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The Salmo lead-zinc deposits : a study of their deformation and metamorphic features MacDonald, Alan Stratton 1973

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nzo? c l THE SALMO LEAD-ZINC DEPOSITS: A STUDY OF THEIR DEFORMATION AND METAMORPHIC FEATURES by ALAN STRATTON MACDONALD B.Sc. University of Glasgow, 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geological Sciences We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1973 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Geoloycal &t<tMats The University of British Columbia Vancouver 8, Canada Date ABSTRACT The p r o b l e m a t i c h i s t o r y o f t h e s t r a t a - b o u n d Salmo l e a d -z i n c d e p o s i t s , w h i c h o c c u r i n h i g h l y deformed, low-grade meta-sediments o f t h e s o u t h e r n Kootenay A r c o f B r i t i s h C o l u m b i a , has been i n v e s t i g a t e d v i a s t r u c t u r a l a n a l y s e s , f a b r i c s t u d i e s , and minor element d e t e r m i n a t i o n s i n t h r e e o f t h e d e p o s i t s : Reeves MacDonald, J e r s e y and H. B. mines. Three phases o f f o l d i n g have been d i s t i n g u i s h e d : an e a r l y phase o f n e a r - i s o c l i n a l f o l d i n g , o v e r t u r n e d toward t h e west, produced t h e major s t r u c t u r e s ; a second phase o f u p r i g h t , more open f o l d i n g m o d i f i e d t h e f i r s t phase f o l d s by near c o a x i a l r e f o l d i n g , by f u r t h e r c l o s u r e and l o c a l f l a t t e n i n g , and u l t i m a t e l y by w e s t w a r d - d i r e c t e d t h r u s t i n g ; a t h i r d phase o f c o n j u g a t e mono-c l i n a l f o l d s and k i n k bands was produced by n o r t h - s o u t h compres-s i o n r e l a t e d t o n o r t h w a r d - d i r e c t e d t h r u s t i n g . The e s s e n t i a l l y t a b u l a r s p h a l e r i t e - p y r i t e - g a l e n a o r e b o d i e s a r e i n v o l v e d , on a l l s c a l e s , i n t h e f o l d i n g and t h e o r e s e x h i b i t i n t e r n a l s t r u c t u r e s a s c r i b e d t o t h e d i f f e r e n t i a l movement o f s u l p h i d e s and h o s t d o l o m i t e and c a l c i t e m a r b l e s . R e g i o n a l metamorphism, t o lower g r e e n s c h i s t f a c i e s , was synchronous w i t h Phase 1 f o l d i n g . C o n t a c t metamorphism by g r a n i t e s t o c k s (K-Ar age: c i r c a 100 m.y. B.P.) p o s t d a t e s a l l phases o f f o l d i n g , and a f f e c t s J e r s e y and H. B. d e p o s i t s , and p o s s i b l y a l s o Reeves MacDonald; e s t i m a t e d t e m p e r a t u r e s a r e i n i i i the range 425-600°C (at 1.5 kb). Seventy-one analyses of minor elements i n the sulphides show that p y r i t e has Co:Ni<l, and that sphalerite has increasingly high Fe, Mn and Cd contents with increasing grade of contact metamorphism, except for an anoma-lous enrichment i n Fe, Cd, Cu and Ag with depth i n Reeves MacDonald mine. Pyrite retains b r i t t l e deformation textures u n t i l hornblende hornfels facies i s attained when r e c r y s t a l l i z a -t i o n becomes increasingly important, and ultimate breakdown to pyrrhotite occurs. Sphalerite and galena t y p i c a l l y have granoblastic-polygonal r e c r y s t a l l i z a t i o n textures but exhibit widespread s l i g h t l a t t i c e bending and subgrain development, believed to postdate annealing r e c r y s t a l l i z a t i o n ; l o c a l deforma-t i o n twinning and kinking, recognized only i n sphalerite, may pre-date annealing r e c r y s t a l l i z a t i o n . X-ray f a b r i c analyses of sphalerite, mainly from Reeves MacDonald mine, show well developed preferred orientation of (111) p a r a l l e l with composition layering, attributed to syntec-tonic r e c r y s t a l l i z a t i o n . Sphalerite from Jersey mine has more varied (111) subfabrics showing development toward s m a l l - c i r c l e patterns of [ i l l ] which probably represent annealing f a b r i c s . Mylonitic sphalerite, from thin zones i n Jersey mine, has a d i s -t i n c t i v e (111) subfabric with orthorhombic symmetry and a pattern approaching (110) [OOl] . Galena, which has variable mylonitic and r e c r y s t a l l i z e d textures, has either a random f a b r i c , or weak (200) subfabrics which may r e f l e c t p l a s t i c deformation on the system (001) [llO] .:: Quartz e-axis subfabrics and orientations of deformation lamellae (determined o p t i c a l l y ) suggest that, i n i v q u a r t z i t i c r o c k s , s y n t e c t o n i c r e c r y s t a l l i z a t i o n o c c u r r e d d u r i n g Phase 1 f o l d i n g , whereas p l a s t i c d e f o r m a t i o n , and a t l e a s t l o c a l r e c r y s t a l l i z a t i o n ( i n f i n e - g r a i n e d m a t e r i a l ) , was produced e s s e n t i a l l y by f l a t t e n i n g d u r i n g Phase 2, and p o s s i b l y d u r i n g Phase 3 f o l d i n g . e - a x i s s u b f a b r i c s i n h o s t d o l o m i t e m a r b l e s may a l s o be i n d i c a t i v e o f r e c r y s t a l l i z a t i o n d u r i n g f l a t t e n i n g . I t i s c o n c l u d e d t h a t t h e s u l p h i d e s e x h i b i t s t r u c t u r e s , on a l l s c a l e s , e q u i v a l e n t t o t h o s e r e c o g n i z e d i n t h e h o s t r o c k s and t h a t t h e s e i n d i c a t e i n v o l v e m e n t i n a l l phases o f d e f o r m a t i o n , i n r e g i o n a l metamorphism, and i n c o n t a c t metamorphism. The d e p o s i t s a r e i n t e r p r e t e d as b e i n g o r i g i n a l l y o f M i s s i s s i p p i V a l l e y t y p e . TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES ix LIST OF ILLUSTRATIONS x i ACKNOWLEDGEMENTS xvi I. INTRODUCTION 1 LOCATION AND PURPOSE OF THE STUDY 1 PREVIOUS WORK 4 II. REGIONAL GEOLOGICAL SETTING 7 STRATIGRAPHY 7 Proterozoic rocks 7 Palaeozoic rocks 10 Mesozoic rocks 15 IGNEOUS HISTORY 15 Basic dykes, s i l l s (and volcanics?) 16 F e l s i t e s i l l s 16 Nelson-type plutonic intrusions 17 Coryell-type plutonic intrusions 19 Lamprophyre dykes and s i l l s 22 STRATIGRAPHIC SETTING OF MINERALIZATION 23 Dolomite i n the Reeves member 2 3 Dolomite i n the Nelway/Metaline formation 25 SUMMARY 27 v v i I I I . STRUCTURAL ENVIRONMENT 30 MINOR FOLDING 30 Phase 1 structures 32 Phase 2 structures 36 Phase 3 structures 37 EFFECTS OF SUPERIMPOSED FOLDING 4 3 Phase 2 superimposed on Phase 1 4 3 Phase 3 superimposed on Phases 1 and 2 46 SUMMARY OF STRUCTURAL STYLES AND RELATIVE AGES OF FOLDING 48 MAJOR FOLDING 48 H. B. mine area 50 Jersey mine area 52 Reeves MacDonald mine area 54 FAULTING 57 MINOR FRACTURES 61 STRUCTURAL SYNTHESIS 63 IV. METAMORPHIC ENVIRONMENT 68 INTRODUCTION 68 REGIONAL METAMORPHISM 70 Textural features of the regionally metamorphosed host rocks 70 Mineral assemblages, metamorphic f a c i e s , and timing of the regional metamorphic event 71 P-T conditions of regional metamorphism 72 CONTACT METAMORPHISM 73 Textural features of the contact metamor-phosed host rocks 73 Nature and d i s t r i b u t i o n of the contact aureoles 74 Reeves MacDonald mine area 75 H. B. mine area 75 Jersey mine area 77 Assemblages of the contact aureoles 80 P-T conditions of contact metamorphism 81 F l u i d phase during contact metamorphism 86 V l l V. THE SULPHIDE DEPOSITS 90 INTRODUCTION 90 NATURE AND FORM OF THE SULPHIDE ORE BODIES 91 Reeves MacDonald mine 92 Jersey mine 96 H. B. mine 100 Summary 102 MINERALOGICAL VARIATION OF THE SULPHIDES 107 Introduction 107 Minor element content of sphalerite 108 Minor element content of p y r i t e 115 Minor element content of galena 121 Occurrence of pyrrhotite 121 Occurrence of a second generation of p y r i t e 127 Summary 12 8 TEXTURAL FEATURES OF THE SULPHIDES 129 Introduction 129 Pyrite 129 Sphalerite 133 Galena 137 Summary and interpretation 13 9 FABRIC OF THE ORES 143 Introduction 143 Sphalerite f a b r i c 146 (111) Subfabric 146 (a) Specimens from Reeves MacDonald mine 146 (b) Specimens from Jersey mine 147 (c) Mylonitized specimens from Jersey mine 150 (220) Subfabric 150 Origin of sphalerite f a b r i c 153 Galena f a b r i c 156 (2 00) Subfabric 156 Dolomite f a b r i c 160 Quartz f a b r i c 163 Summary 168 ORIGIN OF THE ORES 172 v i i i VI. SUMMARY AND CONCLUSIONS 176 STRUCTURE 176 SULPHIDE DEPOSITS 177 DEFORMATION AND REGIONAL METAMORPHISM 178 CONTACT METAMORPHISM 18 0 BIBLIOGRAPHY 183 APPENDIX A. MAGNESIAN CALCITE-DOLOMITE GEOTHERMOMETRY 197 B. X-RAY TEXTURE GONIOMETER ANALYSIS OF PREFERRED ORIENTATION 199 Sample preparation 199 Technique 200 Accuracy of the technique 204 Precision 207 Pole-figures to A = 90° 209 C. MINOR ELEMENT DETERMINATION BY ATOMIC ABSORPTION SPECTROPHOTOMETRY 212 Sample preparation 212 An a l y t i c a l method 214 An a l y t i c a l precision 214 Sphalerite coloration 218 D. ANALYSIS OF SPHALERITE BY ELECTRON MICROPROBE 222 E. MAPS OF STRUCTURAL DATA 225 LIST OF TABLES I. Stratigraphic d i v i s i o n s of the southern Kootenay Arc 8 II. Potassium-argon age determinations on three intr u s i v e igneous rocks from Jersey mine area 2 0 III . Structural elements and t h e i r nomenclature 31 IV. Summary of st r u c t u r a l styles and r e l a t i v e ages of folding 49 V. Structural c o r r e l a t i o n along the southern Kootenay Arc 65 VI. Metamorphic rock types and t y p i c a l mineralogies of the exposed stratigraphic units i n the mine areas: (i) outside contact aureoles, ( i i ) within outer contact aureoles, and ( i i i ) within inner contact aureoles 69 VII. Comparison of mean values of minor element contents of sphalerite samples from the three mines 111 VIII. Comparison of mean values of minor element contents of d i f f e r e n t types of sphalerite from the Annex zone of Reeves MacDonald mine 114 IX. Comparison of mean minor element contents of pyrite samples from the three mines 116 X. Co and Ni contents of A. certa i n sedimentary rock types, and of B. pyr i t e from d i f f e r e n t types of ore deposit 119 XI. d i i 2 and estimated temperatures of c r y s t a l -l i z a t i o n of magnesian c a l c i t e s from Reeves MacDonald and Jersey mines 198 XII. Absorption c o e f f i c i e n t s , 26 angles, and other relevant data for the mineral assemblages analyzed 206 XIII. Numbers and locations of ore specimens used i n X-ray fab r i c analysis 211 ix X XIV. Minor element contents of sphalerite samples from Reeves MacDonald mine 215 XV. Minor element contents of sphalerite samples from Jersey and H. B. mines 216 XVI. Duplicate analyses of minor elements i n sphalerite samples from the three mines 217 XVII. Sphalerite colour notation, based on Munsell Rock Colour Chart 219 XVIII. Minor element contents of p y r i t e samples from the three mines 221 XIX. Analyses by electron microprobe of iron and zinc i n sphalerite 224 LIST OF ILLUSTRATIONS FIGURE 1. Generalized geology of the southern Kootenay Arc showing the location of economically important strata-bound lead-zinc sulphide deposits 2 2. Intrusive rocks i n the Salmo area. Jersey mine area i s enlarged to show location of specimens dated by potassium-argon method 21 3. Examples traced from photographs of minor f o l d styles from the three f o l d generations d i s t i n -guished i n the mine areas 34 4. Equal-area projections of Phase 1 minor struc-t u r a l elements from the three mine areas 35 5. Plots of thickness variations across three Phase 2 minor f o l d hinges, developed i n quartzite, quartz p h y l l i t e 38 6. Equal-area projections of Phase 2 minor struc-t u r a l elements from the three mine areas 39 7. Equal-area projections of Phase 3 minor struc-t u r a l elements from the three mine areas 41 8. Examples of interference f o l d structures r e s u l t i n g from superimposition of Phase 2 folds on e a r l i e r formed Phase 1 folds 45 9. Diagram showing the ef f e c t s of Phase 2 folding on Phase 1 structures: (a) by refolding and (b) by closure and d i f f e r e n t i a l f l a t t e n i n g 47 10. V e r t i c a l cross-sections (subnormal to major f o l d axes) of H. B. mine area 51 11. V e r t i c a l cross-sections (subnormal to major f o l d axes) of Jersey mine area 53 12. Inclined cross-section (subnormal to major F;t f o l d axes) of Reeves MacDonald mine area 55 x i x i i FIGURE 13. Main f a u l t and f o l d patterns i n the southern Kootenay Arc 58 14. Equal-area projections of poles to j o i n t surfaces from the three mine areas 62 15. Contact metamorphic ef f e c t s i n Reeves MacDonald mine area 76 16. Contact metamorphic ef f e c t s i n H. B. mine area 78 17. Contact metamorphic e f f e c t s i n Jersey mine area 79 18. S t a b i l i t y f i e l d s of gros s u l a r i t e and wollas-tonite i n H2O-CO2 mixtures at 2 kb 87 19. Mode of occurrence of grossularite skarn within c a l c i t e marble of the Reeves member 87 20. Schematic representation of the range of contact metamorphic temperatures a f f e c t i n g the three sulphide deposits 89 21. Diagrammatic east-west longitudinal section of Reeves MacDonald mine showing the ore zones 93 22. Level plans of the Reeves ore zone i l l u s t r a t i n g the change i n configuration down plunge 93 23. Plan view and representative cross-sections of Jersey mine workings, showing the main struc-t u r a l features 97 24. a. Isometric view of the H. B. ore zones, showing t h e i r configuration and s p a t i a l r e l a t i o n s , b. Typical v e r t i c a l section of the No. 1 zone, looking north 101 25. Examples of layered ores from the three mines 104 26. Examples of breccia ores from Reeves MacDonald and Jersey mines 105 27. Examples of f o l d structures involving sulphides from Reeves MacDonald and Jersey mines 106 28. Logarithmic p l o t of Cd vs. Fe contents of sphalerite samples from the three mines 109 29. Ternary plot of Mn, Cu and Ag contents of sphalerite samples from the three mines 110 x i i i FIGURE 30. Logarithmic plo t of Co vs. Ni contents of p y r i t e samples from the three mines 118 31. FeS contents (mole %) of sphalerite samples from Jersey mine 124 32. Semi-quantitative microprobe determinations of iron v a r i a t i o n across sphalerite grains 126 33. Grain size v a r i a t i o n of p y r i t e and sphalerite between the three mine areas 130 34. Photographs and photomicrographs of micro-structures and textures developed i n p y r i t e 132 35. Photomicrographs of r e c r y s t a l l i z a t i o n textures developed i n sphalerite, etched with thio-urea + HC1 135 36. Photomicrographs of deformation textures and microstructures developed i n sphalerite, etched with thio-urea + HC1 136 37. Photomicrographs of textures and microstructures developed i n galena, etched with thio-urea + HC1 140 38. ( I l l ) pole figures for sphalerite from Reeves MacDonald mine 148 39. ( I l l ) pole figures for sphalerite from Jersey mine 149 40. ( I l l ) pole figures for a. p a r t i a l l y mylonitized, and b. mylonitized sphalerite from Jersey mine 151 41. (220) pole figures for sphalerite from a. Reeves MacDonald and b. Jersey mines 152 42. a. Translation directions i n the (111) plane of sphalerite, b, c. ( I l l ) pole figures of naturally deformed sphalerite, showing infer r e d i d e a l subfabrics and possible t r a n s l a t i o n directions 154 43. (200) pole figures for galena from Jersey mine 157 44. a. Translation directions i n the (100) plane of galena, b. Translation d i r e c t i o n s i n the (110) plane of galena. c. Example of (200) pole figure of naturally deformed "gneissic" galena 159 xiv FIGURE 45. Preferred orientation of dolomite c-axes i n four dolomite marbles 162 46. Preferred orientation of quartz e-axes i n four quartzites, a quartz phyllonite, and a quartz schist 165 47. Top: Equal area projections of poles to 75 sets of deformation lamellae, and of c-axes of host grains i n each of two quartzites. Centre: Histograms of angles between lamellae pole and e-axis i n each grain. Bottom: Deduced maximum p r i n c i p a l stress directions 167 48. Geometry of the P h i l l i p s X-ray texture gonio-meter set-up for r e f l e c t i o n and transmission modes 201 49. Intensity correction curves established from r e f l e c t i o n scans of random specimens 203 50. Duplicate X-ray r e f l e c t i o n scans for various sphalerite specimens 208 51. Plot of minor element contents vs. colour for a l l sphalerites (49) analyzed by AA spectro-photometry 220 XV PLATE I. Planar structures i n the Reeves MacDonald mine area 226 II. Linear structures i n the Reeves MacDonald mine area 227 III. Major structures i n the Reeves MacDonald mine area 228 IV. Planar structures i n the Jersey mine area 229 V. Linear structures i n the Jersey mine area 23 0 VI. Major structures i n the Jersey mine area 231 VII. Planar (A) and lin e a r (B) structures i n the H. B. mine area 232 VIII. Major structures i n the H. B. mine area 233 ACKNOWLEDGEMENTS This study was done under the supervision of Dr. J . V. Ross who o r i g i n a l l y suggested the Salmo area for a study of t h i s kind. Technical assistance was provided by J . E. Harakal, N. D i l l o n , A. Bentzen, and many other members of the Department of Geological Sciences, and also by R. G. Butters of the Department of Metallurgy, University of B r i t i s h Columbia. Dr. J . T. Fyles of the B r i t i s h Columbia Department of Mines i s thanked for his f r i e n d l y encouragement and in t e r e s t i n the study. The w i l l i n g cooperation, i n the f i e l d , of mine geologists and managers i s g r a t e f u l l y acknowledged, i n p a r t i c u -l a r G. G. Addie, then of Reeves MacDonald Mines Ltd. F i e l d expenses were provided through Grant NRC-A2134 awarded to J . V. Ross, and accommodation was kindly made a v a i l -able by Reeves MacDonald Mines Ltd., Canadian Exploration Ltd., and Consolidated Mining and Smelting Co. Ltd. The author was a r e c i p i e n t of a University of B r i t i s h Columbia Summer Research Scholarship i n 1972. xv i These r o c k s o c c u r i n one o f t h e C o r d i l l e r a n zones o f maximum o r o g e n i c s h e a r i n g and mashing, w i t h complete r e c r y s t a l l i z a t i o n . Numberless c r u m p l i n g s , o v e r t u r n i n g s and f a u l t i n g s c h a r a c t e r i z e t h e r e g i o n , w h i c h , as a l r e a d y n o t e d , has been t h e scene o f r e p e a t e d igneous i n j e c t i o n s i n t h e form o f d i k e s , s i l l s , s t o c k s , and b a t h o l i t h s . . . . To such p r i n -c i p a l d i f f i c u l t i e s i n a n a l y z i n g t h e complex assem-b l a g e o f s t r a t a a l o n g t h e Pend D ' O r e i l l e r i v e r t h e r e was added t h a t common d i s a d v a n t a g e o f t h e g e o l o g i s t on t h e F o r t y - n i n t h P a r a l l e l , t h e dense e v e r g r e e n f o r e s t w i t h i t s deep mat o f b r u s h and f a l l e n t i m b e r . - D a l y , 1912 SECTION I INTRODUCTION LOCATION AND PURPOSE OF THE STUDY The Kootenay Arc (Hedley, 1955) i s a complex arcuate s t r u c t u r a l b e l t l y i n g within the south-central part of the Eastern C o r d i l l e r a n Fold Belt (Fig. 1). I t comprises juxtaposed Proterozoic, Palaeozoic and Mesozoic rocks affected i n varying degrees by polyphase deformation and metamorphism. Within t h i s highly deformed b e l t , mainly Lower Palaeozoic miogeosynclinal rocks separate late Palaeozoic and Mesozoic eugeosynclinal rocks i n the west from Precambrian rocks of the B e l t - P u r c e l l a n t i -clinorium i n the east. Origin of the Arc has been widely debated, over the l a s t decade, i n terms of both i t s geometry (details of which remain to be defined) and i t s evolution. Also problematic i s the metallogenesis and subsequent history of numerous s t r a t a -bound lead-zinc sulphide deposits, occurring i n Cambrian carbonate rocks along the length of the Arc. The Salmo area (Fig. 1) was selected for study because i t includes three major lead-zinc deposits—Reeves MacDonald, Jersey and H. B. mines—which are c l o s e l y located along s t r i k e of a strongly curved section of the southern Kootenay Arc, near the Canada-U.S.A. border. It was considered that a detailed examination of the stratigraphy, structure and metamorphism of both country rocks and enclosed sulphides, together with further 2 Figure 1. Generalized geology of the southern Kootenay Arc showing the location of economically important strata-bound lead-zinc sulphide deposits (compiled from Fyles, 1970; Ross, 1970; and Yates, 1970). 3 laboratory studies, would (i) c l a r i f y d e t a i l s of the geometry of the southern Kootenay Arc and perhaps of i t s evolution (at least i n t h i s segment), ( i i ) elucidate the history of the lead-zinc sulphides, and ( i i i ) provide information on the behaviour of sulphide assemblages under conditions of regional and/or thermal metamorphism. F i e l d work for t h i s thesis occupied four months, during summers of 1969-71, spent on the properties of Reeves MacDonald, Canex Jersey and Cominco H. B. mines. Detailed s t r u c t u r a l mapping was ca r r i e d out on 1 i n to 4 00 f t base maps of surface areas immediate to the mines and numerous v i s i t s were made underground to c o l l e c t oriented sulphide samples (except at H. B. mine which was closed down i n 1966). In the thesis, the stratigraphy of the region i s re-viewed, the various types and ages of int r u s i v e igneous a c t i v i t y are considered, and the nature and stra t i g r a p h i c p o s i t i o n of the strata-bound sulphide deposits are discussed i n r e l a t i o n to that framework. The polyphase nature of deformation i n the three mine areas i s then described together with analyses of the various f o l d geometries and fracture patterns. Major s t r u c t u r a l features of the mine areas are re-interpreted and an attempt made to integrate these into the evolution of t h i s segment of the Kootenay Arc. P-T conditions of regional and of l o c a l con-tact metamorphism are estimated and t h e i r t extural and minera-l o g i c a l e f f e c t s on both sulphides and host rocks determined. The fabrics of the sulphides and of the quartz- and dolomite-rich host rocks are studied by X-ray and o p t i c a l methods and t h e i r 4 responses to deformation and metamorphism compared. F i n a l l y , the implications of the various deformation and metamorphic features are discussed i n terms of the metallogenesis and sub-sequent history of the strata-bound sulphides. PREVIOUS WORK Gold lode-mining i n Ymir and Sheep Creek camps between 1896 and 1916 f i r s t stimulated i n t e r e s t by the Geological Survey of Canada i n the Salmo area, r e s u l t i n g i n the West Kootenay map of McConnel and Brock (1904). In t h i s , the Rossland volcanic group was distinguished from metasediments to the east which were assigned to the N i s c o n l i t h and Selkirk series which were supposed to be of Cambrian age and to young eastward. Daly (1912) also traversed and mapped the southern edge of the area for the International Boundary Commission. He renamed the N i s c o n l i t h series as the Pend d 1 O r e i l l e group and t e n t a t i v e l y equated them with the Cache Creek group, considered to be of Carboniferous age. He also noted t h e i r s t r u c t u r a l complexity. Revival of gold mining a c t i v i t y after 1928 was followed by Walker's (1929, 1934) one inch to one mile geological map and description of the geology and mineral deposits of Salmo area. Walker established the basic st r a t i g r a p h i c framework, subdividing the lower, predominantly c l a s t i c succession into separate formations. A l l of these, together with the Pend d 1 O r e i l l e series were assigned to the Precambrian. He also described lead-zinc occurrences i n carbonate rocks near the base of the Pend d * O r e i l l e series and c l a s s i f i e d them as s t r u c t u r a l l y controlled replacement deposits. 5 Post-1940, the decline of gold mining and the concurrent development and exploitation of the large strata-bound lead-zinc sulphide occurrences i n the area resulted i n renewed mapping and reinterpretation of the geology by both the B r i t i s h Columbia Department of Mines and the Geological Survey of Canada. L i t t l e (1950, 1951, 1960) remapped the Salmo area (later incorporated into the Nelson map-area, west half) and on palaeontological grounds assigned Walker's Pend d 1 O r e i l l e series to the Lower Palaeozoic, subdividing i t into the Laib group (Lower Cambrian), Nelway group (Middle Cambrian) and Active formation (Ordovician). In 1953, Mathews made a detailed study of the declining Sheep Creek gold camp, r e f i n i n g the stratigraphy of the host Reno and Quartzite Range formations and d e t a i l i n g the s t r u c t u r a l controls on gold lode-mineralization. Fyles and Hewlett (1959) mapped (1 i n to 2000 ft) the Lower Palaeozoic rocks east and south of Salmo and redefined the Laib group as a formation subdividing i t into four members. This aided i n interpreting the complex structure developed i n these rocks which was shown to be the product of at least two phases of deformation. From detailed mapping of t h e i r surface geology and from examination of the lead-zinc -sulphide deposits themselves i t was concluded that mineralization was by replacement, s t r u c t u r a l l y controlled by the second phase of folding. Numerous descriptions of i n d i v i d u a l Salmo lead-zinc deposits have also been published by B. C. Department of Mines, company and other geologists and w i l l be referred to i n the body of the t h e s i s . 6 There are too a number of regional studies which have d i r e c t l o c a l application to Salmo area. Hedley (1955) f i r s t defined the Kootenay Arc and described i t s s t r u c t u r a l and metallogenic features. These were further amplified and developed by Fyles (1966, 1967, 1970) and by Yates et al. (1966) and Yates (1970). The evolution of the Arc has been also the subject of wide debate by Wheeler (1966, 1970), Ross and Kellerhals (1968), and Ross (1970). In addition, the metallo-genesis of the regionally d i s t r i b u t e d lead-zinc deposits has been discussed. Muraro (1966) ascribed the gross shapes of the sulphide deposits and t h e i r i n t e r n a l structures to penetrative deformation and suggested that mineralization pre-dated regional metamorphism. However, Fyles (1967) considered the evidence for the l a t t e r suggestion to be very uncertain. S i n c l a i r (1964, 1966) and Reynolds and S i n c l a i r (1971) determined lead isotope abun-dances for deposits i n the southern Kootenay Arc and d i s t i n -guished two populations of anomalous lead isotopes corresponding to strata-bound and to vein-type deposits. Both types were i n t e r -preted as having been emplaced at approximately the same time, c i r c a 150 m.y. ago ( i . e . , pre-regional metamorphism).. Sangster (1970a, b) determined sulphur isotope abundances i n sulphides from the Salmo deposits which showed that these could have been derived from Cambrian sea water sulphate and hence could have been syngenetic-diagenetic i n o r i g i n . SECTION II REGIONAL GEOLOGICAL SETTING STRATIGRAPHY The southern Kootenay Arc, although primarily a tectonic feature, i s outlined by the d i s t r i b u t i o n of Palaeozoic miogeo-sy n c l i n a l and t r a n s i t i o n a l rocks. To the east, these are mar-g i n a l l y infolded with c l a s t i c and minor volcanic rocks of Late Proterozoic age, while to the west they are i n complex s t r u c t u r a l contact with Upper Palaeozoic and Mesozoic eugeosynclinal a r g i l -l i t e s and volcanics. Table I shows the stratigraphic succession and c o r r e l a -tions established for the adjacent Metaline, Salmo and Kootenay Lake areas of the southern Arc. Proterozoic rocks The Late Proterozoic succession forming the east side of the Arc was described and defined as the Windermere Series by Walker (1926). The basal Toby conglomerate formation marks the major unconformity separating these Windermere rocks from the under-lying B e l t - P u r c e l l Series (a mid-Proterozoic fine-grained c l a s t i c assemblage forming the P u r c e l l anticlinorium). It i s of strongly bimodal grainsize and very variable i n l i t h o l o g y and thickness but was considered as being too extensive to represent a true 7 8 .Table 1. Stratigraphic d i v i s i o n s of the southern Kootenay Arc (compiled from L i t t l e , 1960; Fyles, 1970; Ross, 1970; and Yates, 1970). METALINE DISTRICT SALMO DISTRICT LARDEAU DISTRICT PENNSYLVANIAN MISSISSIPPIAN UPPER ORDOVICIAN MIDDLE ORDOVICIAN LOWER ORDOVICIAN UPPER CAMBRIAN MIDDLE CAMBRIAN LOWER CAMBRIAN WINDERMERE ROSSLAND GROUP MT. ROBERTS FN. unnamed formation LEDBETTER SLATE FN. OMETALINE FORMATION MAITLEN PHYLLITE FN. GYPSY QUARTZITE FN. MONK FORMATION LEOLA VOLCANICS SHEDROOF CONGLOMERATE ROSSLAND GROUP / m  /^~YMIR GROUP MT. ROBERTS FN ACTIVE FORMATION • L A F I N. U. L a i b member Emerald member DReeves member Trueman member RENO FORMATION QUARTZITE RANGE FN. THREE SISTERS FN. MONK FORMATION IRENE VOLCANICS TOBY CONGLOMERATE SLOCAN GROUP KASLO GROUP MILFORD GROUP BROADVIEW FORMATION JOWETT FORMATION SHARON CREEK FN. AJAX FORMATION TRIUNE FORMATION INDEX FORMATION C BADSHOT FORMATION MOHICAN FORMATION HAMILL GROUP HORSETHIEF CREEK GP. IRENE VLCS TOBY CONGLOMERATE C Horizons containing Pb-Zn mineralization 9 fanglomerate (Rice, 1941). A recent study (Aalto, 1971) suggests that i t i s actually a t i l l i t e although t h i s p o s s i b i l i t y was also b r i e f l y entertained by e a r l i e r workers. Upwards i t becomes interbedded with the Irene volcanic formation, greenstones of andesitic composition believed to represent a volcanic extrusive and p y r o c l a s t i c assemblage (Rice, 1941). Farther south, i n Washington, M i l l e r (1969) has recognized pillows i n the equiva-lent Leola volcanics which are of t h o l e i t i c composition. These volcanics t h i n both north and south away from the general v i c i n i t y of the International Boundary. Conformably overlying the Irene volcanics i s the Horsethief Creek group or i t s equivalents i n the Salmo area, the Monk and the Three Sisters formations. The lower part, equivalent to the Monk formation, has been described as a "heterogeneous assemblage" by Walker (1934) and as a "waste-basket formation" by Park and Cannon (1943), being predominantly p h y l l i t e with i n t e r c a l a t i o n s of conglomerate, quartzite and arenaceous limestone. In the south, t h i s becomes increasingly arenaceous upwards into massive coarse-grained quartzite and g r i t of the Three Si s t e r s formation (or lower part of the Gypsy quartzite i n the Metaline d i s t r i c t ) . To the north, however, the l i t h o l o g i c a l heterogeneity continues to the top of the undivided Horsethief Creek group, ind i c a t i n g a marked southward facies change corresponding to increasing proximity of source. This variable coarse c l a s t i c and volcanic assemblage appears to represent deposition i n a rapidl y subsiding trough, marginal to the Pu r c e l l anticlinorium, i n which movements were 10 probably epeirogenic and f a u l t controlled (Yates, 1970). Forma-tions generally t h i n northwards and, i n the Metaline area at least, t h i n even more rapidly to the west and southwest. However t h e i r ultimate western l i m i t i s unknown (Park and Cannon, 1943). The boundary between Precambrian and Cambrian has not been accurately defined i n the southern Kootenay Arc due to the poor f o s s i l record and the fact that coarse c l a s t i c sedimentation continued v i r t u a l l y unbroken into the Palaeozoic era. L i t t l e (1960) has a r b i t r a r i l y placed the boundary i n the Salmo area at the base of the Hamill group since the lower part correlates l i t h o l o g i c a l l y with the upper Gypsy quartzite formation i n which Park and Cannon (1943) found t r i l o b i t e fragments. Palaeozoic rocks The Hamill group are the Lower Cambrian representatives of continued c l a s t i c deposition. In the Salmo area, the group i s subdivided into the Quartzite Range and overlying Reno  formations. The former comprises a massive white quartzite of remarkable purity and l a t e r a l persistence which can be recognized as a d i s t i n c t i v e l i t h o f a c i e s as far north as Duncan Lake (Fyles, 1964). Upwards i t becomes increasingly impure and where p h y l l i t e i n t e r c a l a t i o n s occur the Reno formation i s distinguished. In the Salmo area, t h i s Lower Cambrian c l a s t i c succession appears, i n spite of increasing i n t e n s i t y of subsequent deforma-ti o n , to th i n markedly toward the west from the Sheep Creek a n t i c l i n e , to lose cross-bedding and to become f i n e r grained and increasingly argillaceous (Fyles and Hewlett, 1959). 11 Appearance of carbonate rocks marks the t r a n s i t i o n from a hitherto predominantly c l a s t i c succession into the mixed car-bonate and p e l i t i c sequence of the Laib formation ( L i t t l e , 1960) and i t s c o r r e l a t i v e s , the Mohican, Badshot and Index formations (Lardeau d i s t r i c t ) and the Maitlen p h y l l i t e (Metaline d i s t r i c t ) . The t r a n s i t i o n a l rocks, interbedded th i n limestone marble and p h y l l i t e , have been distinguished i n the Salmo area as a separate member (the Trueman) by Fyles and Hewlett (1959)'. In addition to t h e i r varied l i t h o l o g y they are extremely variable i n thickness, apparently as a r e s u l t of intense deformation and thus may not provide a very r e l i a b l e s t ratigraphic marker. They are overlain by grey and white, l o c a l l y dolomitic, limestone/marble of the Reeves member/Badshot formation which provides perhaps the best stratigraphic marker of the Kootenay Arc, by vi r t u e of i t s d i s t i n c t i v e and persistent l i t h o l o g y and palaeontological control (the presence of Lower Cambrian archaeo-cyathids at widely separated l o c a l i t i e s ) . The o r i g i n of the dolomite f a c i e s , important as host to the Salmo-type lead-zinc deposits, has been the subject of some controversy which w i l l be discussed i n d e t a i l below. This limestone i s not without v a r i a t i o n , east-west l i t h o -l o g i c a l changes having been demonstrated by Fyles and Hewlett (1959) i n the Salmo area and by Fyles (1964) i n the Duncan Lake area. Eastwards the limestone becomes impure, passing into a r g i l -laceous limestone and calcareous s i l t s t o n e and the only dolomite i s apparently the product of l o c a l a l t e r a t i o n adjacent to veins and intrusions. 12 Telescoping of east-west facies changes and d r a s t i c thinning by deformation causes l o c a l c o r r e l a t i o n problems, since the Reeves/Badshot limestone may then be confused with limestone units of the Trueman member or i t s equivalent (Fyles and Hewlett, 1959; Fyles, 1964) and with units of the lower Lardeau group (Crosby, 1968). An abrupt upward change to a predominantly p e l i t i c succession follows everywhere along the southern Arc. In the Salmo area, a black a r g i l l i t e - p h y l l i t e member, the Emerald (Fyles and Hewlett, 1959) i s distinguished from over-ly i n g green p h y l l i t e s and micaceous quartzites which comprise the upper part of the Laib formation. This member i s r e s t r i c t e d to the westernmost outcrops of Lower Cambrian st r a t a which may again r e f l e c t facies telescoping. I t does, however, l i t h o -l o g i c a l l y very clo s e l y resemble the Ordovician Active formation and i f equivalent may therefore be s t r u c t u a l l y emplaced either by pre-folding decollement thrusting, or by complex folding and associated thrusting. In the Salmo-Metaline segment there i s a gradual t r a n s i -t i o n from Laib and Maitlen p h y l l i t e formations up into the predominantly carbonate Nelway and Metaline formations, respec-t i v e l y , i n d i c a t i n g the persistence of a shelf environment i n th i s segment of the Arc. To the north i n the Lardeau segment, the p e l i t i c Index formation continues unchanged, r e f l e c t i n g con-tinued subsidence of the Lardeau trough. The Nelway/Metaline formations are divided into lower limestone, middle dolostone and upper limestone members, described 13 i n d e t a i l by Park and Cannon (194 3) and by Dings and Whitebread (1965). The lower member i s composed of dark grey limestones and calcareous p h y l l i t e s and contains Middle Cambrian t r i l o b i t e s . The middle member consists of medium to thick bedded dolostone of various kinds which l o c a l l y i s host to productive lead-zinc mineralization i n the Northport d i s t r i c t , west of Metaline, and to minor mineralization i n the Salmo area near Nelway (Fyles and Hewlett, 1959). Although t y p i c a l l y a massive grey limestone sequence, the upper member i s also dolomitized but only i n i t s uppermost 200 f t which i s host to economically important lead-zinc mineralization at Metaline F a l l s . A l g a l structures i n limestone and shaly limestone have been described from several stratigraphic levels i n the Metaline formation (Dings and Whitebread, 1965). No Upper Cambrian f o s s i l s have been found and the contact with the overlying Ledbetter slate formation i s very abrupt. Since the l a t t e r con-tains Lower and Middle Ordovician gra p t o l i t e s not far above i t s base, a disconformity may separate the two formations (Park and Cannon, 1943) or even a pre-folding decollement, but no regional discordance has been recognized. The Ledbetter slate i s correlated with the Active forma- t i o n of the Salmo area which contains Lower Ordovician grapto-l i t e s at one l o c a l i t y northeast of Salmo v i l l a g e ( L i t t l e , 1960) . They are l i t h o l o g i c a l l y very s i m i l a r , comprising black a r g i l l i t e , slate and p h y l l i t e with minor calcareous and s i l i c e o u s i n t e r -calations, not unlike the Lardeau group to the north. 