. Fractures conchoidally. Upper 0.3 m has IS68F2-38A.6BF2-3M \\dolomlte-«led fenestral vugs. A Dolostone, massive, medium crystalline, medium to thick partings. Open vugs sparsely distributed 6BF2-37A \ in 40 cm-thick layers. Possible milHmetric burrows. Possible fenestrae. StytoKtes. B 6BF2-37 \Dolosilstone. like intervals 14 and 24.

Possibly displaced. Dolosiltstone, similar to Nervals 14 and 24, thin interbeds of intra dast ydolowackestone. greenish grey weathering, well laminated with thin irregular wavy laminations \ (microbial?), silicidastic-silty laminations, miHimetric intradasts. continued

172 Appendix 1*5. Siratiyraphic sections

Section BF07TIC1 (1 of 5) "J* continued

SOm«

Quartz-sandy dotostone, buff weathering, light grey, finely crystalline, thin to thickly laminated, massive, q BF07S1-7A Solution seams cluster together parade! to laminations. Rare 5-10 cm-thick horizon is vuggy. 1-2% • Bf07S1-7 pyrite is disseminated throughout. Scattered spherical dark grey quartz grains <1mm. 40m-

Dotostone, bufl weathering, light grey, very finely crystalline, possiDte taint laminations, thickly parting. n BF07S1-5A PyO Spherical (to elongate) mBlimetric vugs are concentrated in 4 cm-thick layers. Solution seams and r-i BF07S15 \ stytolftes. some with pyrite. Fractures with pyrtte. Dotostone, buff weathering, light grey, very finety crystalline, massive. KS BF07S1-4A to

20m-

U) Ui

Dotostone, light grey weathering, light grey, finely to very finely crystalline, locally poorty paraBel laminated, medium to thickly parting, possibly fenestral. Faint impressions of 1-2 cm intraclasts on O BF07ST-2A toC weathered surface. Vuggy fenestra!? layers with 5-10% vugs alternate gradationalty with less vuggy (2%) layers. Round vugs to 3 cm; elongate (fenestral?) vugs to 1 cm aligned parallel to laminations; • BF07S1-2 & open, some dolomite-lined Some white efflorescence. BF07S1-2-4

Dotostone, orange-grey weathering, light grey, finely crystalline, locally laminated, medium parting. q BF07S1-1A ^"-Dolomite veins, 2% vugs with dolomite and pyrite. Along strike to north is a small exposure of dark grey Q] BF07SM weathering, dark grey dotostone.

Base of section

173 Appendix B. Siratigraphic sections

Section BF07TIC1 (continued, 2 of 5) ' continued fN

*(5 In 0 UV. 1

/ / Dolostone, partly recrystallized, red-brownish grey or beige weathering with fine sandy appearance, light grey, finely to very finely crystalline locally with medium crystalline domains, medium blocky CI BF07SI-14A to C partings, vuggy. Possible intraclasts or broken muddy layers; possible ghost oncoids. Closely spaced r- — CQttDoJ Py2^ solution seams. Most vugs are filled with quartz (including euhedral prisms) and weather up; also • BW7S1-14 dolomite and pyrite-filled and open vugs. Mottled appearance al top is due to bimodal crystal size and weathering colour caused by irregular aleration/recrystaHization. Locally intensely altered (recrystallized dissolution breccia?).

"O Oncoid doioftjdstone, black to dark grey weathering, dark grey, medium (to coarsely) crystalline, thick OB«>7SM2AtoB solution seam partings. Oncoids are 2-4 cm and spherical (to ovoid), local white efflorescence • BF07S1-12

5 (V

Dolostone, black weathering, dark medium grey, medium crystalline, medium solution seam partings. Ghost microbial? laminations are locaHy visible on weathered surface. Cerrtrimetric domains defined by • BF07S1-10A toB fine vs. medium crystal sizes may represent biotubation of layered sediment. A 40cm vuggy. possibly-fenestral interval near top is better laminated. Black colour is imparled by inter- (and intra-?) pi bfo7S1-io crystalline material. Pervasively recrystallized? White, blue, and rusty stains/efflorescence on weathered outcrop.

Dolostone, yellow-grey weathering, dark grey, finely crystalline, possible laminations, wavy medium O BF07S1-9A ODd Py partings. Abundant solution seams. Sparse Ailed vugs. • BF07S1-9

continued

174 Appendix B. Stratigraphic sections

Section BF07TIC1 (continued, 3 of 5) ,i. - =c=:

Dolostone cemented breccia with calcite cement, buff, cream, light grey, and light brown weathering, ^ gpg75^22A to 8 * Qtz Py Cal

/ / •o Dolostone, medium grey weathering, medium dark grey, thinly to thickly laminated, irregular partings. O BF07S1-21A

> t S

OBF07S1-19A Dolostone, buff-grey weathering, light grey, finely crystalline, medium to thick blocky partings. • BF07SH9

/ / '

Cemented breccia in intraciast dolofloatstone, brown-grey weathering with reddish stain, medium to very thick partings. Network of calcite cement around 1 cm. grey, rounded, creamy-dolomite-lined I BF07S1-18A to E dolostone dasts Vugs to 30 cm contain ft-cm calcite crystals. Locally the clasts appear to have grains r—1 ^75^ jg (oncoids or intraciasts). Possibly a primary (collapse) breccia, but samples are suggestive of dissolution. Dolostone. brownish grey weathering, medium solution seam partings, Solution seams resemble laminations. Sparse intraciasts are centimetres long. At top is a SO cm-thick vuggy horizon, vugs <1-3 fs BF07S1-17A —t cm, lined by dolomite and pyrite followed by calcfte and pyrite, 5% vugs. Pyrite as miHimetric \\ dodecahedrons. White efflorescence. 5 \ Skeletal dolowackestone. light grey weathering, finely crystalline. Top of interval is oncoid O BF07S1-16AtoB

(N "75 2 o k.u E

continued -J

175 Appendix IV Stratigraphic suctions

Section BF07TIC1 (continued, 4 of 5) continued

D £ til o3 m / , / Dolostone rock-matrix fault breccia, but weathering, Kght grey, with millimetre-scale clasts. • BF07S1-34 "O *-»aj Dolostone, dolostone cemented breccia, and rock-matnx (fault?) breccia, medium parting. B8sal 2m is c pyrttfc, recessive, white efflorescence. MiHimetric fenestra! vugs are open or filled with dark grey ^3._ dolomite which weathers white and up. Rock-matrix fault breccia cuts fenestra! dolostone, which has a BF07S1-33A to D I Ly * ) >*APvQ-^» been affected by dissolution brecciation. Rock-matrix fioatbreccia has rounded to angular, equant to ro tabular, dark grey weathering dolostone clasts in a light orangey-brown dolostone matrix. LocaRy there O 6F07S1-33 is a preferred orientation of tabular clasts. Locally a dark vuggy fabric grades laterally into A light-coloured, siltcifled dolostone. Interval changes from semi-recessive at base to resistant at top. ar._ Dissolution cemented breccia of laminated doiostone, light yellowish grey weathering, light grey, 0 BF07S1-32A to D medium parting. Centimetre-scale dark grey, elongate clasts, aligned parallel to parting, angular to \amorphous, separated by friable yeltow-grey cement. • BF07S1-32

~r~i

~r~<

Dolostone. yellowish grey weathering, pale grey with dark grey fenestra! fills, finely crystalline, i /' laminated, thick irregular to parallel partings. Alternating fenestral vs nonfless fenestra!. Some fenestral o BF07S1-30A toD £ horizons include very large (centimetre-scale) elongated vugs. Special horizons: 8.1-6.9 m is pyritic, recessive. At 7.3 m is 60 cm of pyritic, recessive, rusty weathering, finely crystalline, medium dark grey Q BF07S1-30& 0J CpJJ^Sii to dark grey (fresh) fenestral dolostone with fine stringers and 1 mm cubes of pyrite. At 7.6-8.1 m is BF07S1-30B siKcified interval, medium to dark grey weathering; and along apparent strike to east is a breccia of calcite network between centimetric dolostone clasts. At 12.1 is a 1-cm layer, traceable for 2 m. of miltimetric intraclast rip-ups. At 15.2 is breccia. r*- ro •D ~~r~7 4^0/ ro C

k- Dolostone, buff to medium grey weathering, light grey, finely crystalline, laminated, medium to thick rtj irregular to blocky partings. Fenestral horizons are interiayered with less- or norvfenestral at a CI BF07S1-29A T3 decimetre scale. • BF07S1-29 —-"Dolostone, buff weathering, pale grey, finely crystalline, laminated, thin (to medium) paraiel to irregular partings. SubmiBimetre to millimetre-scale vugs contain medium crystalline euhedral dolomite CM BF07S1-28A crystals. Top of interval is locally very dark grey and has elongate, miKimetre-scale, open vugs • BF07S1-28 =Z= G>Py (fenestral?). Pervasively recrystallized. White efflorescence StytoWes. /Dolostone, yeltow-burt weathering, pale pinkish grey with dark grey vug fills, finely crystalline, OBF07S1-27AIOD /faintly laminated, medium to thickly parting. Local submiHimetre-thick calcite stringers form breccia Cat — network. Ghost mlni-oncoids? (spheroidal orains <1 cm) • BF07S1-27 PyCalOZX'#* -i Dolostone rock-matrix breccia, yeHow weathering, greenish medium grey, finely crystalline, thinly BF07S1-26A to B \ irregularly parting, porous. Brecciated with dark miilimetric doiostone clasts in paie dolostone matrix. \\5% pyrite in mitlimetric vugs. Calcite in vugs. White efflorescence. • BF07S1-26 \ Dolostone. buff weathering, pale reddish grey with daft grey fenestral fill, finely crystaline, locally \ laminated, irregular medium partings. Filled fenestral vugs are oriented parallel to laminations. O BF07S1-25A \ Centimetric patch of 1-5 mm oncoids occurs in same bed as fenestra! vugs. Abunadnt solution • 8F07S1-25 \ seams. White efflorescence. Doiostone, buff weathering, pale grey, finely to medium crystalline, thinly irregularly parting, locally 06f07S1-24AtoB porous. Fenestral at top; some fenestrae-like vugs near base. Small intraclasts near base. Brecciation creates network appearance at base. • BF07S1-24

Dolostone cemented breccia, medium dark grey weathering, medium dark grey, medium crystalline, I BF07S1-23A toC QPyfc thin to medium irregular parting, vuggy to very vuggy and porous. Variably intense white efflorescence. Mostly brecciated. Pyrite disseminated and in vugs. Some breccia clasts are laminated. TIC Ryan D B(57$1-234r mineralized zone along strike to north. BF07S1-23B

continued |TiTi

176 Appendix B. Stratigraphic sections

Section BF07TIC1 (continued, 5 of 5)

TOD of section 277.5m

ro ft**, / ' Dolostone and dolostone cemented breccia, medium orey weathering, stained reddish brown, light to • 8F07S1-39A to C medium grey on fresh surfaces, medium to thick irregular partings. MiSimetrtc to centimetric, rounded to SilPyCal Dol-^2? angular clasts of dolostone in coarse dolomite and calcite matrix. Upper part of interval is heavily o BF0751-39 -D silicified

pS/ - / , /*

1 I- & Dolostone, light grey weathering, Hght grey, finely crystalline, microbially laminated alternating with ES BF07S1-37A -TT • BF07S1-37 "zzrz: parallel to non-laminated in 10 cm beds.

/ /: 3 • 5 £ 2t3 <3 ~T~T toa* "O

Doloslone and dolostone rock-matrix fauh breccia, buff to light grey weathering, Hght grey, finely crystalline, poorly laminated. Dolomite and calcite fill vugs and fractures. At 9.1m are siBcified microbial 18F07S1-36AtoE laminations and quartz-filled fenestra! vugs. At 9.5m, a 60 cm-wide vein of immensely coarse calcite ODol Cal/\-»-*- • BF07S1-36 trends 300 degrees and contains clasts of dark vuggy dolostone up to 15 cm. Outcrop is coated with z =z ^ white efflorescence.

, / , r

/' r-

177 Appendix li. Siratigraphic sections

Section BF07TIC2 0 of 6) [ continued

Oolostone (and dolomudstone), medium grey weathering, medium dark brownish grey, finely crystalline, medium parting to thickly parting, thin banding defined by mottles. Centimetre-scale mottles O BF07S2-17AtoD are defined by colour and crystal size; intensely bioturtoated Layers of dolomudstone. Rare vugs <1 • BF07S2-17 cm, circular, fitted with dolomite and calcite. / / I Dolostone, yeltow-grey weathering, medium grey, very finely crystalline, thickly laminated, medium a 6F07S2-16A /parting. Parallel to irregular laminations include microbial ones. SBty layers are disrupted to form • BF07S2-16 I rip-up clasts 1-2 cm. Calcite fills subvert!cal veins and en echelon gashes. II Oolostone (to intraciast dolograinstone), pale yellow-grey weathering, medium to pale grey, very j finely crystalline, medium stylolKic partings. Mottled appearance locally enhanced by densely I packed solution seams. Some beds have tiny irregular porosity. Vuggy horizons contain irregular, CI BF07S2-15AtoF //elongate, horizontal vugs with calcite flu. Near top is a bedding plane with burrow-like structures • BF07S2-15 II having rounded ends, up to 9 cm x 0.5 cm, either tubular mud clasts or dense burrowing, similar to 'I interval 13. Subvertical caldte-fWed gashes. Top of first waterfall. =sgs

—/ j Dolostone, medium yellow-grey weathering, medium dark grey, finely (to medium) crystalline, ~ OBF07S2-10A / faint thick laminations defined by differential weathering, no parting. Mottled/bioturtated • BF07S2-10 (centimetric amorphous domains defined by crystal size and colour). Dolostone, medium grey weathering, yellow on fracture surfaces, medium grey, finely crystalline, locally J»~ OBF07S2-9AtoC - thickly laminated, medium parting. Colour mottled in medium and dark grey. Local differential I -"OCalDol • BF07S2-9 weathering defines thick laminations. Centimetric patches on fracture surfaces and veins to 4 mm wide \of light grey to white calcite. OCalDolPy Dolostone or dolomitic mudstone. dark yellow-grey weathering, medium dark grey, finely to medium crystalline, finely laminated, thinly bedded at base, thin to medium parting above. Starved ripples at a BF0752-8A to I base. On fracture surfaces are flat, centimetric, recessively weathering vugs of fine grey calcite and • BF07S2-8 A lesser coarse euhedral dolomite with minor pyrite. Solution seams. Top 1 m is pyritic and vuggy;

l\\ pyrite is oxidized along laminations. Base of first waterfall. \ Dolomitic limestone and calcareous dolostone. medium crystalline, thickly to unlaminated, medium \bedded, medium parting. Solution seams. Dolomitic limestone, finely crystalline, finely laminated, thinly to medium parting. Dark grey. U centimetre-scale, bedding-paraflel limestone lenses separated by resistant, laminated n BF07S2-6A ,\dolosiitstone. Scattered 1-3 mm black calcite crystals float in the limestone lenses. D BF07S2-6 ISiliciclastJc-silty, finely laminated calcareous dolostone, lo dolomitic lime mudstone to ;calcisiltstone. Yellow-grey weathering with medium grey laminations. Medium partings. Soil OBF07S2-5A 1 sediment deformation, millimetric rip-up clasts, local ripples. No quartz. QBF07S2-5

Quartz-sandy dolostone to dolomitic sandstone and sHiciclestic mudstone, orange-grey weathering, medium grey, finely laminated, 10 cm cross-beds, thickly parting. Up to 50% very fine to coarse quartz sand grains, locally quartz-rich, centimetric beds with up to 50% quartz. Irregular, sinuous to OBF07S2-3A to J branching, 3D ripples have 5-10 on wavelength. <1-2 cm amplitude, and are made of quartz sand; 0 BF07S2-3& siliciclastic mud lies in troughs between ripples. Burrow-like structures in a brownish-grey mud layer BF07S2-3-2 i777 \ are bedding-parallel, 1-2 cm long, tapering at both ends, 2*4 mm wide, and orange with fine dark *f/f r fit= \ rim. Rare miHimetric domains of coarse white dolomite. Dolostone, brown-grey weathering, light medium grey, medium parting. Very finely crystalline, finely \ laminated dolostone alternates in centimetric layers with non-laminated, medium crystalline, O BF07S2-2A to B Vpatchily re-crystallized dolostone. Latter contains 1-G mm domains of coarse white dolomite, and • BF07S2-2 —\ \ up to 20% quartz grains, Solution seams separate centimetric 'beds*. \ Oolostone, orange-grey weathering, medium grey, very finely crystalline, thickly laminated, medium OBF07S2-1A \ parting. Trace disseminated pyrite, veins of dolomite miBimetres wide, laminations defined by • BF07S2-2 \ differential weathering and on fresh surface by color (darker grey).

Dolostone. weathers brown-grey with sandy texture, medium grey, finely crystalline. , / , / / Dolostone. orange-brown-grey weathering, medium grey, finely to very finely crystalline, thickly • BF07S2A-4A parting. At 1 m is suggestion of burrows on bedding plane, / Oolostone, laminated, thickly parting. IBF07S2A-3A // Dolostone. oranpe-grev weathering, light a rev, finely crystalline, irregular thick partings, vuggy —/folded and fautt-brecciated (network of filled fractures). Thick bed undulates in low dunes with IBF07S2A-2Ato 2C wavelength 1 -1.2 m, amplitude 30-40 cm. Dolostone (and ooid dolograinstone), orange-grey weathering, light grey, finely crystalline, wavy laminated, thinly (to medium) bedded and parting. At 1 m are thin beds of ooid dolograinstone with \undulatory bedding planes; elsewhere is dolostone without ooids. Base of section

178 Appendix B. Stratigraphic actions

Section BF07TIC2 (continued, 2 of 6) "j" continued

I r-rsj k.03 T5 Py Pyro Dolostone, pinkish grey weattiering, pale greyish pink, medium crystalline, medium parting, porous. \ Abundant (20%) midimetnc porosity, disseminated fine-grained pyrite, fine wtsps of black C* BF07S2-21A \ pyrobitumen? in wispy pores. Centimetre-scale weatherd pits. 'Sugary'texture under lens • BF07S2-21 \ imparted by euhedral dolomite. Intermittently exposed.

r». fN TO S o u E

5 %'t/i

2 is k_O

X Dolostone, buff weathering, pale grey, very finely crystalline, thickly wavy laminated, medium parting. Ol BF07S2-19A 6 Pyritic vugs millimetre to centimetre-scale, open and with pyrite. arranged linearly (possible planar). • 8F07S2-19

Intradast dotofloat stone, dolostone, and cemented dolostone breccia, medium yellow-grey weathering to rusty red-brown, very finely crystalline, massive to medium parting. Intraclast dolofloatstone consists >s of laminated, tabular to lenticular ciasts in a medium wystafline, sandy-weathering matrix; locally the Ol DolCa! Py 2^ horizon, 20-30% 1-cm subsphericai vugs filled with dolomite and pyrite. Dolomite ± pyrite fills irregular 3 vugs and fractures throughout. Interval is marked by: vertical dolomite veiniets; subvertical fracture set > spaced 10-20 cm and very obviously restricted to this interval; and metres-wide areas of pyrite-dolomite cemented breccia. Pyrite is disseminated, is in vugs with dolomite, and occurs as massive veins. Interval includes a recently sampled gossan. Second waterfall

continued

179 Appendix II Simligraphic sections

Section BF07TIC2 (continued, 3 of 6) '[continued

CI BF07S2-29A

Dolostone, yellow-grey weathering, pale pinksih grey, finely crystalline, faintly lamianted, medium to thickly parting, medium-thick vug-rich horizons (beds?). Cliff. Horizons of abundant (20%). aligned, elongated, millimetre and centrimetre-scale vugs which locally have fenestral appearance, alternate with less vuggy horizons. Vugs are Ivied with coarse euhedral dolomite. White efflorescence.

170m-

Dolostone, yellow-grey weathering, pale yellowish grey, finely to medium (to coarsely) crystalline, locally thickly lamianted. medium to thickly parting, porous. Cliff. Variably fenestral in alternating layers a BF07S2-26A to E of fenestra! vs. not fenestra!. Abundant (20%) miilimetric porosity usually arranged linearty, and r-t RFn7<.5 fN centi metric vugs or weathered-out pits. Local laminations defined by differential weathering and accentuated by orientation of pores. Miilimetric pyrite and local miilimetric quartz prisms in pores. Z=

150m- Dolostone, light medium grey weathering, yellowish grey, medium (to coarsely) crystalline, massive to irregularty parting, porous. Cliff. Disseminated pyrite grains to 3 mm. Large vugs (weathered-out pits) to ^ BF07S2-25A toC ODol Qtz 10 cm. Rare millimetre-long quartz prisms in S-mm vugs. Minor white efflorescence. Abundant (20%) miilimetric porosity. Coarse euhedral dolomite lines pores.

140m—

Dolostone, pinkish grey weathering, pale greyish pink, finely (to medium) crystalline, medium patting, porous. Millimeliic to centimetric porosity 10%. Trace pyrite. Large, metre-scale blocks of rubble above • &F07S2-23 basal 2.1 m of outcrop.

130m-

180 ppcndix B. Stratigraphic sections

Section BF07TIC2 (continued, 4 of 6)

Doloslone, light medium grey weathering, light grey, very finely lo finely crystalline, welMamianted, medium parting. Laminations of dolomudstone are separated by milNmetre-wkflh laminations of sill or O BF07S2-32A v fine sand-sized doiosione Soft sediment deformation Some microbial laminations? Pyrite _ \along stytoiites. Dolomite lines vugs, caicile fills. Bf07S2"32

Dolostone, light medium grey weathering, pale grey, very finely to finely (to medium) crystalline, O BF07S2-30A to c weK-lamianted, medium parting. Consistently well-laminated, locally parateMaminated, possibly locally rn 0FO752-3O microbially laminated. Local soft-sediment deformation.

181 Appendix B, Stratigrapliic sections

Section BF07TIC2 (continued, 5 of 6) i continued

Dolostone. black weathering, dark grey, medium crystalline, thickly lamianted, thinly bedded, thinly to no medium parting. Lower 60 cm well laminated. Above this the rock has mottled appearance: lighter grey, J* . centimetric elongate domains with sandy texure (locally ooidic?) which locally define banding, CS BF07S2-40A to I I Ca| py surrounded by finer (but still medium) crystalline black laminated matrix. Compositional banding is 2 cm • BF07S2-40 ra • thick, disrupted. Wspy carbonate (caicite?) veinlets are so abundant they form an incipient breccia. •O Centimt re-scale aggregates of pyrile near the breccia. Patches and veins of carboante. \Miite efflorescence. Blue efflorescence effervesces in HCi.

Dolostone, medium grey weathering, yellow on fractures, pate creamy to light grey, very finely to finely •o crystalline, thickly welHamianted, thinly to medium parting. Cliff. WeK parallel to wavy laminated, locaKy ~~Py • BF07S2-38A CO microbial. Sparse open centimetric vugs. Abundant solution seams and stytolites. hematitic solution BF07S2-388 c seam partings. E 5 03~~

Dolostone, light grey (to bleached cream) weathering, pale grey, very finely to finely crystalline, thickly wavy to I BF07S2-36A to F f , f ' parallel weil-lamianted. thinly parting Cliff. Consistently, wetMaminated parallel to wavy Local soft sediment deformation. 1-2 cm horizons of intradast dotowackestone to doioftoatstone, millimetric intradasts Laminations • BF07S2-36 locally are mud vs silt, locally with millimetre rip-up ciasts of mud in the sitty layer Rare centimetric vug with / / coarse dolomite and caicite

~~Dolostone, medium grey weathering. Hght grey, very finely crystalline, thickly welMamianted. thinly O 8F07S2-34A parting. • BF07S2-34~~

~~182 Appendix H. Ntmtigrapliic sections~~

~~Top of section 360.9m Section BF07TIC2 (continued, 6 of 6)~~

Dolostone conglomerate, and lesser pink, very fine grained sandstone. AH is rubble; heavy carpet of rubble covers hilltop completely. Conglomerate clastsare angular to subangular, tabular, 1 to >10 cm x 1*4 cm, in pack- and fto atbreccia packings. They consist of a variety of dolostone (in shades of light to medium grey, laminated and non-laminated), chert, and rare sikstone. Dolostone dasts are commonly O BF07S2-46A to X partly encased by soft, reddish brown-black crust (of Fe-Mn oxides? insoluble remnants of burial O 8FQ7S2-46A, dissolution?). Conglomerate matrix is tight grey dolostone, commmonly same same colour as dasts. 8F07S2-46B Centimetric vugs are open or calcite-flled. Conglomerate is locally brecciated and cafcite-cemented BF07S2-46C BF07S2-46D and veined therefore calcite event is post-Sekwi. Post-conglomerate compression has caused local inter-clast penetration and fitted clast fabric. Some sandstone is slightly dolomitic, other is lamianted and contains no carbonate.

Quartz-sandy dolomitic limestone and calcareous (and dolomtttc?) sandstone, yellow-brown Pebble or Gi BF07S2-45A cobble-sized rubble. Some pieces are terrigenous sandstone without carbonate cement & are partly • BF07S2-4S encrusted by <1 mm-thick soft black * hematttic crust (Fe-Mn oxides?).

Sandstone, yellow-brown to pink weathering, poker-chip rubble. Flat cobbles of finely laminated sandstone with hematitic layers, locally calcareous. Also cobbles of dolostone conglomerate, with dasts of dolomudstone in faintly dolomitic matrix; abundance of these cobbles increases upward. They may derive from interval 46.

Dolostone. bleached cream weathering, light grey, finely to medium crystalline, locally microbially lamianted. medium (to thinly) parting, vuggy. Local 2-cm colour bands (laminated, white, non-vuggy G> Py Qtz Dol versus non-laminated, grey, vuggy, mottled). Pores are lined by euhedral coarse dolomite t euhedral quartz ± pyrile to 3 mm. Centimetric weathered pits. Pyrite is concentrated along solution seams.

Dolostone. medium grey weathering (localy bleached light grey), light grey, finely crystalline, microbially laminated. Local muddy broken layers 5 mm thick, interbedded with microbially lamianted O 8F07S2-42AtoC dolostone. Local dolostone veins or dykelets are mHlimetnc, medium grey, and cut through bleached, light grey laminated dolostone (across and along laminations); unknown origin; same as interval 29 in • 8F07S2-42 BF07TIC5. Lower 2 m consists of metre-scale slabs. Above that is abundant rubble. / . >

Dolostone. Mack weathering, dark grey, medium crystalline. Pitted, jagged weathered surface. Faint suggestion of laminations. Not mottled. White and blue efflorescence, wispy calcite veinlets. continued J

~~183 Appendix B. Slraligraphic sections~~

~~Section BF07TIC3(1 of 3) continued~~

Dolostone. buff to yellow-grey weathering, light grey, micro crystalline, thinly laminated and thinly to a BF07S3-6A to C —\ medium bedded. Some gritty (silicidastic-silty?) dolomudstone at top. Bedding planes are dart Q BF07S3-6 \\grey (muddy?). Dedication cracks. Load casts on one bedding plane \ Dolostone, buff-grey weathering, light grey, very finely crystalline. mjcrobtaBy laminated. \ Laminations are locally storm?-disrupted. Stylolitic. CNff.

/Dolostone, medium dark grey weathering, medium dark grey, medium crystalline, massive. /Darter and more pyritic than previous interval. Mostly fenestra! (some layers not). Fenestra® are O BF07S3-3AIOE millimetre-sized and filled with pale creamy dotomite. Local cemented breccia (dolomite t calcite t • BF07S3-3 ^•PvDolCal pyrfte) with mm-sized ciasts and cement in veins and domains to 1 cm. White efflorescence. Dolostone, medium grey weathering, yellow-orange on fractures, pale grey, finely to very finely crystalline, massive, cliff-farming. Centimetres-thick bands are either vuggy (1-10 mm open vugs lined d BF07S3-2A to C ODdPyQtZ by dolomite ± pyrfte). skeletal? dolofloatstone? (oddly shaped white dolomite "fragments"), or laminated • BP07S3-2-0.6 (rare, discontinuous). Trace of pyrite is common. BF07S3-2-1.5

~~^ Cover. Base of section is top of intervai 1 of section BF07TIC2. Base of section~~

~~184 Appendix 15. Stratigraphic sections~~

~~Section BF07TIC3 (continued, 2 of 3) I' continued~~

~~o°Go OoH dologralnstone, brown-grey weathering, medium to thickly parting. Ooids 1-2 mm. Floating O 8F07S3-16A toB oncoMs at base. • 8F07S3-16~~

Doiostone and oncoid doiofloatstone, dark brown-grey weathering, dark grey, medium crystalline, oF medium to thickly parting. Cliff. Some horizons have cm-scale colour banding, some are ortco id-rich. '7? / Dol-* Oncoids are ail <1cm and oblong. White and blue efflorescence, wisps of white carbonate; dolomite ' P / veintets.

