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Geology and genesis of the Dolly Varden silver camp, Alice Arm area, northwestern British Columbia Devlin, Barry David 1987

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GEOLOGY AND GENESIS OF THE DOLLY VARDEN SILVER CAMP ALICE ARM AREA, NORTHWESTERN BRITISH COLUMBIA By BARRY DAVID DEVLIN B . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of G e o l o g i c a l S c i e n c e s ) accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA March 1987 (c) Barry David D e v l i n , 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) Page i i F r o n t i s p i e c e . View l o o k i n g n o r t h up the K i t s a u l t R i v e r v a l l e y , w i t h the T o r b r i t mine i n the fo reground and the K i t s a u l t G l a c i e r i n the background . Page i i i ABSTRACT The D o l l y Varden camp, A l i c e Arm ar e a , northwestern B r i t i s h Columbia, i s c h a r a c t e r i z e d by s t r a t i f o r m and v o l c a n o g e n i c s i l v e r - l e a d - z i n c - b a r i t e d e p o s i t s i n E a r l y t o Middle J u r a s s i c c a l c - a l k a l i n e v o l c a n i c r o c k s of the Hazelton Group. These d e p o s i t s , c o n t a i n i n g e x c e p t i o n a l s i l v e r and s i g n i f i c a n t base metal v a l u e s , are i n a n d e s i t i c t u f f a c e o u s r o c k s , and occur t y p i c a l l y as l a y e r s of q u a r t z , carbonate, b a r i t e and j a s p e r , with l e s s e r amounts of p y r i t e , s p h a l e r i t e and galena, and sparse c h a l c o p y r i t e . P r o d u c t i o n from three d e p o s i t s , the D o l l y Varden, N o r t h s t a r and T o r b r i t mines, t o t a l e d 1,284,902 tonnes of ore th a t averaged 484g s i l v e r per tonne, 0.38 percent l e a d and 0.02 percent z i n c . The H a z e l t o n Group i s a t h i c k , widespread assemblage of b a s a l t i c to r h y o l i t i c v o l c a n i c flow r o c k s , t h e i r t u f f a c e o u s e q u i v a l e n t s , and d e r i v e d sedimentary r o c k s . D o l l y Varden camp i s u n d e r l a i n by more than 3,000m of Hazelton Group rocks comprised of one major v o l c a n i c and one major sedimentary f o r m a t i o n . V o l c a n i c r o c k s u n d e r l i e sedimentary r o c k s and have been s u b d i v i d e d i n t o f o o t w a l l and hangingwall u n i t s based on s t r a t i g r a p h i c p o s i t i o n r e l a t i v e to the m i n e r a l i z e d s t r a t i f o r m h o r i z o n . F o o t w a l l v o l c a n i c rocks c o n s i s t of green _+ maroon Page i v b a s a l t i c - a n d e s i t e t u f f , green + maroon p o r p h y r i t i c a n d e s i t e and green a n d e s i t e shard t u f f . S t r a t i f o r m m i n e r a l i z a t i o n r e s t s conformably upon the u n d e r l y i n g green a n d e s i t e shard t u f f . Hangingwall v o l c a n i c rocks above the s t r a t i f o r m l a y e r c o n s i s t of p a l e grey b a s a l t i c - a n d e s i t e ash t u f f , maroon b a s a l t i c - a n d e s i t e a s h - l a p i l l i t u f f , grey-green p o r p h y r i t i c a n d e s i t e , and p a l e green a n d e s i t e ash t u f f . Hangingwall v o l c a n i c s are unconformably capped by sedimentary rocks c o n s i s t i n g of maroon s i l t s t o n e , c a l c a r e o u s and f o s s i l i f e r o u s wacke, and b l a c k s i l t s t o n e and s h a l e ; b l a c k s i l t s t o n e and s h a l e form the youngest rock u n i t of the Hazelton Group i n the D o l l y Varden area. B a s a l t and lamprophyre dykes i n t r u d e a l l rocks of the Hazelton Group. The ro c k s of the Hazelton group exposed i n the D o l l y Varden camp are f o l d e d i n t o a s e r i e s of a n t i c l i n e s and s y n c l i n e s with g e n t l e , northwestern plunges. Two major s e t s of n e a r l y v e r t i c a l b l o c k f a u l t s cut a l l rock u n i t s ; e a r l i e r f a u l t s t r e n d northwest and younger f a u l t s t r e n d n o r t h - n o r t h e a s t . G e o l o g i c a l mapping, combined with p e t r o l o g i c , p e t r o g r a p h i c and i s o t o p i c data, i n d i c a t e t h a t the s t r a t i f o r m d e p o s i t s probably formed as submarine e x h a l a t i v e d e p o s i t s a s s o c i a t e d w i t h a n d e s i t i c v o l c a n i s m of the Hazelton Group d u r i n g the E a r l y to Middle J u r a s s i c . Evidence f o r a v o l c a n o g e n i c o r i g i n i s the c o n f o r m i t y of l a y e r e d m i n e r a l i z a t i o n with s t r a t i g r a p h y , l a t e r a l Page v and v e r t i c a l m i n e r a l z o n a t i o n p a t t e r n s , c o n s i s t e n t hangingwall versus f o o t w a l l c o n t a c t r e l a t i o n s h i p s , fragments of s t r a t i f o r m ore w i t h i n t u f f a c e o u s v o l c a n i c rocks of the hangingwall, c o n s i s t e n t d i f f e r e n c e s i n the s t a b l e i s o t o p i c compositions between the s u l f i d e s versus b a r i t e , quartz and carbonate gangue, and the J u r a s s i c " f i n g e r p r i n t " f o r the l e a d - b e a r i n g d e p o s i t s of the D o l l y Varden camp. The D o l l y Varden d e p o s i t s d i s p l a y c r i t e r i a f o r c l a s s i f i c a t i o n of a new, p r e v i o u s l y unrecognized, s t r a t i f o r m and vo l c a n o g e n i c , d e p o s i t type, named here, the " D o l l y Varden type", and i s c h a r a c t e r i z e d by s i l v e r - r i c h , low s u l f i d e and high oxide s t r a t i f o r m m i n e r a l i z a t i o n w i t h i n a n d e s i t i c v o l c a n i c r o c k s . Page v i TABLE OF CONTENTS page FRONTISPIECE i i ABSTRACT i i i TABLE OF CONTENTS v i LIST OF TABLES v i i i LIST OF FIGURES i x ACKNOWLEDGEMENT xv 1 .0 INTRODUCTION 1 2.0 REGIONAL GEOLOGY 5 2.1 INTRODUCTION 5 2.2 HAZELTON VOLCANIC-SEDIMENTARY UNITS ( 1 TO 6) 6 2.3 TERTIARY INTRUSIVE UNITS (7 TO 9) 11 2.4 STRUCTURE 1 2 2.5 ALTERATION 1 2 3.0 PROPERTY GEOLOGY 14 3.1 INTRODUCTION 14 3.2 LITHOLOGY 21 3.2.1 F o o t w a l l V o l c a n i c Rocks 21 3.2.2 S t r a t i f o r m S i l v e r - L e a d - Z i n c - B a r i t e E x h a l a t i v e M i n e r a l i z a t i o n 26 3.2.3 Hangingwall V o l c a n i c Rocks 38 Page v i i page 3.2.4 Sedimentary Rocks 57 3.2.5 I n t r u s i v e Rocks 62 3.3 CHEMISTRY OF IGNEOUS ROCKS 66 3.4 STRUCTURE 72 3.5 ALTERATION AND VEIN MINERALIZATION 76 4.0 ISOTOPE STUDIES 84 4.1 INTRODUCTION 84 4.2 SULFUR, OXYGEN AND CARBON ISOTOPES 84 4.2.1 S u l f u r Isotopes 85 4.2.2 Oxygen Isotopes 90 4.2.3 Carbon Isotopes 94 4.2.4 D i s c u s s i o n 94 4.2.5 Summary 97 4.3 POTASSIUM-ARGON ISOTOPES 97 4.4 LEAD ISOTOPES 100 5.0 GENESIS OF THE STRATIFORM MINERALIZATION 105 5.1 INTRODUCTION 105 5.2 PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE STRATIFORM MINERALIZATION 105 5.3 GENETIC MODEL 113 6.0 CONCLUSIONS 119 BIBLIOGRAPHY 123 APPENDIX 131 J STABLE ISOTOPE FRACTIONATION EQUATIONS 131 Page v i i i LIST OF TABLES page TABLE 1.1 P r e v i o u s p r o d u c t i o n and r e s e r v e s f o r the D o l l y Varden camp, northwestern B.C. 4 TABLE 2.1 Formations i n the K i t s a u l t R i v e r a r e a , northwestern B.C. 7 TABLE 3.1 Petrography of the v o l c a n i c and sedimentary rocks of the D o l l y Varden camp, northwestern B.C. 16 TABLE 3.2 Mineralogy of the m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( u n i t 3) i n the D o l l y Varden camp, northwestern B.C. 28 TABLE 3.3 Whole rock c h e m i s t r y (XRF) and normative c a l c u l a t i o n s f o r igneous r o c k s from the D o l l y Varden camp, northwestern B.C. 67 TABLE 4.1 S u l f u r , oxygen and carbon i s o t o p e compositions of s u l f i d e s , b a r i t e , q uartz and c a l c i t e i n d e p o s i t s from the D o l l y Varden camp, northwestern B.C. 86 TABLE 4.2 C a l c u l a t e d d e p o s i t i o n a l temperatures f o r p a i r s of s u l f u r and oxygen compounds from the D o l l y Varden camp, northwestern B.C. 89 TABLE 4.3 Whole-rock potassium-argon data f o r v o l c a n i c rocks from the D o l l y Varden camp, northwestern B.C. 98 TABLE 4.4 Galena-lead i s o t o p e analyses from the D o l l y Varden camp, northwestern B.C. 101 Page i x Page x page F i g u r e 3.9 S t e e p l y - d i p p i n g l a y e r s of s u l f i d e s , mostly p y r i t e , i n s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a) from the D o l l y Varden East d e p o s i t . F i g u r e 3.10 P o l i s h e d s l a b of quartz and p y r i t e m i n e r a l i z a t i o n , t y p i c a l of the s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a). F i g u r e 3.11 Anhedral p y r i t e forming massive aggregates and c r u d e l y developed l a y e r s i n s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a). F i g u r e 3.12 Layers of c a l c i t e , q u a r t z , b a r i t e and s u l f i d e s i n c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b) from underground workings at the N o r t h s t a r d e p o s i t . F i g u r e 3.13 V e r t i c a l z o n a t i o n i n d r i l l h o l e U-80-95 i n N o r t h s t a r d e p o s i t , D o l l y Varden camp, northwestern B.C. F i g u r e 3.14 P o l i s h e d s l a b of c a l c i t e , b a r i t e and s p h a l e r i t e m i n e r a l i z a t i o n , t y p i c a l of the carbonate-s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b). F i g u r e 3.15 Massive s p h a l e r i t e and p y r i t e with c o a r s e - g r a i n e d bladed b a r i t e c r y s t a l s i n c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b). F i g u r e 3.16 C o l l o f o r m l a y e r s of hematite and magnetite i n s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . 31 32 32 33 36 37 41 41 Page x i page Figure 3.17 Well developed layers of bar i t e , jasper and su l f i d e s in sul f a t e - o x i d e - s u l f i d e exhalite (unit 3c) from underground workings at the Tor b r i t mine. 42 Figure 3.18 Polished slab of galena and jasper mineralization, t y p i c a l of. massive s u l f i d e ore from the sul f a t e - o x i d e - s u l f i d e exhalite (unit 3c). 43 Figure 3.19 Carbonate boulder, 30cm across, i n pale grey  basaltic-andesite ash tu f f (unit 4) from underground workings at the Northstar deposit. 44 Figure 3.20 Secondary f o l i a t i o n i n pale grey basaltic-andesite  ash t u f f (unit 4). 44 Figure 3.21 Subrounded to subangular maroon t u f f l i t h i c fragments, up to 50cm across, i n maroon- basaltic-andesite a s h - l a p i l l i t u f f (unit 5). 48 Figure 3.22 Platy shards i n a l o c a l p y r o c l a s t i c flow within maroon basaltic-andesite a s h - l a p i l l i t u f f (unit 5). 49 Figure 3.23 Light green, angular to subangular, l a p i l l i -sized l i t h i c fragments, up to 5cm across, i n dark grey andesite l a p i l l i t u f f (unit 6a). 54 Page x i i page F i g u r e 3.24 Hand specimen of dark green a n d e s i t e t u f f ( u n i t 6b) t h a t c o n t a i n s an ore fragment from the u n d e r l y i n g s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . 55 F i g u r e 3.25 T h i n s e c t i o n of dark green a n d e s i t e t u f f ( u n i t 6b) t h a t c o n t a i n s fragments of carbonate and b a r i t e ore from the s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . 55 F i g u r e 3.26 Phenocrysts of p l a g i o c l a s e and hornblende i n grey-green p o r p h y r i t i c a n d e s i t e ( u n i t 7a). 56 F i g u r e 3.27 P l a g i o c l a s e c r y s t a l fragments, and subrounded g r a i n s of quartz and l i t h i c fragments, i n p a l e  green a n d e s i t e ash t u f f ( u n i t 7b). 56 F i g u r e 3.28 Well developed bedding i n c a l c a r e o u s and f o s s i l i f e r o u s wacke ( u n i t 8b). 59 F i g u r e 3.29 Co a r s e - g r a i n e d , p o o r l y s o r t e d fragments i n c a l c a r e o u s and f o s s i l i f e r o u s wacke ( u n i t 8b). 64 F i g u r e 3.30 B a s a l t dyke ( u n i t 9) composed of l a t h s of a u g i t e i n a p l a g i o c l a s e dominated groundmass. 64 F i g u r e 3.31 B a s a l t dyke ( u n i t 9) c r o s s c u t t i n g green +/- maroon b a s a l t i c - a n d e s i t e t u f f ( u n i t 1) on a roadcut near the T o r b r i t mine. 65 Page x i i i page F i g u r e 3.32 AFM diagram f o r igneous rocks i n the D o l l y Varden camp, northwestern B.C. 68 F i g u r e 3.33 T o t a l a l k a l i s i l i c a (TAS) diagram f o r the D o l l y Varden camp, northwestern B.C. 69 F i g u r e 3.34 Si02 vs Zr/Ti02 diagram f o r the D o l l y Varden camp, northwestern B.C. 70 F i g u r e 3.35 Well developed a-c j o i n t s , o r i e n t e d i n a n o r t h e a s t e r l y d i r e c t i o n , and p e r p e n d i c u l a r to the n o r t h w e s t e r l y t r e n d i n g f o l d a x i s . 75 F i g u r e 3.36 The very prominent gossan of the D o l l y Varden Gold B e l t , near Black Bear Creek ( F i g s . 3.1 and 3.4). 82 F i g u r e 3.37 G o l d - s i l v e r - c o p p e r v e i n s of the D o l l y Varden Gold B e l t . 83 F i g u r e 4.1 S u l f u r i s o t o p e p l o t f o r d e p o s i t s from the D o l l y Varden camp, northwestern B.C. 87 F i g u r e 4.2 Range of c a l c u l a t e d dfl 80 v a l u e s f o r ore f l u i d s (Table 4.1.) r e s p o n s i b l e f o r m i n e r a l i z a t i o n i n the D o l l y Varden camp, northwestern B.C. 93 F i g u r e 4.3 P l o t s of 208Pb/204Pb v s . 206Pb/204Pb, 207Pb/204Pb v s . 206Pb/204Pb and 206Pb/208Pb v s . 206Pb/ 207Pb f o r d e p o s i t s l o c a t e d on F i g u r e 3.1 and l i s t e d i n Table 4.4. 104 Page x i v page F i g u r e 5.1 F i g u r e 5.2 F i g u r e 5.3 I d e a l i z e d c r o s s - s e c t i o n of the D o l l y Varden camp, northwestern B.C. 107 Schematic r e c o n s t r u c t i o n of the m i n e r a l i z e d s t r a t i f o r m h o r i z o n i n the D o l l y Varden camp, northwestern B.C. 110 Model f o r ge n e s i s of s t r a t i f o r m m i n e r a l i z a t i o n i n the D o l l y Varden camp, northwestern B.C. 114 Page xv ACKNOWLEDGEMENT I would l i k e to thank C.I. Godwin f o r h i s guidance and s u p e r v i s i o n of t h i s p r o j e c t . Thanks a l s o are extended to A . J . S i n c l a i r , J.K. R u s s e l l and D.J. A l l d r i c k f o r t h e i r help d u r i n g r e s e a r c h and suggestions f o r improvement of the f i n a l manuscript. F i e l d support from Peter T h i e r s c h and V i c t o r Koyanagi, t e c h n i c a l and a n a l y t i c a l a s s i s t a n c e from both the Department of G e o l o g i c a l Sciences and the Department of Oceanography a t The U n i v e r s i t y of B r i t i s h Columbia, and s t a b l e i s o t o p e a n a l yses by H.R. Krouse from the U n i v e r s i t y of C a l g a r y , and K. Muehlenbachs from the U n i v e r s i t y of A l b e r t a , are g r a t e f u l l y acknowledged. S p e c i a l a p p r e c i a t i o n goes t o Karen D e v l i n f o r her e x c e l l e n t d r a f t i n g s k i l l s and moral support. I would a l s o l i k e t o thank W.F. C h r i s t e n s e n of D o l l y Varden M i n e r a l s I n c o r p o r a t e d , W.N. Pearson of Derry, Michener, Booth and Wahl, C o n s u l t i n g G e o l o g i s t s and E n g i n e e r s , and the Science C o u n c i l of B r i t i s h Columbia f o r the o p p o r t u n i t y to make these s t u d i e s . 1 .0 INTRODUCTION The D o l l y Varden s i l v e r camp, centered near l a t i t u d e 55o 77' nort h and 129o 50' west (NTS: 103P), s t r a d d l e s the K i t s a u l t R i v e r 27km upstream from the smal l v i l l a g e of A l i c e Arm, approximately 850km northwest of Vancouver, B r i t i s h Columbia ( F i g . 2.1). Topography i n the area i s rugged and v a l l e y s l o p e s are steep. E l e v a t i o n i n the camp ranges from 275 to 1,050m above sea l e v e l , with most of the s i l v e r d e p o s i t s and prospects o c c u r r i n g below 750m. Present access to the r e g i o n i s by h e l i c o p t e r e i t h e r from Stewart, 41km to the n o r t h , or P r i n c e Rupert, 163km to the south. A g r a v e l road from the v i l l a g e of A l i c e Arm c o u l d be used f o r access to the camp p r o v i d e d minor r e p a i r s were c a r r i e d out. T h i s v i l l a g e , however, i s i s o l a t e d from the town of K i t s a u l t on the other s i d e of A l i c e Arm i n l e t by a 3km barge or f e r r y t r i p . K i t s a u l t i s connected by a p r i v a t e road to the S t e w a r t - C a s s i a r highway. The K i t s a u l t R i v e r area i s p a r t of the C o a s t a l Mountain p h y s i o g r a p h i c r e g i o n . Mean annual p r e c i p i t a t i o n ranges from 250 to 350cm. Mean d a i l y temperature i n January ranges between -10 and -15oC, and i n J u l y , i t i s l e s s than 14oC. V e g e t a t i o n i s p r i m a r i l y s u b a l p i n e Engelmann spruce and s u b a l p i n e f i r , with c o a s t a l western hemlock at lower e l e v a t i o n s ( F a r l e y , 1979). E x p l o r a t i o n and development has been c a r r i e d out i n the K i t s a u l t R i v e r v a l l e y s i n c e the f i r s t c l a i m s were staked i n the 1 e a r l y 1900's. Much of the e a r l y , c o l o r f u l h i s t o r y of the camp i s i n the r e c e n t book " S t e e l R a i l s and S i l v e r Dreams" (Muralt, 1985). Most of the s i l v e r - b a s e metal p r o d u c t i o n , t o t a l i n g 1,284,902 tonnes of ore averaging 484g s i l v e r per tonne, 0.38 percent l e a d and 0.02 percent z i n c , took p l a c e from 1919 to 1921 at the D o l l y Varden and N o r t h s t a r mines, and between 1949 and 1959 at the T o r b r i t mine (Table 1.1, F i g . 2.1). T o t a l g o l d and copper r e c o v e r e d from these mining o p e r a t i o n s was 3836g and 191kg, r e s p e c t i v e l y . E x p l o r a t i o n work c o n s i s t i n g of diamond d r i l l i n g , t r e n c h i n g , underground development, as w e l l as g e o l o g i c a l , geochemical and g e o p h y s i c a l surveys, has been c a r r i e d out i n t e r m i t t e n t l y i n the D o l l y Varden mining camp. T o t a l e s t i m a t e d proven, probable and p o s s i b l e r e s e r v e s f o r the camp (Table 1.1), are 1,354,596 tonnes averaging 326g s i l v e r per tonne, 0.24 percent l e a d and 0.29 percent z i n c . D e t a i l e d (1:5,000) g e o l o g i c a l mapping presented here f o r the D o l l y Varden camp ( F i g s . 3.1 to 3.3) a l l o w s the main m i n e r a l occurrences to be r e c o n s t r u c t e d to a continuous 3km long ore h o r i z o n t h a t conforms to s t r a t i g r a p h y . T h i s mapping was augmented by d e t a i l e d s t u d i e s t h a t i n c l u d e : (1) p e t r o l o g i c a l and p e t r o g r a p h i c a l d e s c r i p t i o n s of ore and host r o c k s , (2) whole-rock geochemical a n a l y s i s and K-Ar d a t i n g , and (3) s u l f u r , oxygen, carbon and g a l e n a - l e a d i s o t o p e a n a l y s e s . S y n t h e s i s of t h i s work shows t h a t the D o l l y Varden camp i s c h a r a c t e r i z e d by s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e d e p o s i t s i n t e r c a l a t e d i n i n t e r m e d i a t e v o l c a n i c rocks of E a r l y to Middle J u r a s s i c age. In 2 a d d i t i o n to s t r a t i f o r m m i n e r a l i z a t i o n , both s i l v e r - l e a d - z i n c and g o l d - s i l v e r - c o p p e r v e i n s occur throughout the camp. These i n t e r p r e t a t i o n s r e p r e s e n t a r a d i c a l departure from p r e v i o u s workers i n the area because they c o n s i d e r e d a l l m i n e r a l i z a t i o n to be e p i t h e r m a l v e i n s (Hanson, 1921; Black, 1951; Campbell, 1959; S k e r l , 1962; C a r t e r , 1970; and M i t c h e l l , 1973). The main focus of t h i s study i s on the nature of the v o l c a n i c rocks and t h e i r r e l a t i o n s h i p to the s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n . 3 TABLE 1.1. Previous production and reserves for the Dolly Warden camp, northwestern B.C. Previous production! Reserves2 (proven, probable and possible) Ag Pb Zn Ag Pb Zn Deposit name tonnes (tons) grams (ounces) percent percent tonnes (tons) grams (ounces) percent percent *" Torbrit 1,251,366 (1,379,372) 463 (13.52 ) 0.40 0.02 786,372 (866,812) 312 (9.10) 0.42 0.50 Dolly Varden 33,434 (36,854) 1,268 (37.03) 0.003 43,040 (47,443) 548 (16.00) Northstar 102 (112 ) 868 ( 25.34) 128,439 (141,577 ) 401 (11.71) Wolf 396,745 (437,329) 306 (8.92) TOTAL 1,284,902 (1,416,338 ) 484 (14.13 ) 0.38 0.02 1,354,596 (1,493,161) 326 (9.51) 0.24 0.29 1. Previous production data i s from the Mineral Policy Sector, 2. Reserve estimates for the Torbrit and Dolly Warden deposits and 1973, and estimates for the Northstar and Wolf deposits Department of Energy, Wines and Resources, Ottawa. are from the Dolly Varden Wines Limited annual reports for 1971 are from Thompson and Pearson, 1981. 2.0 REGIONAL GEOLOGY 2.1 INTRODUCTION The D o l l y Varden mining camp l i e s at the western margin of the Intermontane B e l t , w i t h i n the S t i k i n i a t e r r a n e ( F i g . 2.1; Coney et a l . , 1980). The rocks have been c o r r e l a t e d with the Hazelton Group, which i s a t h i c k and widespread i s l a n d a r c assemblage of b a s a l t i c to r h y o l i t i c v o l c a n i c flow r o c k s , t h e i r t u f f a c e o u s e q u i v a l e n t s and d e r i v e d sedimentary r o c k s , d e p o s i t e d i n the Hazelton Trough d u r i n g the E a r l y to Middle J u r a s s i c (Tipper and R i c h a r d s , 1976). The Hazelton Trough probably r e p r e s e n t s a marginal b a s i n , adjacent to the i s l a n d a r c , formed by c r u s t a l e x t e n s i o n r e l a t e d to back-arc s p r e a d i n g (Carey and Sigu r d s s o n , 1984). E x t e n s i o n generated f r a c t u r e zones and s e a f l o o r grabens t h a t a c t e d as t r a p s and l a r g e s c a l e b a r r i e r s to the d i s p e r s a l and d e p o s i t i o n of the v o l c a n i c and sedimentary rocks and a s s o c i a t e d s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l d e p o s i t s . Most of the v o l c a n i c d e b r i s trapped i n t h i s b a s i n was produced by e x p l o s i v e a n d e s i t i c e r u p t i o n s and by secondary e r o s i o n of the a r c complex. E x p l o s i v e volcanism i s t y p i c a l of shallow subaqueous and/or s u b a e r i a l e r u p t i o n s (Carey and Sigurdsson, 1984). R e g i o n a l geology of the K i t s a u l t R i v e r area was p r e v i o u s l y d e s c r i b e d by McConnell (1913), T u r n b u l l (1916), Hanson (1921, 1922a, 1922b, 1923 and 1928) and Black (1951). Geology of the 5 Unuk R i v e r , Salmon R i v e r and Anyox map-area was compiled by Grove (1982, 1986). Hanson (1921) s u b d i v i d e d rocks of the Haz e l t o n Group i n the upper K i t s a u l t R i v e r v a l l e y i n t o one sedimentary and one v o l c a n i c f o r m a t i o n , whereas Black (1951) r e c o g n i z e d two sedimentary and two v o l c a n i c f o r m a t i o n s . Recent remapping of the area by A l l d r i c k and Dawson ( A l l d r i c k et a l . , 1986; Dawson and A l l d r i c k , 1986), augmented by d e t a i l s here (cf_. D e v l i n and Godwin, 1986a,b), shows t h a t the K i t s a u l t R i v e r v a l l e y i s u n d e r l a i n by s i x v o l c a n i c - s e d i m e n t a r y u n i t s (1 to 6) of the Hazelton Group, and three T e r t i a r y i n t r u s i v e u n i t s (7 to 9) d e s c r i b e d below (Table 2.1, F i g s . 2.1 and 2.2). 