14 The upper l i m i t s of both formations are very poorly defined due to poor exposure and s t r u c t u r a l complexity. In the Metaline area, the Ledbetter i s succeeded by unnamed formations composed of slate with minor exotic, b i o c l a s t i c limestone and pebble conglomerate, containing S i l u r i a n and Devonian f o s s i l s (Dings and Whitebread, 1965). This predominantly black shale assemblage of Ordovician-Devonian age r e f l e c t s the extension southwards and subsequent persistence of a r e s t r i c t e d basin (?) environment along the southern segment of the Arc. These unnamed formations are assumed to be the c o r r e l a -t i v e s of the upper Lardeau group to the north, represented by the volcanic Jowett formation and the overlying c l a s t i c Broadview  formation which are however of unknown age. The provenance of the l a t t e r i s problematic since i t d i f f e r s so r a d i c a l l y from the underlying thick shale sequence. A l t e r n a t i v e l y , the Broadview formation has been equated with the Horsethief Creek group (Read, 1966). Above t h i s , the stra t i g r a p h i c record i s fragmentary and incomplete for the remainder of the Upper Palaeozoic era. This apparently r e f l e c t s the culmination of l o c a l tectonism and the development of a eugeosynclinal environment to the west of the Arc. In the Salmo-Metaline sector the Pennsylvanian i s represented i n limited outcrops west of the Arc by the Mt. Roberts  formation which comprises s l a t e , limestone, andesite and banded t u f f with a Pennsylvanian (and possible Permian) fauna and f l o r a ( L i t t l e , 1960). The same stratigraphic break i s recognized 15 i n the Lardeau trough i n the unconformity separating the Milford group from older rocks below. Mesozoic rocks In the Salmo area, T r i a s s i c - J u r a s s i c rocks are struc-t u r a l l y juxtaposed against the lower and middle Palaeozoic rocks of the Kootenay Arc. These are distinguished as the Ymir and Rossland groups but t h e i r r e l a t i v e ages are obscure, the former being predominantly sedimentary ( a r g i l l i t e , quartzite, and limestone) and the l a t t e r mixed volcanic (andesitic volcanics and pyroclastics) and sedimentary ( a r g i l l i t e , impure sandstone and conglomerate). They are correlated to the north with the Slocan and Kaslo groups which crop out widely to the west of Kootenay Lake. The Slocan group consists of a r g i l l i t e , impure sandstone and limestone of T r i a s s i c age i n part ( L i t t l e , 1960), whereas the Kaslo group i s a greenstone, breccia and t u f f assem-blage of uncertain age, which i s assumed to s t r a t i g r a p h i c a l l y underlie the Slocan group ( L i t t l e , 1960). IGNEOUS HISTORY Igneous a c t i v i t y has been widespread, i n both time and space, throughout the southern segment of the Arc. Types of a c t i v i t y are extremely varied but each i s apparently widely d i s -tributed along some 150 miles of the Arc between the Lardeau and Metaline d i s t r i c t s . Radiometric age determinations on these various types are r e l a t i v e l y few but on the basis of cross-cutting relationships, a l t e r a t i o n and in t e r n a l deformation t h e i r r e l a t i v e ages appear to be (in order of decreasing age): 16 (a) Basic dykes, s i l l s (and volcanics?) (b) F e l s i t e s i l l s (c) Nelson-type g r a n i t i c batholiths and s a t e l l i t e stocks (d) Coryell-type a l k a l i n e stocks (e) Lamprophyre dykes Basic dykes, s i l l s (and volcanics?) A number of older basic, minor i n t r u s i v e and possible volcanic rocks have been described from d i f f e r e n t l o c a l i t i e s i n the southern Arc. Their r e l a t i v e ages are obscure but they are compositionally d i f f e r e n t from the younger lamprophyres and apparently older than a l l other i n t r u s i v e types, being highly altered and i n t e r n a l l y deformed. In the Duncan Lake area, Fyles (1964) has described s i l l -l i k e amphibolite masses i n the upper Hamill group and Mohican formation which vaguely resemble f e l d s p a r - c h l o r i t e schists and greenstones of d e f i n i t e volcanic o r i g i n occurring i n the Lardeau group, much higher i n the succession. Older basic dykes i n the Sheep Creek gold camp (Mathews, 1953) are f o l i a t e d unlike the younger lamprophyre sui t e , and d i s t i n c t l y more s i l i c a - r i c h and soda-poor. Northeast of Reeves MacDonald mine, a thick s i l l - l i k e mass of intensely deformed, augen-textured greenstone with schistose margins occurs within the Quartzite Range formation i n the core of the Salmo River a n t i c l i n e . F e l s i t e s i l l s F e l s i t e s i l l s , commonly as narrow multiple swarms of extraordinary s t r i k e length p a r a l l e l i n g the main f o l i a t i o n , are 17 a d i s t i n c t i v e regional i n t r u s i v e feature. They frequently d i s -play a weak f o l i a t i o n and, i n the Duncan Lake and Ainsworth-Kaslo areas (Fyles, 1964, 1967) may be boudinaged and even folded. In the Sheep Creek area, a s i l l swarm c l o s e l y follows the Reno-Laib formational contact, except where t h i s i s parasi-t i c a l l y folded on the east limb of the Central syncline (Mathews, 1953). To the west, i n the v i c i n i t y of Salmo, they intrude the upper Laib and Active formations, l y i n g west and east respectively of the main Salmo River-Jersey a n t i c l i n a l structure. Locally at least (e.g., on the Salmo River northeast of the Reeves MacDonald mine) they show an i n c i p i e n t f o l i a t i o n , apparently coplanar with the a x i a l planes of Phase 2 folds, suggesting that they may predate or i n part by synchronous with the l a t t e r . Nelson-type plutonic intrusions On the regional scale, g r a n i t i c rocks of the Nelson and Kuskanax batholiths (Fig. 1) dominate the western concave side of the Arc and appear to emphasize i t s curvature. Numerous s a t e l l i t e plutons and stocks are also widely d i s t r i b u t e d along and across the Arc, causing l o c a l complications due to contact thermal metamorphism and marginal deformation. Their d i s t r i b u t i o n appears larg e l y i r r e g u l a r except for a possible weak east-southeast alignment. Marginally, the intrusives may show b r i t t l e i n t e r n a l deformation and l o c a l intense folding of the country rocks, suggestive of f o r c e f u l i n t r u s t i o n . 18 The main in t r u s i v e phase i s composed of p o r p h y r i t i c granite with subordinate phases of nonporphyritic granite, granodiorite, quartz monzonite, d i o r i t e and l o c a l l y syenite. Intrusion everywhere appears to postdate the main phases of fo l d i n g . Potassium-argon age determination of 170 m.y. on b i o t i t e (Leech et al. , 1963) and of 158 m.y. on b i o t i t e and 164 m.y. on hornblende (Nguyen et al. , 1968) indicate intrusion i n the Middle Jurassic which i s consistent with other geological evidence ( L i t t l e , 1960). Stocks are p a r t i c u l a r l y numerous i n the Salmo and Sheep Creek areas and have been described i n a general way by Fyles and Hewlett (1959) and Mathews (1953) as steep-sided i r r e g u l a r masses displaying varied contact e f f e c t s , with margins varying from d i f f u s e to x e n o l i t h i c and cross-cutting. Thermal aureoles are up to several thousand feet wide and may overlap so that l i t t l e of the country rock can have escaped reheating. The stocks are composed usually of b i o t i t e granite or quartz monzonite with only minor amounts, i f any, of other phases. A l l three areas mapped are i n some degree affected by contact thermal metamorphism but only near the Jersey mine do intrusions a c t u a l l y occur close to the lead-zinc ore bodies. There, three small stock-like bodies of b i o t i t e granite, elongate p a r a l l e l with the l o c a l f o l i a t i o n , intrude the main f o l d struc-tures and l o c a l l y cut the ore zones. Skarn-type tungsten mineralization occurs where the intrusions are i n contact with either of the calcareous Trueman or Reeves members, r e s u l t i n g i n complex superimposed mineralization. 19 B i o t i t e from a medium-grained f a c i e s of the Dodger stock gave a potassium-argon age of 100 + 3.0 m.y. (Table I I , F i g . 2 ) . T h i s i s v e r y s i m i l a r t o c i r c a 100 m.y. concordant ages determined from hornblende, muscovite and b i o t i t e from the S p i r i t p l u t o n and Kaniksu b a t h o l i t h i n Stevens County, Washington (Yates and Engels, 1968). However ot h e r s t o c k s i n the Salmo d i s t r i c t which have been dated ( a l s o by potassium-argon method) are the L o s t Creek quartz monzonite stock (119 m.y. b i o t i t e age, Leech et al. , 1963) and the Porcupine Creek g r a n o d i o r i t e stock (128 m.y. b i o t i t e age and 152 m.y. hornblende age, Wanless et al. , 1967) ( F i g . 2). The l a t t e r p a i r of ages suggest t h a t these stocks are r e l a t e d t o the Nelson s u i t e . Although the Dodger and a f f i l i a t e d s m a l l s t o c k s are p o s s i b l y r e l a t e d t o the Cretaceous p l u t o n i c event r e p r e s e n t e d by the S p i r i t p l uton-Kaniksu b a t h o l i t h and perhaps a l s o by the Bayonne and F r y Creek b a t h o l i t h s (100 m.y. b i o t i t e and muscovite ages, Leech et al. , 1963), i t seems more l i k e l y t h a t they belong r a t h e r t o the Nelson s u i t e and have s u f f e r e d argon l o s s , p o s s i b l y by r e h e a t i n g d u r i n g the subsequent Eocene igneous event. C o r y e l l - t y p e p l u t o n i c i n t r u s i o n s A number of very s m a l l p i p e - l i k e s t o c k s of a l k a l i n e a f f i n i t i e s , o c c u r r i n g i n the Salmo area, are c o r r e l a t e d w i t h the s y e n i t i c rocks of Rossland and f a r t h e r west, which have been d e s c r i b e d as the C o r y e l l - t y p e by L i t t l e (1960). The o n l y one r e l e v a n t t o t h i s study, the Salmo R i v e r stock, l i e s a s h o r t d i s -tance t o the west of the Canex Emerald tungsten mine ( F i g . 2 ) . I t was d e s c r i b e d by Daly (1912) as a p o r p h y r i t i c a u g i t e monzonite. Table I I . Potassium-argon age determinations on three i n t r u s i v e igneous rocks from Jersey mine area (specimen locations are shown i n F i g . 2). Specimen number Unit Rock type Mineral %K ± S* 40. ,. A radiogenic 4 0 A t o t a l 40, A radiogenic (10~ 5 cc STP/g) 40. A radiogenic 4 0 K x 10 3 Apparent age (m.y.) CX70-19 Dodger stock B i o t i t e g r a n i t e B i o t i t e 6. 08 + 0.04 0.92 2.467 5.995 100 ± 3.0 CX70-17 Salmo River stock Augite monzonite B i o t i t e 7. 23 i 0.02 0.87 1.467 2.998 50.6 ± 1.5 CX70-21 T e r t i a r y dyke B i o t i t e lampro-phyre B i o t i t e 7. 04 t 0.01 0.88 1.398 2.934 49.5 ± 1.5 O *S = Standard d e v i a t i o n of quadruplicate analyses Potassium analyses by J . E. Harakal and V. Bobik using Baird Atomic KY and KY3 flame photometers Argon analyses by J . E. Harakal using AEI MS-10 mass spectrometer 21 X L O C A T I O N O F CX7CH7. XuJg L O C A T I O N U N D E R G R O U N D O F CX70-19, 21. ( f r o m m a i n D o d g e r d r i f t ) Figure 2. Intrusive rocks i n the Salmo area (after L i t t l e , 1960). Jersey mine area i s enlarged to show location of specimens dated by potassium-argon method. Ages from the Lost Creek stock and from the Porcupine Creek stock are by Leech et al. (1963) and Wanless et al. (1967). 22 B i o t i t e from t h i s stock gave a potassium-argon age of 50.6 ± 1.5 m.y. (Table I I ) . T h i s i s i n c l o s e agreement w i t h potassium-argon ages determined from other a l k a l i n e i n t r u s i v e rocks a s s i g n e d t o the C o r y e l l s u i t e i n Stevens County, Washington (Yates and Engels, 1968) and i n the Rossland d i s t r i c t ( F y l e s et al. , 1973). Lamprophyre dykes and s i l l s B i o t i t e - and o l i v i n e - l a m p r o p h y r e dykes and s i l l s are found throughout the southern segment of the A r c . They d i s p l a y l i t t l e i n t e r n a l deformation and a p p a r e n t l y postdate a l l other i n t r u s i v e and major t e c t o n i c events. In the Salmo and Sheep Creek areas, the lamprophyre dykes are not g e n e r a l l y w e l l exposed but are o f t e n encountered i n underground workings where they c u t m i n e r a l i z a t i o n of a l l types. They may c o n t a i n l o c a l l y d e r i v e d x e n o l i t h s of q u a r t z i t e , p h y l l i t e , s u l p h i d e , e t c . , but more i n t e r e s t i n g e x o t i c x e n o l i t h s of g r a n i t e have a l s o been noted i n the Sheep Creek area (Mathews, 1953), along the Pend O r e i l l e R i v e r near the Reeves MacDonald mine, and w i t h i n zones i n the H. B. mine (Warning, 1960). B i o t i t e from a lamprophyre dyke i n the J e r s e y mine gave a potassium-argon age of 49.5 ± 1.5 m.y. (Table I I , F i g . 2). T h i s i s e s s e n t i a l l y the same age as t h a t determined f o r the a l k a l i n e Salmo R i v e r stock. Yates and Engels (1968) and F y l e s et al. (1973) have a l r e a d y shown t h a t t h i s mid-Eocene event was widespread and t h a t i n t r u s i v e and e x t r u s i v e a c t i v i t y were e s s e n t i a l l y c o e v a l . STRATIGRAPHIC SETTING OF MINERALIZATION Strata-bound lead-zinc deposits i n the southern Arc are r e s t r i c t e d to carbonate units of Lower and Middle Cambrian age which invariably have been dolomitized. The Reeves (Badshot) limestone/marble, which forms the Lower Cambrian host, i s dolomitized only i n r e l a t i v e l y small l e n t i c u l a r zones to which the sulphides, i f present, are large l y confined. In contrast, the Middle Cambrian Metaline (Nelway) formation i s much more extensively dolomitized and indeed i t s middle member i s almost wholly dolomite and forms a productive sulphide host i n the Northport d i s t r i c t . Its upper grey lime-stone member i s also dolomitized but only i n i t s uppermost 200 f t i n the Metaline d i s t r i c t , where i t i s host to economically important sulphide mineralization. There has been considerable argument concerning the o r i g i n of these dolomite-sulphide associations. In p a r t i c u l a r the dolomite has been variously considered as being of epigenetic, diagenetic, or syngenetic o r i g i n . Dolomite i n the Reeves member Within the c a l c i t e marble of the Reeves member, dolomite forms f l a t tabular zones e s s e n t i a l l y conformable with the host; although not confined to one single horizon and therefore not stratiform the zones do seem to be strata-bound. They are located near the base of the Reeves member, l o c a l l y even i n con-tact with the underlying Trueman mamber, and i n general are less than 100 f t thick. However there i s a notable exception at the 24 Reeves MacDonald mine where an easterly s t r u c t u r a l r e p e t i t i o n of the Reeves member has been v i r t u a l l y completely dolomitized throughout i t s t o t a l thickness of 350-400 f t (Plate I I I ) . The dolomite zones are elongate p a r a l l e l with the major s t r u c t u r a l trends and appear to have been involved i n a l l phases of deforma-tio n (see Section I I I ) . Contacts between dolomite and host c a l c i t e marble are usually interlayered v e r t i c a l l y over short distances and f i n e l y and i n t r i c a t e l y interfingered l a t e r a l l y . The dolomite marble i s d i s t i n c t l i t h o l o g i c a l l y since i t i s com-posed usually of more than 80% dolomite i n contrast with c a l c i t e marble which i s more than 80% c a l c i t e (Green, 1954). Quartz, probably r e c r y s t a l l i z e d a f t e r chert, i s ubiquitous, usually i n minor amounts, as small lenses and th i n layers. However the dolomite marble may l o c a l l y be highly s i l i c e o u s i n i t s upper part as i n the s t r u c t u r a l l y repeated eastern outcrop of the Reeves member at Reeves MacDonald mine (Plate I I I ) . Several v a r i e t i e s of dolomite marble can be recognized: (i) massive—pale grey to white homogeneous dolomite ( i i ) banded—alternating pale grey/black layered dolomite ( i i i ) sheared—highly sheared pale grey/black dolomite i n which S-planes are i l l u s t r a t e d by graphitic laminae The dolomite marble may be brecciated also but t h i s i s usually i n association with sulphides where the l a t t e r form the matrix to blocks, fragments and lenses (some i n t r i c a t e l y folded) of dolomite marble. Fyles and Hewlett (1959) and Fyles (1964) believe the dolomite and i t s s i l i c e o u s v a r i e t i e s were formed by epigenetic 25 replacement of host Reeves limestone/marble and that the replace-ment was s t r u c t u r a l l y controlled. An alte r n a t i v e primary or diagenetic o r i g i n i s implied by Sangster (1970a) who believes the carbonates formed, i n association with bedded chert, i n a deep-water euxinic environment. Dolomite i n the Nelway/Metaline formation The middle dolomite member of the Metaline formation i s primarily composed of l i g h t grey, f i n e - to medium-grained, thick bedded dolostone but several subordinate v a r i e t i e s are also distinguished. These range from very fine-grained grey to medium-grained black massive dolostone, together with d i s t i n c t i v e mottled and striped v a r i e t i e s which may be of a l g a l o r i g i n . Because of i t s widespread d i s t r i b u t i o n and great thickness (more than 3000 f t ) , Dings and Whitebread (1965) regard the middle dolomite unit as being of diagenetic o r i g i n . The equivalent Nelway middle member i s composed of l i g h t to dark grey massive dolostone commonly with chert nodules. However i t also includes a unit of f i n e l y interbanded l i g h t grey/ black dolostone i n which the black layers contain abundant ir r e g u l a r small lenses i n f i l l e d with white dolomite and chert resembling "bird's eye" structures, possibly of dessication o r i g i n . L i t t l e (1960) regarded the dolomite as of primary o r i g i n . Fyles and Hewlett (1959), who noted that the limestone-dolostone contact at the base of the middle member was i r r e g u l a r l y trans-gressive on a broad scale and often complexly interbanded, 26 concluded that "the complex pattern re s u l t s from the vagaries of dolomitization" but did not speculate on the o r i g i n of the dolomite. The upper limestone member of the Metaline formation i s dolomitized i n i t s uppermost 200 f t i n the Metaline F a l l s area. This unit, known as the Josephine horizon, consists of i r r e g u -l a r l y but pervasively brecciated dolostone with a matrix of f i n e -grained black carbonaceous dolomite and jasperoid. The brec-ciated dolostone i s t e x t u r a l l y very variable and includes a striped variety which has been interpreted as being of a l g a l o r i g i n (McConnel and Anderson, 1968). The l a t t e r authors propose that t h i s Josephine horizon i s stratigraphic and hence of sedi-mentary and diagenetic o r i g i n whilst Park and Cannon (1943) and Dings and Whitebread (1965) consider the dolomite to be of epigenetic o r i g i n . These various dolomite occurrences are from d i f f e r e n t s t r u c t u r a l , as well as s t r a t i g r a p h i c , l e v e l s and thus display widely d i f f e r i n g i n t e n s i t i e s of deformation. A comparison of the occurrences, allowing for s t r u c t u r a l v a r i a t i o n , suggests that they are a l l strata-bound although t h e i r l i m i t s are not always c l e a r l y or simply defined. There i s no evidence that the dolomitization process was s t r u c t u r a l l y controlled or l o c a l i z e d as proposed by those favouring an epigenetic o r i g i n although of course the dolomite zones are themselves deformed. In general, too, the dolomite zones are frequently more or less s i l i c e o u s , s l i g h t l y carbonaceous and argillaceous. Striped and mottled v a r i e t i e s , distinguished i n the less highly deformed Middle 27 Cambrian units have been interpreted to be of a l g a l and/or diagenetic o r i g i n . However, Zeuger (1972) has pointed out that f i n e l y laminated dolomite and dessication structures developed i n dolomite are not necessarily diagnostic of a supratidal or i n t e r t i d a l o r i g i n and may be found even i n subtidal dolomite bioherms. It i s suggested that the general features of these various dolomite occurrences are more compatible with an early replacement o r i g i n (possibly diagenetic) i n a bank environment rather than with a l a t e r , s t r u c t u r a l l y controlled, epigenetic o r i g i n . SUMMARY Accumulation of a c l a s t i c wedge ( i n i t i a t e d by epeiro-genic movements) marginal to the P u r c e l l Arch extended from Late Proterozoic to Lower Cambrian times. Overstep from the northeast onto the Arch occurred by e a r l i e s t Cambrian period v i a the s t r u c t u r a l l y controlled northeast-trending Eager trough and presumably continued with the progressive denudation of the Arch which i s r e f l e c t e d i n the increasingly f i n e grain size of the e l a s t i c s upwards i n the sedimentary p i l e . A widespread shelf-edge bank carbonate (Reeves/Badshot limestone) marked the culmination of t h i s prograding accumulation i n the middle Lower Cambrian. Carbonate deposition persisted i n the Salmo-Metaline sector at least u n t i l the end of the Middle Cambrian. Most of the dolomite occurrences i n the Lower Cambrian Reeves member/Badshot formation and i n the Middle Cambrian 28 Nelway-Metaline formation are considered to be of a syngenetic-diagenetic o r i g i n as the occurrences are e s s e n t i a l l y s t r a t a -bound i n form, exhibit s l i g h t facies differences from t h e i r "host" limestones, and contain problematic structures possibly of a l g a l and of dessication o r i g i n s . To the north, i n the Lardeau d i s t r i c t , the shelf environment was replaced toward the end of the Lower Cambrian period by deeper, more r e s t r i c t e d slope or basin environment which, by the Lower Ordovician, had developed farther south along the Arc and persisted there u n t i l the S i l u r i a n and perhaps Devonian period when there i s some evidence of i n f l u x of c l a s t i c material from a presumed western source. The unconformity beneath the Mount Roberts formation (and the Milford group) apparently marks mid-Palaeozoic tectonism i n the Kootenay Arc region. The nature of t h i s deformation i s obscure although i t has been postulated as r e f l e c t i n g the develop-ment of eastward-verging nappe structures (Ross and K e l l e r h a l s , 1968). The subsequent depositional record i s of mixed andesitic volcanic/sedimentary eugeosynclinal character with material being derived largely from the west. However t h i s record i s i n -complete, there being l i t t l e evidence of deposition during the Permian and Lower T r i a s s i c periods. The Upper T r i a s s i c - J u r a s s i c Ymir and Rossland groups unconformably o v e r l i e the Pennsylvanian Mount Roberts formation as apparently the Kaslo and Slocan groups s i m i l a r l y o v e r l i e the Milford group, r e f l e c t i n g the continuation (or r e - i n i t i a t i o n ) of tectonism i n the early Mesozoic era. These T r i a s s i c - J u r a s s i c 29 rocks are themselves folded but plutonic intrusion by the Nelson batholith and i t s s a t e l l i t e s post-dates t h i s deformation which must therefore be pre-Middle Jurassic i n age. Many of these s a t e l l i t e s have radiometric apparent ages much younger than those of the Nelson batholith i t s e l f . Several small granite stocks i n the v i c i n i t y of Jersey mine are probably examples of such s a t e l l i t e s . One of them, the Dodger stock, which contact metamorphoses and l o c a l l y intrudes lead-zinc mineralization, was found to have an apparent potassium-argon age from b i o t i t e of 100 m.y. Other potassium-argon age deter-minations on b i o t i t e s from the Salmo River a l k a l i n e stock and from a lamprophyre dyke confirm the occurrence i n t h i s area of the Eocene igneous event which i s found to be widespread i n the southern Kootenay Arc. SECTION III STRUCTURAL ENVIRONMENT The three mine areas are located within a westerly verging, folded and thrust Lower Palaeozoic sequence referred to as the "Mine Belt" by Fyles and Hewlett (1959) and as the "Thrust' Belt" by Yates (1970). Economic mineralization i s r e s t r i c t e d to the Reeves member where i t i s exposed on the upper limb of the major complex a n t i c l i n a l structure which dominates the b e l t . Structural mapping included most of the l a t t e r structure within the mine areas. The same sequence of s t r u c t u r a l events was recognized in a l l three areas although there are marked differences i n the r e l a t i v e i n t e n s i t i e s of these events and lesser differences i n both geometry and sty l e of deformation. Deformation i s polyphase, with three phases of folding and various fracture systems having been recognized. MINOR FOLDING The various s t r u c t u r a l elements associated with folding were distinguished i n the f i e l d on the basis of t h e i r morphology and orientation. These elements with the nomenclature used are l i s t e d i n Table III and t h e i r orientations and locations shown in Plates I, II, IV, V and VII. Relative ages of the d i f f e r e n t phases of folding were established mainly from p a r a l l e l or cross-cutting relationships 31 Table III . Structural elements and t h e i r nomenclature. Surface element Linear element F 0 bedding Phase 1 Fi a x i a l plane micaceous Li F 0 / F i intersections f o l i a t i o n APi f o l d a x i a l surface f o l d axis Phase 2 F 2 crenulation cleavage L 2 crenulation of Fj or a x i a l plane or F 2 trace on cleavage F o- l AP 2 f o l d a x i a l surface f o l d -axis Phase 3 F 3 s t r a i n - s l i p cleavage L 3 kink bands i n Fj or F 3 trace on F 0 - i AP 3 f o l d a x i a l surface f o l d axis 32 between cleavages and f o l d a x i a l surfaces, and from r e f o l d i n g of e a r l i e r cleavages and related l i n e a r structures. S l i g h t d i f -ferences i n f o l d s t y l e of successive phases may also be recog-nized but these are much complicated by the varied response of d i f f e r e n t l i t h o l o g i e s during any p a r t i c u l a r phase of fo l d i n g . Following a convention established by other workers i n the Kootenay Arc, these phases of folding have been designated Phase 1, Phase 2, and Phase 3. However i t should be understood that these are not necessarily equivalent to phases distinguished by other workers beyond the immediate Salmo area, as w i l l be considered below. Phase 1 structures Although gross l i t h o l o g i c a l units are e a s i l y d i s t i n -guished, recognition of in t e r n a l bedding surfaces (F 0) i s frequently obscured by the F i f o l i a t i o n , except where the bedding i s cut at high angles by the l a t t e r as i n Phase 1 f o l d closures. Very commonly the e a r l i e s t recognized f o l i a t i o n (Fi) i s near coincident with bedding so the two surfaces could be d i s t i n -guished only with d i f f i c u l t y . Thus i n many places, p a r t i c u l a r l y i n quartz p h y l l i t e s and i n carbonate units, only a composition layering (designated F 0 - i ) was mapped. The major penetrative f o l i a t i o n comprises a s l i g h t l y micaceous, platy cleavage i n quartzite, an intense micaceous-chloritic f o l i a t i o n or "s c h i s t o s i t y " i n p h y l l i t e s , and a cleavage i n carbonate rocks i l l u s t r a t e d only by sparse micas, or by graphitic partings. The e a r l i e s t recognized li n e a t i o n s (Li) are generally not very obvious structures involving intersections between bedding 33 and the F i f o l i a t i o n . They include bedding traces, usually i l -l u strated by colour bands on the F i s c h i s t o s i t y , mica-edge traces on bedding surfaces, and cleavage mullions developed at f o l d hinges i n q u a r t z i t i c rocks. The e a r l i e s t recognized folds deform only bedding and have a x i a l planes p a r a l l e l with the Fi f o l i a t i o n . They are generally t i g h t to i s o c l i n a l structures, either asymmetric with single hinges or symmetric with multiple hinges and long para-s i t i c a l l y folded limbs. Where strong a x i a l plane cleavage i s developed, as i n more competent rock types, hinges may be more or less serrate or even l o c a l l y o b l i t e r a t e d by transposition. A l l these folds, i r r e s p e c t i v e of l i t h o l o g y involved, display marked limb attenuation (Fig. 3), with the most spec-tacular attenuations being displayed by thin s i l i c e o u s layers within the Trueman and Reeves carbonate members. Rootless i n t r a -f o l i a l folds may also be developed within these l a t t e r u n i t s . The folds are considered to approximate those of " s i m i l a r " type (Ramsay, 1962a) on the basis of the weak d u c t i l i t y contrast displayed by the d i f f e r e n t l i t h o l o g i e s involved and on the basis of cross-sectional shape of the folded layers. Phase 1 l i n e a r structures (fold axes and lineations) have variable low to moderate plunges generally south to south-west or less frequently north to northeast or even northwest (Fig. 4). A x i a l surfaces too have variable orientations but most commonly are moderately i n c l i n e d easterly to southerly. Very similar orientations are exhibited by bedding and Fi f o l i a t i o n surfaces implying that Phase 1 folding i s e s s e n t i a l l y i s o c l i n a l . 34 PHASE 1 MINOR FOLDS PHASE 2 MINOR FOLDS PHASE 3 MINOR FOLDS F i g u r e 3. Examples t r a c e d from photographs o f mi n o r f o l d s t y l e s from t h e t h r e e f o l d g e n e r a t i o n s d i s t i n -g u i s h e d i n t h e mine a r e a s . 35 Figure 4. Equal-area projections (lower hemisphere) of Phase 1 minor s t r u c t u r a l elements (nomenclature as i n Table III) from the three mine areas: a-c from H. B.; d-f from Jersey; g - i from Reeves MacDonald. Data from Plates I-VIII. Inset map (after Fyles and Hewlett, 1959) shows location of mine areas i n r e l a t i o n to the host Reeves member (black) and to i n t r u s i v e stocks. 36 That the variations are lar g e l y a consequence of r e f o l d i n g i s shown by the dispersion of poles to these surfaces along great c i r c l e s centred e s s e n t i a l l y on the modal Phase 2 f o l d axes (Fig. 4a, d, g). Phase 2 structures Phase 2 minor folds are distinguished as open to t i g h t asymmetric fol d s , generally upright to s l i g h t l y overturned i n attitude (Fig. 3). Asymmetry viewed downplunge (usually south-ward) i s almost invariably dextral. Hinge p r o f i l e s vary from rounded to subangular, tending toward the former i n more massive rocks and toward the l a t t e r i n f i n e l y interbedded and/or strongly cleaved rocks. Attenuation of the limbs i s apparently s l i g h t . A x i a l plane cleavage (F 2) i s weakly developed i n massive rocks and i s represented by a crenulation cleavage i n p h y l l i t i c rocks. Mineral alignment along these planes i s l i m i t e d to sparse micas, possibly of mimetic o r i g i n . The crenulation c l e a -vage i s widely developed and the crenulation i t s e l f , or micro-folding of the F i f o l i a t i o n , forms a p a r t i c u l a r l y prominent l i n e a t i o n (L 2) throughout the three areas. Locally a l i n e a t i o n may also be developed on the f o l d limbs perpendicular to the f o l d hinges but the age of t h i s r e l a t i v e to the l i n e a t i o n L 2 i s not known. These Phase 2 folds are considered to be 11 f l e x u r a l - s l i p " folds modified by f l a t t e n i n g (Ramsay, 1962a) because of the con-t r a s t i n response between competent and incompetent units, and the generally s l i g h t attenuation of the f o l d limbs. The l a t t e r was investigated by measuring thickness variations across f o l d 37 hinges i n several mesoscopic folds and i t was found that the orthogonal thickness t tended to maximum values at the hinges whereas the thickness T measured p a r a l l e l to the a x i a l surface tended to minimum values at the hinges (Fig. 5) . This geometry-i s c h a r a c t e r i s t i c of flattened " f l e x u r a l - s l i p " folds (Ramsay, 1962a). Phase 2 l i n e a r structures plunge at low to moderate angles generally south to south-southwest or less frequently north to north-northeast (Fig. 6). They are approximately coaxial with Phase 1 structures i n the H. B. and Jersey areas where modal orientations d i f f e r by only 5-10°. Structural trends diverge more markedly i n the Reeves MacDonald area where modal orientations d i f f e r by approximately 20°. A x i a l planes exhibit considerably less v a r i a t i o n than do Phase 1 a x i a l planes and are usually steeply i n c l i n e d east-southeast to southeast so that Phase 2 folds can be distinguished geometrically from those of the e a r l i e r phase. Phase 3 structures Phase 3 folds are shallow to close asymmetric, monoclinal structures, plunging at moderate to steep angles. The larger folds i n a l l l i t h o l o g i e s tend to have gently rounded hinges whereas smaller representatives, e s p e c i a l l y i n w e l l - f o l i a t e d p h y l l i t e s , have d i s t i n c t l y angular hinges and are r e a l l y small kink folds (Fig. 3). Where deformation i s more intense, c l o s e l y spaced kink bands and, l o c a l l y , crenulations may be developed. However a x i a l plane cleavage i s generally very weak or absent. More commonly 38 distance along layer Figure 5. Plots of thickness variations across three Phase 2 minor f o l d hinges, developed i n quartzite, quartz p h y l l i t e . T, the layer thickness measured p a r a l l e l to a x i a l planes, i s plotted against perpendicular distance from the a x i a l planes. t f the orthogonal thickness of the l a y e r ( s ) , i s plotted against distance along the composition layering.. 39 CONTOUR MAXIMA F i g u r e 6. E q u a l - a r e a p r o j e c t i o n s (lower hemisphere) o f Phase 2 minor s t r u c t u r a l elements (nomenclature as i n T a b l e I I I ) from t h e t h r e e mine a r e a s : a-b from H. B.; c-d from J e r s e y ; e - f from Reeves MacDonald. Data from P l a t e s I - V I I I . I n s e t map ( a f t e r F y l e s and H e w l e t t , 1959) shows l o c a t i o n o f mine a r e a s i n r e l a t i o n t o t h e h o s t Reeves member ( b l a c k ) and t o i n t r u s i v e s t o c k s . 40 a discrete s t r a i n - s l i p cleavage i n p h y l l i t i c rocks or a fracture cleavage i n more massive rocks i s developed. Traces of these planar structures on the F i f o l i a t i o n or on composition layering produce a weak l i n e a t i o n ( L 3 ) with the same orientation as the kink f o l d and larger monoclinal f o l d axes. Phase 3 structures are non-penetrative. They are however widely developed, generally on a mesoscopic scale but l o c a l l y also on a macroscopic scale, as i n H. B. mine area. The folds can be divided, on the basis of t h e i r asym-metry and orientation, into two sets (Fig. 7): (i) S i n i s t r a l folds ( F 3 s ) plunging at moderate to steep angles east to northeast ( i i ) Dextral folds (F 3 (j) plunging at moderate to steep angles east-southeast to southeast A x i a l planes (or kink planes) are generally subvertical to ver-t i c a l . The two sets are believed to be coeval and to form a conjugate system, although only r a r e l y are true conjugate pairs recognized. Both sets may however be recognized i n a l l areas although t h e i r r e l a t i v e i n t e n s i t i e s vary markedly. The orientation of p r i n c i p a l stress axes can be deter-mined from the mutual attitudes of the kink planes of conjugate f o l d systems (Johnson, 1956; Ramsay, 1962c). In t h i s study, modal orientations of kink planes from the two singular sets of folds ( s i n i s t r a l and dextral) were used to determine the stress f i e l d orientation; a procedure which C l i f f o r d (1968) has shown to be v a l i d where t r u l y conjugate arrays are lacking. This shows in the maximum p r i n c i p a l stress b i s e c t i n g the obtuse angle 41 F i g u r e 7 . Equal-area p r o j e c t i o n s (lower hemisphere) of Phase 3 minor s t r u c t u r a l elements (nomenclature as i n Table I I I ) from the three mine areas: a-c from H . B . ; d-f from J e r s e y ; g - i from Reeves MacDonald. Data from P l a t e s I - V I I I . I n s e t a t lower r i g h t shows geometry and m o n o c l i n i c symmetry of the Phase 3 conjugate system. I n f e r r e d p o s i t i o n s of p r i n c i p a l s t r e s s axes are shown i n c, f , and i ; 1, 2, 3 r e f e r to s u b s c r i p t s on ai>02>o"3. between the conjugate kink planes (Fig. 7). This i s a not uncom-mon si t u a t i o n i n naturally deformed rocks (Roberts, 1971) which i s i n accord with the experimental data of Paterson and Weiss (1966) but not with that of Donath (1964, 1968) or Borg and Handin (1966). Herein l i e s a controversy concerning the r e l a -tionship between kink bands and p r i n c i p a l stress orientations; i n p a r t i c u l a r , whether or not kink planes are generated p a r a l l e l with planes of maximum shearing stress. Paterson and Weiss (1966) and Weiss (1968) maintain that no causal r e l a t i o n s h i p exists and propose that kink bands nucleate at a point or l i n e source, grow by kink plane migration (continuously increasing i n width) and that t h i s i s achieved by s l i p within and along the f o l i a t i o n . On the other hand, Donath (1964, 1968) and Dewey (1965, 1969) regard kink bands as f o l i a t i o n segments of constant length, externally rotated between kink planes which p a r a l l e l surfaces of maximum shearing stress. Their positions are con-sidered to be already defined at i n f i n i t e s i m a l s t r a i n and there-after remain fixed. Whatever the mechanism for t h e i r formation, the Phase 3 fo l d systems i n the study areas consistently have monoclinic symmetry and the deduced maximum p r i n c i p a l stress directions are directed approximately north-south (Fig. 7c, f, i ) . In Jersey and H. B. areas, the deduced maximum p r i n c i p a l stress d i r e c t i o n i s sub-parallel with the modal orientation of the composition layering whereas at Reeves MacDonald i t i s more i n c l i n e d to the layering. This v a r i a t i o n i n attitude of the layering r e l a t i v e to the maximum p r i n c i p a l stress may account for v a r i a t i o n i n 43 the r e l a t i v e i n t e n s i t i e s of the two sets of the conjugate f o l d system from one area to another, as has been i l l u s t r a t e d by Roberts (1971). EFFECTS OF SUPERIMPOSED FOLDING Phase 2 superimposed on Phase 1 Phase 2 folding has produced widespread reorientation and hence modification to the geometry of e a r l i e r structures, both l i n e a r and planar. Farther north i n the Kootenay Arc, Ross (1970) has shown that the e a r l i e s t l i n e a r structures (Li) plunge both north and south and are frequently c u r v i l i n e a r . He has proposed that t h i s i s produced by variable s l i p within the f o l i a t i o n p a r a l l e l with the a2-direction of Phase 2 folding and that culminations/ depressions of Li therefore coincide with a x i a l surfaces of Phase 2 fo l d s . Within the mine areas, Phase 1 l i n e a r structures display s i m i l a r plunge variations and c u r v i l i n e a r l i n e a t i o n s have been observed l o c a l l y . However, Phase 2 l i n e a r structures also exhibit plunge culminations/depressions on a broad scale so that, unless there has been d i f f e r e n t i a l f l a t t e n i n g of Phase 2 folds, a l l the v a r i a t i o n i n Li orientation cannot be the product of s l i p during Phase 2 f o l d i n g . That i t i s i n part can be demonstrated on the Phase 2 culminations where L2 i s uniformly horizontal but Li has variable plunge (±10°) as at the northern end of the Jersey mine area (Plate IV). In spite of t h e i r variable orientation, no c l e a r l y de-fined dispersion path (in stereographic projection) of Li l i n e a r structures about the Phase 2 axes of folding can be determined, presumably because of t h e i r near coaxial trends; the difference i n modal orientations i s less than 5° at Jersey, 10° at H. B. and 20° at Reeves MacDonald (compare F i g . 