Physical Volcanology and Hydrothermal Alteration·
of the Footwall Rocks to the
Archean Sturgeon Lake Massive Sulfide Deposit,
Northwest Ontario
A Thesis
Submitted to the Faculty of the Graduate School
of the University of Minnesota
by
Peter K. Jongewaard
In Partial Fulfillment of the Requirements
for the Degree of
Master of Science
January 1989 Acknowledgements
The author would like to acknowledge his advisor, Dr. Ronald L. Morton of the University of Minnesota-Duluth for his support and encouragement, as well as initiation of this thesis. Thanks are also extended to Ors. James A. Grant, John C. Green, and Paul Siders of the University of Minnesota-Duluth for serving on the advisory committee. Thanks are given to Mr. Frank Balint of Minnova, Inc., Thunder Bay, Ont., for access to the property, company records, and financial support. Also acknowledged are Dr. J.M. Franklin of the Geological Survey of Canada , Mr. George Hudak, Mr. J.S. Walker, and Mr. Chris Rog o f the University of Minnesota-Duluth for stimulating discussions in the field. Lastly, the author wishes to thank his family for constant support, encouragement, and patience. ABSTRACT
The f ootwall rocks beneath the Archean Sturgeon Lake massive sulfide deposit consist of a 3 km thick sequence o f steep north-dipping subaqueous volcanic and volcaniclastic rocks intruded by mafic dikes and sills. Preserved primary textures, fragment composition, and regional stratigraphic correlation allow for the volcanic and volcaniclastic rocks to be subdivided into seven distinct units. Mafic volcanic rocks comprise the lowermost units, consisting of massive, pillowed, and amygdaloidal flows, with minor interlayered felsic flows and pyroclastic deposits. These mafic units are overlain in the west half of the field area by a coarse heterolithic volcanic breccia, which grades up into, and is intercalated with quartz-phyric felsic pyroclastic flow deposits. This felsic unit is locally overlain by bedded volcanic debris flows and associated epiclastic sediments. These are in turn overlain by a thick sequence of massive to bedded quartz-phyric felsic pyroclastic flow deposits, the Mattabi series, with minor intercalated volcanic debris flows. These rocks are overlain by the host rocks to the orebody which consist of bedded to massive quartz- & plagioclase-phyric pyroclastic flow deposits. The succession is capped by mafic to intermediate massive and amygdaloidal flows, and was later intruded by two large dioritic sill-like bodies which dilate the stratigraphy. The east half of the field area is underlain by the lowermost mafic units which are overlain by fragment-poor ash-rich felsic pyroclastic flow deposits. A NE trending structure, interpreted to be a synvolcanic normal fault, provides the break between east and west, and may be a major bounding fault to a large caldera system. Convective circulation of hydrothermal fluids within the succession resulted in the formation of distinct alteration assemblages, which include a) silicified; b ) Fe- chlorite; c) chloritoid; d) cordierite; e) aluminum silicate; f) sericite; and g) Mg-chlorite. Field and petrographic evidence suggest that two periods of hydrothermal activity affected the felsic volcanic rocks of the succession: 1) development of silicif ied rocks and Al-silicates from leaching of original constituents, and chloritoid/chlorite alteration by a process of Fe-enrichment, and 2) widespread sericitization from K enrichment, and cordierite alteration, by leaching of Fe and Mn, leaving the rocks enriched in Ca and Mg during the time of development of the Sturgeon Lake massive sulfide deposit. Subsequent regional deformation and metamorphism to upper greenschist facies produced a bedding-parallel foliation and development of metamorphic mineral phases, strongly dependent on pre-metamorphic altered compositions.
i TABLE OF CONTENTS
Abs tr act ...... i Table of Contents ...... ii List of Figures ...... iv Li st of Tables ...... vii List of Plates ...... vii
I. Introduction ...... l
Purpose of Study ...... 1 Location, Access, and Physiography ...... J Methods of Study ...... 5 Regional Geology ...... 6 Previous Work ...... 9
II.Lithology and Stratigraphy ...... 13
Introduction ...... 13 Description of Units ...... 15 Precaldera Volcanic Rocks ...... 15 Mafic Volcanic Rocks ...... 15 Caldera-Related Units ...... 22 Heterolithic Breccia ...... 22 Quartz Pyroclastic Flow (QPYF) ...... 27 Debris Flow Deposits ...... 31 Mattabi Pyroclastic Deposits ...... JS L-Series Pyroclastic Deposits ...... 48 Post-Caldera Rocks ...... 54 Mafic Volcanic Rocks ...... 54 Mafic Intrusive Rocks ...... 55 Volcanic Interpretation ...... 59 Massive Sulfide Orebody ...... 62
III.Hydrothermal Alteration ...... 67
Introduction ...... 6 7 Alteration Assemblages ...... 68 Silicified Assemblage ...... 68 Iron-Chlorite Assemblage ...... 68 Chloritoid Assemblage ...... 72 Cordierite Assemblage ...... 74 Aluminum Silicate Assemblage ...... 77 Sericite Assemblage ...... 78 Magnesium Chlorite Assemblage ...... 81 Distribution of Alteration Assemblages ...... 82
ii IV.Effects of Metamorphism ...... 85
V.Alteration Geochemistry ...... 96
Silicified Assemblage ...... 102 Fe-Chlorite Assemblage ...... 104 Chlori toid Assemblage ...... 107 Cordierite Assemblage ...... 111 Aluminum Silicate Assemblage ...... 114 Ser ici te Assemblage ...... 118 Mg-Chlorite Assemblage ...... 120
VI.Alteration Model ...... 123
VII.Summary and Conclusions ...... 129
References Cited ...... 13 4
Appendix 1: Modal Mineralogy ...... A-1 Appendix 2: Geochemical Analyses ...... A-2 Appendix 3: Modal Mineralogy-Orebody ...... A-3
iii LIST OF FIGURES
1. Location Map ...... 4
2. Location of Subprovinces ...... 7
3. Regional Geology ...... 8
4. Areas of Study ...... 11
5. Outcrop of pillowed lower mafic unit ...... 1 7
6. Amygdaloidal sheet flow of lower mafic unit ...... 1 9
7. Photomicrograph of amygdaloidal mafic flow ...... 1 9
8. Pumice fragments in outcrop, slj-105 ...... 22
9. Blocks within breccia unit ...... 2 4
10. Breccia within drill core ...... 25
11. Fragments within breccia ...... 25
12. Photomicrograph of QPYF matrix ...... 3 0
13. Photomicrograph of amygdules within fragment in QPYF .. 30
14. Large pumice block within debris flow deposit ...... 33
15. Bombs within debris flow deposit ...... 34
16. Bedded debris flow deposits ...... 35
17. Thin laminated debris flow horizon ...... 36
18. Fragments in mafic debris flow deposit ...... 36
19. Drill core intersection of Mattabi pyroclastic rocks .. 4 0
20. Crystal- and ash-rich beds, Mattabi pyroclastic rocks .42
21. Outcrop of siliceous Mattabi pyroclastic rocks ...... 42
22. Mantled quartz phenocrysts, Mattabi pyroclastic unit .. 43
23. Photomicrograph of fragment and phenocrysts in Mattabi pyroclastic rock ...... 4 4
24. Photomicrograph of fine-grained Mattabi matrix ...... 44
iv 25. Photomicrograph of graded silt-sized quartz chips in Mattabi pyroclastic rock ...... 45
26. Drill core intersection of coarse debris flow deposit within Mattabi pyroclastic deposit ...... 47
27. Outcrop of contact between L-series subunits ...... 50
28. Rusty mineralized horizon, L-series pyroclastic rocks.51
29. Photomicrograph of plagioclase phenocryst in L-series.51
30. Thinly laminated ash beds within L-series ...... 52
31. Photomicrograph of phenocrysts within L-series rock ... 53
32. Massive northernmost dioritic intrusion ...... 58
33. Thin dike cutting L-series exposure ...... 58
34. Diagrammatic section through orebody, DDH# SLM-156 .... 63
35. Graph of Sph-Cp zonation in orebody ...... 65
36. Graph of Py-Po zonation in orebody ...... 66
37. Outcrop of silicified L-series rock ...... 69
38. Drill core intersection of Fe-chlorite alteration ..... 70
39. Photomicrograph showing Fe-chlorite assemblage ...... 71
40. Photomicrograph of anomalous blue interference colors of Fe-chlori te ...... - ...... 71
41. Photomicrograph of chloritoid veinlet ...... 73
42. Photomicrograph of chloritoid in sericitic matrix ..... 73
43. Drill core showing cordierite porphyroblasts ...... 75
44. Photomicrograph of cordierite in sericitic matrix ..... 75
45. Photomicrograph of cordierite in quartz-porphyritic Mattabi pyroclastic rock ...... 76
46. Photomicrograph of cordierite with tourmaline ...... 76
47. Aluminum silicate alteration in outcrop of Mattabi pyroclastic rock ...... 79
48. Photomicrograph of andalusite porphyroblasts ...... 79
v 49. Photomicrograph of sericite veinlet ...... 80
50. Photomicrograph of sericite with ilmenite ...... 80
51. Graph of MgO/MgO+FeO ratios within the different alteration assemblages ...... 89
52. Photomicrograph showing possible biotite-forming reaction from chlorite + sericite ...... 89
53. Photomicrograph of staurolite rimming chloritoid ...... 92"
54. Photomicrograph of staurolite porphyroblasts ...... 93
55. P-T diagram of relevant staurolite- and cordierite- forming reactions in the study area ...... 93
56. Graph of CaO/CaO+MgO+FeO ratios for alteration assemblages within study area ...... 94
57. T-solubility diagram of silica at varying pressures .. lOJ
58. Isocon diagram showing Fe-chlorite alteration of silicified rock ...... 106
59. Isocon diagram showing chloritoid alteration of silicified rock ...... 108
60. Composition diagrams of chloritoid and Fe-chlorite alteration assemblages ...... 110
61. Isocon diagram showing cordierite alteration of silicified rocks ...... 113
62. Graph of major oxide ratios for alteration assemblages enriched in Fe and Mg ...... 115
63. Isocon diagram showing aluminum silicate alteration of silicified rocks ...... 117
64. Isocon diagram showing sericitic alteration of silicified rocks ...... 119
65. Isocon diagram showing Mg-chlorite alteration of silicified rocks ...... 122
66. Alteration model showing hydrothermal system during deposition of Mattabi-series rocks ...... 126
67. Alteration model showing hydrothermal system during deposition of L-series rocks ...... 127
vi LIST OF TABLES
V-1. Averaged chemical compositions of alteration assemblages used for comparison purposes ...... 100
V-2. Calculated CIPW norms for compositions shown in tab 1 e V-1 ...... l o 1
V-3. Calculated changes in concentration from isocon of Fe-chlorite vs. silicified alteration ...... 106
V-4. Calculated changes in concentration from isocon of chloritoid vs. silicified alteration ...... 1 08
V-5. Calculated changes in concentration from isocon of cordierite vs. silicified alteration ...... 113
V-6. Calculated changes in concentration from isocon of Al-silicate vs. silicified alteration ...... 117
V-7. Calculated changes in concentration from isocon of sericite vs. silicified alteration ...... 119
V-8. Calculated changes in concentration from isocon of Mg-chlorite vs. silicified alteration ...... 122
LIST OF PLATES
1. Geology of the Sturgeon Lake Mine area ...... back jacket
2. Distribution of alteration assemblages ...... back jacket
3. Composite section through outcrop SLJ-100, UPYF debris flow deposits ...... back jacket
vii I. INTRODUCTION
The Sturgeon Lake massive sulfide deposit was a 2.1
m.t. Zn-cu-Pb-Ag-Au high-grade orebody located within
Archean volcanic rocks of the Wabigoon greenstone belt of
northwest Ontario (Severin, 1982). The deposit was
discovered in 1970 as a result of a ground geophysical
follow-up to an airborne geophysical survey of the volcanic
rocks of the South Sturgeon Lake area. The mine was operated
as an open pit by Sturgeon Lake Mines Ltd., a joint venture
of Corporation Falconbridge Copper and New Brunswick
Uranium, Inc. Milling and concentrating were done on site
from 1974 to early 1980. The open pit is now flooded; the mill was dismantled in 1986 and moved to another location.
The Sturgeon Lake mine site is now vacant, with hardy pio- neer vegetation reclaiming waste piles and tailings ponds.
PURPOSE OF STUDY
The Sturgeon Lake deposit was one of five massive sulfide orebodies discovered between 1969 and 1971 in the volcanic rocks south of Sturgeon Lake. Controversy has reigned in the past regarding the relative stratigraphic positions of these five deposits (Trowell, 1983; Severin,
1982; Franklin et al., 1977). In 1985, the Geological Survey of Canada, the Ontario Geological Survey, and the University of Minnesota-Duluth entered into an agreement to study the
1 stratigraphy, physical volcanology, and hydrothermal
alteration related to massive sulfide deposition in the
South Sturgeon Lake area. This study is a part of that
effort.
The footwall rocks beneath the Sturgeon Lake mine have
been variously described by previous workers with little real attention paid to the volcanic environment and hydrothermal alteration (Friske, 1983; Severin, 1982). It is believed that a detailed study of these rocks will
facilitate a better understanding of the overall volcanological regime in the area, as well as provide detailed information regarding the mineralizing processes involved in the formation of the Sturgeon Lake deposit.
Specifically, the objectives of the study are:
1) To determine the volcanic stratigraphy of the
f ootwall rocks to the Sturgeon Lake mine
and assist in correlation of lateral
equivalents;
2) Develop a model of the volcanic environment;
3) Identify alteration mineral assemblages and
attempt to determine their association with the
processes responsible for ore deposition.
2 LOCATION, ACCESS, AND PHYSIOGRAPHY
The Sturgeon Lake Mine is located 25 km east of the southern tip of Sturgeon Lake in northwest Ontario, approximately 400 km NNE of Duluth, Mn., and 240 km NW of
Thunder Bay, Ontario (Fig.1). Road access is provided by
Trans-Canada Hwy. 17 to Ignace, Ontario, then north on
Ontario 599 for 72 km, then east on the mine access road for
24 km.
The Sturgeon Lake Mine property is characterized by two distinct surficial terrains. The northern third is an open gravelly plain of waste piles and tailings ponds of the former mine and mill site. The southern two-thirds is a dense forest of spruce, balsam, and aspen on low rolling hills with intermittent streams, cedar and spruce swamps, and shallow, bog-rimmed lakes. Variation in topographic relief rarely exceeds 20 meters. Bedrock exposures are severely limited; most of the hills are glacially-derived boulder mounds and sandy till. Outcrops cover roughly 1-2% of the total area, restricted to scattered occurrences along creeks and ridge crests, and several bulldozed strips excavated by mine personnel. Several excellent exposures were provided by large upturned root systems in areas of severe windfall.
3 · ,, .., · · · "' · · --- ·"::B· - ,-· .• -·-• '· / AQOl(our : ti Ji· ' -.. ; . . . :· . :::-:: ,_·;··: '. :·
/ ./ A lli Hwy 11 100 Kilom1ttn u Q) ..0 Q) Ignace ::::i 0 a Study Area Location 0 JOO AFTER ORAMNG BY Fig. 1- Location of study area in NW Ontario. 4 METHODS OF STUDY Field work was conducted during the summer of 1987. Geologic mapping was carried out over the mine property, roughly 10 sq. km, using the pace and compass method on widely spaced cut grid lines. Information obtained was compiled on 1:4800 base maps provided by Minnova, Inc., (formerly Corporation Falconbridge Copper) as well as mylar overlays on 1:15000 scale air photographs. Detailed mapping of a small, but well-exposed, area of outcrops at a scale of 1:120 was conducted to detail local depositional features. Samples were collected at each outcrop. In addition, 15,000 feet of diamond drill core from 18 exploration diamond drill holes was logged and systematically sampled to assist in stratigraphic correlation. From outcrop and diamond drill core samples, 224 thin sections were made and analyzed petrographically for primary textures, mineralogy, and alteration. Modal analyses from these are compiled in Appendix 1. Geochemical analyses for whole-rock major oxides and trace elements on 200 samples from the field area were performed by Metriclab, Inc. Results of these analyses are tabulated in Appendix 2. In addition, 20 polished sections of samples from the orebody were studied for textures and mineralogy. Results are tabulated in Appendix 3. 5 REGIONAL GEOLOGY The study area is situated within Archean volcanic rocks of the Wabigoon subprovince of the Superior province of the Canadian shield (Fig.2). This granite-greenstone subprovince is bounded to the north and south by the English River and Quetico gneiss belts, respectively (Goodwin et al., 1972). A thorough description of the various lithologies and regional stratigraphy is presented by Trowell (1983). He describes the Savant-Sturgeon Lake metavolcanic-rnetasedirnentary belt as consisting of four volcanic-sedimentary assemblages each characterized by cyclic volcanism. The southernmost, the South Sturgeon Lake assemblage, is host to all of the massive sulfide deposits discovered in the region to date, including the Sturgeon Lake deposit (Fig.3). The South Sturgeon Lake assemblage includes a basal mafic unit, approximately 1-2 km thick, overlain by up to 9 km of maf ic to felsic volcanic and volcaniclastic rocks and minor sediments (Franklin et al., 1981). This 10 km thick succession strikes east-west and dips moderately to steeply to the north, forming the southern limb of a major synform centered roughly on the north shore of sturgeon Lake (Trowell, 1983). The volcanic rocks of this assemblage are intruded at their southern extremity by the Southern granitic-gneissic complex, and the Bell Lake alkalic 6 ARCHEAN SUBPROVINCE TYPE .: ·. .,. VOLCAHO-PWTOHIC CHUllCHIU. PROVINCE SOUTHEJIH PROVINCE -i Fig. 2- Location of greenstone-granite subprovinces within Superior province of Canadian Shield (modified after Card and Ciesielski, 1986). 7 .<=• . • • ., .. =.- . STURGEON LAKE . ·- ():) ·;/·-·. ·•. :'' <·-·-· I ., . •...... _,· ..;.·.;_.·._ ·, .'·' ...... ,_ _.;: : ..... r... ! ' :- .. .. _ .·1.- .. -::-::.=-· ''t !·· ...... ·":'·- :.:· ,_. __l ... :: ••.f ··-· .. -..; .-: ... ,;. EJ ALKAUC INTRUSIVES .. •.· (51 GRANITIC INlRUSIVES B LIETASEOILIENTS li!ll!I MASSIVE SULflDE OREBOOIES 13 lRDNOHJEMITlC INTRUSIVES HORl> Fig. 3- Regional geology of the South Sturgeon Lake area (after Trowell, 1983; Franklin et al., 1977). complex. A large sill-like trondhjemitic body, the Beidelman Bay pluton, intrudes the volcanic succession just above its known base (Campbell et al., 1981). Radiometric ages of the Beidelman Bay pluton and the overlying felsic extrusive rocks, which host the massive sulfide mineralization, have been determined by U/Pb zircon methods to be 2733 +/- 3 m.y. (Davis and Trowell, 1982). Extrusive rocks at the top of the South Sturgeon Lake assemblage give a U/Pb zircon date of 2717 m.y. (Davis et al., 1985), indicating a 15 m.y. span of at least intermittent volcanic activity in the area. Regional metamorphism in the area is of lower greenschist grade with local lower amphibolite grade in proximity to intrusive bodies. Metamorphic grade increases from west to east accross the South Sturgeon Lake area (Hudak, 1989: this study). PREVIOUS WORK Early geologic work in the sturgeon Lake area was restricted to descriptive reports concerning several small gold prospects discovered early in this century. Regional reconaissance mapping by the Ontario Department of Mines (Rodgers, 1964) and the Geological Survey of Canada (Skinner, 1969) helped outline the regional geology of the area. 9 Discovery of the Mattabi orebody in 1969 by Mattagami Lake Mines personnel sparked exploration activity in the south Sturgeon Lake area by a number of mining companies. This led to the eventual discovery of four additional massive sulfide deposits in the area by 1972. Grid mapping, geophysical surveys, and diamond drilling by exploration personnel throughout the south Sturgeon Lake area helped to establish a base of data upon which numerous subsequent studies have been built. Extensive detailed geologic study in the area has thus far focused primarily on the Mattabi deposit, the largest orebody discovered to date. A study of the hydrothermal alteration related to the deposit has been carried out by Franklin et al., (1975). Groves (1984) gives the first detailed account of the f ootwall stratigraphy and wide-scale alteration beneath the Mattabi deposit. A synthesis of the volcanology and alteration related to the Mattabi and F- group deposits is described by Morton et al., (1988), and Morton & Franklin (1988). Master's theses describing stratigraphy, volcanology, and alteration include Area 16- Mattabi (Walker, in prep.), the F-group deposit (Hudak, 1989), and the Darkwater property west of the F-group deposit (Rog, in prep.) (Fig. 4). The Sturgeon Lake Mine was discovered by Falconbridge Nickel Mines, Ltd., in October of 1970. Subsequent exploration drilling and grid mapping on the property has to 10 .. , . ··.:--. :'·°;- STURGEON LAKE .. ,, •'..f.' r-· f- ® WALKER, 1887 -•. l •;i;,· •;.'-... El AU (gj TRONOH.DllllC INTRUSI 'tES NORTH FllSIC WE'! Avet.CAN ICS l D WAflC W£TAVCLCANICS y i KILOWElDIS Fig. 4- Areas of study within South Sturgeon Lake area as part of cooperative effort. date failed to delimit additional ore reserves, but has provided the base of information used in this and other subsequent investigations. The .area immediately northwest of the Sturgeon Lake mine, including the Lyon Lake and Creek Zone deposits, has been described by Harvey and Hinzer (1981). They proposed that the three deposits are lateral equivalents of the same ore-forming event, occurring at the same stratigraphic interval. The first thorough summary of the geology in the immediate vicinity of the Sturgeon Lake mine was by Severin (1982), in which he describes the Sturgeon Lake and Mattabi deposits as occupying the same stratigraphic position, contrary to the conclusions of the present study and previous published reports (Harvey and Hinzer, 1981; Franklin et al., 1977). His hypothesis is based on detailed mapping in the open pit as well as diamond drill core logging from the northwestern extremities of the property. Two theses examining the applicability of lithogeochemical analyses to exploration in the Sturgeon Lake-Lyon Lake area have been provided by Friske (1983) and Staargaard (1981). These works have focused on the geochemical characteristics of host rocks and alteration related to the deposits. A regional study of the structure and volcanic environment throughout the South Sturgeon Lake assemblage, (Mumin, 1988), describes the area as having been an oceanic 12 rift environment, with mineralization localized along the rift axis at varying stratigraphic intervals. The predominance of explosive felsic volcanic rocks in the area and other field relations, however, cast doubt upon this hypothesis. The characteristics of the volcanological and depositional environment in the Sturgeon Lake mine area have not, to date, been the focus of any specific work, and, as such, have remained obscure. These questions, and others, are addressed in the present study. II. LITHOLOGY AND STRATIGRAPHY A. INTRODUCTION The regional stratigraphy, volcanology, and alteration of the south Sturgeon Lake volcanic succession has been the focus of ongoing research sponsored by the GSC, OGS, and UMD, of which the present study is a part. Data obtained through detailed field mapping and petrographic analyses have allowed correlation of several distinct volcanic units over a wide area from west of the F-group deposit eastward to the Sturgeon Lake mine, a lateral distance of over 22 km (Fig.4). The distribution of these volcanic units indicates the presence of a large maf ic shield volcano upon which is superimposed what has been termed the Sturgeon Lake caldera complex (Morton et al., 1988). These felsic fragmental 13 volcanic rocks can be correlated eastward to include the footwall succession beneath the Sturgeon Lake mine. The distribution of rocks within the study area is shown on plate 1 (back pocket). Strike of the units remains consistently ESE, with steep northerly dips ranging from 65 degrees to near vertical. No evidence exists for overturned strata within the field area. A pervasive sub-vertical foliation is oriented subparallel to strike, readily observable in outcrop. In thin section, however, bedding- foliation distinction is difficult. Throughout the area the rocks have undergone regional greenschist facies metamorphism, with local amphibolite facies rocks recognized in close proximity to large intrusive bodies in the southern extremities of the study area. Hereafter, for the sake of brevity, the prefix meta- will not be included in the text in reference to the rock types discussed. The metamorphism will be considered in chapter 4. The rocks of the study area have undergone variable amounts of hydrothermal alteration, as evidenced by the modal mineralogies tabulated in Appendix 1. Despite metamorphism and alteration, preserved primary textures and structures allow the identification of the original character of the volcanic rock units. These textures, along with fragment types, composition, and regional stratigraphic correlation have been used to distinguish seven distinct 14 volcanic units within the footwall succession. These units have been assembled into three groups, based on their relationship to the Sturgeon Lake caldera, as follows: 1) Precaldera rocks: mafic flows, flow breccias, and minor interbedded f elsic rocks which form the base of the footwall succession. 