GEOLOGY OF THE SANDHILL ZN-CU-PB-AG PROSPECT AND ECONOMIC POTENTIAL OF THE GIBSON-MACQUOID GREENSTONE BELT, DISTRICT OF KEEWATIN, N.W.T
by
Allan E. Armitage
Graduate Program in Earth Sciences
Submitted in partial fulfilnient of the requirement for the degree of Doctor of Philosophy
Facul ty of Graduate S tudies The University of Western Ontario London, Ontario January, 19%
O Allan E. Armitage, 1998 National library Bibliothèque nationale 141 of,, du Canada Acquisitions and Acquisitions et Bbliographic Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON KiA ON4 OttawaON K1AON4 Canada canada
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The study area is approximately 120 km north-west of the community of Rankin Inlet. and JO km SW of the tidal waters of Cross Bay in Chesterfield Inlet. Geological mapping from l993- 19% in this area covered 350 km' of parts of the Gibson Lake (55N/12)- MacQuoid Lake (55W9)rnaps. This area is underlain by a polydeformed sequence of mafic to felsic metavolcanic rocks and relateci clastic and chernical rnetasedimentary rocks, dlof the Archean Gibson-MacQuoid Greenstone Belt. Granitic gneiss is interlayered with the metavolcanic and metasedimentary rocks. and forms the nonhem and southem boundary to the greenstone belt. Archean granitic intrusions are common in the western pans of the map area. and younger gabbro intrusions and lamprophyre and diabase dykes are cornmon throughout the map area. The Archean stratigraphy in the study area was deposited within a shallow subaquous environment of deposition in a continental marginal arc environment. near the boundary of the back-arc basin and sialic maton. Deposition of the supracrustal rocks was accompanied by the formation of the Sandhill volcanic-hosted massive sulphide prospect. The rocks and mineraiization were then subjected to an Archean (ca 2.6 Ga) tectonothermal event which involved compression. amphibolite grade metamorphism. and diapiric emplacement of granitic bodies. Later. ri fting of the Archean basement and supracrustal rocks resulted in the emplacement of the Suluk Gabbro and Suluk Ni-Cu-Co occurrence at ca. 2.2 Ga. Following a Proterozoic (ca 1.94 Ga) tectonotherrnal event. thermal relaxation and brittle faulting of the cmst was accornpanied by the emplacement of the diamondilerous Akluilâk lamprophyre dyke. The Sandhill prospect, located in the central part of the map area. is comprised of a zone of stratiform base metal suiphide rnineralization hosted within an extensive concordant horizon of pyritic quartz-muscovite schist. This schist horizon is stratabound to a felsic-intermediate metavolcaniclastic unit. Alteration assemblages and weakly sulphidic quartz-muscovite schist horizons extend discontinuously for 12 km eastward dong strike. The host metavolcaniclastic unit is bounded to the north by orthogneiss. and to the south by an interlayered sequence of felsic-mafic metavolcanic rocks, and is terminated to the West by ü late north-west trending fault. Significant Zn rnineralization is hosted within graphitic argillite horizons in the western parts of the map area. In the main Sandhill zone. massive and disseminated sphalerite occurs within multiple 1-2 m horizons in the upper 15-20 m of the quartz-muscovite scliist. Surface samples assayed up to 9.3 % Zn and 160 gtonne Ag. The sulphide mineralization is directly associated with the highly aluminous assemblage of Mn-gamet. Zn-staurolite. and gahnite. a Zn spinel. Several concordant silicified horizons, 0.5- 1.5 rn thick. contain stringer sphalerite and disseminated chalcopyrite. Samples from these horizons assayed up to 3.5 % Zn. 1.0 % Cu. and 185 g/tonne Ag. Mineralogy and whole rock pochemistry indicates the quartz-muscovite schist represents the metamorphosed equivalent of intense sericite alteration of the host metavolcaniclastic unit. This hydrothermal alteration resulted in the loss of Ca. Na and Mg as well as Sr, Ba and the LREE. and ri gain in Mn and Fe as well as Zn. Pb. Cu and S. This schist horizon is enclosed in a much broader envelope of less intensely altered metavolcaniclastic rocks. This alteration is mainly developed in the structural hanging wall to the mineralised zone. Geochemistry indicates less intense but consistent chemical changes, most notably the addition of Mn, which graduaily becornes less intense in an outwards direction. The features which characterise the Sandhill zone define it as a metarnorphosed Cu-Zn type voicanic-hosted massive sulphide prospect. It formed aî a replacement deposit. distal to a hydrothermal discharge zone. The Suluk base metal sulphide occurrence was discovercd during the 1994 field season. Four surface sarnples of massive sulphide were found to contain anomalous concentrations of Ni, Cu and Co. These four samples averaged 2.2 C/o Ni, 1.7 % Cu and 0.14 % Co. The Suluk occurrence is a 045-050" striking zone of massive to semi-massive sulphides that can be traced discontinuously over a strike length of 650 m. The occurrence is hosted in a north-dipping sequence of strongly foliated Archean rnafic metavolcanic rocks. Sulphides. inciuding pyrrhotite. marcasite. chalcopyrite. violarite and pentlandite occur within several vertically dipping zones which are oriented perpendicular to the regional structural trend. These zones Vary from 0.5-1 rn in maximum thickness and taper out over a strike length of 3-4 meters southwards. The sulphides are in sharp contact with the host rock and show no interna1 fabric. Rounded gabbro xenoliths as well as mafic rnetavolcanic xenoliths occur within the sulphide zones. The Suluk occurrence is spatially associrited with a ca 2.2 Ga gabbroic intrusion. referred to as the Suluk gabbro. immediately to the West and may be genetically related. The geological characteristics of the Suluk sulphide zone and Suluk gabbro show similarities to those reported [rom Proterozoic Ni-related gabbro intrusions in the Bah ic Shield. A unique diamond-bearing lamprophyre dyke. the Akluilâk dyke was discovered approxirnately 1.5 km south-west of the Sandhill prospect. The dyke is north-striking, near vertical and crosscuts the Archean stratigraphy. It measures 0.5- 1.5 rn wide and is exposed continuously for 200 m. The Akluilik dyke consists of coarse grained oikocrystic orthoclase separated by aggregates of bioiite. calcite. lesser apatite and accessory rutile and pyrite. indicator minerais. identified in mineral separates. include olivine. chrome spinel. gamet (G9). pyroxene (low chrome and Ti diopside). and homblende. Petrogrüphically and chernical ly. the Akluilâ k dyke is classified as a calc-alkaline. ultrapotassic minette. Diamoods are yellow-brown in colour. but a few are pale yellow and pale green. Larger black crystals are the result of a thin graphite coat. Diamond crystal shapes include octahedra, macles, cubes and dodecahedra. A monazite-bearing apatite from the Akluilâk dyke yielded a Pb-Pb isochron age of 1832 + 28 Ma. The regiondly extensive mineralization and alteration associated with the Sandhill prospect. the newly discovered Suluk Ni-Cu-Co occurrence and diarnondiferous Akluilâk larnprophyre dyke indicates the promising resource potential of this region. ACKNO WLEDGMENTS
1 would like to express my appreciation to n number of people and agencies who helped make this thesis possible. First and forernost. I thank Dr. Neil MacRae for his continued supervision and for his discussions and ideas on various pans of the thesis. His encouragement throughout the term of this project was invaluable. Also Dr. Allan Miller of the Geological Survey of Canada for his ideas and vaiuable geologic discussions on the geology of the western Churchill Province; these discussions help put the geology of my thesis area into perspective. Without these two people and their confidence in rny abilities. this thesis in its present fom would not have been completed. 1 thank Phi1 Mudry, Mumy Pyke and Mark Baiog of Comaplex Minerals Corp. for making avai lable unpubl ished data frorn the Gibson-MacQuoid Lake area and logistical support. 1 aiso thank them for there continuous support and encouragement in completing this thesis. I also thank Cornaplex for the use of their cornputer and photocopying facilities during the completion of this thesis. 1 thank Dean Besserer. Adrienne Jones and Sergio Alvarado for field assistance. 1thank the following people at the University of Western Ontario for lecnical support: John Fonh and Gord Wood in the rock preperation Lab. Charlie Wu in the X-ny Fluoresence Spectrometer Lab. and Bob Bamette and Yves Thibault in the Electrom Microprobe Lab. I thank Melinda Tatty of M&T Enterprises Ltd., Rankin Inlet for excellent expediting services during the two field seasons. 1 thank the following agencies for financial support for this project: Canada- Northwest Territories Minerd Initiatives ( 199 1- 1996) (Project # 8 10024), an initiative under the Canada-Northwest Territories Econornic Development Cooperation Agreement: Indian and Northern Affairs Canada (Contract No. YK-94-95-029) and Natural Sciences and Engineering Research Council of Canada (Grant No. OGP 0005539). TABLE OF CONTENTS
CERTIFICATE OF EXAMINATION ii ABSTRACT iii ACKMOWLEDGMENTS v i TABLE OF CONTENTS vii LIST OF APPENDICES ix LIST OF FIGURES ix LIST OF PLATES xi LIST OF TABLES xi LIST OF MAPS xi
CHAPTER SECTION PAGE NUMBER
1. INTRODUCTION 1.1 Location and Access 1 1.2 Regional Geology 4 1.3 Purpose of Study 11 1.4 Previous work in the Gibson-MacQuoid Lake area 1.4.1 Bedrock Mapping 12 1.4.2 Mineral Exploration 13 1.5 MethodsofInvestigation 14 1.6 Analytical Procedures 1.6.1 Whole Rock Chemical Analysis 14 1.6.2 Mineral Chemical Analysis 16
2. GEOLOGY OF THE GIBSON-MACQUOID LAKE AREA introduction 18 Gibson-MacQuoid Greenstone Belt 2.2- 1 Mafk Metavolcanic Rocks 18 2.2.2 Intermediate Metavoicanic Rocks 25 2.2.3 Intermediate-Felsic Metavolcaniclast ic Rocks 27 2.2.4 Clastic Metasedimentary Rocks 30 2.2.5 Chemical Metasedimentary Rocks 38 Age of the Gibson-MacQuoid Belt 39 Orthogneiss 39 Granitoid Intrusions 40 Gabbro 41 Lamprophyre Dykes 43 Pegmatite Dykes 44 Diabase Dykes 45 Conclusions 45
vii 3. STRUCTURE AND METAMORPHIC PETROLOGY OF THE GIBSON- MACQUOID GREENSTONE BELT 3.1 Introduction 47 3.2 RegionalSinictureandMetmorphism 3.2.1 RankinInletarea 47 3.2.2 Chesterfield Idet/Barbour Bay area 49 3.2.3 MacQuoid Lake are3 50 3.3 Gibson-MacQuoid Lake area 3.3.1 Structure 51 3.3.2 Metamorphism 55 3.4 Conditions of Metamorphism 3.4.1 Petrogenetic Grid 56 3.4.2 Gamet-Biotite Geothermometer 57 3.4.3 Gamet-Hornblende Geothemometer 6 1 3.4.1 Hornblende-Plagioclase Geothermometer 63 3.5 Conclusion 64
4. TECTONIC SETTING OF THE GIBSON-MACQUOID GREENSTONE ELT(PRIV"TE ) 4.1 Introduction 65 4.2 Geological Characteristics of Mafic Metavolcanic rocks 66 4.3 GML Metavolcanic Rocks 4.3.1 Mafic Me tavolcanic Rocks 70 4-32 Felsic-Intermediate Metavolcanic Rocks 73 4.4 Clastic Metasedimentary Rocks 80 4.5 Granitoid Rocks 86 4.6 Conclusions 91
5. THE SANDHILL VOLCANIC-ASSOCIATED BASE METAL MASSIVE SULPHIDE PROSPECT 5.1 Introduction 93 5.2 Volcanic-Associated Massive Sulphide Deposits 5.2.1 General Characteristics 94 5.2.2 Deposit Scale Characteristics 95 5.2.3 Classification 98 5.2.4 Genetic Mode1 10 1 5.3 Sandhill Prospect 104 5.4 Recent Exploration 118 5.5 Classification of the Sandhill Prospect 119 5.6 Conclusion 122
6. GEOLOGICAL CHARACTERISTICS OF THE SULUK OCCURRENCE AND SULUK GABBRO 6. f Introduction 124
viii 6.2 Geology of the Suluk Occurrence 124 6.3 Geochemistry and Mineralogy of the Massive Sulphide Ore 6.3.1 Surface 126 6.3-2 Subsurface 130 6.4 Genetic Association of the Suluk Occurrence 130 6.5 Suluk Gabbro 6.5.1 Geology and Petrography 13 1 6.5.2 Geochemistry 133 6.5.3 RecentExplorationoftheSulukGabbro 137 6.6 Age Constraint of the Suluk Gabbro and Suiuk Ni-Cu-Co Occurrence 137 6.7 Metallogenic Implications 139
7. GEOLOGICAL CHARACTERISTICS OF THE AKLUILAK DYKE AND OTHER LAMPROPHYRE DYKES IN THE GIBSON-MACQUOID LAKE AREA 7.1 introduction 143 7.2 The Christopher Island Formation 144 7.3 The GML Lamprophyre nykes 149 7.3.1 The Akluiliik Dyke 160 7.4 Conclusion 164
8. CONCLUSIONS 174
REFFERENCES 177
LIST OF APPENDICES 1. Modal Mineralogy and Sample Locaticjn Maps 187 2. Whole Rock Chemistry 198 3. Mineral Chemistry 208 4. Results of Geothermometry Calculations 244
LIST OF FIGURES Location of the Gibson-MacQuoid Lake area 2 Major crustal components of the western Churchill Structural Province 5 Geology of the western Churchill Province and location of the Study Area 7 Major elernent classification diagrams for the mafic metavolcanic rocks 22 Plots of mineral chemistry for the mafic metavolcanic rocks24 Major element classification diagrams for the felsic-intermediate metavolcaniclastic rocks 29 Plots of mineral chernistry for the felsic-intermediate metavolcanic 1astic rocks 31 Plots of mineral chemistry for the felsic-intermediate metavolcaniclastic rocks 32 Plots of mineral chemistry for the clastic metasedimentary rocks 36 Plots of mineral chemistry for the clastic metasedimentary rocks 37 Major element classification diagrains for the granitoid rocks 42 Regional conditions of metamorphism 48 Orientation of ptanar and linear fabrics 52 Petrogenetic Grid 58 N-MORB-normalised diagrams for tholeiitic mafic volcanic rocks 69 N-MORB norrnalised multielement diagrarn of the GML rnafic metavolcanic rocks 72 Chondrite-normaiized REE plot of the GML rnafic metavolcanic rocks 74 Tecronic discrimination diagrams for the GML rnafic rnetavolcanic rocks 75 Comparison of mafic volcanic rocks from various tectonic environments with the GML rnafic metavolcanic 76 N-MORB- and Chondrite-normalized plots for the intermediate to felsic metavolcaniclastic rocks 78 Tectonic discrimination diagrams for the intermediate to felsic rnetavolcaniclas tic rocks 79 Spiderplot of selected sarnples of GML metagreywacke 82 A-CN-K diagram for the GML metagreywücke 85 Comparison of the trace element compositions of average granite types with GML granitoid rocks 89 Tectonic discrimination diagrams for the granitoid rocks 90 Evolutionary sequence of the GMB 92 Characteristics of a VMS deposit 96 Classification of VMS deposits 99 Genetic models for VMS deposits 102 The Sandhill Prospect 105 Major element characteristics of alteration in the Sandhill Area Trace element characteristics of alteration in the SandhilI Area REE characterist ics of alteration in the Srindhiil Area 111 Minera1 Chemistry of Alteration Phases in the Sandhill Area Map of Alteration in the Sandhill Area 115 Mineral Chemistry of Alteration Phases in the Sandhill Area Classification of the Sandhill Prospect 120 Geolugy Map of the Suluk Occurrence 125 Geochemistry of the Suluk Gabbro 135 AFM Plot for the Suluk Gabbro Samples 136 Genetic Mode1 for The Suluk Gabbro and Suluk Occurrence Distribution of the Dubawnt Supergroup 145 Location of the GML lamprophyre dykes 150 Plots of minerai chemistry for the GML larnprophyre dykes 152 Plots of minera1 chemistry for the GML lamprophyre dykes 153 Plots of Major element Geochemistry for the lamprophyre dykes 7.6 Major elernent classification diagrarn for the lamprophyre dykes 157 7.7 N-MORB and Chondrite-nonnalized REE plot for the GML larnprophyre dykes 158 7.8 N-MORB and Chondrite-normalized REE plot for the larnprophyre dykes 165
LIST OF PLATES 1.1 Topography in the study area 3 1.2 West-trending gabbl~dykc 3 7.1 Field photographs of the mafïc metavolcanic rocks 20 2.2 Intermediate metavolcanic conglornerate 26 2.3 Felsic-intermediate rnetavolcaniclastic rocks 26 3.1 Stmctural features in the field area 54 6.1 Back-scatter clectron images of sulphides in the Suluk Occurrence 129 7.1 Back-scatter electron images of Feldspar in lamprophyre dykes 154 7.2 Field photognph of the Akluilâk Dyke 161 7.3 Ultamafic Xenolith in the Akluilak Dyke 161 7.4 SEM photograph of micro-diarnonds recovered from Akluilâk Dyke 163
LIST OF TABLES Major element geochemistry of the maFic metavolcanic rocks 21 Major element geochemistry of the felsic-intermediate metavolcaniclastic rocks 28 Major element geochemistry of' the clastic rnetasedimentary rocks 34 Major elernent geochernistiy of the granitoid intrusive rocks 41 Summary of temperatures calculated from geothermorneters 60 Trace element characteristics of tholeiitic mafic voIcanic rocks from various tectonic settings 67 Trace and REE chernistry of the rnafic metavolcanic rocks 71 Trace and REE chemistry of the intermediate to felsic mctavoIcaniclastic rocks 77 Trace element characteristics of the rnetagreywacke. and average Archean greywacke 81 Trace element characteristics of the granitoid rocks, and average granite types 88 Geochemistry of Sphalerite 106 Geochemistry of pyrite, chalcopyrite, galena and stannite 107 Sulphide mineral chemistry 128 Sulphide mineralchemistry 130 Geochernistry of the Suluk Gabbro 134 Major element geochemistry of the Lamprophyre Dykes 147 Trace and REE geochernistry of the Lamprophyre Dykes 148 Electron microprobe analysis frorn the GML Lamprophyre dykes 168
LIST OF MAPS Map. Geology of the Gibson-MacQuoid Lake area In Pocket INTRODUCTION
1.1 LOCATION AND ACCESS The study area Lies in parts of the Gihn Lake (5SNI12) and MacQuoid Lake (55M/9)map sheets and underlies an area of 350 lm2.The area is approxmiately 120 km north-west of the cornmunity of Ra& Idet, District of Keewatm (Fig. 1.1 ), and 40 km south-west of the tidal waters of Chesterfield Inlet. This region is part of the barren lands that is devoid of trees, except for isolateci patches of low bush. The climate is severe with long, col4 windy winters and short, warm, relatively dry summers. The topography in the study area is characterised by abundant Iakes, extensive outcrop, and variable glacial debris (bodder fields, eskers, etc.) (Plate 1.1). Relief is low, typically 60 to 90 meters above sea level, and reaches a maximum elevation of 140 rn in the western part of the area Outcrop is good to excellent with 40-70 % exposure allowing for hi& station density and easy correlation of units. Outcrop inciudes rounded hiUs of mafic volcanic rocks granitoids and gneiss and low-lying feisic voIcanic and sedimentary rocks. West-trending eloogate gabbro dykes (Plate 1.2) form prominent ridges throughout the map area. Most outcrops in the map area are heavily lichen-covered, which obscures geologic textures and structures. The study area is readily accessible by helicopter, or srnail fixed wing aircrafi on skieiwheels until early to mid June and floats fiom emly to mid July until October. Equipment and supplies can also be moved overland by sww machine during the winter months. Rankin Inlet and Baker Lake (Fig. 1.1) are supplied daily by commercial aircraft fiom Yellowlmae, N.W.T or fkom Wmnipeg Manitoba, and have well established expediting services. Dinmg the short shipping season (Jdy to October), water transportation is available fkom Churchill to Rankm Inlet, and Baker Lake via Chesterfield Inlet, Victoria Baffin Island lslan O
District O of ~orthwest~emtories
Mackenzie ,*,' District of Keewatin
Baker Lake Study area*gsterfield
Alberta Hudson Bay
Saskatchewan 1 Ontario
Figure 1.1. Geographical location of the Gibson-MacQuoid Lake study area. Plate 1.1. Topography in the study area (view looking south). Relief in the field of view is approximately 15-20 meters.
Plate 1.2. West-trending gabbro ridge north-west of the Sandhill Prospect (view looking north-west). Relief ofthe tidge is approximately 30 meters.. 1.2 REGIONAL GEOLOGY AND TECTONIC SETTING The study area lies within the western part of the ChurchiU Structural Province of the Canadian Shield (Fig. 1.2). The geology of the western Churchill Province includes Archean gneisses, Archean supracrustal rocks. and unconformable Early Proterozoic sheif sequences. and igneous rocks. The Archean rocks have been subdivided based upon Lithologic-tectonic-geochronologic characteristics: subdivisions include zones, blocks. subprovinces and belts. These rocks record a complex history of polypbase deformation and metarnorphisrn during the Archean Keno ran (ca. 2.6-2.5) and Early Pro terozo ic Hudsonian (ca 2.0-1 -85) orogenies (Stockweil 196 1). The Archean rocks in this region comprise part of the Amer Lake Zone (ALZ) (Zone 4 of Lewry et al. 1985). The ALZ is that portion of the Churchill Province consisting of Archean basement, abundant Early Pro terozo ic granite p luto ns and supracrusta1 remnants which are variab. marked by Proterozoic reworking. The ALZ was Wher subdivided, based on lithologic chatacter and erosional level of exposed cmt. into six structural blocks. Each block is separated by major structural breaks (Hom1980; Heywood and Schau 1978; Fraser 1987; Lewrey et al. 1978. 1985: Wright 1967; and others). The Tdtson and Queen Maud blocks (Fig. 1 2)are essentially hi& grade terranes which represent deep cwtdIeveis; they include amphibole to pyroxene granulite gneisses of quartz diontic to granitic compositions, and rninor high grade supracrustal rocks. The Cornmittee Bay and Armit Lake blocks represent intermediate to deep crusta1 levels; they conskt O f greenschist to granulite facies c haxmoc hit ic, tonalit ic, and granit ic gneisses and greenschist to lower amphibolite supracnistal rocks. The Ennadai and Tulemalu blocks represent shallow to moderate level terranes composed predominantly of low grade supracrusta1 rocks. Tella and Eade (1986) proposed that the Archean rocks in the Kamiiukuak Lake area be subdivided into two major terranes; the terranes king separated by a 5 km wide north-east-trending ductile deformation zone referred to as the Tulemalu huit zone (TFZ) (Fig. 1-2). The TFZ separates a predomulantly Archean granulite terrane to the West and a
relatively lower grade terrane composed of Archean supracrustal rocks to the east. Based on geological, geophysical. and aerornagneric data Tehand Eade ( 1986) postulated that the TF2 represents the northerly extension of the Virgin River fault zone (VRFZ) and BIack Lake fault zone (BLFZ), documented in Saskatchewan (Lewry and Sibbald 1977: Hanmer 1987), which collectively represent a major structural break. Hotnnan (1988) referred to the TFZ. VRFZ and BLFZ collectiveiy as the Snowbird tectonic zone (Fig. 1.2) and used thk major cnistal break as a province bomdary. He subdivided the north-western Churchill Province into the Rae Province (which includes the Taltson Queen Maud? Cornmittee Bay and Arrnit Lake blocks) and the Heam Province (which uicludes the Ennadai and Tulemalu blocks) (Fig. 1.2). This subdivision is based on a distinct set of Archean greenstone belts in each province. Recently, bmer and Teh ( 1995) further subdivided the Archean greenstone kits in the centrai Churchill Province into three tirne Lithostratipphic sequences based on rock associations and age of volcanism (Fig. 1.3). West of the Snowbird tectonic zone (i.e. in the Rae Province), the ca 2.8 Ga (Roddick et al. 1992; Teh et al. 1985) Woodbum Lake Group (WLG) is characterised by a bhodal sequence of komatiitic-tholeiitic dcand ultramafic volcanic rocks and calc- aikaline felsic flo ws and tuffs: interlayered sedimentary rocks include greywacke. iro n formation and quartzite (Henderson et al. 199 1; Annesley 1989; Ashton 1988: Fraser 1987). The volcanic rocks of the WLG are interpreted to have formed in a continental marginal arc environment (hesiey 1989). Rocks of the WLG have ken rnetamorphosed under greenschist to amphibolite facies and intruded by ca 1.6 Ga (Ashton 1988; Roddick et al. 1992) granite plutom. Similar granitic rocks comprise the Tehek Plutonic Complex in the Baker Lake area (Heywood and Schau 1981; Schau et al. 1982). A second major tectonic event at 2.0-1.8 Ga produced north-east-verging structures and minor alkalic plutoaism. Associated themial events resulted in the re-setting of K-Ar and 'OA~/'~A~ age dates (Ashton 1988). Supracrustal rocks lithologically sunilar to the WLG occur to the nonh-east, the Prince Albert Group (Schau 1982; Frish 1982) and to the south-west. the Ketyet River Group (Taylor 1985) (Fig. 1.3).
