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Galena lead isotope study of mineral deposits in the Eagle Bay Formation, southeastern British Columbia 1986

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GALENA LEAD ISOTOPE STUDY OF MINERAL DEPOSITS IN THE EAGLE BAY FORMATION, SOUTHEASTERN BRITISH COLUMBIA by FRANCOISE MELANIE GOUTIER B.Sc UNIVERSITE DE MONTREAL, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER, 1986 @ F r a n c o i s e Melanie G o u t i e r , 1986 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. 1 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) ABSTRACT The Eagle Bay Formation i n the Adams Plateau-Clearwater area, 35km nort h e a s t of Kamloops, hosts s e v e r a l economic and sub-economic m i n e r a l i z e d occurrences. The age and genesis of these mineral d e p o s i t s can be estimated by using a s p e c i f i c growth curve which d e p i c t s the l e a d e v o l u t i o n f o r the Eagle Bay Formation. T h i s curve, named the remodeled curve, represents a l o c a l d e v i a t i o n from the average 'shale' curve of Godwin and S i n c l a i r (1982) f o r the autochthonous p a r t of the Canadian C o r d i l l e r a . This remodeled curve i s s p e c i f i c a l l y a p p l i c a b l e to the Adams Plateau-Clearwater area. The le a d i s o t o p e data from the d e p o s i t s of the Eagle Bay Formation p l o t i n three d i s t i n c t c l u s t e r s along the curve i n d i c a t i n g that the le a d i s o t o p i c s i g n a t u r e of the Eagle Bay Formation i s upper c r u s t a l , and that three p e r i o d s of m i n e r a l i z a t i o n can be recog n i z e d or ' f i n g e r p r i n t e d ' . A c c o r d i n g l y , m i n e r a l i z a t i o n oogenetic with Devonian volcanism, and veins r e l a t e d to Cretaceous magmatism can be d i s t i n g u i s h e d by l o c a t i o n of g a l e n a - l e a d isotope values w i t h i n c l u s t e r s 1 or 3 r e s p e c t i v e l y . C l u s t e r 2 r e f l e c t s a Late T r i a s s i c pulse of m i n e r a l i z a t i o n and i n c l u d e s e p i g e n e t i c veins and s t r a t i f o r m d e p o s i t s . These d e p o s i t s are e i t h e r replacement or oogenetic with t h e i r host. The T r i a s s i c model age f o r m i n e r a l i z a t i o n t h at i s apparently s t r a t i f o r m and oogenetic r a i s e s questions about the c u r r e n t l y assigned Cambrian age of a s s o c i a t e d host rock. To accommodate the l e a d isotope data a new Upper T r i a s s i c u n i t (T-EBG) w i t h i n the Eagle Bay Formation i s d e f i n e d . The d i s t i n c t i v e l e a d i s o t o p i c s i g n a t u r e between d e p o s i t s hosted by the Eagle Bay Formation i s v a l u a b l e as a guide f o r f u t u r e mineral e x p l o r a t i o n programs i n the Adams P l a t e a u - Clearwater area. R e c o g n i t i o n of l e a d i s o t o p i c f i e l d s t h a t f i n g e r p r i n t types of mineral d e p o s i t s , provides a u s e f u l and p r a c t i c a l framework f o r the c l a s s i f i c a t i o n and e v a l u a t i o n of new m i n e r a l i z e d prospects i n the area. i i i Table of Contents ABSTRACT i i LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGMENTS i x 1. GENERAL INTRODUCTION 1 2. GENERAL GEOLOGY OF THE ADAMS PLATEAU- CLEARWATER AREA 4 2.1 INTRODUCTION 4 2.2 STRATIGRAPHY 9 2.3 INTRUSIONS 13 2.3.1 DEVONIAN INTRUSIONS . 13 2.3.2 CRETACEOUS INTRUSIONS 14 2.3.3 LAMPROPHYRE DYKES 17 2.4 STRUCTURE 17 2.4.1 PRE-JURASSIC STRUCTURES 18 2.4.2 JURASSIC STRUCTURES 18 2.4.3 CRETACEOUS STRUCTURES 19 2.4.4 TERTIARY STRUCTURES 20 3. LEAD ISOTOPE SYSTEMATICS 22 3.1 HISTORY OF LEAD ISOTOPE INTERPRETATION 22 3.2 BASIC PRINCIPLES AND EQUATIONS 26 3.3 ANALYTICAL PROCEDURES 31 i v 3.3.1 SAMPLE DESCRIPTION 31 3 .3 .2 ANALYTICAL PRECISION 31 3 .3 .3 CALCULATION OF AVERAGE VALUES FOR THE DEPOSITS 34 3.4 THE REMODELED CURVE FOR THE EAGLE BAY FORMATION 39 3.4.1 DEPARTURE TIME, INITIAL COMPOSITION AND U VALUE 47 3 .4 .2 W VALUE 51 3 .4 .3 SUMMARY 52 3.5 MODEL AGE DETERMINATION 53 4. LEAD ISOTOPES, MINERAL DEPOSITS AND STRATIGRAPHY .- 55 4.1 INTRODUCTION 55 4.2 CLUSTER 1: DEVONIAN COGENETIC DEPOSITS 58 4.3 LEAD DATA BETWEEN CLUSTER 1 & 2 63 4.4 CLUSTER 2: TRIASSIC STRATIFORM AND VEIN DEPOSITS 64 4.4.1 DEPOSITS GEOLOGY 64 4 .4 .2 MULTIPLE INTERPRETATION OF LEAD DATA 70 4 . 4 . 3 SUMMARY 80 4.5 LEAD DATA BETWEEN CLUSTER 2 & 3 80 4.6 CLUSTER 3: CRETACEOUS VEINS 83 v 4.7 LEAD DATA BEYOND CLUSTER 3 87 4.8 SUMMARY 88 5. CONCLUSIONS 90 REFERENCES CITED 93 APPENDIX A 103 APPENDIX B 147 APPENDIX C 149 v i LIST OF TABLES TABLE 3.0 Equations used i n lead i s o t o p i c model c a l c u l a t i o n 28 TABLE 3.1 S t a t i s t i c s r e l a t e d to the c a l c u l a t i o n of mass f r a c t i o n a t i o n f a c t o r s u sing Broken H i l l Standard (BHS:UBC1) 33 TABLE 3.2 Rep r e s e n t a t i v e c a l c u l a t i o n of average galena lead i s o t o p i c values f o r a given d e p o s i t 35 TABLE 3.3 Average galena l e a d isotope values f o r ore de p o s i t s i n the Eagle Bay Formation 37 TABLE 3.4 Lead i s o t o p e values f o r the remodeled shale curve 48 TABLE 4.0 C l a s s i f i c a t i o n and name of d e p o s i t s w i t h i n d i s c r e t e c l u s t e r s of data d e f i n e d i n F i g u r e s 3.3 t o 3.5 56 TABLE A.l M i n e r a l d e p o s i t s i n the Adams P l a t e a u area d e s c r i b e d i n appendix A 104 v i i LIST OF FIGURES FIGURE 1.0 G e n e r a l i z e d t e c t o n i c map of the Canadian C o r d i l l e r a 2 FIGURE 2.0 Regional g e o l o g i c map of the Adams P l a t e a u - Clearwater area 5 FIGURE 2.1 Geology of the Eagle Bay Formation showing major rock u n i t s and f a u l t s 10 FIGURE 3.0 Model e v o l u t i o n of l e a d with time. A: Diagram 207pb/204p D vs. 206pb/204pb B: Diagram 208pb/204pb v s . 206pb/204pb 23 FIGURE 3.1 Schematic e v o l u t i o n of the le a d i n galena from the Eagle Bay Formation 29 FIGURE 3.2 207pb/204pb vs. 206pb/204pb diagram showing the i s o t o p i c d i s t r i b u t i o n of a l l analyses from the B i r k Creek area 36 FIGURE 3.3 207pb/204pb vs. 206pb/204pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3 41 FIGURE 3.4 208pb/204pb vs. 206pb/204pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3 43 FIGURE 3.5 206pb/208pb vs. 206pb/207pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3 45 FIGURE 4.0 Geology of the Eagle Bay Formation with l o c a t i o n of the sampled mineral d e p o s i t s 59 FIGURE 4.1 Folded m i n e r a l i z e d l a y e r s , Lucky Coon d e p o s i t 67 FIGURE A.1 Map of the Homestake pro p e r t y 121 FIGURE A.2 Lower hemisphere equal area p r o j e c t i o n of s t r u c t u r a l elements, Homestake d e p o s i t area 123 FIGURE A.3 V e r t i c a l s e c t i o n (97+00) through the RG 8 s u l p h i d e b a r i t e l e n s , Rea Gold d e p o s i t 126 FIGURE A.4 Equal area p r o j e c t i o n s onto lower hemisphere of s t r u c t u r a l elements Rea Gold d e p o s i t 128 FIGURE A.5 D e t a i l e d s e c t i o n s A-A 1 and B-B' from the north s i d e of B i r k Creek area 131 v n i ACKNOWLEDGEMENTS I acknowledge the B r i t i s h Columbia M i n i s t r y of Energy, Mines and Petroleum Resources f o r f i n a n c i a l support of f i e l d work. Many from the M i n i s t r y were h e l p f u l . I am p a r t i c u l a r l y g r a t e f u l to Trygve Hoy, with whom i t was a pleasure to work, f o r hi s encouragement and su p p o r t i v e a t t i t u d e , and to Paul S c h i a r i z z a f o r ideas and c r i t i c a l d i s c u s s i o n s which i n f l u e n c e d my t h i n k i n g throughout t h i s r e s e a r c h . Sincere thanks are extended to my ad v i s o r Dr. C.I. Godwin for h i s d i r e c t i o n , encouragement and s u p e r v i s i o n of my t h e s i s , and to Dr. R.L. Armstrong f o r p r o v i d i n g access to h i s Geo c h r o n o l o g i c a l Laboratory at The U n i v e r s i t y of B r i t i s h Columbia. I wish to thank a l l students, f a c u l t y and s t a f f members i n the department of G e o l o g i c a l Sciences who c o n t r i b u t e d by t h e i r knowledge and f r i e n d s h i p to the completion of t h i s t h e s i s . I a l s o thank Alex Davidson and Ian P i r i e of C o r p o r a t i o n F a l c o n b r i d g e Copper and Glen Shevchenko of Noranda E x p l o r a t i o n Co. L t d . f o r t h e i r a v a i l a b i l i t y and f o r d i s c u s s i n g some aspects of t h i s p r o j e c t with me. The i n f o r m a t i o n and galena samples they p r o v i d e d are g r e a t l y a p p r e c i a t e d . i x 1 1. GENERAL INTRODUCTION The Eagle Bay Formation i s i n the Adams Plateau-Clearwater area, centred 35km no r t h e a s t of Kamloops i n southeastern B r i t i s h Columbia ( F i g . 1.0). The formation i s a multiply-deformed sequence of low-grade meta-sediments and v o l c a n i c rocks stacked as i m b r i c a t e d s l i c e s on the southwestern f l a n k of the Shuswap Metamorphic Complex. I t hosts s e v e r a l economic and sub-economic l e a d - z i n c - s i l v e r - g o l d occurrences of v a r i o u s types and a f f i n i t i e s t h a t were i n t e r m i t e n t l y i n p r o d u c t i o n during the f i r s t h a l f of the century. Recent d i s c o v e r y of the p o l y m e t a l l i c Rea Gold d e p o s i t , a g o l d - a r s e n o p y r i t e - r i c h volcanogenic Kuroko type d e p o s i t near Johnson Lake, regenerated i n t e r e s t i n the area by p r o v i d i n g evidence of p o t e n t i a l l y s i g n i f i c a n t economic m i n e r a l i z a t i o n . T h i s t h e s i s was i n i t i a t e d to assess whether galena l e a d i sotope s t u d i e s would a i d i n t e r p r e t a t i o n s of the nature and age of the d i f f e r e n t d e p o s i t s o c c u r r i n g w i t h i n the Eagle Bay Formation. I t a l s o was intended to pr o v i d e a p r a c t i c a l and u s e f u l framework f o r g u i d i n g e x p l o r a t i o n programs i n the Adams Plateau-Clearwater area. Observations (and i n some cases d e t a i l e d mapping) were made on 37 m i n e r a l i z e d occurrences which were sampled f o r t h i s study (Appendix A). F i e l d work was conducted over the summers of 1984 and 1985. Remains from past 2 F i g u r e 1.0. G e n e r a l i z e d t e c t o n i c map of the Canadian C o r d i l l e r a showing the major s t r u c t u r a l d i v i s i o n s and l o c a t i o n of the study area ( a f t e r Wheeler and G a b r i e s l e , 1972). 3 mining a c t i v i t i e s and log g i n g roads i n the area f a c i l i t a t e d access to the v i s i t e d p r o p e r t i e s . The f i r s t p a r t of t h i s study presents an overview of the geology of the Eagle Bay Formation and of adjacent areas. The second p a r t o u t l i n e s the b a s i c p r i n c i p l e s which govern uses of the common l e a d method f o r model age d e t e r m i n a t i o n s . A remodeled v e r s i o n of the 'shale' growth curve of Godwin and S i n c l a i r (1982) i s used to i n t e r p r e t the le a d i s o t o p i c data from d e p o s i t s hosted by the Eagle Bay Formation. The t h i r d p a r t of t h i s t h e s i s i n t e r p r e t s galena l e a d model ages of d e p o s i t s d e f i n e d by the remodeled curve. I m p l i c a t i o n s of the c l u s t e r i n g of the data i n t o three d i s t i n c t groups (Devonian, T r i a s s i c and mid-Cretaceous) are presented. The di s c r e p a n c y between T r i a s s i c l ead model age obtained f o r s e v e r a l s t r a t i f o r m d e p o s i t s and t h e i r g e o l o g i c a l s e t t i n g i s d i s c u s s e d , and leads to the i n t e r p r e t a t i o n t h a t i f the m i n e r a l i z a t i o n i s not of T r i a s s i c replacement type, but r a t h e r oogenetic with i t s host then the s t r a t i g r a p h y of the Eagle Bay Formation should i n c l u d e a T r i a s s i c u n i t . The r e s u l t s are fundamental to g e o l o g i c a l understanding and to mineral e x p l o r a t i o n i n the Adams Plateau-Clearwater area. 4 2. GENERAL GEOLOGY OF THE ADAMS PLATEAU-CLEARWATER AREA 2.1 INTRODUCTION M i n e r a l d e p o s i t s and o c c u r r e n c e s i n the Adams P l a t e a u - C l e a r w a t e r area are h o s t e d by the E a g l e Bay F o r m a t i o n , which i s composed of a m u l t i p l y deformed sequence of low-grade meta- sediments and v o l c a n i c r o c k s . The E a g l e Bay F o r m a t i o n l i e s w i t h i n Kootenay Terrane (Monger, 1985) a l o n g the western f l a n k of the Monashee Terrane i n the Omineca B e l t ( F i g . 2.0). The E a g l e Bay F o r m a t i o n ranges i n age from Cambrian t o Permian ( S c h i a r i z z a and P r e t o , 1984). However, as d e f i n e d i n t h i s t h e s i s i t c o n t a i n s r o c k s t h a t may be as young as Upper T r i a s s i c . Much of the a r e a a d j a c e n t t o and e a s t of the Eagle Bay F o r m a t i o n i s c a l l e d the N o r t h w e s t e r n Shuswap Complex ( O k u l i t c h , 1984). T h i s complex, a l o n g w i t h the Monashee Complex (Read and Brown, 1981) and the Okanagan P l u t o n i c and Metamorphic Complex, i s p a r t of the l a r g e r Shuswap Metamorphic Complex t h a t c u r r e n t l y i s i n c l u d e d i n Monashee Terrane (Monger, 1985). The boundary between the E a g l e Bay F o r m a t i o n and the N o r t h w e s t e r n Shuswap Complex now i s r e c o g n i z e d t o be a low a n g l e detachment f a u l t r a t h e r than a metamorphic or i n t r u s i v e c o n t a c t (Brock, 1934; F y s o n , 1970). T h i s f a u l t , named the E a g l e R i v e r f a u l t i n r e c e n t 5 Figure 2.0 Regional geologic map of the Adams Plateau- Clearwater area showing the location of the Eagle Bay Formation r e l a t i v e to other major formations and groups, majors intrusions, and regionaly important faults (modified: from Okulitch and Cameron, 1976; Journeay, 1986; Jung, 1986). 6 LEGEND Jurassic & Cretaceous I***;*) Granitic rocks Upper Triassic | NCL | Undiff. Nicola Group rocks Upper Triassic and older Eagle Bay Formation 1 FNL | Fennell Formation Undetermined age j Sicamous Formation Undiff. Paleozoic rocks Undiff. Paleoz. intrusives Und SYMBOLS High angle faults Eagle River Detachment Quesnel Lake thrust 0.7060 initial 8 7 S r / 8 6 S r ratio, isotopic contour line 7 mapping (Journeay, 1986; F i g . 2.0), i s i n t e r p r e t e d as the break-away zone f o r the southern Okanagan detachment (Journeay, 1986) and t h e r e f o r e i s p a r t of the major e x t e n s i o n a l f a u l t system r e l a t e d to the Eocene thermal event i d e n t i f i e d i n s o u t h - c e n t r a l B r i t i s h Columbia (Ross, 1974; Journeay, 1986: Coney, 1980; Tempelman-Kluit, 1984; Bardoux, 1984; Parkinson, 1985; P a r r i s h , 1985). The Eagle Bay Formation i s bordered on the west by the F e n n e l l Formation of the S l i d e Mountain Group (Campbell and Ti p p e r , 1971). The F e n n e l l Formation i s composed of an oceanic assemblage of p i l l o w e d b a s a l t s , d i o r i t e and r i b b o n c h e r t s (Uglow, 1 9 2 2 ) . These two formations are separated by an e a s t e r l y d i r e c t e d t h r u s t f a u l t ( O k u l i t c h , 1979; S c h i a r i z z a and Preto, 1984). To the south the formation i s i n f e r r e d to be i n f a u l t contact with the Upper T r i a s s i c ( ? ) Sicamous Formation ( O k u l i t c h , 1 984 ; Daughtry i n Preto et a_l.,1985; see s e c t i o n 4.4.3). The formation i s t r u n c a t e d to the north by the Raft b a t h o l i t h ( F i g . 2 . 0 ) . Monashee Terrane (Monger, 1986) i s exposed i n a s e r i e s of domal metamorphic complexes. Each i s c h a r a c t e r i z e d by a core of o l d e r metamorphic p l u t o n i c basement, which e i t h e r crops out or i s covered by polydeformed and r e g i o n a l l y metamorphosed mixed sequences of sedimentary and v o l c a n i c rocks (Brown and Read, 8 1983; Coney, 1980). Rocks w i t h i n the complexes range i n age from p o s s i b l y Archean to e a r l i e s t J u r a s s i c (Duncan, 1982; O k u l i t c h , 1984). The Shuswap Metamorphic Complex i s regarded as the core zone of the Columbian Orogeny which caused major d e f o r - mation i n the Omineca B e l t — a n d i n the Eagle Bay F o r m a t i o n — duri n g J u r a s s i c time (Reesor and Moore, 1970; O k u l i t c h , 1984). Unambiguous evidence f o r p r e - J u r a s s i c deformation i n the b e l t i s l a c k i n g , although some of the s t r u c t u r e s may have been generated i n previous orogenies such as Kenoran, the Hudsonian, or the East Kootenay ( O k u l i t c h , 1979). Evidence of a major Eocene thermal and e x t e n s i o n a l event i s widespread throughout the Intermontane and Omineca B e l t s . P a r r i s h (1985) argues that the un r o o f i n g of metamorphic core complexes i s p r i m a r i l y a r e s u l t of T e r t i a r y e x t e n s i o n a l t e c t o n i c s , r a t h e r than of Mesozoic compression as suggested by Brown and Read (1983). Thus, the Eagle Bay and the F e n n e l l Formations, as w e l l as the Raft and the Baldy b a t h o l i t h s , would have been l o c a t e d above the Monashee Complex at the time of t h e i r formation and would have s l i d o f f the metamorphic complex approximately 50Ma ago. The Eagle River detachment f a u l t zone (Journeay, 1986; F i g . 2.0), and numerous normal f a u l t s of T e r t i a r y age and r e l a t e d T e r t i a r y v o l c a n i c rocks ( S c h i a r i z z a , 1985; Hickson, 1986) are a l s o a t t r i b u t e d to the Eocene thermal and d e f o r m a t i o n a l event. However problems a r i s e when the 9 i n i t i a l 87sr/86sr r a t i o s of the R a f t and the Baldy b a t h o l i t h s are taken i n t o account. Values c o n s i d e r a b l y higher than those present, ranging from 0.7083 to 0.7101, are to be expected from i n t r u s i o n s t hat pass through the Monashee Complex during t h e i r ascent. Therefore, Jung (1986) argues that the present p o s i t i o n of the Raft and Baldy b a t h o l i t h s correspond to t h e i r o r i g i n a l emplacement p o s i t i o n , and t h a t i t i s improbable that they ever were l o c a t e d over the Monashee Complex. This argument i s a l s o i n agreement with the i n t e r p r e t a t i o n of O k u l i t c h (1979) t h a t the r o o t s of the b a t h o l i t h s are i n the Northwestern Shuswap Complex. 2.2 STRATIGRAPHY The Eagle Bay Formation was f i r s t mapped by Dawson (1898) as the Adams Lake and N i s c o n l i t h S e r i e s . Subsequently Daly (1915) d i v i d e d the Adams Lake S e r i e s i n t o three i n f o r m a l formations c a l l e d the Adams Lake greenstone, the T s h i n a k i n limestone, and the B a s t i o n s c h i s t s . Rice and Jones (1948) and Jones (1959) renamed many of the rocks p r e v i o u s l y i n c l u d e d i n the above s e r i e s , and d e f i n e d the Mount Ida Group w i t h i n which the Eagle Bay Formation was the youngest conformable member. The Eagle Bay formation then i n c l u d e d much of Dawson's Adams Lake S e r i e s and Daly's (1915) greenstone formation; i t contained three members: a t h i c k b a s a l s u c c e s s i o n of c h l o r i t i c s c h i s t , a mixed sedimentary sequence i n c l u d i n g the prominent T s h i n a k i n 1 0 Devonian to Permian F e n n e l l F o r m a t i o n 1 1 [ b H U p p e r s t r u c t u r a l d i v i s i o n : p i l l o w e d and m a s s i v e m e t a - b a s a l t , minor cher t I IF I L o w e r s t r u c t u r a l d i v i s i o n : p i l l o w e d and m a s s i v e m e t a - b a s a l t and r i b b o n c h e r t , l i m e s t o n e , d io r i te , g a b b r o , q u a r t z t e l d s p a r , p o r p h y r y , rhyo l i te Mississippian I E8P I P h y l l i t e and s l a t e with i n t e r b e d d e d s a n d s t o n e and gr i ts Devonian and/or Mississippian I EBF | F e l d s p a t h i c phyl l i te ( in termedia te to fe ls ic tuft) Devonian | EB.A | S e r i c i t e - q u a r t z - p h y l l i t e and s c h i s t ( in te rmed ia te to f e l s i c v o l c a n i c s and v o l c a n o c l a s t i c s ) Devonian and/or older | EBS j M i x e d m e t a - s e d i m e n t a r y s e q u e n c e ( p h y l l i t e s ) | EBG [ C a l c a r e o u s c h l o r i t e - s c h i s t . f r a g m e n t a l s c h i s t (mat ic to i n t e r m e d i a t e v o l c a n i c s ) ]j T s h i n a k i n l i m e s t o n e ^ - - ^ mixed phyl l i te ( E B C p ) f—*-j quar tz i te ( EBCq ) f | p o l y m i c t i c c o n g l o m e r a t e ( E B C c g ) | | T-EBC ( ? T r i a s s i c ) Lower Cambr ian a n d / o r older I EBQ | C h l o r i t e - m u s c o v i t e quartz i te . c h l o r i t e - m u s c o v i t e - q u a r t z sch is t and minor m e t a - s e d i m e n t s (SDQl I EBH | Quartzite, grit and chlorite-sericite-quartz schist Intrusives J u r a s s i c & C r e t a c e o u s E;;:' ;l Raft batholith. Baldy batholith, Scotch Creek plug La te Devonian | Dgn I Grani te and g r a n o d i o r i t e o r t h o g n e i s s ' 1 2 3 F o s s i l l oca l i t y : M i s s i s s i p p i a n . P e n n s y l v a n i a n , Permian f C a m b r i a n rk, z. Rb Isotopic date: K / A r , u ran ium- lead , R b / S r F a u l t s Thrust fault ( this s tudy) ^M*' Thrust fault ( S c h l a r l z z a et a l . 1984) F i g u r e 2.1 Geology of the Eagle Bay Formation showing major rock u n i t s and f a u l t s (modified from S c h i a r i z z a and Preto, 1984). 1 2 Limestone, and an upper sequence of c h l o r i t i c s c h i s t . Sub- sequent work by Campbell and Tipper (1971), O k u l i t c h (1979), S c h i a r i z z a and Preto (1984), Preto and S c h i a r i z z a (1985), and S c h i a r i z z a (1986, 1986b) r e f i n e d the understanding of the s t r a t i g r a p h y of both the Eagle Bay Formation and the adjacent F e n n e l l Formation. Recent work by Preto and S c h i a r i z z a (1985) i n d i c a t e s t h at the Eagle Bay Formation i s exposed i n four i m b r i c a t e d s l i c e s separated by southwesterly d i r e c t e d t h r u s t f a u l t s ( F i g . 2.1; S c h i a r i z z a and Preto, 1984; S c h i a r i z z a , 1986b). S t r a t i g r a p h i c ages and/or contact r e l a t i o n s h i p s e s t a b l i s h e d by S c h i a r i z z a and Preto (1984) have been modified to accommodate r e s u l t s o b tained from the l e a d i s o t o p e i n v e s t i g a t i o n of mineral d e p o s i t s o c c u r r i n g throughout the Eagle Bay Formation. D i s c u s s i o n of the l e a d i s o t o p i c composition from these d e p o s i t s , and t h e i r i m p l i c a t i o n s on the i n t e r p r e t a t i o n of the s t r a t i g r a p h y of the Eagle Bay Formation are presented i n Chapter 4. Eagle Bay Formation i s d i r e c t l y c o r r e l a t i v e with other s t r a t i g r a p h i c sequence o c c u r r i n g on the edge of the Shuswap Metamorphic Complex. O k u l i t c h (1979) has c o r r e l a t e d the Formation p a r t l y with the Cambrian to O r d o v i c i a n Lardeau Group, and p a r t l y with the younger M i l f o r d Group of the Kootenay Arc. S t r u i k (1986), based on l i t h o l o g i c , s t r u c t u r a l and age s i m i l a r i t i e s , c o r r e l a t e s the Eagle Bay Formation with both the B a r k e r v i l l e and the Kootenay Arc Terranes. S i m i l a r l y , Ross and 1 3 F i l l i p o n e ( i n press) suggest that some pa r t s of the Eagle Bay Formation, notably the b a s a l q u a r t z i t e and the prominent meta-volcanic carbonate s u c c e s s i o n , are d i r e c t l y c o r r e l a t e d with s i m i l a r rocks i n the Snowshoe Group near Crooked Lake (100km east of Williams Lake). S t r u i k (1986) proposed that a l l three s u c c e s s i o n s were d e p o s i t e d i n a s i m i l a r g e o l o g i c a l s e t t i n g . A c c o r d i n g l y , the Eagle Bay Formation i s now i n c l u d e d by Monger (1985) i n the Kootenay Terrane under " v a r i a b l y metamorphosed Lower P a l e o z o i c s t r a t a comprising p e l l i t e , q u a r t z i t e , g r i t s , b a s i c a c i d i c rocks and Devonian and (?) o l d e r i n t r u s i o n s . " 2.3 INTRUSIONS The Eagle Bay Formation has been i n t r u d e d r e p e a t e d l y . Magmatism and/or volcanism a f f e c t e d the area i n Devonian, Cretaceous and Eocene time. 2.3.1 Devonian I n t r u s i o n s M e t a - b i o t i t e g r a n o d i o r i t e , c o r r e l a t e d with the Mount Fowler o r t h o g n e i s s ( F i g . 2.1), i n t r u d e s Devonian v o l c a n i c rocks of the Eagle Bay Formation. Z i r c o n s from the b a t h o l i t h y i e l d e d upper and lower i n t e r c e p t dates on c o n c o r d i a diagrams of Devonian and of mid-Cretaceous ages ( 372+_6Ma and 92.5Ma: O k u l i t c h , 1975). S i m i l a r bodies of i n t e r m e d i a t e to f e l s i c composition, ranging i n age from Late Devonian to mid- 1 4 M i s s i s s i p p i a n (Mortensen e t a_l. , i n p r e s s ) , o c c u r throughout the Snowshoe meta-sediments i n the B a r k e r v i l l e T e r r a n e . The presence of these i n t r u s i o n s i n both the Eag le Bay Format ion and the Snowshoe Group do not p r o v e , but support c o r r e l a t i o n s between these two s u c c e s s i o n s i n r e g i o n a l l y d i s t i n c t a r e a s . An e x t r u s i v e phase of s i m i l a r c o m p o s i t i o n ( m e t a - r h y o l i t e ) found on the Beca p r o p e r t y a l s o y i e l d e d z i r c o n dates of Devonian age, 399+^1 Ma, from the upper i n t e r c e p t on a c o n c o r d i a diagram (Pre to and S c h i a r i z z a , 1985). The s i m i l a r i t i e s i n age and rock type between the Mt Fowler o r t h o g n e i s s , the f e l s i c i n t r u s i o n s , and some of the m e t a - v o l c a n i c s ( e . g . u n i t EBA, F i g . 2.1) suggest t h a t they are oogene t i c and of Devonian age. The occurrence of these v o l c a n i c and i n t r u s i v e rocks of f e l s i c a f f i n i t i e s on the western margin of the Shuswap Complex and the presence of v o l c a n o g e n i c d e p o s i t s w i t h i n the Devonian v o l c a n i c u n i t s (Rea Gold and Homestake d e p o s i t s , Appendix A ) , p r o v i d e s evidence f o r s u b d u c t i o n r e l a t e d proce s se s d u r i n g the D e v o n i a n . 2 .3 .2 Cre taceous I n t r u s i o n s The Ra f t and Ba ldy b a t h o l i t h s are e l o n g a t e d bod ie s that i n t r u d e the Eag le Bay Format ion ( F i g . 2 . 1 ) . In s e v e r a l l o c a l i t i e s , both b a t h o l i t h s are surrounded by a s t r u c t u r a l and metamorphic h o r n f e l s i c a u r e o l e i n which r e g i o n a l s t r u c t u r e s are r o t a t e d p a r a l l e l to the westward t r e n d of the i n t r u s i o n s 1 5 (Campbell and T i p p e r , 1971). Small i n t r u s i v e bodies, such as the Scotch Creek and the Deep Creek plutons as w e l l as quartz porphyry dykes or s i l l s , occur throughout the area ( F i g . 