Archeocyathan doloboundstone, black to dark grey weathering, dark grey, finely to medium crystalline. Exposed as metre-scale rubble. Two scales of layering; black medium crystalline doiostone is I BF07S3-t4AtoJ irrteriayered with mottled, black and dark grey bands with irregular borders. Common wispy white olQtzH carboante (incipient brecciation) and some large vugs lined with coarse dolomite preceding coarse quartz. Rubble of tiny-ooid dolograinstone.

% Doiostone and Archeocyathan doloboundstone, black to dark grey weathering, dark grey, medium crystalline, medium parting. Spherical to oblong oncoid ghosts, <1-4 cm. Local faint, discontinuous O BF07S3-13AtoE laminations. White carbonate wisps hint of proto-brecciation. Horizons of skeletal? doiostone 10 ^B»% • 6F07S3-13 (mm-scaie fragments of orange resistant dolomite). Stylolitic. White efflorescence. Lower 6.1 m is rubble and sparse outcrop; above is outcrop.

/Doiostone. medium grey weathering, dark medium grey, finely to medium crystalline (polymodal). /microbially laminated, thinly to medium parting. Weathered surface is rough. Domains of BF07S3-12A /proto-breccia with white dolomite cement. Laminations are locally msty. Stylolitic. White O BF07S3-12 efflorescence. Rubble and sparse outcrop. Doiostone, medium grey weathering, medium to dark-medium grey, finely crystalline to microcrystalline. laminated, thinner parting (thin to medium) than interval 10. From 0-0.5 m is well-laminated, hematite. medium crystalline doiostone. At 0.5 m is 1 cm discontinuous horizon of Mack chert Deca metric load O BF07S3-1 lAtoM structures above chert. Above 0.5 m is locally hematitic. locally thickly laminated, with thick dessication • BF07S3*11Ato8 cracks forming 3-5-sided polygons. At - 4 m are discontinous flat tensoid microbial buildups with quartz sand that was caught in the microbial mats. White efflorescence.

v Doiostone and stromatolite doloboundstone. dark buff-grey weathering, medium grey, finely crystalline. Oi BF07S3-10AtO F \very well and finely undulatory laminated, medium parting. Common disrupted laminations, mrn-scale 7 tabular mud clasts, & troughs. Local cm-scale stromatolites. This interval is hematitic along strike to Q BF07S-10 east. Dessication cracks.

~~Cover. Stromatolites and dessication cracks in doiostone rubble.~~

SiNciclastiosilty doiostone, yellow-grey weathering, light grey, finely to very finely crystalline, very thinly I BF07S3-8A to H to thinly interbedded siliciclastic-silty (and sandy) doiostone and siRy mudstone. Polygonal cracks and —\abundant burrows (discrete traces) on bases of bedding (Manes, including trilobite resting traces • BF07S3-8A to C \(Rusophycus). Stylolitic. Cliff. White efflorescence.

Doiostone, buff-grey weathering, light grey, very finely crystalline, finely laminated with irregular wavy 0 BF07S3-7A to I laminations that are commonly disrupted (as in interval 5). Medium parting except top 5 m has thin • 8F07S3-7 partings. Stylolitic. Cliff.

~~continued~~

~~185 Appendix B. Straliyniphic sections~~

~~Section BF07TIC3 (continued, 3 of 3)~~

~~Top of section > 155.7m Dolostone, fenestra!. Corresponds to interval 26 of section BF07TIC2. 19~~

CM Dolostone, light brown-grey weathering, pate grey, finely crystalline, massive to thickly parting. Pyrite, Ot 6F07S3-18A , / , / ODol PyQtz dolomite and quartz in cm-scale vugs. Some horizons are vuggier to 20% vugs, locally laminated at • BF0753-18 ro _ base. Corresponds to interval 25 of section BF07TIC2. "O ! ' ! [ / 18 -r~i 150m—

140m— J*

~~130m--~~

~~120m— continued •~~

~~186 Appendix li. Strniigraphie sections~~

~~T contin Section BF07TIC5(1 of 4)~~

~~Doiostone, dark grey to dark brown weathering, dark grey, finely crystalline, massive to thickly parting, • BF07S5-11 I^PyDol and cemented breccia with up to 20% pyrite-dlomite cement.~~

Oncoid doioflo at stone, dark grey to brown weathering, dark grey, finely crystalline, medium parting. Oncoids are concentrically, irregularly laminated, spherical. 1-2 cm (smaller ones tend to be oblong). a BF07S5-8A to C JoF RJS Sugary texture. Top 30 cm has smaBer oncoids (

Dolostone, dark grey to brown weathering, dark grey, finely to very finely crystalline, mottled and J s*9o banded, thickly parting. Basal 60 cm has irregularly edged colour-banding (1 cm black vs 2 cm mottled O BF07SS-7MOE grey). Above Mat is more subtle variability in colour and crystal size. Few 5 mm oncoids near top. White 17*7 Pol Py- • BF07S5-7 and pink/orange dolomite in cm-wide veins and patches to 30 cm. Pyrite disseminated throughout and in veins. Grades upward into cemented breccia (with wispy to centimetric dolomite cement). i CO

Dolostone, doiomitic siltstone. doiosiltstone, and dolomudstone. Pale yellow-grey to bleached weathering, fight grey, very finely crystalline, very thinly to thick partings. Dolostone is microbial^ laminated, similar to intervals 2 and 4. and is interttedded with doiomitic siltstone and local recessive Ci 8F07S5-5A to €, platy dolosiftstone. Basal 0.2 m is orange-grey weathering dolostone with shiny grey mudstone 6AtoG partings, very thinly bedded with clustered solution seams that resemble laminations. At 8 m is a 4-cm Q BF0755-5 to 6 thick, very thinly parting, finely crystalline dolomudstone with cracks or burrows in mudstone partings. Local alternation between laminated and unlamianted. Stromatolites and possible bioherm at top. Stylolites.

~~/ ; , >~~

Dolostone, pale yellow-grey to bleached weathering, light grey, very finely crystalline, laminated and . microbiafly laminated, regular medium parallel partings. Rare 20-30-cm horizon with no laminations. d BF07S5-2A to C,3A •AArOi^PyOol 1SA Upper 0.3 m is semi-recessive, dark grey weathering, very dark grey, variably becciated with up to 20% • BF07S5-2 to 3 . > / 1 pyrite in veins and as breccia cement with dolomite.

t \ r >N 01 Dolostone, pink weathering, light grey, very finely to medium crystalline, massive. MiBimetre-scale en flecks of resistant dolomite resemble fragments. Local fine pyrite to 10%. Vugs <1-2 cm filled with white BF07S5-1AtoC / s ' ODolPy^t dolomite. Top is vuggier with mm-scale vugs. Pyrite cements a milNmetric breccia at top. Stylolites. • 8F07S5-1 > White efflorescence.

~~, / , / /// ZZZZI Base of section~~

~~187 Appendix B. Stratigmphic sections~~

~~Section BF07TIC5 (continued, 2 of 4) T continued~~

~~T3 4-»~~

Dotostone, medium grey weathering, medium grey, finely crystalline. Rubbte • BF07S5-24 —Dotostone, bleached cream weathering, light grey, finely crystalline, welMaminated, locally thinly banded, medium to thickly parting. Local centimetre-scale bands of better vs. less-well laminated. O BF07S5-23A —\Some microbial laminations. Stylolitic. • BF07S5-23 Dotostone, dark medium grey weathering, dark grey, finely crystalline, very thinly mottle-banded, CI BF07SS-22A to 0 thickly parting. Sandy textured. Very thin (0.5 cm), dark, irregular-edged, parallel bands. Pervasive. • BF07S5-22 Intermittent fine (miBimetric) brecciation in cm- to dm-scale patches.

/ Dotostone, medium dark grey weathering, dark grey, finely crystalline, thinly mottle-banded —/Local hematite stains on bedding planes. Faintly laminated at top. Crude colour & crystal-size O 8F07S5-2QAtoC banding with irregular edges like planar mottled arrays ("mottle-banded"). The darker bands are finer, • BF07S5-20 might have been muddier? White efflorescence. Dotostone, bleached cream to light grey weathering, medium grey, finely crystalline, parallel laminated and locally microbially laminated, thin colour banding near base, medium solution seams partings. a BF0755-19AtoD Well-laminated bands are possibly siliceous. Local 1 cm bands of mm to cm-scale in tradas! • BFQ7S5-19A, 8 dolopackstone. Local stromatolitic humps 20 cm across by 10 cm high. Stylolitic. >\ >\ Dotostone, dark grey weathering with jagged pitted surface, medium dark grey, medium (to finely) crystalline, mottled. Wispy network of dolomite(-pyrte) forms incipient cemented breccia. Few oncoid a BF07S5-18AtoE \ghosts 5 mm barely visible, concentric structure very rarely preserved. Matrix to mottles & • BF07S5-18 \oncokte has been recystallized and coarsened. Dotostone and stromatolitic doloboundstone. light brown-grey weathering, light grey, very finely crystalline, microbially laminated, medium parting. Tall stromatolites up to 40 cm hgh have loaded the KS BF07S5-17A toC underlying laminated beds, cresting non-laminated load/sag structures where beds have thickened and • BF07SS-17 5 been depressed -10 cm. Stylolitic. a>

rN 15 Dotostone and dolosiltstone or dolomitic sittstone, pate buff weathering, light grey with dark stripes, A BF07S5-15ATOC 15 p finely crystaftine, laminated and microbially laminated, medium parting. Some bedding planes have o 1—2. v u.U structures reminiscent of synaeresis cracks, which are preferred sites for pyrrte veins. Stylolitic. • 8F07SS-1S £

mjji IfcP/Dol Dotostone cemented breccia. Not vuggy, otherwise same as interval 12. O Py Qtz Dol 7*7 Dotostone cemented breccia, buff weathering, light grey, finely crystalline, biocky parting, vuggy, CI BF07S5-12A toB porous. Altered dissolution cemented breccia. Broken poorly exposed outcrop. • BF07S5-12