East of the Snowbird Tectonic Zone (the Hearne Province), two ages of greenstone bebs are reco+&ed: the ca 2.69 Ga Kammak greenStone belt (Mortensen and Thorpe 1987; Cavell et al. 1992) and a series of ca 2.66 Ga greenstone belts including the Rankin Inlet Group and the Yathkyed-Angikuni and Ennadai Lake belts (Fig. 1.3). Both ages of greenstone belts are characterised by multicyclic mafic to fekic volcanic piles. intercdated clastic and chemical sedimentary rocks, and composite tonalitic to granitic piutons. The Kamioak greenstone kit (KGB) is the largest and most continuous greemtone belt in the Churchill Province (Fig. 1.3). It extends for approximately 480 km fiom the Hudson Bay Coast south-westward. The belt is characterised by mafk to felsic volcanic rocks and intercaiated c lastic and chernical sediments (Davidson 1970; Ridler I 972, 1973 ;
Ridler and Shilts 1974; Park and Ralser 19%). Davidson ( 1970) O riginally subdivided the rocks of the KGB into three broad groups of volcanic and sedimentary rocks. Ridler (1973) and Ridler and Shilts (1974) re-e? 1.3 PURPOSE OF THIS STUDY The Gibson-MacQuoid Lake area Lies in a region that has received minimal geological mapping and mineral exploration. 'The area is underlain by the Archean Gibson- MacQuoid greenstone belt (GiMB) (Fig. 1.3). and is one of the lem understood vo lcanic- sedimentary sequences in the western Churchill Structurai Province of the Canadian Shield. Despite a limited geological data base for this belt. prelirninary investigations indicate a potential for fiinire mineral exploitation. The Lithological and structural pattern of the GMB is similar to better understood and geologicdy constrained Archean greenstone belts elsewhere in the western Churchill Province which host base metal massive sulphide and other metal deposits. The emphasis of this project is to describe the geological characteristics of the Sandhill Prospect, a base metal massive sulphide zone: the geo log ical c haracterinics of the .4kluilâk diarnondiferous lampro phyre dyke (alias the Thirsty Lake Dyke) and Suluk Ni-Cu-Co occurrence, discovered during this project. are also discussed. The project area is in a region affected by Proterozoic reactivation and consequently the Pro terozo ic tectono thermal overprint on the Archean history must also be evaluated. The proxüriity of the project area to an existing inhstructure (Rankin Met) and a vansportation comdor (Chesterfield Met) (Fig. 1.1) is viewed as a positive economic criterion that signals it as a prime exploration target and suitable for renewed geoscience research. This project wid enhance the Limited data base available on this area and provide usefil guidelines for Merexploration for base-met& and diamonds on a more local scale, Li the Gibson-MacQuoid greenstone belt. The specific project objectives are: to map and document (£iom 1:30 000 scaie base maps) LithologicaL structural and mheralogical features of the Gibson-MacQuoid belt and dehe possible aructural and/or stratigraphie relationslips of the Sandhill zone: to document alteration patterns in and around the Sandhill zone ushg thin-section petrography and whole rock and minerai chemistry; to esvamine the conditions and effects of metamorphism on the Sandhill zone: to discus the ongin of the SandhilI zone and to compare it with other better known base metal massive suiphide deposits: to document the geological characteristics of the Akiuilâk diamondiferou lamprophyre dyke and Suiuk Ni-Cu-Co occurrence; and to conduct geochronological investigations on the volcanic and plutonic rocks to constrain the timing of deformation and metamorphism PREVIOUS WORK IN THE GIBSON-MACQUOID LAKE AREA Bedrock Mapping The Gibson-MacQuoid Lake area was previously mapped by the Geologicd Survey of Canada on a reconnaissance scale (1 inch=8 miles), as part of a regional mapping project (Wright 1967). Results of more recent rnapping in and around the proposed study area are summarised in reports by Reinhardt and Chandler (19731, LeCheminant et ai. (1976,1977), Reinhardt et aL (1980) and Tella et. al. (1 992, 1993). The area is underlain by an ArcheanlProterozoic granite-greenstow-gneiss terrane. Litho 10 gies in the Gibson-MacQuo id Lake area include an extensive east- west- trending greenstone belt, the GMB, which is comprised of an Archean sequence of interbedded dcvolcanic rocks and clastic and chernical sedimentary rocks, wirth lesser proportions of intermediate to felsic volcanic rocks. ail metamorphosed to the amphibolite Eicies. SmaUer gabbro and syenite bodies of uncertain age intrude the volcanic and sedimentary rocks. The volcanic and sedknentûry sequence is bounded to the north and south by granite gneisses and rnigmatites and younger granitoids. 1.4.2 Minerai Exploration The GMB was fïrst investipated for its economic potential in 1986 by Comaplex Minerals Corporation and Asamera Minerals Inc.: a two-person prospecthg team evaluated the potential for precious metal minerakation in the volcanic belt. Samples of sulphidic iron formation and quartz veuiing returned values of up to 5.1 and 21.0 e/t Au respectively. In 1987, a 2% week foilow-up sampling program resulted in values as high as 44 g/t Au fiom samples of sulphidic Bon formation in what are referred to as the Falcon and Camp zones (Hauseux 1987). In the spring of 1988. an extensive reconnaissance and detailed exploration program by Comaplex Minerals Corporation (Staargaard 1988) identified additio na1 auriferous iron formation which returned values as high as 12.9 g/t Au. A major base metal massive sulphide zone, the Sandhill Prospect. was also identined. A 2.3 by 0.8 km grid was connnicted over an east-west trending area containing zinc and pyrite-rich kost heaved boulders. Grid work included detailed geologicai rnapping, sarnpling, and magnetic and VLF-EM surveys. The SandhiU Prospect was found to be comprised of a zone of stratiform sphaierite, chaicopyrite and galena mineralkation whicb is hosted within a 900m long zone of highly altered intermediate to felsic t&. Representative sarnples of mineraiization contain up to 2% each of Zn and Cu; Pb up to 0.25% (Staargaard 1988). Go ld and silver values are up t O 0.1 5 and 15 g/t respectively; a few sarnples yielded up to 311 g/t Ag. In 1992, an airborne magnetic and electromagnetic survey was conducted for Cornaplex Minerals Corp. over the area encompassing the Sandhill Prospect. A number of weakly anornalous electromagnetic and magnetic responses were identitied over the Sandhill Prospect, ho wever, these responses were no t fo ilo wed up. No Mer work was conducted on the SmdhiII Prospect untii initiation of the present PbD. study in 1993. This study resulted in recognition of new and extensive base metai dphide rnineralization and diamonds during the 1993 and 1994 field seasons. and m renewed exploration activity m the Gibn-MacQuoid Belt. E.xploration by Cumberland Resources Ltd during the 1995 and 1996 field seasons consisteci of airborne and ground Ceeophysics. prospecthg detailed geologicai rnapping and diamond drilling (Lewis 1996). The pro gram was multi-purpose with the objective of Merenhancing the base rnetal and diamond potentiai of the GMB. This recent exploration work will be descnbed in successive chapters on the SandhiU Prospect, the Sduk occurrence and the Akluilàk diamondiferous iamprophye dyke. 1.5 METHODS OF INVESTIGATION Bedrock mapping (1:30,000) was conducted during the 1993 and 1994 field seasons (June to August) by a two-person crew. Further mapping was completed in August 1995. Detailed rnapping (1 :2.500) was completed on the SandhiU zone. Field data was processed ushg field- base portable PC, pocket cornputers, and FIELD LOG (Brodaric and Fyon 1989) v. 2.83 and AutoCAD software applications. A suite of samples for standard and poiished thin sections were used to idente Lithologies for the purpose of compiling a geologic map. These sarnples were also used to audy the rnineralogical and tedmrelationship to determine the metamorphic histox and to outline the rnineralogicai characteristics of the SandhiU zone and enclosing alteration envelope. Mole rock and minerai chernicai compositions were determined to c haracterise the volcanic and sedimentary rocks and to document the chernical changes within and away hmthe SandhiU zone. Several samples of volcanic and plutonic rock were chosen for geochronology by 40~r/~'~r and U/Pb techniques, to constrain the timing of volcanism, deformation and rnetamo rp him 1.6 ANALYTICAL PROCEEDURES 1.6.1 Whole Rock Chernical Analysis Llajor, trace, and rare earth element analyses was completed on representative samples of the various lithologies in the study area. Considerable care was taken to sarnple oniy the least-altered rocks to mùumise the effects of secondary aiteration such as that . which occurs dong joints and Eactures and in veins. Samples were also trimmed of weathered material both in the field and pnor to cnishing using a hammer and a water- cooled rock saw. Classification and charactensation of the analysed samples are based on various geochemicai discriminate diagrarns used in the text; data is plotted on a loss-on- ignition-Eee bais for proper cornparison of the data. Sarnpies for which Fd3 and total iron are detemiined. the CIPW nom and Mg # ( molecular WgO / (Mg0 + F~o')] * 100) was calculated using either detertnined values of Fe0 and Fe205 or a tived Fe203ReO ratio which is based on the average of the determined values for each rock tfle. Analysis of representative samples were partially determined at the University of Western Ontario (UWO) with the majority of the samples done at X-ray assay Labs (XRAL) in Don Mills, Ontario. Duplicate samples were in good agreement between labs. Samples analysed at UWO were crushed and milled to about -250 mesh by a mild steel rniii at Activation Lab LTD. in Ancaster, Ontario. Major and trace elements were dysed by X-ray fluorescence (XE) using a Phillips PW 1150 automated wavelength dispersive spectrometer. REE and some trace elements (Sc, Cs, Ta, HE, Th. and U) were determined using Instrumental Neutron Activation Analysis (LNAA) by an Ortec hyper- pure germanium detector comected to a Canberra 8k multichannel analyser. Analysis of standards indicate accuracy in the data is commonly within 5% for the major elements, and within 10% for the trace elements and REE. Major elements were determuied on fused discs. These were prepared using 5g of a mixture of lithium tetraborate, lithium carbonate and lanthanum oxide with the residue fiom LOI detenninations; amonium iodide NHJ was also added as a non-wetting agent. This mixture was placed in a Pt crucible and fked for 20 minutes at approxirnately 1000°C.The mixture was poured into a Pt mould and dowed to set. LOI was determined by heating 1 g of each sample at 1000°C for 2 hom. The loss of weight of each sample reflects the total volatile content. Trace elements were determined on pressed pellets. The pellets were prepared by mkhg 6g of each sarnple with 6 drops of polyvinyl alcohol(2% by weight) solution. The sample in a bric acid backing was placed in a press for 5 minutes at 50 tons per square inch pressure. Powdered samples for REE analysis were irradiated at the McMaster University react O r. Detection Limits are as follows: for the major elements: 0.0 1 wt. %; for Nb. Zr, Y, Sr, Ga and Rb: 2 ppm; for Pb, Zq Cu, Ni. Co, Cr. V. Bi, Ag and Ba: 5 ppm: for As. Cs and Sc:0.5 ppm; for Au: 2 ppb; for Ta and HE 0.1 ppm: and for La, Ce. Nd. SnEu. Tb, Yb and Th 0.2 ppm X-mv Assav Laboratories (XRAL) For sarnples dysed at XRAL, major elements and Rb, Sr, Y, Zr, Nb and Ba were anaiysed by XRF using a Phillips PW 1400 wavelength dispersive spectrometer; Fe0 % and Hz0 % were determined by wet titration; CO2 % was determined by CO2 Coulometer; S was determined by LECO. The remainder of the trace elements were done by inductively-coupled Planna Emission Spectroscopy (ICP). AU REE itnalysis were detennined by ICP- ~MassSpectrometry (MS). Pt and Pd were determined by &me atomic direct current plasma emission spectroscopy. Repiicate analysis of our rock samples suggest uncertainties of B%for major elements and cornmonly <8% for trace elements and REE. Detection Limts are as follows: for major elements (including S): 0.01 W. %; for Rb, Sr, Y, Zr, Nb, Ba, V and Pb: 2 ppm: for Sb: 5 ppm Sn: 10 ppm; As and Bi: 3 ppm; Cr, Co, Ni, Y, Mo and Cd: 1 ppm; Cu, Zn and Zr: 0.5 pprn; La, Ce, Pr, Nd. Sm, Gd, Tb, Dy, Er, Tm Yb, Th and U: O. 1 ppm; Eu, Ho and Lu: 0.05 ppm; 1.6.2 Mineral Chernical Analysis Minerais were analysed at the University of Western Ontario using a JEOL IXA- 8600 Superpro be electron micro probe equipped with Tracor-No rthem TN-5500 automation; matrix correct ions were made using the Traco r-No rthem ZAF pro_gram. analysis were made with four automated wavelength dispersion spectrometers at an accelerating voltage of 15 kV and a bem current of 10 nA for silicate minerals. and 20 kV and 20 nA for sulphide minerals. Beam diameter used was 1 pm for rnost miner&. and 5 pn for muscovite and plagioclase to avoid volatilisation of Na Count times were 20 seconds for each element in the scheduIe. A variety of natural and synthetic minerais (Listed below) were used for standardisation before and during (to check for instrumental drift) each nin. The following mineral standards were used: Si: orthoclase or albite. orthopyroxene or pyrope; Al: anorthite 90. wakefield diopside or kaersutite: Ti: kaersutite or titanite; Ca: grossularite; K: onhoclase; Na: albite; Fe: orthopyroxene or fayalite; Mg: wakefield diopside, orthopyroxene, pyrope or olivine; C 1: tugtupite: F: L iF: P : durango or apatite; Ba: barite; Sr: SrTioz; Mn: spessmine or rhodenite; Cr: chromite; Ni: millerite; Cu: chakopyrite; Pb: gaiena: Zn: sphalerite; S: pyrite, pyrrhotite. sphalente? galena or chalcopyrite; Bi: pure Bi; Cd: greenochite; Co: pure Co; Ag: pure Ag; Sn: pure Sn. iMineral standard used was dependent on schedule used. Simple identification of miner& was completed using the Energy Dispersive Spectrometer connected to the probe. Ail structural formulas except for amphiboles were calculated using a standard computer program developed at the University of Western Ontario. Structural formulas for amphiboles were caiculated with the computer program PAPIKE. The proportion of ~e'-and ~e"in the atomic formula is the %id-point" between ferrous and femc iron for total iron, as determined following the procedure of Papike et. al. (1974). GEOLOGY, PETROGRAPHY AND MAJOR ELEMENT GEOCHEMISTRY OF THE) GIBSON-MACQUOID LAKE AREA 2.1 INTRODUCTION The scudy area is underiain by a polydeforrned and metarriorphosed north-dipping sequence of fèlsic to dcmetavolcanic rocks and mterlayered clastic and chernicd rnetasedimentary rocks (Map 1), al1 of the GMB (hmhge et aL 1994, 1995). Orthogneiss. coILSiStmg of variab& deformed and metamorphosed granitoid rocks, is interiayered with the metav~icaaicand sedimentary rocks, and fom the northern and southern bomdanes of the greenstone beh. Gabbro and @oid mtrusions and iamprophyre and diabase dykes are cormiion throughout the map area Granitoid is used here to descnbe mtnisive rocks mn& in composition fiom diode to tonalite tlnrough grmodiorite to Me. This Chapter descri'bes the lithological features of the Gibson-MacQuoid Lake area and inctudes thin-section petrography, major element who le rock chemistry. and mineral chemistry. Various geochemical plots are used to classi@ and characterise the iithologies and their miwdogy. A complete List of minerai assemblages and sarnple location nmps are presented in Appendix 1; a complete iïst of minerai chemisay is presented in Appendix 2. For clam, appendices wiU not be refend to m the rernainder of this Chapter. Additionai data on petrography and mind chemisny fiom several rock units are contained m a BSc. thesis (Besserer 1994). 2.2 GLBSON-MACQUOID GREENSTONE BELT 2.2.1 Mafic metavoicanic rocks In the eastem part of the map area (Map), n*lnc metavolcanic rocks fom linear, continuous to discontmuous bands up to 500 rn thick m map view. They are massive to bandeci, strongiy foliated to sbeared, and weakiy carbonatized (calcite): primary volcanic feanires are not well preserved m the rocks m this anzq however, relict pillow structures are Iody present. In the western parts of the area the dcrocks tom thicker horizons and are less sheared. but are mon& lineated and display prhmq volcanic features (Le. pillow strucnires) (Plate 2. la). especiaily m the region around Grizzly Lake. niese rocks consist of mteriayered massive to pillowed flows. bounded by metavolcanic breccias. and miwr intemratifed rnetavo lcaniclanic rocks. Weakly defodpiuows up to 1 m in diasneter are well developed north and east of Grizzly Lake. Some piUow structures mdicate that the straticgaphy yoqs to the north. Metavolcanic breccia Layers are typic* several meters thick and are characterised by angular Sagments set m a dark brown-weathering Fecarbonate-rich ma& The breccia is deeply pitted (Plate 2.1 b) as a result of carbonate weathering out Ln conhast, the massive and pillowed layers typiCayr form smooth, rounded outcrop SUTFLces. bletavolcanic bretcias domhate the stratigraphy directly north of Grizzly Lake and fom layers tens of meters thick: Fe-carbonate may form up to 30 % of the outcrop. Fe-carbonate is absent in the rnafic metavolcanic rocks in the eastern parts of the rnap area. Sparse mafic metavolcanichstic rocks form 1-2 m thick layers and consist of 0.4- 1 cm plagioclase clasts. parti* Batteneci paralle1 to the foliation Masive, weakly to swngiy foliated metagabbro sills are common in the dc metavolcanic un& especially m the western part of the map area. The dcmetavolcanic unit pmches out in the extrerne western end of the map area however, dcrocks form a major portion of the stratigraphy to the West in the MacQuoid Lake area (Teh et ai. 1997; Reinharrdt et al., 1980; LeCherninant et al, 1977); the mafk unit continues both to the south and to the east. Twenty-two samp1es of more massive horizons of the mafic metavolcanic rocks were collected for major element geochernistry (Table 2.1). The dcmetavolcanic rocks are predominantly basaltic in composition (<52 wt % Sioz; NazO + &O < 5 wt. %) (Fig. 2.la); few are basaitic andesites (52-57 wt. % Sioz). The rocks are predominantly hypersthene + dio pside + quartz-no mative and show a su baikaiïne tho leüt ic chemical trend (Fig. 2. l b). They have high total iron (FeO* = 9.99- 18.45 wt %), low magnessium Plate 2.1. Field photographs of the inafic metavolcanic rocks; a) small scale pillow structures from east of Grizzly Lake; b) breccia showing pitted surface as a result of weathered-out iron-carbonate north of Grizzly Lake; and, c) strongly foliated, massive and gametiferous (white porphyroblnsts) rocks, from the eastern part of the map area. SiO, (wt %) A-Cation % Figure 2.1. Major element classification diagrams for the volcanic rocks from the snidy area: (a) silica vs. total akalies (fkom Le Maitre 1989); (b) MM plot (fiom Irvine and Baragax 197 1); (c) silica vs. potassium (fiom Le Maitre 1 989); (d) Jenson ( 1976) cation plot. Pertinent fields are HFT - Hi&-Fe Tholeiite, HMT - High-Mg Tholeiite, TA - Tholeiitic Andesite, and CB - Calc-Aikaline Basait (3.61 -7.92 wt. % MgO) and Mg X's (32.02-56.2), low potassium ( Plagioclase varies in abundance fiom 20-50 modai %. It occurs as fine- to medium- graineci subidiobiastic, granoblastic crystals, and disphys relatively weil developed triple junction boundaries. Fme @ed plagioclase commoniy rims gamet crynals and in several samples aggregates of plagioclase form pseudomorphs der garnet. Pkgioclase cxynals are rare@ zoned and twinned and weakly sericitized. although plagioclase is commoniy sericitized adjacent to cross-cutting veiniets mdicatiq hte fluid migration Pkgioclase composition ranges korn oligociase to andesine (Anl7 to hs)(Fig. 2.2b). In generaL plagioclase qds nmmniglreplacjng garnet have a Uer average anorthite component (An3~)than matrix plagiocJ= cnstals (bd- Synvolcanic metagabbro sills (meter-scde) m the rnafic metavolcanic unit are dark green massive to fobed, and contain medium to coarse-grained blue-green amphibole and phgochse, and rare@ gamet; m the western part of the rnap area plagioclase may form 0.5-2 cm phenocrysts in the sills. These metagabbro silis are much more abundant in the western part of the niap area. 2.2.2 Intermediate metavolcanic rocks in the central and western parts of the rnap area (Map l), the dcmetavolcanic rocks grade abmptiy northward mto a preàomhantiy mterrnediate metavolcanic unit consishg pmnady of mterhyered (meter-scale) mono lithic metavo lcanic conglomerate (approximately 20-25 % of the unit) and fmer-grained metavolcaniçlasfc rocks. Conglomerate, as it is used here, refers to a metamorphoseci rnetavoIcaniciastic rock containmg rounded ciasts greater 2 mm (Cas and Wright 1987). The conglornerate (Plate 2.2) is matrix supported and is cornprised of 15-40 %, 10-50 cm long, light grey to green, rounded plagioclase-rich ciasts set m a fine- to medium-graineci laminated to banded ma& of blue-green amphibole + pkgiociase + quartz + gamet. Clasts are elongated pamlel to and are wrapped by the foliation-parallel bandÏng/'iammation Fie- to medium-grained metavolcaniclasfc rocks are characteriseci by 2-10 % subhedral plagiochse and minor quartz crystals m a plagioclase + quartz + biotite f blue- green amphibole f garnet ma& Severai mer-scale layers m the mdc metavolcanic unit CO& of 20-40% dum-to coarse-Wed, raudody orienteci. acicuiar needles of blue- green amphile m a predomhantly white-weathering plagioclase-rich mahn These layers occur within 50- 100 meters of the dc-mtennediate metavolcaic rock contact. 2.23 Intermediate to feisic metavolcaniclastic rocks A linear beit of predombntly intemediate to felsic metavoIcaniclastic rocks enends fiom the east to the central part of the map area where it terminates at a major north-west- trendmg fàdt (Map 1). This unit is host to the Sandhill prospect and associateci discontmuous aiteration horizons to the east (to be discussed m Chapter 5). The metavokaniclastic rocks are in sharp contact and typically interlayered with the southem-bounding dcmetavolcanic rocks and form a sharp contact with the northem-bounding gneiss. In an outcrop at the western end of the bek, a 0.5 m wide metavolcanic congiomerate consists of 6-30 cm long felsic clasts. A second less extensive belt of metavolcaniclastic rocks occurs adjacent to and w-raps around the granitoid and gabbro intrusions West of GaLake. Tnirty-four samples were collected fiom the felsic-mtermediate metavo lc~clasticunit. Because the eastem metavolcanickstic unit hosts the Sandhill prospect, the effects of hydrothermal aiteration mut be evaluated prior to geochemicai classification of vUs unit. Based on whole rock geochemistryTthe samples are subavided mto rnetavolcaniciastic and altered metavoIcaniclastic rocks. Generally, altered samples show a Ioss in NazO and Ca0 and gain in 1Mn0, F~O~and K20 with proxiInity to Sandhill horizon This geochemical variation is reflected m the variation in mineralogy. The change in geochemktry and miwralogy in altered volcaniclastic rocks wiu be discussed in more detail m chapter 5. Here, the major element geochemistry and mindogy of the relative& unabered samples is considered. Badon major element geochemistryTthe unaitered metavolcaniclastic rocks are predominantly dacite in composition (63-68 wt % Sioz; Fig. 2.3a; Table 2.2); few are andesite (57-63 wt % Sioz). The rocks have medium-K levels (0.56-2.09 wt. % &O; Fig. 2.3b) and show a calc-alkaline chernical trend (Fig. 2.3~). Metavolcaniclastic rocks (Piate 2.3) are light grey to pi&, well laminateci to banded on a mm to cm scde and have a fine- to medium-graineci granobhic tem. They consist pnmariiy of plagioclase + quartz t blue-green amphibole I biotite 2 gamet: disconthuous layers. 5-20 cm thick, contain angular 2-5 mm plagiochse clasts. Accessory mlierals include opaques (nmhiy ilmenite and pyrite), titanite, apatite, towrialme and zircon; garnet. I-5 mm m diameter. is sparsely distnIbuted chroughout the sequence. Epidote. sericite. and chlorite are secondary phases. and are more abundant in samples nom the eastern parts of the sequence. adjacent to north-west-trendnig fàuhs (Map 1). Foliation in the rocks is defined by the dipment of blue-green amphile and biotite; layering m the rocks is defineci by variable amphibole, biotite and plagiochse proportions. Blue-green amphibole in these rocks occur as fine- to medium-@ed. idioblastic to nibidioblasfc, nematoblastic to upnoblastic crystals, withm discontinuous 0.52 cm layers. It varies eom rnegnesio-homblende to ferro-tscheWe in composition (Fig. 2.4a) and has an MgFe ratio ranging fiom 0.32-0.56. Fme-grained, subidioblastic. pnobIastic crystais of plagioclase in these rocks shows a m~owrange in composition and is oligoclase to andesine (hgto AnJsr) Vig. 2.4b); subidiobiastic to xenoblastic porphyrobksts of gamet cornrnonly rkdby he-graineci plagioclase is prhady almandine rich (62.4-63.5 mol %) (Fig. 25a) with a significant grossular component (24.7-25.0 moL %); biotite is intermediate m composition (Fig. 2.5b) with an Fe/Mg ratio ranging &om 0.62-0.64. Rocks in the western metavolcaniclastic horizon are Light-grey to white-weaihering, weU Iayered. and consist predomhady of plagioclase and quartz with Iesser biotite, white- mica and sparse gamet. Several 1-2 rn wide layers contain 5- 10 % medium-grained blue-green amphibole. Discontmuous layers, 5- 10 cm thick, contain angular 2-5 mm plagioclase clasts. No mineral chernical data was colIected fiom tbis horizon, 2.2.4 Clastic Metasedimentary Rocks Clastic rnetasedimentq rocks form the most dominant lithology of the supracwtal rocks m the eastem to central parts of the map area but becorne much les abundant to the West. These rocks inchide metagreywacke and metaarpiiiite, and lesser metaqwrtz arenite to rnetaquartzite. In the eastem and southem parts of the rnap area, grey to red-broq gntty " 1 Tremolite Magnesio- homblende Act Hbld Actinolite 1 a Ferro- Ftsch tschenakite Hbld Plagioclase feldspars Figure 2.4. Plots of the minera1 chemistry fiom the felsic-intermediate rnetavolcaniclastic rocks from the GML area. a) Silica venus the ratio of rnagnesium to magnessium and ferrous iron (in atoms formula units) for calcic amphibole classification ((Ca+Na)B >/- 1.34 and NaBc0.67) (after Leake, 1978). b) Classification of the plagioclase feldspar series and high-temperature alkali feldspars (modified fiom Deer et al., 1983). Gro Ca&Si,O., Annite Siderophyllite t .O0 (a> 0.66 . r" & A + a ka Irp L Biotite 2.00 2.50 3.00 3.50 4.00 Phlogopite Al (IV) + Al (VI) Eastonite Figure 2.5. Plots of mineral chemistry from felsic-intermediate volcaniclastic rocks in the GML area. a) Gamet compositions in the Spessartine (Sp)-Almandine (Alm) + Pyrope (Pp) - Grossular (Gr) system. b) Total Al vs the ntio of magnesium and total iron for biotite classification (after Deer et al., 1983). te& and generaily massive metagreywacke domhates. These rocks are he to medium graid and consist of the metamorphic assembiage quartz + biotite + piagioclase + white-mica k gamet t andaiusite i si?imanite (fibrolite). Apatite, zircon and tourmaline are common accwory ph;epidote? sericite and chlorite are variably present as secondary phases. From no& of Thimy Lake westward (Map 1), weiI layered (bedded) metagreywacke to metaargiuae dominates (thinly bedded turbidite sequence). These rocks are cbaracterised by medium to coarse grained stauroiite, andalusite and kyanite-bearing assembiages. iUlnnmosilicate minerais typically occur as 0.46 cm long porphyrobIasts set in a he- to medium-grained biotite + quartz + plagioclase + gamet ma& These porphyroblasts are concentrateci m 5-10 cm wide foliation-parallel horizons which alternate with relative- alunhosilicate and mica-poor. more quartz-feldspar-ric h iayers. This layering may represent primary compositional bancihgheddmg. ~Metagreywacketo rnetaargdlke, fiom West of Thirsty Lake to about Century Lake (Map 1) typicaliy grades northward into lut-grey weathering, metaquartz are* which CO& of the assemblage quartz + biotite + muscovite + plagioclase i biotite + gamet and accessory zircon and toumialine. Minor discontmuous iayers of oligomictic metacongiomerate are associated with the quartz arenite. The rnetaco@omeraîe layers are generally 0.5-1 m thick, and contain pebbles and cobbles of granite and quartzite. Framework chs show variable degrees of flattening due to & White-weathering quartzite forms discontinuous 3-8 m thick bands stmcturaily below and in sharp contact with mafic metavolcanic rocks immediately south of the Sandhill prospect (Map 1). Rare crosîbeds m the metaquartzite indicates yoUngmg to the north, consistant with directions indicated by pre~ervedpillow structures in the western part of the map am Nineteen samples of the clastic sedimentary rocks were chosen for whole rock geochemistry (Table 2.3) to characterise the unit. Samples 005 and 538A are metaquartz arenite and have relathely high Si6 content (76.5-80 wt. %) and low /&O3 (1 1-11.1 W. %) and Na20 (.39-.47 wt. %) contents. Samples 538B and 541A are f?om the same stratigraphie horizon but contain a significant gamet component (25-35 modal %). These cg=- vl==a - vi rC a* '71; i,c=?m =Nec E = 3- n gc- i- w9 @ g;sc ==-= = C3 a- f:.c:vr9 3 Y1g ~EZ?$2~5~2 O9 o in0 '7n u or, i=irY*wO c- i j- - Wvl- 3 VI C 3.3 9 c-mm7 w CI a 3. 7 -!-7c? u-! - g 2-7 5 xc~-vi=rciccvmc i - m 7 Yi m -7 e -r Ozvr-- -m V. -"TT=? 3gg 5 = 2 Z""N ==7't--C - W=- - sz - SI G e93m ttN=*W= 10 vr = *9??"-9?? 3aE- -ror<-ciN 6 E -= - 1 5 7z -t c m c rn C--NN or ici - I!?.?v!q??aq - " Ge; a-Po--mouwI*X~ E3 ---- 2 -T - -9 = 5 =-ln 2 * ~c~-~c~~-rnmo9 - c- 9 7 s 5 -3 a"=*== sao,=z ==YI m O vt* m 52- o m j r +-.*mm A j c- -c f cl 9 - c. - * O CI c34--0 ob* = 9g q qokyq % 3 S88 ic--w,~~rnma t- -c- N rr) * ?* V a =~%=ZX=~~97386 5 -Cam 4~irr)--ma 9 - OI 0 sCu O-== bf!-9P~~C CN~vi 2'4 '9ol *y!5q 3 ?O+ oie roor=immmo 6 -03 a L Yi 3 CV OOOOI ==ze-orbr m m .Y*? .v& 9 TC* Iq - y;Cz-o=~ -c- cc % QI 9 ~cria~~=.**~ao~c C-c 0 3ei gOqbgoX24R~Q~P ?n - a- X 0i w ~~g~cb-CC5OV)CNZ a ?'?