2) Caldera-related units: breccias, ash-flow tuffs, and debris flow deposits which form intra-caldera fill and minor outflow facies 3) Post-caldera rocks: late-stage volcanic and intrusive rocks B. DESCRIPTION OF UNITS 1. PRECALDERA VOLCANIC ROCKS a. Mafic Volcanic Rocks (Unit 1, Plate 1) A 1-2 km thick sequence of basaltic lava flows is poorly exposed in the southern and central portions of the field area, and constitute the lowest member of the footwall succession. Similar units have been identified south of the Mattabi deposit (Groves, 1984), and form the basal portion of the South Sturgeon Lake assemblage over a wide area. These mafic lava flows, which comprise 30-40% of the rocks in the area, are generally massive and/or porphyritic, with 15 amygdaloidal and pillowed flows locally present. Felsic lava flows and ash tuffs are occasionally observed interlayered with the mafic lavas. Poor exposure limits the determination of lateral extent of these flows, and no contacts were observed. The southernmost exposures have been metamorphosed to amphibolite grade due to intrusion of the Southern Granitic Complex (Trowell, 1983). Massive and porphyritic flows are dominant in the basal two-thirds of the mafic sequence, but poor exposure and lack of diamond drill hole data limit thickness estimates. In outcrop these rocks are dark gray, fine- to medium-grained homogeneous amphibolites which exhibit a pronounced foliation due to the alignment of medium-grained amphibole and biotite. Euhedral plagioclase phenocrysts 1-3 mm in diameter (2-3%) are common. Sparse 1-3 cm wide veins of quartz and chlorite occur throughout the rocks subparallel to the foliation, as well as traces of disseminated pyrite. In thin section, these rocks are composed of 1-3 mm euhedral to subhedral plagioclase phenocrysts (2-5%), which have their long axes subparallel to the foliation. 1-2 mm euhedral to subhedral grains of hornblende (40%) exhibit a subparallel alignment and are set in a matrix composed of fine-grained mosaics of quartz ana plagioclase, with minor disseminated biotite, pyrite, and magnetite. The opaque minerals occur in streaks or lenses parallel to the foliation. 16 Fig. 5- Elliptical pillow lavas from exposures NE of Lac David. Hammer measures 38 cm in length, handle points to NNE topping direction. Pillowed amygdaloidal flows are well exposed over a continuous 100 m section immediately NE of Lac David ( plate 1, back pocket). They can be traced laterally for roughly 300 m. The pillows, 1-4 m wide, vary from elliptical to well-rounded, and are defined by 3-5 cm raised selvedges (Fig.5). Shapes of pillows indicate a consistent NNE topping 17 direction. Individual pillows contain from 30-70% rounded to elongate amygdules (.5-1 cm) which are filled by quartz and chlorite. In thin section the pillow lavas consist of rounded 2-10 mm quartz-chlorite amygdules set in a matrix of very fine- grained quartz and plagioclase with abundant radial sprays of fine-grained actinolite and/or chlorite. Biotite (5-10%), magnetite, epidote, and pyrite are present as accessory phases (Appendix 1). A series of thin amygdaloidal sheet flows overlie the pillow lavas, being exposed over a 20 m section (Fig.6), and are intruded at the top by a 10 m thick mafic sill. Determination of lateral extent of the flows is inhibited by lack of outcrop. Individual flows are 3-5 m thick and exhibit flow tops which consist of 10-50% rounded quartz- filled amygdules in a fine-grained dark green matrix. In outcrop the flows display a rough-ribbed weathered surface, and are cross-cut by numerous thick (20-50 cm) quartz veins at a high angle to strike. In thin section the sheet flows are composed of fine- to medium-grained intergrown quartz and plagioclase (20-30%), with 10-15% disseminated biotite, radial sprays of fine- grained actinolite and chlorite (25%), and, locally, 2-5 mm garnet porphyroblasts (3-5%). Magnetite and epidote are present as accessory phases. Amygdules are filled with fine-grained quartz and chlorite (Fig.7). 18 Fig. 6- Amygdaloidal mafic flow overlying pillowed outcrops NE of Lac David. Lens cap is 56 mm in diameter. Note quartz-chlorite filled amygdules. Field of view is 4x3 mm; plane polarized light. 19 Felsic rocks interlayered within the mafic flows represent <5% of the rocks in the area, and consist of fine- grained lavas and ash-tuffs. Felsic lavas were observed only in one outcrop where they overlie the sheet flows. In outcrop, this unit is pale gray in color which is in stark contrast to the underlying basalts, and it reaches a maximum thickness of 10 m. Lateral extent of this unit could not be determined. The lower and upper contacts of this unit are obscurred by mafic sills. The unit is quartz porphyritic, with small (1 mm) blue quartz phenocrysts (2-3%) randomly distributed in a fine-grained matrix of chloritoid (5-10%) and quartzofeldspathic material. In thin section this rock is composed of 1 mm quartz phenocrysts (2%), anhedral chloritoid (5-10%), and anhedral blebs of pyrite (5-7%) set in a streaky fine-grained matrix of intergrown quartz and plagioclase with minor amounts of fine-grained sericite ( <5%) and chlorite ( <1 %). Felsic ash tuffs outcrop south of Lac Andrew and immediately northeast of Lac David (plate 1). In the Lac Andrew location, the rocks are foliated quartz-porphyritic ash tuffs. Both upper and lower contacts are covered by glacial debris, and lateral extent could not be determined . Here 1 mm euhedral blue quartz phenocrysts (1-2%) and 3-4 mm rounded aphanitic siliceous lapilli (5-10%) are enclosed in a siliceous, fine-grained tan-pink matrix. Thin 1-2 mm quartz-tourmaline veins cut the exposure subparallel to the 20 foliation, and small rectangular pits on the weathered surface suggest weathered-out plagioclase phenocrysts. Outcrops northeast of Lac David appear as thin (1-3 m), fine-grained, siliceous quartz-phyric ash-flow tuffs, with a distinctive pumice-rich 0.5 m-thick zone at the top (Fig.8). Thin section examination shows these rocks to be composed predominantly of very fine-grained quartz and feldspar which encloses euhedral quartz phenocrysts (1-2%), angular siliceous microcrystalline lithic fragments (5-10%), and elliptical 2-10 mm pumice fragments. The pumice fragments are now composed of fine-grained recrystallized quartz. Fine-grained sericite is disseminated throughout the rocks and is locally in 3-5 mm. veinlets which in some cases contain rounded cordierite porphyroblasts. Fine-grained chlorite (<2%) and biotite (<2%) are disseminated throughout the matrix. Similar intercalations of thin felsic horizons within maf ic rocks have been noted 8-10 km west of the study area by Groves (1984), and in the area west of Darkwater Lake by Rog (in prep.). This dominantly mafic sequence is limited to a few exposures in the southern portions of the study area. Highly vesiculated pillowed and sheet flows are at the top of this unit, suggesting a shallow water environment during the waning stages of mafic volcanism within the area. 21 Fig. 8- Pumice(?)-rich top of thin felsic ash-flow tuff unit interlayered within mafic sequence. Lens cap is 56 mm in diameter. 2. CALDERA-RELATED VOLCANIC AND VOLCANICLASTIC UNITS a. Heterolithic Breccia (unit 2, Plate 1) Heterolithic breccia directly overlies the mafic volcanic succession in the western half of the field area. This unit is traceable far beyond the western boundary of the field area and is laterally correlative with similar rocks to the west below the Mattabi deposit (Morton et al., 1988; Walker, in prep.) It has a known thickness of 800 m and may be considerably greater; however, lack of outcrop exposure and drill core intersections in the southwestern portions of the field area prevent verification. Outcrops 22 are restricted to the area immediately west of Lac David. Drill intersections occur along the western boundary near Lyon Creek. In outcrop, poorly-sorted lapilli- to block-sized angular f elsic and maf ic volcanic fragments are randomly distributed in a dark gray-green, fine-grained matrix. Locally a weak foliation is defined by alignment of the long axes of fragments subparallel to the strike, possibly an effect of deformation. Two distinct types of maf ic volcanic fragments are identified in outcrop and drill core (Figs.9 & 10). These are: a) angular dark green massive to amygdaloidal, and b) angular gray-green plagioclase-phyric fragments. Together these two mafic rock types constitute up to 60% of the rock, and are thought to represent fragments of material similar to the underlying rnafic lava flows. In thin section, massive fragments are composed of very fine-grained intergrown chlorite (20%), biotite (20%), quartz (20%), plagioclase (20%), and chlorite-actinolite (10-20%), with opaques present in trace amounts. Amygdules, where present, are filled with fine-grained quartz. Porphyritic fragments consist of 2-4 mm euhedral plagioclase phenocrysts (10-20%), locally glorneroporphyritic, enclosed by a fine-grained matrix of quartz (25%), actinolite (10%), biotite (10%), chlorite (25%) and minor carbonate (Appendix 1). Angular, pale gray to tan felsic lithic fragments up to 5 23 Fig. 9- Large plagioclase-porphyritic block (left) and massive mafic block (right) within hetero- lithic breccia unit. Lens cap is 56 mm in diam. cm in diameter comprise 5-10% of the unit. These fragments are distinctive in outcrop by standing out in positive relief and having distinct color contrasts with the surrounding mafic fragments and matrix (Fig.11). Felsic amygdaloidal fragments are also locally present (3-5%). 24 Fig. 10- Amygdaloidal mafic fragments within breccia unit. Pencil measures 14 cm. Fig. 11- Small felsic lapilli and larger blocks within breccia unit. Lens cap is 56 mm in diameter. 25 In thin section, massive felsic fragments are composed of very fine-grained quartz, whereas amygdaloidal fragments contain 30-50% rounded quartz-filled amygdules set in a matrix of fine-grained quartz and sericite with minor chlorite. In outcrop, the matrix of the breccia, which comprises 20-50% Of the total rock, is composed of coarse ash to small lapilli-sized mafic and felsic fragments. Locally, knots of actinolite (20%) are in raised relief. In thin section, the matrix displays variable amounts of very fine-grained quartz-plagioclase-biotite-chlorite-carbonate with fine- grained sprays of intergrown actinolite-chlorite. Magnetite and pyrite are present in trace amounts (Appendix 1). Lenses of ash-flow tuff are intercalated with the breccia unit within its upper 100-200 m, indicating contemporaneous explosive volcanism and breccia deposition. A northeast-trending structure, (hereafter termed the Lac David fault), marks the eastern limit of the recognized extent of the breccia within the field area (plate 1). The heterolithic nature of the unit, its thickness, intercalations with ash-flow tuff, and its conspicuous absence east of the Lac David fault combine to suggest that it is a collapse breccia. The Lac David fault may thus represent the easterri topographic margin of the Sturgeon Lake caldera. Similar field relations and distributions of caldera-collapse breccias have been documented in the 26 Tertiary San Juan volcanic field in the southwestern U.S. (Lipman, 1976), in the Proterozoic Slave province in the Northwest Territories (Hildebrand, 1984), and in Mesozoic submarine volcanic rocks exposed in the southern Sierra Nevada (Busby-Spera, 1984). b. Quartz Pyroclastic Flow (QPYF) (unit 3, Plate 1) Quartz crystal-rich pyroclastic flows, known locally in the district as the QPYF, are situated immediately above, and intercalated with, the coarse heterolithic breccia. The units represent the first large-volume eruption of felsic material in the footwall succession. These quartz crystal- bearing pyroclastic flow units are laterally extensive, and may be traced from the study area some 22 km westward to the Darkwater property (Rog, in prep.). The stratigraphic position and unique characteristics of this unit make it an excellent marker horizon across the South Sturgeon Lake area. The QPYF crops out north of Lac Charles and is intersected in drill core near Lyon Creek (Plate 1). It comprises roughly 10% of the rocks in the field area and has a maximum thickness of 150 m; however original thickness estimates are hindered by the intrusion of several maf ic sills into the succession. The lower contact is irregular due to intercalations with the heterolithic breccia; the upper contact is sharp as observed in both outcrop and drill 27 i ntersections with overlying ash-flow tuff and debris flow deposits. In outcrop, the QPYF is a pale gray to light green, locally fragment-rich, pyroclastic unit exhibiting a wide variety of primary textural features. These include pumice- rich zones, which locally are reversely graded, pumice and felsic lithic fragment-rich zones, and fine-grained quartz crystal tuffs. The upper 10 m of the QPYF is pumice-rich, with 2-4 cm subangular to subrounded pumice comprising 25- 40% of the rock. The lowermost exposures, east of Lac Charles, are fine-grained crystal tuffs, with 1 mm euhedral bluish quartz phenocrysts (to 3%) set in a fine-grained siliceous matrix. The central portion of the unit is massive, with random lapilli- to block-sized angular siliceous lithic fragments (5-10%) and pumice lapilli (10- 20%) enclosed by a gray fine-grained matrix containing 1 mm bluish quartz phenocrysts (2-3%). Round to elliptical, 3-5 cm wide rusty sulfide blebs are locally present within the crystal tuffs, and thin 2-5 cm quartz-chlorite veins are common and cross-cut the rocks at a high angle to strike. A distinctive 50 m. section of fragment- and crystal-poor ash tuff occurs within the upper parts of the QPYF in the western portion of the field area. This section contains small 1-2 mm subhedral biotite flecks (10-15%) distributed within a fine-grained gray aphyric matrix. Thin section analysis shows the QPYF to be quite 28 distinctive from overlying ash-flow tuffs. Euhedral and broken quartz phenocrysts 0.5-1 mm accross (1-5%) are scattered within a "chunky" fine-grained inequigranular matrix of quartz-feldspar and minor sericite (5%) (Fig.12). Fine-grained biotite (0-5%), and chlorite (5-10%) are ubiquitous and locally define a weak foliation. Stringers, veins, and patches of chlorite (0-10%), chloritoid (0-8%), andalusite (0-2%), cordierite (0-5%), epidote (0-5%), and opaques (0-2%), are locally present (Appendix 1). Pumice-rich portions of the unit display rounded or popcorn-shaped pumice lapilli (10-40%) which vary from 0.5- 1.5 cm in diameter. The pumice fragments have well-preserved 1-2 mm round quartz-filled amygdules (30-50%) enclosed by a fine-grained quartz-chlorite-sericite matrix (Fig.13). Three distinctive types of lithic fragments are observed in thin sections: a) small (3-5 mm) angular fragments of fine-grained, intergrown quartz and chlorite (to 10%); b) angular, 5-10 mm fragments of equigranular fine-grained quartz (5-25%); and c) 3-10 mm equigranular masses of intergrown fine-grained quartz and feldspar with a vague spherulitic radial expression. Mantling of quartz phenocrysts by 0.1 mm rims of very fine-grained ash has been observed locally within the unit. These rims are believed to be layers of wet ash accreted around central crystal cores during hydrovolcanic or phreatomagmatic eruption (Fisher and Schminke, 1984, p.94). 29 Fig. 12- Photomicrograph of QPYF displaying inequi- granular quartz-rich matrix typical of unit. Field of view is 4x3 mm; crossed polars. Fig. 13- Quartz-filled amygdules within pumice fragment in QPYF. Field of view is 4x3 mm; plane polarized light. 30 These armored or accretionary lapilli have been noted within this unit to the west in the footwall of the F-group deposit (Hudak,in prep.). The stratigraphic of the QPYF, the fact that it is intercalated with and overlies a thick collapse breccia, suggests contemporaneous felsic pyroclastic eruptions and foundering of the underlying strata at the beginning stages of formation of the Sturgeon Lake caldera. c. Debris Flow Deposits (Unit 4, Plate 1) A series of massive to bedded debris flow and bedded epiclastic deposits overly the QPYF in several localities within the study area. outcrops of these units are limited to a well-exposed section northeast of Lac Charles. The unit is also intersected in drill core just south of the former mill site, and constitutes roughly 5% of the rocks in the study area. Regional stratigraphic correlation of these deposits has been established to the west as far as the Mattabi footwall, a distance of >8 km (Morton et al., 1988); these units are conspicuously absent east of the Lac David fault. Contacts with both over- and underlying units are sharp, with the deposits reaching a maximum thickness of 55 m in the Sturgeon Lake Mine footwall. The unit thins rapidly westward away from the Lac David fault and is locally absent within the succession, suggesting deposition restricted to paleotopographic lows. 31 A composite section of these deposits was constructed from data obtained through detailed mapping of a series of stripped outcrops at a scale of 1:120 (Plate J, back pocket). This detailed mapping showed that the unit consists of a series of 1-10 m thick heterolithic fragment-rich subunits separated by thin (<1 m) interbedded ash or silty horizons. Individual beds exhibit a wide variability in fragment type, ratios of fragments to matrix, and fragment size; this allows for good stratigraphic correlation over strike lengths of >200 m, despite limited exposure. Based on percentage and composition of fragments, the unit can be roughly divided into three dominant groups. The lowermost group consists of coarse heterolithic fragmental units, which vary from lack internal structure. Individual beds contain angular cherty lithic lapilli-sized clasts (20-50%), angular mafic lapilli (10-20%), and angular to subrounded lapilli- to block-sized pumice fragments (20-30%). The fragments are clast-supported within a matrix (5-30%) composed of fine- grained quartz, biotite, and chlorite (Fig.14). A thin (1 I cm) horizon rich in disseminated pyrite occurs at the contact between these fragment-rich beds and the underlying pumice-rich QPYF. This lower group is overlairi by bedded fragmental deposits which alternate between fine-grained lithic-rich beds and beds which contain up to 25% juvenile pumice bombs. 