~~continued <~~

~~188 Appendix B. Stratigraphie sections~~

~~Section BF07TIC5 (continued, 3 of 4) I~~

Oolostone, buff weathering, light medium grey, variably laminated, locally medium bedded, thickly parting. Toward top, soft-sediment-disrupted 20-cm beds alternate with not-disrupted. Two subveitical fracture sets with m-scale spacing: west-trending and undulating south-trending. c '(Z 4-1c oD 5: Rubble of dok>rrutic sandstone and siltstone, siliciclastic siltstone, and dolomudstone with very thin c( beds of phosphate granules (& a variety of sedimentary breccia with finely crystalline dolostone matrix O 6F07S5-34A to C and clasts of siltstone, chert, and dolostone from interval 35). Siltstone is buff, pink, and grey c weathering, varibaly laminated jagged chips of rubble. Local limonKe yellow to gossanous brown stain • BF07S5-34 ro in the lowest 3 m.

~~~r~~) "O Dolostone, white weathering, paraltet-lamianted Rubble. From 6-6.5 m is dark grey weathering.~~

c 1 TO Oolostone, light grey to black weathering, medium grey, finely crystalline, medium bedded with beds defined as laminated and non-laminated. Local network of tan-weathering veins of sand-sized dolomite I 8F07SS-29A to B grains (dykelets as in interval 42 in BF07TIC2).

Dolostone. very dark grey weathering, medium dark grey, finely crystaline, laminated, thinly bedded, thin to thick styiolitic wavy parting. Thin bands defined by colour and crystal size, at least beany laminated. From 0-0.2 m is thinly microbialfy laminated with cm-scale soft-sediment deformation. From I 8F07S5-28A to 6 0> IT5 0.2-2.4 m is colour-banded overlain by colour-mottled. From 2.4 to 4.0 m is oncoid dolofloatstone. Top 4 un "D 2?D0<- m is locally a dolomite cemented breccia, rubbly weathering, dolomite veined, with white efflorescence • BF07S5-28 and abundant solution seams. Intervals 27-28 are reminiscent of intervals 19-20 (fault repeat?) except 28 is better laminated than 20

~~r/'~~

~~, / , / '~~

~~/ /~~

~~• / i ' /-~~

•o /;/ / / / r Dolostone, bleached, similar to interval 25. Well-banded and laminated Color banding <1-2 cm very c similar to interval 19. Soft sediment deformation. Rip-up clasts. Dark brown solution seam residue on I BF07S5-27A toC E parting surfaces. Styiolitic. <0 / ) / ,

> * *

~~\TrTr7* 1 r. / .~~

~~189 Appendix B. Stialigraphic sections~~

~~Section BF07TIC5 (continued, 4 of 4)~~

Top of section §5 c 'tz c D Dolostone conglomerate, buff weathering, medium grey, massive. Same unit as interval 46 of section O CM ^2 BF07TIC2. Clasts are angular to subangular, tabular, pebble to cobble sized, and consist of a variety of 5 5 dolostone (lamianted, unlaminated, shades of grey, red-grey, finely or medium crystalline) and chert. 6F07S5-35A to B c LL. Vfe>Z3; Chert clasts are black. small, and speckled white due to disseminated mm-scale grains or grain aggregates of dolomite (dissolution of which would create the porous texture observed in some of the chert clasts from section BF07TIC2). Some chert clasts are associated with geopetai? dolomite c cement. Dolomite veins and local dolomite cemented breccia. (V •5?i u. -is

~~r— •Ipa 5 LL. continued i~rr~~

~~190 Appendix C. NWT Open File 2010-04 (Geology of the AB area)~~

~~Appendix C. Geology of the AB area, parts of NTS 106C/16 and 106F/01; NWT Open File 2010-04~~

This appendix is reproduced from NWT Open File 2010-04 with the permission of the publisher, the Northwest Territories Geoscience Office. The first part of the appendix is the report, which includes two over-sized pages; the second part is a map, which is in the pocket of this dissertation.

~~191 Appendix C. Reprinted from NWT Open File 2010-04. Dissertation p. 192~~

~~NWT Open File 2010-04~~

~~Geology of the AB area, parts of NTS 106C/16 and 106F/01 B. J. Fischer, C. Atherton, E. Parker, J. Law~~

Recommended Citation: Fischer•, B. Atherton, C., Parker, E., and Law, J., 2010. Geology of the AB area, parts of 106C/16 and 106F/01; Northwest Territories Geoscience Office, NWT Open File 2010-04,1 map, scale 1:20,000, and accompanying report, 66 p.

»> NORTHWEST TERRITORIES GEOSCIENCE OFFICE Author's addresses: C. Atherton, E. Parker and J. Law B. J. Fischer Eagle Plains Resources Ltd. Northwest Territories Geoscience Office Suite 200, 16-11th Ave. S. PO Box 1500 Cranbrook, BC V1C 2P1 4601-B 52 Avenue Yellowknife, NT X1A2R3

~~Northwest Territories Geoscience Office 4601-B 52 Avenue P.O. Box 1500 Yellowknife, NT, XIA 2R3 Canada 867-669-2636 www.nwtgeoscience.ca~~

~~This publication may be obtained from the Northwest Territories Geoscience Office (see address, phone number, and website above).~~

~~NWT Open File Number 2010-04~~

Table of Contents Abstract 3 Introduction 4 Regional geology 6 Stratigraphy 8 Terminology 9 Backbone Ranges Formation 9 Lower Member (PCB1) 9 Middle Member (PCBm) 12 Upper Member (PCBu) 12 Interpretation 12 Sekwi Formation (Cs) 12 Csl 13 Cs2 13 Cs2a 14 Cs2b 14 Cs2c 16 Cs2 (undivided) 17 Cs3 17 Cs4 19 Cs4g 20 Cs2-3(-4) undivided 20 Cs coarse fragmental rocks 21 Interpretation 21 Age and correlation 21 Depositional environment 21 Paleo-erosion 24 Franklin Mountain Formation (COf) 24 COfl basal member 24 COf2 siliceous member 25 COf undivided 26 COf dark vuggy dolostone 29 COf coarse fragmental rocks 29 Interpretation 32 Age and correlation 32 Depositional environment 33 Alteration 33 Paleo-erosion 34 Duo Lake(?) Formation (OSd) 34 OSdl 34 OSd2 35 Interpretation 36 Age and correlation 36 Depositional environment 37 Paleo-erosion 37 Cloudy(?) Formation 37 Interpretation 38

~~\\\ I ( >1 2010-04 (ieoloLi\ ol'llte AU area, parts ol'\IS low l(i and HIM 0 I I \ppendi\ ( , Reprinted from W\ I Open I ile 201(1-04. I)issertalion p. I(>5~~

Structure 40 Alteration and mineralization 46 Sekwi Formation mineralization 47 Franklin Mountain Formation mineralization 51 Duo Lake(?) Formation mineralization 54 Stratigraphic, diagenetic, and structural summary 55 Conclusions 57 Acknowledgements 59 References 60 Appendix I - Classification of carbonate rocks including breccias 64 Appendix II - Grain size and bedding thickness terminology 66

~~List of Figures~~

Figure 1. Physiographic relief map of the Northwest Territories of Canada, and locations of the AB study area, nearby communities, and roads 5 Figure 2. Regional geology of part of the northern Mackenzie Mountains, and location of the study area 7 Figure 3. Locations of mapping stations, zinc showings, faults, and streams in the AB area 10 Figure 4. Generalized stratigraphic column for the AB area 11 Figure 5. Cross-section A-A"" 41 Figure 6. Cross-section B-B' 42 Figure 7. Paragenesis of zinc±lead showings hosted by Sekwi Formation in the AB area 53

~~List of Tables~~

~~Table 1. Sphalerite (-galena-smithsonite) showings in the AB map area 48 Table 2. Habits of minerals in Sekwi Formation showings 49~~

~~\\\ I i >1 2010-1)4 (ieoloiip\ nl ihe \B area, parls ol \ I S I06( W> and 1061 (I \ppendi\( Reprinted from \\\ I Open I ile 20I (MM Dissertation p. I %~~

Abstract the Sekwi Formation, is abundant in the siliceous member 2 of the Franklin Mountain Formation, and is of minor significance in the An area of 38 km2 covering numerous Duo Lake(?) Formation. Mineralization is carbonate-hosted zinc±lead showings, closely associated with the ABC Fault and particularly the AB and AB-C showings, was loosely associated with the AB Fault. mapped and is presented at 1:20,000 scale. The purpose of the study was to elucidate Three first-order controls on mineralization stratigraphic, lithological, and structural are identified. The primary control is controls on localization of mineralization. The structural: regional and property-scale faults, Neoproterozoic to Early Cambrian Backbone although barren, served as conduits, whereas Ranges Formation (quartzite, minor microscopic and mesoscopic fractures dolostone) along the south edge of the map localized precipitation in susceptible rocks. area has been thrust northward over Early The second control is stratigraphic: Cambrian Sekwi Formation limestone and susceptible rock types are more prospective dolostone, Cambro-Ordovician Franklin where they are present at the base of the local Mountain Formation dolostone, and two units stratigraphic succession. The third control is tentatively assigned to Ordovician-Silurian lithologic: susceptible rock types in Sekwi Duo Lake (shale, siltstone, minor limestone) Formation are those with millimetre to and Cloudy (limestone) formations. Another centimetre-scale variations in mineralogy, regional reverse fault (AB Fault) strikes east such as dolograinstone and organic-rich, across the north part of the map area, placing siliciclastic-rich, mottled dolostone. Sekwi and Franklin Mountain formations Prospective Sekwi Formation strata may not against Duo Lake(?) and Cloudy(?) be far below the surface in the north part of formations. The Sekwi, Franklin Mountain, the map area. Also, extensions at-depth and and Duo Lake(?) formations have been along-strike of the cement-breccia zone along divided into informal members. An erosional the ABC Creek are prospective. unconformity between Sekwi and Franklin Mountain formations is indicated by the removal of the uppermost Sekwi units in a paleo-valley 330 m deep. An unconformity between Franklin Mountain Formation and Duo Lake(?) Formation is suggested by variable thicknesses of the former. Duo Lake(?) Formation is gradational with overlying Cloudy(?) Formation.

The structural character of the map area is dominated by faults. Strata trend east to southeast and dip gently except in tight folds parallel to the major faults. Mineralization consists of sphalerite and minor galena in void-filling and disseminated textures, associated with a gangue of dolomite, marcasite, pyrite, barite, and lesser quantities of calcite, quartz, and pyrobitumen. Mineralization is most intense in member 2 of

~~\\\ i ol 2010-04 CieoloL\\ of the Mi area, parts ol \IS I06( I hand I0M 01 \ppendi\ t . Reprinted from W\ I Open lile 2010-04. Dissertation p. I ()7~~

Introduction Eagle Plains Resources Limited geologists and prospectors in 2007 and 2008, and by the first author and Elizabeth Turner of This study is part of a Masters of scientific Laurentian University during visits to the AB research project being carried out by the first and AB-C zinc showings in 2006 and 2007. author at Laurentian University. The objective Some interpretation in the DAB area made of the study was to provide a stratigraphic and use of data from Welcome North Mines structural framework for interpretation of Limited, who first discovered mineralization mineralization in the AB area of the northern in the area (McArthur and McArthur, 1977). Mackenzie Mountains. Twenty carbonate- Although some thin sections were examined, hosted zinc±lead showings, some of which the interpretations are largely based on field were discovered during the course of this work. The bulk of this report is meant to be project, are present in the mapped area. The read while referring to the accompanying AB and AB-C showings hosted by Sekwi map, and may be difficult to follow if this is Formation and the DAB showing in Franklin not done. Mountain Formation are the most significant of these. This study contains the first detailed description of Sekwi Formation lithofacies in The AB area is centred roughly at 65°N, the northern Mackenzie Mountains. 132.25° W in the Northwest Territories in Understanding the factors which control the National Topographic System (NTS) map spatial distribution of sulphide bodies in a sheets 106C/16 and 106F/01. It is roughly carbonate host rock requires a thorough equidistant and 240 km from Norman Wells, understanding of host rock stratigraphy and Northwest Territories and Mayo, Yukon (Fig. lithofacies. The following detailed 1). The terrain of the AB area is moderately descriptions are essential to understanding the rugged, ranging in elevation from 1300 to configuration of the map, and will be useful to 2050 m. Outcrop comprises 20-40% of the anyone wishing to do further work in the area. ground surface, with the remainder being scree, rubble, and thin overburden vegetated Locations are given in Universal Transverse by sedges and other low ground cover. Mercator coordinates for zone 8N, based on North American Datum 1983 (UTM Zone 8N, Mapping at a scale appropriate for NAD83). The GIS database and all presentation at 1:20,000 was carried out over photographs for this project are being approximately 38 km2 during twelve mapping published separately by the Northwest traverses in August 2008: six by Fischer and Territories Geoscience Office (NTGO) as an Law, three by Fischer and Parker, one by NWT Open Report. Fischer and Aaron Higgs, and two by Atherton and Law. Other data used in construction of the map were acquired by

~~\\\ I ( >1 20 I 0-0-4 (>eoloe\ ol the \ I! ;irea. parts ol \ I S 1 06( I () and I OM (11 Appendi\ ( . Reprinled trfin \\\ I Open l ite 201(1-04. I )is--erlatiou p. I~~

~~130°W~~

~~Figure 1. Physiographic relief map of the Northwest Territories of Canada, and locations of the AB study area, nearby communities, and roads. Dark reddish brown represents the highest elevations.~~

~~\\\ 1 Ol 2010-04 ( ichIol!) ot lite \ 15 area, purls i*l N I S 1 (Hit Ihand 1(161 01 \ppendi\ ( . Reprinted Innn \\\ I ()pen file 2010-04. I )issertation p. I')')~~

Regional geology Development of the northwest-trending Misty Creek Embayment in the northeast edge of the The AB area is in the eastern fold and thrust Selwyn Basin during the Middle Cambrian belt of the northern Canadian Cordillera, coincided with uplift and exposure of the which is underlain by Mesoproterozoic to Mackenzie Arch to the east. The Sekwi ramp Devonian sedimentary rocks that were was flooded by this event. In the heart of the deposited on the western margin of Laurentia embayment, the Sekwi Formation is overlain (present-day direction). The Cretaceous to conformably by fine siliciclastic rocks of the Tertiary Laramide orogeny compressed and Middle Cambrian Hess River Formation, uplifted the succession into an arcuate, followed by shale and silty limestone of the concave-westward, generally northwest- Cambro-Ordovician Rabbitkettle Formation, trending belt marked by tight folds and then thin siltstone, limestone, dolostone, and northeast-verging thrusts. Published geology chert of the Ordovician-Silurian Duo Lake maps of the area are at 1:250,000 scale and Formation (Cecile, 1982). Overlying the Duo consist of a preliminary, hand-drawn map for Lake Formation within the Embayment is a NTS sheet 106C (Blusson, 1974), a final, package of thin-bedded, cherty limestone and colour map for sheet 106F (Norris, 1982), and shale known as the Cloudy Formation (Cecile, a digital compilation of the Yukon and parts 1982). of the Northwest Territories (Gordey and Makepeace, 2003). Closer to the edge of the basin, the Hess River Formation is missing and the Sekwi Rocks in the AB region (Fig. 2) are Formation is unconformably overlain by unmetamorphosed. The oldest are middle Rabbitkettle or Duo Lake Formation. Neoproterozoic siliciclastic and carbonate Dolostone of the Franklin Mountain strata of the Mackenzie Mountains Formation represents re-establishment of a Supergroup (Aitken and McMechan, 1992; carbonate platform along the east margin of Narbonne and Aitken, 1995). A post-rift the basin during the late Cambrian, and its glaciation, early sag-phase continental growth through at least the Early Ordovician. separation, and subsidence of a passive Franklin Mountain Formation intertongues margin on the western edge of late with the lower parts of the Duo Lake Neoproterozoic Laurentia are recorded by Formation at the basin edge (Cecile, 1982), siliciclastic and carbonate strata of the including the map area. North and east of the overlying Windermere Supergroup (Narbonne map area, a sub-Upper Ordovician and Aitken, 1995). These strata are overlain unconformity records another hiatus in by fluvial and shallow-marine, quartz arenite- platformal deposition, separating the Franklin dominated strata of the Backbone Ranges Mountain Formation from Ordovician- Formation, which are related to latest Silurian Mount Kindle Formation dolostone. Neoproterozoic to Early Cambrian crustal While Mount Kindle sediments were being extension and renewed subsidence deposited on the platform, Cloudy and upper (MacNaughton et al., 1997, 2008). Early Duo Lake sediments were being deposited in Cambrian marine transgression led to the basin. development of the Selwyn Basin and, on its eastern edge, a mixed carbonate-siliciclastic The overlying carbonate succession records ramp preserved as the Sekwi Formation the history of an Early to Middle Devonian (Krause and Oldershaw, 1978, 1979; Fritz et platform on the subsiding margin of Laurentia al., 1992; Dilliard et al., 2007). (Fritz et al., 1992). Subsequently, during the

\\\ i (>i : asul M>M (i| (i Legend area mapped in this study —— fault Geology Quaternary o Devonian Ota* Earn Group Hume Formation • Landry Formation to Arnica Formation Silurian-Devonian HI Detorme Formation Ordovician-SikJrian Mi Mount Kindle Formation Cambrian-Ordovidan CO* Franklin Mountain Formation COM Franklin Mountain transitional formation (Cambrian-)Ordoviban-Devonian COr Road River Group Earty Cambrian m Sekwi Formation 1 Late Neoproterozoic to Earty Cambrian uPCb Backbone Ranges Formation Neoproterozoic • Windermere Supergroup • Risky Formation • Sheepbod Formation HI Keeie Formation HI Twitya Formation HI Raprtan Group "A HI Tsezotene gabbro Neoproterozoic - Mackenzie Mountains Supergroup • Little Dal Group ufku upper Katharine Group uPfc Katharine Group 'i#H Tsezotene Formation

Figure 2. Regional geology ofpart of the northern Mackenzie Mountains, and location of the study area. Geology after Gordey and Makepeace (2003) and Aitken and Cook (1974). VTMzone 8Nprojection, NAD83 datum. \ppcnciin ( . Rcpi'inlcd from \\\ 1 < 'pen i iIc 2010-114 I )isscrt.nion p. 20

Middle to Late Devonian, a major change in terminus of the Richardson fault array, a tectono-sedimentary regime brought about the long-lived lithospheric feature (Eisbacher, end of the Misty Creek Embayment and 1983; Norris, 1997). Forty kilometres west of Selwyn Basin as depocentres, and initiated a the map area is the northern end of the Snake regional, terrigenous clastic influx from the River Fault, a major structural break that west and north (Gordey et al., 1992). The parallels the Plateau Fault for at least 150 km resulting blanket of sediments, preserved as (Eisbacher, 1981; Norris, 1997). the Earn Group, terminated carbonate deposition on the platform.

Early maps, including those on which Figure 2 is based, did not differentiate among the Hess River, Rabbitkettle, Duo Lake, and Cloudy formations, mapping them together as the Road River Formation. The Road River stratigraphic entity in the Mackenzie Mountains has since been raised to group status by some authors (Fritz, 1985; Gordey and Anderson, 1993), but inconsistencies in its definition have led to a more recent abandonment of the term outside the unit's type area (Cecile, 2000). The latter approach is endorsed in this report.

The AB area is underlain by strata of the Backbone Ranges, Sekwi, and Franklin Mountain formations, and what has previously been mapped as Road River Formation (Fig. 2). It is transected on its north and south edges by regional-scale, contractional faults. On a larger scale, the study area lies between two major deflections in the northern Cordilleran fold-and-thrust belt: as one moves north, the structural grain changes orientation from northwest to west at the Mackenzie Deflection, then from west to north at the Ogilivie Deflection (Norris, 1997). The AB area lies between the deflections, where structural grain is oriented westward. Numerous southwest-dipping fault splays, 20 km east of the map area (Fig. 2), mark the northern terminus of the Plateau Fault, a major southeast-striking structure traceable for over 300 km (e.g., Gabrielse et al., 1973; Cecile, 1982; McMechan et al. 1992). High- angle oblique faults with numerous splays, 40 km WNW of the map area, mark the southern

~~\W I < >1 20 10-04 ol'lhe ABarca. pans of \ IS l()6( 16 and I0M 0 I S \ppcntli\ ( . Reprinted from \\\ 1 Open l ile 2(110-04. I)issertalion p. 202~~

Stratigraphy Terminology The carbonate rock classification scheme of Mapping stations, or points at which features Dunham (1962), as modified by Embry and of the rock were documented, are shown in Klovan (1971), is used in this report. The Figure 3. Geographic locations in the text are modifiers "argillaceous", "silty", and "sandy" referenced to named faults, zinc showings, refer to the presence in a carbonate rock of and streams (Fig. 3; Map). Where formation terrigenous mud, terrigenous silt, and quartz and member thicknesses could not be sand, respectively. Terminology used to measured directly or obtained from cross- describe coarse fragmental rocks in this study section construction, they were estimated follows, for the most part, the suggestions of from dip of the unit, horizontal width of the Morrow (1982). Both the Dunham-Embry- unit perpendicular to strike, and topographic Klovan scheme and Morrow's terminology relief. are explained in Appendix I. Modifiers used to describe crystal and grain size, and bedding Mapping confirmed the presence of lower, thickness are defined in Appendix II. middle, and upper members of the Backbone Ranges Formation along the south edge of the Backbone Ranges Formation map area. These have been thrust northward over the Sekwi Formation, platformal The Neoproterozoic to Early Cambrian Franklin Mountain Formation, and two Backbone Ranges Formation is exposed in the formations tentatively assigned to the Duo hanging wall of Fault 2. It was examined only Lake and Cloudy formations (Fig. 4; Map). briefly as part of this study. Another regional reverse fault trending east Lower Member (PCBI) across the north part of the map area places the Sekwi and Franklin Mountain formations The lower member is in the immediate against the Duo Lake(?) and Cloudy(?) hangingwall of Fault 2 and is at least 90 m formations. The northern fault is designated thick. It is a well-cemented, well-sorted quartz AB Fault and the southern one, Fault 2. Nine arenite with fine to coarse, subangular to other faults are labeled on the map and rounded grains. It is weathered medium grey, referred to by number or name throughout the yellowish grey, or brown, and is white, pink, report. or purplish white on fresh surfaces. It is medium to thickly bedded with common An erosional unconformity between the Sekwi planar-tabular cross-beds and parallel and Franklin Mountain formations is indicated laminations. It is locally speckled with 2-3 by the removal of the uppermost Sekwi units mm, pale brown spots of very fine in a paleo-valley 330 m deep. An hematite(?). At one locality the lower member unconformity between the Franklin Mountain is a clast-supported, quartz-pebble to granule and Duo Lake(?) formations is suggested by conglomerate. the variable thickness of the former. Neither unconformity is exposed in outcrop. The Cloudy(?) Formation lies conformably and gradationally on the Duo Lake(?) Formation. The stratigraphy of the map area is summarized in Figure 4.

~~W\ I Ol 2010-04 CieoloL!} of the \ I? area, parts of \ IS HIM. I 0 and |0M HI <•> J _ ^ ^ Legend~~

~~AB Main * Zn ± Pb showing, 1 name and location~~

~~Mapping stations~~

~~• • First author. 2008; detailed documentation, noted in passing • First author, 2007 t \ « V # • • First author, 2006~~

if Second, third and fourth authors, 2007- • r. 2008 / wJujl Z * •. V » . {fefcL i„ \ AB Fault Fault, with name •^k'T' •• • _ /MyKeryFamt * / Edge of mapped area ** • m * "JKsI ' ' AB Creek Stream, with name

~~Topographic contour (100 ft interval south of 65N, 200 ft north Fault 2 of 6SN)~~

Figure 3. Locations of mapping stations, zinc showings, faults, and streams in the AB area. Topographic data from the National Topographic Database (NTDB), Geomatics Canada. Projection is UTM Zone 8N, datum is NAD83. \ppcndix ( . Reprinted from \\\ I Open Hie 2(1! (1-04. I)issertation p. 204 § CIoudy(?) Legend 5 Formation skeletal graptolites A A intraclasts o oncoids Duo oo ooids c Lake(?) § Forma- peloids i tion bloturbated burrowed parallel laminated microbially laminated 7T7T cross-stratified C3> vuggy siliciclastic silt Franklin 2a 00 O T77T A chert Moun mineralization; tain Fm !b undivided major, minor (COf) (north) (south) cemented breccia

~~Sekwi Carbonate rock Formation limestone (Cs) zzz 00 o ° = dolostone dolomudstone~~

~~calcisiltstone 2-3(-4) (south grainstone, dolograinstone west) rudstone / limstone breccia~~

~~bioherm~~

~~oo o Carbonate rock with siliciclastic component~~

~~argillaceous limestone — ^k Hi silty dolostone Upper Mbr acKDone (PCbu) Ranges Fm sparsely quartz sandy dolostone Bedding characteristics of carbonate rock~~

~~•y Middle Mbr thin bedding | (PCbm) medium bedding +**2 g. Lower Mbr thick bedding £ (PCbm) wavy bedding~~

~~50 m sparsely nodular bedding vertical scale Siliciclastic rock B Om shale~~

~~calcareous shale~~

Figure 4. Generalized stratigraphic column for the AB area. Strati- dolomitic shale graphic ages are on the far left. Informal members are indicated by siltstone numbers 1,2a, etc. and vertical bars. Geographic variation is indicated by a vertical zig-zag division of the column: left side of column for dolomitic siltstone Sekwi Formation represents undivided equivalent of members Cs2, quartz arenite Cs3 and possibly Cs4 in the southwest part of the map area; and right dolomitic quartz arenite side of column for Franklin Mountain Formation represents undivided equivalent of member COflb south of the AB Fault. Wavy horizontal o ° 0; conglomerate lines represent erosional unconformities; the location of the upper one conformable contact might be as high as the base of OSd2 (see text). Horizontal scale of the column is a qualitative representation of weathering resistance. unconformable contact \\\ I (>1 2010-04 ficoloiiN of the \ B arc;), parts of \ I S 1061 16 and 1061 01 \ppcndi\ ( . Reprinted fr<>m W\ I Open l ite 201(1-04. Dissertation p. 205

depositional setting of each member is Middle Member (PCBm) provided by MacNaughton et al. (1997,2008). The well-sorted, cross-bedded quartz sands of The middle member occupies the immediate the Lower and Upper members are fluvial in hangingwall of Fault 2 at the western end of origin. The dolomitic sediments of the Middle the map area and elsewhere overlies the lower Member record a nearshore, shallow marine member in the hangingwall. It consists of setting where carbonate mud and fine to about 90 m of thinly bedded, dolomitic quartz coarse, terrigenous sediment mingled. arenite and thinly bedded, interstratified dolomitic siltstone, dolomitic sandstone, and Sekwi Formation (Cs) intraclast and quartzite-pebble dolostone conglomerate. It is weathered brownish The Sekwi Formation is a lithologically orange, reddish brown, and greyish pink, and variable unit that is a preferred host to is pale grey to pinkish grey on fresh surfaces. sulphide mineralization in the AB area. It is It is fine grained and finely crystalline to exposed between the AB Fault and Fault 2, microcrystalline, commonly laminated or where it occupies the floors and slopes of cross laminated, semi-recessive, and flaggy. It valleys. The base of the formation is not locally contains traces of pyrite. exposed, and its top is an erosional unconformity beneath Franklin Mountain Upper Member (PCBu) Formation. The minimum thickness of the Sekwi Formation ranges from 150 to 700 m in The upper member was examined at one the map area. The formation includes skeletal, locality, where it consists predominantly of a ooid, oncoid, and intraclast packstone, light grey weathered, pink to cream, medium- wackestone, floatstone, and rudstone, bedded quartz arenite. It is well cemented, argillaceous and organic-rich lime mudstone, very fine grained (locally medium to coarse partly to fully dolomitized variants of the grained), locally laminated, and speckled with above, dolomitic arenite, and vuggy pale brown, millimetric hematite(?) spots. dolostone. In this study, the Sekwi Formation Subordinate rock types include: very thinly has been divided into four informal members bedded light brown siltstone; very thin to of limited extent, numbered 1 to 4 in medium-bedded, rusty weathered, pinkish ascending order from base to top. Two of grey to greenish pink, very fine grained these (Cs2 and Cs4) are further divided into glauconitic sandstone with wavy and parallel sub-members. Cs2 hosts significant sulphide laminations; and orangey brown, recessively mineralization, and Csl and Cs3 host minor weathered, fine to coarse-grained, laminated, mineralization. Photo 1 shows the upper part dolomitic(?) sandstone. of the formation. Interpretation Pervasive dolomitization with accompanying The type section of the Backbone Ranges near-complete destruction of primary fabrics Formation was described by Garbielse et al. occurs at two stratigraphic levels, Csl and (1973). Correlation of its members was Cs3. This destructive dolomitization was discussed by Aitken (1989) and MacNaughton clearly constrained by primary stratigraphic et al. (2008). The inferred age of the lower layering. Dolomitization of Cs2, on the other and middle members is Ediacaran (latest hand, has a strong spatial correlation with Neoproterozoic) and that of the upper member sulphide mineralization: it is partial or absent is at least in part Lower Cambrian (Fritz, except near showings, where it is pervasive, 1982; Aitken, 1989). A discussion of the

~~W\ I ( >1 2010-04 (ieolot:\ ol the \B area, parts ol \IS ]0(H Mi and 10(->1 HI Appendix ( . Reprinted from \\\ I Open file 2010-04 i)issenaiion p. 20fi~~

~~AB-C Upper~~

~~AB C l ower~~

* -Jj >. •« •

Wl • N\ •m&ms. Photo I. Looking northwest at members of the Sekwi Formation in the AB-C area. Units labeled in red are beyond (north of) the AB Fault. Cs = Sekwi Formation, COf= Franklin Mountain Formation, OSd = Duo Lake(?) Formation, and OSc = Cloudy(?) Formation. Taken from 63I156E, 7208595N. though partially retentive of primary fabrics. Csl at various locations near the AB Fault, Breccias in the Sekwi Formation are the AB-C showing, and the Point Vug significant, both as hosts of mineralization occurrence is a mosaic breccia with a and as indicators of faulting. marcasite-dolomite cement. Locally near the Point Vug occurrence, dark grey dolostone of Cs1 Csl has a fabric of aligned, elongate, millimetre-scale vugs filled by coarse white Member l is the lowest mapped member of dolomite (Photo 3), grading into zebra fabric the Sekwi Formation, and is exposed only in (discontinuous, planar, 1-2 cm wide bands of ABC Creek, where it hosts the AF and Point drusy dolomite separated by finely crystalline dark, mottled Vug showings. Csl consists of a dolostone). This alteration resembles the dark, dolostone (Photo 2) containing finely vuggy dolostone of the Franklin Mountain disseminated pyrite, overlain by a buff- Formation, described below. weathered, medium grey, finely crystalline dolostone. Fenestral(?) fabric is locally Cs2 preserved as sparse to abundant, millimetre to sub-m i 11 imetre-scale, dolom ite-fi I led, The second member of the Sekwi Formation elongate, aligned vugs. Ghost laminations are consists of an ooid grainstone sandwiched common and defined by colour variations on between two intervals of skeletal wackestone. weathered or fresh surfaces. Lenses of oncoid These three sub-members are termed 2a, 2b, dolofloatstone are rare and less than l m and 2c (Photo l). Each of them is dolomitized thick. near the AB, AB-C and Link showings and calcareous farther from those showings. The

~~\\\ I ()l 20MI-04 (icoloy} ol'the AI! area, pails of \ 1 S 10(i( 16and I 0M (I \ppendi\ ( . Reprinted from \\\ I Open file 2010-04 I)issertation p. 207~~