*?Y09 * 19 n gc=-oooaoruo rc - cc; 0: Qi Pr) *. . two samples are aiso distniguished by there hi@ Mn0 (0.24-0.29 W. %) and FezO3' (1 7.3- 18.7 wt. %) content and low AhQ (13-1 3.1 wt %) and K20(0.2-0.63 wt. %). The elevated Mn0 content may be the result of hydrothed aiteration reiated to the dwelopment of the Sandhill zone. where Mn0 is a ngnincant aiteration component (discussed in Chapter 5). The remainder of the rocks are metag~ywacketo metaargiriite and show a relative@ narrow range m chetnical composition These rocks are generalty intermediate with Sia ranging fkom 53.2-65.4 wt. %. The coiriposition of these rocks expresseci m ternis of wt. % Cao, NazO, %O, F~G',Mgû and Ti@ overlaps that of a typicd granodiorite (Condie, 1993). minerai chernical compositions fkom the metagreywacke and rnetaargiude are relatively consisent, with a few exceptions. Plagioclase (15-30 modal %) and biotite (1545 modal %) are the major minerai phases in the clastic rocks, except in quartz arenite mineralogies (0-15 % plagioclase and 5-15 % biotae). Fine to medium grained, granoblastic plagioclase is comrnoniy t-ed and rarely sericitized. Plagioclase is typically oligoclase m composition (Fig. 2.6a). Samples 360 and 4954 fkom directly south of SandhiU, contain pkgioclase with andesine to iabradorite compositions. Biotite, as fine to medium grained latbs, defines a mong foliation It is homogeneous m composition (Fig. 2.6b), rich m Al (Aio+Al(VI) - 3.5 apfü), and has a low Fe/(Fe + Mg) ratio (0.45-0.53). As m plagioclase compositioq samples 360 and 495A are distinguished by having lower A.io+AIo (3-3.3 apfu) contents. Muscovite is sparse in the metasedimentary rocks but may form up to 20 modal %. Muscovite ranges f?om muscovite to paragonitic muscovite m composition (8-19.5 moL % paragonite) (Fig. 2.6~). Gamet in metagreywacke and metaargiiiite (2-20 modal %) fypicaily occur as 1-5 mm, subidiobiastic to xenobiastic. poikiloblastic porphyrobktq and contain abundant inclusions of fine graineci quartz In a few samples, quartz m&iom niay be alignai pardel to the foliation Foliation m the rocks wraps the gamet crystals but as in the mafic rocks gamet shows no rotation. Occasionaiiy, gamet grains are broken mto several pieces and sinmg out dong the foliation plane. hdividual gamet grains rarely show good crystal fbrm, and are typically altered partly to he grained biotite, chlorite or sericite dong grain bouncianes and cross-cutting fktures. Gamet m the clastic rocks is aimandine (65-76moL %) m chernical composition (Fig. 2.7a) with a signrficant pyrope component (10-23 mL %). Gro Ca3AJ2Si30 12 Figure 2.7. Plots of minera1 chernistry from the clastic metasedirnentary rocks. a) Gamet compositions in the Spessartine (Sp)-Almandine (Alm) + Pyrope (Pp) - Grossular (Gr) system. b) Zn-Fe-Mg + Mn temary diagram for staurolite. Gmss-and spessartine are lesser components. Chernical zoning m gamet shows a generai decrease in the spessartine component and mcrease m grossular and pyrope components. Gamets in samples 360 and 4954 as weii as 485A Eorn the same area contains a sigruficant spessartine component m the cores (up to 17.8 moL %). Gamets m metagreywacke fiorn the eastern end of the study area show simh compositionai variations (Besserer 1994) wRh Mn- rich cores and Mn-poor rims. Stauroiite is a relaweiy abundant phase (2-25 modal %) m rnetaargiiiae m the westem part of the map ara (Map 1) and occurs m much the çame mamer as gamet. It is medium to coarse graine& xenobiastic, poikiloblastic and contain abundant mclusions of quartz Staurohe is commnly altered to sericite. Ln places sericite pseudomorphs staurolite and or@ fine gaineci rounded cores of staurolite mystak are presewed. Staurolite in these rocks is primarily Fe-rich (73-82 mol %) (Fig. 23). 2.2.5 Chernical Metasedimentary Rocks Chernical sedirnentary rocks mciude bamied iron formation and nilphidic-graphaic argillde. Iron forniafion (IF) is typically hosted by metageywacke m the southem and eastern parts of the map area IF hrms discominuou, 1-8 m wide horizons consisting of 2540% gamet. 0.2-3.0 cm m diameter, in a banded quartz + mapetite + amphibole + biotite maUL The IF has a pronounced aeromagnetic signature (Geological Survey of Cariada 1971a). The most extensive band of IF occurs at the contact between dcand fèlsic metavolcaniclastic rocks in the western part of the map area (Map 1). It strikes discontinuousiy for more than 10 km, ranges fkom 2-8 rn thick and is siliceous wdh ody miwr (10-1 5%) rnagnetite + pyrrfiotite * grunerite laminae. Sulphidic-graphitic arpiiiite (metamorphosed graphitic Mes) occurs as thin discontinuous horizons in the dcmetavolcanic rocks and ckstic sedimentary rocks m the cent. parts of the map area. It also occurs as discontmuous horizons at the dc metavolcanic-sedimentary rock contact and rnafic rnetavo lcanic- fèlsic rnetavo Icanïc rock contacts m the western parts of the rnap area These rocks are black and conth 10-25 % pyrite and/or pyrrhotite, which defines a wel developed foliation. 2.3 AGE OF THE GIBSON-MACQUOID GREENSTONE BELT Rocks of the Rankin Inlet Group and theû higher grade equivalents can be traced discontinuously korn Rankin Met northwards to Chesterfield Met (Tella et al. 1993) (Fig. 1.3). In the Chesterfield Met are% the supracnistal rocks are represented by arnphibolite- grade dcto feisic volcanic and volcaniclastic rocks. and sediment. rocks (gamet + biotite f staurolite + andalusite + sillùnanite t cordierite schist). These rocks fom multiple east- to northeast-trending, north-dipping belts which extend westward into the Gibson Lake-MacQuoid Lake areas. herein is referred to as the GMB. Analysis of zircon fiom a sample of felsic volcanic rock fiom the MG. coliected in the Ranh Inlet ares yielded a U-Pb upper concorodia intercept age of 2663 i 3 Ma (Tella et al. 1996). This Archean age for the MG is Mersupported by an Archean U-Pb age of 2.65 I -03 Ga fbm a pegmatite dyke which cuts equivaient supracnistal rocks in the Chesterfield Inlet area (Tek et ai. 1993). Based on the stratigraphie relationships with the MG in the Chesterfield Met are* the supracrustal rocks of the GMB are tentatively interpreted to be Archean in age (ca 2.65-2.66 Ga). More recent data (Telia pers. Cornm.) f?om the MacQuoid Lake map sheet indicate that the rocks of the GiMB may be as old as 2.75 Ga. 2.4 ORTETOGNEISS Orthogneiss is m structural contact, with the metavolcanic and metasedimentary rocks, and forms the northm and southan boundaries of the greenstow beh. The orthogneiss comprises an undifferentiated sequence of variably deformeci and metarnorphosed intrusive rocks that range in composition fiom diorite to tode ttnough granodiorite to granite. contacts of orthogneiss and supracrustal rocks are typicaily migmititic andor sharp and highly strained. These rocks are banded to massive, typically strongly foliated and variably liwated. Stnicturai fàbrics m the orthogeeiss are contormable with the mpracrustd rocks. DiscoriMuous thin metasediwIitas. rocks, amphiboiite aod odeiron formation are present in the orthogneiss m the eastem parts of the map area Tonahtic to granitic composifons are light grey to pink weathering and CO& of variable proportions of pkgiociase, qquartZ K-feldspar, biotite, homblende and gamet Dioritic rocks are a dark salt and pepper cololaed sugary texnned and conskt of fke Ceraineci piagioclase. homblende. &or quartz and rare almandine gamet 2.5 GRANTTOID INTRUSIONS Three large distinct white to -my-weathering granitoid intrusions occur in the western part of the rnap area Contacts with the supraclustaj rocks are sharp, wel foliated to sheared and contain rafts of the supracnisral rocks. IntemaiIy the mtrusions are rrmssive and lmfoliated but dispiay a well developed lineation Eibric (Li) defhed by elongated aggregates of fine -med biotite. The granitoid intrusions are massive, fine- to coarse-med and consist predominantly of plagioclase (40-50 modal %) and quartz (30-36 modal %) with lesser bio tite (6- 12 %) and K-feldspar (5- 10 modal %). Quartz shows undulous extinction and serrated boundaries with plagioclase; plagioclase is weakly aitered to sericite and calcite. Euhedral to subhedral epidote (1-3 modal %) occurs as inclusions in biotite and feldspar (possibly of magmatic origin); some epidote is well zoned. Biotite fom medium-grained aggregates of randomly O riented crystals. Fine- to medium-grained euhedral diarnond shaped titanite crystals ( 1 modal %) and fine grained euhedral rnagnetite ( 1 modal %) are randomly distn'buted throughout the rock. Based on modal minerdogy (Appendix 1) and major element geochemimy (Table 2.4), the intrusions are fèlsic (SiG > 66 wt. %) and tooalitic to granodioritic m composition (Fig. 2.9qb). The rocks are metaluminous to weakiy peraiuminous with molecular A/CNK ratios < 1.O 1 (Fig. 2.9~).The presence of biotite t homblende and accessory phases magnetite and titanite, the absence of mgmatic muscovite or other highly duminous miner&, and the metaluminous to weakiy perduminous chemistry Indicate that the intrusions have 1-type afkities (Pitcher, 1983; Brown et ai., 1984). 41 Table 2.4. Major element geochernistry of the granitoid intrusions in the western part of the GLMLarea. 2.6 GABBRO Gabbro with minor pyroxenite intrusions of possible Proterozoic age (see Chapter 6) are common throughout the map area. In the muthast part of the map ares a 750 m long elliptical plug of pyroxenite mtnides the sedimentary rocks. Gabbro occm as numerous east- trendmg dykes throughout the eastem and centrai parts of the map ara, and as iarger intrusions in the central and western parts of the map area. The east trending gabbro dykes are conformable to and crosscut regional structurai trends, however do not have a structural fàbric. The dykes form prominent topographie ridges (up to 50 m above nurounding Iahologies) and vary Eom 10 m up to 300 m wide. These rocks are typicaiiy dark green, massive, with fine-grained ma.& and medium- to coarse-graineci cores. They consist of pyroxene/amphi'bole + plagioclase-beanng assemblages. Several of the gabbro dykes contain 1-2 % dissemÏnated, fine-@ed pyrrhotite. These gabbro dykes m the eastem and central parts of the rnap area may be equnalent to the east trending Proterozoic (ca 2.2 Ga) Tulemalu dyke swam (Eade 1986). A krge gabbro intrusion m the westem part of the map area wraps around the previoudy descgrandoid intnisions, and a dernitnision is hosted by the metavolcanic rocks m the northeastem part of the map area. The western and eastern intrusions display a weakly to weIl developed lineation fàbric and ail intrusions are variably sheared and cul by epidote and calcite vedets. A d gabbro intrusion m the central part of the map are* mfomdy referred to as the Sduk gabbro, is spatially associateci with the Suluk Cu-Ni-Co deposit and may be genetically reiated. Unlike the aabve descnbed gabbro mnisions, the Suiuk gabbro is tedunirally hhomogeneous with he- to coarse-grained to pegmatitic phases. It consists predominantly of blue-green hornblende/pyroxene (augite) + plagioclase, with rninor biotite and quartz, trace apatite, zircoa magnetite, pyrrhotite and chalcopyrite and secondary epidote. Pyroxenite (altered to arnphilite) is a predominant phase in the eastem portions of the intrusions as is the pegmatitic phases. Layering on the cm to m scale was &O identsed in the eastern end of the rnap area and is defined by variable plagioclase and homblendelpyroxene. A pronounced aerornagnetic signature centred over the eastem part of the Suluk gabbro (Geological Survey of Canada aeromagnetic rnap 197 1) (not displayed by the other gabbro intrusions in the area) is, in part, due to both 3-5 % dissernimted magnetite in the pyroxene-rich phases, and trace dissexninated pyrrhotite. The Suluk gabbro, Suluk suiphide occurrence and their possible genetic relationship wiU be discussed in greater detail in Chapter 6. 2.7 LAMPROPHWUI DYKES The terni lamprophyre, as proposed by MitcheLl(1994), is applied to rocks which are characterised by the presence of euhedrai to subhedral phenocIysts of mica andor amphibole together with lesser clinopyroxew and/or melilite. These minerals are set in a groundmass which consists of one or more of plagioclase, alkali feldspar, feldspathoids, carbonate, mica, amphibole, monticellite, meme, Fe-Ti oxides and ghs. The term lamprophyre is used here as a field term and has no compositionai or genetic significance. Lamprophyre dykes are abundant and widespread in the map area They are typically undeformed, although some dykes are offset by late NW-trending faults. Dykes range fiom 10 cm to approximately 2 rn wide. are aeeply dipping and discordant to local contacts and fabncs? and occur as recessive trenches. Individuai dykes are ody e.xposed for short dinances and have a weU dehed NNW regional trend. The dykes are porphyritic with biotite or amphibole phenocrysts set in a biotite + feldspar matrix. Biotite is rarely aligned paralle1 to the rnargins of the dykes. Xeno iiths are abundant in some larnprophyre dykes and inc lude granite, orthogneiss and metasedimentary rocks. During the 1993 field season a single rnicrodiamond (a80 microns) was discovered in a hand sample fiom a lamprophyre dyke. Processing of subsequent sarnples yielded multiple micro- and macrodiamonds. This lamprophyre dyke is designated the Akluiiâk (alias Thirsty Lake) dyke. Akluilâk means 'richest' in Inuhtut. the laquage of the Inuit. The dyke is unique becaw ifs the first noted lamprophyric rock to hon diarnonds, and the first confïrmed mdti-diamond occurrence in the central Churchill Structural Province. Lamprophyre dykes in the map area are correkted with the ca 1.84 Ga alkalsie ipeous province dehed by the distniution of the Christopher Island Fodon(CIF) of the Baker Lake Group (Gall et ai. 1992; Petemn and Rainbird 1990; LeCheminant et aL l987a). The geological characteristics of the Akluilâk dyke and other lamprophyre dykes in the map area will be detailed in Chapter 7. 2.8 PEGMATITE DYKES Foliated and boudmaged white quartz + plagioclase + tourmaline f gamet-bearing pegmatite dykes are common m the orthogneiss (unit 5), Sedenentary rocks (unit 4) and dc metavolcanic rocks (unit 1). Relatively lmdeformed white to p8ik quartz + K-feldspar + plagrociase + tourmalgie * muscovite 5 beryl pegmatite dykes are cornmon in the centrai to western parts of the map ara; they cut dl units previousiy descriid as weli as the gabbros. Based on structural relationçhips, the white tourmaline pegmatite dykes are assigneci to the Archean and the white to pink dykes to the Proterozoic. 2.9 DIABASE DYKES In the eastem part of the map mea. three northwest-trendmg diabase dykes (Mit 10). up to 1 rn wide, cut the rn~volcanicand Sedimentary rocks and are probabiy related to the 1267 2 Ma Mackenzie dyke n;ÿarm (LeCheminant and Heaman 1989). 2.10 CONCLUSIONS The Gibson-MacQuoid Lake area is underlain by a sequence of cdc-alkaline dacite to rhyoiite metavolCaniclastic rocks. tholeiitic basait to basaitic andesite, and interlayered clastic and chernical metasedimentary rocks compris& the Archean GMB. PUow structures in the dcmetavolcanic rocks and rare cross-beds m metaquartnte mdicate this stratigaphy locaily young's to the north. In the eastem and centrai parts of the mpares relatively nmssive metqpywacke with mterhyered oxide hies iron formation grades northward mto thiniy-bedded turbidites, and gradua& mto metaquartz arenite and rneraquartnre towards the centrai part of the map ara This stratigraphy represents a shallowing upward sequence. hon formations are starved-basin deposits which are deposited in an environment either below or protected fkom active wave- base (Eriksson et aL 1994). The massive nature of the mefagreywacke represents a submarine charnel iàcies. The thdy-bedded turbidites represent a distal horizon possibly in a lower-fan lobe; the absence of cross-beds etc. mdicates deposition below wave-base. Metaquartzite with rare cross beds, mdicate a Salow subaqueous environment of deposition above wave-base. The siïciclastic nature of the clastic metasedimentary rocks, and presence of granitic and quartzite clasts in metacongiomerate horizons and absence of voicanic material suggests a cratonic source for the clastic metasediments. In the western part of the map areq dcmetavolcanic rocks dominate the ssatigraphy. Mafic metavo1canic rocks, comprised of massive and pillowed flows and volcanic breccias, are interlayered with tubedded clastic metasedanentary rocks, cherry iron formation and sulphidic arme (sulphide kies iron formation). Synvolcanic metagabbro siils are abundant. The predominance of mafic metavolc~crocks. Înterlayered with iron formation aml abundance of metagabbro sills indicates a deepened basin-5- possibly adjacent to an extnisive centre. The caic-alkaline geochemical signature of the felsic-intermediate volcaniclastic rocks and their mterhyering and Sarp Iower contacts with the tholeiiiic dcrnetavolcanic rocks mdicates a separate volcanic source. The fine-@ned weii lamoiated nature and the absence of coarse metavolcaniclastic deposits (i-e. volcanicderived congiomerates or other coarse pyrociastic rocks), suggests that these metavoIcaniclasuc rocks are a distal deposit formed in a subaqueous environment, but deriveci fiom a subaerial environment (Fisher and Schmincke 1984). Thek calc-alkaline chemical nffmty and possible subaerial derivation suggests a continentai-marginai arc source (Condie 1993). The continental source of the clastic metasedimentary rocks, a continental-arc source for the felsic-intermediate metavolcaniclastic rocks. and the presence of dcmetavolcanic rocks qgests an overd back-arc basm senhg for the GMB stratigraphy (Eriksson et al. 1994). This proposed tectonic setting will be Merdiscussed m chapter 4 where nrpponing data on trace elernent and rare earth element geochemistxy of the metavolcanic and metasedimentary rocks are presented. Orthogneiss, comprishg severai ages of variably deformed and metamorphoseci moidrocks, is in structurai contact with the metavolcanic and metasedimentary rocks. and tom the northem and southem boundaries of the greenStone belt. 1-type tonalite to granodiorite intrusions are conon in the western part of the rnap a.Proterozoic gabbro and lampro phyre and diabase dykes are common throughout the map area. STRUCTURE AND METAMORPHIC PETROLOGY OF THE GIBSON-MACQUOID GREENSTONE BELT 3.1 INTRODUCTION Regional metarnorphic and structural midies in the western Churchill province indicate that the region has been subjected to at least two major tectonothexmai events. the f2st Archean (ca 2.6 Ga) and the second Early Proterozoic (ca 1-94- 1.9). The effects of both events in the region are weii documented (Tella et al. 1992, 1993, 1997: Teh 1993: Sanbom-Barrie 1994). The purpose of this chapter is to summarise the regional structure and metamorphism in the region adj0 ining the GML area and to evaluate the effects O f the polyphase tectonothermal events on the rocks within the GML area. 3.2 REGIONAL STRUCTURE; AND METAiMORPHISM 3.2.1 Rankin Met area Deformation in the Raakin Inlet area (Fig. 1.3) produced Fi isoclinal fol& and interleaved tectonic siices which have subsequently been folded into a south-em-plunging upright Fz syncline (Teh et al. 1986). Stratigraphie and structurai reversais in the region also suggea the rocks have been affected by both south-west and north-east vergence Fi thnists. Regional metamorphism has reached the lower greenschist facies in the Ranh Inlet area (Tek et al. 1992, 1993) (Fig. 3.1). This deformation and greenschist grade metamorphism is interpreted to be Archean in age (Teh 1995). Early Proterozoic deformation of the RIG is indicated by reactivation of Archean faults (ca 1-94 Ga, UPb; Tek 1995) (ca 1.78 Ga, 40M39~r;Miller et ai. 1994), including the Pyke Fadt in the Rankin Inlet area This is Iocdy evidenced by thnisting of the Archean RIG on to the orthoquartzite of the Eariy Pro terozoic Hu- Group. Figure 3.1. Geologic map of the western Churchill Structural Province (see Ffig. 1.3 for more detail) showing the distribution of the Rankin Inlet Group (RIG), Gibson-MacQuoid Lake Belt (GMB) and grade of Archean and Proterozoic Metarnorphism. Location of the study area is indicated by the box. 3.2.2 C haterfield Inlet/Barbour Bay Area Regional Archean metamo rphism increases rapidly to the no rth and north-east (Tella and Schau 1994) (Fig. 3.1). The higher grade equivalents of the RIG cm be traced discontinuously nom Rankin Inlet no rthwards to Barbour Bay and nonh-eastwards t O Chesterfield Met. These rocks form multiple east- to north-east-trendkg, north-dipping metavo lcanic/metasedmientary belts whic h are bo unded by Arc hem (> 2-63 Ga) quartzofeldspathic gneiss. Locdy, the kits wrap around and dip away 60m domal felsic piutons. Metasedimentary rocks consist of gamet + biotite + staurolite k andalusite f sillllnanite k cordiente k muscovhe + plagioclase + quartz assemblages; interlayered mafic metavolcanic rocks (amphibo iite) consist of hornblende + plagioclase + gamet assemblages; interiayered discontinuous iron formation consists of magnetite + gamet + hornblende + grunerite assemblages. These mineral assemblages indicate rniddle to upper amphibolite facies conditions of regional metamorphism. Thermo barometric calculations. based on a number of different mineral equilibria, fiom rocks in the Chesterfield Met area yielded P-T estimates of ca 3.1 kbar and 635 OC (Teila et al. 1989). P-T estimates for rnetarnorphism in the Barbour Bay area are in the order of 2.8-3.6 kbar and 520-650 OC. Paragneiss (GMB-equivalents?) of similar minerdogy occurs in the Cross Bay area (Sanbom-Banie 1994) (Fig. 3. l), north of the Gibson-MacQuoid Lake area. At lest four sets of fo lds were ident Xed in the metasedimentary/metavolcanic belts (Teh and Schau 1994). These include an early isociinai, doubly plunging, recumbent fold set (Fi) which is refolded by a north-west-plunging open to tight fold set (F?). These FI and F2 fol& were subsequently modified by moderately west-plunging open F3 folds, and no rth- plunging Fr fo lds. The Arc hem met asedimentaryhetavolcanic belts in the Barbour BayKhesterfleld Met area extend continuousIy westward into the Gibson Lake-MacQuoid Lake area Early Pro terozo ic deformation in the Barbour Bay/Chesterfïeld Met area is recorded by rocks of the Archean (ca 2.77 Ga) Uvauk complex (Tella 1995, Teh and Schau 1994). The Uvauk complex is an allochthonous Archean layered gabbro-dc granulite-anorthosite complex. The complex forms a rootless, east-north-east-trending sheet which overiies the relatively lower grade Archean ortho- and paragneiss. The prototith of the Uvauk complex was a layered and well differentiated mafic intrusive body which was subsequently deformed and rnetarnorphosed under granuiite facies conditions. Defomtion textures. metamorphic mineral growth and U-Pb geochronoloey suggest thaî the rnetarnorphism and ductile deformation were episodic. Zircon rnonazite and titanite ages reveal that the Uvauk complex records an Archean (ca 3.59 Ga) ganulite grade mylonitic event and an Early Proterozoic (ca 1.94 Ga) mylonitic event. Thermobarometnc studies (Teh 1995, Tek and Schau 1994) suggest that the fist event occurred at pressures in excess of 10 kbars (- 30 km). The Proterozoic event records exhumation of 2-3 kbars (6-9 km). The data demonstrates the presence of horizontal displacements during bo th the Arc hean and Pro terozo ic. The Uvauk complex is Luiked to other iithologicaliy and tectonically similar ductile hi&-arain zones that are associated with the uplifl of granulite-anorthosite complexes. These include the Kramanituar complex (Sanbom-Bame 1994) in the Cross Bay area, immediately north of the Gibson-MacQuoid Lake are& and the Daly Bay complex (Gordon 1988) to the east. Regionally pervasive semi- brittle to ductile, greenschist grade shear zones are widespread in the western Churchill Province which include the Pyke Fault near Ranh Inlet, and the Amer Fault Zone north-west of Baker Lake (Fig. 3.1). 3.2.3 MacQuoid Lake area West of the study area, in the MacQuoid Lake area (Fig. 3.1). the rocks record both an Archean (2.65-2.61 Ga) and an Early Proterozoic event (between 2.19-1.84 Ga) (TeUa et ai. 1997). At least two Archean deformational events and one amphibolite facies metamorphic event are recorded by the metavolcanic and metasedimentary rocks and layered gneiss complex. DI structures include an So parailel north to north-west-dipping S 1 cleavage, and a north-east to east-north-east-trending Li minerai lineation, and south-east- verging recumbent Fi folds. Dt structures are dehed by north-east and south-west- plunging F2 folds and associated SI axial plana cieavage, and L2 mineral lineations. Metamorphic minerai assemblages in the metavolcanic rocks (gamet + plagioclase + amphile + chopyroxene), and the metasedimentary rocks (aluminosilicates, gamet, staurolite, cordierite) indicate middle to upper amphibolite facies conditions of regional met amo rp hism A diabase dyke swarm (correlative with the ca 2.19 Ga Tuledu swarm) in the MacQuoid Lake rnap area (Tella et al. 1997) documents evidence of a Proterozoic tectono the& overprint. AU dykes are deformed and metamorphosed under greensc hist facies conditions. The MacQuoid Lake map area is ako mected by north-dipping, ductile hi& strain zones and at lem three sets of late brinle faults (east to north-west- trendhg) . The Archean and Early Proterozoic tectonothed events, recorded regiody. si~cantlyaffected the rocks in the Gibson-MacQuoid Lake area The effects of these tectonotherd events wiU be dûcussed below and in subsequent chapters concemhg the minerai prospects in the area. 3.3 GIBSON-MACQUOID LAKE AREA 3.3.1 Structure Bedding (So) in the study area is mdicated by compositional layering in the metasedirnentary and intermediate-felsic metavolcaniclanic rocks, and by the interlayering of flows. breccias. and her grained volcaniclastic rocks in the dcand mtermediate metavolcanic rock sequences. Facing directions are poorly preLcerved;however, m the western part of the rnap area, weakly defonned dcpillow structures mdicate locally the stratigraphy young's to the north: croçsbedding in a metaquartz arenite dÏrectiy south of the Sandhill prospect also mdicates -hy olmg's to the noah. Regionai foliailon (Si) is parailel to beddmg/layering (&=Si) and is dehed by micas and amphibole m the rnetadimentary and inteete-felsic metavolcaniclastic rocks and orthogneiss, and by amphile m the &c metavolcanic rocks. In the north-eastem part of the map area, Si foliation strikes coasistently West and dips moderately to the north (Fig. 3.2). SI fdiations define shailow to moderate east- ami west-plunging isoclinal fol& (FI) Hi the metavolcanic and rrietasedkntary rocks (Plate 3.1 a), however, FI &Id closures have only been observed in kw localities. In the south-eastem part of the rnap are& S1 foliations deke regional shdow north-west-phmgmg antiforms and synform. In the western part of the rnap area FI foliations m the supraclZIStal rocks are variable m dip direction and wrap around two large gmnodiorite intrusions. Moderate mrth-west- to north-east-plmgkg F-2 fol& (Fig. 3.2) (Plate 3.1 b) show both S ami Z asymmetry. Moderate north-west- to wrth-east-plmghg crenulauom. well developed in places, dehe a second cleavage (Sz) which is ad planar to the FZ folds. Localiy. aluminosilicate porphyroblasts m the sedimentary rocks have been rotated mto the plane of the SI foliation 9idiotmp Dz deformation outlasted peak metamorphic conditions. Moderate north- to north-east-plunging L 1 minerai and roddmg line;uions (Fig . 3.1 ) (Plate 3.1~)are wea'developed m the eastem and central parts of the rnap area. This iineation is mady developed along major lithologic contacts. White pegmatite dykes located at the lithologic contacts also tend to have a weU developed rodding iineation This indicates mjor structurai movement dong lithologic contacts. The northerly plunging LI heation fàbric. shallow east and west-plunging isoclinal Fi folds and predominant west-trendmg Si foliation indicates a north-south cornpressional event. The Li iineation &bric is more penetrative m the supracnistal rocks in the western part of the map are% m the regions of the eoidintrusions. LI Lineation is also wel developed throughout the three large grandit mtnisions m the western part of the rnap area. A foliation is oniy deveioped along the mareof the intrusions and is paralle1 to the maqjns. The Iack of a peneuative foliation m the mtrusion and concordancy of the foliation m the nipracnistal rocks with the ~sLT~~Sof the intrusions is typical of diapiric emplacement of granitoids (Condie 1989). The penetrative LI Mcin the granitoids mdicates they are late syntectonic and the peneaative Li Mxic m the supracd rocks m this area may be poa Si and has developed as a rdof the granitoid emplacement. Late north- to north-west-trendmg brittle fàults traosect the map area. A major huit in the centrai part of the map ara shows variabie dedo&t as inclkateci by an east-trendmg gabbro dyke. The felsic-intennediate metavokcziniclasac unit is tnincated on the east side of the fa& and a sedimentary rock sequence is truncaîed on the West side of the huit. A second mjor £a& in the eastern part of the map area is identifid by extensive block fkdting. Numerous dersale îauits, not shown on the map, display limiteci apparent o&ts of bo th Plate 3.1. Structural features in the rnap area; a) moderate west- plunging isoclinal fold (F,) in the clastic metasedimentary rocks in the central part of the rnap area; b)hinge zone of a north-east- plunging F, fold with well developed S, axial planar cleavage; and c) well developed northerly-plunging rodding lineation (L,) in a felsic metavolcaniclastic rock in the western part of the map area. shistrai and dedmovement. Defodonassociated with these fà& affecteci ail rock units, incluàjng the gabbro dykes and iaqrophyre dykes: epidote and K-feldspar retrogression is commoniy asociated with these laie brittle fàults. 3.3.2 Metamorphism Ln the study are% clastic metasedimentary and &c metavolcanic rocks represent the do minant Litho logies; their characteristic mineral assemblages have ken outlined in Chapter 2. In the foUowing section, the minerai and textural relationship of the major rock îiorrning miner& in these rocks are outlined in order to constrain the metamorphic history of the GMB. The clanic metasedimentary rocks mainiy coosist of biotite + piagioclase (oiigociase to andesine) + quartz * muscovite gamet (almandine) k andalusite * stauolite. Kyanite is locally present m the metasedimentary rocks in the central part of the rnap area. Sillifianite (fibroiite) rarely occurs m the eastem end of the map area (Besserer 1994). In generaL almandine gamet, staurolite and the duminosilicate minerais are present as large porphyrobiasts or poikiloblasrs, whereas biotite and muscovite dehe a well developed foliation (Si). Porphyroblasts/poikiloblasts iack an interna1 fàbric and the Si fàbric wraps the porphyroblasts. Such textures kdicate pre-tectonic (DI) growth Gamet and staurolite are typicdly fkctured mto several pieces which are stning out concordantiy with the rock foiiation suggesting they acted as rigid bodies as the rnatrix fabnc formed; porphyrobiasts rarely show evidence of rotaiion Sillimaaite occurs as fibrous aggregates afker foliation-pardel biotite. The above tex-mdicaie the main assemblage represents the peak metamorphic conditions of the region, however, early porphyroblasiic growth aiso hdicates that temperatures were significantly high prior to the onset of compression. Sillimanite growth der rnatrix biotite mdicates temperatures contmued to hcrease der the onset of deformation (Di). Mafic metavolcanic rocks are mabdy composeci of tschermakitic homblende + plagiochse (oligoclase to andesine) + almandine gamet + quartz + ilmenite. Simikr to the metasedimentary rocks, gamet occurs as a porphyrobkstic phase. Hombiende dehes a wel developed fohtion which wraps the garnet porphyroblans. As in the rnetasedimentary rocks, garnet is typicaUy broken mto several pieces which are strung out concordan@ with the rock foliation and mineral grains rarely show evidence of rotation The above mineral assembiage is mterpreted to represent peak metamorphic conditions. Gamet is typically rimmed to completely replaced by piagiochse. The plagioclase rims around gamets (not restncted to pressure Wows) mdicate a pst-tectonic @est-fihic) decompression event. This decompression event is pst-&. The st&Ie rneram~rphicmineral assembiages in the clastic metasedimentary rocks and mafic meiavolcanic rocks indicate amphiiiite facies rnetamorphic conditions. Eiheral assemblages are typical of the Staurolite zone m the Banovian Zona1 Scheme (Yardey 1989) and indiate relative@ low pressures and moderate temperatures of metamorphimL Retrograde metarnorphism der peak metamorphic conditions is locaily present and mdicated by sparse chlorite aiteration of gamet and biotite, sericite after stauroüte, andalusite and plagioclase and epidote and sericite alteration adjacent to crosxutting veinlets. Specific P-T conditions of peak metamorphic conditions are dehed below. 3.4 CONDITIONS OF METAMORPHISM In th* section a petrogenetic gnd. published cabrations of suitable geothermometers, and intemdy consistent sets of thermodynamic data are used to estirnate the P-T conditions of minerai equilibration in the ciastic metasedimentary rocks and mafic metavolcanic rocks. It is assumed that the present mineraiogy of these rocks represents a stable assemblage and the caiculated temperature conditions reflect those achieved at peak metamorphic conditions in the Gibso n-MacQuo id Lake area. Mineral pairs and temperature calculations are presented in Appendix 2 and summarised in Table 3.1. 