2.1). They are i n f e r r e d to be c o g e n e t i c with the Cretaceous Baldy b a t h o l i t h . Both i n t r u s i o n s , are e q u i g r a n u l a r g r a n o d i o r i t e to quartz monzonite and are s i m i l a r c h e m i c a l l y . They c o n t a i n c h l o r i t i z e d b i o t i t e as the only mafic m i n e r a l . Widespread minor concen- t r a t i o n s of s u l p h i d e minerals w i t h i n the i n t r u s i o n s i n c l u d e the g a l e n a - s p h a l e r i t e r i c h quartz veins of the Leemac property (Appendix A), and s e v e r a l molybdenite occurrences i n the B a r r i e r e Lake area r e p o r t e d i n unpublished p r o v i n c i a l open f i l e r e p o r t s a v a i l a b l e at the B r i t i s h Columbia M i n i s t r y of Energy, Mines and Petroleum Resources. Cretaceous Rb/Sr dates were obtained f o r the two b a t h o l i t h s by Jung (1986) with a f i v e p o i n t whole rock and mineral separate i s o c h r o n . A mid-Cretaceous date of 104Ma with an i n i t i a l 87sr/86sr r a t i o of 0.7060 was obtained from a sample from the western p a r t of the Raft b a t h o l i t h . A mid-Cretaceous date of 98.5+2.2Ma with i n i t i a l 87sr/86sr r a t i o of 0.7054 was obtained f o r the Baldy b a t h o l i t h . These s i m i l a r dates and i n i t i a l r a t i o s , p l u s the s i m i l a r i t y i n t e x t u r e and composition 1 6 i n d i c a t e t h a t t h e t w o b a t h o l i t h s a r e p r o b a b l y o o g e n e t i c . F u r t h e r m o r e t w o K-Ar m i d - C r e t a c e o u s d a t e s o f 99+5Ma a n d 82+6Ma w e r e o b t a i n e d b y W a n l e s s e t a ^ L . ( 1966) f o r t h e B a l d y b a t h o l i t h . S i n c e t h e K - A r d a t e s a r e c o n c o r d a n t w i t h t h e R b - S r d a t e s , t h e b a t h o l i t h s w e r e p r o b a b l y n o t s u b s t a n t i a l l y a f f e c t e d b y a n y l a t e r t h e r m a l e v e n t s . H o w e v e r , i n c o m p l e t e n e w u r a n i u m - l e a d d a t a o n z i r c o n s f r o m t h e R a f t b a t h o l i t h i n d i c a t e s s o m e u n c e r t a i n t y i n i t s a s s i g n e d m i d - C r e t a c e o u s c r y s t a l l i z a t i o n a g e ( J u n g , p e r s . c o m m . , 1 986 ) . T h e i n i t i a l 87sr/86sr r a t i o s o f a b o u t 0.7060 f o r t h e R a f t a n d B a l d y b a t h o l i t h s a r e h i g h e r t h a n t h o s e b e l o w 0.7040 f r o m b a t h o l i t h s l o c a t e d t o t h e w e s t i n t h e I n t e r m o n t a n e B e l t . V a l u e s c o m p a r a t i v e l y g r e a t e r t h a n 0.7060 a r e r e p o r t e d t o t h e e a s t i n t h e S h u s w a p M e t a m o r p h i c C o m p l e x ( J u n g , 1986). T h e i n i t i a l s t r o n t i u m i s o t o p e r a t i o o f 0.7060 p a s s e s t h r o u g h t h e E a g l e B a y F o r m a t i o n a s s h o w n o n F i g u r e 2.0. T h i s l i n e p r o b a b l y r e p r e s e n t s a t r a n s i t i o n a t d e p t h c o r r e s p o n d i n g t o t h e w e s t e r n l i m i t o f P r e c a m b r i a n b a s e m e n t r o c k s ( A r m s t r o n g , i n J u n g , 1986). T h e r e l a t i v e l y h i g h i n i t i a l 87sr/86sr r a t i o s f o r t h e R a f t a n d B a l d y b a t h o l i t h s e m p h a s i z e a g e n e t i c l i n k b e t w e e n t h e m a g m a a n d t h e o l d c r u s t a l m a t e r i a l f r o m w h i c h t h e s e b a t h o l i t h s w e r e d e r i v e d . T h e h i g h r a t i o s a p p a r e n t l y r e f l e c t t h e a d d i t i o n o f r a d i o g e n i c 87sr f r o m m a g m a g e n e r a t e d i n , o r c o n t a m i n a t e d b y , a P r e c a m b r i a n b a s e m e n t u n d e r l y i n g t h e E a g l e B a y F o r m a t i o n . T h e i n i t i a l 1 7 strontium r a t i o s are in general agreement with the lead isotopic signature of the deposits in the Eagle Bay Formation—both indicate the presence of upper cr u s t a l material beneath the formation. 2.3.3 Lamprophyre Dykes Lamprophyre dykes are widely d i s t r i b u t e d in the Adams Plateau-Clearwater area, and commonly are noted on properties where sulphide mineralization is reported (see description in Appendix A for Mosquito King, Crowfoot Mountain, and Rexspar). These dykes commonly occur along northerly trending faults and several have yielded mid-Eocene dates (dates by the Geological Survey of Canada are summarized in Jung, 1986). The relationship between these dykes and sulphide mineralization i s discussed in Chapter 4. 2.4 STRUCTURE The Eagle Bay Formation i s complexly deformed. Timing relationships often are neither clear nor consistent, although i t i s generally agreed that a l l the s t r a t i f i e d units were deformed (or re-deformed) during the Jurassic folding event related to the Columbian Orogeny (Campbell, 1973). This orogeny, associated with the accretion of a western allochthonous terrane against the Omineca belt and the craton (Monger et aJL. , 1 982), produced a pervasive f o l i a t i o n and 1 8 southwesterly d i r e c t e d t h r u s t f a u l t s . The Eagle Bay Formation subsequently was deformed and r e f o l d e d by 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 s a s s o c i a t e d to the i n t r u s i o n of the Raft and Baldy b a t h o l i t h s i n the mid-Cretaceous. L a t e r n o r t h e a s t e r l y t r e n d i n g s t r i k e - s l i p f a u l t s , as w e l l as n o r t h e r l y s t r i k i n g normal f a u l t s , cut through the major u n i t s and s t r u c t u r e s of the formation. 2.4.1 P r e - J u r a s s i c S t r u c t u r e s The f i r s t deformation of the Eagle Bay Formation may be as o l d as E a r l y Devonian as i n d i c a t e d by the presence of an e a r l y metamorphic f o l i a t i o n , which i s a x i a l planar to very r a r e , small i s o c l i n a l f o l d s ( S c h i a r i z z a , 1986). However, d i r e c t evidence of such a d e f o r m a t i o n a l event has been masked by subsequent deformation and r e g i o n a l metamorphism. J u x t a p o s i t i o n of the F e n n e l l and the Eagle Bay Formations r e s u l t e d from e a s t e r l y d i r e c t e d t h r u s t s . T h i s t h r u s t i n g event was post mid-Permian, s i n c e conodont bearing s t r a t a of mid-Permian age are repeated by the t h r u s t s . T h r u s t i n g was a l s o e a r l i e r than J u r a s s i c because the t h r u s t s are f o l d e d by s t r u c t u r e s r e l a t e d to the J u r a s s i c Columbian Orogeny ( S c h i a r i z z a and P r e t o , 1 984) . 2.4.2 J u r a s s i c S t r u c t u r e s 1 9 U n i t s of the Eagle Bay Formation e x h i b i t evidence of syn-metamorphic deformation c h a r a c t e r i z e d by: 1) p e r v a s i v e s h i s t o s i t y s u b - p a r a l l e l to the o r i g i n a l bedding and a x i a l planar to i s o c l i n a l f o l d s t h a t verge westward, and 2) lack of c o n t i n u i t y of the u n i t s along s t r i k e due to s h e a r i n g that caused t r a n s p o s i t i o n of the l a y e r i n g and d i s r u p t i o n s of i s o c l i n a l f o l d s ( D i c k i e , 1985). The Nikwikwaia Lake synform on the Adams Pl a t e a u ( F i g . 2.1) i s a l a r g e w e sterly t r e n d i n g f o l d r e l a t e d to t h i s deformation. R e d i s t r i b u t i o n of s u l p h i d e masses i n the c r e s t s of f o l d s i n d e p o s i t s i n the synform area (Appendix A: Lucky Coon, E l s i e , King Tut) i s probably r e l a t e d to t h i s event ( F i g . 4.1). A southwesterly d i r e c t e d t h r u s t i n g event e s t a b l i s h e d the present c o n f i g u r a t i o n of the u n i t s by c r e a t i n g major im b r i c a t e d panels w i t h i n the Eagle Bay Formation ( F i g . 2.1). T h i s t h r u s t i n g probably o c c u r r e d near the end of the Colombian Orogeny 2.4.3 Cretaceous S t r u c t u r e s A prominent u p r i g h t , e a s t e r l y o r i e n t e d set of f o l d s , w e l l exposed i n the v i c i n i t y of the R a f t and the Baldy b a t h o l i t h s , i s r e l a t e d to the presence of the mid-Cretaceous i n t r u s i o n s . The best examples of t h i s phase of f o l d i n g are exposed i n the Clearwater area where i n t r u s i o n s l o c a l l y change 20 the predominantly n o r t h e r l y d i p d i r e c t i o n of bedding and s h i s t o s i t y ( S c h i a r i z z a , 1986). On the Adams P l a t e a u , outcrop s c a l e f o l d s have the same e a s t e r l y o r i e n t a t i o n ; these f o l d s probably were generated d u r i n g or soon a f t e r the i n t r u s i v e event. N o r t h e a s t e r l y t r e n d i n g s t r i k e - s l i p f a u l t s , such as the B a r r i e r e Lakes and Johnson Creek f a u l t ( F i g . 2.1), cut the Eagle Bay Formation and the F e n n e l l Formation and account f o r some major s t r a t i g r a p h i c t r u n c a t i o n s . In the Scotch Creek area, some of these f a u l t s were i n t r u d e d by Cretaceous porphyry dykes and plu g s . However, i n other p l a c e s s i m i l a r f a u l t s extend i n t o the Baldy b a t h o l i t h i n d i c a t i n g that t h i s f a u l t i n g i s Cretaceous or younger. 2.4.4 T e r t i a r y S t r u c t u r e s The youngest phase of deformation, a f f e c t i n g both the Eagle Bay Formation and the adjacent F e n n e l l Formation, i s of Eocene age and i s c h a r a c t e r i z e d by open, n o r t h e r l y plunging f o l d s with u p r i g h t a x i a l p l a n e s . T h i s deformation i s r e s p o n s i b l e f o r r e g i o n a l warping of previous s t r u c t u r e s , such as the f o l d i n g of the a x i a l s u rface t r a c e of the Nikwikwaia Lake synform. The o r i e n t a t i o n of t h i s set of f o l d s i s s i m i l a r to the o r i e n t a t i o n of a set of normal f a u l t s t h a t cut a l l u n i t s of the Eagle Bay Formation. These f a u l t s do not cut the o v e r l y i n g 21 Miocene b a s a l t s ; they l o c a l l y are i n t r u d e d by T e r t i a r y b a s a l t i c and/or lamprophyre dykes. These s t r u c t u r e s probably are r e l a t e d to the T e r t i a r y e x t e n s i o n a l and thermal event. 22 3. LEAD ISOTOPE SYSTEMATICS 3.1 HISTORY OF LEAD ISOTOPE INTERPRETATION Houtermans (1946) and Holmes (1946) were among the f i r s t to t a c k l e the concept of a d d i t i o n of r a d i o g e n i c l e a d , d e r i v e d from r a d i o a c t i v e decay of uranium and thorium, to primeval l e a d and independantly d e r i v e d the fundamental equations which govern the i n c r e a s e of r a d i o g e n i c l e a d over time. The e v o l u t i o n of l e a d with time i n source regions c h a r a c t e r i z e d by d i f f e r e n t uranium and thorium contents are d e p i c t e d i n F i g u r e 3.0. With the i n c r e a s e of a v a i l a b l e data inadequacies i n the model were h i g h l i g h t e d and the term 'anomalous l e a d 1 was i n t r o d u c e d to c a t e g o r i z e ore l e a d data which gave negative or excess model ages. N e v e r t h e l e s s , a s i d e from anomalous l e a d , the i s o t o p i c composition of lead from s e v e r a l conformable ore d e p o s i t s of v a r i o u s ages were used to c o n s t r u c t a growth curve f o r con- formable ore l e a d . Stanton and R u s s e l l (1959), t h e r e f o r e proposed that t h i s curve represented the development of i s o t o p i c composition of d e p o s i t s d e r i v e d from a n e a r l y homogenous source, the upper mantle, which had maintained an almost constant U/Pb and Th/Pb r a t i o s i n c e the formation of the e a r t h . A summary paper (Kanasecwich, 1968) reviewed the the p r i n c i p l e s and the a p p l i c a b i l i t y of l e a d i s o t o p e models as known i n the l a t e 1960's. 23 Single-stage ~1 I 1 1 1 1 1 1 r- 10 12 14 16 18 2 0 6 P b / 2 ° 4 P b F i g u r e 3.0 Model e v o l u t i o n of lead with time (from Koppel and Grunenfelder, 1979). A: Diagram 207pb/204pb vs. 206pb/204pb showing s i n g l e - s t a g e growth curves with u as a parameter and s i n g l e - s t a g e i s o c h r o n s . B: Diagram 208pb/204pb vs 206pb/204pb showing s i n g l e - s t a g e growth curves with u and w as parameters. 24 Refinements of the parameters used to c a l c u l a t e the growth curve (decay constants f o r U and Th, i s o t o p i c composition of primeval l e a d , etc.) as w e l l as improvement i n l e a d chemistry and a n a l y t i c a l methods, r e s u l t e d i n the r e c a l i b r a t i o n of the curve i n the l a t e 1 960's (Stacey e t a_l. , 1 969, Cooper et a l . , 1969). The e f f e c t s of new decay constants on c a l c u l a t e d model ages were reviewed by Oversby (1974). These m o d i f i c a t i o n s emphasized the d e v i a t i o n s of the data from a s i n g l e stage curve, and demonstrated the inadequacy of such curve i n c h a r a c t e r i z i n g the e v o l u t i o n of ore l e a d through time. Se v e r a l mathematical models, i n v o l v i n g mixing of d i f f e r e n t environments and m u l t i - s t a g e growth, were then d e v i s e d to simulate average l e a d i s o t o p e e v o l u t i o n curves that f i t t e d the data more c l o s e l y . Doe and Stacey (1974) changed the parameters r e l a t e d to the age of the e a r t h used i n t h e i r c a l c u l a t i o n s and e x p l a i n e d the departure from s i n g l e stage c o n d i t i o n s by the mixing of s e v e r a l i s o t o p i c heterogeneous source m a t e r i a l s . Stacey and Kramers (1975) e s t a b l i s h e d a two-stage model i n which the departure of the second stage curve at 3.7Ga corresponded a p p a r e n t l y to a time of major c r u s t a l d i f f e r e n t i a t i o n , and g e n e r a t i o n of an uranium-enriched and of an uranium-depleted environment. Cumming and Richards (1975) gave an a l t e r n a t i v e i n t e r p r e t a t i o n to the sudden e p i s o d i c model espoused by Stacey 25 and Kramers (1975) by p r e s e n t i n g a continuous e v o l u t i o n model i n which U/Pb and Th/Pb r a t i o s c o n s t a n t l y i n c r e a s e d i n the source m a t e r i a l f o r conformable ore. F o l l o w i n g development of these e m p i r i c a l models, Doe and Zartman (1979), f o l l o w i n g Armstrong (1968) and Armstrong and Hein (1973), presented the plumbotectonic model t h a t i n c o r p o r a t e d , by means of computer modeling, g e o l o g i c a l processes r e l a t e d to p l a t e t e c t o n i c concepts with l e a d e v o l u t i o n s y s t e m a t i c s . T h e i r i d e a l i z e d model f u r n i s h e d a more g l o b a l approach to l e a d e v o l u t i o n by s i m u l a t i n g mixing between v a r i o u s d i s t i n c t environments — each c h a r a c t e r i z e d by d i f f e r e n t c o n c e n t r a t i o n s and p r o p o r t i o n s of U, Th and Pb. These environments e x i s t e d long enough to produce marked d i f f e r e n c e s i n l e a d e v o l u t i o n with time. Subsequently, Godwin and S i n c l a i r (1982) c o n s t r u c t e d the 'shale' growth curve that was s p e c i f i c a l l y a p p l i c a b l e to the autochthonous p o r t i o n of the Canadian C o r d i l l e r a c h a r a c t e r i z e d by high u/Pb and Th/Pb r a t i o s . T h i s p a r t of the C o r d i l l e r a i s upper c r u s t a l i n l e a d i s o t o p e c h a r a c t e r as d e f i n e d by Doe and Zartman ( i b i d . ) . T h i s study used a remodeled 'shale' growth curve ( c f . Godwin and S i n c l a i r (1981; 1982) to o b t a i n a b e t t e r f i t with the 26 l e a d data on galena from d e p o s i t s i n the Eagle Bay Formation. The reasons f o r these changes are d i s c u s s e d i n s e c t i o n 3.4. 3.2 BASIC PRINCIPLES AND EQUATIONS The wide range i n l e a d i s o t o p i c r a t i o s r e l a t e d to time and g e o l o g i c a l s e t t i n g and geochemical c y c l e s of l e a d , uranium and thorium p r o v i d e a u s e f u l method f o r e s t i m a t i o n s of the age and c o n d i t i o n s of formation f o r ore m a t e r i a l . The common lea d method i s based upon measurement of l e a d that has evolved through time i n one or i n s u c c e s s i v e l y c l o s e d systems or environments. I t i s assumed that these environments, c h a r a c t e r i z e d by d i s t i n c t U/Pb and Th/Pb contents, and broadly corresponding to a major source or r e s e r v o i r f o r magma gen e r a t i o n (e.g. upper mantle or c r u s t ) , have undergone an i s o l a t e d e v o l u t i o n f o r a s u f f i c i e n t length of time to a c q u i r e a s p e c i f i c i s o t o p i c s i g n a t u r e before mixing occurs between them. The t r a n s f e r of l e a d from one system to another g e n e r a l l y i m p l i e s a c t i v e g e o l o g i c a l processes (orogenic episodes, formation of new c r u s t a l segments, e t c . ) c h a r a c t e r i z e d by a change i n the U/Pb and the Th/Pb r a t i o due to the p r e f e r e n t i a l a f f i n i t i e s of uranium and thorium to upper c r u s t a l rocks compared to d e p l e t i o n i n environments i n v o l v i n g mantle and/or lower c r u s t a l m a t e r i a l s . 27 Age determinations on galena using the common lead method r e l y on the measurement of l e a d produced from uranium i s o t o p e s (206pb, 207pb), and from the thorium i s o t o p e (208pb) decay. Galena i s used because a f t e r c r y s t a l l i z a t i o n i t s l e a d i s o t o p i c composition i s 'fro z e n ' due to the absence of r a d i o a c t i v e elements i n i t s s t r u c t u r e . The amount of r a d i o g e n i c component of a sample i s computed and expressed as the r a t i o of the r a d i o g e n i c l e a d over 204pb, whos n a t u r a l abundance does not change with time. The 206pb/204pb, 207pb/204pb, 208pb/204pb r a t i o s w i l l t h e r e f o r e i n c r e a s e with time from t h e i r i n i t i a l r a t i o s from the decay of uranium and thorium. The r a t e of decay and p r o d u c t i o n of the r a d i o g e n i c i s o t o p e i s governed by the h a l f - l i f e of each parent i s o t o p e and the parent abundance. The time taken f o r the 238u to decay i n t o 206pb i s about the same as the age of the e a r t h ; thus about h a l f of the 238u isotope has decayed s i n c e the e a r t h formed. The h a l f - l i f e of 235rj i s c o n s i d e r a b l y s h o r t e r ; a c c o r d i n g l y about 75% of the p r i m o r d i a l 235rj i s o t o p e had decayed to 207pb by 3. OGa (Doe, 1970); and subsequent g e n e r a t i o n of 207pb i s s m a l l . T h i s d i f f e r e n c e i n the r a t e of i s o t o p i c p r o d u c t i o n of l e a d from these two i s o t o p e s over time i s r e f l e c t e d by the smooth f l a t t e n i n g of the i s o t o p i c growth curve toward younger ages ( F i g . 3.0). Model ages can be c a l c u l a t e d from measured i s o t o p i c r a t i o s 28 S c h e m a t i c E v o l u t i o n a r y H i s t o r y of the M u l t i - s t a g e L e a d for O r e D e p o s i t s in the Eagle Bay F o r m a t i o n 5Ga 4Ga 3Ga 2Ga 1Ga P r e s e n t 1st S tage I I I I 2nd S tage I I I 3rd S tage I I I I I I r rz T - * 1 lio n  - * 1 " h L J I ' io n  o f th e  L  / =  3 2 .2  1  c w 5 u = w = 9.74 37. 1 9 c • -5 0 W = 12.16 w = 45.35 a> j 1 </> 1 — 1 u 1 t 2 = 2 .0Ga t 1 = 3 .7Ga T = 4 .55Ga Figure 3.1 Schematic evolution of the lead in galena from the Eagle Bay Formation i s as follows (modified from Faure, 1977): system 1 starts T years ago and exists for a period of time equal to T - t i . At t i the lead is transferred to system 2 and continues to evolve during i n t e r v a l t l - t 2 . At time t2 the lead is transferred to system 3 and resides there for t2-t3 years. At t3 the lead is withdraw and fixed in galena—an environment containing no uranium or thorium--so that between t3 and present no further isotopic evolution occurs. 29 Table 3.0 Equations used i n lead isotope model c a l c u l a t i o n 1 2 (2 0 4 Pb / 2 0 4 Pb), = (2 0 6 Pb/ J 0 4 Pb)0 + u (eXs T - e X » l ) ( e X 5 T _ e A 5 l ) ( « ' P b / * o « P b ) t = (5 0 7 P b / 5 0 4 P b ) 0 + ii ^ X s T - X s t 137.88 3 ( 2 0 8 P b / J 0 4 P b ) t = ( J 0 8 P b / 3 0 4 P b ) 0 + W ( e X 2 T - e X J t ) ( 2 0 6 P b / 2 0 4 P b ) 0 = a0 = 9.307 primordial lead (= Pb isotopic composition ( 2 0 1 P b / 2 0 4 P b ) 0 =b 0 = 10.294 at timeT) ( 2 0 8 Pb. / 2 0 4 Pb) 0 =c 0 = 29.479 (Tatsumoto et a l . 1973) T = age of the Earth (calculated with the new decay constants) = 4.57 b.v. (Tilton, 1973). ( 2 0 7 P b / 2 0 4 P b ) ( - b 0 , (e X s T — e X 5 1 ) . * sT „ X 8 i , (2 0 6 P b / 2 0 4 P b ) t - a0 137.88 ' (eAs 1 - e' This is the equation of a straight line, the so-called isochjon. 7Pb 2 0 4 = b0 + Pb. ( e X sT _ e X s t ) 137.88 ( e X 8 T . . e X 8 t ) 2 06 Pb - a 0 2 0 4 Pb. / J = 2 3 8 u / 2 0 4 p b W = 2 3 2 T h / 2 0 4 p b X 8 , X s , X j : decay constants of 2 3 8 U , 2 3 S U , a n d 2 3 2 Th respectively. (see Steiger and Jager, 1977: Sub- commission on Geochronology: Convention on the use of uniform decay constants in geo- and cosmochronology; EPSL, 36, 359-362). The recommended constants are: Uranium: X ( 2 3 8 U ) = 1.55125 x 10"1 ° / y X ( J 3 5 U ) = 9.8485 x 1 0 - ' ° / y atomic ratio 2 3 8 U / 2 3 5 U = 137.88 Thorium: X ( J 3 2 T h ) = 4.9475 x 10" 1 1 /y 30 of galena by s o l v i n g equations 1 to 3 f o r t2 i n Table 3.0. To use these equations the number, and c h a r a c t e r i s t i c s of each s u c c e s s i v e environment from which l e a d was d e r i v e d must be known or approximated. Change of U/Pb and Th/Pb, due to f r a c t i o n a t i o n i n the environment from which galena was generated, i s assumed to be n e g l i g i b l e . Furthermore any model age should be i n t e r p r e t e d w i t h i n a known g e o l o g i c and t e c t o n i c framework. T h i s i s because the i s o t o p i c composition of galena i s d i r e c t l y r e l a t e d to the time and type of m i n e r a l i z i n g process which formed the galena. In some cases the l e a d system can a l s o be d i s t u r b e d by subsequent events; marked r a d i o g e n i c enrichment i n v e i n d e p o s i t s has been observed ( R u s s e l l and Farquhar, 1960; Watson, 1981), and signs of r e - e q u i l i b r a t i o n of the i s o t o p i c composition of galena due to metamorphism have been rep o r t e d i n s e v e r a l s t u d i e s (Cumming and G u r j u r d i s , 1973; Richards, 1981; B r e v a r t et a l . f 1982). E v o l u t i o n of the l e a d i n the d e p o s i t s hosted by the Eagle Bay Formation f o l l o w s a m u l t i - s t a g e h i s t o r y s c h e m a t i c a l l y d e p i c t e d i n F i g u r e 3.1. The f i r s t two stages of the l e a d e v o l u t i o n are assumed to have f o l l o w e d the Stacey and Kramers (1975) model, i n which the l e a d developed i n i t i a l l y from a primeval composition ( i n f e r r e d to be t h a t of t r o i l i t e l e a d , Tatsumoto et a_l. , 1 973 ) at time T e s t a b l i s h e d at 4.57Ga, fo l l o w e d by a second stage that s t a r t e d at 3.7Ga with higher u 31 and w v a l u e s — d e p a r t u r e of the second s t a g e c o r r e s p o n d s t o the approximate age f o r the i s o l a t i o n of the lower mantle from the m i x i n g system. The l a s t s t a g e of the l e a d e v o l u t i o n f o r the d e p o s i t s of the E a g l e Bay F o r m a t i o n i s approximated by the ' s h a l e ' c u r v e of Godwin and S i n c l a i r (1982). T h i s l a s t s t a g e , however, appears t o more c l o s e l y model the l e a d e v o l u t i o n i n the E a g l e Bay F o r m a t i o n when i t i s anchored t o the S t a c e y and Kramers ( 1 9 7 5 ) c u r v e a t 2.0Ga. C o n s t r u c t i o n of the remodeled c u r v e i s d e v e l o p e d i n s e c t i o n 3 . 4 . 3.3 ANALYTICAL PROCEDURES 3 . 3 . 1 Sample D e s c r i p t i o n Ore samples were c o l l e c t e d from 3 7 d e p o s i t s and m i n e r a l i z e d o c c u r r e n c e s l i s t e d i n T a b l e 4 . 1 and d e s c r i b e d i n Appendices A and C. A l l samples were s e l e c t e d from s u l p h i d e r i c h h o r i z o n s and/or from c r o s s - c u t t i n g m i n e r a l i z e d s t r u c t u r e s . I n s e v e r a l d e p o s i t s both massive ore and v e i n m i n e r a l i z a t i o n were sampled t o determine the e f f e c t s of d i f f e r e n t t y p e s of o c c u r r e n c e on i s o t o p i c c o m p o s i t i o n . A l l the l e a d a n a l y s e d was e x t r a c t e d from hand p i c k e d g a l e n a and p r e p a r e d a c c o r d i n g t o the methods d e s c r i b e d i n Appendix B. 3 . 3 . 2 A n a l y t i c a l P r e c i s i o n Lead i s o t o p i c r a t i o s were measured on a VG Isomass 5 4 R 32 s o l i d source mass spectrometer i n t e r f a c e d with a HP-85 computer i n the Geochronology Laboratory of R. L. Armstrong at The U n i v e r s i t y of B r i t i s h Columbia. S e v e r a l b l o c k s of data were r o u t i n e l y taken f o r each sample l o a d . The r e p o r t e d r e s u l t s (Appendix C) rep r e s e n t the normalized mean of these data. Within run p r e c i s i o n , expressed as the percentage standard d e v i a t i o n , i s u s u a l l y b e t t e r than 0.05%. Repeated measurement of Broken H i l l Standard (BHS-UBC1) and analyses of d u p l i c a t e s (Appendix C) monitored the a n a l y t i c a l p r e c i s i o n of the runs. T h i r t e e n d e t e r m i n a t i o n s of BHS-UBC1, made during the course of t h i s study, were added to 35 p r e v i o u s l y obtained values to compute the average r a t i o given i n Table 3.1. An e m p i r i c a l mass f r a c t i o n a t i o n c o r r e c t i o n f a c t o r was c a l c u l a t e d using accepted values f o r BHS-UBC1 e s t a b l i s h e d by Richards (1981 ). This f a c t o r was used to normalize the i s o t o p i c r a t i o s of a l l a n a l y s e s . The maximum v a r i a t i o n observed i n d u p l i c a t e a n a l y s i s i s l e s s than 1.0%. The averaged d i f f e r e n c e s between the two s e t s of values are 0.023, 0.019 and 0.054 f o r the 206pb/204pb, 207pb/204pb and 208pb/204pb r a t i o s r e s p e c t i v e l y . P a i r e d - t t e s t conducted on the d u p l i c a t e analyses e s t a b l i s h e d with 95% confidence that no systematic b i a s e x i s t s between the d i f f e r e n t s e t s of d u p l i c a t e a n a l y s i s . However, even under optimal c o n d i t i o n s e r r o r s a r i s e from f r a c t i o n a t i o n processes (which TAELE 3.1: Statistics related to the calculaticn of mass f ractkinBticn factors using Broken Hill Standard (BHS-UECI). Lead Isotope ratios Z16/2D4 abs + 207/204 abs + 2D8/2D6 abs + 206/207 abs + 206/20B abs + Maximim rtinimLfn 15.962 15 .m 0.007 O.0D1 15.32^ 15.300 0.005 0.000 35.653 35.359 0.056 0.002 1 .062307 1.061636 0.020032 0.000016 0.650816 0.669966 0.000705 OD000O9 Average (n=66) Std. Dev. % Std. Dev. 15.950 0.0053 0.033 0.003 15.311 O.C060 0.Q39 0.002 35.613 0.0021 0.006 0.010 1.061732 0.00D019 0.002 0.001330 0.650609 0.0COO17 0.0C& 0.000039 BH3dJECl Error Corr. Fact Precision 16.006 0.001 1.003377 0.000112 15.330 0.007 1 .005169 0.000205 35.651 0.007 1.006734 0.000121 1.039696 0.007 0.993237 0.000013 0.66B907 0.018 0.993651 0.00D061 1. BHS:UBC standard v a l L E s fran double s p i k e a n a l y s e s reported b y Richards 1981 . 