and oncoid-intraclast floatstone, and a rare exposure of concretionary dolostone. Near the AB showing, the unit also includes thinly bedded, finely laminated dolostone, nodular mottled dolostone (Photo 6), and a 20-m interval of intraclast dolorudstone. At AB-C Lower, an intraclast dolorudstone containing flat, cobble-sized clasts is restricted to thin, bedding-parallel layers within medium-parted, mottled, argillaceous dolostone.

Sphalerite mineralization at the AB, AB-C Photo 2. Recessive, dark, mottled dolostone ofSekwi Lower, and Point showings is hosted by the Formation member I (Csl) in stratigraphic andfault dark mottled dolostone, the intraclast contact with overlying, finely crystalline, buff dolostone rudstone, and, to a lesser extent, the finely of Csl. Fault oriented at about 035/65 slices through crystalline dolostone of member 2a. The Cs2a left (north) end of the outcrop. Scale provided by Bronwen Wallace, who is collecting samples of very dark mottled dolostone is fine to medium sparsely disseminated sphalerite from the buff unit (AF crystalline, dark grey weathered, and medium showing). Looking north-northeast from 63120IE, grey, with anastomosing black wisps or seams 7209522N. of insoluble residue outlining lighter grey, coarser domains. The Cs2a dark mottled dolostone is thinly bedded with irregular, wavy bedding planes, and fissile to shaly at the AB showing. It is at least locally —V V*.T- * bituminous, and its dark colour is seen in thin section to result from abundant organic material. Up to 20% terrigenous mud and silt is concentrated in burrows and solution seams. Polymict intraclast dolorudstone to floatstone of Cs2a forms a partly covered, 20 m thick interval at AB. This interval is thick bedded and contains poorly sorted, polymict dolostone clasts of millimetre to decimetre- Photo 3. Dark, vuggy fabric due to alteration in Sekwi scale (Photo 7). member I. Elongate, aligned vugs up to 4 cm long and Cs2b 2 mm high are filled or lined with coarse white dolomite. Glove finger is 2.5 cm wide. 630970E, Sekwi member 2b is an ooid(-oncoid 720914IN. ±skeletal) grainstone to dolograinstone and packstone that forms a prominent, 50 m high grainstone subunit Cs2b thins southward and cliff in the vicinity of the AB-C showing westward, and disappears southwestward. (Photo 8). It thins to 15 m in the Mystery Cs2a Fault area south of AB-C, where it has a muddier matrix and a higher percentage of Sekwi member 2a, the lowest, consists of skeletal components, and disappears about 40 m of dark grey, argillaceous to silty, altogether to the southwest. To the west, bioturbated to mottled limestone to dolostone stratigraphically above the AB showing, it (Photos 4, 5). It contains intervals of skeletal consists of a 4-metre interval of ooid-peloid wackestone, isolated lenses of ooid grainstone

~~\\\ I ol 2010-04 (icolo^\ ol lite \B area, parts ol \ I S I0(H' ] 6 and I0(>l 0 14 \ppendi\ ( '. Reprinted from \\\ I Open l ile 2010-04. I)issertation p. 208~~

Photo 6. Mottled, yellow and grey weathered dolostone Photo 4. Dark, mottled dolostone of Sekwi member 2 a of Sekwi member 2a, stratigraphically below the AB at the AB-C Lower showing. Rusty stains are from showing. The irregular yellow bands, reminiscent of weathering of pyrite. Disseminated sphalerite is not nodules, probably derive from diagenetic alteration of visible at this distance. Hammer head is 16 cm across. mildly bioturbated primary layering. Exposed pencil is 630609E, 7209118N. 13 cm long. 627332E, 7210126N.

Photo 5. Burrows in dolostone of Sekwi member 2a Photo 7. Dolostone debrite in Sekwi member 2a at the near the Point showing. Scale in millimetres. 630886E, AB showing. This example has dominantly tabular, 7208865N. muddy clasts. Widest part of pencil is 9 mm. 627310E, 7210070N. millimetric skeletal fragments, and ovoid clasts up to 1.5 cm long made up of spherical, grainstone overlain by eight metres of 1-5 mm microbial clots (Photo 10). These resistant, thin and wavy-bedded oncoid- clasts occur in beds with sparsely scattered, intraclast dolorudstone to dolofloatstone. The unit as a whole is medium grey weathered large ooids. Locally, dolomite has selectively (locally dark grey weathered) and light to dark replaced the allochems, and even where grey. Wavy planes modified by horizontal dolomitization is complete, allochems remain burrows separate thin to medium beds. Cross- clearly defined. bedding is common in oolitic parts. Allochems consist mainly of ooids, with Unit Cs2b is traceable from the Link showing subordinate but significant oncoids and around a southwest-closing exposure aggregate clasts (Photo 9). South of the AB-C (resulting from a northeast-trending creek and Link showings, member 2b includes valley cutting into gently southwest-dipping

~~\\\ I ( )| 2010-04 (ieoluy\ ol'tlie \B area, parts of \ i S I06( 16 and 1061 0 I)issorlaiii>n p. 2()(>~~

(

t 1 i Photo 8. Sekwi member 2b ooid grainstone in thin, Photo 10. Millimetric microbial?) clots packed into I wavy beds, southwest of the AB-C showings. Bronwen cm clusters or clasts. The matrix around these clasts Wallace for scale. 630358E, 720862IN. contains trilobite fragments, scattered ooids, and isolated clots. Sekwi member 2b in the Mystery Fault area, south of the AB-C and Link showings. Metal tip of pencil is 4 mm long. 631030E, 7208275N.

and the ooid dolograinstone at the AB-C showing does not exhibit significant displacement along it (see Structure section). A fold in the Mystery Fault area has placed the thin, southern parts of Cs2b structurally above the AB-C and Link showings. Cs2c Sekwi member 2c is roughly 70 m thick near AB-C but thins to about 50 m near the Photo 9. Oncoid floatstone in partially dolomitized Mystery Fault. Member 2c consists of skeletal ooid grainstone matrix, Sekwi member 2b, SSE of the packstone to floatstone with lesser dark, AB-C showings. Note trilobite skeletal fragments in and silty dolostone, rare matrix and nucleating oncoid grains (arrows). Glove mottled, argillaceous finger is 2.5 cm wide. 630804E, 72088I2N. siliciclastic shale, and two bioherms at its base near the Link showing. The Cs2c skeletal strata) and north to the AB-C Upper showing packstone/floatstone weathers a characteristic (Photo 1). Unit Cs2b hosts both showings, orangey brown and is thin and wavy bedded which are marked by strongly developed (Photo 11). The Cs2c packstone/floatstone is gossans. The unit is not exposed north of AB- medium to dark grey and finely crystalline, is C, though gossanous soils are traceable from burrowed and more-complexly bioturbated the showing northward to the AB Fault. (Photo 12), and contains variable but low Limited exposures in this area are of skeletal- quantities of terrigenous silt and fine quartz oncoid-intraclast-ooid dolofloatstone, locally sand. Allochems consist of intraclasts and with coarsely crystalline dolomite cement fragments of trilobites and brachiopods, filling dissolved burrows and skeletal moulds, intermixed with sparse to abundant ooids and and minor mottled dolostone. This may clasts of microbial clots (as described for represent another abrupt lateral facies change Cs2b). The Cs2c dark, mottled dolostone is in member 2b; a northwest-trending fault thinly bedded, with wavy and rubbly bedding hypothesized to exist between these exposures planes and anastomosing, millimetric seams

~~\\\ I (>| 2011>-04 (icoloy_\ of the \li area, parts ol \ I S l()(>( l(>and I0M (II 16 \ppetuli\ ( . Reprinted lri>m \\\ I Open I ile 2010-04. I Jis'-erlalion p. 2 10~~

Cs2 (undivided) Member 2 (undivided) east of Fault 10 is a poorly exposed package of greyish orange weathered skeletal wackestone and packstone with subordinate lime mudstone, laminated calcisiltite, silty to argillaceous limestone, and skeletal rudstone. Skeletal fragments consist of brachiopods, trilobites, and locally abundant, solitary archeaocyathans(?) up to 1.5 cm in cross-section (Photo 14). Beds are thin (ranging from very thin to medium) with wavy bedding planes, and are commonly Photo 11. Typical outcrop appearance ofSekwi burrowed to bioturbated and partially member 2c skeletal -wackestone/floatstone. Erik Parker dolomitic. for scale. Looking south-southeast from 629733E, 7208056N. Cs3

Sekwi member 3 is roughly 70 m thick in the AB-C area, where it consists of three cliffs approximately 15 m high of finely crystalline, sparsely vuggy dolostone, separated by recessive intervals of approximately the same thickness. The cliffs are finely (very finely to medium) crystalline, buff weathered, light grey dolostone with thin to thick stylolitic partings (Photo 15) and local traces of pyrite. Millimetre-scale vugs, though sparsely distributed, are almost ubiquitous. These are filled or partially filled with dolomite, less Photo 12. Bioturbated skeletal floatstone showing commonly containing barite or pyrite. Ghost trilobite fragments in a large burrow, Sekwi member 2c. Scale in millimetres. 630420E, 7208609N. grains resembling skeletal fragments, intraclasts, and oncoids are rare. The lowest of black, argillaceous, organic material. The cliff has thin to medium-width partings and is Cs2c bioherms are prominent mounds, up to 2 characterized by cross-bedding and cross- m across and 0.8 m high (Photo 13A), of dark lamination (Photo 16). Cross-bed sets are up grey, microcrystalline calcite. Their weathered to 20 cm thick. Cross-strata are thin to thick surfaces show them to be composed of laminations with either tangential or angular millimetre-scale microbial clots, and bases. The angles between cross-laminations brachiopod and trilobite debris (Photo 13B). and set boundaries are consistent within any A concretionary shale in member 2c above the one outcrop, but vary from 5 to 20 degrees Link showing consists of dolostone across the area. Between the cliffs are 10-15 concretions in siliciclastic shale. Sandy m thick intervals of cover, or recessive, carbonate rocks are present along strike at the medium to dark grey, mottled dolostone top of Cs2c to the southwest. Sekwi member exposed as rubble. Trace amounts of fine, red 2c is a minor host of mineralization. sphalerite are locally present in the lowest cliff, and a number of exposures of vein-fill and vug-fill sphalerite near the headwaters of

~~\\\l(»l 20(0-04 (ieol(iL;_\ i'l the \ B aied. pai Is o! \ I S 1 06( I (i and 1 0M 0 \ppenc)i\ ('. Reprinted front \\\ I Open l ilc 2o|(M)4. I lissertation p. 2 I~~

Photo 13. Bioherm in Sekwi member 2c. A) View of the bioherm looking south. Hammer is 40 cm long. B) Weathered surface shows clots ofprobable microbial origin (e.g., left arrow), abundant tiny trilobite fragments (e.g., central black arrow), and shell fragments (e.g., right arrow). Larger fragments (grey arrows) include a brachiopod shell and a trilobite carapace. Scale in millimetres. 630936E, 7208735N.

ABC Creek (not visited as part of this study) grey, sparsely vuggy dolostone with thin to may be in Cs3. medium, non-parallel partings which cut each other at angles of up to 40 degrees. Cs3 is cut In the AB area, Cs3 consists of 3 m of fine to off by a covered, east-northeast-trending medium crystalline, buff weathered, light topographic low, which may coincide with a

~~\\\ I ( )| 20 I (1-04 (ieolou\ of the \ B area, parts of \ I S !()(>( Its and 10(4 0 1 \ppendi\ ( . Reprinted ! i om \\\ I Open l ilc 2010-04 I)issertalion p. 2 12~~

Photo 14. Archeaocyathan(?) rudstone in Sekwi Photo 16. Cross-bedded dolostone at the base of Sekwi member 2 (undivided) adjacent to Fault 10. Metal part member 3. Scale in millimetres. 630389E, 720851 IN. of pencil tip is 4 mm long. 628004E, 7208333N. including very low-angle ones, are common in quartz-rich beds. Normal grading occurs locally in skeletal beds. Horizontal burrows are common. Bedding thickness ranges from very thin to medium, and rock types change vertically over distances of centimetres to a few metres. Skeletal components include fragmented and whole trilobites and * * _. brachiopods, and rare microbial clots in clasts or clusters 1-2 cm long (Photo 18).

North of the AB-C showing, laminated and locally cross-bedded quartz arenite and sandy Photo 15. Finely crystalline, sparsely vuggy, light grey dolostone typical of the resistant intervals in Sekwi dolostone predominate over oncoid (-skeletal) member 3. Closely spaced solution seams give the rudstone, intraclast rudstone-grainstone with appearance of laminations. Hammer is 40 cm long. current-rippled bedding planes, wavy-bedded 630491E, 7209320N. lime mudstone, and dolomitic siltstone. Rock types in the AB showing area include fault that removed the upper parts of Cs3. dolomitic quartz arenite, silty to sandy, locally oolitic dolostone, and argillaceous limestone. Cs4 Southeast of AB, burrowed, thin-bedded The uppermost member of the Sekwi dolostone is interbedded with sandy, Formation is about 250 m thick near the AB-C laminated to cross-laminated dolostone. showing, but thins to 110 m near AB. It Sekwi member 4 in the southwest of the map consists primarily of sandy dolostone (Photo area is exposed mostly as rubble of quartz 17) and skeletal limestone (packstone, arenite, sandy dolostone, and finely wackestone), commonly with muddy crystalline, recrystallized dolostone. In the interbeds. It also contains intervals of ooid southeast valley between Faults 5 and 7, Cs4 dolograinstone, intraclast dolorudstone, includes microbially laminated dolostone oncoid-skeletal dolostone, and a variety of (Photo 19). other minor rock types. Parallel laminations, current ripples, and cross-laminations,

~~\\\ I ( >1 2010-04 of the \I5 area. parts ol \ I S 106( I 6 and I0M 01 \ppciii.1i\ ( . Reprinted from \\\ I Open file 201(1-04. l)i>sertaiion p. 2 I 3~~

Cs4g Unit 4g is a grainstone near the top of member 4. On the hill west of AB, Cs4g is an ooid dolograinstone with well-preserved ooids. In a fault-bounded wedge at the east end of the map area, it is a skeletal floatstone in ooid grainstone matrix that grades into a heavily dolomitized ooid grainstone with only coarse fabric preservation. A quartz arenite underlies the grainstone west of AB, but in the eastern wedge it is underlain by poorly exposed i rubble of heavily dolomitized rock, including Photo 17. Quartz-rich laminations in quartz-sandy vuggy and silicified varieties. dolostone of Sekwi member 4. Metal part ofpen tip is 4 mm long. 630567E, 7207154N. Cs2-3(-4) undivided

Stratigraphic equivalents of Sekwi members 2, 3, and possibly 4 are exposed in the western part of the map area. These consist of limestone and dolostone with skeletal, intraclastic and ooidic grains in a range of textures, and carbonate siltstones and mudstones. In the creek-cut core of an anticline between Faults 2 and 3, the lower half of a 700 m section of Sekwi Formation is extremely well exposed. Subdivisions mapped in the AB-C area are not evident here (as illustrated on the left half of the column in Figure 4). From base to top, the package Photo 18. Ovoid structures (clasts?) consisting of clusters of 1-3 mm microbial clots, in Sekwi member 4. consists of argillaceous limestone and lime Scale in millimetres. 630582E, 7207151N. mudstone with minor skeletal fragments; laminated, sandy dolostone with oolitic, intraclast-bearing, and microbially laminated intervals; well-laminated limestone; ooid grainstone to wackestone; well-laminated calcisiltite; massive limestone with minor skeletal fragments and intraclasts; Salterella packstone interbedded with silty limestone and rare microbially laminated limestone; nodular limestone; and laminated to massive limestone with rare interbeds containing intraclasts and skeletal fragments. Overlying this package is rubble of Cs4.

Immediately west of Fault 10, rocks assigned Photo 19. Microbially laminated dolostone of Sekwi member 4. Scale in centimetres with subdivisions in to Cs2-3(-4) include sandy dolostone rubble millimetres. 632967E, 7208008N. and an outcrop of well-indurated, orangey

\\\ I < il 2010-04 (ieoloe> ol (lie \ U area, parls ol \IS 1061' 16 aril 1061 III 20 Appendix ( . Keprinied Iron) \\\ I Open I ile 2010-04. I)issenution p. 214 rusty brown weathered, medium to dark grey, Another important type of secondary breccia well-laminated, thinly to very thinly bedded, in the Sekwi Formation is a cemented crackle calcareous dolomudstone with alternating to mosaic floatbreccia that hosts the AB-C beds of yellow and grey. In the eastern wedge Upper and Link showings (and is described between the AB Fault and Fault 7, below; see Alteration and mineralization). The stratigraphically below the heavily cemented breccia post-dates the cataclasite. dolomitized rubble of Cs4, are thinly Heavily weathered cemented breccia at the interbedded, pinkish grey and orangey brown AB-C Upper and Triple showings, and on the weathered, laminated dolostone, and hillside north of AB-C, contain rounded laminated to cross-laminated, microcrystalline pebbles, cobbles and boulders of dolostone Salterella dolograinstone with scattered (including cataclasite) in a friable yellow brachiopods (Photo 20). matrix (Photo 22).

In the southeastern region between Faults 2 Interpretation and 5, strata assigned to this member consist of two units. The basal two thirds is a Age and correlation recessive interval of thin to medium-bedded, The Sekwi Formation type section in NTS laminated, brown-weathered, dark grey to map sheet 105P was measured by Handfield black, calcareous siltstone containing (1968). Comparison of Sekwi Formation in abundant trilobite fragments and rare thin the AB map area with measured sections by limestone beds. This is overlain by a resistant Fritz (1976, 1978, 1979), Krause (1979), and unit of massive, light brownish grey Dilliard (2006) in map-sheets 106A, B, and C weathered, very finely crystalline limestone and 105P, suggests the AB area exposes rocks with medium to thick partings suggestive of from the upper part of the formation. The metre-scale cross-bedding. These strata are upper Sekwi Formation is characterized by atypical of the Sekwi Formation and their shallow-water, inner-ramp rock types and assignment to that formation is tentative. belongs to the Bonnia-Olenellus trilobite biozone of the late Early Cambrian (Fritz, Cs coarse fragmental rocks 1972; Krause, 1979). Primary coarse fragmental rocks are described Depositional environment above along with the members in which they Abrupt lateral facies changes characterize the are present. Rock-matrix breccia of probable Sekwi Formation in the map area. Member 1 fault origin (cataclasite) is exposed at the AB- is poorly preserved and poorly exposed so no C Upper showing in a 140 m long, SE- interpretation is attempted here. Member 2a trending zone. The cataclasite (Photo 21) is a was deposited in a subtidal, open-marine rock-matrix rubble packbreccia (to environment with abundant bioturbation and floatbreccia) with polymict, rounded to benthic invertebrates. The predominance of angular dolostone clasts in a wide range of wackestone and absence of deposits resulting grey shades, from granule to cobble but from winnowed sands suggests the unit was dominantly pebble sized, in a finely deposited below fair-weather wave base. crystalline dolostone matrix. Clasts from units Local nodular structures support an origin in Cs2b, Cs2c, and Cs3 were identified. waters of intermediate depth. The presence of Exposures of rock-matrix breccia along ABC possible tempestites (mottled, argillaceous Creek may have been created during dolostone with thin interbeds consisting of movement on the ABC Fault (see Structure). flat-lying, cobble-sized clasts in a muddy matrix) suggests that deposition occurred

~~\\\ 1 ( >1 2010-04 (leoloyx of llie \B area. parts ot \IS 1061 I6and I0(>| (ll \ppendi\ ( . Reprinted from \\\ I Open l ile 2010-04. Dissertation p. 2 I 5~~

~~<•&~~

Photo 20. Salterella dolograinstone in undivided Sekwi member 2-3(-4) at the eastern edge of the map area. A) Typical outcrop appearance, looking NW at medium-bedded dolostone. B) Salterella cones in a microcrystalline matrix show a preferred orientation perpendicular to the plane of the photo. Pencil lead is 0.5 mm wide. 633798E, 7209078N. above the storm wave base. In the AB area dolofloatstone, or debrite. These and other during deposition of Cs2a, there was a characteristics discussed above are consistent temporally (and possibly spatially) restricted with a mid-ramp setting that experienced depositional low that received at least 20 m of significant terrigenous input. sediment gravity flow deposits, preserved as a 20 m interval of intraclast dolorudstone to

~~\\\ I or 2010-04 (ieoloe> ol'the \B area, parts of VI S I06C 16 and !0(>| () Appendix ( . Reprinted from \\\ I Open l ile 2010-04. I)!ssertation p. 216~~

shoal (e.g., Clough and Goldhammer, 2000), lft> or along the seaward shoal face under the influence of longshore currents (Carney and Boardman, 1993). The shoal was replaced by shallow, lagoonal conditions during deposition of Cs2c.

Sekwi member 2c was deposited in subtidal, open-marine conditions in low-energy waters with abundant bottom life and minor terrigenous influence. The bioherms at its base at least superficially resemble Photo 21. Rock-matrix rubble packbreccia in a fault thrombolitic - leiolitic bioherms described by zone cutting Sekwi member 3 above AB-C Upper Riding (2000). Depositional conditions of unit showing. Clasts are polymict dolostone, generally Cs2c are consistent with those of an inner- rounded, and granule to pebble sized in this photo. ramp, back-shoal lagoon with scattered Matrix is a finely crystalline dolostone. Scale in millimetres. 630379E, 7209220N. microbial bioherms. Cs2c is missing in the AB area where a few metres of resistant, recrystallized dolostone of Cs3 lie directly on Cs2b.

Sekwi member 3 retains few primary features. The lowermost of the recrystallized dolostone cliffs of Cs3 derives from cross-bedded carbonate sands, deposited in a high-energy environment free of terrigenous input, lacking fauna and large carbonate grains, and above the fair-weather wave base. The presence of both straight and wavy-crested dunes and ripples, and cross-strata angles range from 5 to 20 degrees, implies variations in energy Photo 22. Well-rounded cobbles and pebbles of and/or grain size. This part of the unit may dolostone, including some fault breccia cobbles, in a friable, gossanous matrix in Sekwi member 2c above represent the foreshore of a ramp which had the AB-C Upper showing. Elizabeth Turner for scale. no shoal to damp the waves. It may Looking west from 630482E, 7209183N. alternatively represent a new sand shoal on the inner ramp. The dark, mottled dolostone Sekwi member 2b formed in high-energy intervals between cliffs may derive from waters as a mobile shoal of cross-bedded burrowed carbonate mud and silt, suggesting ooids on an inner ramp. Lateral drops in an alternation between high and low-energy energy allowed the shoal to collect interstitial environments. This alternation may have been mud, skeletal fragments, and larger, between foreshore/shoreface and offshore irregularly shaped ooids toward what is now zones on an open shelf or ramp. Alternatively, the south, and to thin or dissipate into skeletal it could have been between a mobile sand wackestone to the west and southwest. The shoal on the inner ramp, and bioturbated mud drops in energy may have occurred in the of either an inner-ramp lagoon (shoreward of deeper water between sand ridges (Ball, the shoal) or mid-ramp zone (seaward of the 1967), shoreward of the main body of the shoal). A dramatic facies change might have

\\\ I ( >1 2010-04 (icolot!) of the \B area. part-- of \ I S I0(i( 16 and 1061 01 \ppendi\ ( . Reprinted from \\\ I Open 1 iIc 201(1-04. 1 )isscrtafion p. 217 occurred to the southwest, where the strata Paleo-erosion underlying Cs4 bear no resemblance to Cs2 Deep but geographically restricted sub- and Cs3 as documented at AB-C; but since the Franklin Mountain Formation erosion of amount of displacement on intervening Sekwi Formation (Fig. 4) is indicated by basal Cretaceous to Tertiary faults is not known, the Franklin Mountain Formation resting directly original lateral distance between the localities on the second member of the Sekwi remains unknown. Formation near the Link showing, on the third member 1.5 km to the southwest of Link, and Sekwi member 4, which comprises one third on the fourth member 1.7 km to the west. to one half of the stratigraphic thickness of About 330 vertical metres of strata are exposed Sekwi Formation in the area, is only missing near the Link showing. half as thick at the AB as at the AB-C showing. It is rich in, and locally dominated Sekwi member 4 may be absent in the large by, terrigenous detritus, with subordinate drainage 3.6 km north of the AB Fault, where skeletal material, intraclasts and layered rocks identical to Cs2a and Cs2b are grains in a muddy to silty matrix. Laminations immediately overlain by the Franklin are common. These features suggest a quiet, Mountain Formation. It is not known whether deep-water, marine setting with significant this absence is erosional or a facies change. terrigenous influx. Local lenses of grainstone interbedded with bioturbated wackestones and Franklin Mountain Formation (COf) mudstones could be winnowed storm deposits. The local grading and cross-lamination noted The Franklin Mountain Formation is a pinkish above likewise could be due to storms. These grey weathering dolostone with minor to no characteristics suggest a mid-ramp setting retention of primary structures. It overlies the (below the fair-weather wave base but above Sekwi Formation between the AB Fault and the storm wave base) with heavy terrigenous Fault 2, where it caps many of the peaks input. The increase in terrigenous input in Cs4 (Photo 1), and it forms the plains north of the time was probably due to changing climatic or AB Fault. It ranges from 70 m to over 250 m tectonic conditions that led to increased thick. It has been divided locally into three erosion on land. Sub-member Cs4g was informal members for this study, but across deposited in medium-energy waters as an ooid most of the map area it is undivided. A shoal with a slightly muddy matrix and dolomitization or dolomite recrystallization lacking cross-beds. destroyed primary fabrics in the formation along Fault 3. In total, the exposed Sekwi Formation records first a shallowing sequence from mid-ramp COf1 basal member (Cs2a) to shoal (Cs2b) and inner-ramp lagoon The base of the Franklin Mountain Formation (Cs2c) to back-ramp beach or shoreface (base in the AB area is only locally exposed and of Cs3) environments. A period of fluctuating consists of either a dolomitic arenite (member relative sea level (the rest of Cs3) was then la) or a well-bedded dolostone (member lb). followed by a deepening to mid-ramp COfla is exposed south of the AB Fault, and conditions (Cs4). Cs4g represents a consists of a few metres of medium-bedded, shallowing near the end of Cs4 time. brown to grey-weathered, medium grey, fine to very fine grained, cross-bedded, locally laminated, dolomitic quartz arenite (Photo 23). Rubble of clean, white quartz arenite is locally present. COfl a directly overlies the

~~\\\ I ()L 20 10-()4 CicoIol!) of the \ B area, parts of \ L S I0(>( 16 and I0M (I 24 \ppenili\ ( . Kepnnled from \\\ I Open I ile 2010-114. I)isscruilion p. 2 I S~~

~~roughly 20 m of poorly parted, thickly parted, thickly laminated dolostone. The top of COfl b is placed at the first appearance of ooids.~~

Despite heavy brecciation, rocks along ABC Creek north of the AB Fault can be assigned to COfl b. This is because clasts of the laminated dolostone that is typical of COfl b are common within the breccia, and because a few unbrecciated outcrops consist of typical COfl b rocks, namely thin to medium-bedded, well-bedded, laminated dolostone, with a shallow channel a few metres wide at one locale.

In the eastern wedge of land between the AB Fault and Fault 7, rocks assigned to COfl (undivided) consist of resistant, medium- bedded, microbially laminated dolostone, commonly with fine quartz sand caught in the Photo 23. Fine-grained, medium-bedded, dolomitic laminations, and unlaminated, sandy quartz sandstone of Franklin Mountain member la, dolostone with scattered, centimetric zones south of the AB Fault near the Duce showing. Hammer containing ghost oncoids or intraclasts. Open is 40 cm long. 63I420E, 7209157N. vugs 1-10 cm in diameter lined with quartz±pyrite are common near the top and Sekwi Formation and is overlain by vuggy bottom of this interval. dolostone of the undivided Franklin Mountain Formation. COf2 siliceous member

Although quartz arenite of COfl a was Franklin Mountain member 2a is a silicified documented north of the map area, it is not ooid dolograinstone at least 50 m thick that is exposed within the map area north of the AB very resistant and caps a number of peaks in Fault. Strata immediately above Sekwi the map area. It immediately overlies COflb Formation north of the AB Fault are mostly north of the AB Fault, and overlies vuggy, covered by overburden. Three divisions of undivided Franklin Mountain Formation south COfl b occur above the covered interval. The of the fault. It is light to brownish grey lowest is a 50 m cliff of monotonous, well- weathered, light grey, finely to coarsely bedded, medium-bedded, laminated, brownish crystalline, and massive to medium bedded. It grey weathered, microcrystalline, locally has centimetre-scale trough and planar-tabular argillaceous dolostone with a shallow channel cross-bedding, as well as dunes up to 80 cm in a few metres wide (Photo 24). Overlying this wavelength (Photo 25). Silicification consists is at least 30 m of medium-bedded, thickly to of white or grey, cherty oolite lenses (Photo non-laminated, finely to microcrystalline, pale 26) and irregular centimetric masses of black buff weathered, light grey dolostone, rarely chert. Millimetre and centimetre-scale vugs broken into slightly rotated blocks. This are filled by quartz. Dolomitization was grades up into the third division, which is thorough and largely destructive of pre

~~\\\ I Ol 20 111-04 of the \l! area, pans of \ I S I06( 16 and 1061 (I \ppeiuli\ ( . Reprinted from \\\ I Open I ile 2010-1)4 I)issertation p. 2 1')~~

~~Photo 24. A) Channel in medium-bedded, laminated dolostone of Franklin Mountain member lb. John Law for scale. 630278E, 7212673N. B) Channel is outlined in black~~

existing fabric; ooids are visible only as faint boulder-sized, angular to rounded clasts of ghosts except where preserved by dark grey, laminated dolostone. silicification. Minor beds and lenses of oncoid dolorudstone (Photo 27), laminated dolostone, Franklin Mountain member 2b overlies COf2a vuggy, medium-crystalline dolostone, and along the ABC Creek north of the AB Fault, argillaceous dolostone are common. Oncoids and hosts the DAB showing (J. Ryley, Eagle are recognized by their irregular, Plains Resources, pers. comm. 2008). COf2b discontinuous lamellae (Tucker and Wright, consists of 10-20 m of silicified dolostone 1990). Oncoids in COf2a along the ABC with highly irregular, resistant, silicified, Creek and west of the AB showing have been microbial and mechanical laminations and dissolved and their moulds filled with cherty, coral or sponge-like pseudo-fossils, geopetal sediment overlain by dolospar or perhaps derived from a laminated to coarse quartz (Photo 28). Their origin as burrowed, quartz-rich carbonate precursor oncoids is revealed by the presence of (Photos 30, 31). It is light to brownish grey partially to undissolved oncoids centimetres weathered, pale grey, fine to medium away in the same beds (Photo 29). Rare rock crystalline, locally laminated, and medium types in COf2a include dark, vuggy dolostone bedded. Millimetre-scale vugs are lined or (described below), silicified laminated filled by quartz. dolostone (similar to that found in COf2b, below), and a decimetre-scale gravity flow COf undivided deposit (debrite?) that scoured the laminated Throughout much of the map area south of the dolostone beneath it. The debrite is a rock- AB Fault, the Franklin Mountain Formation is matrix rubble floatbreccia with a matrix of not divisible into members, and north of the finely crystalline dolostone, and pebble to AB Fault it was not mapped in detail during