3.4.1 Petrogenetic Grid As noted above, the stable metamorphic mineral assemblage m the clastic metx&kmtary rocks is typical of the Staurolite zone in the Barrovian Zonai Scheme (Yardley 1989). The coexistence of staurolite, andalunte and aimandine gamet mdicate metamorphiSm at reiativeiy Iow pressures and moderate temperahaes (Yardley 1989). Figure 3.3 is a petmgewbc grid for pelaic metasedmiaaas, rocks m the &O-Fe0-&O3-Si02-H20 (KFASH) chemicai Wern This -tes the pertinent reactions and characteristic mineral asxrnbiages which form m Fe-rich pelibc rocks. at various tempeme ami pressure condaions. during prograde metamorphkm It shodd be noted that with mcreashg Mg content in the system these mictions wodd sNt to slightly higher temperatmes. From Fig. 3 -3. an estimate of the temperanrre and pressure conditions for regionai metamorphism is in the order of 500-580°C and below 3.5 kbars pressure (shaded area) based on the stabihy of Fe- naurolite. gamet and anddusite. The absence of cordierite at these estimated temperatures indicate pressures were above 1.5-2 kbars (Yardey 1989). Kyanite-bearmg meîaedbentary rocks are restricted to a narrow. few hundred meter wide zone (east-west) m the central part of the map area (Map), adjacent ro the north-west- trendmg W. It's occurrence may be due to an abrupt change in structurai relief due to vertical displacement dong this Faut. The rektionship between We,andalusite and stauroiite in this area has not been determitlecl. Smiilar localised occurrences of kyanite are reported by Sanbom-Banie (1994). The rare presence of fiohte der biotite m the eastem part of the map area wgests temperatmes niay have been as high as 580 OC, the andalusite-sillimanite phase b0undaI-y. The stable rnetarnorphic minerai assemblage in the mafic metavolcanic rocks is typical of amphibiite facies regional metamorphism Grom Iow to moderate pressures and rnoderate to high temperatures. The characteristic blue-green amphibie, Ca-plagioclase and almandine gamet in these rocks is a typical assemblage in the Staurolite zone of Barrovian metamorphism and consistent with the P-T conditions estirnated for the metasedimentary rocks. 3.4.2 Gamet-Biotite Geothermometer The partitioning of MgfFe between gamet and biotite has been cahbrated (experimentdy and empincdy) by Thompson (1976), Goldman and Albee (1977), Ferry and Spear (1978), Ganguly and Saxena (1984). hdares and Martignole ( 1985), Berman ( 199 1) . The ion-exc hange reaction for this mineral pair is: 1 l3 pyrope + '13 annite = '/3 aimandine + '/3 bio tite Figure. 3.3 Petrogenetic grid for pelitic rnetasedimentary rocks in the KFASH system (afier Spear and Cheney 1 989). Shaded area represents estimated conditions of metamorphism in the GiML area. Table 3.1 presents calculated temperatures for coexisting gamet-biotite pairs in several clastic metasedimentary rock samples &om across the Gibson-MacQuo id Lake area ushg three caii'bratiom (Ferry and Spear 1978; Indares and Martignole 1982: and Berman 199 2). Temperatures were calculated at 3 kbar of pressure, an approximation based on the interpreted stable minera1 assemblage (Fig. 3.3). The experimentai cak'bration of the gamet-biotite reaction by Feny and Spear (1978) is one of the eariy and more widely used geothermometers. This calibration assumes strictly an MgEe exchange between garnet and biotite. Their geothemometer uses the expression: where & is expressed as (&,/&ab' / (XFe/XMq)lt.However. Li natural systerns, garnet may also contain significant amounts of Ca and Mn. and biotite may contain si@cant amounts of and Ti. These components may significantly affect the temperature of eq3iition (Ganguly and Saxena 1984, Indares and Martignole 1985). Therefore. the experimental calibration of Ferry and Spear (1 978) is only an approximation for natural assemblages of the common presence of Ca, Mn Ti and Al"% the systen Indares and BIartignole (1985) have expanded on the experimental ideal mode1 of Ferry and Spear (1978) by correcting for the effects of Ti and AltVDin biotite and Ca and Mn in gamet. Indares and Martignole (1985) have incorporated the effects on the basis of the compositional data for coexisting gamet and biotite IÏom a suite of grandite facies assemblages. They have isoiated the effect of Mn and Ca concentration in gamet on & according to both Gangdy and Saxena (1984) and Newton and Haselton (1981) modeis, and evaluated the effects of Ti and ~1'~concentrations in biotite f?om statistical treatment of the residud variation of & as a function of these components. Their final expression for the gamet-biotite geothermometer is as foliows: Table 3.1. Summary of temperatures calculated fiom geotherrnamrters. I&S - lndares and Martigiiole (1985), P&S - Ferry and Spear (1978), B - Berman (1988), G&P - Graham and Powell (1984), and HLB - I-lolland and Blundy (1994). ** Al1 teinperatiires calciilated at 3 kbar pressure. Sample Pair T ( "C ) l Sariiple Pair Sample Pair NWT 7A NWT 78 504 360 133 275D 23 1 Average T ( OC): Berman ( 199 1) uses an "intenially consistent" thermo barometric technique referred to as TWEEQU (Thermobarometry With Estimation Of EQUilibration State). In this method, a given equilibria mineral assemblage is computed in P-T-X(C02) - activj. space by the TWQ program. The TWEEQUE calculation is performed utilking a set of intemally consistent thermodynamic data for end members and solution properties. For calculation of the gamet-biotite reaction. the solution properties take hto account Mn and Ca substitution in gamet, and Ti and MVDsubstitution in biotite. Application of the biotite-gamet thennometes on the Gibson-MacQuoid Lake clastic metasedimentary rocks has ken carried out using gamet and biotite rim composf ions fiom 1 1 pairs in 7 samples. Care has been taken to analyse minerds in contact. and to analyse as close to the rixn of each minera1 as possible. Calculated temperatures range kom 484 to 587 OC (average = 533 h 50 OC) when evaiuated with Ferry and Spear's calculation. Temperatures caiculated with the calibration of Indares and Martignole ( 1985), which is based on Ferry and Spear's (1978) experimental calibration but corrects for the effects of Ti and AfV% biotite and Ca and Mn in gamet. are much lower. The? mge fkom 462 to 540 OC (average = 500 OC). Temperatures calcuiated using Berman's (1991) TWQ program, which utilises a set of interndy consistent thermodynamic data for end rnembers and solution properties, range fiom 498 to 620 OC (average = 559 OC). These temperatures on average are 60 OC higher than those calculated fkom Indares and Martignole's caliiration but only 25 OC higher than those calculated by Ferry and Spear's calibration. 3.4.3 Gamet-Horubleude Geothermorneter The Fe-Mg exchange equilriria between garnet and pargasitic homblende has ken calibrated by Graham and Powell (1984). The reaction is: 1 /iFerro-prgasite + '1, Pyrope = '/r Pargasite + Almandine It is a pressure independent reaction and therefore desa good geothermometer. This geothermometer is applicable to rocks with Mn-poor gamet (Xun -C 0.1) and common hornblende with wide1y vmg chemistry? metamorphosed below 850°C. and at low oxygen fbgacities. It uses the expression: T ("K)= 2880 + 3280~c,G[/ (Ln & + 2.426) where % is expressed as (XFJXM~)*/ (xFJXM~)~~. Gamet and homblende assemblages are cornmon in the metamorphosed ntatic rnetavolcanic rocks of the Gibson-MacQuoid Lake area As indicated in Chripter 2. gamet and homblende are generaily homogeneous in chernicd composition, appear to be in chernical equilibrium. and represent peak metamorphic conditions. Mn is generaiiy low in both phases, however. in a couple of samples. gamet cores were > 0.10. In calculating temperatures using this geothermometer. it is recommended by Graham and Poweii (1984) that aii Fe be assumed as ~e?However, this assumption may resuit in temperature overestimates if the prllnary homblende's are nch in femc iron. In fact. a signtncant amount of ~e'~is present in the samples fiom the study area as iderred fiom the 'mid point" of Papike et ai.3 (1974) method. Temperatures fkom 9 mineral pain in 5 samples. cdculated with ~e'-and ~ej-in homblende, range fiom 555-6231 OC (average = 59 1 OC) at 3 kbar pressure. Calculated temperatures are quite a bit higher than those caiculated using the gamet-biotite geothennometer, ho wever, temperatures overlap those estimated fiom Berman's ( 199 1) gamet-biotàe geothermometer pote: caiculated temperatures, not shown here. assurning ail Fe as ~e'-in homblende were consistently 20-30 OC higher than temperatures shown in Table 3.1. 3.4.4 Hom blende-Plagioclase Geothermometer The hornblende-plagioclase geothermometer (Holland and Blundy 1994) involves the exchange of the componems (NaSi) (CaAI)., between homblende and plagioclase. The thennometer has been calibrated agamst an extensive data-set of natural and synthetic amphiboles. The equili'brium exchange reaction is: edenite + dbite = ricterite + anorthite This themorneter is applicable to rocks which formed in the range of 400- 1000 OC and 1- 15 kbar. and over a broad range of bulk compositions including tschermakitic amphiboles from gamet amphilites. The uncertainty of the thermorneter is * 35-40 OC. It uses the expression: where the Ynbm tenn is given by: for XabO.5 the Yab, = 3.0; othenvise Yabm = 12.0(2Xab-1) + 3.0. A procedure for the estimation of ferric iron in amphiboles is presented by HoUand and Blundy (1994), however, for consistency, ferric iron in amphiboles used here was calculated by applying the method of Papike et al. (1974). A test of a couple of amphiboles indicated little Merence in the calculated femc iron between Papike et al.3 (1 974) method and Holland and B lundy's (1994) method. Temperatures were calculated using six minerai pairs fkom 3 sarnples. Cdculated temperatures range fiom 543-600 OC (average = 566 40 OC) at 3 kbar pressure. These temperatures agree with temperatures estimated fiom Berman's (1991) gamet-biotite geo thermomet er and temperatures calculated using the gamet-ho niblende geo thenno meter. 3.5 CONCLUSIONS At least two deformation events and one amphibolite facies metamorphic event are recorded by the north-facing metavolcanic and metasedimentary rocks in the GiML area Di structures include an So pardel no&-dipping SI cleavage, shallow West- and est- plunging isoclinal Fi folds, and a north-plunging LI lineation fabric. D2 structures are defked by rnoderate no&-west- to north-east-plmghg FZ fol& and associateci moderate north-west- to north-east-plmghg crenulation which defines an axial planar cleavage (S2). Metamorphic mineral assemblages in the chic rnetasedimentary rocks (gamet + staurolite + andalusite + biotite + oligoclase) and matic metavolcanic rocks (homblende + plagioclase + gamet). indicate Io wer amphibolite facies conditions of regional metamorphisrn Metamorphic rnineral textures indicate that regional tectonism was prirnarily compressional. Based on regional studies, both deformation events and the amphibolite grade metamorphic event are interpreted to be Archean age. An estimate of the temperature and pressure conditions for regional nietamorphism. based on the stable mineral assemblage, is in the order of 500-580°C and 1.5-3.5 kbars. Geothermornetric calculations yielded temperatures which range f?om 500-625°C at 3 kb pressure. Despite the hi& range in calculated temperatures, they generally fdwithin the range indicated by the rnineral assemblage and confirm that the peak metarnorphism in the GML area has reached lower arnphibolite grades. Temperatures are also consistent with regional studies. Textures in the rnafic volcanic rocks (plagioclase rirns on gamet) suggen a second metamorphic event, which was primarily a decompression and thexmai event in the study area Prelimlliary age dating of metamorphic homblende in the mafic metavolcanic rocks f?om the GML area yielded an Early Proterozo ic age (K-Ar) of (Miller, pers. corn 1996). Inferred fiom resetting temperatures for homblende, a second arnphibolite grade metamorphic event is suggested in the GML area Such a metamorphic event is consistent with regional studies. Further evidence for a Proterozoic amphiboiite grade thermal overprint is indicated by the gabbro intrusions in the study area. This evidence will be discussed in Chapter 6 on the Suluk occurrence. TECTONIC SETTING OF THE GIBSON-MACQUOID GREXNSTONE BELT 4.1 INTRODUCTION Tectonic settings of recent orogenic belts cm be inferred by examining stratigraphy, petrography and major element geochemistry of the volcanic and sedimentary rocks (Pearce 1982). in ancient orogenic belts, however, prirnary volcanic and sedimentary features are commonly modified by deformation, metarnorphism andor erosion. This is tnie in many orogenic belts where only remnants of volcanic terranes exist. In this case. trace and rare earth element (REE) geochemical characterisation of the metavolcanic rocks. associated intrusive rocks. and metasedimentary rocks rnay provide the best evidence. Interpretation of the tectonic setting in which the GMB formed was attempted in Chapter 2 using stratigraphy, petrography and major element geochemistry of the metavolcanic rocks. This work suggested an overall back-arc basin sethg for the GMB stratigraphy. This chapter surmarkes the trace and rare earth element geochemical characteristics of the metavolcanic rocks, as weii as the chic metasedimentary rocks (greywacke), and gmnitoid rocks in the Gibson-MacQuoid Lake area, with the aim of Mer defining a possible tectonic setting for the GMB. This will provide criteria by which the GMB cm be compared to other better understood volcanic belts which host major volcanic-associated massive sulphide deposits. The geochemical data presented here are ftom selected samples which display no obvious alteration associated with the formation of the Sandhill base metal sdphide mineralization (Le. Mn and Fe alteration, see Chapter 5), or epidote/K-feldspar/carbonate veining related to late cross-cuning Gtults. This discrimination of samples was done so that who le-rock analyses wouid closely reflect primary rock compositions. A more complete list of the geochemical data is presented in Appendk 3. The geochemistry of rnafic volcanic rocks in a volcanic sequence has ken used ext ensively to distinguish the tectonic environment O f formation of a vo lcanic-sedimentary Mt. more so than any other rock type. This chapter presents the general characteristics of Mcvolcanic rocks formed in various tectonic settings (Le. withlli plate, convergent or divergent settings). 4.2 GEOCHEMICAL CHARACTERIS'MCS OF MAFIC VOLCANIC ROCKS Various methods have ken used to characterise and compare rnafic volcaaic rocks. The typical method of characterising and comparing analyses of matic rocks is to plot the data on normal mid-ocean ridge basalt (N-M0R.B)-normaiised geochemical variation diagrams (Pearce 1982). N-MORB is used as a nomialising factor because it is interpreted to represent compositions closest to primary made. Other magma types. such as those formed at within plate or collisional tectonic environments, exhibit a selective and systematic enrichment or depletion of certain elernents relative to N-MORB (Table 4.1. Fig. 4.1). Other methods of discriminating b&ts ernploy plotting the geochemistry of basalts on various tectonic discrimination diagrams which deuse of the elements Zr. Y, Nb. Th. La Ti and Yb. These elements are considered to be relatively immobile during metamorphism and can be assumed to represent primary magma compositions. MORBTsare basalts erupted at mid-ocean spreading centres where they fom new oceanic cm; most are tholeiitic in composition. The most primitive of ail basalts (compared to primitive mantie) is the N-MORB which generally have low absolute abundances of large-ion lithophile elements (LILE), high field-strength elements (HFSE) and light rare earth elements (LREE) (Table 4.1 ). They have high ZrNb (> 17) and Y/Nb (B4.5) ratios, and low ZrN (1.8-4.4) ratios, and are chondrite-normaiized LREE depleted (L+a/Yb< 1. l)~(le Roex 1987). Enriched (E)-MORB generally have higher abundances of the LILE and HFSE, have lower ZrNb (5.8-6.8) and Y/Nb (0.9-1.2),and higher Zr/Y (6.1 -7.9), and are strongly e~chedin chondrite-normalized LREE (Lm > 4.5)~. Withh plate tholeiitic basalts (WPB)include those which occur in continental rifts (CRB) and oceanic Islands (OB)(Condie 1989). Oceanic islands form as a result of oceanic lithosphere moving over a rising mantle plume. Volcanic rocks are Fable 4.1. Trace element characteristics of Nod-type Mid-Ocean Ridge Basalt (N-h.IORB) (Sun and McDonough 1989, Oceanic Ishd Bas& (OB) and Continental Rift Basait (CRB) (Basaltic Volcanism Study Project 198 l), Back-arc Basin Bas& (BABB) and Island Arc Badt (IAB) (Saunders and Tarney 199 l), and Chondnte (Taylor and McLennan 1985). N-MORB OIB BABB Chondnte 51 1 1266 742 290 494 275 138 350 Il6 598 UOO 3 154 1 11 6 6 140 74 90 362 180 2.3 18.0 5.7 2.05 4.72 0.00 74 164 1 O6 7608 16127 8093 28 28 28 12.02 1-56 4.86 2.64 5.86 3 -82 3 1-76 9.1 1 18-53 0.12 1 -26 0.70 2.50 15.30 7.36 0.367 7.50 38.00 16.18 0.957 1-32 0.00 0.00 O. 137 7.30 0.00 12.00 0.7 1 1 2.26 6.17 3.63 0-231 1 .O2 0.00 1.19 0.087 3.68 0.00 0.00 0.306 0.00 0.00 0.00 0.058 4.55 0.00 4.97 0.38 1 1 .O 1 0.00 0.00 0.085 1 2.97 0.00 0.00 0.249 0.00 0.00 0.00 0.0356 3 .O5 2.10 2.90 0.248 0.46 0.00 0.00 0.038 1 0.55 4.92 1.72 Note: N denotes chondriîe normalised values. predorninantly of the tholeüuc series, with lesser alkaline rocks: in both series, basaltic compositions (olivine to Fe-ric h tho leiites) dominate over intermediate and felsic compositions. The Hawaiiarl Islands are the best known example of oceanic Island volcanism. Continental rifts form as a result of continental break-up, continent-continent collision or continental hotspots. Magmas in these settings are commonly empted fkom small ro intermediate-sized cinder cones or extensive &sure systems (such as the Columbia River Plateau). Volcanic rocks in continental rifi systerns are characterised by bimodal tholeiitic or alkaline suites and include mdc and felsic mgmas and rarely intermediate members: felsic mapas are cornrnonly less abundant than matic compositions. Geochemically, OB and CRB show similar N-MORB-nomialised geochemical patterns (Pearce 1982; Condie 1989) and are similar to E-MORB. OiB and CRB are typicdy enriched in the LILE, moa HFSE and the LEE FalYb = 4.92 (OIB) and 4.8 1 (CRB)IN(Table 4.1 ; Fig. 4.1). These basalts have much lower ZrNb (9.1 1 and 13.44 respectively) and Y/Nb (1.56 and 3.36), and higher ZrlY (5.86 and 4.0) than N- MORB. Magmas formed in collisional (subduction-related) tectonic settings include those formed in volcanic arc (VAB) and back-arc basin settings. Volcanic arcs are of two mes; those buiit on continental crut (continental-margin arc) and those built on oceanic crust (island arc) (Condie 1989). Continental-margin arcs are primarily subaerial arcs and are composed of flows and associated pyroclastic deposits wbich form large stratovolcanoes. Oceanic arcs are predominantfy submarine and are typicdy comprised of pillowed flows and large volumes of hyaloclastic tuf& and breccias. Both tholeiitic and calc-alkallie magmas c haracterise arcs with andesites and basaltic andesites O ften dominating. Felsic magmas in arcs are generally emplaced as batholiths, although felsic volcanimi is cornmon in mo st continental-margin arcs. Tho leiitic vo lcanic arc basalts (VAB) are characterised by moderate e~chmentin the LlLE relative to the elements Ta to Nb, and are typicdy weakly to strongly depleted in the HFSE and LEE (Condie 1989; Pearce 1982, 1983) (Table 4.1; Fig. 4.1). The enrichment in the LEE and depletion in the Ta-Nb relative to neighbouring LILE is typical of subduction related Wtsand is known as a subduction zone component (Saunders and Tamey 1984); Condie 1989). - O Continental rÏft basalt 2 Oceanislandbasalt - C Back-arc basin basalt 1 4 X Island arc basalt - - N-MORB - - Figure 4.1. a) N-MORB normalized multi elernent variation diagram and b) choncirite normalized diagram, of tholeiitic basait formed in various tectonic environments. (See table 4.1 for data, data sources and normalizing factors). The average VAB has weakly lower YINb (10) and ZrN (2.29) and moderately lower ZdNb (22.9) than N-MORB (Table 4.1). Back-arc basins, a category of marginal basins. form behind the volcanic chahs of volcanic-arc systems (Saunders and Tamey 1984 1991). They fonn as a result of extension and sedoor spreading behind or within a volcanic arc, and are associated with contemporaneous subduction-zone activity. The rnajority of modem back-arc basins are associated with oceanic island arcs, termed intra-oceanic or ensirnatic basuis, and include the Mariana Trough, Lau Basin, and East Scotia Sea Rifting of continental iithosphere &O produce back-arc basins but are less common. Such baskiis, temeci ensialic basins. include the Braosfield Straight and Sea of Japan. The rnajority of the back-arc igneous rocks are quartz-normative tholeütic basait to basaltic andesite. The chemistry of back-arc basin basalts (BABB) is transitional between MORB and VAB although basalts indistinguishable fiom MORB exist. Essentially a BABB is a MORB which has been overprinted with a subduction zone component. That is, they show an enrichment in LILE relative to the HFSE and a weakly to moderately developed negative Ta-Nb anomaly (Fig. 4.1a). BABB are typicdy weakly enriched to weakly depleted in LREE (Fig. 4.lb). The average BABB (Table 4.1) has lower Yhh (4.9 1) and Zr/Nb (18.59) and higher Zrff (3.79) than N-MORB. The difference between BABB and VAB is that BABB have weakly higher total LEE and HFSE and a less defined Ta-Nb anomaly (Fig. 4. la). 4.3 G ibson-MacQuoid Lake Metavolcanic Rocks 4.3.1 Mafic metavolcanic rocks Based on field characteristics, mineralogy and major elernent geoc hemistry (Chapter 2), the mafïc metavolcanic rocks in the GML area are classined as high-Fe, low- K tholeütic, quartz-normative basalt to basaltic andesite and are interpreted to have formed within a subaquous environment. The trace element geochemistry of the reiatively unaltered WCmetavolcanic rocks is presented in Table 4.2. Relative to N-MORB (Fig. 4.2a), the mafic metavolcanic rocks are strongly emiched in the LILE, weakly e~chedin most HFSE, close to unity relative to N-MORB in P, Y, Lu and Yb, and are depleted in Cr and Ni. They show a weak negative Ta-Nb anornaly relative to the neighbouring LILE Table 4.2. Trace and REE chemistry (ppm) of the mafic metavolcanic rocks iiom the GML. area. Sample # P Cr Ni K Rb Ba Sr Ta Nb Hf Zr Ti Y NbN Zrff ZrWb Th La ce Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu (L~/Y~)N Sr K Rb Ba Th Ta Nb La Ce P SmHf Zr Ti Y Yb Lu Cr Ni Figure 4.2. N-MORB normalized multielement variation diagrarns (a) of the GML mafic metavolcanic rocks and (b) of the GML rocks (shaded area) compared with tholeiitic basalt tiom various tectonic environments. (Th and La). REE f5il within a relatively narrow range at approximately 8-20X chondrite abundances (Fig. 4.2). The REE patterns are flat (Fig. 4.3a), range &om weakiy LREE depleted to weakly LREE e~ched[(La/Yb)p0.66-1-59] (Fig. 4.3b) and display a negligible Eu anomaly . The overd pattern defined by the trace element chemistry (Fig 42b) and the ratios YNb (5.2-IO), ZrN (2.7-4.2) and Zr/Nb (13.5-33.0) (Table 4.1) indicate the dc rnetavolcanic rocks of the GML area formed within a collisional (subduction related) tectonic setting. On various major and trace element discriminant diagams (Fig 4.4a-d), the mafic metavolcanic rocks show characteristics of ocean floor basdts (Le. N-MORB or BABB). Based on the mjor and trace element geochemical characteristics. the GbK metavolcanic rocks are not consistent with a MORB or VAB derivation and are therefore interpreted to have formed in a back-arc basin tectonic setting. That is, they show the characteristics of a MORB which has ken overprinted with a subduction zone component (Fig. 4.4d). The trace element geochemistry of the GML metavolcanic rocks is similar to basalts fiom modem back-arc settings (Fig. 4.5). 43.2 Feisic to intermediate metavolcaniclastic rocks Based on field characteristics. mineralogy and major element geochemistry, the metavolcaniclastic rocks which host the Sandhiii deposit are medium-K, calc-alkaline andesite to dacite (Chapter 2). Trace and REE data of these rocks is presented in table 4.3. Relative to N-MORB (Fig. 4.6a), the metavo lcaniclastic rocks are strongiy enriched in the LILE, are moderately to weakiy enriched in most KFSE. are close to unity relative to N-MORB in P and depleted in Ti to Ni. ïhey generdy show a weak negative Ta-Nb anomaly relative to the neighbouring LILE (Th and La). REE fall within a relatively narrow range. The REE patterns are LREE-enriched [(La/Yb)N= 5.6- 10.61 and, like the dcmetavolcanic rocks, display a negiigible Eu anomaly (Fig. 4.6 b, c). The trace element characteristics of the metavo Icaniclastic rocks compare Favourably with those which formed within a volcanic arc tectonic seaing (Fig. 4.7). This seaing fits with the rnafic metavolcanic rocks in that both were formed in a collisional tectonic setting, however, the mafic rocks are interpreted to have formed in a back-arc setting. Figure 4.3. (a) Choncirite-normalized REE plot of the GML mafic metavolcanic rocks. Normalizing values are from Taylor and McLennan (1985). (b) plot of Mg0 vs choncirite- normalized (N) LdYb for the GML mafic metavolcanic rocks. * Tonga Arc * Mariana Trough Lau Basin - * Parece-Vela Basin - a Mariana arc 1 1 1 1 1 III 1 1 1 t f III I .O1 -1 1 Log(Th1N b) ,' Mariana Troucrh - Figure 4.5a,b. Diagrams showing the range in composition of rnafic metavolcanic rocks from various tectonic environrnents (from Saunders and Tarney, 1984). The diagrams show the similarity in chemistry of the GML mafic metavolcanic rocks (open square) to back-arc basin basalts fiom around the world. Table 4.3. Trace and REE chemistry (pprn) of the intermediate to felsic metavolcaniclastic rocks fiom the OML eree. Samplc # P Cr Ni K Rb Ba Sr Ga Ta Nb Hf Zr Ti Y Tb La Ce Pr Nd Sm Eu Cd Tb DY Ho Er Tm Yb Lu \ \ \ \ WlTHlN \ PLATE -. iAVAS '\ \ I \ I I 1 I Zr/117 A - N-type MORB A B - E-type MORB and WPB and differentiates C - Alkaline WPB and differentiates 0 - Destructive plate-rnargin basalts and differentiates '\ \ \, Figure 4.7. Tectonic discrimination diagrams for the intermediate to felsic metavolcaniclastic rocks which host the Sandhill deposit: (a) Zr vs Ti diagram fiom Pearce et al. (1 984); (b) Th-Zr/ 1 17-Nb/ 16 diagram is an analogue of the Th-Hf-Ta diagram of Wood (1 980). The metavolcaniclastic rocks are interpreted to be a distal volCaniclastic deposit fodm a mbaquous environment, but likeS, derived hma nibaeriai environment (Chapter 2). Such distal Mout deposits have been identifiai m back-arc settings and are interpreted to be derived Eom an active island arc (Fisher and Schmincke 1984). The active arc, however. may be 100's of Imi away. This type of environment is interpreted for the GML area in which the intermediate to feisic metavolcaniclastic rocks which host the SandhiU deposit were derived fiom a distal ishd arc and deposited within the back-arc. The calc-an 4.4 CLASTIC METASEDIMENTARY ROCKS (UNIT 4) Vario us geochemical methods have ken devised to characterise and determine the provenance and tectonic setting of Archean greywacke (Nesbitt and Young 1982. 1984 Taylor and McLennan 1985; Bhatia and Crook 1986; Naqvi et al. 1988). Greywacke used in this work includes sandstones of a wide mineralogical range, deposited in a deep sea environment by turbidity currents or other mass- flo w processes. Twelve samples defïned as metagreywacke were COliected f?o m the field area and t heir geochemical characterist ics are summarised in Table 4.4. The geochemistry of the metamorphosed greywacke fiom the study area is plotted on a spidergram (Fig. 4.8), which shows the samples normalised against the average Archean (3.5-2.5 Ga) upper crust (normalisation values [Table 4.41 taken fTom Condie 1993). Cao, Ni, Cr, Co and Y in the study area samples show minor depletion's relative to the average cm, whereas the remahder of the major and trace elements are at average to slightly above average concentrations. The average composition for the GML greywacke is similar to the average Archean upper crut (Table 4.4), suggesting a single source (similar in composition to the average Archean crust) provided most of the detritus. Archean greywacke are known for their low A120JNaz0 ratios (<6) compared to most other sandstones (Taylor and McLennan 1985) indicative of their chernical immatunty and derivation fiom a relatively unweathered source. nie küz03/Na20 ratio of - - - - 1 ------. - + - average Archean - - upper cmst Figure 4.8. Spiderplot of selected samples of metamorphosed greywacke from the GML area normalized against average Archean upper crut (values from Condie 1993). the metagreywacke fkom the study area have an average value of 5.39 (3.97-6.80). which is typical of that for immature sedirnents. The KtO/Na20 ratio of clastic metasediments has ken used to infer crusta1 evolution. It is beiieved that the K20/Na20ratio of most sediments formed prior to 2.5 Ga is generally c 1 (Engel et ai. 1974). This is because K20 was not as abundant in Archean continental crust compared to continental crut in the Proterozoic and Phanerozoic. Archean continental crust was largeIy made up of mafic- ultramafïc rnetavolcanic rocks and tonalitic gneiss. The KZO and Na20 content of the metagreywacke in the study area fdwdhm a relatively oanow range and the weight ratio KrO/Na2O is typicaily Iower than 1, with an average of 0.8 (0.5- 1.4) (Table 4.4). Archean greywacke also contain hi& concentrations of Fe0 and MgO. suggesting natic metavolcanic rocks were an important source rock, with Fe0 + Mg0 ranging fiom 4.1 - 1 1.5 wt. % (Taylor and McLennan 1985). However, there is no difference in major element chemistry between those derived nom a volcanic source or those derived fiom a mixed or granitic source. The average Fe0 + Mg0 for the samples fiom the study area is 9.96 wt. % (range = 7- 19 wt. %), again simiiar to the average Archean crust. The maturity of the metagreywacke in the study area, and the composition of the source rock cm be determined by looking at the degree of chemical weathering of the source rock. Chernical weathering bas important effects on the composition of chic sedimentary rocks. The degree of chemical weathering can be quantitatively measured by cdculating the chemical index of alteration (CM)(Nesbitt and Young 1982) using the molecular proportions: CIA = [Ai203/(Alt0>+ Cao* + Na20 + K20)]* 100 where Cao* is the amount of Ca0 incorporated in the silicate fkction of the rock. A correction is made for the proportion of apatite and calcite iu the rock. Detaiied microscopie studies of the metagreywacke fiom the study area indicates carbonate and apatite are minor, therefore, little error is introduced. The CM-values for the metagreywacke f?om the study area have an average value of 59.46 (53.4-65.6), supporting a previous interpretation that the metagreywacke are generally immature. were deposited rapidly and ctosefy represent the original rock type. The above data for the metagreywacke fÎom the midy area are plotted on an A- CN-K ternary diagram (Fig. 4.9). This triangular plot can be used to constrain the initial composition of the source rock (Nesbitt and Young 1984). Many weathering profiles show a linear trend subparailel to the A-CN join. In the absence of K rnetasornatism. a he can be drawn through the data points and interset the feldspar join at a point diat shows the proportion of plagioclase and K-feldspar of a fkesh rock. Prbay rock types will fall dong or close to this join and the intersection yields a good indication of the type of parent rock for the sediments. A line drawn through the data points representing the study area sarnpies to the feldspar join (Fig. 4.9) is consistent with a derivation fkom a source grnodiontic in composition or a composition which resembles that of the average Archean upper crust. The variable trace element geochemistry of greywacke has been determined to reflect their provenance type and tectonic setting (Bhatia and Crook 1986; Naqvi et al. 1988). The tectonic settings recognised include oceanic Island arc, continental island arc, active continental margb, and passive continental margin. Trace elements used for discrimination include La, Ce, Nd, Y, Tb, Zr, Hf; Nb, Ti and Sc. These are the most usefiil elements for provenance and tectonic setting determination because they tend to be transported quantitatively into clastic sedimentary rocks during wearhering, and because of their relative low mobility during sedimentary processes. Other elements used include Rb, Sr, Ba, Ni Co and V. In general, there is a systematic increase in the LEE (La, Ce, Nd), Th, Nb and the Ba/Sr, Rb/Sr, LaN and Ni/Co ratios and a decrease in V, Sc and the BaiRb, K/Th and WII ratios in greywacke nom oceanic Island arc through continental isiand arc, active continental margin, to passive continental margin. The abundance of Sc, V, Cr, La, Zr and Y and the ratios of these elements VISc, LdY, Sc/Cr, TilZr and LdSc in the metagreywacke fiom the study area (Table 4.4) overlaps that of both a continental island arc and active continental margin setting for their deposition (Bhatia and Crook 1986; Naqvi et ai. 1988). The overall geochemistry of 9. A-Type Granite 8. 