32 Fi g. 14- Large vesicular pumice block within coar se lower debris flow unit. Pipe measures 1 4 cm. Individual beds range from <1-3 m, with a total thickness of 10 m. The fine-grained beds are composed of coarse ash- to small lapilli-sized felsic and mafic lithic fragments which are tightly packed in a fine-grained, gray-green matrix . Beds are massive, and maintain a uniform thickness where exposed. Bomb-rich beds provide perhaps the most striking outcrops seen throughout the entire field area. Dark green bombs (20-50 cm in diameter), some with distinctive fusiform shapes, are scattered through a fine-grained, gray-green matrix composed dominantly of coarse ash- to small lapilli- sized clasts (Fig.15). Bombs exhibit a 2-5 cm wide, fine- grained rind that envelopes amygdaloidal and/ or v esicular 33 Fig. 15- Cored bomb within bomb-rich deposit . Note Note fragmental nature of matrix and glacial striations. Pencil measures 15 cm. cores. Impact structures, such as sagged bedding, were not observed in the matrix surrounding these bombs. This suggests lateral transport of reworked pumice-rich pyroclastic material . The upper third of these deposits show a marked c hange in character and composition from all of the underlying beds. The uppermost group is composed of a series of thin ( sized dark green matrix (Fig.16). Clasts are both felsic and mafic in composition and make up 25% and 10% of the rock, 34 Fig. 16- Small lapilli in vaguely normally-graded debris flow beds, tops away from viewer. Pipe measures 14 cm. respectively. Thin ( <0.5 m) laminated silty deposits are locally interbedded with the clast-rich beds, and display small-scale normal grading (Fig.17). The thickness of individual beds increases upward, and the unit is capped by a 10 m-thick massive clast-rich bed which has local concentrations of subangular cherty lithic fragments which 35 Fio. 17- Close-up of thinly laminated silty horizon separating clast-rich debris flow deposits Fig. 18- Scattered lapilli set in mafic matrix of upper debris flow unit. Lens cap is 56 mm in diam. 36 exhibit a distinctive bedding alignment (Fig.18). These uppermost units reach a total thickness of 30 m and exhibit sharp contacts with overlying ash-flow tuffs. Thin section examination of the deposits reveals that the predominant fragment type consists of felsic lithic lapilli, with subordinate mafic lithic lapilli and pumiceous lapilli and bombs. Felsic lithic fragments are extremely angular and vary from 0.5-1 cm in diameter and 10-50% in abundance. They are composed of very fine-grained and interlocking mosaic-textured quartz with minor chlorite and sericite. Mafic lapilli appear as angular to subrounded clasts (5-25%) composed of fine-grained chlorite, biotite , and actinolite, which commonly exhibit a fine-grained radial intergrowth of actinolite-chlorite; minor opaques and carbonate are usually present. Pumice clasts invariably contain rounded to elliptical, 2-4 mm quartz-filled amygdules (10-25%) in a matrix of fine-grained inequigranular quartz with minor fine-grained chlorite- biotite-sericite. Pumice bombs, in thin section, exhibit intense hydrothermal alteration, with minor fine-grained quartz dispersed through massive sericite which encloses subhedral chloritoid porphyroblasts and rounded 2-4 mm quartz-filled amygdules. Thin section examination shows the matrix of the depo- sits to be composed of variable amounts of fine-grained quartz and feldspar, fine-grained actinolite-biotite- 37 chlorite, and minor sericite and 0.5-1 mm euhedral and broken quartz phenocrysts are present locally in trace amounts. Carbonate, iron-rich chlorite, chloritoid, garnet, and opaques are present in variable amounts in veins and 2-5 mm patches. The presence of these deposits within the footwall ·succession is believed to represent shedding of debris from major paleotopographic features, such as fault scarps, thought to be related to the foundering of the Sturgeon Lake caldera. Such debris flow deposits, intercalated within large-volume ash-flow tuff successions, are common features associated with active caldera margins (Lipman, 1984; Fisher & Schminke, 1984). d. Mattabi Pyroclastic Deposits (unit 5, Plate 1) The Mattabi pyroclastic flows (Morton et al., 1988), form the thickest volcanic unit within the footwall succession to the sturgeon Lake mine, reaching a maximum thickness of 1 km. These pyroclastic rocks consist of massive to well-bedded quartz-phyric ash-flow tuffs and bedded ash units, with minor intercalated debris flow deposits and thin interbedded sediments. These rocks have been traced laterally nearly 20 km to the west (Rog, in prep.;Morton et al., 1988), and may extend to the eastern boundary of the present study area. Their importance in the localization of massive sulfide mineralization cannot be 38 overstated, as these felsic pyroclastic flows form the immediate host to the Mattabi deposit, and the immediate hangingwall to the F-group deposit (Morton et al., 1988; Hudak, in prep.;Walker, in prep.). The Mattabi pyroclastic flows crop out sporadically within the field area, most notably along Lyon Creek as well as scattered outcrops south of the old mill site and eastward along the northeastern property boundary. Correlation of this unit is facilitated by numerous diamond drill holes throughout the northern third of the field area. The unit underlies roughly 30% of the total area of the present study. Petrologically, least-altered samples of these rocks are rhyolitic to rhyodacitic in composition. Massive quartz-phyric pyroclastic flows outcrop along Lyon Creek and again along the northeastern property boundary. Numerous drill core intersections have shown these to reach a maximum thickness of 150-200 m. Contacts with bedded ash-flow tuff s and bedded ashes range from sharp to gradational over a few meters. In outcrop, the massive pyroclastic flows are gray to buff on fresh surfaces and weather to tan to pale gray. Subvertical foliation, defined by fine-grained sericite and chlorite, is readily discernable. Euhedral to subhedral, 1-2 mm bluish quartz phenocrysts are scattered throughout the rocks (1-2%) along with angular to subrounded, 0.5-2 mm felsic lithic fragments (10%) (Fig.19). Subrounded to 39 Fig. 19- Massive pyroclastic flow of the Mattabi se- ries. Note assorted fragments and crystals. elliptical pumice fragments, 0.5-2 cm in diameter, show little if any sign of deformation or flattening, and constitute 5-15% of the rock. Thin section examination of these massive flow units show 1-2 mm euhedral to subhedral to broken quartz phenocrysts, (1-3%), randomly distributed in a matrix of fine-grained recrystallized quartz with minor sericite and chlorite. Angular to subrounded fine-grained siliceous lithic lapilli, (2-15%), and subrounded pumice lapilli, (5- 10%), some with 0.1-1 mm rounded quartz-filled amygdules, are variably present. Zircon, sphene, and opaques are present in trace amounts. Veinlets and patches of fine- 40 grained chlorite (2-25%), biotite (0-15%), sericite (5-35%), chloritoid (0-10%), carbonate (0-10%), andalusite (0-10%), and cordierite (0-10%), representing various alteration assemblages, are present locally throughout the unit (Appendix 1). The predominant rock types within the Mattabi succession are bedded quartz-phyric ash-flow tuffs, consisting of repetitions of thin normally-graded crystal and/or lithic lapilli-rich beds, from a few meters to lO's of meters in thickness, overlain by bedded ash units (Fig.20). Such units outcrop along Lyon Creek and south of the mill site, and comprise up to 50% of the ash-flow tuffs within the field area (Fig.21). Basal crystal and lithic-rich beds are normally graded, containing 5-20% blue quartz phenocrysts (1-2 mm) and 20-50% angular to subrounded pumice fragments (0.5-2 cm) in a gray fine-grained ashy matrix. Crystals are locally mantled by conspicuous 0.5-1 mm-wide rims of very fine-grained quartz (Fig.22); these are thought to be a devitrification feature from originally glassy fine ash. These crystal- and lithic-rich beds grade upward into thin-bedded ash units which exhibit plane parallel bedding, with individual beds ranging in thickness from a few cm. to 1 m. Small (<0.5 mm) broken quartz phenocryst splinters and chips are locally concentrated (to 3-5%) within these ash units. 41 Fig. 20- Thin crystal- and lapilli-rich beds overlain by bedded ash unit, Mattabi pyroclastic SLM-136-997. to the left. Fig. 21- Outcrop of siliceous Mattabi pyroclastic rock, Lyon Creek. Lens cap is 56 mm in diam. 42 Fig. 22- Intersection of Mattabi pyroclastic unit displaying mantled quartz phenocrysts, SLM- 139-460. Petrographic observation shows these bedded pyroclasti c deposits to consist of quartz crystals, lithic fragments , and pumice fragments, in a fine-grained matrix of recrystallized quartz with minor sericite and chlorite (Figs.23,24). Foliation is defined by alignment of fine micaceous grains. Small-scale normally graded bedding is locally present (Fig.25). Preliminary geochemical evidence indicates a distinct trace-element zonation within the Mattabi pyroclastic rocks. Zircon, yttrium, and niobium grade from high (approx. 800 ppm. Zr) to low (approx. 200 ppm. Zr) values with increasing stratigraphic height. 43 Fig . 23- Photomicrograph of crystal-(right) and fragment-(left) bearing Mattabi pyroclastic unit. Crossed polars; 4x3 mm field of view. Fig. 24- Photomicrograph of fine-grained nature of Mat- tabi ash unit. Crossed polars; 4x3 mm. 44 Fig. 25- Photomicrograph of graded silt-sized quartz chips atop ash unit in Mattabi series . Crossed polars; field of view is 3x4 mm. This zonation is repeated up to 9 times, perhaps indicating specific flow units within the Mattabi sequence (Morton & Franklin,1988). Such geochemical zonation of trace elements within specific flow units is believed to be the result of eruptions from compositionally zoned magma chambers (Hildreth, 1979; Smith, 1979). Further investigations of 45 zonation within the Mattabi pyroclastic sequence is being conducted by Morton (pers. comm., 1988). A coarse, heterolithic debris flow deposit lies within the Mattabi pyroclastic rocks immediately west of the Lac David fault in the center of the field area (Plate 1), reaching a maximum thickness of 65 m in the east and thinning rapidly westward. This distinctive unit is not exposed at the surface but is intersected in three diamond drill holes south of the mill site area. Both upper and lower contacts with the Mattabi pyroclastic flows is sharp. This heterolithic debris flow unit is characterized by a high percentage of lithic fragments supported in a dark green matrix (Fig.26). Fragments typically comprise 25-50% of the rock. Fragment types include 1-2 cm round to subangular felsic lithic lapilli (10-50%), large 2-3 cm angular scoriaceous lapilli (5-20%), and 0.5-2 mm massive or amygdaloidal mafic lithic lapilli (10-25%). Petrographic observation of this unit shows the matrix to be composed of very fine-grained quartz (40-60%), chlorite (5-25%), biotite (5-15%), and sericite (2-5%), with minor carbonate (1-5%) and fine-grained opaques (1-4%) (appendix l); 1-2 mm quartz phenocrysts (0-2%) are observed locally in the matrix. Felsic lithic fragments are composed of fine-grained quartz and/or quartz and carbonate. Mafic lithic fragments are typically composed of intergrown fine-grained quartz-plagioclase-chlorite-actinolite, locally 46 Fig. 26- Coarse debris flow subunit within Mattabi series, SLM-137. Note subrounded fragments. surrounded by a 0.5 mm. rim of fine-grained biotite. Scoriaceous fragments are composed predominantly of fine- grained chlorite with carbonate in irregular patches and amygdules. The presence of this subunit within the Mattabi pyroclastic sequence is similar to small or medium-sized rock falls and rock slides from caldera walls which are locally interlayered with intracaldera fill sequences described from other areas (Lipman, 1976, 1984;Hildebrand, 1984). The Mattabi pyroclastic rocks described above are considered to be subaqueous pyroclastic flow deposits, 47 similar to previously described Archean subaqueous pyroclastic flow deposits in the Wawa region of northwest Ontario (Osterberg, 1981; Nebel, 1982; Morton and Nebel, 1984), the Mesozoic Vandever Mountain tuff within the southern Sierra Nevada of California (Busby-Spera, 1984), the Tertiary Ohanaceposh Fm. in Washington (Fiske, 1963), and the Tokiwa Fm. in Japan (Fiske and Matsuda, 1964). Similarities include: a) a lack of welded features (unflattened pumice lapilli); b) alternating of thin graded crystal- and/or lithic-rich beds with thin-bedded ash deposits; and c) small-scale grading of fine-grained ash units, with local silty lenses concentrated at the bottoms of thin 2-3 cm ash beds. e. "L"-series Pyroclastic Rocks (unit 6, Plate 1) The "L"-series felsic pyroclastic rocks constitute the uppermost felsic volcanic units within the footwall succession of the Sturgeon Lake mine. The unit outcrops in the eastern extremities of the area and along Lyon Creek (Plate 1), and is intersected in drill core across the northern part of the field area. The "L"-series are the host rocks to the mineralization at the Sturgeon Lake mine, and underlie roughly 5% of the area of the present study. This pyroclastic sequence has been traced westward to the Darkwater property (Rog, in prep.), a distance of > 20 km, and forms the immediate hangingwall to the Mattabi deposit 48 (Morton et al., 1988; Walker, in prep.). The unit appears to thin and pinch out rapidly beyond the eastern limits of the field area. The "L"-series rocks consist of quartz- and quartz- plagioclase-phyric massive and bedded ash-flow tuffs and bedded ash units, and are distinguished from the underlying Mattabi sequence by the presence of plagioclase phenocrysts. Thickness estimates within the study area are hindered by a large mafic sill which intrudes and dilates the unit beneath the ore zone. Bedded ash-flow tuffs outcrop along the eastern end of the northern property boundary (Plate 1). Here a well- exposed 50 m stripped section exhibits a sequence of thick- bedded lapilli tuffs and thin-bedded ash-tuff units (Fig.27). Lapilli tuffs range in thickness from 1-10 m with 5-15% elliptical pale gray coarse ash- to lapilli-sized siliceous fragments concentrated in basal sections, becoming relatively fragment-free near the top. The lowermost 2 m of one unit displays a rusty weathered appearance throughout, caused by disseminated pyrite mineralization (Fig.28). Thin section examination reveals 1 mm. euhedral quartz and relatively unaltered 1-2 mm plagioclase phenocrysts in a very fine-grained matrix of quartz (65-75%) and sericite (10-20%), which defines a weak foliation (Fig.29). Chlorite (0-10%), garnet (0-5%), chloritoid (0-2%), carbonate (0-8%), and biotite (2-12%), are variably present as minor constit- 49 Fig. 27- Contact (under field book) between laminated ash unit (above) and lapilli tuff ( below ) of L-series pyroclastic rocks along NE boundary . uents (Appendix 1). Bedded ash units are thin (1-2 m), exhibit plane parallel bedding, and sharp parallel contacts with underlying units (Fig.JO). Their composition is similar to the lapilli tuffs except for absence of fragments and crystals. A distinctive unit within the "L"-series is intersected 50 Fia . 28- Rusty horizon at base of lapilli tuff a l ong NE boundary. Hammer measures 38 cm; tops toward viewer. . .• •' ..f!' ·_y .. • ' .,,. • ; "' ...L ·:-a» · , _· "9' . • ...... ,,. ,. roll .. :#_" • . " • ." -:< .... -: ,_. .:/;; . ·- :-: .ft!...... -!- :.I'• .,,, .• ,.: , _.... ;.i '-" • · ,.. " ,&.' • "- ·• • - ,.-· v· . " • -, .•.• •- . . .;...... , ...... ,._ ) .... :..' - ' . •... " •.• ,. . .,.t:fll:__.,..it-".... ' ' . .. .·. • • ,. - • !...... :. · ' .>'....,1 ':. ·.-t .• • !l 'l-::t(•, ---('.· • ¥\. ..• , ,.,,,,. . : ,.. t. .... ; ...... - .. • 4 ...... , .. .,,... • ..i& , ....,,.. ... • • .. • • ...... • .{. - ..r; "..V . • .. J..'. y ...... : • ,, ..,: , .. •' . ' . . . ;. •,.- ..:.·¥!"'', .,,,. .. ..; . · ...... -· ,... ,._. , • •• ""lt-n...... ,. • ·.·.• >·: . •,...... •• •• r.... •. •,... - ...... :t.-. . ... , .·. '"'• • .• .'I 'fl _• ,a J I • • •' • • ... .4 ...... • .. ., , , . .. ••, tt ....:'fT . ...• '·"· ..., · • • .•• . • "\ y, . • ...... " ..j't!-:. >t•!·# • .• i; ·\_.... • ...... ( • "' \ 11. . ,..-l ' ...... ·- "" ., ...... _..., ·""' 1 ••· . ..-JZ • .,r-• "f,. .• . .-. -.• • • . . 4: . •... ., · • . • •• ' • ..,.. .• . • ...... :-::.--.::-· -..Jr - · ) i..•· . • . . . "' ri.. 1._ ..... ,_.. ..• '\- ' 4..... " :_;. . '·'· .$...... :. .. :.NI-... .. "' .: ..... , -.-. - ;.-· . _.;..,, -. • • .., .. . r "\ .. · ..• '-' ...'( ...- •" ··.· . .. . . • • , ,, • . .. • • ) , , .._II 'tr.• -l.t Jt. ; . . • . • . •• .• . . "'r. • Jr ;.·. "' • l ·1 . '111"4'· • • • •' r • \ .,' ... Ja...... • f • ...,.. • ' ., irrrrr.,...,. • ••.• • • ) .J • .... • ... • •1• .. -' • 1 .. J .-,""'- .• • ,, • • ( 40 :_.-.·· ..f...... ,.)."4'."'J .. , : •. t . .._ .... • • •"' . •, ',.,o .. ·t.,.L ,,,.., ._,.,,_._ ...... Ir' ",. ."'i ,.· • .-· ! ··'· . .. ' .,r.. . ., ' •, • ' • .,_ . ._. , "r,.e•_, .... .:2!...... - .. 'r1 - !I .; ...., , I ,, • · ... ' \ • • ' '· ·• .. ••• '• . ., ..,. \.. • , . .. .. l \ .,...... tl'...... -...... ""' ..... •" i., .. ..,...... ,, ....t · - I •T""',. ... r.. ..k _-:, " " • . . '•.. . • • . ""il!" . ' ... ,. ,.. -.,._ ,.,...... :,,,...... ,,. • .• ... ,...... I: . •.1 ·- .. -. . . .., ...... v. . . . t.....:.A ..... ' "'- ...... Fig. 29- Photomicrograph of plagioclase phenocryst (center) in L-series pyroclastic rock, NE boundary. Crossed polars; view is 4x3 mm. 51 Fig. 30- Thinly-laminated ash beds within L-series outcrop along NE boundary. Lens cap measures 56 mm in diameter. in drill core in the northwestern portion of the field area. It shares the characteristics of the rest of the unit with the exception of larger quartz phenocrysts, ranging from 2-4 mm (Fig.31). This distinction can be used to recognize this unit in the hangingwall stratigraphy of the F-group deposit 15 km to the west (Hudak, in prep), but lack of further exposure and/or drill core intersection of this subunit within the Sturgeon Lake mine footwall precludes its usefulness as a marker horizon in the present study. A maximum thickness of 10-15 m is observed. The distinct compositional difference between the "L"- 52 Fig. 31- Photomicrograph of large quartz and plag- ioclase phenocrysts in L-series subunit. Field of view is 4x3 mm; crossed polars. series pyroclastic rocks and the underlying Mattabi sequence indicates that these flows are either frqm separate_ magmatic sources, or the result of evolutionary changes in the same parent magma. Field evidence favors the latter; the two units are, for the most part, in direct conformable contact over their entire strike length, save for thin wedges of epiclastic material and thin lava flows locally occurring west of the field area near the Mattabi mine (Morton et al., 1988). The widespread areal distribution of these "L"-series rocks, extending beyond the eastern topographic margins of the sturgeon Lake caldera, suggest that they constitute a major portion of the outflow facies of pyroclastic rocks as well as part of the intracaldera fill. 53 3. POST-CALDERA VOLCANIC AND INTRUSIVE ROCKS a. Mafic to Intermediate Flows (Unit 7, Plate 1) A series of massive to amygdaloidal lava flows are intersected in drill core at the northernmost edge of the field area. Lack of outcrop exposure of these flows within the sturgeon Lake mine succession prevents determination of field relations with the underlying units. Compositionally similar pillowed flows overlie the L-series pyroclastic rocks in the hangingwall to the Mattabi deposit to the west, and have been correlated in drill core along strike in the area between the two deposits (Morton et al., 1988). The flows are thin (5-10 m), dark green and fine grained, with thin 1 m zones of 2-4 mm. rounded quartz- and/or carbonate- filled amygdules near flow tops. In thin section these flows consist of a fine-grained, streaky, foliated matrix of quartz and plagioclase (50-70%), with fine-grained disseminated biotite (5-10%), chlorite (10-25%), actinolite (3-5%), and scattered fine-grained opaques (Appendix 1). Amygdules are rounded to elliptical, 1-4 mm in diameter, and are filled with fine-grained quartz and/or carbonate. These flows signal the end of felsic volcanism within this particular cycle of the South Sturgeon Lake assemblage. The flows constitute the immediate hangingwall to the sturgeon Lake deposit (Severin, 1982). Their lateral extent was not determined eastward from the present study area. 54 b. Mafic Intrusive Rocks (units 8,9, Plate .1) Two prominent maf ic sills intrude the volcanic stratigraphy in the Sturgeon Lake footwall succession. These intrusive bodies are similar in composition, shape, size, and attitude, and, compared to the volcanic units, are fairly well exposed in outcrop. Together they comprise 20- 30% of ·the rocks within the footwall succession. Individually these intrusions reach a maximum thickness of 300-400 m, and are slightly discordant to the volcanic stratigraphy. They are separated by approximately 700-800 m of extrusive and epiclastic volcanic rocks. The southernmost intrusion, referred to as the "marker andesite" by Friske (1983), intrudes the heterolithic breccia and QPYF units above the northern edge of Lac Charles. The unit outcrops in this area, along Lyon Creek, and just south of the northeastern property boundary, and is intersected in drill core all along the southern edge of the mill site area. The extent of the unit westward beyond the limits of the study area is uncertain, though preliminary field evidence indicates continuation along strike for 1100 m (Morton, pers. comm.). This intrusive body was used as a shut-down rock in which to end diamond drilling in the southern tier of holes drilled by Sturgeon Lake Mines. The unit reaches a maximum thickness of 300 m within the study area and, petrologically, is quartz-gabbroic to quartz- dioritic in composition. 55 In outcrop, the unit is distinctive in its massive , homogeneous, dark green, fine-grained to aphanitic character. It also has an irregular network of thin 1-2 cm raised veinlets of chlorite-quartz, providing a coarse ribbed appearance. Contacts with over- and underlying units are sharp, with chilled margins as thick as 3-5 m common. Thin section examination shows fine-grained euhedral to subhedral hornblende (20-40%) and fine-grained anhedral quartz "plates" (5-10%) in a matrix of fine-grained plagioclase (8-25%), quartz (20-30%), biotite (10-25%),and chlorite (0-10%), with minor magnetite (appendix 1). Within massive outcrops, swirls and trains of 2-5 mm subhedral garnets locally reach 5-10%of the rock, and patches and veinlets of fine-grained carbonate are common. The northernmost of the two intrusions has been ref erred to as the "footwall intrusion" by Severin (1982). It outcrops in the central portion of the mill site area and is intersected in numerous drill holes beneath the ore zone. This unit gave a high magnetic relief signature in the early aeromagnetic surveys conducted over the area in 1969 (Franklin et al., 1977). Within the present study area this intrusive body reaches a maximum thickness of 400 m, and has been traced westward a distance of over 2 km, maintaining a fairly uniform thickness throughout (Morton and Hudak, pers. comm.). In outcrop the unit displays a uniform, homogeneous, dark green fine-grained appearance (Fig.32). Textural 56 variations observed within drill core of this unit include local coarsening of grain size and local concentrations of amphiboles. In thin section, fine- to medium-grained subhedral hornblende phenocrysts (10-40%), fine-grained subhedral plagioclase phenocrysts (0-10%), and fine-grained anhedral quartz "plates" (5-15%) are enclosed in an equigranular fine-grained groundmass of plagioclase (10- 20%), quartz (20-30%), biotite (10-20%), and chlorite (0- 10%), with minor magnetite (Appendix 1). Patches and veinlets of fine-grained carbonate are commonly distributed throughout the rock. Thin, 0.5-1 m mafic dikes are present throughout the study area in both outcrop and drill core, cross-cutting the stratigraphy at varying angles to strike. These are fine- grained to aphanitic, dark green to black, with chilled margins of a few cm in width noted locally (Fig.33). These thin dikes are possibly related to the larger intrusive bodies, both spatially and compositionally, and are widespread throughout the field area. 57 Fig. 32- Outcrop of massive dioritic intrusion 200 m south of Field book for scale. Fig. 33- Thin mafic dike cross-cutting L-series tuffs, NE boundary. Note chilled margins. Lens cap is 56 mm in 58 C. VOLCANIC INTERPRETATION The rocks studied within the thesis area record an interesting and often violent geologic history of this small portion of the Savant-Sturgeon Lake greenstone belt. Volcanic eruption styles range from quiet effusion of basaltic lava to tremendous explosive silicic volcanism related to caldera collapse. Field and petrographic evidence point to the units within the Sturgeon Lake mine footwall playing a major role in the formation of the Sturgeon Lake caldera complex. The lowermost volcanic units within the study area are dominantly mafic flows which are laterally extensive and form the base of the South Sturgeon Lake assemblage (Franklin,1981; Severin,1982). These flows proceeded to construct a large mafic edifice, probably a shield volcano, with minor intermittent felsic volcanism producing small- volume lava flows and ash-tuffs. A considerable volume of felsic volcanics 20 km. west of the study area, the Sackpot Lake succession (Morton et al., 1988; Rog, in prep.) probably contributed to the interlayered felsics within the mafic sequence. Mafic volcanism ceased temporarily after the deposition of the shallow-water pillowed flows and thin amygdaloidal sheet flows observed immediately northeast of Lac David. An abrupt change in eruptive styles and composition 59 follows the dominantly mafic volcanism, with the eruption of the QPYF pyroclastic rocks and contemporaneous beginnings of collapse of the Sturgeon Lake caldera to produce the interlayered breccias and ash-flow tuffs. Blocks of the underlying mafic and felsic volcanic material within the breccia unit, and intercalations of ash-flow tuff within the breccia, attest to the contemporaneous eruption and collapse, similar to that documented in the San Juan volcanic field of the southwestern U.S. (Lipman, 1976,1984), and in the Wopmay orogen region of the Slave province in the Northwest Territories (Hildebrand, 1984). Debris flows and bedded epiclastic deposits follow the eruption of the QPYF, originating from oversteepened fault scarps related to caldera subsidence. The Lac David fault is representative of such a structure within the study area. The bedded and graded nature of the uppermost debris flow horizons possibly signals a vertical transition to a dominantly subaqueous environment with continued caldera subsidence. Local absence of debris flow material indicates topographic control of its deposition, with absence in areas of elevated topography. Large-volume ash-flow tuffs of the Mattabi sequence were subsequently erupted and deposited upon the debris flow deposits and underlying units in a dominantly subaqueous environment within the caldera. Evidence for subaqueous deposition includes; a) absence of welded textures despite 60 substantial thickness of the deposits; b) thin repeating graded crystal-lithic and ash units; c) thin graded sedimentary horizons within the pyroclastic sequence; and d) a large massive sulfide deposit located 8 km west of the study area within these rocks (Mattabi). Subsidence along caldera margins continued, as evidenced by the interlayered debris flow wedges which thin rapidly westward away from the Lac David fault. Volcanism ceased for a short(?) period following the deposition of the Mattabi sequence. This quiescent period is indicated by thin epiclastic rocks atop the Mattabi pyroclastic rocks west of the study area (Morton et al., 1988; Walker, in prep.). Explosive volcanic activity resumed with eruption of the L-series quartz- and plagioclase-phyric pyroclastic sequence which was deposited as widespread ash- flow sheets, filling in and flowing out over the existing caldera margins. Near the end of this pyroclastic episode, hydrothermal activity increased within the study area and the Sturgeon Lake massive sulfide deposit was formed. Final volcanic activity within the field area includes the subaqueous extrusion of maf ic to intermediate lava flows which cap the sequence and immediately overlie the orebody. Subsequent intrusion by mafic sills and dikes complete the stratigraphy. Field and petrographic evidence such as cross- cutting relationships and chilled margins of sills and dikes indicates a late emplacement. 