4 and 6). It i s thus not possible because of the i l l - d e f i n e d L i dispersion paths to deduce the s p e c i f i c deforming process operative during Phase 2 folding. Phase 1 planar elements, both the micaceous-chloritic f o l i a t i o n and f o l d a x i a l surfaces, are c l e a r l y folded about the Phase 2 axes, as i l l u s t r a t e d by the dispersion of poles to both sets of surfaces along great c i r c l e s centred e s s e n t i a l l y on the modal Phase 2 axes (Fig. 4a, d, g). This i s best i l l u s t r a t e d i n Jersey mine area (Fig. 4d) where macroscopic Phase 2 folding i s correspondingly best developed. Interference f o l d structures of two d i s t i n c t types have been recognized (Fig. 8). The basin/dome structures (Type 1 of Ramsay, 1962b) are less common and have been recognized only within c a l c i t e marble units. They are produced by the same mechanism as the c u r v i l i n e a r L i lineations already described. More common, and recognized i n a l l l i t h o l o g i e s , are approximately c o a x i a l l y refolded fo l d s , corresponding to Type 3 of Ramsay (1962b), i n which the Phase 1 axes were oriented close to the Phase 2 a x i a l surfaces (Fig. 8 c - f ) . Flattening of Phase 1 folds has presumably also occurred during Phase 2 folding. This i s believed to be r e f l e c t e d i n the occurrence of intense shearing/transposition i n f o l d closures and perhaps also i n the occurrence of boudinage structures with-i n carbonate units on f o l d limbs, although the l a t t e r structures 45 ON .Figure 8. Examples o f i n t e r f e r e n c e f o l d s t r u c t u r e s r e s u l t i n g from s u p e r i m p o s i t i o n o f Phase 2 f o l d s on e a r l i e r formed Phase 1 f o l d s , a-d a r e d e v e l o p e d i n c a l c i t e m a r b l e ; e-f a r e d e v e l o p e d i n q u a r t z p h y l l i t e and q u a r t z i t e . 46 may have developed wholly during Phase 1. Shearing/transposi-ti o n appear to be p a r t i c u l a r l y intensely developed where Phase 2 macroscopic folds are either absent or weakly developed, as i n the H. B. and Reeves MacDonald mine areas. I t i s also perhaps s i g n i f i c a n t that the nearest approach to coplanarity between modal Fi and F 2 a x i a l surfaces occurs i n the H. B. mine area (compare 4c and 6b). This may suggest that, where Phase 1 structures were already steeply i n c l i n e d , these early folds were tightened up and flattened rather than refolded (s.s.) during Phase 2 deformation (Fig. 9). Phase 3 superimposed on Phases 1 and 2 Phase 3 folding i s a non-penetrative event so that i t s eff e c t s are l o c a l i z e d . These are most c l e a r l y i l l u s t r a t e d i n part of H. B. mine area where several macroscopic s i n i s t r a l folds r e f o l d e a r l i e r structures (Plate VIII). There, Phase 1 li n e a r structures have very variable orientations but are d i s -persed (in stereographic projection), with considerable spread, along an 80° small c i r c l e locus centred on the Phase 3 s i n i s t r a l axis (Fig. 4c). Such constant angles between L 3 S and Li would imply, according to Ramsay (1962), that Phase 3 folds are " f l e x u r a l - s l i p " i n type. (These folds have been referred to, above, as kink folds and the controversy surrounding the mecha-nism of formation of such folds has been referred to.) Poles to the related planar structures, Fi f o l i a t i o n and a x i a l surfaces, are dispersed along a very s i m i l a r small c i r c l e locus (Fig. 4a, b). I n s u f f i c i e n t Phase 2 structures were recognized within t h i s p a r t i c u l a r sub-domain to i l l u s t r a t e t h e i r response to Phase 47 -Figure 9. Diagram showing t h e e f f e c t s o f Phase 2 f o l d i n g on Phase 1 s t r u c t u r e s : (a) by r e f o l d i n g and (b) by c l o s u r e and d i f f e r e n t i a l f l a t t e n i n g . 48 3 s i n i s t r a l f o l d i n g . Elsewhere i n H. B. mine area and through-out Jersey and Reeves MacDonald mine areas no equivalent c l e a r l y defined dispersion of either Phase 1 or Phase 2 l i n e a r s truc-tures can be distinguished. Both, however, do show culmina-tions/depressions within the composition layering ( F o - i ) , as has been referred to above, but the development of the broad culminations/depressions exhibited by Phase 2 l i n e a r structures i s not c l e a r l y understood. The most l i k e l y explanation i s that they developed as a r e s u l t of Phase 3 folding since the trend of the culminations/depressions i n plunge i n the Jersey and H. B. mine areas p a r a l l e l the traces of Phase 3 a x i a l surfaces (Plates VI, VIII). SUMMARY OF STRUCTURAL STYLES AND RELATIVE AGES OF FOLDING Three phases of foldin g , a l l at least of l o c a l s i g n i f i -cance, have been recognized. Their s t y l e s , average orientations and age r e l a t i o n s are summarized i n Table IV. Using l o c a l evidence, only an upper age l i m i t can be placed on these since they a l l pre-date g r a n i t i c i n t r usion i n the area, dated at 100 m.y. (Lower Cretaceous). The r e l a t i v e timing of the phases i s as indicated but the continuity or otherwise cannot be f u l l y established within the small areas studied. MAJOR FOLDING The three strata-bound sulphide deposits are a l l located on the east limb of complex major a n t i c l i n a l structures referred to as the Salmo River a n t i c l i n e and the Jersey a n t i c l i n e i n Table IV. Summary of s t r u c t u r a l s t y l e s and r e l a t i v e ages of fo l d i n g . D i s t r i b u t i o n Surface folded Morphology A x i a l surface f o l i a t i o n Lineation Attitude Phase 1 Minor f o l d s : common Major f o l d s : dominant Tight to i s o c l i n a l , s i m i l a r f o l d s with attenuated limbs Fi s c h i s t o s i t y i n p h y l l i t e , a x i a l plane cleavage i n quartzite and limestone Li i n t e r s e c t i o n s of Fo/Fi Variably i n c l i n e d a x i a l surfaces, va r i a b l e a x i a l trends, low to moderate plunge Phase 2 Minor f o l d s : common but l o c a l l y r e s t r i c t e d Major f o l d s : common but l o c a l l y r e s t r i c t e d Fo, F i Open to close, asym-metric flattened f l e x u r a l - s l i p folds F 2 crenulation cleavage i n p h y l l i t e , weak a x i a l plane cleavage i n massive rocks Phase 3 Minor folds: widespread but variably developed Major fo l d s : l o c a l l y developed o / I i Shallow to open, asym-metric monoclinal folds and kink bands (conju-gate) F 3 s t r a i n - s l i p to crenu-l a t i o n cleavage i n p h y l l i t e , weak fracture cleavage i n massive rocks L 2 crenulation of mica L 3 i n t e r s e c t i o n of and F 2 / F u _ i intersection F 3 / F 0 - 1 Steep a x i a l surfaces, mainly S to SSW a x i a l trends, low to moderate plunge Steep a x i a l surfaces, NW and SE a x i a l trends, moderate to steep plunge Reeves MacDonald and Jersey-H. B. mine areas respectively (Fyles and Hewlett, 1959). Although they are not continuous these appear to be e s s e n t i a l l y the same structure exposed at di f f e r e n t l e v e l s . It i s proposed that the name—Salmo River a n t i c l i n e — b e extended to include the whole structure. Overall plunge i s southward but plunge culminations contribute to per-sistence of the structure along s t r i k e . Structural complexity diminishes with increasing depth i n the a n t i c l i n e which i s re-fl e c t e d i n degree of exposure of the q u a r t z i t i c core rocks. Complications at higher le v e l s are due to multiple hinges, to tectonic thickening/thinning p a r t i c u l a r l y of the Trueman member, and to the eff e c t s of tectonic s l i d e s (Fleuty, 1964) and thrusts (see descriptions on p. 57). H. B. mine area (Plate VIII, F i g . 10) Major structure of H. B. mine area i s the most complex of the three areas. Additional s t r u c t u r a l complications are due to Phase 3 major foldi n g , to obscure stratigraphic r e l a t i o n s between dolomite marble and c a l c i t e marble of the Reeves member, and to the uncertain nature of p h y l l i t e i n t e r c a l a t i o n s within the Reeves member. Phase 1 major folds plunge southward and have a x i a l sur-faces i n c l i n e d steeply eastward. These are most c l e a r l y i l l u s -trated by the a n t i c l i n e s cored by quartz p h y l l i t e / s c h i s t of the Reno formation (Fig. 10). Internal structure of the Reeves member i s obscure due to widespread intense transposition. Dolomite marble within the member forms huge pod-like masses which are d i f f i c u l t to interpret s t r u c t u r a l l y because t h e i r W E S T F i g u r e 10. V e r t i c a l c r o s s - s e c t i o n s (subnormal t o major f o l d axes) o f H. B. mine a r e a . L o c a t i o n s and g e n e r a l g e o l o g y a r e shown on P l a t e V I I I . 52 l i m i t s cannot be assumed to have been, even o r i g i n a l l y , s t r a t i -graphic. Very t h i n i n t e r c a l a t i o n s of p h y l l i t e also within the Reeves member are interpreted as s t r a t i g r a p h i c and not as extremely attenuated i s o c l i n e s as envisaged by Fyles and Hewlett (1959) . Generally weak development of Phase 2 folding and wide-spread development of transposition structure i s interpreted as indicating tightening and hence possible f l a t t e n i n g of Phase 1 folds. Low to high angle thrusting which further complicates the structure i s believed to have occurred toward the end of Phase 2 deformation (Fig. 10). Phase 3 s i n i s t r a l macroscopic folds are well developed in the area. These plunge steeply northeast and have subvertical a x i a l surfaces. E f f e c t s of t h i s folding contribute to subsurface complexities i n structure of the dolomite marble "pods" and hence i n configuration of the ore zones southward downplunge along the main host Phase 1 structure (Fig. 10). The l a t t e r i s inferred to be a t i g h t s y n c l i n a l l y folded dolomite marble lens occupying what has been referred to as the H. B. syncline. Jersey mine area (Plate VI, F i g . 11) The major a n t i c l i n a l structure i n Jersey mine area i s i n part recumbent, with the predominantly phyllite-marble limbs dipping more gently eastward than the more upright q u a r t z i t i c core rocks (Fig. 11). The limbs are folded into r e l a t i v e l y open, upright s l i g h t l y asymmetric Phase 2 f o l d s . These have steep, generally eastward-dipping a x i a l surfaces. Core rocks of the a n t i c l i n e F i g u r e 11. V e r t i c a l c r o s s - s e c t i o n s (subnormal t o major f o l d axes) o f J e r s e y mine a r e a . L o c a t i o n s and g e n e r a l g e o l o g y a r e shown on P l a t e V I . contain only minor Phase 2 folds superimposed on the Phase 1 structure. The l a t t e r i s complicated by tectonic thickening and re p e t i t i o n i n multiple hinges of the Trueman member, and by s l i d i n g at the base of that member. The s l i g h t departure i n ax i a l trends between the two f o l d generations can be appreciated from the d i s t r i b u t i o n of major a x i a l traces i l l u s t r a t e d i n Plate VI. Phase 3 folding i s represented by sparsely developed mesoscopic kink folds; but at the northern end of the area a broad culmination causes northward plunge reversals of both Phase 1 and 2 li n e a r structures. Its trace p a r a l l e l s a x i a l traces of Phase 3 minor s i n i s t r a l folds and so the culmination i s con-sidered to be genet i c a l l y related to Phase 3 deformation. Reeves MacDonald mine area (Plate I I I , F i g . 12) The most d i s t i n c t i v e s t r u c t u r a l feature i n Reeves MacDonald mine area i s the nearly east-west s t r i k e and more southwesterly f o l d a x i a l trends. According to Yates (1970) t h i s abrupt change i n s t r i k e i s produced by aggregate displacement of northward-directed thrusts and associated tear f a u l t s . Appro-p r i a t e l y oriented thrusts e x i s t i n Reeves MacDonald area but cross-cutting f a u l t s exhibit only weakly oblique displacements. Development of the east-west s t r i k e could also be p a r t l y explained by invoking large scale dextral kink folding (Phase 3) accom-panying thrusting, with the northern antiformal hinge located east-northeast of the mine area (Fig. 1) and the middle limb s t r i k i n g east-west through the mine area. A complementary I — 3 0 0 0 FT 1— 2 0 0 0 I — I O O O N O R T H F i g u r e 12. I n c l i n e d c r o s s - s e c t i o n (subnormal t o major F i f o l d axes) o f Reeves MacDonald mine a r e a . L o c a t i o n and g e n e r a l g e o l o g y a r e shown on P l a t e I I I . 56 synformal hinge cannot be located since the structure farther west i s concealed by thrusting. However there i s l i t t l e r e a l evidence that Phase 3 folding occurred on such a large scale. Within the mine area, structure i s dominated by the Salmo River a n t i c l i n e . Its a x i a l surface dips steeply south-southeast and i t s plunge (up to 50°) i s anomalously steep. South of the a n t i c l i n e l i e s the Reeves syncline which conformably encloses dolomite marble and associated sulphide mineralization. This structure was considered by Fyles and Hewlett (1959) to be a secondary (Phase 2) f o l d but was reinterpreted by Macdonald (1970), on the basis of minor f o l d geometry, to be a Phase 1 f o l d . I t i s a steeply plunging, extremely attenuated syncline and the r e l a t i v e l y competent dolomite marble i n i t s core i s highly transposed. The structure i s believed to have been f l a t -tened during Phase 2. The Reeves member i s repeated south of the Reeves syncline and appears to occupy the overturned limb of another syncline, perhaps o r i g i n a l l y a s t r u c t u r a l l y higher part of the Reeves syncline now juxtaposed along a lag surface. Whereas Phase 2 minor structures are ubiquitous and intensely developed (except i n carbonate units) the major folds are r e l a t i v e l y open structures of limited dimensions. A x i a l traces transect Phase 1 traces at 60-70° r e f l e c t i n g a divergence i n trends between the two phases (Plate III) which probably con-tributes to the southward developing curvature of t h i s segment of the Arc. 57 FAULTING Major f a u l t s developed within and adjacent to the so-ca l l e d "Mine Belt" or "Thrust Belt" south of Salmo are shown i n Figure 13 (after L i t t l e , 1960; Frebold and L i t t l e , 1962; Yates, 1970). The f a u l t i n g includes tectonic s l i d e s (not shown i n the Figure) and thrust f a u l t s cut by a vari e t y of transverse f a u l t s . Tectonic s l i d i n g , a l b e i t on a limited scale, has con-tributed s i g n i f i c a n t l y to the development of the complex Salmo River a n t i c l i n e . The main locus of s l i d i n g has been along the Trueman member located between the Reeves marble member and the underlying thick q u a r t z i t i c sequences, r e s u l t i n g i n varied and l o c a l l y d r a s t i c attenuation of that member and bringing Reeves marble into contact with the q u a r t z i t i c rocks (Plates I I I , VI, VIII). From t h e i r d i s t r i b u t i o n i n r e l a t i o n to the major f o l d structures, s l i d e movements are presumed to have been concurrent with Phase 1 folding perhaps also being reactivated by f l a t t e n i n g during Phase 2. The thrust f a u l t s , i n contrast, are discrete s t r u c t u r a l breaks which cut across the stra t i g r a p h i c section and juxtapose widely disparate units. They are represented by the Waneta, A r g i l l i t e , Black Blu f f and other lesser f a u l t s which dip steeply eastward to southward (Fig. 13). The Waneta f a u l t marks the str u c t u r a l contact between Lower Palaeozoic and Mesozoic rocks along the western margin of the "Thrust Belt" whereas the Black Bluf f f a u l t marks the eastern l i m i t of the b e l t . This l a t t e r f a u l t was considered by Ross (1970) to be the southern expression of a major sole thrust separating westerly verging parautochthonous 5 8 Figure 13. Main f a u l t and f o l d patterns i n the southern Kootenay Arc (after L i t t l e , 1960; Frebold and L i t t l e , 1962; Yates, 1970). rocks from easterly verging allochthonous rocks. However within t h i s area no difference i n vergence was recognized across t h i s f a u l t . The A r g i l l i t e f a u l t l i e s between these f a u l t s i n the north but merges southwestwards with, and apparently supercedes the Black Blu f f f a u l t . I t everywhere separates Lower Cambrian rocks from the Ordovician Active Formation to the east and may represent a pre-folding de'collement thrust since the Active Formation i s everywhere apparently i n f a u l t contact with other units. The age of thrust f a u l t i n g i s problematic. Fyles and Hewlett (1959) believe i t to have been i n i t i a t e d during the f i r s t phase of folding and that movement continued during the second phase of folding. They also consider thrusting to have been directed e s s e n t i a l l y westwards. Certainly the north-trending thrust segment, as i l l u s -trated by the A r g i l l i t e f a u l t i n H. B. mine area, has been refolded by, and hence predates Phase 3 event. The southwest to west-southwest trending segment extends into the Metaline-C o l v i l l e quadrangles of northeast Washington where thrusting i s directed e s s e n t i a l l y northward and i s associated with large scale east-west kink folding (Yates, 1970). S i m i l a r l y i n the Reeves MacDonald area, thrusting appears to be related to kink folding, e s p e c i a l l y since p r i n c i p a l stress directions derived from assumed conjugate Phase 3 sets i s compatible with northward-directed movement. 60 Thus thrusting may be of two d i s t i n c t ages comprising (a) pre-Phase 3 (Phase 21) westward-directed movements, and (b) Phase 3 northward-directed movements. Transverse f a u l t s include a va r i e t y of northeast- to northwest-trending f a u l t s which cut across folds and thrusts a l i k e . Some of these may be s t r i k e - s l i p f a u l t s but there i s c o n f l i c t i n g opinion with respect to t h i s . In the Salmo map area, Walker (1934) and Frebold and L i t t l e (1962) have described r i g h t - l a t e r a l s t r i k e - s l i p movements along northwest to west-northwest-trending f a u l t s , such as the Ripple Creek f a u l t cutting the southern end of the Sheep Creek a n t i c l i n e and the Mt. E r i e f a u l t s west of Salmo v i l l a g e . A con-jugate northeast-trending set i s developed but only weakly so. Fyles and Hewlett (1959), however, found no evidence for s t r i k e -s l i p movement on the Ripple Creek f a u l t . A contrasting sense of movement along early, s i m i l a r l y oriented system of s t r i k e - s l i p f a u l t s i n the Sheep Creek area i s described by Mathews (1953). There, l e f t - l a t e r a l s l i p occurs along northwest-trending fractures and r i g h t - l a t e r a l along northeast-trending fractures, with the l a t t e r being the dominant set. No evidence for s t r i k e - s l i p movements was found within the mine areas; north-northwest s t r i k i n g f a u l t s i n the Reeves MacDonald area are either normal d i p - s l i p or s l i g h t l y oblique-s l i p f a u l t s . A group of north to north-northeast s t r i k i n g , normal (?) f a u l t s i s also recognized which appear to both pre- and post-date g r a n i t i c i n trusion both i n the Salmo d i s t r i c t (Fyles and Hewlett, 1959) and i n the M e t a l i n e - C o l v i l l e quadrangles (Yates, 1970). Some are occupied by sheared lamprophyre dykes suggesting that movements continued at least u n t i l the Eocene (see Section I I , p. 22). MINOR FRACTURES Joint orientations measured i n the course of mapping are i l l u s t r a t e d , v i a equal-area projections of poles to j o i n t sur-faces and v i a rose diagrams i n Figure 14. Cross j o i n t s are the dominant fractures i n a l l three areas and may comprise paired, c l o s e l y oriented sets. They are subvertical to v e r t i c a l and s t r i k e normal to the main s t r u c t u r a l trends. If the paired maxima (Fig. 14) are r e a l they may r e f l e c t d i f f e r e n t stress regimes associated with Phase 1 and Phase 2 fol d i n g . In many places, these fractures have opened to form quartz-carbonate-filled gash veins which i n Jersey mine area may be fringed by g r o s s u l a r i t e - a c t i n o l i t e skarn implying that opening of these fractures either preceded or accompanied intrusion of g r a n i t i c stocks i n the d i s t r i c t . It i s suggested that they were formed by s l i g h t extension accompanying i n t r u s i o n . A set of steep j o i n t s , s t r i k i n g north to north-northeast, i s also developed but i t i s not clear whether these represent true longitudinal j o i n t s with respect to Phase l : a n d 2 f o l d structures, or are related to the high-angle, north to north-northeast s t r i k i n g f a u l t s developed throughout the d i s t r i c t . Several other weakly developed j o i n t sets occur. These are generally moderately to steeply i n c l i n e d and s t r i k e either 62 F i g u r e 14. E q u a l - a r e a p r o j e c t i o n s o f p o l e s t o j o i n t s u r f a c e s , and r o s e diagrams o f j o i n t d i r e c t i o n s from t h e t h r e e mine a r e a s : (a) from H. B.; (b) from J e r s e y ; and (c) from Reeves MacDonald. I n s e t map ( a f t e r F y l e s and H e w l e t t , 1959) shows l o c a t i o n o f mine a r e a s i n r e l a -t i o n t o t h e h o s t Reeves member ( b l a c k ) and t o i n t r u s i v e s t o c k s . approximately northeast or northwest, oblique to Phase 1 and 2 f o l d trends. They are subparallel with Phase 3 trends and could represent conjugate shear j o i n t s related to the infe r r e d Phase 3 north-south compression. STRUCTURAL SYNTHESIS Phase 1 and Phase 2 a x i a l trends are near coaxial i n H. B. and Jersey mine areas but diverge more widely i n Reeves MacDonald area. Both phases also have westward vergence. There i s , however, no l o c a l evidence to determine whether they both r e s u l t from a single protracted period of deformation or whether they r e s u l t from two e s s e n t i a l l y d i s t i n c t deformation periods. Phase 1 folding was near i s o c l i n a l and was synmeta-morphic (lower greenschist facies) whereas Phase 2 fold i n g was more open and developed at submetamorphic temperatures. The e f f e c t of Phase 2 folding superimposed on e a r l i e r Phase 1 structures has been to produce refolding and i n some cases tightening up of Phase 1 folds r e s u l t i n g i n f l a t t e n i n g which has led to increased tectonic thinning of incompetent units, shearing of more competent units and ultimately thrusting. Phase 3 deformation i s non-penetrative and i s represented by kink folding (believed to be conjugate) and by weak s t r a i n -s l i p cleavage, both cutting at a high angle across e a r l i e r struc-t u r a l trends except toward the south i n Reeves MacDonald area. The geometry of t h i s phase i s interpreted as r e s u l t i n g from an approximately north-south compression, i . e . , the product of a d i f f e r e n t stress system than that which produced the two e a r l i e r phases. This Phase 3 event would appear to be the d i r e c t 64 equivalent of thrusting and kink folding about east-west axes described by Yates (1970) from M e t a l i n e - C o l v i l l e d i s t r i c t s . The ef f e c t of superimposition of Phase 3 has been to produce e f f e c -t i v e , i f li m i t e d , north-south shortening possibly related to northward-directed thrust f a u l t s developed near and south of the International Boundary. These north-south directed structures could be the r e s u l t of accommodation movements following east-west stacking of Phase 1 and Phase 2 folds. Some of the conju-gate s t r i k e - s l i p f a u l t s recognized by other workers i n Salmo d i s t r i c t may be related to these movements (Mathews, 1953; Frebold and L i t t l e , 1962). B r i t t l e - t y p e extension preceded and/or accompanied g r a n i t i c i ntrusion, dated at 100 m.y. age (see Section I I , p. 19), in the v i c i n i t y of the mines, producing c l o s e l y spaced east-west j o i n t i n g and gash veining. North to north-northeast normal f a u l t i n g and fracturing in part post-dates g r a n i t i c intrusion. Lamprophyre dyke i n t r u -sion dated at 49 m.y. (Yates and Engels, 1968; t h i s study: Section I I , p. 22) i s par t l y controlled by t h i s same fracture system. When a regional s t r u c t u r a l synthesis i s attempted (Table V) i t becomes clear that Phase 3, unlike Phases 1 and 2, cannot be correlated from north to south along the southern Kootenay Arc although there are general s i m i l a r i t i e s i n the character of deformation with open folds and s t r a i n - s l i p or f r a c -ture cleavage having been developed. Farther north, these folds tend to be coaxial with the two e a r l i e r phases and have been T a b l e V. S t r u c t u r a l c o r r e l a t i o n a l o n g t h e s o u t h e r n Kootenay A r c . METALINE (after Yates, 1970) SALMO KOOTENAY LAKE (after Crosby, 1968) SLOGAN (after Ross and K e l l e r h a l s , 1968) DUNCAN LAKE (after F y l e s , 1964) P H A S E Open to t i g h t f o l d s F i : A.P. cleavage dipping SE L i : 20-30 plunge SW Tigh t to i s o c l i n a l s i m i l a r f o l d s F i : A.P. cleavage to s c h i s t o s i t y L i : v a r i a b l e plunge I s o c l i n a l s i m i l a r f o l d s F i : A.P. cleavage to s c h i s t o s i t y L i : or low plunge N I s o c l i n a l , i n t r a -f o l i a l s i m i l a r folds F i : A.P. cleavage to s c h i s t o s i t y L i : v a r i a b l e low plunge I s o c l i n a l , attenuated s i m i l a r f o l d s F i : A.P. cleavage to s c h i s t o s i t y Lj : low plunge N P H A S E Open to cl o s e , asymmetric, f l a t -tened f l e x u r a l -s l i p f o l d s F 2 : c r e n u l a t i o n cleavage dipping steeply E L2: low plunge S-SSW Open to i s o c l i n a l , asymmetric, f l a t -tened f l e x u r a l -s l i p or s i m i l a r f o l d s F 2 : A.P. to crenu-l a t i o n cleavage L2: low plunge N or S Open, asymmetric folds F 2 : crenulation cleavage dips SW L 2 : low plunge S to SE Open to t i g h t , asym-metric f l e x u r a l - s l i p or s i m i l a r f o l d s F 2 : A.P. cleavage t o s c h i s t o s i t y , steep dip E or W L 2 : low .plunge N to NW P H A S E Major kink f o l d F 3 : A.P. dips steeply S L 3 : axis plunges v. steep N80W Conjugate mono-c l i n a l f o l d s , kink bands F 3 : s t r a i n - s l i p cleavage, sub-v e r t i c a l L 3 : steep plunges NE and SE Shallow to open f l e x u r a l f o l d s , kinks F 3 : weak fra c t u r e cleavage, steep dip N or S La: steep plunge W Flattened f l e x u r a l -s l i p f o l d s , kinks F 3 ' : s t r a i n - s l i p or f r a c t u r e c l e a -vage dips NE L3" : low plunge NW or SE Orthorhomic f o l d s F 3 * : conjugate shears dip NE and E L 3" : plunge ESE and S Asymmetric minor and chevron f o l d s F f i weak cleavage, steep dip N L ? : steep plunge W to NW Local intense de-formation marginal to g r a n i t i c i n t r u -sion V a r i a b l y oriented kinks and f r a c t u r e s , r e l a t e d to emplace-ment of Nelson b a t h o l i t h 66 considered as r e s u l t i n g from a single protracted deformation (Ross, 1970) . Whereas i n the south, Phase 3 structures tran-sect e a r l i e r structures except near the Canada-U.S.A. border where there i s the abrupt westward swing i n s t r i k e of the Arc. Yates (1970) has proposed that t h i s abrupt swing or bend i s produced by aggregate displacement of northward-directed thrusts and related tear f a u l t s . This bend i s , however, imposed on a less marked regional curvature which i s related to southward-developing divergence of Phase 1 away from Phase 2 s t r u c t u r a l trends, possibly accompanied by a reduction i n i n t e n s i t y of the l a t t e r . In the Salmo d i s t r i c t , both Phase 1 and Phase 2 struc-tures display westward vergence at the l e v e l s observed. Ross (1970) has suggested that such westerly verging Lower Palaeozoic rocks along the east side of the Kootenay Arc, represent a para-autochthonous cover displaced westward o f f the P u r c e l l Arch, possibly as a consequence of u p l i f t . Further, Phase 2 fold i n g i n these cover rocks developed as a r e s u l t of reaction with allochthonous nappe structures verging easterly towards the P u r c e l l Arch. Farther south, i n the v i c i n i t y of the International Boundary, Phase 1 folds trend more southwest, gradually become more open structures, and are less ( i f at a l l ) affected by Phase 2 folding, suggesting that there eastward crowding was less marked. Timing of the deformation i n the southern segment of the Arc i s problematic. Yates (1970), for example, believes 67 deformation i n M e t a l i n e - C o l v i l l e d i s t r i c t s , although perhaps i n i t i a t e d i n the T r i a s s i c , was a t a maximum producing the main f o l d i n g i n the l a t e J u r a s s i c and was completed b e f o r e 100 m.y. ago (mid-Cretaceous). In Salmo d i s t r i c t , a t l e a s t two s e t s of macroscopic f o l d s have been r e c o g n i z e d i n the J u r a s s i c Rossland group west of the mine areas ( L i t t l e , 1960; F r e b o l d and L i t t l e , 1962). They c o n s t i t u t e u p r i g h t , asymmetric f o l d s p l u n g i n g a t low angles south to southwest (equated by F r e b o l d and L i t t l e w i t h Phase 1 f o l d s i n the mine areas) which l o c a l l y are warped by n o r t h e a s t - t r e n d i n g asymmetric f o l d i n g overturned to the southeast ( F i g . 14). From t h e i r geometry, these f o l d s might more p l a u s i b l y be equated w i t h Phase 2 and Phase 3 s t r u c t u r e s developed i n the mine areas, but even t h i s c o r r e l a t i o n i s very u n c e r t a i n . However, i t i s suggested t h a t Phase 1 f o l d i n g a t l e a s t i s p r e - J u r a s s i c i n age. The chronology of deformation f a r t h e r n o r t h along the Arc i s a l s o a matter of some debate. Ross and K e l l e r h a l s (1968) and Ross (1970) have proposed t h a t the Slocan group of T r i a s s i c age i s a f f e c t e d o n l y by Phase 3 f o l d i n g and hence t h a t Phase 1 and Phase 2 f o l d i n g i s e n t i r e l y of P a l a e o z o i c age. Read (1966) and Wheeler (1970), however, b e l i e v e t h a t (i) Phase 1 f o l d i n g , although P a l a e o z o i c i n age, pre-dates the M i l f o r d group and i s t h e r e f o r e p r e - e a r l y M i s s i s s i p p i a n i n age, and a l s o t h a t ( i i ) Phase 2 f o l d i n g may have a f f e c t e d rocks of Mesozoic age. W h i l s t the meagre c h r o n o l o g i c a l evidence from Salmo d i s -t r i c t c o n t r i b u t e s l i t t l e t o t h i s debate, i t does a t l e a s t permit s t r u c t u r a l c o r r e l a t i o n s to be made wit h the more s o u t h e r l y segment of the Kootenay Arc i n Washington. SECTION IV METAMORPHIC ENVIRONMENT INTRODUCTION The metamorphic character of the Lower Palaeozoic rocks i n the Salmo d i s t r i c t has been b r i e f l y described by Fyles and Hewlett (1959) who distinguished a contact metamorphic event superimposed on low-grade regional metamorphism. In t h i s study, the l i m i t s of the contact aureoles i n the mine areas have been defined and outer/inner contact "zones" distinguished where possible. C h a r a c t e r i s t i c t e x t u r a l and minera-l o g i c a l features of the host rocks are described and thermal metamorphic features are separated from those of regional meta-morphism. The pressure-temperature conditions accompanying both metamorphic events have been estimated from experimentally determined mineral reactions and from X-ray d i f f r a c t i o n deter-minations of c a l c i t e compositions from coexisting c a l c i t e -dolomite assemblages. Such estimates applied to the lead-zinc sulphides at least allow a comparison to be made of t h e i r minera-l o g i c a l and textural responses to contact metamorphism (see Section V). A summary of the relevant stratigraphy, metamorphic rock types and t y p i c a l mineral constituents of the mine areas i s presented i n Table VI. 68 T a b l e V I . Metamorphic r o c k t y p e s and t y p i c a l m i n e r a l o g i e s o f t h e exposed s t r a t i g r a p h i c u n i t s i n t h e mine a r e a s : ( i ) o u t s i d e c o n t a c t a u r e o l e s , ( i i ) w i t h i n o u t e r c o n t a c t a u r e o l e s , and ( i i i ) w i t h i n i n n e r c o n t a c t a u r e o l e s . S t r a t i g r a p h i c U n i t OUTSIDE THE CONTACT AUREOLES ROCK TYPE and t y p i c a l m i n e r a l o g y WITHIN THE OUTER AUREOLES ROCK TYPE and t y p i c a l m i n e r a l o g y WITHIN THE INNER AUREOLES ROCK TYPE and t y p i c a l m i n e r a l o g y A C T I V E FORMATION S L A T E , P H Y L L I T E : g r a p h i t e -q u a r t z - a l b i t e - c a I c i t e -m u s c o v i t e LIMESTONE: g r a p h i t e - q u a r t z -m u s c o v i t e - c a l c i t e S L A T E , P H Y L L I T E : g r a p h i t e -t r e m o l i t e - a l b i t e - c a l c i t e -m u s c o v i t e MARBLE: g r a p h i t e - t r e m o l i t e -m u s c o v i t e - c a l c i t e (not d e t e r m i n e d ) UPPER L A I B MR. P H Y L L I T E : a l b i t e - q u a r t z -c h l o r i t e - m u s c o v i t e PHYLLONITE: q u a r t z and p e r t h i t e p o r p h y r o c l a s t s i n p h y l l i t e m a t r i x P H Y L L I T E : a l b i t e - c h l o r i t e -b i o t i t e - q u a r t z - m u s c o v i t e S C H I S T : p l a g i o c l a s e -c o r d i e r i t e - b i o t i t e -a n d a l u s i t e - q u a r t z - m u s c o v i t e EMERALD MR. P H Y L L I T E : g r a p h i t e - q u a r t z -a l b i t e - c l i n o z o i s i t e -c a l c i t e - m u s c o v i t e LIMESTONE: g r a p h i t e - q u a r t z -m u s c o v i t e - c a l c i t e P H Y L L I T E : g r a p h i t e -t r e m o l i t e - a l b i t e - c l i n o -z o i s i t e - c a l c i t e - m u s c o v i t e MARBLE: g r a p h i t e - t r e m o l i t e -m u s c o v i t e - c a l c i t e (not p r e s e n t ) REEVES MR. C A L C I T E MARBLE: q u a r t z -m u s c o v i t e - d o l o m i t e - c a l c i t e DOLOMITE MARBLE: q u a r t z -p h l o g o p i t e - c a l c i t e -d o l o m i t e C A L C I T E MARBLE: t r e m o l i t e -d o l o m i t e - c a l c i t e and q u a r t z - t r e m o l i t e - c a l c i t e DOLOMITE MARBLE: t r e m o l i t e -c a l c i t e - d o l o m i t e C A L C I T E MARBLE: d i o p s i d e -d o l o m i t e - c a l c i t e DOLOMITE MARBLE: f o r s t e r i t e c a l c i t e - d o l o m i t e TRUEMAN MR. C A L C I T E P H Y L L I T E : q u a r t z -m u s c o v i t e - c a l c i t e P H Y L L I T E , QUARTZ P H Y L L I T E : ( c h l o r i t o i d ) - c h l o r i t e -a l b i t e - q u a r t z - m u s c o v i t e C A L C - S I L I C A T E HORNFELS: p l a g i o c l a s e - a c t i n o l i t e -( d i o p s i d e ) - c a l c i t e - q u a r t z P H Y L L I T E , QUARTZ P H Y L L I T E : a l b i t e - c h l o r i t e - b i o t i t e -m u s c o v i t e - q u a r t z C A L C - S I L I C A T E HORNFELS: g r o s s u l a r i t e - i d o c r a s e -s c a p o l i t e - w o l l a s t o n i t e -d i o p s i d e - p l a g i o c l a s e , e t c . S C H I S T , QUARTZ SCHIST: a l b i t e - b i o t i t e - m u s c o v i t e -q u a r t z RENO FORMATION QUARTZ P H Y L L I T E : a l b i t e -c l i n o z o i s i t e - m u s c o v i t e -c h l o r i t e - q u a r t z Q U A R T Z I T E : c h l o r i t e -m u s c o v i t e - q u a r t z QUARTZ P H Y L L I T E : a l b i t e -c h l o r i t e - b i o t i t e - m u s c o v i t e -q u a r t z QUARTZITE: m u s c o v i t e -b i o t i t e - q u a r t z QUARTZ SCHIST: p l a g i o c l a s e - c o r d i e r i t e -b i o t i t e - a n d a l u s i t e -m u s c o v i t e - q u a r t z QUARTZITE: m u s c o v i t e -b i o t i t e - q u a r t z CTl P H Y L L I T E , QUARTZ P H Y L L I T E : ( c h l o r i t o i d ) - a l b i t e -QUARTZITE RANGE F N . c h l o r i t e - m u s c o v i t e - q u a r t z Q U A R T Z I T E : c h l o r i t e -m u s c o v i t e - q u a r t z P H Y L L I T E , QUARTZ P H Y L L I T E : a l b i t e - c h l o r i t e - b i o t i t e -m u s c o v i t e - q u a r t z Q U A R T Z I T E : m u s c o v i t e -b i o t i t e - q u a r t z SCHIST, QUARTZ S C H I S T : p l a g i o c l a s e - c o r d i e r i t e -b i o t i t e - a n d a l u s i t e - q u a r t z QUARTZITE: m u s c o v i t e -b i o t i t e - q u a r t z 70 REGIONAL METAMORPHISM Textural features of the regionally metamorphosed host rocks Chlor i t e and/or white mica (mainly muscovite (2M), or phlogopite (2M) i n dolomite marble) are aligned p a r a l l e l with both Fo and Fi surfaces i n a l l rock types. In p h y l l i t e s , the muscovite i s commonly bent around L2 crenulations where i t l o c a l l y exhibits subgrain development. It also occurs l o c a l l y as random flakes and as sparse developments along F2 cleavage planes; the l a t t e r possibly as mimetic alignments. C h l o r i t o i d , abundant i n some c h l o r i t i c p h y l l i t e s as elongate metacrysts, displays a marked preferred orientation p a r a l l e l with F i surfaces. Quartz i s generally strained. In dolomite and c a l c i t e marbles, quartz p h y l l i t e s and phyllonites, i t i s intensely so and larger grains display d i s t i n c t dimensional preferred orienta-t i o n , strongly undulose extinction, subgrain development and serrate grain boundaries. These larger grains occur commonly as flattened augen or lenses l o c a l l y i n a matrix of polygonal-shaped, s t r a i n - f r e e quartz of f i n e grain size (15-30 vim) . Such fine-grained polygonal textures are t y p i c a l of quartz occurring in the various fine-grained p h y l l i t e s . In quartzites, the quartz exhibits only s l i g h t dimensional preferred orientation, weak s t r a i n extinction and t y p i c a l l y granoblastic textures. However, crystallographic preferred orientation i s strongly developed, as shown by stereographic plots of d-axes orientations (Fig. 46a,b). In places, sub-basal deformation lamellae are intensely developed (Fig. 47). 