1-Type Granite 5. GranodioriteIDacite 4. Average Archean upper crust (3.5-2.5Ga) 1. GabbrotBasalt Feldspar Join Figure 4.9. An A-CN-K diagram (in molecular propohons) for the GiML metagreywacke samples (asterisks) and average compositions (Nesbitt and Young 1984) of fresh rocks (Solid circle). Note the chernical weathering trend for the GML samples. meragreywacke, and the absence of volcaniciastic or sedimentary rocks characteristic of a an isiand arc mdicates an active continental rnargïn arc sening. 1.5 GRANITOH) INTRUSIONS Based on mineralogy and major element geochemhy, these rocks have been classified as 1-type feisic, metduminous to weakiy periluminous, tonaliiic to granodiontic mtnisions (Chapter 2). This section demithe trace element chemisûy of the graniroids. ïhe mce element chemimy is compd with the major granitoid types mcludmg A-, S-, LM- and 1-types (PRcher 1983; Wenet al 1987) (Table 4.5) . A (anorogenic)-type granRoids are derived @om recycled. dehydrated continental cmand form by tension-related (non-subduction) processes. They are acid-basic and peraIkaine m composition and are enrîched m the WSE. M, 1-, and S-type granitoids form above subduction zones or within coilision belts. M (made)-type granitoids are mantle derived metduminous gabbroquartz diode rocks whic h form m oceanic ishd arc and primitive continental arcs. These rocks are characterised by Iow LILE and HFSE abundances. S (sedimentaq+type @oids form in mature continental arcs and are the products of with-plate made sources with a major cnisfal contniution (sedimentary protolïth). These pnhoids are typicaily granodiorite and two-mica granites with strongiy periiuminous characteristics and hi& concentrations of LILE and HFSE abundances. 1 (igne0us)-type granitoids are intermediate between M- and S-type granitoids. 1-type granitoids are metaluminous to perduminous rock suites tbat show a range m rock types fkom diorite to tonalite to monzogranite to granite. These rocks fom m normal continental arcs and have a mamly made derived precursor with a mhor subduction-relateci source. The GML tooaüte-granodiorite inminons have low Rb, Nb and Y contents relative to Ba, Sr and Ti (Fig. 4.10a). The chernical pattern has some smiilaniies to tbat for average M- type granite (Fig. 4.10b) although the lower Rb and Nb and higher Y values of the GML grandoids are not consistent with this ati;nav. Cornbmed with the mineraiogy and major element chemistry, the mtnisive rocks m the GML area are likely primitive 1-type granites with ckmktry transitional between M- and 1-type grades. The 1-type petrochemical features of the granitoid intrusions suggest they formed in a subduction-related setting (Pitcher 1983). This interpretation is supported by the tectonic setting discrimination diagrams of Pearce et al. (1984) (Fig. 4.1 lab). The granitoid samples plot well within the field for volcanic-arc granites and likely forrned within a continental arc environment. 88 Table 4.5. Trace element characteristics of the granitoîd rocks kom the GML are% and average granite types of Whaien et al. ( 1987). Sample # P Ba Rb Sr Pb Th u Zr Nb Y Ce Sc v Ni Cu Zn Ga (a) . . .O 1 K RbBaSr Y Zr NbThGa PTi V NiCuPbZn GML granitoids .O1 ,,.o. 8,. , . K RbBaSr Y Zr NbThGa PT V NiCuPbZn Figure 4.10. Cornparison of the trace element compositions of: (a) average granite types of Whalen et al. (1987) and @) granitoid rocks fiom the GML ares-Analysis are normalized against the average 1-type granite ofWhalen et al. ( 1 987). VAG ORG a GML granitoids - 1-type granite 2 M-type granite L S-type granite 0 A-type granite 1 WPG ORG Figure 4.11. (a) Rb venus (Y + Nb) and (b) Nb versus Y for the GML kmnitoids. Average granite compositions from Whalen et al. ( 1987) are shown for cornparison. Fields in figures are fiom Pearce et al. (1984). VAG - Volcanic Arc Granite; WPG - Within Plate Granite; ORG - Ocean Ridge Granite; syn-COLG - syn-collisional Granite. 1.6 CONCLUSIONS The tectonic sethg defÏned by the whole rock geochemistry of the mdc volcanic rocks (back-arc basin), the felsic-intermediate volcanic rocks (island arc), the sedimentary rocks (active continental margïu) and the -doids (isld arc) indicates an overall continental- ma@ arc tectonic sening for the GMB. A back-arc basin/co~entai-margin arc tectonic mode1 for the development of Archean granite-greenstone kits was developed by Tarney et aL (1976) and discussed by Condie (1989). An idealised sequence of events leadhg to the production of these belts is illustrated in Figure 4.12. Early stages of development of the back-arc basm succession are characterised by eniption of dc-ultrarrÿlfc lavas and deposition of Sediments derived f?om the continent ador arc (dependnip on the position in the basin and extent of nftmg). The back-arc basm succession is then deformed and mtruded with syn-tectonic granitoids during activation-type orogeny and lata by pst-tectonic granites. Prefèrential uplift and erosion of the sequence is then necessary to expose high grade terraneS. Deformation of the Archean cnist is cornplex and polyphase. Early phases of deformation are dominantiy compressionai as reflected by nappes and thnists. Later diapiric emplacement of plutons is associated with prirnarily vertical forces. Regional metamorphimi of Archean crut is typically low pressure type. The overall Archean çaatigraphy and Arc han deformation (outlined m Chapten 2 and 3) of the GML area £its weil with this modeL The stratigraphy iudicates continental side of a marpuiai arc. Resent mineral assemblages mdicate Iow-pressure regionai metamorphic conditions and stnicturaI &CS indicate an eariy stage of compression foUowed by localjsed diapiric empiacernent of the granitoids (Chapter 3). A Proterozoic tectonothennal event has modified these Archean fm. GML area Continental se diment / Sedimenta phase Deformation + GML area syn-orogenic tonalite Basin closure Phase GML area Figure 4.12. Evolutionary sequence of an Archean greenstone belt in a back-arc basin tectonic setting (frorn Tarney et al. 1976). Box indicates area represented by the GML area. TRE SANDHILL VOLCANIC-ASSOCLATED BASE METAL SULPHIDE PROSPECT 5.1 INTRODUCTION The Sandhill base metal prospect was discovered in 1988 during an extensive reconnaissance and detailed exploration pro gram by Comaplex Minerals Corp. and Asamera Minerals hc. (Staargaard 1988). The prospect is comprised of a zone of stratiform sphalerite, chalcopyrite and galena rnineralization hosted within a 900 m long zone of highly dtered intermediate to felsic metavo lcaniclastic rocks. Representative samples of rnineralization contain up to 2 % each of Zn and Cu, and up to 0.25 % Pb (Staargaard 1988). Gold and silver values are up to 0.15 and 15 g/t respectively. A few sarnples yielded up to 311 g/t Ag. No fùrther work was conducted on the Sandhill Prospect until initiation of the present study. However. recognition of new and extensive base rnetal dphide mineralizaton during this study has dedm renewed interest by Cumberland Resources Ltd. m the Sandhill prospect. Exploration, conducted by Cumberland Resources Ltd. during the 1995 and 1996 field seasons, consisteci of airbome and ground geophysics, pro-, detailed geological qphgand diamond dnlling (Lewis 1996). This chapter presents the mineralogicai and geochemical characteristics of the Sandhill massive sulphide zone and asmciated alteration enveiope, as well as other stratigraphically equivalent sulphide showings. Field observations, petrographic data and whole rock and mineral geochemical data are discussed here; petropphic and representative mineral assemblages and sarnpie location maps, and whole rock, and mineral chemistry are presented in Appendix 1, 2 and 3 respectively. Recent work on the Sandhill prospect by the Cumberland Resomes Ltd is also descfl'bed below. The description of the Sandhill prospect will be preceded by a generai descnption of volcanic-associated massive dphide deposits. This wili provide criteria by which the SandhiU prospect can be classified (i.e. CO pper-MC group or zinc-lead-COpper group). 5.2 VOLCANIC-ASSOCIATED MASSIVE SULPHIDE (VMS)DEPOSITS 5.2.1 General Characteristics Volcanic-associated massive sulphide (W)deposÎts, also referred to as vokcanic- hosted or volcanogenic massive nilphide deposits, have recently ken extensively reviewed by Lydon ( 1988, 1984; general overview), Franklin ( 1993, 1996; Canadian VMS deposits), and Large (1992; Australian VMS deposits). Early reviews of WSdeposits included Ohmoto and Skinner (1983), Franklin et aL (1981), Sangster and Scott (1976), and Hutchllûon (1973). The foilowing section surmnarises the generai characteristics of WlS deposits. prhady extmcted fkom the more recent papers by Lydon (1 988. 1984). Large ( l992), and Franklin ( 1993. 1996). For a more comprehensive description of VMS deposits the readen are referred to the references cited above. VMS deposits mclude all massive or semi-massive accumulations of sulphide minerais which form on or near the sea floor by precipitation of hydrotherrnal fluids. VMS deposits are primarily associated with volcanicdominated terranes and are predominantiy hosted within nibmarine volcanic rocks. However, mdividuai deposits rnay be enclosed in associated sedimentary rocks. Volcanic terranes which host VMS deposits form in a variety of tectonic settmgs, mcluding spreading rnid-ocean rîdges or back-arc basins, island arcs or continental- margin arcs, or intra-plate oceanic islands. Deposits range in age ffom pre 3.1 Ga in the volcanic rocks of the Pilbara Block of Western Ausnalia to the presentiy forming deposits m modern actively spreadnig ridges (eg., East Pacifïc Füse). Wahlli a volcanic terrane, VMS deposits typidiy occur m clusten of ore lenses, seperated by iithologically similar rocks, and most deposits tend to occur withm a singie stratigraphie interval, defïned as the fàvourable horizon The Eivolirable horizon however, may occupy only a small fiaction of the overall volcanic strahgraphy. The ternainder of the Stratigraphy wiU show no evidence for the presence of VMS deposh. Wthm the Givourable horizon mdividuaI VMS deposits or lenses show a saong association with synvolcanic Fauts and occur within topographie lows. 5.2.2 Deposit-seale Characteristics individual sulphide deposits within a volcanic terrane rnay be ckissiûed as either prolàmal or distaI deposits. Proximai deposits are those which occur innnediateiy adjacent to thek e-e vent whereas dÏstai deposh are those which form at some distance fiom the vents either through chemicai or mechanical processes (Ffankjitl et ai. 198 1). in a generalised mode1 (Fig. 5. L). individual proximal WSdeposits are comprkd of a concordant lem of massive sulphide consisting of at least 60 % sulphide minerals (Lydon 1984). Upper contacts of the lens are sharp, but the lower contact is transitional into a discordant stringer or stockwork zone contained within a hydrotherdy altered pipe. The st~geror pipe zone may extend for several tens of meters below the deposit. A single deposit or mine rnay con& of multiple massive sulphide lenses and associated stockwork zone. Shapes of individual deposits Vary fkom steep-sided cones. which form on top or tlank of a topographie feature, to tabuiar sheets which foxm in topogaphic depressions. Many deposits which have undergone penetrative deformation are typically stretched so that the stockwork zone is in apparent lateral confomllty with the massive sulphide lem. The most common suiphide minerals in VMS deposits are pyrite, pyrrhotite. chalcopyrite, sphalerite and galena. The most commo n non-sulp hide minerals include magnetite, hernatite and casiderite. VMS deposits also contain, in variable arnounts. silver, go14 cadmium, bismuth, tin and selenium. Gangue minerals which may precipitate with the sulphides are quartz, chlorite, sericite, bante, gypsum, carbonates and alumliosilicate minerals (and their metamorphic equivalents, i.e. chloritoid, staurolite, andalusite. gamet. cordierite, anthophyllite etc.). Gahnite is an accessory phase in most deposits metamorphosed to the amphibolite grade (Spry 1986; Spry and Scott 1986). Zoniog of suiphide minerals within individual pro'uimiil massive sulphide deposits is ubiquitous (Fig. 5.1) (Lydon 1984). There is a systematic decrease in the Cu/Zn ratio (~halcopynte/sphalerite)upward and outward fiom the core of an alteration pipe. MASSIVE SULPHIDE LENS l-- Sharp hanglng --\ - wall contact -.. 1 '\ 'Exhatite" or Massive, rubbly or brecciated structure (strong chernical zonation pattern) 'Tuf fite' horizon \ - - . / \ Gradational footwall chloritic hydrothermal alteration 11-1 Py + Sp * Gn sulphide mlneralization sericitic-chloritic hydrothermal alteration Figure 5.1. Esscntiül cliüracteristics of'iiii ideitlizcd ~ol~iiiiog~iii~iii;issivc siilpliide dcposit (;iller Lydoii I 084). Barite, when present, commonly occurs with the highest concentrations of sphaierite and galena in the outermost zone of the massive suiphide lem. Pyrite generdy occurs throughout the deposit but tends to achieve its maximum concentration where sphalente becomes predomhant over chakopyrite. Magnetite tends to be concentrated in the core of the stockwork zone and the cennal basai part of the suiphide lem. FUially, a thin bedded siliceous exhalite containing pyrite or hematite typically forms a thh veneer over the top of the sulphide mound and extends laterally away from the deposit for a considerable distance. Nteration zones encompassing the rnineralization also show a distinct Mneralogical and chernical zoning within individual proximal deposits (Fig. 5.1). Surrounding the stockwork zone, the alteration pipe consists of a chloritized core. surrounded by sericitized peripheries. The chloritized core is characterised by additions of Fe. Mg, Cu, Zn and S. and depletions in Ca Na, and K as well as Sr. Nteration in the sericitic zone is a Less intense continuation of the chloritic zone except for the addition of K rather than a depietion. In deposits that have ken metamorphoseci, the major Mg and Fe addition to the alteration pipe is reflected by a cordierite-anthophyuite assemblage. Silica and chlorite alteration aiso fom the predorninant silicate phase in the massive sulphide lem, and occur as cross-cutting veins, as a matrix cernent. or as distinct iithological lenses. Hanging-waii aiteration in VMS deposits is much less intense and contains sirnilar alteration assemblages as in the pipe zone. Continuity in the alteration of the pipe zone into the stratigraphie foot-wall is recognised in many regions (Lydon 1988a). Semi-conforniable foot-wall alteration zones are laterally widespread and rnay extend for rnany kilometres away f?om the deposit. Styles of aiteration recognised include Na depletion and Fe and Mg e~chment,marked by regional staurolite and chlorite bearing rhyolite. Other examples include Si and Na enrichment, accompanied by depletion of Fe, Mg, Ca, Ti, Zn and Cu, which is marked by secondary dbite and epidote and quartz assemblages, or intense silicification in mafk volcanic rocks (result are silicified matic volcanic pillows). ProWdeposits tbat formed in relativeiy shallow water, volcanic rocks comprised of volcanic breccia. debris flows and some subaerial vo lcanic products are characterised by iatedy extensive carbonatized volcanic strata which are depleted in sodium Hydrothennal precipitates such as ferruginous chen. suiphidic nitf and sulphidic sediments are deposited penecontemporaneously with the VMS deposit, and may be laterally extensive. Base metal contents. aithough sub-Ore grade. within these distal horizons may increase and lead into the proximal deposits. Another style of VMS deposits are those with a sheet- or blanket-like morpholou (Large 1992). These deposits ioclude both prod(stratabound replacement deposit. brine pool) and distai (distal brine pools, distal slide sheets or reworked style deposits) sulphide accumulations. Distai deposits are characterised by the absence of sipficant foot-wd alteration, including a pipe zone, and predorninance of Zn-Pb mineralization over Cu. Mn or Fe oxïdes are connwn m aiteration zones associated with distal deposits. 5.2.3 Classification Classification of VMS deposits range fkom those based stnctly on tectonic setting (Le. spreading centres, island arc or continental margin settings), to those based on host iithology, petrochemistry and tectonic setting (Kuroko-, Cpw- or Besshi-types), to those based on host iithology and age of the host Litholog (Le. felsic volcanic rocks in Archean terranes, bimodal volcanic rocks in post Archean sequences, or dcvolcanic- dorninated sequences), to those based on major ore element chemisvy (Zn-Cu-,PbZn- Cu-, Pb-Zn- or Cu-types) (Lydon 1984). The hst two types of VMS classification schemes rely on a genetic classification of the host volcanic stratigraphy, however, a genetic classification is ofien compiicated by deformation, especidy in older terranes. A classification scheme based on metal content eIiminates the uncertainties in det ermining the tectonic setting. Large (1992) has adopted a three-fold classification scheme for VMS deposits based on ore element chemistry for the Australîan deposits. These include the Cu- , Cu-Zn-and Zn-Pb-Cu-types; Cu-type deposits wodd have a Cu ratio (Cu/Cu + Zn) > 60, and a Zn ratio (Zn/Zn + Pb) > 60; Zn-Cu deposits have a Cu ratio < 60 and a Zn ratio > 90; Zn-Pb-Cu deposits have a Cu ratio < 60 and a Zn ratio = 60-90. Franklin (1993, 1996) and Lydon (1988a) have settled on a two-fold classification scheme, Tonnes per 1 % area Figure 5.2. Subdivision of the three principle compositional groups based on tonnes of contained Cu, Pb, and Zn in massive sulphide deposits from around the world (From Franklin et al. 198 1). Volcanic-associated deposits are entirely within the Cu-Znand Zn-Pb- Cu groups; the Pb-Zn group is largely in sediment-hosted deposits. onginaliy defined by Franklin et aL ( 198 1). It is based on total contained Cu. Pb and Zn The two compositional groups are the Cu-Zn group (which includes Cu-type and Zn-Cu- type deposits) (Fig. 5.2) and the Zn-Pb-Cu group. The division between the two groups is set at a ZdZn + Pb ratio of 0.90. Cu-type deposas are not distinguished essentiaiiy because deposits of this classification were only muied for Cu and calcuiations were ody based on mined ore. Many of these deposits contain significant reserves of Pb and Zn. A third classification is distinguished, the Pb-Zn-type. ho wever, these deposits are strictly associated with sedimentary rocks and are no t Licluded as VMS deposits. Deposits of the Cu-Zn group occur within two main geological settings (Franklin 1993. 1996). The fkst setting includes areas dominated by dcvolcanic rocks such as Archean and Proterozoic greenstone belts, and Recent and Phanerozoic spreading ndges and seamounts. Deposits of mafïc volcanic dominated settings rnay have up to 30 % felsic volcanic rocks and subordhate sedimentary rocks in the footwall sequence and the overd sequence commonly has subvolcanic intrusions near its base. The deposits tom concordant to semi-concordant, massive iron-miphide rich bodies, commonly underlain by an extensive st~gerore zone. These deposits are commonly overlain by sedimentary grata including clastic and chernical (graphitic shales and Von formations) sediments. The second maLi geologic setting for Cu-Zn Group deposits includes areas containing nibequal amounts of dcvolcanic rocks and sedimentary rocks, such as in Phanerozoic arc and back-arc sequences (Franklin 1993, 1996). Deposits include those that form close to a tectonic boundary between ocean floor and island arc, ocean floor and continental cm,or ocean floor and cratons. The volcanic component in these deposits is dominated by mafic volcanic rocks, however, some areas also have minor quantities of felsic volcanic rocks. Sedimentary rocks are dominantly pelitic. Deposits in this setting are commonly tabular with distinct layering or bedding within the sulphide bodies and sulphides are locdy interbedded with silicate layers. Iron formations are common at the ore horizon. Alteration is not as pronounced as in volcanic-dominated Cu-Zn deposits. Deposits of the Zn-Pb-Cu group are most comonly Phanerozoic in age, occur in arc-related terranes where felsic volcanic sequences are dominant. Felsic volcanic rocks include calc-allcalùie feisic porphyritic ash-flow tu& rhyolite domes and flows, and some feisic epiclastic rocks. There is Me or no rnafic volcanic rocks in these deposits. As in the Cu-Zn group, deposits of the Zn-Pb-Cugroup include those dominated by felsic volcanic rocks and those which have sedimentary rocks as a si~cantportion of the foot-wall stratipphy. They appear in much the same manner as those in the Cu-Zn goup. i.e. shape, and ore minerai content and zoning. However. deposits of the Zn-Pb-Cugroup are characterised by barite, and gypsum as sigrÿficant gangue minerais. 5.2.4 Genetic Mode1 VMS deposits form hma hydrothermai system which is essentially a convective ce1 consisting predomimntly of searvater with a lessor magmatic and meteoric water cornponent (Fig. 5.3) (Franklin 1993, 1996; Lydon 1988). The driving energy of the convective ceU is eaher the oceanic cnistal kat flow at active spreadhg ridges, or an intnisive body such as a rhyoiite dorne. Durhg its decent, the seawater is heated, and modified in its chemical composition as it picks up met& which it leaches fiom the rock sequences. The remit is a lower semiconformable silicified. epidotized or carbnatized aiteration zone leached in met&. The modified seawater is sutnciently e~chedm met& to produce an ore fonning hydrothemial fluid Mer passing ttirough the hottest part of the convective cycle. the hiay saline, hot (350-400 OC) hydrothed solution begins to Ne rapidiy to the sea tloor dong a pre-existing zone of high permabiiity, mch as a &L& or fkcnire zone. Mixing of the rishg chemically-enhancecl hydrothermal fluîd with cooler sea or pore water causes the precipitation of ore and gangue minerais. uiitial chernid reaction takes pkce in the subsurFace, forrning the alteration pipe and associated sasiger chakopyrite ore zone. Chalcopyrite is the hst suiphide to precipitate because copper solubility decreases rapidly with temperature compareci to lead and zinc. At the seawater-rock interfàce, Mer cooling of the fluid causes rapid chemical precipitaîion of sphalerite and galena resultiog in the accumulation of the suiphide mound. Continued flo w of the solution up through the nilphide mound will redistri'bute the ore minerais resuiting in the characteristidy mned massive suiphide deposa. Cu/(Cu + Zn) ratios decrease upwards and outwards fiom the centrai part of the mound due to the progressive cooiing of the fluid, Replacement style deposits form when the hydrothermal fluids penetrate a porous. unconso lidated Sedimentary or vo lcaniclastic horizon adjacent to the hydrothermai hes (Large 1992). In this modeL the Cu to PbZn zonation is &eh to develop outward fkom the feeder huit rather tban ~lratigrapbidyup through the sulphide rnotmd. Sulphide mounds formed on topopphic hi* or steep slopes rnay becorne unstable as a result of CeraMtationalinstability or hydrauiic lifting and move dom slope and corne to rest at sorne distance away from the vent areas (Fig. 5.3). These distal slump breccia or siide sheets are characteriseci by lead-zinc-rich sulphide fhgnents which may occur withm submarine mass flow horizons dong mike 6om the proXimai deposits. This deposit type lacks the characteristic suiphide zoning, footwall merzone and si@cant footwall alteration (Lydon 1988; Large 1992). Hydrothermal fluid at a discharge site may initially form a dense buopt ore solution withjn the seawater. This buoyant plume m the overlying seawater wiU rnigrate downslope to accumulate as a brhe pool in a topographic depression or settle out m a topographic hi& (Fig. 5.3). If the near bottom seawater k reducing, suiphide Miout wül form a sipificant Zn-Pb deposit. The teSultant sulphide accumulation fom a distal bedded or layered deposit which kicks a characteristic pipe zone, and has no major footwall alteration zone. If the bottom waters. however, are more oxidising, sulphide minerais wiiI be destroyed and barite ador manganese oxides will be formed. As the composition of the uutially disckged fluid evolves widi tirne, silica, iron andor manganese oxides will also precipitate fkther out fiom these brine pools. The buoyant plume may spread laterally m a sWow water environment causHig precipitation of sphalerite and galena resulting in bedded suiphide deposits proximal to the discharge site (Large 1992). Massive nilphide bodies niay undergo intense deformation, and may be partially to completely detached fkom the aberation pipe (Franklin 198 1; Large 1992). Such deposits are apparent diçtal massive dphide accumulations. 53 THE SANDHILL PROSPECT The Sandhill prospect is comprised of a zone of sporadic stratifiom base metal dphide mineralization hosted within an extensive concordant horizon of pyritic quartz-muscovite schist (Fig. 5.4). The strike length of the concordant rnineraiised horizon is approximately 1,300 m and has a maximum thickness of 70-80 m. The sulphide miner& are predominantiy pyrite. sphalerite and chakopyrite. wRh minor pyrhoute and galena. Sigrilfiant concentrations of Ag are also present. Silicate minerais. directly affociated with the sulphide minerakation include gamet. s*iuroIite and gahnite. The mineralised horizon is enclosed by a more extensive envelo pe of hydro thedyaltered feisic-intermediate metavolcaniclastic rocks. Alteration assemblages and multiple weakly sulphidic quartz-muscovite schist horizons extend discontinuousIy for 11 km eastward along strike (Map), and westward. the host aratigraphy is truncated by a north-wea trending fault. The minerakation and alteration that des up the Sandhill prospect is hosted whoily with8i the feisic-intermediate metavolcanickstic unit (see chapter 2). This unit is bomded to the north by orthogneiss, and to the south by a sequence of mterlayered felsic-intemediate metavolcaniciastic and rnafic metavolcanic rock, mtedow chat is rare m the sequence. The main concentration of suiphide rnineralization is within the central part of the Sandhill zone (Fig. 5.4) and extends for approxkmeiy 200 m along de.Less extensive. sporadic suiphide mineraiization occurs near the west end of the pyntic quartz-muscovite schist horizon. Massive to disseminateci, medium- to coarse-grainecl sphalerite with trace interstitial galena occurs as multiple diçcontmuous 2-8 cm wide bands wahin the upper (northem) 15 to 20 meters of the pyritc quartz-muscovite scbist horizon Zinc dues m 27 widely spaced representative chip samples of this style of mineralization range hm0.02-9.3 wt % (average of 1.6 wt %) (Appendix 2); 14 of these samples assayeti >0.5 ghome silver and up to 160 g/t (average of 10 g/t). Several discontinuous concordant chat horizons, 0.5- 1.5 m thick, contain discontinuous 1-4 cm wide bands of coarse-&ed sphalerite * galena with associated 2- 10 % disseminateci fine-grained chaicopyrite. Two representative chip samples (samples 4140, Appendix 2) hma chert hohnwithh the main part of the Saedhill zone averaged 3.9 wt % Zn, 0.9 wt % Cu, 0.2 wt % Pb, 185 g/tonne Ag and 0.2 utonne AU Adym of the dommant suiphide phases identifieci m the niain Sandhill zone are presented m Tables 5.1 and 5.2. S phalerite is generaily hn-rich (5.74-7.4 1 atoms per formula unit (apfù)), with a ngniscant cadmium component (0.1 -0.3 apfù). In several anaiysis pyrite contains a nenificant cohalt component (up to 0.32 apfù). ChaicopyrÏte is pure end rnember. Severai an-of gaiena contain signiscant amounts of silver, bismuth and seleniun Trace amounts of stannite (Table 2), a M suiphide, with associated native tin was identifid m one sample from a chert horizon Trace amounts of native bismuth, typically associated with galena, bismuth telliaides, and a variety of silver-bismuth-anhony-copper-iron sulfosalts were identifieci ushg the Energy Dispersive Spectrometer comected to the e1ectron microprobe at the University of Western Ontario. The trace me& identifid above are sparsely reflected m the whole rock chexnical -sis of the quartz-muscovite scm or chert horizons (Appendix 2). Discontinuous pyritic quartz + muscovite schist horizons persist for up to 12 km eastward dong strke (Map 1). However, sphaierite. chaicopynte and galena were rarely obsexved in these horizons. meen simples ikom the eastern horizons averaged O. lwt % Zn and negligiile Cu and Pb (Appendix 2). Despfe the low base metal values in these zones the 13 samples averaged 8.2 g/tonne Ag. The quartz-muscovite schist which host the suiphide mineralization. both in the Sandhïü area and areas to the east, is mterpreted to be the remit of mtense sericite alteration of the felsic-intermediate metavolcaniciastic rocks. The major element geochemistry of the quartz- muscovite schist is plotted on a nurnber of ternary diagrams (Kg. 5.5) to view the effects of hydrothermal akeratioa Major oxides are plotteci against Ti9 and Ai203as these major oxides are viewed to have ken immobile driring the formation of alteration halos associated with massive miphide deposits (Barrett and MacLean 1994). Cornpareci to the unaltered host feisic- intermediate volcaniclastic rocks, the quartz-muscovite schist shows a depletion in NazO, Cao,and Mg0 and enrichment in Mn0 and F~O*as weii as Cu, Zn, and S (not show on Figure 5.5). K20shows minor enrichment, and Si02 shows no systematic change. Figure 5.6. N-MORB-normalized multi-eliment diagrams of the (a) quartz-muscovite schist and (b) altered felsic-intemediate rnetavolcaniclastic rocks. Unaltered felsic-intermediate metavolcaniclastic indicated by solid pattern. Figure 5.7. Chondrite-normalized REE plots of the (a) quartz-muscovite schist and (b) altered felsic-intemediate metavolcaniclastic rocks. Unaltered felsic-intermediate metavolcaniclastic indicated by solid pattern. Trace and REE chemistry of the quartzmuscovite schist is presented in Figures 5.6a and 5.7â Relative to the host metavo lcmiclast ic rocks. the quartz-muscovite schist, shows a strong depIetion in the LILE Sr and Ba, and the LREE La. Ce. Nd and Sm Except for P and Tb. concentrations of the HFSE and the HREE are simila. to the unaltered metavo~caniclasticrocks. The overall trace and REE characteristics of the quartzmuscovite schist compare favourably with those of the metavo lcaniclastic rocks. The quartz muscovite schist is medium to coarse graine4 white-weathering and consists predomhantly of quartz and muscovite. Muscovite may form up to 30 modal % and ranges lÎom muscovite through paragonitic