2.2 HAZELTON VOLCANIC-SEDIMENTARY UNITS (1 TO 6) U n i t 1 , the lowermost sequence exposed, c o n s i s t s of interbedded, f i n e l y laminated b l a c k s i l t s t o n e , and a r g i l l i t e with minor wacke and limestone. Although the base of t h i s u n i t i s not exposed i n the K i t s a u l t R i v e r v a l l e y , u n i t 1 i s at l e a s t 1,200m t h i c k . U n i t 2, o v e r l y i n g u n i t 1, c o n s i s t s of mixed mafic v o l c a n i c and e p i c l a s t i c r o c k s . A u g i t e , f e l d s p a r , and o l i v i n e p o r p h y r i t i c b a s a l t flows, p y r o c l a s t i c s and d e r i v e d conglomerates are c h a r a c t e r i s t i c of the u n i t . Thickness of u n i t 2 ranges from 150 to 700m. 6 TABLE 2.1. Formations in the Kitsault River area, northwestern B.C. Era Period Epoch Group Rock Unitl Lithology Cenozoic Tertiary Eocene and Younger (22 ma; K-Ar) Early to Middle Eocene (43-55 Wa; K-Ar) Dykes (9) basalt, lamprophyre, diorite, microdiorite Alice Arm quartz monzonite, (Ajax) biotite quartz monzonite porphyry, intrusions (8) sericite quartz monzonite porphyry Coast Range quartz monzonite, granodiorite Batholith (7) mesozoic Jurassic Early to Hazelton Upper basal fossil i ferous uiacke, si l tstone, middle sedimentary shale, sandstone, unit (6) intraformational conglomerate,limestone Epiclastic maroon and green volcanic conglomerate, and fe ls ic breccia, sandstone, black siltstone, volcanic a rg i l l i t e , uiacke, limestone, unit (5) greenish grey dacitic pyroclastic rocks, feldspar porphyritic flows Intermediate green and minor maroon andesite volcanic pyroclastic rocks, unit (4) feldspar + hornblende andesite porphyry black si l tstone, maroon siltstone sandstone, conglomerate, limestone, fossil i ferous limestone, chert Triassic(?) Unconformity(?) middle sedimentary unit (3) black si l tstone, limestone and fossil i ferous limestone, green and purple volcanic breccia, siltstone, sandstone, conglomerate, uiacke, polymictic pebble conglomerate Wafic volcanic olivine porphyry basalt flows, unit (2) augite porphyry basalt flows and pillowed flows, basaltic pyroclastic rocks, basaltic conglomerate, black si l tstone, sandstone, wacke, limestone Lower sedimentary unit (1) black si l tstone, a rg i l l i t e , shale, black wacke, sandstone, limestone Formations and rock units as described by Alldrick et a l . , 1986, and Dawson and Alldrick, 19B6. Numbers in parentheses are rock units as described in Figure 2.2. 7 'MP-182, 1S3 103P-160 103P-016 I03P-147 103P-223 F i g u r e 2.1. Re g i o n a l geology surrounding the D o l l y Varden camp, northwestern B.C. M o d i f i e d from A l l d r i c k et a l . (1986), A l l d r i c k and Dawson (1986), and D e v l i n and Godwin (1986a). 8 LEGEND INTRUtlVI ROCKS TUTUJtV [ 9 j MINOR DYKES: MICAOOlORITE (tl: GflANOOlORITe (Dt: 1 LAMPROPHYRE (C) | 8 1 AJAX INTRUSIONS: QUARTZ FELDSPAR PORPHYRITIC QUARTZ MONZONITE la): BJOTfTTi QUARTZ MONZONTTE (bl. S5.1 Ma(K-Afi | 'y | COAST PLUTONIC COMPLEX. QUARTZ MONZONITE (•): GRAMOOtOfliTE IB). 43-51 Ma (KiArl INTRUSIVE CONTACT WLCAMC AMD SCOHMNTARV "JOCKS WODLC TO UfNI JURASSIC i~3 1 BASAL FOSSILIFEROUS WACKE (tl: BLACK SILTSTONE ANO WACKE (M: MMOR INTHAPORMATONAL CONGLOMERATES AMO LIMESTONE (c) U3WU JUHASSK I S I GREEN AND MAROON WXCANC BRECCIA It); EPCLASTC CONGLOMERATE AND SEDIMENTS (b): LOCAL DACITIC FLOWS AND PVROCLASTCS (cl VOLCJkMC ANO lUNMCffTAJtV ROCKS [CONTINUED! LOWER JURASSIC iCONTINUEDt \A | F E L D S P A R - M O R N B L E N D S PORPHYRITIC ANOESITIC PVROCLASTICS (41 AND FLOWS SILLS (Di: MINOR INTEMEDS OF LIMESTONE. SILTSTONE. SANDSTONE. CHERT. A N D BARITE ic) | 3 ] BASAL POLYMICTIC CONGLOMERATE. MINOR I N T E R B E D D E D uMESTONE. SILTSTONE. GRlT SANDSTONE (al: SILTSTONE. ARGILLITE (01; sOLCANIC BRECCIA. MINOR I N T E R B E O O E D SILTSTONE. SANDSTONE Id. INTERBEDDED SILTSTONE. SANDSTONE. A N O °£BBLE CONGLOMERATE (MARKER -ORIZON) id | 2 | AUGITE (OLIVINE) PORPHYRITIC BASALT FLOWS. PILLOWEO FLOWS I«I, AUGlTEFELOSPAR P O R P H Y R I T I C BASALT PYROCLASTICS AND KXCANtC BRECCIAS Itt: EPKXASTC CONGLOMERATE. MiNOR INTERBEDDED SILTSTONE. ARGILLITE. AND LIMESTONE !C| | 1 j SILTSTONE. A R G I L U T E . WACKE fa): RARE LIMESTONE <D»: BOTTOM OF UNfT NOT SEEN ^ 90LD BELT ALTERATION ZONE SYMBOLS VEIN M W E R A U Z A T W N _ ) C R A C K L E B R E C C I A U IN E R A L I Z A T O N * S T R A T A B O U N D MINERALIZATION P O R P H Y R Y MINERALIZATION F i g u r e 2 . 2 . C r o s s - s e c t i o n from F i g u r e 2.1 of r e g i o n a l geology surrounding the D o l l y Varden camp, northwestern B.C. (see F i g 2.1 f o r source of data.) 9 U n i t 3 i s a sedimentary sequence of s i l t s t o n e , sandstone, wacke, g r i t , pebble to cobble conglomerate, and minor v o l c a n i c b r e c c i a . U n i t 3 v a r i e s i n t h i c k n e s s from 400 to 2,000m and the con t a c t a g a i n s t u n i t 2 i s g r a d a t i o n a l . F o s s i l s c o l l e c t e d from u n i t 3 p o s s i b l y are e i t h e r Permian o r T r i a s s i c i n age (H. Ti p p e r , p e r s . comm. to D. A l l d r i c k , 1986). U n i t 4 i s an a n d e s i t i c p y r o c l a s t i c rock sequence with i n t e r c a l a t e d flows and/or s u b v o l c a n i c s i l l s of s i m i l a r composition. T h i s u n i t , which ranges from 500 to 2,000m i n t h i c k n e s s , hosts the m a j o r i t y of the s i l v e r , g o l d and base metal occurrences i n the K i t s a u l t R i v e r area. U n i t 5, i s g r a d a t i o n a l with u n d e r l y i n g u n i t 4, and c o n s i s t s of a shallow water, marine to s u b a e r i a l assemblage of a l t e r n a t i n g green and maroon v o l c a n i c b r e c c i a s and conglomerates, l e s s e r a n d e s i t e and/or d a c i t e flows and p y r o c l a s t i c s , with minor b l a c k s i l t s t o n e and lim e s t o n e . The th i c k n e s s of t h i s u n i t v a r i e s from l e s s than 100m to a maximum of 1,500m. U n i t 6, the uppermost sequence exposed i n the area, i s a marine assemblage of b l a c k s i l t s t o n e , s h a l e , wacke, with l e s s e r sandstone, limestone and i n t r a f o r m a t i o n a l conglomerate. E a r l y J u r a s s i c f o s s i l s from u n i t 6 ( D e v l i n and Godwin, 1986b; H. T i p p e r , p e r s . comm. to D. A l l d r i c k , 1986) i n d i c a t e t h a t a 10 s i g n i f i c a n t unconformity between T r i a s s i c ( u n i t s 1 to 3) and J u r a s s i c ( u n i t s 4 to 6) v o l c a n i c - s e d i m e n t a r y u n i t s may occur i n the K i t s a u l t v a l l e y (H. T i p p e r , p e r s . comm. to D. A l l d r i c k , 1986). 2.3 TERTIARY INTRUSIVE UNITS (7 TO 9) S e v e r a l T e r t i a r y i n t r u s i v e u n i t s cut a l l rocks of the Hazelton Group i n the K i t s a u l t R i v e r a r e a . U n i t 7, quartz monzonite t o g r a n o d i o r i t e of the E a r l y t o Middle Eocene Coast Range b a t h o l i t h , i s exposed i n the southwest corner of the map-area ( F i g . 2.1). C a r t e r (1982) r e p o r t e d 43 t o 51 Ma potassium-argon dates f o r the e a s t e r n Coast Range B a t h o l i t h . U n i t 8 i s the E a r l y to Middle Eocene Ajax i n t r u s i o n s , which were o r i g i n a l l y named A l i c e Arm i n t r u s i o n s because of t h e i r p r o x i m i t y and abundance i n the A l i c e Arm area ( C a r t e r , 1982). T h i s u n i t occurs as small s t o c k s of qua r t z f e l d s p a r p o r p h y r i t i c quartz monzonite and b i o t i t e q uartz monzonite. B i o t i t e from one of these i n t r u s i o n s y i e l d e d a potassium-argon date of 55.1 + 3 Ma ( C a r t e r , 1982; r e c a l c u l a t e d i n Dawson and A l l d r i c k , 1986, usi n g c o n s t a n t s from S t e i g e r and Jager, 1977). Although Ajax i n t r u s i o n s y i e l d o l d e r dates than the Coast Range B a t h o l i t h , A l l d r i c k ( A l l d r i c k , p e r s . comm., 1987) i s c e r t a i n t h a t they are s a t e l l i t e p l u t o n s or " o u t l i e r s " of the main Coast Range B a t h o l i t h . 11 U n i t 9 i s the numerous T e r t i a r y dykes t h a t c r o s s c u t a l l rock u n i t s i n the K i t s a u l t R i v e r area. They c o n s i s t of b a s a l t , lamprophyre, m i c r o d i o r i t e and g r a n o d i o r i t e . One of the b a s a l t dykes y i e l d e d a whole rock K-Ar date of 22.3 + 0.8 Ma ( D e v l i n and Godwin, 1986b). 2.4 STRUCTURE Three p a r a l l e l r e g i o n a l f o l d s are i d e n t i f i e d i n the v o l c a n i c and sedimentary u n i t s i n the K i t s a u l t R i v e r area ( F i g s . 2.1 and 2.2). These f o l d s , a l l doubly p l u n g i n g , i n c l u d e the Varden G l a c i e r a n t i c l i n e , K i t s a u l t R i v e r s y n c l i n e and the Mount McGuire a n t i c l i n e . Two major s e t s of f a u l t s a l s o t r a n s e c t the a r e a . E a r l i e r f a u l t s t r e n d northwest and younger f a u l t s t r e n d n o r t h e a s t . 2.5 ALTERATION An e x t e n s i v e hydrothermal a l t e r a t i o n zone h o s t i n g numerous g o l d - s i l v e r - c o p p e r occurrences trends s u b p a r a l l e l to the northwest f a u l t t r e n d ( F i g . 2.1). T h i s a l t e r a t i o n zone measures n e a r l y 15km i n l e n g t h and i s c h a r a c t e r i z e d by s e r i c i t i z a t i o n , s i l i c i f i c a t i o n and p y r i t i z a t i o n . A l l Hazelton Group rocks i n the K i t s a u l t R i v e r area have been s u b j e c t e d to e i t h e r g r e e n s c h i s t f a c i e s (Dawson and A l l d r i c k , 1986) or p r e h n i t e - p u m p e l l y i t e f a c i e s (P. Read, p e r s . comm., 1986) r e g i o n a l metamorphism. P r e h n i t e was i d e n t i f i e d by the w r i t e r i n 12 some t h i n s e c t i o n s ( s e c t i o n 3.2) and the lower metamorphic grade i s f a v o r e d f o r the Hazelton Group rocks i n the K i t s a u l t R i v e r area. 13 3.0 PROPERTY GEOLOGY 3.1 INTRODUCTION Geology of the D o l l y Varden camp i s i n F i g u r e s 3.1 to 3.3 ( i n p o c k e t ) , and F i g u r e s 3.4 and 3.5 ( i n t e x t ) . P r e v i o u s d e s c r i p t i o n s of geology i n the area i n c l u d e b r i e f accounts of the g e n e r a l geology by S k e r l (1962) and M i t c h e l l (1973), and more d e t a i l e d g e o l o g i c a l r e p o r t s on: the T o r b r i t s i l v e r mine (Campbell, 1959), the Gold B e l t area northwest of the T o r b r i t mine ( C a l i c h , 1956; C a r t e r , 1970), and the Wolf s i l v e r prospect. ( T h i e r s c h , 1986). Geology of the Kinskuch Lake area, 12km east of the D o l l y Varden camp, was mapped by Gale (1957). Rocks i n the map-area are c h a r a c t e r i z e d by the E a r l y to Middle J u r a s s i c H azelton Group, c o n s i s t i n g p r i n c i p a l l y of v o l c a n i c and sedimentary rocks with a s s o c i a t e d s t r a t i f o r m and vo l c a n o g e n i c s u l f i d e / s u l f a t e d e p o s i t s . There are approximately 3,000m of v o l c a n i c flow, p y r o c l a s t i c and sedimentary r o c k s exposed i n the D o l l y Varden map-area. T e r t i a r y dykes cut a l l of these H a z e l t o n Group r o c k s . The Hazelton Group rocks have been s u b d i v i d e d i n t o u n i t s based on m i n e r a l o g i c a l and t e x t u r a l c h a r a c t e r i s t i c s , and on s t r a t i g r a p h i c p o s i t i o n r e l a t i v e to the m i n e r a l i z e d s t r a t i f o r m h o r i z o n . Rock names used to d e s c r i b e the u n i t s were d e r i v e d from both petrography and whole rock c h e m i s t r y . Petrography of 14 the v o l c a n i c and sedimentary rocks i n the D o l l y Varden camp i s summarized i n Table 3.1. T e x t u r a l c h a r a c t e r i s t i c s of p y r o c l a s t i c fragments and d e p o s i t s , however, were e i t h e r i n f e r r e d or r e c o n s t r u c t e d from p r e s e r v e d t e x t u r e s and the terminology i s c o n s i s t e n t with t h a t of F i s h e r and Schmincke (1984). Chemical c l a s s i f i c a t i o n of the igneous rocks i s d i s c u s s e d i n d e t a i l i n s e c t i o n 3.3. The s t r a t i g r a p h i c sequence, summarized i n F i g u r e 3.6, c o n s i s t s of s t r a t i f o r m m i n e r a l i z a t i o n bounded by f o o t w a l l and hangingwall v o l c a n i c r o c k s , which are a l l o v e r l a i n by sedimentary r o c k s . F o o t w a l l v o l c a n i c rocks c o n s i s t of more than 1,200m of green +_ maroon b a s a l t i c - a n d e s i t e t u f f ( u n i t 1), green _+ maroon p o r p h y r i t i c a n d e s i t e ( u n i t 2a) and green a n d e s i t e shard t u f f ( u n i t 2b). S t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n ( u n i t s 3a, 3b and 3c) o v e r l i e s the f o o t w a l l v o l c a n i c r o c k s , and i s up to 60m t h i c k . Hangingwall v o l c a n i c rocks above the s t r a t i f o r m m i n e r a l i z a t i o n are about 1,000m t h i c k , and c o n s i s t of pale grey b a s a l t i c - a n d e s i t e ash t u f f ( u n i t 4), maroon b a s a l t i c - a n d e s i t e a s h - l a p i l l i t u f f ( u n i t 5), dark grey a n d e s i t e l a p i l l i t u f f ( u n i t 6a), dark green a n d e s i t e t u f f ( u n i t 6b), grey-green p o r p h y r i t i c a n d e s i t e ( u n i t 7a) and p a l e green a n d e s i t e ash t u f f ( u n i t 7b). Hangingwall v o l c a n i c s are o v e r l a i n by sedimentary rocks ( u n i t s 8a, 8b and 8 c ) . T e r t i a r y dykes ( u n i t 9) a f e not shown i n F i g u r e 3.6. 15 TABLE 3.1. Petrography! of the volcanic and sedimentary rocks In the Dolly Uarden camp, northwestern B.C. Unit Rock Intrusive and flow rocks Pyroclastic and sedimentary rocks Total Total Fragments (percent of total) phenocrysts Phenocrysts (percent of total) Groundmass fragments Crystal fragments Uitric Lithic matrix (percent of rock) PL HB C/PX QZ OP AP SP F5 C/PX QZ CH CA SC EP (percent of rock) PL HB C/PX QZ BI PIS OP SP fragments fragments FS QZ CH CA SC 9 Basalt and lamprophyre dykes 20-90 SO 30 15 S tr Be Black siltstone and shale 8b Calcareous and fossiliferous uacke 8a Maroon siltstone 7b Pale green andesite ash tuff 7a Grey-green porphyritic andesite 35-55 65 20 5 10 6b Dark green andesite tuff I—J 6a Oark grey andesite lapilli tuff 5 Maroon basaltic-andesite ash-lapilli tuff 4 Pale grey basaltic-andesite ash tuff 3 Mineralized stratiform horizon n/a 2b Green andesite shard tuff 2a Green + maroon porphyritic andesite 30-65 80 5 5 tr 10 tr tr 1 Green • maroon andesite tuff tr x tr tr x tr • tr 80-100 BO AO 20-40 40-60 45 25-75 30-40 30-70 30-60 65 50 30 50 40 25 50 4 55 • 25 tr 25 20 3 tr 7 tr 45 tr 5 20 30 5 2 15 40 n/a 10 10 30 25 10 20 tr 45 65 30 20 15 65 1. Mineral assemblages estimated from thin sections of each rock unit. Abbreviations: QZ = quartz, PL = plagioclase, C/PX = clinopyroxene, HB = hornblende, BI = biotite, PIS = muscovite, AP = apatite, SP = sphene, OP = opaques, FS = undifferentiated feldspar, SC = sericite, CH = chlorite, CA = undifferentiated carbonate, EP = epidote, x = pervasive, • = minor, tr = trace, n/a = not applicable (unit 3 is described in Table 3.2). Figure 3.4. Geology of the Dolly Varden camp, A l i c e Arm area, northwestern B.C. Cross-sections A-B and C-D are on Figures 3.2 and 3.3 (in pocket), and 3.5 (in t e x t ) . A l l units are within the Early to Middle Jurassic Hazelton Group, except T e r t i a r y dykes, which are not shown. Footwall volcanics (1) = unit 1 (green _+ maroon basaltic-andesite t u f f ) , unit 2a (green +_ maroon porphyritic andesite),. and unit 2b (green andesite shard t u f f ) . Mineralized stratiform horizon (2) = unit 3a ( s i l i c a - s u l f i d e e x h a l i t e ) , unit 3b (carbonate-sulfate-sulfide e x h a l i t e ) , and unit 3c (sulfate-oxide-sulfide e x h a l i t e ) . Hangingwall volcanics  (3) = unit 4 (pale grey basaltic-andesite ash t u f f ) , unit 5 (maroon basaltic-andesite a s h - l a p i l l i t u f f ) , unit 6a (dark grey andesite l a p i l l i t u f f ) , unit 6b (dark green andesite t u f f ) , unit 7a (grey-green po r p h y r i t i c andesite), and unit 7b (pale green andesite ash t u f f ) . Sediments (4) = unit 8a (maroon s i l t s t o n e ) , unit 8b (calcareous and f o s s i l i f e r o u s wacke), and unit 8c (black s i l t s t o n e and shale). 17 18 Figure 3.5. Cross-sections for the Dolly Varden camp, northwestern B.C. Cross-section A-B, looks northwest through the Dolly Varden West, Northstar and T o r b r i t areas. Cross-section C-D, looks northwest through the Wolf deposit. Location and units are described i n Figure 3.4. 19 8c EAST 8c" -8b© - - -F i g u r e 3.6. G e n e r a l i z e d s t r a t i g r a p h i c column f o r rock u n i t s i n the D o l l y Varden camp, northwestern B.C. U n i t s are l o c a t e d and d e s c r i b e d i n F i g u r e 3.4. 20 3 .2 LITHOLOGY 3.2.1 F o o t w a l l V o l c a n i c Rocks U n i t 1 Green + /- maroon b a s a l t i c - a n d e s i t e t u f f ( u n i t 1), exposed i n the southeast corner of the map-area ( F i g s . 3.1 and 3.4), appears to be the o l d e s t u n i t i n the D o l l y Varden camp. I t has an i n d e f i n i t e t h i c k n e s s because i t s bottom i s not exposed i n the map-area. Outcrops are g e n e r a l l y massive c l i f f s e x h i b i t i n g b l o c k y , angular f r a c t u r e p a t t e r n s . Weathered s u r f a c e s , c h a r a c t e r i s t i c a l l y p ale grey with maroon t i n t s , l o c a l l y show bedding and subangular to subrounded l a p i l l i up to 3cm a c r o s s . In hand specimen, u n i t 1 i s t y p i c a l l y green with minor maroon, and f i n e - g r a i n e d . Numerous broken p l a g i o c l a s e c r y s t a l s , and l e s s e r dark green and maroon c l a s t s , are e a s i l y r e c o g n i z a b l e i n hand specimen. In t h i n s e c t i o n , the t u f f s of u n i t 1 c o n s i s t of between 30 to 60 percent randomly o r i e n t e d , m a t r i x supported fragments t h a t range from l e s s than 0.1mm to 15mm but average 1.5mm a c r o s s . The random o r i e n t a t i o n of these fragments might i n d i c a t e an a s h f a l l r a t h e r than an ash flow o r i g i n ( F i s h e r and Schmincke, 1984). Subhedral, p l a g i o c l a s e c r y s t a l s with many broken f a c e s , comprise 25 percent of the fragments. They are a l b i t e i n composition (An5). Anhedral hematite g r a i n s make up approximately 10 percent of the fragments, and subhedral hornblende i s present o n l y i n minor amounts. Subangular ash and c r y s t a l t u f f c l a s t s comprise up t o 65 percent of the fragment component. The f i n e ash matrix c o n s i s t s p r i m a r i l y of c h l o r i t e and carbonate with l e s s e r q u a r t z . M i n e r a l pseudomorphs i n c l u d e p l a g i o c l a s e going to f i n e aggregates of c h l o r i t e and/or carbonate, and hornblende a l t e r i n g to c h l o r i t e and i r o n o x i d e s . Many l i t h i c fragments have been completely r e p l a c e d by carbonate. Randomly o r i e n t e d carbonate and/or q u a r t z v e i n l e t s averaging 0.2mm i n width, are common. Chemical a n a l y s i s of one specimen from u n i t 1 (Table 3.3: s e c t i o n 3.3) i n d i c a t e s a b a s a l t i c - a n d e s i t e composition ( F i g s . 3.33 and 3.34; Winchester and F l o y d , 1977, Le Bas e t a_l., 1 986). U n i t 2 U n i t 2 i s r e p r e s e n t e d by e i t h e r s u b v o l c a n i c dykes and s i l l s ( u n i t 2a) or t h e i r p y r o c l a s t i c e q u i v a l e n t s ( u n i t 2b). P o r p h y r i t i c a n d e s i t e s of u n i t 2a i n t r u d e u n i t 1, and both u n i t s 1 and 2a are unconformably o v e r l a i n by shard t u f f s of u n i t 2b, and maroon t u f f s of u n i t 5 ( F i g . 3.6). Green +/- maroon p o r p h y r i t i c a n d e s i t e (Unit 2a) crops out s p o r a d i c a l l y throughout the so u t h e a s t e r n p a r t of the map-area r e a c h i n g a maximum t h i c k n e s s of n e a r l y 150m. Outcrops are moderately r e s i s t a n t and d i s p l a y the same blocky angular f r a c t u r e p a t t e r n s as u n i t 1. S u r f a c e s weather a pale to medium grey; when f r e s h , u n i t 2a i s pale green t o grey-green with l o c a l maroon t i n t s . The groundmass i s a p h a n i t i c and phenocrysts, 22 g e n e r a l l y 1mm a c r o s s , are dominantly p l a g i o c l a s e with l e s s e r c h l o r i t i z e d mafic m i n e r a l s and hematite f l e c k s . E x t e n s i v e e p i d o t i z a t i o n of p l a g i o c l a s e phenocrysts imparts the pale green c o l o r . F i n e l y d i s s e m i n a t e d magnetite, not d i r e c t l y observed i n hand specimen, imparts a marked magnetism to t h i s rock. C a l c i t e and minor q u a r t z with b a r i t e v e i n s , averaging l e s s than 1mm i n width, are numerous. Common amygdules ( p o s s i b l y i n d i c a t i v e of shallow emplacement or e x t r u s i o n ) are f i l l e d w ith c a l c i t e , c h l o r i t e , e p i d o t e , quartz and t r a c e s of p r e h n i t e ( i n t h i n s e c t i o n ) ; up to 2 percent d i s s e m i n a t e d p y r i t e i s p r e s e n t l o c a l l y . T h i n s e c t i o n s of u n i t 2a e x h i b i t predominantly p o r p h y r i t i c with l e s s e r t r a c h y t i c and i n t e r g r a n u l a r t e x t u r e s . Subhedral phenocrysts, 30 to 65 percent of the rock, range from l e s s than 0.1mm to 5mm and average 1.0mm i n s i z e . These phenocrysts c o n s i s t o f : 80 percent c r u d e l y zoned p l a g i o c l a s e (An23 to An27), 5 percent hornblende ( r a r e l y up to 70 p e r c e n t ) , 5 percent pyroxene, 10 percent i r o n oxides (mainly anhedral magnetite), and t r a c e s of q u a r t z , a p a t i t e , sphene and leucoxene. The groundmass c o n s i s t s of m i c r o g r a n u l a r aggregates of c h l o r i t e , with l e s s e r amounts of s e r i c i t e , q uartz and f e l d s p a r , and sparse e p i d o t e and carbonate. P l a g i o c l a s e c r y s t a l s are s a u s s u r i t i z e d as i n d i c a t e d by i r r e g u l a r c l o t s of carbonate, e p i d o t e and s e r i c i t e t h a t p a r t l y r e p l a c e most phenocrysts ( F i g . 3.7). Rims around hornblende and pyroxene show a l t e r a t i o n to c h l o r i t e and i r o n o x i d e s . 23 I F i g u r e 3.7. S a u s s u r i t i z e d p l a g i o c l a s e phenocrysts i n green +/- maroon p o r p h y r i t i c a n d e s i t e ( u n i t 2a). Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . F i g u r e 3.8. V i t r i c - s h a r d fragments i n green a n d e s i t e shard t u f f ( u n i t 2b). Note t h a t fragments are a l i g n e d s u b p a r a l l e l to the f o l i a t i o n d i r e c t i o n . Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . 24 Green a n d e s i t e shard t u f f ( u n i t 2b) i s a widespread p y r o c l a s t i c rock t h a t crops out near the confluence of K i t s a u l t R i v e r and T i g e r Creek, i n the s o u t h e a s t e r n p a r t of the map-area ( F i g s . 3.1 and 3.4). T h i s u n i t ranges i n t h i c k n e s s from 15m i n the Moose-Lamb area to a maximum of 170m i n the D o l l y Varden West a r e a . Outcrops have smooth, rounded s u r f a c e s , commonly d i s p l a y i n g a p i t t e d s u r f a c e and r e g u l a r , s u b p a r a l l e l j o i n t i n g . Weathered s u r f a c e s are e i t h e r p a l e grey, grey or grey-brown; f r e s h s u r f a c e s are grey to grey-green with minor maroon t i n t s . D e p osits are unbedded, moderately s o r t e d and t u f f a c e o u s with sm a l l p l a g i o c l a s e c r y s t a l fragments and dark green shards s e t i n a f i n e - g r a i n e d m a t r i x . Minor f i n e l y d i s s e m i n a t e d p y r i t e occurs l o c a l l y . T h i n s e c t i o n s show t h a t fragments i n u n i t 2b are m a t r i x supported and p r e f e r e n t i a l l y o r i e n t e d . Fragments comprise between 30 and 70 percent of t h i s u n i t , and range from l e s s than 0.1mm to 10mm and average 1.0mm i n s i z e . They are composed of 55 percent subhedral p l a g i o c l a s e c r y s t a l s , 25 percent p l a t y shards, 15 percent t u f f fragments, 5 percent opaques (probably i l m e n i t e ) , minor hornblende and pyroxene, and t r a c e s of muscovite. Shards and l i t h i c fragments are g e n e r a l l y subangular. Subrounded l i t h i c g r a i n s are l o c a l l y abundant and suggest the p o s s i b l e c o n t r i b u t i o n of a minor e p i c l a s t i c component. The o r i g i n a l v i t r o c l a s t i c m atrix i s r e p l a c e d p r i m a r i l y by s m a l l , ragged g r a i n s of c h l o r i t e and s e r i c i t e with 25 minor carbonate and q u a r t z . P l a g i o c l a s e fragments g e n e r a l l y have been r e p l a c e d by e i t h e r s e r i c i t e and carbonate or c h l o r i t e , whereas most shard and l i t h i c fragments are r e p l a c e d by c h l o r i t e . Hornblende and pyroxene are g e n e r a l l y a l t e r e d to c h l o r i t e and rimmed by i r o n o x i d e s . C a l c i t e v e i n l e t s , averaging 0.2mm i n width, are l o c a l l y abundant throughout t h i s u n i t . Welding i n u n i t 2b i s evidenced by: 1) p r e f e r r e d o r i e n t a t i o n of c r y s t a l and v i t r i c - s h a r d fragments, s u b p a r a l l e l to a c r u d e l y developed f o l i a t i o n ( F i g . 