71 The carbonates, c a l c i t e and dolomite, form r e c r y s t a l -l i z e d equigranular aggregates within which the Fi f o l i a t i o n i s outlined by graphitic partings and aligned white mica. Dolomite exhibits fine-grained (30-80 urn) granoblastic textures and c a l c i t e f i n e - to medium-grained (less than 300 urn) subgrano-b l a s t i c textures. Mineral assemblages, metamorphic f a c i e s , and timing of the regional metamorphic event Mineral assemblages from p e l i t i c rocks, i n parts of Reeves MacDonald and H. B. mine areas which have not been modi-f i e d by contact metamorphism, indicate that regional metamorphism was Barrovian i n type and r e s t r i c t e d to lower greenschist f a c i e s . These assemblages include: chloritoid-chlorite-muscovite-quartz albite-epidote-chlorite-muscovite-quartz calcite-chlorite-muscovite-quartz The presence of c h l o r i t o i d , c h l o r i t e and a l b i t e together with epidote and the general absence of coeval b i o t i t e define the subfacies to be quartz-albite-muscovite-chlorite subfacies (Turner and Verhoogen, 1960, p. 534). Timing of t h i s metamorphism was apparently e s s e n t i a l l y synchronous with Phase 1 deformation, as evidenced by the pre-ferred orientation of p h y l l o s i l i c a t e s and c h l o r i t o i d . To what extent, i f any, metamorphism outlasted t h i s phase of deformation i s not clear as textures were subsequently affected by Phase 2 deformation which appears to have been a purely tectonic event, unaccompanied by mineralogical change. It i s true that i n places 72 white mica i s sparsely aligned p a r a l l e l with Phase 2 a x i a l plane cleavage but, l i k e b i o t i t e , i t i s probably of l a t e r mimetic o r i g i n ( i . e . , post-Phase 3). P-T conditions of regional metamorphism The occurrence of c h l o r i t o i d allows a lower P-T l i m i t to be estimated for the regional metamorphic event i n t h i s d i s t r i c t . Ganguly (1968) and Hoschek (1969) have investigated experimentally the s t a b i l i t y of c h l o r i t o i d and the l a t t e r has proposed the following reaction for i t s formation: c h l o r i t e + k a o l i n i t e (or pyrophyllite) = c h l o r i t o i d + quartz Based on equilibrium conditions for the synthesis of c h l o r i t o i d , t h i s would imply a temperature of formation of approximately 425°C between 4-6 kb t o t a l pressure. The general absence of b i o t i t e would also suggest that temperatures were not much i n excess of 400°C. The temperature of c r y s t a l l i z a t i o n of magnesian c a l c i t e , from calcite-dolomite assemblages, was also determined by X-ray d i f f r a c t i o n using the method of Graf and Goldsmith (1955, 1958) .(see Appendix A). Samples, from the Reeves member at the Reeves MacDonald mine, contained a l i t t l e over 3 mole % MgCC>3, corres-ponding to a temperature of c r y s t a l l i z a t i o n of 450°C ± 25°. This provides only a minimum temperature since l a t e r annealing may have caused exsolution. Goldsmith and Newton (1969) have shown that the e f f e c t of t o t a l pressure on the s o l u b i l i t y of MgCC>3 i n the c a l c i t e structure i s s l i g h t , amounting to only 0.12 mole % per kb (measured i n the range 500-800°C). Although these samples are from outside the l i m i t of the contact aureole, as indicated by 73 the absence of random b i o t i t e , i t i s not possible to be ce r t a i n that the indicated temperature of c r y s t a l l i z a t i o n i s that of regional metamorphism unaffected by l a t e r contact metamorphism, temperature estimates for the two events being very si m i l a r (cf. p. 82). CONTACT METAMORPHISM Textural features of the contact metamorphosed host rocks  Ch l o r i t e , occurring with b i o t i t e i n outer aureoles, i s generally absent from inner aureoles except where i t i s re t r o -gressive, and hence mimetic, aft e r b i o t i t e . The Fi f o l i a t i o n i s therefore i l l u s t r a t e d mainly by white mica and mimetic b i o t i t e . Both of the l a t t e r also occur as random flakes and mimetic a l i g n -ments p a r a l l e l with Fz cleavage. In addition, b i o t i t e forms random p o i k i l o b l a s t s and clust e r s nucleated around magnetite grains. Other post-tectonic porphyroblasts and p o i k i l o b l a s t s are formed by andalusite and c o r d i e r i t e respectively. Quartz, where present, i s generally less intensely strained than outside the contact aureole. In marbles and c a l c i t e p h y l l i t e s , quartz has reacted to form various c a l c - s i l i c a t e s . In both schists and quartz s c h i s t s , the quartz i s t y p i c a l l y s t r a i n - f r e e and has well-developed polygonal-shaped grain boundaries. In quartzites, textures vary from granoblastic to interlocking; the l a t t e r apparently being achieved by sel e c t i v e grain growth. Strain extinction i s generally weak but l o c a l l y may be intense and associated with sub-basal deformation lamellae. 74 Dimensional preferred orientation i s lacking but c r y s t a l l o -graphic preferred orientation p e r s i s t s as i l l u s t r a t e d by c-axes orientations (Fig. 46e-g). Dolomite has a c h a r a c t e r i s t i c medium-grained (80-250 urn) granoblastic to polygonal texture. In contrast, c a l c i t e exhibits wide v a r i a t i o n i n grain size from medium to coarse (0.2-5.0 mm), t y p i c a l l y allotriomorphic textures and r e l a t i v e l y intense twinning development. The c a l c - s i l i c a t e s — t r e m o l i t e , diopside and f o r s t e r i t e — occur as sparse, randomly oriented laths and i d i o b l a s t s within massive dolomite and c a l c i t e marbles. In layered c a l c - s i l i c a t e hornfels, g r o s s u l a r i t e - r i c h layers and/or a c t i n o l i t e - and diopside-rich layers alternate with q u a r t z - c a l c i t e - z o i s i t e s c h i s t and b i o t i t e s c h i s t layers. Associated c a l c - s i l i c a t e minerals include idocrase, scapolite and wollastonite. Closely spaced fractures f i l l e d with quartz-calcite cut through these c a l c -s i l i c a t e assemblages, e s p e c i a l l y the more competent gr o s s u l a r i t e layers. Nature and d i s t r i b u t i o n of the contact aureoles The d i s t r i b u t i o n of g r a n i t i c stocks within and around the mine areas i s shown i n Figure 2, from which i t i s obvious that of the contact metamorphic e f f e c t s described, only those i n Jersey mine area show a close s p a t i a l r e l a t i o n s h i p to exposed intrusions. The outermost l i m i t of contact metamorphism that could be detected mineralogically was taken at the f i r s t appearance 75 of b i o t i t e i n p e l i t i c rocks and of a c t i n o l i t e / t r e m o l i t e i n carbonate rocks. An inner contact aureole was defined by the presence of c o r d i e r i t e i n p e l i t i c rocks and of f o r s t e r i t e + c a l c i t e , or of diopside or g r o s s u l a r i t e i n carbonate rocks. Higher metamorphic grade may be attained l o c a l l y , close to i n t r u s i v e contacts, as evidenced by the presence of f i b r o -l i t e and andalusite. Such occurrences are rare and no additional contact zone was defined. Reeves MacDonald mine area. Figure 15 i l l u s t r a t e s the occurrence of post-tectonic b i o t i t e i n p e l i t i c rocks and of occasional a c t i n o l i t e i n carbonate rocks i n Reeves MacDonald mine area. Andalusite i s not developed. The sporadic d i s t r i b u -t i o n of these indicator minerals outlines an outer contact aureole, limited to the northern overturned limb of the Salmo River a n t i c l i n e . Contact metamorphic e f f e c t s f a l l o f f southward, disappearing near the a x i a l trace of the a n t i c l i n e , approximately 1000 f t north of the outcrop of the Reeves MacDonald ore zone. This f a l l - o f f i n contact e f f e c t s may i n part be due to topography since there i s a 1200 f t increase i n elevation southward from the Salmo River to the a x i a l trace. The nearest exposed i n t r u -sive body i s located 8000 f t north of the Salmo River a n t i c l i n e . Conceivably, closer subsurface intrusions, other than dykes, may ex i s t but none has been encountered i n underground workings. Gran i t i c xenoliths have, however, been found i n lamprophyre dykes. H. B. mine area. Figure 16 shows the d i s t r i b u t i o n of contact metamorphic m i n e r a l s — b i o t i t e i n p e l i t i c rocks and 7 6 F i g u r e 15. C o n t a c t metamorphic e f f e c t s i n Reeves MacDonald mine a r e a . Shown a r e o c c u r r e n c e s o f ( i ) p o s t - t e c t o n i c b i o t i t e i n p e l i t i c and s e m i - p e l i t i c r o c k s , and ( i i ) a c t i n o l i t e s k a r n . 77 tremolite, a c t i n o l i t e and dippside i n carbonate and c a l c -s i l i c a t e rocks—which indicate the existence of a contact aureole i n H. B. mine area. The occurrences, e s p e c i a l l y of diopside, are concentrated on the lower north and south slopes of Sheep Creek, suggesting an increase i n i n t e n s i t y of the metamorphic aureole with depth. As a r e s u l t of the absence of c o r d i e r i t e from p e l i t i c rocks and the sporadic d i s t r i b u t i o n of diopside a d i s t i n c t inner aureole could not be defined. The l o c a l i z e d occurrences of diopside skarn and diopside-bearing hornfels are attributed to the l o c a l i n f l u x of magmatic water causing reductions i n CO2 pressures. The aureole i s developed i n the core and on the upper limb of the complex, major a n t i c l i n e which dominates the struc-ture at H. B. mine. The ore zones l i e at least within the outer contact aureole as tremolite i s commonly developed i n the dolomite-sulphide assemblages of the Garnet Zone and t a l c i s reported (Warning, 1960) as abundant i n the H. B. ore zones. Possible i n t r u s i v e sources for thermal metamorphism are s p a t i a l l y f ar removed; the Dodger and Annie Rooney Creek g r a n i t i c stocks l i e 1.25 miles to the south and the Nevada Mountain g r a n i t i c i n trusion l i e s approximately the same distance to the east (Fig. 2). Jersey mine area. Figure 17 i l l u s t r a t e s outer and inner aureoles distinguished i n Jersey mine area which i n t h i s case are developed "peripheral" to exposed intrusions. The pattern, however, i s much complicated by l i t h o l o g i c a l v a r i a t i o n and by 78 © b i o t i t e A d i o p s i d e i n h o r n f e l s Q a c t i n o l i t e w«& d i o p s i d e s k a r n 0 t r e m o l i t e Geology as i n P l a t e V I I I F i g u r e 16. C o n t a c t metamorphic e f f e c t s i n H. B. mine a r e a . Shown a r e o c c u r r e n c e s o f ( i ) p o s t - t e c t o n i c b i o t i t e i n p e l i t i c and s e m i - p e l i t i c r o c k s , ( i i ) a c t i n o l i t e and t r e m o l i t e i n c a r -bonate r o c k s , and ( i i i ) d i o p s i d e i n c a l c - s i l i c a t e h o r n f e l s and i n s k a r n . 79 OUTER AUREOLE €> b i o t i t e O a c t i n o l i t e 0 t r e m o l i t e INNER AUREOLE c o r d i e r i t e i n p e l i t e s ; d i o p s i d e , f o r s t e r i t e and g r o s s u l a r i t e i n c a r b o n a t e Geology as i n P l a t e V I F i g u r e 17. C o n t a c t metamorphic e f f e c t s i n J e r s e y mine a r e a . Shown a r e ( i ) a d i f f u s e o u t e r a u r e o l e d e f i n e d by o c c u r r e n c e s o f p o s t - t e c t o n i c b i o t i t e i n p e l i t i c and s e m i - p e l i t i c r o c k s , and o f a c t i n o l i t e and t r e m o l i t e i n c a r b o n a t e r o c k s ; ( i i ) an i n n e r c o n -t a c t a u r e o l e d e f i n e d by o c c u r r e n c e s of c o r d i e r i t e i n p e l i t i c and s e m i - p e l i t i c r o c k s , and o f d i o p s i d e , f o r s t e r i t e and g r o s s u l a r i t e i n c a r b o n a t e r o c k s . 80 disruption due to l a t e r f a u l t i n g . Nor are the Emerald'and Dodger stocks simple, steep-sided plugs. They have considerable sub-surface extensions (moderately well known from mining a c t i v i t i e s ) so the subsurface configuration of the contact metamorphic aureoles departs considerably from that observed at the surface. The lead-zinc sulphide ore zones l i e mainly within the inner contact aureole and are themselves l o c a l l y cut by g r a n i t i c off-shoots. Assemblages of the contact aureoles Equilibrium mineral assemblages established for p e l i t i c and carbonate l i t h o l o g i e s i n the contact aureoles of the three areas are summarized below: Outer Aureole P e l i t i c rocks: Carbonate rocks: P e l i t i c rocks: Carbonate rocks quartz-muscovite-chlorite-b i o t i t e - a l b i t e c a lcite-dolomite-talc calcite-dolomite-tremolite c a l c i t e - a c t i n o l i t e - p l a g i o c l a s e -quartz quartz-muscovite-biotite-cordierite(-andalusite) d o l o m i t e - c a l c i t e - f o r s t e r i t e calcite-dolomite-diopside grossularite-diopside-w o l l a s t o n i t e - c a l c i t e grossularite-diopside-plagioclase grossularite-idocrase-diopside-scapolite g r o s s u l a r i t e - z o i s i t e - q u a r t z diopside-quartz-calcite Absence of c h l o r i t e (except for retrogressive material) and presence of c o r d i e r i t e with or without andalusite i n p e l i t i c rocks, plus the various assemblages from c a l c - s i l i c a t e and Inner Aureole C a l c - s i l i c a t e hornfels and skarn: 81 carbonate rocks define the metamorphic facies of the inner contact aureole as hornblende-hornfels facies (Turner, 1968, p. 193). Mineral assemblages from the outer zone of the contact aureole, i n p a r t i c u l a r the association of c h l o r i t e and b i o t i t e i n p e l i t i c rocks and the occurrence of t a l c or more commonly tremolite with dolomite and c a l c i t e i n carbonate rocks, define the metamorphic facies there as corresponding to albite-epidote-hornfels (Turner, 1968, p. 190). P-T conditions of contact metamorphism The p r e v a i l i n g l i t h o s t a t i c pressure at the time of i n t r u -sion (Lower Cretaceous) has been estimated at 2 kb ± 500 bars by Greenwood (1967) from an area 1.5 miles east-southeast of H. B. mine. This estimate was based on stratigraphic work of L i t t l e (1950). In the l i g h t of stratigraphic revisions by Fyles and Hewlett (1959) and L i t t l e (1960), a s l i g h t l y more conservative estimate of 1.5 kb, corresponding to 20,000 f t of overlying rock, i s proposed. Assuming f l u i d pressure was equal to t o t a l pressure, estimates of the range of temperatures e x i s t i n g during contact metamorphism can be arrived at by considering the experimentally determined s t a b i l i t y r e l a t i o n s of certa i n minerals from the assemblages characterizing the contact aureoles established i n both p e l i t i c and carbonate rocks. The lowermost temperature l i m i t s are d i f f i c u l t to deter-mine as the reactions which produce b i o t i t e and tremolite are 82 poorly defined experimentally. These minerals probably formed according to the reactions (Winkler, 1967, p. 25, 99): muscovite + prochlorite = b i o t i t e + A l - c h l o r i t e + quartz + H2O dolomite + quartz + H2O = tremolite + c a l c i t e + C 0 2 Equilibrium data, calculated by Skippen (1971), indicate that tremolite would form either d i r e c t l y according to the above reaction, or i n d i r e c t l y from t a l c + c a l c i t e at temperatures i n the range 415-500°C for p a r t i a l pressures of CO2 greater than 0.2 at a t o t a l f l u i d pressure of 2 kb. This i s i n f a i r agree-ment with estimates for the lower temperature l i m i t of a l b i t e -epidote hornfels facies of metamorphism at the outer edge of contact aureole which i s generally taken to be at approximately 400°C at 1.5 kb (Winkler, 1967, p. 70; Turner, 1968, p. 256). Talc reported i n the H. B. ore zones presumably formed according to the reaction (Winkler, 1967, p. 23): dolomite + quartz + H 20 = t a l c + c a l c i t e + CO2 Its l o c a l i z e d and concentrated occurrence i s attributed to i n t r o -duction (via fractures?) of water and s i l i c a to dolomite marble; according to Winkler (1967, p. 25) high H20:C02 r a t i o s would favour the formation of t a l c over tremolite. This i s confirmed by the experimental data of Skippen (1971) which gives e q u i l i b -rium temperatures for the above reaction of 400-460°C for p a r t i a l pressures of CO2 between 0.2-0.5 at a t o t a l f l u i d pres-sure of 2 kb. At higher p a r t i a l pressures of CO2 tremolite forms in place of t a l c . Elsewhere, even at H. B. mine, tremolite i s the more common hydrous s i l i c a t e presumably because X-,„. values were higher, although Gordon and Greenwood (1970) have suggested 83 t h a t p h l o g o p i t e (a common minor c o n s t i t u e n t o f the dolomite marble) forms i n p l a c e of t a l c where potassium and aluminum are a v a i l a b l e , as i n muscovite, thus a l l o w i n g the d i r e c t f o r m a t i o n of t r e m o l i t e over a wider range of C O 2 p a r t i a l p r e s s u r e s . The temperatures developed w i t h i n the i n n e r c o n t a c t a u r e o l e i n J e r s e y mine area, which i s marked by the presence of c o r d i e r i t e i n p e l i t i c rocks and of f o r s t e r i t e and d i o p s i d e i n c a l c a r e o u s r o c k s , can o n l y be approximately c a l i b r a t e d s i n c e the r e a c t i o n s have e i t h e r been o n l y p a r t l y i n v e s t i g a t e d experimen-t a l l y , or they are d i v a r i a n t . C o r d i e r i t e , which a p p a r e n t l y develops s i m u l t a n e o u s l y w i t h a n d a l u s i t e , p o s s i b l y forms a c c o r d i n g t o the r e a c t i o n (Winkler, 1967, p. 71): c h l o r i t e + muscovite + q u a r t z = c o r d i e r i t e + b i o t i t e + a n d a l u s i t e + H 20 In quartz-, muscovite-bearing p e l i t i c rocks such as these, i t probably becomes s t a b l e a t temperatures near 500°C f o r p r e s s u r e s between 1 and 2 kb (Hirschberg and Winkler, 1968; S e i f e r t and Schreyer, 1970). 84 The experimentally determined, divariant reactions for the appearance of the relevant c a l c - s i l i c a t e minerals are: (a) tremolite + c a l c i t e + quartz = diopside + CO2 + H2O for which equilibrium temperatures have been determined i n the range T = 510-540°C for X >0.2 at P f = 1 kb (Metz and C U 2 ' r Winkler, 1964) and T = 475-540°C for X^ _ >0.2 at P, = 2 kb (Skippen, 1971) L U 2 t (b) tremolite + dolomite = f o r s t e r i t e + c a l c i t e + CO2 + H2O for which equilibrium temperatures have been determined i n the range T = 510-560°C for X0_ >0.2 at P- = 1 kb (Metz, 1967) CO 2 t and T = 535-580°C for X_,~ >0.2 at P. = 2 kb (Skippen, 1971) The d i f f e r e n t determinations are i n reasonable agreement for reaction (b) but not for reaction (a) which i s generally taken as marking the beginning of the hornblende hornfels facies of contact metamorphism. The data of Skippen (1971) suggest lower temperatures for t h i s reaction (a) which are more cl o s e l y i n agreement with the estimate of Turner (1968, p. 258) for the beginning of hornblende hornfels f a c i e s . Grossularite, occurring l o c a l l y within the inner contact aureole, provides some additional information as to pressure-temperature conditions. Its s t a b i l i t y f i e l d i n H2O-CO2 mixtures i s shown i n Figure 18 (Gordon and Greenwood, 1971) which i n -dicates that i t s formation i s favoured by water-rich f l u i d s . Within layered c a l c - s i l i c a t e hornfels of the Trueman member, 85 gros s u l a r i t e probably formed according to the reactions: z o i s i t e + c a l c i t e + quartz = grossularite = CO2 + H2O c a l c i t e + anorthite + quartz = grossularite + CO2 for which equilibrium temperatures are i n the range T = c.500-590°C for X c o <0.15 at P f = 2 kb (Gordon and 2 Greenwood, 1971) However i t s occurrence i n massive skarn suggests a metasomatic o r i g i n (discussed below). Local occurrence of f i b r o l i t e with andalusite i n p e l i t i c rocks close to int r u s i v e contacts permits an estimate to be made of the highest temperatures attained during contact metamorphism. Holdaway (1971) has shown that f i b r o l i t e , due to i t s high sur-face energy, i s more l i k e l y to have formed from muscovite than from andalusite. If so, then the experimentally defined break-down of muscovite (Althaus et al., 1970) to aluminum s i l i c a t e according to the reaction: muscovite + quartz = Al 2SiOs + orthoclase which occurs at T = 600°C for P„ _ = 1.5 kb (Fig. 20) n 2 vJ can be used to c a l i b r a t e the upper temperature l i m i t . A country rock temperature immediately adjacent to the g r a n i t i c intrusions can also be arrived at, using Jaeger's (1957) ide a l model of a dyke-like in t r u s i v e mass losing heat mainly by conduction. Assuming an intr u s i v e temperature of 700°C, a load pressure of 1.5 kb and a geothermal gradient of 30°C/km gives an approximate contact temperature of 600°C. It should be emphasized that because of the assumptions involved t h i s 86 represents a very approximate estimate. Thus i t w i l l be shown below that there was probably considerable flow of H2O accom-panying intrusion so that heat transfer was also, i n part, by convection. As a check on these estimates, the temperature of c r y s t a l l i z a t i o n of magnesian c a l c i t e , from calcite-dolomite assemblages, was determined by X-ray d i f f r a c t i o n , using the method of Graf and Goldsmith (1955, 1958). Samples from the Reeves member at Jersey mine, co l l e c t e d close to or within the inner contact aureole, contained approximately 4 mole % MgCG-3, corresponding to a temperature of formation of 490°C ± 25 (see Appendix A). F l u i d phase during contact metamorphism Local abundance of gross u l a r i t e as skarn, mainly within c a l c - s i l i c a t e hornfels but also as r e s t r i c t e d occurrences within carbonate marble, i n the inner contact aureole at Jersey mine suggests that metasomatism played an important role i n i t s formation. Its occurrence and d i s t r i b u t i o n are apparently con-t r o l l e d by l i t h o l o g i c a l boundaries and fractures. The grossu-l a r i t e tends to be concentrated i n zones p a r a l l e l with composition layering near the top of the Trueman member along i t s gradational contact with the Reeves marble. Locally within the marble i t may form fringes and masses adjacent to fractures (Fig. 19). Such locations are assumed to have been subject to high H 20 p a r t i a l pressures which would favour the formation of grossu-r l a r i t e ; aqueous f l u i d s expelled from the c r y s t a l l i z i n g granite intrusions moving through the layered c a l c - s i l i c a t e Trueman 87 800-1. Zo + Ca + Q = Gr + C 0 2 + H 20 2. Ca + An + Q = Gr + C 0 2 3. Ca + An + Wo = = Gr + C 0 2 4. Ca + Q = Wo + C0 2 5. Zo + C0 2 = Ca + An + H 20 C0 2 F i g u r e 18. S t a b i l i t y f i e l d s o f g r o s s u l a r i t e and w o l l a s t o n i t e i n H 20-C0 2 m i x t u r e s a t 2 kb (from Gordon and Greenwood, 1971) , \ *.S • • • | • •GROSSU/LARITI '. 0-1 15 cm F i g u r e 19. Mode o f o c c u r r e n c e o f g r o s s u l a r i t e s k a r n w i t h i n c a l c i t e m a r b l e o f t h e Reeves member. 88 member and only a f f e c t i n g the overlying Reeves marble i n the v i c i n i t y of fractures. The l a t t e r with i t s presumably higher CO2 p a r t i a l pressures developed diopside and f o r s t e r i t e as the main c a l c - s i l i c a t e minerals. Idocrase and scapolite are commonly associated with grossularite and together they suggest that S i , A l and C l (at least) were also introduced i n the aqueous f l u i d s to contribute to skarn formation. SUMMARY Regional metamorphism i n the three mine areas was re-s t r i c t e d to lower greenschist facies and was apparently syn-chronous with Phase 1 fold i n g . Temperatures accompanying Phase 2 and Phase 3 folding were, i n contrast, submetamorphic. Evidence for post-tectonic overprinting by contact meta-morphism has been found i n a l l three mine areas: i n Reeves MacDonald and H. B. mine areas, d i f f u s e outer aureoles (remote from any intru s i v e source) occur i n which albite-epidote hornfels facies was not generally exceeded, whereas i n Jersey mine area, hornblende hornfels facies was attained within an inner contact aureole developed adjacent to small granite stocks. The various temperatures estimated for contact meta-morphism can be approximated (making allowances for some of the small pressure differences involved) and summarized as follows: Temperature range of outer aureole: 425 - 475°C - 25° Temperature range of inner aureole: 475 - c. 600°C It i s therefore possible to c a l i b r a t e the temperatures to which the lead-zinc sulphide deposits have been elevated, as i l l u s t r a t e d schematically i n Figure 20. 89 I • I i I . I i L_ 3 0 0 4 0 0 5 0 0 6 0 0 700 T°C Figure 20. Schematic representation of the range of contact metamorphic temperatures a f f e c t i n g the three sulphide deposits. Curve (a) indicates approximately the appearance of b i o t i t e (Turner, 1968), and curve (b) the appearance of c o r d i e r i t e (Hirschberg and Winkler, 1968). Curve (c) i s the equilibrium curve for the breakdown of muscovite, i n the presence of quartz, to aluminum s i l i c a t e and orthoclase (Althaus et al. , 1970), and (d) i s the melting curve for granite (Luth et al., 1964). SECTION V THE SULPHIDE DEPOSITS INTRODUCTION Although i t can be r e a d i l y demonstrated that the Salmo sulphide deposits pre-date g r a n i t i c i n t r usion i n the area, there i s controversy as to whether or not they have been involved i n regional metamorphism. Consequently several d i f f e r e n t i n t e r -pretations of t h e i r history have been proposed. Fyles and Hewlett (1959) considered the sulphides to be replacement bodies s t r u c t u r a l l y controlled by and only i n part deformed by Phase 2 fold i n g , i . e . post-metamorphic. In contrast, Muraro (1966) suggested that the sulphides pre-dated both folding and metamorphism and proposed, i n p a r t i c u l a r , that the Duncan Lake deposit (a Salmo type deposit 85 miles farther north) was o r i g i n a l l y of M i s s i s s i p p i Valley type (Muraro, 1962). Callahan (1964, 1967) c l a s s i f i e d the Salmo deposits as Appalachian type ( i . e . , deformed M i s s i s s i p p i Valley type) which were subsequently modified by g r a n i t i c i n t r u s i o n . A pre-regional metamorphic history for the ores has also been implied by Sangster (1970a, b) who proposed a syngenetic-diagenetic o r i g i n for the sulphides "by concentration i n deep-water carbonates, deposited i n a 'shale-starved' basin environ-ment . " 91 Lead isotope abundances from the Kootenay Arc have been determined by S i n c l a i r (1964, 1966), Reynolds and S i n c l a i r (1971) and more recently by LeCouteur (1973). Two isotope populations are recognized, one corresponding to the Salmo strata-bound deposits and the other to the Slocan and Ainsworth vein-type deposits and-rock-leads"from the Nelson ba t h o l i t h . These are a l l anomalous (multistage) leads but they l i e on separate anoma-lous lead l i n e s which indicates that t h e i r parent common leads d i f f e r e d i n composition. It was suggested by S i n c l a i r and by S i n c l a i r and Reynolds that t h e i r subsequent h i s t o r i e s were simi-l a r and that both were emplaced at approximately the same time, 150 m.y. ago ( i . e . , post-regional metamorphism). However, i t i s possible to interpret the "emplacement" of the strata-bound deposits as having occurred as f a r back as the Lower Palaeozoic (LeCouteur, 1973). NATURE AND FORM OF THE SULPHIDE ORE BODIES The three deposits appear to be b a s i c a l l y very s i m i l a r , the major differences i n form apparently being a function of t h e i r s t r u c t u r a l environment and the lesser differences, such as mineralogical and textural v a r i a t i o n , a function of t h e i r varied, subsequent thermal h i s t o r i e s . Their basic mineralogy i s simple, consisting of sphalerite-pyrite-galena. Pyrrhotite and minor chalcopyrite are rare additions possibly related to thermal metamorphism of the ores by lamprophyre dykes and g r a n i t i c intrusions. Gangue consists mainly of dolomite, with lesser c a l c i t e , minor quartz 92 (or various c a l c - s i l i c a t e s within contact metamorphic zones), white mica and graphitized carbonaceous material. The sulphides are present either as disseminations along the composition layering (Fo_i) or as more massive concentra-tions i n which sphalerite and/or galena form the matrix to brecciated or disrupted and folded fragments of p y r i t e and of dolomite and c a l c i t e marbles. These two types of sulphide occurrence w i l l be referred to as layered ore and breccia ore. Reeves MacDonald mine Previous descriptions of the geology of the Reeves MacDonald mine have been published by White (1949), Green (1954), Fyles and Hewlett (1959) and Addie (1970) . The ore body has the form of a steeply plunging, t i g h t syncline i n the core of the Reeves syncline which (as has been discussed i n Section III) i s interpreted as a Phase 1 f o l d . Oblique d i p - s l i p f a u l t s cut the ore body creating separate ore zones (Fig. 21) which display a progressive change i n orientation down plunge: Reeves ore zone Az. 215°/50° E. MacDonald ore zone Az. 235°/48° Annex ore zone Az. 252°/37° The main hinge of the ore body i s apparently much thickened and together with the hinges of p a r a s i t i c minor folds i s t y p i c a l l y serrate and could be interpreted either as a highly attenuated i s o c l i n e or as a l i t h o l o g i c a l contact (F 0) highly transposed along the Fi f o l i a t i o n . The overturned, northern limb of the body has the greater s t r i k e length of the two limbs 93 Figure 21. Diagrammatic east-west longitudinal section of Reeves MacDonald mine showing the ore zones: 1. No. 4; 2. O'Donnel; 3. B. L.; 4. Reeves; 5. East MacDonald; 6. West MacDonald; 7. Point; and 8. Annex (after Addie, 1970). Figure 22. Level plans of the Reeves ore zone i l l u s t r a t i n g the change' i n configuration down plunge. The two leve l s are shown i n t h e i r correct r e l a t i v e positions (from mine records). 94 and t h i s becomes emphasized down plunge as the normal limb and eventually the hinge zone i t s e l f disappear (Fig. 22). Sulphide mineralization i s concentrated near the upper contact of the dolomite marble host with t y p i c a l Reeves c a l c i t e marble. The lower l i m i t i s marked by a well-defined, footwall p y r i t e layer whereas the upper l i m i t , which i s much less d i s t i n c t , approximates the interface between dolomite and c a l c i t e marbles. Sulphides occur either as disseminations p a r a l l e l with composition layering creating a "gneissic" layering or, i n higher concentrations, as the matrix to variable breccias, con-taining rounded to markedly platy fragments of dolomite and c a l c i t e marble. In the "gneissic" layered ore, contacts between sulphides and marble are not sharply defined (Fig. 25a, b) due to the disseminated nature of the sulphides. However massive p y r i t e layers occur i n the footwall of the ore body and these are sharply inter-layered with graphitic layers and dolomite marble. These pyrite-graphite layers may also be t i g h t l y folded and more or less brecciated within intensely f o l i a t e d (Fi) dolomite marble (Fig. 27a). It i s suggested that t h i s well-defined layering represents o r i g i n a l bedding and that the f o l d i n g i s of Phase 1 age. Other mesoscopic folds are outlined by layered, disseminated ore but these have not been c l e a r l y i d e n t i f i e d as to age. Further complications r e s u l t from the presence of numerous detached folds within breccia ore, discussed below. Breccia ore appears to be i r r e g u l a r l y d i s t r i b u t e d and may pass gradationally ( v e r t i c a l l y or l a t e r a l l y ) either into layered ore or into f o l i a t e d or massive dolomite marble. The sulphide matrix may be predominantly either sphalerite or pyrite but not usually galena which i s present i n r e l a t i v e l y minor amounts. The breccia fragments, mostly dolomite marble but also c a l c i t e marble and quartz, may be (i) apparently randomly oriented, or ( i i ) aligned p a r a l l e l with the F i folia^.' t i o n , or ( i i i ) p a r t i c u l a r l y the platy fragments, they may be folded and l o c a l l y boudinaged (Fig. 26a, b, c, 27c). These folds display no systematic geometry and appear to r e s u l t from the deformation of detached, r e l a t i v e l y competent, platy frag-ments within a less competent, sulphide-rich matrix. These structures have been described by Addie (1970) as examples of thixotropic deformation but i t seems un l i k e l y that these would survive unmodified by the subsequent intense deformation which i s r e f l e c t e d i n the dolomite marble host (Fig. 25b). The variable nature of the breccia i s puzzling but appears to be related i n part to whether the host marbles were layered or massive. They very c l o s e l y resemble the "milled" or duvohbewegt ores commonly developed i n sulphide-schist assemblages during regional dyna-mothermal metamorphism (Vokes, 1968, 1969). In these, progres-sive deformation outlasts metamorphism so that fragments of schistose host rocks are t e c t o n i c a l l y incorporated into s t i l l d u c t i l e sulphide layers. Gash and i r r e g u l a r veining by coarse-grained "pegmatitic" sulphides and gangue occur i n both the layered and the breccia ores (Fig. 25c). These are strongly developed downplunge i n the major structure, p a r t i c u l a r l y i n the deepest ore zone—the Annex. They are t e n t a t i v e l y interpreted as representing l o c a l chemical remobilization, i n the sense envisaged by Mookherji (1970), i . e . , l o c a l l y derived and transported some short (but unknown) distance i n solution. They are apparently not deformed to any s i g n i f i c a n t degree and, by analogy with the Jersey mine area (Section I I I , p. 61), t h e i r association with gash-veins suggests a r e l a t i o n s h i p with g r a n i t i c i n trusion i n the area. Jersey mine The geology of Jersey mine has been described by Whishaw (1953), Rennie and Smith (1957), Fyles and Hewlett (1959) and Bradley (1970). The Jersey ore bodies consist of a series of elongate, tabular, folded masses plunging 10-15° southward and converging i n the same d i r e c t i o n . They comprise two, e s s e n t i a l l y separate, main zones subdivided (for mining purposes) into a series of p a r a l l e l subzones, A to J (Fig. 23). Each of these main zones occurs within a dolomite marble host. The more western of these, containing the A-B zones, i s located at the base of the Reeves member i n contact with the Trueman member whereas the eastern host, containing the C-J zones, i s located at a higher l e v e l within the Reeves member but converges downplunge with the lower host. Two d i s t i n c t styles of f o l d i n g , developed on a l l scales, modify the form of the ore bodies: (i) recumbent, t i g h t asymmetric folds (equated with Phase 1) and ( i i ) upright, more open symmetric or s l i g h t l y asymmetric folds (equated with Phase 2). Both were c l a s s i f i e d by Fyles and Hewlett (1959) as L E G E N D do dolomite marble cc calcite marble ph phyl l i te , schist, hornfe ls . lamprophyre dykes + + + granite stock t 200ft | r-4500' -4300 r4400' L4200" ! Fault •Phase 2 ax ia l t races • ^ - V - ^ P h a s e 1 ax ia l traces A - J M i n e zones • • Cross section locations M I N E P L A N ,<— 1000ft— 4500^1 4300-1 4400-1 V E R T I C A L S E C T I O N S F i g u r e 2 3 . P l a n v i e w a n d r e p r e s e n t a t i v e c r o s s - s e c t i o n s o f J e r s e y m i n e w o r k i n g s , s h o w i n g t h e m a i n s t r u c t u r a l f e a t u r e s ( f r o m m i n e r e c o r d s ) . 98 secondary (Phase 2) structures but, from t h e i r geometry, they are separable into d i s t i n c t generations (Fig. 27d, e, f ) . Macroscopic examples of the former are represented by the A-zone and F-zone folds ("skarn r o l l s " i n mine terminology) and of the l a t t e r by the D-zone a n t i c l i n e (Fig. 23). Both types of struc-tures are commonly complicated by low-angle thrusts with d i s -placements of up to several hundred feet. In addition, the tabular ore bodies i n t e r f i n g e r with the dolomite marble hosts so that they are generally complex i n detailed form. An int e r e s t i n g feature of the ore bodies i s that they tend to be much thicker along the macroscopic Phase 2 s y n c l i n a l troughs than on the adjacent Phase 2 a n t i c l i n a l crests (Fig. 23, cross-sections 1 and 2). This led Fyles and Hewlett (1959) and subse-quent mine geologists (e.g., Bradley, 1970) to postulate that emplacement of the ore was somehow s t r u c t u r a l l y controlled by Phase 2 fol d i n g . As i n Reeves MacDonald mine, the sulphides form both layered and breccia ores. The layered ores are the dominant type and, due to the darker colour of the sphalerite and the generally coarser grain size of the sulphides, the layering tends to be more d i s t i n c t than i n the Reeves MacDonald ores. The sulphide layers may be predominantly sphalerite and/or galena or p y r i t e , forming disseminations p a r a l l e l with composition layering ( F 0 _ i ) i n white or grey/white dolomite marble (Fig. 25d, e). Massive pyrite/graphite bands, sim i l a r to those occurring i n the footwall of Reeves MacDonald mine, have been 99 observed l o c a l l y but they are intensely brecciated and p a r t i a l l y obscured by r e c r y s t a l l i z a t i o n . With increased sulphide concentration, the disseminated sulphide layers become increasingly massive and i n many places sphalerite and/or galena layers enclose augen of coarse-grained dolomite, of p y r i t e , and of dolomite marble (Fig. 26d, e). Where sulphide concentrations exceed several inches i n thickness, c h a r a c t e r i s t i c breccia structures are usually developed, as i n the galena-rich bands of the A-, F- and G-zones. Of these, the most spectacular occurs i n the lowermost A-zone where i t i s involved i n Phase 1 f o l d i n g . There the galena layer i s up to six feet thick and contains abundant quartz and dolomite as rounded fragments (Fig. 26f). Mesoscopic folds can be observed at numerous locations within the ore zones. Those involving layered ore have the same geometry as the macroscopic structures a f f e c t i n g the ore bodies as a whole and can be separated into Phase 1 and Phase 2 genera-tions (Fig. 27d, e, f ) . Folds within the breccia ore are generally detached and hence tend to be more ptygmatic. Coarse-grained, "pegmatitic" ore i s uncommon i n Jersey mine but where observed (in the F- and G-zones) i t i s sphalerite-r i c h and associated with minor galena and dolomite. Cross-cutting v e i n l e t s of p y r i t e , p a r a l l e l i n g l a t e gash-veins, also are known but the genetic r e l a t i o n s between these occurrences are unclear. 