34 cause p r e f e r e n t i a l d e p l e t i o n of elements), and from e r r o r i n the measurement of the low i n t e n s i t y 204pb peak. The combination of these e r r o r s generates a spread i n the v a l u e s . I s o t o p i c f r a c t i o n a t i o n , the main source of v a r i a t i o n s i n s i n g l e f i l a m e n t i s o t o p i c determinations (Cooper and R i c h a r d s , 1966; Ozard and R u s s e l l , 1970), i s mass-dependent and r e s u l t s i n the displacement of a p o i n t from i t s t r u e value along a l i n e with slopes that correspond to the product of c o o r d i n a t e r a t i o times the r a t i o of the r e s p e c t i v e mass d i f f e r e n c e — e . g . a slope of 3Y/2X on the 207pb/204pb vs. 206pb/204pb diagram (Ozard and R u s s e l l , 1970; Richards et a l . , 1981). The 204pb e r r o r causes the spread of the values along a slope equal to the 207pb/206pb and 208pb/206pb values s i n c e f o r each of the r a t i o s (206pb/204pb, 207pb/204pb and 208pb/204 Pb) the e r r o r i s r e l a t e d to the 204pb measurement (York, 1969). The slopes of the corresponding e r r o r s i s d e p i c t e d on each diagram ( F i g s . 3.3 to 3.5) . 3.3.3 C a l c u l a t i o n of Average Values f o r the Deposits The average i s o t o p i c composition f o r each d e p o s i t (Table 3.3) are presented on c o n v e n t i o n a l 207pb/ 204pb vs. 206pb/204pb, 208pb/204pb vs. 206pb/204pb, and 206pb/207pb vs. 206pb/208pb diagrams ( F i g s . 3.3 to 3.5). The p l o t t e d average values were obt a i n e d from the computation of repeated analyses of v a r i o u s samples c o l l e c t e d at the d e p o s i t s i t e (Table 3.2; Appendix C). TABLE 3.2: Representative calculation of average galena lead isotopic values 1 for a given deposits. Sample Number2 206/206 Lead Isotope Ratios 207/204 + 208/204 + BIRK CREEK 3050B-001 18.948 30508-001D 18.947 30508-002 18.904 30508-002D 18.882 30508-003 18.901 (3050B-0030 19.026 3050B-004 18.B96 3050B-0040 18.949 30508-005 18.893 30508-506 1B.B78 30508-506D 18.869 Olean (n=11) 18.927 Rejection level at + 2 s t . dev. 0.098 Mean (n=10) 18.907 Std. Error4 0.01 0.02) 0.06) 0.03) 0.03) 0.02) 0.30) 0.02) 0.14) 0.01 ) 0.06) 0.08) 15.718 15.741 15.710 15.699 15.691 15.798 15.705 15.741 15.721 15.708 15.722 15.723 0.059 15.716 0.005 0.02) 0.08) 0.01 ) 0.03) 0.01) 0.30) 0.01) 0.05) 0.01 ) 0.13) 0.10) 38.861 38.856 38.791 38.751 38.744 39.027 38.755 38.9B7 38.829 38.893 38.834 38.848 • .186 38.848 0.03 0.03) 0.08) 0.03) 0.03) 0.02) 0.30))3 0.02) . 0.16) 0.01) 0.18) 0.18) 1. Similar calculation has been made apply to a l l deposits (Appendix C) . 2. 30508 represents the number given to the deposit; 001, 002, etc. defines different samples taken from the deposit; D, indicates duplicate analyses of the same sample. 3. Data from this run was rejected on the basis of more than 2 standard deviations from the mean. 4. Standard error = standard deviation / square root of number of samples (n). 36 tf 003 Birk Creek Deposit Average Calculation 15.75 - CL o CVJ H 003 • • 004 O 001 -LJ CL 005 I v A • T 4 O CM 15.7 1 - 5 0 0 A I i, 002 a v Fractionation / / • 003 j 204 Error i i i 18 .85 18 .95 19.05 2 0 6 P b / 2 0 4 P b F i g u r e 3.2 207pb/204p D vs. 206pb/204pb diagram showing the i s o t o p i c d i s t r i b u t i o n of a l l analyses from the B i r k Creek area. F i l l e d symbols represent i n d i v i d u a l analyses and open symbols d e f i n e t h e i r average. Crossed symbols i d e n t i f y d e l e t e d a n a l y s i s . The average value f o r the B i r k Creek area i s d e p i c t e d with i t s a s s o c i a t e d standard e r r o r (Table 3.2). 37 TABLE 3.3: Average galena lead isotope values from ore deposits in the Eagle Bay Formation. Deposit Name Map Lead Isotope Ratios 1 No2 206/204 207/204 208/204 206/207 Cluster 1 Devonian 206/208 Birk Creek Homestake Rea Gold Ford 508 511 515 53B 18.907 18.854 18.869 1B.8B3 15.716 15.700 15.699 15.698 38.848 38.626 38.755 38.676 1 .20304 1 .20085 1.20192 1.20289 0.48699 0.48845 0.4B6BB 0.4B823 Average (n=4) Std. Error Mean 1B.887 +0.010 15.703 +0.004 38.720 +0.216 1.20211 +.00047 0.48767 +.00039 Between cluster 1 & 2 Art Tuin Mountain 517 519 19.060 19.027 15.737 15.704 39.147 38.B32 1.21110 1.21164 0.4B6B7 0.49027 Cluster 2 Tr iassic Agate Bay 506 19.143 15.701 33.909 1.21922 0.49200 Lucky Coon 518 19.142 15.694 38.900 1 .2196B 0.4920B King Tut 523 19.045 15.688 36.835 1.21718 0.49255 Els ie 524 19.142 15.700 3B.975 1.21925 0.49197 Mosquito King 525 19.090 15.693 38.846 1.21648 0.49142 Pet 526 19.126 15.732 38.980 1.21575 0.49151 Spar 527 19.130 15.690 38.881 1.21927 0.49201 Red Top 531 19.146 15.721 38.939 1.21779 0.49170 Red Mineral 2 534 19.131 15.714 3B.069 1.21747 0.48966 Silver King A 536 19.0B1 15.708 38.899 1.21471 0.49052 Orel l 5P 537 19.128 15.692 38.885 1.21902 0.49191 Sunrise 541 19.105 15.696 3B.B49 1.21716 0.49176 Enargite 504 19.096 15.690 38.9B7 1.21704 0.4B979 Fortuna 513 19.125 15.721 39.018 1.21650 0.49016 White Rock 528 19.151 15.722 39.048 1.21810 0.49046 Vavenby 542 19.191 15.703 38.846 1.21574 0.49145 Silver King-Queen 545 19.104 15.684 38.978 1.21807 0.49012 PS-85-175 54B 19.177 15.721 38.962 1.21987 0.49220 Average (n=18) 19.125 15.701 38.936 1.21775 0.49138 Std. Error Mean +0.007 +0.003 +0.016 +.00365 +.00023 38 TABLE 3.3 (continued) Deposit Map Lead Isotope Ratios'! Name No2 206/204 207/204 208/204 206/207 206/208 Between cluster 2 & 3 Fluke 532 19.223 15.703 39.361 1 .22416 0.48838 mt McClennan 539 19.269 15.698 38.967 1 .22747 0.49448 Foghorn 505 19.208 15.711 39.138 1 .22258 0.49076 Rexspar 516 19.177 15.916 38.986 1.20528 0.49273 Birch Island 540 19.335 15.820 39.235 1 .22200 0.49364 Tindal 543 19.251 15.714 39.080 1 .22509 0.49261 Rouge 547 19.260 15.744 39.156 1.22330 0.49188 Cluster 3 Leemac 546 19.391 15.729 39.336 1 .23279 0.49294 Red Mineral 1 533 19.345 15.699 39.360 1.23229 0.49149 Red mineral 3 535 19.354 15.706 39.383 1.23228 0.49142 Son ja 544 19.356 15.691 39.251 1.23353 0.49313 Beca 507 19.339 15.680 39.016 1 .23338 0.49567 Average (n=5) 19.357 15.701 39.264 1 .23285 0.49293 Std. Error mean +0.040 +0.008 +0.055 +.00026 +.00077 5ide cluster 3 June 521 19.461 15.719 39.504 1.23809 0.49263 1. Lead isotopic ratios represent calculated average values from data in Appendix C (calculation of average value i s described in section 3.3.2). 2. map no. in Appendix C is prefixed by 30 and suffixed by analytical sample number. 39 F i g u r e 3.2 represents an example of such data c o l l e c t e d from the B i r k Creek area. In the average value c a l c u l a t i o n , data f a l l i n g o u t s i d e two standard d e v i a t i o n s from the mean were d e l e t e d (as were o u t l i e r values obtained from runs with poor p r e c i s i o n . Thus means r e p r e s e n t i n g only the 'best' values are presented i n Tables 3.2 and 3.3. Cons i s t e n c y between samples from massive ore and from c r o s s - c u t t i n g s t r u c t u r e s was observed i n a l l d e p o s i t s where both types of samples were c o l l e c t e d . T h i s i n d i c a t e s t h at mineral showings of d i f f e r e n t h a b i t can be co g e n e t i c and formed from s i m i l a r and/or i n t e r a c t i v e hydrothermal systems. In many cases v e i n s may represent feeder zones to massive ore. 3.4 THE REMODELED CURVE FOR THE EAGLE BAY FORMATION The average l e a d i s o t o p i c composition obtained from d e p o s i t s i n the Eagle Bay Formation (Table 3.3) forms a coherent s e r i e s of c l u s t e r s c h a r a c t e r i z e d by high 206pfc>/204pb, 207pb/204pb, and 208pb/204pb v a l u e s . The i s o t o p i c u n i f o r m i t y d i s p l a y e d by the set of data as a whole i s best e x p l a i n e d by the presence of a common u l t i m a t e source f o r the l e a d i n a l l the d e p o s i t s . Because the data p l o t above the average 'orogene' curve of Doe and Zartman (1979), a growth curve r e p r e s e n t i n g the e v o l u t i o n i n an upper c r u s t a l environment i s used to determine the model ages f o r the v a r i o u s d e p o s i t s c l u s t e r e d along i t . 40 F i g u r e 3-3 207pb/204pb vs 206pb/204pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3. F i l l e d symbols denote d e p o s i t s grouped i n s p e c i f i c c l u s t e r s ; open symbols are o u t l i e r s . Deposits i n c l u s t e r 1 to 3 are p l o t t e d with d i f f e r e n t symbols. Bars represent +_ 1 standard e r r o r around the mean of the c l u s t e r . The average growth curves shown are the "shale* curve of Godwin and S i n c l a i r (1982) and the remodeled shale curve (t2 = 2.0Ga, u = 12.16+. 08). 15.75 42 F i g u r e 3.4 208pb/204pb vs 206pb/204pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3. F i l l e d symbols denote d e p o s i t s grouped i n s p e c i f i c c l u s t e r s ; open symbols are o u t l i e r s . Deposits i n c l u s t e r 1 to 3 are p l o t t e d with d i f f e r e n t symbols. Bars represent +_ 1 standard e r r o r around the mean of the c l u s t e r . The average growth curves shown are the ' s h a l e 1 curve of Godwin and S i n c l a i r (1982) and the remodeled shale curve (t2 = 2.0Ga, w = 45.35). 2 0 6 p b / 2 0 4 p b 44 F i g u r e 3.5 • 206p D/208pb vs 206pb/207pb diagram f o r d e p o s i t s hosted by the Eagle Bay Formation using data from Table 3.3. F i l l e d symbols denote d e p o s i t s grouped i n s p e c i f i c c l u s t e r s ; open symbols are o u t l i e r s . Deposits i n c l u s t e r 1 to 3 are p l o t t e d with d i f f e r e n t symbols. Bars represent +_ 1 standard e r r o r around the mean of the c l u s t e r . The average growth curves shown are the 'shale' curve of Godwin and S i n c l a i r (1982) and the remodeled shale curve (t2 = 2.0Ga, u = 12.16+.08). Cluster 3 0 .495 0.024 0 Cluster 2 JQ Q. 0 .49 co o CM X) D_ (0 o CM 0.485 H Remodeled curve - 2.0 Ga 0.44 0.41 Shale curve - 1.887Ga 0.44 0.48 1.190 1.20 1.21 1.22 2 0 6 P b / 2 ° 7 P b 1.23 1.24 46 The approximate c o i n c i d e n c e of the data from the d e p o s i t s of the Eagle Bay Formation with the 'shale' curve of Godwin and S i n c l a i r (1982) supports the u t i l i z a t i o n of such a curve f o r model age e s t i m a t i o n , and i n d i c a t e s t h a t the l e a d i n the d e p o s i t s of the Eagle Bay Formation evolved i n an upper c r u s t a l environment c h a r a c t e r i z e d by high u and w v a l u e s . The curve i s c o n s i s t e n t with the a c t i v e c o n t i n e n t a l margin s e t t i n g assigned to d e p o s i t i o n of the Eagle Bay Formation, and i m p l i e s that there was a s i g n i f i c a n t c o n t r i b u t i o n of m a t e r i a l from r e c y c l e d and homogenized Precambrian c r u s t to c o n s t i t u e n t rock u n i t s of the formation. However, the high 207pb/204pb i s o t o p i c s i g n a t u r e of the galena from the Eagle Bay Formation r e s u l t e d i n the data p l o t t i n g above the average 'shale' curve on the 207pb/204pb vs. 206pb/204pb diagram ( F i g . 3.3). S i m i l a r l y the p l o t t e d 208pb/204pb r a t i o s are s h i f t e d below the 'shale' curve on the 208pb/204pb vs. 206pb/204pb diagram ( F i g . 3.4). P r e s e n t a t i o n of the data on a 206pb/207pb vs. 206pb/208pb diagram ( F i g . 3.5) r e v e a l s that the s l i g h t but systematic d i s c r e p a n c y between the data set and the 'shale' curve i s r e a l and not due to a n a l y t i c a l e r r o r of 204pb ( t h i s diagram minimizes the e f f e c t of t h i s e r r o r by e l i m i n a t i n g the 204pb measurement e r r o r s ) . Consequently the 'shale' curve r e p r e s e n t s an approximation of the average l e a d 47 behavior, but does not f i t the data c l o s e l y enough to permit model age d e t e r m i n a t i o n s . Remodeling of the curve (Table 3.4), by changing the parameters used to d e f i n e i t , r e s u l t e d i n a b e t t e r c o i n c i d e n c e with the data from d e p o s i t s hosted i n the Eagle Bay F o r m a t i o n — e s p e c i a l l y 208pb/204 vs. 206pb/204pb and 206pb/208pb vs. 206pb/207pb ( F i g s . 3.4 and 3.5). The remodeled curve as d e f i n e d here a p p l i e s s p e c i f i c a l l y only to the d e p o s i t s i n the Eagle Bay Formation. I t does not d e t r a c t from the general v a l i d i t y of the 'shale' c u r v e — e s p e c i a l l y as a p p l i e d east of the Adams P l a t e a u . The remodeled curve represent a l o c a l v a r i a t i o n from the average 'shale' curve due to the s p e c i f i c g e o l o g i c a l s e t t i n g c h a r a c t e r i s t i c of the Eagle Bay Formation. The f o l l o w i n g d i s c u s s i o n reviews the changes i n parameters made to o b t a i n the remodeled curve. 3.4.1 Departure Time, I n i t i a l Composition, and u Values The remodeled curve i s anchored to the Stacey and Kramers (1975) curve at 2.0Ga. T h i s date has been favored because i t i s c l o s e to Rb/Sr whole rock dates from g r a n i t i c g n e i s s of the Shuswap Complex (2.0 to 2.25Ga: Duncan, 1982), and to the determined age of the basement by the common l e a d method from three groups of stratabound d e p o s i t s i n t e r r a n e c o r r e l a t e d with the Eagle Bay Formation (Duncan, 1982). The 2.0Ga date i s s l i g h t l y o l d e r than the homogenization time of the c o n t i n e n t a l 48 TABLE 3.4: Lead isotope values for the remodeled curve. Parameters: u = 12.16, u = 45.35, t2 = 2.0Ga Age1 Time Ga1 206/204 Lead Isotope Ratios 207/204 208/204 206/207 206/208 Present 0.0 19.582 15.736 39.515 1.24440 0.49556 Neogene 0.024 19.537 15.734 39.461 1.24171 0.49510 Paleogene 0.066 19.457 15.730 39.366 1.23693 0.49426 Cretaceous 0.14 19.315 15.723 39.19B 1.22846 0.49275 Jurassic 0.21 19.180 15.716 39.044 1.22041 0.49124 Triassic 0.25 19.102 15.711 3e.953 1.21584 0.49039 Permian 0.29 19.023 15.707 38.85B 1 .21112 0.48955 Carboniferous 0.36 18.884 15.698 38.699 1.20296 0.48797 Devonian 0.41 18.7B4 15.692 38.586 1 .19704 0.48681 Silurian 0.44 1B.723 15.688 38.518 1 .19346 0.4860B Ordovician 0.51 18.581 15.678 38.354 1.18516 0.48446 Cambrian 0.57 18.458 15.670 38.218 1.17792 0.48297 Anchor point2 2.0 15.159 15.192 34.799 0.99783 0.43562 1. Time boundaries from DNAG Geologic Time Scale (Palmer, 19B3). 2. Calculated from stage 2 of Stacey and Kramers (1975) u = 9.74, ID = 37.19, ti = 3.7Ga. 49 basement by the Hudsonian orogeny. I t was chosen as the departure p o i n t f o r the model r e l a t e d to galena lead isotopes i n the Eagle Bay Formation. Nevertheless t h i s s t a r t i n g p o i n t r e p r e s e n t s an estimated parameter which i s r e q u i r e d by the m u l t i - s t a g e model adopted i n t h i s study. E s t i m a t i o n of the i n i t i a l r a t i o at 2.OGa i s not unambiguous. However, here i t i s simply assumed that the environment from which the basement was generated evolved along an average curve s i m i l a r to the secondary growth curve of Stacey and Kramers (1975) s t a r t i n g at 3.7Ga (a s i m i l a r assumption was made i n the c o n s t r u c t i o n of the 'shale' c u r v e ) . The i n i t i a l r a t i o s t h e r e f o r e correspond to the e m p i r i c a l data c a l c u l a t e d by Stacey and Kramers (1975, p. 216) and are: 206pb/204pb = 15.159, 207pb/204pb = 15.192, and 208pb/204pb = 34.799. The u value of 12.16 was used to c a l c u l a t e the remodeled curve because i t repr e s e n t s the average U/Pb value f o r the Omineca B e l t c a l c u l a t e d f o r the 'shale' curve (Godwin and S i n c l a i r , 1982). The c a l c u l a t e d u values f o r the data from the Eagle Bay Formation (using equations i n Table 3.0) c o i n c i d e n t l y covered a range centered around a u of 12.0. I s o t o p i c compositions on the remodeled curve were a l s o c a l c u l a t e d with u = 12.08 and 12.24 ( F i g . 3.3) to d i s p l a y the e f f e c t of a v a r i a t i o n of u on the p o s i t i o n of the remodeled curve. 50 U t i l i z a t i o n of 2.OGa as a departure p o i n t generates a curve which p l o t s above the 'shale' curve ( F i g s . 3.3 and 3.4). Consequently, any i s o t o p i c composition a s s o c i a t e d with any model age on the remodeled curve w i l l be g r e a t e r i n both 207pb/204pb and 206pb/204pb r a t i o s r e l a t i v e to the 'shale' curve. The upward displacement of the curve's p o s i t i o n i n c r e a s e s the c o i n c i d e n c e between the curve and c l u s t e r s 1 and 3. This aspect i s s i g n i f i c a n t because these two c l u s t e r s , c o n t a i n i n g d e p o s i t s of known Devonian and Cretaceous age, f a l l a p p r o p r i a t e l y on the remodeled curve at 375Ma and 100Ma r e s p e c t i v e l y . T h i s b e t t e r f i t of the data with the remodeled curve supports the use of 2.OGa r a t h e r than 1.887Ga as the anchor p o i n t f o r the remodeled curve. On the other hand, the v a r i a t i o n s caused by the u t i l i z a t i o n of d i f f e r e n t u values are l e s s s i g n i f i c a n t ( F i g . 3.3), and i t does not appear to be advantageous to change the u value to accommodate the data. 3.4.2 w Value U t i l i z a t i o n of a w value equal to 49.09 (value used f o r the 'shale' curve: Godwin and S i n c l a i r , 1982) to remodel the thorium curve (on the 208pb/204pb vs. 206pb/204pb diagram; F i g . 3.5) i s inadequate. Compared to the uranogenic curve (above s e c t i o n ) the change r e s u l t i n g from the u t i l i z a t i o n of t2 equal to 2.OGa ra t h e r than 1.887Ga does not s e n s i b l y a f f e c t the 51 p o s i t i o n of the remodeled curve r e l a t i v e to the d i s t r i b u t i o n of the data s e t , s i n c e i t only d i s p l a c e s the i s o c h r o n i n t e r s e c t i o n s upward and to the r i g h t ( d e p i c t e d as p o i n t s and crosses i n F i g u r e 3.4). A c l o s e r f i t of the remodeled curve to the data i s obt a i n e d when the w value i s lowered to 45.35. T h i s value i s markedly lower than the 49.09 value used f o r the 'shale' curve; however t h i s value i s higher than the estimated value of 41 .86 used by Doe and Zartman (1979) to c h a r a c t e r i z e the upper c r u s t a l environment f o r t h e i r plumbotectonic model. The geochemical behavior of thorium d u r i n g the f r a c t i o n a t i o n process i s not as w e l l understood as uranium and, the Th/Pb r a t i o i s considered l e s s s p e c i f i c i n d i s c r i m i n a t i n g among v a r i o u s source m a t e r i a l s (Zartman, 1974). T h e r e f o r e , although a s l i g h t l y lower value i s r e q u i r e d to f i t the data from the d e p o s i t s of the Eagle Bay Formation, i t does not imply any major d i f f e r e n c e i n the composition of the p r o t o l i t h f o r these r o c k s . 3.4.3 Summary U n i f o r m i t y w i t h i n d e p o s i t s and the range of the lead i s o t o p i c compositions o b t a i n e d on galena from the d e p o s i t s hosted by the Eagle Bay Formation i n d i c a t e s t h a t the p r o t o l i t h f o r the le a d has an average upper c r u s t a l s i g n a t u r e . T h i s emphasizes the involvement of o l d c r u s t a l basement beneath the Eagle Bay Formation and/or sediment sources f o r the Eagle Bay roc k s . Lead from the d e p o s i t s hosted by the Eagle Bay Formation 52 has g e n e r a l l y s i m i l a r i s o t o p i c compositions to the l e a d i n the Cariboo Gold v e i n s (Andrew, 1982), and i s s i g n i f i c a n t l y d i f f e r e n t (mainly higher 207pb/204pb values) from the l e a d i n the Intermontane B e l t (Andrew, 1982) and the S l i d e Mountain Group (Aggarwal and N e s b i t t , 1984). In a d d i t i o n t h i s s i m i l a r i t y i n the l e a d i s o t o p i c s i g n a t u r e of d e p o s i t s i n the Eagle Bay Formation and i n the B a r k e r v i l l e Terrane supports the c o r r e l a t i o n s e s t a b l i s h e d by S t r u i k (1986). P r o x i m i t y of the data to the 'shale' curve i n d i c a t e s t hat t h i s curve i s a p o s s i b l e approximation to the average behavior of the l e a d . But the d i s t i n c t remodeled curve more c l o s e l y f i t s the data from the Eagle Bay Formation. T h i s remodeled curve i s used throughout the f o l l o w i n g d i s c u s s i o n to a s s i g n model ages to the pulses of m i n e r a l i z a t i o n i n the Eagle Bay Formation mainly represented by three d i s t i n c t c l u s t e r s of data with Devonian, Upper T r i a s s i c , and Cretaceous model ages. 3.5 MODEL AGE DETERMINATIONS Using the m u l t i - s t a g e model d e p i c t e d i n F i g u r e 3.1, model ages f o r the m i n e r a l i z a t i o n can be d e r i v e d from the measured i s o t o p i c r a t i o s of the d e p o s i t s . By combining equation 1 and 2 of Table 3.0, the equation of a f a m i l y of s t r a i g h t l i n e s ( i s o c h r o n s ) passing through the anchor p o i n t of the remodeled 53 shale curve at 2.OGa on Stacey and Kramers' (1975) curve can be obt a i n e d . The slope of the a p p r o p r i a t e i s o c h r o n on which the le a d i s o t o p i c composition l i e s can be used to determine a value of t3 and to a s s i g n a model age f o r the galena. Since the above equation i s t r a n s c e n d e n t a l , t3 cannot be d i r e c t l y c a l c u l a t e d by c o n v e n t i o n a l a l g e b r a i c methods, and computer programs use an i t e r a t i v e c a l c u l a t i o n to approximate the best value f o r t 3 . C a l c u l a t i o n of the slope m, and t3 determinations were made using the average i s o t o p i c values (Table 3.3.) f o r each d e p o s i t . Because the 207pb/204pb, 206pb/204pb slope model ages are very s e n s i t i v e to small changes i n m, v a r i a t i o n s i n the 207pb/204pb i n t e r c e p t of 0.1% (comparable to experimental e r r o r ) r e s u l t e d i n l a r g e v a r i a t i o n s i n the c a l c u l a t e d model ages ( d i f f e r e n c e s of 100Ma were obtained f o r some of the d e p o s i t s i n c l u s t e r 1). Consequently, the slope model ages obtained f o r each d e p o s i t were not used. Instead, ages of the c l u s t e r e d groups of d e p o s i t s were determined by where they p l o t along the remodeled curve. Table 3.3 l i s t s the mean values f o r each c l u s t e r ( c a l c u l a t e d i n the same way as averages f o r each d e p o s i t i n s e c t i o n 3.3.3). These means with t h e i r a s s o c i a t e d standard e r r o r are p l o t t e d on the l e a d diagrams ( F i g s . 3.3 to 3.5). Model age f o r the c l u s t e r s were then e s t a b l i s h e d from the age on the remodeled curve at which the c l u s t e r s — a r o u n d t h e i r mean 54 v a l u e s — i n t e r s e c t e d the curve. These model ages are p r i m a r i l y c o n t r o l l e d by the 206pb/204pb r a t i o s as i t i s these r a t i o s t h a t , e x h i b i t g r e a t e r v a r i a t i o n s . The model ages f o r c l u s t e r s 1,2 and 3 were determined from each diagram ( F i g . 3.3 to 3.5) as being r e s p e c t i v e l y Late Devonian, Late T r i a s s i c , and mid-Cretaceous. These model ages of corresponding c l u s t e r s of d e p o s i t s are d i s c u s s e d i n Chapter 4. 55 4. LEAD ISOTOPES, MINERAL DEPOSITS AND STRATIGRAPHY 4.1 INTRODUCTION The dominant i n f l u e n c e of an upper c r u s t a l component on the lead i s o t o p e composition i n galena of d e p o s i t s hosted by the Eagle Bay Formation was e s t a b l i s h e d i n Chapter 3. T h i s chapter focuses on the d i f f e r e n c e s between these d e p o s i t s as d e f i n e d by the c l u s t e r i n g of the lead data i n t o three main groups along the remodeled curve ( d e p o s i t s i n each c l u s t e r are i n Table 4.0). Deposits s h a r i n g s i m i l a r l e a d i s o t o p e s i g n a t u r e s d e f i n e g e n e t i c l i n k s ; d i f f e r e n c e i n i s o t o p i c composition between the d i s t i n c t c l u s t e r s allow model ages to be assigned and sometimes permits d i s t i n c t i o n s between d e p o s i t s t h a t are oogenetic with, or are markedly younger than t h e i r host r o c k s . S t r a t i g r a p h i c c o r r e l a t i o n and c o n s t r u c t i o n of composite s t r a t i g r a p h i c s u c c e s s i o n s w i t h i n the Eagle Bay Formation has been hampered by i n t e n s e deformation and metamorphism, which commonly obscures c o n t a c t r e l a t i o n s h i p s among the u n i t s . Lead i s o t o p e data are c o n s i s t e n t with the Devonian age f o r the u n i t EBA e s t a b l i s h e d by other c r i t e r a (see s e c t i o n 2.3.1). However le a d data suggest an Upper T r i a s s i c age f o r the s t r u c t u r a l l y lower p a r t of u n i t EBG, which i s c o n s i d e r e d to be Cambrian by TABLE 4.0: Classi f icat ion and name of deposits within discrete clusters of data defined in Figures 3.3 to 3.5 Deposit Host Deposit Map Classi f icat ion Unitl Name No1 Cluster 1 Devonian Volcanogenic EBA Birk Creek 50B Oogenetic with Homestake 511 host rocks Ford 538 E8F Rea Gold 515 Between cluster 1 & 2 Veins EBS Art 517 EBG Twin Mountain 519 Cluster 2 Triassic Stratiform EBG Agate Bay 506 Oogenetic with Lucky Coon 518 host rocks King Tut 523 Els ie 524 Mosquito King 525 Pet 526 Spar 527 Red Mineral 2 534 Silver King A 536 Orell 5P 537 Replacement EBQ Red Top 531 Sunrise 541 Veins EBA Enargite 504 Fortuna 513 EBG White Rock 528 Vavenby 542 Silver King-Queen 545 PS-85-175 548 TABLE 4.0 (continued) Deposit Host Deposit Map Classi f icat ion Unitl Name No1 Between cluster 2 & 3 Stratiform EBG Fluke 532 Replacement EBQ Mt McClennan 539 Uranium (volcanogenic) EBA Rexspar 516 Vein Foghorn 505 Birch Island 540 Tindal 543 Rouge 547 Cluster 3 Vein Baldy Leemac 546 EBG Red Mineral 1 533 Red Mineral 3 535 EBA Sonja 544 Replacement (?) EBA Beca 507 Beyond cluster 3 Vein June 521 1. Host Unit and Map No. are on Figure 4.0. Map no. in Appendix C is prefixed by 30 and suffixed by analytical sample number. 58 S c h i a r i z z a (1986). I n t e r p r e t a t i o n s proposed here, although not completely unambiguous, are c o n s t r a i n e d s u b s t a n t i a l l y by a v a i l a b l e g e o l o g i c a l data. 4.2 CLUSTER 1: DEVONIAN COGENETIC DEPOSITS Two m i n e r a l i z e d d e p o s i t s , Rea Gold and Homestake, and two m i n e r a l i z e d showings, B i r k Creek and Ford, (Table 4.0, F i g . 4.0, Appendix A) are enclosed by c l u s t e r 1 around the Devonian i s o c h r o n on the remodeled curve ( F i g . 