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The Geology and ore deposits of the Howards Pass Area, Yukon and Northwest Territories : the origin of… Morganti, John Michael 1979

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THE GEOLOGY AND ORE DEPOSITS OF THE HOWARDS PASS AREA, YUKON AND NORTHWEST TERRITORIES: THE ORIGIN OF BASINAL SEDIMENTARY STRATIFORM SULPHIDES DEPOSITS by JOHN MICHAEL MORGANTI B.A., B.Sc, Western Washington State University, Bellingham, 1969 M.Sc, Washington State University, Pullman, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Dept., Geological Sciences) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1979 ^cJJohn Michael Morganti , 1979 In presenting th is thes is in p a r t i a l fu l f i lment o f the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i lab le for reference and study. I fur ther agree that permission for extensive copying of th is thes is for scho la r ly purposes may be granted by the Head of my Department or by his representat ives . It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my wri t ten permission. Department of Geological Sciences The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 ABSTRACT i Economically important sedimentary-type stratiform Zn-Pb deposits exist in the Lower Silurian basinal facies of the Selwyn Basin along the Yukon-Northwest Territories border. Three major similar deposits have been defined to date, and are referred to collectively as the Howards Pass de-posits. The Pre-Mesozoic history of the Howards Pass area was dominated by three major basin systems. During the Late Hadrynian to Early Cambrian the 'Grit Unit' was deposited as a clastic wedge with a western source area. In i t i a l l y deep water turbidites were deposited but continued f i l l i n g in of the basin led to shallow water deposition. During the Late Cambrian to Early Devonian the Rabbitkettle and Road River groups were deposited in the Selwyn Basin. The Selwyn Basin is defined by shallow water carbonates on the east and a general deep water environment to the west. The carbonates were succeeded by hemipelagic and pelagic organic-rich sediments with occasional terrigenous material deposited by geostrophic currents. Within the Selwyn Basin the Ordovician to the Early Silurian Howards Pass forma-tion contains three major facies from east to west; a slope facies, a base of slope facies and a chert basin facies. The Howards Pass deposits occur in sub-basins in the base of slope facies. The third major basin system in the region was associated with uplift to the west and is represented by the Earn Group. In this later basin turbidity currents associated with sub-marine fans deposited clastic material derived from the uplifted centre of the Selwyn Basin and underlying rocks. Major barite deposits occur in the Earn Group. i i The individual Howards Pass deposits consist of complex saucer shaped bodies containing laminated to massive sulphides occurring in the Lower Silurian active member of the Howards Pass formation. The deposits are characterized by simple sulphide mineralogy, predominantly sphalerite, galena and pyrite. The sulphides in the deposits may be divided into six textural types which aid in characterizing the sulphides geologically and metallurgically. Types I, II, and III consist of laminated sulphides, types IV and V consist of laminated to massive sulphides and type VI con-sists of late diagentic concretionary sulphides. Types I thru V are as-sociated with specific lithofacies in the active member. The Howards Pass deposits show characteristics common to stratiform-sedimentary deposits such as conformity with bedding, no obvious associ-ation with volcanic rocks, similar age of the three major associated depo-sits, single-stage Pb isotope systematics and association with organic-rich sedimentary rocks. In contrast differences between the Howards Pass depo-sits and other stratiform-sedimentary deposits, include deposition in a starved basin sedimentary environment, a lack of any associated feeder zone within 10 km, a lack of massive pyrite associated with the deposits, rela-tively low Ag and Cu associated with the deposits and a lack of bedded barite near the deposits. This datum suggests that the Howards Pass deposits are unique, and therefore a model is proposed which is relevant to the geologic setting. The most important part of the model is the synsedimentary deposition of Zn and Pb sulphides within sub-basins occurring at the base of slope of the eastern edge of the Selwyn Basin. The formation of biogenetic sulphide from sea water sulphate is suggested by the sulphur isotope data. This data also supports the existence of an ideal cycle of the active member i i i and suggest a possible sub-basin evolution during an individual cycle. The origin of the metals in the deposit is not clear, but the association of volcanic tuffs near the shale-out at the eastern margin of the Selwyn basin suggests that warm fluids may have been expelled onto the sea floor, mi-grated down slope and collected in the topographically low sub-basins, or possibly compaction fluids may have been expelled directly into the sub-basins and concentrated during brine evolution. The abundant evidence for slumping and later folding and the possibi-l i t y of both ordinary and more radiogenic Pb leads to the conclusion that post-depositional mobilization of both sediment and sulphide was important in the final location of Zn and Pb. Exploration for Howards Pass-type deposits, based on the above model, should emphasize the sedimentary nature of the deposits. Regional s t r a t i -graphic exploration should be aimed at defining major, platform-marginal, starved basins. The importance of defining the paleogeography, such as the base of slope and specific sub-basins, appears to be c r i t i c a l . This method emphasizes the petroleum methodology of looking for traps, although in the present case these are paleogeographic sulphide traps. i v TABLE OF CONTENTS Page ABSTRACT , 1 PREFACE xix ACKNOWLEDGMENTS xx CHAPTER I INTRODUCTION 1 PURPOSE AND SCOPE OF THE PRESENT STUDY 1 METHODS OF STUDY 1 LOCATION AND ACCESS 3 TOPOGRAPHY AND CLIMATE 3 LOCAL GEOGRAPHY 7 HISTORY AND PREVIOUS GEOLOGIC INVESTIGATIONS 7 ROCK CLASSIFICATION USED IN THE PRESENT STUDY 8 CHAPTER II - GEOLOGY 10 INTRODUCTION . 10 LOCAL GEOLOGY 13 STRATIGRAPHY 15 Map Unit 2 ( ' G r i t U n i t 1 ) 15 Map Unit 7a (Lower S i l t s t o n e U n i t ) . . 17 Map Unit 7b-l (Massive Limestone Formation) 19 Map Unit 7b-2 (Wavy Banded Limestone Formation).. 23 Map Unit 7b-3 ( T r a n s i t i o n Formation) 28 Map Unit 10a (Howards Pass Formation) 29 In t r o d u c t i o n 29 Map Unit 10a-l ( P y r i t i c S i l i c e o u s Shale Member) 31 Map Unit 10a-2 (Calcareous Mudstone Member) 32 Map Unit 10a-3 (Lower Cherty Mudstone Member) 35 Map Unit 10a-4 ( A c t i v e Member) 37 V Page Facies 1 (Basal Facies) 41 Facies 2 ( L i g h t Grey Basal Limestone Fac i es ) 43 Facies 3 (Graded Limestone F a c i e s ) . . . 44 Facies 4 (Thin Bedded Calcareous Mudstone Facies) 45 Facies 5 (Cherty Mudstone) 47 Facie s 6 (Thin Bedded Cherty Mudstone Fac i es ) 48 Facie s 7 (Whitish Grey Zn-Pb Mudstone) 51 Facies 8 (Grey Chert F a c i e s ) 55 Map Unit 10a-5 (Upper S i l i c e o u s Mudstone Member) 55 Map Unit 10b (Flaggy Mudstone Formation) 59 ORANGE WEATHERING MEMBER 62 FETID LIMESTONE ZONE 67 Map Unit 10c (Upper Chert Formation) 68 Map Unit 18b-l (Iron Creek Formation) 71 Map Unit 18b-2 (Yara Peak Formation) 78 Map Unit 18b-3 (Chert Pebble Conglomerate)... 85 CHAPTER III CORRELATION AND SEDIMENTATION 90 CORRELATION OF UNITS 90 SEDIMENTATION 95 In t r o d u c t i o n 95 Lower Units 96 Howards Pass Formation 98 Upper Units 109 Summary 120 CHAPTER IV - Zn-Pb DEPOSITS 123 INTRODUCTION 123 vi Page DESCRIPTION OF TEXTURAL TYPES 125 Textur a l Type 1 125 Textural Type II 131 Textur a l Type III 138 Textural Type IV 140 Text u r a l Type V 145 Textural Type VI 145 DISCUSSION 150 SUMMARY 156 CHAPTER V STRUCTURE 157 INTRODUCTION 157 PRE-FRANCONIAN STRUCTURES 157 PALEOZOIC STRUCTURES 158 CRETACEOUS STRUCTURES 164 SUMMARY 170 CHAPTER VI GEOCHEMISTRY 171 INTRODUCTION AND METHODS 171 DISCUSSION 183 Zinc and Lead 183 Copper 191 S i l v e r 196 Cadmium • 196 Molybdenum 198 Cobalt and Nickel 198 Manganese 201 Barium and Vanadium 204 Iron 205 Calcium and Magnesium 206 v i i Page P o t a s s ium 206 O r g a n i c C a r b o n ( C ( o r g ) ) 207 S u l p h u r 208 P h o s p h a t e 208 S i l i c a and A l u m i n a 209 M i c r o c hemi s t r y 210 SUMMARY 213 CHAPTER V I I SULPHUR ISOTOPES 215 INTRODUCTION 215 METHODS AND RESULTS 216 D I S C U S S I O N 19 O r i g i n o f S u l p h u r 222 M e c h a n i s m o f S u l p h i d e R e d u c t i o n 222 S u l p h i d e D e p o s i t i o n 227 SUMMARY 232 CHAPTER V I I I LEAD ISOTOPES 233 INTRODUCTION 233 METHODS 235 RESULTS 236 D I S C U S S I O N 238 SUMMARY 243 CHAPTER IX D I S C U S S I O N 246 INTRODUCTION 246 MODEL FOR THE ORIGIN OF THE HOWARDS P A S S -DEPOSITS 246 A C L A S S I F I C A T I O N FOR STRATIFORM - SEDIMENTARY Z n , Pb C u , Ag AND Ba D E P O S I T S : AN E X P L O R A T I O N I S T S VIEW 259 vi i i Page METALLOGENY OF THE EASTERN YUKON 274 REFERENCES 282 APPENDIX A. PLATE LOCATION MAP 308 APPENDIX B. MINERAL IDENTIFICATION METHODS 309 APPENDIX C. LOCATION OF STRATI GRAPH IC SECTIONS 311 APPENDIX D. LOCATION OF MINERAL DEPOSITS IN THE TERRITORIES 312 APPENDIX E. CHEMICAL METHODS AND DATA FOR CHAPTER VI 313 APPENDIX F. SULPHUR ISOTOPE ANALYTICAL METHOD 321 APPENDIX G. LEAD ISOTOPE ANALYTICAL METHOD 323 tx L O C A T I O N OF F I G U R E S P a g e 1-1 L o c a t i o n map o f t h e H o w a r d s P a s s d e p o s i t s . . . . 4 1-2 L o c a t i o n map o f t h e v a r i o u s c l a i m g r o u p s w h i c h c o n s t i t u t e t h e H o w a r d s P a s s c l a i m s 5 I - 3 P h o t o g r a p h s h o w i n g t h e g e n e r a l t o p o g r a p h y o f t h e H o w a r d s P a s s a r e a 6 I I - 1 M a j o r t e c t o n i c f e a t u r e s o f t h e Y u k o n 11 1 1 - 2 R e c o n s t r u c t i o n o f p a r t o f t h e n o r t h e r n C o r d i l l e r a 12 1 1 - 3 C o m p o s i t e s t r a t i g r a p h i c s e c t i o n f o r t h e ' G r i t U n i t ' w i t h a p p r o x i m a t e s c a l e 16 1 1 - 4 C o m p o s i t e s t r a t i g r a p h i c s e c t i o n f o r t h e l o w e r s i l t s t o n e u n i t 18 1 1 - 5 C o m p o s i t e s t r a t i g r a p h i c s e c t i o n o f t h e m a s s i v e l i m e s t o n e f o r m a t i o n 21 1 1 - 6 C o m p o s i t e s t r a t i g r a p h i c s e c t i o n f o r t h e w a v y b a n d e d l i m e s t o n e f o r m a t i o n 24 1 1 — 7 P h o t o g r a p h o f t h e u p p e r m e m b e r o f t h e w a v y b a n d e d l i m e s t o n e f o r m a t i o n 27 1 1 - 8 C o m p o s i t e s t r a t i g r a p h i c s e c t i o n o f t h e H o w a r d s P a s s f o r m a t i o n s h o w i n g t h e v a r i o u s m e m b e r s 3 0 1 1 - 9 P h o t o g r a p h o f a s p e c i m e n o f t h e c a l c a r e o u s m u d s t o n e m e m b e r 3 3 1 1 - 1 0 S t r a t i g r a p h i c c o l u m n s h o w i n g an i d e a l c y c l e w i t h i n t h e a c t i v e m e m b e r 3 8 1 1 - 1 1 D e t a i l e d s e c t i o n s o f t h e a c t i v e m e m b e r i n d r i l l h o l e s 1 2 , 18 a n d 19 3 9 1 1 - 1 2 D e t a i l e d l i t h o l o g i c l o g o f d r i l l h o l e 36 4 0 1 1 - 1 3 S p a c i a l d i s t r i b u t i o n o f t h e b a s a l f a c i e s i n t h e XY a r e a 42 1 1 - 1 4 P h o t o g r a p h o f t h e t h i n b e d d e d c a l c a r e o u s m u d s t o n e f a c i e s o f t h e a c t i v e m e m b e r 4 6 1 1 - 1 5 P h o t o g r a p h o f t h e t h i n b e d d e d c h e r t y m u d s t o n e f a c i e s o f t h e a c t i v e m e m b e r 4 9 1 1 - 1 6 S p e c i m e n o f l a m i n a t e d w h i t i s h g r e y Z n - P b m u d s t o n e 53 X Page 11-17 Photograph of the grey chert f a c i e s of the a c t i v e member 56 11-18 Composite s t r a t i graphic s e c t i o n of the upper s i l i c e o u s mudstone member of the Howards Pass formation 58 11-19 Specimen of a broken limestone c o n c r e t i o n o c c u r r i n g in the upper s i l i c e o u s mudstone member 60 11-20 Composite s t r a t i g r a p h i c s e c t i o n f o r the fl a g g y mudstone formation from DDH 38 61 11-21 Photograph of the orange weathering unit of the fl a g g y mudstone formation 63 1-22 Worm burrows o c c u r r i n g in the orange weathering un i t of the f l a g g y mudstone formation 65 1-23 Composite s t r a t i graphic s e c t i o n f o r the upper chert formation 69 1-24 Composite s t r a t i g r a p h i c s e c t i o n f o r the Iron Creek formation 72 1-25 Graded beds t y p i c a l of d i s t a l t u r b i d i t e s o c c u r r i n g in the Iron Creek formation 74 1-26 S t r a t i graphic s e c t i o n f o r the Selwyn Mountains b a r i t e horizon i n the XY area 76 1-27 Laminated b a r i t e from the Selwyn Mountain b a r i t e horizon 77 1-28 Composite s t r a t i g r a p h i c s e c t i o n of the Yara Peak formation 80 1-29 Photomicrograph of a greywacke from the Yara Peak formation 81 1-30 Photomicrograph of the carbonaceous wacke o c c u r r i n g in the Iron Creek formation 82 1-31 T u r b i d i t e sequences present in the Yara Peak formation and chert pebble conglomerate 84 I- 32 Composite s t r a t i g r a p h i c s e c t i o n f o r the chert pebble conglomerate unit 87 II - 1 B i o s t r a t i g r a p h i c c o r r e l a t i o n of un i t s in the Howards Pass area 93 11-2 L i t h o f a c i e s t i m e - s l i c e i n t e r p r e t a t i o n f o r the eastern Selwyn Basin during d e p o s i t i o n of the wavy banded limestone formation 99 xi Page 111-3 General l i t h o f a c i e s t i m e - s l i c e i n t e r p r e t a t i o n of the eastern Selwyn Basin during d e p o s i t i o n the Howards Pass formation 100 111-4 Composite s t r a t i g r a p h i c s e c t i o n s of the Howards Pass formation across the base of slope f a c i e s 101 111-5 Diagram showing s p a c i a l r e l a t i o n s h i p s between the basin and the edge of the Basin during the lower P a l e o z o i c area 102 111-6 General trends w i t h i n an i d e a l i z e d a c t i v e member cy c l e 107 111-7 General l i t h o f a c i e s t i m e - s l i c e i n t e r p r e t a t i o n f o r the f l a g g y mudstone formation in the Nahanni map-area 110 111-8 General l i t h o f a c i e s t i m e - s l i c e i n t e r p r e t a t i o n f o r the upper chert formation in the Nahanni map-area 117 111-9 General l i t h o f a c i e s time-s1ice i n t e r p r e t a t i o n f o r the Iron Creek formation in the Nahanni map-area 114 111-10 Photograph showing the Iron Creek formation o v e r l y i n g limestone of the carbonate sequence on the northeast side of the South Nahanni River 115 111-11 L i t h o f a c i e s t i m e - s l i c e i n t e r p r e t a t i o n f o r the Yara Peak formation and the chert pebble conglomerate in the Nahanni map-area 118 111-12 Submarine fan environmental model 119 I I I - 13 Facies i n t e r p r e t a t i o n f o r the upper Road River and Earn groups based on the submarine fan model 122 IV- 1 Map of the Howards Pass property showing the l o c a t i o n of the XY, ANN IV and OP deposits and the approximate o u t l i n e of r e l a t e d sub-basins 124 I V- 2 Sample of laminated sulphide of t e x t u r a l type I 126 I V- 3 Photomicrograph of a well preserved p y r i t e framboid 129 x i i P a g e I V -4 P h o t o m i c r o g r a p h o f m o d i f i e d f r a m b o i d s o f p y r i t e 13 2 I V - 6 P h o t o m i c r o g r a p h o f m i c r o f o l d s i n t e x t u r a l t y p e I I 1 3 3 IV - 7 P h o t o m i c r o g r a p h s h o w i n g m a s s i v e p y r i t e i n t e x t u r a l t y p e I I 1 3 4 IV -8 P h o t o m i c r o g r a p h o f p y r i t e c u b e o c c u r r i n g i n t e x t u r a l t y p e I I 1 3 6 I V - 9 S p h a l e r i t e c o n c e n t r a t e d i n f o l d h i n g e o f t e x t u r a l t y p e I I I 1 3 7 I V - 10 P h o t o m i c r o g r a p h o f a f l o w f o l d s o c c u r r i n g i n t e x t u r a l t y p e I I I 1 3 9 I V -11 P h o t o m i c r o g r a p h o f w h i t i s h g r e y Z n - P b m u d s t o n e s h o w i n g t e x t u r a l t y p e I V a 142 I V - 12 P h o t o m i c r o g r a p h o f t e x t u r a l t y p e I V a s h o w i n g b u c k s h o t t e x t u r e 1 4 3 I V - 1 3 P h o t o g r a p h o f p i l l a r s t r u c t u r e s i n t h e w h i t i s h g r e y Z n - P b m u d s t o n e f a c i e s 1 4 4 I V -14 S u l p h i d e f i l l e d c l e a v a g e i n t h e w h i t i s h g r e y Z n - P b m u d s t o n e 1 4 6 I V - 1 5 P h o t o m i c r o g r a p h o f m i n e r a l s e g r e g a t i o n o f s u l p h i d e i n t h e c l e a v a g e i n t e x t u r a l t y p e I V b 1 4 7 I V - 1 6 P h o t o m i c r o g r a p h o f m a s s i v e s u l p h i d e i n t e x t u r a l t y p e V 1 4 8 I V - 1 7 D e t a i l e d s e c t i o n o f t h e w h i t i s h g r e y Z n - P b m u d s t o n e f a c i e s 1 4 9 I V - 18 M a j o r s t e p s i n t h e p r o c e s s o f d i a g e n e t i c p y r i t e f o r m a t i o n 1 5 3 I V - 1 9 A p o s s i b l e m o d e l f o r t h e e v o l u t i o n o f t h e w h i t i s h g r e y Z n - P b m u d s t o n e f a c i e s 1 5 4 V- l S p i r a l s t r u c t u r e o c c u r r i n g i n t h e t h i n b e d d e d c h e r t y m u d s t o n e f a c i e s 1 5 9 V - 2 S c h m i d t s t e r o g r a m b a s e d o n 3 8 2 p o l e s t o c l e a v a g e i n t h e H o w a r d s P a s s a r e a 1 6 7 V - 3 S t r u c t u r a l e v o l u t i o n o f t h e H o w a r d s P a s s a r e a t h r o u g h t i m e 1 7 0 xi i i Page VI-1 Location of diamond d r i l l holes 12, 18, 19 and 36 172 VI - 2 (a,b,c,) Element abundance compared to 173-s t r a t i g r a p h i c s e c t i o n from DDH-12 175 VI-3 (a,b,c,) Element abundance compared to 176-s t r a t i g r a p h i c s e c t i o n from DDH-18 178 VI-4 (a,b,c,) Element abundance compared to 179-s t r a t i g r a p h i c s e c t i o n from DDH-19 182 VI-5 Matrix of c o r r e l a t i o n c o e f f i c i e n t s f o r element p a i r s f o r DDH-12 185 VI-6 Matrix of c o r r e l a t i o n c o e f f i c i e n t s f o r element p a i r s of DDH-18 186 VI-7 Matrix of c o r r e l a t i o n c o e f f i c i e n t s f o r element p a i r s f o r DDH-19 187 VI-8 (a,b) Mean (x) element content f o r f a c i e s in the. 188-a c t i v e member 189 VI - 9 Pb + Zn vs. Zn:Pb r a t i o in the a c t i v e member showing the general trend of decreasing Zn:Pb r a t i o with i n c r e a s i n g Pb + Zn 190 VI-10 Zinc content compared to a c t i v e member l i t h o l o g y 192 VI-11 Pb+Zn content compared to a c t i v e member l i t h o l o g y 193 VI-12 Lead content compared to a c t i v e member l i t h o l o g y 194 VI -13 Copper-zinc-lead diagram f o r s t r a t i f o r m -sedimentary d e p o s i t s 195 VI-14 Organic carbon compared to Cu with r e g r e s s i o n l i n e 197 VI-15 Cd compared to Zn with r e g r e s s i o n l i n e 199 VI-16 Organic carbon compared to Ni with r e g r e s s i o n l i n e 200 VI-17 CaO compared to Mn with r e g r e s s i o n l i n e 203 VI-18 Secondary e l e c t r o n and X-ray scanning photographs of Fe, S, Zn and Pb in framboidal p y r i t e 211 VI-19 Microprobe t r a v e r s e across dewatering s t r u c t u r e in the w h i t i s h grey Zn-Pb mudstone f a c i e s . . . . 212 xi v Page VI- 20 Microprobe t r a v e r s e across lamination in the t h i n bedded cherty mudstone f a c i e s 214 VII- 1 Average <5 -^S values f o r seawater sulphate and sulphur in petroleum through time 217 V11 - 2 D i s t r i b u t i o n of sulphur isotope data from the Howards Pass deposits 220 V11 - 3 Sulphur isotope values f o r a s s o c i a t e d f a c i e s in the a c t i v e member 221 V II - 4 Reaction scheme f o r JJ. d e s u l f u r i c a n s . 225 V II- 5 Diagram showing r e l a t i o n s h i p of H 2 S to su b - b a s i n c o n d i t i o n s at 25 to 50°C 231 VIII - 1 Graph of 2 0 7 P b / 2 0 4 P b p l o t t e d against 206ph/204pb stacey and Kramers' two stage lead e v o l u t i o n curve 239 VIII - 2 Graph of 2 0 8 P b / 2 0 4 P b p l o t t e d against 206pb/204p|:) showing Stacey and Kramers' ( 1 975) two stage lead e v o l u t i o n curve 240 V II I - 3 Data points f o r r e c e n t l y deposited m e t a l l i f e r o u s sediments 244 I X -1 Density of ore forming brines 250 IX- 2 Sedimentary e x h a l a t i v e model f o r the Howards Pass deposits 252 IX-3 Plan view of the model f o r the formation of the Howards Pass Zn-Pb deposits 253 IX-4 Formation of brine in sub-basin 254 IX-5 I n t e r p r e t a t i o n f o r the o r i g i n of the i d e a l c y c l e in the a c t i v e member 256 IX-6 Plan view of major slump i n the XY Zn-Pb deposit 257 I X- 7 Diagramatic e v o l u t i o n of the XY sub-basin.... 258 IX-8 S t r a t i f o r m - s e d i m e n t a r y sulphide deposits grouped by age 212 IX-9 Generalized synsedimentary model f o r the formation of sub-class I s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s 266 I X-10 Gen e r a l i z e d d i a g e n e t i c model f o r formation of sub-class I s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s . . 267 XV Page IX-11 Generalized synsedimentary model f o r the formation f o r sub-class II s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s 270 IX-12 Ge n e r a l i z e d d i a g e n e t i c model of formation f o r sub-class II s t r a t i form-sedimentary deposits 272 IX-13 Water escape curves f o r various temperatures and depths of b u r i a l 273 IX-14 O r d o v i c i a n - S i l u r i a n s i l i c e o u s mudstones of North America 276 IX-15 Late Ordovician pa 1eocontinenta 1 map 277 IX-16 Late S i l u r i a n to Middle Devonian p a l e o c o n t i n e n t a 1 map 278 IX-17 Comparative s t r a t i g r a p h y of the Howards Pass and MacMillan Pass area 280 A - l Location map showing the map areas 308 C-l Location of s t r a t i g r a p h i c s e c t i o n s discussed in text 311 D-1 Location map of Zn, Pb and Ba occurrences in the Yukon and Northwest T e r r i t o r i e s 312 xvi LIST OF TABLES Table Page II — 1 Table of u n i t s from the Howards Pass area.... 14 III — 1 Summary of r e g i o n a l s t r a t i g r a p h i c c o r r e l a t i o n in the eastern Yukon 92 111 - 2 Major d e p o s i t i o n a l environments f o r the s t r a t -i g r a p h i c u n i t s in the Howards Pass area 121 IV-1 Point counts f o r sulphide minerals of t e x t u r a l types I thru V 127 VI-1 Mean (x) element contents f o r various elements in column at l e f t f o r the s t r a t i graphic u n i t s shown at the top of the t a b l e 184 VI- 2 Trace element r a t i o s from s t r a t i g r a p h i c u n i t s in the Howards Pass area 202 VII- 1 Sulphur isotope r a t i o s f o r the Howards Pass dep o s i t s 218 V11 - 2 Values f o r the p a r t i t i o n i n g of sulphur between sulphur spec ies 228 VII I - 1 Lead isotope r a t i o s of sulphide minerals f o r the Howards Pass d e p o s i t s 237 IX- 1 Table showing c h a r a c t e r i s t i c s of proximal, d i s t a l and sedimentary sulphide deposits 249 I X - 2 General s i z e of s t r a t i f o r m - s e d i m e n t a r y sulphide deposits 261 IX- 3 Table of f e a t u r e s a s s o c i a t e d with sub-class I type s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s 265 IX-4 Table of f e a t u r e a s s o c i a t e d with sub-class II type s t r a t i f o r m - s e d i m e n t a r y deposits 269 I X - 5 Table of f e a t u r e s a s s o c i a t e d with sub-class III type s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s 275 E- l Methods used in chemical a n a l y s i s of Howards Pass s amp les 313 E-2 (a,b) Data f o r chemical analyses in core from 314-d r i l l hole (DDH) 12 315 E-3 (a,b) Data f o r chemical analyses in core from 316-d r i l l hole (DDH) 18 317 E-4 (a,b,c) Data f o r chemical analyses in core 318-from d r i l l hole (DDH) 19 320 xvi i Page 6-1 Lead isotope parameters and constants used in the present research 325 x v n i LIST OF PLATES I Regional Geologic Map - Howards Pass _ , , ( s c a l e 1:32, 160) IT T fuckFL II Geologic Map - XY area ( s c a l e 1:4800) In Pockety ir, -„pcc> III Geologic Map - ANN IV area ( s c a l e 1:4800)... I-rr-fVH**** IV Geologic Map - OP area ( s c a l e 1:4800) In- Pockety. PREFACE xix "What now seems to be needed is a substantial increase in our under-standing of primary ores. One possible approach in this endeavour is to accept, as a working hypothesis, that ores are no more or no less than rocks and, provided the relevant conditions for the stability of ore minerals are observed, that they may have formed in all the ways that "or-dinary" rocks have formed. The ores themselves are then seen quite simply as natural polycrystalline aggregates conforming with the principles of physical metallurgy and "materials science". If such an assumption is cor-rect their development, pattern of distribution, and physiochemical charac-te r i s t i c s should conform quite systematically with that of the associated silicates and carbonates. The problem then becomes part of petrogenesis in its broadest sense." from ORE PETROLOGY by R.L. Stanton, 1972 XX ACKNOWLEDGMENTS I am very much indebted to Professor W. C. Barnes, my thesis super-visor, for continued discussions during research on the Howards Pass depo-si t s . His continued emphasis on sedimentalogical aspects of the Zn-Pb deposits has guided the author from overgeneralized concepts to detailed consideration of important aspects of mineral deposition in the sedimentary environments. Throughout the preparation of the manuscript Professor Barnes has provided invaluable guidance, assistance and encouragement for which I am most grateful. I am also indebted to the members of my thesis committee, Professors C. I. Godwin, A. J. Sinclair, D. Perry and R. V. Best for their help throughout the course of my thesis research and for c r i t i c a l reviews of the thesis manuscript. I am grateful for the beneficial discussions I had with Drs. A. E. Soregaroli, M. Barnes, J. W. Murray, J. V. Ross, H. R. Wynne-Edwards, B. Ryan andT.H. Brown and graduate students at U. B. C , especially R. Lett, B. Cooper and G. Ashley and R. 01 sen. Professors H. J. Greenwood and H. R. Wynne-Edwards provided encouragement during periods of low productivity while the manuscript was in preparation. Economic support for the thesis research was supplied mostly by Placer Development Ltd., including f i e l d support and laboratory funds. Funds for microprobe studies and one year teaching assistantship were provided by the Geological Sciences Department of the University of British Columbia. Per-sonal and research expense were partially defrayed by the James Coates Memorial award donated by Redstone Mines Limited during 1973-74. xx i Placer Development personnel also helped the present research by their c r i t i c a l discussions and constant encouragement; most notable of these are D. C. Rotherham, D. A. Howard, I. Borovic, B. Ainsworth, A. D. Drummond, E. A. Scholz, L. Adie, A. Spat, E. A. Lawrence, J. Hylands, E. Lonergan and A. Clendenan. Technical assistance was provided by other Placer employees. J. Taylor and C. Sawyer helped in the typing of early manuscripts; H. Goddard, P. Pacor, J. Libal and A. Kemp assisted in preparation of many of the figures. I am also grateful to the library staff at Placer for obtain-ing those hard to find articles which seem all too common. Drs. H. L. Hosmer, H. C. Ferreira, R. L'Lesperance and Mr. R. Peterson of the United States Steel Corporation have provided many stimulating dis-cussions. Their personal experience with ore deposits throughout the world provided information not obtainable in journals. The thesis topic was originally suggested by A. E. Soregaroli, A. D. Drummond and D. C. Rotherham. Dr. Soregaroli acted as thesis advisor dur-ing the i n i t i a l thesis research. Many stimulating discussions occurred throughout the course of the study in the thesis f i e l d area; these contributed much to my thinking on sedimentary ore deposits. Most influential were D. F. Sangster, W. Krebs, K. Dawson, N. Campbell, C. Smith, I. Borovic, P. Lasnica, R. Macqueen, K. Pride, J. Caja, L. Miller and many others who visited the author in the f i e l d . During the preparation of the manuscript I have received continual support from my fiancee Cheryl. To her go my sincerest thanks for her patience and understanding. 1 CHAPTER I INTRODUCTION PURPOSE AND SCOPE OF THE PRESENT STUDY The purpose of the report investigation is to construct an explora-tion oriented ore genesis model for sedimentary-type stratiform sulphide deposits, based primarily on a detailed investigation of the Howards Pass Zn-Pb deposits in the Summit Lake area of the Yukon and Northwest Territories. The deposits in the Summit Lake area were found in the summer of 1972. L i t t l e geologic information was available for the area, and therefore the geologic framework, a description of the Zn-Pb de-posits and the origin of the deposits are all considered in the present research. The emphasis in the present thesis is on the relationship between Zn-Pb sulphide formation and sedimentation; therefore, the vertical stratigraphic relationships are thought most important. Lateral facies relationships are also considered and appear relevant in the search for the Howards Pass type deposits. Because of the large size of the Howards Pass deposits and the early stage of exploration, lateral zoning within the deposits is not considered in detail. Thus, the present thesis does not represent an exhaustive description of the deposits, but an overall view aimed at defining key parameters thought important in the exploration for similar deposits. To this end the present research uses a multidisciplinary approach. Many of the ideas presented in the present thesis have, to a large extent, been presented by the author previously (Morganti, 1975; 1977a; 1979) and have been tested extensively by d r i l l i n g programs at Howards Pass and by exploration in the surrounding region. 2 METHODS OF STUDY In the course of the present study many methods of investigation were used. All of these were oriented toward the understanding of the origin of the Zn-Pb deposits in the hope of constructing an exploration oriented model of ore deposition. Surface mapping at various scales was used to define spatial, stratigraphic and structural relationships. Data were obtained by mapping 780 km^  at a scale of 1:31,680, and part of this information is presented as Plate I. Detailed mapping at a scale of 1:4800 was also completed in the areas of Zn-Pb mineralization (Plates II, III and IV) (Appendix A). Detailed logging by the author of 10,670 m of diamond d r i l l core at a scale of 1:120 also formed part of the data base. Many fresh samples were collected from the core; and cross-sections are based on both surface mapping and d r i l l core data. Representative samples from each lithologic unit were examined by semi-quantitative x-ray diffraction methods described by Schultz (1964) (Ap-pendix B), owing to limitations of optical methods because of the fine grain size of the rocks. Many samples of the lithologic units and sul-phides were examined microscopically. Other methods were also used and detailed descriptions of these methods are presented with the data, but brief mention of these techniques is made here. Cores from three d r i l l holes which had intersected the mineralized formation were analyzed for various trace and major elements. Over 3000 quantitative analyses by atomic absorption spectrometry and/or x-ray fluorescence spectrometry were completed and organic carbon and carbonate measured by loss on ig-nition. Detailed chemical studies using the electron-microprobe were completed on material from the Zn-Pb deposits; again, distributions of 3 both trace and major elements were studied. Lead and sulphur isotope studies were completed in an effort to locate possible sources for the cationic and anionic components of the ore minerals. All these data were collected with the specific goal of developing an exploration model for the Howards Pass deposits. LOCATION AND ACCESS The Howards Pass area (Lat. 62°27'N., Long. 129°12' W.) is centered 20 km northeast of Summit Lake and straddles the Yukon Territory -Northwest Territories border (Fig. 1-1). The area extends 40 km from the Pelly River to five km southeast of Yara Peak (Fig. 1-2). Access was i n i t i a l l y by float plane from Watson Lake to Summit Lake, a distance of 258 km, and by helicopter from Summit Lake to the main camp. Winter access is by ski plane from Watson Lake to camp or by a winter road originating from Mile 101 on the Nahanni Range Road bet-ween Watson Lake and the town of Tungsten. A 520 m dry weather airs t r i p was constructed in 1973 and improved in 1974. It is suitable for small aircraft such as Otter, Twin Otter and Twin Bonanza. TOPOGRAPHY AND CLIMATE Topography of the Selwyn Mountains in the area of Howards Pass con-sists of broad glaciated valleys, rolling h i l l s and steep alpine-type peaks. Elevation of the study area ranges from 1100 m near the Pelly River to 1986 m at Yara Peak (Fig. 1-2). Major valleys above 1000 m are wide and U-shaped due to Pleistocene alpine glaciation. Much of the area studied in detail consists of gently rolling h i l l s with sparse pe-l i t i c rocks cropping out, and barren glaciated peaks carved from coarse-grained sedimentary rocks (Fig. 1-3). Most of the study area is above 4 Figure 1-1. Location map for the Howards Pass deposits, showing Howards Pass, the Yukon-Northwest Territories border, Tungsten and Watson Lake. Figure 1-2. Location map of the various claim groups which constitute the Howards Pass claims. The main claim groups are the XY, DON, ANNIV and OP. 6 Sugar Mtn. Yara Peak Figure 1-3. The Howards Pass area, showing the rounded peaks and the lack of trees above 1400 m. Photograph taken looking east in the XY area. 7 the 1400 m tree line in the region, and dense spruce forests and willow shrubs are present only in large valleys below 1400 m elevation. Climate in the area is typical of this portion of the Yukon and Northwest Territories with wet cool summers and extremely cold winters. The f i e l d season runs from mid-June to mid-September in an average year. Snow thickness at base camp (elevation 1503 m) ranges from 2 to 5 m based on three years of observations, and temperatures averaged -15°C from October to May. Temperatures during the f i e l d season averaged 7°C to 10°C with moderate shower activity frequent in the afternoons. LOCAL GEOGRAPHY Names given to geographic features in the Howards Pass area are shown in Figure 1-2. Henceforth in this report claim groups (Fig. 1-2) will be referred to as areas, such as the XY, DON, ANNIV and OP areas, while the term Howards Pass area refers to the whole group of claims. The surrounding areas referred to are located relative to the various above claim groups. The Howards Pass map-area refers to the area in Plate 1. The Nahanni map-area or map sheet refers to the area covered by the 4 mi. topographic map (Fig. A-l). HISTORY AND PREVIOUS GEOLOGIC INVESTIGATIONS The Howards Pass Zn-Pb deposits were discovered by Canex-Placer personnel in 1972 following a regional stream sediment geochemical sam-pling program that began in 1966. By 1971, follow-up stream sediment geochemical sampling had delineated several anomalous areas overlying "black shales" that extended for 40 km along the regional strike. Sta-king commenced in 1972 over the geochemical ly anomalous areas and sul-phide showings were subsequently discovered by prospecting. The present 8 study began in 1973 and f i e l d work was concluded during the summer of 1975, during which time 10,670 m of diamond d r i l l i n g were completed on the property. Prior to the present study of the Howards Pass area, geologic in-vestigations were of a regional nature. The Nahanni map-sheet (105-1) was mapped by the Geological Survey of Canada during the early 1960s and a geologic map and legend was published in 1967 (Green et a l . , 1967). Their mapping consisted of aerial photograph interpretation and widely spaced regional check traverses. The published map grouped all Paleo-zoic pelites of the Howards Pass area into unit 18b, host for the Howards Pass deposits. Subsequently, Gabrielse (1967) summarized the geology of the Yukon and correlated the rock units defined by Green et a l . (1967) with other units in the region. Mapping projects similar to that completed by the Geological Survey of Canada in the Nahanni area included the Sekwi Mountain area (Blusson, 1971), Flat River (Gabrielse et a l . , 1973) and Coal River (Gabrielse and Blusson, 1969). These maps provide general regional data, but the method used appears to be better suited to areas with predominatly limestone lithologies rather than the recessive, low colour contrast, basinal facies considered in this study. In 1977 the Geological Survey of Canada began a mapping project in the area on a scale of 1:50,000, this project includes 1/5 of Plate I in the XY area. ROCK CLASSIFICATION USED IN THE PRESENT STUDY The general sedimentary rock classification proposed by Krumbein and Sloss (1953) has been adopted here although their terminology was modified according to Blatt et a l . (1972). "Mudstone" is preferred as a 9 general term because of grain size implications, while shale is defi-nable in terms of fabric. " A r g i l l i t e " , a term used extensively by some for mudstone, is more correctly used for a mudstone hardened by i n c i -pient metamorphism, especially in Precambrian terrains (Blatt et a l . , 1972) and should not be used for diagenetically altered varieties. In the present report, "shale" refers to mudstone which is f i s s i l e parallel to bedding. The Lower Paleozoic rocks in the Howards Pass area contain only minor amounts of shale. The term "black shale" is somewhat mis-leading, for as defined by Swanson (1961) i t is not restricted to a single lithologic type of carbonaceous mudstone, but includes other dark coloured, fine-grained rocks. Demonstrating the range of material con-sidered to be classified as black shale are examples such as the "Chat-tanooga shale" which is chiefly a siltstone (Conant and Swanson, 1961), the graptolitic black shale in the Vinini Formation in Nevada, U.S.A., which is siliceous mudstone (Ketner and Smith, 1963), the Kupfershiefer of Germany and the Green River Formation of the interior of the U.S.A., which are marlstones (Wedepohl, 1964; Bradley, 1931), and Pennsylvanian black shale in western Indiana, U.S.A., which is intermediate in compo-sition beween claystone and coal (Zanger et. a l . , 1963). In this report "black shale" is used only as a general term since the specific use of the term has varied to a great degree in depositional environments and chemical characteristics, both of which are of great importance in con-sidering contained ore deposits. In the present report mudstone, s i l t -stone and shale with appropriate modifiers are preferred. 10 CHAPTER II GEOLOGY INTRODUCTION The Howards Pass Zn-Pb deposits occur in unmetamorphosed Lower Paleozoic basinal facies of the Selwyn Basin in the northern Canadian Cordillera within the Yukon and western Northwest Territories. The nor-thern part of the Cordillera can be divided into two major tectonic ele-ments separated by the Tintina Trench (Fig. 11-1). East of this major geologic and physiographic discontinuity, with an estimated 450 km of displacement (Fig. 11-2) (Tempelman-Kluit, 1977), are Precambrian to Tertiary sedimentary and minor metasedimentary rocks which have been in-truded by Mesozoic granitic plutons. To the southwest of the Tintina Trench are metasedimentary and meta-igneous rocks cut by Mesozoic to Tertiary intrusions (Gabrielse, 1967). Rocks to the southwest of the trench are not considered further in this report. The Selwyn Basin has been defined as a major Paleozoic tectono-stratigraphic feature to the east of the Tintina Trench, and consists of unmetamorphosed pelites and limestones ranging in age from Cambrian to Mississippian (Gabrielse, 1967). Zn-Pb deposits at Howards Pass occur in Ordovician-Si1urian carbonaceous and siliceous mudstones near the edge of the eastern side of the basin. Rocks of the Selwyn Rasin uncon-formably overlie Hadrynian to possibly Cambrian argillaceous and quart-zose rocks with minor limestone informally referred to as the "Grit Unit" (Roddick and Green, 1961; Green and Roddick, 1962). Rocks as young as Mississippian (?) are intruded by Cretaceous granitic rocks, some of which have associated tungsten mineralization. Pleistocene alpine glaciation has carved out the present topography, with granitic n Figure 11-1 - Major tectonic features of the Yukon and western Northwest Territories, showing the relative location of the Selwyn Basin (from Gabrielse, 1967). 12 Figure II-2. Reconstruction of part of the northern Cordillera, showing the original outline of the .Selwyn Basin. Also shown are the Mackenzie Platform, Cassiar Platform and Yukon Cataclastic Complex (modified from Tempelman-Kluit, 1979). 1 3 intrusions, coarse-grained clastic sedimentary rocks and limestones forming most of the sharp alpine type peaks and fine-grained clastic rocks underling lower rolling h i l l s and low mountains. In the present study regional and detailed mapping was confined to the Nahanni Map-Sheet (Green et a l . , 1967) (Appendix A). The terminology used in this report follows the Code of Strati-graphic American Commission on Stratigraphic Nomenclature (in Blackadar, 1972; Hedberg, 1976). The units are rock-strati graphic units based on lithologic characteristics. Two separate identification systems are used in the Howards Pass region. F i r s t , numbers and letters used by Green et a l . (1967) are used with significant sub-divisions and second, local informal names used by many geologists working in the area (e.g. Roberts, 1978) and f i r s t proposed by Morganti (1975). Using this two-fold stratigraphic nomenclature a unit would be presented, for example, as 18b-l (Howards Pass formation (Table I I - l ) ) . LOCAL GEOLOGY The most important geologic aspects pertaining to the Howards Pass Zn-Pb deposits are stratigraphy, sedimentation and structure. As will be evident throughout this report the Howards Pass deposits are synsedi-mentary; thus, subsequent structural evolution of the area has affected the Zn-Pb deposits as well as the other sediments. The stratiform nature of the deposits indicate that regional and local stratigraphy are the best exploration guides in the area. 14 Table I I - l . Table of units from the Howards Pass area. All units in the table are informal. P E R I O D G r e e n e t a l 1 9 6 7 T h i s r e p o r t -b a s e d on m a j o r u n i t s p r o p o s e d by G r e e n e t a l . , 1 9 6 7 T h i s r e p o r t - l o c a l i n f o r m a l u s a g e ( M o r g a n t i , 1 9 7 5 ) . P E N N S Y L V A N I A N MISSISSIPPI DEVONIAN S I L U R I A N O R D O V I C I A N CAMBRIAN ->ADRYNIAN 18b 1 8 b - 3 ! 8 b - 2 10c C H E R T P E B B L E C O N G L O M E R A T E V A R A P E A K F O R M A T I O N I R O N C R E E K F O R M A T I O N U P ^ E ! " 1 ! ! H 1 ' R T ~ ^ 10b FLAGGY MUDSTONE FORMATION 10a H O W A R D S P A S S F O R M A T I O N 7b-3 T R A N S I T I O N F O R M A T I O N W A V Y B A N D E D L I M E S T O N E F O R M A T I O N M A S S I V E L I M E S T O N E F O R M A T I O N L O W E R S I L T S J Q 2 E J I N I J 15 STRATIGRAPHY MAP-UNIT 2 ('GRIT UNIT') The oldest rocks studied in the Howards Pass area are fine-grained clastic rocks (with minor limestone) mapped by Green et a l . (1967) as Map Unit 2 and in the present study lithologically correlated with the 'Grit Unit 1 of Gabrielse (1967). These rocks show intense deformation and are overlain unconformably by the Paleozoic formations. Outcrops mapped as 'Grit Unit' occur to the southwest of the Howards Pass area. The generalized section (Fig. II-3) presented here is tentative due to the reconnaissance nature of the traverses made over these rocks, and to typically recessive outcrops which only locally form steep slopes where capped by more resistant units. The commonest rock types, in order of decreasing abundance, are in-tercalated maroon and green to buff mudstones to siltstones, grey to brown mudstones and siltstones with minor sandstones, green phyllites and minor limestone. The base of this unit was not observed in the Howards Pass area. The lowest rocks noted in the section (Fig. 11 -3) are dark grey to brown mudstones to siltstones which are overlain by orange weathering dolomitic limestone. These are overlain by inter-calated maroon and green mudstones and siltstones which constitute a majority of the 'Grit Unit' near Howards Pass. In areas where the unit is thin, green rocks overlie the maroon rocks, but at thicker sections this sequence can be repeated up to five times. A limestone conglo-merate overlies the brightly coloured pelites and locally is the top of the 'Grit Unit'. The conglomerate contains grey limestone clasts which are slightly rounded occurring in an orange weathering dolomitic 1 6 lower siltstone unit-orange weathering dolomitic siltstone .unconformity (?) Discontinuous light green phyllite unit Conglomeratic limestone with grey limestone clasts in an orange weathering dolomitic limestone matrix. Maroon and green pelite-dusky red to light green mudstone, minor light grey, silver weathering shale, with minor siltstone near contacts. Typically green mudstone overlies maroon mudstone. Mudcracks and cross-beds are present locally. Contacts between maroon and green mudstone are gradational in colour without apparent other lithologic changes. Grey shale and slate. i-Grey siltstone and shale with abundant graded beds. Dolomitic limestone, locally dolostone which weathers orange, but is various shades of grey in fresh outcrops. Grey mudstone, shale and siltstone. Base of section near Summit Lake. Figure 11-3. Composite strati graphic section for the 'Grit Unit' with approximate scale. The section is based on locals between Howards Pass and Summit Lake, southeast of the eastern edge of Plate I. 17 limestone matrix. Locally, clasts of the dolomitic matrix suggest that the unit is an intraformational conglomerate. Pale green phyllites occur throughout the top 100 m of the unit, but are associated with faults and are thought to have been produced by an increase in water pressure associated with these structures (Higgins, 1971). It is also possible that the phyllites constitute a stratigraphic unit (Gabrielse, 1967), but no evidence for this was found in the Howards Pass area. MAP-UNIT 7a (LOWER SILT STONE UNIT) Map-unit 7a, here informally called the lower siltstone unit, con-sists of a sequence of dolomitic siltstones exposed 8 km southeast of the XY camp (Fig. II-4). Only a few outcrops of the unit have been ob-served in stream beds and therefore no thickness estimates are pre-sented. The unit consists of siltstone and minor amounts of sandstone, both of which contain abundant calcite and dolomite cement. Spatial re-lationships between the siltstone and sandstone have not been observed, but the local occurrence of these sandstone bodies suggests that they occur as lenses within the siltstone (Fig. II-4). The siltstones are massive, showing l i t t l e evidence of bedding, whereas the sandstone lenses show a weakly developed low angle (less than 10°) tabular cross-bedding. Locally, minor amounts of dark to pale green mudstone are associated with siIty dolomite. These green mudstone beds can be traced in float along strike for over 10 m. I l l i t e and abundant albite ob-served in thin section suggest that the beds are altered tuffs. Siltstone consists of quartz, K-feldspar and muscovite in order of decreasing abundance, with quartz and K-feldspar occurring as sub-rounded grains. Quartz typically shows overgrowths. Muscovite occurs 18 Massive limestone formation • grey weathering limestone, unconformity (?) massive Orange weathering dolomitic siltstone to s i l t y dolomite with lenses ( ? ) of dolomitic siltstone to sandstone occurring locally. — Pale green tuff float Orange weathering dolomitic siltstone to s i l t y dolomite with lenses. ( ? ) unconformity (?) Grit Unit • light green phyllite unit Figure II-4. Composite stratigraphic section for the lower s i l t -stone unit. The tuff horizon does not outcrop, but can be traced in float. Section is based on area 0.5 km southeast of the southeast cor-ner of Plate I. Scale is approximate. 