3.8), 2) a strung-out g l a s s y - l o o k i n g m atrix and 3) f l a t t e n e d v i t r i c fragments. Shard o u t l i n e s are not w e l l d e f i n e d , as expected i n a n d e s i t i c v o l c a n i c rocks ( F i s h e r and Schmincke, 1984). Chemical a n a l y s i s of f o u r samples from u n i t s 2a and 2b (Table 3.3: s e c t i o n 3.3), show them a l l to be a n d e s i t i c ( F i g s . 3.33 and 3.34). A whole rock K-Ar date of 72.2 +_ 2.5 Ma was a l s o o b t a i n e d f o r one sample from u n i t 2a. T h i s Late Cretaceous date, too young f o r H azelton Group rocks, has been r e s e t by r e g i o n a l metamorphism ( s e c t i o n 4.3). 3.2.2 S t r a t i f o r m S i l v e r - L e a d - Z i n c - B a r i t e E x h a l a t i v e  M i n e r a l i z a t i o n U n i t 3 The rocks of u n i t 3 are t y p i c a l l y l a y e r e d , conformable with e n c l o s i n g w a l l r o c k s and host s i g n i f i c a n t s i l v e r and base metal 26 m i n e r a l i z a t i o n . They are i n t e r p r e t e d here as a s t r a t i f o r m , v o l c a n o g e n i c s i l v e r - l e a d - z i n c - b a r i t e e x h a l i t e h o r i z o n t h a t hosts the f o l l o w i n g d e p o s i t s from south and west to north and east ( F i g s . 3.1 and 3.4): D o l l y Varden West, D o l l y Varden E a s t , N o r t h s t a r , T o r b r i t , Moose-Lamb, a s m a l l , i s o l a t e d occurrence n o r t h of T i g e r Creek on the east s i d e of the K i t s a u l t R i v e r , South Musketeer and p o s s i b l y K i t s o l . T h i s s t r a t i f o r m l a y e r e x h i b i t s p r o p e r t y - s c a l e m i n e r a l zoning from massive s u l f i d e s and quartz ( u n i t 3a) i n the D o l l y Varden East area, through massive carbonates, s u l f a t e s and s u l f i d e s ( u n i t 3b) i n the N o r t h s t a r and D o l l y Varden West area, t o laminated s u l f a t e s , oxides and s u l f i d e s ( u n i t 3c) i n the T o r b r i t and Moose-Lamb a r e a . Mineralogy of the s t r a t i f o r m h o r i z o n ( u n i t s 3a, 3b and 3c) i s summarized i n Table 3.2. P r o p e r t y - s c a l e m i n e r a l zoning i n the e x h a l i t e , mentioned above, i s demonstrated c l e a r l y i n Table 3.2. The summary data presented shows t h a t i n c r e a s e s i n percentages of c e r t a i n m i n e r als i s accompanied by percentage decreases of other m i n e r a l s . Moving from u n i t 3a, through u n i t 3b, to u n i t 3c, b a r i t e , j a s p e r and i r o n oxides s t e a d i l y i n c r e a s e , whereas q u a r t z , carbonate and s u l f i d e s decrease i n abundance. S i l v e r values i n the s t r a t i f o r m h o r i z o n a l s o e x h i b i t zoning a c r o s s the p r o p e r t y . The zoning from west to east i s c h a r a c t e r i z e d by the high grade D o l l y Varden East d e p o s i t ( u n i t 3a) t h a t averages 865g s i l v e r per tonne, through the moderate to high grade N o r t h s t a r and T o r b r i t d e p o s i t s ( u n i t s 3b and 3c) averaging 405g s i l v e r per tonne, to the lower grade Moose-Lamb 27 TABLE 3.2. dineralogyl of the stratiform horizon (unit 3) in the Dolly Warden Camp, northwestern B.C. Property-scale mineral zonation is shown by increases in barite, jasper and iron oxides accompanied by decreases in quartz, carbonate and sulfides, mowing from the silica-sulfide exhalite (unit 3a) , through the carbonate-sulfate-sulfide exhalite (unit 3b), to the sulfate-oxide-sulfide exhalite (unit 3c). Gangue mineralogy (percent of total) Ore mineralogy (percent of total) Unit Rock name QZ SC CH EP CA SO RH BA JA PY SL GN CP HE mG TT PR AR Ag 3c Sulfate-oxide-sulfide exhalite 35 2 15 5 15 7 a 3 1 + 8 5 tr tr tr 3b Carbonate-sulfate-sulfide exhalite 30 40 1Q tr 5 5 7 3 + tr 3a Silica-sulfide exhalite 70 10 tr 20 + tr tr tr 1. Percent mineralogy is estimated from polished thin sections of stratiform ore samples. Abbreviations: QZ = quartz, SC = sericite, CH = chlorite, EP = epidote, CA = calcite, SO = siderite, RH = rhodochrosite, BA = barite, JA = jasper, PY = pyrite, SL = sphalerite, GN = galena, CP -chalcopyrite, HE = hematite, MG = magnetite, TT = tetrahedrite, PR = pyrargyrite, AR = argentite, Ag = native silver, + = minor, tr = trace. 28 d e p o s i t ( u n i t 3c) t h a t averages 135g s i l v e r per tonne. Moving westward from the h i g h grade D o l l y Varden East d e p o s i t , the s i l v e r grade decreases to 15g s i l v e r per tonne f o r the D o l l y Varden West d e p o s i t ( u n i t 3b). The s i l v e r to g o l d r a t i o f o r the s t r a t i f o r m h o r i z o n ranges from 20:1 i n the D o l l y Varden West d e p o s i t , to 15,000:1 i n the T o r b r i t and Moose-Lamb d e p o s i t s , and g e n e r a l l y averages g r e a t e r than 1,000:1. S t r a t i f o r m e x h a l a t i v e m i n e r a l i z a t i o n ( u n i t 3), together with f o o t w a l l and hangingwall t u f f s ( u n i t s 2b and 4, r e s p e c t i v e l y ) , are o v e r l a i n by the maroon t u f f s of u n i t 5 ( F i g . 3.6). Quartz and s u l f i d e e x h a l i t e ( u n i t 3a) i s commonly i n t e r b e d d e d with u n i t 4 a t the D o l l y Varden East d e p o s i t , and.also u n d e r l i e s c a r b o n a t e - r i c h ore ( u n i t 3b) at the N o r t h s t a r d e p o s i t ( F i g s . 3.1 and 3.4). The t h i c k n e s s of these s t r a t i f o r m d e p o s i t s v a r i e s from l e s s than 5m a t the T o r b r i t mine to n e a r l y 60m i n the D o l l y Varden West area; t y p i c a l l y d e p o s i t s average about 20m. S i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a), comprised predominantly of quartz and p y r i t e , i s exposed mainly i n trenches and o l d stopes of the D o l l y Varden mine ( D o l l y Varden E a s t ) . Outcrops are s t a i n e d orange-yellow due to abundant l i m o n i t e , p a r t i c u l a r l y j a r o s i t e . Regular j o i n t i n g and d i s t i n c t , o f t e n c o n v o l u t e d , l a y e r i n g can be observed i n outcrop ( F i g . 3.9). Hand specimen mineralogy i s c h a r a c t e r i z e d by d i s s e m i n a t e d , massive and l e n s o i d a l , f i n e - g r a i n e d , p y r i t e with t r a c e s of c h a l c o p y r i t e hosted i n a gangue of medium g r a i n e d , grey with minor milky 29 white, quartz ( F i g . 3.10). C r o s s - c u t t i n g quartz and s u l f i d e s t r i n g e r s are common and abundant. P o l i s h e d t h i n s e c t i o n study showed t h a t u n i t 3a i s comprise of 70 percent q u a r t z , 20 percent p y r i t e , 10 percent s e r i c i t e , minor c h a l c o p y r i t e and e p i d o t e (up to 5 percent r a r e l y ) , and t r a c e s of a r g e n t i t e , p y r a r g y r i t e and n a t i v e s i l v e r . Angular t u f f fragments have been i d e n t i f i e d i n some specimens. Quartz occurs as anhedral g r a i n s d i s p l a y i n g both undulose e x t i n c t i o n , denoting s t r a i n , and p o l y g o n a l g r a i n boundaries which probably i n d i c a t e s r e c r y s t a l l i z a t i o n . S e r i c i t e occurs e i t h e r i n t e r s t i t i a l l y to q u a r t z or c o n c e n t r a t e d i n f i n e r g r a i n e d l a y e r s . Anhedral and subhedral p y r i t e forms massive aggregates and l e s s f r e q u e n t l y i s o l a t e d g r a i n s , g e n e r a l l y l e s s than 1.0mm i n diameter ( F i g . 3.11). L a y e r i n g , probably bedding, as w e l l a weakly c r e n u l a t e d a x i a l - p l a n e f o l i a t i o n was i d e n t i f i e d i n some t h i n s e c t i o n s . C a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e (Unit 3b), c o n s i s t i n g p r i m a r i l y of c a l c i t e , q u a r t z , s i d e r i t e , b a r i t e and s u l f i d e s , i s r e p r e s e n t e d i n the D o l l y Varden West and N o r t h s t a r d e p o s i t s . Weathered s u r f a c e s d i s p l a y the same l i m o n i t e s t a i n as u n i t 3a, as w e l l as l o c a l l y abundant manganese c o a t i n g s . Outcrops are g e n e r a l l y more r e c e s s i v e than those of u n i t 3a. L a y e r i n g , observed i n o n l y a few o u t c r o p s , i s pronounced i n underground workings and i n d r i l l core from the N o r t h s t a r d e p o s i t ( F i g . 3.12). V e r t i c a l m i n e r a l z o n a t i o n ( F i g . 3.13) c o n s i s t i n g of a p y r i t e - r i c h base, and a s p h a l e r i t e - g a l e n a - r i c h top 30 F i g u r e 3 . 9 . S t e e p l y - d i p p i n g l a y e r s of s u l f i d e s , m o s t l y p y r i t e , i n s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a) from the D o l l y Varden E a s t d e p o s i t . Lens cap i n c e n t e r of photograph to be used f o r s c a l e -i t i s a p p r o x i m a t e l y 5cm a c r o s s . 31 I F i g u r e 3.10. P o l i s h e d s l a b of quartz and p y r i t e m i n e r a l i z a t i o n , t y p i c a l of the s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3a). F i g u r e 3.11. A n h e d r a l p y r i t e f o r m i n g m a s s i v e a g g r e g a t e s and c r u d e l y d e v e l o p e d l a y e r s i n s i l i c a - s u l f i d e e x h a l i t e ( u n i t 3 a ) . Width of p h o t o m i c r o g r a p h i s 7.0mm ( p l a n e , r e f l e c t e d l i g h t ) . 32 F i g u r e 3.12 Layers of c a l c i t e , q u a r t z , b a r i t e and s u l f i d e s c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b) from underground workings a t the N o r t h s t a r d e p o s i t . D i r e c t i o n of bedding i s i n d i c a t e d by hammer. y i n 33 has a l s o been r e c o g n i z e d i n d r i l l core from the N o r t h s t a r d e p o s i t (Thompson and Pearson, 1981). In hand specimen, l a y e r s , d i s s e m i n a t i o n s and s t r i n g e r s of f i n e - g r a i n e d s p h a l e r i t e and galena, with l e s s e r p y r i t e and c h a l c o p y r i t e , occur w i t h i n a c o a r s e - g r a i n e d and l o c a l l y vuggy gangue of manganiferous carbonate, q u a r t z and b a r i t e ( F i g . 3.14). U n i t 3b i n p o l i s h e d t h i n s e c t i o n c o n t a i n s 40 percent c a l c i t e , 30 percent q u a r t z , 10 p e r c e n t s i d e r i t e , 7 percent s p h a l e r i t e , 5 percent b a r i t e and/or w i t h e r i t e , 5 percent p y r i t e , 3 percent galena, minor c h a l c o p y r i t e and t e t r a h e d r i t e , t r a c e r h o d o c h r o s i t e , and r a r e n a t i v e s i l v e r along f r a c t u r e s . Anhedral to subhedral gangue and s u l f i d e m i n e r a l s occur e i t h e r as monomineralic l a y e r s , massive aggregates or d i s s e m i n a t e d g r a i n s . G e n e r a l l y , the g r a i n s have p o l y g o n a l o u t l i n e s and average 1.0mm i n diameter. B a r i t e , however, can occur as c o a r s e - g r a i n e d , subhedral to e u h e d r a l , bladed c r y s t a l s , up to 1.0cm i n l e n g t h ( F i g . 3.15). The c o a r s e - g r a i n e d nature of b a r i t e and p o l y g o n a l g r a i n boundaries f o r the other m i n e r a l s , i s probably i n d i c a t i v e of r e c r y s t a l l i z a t i o n d u r i n g or subsequent t o d i a g e n e s i s . T h i s u n i t i s cut by numerous v e i n l e t s of e i t h e r c a l c i t e or q u a r t z . S u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3c), c o n t a i n i n g p r i n c i p a l l y q u a r t z , c a l c i t e , b a r i t e , hematite, j a s p e r and s u l f i d e s , appears to be the most e x t e n s i v e of the t h r e e d e p o s i t f a c i e s comprising the m i n e r a l i z e d s t r a t i f o r m h o r i z o n . Examples i n c l u d e the T o r b r i t Mine, the Moose-Lamb, the South Musketeer, 34 and p o s s i b l y the K i t s o l p r o s p e c t s . Sporadic outcrops, of u n i t 3c are g e n e r a l l y s m a l l , and r e c e s s i v e . Weathered s u r f a c e s c h a r a c t e r i s t i c a l l y d i s p l a y a w e l l developed l a y e r i n g , r e f l e c t i n g bedding, with l o c a l b r e c c i a t i o n . Where j a s p e r and hematite are abundant, the u n i t i s d i s t i n c t l y reddish-maroon. M e g a s c o p i c a l l y , u n i t 3c g e n e r a l l y c o n s i s t s of l a m i n a t i o n s of q u a r t z , j a s p e r , b a r i t e , carbonate, hematite, magnetite and s u l f i d e s ( F i g s . 17 and 18). L o c a l l y , the l a m i n a t i o n s e x h i b i t c r u d e l y developed rhythmic l a y e r i n g d e f i n e d by repeated s u l f i d e - s u l f a t e - o x i d e m i n e r a l t r i p l e t s , as r e c o g n i z e d i n the T o r b r i t and Moose-Lamb d e p o s i t s . Subangular fragments, d i s p l a y i n g the same laminated mineralogy, but r o t a t e d and s e t i n a f i n e - g r a i n e d j a s p e r - r i c h m a t r ix, were observed l o c a l l y . U n i t 3c, i n p o l i s h e d t h i n s e c t i o n , has a d i v e r s e mineralogy c o n s i s t i n g of 35 percent q u a r t z , 15 percent c a l c i t e , 15 percent b a r i t e and/or w i t h e r i t e , 8 percent hematite, 7 per c e n t j a s p e r , 5 percent s i d e r i t e , 5 percent magnetite, 4 percent p y r i t e , 3 percent s p h a l e r i t e , 2 percent c h l o r i t e , 1 percent galena, minor c h a l c o p y r i t e , and t r a c e s of p y r a r g y r i t e , a r g e n t i t e and t e t r a h e d r i t e . O v e r a l l g r a i n s i z e i s g e n e r a l l y l e s s than 1.0mm but many c o a r s e - g r a i n e d , subhedral b a r i t e l a t h s are up to 2cm i n l e n g t h . B a r i t e c o n t a i n s up to 1 percent s t r o n t i u m (Campbell, 1959). Quartz and carbonate, as w e l l as some b a r i t e , d i s p l a y the same p o l y g o n a l , probably r e c r y s t a l l i z e d , g r a i n boundaries observed i n u n i t s 3a and 3b. S u l f i d e s , hematite and magnetite are f i n e r g r a i n e d than the gangue m i n e r a l s and l o c a l l y d i s p l a y 35 F i g u r e 3.13. V e r t i c a l z o n a t i o n i n d r i l l h o l e U-80-95 i n No r t h s t a r d e p o s i t , D o l l y Varden camp, northwestern B.C. Un i t 2a = green +_ maroon p o r p h y r i t i c a n d e s i t e , p o s s i b l e s i l l ; u n i t 2b = green a n d e s i t e shard t u f f ; u n i t 3b-1 = white, c o a r s e - g r a i n e d b a r i t e > quartz >> c a l c i t e with l e n s e s of p y r i t e ; u n i t 3b-2 = s i d e r i t e >> c o a r s e - g r a i n e d p y r i t e > q u a r t z ; u n i t 3b-3 = white, c o a r s e - g r a i n e d quartz > c a l c i t e > c o a r s e - g r a i n e d , bladed b a r i t e ( p o s s i b l y some w i t h e r i t e ) , n a t i v e s i l v e r along f r a c t u r e s ; u n i t 3b-4 = laminated s u l f i d e s ( s p h a l e r i t e > galena) > quartz > c o a r s e - g r a i n e d , bladed b a r i t e ; u n i t 4 = pa l e grey b a s a l t i c - a n d e s i t e ash t u f f , p y r i t e and quartz fragments; u n i t 5 = maroon b a s a l t i c - a n d e s i t e a s h - l a p i l l i t u f f w i t h minor shards, l a p i l l i and e x t e n s i v e carbonate a l t e r a t i o n . Note t h a t v e r t i c a l z o n a t i o n i s expressed by sy s t e m a t i c v a r i a t i o n i n ore mineralogy going from u n i t 3b-1 to 3b-4. 36 F i g u r e 3.14. P o l i s h e d s l a b of c a l c i t e , b a r i t e and s p h a l e r i t e m i n e r a l i z a t i o n , t y p i c a l of the c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b). " " 37 c o l l o f o r m l a y e r i n g as w e l l as c o l l o f o r m growths around gangue m i n e r a l s ( F i g 3.16). C h l o r i t i z e d shards and shard t u f f fragments have been r e c o g n i z e d w i t h i n the "ore" f a c i e s of some specimens from the T o r b r i t mine. C r o s s - c u t t i n g secondary c a l c i t e v e i n l e t s are numerous. S t a b l e i s o t o p e data from s u l f i d e s and gangue minerals of u n i t 3 ( s e c t i o n 4.2) shows t h a t the e x h a l i t e s probably were d e p o s i t e d as s t r a t i f o r m , v o l c a n o g e n i c m i n e r a l i z a t i o n i n a submarine environment. The genesis of t h i s m i n e r a l i z a t i o n and i t s importance w i l l be d i s c u s s e d f u r t h e r i n chapter 5. 3.2.3 Hangingwall V o l c a n i c Rocks U n i t 4 Pale grey b a s a l t i c - a n d e s i t e ash t u f f ( u n i t 4), r anging from 5 to 85m i n t h i c k n e s s , o v e r l i e s the m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( u n i t s 3a and 3b) i n the v i c i n i t y of D o l l y Varden (East and West) and N o r t h s t a r d e p o s i t s o n l y . Outcrops are e a s i l y r e c o g n i z e d because they d i s p l a y the same orange-yellow j a r o s i t e s t a i n as u n i t s 3a and 3b, and have a c h a r a c t e r i s t i c a l l y moderate to w e l l developed f o l i a t i o n t h a t p a r a l l e l s s t r a t i g r a p h y . The rocks are p a l e grey on f r e s h s u r f a c e s , and are f i n e - g r a i n e d . Most o r i g i n a l f e a t u r e s are wiped out by i n t e n s e s e r i c i t i z a t i o n and s i l i c i f i c a t i o n . L o c a l l y , however, subangular to subrounded l i t h i c and p y r i t i c fragments, p o s s i b l y reworked from the u n d e r l y i n g s t r a t i f o r m h o r i z o n ( u n i t s 3a and 3b), can be 38 r e c o g n i z e d . One l a r g e carbonate boulder, 30cm a c r o s s , was observed underground at the N o r t h s t a r d e p o s i t ( F i g . 3.19). F i n e l y d i s s e m i n a t e d p y r i t e , and e i t h e r quartz or carbonate v e i n s , are l o c a l l y abundant. U n i t 4, i s predominantly v i t r o c l a s t i c with numerous d e v i t r i f i e d shards, p o s s i b l e fiamme', and a weakly developed welded t e x t u r e . M a t r i x supported fragments, most o r i e n t e d p r e f e r e n t i a l l y , comprise between 30 and 40 percent of the u n i t and range from l e s s than 0.1mm to 30mm and average 1.0mm i n diameter. Four unique types of fragments were r e c o g n i z e d and i n c l u d e : (1) 40 percent subrounded aggregates of subhedral p y r i t e , cemented by carbonate and s e r i c i t e , (2) 30 percent v i t r i c fragments, completely a l t e r e d to s e r i c i t e , (3) 20 percent l a r g e , monomineralic, subrounded l i t h i c fragments of e i t h e r c a l c i t e or q u a r t z , and (4) 10 percent s m a l l , c r y s t a l fragments of e i t h e r a nhedral q u a r t z or subhedral p l a g i o c l a s e . P l a g i o c l a s e i s a l t e r e d to s e r i c i t e . Quartz and c a l c i t e d i s p l a y probably r e c r y s t a l l i z e d , p o l y g o n a l g r a i n boundaries, s i m i l a r t o u n i t 3. A l t e r a t i o n of the very f i n e - g r a i n e d m a t r i x i s the same as the f r a g m e n t s - - p r i m a r i l y s e r i c i t e with l e s s e r amounts of q u a r t z . V e i n l e t s a v e r a g i n g 0.1mm i n width, of e i t h e r c a l c i t e or q u a r t z , are numerous throughout u n i t 4. Two d i r e c t i o n s of f o l i a t i o n have been r e c o g n i z e d i n t h i n s e c t i o n . The f i r s t i s c h a r a c t e r i z e d by wispy, u n d u l a t i n g l a y e r s denoted by t r a i n s of s e r i c i t e t h a t wrap around p y r i t e fragments. 39 T h i s i s probably a primary f e a t u r e of f l a t t e n i n g t h a t r e f l e c t s o r i g i n a l bedding. The second d i r e c t i o n i s 70 to 90 degrees to the f i r s t and i s marked by alignment of euhedral p y r i t e p o r p h y r o b l a s t s with w e l l developed s e r i c i t e p r e s s u r e shadows ( F i g . 3.20). T h i s f e a t u r e c r o s s - c u t s the primary f e a t u r e s and i n d i c a t e s a s t r u c t u r a l event a f t e r d e p o s i t i o n . Chemical c l a s s i f i c a t i o n of u n i t 4, based on the a n a l y s i s of one sample from the hangingwall of the N o r t h s t a r d e p o s i t i s b a s a l t i c - a n d e s i t e (Table 3.3: s e c t i o n 3.2; F i g s . 3.33 and 3.34). A r e s e t L a t e Cretaceous date of 70.7 _+ 2.5 Ma was a l s o o b t a i n e d from t h i s u n i t (Table 4.3; s e c t i o n 4.3). U n i t 5 Maroon b a s a l t i c - a n d e s i t e a s h - l a p i l l i t u f f ( u n i t 5) i s the most e x t e n s i v e and e a s i l y r e c o g n i z a b l e u n i t i n the D o l l y Varden camp because of i t s d i s t i n c t i v e c o l o r and fragmental appearance. The u n i t i s exposed w e l l i n the southwestern corner of the map-area, as w e l l as i n the areas of the South Musketeer and Moose-Lamb pr o s p e c t s ( F i g s . 3.1 and 3.4). The base and the top of t h i s u n i t i s marked by l o c a l u n c o n f o r m i t i e s ( F i g . 3.6). South of the Moose-Lamb pro s p e c t , u n i t 5 i s u n d e r l a i n by green t u f f ( u n i t 1 ) . In the D o l l y Varden (East and West) and N o r t h s t a r areas, however, maroon t u f f s o v e r l y the m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( u n i t 3) and r e l a t e d f o o t w a l l and hangingwall t u f f s ( u n i t s 2b and 4, r e s p e c t i v e l y ) . Hangingwall maroon t u f f s i n these areas d i s p l a y unique f e a t u r e s d i s c u s s e d below. 40 I F i g u r e 3.15. Massive s p h a l e r i t e and p y r i t e with c o a r s e - g r a i n e d bladed b a r i t e c r y s t a l s i n c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b). Width of photomicrograph i s 7.0mm (plane, r e f l e c t e d l i g h t ) . F i g u r e 3.16. C o l l o f o r m l a y e r s of hematite and magnetite i n s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . Width of photomicrograph i s 7.0mm (plane, r e f l e c t e d l i g h t ) . 41 F i g u r e 3 .17 . W e l l deve loped l a y e r s of b a r i t e , j a s p e r and s u l f i d e s i n s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3c) from underground workings at the T o r b r i t mine . 42 !^ U r V - ! 8 - P o l i s h e d s l a b o f g a l e n a a n d j a s p e r m i n e r a l i z a t i o n SL1 u n? t S S^. S U l f i d e ° » « » s u l f g t e - o x r ^ s u l r ^ " ' 43 I F i g u r e 3.19. Carbonate boulder, 30cm a c r o s s , i n p a l e grey  b a s a l t i c - a n d e s i t e ash t u f f ( u n i t 4) from underground workings a t the N o r t h s t a r d e p o s i t . T h i s boulder i s p o s s i b l y reworked from the u n d e r l y i n g c a r b o n a t e - s u l f a t e - s u l f i d e e x h a l i t e ( u n i t 3b). Hammer i s o r i e n t e d p e r p e n d i c u l a r to bedding. F i g u r e 3.20. Secondary f o l i a t i o n i n p a l e grey b a s a l t i c - a n d e s i t e  ash t u f f ( u n i t 4 ) . The secondary f o l i a t i o n , o b l i q u e t o p e r v a s i v e f o l i a t i o n t h a t probably r e f l e c t s o r i g i n a l bedding, i s marked by alignment of a euhedral p y r i t e p o r p h y r o b l a s t with a w e l l developed s e r i c i t e p r e s s u r e shadow. Width of photomicrograph i s 1.6mm (plane l i g h t ) . 44 Maroon t u f f s df u n i t 5, range i n t h i c k n e s s from 10m i n the T o r b r i t Mine a r e a , up to at l e a s t 385m i n the D o l l y Varden West area. T h i s u n i t forms massive, c l i f f forming outcrops t h a t are h i g h l y r e s i s t a n t t o weathering. Weathered s u r f a c e s are t y p i c a l l y grey-maroon and d i s p l a y w idely spaced, r e g u l a r j o i n t s . F o l i a t i o n tends to p a r a l l e l bedding, with bedding commonly d e f i n e d by reworked l e n s e s of b r i c k r e d ash t u f f . U n i t 5 i s dominantly maroon on f r e s h s u r f a c e s , but o c c a s s i o n a l l y shows v a r i o u s shades of green. In hand specimen, the r o c k s are f i n e to medium g r a i n e d with abundant broken p l a g i o c l a s e c r y s t a l s . Subrounded, maroon t u f f bombs, up to 50cm i n diameter, have been observed l o c a l l y ( F i g . 