3.3 to 3.5). These four occurrences are hosted by Devonian v o l c a n i c u n i t s (EBA and EBF) of the Eagle Bay Formation. These u n i t s form a conformable s u c c e s s i o n ( l o c a l l y separated by o r t h o g n e i s s bodies) composed of s t r o n g l y f o l i a t e d q u a r t z - s e r i c i t e - p h y l l i t e , c h l o r i t i c p h y l l i t e , and s e r i c i t e s c h i s t , w i t h i n which quartz and p l a g i o c l a s e phenocrysts and r e l i c t igneous t e x t u r e s are l o c a l l y v i s i b l e . T h i s s u c c e s s i o n was i n t e r p r e t e d by Preto (1981 ) as a deformed and r e c r y s t a l l i z e d f e l s i c to i n t e r m e d i a t e v o l c a n i c sequence metamorphosed to g r e e n s c h i s t f a c i e s . U n i t s EBA and EBF are p a r t l y i n t e r l a y e r e d with, but mostly o v e r l a i n e d by, a t u r b i d i t e sequence composed of p h y l l i t e s , a r g i l l i t e , sandstone, g r i t and minor carbonates ( u n i t EBP). Z i r c o n s from the metavolcanic rocks ( F i g . 4.0) y i e l d e d a Devonian, 372+_1lMa date (Preto and S c h i a r i z z a , 1985). Conodonts found i n two limestone beds of u n i t EBP y i e l d e d a m i d - M i s s i s s i p p i a n age (Osagien to e a r l y Devonian to Permian F e n n e l l Formation 5g I UF I Upper structural division: pillowed and massive meta-basalt. minor chert 1 if I Lower structural division: pillowed and massive meta-basalt and ribbon chert, limestone, diorite, gabbro, quartzf eldspar, porphyry, rhyolite Mississippian I EBP I Phyllite and slate with interbedded sandstone and grits Devonian and/or Mississippian I EBF 1 Feldspathic phyllite (intermediate to felsic tuff) Devonian I EBA I Sericite-auartz-phyllite and schist (intermediate to felsic volcanics and volcanoclastics) Devonian and/or older 1 EBS I Mixed meta-sedimentary seouence (phyllites) | EBC I Calcareous chlorite-schist, fragmental schist (mafic to intermediate volcanics) | '•]. 1 Tshinakin limestone fr--^ mixed phyllite ( E B C p ) [ -| quartzite ( EBCq ) \ ) polymictic conglomerate ( E B C c g ) [ I T-EBG ( ? Triassic ) Lower Cambr ian a n d / o r older IEBQ I Chlorite-muscovite quartzite. chlorite-muscovite-quartz schist and minor meta-sediments (SDQ) I EBH I Quartzite. grit and chlorite-sericite-quartz schist Intrusives J u r a s s i c & C r e t a c e o u s [ '• 11 \\ Raft batholith. Baldy batholith, Scotch Creek plug Late Devonian I Qgn I Granite and granodiorite orthogneiss S y m b o l s Mineral occurrences • O Cluster 1 (Oevonian) A & Cluster 3 (Cretaceous) • • Cluster 2 (Triassic) 0 Cluster 4 (Tertiary) X Outliers Faults f^*" Thrust fault (this study) Thrust fault (Schlarizza et al, 1984) F i g u r e 4.0 Geology of the Eagle Bay Formation showing the l o c a t i o n of the sampled mineral d e p o s i t s w i t h i n the major t h r u s t u n i t s (modified from S c h i a r i z z a and Preto, 1984). 60 61 Meramecien: O k u l i t c h and Cameron, 1976). Based on these age de t e r m i n a t i o n s , a bracketed D e v o n o - M i s s i s s i p p i a n age has been assig n e d to these u n i t s . Rea Gold and Homestake d e p o s i t s , l o c a t e d on the limbs of a major overturned and northw e s t e r l y t r e n d i n g s y n c l i n e s i m i l a r l y occur w i t h i n or near the top of a f e l s i c p y r o c l a s t i c sequence i n c l u d e d i n a t h i c k e r more mafic p i l e of t u f f s and minor flows. Deformation has a f f e c t e d the d e p o s i t s and i s marked by a w e l l d e f i n e d p e n e t r a t i v e f o l i a t i o n . D e f i n i t e f o l d s are d i f f i c u l t to o u t l i n e due the s h i s t o s i t y developed i n the r o c k s . Both d e p o s i t s , composed of massive s u l p h i d e lenses and a s s o c i a t e d b a r i t e , e x h i b i t e x t e n s i v e f o o t w a l l a l t e r a t i o n zones c h a r a c t e r i z e d by 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 p y r i t e development. These d e p o s i t s are s i m i l a r i n many re s p e c t s to the syngenetic volcanogenic p o l y m e t a l l i c Kuroko d e p o s i t s (Hoy and G o u t i e r , 1986; Appendix A). A D e v o n o - M i s s i s s i p p i a n l e a d model age f o r the d e p o s i t s i s c o i n c i d e n t with other age de t e r m i n a t i o n s from t h e i r host u n i t s (EBA and EBF), and consequently, the m i n e r a l i z i n g s o l u t i o n s probably were co g e n e t i c with the formation of the host rocks. The l e a d i s o t o p i c s i g n a t u r e of c l u s t e r 1 can t h e r e f o r e be used to f i n g e r p r i n t d e p o s i t s which formed under s i m i l a r c o n d i t i o n s . Thus, although the s i l i c i f i e d p y r i t e - p y r r h o t i - t e r i c h occurrences 62 of the B i r k Creek area and the s t r a t i f o r m massive su l p h i d e zones m i n e r a l i z e d with Pb-Zn-Cu of the Ford property (Table 4 . 0 , F i g . 4 . 0 , Appendix A) are not c o n c l u s i v e l y volcanogenic i n o r i g i n , t h e i r l e a d i s o t o p i c composition suggests such an i n t e r p r e t a t i o n . The oogenetic and volcanogenic m i n e r a l i z a t i o n probably was d e p o s i t e d e i t h e r from s o l u t i o n s a s s o c i a t e d with the volcanism or concentrated from the v o l c a n i c p i l e by c i r c u l a t i n g s o l u t i o n s i n a c o n v e c t i v e c e l l soon a f t e r , or during the formation of the Devonian u n i t s EBA and EBF (Hutchison, 1973; Solomon, 1976; Lydon, 1985). The probable presence of an u n d e r l y i n g l a r g e r i n t r u s i v e mass, which may have set up the c o n v e c t i v e c e l l , i s i n d i c a t e d by the occurrence of quartz porphyry i n t r u s i v e bodies c o n s i d e r e d to be c o g e n e t i c with the v o l c a n i c s (Preto, 1981; Goutier et aJL. , 1 985). The observed i s o t o p i c r a t i o s r e p r e s e n t an average of the l e a d leached by the m i n e r a l i z i n g s o l u t i o n s from the source r o c k s . The l e a d i s o t o p i c compositions from v e i n s a s s o c i a t e d with the d e p o s i t s are s t a t i s t i c a l l y i n d i s t i n g u i s h a b l e from the l e a d e x t r a c t e d from the massive d e p o s i t . T h i s suggests that formation of the v e i n s was contemporaneous with the formation of the massive ore; they may r e p r e s e n t feeders to massive ore bearing h o r i z o n s . Compared to Kuroko type d e p o s i t s (Lambert and 63 Sato, 1974; Sato and S a s a k i , 1976; Sato et a l . , 1980), the l e a d data of c l u s t e r 1 are markedly r a d i o g e n i c . T h i s enrichment i n r a d i o g e n i c l e a d suggests that the u l t i m a t e source of Devonian i n t r u s i v e s i s u n d e r l y i n g Precambrian basement, a c o n c l u s i o n i n agreement with the i n t e r p r e t a t i o n of Armstrong ( i n Jung, 1986) on the western p o s i t i o n of the basement boundary ( F i g . 2.0; see s e c t i o n 2 . 3 . 2 ) . 4.3 LEAD DATA BETWEEN CLUSTER 1 & 2 Two m i n e r a l i z e d v e i n s (Twin Mountain and A r t ; Table 4.0, F i g u r e 4.0, Appendix A) have t h e i r l e a d i s o t o p i c compositions p l o t t i n g d i s t i n c t i v e l y to the r i g h t of c l u s t e r 1. The Twin Mountain v e i n has a lead model age of mid-Pennsylvanian, and occurs i n the Cambrian u n i t EBG ( S c h i a r i z z a and Preto, 1984). The high b a r i t e content of some of the v e i n s at Twin Mountain makes them m i n e r a l o g i c a l l y more s i m i l a r to the nearby Rea Gold and Homestake d e p o s i t (hosted by the De v o n o - M i s s i s s i p p i a n u n i t s EBA and EBF) than to any d e p o s i t s of the Cambrian u n i t EBG. The major t h r u s t i n f e r r e d by S c h i a r i z z a and Preto (1984) which i s o l a t e Twin Mountain from the D e v o n o - M i s s i s s i p p i a n u n i t s has not been confirmed by d e t a i l e d mapping by C o r p o r a t i o n F a l c o n b r i d g e (see Hoy and G o u t i e r , 1986) or by White (1985). The mid-Pennsylvanian model age determined f o r the Twin Mountain v e i n might i n d i c a t e t hat the i n f e r r e d t h r u s t a c t u a l l y r e p r e s e n t s 6 4 an unconformity between separated v o l c a n i c and v o l c a n i c l a s t i c sequences, and that the host u n i t could be younger than Cambrian as c u r r e n t l y i n t e r p r e t e d . However, the mid-Pennsylvanian l e a d model age by i t s e l f does not r e f u t e the Cambrian age a s s i g n to the u n i t EBG. 4.4 CLUSTER 2: TRIASSIC STRATIFORM AND VEIN DEPOSITS C l u s t e r 2 rep r e s e n t s galena l e a d with an Upper T r i a s s i c model age ( F i g . 3.3 to 3.5). S e v e r a l r e m o b i l i z e d s t r a t i f o r m d e p o s i t s hosted by the u n i t EBG, and v e i n s randomly d i s t r i b u t e d through the Eagle Bay Formation have le a d i s o t o p i c compositions that p l o t i n t h i s c l u s t e r . The form of the s t r a t i f o r m d e p o s i t s suggests that they could be oogenetic with t h e i r host u n i t . U n i t EBG, however, has been d e f i n e d as Cambrian ( S c h i a r i z z a , 1986b). Consequently, a major dis c r e p a n c y e x i s t s between the T r i a s s i c model age f o r apparently oogenetic m i n e r a l i z a t i o n and the a s s i g n e d Cambrian age of the host. The f o l l o w i n g c o n s t i t u t e s a b r i e f g e o l o g i c a l d e s c r i p t i o n of the d e p o s i t s of c l u s t e r 2 and pro v i d e s a framework f o r the d i s c u s s i o n of the l e a d i s o t o p e i n t e r p r e t a t i o n s i n s e c t i o n 4.2.2. 4.4.1 Deposit geology S t r a t i f o r m d e p o s i t s Remobilized s t r a t i f o r m d e p o s i t s are represented by the Lucky Coon, E l s i e , King Tut, Mosquito King and Spar d e p o s i t s on 65 the Adams P l a t e a u , and by the Sunrise and Red Top d e p o s i t s i n the Clearwater area (Table 4.0, F i g . 4.0, Appendix A). The term s t r a t i f o r m i s used here to c h a r a c t e r i z e d s u l p h i d e s r i c h l a y e r s conformable with the surrounding rocks (cf_. G l o s s a r y of Geology, American G e o l o g i c a l I n s t i t u t e , 1979). These d e p o s i t s on the Adams P l a t e a u are hosted by u n i t EBG which c o n s i s t s mainly of massive and fragmental g r e e n s c h i s t , of intermediate and mafic v o l c a n i c a f f i n i t i e s , a s s o c i a t e d with sedimentary u n i t s represented by g r a p h i t i c and s i l i c e o u s p h y l l i t e c o n t a i n i n g l a y e r s of p h y l l i t i c limestone, c a l c - s i l i c a t e , and p h y l l i t i c q u a r t z i t e s . The gangue of these d e p o s i t s ' i s s i l i c e o u s ; p y r i t e , the most abundant s u l p h i d e , occurs with dark 'black j a c k ' s p h a l e r i t e and galena. Small amounts of a r s e n o p y r i t e (absent i n the Mosquito King d e p o s i t ) and c h a l c o p y r i t e a l s o occur. None of these d e p o s i t s e x h i b i t c l e a r m ineral z o n a t i o n , and the r a t i o s of the d i f f e r e n t s u l p h i d e s are h i g h l y v a r i a b l e between, as w e l l as w i t h i n , the d e p o s i t s . However, the o v e r a l l content of galena i s g r e a t e r i n these d e p o s i t s than i n those of c l u s t e r 1. The m i n e r a l i z a t i o n i n these d e p o s i t s can e i t h e r be c o g e n e t i c with the Cambrian u n i t EBG, or younger and of replacement type ( s e c t i o n 4.4.2). R e m o b i l i z a t i o n of the s u l p h i d e s d u r i n g deformation i s apparent from c o n c e n t r a t i o n and t h i c k e n i n g of s u l p h i d e horizons i n the hinge zone of i s o c l i n a l f o l d s . For example ( D i c k i e , 66 1985) at the Spar d e p o s i t s u l p h i d e s are concentrated i n an u p r i g h t s l i g h t l y asymmetric f o l d i n which s u l p h i d e apparent t h i c k n e s s at the c r e s t i s twice t h a t on the limbs; s i m i l a r f e a t u r e s are observed i n the Lucky Coon ( F i g . 4.1). F a u l t s a l s o o f f s e t and/or t r u n c a t e s u l p h i d e bearing s t r a t a . On a smaller s c a l e , deformation and r e m o b i l i z a t i o n of s u l p h i d e s are o u t l i n e d by c r y s t a l deformation ( s t e e l galena, undulatory e x t i n c t i o n i n q u a r t z ) , replacement of a r s e n o p y r i t e by galena and s p h a l e r i t e , and overgrowth of euhedral p y r i t e (observed i n p o l i s h e d s e c t i o n from samples of the Lucky Coon and Spar d e p o s i t s ) . The s t r a t i g r a p h i c l e v e l of the s u l p h i d e h o r i z o n s i n the Nikwikwaia s y n c l i n e (Lucky Coon, E l s i e and King Tut) appear e q u i v a l e n t to the Spar d e p o s i t ( D i c k i e , 1985) i n d i c a t i n g t h at these d e p o s i t s may be contemporaneous. The s t r a t i f o r m nature and apparent c o n t i n u i t y of the s u l p h i d e lenses i n the same s t r a t i g r a p h i c u n i t over 8km suggests t h a t these d e p o s i t s are syngenetic but r e m o b i l i z e d by l a t e r f o l d i n g . Near Sqwaam Bay, c l o s e to the lake shore, m i n e r a l i z e d carbonate s w e l l s are common i n c h l o r i t i c s c h i s t (Agate Bay; Table 4.0, F i g . 4.0, Appendix A). Since the i s o t o p i c composition of the le a d from these s w e l l s i s s i m i l a r to the lead from the s t r a t i f o r m d e p o s i t s i n the p l a t e a u , the showing probably r e p r e s e n t s l o c a l c o n c e n t r a t i o n s of disseminated c o g e n e t i c l e a d . The t h r u s t f a u l t of S c h i a r i z z a and Preto 67 F i g u r e 4.1 F o l d e d m i n e r a l i z e d l a y e r s , Lucky Coon d e p o s i t . 68 (1984), assumed to pass s l i g h t l y north of t h i s d e p o s i t , has been r e l o c a t e d southward so that a l l i s o t o p i c a l l y - r e l a t e d d e p o s i t s are w i t h i n s i m i l a r t h r u s t s l i c e s ( F i g . 4.0). (Note that the e x i s t e n c e of t h i s f a u l t was questioned i n s e c t i o n 4.1.1.) Two other d e p o s i t s , Sunrise and Red Top (Table 4.0; F i g . 4.0, Appendix A), p l o t i n c l u s t e r 2. These d e p o s i t s c o n s i s t of semi-conformable lenses and l e n t i c u l a r sheets of s u l p h i d e c o n f i n e d to a s p e c i f i c s t r a t i g r a p h i c p o s i t i o n i n u n i t EBQ ( c l o s e to q u a r t z i t i c and limy zones a s s o c i a t e d with c h l o r i t i c q u a r t z - s c h i s t s t hat are l o c a l l y g r a p h i t i c ) . The m i n e r a l i z a t i o n has a d i s c o n t i n u o u s but conformable d i s t r i b u t i o n . Host u n i t EBQ i s s t r o n g l y f o l d e d around an e a s t e r l y t r e n d i n g open a n t i f o r m that i s p a r t l y d i s r u p t e d by f a u l t i n g . The s u l p h i d e zones e x h i b i t evidence of r e m o b i l i z a t i o n s i m i l a r to that of the Lucky Coon, Mosquito King and Spar d e p o s i t s . The Sunrise and Red Top d e p o s i t s are c l a s s i f i e d i n o l d r e p o r t s as replacement d e p o s i t s r e l a t e d to the emplacement of the Baldy and/or Raft b a t h o l i t h s (Appendix A), implying that the s u l p h i d e s were int r o d u c e d by s o l u t i o n s emanating from i n t r u s i o n s . However, i f the assigned Cretaceous age f o r the b a t h o l i t h s i s c o r r e c t then the f o r e g o i n g c o n c l u s i o n i s untenable on the b a s i s of the l e a d i s o t o p e data, because i t p l o t s i n the Upper T r i a s s i c c l u s t e r . However any i n t e r p r e t a t i o n r e l a t e d to the i n t r u s i v e age of the Raft b a t h o l i t h i s u n c e r t a i n u n t i l new z i r c o n dates e s t a b l i s h a more 69 r e l i a b l e c r y s t a l l i z a t i o n age f o r the b a t h o l i t h . V e i n d e p o s i t s The remaining group of data with i s o t o p i c composition p l o t t i n g i n c l u s t e r 2 i s a s s o c i a t e d with w e l l d e f i n e d v e i n d e p o s i t s (Table 4.0, Appendix A). The l e a d data from the v e i n d e p o s i t s are i n d i s t i n g u i s h a b l e from the l e a d of the above s t r a t i f o r m d e p o s i t s . The occurrence of these veins i s not r e s t r i c t e d to any p a r t i c u l a r u n i t of the Eagle Bay Formation, and i s not s p a t i a l l y c l u s t e r e d ( F i g . 4.0). However, t h e i r d i s t r i b u t i o n i s not t o t a l l y random and can be c a t e g o r i z e d as f o l l o w s : 1) The E n a r g i t e and Fortuna v e i n s (Table 4.0, F i g . 4.0, Appendix A) trend northward and occur c l o s e to w e l l d e f i n e d f a u l t s . These f a u l t s are a s s o c i a t e d with two d i s t i n c t t h r u s t i n g events of post-Permian to p r e - J u r a s s i c age, and of Late J u r a s s i c age ( S e c t i o n 2.3); the bracketed age of the f a u l t i n g i n c l u d e s the Upper T r i a s s i c . 2) The Vavenby, PS-75-185, and White Rock ve i n s (Table 4.0, F i g . 4.0, Appendix A) are hosted by the T s h i n a k i n Limestone. The occurrence of veins i n the Cambrian Limestone with T r i a s s i c model age i n d i c a t e s the occurrence of an e p i g e n e t i c T r i a s s i c pulse of m i n e r a l i z a t i o n . 3) The S i l v e r King-Queen v e i n i s p a r t of a major v e i n system c u t t i n g rocks of u n i t EBG. Since t h i s u n i t a l s o hosts the above 70 s t r a t i f o r m d e p o s i t s , i t demonstrates the occurrence of d i f f e r e n t types of m i n e r a l i z a t i o n of e q u i v a l e n t age i n s i m i l a r r o c k s . 4.4.2 M u l t i p l e I n t e r p r e t a t i o n of Lead i s o t o p e data Three p o s s i b l e i n t e r p r e t a t i o n s are examined below i n an attempt to r e c o n c i l e the l e a d data with the observed g e o l o g i c a l f e a t u r e s . These can be summarized as: 1) the m i n e r a l i z a t i o n i s syngenetic and Cambrian, but deformation and/or metamorphism r e s e t the lead i s o t o p i c system to an Upper T r i a s s i c model age; 2) a l l m i n e r a l i z a t i o n i s e p i g e n e t i c , Upper T r i a s s i c i n age, and r e l a t e d to an e p i g e n e t i c event; and 3 ) the m i n e r a l i z a t i o n i s oogenetic with i t s host, and u n i t EBG, or p a r t of i t , i s T r i a s s i c i n age. R e m o b i l i z a t i o n model Short term growth of r a d i o g e n i c lead i n the host rocks from time of o r i g i n a l d e p o s i t i o n (assumed to be Cambrian) to subsequent r e m o b i l i z a t i o n ( i n J u r a s s i c time) coupled with an i n c r e a s e i n temperature (capable of s t a r t i n g an e f f i c i e n t l e a c h i n g and homogenizing process) might be r e s p o n s i b l e f o r the r e s e t t i n g of the l e a d system and f o r the apparent model age o b tained f o r the s t r a t i f o r m d e p o s i t s . T h i s model r e q u i r e s p r o d u c t i o n of r a d i o g e n i c components from the uranium present i n the r o c k s . Rock l i t h o l o g i e s which have an upper c r u s t a l 71 p r o t o l i t h are e n r i c h e d i n uranium and t h e r e f o r e i n s i t u growth of uranium daughters i s to be expected w i t h i n rocks d e r i v e d from such source. The p r o d u c t i o n of r a d i o g e n i c uranium i s o t o p e s generates an i n c r e a s e i n the 206pb/204pb r a t i o without s u b s t a n t i a l l y a f f e c t i n g the 207pb/204pb r a t i o . The r a d i o g e n i c l e a d produced would be r e l a t i v e l y easy to e x t r a c t due to i t s l o o s e l y h e l d p o s i t i o n i n d e f e c t s t r u c t u r e w i t h i n the mineral l a t t i c e . P o s t - d e p o s i t i o n a l accumulation of r a d i o g e n i c l e a d i n u n i t EBG i s p o s s i b l e , but would be l i m i t e d by the g e n e r a l l y i n t e r m e d i a t e to mafic nature of the v o l c a n i c s . Furthermore the processes r e s p o n s i b l e f o r the l e a c h i n g and r e - t r a n s p o r t a t i o n of metals would have to be e f f e c t i v e over a long p e r i o d of time to permit s u b s t a n t i a l e x t r a c t i o n of metals and r e l a t i v e homogenization of lead i s o t o p e s (Gulson et a_l. , 1 983 ). Could intense deformation i n the E a r l y J u r a s s i c and/or the Cretaceous have caused r e m o b i l i z a t i o n of galena l e a d i s o t o p e ? C e r t a i n l y the present c o n f i g u r a t i o n of the s u l p h i d e masses w i t h i n the d e p o s i t s (see F i g . 4.1) suggests t h a t r e m o b i l i z a t i o n deeply a f f e c t e d the ore and c o n t r o l l e d t h e i r c u r r e n t d i s t r i b u t i o n . L o c a l l y d e r i v e d r a d i o g e n i c l e a d may t h e r e f o r e have been added to the s u l p h i d e s a f t e r t h e i r i n i t i a l formation. In g e n e r a l very l i t t l e i s known about the e f f e c t of metamorphism 72 upon l e a d i s o t o p i c composition (Richards et a_l. , 1981) and even i f r e m o b i l i z a t i o n can account f o r general behavior, s e v e r a l i n c o n s i s t e n c i e s a r i s e when d e t a i l s are c o n s i d e r e d . Radiogenic i s o t o p e s r e l e a s e d from incompatible u n f i t t e d l a t t i c e s i t e s d u r i n g metamorphism might move f a r enough to allow them to become i n c o r p o r a t e d i n t o surrounding mineral d u r i n g r e m o b i l i z a t i o n (Doe and Hart, 1963). However only a high temperature regime or e x t e n s i v e hydrothermal a c t i v i t y would permit complete homogenization of the ore. Moreover, one would expect that any r e m o b i l i z a t i o n mechanism r e s p o n s i b l e f o r such homogenization would r e q u i r e r e c r y s t a l l i z a t i o n to such extent that a l l primary ore t e x t u r e s would have been o b l i t e r a t e d (Le Hurray, 1982). Such an intense process d i d not occur as metamorphism only reached g r e e n s c h i s t f a c i e s , and intense hydrothermal a l t e r a t i o n observed elsewhere (Homestake d e p o s i t , Hoy and G o u t i e r , 1986) i s not observed i n the d e p o s i t s on the Adams P l a t e a u . Thus low temperature a l t e r a t i o n processes apparently at best would leave the d e p o s i t s with an inhomogeneous and s c a t t e r e d i s o t o p i c composition (Cumming and G u d j u r d i s , 1973; Slawson, 1983), but a n a l y s i s of s e v e r a l samples from the same d e p o s i t (Appendix B) r e v e a l s t h a t the l e a d i s o t o p i c composition of the d e p o s i t s do not e x h i b i t such v a r i a t i o n ( s e c t i o n 3.3.2). A l t e r n a t i v e l y galena l e a d i s o t o p e evolved i n the J u r a s s i c from 73 Cambrian source rocks with v a r i a b l e uranium content f a l l along a s t r a i g h t l i n e - - n o t c l o s e to a p o i n t as i n c l u s t e r 2. Comparative evidence between major d e p o s i t s a l s o negates the hypothesis that r e m o b i l i z a t i o n processes caused the T r i a s s i c model age obtained f o r the s t r a t i f o r m d e p o s i t s . I t seems reasonable to assume that i f a Mesozoic re-homogenization of the lead y i e l d e d the T r i a s s i c model age assigned to those d e p o s i t s hosted by the Cambrian u n i t EBG, i t would a l s o have a f f e c t e d the age of the other d e p o s i t s hosted by pre-Mesozoic u n i t s i n the Eagle Bay Formation. The Homestake and Rea Gold d e p o s i t s should t h e r e f o r e a l s o have had t h e i r i s o t o p i c composition a d j u s t e d by the metamorphic event. T h i s i s not the case s i n c e t h e i r model age i s Devonian and concordant with the age of the surrounding rocks. Furthermore the lower galena and l e a d content of Rea Gold and Homestake d e p o s i t s should have made them more s u s c e p t i b l e to r e s e t t i n g s i n c e small a d d i t i o n s of metamorphic l e a d would be more e a s i l y d i s c e r n a b l e from the i s o t o p i c composition of d e p o s i t s c o n t a i n i n g low amounts of l e a d — e s p e c i a l l y when a r e l a t i v e l y s h o r t time i n t e r v a l separates d e p o s i t i o n and metamorphism. Consequently the T r i a s s i c model age obtained f o r the s t r a t i f o r m d e p o s i t s hosted by u n i t EBG i s probably not an e f f e c t of the E a r l y J u r a s s i c d e f o r m a t i o n a l and metamorphic event. 74 Nevertheless t h i s event, d i d c o n t r o l t h e i r s p a t i a l d i s t r i b u t i o n . E p i g e n e t i c , Upper T r i a s s i c model An a l t e r n a t i v e i n t e r p r e t a t i o n f o r the T r i a s s i c model age i s t h a t a l l the d e p o s i t s with l e a d composition p l o t t i n g i n c l u s t e r 2 are e p i g e n e t i c v e i n s , or replacement lodes emplaced i n o l d e r u n i t s d u r i n g an Upper T r i a s s i c event. I f t h i s i s the case the s u l p h i d e s i n the s t r a t i f o r m d e p o s i t s hosted by the Cambrian u n i t EBG would have been d e p o s i t e d i n f a v o r a b l e s t r a t i g r a p h i c h o r i z o n s from s o l u t i o n s that leached and e x t r a c t e d l e a d from the surrounding v o l c a n i c and sedimentary roc k s . R e c o g n i t i o n of a magmatic and/or m i n e r a l i z i n g event a f f e c t i n g the area i n T r i a s s i c time would be s i g n i f i c a n t because i t might i n d i c a t e a p e r i o d of a c t i v e hydrothermal c i r c u l a t i o n t h a t s u p p l i e d r a d i o g e n i c l e a d to the rocks of u n i t EBG j u s t before J u r a s s i c r e m o b i l i z a t i o n . No d i r e c t evidence of such a major event has been i d e n t i f i e d i n the Adams Plateau-Clearwater area. However the v e i n d e p o s i t s which cut the Cambrian T s h i n a k i n Limestone and whose lead i s o t o p i c composition f a l l i n c l u s t e r 2 are examples of e p i g e n e t i c m i n e r a l i z a t i o n of T r i a s s i c age. The a s s o c i a t i o n of the s u l p h i d e r i c h h orizons with p a r t i c u l a r s t r a t i g r a p h i c l e v e l s , and the 1 r e l a t i o n s h i p between the ore and the surrounding rocks suggests s t r o n g l y t h a t the ore masses were o r i g i n a l l y c o n t r o l l e d by the s t r a t i g r a p h y . The a s s o c i a t i o n of the s u l p h i d e h o r i z o n s with chemical sediments i n d i c a t e s that they were 75 probably d e p o s i t e d contemporanously with t h e i r host u n i t (EBG) even i f c l e a r l y r e m o b i l i z e d l a t e r . T r i a s s i c c o g e n e t i c d e p o s i t s I f the m i n e r a l i z a t i o n at the Lucky Coon, Mosquito King and Spar d e p o s i t s i s c o g e n e t i c with the host rocks, and the lead model age i s accommodated, then u n i t EBG, or p a r t of i t , must be T r i a s s i c . U n i t EBG, f a u l t bounded on both s i d e s by other u n i t s of the Eagle Bay Formation, c o n s i s t s mainly of massive fragmental g r e e n s c h i s t of v o l c a n i c a f f i n i t i e s a s s o c i a t e d with an heterogeneous meta-sedimentary s u c c e s s i o n c o n t a i n i n g T s h i n a k i n Limestone, the major marker of the Eagle Bay Formation. A c o r r e l a t e d limestone u n i t i n the Vavenby area c o n t a i n s Archaeocyathids of E a r l y Cambrian age (Norford i n S c h i a r i z z a , 1986), which have been used to i n f e r a Cambrian age f o r the e n t i r e u n i t EBG. The T s h i n a k i n Limestone i s immediately u n d e r l a i n and o v e r l a i n by s i m i l a r sequences of g r e e n s c h i s t s . L o c a l l y the limestone a b r u p t l y lenses out; these t e r m i n a t i o n s r e f l e c t o r i g i n a l margins of the carbonate bank a c c o r d i n g to Preto et al_. ( 1980). However, d e s p i t e the f a c t t h a t t h i s package was mapped as a s i n g l e u n i t r e p r e s e n t i n g a continuous s u c c e s s i o n , a l t e r n a t i v e i n t e r p r e t a t i o n are p o s s i b l e given the s t r u c t u r a l and s t r a t i g r a p h i c c o m p l e x i t i e s of the Eagle Bay 76 F o r m a t i o n . I t i s proposed here t h a t the southern p a r t of u n i t EBG, d e p i c t e d i n F i g . 