muscovite to paragonite in composition (7-93 moi. % paragonite) (Fig. 5.8a; Appendk 3). Samples containhg more paragonitic muscovite's are f?om the main Sandhill area Staurolite and gahnite, lesser gamet and sparse biotite are variably directly associateci with the sulphide minerais m the schist. . Gamet, stauroiite and gahnite occur as subidioblastic to xenobiastic porphyroblasts and are wapped by the foüation individual _gains are typidy broken into muhiple gains and strung out dong the foliation plane; grains rarely show evidence of rotation Gamet is almandine-rich but contains a significant spessartme component; pyrope and grossular are minor components. Gamet contains significantiy les Ca than gamets fi-om unaltered metavolcaniclastic rocks. Chernical zoning in the gamets is minor but shows a general decrease m the spessartme component and increase in the almandine component eom core to rim Staurolite in the schist is prbady Fe-rich but also bas a sign5cant zinc component (13.25- 20.4 moL %). Gahnite. a bluish green &cian spmel contains 77-83 mol % zinc with the remahder king predominiuitiy the iron (hercynite) and magnesiun (spinel sem stricto) component. Rare biotite, associami with this assemblage, is mtermediate in composition and has an FdMg ratio ranging fiom 0.39-0.44. The mineralised horizon is enclosed by a more extensive envelope of moderately to weakly hydrothedy altered feisic-intermediate metavolcaniclastic rocks (Fig. 5.4). However, the alteration is best developed in the structural hanging wall to the mineralised horizon and only weakly developed in the structural footwall. The aiteration envelope may represent the Iess intense transition alteration zone between the quartz-muscovite schist and the ho st felsic-intermediate metavo lcaniclastic unit. As for the quartz-muscovite schist the major element geochemisay of the altered metavolcaniclastic rocks is plotted on a number of termuy diagrams (Fig. 5.5) to view the effects of hydrothemial alteration Meration of the hangmg wall rocks shows the same chemical trends as the quartz-muscovite schist but to a Iesser dep. Wth pro* to the quartz-muscovite schist, the ahered rocks show a depletion in NatO and Ca0 and e~chmentin Mi10 and F~O'as well as Cu. Zn and S (not show on Figure 5.5). KzO. Mg0 and Si02 show no systematic change. Trace and REE chemistry of the altered metavolcaniclastic rocks is presented in Figures 5.6b and 52. Only the most intense- altered rocks fiorn adjacent (north) to the schist horizon shows depletion in the LILE Sr and the LEE La, Ce, Pr, Nd and Sm. Except for and Eu, Gd and Tb. concentrations of the HFSE and the HREE are consistent with the chemistry of' the unaltered metavo lcaniclastic rocks. The chemistry of samples CO ilected Eom pro gressively Mer north of the quartz-muscovite schist horizon approaches that of the unaitered host volcaniclastic rocks (Appendk 2). Samples fiom south of the schist horizon show no O bvious chemical alteration. The variable chernjsay fkom altered to unalterd felsic-intermediate metavo lcaniclastic rocks is reflected by a change in their mineralou (Fig 5.9). As descnt in Chapter 2. undterd rocks are grey to flesh pink weathering, well lammated to bandeci on a mm- to cm- deand have a fine to medium graanied granoblastic texture. These rocks consist of assemblage NaCa-plagioclase (oiigociase to andesine; Fig. 5.1Oa) + quartz + homblende biotite k FeCa-gamet assembiage. Altered metavo1caniclastic rocks are grey to red-brown weathering, weli laminated to banded, and have a niednim to coarse graineci granoblasfc texture. Mered rocks are characterised by a systeniatic change m the abundance and chemisûy of plagioclase and gamet, the disappearance of homblende, and the appearance staurolite and gahnite, and sigmficant amounts of muscovite proximal to the quartz-muscovite schist horizon The least altered rocks are characterised by a plagioclase + quartz + biotite + gamet * muscovite & homblende assemblage (Fig. 5.9). The most mtensely altered rocks are characterised by a qyrtz + muscovite + gamet + biotite + stauroiite + gahnite + pyite magnetite assembiage. Plagioclase in the alterd rocks becornes more Ca-nch with C) Annile Siderophyllile Plagioclase feldspars Tromolite 0.80 -- Magnesio- +h Tschermakite Phlogopite (Y hornblonde Ac1 Q) Actinolite IL Hbld 2 O0 2 50 300 3 50 4 O0 Phlogopile Al (IV) + Ai (VI) Easlonile -Forroactinolite 5.75 6.00 6.25 6.50 6,75 7.00 7.25 7.50 7.75 8.00 Si Figure 5.10. Plots of iniiieral cliciiiistry fsoin the quartz-iiiiiscovitcsçliist (diiitii~iid~)aiid iiltei-cd Sclsic-icitcriiiei1iiilc iiiciiivdciiiii~rocks. a) Calcic aiiipliibole classific;iiioii ((Ca+Na)B >/- 1.34 üiid NiWO.67) (üfter Ixakc, 1978). h) çli~ssilici~tioiiof thc pliigi»cli\~cIèldspiir series and higli-temperature alkali fcldspars (modified from Deer et al., 1983) c) hiotite clüssiFiciitioo (iilicr Deer et al., 1983). Coiiipositioii of iiiinerül pliases froiii the unaltered felsic-iiiterincdiiile iii~tii~~l~iiiii~li~~tIC rocks is ouiliiicd oii eacli diiigniiii. Arrow points iii tlircct ion ol' C C iiicreasiiig intensity ol'üliciïitioii. O\ pro> Falcon zone (Map) iron formation, in 1986 and 1987, averaged 2.2 wt. % Zn and 0.27 % Cu (Hauseux 1987). The Falcon zone is an area previously mvestigated for iron formation- honed gold minerakation (see Chapter 1, section 1.4.2 Minerai Exploration, for details). 5.4 RECENT EXPLORATION ON THE SANDFIEL PROSPECT Recwt work by the JVP was conducted during the 1995 and 1996 field seasons (Lewis 1996). A trenching exercise m 1995 across the main Sandhill zone exposed 2ûm of the rnineralised succession. Tbree limited ssatiforrn horizons of massive and disseminateci nilphides were ident8ed within the mica schist descrii 91 the previous section The most northem horizon is a 5m thick mxydked exhaiatlat chert horizon that contains banded, semi-massive pyrite-sphaterite-chaIcopyrite mineralization at its base. Assay results nom Wedsulphides contain 0.68% Cu, 4.71 % Zn, and 2.65 opt Ag over 0.6h This horizon was aawd for a dinance of 1,300111dong de.A second mineralised horizon 5m below the e.uhalative chert comprises a 1.95 rn mtdof banded pyrite and sphalerite. Thû interval assayed <0.01% Cu, 2.75% Zn and 0.14 opt Ag. This horizon was traceci for a distance of ZOOm eastward where mineralised klsenmeer assayed up to 10.11% Zn Seven meters Mer down the succession a third 1.0 m interval of banded and disseminateci sphalerite and pyrite mineraliraiion assayed 0.04% Cu, 2.77% Zn and 0.09 opt Ag. Grab samples fkom mineralised ch- boulders asayed hi& of 0.85% Cu. 16.24% Zn. O. 11 opt Ag, and 2.05% Cu. 0.80% Zn, 9.15opt Ag. Airborne and ground electromagnetic surveys, and a gravity survey faied to delineate any sigmficant anodes (Lewis 1996) over the min SandhiU zone. The lack of geophysicd anodes is codent with the limaed and disfontinuous suiphide minerakation defined on surface. Four diamoncl driU holes tested the suiphide minerakation to a depth of 300111 Essentidy the drillsig did not enbance the dphide rnineraüzation dehed on mrhce. Assays tiom drill core fiorn three of the hoIes mcluded 7.06% Zn over a 0.36 m interval. 0.66% Cu. 0.27% Zn over a 0.77 m mtervai (mineralised chert), and 1.09% Zn over a 0.44111inted 5.5 CLASSIFICATION OF THE SANDBTLL PROSPECT 'The volcanic hon rock base metai sulphide mineralization honed within a quartz- muscovite schist and associated with a highly aluminous assemblage of gahnite, zincian staurolite and Mn-gamet, the chernicd changes associated with alteration including the loss in Na, Ca and Sr, and gain in Mn, Fe. characterise the Sandhill prospect as a metamorphosed VMS prospect. Based on whole rock chemisay, the quartz-musco vite schist is interpreted to represent the rnetamorphosed equivalent to an intense sericite alteration zone; hydrothedy altered hanging wd rocks show consistent but less intense chemicai changes. Quartz-nch layers within the quartz-musco vite SC hist are interpreted to represent recrystallized silicified horizons. Classification of the Sandhill prospect is based on the total ore element (Zn, Cu and Pb) content in surfàce samples collected during this study (Appendk 2). This data is ploned on the Cu-Pb-Znternary diagram (Fig. 5.1 1) which subdivides Cu-& and Zn-Pb- Cu type VMS deposits. Figure 5.11. Pb-Zn-Cu temary diagram for the buik compositions of samples from the Sandhill prospect. Subdivision of deposit types afier (Franklin et al. 198 1). Based on this plot, and on an average W(Pb + Zn) ratio of 0.98 in mheralised samples (Le. sarnples containing Zn > 2000 ppm: Appendix 2), the SandhiU base metai prospect is ciassZed as a Cu-Zn-type. The abundance of rnetasedimentary rocks. and interpreted back-arc volcanic sethg of the Sandhill metavolcanic rocks, classify the Sandhill Prospect as a sediment-dominated Cu-Zn-typedepost. It is apparent fiom the above description of the Sandhill zone alteration and mineralization, that many of the geological features, such as the chloritic pipe zone with associated aockwork chalcopyrite minerrrlizatioa and a suiphide mound conshing of massive sphalerite mineralization., that characterise the typical proximal VMS deposit are absent (Fig. 5.1). Many deposits Iack a distinct footwall alteration pipe (Franklin 1981). Such deposits are probably distal deposits that were either removed fiom their point of hydrothermal emanation by mechanical means (slumphg of the sdphide body. or structural redistniution of sulphides) or simply have formed at a distance away f?om the point of hydrothed emanation (hydrothermal plume). AU styles have ken described above. The most ubiquitous characteristics of the SmW zone is the intense sencite alteration the extensive hanging wail alteration, and the unusual but extensive Mn alteration. The quartz-muscovite schist may represent the surface expression of a sericite alteration zone (Fig. S. 1) and at sorne depth this schist may grade into a chloritic pipe zone and massive sulphide lem. Altematively, the missing pipe zone and sulphide moud in the Sandhili prospect may have ken tmrqosed into the structurai trend and/or seperated fkom the main SanW zone. However, diarnond drilling has Med to delineate such a chloritic alteration zone or sulphide lem at depth, and airborne and ground geophysics has fXed to dekate a large sulphide body in the axa- Another alternative is that the imer pipe zone and massive nilphide lem has been eroded away. Regional work has faied to delineate mineralised glacial debris. Essentially, the absence of a pipe zone and sulphide moud can not be explained by mechanical means. The Sancthitl deposit is, therefore, interpreted to be a prirnary distal deposit which fomed at a distance fiom a major hydrothermal discharge zone through chemical processes. This is consistent with the iack of a hydrothermal pipe zone (Le. metamorphic equivalent of a chlorite alteration pipe zone), the strong manganese alteration and the predominance of Za and lack of Cu mïneralizatioa The extensive quartz-muscovite sck and hanging wd aiteration halo. and sporadic sulphide minerallzation suggests that the deposit formed below the sedoor &er deposition of the host stratipphy. Fluids may have flowed dong a pre-existing structure or permeable horizon and ponded in a topographie depression previously Wed with porous volcaniclastic rocks. and forming an intense aiteration horizon, and precipitating minor sulphides. ïhe ponded fluids continued to percolate upwards' in a more diffw manor forming a less intense but pervasive hanging wall alteration halo. Fluids probably also fiowed laterally down slope to form O ther minor sulphide zones to the east. The initial channel for the fluids rnay have ken at the stratigraphicdy lower metasedunentary-mafîc-metavolcaniciastic interface. as indicated by the presence of sparse zincian-stauroiites and abundant Mn-gamet (discussed above). The source of the hydrothermai fluids or sulphides is uncertain, however, as concluded in Chapter 2. abundance of metagabbro sills associateci with the dcmetavolcanic rocks in the western part of the map area indicaies the presence of an extrusive centre, the common location of many VMS deposits. It shouid be noted tbat Fe-carbonate alteration of mafk volcanic breccias is quite extensive in this area This carbonate alteration may represent the zone m which the seawater reacted with the upper part of the hydrothed resewoir (Franklin 1996). However. there is no chernical evidence (Le. sodium depletion) to CO& this. 5.6 CONCLUSIONS The Sandhill mineralization and associated alteration envelope is stratabound in felsic-intermediate metavolcaniclastic rocks. Sporadic, stratzed zinc mineralization occurs within a quartz + muscovite schist and is associated with a highly aluminous assemblage consisting of Mn-gamet + zhcian aaurolite + gahnite + biotite; the quartz + muscovite sc hist is interpreted to be the metamorphosed equivaient of intense quartz-sencite hydrothed aiteration of the volcaniciastic rocks. The quartz + muscovite schist is enveloped by weakly altered rocks and is characterised by CaNa-plagioclase + biotite + Mn-gamet + Na-muscovite * zincian staurolite gahnite. Geochemistry of the quartz- muscovite schist, altered and unaitered metavolcanicIastic rocks indicate a loss in Na and Ca and a gain in Mn and total Fe during aiteration. The Sandhill prospect is interpreted to represent the disral sulphide zone of an Archean Sediment dominateci Cu-Zn deposÏt, formed within an ensialic back-arc basin There is no indication of the presence of a pipe zone either laterally or at depth The overall characteristics of the Sandhill Prospect, determined by this study. together wdh other investigations by Cumberland Resources Ltd. indicale suiphide mineralization is Medand iacks both lateral and vertical potentiai. However. extensive carbonate alteration m the mafic metavolcanic rocks. and anomalous Zn in suiphidic shaies in the western part of the map area indicaie a regiod potential for massive nilphide mineralization CHAPTER 6 GEOLOGICAL CHARACTERISTICS OF THE SULUK NI-CU-CO OCCURRENCE AND SULUK GABBRO 6.1 INTRODUCTION During the 1994 field seasoa surface samples containing anomalous concentrations of Ni Cu and Co were collected fiorn a senes of massive sulphide occurrences located approximately 5 km south-west of the Sandhill prospect (Map). The massive sulphide occurrences form the surface expression of what is referred to as the Sduk occurrence. This occurrence is spatidy associated with a gabbroic intrusion immediately to the West, herein referred to as the Suluk gabbro. and may be genetically related. The discovery of the ore grade Ni-Cu-Co mineralization stimulated further exploration by industry ui 1995 and 1996. which included surface sampling, airborne and ground geophysicai surveys, and a driU program over the Suluk occurrence and Suluk gabbro. This chapter presents the field observations, and petrographic and geochemicd data. The foilo wing description of the Suluk occurrence includes work completed by Alain Renault (1 9961, AUan Miller and Neil MacRae (Armitage et ai 1997), and Cumberland Resources Ltd. (Lewis 1 986). 6.2 GEOLOGY OF THE SULUK SULPHIDE OCCURRENCE The Suluk occurrence is a 045-50' sniking zone of massive to semi-massive suiphides that cm be traced discontinuously over a strike length of 650 m (Fig. 6.1 ). The occurrence is hosted in a north dipping sequence of strongS foliated mafic volcanic rocks represented by rraedium to coarse @ed homblende + plagiochse f gamet SCM. The &e expression of the sulphide mne is comprised of several verticdy dipping, V-shaped projections or 'teeth' which are oriented approximately perpendicuiar to the trend of foliation in the host rndc volcanic rocks. These projections Vary kom 0.5- Sarnple Cu % Ni % Co% 1-1 1-1 Mafic Volcanic Rocks [ GneisslPegrnatite - - .-1 --p.- 1-4- Massive Sulphides Sample Cu % Ni % Co % Avg. 2.67 3.63 0.159 Avg. 1.71 2.22 0.14 Figure 6.1. Geology iiiap of ihc Suliik occurrence wiili süiiiple locütioiis ancl üssüy dütü ofsaiiiples collected by the Cuiiiberlaiid Resoiirces Ltd. (Icft) aiid diiriiig iI~isstiidy (right). lm in maximum thichess and taper out southwards over a strike len-gth of 33metres. The sulphides are in sharp contact wbh the host rock and show no intemal fabric. Rounded micro- and macroxenoliths of gabbro and mafc volcanic rocks occur within the nilphide projections. Distances between individuai teeth vary f?om 10 to 250 meters and suiphides are sparsely distniuted between the teeth Minor disseminated to nringer mineraikation occurs in the mafic schist and in quartz or quartz + anenopyrite veins in the stratigraphic hanging wall (north). Ground geophysics over the Suiuk occurrence indicates a continuous conductor for an approximate 800 m strike Iength (Curtis 1996). Initial drilling of this conductor defked a more continuous sulphide zone than seen on dace. The subsurface expression of the Suhik occurrence is defined as an irregular undulating lens that is concordant with the envelo ping dcschist. Drilling intenected bo th dissemuiated and narrow massive to semi-massive suiphide mineralization whic h varies f?o om 0.47 to 4.72 meters thick (along core axis), at vertical depths of up to 140 m (Dickson 1996). Massive and semi-massive mineralization contains abundant micro- and macro-xenoliths, typicaily rounded to subrounded and include hornblende schist, vein quartz and rnetasedimentary rocks. The resdting texture of these suiphides is sirnilar to the suiphide-matrix breccia ores comrnon in many nickel deposits (Annitage et al. 1997). Disseminated to stringer chaicopyrite mineraiization (< 1%) occurs withûi the mafic schist in the stratigraphic hanging wall. As on surface, contacts between massive and semi-massive sulphides are sharp, Little to undefomed and there is no intemal &bric. The lack of deformation texnues along sulphide-wallrock interfaces suggests Wle post-sulphide deformation. 6.3 GEOCHElMISTRY AND MINEFULOGY OF THE MASSIVE SULPHIDES 6.3.1 From Surface The sulphides predominantly weather black to red-brown, and are partially covered by a deep red (strongly oxidised) soii. In places, a white powdery material fonns a coating on the sulphides. This material bas ken identined (X-Ray Difhction) as rozenite, an iron sulphate (Fe(SO4) ' 4&0). The initial four surface sulphide samples collected fiom the Suluk occurrence during the 1994 field seasun averaged 2.2 % Ni, 1.7 % Cu and 0.14 % Co (Fig. 6.1). Twelve widely spaced surlàce samples of the massive sulphides. collected by Cumberland Resources Ltd. during 1995 work, averaged 3.63 % Ni 2.67 % Cu and 0.16 % Co. An additional sample was collected fiom a zone of disseminated mineralization in mafic schist (sample 3674). approlvimately 10 feet north of the massive sulphide horizon. This sample assayed 0.2 % Ni 2.24 % Cu and 0.012 % Co. The massive sulphides are comprised prirnarily of medium to coarse -pined. anhedrai to subhedral nickeliferous pyrrho tite. violante. chalcopyrite. and nickeliferous rnarcasite (Table 6.1) with lesser amounts of magnetite (Plate 6.1). Pvlarcasite predomlliantly rims or pseudomorphs pyrrhotite; magnetite is comrnonly rimmed by hernatite. High-Co violarite (20.55-20.85 aph) (Table 6.1) occurs as rare fine Caained inclusions in common violarite (0.3-2.43); sphalerite. pentlandite and Ni-Co-rich arsenopyite (Table 6.1) occur as fine grained inclusions in pyrrhotite and magnetite. Hematite intergrown with goethite form colloform bands in secondary kactures. Micrometer size inclusions of FeNIBi tellurides and FeNiCo arsenides have been identified using the Energy Dispersive Spectrometer on the electron microprobe. Violarite, the dominant nickel sulphide at surface. typicdy forms as a weathe~g product of nickel sulphide mine& (e.g. pentlandite) and is a cornrnon constituent of weathered nickel deposits in Western Austraiia (McGoldrick and Keays 198 1). A reaction whic h explains this alteration is as follows: Penthdite + Violarite (Thomber 1983) Fe4 jSs+ 2 FeNi& + 0.5 ~i~-+ 2.5 ~e'- + 6 e- As the above reaction proceeds, Ni and Fe are released hto solution and remobilized during weathering. This suggests strong nickel anomalies identified on lake soi1 sediment nwey maps of the Gibson-MacQuoid Lake area (Geological Swey of Canada 1976) represent first order fo Ho w-up targets for exploration of Ni mineralization. Textures including pynho the rimmed and replaced by marcsite, and magnetite rimmed by hematite are consistent with the presence of violarite, and are typical oxidation products of weathered sulphides. Plate 6.1. Back-scatter electron images: a) typical association of violarite (Vi), marcasite (Mc) and rnagnetite (Mt) in oxidized massive sulphides of the Suluk prospect. b) sulphide inclusion in magnetite nom image a: assemblage is pyrrhotite (Po), pentlandite (Pt), flame pentlandite (fPt) and chalcopyrite (Cp). 6.3.2 From Drill Core Dnlling of the Sduk occurrence htesected both massive and disseminated suiphides. The best intersection, a 4.54 m zone (153.15-157.69 dong core axis). is a composite of massive sulphide, and disseminated suiphide in dcschist. This zone assayed 1.35 % Cu. 0.52 % Ni and 0.019 % Co (Dickson 1996). Petrographic and electron micro probe investigations of four suiphide sarnples collected Eom this intersection (Armitage et al. 1995): showed that the sulphides are composed of massive. fine to medium grained undeformed and unaltered pyrrhotite. pent ladite. chaico pyrite (Table 6. l), magnetite and trace amounts of cobaltian pyrite. Table 6.2. Mineral chernical analysis of sulphide minerais fiom drill core (Armitage et al. wt% Ni 36.70 36.49 FE Cu Fe 29.07 29.90 CO Fe Co 0.79 0.89 M Ni S 34.35 34.00 S Co Total 100.00 100.27 Total S Total Atomic % Ni 28.24 28.00 FE Cu Fe 22.65 23.3 1 CO Fe Co 0.0 1 0.67 NI Ni S 48.27 47.77 S Co S P- - 6.4 GENETIC ASSOCIATION OF THE SULUK OCCURRENCE The general characteristics of occurrence of the massive sulphides descnid above suggests that they are stnicturally controiied, genetically unrelateci to the Archean rnafic rnetavolcank host rocks, and may be related to a separate igneous event. The average NiKu ratio hmthe in the weathered massive sulphides f?om the Sduk occurrence is 1.36 (N=ll). Despite an approxirnate 10 % loss in Ni due to weathering (pentlandite to violarite reaction described above), the average NVCu ratio fiom sdcesamples is -picai of NilCu ratios (typically 1-3) of massive suiphides associated with tholeiitic m-c intrusive sequences (Travis et ai. 1976; Naldrett 1989); NVCu ratios kom massive sulphides fiom subsurfàce in the Suluk occurrence are also typicaiiy less than 3. Mafk intrusive sequences which hoa Ni deposits are comprked of gabbro. troctolite. and other related more magnesian rocks such as pyroxenite and peridotite (Naldrett 1989). NUCu ratios of the Suluk occurrence are sig&cantly below ratios typicai of magmatic Ni ores (generally >IO) associated with ultrarnafic host rocks. such as kornatiite or dunite (Naldrett 1989). The Sduk occurrence is spatially associated with a gabbro intrusion (Map). the Suluk gabbro, and may be genetically related. The geological characteristics of the Suluk gabbro are discussed bel0 W. 6.5 SULUK GABBRO 6.5 1 Geology and Petrograp hy The gabbro is an elongated intrusion trending north-east. Its eastem termination of the gabbro approximately 800 meters West of the Suluk occurrence. The gabbro inmides is the metamorphosed dcvolcanic rocks, and contains xenoliths of the mafic metavolcanic rocks. The Suiuk gabbro is textudy and mineralogically inhomogeneous with fine to coane grained to pegmatitic phases, and shows variable degrees of metamorphic recrystallization However, igneous textures are well preserved. Fine to coarse grained pyroxenite (altered to amphibo ke), gabbro (homblende/pyroxene) and lesser pegmatite phases are predorninant in the eastem portions of the intrusion Variable proportions of plagioclase and dcminerais defhe a magmatic layering on a centimene to meter-scde. The eastern part of the gabbro show the lem amount of recrystallization where prllnary mineral assembhges are observed. Gabbro is melanocratic to mesocratic. fine to medium grained, equigrandar to subporphyritic. The least recrystalljzed port io w consist predorninantly of medium phed subhedral to euh- tabular plagioclase crystals with interstitial. medium grained anhedral pyroxene. Plagioclase appears to be the principal cumulus phase and has weii developed polysynthetic twinning, is weakly sencitized. and shows strong unddous extinction. Ciinopyroxene (augite) is CO lourless in plane light. shows inched extinction, and rare simple twins (simple). Strongly pleochroic blue-green homblende occurs as fine medclusters and rosettes rimming pyroxene, (similar to corona texture), as fine grained isolated clusters associated with fine @ed biotite and epido te, and rarely as iso iated medium grained- subhedral crystals. Irregular-shaped fke to coarse grained magnetite is common in these rocks. Coarse graine& subhedral to anhedraL rnagnetite (3-5 modal %) occurs interstitial to plagioclase and pyroxene, and is typicaIiy rimmed by hornblende andor epidote; fine grained magnetite typicdy occun as inclusions in pyroxene or homblende. A pronounced aeromagnetic anornaiy (Geologicd Swey of Canada aeromagnetic map 197 1 ), is centred over the eastern part of the intrusion Where gabbro displays more intense recrystailization, homblende replaces pyroxene and only relict cores of pyroxene may be preserved. Homblende occun as medium to coarse grained. ragged-edged, anhedral crystals which show a weak to moderate blue-green pleochroism (actinolitic homblende) with mowstrongly pleochroic rims. The coarse gained homblende is locaily rimmed by fine-grained, randomly oriented. grano blastic hornblende. Pyroxenite consists of medium to coarse graiued, subhedral homblende with minor inclusions of titanite, and sparse interstitkd plagioclase. Pegmatite consists primarily of very coarse grained, subhedrai to euhedral homblende with interstitial coarse gnined plagioclase, medium to coarse grained euhedral biotite, euhedral to subhedral apatite, and opaque mine&. The western parts of the gabbro intrusion show intense recrystallization. There, the gabbroic rocks are medium graine& relatively homogeneous and rnelanocratic. Magmatic layering is absent. Both homblende and plagioclase bave been completely recrystallized to a medium grained ganoblast ic texture. Homblende displays a strong blue-green pleochroism; plagioclase is, in part, twinned. and shows strong unddose extinction and weli developed polygonal grain boundaries. Ilmenite in these rocks is cornrnonly rimmed by fuie grained titauite. 6.5.2 Geochern istry Fourteen widely scattered dacesamples of the gabbro were collected during this and studies by Cumberland Resources Ltd. The samples represent pyroxene gabbro. homblende gabbro (metamorphosed pyroxene gabbro), pyroxenite (metamorphosed to amphibolite), and hornblende peptite. These samples were CO llected and analysed simply to characterise the Suluk gabbro. More systematic sampling of surface exposures and of drill core of the gabbro û required to determine a possible source for the metais in the Suluk occurrence, and it is beyond the =ope of the present snidy. In general the composition of the pyroxene/hornblende gabbro is variable with Si02 (45.09-51.5 wt. %), Ti02 (0.36-2.13 wt. %), Ah03 (12.61-17.05 W. %). ~e20,~ (6.72-21.45 wt. %), Mg0 (4.82-1 1.16 wt. %), Ca0 (8.25-10.93 wt. %) and NatO (1.71- 3.0 wt. %) (Table 6.2). No linear trends were noted in the data except for Si02 vs ~e20,~ (Figure 6.2). These samples are primarily hypersthene + diopside +- olivine normative; a few are quartz normative. The pyroxenite is MgO-rich (1 1.9 1 W. %) and AlzO1-poor (6.02 wt. %) compared to the average composition of the gabbro, and is strongly diopside-normative. In contrast, the pegmatire is more MgO-poor (5.2) and A1201-rich (16.33); it is strongly olivi~enorrnative but &O contains normative nepheline. The Suluk gabbro shows a subalkaline tholeiitic chernical trend (Fig. 6.3). In terms of trace element chemistry, with a couple of exceptions, the gabbro is deficient in Ni, Cu, Co and, where analysed, Cr (Table 6.2, Fig. 6.2). Table 6.3. Geochemistry and CIPW norrn calculations of selected samples fioin the Suluk Gabbro. Daia Source: Samples 1000-1002 and 568, this study; 90701-02, Comaplex Minerals Corp.; 3680-3690, Cumberland Resources Ltd. Samplo # Si01 ïïOI Alla FQO,' Mn0 M8O Ca0 Na10 K2Q Pa03 1.01 Total Trace cltnicnrs Cr Ni Co Cu ClPW iionn Quartz Orthoclase Alhite Anorthiie Nrphclinc Diopside I lypersihcnr: Qlivinc Magnetilr: Ilmcriitc FeO* / Tholeiitic \,, Figure 6.3. AFM plot (from Irvine and Baragar, 197 1) of samples from the Suluk gabbro. Filled circle = pyroxenite; filled square = pegmatite. 6.5.3 RECENT EXPLORATION OF THE SULUK GABBRO ïhree near-vertical holes. to depths of up to 425 meters. were driUed to test a gravity anondy associated with the Suluk Gabbro (Lewis 1996). It is thought that the gravity anornaly rnight represent a massive sulphide body within the gabbro. Compositionally layered gabbro was encountered throughout aii three holes. and only trace amounts of pyrrhotite. pyrite and chakopyite minerakation were encountered. A down-hole electrornagnetic survey was performed on aii three holes to test for the presence of a deep sulphide body, but no conductive sulphide bodies were detected at least to a depth of 500-550 meters. The above results may indicate the absence of a significant massive sulphide body to these depths. The gravity anomaly may represent simply a regional anomaly or a sulphide body at much greater depths. 