19 both as randomly oriented grains and as grains aligned sub-parallel to cleavage in thin section forming a microscopic slaty cleavage not evi-dent in outcrop. Sandstones show the same mineralogy but with less muscovite. Calcite and dolomite cement constitute up to 5 to 10% of the rock with the higher values occurring in the sandstone. Calcite forms simple cement bonds (Dapples, 1967) between quartz and K-feldspar grains; this calcite is in part replaced by later stage dolomite. Late stage recrystallization of muscovite, minor chert and clay accompanied development of slaty cleavage. The contact between the lower siltstone unit and the 'Grit Unit' has not been seen by the author, although angular discordance and the lack of intense folds similar to that found in the 'Grit Unit' are evi-dent suggest an unconformity. A pre-Franconian regional unconformity with low angular discordance has been proposed by Douglas et a l . (1970). Using the stratigraphic sequence of this report, the uncon-formity should occur between the lower siltstone and the overlying mas-sive limestone formations, but no evidence for or against this proposal could be found, as the contact is everywhere covered. Regional correla-tion of the lower siltstone is tentative owing to the lack of fossils and major east-west facies changes that occur in unit. Lithologically similar rocks occur in the Sekwi Formation of Early Cambrian aqe in the Sekwi Map Sheet to the north (Blusson, 1971; W. J. Crawford, Oral Commun., 1976). MAP UNIT 7b-l (MASSIVE LIMESTONE FORMATION) Map unit 7b-l is informally termed the massive limestone formation and is mappable on a regional scale. The formation consists of massive grey, micritic siliceous limestone which crops out in the northeastern 20 part of the XY map area (Plate I). Although outcrops are abundant along ridge tops, valley occurrences are poorly exposed. There is no type section for the unit owing to the discontinuous and spotty nature of the outcrops, although an idealized section is proposed (Fig. 11-5). It is estimated that the formation is 100 to 300 m thick, although folding may account for some of this thickness. Contacts between the massive limestone and overlying wavy banded limestone are faults in the XY map area (Plate II), although gradational contacts between these two formations are present northeast of the DON area. Continuous deposition is further supported by lithologic simi-lar i t y between the massive limestone and the thick microsparite beds of the lower member of the wavy banded limestone. Two major rock types are present within the formation (Fig. 11-5). Over 90% of the outcrops consist of generally massive microspar grading locally into micrite. Minor occurrences of biomicrite occur as lenticu-lar masses in the lower part of the formation. The massive microspar constitutes most of the lower 50 m and all upper portions of the forma-tion, and is easily identified by its massive grey outcrops showing rough, elephant hide-like surfaces. The main sedimentary structure noted in this rock type is parallel bedding which is weakly defined by darker detrital laminae 2 mm to 1 cm thick. These quartz-rich carbona-ceous laminae are typically irregular. Two types of calcite concretions occur: (1) Minor light calcite-quartz lenticular concretions 2 to 5 rrm thick and 20 mm to more than 10 cm long occur parallel to bedding. Gradational contacts and minor folding indicate that these were formed soon after deposition of the surrounding limestone, before complete 21 i n ro CM t i ' ' 1 i -i s "1 k » i Wavy banded limestone formation consisting of intercalated microsparite and micrite Upper unit - grey weathering, poorly bed-ded microspar and micrite, with micrite occurring as isolated patches. Lower unit - grey weathering, weakly bedded microspar with patches of micrite, also present are lenses of biomicrite up to 75m across. unconformity (?) Lower siltstone unit - orange weathering dolomitic siltstone. Figure 11-5. Composite stratigraphic section of the massive lime-stone formation. Based on cl i f fs north of Don Creek (Location 7b-l, Appendix C). 22 1ithification. Grain sizes within these concretions are less than 10 ym. (2) Coarse-grained (150 ym to 500 ym) calcite occurs in semi-spherical concretions and veins. These concretions are 5 to 20 cm across; bedding is draped over them indicating that they were present before 1ithification. The two types of concretions are considered to have similar origins although the slightly higher clay content of the smaller concretions may have hindered crystal enlargement during neomor-phism. The greater extent of deformation noted in the concretions with less evidence of crystal enlargement may be explained by the greater strength associated with larger crystal size (Fuchtbauer, 1974). Calcite veins are abundant in the unit, and appear to cut a l l sedimentary features. Many of the micrite laminae are argillaceous. The micrite appears dark in thin section with grain sizes generally less than 10 ym across, and occurs as patches within a s i l i c i c microspar (Folk, 1962). The microspar grains are 5 to 40 ym across, showing t r i p l e junctions and serrated edges suggestive of neomorphism (Bathurst, 1975). Calcite con-stitutes 90% of the microspar with approximately 10% quartz and trace amounts of organic matter and clay. Locally the microspar-micrite is intercalated with argillaceous microspar laminae up to 2 cm thick, a l -though most are less than 1 cm thick. These contain up to 30% clay, the rest being microspar and minor amounts of organic matter. The mixed microspar and micrite contain up to 30% intraclasts, some of which show deformed twin lamellae. The lower 50 m of the massive limestone formation contain lenses of calcarenite (packstone of Dunham, 1962) showing poorly developed 23 bedding. The grain-supported limestone contains up to 60% intraclasts which appear to be composed of fossil and possibly oolith fragments. Some of the fragments show attached calcite and/or dolomite cement indicating 1 Unification had occurred before the clasts were deposited in the unit. The matrix is similar to micrite noted elsewhere in the formation, with microspar and quartz grains common. MAP UNIT 7b-2 (WAVY BANDED LIMESTONE FORMATION) The wavy banded limestone formation is a regionally significant clastic deposit which shows characteristic "chain-link" outcrop surface texture in the upper part. The unit is correlated 1 ithologically with part of the Rabbitkettle Formation to the south and east (Gabrielse et a l . , 1973). Rocks of the wavy banded limestone crop out in areas surrounding the XY area, and are present along the edge of the DON area and the northern edge of the ANNIV and OP areas (Plate I). The unit is esti -mated to be 250 to 300 m thick (Plates I - IV), although i t is apparent-ly thickened to over 500 m by minor folding which is pervasive through-out the upper member of the formation. As discussed previously, the lower part of the unit is interdigitate with the massive limestone for-mation. The upper contact with the transition formation is gradational over 10 to 30 m. The wavy banded limestone is divided into two informal members (Fig. 11-6) based on the amount of argillaceous material in some beds, as expressed at outcrops in the thickness and evenness of bedding. The lower member consists of intercalated microspar and micrite, and shows even bedding, whereas the upper member consists of intercalated 24 — — V 1 ! i - 1 -7 1 _ l I - 1 — i— — 1 ' i ' l ' ) 1 1 1 L 1 1 1 1 j ^ J ) / Transition formation - laminated mudstone Upper member - intercalated light grey microsparite and micrite and calcareous mudstone, laminae are 1 to 5 cm thick. The top 50 m shows a characteristic chain link structure. Carbonate content of the mudstone laminae decreases up section. Green tuff occurs in lower 30 m of member. Lower member - intercalated light grey microspar and dark grey micrite beds which are 5 to 40 cm thick. Massive limestone - light grey weathering massive microsparite. Figure 11-6. Composite strati graphic section for the wavy banded limestone formation. Based on exposures on a h i l l southeast of the XY area (Location 7b-2, Appendix C). Scale is approximate. 25 s i l i c e o u s m i c r i t e and a r g i l l a c e o u s m i c r i t e beds s h o w i n g a " c h a i n - l i n k " s t r u c t u r e . A g r a d a t i o n a l c o n t a c t s e p a r a t e s t h e s e two members. The l o w e r member o f t h e wavy banded l i m e s t o n e c o n s i s t s o f i n t e r b e d r i e d m i c r o s p a r i t e and m i c r i t e . Most beds a r e 5 t o 30 cm t h i c k w i t h some m i c r i t e b eds o v e r 10 cm t h i c k s h o w i n g an a p p a r e n t g r a d e d b e d d i n g . T e x t u r e s i n d i c a t i v e o f b o t t o m c u r r e n t d e p o s i t i o n h a v e n o t been n o t e d . P e t r o g r a p h y o f t h e l o w e r member shows t h a t t h e d a r k g r e y m i c r i t e b eds ( t y p e I I I M o f F o l k , 1959) l o c a l l y c o n t a i n t r a c e q u a n t i t i e s o f p e l l e t s . B e s i d e s m i c r i t i c c a l c i t e w i t h g r a i n s i z e s up t o 10 ym, c l a y s and q u a r t z i n t h e same s i z e r a n g e c o n s t i t u t e up t o 10% and a r e d i s t r i b u t e d e v e n l y t h r o u g h o u t t h e r o c k . The f i n e g r a i n e d n a t u r e o f t h e m i c r i t e and p r e s e n t s o f t r a c e amounts o f o r g a n i c m a t e r i a l g i v e t h e r o c k a b r o w n i s h t i n t i n t h i n s e c t i o n s . L i g h t g r e y m i c r o s p a r beds a r e i n t e r c a l a t e d w i t h t h e d a r k e r m i c r i t e b e d s i n t h e l o w e r member. T h e s e beds a r e 5 t o 40 cm t h i c k and show no p r i m a r y d e p o s i t i o n a l s t r u c t u r e s . X - r a y d i f f r a c t o g r a m s i n d i c a t e t h a t t h e m i c r o s p a r c o n t a i n s 9 5 % c a l c i t e w i t h 5% q u a r t z g r a i n s and o n l y t r a c e s o f m i x e d l a y e r e d c l a y s and o r g a n i c m a t t e r . The c a l c i t e and q u a r t z a r e 10 t o 40 ym a c r o s s and a r e t y p i c a l l y e q u i g r a n u l a r ; w i t h an i n t e r l o c k i n g m o s a i c o f c a l c i t e g r a i n s s h o w i n g t r i p l e j u n c t i o n s . L e s s t h a n 2% o f t h e t r i p l e j u n c t i o n s show e n f a c i a l j u n c t i o n s , i n d i c a t i n g a g g r a d i n g n e o m o r p h i s m ( B a t h u r s t , 1975) d u r i n g d i a g e n e s i s . The m a j o r d i f f e r e n c e b etween t h e m i c r o s p a r and t h e m i c r i t e i n t h e l o w e r member a r e t h e low c l a y and o r g a n i c m a t t e r c o n t e n t s i n t h e m i c r o -s p a r . A c c o r d i n g t o S p r y ( 1 9 6 9) i m p u r i t i e s s u c h as c l a y and q u a r t z h i n d e r r e c r y s t a l 1 i z a t i o n . T h u s , w h i l e t h e " p u r e r " m i c r i t e b e d s u n d e r g o r e -26 crystallization producing microspar, impurities in the clay rich micrite inhibit recrystal1ization. The sharp contacts between beds indicate that the original contacts between clay-rich and clay-poor micrite were also sharp. A green aquigene tuff breccia occurs in the lower 30 m of the upper member of the wavy banded limestone. In hand specimen coarse ash and l a p i l l i are over 2 mm across and are elongate parallel to bed-ding in the limestone. In thin section the tuff shows abundant r e l i c t glass shards. The best outcrops of this rock type are 7 km north of Yara Peak where the tuff is 12 m thick. The upper member of the wavy banded limestone formation is charac-terized by "chain link" structure which consists of intercalated light grey micrite and calcareous mudstone, and appears wavy owing to varying bedding thickness. Bedding is in general thinner than the lower member, with micrite beds ranging from 1 to 5 cm thick, and showing rapid lateral variation. Many of the beds show a weak grading. In thin sec-tions the micrite consists of 70 to 80% calcite with grains generally less than 10 pm across, although some grains are up to 20 ym across. Grey to tan laminated calcareous mudstone is interbedded of the micrite. These beds are 5 mm to 3 cm thick and consist of 5 to over 50 thin laminae. The mudstone beds generally drape over the discontinuous micrite beds forming a "chain-link" structure (Fig.II-7). In thin section the calcareous mudstone contains 20-30% calcite, 15-25% quartz and 45-65% clay. X-ray diffraction patterns from selected samples indi-cate the clay consists of mixed I M Q clay and 2M muscovite. Minor amounts of organic matter darken some laminae, and locally are concen-trated in the cleavage. Trace amounts of cubic pyrite are present in the mudstone and are much more abundant than in micrite beds. 27 Figure II-7. Photograph of the upper member of the wavy banded limestone formation. The wavy nature of the bedding is the result of the intersection of bedding and cleavage and constitutes the "chain-link" structure referred to in the text. The pencil near the top of the photograph is for scale. 28 Mineral species in the upper member vary progressively through the sequence. Quartz increases from 10% in the micrite at the base to 30% near the top. The calcareous mudstone also shows a progressive decrease in carbonate content at the top of the member. Thus, the combination of progressive increase in the relative abundance of mudstone and the dec-rease in carbonate defines a transitional contact with the overlying transition formation. MAP-UNIT 7b-3 (TRANSITION FORMATION) The transition formation consists of laminated mudstone and minor intercalated limestone, which separates the wavy banded limestone and the Howards Pass formations. This informal unit is mappable on a re-gional scale and is therefore given formational status. Texturally, the unit is similar to the wavy banded limestone; the main difference being the lower carbonate content. As the name implies, the unit is gradati-onal between the underlying limestones and the overlying carbonaceous mudstone. The lower contact with the wavy banded limestone is gradati-onal over 1 to 10 m, and is based on the calcite content. Rocks having less than 50% calcite are placed in the transition formation. The upper contact with the Howards Pass formation is also gradational, over 0.5 to 5 m, and is based on the organic matter content. The unit ranges from 10 to 80 m in thickness and is distinctive on a regional scale (Plate I ) . The formation consists predominantly of brown to grey weathering laminated mudstone. Three basic types of laminae have been recognized: (1) pale grey siliceous laminae, (2) brown clay-rich laminae and (3) pale grey calcareous laminae. The laminae are 1 to 10 mm thick; most 29 are over 5 mn thick and are both calcareous and more abundant near the base of the unit. Clay-rich laminae tend to occur in beds consisting of 5 to 50 laminae. Sedimentary structures other than parallel lamination are rare, with only a few graded beds evident near the base of the unit. X-ray diffractograms indicate a large range in mineral contents with 15 to 65% quartz, 20 to 45% 2 M muscovite, 0 to 45% calcite and up to 10% pyrite. MAP-UNIT 10a (HOWARDS PASS FORMATION) INDR0DUCTI0N The Howards Pass formation contains all economically significant Zn-Pb deposits in the Howards Pass area. The unit is given informal for-mational status, because of regional mappability and economic s i g n i f i -cance. The Howards Pass formation consists of highly carbonaceous, siliceous mudstones with minor chert and limestone. Detailed study both of surface outcrops and d r i l l core allows division into distinct members (Fig. 11-8). The active member, which contains the Howards Pass Zn-Pb deposits, is further subdivided into lithologic facies. The formation is moderately homogeneous, consisting of carbonaceous mudstones, most of which are siliceous. An exception is the active member, a heterogeneous unit consisting of intercalated carbonaceous mudstone, limestone and chert, with some mudstone containing up to 50% Zn+Pb. Mapping (Morganti, 1976) has shown that the Howards Pass formation is of regional extent (Plate I). The active member occurs discon-tinuously in a linear belt about 10 km wide for approximately 220 km between Flat Lakes and the Itsi Mountains along a 300° azimuth. Within 30 131 I r l r l r l - . =1 10b (flaggy mudstone formation) 10a-5 (upper siliceous mudstone member) -laminated, siliceous carbonaceous mudstone with abundant limestone concretions, and a graptolite zone 1 m thick occurring near the top of the member. 10a-4 (active member) - intercalated mudstone, limestone and chert with economically significant amounts of Zn and Pb with a poorly preserved graptolite horizon. 10a-3 (lower cherty mudstone member) -massive, carbonaceous siliceous mudstone with blocky fracture and up to 12% C( ) 10a-2 (calcareous mudstone member) -calcareous carbonaceous mudstone with 0.2 m graptolite zone. 10a-l (pyritic silceous shale) - siliceous carbonaceous f i s s i l e shale with common pyrite concretions. 7b-3 (transition formation) Figure 11-8 - Composite stratigraphic section of the Howards Pass forma-tion showing the various members. Numbers refer to Geological Survey of Canada nomenclature (Green et a l . , 1967). Based on data from DDH 18, 19, 36, 32 and 80 in the XY area (Plate II). 31 the Howards Pass area, the active member is limited to the XY, ANNIV and OP areas (Morganti, 1975). Lateral thinning of the member suggests deposition in small isolated sub-basins, elongate parallel to the regi-onal strike, within the larger Selwyn Basin in which the Howards Pass formation was deposited. MAP-UNIT 10a-l (PYRITIC SILICEOUS SHALE MEMBER) The pyritic siliceous shale member is stratigraphically the lowest carbonaceous rock unit to occur in the Paleozoic section in the Howards Pass area. The member is 2 to 10 m thick, and is generally uniform in thickness over distances less than 0.5 km. Its two most distinctive features are well developed f i s s i l i t y and abundant, 1 to 10 mm, lenti-cular pyrite concretions which define the lamination. The member con-sists of interlaminated carbonaceous shale and pyritic carbonaceous shale. Some of the pyrite concretions are folded; and all pyrite con-cretions weather to limonite pods which aid in the identification of the member at surface. Other structures noted include quartz veins which parallel bedding and are termed "pseudo beds" in the present re-port. The pyritic siliceous shale member contains quartz, muscovite and pyrite, with minor dolomite; and is the oldest unit in the Paleozoic section to contain over 1% organic carbon. Quartz is the most abundant mineral in the shale; x-ray diffractograms indicate 40 to 60% quartz in samples studied. Muscovite constitutes 35 to 50% of the shale, and in thin section is aligned parallel to bedding. Pyrite ranges from less than 5 to 10%, most of which occurs as fine grained (less than 0.1 mm) concretions. These differ from concretions which are ubiquitous in the 32 rest of the Howards Pass formation because the pyrite is fine grained and more abundant than in other members in the formation, and because the concretions are elongate parallel to bedding. Trace amounts of calcite and dolomite occur as segregations. The upper contact with the overlying calcareous mudstone member is sharp and marked by a decrease in pyrite content, and an increase in car-bonate content. The lower contact with the transition formation is gra-dational and demonstrates a continuity between the Howards Pass for-mation and the underlying limestones; previously this contact was thought to be an unconformity (S.L. Blusson, Oral Commun., 1975). MAP-UNIT 10a-2 (CALCAREOUS MUDSTONE MEMBER) The calcareous mudstone member consists of massive, calcareous, carbonaceous mudstone. Calcite occurs as cement and as microscopic con-cretions. The unit has been identified in outcrop and d r i l l core in the XY, ANNIV and OP areas. Rocks in the member are dark grey where fresh and pale brown where weathered. Although most of the member is massive, rare poorly defined bedding and pyrite-calcite microconcretions are present. Poorly developed beds are defined by variable carbonate content ranging from an estimated less than 5% to 40% CaC03 based on the HC1 reaction f i e l d test. Within calcareous beds individual laminae show a variation in organic matter and pyrite content. The most diagnostic structures in the calcareous mudstone member are what are descriptively termed "feathery" calcite beds (Fig. II-9), which consist of thin calcite-cemented concretions, many of which contain pyrite cores. The concentrations range up to 5 rrm in diameter and are elongate parallel to cleavage and microfaults, giving a feathery appearance to the beds containing them. These micro-faults show displacement up to 15 mm, and curve over distances of a few 33 Figure II-9. Specimen of the calcareous mudstone member of the Howards Pass formation. Shown are the laminated nature, the high con-tent of organic matter and a feathery calcite bed. In this instance the calcite concretions contain pyrite cores. This particular mudstone con-tains 20% carbonate. cm sometimes coalescing downward within 3 to 5 cm indicating that they formed before 1ithification (Fairbridge, 1946). The occurrence of car-bonate locally associated with the microfaults suggests that the elonga-tion of the concretions is due to growth parallel to migration paths (Berner, 1968). The lack of disturbed laminae associated with the con-cretions suggests that physical rotation of the concretions did not occur. Another structure typical of the calcareous mudstone member is cal-cite "pseudo-beds". These are veins, ranging in thickness from 1 to 3 cm which parallel bedding. Within the total thickness of the member, 10 to 25 "pseudo-beds" have been observed The veins consist mostly of f i b -rous calcite and minor fibrous quartz; the long axes of the fibres are perpendicular to the vein walls and also bedding. Late stage calcite veins f i l l e d with white sparry calcite cut all the above structures. These veins are abundant and range from 5 nm to 1 cm across, and in some cases the crystal terminations are visible. Minerals identified by x-ray diffraction in the calcareous mudstone member include calcite, quartz, muscovite, pyrite and dolomite. Gypsum and mountain leather were identified in minor amounts in the ANNIV area at outcrops. Organic matter is also important and gives the rocks their dark colour. Calcite constitutes 5 to 35% of the rock, occurring as in t e r s t i t i a l crystals in quartz and carbonaceous matter, and irregular masses surrounded by organic matter. Individual grains range from 1 to 10 urn across, although local segregations are up to 0.2 mm across. All calcite grains noted in thin section are elongate parallel to bedding. Quartz, which ranges from 1 to 10 ym across, constitutes 20 to 50% of the rock and is elongate parallel, to bedding. Quartz also occurs in elongate lenses 100 ym to 10 mm long perpendicular to bedding, and is associated with ptygmatic folds. Muscovite ranges from 20 to 30%, with the flakes parallel to bedding, however, the unit is non-fissile. Pyrite in minor amounts up to 3%, is associated with calcite spatially, both as disseminated pyrite blebs (Zangerl et a l . , 1969) associated with carbonate masses and as cores of calcite microcon-cretions. MAP-UNIT 10a-3 (LOWER CHERTY MUDSTONE MEMBER) The lower cherty mudstone member consists of monotonous, poorly bedded, siliceous carbonaceous mudstone. The unit has been observed throughout the Howards Pass area with only slight lithologic change. To the northeast, near the South Nahanni River, the member contains up to 20% carbonate, where as to the southwest, near Summit Lake, a carbona-ceous bedded chert is the major rock type. In the Howards Pass area the member is 20 to 90 m thick. Typically, outcrops are dark grey to black and massive with blocky to conchoidal fracture. Sedimentary structures are sparse and include weakly defined lami-nation, abundant quartz "pseudo-beds" and pyrite concretions. Indivi-dual laminae are 2 to 10 mm thick and differ in quartz, carbonate and pyrite content. Contacts between laminae are uneven, with lateral vari-ation over a few centimeters common. The most obvious structure in the member is quartz "pseudo-beds". These are similar to those occurring in the calcareous mudstone member except for the predominance of quartz over calcite. They are also more abundant; up to 30% quartz "pseudo-beds" have been found over a stratigraphic thickness of 70 m. These are generally parallel to bedding with fibrous quartz elongate perpen-dicular to the walls, and are 5 mn to 2 cm thick, but vary considerably along their length. Typically they have a geopetal fabric with sharp, slightly wavy, bases and serrate tops which are related to quartz crystal terminations. Penecontemporaneous microfaults locally displace some of the veins, but occasionally the veins displace microfaults, suggesting contemporaneous formation. Pyrite nodules are common throughout the lower cherty mudstone member, constituting about 1% of the unit. Pyrite may occur alone, but approximately 90% of the con-cretions observed are surrounded by fibrous quartz which is elongate at a high angle to bedding. Unlike similar structures in the calcareous mudstone member these do not occur in localized zones but are dissemi-nated throughout the unit. Individual concretions are 2 to 10 mn wide and up to 20 mm long. The similarity between fibrous quartz in the nodules and veins suggests similar modes of formation. The mineralogy of the lower cherty mudstone is only known in a general way because of a high organic carbon content (4 to 12%) which limits microscopic identification and the possibility of identifying minor minerals which would be below the 5% limit for x-ray diffraction detection (Appendix B). Quartz is the most abundant mineral, consti-tuting between 40 and 80% of the rock. Approximately 60% occurs as grains 2 to 10 pm across, associated with organic matter, and 40% occurs in the "pseudo-beds". The most obvious mineralogical feature of the lower cherty mudstone is the low clay content compared to most mudstones (Pettijohn, 1975). Muscovite constitutes 10 to 25% of the samples analyzed. Calcite constitutes 5 to 15% of the lower 10 to 30 m of the unit. Bitumen is associated with pyrite in quartz veins, and shows a cubic outline with conchoidal fracture. The lower contact with the calcareous mudstone member is tran-sitional over 10 to 25 m, and is distinguished by an increase in carbon-ate content and concomitant decrease in s i l i c a down section. The upper contact with the active member is sharp. MAP-UNIT 10a-4 (ACTIVE MEMBER) The active member consists of a repetitive, possibly rhythmic, sequence of intercalated carbonaceous mudstone, cherty mudstone, chert and limestone and locally contains economically significant Zn and Pb sulphides. Because of it s heterogeneity, the member is distinctive and easily identified, both at outcrops and in d r i l l core. The unit is established as a member because i t is advantageous to recognize i t as a specially developed part of the Howards Pass formation. Since i t is a geographically restricted member that appears to terminate on a l l sides (?) it may be a l e n t i l , but in the present thesis the term member is thought to be suitable. Detailed logging of diamond d r i l l cores has allowed sub-division of the member into nine 1ithologically homogeneous facies (Fig. 11-10). Eight of these are repeated up to 8 times vertically within the member (Figs. 11-11, 11-12). In the present thesis the member is presented as an idealized cycle, a composite sequence of the lithologies in which each facies occurs only once. This ideal cycle does not imply that all sections of the member will show a complete cycle (Wells, 1960; Duff and Walton, 1962); in fact, a complete cycle in the active member is a rarity. Weller (1956) distinguished two categories of cycle: those re-ferred to as "typical", "normal", etc., which might be expected to be of 38 — — -X -x - t X-• i i i i i i T - — A - X —-I 1 1 , 1 1 1 y - y - y -— i — > — I — I — I — T I — I — l -T~~T i — r I I i i i I I I ' I ' ' ' I t Grey Chert - Light grey laminated chert Whitish grey Zn-Pb Mudstone chert with up to 50% Zn + and galena. Water escape - Light grey laminated Pb present as sphalerite structures are common. Thin Bedded Cherty Mudstone - Laminated siliceous mudstone with up to 12% organic carbon (LOI). Some laminae contain framboidal pyrite and/or sphalerite with trace amounts of galena. Slump structures are abundant. Cherty Mudstone - Dark grey to black siliceous carbonaceous mudstone showing weak lamination; 'pseudo-beds' are abundant. Mixed Cherty Mudstone and Limestone - Mixed cherty mudstone and light grey basal limestone. Contacts between lithologies are sharp and cross-cutting. Thin Bedded Calcareous Mudstone - Laminated calcareous carbonaceous mudstone with up to 5% organic carbon (LOI). Some laminae contain framboidal pyrite and/or sphalerite with traces of galena. Slump structures are abundant. Graded Limestone - Laminated limestone with carbonaceous matter at the top of laminae. Light Grey Basal Limestone - Light grey laminated limestone with up to 35% muscovite. Figure 11-10. Stratigraphic column showing an ideal cycle within the active member, with the eight cyclical facies noted in the member identified by local informal name. No scale implied. 39 D D H 18 5 2 SiWcco Lower Cherty (1) B a s a l (2) L i g h l G r e y Basa l L imes tone (3) G rodded L imes tone (4) Th in Bedded C o l c a r e o u s Mudstone (5) M i x e d L i m e s t o n e and Mudstone u d s t o n e Member 9 4 6 7 2 7 6 4 2 Fau l t 2 4 Mudstone Member (6) C h e r t y M u d s t o n e (7) T h i n B e d d e d C h e r t y Muds tone (8) W h h i s h G r e y Z n - P b Muds tone (9 ) Grey C h e r t 2 4 6 7 4 6 2 7 6 rr LU CD ui 2 UJ > O < Figure 11-11. Detailed sections of the active member in d r i l l holes 12, 18 and 19. Numbers represent the individual facies of the active member. Note that the presence of a complete ideal cycle of the active member is rare in these d r i l l holes. 40 UPVCR SILICEOUS 2 BASAL »cltS~ LOWER CMfRTY | HUDSTDW • Figure 11-12. Detailed lithologic log of d r i l l hole 36, showing repeditive nature of facies occurring in the active member. Bedding is 90° to core axis, and total length of active member is 70.82 m. Numbers refer to active member facies: 1) basal, 2) light grey basal limestone, 3) graded limestone, 4) thin bedded calcareous mudstone, 5) mixed cherty mudstone and limestone, 6) cherty mudstone, 7) thin bedded cherty mud-stone, 8) whitish grey Zn-Pb mudstone and 9) grey chert facies. 41 common occurence and those, like the "idealized standard" here referred to as the ideal cycle which may be rarely developed, but which express some characteristic order of the lithological units. Duff et a l . (1967) have correctly suggested that a theoretical, or in the present context, an ideal cycle, is one to which the observed sedimentary sequence can be referred, and through which the observed sedimentary successions can be understood. This ideal cycle is one which can be constructed from theoretical considerations and from accumulated data from modern en-vironments and experimental evidence. Such is the case of the ideal cycle of facies occurring in the active member. Research aimed at con-struction of a "modal" or most typical cycle is s t i l l in progress. To date, wherever the facies of the ideal cycle have been found in their suggested sequence, their contacts are gradational; in contrast, where the same facies are found out of the proposed sequence the contacts are generally sharp. Furthermore, i t is the author's experience that the ideal cycle order is most common of any sequence which includes a l l elements of the cycle. FACIES 1 (BASAL FACIES) The basal facies is a highly contorted and locally foliated (in the sense of Hobbs et a l . , 1976) carbonaceous mudstone. Unlike the other facies i t is not repeated higher in the member. Its distribution appears to be important; because i t appears locally to contain the sli p zone of a major slump; to date, the facies has only been observed in the XY area, where i t occurs only in d r i l l holes southwest of Yara Peak (Fig. 11-13) and is 10 cm to 2 m thick. The facies consists of massive carbonaceous siliceous mudstone with lenses and laminae of contorted, slightly carbonaceous chert. The similarity between the lenses and the I,-H 71 O j NO I NAME PEAK SUGAR MTN \ H 45 r> YARA PEAK / v.. / • — X < : V \ \ \ I XY CAMPj I I \ 0 1_ \ H 19 O 625 metres Figure 11-13. Spacial distribution of the basal facies in the XY area. Location of some d r i l l holes are shown for location reference. The stippled area represents the basal facies as seen in d r i l l core, and may be more widespread than is indicated (see Plate II). 43 laminae and the abundance of flow folds (de Sitter, 1958) indicate that the lenses are disrupted laminae. Locally, the facies is foliated, with light grey chert lenses occurring in the plane of the foliation which parallels bedding of nearby units. At least part of the foliation appears to be the result of bedding plane slippage formed during later folding. X-ray diffractograms indicate a similar mineralogy to the under-lying lower cherty mudstone member, but quartz is more abundant, up to 75% locally. Muscovite and organic carbon (4 to 6%) are minor con-t i n e n t s . Pyrite is present in amounts up to 3%, but differs texturally from that of the underlying unit, because the nodules are broken and/or elongate parallel to the plane of the foliation. Contacts with the underlying lower cherty mudstone and the other overlying facies of the active member are in general sharp; although in two instances fragments of limestone up to 3 cm in diameter were found within the basal facies. FACIES 2 (LIGHT GREY BASAL LIMESTONE FACIES) The light grey basal limestone facies consists of laminated a r g i l -laceous limestone. The facies occurs from one to five times within the active member, most commonly occurring near the base, just above the basal facies in the XY area and at the base of the member northeast of Yara Peak in the XY area (Plate II) and in the ANNIV and OP areas (Plates III and IV). Individual facies are 70 cm to 11 m thick. The limestone consists of 60 to 70% calcite, 20 to 35% 2M muscovite and minor amounts of quartz, with traces of pyrite and organic matter. Calcite occurs as microspar and micrite with the latter being associated 44 with clays. The microspar grains are 5 to 30 urn across, the same size range as quartz. Micrite grains are less than 10 urn in diameter. Car-bonaceous matter and associated pyrite microconcretions occur in the clay-rich laminae. Laminae are 500 ym to 15 mm thick and are defined by variations in calcite and clay content. Other structures evident in the facies are stylolites and calcite veins. Stylolites are abundant within the limestone and may be parallel to lamination or cut i t at a high an-gle. Quartz and organic matter are contained in the st y l o l i t e seams. Contact with the basal facies in the southwestern part of the XY area is sharp, although clasts of limestone do occur in the basal facies in a few instances. In the northeast part of the XY area and in the ANNIV and OP areas the contact between the limestone and the lower cher-ty mudstone member is gradational over 1 to 5 cm. The upper contact with the graded limestone facies is gradational over 1 to 30 cm. FACIES 3 (GRADED LIMESTONE FACIES) The graded limestone facies is a laminated argillaceous limestone with intercalated carbonaceous limestone laminae. The thicker laminae (>5mm) appear inversely graded because of upward decreasing proportions of carbonaceous matter. The graded limestone is present in both the XY and ANNIV areas. As with the other facies in the active member the graded limestone is repetitive and occurs up to 5 times within the member, with individual occurrences being 25 cm to 2 m thick. The main rock type in the facies is laminated limestone with lami-nae 100 ym to 7 mm thick. These laminae contain microspar which con-sists of calcite grains up to 10 ym across and quartz grains which are slightly smaller. Thin sections show the microspar to have a brown tint 45 indicating minor amounts of organic matter (Greensmith, 1978); the pro-portion of organic matter increases near the top of most microspar laminae. Patches of calcite grains 100 to 400 um across contain grains up to 20 ym. Triple junction grain boundaries and the lack of brown or-ganic matter suggest that oxidation and recrystal1ization have produced these patches. X-ray diffractograms of samples from the graded lime-stone indicate 50 to 60% calcite, 25 to 30% muscovite and 10 to 20% quartz. Thus the main compositional differences between the light grey basal limestone and the graded limestone facies are the increase in quartz and a slight increase in carbonaceous matter in the latter. The contacts with the light grey basal limestone and the thin bed-ded calcareous mudstone facies are gradational over 5 to 40 cm. In con-trast, contacts with a l l other facies in the member are relatively sharp. FACIES 4 (THIN BEDDED CALCAREOUS MUDSTONE FACIES) The thin bedded calcareous mudstone facies consists of laminated carbonaceous mudstone containing 20 to 40% calcite. The facies is re-peated up to five times in the member in the XY area and four times in the ANNIV area. In the XY area i t is usually the lowest facies in the section to contain laminated sulphides. The facies is 2 cm to 10 m thick, and may vary in thickness by 100% within 200 m along strike. Individual laminae are 200 ym to 5 mm thick and differ in colour as a result of varying amounts of pyrite, organic matter, calcite and Zn and Pb sulphides (Fig. 11-14). These laminae are traceable over at least 1 m, but poor exposures prevent study of their f u l l extent or demonstration of their continuity, and laminae can not be correlated between d r i l l holes 160 m apart. X-ray diffractograms indicate that 46 Figure 11-14. Photograph of the thin bedded calcareous mudstone facies of the active member. The laminae are the result of variations in amounts of calcite, organic matter, quartz, pyrite, sphalerite and galena. 47 the facies contains 20 to 40% calcite, 40 to 55% quartz and 10 to 20% muscovite, with minor dolomite (?). Calcite occurs as microspar with crystals ranging from 1 to 40 pm in diameter. In thin section, quartz is microcrystal1ine and is to a large extent masked by carbonaceous matter. Accessory minerals could not be identified in thin section because of organic matter (1 to 5% organic carbon); but polished sec-tions indicate that sulphides are most abundant within the carbonaceous mudstone laminae. Within this facies sphalerite and galena tend to occur in laminae from pyrite separate, but minor mixing of all three sulphides is common. Structures identified in the facies include pseudo-graded laminae, "pseudo-beds", microfolds, spiral structures (Fairbridge, 1946), con-volute lamination, pull-aparts, decollement structures and penecontem-poraneous microfaults. Pseudo-graded lamination consists of a size grading of framboidal pyrite, which is believed to form during dia-genesis (Love, 1965; Sweeney and Kaplan, 1973). The other structures mentioned above are all typical of sediments that have slumped and have rapidly lost associated water (Williams, 1963). Contacts with other facies within the active member are gradational to sharp. Gradational contacts with the underlying graded limestone facies are from 5 mm to 5 cm, and with the overlying thinbedded cherty mudstone facies are 1 to 10 cm. Contacts with other facies in the active member are sharp. FACIES 5 (CHERTY MUDSTONE) The cherty mudstone facies is a greyish black monotonous siliceous, 48 carbonaceous mudstone which is repeated up to 9 times within the active member. It is most typically found overlying the thin bedded calcareous mudstone facies. In a few instances in d r i l l core argillaceous lime-stone is intercalated with mudstone, but the sharp contact between the two cross-cuts the laminae of the limestone, indicating post-depositi-onal juxtaposition. The facies ranges in thickness from 50 cm to 7 m. Mineralogically the facies is the same as the lower cherty mudstone mem-ber. The distinguishing characteristics of the cherty mudstone facies is the presence of abundant quartz "pseudo-beds" which may occur up to 15 times in 1 m of stratigraphic thickness and locally constitute 10 to 15% of the lithology. The presence of microfolding is suggested by the occurrence of folded "pseudo-beds" and is typically more intense than in the lower cherty mudstone member. FACIES 6 (THIN BEDDED CHERTY MUDSTONE FACIES) The thin bedded cherty mudstone facies consists of rhythmic (Gross et a l . , 1963; Muller and Blaschke, 1969) intercalated laminae of chert, carbonaceous mudstone (with or without visible pyrite, sphalerite or galena) and minor micrite. Colours range from very light grey (N 8) or light grey (N 7) to greyish black (N 2) and dark yellowish orange (10 YR 6/6) and emphasize the laminated nature of the facies (Fig. 11-15). There are two variants: in the XY area a laminated siliceous carbona-ceous mudstone is dominant compared to the ANNIV and OP areas where a moresiliceous laminated cherty carbonaceous mudstone is dominant. Both variants occur in all three Zn-Pb deposits. The facies is of economic importance because i t contains significant amounts of Zn and Pb sul-phides. Stratigraphic thicknesses ranges from 5 cm to 6 m; i t is 49 Figure 11-15. Photograph of the thin bedded cherty mudstone facies of the active member. The laminae are the result of variations in quartz, organic matter, pyrite, sphalerite and galena content. Micro-folds and faults evident in the specimen are the result of minor slump-ing, concretion growth and later regional deformation. 50 thickest in the XY area, although i t is repeated more commonly in the ANNIV area where i t occurs up to 8 times in the member. The XY thin bedded cherty mudstone facies variant consists of in-tercalated laminae of siliceous carbonaceous mudstone (many of which are sulphide bearing) chert and occasional carbonaceous limestone. The laminae are 300 ym to 1 cm thick and average 500 ym. The most abundant laminae in the facies are siliceous carbonaceous mudstones, containing 60 to 70% quartz, 20 to 35% muscovite and 4 to 12% organic carbon. Ap-proximately 37% of the 356 laminae examined in polished section contain sulphides and some consist of massive sulphide. In general, the laminae are dominated by sphalerite or pyrite with only minor mixing of these two. The black chert and limestone laminae do not contain sulphides or more than 1% organic carbon. The laminae are rhythmically interlayered (Reineck and Singh, 1975), but to date no repetitive sequence has been found. Structures observed include microscopic folds, penecontem-poraneous faults, intraformational breccias, spiral structures, con-volute lamination, pull-aparts and decollement structures, all of which indicate slumping. The abundance of these structures indicate that slumping was common and occurrences of the facies without these struc-tures are rare. The ANNIV variant of the facies consists mostly of intercalated carbonaceous cherty mudstone and carbonaceous chert laminae; either may contain abundant sulphides. Individual laminae are 500 ym to 1.5 cm thick, thicker than those in the XY variant. X-ray diffraction and chemical analyses show the rhythmites to contain 65 to 90% quartz, and up to 10% muscovite, with the remaining rock made up of sphalerite, 5 1 pyrite and galena. Organic carbon constitutes up to 3% of the rock. Thus, the ANNIV variant (i.e. rhythmites) is more siliceous than the XY type. The sulphides occur in the carbonaceous laminae, but do not con-stitute massive sulphide as in the XY variant. Of the 220 laminae examined in polished section 68% contain greater than 5% sulphide. Unlike the XY variant, the ANNIV variant shows abundant mixing of Fe, Zn and Pb sulphides in individual laminae. Structures indicative of slumping, which are abundant in the XY variant are not present in the ANNIV variant, where st y l o l i t e s , many of which contain sphalerite, galena and organic matter, were the only structures noted. Contacts with the thin bedded cherty mudstone and thin bedded cal-careous mudstone facies are gradational over 1 mm to 5 cm. In the for-mer the contact is marked by an increase in lamina definition, whereas the latter is marked by a decrease in carbonate content. All other con-tacts are sharp. FACIES 7 (WHITISH GREY Zn-Pb MUDSTONE FACIES) The whitish grey Zn-Pb mudstone facies is a laminated cherty rock containing up to 70% sulphides. The relatively low chert content neces-sitates the use of the term mudstone (Blatt et a l . , 1972). The term sulphide mudstone could also be used, but the presence of less than 5% pyrite leads the present author to conclude that the term whitish grey Zn-Pb mudstone facies sufficiently describes the facies at present. The high Zn and Pb content makes the facies the most economically s i g n i f i -cant in the area; and constitutes 80% of the 11 original showings which led to the staking of the XY, ANNIV and OP claims. The facies is best observed in d r i l l cores, but also occurs as resistant outcrops at 52 showings in the area (Plates II, III and IV). The facies is repeated up to 9 times and is 1 cm to 12 m thick. Both repetition and thickness are greatest in the XY area. The mineralogy of the facies is simple. X-ray diffraction studies indicate that quartz, sphalerite and galena are the only major minerals present with only minor amounts of pyrite and locally calcite. Overall, organic carbon constitutes less than 0.2% of the facies, suggesting that nearly all planktic organic matter was oxidized above the chemocline or during sulphate reduction. Sedimentary diagenetic structures are common and well displayed in the facies, and include lamination, "pseudo-beds", calcite nodules, and abundant penecontemporaneous water escape-structures (ie. p i l l a r struc-ture of Lowe, 1975). Lamination is defined by variation in colour due to organic matter, quartz and sulphide content; laminae are 100 to 500 urn thick and occur in beds 500 urn to 2 cm thick, each consisting of 5 to 50 laminae (Fig. 11-16). Laminae are traceable over 50 cm, but vary considerably in thickness because of differential compaction. Beds are also variable, but can be traced over a few meters. Quartz "pseudo-beds" are present in the facies, occuring up to four times in 1 m of strati graphic section. Locally these veins are terminated by penecon-temporaneous microfaults. The most obvious structures in the facies are cross-cutting veins containing massive sphalerite and galena with minor pyrite (Fig. 11-16); and range in width from 500 pm to 1 cm, varying by a factor of five over a few centimetres. The veins are irregular and sinuous in outline and locally are anastomosing where not modified by axial plane cleavage. Internally the veins show structures similar to the p i l l a r structures 53 Figure 11-16. Specimen of laminated whitish grey Zn-Pb mudstone. Light grey laminae contain chert, sphalerite and galena with minor organic matter. The dark grey laminae are similar except for a relatively higher organic carbon content. Water escape structure at right contains massive sphalerite and galena. described by Lowe (1975, 1976). The matching of beds across the struc-tures demonstrates that differential compaction is associated with for-mation of the p i l l a r structures. Terminations of the structures at the base of the facies are sharp, and where the facies is greater than 25 cm thick massive sulphide commonly occurs at the base. At the s t r a t i -graphic top of the facies the veins may protrude a few mm into the over-lying facies. The veins cut the facies at nearly right angles where axial plane cleavage is not evident. The p i l l a r structures have only been observed in the whitish grey Zn-Pb mudstone and are considered to be related to the occurrence of a high sulphide content. According to Lowe (1976), p i l l a r structures are the result of rapid fluid escape from fine-grained sediments and are therefore penecontemporaneous. Quartz "pseudo-beds" and limestone nodules are present with facies, occurring up to 8 times in 1 m of section. The "pseudo-beds" show flat bottoms and serrate tops due to upward crystal growth, and are locally terminated by the modified p i l l a r structures; no instances of "pseudo-beds" cross-cutting modified p i l l a r structures have been noted. Lime-stone nodules are poorly developed in the facies, and even though coarse crystals of calcite with a radiating structure occur, ghost structures are well displayed, indicating that the nodules formed after the unmodi-fied p i l l a r structures. Most contacts between the whitish grey Zn-Pb mudstone facies with other facies in the member are sharp. Exceptions to this are contacts with the grey chert and the thin bedded cherty mudstone facies. The contact with the grey chert the contact is marked by an increase in sulphide and a slight increase in carbonaceous matter. 55 FACIES 8 (GREY CHERT FACIES) The grey chert facies consists of laminated medium light grey (N 6) to medium dark grey (N 4) chert. The facies is repeated up to 4 times within the member; i t is 5 cm to 1 m thick in the XY area and up to 2 m thick in the ANNIV and OP areas. Individual laminae are 500 pm to 8 mn thick, and are separated by dark carbonaceous laminae less than 100 pm thick (Fig. 11-17). Locally, the lamination has been destroyed by re-crystallization of the chert. This type of destruction of bedding is thought to be a result of chertification (Park and Croneis, 1969). The mineralogy of the facies is extremely simple; quartz constitutes 95 to 99%, secondary calcite up to 5% and organic carbon up to 0.5% locally. Except for the lack of laminated sulphides, the grey chert facies is mineralogically the same as the whitish grey Zn-Pb mudstone facies. The only structures noted in the facies, other than lamination, are common sty l o l i t e s . They are rectangular to sutured in style (Park and Schot, 1968), both parallel and perpendicular to lamination and contain quartz and organic matter. Contacts with all other facies of the active member are sharp ex-cept with the whitish grey Zn-Pb mudstone. Here the contact is gra-dational over 2 to 4 cm and is marked by an increase in sulphide con-tent. The contact with the upper siliceous mudstone member is also sharp, although distinguishing between the grey chert facies and dark grey chert in the overlying unit is not always easy. MAP-UNIT 10a-5 (UPPER SILICEOUS MUDSTONE MEMBER) The upper siliceous mudstone, the uppermost member of the Howards Pass formation, directly overlies the active member in the XY, ANNIV and 56 Figure 11-17. The grey chert facies of the active member. The laminae are the result of variation of chert (quartz) and organic matter content. The specimen contains up to 1% organic carbon. Stylolites and veins present in the specimens are quartz f i l l e d . 