4.0 as u n i t T - E B G , i s l i t h o l o g i c a l l y d i s t i n c t from the n o r t h e r n p a r t , and r e p r e s e n t an a d d i t i o n a l t h r u s t s l i c e w i t h i n the Eag le Bay Format ion w i t h a bounding t h r u s t f a u l t on the southern s i d e and near the base of the T s h i n a k i n L imes tone . T h i s t h r u s t i f p re sen t would separa te the l imes tone and the g r e e n s c h i s t v o l c a n i c rocks to the n o r t h from the meta- sedimentary sequence to the s o u t h . As p r e s e n t l y mapped by S c h i a r i z z a and P r e t o (1984) , the meta-sedimentary s u c c e s s i o n , c o n t a i n i n g both the f o l d e d c o n g l o m e r a t i c and the p h y l l i t i c q u a r t z i t e member ( s u b - u n i t s EBGcg and EBGq), occurs on ly on the southern s i d e of the T s h i n a k i n L imes tone . F u r t h e r m o r e , the s u b - u n i t EBGp seems r e s t r i c t e d to the area n o r t h of the l i m e s t o n e . A l t h o u g h the T s h i n a k i n Limestone i s i n t e r b e d d e d w i t h g r e e n s c h i s t i n s e v e r a l p l a c e s , i t i s never i n d i r e c t c o n t a c t w i t h the metasediments . Even though the metasedimentary s u c c e s s i o n appears to be i n s t r a t i g r a p h i c c o n t a c t , and l o c a l l y i s i n t e r d i g i t a t e d w i t h g r e e n s c h i s t , the c o n t a c t r e l a t i o n s h i p s have been obscured by f o l d i n g . Thus the apparent c o n t a c t between some of these u n i t s c o u l d be s t r u c t u r a l r a t h e r than s t r a t i g r a p h i c ( i . e . deformed and t r a n s p o s e d c o n t a c t ) . The d i v i s i o n between u n i t s EBG and T-EBG a l s o i s supported 77 b y m a r k e d d i f f e r e n c e s i n d e f o r m a t i o n a l i n t e n s i t y a n d s t y l e b e t w e e n t h e T s h i n a k i n L i m e s t o n e t h e g r e e n s c h i s t v o l c a n i c s , a n d t h e m e t a - s e d i m e n t a r y s e q u e n c e . G e n t l e w a r p i n g o f t h e T s h i n a k i n l i m e s t o n e c o n t r a s t w i t h t h e t i g h t N i k w i k w a i a L a k e s y n f o r m , w h i c h w a s f o r m e d b y t h e C o l o m b i a n O r o g e n y , a n d w h i c h r e p e a t s t h e p h y l l i t i c q u a r t z i t i c b e d s ( s u b - u n i t E B G q , F i g . 4 . 0 ) . O l d e r s t r u c t u r e s w i t h i n u n i t T - E B G h a v e n o t b e e n i d e n t i f i e d a n d D e v o n i a n o r t h o g n e i s s h a s n o t b e e n m a p p e d . T h e r e f o r e t h e T - E B G p a r t o f t h e u n i t E B G d o e s n o t c o n t a i n a n y r e c o g n i z a b l e p r e - T r i a s s i c e l e m e n t s . I m p l i c a t i o n s o f t h e p r e s e n c e o f a T r i a s s i c u n i t w i t h i n t h e E a g l e B a y F o r m a t i o n a r e n u m e r o u s . C e r t a i n l y m o r e d e t a i l e d m a p p i n g a n d b e t t e r s t r u c t u r a l a n d s t r a t i g r a p h i c u n d e r s t a n d i n g a r e r e q u i r e d t o r e s o l v e w h e t h e r o r n o t t w o t h r u s t f a u l t e d u n i t s ( E B G a n d T - E B G ) e x i s t w i t h i n t h e p r e s e n t l y d e f i n e d t h r u s t s l i c e E B G ( F i g . 4 . 0 ) . C o n t a c t r e l a t i o n s h i p s b e t w e e n t h e E a g l e B a y F o r m a t i o n a n d t h e S i c a m o u s F o r m a t i o n ( e x p o s e d o n t h e s h o r e s o f S h u s w a p L a k e , F i g . 2 . 0 ) , a s w e l l a s t h e a g e o f t h e S i c a m o u s F o r m a t i o n , a r e f u r t h e r c o n s t r a i n t s o n t h e U p p e r T r i a s s i c a g e f o r u n i t T - E B G i n t h e E a g l e B a y F o r m a t i o n - - t h i s i s e l a b o r a t e d o n b e l o w . T h e S i c a m o u s F o r m a t i o n u n t i l r e c e n t l y w a s c o n s i d e r e d U p p e r T r i a s s i c a n d v i e w e d a s a f a c i e s e q u i v a l e n t o f r o c k s o f t h e 78 Slocan assemblage, but there i s no d i r e c t p a l e o n t o l o g i c a l evidence to support t h i s c o r r e l a t i o n ( O k u l i t c h , 1979). The contact between the Sicamous and the Eagle Bay Formation t h e r e f o r e was assumed to be a t h r u s t f a u l t which juxtaposed D e v o n o - M i s s i s s i p p i a n rocks ( u n i t EBA) on Upper T r i a s s i c rocks of the Sicamous Formation ( O k u l i t c h , 1979). However, recent mapping and d r i l l core from the upper contact between the Sicamous and the Eagle Bay Formation i n the B l i n d Bay area (Daughtry in. Preto and S c h i a r i z z a , 1985) supports a gradual t r a n s i t i o n between a limestone member of the Sicamous Formation and a c h l o r i t i c green c a l c a r e o u s s c h i s t of the Eagle Bay Formation. T h i s conformable contact r e l a t i o n s h i p between these two formations has been i n t e r p r e t e d i n two d i f f e r e n t ways: 1. The Sicamous Formation u n d e r l i e s Devono-Mississippian u n i t EBA of the Eagle Bay Formation and i s t h e r e f o r e older ( i . e . Cambro-Ordovician) than u n i t EBA. In t h i s case some limestone members of the Sicamous Formation could be c o r r e l a t i v e with the Index Formation of the Lardeau Group i n the Kootenay Arc ( O k u l i t c h , pers. comm., 1986). 2. The contact between the Sicamous and the Eagle Bay Formation i s g r a d u a l , even though not n e c e s s a r i l y conformable, and i n v e r t e d by a synformal s t r u c t u r e overturned to the south (Daughtry, p e r s . comm., 1986). The Sicamous then could be Upper T r i a s s i c and pa r t of i t could be e q u i v a l e n t to rocks of the Slocan Group or to some black shale of the N i c o l a Group. These 79 s h a l e s , which may r e p r e s e n t a deeper d e p o s i t i o n a l f a c i e s of the Sicamous F o r m a t i o n form a more or l e s s c o n t i n u o u s band down t o the Vernon a r e a where they c o n t a i n s conodonts of N o r i a n age (Daughtry, p e r s . comm., 1986; O k u l i t c h , 1979). However, because d i r e c t p a l e o n t o l o g i c a l e v i d e n c e i s l a c k i n g near Adams Lake, and s t r u c t u r a l and s t r a t i g r a p h i c r e l a t i o n s h i p s ambiguous, n e i t h e r of the two i n t e r p r e t a t i o n s above can be u n e q u i v o c a l l y f a v o r e d or r u l e d o u t . I m b r i c a t i o n of T r i a s s i c r o c k sequences w i t h i n a s u c c e s s i o n w i t h p e r i - e r a t o n i c a f f i n i t i e s has been documented by Ross e t a l . (1985) from the Crooked Lake area--100km e a s t of W i l l i a m s Lake. I n t h i s a r e a a T r i a s s i c sequence of b l a c k p h y l l i t e s , c o r r e l a t e d t o the Q u e s n e l l i a t e r r a n e , were m e c h a n i c a l l y i m b r i c a t e d w i t h i n the Snowshoe Group, which i s p a r t of the B a r k e r v i l l e T e r r a n e . A s i m i l a r type of i m b r i c a t i o n c o u l d be p o s s i b l e w i t h i n the E a g l e Bay F o r m a t i o n . However, the l e a d i s o t o p i c c o m p o s i t i o n of the d e p o s i t s h o s t e d by u n i t EBG are u n l i k e those h o s t e d elsewhere by Q u e s n e l l i a r o c k s (and t h e r e f o r e any N i c o l a Group r e l a t e d r o c k s ) , which have l e a d i s o t o p i c c o m p o s i t i o n t h a t p l o t below the s h a l e c u r v e (Andrew, 1982) r a t h e r than i n the p o s i t i o n of c l u s t e r 2. C o r r e l a t i o n of u n i t T-EBG w i t h a S l o c a n type assemblage would be b e t t e r s u p p o r t e d by l e a d i s o t o p i c e v i d e n c e s i n c e a t l e a s t p a r t of the S l o c a n Group l e a d was p r o b a b l y d e r i v e d from c r a t o n i c r o c k s (D. Gosh, i n Logan 1985). 80 4.4.3 Summary Although model ages f o r s t r a t i f o r m d e p o s i t s with lead i s o t o p i c composition en c l o s e d by c l u s t e r 2 i s s i m i l a r to, or c l o s e t o , the orogenic and metamorphic E a r l y J u r a s s i c Colombian Orogeny, i t i s u n l i k e l y that the l e a d i s o t o p e composition of the s t r a t i f o r m s u l p h i d e ores from the Adams P l a t e a u (hosted by the u n i t EBG) was a f f e c t e d by metamorphism to the p o i n t of complete r e s e t t i n g . The T r i a s s i c model age f o r the s t r a t i f o r m d e p o s i t s i n c l u s t e r 2 can be i n t e r p r e t e d as f o l l o w : 1) the m i n e r a l i z a t i o n i s of replacement type and r e l a t e d to a T r i a s s i c event, i n which case c l u s t e r 2 can be used to f i n g e r p r i n t that event, or 2) the m i n e r a l i z a t i o n i s cogenetic with u n i t EBG and, a s t r u c t u r a l s u b d i v i s i o n of the u n i t EBG i n t o two separate u n i t s of Cambrian and T r i a s s i c age i s r e q u i r e d . U n t i l the o r i g i n of these s t r a t i f o r m d e p o s i t s i s more c l e a r l y d e f i n e d or the suggestion that a t h r u s t e x i s t s w i t h i n the u n i t EBG i s t e s t e d i n the f i e l d , these are e q u a l l y v a l i d . 4.5 LEAD DATA BETWEEN CLUSTER 2 & 3 Model ages f o r d e p o s i t s with l e a d i s o t o p i c compositions t h a t p l o t between c l u s t e r 2 and 3 are not i n t e r p r e t a b l e . The random d i s t r i b u t i o n of some of these data probably r e f l e c t s an h i g h l y r a d i o g e n i c component generated by proximal uranium and thorium m i n e r a l i z a t i o n ( i . e . Rexspar d e p o s i t Table 81 4.0, F i g . 4.0, Appendix A). The h i g h l y anomalous le a d i s o t o p i c composition i n galena from the Rexspar d e p o s i t s i s a s s o c i a t e d d i r e c t l y with the high uranium and thorium c o n c e n t r a t i o n found t h e r e . T h i s d e p o s i t , hosted by a t u f f a c e o u s t r a c h y t i c to a n d e s i t i c member of u n i t EBA, c o n t a i n s two m i n e r a l i z e d zones: an uranium bearing zone composed of abundant p y r i t e a s s o c i a t e d with f l u o r p h l o g o p i t e , and a f l u o r i t e zone c o n t a i n i n g t r a c e s of galena and molybdenite but mainly barren of uranium and thorium. A K-Ar date of 236 +_ 8Ma (Preto, 1977) obtained from f l u o r p h l o g o p i t e at Rexspar r u l e d out the Cretaceous Baldy b a t h o l i t h as a p o t e n t i a l source f o r the m i n e r a l i z a t i o n . Preto (1977) t h e r e f o r e proposed that the m i n e r a l i z a t i o n was 'syngenetic' with the host r o c k s . The 207pb/204pb value f o r the galena at Rexspar (Table 3.3) i s much great e r than the average value f o r the other d e p o s i t s hosted by the Eagle Bay Formation; i t consequently p l o t s w e l l above the remodeled curve i n F i g u r e 3.3. The 206pb/204pb and 208pb/204pb values (Table 3.3) are not as extreme and f a l l w i t h i n the expected range f o r the d e p o s i t of the Eagle Bay Formation, however, s i n c e Rexspar i s l i k e l y oogenetic with the De v o n o - M i s s i s s i p p i a n sequence, these values should be lower and w i t h i n the range of values d e l i m i t e d by the d e p o s i t s i n c l u s t e r 1. 82 The Foghorn, Rouge, B i r c h I s l a n d and T i n d a l d e p o s i t s (Table 4.0, F i g . 4.0, Appendix A) are veins i n an area dominated by the same f e l s i c v o l c a n i c rocks (Devonian u n i t E B A - - t r a c h y t i c member) that host the Rexspar d e p o s i t . The l e a d data f o r these e p i g e n e t i c veins f a l l to the r i g h t of c l u s t e r 2 . The high l e a d r a t i o s r e f l e c t i n c o r p o r a t i o n i n the m i n e r a l i z i n g s o l u t i o n s of a h i g h l y r a d i o g e n i c component generated by the i n s i t u decay of uranium and thorium i n the surrounding rocks, most of which was probably generated and r e l e a s e d from uranium and thorium r i c h m inerals l i k e those i n the Rexspar d e p o s i t . Model age d e t e r m i n a t i o n s f o r these v e i n s i s ambiguous and i n v o l v e s c o n s i d e r a t i o n of a short term growth of r a d i o g e n i c l e a d from a l o c a l l y uranium and thorium r i c h environment. Consequently the remodeled curve cannot be used d i r e c t l y to estimate the model age f o r these v e i n s . Because an i n c r e a s e i n r a d i o g e n i c l e a d would generate model ages younger than the m i n e r a l i z a t i o n event and the l e a d i s o t o p i c composition i s l e s s than that a s s o c i a t e d with the m i n e r a l i z a t i o n caused by the Baldy b a t h o l i t h ( c l u s t e r 3), these veins more l i k e l y are r e l a t e d to the J u r a s s i c deformation a s s o c i a t e d with the Colombian orogeny. However new o l d e r dates from the R a f t b a t h o l i t h (Jung, pers. comm., 1986) may l i n k the formation of these veins to i t s i n t r u s i o n . The F l u k e d e p o s i t (Table 4.0, F i g . 4.0, Appendix A) c o n s i s t s of d i s c o n t i n u o u s s u l p h i d e r i c h l a y e r s that are 83 semi-conformable with the s h i s t o s i t y and c o m p o s i t i o n a l l a y e r i n g of host u n i t EBG. The s u l p h i d e zones a s s o c i a t e d with a c a r b o n a t e - r i c h s c h i s t member t h e r e f o r e appear to be a t r u e replacement. P r o x i m i t y of the d e p o s i t to g r a n i t i c i n t r u s i o n s may i n d i c a t e that the m i n e r a l i z a t i o n was concentrated i n the limy h orizons by l a t e r a l c i r c u l a t i o n of f l u i d s emanating from the i n t r u s i o n . The lead p l o t s ( F i g 3.3 to 3.5) f o r the Fluke d e p o s i t l i e between c l u s t e r 2 and 3, but i t i s c l o s e s t to c l u s t e r 3. The s l i g h t l y lower l e a d i s o t o p i c composition, compared to those from v e i n s of c l u s t e r 3, i s probably r e l a t e d to a l a r g e r component of w a l l r o c k l e a d . 4.6 CLUSTER 3: CRETACEOUS VEINS The Leemac v e i n , two u n c l a s s i f i e d small s i z e d occurrences, and the s t r a t i f o r m Beca d e p o s i t p l o t i n c l u s t e r 3 (Table 4.0, F ig.4.0, Appendix A). The Leemac v e i n , i n the Cretaceous Baldy b a t h o l i t h has a l e a d i s o t o p i c composition c o i n c i d e n t with the Cretaceous i s o c h r o n on the remodeled curve ( c l u s t e r 3; F i g . 3.3 to 3.5) T h i s r e l a t i o n s h i p suggests a g e n e t i c l i n k between the i n t r u s i o n and the m i n e r a l i z a t i o n . The f a c t t h a t the l e a d i s o t o p i c composition of the v e i n i n the b a t h o l i t h p l o t s on the remodeled curve a l s o i n d i c a t e s that the l e a d of the b a t h o l i t h has evolved 84 from a s i m i l a r p r o t o l i t h source as the surrounding rocks of the Eagle Bay Formation. S p e c i f i c a l l y , the le a d i s o t o p i c composition r e f l e c t s the d i r e c t i n f l u e n c e of an upper c r u s t a l basement i n the o r i g i n and gen e r a t i o n of the i n t r u s i o n ; t h i s supports the i n t e r p r e t a t i o n t h a t the r o o t s of the b a t h o l i t h are i n the adjacent Shuswap Complex ( O k u l i t c h , 1979; see s e c t i o n 2.4.4) . C l u s t e r 3, t h e r e f o r e , i s the f i n g e r p r i n t f o r Cretaceous d e p o s i t s that are cogenetic with the i n t r u s i o n of the b a t h o l i t h . A c c o r d i n g l y , two small m i n e r a l i z e d s i l i c e o u s zones c a r r y i n g v a r i a b l e values of l e a d , z i n c and s i l v e r , sampled i n the v i c i n i t y of Li c h e n Mountain on the Adams Platea u (Red Mi n e r a l Claim 1 and 3, Table 4.0, F i g . 4.0, Appendix A) that were p r e v i o u s l y i n t e r p r e t e d as syngenetic e x h a l a t i v e d e p o s i t s , seems more a p p r o p r i a t e l y r e l a t e d to a small g r a n i t i c plug i n the Scotch Creek area ( F i g . 4.0) which i s probably a s a t e l l i t e of the Baldy b a t h o l i t h . Four other showings around L i c h e n Mountain on Adams P l a t e a u : Pet, Red mineral c l a i m 2, O r e l l 5P and S i l v e r King-A (Table 4.0, F i g . 4.0, Appendix A) y i e l d e d l e a d i s o t o p i c s i g n a t u r e s that were d i s t i n c t l y d i f f e r e n t from the two Cretaceous showings by f a l l i n g i n c l u s t e r 2 i n s t e a d of c l u s t e r 3. The s p a t i a l r e l a t i o n s h i p s between these u n c l a s s i f i e d 85 occurrences and the Spar and Mosquito King, coupled with t h e i r i s o t o p i c composition, i n d i c a t e s t h a t they probably represent l o c a l accumulation of oogenetic m i n e r a l i z a t i o n s i m i l a r to the other nearby s t r a t i f o r m d e p o s i t s . The d i s t i n c t i o n between two d i f f e r e n t types of m i n e r a l i z a t i o n among these s i x m i n e r a l i z e d occurrences i s a good example of the a p p l i c a b i l i t y of the l e a d method f o r d i s c r i m i n a t i n g d i f f e r e n t ages and o r i g i n f o r otherwise s i m i l a r l o o k i n g d e p o s i t s . The Sonja v e i n (Table 4.0, F i g . 4.0, Appendix A) cuts through the Devonian u n i t EBA near Clearwater. I t occurs as a d i s c o n t i n u o u s s i l i c i f i e d zone along the s i d e of a major dyke from g e o l o g i c a l evidence, and l e a d data that p l o t s i n c l u s t e r 3, the m i n e r a l i z a t i o n on the Sonja property i s e p i g e n e t i c and Cretaceous. Another d e p o s i t with lead data p l o t t i n g i n c l u s t e r 3 i s the Beca d e p o s i t (Table 4.0, F i g . 4.0, Appendix A). However, i n a l l l ead diagrams ( F i g s . 3.3 to 3.5) Beca p l o t s f u r t h e s t from the mean value of c l u s t e r 3. I n t e r p r e t a t i o n r e g a r d i n g the g e o l o g i c a l s e t t i n g of the Beca p r o p e r t y i s u n c e r t a i n . The d e p o s i t has been c l a s s i f i e d as a syngenetic volcanogenic d e p o s i t (Preto et a l . , 1985; BCDM Assessement Report no. 7040) because i t c o n t a i n s conformable s u l p h i d e r i c h h o r i z o n s a s s o c i a t e d with p y r i t i c c herty bands, and because i t occurs w i t h i n the same 86 Devonian f e l s i c v o l c a n i c sequence as the Homestake and Rea Gold d e p o s i t s ( u n i t EBA). However the lead i s o t o p i c s i g n a t u r e of the Beca d e p o s i t f a l l s i n c l u s t e r 3 , and i s markedly d i s t i n c t from the lead from the Rea Gold, Homestake and Ford d e p o s i t s . These is o t o p e data i n d i c a t e t hat the m i n e r a l i z a t i o n i s e p i g e n e t i c and Cretaceous r a t h e r than syngenetic and De v o n o - M i s s i s s i p p i a n . Z i r c o n s from Beca property ( F i g . 4.0), y i e l d e d a d i s c o r d a n t chord i n t e r c e p t i n g the Concordia curve at p o i n t s corresponding to 399 and 100Ma (Preto, 1 9 8 1 ) . The Devonian date i s i n t e r p r e t e d as the time of c r y s t a l l i z a t i o n f o r the v o l c a n i c s . A subsequent Cretaceous event i s advocated to account f o r le a d l o s s and r e s u l t i n g z i r c o n d i s c o r d a n c e . I t i s i n t e r e s t i n g to note that the Cretaceous age of t h i s subsequent event corresponds to the model age of c l u s t e r 3 . Therefore lead r e m o b i l i z a t i o n and homogenization of the le a d i n the Cretaceous might have o c c u r r e d . The Cretaceous i n t r u s i o n of the Baldy b a t h o l i t h o f f e r s g r e a t e r p o t e n t i a l f o r genera t i o n of c i r c u l a t i n g s o l u t i o n s than does the J u r a s s i c event r e l a t e d to deformation and metamorphism. Nev e r t h e l e s s the same argument a g a i n s t the re-homogenization process (see s e c t i o n 4.2.2) a p p l i e s here, as the lead i s o t o p i c composition of the d e p o s i t s hosted by the same Devonian u n i t (the co g e n e t i c d e p o s i t s of c l u s t e r 1) has not been re-homogenized to a Cretaceous age. U n f o r t u n a t e l y , the Beca d e p o s i t i s not l o c a t e d c l o s e r than other d e p o s i t s i n the area to the b a t h o l i t h and t h i s cannot be used to j u s t i f y why i t s lead 87 composition could have been more s i g n i f i c a n t l y a f f e c t e d by the i n t r u s i o n . The m i n e r a l i z a t i o n might be an e p i g e n e t i c replacement. 4.7 LEAD DATA BEYOND CLUSTER 3 M i n e r a l i z a t i o n of the June v e i n i s probably l a t e and r e l a t e d to a T e r t i a r y event sinc e i t s lead data p l o t s c l o s e to a T e r t i a r y model age along the remodeled curve. The only u n c e r t a i n t y surrounding t h i s i n t e r p r e t a t i o n i s t h a t , although i t i s based on three d u p l i c a t e a n a l y s i s from the same d e p o s i t , no a n a l y s i s from any other d e p o s i t has a s i m i l a r l e a d i s o t o p i c composition. T e r t i a r y lamprophyre dykes are widespread i n the map area and occur i n c l o s e v i c i n i t y of the Mosquito King, Spar and Fluke d e p o s i t s . The i s o t o p i c s i g n a t u r e of l e a d , m i n e r a l i z a t i o n from c r o s s - c u t t i n g s t r u c t u r e s , s p a t i a l l y r e l a t e d to these dykes, cannot be s t a t i s t i c a l l y d i s t i n g u i s h e d from the lead from the massive s u l p h i d e zones (Appendix C ). Consequently, the i n t r u s i o n of these l a t e dykes d i d not a f f e c t the o v e r a l l l e a d i s o t o p i c composition of those d e p o s i t s . I f the Eocene thermal and d e f o r m a t i o n a l event d i d a f f e c t e d the Eagle Bay Formation, the p a u c i t y of le a d of T e r t i a r y composition i s another argument a g a i n s t r e m o b i l i z a t i o n as a common process r e s p o n s i b l e f o r v a r i a t i o n s i n the le a d i s o t o p i c composition of galena. 88 4.8 SUMMARY The lead isotopic composition of deposits hosted by the Eagle Bay Formation indicates that three pulses of mineralization were responsible for sulphide concentration within the units of the Formation. The oldest mineralization i d e n t i f i e d in the Eagle Bay Formation is represented by cluster 1 with a model age of Devonian. This cluster characterized lead from polymetallic deposits which are cogenetic with f e l s i c to intermediate volcanic rocks of Devono-Mississippian age. Therefore, cluster 1 can be used to fingerprint such type of mineralization occurring in the Eagle Bay Formation. The second period of mineralization is Upper T r i a s s i c , and i s represented by cluster 2. This cluster contains almost half of the deposits — mainly veins and stratiform deposits — sampled for this study. The vein deposits indicate that there was a pulse of mineralization occurring during that period that i s mainly characterized by i n f i l l i n g of suitable structures. The stratiform deposits within this cluster may be either replacement or cogenetic in o r i g i n . If cogenetic, the part of the unit which host these deposits must be Upper T r i a s s i c rather than Cambrian as currently mapped (Schiarizza and Preto, 1984) since ressetting of the lead isotopic composition by 89 metamorphism cannot account f o r the T r i a s s i c model age of these d e p o s i t s . Based upon the upper c r u s t a l s i g n a t u r e of the Eagle Bay Formation, the Upper T r i a s s i c u n i t would probably be e q u i v a l e n t to rocks of the Slocan Group. Some d e p o s i t s , which have t h e i r lead i s o t o p i c composition f a l l i n g o u t s i d e of and to the r i g h t of c l u s t e r 2 , are hosted by an uranium r i c h member of the formation which i s probably the cause f o r the r a d i o g e n i c s i g n a t u r e . F i n a l l y , the l a s t major p e r i o d of m i n e r a l i z a t i o n recorded by the le a d i s o t o p e data from t h i s study i s mid-Cretaceous and represented by c l u s t e r 3 . T h i s event i s r e l a t e d to the i n t r u s i o n of the Baldy b a t h o l i t h . Lead i s o t o p i c compositions, of T e r t i a r y model age, are markedly absent and i n d i c a t e t hat even i f the Formation was a f f e c t e d by a thermal T e r t i a r y event no important m i n e r a l i z i n g processes were a s s o c i a t e d with i t . 