3.21). Fragments, between 25 and 75 percent of u n i t 5, range from 0.1mm to 20.0mm and average 2.0mm a c r o s s . They are m a t r i x supported, randomly o r i e n t e d and c o n s i s t of 50 p e r c e n t p l a g i o c l a s e (An23 to An32), 30 percent maroon t u f f l i t h i c fragments ( l o c a l l y up to 70 p e r c e n t ) , 15 percent hematite and 5 percent broken, subhedral pyroxene g r a i n s . Rare f l a t t e n e d , fiamme'-like shards occur i n a p o s s i b l y welded m a t r i x . T h i s f i n e - g r a i n e d m a t r i x i s an aggregate of r e l i c t f e l d s p a r s and s e r i c i t e , minor q u a r t z and t r a c e s of carbonate and c h l o r i t e . Most p l a g i o c l a s e c r y s t a l s have been a l t e r e d t o s e r i c i t e ; pyroxene i s pseudomorphed by c h l o r i t e and i r o n o x i d e s . The unique hangingwall maroon t u f f s of u n i t 5, noted above, 45 near the D o l l y Varden (East and West) and N o r t h s t a r d e p o s i t s , formed as a p y r o c l a s t i c flow of l i m i t e d a e r i a l e x t e n t . T h i s u n i t tends to be l e s s r e s i s t a n t to weathering and hand specimens l a c k green c o l o r when compared to the r e s t of u n i t 5. Fragments are f i n e r g r a i n e d and more angular, with numerous dark green shards seen i n p l a c e s ( F i g . 3.22). C a l c i t e v e i n s , a v e r a g i n g l e s s than 1mm i n width, occupy up to 10 percent of t h i s u n i t . These maroon t u f f s i n t h i n s e c t i o n are dominantly v i t r o c l a s t i c . Fragments average 1.0mm i n l e n g t h and c o n s i s t of 50 percent p l a t y shards ( s i m i l a r t o those i n f o o t w a l l u n i t 2b), 10 percent l i t h i c fragments, 10 percent p l a g i o c l a s e , 5 percent q u a r t z , t r a c e s of hornblende and 25 percent anhedral hematite g r a i n s . Rare, subrounded carbonate fragments may r e p r e s e n t reworked ore c l a s t s from the u n d e r l y i n g c a r b o n a t e - r i c h s t r a t i f o r m l a y e r ( u n i t 3b). The m a t r i x i s dominated by carbonate, l e s s e r s e r i c i t e and q u a r t z , and sparse r e l i c t f e l d s p a r s and hematite dust. Shards are g e n e r a l l y r e p l a c e d by e i t h e r carbonate, s e r i c i t e or c h l o r i t e ; l i t h i c fragments have a l t e r e d to carbonate and l e s s e r c h l o r i t e , hematite and s e r i c i t e . Hematite a l s o occurs as c o a t i n g s on shards and p l a g i o c l a s e c r y s t a l s . Chemical a n a l y s i s (Table 3.3: s e c t i o n 3.3) of one sample from u n i t 5 u n d e r l y i n g the Moose-Lamb d e p o s i t ( F i g s . 3.1 and 3.4), y i e l d e d an a n d e s i t e composition ( F i g s . 3.33 and 3.34), whereas two samples from the hangingwall maroon t u f f s i n the N o r t h s t a r and Moose-Lamb areas, showed a b a s a l t i c composition ( F i g s . 3.33 and 3.34). A r e s e t Late Cretaceous date of 68.1 + 46 2.5 Ma was o b t a i n e d by K-Ar a n a l y s i s of the same sample, mentioned above, from the f o o t w a l l of the Moose-Lamb d e p o s i t (Table 4.3: s e c t i o n 4.3). U n i t 6 Tuffaceous rocks of u n i t 6 are most widespread i n the c e n t r a l p a r t of the map-area, near the N o r t h s t a r and T o r b r i t d e p o s i t s , and the South Musketeer p r o s p e c t ( F i g s . 3.1 and 3.4). T h i s u n i t i s s u b d i v i d e d i n t o dark grey l a p i l l i t u f f ( u n i t 6a) which grades upwards and l a t e r a l l y to the no r t h e a s t i n t o dark green t u f f ( u n i t 6b). U n i t s 6a and 6b o v e r l i e both green shard t u f f ( u n i t 2b) and maroon t u f f ( u n i t 5), and have a l s o been r e c o g n i z e d i n the hangingwall of the N o r t h s t a r and T o r b r i t d e p o s i t s . Dark grey a n d e s i t e l a p i l l i t u f f ( u n i t 6a) has a l i m i t e d a e r i a l extent and a maximum t h i c k n e s s of 165m. Outcrops are small and s p o r a d i c . Weathered s u r f a c e s are smooth and grey, with r e g u l a r j o i n t p a t t e r n s , c r u d e l y developed f o l i a t i o n and a p i t t e d t e x t u r e where b r e c c i a fragments have weathered out. Fres h s u r f a c e s show an a p h a n i t i c , dark grey matrix h o s t i n g numerous l i g h t green, p o o r l y s o r t e d , angular to subangular, l a p i l l i s i z e d fragments up to 5cm acr o s s ( F i g . 3.23). Fragments average 45 percent of the rock and g e n e r a l l y range from 0.1 to 10.0mm and average 2.0mm a c r o s s . They are matrix supported, randomly o r i e n t e d , and c o n s i s t of 65 percent l i t h i c 47 F i g u r e 3.21. Subrounded to subangular maroon t u f f l i t h i c fragments, up to 50cm a c r o s s , i n maroon b a s a l t i c - a n r l p g i t e  a s h - l a p i l l i t u f f ( u n i t 5 ) . " 48 I F i g u r e 3 .22 . P l a t y shards i n a l o c a l p y r o c l a s t i c f l ow w i t h i n maroon b a s a l t i c - a n d e s i t e a s h - l a p i l l i t u f f ( u n i t 5 ) . Opaques are p r i m a r i l y h e m a t i t e , which o c c u r s as bo th a n h e d r a l g r a i n s and c o a t i n g s on s h a r d s . Width of photomicrograph i s 4.2mm (p lane l i g h t ) . 49 fragments, 25 percent subhedral p l a g i o c l a s e c r y s t a l s , 8 percent b i o t i t e and 2 percent i r o n o x i d e s . The green matrix i s very f i n e - g r a i n e d and dominated by c h l o r i t e . P l a g i o c l a s e c r y s t a l s are pseudomorphed by s e r i c i t e and c h l o r i t e ; b i o t i t e has been a l t e r e d to carbonate with r i b s of i r o n oxides t h a t f o l l o w b a s a l cleavage. L i t h i c fragments have been r e p l a c e d completely by carbonate w i t h minor c h l o r i t e and s e r i c i t e . Dark green a n d e s i t e t u f f ( u n i t 6b) i s widespread and reaches a maximum t h i c k n e s s of 225m i n the North Musketeer a r e a . Outcrops are l i g h t grey-brown and c r u d e l y f o l i a t e d . T h i s rock, grey-green when f r e s h , i s f i n e to medium g r a i n e d and has abundant dark green l i t h i c and v i t r i c c l a s t s and minor p l a g i o c l a s e c r y s t a l fragments. F i n e l y d i s s e m i n a t e d p y r i t e i s g e n e r a l l y l e s s than 1 p e r c e n t . Fragments i n u n i t 6b comprise between 40 and 60 percent of the u n i t . They are subangular, matrix supported, randomly o r i e n t e d , range from l e s s than 0.1 to 10.0mm and average 1.0mm a c r o s s , and c o n s i s t of 45 percent l i t h i c fragments ( l o c a l l y up to 85 p e r c e n t ) , 40 percent p l a g i o c l a s e fragments, 10 percent c h l o r i t i z e d shards, and 5 percent opaques, t h a t are mainly p y r i t e . The mat r i x i s dominantly c h l o r i t e , with l e s s e r s e r i c i t e and carbonate, and sparse q u a r t z . Underground a t the T o r b r i t mine, u n i t 6b d i r e c t l y o v e r l i e s s t r a t i f o r m m i n e r a l i z a t i o n ( u n i t 3c) and c o n t a i n s subrounded 50 fragments of the u n d e r l y i n g o r e . These ore fragments r e p r e s e n t both massive and l a y e r e d ore types, and c o n t a i n b a r i t e and qu a r t z , l e s s e r carbonate and t r a c e s of j a s p e r ( F i g s . 24 and 25). Coarse-grained, s u b h e d r a l , bladed b a r i t e and/or w i t h e r i t e , was i d e n t i f i e d i n many fragments. The chemical composition of u n i t 6 (Table 3.3: s e c t i o n 3.3), based on a n a l y s e s of one sample from each of u n i t s 6a and 6b, i s p r i n c i p a l l y a n d e s i t i c ( F i g s . 3.33 and 3.34). U n i t 7 Su b v o l c a n i c s i l l s or flows of p o r p h y r i t i c a n d e s i t e ( u n i t 7a), together with a p y r o c l a s t i c e q u i v a l e n t of a n d e s i t e ash t u f f ( u n i t 7b), occur throughout most of the n o r t h e r n and southwestern p a r t s of the map-area ( F i g s . 3.1 and 3.4). Grey-green p o r p h y r i t i c a n d e s i t e ( u n i t 7a) covers a v a s t area and reaches a maximum width of n e a r l y 1km, near the Combination showing ( F i g s . 3.1 and 3.4). Dimensional v a r i a t i o n s i n t h i s u n i t w i t h i n the map-area are not w e l l known. C h a r a c t e r i s t i c a l l y p a l e grey-brown outcrops form steep c l i f f s with b l o c k y , i r r e g u l a r f r a c t u r e s . Limonite p e r v a s i v e l y s t a i n s these rocks e i t h e r an orange-brown or orange-yellow; l o c a l l y they are bleached pale grey or white. When f r e s h , u n i t 7a i s grey-green, has a f i n e - g r a i n e d m a t r i x w i t h phenocrysts of p l a g i o c l a s e , hornblende, and t r a c e pyroxene. S e r i c i t i z a t i o n and/or s i l i c i f i c a t i o n imparts a massive appearance t o some of these 51 r o c k s . F i n e l y d i s s e m i n a t e d p y r i t e i s u b i q u i t o u s . U n i t 7a r o c k s are a s s o c i a t e d c l o s e l y with zones of s e r i c i t i z a t i o n and p y r i t i z a t i o n ( u n i t 7 a ( s ) ) , and s i l i c i f i c a t i o n and p y r i t i z a t i o n ( u n i t 7 a ( q ) ) , d i s c u s s e d i n d e t a i l l a t e r i n t h i s chapter ( s e c t i o n 3.5). U n i t 7a, i n t h i n s e c t i o n , i s s i m i l a r i n t e x t u r e and mineralogy to the green _+ maroon p o r p h y r i t i c a n d e s i t e of u n i t 2a, except i t l a c k s t r a c h y t i c and amygdaloidal t e x t u r e s ( F i g . 26). Subhedral, randomly o r i e n t e d phenocrysts comprise between 35 and 55 percent of t h i s u n i t , and range from l e s s than 0.1 to 5.0mm and average 1.0mm a c r o s s . The phenocryst assemblage c o n s i s t s of 65 percent unzoned p l a g i o c l a s e (An25), 20 percent hornblende ( l o c a l l y up to 45 p e r c e n t ) , 5 percent pyroxene and 10 percent opaques, mainly p y r i t e . Phenocrysts of p l a g i o c l a s e have a l t e r e d mainly to s e r i c i t e and minor c h l o r i t e , hornblende has p a r t i a l l y gone to c h l o r i t e and opaques, and pyroxene i s pseudomorphed by c a l c i t e and c h l o r i t e l o c a l l y . The f i n e - g r a i n e d groundmass i s u n o r i e n t e d and dominated by c h l o r i t e , l e s s e r quartz and sparse s e r i c i t e , carbonate and f e l d s p a r . Pale green a n d e s i t e ash t u f f ( u n i t 7b) ranges i n t h i c k n e s s from 50m i n the North Musketeer area, up to 52 5m i n the Wolf area ( F i g s . 3.1 and 3.4). Outcrops are g e n e r a l l y s t r u c t u r e l e s s , except f o r l o c a l b l o c k y , i r r e g u l a r f r a c t u r i n g . T h i s u n i t i s c h a r a c t e r i s t i c a l l y grey-brown where weathered, pale grey-green on f r e s h s u r f a c e s , and massive with an i n d i s t i n c t t u f f a c e o u s 52 t e x t u r e , which on c a r e f u l i n s p e c t i o n of sawn s l a b s r e v e a l s dark green, l i g h t green and r e d fragments g e n e r a l l y l e s s than 1mm a c r o s s . U n i t 7b, as viewed i n t h i n s e c t i o n , has fragments t h a t are subangular and m a t r i x supported; f a b r i c s are both random and d i r e c t e d ( F i g . 3.27). An e p i c l a s t i c component i s i d e n t i f i e d by numerous subrounded g r a i n s of quartz and l i t h i c fragments. Fragments comprise between 20 and 40 percent of t h i s u n i t , and range from l e s s than 0.1 to 10.0mm and average 0.3mm i n diameter. They c o n s i s t of 50 percent broken p l a g i o c l a s e c r y s t a l s (An20), 30 p e r c e n t q u a r t z , 3 percent b i o t i t e , 7 percent i r o n o x i d e s , 10 percent g l a s s shards and t r a c e s of rounded l a p i l l i of the same ash t u f f m a t e r i a l . The matrix, although c r y p t o c r y s t a l l i n e , probably i s dominated by s e r i c i t e and carbonate because of i t s h i g h b i r e f r i n g e n c e . S e r i c i t e and carbonate occurs i n p l a g i o c l a s e pseudomorphs and i n t e r s t i t i a l , r a d i a t i n g aggregates of p r e h n i t e was i d e n t i f i e d i n some specimens. The chemical composition of u n i t 7 (Table 3.3: s e c t i o n 3.3; F i g s . 3.33 and 3.34) i s p r i n c i p a l l y a n d e s i t e , based on the a n a l y s i s of two samples from u n i t 7a and one sample from u n i t 7b. One of the samples from u n i t 7a, however, was a l t e r e d l e s s and i n d i c a t e d a b a s a l t i c - a n d e s i t e c o m p o s i t i o n . A n d e s i t i c composition of host rocks to m i n e r a l i z a t i o n i n the Wolf area ( u n i t 7b), was confirmed by T h i e r s c h (1986). 53 F i g u r e 3.23. L i g h t green, angular t o subangular, l a p i l l i - s i z e d l i t h i c fragments, up to 5cm a c r o s s , i n dark grey a n d e s i t e  l a p i l l i t u f f ( u n i t 6a). The fragments have been completely a l t e r e d to carbonate and c h l o r i t e . 54 I F i g u r e 3.24. Hand specimen of dark green a n d e s i t e t u f f ( u n i t 6b) th a t c o n t a i n s an ore fragment from the u n d e r l y i n g s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . The ore fragment i n t h i s specimen, taken from underground workings at the T o r b r i t mine, c o n t a i n s l a y e r s of q u a r t z , carbonate, b a r i t e and j a s p e r . F i g u r e 3.25. T h i n s e c t i o n of dark green a n d e s i t e t u f f ( u n i t 6b) th a t c o n t a i n s fragments of carbonate and b a r i t e ore from the s u l f a t e - o x i d e - s u l f i d e e x h a l i t e ( u n i t 3 c ) . The ma t r i x i s dominantly c h l o r i t e . Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . 55 1 F i g u r e 3.26. Phenocrysts of p l a g i o c l a s e and hornblende i n grey-green p o r p h y r i t i c a n d e s i t e ( u n i t 7a). Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . F i g u r e 3.27. P l a g i o c l a s e c r y s t a l fragments, and subrounded g r a i n s of quartz and l i t h i c fragments, i n pal e green a n d e s i t e  ash t u f f ( u n i t 7b). The matrix i s f i n e - g r a i n e d t u f f a c e o u s m a t e r i a l t h a t has been a l t e r e d to s e r i c i t e and carbonate. Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . 56 Lead i s o t o p e a n a l y s i s of galena from a quartz v e i n c u t t i n g u n i t 7a suggests t h a t m i n e r a l i z a t i o n i s J u r a s s i c ( c f . A l l d r i c k e t a l . , 1987). T h i s i n d i c a t e s t h a t the age of u n i t 7a i s probably J u r a s s i c or o l d e r . I n t e r p r e t a t i o n of l e a d i s o t o p e data from the D o l l y Varden camp w i l l be d i s c u s s e d i n d e t a i l i n a l a t e r chapter ( s e c t i o n 4.4). 3.2.4 Sedimentary Rocks U n i t 8 Sedimentary rocks of u n i t 8 exposed ( F i g s . 3.1 and 3.4) i n the s o u t h e a s t e r n and n o r t h e a s t e r n p a r t s of the map-area, and i n the K i t s a u l t R i v e r v a l l e y to the northwest, are the youngest rocks of the Hazelton group i n the D o l l y Varden camp because a l o c a l unconformity separates these rocks from the u n d e r l y i n g v o l c a n i c r o c k s . They c o n s i s t of a lowermost maroon s i l t s t o n e ( u n i t 8a), o v e r l a i n by c a l c a r e o u s and f o s s i l i f e r o u s wacke ( u n i t 8b), which i s capped by b l a c k s i l t s t o n e and shale ( u n i t 8 c ) . Maroon s i l t s t o n e ( u n i t 8a) c o n s i s t s of d i s c o n t i n u o u s beds up to 90m t h i c k t h a t o v e r l y ash t u f f s of u n i t 7b near the Wolf and Moose-Lamb p r o s p e c t s ( F i g s . 3.1 and 3.4). Outcrops of t h i s u n i t are s p o r a d i c , r e c e s s i v e l y weathered and l i g h t maroon. C l o s e l y spaced, s u b p a r a l l e l j o i n t s and d i s t i n c t bedding are a l s o c h a r a c t e r i s t i c . F r e s h s u r f a c e s are t y p i c a l l y maroon to b r i c k r e d . The u n i t i s mainly f i n e - g r a i n e d and massive, with l o c a l 57 i n t e r b e d s of conglomerate with d i s t i n c t i v e but minor, l o c a l , rounded, grey and white c l a s t s , up to 2cm i n diameter. In some p l a c e s , t h i s u n i t c o n t a i n s j a s p e r , which d i s p l a y s c o n c h o i d a l f r a c t u r e s . T h i n s e c t i o n examination of u n i t 8a shows bedding; and abundant subangular fragments suggests t h a t u n i t 8a i s a mixed p y r o c l a s t i c - e p i c l a s t i c rock or t u f f i t e (Schmid, 1981 i n F i s h e r and Schmincke, 1984). Fragments comprise 40 pe r c e n t of t h i s u n i t and range from l e s s than 0.1 to 0.5mm and average 0.1mm i n diameter. They c o n s i s t of 45 percent q u a r t z , 30 percent i n d i s t i n c t f e l d s p a r g r a i n s (probably p l a g i o c l a s e but are now completely a l t e r e d to s e r i c i t e and c a r b o n a t e ) , 20 percent hematite, 5 percent muscovite and t r a c e s of b i o t i t e . They are moderately s o r t e d and set i n an a l t e r e d matrix of s e r i c i t e with minor carbonate and q u a r t z . Calcareous and f o s s i l i f e r o u s wacke ( u n i t 8b) c o n s i s t s of r e l a t i v e l y continuous beds up to 80m t h i c k t h a t o v e r l i e s e i t h e r p ale green ash t u f f ( u n i t 7b) or maroon s i l t s t o n e ( u n i t 8a), near the Moose-Lamb, North Musketeer and Wolf prospects ( F i g s . 3.1 and 3.4). Outcrops g e n e r a l l y weather grey except where s u l f i d e s are abundant they are orange-yellow l i m o n i t e s t a i n e d . T h i s u n i t i s moderately w e l l bedded, c r u d e l y f o l i a t e d and r e g u l a r l y f r a c t u r e d ( F i g . 28). C e r t a i n beds of wacke c o n t a i n f o s s i l m a t e r i a l t h a t i s most r e c o g n i z a b l e on weathered s u r f a c e s . Fresh s u r f a c e s are dark grey, f i n e - g r a i n e d and c a l c a r e o u s . 58 F i g u r e 3 .28 . W e l l d e v e l o p e d bedding i n c a l c a r e o u s and  f o s s i l i f e r o u s wacke ( u n i t 8 b ) . T h i s o u t c r o p i s s i t u a t e d b e s i d e the K i t s a u l t R i v e r , near the K i t s o l showing ( F i g s . 3.1 and 3.4), and c o n t a i n s numerous b e l e m n o i d , r h y c h o n e l l i d b r a c h i o p o d and p e l e c y p o d f o s s i l s . 59 P y r i t e and t r a c e s of s p h a l e r i t e and galena occur e i t h e r as f i n e - g r a i n e d d i s s e m i n a t i o n s or co n c e n t r a t e d along bedding planes i n minor amounts. Showings of galena and s p h a l e r i t e i n u n i t 8b were d i s c o v e r e d approximately 400m due south of the Wolf pr o s p e c t ( F i g . 3.1). T h i n s e c t i o n s of u n i t 8b show abundant p o o r l y s o r t e d fragments i n a c a l c a r e o u s and arenaceous m a t r i x . Fragments average 60 percent of the u n i t and are subrounded t o subangular, fragment supported and both randomly and p r e f e r e n t i a l l y o r i e n t e d . They range from l e s s than 0.1 to 3.5mm and average 0.5mm a c r o s s . T h e i r composition c o n s i s t s of 50 percent f e l d s p a r (mainly p l a g i o c l a s e and a l l s e r i c i t i z e d ) , 20 percent q u a r t z , 10 percent c a l c i t e fragments, 10 percent f e l d s p a r porphyry fragments, 7 perc e n t s c a t t e r e d opaques ( p r i m a r i l y p y r i t e ) , 3 percent b i o t i t e and t r a c e s of muscovite and sphene. P o r p h y r i t i c a n d e s i t e ( u n i t 7a) i s the most l i k e l y source of the f e l d s p a r porphyry rock fragments ( F i g . 3.29). The matrix i s dominated by s e r i c i t e and carbonate with minor q u a r t z ; and most of the f o s s i l s have been r e p l a c e d by i r o n carbonate. A s u i t e of f o s s i l s c o l l e c t e d from u n i t 8b were submitted to H.W. T i p p e r of the G e o l o g i c a l Survey of Canada, Vancouver, f o r i d e n t i f i c a t i o n . The fauna were s i m i l a r t o others i n northwestern B r i t i s h Columbia and i n c l u d e d ( T i p p e r , w r i t t e n communication, 1986) belemnites, r h y n c h o n e l l i d brachiopods and v a r i o u s pelecypods. Pelecypods were i d e n t i f i e d as Chlamys sp. 60 and a fragment of a coarse r i b b e d v a r i e t y , p o s s i b l y Weyla spp. U n f o r t u n a t e l y , the fauna d i d not g i v e a d e f i n i t e age to t h i s u n i t , but a c c o r d i n g to T i p p e r i t i s probably of E a r l y J u r a s s i c , T o a r c i a n age. Other f o s s i l s u i t e s c o l l e c t e d from Hazelton Group rocks i n the K i t s a u l t R i v e r area (Hanson, 1921; Campbell, 1959; and D. A l l d r i c k , p e r s . comm., 1986) a l s o f a v o r an E a r l y J u r a s s i c age. Black s i l t s t o n e and shale ( u n i t 8c) has ah i n d e f i n i t e t h i c k n e s s and the top of the u n i t i s not exposed i n the map-area. U n i t 8c o v e r l i e s both the p o r p h y r i t i c and t u f f a c e o u s r o c k s of u n i t 7 and wackes of u n i t 8b. Outcrops are r e c e s s i v e but when exposed are t y p i c a l l y w e l l bedded and f o l i a t e d with r e g u l a r , c l o s e l y spaced j o i n t s . F r e s h s u r f a c e s are g e n e r a l l y b l a c k , f i n e - g r a i n e d and laminated. L i g h t grey mudstone and sandstone i n t e r b e d s occur l o c a l l y . Graded and cro s s - b e d d i n g have a l s o been r e c o g n i z e d . Beds vary i n t h i c k n e s s from m i l l i m e t e r s to tens of meters, but average about 5cm. F i n e - g r a i n e d p y r i t e c o n c e n t r a t e s along some bedding p l a n e s , and when presen t i n gre a t amounts, the rocks d i s p l a y a red-brown l i m o n i t e s t a i n . B l a c k s i l t s t o n e s and s h a l e s of u n i t 8c c o n s i s t predominantly of subangular, randomly o r i e n t e d g r a i n s ranging from 0.1 to 1.0mm and averaging 0.2mm a c r o s s . L o c a l fragments i n s i l t s t o n e occur i n a d i r t y c r y p t o c r y s t a l l i n e m a t r ix, c o n s i s t i n g of 65 percent s e r i c i t e a l t e r e d f e l d s p a r , 25 percent q u a r t z , 3 percent 61 b i o t i t e and 7 percent g r a i n s of carbonaceous m a t e r i a l and minor hematite. Grey s i l t s t o n e beds are f i n e r g r a i n e d ( g e n e r a l l y l e s s than 0.1mm) and have a s i m i l a r mineralogy, except f o r l e s s carbonaceous m a t e r i a l , hematite and b i o t i t e . 3.2.5 I n t r u s i v e Rocks U n i t 9 B a s a l t and lamprophyre dykes ( u n i t 9) cut a l l other u n i t s i n , and are d i s t r i b u t e d throughout the map-area ( F i g s . 3.1 and 3.4). The dykes erode e a s i l y and t y p i c a l l y form s m a l l g u l l i e s where they crop out. Weathered s u r f a c e s are^grey-brown with g r a n u l a r , s a n d - l i k e s u r f a c e t e x t u r e s . Columnar j o i n t i n g and c h i l l e d margins are w e l l developed i n p l a c e s . These dykes occur as e i t h e r swarms or s i n g l e dykes, r a n g i n g i n width from a few centimeters t o more than 10m, but average about 1m ( F i g . 3.31). In hand specimen, dyke rocks are dark grey-green, f i n e - g r a i n e d and s o f t , with v a r i a b l e t e x t u r e s i n c l u d i n g massive, p o r p h y r i t i c and amygdaloidal. Phenocrysts i n p o r p h y r i t i c v a r i e t i e s i n c l u d e : hornblende, pyroxene and minor p l a g i o c l a s e . Amygdules are f i l l e d with c h l o r i t e , c a l c i t e and z e o l i t e (probably a n a l c i t e from t h i n s e c t i o n e xamination). T h i n s e c t i o n s of u n i t 9 ( F i g . 3.30) show the groundmass to c o n s i s t of a c i c u l a r l a t h s of p l a g i o c l a s e and pyroxene with i n t e r s t i t i a l c h l o r i t e and c a l c i t e . Phenocrysts are subhedral t o euhedral and randomly o r i e n t e d ; they range from 0.1 to 3.0mm and 62 average 0.5mm i n s i z e . The p r o p o r t i o n of phenocrysts v a r i e s from 20 to 80 percent among dykes. The phenocryst assemblage t y p i c a l l y c o n s i s t s of 50 percent p l a g i o c l a s e (An67) wi t h minor zon i n g , 30 per c e n t hornblende, 15 percent a u g i t e , 5 percent magnetite and t r a c e s of a p a t i t e . P l a g i o c l a s e has been a l t e r e d to c h l o r i t e i n p l a c e s , whereas most of the hornblende and a u g i t e phenocrysts have gone to c h l o r i t e , i r o n oxides and, l o c a l l y , carbonate. The composition (Table 3.3: s e c t i o n 3.3) of a dyke c r o s s c u t t i n g s t r a t i f o r m m i n e r a l i z a t i o n ( u n i t 3b) a t the N o r t h s t a r d e p o s i t ( F i g . 