100 H. B. mine The geology of the H. B. mine has been described i n part by Green (1954) and more f u l l y by Irvine (1957), Fyles and Hewlett (1959) and Warning (1960). As production ceased i n 1966, the writer was able to examine only surface exposures so that the following description of the ore bodies i s largely based on the above previous work. There are two d i s t i n c t occurrences of productive ore, the H. B. and Garnet ore bodies (Plate VIII, F i g . 10). The H. B. ore bodies take the form of three elongate, crudely e l l i p s o i d a l zones dipping steeply toward the east and plunging 15-20° south-ward. These are connected by gently dipping tabular ore breccia zones which plunge southward at the same angle (Fig. 24). The system, with a plunge length of greater than 3000 f t , i s located i n the core of a complex major syncline, the H. B. syncline, which i s considered (Section I I I , p. 52) to be a Phase 1 f o l d , modified by f l a t t e n i n g during Phase 2 deformation. The Garnet ore body i s located southwest of the H. B. ore bodies across the Garnet f a u l t (Fig. 10). It occurs as a single i s o l a t e d zone, also steeply dipping to the east and plunging at a low angle southwards. I t has a plunge length of approximately 2000 f t and i s exposed at the surface i n glory-hole workings. The steeply dipping ore zones consist of numerous d i s -seminated sulphide layers and lenses p a r a l l e l i n g an intense cleavage f o l i a t i o n (Fj?) developed i n the host dolomite marble (Fig. 25f). These have been described as mineralized shear 101 CS. b . r 3 7 0 0 H.B. ORE ZONES Lamprophyre dykes K j a o o ' VERTICAL SECTION No. I ZONE after Warning, i960 sho£?n« ? w I S O m e t r i c . v l e " of the H. B. ore zones, showing t h e l r configuration and s p a t i a l r e l a t i o n s . n o r t h " 1 v e r t l c a l section of the No. 1 zone, looking 102 zones which were developed p a r a l l e l to an e a r l i e r a x i a l plane cleavage related to major folding (Irvine, 1957; Warning, 1960). The connecting f l a t breccia zones, which are apparently truncated by the steeply dipping ores, are interpreted by the same authors as zones of shearing and brecciation formed at a late stage of the main folding and subsequently mineralized. As these breccias also contain fragments of cleaved dolomite marble, Warning (1960) proposed the following sequence of struc-t u r a l events preceding mineralization: (i) folding and development of a x i a l plane cleavage, ( i i ) low angle shearing and brecciation and ( i i i ) steep shearing. Fyles and Hewlett (1959) related the gently dipping breccia zones to thrust zones which were considered to be secondary structures (Phase 2) and the control for mineralization. The breccia ores have higher sulphide contents than the steep layered ores and from t h e i r descriptions c l o s e l y resemble the breccia ores of Reeves MacDonald and Jersey mines which are believed to be post-mineralization breccias. If the breccias of H. B. mine also post-date mineralization, then t h e i r formation could have accompanied folding and the steep layered ores could have formed by transposition of breccia ore (or i t s precursor) along F i a x i a l cleavage either during Phase 1 fold i n g or during Phase 2 closure of Phase 1 fol d s . Summary It i s concluded that no unique s t r u c t u r a l control of the emplacement of mineralization can be demonstrated as the ores are either located i n , and apparently deformed by, Phase 1 major 103 structures (the Reeves and H. B. synclines at Reeves MacDonald and H. B. mines re s p e c t i v e l y ) , or are apparently deformed by both Phase 1 and Phase 2 f o l d structures of smaller dimensions (Jersey mine). Internally, mesoscopic structures of the ores themselves suggest that the ores have indeed been deformed as: (i) layered disseminated ores outline mesoscopic folds with the same geometry as the macroscopic structures; ( i i ) layered, more massive ores show flaser/augen structures in d i c a t i n g d i f f e r e n t i a l response of the various sulphides to deformation; ( i i i ) breccia ores record intense and prolonged post-minerali-zation deformation. 104 P Figure 25. Examples of layered ores from the three mines. a. Typical layered sphalerite-pyrite/dolomite ore from Reeves MacDonald mine. Note t r a n s i t i o n into breccia ore at upper r i g h t . Reeves MacDonald mine, E. MacDonald zone, 610' l e v e l . b. D e t a i l of dolomite marble/sulphide r e l a t i o n s i n layered ore. Note dark graphitic laminae o u t l i n i n g f o l i a t i o n within the white dolomite marble. Reeves MacDonald mine, Annex zone, 925' l e v e l . Specimen RM71-48. c. "Pegmatitic" sphalerite-dolomite-quartz i n irregular/gash veining. Reeves MacDonald mine, Annex zone, 800' l e v e l . d. Layered dark dolomite marble and sphalerite, with augen and lenses of white c a l c i t e . Hammer for scale at lower l e f t . Jersey mine, F-zone. e. D e t a i l of t y p i c a l layered dark sphalerite/white dolomite ore from Jersey mine. Jersey mine, G-zone. Specimen CX69-22. f. D e t a i l of dark sphalerite/white dolomite-calcite ore, trans-posed along Fi f o l i a t i o n (?). H. B. mine, Garnet zone. Specimen HB70-18. 104 F i g u r e 25. Examples of l a y e r e d o r e s from the t h r e e mines. Figure 26. Examples of breccia ores from Reeves MacDonald and Jersey mines. a. Contorted and brecciated dolomite marble within and adjacent to dark sphalerite-pyrite layer. Reeves MacDonald mine, E. MacDonald zone, 400' l e v e l . b. Platy fragments of layered dolomite marble i n sphalerite-r i c h matrix of breccia ore. Reeves MacDonald mine, Annex zone, 875' l e v e l . Specimen RM70-34. c. Det a i l of re l a t i o n s between black gr a p h i t i c dolomite marble and sphalerite i n s p h a l e r i t e - r i c h breccia ore. Same speci-men as b. above. d. White c a l c i t e and grey dolomite augen and lenses within streaky sphalerite-galena ore. Jersey mine, open p i t west of 4050* ad i t . e. White c a l c i t e and grey dolomite augen and lenses within galena-rich matrix (dark grey). Jersey mine, open p i t west of 4050' ad i t . Specimen CX69-11. f. D e t a i l of galena and s p h a l e r i t e - r i c h breccia ore containing rounded, white dolomite fragments. Jersey mine, D-zone. Specimen CX69-55. 105 F i g u r e 26. Examples o f b r e c c i a o r e s from Reeves MacDonald and J e r s e y mines. I06P F i g u r e 27. Examples o f f o l d s t r u c t u r e s i n v o l v i n g s u l p h i d e s from Reeves MacDonald and J e r s e y mines. a. I n t e r b e d d e d and f o l d e d m a s s i v e p y r i t e (white) and g r a p h i t i c d o l o m i t e ( g r e y ) . Reeves MacDonald mine, Reeves zone " g l o r y - h o l e " i b. D i s s e m i n a t e d p y r i t e (grey) o u t l i n i n g f o l d i n c a l c i t e m arble ( o b l i q u e s e c t i o n ) . Reeves MacDonald mine, Reeves zone " g l o r y - h o l e " : c. B r e c c i a o r e c o n t a i n i n g f o l d e d d o l o m i t e m a r ble l a y e r s i n p y r i t e - s p h a l e r i t e m a t r i x . Note r o o t l e s s c l o s u r e a t l o w e r r i g h t and l a c k o f s y s t e m a t i c f o l d geometry. Reeves MacDonald mine, Reeves zone " g l o r y - h o l e " : d. Recumbent Phase 1 f o l d i n l a y e r e d w h i t e d o l o m i t e m a r b l e / s p h a l e r i t e - g a l e n a - p y r i t e o r e , c u t by t h r u s t f a u l t s . J e r s e y mine, E-zone. e. Recumbent Phase 1 f o l d i n g r e y / w h i t e d o l o m i t e marble w i t h minor s p h a l e r i t e - r i c h l a y e r s . J e r s e y mine, F-zone. f . U p r i g h t Phase 2 f o l d i n w h i t e d o l o m i t e marble and i n t e r -l a y e r e d d a r k d o l o m i t e m a r b l e / s p h a l e r i t e . J e r s e y mine, F-zone. 106 F i g u r e 27. Examples o f f o l d s t r u c t u r e s i n v o l v i n g s u l p h i d e s from Reeves MacDonald and J e r s e y mines. 107 MINERALOGICAL VARIATION OF THE SULPHIDES Introduction A s u p e r f i c i a l comparison of the ores from the three deposits reveals r e l a t i v e l y obvious mineralogical, as well as te x t u r a l , variations between them. The former comprise: (i) a general increase i n the iron content of sphalerite from Reeves MacDonald to H. B. to Jersey mines, ( i i ) l o c a l association of pyrrhotite with p y r i t e i n H. B. and Jersey mines, and ( i i i ) super-imposition of scheelite-molybdenite skarn mineralization on the older sphalerite-galena mineralization at Jersey mine. Other more cr y p t i c v a r i a t i o n s , which have also been noted i n the past, include: (a) a general increase i n the cadmium content of sphalerite from north to south implied by mine production figures ( S i n c l a i r , 1964); (b) increased cadmium and s i l v e r values i n the Annex ore zone at Reeves MacDonald mine (G_. G. Addie, 1971, pers. comm.); and (c) l o c a l change i n the antimony and bismuth contents of galena said to be a r e s u l t of contact metamorphism at Jersey mine ( S i n c l a i r , 1964). Many of these changes appear to be connected with contact metamorphism which i s generally accepted as post-dating lead-zinc mineraliza-t i o n (Muraro, 1966). The mineralogical e f f e c t s of contact metamorphism on strata-bound sulphide ores i n general have been reviewed by Vokes (1969) and may be summarized as including: (a) p a r t i a l melting of sulphides (Fe-Pb-Zn-S system) (b) d i s s o c i a t i o n of primary p y r i t e to pyrrhotite and/or magnetite 108 (c) exsolution and concentration of chalcopyrite (d) increased iron content of sphalerite In t h i s study, the mineralogical e f f e c t s were i n v e s t i -gated primarily v i a quantitative determinations of minor element contents of sulphides. Seventy-one determinations were ca r r i e d out using atomic absorption spectrophotometry (49 sphalerite and 17 p y r i t e analyses) and electron microprobe (5 sphalerite analyses). Details of sample preparation, a n a l y t i c a l methods and precision are given i n Appendix C. Minor element content of sphalerite Iron, cadmium, manganese, s i l v e r and copper values i n 49 sphalerite samples from the three deposits were determined by A. A. spectrophotometry (Tables XII and XIII of Appendix C). Lead values determined as measure of sample contamination, varied from n i l to 4.7 wt. % but showed no systematic c o r r e l a -t i o n with other minor element values. Mean values of minor element contents of sphalerites from the three deposits are compared i n Table VII. In t h i s Table, the Reeves MacDonald mine samples have been subdivided into those from Reeves MacDonald zone vs. those from Annex zone as there are s i g n i f i c a n t differences between them, as w i l l be discussed below. Scatter diagrams of i n d i v i d u a l sample values are i l l u s t r a t e d v i a a logarithmic pl o t of cadmium against iron (Fig. 28), and a ternary plo t of logarithmically transformed manganese, s i l v e r and copper values (Fig. 29). These indicate differences between the four sample groups which were s t a t i s t i c a l l y tested using the 109 10.0 0.1 -o 0 o -© • < 0 O-^CO o 1 1 1 1 I I I I i i i i I I I I , A Jersey E3 H.B. @ R.MacC O R.MacC i i i i I I I I , )onald )onald Annex i i i i i i i i , . 0.01 0.1 1.0 10.0 100.0 wt% Fe -Figure 28. L o g a r i t h m i c p l o t o f Cd v s . Fe c o n t e n t s o f s p h a l e r i t e samples from t h e t h r e e mines. 110 F i g u r e 29. T e r n a r y p l o t o f Mn, Cu and Ag c o n t e n t s ( i n ppm l o g a r i t h m i c a l l y t r a n s f o r m e d ) o f s p h a l e r i t e samples from t h e t h r e e mines. Table VII. Comparison of mean values of minor element contents of sphalerite samples from the three mines (G = geometric mean i n ppm; S.D. = standard deviation expressed as logarithms). Reeves MacDonald mine Annex zone Reeves MacDonald z. H. B. mine Jersey mine Minor element (15 samples) G S.D. (10 samples) (9 G S.D. G samples) S.D. (15 samples) G S • D. Fe 14100 0.127 9900 0.138 27300 0.128 43600 0. 158 Cd 10400 0.078 4000 0.177 4100 0.071 6100 0. 056 Mn 60 0.275 75 0.423 385 0.239 545 0. 309 Ag 71 0.551 11 0.313 7 0.402 9 0. 592 Cu 51 0.177 21 0.236 17 0.205 30 0. 253 Annex zone vs. Reeves MacDonald zone Reeves MacDonald zone vs. H. B. mine H. B. vs Jersey mine « mine t-values Degrees of freedom Degrees of t-values freedom t-values Degrees of freedom Fe -2.8371 23 7.1561 17 3.2521 22 Cd -6.8911 11 0.045 12 6.5921 22 Mn 0.698 23 4.4361 17 1.256 22 Ag -4.1961 23 -1.047 17 0.345 22 Cu -4.7081 23 -0.870 17 2.4071 22 Indicates mean values are s i g n i f i c a n t l y d i f f e r e n t at the 95% confidence l e v e l 112 standard t - t e s t of the mean values at the 5% l e v e l of s i g n i f i -cance. The t-values were computed using a FORTRAN program, STRIP (Seagraves, 1971) and the re s u l t s are l i s t e d i n Table VII. These suggest that there i s a general increase i n the ir o n , cadmium and manganese values of sphalerite i n the order—Reeves MacDonald (exclusive of the Annex zone), H. B., Jersey. This i s however c l e a r l y systematic only i n the case of iron although moderate correlations do ex i s t between iron and manganese (r = 0.62) and between iron and cadmium values (r = 0.56). Similar correlations between the iron and manganese contents of sphalerites have been noted i n other occurrences by Fryklund and Fletcher (1961), Sims and Barton (1961) and Boyle and Jambor (1963) but according to Fryklund and Fletcher no c o r r e l a t i o n existed between iron and cadmium contents i n t h e i r study. The general trend of these minor element values corre-sponds with the observed increase i n i n t e n s i t y of contact meta-morphic e f f e c t s , implying a relat i o n s h i p that i s at least p a r t l y temperature dependent. Obviously, the other conditions atten-dant upon r e c r y s t a l l i z a t i o n (pressure, sulphur fugacity, etc.) and the pre-existing minor element concentrations are largely unknown so that t h e i r value as geological thermometers must remain at best q u a l i t a t i v e . In t h i s respect, the significance of the iron content (in particular) of sphalerite has been discussed by Kullerud (1953), Barton and Kullerud (1958) and Barton and Toulmin (1966) and has been shown, i n p y r i t e + sphalerite assemblages, to be sensitive to not only temperature but also sulphur fugacity. 113 Differences i n the minor element content of sphalerites are most marked between samples from the Reeves MacDonald ore zones and samples from the Annex ore zone at Reeves MacDonald mine. Those from the Annex zone are d i s t i n c t l y r i c h e r i n ir o n , cadmium, s i l v e r and copper (Table VII and F i g . 28, 29). The reasons for t h i s change down the plunge length of, what was pr i o r to f a u l t i n g , a continuous ore body are obscure; no increase in metamorphic grade has been recognized, although a contact metamorphic aureole could conceivably ex i s t at t h i s depth (see Section IV, p. 75). The most obvious physical difference down-plunge i s an increase i n very coarse-grained, s p h a l e r i t e - r i c h "pegmatitic" ore veining i n the Annex zone. This may be i n either gash veins or i n i r r e g u l a r veining which grades into t y p i c a l r e c r y s t a l l i z e d , fine-grained sphalerite of the layered and breccia ores (Fig. 25c). When the minor element contents of the "pegmatitic" and the fine-grained sphalerites are compared, i t i s found that the only s i g n i f i c a n t difference i s i n the iron contents (Table VIII). Thus i t i s not clear how the zonation i n minor elements down-plunge i s related, i f at a l l , to the development of the coarse-grained, s p h a l e r i t e - r i c h ore. Many writers (Ramdohr, 1953; Juve, 1967; Lawrence, 1967; McDonald, 1967; Mookherjee, 1970; Vokes, 1971) suggest that coarse-grained, pegmatite- or v e i n - l i k e sulphide-gangue bodies within strata-bound ores i n metamorphic t e r r a i n are segregations mobilized during metamorphism. Such mobilization i s believed, i n general, to involve limited f l u i d transport (although the actual Table VIII. Comparison of mean values of minor element contents of d i f f e r e n t types of sphalerite from the Annex zone of Reeves MacDonald mine (G= geometric mean i n ppm; S.D. = standard deviation expressed as logarithms). Coarse-grained pegmatitic sphalerite (7 samples) G S.D. Fine-grained sphalerite (7 samples) G S.D. t-values Degrees of freedom Fe 16900 0.140 11900 0.068 -2.5841 12 Cd 10000 0.091 10700 0.072 0.701 12 Mn 77 0.358 45 0.120 -1.636 7 Ag 47 0.521 67 0.233 0.735 12 Cu 43 0.177 61 0.166 1.721 12 1Indicates mean values are s i g n i f i c a n t l y d i f f e r e n t at the 95% confidence l e v e l 115 physico-chemical nature of the transporting medium i s r a r e l y discussed), or i n rarer cases to involve p a r t i a l melting i n the Fe-Pb-S, Fe-Pb-Zn-S, and Cu-Fe-Pb-S systems (Brett and Kullerud, 1967; Lawrence, 1967; Vokes, 1971). I t i s also suggested that the mobilization takes place s e l e c t i v e l y as r e l a t i v e enrichments of s e g r e g a t i o n s f o r example, i n Pb, As, Sb, and Ag concentra-tions, have been described (Vokes, 1963, 1971). In t h i s study, the "pegmatitic" ore commonly occupies gash veins (which i n the Jersey mine area are considered to have formed at a l a t e stage of granite i n t r u s i o n ) , appears to be e s s e n t i a l l y undeformed, and hence post-dates a l l three phases of folding and regional metamorphism. Therefore, i f i t s mobiliza-t i o n i s indeed of metamorphic o r i g i n , i t can only be of contact metamorphic o r i g i n , perhaps e x o t i c a l l y related to granite i n t r u -sion at depth i n the area and r e s u l t i n g from upward migration of magmatic water through the ore body. Minor element content of p y r i t e The cobalt, n i c k e l , copper and manganese contents of 17 p y r i t e samples from the three deposits were determined by A. A. spectrophotometry (Table XIX of Appendix C). Lead and zinc values, determined as a measure of sample contamination, are e r r a t i c and often r e l a t i v e l y high (0.002 - 2.2%) but show no systematic c o r r e l a t i o n with the other minor element values. Means and standard deviations for the values are given i n Table IX. The only s i g n i f i c a n t difference (at the 95% confidence level) between the mean values of the three deposits i s i n the higher mean n i c k e l content of the Reeves MacDonald p y r i t e s . Table IX. Comparison of mean minor element contents of p y r i t e samples from the three mines (G = geometric mean i n ppm; S.D. = standard deviation i n logarithms). - R. MacDonald mine Minor (7 samples) element G S.D. H. B. mine (5 samples) G S.D. Jersey mine (5 samples) G S.D. Synoptic (17 samples) G S.D. Co 11 0.148 4 0.355 5 0.473 6 0.376 Ni 149 0.163 16 0.351 38 0.397 52 0.506 Cu 10 0.131 8 0.507 7 0.496 8 0.372 Mn 2 0.147 21 0.506 4 0.211 5 0.554 Co:Ni .07 .25 .13 .12 R. MacDonald mine vs. Jersey mine t-values Degrees of freedom Co -1.545 5 Ni -3.6341 10 Cu -0.832 4 Mn 3.8181 10 1 Indicates mean values are s i g n i f i c a n t l y d i f f e r e n t at the 95% confidence l e v e l 117 There i s also a high c o r r e l a t i o n (r = 0.81) between cobalt and nic k e l values which are shown, plotted on a logarithmic scale, i n Figure 30. The genetic significance of Co:Ni r a t i o s , i n r e l a t i o n to strata-bound, disseminated copper deposits, was discussed by Davidson (1962) who noted t h e i r d i s t i n c t i v e l y high Co:Ni r a t i o s which more cl o s e l y resembled those of a c i d i c igneous rocks and a f f i l i a t e d skarn sulphides than those of either ancient or modern sediments. Cobalt and ni c k e l contents of sedimentary rocks tend to be low and Co:Ni r a t i o s are generally less than unity (Table X).. Lo f t u s - H i l l s and Solomon (1967), from a study of p y r i t i c ores i n Lower Palaeozoic rocks of the Tasman geosyncline, found that sedimentary p y r i t e i n shales i s characterized by low Co:Ni ra t i o s (<0.35) and by moderately high Ni contents (>200 ppm), although p y r i t e from g r a n i t i c rocks (and associated ore) and from stratiform lead-zinc ores with volcanic associations had similar low ra t i o s but much lower Ni contents. A recent s t a t i s t i c a l study of analyses of minor elements i n p y r i t e from many sources by Price (1972) shows that the mean (geometric) cobalt and n i c k e l contents of sedimentary p y r i t e are s i g n i f i c a n t l y lower than those of py r i t e from either massive sulphide-volcanic exhalative deposits or hydrothermal vein-type deposits, and that the mean Co:Ni r a t i o i s less than one (Table X). Very l i t t l e information i s available on the cobalt and ni c k e l contents of py r i t e from M i s s i s s i p p i Valley type deposits, 118 100 E a a o 10 --A ® 0 1 I I I I I I I ! ® m A i i i i , i i i A Jersey m H.B. © R.MacD ...i... i i i i . i 11 onald 1 10 100 1000 Ni p p m F i g u r e 30. L o g a r i t h m i c p l o t o f Co v s . N i c o n t e n t s o f p y r i t e samples from t h e t h r e e mines. 119 Table X. Co and Ni contents (in ppm) of A. c e r t a i n sedimentary rock types, and of B. p y r i t e from d i f f e r e n t types of ore deposit. Co Ni Co:Ni A. Average shale 19 68 0.57 (Turekian and Wedepohl, 1961) Average black shale 10 50 0.2 (Vine and Tourtelot, 1970) - 126 41 ? ? (Weber, 1964) Carbonates 4 11 0.36 (Graf, 1962) B. Sedimentary ores 41 65 0.63 Hydrothermal ores 141 121 1.17 (Price, 1972) Massive sulphide ores 486 56 8.70 120 few analyses having been done and these mostly semi-quantitative spectrographic analyses. A few analyses (20) from the s t r a t i -form zinc-lead ores of the Upper M i s s i s s i p p i Valley d i s t r i c t indicate that p y r i t e and marcasite (common i n these deposits) generally have low cobalt and n i c k e l contents and Co:Ni r a t i o s close to unity (Bradbury, 1961), although p y r i t e of d i f f e r e n t generations may have cobalt and n i c k e l contents of up to 1% (Hall and Heyl, 1968). The available data, however, are insuf-f i c i e n t to accurately characterize p y r i t e from these deposits. Although cobalt and ni c k e l contents of the Salmo pyrites most cl o s e l y resemble those of syngenetic p y r i t e and of sedimen-tary rocks, they have almost c e r t a i n l y been modified by meta-morphism (possibly both contact and regional), e s p e c i a l l y where a new phase, such as pyrrhotite, has been generated. Cambel and Jarkovsky (1969), i n a study of the p y r i t i c deposits of the Western Carpathians, showed i n coexisting p y r i t e and pyrrhotite that n i c k e l was concentrated i n the pyrrhotite l a t t i c e and cobalt i n the py r i t e l a t t i c e , under medium- to high-grade metamorphic conditions. Sangster (1967) has also proposed r e d i s t r i b u t i o n of cobalt and ni c k e l between pyrrhotite and sphalerite as a consequence of the metamorphic conversion of pyrite to pyrrhotite i n the New Calumet deposit, Quebec. Although the Salmo py r i t e data are too few, there i s a suggestion that contact metamorphism and the appearance of pyrr-hotite may be the cause of the s i g n i f i c a n t l y lower nickel': values at Jersey and H. B. mines. 121 Even more uncertain are the e f f e c t s , i f any, of p r i o r regional metamorphism, since pyrrhotite was not formed under these conditions. However, p a r t i c u l a r l y at Reeves MacDonald mine (least affected by contact metamorphism), the bedded nature of some of the p y r i t e , i t s common association with g r a p h i t i c dolomite and the generally low cobalt and n i c k e l contents, with Co:Ni r a t i o s <1, suggest that the p y r i t e i s sedimentary i n o r i g i n and that cobalt-nickel values are perhaps l i t t l e f r a c -tionated under conditions of lower greenschist metamorphism. Minor element content of galena No determinations were made, i n t h i s study, of minor element contents of galena as suitable galena-rich material was available only from Jersey mine. It has already been shown (S i n c l a i r , 1964) that galena (six analyses) from Jersey mine has high Sb:Bi r a t i o s which are probably i n d i c a t i v e of a low tempera-ture o r i g i n (Malakhov, 1969). One additional sample, believed to be highly contact metamorphosed, had a very low Sb:Bi r a t i o which i s more i n d i c a t i v e of a high temperature o r i g i n as i n skarn-type mineralization (Malakhov, 1969) . Occurrence of pyrrhotite Pyrrhotite coexisting with sphalerite + p y r i t e occurs l o c a l l y i n a l l three deposits. At Reeves MacDonald mine, the occurrence of the three phase assemblage i s very r e s t r i c t e d and has been observed only i n rare sulphide xenoliths from lampro-phyre dykes cutting the ore body. In the H. B. mine, pyrrhotite occurs sparingly and then mostly as l o c a l concentrations i n the 122 No. 1 ore zone (Warning, 1960) . I t i s not know how i t s d i s t r i -bution r e l a t e s , i f at a l l , to lamprophyre dykes cross-cutting the ores. Pyrrhotite occurrence i s most abundant and widespread at Jersey mine where i t i s found near the base of the A-zone and sporadically throughout the eastern zones (F, G and H). Its d i s t r i b u t i o n i s apparently related to proximity of the Emerald and Dodger stocks (Fig. 17), but i t s mode of occurrence i s apparently complex i n that i t not only i s associated with sphalerite-pyrite-galena mineralization but possibly also occurs as a primary (?) constituent of skarn-type scheelite-molybdenite mineralization at the margins of the granite stocks. The assemblage sphalerite + pyrrhotite + p y r i t e i s of pa r t i c u l a r i n t e r e s t as the sulphur fugacity i s fixed at given temperatures by the coexisting iron sulphides (Barton and Toulmin, 1966). It has been shown (Boorman, 1967; Scott and Barnes, 1971; Boorman, Sutherland and Chernyshev, 1971) that the sphalerite-pyrrhotite-pyrite solvus i s v e r t i c a l between 550° and 304°C so that the FeS content of sphalerite i n equilibrium with hexagonal pyrrhotite + p y r i t e i s fixed at approximately 21 mole % (at 1 bar) and i s not therefore temperature se n s i t i v e . I t i s however pressure sensitive, as has been calculated by Barton and Toulmin (1966) and Scott and Barnes (1971), and appears to pro-vide a useful geobarometer, providing the attainment of e q u i l i -brium can be established. Five samples of sphalerite coexisting with pyrrhotite + pyr i t e were analyzed by electron microprobe for zinc and iron (see 123 Appendix D). Four of these samples were from Jersey mine and one from Reeves MacDonald mine. Apart from comparing FeS con-tents of these sphalerites with those from sphalerite + p y r i t e assemblages, a further purpose was to attempt to use the former assemblages as geobarometers to check estimates of t o t a l pres-sure during contact metamorphism. However, the lack of a t t a i n -ment of equilibrium i n the ore during contact metamorphism (discussed below) has precluded t h e i r use as geobarometers. The Reeves MacDonald sample was from a sulphide xenolith i n a lamprophyre dyke of Eocene age. Sphalerite from i t con-tained 17.82 ± 1.2 mole % FeS and was not, on the basis of t h i s microprobe data, very homogeneous. Further, the presence of abundant blebs of pyrrhotite (possibly exsolved) i n the sphalerite suggested that the FeS content might not be " o r i g i n a l . " FeS contents of the Jersey sphalerites coexisting with py r i t e + pyrrhotite were i n the range 10.83-12.66 mole % (mean: 11.94 ± 0.64 mole % FeS). In comparison, the FeS contents of sphalerite coexisting with p y r i t e alone (analysed by A. A. spec-trophotometry) were i n the range 2.42-11.31 mole % (mean: 7.86 ± 1.92 mole % FeS). These re s u l t s are inset as histograms i n Figure 31 to i l l u s t r a t e t h e i r range i n r e l a t i o n to the composi-tion of sphalerite i n equilibrium with pyrrhotite + p y r i t e between 550° and 304°C. The l o c a l i z e d d i s t r i b u t i o n of pyrrhotite, together with the wide v a r i a t i o n i n sphalerite compositions (Fig. 31), indicate that equilibrium was not attained throughout the Jersey ores during contact metamorphism. Further, the coexisting pyrrhotite 124 Figure 31. FeS contents (mole %) of sphalerite samples from Jersey mine. Contents and locations of i n d i v i d u a l samples are shown on plan of mine workings. Inset shows projection (on the FeS-Zns binary) of part of the system Fe-Zn-S at 1 bar (after Scott and Barnes, 1971). In r e l a t i o n to t h i s , the histogram shows range i n FeS contents of sphalerites from Jersey mine (white from sph + py and black from sph + py + po assemblages). 125 i s mixed monoclinic and hexagonal, as determined d i r e c t l y by X-ray d i f f r a c t i o n (Arnold, 1966), so that i t s association with py r i t e suggests disequilibrium within the iron sulphide assem-blage. The hexagonal pyrrhotite has a composition of approxi-mately 47.5 atomic % Fe (determined from the curve for d j | ^ j versus composition of Arnold, 1962) which i s usual i n ores containing both hexagonal and monclinic pyrrhotite (Arnold, 1967). This has been interpreted as r e s u l t i n g from inversion below 304 C of hexagonal high-temperature pyrrhotite (composition: 46.5-47.5 atomic % Fe) to hexagonal low-temperature pyrrhotite and metastable monoclinic pyrrhotite (Arnold, 1969). This could be the r e s u l t , i n t h i s case, of retrogressive contact metamorphism as indicated by the development of c h l o r i t e a f t e r b i o t i t e porphyroblasts i n schists elsewhere i n the contact aureole. Sphalerite coexisting with pyrrhotite + p y r i t e l o c a l l y contains minute blebs and lamellae (possibly exsolved) of chal-copyrite and/or pyrrhotite. Rare l o c a l i z e d , minor concentrations of chalcopyrite have also been noted either i n contact with both sphalerite and pyrrhotite, or with pyrrhotite alone. In general, even where no "exsolution" i s observed, sphalerite i s s l i g h t l y less homogeneous (on the basis of semi-quantitative microprobe traverses for iron) than i n sphalerite-pyrite assemblages, par-t i c u l a r l y when compared with specimens from H. B. and Reeves MacDonald mines (Fig. 32), which further suggests that e q u i l i -brium was not f u l l y attained on the micro-scale. 126 LU Po CX69-55 c. HB70-I9 RM70-100/jm Figure 32. Semi-quantitative microprobe determinations of iron v a r i a t i o n across sphalerite grains i n samples from (a, b) Jersey mine; (c) H. B. mine; (d) and Reeves MacDonald mine. (a) shows traverse of sphalerite adjacent to pyrrhotite. 1 2 7 Occurrence of a second generation of p y r i t e A second generation of p y r i t e within sphalerite + pyrrhotite + p y r i t e assemblages i n the Jersey ore i s indicated by the l o c a l development of large i d i o b l a s t i c p y r i t e c r y s t a l s (Fig. 34f) and of inclusion-bearing p y r i t e overgrowths on p r i -mary py r i t e i n contact with pyrrhotite. Late, cross-cutting pyrite v e i n l e t s elsewhere i n the ore may also be of t h i s genera-t i o n although i t has been suggested that these and other cross-cutting veins of arsenopyrite, pyrrhotite and chalcopyrite (not observed i n t h i s study) r e s u l t from a separate episode of minera-l i z a t i o n accompanying intrusion of the granite stocks and perhaps related to scheelite-molybdenite skarn mineralization ( S i n c l a i r , 1964) . The o r i g i n of t h i s second p y r i t e generation i s not known but may r e s u l t from late-stage sulphurization of pyrrhotite. Such an increase i n sulphur vapour pressure might also explain the occurrence of "exsolved" pyrrhotite i n sphalerite from these assemblages (Barton and Toulmin, 1966). Similar occurrences of secondary p y r i t e from dyke-contact aureoles i n massive sulphides have been described by Johnson ( 1 9 6 6 ) , Graham ( 1 9 6 8 ) , and Mookherjee and S u f f e l ( 1 9 6 8 ) . These are ascribed to sulphurization of pyrrhotite and of ferromagnesian s i l i c a t e s near the i n t r u s i v e contacts either by the sulphur released during the breakdown of the pyrrhotite (in the presence of O 2 ) to magnetite, or by the migration inwards towards the intrusion of sulphur released by the transformation of p y r i t e to pyrrhotite. Breakdown of pyrrhotite has not been observed, 128 however, i n the Jersey ore nor does such a breakdown appear to have been l i k e l y i f carbonaceous/graphitic material was associated with the ore at the time of contact metamorphism i n s i m i l a r abundance to that presently observed i n Reeves MacDonald ore. Summary A number of mineralogical e f f e c t s r e s u l t i n g from contact metamorphism of the sulphide assemblages have been determined. Some of these are tentative because of i n s u f f i c i e n t data. The e f f e c t s include changes i n the minor element contents of the sulphides, the appearance of new mineral phases, and perhaps also l o c a l mobilization of both sulphides and gangue. They may be summarized as follows: (i) Changes i n minor element contents: a. progressive increases i n the Fe, Mn and Cd contents of sphalerite b. a possible decrease i n the Ni content of p y r t i e c. a possible decrease i n Sb:Bi r a t i o s i n galena at the highest metamorphic grade ( S i n c l a i r , 1964) ( i i ) Appearance of new minerals within the inner aureole of contact metamorphism: a. transformation of p y r i t e to pyrrhotite giving the d i s -equilibrium assemblage sphalerite + p y r i t e + pyrrhotite b. possible exsolution of pyrrhotite and chalcopyrite from sphalerite c. c r y s t a l l i z a t i o n of a second generation of p y r i t e 129 ( i i i ) Formation of "pegmatitic" s p h a l e r i t e - r i c h ore (in the Reeves MacDonald Annex zone) possibly by mobilization v i a a f l u i d phase of magmatic o r i g i n ; enrichment of Fe, Cd, Ag and Cu i s observed i n both "pegmatitic" and host fine-grained ore. Mineralogical evidence that the sulphides have undergone regional metamorphism i s extremely s l i g h t . I t i s suggested by the cobalt-nickel contents of p y r i t e which appear to indicate a sedimentary, and hence pre-metamorphic, o r i g i n and also by the remarkable homogeneity, on the microscale, of sphalerite i h the least contact metamorphosed specimens which may imply p r i o r e q u i l i b r a t i o n of the sulphides. TEXTURAL FEATURES OF THE SULPHIDES Introduction The sulphide minerals were examined i n both t h i n and polished sections for variations i n grain size and shape, grain boundary configuration and deformation structure. Structure etching of the polished sections was used extensively to reveal grain and subgrain boundaries and intragranular microstructure. A thiourea + HC1 solution was used for sphalerite and galena (Brebrick and Scanlon, 1957) and a KMnOit + RzSOn solution for p y r i t e (Cameron, 1961, p. 210-211). Pyrite P y r i t e occurs i n a wide range of grain s i z e s , these being i l l u s t r a t e d semi-quantitatively for the three areas i n Figure 33. Its forms too are varied and include the following: 130 10.0 3.0-1.01— E E c 0.3 a> N w c O.lh-C3 o .03-Poiklloblosts mM BEjaAveroge els H.B. JERSEY REEVES MACDONALD JERSEY H.B. REEVES MACDONALD P Y R I T E S P H A L E R I T E F i g u r e 33. G r a i n s i z e v a r i a t i o n o f p y r i t e and s p h a l e r i t e between t h e t h r e e mine a r e a s . 131 (i) folded/brecciated massive, prismatic layers associated with graphitic laminae ( i i ) fractured porphyroclasts ( i i i ) s u b i d i o b l a s t i c grains and granoblastic-polygonal grain aggregates (iv) large p o i k i l i t i c i d i o b l a s t s (v) l a t e cross-cutting v e i n l e t s At Reeves MacDonald mine, (i) and ( i i ) are the common forms observed. Where massive layers occur, they are invariably folded and/or brecciated (Fig. 34a). More commonly, p y r i t i c layers contain numerous, strongly fractured, angular fragments or porphyroclasts. The fracturing i s usually i r r e g u l a r but regular conjugate fracturing has also been observed (Fig. 34b, c ) . Both these types may be healed with inclusion-free p y r i t e . Disseminated, fine-grained p y r i t e has a more widespread occur-rence throughout the ores and tends to be either angular to subangular and s l i g h t l y fractured or subi d i o b l a s t i c and i n places embayed. Large i d i o b l a s t i c forms are rare and are apparently r e s t r i c t e d to l a t e , "pegmatite"-ore veining. Average grain size tends to be higher at Jersey mine and granoblastic-polygonal and i d i o b l a s t i c p y r i t e are more common (Fig. 34e, f ) . In numerous places the configuration of grano-blastic-polygonal aggregates within sphalerite-galena layers suggests that they represent r e c r y s t a l l i z e d augen or porphyro-c l a s t s (Fig. 34d). In contrast the large p o i k i l i t i c i d i o b l a s t s are suggestive of n e o c r y s t a l l i z a t i o n (Fig. 34f). Perhaps related to the l a t t e r are late v e i n l e t s of massive p y r i t e which I32f Figure 34". Photographs and photomicrographs of microstructures and textures developed i n p y r i t e . a. Folded and cleaved p y r i t e (grey), interlayered with highly graphitic dolomite. Reeves MacDonald mine, Reeves zone "glory-hole". Specimen RM69-17. b. Typical i r r e g u l a r l y fractured and fragmented p y r i t e . Reeves MacDonald mine, Reeves zone "glory-hole". Specimen RM69-21. Magnification 8OX. c. Conjugate fracture system i n p y r i t e porphyroclast. Reeves MacDonald mine, Annex zone. Specimen RM71-32. Magnifica-t i o n 100X. d. Pyrite augen i n dark sphalerite-galena layer. Jersey mine, D-zone. Specimen CX69-53. e. Rec r y s t a l l i z e d , polygonal texture i n p y r i t e . Jersey mine, D-zone. Specimen CX69-55. Magnification 50X. f. P o i k i l o b l a s t i c p y r i t e (arrowed) i n layered sphalerite-pyrrhotite-dolomite matrix. Jersey mine, F-zone. Specimen CX69-95. 132 F i g u r e 34. Photographs and p h o t o m i c r o g r a p h s o f m i c r o s t r u c t u r e s and t e x t u r e s d e v e l o p e d i n p y r i t e . 