90 5. CONCLUSIONS T h i s l e a d i s o t o p i c study of 37 m i n e r a l i z e d occurrences hosted by the Eagle Bay Formation i n the Adams P l a t e a u - Clearwater area allowed e v a l u a t i o n of the a p p l i c a b i l i t y of the 'shale' curve of Godwin and S i n c l a i r (1981) to d e p o s i t s i n the Adams Plateau-Clearwater area. The le a d i s o t o p i c composition of these d e p o s i t s p l o t g e n e r a l l y along the 'shale' curve i n d i c a t i n g t h a t the model i s s u b s t a n t i a l l y c o r r e c t . T h i s shows that the lea d source i s upper c r u s t a l i n o r i g i n , was d e r i v e d from autochthonous p o r t i o n of the Canadian C o r d i l l e r a , and i n v o l v e d Precambrian basement under the Eagle Bay Formation. I t a l s o r e i n f o r c e d the c o r r e l a t i o n of the Eagle Bay Formation with other p e r i - c r a t o n i c s u c c e s s i o n s , p a r t i c u l a r l y i n the Kootenay Arc and B a r k e r v i l l e Terranes. The 'shale' curve was inadequate f o r p r e c i s e model age det e r m i n a t i o n from the g a l e n a - l e a d data from the Eagle Bay Formation. B e t t e r c o i n c i d e n c e of the data was obtained with a remodeled curve using 2.OGa as departure time from the average growth curve of Stacey and Kramers (1975). T h i s curve has the same u value as the 'shale' curve, but has a lower w value of 45.35. The 2.OGa departure time approximates the time of formation of the C o r d i l l e r a n c r u s t , and was chosen because i t corresponds to ages determined by others f o r the Shuswap 91 Metamorphic Complex (c|_. Duncan , 1 9 8 2 ) . The l e a d i s o t o p i c c o m p o s i t i o n o f g a l e n a from the d e p o s i t s i n t h e E a g l e Bay F o r m a t i o n p l o t i n t h r e e d i s t i n c t c l u s t e r s a l o n g t h e r emode led c u r v e . The D e v o n i a n c l u s t e r 1 e n c l o s e s l e a d i s o t o p i c c o m p o s i t i o n s w h i c h c h a r a c t e r i z e o o g e n e t i c m i n e r a l i z a t i o n a s s o c i a t e d w i t h D e v o n o - M i s s i s s i p p i a n v o l c a n i c r o c k s . T h i s c l u s t e r t h e r e f o r e can be used t o f i n g e r p r i n t p o l y m e t a l l i c v o l c a n o g e n i c d e p o s i t s h o s t e d by t h e E a g l e Bay F o r m a t i o n . S i m i l a r l y , t h e m i d - C r e t a c e o u s c l u s t e r 3 can be used t o d i s t i n g u i s h v e i n d e p o s i t s r e l a t e d t o t h e i n t r u s i o n of t h e B a l d y b a t h o l i t h and of i t s s a t e l l i t e s . The Upper T r i a s s i c c l u s t e r 2 c o n t a i n s d e p o s i t s of v a r i o u s t y p e s so t h a t a u n i q u e i n t e r p r e t a t i o n cannot a p p l y t o a l l of t h e d e p o s i t s r e p r e s e n t e d . Some of them a r e e p i g e n e t i c v e i n s , and t h e i r f o r m a t i o n m i g h t be r e l a t e d t o j u x t a p o s i t i o n of t h e F e n n e l l F o r m a t i o n w i t h t h e E a g l e Bay F o r m a t i o n , or t o a y e t u n d e f i n e d e v e n t w h i c h a f f e c t e d t h e a r e a i n t h e T r i a s s i c . The s t r a t i f o r m d e p o s i t s on the Adams P l a t e a u , w h i c h a l s o p l o t i n t h a t c l u s t e r , a l s o may have formed d u r i n g such e v e n t , h o w e v e r , i f t h e m i n e r a l i z a t i o n i n t h e s e d e p o s i t s i s o o g e n e t i c w i t h t h e Cambr ian u n i t EBG, t h e i n t e r p r e t a t i o n of the l e a d model age i m p l y s t r a t i g r a p h i c r e c o n s i d e r a t i o n and the u n i t EBG s h o u l d be s u b d i v i d e d i n t o two d i s t i n c t members of Cambr ian ( u n i t E B G ) , and of Upper T r i a s s i c ( u n i t T-EBG) age t o accommodate t h e d a t a . 92 The galena l e a d i sotope study developed here f u r t h e r i l l u s t r a t e s the a p p l i c a b i l i t y of the common le a d method i n c a t e g o r i z i n g m ineral d e p o s i t s w i t h i n a given r e g i o n . 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G e o l o g i c a l A s s o c i a t i o n of Canada S p e c i a l paper 11, pp. 1-18. YORK, D. 1969. Least squares f i t t i n g of a s t r a i g h t l i n e with c o r r e l a t e d e r r o r s . E a r t h and P l a n e t a r y Science L e t t e r s , 5, pp. 320-324. ZARTMAN, R.E. 1974. Lead i s o t o p i c p r o v i n c e s i n the C o r d i l l e r a of the western United S t a t e s and t h e i r g e o l o g i c s i g n i f i c a n c e . Economic Geology, 69, pp. 792-805. 103 APPENDIX A ADAMS PLATEAU-CLEARWATER AREA DEPOSIT DESCRIPTIONS The f o l l o w i n g d e s c r i p t i o n s c o n s t i t u t e a b r i e f summary of l i t e r a t u r e review on the d e p o s i t s of the Adams P l a t e a u - Clearwater area augmented by o b s e r v a t i o n s , and i n some case d e t a i l e d work, made by the w r i t e r i n the summers 1984 and 1985. The c o m p i l a t i o n map of S c h i a r i z z a e t a_l.(1984) has been used to a s s i g n l i t h o l o g i c names to host u n i t s of the d e p o s i t s . The ab b r e v i a t e d names f o r these u n i t s (and subunits) appear i n parentheses. D e s c r i p t i o n s of these u n i t s and subunits appear on S c h i a r i z z a ' s map (op. c i t . ) and i n BCDM f i e l d w o r k papers from S c h i a r i z z a and/or Preto on the Adams P l a t e a u Clearwater area between 1978 and 1986. Table A.1: Mineral deposits in the Adams Plateau-Clearwater Area Deposit Name Deposit Type ADAMS PLATEAU AREA Beca Lucky Coon Spar Mosquito king BC Zn 1 Crowfoot Mtn Ford property Silver king Silver king-Queen Pet Red Mineral Claims Stratabound Stratiform/Remobilized Stratiform/Remobilized Stratiform/Remobilized Disseminations Replacement Volcanogenic Vein Vein Vein Vein JOHNSON LAKE AREA Agate Bay Twin Mountain Art Homestake Rea Gold Mineralized pods Vein Vein Volcanogenic/polymetal. Volcanogenic/polymetal. BARRIERE LAKES AREA Birk Creek Showings Enargite Fortuna White Rock June/Kajun Broken Ridge Leemac Strat i f orm/Volcanogenic Vein Vein Vein Vein Disseminations Vein VAVENBY-CLEARUATER AREA Chu-Chua Foghorn Rexspar Mt McClennan Vavenby Ps-75-185 Sonja Birch Island Tindal Volcanogenic/cyprus Vein Volcanogenic/Uranion Replacement Vein Vein Vein Vein Vein 1 05 ADAMS PLATEAU AREA: BECA: A l s o known as: Quest Group, Lucky S t r i k e , Rhode I s l a n d , Lakeview-Joe, Tom M i n f i l e number: 082M-054,055 M i n e r a l Inventory number: 82M4-PB4 Map number: 007; L a t . 51.050N long. 119.710W Pr o d u c t i o n , as l i s t e d i n M i n f i l e : 5 tonnes of ore (1926): 31 g Au 2,395 g Ag 1 , 496 kg Pb L o c a t i o n : The Beca property on the shore of Adams Lake, due east of Squaam Bay i s d i r e c t l y a c c e s s i b l e by boat. A switchback road dropping 1,800m from Nikwikwia lake on the western edge of the p l a t e a u , a l s o leads to the p r o p e r t y . Host rock: The area c o n s i s t s of a r e p e t i t i v e s u c c e s s i o n of a n d e s i t i c to r h y o l i t i c v o l c a n i c rocks and a s s o c i a t e d q u a r t z i t i c and a r g i l l a c e o u s meta-sedimentary rocks (EBA). The rocks are metamorphosed to g r e e n s c h i s t f a c i e s and show a high degree of s c h i s t o s i t y t h a t s t r i k e s about N85W and d i p s 25 to 45 degrees n o r t h . The more f e l s i c phase has c l e a r l y invaded a n d e s i t i c rocks which are preserved as x e n o l i t h s i n the f e l s i c rocks. Small g r a n i t i c i n t r u s i o n s immediatly south of the property boundary produced a thermal metamorphic aureole t h a t o v e r p r i n t s r e g i o n a l low grade metamorphism. The chemical s i m i l a r i t y between the g r a n i t i c rocks and the f e l s i c v o l c a n i c rocks may i n d i c a t e a comagmatic r e l a t i o n s h i p between these two rock types. M i n e r a l i z a t i o n : The two m i n e r a l i z e d areas found on the property are a s s o c i a t e d with p y r i t i c c h e r t y bands. The s u l p h i d e s occur as f i n e g r a i n e d conformable lenses c o n t a i n i n g p o r p h y r o b l a s t s of a r s e n o p y r i t e and l o c a l l a y e r s of s p h a l e r i t e . L o c a l l y , a l t e r e d r h y o l i t e i s l a c e d with narrow (1 to 25mm), c l o s e l y spaced quartz v e i n s which are s p o r a d i c a l l y m i n e r a l i z e d with galena and more r a r e l y with s p h a l e r i t e . Sample d e s c r i p t i o n : Samples are a f i n e g r a i n e d mixture of p y r i t e , c h a l c o p y r i t e , galena, and s p h a l e r i t e a s s o c i a t e d with c a l c i t e and minor q u a r t z . The samples were c o l l e c t e d from massive s u l p h i d e r i c h l a y e r s w i t h i n the s c h i s t beside the o l d a d i t s near the lake shore. References: BCDM ASS RPT 6680, 7040. BCDM GEM 1970 p. 314. 106 LUCKY COON: Al s o known as Mc G i l l i v a r y group, E l s i e , Speedwell, King Tut. M i n f i l e number: 082M-012 to 015 M i n e r a l Inventory number: 82M4-PB4 to PB7 Map number: 018; L a t . 51.070N Long. 119.600W Grades, as l i s t e d i n M i n f i l e : T o t a l d e p o s i t ( i n d i c a t e d 1972): 68,040 tonnes, cut o f f used: 296.0 g/t Ag 7.1 % Pb 4.8 % Zn P r o d u c t i o n , as l i s t e d i n M i n f i l e : from Lucky Coon, 496 tonnes of ore (1976-1977): 274 g Au 228,669 kg Ag 62,03 3 kg Pb 41,367 kg Zn 114 kg Cd : from East Lehmi, 30 tonnes of ore (1956): 31 g Au 35,146 g Ag 8,330 kg Pb 2,393 kg Zn L o c a t i o n : Lucky Coon i s on the Adams Pl a t e a u at an e l e v a t i o n of 1,830m. The property i s a c c e s s i b l e by logging roads e i t h e r from Scotch Creek across the p l a t e a u to the o l d open p i t , or from the south end of Adams Lake to w i t h i n 2km of the p r o p e r t y . Host Rock: The m i n e r a l i z a t i o n i s a s s o c i a t e d with black and dark brown s i l i c e o u s and g r a p h i t i c p h y l l i t e , and with p h y l l i t i c limestone (EBG). Wide bands of f i n e - g r a i n e d s e r i c i t i z e d q u a r t z i t e , i n t e r l a y e r e d with s m a l l e r c h l o r i t e - c a l c i t e r i c h bands occur c l o s e to s u l p h i d e - r i c h h o r i z o n s . These metasedimentary u n i t s are f o l d e d by the Nikwikwaia Lake synform and are surrounded by g r e e n s c h i s t s t h a t are d e r i v e d from mafic flows and t u f f s . Quartz f e l d s p a r porphyry dykes c r o s s c u t p a r t of the southern limb of the synform and show evidence of subsequent f o l d i n g . B a s i c dykes are a l s o present but are not w e l l exposed. S t r u c t u r e : I s o c l i n a l and asymmetric f o l d s , e s p e c i a l l y w e l l exposed i n the northern p i t , demonstrate the prominent r o l e of the s t r u c t u r e i n c o n t r o l l i n g the d i s t r i b u t i o n of the s u l p h i d e s . In such f o l d s , s u l p h i d e beds 25cm t h i c k on the limbs reach a t h i c k n e s s of 45cm i n the hinge zone. O r i g i n a l t e x t u r e i n the s u l p h i d e horizons has been o b l i t e r a t e d by the deformation. 107 M i n e r a l i z a t i o n : S i l v e r , l e a d and z i n c s u l p h i d e s are g e n e r a l l y r e s t r i c t e d to a s p e c i f i c s t r a t i g r a p h i c h o r i z o n ( s i l i c e o u s and g r a p h i t i c p h y l l i t e s , p h y l l i t i c limestones) that i s g e n e r a l l y continuous along s t r i k e f o r 2000m. In d e t a i l , however, the su l p h i d e zones are d i s c o n t i n u o u s due to r e m o b i l i z a t i o n and d i s r u p t i o n during f o l d i n g ( D i c k i e , 1985). The su l p h i d e s are f i n e - g r a i n e d and occur as bands, from 15cm to 1m wide separated by 30 to 90cm of s i l i c e o u s p h y l l i t e , or as vei n s i n s e r i c i t i c s c h i s t s . The m i n e r a l i z a t i o n c o n s i s t s of a r s e n o p y r i t e , p y r i t e , s p h a l e r i t e , galena, a r g e n t i t e and a l i t t l e t e t r a h e d r i t e . The r a t i o of the d i f f e r e n t s u l p h i d e s throughout the d e p o s i t i s v a r i a b l e ; the a r s e n o p y r i t e content v a r i e s from 1 to 25% (commonly diamond shaped g r a i n s are l o c a l l y e x t e n s i v e l y r e p l a c e d by s p h a l e r i t e and g a l e n a ) . The p y r i t e can comprise as much as 75% of the su l p h i d e zone but i s o f t e n embayed and/or r e p l a c e d by s p h a l e r i t e and galena; however, euhedral unbroken p y r i t e c r y s t a l s (probably formed by r e c r y s t a l l i z a t i o n ) do occur. The s p h a l e r i t e and galena are i n t i m a t e l y a s s o c i a t e d . Embayed i s l a n d s of s p h a l e r i t e with cusp-shape borders are common. Sample d e s c r i p t i o n : M a s s i v e sulph the s e r i c i t i c s c h i s t u n i t i n the c o n s i s t of small blebs of galena c a l c i t e i n a f i n e - g r a i n e d matrix and p y r i t e . i d e samples were c o l l e c t e d from o l d p i t number 1. The samples a s s o c i a t e d with quartz and composed mainly of s p h a l e r i t e References: BCDM ASS. RPT. 11,521. BCDM MMAR 1936 pp. D41-D43. BCDM MMAR 1930 pp. A184-A186. DICKIE, G.J. 1985. 108 S P A R : A l s o known as: Ex 1, Bel M i n f i l e number: 082M-017, 018 M i n e r a l Inventory number: 82M4-PB2, PB5 to PB7 Map number: 027; L a t . 51.060N Long. 119.540W Pr o d u c t i o n , as l i s t e d i n M i n f i l e : 274 tonnes of ore, (1952, 1953, 1955, 1976): 435 g Au 249,383 g Ag 4,953,594 kg Pb 891,766 kg Zn 291 kg Cu L o c a t i o n : The Spar d e p o s i t i s on the southeastern edge of the Adams Pl a t e a u l e s s than 2km west of the Mosquito King d e p o s i t . I t i s a c c e s s i b l e by the logging roads p a r a l l e l to Scotch Creek. Host Rock: M i n e r a l i z a t i o n i s hosted by f o l d e d limy p h y l l i t e s a s s o c i a t e d with minor s e r i c i t e q u a r z t i t e s , limestone and c h l o r i t i c meta-volcanics (EBGs). The s u l p h i d e h o r i z o n s and the host rocks are enclosed w i t h i n the same in t e r m e d i a t e to mafic v o l c a n i c and v o l c a n i c l a s t i c sequences encountered at the Mosquito King and Lucky Coon d e p o s i t s . M i n e r a l i z a t i o n i s a l s o cut by small f i n e - g r a i n e d d i o r i t e and g r a n i t e porphyry dykes. S t r u c t u r e : The rocks i n the v i c i n i t y of the d e p o s i t are s t r o n g l y f o l i a t e d , have a general east-west s t r i k e , and d i p g e n t l y northward. S t r a t a show d r a g f o l d i n g and c r e n u l a t i o n cleavage; f o l d axes s t r i k e S600w with low plunge (the c r e s t plunges 100sw). Two sets of f r a c t u r e s cut the r o c k s : one d i p p i n g s t e e p l y north-south and the other d i p p i n g more s h a l l o w l y d i p p i n g east-west. The n o r t h - south set seems to have acted as a channel way f o r m i n e r a l i z i n g s o l u t i o n s i n c e f a i r l y massive f i n e - g r a i n e d s p h a l e r i t e i s found i n the f o l d e d zones d i r e c t l y above such f r a c t u r e s ( D i c k i e , 1985). The east-west set terminates a b r u p t l y some m i n e r a l i z e d h o r i z o n s and thus may be p a r t of a l a t e f r a c t u r i n g event. M i n e r a l i z a t i o n : S t r a t i f o r m s u l p h i d e masses occur as f o l d e d elongated bodies (extending over 400m). The m i n e r a l i z a t i o n d i s t r i b u t i o n does not appear to be c o n f i n e d to only one l a y e r . However the m i n e r a l i z a t i o n i s a p p a r e n t l y stratabound and was o r i g i n a l l y d e p o s i t e d w i t h i n a s i l i c e o u s u n i t . T h i s u n i t has been f o l d e d and metamorphosed, r e s u l t i n g i n the m i g r a t i o n and c o n c e n t r a t i o n of the s u l p h i d e m i n e rals along the c r e s t s of f o l d s or crumpled zones i n the e n c l o s i n g s e r i c i t i c sequence ( D i c k i e , 1 985 ) . 109 The s u l p h i d e h orizons are composed of massive l a y e r e d galena bordered by a f r i n g e zone of galena, s p h a l e r i t e , p y r i t e , p y r r h o t i t e and c h a l c o p y r i t e . Minor amounts of t e t r a h e d r i t e , a r s e n o p y r i t e and a r g e n t i t e a l s o occur. The bands of massive m i n e r a l i z a t i o n (40cm t h i c k ) are separated by s e r i c i t i z e d a r g i l l i t e . Sample d e s c r i p t i o n : Samples were c o l l e c t e d from the main o l d a d i t s from which most of the minerals were e x t r a c t e d i n the 1950's. F i n e - g r a i n e d galena i s a s s o c i a t e d with s p h a l e r i t e and p y r i t e i n a quartz carbonate matrix. A v e i n c o n t a i n i n g abundant f l u o r i t e was a l s o sampled. References: BCDM MMAR 1953 pp. 102-103. HAINSWORTH, W.G. 1973. Unpublished r e p o r t on the Giant M e t a l l i c Mines. JAMES, D.H. 1949. 1 1 0 MOSQUITO KING: A l s o known as: Oro, King Tut, Garnet M i n f i l e number: 082M-016, 140 M i n e r a l Inventory number: 82M4-AG2, CU2 Map number: 025; Lat. 51.060N Long. 119.520W Reserves, as l i s t e d i n M i n f i l e 40,824 tonnes @ (Ind. 1981): 1.25 g/t Au 21.70 g/t Ag 10.0 % Pb 8.5 % Zn P r o d u c t i o n , as l i s t e d i n M i n f i l e 419 tonnes of ore (1972-73, 1976): 219 g Au 232,154 g Ag 22,721 kg Pb 18,328 kg Zn L o c a t i o n : The Mosquito King p r o p e r t y i s l o c a t e d at an approximate e l e v a t i o n of 1,750m on a r i d g e on the Adams P l a t e a u . A l o g g i n g road between Nikwikwain Gold Creek and Kwikoit Creek leads to the p r o p e r t y . Host Rock: Sulphide lenses are enclosed w i t h i n i n t e n s i v e l y s i l i c i f i e d beds of a r g i l l i t e s and quartz s e r i c i t e rocks. These c l a s t i c rocks are p a r t of a predominantly mafic v o l c a n i c s u c c e s s i o n (EBGs). These u n i t s have been metamorphosed to g r e e n s c h i s t f a c i e s and c o n t a i n abundant c h l o r i t e and s e r i c i t e . S i l i c i f i c a t i o n and b l e a c h i n g i s u b i q u i t o u s i n the limy a r g i l l i t e s and i n the q u a r t z i t e , but not i n the g r e e n s c h i s t . The sequence i s cut by a n d e s i t e and hornblende porphyry dykes which are s i m i l a r to those o c c u r r i n g on the Lucky Coon property. S t r u c t u r e : F o l d s on the p r o p e r t y have a predominent east-west t r e n d but axes s t r i k i n g north-south are not uncommon; d r a g - f o l d i n g i s u b i q u i t o u s i n most exposures. J o i n t s and small north s t r i k i n g f a u l t s seem to c o n t r o l , at l e a s t l o c a l l y , the mineral d i s t r i b u t i o n . M i n e r a l i z a t i o n : At the main showing m i n e r a l i z a t i o n v a r i e s i n t h i c k n e s s from 60cm to 3.5m (average 1.5m). I t c o n s i s t s of s e v e r a l t h i n , c l o s e l y spaced beds composed of black s p h a l e r i t e , galena, p y r i t e , c h a l c o p y r i t e and f i n e - g r a i n e d p y r r h o t i t e which are more or l e s s concordant with the e n c l o s i n g host. Lower i n the s u c c e s s i o n , beds have been m i n e r a l i z e d with i r o n s u l p h i d e s (mainly p y r r h o t i t e ) and minor s p h a l e r i t e . P y r r h o t i t e and p y r i t e r i c h lenses (up to 60cm wide) are e x t e n s i v e i n the limy a r g i l l i t e s . Disseminated p y r i t e a l s o occurs along bedding planes and i n f r a c t u r e s a s s o c i a t e d with s i l i c i f i e d zones. M i n e r a l i z e d beds can be t r a c e d over 915m along a N700E s t r i k e 111 but they are not uni f o r m l y or c o n t i n u o u s l y d i s t r i b u t e d . Veins of galena and s p h a l e r i t e occur l o c a l l y i n the s c h i s t s and i n the limy beds. Magnetite and secondary copper minerals are l o c a l l y abundant i n the mafic v o l c a n i c s . Minor m i n e r a l i z a t i o n a l s o occurs a s s o c i a t e d with the porphyry dykes (James, 1949). Sample d e s c r i p t i o n : Well c r y s t a l l i z e d but deformed galena i n a quartz and c a l c i t e matrix c o n t a i n i n g a minor amount of p y r i t e and s p h a l e r i t e i s c h a r a c t e r i s t i c of the main m i n e r a l i z a t i o n . The samples come from the main m i n e r a l i z e d area of the d e p o s i t i n the open o l d workings. Galena was a l s o c o l l e c t e d from c r o s s - c u t t i n g v e i n s near a dyke. References: BCDM ASS RPT 45, 7019. BCDM MMAR 1949 pp. A134-136. BCDM MMAR 1930 pp. A186-188. DICKIE, G.J. 1985. JAMES, D.H. 1949. 1 1 2 BC ZN 1: Al s o known as: Cu 1, Cu 5 M i n f i l e number: 082M-138, 139 Mi n e r a l Inventory number: 82M4-CU1, ZN2 Map number: 022; L a t . 51.01 ON Long. 1 1 9.520W Grades, as l i s t e d i n M i n f i l e : I n d i c a t e d : 148,000 tonnes P o s s i b l e : 272,000 tonnes @ 0.19 % Cu Reserves: 326,000 tonnes @ 0.35 % Cu 38 G/t 6 % Pb 2.41 % Zn 0.19 % Cu 0.14 % Mo L o c a t i o n : T h i s m i n e r a l i z e d occurrence i s about 5.5km south of the Mosquito King d e p o s i t near the l o c a l l y named China Creek. I t i s a c c e s s i b l e from one of the numerous log g i n g roads on the Adams P l a t e a u . Host Rock: A r g i l l a c e o u s p h y l l i t e s are i n t e r c a l a t e d with limy and s i l i c e o u s h o r i z o n s interbedded with abundant greenstone d e r i v e d from mafic v o l c a n i c s and v o l c a n o c l a s t i c s (EBG). The sequence i s in t r u d e d by a s e r i e s of minor d i a b a s i c dykes and s i l l s . One dyke sampled c o n s i s t s of hornblende, q u a r t z , andradite and minor c l i n o p y r o x e n e , c l i n o z o i s i t e , c h l o r i t e and p l a g i o c l a s e . S c h i s t o s i t y of the host rock s t r i k e s e a s t - n o r t h e a s t and dips moderately to the northwest. M i n e r a l i z a t i o n : A s t r a t i f o r m zone c o n t a i n s disseminated s p h a l e r i t e and galena with minor p y r r h o t i t e and l o c a l l y abundant magnetite. Some zones of high i r o n content y i e l d good Cu and Au va l u e s . One zone may be continous f o r over 510m; i t has a width of as much as 1.65m. Sample d e s c r i p t i o n : F i n e - g r a i n e d disseminated i n h i g h l y c h l o r i t i c m i n e r a l i z a t i o n . s p h a l e r i t e and minor galena s c h i s t i s c h a r a c t e r i s t i c of the References: BCDM ASS RPT 5132 BCDM GEM 1978, p. E101. BCDM GEM 1974, p. 95. 11 3 CROWFOOT MOUNTAIN: A l s o known as: Fluke, Saul M i n f i l e number: 082M-104, 105 Map number: 032; L a t . 51.060N Long. 119.250W Grade: composite sample, gross average: 0.34 g/t Au (From ASS.RPT.) 170.0 g/t Ag 0.1 % Cu 5.0 % Pb 8.0 % Zn 0.18 % Sn L o c a t i o n : The Fluke claims on Crowfoot Mountain are approximatly 16km north of Magma Bay on the north shore of Shuswap Lake, and are a c c e s s i b l e by f o r e s t r y roads. Host Rock: M i n e r a l i z a t i o n i s hosted by p h y l l i t i c marble and a l t e r e d limestone a s s o c i a t e d with p h y l l i t e , q u a r t z i t e and greenstone s i m i l a r to those found i n the other d e p o s i t s on the P l a t e a u (EBG). These rocks are s t r o n g l y f o l i a t e d and l i n e a t e d . The area i s i n t r u d e d by an enormous number of dykes, s i l l s and small i r r e g u l a r bodies of g r a n i t i c and d i a b a s i c r o c k s . S i l i c i f i c a t i o n i s e x t e n s i v e i n the v i c i n i t y of the s u l p h i d e r i c h zones. S t r u c t u r e : Intense drag f o l d i n g , d i s r u p t i o n of limy horizons and g r e e n s c h i s t f a c i e s i n the meta-volcanic rocks are i n d i c a t i o n s t h a t the area has the same de f o r m a t i o n a l c h a r a c t e r i s t i c s as the r e s t of the Adams P l a t e a u . S t r u c t u r a l d e t a i l s of the deformation i n the v i c i n i t y of the d e p o s i t are not known. M i n e r a l i z a t i o n : M i n e r a l i z a t i o n has been d e s c r i b e d as s u l p h i d e replacement i n bands of limestone and marble. On a l a r g e s c a l e the s u l p h i d e s are c o n f i n e d to h o r i z o n s w i t h i n the limestone, but the d i s t r i b u t i o n of the s u l p h i d e s i s h i g h l y e r r a t i c . Galena and s p h a l e r i t e occur i n pods as w e l l as i n d i s s e m i n a t i o n s throughout the rock. Sulphides are a l s o found i n v e i n s c u t t i n g c h l o r i t i c s c h i s t . These v e i n s s t r i k e i n the same d i r e c t i o n as the main f o l i a t i o n ( s t r i k i n g N400N and d i p p i n g moderately northwestward) but d i p i n the o p p o s i t e d i r e c t i o n . Veins are unevenly m i n e r a l i z e d with galena, p y r i t e , s p h a l e r i t e and c h a l c o p y r i t e . Sample d e s c r i p t i o n : Blebs of c a l c i t e , p y r i t e , galena and s p h a l e r i t e p l u s minor quartz i n laminated but c o n t o r t e d and d i s c o n t i n u o u s limestone lenses were sampled on the p r o p e r t y . V e i n m i n e r a l i z a t i o n c l o s e to a lamprophyre dyke was a l s o sampled. References: BCDM ASS RPT 609, 3821, 4031, 6230, 6857. 1 1 4 FORD PROPERTY: Map number: 038; L a t . 51.000N Long. 119.600w L o c a t i o n : The Ford p r o p e r t y i s centred near the head of Woolford Creek. Access i s f a c i l i t a t e d by a network of logging roads. Host Rock: The main rock types i n the area are s e r i c i t e quartz p h y l l i t e and s e r i c i t e f e l s p a r quartz p h y l l i t e c o n t a i n i n g abundant medium to f i n e - g r a i n e d angular c l a s t s ( u n i t EBA). I t i s l i k e l y t h a t these rocks are a l t e r e d i n t e r m e d i a t e to f e l s i c t u f f s . The u n i t s have a fragmental and p o r p h y r o b l a s t i c appearance due to metamorphism. A g r a p h i t i c limestone c o n t a i n i n g u n f o l i a t e d white quartz sandstone a l s o occurs i n the area. A l l these rocks have undergone g r e e n s c h i s t f a c i e s r e g i o n a l metamorphism and l o c a l l y c o n t a i n abundant c h l o r i t e . Post metamorphic i n t r u s i o n of d i o r i t e and lamprophyre dykes, cut through the rocks of the p r o p e r t y . S t r u c t u r e : The contact between the d i f f e r e n t u n i t s appear i n s e v e r a l p l a c e s to be planar but not continous along s t r i k e . The w e l l developed f o l i a t i o n , p a r a l l e l to s u b - p a r a l l e l with the l i t h o l o g i e s , i s g e n t l y warped; t h i s probably i n d i c a t e s the presence of a l a r g e open f o l d plunging to the north across the p r o p e r t y . S t e e p l y d i p p i n g n o r t h - n o r t h e a s t e r l y t r e n d i n g f a u l t s t r u n c a t e and o f f s e t some of the u n i t s . M i n e r a l i z a t i o n : The property i s the probable host of s t r a t i f o r m massive s u l p h i d e d e p o s i t s as four zones c o n t a i n m i n e r a l i z a t i o n : 1 ) a s e r i e s of f i v e lenses (5 to 20cm t h i c k ) of massive s u l p h i d e c o n t a i n i n g mainly p y r r h o t i t e and small amounts of s p h a l e r i t e and c h a l c o p y r i t e a s s o c i a t e d with abundant s i l i c a (the m i n e r a l i z e d lenses are conformable to the f o l i a t i o n ) , 2) a s e r i e s of narrow l a y e r s (1 to 3cm t h i c k ) of massive p y r i t e w i t h i n a c h l o r i t i c quartz p h y l l i t e u n i t , 3) p y r i t e r i c h m e t a - r h y o l i t e that may be a metamorphic e q u i v a l e n t of a q u a r t z - p y r i t e e x h a l a t i v e u n i t , and 4) a narrow (1 to 3cm t h i c k ) s i l v e r r i c h , g a l e n a - c h a l c o p y r i t e - q u a r t z - c a l c i t e v e i n c u t t i n g through s e r i c i t i c c h l o r i t e quartz s c h i s t . An a l t e r a t i o n zone c o n s i s t i n g of secondary q u a r t z , muscovite, b i o t i t e and a c t i n o l i t e i s present i n the lower p a r t of the s e c t i o n . T h i s zone has c h a r a c t e r i s t i c s s i m i l a r to a thermal metamorphic aureole and i s i n t e r p r e t e d by Robinson (1986) to have been generated by a i n t r u s i v e at depth. Sample D e s c r i p t i o n : Samples c o l l e c t e d c o n s i s t of f i n e g r a i n e d massive s u l p h i d e s c o n t a i n i n g galena a s s o c i a t e d with abundant p y r r h o t i t e and minor s p h a l e r i t e . Reference ROBINSON, C. 1986. Geology of the Ford p r o p e r t y Adams Pl a t e a u , south c e n t r a l B r i t i s h Columbia. Unpublished BSc T h e s i s , U n i v e r s i t y of B r i t i s h Columbia. 1 1 5 SILVER KING-A: M i n f i l e number: 082M-129 Mi n e r a l Inventory number: 82M4-AG3 Map number: 036; L a t . 