3.1), was b a s a l t ( F i g s . 3.33 and 3.34). A whole rock K-Ar date of 22.3 +_ 0.8 Ma f o r the same dyke (Table 4.3: s e c t i o n 4.3) i n d i c a t e s emplacement d u r i n g Miocene time. 6 3 I F i g u r e 3.29 Coar s e - g r a i n e d , p o o r l y s o r t e d fragments i n ca l c a r e o u s and f o s s i l i f e r o u s wacke ( u n i t 8b). Note the l a r g e f e l d s p a r porphyry rock fragment. Width of photomicrograph i s 4.6mm ( p o l a r i z e d l i g h t ) . I F i g u r e 3.30. B a s a l t dyke ( u n i t 9) composed of l a t h s of a u g i t e i n a p l a g i o c l a s e dominated groundmass. Width of photomicrograph i s 2.2mm ( p o l a r i z e d l i g h t ) . 64 F i g u r e 3 . 3 1 . B a s a l t dyke ( u n i t 9) c r o s s c u t t i n g g reen + / - maroon  b a s a l t i c - a n d e s i t e t u f f ( u n i t 1) on a roadcu t near the T o r b r i t mine . Note columnar j o i n t i n g p e r p e n d i c u l a r to w a l l s of d y k e . 65 3.3 CHEMISTRY OF IGNEOUS ROCKS Chemical analyses of s e l e c t e d , r e p r e s e n t a t i v e igneous rocks from the D o l l y Varden camp ( F i g . 3.1) are i n Table 3.3. Hazelton Group v o l c a n i c rocks are s u b a l k a l i n e , d i s p l a y i n g a c a l c - a l k a l i n e t r e n d on an AFM diagram, and the T e r t i a r y dyke p l o t s i n the t h o l e i i t i c f i e l d ( F i g . 3.32). The Haz e l t o n Group rocks are a l s o i n t e r m e d i a t e i n composition and c h a r a c t e r i z e d by the predominance of a n d e s i t i c v o l c a n i c s . D o l l y Varden v o l c a n i c s , hypersthene-normative and aver a g i n g 55 weight pe r c e n t Si02, are b a s i c a n d e s i t e s a f t e r G i l l (1981)1. G i l l a l s o e s t a b l i s h e d c r i t e r i a f o r c l a s s i f i c a t i o n of t y p i c a l c a l c - a l k a l i n e " o r o g e n i c " a n d e s i t e s . These are d i s t i n g u i s h e d c h e m i c a l l y from other types of a n d e s i t e s by having K20 < (0.145 x Si02 - 5.135) and Ti02 < 1.75 weight p e r c e n t . V o l c a n i c rocks i n the D o l l y Varden camp s a t i s f y the requirements f o r Ti 0 2 , but a K20 average of 5 percent i s too high f o r or o g e n i c a n d e s i t e . Nonetheless, the a n d e s i t e s are probably o r o g e n i c — t h e high K20 va l u e s might r e f l e c t e i t h e r potassium metasomatism accompanying e i t h e r metamorphism or hydrothermal a l t e r a t i o n . 1. A n d e s i t e s , as d e f i n e d by G i l l (1981), are hypersthene-normative v o l c a n i c rocks with between 53 and 63 weight percent Si02, c a l c u l a t e d on an anhydrous b a s i s . He f u r t h e r s u b d i v i d e s them i n t o b a s i c a n d e s i t e s , with 53 t o 57 weight percent Si02, and a c i d a n d e s i t e s with 57 t o 63 weight percent Si02. TABLE 3.3. Whole rock chemistry (XRF)1 and norma t iye ca lcula t ions^ for igneous rocks from the Dol ly Warden camp, northwestern B . C . Sample locat ions are p lot ted on f igure 3.1. Data are plotted in Figures 3.32 to 3.34. Unit 1 2a 2b 2b 2b U 5 5 5 6a 6b 7a 7a 7b 9 Sample number T177 T37a 0227 0376 T123 0U84-NS1 035 0335 D364a 085 0382b 030ft T263 D32 G19 Major Elements (weight percent) S102 50.93 53.16 54.19 55.77 60.04 52.55 60.24 51.78 51.52 57.76 61 .88 46.13 54.40 61 .22 41.25 U02 0.74 0.66 0.79 0.59 0.72 0.69 0.60 0.68 0.62 0.56 0.53 0.71 0.52 0.85 3.02 A1203 17.06 17.60 18.93 17.91 16.73 16.35 16.14 16.05 15.28 1E.06 15.16 16.40 15.51 16.80 15.0B Fe2Q33 8.49 6.75 8.09 6.52 6.94 6.52 5.40 7.54 6.90 4.43 3.01 11.24 6.18 6.24 12.10 PlnO 0.25 0.09 0.28 0.37 0.09 0.11 0.15 0.19 0.29 0.15 0.21 0.27 0.20 0.11 0.2B PlgO 2.55 2.45 1.98 1.48 • 2.53 1.46 1.43 1.97 2.69 1.49 0.76 7.14 1.41 3.62 4.99 CaO 3.69 3.04 2.44 D.B7 1.30 1.48 3.41 6.01 6.90 6.62 1.21 6.33 3.03 2.22 10.38 Na20 0.B4 1.82 0.09 0.15 0.92 0.15 2.39 0.30 1.32 1.56 0.16 1 .64 0.45 0.88 1 .91 K20 5.40 3.94 5.30 10.70 3.70 4.57 4.34 4.12 6.08 2.66 8.61 2.59 6.46 3.30 0.78 P20S 0.66 0.53 0.55 0.62 0.32 0.52 0.44 0.48 0.50 0.48 0.57 0.92 0.34 0.17 2.25 S 0.00 0.00 0.00 0.02 0.00 0.66 0.00 0.00 0.01 0.00 0.00 0.04 0.27 0.0 0.01 L D H 5.62 4.98 5.53 2.75 4.26 6.89 3.53 B.32 7.02 6.71 2.61 3.15 2.74 4.34 6.23 Totals 96.23 95.04 98.17 97.75 97.55 96.97 98.07 97.44 99.13 98.50 94.71 96.56 91.51 99.75 9B.2B Trace Elements (ppm) Ba 1828.68 2571.44 1203.50 2559.39 1507.19 3391.86 3213.42 3313.38 2843.99 1089.21 4516.72 922.96 3557.B4 1518.60 486.54 Co 21.3B 19.39 9.55 14.75 17.23 17.67 15.83 12.78 15.93 15.63 4.20 27.83 14.96 16.54 30.70 Cr 39.73 40.27 16.75 39.82 31.83 52.14 62.16 51.68 18.51 30.93 30.48 82.95 44.76 32.78 69.01 Cu 16.90 23.49 15.04 9.34 11.52 32.56 26.04 7.17 20.19 14.46 6.64 95.84 16.42 25.20 33.30 Kb 3.92 5.91 4.63 7.03 7.01 5.32 5.94 5.05 5.34 5.31 5.54 4.48 5.87 11 .36 18.44 Ni 10.17 8.50 3.48 7.58 B.76 7.63 5.65 3.16 7.61 5.43 5.07 18.92 7.94 10.24 30.B2 Pb 21.65 16.61 11.40 54.78 3.16 166.22 20.68 10.06 17.76 20.53 29.40 6.09 21 .52 15.20 10. B6 Rb 181 .97 120.49 150.16 272.73 128.10 185.08 121.62 142.01 150.47 70.97 205.41 52.97 176.89 103.24 8.31 Sr 95.04 388.81 88.27 96.61 89.99 61 .17 862.90 216.05 261.60 557.49 85.30 647.53 168.70 465.83 755.88 V 141 .10 131.40 168.68 107.23 128.49 145.09 104.48 154.41 124.0B 126.38 120.36 205.60 116.71 92.94 227.53 Y 17.24 15.42 19.14 20.31 15.46 16.80 17.64 17.15 17.37 14.01 18.39 15.56 18.60 35 .S1 26.18 Zn 242.56 105.37 434.96 293.42 93.B6 390.00 126.90 78.15 137.95 97.87 135.20 216.81 81 .93 111 .96 111.73 Zr 71.21 130.29 81 .03 105.72 105.81 74.84 133.94 77.06 85.86 112.87 92.39 71.05 102.75 172.6B 201 .82 Normative Minerals (weight percent) Quartz 11.49 16.26 23.12 8.86 32.23 24.71 19.89 16.50 3.06 22.74 25.88 0.00 17.IB 31 .98 2.64 Orthoclase 31.91 23.28 31.32 63.23 21.86 27.01 25.65 24.35 35.93 15.72 50. BB 15.30 38.17 19.50 4.61 Alb i te 7.11 15.40 0.76 1.27 7.78 1 .27 20.22 2.54 11.17 13.20 1.35 13.88 3.81 7.45 16.16 Arorthi te 13.99 11.62 8.51 0.27 4.36 3.94 14.04 26.68 17.81 28.96 2.2B 25.39 12.81 9.90 30.27 Diopside 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.B7 0.60 0.00 0.00 0.00 0.00 5.27 Hyperstnene 15.22 11.74 12.91 9.77 12.11 15.92 7.17 12.18 7.84 5.34 1 .69 26.90 8.44 13.02 15.58 Ol iv ine 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.58 0.00 0.00 0.00 Caruidun 4.70 6.08 9.93 5.98 9.61 9.71 2.36 1 .32 0.00 0.00 4.74 1.59 3.08 B.15 0.00 Apatite 1.56 1 .26 1.30 1.47 0.76 1.23 1.04 1.14 1.18 1 .14 1.35 2.18 0.B1 0.40 5.33 Placrietite 3.25 3.16 3.32 3.03 1.22 3.18 3.04 3.16 3.07 3.02 2.31 3.20 2.93 3.41 6.55 Ilmenite 1.41 1.29 1.50 1.12 1.37 1.31 1 .14 1.29 1.18 1.10 1.01 1.35 0.99 1.61 5.74 Hematite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0 . X 0.44 0.00 0.00 0.00 0.00 Pyri te 0.00 0.00 0.00 0.04 0.00 1 .61 0.00 0.00 0.O2 0.00 0.00 0.07 0.51 0.00 0.02 1. Chemical analyses by Department of Oceanography, The University of B r i t i s h Columbia. 2. Normative minerals calculated at the Computing Centre, The Universi ty of B r i t i s h Columbia. Calculat ions were made u i th Fe = 0.899BFe2D3 ( Irvine and Baragar, 1971). 3. Total iron expressed as Fe203. 4. L .O . I . = Loss on i g n i t i o n . F F i g u r e 3.32. AFM diagram f o r igneous rocks i n the D o l l y Varden camp, northwestern B.C. Haz e l t o n Group v o l c a n i c r o c k s are g e n e r a l l y c a l c - a l k a l i n e and the T e r t i a r y dyke p l o t s i n the t h o l e i i t i c f i e l d . L i n e separates t h o l e i i t i c from c a l c - a l k a l i n e rocks ( I r v i n e and Baragar, 1971). A = Na20 + K20; F = 0.8998 Fe203; M = MgOj a l l are i n weight p e r c e n t . Symbols used are as f o l l o w s : O = Hazelton Group v o l c a n i c r o c k s , • = average composition of Hazelton Group v o l c a n i c rocks i n the D o l l y Varden camp,A= T e r t i a r y dyke. 68 9 O CM + o CM o z 12 -10 -8 -6 -FOIOITE RHYOLITE 37 PICRO-SASALT F i g u r e 3.33. T o t a l a l k a l i s i l i c a (TAS) diagram f o r the D o l l y Varden camp, northwestern B.C. Hazelton Group v o l c a n i c rocks are g e n e r a l l y b a s a l t i c - t r a c h y a n d e s i t e s . The T e r t i a r y dyke p l o t s i n the p i c r o b a s a l t f i e l d . V o l c a n i c rock names and the chemical c l a s s i f i c a t i o n i s a f t e r Le Bas et a_l. ( 1 986). Symbols are as i n F i g u r e 3.32. 69 F i g u r e 3.34. Si02 vs Zr/Ti02 diagram f o r the D o l l y Varden camp, northwestern B.C. Hazelton Group v o l c a n i c rocks are g e n e r a l l y a n d e s i t e s . The T e r t i a r y dyke p l o t s i n the a l k a l i b a s a l t f i e l d . The f i e l d s f o r common v o l c a n i c rocks are a f t e r Winchester and F l o y d (1977). Symbols are as i n F i g u r e 3.32. 70 Using the t o t a l a l k a l i s i l i c a (TAS) diagram f o r the chemical c l a s s i f i c a t i o n of v o l c a n i c rocks (Le Bas et a l . , 1986), f o u r of f o u r t e e n a n a l y s e s from the Hazelton Group v o l c a n i c rocks i n the D o l l y Varden camp are b a s a l t i c - t r a c h y a n d e s i t e , t h r e e are a n d e s i t e , two are b a s a l t i c - a n d e s i t e , two are b a s a l t , one i s t r a c h y a n d e s i t e , one i s t r a c h y d a c i t e , and one i s t e p h r i p h o n o l i t e ( F i g . 3.33). The average composition of the v o l c a n i c rocks i n d i c a t e s they are b a s a l t i c - t r a c h y a n d e s i t e . The T e r t i a r y dyke i s c h e m i c a l l y d i f f e r e n t from the Hazelton Group v o l c a n i c rocks and p l o t s i n the p i c r o b a s a l t f i e l d . T h i s c l a s s i f i c a t i o n f o r the T e r t i a r y dyke, however, i s erroneous and the proper c l a s s i f i c a t i o n , based on petrography ( s e c t i o n 3.2.5), i s b a s a l t . The AFM and TAS diagrams, however, use elements t h a t are probably mobile d u r i n g e i t h e r metamorphism or hydrothermal a l t e r a t i o n . T h i s may e x p l a i n the wide range of chemical an a l y s e s d e p i c t e d on these diagrams. To overcome t h i s problem, Winchester and F l o y d (1977) e s t a b l i s h e d a chemical scheme of d i s c r i m i n a t i n g a l t e r e d v o l c a n i c rock types u s i n g immobile elements, such as t i t a n i u m and z i r c o n i u m . The Si02 vs Zr/Ti02 p l o t of Winchester and F l o y d ( F i g . 3.34) shows t h a t e i g h t of f o u r t e e n a n a l y s e s are a n d e s i t e , f o u r are s u b - a l k a l i n e b a s a l t , one i s t r a c h y a n d e s i t e and one i s a l k a l i b a s a l t . The average composition confirms the Hazelton Group v o l c a n i c r o c k s i n the D o l l y Varden camp to be a n d e s i t e . T h i s c l a s s i f i c a t i o n a l s o shows t h a t the T e r t i a r y dyke i s d i f f e r e n t from H a z e l t o n Group v o l c a n i c rocks and p l o t s i n the probable e x t e n s i o n of the a l k a l i 71 b a s a l t f i e l d . As d i s c u s s e d p r e v i o u s l y , t h i s c l a s s i f i c a t i o n i s erroneous and the T e r t i a r y dyke i s a b a s a l t , based on petrography ( s e c t i o n 3.2.5). In summary, Hazelton Group v o l c a n i c rocks i n the D o l l y Varden camp- are c a l c - a l k a l i n e b a s a l t s and a n d e s i t e s , with chemical s i m i l a r i t i e s to ot h e r Hazelton Group v o l c a n i c s u i t e s of n o r t h - c e n t r a l B r i t i s h Columbia ( T i p p e r and R i c h a r d s , 1976). Ha z e l t o n Group rocks g e n e r a l l y show trends t y p i c a l of c a l c - a l k a l i n e v o l c a n i c t e r r a n e s , r a n g i n g i n composition from b a s a l t t o r h y o l i t e , depending on s t r a t i g r a p h i c l o c a t i o n . These rocks are a l s o c h e m i c a l l y analogous to oth e r E a r l y J u r a s s i c c a l c - a l k a l i n e v o l c a n i c s u i t e s i n the Canadian C o r d i l l e r a , namely the Toodoggone V o l c a n i c s , Bonanza V o l c a n i c s , Yakoun Formation and Rossland Formation (Souther, 1977; F o r s t e r , 1984). 3.4 STRUCTURE F o l d geometry i n the D o l l y Varden camp i s dominated by a s i n g l e phase of deformation. V o l c a n i c and sedimentary beds of the H a z e l t o n Group form broad u p r i g h t f o l d s with g e n t l e , n o r t h w e s t e r l y plunges ( F i g s . 3.1 to 3.5). Thus, sedimentary rocks exposed e a s t of the T o r b r i t Mine l i e i n the core of a s y n c l i n e , which when p r o j e c t e d to the northwest, f o l l o w s the K i t s a u l t R i v e r v a l l e y . M i n e r a l i z e d s t r a t i f o r m h o r i z o n s of the D o l l y Varden (East and West), N o r t h s t a r , T o r b r i t and Moose-Lamb d e p o s i t s occur on the s t e e p l y n o r t h - d i p p i n g , western limb of 72 t h i s s y n c l i n e . T h i s simple f o l d p i c t u r e , however, i s c o m p l i c a t e d by numerous s t e e p l y - d i p p i n g b l o c k f a u l t s t h a t cut a l l rock u n i t s and make s t r a t i g r a p h i c c o r r e l a t i o n d i f f i c u l t . R e l i a b l e bedding measurements were o b t a i n e d from c o m p o s i t i o n a l l a y e r i n g , p r i m a r i l y i n sedimentary u n i t s , and alignment of t u f f and l a p i l l i fragments i n the t u f f a c e o u s u n i t s . Synsedimentary deformation s t r u c t u r e s are r a r e . Sedimentary rocks of u n i t 8 are t i g h t l y , d i s h a r m o n i c a l l y f o l d e d , whereas the more competent v o l c a n i c rock u n i t s are deformed i n t o broader, open f o l d s forming a s e r i e s of n o r t h w e s t e r l y t r e n d i n g a n t i c l i n e s and s y n c l i n e s with moderate d i p s on the limbs t h a t seldom exceed 60 degrees. Where marked r o t a t i o n of f a u l t b l o c k s has o c c u r r e d , such as i n the N o r t h s t a r and T o r b r i t areas, steeper d i p s are observed consequently i n the v o l c a n i c rock u n i t s . Sedimentary and v o l c a n i c rocks e x h i b i t prominent f o l i a t i o n s t h a t are both s u b p a r a l l e l t o bedding and approximately a x i a l p l a n a r to the f o l d s . F o l i a t i o n planes t h a t are s u b p a r a l l e l to bedding occur p r i m a r i l y i n t u f f a c e o u s rocks and probably r e s u l t e d from dewatering and f l a t t e n i n g of the beds d u r i n g metamorphism. A x i a l plane f o l i a t i o n s , however, occur i n a l l sedimentary and v o l c a n i c rock u n i t s and g e n e r a l l y t r e n d n o r t h w e s t e r l y with steep to v e r t i c a l n o r t h e a s t e r n d i p s . A x i a l plane f o l i a t i o n s i n f i n e - g r a i n e d , incompetent sedimentary u n i t s are w e l l developed s l a t y and f r a c t u r e c l e a v a g e s ; v o l c a n i c u n i t s show onl y c r u d e l y developed f r a c t u r e c l e a v a g e s . Bedding 7 3 l i n e a t i o n on a x i a l plane cleavage, r e c o g n i z e d p r i m a r i l y i n the sedimentary r o c k s , plunges c o n s i s t e n t l y 25 degrees to the northwest. Most j o i n t s i n the map-area are d i l a t i o n a l f r a c t u r e s , commonly o r i e n t e d i n a n o r t h e a s t e r l y d i r e c t i o n , p e r p e n d i c u l a r to the f o l d a x i s as i n the a-c plane ( F i g . 3.35). F o l d s , f o l i a t i o n and j o i n t s are a l l r e l a t e d to a major southwest-northeast d i r e c t e d compression. Block f a u l t i n g i n the D o l l y Varden area i s g e n e r a l l y d e f i n e d by an abrupt change i n l i t h o l o g y , o f t e n marked by p a r a l l e l s t e p - l i k e c l i f f s , e a s i l y r e c o g n i z e d both i n the f i e l d and on a i r photos. These f a u l t s have e i t h e r normal or r e v e r s e movements. In some cases, f a u l t s which appear to be normal c o u l d have been r o t a t e d so t h a t they now appear to be r e v e r s e ( c f . McKlay., 1 984 ) . F a u l t s are dominated by two d i r e c t i o n s , and the t i m i n g of t h e i r f o r m a t i o n can be d e f i n e d by the r e l a t i v e displacements of u n i t s ( e s p e c i a l l y the m i n e r a l i z e d s t r a t i f o r m l a y e r s ) , and of e a r l i e r f a u l t s by younger f a u l t s . Schematic r e c o n s t r u c t i o n of the f a u l t s and m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( F i g . 5.2) i s d i s c u s s e d i n d e t a i l i n s e c t i o n 5.2. The e a r l i e s t s e t of f a u l t s t r e n d s northwest; examples i n c l u d e the D o l l y Varden and Moose-Lamb f a u l t s ( F i g s . 3.1, 3.4 and 5.2). G o l d - s i l v e r - c o p p e r v e i n s , such as those d i s c o v e r e d a t the Red P o i n t and Red P o i n t E x t e n s i o n p r o s p e c t s , are s u b p a r a l l e l 74 F i g u r e 3.35. W e l l d e v e l o p e d a-c j o i n t s , o r i e n t e d i n a n o r t h e a s t e r l y d i r e c t i o n , and p e r p e n d i c u l a r to the n o r t h w e s t e r t r e n d i n g f o l d a x i s . 75 to these e a r l i e r n o r t h w e s t - t r e n d i n g f a u l t s . The l a t e r s e t of f a u l t s t r e n d n o r t h - n o r t h e a s t and have s t r o n g l y i n f l u e n c e d the physiography and drainage p a t t e r n s i n the map-area. These f a u l t s i n c l u d e the Campbell, Hanson and M i t c h e l l f a u l t s (Figs.. 3.1, 3.4 and 5.2). Apparent displacement along these f a u l t s i s p r i n c i p a l l y r i g h t - l a t e r a l ; s l i c k e n s i d e s suggest both s t r i k e - s l i p and d i p - s l i p motion. T e r t i a r y dykes and s i l v e r - b a s e metal v e i n s , such as those of the Wolf d e p o s i t , are s u b p a r a l l e l to and commonly f o l l o w the l a t e r n o r t h - n o r t h e a s t f a u l t s . 3.5 ALTERATION AND VEIN MINERALIZATION P e r v a s i v e and f r a c t u r e c o n t r o l l e d hydrothermal a l t e r a t i o n a f f e c t s a l l rock u n i t s i n the D o l l y Varden camp. P e r v a s i v e p r o p y l i t i c a l t e r a t i o n predominates, p r i m a r i l y due to the combined e f f e c t s of r e g i o n a l metamorphism and hydrothermal a c t i v i t y . P r o p y l i t i c a l t e r a t i o n i s c h a r a c t e r i z e d by the development of c h l o r i t e , carbonate and e p i d o t e from mafic m i n e r a l s and a n o r t h i t i c p l a g i o c l a s e ; s a u s s u r i t i z a t i o n of p l a g i o c l a s e phenocrysts i s t y p i c a l of t h i s a l t e r a t i o n s t y l e . Other hydrothermal a l t e r a t i o n types i n c l u d e widespread s e r i c i t i z a t i o n and s i l i c i f i c a t i o n , the l a t t e r more commonly a s s o c i a t e d with f r a c t u r e s . O r i g i n a l f a b r i c s of the r o c k s tends to be completely obscured by s i l i c i f i c a t i o n , and to a l e s s e r degree by s e r i c i t i z a t i o n . P y r i t e i n v a r i a b l y i s a s s o c i a t e d with a l l t h ree a l t e r a t i o n s t y l e s . Late carbonate s t r i n g e r s o v e r p r i n t the e a r l i e r e f f e c t s of hydrothermal a c t i v i t y i n a l l rock u n i t s . 76 F o o t w a l l v o l c a n i c r o c k s ( u n i t s 1, 2a and 2b) d i s p l a y moderate, p r o p y l i t i c a l t e r a t i o n . P y r i t e , however, i s g e n e r a l l y more abundant i n u n i t s 2a and 2b, e s p e c i a l l y w i t h i n the immediate f o o t w a l l of the m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( u n i t 3). Minor s i l i c i f i c a t i o n a l s o i s a s s o c i a t e d with p y r i t e i n u n i t 2b. In c o n t r a s t to the f o o t w a l l sequence, hangingwall v o l c a n i c rocks ( u n i t s 4 and 5) o v e r l y i n g s t r a t i f o r m m i n e r a l i z a t i o n ( u n i t 3) of the D o l l y Varden and N o r t h s t a r d e p o s i t s , have been extremely s e r i c i t i z e d . S e r i c i t e i n v a r i a b l y i s a s s o c i a t e d with quartz and p y r i t e i n the pale grey ash t u f f of u n i t 4. Maroon t u f f s ( u n i t 5), however, are n e i t h e r s i l i c i f i e d nor p y r i t i z e d but r a t h e r have been a l t e r e d e x t e n s i v e l y to carbonate, s e r i c i t e and hematite. Hematite imparts the c h a r a c t e r i s t i c maroon c o l o r to u n i t 5 and i m p l i e s o x i d i z i n g c o n d i t i o n s r e l a t e d to d e p o s i t i o n and e a r l y d i a g e n e s i s . The maroon c o l o r might a l s o i n d i c a t e a v o l c a n i c source from s u b a e r i a l e r u p t i o n s subsequently d e p o s i t e d i n a marine environment. No s i n g l e c r i t e r i o n , however, i s r e l i a b l e f o r i n t e r p r e t a t i o n of such a d e p o s i t i o n a l h i s t o r y (Tipper and R i c h a r d s , 1976). Other hangingwall v o l c a n i c rocks ( u n i t s 6 and 7) d i s p l a y the same p e r v a s i v e , moderate p r o p y l i t i z a t i o n observed i n the f o o t w a l l u n i t s 1 and 2. Moderate s e r i c i t i z a t i o n and c a r b o n a t i z a t i o n r e p r e s e n t hydrothermal a l t e r a t i o n e f f e c t s on the sedimentary rocks ( u n i t 8). U n i t s 8b and 8c host l o c a l l y abundant p y r i t e , which might be hydrothermal and/or synsedimentary. 77 T e r t i a r y dykes ( u n i t 9) show s l i g h t to moderate p r o p y l i t i c a l t e r a t i o n . T h i s i s r e p r e s e n t e d by c h l o r i t e and c a l c i t e , with l e s s e r z e o l i t e , i n p e r v a s i v e a l t e r a t i o n and amygdules. Deformation and metamorphic t e x t u r e s , such as g r a i n growth and r e c r y s t a l l i z a t i o n , dominates the a l t e r a t i o n s t y l e of the m i n e r a l i z e d s t r a t i f o r m h o r i z o n ( u n i t 3 ) . Although r e c r y s t a l l i z a t i o n of the mi n e r a l s due to tec t o n i s m i s q u i t e e v i d e n t , there does not appear to have been major r e m o b i l i z a t i o n . U n i t 3 i s a l s o h y d r o t h e r m a l l y a l t e r e d , i n a s i m i l a r but l e s s e r degree than the host r o c k s . S e r i c i t e and c h l o r i t e are the main a l t e r a t i o n m i n e r a l s a s s o c i a t e d with the s t r a t i f o r m m i n e r a l i z a t i o n . V e i n m i n e r a l i z a t i o n i n the D o l l y Varden camp occurs e i t h e r as s i l v e r - b a s e metal or g o l d - s i l v e r - c o p p e r v e i n s i n Haz e l t o n Group r o c k s . These are d e t a i l e d below. S i l v e r - b a s e metal v e i n s c a r r y s i g n i f i c a n t s i l v e r , l e a d and z i n c v a l u e s and occur as s t r u c t u r a l l y c o n t r o l l e d d e p o s i t s a s s o c i a t e d w i t h replacement. Examples of t h i s type i n c l u d e the Wolf d e p o s i t , and the David C o p p e r f i e l d , M i t c h e l l , North Musketeer, S u r p r i s e and T i g e r p r o s p e c t s ( F i g s . 3 . 