133 cross-cut the composition layering and have the same orientation as the late fractures and gashes f i l l e d with quartz and c a l c i t e previously described (Section I I I , p. 61).. P y r i t e - r i c h layers are commonly p a r t i a l l y r e c r y s t a l l i z e d (granoblastic-polygonal texture) but within them survive brecciated, massive p y r i t e frag-ments, c h a r a c t e r i s t i c a l l y associated with graphitic laminae. Pyrite from H. B. mine commonly occurs as layered, prismatic fragments associated with minor g r a p h i t i c material. These c l o s e l y resemble the form (i) described above but they also occur as nodular masses up to 1 cm i n diameter which have an in t e r n a l r a d i a t i n g , prismatic structure and may look coarsely colloform; X-ray d i f f r a c t i o n studies did not reveal the presence of marcasite i n any of t h i s material. These forms are found both as r e l a t i v e l y i s o l a t e d masses within dolomite and c a l c i t e gangue and as a component of brecciated, highly p y r i t i c layers. Dis-seminated, fine-grained p y r i t e varies from angular to rounded, subi d i o b l a s t i c grains, with the former occurring more t y p i c a l l y i n the brecciated p y r i t e layers and the l a t t e r t y p i c a l l y i n sphalerite-galena layers where the grains may be embayed. Sphalerite Sphalerite generally forms granoblastic aggregates com-posed of strongly twinned equidimensional grains. The twin lamellae are broad and mostly coherent and are thus considered to be mainly r e c r y s t a l l i z a t i o n or annealing twins (Klassen-Nekhudova, 1964; Stanton and Gorman, 1968) rather than deforma-ti o n twins (compare Fig.. 35d and 36f) . Average grain size 134 increases progressively from Reeves MacDonald through H. B. to Jersey mines (Fig. 33), presumably r e f l e c t i n g increasing i n t e n s i t y of contact metamorphism. Numerous specimens from Jersey mine exhibit l o c a l i z e d exaggerated grain growth as a r e s u l t of t h i s annealing r e c r y s t a l l i z a t i o n (Fig. 35d, upper r i g h t ) , possibly analagous to secondary r e c r y s t a l l i z a t i o n i n metals. Grain size i n the other deposits tends to be more uniform l o c a l l y except i n the deepest zone (the Annex) of Reeves MacDonald mine where patches of coarser grain size (circa 200 um) occur l o c a l l y and are possibly related to the development of late "pegmatitic" sulphides. Etching reveals i n t e r n a l grain boundaries within many larger sphalerite grains (Fig. 36d). These outline a substructure of rounded "grains" which are d i s t i n c t l y bimodal i n grain size (averaging 80 ym and 10 ym). Twin lamellae cut across these without d e f l e c t i o n . They probably represent true subgrains since they are terminated at host grain boundaries. Mylonitized sphalerite, forming th i n f l i n t y - l o o k i n g layers (less than 1 cm thick) p a r a l l e l with composition layering, has been recognized at several l o c a l i t i e s i n Jersey mine (in the F-zone)(Fig. 36a-c). The only other recorded occurrence of similar material appears to be that described by Butler (1935) from the F r i e d e n s v i l l e Appalachian-type deposit. On the micros scale the mylonitized sphalerite consists of ribbon-like or lensoid concentrations forming zones within sphalerite and car-bonate gangue of normal grain s i z e . When etched these concentra-tions are revealed as consisting of very fine-grained polygonal 135 f -Figure 35. Photomicrographs of r e c r y s t a l l i z a t i o n textures developed i n sphalerite, etched with thio-urea + HC1. a-c Examples of fine-grained granoblastic textured sphalerite from Reeves MacDonald mine. These textures are i n t e r -preted as e s s e n t i a l l y primary r e c r y s t a l l i z a t i o n textures. Sphalerite i s l i g h t grey i n colour and strongly twinned, dolomite i s black (from etching), and p y r i t e i s white. A l l magnifications 28X. a. Annex zone, l e v e l unknown. Specimen RM71-34. b. Annex zone, 800* l e v e l . Specimen RM71-52. c. Annex zone, l e v e l unknown. Specimen RM71-32. d-f. Examples of r e l a t i v e l y coarse-grained subgranoblastic sphalerite from Jersey mine. These textures are i n t e r -preted as annealed textures r e s u l t i n g from grain growth. The coherent lamellar twinning i s believed to be annealing or r e c r y s t a l l i z a t i o n twinning. Note exaggerated grain growth at top centre of Figure 35d, and also bending of twin lamellae i n Figures 35e, f. Sphalerite i s grey and strongly twinned, p y r i t e i s white, dolomite i s black, and galena i s mottled grey (from etching). A l l magnifi-cations 28X. d. D-zone. Specimen CX69-53. e. D-zone. Specimen CX69-44. f. C-zone. Specimen CX69-45. 135 F i g u r e 35. Photomicrographs o f r e c r y s t a l l i z a t i o n t e x t u r e s d e v e l o p e d i n s p h a l e r i t e , e t c h e d w i t h t h i o - u r e a + HC1. 1 3 6 f -Figure 36. Photomicrographs of deformation textures and micro-structures developed i n sphalerite, etched with thio-urea + HC1. a. Mylonitic sphalerite. Section i s normal to the lamination. Jersey mine, F-zone. Specimen CX69-25. Magnification 50X. b. Detail of sphalerite "ribbons" from mylonitic layer, showing very fine-grained polygonal texture. Jersey mine, F-zone. Specimen CX69-25. Magnification 320X. c. Extreme d e t a i l of polygonal texture developed i n mylonitic sphalerite. Jersey mine, F-zone. Specimen CX69-25. Magnification 1000X. d. Subgrain structure developed within a single twinned sphalerite grain. Jersey mine, D-zone. Specimen CX69-55. Magnification 1000X. e. Kinking of r e c r y s t a l l i z a t i o n twins and the development of deformation twinning i n sphalerite. Note also the serrate grain boundaries. Jersey mine, D-zone. Specimen CX69-56. Magnification 80X. f. Intense deformation twinning i n sphalerite from "gneissic" sphalerite-galena. Jersey mine, A-zone, A-zone. Specimen CX69-27. Magnification 80X. 136 F i g u r e 36. Photomicrographs o f d e f o r m a t i o n t e x t u r e s and m i c r o -s t r u c t u r e s d e v e l o p e d i n s p h a l e r i t e , e t c h e d w i t h t h i o - u r e a + HC1. 137 aggregates with an average grain size of 5-10 urn (Fig. 36c) which shows them to be t o t a l l y r e c r y s t a l l i z e d . Evidence of s l i g h t i n t e r n a l deformation i n sphalerite aggregates i s widespread. The most common i s a weak to moderate bending of the annealing or r e c r y s t a l l i z a t i o n twin lamellae (Fig. 35e, f ) . Locally, more intense deformation i s indicated by the development of kink bands, s l i p l i n e s and serrate grain boundaries i n host grains (Fig. 3 6e). The most intense defor-mation i s shown by sphalerite porphyroclasts within mylonitic galena layers. These may have intensely developed deformation twinning (closely spaced, narrow, non-coherent lamellae), marked dimensional preferred orientation, and sparse matrix of f i n e -grained (5 \im) , polygonal-shaped grains (Fig. 36f) . The less intense deformation e f f e c t s are recognized i n even the most highly annealed sphalerite aggregates from Jersey mine and t h e i r development i s therefore believed to post-date, wholly or i n part, contact metamorphism. It i s not clear to what extent the intense s t r a i n shown by sphalerite porphyro-c l a s t s within galena layers also post-dates contact metamorphism; i t may, i n fact, represent p l a s t i c deformation which has survived annealing r e c r y s t a l l i z a t i o n . Galena The highest galena concentrations, i n a l l three deposits, occur i n breccia ores. Minor concentrations elsewhere i n the ore bodies are l o c a l i z e d i n such tensional features as cross-fractures and boudinage "necks," suggesting that s o l i d - s t a t e movement of the galena may have occurred. 138 There do not appear to be any widespread s i g n i f i c a n t differences i n texture or microstructure among the galenas from the three deposits, except that mylonitic lamination (see below) was not observed i n the galena-poor ores of Reeves MacDonald mine. Unetched galena t y p i c a l l y has xenoblastic form i n r e l a t i o n to the other sulphides and to dolomite gangue. Etching reveals straight, or s l i g h t l y curved, grain boundaries and uniformly granoblastic-polygonal textures (Fig. 37a). Although the average grain size i s about 50 urn, s u r p r i s i n g l y wide variations i n grain size occur l o c a l l y (from less than 1 urn to 300 urn) even on the microscale (Fig. 37c). Grain shapes, whatever the grain s i z e , are generally equidimensional except for some coarse-grained material from Reeves MacDonald mine which exhibits length/width r a t i o s for the grains of up to 2:1 (Fig. 37b). Such dimensional preferred orientation could perhaps be attributed to s l i g h t f l a t t e n i n g . However, similar textures have been induced experi-mentally by s t a t i c r e c r y s t a l l i z a t i o n of deformed (kinked), coarse-grained galena (Stanton and Willey, 1972); continued heating of these reduced length/width r a t i o s of the grains by sideways growth and indicated development toward equidimensional grain structure. L y a l l and Paterson (1966) also noted development of elongate grain shapes r e s u l t i n g from s t a t i c r e c r y s t a l l i z a t i o n of some single c r y s t a l s of galena experimentally deformed by 001 s l i p . At many places within the galena-rich breccia ores of H. B. and Jersey mines, mylonitic lamination (grain size from less than 1 to 5 ym) i s developed which may enclose 139 porphyroclasts of p y r i t e and of p o l y c r y s t a l l i n e sphalerite together with highly deformed fragments of dolomite marble and patches of coarser-grained galena (Fig. 37d, e). This mylonitic material, as far as can be determined (the f i n e s t grains aft e r etching are not e a s i l y resolved with the microscope), generally forms equidimensional granoblastic-polygonal textures. The coarser-grained patches of galena, by analogy with the accom-panying porphyroclasts of p y r i t e and sphalerite, may represent textural r e l i c t s which survived mylonitization and were subse-quently annealed. Such annealing might be expected to be more e f f e c t i v e , i n terms of grain boundary adjustment and grain growth, than i n the matrix as a r e s u l t of higher stored s t r a i n energy i n the r e l i c t material. Subgrain boundaries were detected by etching i n much of the coarser-grained galena, whether equidimensional or elongate i n shape (Fig. 37b). These subgrains (grain size c i r c a 5 ym) are produced by polygonization, presumably as a r e s u l t of l a t e minor deformation. Curvilinear cleavage traces a t t e s t to bend g l i d i n g also having occurred. Summary and inte r p r e t a t i o n P y r i t e , of the three sulphides, undoubtedly provides the most obvious evidence that the ores have been deformed because of i t s f a i l u r e by b r i t t l e fracture under a wide range of con-di t i o n s (Graf and Skinner, 1970), and because the r e s u l t i n g fractured grains and porphyroclasts survive annealing at least u n t i l conditions of hornblende hornfels facies are reached. 14-of Figure 37. Photomicrographs of textures and microstructures developed i n galena, etched with thio-urea + HC1. a. Polygonal textured, coarse-grained galena. Jersey mine, A-zone. Specimen CX69-78. Magnification 80X. b. Galena aggregate showing dimensional preferred orie n t a t i o n . Equant subgrains are f a i n t l y v i s i b l e within the large elongate grains. Reeves MacDonald mine, Annex zone, 950' l e v e l . Specimen RM71-47. Magnification 80X. c. Granoblastic to polygonal textured galena, showing wide grain-size v a r i a t i o n on the microscale. Subgrains are developed within the coarser-grained material on the r i g h t . Jersey mine, A-zone. Specimen CX69-73. Magnification 28X. d. Fine-grained, polygonal textured galena, associated with th i n mylonitic sphalerite layer. Jersey mine, A-zone. Specimen CX69-78. Magnification 80X. e. Very fine-grained, mylonitic galena containing porphyro-c l a s t s of p y r i t e and of p o l y c r y s t a l l i n e sphalerite. H. B. mine, X-2 zone. Specimen HB71-3. Magnification 28X. 140 Figure 37. Photomicrographs of textures and microstructures developed i n galena, etched with thio-urea + HC1. 141 Under these conditions increasing r e c r y s t a l l i z a t i o n , formation of pyrrhotite and of a second generation of p y r i t e , may a l l con-tr i b u t e to development of new textures. Textures of the other sulphides, sphalerite and galena, are lar g e l y those of r e c r y s t a l l i z a t i o n — t y p i c a l l y granoblastic to polygonal. In the H. B. and Jersey ores which are located within contact metamorphic aureoles these textures appear to r e s u l t largely from annealing r e c r y s t a l l i z a t i o n . However, i n the Reeves MacDonald ore, which i s located approximately 1000 f t away from the outermost l i m i t of a contact aureole detectable i n p e l i t i c rocks, i t i s not clear to what extent the r e c r y s t a l l i z a -t i o n textures r e s u l t from syntectonic r e c r y s t a l l i z a t i o n , from l a t e r annealing r e c r y s t a l l i z a t i o n , or from some combination of both. Grain sizes, as i l l u s t r a t e d by pyrite and sphalerite, show a progressive increase with increasing i n t e n s i t y of contact metamorphism from Reeves MacDonald to Jersey mines. In general, galena has better equilibrated textures than does sphalerite; a contrast i n behaviour which has been demon-strated experimentally i n s t a t i c r e c r y s t a l l i z a t i o n of deformed galena-sphalerite ore from Broken H i l l (Stanton and Willey, 1970) and attributed to the very low annealing a c t i v a t i o n tem-perature (perhaps as low as 10-20°C) required for grain boundary readjustment i n galena (Stanton and Gorman, 1968). Much higher temperatures (generally above 300°C) are required to produce appreciable grain growth during experimental annealing of galena aggregates (Siemes, 1964; Stanton and Gorman, 1968); growth rates 142 apparently being affected by the degree of p l a s t i c deformation and of preferred orientation previously developed i n the aggre-gates (Stanton and Willey, 1972). The o r i g i n of some of the more varied textures developed i n the sulphides of the study area can perhaps be explained by these experimental observations. In the mylonitic galena layers, patches of coarser grain size are attributed to areas of higher stored s t r a i n energy p r i o r to annealing. Both fine-grained matrix and coarse-grained lenses now exhibit granoblastic-polygonal textures and the only i n t e r n a l microstructures observed are bent cleavage planes and subgrains developed within larger i n d i v i d u a l grains, including w e l l - e q u i l i -brated polygonal-shaped grains. Sphalerite porphyroclasts within galena aggregates (whether mylonitized or not) exhibit a wide range of in t e r n a l e f f e c t s , from intense p l a s t i c deformation to t o t a l r e c r y s t a l l i z a t i o n , suggesting that sphalerite was, i n general, less responsive than galena to annealing. Layered p o l y c r y s t a l l i n e sphalerite aggregates, i n com-parison with galena, have only l o c a l , t h i n mylonitic layers developed within them. The l a t t e r have well-equilibrated poly-gonal textures whereas the unmylonitized aggregates have less well-equilibrated granoblastic textures which, i n many places, show the eff e c t s of minor def o r m a t i o n — s l i g h t bending of annealing twin lamellae, and the development of subgrains post-dating grain growth and hence annealing. Localized more intense s t r a i n — shown by kinking of twin lamellae and the development of s l i p lines—may be of the same age, or more probably i t i s r e l i c t as in the sphalerite porphyroclasts already described. 143 The widespread s l i g h t deformation and recovery e f f e c t s observed i n sphalerite and galena could have developed at any time since contact metamorphism by g r a n i t i c stocks i n the area produced annealing; f a u l t i n g continued at least u n t i l the Eocene thermal event represented by intrusion of lamprophyre dykes and alka l i n e stocks. Equivalent e f f e c t s have been described from only s l i g h t l y deformed vein-type sulphide deposits (Burn, 1971) and may be a feature of many sulphide ores as has been suggested by Stanton and Gorman (1968). In addition, i t has been suggested that creep within mine p i l l a r s and i n unsupported stopes might be s u f f i c i e n t to induce these features. However, considering sphalerite's somewhat higher annealing a c t i v a t i o n temperature (perhaps 60°C compared to 10-20°C for galena, according to Stanton and Gorman, 1968), temperatures within the mines are probably i n s u f f i c i e n t to promote recovery i n sphalerite at le a s t . FABRIC OF THE ORES Introduction The o p t i c a l determination of crystallographic preferred orientation i n opaque minerals, such as sulphides, i s d i f f i c u l t i f not impossible, p a r t i c u l a r l y where fine-grained p o l y c r y s t a l -l i n e aggregates are involved. X-ray methods have, however, been used extensively. Bradshaw and P h i l l i p s (1970) have reviewed these methods and th e i r application to petrofabric studies. They include: (a) stationary and moving camera methods (Sander and Sachs, 1930; Wenk, 1963, 1965; Starkey, 1964) 144 (b) diffractometer and texture goniometer methods (Schulz, 1949a, b; Gehlen, 1960; Higgs et al. , 1960; Davis, 1966; Baker et al. , 1969) (c) the X-ray universal stage (Paulitsch, 1963) Applications to sulphide f a b r i c s are r e l a t i v e l y few. Gehlen (1960) f i r s t discussed the application of an X-ray texture goniometer method to the determination of preferred orientation i n ore minerals, using the Schulz (1949a) r e f l e c t i o n technique. Various error sources were also investigated and examples of preferred orientation were determined for pyrrhotite, hematite, p y r i t e , sphalerite and chromite. Siemes (1964) and Siemes and Schachner-Korn (1965), using the same method, determined the fabric s developed i n "gneissic" galena (bleisehweif) and the eff e c t s on them of annealing. Experimental deformation of galena at room temperature and i t s f a b r i c development have also been studied by Siemes (1970). A similar study of sphalerite was con-ducted by Saynisch (1970) who also compared the experimentally produced f a b r i c s with those of naturally deformed sphalerite. Chakrabarti (1969) b r i e f l y compared natural f a b r i c s developed i n both ore and gangue minerals from the Zawar (Rajasthan) lead-zinc deposits which occur i n regional metamorphic t e r r a i n . An X-ray photographic method (Starkey, 1964) was used by Bertrand (1969) to te s t for preferred orientation i n the regionally meta-morphosed sulphide ore of the Normetal mine (N. W. Quebec) but subfabrics were found to be completely random and presumed annealed. 145 In t h i s study, i n v e s t i g a t i o n of p r e f e r r e d o r i e n t a t i o n i n the s u l p h i d e aggregates was undertaken t o determine the nature and degree of any c r y s t a l l o g r a p h i c p r e f e r r e d o r i e n t a t i o n deve-loped i n the or e s , and to determine what f a b r i c changes o c c u r r e d as a consequence of i n c r e a s i n g i n t e n s i t y of c o n t a c t metamorphism. In m e t a l l u r g i c a l experience, a t l e a s t , i t i s g e n e r a l l y accepted t h a t annealed f a b r i c s may e i t h e r resemble the p r e - e x i s t i n g de-formation f a b r i c , or be completely d i f f e r e n t , o r even be random (Barret and M a s s a l s k i , 1966, p. 568-569; Byrne, 1965, p. 105). However, the deformation f a b r i c s r e f e r r e d t o are g e n e r a l l y the r e s u l t of c o l d working ( p l a s t i c deformation a t low temperatures) whereas i n n a t u r a l l y o c c u r r i n g m i n e r a l assemblages the p r e -annealing f a b r i c s may r e s u l t e i t h e r from p l a s t i c deformation (c o l d working), from s y n t e c t o n i c r e c r y s t a l l i z a t i o n (hot working), or from both these p r o c e s s e s . To t e s t f o r the e x i s t e n c e of p r e f e r r e d c r y s t a l l o g r a p h i c o r i e n t a t i o n , o r i e n t e d s l a b s of s u l p h i d e s , c u t p a r a l l e l t o com-p o s i t i o n l a y e r i n g ( F o - i ) , were X-rayed u s i n g a standard P h i l l i p s t e x t u r e goniometer. The Schulz (1949a) method was used t o measure v a r i a t i o n s i n r e f l e c t i o n i n t e n s i t y of the Bragg angle f o r s e v e r a l c r y s t a l l o g r a p h i c forms of s p h a l e r i t e and galena. T h i s i n v o l v e s simultaneous r o t a t i o n about i t s own a x i s and t i l t i n g of the specimen s l a b i n the i n c i d e n t X-ray beam which permits measurement of r e f l e c t i o n i n t e n s i t i e s throughput h e m i s p h e r i c a l space above the s l a b s u r f a c e w h i l s t keeping the Bragg angle c o n s t a n t . The method s u f f e r s from the l i m i t a t i o n t h a t i t pro-v i d e s l i m i t e d coverage of the h e m i s p h e r i c a l r e f l e c t i o n geometry 146 due to defocussing of the X-ray beam when the sample i s t i l t e d to high angles. Thus coverage was r e s t r i c t e d to within 70° from the f o l i a t i o n pole. Details of instrument setting and possible error sources are given i n Appendix B. Measured r e f l e c t i o n i n t e n s i t i e s were plotted i n equal-area polar projection and contoured as multiples of a uniform d i s t r i b u t i o n , taken to be the mean in t e n s i t y expressed as unity (Baker et al., 1969). Such in t e n s i t y plots are known as pole  figures and are defined (Green et al. , 1970) as the d i s t r i b u t i o n on an equal-area projection of the poles to a l l planes of a c r y s t a l form with reference to a set of specimen coordinates. Sphalerite f a b r i c Pole figures were constructed from r e f l e c t i o n i n t e n s i t i e s obtained from (111) and (220) forms to determine the nature of preferred orientation developed i n p o l y c r y s t a l l i n e sphalerite. These are the two most intense r e f l e c t i o n s of sphalerite. In addition, (111) planes constitute the p r i n c i p a l g l i d e planes operative during p l a s t i c deformation (Buerger, 1928) and might therefore be expected to show preferred orientation. ( I l l ) Subfabric. Various patterns of preferred orienta-t i o n are i l l u s t r a t e d by the (111) r e f l e c t i o n s . These are separable into several types which can be q u a l i t a t i v e l y related to observed textural v a r i a t i o n s . (a) Specimens from Reeves MacDonald mine generally display primary r e c r y s t a l l i z a t i o n textures although these may be l o c a l l y modified ( p a r t i c u l a r l y i n the Annex zone) by areas of increased grain growth. Pole figures show a central 147 maximum of [i l l ] f a l l i n g within 20° of the normal to the specimen f o l i a t i o n , i n d i c a t i n g a preferred orientation of (111) planes p a r a l l e l to subparallel with the composition layering i n the ore (Fig. 38). The symmetry i s usually a x i a l but l o c a l departures to near orthorhombic symmetry also occur (Fig. 38a, e) .. The l a t t e r may r e s u l t from superimposition on the a x i a l f a b r i c of a l a t e r f a b r i c e l e -ment, or from modification to the a x i a l f a b r i c , for example by bend g l i d i n g — i n t h i s case about a southerly plunging axis (equivalent geometrically to the Phase 3 dextral axis recognized i n the host rocks?). The only specimen of p o l y c r y s t a l l i n e sphalerite from H. B.  mine which was analyzed was found to have a (111) subfabric very s i m i l a r — i n pattern, i n t e n s i t y and a x i a l symmetry—to those of specimens from Reeves MacDonald mine. (b) Specimens from Jersey mine, with average grain sizes two to three times larger than those of Reeves MacDonald specimens, are assumed to be highly annealed. In addition grain growth i s exaggerated i n many places as a r e s u l t of secondary recrys-t a l l i z a t i o n . Pole figures show a range of patterns i n which [i l l ] sub-maxima are dispersed increasingly outwards to form a small c i r c l e annulus 40-45° from the f o l i a t i o n normal (Fig. 39). This implies the development toward a preferred orientation of (001) planes p a r a l l e l with the layering i n the ore. Such a subfabric (Fig. 39f) vaguely resembles the "cube texture" commonly developed by annealing i n FCC metal 148 F i g u r e 38. ( I l l ) p o l e f i g u r e s f o r s p h a l e r i t e from Reeves MacDonald mine. S e c t i o n s a r e c u t p a r a l l e l w i t h c o m p o s i t i o n l a y e r i n g (Fo-i) and o r i e n t e d n o r t h - s o u t h . The average l i n e a -t i o n (Li) d i r e c t i o n i s i n d i c a t e d . The broken c i r c l e r e p r e s e n t s a r e f e r e n c e h o r i z o n t a l p l a n e . I n t e n s i t y c o n t o u r s a r e drawn a t 0.55, 0.70, 0.85, 1.00., 1.15, 1.30,>1.45 X u n i f o r m d i s t r i b u t i o n (maximum i n t e n s i t i e s a r e shown a t l o w e r r i g h t o f each f i g u r e ) . Specimen numbers and l o c a t i o n s a r e g i v e n i n T a b l e X I I I (Appendix B ) . 149 Figure 39. ( I l l ) pole figures for sphalerite from Jersey mine. Sections are cut p a r a l l e l with composition layering ( F 0 - i ) and oriented north-south. The average l i n e a t i o n (Li) d i r e c t i o n i s indicated. The broken c i r c l e represents a reference horizontal plane. Intensity contours are at 0.70, 0.85, 1.00, 1.15, 1.30,> 1.4 5 X uniform d i s t r i b u t i o n (maximum i n t e n s i t i e s are shown at lower r i g h t of each f i g u r e ) . Specimen numbers and locations are given i n Table XIII (Appendix B).. 150 sheet (Barret and Massalski, 1966, p. 570). It cannot, however, be c l e a r l y demonstrated that t h i s represents a systematic trend related to increasing i n t e n s i t y of annealing. (c) Mylonitized specimens from Jersey mine are very fine-grained and completely r e c r y s t a l l i z e d with a well developed poly-gonal texture. Pole figures show a preferred orientation i n which there i s a tendency for two concentrations of [ l l l i to develop (Fig. 40). This, i n one of the specimens, approximates an i d e a l (110) [OOl] or (110) [110] subfabric i n which there i s a tendency for (110) planes to become aligned with the composition layering (Fig. 42c). (An i d e a l sub-fabr i c i s defined as the pattern assumed by the pole figure maxima when superimposed on a standard projection (in t h i s case cubic) of the form being analyzed.) The other specimen contained both mylonitized and unmylonitized sphalerite and i s assumed, therefore, to show a hybrid f a b r i c (Fig. 40a). (220) Subfabric. Several pole figures of (220) r e f l e c -tions were also constructed (Fig. 41) to check that the (111) preferred orientations were expressed by other crystallographic forms. In p a r t i c u l a r , the (220) pole figure of the specimen from Reeves MacDonald mine (Fig. 41a) c l e a r l y confirms the existence of a central [ i l l ] maximum. Further, the d i s t r i b u t i o n of [llO] maxima suggests a weak d i r e c t i o n a l f a b r i c corresponding to the id e a l (111) [112] pattern. The (220) pole figure of the speci-men from Jersey mine i s somewhat more complex, r e f l e c t i n g the 151 i Figure 40. ( I l l ) pole figures for a. p a r t i a l l y mylonitized, and b. mylonitized sphalerite from Jersey mine. Sections are cut p a r a l l e l with the f o l i a t i o n and oriented north-south. Intensity contours are drawn at 0.85, 1.00, 1.15, 1.30, 1.45, >1.60 X uniform d i s t r i b u t i o n (maximum i n t e n s i t i e s are shown at lower r i g h t of f i g u r e s ) . Superimposed on Figure b i s the id e a l subfabric (110) [001] . Specimen numbers and locations are given i n Table XIII (Appendix B). 152 F i g u r e 41. (220) p o l e f i g u r e s f o r s p h a l e r i t e from a. Reeves MacDonald and b. J e r s e y mines. S e c t i o n s a r e c u t p a r a l l e l w i t h c o m p o s i t i o n l a y e r i n g ( F 0 - i ) and o r i e n t e d n o r t h - s o u t h . The average l i n e a t i o n ( L i ) d i r e c t i o n i s i n d i c a t e d . The b r o k e n c i r c l e r e p r e s e n t s a r e f e r e n c e h o r i z o n t a l p l a n e . I n t e n s i t y con-t o u r s a r e drawn a t 0.8, 1 .0 , 1 .2 , 1 .4 , >1.6 X u n i f o r m d i s t r i b u -t i o n (maximum i n t e n s i t i e s a r e shown a t lower r i g h t o f each f i g u r e ) . Superimposed i s t h e i d e a l s u b f a b r i c (111) [ l l2J . Specimen numbers and l o c a t i o n s a r e g i v e n i n T a b l e X I I I (Appendix B) . 153 complexity of the (111) subfabric. However, a weak 3-fold sym-metry can be detected which i s also suggestive of the i d e a l d i r e c t i o n a l f a b r i c (111) [ll2"] (Fig. 41b). Origin of sphalerite f a b r i c . Buerger (192 8) u n i a x i a l l y compressed sphalerite and showed that i t deformed by twin g l i d i n g on the system (111) [ll2] (Fig. 42a) . Saynisch (1970) found that [lio] axes were aligned with the compression axis during a x i a l deformation of p o l y c r y s t a l l i n e sphalerite. He also demonstrated, by X-ray f a b r i c analysis, that (111) [ll2] and (110) [OOl] (Fig. 42b, c) were commonly developed subfabrics i n naturally deformed sphalerite aggregates. Assuming deformation to have been produced by simple shear, he showed, by applying the theory of Schmid and Boas (1950) to the 24 t r a n s l a t i o n systems of {111$ [ll2] , that both (111) [112] and (110) [OOl] were stable "end positions." No d e t a i l s are given of the texture and microstructure of these naturally deformed sphalerite aggregates but i t i s implied that the f a b r i c s r e s u l t from p l a s t i c deformation. Nearly a l l of the Salmo material has been r e c r y s t a l l i z e d (prior to minor late straining) so that i t i s not clear from the textures whether the pre-annealing f a b r i c was produced mainly by syntectonic r e c r y s t a l l i z a t i o n , or by p l a s t i c deformation. The very weak d i r e c t i o n a l anisotropism of most of the f a b r i c s , unlike those figured by Saynisch (1970) (Fig. 42b, c ) , suggests that p l a s t i c deformation per se was not the main orienting.process; syntectonic r e c r y s t a l l i z a t i o n appears more l i k e l y . Certainly, syntectonic r e c r y s t a l l i z a t i o n would be expected under the 154 a. ( I l l ) plane [121] b. _ L _t c. Figure 42. a. Translation directions i n the (111) plane of sphalerite, b, c. ( I l l ) pole figures of naturally deformed sphalerite, showing inferred i d e a l subfabrics and possible t r a n s l a t i o n directions (from Saynisch, 1970). 155 synmetammorphic conditions of Phase 1 folding and possibly also under the submetamorphic conditions of Phase 2 f o l d i n g . Under these conditions, with estimated temperatures of approximately 425°C and 350°C respectively (±50°C), i . e . , with T/T m = 0.5-0.6 for sphalerite (where T m i s the absolute M.P.), recovery would be expected to be an important process, producing polygonization and ultimately r e c r y s t a l l i z a t i o n . It i s proposed, therefore, that the widespread preferred orientation of (111) planes p a r a l l e l with composition layering i n the ores r e s u l t s from syn-tectonic r e c r y s t a l l i z a t i o n . The weak ( 1 1 1 ) [ l l 5 ] element within the more general (111) a x i a l l y symmetric f a b r i c i s ascribed to minor, pervasive p l a s t i c deformation superimposed on the l a t t e r f a b r i c . Age of t h i s defor-mation i s problematic; t r a n s l a t i o n i s indicated as having occurred within the plane of the composition layering i n a d i r e c t i o n normal to the main f o l d axes so that i t could be related perhaps to Phase 2 folding but then would have to have survived annealing r e c r y s t a l l i z a t i o n . Indeed, there i s some evidence that t h i s may have occurred even i n Jersey mine (p. 137). It i s not known to what extent the s l i g h t deformation and recovery e f f e c t s , which post-date annealing r e c r y s t a l l i z a t i o n , contribute to the observed subfabric elements. Possibly t h i s i s limited to very minor modifications of the pre-existing sub-fabrics by bend g l i d i n g . Mylonitic sphalerite, with i t s very fine-grained poly-gonal, st r a i n - f r e e grains, has a (111) subfabric which approaches an i d e a l (110) [00l] pattern with orthorhombic symmetry. Such 156 mylonitic textures have been interpreted as forming i n zones of r e s t r i c t e d extensional flow at high s t r a i n rates (Ross, 1973). Flattening, as during Phase 2 foldi n g , could produce these mylonite zones but there i s l i t t l e evidence for t h i s within the ore zones of Jersey mine; there, re f o l d i n g , rather than closure, of Phase 1 folds occurred. It i s postulated, therefore, that the mylonite zones were formed by simple shear during the thrust movements which occurred at a late stage of Phase 2 f o l d i n g . As observed by T u l l i s et al. (1973), i n experimental deformation of quartzite, the magnitude of f i n i t e s t r a i n determines the microstructure, not whether the deformation i s a x i a l or r o t a t i o n a l . Galena f a b r i c The (200) form of galena was investigated because of i t s r e l a t i v e l y high d i f f r a c t i o n i n t e n s i t y . Measured i n t e n s i t i e s , however, were so weak for t h i s form that analyses of other forms were not made. Only specimens from Jersey mine were used, other available material being either too low i n galena content (Reeves MacDonald specimens) or of unknown orientation (H. B. specimens). (200) Subfabric. The (200) subfabric of variably mylonitized galena specimens from Jersey mine i s either random or weakly developed as might be inferred from t h e i r generally well-equilibrated, granoblastic-polygonal textures. Their pole figures, where the subfabric i s not random, show maxima r e s t r i c t e d to within 15-20° of the normal to the specimen f o l i a t i o n and i n some cases d i s t i n c t l y elongated north-northeast to south-southwest (Fig. 43). A preferred orientation of (001) planes p a r a l l e l with the composition layering (Fo-i) i s thus indicated. 157 Figure 43. (200) pole figures for galena from Jersey mine. Sections are cut p a r a l l e l with composition layering ( F 0 - i ) and oriented north-south. Broken c i r c l e represents reference h o r i -zontal plane. Average L i l i n e a t i o n d i r e c t i o n i n the f o l i a t i o n plane i s indicated. Intensity contours are drawn at 0.75, 1.00, 1.25, >1.50 X uniform d i s t r i b u t i o n (maximum i n t e n s i t i e s are shown at lower r i g h t of each f i g u r e ) . Specimen numbers and locations are shown i n Table XIII (Appendix B). 158 The elongation of the central maxima, which changes the f a b r i c symmetry from a x i a l to orthorhombic, may r e s u l t from bending of the (001) planes; such bend g l i d i n g i s attested by the l o c a l development of curviplanar cleavage i n these galena aggregates. The bend gli d e axes (from F i g . 43b, d) plunge at low angles southeast or northwest and therefore have somewhat si m i l a r orientations to Phase 3 dextral axes i n the host rocks. However, the o r i g i n of t h i s preferred orientation of (001) planes i s problematic. Mugge (1898) and Buerger (1928) ob-served that galena deformed p l a s t i c a l l y by s l i p on the system (001) [llO] (Fig. 44a) . This has been v e r i f i e d for deformation of p o l y c r y s t a l l i n e galena by L y a l l and Paterson (1966) who also offered evidence that an additional s l i p system (110) [llO] opera-ted at higher stresses when orientation was unfavourable for s l i p on (001) [llO] (Fig. 44b) . In addition, i t has been shown by Siemes (197 0) that a x i a l deformation of p o l y c r y s t a l l i n e galena at room temperature, between 0.3-5.0 kb confining pressure, res u l t s i n uniform flow and the alignment of [llO] poles p a r a l l e l with the compression axis. Conceivably, the observed (001) preferred orientation could r e s u l t from p l a s t i c deformation but textures are r e c r y s t a l -l i z e d and deformation e f f e c t s , as far as can be determined, are limited to l a t t i c e bending and subgrain development. Textures are mylonitic i n many places but the subfabric does not resemble those developed i n naturally deformed "gneissic" galena (bleisohweif) which has various well developed (200) subfabrics approximating the i d e a l (110) [001] pattern (Fig. 44c) . The 159 i] a. [on] b > Figure 44. a. Translation d i r e c t i o n s i n the (100) plane of galena. b. Translation d i r e c t i o n s i n the (110) plane of galena. c. Example of (200) pole figure of natu r a l l y deformed "gneissic" galena (from Siemes, 1970), showing inferred i d e a l sub-f a b r i c and possible t r a n s l a t i o n d i r e c t i o n s . 