57 OP areas. Outside of these three areas the member overlies the lower cherty mudstone member. Within the Howards Pass area the member is 25 to 120 m thick compared to 20 to 65 m thick regionally. It consists of interlaminated dark grey (N 3) to greyish black (N 2) mudstone and light grey (M 7) to medium grey (N 5) chert. In areas where the member over-lie s the active member i t can be divided into lower, middle and upper units (Fig. 11-18). The lower unit consists of laminated carbonaceous mudstone and mi-nor intercalated medium grey chert; the mudstone contains abundant lime-stone concretions. The dominant rock type in the unit is a laminated, siliceous carbonaceous mudstone which contains 20% grey chert laminae. The carbonaceous laminae are 200 um to 8 mm thick and contain 2 to 4% organic carbon whereas the chert laminae are 500 ym to 5 mm thick and contain only trace amounts of organic matter. The chert laminae have quartz veins or "pseudo-beds" overlying them commonly where microfolding was most intense. Laminated medium grey (N 5) to medium dark grey (M 4) chert 3 to 16 cm thick is intercalated with the carbonaceous mudstone. The chert beds constitute 10 to 15% of the unit; and are in gradational contact with the mudstone. Carbonate in the mudstone consists of the following types: (1) elongate coarsely crystalline carbonaceous con-cretions 3 to 40 cm long perpendicular to bedding, with radiating or banded internal structure; (2) light grey; bedded microspar clasts 5 mm to 10 cm long, parallel to bedding. The latter are found only within the lower 10 m of the unit. The laminated carbonaceous mudstone is bent around both types of carbonate, but more so around the bedded types. 58 o V- 'i flaggy mudstone formation - buff to dark grey intercalated laminae of carbonaceous and non-carbonaceous mudstone. upper unit - laminated carbonaceous mudstone with graptolite horizon (F) approximately 15 m from the upper contact. middle unit - laminated carbonaceous mudstone with intercalated light grey cherty mudstone laminae, fetid coarse crystalline carbonate concretions are abundant, frequently with radiating structure. The unit shows abundant microfolds which may be related to the limestone concretions. lower unit - laminated carbonaceous mudstone with intercalated light grey cherty mudstone, fetid coarse crystalline limestone concretions are abundant, frequently with radiating or banded structure, medium grey laminated chert and cal c i l u t i t e clasts are also present. Galena and sphalerite micro-concretions occur locally near the base of the unit. active member -laminated and mudstones and intercalated chert, massive carbonaceous 1imestone. Figure 11-18. Composite stratigraphic section of the upper siliceous mudstone member of the Howards Pass formation. The section is based on data from d r i l l holes 18, 36 and 39 in the XY area. 59 The middle unit of the member is similar to the lower, being mainly composed of laminae of carbonaceous mudstone and light grey chert, but lacks the laminated grey chert beds. Coarsely crystalline spherical carbonate concretions 5 to 20 cm in diameter only occur in the middle unit, and show mostly radial internal structures (Fig. 11-19). The upper unit of the member is composed of laminated carbonaceous mudstone, and ranges from 10 to 30 m thick with individual laminae being 500 ym to 4 mm thick. Approximately 20% of the laminae are light grey chert. The upper unit does not show the intense bending of laminae no-ted in the lower two units. A regionally significant 1 m thick grap-t o l i t e zone occurs 15 m below the top of the unit, and is a good marker horizon for correlation. In areas not overlying the active member the upper siliceous mudstone member is similar to the upper unit overlying the active member and s t i l l contains the graptolite zone. Contacts between the upper siliceous mudstone member and other units are sharp, although the upper contact with the flaggy mudstone is interdigitate. MAP-UNIT 10b (FLAGGY MUDSTONE FORMATION) The flaggy mudstone formation is a regionally distinctive unit which overlies the Howards Pass formation and marks a major change in the depositional environment of the Selwyn Basin. As with all units of map-unit 10, the formation is used in an informal sense. It is divided into two units: a lower, generally orange weathering member, and a fe-tid limestone zone (Hedberg, 1976) (Fig. 11-20). The lithologic forma-tion has been observed in an 80 km radius from Howards Pass except to 60 Figure 11-19. Specimen of a broken limestone concretion occurring in the upper siliceous mudstone member of the Howards Pass formation. Most of the concretions show a radiating structure similar to that evi-dent in the specimen, although banded structures are also evident in many of the concretions. 61 1 1 1 Bo Upper chert format ion, conta in ing c a l c a r e -ous, carbonaceous chert with c lay c l a s t s . Carbonaceous f e t i d limestone with abundant burrows. In terca la ted carbonaceous mudstone and non-carbonaceous mudstone with local s i l t s t o n e lenses conta in ing bar i te c o n c r e t i o n s . Dark grey, carbonaceous mudstone, laminae are 0.5 to 3 cm t h i c k . Intercalated laminae of carbonaceous and non-carbonaceous mudstone. Buff weathering quartz-muscovite s i l t s t o n e . Intercalated laminae of carbonaceous and non-carbonaceus mudstone. Laminated, carbonaceous mudstone. Intercalated carbonaceous and non-carbona-ceous mudstone. S l i g h t l y ca lcareous , carbonaceous and non-carbonaceous mudstone. Intercalated laminae of carbonaceous and non-carbonaceous mudstone. Laminated, carbonaceous mudstone. Howards Pass formation - upper s i l i c e o u s mudstone member, laminated carbonaceous mudstone. Figure 11-20. Composite s t r a t i g r a p h i c sect ion for the f laggy mudstone formation from d r i l l hole 38 and the northeast side of Yara Peak (Plate II, Locat ion 10b in Appendix C ) . 62 the northeast where a facies change occurs 10 km from Yara Peak. Within the Howards Pass claim groups the formation is exposed in the XY, ANNIV, DON and OP areas. Locally the XY area, a few outcrops appear similar to flagstone, from which the formation derives its name. ORANGE WEATHERING MEMBER The orange weathering member consists of orange weathering mudstone to siltstone intercalated with minor carbonaceous mudstone. Quartz, the most abundant mineral constitutes 50 to 70% of the mudstone, and mus-covite up to 45%. Pyrite, calcite and traces of barite and gypsum con-stitute the remaining minerals. The regional stratigraphic thickness is relatively uniform compared to units in the Howards Pass formation. The estimated thickness is 60 to 200 m in the XY area, 75 to 300 m in the ANNIV area and 80 to 300 m in the DON and OP areas. To date, no system-atic variation can be demonstrated, although thicknesses over 75 m are present only overlying the sub-basins in which the active member of the Howards Pass formation was deposited. Outcrops of the orange weathering unit are greyish orange (10 YR 7/4) through light brown (5 YR 5/6) to moderate brown (5 YR 3/4), and fresh samples are dark grey (N 3) to light brown (5 YR 5/6). Intercalated laminae of light coloured mudstone and dark grey car-bonaceous mudstone constitute approximately 70% of the unit (Fig. 11-21). Sedimentary structures include lamination, burrows, dolomitic siltstone and mudstone clasts and p i l l a r water escape structures a l l of which have been overprinted by later cleavage. All the above structures are easy to recognize because of a colour contrast between the light coloured slightly carbonaceous and dark carbonaceous intercalated mud-63 Figure 11-21. Outcrop of the orange weathering unit of the flaggy mudstone formation. The orange weathering areas consist of quartz and muscovite with minor dolomite and pyrite. The darker grey areas are discontinuous laminae of carbonaceous mudstone. 64 stones in the member. Laminae 5 mm to 2 cm thick make up the member and typically show light mudstone bases and carbonaceous mudstone tops. Light grey rounded dolomitic quartzose siltstone clasts occur throughout the member, constituting up to 3% by volume. Uncommon dark grey l e n t i -cular mudstone clasts are present and are bent, suggesting that the mud in the clasts was not l i t h i f i e d when later deposited in the siltstone. The mudstone clasts are similar to carbonaceous mudstone in the member, but the siltstone clasts are sufficiently different to be termed exotic. Many thin beds and laminae that contain 2 to 3% carbonaceous matter also contain burrows parallelto bedding (Fig. 11-22), which show three-dimensional geometry indicative of simple to highly organized mining or feeding of the nereites-facies (Seilacher, 1967). Two types of concretions are present in the member. Coarsely crystalline limestone concretions 5 cm to 1.5 m in diameter are found within the lower 25 m of the member, but most are found in an interval 10 to 25 m above the base of the member, forming a stratigraphic hori-zon. Many are similar to those present in the upper part of the Howards Pass formation in that they are fetid and contain a radial or banded internal structure. Most of the concretions are spherical, but some are elongate parallel to bedding. Pyrite is abundant throughout the member; in the form of pyritohedrons, cubes and spherical concretions. Ir-regular oblate concretions represent 80% of the pyrite; many have rims of fibrous calcite and quartz which may in turn be rimmed by gypsum. Slightly elongate pyrite concretions are perpendicular to bedding. Dish structures (Middleton, 1967; Lowe, 1975) are common in the orange weathering member, and consist of strongly curved dishes and 65 Figure 1 1 - 2 2 . Worm burrows in the orange weathering unit of the flaggy mudstone formation. The burrows are typically parallel to lami-nation indicating nereites, deep water facies. 66 closely spaced hair-line p i l l a r s . The elutriation of carbonaceous mat-ter emphasizes the structures by their colour contrast. The dish struc-tures are outlined by the upturned edges of discontinuous 500 um to 1 cm thick carbonaceous laminae. These structures do not occur in the lower 2 or 3 m of the member nor in those intercalated carbonaceous beds which are over 1 cm thick. Dish structures are locally d i f f i c u l t to recognise because of overprinting by the later regional cleavage. . Lens shaped bodies of fine to medium grained orange weathering siltstone and laminated carbonaceous mudstone are contained in the mem-ber. The former which consist of fine-grained quartz-muscovite s i l t -stone with only traces of organic matter, are 2 to 15 m thick and up to 150 m in length. These lenses are present in the XY and ANNIV areas where the member overlies areas where the active member was deposited. Lenticular bodies of laminated carbonaceous mudstone 5 to 40 m thick have been traced in d r i l l holes for over 500 m, and are common regional-ly. None of the sedimentary structures noted in the rest of the member are present in the carbonaceous mudstone. The contact between the orange weathering member and the Howards Pass formation is generally sharp, although locally the lower 1 to 3 m of the orange weathering member is more carbonaceous than is typical. Intercalation of the orange weathering member and the Howards Pass for-mation over 3 to 7 m in d r i l l core further suggests a local interfinger-ing of the two units. The upper contact with the upper chert formation is also sharp or is gradational over less than 0.5 m. 67 FETID LIMESTONE ZONE The fetid limestone zone is a discontinuous limestone at the top of the flaggy mudstone formation. The present author has identified this zone in the XY, ANNIV and OP areas and locally to the southwest of Howards Pass area although i t is mappable only in the XY area. The unit is thickest near Yara Peak (Plate II) and thins rapidly to zero along the regional strike. In the Yara Peak area the zone is 20 m thick, locally, and in the ANNIV and OP areas a maximum thickness of 5 m was observed. Detailed descriptive data for the fetid limestone zone is incom-plete owing to poor exposure, but a general description is possible. The limestone is greyish black (N 2) on fresh surfaces, and weathers to darkgrey (N 3). A strong fetid odour is characteristic at broken sur-faces. Bioturbation structures are abundant in the zone and are similar in morphology to those burrows found in the rest of the flaggy mudstone formation, except that they are larger, up to 2 cm across, and more abundant. These feeding traces do not follow bedding as they do in the rest of the formation, but instead have a random orientation. The lack of any noticeable bedding in the zone may be the result of destruction of bedding by burrowing animals. The mineralogy of the zone is simple, consisting of calcite, pyrite and muscovite and only minor quartz. Coarsely crystalline sparite grains 0.2 to 1 mm across constitute 90% of the limestone. Limestone in thin section shows organic matter (1 to 4%) disseminated throughout, and is similar in appearance texturally to the coarse crystalline limestone 68 limestone concretions present elsewhere in the formation and the upper siliceous mudstone. Pyrite is present in quantities up to 5%, occurring as cubes and pyritohedrons 0.1 to 0.5 mm in diameter. The contact with the underlying mudstone is sharp, although the carbonate content in the underlying mudstone increases up-section toward the contact over 3 m. The contact with the overlying upper chert formation is also sharp. The discontinuous nature regionally and the lenticular shape local-ly of the fetid limestone zone suggest the development of local environ-ments favourable to its deposition. The similarity of textures of the fetid limestone zone and the fetid limestone concretions stratigraphi-cally below raises the question of a sedimentary or a diagenetic origin for the zone. The presence of bedding locally and bioturbation indi-cates that a sedimentary origin is more probable. MAP-UNIT 10c (UPPER CHERT FORMATION) The upper chert formation consists of a sequence of dark grey weathering chert and mudstone, showing characteristics of both the Road River group (see chapter III) and Earn Group (Campbell, 1967) (Fig. 11-23). It contains laminated cherts and mudstones which are similar to the Road River group and also local current marks typical of the Earn Group. The unit is best exposed on the northeast slope of Yara Peak (Appendix C) and is also exposed locally from just west of the South Nahanni River to Summit Lake and from the Itsi Mountains in the north-west to Tungsten. Regionally, the formation is 50 to 400 m thick; in the Howards Pass area i t is 110 to 400 m thick. The formation contains chert and siliceous mudstone, both of which are greyish black (N 2) and weather to a lighter medium dark grey (N 4). 69 Iron Creek formation - massive carbonaceous mudstone to siltstone. ~ — r — ' I n " i TT Ti unconformity mm I I — r l I [ Upper chert containing carbonaceous chert with beds ranging from 2 to 10 cm, but is locally massive. Siliceous carbonaceous mudstone with cherty mudstone occurring locally. Minor bulbous flute casts are present in siIty portions. Lower chert containing carbonaceous chert with beds ranging from 2 to 10 cm thick. Slightly calcareous, carbonaceous chert with clay clasts locally. Flaggy mudstone formation (fetid limestone unit) containing dark grey fetid limestone with abundant burrows. Figure 11-23. Composite strati graphic section for the upper chert formation, from the northeast side of Yara Peak (Location 10c in Appendix 70 The cherts are thin bedded, ranging from 2 to 10 cm thick and show l i t t l e internal lamination except for rare light grey chert laminae 0.5 to 3 cm thick. Chert textures are evident in thin section despite par-t i a l masking by organic matter. X-ray diffractograms indicate 75 to 95% quartz and up to 20% mixed lMp. i l l ite and 2M muscovite, with minor calcite which exceeds 10% only in the lower 15 m of the unit. Only 0.3 to 2% organic carbon is present in the formation. The mudstone in the formation is similar to the cherts except for the greater abundance of mica relative to quartz. The mudstone contains up to 40% mixed I M Q i l l i t e and 2M muscovite and only 40 to 60% quartz. Beds are 1 to 5 cm thick and do not contain light grey chert laminae. Weakly graded mud-stone to siltstone is present where the formation is thinnest. These same areas contain bulbous flutes associated with siltstone. The top 10 to 30 m of the formation consists of calcareous mud-stone which contains from 20 to 35% calcite. Beds of this lithology are 10 to 30 cm thick with no other sedimentary structures evident. The calcite is very fine-grained (less than 5 ym in diameter). Contacts between the upper chert formation and other units are sharp. The lower contact with the orange weathering member is sharp, although within approximately 1 to 2 m of the contact the proportion of carbonaceous matter in the lower unit is greater than typical. In areas where the fetid limestone zone occurs, the contact between the chert and the limestone is extremely sharp. The upper contact with the Iron Creek formation is sharp and is marked by the occurrence of mudstone and ob-vious graded bedding in the upper unit. Regional mapping indicates that 71 this contact is an unconformity with a slight angular discordance which in some areas accounts for the top 5 to 40 m of the upper chert forma-tion being absent. MAP-UNIT 18b-l (IRON CREEK FORMATION) The Iron Creek formation is an informal map unit consisting of s i l -ver-grey weathering mudstones to fine-grained sandstones showing ubi-quitous graded beds in the Howards Pass area. The formation is present regionally, although outside the immediate Howards Pass area major facies changes occur. Within the area the formation is 100 to 350 m thick. The type locality for the formation is Iron Creek in the XY area (Plate II) which has an orange coloured valley bottom where the creek cuts through the formation. The formation is subdivided into six in-formal units: a lower carbonaceous mudstone, lower graded beds, car-bonaceous wacke, the Selwyn Mountains barite horizon, upper graded beds and upper carbonaceous mudstone (Fig. 11-24). The most significant unit regionally is the Selwyn Mountains barite horizon. The lower and upper carbonaceous mudstone units consist of dark grey (N 3) to greyish black (N 2) mudstone, the lower being 10 to 40 m thick and the upper 20 to 45 m thick in the Howards Pass area. Beds are 1 to 10 cm thick, and are weakly graded from siltstone at the base to mudstone at the top. In a few instances bulbous loaded flute casts are found in float from the unit. X-ray analyses indicate that quartz ranges from 30 to 60% and mixed IMQ i l l ite and 2M muscovite from 40 to 60%. Traces of plagioclase (?) are indicated by x-ray diffraction, but 72 Yara Peak formation - brown weathering mudstone to siltstone with abundant graded beds. unconformity Carbonaceous mudstone - siliceous, _ carbonaceous mudstone to coarse siltstone with abundant graded beds. Upper graded beds containing carbonaceous mudstone to coarse siltstone with abundant graded beds. Selwyn Mountains barite horizon (See Fig. 11-28 for details). Carbonaceous wacke. Lower graded beds containing carbonaceous mudstone to coarse siltstone with abundant graded beds. Massive carbonaceous mudstone unconformity Upper chert formation - carbonaceous chert with local patches of carbonaceous mudstone. Figure 11-24. Composite stratigraphic section for the Iron Creek formation, from Iron Creek in the XY area (Location 18b-l in Appendix C). the low intensity of these peaks precludes positive identification. The unit contains less than 1% organic carbon. The lower and upper graded beds are light grey (N 7) to medium dark grey (N 4), depending on the grain size and related carbon content. Beds are 1 to 15 cm thick, averaging about 4 cm. As the name implies, the units are characterized by wel1-developed graded beds (Fig. 11-25) and locally exhibit flute casts, tool mark casts, flame structures and load casts at the bases of the graded beds. Typically, the beds have bases rich in coarse s i l t - s i z e chert grains, grading upward through fine s i l t to carbonaceous mudstone tops. At the tops of some beds disconti-nuous light grey chert laminae are present. Carbonaceous wacke ranges from 1 to 5 m thick in the XY area, but is up to 20 m thick in the OP area. Both fresh and weathered samples are dark grey (N 3). The wacke is characterized by subangular chert grains 100 pm to 2 mm in diameter, contained within a carbonaceous mud-stone matrix. The matrix consists mostly of quartz and clays with 0.5 to 10% organic carbon. To the northwest of the OP area this unit grades laterally into a conglomerate. Barite occurs sporadically throughout the Howards Pass area at the same stratigraphic horizon in the formation and is therefore a s i g n i f i -cant regional marker horizon. Because of its regional extent and separate stratigraphic position from the bedded barite horizon hosting the Tom Pb-Zn-Ag deposit in the MacMillan Pass area, the barite occur-ring in the Iron Creek formation is given the informal name Selwyn Moun-tains barite horizon. The horizon crops out as a resistant unit and weathers to a light greyish yellow colour which is easily distin-74 Figure 11-25. Graded beds typical of distal turbidites occurring in the Iron Creek formation. These distal turbidites generally only show intervals A, B and E of the Bouma sequence. guished. In the Howards Pass area the horizon occurs in the XY, DON, ANNIV and OP areas and ranges from 0 to 12 m thick in the XY area, but is less than 1 m thick in the ANNIV area. The horizon locally exceeds 25 m in thickness, but regionally most stratigraphic sections examined is represented by barite concretions less than 1 cm in diameter which occur in carbonaceous mudstone over a 50 cm to 5 m stratigraphic thick-ness. In areas where the barite horizon is more obvious, the barite is laminated and contains limestone concretions and carbonaceous chert beds (Fig. 11-26). In the areas of laminated barite the laminae are 2 nm to 2 cm thick and are intercalated with thinner carbonaceous mudstone laminae (Fig. 11-27). Some of the thicker laminae are size graded, with thin carbonaceous tops. The lower parts of the laminae contain 50 to 90% BaS04 and decrease upwards in barite content. Clay varies inversely with barite. Pyrite concretions less than 1 cm in diameter constitute up to 5% of the organic rich baritic laminae; i n t e r s t i t i a l calcite is usually associated with the pyrite. The baritic laminae occur in beds 10 cm to 20 m thick which show spiral structures, convolute bedding and de'collement structures, all indicative of internal slumping of these beds, which contain limestone lenses and spherical concretions of dark grey carbonaceous coarsely crystalline carbonate. In addition, light grey bedded limestone occurs as rounded clasts 2 to 5 cm across and elongate lenses which are 25 cm to 2 m thick and up to 10 m in length in the plane of bedding. Laminae of baritic mudstone wrap around these large limestone bodies. Thus, two stages of carbonate deposition may have occurred. F i r s t , limestone was deposited with the baritic mudstone and was involved in the slumping of these beds; secondly, after slumping carbonate concretions developed. 76 V I ! I ! I ! I / i . i . i . i i Upper graded beds with coarse siltstone to mudstone showing abundant graded beds. Laminated barite intercalated with minor baritic carbonaceous mudstone. The laminated barite contains limestone clasts and concretions. Thin bedded carbonaceous chert Intercalated laminated barite to highly baritic mudstone and laminated baritic mudstone with abundant barite concretions. Limestone clasts and concretions occur in the laminated barite. Locally siltstone beds occur near the base of the unit. Thin bedded carbonaceous chert with 1 to 8 cm thick. beds Carbonaceous wacke containing chert clasts with a carbonaceous mudstone matrix. Figure 11-26. Stratigraphic section for the Selwyn Mountains barite horizon, taken from the XY area (Location Ba in Appendix C). 77 Figure 11-27. Laminated barite from the Selwyn Mountains barite horizon. Light laminae contain more than 90% barite and darker laminae consist of baritic laminae with organic matter. 78 Carbonaceous mudstone beds 10 cm to 3 m thick containing abundant barite concretions 2 mm to 1 cm in diameter are intercalated with the baritic beds. Some of the larger concretions show a rosette structure, although most are elongate in the plane of the bedding. These carbona-ceous mudstone beds are identical to the carbonaceous mudstones which occur regionally at the same stratigraphic horizon, even in areas where laminated barite is not present. The carbonaceous mudstone does not show any of the slump structures evident in the laminated barite beds, suggesting that the gravitational instability which caused slumping in the laminated barite did not cause similar structures in the mudstone. Carbonaceous chert beds 0.5 to 5 m thick are associated with the laminated baritic beds. Laminae within the chert beds range from 0.5 cm to 3 cm thick and contain no visible internal sedimentary structures. The thickness of the chert beds are directly proportional to the thick-ness of laminated barite in the deposits examined. MAP-UNIT 18b-2 (YARA PEAK FORMATION) The Yara Peak formation is an informal unit that is present re-gionally and consists of brown-weathering clastic sediments which over-l i e the grey weathering units described earlier. The formation is at least 100 to 200 m thick in the Howards Pass area and forms the top of the stratigraphic section in most of the area (Plate I). The main characteristic of the Yara Peak formation is its weathering colour, which ranges from brown (5 YR 3/4) to dusky brown (5 YR 2/2). Fresh samples range greatly in colour, from moderate yellow brown (10 YR 5/4) to dark grey (N 3). 79 The rock types present in the Yara Peak formation are diverse and, typical of a flysch assemblage (Lajoie, 1970), include mudstone, shale, slate, siltstone and sandstone. The best exposures of the formation found to date are southwest of the DON area and west of the OP area (Plate I). In these the formation may be sub-divided into four informal units, designated A through D (Fig. 11-28). Regional facies changes make the four-fold division applicable only to the Howards Pass area. Unit A forms the lower 50 to 70 m of the formation and comprises a sequence of thin graded beds of siltstone to mudstone and, locally, mud-stone and associated slate. The graded beds are 1 to 5 cm thick of coarse siltstone grading upwards into finer mudstone. The graded beds are similar to those in the Iron Creek formation except for the presence of the quartz grains, the proportion of organic matter and the valence state of Fe. The Yara Peak formation contains monocrystal1ine quartz grains (Fig. 11-29) compared to chert grains in the Iron Creek formation (Fig. 11-30). The ratio of organic matter to clay is also lower in the Yara Peak formation than in the underlying units. Mixed mudstone and slate occur locally in unit A; for example, in the XY area they con-stitute 10 to 15% of the unit. The mudstone is massive and lacks ob-vious bedding. Slate is associated with the mudstone but shows clay minerals aligned parallel to the regional cleavage. Within the graded beds of the unit there are abundant flame structures and poorly developed flute casts and load casts which are best observed in beds over 4 cm thick. Lenticular pyrite concretions 1 to 5 cm long are present throughout the unit with their long axis parallel to bedding. These weather to limonite and are common in the unit. 80 chert pebble conglomerate - dark brown, weathering chert and shale clast mudstone matrix conglomerate. nconformity UNIT D - Brown weathering mudstone to greywacke showing large scale graded beds; greywacke is more abundant than mudstone. UNIT C - Brown weathering mudstone to greywacke showing abundant graded beds with siltstone and mudstone more abundant than greywacke. UNIT B - Brown weathering slightly carbonaceous mudstone to fine-grained sandstone with abundant graded beds; same as unit B except greater proportion of siltstone and sandstone, also noted are occasional greywacke beds. UNIT A - Brown weathering slightly carbonaceous mudstone to fine-grained sandstone with abundant graded beds. unconformity Iron Creek formation - Grey weathering massive carbonaceous mudstone. Figure 11-28. Composite stratigraphic section of the Yara Peak formation from a ridge southwest of Don Creek (Location 18b-2 in Appendix C). 81 Figure 11-29. Photomicrograph of a greywacke from the Yara Peak formation. The clasts are predominatly quartz grains; the matrix con-sists of mudstone. The quartz grains are similar to those in the 'Grit Unit'. 82 Figure 11-30. Photomicrograph of carbonaceous wacke occurring in the Iron Creek formation. The clasts are predominantly chert; the matrix consists of carbonaceous mudstone. The chert clasts are similar to chert occurring in the basinal facies of the Howards Pass formation. 83 Unit B is 70 to 120 m thick and consists of thin graded beds with minor greywacke lenses and slate. The graded beds have fine sandstone to coarse siltstone bases and grade upward to finer mudstone at the top. Sedimentary structures include flame structures and groove casts. Len-ticular massive greywacke beds 10 cm to 2 m thick are interbedded with the finer-grained beds and constitute less than 10% of the unit. Quartz grains are up 2.5 cm in diameter, but average 0.5 to 2 mm; quartz s i l t and clay constitute the matrix of the greywacke. The greywacke beds are traceable for up to 150 m along strike, but eventually pinch out. In two instances where greywacke beds have been traced, they are found to turn into the cleavage; here they can be traced across bedding for up to 25 m forming clastic dikes. Unit C is 50 to 130 m thick and consists of intercalated fine-grained graded beds and greywackes; the latter making up 30 to 50% of the unit. The graded beds are similar to those found in units A and B. The greywacke beds are also similar to those found in unit B, but are traceable over 500 m and occur at the base of the finer graded beds. Flute casts and groove casts are common at the base of the greywacke beds. To the south of the XY area, six measurements on in-place casts indicate local current directions were from the west to southwest. Partial Bouma sequences are present in the unit (Fig. 11-31). Unit D, the uppermost unit in the Yara Peak formation is 30 to 110 m thick and consists of intercalated greywackes, quartzose sandstones and minor siltstones and mudstones. Beds range from 3 cm thick in the mudstones to over 5 m in the greywackes. Complete Bouma sequences are found locally, and include coarse greywackes (division A) with bases 84 PELAGIC SHALE HORIZONTAL LAMINATION CURRENT RIPPLE & CONVOLUTE LAMINATION HORIZONTAL LAMINATION BEDDING (B) tvcr»i^>accostTO Figure 11-31. Turbidite sequences present in the Yara Peak forma-tion and the chert pebble conglomerate; A) ideal Bouma cycle, B and C) partial cycles from the Yara Peak formation, D) partial cycle from the chert pebble conglomerate. Not drawn to scale. 85 containing groove and flute casts which indicate a western source, a l -though only a few measurements were obtained. Quartz-rich cross-bedded siltstone and sandstone are found in division C. The mudstones at the top of the sequences are similar to those present in unit A at the base of the formation. The Yara Peak formation is bounded by unconformities. The lower contact is locally conformable, but 1 km northeast of the DON area the formation overlies the lower graded beds of the Iron Creek formation, suggesting an unconformity. The chert pebble conglomerate unconformably overlies the Yara Peak formation, locally directly overlying unit A. MAP-UNIT 18b-3 (CHERT PEBBLE CONGLOMERATE) The chert pebble conglomerate is an informal unit over 400 m thick in the Howards Pass area and consists of disorganized conglomerates (Walker and Mutti, 1973) with chert, quartz and minor shale clasts, locally intercalated with brown weathering mudstones and sandstones. The unit contains complex facies relationships and has not been studied in detail, and is therefore considered an informal unit. The unit weathers brown (5 YR 3/4) to dusky brown (5 YR 2/2) and at a distance appears similar to the underlying Yara Peak formation, except that the outcrops of the conglomerate appear rubbly. The conglomerate was studied mainly to the southwest of Howards Pass where i t is contain-ed in a syncline which extends for approximately 35 km along strike (Plate I), although the unit does occur elsewhere. The top of the con-glomerate was not observed in the Howards Pass area, but is similar to the chert pebble conglomerate in the Canol Formation near MacMillan Pass (Smith, 1978) where i t underlies the Tom Ba-Pb-Zn-Ag deposit, and is similar to the Earn Group to the west. 86 In the Howards Pass area the best exposures are to the west of the OP area, where a stratigraphic sequence has been developed which applies to the unit in the syncline south of Howards Pass. Elsewhere all the sub-units described occur, but their interrelationships cannot be demon-strated. The matrix is similar in a l l the subdivisions of the chert pebble conglomerate, consisting of siliceous mudstone, siltstone and chert similar to that noted in the greywackes of the Yara Peak for-mation. The chert pebble conglomerate can be subdivided into five sub-units (A thru E) based on clast type and grain size (Fig. 11-32). All of these sub-divisions are present in the OP area, but regionally only partial sections occur suggesting laterial facies changes. Sub-unit A is the stratigraphically lowest recognizable division of the chert pebble conglomerate; i t is 10 to 40 m thick and is charac-terized by up to 20% lenticular carbonaceous mudstone clasts. The re-maining 80% of the clasts consist of sub-rounded black to white chert and minor quartz ranging from 1 to 10 cm in diameter. On cut surfaces the clasts appear to be supported. The mudstone clasts are aligned parallel to bedding found elsewhere in the unit and represent the only sedimentary structures. Sub-unit B is 25 to 40 m thick in the OP area and consists of a pebbly mudstone containing pebbles 5 nm to 2 cm in diameter. Black to dark grey chert clasts constitute 80 to 90% of the pebbles, whereas light grey chert pebbles make up the remainder. Pebbles are sub-rounded and equant with the pebble:matrix ratio being approximately 2:3, which is lower than other sub-units. The matrix consists of slightly carbona-ceous mudstone to siltstone. 87 o in oo •»•>•..*•.. •'.,„,...r » o • &»T> -o, •staler •o ' Q U | Top of the s t r a t i g r a p h i c sect ion in the Howards Pass area . SUB-UNIT E - Light grey to white c l a s t , chert pebble conglomerate with no bedding ev ident . SUB-UNIT D - L ight brown weathering in te rca la ted quartz areni te to sub-greywacke and greywacke sandstone with weakly graded beds. SUB-UNIT C - Brown weathering, black chert . c l a s t pebble conglomerate, with massive lower part and upper th ick graded beds. L o c a l l y upper part grades into brown mudstone. SUB-UNIT B - Fine black c l a s t chert pebble conglomerate. SUB-UNIT A - Chert and shale c l a s t conglomerate nconformity YARA PEAK FORMATION - Mudstone to greywacke showing abundant graded beds. F igure 11-32. Composite s t r a t i g r a p h i c sect ion for the chert pebble conglomerate u n i t , from a r idge southeast of the OP area (Locat ion 18b-3, Appendix C ) . 88 S u b - u n i t C i s 300 t o 350 m t h i c k and i s d i s t i n g u i s h e d , by a b u n d a n t b l a c k c h e r t p e b b l e s w h i c h a r e 0.5 t o 10 cm i n d i a m e t e r , s u b - r o u n d e d and e q u a n t ; b l a c k c h e r t c o n s t i t u t e s 70 t o 80% and l i g h t g r e y c h e r t 20 t o 30%. The l o w e r p a r t o f t h e s u b - u n i t i s m a s s i v e and d o e s n o t show b e d d i n g o r i m b r i c a t i o n . The u p p e r p a r t c o n t a i n s a g r e a t e r p r o p o r t i o n o f o b l a t e p e b b l e s , shows weak i m b r i c a t i o n m o d i f i e d by c l e a v a g e and i s c r u d e l y b e d d e d . T h e s e beds a r e 10 t o 40 m t h i c k and a r e p o o r l y g r a d e d , a l t h o u g h t h e t o p s o f t h e b e d s a r e s t i l l f i n e c o n g l o m e r a t e . S u b - u n i t D o c c u r s o n l y l o c a l l y w e s t o f t h e OP a r e a and has n o t been i d e n t i f i e d e l s e w h e r e . I t i s 20 t o 150 m t h i c k and c o n s i s t s o f b e d d e d v e r y c o a r s e l i t h i c a r e n i t e and i n t e r c a l a t e d g r e y w a c k e . Q u a r t z g r a i n s a r e 1 t o 3 mm i n d i a m e t e r w i t h o n l y m i n o r c h e r t g r a i n s p r e s e n t e x c e p t i n t h e g r e y w a c k e . In t h e OP a r e a t h e t o p o f t h e c h e r t p e b b l e c o n g l o m e r a t e , and t h e h i g h e s t s t r a t i g r a p h i c u n i t i n t h e Howards P a s s a r e a , i s s u b - u n i t E, w h i c h i s o v e r 200 m t h i c k . The s u b - u n i t c o n s i s t s o f m a s s i v e c o n g l o m e r a t e w i t h 90 t o 9 5 % l i g h t g r e y t o w h i t e c h e r t p e b b l e s , w i t h o n l y m i n o r q u a r t z a r e n i t e and d a r k c h e r t c l a s t s . The s u b - u n i t w e a t h e r s l i g h t brown (5YR 6/4) due t o t h e p r e s e n c e o f i r o n o x i d e s i n t h e s i l t s t o n e m a t r i x w h i c h c o n s t i t u t e s 10% o f t h e c o n g l o m e r a t e . No o b v i o u s b e d d i n g o r i m b r i c a t i o n i s p r e s e n t . R e g i o n a l f a c i e s c h a n g e s a r e e v i d e n t i n t h e c h e r t p e b b l e c o n g l o m e r a t e . W i t h i n t h e s y n c l i n e m e n t i o n e d p r e v i o u s l y ( P l a t e I ) , c o n g l o m e r a t e s a r e a b u n d a n t w h i l e t o t h e e a s t t h e y a r e l e s s a b u n d a n t ; s i l t s t o n e s and g r e y w a c k e s o c c u r a t t h e same s t r a t i g r a p h i c l e v e l . T h i s same e a s t w a r d f i n i n g a l s o o c c u r s t o t h e s o u t h and o n l y s a n d s t o n e s o c c u r a t t h i s s t r a t i g r a p h i c l e v e l n e a r T u n g s t e n . 89 The chert pebble conglomerate typically overlies the Yara Peak for-mation, and appears to be the culmination of the upwards coarsening ob-served in that formation. The presence of an unconformity at the base is indicated by the chert pebble conglomerate overlying various units throughout the stratigraphic section, including the wavy banded lime-stone; although local faults may also bring these two units into con-tact. 90 CHAPTER III CORRELATION AND SEDIMENTATION CORRELATION OF UNITS The problem of biostratigraphic correlation in the Howards Pass area has been accentuated by the sparseness of megafossils. Conodonts may provide better biostratigraphic control in the future, but this method is just beginning to be used in the area. In the present study lithologic correlation was the method used, although graptolite fossil assemblages provided further control within the Howards Pass formation. In the present study the term group is used informally for the Rabbit-kettle and Road River strata. At present these are considered of forma-tion status, but confusion has resulted in part because of the more detailed stratigraphy available in the Howards Pass area (Morganti, 1975, 1977a, 1979). The informal use of groups and formations in the present work appears justified because of stratigraphic hierarchy. The lack of detailed biostratigraphy in the area at present makes, in the view of the present author, a strong case against the use of time-stratigraphic units. As more definite biostratigraphic correlation is completed, new, more regional, names will obviously be formally pro-posed. The oldest units in the Howards Pass area are the fine grained elastics and phyllite occurring below the Franconian unconformity; these are correlated with the 'Grit Unit' as described by Gabrielse et a l . (1973). They stated that the lithological characteristics of the 'Grit Unit' and its stratigraphic relationships with Lower Cambrian rocks sug-gest correlation with the Hadrynian Kaza, Miette and Windermere strata occurring farther south in the Canadian Cordillera. The same assemblage 91 is recognized in the Flat River area (Gabrielse et a l . , 1973) and Frances Lake map-area (Blusson, 1966) and as far west as the Tintina Trench in the Finlayson Lake map-area (Green et a l . , 1960). The lower siltstone unit (map unit 7a) also occurs below the Franconian unconformity. The general lithology and relative s t r a t i -graphic position of the unit suggest that i t correlates with the Sekwi Formation (Blusson, 1971; Gabrielse et a l . , 1973), but the former is a siltstone in contrast to the latter which is a dolomitic limestone. Furthermore this correlation is tentative because of the limited amount of exposure of the unit and the lack of f o s s i l s . The Sekwi Formation consists of orange weathering s i l t y dolomite whereas the more westerly lower siltstone is an orange weathering dolomitic siltstone. A facies change, related to the easterly source was proposed by Gabrielse et al.(1973), and may explain this discrepancy. The massive limestone, wavy banded limestone and transition for-mations are all correlated with the Rabbitkettle Formation as defined by Gabrielse et a l . (1973). This correlation is based on lithology, fossil data and the tracing of the unit from the Coal River to the Pelly River by (Gabrielse and Blusson, 1969). The presence of three informal forma-tions in the present study indicates that the Rabbitkettle should be given informal group status (Table I I I - l ) . Further correlation of the Rabbitkettle and the Broken Skull formation to the east can be made based on evidence presented by Gabrielse et a l . (1973). The Howards Pass, flaggy mudstone and all or part of the upper chert formations are equivalent to the Road River Formation as described by Gabrielse et a l . (1973). This correlation is supported by lithology and megafossils found in the Howards Pass area (Fig. I I I - l ) . The 92 Table I I I - l . Summary of regional stratigraphic correlation in the eastern Yukon. Regional units are shown in column at right. The use of formations as presented in the present thesis would elevate the Road River and Rabbitkettle formations to group status. PERIOD •This r e p o r t -based on major u n i t s p roposed by Green e t a l . T h i s r e p o r t - l o c a l i n f o r m a l usage (Morgant i , 1975) Reg iona l uni ts wh ich c o r r e l a t e w i t h the l o c a l s e c t i o n , some o f wh ich meet group requ i remen ts PENNSYLVANIAN M I S S I S S I P P I 18b-3 CHERT PEBBLE CONGLOMERATE 18b-2 YARA PEAK FORMATION DEVONIAN 18b-1 IRON CREEK FORMATION EARN GROUP 10c UPPER CHERT FORMATION ROAD RIVER FORMATION (GROUP) SILURIAN 10b FLAGGY MUDSTONE FORMATION 10a HOWARDS PASS FORMATION ORDOVICIAN 7b-3 TRANSITION FORMATION RABBITKETTLE FORMATION (GROUP) CAMBRIAN 7b-2 WAVY BANDED LIMESTONE FORMATION 7b-1 MASSIVE LIMESTONE FORMATION 7a LOWER SILTSTONE UNIT ^ SEKWI FORMATION 2 'GRIT UNIT' 'GRIT UNIT' HADRYNIAN cc Ul o _J I o > UJ Q TIME FOSSIL (RANGE) ROCK UNIT _ J CO o > o Q o COUVINIAN EMSIAN SIEGENIAN GEDINNIAN DOWNTONIAN LUDLOVIAN WENLOCKIAN LLANDOVERIAN ASHGILLIAN CARADOCIAN LLANDEILIAN LLANVIRNIAN ARENIGI AN TREMADOCIAN oo Ul fc or l -< t cr >-o FETID LIMESTONE Q: UI u o 2 O (O UJ o < UJ Q O _J (-i UPPER SILICEOUS MUDSTONE ACTIVE MEMBER CALCAREOUS MUDSTONE 2 O tr e to to Q I o X TRANSITION ZONE Figure I I I - l . Biostratigraphic correlation of units in the Howards Pass area using known worldwide ranges of identified genera. The Early Silurian age for the active member is for all three Zn-Pb deposits in the area. Fossil locations are marked on Plates II, III and IV. 94 identification of the better preserved fossils were made by the present author, but a suite of fossils collected from the Cyrotograptus zone in the XY area and sent to Dr. C.R. Stelk (Stelk, written commun. to A.D. Clendenan, 1974) confirm the Lower Silurian age of the upper siliceous mudstone member of the Howards Pass formation. The present fossil data, although preliminary in nature, does allow placement of the Howards Pass formation and i t s contained Zn-Pb deposits in a useful time-strati-graphic framework. The Road River is given informal group status in the present report because of the presence of three regionally mappable units within i t as previously defined, as well as the importance of the abili t y to trace the unit containing the Howards Pass Zn-Pb deposits. Correlation of the Road River with the Whittaker Formation to the east has been proposed by Gabrielse et a l . (1973). The Iron Creek and Yara Peak formations and the chert pebble con-glomerate unit can be traced to the MacMillan Pass area where they have been correlated with the Canol Formation, but major facies changes between the formation at the type locality in the Arctic make this later correlation questionable (Mackenzie, 1970). The distinctive lithology of the chert pebble conglomerate is also similar to that of the Earn Group in the Glenlyon map-area (Campbell, 1967). Thus the three formations in the Howards Pass area may be better correlated with the Earn Group. Mapping in the Howards Pass region has significantly refined the stratigraphic section there (Morganti, 1975, 1976, 1977a). It is pro-posed that the Rabbitkettle and Road River formations be given informal group status, and that term Earn Group be used in the Howards Pass area 95 for the Middle Devonian to Mississippian (?) units. This would not only help define locations in the stratigraphic section but also allow for lithofacies time-slice reconstructions to be made, as has been done in this study with the Howards Pass formation. The age of the active mem-ber is tentatively thought to be Early Silurian in age, based on the fossil evidence presented here. The fossil data also indicate that the sedimentary rate of deposition for the Howards Pass formation in the Howards Pass area was in the range of 1 to 6 mm/1000 yrs., depending on assumptions made concerning the percent compaction. SEDIMENT AT ION  INTRODUCTION The sedimentary environments which evolved in the Paleozoic in the eastern Yukon area are complex, and in this report are presented in a separate section because of economic ramifications. The major s t r a t i -graphic-tectonic feature in the area is the Selwyn Basin which, based on data presented .here, was in existence from the Cambrian to the Early Devonian, and not Late Devonian to Mississippian as previously proposed (Gabrielse, 1967; Green et a l . , 1967). This is based on the presence of poorly preserved Monograptus (cf. M_j_ Yukonensis) near the top of the upper chert formation. Sedimentary sulphides were deposited in the Selwyn Basin during the Lower Silurian in the Howards Pass formation. Post-Road River sediments were deposited in a different basin than the Selwyn Basin and included fine to coarse elastics derived from a wester-ly source. A later basin had a different geometry than the Selwyn Basin and the associated Zn-Pb deposits have no direct genetic link with the Howards Pass deposits. 96 LOWER UNITS The 'Grit Unit' consists of a lower unit with abundant graded beds and an upper unit with abundant shallow water structures. The depth of water during deposition of the lower graded beds is unknown, but similar turbidites are generally considered to have formed in deep water (Walker, 1969). The upper part of the unit contains abundant evidence for shallow water deposition, including mudcrack casts, cross-bedding and intra-formational conglomerates. This sequence of deep to shallow water deposition suggest f i l l i n g of the basin. The source area for the 'Grit Unit' is not clear from the present study, but Gabrielse (1967), in summarizing the unit regionally, stated that the source was crystal-line and probably lay to the west or southwest, and that the unit was deposited as a clastic wedge. The lower siltstone appears to be a clastic basinward facies of the Sekwi Formation which, in the Sekwi Mountain map-area (Blusson 1971), consists of dolomites and sandy, s i l t y dolomites and limestones. Simi-lar shelf carbonate-basinal terrigenous facies relationships have been described by Selley (1970). These conditions can be brought about by three factors acting singly or in concert. Low input of terrigenous sediment to the shoreline may be due to low runoff or, i f the hinterland is low-lying, low sediment availability. Third, i f the shoreline has a very gentle seaward gradient i t will have an extremely broad tidal zone and an extremely wide development of the facies. belts paralleling the shore. Regional relationships in the Sekwi Formation indicate that a broad tidal zone may be at least in part the reason for the mixed clastic-carbonate relationship (Fritz, 1976). 