1 and 3.4). G e n e r a l l y , t h i s type of m i n e r a l i z a t i o n i s not r e s t r i c t e d to any s p e c i f i c rock u n i t , but the permeable t u f f a c e o u s rocks, e s p e c i a l l y the ash t u f f s of u n i t 7b, are f a v o r e d . T h i s f e a t u r e 78 of host rock preference along with widespread a l t e r a t i o n of the enclosing host rocks to mineralization, has lead to the nomenclature of "replacement veins" (Thiersch, 1986). The silver-base metal veins s t r i k e northeast and dip steeply to the east and west, subparallel to the youngest set of fa u l t s i n the area. Veins vary i n thickness from less than one meter up to several meters across, and are usually discontinuous. One of the veins at the Wolf deposit varies between 2 and 8m i n width and was traced for over 250m along i t s length (Thiersch, 1986). Mineralization consists of a quartz-carbonate gangue, with l o c a l concentrations of barite and/or witherite and jasper, hosting p y r i t e , lesser sphalerite and galena, sparse chalcopyrite and traces of pyrargyrite, tetrahedrite and native s i l v e r . Barite i s ra r e l y completely replaced by p y r i t e . Metal values are generally e r r a t i c as indicated by d r i l l i n g at the Wolf deposit (Thompson and Pearson, 1981). Open space textures, described by Thiersch (1986) for the Wolf deposit and recognized for the other vein occurrences of t h i s type, include colloform bands of grey, white and jasperoid quartz, comb structures and well terminated quartz c r y s t a l s . Breccia textures, primarily wallrock fragments enclosed by vein material, are common. Hydrothermal a l t e r a t i o n related to the silver-base metal mineralizing systems i s dominated by s i l i c i f i c a t i o n and p y r i t i z a t i o n i n poorly defined envelopes surrounding the veins. The envelopes are characterized by intense bleaching of the host 79 rocks and l o c a l l i m o n i t e s t a i n . No d i f f e r e n c e i n hangingwall and f o o t w a l l a l t e r a t i o n was noted a t the Wolf d e p o s i t ( T h i e r s c h , 1986). G o l d - s i l v e r - c o p p e r v e i n s occur w i t h i n the D o l l y Varden Gold B e l t , an area c h a r a c t e r i z e d by a very prominent gossan ( F i g . 3.36), which i s r e l a t e d to h y d r o t h e r m a l l y a l t e r e d p o r p h y r i t i c a n d e s i t e of u n i t 7a ( F i g s . 3.1 and 3.4). Hydrothermal a l t e r a t i o n a s s o c i a t e d w i t h t h i s zone i s expressed e i t h e r as s i l i c i f i c a t i o n and p y r i t i z a t i o n ( F i g . 3.1: u n i t 7a(q)) or s e r i c i t i z a t i o n and p y r i t i z a t i o n ( F i g . 3.1: u n i t 7 a ( s ) ) . The g o l d - s i l v e r - c o p p e r v e i n s g e n e r a l l y s t r i k e northwest with steep n o r t h e a s t e r l y d i p s and widths ranging from a few centimeters to tens of meters. V e i n mineralogy i s mainly p y r i t e and l o c a l l y abundant c h a l c o p y r i t e hosted w i t h i n a s i l i c i f i e d and c h l o r i t i z e d gangue. The o v e r a l l s i l v e r to g o l d r a t i o i s 7 to 1. T y p i c a l m i n e r a l i z e d zones are stockworks or v e i n - f i l l i n g s e x h i b i t i n g open space f r a c t u r e f i l l i n g t e x t u r e s ( F i g . 3.37). Examples of t h i s type of m i n e r a l occurrence i n c l u d e s the Maud McPhee, Red P o i n t , Red P o i n t E x t e n s i o n , Combination and Dan Patch p r o s p e c t s ( F i g s . 3.1 and 3.4). S i l i c i f i c a t i o n , s e r i c i t i z a t i o n and c h l o r i t i z a t i o n are the main e x p r e s s i o n s of w a l l r o c k a l t e r a t i o n immediately a d j a c e n t to the v e i n s ; but i n g e n e r a l , hydrothermal a l t e r a t i o n i n the Gold B e l t i s dominated by s e r i c i t i z a t i o n ( F i g . 3.1: u n i t 7 a ( s ) ) . In the c e n t r a l p a r t of the Gold B e l t a r e a , an i n t e n s e l y s i l i c i f i e d zone ( F i g . 3.1: 80 u n i t 7a(q)) c h a r a c t e r i z e d by stockworks of milky white q u a r t z and b a r i t e , p o s s i b l y r e p r e s e n t s the uppermost l e v e l s a hydrothermal system, o f t e n r e f e r e d to as a s i l i c a cap ( c f . Buchanan, 1981 ). A northwest t r e n d i n g g o l d zone, approximately 600m i n l e n g t h , was d i s c o v e r e d d u r i n g a r e c e n t e x p l o r a t i o n program i n the Gold B e l t area ( D e v l i n , 1986). T h i s program i n v o l v e d s u r f a c e and underground g e o l o g i c a l mapping, rock and s o i l geochemical sampling and channel sampling of o l d trenches and g o l d showings. At the Red P o i n t prospect ( F i g s . 3.1 and 3.4), near the south end of t h i s g o l d zone, a m i n e r a l i z e d showing was o u t l i n e d t h a t measured 38m long and 4.6m wide, g r a d i n g 5.7g g o l d per tonne. One of the samples taken a c r o s s t h i s showing assayed 15.5g g o l d per tonne over a 2.0m width. Another m i n e r a l i z e d showing was d i s c o v e r e d a t the Red P o i n t E x t e n s i o n p r o s p e c t , near the north end of the g o l d zone. T h i s showing i s 50m i n l e n g t h , 3.7m i n width, and grades 3.6g g o l d per tonne. S i g n i f i c a n t g o l d v a l u e s were a l s o d i s c o v e r e d a t the Combination p r o s p e c t ( F i g s . 3.1 and 3.4). 81 Figure 3.36. The very prominent gossan of the Dolly Varden Gold Belt, near Black Bear'Creek (Figs. 3.1 and 3.4). This zone i s related to hydrothermally altered grey-green porphyritic  andesite (unit 7a). 82 F i g u r e 3 . 3 7 . G o l d - s i l v e r - c o p p e r v e i n s o f t h e D o l l y V a r d e n G o l d B e l t . T y p i c a l m i n e r a l i z e d z o n e s a r e q u a r t z s t o c k w o r k s a n d v e i n f i l l i n g s . 8 3 4.0 ISOTOPE STUDIES 4.1 INTRODUCTION S t a b l e and r a d i o g e n i c i s o t o p e s t u d i e s were undertaken to prove t h a t s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n i s contemporaneous wi t h the E a r l y to Middle J u r a s s i c v o l c a n i c rocks of the H a z e l t o n Group. The s t a b l e i s o t o p e s of s u l f u r , oxygen and carbon were used to determine: (1) the source of s u l f u r , oxygen and carbon i n s u l f i d e s , b a r i t e , q u a r t z and carbonates (2) the d e p o s i t i o n a l temperature of m i n e r a l i z a t i o n , and (3) the d e p o s i t i o n a l environments of the d i f f e r e n t components of the m i n e r a l i z a t i o n , p a r t i c u l a r l y s u l f i d e s v s . b a r i t e . Radiogenic i s o t o p e s of l e a d were used to determine the source of l e a d i n galena, and r a d i o g e n i c i s o t o p e s of both K-Ar and l e a d helped to r e s o l v e the age of w a l l r o c k s of the s t r a t i f o r m m i n e r a l i z a t i o n . I s o t o p i c d a t a , combined with the d e t a i l e d g e o l o g i c s t u d i e s , was a l s o c r i t i c a l i n r e f i n i n g a g e n e t i c model f o r s t r a t i f o r m m i n e r a l d e p o s i t s i n the D o l l y Varden camp. 4.2 SULFUR, OXYGEN AND CARBON ISOTOPE STUDIES S u l f u r , oxygen and carbon i s o t o p e s were an a l y z e d i n s u l f i d e , b a r i t e , q uartz and carbonate from d e p o s i t s w i t h i n the D o l l y Varden camp ( F i g . 3.1 and Table 4.1). Data are r e p o r t e d as per m i l d e v i a t i o n (<T) from a standard c a l c u l a t e d as: <S = {(RSample - RStandard) / (RStandard)} x 1 ,000 ( %• ), 84 where RSample i s 34S/32S, 180/160 or 13C/12C i n the sample and RStandard i s the corresp o n d i n g r a t i o f o r the standard (Ohmoto and Rye, 1979; T a y l o r , 1979). The standards are Canon D i a b l o t r o i l i t e (CDT) f o r s u l f u r , Standard Mean Ocean Water (SMOW) f o r oxygen, and U n i v e r s i t y of Chicago standard, Peedee Belemnite (PDB) f o r carbon. The r e p r o d u c i b i l i t y at 1 sigma of cf34S v a l u e s i n s u l f i d e s and b a r i t e , and <fl3C i n carbonates, i s _+ 0.2%o and _+0.1 %» , r e s p e c t i v e l y (H. R. Krouse, p e r s . comm., 1 987), and + 0 . 1 4 % o f o r cfl 80 i n quartz (K. Muehlenbachs, p e r s . comm., 1987). 4.2.1 S u l f u r Isotopes S u l f u r i s o t o p e v a l u e s f o r s u l f i d e and b a r i t e samples i n Table 4.1 are p l o t t e d i n F i g u r e 4.1. S u l f i d e rf34S v a l u e s range from -7.0 to +20.4 per m i l , with most of the value s e i t h e r very c l o s e to zero or s l i g h t l y n e g a t i v e ; more p o s i t i v e v a l u e s occur i n the D o l l y Varden East and Wolf d e p o s i t s . The i s o t o p i c c omposition of s u l f u r i n the s u l f i d e m i n e r als i s t y p i c a l of val u e s d i s p l a y e d f o r v o l c a n o g e n i c massive s u l f i d e d e p o s i t s where s u l f i d e s c h a r a c t e r i s t i c a l l y have <f34S v a l u e s t h a t c l u s t e r around zero per m i l , which i s i s o t o p i c a l l y s i m i l a r to me t e o r i t e s and igneous rocks (Ohmoto and Rye, 1979). B a r i t e has c o n s i d e r a b l y h i g h e r df34S v a l u e s , ranging from +12.6 to +25.1 per m i l . High p o s i t i v e d34S v a l u e s f o r b a r i t e are a l s o t y p i c a l of s u l f a t e m i n e r a l s i n v o l c a n o g e n i c massive s u l f i d e d e p o s i t s . These values are g e n e r a l l y c l o s e to contemporaneous 8 5 TABLE 4.1. Sulfur, oxygen and carbon isotope compositions of sulfides, barite, quartz and calcite in deposits from the Dolly Warden Camp, northwestern B.C. Sample locations are plotted on Figure 3.1. Data are plotted in Figures 4.1 and 4.2. Sample Deposit mineral d34S1 cfl801,2 rfl803 <f!3C1 Number Name Analyzed fr> CDT %. SNOW Ore Fluids %* PDB 0272a Dolly Varden West Sphalerite -1.1 0272a Dolly Varden west Galena -2.0 0272a Dolly Varden west Barite +25.1 +11.7 +1.5 to +11.8 DV-2 Dolly Varden East Pyrite +9.2 DV-2 Dolly Varden East Sphalerite +3.6 DV-2 Dolly Varden East Pyrargyrite -3.5 D258 Dolly Varden East Pyrite +11.4 D258 Dolly Varden East Sphalerite +7.8 0258 Dolly Varden East Galena +1.8 D258 Dolly Varden East Calcite +9.0 -4.2 to +5.2 D258 Dolly Varden East Quartz +11.2 -5.2 to +6.1 D333b-1 Northstar Pyrite -4.5 D333b-1 Northstar Sphalerite -4.7 D333b-1 Northstar Galena -5.2 D333b-1 Northstar Barite +12.B +10.8 +0.6 to +10.9 0333b-1 Northstar Quartz +13.1 -3.0 to +8.4 D333b-2 Northstar Sphalerite -1.2 D333b-2 Northstar Galena -0.8 D333b-2 Northstar Barite +15.9 n.d. D326-1 Torbrit Pyrite +0.4 D326-1 Torbrit Sphalerite -3.8 D32B-1 Torbrit Galena -7.0 D326-1 Torbrit Barite +13.6 n.d. D326-1 Torbrit Quartz +12.7 -3.4 to +8.0 D32B-2 Torbrit Sphalerite -0.9 D326-2 Torbrit Galena -2.9 D326-2 Torbrit Barite +14.6 n.d. 41081-14 Wolf Pyrite +20.4 41081-14 Wolf Sphalerite +3.0 41081-14 Wolf Galena +8.9 41081-14 Wolf Witherite +10.2 -0.5 to +8.3 41081-14 Wolf Calcite +13.0 -0.3 to +9.2 41081-14 Wolf Quartz +15.4 -0.7 to +10.7 41081-24 Wolf Pyrite +16.0 D72a Tiger Quartz +15.9 -0.2 to +11.2 T248 Red Point Extension Quartz +6.9 -9.1 to +2.2 1. Isotopes of sulfur from sulfides and barite, oxygen from barite and carbonate, and carbon from calcite were analyzed by H.R. Krouse, Department of of Physics, University of Calgary, Calgary, Alberta T2N 1N4; CDT = Canyon Diablo t r o i l i t e standard; SmOW = Standard mean Ocean Water; PDB = University of Chicago standard, Peedee Belemnite. 2. Isotopes of oxygen from quartz were analyzed by K. muehlenbachs, Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E0; n.d. = not determined. 3. Calculated from the dl80 values of barite, quartz and carbonate using oxygen isotope fractionation equations in Appendix "JJ. Calculated range of ore f l u i d compositions are calculated from the temperature range of 143oC to 375oC (estimated in Table 4.2 from sulfur and oxygen isotope data for pairs of sulfur and oxygen compounds from the Dolly Varden camp). 4. Data is also in Thiersch (1986). 86 634S, °/oo DOLLY VARDEN EAST NORTHSTAR A A TORBRIT • BARITE A SPHALERITE • GALENA • PYRITE • PYRARGYRITE WOLF Range of seawater sulfate at approx. 190 Ma c F i g u r e 4.1. S u l f u r i s o t o p e p l o t f o r d e p o s i t s from the D o l l y Varden camp, northwestern B.C. The range f o r e a r l y J u r a s s i c seawater s u l f a t e i s seawater s u l f a t e i s from C l a y p o o l et a l . , 1980. Diagram shows a dominantly magmatic o r i g i n f o r the s u l f i d e s (rf34S =• 0%o ), and an o r i g i n from oxygenated seawater of E a r l y J u r a s s i c age (ca. 190 Ma) f o r b a r i t e (df34S = 15 % „ ) . 87 oxygenated seawater as r e p r e s e n t e d by i s o t o p e age curves f o r marine s u l f a t e m i n e r a l s i n e q u i l i b r i u m with seawater (Holser and Kaplan, 1 966 i n Faure', 1 977; C l a y p o o l et a l . , 1 980). Most of the b a r i t e samples from the D o l l y Varden camp f a l l w i t h i n the range of seawater s u l f a t e p r e c i p i t a t e d d u r i n g the E a r l y J u r a s s i c p e r i o d at approximately 190 Ma ( F i g . 4.1). Temperatures of d e p o s i t i o n as i n d i c a t e d from p a i r s of s u l f u r compounds u s i n g the s u l f u r i s o t o p e a n a l y s e s from the D o l l y Varden camp (Table 4.1) c a l c u l a t e d from s u l f u r i s o t o p e f r a c t i o n a t i o n equations (Appendix J) are i n Table 4.2. Most of these temperatures are u n r e a l i s t i c a l l y low or h i g h , s u g g e s t i n g i s o t o p i c d i s e q u i l i b r i u m , and non-contemporaneous p r e c i p i t a t i o n . The range of c a l c u l a t e d temperatures f o r e x c e p t i o n a l p a i r s of s u l f u r compounds from the D o l l y Varden camp (143oC and 375oC), however, f a l l s c l o s e t o : (1) e x i t temperatures (260oC to 350oC) measured i n a c t i v e hydrothermal vents on the E a s t P a c i f i c R i s e , 21oN l a t i t u d e ( S t y r t et a l . , 1981), (2) f l u i d i n c l u s i o n temperatures (150oC to 360oC) determined f o r s u l f i d e and s u l f a t e m i n e r a l s i n Kuroko d e p o s i t s , Japan, and a n h y d r i t e s from the E a s t P a c i f i c R i s e (Kusakabe et a l . , 1982; Pisutha-Arnond and Ohmoto, 1983) and (3) d e p o s i t i o n a l temperatures (115oC to 305oC) c a l c u l a t e d from s u l f u r i s o t o p e data f o r s p h a l e r i t e - g a l e n a p a i r s from the M i s s i s s i p p i a n s t r a t i f o r m , z i n c - l e a d - b a r i t e Red Dog Creek and Drenchwater Creek d e p o s i t s , A l a s k a (Lange e t a l . , 1980). These temperatures are a l s o i n c l o s e agreement with the 88 TABLE 4.2. Calculated depositional temperaturesl for pairs of sulfur and oxygen compounds from the Dolly Varden Camp, northwestern B.C. Sulfur and oxygen isotope data used in estimates are in Table 4.1. Underlined values represent potentially r e a l i s t i c depositional temperatures—see text. Variation in estimated temperatures are due to analytical error in the sulfur and oxygen analyses and i s approximately + 30oC. Temperature (oC) Sample Deposit Barite- Barite- Barite- Pyrite- Pyrite- Sphalerite- Quartz- Quartz- Quartz- Calcite-Number Name Galena Sphalerite Pyrite Galena Sphalerite Galena Calcite Barite Uitherite Witherite D272a Dolly Varden West 143 192 623 0V-2 Dolly Varden East -41 D258 Dolly Varden East 53 17 74 D333b-1 Northstar 2B3 349 375 934 957 929 D333b-2 Northstar 311 354 1071 D32B-1 Torbrit 227 346 532 96 -5 202 D326-2 Torbrit 290 405 328 41081-1 Wolf 25 -141 77 190 c.i.2 174 152 108 1. Calculated from the d34S values for sulfides and barite, and the 0*180 values for quartz, barite and carbonates, using sulfur and oxygen isotope fractionation equations in Appendix T_. 2. c i . = calculation invalid. temperature (270oC) determined f o r s p h a l e r i t e f o r m a t i o n by p l o t t i n g the FeS content of s p h a l e r i t e from the T o r b r i t d e p o s i t on a p o r t i o n of the system ZnS-FeS-S, and by employing the a r g e n t i t e - s i l v e r assemblage as a s u l f u r barometer (Campbell, 1959). The u n c e r t a i n t i e s of the data i n t h i s l a t e r study i n d i c a t e d t h a t the temperature of s p h a l e r i t e f o r m a t i o n c o u l d range between 230oC and 310oC. Thus the e x c e p t i o n a l p a i r s of s u l f u r compounds an a l y z e d i n d e p o s i t s of the D o l l y Varden camp may have been near i s o t o p i c e q u i l i b r i u m a t the time of d e p o s i t i o n . I f so, c a l c u l a t e d temperatures approximate d e p o s i t i o n a l temperatures. 4.2.2 Oxygen Isotopes Oxygen i s o t o p e compositions of q u a r t z , b a r i t e and carbonate samples from d e p o s i t s i n the D o l l y Varden camp range from +6.9 to +15.9 per m i l (Table 4.1). Most of the a*180 v a l u e s are hig h e r than +9.6 p a r t s per m i l , the analyzed v a l u e of BaS04 prepared from d i s s o l v e d s u l f a t e i n present-day s u r f a c e water of the c e n t r a l P a c i f i c Ocean ( S a k a i , 1977 i n Kusakabe e t a l . , 1 982). The <fl 80 v a l u e s are a l s o very c l o s e t o those of a n h y d r i t e s from the East P a c i f i c R i s e , which range from +10.2 to +11.5 per m i l (Kusakabe e t a l . , 1982). S i m i l a r v a l u e s were observed from: (1) v o l c a n o g e n i c s u l f a t e s and hangingwall f e r r u g i n o u s c h e r t s of Kuroko d e p o s i t s (Matsukuma and H o r i k o s h i , 1970; Kusakabe and Chiba, 1983; Tsutsumi and Ohmoto, 1983; Watanabe and S a k a i , 1983), (2) quartz and hematite samples from 90 the B i g Mike v o l c a n o g e n i c massive s u l f i d e d e p o s i t i n Nevada (Rye et a l . , 1984), and (3) ores and a l t e r a t i o n zones of the Kidd Creek v o l c a n o g e n i c massive s u l f i d e d e p o s i t s , O n t a r i o (Beaty and T a y l o r , 1979, 1980 i n F r a n k l i n et a l . , 1980). Temperatures of d e p o s i t i o n were a l s o c a l c u l a t e d from p a i r s of oxygen compounds (Table 4.2) u s i n g the oxygen i s o t o p e a n a l y s e s ( F i g . 4.1) and oxygen i s o t o p e f r a c t i o n a t i o n equations (Appendix X) • R e a l i s t i c d e p o s i t i o n a l temperatures f o r oxygen compounds range from 152oC to 190oC, and are w i t h i n the range of c a l c u l a t e d temperatures f o r p a i r s of s u l f u r compounds from the D o l l y Varden camp (143oC to 375oC). The <f 1 8 v a l u e s of ore f l u i d s f o r the D o l l y Varden d e p o s i t s can be es t i m a t e d i f i t i s assumed t h a t oxygen-bearing m i n e r a l s and the s o l u t i o n s from which they p r e c i p i t a t e d are i n i s o t o p i c e q u i l i b r i u m . Oxygen i s o t o p e compositions of the ore f l u i d s are g e n e r a l l y c a l c u l a t e d from the dfl80 v a l u e s and f i l l i n g temperatures of f l u i d i n c l u s i o n s of e i t h e r the oxygen-bearing m i n e r a l s or a s s o c i a t e d ore m i n e r a l s , together with the e x p e r i m e n t a l l y determined f r a c t i o n a t i o n f a c t o r s f o r v a r i o u s mineral-water systems. In t h i s study, because the f i l l i n g temperatures of f l u i d i n c l u s i o n s were not measured, the o v e r a l l i s o t o p i c temperature range of 143oC t o 375oC estimated f o r p a i r s of s u l f u r and oxygen compounds from the D o l l y Varden camp was used i n the c a l c u l a t i o n s . The c l o s e approximation of t h i s temperature range to those of s u l f i d e and s u l f a t e m i n e r a l s i n 91 Kuroko d e p o s i t s and on the Ea s t P a c i f i c R i s e j u s t i f i e s i t s use i n determining the oxygen i s o t o p e compositions of the ore f l u i d s . Oxygen i s o t o p e f r a c t i o n a t i o n equations used i n the c a l c u l a t i o n s are i n Appendix J . C a l c u l a t e d oxygen i s o t o p e compositions of the ore f l u i d s r e s p o n s i b l e f o r m i n e r a l i z a t i o n i n the D o l l y Varden camp, c a l c u l a t e d i n Ta b l e 4.1, are p l o t t e d i n F i g u r e 4.2. The rfl 80 val u e s f o r ore f l u i d s range from -9.1 t o +11.8 per m i l with most of the va l u e s e i t h e r c e n t e r e d on zero, which i s very c l o s e t o seawater (SMOW i n F i g . 4.2), or s l i g h t l y e n r i c h e d i n the h e a v i e r oxygen i s o t o p e . The range of va l u e s are l a r g e l y c o i n c i d e n t with those f o r Kuroko d e p o s i t s (Pisutha-Arnond, 1983); the upper p a r t of the range o v e r l a p s those presented by T a y l o r (1979) f o r magmatic waters, and a s m a l l p a r t of the lower range f o r metamorphic waters. F i g u r e 4.2 shows t h a t the most com p e l l i n g c o i n c i d e n c e t o be of data from the D o l l y Varden camp with seawater. No s y s t e m a t i c v a r i a t i o n between d e p o s i t s sampled and m i n e r a l s a n a l y z e d was observed f o r oxygen i s o t o p e data from the D o l l y Varden camp. Since oxygen i s o t o p e exchange i n hydrothermal systems i s l a r g e l y a f u n c t i o n of temperature ( T a y l o r , 1979), i t should be p o s s i b l e to e x t r a p o l a t e the temperature of fo r m a t i o n f o r the m i n e r a l i z a t i o n i n the D o l l y Varden camp from the range of temperatures determined by s u l f u r and oxygen i s o t o p e geothermometry and the cor r e s p o n d i n g c a l c u l a t e d d*180 v a l u e s f o r the ore f l u i d s ( F i g . 4.2). Thus, i f the oxygen-bearing minerals -20 -10 0 +10 +20 81aO, ° / o o F i g u r e 4.2. Range of c a l c u l a t e d 4*180 v a l u e s f o r ore f l u i d s (Table 4.1) r e s p o n s i b l e f o r m i n e r a l i z a t i o n i n the D o l l y Varden camp, northwestern B.C. Temperatures of 143oC and 375oC were esti m a t e d from s u l f u r and oxygen i s o t o p e data f o r p a i r s of s u l f u r and oxygen compounds (Table 4.2) from the D o l l y Varden camp. Diagram ( m o d i f i e d from T a y l o r , 1979) a l s o shows SM0W (Standard Mean Ocean Water), the c a l c u l a t e d f i e l d s of primary magmatic and metamorphic waters, k a o l i n i t e and meteoric water l i n e s , and a p l o t of the range of dD of f l u i d i n c l u s i o n s v s . c a l c u l a t e d <fl 80 v a l u e s f o r Kuroko v o l c a n o g e n i c massive s u l f i d e d e p o s i t s (Pisutha-Arnond and Ohmoto, 1983 ). Th'is p l o t s t r o n g l y supports a d e r i v a t i o n from hot seawater ( c a . 245oC) of the oxygen i s o t o p e s i n b a r i t e , carbonate and q u a r t z . 93 were p r e c i p i t a t e d from seawater, as e s t a b l i s h e d by the s u l f u r i s o t o p e data on b a r i t e , the temperature of f o r m a t i o n was about 245oC. 4.2.3 Carbon Isotopes Carbon i s o t o p e compositions were determined f o r c a l c i t e samples from the D o l l y Varden E a s t and Wolf d e p o s i t s . Values of dfl3C i n (Table 4.1) are -9.8 and -11.8 per m i l , r e s p e c t i v e l y . Ore d e p o s i t s i n which carbonate m i n e r a l s have <fl3C v a l u e s near -5 p a r t s per m i l are i n t e r p r e t e d g e n e r a l l y to have formed from magmatic f l u i d s , whereas values i s o t o p i c a l l y more n e g a t i v e than magmatic carbon are e i t h e r b i o g e n i c , with reduced carbon from b i o l o g i c p r o c e s s e s , or have a metamorphic o r i g i n (Ohmoto and Rye, 1979). Sedimentary marine carbonates and seawater have rfl 3C v a l u e s c l o s e t o zero p a r t s per m i l . None of the o r i g i n s above c l e a r l y e x p l a i n the carbon i s o t o p e compositions o b t a i n e d here. The dfl 3C v a l u e s , however, are w i t h i n the -4 to -12 p a r t s per m i l range f o r C02 i n f l u i d i n c l u s i o n s from most hydrothermal ore d e p o s i t s (Faure, 1977). 