50.950N Long. 119.480W L o c a t i o n : T h i s small showing i s l e s s than 500m north of the Spar d e p o s i t along the log g i n g road l e a d i n g to the Lucky Coon d e p o s i t . D e s c r i p t i o n : M i n e r a l i z a t i o n occurs i n a l t e r e d limestone i n c l o s e p r o x i m i t y to b r e c c i a t e d rock c o n t a i n i n g fragments of a r g i l l i t e ( f r e s h and p a r t i a l l y replaced) cemented by sugary q u a r t z . The su l p h i d e s do not occur d i r e c t l y i n the b r e c c i a and seem r e s t r i c t e d to the surrounding limestone. Zones r i c h i n c a l c i t e , f l u o r i t e and porcelaneous quartz occur adjacent to the s u l p h i d e s . Sample d e s c r i p t i o n : Small seams of f i n e g r a i n e d galena mixed with c o a r s e r s p h a l e r i t e g r a i n s i n a c a l c i t i c gangue are c h a r a c t e r i s t i c of the sampled specimens. Reference: BCDM GEM 1971, p. 436. SILVER KING-SILVER QUEEN: Al s o known as: King James M i n f i l e number: 082L-NW044 Map number: 045; L a t . 50.950N Long. 119 . 4 8 0 w L o c a t i o n : A l a r g e exposure of t h i s v e i n occurs on the east s i d e of Scotch Creek 8km north of the post o f f i c e of Scotch Creek along the l o g g i n g road that f o l l o w s the power l i n e . D e s c r i p t i o n : M i n e r a l i z a t i o n occurs i n a v e i n system which i s about 30m wide and s t r i k e s n o r t h w e s t e r l y through the c h l o r i t i c s c h i s t and c a l c a r e o u s p h y l l i t e of u n i t EBG. The v e i n contains pockets of coarse g r a i n e d galena and s p h a l e r i t e i n q u a r t z - c a l c i t e gangue. References: BCDM GEM 1977, p. E85. BCDM GEM 1975, p. E55. 11 6 PET: M i n f i l e number: 082M-143 Map number: 026; L a t . 51.050N Long. 119.530W L o c a t i o n : T h i s showing i s exposed i n a t r e n c h , about 1km south of the main workings of the Spar d e p o s i t . D e s c r i p t i o n : Small amounts of galena and s p h a l e r i t e (marmate) occurs as d i s s e m i n a t i o n i n c h l o r i t i c s c h i s t . Sample d e s c r i p t i o n : No d e s c r i p t i o n i s a v a i l a b l e . Data used came from analyses by the GSC (GSC number: G79PE). Refernces: BCDM ASS RPT 5919. BCDM GEM 1976, p. E59. RED MINERAL CLAIMS: A l s o known as: Fox, Deer, F i r , Pat, Joe M i n f i l e number:82M-154 Map numbers: 033 L a t . 51.080N Long. 119.380W 034 51.100N 119.380W 035 51.070N 119.380w 037 51.050N 119.540w L o c a t i o n : The m i n e r a l i z e d showings are c l u s t e r e d around Lichen Mountain, l o c a t e d northwest of the Mosquito King d e p o s i t , about 3km e a s t - s o u t h e a s t of the j u n c t i o n of Cross and Kwikoit Creeks. Host Rock: The m i n e r a l i z a t i o n i s mostly found i n carbonate l a y e r s a s s o c i a t e d with a r g i l l i t e s and meta-volcanics (EBG). L o c a l l y manganese r i c h bands occur near the m i n e r a l i z e d zones. The rocks are f o l d e d and metamorphosed, as are t h e i r e q u i v a l e n t s elsewhere on the Adams P l a t e a u . The main f o l i a t i o n i n the rocks s t r i k e s n o r t h e a s t and d i p s n o r t h . M i n e r a l i z a t i o n : These mineral occurrences are of small s i z e , outcrop on s u r f a c e , and do not have any known underground extent. Quartz v e i n s c o n t a i n i n g a r g e n t i f e r o u s galena cut through both v o l c a n i c rocks and limestone. The m i n e r a l i z a t i o n has been d e s c r i b e d as conformable lenses of c y l i n d r i c a l shape; but t h i s geometry could not be confirmed i n the f i e l d . Sample d e s c r i p t i o n : A l l the c o l l e c t e d samples c o n t a i n coarse galena i n quartz gangue a s s o c i a t e d with v a r i a b l e amounts of s p h a l e r i t e and p y r i t e . The galena from the occurrence number 033, above, c l e a r l y shows evidence of deformation. References: BCDM Open F i l e . BCDM E x p l o r a t i o n i n BC 1979 11 7 JOHNSON LAKE AREA: AGATE BAY: A l s o known as: Try Me, Rankin Group, Karen, Joe M i n f i l e number: 082M-053 Map number: 006; L a t . 51.08ON Long. 119.75oW L o c a t i o n : The showing i s exposed at the shore l i n e near the northern end of Squaam Bay. Host Rock: F i n e - g r a i n e d q u a r t z - s e r i c i t e s c h i s t s are interbedded with c h l o r i t i c s c h i s t (EBAa). These greenstones are h i g h l y a l t e r e d and c o n t a i n s w e l l s of carbonates ( c a l c i t e and a n k e r i t e ) . T h i s u n i t , mapped as part of the f e l s i c package of the Eagle Bay Formation, bear more resemblance to the more mafic sequence ( u n i t EBG) found to the north, and on the other s i d e of Adams Lake. S t r u c t u r e : The m i n e r a l i z a t i o n occurs w i t h i n a h i g h l y a l t e r e d s c h i s t package. The main f o l i a t i o n s t r i k e s i n average at N70oW and d i p s from 22o to 55o n o r t h e a s t . Abundant small f a u l t s cut the s c h i s t . M i n e r a l i z a t i o n : Low grade Pb-Zn-Cu occurs i n quartz v e i n s . Two types of ve i n s cut the host rocks: 1) narrow (1 to 3cm t h i c k ) c l o s e l y spaced v e i n s more or l e s s conformable to the s c h i s t o s i t y , 2) d i s c o n t i n o u s l a r g e r veins (8 to 40cm t h i c k ) s c a t t e r e d through the s c h i s t s , as pods or l e n s e s . A l l the v e i n - l i k e masses pinch and s w e l l e r r a t i c a l l y and are truncated by f a u l t s . In both types of occurrences, the su l p h i d e s are e r r a t i c a l y d i s t r i b u t e d and c o n s i s t of p y r i t e and s p h a l e r i t e with t r a c e s of galena and c h a l c o p y r i t e i n a qu a r t z , c a l c i t e and a n k e r i t e gangue. Tourmaline has been r e p o r t e d i n these veins (BCDM, 1961). Sample d e s c r i p t i o n : Euhedral galena g r a i n s i n q u a r t z - c a l c i t e v e i n s c u t t i n g a l t e r e d greenstone. References: BCDM ASS RPT 4135. BCDM MMAR 1961 pp. 53-55. 11 8 TWIN MOUNTAIN: Al s o known as: S t a r , Max, Hope M i n f i l e number: 082M-020 Mi n e r a l Inventory number: 82M4-PB3 Map number: 019; L a t . 51.13ON Long. 119.80OW Grade: S u b j e c t i v e average value of 11 samples co n s i d e r e d to be r e p r e s e n t a t i v e of the m i n e r a l i z e d zone (BCDM ASS RPT 9882) are: B a r i t e i s a l s o present i n q u a n t i t i e s s u f f i c i e n t to be of p o s s i b l e economic i n t e r e s t . L o c a t i o n : The showing occurs on the south-east f l a n k of Samatosum Mountain at an e l e v a t i o n of 1,200 to 1,500m. The o l d workings are a c c e s s i b l e v i a l o g g i n g roads. Host Rock: Two conformable m i n e r a l i z e d zones or veins are hosted by g r e e n s c h i s t and c h l o r i t e s c h i s t d e r i v e d from mafic to i n t e r m e d i a t e v o l c a n i c and v o l c a n i c l a s i c rocks (EBGq). These rocks c o n t a i n abundant t h i n carbonaceous l a y e r s and f r a c t u r e f i l l i n g s , and show remnant p i l l o w s t r u c t u r e s . Tuffaceous and more s i l i c e o u s horizons occur w i t h i n the g r e e n s c h i s t . T h i s package of rocks i s o v e r l a i n by the T s h i n a k i n Limestone. S t r u c t u r e : Rocks i n the area are moderately c o n t o r t e d and i n p l a c e s e x h i b i t kink banding. The main f o l i a t i o n s t r i k e s N40OW and d i p s 430NW. M i n e r a l i z a t i o n : The v e i n s or m i n e r a l i z e d zones c o n t a i n p y r i t e , c h a l c o p y r i t e , s p h a l e r i t e and galena i n a carbonate gangue with minor q u a r t z , and b a r i t e ; the zones l o c a l l y are a z u r i t e s t a i n e d . M i n e r a l i z e d zones range i n width from 20cm to over 1m. An a p p a r e n t l y u n r e l a t e d v e i n l a c k i n g v i s i b l e m i n e r a l i z a t i o n c o n t a i n s up to an estimated 30 percent b a r i t e . Sample d e s c r i p t i o n : The analysed samples are from an open trench c l o s e to the o l d a d i t s . They c o n t a i n blobs of s p h a l e r i t e , p y r i t e and galena i n a c a l c i t i c matrix. 0.170 8.84 0.90 2.15 0.18 g/t Au g/t Ag % Pb % Zn % Cu References: BCDM ASS RPT 9882, 2093. BCDM MMAR 1936, p. D39. 11 9 A r t : M i n f i l e number: 082M-124 Map number: 0 1 7 ; L a t . 5 1 . 1 0 O N Long. 119.95ow L o c a t i o n : T h i s showing i s adjacent to the road between Louis Creek and Squaam Bay, near the east end of F o r e s t Lake. Host Rock: M i n e r a l i z a t i o n i s hosted by a spotted quartz muscovite s c h i s t c o n t a i n i n g limy q u a r t z i t i c pods. T h i s s c h i s t i s p art of the subunit EBSs c h a r a c t e r i z e d by p h y l l i t i c sandstone, g r i t , p h y l l i t e , c h l o r i t e s c h i s t , and q u a r t z i t e with a small amount of limestone. M i n e r a l i z a t i o n : Quartz carbonate v e i n s c o n t a i n i n g minor p y r i t e and galena cut the s c h i s t . Traces of f u c h s i t e are a l s o present. Sample d e s c r i p t i o n : Quartz v e i n s i n the s c h i s t c o n t a i n pods of galena a s s o c i a t e d with minor carbonates. References: BCDM M i n f i l e number 082M-124. 120 HOMESTAKE: M i n f i l e number: 082M-025 Mi n e r a l i n v e n t o r y number: 82M4-AG1 Map number: 011; L a t . 51.11 O N Long. 119.83ow Reserve: proven (The F i n a n c i a l Post, Jan. 1973) are 1,010,800.0 tonnes of ore: 240.0 g/t Ag 2.5 % Pb 4.0 % Zn 0.6 % Cu 28.0 % b a r i t e P r o d u c t i o n , as l i s t e d i n M i n f i l e : 6,965 tonnes of ore (between 1935 to 1941) 12,400 g Au 9,565,900 g Ag 11,080 kg Cu 171,325 kg Pb 426,520 kg Zn L o c a t i o n : Access to the property i s by a switchback road that leaves the main road 5km northwest of Squaam Bay. Host Rock: The m i n e r a l i z e d b a r i t e lenses are o v e r l a i n by s i d e r i t i c p h y l l i t e that c o n t a i n interbedded a r g i l l i t e , and by a t u f f a c e o u s c h l o r i t i c s c h i s t u n i t (EBAa). A wide zone of a l t e r e d rock occurs below the m i n e r a l i z e d l e n s . Regional metamorphism and l o c a l hydrothermal a l t e r a t i o n have obscured the primary composition of the host rocks; consequently, the f o l l o w i n g u n i t d e s c r i p t i o n s are based on mineral assemblages (Table ). A p o o r l y exposed c h l o r i t e p h y l l i t e ( u n i t 1) occurs i n the southern p a r t of the map area ( F i g . A.1). I t i s a t h i n l y laminated brownish green c h l o r i t e p h y l l i t e t h a t i s n o t i c e a b l y l e s s f o l i a t e d than the o v e r l y i n g s c h i s t s . U n i t 2 comprises dominantly s e r i c i t e - q u a r t z s c h i s t with abundant disseminated p y r i t e throughout. U n i t 2a i s a more massive phase of the "paper" s c h i s t of u n i t 2b and c o n t a i n s l e n t i c u l a r , s i l i c a - r i c h s e g r egations up to 6 cm i n l e n g t h . U n i t 2b, r e f e r r e d to as a s e r i c i t e - q u a r t z "paper" s c h i s t , i s the most conspicuous u n i t i n the map area. In outcrop, the paper s c h i s t u n i t i s e a s i l y d i s c e r n i b l e by i t s f i s s i l e appearance and by i t s weathered c o a t i n g of yellow f e r r i c s u l p h a t e . I t i s the host and the f o o t w a l l to the b a r i t e - s u l p h i d e lenses and i s i n t e r p r e t e d to be a h i g h l y a l t e r e d , predominantly f e l s i c t u f f u n i t . A number of quartz v e i n s up to a metre t h i c k are found w i t h i n the paper s c h i s t below the b a r i t e OJ nj O H- 0 ua CD C W H 01 CD H > O • OJ -> a cn 3: OJ r-h M O O M l 3 rr O fD » OJ o 3 3 D-. CD tn O rt O OJ C X n- ro (D TJ M M - O •o -» CD *X> M 00 rt cn • in M " o H- ua ua CD o 1-' o ua •<: OJ a 0N. 'IT UNIT 5. zt UNIT 2b •'C|;UNIT 4 1 1 \ \ v . UNIT 3 \ LEGEND EAGLE BAY FORMATION I 5 I TUFFACEOUS CHLORITIC SCHIST I 4 I ANKERITIC PHYLLITE. 4a — ARGILLITE [~3~| CHLORITE SCHIST I 2c j MINERALIZATION: BARITE BLUFF I 2b I SERICITE-QUARTZ PAPER SCHIST I 2o I SERICITE-QUARTZ SCHIST I I I CHLORITE PHYLLITE UNIT 2o UNIT I 122 l e n s e s ; they c o n t a i n p y r i t e but are g e n e r a l l y barren of other s u l p h i d e s . A dark green laminated c h l o r i t e s c h i s t ( u n i t 3) occurs s t r a t i g r a p h i c a l l y above and l a t e r a l l y west of u n i t 2b. I t c o n s i s t s of carbonate phenocrysts w i t h i n a f i n e - g r a i n e d c h l o r i t e - f e l d s p a r matrix. These phenocrysts, which may be pseudomorphic a f t e r p l a g i o c l a s e , are rimmed and p a r t i a l l y r e p l a c e d by c h l o r i t e . T h i s u n i t i s probably a l t e r e d andesite t u f f ; i t s c o n t a c t with u n i t 2b i s i n pa r t an i n t e r f i n g e r i n g of f e l s i c and intermediate t u f f s but may a l s o r e f l e c t an i r r e g u l a r p e r v a s i v e p o t a s s i c and s i l i c i c a l t e r a t i o n boundary. A f i n e - g r a i n e d a n k e r i t i c p h y l l i t e ( u n i t 4) composed of interbedded l a y e r s of a n k e r i t e - b e a r i n g c h l o r i t i c p h y l l i t e occurs above u n i t s 2b and 3. In outcrop l i m o n i t i c pseudomorphs a f t e r i r o n - r i c h carbonate g i v e the rocks a c h a r a c t e r i s t i c brown t i n g e . Some f i n e - g r a i n e d p y r i t i c a r g i l l i t e s w i t h i n the p h y l l i t e package are the most continuous and r e l i a b l e marker u n i t s at Homestake. These a r g i l l i t e l a y e r s c o n t a i n elongated quartz eyes and augen-shaped c l a s t s up to 0.8 mm i n diameter. The quartz eyes have cores of euhedral p y r i t e c r y s t a l s and are set i n a f i n e - g r a i n e d p y r i t i c carbonaceous matrix of p h y l l o s i l i c a t e s , q u a r t z , and f e l d s p a r . U n i t 4 i s i n t e r p r e t e d to be l a r g e l y a sedimentary c l a s t i c rock with interbedded c h l o r i t i c t u f f l a y e r s . A t u f f a c e o u s c h l o r i t e s c h i s t ( u n i t 5) occurs on the steep c l i f f s i n the upper, northern p o r t i o n of the Homestake area. The rock c o n t a i n s massive and t u f f a c e o u s zones composed of c h l o r i t e and carbonate (probably developed from r e g i o n a l metamorphism of rocks of int e r m e d i a t e compositon such as a n d e s i t e ) . R e l i c t f l a t t e n e d f e l s i c c l a s t s imply a p y r o c l a s t i c o r i g i n f o r at l e a s t p a r t of t h i s u n i t . P y r i t i c quartz v e i n s and c a l c i t e s t r i n g e r s occur throughout the s c h i s t , and i n s e v e r a l p l a c e s cut the f o l i a t i o n . L o c a l l y , c h e r t y pods and a r g i l l i t e l a y e r s are interbedded with the s c h i s t . T h i s u n i t i s o v e r l a i n by a t h i c k greenstone sequence (V.A. Preto, p e r s . comm., 1985). S t r u c t u r e : A w e l l d e f i n e d p e n e t r a t i v e mineral f o l i a t i o n i s u b i q u i t o u s throughout the Homestake area. The f o l i a t i o n i s o u t l i n e d by the p r e f e r r e d o r i e n t a t i o n of p l a t y minerals such as s e r i c i t e and c h l o r i t e , and l e n t i c u l a r s i l i c a - r i c h s egregations i n u n i t 2. F o l i a t i o n p l o t t e d on a st e r e o n e t ( F i g . A.2), has a reasonably t i g h t c l u s t e r around a maximum t h a t s t r i k e s 120 degrees and d i p s 30 degrees n o r t h e a s t . O r i g i n a l c o m p o s i t i o n a l l a y e r i n g g e n e r a l l y i s d i f f i c u l t to see. Except w i t h i n the a r g i l l i t e bands of u n i t 4, i t has been l a r g e l y obscured by e i t h e r metamorphism or the in t e n s e deformation. In g e n e r a l , however, i t s t r i k e s between 120 and 160 degrees with 123 N F i g u r e A.2. Lower hemisphere equal area p r o j e c t i o n s of s t r u c t u r a l elements Homestake d e p o s i t area: A- Poles (92) to f o l i a t i o n , maximun concentration-30% B- Poles (15) to co m p o s i t i o n a l l a y e r i n g , maximum c o n c e n t r a t i o n -33%. Contour i n t e r v a l s - 1 , 10 (from Hoy and Go u t i e r , 1986). 124 an average d i p of 35 degrees northeast ( F i g . A.2). The s i m i l a r i t y between f o l i a t i o n and bedding a t t i t u d e s i n d i c a t e s e i t h e r t i g h t or i s o c l i n a l f o l d i n g or a constant f a c i n g d i r e c t i o n . No l a r g e f o l d s have been i d e n t i f i e d i n the c h l o r i t e or s e r i c i t e p h y l l i t e s beneath the b a r i t e l e n s e s . Nearly a l l bedding-cleavage i n t e r s e c t i o n s i n these p h y l l i t e s have a common vergence. T h e r e f o r e , the s u c c e s s i o n c o u l d be a homoclinal, non-folded sequence on the lower, u p r i g h t limb of a t i g h t s y n c l i n e . However, r o o t l e s s t i g h t to i s o c l i n a l minor f o l d s throughout the s u c c e s s i o n and the presence of l a r g e f o l d s o u t l i n e d by a r g i l l i t e beds i n o v e r l y i n g rocks ( u n i t 4) suggest t h a t l a r g e r f o l d s a l s o occur w i t h i n the p h y l l i t e s . These f o l d s would be asymmetric, e s s e n t i a l l y c o n f i n e d to a s i n g l e u n i t , with shortened or sheared-out overturned f o l d s limbs. On a r e g i o n a l s c a l e the Homestake property i s l o c a t e d on the southern limb of a l a r g e overturned s y n c l i n e ( S c h i a r i z z a and Preto 1984; Preto and S c h i a r i z z a , 1985). Evidence i n the Homestake area, i n c l u d i n g f o l d c l o s u r e s and vergences obtained from bedding-cleavage i n t e r s e c t i o n s , supports a s y n c l i n a l f o l d c l o s u r e to the n o r t h e a s t . M i n e r a l i z a t i o n : A number of b a r i t e s u l p h i d e lenses with v a r i a b l e amounts of s u l p h i d e occur w i t h i n the upper pa r t of u n i t 2b. They are d e s c r i b e d i n d e t a i l i n e a r l y M i n i s t r y of Mines Annual Reports (1927, 1936) and are b r i e f l y reviewed here. At l e a s t three l e n s e s , separated by s e r i c i t e s c h i s t , are r e c o g n i z e d . They range i n t h i c k n e s s from l e s s than a metre to at l e a s t 10 metres; underground some have been t r a c e d s e v e r a l hundred metres. M e t a l l i c m i n e r als w i t h i n these lenses i n c l u d e t e t r a h e d r i t e , galena, s p h a l e r i t e , p y r i t e , c h a l c o p y r i t e , a r g e n t i t e , minor n a t i v e s i l v e r , and t r a c e ruby s i l v e r and n a t i v e g o l d . The lenses may c o n s i s t e i t h e r of massive to banded b a r i t e with only s c a t t e r e d m e t a l l i c minerals throughout, or i n t e r l a y e r e d b a r i t e , s c h i s t , and s u l p h i d e s . Two lenses are exposed on s u r f a c e . The l a r g e s t , r e f e r r e d to as the " b a r i t e b l u f f " ( u n i t 2c), has an exposed t h i c k n e s s of 5 to 6 metres. I t pinches out r a p i d l y along s t r i k e , has a sharp hangingwall c o n t a c t with s e r i c i t e s c h i s t , and grades downward i n t o massive s e r i c i t i c c h e r t . A smaller l e n s , 1 to 2 metres t h i c k , occurs below the " b a r i t e b l u f f " u n i t ; i t i s banded but c o n t a i n s only minor s u l p h i d e s . Sample d e s c r i p t i o n : Samples were c o l l e c t e d from the b a r i t e b l u f f and are composed of e r r a t i c a l l y d i s t r i b u t e d medium gra i n e d p y r i t e , s p a l e r i t e and galena. Galena sample from quartz v e i n m a t e r i a l was a l s o a n a l y s e d . References: HOY,T.,and GOUTIER,F. 1986. 125 REA GOLD: Al s o known as: H i l t o n M i n f i l e number: 082M-091 Map number: 015; L a t . 51.13ON Long. 119.81ow P u b l i s h e d d r i l l i n d i c a t e d r e s e r v e s : 120,000 tonnes of ore. 18.2 gt Au 141.2 gt Ag 0.85 % Cu 4.11 % Zn 3.67 % Pb L o c a t i o n : The Rea Gold property i s l o c a t e d west of Samatosum mountain and i s a c c e s s i b l e v i a log g i n g road from Squaam Bay. Host Rock: The d e p o s i t d e s c r i p t i o n i s from Hoy and Goutier (1986). The d e p o s i t i n c l u d e s two t h i n , l a t e r a l l y continuous lenses that l i e s t r a t i g r a f i c a l l y above a h i g h l y a l t e r e d sequence of dominantly mafic and minor f e l s i c t u f f s ( F i g . A.3). S t r a t i g r a p h i c a l l y above these lenses i s a t h i n mafic t u f f sequence and a t h i c k e r sequence of a r g i l l i t e , s i l t s t o n e , and g r i t s ( E B F f ) . The s u c c e s s i o n i s i n v e r t e d ; hence, the " f o o t w a l l a l t e r a t i o n zone" or "stockwork feeder zone" now forms the hangingwall of the l e n s e s . Rock U n i t s : The o l d e s t u n i t w i t h i n the d e p o s i t area comprises predominantly mafic t u f f ( u n i t 1) that l i e s at the s t r u c t u r a l top of the s u c c e s s i o n . T h i s t u f f u n i t i n c l u d e s ash, c r y s t a l , and l a p i l l i t u f f s with v a r i a b l e amounts of disseminated p y r i t e . They are s t o n g l y f o l i a t e d , producing green p h y l l i t e s and s c h i s t s ; more massive "greenstone" u n i t s may be d e r i v e d from mafic flows. There are t h i n c h e r t bands and a n o t i c e a b l e i n c r e a s e i n s e r i c i t e content toward the con t a c t with u n i t 2. In g e n e r a l , t h i s contact i s g r a d a t i o n a l and r e f l e c t s , i n p a r t , an i n c r e a s e i n a l t e r a t i o n i n the s t r a t i g r a p h i c f o o t w a l l of the d e p o s i t . U n i t 2 i s the f o o t w a l l a l t e r a t i o n or stockwork feeder zone of the s u l p h i d e l e n s e s . I t i s very e x t e n s i v e i n the hangingwall of the more n o r t h e r l y of the two l e n s e s , but i s only a few metres t h i c k i n the hangingwall of RG8, the southern l e n s . I t i n c l u d e s e x t e n s i v e l y a l t e r e d mafic t u f f s , otherwise s i m i l a r to those of u n i t 1, c h e r t l a y e r s , and t h i n more f e l s i c ( d a c i t e ?) ash t u f f l a y e r s . These u n i t s now appear as pale tan to pale green s i l i c e o u s p h y l l i t e s and s c h i s t s interbedded with pure to s e r i c i t i c c h e r t . A l t e r a t i o n i n c r e a s e s d r a m a t i c a l l y toward the co n t a c t with the s u l p h i d e l e n s e s . I t i n c l u d e s : a) s i l i c i f i c a t i o n through i n t r o d u c t i o n of s i l i c a i n the form of quartz v e i n s , and of t h i n to r e l a t i v e l y t h i c k c h e r t l a y e r s , d i s c o n t i n u o u s c h e r t l a m e l l a e , and fragmental c h e r t ; 126 o 8 T" o s T" o I580- LEGEND UNIT 6 ARGILLITE: MINOR WACKE. GRIT WACKE. GRIT: MINOR ARGILLITE UNIT 5 | 6 | MAFIC TUFF: MINOR ARGILLITE f"c~| DARK GREY TUFFACEOUS ARGILLITE UNIT 4 BARITE: MINOR SULPHIOES UNIT 3 MASSIVE' SULPHIDES UNIT 2 | | MAFIC TUFF. SILICIFIED. CHERT MINOR DACITE (?) TUFF UNIT 1 | | MAFIC TUFF: MINOR SILICIFICATION F i g u r e A.3 V e r t i c a l s e c t i o n (97+00) t h r o u g h t h e RG 8 s u l p h i d e b a r i t e l e n s , Rea G o l d d e p o s i t ( f r o m Hoy and G o u t i e r , 1986). 127 b) p y r i t e , which i s disseminated, i n v e i n s , and i n d i s c o n t i n u o u s s t r e a k s ; i t i n c r e a s e s from 1 to 2 per cent i n u n i t 1 to commonly 10 to 20 per cent near the s t r a t i g r a p h i c top of u n i t 2; and c) s e r i c i t e which becomes u b i q u i t o u s w i t h i n u n i t 2. White (1985) noted both l o c a l soda enrichment (as massive a l b i t e and paragonite) and c a r b o n i z a t i o n (as dolomite, i r o n - r i c h magnesite, and c a l c i t e ) . S t r a t i g r a p h i c a l l y o v e r l y i n g the s u l p h i d e or s u l p h i d e - b a r i t e lenses i s a t h i n sequence of predominantly mafic t u f f s ( u n i t 5) tha t grades up i n t o a r g i l l i t e s . These t u f f s are pale grey to brown-weathering thin-bedded c h l o r i t e p h y l l i t e s . S i l i c i f i e d zones occur only l o c a l l y and p y r i t e content i s g e n e r a l l y low. A dark grey t u f f a c e o u s " a r g i l l i t e " ( u n i t 5c) with high Ba content ( I . P i r i e , p ers. comm., 1985) occurs i n the intermediate f o o t w a l l of the RG8 l e n s , at the s t r a t i g r a p h i c base of u n i t 5. Unit 5 i s g e n e r a l l y i n f a u l t c o n t a c t with u n i t 6, but i n some d r i l l i n t e r s e c t i o n s i t grades through an i n t e r v a l of interbedded green p h y l l i t e and a r g i l l i t e ( F i g . ). A sequence of m e t a c l a s t i c rocks ( u n i t 6) at the s t r u c t u r a l base of the s u c c e s s i o n are the yougest rocks i n the d e p o s i t area. They comprises grey laminated a r g i l l i t e , s i l t s t o n e , wacke, and l o c a l pebble comglomerate with both v o l c a n i c and sedimentary c l a s t s . Bedding and graded beds are w e l l preserved. Thin mafic ash t u f f l a y e r s occur i n the b a s a l p a r t of u n i t 6. S t u c t u r e : The d e p o s i t and host rocks are w i t h i n a northwest-trending, n o r t h e a s t - d i p p i n g homoclinal s u c c e s s i o n t h a t has been s t r u c t u r a l l y i n v e r t e d . A pronounced mineral s c h i s t o s i t y l a r g e l y masks primary bedding except i n s t r u c t u r a l f o o t w a l l rocks where well-bedded and commomly graded m e t a c l a s t i c rocks occur. The observed bedding i s s u b - p a r a l l e l to the s c h i s t o s i t y ( F i g . A.4), i n d i c a t i n g t i g h t to i s o c l i n a l f o l d i n g . Changes i n the vergence of the b e d d i n g - s c h i s t o s i t y i n t e r s e c t i o n s and the many s m a l l , r o o o t l e s s i s o c l i n a l f o l d s i n d i c a t e , however, th a t the s u c c e s s i o n i s f o l d e d . F o l d i n g i s asymmetrical i n s t y l e and i n d i v i d u a l f o l d s are c o n f i n e d to s p e c i f i c u n i t s since r e p e t i t i o n of the major l i t h o l o g i c s u b d i v i s i o n s i s not apparent. W i t h i n u n i t 2, cleavage-bedding i n t e r s e c t i o n s i n d i c a t e a synformal a x i s l o c a t e d to the n o r t h e a s t . R e l a t i o n s h i p s between the massive s u l p h i d e , b a r i t e , and a l t e r a t i o n zone i n d i c a t e t h a t the d e p o s i t i s i n v e r t e d ; t h i s suggests that the observed s c h i s t o s i t y and a s s o c i a t e d f o l d s are second g e n e r a t i o n s t r u c t u r e s superimposed on a p r e v i o u s l y i n v e r t e d p a n e l . Within more competent s t r u c t u r a l f o o t w a l l rocks ( u n i t 6), these f o l d s are r e l a t i v e l y open and the l o c a t i o n of f o l d hinges can be d e f i n e d . A l a t e s o u t h e a s t - t r e n d i n g c r e n u l a t i o n cleavage, a s s o c i a t e d with minor open f o l d s , i s superimposed on the e a r l i e r s c h i s t o s i t y . F a u l t s p a r a l l e l to s c h i s t o s i t y are common but only the l a r g e s t N -L T F i g u r e A.4 Equal area p r o j e c t i o n s onto lower hemisphere s t r u c t u r a l elements Rea Gold d e p o s i t : A- Poles to f o l i a t i o n B- Poles to compositional l a y e r i n g (from Hoy and G o u t i e r , 1986). 