97 The depositional environment of the massive limestone formation is speculative due to poor exposures, but the abundance of micrite suggests deposition below wave base (Bathurst, 1975). Lenses of transported fos-s i l material in the lower part further suggests deposition i n i t i a l l y was by currents with a reef or bioherm source, possibly to the east (Gabrielse et a l . , 1973). The upper part of the unit contains micrite, suggesting l i t t l e current activity; this and the high s i l i c a content indicate deposition below wave base (Selley, 1970). The carbonate plat-form to the east - basin to the west geometry and possible eastward shallowing of the depositional environment for the massive limestone formation suggest that the unit had a geometry similar to the units deposited in the Selwyn Basin. Therefore the massive limestone may mark the beginning of the existence of the Selwyn Basin. The wavy banded limestone is the f i r s t formation to definitely show the typical geometry of the Selwyn Basin (Gabrielse, 1967). The lower member consists of graded micrite beds typical of proximal limestone rhythmites of the basin-slope facies of Hoffman (1974). He suggested that the facies is "deep water", but the lack of wave related features in the wavy banded limestone only indicates that deposition was below wave base. The overlying upper member consists of laminated micrites which locally show penecontemporaneous folds and are more typical of the distal-limestone rhythmite facies (Hoffman, 1974). These laminae in the upper member are locally graded and show spiral structures suggestive of clastic deposition and subsequent slumping. The laminae may be the result of distal turbidity current deposition, sedimentation or basinal currents, although the formation of microspar has obscured the original 98 nature of the laminae. If, as has been suggested (Gabrielse et a l . , 1973), the source area for the formation was to the east, then the pro-ximal facies overlain by a distal facies could be a result of either basin deepening or eastward shelf migration (i.e., transgression) of the Broken Skull Formation. The roughly synchronous nature of the format-ions (Gabrielse et a l . , 1973) and the same location of facies changes in the massive limestone suggest that the basin deepened during the late Cambrian (Fig. Ill-2)-The transition formation is the result of a depositional environ-ment similar to that in which the wavy banded limestone was deposited, except for a higher silicate/carbonate ratio. The dominance of clay and quartz over carbonate suggest that the relative rate of sil i c a t e input increased gradually, or that the Selwyn Basin continued to subside below the carbonate-compensation depth. HOWARDS PASS FORMATION The Howards Pass formation marks the beginning of "black shale" deposition in the Selwyn Basin, and because of its economic importance is considered in some detail. The formation is subdivided regionally into three major facies (Morganti, 1977), from west to east, these are: a chert basin facies, a base of slope facies and a slope facies (Fig. Ill-3), s t i l l further east, near the south Nahanni River, are shallow water shelf and locally reef limestone facies of the Whittaker Formation (Gabrielse et a l . , 1973). The Howards Pass formation is thickest in the area of Howards Pass, where the base of slope facies occurs (Fig. III-4). Characteristics such as the high organic matter content, lamination and slow deposition rate of less than 6 mm/1000 yrs. are 99 Figure III-2. Lithofacies time-slice interpretation for the east-ern Selwyn Basin during deposition of the wavy banded limestone forma-tion. The area shown is the Nahanni map sheet. 1 0 0 Figure 111-3. Lithofacies time-slice interpretation for the east-ern Selwyn Basin during deposition of the Howards Pass formation in the Nahanni map-area. Arrows indicate the direction of sediment transport. Figure III-4. Composite stratigraphic sections of the Howards Pass formation across the base of slope facies in the Howards Pass area. These sections show a general thickening of the formation in the area of the Howards Pass sub-basins (section C). 102 typical of a starved basin (Lineback, 1968, 1969; Conant and Swanson, 1961). Pelagic deposition in the eastern Selwyn Basin was preceded by basinward migration of the top of the slope due in part to local reef de-velopment (Fig. III-5). This migration was on the order of 10 km, based on the difference in location of the contacts between the wavy banded limestone formation and Broken Skull Formation and that between the Howards Pass formation and Whittaker Formation. Within the three basinal facies, the slope facies is characterized by a thin sequence of calcareous mudstones similar in appearance to the calcareous mudstone member in the Howards Pass area. This lithology has been found from 6 km to 20 km east of Yara Peak (Fig. Ill-3) and inter-fingers with the Whittaker Formation to the east. Within the slope facies, blocks of al1ochthonous limestones up to 30 m across and 10 m thick are present up to 5 km from the reef. The presence of rudites and poorly preserved fossils suggests that this material has come from the fore-reef (Wilson, 1975; Krebs, 1976a). These blocks have apparently rolled or slid down the slope as is evidenced by the lack of significant associated slump structures. In the Howards Pass area, laminated, siliceous, highly carbonaceous mudstone defines the base of slope facies of the Ordovician-Silurian Selwyn Basin (Fig. III-3). An extreme thickening of the formation is associated with this facies, suggesting a weakly developed trough at the base of the slope. This trough is most clearly developed in areas of sub-basin development where the active member occurs (Fig. Ill-4). The sub-basins are elongate sub-parallel to the trend of the major facies H O W A R D S P A S S S O U T H NAHANNI R IVER B R O K E N S K U L L RIVER R E E F CARBONATE P L A T F O R M SHORE B A S I N A L C L A S T I C S ~ 10 km I 1 R E S T R I C T E D S H E L F DURING DEPOSITION OF WAVY BANDED L IMESTONE FORMATION f - ^ , 'SHF I F CARBONATES — ^ I ( B R O K E N S K U L L FM.) Figure III-5. Diagram showing spacial relationships between the basin and the edge of the Selwyn Basin during deposition of the wavy banded limestone formation and the Howards Pass for-mation. Not drawn to scale. 104 changes in the area, and define a trend sub-parallel to major facies changes. This suggests that the origin of the sub-basins is directly or indirectly related to the formation of the regionally significant facies changes. West of Howards Pass, near Summit Lake, chert is the major rock type in the Howards Pass formation. The chert is dark grey to black, but to the north near Mount Sheldon equivalent varicoloured cherts with only traces of organic carbon occur. Abundant white chert blebs, barely visible in hand specimens, appear to be replaced radiolarian tests in thin section. This suggests that mainly pelagic sediments were deposited on the basin floor. Only minor amounts of terriginous sediments were deposited in the starved Selwyn Basin and regional mapping has not indicated any chan-nels, canyons or fans (Silver and Todd, 1969) along the eastern edge of the Ordovician-Silurian Selwyn Basin. The extensive shallow water car-bonate environment in the Whittaker Formation (Gabrielse et a l . , 1973) could have prohibited significant terriginous material from entering the basin from the east (Fig. 111 —5) -The large amount of thickening in the base of slope facies of the Howards Pass formation is not typical of most black shale deposits (Conant and Swanson, 1961). This may be due to either the fact that most black shales described in the literature are intracratonic (Heckel , 1969), whereas the Selwyn Basin may be platform-marginal, or that local thickening is due to the presence of a fault bounded trough (Weeks, 1952). Similar platform marginal graptolitic shales in Nevada (Churkin, 1974) are less than one-third the thickness with no significant thick-ness changes reported. The coincident alignment of regional facies 105 change, major faults in the Proterozic units and the Howards Pass sub-basins suggest that differential movement in the basement rocks in-fluenced sedimentation. The lack of coarse elastics near the edges of the sub-basins further suggests that the rate of subsidence in the sub-basins was slow, and possibly that reactivation of the basement did not produce fault scarps in the sub-basins. The regional facies distribution, within the Howards Pass for-mation, (Fig. 111-3) of slope, base of slope and chert basin are typical of an increase of water depth toward the basin floor (Selley, 1976). While there has been general agreement that marine carbonaceous shales with a sparse or non-existent benthic fauna have formed in stagnant bot-tom conditions, opinions have varied widely on the probable depth of deposition. At one extreme, i t has been suggested that many carbona-ceous shales in the geologic past have been deposited in extremely shal-low water, no more than a metre deep, with benthic algae acting as baf-fles restricting water movement (Twenhofel, 1939; Conant and Swanson, 1961; Hal lam, 1967). An alternative view has been for a deep water ori -gin ranging from several hundred to several thousand metres, at the bot-tom of marine basins (Wodnough, 1937). The latter deep water depositi-onal model is supported by modern analogies such as the Gulf of Cali-fornia (Calvert, 1964; 1966) and the Black Sea (Ross and Degens, 1974). In the Howards Pass area allochthonous blocks of limestone are present 5 km down the slope from the nearest carbonate buildup from which they appear to be derived. This type of submarine talus suggests slopes of over 5° (King, 1948) If the slope was consistent over the 18 km from the reef front to the base of slope a water depth of approximately 500 to 1600 m is indicated. 106 Evidence suggestive of water depth during deposition of the base of slope facies of the formation includes the association of graptolitic carbonaceous mudstones with well preserved lamination and the lack of benthic fo s s i l s , both suggestive of deposition below wave base. Evi-dence against the "shallow water - algal baffle model" consists of the presence of hydrodynamically aligned graptolites which indicate weak undirectional bottom currents (Moors, 1969). Thus there is no evidence conflicting with the proposed water depth of 500 to 1600 m presented above. The shallow limits of water depth is suggested by the preserva-tion of limestone in the active member which indicates that the member was deposited above the carbonate compensation depth of 4,500 m (Hudson, 1967) to 5,400 m (PettiJohn, 1975). This deep limit applies only to the base of slope facies since the lack of carbonate in the radiolarian chert in the basin floor faces could be a result of deposition below the compensation depth. The above data and considerations suggest that the Ordovician-Silurian Selwyn Basin had a deep water base of slope and basin floor. All three major Howards Pass Zn-Pb deposits occur in the active member which in turn was deposited only in the base of slope facies. The active member contains recurring facies which may be cyclical in nature, but the ideal cycle is not often developed, in part because of breaks in sedimentation related to slumping. The ideal cycle shows four generalized trends (Fig. III-6), including a sphalerite-galena and quartz increase up-section, a carbonate decrease up-section and an organic matter maximum in the middle. The occurrence of limestone in a deep water environment is not com-mon, but may be related to sulphate reduction in the sub-basins. If the 1 0 7 Figure III-6. General trends within an ideal active member cycle. A. sphalerite + galena content, B. carbonate content, C. organic car-bon content, D. quartz content. Facies of the active member are shown by numbers; 1) light grey basal limestone, 2) graded limestone, 3) thin bedded calcareous mudstone, 4) mixed cherty mudstone and limestone, 5) cherty mudstone, 6) thin bedded cherty mudstone, 7) whitish grey Zn-Pb mudstone and 8) grey chert. Scale not implied. 108 sub-basins were closed by a chemocline, which seems probable, two models for limestone production are possible, both of which require bacteria and sulphate. The occurrence of calcilutites occurring in deep water environments at the expense of sulphate in salt lakes, in the Dead Sea and in ancient evaporite deposits has been documented thoroughly (Neev, 1963; Neev and Emery, 1967; Friedman, 1965; Sanders and Friedman, 1969; Schmalz, 1969). Specifically, Neev, (1963) found that low-magnesium calcite in the Dead Sea forms as a result of the breakdown of calcium sulphate by sulphate reducing bacteria, particularly in the reducing environment of the sub-basin. Hydrogen sulphide, the intermediate product in gypsum degradation, can evolve on the sea floor from gypsum in violent eruptions (Butlin, 1953). The lack of any remaining sulphate minerals in the active member suggests that sulphate was not present in a solid form. In the absence of solid calcium sulphate, calcium carbonate can s t i l l be formed from calcium and sulphate ions in sea water. In the laboratory Zobell (1958) studied sulphate reduction by Desulfovibrio using soluble compounds such as MgSO^  or Na2S04. Under these laboratory conditions the bacteria at-tack the sulphate ion directly in solution (Friedman, 1972). The generalized equation for sulphate reduction under these conditions is: 2CH20 + S04= 2H20 + S = where 2CH20 represents organic matter (Richards, 1965; Nissenbaum et a l . , 1972), or the more general form presented by Berner (1971): 2CH20 + S04= 2HC03- + H2S with the high HCO3- ion concentration possibly bringing about precipi-tation of dissolved Ca + + as CaC03 (Feely and Kulp, 1957; Presley et a l . , 1968). The change in pH as a result of bacterial sulphate reduc-109 tion depends upon the nature of the organic source (Berner, 1971). How-ever there is some suggestion that the overall reaction in marine sedi-ments and in anaerobic waters cause a slight increase in pH (Emery and Rittenberg, 1952; Kaplan et a l . , 1963; Tissot and Welte, 1978). Similarly, deamination of nitrogenous organic matter, which occurs largely through the agency of biological processes in the presence or absence of dissolved oxygen, leads to the development of ammonia. With-in aerobic environments the ammonia may build up to considerable levels and may sometimes exceed concentrations of 10-3 M, (Rittenberg et a l . , 1955) and hence may raise the pH of the environment. Consideration of the ideal cycle of the active member suggests that pH could be very important. The inverse relationship of carbonate and organic matter and the inverse relationship between carbonate and chert suggests that pH could be a controlling factor (Fig. 111-6). Experi-mental work has shown that the deposition of SiO2 and CaC03 is pH depen-dent and that at higher pH CaCOg is' preserved while at lower pH chert is preserved (Freidman and Sanders, 1978). UPPER UNITS The flaggy mudstone occurs throughout the Nahanni map-area (Plate I) and is everywhere similar in thickness and in the sedimentary struc-tures present, except in the Howards Pass area where the formation thickness increases to over 75 m (Fig. I l l - 7 ) - Regional distribution indicates that the formation was deposited to within 3 km of the carbo-nate front to the east, and that this distance is uniform along strike. This, combined with the nereites facies trace fossils (Seilacher, 1967) and laminated nature of the sediments indicate a deep water environment at the time of deposition. Alternating laminae of quartz-muscovite mud-n o Figure III-7. General lithofacies time-slice interpretation for the flaggy mudstone formation in the Nahanni map-area. The unit is characterized by regional homogeneity and the lithology is identical over thousands of knr. Area with vertical lines indicates thickness of the formation greater than 75 m. I l l stone and non-terrigenous carbonaceous mudstone and local thickening of the formation where there apparently were sub-basins such as in the Howards Pass area, are suggestive of contourites (Hoilister and Heezen, 1972). These are deposited by contour or geostrophic currents which can transport sediments parallel to topographic contours in deep water (Bouma and Hollister, 1973). The occurrence of minor distal turbidites, abundant burrows and pelagic deposits in the form of the carbonaceous mudstone beds are in general supportive of the deep water contourite mode of deposition (Stow and Lovell, 1979). The sediments of the flaggy mudstone blanketed the eastern Selwyn Basin and at least partially f i l l e d in basin irregularities such as at the base of the slope. The paleogeographic distribution of the upper chert formation is similar to that of the flaggy mudstone (Fig. III-8), although the uncon-formity at the base of the Iron Creek formation hinders paleogeographic interpretation. The uniformity of thickness of the upper chert suggests that the trough at the base of the slope had been f i l l e d by the end of deposition of the flaggy mudstone. The presence of sparse radiolarians in the cherts, and minor small scale sole marks in the mudstone suggest that the unit was deposited by a combination of pelagic and hemipelagic sedimentation and weak local turbidity currents, similar to that des-cribed by Bramlette (1946, 1961). The distribution of the flaggy mud-stone and the upper chert formations may be significant. Neither unit has been found east of the South Nahanni River. This distribution could be the result of either a facies change or removal of the units from the east side of the river by erosion. Although detailed geologic mapping has not been completed in this inverval to the east, the proposal that the flaggy mudstone and the upper chert formations contain pelagic sedi-ments and contourites suggests that these lithologies would not have 112 Figure 111-8. General lithofacies time-slice interpretation for the upper chert formation in the Nahanni map-area. Within the map sheet the formation is lithologically uniform with only relatively minor thickness variations. 113 been deposited on the carbonate platform, and therefore a facies change is suggested. The Earn Group, which consists of the Iron Creek and Yara Peak for-mations and the chert pebble conglomerate in the Nahanni map-area (105-1), contains clastic sequences and marks a major change in the type of deposition in the eastern Yukon. The Iron Creek formation is the f i r s t major clastic unit in the Paleozoic sequence to have been obvious-ly deposited by turbidity currents (Kuenen and Migliorini, 1950; Walker, 1973). In the Howards Pass area the formation consists predominantly of coarse siltstone to mudstone deposited as graded beds, and is similar to distal turbidite sequences, with abundant s i l t and mud compared to sand and the presence of only Bouma A, B and E divisions, on the fringes of submarine fans (Nelson and Nil sen, 1974). To the west of the OP area the relative amount of sand increases and a conglomerate with chert clasts 2 to 5 rrm across locally occurs (Fig. I l l - 9 ) . The conglomerate contains a mudstone matrix and is similar to upper fan deposits (Walker, 1976). To the east, the formation overlies the limestones of the Delorme Formation (Fig. 111-10); here the formation consists of fine-grained mudstone and chert and is similar to the hemipelagic upper chert formation. This regional facies pattern is suggestive of a small sub-marine fan originating just west of the OP area near the Pelly River and grading eastward into distal turbidites (Walker, 1967) and hemipelagic deposits. This distribution implies a source to the west and a reversal in basin polarity between the times of deposition of the Howards Pass - and Iron Creek formations. The distinct differences in lithology and provenance between the Iron Creek and underlying formations indicate that this unit was not deposited in the Selwyn Basin as defined in this 114 « * <* - KHOUCTBCS Figure 111-9. General lithofacies time-slice interpretation for the Iron Creek formation in the Nahanni map-area. This interpretation is based mainly on the grain size distribution within the formation. Two general features are evident and include a source area to the west of the OP area and two small chert basins along the margin of the coarse grained fan complex. 115 Figure 1 1 1 - 1 0. Photograph showing the Iron Creek formation overlying limestones of the carbonate sequence on the east side of the South Nahanni River looking northeast. In this area the Iron Creek formation consists of laminated mudstone with minor graded beds. 116 thesis. The presence of clasts of radiolarian chert in the Iron Creek formation, furthermore, suggests that the source material may have been the central part of the Selwyn Basin, where the Howards Pass formation consists of radiolarian chert. The depositional environment for the Selwyn Mountains barite hori-zon is important because of the local association of Pb, Zn and Ag. The presence of minor amounts of barite in this horizon regionally has been demonstrated (Morganti, 1976) and may be equivalent to sediments con-taining barite nodules and diagenetic barite further south in north-eastern British Columbia. Surface grab samples from this horizon regionally contain over 5000 ppm Ba which suggests the presence of a Ba rich time horizon regionally. The presence of laminated barite associated with carbonaceous chert suggests deposition in local sub-basins on the sea floor. In areas of drastic thickening of the laminated barite (e.g. at the 0R0, GHMS and NOR claims, Appendix D), rapid termination along one edge and penecontemoraneous folds in the underlying rocks suggest that these local basins are fault bounded (Weeks, 1952). The faults could have channeled Ba-rich fluids into the local basins making the faults important in both the source of Ba and the concentration of Ba. The delicate lamination and abundance of slump structures in the barite further suggest a synsedimentary origin for the laminated barite. The Yara Peak formation and chert pebble conglomerate have most of the attributes of flysch sequence (Dzulynski and Smith, 1963; Hsu, 1970): (1) the succession is made up of alternating shales, mudstones and siltstones, with sandstones; (2) in the Yara Peak formation the sandstones are greywackes; (3) graded beds and sole marks are common; 117 (4) slump deposits are present; (5) fo s s i l s are rare; (6) volcanic rocks are absent; (7) large scale cross-stratification is virtually absent and (8) no features suggestive of sub-aerial conditions are present. Regional mapping (Plate I) has demonstrated that distinct facies occur in the formation, and the regional distribution of lithologies (Fig. I I I - l l ) indicates a westerly source area for these sediments. This distribution further suggests deposition associated with fan development (Normark, 1974; Nelson and Nil sen, 1974). The general re-gional grain size distribution indicates that the fan head was west of the OP area, although a few paleocurrent features found south of the DON area in the chert pebble conglomerate indicate a southwesterly source. This inconsistency may be explained by local current perturbations (Potter and Petti John, 1977). To date, only one major fan has been de-fined, but the possibility of multiple fans (Fig. 111-12) is possible and would explain the various chert pebble conglomerate sub-units. The lithology of the clasts in the Yara Peak and Iron Creek for-mations indicates either a different source area or a different source material. In the Yara Peak formation quartz grains are more abundant than chert grains, but the similar regional spacial distribution of lithologies indicate that the fan systems for both units originated in approximately the same area. The difference between the dominant clasts can be explained by continued up-lift and erosion of the sedimentary se-quence to the west of the Howards Pass area. If, as has been proposed earlier, the Howards Pass formation and/or the upper chert formation constituted the source material for the Iron Creek formation, continued up-lift would eventually cause stripping off of the Paleozoic strata and 113 Figure I I I - l l . Lithofacies time-slice interpretation for the Yara Peak formation and the chert pebble conglomerate in the Nahanni map-area. The grain size distribution indicates a general source area to the west of the OP area and major sediment transport to the east (indi-cated .by arrows). 11 BASIN FLOOR Figure 111-12. Submarine fan environmental model, showing genera-lized location of channels, fan and outer fan. No scale is implied (modified from Nelson and Kulm, 1973). 120 exposure and erosion of the 'Grit Unit' which contains quartz clasts and Fe + 3, both characteristic of the Yara Peak formation. The occurrence of abundant chert clasts in the chert pebble conglomerate suggests that continued uplift may have eventually exposed the sediments undelying the Grit Unit (Green et a l . , 1967). SUMMARY The general depositional history of the Howards Pass area, and of the Nahanni map-area in general, during the Paleozoic consisted of three main stages (Table 111-2). The f i r s t was deposition of carbonaceous sediments in a starved basin with shallow water carbonates on its eastern margin, with minor amounts of terrigenous sediments originating from the east. Sub-basin deposits which host the Howards Pass deposits occur only in the base of slope facies. Subsequent deposition of the flaggy mudstone was by a combination of pelagic sedimentation and t e r r i -genous material deposited by basinal currents. The upper chert forma-tion was deposited in a similar manner, but with a greater proportion of pelagic sedimentation with some deposition as distal turbidites. The last stage preserved in the area was the formation of clastic fan com-plexes, which developed to the west of the Howards Pass area with the transport of sediment from west to east. These rocks record the uplift and erosion of the central part of the underlying Selwyn Basin sediments and older rocks and deposition in fan complexes which, in general, show a coarsening upward sequence (Fig. 111-13). The third stage is not considered to be part of the Selwyn Basin, but constitutes deposition in a subsequent basin. 121 Tab le 111-2 - Major d e p o s i t i o n a l environments f o r the s t r a t i g r a p h i c un i t s i n the Howards Pass a r e a . Note tha t two separate d e p o s i t i o n a l bas ins o c c u r , the O r d o v i c i a n - E a r l y Devonian Selwyn Bas in and the post -E a r l y Devonian f l y s c h b a s i n . STRATIGRAPHIC UNIT MAJOR TYPE OF DEPOSITION CHERT PEBBLE CONGLOMERATE TURBIDITE DEPOSITION (submarine fan r e l a t ed depos i t i on ) YARA PEAK FORMATION IRON CREEK FORMATION UPPER CHERT". FORMATION DEPOSITION BY MIXED GEOSTROPHIC AND TURBIDITY CURRENTS WITH VARYING AMOUNTS OF PELAGIC SEDIMENTATION FLAGGY MUDSTONE FORMATION HOWARDS PASS FORMATION STARVED BASIN DEPOSITION TRANSITION FORMATION TRANSITIONAL WAVY BANDED LIMESTONE FORMATION BASINAL LIMESTONE DEPOSITION 122 ROCK UNIT FACIES SEQUENCE INTERPRETATION CHERT PEBBLE CONGLOMERATE UNIT YARA P E A K FORMATION IRON C R E E K FORMATION UPPER CHERT FORMATION F -U(? ) F - U C - U C - U F-U F-U C - U F-U 4- C - U C - U F - U C - U INNER FA~N C H A N N E L FILL CHANNELLED PORTION OF SUPRAFAN L 0 8 E 3 z < CHANNELLED u. i i 1 a 2 Z sMoarH o w UJ SMOOTH CQ Q _l PORTION OF z SUPRAFAN < u. < L O B E S cc CL in OUT ER FAN B AS IN FLOOR Figure II1-13. Facies interpretation of the upper Road River and Earn groups based on the submarine fan model of Walker and Mutti (1973). The Earn group consists of the Iron Creek and Yara Peak formations and the chert pebble conglomerate; and was deposited in a basin overlying the earlier Selwyn Basin. 123 CHAPTER IV Zn-Pb DEPOSITS INTRODUCTION All significant Zn-Pb sulphide discoveries at Howards Pass have been in the active member of the Howards Pass formation. Three main Zn-Pb deposits have been identified, and include the XY, ANNIV and OP deposits (Fig. IV-1). These are stratiform and stratabound complex saucer-shaped Zn-Pb sulphide deposits with local areas containing mas-sive sulphides. Texturally the deposits are similar to one another and for descriptive purposes are subdivided into six textural types, five of which occur within specific facies of the active member. These deposits also show similar geometry and association with sub-basins in the base of slope facies of the eastern Selwyn Basin. The textural types are based on hand specimen and microscopic properties, but chemical and mineralogical differences are evident between them. Type I consists of laminated, sulphide-rich carbonaceous mudstones. Sulphides are found in only some of the carbonaceous laminae, which are intercalated with simi-lar laminae containing only trace amounts of sulphides. Laminae are only slightly folded and in sulphide-rich laminae can be traced lateral-ly with no change in sulphide concentration. Type II contains sulphide rich laminae similar to those of type I, but open to closed microfolds are abundant; and many of these folds show fracturing in the hinge areas. Sphalerite and trace amounts of galena are more concentrated in the fold hinges. Type III also consists of laminated sulphides, but folding is more intense than in types I or II. Flow folds (de Sitter, 1958) are common, and sulphides associated with them are massive and are not as obviously associated with specific laminae as in types I and II. Figure IV-1. Map of the Howards Pass property showing the locations of the XY, ANNIV and OP deposits and the approximate outline of the original related sub-basins. ro 125 Type IV is sub-divided into two sub-types; sub-type IVa consists of macroscopic laminated sphalerite and galena occurring in a siliceous laminated mudstone. Type IVb is associated with type IVa and consists of massive sphalerite and galena occurring in dewatering structures and later cleavage that cross-cut mudstone laminae. Type V consists of massive sphalerite, galena and pyrite. Type VI is of l i t t l e economic consequence and consists of isolated sphalerite and/or galena associated with pyrite concretions, or galena occurring along microfault planes or in s t y l o l i t e seams not associated with other textural types. The present chapter describes the textural types occurring in the three deposits. Because of the facies-specific nature of the textural types, the combination of the description of the textural types and the des-cription of the active member (Chapter II) provides a general descrip-tion of the Howards Pass deposits. Thus, the description of the depo-sits has the same emphasis on vertical stratigraphic sequences rather than on lateral variations. DESCRIPTION OF TEXTURAL TYPES  TEXTURAL TYPE I Type I consists of laminated sulphides (Fig. IV-2) and interbedded laminated carbonaceous mudstones. To date, this type has been observed only within the thin bedded cherty mudstone and thin bedded calcareous mudstone facies of the active member. The major sulphide minerals in-clude pyrite, sphalerite and minor galena, in order of decreasing abun-dance (Table IV-I). Pyrite occurs as framboids, atolls (pyrite type B of Blanchard and Hall, 1942) and as cubes. Framboids which constitute 90% of the pyrite 126 Figure IV-2. specimen contains varying amounts of Sample of laminated sulphide of textural type I. The alternating laminae of carbonaceous mudstone with pyrite, sphalerite and minor galena. 127 TABLE IV-1 POINT COUNTS FOR SULPHIDE MINERALS OF TEXTURAL TYPES I THRU V TEXTURAL PYRITE SPHALERITE GALENA CHALCOPYRITE GANGUE TOTAL TYPE (%) (%) (%) (%) (%) COUNTS NO. I 15.9 4.0 0.1 79.8 758 I 21.2 5.1 0.1 63.6 711 1 16.0 10.2 0 73.7 293* II 13.9 17.1 0.3 68.7 709 II 9.1 17.2 0 73.1 871 13.4 13.3 0 73.3 730 I I I 26.6 8.8 0 1.1 63.6 730 I I I 25.9 22.2 0 0 51.9 769 [II 26.0 20.0 0 0.3 53.6 731 t i l 12.3 55.3 2.9 0.2 29.3 624 I I I 9.2 50.6 2.2 0.4 37.7 741 IV 0.4 32.8 3.5(13.8)** 49.6 690 IV 1.4 39.0 7.1(7.1) 45.3 644 IV 0.8 33.9 2.4(7.6) 55.3 838 IV 0 51.9 7.7(7.7) 40.3 856 V 15.2 30.3 19.0 35.1 564 V 1.2 53.9 41.3 3.5 748 V 2.0 40.3 44.6 3.2 650 V 0.4 22.3 20.2 57.0 703 V 0.4 27.1 23.9 64.3 723 * not enough space was present on section for 600 counts ** pits present in section which may represent plucked galena 128 observed, range in size from 5 to 50 ym, and are well preserved so that the individual cubes forming the "raspberry" texture are visible (Fig. IV-3). These cubes are less than 1 ym in diameter and occur in a matrix of organic matter, a feature also noted by Love (1965) in the Marl Slate. Locally, framboids are present in attached groups (Fig. IV-4) which are usually found associated with the hinges of open folds. These attached groups contain 2 to 6 individual framboids sharing common boun-daries. The tiny internal cubes are preserved in most instances; a few groups lack the internal texture, but do have a highly pitted surface similar to that described as "dirty pyrite" at Mt. Isa by McDonald (1970). Atoll-texture pyrite consists of grains 10 to 30 ym across and constitutes 5% of the pyrite in type I; the grains have an octagonal cross section with their centres containing sphalerite or quartz. Atoll-texture pyrite is invariably associated with framboidal pyrite. Similar atoll texture pyrite has been reported from other base metal bearing carbonaceous mudstones, including those at Mt. Isa (Blanchard and Hall, 1942) and in the Marl Slate (Love, 1962). Pyrite is also present as disseminated cubes 0.1 to 0.5 mm across constituting 5% of the pyrite in type I. These cubes are not typically associated with the framboidal pyrite laminae. Sphalerite, the dominant base metal sulphide in the textural type (Table IV-1) appears in some laminae as disseminated grains which are typically elongate with their major axis in the plane of the regional cleavage. They range from 9 to 50 ym in width and 20 to 200 ym in length. Approximately 80 to 90% of the sphalerite occurs as free grains in quartz and organic matter and 10 to 20% as simple intergrowths 129 Figure IV -3 . Photomicrograph of a well preserved pyrite framboid. The internal structure is shown by the arrangement of individual pyrite cubes less than 1 um across. 130 Figure IV-4. Photomicrograph of modified framboids of pyrite. Evidence of alteration includes destruction of internal texture and com-bination of individual framboids into masses. 131 (Kraft, 1967; Amstutz, 1962) partially rimming framboidal pyrite. Sphalerite in the deposits has a metallic luster even though i t contains l i t t l e iron. Galena is present only in trace amounts and is associated with isolated grains of sphalerite. Simple intergrowths are most com-mon; with sphalerite being the most abundant phase. Some of the organic matter in this textural type has properties in reflected light similar to those of shungite (Marmo, 1960), a mineral with a crystal structure similar to, but not as well ordered as, gra-phite. TEXTURAL TYPE II Type II consists of laminated sulphides which are similar to type I, but contain greater amounts of Zn and Pb, and is more structurally complex (Figs. IV-5, IV-6). The sulphide mineralogy is the same as that of type I, but the proportions are different (Table IV-1). Textural type II is present in the thin bedded cherty mudstone and the thin bedded calcareous mudstone facies. Approximately 70% of the samples examined of this textural type (p250) are in the thin bedded cherty mud-stone facies. Pyrite occurs as framboids, atolls and irregular masses. Framboids constitute 55 to 60% of the pyrite, with most showing the typical spherical outline but lacking the internal detail, having only pitted massive interiors. Most of the altered framboids are in groups of two to five which coalesce into masses in which part of the outlines of the original framboids are s t i l l distinguishable (Fig. IV-7). Atoll pyrite is associated in minor amounts with framboidal pyrite, and is well pre-served, indicating that the atolls were more resistant or formed 132 Figure IV-5. Textural type II consists of laminated sulphides showing open folds. Individual laminae shown are generally rich in py-rite and/or pyrite intercalated with carbonaceous mudstone. Scale is in cm. 133 Figure IV-6. Photomicrograph of microfold in textural type II. Note that mobilized sulphides are locally associated with the hinges of the folds although the laminated nature of sulphides is s t i l l evident. 134 Figure IV-7. Photomicrograph of massive pyrite in textural type II. The outline of the individual pyrite framboids is s t i l l v isible. 135 later. Irregular masses of pyrite and occasional cubes constitute 40 to 45% of the pyrite in this textural type. The abundance of rel i c t fram-boids in cubes and masses of pyrite (Fig. IV-8) suggests that most or possibly all of the pyrite occurring in textural type II is an altera-tion product of framboidal pyrite. Sphalerite occurs as disseminated grains in individual carbonaceous mudstone laminae. In the XY area the grains are elongate parallel to axial plane cleavage, but in the less disturbed ANNIV and OP deposits the sphalerite grains are close to equidimensional. Grains are 5 to 60 pm across, although some elongate grains in the XY deposit are up to 200 pm long. The grains are disseminated, although the control by lamina-tion is obvious. In some cases elongate sphelerite grains in the XY deposit are in end-to-end contact, combining to form elongate masses up to 500 pm long in the plane of the cleavage. In general, sphaleriterich laminae in type II have more sphalerite than type I; samples not showing obvious microfolds have laminae containing 40 to 50% sphalerite whereas those of type I contain less than 25%. Massive sphalerite up to 100 pm across is associated with microscopic fold hinges (Fig. IV-9). The increase in the sphalerite in these hinge zones may be a result of both structural thickening of the sphalerite-rich laminae (Ramsey, 1967) and a higher concentration of sphalerite relative to other minerals in the hinge zones. The association of higher sphalerite with slump folds suggests mobilization of Zn and Pb during slumping and only reorien-tation of sphalerite grains during later folding associated with re-gional cleavage formation. Sphalerite is not typically intergrown with 136 Figure IV-8. Photomicrograph of a pyrite cube occurring in textural type II. The presence of re l i c t framboids (outlined in ink) suggests that the cube is a result of alteration of framboids. The abundance of re l i c t framboids in the active member further suggests that most, or possibly a l l , of the pyrite in the member was originally framboidal in nature. 137 Figure IV-9. Sphalerite may be concentrated in the hinge areas of micro-folds occurring in textural type III. In the specimen shown the mobili-zation of zinc relative to the pyritic laminae is evident. 138 other sulphides away from microscopic fold hinges. The minor amount of sphalerite-pyrite intergrowth that does occur shows sphalerite partially surrounding framboidal pyrite. In the microfold hinge areas massive sphalerite contains modified framboids in a buckshot (Amstutz, 1962) texture. Galena occurs in trace amounts as irregular grains 10 to 200 um across and these show simple intergrowths with sphalerite. Galena has only been identified in the microfold hinges in the same laminae as sphalerite. TEXTURAL TYPE III Type III consists of laminated to massive sulphides which are locally related to laminae, but are also structurally controlled by microfolds (Fig. IV-10). The sulphide mineralogy is similar to that of types I and II except for a greater abundance of galena and the presence of trace amounts of chalcopyrite (Table IV-I). Textural type III occurs in the thin bedded cherty mudstone facies. Pyrite occurs as irregular masses; approximately half of these are modified enough that the internal cubes are not identifiable. These framboids range in size from 10 to 70 um but are commonly in coalesced masses over 100 um across. Near microfold hinges some framboids are broken. The second major form of pyrite, irregular masses, is only associated with microfolds and is 0.1 to 2 mm across. Some of these are elongate in the plane of cleavage. The characteristic "dirty pyrite" texture and colloform-1ike edges suggest that these too are formed from alteration of framboidal pyrite. 139 Figure IV-10. Flow folds which are typical of textural type III. Dashed lines outline some of the folds. 140 Sphalerite occurs as individual grains 10 to 60 um across and as irregular masses 150 to over 1000 um in diameter. Individual grains constitute approximately 30 to 35% of the sphalerite in type III and are associated with specific laminae. Some of these are associated with shungite and pyrite with simple intergrowths of pyrite-sphalerite being most common. Most of the sphalerite occurs as large (greater than 100 pm) irregular masses associated with microfolds. These irregular masses occur only in slump folds and are not elongate parallel to cleavage as in type II. Also, massive sphalerite does not show confinement to specific laminae as in types I and II, but may cut lamination at various angles in fold hinges. Intergrowths with galena and pyrite are common, typically with the latter minerals occurring as inclusions. Galena and chalcopyrite are present in minor amounts, galena being more abundant than in types I and II and chalcopyrite being unique to type III (Table IV-1). Galena occurs as irregular grains 10 to 50 pm across only in the hinge areas of microfolds, where i t is intergrown with sphalerite. The few grains of chalcopyrite noted in this textural type are also intergrown with sphalerite in fold hinges. TEXTURAL TYPE IV Textural type IV can be divided into two sub-types, IVa and IVb. Sub-type IVa consists of laminated sphalerite and galena with the indi-vidual grains being disseminated in the laminae. Sub-type IVb, in con-trast, consists of massive sphalerite and galena with minor pyrite in cross-cutting veins. The two sub-types are always associated on the scale of a hand specimen. 141 Textural type IVa consists of mesoscopically laminated sulphides in laminated chert. This sulphide mudstone is by definition the whitish grey Zn-Pb mudstone facies. Microscopic investigations have shown that while the sulphides appear laminated to the unaided eye the individual laminae contain microscopically disseminated sphalerite and galena as equant grains 3 to 45 urn across (Fig. IV-11). Approximately 60% of these minerals occur as free grains and 40% are intergrown. Some intergrowths are simple, but most have complex or buckshot textures. The most complex type of intergrowth is a buckshot texture in which individual sphalerite grains 20 to 40 ym across contain up to 30 or 40 blebs of galena (Fig. IV-12) in a manner similar to myrmekitic intergrowths in granitic rocks. Up to 80% of the galena in sub-type IVa is intergrown in this manner; the rest occurs as free grains. Pyrite in sub-type IVa occurs in a manner similar to that of types I, II and III, consisting of framboidal pyrite in a few of the more car-bonaceous laminae in the facies; i t appears in 0.5 to 1% of the laminae, compared to 10 to 20% in types I and II. Textural type IVb consists of massive sphalerite and galena, with traces of massive pyrite occurring in 500 ym to 1 cm wide veins that crosscut laminae, and represent fluid escape structures (Fig. IV-13). These veins occur only in the whitish grey Zn-Pb mudstone and are specifically associated with textural type IVa. Within these veins, irregular massive grains of sphalerite 100 ym to more than 1 mm across. Galena grains 50 to more than 500 ym long appear in a similar manner. Elongation of these two minerals in the plane of the vein give the 142 Figure IV-11. Photomicrograph of whitish grey Zn-Pb mudstone showing textural type IVa. At this scale (microscope) the sulphides are disseminated, but in hand specimen the sulphides appear laminated. 143 Figure IV-12. Photomicrograph of individual sphalerite grain in textural type IVa. Galena grains less than 2 ym across occur in a buck-shot texture within the sphalerite grain. 144 Figure IV-13. Photograph of whitish grey Zn-Pb mudstone with p i l -lar structures and sulphide concretions. These sulphide f i l l e d struc-tures are irregular and anastomosing which suggest that they are the result of compaction related to fluid escape. 145 veins a streaky appearance which i s most prominent in those veins ob-v ious ly modif ied by l a t e r cleavage ( F i g . IV-14). Genera l l y , galena i s concentrated at the edges and/or in the centre of the vein ( F i g . IV-15) . P y r i t e occurs in t race amounts in the sub-type and c o n s i s t s of i r r e g u l a r grains 5 to 80 urn a c r o s s . The p i t ted surface t y p i c a l in these grains suggests that they are a l te red framboids. The framboidal p y r i t e conta in ing laminae noted in sub-type IVa c a n , in some instances be traced through the veins where the massive pyr i te occurs , although t h i s i s not poss ib le where the veins have been modified by l a t e r c leavage. TEXTURAL TYPE V Type V cons is ts of approximately equal proport ions of complexly intergrown massive spha le r i t e and galena with minor pyr i te (Table IV - I ) , and shows no obvious laminat ion ( F i g . IV-16). Both spha le r i t e and galena occur as i r r e g u l a r massive grains 20 pm to 1 mm a c r o s s . Buckshot texture i s common, with 5 t o 20 pm s p h a l e r i t e blebs across in l a rger galena masses 200 pm to 1 mm a c r o s s . Minor i r r e g u l a r massive p y r i t e 40 to 150 pm across i s t y p i c a l l y intergrown with the s p h a l e r i t e and galena. Textural type II i s t y p i c a l l y at the base of the whit ish grey Zn-Pb mudstone f a c i e s and shows s p i r a l textures ( F a i r b r i d g e , 1946) in the sulphides i n d i c a t i v e of slumping. In some instances the veins in the whi t ish grey mudstone f a c i e s appear to be re la ted to type V sulphides ( F i g . IV-17) , suggesting that slumping and water escape occurred s imul taneously . TEXTURAL TYPE VI Type VI c o n s i s t s of concret ions of galena and/or spha le r i t e 100 pm 146 Figure IV-14. S u l f i d e f i l l e d cleavage in the whi t ish grey Zn-Pb mudstone. In contrast to those p i l l a r s t ruc tures formed during compac-t i o n these show s t ra igh t contacts and in the f i e l d show a coherent s t r i k e p a r a l l e l to the regional s t r i k e of c leavage. Note the segregation of s p h a l e r i t e and galena in the c leavage. 147 Figure IV-15. Photomicrograph of mineral segregat ion in textura l type IVb. Galena (Gn) occurs in segregations p a r a l l e l to cleavage and in contact with s i l i c a t e s . T h i s p a r t i c u l a r specimen shows cleavage modif ied textura l type IVb. 148 Figure IV-16. Photomicrograph of massive sulphide in textura l type V. There is no evidence of lamination in t h i s textura l type . Note that buckshot texture is common with both spha le r i t e in galena and galena in s p h a l e r i t e . 149 Grey chert facies with abundant stylolites Massive sphalerite and galena in p i l l a r structures (textural type IVb). Laminated whitish grey Zn-Pb mudstone with intercalated laminae of chert and carbonaceous chert with laminated sphalerite and galena, (textural type IVa). • 'Massive Zn-Pb sulphides with local development of spiral structures indicating that slumping has occurred (textural type V). Thin bedded cherty mudstone facies Figure IV-17. Detailed section of the whitish grey Zn-Pb mudstone facies showing relationship between textural types IVa, IVb and V. Section is based on DDH-66 in the XY area (Plate II). 150 to 2 cm a c r o s s , most of which are assoc ia ted with pyr i te c o n c r e t i o n s . T h i s textura l type occurs not only in the ac t ive member, but a lso in the lower 10 m of the upper s i l i c e o u s mudstone member. In the a c t i v e member type VI cons is ts of massive galena or spha le r i t e in f rac tures and s t y l o -l i t e seams or as c o n c r e t i o n s . These always occur s t r a t i g r a p h i c a l l y above the f i r s t occurrence of one of textura l types I through V. In the upper s i l i c e o u s mudstone member, the textura l type cons is ts of galena and/or spha le r i t e which have p a r t i a l l y replaced pyr i te concret ions which are s i m i l a r to the small pyr i te concret ions found throughout the Howards Pass format ion. The spotty nature of t h i s textura l type and the lack of s t r i c t s t r a t i g r a p h i c control suggest that the sulphides may be d i a g e n e t i c . The l o c a t i o n of the s u l p h i d e , above prev ious ly deposited Zn-Pb s u l p h i d e , fu r ther suggests that the metal was suppl ied by la te stage, v e r t i c a l l y migrat ing f l u i d s of d iagenet ic o r i g i n . DISCUSSION The grouping of the sulphides into s ix textura l types is advanta-geous in two ways: (1) It al lows fo r proposals of o r i g i n of the i n d i v i -dual t y p e s . (2) It has allowed fo r quick charac te r i za t ion of sulphides f o r meta l lu rg ica l purposes, only the former use i s considered here. The s i x textura l types def ined in the Howards Pass deposits may be grouped into o r i g i n - r e l a t e d types . Textura l types I, II and III are s i m i l a r , c o n s i s t i n g of laminated sulphides occurr ing in the th in bedded cherty mudstone and the th in bedded calcareous mudstone f a c i e s . The main d i f f e rences between these textura l types are in s t ruc tura l complexi ty , which ranges from nonfolded in type I to flow fo lds in type II I , and 151 in sulphide gra in s i z e and amount; type I having the lowest sulphide content and f i n e s t gra in s ize grading to type III with the highest s u l -phide content and coarsest gra in s i z e , l o c a l l y containing massive s u l -phide (Morganti , 1973). The increase in s t ructura l complexity of slump-ing and a lso l a t e r regional f o l d i n g (Chapter II provides de ta i led des-c r i p t i o n s of these s t r u c t u r e s ) . Much of the mobi l ized sulphides are associa ted with slump re la ted s t ructures (sp i ra l s t r u c t u r e s , e t c . ) . Previous inves t iga t ions on metamorphosed s t ra t i fo rm deposi ts have i n t e r -preted sulphide mobi l i za t ion and gra in s i ze change as evidence for s u l -phide remobi l i za t ion which occurred during metamorphism (McDonald, 1970; Stanton, 1972; Lambert, 1973). The presence of textures i n d i c a t i v e of remobi l i za t ion in the Howards Pass d e p o s i t s , but with no evidence fo r metamorphism, suggests that mob i l i za t ion associa ted with increas ing s t ructura l complexity occurred mainly during slumping and compaction. At low temperatures of less than 100° metal movement would be in s o l u -t i o n (Vokes, 1969) and not in the s o l i d state as proposed by Stanton and Gorman (1968) fo r higher temperatures. The modi f ica t ion of s u l -phides by slumping fur ther ind ica tes that at least some of the metal sulphide was formed before slumping. The timing of i n i t i a l sulphide formation in textura l types I, II and III i s suggested by experimental evidence and observations on recent sediments. These resu l ts and observation suggest that at least some of the sulphides are d iagenet ic in o r i g i n . For example, Lambert and Bubela (1970) produced monomineralic sulphide bands in the laboratory at 53°C using bacter ia l" sulphide and a mult i -element s o l u t i o n . These laminae were up to 50 ym t h i c k . Farrand (1970), in a s i m i l a r experiment, ob-ta ined meta l l i c (Fe, Zn , Cu) sulphides in the form of f ramboids. 