4.2.4 D i s c u s s i o n M i n e r a l i z a t i o n i n v o l c a n o g e n i c massive s u l f i d e d e p o s i t s p r e c i p i t a t e s a djacent to vents near the s e a f l o o r due to mixing of seawater and hydrothermal s o l u t i o n s . S ince e q u i l i b r i u m between seawater s u l f a t e and hydrothermal H2S does not occur 94 g e n e r a l l y , the i s o t o p i c composition of s u l f u r i n s u l f i d e m i n e r a l s r e f l e c t s the i s o t o p i c composition of s u l f u r i n the hydrothermal s o l u t i o n s p r i o r to mixing with seawater ( S t y r t e t a l . , 1981). T h e r e f o r e , n e a r l y zero df34S v a l u e s of s u l f i d e s i n the D o l l y Varden d e p o s i t s suggest t h a t s u l f u r was d e r i v e d p r i m a r i l y from e i t h e r a magmatic source or from the u n d e r l y i n g a n d e s i t i c v o l c a n i c r o c k s . S l i g h t l y n e g a t i v e values f o r many of the s u l f i d e s , however, may mean t h a t the hydrothermal f l u i d s i n c o r p o r a t e d minor amounts of t y p i c a l l y n e g a t i v e b i o g e n i c s u l f u r , probably d e r i v e d from the sedimentary rock u n i t s u n d e r l y i n g the m i n e r a l i z e d s t r a t i f o r m h o r i z o n and v o l c a n i c host rocks of the D o l l y Varden camp ( A l l d r i c k e t a l . , 1986; Dawson and A l l d r i c k , 1986). A seawater s u l f a t e o r i g i n f o r b a r i t e s u l f u r i s i n d i c a t e d by the h i g h p o s i t i v e d*34S v a l u e s which are c l o s e to E a r l y J u r a s s i c seawater s u l f a t e v a l u e s . Seawater i s o t o p i c v a l u e s f o r s u l f u r , e s s e n t i a l l y i d e n t i c a l to normal seawater, have been observed i n s u l f a t e d e p o s i t s on the East P a c i f i c R i s e ( S t y r t e t a_l., 1981; Kusakabe et a l . , 1982); s i m i l a r l y Kuroko s u l f a t e s r e f l e c t Miocene seawater s u l f a t e v a l u e s (Kusakabe and Chiba, 1983; Watanabe and S a k a i , 1983). A seawater source f o r oxygen i n b a r i t e , quartz and carbonate i n D o l l y Varden ores i s c o n s i s t e n t with the s u l f u r i s o t o p e data f o r the b a r i t e . The <fl 80 v a l u e s , however, are s l i g h t l y e n r i c h e d compared to present-day seawater. T a y l o r (1979) noted t h a t 9 5 e q u i l i b r i u m i s o t o p i c f r a c t i o n a t i o n f o r oxygen i s l a r g e l y temperature dependent. T h e r e f o r e , enrichment of h e a v i e r i s o t o p e s i n the oxygen-bearing minerals may have been caused by oxygen i s o t o p e exchange between oxygenated seawater and hydrothermal f l u i d s d u r i n g c o n d i t i o n s of i n c r e a s e d temperature. P o s i t i v e v a l u e s o b t a i n e d f o r s u l f i d e m i n e r als from the D o l l y Varden East and Wolf d e p o s i t s appear t o r e p r e s e n t mixing between magmatic and seawater s u l f u r . S u l f u r was probably d e r i v e d i n p a r t from e i t h e r v o l c a n i c r o c k s or magma and i n p a r t from seawater s u l f a t e which had been reduced e i t h e r by b a c t e r i a at the s u r f a c e or d u r i n g subsurface i n t e r a c t i o n between v o l c a n i c s and seawater. A combined magmatic and seawater source f o r s u l f u r i n s u l f i d e s has been suggested f o r s u l f i d e s from a c t i v e vents on the E a s t P a c i f i c R i s e ( S t y r t et a l . , 1 9 8 1 ) , f o r the B i g Mike c u p r i f e r o u s v o l c a n o g e n i c massive s u l f i d e d e p o s i t (Rye e t a l . , 1 9 8 4 ) , and f o r the s t r a t i f o r m and v o l c a n o g e n i c z i n c - l e a d - b a r i u m d e p o s i t s of the Red Dog Creek and Drenchwater Creek areas (Lange e t a l . , 1 9 8 0 ) . The « f l 3 C v a l u e s i n c a l c i t e from the D o l l y Varden East and Wolf d e p o s i t s are i s o t o p i c a l l y more n e g a t i v e than seawater and might be due to the d e p l e t i o n of the h e a v i e r carbon i s o t o p e d u r i n g c i r c u l a t i o n of seawater through the u n d e r l y i n g a n d e s i t i c v o l c a n i c r o c k s . T h i s i s supported by s i m i l a r <3(l 3C v a l u e s ( - 1 4 . 6 to 0 . 9 p a r t s per m i l ) f o r c a l c i t e i n hydrothermally a l t e r e d b a s a l t s of the Miocene Macquarie I s l a n d o p h i o l i t e , south of New 96 Zealand (Cocker e t aj.., 1 982). 4.2.5 Summary S t a b l e i s o t o p e data from s u l f i d e and gangue m i n e r a l s from the D o l l y Varden camp g e n e r a l l y support a d u a l source f o r the "ore" m i n e r a l i z a t i o n . A dominantly magmatic o r i g i n f o r the s u l f u r i n the s u l f i d e s c o n t r a s t s with a probable seawater o r i g i n f o r s u l f u r and oxygen i n b a r i t e , q u a r t z and carbonate gangue. S u l f u r i s o t o p e s of s u l f i d e s show them to be mainly magmatic with a minor component of sedimentary s u l f u r . On the oth e r hand, s u l f u r i s o t o p e s i n b a r i t e r e f l e c t c l o s e l y an o r i g i n from oxygenated seawater of a p p r o p r i a t e E a r l y J u r a s s i c age. Given then t h a t the b a r i t e i s from seawater, a s s o c i a t e d gangue mi n e r a l s probably are t o o . Thus, oxygen i s o t o p e s i n b a r i t e , q uartz and carbonate are compatible with a sedimentary marine o r i g i n , and were d e r i v e d from hot ( c a . 245oC) seawater. 4.3 POTASSIUM-ARGON ISOTOPES Whole-rock potassium-argon ages on samples from the D o l l y Varden camp are l o c a t e d on F i g u r e 3.1 and presented i n Table 4.3. One sample of f e l d s p a r - h o r n b l e n d e p o r p h y r i t i c a n d e s i t e from the f o o t w a l l v o l c a n i c sequence i n the v i c i n i t y of the T i g e r p r o s p e c t , near the T o r b r i t mine, y i e l d e d a Late Cretaceous age of 72.2 + 2.5 Ma. S i m i l a r Late Cretaceous ages were determined f o r samples from the hangingwall v o l c a n i c sequence, which 97 TABLE 4.3. Whole-rock potasium-argon datal for uolcanic rocks from the Dolly Varden camp, northwestern B.C. Sample locations are plotted on Figure 3.1. Sample number Location Rock name and rock unit2 55K (±) 40Ar * -i AOAr* "i Apparent age (Fla^ lat(oN) long(oUl) 40Artotal 106 cm3 STP/g Time5 T37a 55.6B 129.50 Feldspar-hornblende porphyritic andesite (unit 2a) 3.35 0.01 0.878 9.590 72.2 + 2.5 Late Cretaceous DVB4-NS1 55.68 129.51 Sericitized andesite ash tuff (unit 4) 4.18 0.07 0.844 11.713 70.7 + 2.5 Late Cretaceous D35 55.68 129.50 Andesite l a p i l l i tuff (unit 5) 3.80 0.03 0.871 10.246 68.1 + 2.5 Late Cretaceous G19 55.68 129.51 Basalt (unit 9) 0.676 0.005 0.523 .5905 22.3 + 0.8 Miocene 1. Argon analyses are by J. Harakal and potassium analyses are by K. Scott; a l l analyses were done at the Geochronology Laboratory, The University of British Columbia. 2. Units are described in Chapter 3. 3. Ar* indicates radiogenic argon. 4. Constants used are from Steiger and Jager (1977):\e = 0.581 x 10-10 yr-1 ;\fi = 4.962 x 10-10yr-1; 40K/K = 1.167 x 10-4. 5. Time designation is from Palmer (1983). i n c l u d e d a 70.7 +_ 2.5 Ma age f o r a s e r i c i t i z e d a n d e s i t e ash t u f f immediately o v e r l y i n g the N o r t h s t a r d e p o s i t and a 68.1 +_ 2.5 Ma age f o r an a n d e s i t e l a p i l l i t u f f s i t u a t e d southeast of the T o r b r i t mine. An E a r l y Miocene age of 22.3 +_ 0.8 Ma was o b t a i n e d f o r a b a s a l t i c dyke t h a t c r o s s c u t s s t r a t i f o r m m i n e r a l i z a t i o n of the N o r t h s t a r d e p o s i t ( D e v l i n and Godwin, 1986b). T h i s date i s i n c l o s e agreement with T e r t i a r y potassium-argon ages determined f o r s i m i l a r dykes i n the A l i c e Arm area ( C a r t e r , 1982) and i n the v i c i n i t y of the P r e m i e r - S i l b a k mine, near Stewart (D. Brown, p e r s . comm., 1986). Analyses of the a n d e s i t i c v o l c a n i c rocks were expected to r e v e a l the age of rocks h o s t i n g the s t r a t i f o r m m i n e r a l i z a t i o n i n the D o l l y Varden camp. Late Cretaceous dates o b t a i n e d f o r these r o c k s , however, are too young i n comparison to the E a r l y to Middle J u r a s s i c age accepted f o r the Hazelton Group rocks i n the K i t s a u l t R i v e r a r e a . T h e r e f o r e , i n t e r p r e t a t i o n of the dates as a d i r e c t measurement of the age of host rocks appears to be i n v a l i d . Potassium-argon a n a l y s e s have a l s o been conducted on whole-rock samples and on hornblende, b i o t i t e and potassium f e l d s p a r m i n e r a l separates o b t a i n e d from v a r i o u s rock u n i t s i n the nearby Stewart area (Smith, 1977; A l l d r i c k e t a l . , 1987). E a r l y t o Late Cretaceous ages were r e p o r t e d f o r s e v e r a l samples and are somewhat younger than Late T r i a s s i c to E a r l y J u r a s s i c ages determined by uranium-lead d a t i n g of z i r c o n s f o r the same 99 rock u n i t s ( A l l d r i c k et a l . , 1 9 8 6 ; D. Brown, pe r s . comm., 1 9 8 6 ) . A l l d r i c k et a_l. ( 1 9 8 7 ) attempted to e x p l a i n the v a r i e d potassium-argon dates f o r samples of the same rock u n i t by u s i n g the "metamorphic v e i l " concept (Armstrong, 1 9 6 6 ) ; where argon i s d r i v e n o f f and potassium-argon dates r e s e t by temperature i n c r e a s e s d u r i n g r e g i o n a l metamorphism. They a l s o argued t h a t f o r c e r t a i n m i n e r a l s , such as b i o t i t e and p o s s i b l y s e r i c i t e , lower g r e e n s c h i s t f a c i e s metamorphism p r o v i d e s s u f f i c i e n t temperature i n c r e a s e s to cause argon l o s s and r e s e t t i n g of potassium-argon d a t e s . T h e r e f o r e , the same argument p r o v i d e s an e x p l a n a t i o n of why the lower g r e e n s c h i s t a l t e r e d H a zelton Group rocks c h a r a c t e r i s t i c of the D o l l y Varden camp, y i e l d o n l y Late Cretaceous ( c a . 7 0 Ma.) potassium-argon d a t e s . 4.4 LEAD ISOTOPES Lead i s o t o p e r a t i o s , on galena samples from f i v e d e p o s i t s w i t h i n the D o l l y Varden camp ( F i g . 3 . 1 and Table 4.4), are p l o t t e d on c o n v e n t i o n a l l e a d i s o t o p e diagrams (207Pb/204Pb vs 206Pb/204Pb, 208Pb/204Pb vs 206Pb/204Pb and 206Pb/208Pb vs 206Pb/207Pb) i n F i g u r e 4 . 3 . Lead i s o t o p e a n a l yses on galena samples c o l l e c t e d p r e v i o u s l y from the D o l l y Varden and T o r b r i t mines (Godwin et a l . , 1 9 8 0 ) were not used i n t h i s study; they are c o n s i d e r e d to be of poor q u a l i t y . Table 4.4 l i s t s the sample number, d e p o s i t name, l o c a t i o n , h ost l i t h o l o g y , d e p o s i t type and the B r i t i s h Columbia M i n e r a l 100 TABLE 4 .4 . Galena-lead Isotope analyses! from the Dolly Varden camp t northuestern B . C . Sample locat ions are p lot ted on Figure 3 .1 . Data are p lot ted in Figure 4 .3 . H O Sample Deposit NTS acni Lat.o Long.o Lead Isotope Ratios (one sigma uncertainty) Nunber Name Nap Numbers North litest Li thology Deposit type 206Pb/2O4P8 207Pb/204Pb 208Pb/204Pb 206Pb/207Pb 206Pb/20BPb 30555-001 Red Point 103P/12E 103P--196 55.69 129.52 a l tered andesite porphyry Au-Ag-Cu vein 18.814 (0.02) 15.608 (0.02) 38.394 (0.02) 1.20546 (0.01) 0.490034 (0.00) 30555-001 Red Point 103P/12E 103P--196 55.69 129.52 a l tered andesite porphyry Au-Ag-Cu vein 18.824 (0.01) 15.612 (0.00) 38.427 (0.02) 1.20569 ( 0.01) 0.489854 (0.01) 30556-001 Nartfistar 103P/12E 103P--1B9 55.68 129.51 andesite tuf f st rat i form Ag-Pb-Zn-Ba 1B.B74 (0.02) 15.623 (0.01) 38.482 (0.02) 1.20810 ( 0.01) 0.490468 (0.01 ) 30557-001 Torbr i t 103P/12E 103P--191 55.68 129.50 andesite tuf f strat i form Ag-Pb-Zn-Ba 18.875 (0.01) 15.625 (0.01) 38.485 (0.02) 1.20805 (0.01) 0.490453 (0.01) 30771 -003 Ool ly Uarden 103P/12E 103P--1BB 55.68 129.51 andesite tuf f strat i form Ag-Pb-Zn-Ba 1B.B52 (0.01) 15.612 (0.01) 38.452 ( 0.01) 1.20753 (0.01) 0.490274 (0.01) 30771-004 Dol ly Uarden 103P/12E 103P--188 55.6B 129.51 andesite tuf f strat i form Ag-Pb-Zn-Ba 1B.B9B (0.01) 15.624 (0.01) 38.519 (0.01) 1.20955 (0.00) 0.490617 (0.01) 30904-001 Wolf 103P/12E 103P--198 55.71 129.52 andesite tuff Ag-Pb-Zn-Ba vein IB.859 (0.01) 15.613 (0.01) 38.464 ( 0.01) 1.20789 (0.00) 0.490291 (0.01) AUG Dol ly Uarden Camp (n = 7) 103P/12E 55.69 1 29.51 andesite mineral izat ion 18.857 (0.01) 15.617 (0.01) 38.460 (0.02) 1.20747 ( 0.01) 0.49D2B4 (0.01) AUG Jurassic (n = 8)2 IB.818 (0.02) 15.611 (0.00) 38.437 (0.03) 1 .20544 ( 0.00) 0.489567 (0.00) AUG Ter t iary (n = 12)2 19.148 (0.04) 15.622 (0.00) 38.629 (0.04) 1.22572 (0.00) 0.4956B4 (0.00) 1. A l l sample preparation and analyses are by J .E .Gabi tes and were done in the Geochronology Laboratory, Department of Geological Sc iences, The Univers i ty of B r i t i s h Columbia. Lead isotope ra t ios were analyzed using phosphoric ac id and s i l i c a g e l , measured on a Vaccuum Generators Isomass 54R s o l i d source mass spectrometer l inked to a Hewlett-Packard HP-B5 computer. A l l analyses are judged to be of good q u a l i t y . Abbreviations used in table are: NTS = National Topographic Survey, DCCII = B r i t i s h Columbia Mineral Inventory, AUG = Average. 2. Data from Stewart mining camp (A l ldr ick et a l . , 19B7). Inventory (MINFILE) number f o r each sample a n a l y z e d . Samples were o b t a i n e d from s t r a t i f o r m and v e i n s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n w i t h i n a n d e s i t e t u f f , and g o l d - s i l v e r - c o p p e r veins hosted by a l t e r e d a n d e s i t e porphyry. The average l e a d i s o t o p i c r a t i o s f o r galena from J u r a s s i c and T e r t i a r y m i n e r a l d e p o s i t s i n the Stewart mining camp ( A l l d r i c k e t a l . , 1987) are a l s o i n c l u d e d i n Table 4.4. The i s o t o p i c c omposition of g a l e n a - l e a d i n the D o l l y Varden ores are uniform, p l o t t i n g w i t h i n the d i s t i n c t c l u s t e r 1 on F i g u r e 4.3. A l l l e a d i s o t o p e v a l u e s i n the c l u s t e r , p l o t below the growth curve of Stacey and Kramers (1975) and the "orogene" e v o l u t i o n curve of Doe and Zartman (1979; 1981), segments of which are p l o t t e d on F i g u r e 4.3. Growth curves of Stacey and Kramers and the "orogene" e v o l u t i o n curve do not apply to the D o l l y Varden data because they would p r e d i c t a f u t u r e model age f o r m i n e r a l i z a t i o n . O l i v e r (1982) a l s o noted t h i s from a p r e l i m i n a r y study of 123 g a l e n a - l e a d i s o t o p e a n a l y s e s from d e p o s i t s w i t h i n the Intermontane B e l t ; these d e p o s i t s occur i n s i m i l a r t e r r a n e s of the Intermontane B e l t and most were hosted i n H a z e l t o n Group r o c k s . Lead i n the D o l l y Varden d e p o s i t s appears to be d e r i v e d p r i n c i p a l l y from an average orogene r e s e r v o i r (Doe and Zartman, 1979 and 1981), which i s t y p i c a l of a mature i s l a n d a r c s e t t i n g 102 comprised of c o n t i n e n t a l c r u s t , and p e l a g i c sediments. The c l u s t e r of g a l e n a - l e a d i s o t o p e data i n F i g u r e 4.3 suggests t h a t a l l m i n e r a l d e p o s i t s i n the D o l l y Varden camp are r e l a t e d c l o s e l y g e n e t i c a l l y and i n age. The data a l s o p l o t very c l o s e t o average l e a d i s o t o p i c r a t i o s f o r galena from J u r a s s i c m i n e r a l d e p o s i t s i n the Stewart mining camp, which are d i s t i n c t from T e r t i a r y d e p o s i t s ( A l l d r i c k e t a l . , 1987). Although, l e a d i s o t o p e r a t i o s do not p r o v i d e a b s o l u t e model ages f o r the forma t i o n of these m i n e r a l d e p o s i t s d i r e c t l y , t h e i r a s s o c i a t i o n with known J u r a s s i c d e p o s i t s i n the Stewart a r e a , e f f e c t i v e l y date them on a " f i n g e r p r i n t " b a s i s . D e p o s i t s from the D o l l y Varden camp, on the b a s i s of l e a d i s o t o p e s , formed d u r i n g a s h o r t - l i v e d m i n e r a l i z i n g event i n the J u r a s s i c . Note t h a t they f a l l i n c l u s t e r 1 ( F i g . 4.3), separated from another c l u s t e r of l e a d i s o t o p e v a l u e s from T e r t i a r y d e p o s i t s ( c f . A l l d r i c k e t a l . , 1987). These r e s u l t s support the h y p o t h e s i s espoused elsewhere ( c f . Chapter 3) i n t h i s t h e s i s t h a t g a l e n a - b e a r i n g d e p o s i t s of the D o l l y Varden camp formed c o g e n e t i c a l l y with c a l c - a l k a l i n e H azelton Group v o l c a n i c r o c k s at about 190 Ma. 103 F i g u r e 4.3. P l o t s of 208Pb/204Pb v s . 206Pb/204Pb / 207Pb/204Pb vs . 206Pb/204Pb and 206Pb/208Pb vs. 206Pb/207Pb f o r d e p o s i t s l o c a t e d on F i g u r e 3.1 and l i s t e d i n Table 4.4 .•= d e p o s i t s from the D o l l y Varden campfO= d e p o s i t s with J u r a s s i c l e a d s i g n a t u r e andQ= d e p o s i t s with T e r t i a r y l e a d s i g n a t u r e from the Stewart camp ( A l l d r i c k et a l . , 1987). C l o s e d symbols r e p r e s e n t group means. F r a c t i o n a t i o n s l o p e and Pberror were determined u s i n g equations from R i c h a r d s (1983). A n a l y t i c a l e r r o r shown i s 2 f from 46 analyses of the Broken H i l l galena standard (BHS-UBC1). The growth curve marked "S & K" i s a f t e r Stacey and Kramers (1975); the e v o l u t i o n curve marked "orogene" i s " V e r s i o n 1" a f t e r Doe and Zartman (1981). The f i e l d of p e l a g i c sediments i s a f t e r Doe and Zartman (1979 and 1981). 104 5.0 GENESIS OF STRATIFORM MINERALIZATION 5.1 INTRODUCTION S e v e r a l t h e o r i e s have been proposed f o r the genesis of the m i n e r a l i z e d s t r a t i f o r m d e p o s i t s i n H a z e l t o n Group rocks i n the D o l l y Varden camp. Hanson (1921) i m p l i e d t h e i r s t r a t i f o r m nature by s u g g e s t i n g t h a t they r e p r e s e n t e d "bedded v e i n s " . Black (1951), Campbell (1959) and S k e r l (1962) c o n s i d e r e d them to be replacement-vein d e p o s i t s formed d u r i n g e i t h e r Cretaceous or E a r l y T e r t i a r y time. S i m i l a r l y , M i t c h e l l (1973) f a v o r e d an epithermal-replacement o r i g i n but r e l a t e d them to J u r a s s i c v o l c a n i s m i n s t e a d . T h i s study, however, i n d i c a t e s t h a t most s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n probably formed as h y d r o t h e r m a l l y d e r i v e d , submarine e x h a l a t i v e d e p o s i t s t h a t comprise p a r t of the v o l c a n i c s t r a t i g r a p h y . The term " e x h a l a t i v e " used here, r e f e r s to the l o c a l i z e d e x p u l s i o n of f l u i d s i n t o the hydrosphere ( F r a n k l i n et a l . , 1981), and products of the e x h a l a t i v e process are c a l l e d e x h a l i t e s ( R i d l e r , 1973). 5.2 PHYSICAL AND CHEMICAL CHARACTERISTICS  OF THE STRATIFORM MINERALIZATION A s t r a t i f o r m and v o l c a n o g e n i c o r i g i n f o r these d e p o s i t s i s supported by f i e l d mapping, which shows t h a t the main mi n e r a l occurrences can be r e c o n s t r u c t e d to one continuous ore h o r i z o n 105 t h a t conforms to bedding. As i l l u s t r a t e d i n an i d e a l i z e d c r o s s - s e c t i o n f o r the D o l l y Varden camp ( F i g s . 3.1 to 3.5, and 5.1), c o n f o r m i t y of s t r a t i f o r m m i n e r a l i z a t i o n ( u n i t s 3a, 3b and 3c: s e c t i o n 3.2) to e n c l o s i n g host r o c k s , i s key support f o r t h i s h y p o t h e s i s . Another important f e a t u r e i s the c o n s i s t e n t -s t r a t i g r a p h i c p o s i t i o n of the m i n e r a l i z e d sequence between a green f o o t w a l l ( u n i t 2b) and a maroon hangingwall ( u n i t 5 ) . Fragments of s t r a t i f o r m ore a l s o occur w i t h i n t u f f a c e o u s hangingwall r o c k s ( u n i t s 4, 5 and 6b). Hangingwall p y r i t i c t u f f s ( u n i t 4) a l s o bear c l o s e resemblance to s i l i c e o u s and p y r i t i c t u f f s thought to be e x h a l a t i v e l a y e r s t h a t commonly o v e r l y s t r a t i f o r m and v o l c a n o g e n i c d e p o s i t s elsewhere ( R i d l e r , 1973). In g e n e r a l , the i d e a l i z e d s t r a t i g r a p h i c s y n t h e s i s can be d e s c r i b e d as a f o o t w a l l sequence of i n t r u s i o n s and t u f f s , unconformably o v e r l a i n by maroon t u f f s t h a t e n c l o s e m i n e r a l i z e d s t r a t i f o r m d e p o s i t s and a s s o c i a t e d p y r i t i c t u f f h o r i z o n s . The maroon t u f f s are capped unconformably by sequence of flows and r e l a t e d t u f f s , which are unconformably o v e r l a i n by e p i c l a s t i c r o c k s , mainly b l a c k s h a l e and s i l t s t o n e . V e r t i c a l m i n e r a l z o n a t i o n , from a p y r i t e - r i c h base t o a g a l e n a - s p h a l e r i t e - r i c h top, has been r e c o g n i z e d i n some of the s t r a t i f o r m ore d e p o s i t s of the D o l l y Varden camp and i s p a r t i c u l a r l y e v i d e n t i n d r i l l c o r e from the N o r t h s t a r d e p o s i t ( F i g . 3.13). V e r t i c a l m i n e r a l zoning i s probably one of the most widely r e c o g n i z e d f e a t u r e s of v o l c a n o g e n i c e x h a l a t i v e d e p o s i t s (Large, 1977). S t r a t i f o r m ore u n d e r l a i n by stockwork 1 0 6 WEST EAST F i g u r e 5.1. I d e a l i z e d c r o s s - s e c t i o n of the D o l l y Varden camp, northwestern B.C. The s e c t i o n , drawn l o o k i n g n o r t h , approximates the r e l a t i o n s h i p s of the i n v o l v e d E a r l y to Middle J u r a s s i c H azelton Group rocks but i s not drawn to s c a l e ; e f f e c t s of f o l d i n g and f a u l t i n g have been removed. U n i t s are d e s c r i b e d i n F i g u r e 3.4. Ore d e p o s i t s , w i t h i n t h e i r r e s p e c t i v e e x h a l i t e f a c i e s ( c f . F i g . 5.3), a r e : 1 = D o l l y Varden West, 2 = D o l l y Varden E a s t , 3 = N o r t h s t a r , 4 = T o r b r i t , and 5 = Moose-Lamb. A b b r e v i a t i o n : u = unconformity. 107 ore, as r e p r e s e n t e d by d i s s e m i n a t e d and f r a c t u r e f i l l i n g q u a r t z and p y r i t e m i n e r a l i z a t i o n a s s o c i a t e d with i n t e n s e a l t e r a t i o n i n p r e - e x i s t i n g , f o o t w a l l r o c k s , i s another c h a r a c t e r i s t i c f e a t u r e of v o l c a n o g e n i c e x h a l a t i v e d e p o s i t s . T h i s type of stockwork m i n e r a l r z a t i o n i n the f o o t w a l l of the D o l l y Varden E a s t d e p o s i t probably r e p r e s e n t s the vent or source area of m i n e r a l i z a t i o n . V e r t i c a l m i n e r a l z o n a t i o n , stockwork m i n e r a l i z a t i o n and i n t e n s e f o o t w a l l a l t e r a t i o n , have not been documented i n the other s t r a t i g r a p h i c a l l y e q u i v a l e n t ore d e p o s i t s , such as the T o r b r i t and Moose-Lamb d e p o s i t s . Another l i n e of evidence f o r a v o l c a n o g e n i c o r i g i n i s the l a t e r a l z o n a t i o n of gangue mi n e r a l s (Table 3.2). Moving eastward, over 2km, a c r o s s the map-area ( F i g s . 3.1, 3.4 and 5.1), zones vary from the q u a r t z - r i c h lodes of the D o l l y Varden E a s t d e p o s i t ( F i g s . 3.9 t o 3.11), through the q u a r t z - c a r b o n a t e - b a r i t e N o r t h s t a r lode ( F i g s . 3.12 to 3.15), to the b a r i t e - j a s p e r m i n e r a l i z a t i o n of the T o r b r i t and Moose-Lamb d e p o s i t s ( F i g s . 3.16 to 3.18). L a t e r a l z o n a t i o n a l s o i s r e f l e c t e d i n s i l v e r grades t h a t vary from 865g s i l v e r per tonne f o r the D o l l y Varden E a s t , 405g s i l v e r per tonne f o r the N o r t h s t a r and T o r b r i t , and 13 5g s i l v e r per tonne f o r the Moose-Lamb. Moving westward from the D o l l y Varden East d e p o s i t , the s t r a t i f o r m l a y e r i s c h a r a c t e r i z e d by the quartz-carbonate m i n e r a l i z a t i o n of the D o l l y Varden West d e p o s i t , which has a s i l v e r grade of 15g s i l v e r per tonne. 108 Two major s e t s of f a u l t s bound s t r u c t u r a l b l o c k s t h a t c o n t a i n the s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e d e p o s i t s ( F i g s . 3.1 to 3.5, and 5.2). In i t s present p o s i t i o n , the s t r a t i f o r m l a y e r appears to have been segmented by these f a u l t s i n t o f i v e major, separate b l o c k s . ( F i g . 5.2 J : b l o c k s 1 to 5); f i r s t by the e a r l i e r n o r t h w e s t e r l y t r e n d i n g D o l l y Varden ( F i g . 5.2 X : f a u l t A) and Moose-Lamb (B) f a u l t s , and l a t e r by the n o r t h e a s t e r l y t r e n d i n g Hanson (C) and Campbell (D) f a u l t s . I n d i v i d u a l s t r a t i f o r m ore bodies w i t h i n each s t r u c t u r a l b l o c k i n c l u d e the D o l l y Varden West ( F i g . 5.2 X: d e p o s i t 1), D o l l y Varden E a s t ( 2 ) , N o r t h s t a r ( 3 ) , T o r b r i t (4) and Moose-Lamb (5) d e p o s i t s . F a u l t displacement i s e i t h e r normal or r e v e r s e , with the e x c e p t i o n of the Hanson f a u l t (C), which appears to have exp e r i e n c e d s c i s s o r - l i k e r o t a t i o n about a p o i n t between the D o l l y Varden East (2) and N o r t h s t a r (3) d e p o s i t s ( F i g . 