160 l a t t e r are considered to have been produced by shearing deforma-t i o n (Siemes and Schachner-Korn, 1965) but the a x i a l deformation experiments of Siemes (1970) would suggest that preferred orien-tation of (110) planes, p a r a l l e l with composition layering, could also be produced by f l a t t e n i n g . However, as with mylonitic sphalerite from Jersey mine, these mylonite textures are con*'..v sidered as re s u l t i n g from l o c a l i z e d shear within the galena-rich layers, perhaps related to thrusting at a late stage of Phase 2 folding. The (200) subfabric, since i t does not appear to be related to shearing, may r e s u l t from annealing r e c r y s t a l l i z a t i o n , or from weak p l a s t i c deformation (either surviving annealing or imposed on an annealed random f a b r i c ) . Dolomite f a b r i c The orientations of c-axes of dolomite i n four specimens of dolomite marble were determined, using a p o l a r i z i n g micro-scope and universal stage. Two of the specimens were from Reeves MacDonald mine and two from Jersey mine. Due to a general lack of twinning and the r e l a t i v e l y low birefringence the c-axes were measured d i r e c t l y (Turner and Weiss, 1963, p. 239). For each specimen, 2 00 grains were measured i n a pair of mutually perpen-dicul a r t h i n sections and the data combined i n a single diagram normal to the Li l i n e a t i o n d i r e c t i o n . The preferred orientations (Fig. 45) show r e l a t i v e l y consistent, strong concentrations of c-axes subperpendicular to the composition layering ( F 0 - i ) . Such patterns are apparently t y p i c a l of many dolomite tectonites (Ladurner, 1953; C h r i s t i e , 1958), i n p a r t i c u l a r the so-called S-tectonites. Neumann (1969) has produced similar 161 patterns by experimental r e c r y s t a l l i z a t i o n of Dover Plains and Knox dolomite under directed stress. Neuman also suggested, because of the common s i m i l a r i t y between the preferred orientar tions of e-axes i n r e c r y s t a l l i z e d c a l c i t e and dolomite, that s l i p and twinning processes do not contribute to the development of the preferred orientations; p l a s t i c deformation, under experi-mental conditions at least, r e s u l t s i n d i f f e r e n t e-axis sub-fa b r i c s for the two minerals r e f l e c t i n g t h e i r d i f f e r e n t trans-l a t i o n and twinning systems (Handin and F a i r b a i r n , 1955; Higgs and Handin, 1959; Griggs et al., 1960). R e c r y s t a l l i z a t i o n , i n -volving the nucleation of new s t r a i n - f r e e grains, i s proposed by Neumann (1969) as the orienting process where p l a s t i c deformation cannot be demonstrated. The dolomite specimens from the Salmo area, examined for preferred orientation, t y p i c a l l y have uniform grain sizes, granoblastic to polygonal textures and exhibit only limited f-twinning (shown by less than 5% grains). Grain size d i f -ferences, -which e x i s t between Reeves MacDonald (average 55 urn) and Jersey (average 125 um) dolomite, and the d i s t i n c t l y more polygonal texture of the l a t t e r , imply that annealing r e c r y s t a l -l i z a t i o n has affected at l e a s t the dolomite marble from Jersey mine area. There i s also a s l i g h t suggestion that preferred orientation i s more sharply developed i n the Jersey dolomite (compare maxima i n F i g . 45). The concentrations of c-axes subnormal to composition layering i n a l l the specimens are similar to those developed experimentally by a x i a l deformation and are consistent with and 162 Figure 45. Preferred orientation of dolomite e-axes (lower hemisphere, equal-area projection) i n four dolomite marbles. Sections are cut normal to the Li l i n e a t i o n . 200 grains were measured for each diagram and contours drawn at 1, 2, 3, 4, >5% per 1% area (maximum values are shown at lower r i g h t of each f i g u r e ) . a. Reeves MacDonald mine, Reeves zone "glory-hole". Specimen RM69-18. b. Reeves MacDonald mine, Reeves zone, 1900' l e v e l . Specimen RM69-60. c. Jersey mine, D-zone. Specimen CX69-47. d. Jersey mine, E-zone. Specimen CX69-43. 163 perhaps related to f l a t t e n i n g perpendicular to the layering during r e c r y s t a l l i z a t i o n , as has been suggested for c e r t a i n other dolomite tectonites (Neumann, 1969). These preferred orientations are interpreted as r e s u l t i n g from syntectonic r e c r y s t a l l i z a t i o n probably during Phase 1 deformation and possibly also during Phase 2 deformation. However, the dolomite may have been wholly, or p a r t l y , p l a s t i c a l l y deformed during Phase 2 with much of the s t r a i n being subsequently annealed out during contact metamor-phism. Experimental r e c r y s t a l l i z a t i o n of dolomite suggests that early formed, well developed f a b r i c s may be retained, or only s l i g h t l y modified, during syntectonic r e c r y s t a l l i z a t i o n or during p l a s t i c deformation followed by annealing. Such modifications to the c-axes fa b r i c s generally involve the development of small-c i r c l e g i r d l e s i n place of concentrations close to the axis of compression; these appear to r e s u l t from nucleation and growth of new s t r a i n - f r e e grains with c-axes tending to be i n c l i n e d 30-60° to those of old host grains (Neumann, 1969). Quartz f a b r i c Quartz c-axes orientations i n four quartzite and i n two quartz p h y l l i t e / s c h i s t specimens were determined by the standard universal stage method. Relatively consistent preferred orien-tations were obtained (Fig. 46). The subfabric diagrams for the four quartzites show peripheral "split-maximum" g i r d l e s with approximate orthorhombic symmetry but the symmetry axes are not symmetrically disposed with respect to specimen f o l i a t i o n and l i n e a t i o n (Fig. 46a,b,e,f). These patterns somewhat resemble, and are found i n association 164 with, the "crossed-girdle" patterns commonly developed i n other S-tectonites. The l a t t e r , however, have symmetry axes symmet-r i c a l l y disposed with respect to f o l i a t i o n and l i n e a t i o n and are interpreted as r e s u l t i n g from f l a t t e n i n g perpendicular to the f o l i a t i o n , with the l i n e a t i o n approximating the d i r e c t i o n of elongation (Sylvester and C h r i s t i e , 1968). The patterns are thus correlated, i n a general way, with s t r a i n . However, i n situations of polyphase deformation, e-axes d i s t r i b u t i o n s probably also r e f l e c t e f f e c t s of stress v a r i a t i o n and f a b r i c anisotropism i n addition to a more general type of s t r a i n . Because of t h e i r o v e r - a l l low symmetry and uniform patterns, the c-axes subfabrics of these Salmo quartzites are ascribed to more general s t r a i n than that r e s u l t i n g from f l a t t e n i n g . The development of these subfabrics i s presumed to r e s u l t from syntectonic r e c r y s t a l l i -zation during Phase 1 deformation, i . e . p r i o r to f l a t t e n i n g . The quartz phyllonite from Reeves MacDonald mine area has an i n t e r e s t i n g f a b r i c composed of two elements: (a) elongate highly strained augen with a symmetrical "crossed-girdle" pattern of c-axes (Fig. 46c), and (b) small polygonal s t r a i n - f r e e grains with a s m a l l - c i r c l e g i r d l e of c-axes normal to the f o l i a t i o n (Fig. 46d). The quartz schist from Jersey mine area has a uniform well-equilibrated polygonal texture and a weak s m a l l - c i r c l e g i r d l e of c-axess(Fig. 46g) resembling that of the small s t r a i n - f r e e grains i n the phyllonite from Reeves MacDonald mine area. Similar s m a l l - c i r c l e g i r d l e s of c-axes have been pro-duced i n experimental syntectonic r e c r y s t a l l i z a t i o n of f l i n t 165 Reeves MacDonald area J e r s e y area Figure 46. Preferred orientation of quartz c - a x e s (lower hemisphere, equal-area projection) i n four quartzites (a, b, e, f ) , a quartz phyllonite (c, d), and a quartz s c h i s t (g). Sections are cut normal to the L i l i n e a t i o n . In the quartz phyllonite, 200 elongate strained grains (c), and 200 poly-gonal s t r a i n - f r e e grains (d) were measured. In a l l other specimens 300 grains were measured. Contours drawn at 1.0, 2.0,3.0,>4.0% per 1% area (maximum values shown at lower r i g h t of each f i g u r e ) . a. Specimen RM69-23 b. Specimen RM69-24 Quartzite Range Fn., core of Salmo River a n t i c l i n e c-d. Specimen RM69-13, U. Laib mamber, overturned limb of Salmo River a n t i c l i n e e. Specimen CX69-3 f. Specimen CX69-38 g. Specimen CX69-4 Q u a r t z i t e Range Fn. J e r s e y a n t i c l i n e core of 166 i n the alpha quartz f i e l d during a x i a l compression (Green et al. , 1970), and i n a x i a l deformation experiments (under si m i l a r con-ditions) on quartzite ( T u l l i s et al., 1973). There i s , however, some doubt as to the r e l a t i v e roles of syntectonic r e c r y s t a l l i -zation and of p l a s t i c deformation i n the development of such preferred orientation. "Crossed-girdle" patterns, s i m i l a r to those observed i n quartzites naturally deformed by f l a t t e n i n g (Sylvester and C h r i s t i e , 1968), have also been produced by r e c r y s t a l l i z a t i o n during non-axially symmetric compression (Green et al., 1970) which suggests that these patterns are a more general s t r a i n equivalent of the s m a l l - c i r c l e patterns of preferred orientation. Thus the preferred orientations i n the two fine-grained quartz-rich rocks which have been examined are assumed to have been produced by f l a t t e n i n g , presumably during Phase 2 f o l d i n g . Deformation lamellae may or may not be developed i n the quartzites. Two of the four specimens contained abundant well developed lamellae. The orientations of 75 sets of lamellae were measured i n each together with the e-axes orientations of host grains. Histograms (Fig. 47) of the angular r e l a t i o n s be-tween these elements show the lamellae to be predominantly sub-basal, as commonly developed i n quartzite tectonites (Friedman, 1964; Carter and Friedman, 1965). Ave Lallement and Carter (1971) have shown that i d e n t i c a l sub-basal lamellae can be produced experimentally i n quartz at moderate temperature and low pressure and propose that natural sub-basal lamellae should form below -13 500°C for s t r a i n rates <10 /sec. In Figure 47, the "arrow 1 6 7 Figure 47. Top: Equal area projections of poles to 75 sets of deformation lamellae (arrow heads), and of c-axes of host grains (arrow t a i l s ) i n each of two quartzites (a. RM69-24 from Reeves MacDonald mine area; b. CX69-3 from Jersey mine area). Centre: Histograms of angles between lamellae pole and c-axis i n each grain. Bottom: Deduced maximum p r i n c i p a l stress d i r e c t i o n s (see text for explanation). 168 method" (joining e-axes to corresponding deformation lamellae poles) i s employed to locate the orientation of the p r i n c i p a l stress axes (Carter and Raleigh, 1969). The deduced positions indicate maximum compressive stresses oriented approximately normal to the specimen f o l i a t i o n s implying that the p l a s t i c deformation was produced by f l a t t e n i n g . For the specimen from Jersey area (Fig. 47b), t h i s orientation appears symmetrically related to Phase 2 folding deformation whereas for the specimen from Reeves MacDonald area (Fig. 47a), the orientation most close l y approximates that deduced from Phase 3 folding (Fig. 7 i ) . Annealing, as a r e s u l t of contact metamorphism, appears to have had some e f f e c t on preferred orientation of e-axes; those of Jersey specimens are very similar to, but s l i g h t l y weaker than, these of Reeves MacDonald specimens (Fig. 46). This agrees with annealing experiments i n the a-quartz f i e l d (Green et at., 1970) which have produced only weak to moderate changes i n pre-ferred orientation of e-axes (over limited time periods) p a r t i c u -l a r l y for s m a l l - c i r c l e g i r d l e patterns. Summary X-ray f a b r i c analyses show that the sulphide minerals possess varying degrees of preferred orientation. Galena, sampled from Jersey mine only, has a very weak fa b r i c and corresponding, generally well-equilibrated polygonal texture. Sphalerite, i n contrast, has well-developed, varied f a b r i c , even where coexisting with galena. Specimens of sphalerite from Reeves MacDonald mine have r e l a t i v e l y systematic subfabric elements i n which (111) planes 169 exhibit a preferred orientation p a r a l l e l with composition layering i n the ores. (220) subfabric patterns r e f l e c t t h i s same preferred orientation and also indicate a very weak d i r e c t i o n a l element for the combined f a b r i c , corresponding to (111) [ll5] which i s the twin g l i d i n g system operative i n p l a s t i c deformation of sphalerite. This element i s believed to post-date the a x i a l l y symmetric (111) subfabric and may r e f l e c t p l a s t i c deformation features observed i n the texture. Sphalerite from Jersey mine shows more varied (111) sub-f a b r i c s , ranging from Reeves MacDonald-type subfabrics to more complex, s m a l l - c i r c l e patterns of submaxima. The l a t t e r are interpreted as representing true annealing subfabrics, developed from the Reeves MacDonald patterns which are believed to repre-sent r e l a t i v e l y unmodified, pre-existing deformation fabr i c s produced by syntectonic r e c r y s t a l l i z a t i o n . Mylonitic sphalerite from conformable th i n zones within the Jersey ores has a d i s t i n c t i v e orthorhombic (111) subfabric approaching an i d e a l (110) [OOl] pattern and i s considered to r e s u l t from simple shear within the composition layering,vperhaps i n association with thrusting at a late stage of Phase 2 fol d i n g . The variably developed mylonite textures i n galena from Jersey mine are believed to have formed i n the same manner but the (200) subfabric, i f developed, i s very weak and does not resemble the patterns of preferred orientation observed i n "gneissic" galena (Siemes and Schachner-Korn, 1965). The (200) subfabric i s , therefore, considered to represent either a weak 170 a n n e a l i n g s u b f a b r i c , o r a weak s u b f a b r i c produced by s l i p on t h e system (001)[ll0] , e i t h e r s u r v i v i n g a n n e a l i n g o r superimposed on an a n n e a l e d random f a b r i c . Q u a r t z i t e s have p e r i p h e r a l "split-maximum" g i r d l e p a t -t e r n s o f c-axes, r e s e m b l i n g " c r o s s e d - g i r d l e " p a t t e r n s b u t t h e y a r e n o t s y m m e t r i c a l l y d i s p o s e d w i t h r e s p e c t t o t h e f o l i a t i o n / l i n e a t i o n . O r i e n t a t i o n s o f s u b - b a s a l d e f o r m a t i o n l a m e l l a e , measured i n two o f t h e q u a r t z i t e s , s u ggest t h a t p l a s t i c deforma-t i o n (assumed t o p o s t - d a t e s y n t e c t o n i c r e c r y s t a l l i z a t i o n ) was produced by f l a t t e n i n g . R e c r y s t a l l i z e d g r a i n s i n two f i n e - g r a i n e d q u a r t z - r i c h r o c k s were found t o have s m a l l - c i r c l e g i r d l e p a t t e r n s o f c-axes d i s p o s e d s y m m e t r i c a l l y w i t h r e s p e c t t o t h e f o l i a t i o n / l i n e a t i o n . These were i n t e r p r e t e d as i n d i c a t i n g r e c r y s t a l l i z a -t i o n a l s o produced d u r i n g f l a t t e n i n g . P r e f e r r e d o r i e n t a t i o n s o f c-axes i n f o u r d o l o m i t e m a r b l e s show s i n g l e o r s m a l l - c i r c l e maxima o r i e n t e d a p p r o x i m a t e l y normal t o c o m p o s i t i o n l a y e r i n g i n t h e m a rbles w h i c h may a l s o be i n d i c a -t i v e o f f l a t t e n i n g . A n n e a l i n g r e c r y s t a l l i z a t i o n d u r i n g c o n t a c t metamorphism has g e n e r a l l y weakened c - a x i s s u b f a b r i c s i n t h e q u a r t z - r i c h r o c k s b u t appears t o have had l i t t l e e f f e c t on c - a x i s s u b f a b r i c s i n d o l o m i t e m a r b l e , a l t h o u g h b o t h groups show e v i d e n c e o f t e x t u r a l changes. The main f a b r i c s o f t h e h o s t r o c k s a r e a s c r i b e d , t h e r e f o r e , t o s y n t e c t o n i c r e c r y s t a l l i z a t i o n w i t h minor m o d i f i c a t i o n s , i n t h e form of p l a s t i c d e f o r m a t i o n and/or r e c r y s t a l l i z a t i o n , b e i n g 171 produced, at least i n part, by f l a t t e n i n g during Phase 2 foldi n g and possibly also, i n the Reeves MacDonald area, during Phase 3 foldi n g . No subfabric elements recognized i n the sulphides can be attributed d i r e c t l y to f l a t t e n i n g , although mylonite textures i n Jersey mine can be related to Phase 2 fold i n g . It i s by no means clear what the response of sphalerite i n the Reeves MacDonald ores was to the f l a t t e n i n g which occurred there during Phase 2 folding (see Section I I I , p. 56); the r e l a t i v e roles of syn-tectonic r e c r y s t a l l i z a t i o n and p l a s t i c deformation are not known. A preferred orientation of (110) planes p a r a l l e l with the com-position layering might be expected from a x i a l deformation experiments (Saynisch, 1970) but i s not observed. Syntectonic r e c r y s t a l l i z a t i o n , as during Phase 1 foldin g , may be the main orienting process. The mechanism for the development of the preferred orientation by r e c r y s t a l l i z a t i o n i s not known but current experimental workers (e.g., Green et al. , 1970) appear to favour the "oriented growth" theory, based on the mobility of high-energy grain boundaries (Barret and Massalski, 1966, p. 579). However, i t should be noted that the thermodynamic theory of Kamb (1959) for selective grain growth, due to differences i n st r a i n energy under non-hydrostatic stress, predicts the develop-ment of preferred orientation of (111) or (001) planes i n cubic c r y s t a l s normal to the unique stress axis. 172 ORIGIN OF THE ORES Evidence from t h i s study as to the o r i g i n of the lead-zinc ores i s largely inconclusive, or, to put i t i n the ter-',.. minology of Snyder (1967), "permissive" ( i . e . , subject to dual in t e r p r e t a t i o n ) . The s t r u c t u r a l evidence shows that the ores have been penetratively deformed and are involved i n both Phase 1 and Phase 2 f o l d structures. Mineralization, therefore, pre-dates Phase 1 deformation. The age of t h i s deformation could not be defined within the study areas but, from regional s t r a t i g r a p h i c considerations, i t i s believed to have occurred during the Devonian-Mississippian hiatus. If t h i s interpretation i s correct mineralization could have occurred at any time between the Lower Cambrian and Devonian periods, although similar mineralization i n the Nelway/Metaline formation may further l i m i t t h i s i n t e r v a l to between Middle Cambrian and Devonian periods. The l o c a l s t ratigraphic evidence shows that the ores are located i n a dolomitic facies of the Lower Cambrian Reeves member and that they are e s s e n t i a l l y strata-bound. The Reeves member i s considered to have been deposited i n a shelf environment with the l o c a l i z e d dolomitic facies having developed on shallow banks. Where the host dolomite marble has not been r e c r y s t a l l i z e d during contact metamorphism, the sulphides ( p a r t i c u l a r l y pyrite) are commonly associated i n the marble with minor amounts of graphir t i z e d carbonaceous material and with quartz. Mineralogy of the ores i s simple, comprising mainly sphalerite, p y r i t e and galena with only minor pyrrhotite and 173 and chalcopyrite l o c a l l y i n addition. Cobalt and n i c k e l contents of p y r i t e are suggestive of a syngenetic-diagenetic o r i g i n for that mineral at l e a s t . Where least affected by contact metamor-phism, sphalerite has uniformly low iron and manganese contents which are suggestive of a low temperature of formation. The sulphur isotopic character of the Salmo ores (Sangster, 1970b) indicates derivation by biogenic reduction of sea water sulphate; <5S31* values are p o s i t i v e and r e s t r i c t e d i n range for the i n d i v i d u a l deposits. Sangster has interpreted these as i n d i c a t i n g a syngenetic o r i g i n for the ores as the 6 S ^ values are somewhat i s o t o p i c a l l y l i g h t e r than those determined for sea water sulphate of Cambrian age (Thode and Monster, 1965). However, i n practice i t i s not possible to d i f f e r e n t i a t e between isotopic compositions of Cambrian and Ordovician sulphates so that, although the sulphur i s derived from sea water, i t need not be syngenetic with respect to the host rocks. Lead isotope abundances i n the Salmo deposits are anama-lous ( S i n c l a i r , 1966; Reynolds and S i n c l a i r , 1971). According to Snyder (1968), anomalous leads which are c h a r a c t e r i s t i c of the M i s s i s s i p p i Valley deposits are diagnostic of an epigenetic o r i g i n for the ores. However, numerous M i s s i s s i p p i Valley type deposits have non-radiogenic or single-stage leads, for example the Pine Point and Monarch deposits (Baadsgaard et al. , 1965; LeCouteur, 1973) which suggest that the lead isotopic character of ores i s not diagnostic as to o r i g i n . In many of the above c h a r a c t e r i s t i c s , s t r a t i g r a p h i c , mineralogical and i s o t o p i c , the Salmo deposits resemble t y p i c a l 174 M i s s i s s i p p i Valley deposits, as described by Ohle (1959) and by Snyder (1967, 1968). On similar grounds, Muraro (1962) con-sidered the Duncan deposit, occurring i n a very s i m i l a r geologi-c a l setting 80 miles north of Salmo (Fig. 1), to have been a M i s s i s s i p p i Valley type deposit p r i o r to regional metamorphism. Some of the obvious differences i n character, such as the fine grain s i z e , r e l a t i v e l y homogeneous nature of the sulphides and the lack of voids and open spaces, can be attributed to penetra-t i v e deformation and r e c r y s t a l l i z a t i o n . Current theories as to the genesis of M i s s i s s i p p i Valley type deposits invoke various f l u i d transport and p r e c i p i t a t i o n systems operative at the flanks of large sedimentary basins (Callahan, 1964; Jackson and Beales, 1967; White, 1968; Beales and Onasick, 1970; Hoagland, 1971; and others). The transporting f l u i d s are generally considered, as a r e s u l t of f l u i d i n c l u s i o n studies (Hall and Friedman, 1963; Roedder, 1967), to be chloride brines of lar g e l y connate o r i g i n , with l o c a l contributions of meteoric or magmatic water being invoked i n s p e c i f i c s i t u a t i o n s . -Source of the brines and transported metals i s assumed to be shales of the sedimentary basins undergoing diagenesis, compac-tio n and eventual b u r i a l metamorphism. Two models for these metal-bearing brines are envisaged—one sulphur-rich and involving metal-sulphide complexes, and the other sulphur-deficient and involving metal-chloride complexes (White, 1968). I t was to the second of these that Jackson and Beales (1967) subscribed. They proposed that sulphur-deficient brines escaping from deep sedi-mentary basins mix at shallow depths with H2S-rich brines i n 175 c a r b o n a t e r e s e r v o i r s , r e s u l t i n g i n p r e c i p i t a t i o n o f o r e m i n e r a l s . A v a r i a t i o n on t h e i r model i s suggested f o r t h e f o r m a t i o n o f t h e Salmo o r e s . B l a c k s h a l e s o f t h e A c t i v e f o r m a t i o n o f O r d o v i c i a n -Devonian age may have been t h e s o u r c e f o r l e a d and z i n c . The c l o s e a s s o c i a t i o n o f p y r i t e (Co:Ni r a t i o s <1) w i t h g r a p h i t i z e d carbonaceous m a t e r i a l i n t h e d e p o s i t s s u g g e s t s t h a t a s u l p h i d e -r i c h environment may have been d e v e l o p e d s y n g e n e t i c a l l y o r d i a g e n e t i c a l l y i n t h e h o s t c a r b o n a t e s and hence been a v a i l a b l e t o p r e c i p i t a t e o r e s from z i n c - and l e a d - b e a r i n g b r i n e s moving upward and eastward out o f t h e s h a l e b a s i n . Such a model would s a t i s f y b o t h t h e s u l p h u r and l e a d i s o t o p i c d a t a . The n a t u r e o f t h e o r e - b e a r i n g s t r u c t u r e s i n t h e Salmo d e p o s i t s p r i o r t o d e f o r m a t i o n i s : o b s c u r e . B r e c c i a s a r e e x t e n -s i v e l y d e v e l o p e d and a r e i n t e r p r e t e d as b e i n g l a r g e l y o f t e c t o n i c o r i g i n but t h i s does n o t p r e c l u d e t h e p r i o r e x i s t e n c e o f b r e c c i a s o f o t h e r o r i g i n s — b y s e d i m e n t a r y p r o c e s s e s , o r by s o l u t i o n and c o l l a p s e . Indeed, i n p l a c e s d o l o m i t e b r e c c i a r e s e m b l e s c r a c k l e b r e c c i a b u t t h i s resemblance may be s u p e r f i c i a l as a wide v a r i e t y o f t r a n s p o s i t i o n s t r u c t u r e s a f f e c t t h e d o l o m i t e m a r b l e . SECTION VI SUMMARY AND CONCLUSIONS STRUCTURE The structures of the three mine areas reveal a complex history involving at least three phases of fo l d i n g : Phase 1 overturned, n e a r - i s o c l i n a l folds of "s i m i l a r " type, with westward vergence. Phase 2 upright, asymmetric folds of flattened " f l e x u r a l -s l i p " type, with westward vergence. These are associated with westward-directed thrust f a u l t s . Phase 3 monoclinal folds and kink bands forming a conjugate system with monoclinic symmetry. Deduced maximum p r i n c i p a l stress directions are oriented approxi-mately north-south, suggesting an association with northward-directed thrust f a u l t s . Shearing and transposition i n the cores of Phase 1 folds indicate that closure and f l a t t e n i n g of these structures occurred, i n addition to re f o l d i n g , during Phase 2 deformation. Culminations and depressions i n the attitude of Phase 1 l i n e a r structures r e s u l t from interference between Phase 1 and Phase 2 f o l d struc-tures whereas broad culminations and depressions a f f e c t i n g both Phase 1 and Phase 2 l i n e a r structures r e s u l t from Phase 3 f o l d i n g . 176 177 The marked curvature of the southern Kootenay Arc near 49°N i s believed to be a composite e f f e c t produced by (i) souths, ward developing divergence between Phase 1 and Phase 2 struc-t u r a l trends, and ( i i ) northward thrusting and associated steeply plunging monoclinal and kink folding of Phase 3 age. The chronology of these phases of deformation cannot be determined within the mine areas although i t can be shown that the l a s t phase must pre-date g r a n i t i c i n trusion for which a minimum age of 100 m.y. B.P. was determined. SULPHIDE DEPOSITS The tabular sulphide bodies are shown to have been involved i n both Phase 1 and Phase 2 f o l d i n g . Layering within the sulphides and i n the ores p a r a l l e l s composition layering i n the host dolomite marbles and some places outlines mesoscopic folds of both ages. In other places, the sulphides may be trans-posed along the Fi f o l i a t i o n . Internal deformation i s indicated by the development of augen/flaser structures involving both sulphides and marble, and by the development of mylonitic layers within the sulphides, sphalerite and galena. In many places too, the sulphides form the matrix to extensive tabular bodies of breccia which are e s s e n t i a l l y conformable with the composition layering. In the past, these were interpreted as mineralized breccias but are now interpreted as being largely of post-minera-l i z a t i o n , tectonic o r i g i n r e s u l t i n g from d i f f e r e n t i a l movement between dolomite marble and more highly d u c t i l e sulphide, and also between sulphides of d i f f e r e n t d u c t i l i t i e s . Detached folds within these breccia bodies display no systematic geometry and 178 and cannot be a s s i g n e d t o any p a r t i c u l a r phase o f f o l d i n g . M i c r o s t r u c t u r a l e v i d e n c e f o r i n t e r n a l d e f o r m a t i o n i s g i v e n m a i n l y by p y r i t e w h i c h t y p i c a l l y forms f r a c t u r e d g r a i n s and augen w i t h i n e q u i d i m e n s i o n a l , r e c r y s t a l l i z e d s p h a l e r i t e and/or g a l e n a . The d e p o s i t s a r e c o n s i d e r e d t o be u l t i m a t e l y o f e p i -g e n e t i c o r i g i n and were p r o b a b l y o f M i s s i s s i p p i V a l l e y t y p e p r i o r t o d e f o r m a t i o n and metamorphism. They a r e t h u s n o t b e l i e v e d t o d i f f e r f u n d a m e n t a l l y from t h e M e t a l i n e d e p o s i t s o f M i d d l e Cambrian age; t h e d i f f e r e n c e s t h a t do e x i s t p r o b a b l y r e s u l t i n g from ( i ) s l i g h t f a c i e s d i f f e r e n c e s i n t h e h o s t c a r b o n a t e s , ( i i ) more i n t e n s e d e f o r m a t i o n , and ( i i i ) t h e more complex meta-morphic h i s t o r y o f t h e Salmo d e p o s i t s . DEFORMATION AND REGIONAL METAMORPHISM The e f f e c t s o f d e f o r m a t i o n and r e g i o n a l metamorphism on th e s u l p h i d e s a r e r e l a t i v e l y o b s c u r e , l a r g e l y because t h e y i n v o l v e r e c r y s t a l l i z a t i o n w h i c h i n many p l a c e s i s o v e r p r i n t e d by t h e e f f e c t s o f c o n t a c t metamorphism; o f t h e t h r e e d e p o s i t s , t h e Reeves MacDonald i s l e a s t a f f e c t e d by t h e o v e r p r i n t i n g . S p h a l e -r i t e from i t shows re m a r k a b l e homogeneity o f c o m p o s i t i o n on t h e m i c r o s c a l e , as de t e r m i n e d s e m i - q u a n t i t a t i v e l y by e l e c t r o n m i c r o -probe. T e x t u r e s a l s o t e n d t o be more u n i f o r m , w i t h p y r i t e g e n e r a l l y e x h i b i t i n g t h e e f f e c t s o f b r i t t l e f r a c t u r i n g , and s p h a l e r i t e and g a l e n a d i s p l a y i n g t y p i c a l l y g r a n o b l a s t i c - p o l y g o n a l t e x t u r e s and g e n e r a l l y equant g r a i n shapes. X-ray f a b r i c d e t e r m i n a t i o n s show t h a t s p h a l e r i t e a g g r e -g a t e s ,, m a i n l y from Reeves MacDonald b u t a l s o l o c a l l y i n H. B. and J e r s e y mines, have w e l l d e v e l o p e d p r e f e r r e d o r i e n t a t i o n o f 179 (111) p l a n e s p a r a l l e l w i t h c o m p o s i t i o n l a y e r i n g i n t h e o r e . The o r i g i n o f t h i s w i d e l y d e v e l o p e d f a b r i c i s a s c r i b e d t o s y n t e c -t o n i c r e c r y s t a l l i z a t i o n . Conformable, t h i n m y l o n i t e l a y e r s w i t h i n the s p h a l e r i t e a g g r e g a t e s , a t J e r s e y mine, have a q u i t e d i f f e r e n t s u b f a b r i c w h i c h approaches an i d e a l (110) [bol] p a t t e r n and has o r t h o r h o m b i c as opposed t o a x i a l symmetry. The m y l o n i t e t e x t u r e s , a l s o d e v e l o p e d i n g a l e n a from J e r s e y mine, a r e con-s i d e r e d t o be t h e r e s u l t o f i n t e n s e movement caused by s i m p l e shear d u r i n g Phase 2 f o l d i n g . A weak ( l l l ) [ l l 2 J element w i t h i n the more g e n e r a l (111) s p h a l e r i t e f a b r i c p r o b a b l y r e s u l t s from p l a s t i c d e f o r m a t i o n w i t h s l i p b e i n g i n d i c a t e d w i t h i n t h e l a y e r i n g and a c t i n g i n a d i r e c t i o n a p p r o x i m a t e l y normal t o t h e Phase,1/ Phase 2 f o l d a x i a l t r e n d s . There i s w i d e s p r e a d t e x t u r a l e v i d e n c e o f minor p l a s t i c d e f o r m a t i o n i n t h e form o f s l i g h t l a t t i c e b e nding and s u b g r a i n development (observed i n b o t h s p h a l e r i t e and g a l e n a ) ; much o f t h i s a p p a r e n t l y p o s t - d a t e s g r a i n growth and hence a n n e a l i n g . However, l o c a l more i n t e n s e d e f o r m a t i o n shown by k i n k i n g and d e f o r m a t i o n t w i n n i n g i n s p h a l e r i t e a l o n e may p r e -d a t e a n n e a l i n g , and may c o n t r i b u t e t o t h e obser v e d weak (111) [ l l2] s u b f a b r i c element. O p t i c a l d e t e r m i n a t i o n s were a l s o made o f q u a r t z and d o l o -m i t e f a b r i c s . Q uartz c-axes d i s p l a y " s p l i t maximum" p e r i p h e r a l g i r d l e s w h i c h a r e s l i g h t l y asymmetric w i t h r e s p e c t t o f o l i a t i o n / l i n e a t i o n and a r e b e l i e v e d t o r e f l e c t a g e n e r a l t y p e o f s t r a i n r e s u l t i n g from s y n t e c t o n i c r e c r y s t a l l i z a t i o n d u r i n g Phase 1 d e f o r -m a t i o n . Quartz d e f o r m a t i o n l a m e l l a e were used t o d e r i v e p r i n c i p a l s t r e s s d i r e c t i o n s w h i c h i n d i c a t e t h a t t h e l a m e l l a e were produced 180 during f l a t t e n i n g ; the orientations of the maximum p r i n c i p a l stress axes suggesting that f l a t t e n i n g occurred during Phase 2 deformation (Jersey mine area) and possibly during Phase 3 defor-mation (Reeves MacDonald mine area). R e c r y s t a l l i z e d grains from a quartz phyllonite and a quartz schist (contact metamor-phosed) have c-axis subfabrics i n which s m a l l - c i r c l e g i r d l e s are developed normal to the f o l i a t i o n which indicates that recrys-t a l l i z a t i o n , at least l o c a l l y , was also produced by f l a t t e n i n g . Dolomite displays c-axes patterns strongly concentrated subnormal or normal to composition layering which may also be i n d i c a t i v e of f l a t t e n i n g although i t i s not clear what the r e l a t i v e roles of syntectonic r e c r y s t a l l i z a t i o n and p l a s t i c deformation (with subsequent annealing) were i n the development of t h i s subfabric. CONTACT METAMORPHISM The conditions of contact metamorphism and some, at l e a s t , of i t s e f f e c t s on the sulphide deposits have been investigated. The Reeves MacDonald deposit i s located close to the detectable l i m i t of a contact aureole, the H. B. deposit l i e s within an outer aureole (albite-epidote horfels facies) and the Jersey deposit i s located mainly within an inner aureole (hornblende hornfels f a c i e s ) . Only i n the l a s t case can the contact aureole be s p a t i a l l y related to an in t r u s i v e igneous source. Estimated temperatures attained during contact metamorphism are i n the range 425-600°C (±25.°) for an assumed t o t a l pressure of 1.5 kb. Grain sizes of sphalerite and p y r i t e show a r e l a t i v e l y systematic increase i n diameter with increasing metamorphism. Grain shapes are t y p i c a l l y equant (although not e x c l u s i v e l y ) , 181 w i t h s p h a l e r i t e t e n d i n g t o have g r a n o b l a s t i c t e x t u r e and g a l e n a a w e l l d e v e l o p e d p o l y g o n a l t e x t u r e . P y r i t e , however, d e v e l o p s p o l y g o n a l g r a i n b o u n d a r i e s o n l y under c o n d i t i o n s o f h o r n b l e n d e h o r n f e l s metamorphism, whereas s p h a l e r i t e , under t h e s e c o n d i -t i o n s , d e v e l o p s more i r r e g u l a r b o u n d a r i e s as a consequence o f e x a g g e r a t e d g r a i n growth. D e f i n i t e changes t o t h e (111) p r e -f e r r e d o r i e n t a t i o n o f s p h a l e r i t e a g g r e g a t e s a l s o b e g i n t o o c c u r under t h e s e c o n d i t i o n s , perhaps as a r e s u l t o f t h i s e x a g g e r a t e d g r a i n growth. There i s some s u g g e s t i o n t h a t t h e new a n n e a l i n g s u b f a b r i c u l t i m a t e l y approaches a p a t t e r n i n w h i c h (001) p l a n e s ar e d e v e l o p e d p a r a l l e l w i t h t h e c o m p o s i t i o n l a y e r i n g . G a l e n a , r e c r y s t a l l i z e d under t h e s e c o n d i t i o n s , has e i t h e r a random f a b r i c o r a p r e f e r r e d o r i e n t a t i o n o f (001) p l a n e s p a r a l l e l w i t h c o m p o s i t i o n l a y e r i n g but t h e o r i g i n o f t h i s i s u n c e r t a i n as a comparison c o u l d not be made w i t h l e s s h i g h l y a nnealed m a t e r i a l ; p o s s i b l y i t i s r e l a t e d t o p l a s t i c d e f o r m a t i o n on t h e system (001) [no] . Seventy-one a n a l y s e s o f minor element c o n t e n t s o f s p h a l e r i t e and p y r i t e i l l u s t r a t e c e r t a i n m i n e r a l o g i c a l changes a l s o o c c u r r i n g w i t h i n c r e a s i n g metamorphism. Thus s p h a l e r i t e shows a p r o g r e s s i v e , i f not v e r y s y s t e m a t i c , i n c r e a s e i n i r o n , manganese and cadmium c o n t e n t s . A t t h e h i g h e s t metamorphic gr a d e , c h a l c o p y r i t e and p y r r h o t i t e may l o c a l l y be e x s o l v e d from s p h a l e r i t e w h i c h i n g e n e r a l becomes much l e s s homogeneous i n c o m p o s i t i o n . P y r i t e shows s l i g h t changes i n n i c k e l c o n t e n t w i t h i n c r e a s i n g metamorphism w h i c h may o r may not be s i g n i f i c a n t . Under t h e h i g h e r c o n d i t i o n s o f h o r n b l e n d e h o r n f e l s f a c i e s , i t b e g i n s t o break down t o p y r r h o t i t e and, i n t h e J e r s e y d e p o s i t , 182 forms a s p o r a d i c a l l y d e v e l o p e d d i s e q u i l i b r i u m assemblage: s p h a l e r i t e + p y r i t e + p y r r h o t i t e i n w h i c h t h e s p h a l e r i t e c o n t a i n s l e s s t h a n 13 mole % FeS. The c e n t r a l c o n c l u s i o n a r i s i n g from t h i s s t u d y i s t h a t t h e s u l p h i d e d e p o s i t s have i n d e e d been deformed and t h a t t h e y have been i n v o l v e d i n a l l phases o f d e f o r m a t i o n , i n r e g i o n a l metamorphism and i n c o n t a c t metamorphism. The v a l u e o f a p p l y i n g p e t r o f a b r i c t e c h n i q u e s t o opaque m i n e r a l s has h o p e f u l l y been demonstrated; s y n t e c t o n i c r e c r y s t a l l i z a t i o n b e i n g an even more c r y p t i c p r o c e s s i n s u l p h i d e s t h a n i n o t h e r r o c k s . 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In: Tectonic history and mineral deposits of the western C o r d i l l e r a . Can. Inst. Min. Metall. Spec. Vol. 8_, 27-45. . 1970. Summary and discussion. In: Structure of the southern Canadian C o r d i l l e r a . Geol. Assoc. Can. Spec. Paper 6_, 155-166. Whishaw, Q. G. 1954. The Jersey lead-zinc deposit, Salmo, B. C. Econ. Geol. 49_, 521-529. White, D. E. 1968. Environments of generation of some base-metal ore deposits. Econ. Geol. 6_3_, 301-331. White, W. H. 1949. Reeves MacDonald Mine. B. C. Dept. Mines Ann. Rept. 1949, A169-A174. Williams, K. L. 1967. Electron probe microanalysis of sphalerite. Am. Mineral. 5_2, 475-492. Winkler, H.G.F. 1967. Petrogenesis of metamorphic rocks. Springer-Verlag, N. Y., 237 p. Yates, R. G. 1970. Geologic background of the Metaline and Northport mining d i s t r i c t s . Washington Div. Mines and Geol. B u l l . 