1 5 2 A diagenet ic o r i g i n for the framboidal pyr i te is supported by the data of Garre ls and C h r i s t (1965) which ind ica tes that pyr i te is not s tab le in normal seawater. T h i s has been demonstrated in the laboratory by Berner (1971) and proposed fo r Mesozoic sediments ( E l v e r h o l , 1977). Invest igat ions by Berner (1969) and Sweeney and Kaplan (1973) have shown that the marine formation of framboidal pyr i te involves the i n i t i a l f o r -mation of mackinawite (FeS i_ x ) or h y d r o t r o i l i t e (FeS) and subsequent react ion of t h i s phase with b a c t e r i a l elemental sulphur to form g r i e g i t e (Fe3S4) or pyr i te (FeS2) ( F i g . IV-18). A t o l l textured pyr i te associated with framboidal p y r i t e may be derived from the l a t t e r . The author has recent ly observed framboidal pyr i te from a modern bog c o n s i s t i n g of an outer rim replaced by marcasite surrounding a core of pyr i te showing a "raspberry" t e x t u r e . I f the core were d i s s o l v e d subsequently and the rim replaced by p y r i t e , a t y p i c a l a t o l l texture would r e s u l t . It i s suggested that a t o l l textures may be the resu l t of a l t e r a t i o n of fram-b o i d s . The a s s o c i a t i o n of a t o l l s with framboidal pyr i te supports t h i s mode or o r i g i n . The occurrence of spha le r i t e and galena in carbonaceous laminae is s i m i l a r to that of framboidal pyr i te and suggests a l l three o r ig ina ted during ear ly d i a g e n e s i s . Where s p h a l e r i t e or galena i s intergrown with framboids of pyr i te the former two always surround the f ramboids, i n d i c a t i n g a l a t e r o r i g i n . Textural types IV and V cons is t of laminated sulphides (type IVa) and associated massive sulphides (types IVb and V) and only occur in the whi t ish grey Zn-Pb mudstone f a c i e s , and are associa ted with the d iagenet ic h is to ry of the f a c i e s ( F i g . IV-19). Type IVa is associated with laminae ( F i g . IV-19a) whereas type IVb is associated with water 1 5 3 Pyrite FeS 2 Figure IV-18. Major steps in the process of d iagenet ic pyr i te f o r -mation. Although pyr i te can form d i r e c t l y from H 2S and F e 2 + in modern sediments, framboids form only during the FeS stage . (Berner, 1971, Sweeny and Kaplan, 1973; Howarth, 1979). 154 Stage 1 - br ine formation and i n i t i a l Zn and Pb d e p o s i t i o n ; formation o f tex tura l type IVa. Stage 3 - f l u i d escape due to compact ion, f o r -mation of tex tura l type IVb. Stage 2 - i n i t i a l compaction and/or slumping due to g r a v i t a t i o n a l i n s t a -b i l i t y , formation of tex tura l type V. D. Stage 4 - Cretaceous cleavage formation which modi f ied most p i l l a r s t ruc tu res and formed s u l -phide f i l l e d c leavage , forma-t i o n of tex tura l type IVb. Figure IV-19. A possib le model for the evolut ion of the whit ish grey Zn-Pb mudstone. Stage I - br ine d e p o s i t i o n , stage 2 - compaction and/or slumping, stage 3 - f l u i d escape, stage 4 - Cretaceous cleavage format ion. 155 escape s t ructures ( F i g . IV-19b) and type V represent the massive s u l -phide at the base of some ind iv idua l beds in the fac ies ( F i g . IV-19c) . A l l these sulphide textura l types are crosscut by c a l c i t e nodules. The occurrence of framboidal pyr i te laminae only every 20 to 150 laminae compared to every 2 to 5 laminae in the carbonaceous mudstones suggests the p o s s i b i l i t y of a 10 to 15 f o l d increase in the r e l a t i v e rate of sediment d e p o s i t i o n , and a s i m i l a r increase in sedimentation rate assum-ing a constant rate of i ron in f lux and the F e 2 + i s the r a t e - c o n t r o l -l i n g f a c t o r in pyr i te format ion. T h i s suggested increase in the s e d i -mentation rate in the sub-basins during deposi t ion of the whit ish grey Zn-Pb mudstone and associated limestone is analogous to sub-basin depo-s i t i o n in the Red Sea ( B i g n e l l , 1975) where the deposi t ion rate i s orders of magnitude f a s t e r than those of the surrounding non-brine areas . The syngenetic deposi t ion of Zn in s i l i c e o u s sediments has been documented in the br ine environment at Lake Kivu (Degens et a l . , 1972) and the Red Sea br ine pools ( B i g n e l l , 1975). The above reasoning leads to the conclus ion that the whit ish grey Zn-Pb mudstone and associated tex tura l type IV sulphides could have been syngenet ica l ly deposited by br ines and subsequently modif ied by slumping and compaction due to g r a v i t a t i o n a l i n s t a b i l i t y re la ted to extreme densi ty c o n t r a s t s . Deposi -t i o n by br ines i s fu r ther suggested by loca l th ick sect ions of the f a c i e s in the central -downslope part of the s u b - b a s i n s . Textura l type VI t ransgresses stata and o v e r l i e s the other textura l t ypes . T h i s r e l a t i o n s h i p a lso occurs at White P ine , Michigan (Ensign et a l . , 1968) and above some volcanogenic deposits (Govett and Goodfel low, 1 5 6 1975) and i s a r e s u l t of upward migrat ing f l u i d s passing through metal -l i f e r o u s m a t e r i a l . At Howards Pass, t h i s was most l i k e l y la te diagenet-i c upward migrat ion of compaction re la ted f l u i d s . The replacement of pyr i te by spha le r i t e and galena above the ac t ive member fur ther i n d i -cates that sulphide as free H 2S was r a r e , and that the only sulphide a v a i l a b l e was in the pyr i te concret ions occurr ing in the carbonaceous mudstones. Even though type VI may not be of economic in terest in i t s own r i g h t , i t s a s s o c i a t i o n with the other textura l types may prove to be an ore guide f o r p rospec t ing . SUMMARY The economical ly s i g n i f i c a n t Zn-Pb sulphides in the Howards Pass area occur in three d i s t i n c t s t ra t i fo rm deposits which occur in sub-basins where the ac t ive member was depos i ted . The sulphides can be sub-d iv ided in to s ix textura l types which are re la ted to sedimentary f a c i e s in the a c t i v e member. Textural types I, II, and III occur in laminated carbonaceous mudstones and show increas ing s t ruc tura l complexity due mostly to slumping. Textura l types IV and V occur in the whi t ish grey Zn-Pb mudstone and could be the resu l t of synsedimentary deposi t ion and subsequent compaction modif ied by l a t e r cleavage format ion. Textura l type VI cons is ts of la te d iagenet ic sulphide concret ions and nodules. The sulphide textures and minerals are s i m i l a r in the XY, ANNIV and OP d e p o s i t s , although the proport ions of the s ix textura l types vary between d e p o s i t s . T h u s , the textura l study supports the s t r a t i g r a p h i c evidence i n d i c a t i n g that the three deposits formed in the same env i ron-ment, and that var iants of the same ore genesis model apply to a l l three d e p o s i t s . 157 CHAPTER V STRUCTURE INTRODUCTION Secondary s t ructures present in the Howards Pass area record a h i s -tory of local penecotemporaneous fo ld ing and f a u l t i n g and p o s t l U n i f i c a -t i o n f o l d i n g and f a u l t i n g , low grade metamorphism at the base of the sect ion and igneous i n t r u s i o n . The s t ructura l h is tory of the area i s complex, although the predominance of f a u l t i n g and open f o l d s on a re -gional sca le has resu l ted in f a i r l y f l a t l y i n g s t ra ta occurr ing above the ' G r i t Uni t ' (Plate I ) . For the sake of c l a r i t y the s t ructures are sub-d iv ided into three age groups which show d i f f e r e n t types of deforma-t i o n ; these are: Pre -Francon ian , which a f f e c t rocks underlying the massive l imestone format ion, Paleozoic s t ructures which a f fec t most rocks in the Howards Pass region to varying degrees and Mesozoic s t r u c -tures which a f fec t a l l rocks in the reg ion . PRE-FRANCONIAN STRUCTURES Low grade metamorphism and open fo ld ing have a f fected rocks of the ' G r i t Un i t ' to the southwest of the Howards Pass area (Green et a l . , 1967). Regional ly pervasive s la ty cleavage and loca l p h y l l i t e within the uni t are a r e s u l t of t h i s deformat ion. The lack of these s t ructures in the Sekwi formation ind ica tes that t h i s unit was not a f fected by the deformation and that there is an unconformity between the two u n i t s . A Pre-Franconian angular unconformity at the base of the massive l imestone formation i s i n f e r r e d from regional mapping (Douglas et a l . , 1970; Gabr ie lse et a l . , 1973), although in the Howards Pass area the angular discordance observed could a lso be due to f a u l t i n g . 158 PALEOZOIC SFRUCfURES Structures formed during the Paleozoic are economical ly important because some have produced local r e d i s t r i b u t i o n of base metals in the Howards Pass d e p o s i t s , and the bar i te d e p o s i t s , and a lso because they record a l i t t l e known part of the t e c t o n i c h i s t o r y of the a r e a , yet these s t ructures are poorly understood owing to l a t e r Cretaceous s t ruc tura l o v e r p r i n t i n g . The major s t ructures that were formed in the Paleozoic include loca l penecontemporaneous fo lds in the Howards Pass area and a few regional f a u l t s which are associated with sedimentation of the Earn Group. Abundant evidence for slumping occurs in the a c t i v e member of the Howards Pass formation and in the Selwyn Mountains b a r i t e hor i zon . In the a c t i v e member two d i s t i n c t types of slumping occur: mesoscopic and microscopic in t ra laminar slumping and, in the XY d e p o s i t , megascopic slumping of parts of the a c t i v e member. The smal ler sca le slump s t r u c -tures are most obvious in the th in bedded cherty mudstone and t h i n bed-ded calcareous mudstone f a c i e s . In both f a c i e s s p i r a l and decollement s t ructures ( F i g . V - l ) are present and these post-date the emplacement of most s u l p h i d e s , which are deformed by the s t r u c t u r e s . Abundant s l i d e c l a s t s of pyr i te in a mudstone matrix ind ica te that local i n t r a f o r m a t i -onal b r e c c i a t i o n occurred during slumping. Many of the microscopic fo lds show evidence of int ra laminar slumping and inc lude complete con-volute f o l d s (Wi l l iams, 1963) and subsuperf ica l in t ra format ional f o l d s ( F a i r b r i d g e , 1946) which show th ickening in the hinge areas . Many of the microfo lds in the ac t ive member have a poorly developed axia l plane s la ty c leavage. These fo lds are open to c losed and are 159 Figure V - l . Sp i ra l s t ructure occurr ing in the th in bedded cherty mudstone f a c i e s of the act ive member. Textures such as t h i s are common in the XY Zn-Pb deposit and ind icate intralaminae slumping contempora-neous with d e p o s i t i o n . 160 found in the same f a c i e s as the int raformat ional slump fo lds descr ibed above. The cleavage shows convergent fans (Ramsay, 1967) re la ted to the m i c r o f o l d s . The cleavage and associa ted micro fo lds have caused much r e d i s t r i b u t i o n of Zn and Pb sulphides in textura l types II and III. The r e l a t i v e age of cleavage and f o l d s is indicated by involvement of s u l -phides in the fo ld ing and the lack of t h i s cleavage cut t ing l imestone nodules, suggesting an ear ly d iagenet ic o r i g i n . The cleavage associated with p r e - l i t h i f i c a t i o n fo lds i s not common, but has been documented by Wi l l iams et a l . (1969). They suggested that these st ructures formed by rapid load ing ; a mechanism that is probable in a su lph ide -depos i t ing environment l i k e that of the Howards Pass d e p o s i t s . In the ANNIV and OP deposits the above st ructures are present , but to a l e s s e r degree. An explanat ion of t h i s may be that the lower organic carbon and high SiO2 contents in the th in bedded cherty mudstone f a c i e s of the ANNIV and OP a r e a s , may have i n h i b i t e d slumping. T h i s aspect of slump control by mud chemistry is not new and was f i r s t pro-posed by Boswell (1961). The a s s o c i a t i o n of in t ra format ional slumps with the sulphide deposits appears to be the resu l t of a combination of g r a v i t a t i o n a l i n s t a b i l i t y associa ted with base metal d e p o s i t i o n , and high f l u i d content of the carbonaceous muds. The deposi t ion of dense s u l p h i d e - r i c h muds would in e f fec t act as a rap id ly deposited sediment producing high f l u i d pressures and rapid load ing . The slow rate of sedimentation and the nature of d e p o s i t i o n , both of which suggest r e l a -t i v e tec ton ic quiescence, suggest that the p o s s i b i l i t y of earth tremors re la ted to rapid c rus ta l movements (Wi l l iams, 1963) as of cause of slumping was minimal. 161 In the XY deposi t the asymmetry of the s u b - b a s i n , apparent r e d i s -t r i b u t i o n of the member, l o c a l l y a basal s l i p zone at the base of the a c t i v e member and local v a r i a t i o n s in the thickness of the over ly ing sediment a l l suggest megascopic slumping of the ac t ive member. The asymmetry of the sub-basin is def ined by d r i l l hole data . To the northeast of Yara Peak the ac t ive member i s t h i n (5 to 15 m) and shows only minor int raformat ional slump s t r u c t u r e s . Near the centra l part of the sub -bas in , s l i d e c l a s t s of l i g h t grey basal l imestone f a c i e s and the f o l i a t e d basal f a c i e s occur where there is usua l ly 30 to 50 m of ac t ive member. Th is is in terpreted to be a block of the ac t ive member which has s l i d down s l o p e . The a c t i v e member in the southern part of the sub-basin is th ick (50 to 80 m) and contains abundant whit ish grey Zn-Pb mudstone compared to the a c t i v e member or the northern part of the s u b - b a s i n . Slump features ( e . g . s p i r a l and decollement s t ructures) are more abundant in the southern, down-slope, port ion of the ac t ive member, and here a lso the basal zone of the ac t ive member is highly f o l i a t e d . Where the member i s m i s s i n g , the upper s i l i c e o u s mudstone i s t h i c k e r than where i t o v e r l i e s the ac t ive member and 2 to 3 times t h i c k e r than areas away from the s u b - b a s i n . The asymmetry of the a c t i v e member and the suggested f i l l i n g in by the upper s i l i c e o u s mudstone where proposed a c t i v e member displacement i s proposed, is suggest ive of major slump movement (Lewis, 1971). Small s c a l e , intralaminae slump st ructures are a lso abundant in the Selwyn Mountains ba r i t e hor izon . These occur only in the laminated b a r i t e deposi ts where BaS04 c o n s t i t u t e s from 50 to 95% of the rock . 162 Spi ra l and decollement s t ructures are abundant and post-date emplacement of the b a r i t e . M i c r o s c o p i c - s c a l e r e d i s t r i b u t i o n of BaS0 4 s i m i l a r to that noted for ZnS and PbS in the Howards Pass deposits was not observed in the b a r i t e d e p o s i t s . In the b a r i t e deposi ts both g r a v i t a t i o n a l i n s t a b i l i t y and shock induced slumping may have been important . The higher s p e c i f i c grav i ty of ba r i t e ( S . G . = 4.5) over ly ing less dense mud may have caused slumping. Shock induced slumping may a lso have been important because the b a r i t e horizon was deposited during tec ton ic up-l i f t to the west, and l o c a l l y f a u l t s are associated with deposi t ion of the ba r i t e deposi ts ( for example at the 0R0 and NOR b a r i t e d e p o s i t s ) . F a u l t s , unconformit ies and s l a t y cleavage ind ica te t e c t o n i c a c t i -v i t y from Middle-Devonian to M i s s i s s i p p i a n (?) t ime. Faul ts considered to have occurred in t h i s time in terva l include those which are te rmi -nated by unconformi t ies , and those associa ted with laminated b a r i t e . Faul ts s t r i k i n g roughly 300° and terminated by unconformit ies underlying the Iron Creek and Yara Peak formations occur in the Howards Pass map-area . These show a maximum displacement of 200 m and are apparently due to block f a u l t i n g during the Middle-Devonian to E a r l y M i s s i s -s ipp ian ( ? ) . L o c a l l y , f a u l t s and f a c i e s changes are associa ted with laminated b a r i t e in the Selwyn Mountains bar i t e hor i zon . These f a u l t s are present along the edges of the GHMS, NOR and 0R0 bedded b a r i t e deposi ts (Appendix D) and in part explain the loca l rapid th ickening of the b a r i t e and chert and f a c i e s changes between them. These features suggest that the f a u l t s were penecontemporaneous with sedimentation and re la ted to d i f f e r e n t i a l compaction. Minor f a u l t s s t r i k i n g 3 0 0 ° a lso occur in the wavy banded l imestone. These have dolomit ic a l t e r a t i o n 163 up to 3 m wide associated with them, but do not cut the Howards Pass format ion. The age of these f a u l t s is not known and more de ta i led i n -ves t iga t ion i s needed to understand t h e i r r e l a t i o n s h i p to the fau l ts noted higher in the s e c t i o n . The age of s l a t y cleavage in the basal 100 m of the Yara Peak formation cannot be demonstrated, but the associa ted s t r u c t u r e s , and fac t that the major Cretaceous cleavage c r o s s - c u t s t h i s cleavage suggest a pre-cretaceous age. The s la ty cleavage s t r i k e s 265° to 2 8 5 ° , d ips 75 to 9 0 ° nor th . Poorly def ined bodies of massive mudstone up to 150 m across in the bottom 100 m of the Yara Peak formation fol low the s t r i k e of the s la ty c leavage. The a t t i tude is defined by p a r a l l e l alignment of micas and is the only s t ructure noted in the mudstone. Greywacke dikes up to 75 m long fo l low the c leavage, and show i r r e g u l a r to s t ra ight con-t a c t s . The dikes are t raceable into greywacke beds from which they o r i g i n a t e d , occurr ing below the mudstone b o d i e s . The a s s o c i a t i o n with c l a s t i c dikes ind ica te that these features formed while the Yara Peak greywackes were s t i l l unconsolidated (Maxwell, 1962). The s la ty c leav -age could be a var iant of the 300° f rac ture c leavage, but th is would require the maintenance of high f l u i d pressures over an u n r e a l i s t i c a l l y long t ime. The occurrence of these features in t u r b i d i t y current de-pos i ts suggest that abnormal p o r e - f l u i d pressures were involved in the cleavage formation (Rubey and Hubbert, 1959; Wil l iams et a l . , 1969; Al terman, 1973). Condit ions favouring the development of abnormally high pore-water pressures which are t y p i c a l of deposits such as the Yara Peak formation include (1) the presence of compactible and r e l a t i v e l y impermeable p e l i t e beds to retard escape of pore f l u i d s ; (2) interbeds 164 of l ess compact ib le , more permeable greywackes as reservo i rs fo r the f l u i d s ; and (3) a great tota l thickness of a rap id ly deposited over ly ing unit such as the chert pebble conglomerate to produce loading at a rate greater than that of escape of pore water. The imp l ica t ions of s l a t y cleavage are quest ionable . For example, de ta i l ed studies in the French Alps have shown that weak s la ty cleavage there was caused by 25% f l a t -t e n i n g ; in c o n t r a s t , experimental studies have suggested that the in ten-s i t y of deformation is not indicated by i n t e n s i t y of s la ty cleavage (Wi l l i ams, 1977). The abundance of unconformit ies , f a u l t s and coarse c l a s t i c s e d i -ments in the Earn Group suggest that the Middle Devonian to M i s s i s s i p p i -an (?) in terva l was r e l a t i v e l y t e c t o n i c a l l y a c t i v e . A western source for the coarse e l a s t i c s ind icates that the major u p l i f t occurred west of the Howards Pass a r e a . T h i s Middle Devonian to M i s s i s s i p p i a n (?) u p l i f t occurred throughout the C o r d i l l e r a n be l t (Burchf ie l and Dav is , 1972; Boucot et a l . , 1974; Poo le , 1972; Stewart and Poo le , 1972; Churk in , 1974) and is c a l l e d the Ant le r orogeny in Nevada and parts of C a l i -f o r n i a . CRETACEOUS STRUCTURES Mesoscopic and macroscopic f o l d s , regional f rac tu re c leavage, and f a u l t s are the resu l t of Cretaceous deformation and associated igneous i n t r u s i o n . Mesoscopic and megascopic (Turner and Weiss, 1963) fo lds are abun-dant in the Howards Pass area . Mesoscopic fo lds have wavelengths that range from 0.5 to over 100 m and amplitudes of 0.5 to 25 m. These may be open to i s o c l i n a l , but in general the smal ler fo lds are c losed and 165 l o c a l l y i s o c l i n a l whereas the l a r g e r ones are more open. Megascopic fo lds have wavelengths that range from 2 to 10 km and amplitudes of from 0.5 to 2 km, and are t y p i c a l l y open. The loca l occurrence of bedding plane f a u l t s between the f laggy mudstone and Howards Pass formation and the lack of s i g n i f i c a n t d i f f e r e n t i a l th ickening in f o l d hinges ind ica te a f l e x u r a l - s l i p f o l d mechanism. Mesoscopic f o l d s are associated w i th , and have axia l planes that p a r a l l e l , the regional f rac ture cleavage and are most evident in the Howards P a s s , upper chert and the t r a n s i t i o n format ions. The trend of the fo lds ranges from 290 to 3 0 5 ° ; plunge ranges from 45° northwest to 5 ° southeast . In the XY a r e a , long i tud ina l sect ions based on d r i l l h o l e information i n d i c a t e an average plunge of 5 t o 15° northwest. The Zn-Pb deposi ts in the Howards Pass area have been d isp laced by these f o l d s (Plate IV) . Within f o l d h inges, sulphides have been l o c a l l y r e d i s t r i -buted by th ickening of the th in bedded calcareous mudstone and th in bedded cherty mudstone f a c i e s , with resul tant concentrat ion of a s s o c i -ated Zn and Pb su lph ides . Megascopic fo lds are responsib le for the major formation o u t l i n e s on the 1:30,000 sca le map (Plate I ) . Regional f o l d trends are 290 to 315° with axia l planes dipping 80 to 85° to the northeast . One such f o l d studied in de ta i l in the XY area shows a 1 0 ° plunge to the north-west. A l l megascopic fo lds in the Howards Pass area (Plate I) are open, although they may be c losed near major i n t r u s i v e centres such as near Tungsten and in the I ts i Mountains. A regional f rac ture cleavage a f f e c t s a l l units in the s t r a t i g r a p h i c s e c t i o n , but is most obvious in the Yara Peak and Iron Creek formations 166 and in the whit ish grey Zn-Pb mudstone f a c i e s of the Howards Pass forma-t i o n . The cleavage s t r i k e s 290 t o 3 1 5 ° , averaging 3 0 0 ° , d ips 75 to 85° northeast and is d i s t i n c t from the s l a t y cleavage which occurs l o c a l l y ( F i g . V - 2 ) . The r e l a t i v e age of the cleavage can be bracketed because i t c r o s s - c u t s slump f o l d s and s t y l o l i t e s and i s not deformed by meso-scopic nor megascopic f o l d s , but is cut by la te longi tud ina l and cross f a u l t s . In the whi t ish grey Zn-Pb mudstone f a c i e s the cleavage i s f i l l e d with s p h a l e r i t e and galena and i s most abundant in the hinges of mesoscopic f o l d s . These sulphide f i l l e d s t ructures d i f f e r from the penecontemporaneous water escape s t ructures described e a r l i e r in that they have s t ra igh t p lanar contacts and occur at i r r e g u l a r i n t e r v a l s whereas the sulphide f i l l e d veins a t t r ibu ted to cleavage have sharp planar contacts and are c l o s e l y spaced ( F i g . IV-14). The e f f e c t s of the cleavage on the sulphides are: (1) loca l r e d i s t r i b u t i o n of Zn and Pb and (2) a coarsening of sulphide gra in s i z e in the c leavage. S t r i k e f a u l t s are common throughout the Howards Pass area and s t r i k e approximately 300° with steep dips to the nor theast . These f a u l t s cut a l l rock units and mesoscopic and microscopic fo lds in the a r e a , and are in turn d isp laced by c r o s s - f a u l t s . Some of these s t r i k e f a u l t s are over 20 km long and contain gouge zones up to 25 m wide (Plate I ) . The presence of mul t ip le p a r a l l e l f a u l t zones and divergent s l i c k e n s i d e s showing r e l a t i v e movement of v e r t i c a l to 45° suggests that movement recurred along these f a u l t zones. Most of the s t r i k e f a u l t s show movement that postdates the fo lds and c leavage, but the p a r a l l e l o r i e n t a t i o n of both suggests that the same forces produced both f e a t u r e s , or that the f a u l t s formed along planes of weakness provided by 167 Figure V - 2 . Schmidt stereogram based on 382 poles to cleavage in the Howards Pass area . Two major s t r i k e d i r e c t i o n s are ev ident , 300° and 2 7 0 ° . The 300° cleavage is a f rac ture cleavage whereas the 2 7 0 ° cleavage shows both f rac ture and s la ty c leavage. 168 the cleavage (Spencer, 1969). Both the s t r i k e f a u l t s and the f rac ture cleavage are cut by dikes associa ted with the Cretaceous i n t r u s i o n s found outside the Howards Pass a r e a . The a s s o c i a t i o n of the most ex-tensive f a u l t s with fac ies changes and major f a u l t s in the ' G r i t Un i t ' suggests that r e a c t i v a t i o n of "basement" f a u l t s may be an important fac tor in the loca t ion and or ien ta t ion of some of the s t r i k e f a u l t s , as i s well es tab l ished elsewhere (C loos , 1955). Late c r o s s - f a u l t s cut a l l mesoscopic and macroscopic f o l d s , f r a c -ture cleavage and longi tud ina l f a u l t s in the Howards Pass area (Plates I thru IV). These c r o s s - f a u l t s s t r i k e approximately 060° and have nearly v e r t i c a l d i p s , p a r a l l e l to AC extension j o i n t s associated with mega-scopic f o l d s . Ver t i ca l separat ion along these f a u l t s ranges from 5 to 20 m. In the XY area the c r o s s - f a u l t s d iv ide the XY sub-basin into s t r u c -tura l blocks which have the northwest s ide downthrown, producing a s tep-l i k e se r ies of displacements of the a c t i v e member. In the ANNIV area the development of s t ruc tura l blocks re la ted to c r o s s - f a u l t s is a lso ev iden t , but no order ly stepping occurs (Plate I I ) . Late thrust f a u l t s have been i d e n t i f i e d in a small area in the XY area (Plate I I ) . Evidence fo r thrust f a u l t i n g includes a nearly h o r i -zontal f a u l t plane 80 cm th ick with s l i c k e n s i d e s i n d i c a t i n g reverse movement and displacement of f rac tu re cleavage by th is f a u l t p lane. The amount of movement along th is plane is unknown because i t cuts no s t r a -t i g r a p h i c markers. SUMMARY The tec ton ic h is to ry in the Howards Pass area is s i m i l a r to that found fo r other areas in the western C o r d i l l e r a . Most of the t e c t o n i c 169 events have a f fec ted the Howards Pass deposits ( F i g . V -3 ) . During the Paleozoic Era two major sedimentary- tectonic regimes were dominant. During the Ordovic ian to Ear ly Devonian, the Selwyn Basin may have been t e c t o n i c a l l y stable and consisted of a starved b a s i n . Penecontempora-neous slumping caused much of the small sca le r e d i s t r i b u t i o n of metals in the Zn-Pb deposits and major southwest t ransport and upgrading in the XY a r e a . Subsequent orogeny beginning in the Middle Devonian produced an u p l i f t to the west of Howards Pass which shed de t r i tus to the eas t ; the l a t e r stages of which co inc ide with the Ant le r Orogeny in the wes-tern United S ta tes . A Cretaceous orogeny produced major fo lds and f a u l t s , fol lowed by igneous i n t r u s i o n . A l l tectonism a f te r the Ear ly Devonian a f fected the Howards Pass d e p o s i t s . The Mid-Devonian to Mis -s i s s i p p i a n and Cretaceous tectonism d isp laced the d e p o s i t s , but only l o c a l l y have they r e d i s t r i b u t e d the Zn-Pb concentrat ions within them. PERIOD STRUCTURAL AND IGNEOUS PRODUCTS FAULTS Cross f a u l t s S t r i k e f a u l t s T h r u s t f a u l t s FOLDS M i c r o s c o p i c f o l d s Mesoscop i c f o l d s Megascop ic f o l d s CLEAVAGE F r a c t u r e c l e a v a g e S l a t y C leavage I oca l r e g i o n a l SLUMPS STRUCTURES PHYLLITIC TEXTURE UNCONFORMITY VOLCANIC FLOWS VOLCANIC TUFFS INTRUSIVE ROCKS o TO T7 TO 3> 1. y4 V). 3» Figure V - 3 . S t ructura l evolut ion of the Howards Pass area through t ime. Bars i n d i -cate time of formation of s t ructures and igneous a c t i v i t y . Time of Zn-Pb minera l i za t ion and top of the s t r a t i g r a p h i c sect ion are shown for comparison. The volcanic flows and t u f f s contemporaneous with the Zn-Pb minera l i za t ion are not within the Howards Pass area (Plate I ) , but occur near the shale-out near the South Nahanni R iver . 171 CHAPTER VI GEOCHEMISTRY INTRODUCTION AND METHODS Rock geochemistry of the Howards Pass and other formations was i n -vest igated in an attempt to charac ter i ze the sediments associated with the Howards Pass d e p o s i t s . Three approaches were attempted. F i r s t , three complete d r i l l cores from the XY deposit ( F i g . VI-1) were s p l i t in to i n t e r v a l s less than 3.2 m long and analyzed for twenty-one elements (Mo, Cu, Zn, Pb, Cd, N i , Co, Ag, Mn, V, Ba , Fe, Ca, Mg, K, C(org ) , C 0 2 , P, S , SiO2> AI2O5) by various quant i ta t ive and semi -quant i ta t ive methods (Appendix E ) ; the data were reca lcu la ted to 3.2 m i n t e r v a l s when com-pared to l i t h o l o g y . Second, samples of the various f a c i e s in the a c t i v e member were a lso analyzed by the same methods; t h i s data helped charac-t e r i z e the ind iv idua l f a c i e s . T h i r d , laminated samples of the th in bedded cherty mudstone and the whi t ish grey Zn-Pb mudstone fac ies were examined by e lec t ron microprobe fo r Zn, Pb, F e , Ca , Mg, K, Si and A l . The probe data are only r e l a t i v e and show only va r ia t ions and t rends . Two techniques were used to obtain data on chemical v a r i a t i o n , between laminae and across st ructures beam traverses were used and ind iv idua l gra ins were analyzed using scanning images f o r element a s s o c i a t i o n (Appendix E ) . The data obtained from the three d r i l l holes are sum-marized three ways. F i r s t , the data are cor re la ted with l i t h o l o g i e s g r a p h i c a l l y ( F i g s . VI-2 thru V I -4 ) . Second, the means for elements •analyzed are compared to published chemical data on black shales ( e . g . Vine and T o u r t e l o t , 1970) and other s t r a t i f o r m Zn-Pb deposi ts (Lambert and S c o t t , 1973) (Table V I -1 ) . T h i r d , elementary s t a t i s t i c a l techniques are used to aid in determining element d i s t r i b u t i o n s and i n t e r r e l a t i o n -ships ( F i g . V I -5 , VI -6 , V I -7 ) , although the v a l i d i t y of t h i s approach Figure VI -1 . Locat ion of diamond d r i l l holes 12, 18, 19 and 36. Core from these holes were used fo r chemical -1 i t h o l o g i c a l analyses discussed in the tex t . DDHI2 log Zn (ppm) log Pb (ppm) to1 to* io* 10* to* & 10* io* to* B*ipr« iff* io° to* io* la^w* log V (ppm) log Bo (ppm) to* id* to* to' to* 7 Figure VI-2a. Element abundance (Zn, Pb, Cd, V, Ba) compared to s t r a t i g r a p h i c sect ion from DDH 12. USMS = upper s i l i c e o u s mudstone, AM = act ive member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member. Total length of core is 180 m. Figure VI -2b. Element abundance (Ag, Cu, N i , Co, Mn) compared to s t r a t i g r a p h i c sect ion from DDH 12. USMS = upper s i l i c e o u s mudstone member, AM = act ive member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member. Total length of core i s 180 m. -p. Figure V I -2c . Element abundance (K 2 0 , Fe , caO, MgO, C ( o r g ) , S, P) compared to s t r a t i g r a p h i c sec t ion from DDH 12. USMS = upper s i l i c e o u s mudstone member, ,AM = ac t ive member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member. C U ) r e f e r s ' t o organic carbon. Tota l length of core is 180 m. ODH 18 log Zn (ppm) log Pb (ppm) bgCd(ppm) log V (ppm) log Bo (ppm) Figure V I -3a . Element abundance (Zn, Pb, Cd, V, Ba) compared to s t r a t i g r a p h i c sect ion from DDH 18. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = a c t i v e member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member. Tota l length of core i s 198 m. DOH 18 log Aa (ppm) log Cu (ppm) log Ni (ppm) log Cot ppm) log Mn (ppm) Figure. VI -3b. Element abundance (Ag, Cu, N i , Co, Mn) compared to s t r a t i g r a p h i c sect ion from DDH 18. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = ac t ive member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member. Tota l length of core i s 198 m. Figure V I -3c . Element abundance ( K 2 C 1 , Fe , CaO, MgO, C ( o r g ) , S, P) compared to s t r a t i g r a p h i c sect ion from DDH 18. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = act ive member, LCMS = lower cherty mudstone member, C a l c . MS .= c a l -careous mudstone member. C(%) re fers to organic carbon. Total length of core is 198 m. log Zn (ppm) log Pb (ppm) log Cd (ppm) log V (ppm) log Bo (ppm) Figure V I -4a . Element abundance (Zn, Pb, Cd, V, Ba) compared to s t r a t i g r a p h i c sec-t i o n from DDH 19. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = ac t ive member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone member, PSSh = p y r i t i c s i l i c e o u s shale member, TZ = t r a n s i t i o n format ion, WB = wavy banded l imestone format ion. Tota l length of core is 225 m. log A g (ppm) log C u (ppm) log Ni (ppm) log C o ( p p m ) log M n (ppm) Figure VI -4b. Element abundance (Ag, Cu, N i , Co, Mn) compared to s t ra t ig raph ic sec-t i o n from DDH 19. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = a c t i v e member, LCMS - lower cherty mudstone member, C a l c . MS = calcareous mudstone member, PSSh = p y r i t i c s i l i c e o u s shale member,.TZ = t r a n s i t i o n formation, WB = wavy banded l imestone format ion. Total length of core is 225 m. DDHI9 K,OfW F«(t)fW CoO(%) MgOft) C(%) FMS USMS i i i r* ' ' ' v « • t » • r i « - p d — - - , v m * w m iv —, i * i r i *-> > AM r [ •—j LCMS Calc.MS PSSh I > T Z -4 -1 4 Figure VI - 4 c . Element abundance ( K 2 O , Fe , CaO, MgO, C ( o r q ) ) compared to s t r a t i -graphic sect ion from DDH 19. .FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mud-stone member, AM =• ac t ive member, LCMS = lower cherty mudstone member, C a l c . MS = c a l c a -reous mudstone member, PSSh = p y r i t i c s i l i c e o u s shale member, TZ = t r a n s i t i o n format ion, WB - wavy banded limestone format ion. C(%) refers to organic carbon. Tota l length of core i s 225 m. Figure VI -4d. Element abundance (S, P, S i 0 2 , AI2O3) compared to s t ra t ig raph ic sec-t i o n from DDH 19. FMS = f laggy mudstone format ion, USMS = upper s i l i c e o u s mudstone member, AM = a c t i v e member, LCMS = lower cherty mudstone member, C a l c . MS = calcareous mudstone ^ member, PSSh = p y r i t i c s i l i c e o u s shale member, TZ = t r a n s i t i o n formation, WB = wavy banded ro l imestone format ion. Tota l length of core is 225 m. 183 may be questioned on the grounds of sampling pract ice (Koch and L i n k , 1971), which was not s t r i c t l y random in the present study. The Kolmogorov-Smirnov test (Winkler and Hays, 1975) was used to compare the sample d i s t r i b u t i o n with theore t i ca l d i s t r i b u t i o n s for goodness of f i t and showed that t race elements (Zn, Pb, Mo, Cu, Cd, N i , Co, Ag, Mn, V and Ba) approximate a lognormal d i s t r i b u t i o n (Ahrens, 1954; A i t c h i s o n and Brown, 1957) whereas major elements (Fe, Ca , K, Mg, C ( o r g ) , P, AI2O3 and Si02) more c l o s e l y approximate a normal d i s t r i b u t i o n . DISCUSSION ZINC AND LEAD Zn and Pb are h ighly concentrated in the Howards Pass formation r e l a t i v e both to carbonaceous mudstones analyzed by Vine and T o u r t e l o t (1970), and to other uni ts in the Howards Pass area (Table V I -1 ) . The highest Zn and Pb concentrat ions occur in the ac t ive member, which has a mean Zn content of 1.23% whi le that of Pb is 0.35%. T h i s data confirms the visual genera l i za t ion that the Zn and Pb contents of the ac t ive mem-ber are the only concentrat ions in the formation that could be cons ider -ed of ore grade. There i s a d e f i n i t e assoc ia t ion of Zn and Pb with l i t h o l o g y in the ac t ive member, which i s best demonstrated by comparing data from samples taken from each of the f a c i e s in the member ( F i g . V I -8 ) . Zn: Pb ra t ios a lso vary between l i t h o l o g i e s and show a general trend of decreasing Zn: Pb r a t i o with increas ing grade ( F i g . V I -9 ) . To fur ther inves t iga te t h i s r e l a t i o n s h i p between Zn-Pb content and l i t h o l o g y in the ac t ive mem-b e r , samples from DDH-36 were c o l l e c t e d and analyzed on a 0.3 m i n t e r -c 184 Table V I - 1 . Mean (x ) element contents for various elements in column at l e f t fo r the s t r a t i g r a p h i c units shown at the top of the t a b l e . Published chemical content averages for black shales and non-carbonaceous shales are shown fo r comparison. Concentrat ion of S i02 f o r average black shale is taken from Pet t i john (1975). Numbers l i s t e d under heading "S t ra t ig raph ic Uni ts" re fers to N used in c a l c u l a t i n g the mean concent ra t ion , fo r example, next to f laggy mudstone the terms 10/3 re fers to the use of N=10 to determine mean for a l l elements and com-pounds except S i 0 2 and AI2O3, fo r which N=3. S t r a t i g r a p h i c U n i t s c 0 u l T3 3 2 >* o> o> a U. Upper Siliceous 70, ! Mudstone 38 u CO a> c o NJ a> •> u < \ 2 >. i _ 93 £ . 93 ° § 11 3 <U O <= 93 O O VI O T 3 a = u 5 CA 3 O 93 U CO y « c ° a. co ao\ 01 c o M C .2 c o 93 O J C CT> co 7> u <u 3 Z «> r -§>cO c: v <u c 3 > Average Shole (Green 1959) c g 2 •— i2 <3 \L cn — — S. » ° "2 % 5 < aJ Mo 2 9 2 4 21 1 6 8 1 0 1 0 I 3 Cu 2 6 6 1 5 7 6 0 6 0 1 7 2 4 7 0 3 8 4 5 Zn 2 5 9 8 6 1 2 2 9 5 4 7 8 '12a 3 5 1 0 4 2 0 0 2 0 0 1 6 0 Pb 8 1 9 7 3 4 6 3 1 6 2 4 5 2 0 1 7 2 0 2 0 2 0 Cd 0 - 2 11-9 6 2 4 7 1 0 0 1 • 4 — — — Ni 2 7 9 3 7 7 1 4 6 1 1 7 3 9 4 3 5 0 2 1 6 8 1 c Co 1 7 1 4 1 8 1 4 1 5 1 4 1 7 1 0 1 2 1 9 c Ag • 3 • 7 8 2 - 4 7 1-55 • 9 • 1 8 • 2 7 <l • 9 • 0 7 Mn 1 9 8 1 1 2 2 0 0 8 9 1 1 3 1 9 8 1 5 9 1 5 0 6 7 0 0 8 5 0 V 1 0 8 3 8 4 5 1 6 1 0 9 1 6 0 3 1 6 0 2 7 1 1 5 0 1 3 0 1 3 0 Ba 8 6 2 1 1 3 1 6 4 5 3 8 1 3 1 0 6 1 2 2 1 4 1 8 2 5 3 0 0 8 0 0 5 8 0 Felt) 2 0 1 1 - 9 6 2 - 5 1 2 2 5 2 - 4 5 1 9 7 2-11 2 0 4 - 3 4 - 7 2 Ca 0 5 1 7 9 3 1 1 7 - 6 3 5 - 5 1 1 4 - 2 9 7- 6 3 9 - 0 5 2 1 7 - 3 3 1 MgO 2 - 8 8 0 - 6 8 0 - 2 2 0 - 7 4 3 - 7 9 4 1 4 3 - 2 5 0 - 9 2 5 1-9 K 2 0 3 9 2 1 - 6 7 0 - 6 9 3 9 4 3 - 6 4 4 - 3 5 4 - 8 1 2 4 3 - 3 7 3 - 2 0 C(org I - 0 2 4 - 9 0 4 - 4 9 6 - 5 0 3 - 7 3 I - 0 3 1 1 5 3 - 2 • 6 5 — C 0 2 6- 0 2 6 2 3 1 0 - 7 3 6 - 0 5 1 4 - 5 3 8 - 9 5 9 - 9 8 — — — p2o5 • 1 1 3 II 7 • 5 2 9 • 3 0 2 • 2 1 1 • 3 6 3 • 3 5 4 — — s 1 2 S 1 - 6 4 2 9 5 2 - 6 2 1 - 6 • 8 2 • 7 7 — — 7 - 7 4 3 - 7 8 0 - 6 7 6 8 4 8 4 1 7- II 9 0 6 1 3 2 3 1 4 - 7 4 1 5 1 2 Si o2 S 2 - 6 7 6 4 - 7 9 4 8 9 3 6 3 - 9 0 5 7 - 3 9 5 7 0 5 5 4 - 7 2 5 1 - 0 3 — 185 Cu Z n Pb Cd A, So Fell) CoO MgOl C% C0 2 iLoir Mo Cu Zn Pb -•2794-8147 406a-07«9i Ag Ba Felt! ••327d--5705f MgO|. -2850--2575 ! K,0 c % (LOI1 CO, Figure VI-5. Matr ix of c o r r e l a t i o n c o e f f i c i e n t s fo r element pai rs f o r DDH 12. Sign before c o e f f i c i e n t ind ica tes d i r e c t i o n of slope of re -gression l i n e . C(LOI) represents organic carbon C02(|_0I) represents CO32-. 1 Cu Zn Pb- Cd Co A9 Bd Felt) CoO MgO K2° C% (LOI) Si 0, A,2°J Mo Cu 0002^3670-3481 Zn -•06831-2596 • Pb Cd -3898)--4874 Co Ag -45aa-6297 —27981-2624: -0102-04671 CoO MgO >-•378M-4637 C V. (LOI) C0 2 :LOD SiO, Figure VI -6 . Matrix of c o r r e l a t i o n c o e f f i c i e n t s for element pai rs f o r DDH 18. Sign before c o e f f i c i e n t ind ica tes d i r e c t i o n of slope of regression l i n e . C(|_oi) represents organic carbon, c ^ 2 ( L O I ) represents C O 3 2 " . 1 C u Z n P b C d N i C o A , M n V B d Felt) C o O M g O K 2 0 C % (LOI) C 0 , (LOI) P 2 0 5 s S i A l . , 0 , M o •2137 • 0908 -0608 •1065 •4856 •2754 •2199 •0394 •6248 - 3 1 9 3 —1874 •0775 -1443 •0337 •2950 •0529 -1541 •0822 -1764 -0311 C u 1881 •2587 •2420 •1842 -•1839 •HOI - 0 9 7 ! •0893 -1149 •2933 -1837 -1350 -1476 •2957 - 2 7 5 4 •2546 •3050 •1425 - 2 0 0 6 Z n •7697 •8369 --0940 -1546 •3055 •1619 - 0 5 9 7 -2109 •0876 •1549 - 2 2 6 4 -3187 - 0 3 9 9 - 0 4 4 4 -1760 -1378 -1691 -3116 Pb •6336 -1797 -1268 •1990 •1808 -•1507 -1679 -0316 •2093 - 1 8 5 0 -3160 -•1593 -0153 - 2 0 8 C •3603 -2127 - 2 7 6 5 C d - 0 6 7 2 - 0 5 0 6 •3979 •2775 •0192 - 2 5 4 7 •0892 •1218 - - 2 7 2 5 •0204 - 0 7 5 2 -2186 •5314 -2107 -2685 N i •1457 - 0 7 2 5 -4821 •7164 - 1 5 9 5 - 0 3 9 8 - 3 9 9 3 •0518 •5457 •4946 - 3 3 3 9 •2576 •1699 • 2051 •4239 C o •2726 •4965 •0432 •1785 -•I960 • 5125 •3276 •2691 -0681 •5613 • 0 8 5 5 - o a i - 6 0 2 0 -2671 A g •3211 •0881 -3848 •0186 •4157 - 3 2 7 0 • 3020 1153 •3223 -2133 •3291 - 3 4 5 6 -•3230 M n - 3 5 9 6 -1338 - 0 9 9 6 •8261 -1043 - 3 9 8 3 - 3992 •76 8 9 -1972 -0092 - 7 6 2 6 - 3 2 2 5 V —3388 - 0 2 6 2 - 3 3 7 0 -1299 •4045 •4886 -•2911 - 2 0 4 0 •1927 -1927 •3157 B a •034 5 -•2B65 •8443 •5567 -1160 -2108 •1609 — 1611 •0801 •5392 Fell) - 2 2 4 3 •0222 •0298 •3039 - 2 5 9 8 - 0 9 4 5 •6060 •1284 -•0089 C a O -2274 - 4 9 2 2 -3811 ' 9 4 6 -•0642 -1215 -•8142 —»728 M g O •6432 •0840 -1306 •1644 -•1052 - 0 3 6 •6235 K 2 0 •2234 - 3 3 8 9 •0361 •0158 •1705 •9167 C% (LOI) - 4 2 6 5 0653 • 3165 •2770 •1490 C 0 2 (LOI) - 0 5 1 5 - 2577 - 7 5 4 4 - 2 8 4 4 P 2 0 5 -1751 •0982 •0061 s - 0 4 0 2 - 0 2 5 2 S i 0 2 •0404 Figure VI -7 . Matrix of c o r r e l a t i o n c o e f f i c i e n t s for element pai rs fo r DDH 19. Sign before c o e f f i c i e n t ind ica tes d i r e c t i o n of slope of regression l i n e . C(|_OI) represents organic carbon C 0 2 ( i _ 0 I ) represents C O 3 2 " . 188 Ag Ba Mn Mo Co Ni Cu Cd Pb Zn Figure IV-8a. Comparison of mean (x) element content values for f i v e samples from each of 10 rock categor ies represent ing fac ies of the a c t i v e member and associated rocks . Rock l i t h o l o g i e s are represented by numbers; (1) upper s i l i c e o u s mudstone member, 2-9 represent f a c i e s of the ac t ive member (2) grey c h e r t , (3) whi t ish grey Zn-Pb mudstone, (4) th in bedded cherty mudstone, (5) cherty mudstone, (6) th in bedded calcareous mudstone, (7) graded l imestone, (8) l i g h t grey basal l ime-stone, (9) basal f a c i e s and (10) lower cherty mudstone member. 189 Figure IV-8b. Comparison of mean (x) element content values fo r f i v e samples from each of 10 rock f a c i e s of the ac t ive member and as -soc ia ted rocks . Facies are represented by numbers; (1) upper s i l i c e o u s mudstone member, 2-9 represent f ac ies of the ac t ive member 2) grey c h e r t , 3) whi t ish grey Zn-Pb mudstone, 4) th in bedded cherty mudstone, 5) cherty mudstone, 6) th in bedded calcareous mudstone, 7) graded l imestone, 8) l i g h t grey basal l imestone, 9) basal f a c i e s and 10) lower cherty mudstone member. 190 Pb+ Zn (%) Figure V I -9 . Pb+Zn vs Zn:Pb r a t i o in the act ive member showing the general trend of decreasing Zn:Pb r a t i o with inc reas ing Pb+Zn. F i e l d s of textura l types are p lot ted fo r comparison. 191 v a l . The most obvious r e l a t i o n s h i p s are that the l i gh t grey basal l ime-stone and graded limestone fac ies contain only t races of Zn and Pb (<500 ppm Zn and <100 ppm Pb) and that the whit ish grey Zn-Pb mudstone f a c i e s contains the highest concentrat ions of these metals (>10% Zn and >5% Pb); the th in bedded cherty mudstone and th in bedded calcareous mudstone f a c i e s contain varying concentrat ions of Zn and Pb, but in g e n e r a l , range from 2 to 15% Zn and 0.5 to 4% Pb ( F i g s . VI-10 and V I -11) . These grade-1 i tho fac ies r e l a t i o n s h i p s are fur ther supported by analyses of v i s u a l l y t y p i c a l samples of the various a c t i v e member f a c i e s ( F i g . V I -8 ) , and de ta i led sampling of core from d r i l l hole 36 in the XY area ( F i g s . VI-10, VI-11, VI -12) . Comparison of Zn: Pb: Cu ra t ios in s t ra t i fo rm deposi ts has been sug-gested by Stanton (1972). The Howards Pass deposi ts d i f f e r in both Cu: (Zn+Pb) and, to some degree, Zn: Pb from other "s im i l a r " stratabound deposi ts ( F i g . VI-13) supporting one of the major proposals of t h i s the-s i s , that the Howards Pass deposi ts cons t i tu te a new sub-c lass of Zn-Pb deposi t (Chapter IX). COPPER The Cu concentrat ion within the Howards Pass formation is r e l a t i v e -ly uniform ( F i g s . VI -2 , V I -3 , V I -4 ) , and is s i m i l a r to the average Cu concentrat ion of 50 ppm reported by Vine and Tour te lo t (1970) for black s h a l e s . The Cu content of the ac t ive member is s i m i l a r to that of the rest of the format ion, an a typ ica l s i t u a t i o n fo r s t r a t i f o r m Zn-Pb depo-s i t s (Lambert, 1976; Krebs, 1976b); furthermore, there are no s a t e l l i t e copper deposi ts in the Howards Pass area s i m i l a r to those found at McArthur River (Lambert, 1976), Mt. Isa (Bennet, 1967), or Lady Loret ta 192 za ma 8 10 IS 20 28 Figure VI-10. Zinc content compared to ac t ive member l i t h o l o g y based on de ta i l ed l i t h o l o g i c log of core from d r i l l hole 36 compared to 0.328 m samples analyzed fo r Zn . Three major zones of high Zn are re-la ted to the presence of whi t ish grey Zn-Pb mudstone f a c i e s . Tota l length of ac t ive member is 70.82 m, bedding is 90° to core a x i s . Num-bers re fe r to ac t ive member f a c i e s : 1) b a s a l , 2) l i g h t grey basal l imestone, 3) graded l imestone, 4) th in bedded calcareous mudstone, 5) mixed cherty mudstone and l imestone, 6) cherty mudstone, 7) th in bedded cherty mudstone, 8) whi t ish grey Zn-Pb mudstone and .9) grey chert f a c i e s . 193 Figure VI -11. Lead + Zn content compared to ac t ive member l i t h o -logy based on d e t a i l e d l i t h o l o g i c log of core from d r i l l hole 36 com-pared to 0.328. m samples analyzed fo r Zn + Pb. Three major zones of high Zn + Pb are re la ted to the presence of whi t ish grey Zn-Pb mudstone f a c i e s . Tota l length of ac t ive member is 70.82 m, bedding is 9 0 ° to core a x i s . Numbers re fer to act ive member f a c i e s : 1) b a s a l , 2) l i g h t grey basal l imestone, 3) graded l imestone, 4) th in bedded calcareous mudstone, 5) mixed cherty mudstone and l imestone, 6) cherty mudstone, 7) th in bedded cherty mudstone, 8) whi t ish grey Zn-Pb mudstone and 9) grey chert f a c i e s . 194 10 m LOWCB CMtRTY MUOSTONC Figure VI-12. Lead content compared to ac t ive member l i t h o l o g y based on d e t a i l e d l i t h o l o g i c log of core from d r i l l hole 36 compared to 0.328 m samples analyzed f o r Pb. Three major zones of high Pb are re la ted to the presence of whi t ish grey Zn-Pb mudstone f a c i e s . Tota l length of ac t ive member i s 70.82 m, bedding is 90° to core a x i s . Numbers re fe r to a c t i v e member f a c i e s : 1) b a s a l , 2) l i g h t grey basal l imestone, 3) graded l imestone, 4) th in bedded calcareous mudstone, 5) mixed cherty mudstone and l imestone, 6) cherty mud-stone, 7) th in bedded cherty mudstone, 8) whi t ish grey Zn-Pb mudstone and 9) grey chert f a c i e s . 195 Pb Figure VI-13. Copper-z inc lead diagram with the fo l lowing plot ted: Howards Pass, s t rat i form-sedimentary deposi ts (Stanton, 1972) and the general trend of temperature decrease in a brine (Sato, 1972; Large, 1977; Wi l l i ams, 1978). The use of t h i s model suggests that the low copper con-tent in the Howards Pass deposits could be the resu l t of a low temperature ore forming f l u i d . 