61 D. Mlo. SSTVE SULFIDE OREBODY The Sturgeon Lake massive sulfide deposit produced 2.1 m.t. of high-grade Zn-Cu-Pb-Ag-Au ore during the life of the mine from 1974 to 1980. To better understand the nature of the ore, 20 polished sections were analyzed from DDH# SLM- 156 (Fig. 34) which intersected significant massive sulfide mineralization. Modal mineralogy from these sections is presented in Appendix 3. The orebody has been described as a lens of massive sulfide mineralization with an underlying stringer zone (Severin, 1982). Pyrite (0-65%) is the dominant sulfide mineral present, with lesser amounts of sphalerite (0-40%), chalcopyrite (0-50%), and minor pyrrhotite, galena, arseno- pyrite, and magnetite. Pyrite occurs chiefly as aggregates of blocky euhedral grains. Sphalerite is massive and locally contains minute chalcopyrite exsolutions. Chalcopyrite occurs as massive blebs, veinlets, and locally as fracture- fillings in pyrite and sphalerite. Galena and arsenopyrite are minor constituents of sphalerite-rich ore, occurring as discrete euhedral grains, while pyrrhotite is closely associated with chalcopyrite as rounded anhedral blebs. Magnetite is seen as rounded poikilitic grains with numerous tiny pyrite and chalcopyrite inclusions. These ore minerals display a zoning pattern character- istic of proximal volcanogenic massive sulfides (Franklin 62 SURFACE ELEVATION O' . .•: ·.· 'I ' TOPPING ... .\' --,_ __ _ • I . , \ MASSIVE . . \ . ' SULFIDES ..· ' ,\ . .... __ ...... _ ··-: • . . ;., . \ / . •\ .. _.....,.. ... ' .' / . STRINGER ORE SLM-156 500' z z 0 0 0 0 0 U) 0 0 0 100 I I FEET SECTION 1 0000 EAST Fig. 34- Vertical N-S section through orebody, looking west, showing location of DOH # SLM-156 (from Minnova,Inc. unpublished 1980). 63 et al . ! 1981; Lydon,1988), exhibiting an increase in the Zn/Zn+Cu ratio with increasing stratigraphic height. This is illustrated for the Sturgeon Lake deposit in Fig. 35. Pyrite and sphalerite are most abundant in the upper portions of the ore lens as bedded or layered ore, with chalcopyrite and pyrrhotite increasing with depth (Fig. 36). The lowermost ore, the underlying stringer zone, is dominantly composed of chalcopyrite. Recent seafloor studies and experimental work have shown the zonation typical of volcanogenic massive sulfide deposits to be due to progressive cooling and evolution of the ore solutions, due in turn to the relative solubilities of chalcopyrite and sphalerite as a function of temperature (Lydon, 1988). Early precipitation of sphalerite and pyrite forms a blanket which further insulates the hotter ore solutions below, enabling precipitation of chalcopyrite. Within the Sturgeon Lake deposit, this copper-rich fluid is seen locally to break through the overlying sphalerite- pyrite ore (Severin, 1982). The zonation of ore minerals, the presence of a stringer zone beneath the massive ore, and the height-width ratio of the deposit all support the suggestion that the Sturgeon Lake massive sulfide orebody is a proximal deposit. The ore lens formed directly over its own hydrothermal feeder conduit, with little if any transport of the ore away from the vent area. 64 0 I \ \ \ 40 --- -- CHALCOPYRITE --- . ,...... -- ::;.. - ·------SPHALERITE '-.-'--- ...... -- - --...... >- ...... -... 0 ...... 0 80 ...... m w 0:::: 0 -... --- ...... z ' 120 ' '-. I I- ., CL w ' 0 ' I _J I <( --- u 160 ( -· - I- \ 0:::: w > " " " \ 200 ' '' 240 0 20 40 60 80 100 i\.10DAL % Fig. 35- Graph showing zonation of sphalerite vs. chal- copyrite in orebody. Data from Appendix 3. 65 0 \ I \ '- - .. __ _ 40 --- -::. __ PYRITE ,...... PYRRHOTITE-- _..------;.- >- 0 0 80 Cl w ;. a:: 0 ---- - '("--· - z ' 120 I --- I- CL w 0 _J <{ u 160 I-a:: w > 200 240 0 20 40 60 80 100 NORMALIZED MODAL ·: MINERALOGY Fig. 36- Graph showing zonation of Fe-sulfides with depth in orebody. Data from Appendix 3. 66 III. HYDROTHERMAL ALTERATION I. INTRODUCTTON Volcanic and volcaniclastic rocks within the study area have undergone variable amounts of hydrothermal alteration, as well as regional greenschist to lower amphibolite facies metamorphism (Trowell, 1983; Severin, 1982). Sericite, chlorite, carbonate, cordierite, chloritoid, biotite, aluminum silicates (andalusite, kyanite), and garnet occur in modal abundances too high to be explained by original igneous chemical compositions. These abnormal abundances (Appendix 1), coupled with textural and other geochemical evidence, have led to the identification of mineral assemblages which are believed to represent distinct zones of original hydrothermal (metasomatic) alteration. These assemblages can be classified on the basis of their modal mineralogy and are named to reflect the most abundant alteration mineral present, including; a) silicified (quartz-rich); b) iron-chlorite; c) chloritoid; d) cordier- ite; e) aluminum silicate; f) sericite; and g) magnesium chlorite assemblages. Note that all present mineral assem- blages result from regional metamorphism of rocks which had been hydrothermally altered to varying degrees. Following is a description of each assemblage as observed in outcrop, drill core, and thin section, along with a brief discussion of their distributions throughout the study area. 67 II. ALTERATION ASSEMBLAGES 1.SILICIFIED ASSEMBLAGE Silicif ied rocks form a broad semiconformable zone which extends throughout the felsic pyroclastic rocks of the Mattabi and "L" successions (Plate 2). It reaches a thickness of 1500-2000 feet and has a strike length extending the full width of the study area. SilicifLed rocks are locally cross-cut by chloritoid- and chlorite-rich rocks, and grade laterally into sericite- or cordierite-rich rocks. Rocks are considered to have been silicified if they have an Si02 content of greater than 77 wt.%, 10-20% higher than typical values reported from intracaldera ash-flow tuff from more than 50 caldera systems summarized by Lipman (1984). Silicified rocks are light gray to buff in color (Fig.37), and in thin section are composed of quartz (70- 80%) and sericite (5-15%), with minor chlorite, biotite, and carbonate. Chloritoid, cordierite, and aluminum silicates (andalusite and kyanite) may also be present in minor amounts (Appendix 1). Lithic and pumice fragments are composed primarily of fine-grained mosaics of quartz, and thin 1 mm. quartz veins are locally present. 2.IRON-CHLORITE ASSEMBLAGE (iron-chlorite,quartz +/- iron- carbonate,garnet,biotite,magnetite,sericite) This assemblage occurs within all of the stratigraphic units in the northernmost part of the field area, and is 68 Fig . 37- Outcrop of silicified L-series pyroclastic flow deposit, SLJ-13, in northeastern corner of field area. found as isolated stringers within the lower units of the footwall succession (Plate 2). Iron-chlorite occurs as thin veins, a few cm to meters in width, which cross-cut stratigraphy, and thin conformable zones 2-3 m in width and lO's of meters in lateral extent. Contacts between iron- chlorite-rich and other assemblages are generally sharp, although locally iron-chlorite rich rocks may grade into silicified rocks. Iron-chlorite rich rocks are easily identified in hand specimen, because massive dark-green chlorite, pink garnet, and rusty-stained iron-carbnate veins and patches replace the original rock (Fig.38). Fine-grained euhedral magnetite 69 and minor pyrrhotite and pyrite may also be present in varying amounts. In thin section iron-chlorite (5-50%) occurs in discrete veinlets, as well as patches and disseminations throughout the host rock (Figs.39-40). Garnet (0-10%) occurs as subhedral 1-10 mm porphyroblasts, as ragged anhedral patches, and as stringers flanking chlorite-rich veins. Veinlets and patches of iron-carbonate (0-25%) are developed within chlorite-rich veins. Magnetite porphyroblasts (0-10%) are locally well developed within the chlorite-carbonate veins and patches, whereas sericite (0-20%), biotite (0- 10%), and pyrite or pyrrhotite (0-5%) may be present in varying amounts. Quartz is ubiquitous as a fine-grained component of the matrix. Fig. 38- Drill core intersection of Fe-chlorite alter- ation in Mattabi series pyroclastic deposits. 70 Fig. 39- Photomicrograph showing Fe-chlorite alter- ation with associated garnet and carbon- ate. Plane polarized light; view is 4x3 mm. Note strong pleochroism in chlorite. Fia. 40- Photomicrograph showing typical dark blue interference colors of Fe-chlorite. 71 3 . CHLORITOID ASSEMBLAGE (chloritoid,quartz +/ - iron- chlorite,biotite,sericite,garnet) Chloritoid-rich rocks form two distinct zones within the footwall succession, and may also occur as isolated patches elsewhere within the field area (Plate 2). The northernmost zone is located within the Mattabi pyroclastic flow deposits east of the former mill site; here chloritoid is developed in thin mm to cm scale veinlets within sericitic or silicified rocks in a north-trending linear zone which is approximately 150 m in thickness. The southern zone is within the debris flow deposits west of the Lac David fault and has a strike length of 100-200 m. Chloritoid-rich rocks grade laterally into silicified, sericitic, or cordierite-rich rocks. Rocks which contain chloritoid are pale- to dark-green in color, with chloritoid visible as small 1 mm porphyro- blasts with characteristic square cross-sections. Thin section examination shows that chloritoid occurs in two different habits: a) euhedral 1-2mm porphyroblasts in veins within quartz- or sericite-rich rocks (Fig.42); and b) thin ragged veinlets with iron-chlorite within sericite-rich rocks (Fig.41). Fine-grained quartz (40-75%) is ubiquitous as a component of the matrix whereas fine-grained iron- chlori te (0-25%), sericite (0-30%), biotite (0-10%), garnet (0-5%), and pyrite or pyrrhotite (0-5%) may be present. 72 Fig. 41- Photomicrograph of thin chloritoid vein within Mattabi pyroclastic rock, SLM-175-893. Pl ane polarized light; field of view is 4x3 mm. Fig. 42- Photomicrograph of lath-like chloritoid within sericitic debris flow matrix, SLJ-101. Crossed polarizers; field of view is 4x3 mm. 73 4.CORDIERITE ASSEMBLAGE (cordierite,chlorite,biotite,quartz +/-sericite,epidote,ilmenite,tourmaline) This alteration assemblage occurs throughout the felsic rocks of the footwall succession, and is particularly well developed in a stratabound zone extending the width of the field area within the lower portions of the Mattabi pyroclastic flow deposits (Plate 2). Cordierite-rich rocks grade outward into sericite-rich or Mg-chlorite-rich rocks. Cordierite-rich rocks are pale grey to dark green in color, with cordierite visible in hand specimen as pale 1-2 mm spots occurring in veinlets of a few mm to a few cm in width (Fig. 43). Biotite is locally visible as dark veinlets and patches flanking cordierite-rich veins. In thin section, cordierite (5-35%) occurs as discrete, rounded 1-2 mm porphyroblasts_and displaying characteristic flame-like sector twinning and low interference colors (Fig. 44), and as vague inclusion-filled patches within the matrix of the rock (Fig. 45). Quartz (45- 75%) is ubiquitous as a fine-grained component of the matrix. Biotite (2-30%) and Mg-rich chlorite (2-25%) are essential components of this assemblage, occurring as fine- grained patches and disseminations. Sericite (0-30%) is present in varying amounts, locally enclosing euhedral cordierite porphyroblasts. Ilmenite (0-3%) occurs as thin spindly grains concentrated within patches of cordierite, and locally, fine-grained tourmaline (0-10%) (Fig. 46). 74 Fig. 43- Cordierite porphyroblasts developed within Mattabi pyroclastic rock, DDH# SLM-140-260. Fig. 44- Photomicrograph of cordierite within sericite, SLM-136-477. Field of view is 4x3 mm; crossed polarizers. 75 Fi g. 45- Cordierite patches within quartz-phyric Mattabi pyroclastic rock, SLM-134-340. Field of view is 4x3 mm; crossed polars. Fig. 46- Photomicrograph of cordierite (gray) with tourmaline, SLM-140-263. Field of view is 4x3 mm; crossed polarizers. 76 5 . ALUMitDJM-SILICATE ASSEMBLAGE (andalusite/kyanite,sericite, quartz +/- chlorite) Rocks of this assemblage form three distinct stratiform zones within the Mattabi pyroclastic flow deposits. These narrow zones, 10-30 m in thickness and 100-400 m in strike length, occur within a) the lower portion of the Mattabi series rocks on the west side of the Lac David fault; b) the lower section of the caldera outflow pyroclastic rocks east of the Lac David fault; and c) the northernmost parts of the Mattabi succession immediately south of the maf ic sill in the vicinity of the former mill site (Plate 2). Aluminum-silicate assemblage rocks cross-cut silicif ied rocks, and are themselves cross-cut by sericitic or cordierite-rich rocks. In hand specimen, it is difficult to distinguish anhedral andalusite from ovoid or rounded cordierite porphyroblasts; the matrix material to each is very similar as well. In outcrop, aluminum-silicate-rich rocks are fine- grained and pale gray in color, with pale gray-white porphyroblasts of andalusite locally present (Fig. 47). Thin section examination reveals 1-5 mm inclusion-filled andalusite porphyroblasts (2-25%) which occur within thin patches and stringers (Fig. 48). Sericite (5-30%) and quartz (50-75%) are essential constituents of this assemblage, whereas fine-grained chlorite (0-10%), biotite (0-10%), epidote (0-2%), and opaques (0-1%) are scattered throughout 77 t h e matrix in varying amounts. Kyanite (0-3%), in subhedral 0.5-1 mm porphyroblasts, is locally present. 6.SERICITE ASSEMBLAGE (sericite,quartz +/-biotite, chlorite,carbonate,ilmenite,epidote/zoisite) Sericite-rich rocks are widespread throughout the felsic pyroclastic rocks of the Sturgeon Lake Mine footwall succession, occurring in discontinuous patches and zones on a scale of lO's of meters at various stratigraphic intervals (Plate 2). Rocks displaying this assemblage are yellow-tan to pale green-gray in color and commonly exhibit a well- developed foliation and phyllitic partings. Rocks of this assemblage grade laterally into chloritic, silicified, or cordierite-rich rocks. Sericite (15-40%) is the dominant alteration mineral, occurring in very fine-grained wispy veinlets, patches, and massive veins (Fig. 49). Quartz (55-75%) is an essential constituent; other minerals present include chlorite (0- 20%), chloritoid (0-5%), and carbonate (calcite/dolomite? ) (0-5%). Fine-grained anhedral biotite (0-30%) and epidote/zoisite (0-2%) may be present along margins of thick sericitic veins. Thin spindly rods of ilmenite may occur in trace amounts within thick sericitic veins (Fig. 50). 78 Fi g. 47- Outcrop of Mattabi pyroclastic rock showing pale gray andalusite porphyroblasts, SLJ-3A. Fig. 48- Inclusion-filled andalusite porphyroblasts, SLM-140-287. Field of view is 4x3 mm; crossed polarizers. 79 Fig. 49- Wispy sericitic vein within ash-rich Mattabi pyroclastic rock, SLM-173-500. Field of view is 4x3 mm; crossed polarizers. Fig. 50- Photomicrograph of a fine-grained sericite vein with ilmenite (opaque) in vein center, SLM-163-394. 4x3 mm field; crossed polars. 80 7.MG-CHLORITE ASSEMBLAGE (Mg-rich chlorite,quartz +/- biotite,sericite,cordierite,carbonate) Rocks of this assemblage occur as discontinuous patches (up to lO's of meters in length and width) within the lower Mattabi f elsic pyroclastic rocks of the footwall succession (Plate 2). Although Mg-rich chlorite is found in minor amounts within other alteration assemblages, only rarely is it abundant enough to comprise the dominant alteration mineral of any given area. Rocks of this assemblage display a dark green to mottled green color, depending on alteration intensity. Mg-chlorite alteration grades laterally into cordierite- or sericite-rich rocks. Mg-rich chlorite is distinguished from Fe-rich chlorite primarily on the basis of optical properties, such as pale pleochroism and· green to brown interference colors (Hey, 1954; Deer et al., 1966), and whole-rock geochemical analyses (Appendix 2). Mg-rich chlorite (15-30%) occurs as fine-grained disseminations, networks of thin veinlets, and diffuse patches. Quartz (50-75%) is invariably present as a fine-grained component of the matrix, and locally as thin veinlets. Other minerals present may include biotite (0- 10%), sericite (0-10%), cordierite (0-5%), and patches of fine-grained carbonate (0-5%). 81 III. DISTRIBUTION OF ALTERATION ASSEMBLAGES The spatial distribution of the various alteration assemblages is shown on Plate 2. It should be noted that the zones indicated on this plate are generalized, and are not intended to exclude local variations where more than one assemblage may be present within the same outcrop. The distribution exhibits similarities to alteration zone geometries of other Mattabi-type massive sulfide deposits (Morton & Franklin, 1987), in which alteration is over broad semiconformable areas with ill-defined proximal alteration pipes. Both iron-chlorite and chloritoid alteration zones show cross-cutting relationships with respect to the other alteration types. Silicified, sericite, and cordierite assemblages are, in a general sense, stratiform and of considerable lateral extent. Aluminum silicate alteration displays a stratiform distribution as well, but on a significantly smaller scale. Silicif ied rocks form a broad semiconformable zone which extends throughout the thickness of the Mattabi and "L" series pyroclastic rocks, and has also been noted near the top of the succession in the vicinity of the orebody (Severin, 1982). The silicification seems to have occurred at the earliest stages of alteration, as other assemblages (Fe-chlorite, chloritoid) cross-cut the silicified rocks. Fe-chlorite alteration, as noted previously, is well- 82 developed in the northwestern portions of the study area, and occurs in veins and stringers elsewhere within the footwall succession. The absence of a wide areal distribution of this assemblage, and its restriction to veins and fracture fillings suggest a structural (fracture permeability) control on the distribution. Similarly, chloritoid-bearing rocks are restricted to zones within the footwall succession which cross-cut stratigraphy, especially just east of the former mill site. In contrast, cordierite is widespread within the lower portion of the Mattabi succession, and extends the entire width of the field area. The apparent stratigraphic control of cordierite suggests that its distribution is related to the original permeability of the host felsic pyroclastic rocks, with cordierite development controlled by the pre- metamorphic bulk composition of the altered rock. Aluminum silicates are noted within narrow stratiform zones within the lower section of the Mattabi pyroclastic flow sequence flanking the Lac David fault. Highly aluminous assemblages such as this are possibly indicative of leaching of original constituents of the rocks (Valliant et al., 1983; Vernon et al., 1987). These zones may represent fluid channelways and/or discharge areas for evolved ore bearing solutions (Morton & Franklin, 1987). Sericite-altered rocks occur in relatively widespread but discontinuous zones at various stratigraphic intervals 83 throughout the f elsic pyroclastic rocks of the f ootwall succession. Pervasive sericitization is well-developed within the central section of the Mattabi series rocks in the vicinity of the former mill site, the western boundary of the field area, and in the "L" series rocks in the vicinity of the orebody. The widespread areal extent of this assemblage suggests that its distribution is related to the original permeability of the host rocks, noted in similar Archean felsic pyroclastic units in Wawa (Morton & Nebel, 1984) and at the Onaman River (Osterberg, 1985) area of the Geraldton-Beardmore district of northwest Ontario. Mg-rich chlorite alteration is the least widespread of the alteration assemblages recognized. This assemblage is most prevalent in the lower sections of the Mattabi pyroclastic flow deposits south of the former mill site, occurring as thin discontinuous patches of small extent. As noted earlier, Mg-chlorite is present in minor amounts within sericite- and cordierite-rich rocks. The alteration in the footwall rocks beneath the Sturgeon Lake massive sulfide deposit differs substantially from that observed beneath the Mattabi deposit 8 km to the west by the notable lack of widespread distribution of carbonates (Groves, 1984; Groves et al., 1988). Carbonates occur locally within the field area, but are of minimal extent, usually being found as late thin carbonate veinlets or minor constituents of other alteration assemblages. The 84 lack of carbonates in this area is problematical, as the lithologies between the two deposits correlate well over a strike distance of 8 km. The Lyon Lake and Creek Zone deposits occupy a stratigraphic position roughly 500 m above the study area which is carbonate-poor. Fe-carbonate is enriched within the immediate footwall of these deposits (Harvey & Hinzer, 1981). It is possible that the hydrothermal fluids related to the oveilying orebodies were responsible for decarbonatization beneath the Sturgeon Lake deposit. Quite possibly the Mattabi deposit (and rocks further to the west) did not undergo the effects of this second major ore-forming hydrothermal event. The implication drawn by this hypothesis is that the Sturgeon Lake Mine footwall rocks display the effects of two major hydrothermal events. IV. EFFECTS OF METAMORPHISM The Sturgeon Lake Mine footwall succession offers an opportunity to study the effects of regional metamorphism on rocks of altered compositions. Altered felsic rocks locally contain abundant quartz, sericite, chlorite, biotite, and minor chloritoid, aluminum silicates,and carbonate; altered mafic rocks are composed primarily of plagioclase, chlorite, actinolite, epidote, and quartz (Appendix 1). For the most part, these assemblages fall somewhere within the range of greenschist facies metamorphism (Winkler, 1979, p.82). 