~~\\\ I ( >1 2010-04 (ieoli>L!\ of the \B area, parts of \ I S 1061' 16 and 1061 Ul 26 Xppemlix ( . Reprinted from \\\ I Open I ile 2010-04. Dissertation p. 220~~

Photo 25. Symmetrical dune of 80 cm wavelength (pencil is below trough) in medium-bedded ooid dolograinstone of Franklin Mountain member 2a. Dark laminations are argillaceous. Although most exposures of COf2a are extensively silicifled, this one is not. Pencil is 14 cm long. Looking west from 627904E, 7209365N. \

Photo 26. Silicified ooids in Franklin Mountain Photo 27. Oncoidf?) dolorudstone rubble from member 2a. Pencil lead is 0.5 mm wide. 629608E, Franklin Mountain member 2a. 1.5 cm ghost oncoids 7211691N. are visible largely because of dissolution and subsequent cementation in inter-grain spaces. Dolomite rims the inter-oncoid vugs and quartz cores them. Blue part of pencil is 1 cm wide. 629784E, 7209103N.

~~\\\ i (>1 2010-04 (leoloL!) ot the AR urea, parts of N I S 106( Ih aiul 10(4 0 Appendix ( . Reprinted Irom \\\ I Open I i!e 201(1-04. I)is^ertalion p. 221~~

Photo 28. Geopetal oncoidfrom rubble of Franklin Mountain member 2a in the west part of the map area. Internal sediment, which partly filled the oncoid mould after dissolution of the oncoid, has been replaced by fine, beige dolomite. Coarse, white quartz fills the remainder of the void, above the fine dolomite. Large divisions on the scale-bar are centimetres, small lines are millimetres. 626521E, 7210514N.

I Photo 29. Geopetal oncoids in outcrop of Franklin Mountain member 2a in the east part of the map area. Undissolved ghost oncoids (e.g., at left ofphoto) confirm interpretation of the geopetal structures as oncoidal. Coarse dolomite rims the structures and very coarse, orange dolomite±quartz fills their upper parts. Small skeletal fragments in the rock have also been dissolved andfilled with coarse dolomite. Transparent part of pencil is 1.5 cm long. 631497E, 7210635N. this study. Undivided Franklin Mountain fabric destructive, so that only local, faint Formation is predominantly a vuggy, fine to laminations remain. Vugs are sparse to medium crystalline, pinkish grey weathered, abundant, millimetre to centimetre-scale, and light grey dolostone. Dolomitization was variably filled with dolomite or quartz, open,

~~\\\ I ( >1 20 10-04 (leoloy) of the \ H area, parts of \ I S I0ft( I ft and lOftl (II 28 \ppeiuli\ ( . Repnnieil from \\\ I'Open I ile 2010-04. I )issertalion p. 222~~

fabric consists of a dense array of vugs up to 1 cm long, concentrated in planes grossly parallel to bedding, within a dark grey weathered, finely crystalline dolostone (Photo 32). White dolomite or quartz lines or fills the vugs, which are commonly elongate and aligned parallel to their axes of elongation. The vugs locally resemble filled fenestrae. The dark, vuggy fabric is gradational with its host dolostone and difficult to trace at outcrop scale. From a distance, however, the dark, vuggy dolostone can be seen to occur in Photo 30. Pale brown, silicified laminations and grossly concordant, metre-scale bands and irregular silica-rich ridges in grey dolostone of bundles of decimetre-scale bands at a low Franklin Mountain member 2b. Glove finger is 2 cm angle to bedding (Photo 32B, 33). In restricted wide. 631259E, 7210638N. areas the dark, vuggy fabric grades through increasing vug interconnectedness into zebra fabric with discontinuous, millimetre-scale bands crustified with white dolomite (Photo 34). A similar dark, vuggy dolostone grading into centimetre-scale zebra fabric is exposed in Sekwi Formation member 1 along the ABC Creek.

~~COf coarse fragmental rocks~~

Primary breccias are described above along with the member in which they are present. In COf undivided and COf2, rock-matrix rubble floatbreccia and packbreccia in thick, crudely Photo 31. Silica pseudo-fossil in Franklin Mountain member 2b. These structures, which occur in a wide defined beds may be of diagenetic origin. The variety of shapes, are composed of minute silica matrices of these breccias are finely crystals perpendicular to the structure's walls. Pencil crystalline dolostone, with subordinate lead is 0.5 mm wide. 631400E, 72I0639N. amounts of coarse calcite or dolomite cement. Fragments are pebble to cobble-sized, or lined by dolomite and cored by euhedral rounded (to subangular), equant (to tabular), quartz. Rock types characteristic of COf2a oligomict, finely crystalline dolostone (Photo and COf2b are present in rubble south of the 35). A breccia of unknown origin in COf2a AB Fault, but were not mappable. north of the AB Fault consists of black chert fragments in a matrix that grades from COf dark vuggy dolostone dolostone to chert along strike. The breccia is underlain by a bed of black chert and overlain A dark, vuggy fabric is common in the by ooid dolograinstone with patchy Franklin Mountain Formation. It is common chertification. A dark grey chert breccia near in undivided COf near Fault 3, and in COflb the DAB showing is roughly along strike from along the ABC Creek, as breccia clasts as well it, suggesting a stratigraphic control on as in unbrecciated outcrop. One small formation of these chert-dolostone breccias. occurrence was noted in COO. Dark, vuggy

~~\\\ I ( >1 2010-04 (icok>L!\ c! llic \R area, parts of \ I S 1061 Ihard 10(>l 01 2') Appendix ( . Reprinted from \\\ I Open I ile 2010-04. Dissertation p. 22"~~

Photo 33. Undivided Franklin Mountain Formation immediately below member 2a. Dark bands in the cliff are dolostone with dark, vuggy fabric (see text for explanation). Each band is a metre or more in Photo 32. Dark, vuggy fabric in Franklin Mountain thickness. Bands change in thickness along strike due member lb along ABC Creek. A) Close-up. B) From a to a changing number of component subsidiary bands. distance. Divisions on stick are 10 centimetres each. 629642E, 7209098N. 6316I3E, 72I0603N.

Polymict rock-matrix breccias of probable fault origin (cataclasite) occupy a zone over a kilometre long in COfl and COf2a along the ABC Creek, and in a small (10 x 20 m), possibly discordant zone in COf2a on a hillside southeast of the AB showing. These are rubble floatbreccias with a buff or light or dark grey, finely crystalline dolostone matrix, and a poorly sorted variety of angular to rounded, granule to boulder-sized dolostone clasts. Clast rock types (Photo 36) include laminated and unlaminated dolostone in Photo 34. Dark, zebra dolostone in Franklin Mountain various shades of grey, the dark grey, vuggy Formation near Fault 3. White dolospar in millimetres- dolostone described above, polymict rock- thick bands is separated by dark grey dolostone. This matrix breccia (indicating two generations of example grades into dark, vuggy fabric 20 cm to the brecciation), and plastically deformed clasts right, and is an evolved variant of that more common of microcrystalline black material. The fabric. Pencil is 1 cm wide at its widest visible part. 627899E, 7208583N. polymict nature of the breccia and the

~~W\ i (>1 2010-04 (ieok>;j_\ cflhe \B area, parts of \I S I06( 1 (> and !0(>l 01 \ppeiuli\ ( . Reprinted InMil \\\ I Open i ile 2010-04. Dissertation p. 224~~

Photo 35. Rock-matrix rubble packbreccia of probable B sedimentary origin in Franklin Mountain member 2a. Clasts and matrix weather almost the same colour, making the fragmental nature of the rock difficult to see from a distance. The matrix is a coarsely crystalline dolomite cement. Clasts are of well-rounded, finely crystalline dolostone. The outcrop is crudely bedded * (not visible in photo). 629583E, 7211636N. presence of dark, vuggy dolostone clasts within it, as well as an unbrecciated dark, vuggy fabric at the same stratigraphic level, indicate a secondary origin for the breccias. Both generations of breccia are therefore inferred to be cataclasites.

Replacement-matrix breccias along the ABC Creek are pseudo-breccias created by replacement of the original rock around clast- like, unaltered remnants. In one example, finely crystalline dolomite has heterogeneously replaced an ooid dolograinstone to create round, pebble-sized remnants and isolated ooids that 'float' in the finely crystalline replacement matrix (Photo 37). The age of this and other dolomitization Photo 36. Rock-matrix fault breccia in Franklin with respect to faulting is ambiguous. Most Mountain Formation along the ABC Creek. A) fragments in the rock-matrix breccias have Subangular to rounded, granule to cobble-sized clasts sharp boundaries, suggesting that of light and dark grey dolostone, laminated dolostone, dolomitization pre-dated faulting, but some and breccia, in a matrix of finely crystalline dolostone. fragments are gradational with the matrix, Breccia in clasts is a previous generation of rock- matrix fault breccia. Scale in millimetres. B) Same as implying that at least some dolomitization or A. Note large, cobble-sized clast of pebble breccia in dolomite re-crystallization post-dated faulting. the middle. Scale in millimetres. C) Black, plastically deformed clasts in dolostone fault breccia. Blue part of hammer handle is 19 cm long. A andB from 63I473E, Two types of cemented breccia are common 7210390N ± 70m NE/SW. Cfrom 631213E, 72098I9N in the Franklin Mountain Formation. ± 100m NE/SW.

~~\\\ I Ol 2010-114 (ieoloy\ of the \M area, parts of \ IS I0K lOaiul I 0M III \ppcndi\( . Reprliiled from \\\ I Open lile 201(1-04, Dissertaiion p. 22?~~

~~Interpretation~~

Age and correlation The type section of the Franklin Mountain Formation in the front ranges of the Franklin Mountains was described by M. Y. Williams in 1922 (as referenced by Norford and Macqueen, 1975). Re-examination of the type section and regional studies (Norford and Macqueen, 1975) led to the recognition of three widespread members: a basal cyclic member, a middle rhythmic member, and an Photo 37. A replacement mosaic packbreccia in ooid upper cherty member. The cyclic member is dolograinstone of Franklin Mountain member 2a has a not known west of the Mackenzie Arch. In the finely crystalline dolomite matrix, rounded pebble- interior ranges of the Mackenzie Mountains sized remnants of ooid dolograinstone, and isolated ooids which "float" in the matrix. This texture was and westward, the entire formation tends created by inhomogenous replacement of pebble-sized toward uniformity because the rhythmic areas, and preferential replacement of the grainstone character of the middle member is lost, and matrix over the ooids. 631287E, 7210085N ± 70m the cherty member becomes less siliceous NE/SW. (Norford and Macqueen, 1975). A basal "red- beds" sandstone Dolomite± marcasite/pyrite cemented breccia sub-member, correlative with along the ABC Creek post-date both the base of the rhythmic unit, was identified generations of polymict rock-matrix breccia, along the Mackenzie Arch, east and southeast and correlate with sulphide-dolomite-barite of the present study area (Aitken et al., 1973, cemented breccia in the Sekwi Formation to 1982; Gordey et al., 2009). A cherty member the south. (Evidence is equivocal in Franklin described from map sheets to the east- Mountain Formation exposures, allowing for a northeast (106G and H; Aitken et al., 1982) synchronous origin for the cataclasite and the has white chert nodules, quartz-lined vugs, cemented breccia, but relative timing is clear and silicified oncoids. The basal unit of the in two Sekwi Formation exposures.) The formation has not been dated, but the base of dolomite±marcasite/pyrite cemented breccias the rhythmic unit, to the southeast of the map have rubble to mosaic textures and include area in the Canyon Ranges, is Late Cambrian, fragment and matrix-supported end-members and at the Arctic Red River to the east of the (Photos 38, 39). The second type of cemented map area the cherty unit and at least part of breccia is calcite cemented. Crackle and the rhythmic unit are Early Ordovician in age. mosaic calcite breccias, calcite veins, and Norford and Macqueen (1975) hypothesize large (decimetre-scale) calcite vugs are the presence of a minor unconformity between spatially associated with Faults 3 and 4. A the rhythmic and cherty members. calcite breccia is documented in a metre-scale, bedding-discordant zone in COf2b near the In the AB map area, COfla arenite may ABC Creek, and calcite veins are associated correlate with the basal red-beds of the with minor sphalerite at the Twice showing, rhythmic member to the east, and therefore approximately 300 m to the north. may be as old as Late Cambrian. COflb is interpreted to be a manifestation of the rhythmic member because it is well bedded and directly underlies COf2, which is lithologically similar to the cherty member

~~\\\ I ( >1 2010-04 Cicolos:\ ol the \B urea. parl> ol \ I S 10ft( 1ft and I0(>l 0 \ppemJI\( . Reprinted 1 rom \\\ I Open I ile 2010-04. I)is--ertation p. 226~~

Photo 38. Pyrite-dolomite cement at lower right penetrates the matrix ofpre-existing fault breccia in Franklin Mountain Formation along the ABC Creek. Dissolution of the fault breccia matrix and rounding of its fragments preceded cementation. Divisions on stick are 10 centimetres each. 63I473E, 7210390N± 70m NEJSW. described by Norford and Macqueen (1975). COf (undivided) south of the AB Fault occupies the same stratigraphic position as COflb but has a very different lithological character which is currently unexplained. Depositional environment Photo 39. Marcasite-dolomite cement in a breccia in Franklin Mountain Formation along the ABC Creek A) Basal Franklin Mountain Formation member Marcasite rim was partially torn up and displaced la is a cross-bedded quartz arenite deposited prior to dolomite precipitation. B) Close-up of bladed from a terrigenous source by strong currents marcasite crystals displaying cockscomb texture. Scale in a heavily eroded valley. Well-bedded in millimetres. 631216E, 7209645N. dolostone of COflb records high-energy, marine deposition of silt-sized carbonate tidal(?) currents, with intervening lower- particles without appreciable terrigenous energy areas of laminated sediment deposition. These sediments influx. The microbially laminated, sandy were overlain by dolostone of undivided member COfl in the laminated to burrowed, sandy to silty eastern wedge was deposited in low-energy, carbonate sediment with patchy microbial shallow, marine water with a minor mats, indicating that a lower energy terrigenous influence and may represent, environment replaced the shoal. along with some of COf (undivided), a lateral Alteration variant of the deeper-water, higher-energy Dissolution of oncoids is inferred to have COflb. occurred during early seafloor diagenesis, when internal sediment could create the Franklin Mountain member 2 has lost much of geopetal texture. The mineralogical its primary depositional character through composition of these oncoids must have silicification and pervasive dolomitization. A differed from that of the surrounding discontinuous ooid shoal developed dune- sediment, and probably consisted of one of the scale cross-beds under the influence of strong common metastable carbonate minerals,

\\\ I (>1 2010-04 Cicoloy\ of the \B area. parK ol \I S 1061 16 arnl 1061 01 \ppcntlix t . Reprinted from \\\ I Open file 201(1-0-1 Dissertation p. 227 aragonite or magnesian calcite. Later south of the fault, and particularly deep crystalline fills which completed the geopetal erosion in the Link area. In this same area, texture were either deposited or replaced dramatic erosion of the Sekwi Formation during burial diagenetic silicification and occurred prior to Franklin Mountain dolomitization events. At least some deposition. An unidentified tectonic control silicification preceded pervasive must have influenced topography from the dolomitization of the host rock, preserving Early Cambrian until at least the Early ooids that in the surrounding, unsilicified rock Ordovician, causing deep erosion in the same are barely visible ghosts. place at two separate times.

The dark, vuggy dolostone noted above has Duo Lake(?) Formation (OSd) both primary and secondary characteristics. Restriction of the vuggy fabric to dark bands The Duo Lake(?) Formation is present and the gross bedding concordance of those between the AB Fault and Fault 2 in a number bands speak for a primary origin. The slight of small, separated areas. It also underlies discordance, however, suggests a secondary much of the mountainsides that form the origin. This discordance is best visible in an western part of the map area, and underlies exposure in ABC Creek, where the dark bands some hills immediately north of the AB Fault. are at a slight angle to laminations and The Duo Lake(?) Formation is a recessive, lamination-parallel colour changes (relict thinly to very thinly bedded, shaly siltstone at bedding?), and fade out along strike (Photo its base, grading upward into mixed 32B). It is likely that a primary depositional calcareous and siliciclastic shale with an unit controlled the locus of later alteration; upward-increasing proportion of resistant without such a constraint it is difficult to limestone or dolostone and black chert beds. explain the near-coincidence of the alteration For this study, it is divided into a lower, with bedding, and the restriction of dense vug siliciclastic-dominated member, OSdl, and an development to layers. This fabric in upper, carbonate-dominated member, OSd2. undivided Franklin Mountain Formation These appear to be intergradational, as best as underlies COO, in the same stratigraphic can be judged given the paucity of exposure, position as COfl b. and OSd2 is gradational with the overlying Cloudy(?) Formation. The Duo Lake(?) The lowest member of the Sekwi Formation Formation is 150 m thick north of the AB also contains a dark, vuggy dolostone grading Fault in the west, 230 m thick in the east, and into zebra dolostone. It is not well-enough at least 375 m thick south of the AB Fault in exposed to allow comment on its relationship the west part of the map area. to the similar Franklin Mountain rock type, although it is in the same vicinity (Map). OSd1 Paleo-erosion Duo Lake(?) member l comprises the lower North of the AB Fault, the Franklin Mountain two-thirds of the formation. It is a poorly Formation is about 190 m thick. South of the exposed, black (on weathered and fresh fault it ranges from over 250 m on the hill surfaces), recessive, siliciclastic mudstone, southeast of the AB showing, to about 100 m shale, siltstone, and rare very fine sandstone on the southern plateau north of Fault 5, and (Photo 40). It is generally finely parallel- 70 m east of the Link showing. These laminated and contains abundant graptolites thicknesses indicate uneven, post-Franklin and unidentified carbonaceous compressions Mountain, pre-Duo Lake(?) (OSd2) erosion on bedding planes. Traces of pyrite are common. Thin black chert beds are very rare.

~~\\\ I Oi 2010-04 (ieoloy_\ of the \B area, parts ol \I S I0M U> and I06l Oi 34 \ppendi\ ('. Reprinted fiom \\\ i Open lile 2D 10-0-1 I)isserialion p. 228~~

~~OSd2~~

The base of Duo Lake(?) member 2 is placed where the proportion of carbonate first exceeds 10% of the rock. It is 60 m thick north of the AB Fault and at least 100 m thick south of it. OSd2 consists of limestone, dolostone, black chert, calcareous shale, and rare siliciclastic shale. The amount of carbonate and chert increases upward as the amount of shale decreases.

South of the AB Fault in the east part of the map area, OSd2 is partly to fully dolomitized. North of the AB Fault and in the far west, it is calcareous. OSd2 consists of thinly bedded, yellow and grey, nodular to banded lime mudstone and calcisiltite or their dolomitized equivalents (Photo 41), microcrystalline dolostone in thin to very thin beds, and light grey limestone. Interbeds of calcareous and dolomitized shale are common. Black chert is Photo 40. Looking south at Duo Lake(?) member 1 in a rare creek-cut exposure. Thin to medium beds of present in increasing amounts up-section as siliciclastic siltstone and very fine sandstone are thin interbeds in shale, and as lenses and separated by thick intervals of black, crumbly shale. irregular bands in limestone. Skeletal Cloudyf?) Formation tops the hill in the background fragments are rare. Platy limestone is present and has shed light grey scree down its slope. 628814E, in subordinate amounts. Minor rock types, 7210797N. exposed mainly as rubble and restricted to the area south of the AB Fault in the eastern part In one exposure near the base of the of the study area, include fine-grained, thinly formation, a few 15 cm thick beds of bedded, calcareous to dolomitic sandstone; dolostone are interspersed 1-2 m apart within platy, microcrystalline dolostone with the siliciclastic rocks. Minor black calcareous millimetre-scale lags of quartz sand, shale increases up-section. In the western part intraclasts, and chips of black chert; platy of the map area, an 80 m thick sub-member, limestone; silicified lime mudstone and black OSdlb, is distinguished by the first ooid grainstone; and a variety of post- appearance of widely spaced limestone depositionally modified, sediment gravity intervals 2-5 m thick (massive ash-grey flow breccias. The breccias generally form limestone or platy, dark grey, microcrystalline bedding-parallel bodies less than 1 m thick, limestone), and an increase in calcareous and consist of rubble packbreccia (to shale. Duo Lake(?) member 1 is 90-150 m floatbreccia) with clasts of limestone, thick north of the AB Fault, where member 1 polymict dolostone, and chert that are pebble directly overlies the Franklin Mountain to cobble-sized and subangular to rounded. Formation. In the west, member 1 (including Matrices range from finely crystalline sub-member 1 b) has a faulted base and is at dolostone invaded by later coarse, vuggy least 280 m thick. Member 1 is completely dolomite cement, to medium and coarsely missing in the east, where OSd2 overlies crystalline limestone or dolostone derived by Franklin Mountain Formation.

~~\\\ I ( i| 2(110-04 (>eoli>L!_\ (>l llie \B area, parts ol \I S I06( 16 and 1061 01 \ppcndi\ ( . Reprinted from \\\ I Open I ile 2010-04. I )issertation p. 22')~~

subangular to rounded, granule to cobble- sized, tabular or elongate, and aligned. Clast compositions are dolostone, laminated dolostone, and sandy dolostone. The matrix is finely crystalline dolostone, and locally coarse vuggy cement. The cement consists of orange dolomite rims, white calcite centres, black pyrobitumen smears on the calcite, and local quartz, sphalerite, and pyrite (Fog showing). In some samples, a mixture of calcite, sphalerite, pyrite, and pyrobitumen has replaced clasts. Photo 41. Looking west at thin-bedded, banded limestone of Duo Lake(?) member 2. Light grey Duo Lake(?) member 2 is partly to fully limestone bands are separated by very thin, yellow- dolomitized where it overlies the Franklin brown, silty, dolomitic limestone layers. Folding is due to Fault 2 footwall deformation. Hammer is 40 cm Mountain Formation in the southeast part of long. 630583E, 720728IN. the map area. In the far west, and north of the AB Fault, it overlies OSdl and is not replacement or recrystallization of particulate dolomitized. matter. Cone-in-cone structure is common in OSd2 south of the AB Fault, at the tops of Interpretation lime mudstone beds and around the tops of Age and correlation calcareous nodules (Photo 42). The Duo Lake Formation (Cecile, 1982) is a In the west part of the study area, a thick recessive unit up to 415 m thick, consisting of skeletal-intraclast rudstone is present near the black graptolitic shale, siliceous shale, and base of OSd2. South of the AB Fault, it has a thinly, rhythmically interstratified silty finely crystalline, brownish grey weathered limestone and shale with minor chert and limestone matrix (locally a skeletal volcanogenic sandstone. At its type section it wackestone matrix), and rounded, pebble to consists of a lower division of interbedded cobble-sized clasts of limestone, broken coral, shale and silty limestone overlain by an upper and skeletal wackestone (brachiopod, coral, division of siliceous shale, but it is not crinoid, graptolite?). The clasts form a divisible into members regionally, and varies randomly oriented framework. This unit is a great deal in carbonate, silica, and black tentatively correlated with a rudstone in OSd2 shale content. In the AB map area, the Duo north of the AB Fault. The latter is a Lake(?) Formation consists of a lower, yellowish grey weathered, graded, dolomitic recessive, black, graptolitic shale that floatbreccia with thick, poorly developed unconformably overlies the Franklin partings, a matrix of finely crystalline Mountain Formation, and an upper, siliceous dolostone, and boulder to pebble-sized clasts member that grades upward into the of limestone and isolated fossils that fine and Cloudy(?) Formation. These attributes suggest decrease upward to a laminated top. that the unit is equivalent to the Duo Lake Formation. An exposure of dolostone beds Of economic interest is a polymict rubble interstratified with black shale near the base packbreccia (to floatbreccia) in the southeast. of the formation (OSdl, above) may represent Exposed rubble traces the trend of a bed a tongue of Franklin Mountain Formation approximately 0.5 m thick. Clasts are (Cecile, 1982).

~~\\\ I <)l :0l0-04 of the \li area, parts ot \ I S lOftC I ft anil lOftl 01 \ppendi\ ( . Reprinted from \\\ I Open file 2(110-04. Dissertation p. 2.i(i~~

A presence of carbonate beds show that most deposition occurred below the storm wave base and above the carbonate compensation depth. The upward increase in carbonate and appearance of mottles reminiscent of A H burrowing activity suggest an overall shallowing and a concomitant increased oxygenation of the water over time. Decimetre-scale breccia bodies and metre- scale rudstone beds are attributed to sediment gravity flows, suggesting that the uppermost part of the unit was deposited on a slope. Most chert in the upper part of the unit exhibits evidence of secondary origin (in-situ growth structures and lenses that cross-cut bedding). Paleo-emsion In the east, south of the AB Fault, OSdl is missing; OSd2 lies directly on Franklin Mountain Formation. In this same area, the Franklin Mountain Formation is thinner than elsewhere. A single pre-OSd2 erosional hiatus could explain both the absence of OSdl and the thinner COf, but would require an unlikely transition of the depositional environment Photo 42. Cone-in-cone structure in Duo Lake(?) from basinal to subaerial and back again with member 2 just north of Fault 2. A) The top of a bed, no record of intervening shallow water. It is viewed perpendicular to bedding, showing long axes of more likely that OSdl was not deposited in prismatic calcite crystals. Pencil is 8 mm wide at this area or was substantially different than to widest visible part. 630586E, 7207288N. B) Bedding the north and west, and that movement on plane view of triangular cross-sections ofprismatic calcite crystals. Small lines on scale bar are 1 mm intervening faults placed the areas in apart. 630674E, 7207549N. proximity to each other.

The base of the Duo Lake Formation ranges Cloudy(?) Formation from earliest to latest Early Ordovician and its top ranges from latest Middle Ordovician to The Cloudy(?) Formation, exposed on late Early Silurian (Cecile, 1982). Both base mountain tops north of the AB Fault and and top young to the south, suggesting that in along the western edge of the map area, is at the AB map area, the Duo Lake(?) Formation least 130 m thick. It consists of thin to was deposited from Early through to Middle medium-bedded, ash grey weathered, dark Ordovician. grey lime mudstone (and locally, finely laminated calcisiltite) with up to 50% black Depositional environment chert in thin beds, lenses, and cross-cutting Black shale, thin primary chert beds, and amorphous bodies (Photos 43,44). The graptolites indicate that the unit was deposited limestone is finely to micro-crystalline and in quiet, deep, euxinic waters with a dearth of contains minor rugose coral debris. Intervals terrigenous input (i.e. sediment-starved). A 10-20 m thick are chaotically folded due to lack of current structures combined with the early post-depositional slumping. The

~~\\\ I Ol 2010-04 (ieoiou\ ol the \li area, parts ol \I S I0M Ktand I0M (II Xppciulix ( . Reprimed from \\\ I Open lite 201(1-04. I)i"«scriat!on p. 2~~

~~• > V- •/~~

Photo 43. Thin-bedded, dark grey lime mudstone with shaly partings, in Cloudy(?) Formation. The light grey bed at the hammer's head is of intraclast(-skeletal) rudstone to grainstone and represents a small debris flow. Hammer is 40 cm long. 628415E, 7210190N.

Photo 45. Heavily silicified intraclast(-skeletal) rudstone with skeletal(-intraclast) grainstone matrix in Cloudy(?) Formation debrite. A) Rubble. B) Outcrop showing normally graded bed. Clear pencil tip is 1.5 cm long. 628425E, 7210144N.

Photo 44. Lime mudstone of Cloudy (?) Formation. and solitary rugose corals, crinoids, bryozoa, Secondary black chert forms bedding-parallel bands and unidentified fragments. and cross-cutting masses. Hammer is 40 cm long. 626383E, 7211424N. Interpretation

limestone and chert are cut by irregular The Cloudy Formation in the Misty Creek veinlets of calcite and bitumen with quartz as Embayment ranges in age from Late the latest phase. Ordovician to Early Silurian (Cecile, 1982). It consists of up to 470 m of thin-bedded, sooty Overlying the limestone-chert succession, at grey weathered skeletal limestone, and minor least locally, is a coarse skeletal-intraclast(- shale, chert, and yellow limestone. Skeletal chert clast) rudstone with a skeletal packstone debris is silt to sand-sized. The purported matrix, in thick to medium beds which are Cloudy Formation in the AB map area differs rarely graded and locally silicified (Photo 45). somewhat from this description, in that it This rudstone is interstratified with medium contains markedly more chert and a beds of black chert and thin beds of recessive conspicuous interval of chaotic skeletal calcisiltite and lime mudstone. Skeletal rudstone; however, its overall lithological fragments in the rudstone beds are colonial characteristics and stratigraphic position

\\\ I (>| 2I» 10-04 (icoloyx ol tile \ B area, parls ol \ I S I06( 16 and 1061 01 .-N \ppeiu!i\ ( . Reprinted troni \\\ I Open 1'tic 2010-04. Disscrtaiioii p. 2M suggest it is equivalent to the Cloudy Formation. Cecile (1982) defines the base of the Cloudy Formation as the base of the first "thick" grey limestone above Duo Lake Formation shale, chert, or yellow limestone, and further states that the Cloudy Formation, above that basal limestone, can contain up to 40% shale that is indistinguishable from Duo Lake Formation shale. There is an interval of rudstone in the western part of the present map area that might conceivably be regarded as "thick", and therefore the base of the Cloudy Formation, but it is less than 10 m thick and has weathered a yellowish to brownish grey. It is therefore assigned to OSd2.

Cloudy(?) Formation limestone was deposited below the wave-base on a slope that became unstable after seafloor cementation had begun. Chert formation at least partially post-dated mesoscopic slumping and folding, because amorphous concentrations of chert cut across folded bedding planes. Chert also is present in bedding-parallel bands. Biological activity was low, at least at the base of the formation. Chaotic, graded beds of rudstone, separated from each other by thin beds of mudstone, were deposited as sediment gravity flows on the foreslope of a reef, which probably existed in the laterally equivalent Mount Kindle Formation on the platform to the (present-day) north.

~~\\\ i (>i :oio-o4 (icoloyx el'the \B area, parts ot \ I S I06( 16 and 1061 (.11 \|ipundi\ ( . Reprinted from \\\ I Open I ile 21)10-04. I)issciialion p. 2 >~~