196 (Loudon et a l . , 1975). There is a p o s i t i v e c o r r e l a t i o n between Cu and C ( o r g ) at rg.005 level of s i g n i f i c a n c e suggesting that the Cu is a s s o c i -ated with organic matter ( F i g . V I -14) , although occasional cha lcopyr i t e grains ind ica te that at least part of the Cu occurs as a su lph ide . SILVER The s i l v e r content of the Howards Pass formation is s i m i l a r to that of other carbonaceous mudstones (Table V I -1 ) , with means for the members ranging from 0.18 to 2.47 ppm, compared to s l i g h t l y less than 1 ppm re -ported by Vine and T o u r t e l o t (1970). The highest Ag values (up to 4 ppm) occur in the ac t ive member, associated with high Zn and Pb va lues , a l -though no d i s c r e t e Ag-bearing mineral has been noted. The Ag content of the Howards Pass deposits are anomalously low compared to s i m i l a r s t r a -t i f o r m d e p o s i t s , such as Mt. Isa (Mathias and C l a r k , 1975), McArthur River (Lambert, 1976), Meggen (Dornsiepen, 1976) and Tom (Freberg, 1976), again i n d i c a t i n g a geochemical d i f f e rence from these other depo-s i t s . Selected surface samples from the Iron Creek formation contain up to 6 ppm Ag and samples from the Yara Peak formation contain less than 0.5 ppm Ag, but to date not enough data is a v a i l a b l e to ind ica te the s i g n i f i c a n c e of these r e s u l t s . CADMIUM Cadmium is h ighly concentrated in the a c t i v e member, which contains a mean value of 620 ppm, with 1000 to 1600 ppm in the whit ish grey Zn-Pb mudstone f a c i e s . Other members in the Howards Pass formation contain less than 5 ppm and are s i m i l a r to the 1.4 ppm Cd mean reported f o r 84 samples from bituminous P ie r re Shale (Tourtelot et a l . , 1964). Cadmium shows a high degree of c o r r e l a t i o n with Zn ( for example DDH 12 r = .837 Figure VI-14. Organic carbon (C%) compared to Cu (ppm) with reg-ress ion l i n e , showing p o s i t i v e c o r r e l a t i o n between organic carbon and Cu. 198 where r.Q05=0.27 ( F i g . V I -15) ) . The a s s o c i a t i o n of Cd with Zn in the Howards Pass formation may be explained by the s u b s t i t u t i o n of Cd in the s p h a l e r i t e s t ructure (Walkita and Schmit t , 1972). In the Howards Pass deposi ts up to 1.4% Cd has been found in s p h a l e r i t e , which is c lose to the 1.66% maximum reported by Mason and Berry (1968). MOLYBDENUM The Mo content of the Howards Pass formation ranges from 8 to 24 ppm with higher values obtained from the ac t ive member. The high v a r i a b i l i t y at low concentrat ions makes any genera l i za t ions ten ta t i ve and therefore the datum is not compared to s t ra t ig raphy . There is a weak c o r r e l a t i o n between Mo and C ( o r g ) ; f o r example in DDH 18, r = .275 (where r .Q05 = .267). T h i s a s s o c i a t i o n was a lso noted experimental ly by Ber t ine (1972) in anoxic waters where slow absorpt ion of Mo onto organic matter is the major fac tor in Mo deposi t ion in sediment and found up to 2700 ppm Mo in marine humic a c i d s . Ber t ine a lso found the c o p r e c i p i t a t i o n of Mo with i ron sulphide to be important in some s e d i -ments, although the low c o r r e l a t i o n between Fe and Mo in the Howards Pass formation suggests that t h i s mechanism was not important. COBALT AND NICKEL Cobalt and Ni abundances in the Howards Pass formation are t y p i c a l of black shales (Vine and T o u r t e l o t , 1970). The means of Co content fo r the various members of the formation are r e l a t i v e l y homogeneous, ranging from 14 to 19 ppm. Nickel on the other hand is more v a r i a b l e , but s t i l l wi thin the range of t y p i c a l black s h a l e s . Cor re la t ion shows Ni re la ted to organic carbon and other elements a lso associated with organic carbon ( F i g s . V I -5 , V I -6 , V I -7 , VI-16) such as V, Cu and Mo. The high a f f i n i t y / 199 1500 3000 4500 6000 7500 9000 Zn (ppm) Figure VI-15. Cd (ppm) compared to Zn (ppm) with regression l i n e , showing p o s i t i v e c o r r e l a t i o n between Zn and Cd. No s p e c i f i c Cd mineral has been found which suggests that Cd is subst i tu ted in the spha le r i te s t r u c t u r e . 200 Figure VI-16. Organic carbon (C(%)) compared to Ni (ppm) with reg-ression l i n e showing p o s i t i v e c o r r e l a t i o n between organic carbon and N i . 201 f o r Ni to occur in metal 1 organic complexes has been discussed at length by Burns et a l . (1972). Cobalt on the other hand, is associated with carbonates in the Howards Pass format ion, but c o r r e l a t i o n here is c lose to the c r i t i c a l value for s i g n i f i c a n c e (ir .rj05 = -267). The Co: Ni r a t i o for s p e c i f i c sulphide minerals have been used ex-t e n s i v e l y as an environmental i n d i c a t o r in s t ra t i fo rm deposit minerals ( e . g . , p y r i t e , Rankama and Sahama, 1950), but some general comments can be made concerning whole rock r a t i o s (Lambert and S c o t t , 1973). Tab le V I - 2 shows that Co:Ni r a t i o s , ca lcu la ted from mean values f o r the various members of the Howards Pass format ion, are s i m i l a r throughout the formation and are less than 1. T h i s is in contrast to the McArthur River deposit in which the Co: Ni r a t ios are greater than 1 in the o r e s , but less than 1 away from the Zn-Pb sulphides (Lambert and S c o t t , 1973). Using Lambert and S c o t t ' s reasoning t h i s r e l a t i v e constancy of Co: Ni r a t i o may be the r e s u l t of a greater proport ion of control on the depo-s i t i o n of sulphides by the sedimentary environment rather than by p r o x i -mal v o l c a n i c - r e l a t e d ore f l u i d s . MANGANESE Manganese concentrat ions in the Howards Pass Formation range from x= 89 ppm in the lower cherty mudstone to x = 200 ppm in the ac t ive member, s i m i l a r to an average of 150 ppm fo r black shales (Vine and T o u r t e l o t , 1970), and much lower than that of non-carbonaceous s h a l e s , which average 6700 ppm (Green, 1959). Within the Howards Pass formation c o r r e l a t i o n of Mn with Ca ( F i g . V I -5 , V I - 6 , V I - 7 ) is s i g n i f i c a n t (r = .826 where r .QO5 = .283, F i g . V I - 1 7 ) . T h i s i s p o s s i b l e , where fe^^ i s unstable , only in a reducing environment (Garrels and C h r i s t , 1965). Tab le VI -2 . Trace element ra t ios from s t ra t ig raph ic units in the Howards Pass area , Upper part of t ab le shows data f o r Co:Ni r a t i o s , lower part is for Ba: V r a t i o s . Co/Ni S t r a t i g r a p h i c Unit DDH-18 DDH-19 DDH-: FLAGGY MUDSTONE FORMATION 0.70 0.52 HOWARDS PASS FORMATION upper s i l i c e o u s mudstone 0.13 0.15 0.16 a c t i v e member 0.18 0.22 0.28 lower cherty mudstone 0.09 0.11 0.09 calcareous mudstone 0.13 p y r i t i c s i l i c e o u s shale 0.36 TRANSITION FORMATION 0.40 Ba/V FLAGGY MUDSTONE FORMATION 78.57 82.10 HOWARDS PASS FORMATION upper s i l i c e o u s mudstone 2.26 3.99 ac t ive member 0.92 1.05 4.50 lower cherty mudstone 0.89 0.57 0.74 calcareous mudstone 1.76 p y r i t i c s i l i c e o u s shale 13.84 TRANSITION FORMATION 6.73 Average black shale 2.00, Average shale 6.15 (Table V I -1 ) . 203 Figure VI-17. CaO (%) compared to Mn (ppm) with regression l ine showing p o s i t i v e c o r r e l a t i o n between CaO and Mn. 204 rhe low Mn content associated with the Howards Pass deposits is unl ike the Mn content associa ted with the Meggen deposit (Krebs and Gwosdz, Oral Commun., 1976; Gwosdz and Krebs , 1977) and hydrothermal a c t i v i t y in r i f t i n g regions (Bonat t i , 1975). BARIUM AND VANADIUM Barium and V are concentrated in some areas of the Nahanni map-area but occur only in t race amounts within the Howards Pass formation in the Howards Pass area . For example, the Selwyn Mountains b a r i t e horizon l o c a l l y contains laminated bar i t e deposits with up to 30% B a , while a few grab samples taken from the Iron Creek formation average approximately 1% B a . The Howards Pass format ion , in c o n t r a s t , contains less than 2000 ppm Ba and reg iona l l y i s a Ba-poor u n i t , even though com-parison with Vine and T o u r t e l o t ' s (1970) data shows i t to contain 3 times the Ba in an average black sha le . Comparison of Ba analyses from d r i l l core and surface chip samples show that Ba is r e l a t i v e l y low in the Howards Pass format ion, increas ing up sect ion unt i l i t reaches a high in the b a r i t e horizon and dropping s u b s t a n t i a l l y in the Yara Peak format ion. The Howards Pass deposits are unique in t h e i r lack of associa ted bar i t e when compared to other s t r a t i f o r m Zn-Pb d e p o s i t s . Other deposi ts t y p i c a l l y have b a r i t e e i t h e r d i r e c t l y associa ted with the Zn-Pb s u l -phides, as in the Tom deposi ts (Morganti , 1975; Dawson, 1977; Carnes, 1978) or marginal to the sulphide b o d i e s , as in the case of Meggen (Dornsiepen, 1976). The Howards Pass formation l o c a l l y contains up to 1500 ppm V and averages more than 150 ppm of the t y p i c a l black shale (Vine and 205 T o u r t e l o t , 1970). Within the formation the highest values are in the lower cherty mudstone member (Morganti , 1977a) with an average of over 1000 ppm V. Vanadium shows a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n with C(org) ( f o r example, r f o r V : C ( o r g ) in DDH 18 i s 0.542 where r.005=.283) suggesting that V i s present in organic complexes, s ince no V-conta in ing mineral has been i d e n t i f i e d . F ischer (1973) observed that V can a lso be concentrated by reduction in the presence of organic matter or biogene-t i c a l l y generated H2S, although the a s s o c i a t i o n of V and P noted by F ischer (1973) and in the present study ind ica tes an a s s o c i a t i o n with organic matter. There is a general trend of increas ing Ba up-sect ion above the ac-t i v e member and decreasing V, but the use of ind iv idua l elements f o r determining fac ing is masked by l a t e r a l va r ia t ions in the u n i t s . In c o n t r a s t , Ba: V ra t ios appear to be more consis tent (Table V I -2 ) ; thus Ba: V r a t i o s may prove to be an important s t r a t i g r a p h i c guide in areas where v isual s t r a t i g r a p h i c r e l a t i o n s h i p s are not c l e a r . IRON Tota l i ron content in the Howards Pass formation ranges from 1.92 to 2.51% in the various members (Table VI-1) which is s i m i l a r to the 2.0% average for black shales reported by Vine and T o u r t e l o t (1970). The Howards Pass deposits are unique in that the Zn-Pb sulphides are not associated with massive pyr i te or pyr rhot i te and lack the high i ron con-cent ra t ions t y p i c a l of s t r a t i f o r m Zn-Pb deposi ts (Lambert, 1976; Krebs, 1976b; V o l k s , 1976). Consider ing Howards Pass formation as a whole, the major d i f fe rence between the a c t i v e member and other members is not in the proport ions of Fe or p y r i t e , but is t e x t u r a l ; the ac t ive member i s 206 the only member where framboidal p y r i t e i s dominant. In a l l c a s e s , FeS2 content ca lcu la ted from the Fe analyses and the pyr i te content are s i m i l a r ind ica te that nearly a l l the i ron occurs in p y r i t e . CALCIUM AND MAGNESIUM The mean CaO content of the various members of the Howards Pass formation is greater than the average of 2.1% reported by Vine and T o u r t e l o t (1970), but t h i s is in part due to the presence of i n t e r c a -la ted limestones rather than to an abundance of calcareous mudstone. The highest CaO content and a lso the most l imestone occurs in the a c t i v e member. Within the ac t ive member the l imestone is not associated s p e c i -f i c a l l y with the Zn-Pb su lph ides . Comparison of CaO vs l i t h o l o g y of an i d e a l i z e d cyc le of the ac t ive member ( F i g . VI-8) shows a general de-crease upward in calcium content . The MgO content in the Howards Pass formation is low compared to that of the average black s h a l e . Most Mg appears to be in p h y l l o s i l i -c a t e s , based on the assoc ia t ion of MgO, K 2 0 and Al2^3* which suggests that these elements are present in c lay minerals (Grim, 1968); the i n -verse r e l a t i o n s h i p of C 0 2 and MgO suggests that dolomite is not present in substant ia l q u a n t i t i e s . The r e l a t i v e l y high MgO content in the f l a g -gy mudstone formation compared to the Howard Pass formation is the re -s u l t of a higher p h y l l o s i l i c a t e content and dolomi t ic cement. POTASSIUM The average potash (K 2 0) content of the Howards Pass formation i s s i m i l a r to that reported to be t y p i c a l of black shales (Vine and T o u r t e l o t , 1970) (Table V I -1 ) , although there is a large range of mean va lues; for example, in the ac t ive member x = 0.69% K 2 0 whereas in the 207 lower cherty mudstone member x= 3.9%. T h i s is c lose to C l a r k e ' s (1924) 3.24% K 2 0 average for a l l s h a l e s . Grim (1968) has shown that most K 2 0 in shales is associated with c lays or micas. T h i s is supported in the present study by a strong p o s i t i v e c o r r e l a t i o n ( F i g . VI-7) between K 2 0 and A l 2 O 3 • Further de ta i led examination of the K 2 0 content consisted of K2O s ta in ing techniques to check for any high K 2 0 areas . T h i s was done to check f o r any t u f f beds as noted by Bennet (1967) in the Mt. Isa depos i t , where high K 2 0 t u f f beds are considered by some workers to have o r i g i n a t e d from the same source as Zn and Pb f o r that deposit (Bennet, 1967). No such beds were found in the Howards Pass format ion. ORGANIC CARBON ( C ( o r g ) l Up to 12% organic carbon (C( 0 rg ) ) ^ s P r e s e n t in the Howards Pass format ion , based on est imat ion by loss on i g n i t i o n at 550°C (Dean, 1974). Since an organic carbon content of less than 0.5% and/or t races of f i n e grained pyr i te can cause the dark co lour of "black s h a l e s " , est imat ion of organic carbon C ( o r g ) should be given fo r mudstones. The Howards Pass format ion, for example, i s the only major rock unit in the map area (Plate I) which contains over 1% C ( o r g ) whereas x-= 4.95% i s t y p i c a l of black shales analyzed by Vine and T o u r t e l o t (1970). The highest values f o r C ( o r g ) found in the Howards Pass area are in the lower cherty mudstone member, in which x= 6.50%. T h i s is much higher than the organic carbon content of host rocks associa ted with other s t r a t i f o r m d e p o s i t s . For example, "black shales" in the McArthur River deposi t contain less than 1% C ( o r g ) (Lambert, 1976) and there i s less than 0.5% carbon in sediments near the Red Sea br ine pools 208 (Sweeney and Kaplan , 1973). T h u s , the Howards Pass formation has an organic carbon content more t y p i c a l of h ighly carbonaceous black shales than those sediments associated with other s t r a t i f o r m ore d e p o s i t s . SULPHUR Sulphur i s most abundant in the a c t i v e and lower cherty mudstone members, with means of 2.95 and 2.62% r e s p e c t i v e l y . The high concentra-t i o n s of spha le r i t e and galena and the presence of pyr i te explains the high concentrat ions of S in the ac t ive member. In the lower cherty mud-stone the sulphur could occur in pyr i te and organic sulphur which, ac-cording to Smith and Batts (1977), may cons t i tu te up to 3 wt.% of the organic matter. PHOSPHATE The mean P 2 O 5 contents of the members of the Howards Pass formation range from 0.2% to 1.17%, and are in general higher than the average of 0.15% f o r carbonaceous shales reported by McKelvey (1967). In the Howards Pass formation phosphate shows no s i g n i f i c a n t c o r r e l a t i o n with any other element. The upper s i l i c e o u s mudstone member is character ized by a high P 2 O 5 content compared to the rest of the formation ( F i g . V I - 3 c ) , and shows the highest P2O5 concentrat ion associa ted with the g r a p t o l i t e zone near the top of the member. C l a s s i c a l l y , in the study of phosphor i tes , upwell ing has been considered of great importance in the concentrat ion of phosphate (Freas and Eckstrom, 1968). Cook (1970) has shown that d iagenet ic phosphat iza t ion , c a l c i t i z a t i o n and s i l i c i f i c a -t ion w i l l occur r e a d i l y , and are probably in response to changes of pH. Deposi t ion of phosphate at the sediment-water in te r face does not appear 209 to be s i g n i f i c a n t , but the presence of organic matter and/or bacter ia (Trudinger, 1976) and a genera l ly reducing environment (Senin, 1970) are usua l ly associated with high phosphate (Cook, 1970). The lack of a s p e c i f i c C ( o r g) -P205 a s s o c i a t i o n in the Howards Pass formation suggest that d iagenet ic deposi t ion may have been important. SILICA AND ALUMINA The means fo r SiO2 content of the members of the Howards Pass f o r -mation range from 48 to 93% (Table VI-1) and the mean for the formation i s 64.8%, which is s i m i l a r to 55 to 64% reported by Clark (1924) for 51 Paleozoic s h a l e s . Most of the S i02 in the Howards Pass formation i s chert which was deposited as amorphous s i l i c a (Friedman and Sanders, 1978); therefore the S i 0 2 content r e f l e c t s the proport ions of chert r e l a t i v e to carbonate, carbonaceous matter , p h y l l o s i l i c a t e s and s u l -phides. For example, the lower S i02 content of 50% in the ac t ive member i s because of r e l a t i v e l y more carbonate and s u l p h i d e . T h u s , the l i g h t grey chert f a c i e s contains over 99% S i 0 2 compared to the whit ish grey Zn-Pb mudstone which contains 50 to 60% Si02> suggesting that the change between the two is because of a change in the S i 0 2 : ZnS + PbS r a t i o ; away from the s u b - b a s i n s , sedimentation continued with e s s e n t i a l l y constant S i 0 2 : C ( o r g ) + carbonate + p h y l l o s i l i c a t e + sulphide r a t i o s . The Al2O3 content of the Howards Pass formation is low compared to that of other black shales and to that of other mudstones in the area . For the Howards Pass formation x =0.67% AI2O3 compared to an average of 13.23% reported by Vine and T o u r t e l o t (1970). The s i g n i f i c a n t p o s i t i v e 210 c o r r e l a t i o n between Al2 O 3 and K 2 0 and the lack of fe ldspar suggest that A l 2 O 3 occurs in micas and c l a y s , which are rare in the Howards Pass format ion . MICROCHEMISTRY The chemistry of ind iv idua l laminae, modif ied water escape s t r u c -tures and ind iv idua l grains of sulphide were invest igated by e lec t ron microprobe. Nine elements were analyzed f o r , Zn , Pb, Fe , S, K, Ca , Mg, Si and A l . Within the th in bedded cherty mudstone f a c i e s , Zn occurs predominantly in monomineralic ZnS laminae, but a lso to a l esser degree in F e - r i c h laminae. T h i s supports the microscopic observat ion that most s p h a l e r i t e in the XY deposi t occurs as monomineralic laminae. Micro-scopic study of textura l type I did not ind ica te enough galena to ac-count f o r concentrat ions of Pb in the samples. Probe i n v e s t i g a t i o n of t h i s textura l type shows that Pb is associated with framboidal pyr i te ( F i g . V I -18) , but i t i s not known i f the pyr i te contains enough Pb to account f o r the discrepancy between v isua l and chemical data f o r Pb. Zinc and Pb have been reported associated with organic matter in s i m i l a r carbonaceous mudstones (Macqueen et a l . , 1975), but no such a s s o c i a t i o n was found in the Howards Pass format ion; i t appears that a l l Zn and Pb occurs in su lph ides . If Zn and Pb previously existed in metal1-organic complexes these have since been a l t e r e d , with the metals forming s u l -phides. Microprobe t raverses across t e c t o n i c a l l y modif ied water escape st ructures which are f i l l e d with textura l type IVb sulphides show great -er concentrat ions of Zn, Pb, Fe and S than are found in other parts of the whit ish grey Zn-Pb mudstone fac ies ( F i g . VI -19) . Local increases in 211 c . d . F igure VI-18. Microprobe scanning images of framboidal pyr i te g r a i n s , a . Fe Ka x-rays showing o u t l i n e of framboids, b. S Ka x- rays showing o u t l i n e of framboids, c . Si Ka x-rays showing s i l i c a t e s surrounding p y r i t e and d. Pb Ka x-rays showing that minor amounts of Pb occur in the framboidal p y r i t e . Largest framboid is 45 pm a c r o s s . Figure VI-19. Microprobe t raverse across dewatering structures in the whit ish grey Zn-Pb mudstone f a c i e s , showing chemical d i f fe rences between cleavage and sedimentary l i t h o l o g i e s . Num-bers at l e f t re fe r to l i t h o l o g i e s ; 1) textural . type II, 2): textural type IVa, 3) textural type IVb. Tota l length of t raverse i s 7.0 mm. 213 K, Mg and Al ind ica te the presence of c lays in t h i s textura l type . Com-parison of data for Zn and Pb ( F i g . VI-19) show that galena occurs in narrow d i s c r e t e bands in the massive s p h a l e r i t e . Ca lc ium, in the form of c a l c i t e , is a lso concentrated along the contacts of the water escape s t r u c t u r e s , but only where cleavage is present . Microprobe t raverses across laminae present in the whi t ish grey Zn-Pb mudstone ind ica te that chemical v a r i a t i o n i s complex ( F i g . V I -20) , and that more de ta i l ed microprobe studies are warranted. SUMMARY The geochemical data from' the Howards Pass formation and the asso-c ia ted deposi ts ind ica te that the environment of base metal deposi t ion d i f f e r s from that proposed for apparently s i m i l a r deposi ts elsewhere. Chemical c h a r a c t e r i s t i c s of the deposi ts are: (1) low Ba content in and near to the d e p o s i t s , (2) homogeneity of Fe content throughout the s t r a t i g r a p h i c s e c t i o n , inc lud ing that part of sect ion contain ing Zn-Pb s u l p h i d e s , (3) lack of increase in Ag content in the sulphide d e p o s i t s , (4) consistency of Co: Ni r a t i o s throughout the Howards Pass format ion , (5) V concentrat ion in the lower cherty mudstone member, (6) lack of high-K20 t u f f beds underly ing the Zn-Pb deposi ts and (7) lack of Cu associa ted with the Zn-Pb d e p o s i t s . These chemical c h a r a c t e r i s t i c s help d i f f e r e n t i a t e the Howards Pass deposi ts from other s t ra t i fo rm sedimen-tary sulphide d e p o s i t s . Figure VI-20. Microprobe t raverse across lamination in the th in bedded cherty mudstone f a c i e s , showing v a r i a t i o n s in chemistry with Zn and Pb. Data is semi-quant i ta t ive with i n -c reas ing concentrat ion towards the r i g h t . Numbers re fer to l i t h o l o g i e s ; 1) carbonaceous mud-s tone , 2) s i l i c e o u s mudstone, 3) spha le r i te r i ch mudstone, 4) spha ler i te -ga lena r ich mudstone, 5) s p h a l e r i t e - g a l e n a - p y r i t e r i c h mudstone. Tota l length of t raverse is 8.2 mm. 215 CHAPTER VII SULPHUR ISOTOPES INTRODUCTION The o r i g i n of the sulphur component of the Howards Pass Zn-Pb de-pos i ts i s important because p r e c i p i t a t i o n and therefore f i x a t i o n , of base metals i s re la ted to the a v a i l a b i l i t y and valence state of s u l -phur. Sulphur has four stable isotopes with the fo l lowing natural abun-dances: 3 2 S = 9 5 . 0 2 % , 3 3 s = 0.76%, 3 4 s = 4 . 5 5 % , 3 6 s = o.014%. The i s o t o p i c composition of sulphur in nature ranges widely and as such may be used as an i n d i c a t o r of the source of the sulphur and the mode of formation of su lph ide . An a t t r i b u t e of sulphur that makes i t p a r t i c u -l a r l y valuable in the present context i s i t s apparent a b i l i t y to re ta in i t s o r i g i n a l i s o t o p i c composition throughout most, i f not a l l , the post-deposi t iona l processes a f f e c t i n g the deposit in which i t is contained (Sangster , 1976). Some i s o t o p i c exchange may take place between minerals at high metamorphic grades, but the Howards Pass deposits are unmetamorphosed, so th is is not important. Sulphur isotope v a r i a t i o n s are genera l ly considered in terms of the abundance r a t i o of the two p r inc ipa l i so topes . The range of v a r i a t i o n of 345/325 ^ n a t U r e i s approximately 10% and when r e f e r r i n g to d i f fe rences of isotope abundance ra t ios between samples i t i s most common prac t ice to use the "de l " notat ion where: 6 3 4 s (o/oo) = (34s/32 S ) s a m p 1 e - ( 3 4 S / 3 2 S ) standard y IQOO ( 3 4S/32s) standard gives the permil d i f fe rence in isotope r a t i o between a sample and a standard (Thode et a - ! . , 1961). The genera l ly accepted standard is 216 34 32 t r o i l i t e f r o m t h e Canyon D i a b l o m e t e o r i t e , w h i c h has a S/ S r a t i o o f 22.22 o/oo ( T h o d e , 1970).. In n a t u r e , t h e d i f f e r e n t f o r m s o f s u l p h u r show an o v e r a l l r a n g e o f 34 34 i s o t o p i c v a l u e s o f a b o u t 100 o/oo f o r & S. V a l u e s f o r 6 S a r e r e m a r k a b l y c o n s t a n t f o r a l l p r e s e n t d a y o c e a n s and s e a s and i t i s r e a s o n a b l e t o assume t h a t t h e y have been u n i f o r m a t any p a r t i c u l a r t i m e i n t h e p a s t ( T h o d e and M o n s t e r , 1 9 6 5 ) . The s t u d y o f m a r i n e e v a p o r i t e s a s s o c i a t i e d w i t h a n c i e n t o c e a n s ( T h o d e and M o n s t e r , 1965; H o l s e r and N 34 K a p l a n , 1966) show t h a t t h e 6 S v a l u e o f s e a w a t e r s u l p h a t e has v a r i e d w i d e l y o v e r g e o l o g i c t i m e , between a p p r o x i m a t e l y +30o/oo and + I O 0 / 0 0 ( F i g . V11 - 1 ) . B a s e d on t h e same methods u s e d by T h ode e t a l . (1958) f o r s h o w i n g t h a t p e t r o l e u m and c o e v a l s e a w a t e r s u l p h a t e a r e r e l a t e d , S a n g s t e r (1968, 1971) made a s t r o n g c a s e f o r t h e d e r i v a t i o n o f s t r a t a b o u n d m a r i n e s u l p h i d e d e p o s i t s f r o m c o e v a l s e a w a t e r s u l p h a t e ( F i g . V11 - 1 ) . T h u s , i f s e a w a t e r s u l p h a t e i s t h e s o u r c e o f s u l p h u r f o r t h e s u l p h i d e s t h e s e may be u s e d as a r o u g h age d a t i n g t e c h n i q u e . METHODS AND RESULTS S a m p l e s f o r s u l p h u r i s o t o p e s t u d y were c o l l e c t e d on t h e b a s i s o f l i t h o l o g y d r i l l c o r e s f r o m t h e Howards P a s s f o r m a t i o n , and i n c l u d e t h e w h i t i s h g r e y Zn-Pb m u d s t o n e , t h e t h i n b e d d e d c h e r t y m u d s t o n e and t h e t h i n b e d d e d c a l c a r e o u s m u d s t o n e f a c i e s . T h e s e were e x a m i n e d , c r u s h e d and s e n t t o t h e U n i v e r s i t y o f A l b e r t a where t h e y were a n a l y z e d f o r S i s o t o p i c c o m p o s i t i o n s u s i n g a N i e r - t y p e d o u b l e - i n l e t g a s s o u r c e mass s p e c t r o m e t e r ( A p p e n d i x F ) . The r e s u l t s o f t h e a n a l y s e s a r e p r e s e n t e d i n T a b l e V 1 1 - 1 . T h e s e d a t a show t h a t g a l e n a has a mean 6 *^S o f 15.17 0 / 0 0 (S = 3 . 6 8 % ) , s p h a l e r i t e = 19.68 0 / 0 0 , (S = 3.30%) and p y r i t e 2 1 7 PERIOD Q U A T E R N A R Y T E R T I A R Y C R E T A C E O U S J U R A S S I C T R I A S S I C PERMIAN C A R B O N I F E R O U S D E V O N I A N S I L U R I A N O R O O V I C I A N C A M B R I A N 21.50 21.75 22.C0 22 2 5 22.50 Figure V I I -1 . Average 6^4$ values for seawater sulphate for geologic time ( s o l i d l i ne ) and sulphur in petroleum (dashed l i n e ) . F rac t iona t ion f a c -to r average = 13.8 (modified from Thode et a l . , 1958). 218 Tab le VI I -1 . Sulphur isotope ra t ios for the Howards Pass d e p o s i t s . Sample No. 6 34 s ( 0 / o o ) Galena Spha le r i te Pyr i t e HP-S-1 22.3 26.2 HP-S-2 17.6 21.2 22.7 HP-S-3 11.1 15.0 HP-S-4 17.9 21.9 23.5 HP-S-5 18.2 22.1 21.1 HP-S-6 10.7 16.9 17.0 HP-S-7 17.7 21.6 HP-S-8 11.9 4.1 HP-S-9 13.0 18.1 HP-S-10 12.0 20.1 19.6 HP-S-11 11.3 15.3 1.4 HP-S-12 12.6 16.6 HP-S-13 13.6 21.0 HP-S-14 20.4 24.6 HP-S-15 11.8 15.8 HP-S-16 13.3 19.4 -3 .2 HP-S-17 8.5 16.6 HP-S-18 14.8 HP-S-19 19.3 HP-S-20 17.3 21.3 HP-S-21 19.3 HP-S-22 17.7 21.6 23.0 HP-S-23 13.2 16.8 14.8 HP-S-24 18.5 22.4 X 15.17 19.68 15.6? S 3.68 3.30 9.0' B a r i t e from f laggy mudstone formation Standard NBA 1.1 23.7 24.6 219 15.69 o/oo (S = 9.04%). An ana lys is of b a r i t e from the f laggy mudstone formation produced a value of 6 ^ = 23.7 o/oo which is very c lose to that of S i l u r i a n seawater sulphate (Holser and Kaplan, 1966). DISCUSSION A histogram of the i s o t o p i c data ( F i g . VII-2) shows a d i s t i n c t b i -modal d i s t r i b u t i o n fo r data from spha le r i t e and ga lena. Pyr i t e on the other hand shows a wide range of values and only a weak bimodal d i s t r i -b u t i o n . T h i s and the abundance of d i s e q u i l i b r i u m textures (Stanton, 1972) between framboidal pyr i te and the other sulphides suggest that p y r i t e and the other sulphides have a separate o r i g i n and/or time of format ion. Spha le r i t e i s the major sulphide phase in the deposits and is thus the most important phase to cons ider . Isotopic values for s p h a l e r i t e were s t r a t i g r a p h i c a l l y grouped, fo r the th in bedded calcareous mudstone ( x= 15.37 o / o o ) , the th in bedded cherty mudstone ( x = 17.96 o/oo) and the whi t ish grey Zn-Pb mudstone ( x = 22.56 o/oo) f a c i e s ( F i g . V I I -3 ) . Two s p h a l e r i t e samples from textura l type V are not included because they may have formed subsequent to the other spha le r i t e in the f a c i e s . The theory of i s o t o p i c e f f e c t s has been discussed by var ious authors (Thode, 1970, Hoefs , 1973). There are three bas ic problems which must be considered in the o r i g i n of the Howards Pass su lph ide ; (1) source of the su lphur , (2) nature of the processes operat ive during formation of the sulphide and (3) the formation of the sulphide miner-a l s . In the present d iscuss ion sulphur isotopes and other geologic data are used to evaluate each of the three s teps . Barite Sph Gn Py SULPHUR ISOTOPE DATA FOR HOWARDS PASS -Estimated seawater sulphate •i—h Hill II I • III I I I till 1 l l l l l l IIII I I H—I I i i t 26 24 I 20 I ie i 12 4 I I -4 c f M S % 'oo 6 5 o z Iii z> a u tr a. j 5 TTJI <f" S INTERVAL -17 OBSERVATIONS P 5 > O z 3 o UJ cr u. 5 s 8 i ± cf^S INTERVAL T 24 OBSERVATIONS Figure VI1-2. D i s t r i b u t i o n of sulphur isotope data from the Howards Pass d e p o s i t s , a . Individual analyses p lo t ted r e l a t i v e to S i l u r i a n seawater sulphate, b. Frequency d i s -t r i b u t i o n for i s o t o p i c data from spha le r i te and galena. 221 Figure VI I -3 . Sulphur isotope values fo r associated fac ies in the act ive member. Isotopic values are p lot ted with associated ac t ive member f a c i e s . Squares represent samples with s i g n i f i c a n t amounts of textura l types V and/or VI . Facies of the ac t ive member are shown by number: 1) l i g h t grey basal l imestone, 2) graded l imestone, 3) th in bedded calcareous mudstone, 4) mixed cherty mudstone and l imestone, 5) cherty mudstone, 6) th in bedded cherty mudstone, 7) whi t ish grey Zn-Pb mudstone and 8) grey c h e r t . Within the ideal cyc le there is a general trend of greater 6 34$ values proceeding up sect ion wi thin the c y c l e . 222 ORIGIN OF THE SULPHUR Three major sources of sulphate are poss ib le in sulphide deposi ts: magmatic su lphur , sulphur leached from nearby rock or sediments and sea-water sulphate (Hoefs, 1973). In the case of sedimentary s t r a t i f o r m deposi ts s i m i l a r to those at Howards Pass , the sulphur may be S04= from contemporaneous seawater, from geothermal emanations, which may or may not be volcanogenic , or a combination of the two (Hoefs, 1973; Faure, 1977). The lack of evidence fo r an external source for sulphur ( i . e . magmatic or hydrothermal) in the Howards Pass formation suggests that seawater sulphate was the major source fo r the su lph ide . Deta i led i s o -top ic inves t iga t ions on other high organic carbon environments such as high sulphur coals have demonstrated the seawater sulphate is the major ( > 90%) source of sulphur (Smith and B a t t s , 1977). MECHANISM OF SULPHATE REDUCTION The reduct ion of sulphate to sulphide may be the resu l t of inorga-nic or b i o l o g i c a l reduct ion . The former has been proposed as the domi-nant process in hydrothermal ore deposits (Rye and Ohmoto, 1974) while the l a t t e r is the major process operating in modern sedimentary env i ron-ments (Berner, 1971; 1974). C i r c u l a t i o n of marine sulphate through the sedimentary p i l e could resu l t in chemical reduct ion by react ion with organic compounds above 80°C (Orr , 1974) or by react ion with inorganic compounds (Bonat t i , 1975). Regional mapping of over 700 km 2 at a sca le of 1:31 ,680 (Morganti , 1976) (Plate I) shows no evidence of hydrothermal a l t e r a t i o n which would be suggestive of such a hydrothermal c i r c u l a t i o n system in the Howards Pass area (Plate I ) . T h i s is s i g n i f i c a n t , because in most cases where a model of large sca le c i r c u l a t i o n has been pro-223 posed, using C, D and H i s o t o p i c r a t i o s , evidence of the c i r c u l a t i o n system is obtainable by f i e l d techniques (Rye and Ohmoto, 1974; T a y l o r , 1974; Sheppard et a l . , 1971). Deta i led mapping of the 190 km2 su r -rounding the Howards Pass c la im group at a scale of 1:4800 (Morganti , 1976) and de ta i led logging of diamond d r i l l core has not ind icated any evidence of a l t e r a t i o n or a "feeder system" for the deposits within the area covered in P la te I. The only poss ib le hydrothermal a l t e r a t i o n noted in the area is weak dolomi t ic a l t e r a t i o n associated with f a u l t s in the wavy banded limestone format ion. These a l t e r a t i o n zones are genera l ly less than 5 m a c r o s s , are associated with a l l ages of s t r i k e f a u l t s and are therefore considered to be unrelated to the o r i g i n of the d e p o s i t s . Furthermore no evidence of sulphide minera l i za t ion has been found associated with these f a u l t s , and veins which are present within the Howards Pass formation are rare: those that are present r e f l e c t the composition of the host rock. For example, veins which cut the c a l c a -reous mudstone member are predominantly ca lcareous , while those cu t t ing the lower cherty mudstone member are predominantly s i l i c e o u s . T h i s suggests that material in veins was derived from the surrounding areas and not in t roduced. T h u s , there i s no evidence fo r the addi t ion of material to the formation such as would be the case i f deep c i r c u l a t i o n were to have produced the sulphide (Bona t t i , 1975; Spooner and F y f e , 1973). Regional mapping and d e t a i l e d inves t iga t ions of d r i l l c o r e , using both quant i ta t ive chemical analyses and chemical s ta in ing techniques (Bennett , 1967) ind ica te that there are no tuffaceous horizons or other evidence of volcanism in the the Howards Pass formation in the map-area (Plate I ) . The only d iagnost ic evidence of tuffaceous horizons in the 224 Pa leozo ic s t r a t i g r a p h i c sect ion in the map area is in the lower s i l t -stone, wavy banded limestone and f laggy mudstone formations It may be s i g n i f i c a n t that there are minor dark green t u f f s and basa l t in the Howards Pass formation wi th in 1 km of the shale-out at the South Nahanni R i v e r , but s t i l l there is no evidence of an abnormally high geothermal gradient which could have caused shallow chemical reduction of sulphur in the Howards Pass map a rea . Since at low temperatures the chemical reduct ion of sulphate to sulphide is van ish ing ly low, the metabolic a c t i v i t y of anaerobic sulphate-reducing b a c t e r i a , notably forms such as Desu l fov ib r io and Desulfotomaculum ( Z o b e l l , 1958; McReedy, 1975), could become an important fac tor in the formation of s u l p h i d e . Many studies have been made concerning microbia l f r a c t i o n a t i o n of sulphur isotopes (Kaplan and R i t tenberg , 1964; Kaplan et a l . , 1963). The normal maximum b i o l o g i c a l f r a c t i o n a t i o n of 25 o/oo is fa r less than the t h e o r e t i c a l f r a c t i o n a t i o n of 74 o/oo at 25°C and i s a measure of the e f fec t iveness of these bacter ia in reaching e q u i l i b r i u m . The general scheme ( F i g . VII-4) shows that the f r a c t i o n a t i o n occurs in several steps with the f i n a l 6 34 S showing the combined e f f e c t . The isotope e f fec ts poss ib le in these steps have been discussed by Harr ison and Thode (1958), Kaplan and Rit tenberg (1964), Kemp and Thode (1958), Rees, (1973). Large sulphur isotope e f fec ts are associated with the react ion steps which invo lve the breaking of sulphur-oxygen bonds; the conversion of APS (adenosine - 5' - phosphosulphonate) to su lph i te and of su lph i te to hydrogen su lph ide . The assignment of values of 25 o/oo to each of these ind icated in f i g u r e VI1-4 is only an approximation and represents CELL WALL ENZYME AND METABOLITES A T P ATP SULPHURYLASE H + Fe 2 + APS REDUCTASE ® ( 3%o) EXTERNAL SULPHATE 10) t25%o) ® (25%o) INTERNAL SULPHATE APS SULPHITE HYDROGEN SULPHIDE Figure VI I -4. Reaction scheme fo r D. d e s u l f u r i c a n s . The various sulphur species are shown together with enzymes and metabolites required to promote react ions to the r i g h t . The numbers in brackets are the isotope e f fec ts assigned to the indiv idual react ion steps (based on data from Rees, 1973). cn 226 a combination of the information a v a i l a b l e from inorganic isotope studies and theore t i ca l cons idera t ion (Thode, 1970; Rees, 1973). Proposed models fo r the i s o t o p i c f r a c t i o n a t i o n produced in the re -duct ion of sulphate by Desul fov ibro have assumed react ion sequences which are f i r s t order with respect to sulphur species concent ra t ions . Harr ison et a l . (1957) observed tha t , fo r rest ing stage c e l l suspensions of the bacter ium, the rate of hydrogen sulphide production was indepen-dent of reactant sulphate concentrat ion values greater than 10~ 2 M. The existence of the rate plateau (Caspers, 1957) ind ica tes that the uptake of sulphate by Desu l fov ib r io is f i r s t order with respect to sulphate at low sulphate concentrat ions on ly . At higher concentrat ions the rate of uptake is l imi ted by some other f a c t o r s , such as the concentrat ion of b a c t e r i o l o g i c a l l y u t i l i z a b l e organic carbon (Berner , 1971; R i c k a r d , 1973). Such a s teady-s ta te system is reasonable for a high organic car -bon environment such as the Howards Pass format ion, but with sulphate u l t imate ly l i m i t i n g sulphide product ion. The above model of microbial sulphur reduct ion has been appl ied to sulphur associa ted with petroleum deposi ts (Thode et a l . , 1958; Harr ison and Thode et a l . , 1958) and summarized by Thode and Rees (1970). Thode and Monster (1965) compared 6 34$ of sulphide in petroleum with contem-poraneous seawater and found that the sulphide was depleted in 6 ^^s by 15 o/oo compared to the contemporaneous seawater sulphate . Only major consumption of most S04= within a c losed basin could account f o r a system in which the f i n a l i s o t o p i c composition equals the o r i g i n a l i s o -top ic composition of seawater sulphate (Sangster , 1976; Rees, 1973). In such a system sulphate would be the l i m i t i n g f a c t o r . Such a system 227 would have a higher H2S/SO4 r a t i o than an organic carbon l i m i t i n g case because most of the SO4 would be consumed. SULPHIDE DEPOSITION Sakai (1968) presented data that ind ica te that the composition of the sulphur in sulphide phases forming in equ i l ib r ium was a f fec ted by i s o t o p i c f r a c t i o n a t i o n f a c t o r s . Ohmoto (1972) quant i f i ed these fac to rs and produced an i s o t o p i c geothermometer fo r the p a r t i t i o n i n g of sulphur between various sulphur s p e c i e s . These data , presented by Sakai (1968) and summarized by Ohmoto (1972) fo r 1 5 0 ° C , have been extrapolated to more reasonable temperatures for sediments by Campbell et a l . (1978) (Table V I I -2 ) . The int imate intergrowth of spha le r i t e and galena in the Howards Pass deposits ind ica tes that equ i l ib r ium may have been approach-ed during t h e i r format ion. The lack of an "ore stage" pyr i te and the large range of pyr i te i s o t o p i c values suggest that pyr i te may not have been in equ i l ib r ium with the other two sulphide s p e c i e s . The major fac tors which control the sulphur i so top ic composition in minerals forming in equ i l ib r ium are: (1) temperature, which determines the f r a c t i o n a t i o n between sulphur-bear ing s p e c i e s , (2) 6 ^^S, which is c o n t r o l l e d by the source of the sulphur and (3) the proport ions of o x i -dized and reduced sulphur species in s o l u t i o n . The lack of evidence of thermal a c t i v i t y during deposi t ion of the Howards Pass deposits suggests that the temperature was low, poss ib ly 25° to 5 0 ° C , and that the sulphur source was constant , poss ib ly seawater sulphate or an immediate d e r i v a -t i v e of seawater sulphate . I f th is were so then f r a c t i o n a t i o n would be the resu l t of the proport ions of oxid ized and reduced sulphur s p e c i e s . TABLE VI1-2 VALUES FOR THE PARTITIONING OF SULPHUR BETWEEN SULPHUR SPECIES 25°C 50°C 100°C 150°C A H 2S 0 0 0 0 A S 0 4 2 " 73.5 64 50 39 A ZnS +1.5 +0.6 -0 .8 -0 .9 A PbS -8.2 -7 .4 -6 .0 -5.1 A FeS 2 +4.2 +3.3 +1.6 +0.8 Taken from Ohmoto (1972, F i g . 1 . ) . 229 T h r e e f u r t h e r a s s u m p t i o n s must be made i f i s o t o p i c c o m p o s i t i o n i s t o be a f u n c t i o n o f t h e p r o p o r t i o n s o f t h e o x i d i z e d and r e d u c e d s u l p h u r s p e c i e s : (1) T h a t t h e r e was l i t t l e c h a n g e i n t h e pH d u r i n g s u l p h i d e d e p o s i t i o n . T h i s i s s u p p o r t e d by e v i d e n c e f r o m t h e Red S e a ( B r o o k s e t a l . , 1969) and g e o c h e m i c a l m o d e l l i n g o f low t e m p e r a t u r e b r i n e s ( S h a n k s and B i s c h o f f , 1 9 7 7 ) , b u t i s q u e s t i o n a b l e f o r Howards P a s s u n l e s s i t i s assumed t h a t w i t h i n t h e i n t e r v a l o f s u l p h i d e d e p o s i t i o n t h e pH was r e a s o n a b l y c o n s t a n t . (2) T h a t t h e s u l p h u r i s o t o p i c c o m p o s i t i o n o f s p h a l e r i t e and g a l e n a have n o t c h a n g e d s i n c e f o r m a t i o n i s s u p p o r t e d by t h e l a c k o f any met a m o r p h i s m o f t h e d e p o s i t s . (3) T h a t t h e s u l p h u r s o u r c e had an e s s e n t i a l l y c o n s t a n t i s o t o p i c c o m p o s i t i o n , w h i c h i s r e a s o n a b l e i f s e a w a t e r s u l p h a t e o r a c o n s t a n t d e r i v a t i v e i s t h e s u l p h u r s o u r c e ( R e e s , 1 9 7 3 ) . B a s e d on Ohmoto's (1972) o r i g i n a l c a l c u l a t i o n s , C a m p b e l l e t a l . (1978) have shown t h a t t h e f o l l o w i n g r e l a t i o n s h i p s a r e a p p l i c a b l e t o a s e d i m e n t a r y e n v i r o n m e n t . 5 3 l + S i = *3khS + AH 2S_i - C A S 0 = _ H 2S ( 1 - X H 2 S ) ] ( 1 ) w i t h , f o r an o r i g i n a l homogeneous s u l p h a t e s o u r c e where 6 3 4 S ^ s a n < ^ 6 3 L T S 0 4 = A R E E 1 u a t e d , c a n be t r a n s f o r m e d t o ( S 3' +S i)-(6 3 1 +S< ; N= «. 0= u C X A P _ c \ X S 0 4 - S0 4-H2S+ H 2S-S-j -) H2<> = — (2) AS04-H 2S F o r a s e d i m e n t a r y e n v i r o n m e n t where t h e t h r e e above a s s u m p t i o n s a p p l y , e q u a t i o n (2) may be s i m p l i f i e d t o c a l c . XH 2S = : : — (3) AS04-H 2S where XL|2$ i s t h e m o l e f r a c t i o n H 2S a s s u m i n g H 2S and S04 = a r e t h e 230 s i g n i f i c a n t S species (Nissembaum et a l . , 1972), ( 6 3 4 S m - j n ) i s f o r the observed mineral and ( 6 3 4 S m - j n ) c a l c . i s f o r the ca lcu la ted mineral s p e c i e s . The three groups of i s o t o p i c data ( F i g . VII-3) when subst i tu ted into the appropriate formulae suggest that possib ly the idea l i zed ac t ive member cyc le records the evolut ion of the s u b - b a s i n , and shows a general increase in the XL^S during development of a c y c l e . The general i n -crease in XLJ^S suggests a general increase in the i s o l a t i o n of the sub- basin in which the a c t i v e member was depos i ted , s ince the reducing nature of the sub-basin is a measure of i s o l a t i o n (Ca lve r t , 1964). A comparison of sulphate source i s o t o p i c compositions ( F i g . VII-5) shows that i f the sub-basin was a system open to sulphate during b a c t e r i -al r e d u c t i o n , spha le r i t e should be much more depleted in 3 4 S than the source seawater sulphate . If i t i s assumed that the sub-basin was a system c losed with respect to sulphate then a more reasonable comparison is obtained between the ca lcu la ted and observed va lues . Comparison of the XLJ^S values obtained from the i s o t o p i c com-p o s i t i o n of sulphides from the Howards Pass deposits and those obtained from the Red Sea and the S u l l i v a n Mine (Kaplan et a l . , 1969; Campbell et a l . , 1978) suggest that the Howards Pass sub-basins were more reducing than those of these more thoroughly studied d e p o s i t s . The reason fo r t h i s d i f f e rence may be re la ted to the occurrence of magnetite in the other two d e p o s i t s . As demonstrated by Shanks and B i s c h o f f (1977) the f0£ in low temperatures br ines may be buffered by magnetite-hematite e q u i l i b r i u m . The Howards Pass d e p o s i t s , on the other hand, show no e v i -dence of the presence of F e 3 + during sulphide format ion. .231 5 0 ° C XH 2 S = 1.0 Sph = +24.6%«J XH Z S =0.75 Sph =+8.6 %o XH 2 S*0 .50 sph= -r.4%oi XH,S = 0.25 Sph=-23.4%ol XHJS = 0 S04 2 "»+24%ol 2 5 ° C XH«S«"|.0 Sph= + 22.3%© XH 2 S * 0.75 Sph =+4.12 % o XH 2S = 0.50 sph = - U 3 % o XH 2 S = 0.25 sph* -32.63%o XH 2S = 0 S042"=+24%o Totally Closed A A A A at w C» a -a « •o — a> *• s-l •"5 c • M O to a « w U e tn «i x X CO 4> VI O « w o . in •o o . c o o ut 8 m O <D w <J C UJ « 3 UJ .5 »• VI o i -O 3 CO c e o u (O s Totally open no sphalerite formed. Figure VII-5- Diagram showing r e l a t i o n s h i p of X^„s t o sub-basin condi t ions at 25° C and 50°C, assuming a seawater sulpriate source fo r sulphur of 24.0 o /oo . A l l examples are based on c a l c u l a t i o n s that spha le r i t e i s the major sulphide mineral forming. The f o r 50° C more c l o s e l y approximate the data from Howards Pass f o r 25° C. and assume X H 2s value tfran those 232 SUMMARY Sulphur i so top ic and geologic data are consistent with the sugges-t i o n that seawater sulphate was the source of sulphide in the Howards Pass d e p o s i t s . Four models of sulphide generation are possib le for a sedimentary environment such as that present during deposi t ion of the Howards Pass d e p o s i t s . These include: (1) d i rec t bac te r i a l reduct ion of su lphate , (2) sulphate reduction by biogenic methane, (3) sulphate reduct ion by abiogenic methane and (4) reduct ion by deep c i r c u l a t i n g waters in the underlying sediments. The lack of any evidence of a geo-thermal system suggestive of temperature > 80°C (Or r , 1976) suggests that bac te r ia l reduction of sulphate is a most probable mechanism. If c o r r e c t , the lack of ^2$ enrichment noted in H 2S from o i l deposi ts (Thode and Rees, 1970) suggests a r e s t r i c t e d system in which sulphate was the l i m i t i n g f a c t o r during formation of s u l p h i d e . G e o l o g i c a l l y reasonable assumptions al low f o r an est imation of X ^ s during s u l -phide d e p o s i t i o n , which is a lso an est imation of r e l a t i v e i s o l a t i o n of the sub -bas in . Grouping of i s o t o p i c data by l i t h o l o g y ind ica tes that the t h i n bedded calcareous mudstone, the th in bedded cherty mudstone and the whit ish grey Zn-Pb mudstone fac ies ind ica te inc reas ing ly reducing c o n d i -t ions and progressive r e s t r i c t i o n of the s u b - b a s i n s . T h i s reasoning in turn supports a model postulat ing the existence of an ideal c y c l e sequence in the ac t ive member. 