85 However, locally abundant cordierite and garnet, along with isolated occurrences of staurolite, require further consideration of metamorphic grade. Cordierite formation has been regarded as a key indicator of the beginning of medium-grade metamorphism for rocks of pelitic composition (Winkler, 1979, p.80), whose bulk compositions the altered felsic volcanic rocks of the area most closely approximate. Common metamorphic reactions leading to the formation of cordierite are as follows: (1) chlorite + muscovite + qtz = cordierite + biotite + aluminum-silicate + vapor (Winkler, 1979, p.224) This reaction takes place at temperatures of 490- 550 0 c and pressures of 0.5-4 kb, provided the MgO/MgO+FeO ratio of the chlorite is >0.25. If this ratio is lower, staurolite will form instead of cordierite. (2) chlorite + aluminum-silicate + quartz = cordierite + vapor (Schreyer, 1976, p.372) at temperatures of 400-500 0 C, and pressures of 0.3-2 kb, and (3) chlorite + muscovite + quartz = cordierite + biotite + vapor (Schreyer, 1976, p.372) 86 at temperatures of 470-540°C and pressures of 0.5- 2 kb. These three reactions are with evidence from experimental work by Hess (1969) showing a first appearance of cordierite in muscovite(sericite)- and quartz-bearing pelitic rocks at temperatures of 450-500°C and pressures of 1-4 kb. Figure 51 is a graph showing the relative MgO/MgO+FeO ratio among the altered pyroclastic rocks of the study area. Average compositions of the cordierite assemblage rocks have an MgO/MgO+FeO value of approximately 0.40. Assuming that whole-rock MgO/MgO+FeO values approximate those of the chlorites within those samples, the conditions necessary for cordierite formation from reaction (1) have been satisfied. Note also that the only alteration within the study area with an appropriate MgO/MgO+FeO ratio for staurolite formation is that of the chloritoid assemblage. The presence of biotite as a common constituent of cordierite-rich rocks is further evidence of reactions (1) and (3) as possible cordierite-forming reactions within the study area. Lack of the coexistence of aluminum-silicates and cordierite, however, is a problem, leaving reactions (2) and (3) above as most likely for the cordierite-forming conditions in the study area. Reaction (3) becomes suspect when the abundant examples of coexisting chlorite-sericite-quartz without cordierite 87 are examined. Petrographic evidence exists for these reac- tants to have formed biotite (Fig.52), from the reaction: (4) chlorite + sericite = biotite + Al-rich chlorite + quartz (Turner,1948) This would suggest that reaction (2) perhaps played a more significant role in the formation of cordierite in the study area, dependent on the pre-existence of an aluminum silicate phase (pyrophyllite, kaolinite) throughout much of the Mattabi series rocks. Stanton (1984) gives evidence for the derivation of cordierite from similar altered felsic volcanic rocks from the Geco Mine in Manitouwadge, Ontario. He reports that the Geco cordierites are directly derived from a mixed chlori te-al uminous clay miner.al. Mixed layer clay-chlorites are produced as alteration phases in fluid- rock experimental studies of basalts and rhyolites over a range of temperatures at varying water/rock ratios (Hajash and Chandler, 1981; Seyfried and Bischoff, 1981). Various mixed-layer clays and chlorites form a distinct alteration zone around Kuroko-type massive sulfide deposits in Japan (Scott and Urabe, 1983; Franklin et al., 1981). It is conceivable that a suite including mixed-layer clays and chlorites were precursors to the alteration phases present in the study area. Winkler (1979,p.224) states that the first appearance of staurolite or cordierite is linked to the beginning of 88 t •iuc.m>.... Fic1. 51 - MgO / MgO+FeO ratios of alteration assemblages within the Mattabi pyroclastic rocks of the study area; n = # of samples. Diamond average, lines denote range. Fig. 52- Photomicrograph showing biotite-forming reaction (4) from chlorite and sericite. View is 4x3 mm, crossed polarizers. 89 medium-grade (amphibolite) conditions of metamorphism in rocks of appropriate composition. Reactions producing staurolite may include: (5) chlorite + muscovite = staurolite + biotite + quartz + vapor (Hoschek,1969) (6) chlorite +muscovite + almandine = staurolite + biotite + quartz + vapor (Froese and Gasparrini, 1975) Both of these reactions are possible at 0 495-575 C and 0.5-7 kb. (7) chloritoid + 02 = staurolite + magnetite + quartz + vapor (Ganguly and Newton, 1969) This reaction takes place at approximately 545 C and 5 kb. (8) chloritoid + aluminum-silicate staurolite + cordierite (Richardson, 1968) Winkler (1979, p.223) states that if chloritoid is present in low grade rocks, it is a principal reactant in staurolite-producing reactions at the beginning of medium grade metamorphism. Chloritoid is locally abundant within the altered felsic pyroclastic rocks of the area, whereas staurolite is not. However, in one sample, SLM-137-267 (Fig. 53), staurolite and cordierite are seen as clean euhedral 90 grains, whereas andalusite (where present) and chloritoid are corroded and rimmed by staurolite. These textural relations would suggest a reaction such as (8) above. It is emphasized here that this is a single isolated occurrence, despite the relative abundance of chloritoid in other parts of the study area (Appendix 1). The difference apparently lies in the coexistence of chloritoid and andalusite, not observed in other samples. It can be suggested here that the chloritoid-forming reaction: (9) chlorite + aluminum-silicate = chloritoid + quartz + vapor (Frey, 1978) was limited in other locations by the amount of aluminum- silicate present. Petrographic evidence shows this to be the case; the other chloritoid-bearing samples have the assemblage chloritoid-chlorite. If appropriate grade is reached, reaction (9) would not allow the assemblage chlorite-andalusite-chloritoid to persist. In the sample SLM-137-267, the limiting factor was chlorite. Staurolite was also identified in two other samples, neither of which contain chloritoid. Fig. 54 shows euhedral staurolite grains associated with biotite, quartz, and sericite, restricted to what is interpreted to be a crenulated bedding These isolated occurrences of staurolite help to illustrate the variability in composition found on a thin section scale within these altered 91 pyrocl a s t ic rocks . Seifert ( 1970a) illustrates compatibility relationships within the quartz-saturated portion of the system KMASH (Fig.55). Reactions (2) and (3) above are shown to extend to temperatures well below the stability field of stauroli te , represented on the diagram by reaction (8) . It should be noted here that reaction (8) is from the experimental system Fe0-Al203-SI02-H20, so that the diagrammatic relationships shown by these reactions are not certain. Fig. 53- Photomicrograph showing staurolite grains rimming chloritoid, SLM-137-267. Field of v iew is 4 mm; crossed polarizers. 92 Fig. 54- Photomicrograph of staurolite grains, SLM-136-665, field of view is 1.8 mm. / / / Kyanite Sillim•nite 5 t 4 ...... :; \ \ ::3• \ A: \ CJcv'i;' Aud &. lusile \ \ \ 2 1 400 500 600 700 TC C> Fig. 55- P-T diagram showing relevant cordierite and staurolite-forming reactions listed in text (after Seifert, 1970A, and Richardson, 1968). 93 It should be noted here that the experimental reactions listed above are restricted to rocks of appropriate compositions. Varying proportions of other components not involved in these reactions may play a significant role in cordierite formation at Sturgeon Lake. Figure 56 is a graph illustrating the abundance of Cao relative to MgO and FeO within the various alteration types of the study area. Note that Cao is most abundant within the cordierite assemblage rocks. Petrographic examination shows that epidote/zoisite is the only abundant Ca-bearing phase within these rocks. The relationships between these delicately balanced compositions and cordierite requires further investigation. 0.80 0.80 I 0.40 I II o.ao 0.20 0.10 t t <} UJCll'll!D R-CILOll COlllllEln'm CILOlllTC>m AL ..tIUCATll IEllCITllt IMM:ILOll n•6 n•3 n•15 n•9 n-6 n•7 n•3 Fig. 56- CaO/CaO+MgO+FeO ratio for various alteration assemblages of the study area. n = number of samples in average, diamond = average, lines denote range of values. 94 The presence of garnet within the area may also be useful as a supplemental indicator of metamorphic grade. Common garnet-forming reactions may include: (10) chlorite + muscovite + quartz = garnet + biotite + vapor and (11) chloritoid + chlorite + quartz = garnet + vapor (Thompson & Norton,1968, cited in Winkler,1979) (12) chlorite + muscovite + epidote = almandine-rich garnet + biotite + vapor (Brown, 1969) These reactions are common in low-grade metamorphism of rocks of appropriate composition (Winkler, 1979, p.224). Reaction (11) above can be discounted due to lack of petrographic evidence such as pseudomorphic textures, relict chloritold, etc. Tpe samples which do have garnet coexisting with chloritoid (SLM-175-830 & 562, Appendix 1) have an additional phase, carbonate. Variability in the compositions of garnet corresponds to variability in the T and P of formation (Winkler, 1979, p.222; Hynes & Forest, 1988). Microprobe analyses of garnets from the Lyon Lake Mine area, less than 1 km north of the study area, locally show MnO values in excess of 18 wt% (Mumin, 1988). These factors suggest that manganese may play a role in garnet stabilization within rocks of appropriate composition within the area, and that the carbonate coexisting with garnet and chloritoid may be an iron-rich variety with considerable 95 MnO-FeO substitution. Petrographic evidence, such as lack of biotite and epidote coexisting with garnet, is lacking for reactions (10) and (12) to have been significant during metamorphism within the area. The above analysis of metamorphic grade for the rocks of the study area can be summarized as follows; a) the limit on temperature and pressure would appear to be in the vicinity of reaction (8) shown on Fig. 56, allowing the formation of staurolite, 0 probably between 450-500 c and pressures of <4 kb (upper greenschist-lower amphibolite facies). b) the compositional variation of the altered rocks prior to the onset of metamorphism is the principal control on the distribution of phases present. V. ALTERATION GEOCHEMISTRY The first objective in studying a suite of hydrothermally altered rocks is to determine the mineralogy of the alteration assemblages present. Geochemical data can then be examined to determine the gains and losses of principle chemical components from the same rock type under differing conditions of alteration. Only then is it possible to explain the nature of the hydrothermal fluids which acted upon the rocks, and to propose a model for the evolution of the system which led to the formation of the ore deposit. 96 Geochemical analyses of 193 samples representative of the rocks from the study area were carried out by Metriclab, Inc., of Ste. Marthe sur le Lac, Quebec. Major element oxides and C02 were reported in weight percent, and various base and precious metals and trace elements are reported in ppm . These results are tabulated in Appendix 2. Plate 1 shows the relative distribution of lithologic units within the study area. Due to lack of sufficient outcrop within the area, the majority of samples were taken from drill core from exploration diamond drilling done by Sturgeon Lake Mines in the years prior to the closing of the mine. As is clearly visible on Plate 1, these holes were drilled primarily within the Mattabi series pyroclastic and volcaniclastic rocks which make up >60% of the footwall stratigraphy of extrusive origin. For these r_easons, mass balance calculations and geochemical comparisons will be made only on rocks of this unit. The wide variety of altered compositions exhibited within this unit provides ample data from which to determine the nature of the hydrothermal system. The method employed to determine gains and losses of chemical components due to alteration is the isocon method developed by Grant (1986). The method described therein employs a graphical solution to Gresens' (1967) equation relating changes in volume, mass, and concentrations of components during metasomatism. Since the introduction of 97 this simple yet powerful tool for analysis of geochemical data, the method has been widely used with results that agree with geochemical, petrographic, and field evidence (Davis, 1987; Osterberg et al., 1987; Lockwood and Franklin, 1986). Raw geochemical data (i.e. wt.% of oxides, ppm trace elements) from samples displaying particular alteration assemblages (or, as in this study, averaged values from a group of samples with the same alteration type) are plotted on an x/y graph. The set of data points corresponding to concentrations of individual components is examined for a best fit line from the origin through as many data points as possible. This line generated is the isocon, a line connecting points of equal chemical concentration (Grant, 1986). Those components whose data points fall on or very near the isocon are considered to be relatively immobile, whereas species plotting above the line are considered to be gained, and those below are considered to be lost during alteration. Comparisons of the slopes of lines from the origin through individual data points with the slope of the isocon can give the relative gain or loss of that component. The slope of the isocon, furthermore, gives the % of mass change during alteration. Negative values represent % mass lost, and positive values represent a mass gain. The reader is referred to the original article by Grant (1986) for verification of the mathematical validity of the method. 98 As will be seen below, the constant alumina isocon generally agrees with the best fit line through the data points. Ti02 and Zr generally plot close to the constant alumina isocon. These elements have been considered immobile during hydrothermal alteration in other studies of Archean altered felsic volcanic rocks because of their noted colinear variations within differing alterations of similar rocks (Morton & Nebel, 1984; Osterberg, 1985; Lockwood & Franklin, 1986; Davis, 1987). In order to avoid excessive graph size and clustered points, the concentrations of the different components have been scaled by a numerical factor appropriate for each element. In this way, significant percentage changes for trace elements in ppm as well as major oxide weight percents can be readily observed on one graph. The scale factor for each element is given alongside each data point. The felsic volcanic rocks of the area have all undergone variable amounts of hydrothermal alteration. Within the limits of the study area, no consistent analyses are available to show an unaltered stratigraphic equivalent to the altered rocks. Table V-1 below shows average compositions of the various alteration assemblages used for comparison purposes. Table V-2 gives calculated CIPW norms for these averaged compositions. 99 SIL FECHL CTD CDT AL-SIL SER MGCHL SI02 80.98 73.77 79.80 71.86 72.42 72.59 74.90 TI02 0.36 0.42 0.34 0.63 0.71 0.40 0.39 AL203 8.48 10.50 8.83 12.55 13.14 13.94 9.82 FEO 3.06 5.49 5.09 3.71 4 . 19 3.00 5.09 MGO 1. 61 1. 91 1. 22 2.82 3 .. 47 2.14 4.12 CAO 1. 71 1.83 0.45 2.80 1. 32 0.66 0.66 K20 1.76 2.50 1. 67 2.12 1. 31 3.51 1. 26 NA20 0.25 0.24 0.21 0.67 0.35 0.69 0.19 MNO 0.08 0.12 0.10 0.17 0.06 0.07 0.27 C02 1.12 1.21 1. 20 1. 21 1. 27 1.14 1. 35 TOTALS 99.41 97.99 98.91 98.54 98.24 98.14 98.05 ZR( ppm) 382 430 366 437 787 608 370 ZN(ppm) 65 72 80 74 65 62 167 n= 6 J 9 15 5 7 J TABLE V-I- Chemical compositions of the various alteration assemblages used for comparisons in this study. n= number of samples averaged. SIL=silicified, FECHL=Fe-chlorite,CTD=chloritoid,CDT=cordierite, AL-SIL=aluminum silicate,SER=sericite,MGCHL= Mg-chlorite. 100 SIL FECHL CTD CDT AL-SIL SER MGCHL Ilmenite 0.68 0.80 0.65 1. 20 1. 35 0.76 0.74 Orthoclase 10.39 14.76 9 . 86 12.52 7.73 20.73 7.44 Albite 2.11 2.03 1.78 5.67 2.96 5.84 1.61 Anorthite 8.48 9.07 2.23 13.89 6.55 3.27 3.27 Hypersthene 9.17 14.36 12.00 13.09 15.25 10.29 19.44 Corundum 3.06 4.07 5.86 4.07 8.75 7.81 6.95 Quartz 64.40 51.69 65.34 46.90 54.38 48.30 57.25 Total 98.29 96.78 97.71 97.33 96.97 97.00 96.70 Table V-2- calculated CIPW norms for compositions shown in Table V-1. Major oxides only, excluding trace elements and volatiles. 101 A. SILICIFIED ROCKS Silicified felsic rocks are found within a broad semiconformable zone extending the entire width of the field area. Silicified rocks have been defined as those whose Si02 content exceeds 77 wt %, nearly 5 wt. % higher than that of average rhyolites described by Irvine & Baragar (1971). Petrographic evidence indicates that nearly all other alteration assemblages grade into or sharply cross-cut silicified rocks. The silicif ication of volcanic rocks due to hydrothermal fluids has been noted in footwall successions beneath Archean massive sulfide deposits in various locations throughout the Canadian shield (MacGeehan & MacLean, 1980; Gibson et al., 1983; Morton & Franklin, 1987). As hydrothermal fluid circulated through the Sturgeon Lake Mine footwall succession, it was in contact with very reactable felsic volcanic glass (ash and pumice) and, upon heating, could rapidly become saturated with silica (Fournier, 1985). Fig. 57 is a diagram showing silica solubility in an aqueous sodium chloride solution at various temperatures and pressures (Franklin, 1986). Rapid heating (isobaric) would cause the conditions to shift to higher temperature, exceeding the solubility maximum, and precipitating silica from solution. Rapid heating may come about from a) injection of new magma into a subvolcanic intrusion which is providing heat for the hydrothermal 102 30 • ii • e 10- 4 0 0 T<-C> Fig. 57- Solubility of quartz in aqueous sodium chloride solution at various temperatures and pressures (after Franklin, 1986). system (Franklin,1986); orb) intrusions of synvolcanic sills and dikes into the volcanic pile. Isothermal upward movement of a silica-saturated fluid towards areas of decreased pressure could also cause precipitation of silica from solution, as can be seen from the diagram. Arguments for each of the above possibilities can be given for the probable conditions in the Sturgeon Lake Mine footwall succession. As noted in a previous chapter, the Mattabi series pyroclastic rocks were deposited from a series of eruptions resulting from differentiation of the parent 103 maqma, evidenced by the strong zonation of certain trace elements in successive flow units. Injection of new magma into the subvolcanic feeder for the system probably played a role in the evolution of this magma, and rapid heating of the overlying volcanic pile was a possible result. Abundant rhyolitic ash and pumice was available for reaction with the hydrothermal fluid, resulting in silica-saturated solutions early in the evolution of the hydrothermal system. B. FE-CHLORITE ALTERATION Iron-rich chlorite, with associated iron carbonate, garnet, and magnetite, form thick veins and, locally, thin conformable pods. Field evidence demonstrates that rocks of this assemblage exhibit cross-cutting relationships with silicified rocks, and thus these two assemblages will be geochemically compared to determine the gains and losses of individual components. Changes in mass resulting from Fe-chlorite alteration of silicified rocks are shown in Fig. 58, corresponding to a 19% decrease. Table V-3 shows the range of relative gains and losses of the individual components due to Fe-chlorite alteration of silicified rocks. C02, Ti, Mg, K, Zn, and Zr plot on or very near the constant-alumina isocon. Si shows a significant loss of 26%, while Fe shows a significant increase of 45%. Within silicified rocks, formation of Fe-chlorite may be 104 the result of a reaction such as: • ++ (13) Albite + Fe + Quartz + H20 = Chlorite + + H4Si04 + Na+ (Morton & Nebel, 1984) If the silicif ication process affected these rocks soon after they were deposited (i.e. early in the evolution of the hydrothermal system), then the subsequent addition of Fe could produce an Fe-rich chlorite according to the above reaction. Silicification need not disrupt the alkali component of unaltered felsic volcanic rocks; this has been found to be the case with the silicification of the Amulet Rhyolite in the Noranda, Quebec area (Gibson et al., 1983). The above reaction is consistent with the data presented in the isocon diagram, which indicates a substantial increase in Fe and a decrease in Si. Similar gains and losses have been reported from chlorite alteration at the Phelps Dodge massive sulfide deposit near Mattagami, Quebec (Krandiotis & MacLean, 1987). The strong Fe and Mn enrichment associated with this alteration is presumably due to hydrothermal fluids that had leached these elements from the underlying rocks in the volcanic succession. Such a process is consistent with experimental findings in studies of seawater-basalt D interactions, where, at temperatures of 150- >300 c, seawater loses Mg to the surrounding rock, with a corresponding drop in solution pH and an increased ability 105 40 - 0.5 SI 30 ,...w a: 0 ...I 4 Fe :c 0 SK • 0.05 Zr iii 20 I&. · 0.25 Zn ·8 Mg 100 Mn. . ·7 C• 0 Tl 10 . • 7 C02 .25 ... 