5.2 J : the r o t a t i o n p o i n t , about which the western s i d e has been r o t a t e d c o u n t e r - c l o c k w i s e with r e s p e c t to e a s t e r n s i d e , i s marked by an a s t e r i s k ) . Evidence of t h i s s c i s s o r - l i k e motion i s the asymmetrical displacement of both the s t r a t i f o r m h o r i z o n and the e a r l i e r northwest t r e n d i n g f a u l t s ( d i s t a n c e s between d e p o s i t s 1 and 3 and f a u l t s A and B are l e s s on the western s i d e of the Hanson f a u l t (C) than on the e a s t e r n s i d e between d e p o s i t s 2 and 4 and f a u l t s A and B), and a l s o by shallower d i p to the D o l l y Varden West and N o r t h s t a r d e p o s i t s on the west s i d e of the Hanson f a u l t , compared to those of the T o r b r i t on the e a s t s i d e of t h i s f a u l t . 1 0 9 T F i g u r e 5.2. Schematic r e c o n s t r u c t i o n of the m i n e r a l i z e d s t r a t i f o r m h o r i z o n i n the D o l l y Varden camp, northwestern B.C. X i s present p o s i t i o n of the s t r a t i f o r m h o r i z o n , showing r e l a t i o n s h i p to both e a r l i e r northwest and l a t e r n o r t h e a s t f a u l t s (cf_. F i g s . 3.1 to 3.5). S c i s s o r - l i k e r o t a t i o n occurs on the Hanson f a u l t (A) around a p o i n t marked by a s t e r i s k . JX i - s the p o s i t i o n of the s t r a t i f o r m h o r i z o n a f t e r movement on n o r t h e a s t t r e n d i n g f a u l t s C and D have been removed. T n i s p r e - f a u l t p o s i t i o n of the s t r a t i f o r m h o r i z o n a f t e r movement on the northwest t r e n d i n g f a u l t s A and B have been removed. F a u l t s a r e : A = D o l l y Varden, B = Moose-Lamb, C = Hanson, D = Campbell. D e p o s i t s are : 1 = D o l l y Varden West, 2 = D o l l y Varden E a s t , 3 = N o r t h s t a r , 4 = T o r b r i t , 5 = Moose-Lamb. 1 1 0 R e s t o r a t i o n along the l a t e , n o r t h e a s t f a u l t s ( F i g . 5.2 TT: f a u l t s C and D), shows t h a t southwest of the D o l l y Varden f a u l t (A), the D o l l y Varden West d e p o s i t (1) a d j o i n s the east end of the D o l l y Varden East d e p o s i t ( 2 ) . On the n o r t h e a s t e r n s i d e of the D o l l y Varden f a u l t (A), the N o r t h s t a r ( 3 ) , T o r b r i t (4) and Moose-Lamb (5) d e p o s i t s form a plane t h a t i s terminated to the no r t h e a s t by the Moose-Lamb f a u l t ( B ) . R e s t o r a t i o n along the D o l l y Varden (A) and Moose-Lamb (B) f a u l t s t o t h e i r o r i g i n a l p r e - f a u l t p o s i t i o n ( F i g . 5.2 JJ"J) shows t h a t a l l f i v e d e p o s i t s form a continuous s t r a t i f o r m h o r i z o n t h a t has a r e c o n s t r u c t e d s t r i k e l e n g t h of n e a r l y 3km. Isotope s t u d i e s have been e s s e n t i a l f o r r e s o l v i n g the problem of ge n e s i s of the s t r a t i f o r m m i n e r a l i z a t i o n i n the D o l l y Varden camp. Lead i s o t o p i c r a t i o s f o r galena from the s t r a t i f o r m o c c u r r e n c e s ( s e c t i o n 4.4) have a narrow range, which i s very c l o s e to the r a t i o s of known J u r a s s i c d e p o s i t s but which are markedly l e s s than r a t i o s a s s o c i a t e d with Cretaceous and T e r t i a r y d e p o s i t s i n the Stewart area ( A l l d r i c k e t a l . , 1987). T h i s i n d i c a t e s t h a t the s t r a t i f o r m m i n e r a l i z a t i o n i s consanguinous with the e n c l o s i n g E a r l y to Middle J u r a s s i c H a zelton Group v o l c a n i c r o c k s . S u l f u r i s o t o p e s i n b a r i t e ( s e c t i o n 4.2.1) a l s o are c o n s i s t e n t with an E a r l y J u r a s s i c d e r i v a t i o n from seawater s u l f a t e . A seawater o r i g i n i s supported f u r t h e r ( s e c t i o n 4.2.2 and 4.2.3) by oxygen and carbon i s o t o p e s i n carbonate, q u a r t z and b a r i t e . Thus, i f s u l f u r i n b a r i t e p r e c i p i t a t e d from the same J u r a s s i c seawater as the 111 oxygen and carbon i n a s s o c i a t e d gangue m i n e r a l s , then they too must be J u r a s s i c . T h i s does not c o n f l i c t with from another c o n c l u s i o n t h a t the s u l f u r i n s u l f i d e s was d e r i v e d e i t h e r from a dominantly magmatic source with a minor c o n t r i b u t i o n of sedimentary s u l f u r , or from the u n d e r l y i n g a n d e s i t i c v o l c a n i c rocks ( s e c t i o n 4.2.1). Metals i n the s t r a t i f o r m ore d e p o s i t s w i t h i n the D o l l y Varden camp are predominantly Pb, Zn, Fe and Ba, with l e s s e r amounts of Cu and Ag. These metals were probably leached from the rocks through which the ore-forming hydrothermal f l u i d s c i r c u l a t e d , and t r a n s p o r t e d i n n e u t r a l to weakly a c i d i c s o l u t i o n s as s o l u b l e c h l o r i d e complexes ( F r a n k l i n e t a l . , 1981). However, s i l v e r content i n the D o l l y Varden camp o r e s , with grades g e n e r a l l y a v e r a g i n g more than 400g s i l v e r per tonne, i s hi g h e r than i s normally found i n v o l c a n o g e n i c e x h a l a t i v e d e p o s i t s . T h i s might be due i n p a r t to the h i g h e r c o n c e n t r a t i o n s of s i l v e r i n b a s a l t s and a n d e s i t e s than i n other igneous rock type ( T u r e k i a n , 1972; T a y l o r , 1968 and 1969 i n Amcoff, 1984). Furthermore, the amount of l e a d i n the s t r a t i f o r m d e p o s i t s i n the D o l l y Varden camp i s lower than f o r many v o l c a n o g e n i c e x h a l a t i v e d e p o s i t s , and t h i s a l s o probably r e f l e c t s the a n d e s i t i c source f o r metals (cf_. Solomon, 1 976). The a n d e s i t i c source a l s o i s compatible with the magmatic s i g n a t u r e i n the s u l f u r i s o t o p e s of s u l f i d e s ( s e c t i o n 4.2.1). D e p o s i t i o n a l temperatures of the o r e - f l u i d s forming the 112 s t r a t i f o r m m i n e r a l i z a t i o n , e x t r a p o l a t e d from the range of temperatures determined by s u l f u r i s o t o p e geothermometry and the corre s p o n d i n g c a l c u l a t e d oxygen i s o t o p e v a l u e s f o r the ore f l u i d s , was around 245oC. T h i s temperature i s comparable to the temperature of 250oC assumed f o r the f o r m a t i o n of most minerals i n Kuroko d e p o s i t s (Ohmoto and Skinner, 1983). However, d e t a i l e d f l u i d i n c l u s i o n s t u d i e s by Pisutha-Arnond and Ohmoto (1983), i n d i c a t e t h a t most s u l f i d e and s u l f a t e m i n e r a l s i n Kuroko d e p o s i t s formed through a temperature range of 150o to 350oC. S i l v e r content a l s o i n c r e a s e s with temperature of ore fo r m a t i o n ( T i s c h e n d o r f , 1955 i n Amcoff, 1984), p o s s i b l y i n d i c a t i n g t h a t h i g h e r temperatures might fa v o r p r o d u c t i o n of the e x c e p t i o n a l l y high s i l v e r grades i n the D o l l y Varden camp ore d e p o s i t s . 5.3 GENETIC MODEL The g e n e t i c model f o r the s t r a t i f o r m and v o l c a n o g e n i c e x h a l a t i v e d e p o s i t s i n the D o l l y Varden camp i n v o l v e s p r e c i p i t a t i o n from e x h a l a t i v e hydrothermal f l u i d s of s u l f i d e s and a s s o c i a t e d gangue m i n e r a l s on the s e a - f l o o r ( F i g . 5.3). The e x h a l a t i v e , ore-forming s o l u t i o n s were probably m o b i l i z e d by a c o n v e c t i v e hydrothermal c e l l , d r i v e n by the heat of a c o o l i n g , s u b v o l c a n i c igneous body, i n t h i s case p o r p h y r i t i c a n d e s i t e ( F i g . 5.1, u n i t 2a). During a l u l l i n v o l c a n i c a c t i v i t y , the seawater c i r c u l a t e d through, a l t e r e d and leached permeable, a n d e s i t e p y r o c l a s t i c s . The o r e - b e a r i n g hydrothermal s o l u t i o n s 113 WEST DOLLY VARDEN WEST CARBONATE FACIES DOLLY VARDEN EAST SULFIDE FACIES NORTHSTAR CARBONATE FACIES ~ TORBRIT EAST MOOSE - LAMB •OXIDE FACIES SEA LEVEL DISPERSAL BY CURRENTS F i g u r e 5.3. Model f o r genesis of s t r a t i f o r m m i n e r a l i z a t i o n i n the D o l l y Varden camp, northwestern B.C. Model suggests t h a t s u l f i d e s and a s s o c i a t e d gangue m i n e r a l s i n the s t r a t i f o r m d e p o s i t s were p r e c i p i t a t e d from hydrothermal s o l u t i o n s exhaled onto the s e a f l o o r . Note the b a s i n i s about 3km a c r o s s when r e c o n s t r u c t e d ( c f . F i g . 5.1). North-south e x t e n t and v e r t i c a l s c a l e are unknown. A b b r e v i a t i o n s a r e : LAM = laminated e x h a l i t e u n i t 3c, MAS = massive e x h a l i t e u n i t s 3a and 3b, STK = stockwork, SX = s u l f i d e s , SU = s u l f a t e s , CB = carbonates, OX = o x i d e s , QZ = q u a r t z . 114 were subsequently d i s c h a r g e d along e x t e n s i o n a l f a u l t s , d i s p e r s e d by c u r r e n t s , and f i n a l l y accumulated i n s e a - f l o o r d e p r e s s i o n s . A shallow subaqueous environment f o r d e p o s i t i o n of the m i n e r a l i z a t i o n i s i m p l i e d by the e x p l o s i v e c h a r a c t e r of the a s s o c i a t e d a n d e s i t i c v o l c a nism, and to a l e s s e r degree by the presence of amygdules i n flows and s u b v o l c a n i c s i l l s . Marine f o s s i l s i n the o v e r l y i n g sedimentary rocks i n d i c a t e t h a t the subaqueous medium was marine. The abundance of b a r i t e and other oxygen-bearing gangue m i n e r a l s , mainly i r o n oxides and carbonates, i n the s t r a t i f o r m ore and e n c l o s i n g host r o c k s , i n d i c a t e s t h a t oxygenated, s u l f a t e - l a d e n sea-water must have been a v a i l a b l e c l o s e to the s i t e of m i n e r a l i z a t i o n and f u r t h e r supports a shallow d e p o s i t i o n a l environment. The b a s i n i s about 3km a c r o s s when r e c o n s t r u c t e d ( F i g s . 5.1 to 5.3), but o n l y the east-west dimension has been e x p l o r e d — n o r t h - s o u t h extent and v e r t i c a l s c a l e are unknown. The b a s i n i n t o which hydrothermal f l u i d s were exhaled was probably s t r a t i f i e d , with anoxic bottom waters o v e r l a i n by o x i c s u r f a c e waters. P r e c i p i t a t i o n of s u l f i d e m i n e r a l s o c c u r r e d d u r i n g the quenching of the hydrothermal s o l u t i o n s with seawater under r e d u c i n g , anoxic c o n d i t i o n s , a t or near the sediment-seawater i n t e r f a c e . The oxygen-bearing gangue m i n e r a l s , however, were p r e c i p i t a t e d subsequently from o x i c seawater. Abundant o x i d e s , p a r t i c u l a r l y hematite, i n the s t r a t i f o r m m i n e r a l i z e d beds, a l s o i n d i c a t e s t h a t the redox 115 boundary between anoxic and o x i c waters must have been a c c e s s i b l e to the hydrothermal f l u i d s . T h i s might be r e l a t e d a l s o to the marked decrease i n massive s u l f i d e m i n e r a l i z a t i o n away from the D o l l y Varden East d e p o s i t . M i n e r a l zoning w i t h i n and between m i n e r a l i z e d s t r a t i f o r m d e p o s i t s of the D o l l y Varden camp can be e x p l a i n e d by p r o g r e s s i v e changes i n s o l u t i o n chemistry and p h y s i c a l c o n d i t i o n s as the hot e x h a l a t i v e f l u i d mixes with c o l d sea-water on or near s e a - f l o o r . The development of v e r t i c a l m i n e r a l z o n a t i o n , such as t h a t observed i n the N o r t h s t a r d e p o s i t ( F i g . 3.13), p o s s i b l y i s r e l a t e d to i n i t i a l p r e c i p i t a t i o n of p y r i t e i n the f o o t w a l l from h i g h temperature f l u i d s and subsequent p r e c i p i t a t i o n of s p h a l e r i t e and galena from c o o l e r f l u i d s to form the upper p a r t of the d e p o s i t (Sato, 1977; Large, 1977; Ohmoto et a l . , 1983). A l t e r a t i o n accompanied by replacement may a l s o c o n t r i b u t e to the o v e r a l l z o n a t i o n . The s p e c t a c u l a r asymmetrical l a t e r a l z o n a t i o n of the gangue mi n e r a l s among the m i n e r a l i z e d s t r a t i f o r m D o l l y Varden d e p o s i t s , however, might be r e l a t e d to a b a s i n shape t h a t shallows to the ea s t and west away from the D o l l y Varden East d e p o s i t . Thus, as the e x h a l a t i v e f l u i d moved away from the deeper emanative c e n t e r i n t o a s h a l l o w i n g s e a - f l o o r environment, the gangue and a s s o c i a t e d s u l f i d e m i n e r als were d e p o s i t e d and d i f f e r e n t i a t e d 116 i n t o d i s t i n c t ore f a c i e s (Table 3.1, F i g s . 3.9 to 3.18; c f . R i d l e r , 1970 and 1973, and R i d l e r and S h i l t s , 1974). These are r e p r e s e n t e d by an i n n e r s u l f i d e f a c i e s ( D o l l y Varden E a s t ) , a marginal carbonate f a c i e s ( D o l l y Varden West and N o r t h s t a r ) , and an o u t e r oxide f a c i e s ( T o r b r i t and Moose-Lamb). The D o l l y Varden E a s t d e p o s i t p o s s i b l y o v e r l i e s stockwork q u a r t z - p y r i t e m i n e r a l i z a t i o n and i s c o n s i d e r e d to be proximal to the e x h a l a t i v e vent, whereas the w e l l l a y e r e d m i n e r a l i z a t i o n of the T o r b r i t and Moose-Lamb d e p o s i t s r e p r e s e n t s d i s t a l , s h allower d e p o s i t i o n . D e n s i t y d i f f e r e n c e between sea-water and ore s o l u t i o n s , along with the p o s s i b l e f o r m a t i o n of a buoyant plume above the e x h a l a t i v e vent, can be other important f a c t o r s i n the d i s t r i b u t i o n of the hydrothermal f l u i d s (Sato, 1977; Turner and Gustafson, 1978). Laminated m i n e r a l i z a t i o n probably r e s u l t e d from r e p e a t e d e x h a l a t i v e p u l s e s t h a t generated o s c i l l a t o r y flow of the ore s o l u t i o n s away from the emanative cent e r (Turner and Gustafson, 1978). Temperature, another important f a c t o r i n the development of l a t e r a l m i n e r a l z o n a t i o n , l i k e l y made a major c o n t r i b u t i o n to s i l v e r d i s t r i b u t i o n . There i s a decrease i n s i l v e r content of the s t r a t i f o r m ores away from the h i g h grade D o l l y Varden E a s t d e p o s i t , through the moderate to h i g h grade N o r t h s t a r and T o r b r i t d e p o s i t s , to the lower grade D o l l y Varden West and Moose-Lamb d e p o s i t s . Since s i l v e r grade appears to be t e m p e r a t u r e - r e l a t e d , s i l v e r d i s t r i b u t i o n i n the s t r a t i f o r m ores may imply a g r a d i e n t i n which s i l v e r grade decreases with 117 temperature as the hydrothermal f l u i d s move away from the e x h a l a t i v e vent. 118 6.0 CONCLUSIONS D e t a i l e d f i e l d mapping was paramount i n r e s o l v i n g the geology and genesis of d e p o s i t s i n the D o l l y Varden s i l v e r camp. Pre v i o u s attempts to map the a r e a g e o l o g i c a l l y had been hi n d e r e d by the ruggedness and i n a c c e s s i b i l i t y of the t e r r a i n , compounded by inadequate topographic base maps f o r the K i t s a u l t R i v e r a r e a . Thus, most of the e a r l i e r s t u d i e s had to be l i m i t e d t o i n d i v i d u a l d e p o s i t s and pr o s p e c t s w i t h i n the camp. H e l i c o p t e r -a s s i s t e d mapping on an orthophoto base by the w r i t e r over two f i e l d seasons, however, overcame these o b s t a c l e s and r e s u l t e d i n the f i r s t d e t a i l e d c o m p i l a t i o n of the geology of the D o l l y Varden camp. Work by the w r i t e r , here, a l s o was the f i r s t study i n the D o l l y Varden camp s i n c e s t r o n g v o l c a n o g e n i c models have been developed. Most of the s i g n i f i c a n t c o n t r i b u t i o n s to c u r r e n t g e n e t i c models were made d u r i n g the 1970's, a f t e r completion of the e a r l i e r g e o l o g i c a l s t u d i e s i n the D o l l y Varden camp. Using v o l c a n o g e n i c models, i t was p o s s i b l e to d e f i n e p r o s p e c t s i n the camp w i t h i n a modern o r e - d e p o s i t framework. T h i s r e v e a l e d t h a t : (1) although s i l v e r - b a s e metal and g o l d - s i l v e r - c o p p e r v e i n s are present i n the D o l l y Varden camp, t h i s m i n e r a l i z a t i o n does not occur c l a s s i c a l l y i n e p i t h e r m a l v e i n s , as proposed by e a r l i e r workers; (2) the main m i n e r a l occurrences can be r e c o n s t r u c t e d along block f a u l t s to form one continuous ore h o r i z o n t h a t conforms to s t r a t i g r a p h y , and (3) f e a t u r e s of the s t r a t i f o r m 119 l a y e r are c o n s i s t e n t with a v o l c a n o g e n i c o r i g i n . Evidence f o r a vo l c a n o g e n i c o r i g i n f o r the main m i n e r a l occurrences i n c l u d e s : the c o n f o r m i t y of l a y e r e d m i n e r a l i z a t i o n with s t r a t i g r a p h y , l a t e r a l and v e r t i c a l m i n e r a l z o n a t i o n p a t t e r n s , c o n s i s t e n t hangingwall versus f o o t w a l l c o n t a c t r e l a t i o n s h i p s , fragments of s t r a t i f o r m ore w i t h i n t u f f a c e o u s v o l c a n i c rocks of the hangingwall, c o n s i s t e n t d i f f e r e n c e s i n the s t a b l e i s o t o p i c compositions of the s u l f i d e s v ersus b a r i t e , quartz and carbonate gangue, and the J u r a s s i c " f i n g e r p r i n t " f o r the l e a d - b e a r i n g d e p o s i t s of the D o l l y Varden camp. R e c o g n i t i o n of the s t r a t i f o r m and v o l c a n o g e n i c c h a r a c t e r of the D o l l y Varden d e p o s i t s i s of s p e c i a l importance because of i t s p o s i t i v e e x p l o r a t i o n i m p l i c a t i o n s . The most important of these i s t h a t s t r u c t u r a l b l o c k s h o s t i n g s t r a t i f o r m o r ebodies are c o n f i n e d by two major s e t s of f a u l t s . So f a r , f i v e s i g n i f i c a n t s t r u c t u r a l b l o c k s have been i d e n t i f i e d ; they host the f o l l o w i n g ore zones: D o l l y Varden West, D o l l y Varden E a s t , N o r t h s t a r , T o r b r i t , and Moose-Lamb. Three of these b l o c k s , D o l l y Varden E a s t , N o r t h s t a r and T o r b r i t , have been mined. S e v e r a l other p r o s p e c t s , e s p e c i a l l y the South Musketeer and K i t s o l , are probable e x t e n s i o n s of the s t r a t i f o r m l a y e r . C o n t i n u a t i o n of the known ore zones, p a r t i c u l a r l y northward, i s l i k e l y . M i n e r a l zoning, r e l a t e d to b a s i n c o n f i g u r a t i o n and ore c o n t r o l s i n i t s g e n e s i s , was another key f a c t o r i n the r e c o g n i t i o n of the vo l c a n o g e n i c nature of these d e p o s i t s . The s e t t i n g u n r a v e l l e d here w i l l undoubtedly b e n e f i t the search f o r ext e n s i o n s of known 120 ore d e p o s i t s i n the camp; i t may a l s o h e l p focus e x p l o r a t i o n on d e p o s i t s elsewhere i n Hazelton Group rocks i n western B r i t i s h Columbia. In summary, g e o l o g i c a l mapping, combined with p e t r o l o g i c , p e t r o g r a p h i c and i s o t o p i c data, i n d i c a t e t h a t the s t r a t i f o r m s i l v e r - l e a d - z i n c - b a r i t e m i n e r a l i z a t i o n i n the D o l l y Varden camp probably formed as submarine e x h a l a t i v e d e p o s i t s a s s o c i a t e d with E a r l y to Middle J u r a s s i c c a l c - a l k a l i n e a n d e s i t i c v o l c a n i s m of the Hazelton Group. T h i s g e o l o g i c a l s e t t i n g f o r s t r a t i f o r m m i n e r a l i z a t i o n i s s i m i l a r to t h a t f o r other v o l c a n i c - h o s t e d , submarine e x h a l a t i v e d e p o s i t s , and t h e r e f o r e belong to the worldwide c l a s s of v o l c a n o g e n i c massive s u l f i d e d e p o s i t s . The D o l l y Varden d e p o s i t s , however, d i s p l a y a combination of unique f e a t u r e s not g e n e r a l l y found i n other v o l c a n o g e n i c d e p o s i t s . One of the most o u t s t a n d i n g f e a t u r e s i s the w e l l developed l a t e r a l z o n a t i o n of ore f a c i e s , from the i n n e r s u l f i d e , through marginal carbonate, to out e r oxide f a c i e s . T h i s probably r e p r e s e n t s a b a s i n s h a l l o w i n g away from the e x h a l a t i v e vent. The l a r g e b a s i n , over 3km a c r o s s , and the e x t e n s i v e s t r a t i f o r m h o r i z o n t h a t accumulated w i t h i n i t , are other e x c e p t i o n a l f e a t u r e s of the D o l l y Varden d e p o s i t s . The preponderance of oxide m i n e r a l s over s u l f i d e m i n e r a l s i n the ore, a l s o i s unique and p o s s i b l y i n d i c a t e s t h a t the d e p o s i t i o n a l b a s i n i s shallow. T h i s f e a t u r e a l s o makes i t d i f f i c u l t t o c l a s s i f y these d e p o s i t s as massive s u l f i d e s , because by d e f i n i t i o n , the s t r a t i f o r m p o r t i o n of these d e p o s i t s should be composed of a t l e a s t 60 121 percent s u l f i d e m i n e r a l s (Sangster and S c o t t , 1976 i n F r a n k l i n et a l . , 1981). S t r a t i f o r m d e p o s i t s i n the D o l l y Varden camp, however, average on l y about 15 percent s u l f i d e m i n e r a l s , with the remainder of the h o r i z o n comprised of mainly quartz and carbonate, with l e s s e r b a r i t e , hematite and magnetite. E x t r a o r d i n a r y s i l v e r grades r e p r e s e n t another unique f e a t u r e of the D o l l y Varden camp o r e s . High s i l v e r grades and many of the other f e a t u r e s of the s t r a t i f o r m D o l l y Varden ores d e s c r i b e d above, may r e l a t e t o i t s unique, a n d e s i t i c t e c t o n o s t r a t i g r a p h i c s e t t i n g , and to i t s d e p o s i t i o n a l temperature. The combination of a l l of the above-mentioned f e a t u r e s makes i t d i f f i c u l t to pigeonhole the s t r a t i f o r m s i l v e r - l e a d -z i n c - b a r i t e d e p o s i t s of the D o l l y Varden camp i n t o any e s t a b l i s h e d g e n e r a l i z e d v o l c a n o g e n i c model. T h e r e f o r e , the D o l l y Varden d e p o s i t s p o s s i b l y d i s p l a y c r i t e r i a f o r c l a s s i f i c a t i o n of a new, p r e v i o u s l y unrecognized, s t r a t i f o r m and vol c a n o g e n i c d e p o s i t type t h a t i s i d e n t i f i e d as " D o l l y Varden type". 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Geology, v. 20, p. 325-343. 130 APPENDIX J STABLE ISOTOPE FRACTIONATION EQUATIONS uxygen 1 . Quartz-Water (250 to 500oC) 103lnc< = 3.34(106/T2) - 3.31 ref. Matsuhisa et a l . , 1979 2. Barite-Water (110 to 350oC) 103ln « = 3.01(106/T2) - 7.30 ref. Kusakabe and Robinson, 1977 3. Calcite-Water (0 to 500oC) 103ln <* = 2.78(10B/T2) - 2.B9 ref. Friedman and O'Neil, 1977 4. Witherite-Water (0 to 500oC) 103lnc< = 2.57(10B/T2) - 4.23 ref. Friedman and O'Neil, 1977 5. Quartz-Barite 103ln<< = 0.33(10B/T2) + 3.99 determined by subtracting (2) from (1) above 6. Quartz-Calcite 103lnoC = D.56(106/T2) - 0.42 determined by subtracting (3) from (1) above 7. Quartz-Witherite 103lnoc = 0.77(106/T2) + 0.92 determined by subtracting (4) from (1) above 8. Calcite-Witherite 103ln oc = 0.21(106/T2) + 1.34 determined by subtracting (4) from (3) above Sulfur 9. Sphalerite-Galena 103lnoc = 0.72(10B/T2) ref. Ohmoto and Rye, 1979 10. Pyrite-Galena 1D3lnoC = 1.02(10B/T2) ref. Ohmoto and Rye, 1979 11. Pyrite-Sphalerite 103ln <* = 0.30(10B/T2) ref. Ohmoto and Rye, 1979 12. Sulfates-Pyrite 103lnc< = 4.67(106/T2) + 6.00 ref. Ohmoto and Rye, 1979 13. Sul fates-Galena 103ln oC = 3.65(106/T2) + 6.00 determined by subtracting (10) from (12) aboi 14. Sul fates-Sphalerite 103lnoC = 4.37(106/T2) + 6.00 determined by subtracting (11) from (12) abo\ 

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