233 CHAPTER VIII LEAD ISOTOPES INTRODUCTION The rad ioac t ive decay of uranium and thorium to lead as well as the i s o -top ic va r ia t ions of lead in uranium-free ores are of great importance f o r an understanding of the genesis of ore d e p o s i t s . Only the common lead method was used on samples from the Howards Pass d e p o s i t s . Common lead i s any lead from a mineral phase with a low value of U/Pb and/or Th/Pb such that no s i g n i f i c a n t radiogenic lead has been generated in  s i t u s ince the phase formed. Such phases are galena and other sulphides such as pyr i te and spha le r i t e and a lso some fe ldspars and micas. The use of common leads dates back to Nier (1938) with the develop-ment of the mass spectrometer. Since that time to 1959 continued pro-gress was made, but in the e a r l y 1960s refinement of spectrometr ic techniques and mathematical in te rpre ta t ions star ted a new era in lead isotope inves t iga t ions (Russel l and Farquhar, 1960; Kanasewich, 1968; Doe and Stacey, 1974). Over the past few years the a p p l i c a t i o n of new geologic models to the in te rp re ta t ion of lead isotopes seems to have caused another period of rapid evolut ion in the f i e l d of lead isotopes (R ichards , 1971; Stacey and Kramers, 1975; Sangster , 1976; Faure, 1977). Natural va r ia t ions in the i s o t o p i c composition of lead resu l t from the generation of 2 0 6 P b ^7Pb and 208pb as the stable end products of 238y } 235u a n ( j 232 j n r e s p e c t i v e l y . Because of i t s ion ic chemistry , high atomic mass and r e l a t i v e l y small d i f fe rences in mass between i s o t o p e s , lead i s not suscept ib le to natural physicochemical or biochemical f r a c t i o n a t i o n processes which cause i s o t o p i c var ia t ions in many of the l i g h t e r elements such as sulphur (Love less , 1975) . To date, attempts to 234 i n te rp re t common lead isotope abundances have been based on two main types of lead models, d iscussed below. (1) S ing le -s tage (ordinary) models of lead i s o t o p i c evolut ion as-sume that the earth began with a s ing le primeval lead i so top ic composi-t i o n (see Appendix G for l i s t of symbols) and that the only changes in the ra t ios of the rad ioac t ive parent isotopes to the s table daughter index isotopes ( 2 3 8 U / 2 0 4 P b , 2 3 5 u / 2 0 4 p b a n d 2 3 2 T n / 2 0 4 P b ) a r e due to rad ioac t ive decay. Withdrawal of some l e a d , uranium and thorium from the s i n g l e - s t a g e source by f l u i d s or other means is not excluded so long as the s i n g l e stage source i s large enough so that the ra t ios invo lv ing the rad ioac t ive parent isotopes are not s i g n i f i c a n t l y d is t rubed ; that i s , the source of the f l u i d s is an " i n f i n i t e - r e s e r v o i r " (Doe and Stacey, 1974) . The best examples of ordinary leads are those contained wi th in volcanogenic hosted s t ra t i fo rm deposi ts (Stanton and R u s s e l l , 1959; O s t i c et a l . , 1967); although s i n g l e - s t a g e condi t ions are approached for these d e p o s i t s , they are hot a perfect f i t fo r the model. The small departures from s i n g l e - s t a g e c o n d i t i o n s , shown to be evident even in those deposits that most c l o s e l y approach i t , seem best explained by the mixing of several i s o t o p i c a l l y heterogeneous source mater ia ls (Shaw, 1957; R ichards , 1971) . T h i s mixing may be done through processes such as mul t ip le reworking of lead from very large volumes of rock, in such a way that a s ing le -s tage system is approached; subduction is such a pro-cess (Armstrong, 1968) that would apply to volcanogenic s t r a t i f o r m de-p o s i t s . Thus , s o - c a l l e d s ing le -s tage leads only approximate an evo lu -t ion under s i n g l e - s t a g e c o n d i t i o n s . More r e c e n t l y , a "two-stage" evo lu -t ionary lead model has been proposed to bet ter f i t the volcanogenic lead 235 data (Stacey and Kramers, 1975). T h e i r model is based on new values for various parameters and comparison with lead data from conformable de-pos i ts and various f e l d s p a r s . The new model postulates the i n i t i a l development of lead from a primordial composi t ion, assumed to be that of t r o i l i t e l e a d , beginning at 4.57 Ga . D i f f e r e n t i a t i o n processes brought about the condi t ions of a second stage at approximately 3.7 Ga. E i t h e r the s i n g l e - s t a g e model or Stacey and Kramers' modif ied model, even though imperfect , provides valuable information on the age of formation of the Pb minerals (model-lead ages) . (2) Anomalous leads contain excess radiogenic l e a d . The simplest example of an anomalous lead i s a two-stage process . In the f i r s t s tage , the lead i s o t o p i c composition evolved by a s i n g l e - s t a g e process u n t i l some l a t e r event occurred that caused the 238u/204pD r a t i o to be changed. The r e s u l t i s lead isotope data that l i e along s t ra igh t l i n e s ( in p lots of 2 0 7 P b / 2 0 4 P b versus 2 0 6 P b / 2 0 4 P b ra t ios ) c a l l e d secondary i s o -chrons (Kanasewich, 1968). If the age of m i n e r a l i z a t i o n is known ap-proximately , the age of the soure material fo r the lead may be c a l c u -l a t e d . The transcendental nature of the equation for the secondary i s o -chrons means the so lu t ion is one of successive approximations. Higher order mult istage leads are formed from lead that may have been a s s o c i -ated with several systems having d i f f e r e n t U/Pb and Th/Pb r a t i o s and may have resided in these systems fo r varying lengths of time (Faure, 1977). METHODS Lead samples were c o l l e c t e d from d r i l l cores from the XY deposi t and stored in p l a s t i c sample bags for three months. Subsequently, sam-ples were broken and sub-samples were taken only from the inner parts of 236 the c o r e s . (Doe, 1970; Doe and Delevaux, 1972). These were sent to the Un ivers i ty of Alberta fo r ana lys is of the lead i s o t o p i c r a t i o s . De ta i l s of the a n a l y t i c a l method are given in Appendix G. B r i e f l y , ga lena , spha le r i t e and p y r i t e separates were d i s s o l v e d using var ious a c i d s , loaded on a Re-f i lament and analyzed on a s o l i d source , 90° s e c t o r , 12" r a d i u s , s ing le f i lament mass spectrometer housed in the Department of Physics at the Un ivers i ty of A l b e r t a . F i f t een scans were made fo r each ana lys is and the resul tant raw data processed by computer. F i f t een runs on N .B .S . # 981 Pb standard were completed before and a f te r each sample ana lys is (Kuo and Fo l insbee , 1974). For i n t e r p r e t a t i o n , the lead data were compared to the ordinary l e a d , two stage and mul t ip le stage models to check for model f i t (Slaw-son and R u s s e l l , 1967; Kanasewich, 1968; Koppel and Saager, 1976), and a lso compared to geologic data as another check. RESULTS Data obtained from the lead analyses are presented in Tab le V111-1. Two types of sulphides were sampled; samples HP 1, 2, 5 and 6 are from textura l type IV, occurr ing in the whit ish grey Zn-Pb mudstone, and are of synsedimentary o r i g i n . Samples HP 3,4 , 7 and 8 are from textura l type VI , from sulphide concret ions in the ac t ive member. To check f o r the a p p l i c a b i l i t y of the data to an anomalous lead model, the data were p lot ted on a 2 0 7 P b / 2 0 4 P b versus 2 0 6 P b / 2 0 4 P b d i a -gram. When a l l lead data are p lot ted in t h i s manner a weak l i n e a r pat-tern suggests that an anomalous lead in te rp re ta t ion may be a p p l i c a b l e . The slope and intercept of the 2 0 7 P b / 2 0 6 P b versus 2 0 6 P b / 2 0 4 P b anomalous lead l i n e were ca lcu la ted by computer using the least -squares cubic TABLE VIII-1 Lead Isotope Ratios of Sulphide Minerals for the Howards Pass Deposits Sample No. Mineral 2 0 6 P b / 2 0 4 P b 2 0 7 P b / 2 0 4 P b 2 0 8 P b / 2 0 4 P b HP-Pb-1 Galena 18.6930 15.7365 38.8640 ± .0112 ± .0093 ± .0229 HP-Pb-2 Pyr i te 18.6722 15.6902 38.8395 ± .0211 ± .0176 ± .0434 HP-Pb-3 Galena 18.4046 15.6635 38.6610 ± .0281 ± .0236 ± .0576 HP-Pb-4 P y r i t e 18.6109 15.6707 38.4602 ± .0211 ± .0176 ± .0434 HP-Pb-5 Galena 18.6765 15.7358 38.8275 ± .0210 ± .0174 ± 0.429 HP-Pb-6 Spha le r i te 18.6248 15.6723 38.6791 ± .0119 ± .0099 ± .0244 HP-Pb-7 Galena 18.7944 25.6947 38.7028 ± .0283 ± .0238 ± .0582 HP-Pb-8 Pyr i t e 18.6320 15.7095 38.8386 ± .0171 ± .0141 ± .0348 The normal izat ion fac tors are: 2 0 6 P b / 2 0 4 P b X 1.00315 2 0 7 P b / 2 0 4 P b X 1.00383 2 0 8 P b / 2 0 4 p b X 1.00585 The absolute isotope ra t ios of N .B.S . # 981 s t d / are: 16.9371 15.4913 36.7213 238 method (York, 1969). Data from samples be l ieved to contain synsedimen-tary lead and those containing both synsedimentary lead and c o n c r e t i -onary lead were used. The whole data l i n e show an unacceptable standard er ror of estimate (at 95% confidence ± 0 . 1 3 5 1 ) ; the synsedimentary data do not appear to show a l i n e a r trend on the 207ph/204pD versus 206ph/204pL) c | - j a g r a m > Thus , the present lead i s o t o p i c data do not appear to f i t an anomalous lead model, although more data are required to v e r i f y t h i s . The lead i s o t o p i c data from the Howards Pass deposi ts were a lso compared to the two stage model developed by Stacey and Kramers (1975). F igures V111-1 and VII1-2 are rep lot ted from t h e i r data fo r the present work. Only the lead data from the synsedimentary sulphides are con-s idered s ince they show less heterogeneity than the l a t e r d iagenet ic su lph ides . The mean i s o t o p i c ra t ios for the four synsedimentary lead r a t i o s p lo t ted on the 2 0 7 P b / 2 0 4 P b versus 206ph/204pb diagram show an isochron ind ica t ing a time of Pb minera l i za t ion ( t m ) , of 187 Ma, which i s much younger than the age of m inera l i za t ion ind icated by other e v i -dence. DISCUSSION Three explanations are poss ib le for the age discrepency in the use of common leads (Oversby, 1974). The d i f fe rences (A) between accepted age and model age are small fo r the o ldest deposi ts at Barberton and Manitouwadge, but A increases s u b s t a n t i a l l y f o r younger samples such as those for the Howards Pass d e p o s i t s . T h i s discrepancy at younger ages was one of the main reasons fo r Stacey and Kramers (1975) developing the two stage model which has reduced, but not e l im ina ted , t h i s e r r o r . 239 Figure VIII-1. Graph of 2 0 7 P b / 2 0 4 P b p lo t ted against 2 0 6 P b / -2 0 4 P b showing Stacey and Kramers' two stage lead evolut ion curve . Upper diagram shows, a de ta i l plot of the Howards Pass d a t a , c i r c l e s represent synsedimentary s u l p h i d e s , squares ind ica te data from concret ionary s u l -ph ides . Points along Stacey and Kramers lead evolut ion cure are shown by x. 240 .a a. o CM CL 00 O CM 3 5 0 h-300. 90 2 0 6 2 0 4 150 Pb 20-0 Figure VI11-2. Graph of 2 0 8 p b / 2 0 4 P b p lo t ted against 2 0 6 P b / -2 u 4 P b showing Stacey and Kramers' (1975) two stage lead evolut ion curve . Upper diagram shows a de ta i l plot of the Howards Pass da ta , c i r c l e s represent synsedimentary su lph ide , squares ind ica te data from con-cre t ionary su lph ides , X represents points on the lead evolut ion curve . 241 Using the two-stage model, er rors between accepted age and model age fo r deposits less than 500 Ma range from 12 to 15% (N=3), as compared to 55% f o r the Howards Pass d e p o s i t s . It thus appears that only part of the d i f f e rence can be explained by the inherent A va lue , but i t must be remembered that the growth curve is based on volcanogenic d e p o s i t s . The second poss ib le explanation for the lead model-geologic model age d i s -crepancy i s that the leads are anomalous; as mentioned p rev ious ly , only more data w i l l adequately answer th is quest ion . A t h i r d reason for the discrepency could be a more radiogenic Pb source . That leads from non-volcanic black shales are more radiogenic than those of the is land arc a s s o c i a t i o n (Stanton and R u s s e l , 1959) has been shown by Gulson (1976, 1977). The 2 3 8 U / 2 0 4 P b (u) fo r the source material fo r the Howards Pass leads was ca lcu la ted for the mean lead using the fo l lowing equation: 2 0 6 P b V2- 2 ° 4 P b • a 2 e A 8 T l - e x 8 * where a 2 = 206p b / 204 P b r a t i o a t t i m e t ^ X l = 1.55125 x i r j - 1 0 y - l (Appen-dix G) , T]_ = time of beginning of the second stage lead evolut ion and t = time elapsed s ince removal of a common lead sample from i t s source. Using t h i s procedure v>2 = 9 .89, which is higher than for most volcano-genic massive sulphide deposi ts (Sangster , 1976; Koppel and Sagger, 1976). The heterogeneity of the concret ionary sulphide lead data from Howards Pass i s s i m i l a r to that noted in most sediments (Doe, 1970; Cooper and Richards , 1969), and is poss ib ly due to various ages of f o r -mation and local U-Pb v a r i a t i o n s . 242 Comparison of the Howards Pass leads with those found in the Red Sea deeps suggests that a s i m i l a r mode of formation is p o s s i b l e . In review, the Red Sea basin contains over twenty s u b - b a s i n s , many of which contain meta l l i f e rous br ines and associa ted br ine deposi ts (Bignel l et a l . , 1976). The f i r s t deeps to be studied were the A t l a n t i s II , Chain and Discovery deeps (Degens and Ross, 1969). At present , i t is thought that the three br ines are the resu l t of vo lcanic emanations in the At -l a n t i s II Deep and that br ines in the Chain and Discovery deeps o r i g i -nated as overflow from the A t l a n t i s II Deep. The overflow br ines have t r a v e l l e d a d istance of up to 6 km and are d i l u t e compared to the A t l a n -t i s II br ine (Brooks et a l . , 1969). Lead i s o t o p i c data (Cooper and Richards , 1969) ind ica te that although homogeneous lead is present in the A t l a n t i s II Deep, lead from the Chain and Discovery deeps are pro-g r e s s i v e l y more heterogeneous. Based on chemical composition of br ines and bathimetry, Cooper and Richards (1969) proposed that overf low br ine from the A t l a n t i s II Deep moved through the Chain Deep and f i n a l l y into the Discovery Deep. They fur ther proposed that the increase of lead he-terogenei ty r e f l e c t e d the increasing cont r ibu t ion of lead from the s e d i -ments. The lead i s o t o p i c data from the Howards Pass area show a s i m i l a r t r e n d ; that i s , the i s o t o p i c data from textura l type VI i s more hetero-geneous than that from the proposed br ine deposit of textura l type IV. The concret ions were formed during l a t e r d i a g e n e s i s , probably at various times and in a system where Pb and U were mobi le . Another s i m i l a r i t y between the eastern Selwyn Basin and the Red Sea is a Precambrian t e r -ra in source area . The l imi ted terr igenous material that did enter the 243 Selwyn Basin appears to have or ig ina ted to the e a s t . T y p i c a l l y , s e d i -ments in r e s t r i c t e d b a s i n s , such as the B a l t i c Sea or the Red Sea which dra in Precambrian t e r r a i n s , contain h igh ly radiogenic lead i s o t o p i c r a t i o s , e s p e c i a l l y in f i n e grained sediments (Chow, 1965; Hart and T i l t o n , 1966). Data from the Howards Pass deposits are compatible with regional lead i s o t o p i c zoning proposed by Kuo and Fol insbee (1974), but may be due to proximity to the Sh ie ld rather than to distance from the Anvi l depos i t . Another common c h a r a c t e r i s t i c between the Howards Pass and the Red Sea data is the age discrepancy between the geologic and lead model ages A = 189 m.y. fo r the Howards Pass deposits and A = 500 m.y. f o r the Red Sea. A large age discrepancy is a lso evident in Mn nodules (Reynolds and Dasch, 1971) ( F i g . VI11 -3) . T h i s suggests that the lead from the Howards Pass deosi ts is more s i m i l a r to sedimentary leads than to volcanogenic l eads . SUMMARY Lead i s o t o p i c data are compatible with other data from the Howards Pass d e p o s i t s . The pre l iminary data presented here can be d iv ided into two types: (1) synsedimentary lead data plot near the Stacey-Kramer two stage model curve and (2) l a te stage d iagenet ic sulphides which show a very heterogeneous d i s t r i b u t i o n of lead p l o t s . The r e l a t i o n between the Howards Pass data and the lead growth curve is s i m i l a r to those of pe la -g ic sediments and Red Sea br ine sediments and not to those of volcano-genic deposi ts such as the Kuroko type (Sato and S a s a k i , 1973). T h i s suggests that the lead is derived mainly from sediments, with an unknown proport ion of mantle-derived l e a d . Regional lead zoning as presented by Kuo and Fol insbee (1974) fur ther suggests that material derived from the 244 f155 Mn nodules (Reynolds ond Oascft. 1971) Oceanic basalts » metalliferous sediments. Red Sea • basalt. Red Sea s sediments. Red Sea » metalliferous sediments. East Pacific Rise (Dasch et ot, 1971) • conformable ore deposits Cooper and Richards (1969) Delevoux and Oo* (1974) J_ 17.S no 193 3001 380 tvo-stoge growth curves, S O Figure VI11-3. Lead i s o t o p i c data points fo r recent ly deposited meta l l i f e rous sediments (Red Sea and East P a c i f i c R i s e ) . The two-stage growth curves are for d i f f e ren t u va lues . Note that lead data give nega-t i v e ages even though they are from conformable d e p o s i t s . Numbered points represent data from conformable deposits (from Koppel and Saager, 1976). Precambrian Shie ld could have been a major source of lead in the Howards Pass d e p o s i t s . 246. CHAPTER IX DISCUSSION INTRODUCTION The data presented in the present research leads the author to con-clude that the Howards Pass Zn-Pb deposi ts are unique compared to other sedimentary-type s t r a t i f o r m d e p o s i t s . T h i s has a lso led to the develop-ment of poss ib le ore genesis models or iented toward explorat ion fo r s i m i l a r deposits elsewhere (Morganti , 1975; 1977a; 1979). In par t , t h i s chapter presents an exp lora t ion -or ien ted ore genesis model for the Howards Pass d e p o s i t s . Furthermore, a review of published data has allowed fo r the const ruct ion of a t h r e e - f o l d exp lora t ion -or ien ted c l a s -s i f i c a t i o n of sedimentary-type s t r a t i f o r m d e p o s i t s . At the end of the chapter some cons idera t ion is given to regional metallogeny in the eas-tern Yukon. MODEL FOR THE ORIGIN OF THE HOWARDS PASS DEPOSITS The generat ion of an ore deposit that involves a hydrous f l u i d has four c r i t i c a l aspects (White, 1968): (1) A source for the ore c o n s t i -tuents must e x i s t ; the most commonly envisioned sources are metals d i s -persed in products of weathering, in sediments, in rocks being metamor-phosed, associated with magmas, in the mantle, or in prev ious ly formed ore d e p o s i t s . (2) D i s s o l u t i o n of ore c o n s t i t u e n t s , and re la ted e l e -ments at l eas t in part in the hydrous phase in the i n t e r s t i c e s of the rocks of the environment. (3) Br ine migrat ion in d i r e c t i o n s c o n t r o l l e d by physical and/or chemical d i f f e r e n t i a l s . (4) Mineral deposi t ion by s e l e c t i v e p r e c i p i t i o n of c e r t a i n const i tuents in response to physical and/or chemical change as the f l u i d migrates in to new environments (Anderson, 1978). 247 In the Howards Pass d e p o s i t s , two major sources of metal are geolo-g i c a l l y possib le : (1) the Howards Pass formation i t s e l f , with advec-t i o n (Berner, 1975) provid ing low temperature br ines (Morganti , 1975, 1977a), or (2) the rocks underlying the Selwyn B a s i n , such as the ' G r i t Un i t ' with high temperature (greater than 50°C) br ines exhaled outside of the Howards Pass map-area ( i . e . outside of the area covered by Plate I ) . There i s no experimental evidence fo r movement of the quant i t ies of f l u i d required for such a model of br ine development, the formation of a very low ( less than 50°C) temperature br ine or the v e r t i c a l migration of such a br ine in sediments s i m i l a r to those which formed the Howards Pass format ion. T h u s , the l a t t e r source appears more reasonable at present because of the temperature required fo r the formation of a metal r i c h br ine (150 to 200°C according to Shanks and B i s c h o f f , 1977) and the nature of f l u i d flow away from basin centres (Nixon, 1973; Zarkharov, 1977) and not across bedding (T issot and Welte, 1978) as would be re-quired in the f i r s t source. Such f l u i d movement usual ly occurs because of with crusta l subsidence and elevated heat flow commonly associated with basin formation and/or deepening ( F i s c h e r , 1975). In cons ider ing br ine migra t ion , the main question is where the br ine vent or exhalat ion centre was l o c a t e d . There is no evidence of b r ine migrat ion or of an out le t to the surface in the Howards Pass map area (Plate I ) , suggesting that i f heated br ines did supply metals fo r the formation of the Zn-Pb deposits they must have been expel led to the surface outside of the Howards Pass map area . Following the above reasoning, the problem of the exhalat ion centre associated with br ine migrat ion is to locate an area of high heat flow during deposi t ion of the Howards Pass format ion. 2 4 8 Comparison of the r e l a t i v e importance of br ine source vs paleogeo-graphic control on ore deposi t ion (Table IX-1) shows that the Howards Pass formation represents an end-member group of deposits with paleogeo-graphic control dominating sulphide d e p o s i t i o n . T h i s suggests that the source of the b r i n e s , i f exhaled at r e l a t i v e l y high (greater than 50°C) temperature would be outside the Howards Pass area . T h i s estimate i s empir ica l and based on descr ip t ions of s t r a t i f o r m ore deposi ts (Wolf, 1976; Ta tsumi , 1970; Krebs, 1976b; Large, 1977). The simple mineralogy in the Howards Pass d e p o s i t s , the lack of Cu and the confinement of the deposi ts to paleotopographic lows suggest de-p o s i t i o n of metals from a dense, low temperature b r i n e . That c h l o r i d e br ines (Anderson, 1975, 1978) are denser than seawater has been shown exper imental ly ( E l l i s , 1967; Sato , 1972) ( F i g . IX-1) . Observat ions by Turner (1969) in the Red Sea br ine pools have demonstrated that dense br ines do e x i s t in natural systems and that such br ines can ex is t as i s o l a t e d bod ies . However, d i f fe rences in mineralogy suggest d i f fe rences in chemistry between the Red Sea br ines (Degens and Ross, 1969; Shanks and B i s c h o f f , 1977) and those which may have formed the Howards Pass d e p o s i t s , although the general physical evo lu t ion of the Red Sea br ines may be s i m i l a r to those of the Howards Pass d e p o s i t s . Thus , the most reasonable source area f o r a br ine would be up-slope from the Howards Pass d e p o s i t s , s ince denser b r i n e s , compared to seawater, migrate down-slope in response to g r a v i t a t i o n a l forces (Turner, 1973; Turner and Gustafson, 1978). The only evidence of a poss ib le high heat f low during deposi t ion of the Howards Pass formation cons is ts of minor amounts of t u f f within 1 Table IX-1. Table showing c h a r a c t e r i s t i c s of proximal , d i s t a l and sedimentary sulphide d e p o s i t s . The tab le suggests the r e a l i t i v e importance of brine source and paleogeogeography in the l o c a l i z a t i o n of ore d e p o s i t s , even though discrepancies do occur (based on data from Ander-son, 1975; Lambert and Sato , 1974; Large, 1977; Lydon, 1978; Morganti , 1979; Sangster, 1972, Sa to , 1972. C H A R A C T E R I S T I C P R O X I M A L D E P O S I T D I S T A L DEPOSIT SEDIMENTARY D E P O S I T M e t a l c o n t e n t . A l t e r a t i o n I r o n s u l p h i d e s a n d o x i d e s F o r m Z o n i ng G e o l o g i c S e t t i n g S u l p h u r i s o t o p e s C u - r i c h ( w i t h A u , A g ) ; Zn may be p r e s e n t i n e c o n o m i c q u a n t i t i e s , Pb i s g e n e r a l l y l o w . U n d e r l a i n b y a d i s t i n c t a l t e r a t i o n z o n e o r p i p e . P y r i t e a n d p y r r l i o t i t e - d o m i n a n t s u l p h i d e s . M a g n e t i t e o f t e n i n f o o t w a l 1 . P i p e l i k e o r m u s h r o o m s h a p e d g e n e r a l l y m a s s i v e a n d c r o s s - c u t t i n g . B a n d i n g o n l y i n h a n g i n g w a l l . G o o d z o n i n g , C u i s c o n c e n t r a t e d t o w a r d f o o t w a l l . Z n / C u r a t i o i n c r e a s e s u p w a r d , Pb o c c u r s i n h a n g i n g w a l l o f d e p o s i t . T o w a r d t h e t o p o f a p i l e o f m a s s i v e p y r o c l a s t i c s , f r a g m e n t a l v o l c a n i c s a n d l a v a s . P h a n e r o z o i c o r e e x h i b i t d i s t i n c t d e c r e a s e i n a 3 4 S f r o m s t r a t i g r a p h i c f o o t w a l l t o h a n g i n g w a l l . P b - Z n r i c h , Cu p o o r may h a v e e c o n o m i c A g . No d i s t i n c t f o o t w a l l a l t e r a t i o n z o n e . P y r i t e d o m i n a n t , p y r r h o t i t e a b s e n t . M a g n e t i t e may be i n h a n g i n g wal1. W e l l b a n d e d , s t r a t i f o r m , a n d b l a n k e t s h a p e d . G e n e r a l l y l a c k s d i s t i n c t m e t a l z o n i n o . W i t h i n m i x e d s e d i m e n t a r y v o l c a n i c p i l e . 8 S v a l u e s a r e e i t h e r v a r i a b l e a n d e r r a t i c , o r show a d i s t i n c t i n c r e a s e f r o m f o o t w a l l t o h a n g i n g w a l l . Z n - P b r i c h , l o w Cu a n d l o w A g . No e v i d e n c e o f a n y f o o t w a l l a l t e r a t i o n . S p h a l e r i t e a n d g a l e n a m a j o r s u l p h i d e s o n l y m i n o r p y r i t e , n o m a g n e t i t e . L a m i n a t e d b l a n k e t s h a p e . None e v i d e n t . S e d i m e n t s ; o n l y v o l c a n i c s p r e s e n t a r e up s l o p e . D i s t i n c t i n c r e a s e i n i$34s i n c r e a s i n g up s e c t i o n w i t h i n c y c l i c e v o l u t i o n o f t h e s u b - b a s i n . 250 01 r i 1 1——i 1 1 1 1—!—i 1 1 r _i i i i • 1 1 ' 1 1 ' 0.95 1.00 1.05 OENSITY, g / c c Figure IX-1. Density of ore forming b r i n e s , a) Comparison of den-s i t y of various b r i n e s , 0.5m so lu t ion would approximate seawater (from E l l i s , 1967). b) Three brine types according to Sato (1972) the low tem-perature dense br ine (type I) would most c l o s e l y approximate a br ine moving along the sea f l o o r or trapped in a s u b - b a s i n . 251 km of the shale-out near the South Nahanni River and 12 km northeast of Howards Pass. These vo lcan ics suggest a high heat flow at the sha le -ou t , where hot br ines could have been exhaled contemporaneously with formation of the Howards Pass sub -bas ins . Br ines exhaled at the sha le -out could move down slope un t i l conf ined in the sub-basins at the base of slope ( F i g s . IX-2 and IX-3) . Evidence from studies on the Red Sea br ines (Degens and Ross, 1969) and experimental modell ing with s a l t so lu t ions (Turner, 1973) show that once a br ine is confined in a depres-s i o n , such as those of the Howards Pass s u b - b a s i n s , upgrading can occur due to densi ty and/or thermal s t r a t i f i c a t i o n ( F i g . IX-4) which may ex-p la in the genera l ly increas ing metal contents proceeding up sect ion in an idea l i zed act ive member c y c l e . Deposit ion of Zn and Pb sulphides in the sub-basins may have occur red , poss ib ly through intermediate steps to sulphide formation (Lydon, 1978). Anderson (1978) has reviewed the generat ion of br ines responsib le fo r the formation of M i s s i s s i p p i V a l l e y type deposi ts and concluded that those br ines must have had a low s u l -phur content and therefore that sulphur was added at the s i t e of depos i -t i o n . Sulphur isotope data from the Howards Pass deposits suggest that the sulphide was generated at the s i t e of d e p o s i t i o n , perhaps b i o g e n i -c a l l y . The above model app l ies to the formation of the Howards Pass type sulphide deposi ts ( e . g . XY, ANNIV and OP). The c y c l i c i t y of the ac t ive member could be the resu l t of the i n t e r a c t i o n of br ine supply and evo lu -t ion of the sub-basin environment. The deposi t iona l trends noted in the ideal cyc le of the a c t i v e member ( F i g . I l l - 6 ) can be explained by as-suming the X ^ o s and pH were major c o n t r o l l i n g fac to rs in depos i t ion Shale out and /or Sea Level Fault I Figure IX-2. Sedimentary exhalat ive model fo r the Howards Pass depos i ts . Deep migrat ing f l u i d s move to and up shale-out and/or f a u l t and migrate down s lope , where they are trapped in s u b - b a s i n s . Br ine moving down slope would be a Zn r i c h , Cu poor, low temperature high density br ine (type I of Sato , 1972). 253 Figure IX-3. Plan view of the model fo r the formation of the Howards Pass Zn-Pb depos i ts . Br ines are exhaled along the shale-out at the edge of the Selwyn Basin with associated basic vo lcanic material ( l i ne pa t te rn ) . These brines migrate down slope (arrows) because of t h e i r den-s i t y and c o l l e c t in the sub-basins at the base of the slope where depos i -t i o n o c c u r s . P~=3> OVERSPILL NORMAL SEAWATER DENSE BRINE MOVING DOWN SLOJ SLOPE MOST SALINE T HIGHEST TEMPERA-' ! * U B . - p A b l N TURE SOLUTION Figure IX-4. Formation of brine in sub-bas in . Brine f i l l s in sub-basin from below with continuous flow eventual ly forming a s table s t r a t i f i c a t i o n br ine with more dense br ine concen-t r a t i n g at base of sub-basin (Based on data from Turner , 1969, adapted to geology of the Nahanni map-area). 255 wi thin the sub -bas ins . The pH of the o r i g i n a l sediments may have been c o n t r o l l e d to a large extent by sulphide and/or ammonia formation both of which can cause a r i s e in the pH favorable to CaCC>3 p r e s e r v a t i o n . A pH drop, associated with br ine b u i l d up, could cause d i s s o l u t i o n of CaC03 and p r e c i p i t a t i o n of Si02 ( F i g . IX-5) . Sulphide depos i t ion could be the resu l t of both reduction and pH change and poss ib ly mixing and assoc ia ted coo l ing (Anderson, 1978; Sato , 1972). These deposits were subsequently modif ied by compaction, slumping, and l a t e r , regional f o l d s and f a u l t s . For example, part of the XY sub-basin was upgraded by major impl ied slumping of much of the ac t ive member and subsequently contorted by f o l d i n g and f a u l t i n g ( F i g . IX-6) . To date , no such large sca le slumps have been found in s i m i l a r d e p o s i t s , but a l l have been geometr ica l ly modif ied by l a t e r f o l d i n g and f a u l t i n g (see c r o s s - s e c t i o n s on Plates II, III and IV) ( F i g . IX-7) . Considerat ion of the above model fo r the o r i g i n the Howards Pass deposi ts has economic i m p l i c a t i o n s . Regional exp lora t ion -p lays for such deposi ts should be aimed at f ind ing ear ly Paleozoic platform marginal starved basins (Appendix I) showing s h e l f (or r e e f ) , s l o p e , base of s l o p e , chert basin f a c i e s . S p e c i f i c targets should be geochemical l y anomalous (Zn and Pb) sub-basins at the base of s lope . The importance of paleogeography i s obvious; and may ind ica te that the chasing of poss ib le sulphide traps would be more rewarding than def in ing base metal sources . Once the sub-basin environment has been d e f i n e d , i n i t i a l d r i l l i n g should attempt to def ine grade trends and the loca t ion of slumps within the sub-basin s i n c e , in the case of the XY d e p o s i t , i t appears that these are of higher grade than the rest of the depos i t . ^ 3 CaCOj or S i0 2 [min. max} J V 7"V / \ \ B X H 2 S / / -A c pH 5 6 7 8 / \ / \ I \ INTERPRETATION Opening of sub-basin and/or destruction of chemocline. Intermittent deposition of sulphide (evolution and upgrading of brine) . Isolation of sub-basins (sedimentary l i p and/or chemocline develops). Figure IX-5. In terpreta t ion fo r the o r i g i n of the ideal cyc le in the act ive member. The ideal cyc le i s shown at the l e f t with numbers r e f e r r i n g to ind iv idua l f ac ies : 1) l i g h t grey basal l imestone, 2) graded l imestone, 3) th in bedded calcareous mudstone, 4) mixed cherty mud-stone and l imestone, 5) cherty mudstone, 6) th in bedded cherty mudstone, 7) whit ish grey Zn-Pb mudstone, 8) grey chert f a c i e s . Column A shows r e l a t i v e proportions of CaC03 and S i 0 2 . Column B shows the X^^s based on the sulphur i s o t o p i c data . Column C shows probable pH for brine and sediment (Anderson, 1975, 1978; Berner , 1971). The in te rpre ta t ion column explains the events associated with these t rends . The diagram is schematic and no s p e c i f i c numbers are imp l i ed . metres Figure IX-6. Plan view of the proposed major slump in the XY Zn-Pb depos i t . Cross-hatched area del ineates up-graded slump area , s t i p p l e d area del ineates slump source, arrows show d i r e c -t i o n of t r a n s p o r t , .heavy dashed l i n e shows out l ine of XY sub-bas in . The locat ion of some d r i l l holes and peaks are shown fo r l o c a t i o n re ference . cn 258 Figure IX-7. Diagrammatic evolut ion of the XY s u b - b a s i n , a) O r i g i -nal deposi t ion of synsedimentary Zn and Pb in sub-bas ins , b) major large sca le slumping of the ac t ive member in the XY area a f te r deposi t ion of the ac t ive member, poss ib ly during i n i t i a l deposi t ion of the upper s i l i c e o u s mudstone member, c) Cretaceous fo ld ing and f a u l t i n g of the s u b - b a s i n . The d e t a i l e d evo lu t ion i s more complex than shown, but these three events have produced the major c h a r a c t e r i s t i c s of the XY d e p o s i t , while a and c have been important in a l l three d e p o s i t s . 259 A CLASSIFICATION FOR STRAT I FORM-SEDIMENT ARY Zn , Pb, Cu , Aq AND Ba  DEPOSITS: AN EXPLORATIONISTS VIEW The present i n v e s t i g a t i o n is aimed at const ruct ing an explorat ion or iented geologic model for the Howards Pass d e p o s i t s . One resu l t of t h i s research is the r e a l i z a t i o n that even though a l l s t r a t i f o r m - s e d i -mentary ore deposi ts are not i d e n t i c a l , explorat ion for other s i m i l a r deposi ts is done by analogy. Although s t i l l a v a l i d bas is for exp lora -t i o n , be t te r exp lora t ion e f f i c i e n c y may be obtained by cons idera t ion of the t e c t o n o - s t r a t i g r a p h i c se t t ing of the s t r a t i f o r m d e p o s i t s . Here an attempt i s made at c l a s s i f y i n g s t ra t i fo rm deposi ts which may aid in ex-p lor ing fo r s p e c i f i c types . Ore deposi ts must be c l a s s i f i e d in a framework which aids in t h e i r i n t e r p r e t a t i o n (L indgren, 1933); to da te , the lack of a s a t i s f a c t o r y c l a s s i f i c a t i o n has to some extent caused general confusion ( e . g . Stan-t o n , 1972; Raybould, 1978). By d e f i n i t i o n s t r a t i f o r m sulphide deposits are conformable with the enclosing rocks . Examples such as the Kuroko deposi ts of Miocene age in Japan (Tatsumi, 1970; Ishahara, 1974; Lambert and Sato, 1974), the Kidd Creek deposit (Walker and Mannard, 1974) and the Bathurst deposit in New Brunswick ( M c A l l i s t e r and Lamarche, 1972) are most l i k e l y the resu l t of submarine vo lcanic processes because they are in t imate ly a s s o c i a t e d , both s p a t i a l l y and temporal ly , with products of submarine volcanism. Such deposits are v o l c a n i c - e x h a l a t i v e s t r a t i f o r m sulphide deposi ts (Sangster , 1972; Sangster and S c o t t , 1976). Deposits which are somewhat s i m i l a r to the Howards Pass d e p o s i t s , and are con-s idered here , do not show such an obvious a s s o c i a t i o n with submarine 260 v o l c a n i c r o c k s , b u t a r e s e d i m e n t a r y - t y p e s t r a t i f o r m s u l p h i d e d e p o s i t s . E x a m p l e s o f t h i s c l a s s i n c l u d e Howards P a s s , S u l l i v a n , t h e Zambian C o p p e r B e l t and t h e Mt. I s a a r e a d e p o s i t s . G e n e r a l c h a r a c t e r i s t i c s o f t h i s c l a s s o f d e p o s i t s a r e l i s t e d b e l o w . (1) The d e p o s i t s a r e g e n e r a l l y c o n f o r m a b l e w i t h t h e b e d d i n g o f t h e s u r r o u n d i n g s e d i m e n t a r y r o c k s , and a r e t a b u l a r t o l e n t i c u l a r i n s h a p e . (2) T h o s e d e p o s i t s o c c u r r i n g i n m e t a m o r p h o s e d s e d i m e n t a r y r o c k s show s u l p h i d e t e x t u r e s i n d i c a t i v e o f m e t a m o r p h i s m . (3) The d e p o s i t s show no o b v i o u s a s s o c i a t i o n w i t h v o l c a n i c o r p l u t o n i c r o c k s . (4) D e p o s i t s o f t h e same age and s h o w i n g t h e same c h a r a c t e r i s t i c s f r e q u e n t l y o c c u r g r o u p e d i n t o m e t a l l o g e n i c p r o v i n c e s . (5) The d e p o s i t s , when g r o u p e d , o c c u r i n one m a j o r s e d i m e n t a r y b a s i n , a l t h o u g h i n d i v i d u a l d e p o s i t s may o c c u r w i t h i n s e p a r a t e s u b - b a s i n s . (6) M o st o f t h e d e p o s i t s show o r d i n a r y Pb i s o t o p e s y s t e m a t i c s . (7) In g e n e r a l , t h e d e p o s i t s a r e a s s o c i a t e d w i t h c a r b o n a c e o u s s e d i m e n t a r y r o c k s . Much o f t h e w o r l d ' s Zn, Pb and Cu i s won f r o m s t r a t i f o r m - s e d i m e n t a r y d e p o s i t s and i n g e n e r a l t h e d e p o s i t s a r e l a r g e . The t h i c k n e s s e s and l a t e r a l d i m e n s i o n s o f t h i s c l a s s o f d e p o s i t s v a r y w i d e l y ( T a b l e I X - 2 ) , b u t a l l d e p o s i t s a r e , however, t a b u l a r i n s h a p e , and t h e i r t h i c k n e s s e s a r e s m a l l r e l a t i v e t o t h e i r l a t e r a l d i m e n s i o n s . When g r o u p e d by age, t h e d e p o s i t s show t h e p r e s e n c e o f m e t a l l o g e n i c e p o c h s ( F i g . I X - 8 ) . Table IX-2. General s i z e of strat i form-sedimentary sulphide depos i ts . These deposits s t i t u t e the major world deposi ts of t h i s c l a s s . DEPOSIT AREAI- EXTENT THICKNESS REFERENCES Zambian Copper Overal l ? Variable Mendelsohn, 1961; Be l t 3 .5x l0 3 km . Individual Deposits 50 cm - 10 cm Fle ischer et a l . , 1976 > 3 km2 West Texas - Overal l 8 - 30 m Smith, 1976; Johnson and Croy, Oklahoma 5 x l 0 3 km 2 . Indiv idual Deposits 1976 10 km2 White P ine , 16 km' Mi ch i gan Bel t Super Group = 1.4 km 15 m Harr ison, 1974 (U.S.A. ) Grinnel Formation, A lbe r ta , Canada 3 2 Overal l 1x10' km . Individual occurrences < 5 km2 30 cm - 5 ni Morton et a l . , 1973 Kupferschiefer Germany Overal l 1 . 2 x l 0 3 k m 2 . Individual Deposits) 100 km2 30 - 50 cm Wedepohl, 1971; Rentzsch, 1974 Mt. I sa , Aust. Major Trough ~ e.OxlO'1 km 2 . Individual Deposits 0.5 km2 1 -• 50 m Bennett, 1967; Mathias, , and Clark , 1975 McArthur Ri ver , Aust. H.Y.C. 1.5 km2 up to 130 m Lambert, 1976 Dshezkazgan (U .S .S .R . ) not given up to 700 in Assanov et a l . , 1974 Tom-Jasen (Yukon-NWT, Cdn.) 0.4 km2 up to 60 m Smith, 1978 Sul1i van 2.5 km2 up to 25 m Freeze 1966, Ethier et a l . , 1976 ( B . C . , Canada) 1 - 8 m White and Wri te, 1954 , Ensign et a l . , 1968 Howards Pass Base of S lope" 750 km 2. Individual deposits up to 60 m. (Yukon, N.W.T.) deposits 25 km2 PERIOD TRIASSIC P E R M I A N PENSYLVANIAN MISSISSIPPIAN DEVONIAN S ILURIAN ORDOVICIAN CAMBRIAN HADRYNIAN |== HELIKIAN — 10 2 0 3 0 l i 1 NUMBER OF DEPOSITS Figure IX-8. Strat i form-sedimentary sulphide deposits grouped by age. Two metal logenic epochs are ev ident ; the Proterozoic and the Permian. Blank bars represent sub-c lass I d e p o s i t s , hor izontal l i n e s represent sub-c lass II, v e r t i c l e l ines represent sub-c lass III depos i ts . 263 S t r a t i form-sedimentary type sulphide deposi ts can be d iv ided into three sub-c lasses based on sedimentary environment; t h i s c l a s s i f i c a t i o n a l s o has textura l and geochemical impl ica t ions which may fur ther def ine these three s u b - c l a s s e s . The three sub-c lasses are: (1) shallow i n t r a -c ra ton ic b a s i n , (2) t u r b i d i t e basin and (3) platform-marginal starved basin environments. T h i s c l a s s i f i c a t i o n has important impl ica t ions from both an ore genesis and an explorat ion s tandpoint . The three sub-c lasses are best studied from a regional viewpoint and to a great extent may not be d i f f e r e n t i a t e d by examination of just the sulphide deposits by them-s e l v e s . The occurrence of s i m i l a r c h a r a c t e r i s t i c s of the deposits wi thin a sub-c lass suggests that they have roughly s i m i l a r o r i g i n s . Sub-c lass 1 cons is ts of sulphide deposi ts in shallow water, usua l ly t r a n s g r e s s i v e sequences. Included in s u b - c l a s s 1 are s i g n i f i c a n t de-posi ts such as those in the Kupfersch ie fer of Europe, Creta (USA), the Zambian Copper B e l t , the Redstone occurrences and Spar Lake in the C o r d i l l e r a , White Pine (U .S .A. ) and McArthur River ( A u s t r a l i a ) . These deposi ts : (1) Always occur in carbonaceous sedimentary rocks r ich in p y r i t e that formed in shallow-water near-shore environments. (2) Frequently o v e r l i e red or hemat i te-sta ined sedimentary rocks (rote f a u l e ) . (3) Usual ly occur in evapor i te -bear ing sedimentary sequences. (4) Often occur near major f a u l t zones and basement l ineaments. (5) Usual ly are zoned with respect to t h e i r Cu, Pb and Zn content ; t h e i r zoning can be q u a l i t a t i v e l y described by a simple zoning scheme. 264 Tab le IX-3 summarizes the c h a r a c t e r i s t i c s for the major deposits i n c l u d -ed in s u b - c l a s s 1. The three most consis tent general models fo r sub-c lass I deposi ts are the f a u l t re la ted br ines (Smith, 1969), the sabkha diagenet ic model (Renfro, 1974) and the epigenet ic model (Ensign et a l . , 1968). Smith (1969) proposed that br ines associated with volcanism deposited metals in nearby shales at Mt. I sa , the associated Cu deposit in t h i s model, is considered a replacement deposit re la ted to th is same f a u l t at a l a t e r t ime. In the Sabkha model, an a r i d cl imate with a large evaporation debit produces a coastal sabkha environment which leads to d iagenet ic f l u i d migra t ion ; sulphide i s the r e s u l t of bac te r i a l dest ruct ion of algae and reduction of su lphate . The H2S laden a lgal mat acts as a re-duct ion membrane that causes the t race metals in the ascending f l u i d s to be p rec ip i t a ted as d iagenet ic sulphides (Ca ia , 1976; Van Eden, 1974). The Copper Be l t deposits of A f r i c a are considered the best example of deposits formed in t h i s way (Renfro, 1974; Lee and G l e n i s t e r , 1976). In the epigenet ic model movement of f l u i d s through aqui fe rs permiates s u l -phide r i c h hor izons. Replacement of the sulphides form base metal s u l -phide deposi ts which are not s t r i c t l y s t r a t i f o r m in d e t a i l . The o r i g i n a l sulphide may be the resu l t of b iogenic a c t i v i t y or replacement of s u l -phide minerals (Brown, 1978). The c l a s s i c example of a deposit formed in t h i s way is White P ine , Michigan (Ensign et a l . , 1968). Thus sub-c lass 1 deposi ts may form syngenet ica l l y or d i a g e n e t i c a l l y ( F i g s . IX-9, IX-10). Exp lora t ion fo r t h i s sub-c lass of deposi ts should focus on i n t e r i o r or i n t r a c r a t o n i c basins with associated red beds and evapori te se-Tab le IX-3. Tab le of features associated with sub-c lass I type strat i form-sedimentary de-pos i ts (Assanov et a l . , 1974; Ensign et a l . , 1968; F l e i s c h e r et a l . , 1976; Har r ison , 1974; Johnson and Croy, 1976; Jung and Kn i tzschke , 1976, Kirkham, 1974; Krebs, 1976a, Mathias and C l a r k , 1975; Murray, 1975; Rentzsch, 1974; Wedepohl, 1971). DEPOSIT SHALLOW WATER CONGLOMERATE MUDCRACKS CROSS-BEDS SHALLOW-WATER MARINE CARBONATES DOLOMITE EVAPORITES RED BEDS KUPFERSCHIEFER (Germany) CRETA (U.S.A. ) DZHEZKAZGAN (U.S .S .R. ) X ZAMBIAN Cu BELT X REDSTONE N.W.T. (Canada) BELT-GRINNEL-U. S.A.-CANADA WHITE PINE (U.S.A) Mt. ISA-HILTON ( A u s t . ) McARTHUR RIVER (Aus t . ) Figure IX-9. General ized synsedimentary model for the formation of sub-c lass I s t r a t i f o r m -sedimentary d e p o s i t s . Br ine migrat ion due to compaction or a thermal high cause migrat ion through red beds into shales where deposi t ion occurs in sub-bas ins . Zoning is evident in fau l t c o n t r o l l e d deposit on r i g h t . r\3 Figure IX-10. General ized d iagenet ic model of formation for sub-c lass I strat i formsedimen-tary d e p o s i t s . Deposit on l e f t formed by brine, migration through red beds into carbonaceous mud-s tones , deposit on r ight formed by l a te ra l migra t ion . In both cases zoning ind icates migration path. * ro 268 quences. S p e c i f i c areas of in te res t appear to be near basement highs during deposi t ion of the host beds. Sub-c lass II s t rat i form-sedimentary deposi ts are associated with th ick t u r b i d i t e sequences cons is t ing of graded beds which contain f i n e s i l t s t o n e to conglomerate. Examples of sub -c lass II inc lude Meggen (Germany), Tom-Jason (Canada), S u l l i v a n (Canada). The major de f in ing c h a r a c t e r i s t i c s of t h i s group are: (1) They are always associated with t u r b i d i t e s of f l y s c h sequences. (2) They are f requent ly associated with a major penecontemporaneous f a u l t . (3) They are f requent ly associated with bar i t e and in fact many are r e a l l y b a r i t e deposi ts with r e l a t i v e l y minor, but in some c a s e s , economic Zn and Pb. T h i s sub -c lass has not been as extensive ly studied as sub-c lass type I and as more s i m i l a r deposits are discovered more c r i t e r i a w i l l hopefu l ly be de f ined . Tab le IX-4 l i s t s examples of sub-c lass II deposits and t h e i r di s t i nqui shi ng character!' s t i c s . Models for the o r i g i n of t h i s group of deposits are not as obvious as fo r sub-c lass I, but two appear most re levan t . F i r s t , some of the deposits may be the resu l t of syngenetic sulphide deposi t ion from f l u i d s ascending through the associated f a u l t s . These f l u i d s may or ig ina te due to a heat source at depth (Hodgson and Lydon, 1977) or may o r i g i n a t e from compaction f l u i d s (Morgant i , 1977b; Godwin et a l . , 1979) ( F i g . IX-11). A second poss ib le o r i g i n f o r deposi ts which contain mostly mas-s ive sulphides instead of laminated sulphides i s that sulphate that Table IX-4. Tab le of features associated with sub-c lass II type strat i form-sedimentary deposits (Doriepen, 1976; Dawson, 1977; E t h i e r et a l . , 1976; Freeze , 1966; Fredberg, 1976, Krebs , 1976b; Smith, 1978). GRADED DEEP WATER SILTSTONE & CHERT ASSOCIATED DEPOSIT BEDS CONGLOMERATE SANDSTOME (R)=RADIOLARIAN FAULTS BARITE SULLIVAN, (B .C . ) X X X X X minor MEGGAN, (Germany) X X X X X X RAMMELSBERG, (Germamy) X X X X X X DRIFTPILE, (B .C . ) X X X X ? X TOM-JASON, (Yukon) X X X X X X ORO, (Yukon) X X X X (R) X X NOR, (N.W.T.) X X X X (R) X X GHMS, (N.W.T.) X X X X (R) X X Figure IX-11. General ized synsedimentary model for the formation for sub-class II s t r a t i -form-sedimentary d e p o s i t s . Shallow source deposits ( l e f t ) contain only b a r i t e , while deeper source deposi ts contain Zn-Pb and Ag with bar i te ( r i g h t ) . o 271 was o r i g i n a l l y syngenetic b a r i t e was reduced during d i a g e n e s i s . Late compaction f l u i d s ( F i g . IX-12) could provide metals to these reduced zones (Carpenter et a l . , 1974). T h i s model i s very s i m i l a r to the general model for M i s s i s s i p p i Val ley type deposi ts (Jackson and B e a l e s , 1967; Anderson, 1978; Dozy, 1970) and a lso s i m i l a r to the model fo r f l u i d escape for o i l migrat ion ( F i g . IX-13) (T issot and Welte, 1978). Exp lora t ion fo r sub-c lass II deposi ts should focus on major f l y s c h sequences with s p e c i f i c explorat ion guided by the search for graben s t ructures and submarine fan geometry. Sub-c lass III deposi ts occur in major platform-marginal starved b a s i n s . To date , the Howards Pass deposits are the only major sulphide concentrat ions which are known to occur in t h i s environment. Even though the present t h e s i s has examined the key parameters of sub -c lass III d e p o s i t s , the lack of comparison with other deposi ts makes the a p p l i c a b i l i t y of these c h a r a c t e r i s t i c s elsewhere t e n t a t i v e . The present study has shown that the fo l lowing c h a r a c t e r i s t i c s are important in de f in ing the sub -c lass : (1) G r a p t o l i t i c o r g a n i c - r i c h mudstones are associa ted with the s u l -phide d e p o s i t s . (2) Paleogeographic in te rp re ta t ion shows that sub-c lass III depo-s i t s occur in the base of slope f a c i e s of an platform-marginal b a s i n . (3) The sulphide deposits are l im i ted to sub-basins within la rger deepwater starved bas ins . Sulphides are associated with l ime-stone and c h e r t , both of which are not common away from the sub-basin environment. Figure IX-12. Genera l ized d iagenet ic model of formation for sub-c lass II s t r a t i f o r m -sedimentary d e p o s i t s . Migrat ion of la te stage compaction f l u i d s migrate along sandstone aqu i fe rs and minera l ize synsedimentary bar i te d e p o s i t . HYDROCARBONS GENERATED (SCHEMATIC) B iochsmJcd CH,, H 2S WATER ESCAPE CURVE FOR MONTMORILLONTTE RICH MUD (SCHEMATIC) water available for migration Stage I dehydration 8. lattice water stability zone Stage II dehydration Stage M dehydration Stage TV dehydration WATER CONTENT OF SHALES FOR MONTMO-RILLONTTE RICH MUDS % WATER 1 50 80 turfoct sediment Pore 81 excess interlayer water expulsion Lattice water stability zone Interlayer water expulsion by random collapse of montmorillonite-lllite layers krterloyer wal«r expulsion by ordered IntsrtoyiftQ of illile loyers Deep burial water loss Interlayer water expulsion complete conversion toilite Figure IX-13. Water escape curves for various temperatures and depths of b u r i a l . These curves are useful in rap id ly deposited sediments, but may not be appl icable to starved basins (data from Powers, 1967; B u r s t , 1969; Chapman, 1972). Expulsion of ore forming f l u i d s could occur dur ing Stage II dehydration of Stage I i f a high geothermal gradient is present . 