10 20 30 40 SILICIFIED Fig. 58- Isocon diagram showing Fe-chlorite alteration vs. silicified rocks of the Mattabi series pyroclastic flow deposits. Si02 -26% K20 +15% Ti02 -05% Na20 -23% Al203 n/c MnO +21% FeO +45% C02 -13% MgO -04% Zr -09% cao -13% Zn -11% Table V-3- percentage change of components calculated from Fig. 58. 106 to carry Fe, Mn, and base metals in solution, dependent on the water(fluid)/rock ratio (Seyfried and Mottl, 1982). Experimental work involving seawater-rhyolite interactions shows similar increased ability of fluids to carry Fe and Mn with decreasing pH and increasing temperatures (Hajash and Chandler, 1981). It can be said, therefore, that the fluids responsible for development of the protolith of Fe-rich chlorite were of sufficient temperature and acidity to carry Fe and Mn. C. CHLORITOID ASSEMBLAGE Field and petrographic evidence indicates that this assemblage cross-cuts the silicified rocks. There is relatively little mass change resulting from the chloritoid alteration of silicified rocks (4% mass loss). Fig. 59 shows the results of chloritoid alteration of silicified rocks. Table V-4 gives accompanying percentage changes of components. C02, Ti, K, Si, and Zr plot alonq or near the isocon, indicating the relative immobility of these elements. Fe registers a strong increase of 60%, and Ca shows a significant 75% decrease. Figure 60 is a composition diagram of an empirically delineated field for chloritoid stability (Hoschek, 1967). Average compositions of chloritoid assemblage rocks from this study are shown by the o, whereas Fe-chlorite altered rocks are shown by the dot. As can be seen, the bulk 107 40 30 Q ....0 a: g 20 :z:: () 10 10 20 30 40 SILICIFIED Fig. 59- Isocon diagram showing chloritoid alteration vs. silicified rocks of the Mattabi series pyroclastic flow deposits. Si02 -05% K20 -09% Ti02 -09% Na20 -19% Al203 n/c MnO +20% FeO +60% C02 -03% MgO -27% Zr -08% cao -75% Zn +18% Table V-4- percentage changes of components calculated from Fig. 59. 108 compositions of chloritoid altered rocks fall within the range of each of the fields. Fe-chlorite altered rocks without chloritoid are also within two of the fields shown, but fall outside of the chloritoid stability field in the CaO-FeO+MgO-Al203 diagram. This diagram may indicate that locally an excess of Cao present within the rocks precluded the formation of chloritoid. As stressed by Lockwood and Franklin (1986), chloritoid formation within volcanic rocks requires a peraluminous composition and major additions of Fe over Mg. With losses of Na, K, and Ca to alteration, excess Fe combined with the peraluminous composition to form an iron-rich chlorite, which upon regional metamorphism combined with an aluminum-silicate phase to form chloritoid as shown in the reaction: (9) chlorite + pyrophyllite = chloritoid + Qtz + H20 (Frey, 1978) This reaction has been demonstrated to occur in various chloritoid-bearing volcanic rocks of the Canadian shield (Nebel, 1982; Osterberg, 1985). Such a reaction as (9) above should lead to the assemblages Chl + Ctd + Qtz or Al-Sil + Ctd + Qtz but would effectively rule out the assemblage Chl + Al-Sil + Ctd + Qtz. Coexisting chlorites within chloritoid-bearing rocks of the area are invariably iron-rich. Chloritoid and sericite form a common assemblage within 109 Al203 Al203 '· • O '··. Na20 Foo Moo '------....FoO Al203 • 0 FoO c.o L------' - fig. 60- of chloritoid-altered (open circles) and Fe-chlorite-altered (filled circles) rocks of this study on diagram showing empirically delineated chloritoid stability fields (according to Hoschek, 1967). 110 sericite-rich rocks of the study area. Petrographic evidence shows chloritoid as clean euhedral porphyroblasts (Fig. 43), leading to the conclusion that the rocks were first sericitized. Introduction of a K-rich fluid to a rock containing the assemblage Fe-chlorite + quartz + an aluminum silicate phase (pyrophyllite, kaolinite) produces the pre- metamorphic assemblage sericite + Fe-chlorite + (pyrophyllite, kaolinite) which, upon regional metamorphism, could form the assemblage sericite + chloritoid. Comparison of Figs. 58 & 59 illustrates that the processes responsible for alteration of silicified rocks to chloritoid or Fe-chlorite were essentially the same. Additions in both cases of Fe and Mn suggest an Fe-rich acidic solution was responsible for the formation of pre- metamorphic Fe-chlorite which, in a suitable host rock, would later produce chloritoid. D. CORDIERITE ASSEMBLAGE Cordierite alteration is found predominantly throughout sericitic or chloritic Mattabi series pyroclastic rocks, and occurs as pods and veins. Difficulties arise in geochemical comparisons of cordierite alteration with other alteration assemblages, due to lack of an obvious least-altered equivalent composition. However, previous determination of silicified rocks representing an early alteration assemblage in the area of this study provides a composition with which 111 to compare geochemical trends observed in cordierite-altered rocks. Mass balance calculations indicate that cordierite alteration occurs at a 32% mass loss with respect to silicified rocks. Fig. 61 shows that the isocon in this comparison is again that of constant alumina. Ca, Ti, and Mg plot along the isocon, and are thus considered relatively immobile. Major gains are shown by Na (+85%) and Mn (+44%), with a 39% loss of silica. Table V-5 shows relative gains and losses of components involved in cordierite alteration of silicified rocks. Petrographic examination of cordierite-altered samples confirms the geochemical trends displayed in these isocon diagrams. Na shows consistent increases with cordierite alteration, ranging from 0.2 to 1.31 wt. % (Appendix 2). The only petrographically identified Na-bearing phase is associated tourmaline, which may be present up to 2-3%. Na may also be present in a paragonite component of sericite, though data from microprobe or x-ray diffraction is unavailable to confirm this speculation. Ca increases, though not obvious from examination of the isocon data, are also shown in cordierite-altered rocks, with values ranqing from 1.44 to 4.43 wt.% (Appendix 2). Fine-grained anhedral masses of epidote/zoisite are distributed along the margins of cordierite-bearing veins, and appear to be the principal 112 40 --- .5 SI LIJ30 -- !:: /// " a: ,,,,.·"'' 8 Mg // 0 • .06 Zr 7 c. / / 0 100 Mn . . 25 Zn (.) 26 N•. •/ 30TI .aK . 4 Fe 10 . 7 C02 10 20 30 40 SILICIFIED £.ig__,_ 61- Isocon diagram showing cordierite alteration of silicif ied rocks of the Mattabi series pyroclastic flow deposits. Si02 -39% K20 -23 % 'l'i02 +09 % Na20 +85'8 Al203 n/c MnG +44 :t FeO -24% C02 -25% MgO +15% Zr -19% cao +11 % Zn -24 % Table V-5- percentage changes of components calculated from Fig. 61. llJ Ca-bearinq phases. Biotite is a common constituent within cordierite-altered rocks, possibly as a result of reaction (3) where biotite is a product of a cordierite-forming metamorphic reaction. The isocon diagram indicates that the fluids responsible for the protolith for the cordierite assemblages had the ability to leach Si. Increases in Ca and Na could be attributed to addition to the rock by this same fluid. Textural relations, such as epidote-zoisite along the margins of cordierite-bearing veins, favor this explanation. High temperature (350-425°C) acidic fluids (pH 4.8-2.7) with grossly similar alteration products have been described by Seyfried and Janecky (1985). The major differences exhibited by the geochemical trends of cordierite, chlorite, and chloritoid assemblages are illustrated by the oxide ratios \ shown in Fig. 62. The major differences include higher Al203/Al203+FeO+MgO, MgO/MgO+FeO and CaO/CaO+MgO+FeO ratios of cordierite alteration with respect to other alteration types which are enriched in both iron and magnesium. E. ALUMINUM SILICATE ASSEMBLAGE Field and petrographic evidence shows that aluminum silicate alteration is developed prior to sericite or cordierite. Andalusite and/or kyanite porphyroblasts are developed in veins or patches which are cross-cut by these alteration types. Again, lack of a suitable least-altered 114 U.70 u (i0 (J ll -111 0:10 0 f (> ll gO 1 l\·O u 10 Q l'.oO _ ('.oll1Mgllof't·O Ft: l"lduril<" l'urd1t·nl.t· rlilunl1· 62.- Graph showing selected ma jol'." oxide l'."atios for various alteration assemblages enriched in Fe and Mg. symbols denote averages, vertical lines denote range of values. 115 composition precludes direct comparison of the qeochemical trends related to aluminum silicate development with a suitable precursor. Early silicification provides the most relevant composition with which to compare these trends. Mass changes involved in the production of an aluminum silicate assemblage from a silicified precursor show a 35% decrease. Fig. 63 shows Na and Fe plotting very near the constant alumina isocon. Strong depletions are shown by Mn (-51%), Ca (-50%), K (-52%), and Si (-42%). Table V-6 shows relative percentage change of component concentrations during this alteration. The geochemical trends illustrated by this isocon diagram are consistent with other observed trends of aluminum silicate alteration in volcanic rocks of the Canadian. shield (Osterberg et al., 1987; Morton & Franklin, 1987; Morton et al., 1988). The gains shown by Mg and Ti are attributable to late Mg-chlorite development. Otherwise, the trends show that this alteration was effective in leaching components from the rock, leaving a composition suitable for production of quartz and a pre-metamorphic aluminum-rich phase (such as pyrophyllite or kaolinite). Subsequent metamorphism would produce andalusite or kyanite from the reactions: (10) pyrophyllite = aluminum-silicate + quartz +vapor (11) kaolinite = aluminum-silicate + quartz + vapor 116 40 . .05 Zr 3Al./ .5 SI. w30 8 Mg ct- 0 ...J 30 Tl ...J c • 4 Fe · .25 .Zn BK 10 25 N• 1 C02 100 Mn 7 Ca 10 20 30 40 SILICIFIED Fig. 6J- Isocon diagram showing aluminum silicate alteration of silicified rocks of the Mattabi series pyroclastic flow deposits. Si02 -42% K20 -52% ·r102 +28 % Na20 Al203 n/c MnO -51% FeO -11 % C02 -26 % MgO +40% Zr +34 % cao -50% Zn -34% Table V-6- percentage change of components calculated I I from Fig. GJ. \ 117 Petrographic evidence such as andalusite porphyroblasts including a preexisting foliation suggests metamorphic production of aluminum silicates. Chloritoid was precluded from developing despite the preexistence of a peraluminous composition, perhaps due to the value of the Mgo/Mgo+FeO ratio (as shown in Fig. 51). Had more iron been available, the peraluminous composition may have produced chloritoid rather than Mg-rich chlorite. F. SERICITE ASSEMBLAGE Field and petrographic evidence from the study area indicate that sericite-altered rocks cross-cut other alteration assemblages (silicified, Al-silicate, Mg- chlorite) and therefore was formed at a later stage in the development of the hydrothermal syBtem. Consequently, sericitic alteration will be compared to silicified rocks for purposes of determining gains and losses of components due to sericitization. Mass balance calulations show a 39% decrease in mass in sericitic alteration of silicified rocks. Fig. 64 and table V-7 illustrate relative gains and losses of components. In this instance, the isocon passes approximately through Al and Zr. Losses are indicated by Si (-46%), Fe (-41%), Ca (-77%), and Mn (-47%). Gains are shown by K (+15%) and Na (+65%). Fig. 64 shows that the sericitization _process 118 40 ·- .6 SI 1'.I 30 SK .... § a: I.LI 20 - rn . S Mg · .25 Zn /30TI . · 4 Fe 10 - C02 ·.100 Mn ·7 c. 10 20 30 40 SILICIFIED Isocon diagram showing secicitic alteration of silicified rocks of the Mattabi series pyroclastic flow deposits. Si02 -46% K20 +15% r[j_ 0 2 -JJ% Na20 +G5 % Al203 n/c MnO -47% FeO -41% C02 -39% MgO +20% Zr n / c cao -77% Zn -42% Table V-7- percentage change of components calculated from Fig. 64. 119 successfully removed Ca, Fe, Mn; C02, and Si from the rocks, with substantial gains in K and Na. Within silicified rocks, sericite production may be the result of reaction of a K- rich acidic fluid with an early-formed (diagenetic?) clay mineral or pyrophyllite which persisted through the silicification process. The strong enrichment of Na during ·the sericitization process may possibly be due to formation of paragonite, however, lack of X-ray diffraction and microprobe data precludes further discussion. Because of the very low Na20 values in the rocks, the significance of the observed increases in Na20 are questionable. G. MG-CHLORITE ALTERATION Mg-chlorite is widespread within the rocks of the study area; however, only within limited locations Qoes Mg- chlorite appear as the predominant alteration mineral. Petrographic evidence exists for Mg-chlorite to have formed subsequent to the development of the silicified assemblage, and will be compared to determine related trends. Mass changes show a 14% decrease, and. Fig. 65 and table V-8 illustrate the relative gains and losses in the chloritization of silicified rocks. C02 and Ti plot along the constant alumina isocon. Losses are shown by Na (-34%), Ca (-67%), and K (-38%). Increases are shown by Fe (+43%), with strong increases shown by Mg (+120%), Mn (+190%), and Zn (+121%). The textural and field relationships shown by 120 development of Mg-chlorite may suggest a mixing of hydrothermal fluid with unreacted seawater to produce the observed assemblages. Addition of Mg from seawater to a hydrothermal fluid already enriched in Fe and Mn (and depleted in Mg) could produce chlorite by a reaction such as follows: ++ (15) pyrophyllite + (Mg,Fe) + H20 = chlorite + quartz + 2H+ Lack of widespread distribution of Mg-chlorite in major modal percentages places constraints on how effectively reactions of this sort took place within the study area. 121 .25 Zn· 40 - •.6 SI 8 Mg· -- 3 Al. a: 100 Mn. ....0 l: 0 4 Fe. I 20 -- CJ · .06 Zr :::ll 30 T. 10 - 7 C02 · ·8 K · 25 Ne · 7 Ce 10 20 30 40 SILICIFIED Fig. 65- Isocon diagram showing Mg-chlorite alteration of silicified rocks of the Mattabi series p y roclastic flow d e posits. Si02 -20% K20 -J8 5ci Ti 0 2 -07% Na20 -34 % Al203 n / c MnO +190% FeO +43 % C02 +OJ % MgO +120% Zr -17% cao -67% Zn +1216 Table V-8- percentage change of components calculated from Fig. 65. 12 2 VI . MODEL A hydrothermal system has been described as a geothermal system in which fluids circulate within crustal rocks, generally in an area of high heat flow (Elder, 1981). Several preconditions are necessary for development of such a circulation. These include: a) an aquifer zone of heated fluid; b) a cap-rock unit which serves to contain and insulate the aquifer; c) discharge zones where the fluid is released upward; d) recharge zones where the fluid is replenished; and e) a heat source to raise the temperature of the reservoir fluid (Hodgson & Lydon, 1977). With these preconditions established, changes in the chemical composition and temperature of the fluid from original seawater (Lydon, 1988) facilitate the extraction of metals from silicate phases in the rock through which this fluid passed. Subsequent upward transport through suitable structures to areas of lower pressure and/or temperature cause the precipitation of these dissolved components (Hutchinson, 1982). Recent experimental studies of fluid/rock interaction, as well as direct observations of modern hydrothermal systems on the seafloor, have led to the characterization of the nature of the hydrothermal fluids at various stages within a hydrothermal system. Within the early stages of downward movement of seawater into the system, a consistent 123 observation is the loss of Mg from seawater to the rocks, in the form of a Mg(OH) component of mixed layer clay- chlorites, in exchange for Ca, Na, and K (Seyfried & Mottl, 1982). This process has been shown to be effective at varying water/rock ratios and is relatively independent of rock composition (Hajash & Chandler, 1981). A drop in solution pH by production of H accompanies this process. With continued downward movement of this fluid into the reservoir zone, water/rock ratios would decrease and temperatures increase. Mg would be depleted from the fluid, and pH would continue to decrease by the loss of Ca and Na to the rock, enhancing the ability of the fluid to carry Fe, Mn, and base metals in solution (Seyfried & Janecky, 1985). Subsequent tectonically-induced upward release of this evolved fluid to areas of lower temperature and pressure cause the precipitation of sulfides and potential formation of ore. The f elsic volcanic and volcaniclastic rocks of the Sturgeon Lake Mine f ootwall show marked changes in composition and texture from their assumed original state, reflected primarily in modal abundances of minerals not considered to be of primary igneous origin or their metamorphosed equivalents. Within the above-mentioned constraints of hydrothermal systems, a proposed model of hydrothermal activity within the study area follows, as illustrated in Figs. 66 & 67. 124 Within the South Sturgeon Lake volcanic succession, hydrothermal activity was initiated by intrusion of the Beidelman Bay pluton which acted as a heat source to drive convective circulation (Franklin et al., 1977), as well as being the probable parent magma to the extensive felsic pyroclastic deposits of the area (Morton & Franklin, 1988). Voluminous deposits of caldera-related breccias and debris flows provided a suitable lithology for a reservoir for the system. Early focused discharge zones centered on the F- group (Hudak, in prep.) and Mattabi deposits (Morton et al., 1988) to the west of the present study area. Within the Sturgeon Lake Mine footwall, early-stage hydrothermal alteration was limited to silicification of felsic rocks to produce a partial self-sealed cap to the system. Local focussed discharge of evolved fluids created restricted zones of aluminum silicate and chloritoid/Fe-chlorite alteration; however, thick accumulations of felsic pyroclastic material may have effectively snuffed out development of more extensive alteration during this period. As this phase of hydrothermal activity waned, cooler, less evolved shallow-circulating waters were responsible for development of late-stage Mg-rich chlorite and sericite, similar to that described at the Mattabi Mine by Groves (1984), and the F-group deposit (Hudak, in Hydrothermal activity resumed, probably facilitated by continuation of caldera-forming activity such as synvolcanic 125 SEA L.E-.n. SEAFlOOR +Mg. +K +Mg. +K - +Mg. +K +SI +SI I-' l\J °' lgh Temp.-ature \ I Acldlc Flulda I \ -1 -,- +CoT, +Hof +CoT, +Not -re. -Mn -re. -Mn Molle Volconlc9 HEAT + + Subvolconlc+ lntru.i ... + Body + + + + + + + + + Fig. 66- Diagram of early alteration of the Sturgeon Lake Mine footwall succession. Not to scale, symbols represent components gained or lost by the rock due to fluid interaction. Arrows represent fluid flow, dashed lines faults. 9EA L£'f£l. LAb o.poell ICNUXIR •turveon +r.,wn, llOM meta• I +MG L-s.n.. r•.ic: P,.-odoetlc ltocka I I Mottai Ser'- ,.8lllc p ,.-odoeUc ltocka I ,_.. tv ·..J .._..... Debr19 flow o.,o.tt. \ ...... ,, \ - llOM IM'tclll \ HEAT \ lubwilomik:+ + locty + + + + + + + Fig. 67- Alteration system responsible for deposition of Sturgeon Lake deposit. Not to scale, symbols represent components gained or lost by the rock due to interaction with hydrothermal fluids. Arrows represent fluid flow, dashed lines faults. faulting and continuing ash-flow eruptions of the "L''- series. Under conditions of low water/rock ratios and high temperatures, an acidic fluid was circulated through the Sturgeon Lake Mine f ootwall which enriched the rocks in K and Na to create the extensive sericitic precursor alteration, leaching the rocks of Fe, Mn, silica, and possibly base metals. Deeper-circulating fluids enriched the rocks in Mg and Ca to produce the protolith to the cordierite assemblage rocks. The sequence of alteration events can be summarized as follows: 1) silicification 2) minor aluminum-silicate and/or Fe-enrichment 3) minor Mg-chlorite, sericite 4) sericite, cordierite-precursor 5) late Fe-enrichment The relationship of these alteration trends to the ore- forming fluid responsible for the Sturgeon Lake massive sulfide deposit remains unclear; however, it can be stated that the ore forming event closely coincides with either (4) or (5) above. Several problems remain from examination of the above model. Throughout the study area, no evidence exists for alteration due to downwelling fluids; consequently, it must be assumed that this took place outside of the area, perhaps on a scale of km as noted in previous studies of base-metal 128 sulfide prospects in .NW Ontario (Davis, 1987; Osterberg, 1985). Also of interest is the lack of definition within the f ootwall of a focused zone of upward-moving ore-forming fluid, or alteration pipe. Stockwork ore existed beneath the deposit prior to mining, and was suggested by Severin (1982) to be the upper expression of an alteration pipe structure. diamond drilling during the life of the mine failed to intersect an alteration pipe at depth. VII. SUMMARY AND CONCLUSIONS The stratigraphy of the footwall rocks beneath the Sturgeon Lake massive sulfide deposit is dominated by volcanic rocks of varying composition and eruptive styles which serve well to document the evolution of the Sturgeon Lake caldera complex. Field mapping conducted during 1987 allowed the identification of seven distinct units based on stratigraphic position, preserved primary textures, and composition. The lowermost rocks encountered in the f ootwall are a thick series of mafic lava flows, flow breccias, and minor intercalated felsic flows and tuffs, believed to be correlative with similar rocks to the west of the area as a part of a broad shield volcano. Pillowed and highly amygdaloidal flows at the top of the sequence suggest a shallow water environment during the waning stages of mafic 129 volcanism within the area. These maf ic volcanic rocks are overlain by a thick sequence of heterolithic breccias with intercalated felsic quartz-porphyritic ash-flow tuffs, grading upward into the rhyolitic lapilli- and ash-tuffs of the QPYF series. Blocks and fragments of the underlying mafic rocks within the breccia, and the inter-fingering of lenses of ash-flow tuff, indicate contemporaneous collapse and eruption of f elsic volcanics during the early stages of the development of the sturgeon Lake caldera. Volcanism ceased within the area allowing the deposition of a series of debris flow deposits and thin bedded epiclastic deposits, a result of slumps and rock falls from oversteepened fault scarps. Thinning of these deposits to the west within the area suggest that the Lac David fault is representative of such synvolcanic structures. Large volumes of the Mattabi series rhyolitic quartz- porphyritic ash-flow tuff were deposited upon the debris flows and underlying units. A subaqueous environment is evidenced by normal grading of repeating crystal-lithic and ash beds and thin graded fine-grained sediments within the pyroclastic sequence. Continued subsidence of the Sturqeon Lake caldera is indicated by wedges of debris flow deposits, intercalated with the ash-flow tuff, which thin rapidly away from the Lac David fault. These felsic pyroclastic units are 130 ov erlain locally by thin horizons of fine-grained bedded· sediments which signal an end to this stage of volcanic activity. Explosive volcanic activity resumed within the area with the deposition of quartz- and plagioclase-porphyrtitic ash-flow tuffs of the "L" series pyroclastic rocks, marking a change in composition of the erupting felsic magma. Hydrothermal activity in the area peaked during this time with the deposition of the Sturgeon Lake massive sulfide deposit within the rocks of this series. Final volcanic activity within the area consisted of subaqueous deposition of mafic amygdaloidal lava flows which cap the succession and form the immediate hangingwall to the deposit. Subsequent intrusion of mafic sills and dikes completes the stratigraphy recorded within the area. Thin cross-cutting mafic dikes within the felsic rocks may, in part, be feeders to the overlying mafic flows. Hydrothermal alteration of the footwall succession is indicated by modal abundances of mineral phases too high to be explained by primary igneous compositions or their metamorphosed equivalents. Field, petrographic, and geochemical evidence have led to the identification of distinct alteration mineral assemblages classified on the basis of their modal mineralogy. These include a) silicified (quartz-rich), characterized by Si02 values in excess of 77 wt.