6.6 AGE CONSTRAINT ON THE SULUK GABBRO AND SULUK OCCURRENCE No dates are cunently available on the magmatism in the GMB, thus the age of the Suluk gabbro can only be constrained by metamorphic and structurai criteria and by correlation with regional magmatic events. As discussed in Chapter 3, the rocks of the GMB have undergone two amphibolite grade metamorphic events. which rnay correlate to an Archean (ca2.59 Ga) tectonothermal event and a Proterozoic thermal event (ca 1.94- 1.90 Ga) tectonothermal event defined regionaliy. The main penetrative fabric in the rocks is interpreted to have developed during the Archean event (Chapter 4). Absence of a structural fabric in the Suluk gabbro indicates that it post-dates the major Archean amphibo iite grade metamo rp hic event and may represent an Early Pro terozoic intrusion The presence of honiblende der pyroxene in the eastern part of the Sui& gabbro, and polygonal ganoblastic textures developed in the western parts of the intrusion suggest that it was partially recrystallized under amphihlite facies conditions, possibly during the ca 1.94-1.90 Ga tectonothemial event. The Suluk gabbro was intruded by an unmetarnorphosed lamprophyre dyke correlated with the ca 1.84 Ga Christopher Island Formation (Gall et al., 1992; Peterson and Rainbkd, 1990; LeCheminant et al, l987a). This MercoDstrams the upper limit of crydhation of the gabbro. The east trendhg gabbro dyke swarm m the eastern and centrai part of the map area (Map) also displays an arnphibolite Memetamorphic overprint but kksa petrative fàbric. They cross-cut the metamorphoseci and foiiated roc- and are thernseives cut by dykes of the CEThe dykes rnay be of a similar age as the Suiuk Gabbro. In the Tulemalu Lake - Yathkjed Lake map area, south-west of the Gibson- MacQuoid Lake are& Eade (1986) identified an east-trading diabase dykes swarm. the Tulemalu Dyke Swarm (TD).They lie within a structural domain referred as the Tulemaiu Block (Fig. 1.2), which is bounded by two regional-scale no&-east trending mylonite zones. The TFZ to the nonh-west, and an unnamed subparaliel fauit zone to the south- east. The TD were affected by variable degrees of alteration. In relatively unaltered dykes. ophitic textures are preserved. These dykes consist, in variabk proportions. of labradorite and augite with minor homblende; hornblende is an alteration phase of pyroxene. Chlonte and saussurite alteration is minûnal. More strongly altered dykes are greenish with augite alrnost completely replaced by homblende. and plagioclase intensely dtered; primary igneous textures are, however, well preserved. The TD swm display Little or no structural fàbric and are unmetamorphosed. Based on structural data and lack of a metamorphic overprint, the TD were assigned to the Early Proterozoic and are interpreted to have ken emplaced during an early period of extension at the omet of the Hudsonian Orogeny (Eade 1986). An intrusive age of ca 2200 Ma was established using pdeomagnetic data (Fahrig et al. 1984). One sample fÏom an east-trendhg dyke fkom the MacQuoid Lake area, a possible correlation to the TD swarm, yielded a preliminary U-Pb age of 2.19 Ga (Teila et al. 1997). Additional LLPb baddeleyite ages fiom rnafic intrusive rocks include a Hunvitz gabbro at 21 1 1 Ir: 0.6 Ma (Heaman and LeCheminant, 1993). The east trending gabbro dykes swm m the Gihn-MacQuoid Lake area have the same generaf orientation as the TD, and the Suluk gabbro and Gibson-MacQuoid dykes lie within the same senirrural domain as the TD.Based on this regionai tectonic relationship, the metamorphic history of the gabbros m the Gihn-MacQuoid Lake ma, ant the cross-cutthg relationshp of the gabbros with CIF dyke$ the gabbro intrusions m the GMB may be correiated to the TD and their intrusive age tnay be ca 2.19 Ga Alternatively, the recrystallized Suluk gabbro rnay be a syntectonic pluton and the emplacement age rnay correlate with the suggested 1.94 Ga metaxnorphic overprint, although gabbro dykes of this age have not ken recognised elsewhere in the Keewatm. In summq, the Sduk Gabbro and east-trending dykes in the study area appear to have ken emplaced at ca 2.2 Ga and perhaps as late as 1.94 Ga. 6.7 METALLOGENIC IMPLICATIONS Ensialic rifihg of many of the world's Archean cratons appean to have occurred during the period 2.5 Ga - 2.0 Ga. This globally extensive &hg episode produced numerous large, mafic-ultrarnafic intrusive complexes and associated nickel dphide deposits. Examples include the Nipissing Gabbro in the Archean Southern Province, northem Ontario, Canada (Lightfoot and Naidrett 1996), and dc-ultramafic intrusions of the Baltic Shield in Finiand and Russia (Turchenko 1992; Alapieti et ai. 1990; Gorbunov 1985) The generai geological and tectonic characteristics of the Baitic Shield are sVnilar to those of the western ChurchiU Province. Simrlarities inciude the presence of an Archean-Early Proterozoic stratigraphy, multiple penods of &c intrusions, and multiple orogenic events, the later culminahg at ca 1-8 Ga. Archean cratonization of the Baitic Shield occurred during the ca 2.9-2.6 Ga Lopian Orogeny (Turchenko 1992). Repeated rifting of the Archean basement fiom 2.5-2.0 Ga resulted in the develo pment of volcanic- sedimentary kits and associated mafic and ultramafic intrusions, within Mtbounded bains. The ca 2.0- 1.8 Ga Svencofennian Orogeny deformed the Early Pro terotoic rocks and reworked the Archean basement. Early Proterozoic nickel-copper metallogeny of the Baitic Shield is directly iinked to continental rifting, and mafic-ultramafïc magrnatism The older of the Eariy Proterozoic mineralishg events (2.45-2.35 Ga) produced Ni-Cu, PGE, Cr, V and Ti deposits hoaed by layered dc-uitramafic complexes belonging to the pendo tite-pyroxenite-gabbro- norite suite (Turchenko 1992: Alapieti et al. 1990). The younger of the events (ca 2.3-2.0 Ga) produced NiCu deposits associated with wehriite-pyroxenite-gabbro intrusive rocks (Gorbunov et aL 1985). The younger event produced the Ni-Cu deposits of the Pechenga region. These deposits are descnid in detail by Gorbunov et al. (1985) and summarked by Naldrett ( 1989). Naldrett ( 1989), in hct. uses the Pechenga region as an example of a deposit associated with tholeütes hosted by Precambrian greenstone belts (Setting IIU). This is also the type of deposit sening suggested by the Ni/Cu ratios of the massive sulphides in the Suluk occurrence. The foilowing description is taken f?om Naldrett (1989). The Pechenga deposits occur at the north-east end of the Kola Peninsula where more than 20 Ni-Cu deposits and prospects are dehed. Many of the ore deposits have ken extensively deformed during the Svencofe11Ilj.m Orogeny redting in O biiteration of intrusive contacts and mobilisation of sulphides into tectonic zones. However. studies of the least deformed bodies have shown the intrusions to be layered with an upward progression fÏom peridotite (Iargely altered to serpentinite) through pyroxenite to gabbro. Ni-Cu sulphides are associated with pendotite or serpenthite and become more abundant where these rocks are thicker. Ore types include 1) dissemhated pendotite hosted ore, 2) breccia ores located within tectonic zones but passine laterally into the pendo tire- hosted ore type, 3) massive ores, economically the moa important ores, which are related spatiaily to the breccia ores, and 4) veullets in the country rock. The Kada deposit is typical of one of the less deformed deposits. A schematic plan rnap of this deposit is presented in Figure 6.4. In this deposit, the minerakation is confined to the lower part of a differentiated massif composed mainly of serpentinite. Much of the sulphide ore is confined to a shear zone adjacent to the associated intrusion, but extends for a distance into the host rock dong the foüation and into discordant hctures. The massive, breccia- and host rock disseminated ore gradually thout with distance Eom the intrusion Coincident with this is a decrease in the percentage of Cu and Ni to the extent that the ore is predominantly barren pyrrhotite. The Suiuk gabbro and related sulphide mineralization may be temporally equivaient to the younger mineraking event in the Baltic Shield. The Suluk occurrence and associated Suluk gabbro show suEcient similanties to the Kaula deposit in terms character of exposed portions, chemistry (Le. tholeiitic chemistry of the gabbro and CuMi ratio of sulphides), and age (i.e. Proterozo ic) that they deserve cornparison. Superimposed on Figure 6.4 is a hypothetical reiationship of the Suluk occurrence and Suluk gabbro. The Suluk occurrence would represent an exposed portion of the massive and breccia ore hosted within the country rock, in this case the metamorphosed mafic volcanic rocks. The Suluk gabbro wodd represent the exposed portion of the upper gabbro of an intrusive body. The remallider of the intrusive sequence king unexposed. The V-shaped projections of massive sulphides observed on suface. and the more continuous dphide mineralization defined bel0 w shceby drillin& rnay have fomed in a tectonic zone. and at some depth may be traced hto a muieralised intrusive body such as that in the Kaula deposit. Thus. if the Suiuk occurrence and Sul& gabbro are geneticaily related. they rnay represent the exposed portions of a larger tholeiitic intrusive sequence and associated nickel suiphide deposit. sùnilar in nature to the Kada deposit. IL) > THE AKLuILÂK LAMPROPti[YRE DYKE AND OTHER CIF LAMPROPHYRE DYKES 7.1 INTRODUCTION During the 1993 field season a unique diarnond-bearing lamprophyre dyke. the Akluilâk dyke (alias the Thirsty Lake Dyke), was discovered approximately 1.5 km south- West of the Sandhill prospect. A single rnicrodiamond (-280 microns) was recovered tiom a 2 kg hand sample. A 22 kg bulk sample coliected at the same location the foiiowing year yielded 1765 microdiamonds (600 p)and 2 macrodiamonds (> 500 pm). Independent samples also coilected ftom the same localj. in the foUowing 2 years yielded sùnilar results: a 32.8 kg sarnple returned 1 163 diamonds Încluding 6 macrodiamonds: a 7.8 kg sample renimed 6680 diamo nds including 3 macrodiarnonds; and. a 1,146 Kg bulk sample tested ody for macrodiamonds returned two measuring 1.4 and 2.9 mm. This is the first conI'rrmed rnulti-diamond occurrence in the Central Churchill Province and the first recorded occurrence of a significant number of diamonds in a lamprophyre host rock. This chapter descnis the geo logical characteristics of the Akluilâk dyke and other lamprophyre dykes discovered in the GML area. Field observations. and petrographic and geochemical data are discussed. The foiiowing descriptions of the Akluilâk dyke are based on the work by thk author, and on previous work (MacRae et al. 1995, 1996). The Akluilâk dyke and other larnprophyre dykes fiom the study area are correlated with the ca 1-84 Ga akheigneous province dehed by the dish-iiution of the Christopher Island Formation (CF) of the Baker Lake Supergroup. The geologid characteristics of the CIF will be discussed m this chapter and a cornparison wilI be made with the iamprophyre dykes m the study area Lamprophyres are commoniy descriid by various molecular ratios of their aikali and alurnina content (Mitchell and Bergman 1991). A lamprophyre is classïfied ultrapotassic if the KrO/Na20 > 3, potassic if this ratio is 1-3 and sodic if it is < 1. The (KzO '- Na20)/Ai203 indicates if a rock is perdkaline (Le. ratio > 0.7) or perpotassic (< 0.7). If this ratio is < 1 and the ratio (&O + NatO)lSi02 is < 0.17. the rock is cab alkaline; otherwise, it is alkaline. Major, trace and FEE element whole-rock geocheminry and CIPW nom for the lamprophyre dykes fiom the GML area are presented in Tables 7.1 and 7.2. Relevant molecular ratios for the lamprophyre dykes are also presented in Table 7.1. Because of the numerous mineral chemical analyses £iom GML lamprophyre dykes, and in order to separate the data kom the data for the GMB rocks. the dyke minerai data are grouped in Table 7.3 at the end of this chapter. 7.2 THE CHRISTOPHER ISLAND FORiATION (Cm: PREVIOUS WORK The lamprophyre dykes in the Gibson-MacQuoid rnap area are correlated with the ca 1.84 Ga alkaline igneous province deked by the distriion of the Christopher Island Formation (CF)of the Baker Lake Supergroup (Donaldson 1965; Blake 1980: Lecheminant et al. 1987a; Peterson and Rahbird, 1990; Gall et aL, 1992; Peterson 1994; Jones 1996). The unmetamorphoseci, Early Proterozoic volcanic and sedimentary sequences of the Dubawnt Supergroup were deposited unconfombly on the older Proterozoic and Archean rocks of the Churchill Province and comprise the Baker Lake and younger Thelon Basins (Fig. 7.1). The Baker Lake Basin is cornprised of several fault-bounded sub-basins which extend &orn Dubawnt Lake to Baker Lake. Extensive potassic to ultrapotassic igneous rocks of the CEaccompanied the early stages in the formation of the Baker Lake Basin. The bas& of the CIF are surrounded by a swarrn of hprophyre dykes which extends over an area of at least 100,000 km2 within the ChurchiU Province (Fig. 7.1). These dykes are interpreted to be feeder dykes to the CE fIows (Peterson 1994). The mineraiogy and geochemistry of the volcanic rocks and dykes of the CE are sumrriarised by LeCheminant et al. (1987), Peterson (1994) Peterson et al. (1994) and Baker Inke Croup (mainly I'rotcrozoic covcr rocks, 1.84 Ga potassic volcanics) . .. 51.75 Ga (sandstonc, rhyolite) Archcan Anorogenic granites . : (Churchill Province) (1.75 Ga) Figurc 7.1. Cieologicnl iiiilp of tlie ceiitrul Clitircliill Proviiicc sliowiiig the distrit~iitioiiO&' tlic Diihiiwni Siipeigroiip (lioiii I>cteisoiiiiiid LeClieiiiinaiit 1990). BL=l)uker Lake, DL=Dubawnt 1-iikc, AK-Akliiildk Dykc. bnes ( 1996). These rocks range fiom mafic to felsic minettes and sanidine porphyries. At Dubawnt Lake. the CIF is subdivided into mafic minette and two varieties of felsic minettes (Upper and Lower) (Table 7.1) (Peterson 1994). Mafic minettes (Mg # 5 60; Mg0 > 8 wt. %; SiOt z 47-57 wt. %) consist of phlogopite, diopside. apatite t olivine t rnagnetite phenocrysts within a matrix of phiogopite. Ba-rich K-feldspar, diopside, olivine. magnetite, titanite, nchterite and rutile. The feisic minettes (Mg # < 60; Mg0 < 8 wt %: Si02 z 50-64 wt. %) are typicaily aphanitic with little to no phenocryns (< 5 %) of phlogopite and/or K-feidspar. Secondary minerais in the &c and feisic rocks include quartz, aibite, amphiboles. titanite and calcite (veins and vesicle fills). The dcminettes of the CIF are ultrapotassic with KzO/ Na20 > 3 (wt. %) (rarely < 3) (Table 7.1), and few are peralkaline with WAi > 0.7 (atomic %). The felsic minettes are generally higher in Nz03and NazO, lower in KzO and are generaily potassic with KrOMazO < 3. In general, the rocks of the CIF have high incompatible element contents (K, Rb, Sr, Ba and Th) (Tabie 7.2), and are depleted in the HFSE (Zr, Y' Nb and Ti) relative to the incompatible elements. The rocks have hi& total REE contents and are strongly enriched in the LEE relative to the KREE. The mafie minette tends to be more enriched in the REE. Age consnaints of the CIF ultrapotassic maptism are based on few published ages. A U-Pb zircon age of 1850 +30/- 10 Ma was deterrnined on a quartz syenite body related to the CF mgmatisrn (Teh et al. 1985). An upper age Limit of 1753 +3/-2 Ma (U-Pb zircon age) (Loveridge et ai. 1987) was established on a cross-cutting intrusion. In the Dubawnt Lake are* an "A~/~~AI=age (homblende) of 1825 + 12 Ma (Roddick and Miller 1994) was obtained ~oman undeformed ultrapotassic intrusion which is geneticaiiy Med to the CF. LeCherninant et ai. (1987a), Peterson and Rainbird (1990), and Peterson et al. (1994) proposed that the potassic to ultrapotassic rocks of the CF were formed as a resuit of subduction of oceanic lithosphere beiow the Churchill Province during the Slave (ca 2.0 Ga) and Superior (ca 1.9 Ga) collisions. Dehydration of the subducted lithosphere converted the overlying subkhospheric made to phiogopite peridotite by metasomatism. Continental collision caused cnistai ùiic kening and fo rced the metasomatized rnantle into Table 7.2. Trace and rare earth element geochemistry and CIPW-norm calciilations Ior the GML lamprophyre dykes, and average geochemistry for minettes fiom the CIF (From Peterson 1994). Samplc # OOSC llppcr Felsic hllncltr l'racc clcntrnis Cr 282 137 NI 208 32 Co 45 Sc 25.3 v 174 Cu 70.3 1% O Zn 21(i Ali 1.5 Hb 54 2 1 4 Ba 1570 4526 Sr 707 1273 Nb 1 0 43 Zr 366 535 Y 23 Tb 27.6 Il 3.5 Hrrc cirtb clcrncnl~ 1a 196 Il7 cc 379 240 Pr 44.3 Nd 164 1 O7 Sm 25.6 16 Eu 5.H3 4.3 Cd 17.3 11.4 ï'b 1.5 DY 6.8 6.2 Il0 0.89 Er 2.4 'lin 0.3 Yb 17 I .H Lu O 25 (1Jl'h)N -77.0 J3 9 the hotter asthenosphere. As a result of the& relaxation and post-tectonic extension the ultrapo tassic melts empted through ûanslithospheric fkactures inc luding the Mc Donald and Bathurst faults. Isotopic compositions (Sr, Nd and Pb) suppons this mode1 (Peterson et al. 1994). Peterson et al. (1994) proposed the existence of an ultrapotassic superprovlice based on the overail chemistry and isotopic composition of the CIF rocks that are similar to the lamproites and minettes of western Greeniand (Sismiut lamproites) and Wyoming Province (Smoky Butte and Leucite HiUs) and 7.3 THE GML LAiMPROPHYRE DYKES More than 20 larnprophyre dykes have ken mapped within the nudy area (Fig. 7.2). The density of dykes increases towards the West. Most dykes are undeformed. typicaüy less than 2 m thick, and have straight near vertical contacts. They weather recessively into the host rocks. ChilIed margins are absent. and the host rocks lack obvious contact thermal effects; phenocrystic phases. hcluding biotite and amphibole. rarely show Bow foliation. nie dykes contain sparsely distributed, ro unded xeno liths O C granit ic rocks and gneiss. Dyke trends are typicdy north-west (340-350") in the eastern and central parts of the map area, suggesting they were emplaced dong pre-edvistingstructures such as joints and fault zones. Two distinct dyke trends (340-350" and 290-300') were observed in the western part of the map area, however, their relative age relationships are not clearly established. Dykes in the western part of the map area rnay have ken emplaced into a conjugate joint set. Besides the Akluilak dyke (descnid below), three types of larnprophyre dykes, have ken identined in the study area (based on mineralogy and geochernistry). Light to dark bro wn-to blue-grey weathering, no rth-west- trending (340-3 50°) dy kes are CO mmo n in the east and centrai parts of the map area; dykes of similar composition trend 290-300° in the western part of the map area. These dykes are represented by samples 127, 137, 146, 614A and 700B (Fig. 7.2). They consist of medium to coarse grained phlogopite- biotite * amphibole phenocrysts in a fine grallied to aphanitic matrix of the same miner& plus alkali feldspar, plagioclase, apatite and carbonate. Zircon + danite are cornmon accessory phases; ilmenite. titanite. pyrite, chalco pyrite and nit ile are mino r accessory phases. Few dykes CO ntain rounded carbonate-6lied amygdules. Bio tite phenocrysts are euhedral to subhedral, display ragged edges and are typicdy kinked. In several samples. biotite phenocrysts contain fine grained rutile needles, crystaiiographicdy oriented in three directions to show a trianguiar pattern. suggesting that the biotites were originally very Ti-rich Groundmass biotite is fine grained. subhedral to anhedrai. and randomly oriented. Chlorite alteration of biotite is rninor and restricted to few samples. Biotites are generally uniform in composition and range from Mg-biotite to phlogopite (Fig. 7.3a) (FIFM = 0.28-0.35), are moderately e~chedin TiOz ( 1.1-2.0 wt. %) and weakly enriched in Cr203(O. 1-1.8 wt %), Ba0 (0.2-1.6 wt. %) and F (0.45-0.7 wt. %) (Table 7.1). They show little cornpositional variation f?o m p henocryst to matrk bio t ite. Amphiboles are present in moa sections in the groundmass. less commoniy as phenocrysts, and may represent an alteration phase of pyroxene. Amphibole. in turn, is commody altered to £ïne gahed biotite or chlorite. Amphibole phenocrysts. where present, are medium grained. anhedral. and colo urless to weakly pleoc hoic green. Groundmass amphibole is fme grained and typicaliy forms randomly oriented acicular needles. Amphibole is actinolite (Fig. 7.3b) (WbF = 0.72-0.82; Si = 7.69-7.86 aph) and is uniform in composition both in the phenocrysts and in the groundmass. Alkali feldspar is a major constituent of these lamprophyres and is restricted to the groundmass. It is he grained, decirai and typicdy uitergrown with biotire. Alkali feldspar (Fig. 7.4) is irregularly zoned fiom Ba-rich zones (up to 10 wt. % BaO) (Plate 7.1) to relatively pure K-feldspar (Table 7.3, end of chapter). In a few samples K-feldspar contains albite exo lution (microperthite) (Plate 7. l c). P hgioclase in the groundmass, comrnonly associated with quartz, varies kom albite to oligoclase (Fig. 7.3) and appean to be an alteration phase of K-feldspar (Plate 7. la). Apatite is common in d samples (up to 5 modal %) as euhedral crystals randomly dimbuted in the rnatrix and may occur as euhedral, poikilitic microphenocrysts. It is generally uniform in composition (fluor-apatite [3.0-3.65 wt. % FI with up to 0.9 wt. % SrO; Table 7.3). Calcite is present in ail sections and occurs as segregated patches interstitiai to feldspar and biotite, as medium grained, subhedrai crysîals in secondary vedets and in one case as coarse grained Siderophyllite Biotite & a Phlogopite @, 2.00 2.50 3.00 3.50 4.00 Phlogopite Al (IV) + Al (VI) Eastonite GML larnprophyre Dykes Mafic FeIsic 2 Kersantite i Mciuildc (3250) 1 .O0 1 (Na+K), PY -, 0.40 -- 2 -- Fact !t,h&rnakite FtschHbld Ferro-homblende Hbld Ferroactinolite 0.00 I 41 1I 1 Figure 73. Plots of the mineral chemistry from the lamprophyre dykes . a) classification of biotite (fkom Deer et al. 1983). Biotite analyses fkom the Akluilâk dyke shown for cornparison. b) Silica venus the ratio of rnagnesium to magnessium and ferrous iron (in atoms formula units) for calcic amphibole classification ((Ca+Na), >/- 1.34 and NaB<0.67) (afier Leake, 1978). Plagioclase feldspars Figure 7.4. Classification of the plagioclase feldspar series and high-temperature alkali feldspars (modified from Deer er al., 1983) for the GML lamprophyre dykes. Symbols as in Figure 6.2. Plate 7.1. K-feldspar (K) in lamprophyres from the GML area. (a) Strongly zoned K- feldspar in a mafic minette (10.1 wt. % Ba in brighter area as apposed to 7.6 wt. % Ba in the darker area) (sample 146); (a) Weakly zoned K-feldspar rimmed by plagioclase (P) (oligoclase) in a mafic minette (sample 146). Lighter areas correspond to enrichment in Ba (2.61 wt. % vs 2.08 wt. % in the darker zones). (c) K-feldspar with albite (Ab) exolution in sarnple 137. (d) Sector zoning defined by Ba-enrichment (up to 4.56 W. % in lighter areas to 0.68 wt. % in darker areas) in a K-feldspar in a felsic minette (sample 705). euhedral crystds with quartz in vesicles. The above described dykes (represented by samples 127. 137, 116. 6 1 ?A and 7008) are predominantly mafic in composition (SiO? < 52 %) (Table 7.1). have hi& Mg0 (> 8 wt. %) contents (Fis 7.5qb) and hi@ Mg # 's (62.7-76.3). They are moderately emiched in K20and PzOs. CPW-nom calculations show the dykes to be predominantly olivine + hypersthene + orthoclase normative, with only one dyke (sample 6143) king weakiy nephehe-normative. The dykes are potassic to ultrapo tassic (Fig . 7.6) with molar K2OMa20 ranging fkom 1.5 8-3 .X. and calc-alkaline and perpo tassic to weakiy peralkaline with molar (&O + Na20)/Ai203 ranging Born 0.52-0.73. One sample. # 137 (Table 7.1). is sodic in composition (K20/Na20 < 1). has high Si@ (57.9 W. %) and is strongly quartz normative. Based on rnineralogy and major element chemistry these dykes are correlated with the rnatlc minette of Peterson (1994). In terrns of trace element geochemistry. the mafïc minettes are strongly enriched in the LILE K, Rb, Ba and Th. and LREE La and Cc. moderately enriched in Nb. P, Sm and Zr. weakly depleted in Ti, Y, Lu and Yb, and close to uuity in Cr and Ni (Fig. 7.7a). They show a strong negative Nb anomaiy relative to the neighbouring LILE (Th and La). The REE patterns (Fig. 7.7b) are neep, are strongly LREE enriched [(La/Yb)N= 24-8-146.71 and display a negligible Eu anomaly. The abundance in LREE is attnbuted to the common presence of zircon and aiianite. Three dykes (samples 325c, 005c and 605B) (Fig. 7.2), sirnilar in appearance to the mdc minettes, have been sampled in the central part of the map area, however, the predominant feldspar in these samples is plagioclase rather than K-feldspar. Fo Uo wing the classification scheme of Le Maitre et al. (1989), the plagioclase-bearing lamprophyres are referred to as kersantite. Kersantite dykes, as part of the CIF, have not ken descnid in the literatwe. These rocks consist primarily of biotite and amphibole phenocrysts set in a fine grained ma& of the same minerals, and plagioclase, apatite, carbonate, epidote and opaque minerals. Biotite in the kersantite is Mg-biotite to phlogopite (Fig. 7.3a) (Fm= 0.3 1-0.35) and is generally similar in composition to the biotite/phIogopite ftom the mafic minettes descnid above. They are moderately enriched in TiOI and weakiy enriched in CrZ03, GML lamprophyre Dykes 0 Mafic A Felsic û Kersantite i Akluilâk (3250) SiO, CIF (Peterson 1 994) A Upper Felsic Minette Lower Felsic Minette Mafic Minette Figure 7.5. (a) P,O,-MgO--0 and (b) P,O,-Si0,-KO (W. %) plots for the GML lamprophyre dykes. For cornparison, average CIF compositions are plotted (Peterson 1994). ------alkaline calc-alkaline Peralkaline L, Perpotassic Figure 7.6. &O/N+O versus (K10+Na&3)/A120,(molecular %) plot for the GML lamprophyre dykes. For cornparison, average CIF compositions are plotted . Symbols as in Figure 7.4. Ba0 and F. Amphibole is actinolite to actino iitic hornblende (Fig. 7.3 b). Plagioclase in the kersantite dykes ranges fiom oligoclase, in samples OOSC and 605B, to andesine to labradorite, in sample 325C (Fig. 7.4). Plagioclase in sample 325C is variably zoned with andesine-rich cores and labradorite-rich rims. Apatite is generaIly unifonn in composition and is fluor-apatite (3.0-3.64 wt. % F) wnh up to 0.53 W. % Sr0 (Appendk 7.1). Sirnilar to the mafic minettes. the kersantite dykes are rnafic in composition (Si02 < 52 %)?have hi& Mg0 (> 8 wt %) contents (Fig. 7.5ab) and hi& Mg # 's (68.8 1-69-41) (Table 7.1 ). However, the kersantite dykes contain less KZO and are strongly plagioclase- normative. These dykes Vary tiom sodic to ultrapotassic with molar K20/Na20 = 0.43- 3.48 (Fig. 7.6), and calc-aikalùie and perpotassic with molar (&O + Na20)/d20, c 0.7. in terms of trace and rare earth elements (Fig. 7.74b), the kersantite dykes are very similar to the mafic minettes although K, Sr, and Ba show Iower concentrations. consistent with the absence of K-feldspar. Sampte 6058 is also much more depleted in the W SE and the LREE. The third type of larnprophyre dyke, common in the western part of the map area is a medium to coane grained, pink-green weathering north-west-trending (3 50°) dyke. This type of dyke is represented by sarnples 705 and 700A (Fig. 7.2). They consist predominantly of arnphibo le phenocrysts with lesser bio tite phenocrysts, set in a medium grained matrix of essentidy K- feldspar, minor apatite and carbonate. Secondary chlorite may form after amphibole or biotite, and albite and quartz rim K-feldspar. Biotite occurs as individual grains or clusters of euhedrai crystals. As in the rnafic minettes, bio tite contains abundant crystdographically oriented rutile needles. Biotite is Mg-biotite in composition (Fig. 74, contains less Mg0 and &O3 than biotites in the mafïc minettes but are more emiched in F (0.9-1.2 wt. %) (Appendix 7.1). Amphïbole phenocrysts are euhedral to subhedd, equant to elongate, some nÿinned, and appear to be psudomorphes after pyroxene. They are act hoiite in composition. K-feldspar (Fig . 7.4) are aligned (trachytic texîure) euhedral, lathshaped crystais; some crystals have pink pleochroic cores (hematte inclusions). IrreguIarly to sector and concentric zoning (Plate 7.1D) in the feldspar is deked by Ba-rich mnes with up to 4.56 W. Ba0 % to relatively pure K-feldspar (Appendix 7.1). Apatite (1-2 modal %) is randomly distniuted in the mat& is generally unifonn in composition. and similar to the other larnprophyre dykes in tbat it is fluor-apatite (3.3-3.65 wt. % F) with up to 0.59 wt. % SrO. The above dykes are intermediate in composition (SiOZ= 54.7 and 55.2 W. %). have low Mg0 (< 8 wt. %) contents (Fig. 7.5ab) and low Mg # 's (< 60) (Table 7.1 ) relative to the rnafic minettes and are enriched in KZO and Na20 relative to the mafk minettes. CIP W-nom calculations show the dykes to be olivine-normative and much more orthoclase normative than the rnafic minettes. They are potassic with molar K20/Na20 < 3 (1.56 and 1.5) (Fig. 7.6), and cak-alkaline and perdkaline with molar (KzO + Na20)/Ai203> 0.7 (0.83 and 0.88). Based on mineralog and major element chemistry. the dykes are correlated with the felsic minette of Peterson (1994). As in the mafic minettes. the felsic minettes are strongly enriched in the LILE K, Rb. Ba and Th. and LREE La and Ce. moderately enriched in Nb. P, Sm and Zr, and weakly depleted in Ti Y. Lu and Yb, ho wever. the felsic minettes are depleted in Cr and Ni (Fig. 7.7a). The REE patterns (Kg. 7.7b) are similady steep. are arongly LREE e~ched[(LalYb)~ = 43.5- 44.11 and display a negiigible Eu anornaly. 7.3.1 THE AKLUTLÂK DYKE The Akluilâk dyke (sarnple 3XD) intrudes the metamorphosed volcanic and sedimentary rocks of the GMB (Fig. 7.2). It suikes 340-35O0,is nearly vertical and has weathered recessively into the host rocks. The wahocks lack obvious thermal contact effects. At the discovery site, the dyke mesures 1.5 m wide but pinches to 30 cm approximately 175 m to the north where it is covered by glacial debris. The dyke cm be traced discontinuously for approximately 200 m south of the discovery site. It weathers blue-grey to brown with a knobbly poikilitic texture (Plate 7.2), and contains sparseiy distributed rounded to ovoid xeno liths of granitic gneiss and metamorphosed sedimentary rocks, and rare dtrarnafïc rocks (Plate 7.3), that show moderately developed reaction rims. Ln thm section, the dyke is characterised by clearly dehed and closely packed O rthoc lase oikocrysts separated by aggregates of bio tite and calcite wit h lesser apatite, pyrite, and accessory titanite, rutile, ilmenite and zircon (MacRae et al. 1995). Inclusions Plate 7.2. Blue-grey knobby, poikilitic texture in the Akluilâk lamprophyre dyke. Note the ovoid xenolith of granite in upper part of photograph. Plate 7.3. Ultramafîc xenolith in the Akluilâk lamprophyre dy ke. within the oikococryns are biotite, calcite and apatite crystals and crynal Eagments. but minor pyrite, zircon and rutile are also apparent. Modal mineralogy is approximately 42% biotite. 40% orthoclase, 10% cakite. 7% apatite and 1% accessories including allanite and &con. ChIorite, after biotite. quartz and albite. after orthoclase. and calcite are the result of late stage tluid activity. Matra< biotites fkom the Akluilâk dyke are generaiiy uniform in composition with high Mg0 and N203(Fig. 7.3a), and moderate TiOz (MacRae et al. 1995). Orthoclase oikocrysts are characterised by having subgain boundaries with hi@ Ba concentrations: cores are generally Ba-poor and relatively pure K-feldspar. Apatite phenocrysts are fluor- apatite and most show a slight but consistent Sr0 zonation which increases from core to rim (0.3-0.5 mol %). Minerats noted from bulk-rock sarnples include forsterite (Fo92-98). chrome spinel. gamet (G9chrome-pyrope composition), py~oxene (low Cr and Ti diopside), homblende. and magnetite. Diamonds fiom mineral separates are primarily yeiiow-brown. but range Eom deep yellow through pale yellow and pale green to black. Crystals (Plate 7.4) are sharp-edged octahedra, tetrahexahedroida ('dodecahedra'), cubes, macles (t winned octahedra). aggregates, indeterminate fom, and crystal hgments. Black crynals are the result of graphite sheaths. In the Akluilâk sarnples processed to-date, only one crynal greater than I mm in diameter and about a dozen crystals greater than 0.5 mm have been identified tiom a population of severai thousand diamonds; a large proportion of the diamonds occur in the 0.025 to 0.0 10 mm range, but the majority are smaller than 0.075 mm. Approximately 2 km south of the Akluüâk dyke (Fig. 7.2), an identical 2-3 m wide dyke, the Akluilâk South dyke with the same orientation, appearance and mineralogy extends for approximately 3 km dong strike. Xenoiiths of rounded to angular granitoid rocks and adjacent country rocks are abundant. Rare, highly altered and recessively weathered ultramafic xenoliths are also present (MacRae et al. 1995). Although indicator minerais, such as those recovered in the Akluilâk dyke (i.e. forstente chrome spineL and G9 gamet), and diamonds were not discovered in the original sample site. diamonds have been dkovered in the southern-most outcrop of the Akluiliik South dyke (MacRae. pers. comm.). This dyke is currently king studied by Shaniff Habib. an M-Sc. student at the University of Western Ontario. A third diarnondiferous dyke was discovered by Marcelle Hauseux and Sean Surmacz of Comaplex Minerals Corporation and it is located West of the Akluilâk dyke (Fig. 7.2). This dyke is currently king audied by Chris Holmes, a B.Sc. student at the University of Western Ontario. Compared to the other G;ML lamprophyre dykes. and average compositions of the CIF, the Akiuilâk dyke is characterised by low SiOZ(42.8 wt. %) and Mg0 (4.47 wt. %) contents (Fig. 7.5kb), a Iow Mg # (53.57) and hi& K20 (9.27 wt. %) and P205(2.81 wt. %) contents (Table 7.1). CIPW-nom calculations show the dyke to be leucite + nepheline and orthoclase normative. It is ultrapotassic with moiar K20/Na20 = 8.36 (Fig. 7.6). and calc-alkaline and weakly peralkaline with molar (KzO + Na20)lAltOj = 0.79. The Akluilâk dyke has hi& Rb and Ba, but overafl it is compositionally similar to the GML dykes and CIF dykes (Fig. 7.8a). The REE pattern is flat (Fig. 7.8b) but still strongiy LREE - enriched [(LalYb)N= 36.491 (Table 7.1) and display a negligible Eu anomaly. An age of 1832 f 28 Ma Eom a monazite-bearing apatite f?om the Akluilâk lamprophyre dyke was obtained by MacRae et al. (1996), thus confirming its affinity to the CIF. Figure 7.8. (a) N-MORB nomalized multielement variation diagams and (b) chondrite- normalized REE plot of the GML dykes (shaded area) compared with the Akluilak Dyke and average minette compositions from the CIF. Symbols as in Figure 7.4. N-MORB normalizing values from Sun and McDonough (1 989). REE normalizing values are from Taylor and McLennan ( 1985). 