61, 19-39. , Becraft, G. E., and Campbell, A. B. 1966. Tectonic framework of northeastern Washington, northern Idaho, and northwestern Montana. In: Tectonic history and mineral deposits of the western C o r d i l l e r a . Can. Inst. Min. Metall. Spec. Vol. 8_, 47-59. , Engels, J . C. 1968. Potassium-Argon ages of some igneous rocks i n northern Stevens county, Washington. U. S. Geol. Surv. Prof. Paper 600-D, D242-D247. Zeuger, D. H. 1972. Significance of supratidal dolomitization i n the geologic record. B u l l . Geol. Soc. Am. 83, 1-12. APPENDIX A MAGNESIAN CALCITE-DOLOMITE GEOTHERMOMETRY The X-ray d i f f r a c t i o n method of Graf and Goldsmith (1955, 1958) was used to determine equilibrium temperatures of coexisting c a l c i t e and dolomite. The d-spacing (112) of mag-nesian c a l c i t e i n the samples was measured r e l a t i v e to the (111) peak of an i n t e r n a l s i l i c o n standard (26 = 28.466°), each sample being o s c i l l a t e d at 1/2° 28/min three times across the relevant peaks. ^ ( 1 1 2 ) w a s *-hen found for each sample by subtracting o the mean d, x from d, . for pure c a l c i t e (3.036A). From t h i s ( 1 1 2 ) ( 1 1 2 ) the mole % MgCC-3 i n the c a l c i t e of each sample was determined using the Ad, . vs. mole % MgCC-3 graph of Graf and Goldsmith 1 1 1 2 ; (1955). The equilibrium temperature was then determined from the calcite-dolomite solvus curve of Goldsmith and Newton (1969) which extends down to 400°C (equivalent to approximately 2 mole % MgCG-3 i n c a l c i t e ) . The 29 angle of the relevant peaks cannot be measured with greater accuracy than +0.025 26 which i s approximately equivalent to ±0.8 mole % MgC03 or ±30°C. 197 Table XI. 6I112 and estimated temperatures of c r y s t a l l i z a t i o n of magnesian c a l c i t e s from Reeves MacDonald and Jersey mines. Sample number Location di i 2 (&) A d i i 2 * ( A ) 0 Mean Adii 2(A) ± Std. Dev. Mole % MgC03 Minimum temp. (°C) REEVES MACDONALD MINE RM69-65 1900' l e v e l . Reeves zone 3.0297 0.0060 RM69-75 RM69-39 550' l e v e l , E. MacDonald zone 460' l e v e l , E. MacDonald zone 3.0307 3.0269 0.0050 0.0088 0.0066±0.0014 3.2±0. 5 450125 RM69-81 420' l e v e l , E. MacDonald zone 3.0292 0.0065 JERSEY MINE CX69-6 SW of Jersey town-site 3.0248 0.0109 CX69-24 CX69-74 70G haulage d r i f t , G-zone 74J r i b p i l l a r , J-zone 3.0257 3.0261 0.0100 0.0096 0.009110.0019 4.0±0. 7 490125 CX69-92 671F p i l l a r , F-zone 3.0299 0.0058 0 * A d i i 2 = d i i 2 (pure c a l c i t e ) - d i i 2 (sample) where d i i 2 (pure c a l c i t e ) = 3.0357 A APPENDIX B X-RAY TEXTURE GONIOMETER ANALYSIS OF PREFERRED ORIENTATION An X-ray analysis of preferred orientation i n poly-c r y s t a l l i n e sphalerite and galena samples was carr i e d out using a Norelco diffractometer unit with standard P h i l l i p s texture goniometer attachment belonging to the Department of Metallurgy, University of B r i t i s h Columbia. The Schulz (1949a) r e f l e c t i o n technique was used. Its application to sulphides has been explored by Gehlen (1960) and to deformed quartz aggregates by Baker et al. (1969). More general descriptions of the method are given by C u l l i t y (1956, p. 285-292) and Barret and Massalski (1966, p. 200-203). Sample preparation Oriented ore samples were cut p a r a l l e l with composition layering. A reference d i r e c t i o n , usually the average L i d i r e c -t i o n for that l o c a l i t y , was marked on the cut plane. P o l y c r y s t a l -l i n e samples of sphalerite or galena, as homogeneous as possible i n the plane, were selected and oriented, and small plane p a r a l l e l slabs (approximately 15-20 mm square by 2 mm thick) prepared. The upper surfaces were then ground and f i n e l y polished. The numbers and locations of a l l specimens used are given i n Table XIII. 199 200 Technique The geometry of the goniometer set-up i s i l l u s t r a t e d i n F i g u r e 48. The specimen s l a b was o r i e n t e d a t an angle 8 to the i n c i d e n t beam (so t h a t the Bragg angle, 20, f o r the m a t e r i a l being analyzed i s s a t i s f i e d ) . The i n c i d e n t beam (Ni f i l t e r e d Cu Ka r a d i a t i o n generated a t 35 kv and 13 mA) i r r a d i a t e s the specimen over a narrow r e c t a n g u l a r area. The s l a b i s r o t a t e d i n i t s own plane (a r o t a t i o n ) through 360° i n 8 minutes and s i m u l -t a n e o u s l y t i l t e d (<£ r o t a t i o n ) 5° sideways i n the i n c i d e n t beam f o r each s u c c e s s i v e a ; r o t a t i o n so t h a t the r e f l e c t i o n geometry assumes a s p i r a l c o n f i g u r a t i o n . During these r o t a t i o n s the s l a b i s a l s o o s c i l l a t e d i n i t s own plane p e r p e n d i c u l a r t o the i n c i d e n t beam d i r e c t i o n so t h a t a l a r g e r s u r f a c e area o f the specimen i s i r r a d i a t e d . The d i f f r a c t e d beam i s r e c e i v e d a t a g e i g e r counter and i n t e n s i t i e s are recorded on a s t r i p c h a r t w i t h a speed of 0.5 i n c h per minute. S c a l e f a c t o r and m u l t i p l i e r s e t t i n g s on the r a t e meter were adjus t e d so t h a t the f u l l range of the c h a r t r e c o r d e r was used. The s h o r t e s t time c o n s t a n t s , g e n e r a l l y 8-16 seconds, which y i e l d e d r e l a t i v e l y smooth p r o f i l e s were used,.:as recommended by Baker et al. (1969). T i l t i n g (ti r o t a t i o n ) causes p r o g r e s s i v e r e d u c t i o n i n i n t e n s i t y of the d i f f r a c t e d beam due to d e f o c u s s i n g of the p r i -mary beam. R e f l e c t i o n scans were made only up t o t i l t angles of 70° which i s the normal l i m i t f o r t h i s technique because of severe r e d u c t i o n i n i n t e n s i t y . In t h i s study the specimen was i r r a d i a t e d over a narrow r e c t a n g u l a r area approximately 5 mm x 1 mm. as i n d i c a t e d by a f l u o r e s c e n t t a r g e t . The width of t h i s area i s b e l i e v e d t o have caused i n c r e a s e d d e f o c u s s i n g and hence 201 F i g u r e 48. Geometry of t h e P h i l l i p s X-ray t e x t u r e g o n i o m e t e r s e t - u p f o r r e f l e c t i o n and t r a n s m i s s i o n modes. 202 absorption of the incident beam with increasing angles of t i l t . In d i f f e r e n t goniometer set-ups described by Barrett and Massalski (1966, p. 202) and Gehlen (1960), specimens were ir r a d i a t e d over narrower rectangular areas (e.g., 8 mm x 0.5 mm and 3.7 mm x 0.6 mm respectively). To correct for t h i s e f f e c t , empirical curves were established by scanning a prepared specimen of randomly oriented sphalerite and a near-random specimen of naturally occurring galena. These curves, corrected for background, i l l u s t r a t e the decrease i n i n t e n s i t y of the d i f f r a c t e d beam with increasing t i l t (Fig. 49). Using these curves, the in t e n s i t y (or pole density q) i n the deformed specimen at any point on the s p i r a l scan path (defined by the coordinates a , cj>) i s given by: q(a, cj>) * (Baker et at., 1969) random The background corrections ( Ij 3] Cg) were made by setting the specimen o f f the Bragg angle and recording i n t e n s i t i e s at several values of cj>. I n t e n s i t i e s are read off the chart record at 5° i n t e r -vals of a, giving 504 data points for each r e f l e c t i o n scan to (j) = 70°. The values are then corrected and plotted i n s p i r a l configuration on an equal-area polar projection. These are contoured, as multiples of a uniform d i s t r i b u t i o n (taken to be the mean in t e n s i t y expressed as un i t y ) , to produce a pole figure. 200 g a l e n a T I L T ANGLE $ F i g u r e 49. I n t e n s i t y c o r r e c t i o n c u r v e s e s t a b l i s h e d f r o m r e f l e c t i o n s c a n s o f r andom s p e c i m e n s . 204 Accuracy of the technique Possible sources of inaccuracy i n the technique have been explored by Gehlen (1960) and include those r e s u l t i n g from: (a) specimen shape and misalignment (b) grain size e f f e c t s (c) e f f e c t s of d i f f e r e n t minerals i n the specimen (d) " b u i l t - i n " e f f e c t s — a rotation at constant angular v e l o c i t y ; collimator shape These problems were treated during t h i s study as described below. (a) Specimen shape and misalignment A fluorescent target was used for aligning specimens and checking that the incident beam did not leave the specimen during rotation and o s c i l l a t o r y t r a n s l a t i o n . Alignment was also checked by testing at high t i l t angles (cf>) that the specimen was s t i l l on the appropriate Bragg angle. (b) Grain size e f f e c t s i . O s c i l l a t i o n i n the plane of the specimen helps reduce the e f f e c t of d i f f r a c t i o n by large i n d i v i d u a l grains. In t h i s study fine-grained sulphides (e.g., c i r c a 100 urn sphalerite from Reeves MacDonald mine) were o s c i l l a t e d ±4.5 mm whereas coarser-grained sulphides (e.g., c i r c a 300 ym sphalerite from Jersey mine) were o s c i l l e r a t e d ±7.5 mm. i i . Haessner (1958) has shown that i d e a l l y 10** to 10 5 grains should be i r r a d i a t e d for representative and hence repro-ducible pole-figures to be obtained. This condition appears to have been s a t i s f i e d for specimens of Reeves MacDonald sphalerite and Jersey galena analyzed, but not i n general for specimens of 205 Jersey sphalerite i n each of which approximately 103. grains were i r r a d i a t e d . (c) E f f e c t s of d i f f e r e n t minerals i n the specimen None of the specimens were monomineralic. A l l con-tained a proportion of dolomite and/or py r i t e i n addition to the main sulphide of i n t e r e s t . A few contained both sphalerite and galena. Two possible e f f e c t s of these associations are: (i) i n t e r f e r i n g r e f l e c t i o n s and ( i i ) reduction i n i n t e n s i t i e s due to r e l a t i v e l y high absorbances of associated minerals (Table XII). The f i r s t e f f e c t was r e s t r i c t e d to associations of sphalerite and p y r i t e and was minimized as far as possible by selecting specimen slabs with the lowest p y r i t e concentrations (0-5% by volume). The second e f f e c t was most serious where accessory minerals had higher l i n e a r absorption c o e f f i c i e n t s than the mineral being analyzed, e.g., galena or p y r i t e occurring with sphalerite. This e f f e c t has been quantified by Gehlen (1960) but i t s application i s v a l i d only i f there are no overlapping peaks, component grains are randomly d i s t r i b u t e d , and grain size i s very small i n comparison with mean depth of penetration (1/y for the material being analyzed). Only the second of these conditions could be s a t i s f i e d so that i n the few cases where the specimen contained both sphalerite and galena i n near equal proportions, analyses were made only for the more highly ab-sorbing galena f r a c t i o n s . 206 Table XII. Absorption c o e f f i c i e n t s , 20 angles (after Gehlen, 1960), and other relevant data for the mineral assemblages analyzed. Density (g/cm3) Cu U*(cm2/g) Ka y (cm - 1) Cu Ka 29 hkl Interfering r e f l e c t i o n s Sphalerite 4.09 70 285 28.55 47.60 111 220 Pyrit e P y r i t e Galena 7.58 221 1674 30.08 200 -Pyrite 5.02 200 1002 28.53 47.46 111 220 -Dolomite 2.85 50 143 30.96 104 -u* = mass absorption c o e f f i c i e n t y = l i n e a r absorption c o e f f i c i e n t 207 D o l o m i t e o c c u r s i n many o f t h e specimens b u t due t o i t s low absorbance and l a c k o f i n t e r f e r i n g ( h k l ) r e f l e c t i o n s (Table X I I ) i t s e f f e c t was i g n o r e d . (d) B u i l t - i n e f f e c t s i . A c c u r a c y o f any s i n g l e scan i s reduced a t h i g h t i l t a n g l e s . T h i s i s because a r o t a t i o n p r oceeds w i t h c o n s t a n t a n g u l a r v e l o c i t y so t h a t t h e s c a n n i n g r a t e a l o n g t h e s p i r a l p a t h i n c r e a s e s w i t h i n c r e a s i n g (J) t i l t . T h e o r e t i c a l l y t h i s c o u l d be r e c t i f i e d by m o d i f y i n g t h e goniometer so t h a t t h e a n g u l a r v e l o c i t y o f a r o t a t i o n i s reduced w i t h i n c r e a s i n g <j>. I n p r a c t i c e , however, t h i s l o s s i n a c c u r a c y i s g e n e r a l l y a c c e p t e d because t h e r e i s a l s o l o s s i n a c c u r a c y o f d e t a i l a t low t i l t a n g l e s due t o t h e smoothing e f f e c t o f c o n t o u r i n g c e n t r a l d a t a p l o t t e d on p o l e - f i g u r e s . i i . C o l l i m a t o r d e s i g n , i n c l u d i n g p o r t l i n e f o c u s s l i t and a p e r t u r e s l i t d i m e n s i o n s , d i r e c t l y c o n t r o l t h e shape and s i z e o f i r r a d i a t e d a r e a o f specimens and hence, as has been d e s c r i b e d above, t h e q u a l i t y o f i n t e n s i t y p r o f i l e s . P r e c i s i o n R e p r o d u c i b i l i t y was checked by p e r i o d i c a l l y r e - s c a n n i n g s e l e c t e d specimen s l a b s ( F i g . 50b). To check r e p r o d u c i b i l i t y on t h e m i c r o s c a l e , a s e l e c t e d specimen s l a b w h i c h had a l r e a d y been scanned was d e e p l y e t c h e d and r e - s c a n n e d . The r e s u l t i n g i n t e n s i t y p r o f i l e s a r e e s s e n t i a l l y t h e same ( F i g . 5 0 c ) . T h i s a l s o s e r v e s t o demonstrate t h a t no s u r f a c e "working" o f t h e specimen had o c c u r r e d d u r i n g p o l i s h i n g , a problem e n c o u n t e r e d i n m e t a l l u r g i c a l s t u d i e s . 208 a. ( I l l ) random sphalerite time constant = 8 sec b. ( I l l ) sphalerite - RM70-3 time constant = 16 sec c. ( I l l ) sphalerite - RM70-1 time constant = 16 sec d. ( I l l ) sphalerite - CX69-47 time constant = 4 sec (1) and 8 sec (2) 360 270 180 90 0 20° 15° 10° 5° ' ' ' I Figure 50. Duplicate X-ray r e f l e c t i o n scans for various sphalerite specimens. Shown for reference i s the r e f l e c -t i o n p r o f i l e obtained from randomly oriented sphalerite. 209 To check whether pole-figures were representative of the subfabric developed on the hand-specimen scale, several pairs of s i m i l a r l y oriented slabs from d i f f e r e n t layers i n the same hand specimen were scanned and compared. It was found that pole-figures from any one hand specimen were approximately si m i l a r at least i n the d i s t r i b u t i o n of i n t e n s i t y maxima (Fig. 50d). Pole-figures to 4> = 90° Gehlen (1960) pointed out that a single r e f l e c t i o n scan usually s u f f i c e s for the investigation of preferred orientation i n ore minerals. However, attempts were made by two d i f f e r e n t techniques to produce complete pole-figures because maxima may be developed close to (j) =70 for certain preferred orientations of sphalerite (Saynisch, 1970; see also Section V, F i g . 42b). D e f i n i t i o n of such maxima would be improved i n a complete pole-figure. i . Transmission method A t h i n section made from a specimen slab (previously scanned by r e f l e c t i o n ) was mounted on Scotch tape as advised by Baker et al. (1969) and set up v e r t i c a l l y i n the incident beam so that the Bragg angle was s a t i s f i e d (Fig. 48). The specimen was rotated i n t h i s plane through 360° i n 16 minutes, and simul-taneously translated i n the incident beam. With t h i s geometry the incident beam i s d i f f r a c t e d by (hkl) planes perpendicular to the specimen surface—analagous i d e a l l y to r e f l e c t i o n scan-ning with t i l t angle cf> = 90°. 210 The specimen was then t i l t e d manually 5° for each rota-t i o n through 360°, so that a series of concentric c i r c u l a r scans was obtained covering the pole-figure i n the range cb = 70°-90° which i s inaccessible to r e f l e c t i o n scanning. In the P h i l l i p s goniometer used for t h i s work, a 70° t i l t was the minimum mechanically possible i n transmission mode. Hence, there was lack of overlap between r e f l e c t i o n and transmission scans and i t was not possible to e f f e c t i v e l y normalize and then match transmission data with the r e f l e c t i o n data to obtain a complete pole-figure. i i . Mutually perpendicular specimens Attempts to produce complete pole-figures were also made using three"mutually perpendicular slabs. These were analyzed by r e f l e c t i o n scanning and a composite pole-figure produced by rotation of the data into one plane. In prac t i s e , t h i s approach was unrewarding due to the inhomogeneous d i s t r i b u t i o n (layering) of the sulphides i n sections normal to composition layering, and to the increased time involved, both i n X-ray scanning and i n data reduction. 211 Table XIII. Numbers and locations of ore specimens used i n X-ray f a b r i c analysis. Text Specimen figure. No. Location Pole figure pattern ( I l l ) Sphalerite REEVES MACDONALD MINE 38b RM69-37 460' l e v e l central maximum - RM69-76 500' l e v e l II II 38a RM7 0-1 Annex, 800' l e v e l II H - RM70-2 Annex, 800' l e v e l II I I 38d RM70-3 Annex, 800' l e v e l H n 38c RM71-32 Annex, dump II II 38f RM71-43 Annex, 1000' l e v e l H I I 38e RM71-44 Annex, 975' l e v e l H II H. B. MINE - HB70-19 Garnet zone, p i t central maximum JERSEY MINE 40b CX69-25 7IF heading two maxima - CX69-44 49D stope central maximum 39d CX69-47 E-zone, 5500N central maxima 39e CX69-53 D-zone e x i t s m a l l - c i r c l e maxima 39f CX69-55 D-zone e x i t s m a l l - c i r c l e maxima 39c CX69-56 D-zone e x i t s m a l l - c i r c l e maxima 39b CX69-64 E-zone, 5200N Central maxima 40a CX69-73 74J p i l l a r two maxima 39a CX69-89 659F p i l l a r c e n t r a l maximum (220) Sphalerite REEVES MACDONALD MINE - RM71-43 Annex, 1000' l e v e l s m a l l - c i r c l e maxima 41a RM71-44 Annex, 975' l e v e l s m a l l - c i r c l e maxima JERSEY MINE 41b CX69-47 E-zone, 5500N sm a l l - c i r c l e maxima (200) Galena JERSEY MINE - CX69-45 C-zone random 43d CX69-53 D-zone e x i t elongate central maximum 43c CX69-69 537A p i l l a r weak central maximum 43b CX69-73 74J p i l l a r elongate central maximum 43a CX69-78 7OA stope near random APPENDIX C MINOR ELEMENT DETERMINATION BY ATOMIC ABSORPTION SPECTROPHOTOMETRY Sample preparation A. Sphalerite Samples were crushed by hand, f i r s t roughly using an iron mortar and pestle and then more f i n e l y using a refractory mortar and pestle. After sieving to -50+80 mesh (or -80+200 mesh for some fine-grained samples from Reeves MacDonald mine) the samples were panned to wash and concentrate them. Separate galena grains were e f f i c i e n t l y removed i n t h i s way. Further concentration was effected for many of the samples by the use of Bromoform i n a separatory funnel to separate dolomite, c a l c i t e and quartz. F i n a l concentration was achieved by running samples two or three times through a Frantz Isodynamic magnetic separator. Low iron sphalerites required a cross-slope of 10-11° and an operating current of 1 amp for e f f i c i e n t separation. With increasing iron content the cross-slope was increased to 15-16° and the current reduced to 0.8 amps. Diopside occurring i n some of the Jersey mine samples had f i r s t to be removed at a current of 0.4-0.5 amps. F i n a l l y the sphalerite concentrates were ground for 2-3 minutes in an agate mortar. Preparation of samples thereafter was organized i n separate batches of 12, made up of 10 samples with one duplicate and one blank. 212 213 200 mg of each sample was weighed out into a beaker, dissolved i n 10 ml concentrated HC1 and evaporated to dryness. The residue was dissolved i n 1.5 M HC1, made up to 25 ml i n a volumetric flask and then transferred to a polyethylene b o t t l e ready for analysis. B. Pyrite I n i t i a l preparation of p y r i t e concentrates was si m i l a r to that for sphalerite. After crushing (generally to -80 mesh), sieving and panning, concentrates were passed through the magnetic separator to remove sphalerite. Then leaching with hot 6 M HC1 helped remove galena, dolomite, c a l c i t e , and re-maining sphalerite. For a number of samples, further concen-t r a t i o n using Bromoform i n a separatory funnel was required to remove quartz and remaining dolomite. The f i n a l concentrates were ground i n an agate mortar for 2-3 minutes. Marked interferences from iron are encountered i n the analysis of p y r i t e for cobalt and n i c k e l ( L o f t u s - H i l l s and Solomon, 1967). This was overcome by the extraction of iron from the system, using a method described by Price (1972). 25 mg of sample was weighed into a beaker and then roasted i n a muffle furnace for 2-3 hours at 550°C to remove sulphur. The res u l t i n g oxide was dissolved i n several ml of 6 M HC1 and evaporated to dryness. The residue was redissolved i n 6 M HC1 and made up to 25 ml i n a volumetric f l a s k . This solution was shaken up with methyl iso-butyl ketone (MIBK) i n a separatory funnel so that the iron, as F e 3 + , i s taken up i n the MIBK which i s then separated. The sample solution i s then ready for analysis. 214 A n a l y t i c a l method Sphalerite sample solutions were analyzed for Fe, Cd, Mn, Ag, Cu and Pb. Pyrite sample solutions were analyzed for Co, Ni, Mn, Cu, Zn and Pb. Analyses were done on a Techtron AA-4 Spectrophotometer; operating procedure was as outlined by Fletcher (1970). The most sensitive absorbance l i n e was used for each of the metals determined. Standard solutions were used to establish c a l i b r a t i o n curves for absorbance vs. concentration from which the sample concentrations were read o f f . A l l standard solutions were i n 1.5 M HC1 except for the s i l v e r standard which was i n 3 M HC1. Corrections for background absorption (measured using a hydrogen lamp) were necessary for determinations of cobalt, n i c k e l and lead, and were t r i e d but found unnecessary for cadmium and s i l v e r determinations. S i l v e r and cobalt concentrations were very low i n many samples, requiring the use of expanded scale on the indicator unit; under t h i s condition meter s t a b i l i t y was improved by increasing the lamp current. The re s u l t s are tabulated i n Tables XIV, XV and XVIII. A n a l y t i c a l precision Duplicate analyses (Tables XVI, XVIII) indicate that a n a l y t i c a l precision was s a t i s f a c t o r y . Differences can probably be attributed to sample inhomogeneities (inclusions of other minerals) and sample weighing and d i l u t i o n errors. 215 T a b l e XIV. Mi n o r element c o n t e n t s o f s p h a l e r i t e samples from Reeves MacDonald mine. Sample number Fe Colour 2 % Cd % Mn ppm Ag ppm Cu ppm ppm Location REEVES MACDONALD MINE RM69-17a PB 1.21 0.37 134 9 21 0 Glory hole, Reeves zone RM69-35 DY 0.58 0.35 38 7 23 2250 460' l e v e l , E. MacDonald zone RM69-37 MYB 1.04 0.30 35 19 21 17800 460' l e v e l , E. MacDonald zone RM69-60 MYB 1.38 0.78 19 12 40 860 1900' l e v e l , Reeves zone RM69-66a MYB 1.17 0.51 28 21 14 4120 1900' l e v e l , Reeves zone RM69-66b MYB 1.27 0.46 53 21 16 1050 1900' l e v e l , Reeves zone RM69-69a MYB 1.07 0.45 113 18 30 7450 1900" l e v e l , Reeves zone RM69-69b PB 1.10 0.46 93 14 31 6190 1900' l e v e l , Reeves zone RM69-74 DY 0.91 0.48 315 8 31 1510 1900' l e v e l , Reeves zone RM71-17 DY 0.55 0.16 278 2 6 15400 2650' l e v e l . Reeves zone REEVES MACDONALD ANNEX RM70-1 MYB 1.27 1.11 74 1940 51 2000 800' l e v e l , Annex zone RM70-2 MYB 1. 37 1.09 35 36 61 138 800' l e v e l , Annex zone RM70-3 MYB 1.13 0.96 54 96 63 1420 800' l e v e l , Annex zone RM70-4a MYB 1.27 1.01 58 126 38 1300 875' l e v e l , Annex zone RM70-4b PB 1.40 1.11 39 46 63 69 875' l e v e l , Annex zone RM70-5 MYB - 0. 93 1.25 123 109 41 410 875' le v e l , Annex zone RM70-8 MB 2.21 1.12 131 13 44 6 875' l e v e l , Annex zone RM71-34 MYB 0.97 1.00 43 76 93 1140 Annex dump RM71-42 PB 1.66 0.98 40 164 49 1500 1000' l e v e l , Annex zone RM71-44 DY 0.97 0.91 31 112 100 2430 . 975" le v e l , Annex zone RM71-45 MYB 1.31 1.51 61 36 38 62 950' l e v e l , Annex zone RM71-46 MB 1.37 1.16 59 34 40 120 950' l e v e l , Annex zone RM71-49 MB 2.44 0.94 105 107 45 25 925' l e v e l , Annex zone RM71-53' MB 1.86 0.99 212 81 20 125 800' l e v e l , Annex zone RM71-54 GB 1.84 0.66 * 19 7 80 6 " s a t e l l i t e " 1000' l e v e l . o. z. , Annex zone 'Analyses by A. S. Macdonald using Techtron AA-4 Spectrophotometer 2See Table XV . for explanation of colour notation 216 T a b l e XV. M i n o r element c o n t e n t s o f s p h a l e r i t e samples from J e r s e y and H. B. mines. Sample Fe Cd Mn Ag Cu Pb number C o l o u r 2 % % ppm ppm PPm ppm L o c a t i o n JERSEY MINE CX69-22 DB 3 10 0.63 1620 7 18 87 90G b e n c h , G - z o n e CX69-25 BR 4 75 0.49 411 29 38 . 4750 71F h e a d i n g , F - z o n e CX69-42 BR 4. 52 0.68 994 4 31 2750 514E p i l l a r , E - z o n e CX69-43 DB 4. 34 0. 51 1390 21 35 10600 512E p i l l a r , E - z o n e CX69-44 DB 5. 58 0 .50 536 0 100 1590 49D s t o p e , D-zone CX69-47 BR 4. 13 0.70 558 0 24 680 5500N, E - z o n e CX69-50 BR 4. 47 0.69 241 1 34 6 A n t i c l i n e E . l i m b , D-zone CX69-53 BR 6. 59 0.51 344 48 38 47500 W. w a l l o f e x i t , D-zone CX69-55 BR 4. 78 0.69 204 13 7 2500 E . w a l l o f e x i t , D-zone CX69-56 BR 4. 94 0.58 181 36 50 106 E . w a l l o f e x i t , D-zone CX69-64 MB 1. 40 0.59 356 3 25 94 5200N c r o s s c u t . E -zone CX69-71 DB 3. 80 0.59 1110 45 20 13400 556A p i l l a r , A - z o n e CX69-89 BR 5. 75 0.64 352 13 38 4500 659F p i l l a r , F - z o n e CX69-93 BR 5. 84 0 .65 1080 8 20 62 70G s t o p e , G - z o n e CX69-95 BR 4. 53 0.68 860 23 38 7620 654F p i l l a r , F - z o n e H. B. MINE HB70-2 VDR 4. 09 0.34 180 7 14 38 3200* a d i t dump, G a r n e t zone HB70-6 GB 2 . 38 0.53 560 18 21 100 Open p i t , G a r n e t zone HB70-8 MB 2. 38 0 .35 615 10 16 25 Open p i t . G a r n e t zone HB70-9 PB 2. 40 0.45 432 8 7 0 Open p i t , G a r n e t zone HB70-11 BR 4. 45 0.46 677 6 18 6 Open p i t . G a r n e t zone HB70-14 GB . 2 . 21 0.38 465 3 34 25 2800 ' a d i t dump, S s i d e Sheep C r e e k -HB70-15 GR 2: 81 0.33 556 1 20 31 2800' a d i t dump, S s i d e Sheep C r e e k HB70-19 PB i . 76 0 .40 162 29 11 62 Open p i t , G a r n e t zone HB70-21 VDR 2. 95 0.46 238 10 27 8500 Open p i t , G a r n e t zone A n a l y s e s by A . S . Macdona ld u s i n g T e c h t r o n AA-4 S p e c t r o p h o t o m e t e r . See T a b l e XV f o r e x p l a n a t i o n o f c o l o u r n o t a t i o n 217 Table XVI. Duplicate analyses of minor elements i n sphalerite samples from the three mines. Sample Fe Cd Mn Ag Cu Pb number % % ppm ppm ppm ppm RM71-42 a 1.66 0.99 40 164 49 1500 b 1.63 1.02 40 170 51 1630 RM69-74 a 0.91 0.49 315 8 31 1510 b 0. 81 0.49 313 9 34 1550 HB70-14 a 2.21 0.37 465 3 34 25 b 2.15 0.39 452 3 34 25 CX69-89 a 0.57 0.64 352 13 38 4500 b 0.58 0.61 354 .13 38 4690 RM71-45 a 1.31 1.15 61 36 38 62 b 1.31 1.16 59 34 38 62 218 Sphalerite coloration Coloration i n sphalerite specimens from the three deposits shows a progressive change from dusky yellow to blackish red, apparently with increasing grade of contact metamorphism (Tables XIV, XV, XVII). Such colour v a r i a t i o n i n sphalerite i s commonly attributed to differences i n iron content. However, Roedder and Dwornik (1968), i n an electron microprobe study of colour banding i n sphalerite from the Pine Point deposit, found no c o r r e l a t i o n between colour and iron content and could not s a t i s f a c t o r i l y explain the colour banding. Graeser (1969) sug-gested from a study of minor elements i n sphalerite of r e l a t i v e l y low iron content, from the Binnatal deposit, that colour was strongly influenced by small variations i n manganese content which might not be detectable by electron microprobe. More recently, Scott and Barnes (1972) have shown that nonstoichio-metry af f e c t s sphalerite coloration and they suggest that metal deficiency, due to formation under highly sulphidizing conditions, may cause dark coloration i n sphalerite rather than increases i n iron content. A pl o t of minor element contents of sphalerite specimens from t h i s study against colour v a r i a t i o n suggests a c o r r e l a t i o n between iron, and also manganese (to a lesser extent) contents and coloration (Fig. 51). Such a c o r r e l a t i o n does not preclude metal deficiency e s p e c i a l l y since increasingly high sulphidizing conditions were probably attained during contact metamorphism i n H. B. and Jersey mine areas. Hence t h i s study suggests that sphalerite coloration i s ^ p o s s i b l y a function both of the nature of the metals involved i n the l a t t i c e as well as of an o v e r a l l metal-deficiency. 219 Table.XVII. Sphalerite colour notation, based on Munsell Rock Colour Chart (Goddard, et a l . , 1963). Notation Colour Colour code REEVES MACDONALD MINE DY dusky yellow 5Y 6/4 MYB moderate yellowish brown 10YR 5/4 PB pale brown 5YR 5/2 REEVES MACDONALD ANNEX DY dusky yellow 5Y 6/4 MYB moderate yellowish brown 10YR 5/4 PB pale brown 5YR 5/2 MB moderate brown 5YR 3/4 GB greyish brown 5YR 3/2 H. B. MINE PB pale brown 5YR 5/2 MB moderate brown 5YR 3/4 GB greyish brown 5YR 3/2 VDR very dusky red 10R 2/2 GR greyish red 5R 4/2 BR blackish red 5R 2/2 JERSEY MINE MB moderate brown 5YR 3/4 DB dusky brown 5YR 2/2 BR blackish red 5R 2/2 220 0.01 a o o i — Figure 51. Plot of minor element contents vs. colour for a l l sphalerites (49) analyzed by AA spectrophotometry. Colour be-comes darker toward the r i g h t . Colour notation i s as defined i n Table XVII. 221 T a b l e X V I I I . M i n o r element c o n t e n t s o f p y r i t e samples from t h e t h r e e mines. Sample number Form Co ppm N i ppm Mn ppm Cu ppm Zn ppm Pb % L o c a t i o n ' REEVES MACDONALD MINE RM69-18 a b m a s s i v e 11 14 139 146 1 3 17 18 2 1 2.18 2 .89 S . s i d e o f Reeves g l o r y h o l e RM69-20 a b m a s s i v e 8 .12 92 94 2 2 6 7 219 247 . 0.11 0.12 S . s i d e o f Reeves g l o r y h o l e RM69-21 a b d issen t . 9 8 147 147 2 2 10 12 159 184 0.16 0.18 N . s i d e o f Reeves g l o r y h o l e RM70-26 a b d i s s e m . 11 11 135 142 2 3 10 11 322 322 0.43 0.43 Reeves g l o r y h o l e RM69-36 a b m a s s i v e 12 12 217 204 2 2 10 5 77 76 0.20 0.19 460 ' l e v e l , E . MacDonald zone RM69-52 d i s s e m . 23 266 1 11 1560 0 .70 1900' l e v e l , Reeves zone RM69-77 a b d i s s e m . 9 9 265 265 2 0 10 10 269 269 0.19 0.20 500' l e v e l , E . MacDonald zone JERSEY MINE CX69-20 a b d i s s e m . 0 1 12 15 2 2 2 4 1030 1015 0.03 0.03 65J s t o p e , J - z o n e CX69-23 a b d i s s e m . 11 8 57 72 3 4 38 40 937 1000 0.09 0.09 90G2 b e n c h , G - z o n e CX69-26 a b m a s s i v e 14 14 96 100 6 6 6 8 24 30 0.10 0.12 44C s t o p e , C - z o n e CX69-44 a b m a s s i v e 8 9 68 68 5 5 9 11 275 306 0 .20 0.21 49D s t o p e , D-zone CX69-75 a b d i s s e m . 3 3 17 15 6 7 3 2 3060 2970 0.69 0.67 70G s t o p e , G - z o n e H. B . MINE HB70-1 a b m a s s i v e e 3 16 15 23 23 9 9 1860 1860 0.51 0.52 3200' a d i t dump, G a r n e t zone HB70-4 a b d i s s e m . . 8 3 15 16 6 6 7 9 52 61 0.02 0.02 3500' a d i t dump, G a r n e t zone HB70-10 a b m a s s i v e 0 0 11 9 51 53 3 3 0 .20 0.19 S . S i d e o f open p i t , G a r n e t zone HB70-12 a b d i s s e m . 2 2 7 7 82 83 4 3 i 0.11 0.11 O l d p i t N. o f G a r n e t zone HB70-17 a b d i s s e m . 1 3 61 61 7 8 59 139 2 1.79 1.87 O l d a d i t s , W. Edge o f mine a r e a A n a l y s e s by A . B e n t z e n u s i n g T e c h t r o n AA-4 S p e c t r o p h o t o m e t e r i n d i c a t e s z i n c v a l u e s >3000 ppm APPENDIX D ANALYSIS OF SPHALERITE BY ELECTRON MICROPROBE Five polished specimens of sphalerite co-existing with pyrrhotite and p y r i t e were selected for analysis. Analyses were ca r r i e d out p r i n c i p a l l y by J. E. Harakal on a J.E.O.L. JXA-3A electron microprobe belonging to the Department of Metallurgy, University of B r i t i s h Columbia. Specimens were analyzed for zinc and iron by comparing i n t e n s i t i e s of charac-t e r i s t i c radiations (Ka) with those of pure metal standards. Operating voltage was 25 kv. Five grains i n each specimen were analyzed. Duplicate analyses were made at several d i f f e r e n t points within the grains, a minimum of 10 analyses being made on each grain. Counting time for each analysis was 10 seconds. Standards were analyzed before and aft e r each specimen run and background determinations were made for both standards and specimen at the end of each run. Williams (1967) has described simple matrix correction parameters which can be applied to observed i n t e n s i t y r a t i o s i n the microanalysis of sphalerite. These, however, apply to measurements made at 20 kv on an instrument of d i f f e r e n t geometry than the above. In t h i s study, the data was processed for instrumental corrections (deadtime, background) and matrix corrections (back scatter, ionization-penetration, absorption and fluorescence) using a FORTRAN program, "MAGIC" (made 222 223 available by L. C. Brown, Department of Metallurgy). Sulphur concentration was determined by difference so that a l l analyses t o t a l l e d 100%. Assuming stoichiometric d i s t r i b u t i o n of sulphur, the mole % FeS and ZnS present were calculated from each analysis and t o t a l l e d to obtain some measure of the accuracy of the analyses (Table XIX). These r e s u l t s indicate that accuracy i s adequate for the purposes of t h i s study (see Section V, p. 122). CdS and MnS contents were not determined but on the basis of mean analyses of sphalerite from Jersey mine by AA spectropho-tometry, these were assumed to t o t a l 0.85 mole %. A number of semiquantitative analyses of sphalerite specimens from a l l three deposits were also c a r r i e d out, usually v i a stepwise traverses, to check t h e i r homogeneity or otherwise (see Section V, p. 126). The analyses were made for Zn and Fe, and for Fe and Cd. Fe values are generally within 10% of values determined by AA spectrophotometry on samples from the same hand specimens. RM69-39 RM69-60 RM70-1 CX69-55 HB70-19 AA: 1.04 1.38 1.27 4.78 1.76 wt. % Fe EMP: 1.08 1.33 1.18 4.75 2.00 Similar comparisons of Cd values indicate that the semiquantita-t i v e microprobe analyses are unreliable, perhaps because of r e l a t i v e l y low Cd concentrations. Zn was not determined by the AA method. 224 Table XIX. Analyses by electron microprobe of iron and zinc i n sphalerite (sulphur contents determined by difference, assuming stoichiometry). Total corrected Sample Weight Mole for number % % Total CdS + MnS* CX69-9 Fe 6.89 + 0.97 FeS 10. 83 + 1.52 101.92 102.77 Zn 61.04 + 0.90 ZnS 91. 09 + 1.34 S 32.07 + 0.15 CX69-77 Fe 8.06 + 0.30 FeS 12. 67 + 0.47 55.82 95.97 96.82 Zn + 0.68 ZnS 83. 30 + 1.01 ••;s 36.12 + 0.72 CX69-76 Fe 7.63 + 0.14 FeS 11. 99 + 0.22 98.84 99.69 Zn 58.20 + 0.34 ZnS 86. 85 + 0.50 S 34.17 + 0.45 CX69-53 Fe 7.82 + 0.21 FeS 12. 29 + 0.33 99.32 100.17 Zn 58.32 + 0.25 ZnS 87. 03 + 0.37 S 33.86 + 0.11 RM69-54B Fe 11.34 + 0.77 FeS 17. 82 + 1.21 52.87 96.92 _ Zn + 0.81 ZnS 78. 90 + 1.21 S 35.79 + 0.30 *Mean CdS + MnS content of Jersey sphalerites = 0.85 mole % (by AA spectrophotometry) APPENDIX E MAPS OF STRUCTURAL DATA 225 PLANAR STRUCTURES IN THE REEVES MACDONALD MINE AREA. Si U £ — 3 ^ *tf '^K= = ------/ L E G E N D F o l i a t i o n B e d d i n g F o l d A x i a l S u r f a c d ^ J*' Phase 1 Phase 2 Phase 3 L i t h o l o g i c a l c o n t a c t S l i d e T h r u s t F a u l t No e x p o s u r e . N E P i t U n i t s a s l n P l a t e Ml. A p p r o x . / I n f e r r e d A d i t S t r u c t u r a l mapping by A.S.Macdonald. Main g e o l o g i c a l b o u n d a r i e s s l i g h t l y m o d i f i e d a f t e r F y l e s and H e w l e t t (1959). S C A L E : 500 1000 ft P L A T E I. L I N E A R S T R U C T U R E S I N T H E R E E V E S M A C D O N A L D M I N E A R E A . Hi :/. 101 •"t TC &iJ4*vUz V -fi. -- J M k -, s-.-, » r ..W; -v N E L E G E N D Lineation Minor fold axis with vergence Phase 1 Phase 2 Approx./Inferred Phase 3 Lithologlcal contact Slide Thrust Fault Units as ln Plate IM. No exposure ; N E } Pit (1 Adit Structural mapping by A.S.Macdonald. Main geological boundaries slightly modified after Fyles and Hewlett (1959). S C ALE : 500 1000 ft P I A T E II M A J O R S T R U C T U R E S I N T H E R E E V E S M A C D O N A L D M I N E A R E A II M A P C O M P I L E D F R O M P L A T E S I & II L E G E N D r_H A C T I V E F N . U. LAIS MR. graph i t i c phy 11 i t e ( s la te , l i m e s t o n e , c h l o r i n e p h y l l i t e , phy l lon i t e . E M E R A L D MR. graphi t i c p h y l l i t e , ( la te , l i m e i t o n e . R E E V E S MR. c a l c i t e m a r b l e . sil iceous dolomite m a r b l e , do lomite marble . T R U EM A N MR. q u a r t i ca lc i te p h y l l i t e morble . R E N O F N . q u a r t i p h y l l i t e , q u a r t i l t e . p h y l l i t e , quartz phyl l i t e , quartz i t e . Q U A R T Z I T E RANGE FN. q u a r t zite . anticline syncline inferred P H A S E I A X I A L TRACE P H A S E 2 A X I A L TRACE S L I D E T H R U S T F A U L T N O E X P O S U R E ant i form synform A -S- — • SCALE 1 0 0 0 ft P L A T E III. i 1 } K, V N E hi I ) / / < , / /, / + + + ' /?77 + + + +N E 7 1 § A / + A + + b H7 40 87 • ' / //; J i / , + + / ' * i s / / / / + 4 4 (/ A ' //' f i 4 + + +, ./ / / / , , / / / : /)/4 4 + + +c ft f , fh IO + + + 4 j /yV ,s\ IT ; / + + + /4/ / 4 * / fi* r A /? imV /7 4 \ •+ + +v ^ 7 / J ' d if y if / / 1 3 ' 4 8 . V + + A v ' ' 11 f / + I 4 -f-i + / 1 L E G E N D b r i c r i nal r o l i a t l o n F o l d A x i a l S urface Phase 1 Phase 2 Phase 3 L i t h o l o r l c a l c o n t a c t I n t r u s i v e c o n t a c t S l i d e Fault Units as i n f l a t e VI. l-o exposure N E .Approx. / I n f e r r e d ^ " 4 " + " " + " * P i t . ^ \ A d i t S t r u c t u r a l mapping by A.S.Macdonald Main p - e o l o r l c a l b o undaries s l l s r h t l y m o d i f i e d a f t e r F v l e s and Hewlett (19^9) .  S C A L E : looo ft P L A N A R S T R U C T U R E S I N T H E J E R S E Y M I N E A R E A . i 41 10 / / 17 ;\+; T \ lis •2 II I r • • i / • 4 7.. /// / . 7 * i k r • • 7fiW//// + + + + / • ' ftWiVW' + + + + + /+ y--y'*w±>i//. + + + + + r A / + + i / - r + -(- -r +• I + 1 / 1 + + + + , ; fr f' >+ + + + - :"// J I ',1 ' ' ' 7 / • - 4 - x / [ 20 T I 5 fl \ / 1**11 , r / +   +f J ^ y i / / • ; / + + + + < 15*4 f 8 /)/+ + + + 5kv i 18 A.e / + + + ' / + + + A-/ / fr + + ' / / ' / / ; r t i i i * 7 i i { j 1 „ i + v . > i if' MILL 2 6 S<> . . , / Ml • / '' ''lid 1 m i J I / 1 U i JK V-\ \ / 28 r 2 2 ' 2 4 y, \ I / \ N E f 1 J t l ^» .. 2 6 14-/ .'8 f l 8 L / / / •18 ) v / urur i Ijpni w // • ( '•-HI I I / 'Z4- N r / / / / / L E G E N D Phase 1 Phase 2 Phase 3 Lineation * Minor fold axis Vercence Approx./Inf erred Intrusive contact /*"+""+ + + Slide « — — Fault Units as In Plate VI. t V M M W •«• W Ko .exposure ' N E • Pit Adit > Structural mapping by A.S.Macdonald Main creoloclcal boundaries slightly after Fyles and Hewlett (1959). modi fled' SCALE: 0 500 1000 ft L I N E A R S T R U C T U R E S I N T H E J E R S E Y M I N E A R E A Lu. B i t ) -\ * ; V i 4 /' ,' I IT / , " ' / ' ' ' , ' J ' 4«l ' Ii I Hi t L E G E N D A. PLANAH ELEMENTS F o l i a t l o r i Bedding Phase 1 Phase 2 Phase 3 F o l d A x i a l S u r f a c ^ ^ ' ^ X S B. LINEAR ELEMENTS . L i n e a t i o n Minor Fold Axis with vergence Phase 1 Phase 2 Phase 3 L i t h o l o g i c a l contact S l i d e Thrust F a u l t No exposure P i t Un i t s as l n PlateVUI A d i t S t r u c t u r a l mapping by A.S.Macdonald. Main g e o l o g i c a l boundaries s l i g h t l y modified a f t e r F y l e s and Hewlett (1959). S C A L E 500 1000 ft a M • M I — 233 n. « T r .mi Kii A ir\D C T D I i r T I I R F Q IM T U F U R M I M P A C T A 

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