%; b) iron-chlorite, with associated garnet, magnetite, 131 and iron-carbonate; c) chloritoid, +/- iron-chlorite, sericite, biotite); d) cordierite, with associated sericite, magnesium-chlorite, and biotite; e) aluminum-silicate (andalusite/kyanite) +/- sericite; f) sericite; and g) magnesium-chlorite. Within the South Sturgeon Lake assemblage hydrothermal alteration was probably initiated by the intrusion of the Beidelman Bay trondhjemite, a sill-like body which intrudes the lower maf ic volcanic rocks of the succession and acted as a heat source to drive convective circulation of hydrothermal fluids. Early hydrothermal activity within the study area resulted in the silicification of felsic volcanic and volcaniclastic rocks of the QPYF and Mattabi series. Silicification provided a partial self-sealed cap to the system, breached locally by deeper-circulating higher temperature fluids to form limited development of aluminum- silicate and chloritoid/Fe-chlorite alteration, related to the formation of the Mattabi deposit to the west. As this stage of alteration waned, less-evolved shallow circulating solutions were responsible for development of Mg-chlorite. Hydrothermal activity within the study area intensi- fied with the circulation of a high-temperature acidic fluid enriching the rocks in K and Na while leaching Si and Ca to develop the protolith of the widespread sericite assemblage. Possible deeper circulation of this same fluid enriched the rocks in Ca and Mg to develop the protolith to the 132 cordierite assemblage. The relationship of these assemblages to ore deposition remains unclear and requires further study. \ Subsequent deformation and accompanying metamorphism were responsible for pervasive bedding-parallel foliation I I 1 and growth of metamorphic phases such as staurolite, garnet, I \ cordierite, and biotite throughout the area, strongly I dependent on pre-metamorphic altered composition. 133 REFERENCES Brown, E.H., 1969. Zoned Garnets from the Greenschist Facies; American Mineralogist, vol. 54, pp. 1662- 1677. Busby-Spera, C.J., 1984. Large-Volume Rhyolite Ash-Flow Eruptions and Submarine Caldera Collapse in the Lower Mesozoic Sierra Nevada, California; Journal of Geo- physical Research, vol. 89, # BlO, pp. 8417-8427. Card, K., and Ciesielski, A., 1986. Subdivisions of the Superior Province of the Canadian Shield; Geoscience Canada, vol. 13, #1, pp. 5-13. Campbell, I.H., Franklin, J.M., Gorton, M.P., Hart, T.R., and Scott, S.D., 1981. The Role of Subvolcanic Sills in the Generation of Massive Sulfide Deposits; Econ. Geology, vol. 76, p. 2248-2253. Davis, D.S., 1987. Stratigraphy and Hydrothermal Alteration of the Gagne Lake Prospect; An Occurrence of Volcano- genic Type Massive Sulfides near Mine Centre, NW Ont.; Unpublished M.Sc. thesis, University of Minnesota, Duluth, Minn., 125 p. Davis, D.W., and Trowell, N.F., 1982. U-Pb Zircon Ages from the Eastern Savant Lake-Crow Lake Metavolcanic-Metasedi- mentary Belt, NW Ontario; Can. Jour. of Earth Sciences, vol. 19, p.868-877. Davis, D., Krogh, T.E., Hinzer, J., and Nakamura, E., 1985. Zircon Dating of Polycyclic Volcanism at Sturgeon Lake and Implications for Base Metal Mineralization; Economic Geology, vol. 80, p. 1942-1952. Deer, W.A., Howie, R.A., and Zussman, J., 1966. Tntroduction to the Rock Forming Minerals; Longmans, Green & Co. Ltd. London, 528 p. Dube, B., Koopman, E.R., Franklin, J.M., and Poulsen, K.H., (in press). Preliminary Study of the Stratigraphic and Structural Controls of the Lyon Lake Massive Sulfide De- posit, Wabigoon Subprovince, NW Ontario; Geological Survey of Canada Current Research (1989). Elder, John, 1981. Geothermal Systems; Academic Press, London, 508 p. Fisher, R.V., and Schminke, H.V., 1984. Pyroclastic Rocks; Springer-Verlag, New York, 472 p. 134 Fiske, R.S . , 1963; Subaqueous Pyroclastic Flows in the Ohanapecosh Formation, Washington; Geol. Soc. America Bulletin, vol. 74, p. 391-406. ------, and Matsuda, T., 1964. Submarine Equivalents of Ash Flows in the Tokiwa Formation, Japan; American \ Journal of Science, vol. 262, pp. 76-106. Fournier, R.O., 1985. The Behavior of Silica in Hydrothermal Solutions; in Berger, B.R., and Bethke, P.M., eds., I \ Geology and Geochemistry of Epithermal Systems; Reviews \ in Economic Geology, vol. 2, Society of Economic Geol- ogists, p. 45-62. Franklin, J.M., 1986. Volcanogenic Massive Sulfide Deposits: An Update; in Andrew, C.J. et al., eds., Geology and Genesis of Mineral Deposits in Ireland; Irish Assoc. for Economic Geology, Dublin, p. 49-69. ------, Gibb, W., Poulsen, K.H., and Severin, P., 1977. Archean Metallogeny and Stratigraphy of the South Stur- geon Lake Area; Mattabi Trip, 23rd Annual Institute on Lake Superior Geology, 73 p. ------, Kasarda, J., and Poulsen, K.H., 1975. Petrology and Chemistry of the Alteration Zone of the Mattabi Massive Sulfide Deposit; Economic Geology, .vol. 70, p. 63-79. ------, Sangster, D.M., and Lydon, J.W., 1981. Volcanic Associated Massive Sulfide Deposits; in Skinner, B.J., ed., Economic Geology 75th Anniversary Volume; Economic Geology Publishing Co., p. 485-627. Frey, M., 1978. Progressive Low-Grade Metamorphism of a Black Shale Formation, Central Swiss Alps, with Special Reference to Pyrophyllite and Margarite Bearing Assem- blages; Journal of Petrology, vol. 19, p. 95-135. Friske, P., 1983. Wall-Rock Alteration and Ore Genesis at the Lyon Lake Deposits, NW Ontario; Unpublished Ph.D. Thesis, University of New Brunswick, 210 p. Froese, E., and Gasparrini, E., 1975. Metamorphic Zones in the Snow Lake Area, Manitoba; Canadian Mineralogist, vol. 13, p. 162-167. Ganguly, J., and Newton, R.C., 1968. Thermal Stability of Chloritoid at High Pressure and relatively High Oxygen Fugacity; Journal of Petrology, vol. 9, p. 444-466. 135 Gibson , H.L., Watkinson, D.H., and Camba, C.D.A., 1983. Silicification: Hydrothermal Alteration in an Archean Geothermal System within the Amulet Rhyolite Formation, Noranda, Quebec; Economic Geology, vol. 78, p. 954-971. Goodwin, A.M., et al., 1972. The Superior Province; Geolog- ical Association of Canada Special Paper 11, p. 527-624. Grant, J.A., 1986. The Isocon Diagram -- A Simple Solution to Gresens' Equation for Metasomatic Alteration; Econ. Geology, vol. 81, p. 1976-1982. Gresens, R.L., 1967. Composition-Volume Relationships of Metasomatism; Chemical Geology, vol. 2, p. 47-55. Groves, D.A., 1984. Stratigraphy and Alteration of the Footwall Rocks beneath the Archean Mattabi Massive Sul- fide Deposit, Sturgeon Lake, Ontario; unpublished M.Sc. thesis, University of Minnesota-Duluth, 115 p. ------,Morton, R.L., and Franklin, J.M., 1988. Physical Volcanology of the Footwall Rocks near the Mattabi Massive Sulfide Deposit, Sturgeon Lake, Ontario; Can. Journal of Earth Sciences, vol. 25, p. 280-291. Hajash, A., and Chandler, G.W., 1981. An Experimental Inves- tigation of High Temperature Interaction between Sea- water and Rhyolite, Andesite, Basalt, and Peridotite; Contr. to Mineralogy and Petrology, vol. 78, p. 240-254. Harvey, J.D., and Hinzer, J.B., 1981. Geology of the Lyon Lake Ore Deposits, Noranda Mines Ltd., Sturgeon Lake area, Ontario; Can. Inst. Mining & Metallurgy Bull., vol. 74, #833, p. 77-84. Hess, P.C., 1969. The Metamorphic Paragenesis of Cordierite in Pelitic Rocks; Contr. Mineral. and Petrol., vol. 24, p. 191-207. Hey, M.H., 1954. A New Review of the Chlorites; Mineralog- ical Magazine, vol. 30, p.277-292. Hildebrand, R.S., 1984. Folded Cauldrons of the Early Pro- terozoic LaBine Group, Northwestern Canadian Shield; Journ. of Geophys. Res., vol 89, #BlO, p. 8429-8440. Hildreth, W., 1979. The Bishop Tuff: Evidence for the Origin of Compositional Zonation in Silicic Magma Chambers; Geological Soc. Amer. Special Paper 180, p. 43-75. 136 Hodgson, C.J., and Lydon, J.W., 1977. Geological Setting of Volcanogenic Massive Sulfide Deposits and Active Hydro- thermal Systems: Some Implications for Exploration; Can. Inst. Min. and Metallurgy Bull., vol. 70, p. 95-106. Hoschek, G., 1967. Untersuchungen zum Stabilitatsbereich von \ Chloritoid und Staurolith; Contr. Min. Petrol. vol. 14, I p. 123-162. I ------, 1969. The Stability of Staurolite and Chloritoid \ and their Significance in Metamorphism of Pelitic Rocks; Contr. Mineral. and Petrol., vol. 22, p. 208-232. Hudak, G.J.H. III, 1989. Physical Volcanology and Hydro- thermal Alteration Associated with the Archean F-Zone Volcanogenic Massive Sulfide Deposit, Sturgeon Lake, NW Ontario; Unpublished M.Sc. Thesis, University of Minne- sota-Duluth, Duluth, Minn., 167 p. Hutchinson, R.W., 1982. Syndepositional Hydrothermal Pro- cesses and Precambrian Sulfide Deposits; in Hutchinson, et al, eds., Precambrian Sulfide Deposits; Geological Assoc. of Canada Special Paper 25, p. 761-791. Hynes, A.H., and Forest, R.C., 1988. Empirical Garnet-Musco- vite Geothermometry in Low-Grade Metapelites, Selwyn Range, Canadian Rockies; Journal of Metamorphic Geol., vol. 6, p. 297-309. Irvine, T.A., and Baragar, W.R.A., 1971. A Guide to the Chemical Classification of Common Volcanic Rocks; Can. Journal of Earth Sciences, vol. 8, p. 523-550. Kranidiotis, P., and MacLean, W.H., 1987. Systematics of Chlorite Alteration at the Phelps Dodge Massive Sulfide Deposit, Matagami, Quebec; Economic Geology, vol. 82, p. 1898-1911. Lipman, P.W., 1976. Caldera-Collapse Breccias in the Western San Juan Mountains, Colorado; Geol. Soc Arner Bull., vol. 87, p. 1397-1410. ------, 1984. The Roots of Ash-Flow Calderas in Western North America: Windows Into the Tops of Granitic Bath- oliths; Journal of Geophysical Research, vol. 89, #BlO, p. 8801-8841. Lockwood, M.B., and Franklin, J.M., 1986. Implications of Chemical Trends within the Chloritoid-Altered Volcanic Rocks of the Wawa Belt; Geological Survey of Canada Cur- rent Research Vol. , p. 54-64. 137 Lydon, J.W., 1988. Volcanogenic Massive Sulfide Deposits Part 2: Genetic Models; Geoscience Canada, vol. 15, #1, p. 43-65. MacGeehan, P.J., and MacLean, W.H., 1980. An Archean Sea- floor Geothermal System, Cale-Alkali Trends, and Massive \I Sulfide Genesis; Nature, vol. 286, p. 767-771. \ I Morton, R.L., 1988. (Personal communication). Nebel, M.L., 1984. Hydrothermal Alteration of Felsic Volcanic Rocks at the Helen Siderite Deposit, Wawa, Ontario; Economic Geology, vol. 79, p. 1319-1333. ------, and Franklin, J.M., 1987. Two-Fold Classification of Archean Volcanic Associated Massive Sulfide Deposits; Economic Geology, vol. 82, p. 1057-1063. G.J.H., and Walker, J.S., 1988. Geology and Metallogeny of the South Sturgeon Lake Greenstone Belt, NW Ontario; Geol. Survey of Canada Current Acti- vities Forum Program with Abstracts, Ottawa, Jan. 88. ------, and Franklin, J.M., 1988. An Archean Submarine Caldera Complex: The Mattabi Ash-Flow Tuff and its Re- lationship to the Mattabi Massive Sulfide Deposit; Ontario Geol. Survey Current Activities Forum, Program with Abstracts, Toronto, Dec. 1988. Mumin, A.H., 1988. Hydrothermally Altered Rocks Associated with the Lyon Lake Archean Volcanogenic Massive Sulfide Ore Deposits, Sturgeon Lake, NW Ont.; Unpuplished M.A.S. Thesis, University of Toronto, Toronto, Ont., p. 64-123. Nebel, M.B., 1982. Stratigraphy, Depositional Environment, and Alteration of Felsic Volcanics, Wawa, Ont.; Unpub. M.Sc. thesis, University of 114 p. Osterberg, M.O., 1981. Felsic Pyroclastic Rocks in the Vi- cinity of the Helen Iron Mine, Wawa, Ont.; Unpublished M.Sc. Thesis, University of Minnesota-Duluth, 95 p. Osterberg, S.A., 1985. Stratigraphy and Hydrothermal Alter- ation of Archean Volcanic Rocks at the Headway-Coulee Massive Sulfide Prospect, Northern Onaman Area, NW Ont.; Unpub. M.Sc. Thesis, University of Minnesota-Duluth, 114 p. 138 ------;Morton, R.L., and Franklin, J.M., 1987. Hydro- thermal Alteration and Physical Volcanology of Archean Rocks in th Vicinity of the Headway-Coulee Massive Sul- fide Occurrence, Onaman Area, NW Ont.; Econ. Geol. vol. 82, p. 1505-1520. Richardson, S.W., 1968. Staurolite Stability in a Part of \\ the System Fe-Al-Si-O-H; Journal of Petrology, vol. 9, p. 467-488. Riverin, G., and Hodgson, C.J., 1980. Wall-Rock Alteration at the Millenbach Cu-Zn Mine, Noranda, Quebec; Economic Geology, vol. 75, p. 424-444. Rodgers, D.P., 1964. Geology of the Metionga Lake Area, Dis- tricts of Thunder Bay and Kenora; Ont. Dept. of Mines, Geological Report 24, 53 p. Rog, C.J.,(in prep.). Stratigraphy and Hydrothermal Altera- tion of Archean Volcanic Rocks of the Darkwater Area, Sturgeon Lake, NW Ontario; unpub. M.Sc. thesis, Univer- sity of Minnesota-Duluth, Duluth, Minn. Schreyer, W., 1976. Experimental Metamorphic Petrology at Low Pressures and High Temperatures; in Bailey, D.K., and McDonald, R., eds., The Evolution of Crystalline Rocks; Academic Press, London, 484 p. Seifert, F.,1970a. Low Temperature Compatibility Relations of Cordierite in Haplopelites of the System K20-Mg0- Al203-Si02-H20; Journal of Petrology vol. 11, p. 73-99. Severin, P.W.A., 1982. The Geology of the Sturgeon Lake Cu- Zn-Pb-Ag-Au Deposit; Can. Inst. Min. and Met. Bull., vol. 75, p. 107-123. Seyfried, W.E., and Bischoff, J.L., 1981. Experimental Sea- water-Basalt Interaction at 300 c, 500 Bars: Chemical Exchange, Secondary Mineral Formation, and Implications for Transport of Heavy Metals; Geochim. et Cosmochim. Acta, vol. 45, p. 135-147. ------, and Mottl, M.J., 1982. Hydrothermal Alteration of Basalt by Seawater under Seawater-Dominated Conditions; Geochim. et Cosmochim. Acta, vol. 46, p. 985-1002. ------,and Janecky, D.R., 1985. Heavy Metal and Sulfur Transport during Subcritical and Supercritical Hydro- thermal Alteration of Basalt: Influence of Fluid Pres- sure and Basalt Composition and Crystallinity; Geochim. et Cosmochim. Acta, vol. 49, p. 2545-2560. 139 Skinner , R . , 1969. Geology of the Sioux Lookout Map Area, Ont., a Part of the Superior Province of the Canadian Shield; Geel. Surv. of Canada, paper 68-45, 10 p. Smith, R.L., 1979. Ash-Flow Magmatism; Geological Society of America Special Paper 180, p. 5-27. \' Stanton, R.L., 1984. The Direct Derivation of Cordierite from a Clay-Chlorite Precursor: Evidence from the Geco Mine, Manitouwadge, Ontario; Economic Geology, vol. 79, p. 1245-1264. Thompson, J.B.,Jr., and Norton, S.A., 1968. Paleozoic re- gional Metamorphism in New England and Adjacent Areas; in E-an Zen et al., eds., Studies of Appalachian Geo- logy. Interscience Publishers, New York, p. 319-327. Trowell, N.F., 1983. Geology of the sturgeon Lake Area, Dis- tricts of Thunder Bay and Kenora; Ontario Geological Survey, Report 221, 97 p. Turner, F.J., 1948. Evolution of Metamorphic Rocks; Geol. Soc. Amer. Memoir . #30. Urabe, T., Scott, S.D., and Hattori, K., 1983. A Comparison of Footwall-Rock Alteration and Geothermal Systems Be- neath Some Japanese and Canadian Volcanogenic Massive Sulfide Deposits; in Ohmoto, H., and Skinner, B.J., eds. The Kuroko and Related Massive Sulfide Deposits, Econ. Geology Monograph 5, Economic Geology Publishing Co., p. 345-364. Valliant, R.I., Barnett, R.L., and Hodder, R.W., 1983. Alum- inum Silicate Bearing Rock and its Relationship to Gold Mineralization, Bousquet Mine, Bousquet Twp. Quebec; Can. Inst. Min. and Met. Bull., vol. 85, p. 81-90. Vernon, R.H., Flood, R.H., and D'Arcy, W.F., 1987. Silliman- ite and Andalusite Produced by Base Cation Leaching and Contact Metamorphism of Felsic Igneous Rocks; Journal of Metamorphic Geology, vol. 5, p. 439-450. Walker, J.S., (in prep.). Stratigraphy and Hydrothermal Alt- eration of the Archean Mattabi Massive Sulfide Deposit, Sturgeon Lake, NW Ontario; unpub. M.Sc. thesis, Univ. of Minn.-Duluth, Duluth, Minn. Winkler, H.W., 1979. Petrogenesis of Metamorphic Rocks; Springer-Verlag, New York, 366 p. 140 APPENDIX l MODAL MINERALOGY I I \I Thin sections were prepared from 220 samples gathered from the study area during the field season of 1987. Petro- graphic study resulted in the following table of modal mineralogy, as determined by visual estimation of the con- of each thin section. Included also are columns indicating lithologic unit (as defined in text) and alteration assemblages. ABBREVIATIONS USED A) LITHOLOGIC UNITS DWML-- Darkwater maf ic lavas DWMLA- " , amygdaloidal DWFL- Darkwater f elsic lava DWPYF- " , felsic ash-flow tuf f s INTR- Mafic Intrusive dikes and sills INTQP- Mafic "quartz-plate" intrusive LA- L-series ash-rich pyroclastic rock LAF- II , f ragmental LQ- L-series quartz-phyric ash-flow tuffs LQF- II , fragmental LQP- L-series quartz- and plagioclase phyric ash-flow tuff s MESBX- Heterolithic volcanic breccia MTA- Mattabi series ash-rich pyroclastic rock MTAF- II , fragmental MTM- Mattabi series mixed fragmental/debris flows MTQ- Mattabi series quartz-phyric ash-flow tuffs MTQF- II , f ragmental NNLA- No-Name-Lake Andesitic Flows QPYF- Quartz-Pyroclastic Flow Unit UPYF- Volcanic debris flows and bedded epiclastic rocks Al-a B) ALTERATION CODES: the following codes have been estab- lished based on alteration assemblages and relative timing of different alteration events (where determinable). PA- primary alteration SA- secondary alteration TA- tertiary alteration 1- least altered 2- Silicif ied assemblage 2A- Carbonate 4- Fe-chlorite assemblage 5- Chloritoid assemblage SA- Cordierite assemblage 7- Aluminum-silicate assemblage 8- Sericite assemblage 9- Mg-chlorite assemblage C) MINERALOGY: QT Z- quartz CD- cordierite SER- sericite PL- plagioclase MGC- mg-chlorite GT- garnet FEC- fe'-chlorite AM- hbld/actinolite CT- chloritoid EP- epidote/zoisite AND- andalusite TO- tourmaline KY- kyanite OP- opaques CB- carbonate ST- staurolite BI- biotite Al-b SAHPLE RXTYPE PA SA TA QTZ SER H6C FEC CT AND CB Bl CD PL 6T AH EP TD DP ST c su-106-0 dwfl . 5 BO. 5. 1. J. 4. 5. sl i-30 diiil 1 30. 0. 20. 40. 2. \ \ sli-106-B dnla 4 20. 25. 10. 20. 5. 20. 1. 1. I sli-87 dwpyf SA S 40. 40. sli-105-B dlipyf 2 a BO. IS. • 2. 3. c sli-143-540 i1la 4 2A so. • 10. 2. IS. lS. J, I. sli-143-560 i•la 2A 40. 30. 10. 10. 10. 1. sla-143-116S intqp 2A 20. 30. 20. 10. 20. c intqp 2A 30. J. 25. 35. 5. sll-162-1150 intqp 2A 30. 10. 5. 10. 38. 2. "J, slm-162-520 in tr 2A 30. 3. 15. 10. 4v. 5. sli-138-622 intr SA 40. 30. IS. 10. 2. 4. slm-136-403 in tr 2A ·1 10. 40. 50. 1. sla-148-28 · intr ·4 60. a. s. a. IS. sim-139-288 intr SA 50. 20. 20. 8. 1. 1. sli-162-445 intr 20. 10. 40. 30. 5. sla-143-660 intr 2A 50. 10. IS. 10. 12. 3. c sl1-132-87S intr 4 40. 10. 20. J. 20. 1. 2. sli-132-1177 intr 4 20. 20. ?C 25. 10. 10. sla-143-700 intr 2A 30. 25. 10. 2. 10. 25. slm-164-aBS intr 30. 2. 8. so. 4. 4. c sli-143-BSO la I 60. 10. 10. 15. Jo !. 1. ') 7 c sli-132-888 la 4 7i>. 10. 3. '-• 3. J. sla-132-256 la 4 75. 10. a. 3. 2. !. 1. slm-132-160 la 2 75. a. 3. sli-13 la 2 8S. 10. T I. sl1-132-1063 laf 8 oO. 33. 1. 4. 2. !. c sla-164-534 laf 4 60. 18. 1. 2. J, 10. sl1-132-b2B laf 4 2 75. 10. 10. 2. 1. !. laf SA bO. 3. 10. 10. a. 1. sl1-164-3SS lq 8 bO. 33 . 5. 1. 1. sli-132-79 1q 7S. 5. 12. 3. 1. 8. sli-162-301) lq a 70. 15. iO. !. lq a 68. 18. 10. !. !. la a 60. 30. 10. I. ') slj-140 lqf 8 65. 30. I. 2. L• sl1-164-S30 lqf SA 5S. IS. 15. 15. sli-110 lqp 2 8 7S. 20. 1. !. I. 2. c c sla-143-i40 lqp 4 70. 15. J. J. c c sl1-143-38S lqp 75. 5. ..J. .J. 8. !. sll-143-260 1qp ZA a 55. 5. 10. 3. c IS. sl1-135-161S so. 30. "' 20. !. c sl1-133-l194 1esbx SA 7S. J. 10. 10. 1. c sla-133-1147 SA 2A 9 30. 8. 20. 20. IS. J. 3. sl1-13S-1S76 2A so. 1. l. 20. 20. !. 8. sl j-S4 1esbx 1 40 . 4. 10. 2. 10. 30. 4. sli-140 1esbx SA 70. 2. T 10. 8. 2. 1. 2. < c sl1-13S-1220 mta SA so. 30. 8. .J. J. c slm-13S-216 1ta 1 oO. 10. J. 15. 2. 3. !. 1. c c sla-175-742 1ta SA 2 7S. 2. 2. 2. •·'- J. 1. sla-136-66S 8 5v. 45. !. I. !. 1. sli-136-690 1ta SA 2 60. lS. 10. 10. 2. 1. sla-138-392 1ta 2A 4S. 10. 20. 25. sli-136-477 ata SA 8 40. 40. 0. 2. IC. 1. slm-173-500 1ta a 115. 30. !. 2. c sla-172-474 ata SA 8 7S. 15. J, "J, Al-c RXTYPE PA SA Ttt QTZ SER tt6C FEC CT AND KY CB BI CD Pl GT AH EP TO OP ST ·sla-134-110 11ta \I 10 BO. 5. 3. "...... " 3. ·sl1-1)3-40S ,ta a OU. 25. ".... 10. I. \ slj-IS iata SA 2 I 65. 20. 3. \ sh-174-6SO · 11ta 6S. 10. 3. 3. 10. 8. \ sh-138-681 1ta SA 8 I 65. 2li. 10. 3. 1. I sl i-1 11ta SA 8 65. ·· is: 1. 3. 3. I. 1. 1. slj-2 1ta 8 65. 2S. 10. I. sli-175-362 11ta S 60. 15: 12. 10. 4. s} 1-133-784 ata SA B 60. 2S. 10. 7. sh-172-S62 11t;. SA 55. 15. 5. 5. 2. 2. "J, sh-174-809 •ti 115. 12. ".... a. ..." •sla-172-741 1ta a 75. 20. I. 1. I. slH 1ta SA 2 BO. 8. 2. 2. 1. sla-174-857 •ta . SA 2A 55. a. 12. 10. 12. 1. \ ·· sli-172-9SO ata 70. 15. 12. ".... 2. sl1-13S-al ata 8 50. 30. 2. 17. 1. 1. 1. sl1-f39-201 1ta SA a 50. 20. 15. B. 8. sl1-13S-978 1ta 75. 10. 15. I. 1. 1. sl1-17S-974 •ta 5 2 75. 8. 4. 4. 5. sli-21 1ta 7S. 15. 4. 4. 1. 1. sl1-172-S86 1taf 4 5A 70. 3. 20. .,•• ,j,' 2. sli-68-194 1taf 9 1s. 0. 12. sla-172-508 1taf 70. B. 10. B. 5. 1. sla-148-810 1taf 7(1. 12. B. B. 2. sli-68-438 1taf 8 60. 30. 10. sla-68-314 1taf 2 a 7S. 15. 10. I. sl1-13S-84 1t1 2A 30. 30. 40. 2. 2. sla-137-407 1t1 SA 2A 40. 3. 1. 35. 15. "Jo 1. 3. sl1-138-b08 1t1 SA 9 60. 2. 25. ...." 3. 2. sla-133-238 1t1 40. 20. 1. 30. 3. 1. sl1-13B-S25 1t1 5A 60. 3. 20. ...." 8. 2. 5. 1. slc-137-512 11t1 SA 60. 2. 15. 10. 8. 1. 1. sla-133-278 1t1 2A 10 40. 10. 1. 20. 35. I. 1. 1. sla-133-248 1t1 5A 50. 5. 2. 2. 35. 2. 2. 1. sla-137-661 1t1 SA 2A 60. 20. e. 8. 4. 3. sli-138-560 1t1 Sh 50. 2. 1. 1. 10. a. 20. 1. 2. sl1-163-S60 atq 2 a 70. IS. 12. 1. sli-17 1tq 2 74. 10. 4. 1. ".... 4. sla-135-1133 1tq B 65. 20. 2. 8. 3. 1. sla-163-701 1tq 65. 15. 15. 4. 1. ., sla-134-340 1tq SA 60. 15. 2. 2. a. 15. .. .:.. sla-134-490 atq SA a 65. 20. 2. 5. 10. sla-140-287 1tq 7 so. 30. 10. 15. sla-173-330 11tq 2 ii 70. 20. 5. I. I. . 2. sla-175-754 · 1tq 5 2 7S. ...." 10. 2. 4. 4. sli-156-927 1tq 5A 65. 10. 10. 1. I. 15. I. sl1-17S-65S 1tq 5 6 70. 20. 5. ".... I. sla-139-353 atq 2 a 75. 20. 2. 3. sli-19 1tq SA 2 75. 8. B. 2. "•" 3. I .. slc-134-636 1tq 2 75. 