7.4 CONCLUSIONS Four mineraiogical and compositional types of lamprophyre dykes have been discovered in the GML area. Two types correlate to the matic and felsic minettes of the CIF, as delineated by Peterson ( 1994). A third type. classified as a kersantite. has not ken descnid previously in the CEHowever. overd chernical composition of the kersantite dykes is consistent with average compositions of the CIF dykes and they are tentatively interpreted in this study to be part of the CIF. The fourth type, the Akluilâk dyke. is unique in that it hosts an unusuai concentration of diamonds. and is the fia multidiamond occurrence in the Churchill Province. However. mineralogicaiiy and geochemicaily. it is similar to the CIF rocks, and an age determination (ca 1.832 Ga) also conhns its af&ity to the CIF. The 1st geotectonicaily significant event to mod* pre-CF rocks in the GiML area was a major tectonothermal event at ca 1.94 to 1.90 Ga. This event was accompanied by arnphibolite grade metamorphism of the Archean strati-pphy and Early Pro terozoic rocks. The predominant north to north-west dyke trends in the GML area indicate em-west extension after this tectonothermal event, at about 1.84- 1.83 Ga. It was suggested by MacRae et al. (1995) that the amphibolite grade rocks of the GML area were aiU at depth at the time of dyke emplacement and that the ambient background temperature was in the 400°C range. This ambient temperature may be the result of the Proterozoic amphibolite grade metamorphism which affected the GML area. The lack of chill rnargins on the lamprophyre dykes, the annealing textures and sub-grain boundary development of orthoclase and the replacement of primary pyroxene by actinolite indicate slow coohg of the dykes. A study by Jones (1 996) indicates that the lamprophyre dykes in the Tnirty Mile Lake (TML) ares West of the GML area, are fiesh show no evidence of recrystahtion and have weii-developed chiU rnargins. This may indicate the dykes in the TML. area intruded at a higher level of cm, and the arnbient background temperature was very low. As discussed Ui Chapter 4, the Archean rocks in the MacQuoid Lake area (TML area) record similar Archean metamorphic temperatures as the Archean rocks in the GML area suggesting a simk level of exposed crust. However, gabbro dykes in the MacQuoid Lake area record greenschist facies Proterozic metamorphic conditions (Tella et al. 1997). This indicates that the low ambient temperature of the rocks which hoa the TblL iamprophyre dykes was a resdt of the Proterozoic metamorphic event and has no relation to the depth of emplacement. The si@cance of diamonds in the Akluilâk dyke is extensively discussed by Macke et aL (1995) and will not be discussed further. However. it should be pointed out that the Churchill Province as a who le. and the GML area in particular has a high diamond potentiai and that the CIF is a highhr prospective host rock. Subsequent work in the area (MacRae pers. corn.) discovered diamonds in the Akluilâk South dyke and the V-Day dyke (Fig. 7.2). SUMMARY OF CONCLUSIONS The Gibson-MacQuoid Lake area lies in a region that has in the past received minimal geologicai rnappùig and minerai exploration. Despite a Limited data base, previous investigations in diis region indicated a potential for fhre mineral exploitation. The proximity of the study area to an existing idktmcture and a commercial transportation corridor is Yewed as positive economic critena that identifies this area as a prime exploration target suitable for renewed geoscience research. In 1992, Ailan Miller of the Geological Survey of Canada, initiated a detailed mapping project in the Sandhill region. That fomed the basis of this Ph. D. thesis. Field mapping, sampling, and follow-up laboratory research completed kom 1993 to 1997 in the Gibson-MacQuoid Lake area has: 1) better defined and extended the previously discovered Sandhill base metal prospect. 2) led to the discovery of the Akluilâk diamond-bearing lampro phyre dyke and, 3) discovered the Sduk Ni-Cu-Co prospect. The foUowing is a su- of signiticant conclusions arrived in this project: 1) The study area is underlasi by a north-dïpping sequence of polydeformed dcto felsic metavo lcanic rocks and related chic and c hemical metasedimentary rocks that form a part of the Archean Gibson-MacQuoid Greenstone Belt. Granitic gneiss is in structurai contact with the metavolcanic and metasedimentary rocks, and forms the nonhem and southem boundary to the greenstone Mt. Archean granitic intrusions are common in the western parts of the map area, and younger gabbro intrusions and lamprophyre and diabase dykes are common throughout the map area. 2) At least two tectonothermai events are recorded by the Archean metavolcanic and metasedimentary rocks in the area Di structures are defined by So pardel north-dipping S 1 cleavage, shaliow West- and east-plunging isoclinal FI folcis, and a north-plunging LI lineation fabric. Dz structures define mohenorth-west- to no&-east-plunging F2 folds and associated moderaîe north-west- to north-east-plimging crenulations which dehes an axiai planar cleavage (Sz). Metamorphic mineral assemblages in the metasedirnentary rnetavolcanic rocks indicate Io wer amphilite facies conditions of regional metarnorphism. P-T estimates, based on stable mineral assemblages data are in the order of 500-625°C at around 3 kbars. This deformation and metamorphkm represents the effects of an Archean compressional and amphiiiite grade metamorphic event at ca 2.6 Ga, and an overprinting Early Proterozoic uplift. and amphibolite grade metamorphic event at ca 1 -94- 1.9 Ga 3) Features which characterise the Sandhill base metai prospect include: a) a volcanic host rock, b) the presence of Zn and Cu mineraiization hosted within a quartz-muscovite SC hist (hydrothermdy aitered fekic-intermediate me tavo lcaniclastic rocks). c) an associated highly duminous assemblage of gahnite, zincian staurohe and ;Mn-gamet. and d) a loss in Na and Ca and gain in Fe and Mn during hydrothermal alteration. These features c haracterise the Sana zone as a met amo rpho sed vo lcanic -ho aed massive sulphide prospect. The absence of a pipe zone or massive sulphide lem characteristic of a typicai proximal volcanic-hosted massive sulphide deposit, and the extensive Mn alteration suggest the Sandhill zone represents a dista1 deposit which formed at some distance fiom the hydrothermal discharge zone. The similarity in the chernistry of the quartz-muscovite schist horizon with the ho st rnetavolcaniclastic rocks, and the extensive hanging-wall alteration indicates that the Sandhiii zone formed bel0 w the sea floor. as a replacement deposit . 4) A Ni-Cu-Co massive sulphide prospect, the Sul& Zone, was discovered approximately 4 km south-west of the Sandhill prospect. Multiple 3-4 m by 0.5-1 m pods of massive sulphides occur over a strike length of 650 m. The Suluk zone is spatially associated with a Proterozoic gabbro intrusion. The geo logical characteristics of the Suluk sulphide zone and Suiuk gabbro are similar to those reported fiom Proterozoic Ni-related gabbro intrusions in the Baltic Shield, and indicate that a potentiai for signincant Ni- rnineralization edsin the Gïbson-iMacQuoid Lake area 5) A unique diamond-bearing dyke. the Akluillk dyke was discovered south-west of the SandhiU prospect. This is the fint reported rnulti-diarnond occurrence in the central Churchill Province. and the îïrst reported occurrence of a sipficant nurnber of diamonds in a lamprophyre host rock. A monazite-bearing apatite fkorn the Alduilâk dyke yielded a Pb-Pb isochron age of 1832 + 28 Ma. This age correlates the dyke to the potassic- ultrapotassic volcanism of the ca 1.84 Ga Christopher Island Formation, Dubawnt Supergroup. The discovery of diamonds indicates that the Churchill Province has a hi& diamond potemial, and that the rocks withli the Christopher Island Formation are prospective hosts. 6) The Archean stmtigraphy was deposited within a sWow subaquous environment of depostion in a continental marginal arc environment, near the bo undary of the bac k-arc basin and siaiic craton. This was accompanied by the formation of the Sandhiu VMS prospect. These rocks were then subjected to an Archean (ca 2.6 Ga) tectonothed event which involved compression, amphibolite grade metamorphism, and diapiric emplacement of granitic bodies. 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Contributions to Mineralogy and Petrology, 95: 4074 19. Wood, D.A. 1980. The application of a Th-Hf-Ta diagram to problerns of tectonomagmatic classification and to establishing the nature of crustal contamination of basaitic lavas of the British Tertiary Volcanic Province. Earth and Planetary Science Letters, 50: 1 1-30. Wright, G.M., 1967. Geology of the southeaskm barren grounds, Parts of the Districts of Mackenzie and Keewatin. Geological Survey of Canada, Mernoir 350. Yardley, B. W.D. 1989. An introduction to metamorphic petrology. Longman, London. APPENDIX I MODAL MINERALOGY AND SAMPLE LOCATION MAPS Abbreviations used in modal mineralogy tables. Actinolite Ac Andalusite An Apatite AP Biotite Bi Calcite Cc Chaicopyrite CP ChIo rite Chl Epido te EP Gamet Gt Gahnite Gn Galena Ga HornbIende Hbl l lmenite 1lm Ky anit e KY K-felds par KtP Magnetite Mt Muscovite Mu Plagioclase Pl Pyroxene Px Pyrite PY Quartz Qtz Sericite Se Sillimanite Si S phalerite SP Titanite Ti Tourmaline Tou Zircon Zr Secondary Sc Trace (< 1%) Tr Location (UTM coordinates) and modal mineralogy of representative samples from the study area. Samplc Nonhing Easting Ac An Ap Bi Cc Chl Cp Ep Ga Gn Gt Hbl Ilm Kfp Ky Mt Mu Op Pi Py Px Qtï. Sr Si Sp Si Ti Tou Zr Ihlaflc mrtavo~can~croclu I Location rnap of the niafic metavolcanic rock samples. I I 55119 1 55N112 LEGEND ARCHEAN ANOlOR PROTEROZOIC PROTEROZOIC Metasedimenlary rocks Gabbro intrusions Diabase dykes 0(not shown on map) 1-1 1-1 Intermediate-felsic rnetavolcaniclaslic rocks Dykes 1-1 1-1 Lamprophyre dykes U(no1 shown on map) GZD Muscovite-quartz-pyr~teschist [-1 Graniloid ~ntmsions Intermediale metavolcanic rocks Orîhogneiss Mafic melavolcanic racks OOP 1 ~sa~duies)s!y~s a~!~o~snui-z)~nnb~o uo!jmol4)!~ saie ~~adso~d~~!qputrs Location map of the metnsedimentarv rock saiiides. ,.. LEGEND ARCHEAN ANDIOR PROTEROZOIC PROTEROZOIC r)Melaedimeniary rocks [-] Gabbro intrusions Diabase dykes 0(no, show on rnap) Inlermediale-felsicmetavolcaniclaslic rocks Dykes - - W Lamprophyre dykes (no1 shown on map) aXED Muscovite-quark-pyriteschist Granitoid intrusions O Intermediate metavolcanic rocks 1-1 Orlhogneiss Mafic metavolcanic rocks APPENDIX 2 WHOLE-ROCK CHEMICAL ANALYSES ks.- -357 48.91 1.25 14.3: 15.58- 0.20 7.08 8.73 2.32 0.38 0.08 98.95- - 0.70 1O9 96.1 49 45.3 334.7 60.3 O 123- -4 - 8 O O 11 123 7.6 86.4 108 16.9 O 3 2.4 84 -2 Y 23.2 Th 0.3 U O Be - Rare Earth la 3.94 Ce 12.18 Pr - Nd 9.6 Sm 3 .26 Eu 1.12 Gd - Tb 0.72 rs - Ho - Er - Tm - Yb 2.85 tu -0.45 Mdic metavolcanic rocks con't, I Sarnplc # si01 *rio2 A1201 FCIW Fe0 Mn0 Mg0 Ca0 Na20 K:O P?05 Toul th0 CO: LOI Trnce Elcr 20 1 Unaltered felsic metavolcaniclastic rocks. 'Trace Ela Cr Ni Co Sc v Cu Pb Zn S Bi As Sb AB Au Rb Cs Ba Sr Ga Tn Nb Hf Zr Y ni U Be Rnrc Earth La fe Pr 'Jd Sm Eu 3d rb Dy Y0 3 Tm Yb --Il Sc v Cu Pb Zn S i3 i Sb As Au Rb Cs Ba Sr Ga Ta Nb tif Zr Y Ill U Be Rare brth Altered feIsic volcaniclas ic rocks. I Samplc U Si02 TiO: AIPI Fez01 Fe0 Mn0 Mg0 Ca0 Na20 Kt0 P:O. Total Hz0 CO1 LOI Trace Elainc Cr Ni Co Sc v Cu Pb Zn S Bi As Sb 43 Au Rb Cs Ba Sr Ga Ta Nb I If Zr Y n 1J Be Rare Eanh 1 E La Cc Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu œ Muscovite-quartz schist. Samplc # 3558 373 384A 384B 394 S i0: 60.13 59.11 59.02 61.oo a.4a Ti02 0.59 0.65 1 .O6 0.72 0.71 A1209 14.77 15.22 25.15 15.10 15.63 FeIO1 17.59 14.23 3.10 5.86 5.44 Fe0 - - - 2.80 - Mn0 ~fl@ Ca0 Na:O Kr0 &Or Total t 120 CO2 LOI Trace Ele Cr Ni Co Sc v Cu Pb Zn S Bi Cd Sn Mo As Sb Ag Au Rb Cs Ba Sr Ga Ta Nb Itf Zr Y Th U Be Rare brt La Cc Pr Nd Sm Eu Gd Tb Yb Lu Muscovite-quartz schist con't. Fer Oi Fe0 Mn0 MI30 Cs0 NszO K20 Pz01 Toial If20 CO2 1.01 Tmcc Elc U Be Rare Eanh I La 2.72 Cc 7.2 Pr - Nd 6.4 Sm 1-15 Eu 0.72 Gd - -rb 0.63 Yb 4.22 1 in n 33 Muscot Sample U SiO2 TiOr A120t FaOs Fe0 Mn0 Me Ca0 Na:O K*0 Pz09 Total ri20 CO2 LOI Tnce Elements 1 Cr 50 28 Ni 33 11 Co 18 74C Sc 13 29.é v 96 IOC Cu 451 4.3 Pb 3 C Zn 250 138C S 35400 3250C i3 i O 125 Cd O O Sn O 2a Mo O a As O 142 Sb O a 43 2.4 27.3 Au - - Rb 71 43 Cs - - Ba 1210 973 Sr O 13 Gû - - Ta - - Nb 19 21 III- - - Zr 189 128 Y 26 34 Th - - U - - Be 1 0.9 Rare Eatth Elmenci La 17.7 Cc - Pr - Nd - Sm - Eu - Gd - Tb - Yb - Lu - Quart: Sample # SiOt TiOt A1:Oi FqO, Fe0 Mn0 M@ Ca0 NazO KzO P:Or 'rotal HZ0 CO2 1.01 Tract Elements Cr Ni Co Sc v Cu Pb Zn S Bi Cd Sn W Mo As Sb Pd Ag Au Rb Cs Ba Sr Ga Ta Nb flf Zr Y Th U Be La APPENDIX 3 MINERAL CHEMICAL ANALYSES Amphibole analysis from a) unaltered and b) altered felsic-intermediate metavolcaniclastic rocks. a) Arialvsu Siû, Ti4 MA Cr& FcO Fc24 Mn0 Ml@ Co0 KtO NA@ F a Total Si Al (LW Ta Siic AI (VI) ~2' FC" Me Mn Ti Cr Oct Site Ca Na M4 or B Siic Na K A sib F C1 c~~~2*t~g I AA9347,dAmdubolc 2 AA9347W Amphibole 3 AA93-100~bolc 3 AA93-ITLA Amphibole 7 AA93 JRII Amphibole 4 AA93-326 Amphibole 4 AAY3472A I\niphihlc 8 AA93472H Amphibolr 5 AA93-326 Amphibole 9 Ah9347211 Amphibole 6 AM3033 Amphibole 7 AA93-033 Amphibole mmm oowv)~ CI ctmloorza-O Y)--t -0in8vfq-9 2 PI?C'.*.999 - 0~00'0in000 N-000000 \O N m 4-4 F -.. ViOIONCIyFmqoqg5g 12 emccorn oo nt-- * mint-ow~oo 2 '91'99?8qqN-000000 090.-Nt-O-~ E v) N O\ - .x .X .x OI OI--?N-?O 00OI0a00 ,-,Esse Y) 3 clsols08 crrs gg~~ 06CIO~OOOo%?qlsoq QI N-OO~OOO \O Pl OI msO -,ce NY>-?OEIO 79~4-"0 r-m *190"+ am " --ooool *ci u 8 -9 evi01Czf O 9V)70'nO -mC ILrjnqCIot9 n7nOT0 p c C;NOO"? 1 = N-0000 1 =-)e i . ' -VI a--O 9m00-0 00 0i9-.919 =?*?.?9 &: oenwcwo - m-oooo mec-?* ",O 1 01 1 me . QON~O~O -rm28;28 '4"'40?0 7NC = Pi6040 1 2 N-oooo 1 gs2 5 PSI 3 8 3 1 YIN Q* 3 y ozQ~s-~= -. min00 rCrIWON0 c ?qoq~pq s?*qTq s+0.Z.k.8-X.S.B.&Z ' X,""O"O 1 "- "-0000 1 P4%2 Q* 2 gg 2 n&af&ac&------C, cnm-ooo e-7838 q q?$o?o ,~~wwrrrrc~< &6tc&~s1 01 m-e~oO1 222 =\o~)~)\o\o~r(------* YIN OI rlro 977T7777 a *"**O0 wC+OomO rrmmmmmmm FFV)OOIO'?Cqqo 1 9 1 222 (*Q*hDQ*PQ* , "N Wf?XXX *- ~6224632 Cl , 8 mmmo-O N I- yo=8%!! 7 q7.070 mm ~iloaoo-~~ wr'aaoao I * N-oaoo 1 r*i~Sm~Nmmr?mm -2 ",, b* -?", 2 19S538 335878 =fiCV O 2 ~~Y)o~~I2 cc-oooo 1 442 2 01 an N-0000 77.5 -mwo *am-90 ?q'=!=!lc! rci?'??S 909 -3w0nu m Cr-0000 WC( rn NPC FCi~oOaOO -7707 OOC 9 ?9'?9-9 c'cJY~~!~ CI Crctmovro N-0000 crnc rCN 3 PJ w - 1 OrnoOO eecr*-mo C ?'Y99b.4 ~C!l.Or!O. 'nqiri ~*mr~-r~op-ta-mo N-O =?m.-cqq 9 yN?9q9 p1q mmmb-rb O N-O000 NWC *N 0 Ne5 v)wOQo awb-000 141'4909 9199m9 -77 ~-v>babe oo* CJ-0000 &mo'.-.-.-288 YIN QI "'O -v)v)O b~0070 ~1'91-qcea- kz\00100 2 Feldspe c hernist ry fiom the metasedimentsuy rocks Icontinued). Anntv~ic Si01 Ah01 NalO Ki0 Ca0 Ba0 Toul Si Al Na K Ca Ba Anonhite Albite 28 AA94438B Planioclase 32 AA94-538B Planioclasc 29 AA94-5388 Planioclase 33 AA94-538B Pla~ioclase 30 AA94438B Planioclasc 31 AA94-538B Plaaioclaw 35 AA94-54 1 A Plagioclase 36 AA94-5 4 IA Plaaioclase 37 M94-54 1 A Planioclaur: Gamet analysis fiom the mafic metavolcanic rocks (calculated on the basis of 24 oxygen). r con,at amphibolc inclusion r am,at amphibole inclusion tan'c t t nqadj ioamph t I Garnct chemistry fiom the clastic metasedimentnry rocks. Gamet chemistry fiom the quartz-muscovite (continued). Gamet chemistry fiom the quartz-muscovite (continued). 45 46 47 48 49 50 51 37.04 37.61 MO3 3763 3738 37.46 377ï 004 007 0.15 O04 O00 0.02 0.01 21.17 21.45 20.26 21.34 21.14 21.35 21.38 0.00 0.00 0.00 0.03 0.04 0.00 0.01 12.59 12.33 17.52 11.81 11.69 11.39 11.30 23.17 24.25 21.64 25.31 25.85 2616 25R 4.22 3 95 1.92 2.50 2.64 2.39 2.55 1.99 1 56 1.55 1.97 1.53 2.25 2.08 100.22 101.22 9907 100.63 10027 101 02 L00.82 5.93 S.% 5.N 6 02 6.01 5 99 6 02 0.08 0.04 0.06 0.00 0.00 0.01 0.00 3.92 3 W 3.88 1.02 1.01 401 4.02 0.01 0.01 0.02 ooi o.oo o.oo ooo 0.00 0.00 0 00 0.00 0.01 0.00 000 1.01 0.93 0.47 0.60 063 0.57 061 3.10 3 21 298 3.38 3.48 3 50 3 43 0.34 0.27 0.27 0 34 0.26 0.39 O36 1.71 1.65 2.45 1.60 1.59 1.54 1.53 16.35 15 37 7.64 10.07 10.61 950 1024 50.38 52.98 4831 5720 58.27 5834 5798 5.54 4.37 4.44 570 4.43 6.43 600 27.73 27.28 39.61 27.03 26.69 Z.73 25 79 45 M3-338Gemet mile 36 AA93-338 ûamei nm 47 AA93-338Gamcla>ri: 48 AA93-US 2 AA93-IOOBioliic 6 AA93-137 Biorilc 10 M3416ABiouic 17 AA93-4 16E Biouic 3 AA93-KX)Bio~ic 7 AA93-349 Bi~~ic II AA93416A Biaite l il AA93-î l6E Biaiic 4 AA934 Biotiic 8 AA93-3.19 Bimic 12 AA9W16D Biotirc 19 AA93416E Biotiic 13 AA93416D Bioiiic 20 AM34i6E Bioritc 14 AA93-i l6D Bioiirc nm ? I AA93-i l6F Biauic 15 AA93416D Bioiitc 22 M93-i lbF BIM~ Biotite chernistry fiom the altered felsic-intermediate metavolcaniclastic rocks (continued). 8X€JSS~?SSSi~%Ô8 =Zëi~8ZP~~~~8OoZ ~-soa~goow7ooog nmooa0'--00-000 O - ~-~oo~~oosotioG5=86?388?3=B %t- X~~~oEnrno?-~~~""== 887F88.OSE %O m .-22 .- Y 2 S 8oo&s8na=8 ~p~~~~ a'-Ci) n=ssc=swa= -~OOzauOOmOOO 2 y~~ooneaoo-ooo -YI<<< ?%$8=Nfl3F7583 " '-"i--m~-""mZ'tut" 49'?*442808 z 5 Ci)0-000=g000000 2 6~0000r4n00 0 '#".OP$? nras8~=on;~~a?5:s~oo~;18~:eS~5 ng,gpzg 2 g-=+002=30Q330 'nNOOOONP+00- Q~~asn Qnn00 00 01 a~sôr~i=qon=g? X~?~G~?BGP$~~FIKXIJ 9 ~-~00~=000000'n~oooo~P+oo- " 53333 nqnôz-~an~nsôo sa$r8gq?ooçsas w7-ooazo_=o:mooo nnaooorcccoa-ooo 0 ,, r? Pi OI :mTnoc =eas=s?a?aas8 2 ~~~~~~~~g~$~g~2 2 g-~oo'aogooaooo - X%G8Zae88="----~0o-=ooc6~oo9 So S8$288RX88%888-~~596cidt+o8-~oo %O Ci) 0, S8ZZ!2S~~ZÔ8 ?~%ZS~SX8SF?~~8 3 i?Wodooaoaooo g nnoooon-oo-ooo o cl?,q~2rq0%~+~8 n $2~2~"~ 30m%80m'"~- ,.Y2 Y%%?! n-oodozoo~e~on0 i,6a,,n,onz~~~ 2 %.8a..f'%mmmmrnm 888S;Y;C; vw~~353zm2~'4- 2 =:q9;~ggqq-aqs.o 3 ~~:~~~ a ~-~oo~~~oomoo'o8 ~NOOOO~NOO-300 '(35599% ms~=ô~~8Z~!2Na3 ~;s~o8$?8z~~So 3 - t-~s-zoOo-e?mod6 - - $ VINOOOO~~NOO-000O PIW~==C( -N zeqz8#mPmW N WN*=N p?,,,,oo~~~~-na 0o3c86R58G - - - 2 ndodao-moo-ooo o ~~?~e~+8~%"?ôi eZZLEtg?G8g???- 3 n ~-=oo~~oomooog neiti,oommoO-ood , q$SZ2ZgZZGN??o 3 3880GZZZ8S0688 54 e-~~~g~od&ao'Og ~e4oô0o~rioo-oo8 Q n --nr-inzg oa F 8%388Z-ommm qerss~~saqs~on n-~oo~~~60~'0002 Zmaooonm~o-d~d ti~~,amm ,$f;:i.: Ci) 23m33 oqC8gXG83OROô4-2dd666e6600 s7 38Z=853=8=F68-uit461d0~~406-oe~ ZAA~AAA 555451 qX2808Z8RXZ=8 - ""-r.n?&8=XN8gce-8 G - ~-~00$~906008YI~QOOO~~~~-**O O-mmvne Muscovite chemistry fiom the quartz-muscovite schist (continued). Staurolite chernistry fiom the quartz-muscovite schist. Staurolite chemistry bom the quartz-muscovite schist (continued). 27 AA93-145 Staiiiolitc 28 AA93-145 Stiuirdiic ain 29 -3- 145 Siaiirolitc mamle 30 AA93-145 Staumiirc nm 31 AA93-241 SLaurdiic 32 AA93-241 Sirwrdiie 33 AA93-241 Stauroliie Staurolite chernistry from the quartz-muscovite schist (continued). Gahnite chemisiry from the altered felsic-intermediate metavolcaniclastic rocks (first two analysis) and the quartz-muscovite schist. 9 AA93436C Gahnrte nrn 16 AAY3-042ûahn1tanm 10 AA93436C Gahmic awc 17 AA93-042 Gahruto am I I AA93-042 Gahniic inclusion in staumliie 18 AA93-042G8hniturnanilc 12 N\9UM2 Gnhnite 19 AA93-042Gahnitcnm 13 AA93-042 Gahnitc am 20 fi93442 Gahnitc con 1.) AA93-U.12 Gahnitr mantlc 2 1 AA93-042 Ciahmie rim Gahnite chernistry fkom the quartz-muscovite schist (continued). APPENDIX 4 RESULTS OF GEOTHERMOMETRY CALCULATIONS Gamet-Biotite Geothermometer --4 Biotiic Gama--- Biotitc Gama Biotitc Garncr 2, -4 ;5 07 ;7 44 0.04 1 01 9.00 Tl 59 Io 62 2 1.60 1) 03 O w O 05 36.71 I9 69 36.04 0 34 O OS 0.33 2.7'6 9 39 2 .97 2.53 0 00 2.3 1 O II 0. 13 3.89 ICO 71 45 11 100.7J 5.95 5 42 5.97 O O5 2.5s o.03 0 00 0.19 0.00 4.02 0.93 4.03 0 00 0 00 1) 01 4 84 1.50 -lII O 05 0.0I 0.04 O 66 2-13 O.? 1 0.43 0.00 0.39 0.01 0.04 1.72 1 171 0 032 O. 162 - .--8 ;.>2> 6.775 0.008 0.007 0.072 0.066 +rry and Speir (1978). (P=3lctnn) - 1.68 -1.91 587 1 ':R 514 odrrts and Notes: F/M is the atomic ratio of Fe/Mg; XMn is Mn/(Mg + Mn + Ca + Fe) molar ratio; XCa is Ca/(Mg + Mn + Ca + Fe). XTi is Ti/(Ai(VI)+ Ti + Mn + Fe + Mg): XA"" is ~l'~/(~l~~+ Ti + Mn + Fe + Mg). Gamet-Biotite Geothermometer con' t %mpk Pair Bioutc Gama ." -.- 37 76 >I Ji 1.37 il il7 18.60 II48 O 14 O 03 18.19 3.27 0.09 4.26 12.16 2.73 0.00 1) 98 0.24 O. 17 8.84 97 26 lOl.24 5.48 5.97 2.52 0.03 0.17 0.01 0.71 4.01 0.02 0.00 2.24 4 58 0.0 1 0 58 2.67 0.66 0.00 cl. 17 0.0 1 0.05 1.66 0.839 0.030 0.13 6.939 0.096 0.028 idam aod .MirtiaguoIe (1995). (P=3 kban) -1.87 -1.96 -2.02 534 1 471 ermrn (19911, (+3 khn) Carnet' 3iotite Geothermometer con't pplc ffSD Pair 13i 1 -1.79 -1.93 55 1 1 101 ohmand .Hwtiognole (1995). (P3khi ~4.c-tccm -ce- n - $ -I=YIO~=m7 *.I ZSzSr S;S%, in.c fiPJ ~~=;2-0*0--a w==n= -2s- 5 YN - 3 = a e =TC-=-= sa Q-=ccsP~=-- == - c = - 3 - * in. Geothermometer (Hoiland and Blundy 1994) (P=3kb) k Samplc 409 mu 1 SiO: 43-70 61.0 TiO: 1 .O4 1229 24.41 Cr:O, 0.00 FCO 18.22 O.! Fc:O~ 1.33 Mn0 0.26 M@ 7.85 CIO 11.90 6.0. NA:O 1.37 8.1( K:O 0.33 0.0: Total 98.28 99.81 S1 6.54 2.7; A (IV1 1.46 I.21 Ti 0.12 Al (VI) 0.71 Cr 0.00 FC" 0.15 ~r:' 2-28 0.01 Mn 0.03 Mg 1.75 Ca 1.91 0.15 Na 0.40 0.7C K 0.06 0.M: cm 0.04 .VISi 0.64 XT1 AI 0.36 xM2Al 0.36 XAK 0 .O6 .UZ 0.59 XAVa 0.35 .iMJNa 0.02 .LX 4Ca 0.95 Inlin 4.87 543 Notes: cm = Si + Ai + Ti + ~e'-+ ~e"+ Mg + Mn - 13; XTlSi = (Si4)/4; XTiAl= (8- Si)/4; XM2AI = (Al + Si-8)/2; XAK = K.; XAI = 3 - Ca - Na - K-cm; Ma= Ca + Na + cm - 2: XIM4Na = (2 - Ca - cm)/2; XM4Ca = Cd2 Resume ALLAN ARMITACE 242 1-3rd Avenue N. W. Calgary, AB. T2N OL2 (403) 270-943 1 DATE OF BWTH August 19, 1965 EDUCATION 1993 - 1998 Ph. D. Geology University of Western Ontario, London, Ontario 1 989 - 1992 MSc. Geology Laurent ian University, Sudbury, Ontario 1985 - 1989 BSc. (Honors) Geology Acadia University, Wol fville, Nova Scotia WORK EXPERIENCE 1997 GEOLOGIST March- Present Comaplex Minerais Corp. Duties - Geological mapping and prospecting, Meliadine Gold Property near Rankin fnkt, NWT. Project Manager, Victory Lake Property - GeoIogicaI mapping and prospecting of VMS prospect, north of Kaminak Lake, NWT. Office work includes assessrnent report writing, budget preparation, etc. 1996 GEOLOCIST May- Decem ber Comaplex Minerals Corporation, Calgary -Duties - Gridding, geophysical work, drill core logging, and mapping and prospecting of gold and base VHMS properties in the Rankin InIet and Kaminuriak Lake areas, NWT. Office work included witing of assessment reports and computw drafting. GEOLOGIST Comaplex Minerals Corporation, Calgary -Duties - Gridding, geophysical work, drill core logging and mapping and prospecting of gold, base metal and diamond properties in the Rankin Met and Gibson-MacQuoid Lake areas, NWT. Office work included writing of assessment reports. 1994 - Surnmer SENIOR FIELD ASSISTANT Geological Survey of Canada -Duties - Continueci 1:30 000 field mapping of the Sandhill VHMS prospect, and mapping of a newly discovered diamondiferous lamprophyre dyke hosted with in the sarne Archean greenstone kit, Gibson-MacQuoid Lake area. northwest of Rankin Inlet, NW. 1993 - Surnmer SENIOR FIELD ASSISTANT Geological Survey of Canada -Duties - 1 :30 000 field mapping of the Sandhill VHMS prospect hosted within an Archean greenstone belt, Gibson-MacQuoid Lake are% northwest of Rankin Inlet, N WT. 1992 - Summer SENIOR FIELD ASSISTANT Geological Survey of Canada -Duties - 150 000 field mapping of Archean anorthosite, granulite, granite and meta-volcanic rocks north of Chesterfield Inlet NWT, and 1:30 000 field mapping of iron formation-hosted gold mineralization within the Archean Rankin Inlet Group, Meliadine Lake area. north of Rankin Inlet, NWT. 199 1 - Summer SENIOR FIELD ASSISTANT Geological Survey of Canada -Duties - 150 000 field mapping of Archean migmitites and granitoids. Proterozoic granitoids, and metamorphosed volcanic and sedimentary rocks of the Archean Rankin Inlet Group, Gibson Lake-Meliadine Lake region, northwest of Rankin Inlet, NWT. 1990 - Summer THESIS MAPPUYC; Completion of MSc. field work, including mapping and drill core logging, Third Portage Lake area, north of Baker Lake, NWT. 1989 - Summer SENIOR FIELD ASSISTANT Department of Indian Affairs and Northem Development, NWT. Duties - 1:30 000 field mapping of meta-volcanic-sedimeritary rocks of the Archean Woodburn Lake Group north of Baker Lake, N WT. 1988 - Summer FLELD ASSETANT Nova Scotia Department of Mines and Energy -Duties - Locating, mapping, sarnpling and assesing mineral occurrences of varid types, ages and mineralogy throughout Nova Scotia. 1987 - Summer FiELD ASSISTANT Acadia University, Wolhille, Nova Scotia -Duties - Assisting MSc. student in 1:10 000 mapping of Proterozoic meta- sedimentary rocks and Carboniferous sedimentary rock, Cape Breton Island, Nova Scotia. Ph. D, Thesis: Geology of the Sandhill Zn-Cu-PbAg prospect and economic potential of Gibson- MacQuoid Greenstone Belt, Keewatin District, NWT, University of Western Ontario. London, 1998 MSc. Thesis: Geology and Petrology of gold-bearing banded iron formation, Keewatin District, NWT, Laurentian University, Sudbury, 1992. BSc. Thesis: Geology and petrology of the crystalline rocks of the Whycocomagh Area, Cape Breton Island, Nova Scotia, Acadia University, Wolhille, 1989. REFEREED PUBLICATIONS Armitage, A E., James, R S. and Goff, S.P., 1996: GoId mineralization in Archean banded iron formation, Third Portage Lake area, Northwest Territories. Explor. Mining Geol. Vol. 5, No. 1, p. 1- 15. MacRae, N.D., Armitage, A.E., and Miller, &R, 1996: A diamondiferous Lamprophyre dike, Gibson Lake axa, Northwest Territcries- International Geology Review, Vol. 37, p. 212-229. Armitage, A.E., Miller, AR, and MacRae, N.D., 1997: Paleoproterozoic Ni-Cu-Co sulphide mineralization, Suluk occurrence, Gibson-MacQuoid Lake area, western Churchill Province, Northwest Territories. Current Research 1997-C; Geological Survey of Canada, p. 6 1-70 MacRae, N.D., Armitage, AE,, Miller, AR, Roddick, J.C., Jones, AL., and Mudry, M.P.: The diamondiferous Akluilâk lamprophyre dyke, Gibson Lake area, N. W.T.; Searching for Diamonds in Canada, A.N. LeCheminant, D.G. Richardson, RN-W.DiLabio, and K.A. Richardson (ed.); Geological Survey of Canada, Open File 3228, p. 10 1- 107. Armitage, A.E., Miller, AR, and MacRae, ND., 1995: Geological setting of the Sandhill Zn-Cu-Pb Ag prospect in the Gibson-MacQuoid Lake area, District of Keewatin, Northwest Territories; & Current Research 1995-C; Geological Survey of Canada, p. 2 13-224. Jones, AL, Miller, AR, Armitage, A.E., and MacRae, N.D., 1995: Lamprophyre dykes of the Christopher Island Formation, Thirty Mile Lake, District of Keewatin, Northwest Territories; & Current Research 1 995-C; Geological Survey of Canada, p. 187- 194. Armitage, kE., Miller, AR, and MacRae, N.D., 1994: Geology of the Sandhill Zn-Cu showing in the Gibson Lake axa, District of Keewatin, Northwest Territories; & Current Research 1994-C; Geologicai Survey of Canada, p. 147-155. Armitage, A.E., Tells, S., and Miller, AR 1993: Iron formation-hosted gold mineralization and its geologic setting, Meliadine Lake are% District of Keewatin, Northwest Tenitories in Current Research, Part C; Geological Survey of Canada, Paper 93- 1 C, p. 18% 195. Tella, S., Schau, M., Armitage, AE., and Loney, B.C. 1993: Precambrian geology and econornic potential of the northeastern parts of the Gibson Lake map area, District of Keewatin, Northwest Territories; Current Research, Part C; Geological Survey of Canada, Papet 93-IC, p. 197-208. Tella, S., khau, M., Armitage, AE., Seemayer, B.E., and Lemkow, D. 1992: Precam brian geology and econornic potential of the Meliadine Lake-Barbour Bay region, District of Keewatin, Northwest Territories; in Current Research, Part C; Geological Survey of Canada, Paper 92- 1 C, p. I - 1 1. KE. Northcote, G. Demont and A. Armitage 1988: Investigation of metaIlic mineral occurrences, Metallotectonic Project-Nova Scotia Department of Mines and Energy Report of Activities fart A, Report 88-3. ABSTRACTS Arrnitage, A.E., 1997: The Victory Lake Volcanic-Associated Base Meta1 Prospect, Kivalliq District, Nunavut Region, N. W.T.: A: Project Summary; &J Exploration Overview 1997, Northwest Temitories Armitage, AE., Miiler, AR, and MacRae, N.D., 1995: Geology and mineral potential of the Gibson- MacQuoid lake area, District of Keewatin, NW, Exploration Overview 1995, Northwest Territories. Compiled by E.I. igboji. Armitage, A.E., MacRae, N.D., and Miller, A.R, 1994: Alteration and mineralization associated with the Sandhill Zn-Cu-Pb-AgProspect in the Gibson-MacQuoid Lake area, District of Keewatin, Northwest Territories; in Exploration Overview 1994, Northwest Territories. Compiled by R Kusick and S.P. GoK MacRae, ND., Armitage, A.E., and Miller, AR, 1994: Diamond-bearing potentiai of aikaline dykes in the Gibson Lake ara, District of Keewatin, Northwest Territories. GAC/MAC Prograrn with Abstracts, 19. Armitage, A.E., MacRae, N.D., and Miller, AR, 1993: Alteration and mineralization of the SandhilI Zn-Cu showhg in the Gibson Lake ara, District of Keewatin, Northwest Tmitories; in Exploration Overview 1993, Northwest Territories. Compiled by S. P. Goff Tella, S., Schau, M., and Armitage, A.E., 199k The Uvauk GabbreAnorthosite-Grdite Complex - An Archean? aIlochthonous tectonic remnanf District of Keewatin, N. W.T. GAUMAC Program with Abstracts, 18. Armitage, A, and James, R 1992: Alteration associated with gold mineralization in banded iron formation, Third Portage Lake ara, Keewatin District, NWT.GACIMAC Program with Abstracts, 17. Armitage, A.E., James, RS. and Goff, SP. 1991: Auriferou iron fmations, Third Portage Lake ares Keavatin District, NW.GAC/MAC Program with AbWcts, 16. Armitage, A. 1990: Gwlogy and petrology of gold bearing iron formation in the Third Portage Lake ara, Keewatin District. Exploration Overview 1990, Northwest Territories, Ed. S.P. GoE NOTE TO USERS Oversize maps and charts are microfilmed in sections in the following manner: LEFT TO RIGHT, TOP TO BOTTOM, WlTH SMALL OVERLAPS The following map or chart has been microfilmed in its entirety at the end of this manuscript (not available on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover. Black and white photographic prints (17"x 23") are available for an additional charge. ARCHEAN ANDIOR PROTEROZOIC sser arenite, rnetamorphosed to biotite+ .-Granodiorite:light grey, +/- kyanite schist, minor interlayered lamprophyre dykes iulphidic-graphitic argillite Gabbro: minor pyroxeni -grained,well laminated to banded, rare + plagioclase ihnite-garnet- ~illMineralization Orthogneiss: diorite to c c conglomerate and finer grained margins, rafts of mafic avolcaniclastic rocks -. irs, metavolcanic breccias, metavolcanic 1 Map. Geology of the Gibsc :ks, and gabbro sills; intercalated felsic ( Cu-Co occurrence, the Sai ; mafic volcanic rocks metamorphosed to Day diamondiferous lampr PROTEROZOIC A a Andalusite Diabase dykes (MacKenzie Swarm?) 0-(not shown on map) Andalusite Lamprophyre dykes (Christopher Island Formation) (not shown on map) v Mn-gamet Metasedirn IF - iron formation e Location 01 GRA - graphitic schist ed Minerall Qtz - Quartzite 1st gene 35 Suluk Ni- - - 0- Foliation: 1st generation %Axial tract ik and V- direction c \ \ Trace of fault Axial tracc \ direction c Andalusite + Staurolite ; (MacKenzie Swarm?) . Andalusite + Staurolite + Kyanite ykes (Christopher Island t shown on map) v Mn-garnet + Zn-Staurolite in Metasediments Location of diamond discovery Minerallrodding Iineation: 1st generation ation: 1st generation Axial trace of synform showing -direction of plunge ace of fault Axial trace of antiform showing direction of plunge Suluk Ni-Cu-Co Prospect IMAGE EVALUATION TEST TARET (QA-3)