Structure plunge of this syncline is responsible for an increase in the apparent thickness of Duo Lake(?) Formation in the west. Fault 9 is a Strata in the map area trend east to southeast steep fault forming a distinct, narrow trough and dip gently north and south. Steep bedding offsetting poorly exposed, shaly subunits of is present only in association with folds in the Duo Lake(?) Formation. Fault 4, which footwalls of reverse faults. Duo Lake(?) and juxtaposes Franklin Mountain Formation with Cloudy(?) Formation strata dip shallowly to Sekwi Formation, apparently terminates moderately north. Franklin Mountain against the AB Fault, though cover to the Formation bedding is flat lying to shallowly north precludes confirmation of this. north or south dipping. Sekwi Formation strata generally dip shallowly to moderately Fault 8 is an unusual, shallowly dipping northeast, with undulations creating flat to normal fault which has removed a significant southerly dips. Figures 5 and 6 are north-south thickness of Franklin Mountain Formation in cross-sections across the east and west ends of the west part of the map area (Fig. 6). There the map, respectively. are poor to no constraints on the mutual relationships of Faults 3, 4, 8, 9, and 10; the The structural character of the map area is interpretation on the map and cross-sections is dominated by faults. Eleven significant faults one of a few possible. are shown and labeled on the map; numerous faults of more limited extent are not shown. The ABC Fault is inferred by various lines of Additional mapping would certainly reveal evidence to have minimal offset (Fig. 5) and more faults. Two regional contractional faults to trend east from near the eastern termination traverse the area. The AB Fault is a steep of Fault 3, bending to trend northeast past the reverse fault that strikes east across the centre AB-C and Link showings. The evidence is, of the map, juxtaposing Cambrian and Early from west to east: destructive recrystallization Ordovician strata to the south against and patches of calcite-cemented brecciation in Ordovician-Silurian strata to the north (Photo Franklin Mountain Formation dolostone near 46). A regional syncline parallels the fault in the inferred western end of the fault; its footwall, and thin shale and limestone beds brecciation of a poorly exposed ooid in its immediate footwall are contorted. Fault dolograinstone in Sekwi Formation member 4 2, which strikes east across the south edge of near the head of ABC Creek; the westward the map, is a steep to moderately dipping termination of the three cliffs of Cs3; a slight reverse to thrust fault that brings Backbone offset in the ooid grainstone member 2b of the Ranges Formation up over younger units. Sekwi Formation; minor faults of the same trend offsetting Csl vuggy dolostone and Fault 3 is a steep splay of Fault 2 in the underlying dark, mottled dolostone at the western part of the map area. It has significant inferred eastern end of the fault; and negative displacement at its western end but less at its chargeability anomalies associated with the eastern end, suggesting rotation about a pin at northeastern-trending part of the fault (Eagle its east end. Destructive recrystallization Plains Resources Ltd. induced polarization (Photo 47), heavy multi-directional fracturing survey conducted in 2008, results and calcite veining, and minor calcite- proprietary). Two generations of rock-matrix cemented mosaic breccia are associated with fault breccia in the valley of ABC Creek north parts of Fault 3. A regional syncline parallels of the AB Fault (see COf coarse fragmental Fault 3 to its north, at least locally separated rocks) are on strike with the inferred ABC from it by a very tight anticline. The westerly Fault, which allows entertainment of the

~~\\\ I Ol 2IH0-O4 (,coK>y\ of ihc \B area. pariM>i \IS I06( I hand 1061 "(II 40 Dissertation p. 230~~

~~200~~

~~0Sd2 PCbu Cs4 PCbm~~

~~PCbi~~

~~Fault 2 Fault 5~~

~~nit contact lit contact nit contact, projected in air nit contact, projected in air~~

~~1QQQ91 axis~~

~~il axis~~

~~ith sense of movement~~

Figure 5. Cross-section A-A"". Note southeastward disappearance of Cs3 and Cs4, interpreted as their thinning on the flank of a deep, post-Sekwi, pre-Franklin Mountain paleovalley whose axis lay somewhere in the vicinity of A"'. PCb = Neoproterozoic - Lower Cambrian Backbone Ranges Formation; Cs = Early Cambrian Sekwi Formation; COf = Cambro-Ordovician Frank lin Mountain Formation; OSd = Ordovician-Silurian Duo Lake(?) Formation; OSc = Cloudy(?) Formation. Suffixes (1, lb, etc.) refer to members and sub-members described in the text See accompanying map for section location. Elevation in metres above mean sea leveL

~~NWT OF 20 41 I >!'-•. I1~~

~~2000m~~

~~OSc Cs4 »Sd2 OSdl~~

~~COf :bm~~

~~Cs2-3? PCbl~~

~~Fault 2~~

~~1000m Fault 3~~

~~Cs2-3?~~

~~Figure 6. Cross-section B-B'. PCb =tuntain Formation; OSd = Ordovi~~

~~\\\ i (>r :oio-o4 Appendix ('. Reprinted from \\\ I Open I'i'e 20i(1-04. Oi^ertation p. 22>6~~

Photo 46. A) Looking east along the AB Fault. Grassy hills of Duo Lake(?) member I are to the left of the fault. Sekwi (reddish brown) and Franklin Mountain (grey) formations are to its right, in the center and right of the photo. 628776E, 7209584N. B) Annotated photo. COfis Franklin Mountain Formation, Cs4 is member 4 of Sekwi Formation, OSdl and OSd.2 are members 1 and 2 of Duo Lake(?) Formation. Red labels refer to locations on the opposite (east) side of ABC Creek. map but the possible fault is not). Displacement along this fault is known to be minimal, because Cs2b is not offset southeast of the Point showings. How this fault intersects the ABC Fault, if it does extend to the Point showings, is unclear because the projected intersection is covered. A metre- scale offset in strata defines a west-trending fault (not shown on the map) that intersects the northwest fault in a zone of mineralized cemented breccia comprising the AB-C Upper showing. Sub-horizontal bands of gouge and dark, comminuted material at both AB and Photo 47. Destructively recrystallized dolostone typical AB-C Upper showings are indicative of sub- of Franklin Mountain Formation along Fault 3. Erik horizontal shearing related to regional Parker for scale. 628508E, 7208647N. compressive faulting.

possibility that movement or final movement The Mystery Fault is an east-striking, along the ABC Fault post-dates that along the moderately to steeply dipping reverse fault dolomite- AB Fault. The most extensive that developed during tight folding of the pyrite/marcasite±sphalerite±barite cemented Sekwi and overlying Franklin Mountain breccias are spatially associated with the ABC formations. The eastern end of the Mystery Fault and with the rock-matrix breccias in Fault is a blind thrust terminating beneath a lower ABC Creek. monoclinal anticline in the Franklin Mountain Formation. The monocline is also exposed 1.6 Rock-matrix breccia in the Sekwi Formation km to the east in the Sekwi Formation, northwest of the AB-C Upper showing suggesting that it is more than a local feature. indicates the presence of a northwest-trending Westward, the anticline tightens and Mystery fault, which may extend southeast as far as an Fault breaks through to the surface (Photo 48, exposure of rock-matrix breccia near the Point Fig. 5). Stratigraphic relations indicate about showings. (The breccias are shown on the 130 m of reverse displacement. Farther west

~~\\\ I (>1 2010-04 (icoIo^n of ihc \B area, parts oi \ i S !06( 16 and 1061 nl A} \ppeiuli\ ( . Reprinted from \\\ 1 Open I ile 201(1-04. Dissertation p. 237~~

Photo 48. Looking southeast from about 63032IE, 7208799N at Mystery Fault exposure. The associated anticline is right (south) of the fault. A) Sekwi member 2 is reddish brown; resistant band at top is member 2b. Franklin Mountain Formation and Sekwi member 3 (foreground) are light grey. B) Same photo, annotated Stratigraphic contacts are dashed black, Mystery Fault is solid blue, anticline/monocline axis is short-dashed grey. Cs2 and Cs3 are Sekwi members 2 and 3; COf is Franklin Mountain Formation.

~~\\\ I Of 2010-04 (leoloy) of the \B area, parts of \ 1 S I06C 16 and 1061 ()i 44 \ppcndi\ ( . Reprinted Irom \\\ I Open I ile 2010-04. Dissertation p. 2.^8~~

near the headwaters of the ABC Creek, the fault is inferred for stratigraphic reasons to follow the top of Sekwi member 3: recessive, orange-brown weathered strata above Cs3 (not visited) are along strike with strata identified as Cs2 above the Mystery Fault to the east; therefore, the fault here is inferred to separate Cs2 from structurally underlying, younger Cs3, as it does to the east. The Mystery Fault and associated folds may have developed in response to north-directed compressional forces in the footwall of Fault 2.

An alternative interpretation of Mystery Fault assigns the strata structurally above it to Sekwi Formation member 4. This is not unreasonable in itself, as Cs2 and Cs4 are lithologically similar; it would require only a facies change from detrital quartz-rich, locally oncolitic and oolitic limestone to quartz-poor, bioclastic limestone with a prominent ooid-skeletal interval. This interpretation would juxtapose Cs4 against a succession in which Cs4 is missing (north of Mystery Fault, Franklin Mountain Formation directly overlies Cs3 due to paleoerosion), which requires post-Sekwi, pre-Franklin Mountain faulting, assuming limited lateral motion on the fault. The absence of any specific evidence of pre-Franklin Mountain faulting has guided the interpretation shown on the map, but the alternative should be kept in mind, especially given the indirect evidence of tectonic activity in the Cambrian and Early Ordovician (see Franklin Mountain Formation - Interpretation - Paleo-erosion).

~~\\\ 1 Ol 2010-04~~

Alteration and mineralization compressive stress was roughly vertical (Cox et al., 2001). Fluid movement in such a stress regime would have acted on primary rock Pervasive and largely fabric-destructive layers with internal compositional variations, to dolomitization of Sekwi members 1 and 3 and produce these fabrics characterized by Franklin Mountain Formation is interpreted horizontal planes of vertically opening vugs. tentatively to be of burial-diagenetic origin, based on its lateral extents (which suggest it is Rock-matrix breccias formed in response to not due to localized fluid movement) and its either two separate faulting events or a single relative coarseness combined with vertical protracted one. Both events pre-date formation extents (which preclude it being primary). The of mineralized cemented breccia but post-date dolomite in dolomitic packstone, wackestone, burial diagenesis of Sekwi and Franklin and arenite of Cs2 and Cs4 is probably of Mountain formations and development of the burial diagenetic origin as well (it is selective dark, vuggy fabric. and of wide lateral extent). Dolomitization that affects Sekwi member 2 is fabric-retentive and Cemented breccias (described above in COf spatially related to mineralization. This coarse fragmental rocks and below in Sekwi dolomitization varies from complete (near Formation mineralization) appear to have showings), to partial or absent (between and formed during two separate events. The first, a away from the showings). Dolostone in the dolomite-sulphide ±barite event, cross-cuts and Duo Lake(?) Formation is of unidentified therefore postdates rock-matrix brecciation in origin. It is noteworthy that the only both formations. The second, a calcite event, is dolomitized rocks in Duo Lake(?) Formation best developed in Franklin Mountain are in the southeast part of the map area, where Formation, in association with destructive the greatest concentration of mineral showings dolomite recrystallization along Fault 3. There occurs; perhaps there is a genetic relationship. is no cross-cutting evidence of the age of the A fabric-destructive dolomite recrystallization calcite event with respect to the sulphide event of the Franklin Mountain Formation is or later dolomite veining, although calcite associated with Fault 3 (Photo 47). occurs as a late phase in some breccias of the sulphide event. Movement and fluid migration At least some silicification of the Franklin continued or recurred after the sulphide event, Mountain Formation preceded pervasive as recorded by dolomite-filled tension gashes dolomitization, preserving ooids that in and veins that cross-cut and displace earlier surrounding, unsilicified rock are barely visible marcasite-dolomite cemented breccia and veins ghosts. Remobilization of detrital quartz is (Photo 49). likely to have played a role in this early- diagenetic silicification (Hesse, 1990). The Mineralization is associated with the sulphide dark, vuggy fabric and zebra fabric in the cemented breccia, and occurs in Sekwi, Franklin Mountain and Sekwi formations are Franklin Mountain, and Duo Lake(?) restricted to locations along ABC Creek and formations. Host, size, and other basic Faults 3 and 4. Field evidence also indicates information for the main showings in the map that the dark, vuggy fabric and zebra fabric are area are presented in Table 1. Showings are variants of each other, and their occurrence is located on the accompanying map and in constrained by primary layering. It is therefore Figure 3. assumed that these fabrics were produced by fluid movement during the Cretaceous-Tertiary compressional orogeny, when the minimum

~~\\\ I Ol 2010-04 (>eolo-_\ of the \ B area, parts of \ I S ]()(,( I6and IOft I o; 4fi \ppcikli\ ('. Reprinted from N\\ I Open f ile 2010-04. Dissertation p. 240~~

and Jolt showings. Non-sulphide gangue consists of dolomite and barite, with subordinate local calcite, quartz, and pyrobitumen. The habits of these minerals, regarding all the Sekwi Formation showings collectively, are described in Table 2.

The disseminated to semi-massive style of mineralization at the AB and AB-C Lower showings consists of up to 40% coarse sphalerite concentrated in millimetre to centimetre-scale, anastomosing seams, bands Photo 49. Marcasite-rimmed, dolomite-cored vein is and lenses of dark, siliciclastic and organic-rich displaced by en echelon, dolomite-filled tension gashes, material in dark, mottled dolostone (Photo 52) indicating that at least some movement postdates the and (at AB only) in the matrix of an intraclast sulfidic cemented breccia event. Sekwi member 1 near dolorudstone (Photo 58). In showings the AF showing. Scale in millimetres. 631200E, 7209523N. dominated by the void-filling style, disseminated mineralization is present along Sekwi Formation mineralization the edges of breccia clasts (Photo 59) and at the peripheries of the showings (for example, there The bulk of the mineralization in the Sekwi is minor sphalerite in dark, mottled dolostone Formation is hosted within members 2a and 2b. overlying the AB-C Upper zone). At the AF In Cs2a, the most commonly mineralized rock showing, fine sphalerite and galena are type is a dark, bioturbated, mottled dolostone, disseminated along a 100 m strike length of but intraclast rudstone is a significant finely crystalline dolostone. secondary host. In Cs2b, ooid(-oncoid) dolograinstone is the mineralized lithofacies. The void-filling style of mineralization in the Restricted mineralization is present in finely Sekwi Formation is volumetrically the most crystalline dolostone of Csl and Cs3, and dark, abundant style. Sphalerite is present primarily mottled dolostone of Cs2c. In total, 12 as breccia cement, and less abundantly as zinc±lead showings hosted by Sekwi fracture-fill and vug-fill. At the AB-C Upper Formation have been found in the AB area. The and Link showings, sphalerite dominates the largest of these are AB, AB-C Lower, AB-C cement of a crackle to mosaic floatbreccia in Upper, and Link (Table 1). There are two dolograinstone. Centimetre to decimetre-scale, dominant styles of mineralization, disseminated cemented veins and voids separate to semi-massive and void-filling. Both styles characteristically angular dolograinstone are present at many of the showings. The AB-C fragments. The cement consists of marcasite- Lower showing is dominated by the sphalerite-dolomite-barite±quartz±calcite (in disseminated to semi-massive style. The AB order of deposition). The cement initially showing displays both styles in roughly equal precipitated along bedding planes (Photo 60), proportions. The AB-C Upper and Link but eventually brecciated the beds themselves. showings are dominated by the void-filling At the AB showing, the sphaleritic cemented style. rubble floatbreccia has been strongly affected by dissolution. Well-rounded, centimetre-scale Sulphide minerals at the Sekwi Formation clasts partly replaced by sphalerite float in showings are sphalerite, marcasite, pyrite, and sphalerite-barite-dolomite cement (Photo 59). galena. Smithsonite was noted at the Red Devil Unmineralized breccias at a number of

~~\\\ I ( >i 20 10-04 (n.'oloy\ of ilk- \B area. parts of \ IS 1 06C If> arid 106i 0 1 Appendix ( . Reprinted from \\\ I Open l ile 2D I (1-04. Dissertation p. 241~~

Table 1. Sphalerite (-galena-smithsonite) showings in the AB map area. The most important showings are shown in bold text. exposed size examined (thickness is Host for this stratigraphic/vertical Showing unit study exposure thickness) ore minerals mineral texture AF Csl no outcrop ~10m thick x 100 m sphalerite, finely, sparsely strike length, sparse galena disseminated & erratic Point vug Csl yes outcrop single isolated vug sphalerite, vug-filling galena AB Cs2a yes outcrop 2 zones 8 m apart sphalerite void-filling in dissolution stratigraphically, breccia 8t fractures, upper one 25 m, disseminated to semi- lower one 21.5m, massive covered between and along strike Point Cs2a yes outcrop localized sphalerite vug-filling, burrow/mould AB-C Cs2a yes outcrop <20 m along strike x sphalerite disseminated to semi- Lower 15 m thick massive AB-C Cs2b yes outcrop 50 m along strike x sphalerite void-filling in mosaic Upper 40 m across x 25 m breccia thick Link Cs2b yes outcrop 20 m along strike x sphalerite void-filling in mosaic 10 m across breccia Triple Cs2c yes weathered localized sphalerite void-filling in gossanous outcrop breccia, disseminated Grubby Cs3? no outcrop? localized sphalerite vug-filling Red Devil Cs3? no outcrop localized sphalerite, void-filling in veins smithsonite Jolt Cs3? no outcrop localized sphalerite, void-filling in veins smithsonte Smoke Cs4? no outcrop localized sphalerite void-filling in vein and breccia Duce COfla? no outcrop localized sphalerite, disseminated chalcopyrite Brisk COf yes rubble localized sphalerite vug-filling, disseminated DAB COf2b no outcrop 85 m along strike x sphalerite void-filling in dissolution 20m thick breccia, disseminated Twist COf no outcrop 15m x 30m sphalerite, void-filling in dissolution smithsonite breccia Twice COf no outcrop < 10m x 10m sphalerite, vug-filling, disseminated smithsonite Berger COf no outcrop localized smithsonite, disseminated sphalerite JJ COf no outcrop 75 m along strike x sphalerite, disseminated, void-filling in 15 m thick smithsonite veins Fog OSd2 Yes rubble localized sphalerite void-filling in mosaic breccia, disseminated

~~\\\ I Ol 2010-04 (ieoloy\ o! the \U area, parts of'\I S I06( 16 aiul 1061 01 48 Appendix ( . Reprinted from \\\ 1 < 'pen l ile 2010-04. Dissertation p. 242~~

Table 2. Habits of minerals in Sekwi Formation showings. Mineral Description Marcasite / Marcasite forms cockscomb rims of bladed crystals, up to 2 cm long, perpendicular to vein pyrite edges and breccia fragments. It also occurs alone, in veins (Photo 50), and in masses decimetres across (Photo 51). Marcasite is identified solely by its habit and may have reverted to pyrite. Fine pyrite forms rims on breccia fragments, invades the edges of fragments, fills fine fractures, collects along stylolites, and forms centimetre-scale clots in the host rock. Sphalerite Sphalerite occurs as fine to coarse, red or yellow, disseminated grains and aggregates from <1 mm to 2 cm in diameter, which commonly weather to a chalky white (Photo 52). Sphalerite in breccias commonly forms pale grey or yellowish green, 1cm thick rims, which locally consist of hemispherical, microcrystalline aggregates of sphalerite. These rims are present on host dolostone fragments (Photo 53, 54, 55) or on earlier rims of pyrite/marcasite. In vugs, sphalerite forms dull red weathered, equant crystals up to 3 cm in diameter (Photo 56) or 1-2 mm, green crystals. Galena Galena is not common. It is present as 1-2 mm, euhedral crystals in vugs, is disseminated as very fine grains, and fills hairline fractures. Dolomite Coarsely crystalline, white to orange dolomite, along with barite, occupies the central parts of breccia cements. Barite Coarsely crystalline, white barite, along with dolomite, occupies the central parts of breccia cements. Barite commonly assumes a bladed habit in radial aggregates (Photo 57). Quartz Rare quartz occurs as colourless, translucent, euhedral prisms up to 2 cm long, toward the centres of vugs and dolomite-barite veins. Calcite Coarse white calcite is a rare, late phase. Pyrobitumen Pyrobitumen occurs as amorphous globular masses 1 to 2 mm in diameter and as a sub- millimetre rim on a 3-cm sphalerite crystal from the Point showing (Photo 56).

~~t *** ji J-~~

Photo 50. Vein of marcasite at AB-C Upper showing Photo St. Cemented mosaic floatbreccia in Sekwi hosted by Sekwi member 2 b. Clear portion of pen is 8 member 2b at the AB-C Upper showing. All that cm long. 630482E, 7209183N. remains of the host rock is scattered, dark grey, angular fragments 2-4 cm in size, 'floating" in massive marcasite (ma). Openings within the marcasite are rimmed by dull, pinkish grey weathered sphalerite (sp) locations along ABC Creek have the same and filled by coarse, white barite (ba). 630482E, style as the mineralized breccias, for example, 7209183N. a marcasite-dolomite cemented breccia near the AF showing, and a marcasite-dolomite- Fracture and vug-filling mineralization is of barite breccia with barite crystals up to 10 cm subordinate importance to breccia-filling long near the Point showings (Photo 61). mineralization (Photo 62). Vug-filling

~~\\\ 1 Ol-2010-D4 lieoloLiN ol the \ B area, parts of \ 1 S H)(i( Hi and 10M 1)1 4<> \ppendi\( . Reprinted Irom \\\ IOpen I ile 201(1-04. Dissertation p. 243~~

~~dgst~~

Photo 52. Dark, mottled dolostone of Sekwi member 2a Photo 54. Sphalerite (sp) at the AB-C Upper showing at AB-C Lower showing. White-weathered sphalerite is forms a rim on a dolomite-barite (dm-ba)-filled vein in concentrated along argillaceous seams and ooid dolograinstone (dgst) of Sekwi member 2b. Scale disseminated lightly to moderately elsewhere. Slightly in millimetres. 630482E, 7209183N. rusty colour reveals similar, patchy distribution of pyrite. White at the bottom of the outcrop is an efflorescence due to weathering. Hammer handle is 2 , ! cm across. 630609E, 7209118N. 4'

~~> t ;.A~~

~~iv* '~~

Photo 55. Mineralized cemented breccia at the Link showing. A 6-10 mm rim of sphalerite (sp!) on ooid dolograinstone (dgst) of Sekwi member 2b is succeeded locally by development of sphalerite spheres of a Photo 53. Sphalerite (sp) at AB-C Upper showing in different colour (sp2), and by dolomite (dm). Barite Sekwi member 2b forms macrocrystalline hemispheres (ba) and quartz (qz) are the latest phases. Large on angular dolostone fragments. Orange dolomite fills divisions on scale-card are in centimetres. 631397E, the gaps. Scale in millimetres. 630482E, 7209183N. 7209410N. mineralization is the main style at the Point There is variability among the Sekwi showing, where one vug in dark, burrowed Formation showings in terms of detailed dolostone contains a 3-cm sphalerite crystal mineral paragenesis, but some generalizations (Photo 56). Also at the Point showing, can be made (Figure 7). The earliest phases sphalerite fills the spaces between detrital are marcasite and pyrite, and the latest are quartz grains in burrows or moulds (Photo usually calcite and quartz. At the Point Vug 63). A number of localized showings of minor occurrence, however, sphalerite grew in a vein and vug-filling sphalerite are present in void, attached to the intersection of two quartz Cs3. prisms, which had to have been there prior to the sphalerite crystal's growth. Sphalerite precipitated immediately after marcasite.

~~\\\ I Ol 2010-04 (ieolo:i\ of the \ B area. parts of N IS 106( 16 and 1061 0 50 Appendix ( . Reprinted Iroi \\\ 1 Open I lie 2010-04. Dissertation p. 244~~

Photo 56. Part of a 3 cm equant grain of red sphalerite Photo 58. Intraclast dolorudstone of Sekwi member 2 a from the Point showing in dark, mottled dolostone of at the AB showing is mineralized with sphalerite (sp), Sekwi member 2a. This sphalerite pre-dates dolomite, which is disseminated heavily in the matrix and weakly quartz, and pyrobitumen. The latter forms a visible, in clasts. Metal tip of pencil is 2 cm long. 627401E, sub-millimetre, black rim on the sphalerite. Scale in 7210079N. millimeters. Sample from 630900E, 7208895N. showing, which is in the west part of the map area, is markedly poor in iron sulphides, J* whereas the AB-C Lower showing contains a moderate amount, and the AB-C Upper and • .. Link showings contain abundant iron sulphides.

~~!• Sphaleritic cemented breccia in the Sekwi Formation cross-cuts rock-matrix fault breccia at the AB-C and Point showings, and is~~

X' therefore younger. It is texturally and compositionally identical to the cemented breccia affecting Franklin Mountain Photo 57. Radiating blades of barite, AB-C Upper Formation along the ABC Creek north of the showing. Scale in millimetres. 630506E, 7209I66N. AB Fault, except for the presence of barite and sphalerite in the Sekwi Formation; Dolomite, perhaps of more than one therefore, cemented breccias in the two generation, is inter-grown with all other formations are considered to be cogenetic. phases. Barite largely post-dates the main phase of dolomite. An early generation of Franklin Mountain Formation sphalerite or an early pulse of the same generation, predating all of the above, may be mineralization represented by the dark red grains of the Point showing, which are corroded along their Mineralization in the Franklin Mountain edges and replaced by pyrite, dolomite, and Formation is largely restricted to silicified quartz. dolostone and ooid dolograinstone of COf2, and consists primarily of void-filling There is variability in iron sulphide content sphalerite. Minor smithsonite has developed at among showings, but it cannot be described as many of the showings. Marcasite is a common zonation with the available data. The AB accessory mineral. Other gangue minerals are

\\\ I Ol 2010-04 (,eoloy\ iif the \ 15 area, parts of \ I S 1 <)<>(' 16 and 1061 Oi Photo 60. Beds of ooid dolograinstone 10-15 cm thick have been penetrated along bedding planes by marcasite-sphalerite-dolomite-barite cement. Sekwi member 2 b at the Link showing. Hammer is 40 cm long. 631397E, 7209401N.

Photo 59. Mineralized dissolution breccia in Sekwi member 2a at the AB showing. Sphalerite is disseminated in corroded host clasts (dst), and forms a cement (sp 'c) surrounding the clasts. Minor white dolomite/barite (dm/ba) fills gaps between the earlier sulfides. Sphalerite grains are pale greenish yellow (spl), commonly with red tips (sp2). and loaded with Photo 61. Cemented rubble packbreccia in Sekwi abundant fluid inclusions that give them a dusty member 1 near the Point showing. Rims of equant appearance, even in hand sample. Scales in dolomite grains line each rounded clast. Where clast millimetres. A) Sawn hand sample. B) Close-up of separation is great enough, the rim of dolomite is sawn hand sample. 627401E, 7210079N. followed by a rim of cockscomb marcasite and the gap is cored by barite and open space. Blue part of hammer handle is 19 cm long. 360916E, 7209006N. dolomite, quartz, and calcite. Sphalerite is fine to coarse-grained and red, green, or yellow. It extends for at least 85 m along strike. Its occupies the centres of centimetre-scale vugs, cement is dominated by coarse, pale green which are commonly rimmed by dolomite. It sphalerite with minor coarse, euhedral also lines the peripheries of carbonate±quartz dolomite. Smithsonite is a minor component. veins, in both vein and host. Together with The Twist showing, 400 m away and roughly dolomite, sphalerite forms the cement in along strike to the southeast, is similar, dissolution breccias, and locally is whereas the Twice showing, 500 m farther disseminated in unveined dolostone. along strike, is characterized by fine-grained sphalerite adjacent to calcite veins and The DAB showing is a dissolution breccia, concentrated in the darker, more- characterized by rounded fragments, that carbonaceous mottles of the host. South of the

~~\\\ I Oi 2(11 (1-04 (icoliiy \ ot ihc \ Huron, pans of VIS I<)(>(' I6aiul ]06i 01 Appendix ( . Reprinted from \\\ 1 Open 1 ile 2010-04. Dissertation p. 246~~

~~•• • ,M~~

Photo 62. Dark, mottled dolostone of Sekwi member 2a Photo 63. Coarse, reddish yellow sphalerite in at the AB showing. Fractures are filled with sphalerite, dolostone of Sekwi member 2 a at the Point showing is which is also concentrated in the rock adjacent to the restricted to burrows or moulds rich in terrigenous fractures. Pencil is 14 cm long. 630609E, 7209118N. detritus. 630885E, 7208864N. (Photo by Elizabeth Turner.)

~~pre-brecciation (deposition, diagenesis, localized cataclasis, preliminary brecciation -> post-brecciation mineralization-related dolomitization)~~

~~dolomite~~

~~pyrite/marcasite~~

~~sphalerite-galena~~

~~barite~~

~~quartz~~

~~calcite~~

~~Time:~~

~~Figure 7. Paragenesis of zinc±lead showings hosted by Sekwi Formation in the AB area.~~

AB Fault, the Duce showing differs from the mineralization is not accompanied by highly other Franklin Mountain Formation showings, visible signs of weathering such as gossan or in that it consists of fine chalcopyrite and fine heavy smithsonite development, and is easily grains to coarse blebs of sphalerite in a overlooked. laminated host (tentatively identified as dolomitic quartz arenite of COfl, though the showing was not visited as part of this study). In general, Franklin Mountain Formation

~~W\ I Ol 2010-04 (ieolou\ of the \B area, parts of \I S I06( Kianil MI (i| Appendix ( . Reprinted from \\\ I Open I ile 20 10-04. Dissertation p. 247~~

~~Duo Lake(?) Formation mineralization~~

Lead-zinc ineralization in Duo Lake(?) Formation is not widespread in the exposures visited, although pyrite is a common accessory mineral in siliciclastic siltstone and shale. The Fog showing in OSd2 contains sphalerite cement and disseminated sphalerite in a pre-existing rock-matrix dolostone breccia (debrite?). A dolomite-calcite- pyrobitumen-quartz-sphalerite-pyrite cement invaded the matrix of the breccia, re- brecciating it in places, and certain clasts have been replaced by a coarse mixture of calcite- sphalerite-pyrite-pyrobitumen.

~~\\\ I Ol 2010-04 (icoIplin ol the \B area, purls ol \I S I06( i(>und I0(>i t> I \ppendi\ ( . Reprinted from WV'I Open file 2010-0-1. Dissertation p. 248~~