274 (4) The rate of deposi t ion fo r the r e l a t i v e l y th ick starved basin deposits is slow, less than 10 mm/1000 y r s . (5) The sulphide deposi ts are not associated with anomalous amounts of p y r i t e compared to that found in assoc ia ted sedimentary r o c k s . S p e c i f i c c h a r a c t e r i s t i c s noted in ind iv idua l deposi ts of sub-c lass III are presented in Table H-5. The general model for the sub-c lass III d e p o s i t s , as presented in the present study, proposes that br ines derived by compaction or c rusta l movements are trapped in sub-bas ins . Sulphide deposi t ion from these br ines could be due to pH change, mixing and s u l p h i d a t i o n . Explorat ion for sub-c lass III deposi ts should be aimed at loca t ing key sedimentary environments (Table IX-5) . The prime regional ob ject ive in such a search should be to locate major platform-marginal starved b a s i n s . Such basins do e x i s t , f o r example the O r d o v i c i a n - S i l urian in Central Nevada and in the Ouachita g e o c l i n e , both of which contain g r a p t o l i t i c o r g a n i c - r i c h mudstone sequences (Churkin , 1974; Ross, 1977) ( F i g . IX-14). Paleopole reconstruct ions may aid in loca t ing such se-quences because of the c l i m a t i c control of the deposi t ion of organic matter (Twenhofel, 1939; Ryan and C i t a , 1977; Berry and Wi lde, 1978) ( F i g s . IX-15, IX-16). Once such a basin has been found d e f i n i t i o n of the f a c i e s , e s p e c i a l l y the base of slope f a c i e s , the loca t ion of poss ib le sub-basins and/or geochemical anomalies should a id in evaluat ion of the potent ia l of the major basin for sub-c lass III Zn-Pb d e p o s i t s . METALLOGENY OF THE EASTERN YUKON Aho (1969) suggested that the eastern Yukon i s a Zn-Pb and W pro-v i n c e ; over the past 10 years his genera l i za t ions have proven e s s e n t i a l -Table IX-5. Table of features associated with sub-c lass III type strat i form-sedimentary d e p o s i t s . DEPOSIT GRAPTOLITES PYRITE CONTENT OF HOST ROCKS' ol lo PYRITE CONTENT OF DEPOSIT SUB-BASIN BASE OF SLOPE FACIES MIXED LIMESTONE AND CHERT XY X 2-5 2-5 X X X ANNIV X 2-4 ' 2-4 X X X OP X 2-4 2-4 X X X ITSI X 5 5 X X X PAB-HUG X 1-4 1-4 X X X 276 Figure IX-14. O r d o v i c i a n - S i l u r i a n s i l i c e o u s mudstones of North America. Dash l i n e s show areas of organic r i c h mudstones s i m i l a r to those deposited in the Selwyn-Basin during the same time per iod . (Based on data from Ross, 1977; Pat te rson , 1961; Ber ry , 1970). These s i l i c e o u s mudstones are prime target areas for explorat ion for Howards Pass type d e p o s i t s . Figure IX-15. Late Ordovic ian paleocontinental map, using X path and Y path. 'S(N) i s the south (north) geographic pole determined from apparent polar wandering paths (from Morel and I r v i n g , 1978). At t h i s time Howards Pass (X) was not fa r from the equator. The closeness to the paleo-equator may be s i g n i f i c a n t s ince sediments near the equator tend to contain higher organic carbon. ro Figure IX-16. Late S i l u r i a n to Middle Devonian paleocontinental map, using X path and Y path. S(N) is the apparent polar wandering paths (from Morel and I rv ing , 1978). Note that dur-ing t h i s time the Howards Pass area was s t i l l near the equator. ro oo 279 l y c o r r e c t , but whereas models fo r ind iv idua l deposi ts have been pub-l i s h e d (Morganti , 1975; Smith, 1978; Dawson and D ick , 1978) overa l l models have not been presented based on regional geologic environments. It is evident that most sulphide and sulphate deposits in th is area are re la ted to s t ra t ig raphy . Exceptions to th is are the W d e p o s i t s , which show a c lose spat ia l and temporal a s s o c i a t i o n with Cretaceous g r a n i t i c i n t r u s i o n s , although st ra t igraphy appears to have some control on these d e p o s i t s . Te t rahedr i t e -quar t z veins occur in the Iron Creek and Yara Peak formations throughout the Howards Pass area and l o c a l l y above the chert pebble conglomerate unit in the MacMillan Pass a rea . These veins occur p a r a l l e l to the Cretaceous regional cleavage in uni ts that contain over 150 ppm Cu. The a s s o c i a t i o n of copper - r i ch veins and copper r i c h sediments of regional extent suggests a l a te ra l secre t ion o r i g i n for the v e i n s . The major Zn-Pb and/or b a r i t e occurrences in the eastern Yukon are s p e c i f i c a l l y associated with three major horizons ( F i g . IX-17). L i t h o -l o g i c c o r r e l a t i o n of these p o t e n t i a l l y economical ly s i g n i f i c a n t horizons i s d i f f i c u l t because of f a c i e s changes. For example, between Tungsten and the I ts i Mountains the s t r a t i g r a p h i c sect ion descr ibed at Howards Pass i s a p p l i c a b l e , with r e l a t i v e l y minor m o d i f i c a t i o n , while the s t r a t i g r a p h i c sect ion in the MacMillan Pass area i s d i f f e r e n t due to a loca l graben s t ructure there (Smith, 1978). Recently Dawson (1977) reported on l im i ted f o s s i l c o l l e c t i o n s from the MacMillan Pass a rea . " . . . A l imestone bed immediately underlying the Pb-Zn-Ba horizon on the PETE claims contains la te Devonian conodonts ( B . E . B . Cameron, pers . comm., 1976). A limestone bed about 100 m. s t r a t i g r a p h i c a l l y below w i t h e r i t e - b a r i t e beds on the BAR claims contains ear ly to 280 PERIOD STRATIGRAPHIC SECTION AT HOWARDS PASS STRATIGRAPHIC SECTION AT MAC-MILLIAN PASS (a f ter Smith. 1978) MINERAL DEPOSITS (see appendix D for locat ions) M iss i ss ipp i an Devoni an Si l u r i an Ordovi ci an Cambri an Iron Creek fm. f£SS3 Selwyn Mtns. bari te hori zon top of sect ion in the Howards Pass area 'cKerf pebble conalomerate unit Yara Peak fm. upper chert fm. flaggy mudstone fm. Howards Pass fm. . act ive member Howards Pass fm. t rans i t i on fm. uni t ' 3 bar i te horizon unit 2 bar i te horizon unit 1 V V V M bar i te horizon Road River fm. MacPass graben establ ished bottom of sect ion in the MacPass area Pete (Ba) Tom-Jasen (Ba, Zn, Pb, Ag), Tea (Ba). GHMS (Ba), 0R0 (Ba), NOR (Ba, Pb), Moose (Ba). XY (Zn, Pb), ANNIV (Zn, Pb), OP (Zn, Pb). ITSI (Zn), PAB-HUG (Zn) Figure IX-17. Comparative s t ra t igraphy of the Howards Pass and Mac-Mi l l an Pass area showing s t r a t i g r a p h i c pos i t ion of Zn-Pb and/or ba r i t e d e p o s i t s . 281 Middle Devonian conodonts (Cameron, pe rs . comm., 1976). In the same area , but 1 km. to the south noted la te Devonian cora ls in reefa l carbonates underlying ba r i t e beds. A la te Devonian age of these b a r i t e beds i s i n d i c a t e d . Limestone beds within the th ick TEA b a r i t e sequence contain Devono-Mississ ippian conodonts and a brachiopod t e n t a t i v e l y assigned to the same broad range by Comeron (pers . comm., 1976). Carbonized wood of indeterminate genus was c o l l e c t e d a few metres below minera l i za t ion beds at TOM by Sangster (1971), and s i m i l a r material was found at about the same horizon at JASON by C L . Smith (pers. comm., 1976). These deposits may be M i s s i s s i p p i a n , as may the widespread nodular and lamel lar ba r i t e occurences higher in the Canol Formation, but d e f i n i t i v e f o s s i l evidence is l a c k i n g . " Further f o s s i l information on the MacMil lan Pass area was recent ly reported by Carne (1979). " . . . N o f o s s i l s or t race f o s s i l s were seen in rocks of Unit 1" (same nomenclature as F i g . IX-17 page 280). "An ammonite was c o l l e c t e d in 1976 by J . A . Morin from a dense, b lack , non-calcareous mudstone which under l ies beds of Unit 1 about 1 km. east of the de ta i led study area ( J . A . Mor in , pe rs . comm., 1976. The f o s s i l was sub-sequently i d e n t i f i e d as Ponticeras c f . P. tschernyschewi (Hozapfel) of Upper Devonian (Frasnian) a g e . . . " Thus the age of the TOM bar i t e deposit should be Frasnian or younger. More recent ly f o s s i l s have been c o l l e c t e d from the Earn Group in the Howards Pass map-area (S .P . Gordey, wr i t ten Comm., 1979). These inc lude conodonts Palmatelepsis glabra of Famennian (Upper Devonian) age. There appears to be disagreement as to the s t r a t i g r a p h i c pos i t ion of the f o s s i l s c o l l e c t e d from the Earn Group in the Howards Pass a rea , because the conodonts were extracted from carbonaceous mudstones which are s i m i l a r to several d i f f e r e n t s t r a t i g r a p h i c hor i zons . The author 's mapping ind ica tes that the conodonts are from grey weathering carbona-ceous mudstone which occur within the chert pebble conglomerate, s i m i l a r lenses have a lso been observed in the brown weathering Yara Peak Forma-t i o n . These grey weathering lenses may cause s t r a t i g r a p h i c problems in areas of poor exposure. Two p o s s i b i l i t i e s ex ist : (1) If the f o s s i l s are from carbonaceous mudstones of the Yarrow Peak formation or the chert pebble conglomerate, as is proposed here, then the MacMillan Pass b a r i t e h o r i z o n , which hosts the Tom d e p o s i t , is cor re la ted with eroded rocks that would o v e r l i e the chert pebble conglomerate in the Howards Pass a r e a . (2) If the f o s s i l s are from the Iron Creek format ion , as is proposed by members of the Geological Survey of Canada (S .P . Gordey and K. Dawson, Oral Comm., 1979), then the Selwyn Mountain Bar i t e Horizon and the MacMil lan Pass b a r i t e hor i zon . More conodont data c o l l e c t e d from areas of good s t r a t i g r a p h i c control would be useful in so lv ing th is s t r a t i g r a p h i c problem, but the a v a i l a b l e data supports the c o r r e l a t i o n presented in the present t h e s i s . T h u s , the sulphide horizons in the Howards Pass and MacMil lan Pass areas are to a great extent d i f f e r e n t ( F i g . IX-17). Within both areas the major Zn-Pb and/or Ba horizons are the Howards Pass format ion , the Selwyn Mountains and MacMillan Pass ba r i t e horizons and a s t r a t i g r a p h i c a l l y h igher , l i t t l e understood, bar i te h o r i -zon . A l l deposi ts observed by the present author in these horizons are s t r a t i f o r m . The Howards Pass deposits def ine sub-c lass III, while a l l the b a r i t e deposi ts with or without Zn and Pb (Ag) have c h a r a c t e r i s t i c s t y p i c a l of sub-c lass II. The reason fo r the Zn-Pb province is not c l e a r . Three separate sedimentary- tectonic features are present in the reg ion . The Howard Pass deposits are associated with the starved Selwyn B a s i n , the Selwyn 283. Mountains b a r i t e horizon is associated with t u r b i d i t e s in the Iron Creek formation and the Tom-Jason deposi ts are associated with a graben in the MacMil lan Pass a r e a . A l l appear to be assoc ia ted with evo lu t ion of basins and re la ted f l u i d migra t ion . Loca l l y organic matter appears to be important because of i t s a s s o c i a t i o n with the sulphides in the de-pos i ts in genera l . The e f fec t iveness of metal -organic complexing in producing metal r i c h sediments has been demonstrated (Rashid , 1972, 1974; Degens, 1974), but in the case of the Paleozoic sediments in the region considered here i t i s more l i k e l y that organic carbon is more important in the generat ion of sulphide (Berner, 1971; R ichard , 1973) than concentrat ing the metals by che la t ion or adsorp t ion . 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Z a n g e r l , P . , Ra iner , D . , and Richardson, E . , 1963, The pa leoecologica l h is tory of two Pennsylvanian black shales: F i e l d i a n a - G e o l . Mem. v . 4 , 352 p. Z o b e l l , C . E . , 1958, Ecology of su l fa te - reduc ing bacter ia : Producers Monthly, v. 22, p. 12-29. 310 APPENDIX A- PLATE LOCATION MAP Figure A - l . Locat ion map showing the map areas fo r P la tes I, II, III and IV in the Nahanni map-area. 311 Appendix B MINERAL IDENTIFICATION METHODS The method of semi -quant i ta t ive mineral i d e n t i f i c a t i o n used in the present study is that of Schultz (1964). Clay minerals were fur ther studied by methods descr ibed by C a r r o l l (1970). Representat ive rock samples from d r i l l cores were analyzed by x-ray d i f f ractometer using an aluminum pack-type mount. (McCreery's procedure; Klug and Alexander , 1962). Locat ion and i n t e n s i t y was measured from the s t r i p chart and re-corded. Sample data was compared with that of standards to der ive the mineral percentages. Schultz (1964) found that repeated analyses ind icated that v a r i a -t i o n s in sampling, sample prepara t ion , machine response and i n t e r p r e t a -t i o n by the operator a l l a f fec t the p r e c i s i o n of x-ray determinat ions. Inconsistency of in te rp re ta t ion has the greatest e f f ec t on the determi-nat ion of the c lay minera ls . If a mineral i s present in an amount greater than 15% of the sample, the p r e c i s i o n of i t s determination gen-e r a l l y i s ± 10%. Minerals present in amounts of a few percent or l ess are not c o n s i s t e n t l y detected. Minerals with less than 5% were undetect-able due to a broad increase in background bel ieved to be a resu l t of carbon compounds in the mudstones. Cubi t t (1975) has reduced the error to 6% by complex sample prepara t ion , but his modi f ica t ions were not used because of the general nature of the present study. The x-ray d i f f r a c t i o n methods used to i d e n t i f y c lay minerals are those recommended by C a r r o l l (1970). Samples were prepared in a way which enhanced basal r e f l e c t i o n s of the p h y l l o s i l i c a t e s . A sample s l u r -ry was placed on a glass s l i d e and di f f ractograms made a f te r drying 3 1 2 overnight in a d e s i c c a t o r . Samples were then heated at 500°C fo r one hour in a furnace; a f te r coo l ing to room temperature in a d e s i c c a t o r , another d i f f ractogram was made of the s l i d e . The major c lay mineral d i f -fractogram peak noted was at approximately 1 0 ° . Thus, the poss ib le c lay minerals present were l imi ted to i l l i t e and/or muscovite . The d i s t i n c -t i o n between the minerals was based on the sharpness of the 8 . 1 ° peak, the i l l i t e peak (IMQ) being more d i f f u s e than the muscovite (2M) peak (Figure 4 , C a r r o l l , 1970; Grim, 1968). APPENDIX C LOCATION OF STRATIGRAPHIC SECTIONS Figure C - l . Locat ion of s t r a t i g r a p h i c sect ions discussed in t e x t . I d e n t i f i c a t i o n is by G . S . C . nomenclature, and re fe rs to the composite s t r a t i g r a p h i c sect ions presented in chapter II. Ba denotes bar i te sect ion ( F i g . 11-26). Figure D - l . Locat ion map of Zn, Pb and Ba occurrences in the Yukon and Northwest T e r r i t o r i e s re fer red to in the t e x t . T r i a n g l e s mark s p e c i f i c l o c a t i o n s . APPENDIX E . CHEMICAL METHODS AND DATA FOR CHAPTER VI TABLE E - l . Methods used in chemical analyses oF Howards Pass sampl ELEMENT METHOD DETECTION PRECISION LIMIT (ppm) Mo AAS 1 ± 10% Cu AAS 2 ± 5% Zn AAS 2 ± 5% Pb AAS 2 ± 5% Cd AAS 0.2 ± 5% Ni AAS 2 ± 5% Co AAS 2 ± 5% Ag AAS 0.02 ± 10% Mn AAS 2 ± 5% V AAS 10 ± 15% Ba AAS 400 ± 20% Fe AAS 2 ± 10% Ca AAS 500 ± 15% Mg AAS 500 ± 15% K AAS 500 ± 15% Na AAS 200 ± 15% P AAS 500 ± 10% S LECO 500 ± 10% C ( o r g ) L 0 I ( 5 5 0 ° C ) 300 ± 15% C (C0 3 =) L 0 I ( 1 0 5 0 ° C ) 500 ± 15% S i 0 2 XRF 0.5% ± 10% A 1 2 0 3 XRF 0.1% ± 15% AAS = atomic absorpt ion spectrometry LOI = loss on i g n i t i o n XRF = x-ray spectrochemistry ( f lourescence) Tab le E-2a . Data f o r chemical analyses on core from d r i l l hole (DDH) 12, shown with depth in terva l from surface ( in f e e t ) . PPM I * D e p t h ( f t ) Mo Cu Zn Pb Cd Ni Co Ag Mn V Ba F e ( t ) CaO MgO K 2 0 C(LOI) P ? 0 5 S 22 -30 23 91 120 90 l .0 97 11 l .17 90 530 6200 3 .30 .98 1.25 1.66 6 .7 .643 .30 30-10 33 88 100 110 .9 130 19 l .10 102 550 5600 3.70 2 .66 1.07 4 .49 8.6 .371 .20 1 0 - 5 0 29 58 150 60 2 .0 111 11 1 .01 171 660 3500 2 .03 12 .01 1.75 3.65 6.4 1.177 .31 50-57 37 69 160 60 3 .0 125 11 .92 192 500 3300 2 . 0 3 9 .10 3.35 3.34 11.5 .934 .44 01-90 5 51 230 30 .7 82 8 .25 29 300 1700 .29 7 .04 .79 2 .23 7.2 2 .279 .50 90-100 7 39 230 30 .7 77 8 .18 17 210 1200 .43 7 .11 .73 2 .57 6.4 1.061 .60 100-110 5 39 120 30 .7 GO 11 . 15 112 190 1300 .62 15 .96 .57 1.60 5.6 1.805 .42 110-120 16 60 070 7100 38 0 52 10 .90 170 270 200 2.71 19 04 .11 .21 1.9 .210 2 .32 120-130 6 58 190 120 3 .0 68 10 .36 108 130 1000 1.30 13 72 .42 1.75 4 . 8 2 .180 1 .21 130-110 7 51 760 170 I .0 01 12 .31 210 130 1600 1.05 19 00 .39 l .31 1.1 1.807 1 .21 110-112 15 00 1700 1030 100 0 105 25 .18 137 210 1500 1.59 0 82 .35 l .51 3.2 .199 1 .36 112-115 10 91 5000 1650 100 0 110 21 .10 107 220 1900 1.89 9 30 .39 1.68 4 .7 .179 2 .02 115-150 5 71 1300 110 100 0 120 17 .11 03 300 1600 1.36 8 26 12.04 1 .07 2 .2 2 .157 1 .10 150-152 7 83 2000 120 100 0 112 21 .16 91 200 1100 1.63 fl 26 .71 1.91 2 .0 2 .038 1 .70 152-151 10 59 2000 770 100 0 100 22 .62 111 200 1100 1.95 10 78 .73 1.61 2 .7 2 .036 1 .78 151-157 2 101 15100 53000 100 0 120 19 1 .67 117 320 800 5 .50 10 00 .60 1.46 5 .3 1.626 4 .00 157-159 13 61 2800 110 100 .0 111 21 .52 120 330 900 1.86 3 92 .55 1.63 4 . 3 2 .290 1 .70 159-163 0 59 2500 290 100.0 H O 21 .11 220 210 1100 1.34 16 94 .36 1.15 3.5 1.189 1 .52 163-167 11 38 3300 370 100 0 95 20 .39 115 270 900 .99 10 92 .19 .06 2 .8 1.626 .92 167-169 10 61 6200 750 100.0 120 20 .17 102 100 900 1.52 8 40 .21 1.20 4 . 9 2 .155 1 .66 169-171 9 59 1320 70 100 0 90 21 .23 103 250 500 1 .62 5 04 .21 .01 2 .9 1.027 1 .32 171-173 7 75 18800 2100 100 0 95 23 6 .00 no 310 800 2 .15 5 18 .18 .09 3.6 1.637 2 06 173-176 10 30 1580 510 100 0 101 21 .10 120 300 700 1.30 1 34 .19 .82 3.2 1.591 1 00 176-181 11 31 2300 180 100 0 81 26 .27 135 110 700 1.35 1 62 .16 .80 3.1 1.321 1 02 181-181 21 36 1110 200 100 0 100 22 1 .00 101 520 000 1 .53 6 02 .21 .91 3.4 2 .500 1 01 181-189 11 32 1700 no 100 0 71 32 .61 117 560 500 1.99 3 36 .19 .67 3.6 .010 1 86 189-191 23 18 3000 110 100 0 95 15 1 .23 76 1020 700 1.05 2 66 .31 1 .15 4 .6 .689 1 18 191-195 11 81 19600 I I300 200 ,0 80 30 2 .10 103 520 100 5.05 6 86 .19 .60 5.1 .279 1 00 195-197 31 12 16200 1700 100 0 86 37 .51 180 110 100 2.21 7 00 .11 .43 1.1 .170 2 61 198-201 30 53 l l 000 OOOO 100 .0 98 35 1 .00 163 . 610 900 3.60 6 30 .15 .62 1.9 .110 1 00 201-205 51 58 31800 6000 100 0 108 29 1 .21 210 630 1300 2 .57 9 66 .23 1.01 4 . 9 .172 3 71 205-210 11 29 31600 12600 100.0 50 22 .03 160 210 100 1.82 31 16 .21 .36 1.6 .229 1 02 210-211 18 29 29200 8000 100 0 62 23 .88 350 310 500 2 .37 29 40 .21 .55 2 .5 .251 1 00 211-218 25 37 13600 13100 200 0 72 27 1 .35 310 160 400 3 .20 16 94 .23 .50 2 .0 .222 1 00 210-223 26 13 UOOO 5900 100 0 00 23 1 01 260 520 600 3.50 23 24 .28 .65 3.4 .309 1 06 223-227 20 58 7800 3800 100.0 85 23 1 06 205 530 600 2 .50 10.06 .26 .71 3.7 .160 3 02 227-220 26 11 I OOOO 5000 100 0 100 28 1 28 123 610 400 2 . 2 0 5 88 .21 .71 5 .3 .202 2 52 220-231 16 70 161000 176000 700 0 68 11 11 00 167 350 400 4 . 0 0 6 02 .08 .22 .1 .133 1 00 231-233 5 85 100000 27200 100 0 75 15 7 00 122 350 500 3.25 3 64 .15 .12 1.0 .316 4 00 233-235 35 72 36 000 26100 100 0 91 16 6 00 158 730 600 1.39 8 82 .26 .82 5.1 .710 3 50 235-239 21 72 50000 10200 200 .0 63 21 1 16 380 450 300 1 .67 35 70 .31 .31 2.1 .536 1 22 239-211 75 196 26100 7100 100.0 129 37 5 00 99 1070 500 2 . 0 3 9 94 .16 .48 1.9 2 .153 1 00 211-216 65 113 15500 2000 100 0 90 23 1 18 196 1100 400 1.72 29 12 .21 .53 5.2 .992 2 18 216-217 10 210 10200 2900 100 0 110 27 2 11 12 1350 100 7 .90 9 . 10 .19 .62 7.6 1.333 1 00 217-219 21 210 15700 2100 100 0 120 36 1 59 111 1160 100 7 .20 0 54 .16 .48 7.0 .580 1 00 219-250 35 85 13300 3100 100.0 76 20 1 21 175 810 300 1.15 20. 50 .10 .34 3.1 .758 87 250-260 62 125 16600 1000 65 . 0 127 10 3 00 109 1320 200 1.41 11 . 31 .21 .62 7.4 .735 2 32 260-270 63 170 10500 5700 1fi .O 200 10 5 00 51 2050 500 1.90 7. 81 .37 1.32 9 .9 2 .213 2 64 Table E-2b. Data for chemical analyses on core from d r i l l hole (DDH) 12, shown with depth in terva l from surface ( in f e e t ) . Depth ( f t ) PPM % Mo Cu Zn Ph Cd Ni Co l\g Mn V Ba fe(l) CaO MgO K ; >° C ( L 0 ! ) P 2 0 & S 2 / 0 - 2 0 0 31 72 4500 8900 15 0 146 12 4 .00 102 1030 600 2 31 7 94 .42 2 59 6 .7 .492 2 80 280-290 22 50 1000 620 4 5 140 12 1.10 63 1020 1000 2 38 2 94 .58 3 98 6 .3 .275 2 70 290-300 25 54 2400 110 10 5 140 11 1.05 93 1150 600 2 11 5 74 .52 3 65 5.9 .218 2 32 300-310 36 52 3300 220 17 1 150 11 1.22 70 1530 1000 1 98 3 64 .47 3 07 6 . 3 .247 2 42 310-320 36 60 3300 540 18 2 154 10 1 .24 73 1530 900 2 00 3 22 .45 2 95 6 .9 .170 2 26 320-330 46 65 3000 460 17 0 143 13 1.02 111 1330 500 2 27 6 0? .60 3 41 7.0 .263 2 56 330-310 38 52 1220 400 10 0 166 13 1.27 93 1370 600 2 35 4 90 .66 3 55 6 .7 .309 2 70 340-350 50 59 123 96 6 146 14 1.09 147 1360 600 2 80 9 38 .62 3 07 7.2 .307 2 96 350-360 44 66 122 84 1 170 12 1.13 84 1700 800 1 33 4 48 .79 3 94 9 .3 .488 2 80 360-370 46 63 1830 70 18 3 143 12 1 .42 54 1950 1000 2 15 2 66 .76 4 13 8.9 .275 2 30 370-380 21 60 3900 280 14 4 122 11 1.27 73 1390 600 2 28 3 64 .63 3 72 7 .3 .376 2 58 380-390 16 50 1740 1640 6 7 15? 11 1.67 51 1170 900 2 75 1 96 .63 3 94 6 .6 .279 3 16 390-400 19 61 1700 360 7 0 158 12 1.15 106 1000 800 2 46 5 74 .58 3 70 5 .5 .192 2 86 400-410 31 50 4 300 380 31 0 166 11 1.15 64 1480 1000 1 89 2 24 .51 3 12 6 .7 .236 2 18 410-420 27 57 2500 420 12 6 154 12 1.11 90 1240 1400 1 93 4 34 .60 3 60 5.1 .241 2 14 420-430 37 64 3800 30 3 5 82 17 1.30 189 720 3000 2 24 15 54 5.51 3 31 2 .8 .247 1 08 430-440 35 84 2010 200 11 0 195 12 1.33 63 1520 1500 3 12 2 94 .60 3 55 7.2 .250 3 26 440-450 12 44 2400 130 7 4 72 18 1.26 77 550 800 73 7 28 .65 3 40 2 . 9 .275 3 02 450-460 45 63 230 360 2 0 181 14 1.56 154 1370 1500 2 78 9 10 .63 3 55 5 .9 .309 2 94 460-470 29 83 930 600 11 1 270 12 2 .08 53 1700 2200 2 70 2 94 .74 3 79 7.2 .392 2 84 470-480 23 74 66 50 1 1 180 14 1.62 151 1440 2000 2 42 10 64 .66 3 41 5.7 .346 2 54 480-490 30 75 95 66 1 5 200 13 1.62 97 1410 2900 2 90 6 44 .71 3 72 7.7 .296 2 92 490-500 21 46 550 27 4 0 104 16 .90 129 540 8200 2 70 9 66 2.77 4 66 4 . 5 .256 2 40 500-510 35 38 130 20 1 4 60 18 .69 159 440 8600 2 51 17 08 2 .96 4 42 3 .3 .213 1 92 510-520 47 52 340 5 2 7 02 16 .70 142 530 6500 2 69 16 24 4 .55 3 89 3.5 .190 2 08 520-530 42 42 460 13 4 0 74 17 .55 175 400 4400 3 15 17 50 5 .10 3 36 3.1 .160 2 10 530-540 26 52 210 20 2 0 74 16 .78 160 510 4100 2 66 13 72 4 .54 3 74 3.0 .131 1 54 540-550 29 58 270 20 1 9 68 15 .87 163 550 3800 2 33 9 94 3.76 4 01 3.1 .200 1 14 550-560 28 59 56 28 1 60 15 1.00 188 520 3400 2 48 12 41 6.35 3 98 3.2 .160 1 08 560-570 21 58 280 77 15 0 155 10 1.11 60 1420 1400 1 85 2 38 .52 3 10 6 .2 .236 2 14 570-580 39 50 460 70 2 7 128 16 2 .50 135 1300 2500 2 06 10 76 3.66 2 95 3.9 .176 1 42 580-590 42 48 450 73 3 1 132 17 .77 135 800 3700 2 67 11 62 2.07 4 27 4 . 9 .311 1 84 590-600 43 60 420 20 3 2 23 16 1.01 189 760 2900 2 14 20 44 4 .37 2 90 3.7 .215 1 04 600-610 50 110 930 16 6 9 89 16 1.96 167 1130 3000 2 18 19 18 3.04 3 07 3 .5 .147 1 20 610-620 32 43 760 400 3 4 108 17 .64 166 690 3100 2 70 12 18 2 .98 4 03 3.4 .389 1 70 Tab le E-3a . Data for chemical analyses on core from d r i l l hole (DDH) 18, shown with depth in te rva l from surface ( in f e e t ) . PPM % Depth ( f t ) Mo Cu Zn Pb Cd Ni Co Ag Mn V Ba F e ( t ) CaO MgO K ? 0 C(L01) P 2 ° 5 S 86 -90 I 27 42 3 2 18 12 111 120 10000 99 3 08 1.60 3.94 .6 .073 42 90-100 I 30 37 6 2 31 25 - 250 130 10000 2 77 6 44 2.71 3.55 .9 .087 2 10 100-110 I 44 27 4 2 28 17 - 171 130 11500 l 24 1 20 2 .30 4 .13 .3 .076 53 110-120 I 14 26 2 2 28 18 - 270 110 11700 2 53 5 88 3.32 3.72 .8 .080 1 29 120-130 l 16 24 3 2 20 16 - 176 110 9500 I 71 4 20 2 .48 3.89 .5 .069 93 130-110 l 22 22 2 2 12 25 - 350 120 7600 4 45 7 14 3.74 3.46 1.5 .076 3 34 140-150 l 32 24 8 2 25 20 - 250 100 5100 l 95 6 44 3.56 3.43 1.1 .064 83 150-160 2 20 40 2 2 27 18 2 .00 173 130 3800 l 85 4 20 2 .99 3.60 1.2 .048 1 15 160-170 13 51 55 38 2 112 30 .75 207 180 3600 3 70 6 16 2.87 3.74 5 .9 .073 2 56 170-180 8 90 290 33 5 121 16 .58 176 200 1900 2 46 12 18 .73 1.73 6 .3 1.706 1 32 130-190 15 63 54 26 2 106 20 .48 206 250 1100 2 44 19 46 .79 1.68 5.4 1.621 1 56 190-200 7 98 70 34 3 144 14 .45 89 240 1500 2 62 7 11 .65 1.78 7 .8 1.811 1 86 200-210 3 90 37 40 2 133 • 17 .40 155 220 1500 2 32 13 86 .57 1.21 6 .3 1.903 1 72 210-220 8 136 330 70 6 131 19 .50 147 310 1100 2 98 10 50 .62 1.32 6 .7 1.926 1 86 220-230 7 94 330 30 2 127 20 .32 191 200 1200 l 80 14 14 .55 1 .60 5.9 1.793 1 38 230 -240 1 71 58 50 2 116 14 2 .00 55 240 2000 l 46 8 12 .55 1.81 7.0 .854 1 56 240-250 2 61 900 40 2 3 105 12 2 .00 51 150 1800 l 25 8 68 .45 1.84 7.6 .813 1 09 250-260 1 66 260 30 C 100 12 2 .00 60 150 2300 97 8 68 .37 1.79 5.1 .813 1 02 260-270 3 75 640 32 I 1 112 14 2 .00 73 170 1900 l 43 9 38 .34 1.64 5.6 .813 1 50 270-280 6 74 55 71 1 0 106 16 4 .00 195 180 1900 l 72 19 71 .31 1.28 5.1 .802 1 78 280-290 7 78 2900 200 8 0 98 10 4 .00 77 520 1100 2 19 8 68 .28 1.02 5.6 .866 2 80 290-300 11 51 3300 162 8 7 102 9 4 .00 52 650 1600 90 5 71 .31 1.02 5 .5 .829 1 07 300-310 8 30 710 . 120 2 1 63 9 2 .00 119 400 900 87 8 54 .24 .87 2 .9 .760 91 310-320 10 35 900 520 2 7 60 9 1.50 180 470 1000 l 20 3 78 .32 1.08 2 .2 .845 90 320-330 13 55 1310 350 3 6 77 10 .96 300 580 1200 2 09 14 98 .36 1.08 4 . 0 .341 2 06 330-340 11 58 2200 185 6 5 80 7 .82 77 490 1300 87 4 76 .26 1 .23 3.6 1.218 82 340-350 20 40 1470 180 5 1 79 10 .84 230 550 1000 95 11 98 .28 1.09 5 .0 1.310 94 350-360 15 30 370 128 1 3 71 5 .62 109 620 900 63 3 61 .26 1.30 5.7 .632 50 360-370 16 28 3400 62 9 0 76 4 1.10 45 630 900 72 1 12 .39 1.62 6 .8 .135 80 370-380 12 110 5300 1770 13 3 82 12 1.21 260 510 400 2 38 18 76 .42 1.23 4 . 0 .332 2 48 380-390 9 40 3000 150 8 1 70 6 .80 75 500 700 l 05 9 66 .34 1 .02 3.9 .465 1 30 390-400 15 36 2300 79 6 0 60 7 1.93 82 160 300 82 6 30 .22 .87 3.1 .909 84 400-410 11 28 2700 65 7 0 65 5 .60 55 190 100 49 3 22 .21 .97 3.6 .627 68 410-420 18 29 3300 1830 8 5 92 7 1.26 58 770 800 77 3 61 .31 1.39 5.4 .858 94 420-430 9 60 720 320 2 2 81 8 .83 87 510 300 2 27 7 12 .28 1.36 ' 4 . 7 1.150 2 34 130-441 12 52 800 410 2 1 80 8 1.00 92 600 100 2 30 4 18 .31 1.26 5 .3 .875 •1 24 141-443 28 47 21900 17800 237 0 93 8 4 .00 116 900 800 2 13 3 92 .28 1.19 5.6 .195 3 82 143-444 28 108 81600 11800 283 0 100 8 4 . 0 0 109 660 100 8 00 70 .21 1.23 1.1 .302 4 00 446-419 16 63 52000 15400 158 0 73 9 1.52 157 180 800 7 00 5 71 .18 .81 7.8 .172 4 00 449 -453 23 22 1800 500 12 0 58 13 2 .00 280 390 500 l 51 14 00 .11 .43 8 .3 .211 1 92 153-154 70 19 15500 120 62 0 156 17 2 .00 112 1250 1100 2 30 7 70 .32 1.61 3.2 .309 3 42 454 -158 25 90 90000 32000 298 0 78 10 4 . 0 0 320 500 700 4 60 10 50 .15 .82 10.2 .220 4 00 458 -463 9 15 19100 9900 79 0 39 16 4 . 0 0 530 170 300 l 11 37 52 .16 .19 6 .3 .208 2 20 163-167 15 29 38400 10600 121 0 60 14 4 . 0 0 300 320 100 2 08 22 12 .19 .58 .6 .277 4 00 467-170 13 32 80800 23600 296 0 47 12 4 . 0 0 250 260 500 l 61 15 96 .13 .54 3 .3 .261 1 00 470-173 13 21 14500 6600 51 0 39 17 4 . 0 0 370 170 300 8 90 28 56 .13 .29 3.6 .316 4 00 173 -178 23 50 84800 16100 210 0 65 14 4 . 0 0 410 370 400 4 30 20 02 .19 .50 4 . 3 .288 4 00 478-179 21 12 68000 32800 201 0 60 13 6 .00 370 370 300 2 56 22 54 .22 .56 2 .9 .213 1 00 179 -183 16 31 24800 8600 80 0 64 13 2 .00 250 360 500 2 18 16 24 .21 .57 4 . 3 .252 1 08 Table E-3b. Data for chemical analyses on core from d r i l l hole (DDH) 18, shown with depth in terva l from surface ( in f e e t ) . Depth ( f t ) PPM % Mo Cu Zn Ph Cd Ni Co Ag Mn V Ba F e ( t ) CaO MgO C(LOI ) P 2 ° 5 S 1 0 3 - 1 8 5 21 32 23700 0600 7 5 . 0 64 12 4 . 0 0 230 300 300 2 . 1 3 15 .26 .21 .56 3.9 .231 3 .98 1 8 5 - 1 0 0 21 20 22600 6200 7 1 . 0 62 12 2 . 0 0 220 370 500 1.06 17 .22 .19 .55 3.9 .108 3 . 4 8 108 -190 22 61 55600 12600 1 5 0 . 0 60 12 2 . 0 0 240 100 600 2 . 5 0 13.44 .24 .72 4 .7 .199 4 . 0 0 190 -195 17 31 31600 7300 8 2 . 0 60 11 2 . 0 0 170 350 500 2 . 4 9 1 4 . 0 0 .21 .50 5 .3 .254 4 . 0 0 1 9 5 - 4 9 0 20 28 1300 680 6 . 0 51 16 2 . 0 0 107 340 500 1.97 2 6 . 3 2 .24 .59 3.7 .298 2 . 6 6 4 9 8 - 5 0 3 14 32 26100 23400 1 5 1 . 0 55 16 4 . 0 0 205 300 400 2 . 5 0 26 .32 .23 .50 2 . 0 .126 4 . 0 0 503 -506 30 32 10000 0200 3 7 . 0 01 16 2 . 0 0 185 630 500 1.36 2 0 . 7 2 .28 .79 4 . 5 .250 2 .02 5 0 6 - 5 ) 0 14 22 2600 OOOO 8 . 0 60 14 2 . 0 0 203 310 400 1.32 1 9 . 6 0 .15 .28 2 .9 .007 1.60 5 1 0 - 5 1 3 27 50 13000 7100 4 3 . 0 95 17 4 . 0 0 340 580 300 3 .95 24 .22 .26 .46 5.2 .763 4 . 0 0 513 -516 I'l 130 18000 3000 5 7 . 0 128 17 2 . 0 0 105 1000 600 2 . 9 9 5 .60 .20 .70 6 . 3 .829 3 .88 516 -517 21 29 9000 630 3 1 . 0 70 10 2 . 0 0 86 640 400 .45 7.56 . 1 3 .29 4 . 5 .918 . 0 0 517 -522 43 90 6100 1210 3 3 . 0 90 20 4 . 0 0 270 850 400 1.74 30 .66 .21 .30 4 . 9 1 .337 2 . 2 6 522 -526 65 151 16300 2300 1 8 . 0 124 13 4 . 0 0 96 1540 500 1.84 9 .24 .26 .67 8 . 3 .072 2 . 7 0 526-531 42 00 7100 3000 2 5 . 0 153 10 6 . 0 0 131 1410 700 2 . 2 7 15 .96 .42 2 . 0 0 7.9 1 .718 2 . 0 0 531 -533 23 136 700 590 1.7 160 20 2 . 0 0 160 980 600 4 . 7 5 1 4 . 9 8 .45 2 . 6 0 8 . 3 .634 4 . 0 0 533 -536 11 69 3800 217 1 6 . 3 160 15 2 . 0 0 70 1300 700 2 . 4 8 3 .22 .50 3 .77 13 .9 . 527 . 2 . 6 2 536 -540 15 65 1620 212 7 .0 1 70- 15 2 . 0 0 50 1670 500 2 .75 1.96 .62 4 . 0 0 8 .6 .424 2 .62 540 -550 17 60 2300 167 1 0 . 7 144 13 1.00 73 1250 500 2 .15 3 .50 .57 4.01 5 .9 .314 2 . 4 1 550 -560 15 60 640 108 4 . 7 145 12 75 1200 500 2 .64 4 .34 .60 4 . 3 2 5 .6 .339 2 .71 5 6 0 - 5 7 0 18 60 300 156 3 .0 147 11 76 1230 700 2.61 3.64 .60 4 . 2 0 7.1 .236 2 . 0 0 570 -500 37 61 2600 00 2 0 . 5 157 11 74 1510 800 2 .34 3 .08 .47 3 .70 6 . 3 .256 2 . 5 6 500 -590 40 62 1920 70 18.1 164 12 127 1400 100 2 . 6 2 7 .42 .57 3 .72 5 .8 .259 2 . 9 2 590 -600 33 60 450 96 5 . 2 185 13 133 1500 800 2 . 6 8 7 .28 .65 3 .02 7.0 . 298 2 .64 6 0 0 - 6 1 0 10 65 870 66 11 .6 196 12 n o 1600 600 2 . 6 3 6 . 1 6 .63 3 .86 0 .5 .332 2 .61 6 1 0 - 6 2 0 30 69 400 61 5 . 8 200 12 n o 1670 700 3.01 6 . 0 2 .70 4 . 1 0 8 .9 .371 2 . 0 0 6 2 0 - 6 3 0 25 71 60 56 1.0 197 11 118 1500 600 2 . 7 0 6 . 1 6 .60 4 . 0 8 7 .3 . 3 0 0 2 .64 6 3 0 - 6 4 0 25 68 136 16 1.1 185 14 155 1230 700 2 . 8 7 9 .24 .79 4 . 4 6 8 .4 .424 2 .04 6 4 0 - 6 5 0 13 14 83 36 .2 122 15 210 490 900 2 . 1 2 2 0 . 5 8 .62 3 .06 3 .5 .371 2 . 0 2 6 5 0 - 6 6 0 9 03 130 10 .7 192 13 00 530 1100 1 .45 3 .08 .97 5 .94 8 .7 .364 2 .72 6 6 0 - 6 7 0 0 88 290 33 1.4 106 12 83 560 1100 2 . 4 5 3 . 5 0 .92 5 . 9 0 6 .5 . 410 2 . 4 0 6 7 0 - 6 8 0 10 63 44 20 .2 148 13 121 420 1000 2 .24 5 .74 .89 5 .09 5 .9 .289 2 . 3 0 6 8 0 - 6 9 0 2 58 25 20 .2 114 13 77 350 000 2 .06 4 . 4 8 .99 6 .24 5 .2 .279 2 . 2 0 6 9 0 - 7 0 0 3 63 32 30 .2 112 13 39 410 900 1.89 1.96 1.05 6 . 6 2 5 . 3 .426 l . 88 700 -710 2 68 30 33 .2 114 13 43 310 1400 2 . 3 3 1.02 1.00 6 . 2 9 4 . 9 .364 2 . 3 0 710 -720 3 40 24 27 .2 83 14 101 240 1000 1.58 5 . 1 0 1.02 5 .66 4 . 0 .344 1.54 720 -730 2 41 29 26 .2 77 13 75 210 1200 1.80 5 .32 .98 5 .47 4 . 0 .836 l .82 730-735 3 43 20 26 .3 80 12 73 210 1200 1.17 3 .50 1.13 6 .17 5 .5 .742 l .22 Table E-4a . Data fo r chemical analyses on core from d r i l l hole (DDH) 19, shown with depth in te rva l from surface ( in f e e t ) . Depth ( f t ) PPM % Mo Cu Zn Pb Cd Ni Co An Mn V Ba F e ( t ) CaO MgO K20 C(LOI) P 2 0 5 S S i 0 2 A l 2 0 3 220-230 3 30 22 10 .2 26 13 .4 200 90 8500 2 .00 5 74 3 .13 3.41 1 3 .144 1 42 61 52 6 .81 230-210 3 25 28 11 .2 29 16 .52 229 100 8700 1 .94 5 46 3.19 4 .49 1 1 .222 1 22 62 45 8 .02 210-250 2 23 16 13 .2 27 13 .40 111 no 7200 1 .40 3 70 2.51 4 .41 1 3 .087 98 64 03 8 .36 250-260 5 43 42 13 .2 66 21 .75 101 170 6000 5 .30 5 74 2 .69 3.36 3 5 .282 4 00 57 37 9 .20 260-270 8 38 93 33 .2 66 20 1.00 123 200 6900 2 30 2 80 2 .35 4 .90 3 5 .543 2 22 61 24 9 .50 270-280 25 16 46 50 .2 89 17 .70 204 500 3100 2 22 12 74 1.20 3.10 6 7 .515 2 04 54 50 6 .55 280-290 18 80 64 30 .4 90 18 .90 241 420 5200 2 35 11 90 3.08 3.81 6 5 .366 2 28 10 15 7.16 290-300 25 54 000 31 3 .5 104 20 1.00 185 500 1100 2 22 13 44 3 .43 3 .10 6 7 1.560 2 20 18 60 6.19 300-310 12 57 72 40 .7 122 17 .84 99 580 3200 1 85 9 10 3.14 3.12 6 2 1.981 1 72 57 43 6 .69 310-320 8 96 166 43 :5 148 16 .79 01 300 3600 1 90 8 96 2.17 3.60 10 6 1.947 1 86 58 73 6 .16 320-330 6 «6 400 40 1.3 130 15 .83 80 320 3000 1 78 8 12 1.59 3.12 5 7 1.743 1 80 63 43 6 .02 330-310 15 86 2000 154 6 . 7 114 15 1.35 121 650 3000 1 57 12 04 2.01 2 .95 5 0 1.791 1 96 56 23 5 .79 310-350 8 89 700 62 2 . 0 130 17 1.02 122 460 2900 1 96 13 44 1.56 2 .90 7 6 1.578 2 01 54 25 5 .77 350-360 9 72 420 54 1.0 105 16 .87 120 390 2100 1 59 13 72 1.22 2.71 1 9 1.626 1 62 56 18 5 .25 360-370 3 82 420 44 1.0 112 15 .49 80 200 2000 1 34 10 64 .62 2 .06 9 1.667 1 38 61 22 1.34 370-380 1 82 380 103 .9 99 14 .37 77 130 2200 1 24 8 40 .45 2 .10 1 3 1.495 1 34 68 65 4 .25 300-390 5 74 1400 65 2 . 6 97 13 .40 51 170 2600 1 14 7 14 .34 2.26 l 3 1.770 1 24 70 91 3 .10 390-100 8 60 148 89 .5 78 16 .16 228 200 1800 1 65 17 92 .34 1.30 2 1.477 1 76 51 49 2 .29 100-110 8 49 300 59 .7 69 17 .21 570 130 1100 90 27 58 .31 1.25 3 1.312 1 00 12 29 4 . 2 0 110-120 8 99 1460 640 2 . 5 168 16 .83 63 210 1800 1 47 9 94 .58 2 .14 1 0 1.953 1 66 65 25 5.31 120-130 10 102 330 110 .7 111 15 .71 113 260 2200 2 48 12 60 .87 2 .09 1 6 1.669 2 66 59 22 3.97 130-410 21 116 2100 330 5 .7 74 12 1.12 116 470 1400 1 99 7 20 .24 1.27 2 4 1.115 2 16 66 24 2.61 440-150 8 66 1580 123 3.1 92 13 .16 225 220 1000 1 20 18 62 .28 .98 1 0 1.850 1 36 53 82 1.23 450-156 9 27 1630 60 4 . 5 53 10 .68 37 500 1100 57 2 24 .21 .79 6 9 . .756 62 87 36 1.60 156-158 10 70 1500 80 3.2 60 10 .90 72 600 • 1000 2 60 6 02 .26 .86 5 4 .504 1 02 75 06 2 .05 458-160 19 152 1180 230 3 .0 89 , 11 1.53 111 160 1200 6 40 8 96 .39 1.10 1 9 .355 4 00 64 01 4 . 3 0 460-165 20 68 1160 80 .5 68 7 .81 71 530 1100 77 4 06 .28 .77 3 4 .247 86 24 01 6.92 165-170 4 57 1000 192 2 . 2 60 7 1.00 62 440 1200 4 30 3 50 .23 .72 10 6 .621 4 24 83 22 1.24 170-172 7 34 2300 85 4 .6 72 9 2 . 0 0 50 560 800 1 28 3 36 .26 .86 1 4 1.072 1 36 81 72 1.98 173-177 16 56 1580 169 3 .5 84 8 2 . 0 0 18 • 480 900 1 08 1 96 .29 .86 4 3 .266 1 04 85 87 2 . 1 3 477-180 2 41 3000 7200 6.6 80 10 2 . 0 0 69 560 1000 2 39 4 48 .32 .98 5 1 .275 2 62 75 91 2 .65 180-105 16 42 2000 187 4 . 5 96 14 2 . 0 0 106 700 1100 1 61 7 56 .37 1.27 4 5 .753 1 66 70 03 3.02 185-190 11 25 1110 175 2 . 8 66 9 2 . 0 0 82 360 800 72 5 60 .21 .79 2 5 .708 86 78 55 1.42 490-193 2 111 1200 560 2 . 6 64 12 2 . 0 0 no 420 900 8 00 10 36 .24 1.58 7 1 1.195 4 00 61 11 1.64 193-196 1 69 560 211 1.2 47 8 2 . 0 0 70 270 700 5 20 3 78 .16 .55 4 7 .735 4 00 83 14 5 .67 196-499 1 290 1900 1900 3.6 75 7 1.00 20 330 1100 10 70 2 66 .16 .67 10 4 .788 4 00 71 51 1.13 499-503 6 108 93 1750 .2 68 13 1.00 107 300 1200 2 05 9 66 .18 .79 3 5 1.216 3 50 72 29 1.25 503-509 15 65 2000 320 1.0 60 10 1.00 380 340 800 1 54 27 44 .29 .62 3 1 .829 1 58 45 05 1.60 509-511 10 38 3500 370 6.0 64 10 1.00 137 680 800 1 07 10 64 .21 .71 3 2 1.071 1 20 70 36 1.92 514-518 19 83 4900 590 8 .7 110 13 2 . 0 0 81 1050 1200 1 48 4 34 .32 1.22 6 0 .715 1 74 75 68 3.05 518-522 13 127 17900 5800 1 4 . 7 114 13 2 . 0 0 114 840 700 4 10 6 58 .21 .77 7 7 .437 4 00 71 55 1.45 522-526 23 58 33200 1180 63 .0 92 9 2 . 0 0 75 810 800 1 67 2 02 .19 .86 5 3 .069 2 64 81 27 1.41 Tab le E-4b. Data f o r chemical analyses on core from d r i l l hole (DDH) 19, shown with depth in te rva l from surface ( in f e e t ) . PPM Depth ( f t ) 526-530 530-535 535-537 537-510 540-543 513-516 546-550 550-553 553-557 557-560 560-564 564-567 567-572 572-577 577-501 581- 582 582- 587 587- 588 588- 592 592- 593 593- 598 598-600 600-605 605-607 607-610 610-616 i 615-620 620-624 624-626 626-630 630-633 633-635 635-637 637-640 640- 641 641- 643 643-645 645-647 647-650 650- 651 651- 660 660-670 670-680 680-690 690-700 700-710 Mo Cu 38 29 17 23 46 69 31 15 62 41 28 124 0 9 10 15 11 21 14 17 21 13 26 23 10 9 35 23 23 23 19 16 21 20 29 20 22 35 30 50 60 23 35 27 23 18 33 57 20 53 46 11 178 23 49 26 66 24 720 23 380 8 38 15 52 32 80 32 60 63 120 106 260 11 196 23 20 65 90 42 56 42 43 46 74 48 53 58 55 54 60 58 Zn 1800 480 530 530 6000 77600 5500 2040 6200 8000 9600 5700 21500 34000 68 173 102 160 540 80800 60800 22000 620 42000 1250 27000 5200 1800 30000 2200 48 82 24 2100 960 8000 8000 5100 3000 5800 510 330 450 1340 300 260 Ph 6500 1600 110 141 3600 16500 2000 7000 16400 1600 2100 1670 l l 500 0600 100 350 I 5 l 1410 390 65600 60800 39200 52 23000 400 221 145 310 240 I 4 l 61 152 198 147 420 149 204 930 390 270 199 105 130 93 70 72 Cd 101.0 3 .8 1.2 .9 2 8 . 0 2 3 1 . 0 14.6 4 3 . 0 70 .0 30 .0 4 4 . 0 2 7 . 0 102.0 101 .0 .2 .2 .2 .2 2.1 125 .0 128.0 130.0 1.1 146 .0 4.1 8 . 8 31 .0 8 . 7 170 .0 9 .4 .2 .2 .2 12 .5 6 . 3 6 4 . 0 6 1 . 0 4 8 . 0 18.1 4 6 . 0 3.1 2.1 3 .6 18.1 3 .8 3 .5 Ni 85 69 49 50 100 70 34 50 67 50 52 43 55 77 50 70 69 64 06 79 60 50 02 02 04 78 120 165 140 49 48 136 .60 137 140 135 133 144 136 120 120 126 130 152 167 166 17 17 18 16 11 14 21 16 18 16 18 17 13 13 13 16 16 7 10 11 11 13 13 17 17 14 20 20 13 19 22 10 19 14 16 13 14 14 14 16 Mn V Ba F e ( t ) CaO MgO K 2 0 C(LOI ) P 2 ° 5 S SI 02 A 1 2 ° 3 4 .00 430 650 600 2 .46 21.56 .26 .74 4 . 2 .188 4 .66 20 .98 1.22 2 .00 360 450 200 2 .19 21.84 .19 .53 4 . 5 .199 2 .36 42 .02 0 .20 2 .00 330 350 300 .37 30 .50 .13 .24 1.8 .021 .48 37 .64 4 . 0 0 250 420 500 1.06 24.92 .14 .34 3 .0 .226 1.04 51 .38 0 .29 6 .00 110 680 900 1.20 4 . 9 0 .19 .84 6 .6 .101 1.62 76 .12 1.50 4 . 0 0 450 390 500 7.30 17 .08 .22 .62 6 . 3 .215 4 . 0 0 41 .25 0 .19 6 .00 500 120 200 .48 50 .68 .20 .07 .7 .112 .80 21 .89 4 . 0 0 290 250 500 1.70 22.51 .19 .43 2 . 0 .293 2.94 49 .49 0 .15 4 .00 370 320 300 3 .50 22.54 .21 .62 4.1 .245 4 . 0 0 45 .36 4 .00 350 210 300 2 .63 28 .28 .13 .26 2 .7 .176 3 .10 45 .70 0 .46 2 .00 370 200 400 2 .20 32.90 .18 .41 3 .3 .208 2 . 5 8 37 .64 4 . 0 0 410 220 300 1.02 41 .72 .13 .19 6 .7 .108 1.32 31 .11 _ 4 . 0 0 310 270 500 2 .00 20 .72 .14 .43 2 .2 .115 3.26 50 .59 _ 1.19 340 440 700 2 .57 21.84 .19 .62 2 . 8 .206 4 . 0 0 47.91 0 .48 4 . 0 0 250 330 400 .54 25 .90 .10 .11 2 .6 .167 .70 50 51 0.11 .300 200 530 500 1.72 28 .98 .24 .60 2 . 5 .179 1.50 45 14 0 .66 4 . 0 0 280 410 400 1.17 29 .40 .22 .53 3.7 .156 1.26 43 .72 0 .62 .320 74 340 700 2 . 5 3 1.82 .11 .21 2 . 9 .183 .86 89 35 0 .50 .360 125 420 100 1.76 7.42 .24 .62 3.2 .179 1.10 76 14 1.04 2.81 147 280 500 1.60 30.52 .10 .07 1.2 .133 4 . 0 0 33 31 1.09 4 .00 220 340 • 450 1.02 25 .06 .13 .12 2 .4 .165 3 .76 45 60 1.20 2 . 3 7 420 420 400 .80 12.46 .16 .36 3 .8 .453 2 . 8 0 59 34 .17 215 360 1400 .80 22 .12 .35 1.30 3 .8 1.385 .50 51 07 _ 4 . 0 0 101 640 500 1.36 4 .31 .13 .58 5.1 .339 3.72 70 57 0 .45 4 . 0 0 320 750 300 1.65 28 .28 .19 .41 5.2 1.800 1.86 43 48 4 . 0 0 174 620 300 1.42 19.88 .14 .41 4 . 0 1.191 1.98 57 33 _ 4 . 0 0 187 1140 300 1.30 25 .76 .22 .62 6 .8 1.750 1.70 44 84 0 .60 4 . 0 0 147 1660 500 .05 16.94 .30 .94 9 .5 1.230 2 . 3 0 55 57 1.37 8 .00 96 1050 900 1.12 7.14 .42 2 .17 7.6 1.555 4 .74 62 10 4 .17 4 . 0 0 240 210 700 2 .26 28 .14 .50 1.91 1.5 .305 2 . 5 0 40 .69 2 .69 8 .00 3C0 900 500 2 .35 35 .70 .61 2 .16 1.0 .105 2 . 3 0 32 66 3.37 4 . 0 0 142 990 700 .29 12.46 .58 3.05 7 .5 .362 2 . 1 0 54 08 5 .03 0 .00 127 820 1000 2 . 6 8 - 10.50 .62 3.84 0.1 .529 4 . 0 0 54 15 6 .05 1.00 50 1450 600 .82 1.82 .62 3 .53 9 .5 .270 2 . 1 0 69 74 6 .10 1.00 96 1410 700 2 .65 6 . 3 0 .62 3.62 0.1 .105 2 . 6 8 6 1 . 87 6 .95 1.00 54 1250 900 2 .02 1.82 .59 3.46 8.1 .309 2 .42 68 . 82 9 .03 2 .00 66 1370 800 2 .37 2 .94 .59 3.40 8 .6 .373 2 . 7 8 67 . 47 7.40 2 .00 90 1390 700 2 .72 4 . 2 0 .59 3.00 4.1 .291 3 .00 66. 90 6 .62 2 .00 88 1420 400 3 .40 4 .48 .58 3.34 4 . 7 .204 3 .68 6 5 . 96 6.62 1.00 83 1560 300 2 .10 4 . 2 0 .67 3.55 3 .0 .160 2 . 3 6 64 . 24 7.45 1.32 83 640 1000 2 : 3 3 4 .06 .50 4 .06 4 .7 .275 2 .62 64 . 93 6.34 1.30 107 1720 1000 2.31 6 .58 .56 3.72 5.4 .199 2 . 4 8 6 2 . 76 6 .30 1.18 72 1380 800 1.98 3 .78 .51 3.58 5.1 .135 2 .22 6 0 . 94 6.31 1.32 48 1360 600 1.98 2.24 .64 4 .27 5.1 .236 2 .24 6 7 . 54 7.39 1.30 111 1430 800 2 .59 7.14 .69 3.77 6 . 3 .401 2 .84 6 0 . 65 6 .87 1.30 130 1420 800 2 .54 B.40 .58 3.60 5 .7 .160 2 .72 59 . 74 6 .12 CO ro Table E -4c . Data for chemical analyses on core from d r i l l hole (DDH) 19, shown with depth in terva l from surface ( in f e e t ) . Depth ( f t ) PPM % Mo Cu Zn Pb Cd Ni Co Ag Mn V Ba F e ( t ) CaO MgO K ? 0 C(LOI ) P 2 0 5 S s i o 2 A 1 2 0 3 710-720 45 57 22 49 1 .2 166 15 1.52 97 1610 700 2 .20 6 16 .69 3.89 6 3 .202 2 .39 61 93 7.36 720-730 38 64 310 90 2 .8 145 16 1.36 173 1120 900 2 .30 10 64 .72 3.74 3 9 .231 2.46 56 83 6 . 8 8 730-710 20 03 84 44 1 .0 160 16 1.50 115 1120 1000 3.60 8 02 .91 3.74 4 6 .234 3.50 56 28 8 .08 740-750 21 60 98 36 1 .0 126 15 1.00 118 560 1100 2 .96 7 56 1.55 4 .34 5 7 .325 2 .70 56 59 8 .94 750-760 7 60 29 26 .2 120 13 .6B 58 350 1200 1.97 2 00 1.17 5.81 7 0 .211 2 .10 58 72 11.36 760-770 5 05 32 30 .7 110 15 .87 118 260 1200 3.40 7 42 1.14 5.64 5 8 .222 3.40 53 89 11.30 770-700 3 62 830 35 4 .2 100 15 .53 82 210 1400 2 .20 4 34 1.10 5.74 5.4 .275 2 .10 58 73 11.38 700-790 6 45 100 24 .5 00 13 .55 80 300 1200 1.83 4 06 1.54 5.01 4 3 .247 1.52 49 40 11 .10 790-000 7 68 27 40 .2 04 18 .55 260 260 1600 4 . 2 0 13 02 3 .50 4 . 7 0 4 0 .854 3 .08 45 03 8 .8 9 800-810 7 64 27 31 .2 88 18 .68 172 360 2000 1.81 13 16 1.63 5.74 4 6 1.683 1.58 49 20 9.64 810-820 11 38 100 21 .2 56 22 .37 300 220 1500 1.56 27 44 1.73 2 .03 2 1 .577 1.20 12 05 4 .66 820-830 8 16 17 12 2 35 15 .15 330 100 2000 1.48 17 78 3.54 3.38 8 .247 .72 45 27 4 . 4 8 830- 840 10 15 50 16 2 36 16 .15 260 80 2300 1.74 11 40 4.21 4 . 6 3 8 .318 .82 52 93 5 .52 840-850 9 18 22 20 2 39 13 .18 195 180 2300 1.86 7 00 4 .35 4 . 6 3 1 4 .403 .82 57 60 7 .68 850-060 7 18 22 14 2 42 12 .18 156 230 2300 1.64 5 32 3.34 4 .06 9 .339 .72 62 22 7 .38 860-870 8 17 62 18 2 40 16 .20 199 200 2000 2 .65 6 72 4 .64 4 .08 1 0 .329 .92 55 45 7.87 070-880 11 19 106 12 2 40 16 .28 182 370 1900 2 .10 7 14 3 .90 4 .44 8 .483 .58 57 62 9 .00 880-890 8 18 32 14 2 37 16 .20 162 250 2000 2.11 5 60 3.41 4 .56 8 .463 .64 57 62 9.21 090-900 8 18 36 19 2 38 15 .22 178 280 1700 2.17 6 86 3.63 4 .32 9 .311 .00 56 35 9 .12 900-910 10 21 146 13 4 38 16 .20 187 240 1800 2 .02 7 98 3.26 4.01 7 .275 .60 55 31 8.61 910-920 11 24 120 15 2 41 17 :31 159 340 2300 2 .09 . 6 16 2 .99 4 .92 1 4 .415 .02 56 42 9.81 920-930 9 28 180 23 7 40 17 .62 159 360 2200 2 .05 8 96 2 .82 4 .85 1 3 .339 .80 53 96 9 .43 930-940 9 29 184 19 1 5 57 20 .32 180 470 1900 1.95 10 22 3.02 4 .80 1 6 .424 .78 59 10 10.60 940-950 32 46 750 19 4 3 63 18 .38 440 470 1900 2.11 11 34 3 .26 4 .39 1 5 .469 .88 50 65 8 .97 950-960 8 16 25 15 2 37 17 .13 380 60 1100 2 .40 15 26 3 .58 3.62 1 0 .137 .84 48 35 6 .76 960-970 8 17 20 14 2 34 20 .12 180 70 1600 2 . 1 0 17 92 2 .77 4 . 2 0 1 0 .128 .90 46 67 6 .87 323 Appendix F SULPHUR ISOTOPE ANALYTICAL METHOD Sulphur isotope analyses were performed at the Un ivers i ty of A lber ta using the fo l lowing methods. SULPHIDE SEPARATION (1) Samples were crushed to -200 to -325 mesh. (2) The sample power was washed in warm d i l u t e phosphoric acid to remove carbonate. (3) The sample was then t reated in a s p e c i a l l y b u i l t sulphate r e -duct ion l i n e in a nitrogen atmosphere to generate H2S from each sulphide phase as fo l lows: (A) Galena phase - d i l u t e ( ~ IN) co ld HC1 was used, with SiC or Sn as a reducing agent (B) Spha le r i te phase - 3N to 6N HC1 with moderate heat ing , with Sn as a reducing agent. The H2S was bubbled through d i s t i l l e d water and then cadmium-acetate s o l u t i o n , from which CdS was p r e c i p i t a t e d . (C) P y r i t e - the remaining pyr i te + rock residue powder was d r i e d , ca r r i ed through conventional heavy l i q u i d and mag-ne t ic separa t ion , and pure pyr i te was separated. SO 2 COMBUSTION (1) CdS p r e c i p i t a t e was converted to Ag2S by Ag(N03)2 (0.5N) s o l u -t i o n and f i l t e r e d in T e f l o n f i l t e r cups with concentrated NH3 wash. (2) Ag2S was dr ied in an e l e c t r i c oven at 110°C and c o l l e c t e d . (3) Ag2S or pyr i te sample was mixed with pre-heated cupr ic oxide 324 with a mole r a t i o of 0:S of 4 to 5 and the mixture was placed in a small s i l i c a tube with both ends sealed by quartz wool . (4) The s i l i c a tube was placed in a s i l i c a tube furnace attached to an ex t rac t ion l i n e and evacuated before the sample tube was combusted to ~ 1000°C fo r AgS or ~ 1100°C for p y r i t e . (5) The generated SO2 was p u r i f i e d using c o l d - t r a p s to remove im-p u r i t i e s ( i . e . , H20(g), N2 CO2, e t c . ) . (6) The p u r i f i e d SO2 gas was measured in a Hg manometer and combus-t i o n y i e l d est imated. The sample gas was then c o l l e c t e d in a standard break-seal bo t t l e using an oxygen-natural gas t o r c h . MASS SPECTROMETER MEASUREMENT OF ISOTOPIC RATIOS (1) The break-seal bot t les conta in ing SO2 samples were attached to the sample l i n e of a modif ied N ier - type d o u b l e - i n l e t gas-source mass spectrometer, and evacuated. (2) SO2 sample gas was measured against a commercial grade SO2 l i n e standard, which had been c a l i b r a t e d extensive ly against many working sulphur standards with p r e c i s e l y determined i s o t o p i c composi t ion. (3) The isotope r a t i o of SO2 was measured at c o n t r o l l a b l e constant Hg pressure and was expressed as r a t i o s of mass 66 (34sl602) to mass 64 (32s 16o 2) and were pr inted by an o n - l i n e computer. (4) The isotope r a t i o of SO2 masses was corrected by the working c a l i b r a t i o n curve using the SO2 standard and working standards to c a l c u l a t e the <S 3 4 S . Appendix G LEAD ISOTOPE ANALYTICAL METHOD 325 Lead isotope analyses were performed at the Un ivers i ty of A lber ta using the fo l lowing methods. LEAD EXTRACTION OF SULPHIDES (1) Galena was d isso lved in concentrated HNO3*, evaporated to dry-ness, and red isso lved in d i l u t e HNO3. (2) The so lu t ion was extracted with p u r i f i e d d iphenyl th iocarbazo-nate in the presence of KCN and ammonia-citrate at a p^ of > 8 .5 . (3) The extracted Pb diphenylthiocarbazonate was back extracted with 2% HNO3 and the acid so lu t ion c o l l e c t e d . (4) Pyr i te was d isso lved in concentrated HNO3, to dryness and then red isso lved in 1 N HCL; the HC1 so lu t ion was r insed through cat ion exchange res in column pre-set with IN HC1. (5) A f t e r extensive acide r inse through the column, Pb was separat-ed from the column with pure H2O and c o l l e c t e d . (6) Spha le r i t e was t reated in the same manner as ga lena, except that a double ext ract ion with and without KCN, at pH 8.5 and 6.5 r e s p e c t i v e l y , was employed. (7) A l l p u r i f i e d sample so lu t ions from ga lena , spha le r i t e and py-r i t e were evaporated to dryness and s to red . SAMPLE LOADING ON RE-FILAMENT (1) One drop of 0.75 N pur H3PO4 was placed in the sample evaporate and picked up by a clean c a p i l l a r y tube. * A l l reagents were d o u b l y - d i s t i l l e d . 326 (2) The H3PO4 sample drop was placed on the centre of an outgassed r e - f i l a m e n t , fo l lowing a drop of s i l i c a - g e l s o l u t i o n , and eva-porated with ~ 1 A. D.C. (3) Slow evaporation and homogenization was accomplished with slow increase in e l e c t r i c current up to ~ 2 amp.; a rapid growth of the Pb s i l i ca -phospha te on the f i lament was achieved at ~ 2.2A. the f i lament button was removed from the loading apparatus and was ready for mass spectrometer measurement. MASS SPECTROMETER MEASUREMENT (1) Lead i s o t o p i c measurement was carred out with a s o l i d source , 90° s e c t o r , 12" r a d i u s , s ing le - f i l ament mass spectrometer. (2) The sample f i lament was ionized at 1.6 to 2.2 A f i lament cur-rent in a vacuum of 10"^ atm. and accelerated to 4.5 IV. (3) Recording of peak heights f o r Pb isotopes was made on magnetic tape with a scan speed of 514 mi l l i seconds per s tep ; an average of 15 scans were made fo r each a n a l y s i s . (4) Data were processed using a Fortran IV program designed to c a l c u l a t e and d iscr imina te base - l ine and peak heights and to do polynomial f i t t i n g , and to c a l c u l a t e the corrected Pb isotope r a t i o s with t h e i r standard d e v i a t i o n s . (5) A l l connected Pb isotope ra t ios were normalized by f a c t o r s determined by c a l i b r a t i o n s of N .B .S . # 981 Pb standard (about 15 analyses were done p r io r to and a f t e r each sample a n a l y s i s ) . 327 Table G - l . Lead isotope parameters and constants used in the present research (from Stacey and Kramers, 1975, Faure, 1977). Phrase Isotopic Expression Val ue Symbol Staae 1 Stage 2 Age of .trail ite-lead 4.57 Ga Beginning of second stage 3.7 Ga Primordial lead (Pb 2 0 6 /Pb 2 0 l * ) T a 0 9.307 11.152 (Pb 2 0 7 /Pb 2 0 1 * ) T bo 10.294 12.998 ( p b 2 Q 8 / P b 2 0 - ) T c o 29.487 31 .23 Modem lead ( P b 2 0 S / P b 2 0 1 ) t o ( P b 2 0 7 / P b 2 D - ) t o ( P b 2 ° 8 / P b 2 0 - ) t o V A Y Z 18.70 15.628 38.63 Urani um-lead system (ua38 / P b 20U) T ^ t l (U 2 38/Pb 2 '"*) t l ^ t . 0 (U23S /p b 20i») T ^ t l ( U 2 3 V P b 2 0 - ) t M o 137.38U1 137.88u2 ul U2 7.19 0.05215 9.74 0.07064 Thori um-lead sys tem ( T h 2 3 2 / P b 2 0 I ' ) T ^ 1  ( T ^ 2 3 2 / P b 2 0 , ) t ^ t o w2 33.21 36.84 Thorium-uranium system ( T h 2 3 2 / U « 8 ) T + t l  ( T h 2 3 2 / u 2 3 8 ) t i ^ 4.62 3.78 Uranium isotope raf'o ( U 238 / U 23S) 137 .38 Meteori tic isochron slope ( p b 207 / p b 20 t ) (p b 20S /p b 20t) 0 .625208 Decay constants y238 IJ23S T h 232 *2 0.155125 x 0.98485 x 0.049475 x 10" 10-9 io-9 y r - l yr-l 9 y r - l where: T is the age of the earth, ti is the time at which the second stage formed, and ^ is present day. P u b l i c a t i o n s : M i l l s , J . W., C a r l s o n , C. L . , Fewkes, R. H . , Handlen, L. W., Jayprakash, G. P . , John, M. A . , Morgant i , J . M. , N e i t z e l , T . W., Ream, L. R. , Sanford , S. S . , and Todd, S. G. , 1974, Bedded b a r i t e deposi ts of Stevens County, Washington: Econ. G e o l . , v. 66, p. 1157-1163. Morgant i , J . M. , 1975, S t ra t igraphy and ore deposi ts of the Howards Pass area: Presented a t , Northern Geoscience Conference, Dec. 1975, Ye l lowkn i fe , N.W.t. Morgant i , J . M. , 1977(a), Howards Pass: an example o f sedimentary exha la t ive base metal depos i t : Presented a t , Geol . A s s . Can. Ann. M t g . , A p r i l 16, 1977, Vancouver, B. C. Morgant i , J . M. , 1977(b), Some models f o r l e a d - z i n c in sedimentary enviornments: Presented at Can. Mining Met. D i s t r i c t 6 M t g . , Oct. , 1977, V i c t o r i a , B. C. Morgant i , J . M. , 1979, Geology of the Howards Pass Zn-Pb depos i ts - the o r i g i n of Zn-Pb deposi ts during basin e v o l u t i o n : Presented at the 108. Am. Inst . Mining Eng. F e b . , 1979, New Or leans , La . 

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