12. 5. 1. 1. I. sla-139-780 1tq 50. 15. 10. 20. 1. sln-148-523 1tq 8 75. 23. sla-175-417 1tq 8 70. 30. 1. ., sla-134-300 atq 5A 9 60. 5. 25. 1. 2. Lo 5. l • sla-172-240 1tq 2 a 70. 15. 10. 2. sla-133-656 1tq 2A 50. 5. 10. 25. 12. I. sla-173-360 1tq 2A 75. 10. 1. 10. 1. 2. sla-133-826 1tq SA 70. 15. ,,. 5. 5. Al-d SAMPLE RHYPE PA SA TA llTZ SER tlGC FEC CT ANil C& &I CD PL ST AH EP TO OP ST sli-B 11tq 4· 80. 5. JO. sli-138-419 1tq 5A 50. JO. 10. 1. 15. lS. 10. 1. 1. sll-Jt.3-394 11tq 8 60. 38. 2. s!l-J75-St.2 · 1tq 5 2 7S. 5. 8. 1. 10. slm-173-255 111tq 70. 2.Q. 2. 2. 1. 1. 1. \ sla-137-118 itq 2 80. 10. 1. 1. sh-148-544 lltq 75. 15. 10. 1. slt-175-803 1tq 5 2 7u. 8. 2. 10 . 8. •sl11-148-749 1tq s 2 72. 8. 10. 10. ·sh.-139-90 1tq SA 70. 15. 3. fi. 5. 1. 1. sla-140-807 1tq 2 75. 10. 10. 15. 1. 1. sll-172-J70 1tq 9 70. 12. 15. 1. slj-33 1tq 5ti 8 65. 25. 1. 1. sll-r.35-795 11tq 5A 2 65. 20. 5. I. 1. sl1-J39-460 11tq 8 70. 20. 2. I. 1. 2. slt-J74-436 1tq 8 9 65. IS. lS. 2. sl1-lb3-285 11tq 5 2 71. 12. 12. 4. 1. 1. sla-Jb3-3JOA atq 4 70. 8. 12. 5. 1. 3. I. sl1-J38-1084 i:1tq SA 8 00. 23. 3. 5. 4. 2. 1. 1. slt-138-J 139 atq 2 80. S. 3. 1. ..J, I. 2. I. sl11-137-83 11tq SA o5. 10. 3. 3. 2. 10. ..J, 1. 1. sla-140-:25 1tq 7 60. 30. 5. JO. sl11-lli3-775 11tq I 70. 12. 10. 3. sla-J38-823 11tq 7 0 60. 20. 1s. 2. I. sli-138-848 &tq I 70. 15. IS. 1. sla-136-957 11tq 7 70. 15. 10. 2. .-r,, sl11-J39-174 1tq 55. 20. .. 10. 5. 1. sla-135-592 1tq SA 6 60. 25. 10."' sla-140-160 1tq 5A 9 65. 15. 15. I. 1. sla:-l 74-!9J 1tq 8 9 SS. 25. 20. 1. 1. sl1-138-124 1tq SA 65. 8. 2. lS. 8. 2. 1. sla-J75-163 1tq 4 8 75. 10. 12. 1. sla-175-349 1tq 75. 10. 5. .. slia-140-665 atq 75. 2. 10. "' 15. sl11-68-492 1tq 2 a 65. 15. 10...... 1. , sla-133-3J8 ltq 5A 8 70. 15. 7. 8. .J, I. 1• Slll-174-140 1tq 7 8 55. 20. 15. 2. 7. I. slj-3a 11tq Ii 7S. 5. 2. 2. J5. 2. 1. sli-137-267 atq 5A 60. 20. 10. 10. 1. sl1-137-33J 1tq 6S. 18. 10. 0. 2. sli-175-830 1tq 4 72. 10. 7. 4. 2. 1. sla-J73-628 1tq SA 70. 10. .. 5. 4. 4. 3. slo-J35-537 11tq 9 65. a. 1s. "' 4. sl1-J37-943 mtq SA 50. JO. 20. 1. 10. 10. 1. sl1-J33-545 1tq 5A 70. 5. 10. 10. 5. 1; 1. slj-34 atq 5A 75. a. 5. 10. sla-J35-824 atq 65. IS. ..J, 10. 3. 1. -, sla-J38-335 1tq 2 9 75. 2. 18. ... 4. sl1-J74-519 atq a 60. 3u. 9. 1, sla-J39-818 atq SA 65. 5. 10. 1. 10. 8. 1. sl11-134-220 1tq 4 70. 8. 15. 2. I. 2. sla-140-60 atq 5A 40. lS. 2. 2v. 20. 3. sl11-J37-1093 1tq 7 60. 15. 8. 5. 2. I. sl1-137-IJ25 11tq I 75. 4. ... 15. 1. sl1-J34-5oO 1tq 2 a 70. 15. I. 10. 2. 1. I. 1. sl1-133-187 1tq 2a 8 65. 18. 5. 10. 1. sli-68-347 11tq 8 6S. 25. 10. I. sl1-J34-175 •tq 75. 8. ..J, I. 8. 3. 1. Al-e SAHPlE RXTYPE PA SA TA QTZ SER H6C FEC CT MID KY CB Bl CD PL GT AH EP TO OP ST sl1-140-225A mtq 7 60. 5. 10. sli-6 mtq 5 2 7S. lS. 2. 3. 3. 5Jj-23 1tq SA 2 70. 10. I. s. 8. 2. 1. 1 5}11-148-615 · 11tq 2 7S. 20. L• 1. \ 5lm-163-930 1tq 5 60. 10. 20. 2. 2. 3. 2. sl .-140-263 1tq SA 45. j... 5. 3S. 10. I. 5}1-163-865 1tq 9 65. 10. 20. sl11-136-BS4 11tqf SA B so. 30. 1. LO. B. 1. slr.-175-919 11tqf s 70. 2. 4. 10. 1. B. : slm-68-166 11tqf a 70. 22. 8. I. s!l-68-61 1tqf SA 2 75. 15. 3. 2. I. sl1-175-893 5 6S. B. s. 12. B. 1. sh-174-377 atqf . B 9 60. 18. lS. 1. 3. 2. sl11-13b-380 etqf SA · 9 so. s. 20. 2. 10. 2. 4. sl1-136-1013 itqf 7 B 60. 20. 10. 10. 1. 1. slo1-163-466 11tqf I 7(1. 15. 12. I. I. Slia-136-174 litqf 1 70. 10. 4. 12. 3. 1. sl11-139-649 atqf 6 8 so. 25. 10. 2. .7;. 10. l. 511-135-693 ;tqf 6S. 2. IS. 12. 4. 1. I. slli-164-19S nnla 2A 20. 40. 12. I. 3. 1. sl1a-13S-1295 qpyf 72. IS. .), 1. B. slia-13S-1S07 qpyf 5 B 70. 20. 4. 2. sll-139-1340 qpyf 5A 60. 10. I. LB. 12. 1. sl 1-133-1035 qpyf 5A 9 6S. 1. 12. 12. 5. J,7 slj-102-A qpyf S 5A 60. 10. B. b. I. sl111-13S-1376 qpyf 5 70. 12. 7 I. 12. I. slfi-133-973 qpyf 2 70. 10. LO. LO. sl11-139-1279 qpyf 2A 50. 10. 10. 30. slia-133-1231 qpyf 70. 2. 12. 1. p 2. sl11-139-l 17S qpyf 5A 9 55. 20. 1. 15. 5. sl11-134-B50 qpyf 70. 12. 2. 1. I. 2. 1. 3. sh-134-91S qpyf l 7S. LS. Iii. 1. I. slia-133-1102 qpyf SA 9 60. LS. IS. Iv. 3. 1. slm-134-1320 qpyf I 7S. 12. "... B. I. sli-135-1492 qpyf 5 65. 5. 20. 2. sl11-133-1214 qpyf 2A 60. 20. 10. LO. slj-104-6 qpyf 2 75. 10. IS. I. slid 40-1S9 I Qp)'f s 6S. LS. 2. 15. I. sli-136-1293 qpyf SA so. 10. 10. 2. 5. 1. 1. slHOH qpyf SA 67. 10. 15. 3. 10. I. 5}11-134-1214 qpyf 2A 8 65. 12. 12. 10. 1. slj-32-A qpyf 70. LS. LO. I. sli-139-1210 qpyf 10 60. 15. 20. slj-103-A qpyi SA 74. 7. 10. 2. I. slj-101F2 upyf 40. 4. 40. 10. 4. 2. 1. sl1-136-12SO upyf SA so. 2. 5. 26. a. 10. 5. 1. sla-136-1197 upyf 60. ""'· 3. 2. 25. 1. 1. slj-2S upyf SA 9 so. 20. 20. 5. 3. 1. I. 5}1-139-993 upyf 7 2 65. LO. 15. B. 3. sJj-102-E upyf 9 50. 25. 3. LO. 10. 2. sJj-IOlFI upyf S B lS. 45. 10. 30. I. I. sla-136-1128 upyf 4 65. a. B. 3. 2. s. 4. 1. Al-f APPENDIX 2 The f ollowinq table is compiled from whole-rock and trace element qeochemical analyses of 193 samples from the \ field area determined by Metriclab, Inc., Ste. Marthe Sur Le Lac, Quebec. Major oxides and C02 are reported in wt. %, trace elements in ppm (Au in ppb). Sample numbers given coincide with footages from selected diamond drill holes (SLM-) or outcrops (SLJ-), and as such are easily located on Plate 1. Rock types (rxtype) and alteration codes listed for each sample are explained in Chapter 2 and in Appendix 1. \\ I \ I A2-a SAKPLE"I RXTYPE PA SA TA 5!02 TI02 AL:o3 FED M6D CAD K2D NA2D MND C02 ZR NB ZN CU AU A6 slj-!Ob-D dNfl 5 69.8 1.4i 15.51 4.45 0.82 3.46 2.73 !J.11 0.58 202. I. 34. 11. 9. 6. 0,1 12. sl j-30 dNI) I 54. 1.33 10.37 5.41 b.31 0.73 3.17 i).!2 1),74 150. I. 35. 4(). 55. b. 0.4 22. slj-!Ob-B dNlla 4 55. 4 2.1 14.45 13.i4 5.36 5.35 0.42 0.59 1).44 0.71 132. 2. 23. 53. 2. 5. 0.9 11. sl j-87 dwoyf SA 8 74.2 i).48 14.2 ° 0 1.39 0.33 3.44 0.92 0.02 1.36 57b. 26. 59. 34. 29. 5. 0.1 b. sl e-lb4-885 intr I S6. I 1.5 18.13 2.11 3.11 I.I 2.83 0.26 2.09 118. 1. 35. 67. 62. 7. 0.6 18. sl1-m-2ea intr SA 71. 3 0.86 10.7b 4.47 4.9b 3.38 0.64 0.2i 0.12 I.I 372. b. 55. BO. b. b. I. 9. sll-162-445 intr 1 52.7 1.84 15.3 14.2b 2.59 b.bl I.IS 2.03 0.44 1.9 101. I. 30. bl. 58. b. 0.8 17. s l 1-138-b22 intr SA 9 75. 9 o.44 11.05 4.14 2.B3 o.8b 2.oa 0.2 o.o9 1.01 202. 1. 3b. b2. 2. 1. o.a 4. sli-143-700. in tr 2A 79.3 0.46 10.52 0.85 1),3 3.17 0.68 2.93 0.05 I. 438. 2. 50. 25. 41. 5. 0.3 19. sh-132-868 la 74. 7 0.44 12.42 2.9 0.72 3.b8 0.85 2.11 0.32 1.36 392. I. 84. 13. :;2. S. 0.2 15. sh-143-850 la 6S.3 1.03 IS.b2 6.SS l.i7 2.33 2.S5 2.45 0.2 1.17 320. !. 54. 98. 38. 7. O.b 18. slj-13 la 84.5 1).33 9.37 0.28 O.lb 0.53 1.23 2.b4 0.01 1.4 52b. 1. 72. 3l. 8. 5. O.l 6. sli-132-lbO la 4 2 80.6 1).18 3.6b 6.22 2.05 2.b4 0.8 0.05 0.42 3.08 118. I. 35. b7. 18. 8. 0.5 12. sll-132-10b3 8 65.6 1.03 lb.47 2.39 i),63 3.97 3.42 1.97 0.05 2.46 119 .•• 47. 17. 30. b. 0.3 15. sh-132-628 laf 2 80. 7 •l.43 8.93 3.47 0.88 1.61 1.37 0.97 0.09 I.Ob 353. I. bb. 50. 9. b. 0.4 9. sll-lb4-534 laf 56. 0.15 3.65 29.54 3.bB 2.4 0.03 0.22 1.4 2.3b 65. ! •. 27. 148. 33. i. 0.7 9. slll-lb2-135 lq 8 69. 9 0.39 13.48 5.1 3.29 0.82 2.b3 0.27 v.2 1.04 502. 17. bO. 171. 4. 5. 2.2 4. , s!H32-i9 lq ..;,J,/ - (•.38 i.b 9.12 1.95 1.07 2.02 0.98 0.1 O.Bb 235. 2. 53. 90. 38. 1. 0.7 18 • slll-162-300 lq 8 lb. I 0.36 11.33 3.16 0.28 2.32 0.27 0.09 1.2 458. 14. 7b. 43. 2. b. 0.3 3. sl1-lb2-175 lq 8 78.5 'l.25 l:l.23 3.lo 2.22 0.28 2.12 0.25 O.OB 0.4b 460. 18. b3. 245. IB. 5. O.b ;,, sl11-lb4-3BS 1q 8 6b.b 0.55 15.27 4.11 4.8 0.75 3. 0.93 0.09 1.2 b46. 31. BO. 644. b2. 5. 0.5 4. sll-lb4-530 lqf SA 63. 1).53 15.62 8.61 3.26 3.17 o.b9 1.42 0.23 1.15 480. 18. 76. m. a. 10. o.e 14. sli-14D lqf B bl.6 O.S4 18.4i 4.Sb 2.15 2.17 5.36 0.47 0.06 1.29 679. 39. IOI. b5. 3. 9. I. 7. sli-llD lqp 0 78.9 0.3b 12.38 1.4 O.b:i 0.43 3.35 0.44 J.01 0.57 579. b. 86. lb. 2. 5. 0.1 4. slll-143-740 lqp 71. 9 12.SB 5.33 1.19 1.21 3.63 0.39 0.04 1.04 482. :5. 68. 122. 42. b. 0.5 17. sll-143-2b0 1qp 2A 8 69.S 0.5 14.18 4.39 1.62 3.b8 l.b 2.02 0.04 2. 205. I. 27. 37. Sb. 8. 0.9 II. sla-143-385 lqo 75. 0.44 12.12 2.29 1.26 1.73 3.21 1.33 O.Ob 1.2 51V. 75. 72. 11. 7. 0.4 b. slj-54 1esbx b4. 7 1.09 13.22 7.89 2.85 4.69 1.5 2.25 O.lb 1.38 257. I. 39. 53. 46. 5. 0.4 11. sh-133-1194 1esbx SA 73.4 O.b7 11.3 2.81 3.94 3.45 l.34 0.5 0.11 1.27 357. 2. 53. 110. 2. 5. 0.7 8. sh-133-1147 1esbx 5A 2A 9 1.15 14.2 7.76 7.87 b.37 1.54 1),43 0.23 2.lb 132. !. 28. 103. 4. 5. 1.3 34. sli-140 Hsbx SA 73.5 l.l'i 14.19 4.01 l.b5 2.1 1.97 0.26 0.06 1.38 S63. 23. 62. b. 9. 7. 0.5 9. s 11-135-157 b 1esbx 2a 54. 2 1.03 13.48 7.73 5.92 7.22 2.19 0.43 0.58 b.23 172. !. 39. 185. 8. b. 1.2 22. sl1-135-lbl5 1esbx 57.1 1.24 15.41 9.21 b.27 5.29 3.29 0.74 0.18 0.81 113. I. 31. 78. 4. 7. 1.2 b3. sl1-13HIO 1ta 10 72.8 o.48 10.49 5.3b 2.73 3.47 2.33 o.44 0.13 1.24 432. 11. 66. m. 4. s. 0.1 1. sl•-135-1220 eta SA 8 b4.4 0.67 19.18 4.34 2.63 1.19 4. 72 1).52 O.Ob 0.83 6SO. 36. BB. 104. 3. 5. 0.4 4. sli-135-bl 1ta B 63.6 O.al 17.79 4.08 2.45 2.91 3.7 2.14 0.52 1.24 72'?. 40. 91. 107. 8. 5. O.b 9. s!l-175-742 eta SA 2 79.5 0.4i 9.52 :;,3 1.02 2.lb l.4S (J.79 0.05 1.04 394. lb. b2. 33. IC. 5. O.S 12. sl1-13b-477 11h SA 8 58.8 1).43 l?.2i 5.57 5.27 4.58 1.54 1.02 0.16 1.27 591. 33. bb. 288. 9. 5. I. 7. sl11-174-B57 1ta SA 2A S8.2 1.13 14.63 b.18 6.5 5.9 1.68 0.4b 0.23 2.3i 17S. 1. 38. 22b. 2. b. 1.4 20. sli-172-474 eta SA 8 75.8 o.54 13.24 1.1s 1.91 0.14 3.36 0.21 o.o3 1.2 21. 01. 41. 2. 5. 0.1 2. sh-13b-bbS mta 0 11.1 0.39 12.42 2.27 1.58 0.3 3.44 0.22 o.os 1.24 ::i87. 21. 79. 37. 3. 5. 0.1 2. sl1-172-5b2 1ta SA bl. b o.ss 11.2b 4.47 3.lb 4.17 1.13 0.29 0.1 4.32 423. b. ao. bo. 23. b. 0.0 8. sh-138-bBI 1ta SA 8 b7.b 0.47 lb.42 3.27 3.04 0.9b 3.88 0.32 0.05 0.74 438. 7. b3. 101. 3. 5. O.b 3. slj-IS 1ta SA 2 79.b 0.44 10.51 2.1 !.27 2.03 1.8 0.44 O.Ob 1.36 421. !. 71. 49. 2. 5. 1),3 i. sla-172-741 1ta 74.5 0.5 !S.73 1.27 0.35 1.25 3.19 0.41 0.03 fJ.6 781. 45. 103. 15. 21. 6. 0.2 3. sl1-175-3b2 1ta s 68.b t),b lb.02 5.99 1.67 0.23 3.b2 0.25 0.11 0.99 512. 19. 71. 55. 4. 12. 0.7 9. sh-174-650 1ta I 67. o.s7 12.19 4.58 4.63 4.45 2.22 o.3b 0.11 1.5 m. 2. 56. 98. 3b. 5. o.8 s. sll-13b-b90 1ta SA 2 77.3 0.32 10.22 3.78 2.83 0.6 2.34 0.18 O.Ob O.b7 496. 19. 71. 70. 2. 6. 0.4 4. sla-133-784 1ta SA 8 76.8 o.41 11.79 2.04 2.s0 o.57 2.bl o.32 o.o4 1.33 m. 13. 85. 51 •. b. 5. o.3 3. sh-173-SOO 1ta 0 7b. 0.49 11.9 3.22 l.bl 0.35 3.2S 0.19 0.09 1.47 4?6. 19. 71. !OB. 24. 8. O.S 8. slj-21 1ta 72.9 0.45 10.91 5.i9 3.33 2.87 1.98 0.22 0.(•6 1.36 374. !. b9. 133. 86. 6. 1.3 10. sh-174-809 1ta i0.2 0.41 12.iB 3.02 2.74 3.02 2.94 0.48 0.07 2.C7 433. 9. 71. 65. 3. 5. 0.4 4. sli-138-392 1ta 2A 9 53.S 1.14 13.12 b.76 6.41 8.47 1.S9 0.31 1),12 i.4 160. !. 39. 91. 91. b. 1.4 41. sl1-135-2lb 11ta b8.5 1).55 13.S2 5.35 3.45 2.84 3.2b O.b3 0.2b 1.22 414. 26. bl. 12b. 6. _s. I. 9. slll-135-978 1ta 74.2 0.39 11.45 3.83 2.82 2.92 2.4S 0.3b 0.3 0.88 473. 14. 75. 108. 13. 5. 0.9 8. sl1-139-201 ata SA 8 12.1 0.48 13.lb 3.28 3.74 0.99 2.15 1),37 o.os O.b7 bl7. 19. 84. es. 10. 8. 0.4 5. A2-b SAMPLE I RXTYPE PA SA TA SI02 no:;: AL203 FED KGO CAO !(20 NA2G HNO C02 ZF. NB y rn cu AU AG NI sh-172-950 1ta il.S o.46 12.1,1 4.o7 4.3? o.3 2.19 0.11 0.14 1.:;:; 4S6. 15. bO. 114. 6. o.e 4. slt-175-974 •ta s. 2 i9.a •).41 I.Ob I.SI 0.::1 1.93 0.1:: :),01 1.36 359. a. 58. 44. 2. 5. o.s 4. sh-68-114 77.9 u.2a 1.1 3.52 4.:s .1.b6 0.14 0.1 1.11 418. 2. 66. 90. ' 1. 1).5 3. sh-68-314 ttaf 2 5 11.,, 0.3 Ht07 4.Jl8 1.H 0.1:: Z.53 0.22 •i.Ci 1.36 487. 8. 73. 49. 2. 7. 0.3 3. sh-172-508 1taf SA 2 78.i 0.38 9. 3.12 3.22 1.09 1.36 0.54 0.08 1.27 380. 7. Si. 75. 3. 7. 0.6 4. sla-148-810 1taf 2 78. 0.43 9.71 S.14 1.29 0.32 1.77 \l,18 0.11 1.22 353. I. S3. IS7. 169. 10. 0.7 5. sli-68-438 •hf B 75.e o.35 11.6 4.01 2.2e 0.13 2.66 0.11 o.o9 1.24 m. 14. 11. a;. 4. 6. o.4 s. sh-138-698 •ti SA 65.4 1.42 12.66 7.97 5.47 2.32 I. 0.46 0.12 0.99 215. I. H. 91. 27. 8. 0.9 IB. sh-135-84 1t1 2A 35.J 1.44 17.68 10.14 8.66 JO.Ob 4.51 1.04 0.61 7.57 183. 2. 42. m. 68. 5. 1.9 35. sh-138-525 1t1 SA 66.a 0.97 12.48 4.95 3.92 5.79 1.12 C.4 0.17 1.66 204. I. 35. 46. 21. 7. 0.9 21. sli-133-248 •t• SA 64.7 J.28 13.53 7.76 J.91 2.83 3.li3 0.56 ('.15 1.04 2:;b. 3. 49. IOI. 39. 6. I.I IS. sll-13l-278 •h 2A 10 SS.6 1.37 12.39 7.94 5.12 6.48 3.37 0.39 1.02 5.77 131. I. 33. 105. 23. 5. I.I 25. sh-137.-661 1t1 SA 2A 53.6 1.43 18.09 7.54 b,48 5.74 1.14 I. 0.21 1.33 214. I. 27. 7i. 6. 5. 1.5 37. sl11-m-407 1t1 SA 2A v.85 10.99 s.a3 s.12 9.93 1.41 o.73 0.11 6.76 167. 1. 38. 54. 4. s. 1.3 32. sh-HS-S44 •tq 1 69.b o.43 11.11 3.os !.64 o.32 4.19 o.:6 o.o9 1.29 690. 45. eo. 94. 2. 6. o.6 3. sl1-l:i5-1133 1tq B 71.5 o.4 1s.31 2.1 1.ss 1.44 4.13 o.36 0.1 1.01 103, :1; 97. 61. 16. 0. o.s 3. slj-17 'tq 2 1a.5 o.41 9.28 3.04 1.84 2.1;1 2.19 o.n 0.06 1.13 :;29, 1. 55. 74. 2. s. o.6 a. si1-13B-9S7 •ta I 54.7 1.93 18.35 2.94 5.84 5.2 1.18 0.44 0.14 1.5 711. 44. 86. 11. 6. 1.4 33. sh-136-124 1tq SA 70.7 tl.58 13.45 3.71 j,35 2.69 2.84 0.52 0.1 I.OB 466. 14. 79. 67. 4. 6. O.S 5. sh-133-826 •tq 5A 76.1 o.32 12.20 1.8 1.74 1.93 2.01 o.:i:: o.o4 1.::1 m. ao. 45. s. 5. o.s 3. sh-134-175 1tq 1 76.6 0.:3 9.99 3.96 1.99 3.23 1.57 O.:ib 0.14 I.I 435. 10. 67. 105. 3. 6, 0.6 4. sh-14•)-287 1tq 7 76.e o.39 12.94 2.69 2.56 o.o9 1.54 o.63 0.02 1.4 B42. 23. 6i. 53. 1. o.3 4. sh-134-490 1tq SA 8 75. 0.42 2.92 1.92 j,7J 2.15 0.63 0.09 i).81 561. 17. 69. 137. 4. 6. 0.7 5. sh-174-436 1tq 8 9 68.3 0.58 12.3j 5.85 6.23 0.42 1.79 0.23 ii.JS 1.7 345. 3. 56. 130. 29. 6. 0.8 S. sh-68-347 1tq 8 70.9 0.37 14.34 4.76 :!.61 0.16 3.23 0.24 0.1 1).71 570. 36. i6. 79. 3. s. 0.4 3. sl1-m-03 ttq SA 72. 0.56 11.6 4.2 2.07 4.43 2.17 0.32 1),J 1.89 358. 5. 53. 68. s. s. 0.9 6. sh-173-360 •tq 2A 82.4 0.53 7.49 2.?I 1.44 1.78 0.4 0.29 0.06 1.71 3v6. 2. 33. SS. 3. 11. 0.4 B. sla-148-523 1tq 8 76.9 o.3s u.29 1.s3 1.02 0.10 3.77 o.2e o.o4 1.22 60o. 3o. as. 37. 2. 6. 0.2 2. sll-137-331 1tq 2 a:;,9 o.32 1.s 1.99 1.21 1.12 1.22 0.25 0.02 1,3 m. 2. 53. 37. 9. 5. 0.2 s. s11-m-101 1tq 2A 8 75.6 0.45 9.99 3.08 1.74 2.28 3.24 0.51 0.09 2.37 384. 2. 60. 67. 4. 7. 0.5 5. sli-140-665 •tq 2 79.4 0.21 s.31 3.86 2.65 1.69 2.13 0.22 0.1 o.e4 m:. 1. 72. 94. 2. 6. 0.1 6. sli-173-330 1tq 2 78.1 0.35 8.95 3.81 1.9 J.82 2.13 0.23 0.1 1.5 380. 2. 54. BO. 13. 7. 0.3 4. sla-139-174 1tq SA 8 73. J O. 45 12.62 2.39 2. 6 3.11 2.31 0.56 O. Ob 1.31 573. 18. 83. 58. 2. 5. O.S 4. sh-134-560 ·etq 2 77.1 0.36 11.3 2.77 1.27 2.28 2.6 0.41 0.04 1.28 515. 2S. 77. 82. 14. 5. 0.6 4. sl1-l37-l18 1tq 2 82.2 0.35 B.06 2.74 0.84 2.13 1.89 0.18 0.06 I.OB 340. 3. 66. 55. 7. 6. 1).4 4. sh-139-353 •tq 2 82.5 C.3 JO.bl 0,4Q 0.43 0.75 2.64 0.26 0.01 0.64 440. 7. 63. 9. 2. 6. 0.1 !, sll-140-263 •tq 5A 76.7 0.35 11.04 :.:i3 :.64 2.01 0.31 1.73 0.02 l.43 802. 27. bi. 49. 2. s. 0.3 4. sla-172-170 1tq 76. il.43 B.69 5.02 4.81 O.JB 0.87 0.08 0.54 l,04 347. I. b4. 309. 75. 6. 0.6 S. sl1-175-830 •tq 4 75.2 0.42 9.29 b.45 0.63 2.18 0.1 0.14 o.97 309. 3. 57. 55. :1. 5. 0.5 7. sli-139-818 1tq SA 74.7 0.44 11.01 3.38 3.12 3.29 1.09 0.75 0.1 1.75 368. 3. SO. BB. 3. 6. 0.7 5. sh-163-560 1tq 2 7U 0.27 9.44 3.4 1.79 0.23 2.23 0.15 0.1 1.66 429. 11. 55. 45. 4. 7. 0.3 4. sli-138-335 •tq 2 79.8 o.47 0.a1 1.94 1.1s 1.2e o.2b 0.01 1.04 379. a. 34. 59. 3. 6. o.6 4. sh-174-140 1tq 7 8 66.8 1).86 15.55 3.65 4.71 1.14 2.73 0.51 O.Ob l.43 778. 54. 100. 64. 4. 7. 0.4 4. sh-174-191 1tq 8 9 66.1 0.62 16.62 4.43 0.32 j,33 0.36 0.05 o. 99 555. 19. 99. 92. 2. 6. 0.4 3. sh-163-285 1tq 5 2 n.9 0.26 7.4B 7.95 2.35 o.45 o.e 0.1 o.o9 1.31 322. 1. 46. 200. 121. 6. o.a 10. sll-134-220 1tq . . 4 76.3 0.44 11.64 3.47 1.15 1.91 2.55 0.44 0.11 1.06 596. 21. 94. 98 •. 34. 5. 0.4 4. sh-173-255 1ta I 73.9 0.38 9.48 7.85 1.73 1.24 2.49 0.17 0.25 1.17 m. 2. 60. 94. 35. 12. 0.5 8. sla-139-90 1tq SA 76.6 o.42 11.n 2.49 1.a3 2.01 2.6 o.35 o.o5 o.46 550. 1a. as. 68. 4. 6. o.s 4. sh-133-545 1tq SA 74.4 :).48 11.7 0.92 0.07 1.44 2.62 1.31 1.32 1.29 423. 2. 54. 69. 15. 5. 0.5 4. slt-133-656 1tq 2a 60.9 0.37 9.01 4.81 S.12 8.24 2.48 0.26 0.37 7.59 273. I. 49. 110. 5. • 5. I.I 10. slt-138-1084 1tq SA 8 78.5 0.3 8.04 3.73 3.06 1.92 1.58 O.JB 0.16 0.58 641. 30. IOI. 95. 17. 5. 0.5 5. sh-140-225A •tq 7 77.3 0.45 12.38 3.02 2.97 0.23 0.74 0.18 0.04 1.24 IE3 35. 46. 69. 11. 6. 0.4 4. sla-139-460 1tq B 76. 0.34 11.34 2.49 2.07 1.45 2.93 1).IB 0.05 1.22 543. 19. 76. BB. 9. 7. 0.3 4. sl1-163-310A 1tq 4 69.s o.4 10.sa 6.56 3. 2.94 2.11 o.ra 0.1 1.61 384. 19. b2. 62. 12. 13. 0.1 11. sla-172-240 1tq 2 B 7B. 0.44 10.31 3.32 2.81 O.JS 1.96 0.2 0.1 1.43 :i66. I. 53. 13B. 34. 6. 0.7 4. sli-140-807 •tq 2 79.4 0.32 9.27 3.66 1.71 1.33 Z.66 0.24 0.13 1.03 414. 7. 66. 39. 2. 6. 0.4 S. sh-137-109:i 1tq 7 76.2 0.43 10.93 3.03 2.45 0.78 2.1 0.22 0.06 1.22 648. 30. 89. 44. 3. 6. 0.4 4. slt-163-775 •tq I 76.6 0.3 ll.S2 3.86 2.14 0.22 2.65 0.22 O.J 1.31 500. 12. 66. SB. 4. 6, 0.4 3. A2-c SAKPLE I RITYPE PA SA TA 5!02 TI02 AL203 FED H60 CAO NA:W KNO m ZR N& ZN CU AU it6 NI sh-163-865 1tq iU o.H 11.s 4.ac. 2.2s o.s9 2.55 0.2 0.1 1.6e 428. a. s7. 57. 2. 1. o.5 4. sle-163-930 1tq 5 73.3 0,45 9.74 B.0·1 3.02 o.s2 1.36 0.12 o.2e 1.1:; 303. ?. 4B. 117. 102. 9. o.e s. sl1-11s-:m atq 5 88.6 0.19 S.Sl 2.0o 0.4S 0;42 1.:a 0.1 0.05 1.03 297. I. SS. l2. 21. 5. 0.1 8. sh-148-615 1tq 7 2 BJ,j o.46 o.5 o.1e o.46 2.s o.:;s o.o5 49i. 11. 85. 1:. 4. s. 0.1 3. sh-16:1-394 1tq 8 74.S 0.34 1:.56 :.62 1.46 0.65 3.45 0.25 ii.Ob 1.73 6b5. 23. B2. 29. 3. 7. 0.4 4. sl1-m-srn 1tq SA 6 6B.4 0.6 13.0S 4.::;: 3.98 1.49 2.14 O.J. 2.22 0.92 425. 5. 65. 103. 32. 6. I. 19. sil-138-848 1tq I 72.9 o.45 13.62 :;.13 2.:a o.s2 o.:a 0.08 o.6 m. i. 74. 9B. 2. 6. o.4 4. s1a:m-m 1tq 5A 2 77. 0.3b JO.a 2.B2 2.92 1.47 2.53 0.31 0.12 1.4 5:0. 9. 76. 122. 3. 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S. 0.9 19. etq SA 8 ]j,4 0.3? 14. JS 2.88 1.26 1.67 3.75 O.li O.Oa o.n 610. ZS. 98. so. 3. 10. 0.3 5. sh-174-Sl9 1tq 8 b6. j o.s1 14.42 4.97 5.61 o.5B 2.19 1> • .<5 0.12 1.3b m. e. B4. m. s. 6. o.6 4. sli-69-492 1tq 0.29 S.i8 4.&S 2.85 0,19 I.Bl 0.12 0.09 1.27 324. 9. 65. 92. ISi. 5. 0.7 5. sh-134-340 1tq SA i7. 0.::1 9.91 :.63 2.5s 2.94 1.45 o.44 0.1 1.26 405. Ii. 59. 121. B. B. o.B 5. sil-175-S6: 1tq s 2 77.:: 0.2: b.94 9.:li 1.1; O.SI 0.93 0.2a 0.06 1.96 Z:lb. ,. 42. 61. 149. 52. I. 24. sl1-140-160 1tq 5A BO. 7 0.ee :.es 1.95 2.06 o.8S v.4V o.oe 0.11 m. 0. 1. 73. 3. s. a.s 4. sl1-ll5-S37 •ta i4.2 0.26 9.26 s. 4 s.:1 1.22 o.39 o.:: 0.11 1.:;: m. 1. 54. m. 10. 1. o.6 1. slhi4 •ta 5A o.3a 1.17 1.;2 1.s6 2.97 o.6 o.o3 1.31 6C•e. 31. 92. 41. 2. b. 0.2 3. sla-m-iBO 1tq 70.4 o.43 14.BB ::.2s 2.16 4.22 2.01 o.B3 o.oe 1.14 631. ;: •• ie. B9. 6. 5. o.6 4. sli-19 1tq SA 2 7B.6 o.3 9.91 1.ss 1.16 2.64 0.22 1,33 405. 11. 11. 129. 5. 6. o.6 e. sl1-14B-749 atq S 2 83.3 o.41 e.44 3.37 o.9e c.15 1.24 o.11a o.oe o.s1 1. Sb. 1:1&. 20. a. 0.2 l. slj-23 1tq SA 2 Bl.S o.2b 8.B5 1.51 1.44 2.12 1.57 o.42 0.03 1.31 m. 1•. 50. 4o. 4. 1. o.B a. sh-175-417 1tq B il.3 0.4 IS.32 1.92 0.17 4.26 3.27 0.04 0.74 6B7. 37. BS. 22. 2. S, 0.3 3. s1.-m-m 1tq 4 8 n.6 o.:n 10.64 6.9; z.B7 0.31 1.43 0.24 o.36 o.69 414. 12. 53. 687. 3. 6. o.6 B. sl1-1n-31B 1tq SA 8 77.l o.36 10.5B 3.47 2.5 1.12 2.u Q.3B u.o9 o.69 m. 1a. 11. 97. 4. 5. o.4 4. sl1-13B-B23 1tq 1 a .· ... ..;- o.45 13.19 3.11 2.64 1.3S 2.79 0.2 o.o5 0.11 m. n. 85. a2. 5. 6. o.3 2. sl1-137-943 ittq SA 64. 7 1.31 15.06 4.2q 5.69 1.89 2.12 O.B2 0.06 1.06 304. I. 40. 54. 4. 5. 0.6 19. siia-174-377 1tqf e ob. 9 o.5 1:z.1s s.12 s.B4 1.61 1.B3 o.54 0.12 1.36 m. 17. 1e. m. ..,. 6. 0.1 5. sl1-m-:Bo •taf SA l.2B ll.51 7.0B ii.17 j.38 1.35 u.39 0.2 1.17 m. I. 47. 114. SI. 7. 0.9 IS. sl1-175-119 •lqf s 76.C 0.5 9.S5 6.5 2.08 0.3B 1.62 0.06 0.15 I.Ob 316. 3. 46. S3. 3. 5. O.S 5. slrl36-B54 1taf SA 8 <1.SI IB.05 2.2B 2.:2 1,61 4.74 0.53 0.05 O.SS 846. 42. 97. 107. 3. S. 0.3 3. sl1-135-69:l 1tqf I bi.? 0.6 11.15 5.53 5.64 l.97 2.13 0.47 0.56 I.OB 393, IC. 65. ISl. 15. 7. J.l 13. sl1-l:i6·1013 1tqf 7 8 75.S 0.34 10.93 2.99 1.43 l.9B 0.29 0.11 0.62 4BB. IS. BO. 70. 3. 5. 0.4 4. slia-139-649 1tqf 6 8 73.7 o.5B 13.35 3.41 2.:11 1.26 2.6b o.25 o.oe 1.2 m. 14. n. 4S. 8. 6. o.s s. sl1·6B-l66 •tqf 8 75.6 0.37 12.09 2.9S 2.BS 0.33 2.76 0.21 0.04 1.06 S30. ... 76. 34. 2. S. 0.2 3. slia-69-61 1tqf SA 2 90.3 0.31 10.3 1.7B I.OB 0.7S 3.04 0.19 0.03 0.69 4SB. 6. 66. 31. 10. 6. 0.1 3. slm-136-174 1tqf I 70.9 0.49 12.01 3.96 4.12 4.31 1.65 0.28 0.1 1.27 m. i. S3. 75. 9. 5. 0.9 7. sh-I 75-B93 1taf ·s 76. o.57 9.i6 7.29 1.1B 0.25 2.08 0.12 0.14 1.04 26b. 2. s2. 67. 9. 6. o.s s. slm-163-466 1tqf I 74.1 v.45 10.62 5.66 3.42 0.41 1,94 0.14 O.lb 1.61 360. B. 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Z3. 7. o. 7 2. sl.1-133··973 qpyf 2 77.7 o.: 10.54 "· Q?·-- 2. 4 2.05 1.86 1),29 0.1 1.38 H6. 19. 71. 81. .,,, 5• O.b 5. sli-133-1214 qpyf 2A 75.3 0.57 9. 76 Z.34 1.95 2.95 2.3 0.19 0.05 2.85 358. 1, 60. 59. 2. 6. 0.4 5. slj-102-A qpyf 5 SA 74.Z 1),58 12.58 4. 47 1.99 1.77 1.97 0.29 0.1 1.27 508. 20. ib. ••• 4. 5. 0.4 5. slj-32-A qpyf s 74.3 0.66 10.3 7.01 2.86 o. 6 1.16 0.37 0.12 1.22 274. 1. 35. 39. 105. b. O.b 10. sla-136-1293 qpyf SA b4. O.b4 13.69 5.22 4.97 4.19 2.49 1.03 0.07 1.66 240. I. 39. 91. IS. s. I. 4 136. sli-135:1295 qpyf I 70. 4 . :;,n 0. 58 15.29 -V1wJ 2.06 1.33 o.:3 0.13 1.22 57-i. 19. 88. 174. 11. 6. 0.5 10. sla-133-i231 qpyf 1 72.? 0.53 11.95 4. ::1 3.06 Z.36 1.74 o. 99 O.IS 1.36 m. 12. 60. 92. 7. o.s 13. sla-135-1492 qpyf 5 i0.6 0.77 13. 6S 1.92 0.61 1.29 0.09 0.32 1.29 m. 20. 44. SB. 17. 6. 0.7 8. s!l-m-1376 qpyf s 75.6 0.47 12.09 3.34 1.86 1.72 2.53 O.Z6 0.21 1.29 483. 20. 63. 69. 6. 0.6 7. slHOl-F2 upyf 5 66.S 0.76 12.01 11.:i.4 3.95 C.6 1.24 0.33 0.29 1.24 199. 1. 36. 67. 31.'· b. o. i 28. sh-t:i9-993 upyf 7 2 77.3 1).52 9.82 3.22 2.67 2.06 1.37 0.2S 0.12 I. 4 398. l. 55. so. 3. 6. 0.6 5. sli-102-E upyf 9 61.1 1.94 13.22 10.54 5.19 3.86 1.13 0.31 0.14 1.31 171. 1. 44 . 97. 30. 5. I.I 14. sli-25 upyf SA 69.5 •i.69 11. 6.09 5.56 2.4 1.91 0.29 0.13 o. 97 320. 52. 94. ,. 7. I. 9. sh-136-1250 upyf SA o.6a 13.57 4.63 3.67 S.87 1.72 o. 98 0.14 0.92 261. I. 39. 84. 9. I. 26. .,., e. sla-136-1197 upyf I 75.1 1).27 9.18 4.29 .; • 5.07 0.42 0.39 0.14 1.36 305. I. 45. 28. 4. 6. o.s s. sli-136-1128 uovf 4 ]j,4 v.32 10.42 5.7 2.29 4. 41 0.77 0.32 0.19 1.22 428. 2S. SB. 50. 3. s. 0.6 10. sl i-101-FI upyf s B 65. 1.35 19.54 S.bl 0.99 0.29 3. 77 0.4 0.15 1.33 188. I. 44. l'?. s. 7. 0.3 11. A2-e ..Z..PPE.NDIX 3 MASSIVE SULFIDE OREBODY MODAL MINERALOGY 17 polished sections were prepared from samples taken from mine development DOH# SLM-156 to study rnineraloqy and textures. The followinq table is a result of petroqraphic analysis of these samples as determined by visual .estimation, qiven in modal percentaqes. SAMPLE NUl1BER PYRITE PYRRHOTITE CHALCOPYRI TE SPHALERITE GALENA MAGNETITE ARSENOPYRITE GAN6UE 7 'l ' SLH-156-012 30. o. 1. 40. ·j' o. o. .. a. SLH-156-022 30. 0. 1. 30. .J." 0. ".J. 30 • r: SLH-156-032 65. 1. .J. 17. 2. o. 1• 10. SLH-156-052 8. ..,,< 20. 8. 0. o. 0. 60 . SUl-156-073 60. (I, o. 15. 2. o. 1. 25. SLM-156-087 50. !), 20. 30. o. o. 1. 0. c: SUl-156-092 60. .J, 20. 15. 0. 0. o. 3• 1' 1' SLM-156-100 40. ·Jo 30. 10. 0. 12. o. ,,, SLH-156-110 1. 8. 40. 28. (I, 18. 0. 10. c: c: 7 SLM-156-120 .J, .J, 40. 0. 30. 0. 17. c: -"c: SLH-156-130 0. .J, 30. .J. 0. o. 1. 60. SLM-156-140 0. 10. 50. 1. o. 0. 1. 40. 7 SLH-156-150 0. ,;, 15. 1. o. 0. 0. 81. SLM-156-160 o. 8. 20. 2. 0. o. o. 70. ') SLH-156-169 '-• 10. 35. 2. 0. o. 1. 53. SLM-156-188 0. 2. 8. 0. 0. 0. 0. 90. c: SLH-156-208 o. 10. 80. .J, 0. 0. 0. 5• A3