Stratigraphic, diagenetic, and the possibility of significant movement along intervening faults cannot be discounted. structural summary Mapping outside the AB area and a detailed structural study are required to improve stratigraphic understanding. The Sekwi Formation in the AB area records development of a carbonate ramp with ooid Burial diagenesis of the Sekwi Formation shoals and a shallow, biologically active filled pore spaces with calcite cement, caused lagoon in the Early Cambrian. A mid-ramp minor dolomitization of selected grains in lithofacies is succeeded by a shallowing-up skeletal units, and caused pervasive sequence, consisting consecutively of a dolomitization of member Cs3. Pervasive mobile shoal, an inner-ramp lagoon, and a dolomitization of Cs2 is spatially restricted to possible back-ramp foreshore. This succession the vicinity of showings, and was caused by is overlain by deeper-water, mid-ramp facies. the mineralizing fluids. The unique diagenetic history of the Franklin Mountain Formation An interval of erosion is recorded by a deep included early, pervasive silicification of the valley incised into the Sekwi Formation. Early upper part of the unit, perhaps because it was Ordovician deposition of the Franklin rich in primary quartz detritus, and later, Mountain Formation began with cross-bedded pervasive dolomitization of the entire sands in the eroded valley and a thick formation. There is no relationship between succession of well-bedded carbonate silt and dolomitization and mineralization in the sand elsewhere, and later consisted of quartz- Franklin Mountain Formation. sandy, microbial, and oolitic carbonates deposited on a shallow, open marine shelf. An Bedding trends east to southeast and dips interval of erosion after Franklin Mountain gently north or south. Numerous compressive time is suggested by local thinning of that and normal faults of probable Cretaceous to unit, which is most intense above the Sekwi Tertiary age disrupt the strata. The AB Fault paleo-valley. Fine, siliciclastic sediment of the and Fault 2 are sub-parallel, east-striking, basal Duo Lake(?) Formation reflects deep, thrust to reverse faults of regional extent that quiet, euxinic waters of the Misty Creek dominate the map. Tight folds, which parallel Embayment, which encroached into the area these major compressive faults in close from the southwest in the late Early proximity to them, developed in response to Ordovician and Middle Ordovician. The local the same stress regime. The best-developed absence of lower Duo Lake(?) Formation mineralization is in the Sekwi Formation remains unexplained. Shallowing of the between these two regional faults. Important embayment proceeded with deposition of mineralization is also present in Franklin increasing amounts of limestone interstratified Mountain Formation north of the AB Fault. with siliciclastic sediment of the upper Duo Lake(?) Formation. The overlying limestone Faulting created a major zone of dual- of the Cloudy(?) Formation records further generation cataclasite in the Franklin shallowing and development of a carbonate Mountain Formation as well as minor zones in slope, as a carbonate platform to the east the Sekwi and Franklin Mountain formations. (Mount Kindle Formation) prograded into the This faulting preceded development of embayment. mineralized cemented breccia in the Sekwi Formation and cogenetic, unmineralized Stratigraphic correlations among different cemented breccia in the Franklin Mountain areas of the map must remain tentative, since Formation, but its temporal relationship with

~~\\\ I (>1 2010-0-1 (leoloyx ofthe \ B are;i. parts ol \I S ] 06( l(>and 1061 ol \ppendi\ ('. Reprinted from \\\ I Open file 201(1-04. I)issertulion p. 249~~

Laramide faulting is unknown. Calcite- cemented veins and breccias post-date the main mineralization, but it is not known by how much. Fault 3 was a major fluid conduit, as expressed by destructive dolomite recrystallization and decimetric patches of void-filling calcite. The close association between sphalerite and calcite veins at the Twice showing indicates that the calcite event at least locally remobilized or precipitated sulphides.

~~\\\ I Ol 20 10-04 (leoioyx of the \B area, parts of \ IS ]06< 16 and 1061 01 \ppendi\ ( . Reprinted from WVIOpen I ile 2010-04. Dissertation p. 250~~

Conclusions suggested for deposits in the Irish Midlands (Hitzman and Beaty, 1996). • Susceptible rock types in Sekwi This study has highlighted three key controls Formation are those with millimetre to on mineralization, which are structural, centimetre-scale variations in stratigraphic, and lithologic: mineralogy, and therefore in alteration • Fractures and faults at multiple scales, potential. These consist primarily of from microscopic to regional, are clean (mud-free), ooid-dominated spatially associated with all dolograinstone, and dark, burrow- mineralization, and are a first-order mottled dolostone with high organic control. It is likely that regional and and siliciclastic content. These rock property-scale faults, although barren, types are common throughout the served as conduits, whereas Sekwi Formation, but are an important microscopic and mesoscopic fractures control on mineralization only in localized precipitation in susceptible proximity to fluid conduits and low in rocks. Furthermore, it has been the local stratigraphic succession. Less mentioned (in Franklin Mountain is known about prospective rock types Formation - Interpretation - Paleo- in the Franklin Mountain Formation, erosion) that an unidentified tectonic but known showings are largely control must have influenced restricted to the upper silicified unit, topography from the Early Cambrian member COf2b. until at least the Early Ordovician, causing deep erosion in the same place Consideration of the first-order controls on at two separate times. The location of mineralization, in conjunction with the the AB-C and Link showings along the mapped geology, leads to identification of edge of this paleo-valley suggests that areas both inside and external to the map area, mineralization may have been where mineralization is likely to be present: influenced by the same, underlying • Prospective Sekwi Formation strata tectonic control. may not be far below the surface in the • Susceptible rock types are more north part of the map area. These prospective where they are present at covered strata are likely to be the the base of the local stratigraphic lowest susceptible units and may host succession. For instance, the greater concentrations of metals than dolograinstone of Sekwi member 4 is the stratigraphically higher DAB not mineralized whereas that of showing. member Cs2 is. As another example, • At-depth and along-strike extensions Franklin Mountain Formation is not of the cement-breccia zone along the well mineralized south of the AB ABC Creek are prospective. The Fault, where it overlies susceptible absence of barite and sphalerite in the lithofacies in the Sekwi Formation. Franklin Mountain Formation breccia, These empirical observations can be and their presence in presumably explained by fluids rising along cogenetic Sekwi Formation breccia, structural conduits and precipitating supports the notion of a stratigraphic their metal content in the first- control (if brecciation pre-dates encountered (stratigraphically lowest) faulting) or a lithologic control (if suitable rock units, as has been brecciation post-dates faulting).

~~\\\ I (>1 2010-04 (ieoloL:\ of the \R area, parts of\IS !06( I<>andl06| [)| \ppeiidi\ ( . Reprinted from \\\ I Open l ile 201 f 1-04 Dissertation p. 25 I~~

~~• Regionally, the hanging wall of the AB Fault is prospective where it contains Sekwi Formation rocks that are susceptible to mineralization (as explained above) and cross-cut by meso-scale faults.~~

~~\\\ I ()l 20 10-(M (ieok-L!\ ol'the \R area, parts ol\ IS I0M ihaiuMOM ()| Appendix ( . Reprinted trom \\\ I Open file 2010-04. Dissertation p. 252~~

~~Acknowledgements~~

This study was part of an M.Sc. project being carried out at Laurentian University and supervised by Elizabeth Turner and Dan Kontak. The project was made possible by the Northwest Territories Geoscience Office (Sekwi Mountain Project) and Eagle Plains Resources Limited. We especially thank Bob Sharp (Trans Polar Geological Consultants Inc.) and Edith Martel who collaborated on logistical details, Aaron Higgs who facilitated the mapping with good management, Glen Hendrickson who provided data and network support in the field, the entire 2009 Eagle Plains crew, Brent Vansickle of Fireweed Helicopters, and Elizabeth Turner of Laurentian University.

Legend layout, map surrounds, and annotation were created in ArcGIS 9 by Kelly Pierce. Drafting assistance was provided by Ben Borkovic. The final product was enhanced by a detailed review from Luke Ootes. An earlier draft was reviewed by Elizabeth Turner.

~~W\ I ( >1 2010-04 (leokigv ci the \B are,i. parts ot \IS I06C Kiand 1061 01 \ppendi\ ( . Reprinted I'roni \\\ I Open I ile 2010-04. Dissertation p. 25~~

~~References~~

~~Aitken, J.D., 1989. Uppermost Proterozoic formations in central Mackenzie Mountains, Northwest Territories; Bulletin 368, Geological Survey of Canada, Ottawa, Canada, 26 p.~~

Aitken, J.D. and McMechan, M.E., 1992. Chapter 5, Middle Proterozoic assemblages; In Geology of the Cordilleran Orogen in Canada, edited by H. Gabrielse and C.J. Yorath; Geology of Canada, n. 4, p. 151-218, Geological Survey of Canada, Ottawa (also published as The Geology of North America, vG-2; Geological Society of America).

Aitken, J.D., Macqueen, R.W., and Usher, J.L., 1973. Reconnaissance studies of Proterozoic and Cambrian stratigraphy, lower Mackenzie River area (Operation Norman), District of Mackenzie. Paper 73-9, Geological Survey of Canada, Ottawa, Canada, 178 p.

Aitken, J.D., Cook, D.G., and Yorath, C.J., 1982. Upper Ramparts River (106G) and Sans Sault Rapids (106H) map areas, District of Mackenzie, Memoir 388, Geological Survey of Canada, Ottawa, Canada, 48 p.

~~Ball, M.M., 1967. Carbonate sand bodies of the Bahamas and Florida; Journal of Sedimentary Petrology, v. 37, n. 2, p. 556-591.~~

~~Blusson, S.L., 1974. Five geological maps of northern Selwyn Basin (Operation Stewart), Yukon Territory and District of Mackenzie, NWT; Open File 205, Geological Survey of Canada, Ottawa, Canada.~~

~~Boggs, S., 1987. Principles of Sedimentology and Stratigraphy; Pearson Prentice Hall, Upper Saddle River, USA, 662 p.~~

Carney, C. and Boardman, M.R., 1993. Trends of sedimentary microfabrics of ooid tidal channels and deltas; In Carbonate Microfabrics, edited by R. Rezak and D.L. Lavoie; Frontiers in Sedimentary Geology series, p. 29-39, Springer-Verlag, New York, USA.

~~Cecile, M.P., 1982. The Lower Paleozoic Misty Creek Embayment, Selwyn Basin, Yukon and Northwest Territories; Bulletin 335, Geological Survey of Canada, Ottawa, Canada, 78 p. and 1 map.~~

~~Cecile, M.P., 2000. Geology of the northeastern Niddery Lake map area, east-central Yukon and adjacent Northwest Territories; Bulletin 553, Geological Survey of Canada, Ottawa, Canada, 119 p.~~

Clough, J.G. and Goldhammer, R.K., 2000. Evolution of the Neoproterozoic Katakturuk Dolomite ramp complex, northeastern Brooks Range, Alaska; In Carbonate Sedimentation and Diagenesis in the Evolving Precambrian World, edited by J.P. Grotzinger and N.P. James; Special Publication No. 67, p. 210-241, SEPM (Society for Sedimentary Geology), Tulsa, USA.

~~Cox, S.F., Knackstedt, M.A., and Braun, J., 2001. Principles of structural control on permeability and fluid flow in hydrothermal systems; Society of Economic Geologists, Reviews v. 14, p. 1-24.~~

~~\\\ I Ol 2010-04 (,eoloy\ of the \IS area, parts ofA I S I0M 16 and ] 061 (II 60 \ppetuli\ ( . Reprinted Ironi W\ I Open I ile 20 10-1)4. Dissertation p. 25-1~~

~~Dilliard, K.A., 2006. Sequence stratigraphy and chemostratigraphy of the Lower Cambrian Sekwi Formation, Northwest Territories, Canada; Ph.D. Thesis, Washington State University, Pullman, Washington.~~

Dilliard, K., Pope, M.C., Coniglio, M., Hasiotis, S.M., and Lieberman, B., 2007. Stable Isotope Geochemistry of the Lower Cambrian Sekwi Formation, Northwest Territories, Canada: Implications for ocean chemistry and secular curve generation; Palaeogeography, Palaeoclimatology, and Palaeoecology, v. 256, p. 174-194.

~~Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture; AAPG Memoir 1, American Association of Petroleum Geologists, p. 108-121.~~

~~Eisbacher, G.H., 1981. Sedimentary tectonics and glacial record in the Windermere Supergroup, Mackenzie Mountains, northwestern Canada; Paper 80-27, Geological Survey of Canada, Ottawa, Canada, 40 p.~~

~~Eisbacher, G.H., 1983. Devonian-Mississipian sinistral transcurrent faulting along the cratonic margin of western North America: A hypothesis; Geology, v. 11, p. 7-10.~~

~~Embry, A.F. Ill and Klovan, J.E., 1971. A late Devonian reef tract on northeastern Banks Island; N.W.T. Bulletin of Canadian Petroleum Geology, v. 19, n. 4, p. 730-781.~~

~~Fritz, W.H., 1972. Lower Cambrian trilobites from the Sekwi Formation type section, Mackenzie Mountains, northwestern Canada; Bulletin 212, Geological Survey of Canada, Ottawa, Canada, 90 P-~~

~~Fritz, W.H., 1976. Ten stratigraphic sections from the lower Cambrian Sekwi Formation, Mackenzie Mountains, northwestern Canada; Paper 76-22, Geological Survey of Canada, Ottawa, Canada, 42 p.~~

~~Fritz, W.H., 1978. Fifteen stratigraphic sections from the Lower Cambrian of the Mackenzie Mountains, northwestern Canada; Paper 77-33, Geological Survey of Canada, Ottawa, Canada, 19 p.~~

~~Fritz, W.H., 1979. Eleven stratigraphic sections from the Lower Cambrian of the Mackenzie Mountains, Northwestern Canada; Paper 78-23, Geological Survey of Canada, Ottawa, Canada, 19 P-~~

Fritz, W.H., 1982. Vampire Formation, a new upper Precambrian(?)/Lower Cambrian Formation, Mackenzie Mountains, Yukon and Northwest Territories; Paper 82-IB, Geological Survey of Canada, Ottawa, Canada, p. 83-92.

Fritz, W.H., 1985. The basal contact of the Road River group - a proposal for its location in the type area and in other selected areas in the northern Canadian Cordillera; Current research part B, Paper 85-IB, p. 205-215, Geological Survey of Canada, Ottawa, Canada.

Fritz, W.H., Cecile, M.P., Norford, B.S., Morrow, D., and Geldsetzer, H.H.J., 1992. Chapter 7, Cambrian to Middle Devonian assemblages; In Geology of the Cordilleran Orogen in Canada, edited by H. Gabrielse and C.J. Yorath; Geology of Canada, n. 4, p. 151-218, Geological Survey of

~~\\\ I Ol 2(1 i(MM (leolo^N ol the \B area, parts ol \ 1 S HIM Hi and 10M 01 \ppendi\ ( . Reprinted troni \\\ I Open 1'ile 2010-04. Dissertation p. 2~~

~~Canada, Ottawa, Canada {also published as The Geology of North America, vG-2, Geological Society of America).~~

Gabrielse, H., Blusson, S.L., and Roddick, J.A., 1973. Geology of Flat River, Glacier Lake, and Wrigley Lake map-areas, District of Mackenzie and Yukon Territory; Memoir 366, Geological Survey of Canada, Ottawa, Canada, 153 p., 3 maps.

Gordey, S.P. and Anderson, R.G, 1993. Evolution of the northern Cordilleran miogeocline, Nahanni map area (1051), Yukon and Northwest Territories; GSC Memoir 428, Geological Survey of Canada, Ottawa, Canada, 214 p.Gordey, S.P. and Makepeace, A.J. (compilers), 2003. Yukon digital geology, version 2.0; YGS Open File 2003-9(D), Yukon Geological Survey, Whitehorse, Canada, 1 disc.

Gordey, S.P., Roots, C.F., Martel, E., MacDonald, J., Fallas, K., MacNaughton, R., Leslie, C., and Fischer, B., 2009. Preliminary bedrock geology, Mount Eduni (106A), Northwest Territories, Canada; NWT Open Report 2008-014, Northwest Territories Geoscience Office, Yellowknife, Canada, 1 map, 1:125,000 scale (also published as Open File 5984, Geological Survey of Canada, Ottawa, Canada).

Gordey, S.P., Geldsetzer H.H.J., Morrow D.W., Bamber E.W., Henderson C.M., Richards B.C., McGugan A., Gibson D.W., Poulton T.P., 1992. Chapter 8, Upper Devonian to Middle Jurassic assemblages. In Geology of the Cordilleran Orogen in Canada; Gabrielse, H. and Yorath, C.J. (editors), Geology of Canada, n. 4, p. 151-218, Geological Survey of Canada, Ottawa, Canada (also published as The Geology of North America, vG-2, Geological Society of America).

Handfield, R.C., 1968. Sekwi Formation, a new Lower Cambrian formation in the southern Mackenzie Mountains, District of Mackenzie (95L, 1051,105P); Paper 68-47, Geological Survey of Canada, Ottawa, Canada, 23 p.

~~Hesse, R., 1990. Silica diagenesis: origin of inorganic and replacement cherts; In Diagenesis; p. 253-275, Geological Association of Canada, St. John's, Canada.~~

Hitzman, M.W. and Beaty, D.W., 1996. The Irish Zn-Pb(-Ba) orefield; In Carbonate-Hosted Lead- Zinc Deposits, 75th Anniversary Volume, edited by D.F. Sangster; Society of Economic Geologists, Special Publication No. 4, p. 112-143.

~~Ingrain, R.L., 1954. Terminology for the thickness of stratification and parting units in sedimentary rocks; Bulletin of the Geological Society of America, v. 65, p. 937-938.~~

Krause, F.F. (Schroeder-), 1979. Sedimentology and stratigraphy of a continental terrace wedge: the Lower Cambrian Sekwi and June Lake formations (Godlin River Group), Mackenzie Mountains, Northwest Territories, Canada; Ph.D. Thesis, University of Calgary, Calgary, Canada.

Krause, F.F. and Oldershaw, A.E., 1978. Stratigraphic and paleoenvironmental analysis of the Sekwi Formation, Mackenzie Mountains, Northwest Territories; In Mineral Industry Report 1975, Northwest Territories, edited by P.J. Laporte, W.A. Gibbins, E.J. Hurdle, C. Lord, W.A. Padgham, and J.B. Seaton; EGS Open File 1978-5, p. 136-156, Dept. Indian Affairs and Northern Development, NWT Geology Division, Yellowknife, Canada.

~~\\\ I Ol 20 ! 0-04 (iei>lou\ (if the \B area, parts ot \ I S 106( 16 and |0~~

Krause, F.F. and Oldershaw, A.E., 1979. Submarine carbonate breccia beds; a depositional model for two-layer, sediment gravity flows from the Sekwi Formation (Lower Cambrian), Mackenzie Mountains, Northwest Territories, Canada; Canadian Journal of Earth Sciences, v. 16, n. 1, p. 189- 199.

~~MacNaughton, R.B., Dalrymple, R.W., and Narbonne, G.M., 1997. Early Cambrian braid-delta deposits, Mackenzie Mountains, north-western Canada; Sedimentology, v. 44, p. 587-609.~~

MacNaughton, R.B., Roots, C.F., and Martel, E., 2008. Neoproterozoic-(?)Cambrian lithostratigraphy, northeast Sekwi Mountain map area, Mackenzie Mountains, Northwest Territories: new data from measured sections; Current Research 2008-16, Geological Survey of Canada, Ottawa, 15 p.

McArthur, G.F. and McArthur, M.L., 1977. Geological and geochemical report on the AB-BB- DAB mineral claims (AB Project), Mackenzie Mining District, NTS 106C16, Northwest Territories, Canada, Work performed July 15 - September 2, 1976; Unpublished Assessment Report 080621, Dept. Indian Affairs and Northern Development, NWT Geoscience Office, Yellowknife, Canada.

McMechan, M.E., Thompson, R.I., Cook, D.G., Gabrielse, H., and Yorath, C.J., 1992. Structural styles Part E: Foreland Belt; In Geology of the Cordilleran Orogen in Canada, edited by H. Gabrielse and C.J. Yorath; Geology of Canada n. 4, p. 634-650, Geological Survey of Canada, Ottawa, Canada. (also published as The Geology of North America, v. G-2, Geological Society of America.)

~~Morrow, D.W., 1982. Descriptive field classification of sedimentary and diagenetic breccia fabrics in carbonate rocks; Bulletin of Canadian Petroleum Geology, v. 30, p. 227-229.~~

~~Narbonne, G.M. and Aitken, J.D., 1995. Neoproterozoic of the Mackenzie Mountains, northwestern Canada; Precambrian Research, v. 73, p. 101-121.~~

Norford, B.S. and Macqueen, R.W., 1975. Lower Paleozoic Franklin Mountain and Mount Kindle formations, District of Mackenzie: Their type sections and regional development; Paper 74-34, Geological Survey of Canada, Ottawa, Canada, 37 p.

~~Norris, D.K., 1982. Geology, Snake River, Yukon-Northwest Territories; Map 1529A, Geological Survey of Canada, Ottawa, Canada.~~

Norris, D.K. (editor), 1997. Geology and mineral and hydrocarbon potential of northern Yukon Territory and northwestern District of Mackenzie; Bulletin 422, Geological Survey of Canada, Ottawa, Canada, 401 p.

~~Riding, R., 2000. Microbial carbonates: the geological record of calcified bacterial-algal mats and biofilms; Sedimentology, v. 47 (Suppl. 1), p. 179-214.~~

~~Tucker, M.E. and Wright, V.P., 1990. Carbonate Sedimentology; Blackwell Science, Maiden, USA, 482 p.~~

~~\\\ I ( >1 2010-04 (leoloys ol the \ 1! area, part1- of \ I S |0(i( 16 and 1061'01 \ppeiuli\ ( . Rqirintal from \\\ 1 Open 1 ilc 20 1(1-04. Dissertation p. 257~~

~~Appendix I - Classification of carbonate rocks inciuding breccias~~

~~The classification of carbonate rocks used in this study is shown in Table 1-1. This classification is derived largely from Dunham (1962) as modified by Embry and Klovan (1971).~~

Terminology for carbonate breccias follows the suggestions of Morrow (1982). In brief, Morrow suggests a three-part, non-genetic name. The root, or third, term is either "packbreccia" or "floatbreccia", and expresses the tightness of fragment packing. Comparable adjectives are "fragment-supported" and "matrix-supported", respectively.

The second term is one of "crackle", "mosaic", or "rubble", expressing a continuum in degree of dissociation and rotation of fragments with respect to each other. Equivalent terms include "fitted- fabric" for mosaic and crackle breccias, and "fracture pseudo-breccia" for crackle breccia.

The first term is either "cement" or "particulate" and refers to the nature of the matrix. In this report, the term "particulate" is replaced with "rock-matrix". The term "particulate" is misleading in the area studied, because it implies that the original matrix was particulate, not cement. It is sometimes difficult in the field to distinguish between a replaced or recrystallized particulate matrix and a finely crystalline cement. "Vein breccia" is an equivalent term to "cemented breccia".

Typical carbonate breccia names therefore include the following: cemented rubble packbreccia, rock-matrix rubble floatbreccia, cemented mosaic packbreccia. Modifiers pertaining to fragment size, composition, sorting, angularity, and other characteristics are generally required to complete the description. The term "cemented" may be substituted for by the names of constituent cement phases, as in dolomite-marcasite crackle packbreccia.

\\\ I Ol 2010-04 (icoloy> ot tlk' \B area. parts ol \ I S ]()(>( I (> and 1061 0 I 1 '• |>|V!k]l\ < h.v'pi IliU'd Ml'III W\ j I >[V1. I -U 2' • i I :1 Kil !«'!:(• r Depositions textire Depositions texture recognizable NOT recognizable Autochthonous (components organically Alfochthonous bound during deposition) by by by organisms organisms GRAINS BIG (>10% organisms GRAINS MOSTLY SMALL (<10% components >2mm) that build a that components >2mm) that act as rigid encrust baffles framework and bind cement Matrix- Grain- Contains lime mud (<0.03mm) instead of supported supported mud GRAIN Mud/silt-supported doloetone (if made SUPPRTD of dolomite) MOSTLY MANY framestone bindstone bafflestone MOSTLY MUD SILT (<10% GRAINS (stalk- or recryatallized (<10% grains) grains) (>10% grans) (skeleton- (matrix- shaped limestone (if made grainstone floatatone rude tone supported) supported) fossils) of calcite) lime mudatone calcisHttte wackestone Imat cist wet P*t gat fat rat frst bnst bfst dst or xlst boundstone (bet) add crystal-size add granviype prefix* add organism prefix* prefix* I I I I orve a full name to the matrix add dolomite prefix* add temoenous-cornponent prefix* 'prefixes: • arain-tvDe prefix: e.g., ootd (usually <2mm, regular concentric lamellae), oncoid (>2 mm, irregular lamellae), peloid («mm, no fabric), tntrectast, tkefetal (or name(s) of organisms) • organism prefix: e.g., coral, bryozon, stromatoporoid, etc. • lerrioenous-component prefix for mixed terrigenous-carbonate rocks where carbonate > 50%: one of argillaceous, silicidastic-silty, quartz-sandy for mud, silt, and sand-sized terrigenous particles, respectively • dolomite prefix: doiomittc if partially dolomitized; dofo- or dolomitized if fully dolomitized For use vrtren depositions texture is visible; use 'dolostone' if not. • crvami-size prefix from Table 1-2

Examples: Ooid-intraclast-sketetal wackestone. Argillaceous lime mudstone. Microbial boundstone. Dotomrtic oncoid ftoatstone with ooid grainstone matrix. Trilobite dolofloatstone Finely crystalline dolostone

The above applies to carbonate rocks, defined as those with >50% carbonate component. For mixed terrigenous-carbonate rocks where the carbonate component is < 50%, use carbonate modifiers with the terrigenous-rock root name, as follows: 1. if the carbonate occurs as a cement, use calcareous (bound by calcite cement) or dolomltic (bound by dolomite cement), for example, calcareous siftstone; 2. if the carbonate occurs as grains, create an appropriate modifier from the carbonate mineral type and grain type (e.g. limestone intrsiciastic sandstone).

~~Table 1-1. Classification of carbonate rocks. Based on Embry and Klovan's (1971) modification of Dunham (1962). \ppendi\ ( . Reprinted !ixnn \\\ i ('pen lile 20 10-0-1 Dissertation p. 259~~

~~Appendix II - Grain size and bedding thickness terminology~~

Grain and crystal size terminology used in this study is based on the Udden-Wentworth scale (e.g., Boggs, 1987), modified for use with carbonate crystal sizes (Table II-l). Microcrystalline and cryptocrystalline sizes cannot be distinguished with a hand lens, therefore the term microcrystalline is used to encompass both during fieldwork.

Crystal size mm (decimal) Grain size urn mm (fraction) >256 boulder megacrystalline >4 64-256 cobble 4-64 pebble 2-4 granule very coarsely crystalline 1-4 1-2 very coarse sand coarsely crystalline .5-1 coarse sand 500-1000 %-1

medium crystalline .25 - .5 medium sand 250 - 500 1A - 7* finely crystalline .125-25 fine sand 125-250 1/8-% very finely crystalline .063- 125 very fine sand 63 -125 1/16-1/8 .032 - .063 coarse silt 32-63 1/32 -1/16 .016 - .032 medium silt 16-32 1/64 -1/32 microcrystalline .004 - .063 .008-.016 fine silt 8-16 1/128-1/64 .004 - .008 very fine silt 4-8 1/256-1/128 cryptocrystalline <004 clay <4 < 1/256

~~Table II-l. Grain and crystal size terminology.~~

Bedding and parting thickness terms (Table 11-2) follow those suggested by Ingram (1954), with the exception that his "extra thinly parted" and "super thinly parted" have been combined here into one term.

Thickness (cm) Term for stratification Term for parting >100 very thickly bedded very thick 30-100 thickly bedded thick 10-30 medium bedded medium 3-10 thinly bedded thin 1-3 very thinly bedded very thin 0.3-1.0 thickly laminated extremely thin <0.3 thinly laminated

~~Table II-2. Stratification and parting thickness terminology.~~

\\\ I < >1 20 I 0-04 (tcoloy) of the \H area, parts ot \ I S I06C 16 and |06i 0 Appendix D. Use of the cycling technique for microthermometric measurements of temperatures of homogenization in fluid inclusions

Goldstein and Reynolds (1994) describe a cycling technique used to determine a range within which the temperature of homogenization (Th) of an inclusion lies. It is particularly suited to getting accurate Th values for small inclusions. The technique was used exclusively in this study.

Using the cycling technique, the inclusion is heated until the vapor bubble disappears, after which the inclusion is cooled rapidly. The manner and temperature of return of the vapor phase is diagnostic: a sudden return of the bubble at full size in a spot other than where it disappeared and at a temperature significantly lower than that at which it disappeared indicates that the inclusion had homogenized at the higher temperature. Return of a small bubble that grows at a visible rate to full size, especially from the same spot it disappeared and at a temperature close to that at which it disappeared, indicates that the inclusion had not homogenized. If return behavior indicates the inclusion had not homogenized at a given temperature, the inclusion is heated incrementally higher, then again cooled rapidly. This process is repeated until homogenization is achieved. At that point, Th is known to be within the last and second- last temperature increments.

~~References, Appendix D~~

~~Goldstein, R.H. and Reynolds, T.J., 1994. Systematics of Fluid Inclusions in Diagenetic Minerals: SEPM Short Course 31, Society for Sedimentary Geology, 199 p.~~

~~260 Appendix E. SEM-EDS data from evaporate mounds~~

In order to determine the cation composition of fluid-inclusions semi- quantitatively, a number of the polished-section chips (broken pieces of doubly-polished 100-p.m thin sections) that had previously been studied microthermometrically were chosen for evaporate-mound analysis. In this procedure, the sample is heated on the microthermometry stage to cause decrepitation of the fluid inclusions. The contents of an inclusion expand rapidly upon decrepitation, so that part of the material is expelled as a fine spray while the rest divides into volatiles that escape and salts that precipitate on the surface of the chip, characteristically in a mound or halo around the emptied inclusion (Haynes and Kesler, 1987; Roedder and Bodnar, 1997; Kontak, 2004). The salts or evaporates are analyzed with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS).

The samples analyzed by this method are listed in Table E-l. Three chips from polished-section samples of the TIC showings were brought to 420°C, which caused decrepitation of most of the fluid inclusions. A fourth chip (slide area A) was brought to 500°C without the primary inclusions, which were all small and equant, decrepitating; the inclusions that decrepitated were mostly secondary. The chips were examined petrographically in reflected light to ensure the presence of evaporate mounds, then placed on double-sided carbon tape on a glass slide, mound-side up, and sprayed with carbon before being placed into the electron-microscope vacuum chamber.

A JEOL JSM 6400 scanning electron microscope with a light-element energy- dispersive X-ray emission spectrometer was used. Back-scattered images (Fig. E-l) were used to select evaporate mounds for analysis. One or more spectra were obtained for each site of interest (SOI), usually including both point and field analyses and for some sites including a background spectrum (of the host mineral). The "point" beam covers an effective area of about 5 |im, whereas different sizes were chosen for fields that were

~~261 Appendix E. SEM-EDS data from evaporate mounds~~

Slide Polished previously studied Max Area Showing section chip FIAs on the chip1 Host2 T3 Notes A TIC C 824A1 chip 2 824A1 #6, #7 Sph 500 Only dark secondary inclusions decrepitated; primary ones were all small and equant B TIC C 824A2-1 chip 1 824A2-1 #1,4, #5, #7 Sph, 420 Gal C TIC Ryan 827C1-2 chip 2 827C1-2 #3, #4, #6 Sph, 420 Gal D TIC C 824A1 chip 3 824A1 #2 Sph 420 FIA = fluid inclusion assemblage 2 Host mineral of SEM-analyzed evaporates 3 Maximum temperature to which the chip was subjected during experimental decrepitation

Table E-l. Correlation of areas on the SEM slide with chips of polished sections containing decrepitated fluid inclusions. scanned by the beam. A total of 31 spectra, 19 of these from raster field scans, were acquired from evaporate mounds. A software package designed for the SEM-EDS was used to calculate element concentrations from the spectra. Concentrations for Ma, Mg, CI, K, and Ca were normalized to 100 and are presented in Table E-2. These data were further normalized to create ternary plots of Ca-K-Na, Mg-K-Na, and Mg-Ca-Na+K (Fig. E-2).

A striking feature of the data is the excess of cations over anions. According to Haynes et al. (1988), chloride volatizes at a temperature T where 420°C < T < 500°C. Although Area A was subjected to experimental heating to 500°C, it is no more deficient in chlorine than the other three areas. Volatization due to excessive current-beam density is another possible cause of low CI. A current-beam density as low as 0.35 nanoamps/|xm2 will volatize CI (depending on various analytical conditions and possibly also on other substances present in the mound), whereas K and Na volatize at densities below 2.5 and 3.5 nanoamps/|jm2, respectively, and Ca and Mg are relatively stable (Morgan and Davies, 1981). This is unlikely to be the cause of low CI analyses, however, because there are definitely chloride salts in the mounds (Fig. E-l). Also, a greater loss of the more-easily volatized elements would be expected in point samples than in rasterized field samples, whereas Table E-3 shows no such relationship in terms of CI loss, and Fig. 2-E-2b shows no such relationship in terms of Na or K loss.

~~262 Appendix E. SEM-EDS data from evaporate mounds~~

~~50um~~

Figure E-l. Back-scattered electron images of fluid inclusion evaporate mounds. Clockwise from top left: evaporate minerals that precipitated in fractal, cross-branching crystals at SOI 11 (Spectrum 1 covers a small field in the lower left part of the mound); fractal, cross-branching evaporate crystals at SOI 10 (Spectrum 1covers most of this mound); a group of regular, equant crystals at SOI 21 (Spectrum 2 covers the bright grains); a low splatter of coalesced crystals at SOI 20 (Spectrum 2 covers the brighter grains and some of the surrounding gray material; Spectrum 1 covers Spectrum 2 plus areas to its top and left); and a group of small, equant crystals at SOI 14 (Spectrum 1 covers the brighter crystals or mounds).

The ternary plots in Figure E-2a show that the inclusion fluids were mostly low in Ca and Mg, and consisted of three end-members: a Na-rich fluid, a K-rich fluid, and a mixed fluid containing Na, K, Ca and Mg that probably evolved as a mixture of the other two fluids interacted with the carbonate rocks through which it travelled.

~~263 Ca Slide area~~

~~A c~~

~~e-B Ca Na~~

~~Na+K Ca~~

~~Type Point o Field •~~

~~wi^iiiinfiu p v~~

~~Na+K Ca~~

Figure E-2. Ternary plots of SEM-EDS analyses of decrepitated fluid inclusions in sphalerite and galena. A) Symbolized by Slide area. Each area contains a polished-section chip that was used for fluid inclusion microthermometry (Table E-l). B) Symbolized by type of electron-beam scan, either a focused point or a raster scan of a field. Field Normalized Spectr Area SOI Type size Mound description Interpretation Host Sum um Na Mg CI K Ca (um) A 2 1 point Bright, white mound (3 um) surrounded by low Fluid inclusion evaporate Sph 83 0 7.4 9.61 0 100 gray splatter A 2 2 field ~4x4 Bright, white mound (3 um) surrounded by low Fluid inclusion evaporate Sph 75.3 0 10.6 14.1 0 100 gray splatter A 3 1 field -12x12 Clustered gray lumps forming a circular splatter Fluid indusion(s) evaporate Sph 66.2 0 12.4 18.2 3.21 100 about 30 iim A 15 1 field -70x30 Group of light gray mounds (5-10 jim) Fluid incluston(s) evaporate Sph 100 0 0 0 0 100 B 5 1 field -30x30 Irregular shaped, low gray splatter (20 um) Fluid inclusion evaporate Sph 67.2 0 6.75 6.11 19.9 100 B 6 1 field -10x10 Bright to gray, elongate, sharp-edged mound Evaporate of multiple fluid Sph 47.1 6.2 20.1 19.7 6.92 100 (70x15 m) inclusions with minor silicate contamination B 8 1 field -12x8 Bright to gray, small, equant mound or grain Fluid inclusion evaporate with Sph 88.6 0 0 11.4 0 100 (5 um); same view as SOI 6 minor silicate contamination

B 9 1 point Roughly circular splatter of gray crystals (400 um) Evaporate of multiple fluid Sph 62.5 0 21.1 16.5 0 100 inclusions B 9 2 point Dark area (without visible evaporate) Host crystal with dusting of Sph 73.3 16.8 0 0 9.88 100 between numerous large, round patches of fluid inclusion(s) evaporate evaoorate B 9 3 point Roughly circular splatter of gray crystals (200 |im) Evaporate of multiple fluid Sph 95.7 0 0 4.32 0 100 inclusions B 9 5 point Roughly circular splatter of gray crystals (100 jim) Evaporate of multiple fluid Sph 100 0 0 0 0 100 inclusions

Table E-2. SEM-EDS analyses of Na, Mg, CL, K and Ca for evaporate mounds from experimentally decrepitated fluid inclusions. Data are normalized to 100. Type refers to the type of electron-beam scan; focused points sample an area effectively 5 urn in diameter, whereas fields are scanned and rasterized over the indicated areas. Host is the mineral that hosted the fluid inclusion(s) before decrepitation; Sph = sphalerite, Gal = galena. Field Normalized Spectr Area SOI Type size Mound description Interpretation Host Sum um Na Mg CI K Ca (um) B 9 6 point Dark area (without visible evaporate) Host crystal with dusting of Sph 100 0 0 0 0 100 between numerous large, round patches of fluid inciusion(s) evaporate evaoorate B 10 1 field 72x98 Zoom to part of SOI 9. Large splatter (100 um) of Fluid inclusion evaporate Sph 63.5 0 22.6 13.9 0 100 gray evaporate crystals in fractal cross-patterns; cross-branches at ~90 deg B 11 1 field 17x25 Zoom to part of SOI 9. Large splatter (100 |im) of Fluid inclusion evaporate Sph 58.9 0 23.4 17.7 0 100 gray evaporate crystals in fractal cross-patterns; cross-branches at "120 and -60 degrees

B 12 2 point Small crystal or crystal cluster Fluid inclusion evaporate Gal 5.68 0 44.6 46.6 3.08 100 B 12 3 point Small crystal or crystal cluster Fluid inclusion evaporate Gal 7.35 0 24.1 17.1 51.5 100 B 12 4 point Small crystal or crystal cluster Fluid inclusion evaporate Gal 10.4 0 49.6 38.6 1.38 100 B 12 6 field -10x15 Low gray splatter adjacent to small white mound Fluid inclusion evaporate? Gai 30 7.04 21.5 17.5 23.9 100

B 12 7 field "10x8 Low gray splatter in a ring 30 um wide Fluid inclusion(s) evaporate Gal 26.1 0 44.3 29.7 0 100 B 13 1 field ""12x12 Very low, faint dusting of evaporate? Fluid inclusion evaporate? Gal 21.7 0 48.4 30 0 100 B 13 2 point Small grain or mound (10x7 jim) Fluid inclusion evaporate? Gal 18.5 17.9 27.9 31.9 3.78 100 B 13 3 field -10x5 Very low, faint dusting and tiny (1-2 pim) mound? Fluid inclusion evaporate Gal 14.5 0 49.3 36.2 0 100

B 14 1 field 20x17 Group of smatt gray to white, equant mounds or Fluid indusion(s) evaporate Sph 65.2 0 16.5 13.1 5.19 100 crystal grains about 2-3 (im each C 18 1 point gray mound or crystal (5 \xm) in a field of such Fluid inclusion evaporate Sph 100 0 0 0 0 100 mounds C 21 1 point Low gray mound (40 um), oblong Fluid inclusion(s) evaporate? Sph 95.8 0 0 4.23 0 100 C 21 2 field -30x20 White crystals (5 um) on dark background Fluid inclusion evaporate Sph 80.5 0 0 19.5 0 100 C 22 1 field -40x30 Very low gray splatter (250 um) Evaporate of multiple fluid Sph 82.9 0 9.19 7.92 0 100 inclusions

Table E-2. (continued, 2 of 3) Field Normalized Spectr Area SOI Type size Mound description Interpretation Host Sum um Na Mg CI K Ca (um) D 19 2 field **23x12 Low groups of smaii gray mounds/crystals and a Evaporate of multiple fluid Sph 74.9 0 19.9 5.26 0 100 higher white mound inclusions D 19 3 field 10x10 A low, circular group of small gray mounds/crystals. Fluid inclusion evaporate Sph 73.6 0 13.3 11.2 1.86 100 Covers part of spectrum 2

D 20 1 field 25x22 Splatter of gray, equant, coalesced Evaporate of multiple fluid Sph 55.6 0 24.8 18 1.58 100 mounds/crystals and a group of white, equant inclusions angular (cubic?) grains 3 um D 20 2 field 15x17 Group of white, equant angular (cubic?) crystals (3 Fluid inclusion evaporate Sph 46.1 0 31.6 20.6 1.75 100 jirn) surrounded by gray, equant, coalesced mounds/crystals. Part of spectrum 1

~~Table E-2. (continued, 3 of 3) Appendix E. SEM-EDS data from evaporate mounds~~

Atomic% cations detected Atomic% anions Spec Na+K Area SOI Type trum (mono Ca+Mg required to valent) (divalent) balance cations detected difference 4 point B 12 50.08 1.21 50.69 48.71 2.0 B 13 3 field 52.75 0.00 52.75 47.25 5.5 B 12 2 point 51.88 2.77 53.27 45.34 7.9 B 13 1 field 55.74 0.00 55.74 44.26 11.5 B 12 7 field 60.31 0.00 60.31 39.69 20.6 B 12 3 point 27.80 47.24 51.42 24.96 26.5 B 13 2 point 50.08 25.60 62.88 24.31 38.6 D 20 2 field 73.00 1.26 73.63 25.74 47.9 B 12 6 field 54.02 27.32 67.68 18.66 49.0 D 20 1 field 79.54 1.10 80.09 19.36 60.7 B 6 1 field 71.92 12.08 77.96 16.00 62.0 B 11 1 field 82.04 0.00 82.04 17.96 64.1 B 10 1 field 83.00 0.00 83.00 17.00 66.0 B 9 1 point 84.14 0.00 84.14 15.86 68.3 0 19 field 85.81 0.00 85.81 14.19 71.6 B 14 1 field 84.19 3.45 85.92 12.35 73.6 D 19 field 89.22 1.19 89.81 9.60 80.2 A field 3 1 88.59 2.14 89.66 9.27 80.4 B S 1 field 81.78 13.15 88.36 5.07 83.3 A 2 2 field 92.42 0.00 92.42 7.58 84.8 C 22 1 field 93.62 0.00 93.62 6.38 87.2 B 9 point 77.26 22.74 88.63 0.00 88.6 A 2 1 point 94.89 0.00 94.89 5.11 89.8 C 21 1 point 100.00 0.00 100.00 0.00 100.0 A 15 1 field 100.00 0.00 100.00 0.00 100.0 B 8 1 field 100.00 0.00 100.00 0.00 100.0 B 9 3 point 100.00 0.00 100.00 0.00 100.0 B 9 5 point 100.00 0.00 100.00 0.00 100.0 B 9 6 point 100.00 0.00 100.00 0.00 100.0 C 18 1 point 100.00 0.00 100.00 0.00 100.0 C 18 2 point 100.00 0.00 100.00 0.00 100.0 C 21 2 field 100.00 0.00 100.00 0.00 100.0 D 19 1 point 100.00 0.00 100.00 0.00 100.0

Table E-3. Normalized atomic percents of cations (Na, K, Ca, Mg) and anions (CI) detected in the evaporate mounds. The amount of anions needed to chemically balance the cations is consistently more than the detected amount of anions. The table is sorted by the difference between anions required and detected.

~~268 Appendix E. SEM-EDS data from evaporate mounds~~

~~References, Appendix E~~

~~Haynes, F.M. and Kesler, S.E., 1987, Chemical evolution of brines during Mississippi Valley-type mineralization: Evidence from East Tennessee and Pine Point: Economic Geology, v. 82, p. 53-71.~~

Haynes, F.M., Sterner, S.M. and Bodnar, R.J., 1988, Synthetic fluid inclusions in natural quartz. IV. Chemical analyses of fluid inclusions by SEM/EDA: Evaluation of method: Geochimica et Cosmochimica Acta, v. 52, p. 969-977.

Kontak, D.J., 2004, Analysis of evaporate mounds as a complement to fluid-inclusion thermometric data: Case studies from granitic environments in Nova Scotia and Peru: The Canadian Mineralogist, v. 42, p. 1315-1329.

Morgan, A.J. and Davies, T.W., 1982, An electron microprobe study of the influence of beam current density on the stability of detectable elements in mixed-salts (isoatomic) microdroplets: Journal of Microscopy, v. 124, Pt. 1, p. 103-116.

Roedder, E. and Bodnar, R.J., 1997, Chapter 13, Fluid inclusion studies of hydrothermal ore deposits, in Barnes, H.L., editor, Geochemistry of Hydrothermal Ore Deposits, 3rd ed.: New York, USA, Wiley, p.657-698.

~~269 Appendix F. Sulfur isotope systematics~~

~~Introduction~~

The following discussion provides a theoretical background that supplements the discussion of sulfur isotopes in Chapter 2. The sulfur in base metal sulfides is sourced from either magmatic sulfur, seawater sulfate, or organically bound sulfur (Ohmoto and Goldhaber, 1997). Magmatic sources, however, are not invoked for carbonate-hosted Zn- Pb deposits, which are typically low temperature and distal to any contemporaneous igneous activity (eg. Leach et al, 2005). The sulfur species that predominate in fluids below about 350°C, thus in fluids that precipitate carbonate-hosted zinc deposits, are H2S,

9 *) HS", and SO4" (Ohmoto and Rye, 1979). Only H2S and SO4" need be considered, since the fractionation between HS" and H2S is negligible (Ohmoto and Rye, 1979). Both the isotopic fractionation between H2S and SO42" and their relative concentrations in the fluid have a significant impact on the isotopic composition of sulfide minerals precipitated from the fluid. The possible sources of sulfur and processes by which it may be transferred from source reservoir to ore, and the kinetic isotopic effects associated with those processes, are discussed next.

~~Bacterial reduction of seawater sulfate~~

Seawater S sources must first be reduced to H2S or HS" in order to be available for fixation with base metals. Bacterial sulfate reduction (BSR) operates at temperatures generally under 85°C, although locally it can slightly exceed 100°C (Jorgenson et al., 1992), therefore BSR is restricted to operate on or near the seafloor. BSR is a process by which bacteria mediate the transfer of oxygen from sulfate to organic carbon or H2 gas, producing H2S or HS", water or OH", and bicarbonate, CO2, or residual carbon compounds of lower molecular weight, depending on the nature of the reductant (Strauss, 1999; Canfield, 2001). Sedimentary pyrite is the most voluminous product of BSR in marine sediments. BSR causes a strong negative fractionation in open systems, of - 45±20%o (Ohmoto and Goldhaber, 1997). BSR acts on seawater sulfate that is contemporaneous with the reduction process. The 534S of seawater sulfate has ranged 270 Appendix F. Sulfur isotope systematics through the Paleozoic from a high of about +32%o at the Neoproterozoic-Cambrian boundary to a low of+10%o in the Permian; modern seawater is +20%o (Faure and

Mensing, 2005; Veizer et al., 1999; Srauss; 1999). Sedimentary pyrite can be directly replaced during interaction with base-metal-rich hydrothermal fluids, or dissolved during metamorphism to release H2S which is then available to bind with base metals encountered in hydrothermal fluids (Ohmoto and Goldhaber, 1997). There is negligible fractionation during the replacement or dissolution of sedimentary pyrite, so base metal sulfides whose sulfur originates either directly or indirectly from BSR have negative to strongly negative 534S values, or if produced in a partially closed system, a sampling of such sulfides will have a strong negative peak with values skewed in the positive direction (Ohmoto and Goldhaber, 1997).

~~Thermochemical reduction of seawater sulfate~~

Thermochemical sulfate reduction (TSR) operates at temperatures greater than ~140-160°C (Worden et al., 1995), and therefore is an important process in reduction of seawater-derived sulfate that was precipitated as evaporitic sediments then re-dissolved in deep, warm, basinal fluids. TSR is a process by which organic matter, often in the form of gaseous hydrocarbons, is oxidized and sulfate is reduced, producing H2S, CO2 or carbonate, and water, with or without residual organic matter (Orr, 1974; Anderson, 1991). The products of BSR and TSR are fundamentally the same. In a second form of TSR restricted to volcanic environments and dominated by equilibrium fractionation, evaporitic or seawater sulfates are reduced by oxidation of Fe2+ (Ohmoto and Goldhaber, 1997); this is the mechanism by which VMS deposits acquire their sulfur and is not applicable to carbonate-hosted (MVT) base metal deposits. The mechanism of reduction in TSR is not known and may ultimately involve reduction of H+, with the organic matter or ferrous iron acting as H+ generators by reacting with H2O (Kiyosu and Krouse, 1990; Ohmoto and Goldhaber, 1997). Geological and isotopic evidence show that TSR by oxidation of organic matter is a common process (Orr, 1974; MacQueen and Powell, 1983; Anderson, 1991; Worden et al., 2000). Experimental data and their judicious extrapolation show that this type of TSR is capable of proceeding at fast enough rates to

271 Appendix F. Sulfur isotope systematics produce an MVT orebody at the site of reduction within a geologically reasonable amount of time, at temperatures of 150-250°C (Thorn and Anderson, 2008; previous work by Ohmoto and Lasaga, 1982 as quoted by Anderson, 1991).

There is very little fractionation of S isotopes during dissolution or precipitation of sulfate minerals (+1.65 ± 0.12%o during precipitation; Faure and Mensing, 2005), therefore the sulfate on which TSR operates has 834S very close to that of its source seawater. Experimental data for geologically relevant conditions suggest that TSR is associated with a kinetic isotope fractionation from sulfate to sulfide of -5 to -14%o at temperatures of 140° to 300°C (Kiyosu and Krouse, 1990; see also Kiyosu, 1980 and discussion in Ohmoto and Goldhaber, 1997), but observations in the field are that most H2S reservoirs have 834S identical to nearby evaporite sources (eg. Worden et al, 2000). The observations are what would be expected from a closed system, where all the available sulfate was consumed (Ohmoto and Goldhaber, 1997). An effectively closed system is produced by limiting the availability of sulfate, so that each small amount of sulfate released is fully consumed. Sulfate availability has been shown to have controlled reaction rates during TSR in one gas field, and is suggested to have done so in many, accounting for the observed close correspondence between 834S of H2S gas and nearby evaporites in many gas fields (Worden et al., 2000).

~~Reduced sulfur released during de-sulfurization of organic matter~~

Organically bound sulfur is already reduced when it is released as H2S by thermal maturation, either during burial or during interaction with hydrothermal fluids (Ohmoto and Goldhaber, 1997). The yield of sulfur by this method is low due to the low S content of organic matter; yield is estimated to reach a maximum of 3% H2S by volume (Ohmoto and Goldhaber, 1997 quoting Orr 1977). Kesler et al. (1994) invoke thermal degradation of oil as the source of S in MVT deposits of the Cincinnati Arch, and suggest that wall- rock disseminations are as attractive a source as pooled concentrations. Ohmoto and Goldhaber (1997) list organic matter as a potential source of light S in ore deposits. Leach et al. (1996) invoke coal beds as a source of S for the Silesian carbonate-hosted Zn±Pb deposits, and Farquhar et al. (2010) suggest that sulfidic hydrocarbons contributed 272 Appendix F. Sulfur isotope systematics

~~S to sediment-hosted copper deposits. Organic sulfur has more commonly been invoked to provide the catalytic H2S necessary to jump-start TSR (eg. MacQueen and Powell, 1983).~~

~~The 534S values of sulfur in marine organic matter are age-specific and 5 to 20%o~~

(averaging about 15%o) lighter than seawater sulfate that is contemporaneous with the source organic matter (Thode et al., 1960; Thode and Monster, 1963; Orr, 1974). Organic sulfur separated from sedimentary rocks ranges from -23 to +23%o, and is 3 to 26%o heavier than contemporaneous pyrite (Anderson and Pratt, 1995). The 534S values of petroleum range widely, from -8 to +32%o (Faure and Mensing, 2005). There is no isotopic selection during plant metabolism of marine sulfate (Thode, 1981), therefore metabolically derived S is as heavy as seawater sulfate. However, the contribution of metabolic S to the total S in marine organic matter is small; the S-isotopic signature of organic matter is dominated by early-diagenetic addition of bacterially reduced, isotopically light sulfur from the source rock sediments (Thode et al., 1960; Thode, 1981). This explains the observed relationship between 534S of marine sulfate and 534S of contemporaneous organic matter. The sulfides in this study were deposited sometime after the Cambrian; organic matter that could potentially be their sulfur source would have 834S of 5 to 20%o less than +12 (the Permian-Triassic low) to +32%o (the Early Cambrian high), which represents a possible range of -8 to +28%o.

There is little or no fractionation during migration or low-temperature maturation of oils, however, high-temperature maturation (>135°C) in the presence of evaporitic sulfate causes an increase in 534S of the oil to values that may approach those of the sulfate reservoir, due to isotopic exchange during kinetically competing sulfurization- desulfurization reactions between the oil and H2S produced by TSR (Orr, 1974). De- sulfurization itself does not cause fractionation, thus the 534S of a base metal sulfide mineral derived from an organic-matter source will be similar to the 534S of the parent organic matter, which may be almost as light as contemporaneous pyrite or, in the case of high-temperature petroleum, as heavy as nearby evaporites.

~~273 Appendix F. Sulfur isotope systematics~~

~~Equilibrium fractionation vs. kinetic effects~~

~~The purpose of the type of isotopic study reported on herein is to estimate the isotopic ratio of the source reservoir, from which information it is hoped to determine the~~

~~34 34 34 nature of the reservoir. The 5 S of the total sulfur in the fluid (5 Sfluid) reflects the 8 S of the source reservoir, but the 534S of dissolved H2S (834Sh2s) and of precipitated~~

34 minerals is not necessarily the same as 8 Sflu,d. It is necessary to establish whether equilibrium prevailed among S species in a mineralizing fluid before interpreting the meaning of isotope values measured in sulfide minerals. If the fluid was in S-isotopic

34 equilibrium, the isotope ratio of the fluid (5 Sf]Uid) cannot be determined from the isotope ratio of precipitated sulfides alone. The amount of isotopic fractionation among dissolved sulfur species at equilibrium is primarily temperature dependant (Ohmoto and Goldhaber,

~~1997, p. 523). An equilibrium fractionation factor for aqueous SO42" with respect to H2S (ASO4-H2S, or A) has been determined that is valid between 200° and 400°C (Ohmoto and~~

Goldhaber, 1997, Table 11.1), thus it is calculated that in a fluid in which SO42" and H2S are in equilibrium at 211°C (the average Th in this study), S isotopes will fractionate between species such that SO4 " is 29%o heavier than H2S. Precipitated sulfide minerals

~~34 34 will have the same 8 S as this dissolved H2S (that is, S SH2S)- Clearly, because of this fractionation, the 834S of the total fluid in an equilibrium system, rather than of just the~~

~~34 H2S, is needed to draw any inferences about the source of sulfur. Although the 5 S of the~~

34 2 total S in the fluid is easily found if the 8 S of both H2S and SO4 " and their relative proportions are known, typically neither the proportions nor 834Sso« is known and the only measurable quantity readily available is the 834S of sulfide minerals (equivalent to

~~34 34 8 Shis of the equilibrium fluid). The 8 S value of total S in the fluid can be stated as the~~

~~34 sum of this measured 8 SH2S and a the second term that varies with the molar ratio of dissolved SO42" to H2S (m):~~

~~34 34 8 Sfiuid = 8 SH:S + A(m/(l+m))~~

~~34 (Ohmoto and Rye, 1979). The molar ratio m and therefore S Sfiuid are sensitive to pH,y02, and the activities of cationic species (Ohmoto and Rye, 1979). For example, for~~

~~34 34 an equilibrium fluid at 211°C, as m varies from 0.01 to 20, S SH2s-8 SflUjd varies from 0~~

274 Appendix F. Sulfur isotope systematics to -25%o; in other words, an equilibrium fluid dominated by H2S will precipitate sulfide minerals whose 834S is close to that of the fluid, but equilibrium fluids with more SO42" relative to H2S will precipitate sulfides whose 534S can be dramatically less than that of the total fluid. Since pH and JO 2 can have a profound effect on m, they also have a profound effect on the 834S of precipitated sulfides in equilibrium systems. For an equilibrium fluid at 250°C, near neutral pH, and in a redox state near the S0427H2S

~~34 boundary, a change in jOi of 10 or in pH of 1 will cause 8 SH2S to decrease by 10 to 15%o~~

~~34 34 with respect to S SflUjd. It becomes obvious from this discussion that the 8 SflUjd~~

(therefore 834S of the source sulfur) is impossible to determine with certainty for a system in isotopic equilibrium from only the measured 834S of sulfide minerals when those have negative or low positive values, since there are too many routes by which such values can arise. However, strongly positive values in sulfides have no way to arise other than from a strongly positive source.

If the studied system was not in S-isotopic equilibrium, the H2S and SO42" in the fluid will be effectively non-reactive and independent of each other (Ohmoto and Goldhaber, 1997). The observed 834S values of sulfide minerals can be considered in combination with geological constraints and known kinetic fractionation effects to hypothesize which of a number of sulfur sources/processes produced such values. For example, TSR causes a fractionation of -5 to -14%o, so it is a viable process to have produced sulfide minerals with 834S of+15%o from an evaporite with 834S +25%o. BSR causes a fractionation of -65 to -25%o, so it is a viable process to have produced sulfide minerals with 834S of -30%o from a Phanerozoic oceanic sulfate reservoir.

Isotopic equilibrium is attainable but not inevitable within 100-1000 years in fluids that have geologically reasonable characteristics (pH 5-7, 0.01 moles total S at 200°C; Ohmoto and Goldhaber, 1997). Since chemical and isotopic equilibrium are directly related (Ohmoto and Goldhaber, 1997), equilibrium or its absence can be detected by petrographic evidence, or sulfur isotope geothermometry on sulfide-sulfate mineral pairs (Ohmoto and Rye, 1979). If isotopic equilibrium between co-precipitated sulfate and sulfide minerals is established, this indicates that there was equilibrium of dissolved sulfur species in the precipitating fluid, since there is little or no isotopic 275 Appendix F. Sulfur isotope systematics fractionation on precipitation. Geothermometry on sulfide-sulfide mineral pairs is of less value as an indicator of equilibrium, since equilibrium is so commonly masked by fluctuating temperature and 534Sh2S of the fluid, causing even a single pair of petrographically co-genetic minerals to appear to be out of equilibrium (Ohmoto and Rye, 1979).

From the discussion above on equilibrium fluids, it is evident that sulfides with low or even negative 834S can be precipitated from an equilibrium fluid in which SO42" is in far greater proportion than H2S. The conditions under which such a fluid might exist in nature, however, are inferred to be unusual. An oxidized fluid containing dissolved evaporitic sulfate might encounter strata containing organic matter or hydrocarbons and undergo TSR. If the amount of reductant was sufficient to reduce only some of the SO42", leaving most of the SO42" unaltered, then after all the reductant was consumed, there could exist an equilibrium fluid containing H2S but dominated by SO42", This type of fluid, as discussed, would allow the precipitation of sulfides with low or negative 534S from a dissolved evaporitic source with high 534S. By contrast with those perhaps-rare circumstances, disequilibrium fluids are expected to be the rule during TSR. Where SO42" and H2S are derived from each other by oxidation or reduction reactions like TSR, disequilibrium effects will control their isotopic relationship for as long as they remain in disequilibrium (Ohmoto and Rye, 1979); that is, as long as TSR is on-going and there is a supply of reductant and SO4". Thus, the simplest explanation for the presence of both negative and strongly positive 834S in sulfides is mixing of a fluid containing TSR- derived sulfides with a fluid containing dissolved BSR-derived sulfides.

~~References, Appendix F~~

~~Anderson, G.M., 1991, Organic maturation and ore precipitation in southeast Missouri: Economic Geology, v. 86, p. 909-926.~~

~~276 Appendix F. Sulfur isotope systematics~~

Canfield, D.E., 2001, Biogeochemistry of sulfur isotopes, in Valley, J.W. and Cole, D.R., editors, Stable Isotope Geochemistry: Mineralogical Society of America, Reviews in Mineralogy and Geochemistry v. 45, p. 607-636.

~~Farquhar, J., Wu, N., Canfield, D.E., Oduro, H., 2010, Connections between sulfur cycle evolution, sulfur isotopes, sediments, and base metal sulfide deposits: Economic Geology, v. 105, p. 509-533.~~

~~Faure, G. and Mensing, T.M., 2005, Isotopes, Principles and Applications, 3rd edition: John Wiley and Sons, Inc., Hoboken, NJ, USA, 897 p.~~

~~Jorgensen, B.B., Isaksen, M.F., Jannasch, H.W., 1992, Bacterial sulfate reduction above 100°C in deep-sea hydrothermal vent sediments: Science, New Series, v. 258, p. 1756- 1757.~~

~~Kiyosu, Y., 1980, Chemical reduction and sulfur-isotope effects of sulfate by organic matter under hydrothermal conditions: Chemical Geology, v. 30, p. 47-56.~~

~~Kiyosu, Y. and Krouse, H.R., 1990, The role of organic acid in the abiogenic reduction of sulfate and the sulfur isotope effect: Geochemical journal, v. 24, p. 21-17.~~

~~MacQueen R.W. and Powell T.G., 1983, Organic geochemistry of the Pine Point lead- zinc ore field and region, Northwest Territories, Canada: Economic Geology, v. 78, p. 1- 25.~~

~~Ohmoto, H. and Rye, 1979, Isotopes of sulfur and carbon, in Barnes, H.L., editor, Geochemistry of Hydrothermal Ore Deposits, 2nd edition, New York, USA, Wiley, p. 509-567.~~

~~Orr, W.L., 1974, Changes in sulfur content and isotopic ratios of sulfur during petroleum maturation - Study of Big Horn Basin Paleozoic oils: AAPG Bulletin, v. 58, p. 2295- 2318.~~

~~Strauss, H., 1999, Geological evolution from isotope proxy signals - sulfur: Chemical Geology, v. 161, p. 89-101.~~

~~277 Appendix F. Sulfur isotope systematics~~

~~Thode, H.G., 1981, Sulfur isotope ratios in petroleum research and exploration, Williston Basin: AAPG Bulletin, v. 65, p. 1527-1535~~

~~Thode, H.G., Harrison, A.G., and Monster, J., 1960, Sulfur isotope fractionation in early diagenesis of Recent sediments of northeast Venezuela: AAPG Bulletin, v. 44, p. 1809- 1817.~~

~~Thom, J. and Anderson, G.M., 2008, The role of thermochemical sulfate reduction in the origin of Mississippi Valley-type deposits. I. Experimental results: Geofluids, v. 8, p. 16- 26.~~

Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, F., Carden, G.A.F., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O.G., and Strauss, H., 1999, 87Sr/86Sr, 513C and 5180 evolution of Phanerozoic seawater: Chemical Geology, v. 161, p. 59-88.

~~Worden, R.H., Smalley, P.C., and Oxtoby, N.H., 1995, Gas souring by thermochemical sulfate reduction at 140 °C: AAPG Bulletin, v. 79, p. 854-863.~~

Worden, R.H., Smalley, P.C., and Cross, M.M., 2000, The influence of rock fabric and mineralogy on thermochemical sulfate reduction: Khuff Formation, Abu Dhabi: Journal of Sedimentary Research, v. 70, p. 1210-1221.

~~278 Appendix G. List of publications and contributions generated by this project~~

~~Papers and maps~~

Fischer, B.J. and Turner, E.C., 2007. Preliminary Observations on Stratigraphy and Mineralization at the AB-C Showing, NTS 106 CI6, Mackenzie Mountains, NWT. Internal report for Eagle Plains Resources, Ltd.

Fischer, B. J., Atherton, C., Parker, E., and Law, J., 2010. Geology of the AB area, parts of 106C/16 and 106F/01: NWT Open File 2010-04, Northwest Territories Geoscience Office, 1 map, scale 1:20,000, and 1 report, 66 p.

Fischer, B.J., 2011, Chapter 7.3, Carbonate-hosted Zn-Pb (± Ag, Cu, Ba) and Carbonate- hosted Cu (± Ag, Zn), in Martel, E., Turner, E.C. and Fischer, B.J., editors, Geology of the central Mackenzie Mountains of the northern Cordillera; Sekwi Mountain (105P), Mount Eduni (106A), and northwestern Wrigley Lake (95M) map areas, Northwest Territories: NWT Special Volume 1, Northwest Territories Geoscience Office, Yellowknife, Canada, p. 260-264

~~279 Appendix G. List of publications~~

~~Chapter 2 of this document will be modified and submitted for publication to Economic Geology by Fischer, Turner, and Kontak.~~

~~Abstracts~~

Fischer, B. and Turner, E.C. 2006. Preliminary investigation of zinc showings hosted by the Sekwi Formation, Mackenzie Mountains (poster). 34th Yellowknife Geoscience Forum, Program and Abstracts, November 21-23, 2006.

Fischer, B. and Turner, E.C. 2007. Stratigraphy and Mineralization at the AB-C Carbonate-Hosted Zinc (-Lead) Showing, Mackenzie Mountains: Preliminary Observations. Program of Talks and Abstracts, 35th Yellowknife Geoscience Forum, Yellowknife, NT.

Fischer, B., Turner, E.C., and Kontak, D., 2009. Controls on Zn(-Pb) mineralization in the Early Cambrian Sekwi Formation, Mackenzie Mountains zinc district, Northwest Territories; Geological Association of Canada Annual Meeting, Toronto 2009, Program with Abstracts v. 34.

~~280 Appendix H. Table of abbreviations pertaining to fluid inclusion study~~

Abbreviation Meaning FIA Fluid inclusion assemblage Td The temperature at which the vapor bubble disappears (but does not homogenize) during heating of an inclusion that displays vapor- phase persistence Th Temperature of homogenization

~~ThHA Temperature of homogenization of an FIA.~~

Calculated as the average Thinc for a given assemblage, but only for assemblages that yielded mutually consistent Thinc (90% within 10°C) ThpiAm Miniumum temperature of homogenization of an FIA. Calculated as the average Ty for a given assemblage, but only for assemblages that yielded mutually consistent Ty (90% within 20°C) Thine Temperature of homogenization of an inclusion, taken to be the mid-point of the range determined by the cycling technique (Appendix D)

Th|ncm Miniumum Thinc, as represented by the lower end of a Th range determined by the cycling technique, in the situation where the upper end of the range could not be determined because of inclusion stretching or darkening Tm Temperature of melting

~~Tmhh Temperature of melting of hydrohalite~~

Tmice Temperature of melting of ice Ty The temperature at which the vapor bubble becomes tiny (reaches its minimum size, after which it shrinks no more), during heating of an inclusion that displays vapor-phase persistence. Although Ty represents a

~~minimum possible Thlnc, it is obtained under~~

~~different circumstances than Thincm~~

~~281~~