129 are shown on the map. The most prominent f a u l t s t r i k e s northwest, j u x t a p o s i n g u n i t 5 a g a i n s t u n i t 6. The displacement on the f a u l t i s probably not l a r g e as there does not appear to be much l o s s of s t r a t i g r a p h y across i t ; the f a u l t cuts l o c a l l y up i n t o u n i t 5 l e a v i n g a normal s t r a t i g r a p h i c contact between u n i t s 5 and 6. M i n e r a l i z a t i o n : The s u l p h i d e s , w i t h i n t h i s volcanogenic s u l p h i d e - b a r i t e bearing d e p o s i t , are contained i n two main l e n s e s . The more southern, the RG8 l e n s , appears to be at a s l i g h t l y higher s t r a t i g r a p h i c l e v e l than the L100 l e n s . I t has a l e s s e x t e n s i v e f o o t w a l l a l t e r a t i o n zone, and i s "capped" by massive b a r i t e . D e s c r i p t i o n of these s u l p h i d e lenses are based on v i s u a l examination of d r i l l core and mapping of trenches. The RG8 lens i s w e l l exposed i n two trenches. I t has a r e l a t i v e l y sharp c o n t a c t with a l t e r e d " f o o t w a l l " rocks of u n i t 2 and grades s t r a t i g r a p h i c a l l y up i n t o massive b a r i t e of u n i t 4. However i t i s i n sharp c o n t a c t with t u f f a c e o u s muds or mafic t u f f s of u n i t 5 at i t s f r i n g e s . The b a r i t e "cap" c o n s i s t s of grey to white, massive or f a i n t l y banded b a r i t e with v a r i a b l e amounts of disseminated s u l p h i d e s . The s u l p h i d e content of the b a r i t e g e n e r a l l y decreases away from the u n d e r l y i n g massive s u l p h i d e ( F i g . A . 3 ) . The L100 lens has a s u r f a c e s t r i k e length of approximatly 50 metres and a down di p p r o j e c t i o n of at l e a s t 120 metres. A t h i c k zone of intense s i l i c a a l t e r a t i o n s t r a t i g r a p h i c a l l y below the lens i s a b r u p t l y o v e r l a i n by mafic t u f f s of u n i t 5a. I t does not have a b a r i t e "cap". Sulphide mineralogy i n both lenses i n c l u d e s p y r i t e , arseno- p y r i t e , s p h a l e r i t e , galena, 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 e n n a n t i t e (White, 1985). Sulphides are f i n e - g r a i n e d and massive, c r u d e l y laminated or b r e c c i a t e d . Gold occurs mainly i n the massive s u l p h i d e s but i s a l s o found i n b a r i t e , i n f o o t w a l l stockwork, and i n f a u l t gouge ( I . P i r i e , p ers. comm., 1985). S i l v e r i s a s s o c i a t e d with both b a r i t e and massive s u l p h i d e s , while z i n c , l e a d , and copper occur p r i m a r i l y i n massive s u l p h i d e s . Sample d e s c r i p t i o n : The sample was c o l l e c t e d from the massive s u l p h i d e zone o c c u r r i n g on s u r f a c e and i s composed of extremely f i n e - g r a i n e d s u l p h i d e ore c o n t a i n i n g e s s e n t i a l l y p y r i t e , a r s e n o p y r i t e , and s p h a l e r i t e , with only minor galena. Vein samples c o n t a i n i n g c o a r s e r galena was a l s o analysed. References: HOY,T.,and GOUTIER,F. 1986. 1 30 BARRIERE LAKES AREA: BIRK CREEK SHOWINGS: A l s o Known as: Anaconda, Lynx, Rainbow, Copper C l i f f , M i n f i l e number: 082M-067, (059, 131) M i n e r a l Inventory number: 82M5-CU3 Map number: 008; L a t . 51.33ON Long. 119.90ow L o c a t i o n : The area i s s i t u a t e d 3km west of North B a r r i e r e Lake. The showings are a c c e s s i b l e by t r a i l t h a t f o l l o w s the n o r t h - e a s t s i d e of B i r k Creek. Host Rock: The area i s u n d e r l a i n by s e r i c i t e s c h i s t , c h l o r i t e s c h i s t , black p h y l l i t e , and some r e c r y s t a l l i z e d limestone ( u n i t EBAa). Two s t r a t i g r a p h i c s e c t i o n s ; A-A 1, B-B 1 and a l o n g i t u d i n a l s e c t i o n D-D' c r o s s i n g the s e c t i o n C-C', are shown on the F i g u r e s , and are d e s c r i b e d i n the f o l l o w i n g paragraphs. S e c t i o n A-A' A c l i f f s e c t i o n i s exposed from an e l e v a t i o n of 970m at the creek to 1,102m up s e c t i o n . I t c o n s i s t s dominantly of quartz-eye s e r i c i t e s c h i s t . The s t r i k e of the f o l i a t i o n v a r i e s from 265 to 290 degrees and d i p s 5 to 20 degrees to the n o r t h . The o v e r a l l minimum t h i c k n e s s ( p e r p e n d i c u l a r to f o l i a t i o n , which i s approximately c o i n c i d e n t with bedding) i s 175m ( F i g . A.5). At the base of the s e c t i o n the s c h i s t s c o n t a i n 15 per cent phenocrysts (maximum s i z e 2mm) of quartz and p l a g i o c l a s e i n a q u a r t z - m u s c o v i t e - p l a g i o c l a s e matrix. The p l a g i o c l a s e i s a l t e r e d to c a l c i t e but up s e c t i o n t h i s a l t e r a t i o n i s not apparent because the p l a g i o c l a s e content decreases. A u t o l i t h i c fragmental u n i t s (average fragment s i z e 1.5mm), occur l o c a l l y . Disseminated p y r i t e with an average g r a i n s i z e of 0.5mm, c o n s t i t u t e s up to 8 per cent of the rock. Trace amounts of i n t e r s t i t i a l c h a l c o p y r i t e are present with the p y r i t e . No markedly s u l p h i d e - r i c h horizons were observed. S e c t i o n B-B' T h i s s e c t i o n ( F i g . A.5) passes c l o s e to s e v e r a l o l d workings. Exposure i s l i m i t e d to one or two outcrops and the c o l l a r s of two slumped a d i t s . A well-developed f o l i a t i o n , p a r a l l e l to c o m p o s i t i o n a l l a y e r i n g , trends 265 to 275 degrees and d i p s g e n t l y north (3 to 20 degrees). Observable bedrock i s composed of q u a r t z - s e r i c i t e and c h l o r i t e s c h i s t with l i m o n i t e a l t e r e d p y r i t e - r i c h l a y e r s , and minor laminated black p h y l l i t e s . T h i n s e c t i o n s of the s c h i s t s show zones with elongated fragments (up to 3mm) of p o l y c r y s t a l l i n e quartz g r a i n s . Disseminated p y r i t e i s present throughout much of the s e c t i o n . S i l i c i f i e d massive p y r i t e lenses with minor c h a l c o p y r i t e were observed w i t h i n an 8-metre s e c t i o n near the o l d a d i t s . The p y r i t e i s e uhedral, but fragmented, and a s s o c i a t e d with c h a l c o p y r i t e which g e n e r a l l y i s l o c a t e d at the borders of the p y r i t e g r a i n s . M a t e r i a l observed on a dump i n the immediate area c o n t a i n s 1 31 F i g u r e A.5 D e t a i l e d s e c t i o n s A-A 1 and B-B1 from the north s i d e of B i r k C r e e k — s e c t i o n s about 350m apart (from Goutier et a l . , 1985). 1 32 s i m i l a r m i n e r a l i z a t i o n , as w e l l as a few blocks of v e i n quartz with blebs of s p h a l e r i t e and galena. The l a t t e r type of m i n e r a l i z a t i o n was not observed i n outcrop. S e c t i o n s C - C and D-D' Sec t i o n s C-C* and D-D' cr o s s a major showing along a c l i f f s e c t i o n on the south s i d e of B i r k Creek. Three short a c c e s s i b l e a d i t s , about 9 metres long are p a r a l l e l to a major j o i n t d i r e c t i o n (012 degrees). Other workings i n the immediate v i c i n i t y have been f l o o d e d by the creek and are observable when water l e v e l s are low (V. Preto, pers. comm., 1984). This s e c t i o n i s composesd of s u l p h i d e - r i c h s e r i c i t e s c h i s t i n f a u l t c o n t a c t with an impure limestone u n i t . S t r u c t u r e : A w e l l developed f o l i a t i o n p a r a l l e l to bedding s t r i k e s east-west and di p s v a r i a b l y to the south and north. A superimposed north s t i k i n g , s h a l l o w l y e a s t - d i p p i n g c r e n u l a t i o n cleavage i s pronounced on outcrops near the creek. E a r l y mesoscopic recumbent i s o c l i n a l f o l d s with a x i a l planes p a r a l l e l to the pronounced s c h i s t o s i t y and axes plunging p a r a l l e l to the mineral l i n e a t i o n , probably i n d i c a t e a l a r g e s t r u c t u r e which c o n t r o l s the d i s t r i b u t i o n of the s t r a t i f o r m m i n e r a l i z e d zones (Preto, pers. comm., 1984). M i n e r a l i z a t i o n : M i n e r a l occurrences are s t r a t i f o r m massive p y r i t e d e p o s i t s with minor c h a l c o p y r i t e s p h a l e r i t e and galena. Sulphides occur as massive pods (up to 1m t h i c k ) , as l a y e r s (up to 10cm t h i c k ) and as fragments i n s i l i c i f i e d b r e c c i a . Sulphide m i n e r a l i z a t i o n i s composed mainly of well-formed but d i s r u p t e d p y r i t e g r a i n s (average s i z e 2.5mm across) with minor c h a l c o p y r i t e i n an a n k e r i t i c quartz matrix. T h i s u n i t looks l i k e a p y r i t e - s i l i c a e x h a l i t e . L o c a l l y the s u l p h i d e horizons are w e l l l a y e r e d ( l a y e r s are 8cm t h i c k over an exposed t h i c k n e s s of 3.5m). A t t i t u d e s of l a y e r i n g and c o i n c i d e n t f o l i a t i o n are the same as those observed i n the limestone. Most m i n e r a l i z a t i o n appears to be stratabound and syngenetic with the host f e l s i c s c h i s t s . Sample d e s c r i p t i o n : C o l l e c t e d samples c o n s i s t of f i n e g r a i n e d galena disseminated through massive i r o n s u l p h i d e h o r i z o n s . V e i n m a t e r i a l , a l s o analysed, c o n t a i n s c o a r s e r galena and s p h a l e r i t e i n quartz gangue. Reference: GOUTIER et a l , 1985. 133 ENARGITE: A l s o known as: North S t a r , Ace M i n f i l e number: 082M-064, 065 Map number: 004; L a t . 51.35ON Long. 119.99ow Pr o d u c t i o n as l i s t e d i n M i n f i l e : From the south showing 31 tonnes of ore (1954) 280 g Ag 1 ,561 kg Cu From the north showing 5 tonnes of ore (1972) 3,452 g AG 1,341 kg Pb 651 kg Zn L o c a t i o n : The property at the head of B i r k Creek i s at the summit between the v a l l e y of B a r r i e r e Creek and the North Thompson R i v e r . Host rock: The E n a r g i t e v e i n occurs a t , or adjacent to, the contact between a f i n e g r a i n e d meta-sedimentary package of the Eagle Bay Formation (composed of p h y l l i t e , s l a t e , interbedded s i l t s t o n e and sandstone, and v a r i o u s limestone h o r i z o n s , subunit E B P l ) , and the meta-basalt of the F e n n e l l Formation ( l F u ) . S t r u c t u r e : The v e i n s t r i k e s N15ow and d i p s 45ow. The rocks i n the area s t r i k e almost v e r t i c a l l y ; near the v e i n the host rocks are h i g h l y d i s t u r b e d . M i n e r a l i z a t i o n : The s u l p h i d e s are hosted by a strong quartz v e i n (45cm wide) bordered by gouge m a t e r i a l probably r e l a t e d to a f a u l t between the two formations above. The s u l p h i d e s , mainly galena, are i r r e g u l a r l y d i s t r i b u t e d and occur i n pockets. L o c a l l y disseminated s u l p h i d e s occur i n the adjacent carbonate host r o c k s . Sample d e s c r i p t i o n : Coarse galena i n quartz v e i n was sampled; no other s u l p h i d e s were present i n the sample. References: BCDM EXPL. IN BC. 1978, pp. E108. BCDM GEM 1974 , p. 97. BCDM MMAR 1927, p. 190. 134 FORTUNA: A l s o known as: Kuno M i n f i l e number: 082M-070 to 072 Map number: 013; L a t . 51.37C-N Long. 119.93ow L o c a t i o n : The property i s on the f l a n k of Fortuna h i l l . The aluminium roof of an o l d c a b i n on the property i s v i s i b l e from great d i s t a n c e and can be used to guide access to the workings along o l d t r a i l s . Host rock: Quartz lenses (or v e i n segments) cut through l i g h t to dark green c h l o r i t i c p h y l l i t e s , s i l s t o n e , limestone and q u a r t z i t e ( E B U ) . The s c h i s t s c l o s e to these lenses are very a l t e r e d and i n pl a c e s s i l i c i f i e d . S t r u c t u r e : The f o l i a t i o n i n the host rocks s t r i k e s at N45ow and d i p s 24o to the southwest. The o v e r a l l s t r i k e of the m i n e r a l i z e d bodies p a r a l l e l s the f o l i a t i o n . M i n e r a l i z a t i o n : S c a t t e r e d pockets of galena occur i n the q u a r t z . The v a r i o u s m i n e r a l i z e d zones are more or l e s s p a r a l l e l to each other, and although they occur at s e v e r a l places on the slope of the h i l l , t h e i r c o n t i n u i t y has not been determined. Sample d e s c r i p t i o n : Well c r y s t a l l i z e d galena a s s o c i a t e d with minor amounts of p y r i t e was sampled from one of these bodies o c c u r i n g near the o l d workings. References: BCDM MMAR 1927, p. 190. 135 WHITE ROCK: M i n f i l e number: 082M-066 Mi n e r a l Inventory number: 82M5-PB1 Map number: 028; La t . 51 . 30ON Long. 119.91ow Grade as l i s t e d i n BCDM MMAR 1950: Composite sample: 0.3 4 g/t Au 91.80 g/t Ag 2.2 % Pb 0.8 % Zn L o c a t i o n : The d e p o s i t i s a p p r o x i m a t i v e l y 1.6km e a s t , and 500 to 800 metres above B a r r i e r e River at the south end of North B a r r i e r e ' L a k e . Host Rock: The m i n e r a l i z a t i o n i s hosted by the T s h i n a k i n limestone (EBGt) which occurs i n t e r d i g i t a t e d with green c a l c a r e o u s c h l o r i t i c s c h i s t (EBG). S t r u c t u r e : The main f r a c t u r e system which hosts the v e i n s s t r i k e s n o r t h e a s t e r l y and cuts the limestone at high a n g l e s . These f r a c t u r e s have been i n t e r r u p t e d by l a t e f a u l t s both along and across the plane of the i n f i l l i n g v e ins (BCDM, 1950). A l a r g e number of small v e i n s , exposed on s u r f a c e , are of i r r e g u l a r width and of unknown l e n g t h . These v e i n s g e n e r a l l y s t r i k e N10OS and d i p s t e e p l y to the e a s t . M i n e r a l i z a t i o n : Quartz v e i n s , c l o t s and s t r i n g e r s , c a r r y i n g mainly a r g e n t i f e r o u s galena, occur i n a s e r i e s of f r a c t u r e s which are probably r e l a t e d to the main f a u l t zone along the B a r r i e r e R i ver v a l l e y . In s e v e r a l p l a c e s the c o n t a c t of the limestone and the surrounding s c h i s t i s a l s o w e l l m i n e r a l i z e d . The veins are of i r r e g u l a r l e n g t h ; widths vary from 5cm to 45cm. Sample d e s c r i p t i o n : C o n c e n t r i c galena blebs surrounded by a q u a r t z - c a l c i t e gangue was sampled from a v e i n on the p r o p e r t y . References: ECONOMIC GEOLOGY SERIES NO. 8, GSC 1930, p. 302. BCDM MMAR 1950, pp. 111-112. BCDM MMAR 1928, p. 212. BCDM MMAR 1927, p. 189. 1 36 JUNE KAJUN: A l s o known as: Rennings, Kajun. M i n f i l e number: 082M-058 Map number: 021; L a t . 51.26QN Long. 119 . 8 0 O W L o c a t i o n : A l a r g e north-south t r e n c h (120m long) exposed a m i n e r a l i z e d v e i n on the southeast s i d e of East B a r r i e r e Lake at the mouth of D e a d f a l l Creek. Host rock: A f o l d e d m i n e r a l i z e d v e i n i s hosted by grey to white limestone (EBGl) a s s o c i a t e d with black g r a p h i t i c p h y l l i t e . A l a r g e f a u l t , near the base of the exposure i n the t r e n c h , i s u n d e r l a i n by black s i l i c e o u s and limy gouge and by u n c o n s o l i d a t e d b r e c c i a . Above the v e i n , the limestone i s not d i s t u r b e d and s t r i k e s from N20ow to 45ow with d i p s near 4 0O E . S t r u c t u r e : The m i n e r a l i z e d v e i n i s a s s o c i a t e d with a p o s s i b l e f a u l t i n d i c a t e d by the presence of gouge m a t e r i a l . The v e i n s t r i k e s N70ow and d i p s 65osw. In s e v e r a l p l a c e s m i n e r a l i z a t i o n i s c o ncentrated i n the c r e s t s of small drag f o l d s . M i n e r a l i z a t i o n : In the c r e s t of a open l a r g e f o l d a m i n e r a l i z e d zone, appproximatively 7m long by 4m high, i s composed of s i l i c e o u s c a l c i f i c and d o l o m i t i c gangue c o n t a i n s e c t i o n s up to 1.3m t h i c k which are m i n e r a l i z e d with galena, s p h a l e r i t e and minor c h a l c o p y r i t e . Patches and s t r e a k s of s p h a l e r i t e , galena, c h a l c o p y r i t e and p y r i t e extend l o c a l l y i n t o the surrounding limestone. Sample D e s c r i p t i o n : Well c r y s t a l l i z e d a s s o c i a t e d with p y r i t e and s p h a l e r i t e exposed quartz mass. The samples were and 5m away from the gouge r i c h zone. References: BCDM ASS. RPT. 2232, 2230. but f i n e g r a i n e d galena was sampled from the c o l l e c t e d both adjacent to 1 37 LEEMAC: A l s o known as: Boomac. M i n f i l e number: 082M-056 Map number: 046; L a t . 51.35ON Long. 119.70ow L o c a t i o n : The Leemac group of claims are a c c e s s i b l e by logging roads from the east s i d e of the town of B a r r i e r e . The claims are along F e n n e l l Creek. Host rock: The v e i n occur w i t h i n the Cretaceous Baldy b a t h o l i t h . Near the v e i n the i n t r u s i o n i s p o r p h y r i t i c , r e d d i s h i n c o l o r and n e a r l y devoid of mafic m i n e r a l s . S e r i c i t e i s l o c a l l y abundant i n the v i c i n i t y of the v e i n s t r u c t u r e . Narrow mafic dykes ( s t r i k i n g p a r a l l e l to the m i n e r a l i z e d v e i n and d i p p i n g to the north) occur throughout the b a t h o l i t h . S t r u c t u r e : The v e i n s t r i k e s N25OE with a moderate d i p to the northwest. I t i s bordered on both s i d e s by f a u l t gouge, i n d i c a t i n g t h at the v e i n has been subjected to movement or that i t f i l l s a shear zone r e l a t e d to a f a u l t i n g event. M i n e r a l i z a t i o n : The m i n e r a l i z a t i o n i s hosted by a w e l l d e l i n e a t e d quartz v e i n having an average width of 90cm. The s u l p h i d e s , p y r i t e , s p h a l e r i t e and galena, are coarse and we l l c r y s t a l l i z e d . T h i s m i n e r a l i z e d v e i n i s surrounded by a s u b s i d i a r y v e i n system mostly barren of s u l p h i d e m i n e r a l s . References: BCDM ASS. RPT. 59 39. BROKEN RIDGE: A l s o known as: May. M i n f i l e number: 082M-130 Map number: 009; L a t . 51.350N Long. 119.88ow L o c a t i o n : The m i n e r a l i z e d zone occurs on Harper Creek 2km northwest of the west end of North B a r r i e r e Lake. D e s c r i p t i o n : Lenses and blebs of p y r i t e and p y r r h o t i t e with minor amounts of c h a l c o p y r i t e , s p h a l e r i t e and t r a c e of galena occur semi-conformably with the f o l i a t i o n i n the c h l o r i t i c member of the q u a r t z - s e r i c i t e s c h i s t u n i t EBA. Numerous i r o n gossans i n the area are r e l a t e d to abundant i r o n s u l p h i d e s ( p y r i t e and p y r r h o t i t e ) i n the s c h i s t . Sample d e s c r i p t i o n : The data used come from analyses made by the G e o l o g i c a l survey of Canada, analyse no. G79BN-001. References: BCDM EXPL. i n BC 1976, p. E62 BCDM GEM 1971, p. 440. 1 38 BIRCH ISLAND-CLEARWATER AREA: CHU-CHUA: M i n f i l e number: 092P-140 Map number: 003; L a t . 5 1 . 3 8 O N Long. 120.07OW L o c a t i o n : The Chu-Chua pro p e r t y i s a p p r o x i m a t i v e l y 20km no r t h - northwest from the town of B a r r i e r e , on the r i d g e east of Chu-Chua mountain. Host Rock: The d e p o s i t i s hosted i n the upper s t r u c t u r a l d i v i s i o n of the F e n n e l l Formation (ufb) composed mainly of b a s a l t with a l k a l i c a f f i n i t i e s (Aggarwall e t a_l. , 1984), i n which primary t e x t u r e s and p i l l o w s (1 to 3m a c r o s s ) are s t i l l v i s i b l e . The margins of the p i l l o w s are s l i g h t l y c h i l l e d and are c h l o r i t i z e d or bleached. Massive t a l c zones and s i l i c e o u s rocks are l o c a l l y abundant w i t h i n t h i s package, p a r t i c u l a r i l y near the s u l p h i d e r i c h zones. Chert and/or t u f f i t e o v e r l i e the m i n e r a l i z a t i o n and are b e l i e v e d to be e x h a l a t i v e i n o r i g i n (Aggarwall e t a l . , 1984). S t r u c t u r e : Rocks of the F e n n e l l Formation are g e n e r a l l y not h i g h l y f o l i a t e d . The s c h i s t o s i t y , were developed, i s a x i a l p lanar to e a r l y , g e n e r a l l y northeast plunging i s o c l i n a l f o l d s . Two generations of l a t e r f o l d s ( e a s t e r l y and n o r t h w e s t e r l y t r e n d i n g , S c h i a r i z z a , 1980) r e f o l d e d the main s c h i s t o s i t y and may be r e s p o n s i b l e f o r r e p e t i t i o n of the m i n e r a l i z e d h o r i z o n s . M i n e r a l i z a t i o n : The b a s a l t c o n t a i n s two major (east e r n and western), and two minor l e n t i c u l a r bodies of massive s u l p h i d e s t h a t appear to be stratabound. In g e n e r a l the d e p o s i t s trend north-south, d i p s t e e p l y west, and plunge g e n t l y south. The s u l p h i d e s are i n sharp c o n t a c t with the hangingwall rocks, but the e x t e n s i o n of the bodies down d i p are i r r e g u l a r and i n s e v e r a l p l a c e s lens out i n t o c h e r t y rocks (McMillan, 1980). The m i n e r a l i z e d zones are a s s o c i a t e d with massive t a l c magnetite l e n s e s , and are composed mainly of p y r i t e and c h a l c o p y r i t e with minor s p h a l e r i t e , cubannite, s t a n n i t e , and quartz and c a l c i t e . Bedding i s not common and occurs only l o c a l l y where i t i s o u t l i n e d by c h a l c o p y r i t e - r i c h l a y e r s or by a l t e r n a t i n g l a y e r s of p y r i t e of d i f f e r e n t s i z e s . The massive s u l p h i d e s are cut by q u a r t z - t a l c veins and, i n one h o l e , by molybdenite s t r i n g e r s (McMillan, 1980). 139 The Chu-Chua d e p o s i t i s b e l i e v e d by Aggarwall et a_l. (1984) to repre s e n t d e p o s i t i o n from s a t u r a t e d s o l u t i o n on the sea f l o o r and/or nearby seamounts. The d i f f e r e n t lenses formed from d i f f e r e n t vent sources. The a s s o c i a t e d magnetite and t a l c r i c h zones probably represent areas where a higher component of sea-water was i n v o l v e d i n a l t e r a t i o n and m i n e r a l i z a t i o n . S i m i l a r l y the apparent lack of f o o t w a l l a l t e r a t i o n i s most l i k e l y due to a la c k of s i g n i f i c a n t i n t e r a c t i o n between the hydrothermal s o l u t i o n and the host r o c k s . Sample d e s c r i p t i o n : Lead data r e f e r r e d to i n the present study are from Aggarwall and N e s b i t t (1984). T h e i r analysed l e a d was e x t r a c t e d from p y r i t e and c h a l c o p y r i t e r a t h e r than galena and the data are only used here on a comparative b a s i s . References: AGGARWALL,P.K.,and NESBITT,B.E. 1984. AGGARWALL,P.K.,FUJJI,T.,and NESBITT,B.E. 1984. MCMILLAN,W.C. 1980. 140 F O G H O R N : A l s o known as: Gopher, Shamrock M i n f i l e number: 082M-008, 029, 030, 040, 108 M i n e r a l Inventory number: 82M12-Cu2, Ag1 Map number: 005; L a t . 5 1 . 5 4 O N Long. 119.93ow Pr o d u c t i o n as l i s t e d i n M i n f i l e : Foghorn 73 tonnes of ore (1916-17) 88,364 g Ag 57,276 kg Pb L o c a t i o n : The property i s at a p p r o x i m a t i v e l y 2,000m e l e v a t i o n on Foghorn Mountain, 6.5km south of B i r c h I s l a n d . Host Rock: The property i s u n d e r l a i n by r u s t y weathered f e l d s p a r - c h l o r i t e s c h i s t and s e r i c i t i c q u a r t z i t e s (EBFq), but the m i n e r a l i z e d veins are hosted by s i l i c e o u s and limy s c h i s t s . The Baldy b a t h o l i t h , exposed i n the southern part of the property at G r a n i t e Mountain, i s surrounded by f i n e to medium gr a i n e d b i o t i t e quartz gneiss with i n t e r l a y e r e d amphibolite and p e l i t i c h o r n f e l s . F e l s i c porphyry dykes occur near the m i n e r a l i z e d zones and may be r e s p o n s i b l e f o r both the s i l i c i f i c a t i o n of the host rocks and f o r the s u l p h i d e v e i n s . S t r u c t u r e : The Foghorn showings are l o c a t e d on the northern limb of an east-west s t r i k i n g a n t i f o r m i n very c l o s e p r o x i m i t y to a major n o r t h e r l y s t r i k i n g t h r u s t f a u l t . The n o r t h e a s t e r l y s t r i k e of the v e i n i s at a high angle to the t h r u s t f a u l t . Small s c a l e s t r u c t u r e s , drag f o l d s f o r example, i n d i c a t e that o r i g i n a l bedding has been deformed and probably transposed i n t o t i g h t i s o c l i n a l f o l d s now seen as f o l i a t i o n ( s t r i k i n g N 3 0 O E and d i p p i n g 80ow). M i n e r a l i z a t i o n : Quartz v e i n segments occur throughout the s c h i s t ; t h e i r d i s t r i b u t i o n i s not continuous and may t h e r e f o r e r e p r e s e n t a system of small v e i n s r a t h e r than a major s i n g l e d i s c o n t i n u o u s v e i n . These v e i n segments are l o c a l l y h e a v i l y m i n e r a l i z e d with galena, s p h a l e r i t e and p y r i t e . In p l a c e s c h a l c o p y r i t e a l s o occurs but only i n minor amounts (disseminated c h a l c o p y r i t e i s found i n g r e a t e r amounts i n the nearby L y d i a p r o s p e c t ) . The width of the v e i n segments i s approximatly 35cm; they s t r i k e about N 3 5 O E and d i p i n v a r i o u s d i r e c t i o n s —some of them are v e r t i c a l . Sample D e s c r i p t i o n : Samples were c o l l e c t e d from the o l d workings. The galena occurs with minor amounts of s p h a l e r i t e and p y r i t e i n quartz gangue specimens. References: BCDM ASS. RPT. 11381, 3820. BCDM OPEN FILE. 141 REXSPAR: A l s o known as: Smuggler, Spar, Black Diamond M i n f i l e number: 082M-021 Mi n e r a l Inventory number: 082M12-U1, FSP1 Map number; 016 L a t . 51.570N Long. 119 . 9 0 O W Reserves as l i s t e d i n M i n f i l e : Rexspar, t o t a l d e p o s i t (dec. 1976): 1,114,000 tonnes @ 1.55% U cut o f f used. L o c a t i o n : The Rexspar d e p o s i t 5km, south of B i r c h I s l a n d , i s on the south slope of the North Thompson v a l l e y between Lute and Foghorn Creeks. Host Rock: M i n e r a l i z a t i o n at Rexspar i s d i r e c t l y a s s o c i a t e d with the t r a c h y t i c member of the f e l s i c u n i t EBA. The t r a c h y t e i s massive or b r e c c i a t e d and s t r o n g l y f o l i a t e d . The surrounding rocks, c h l o r i t e s e r i c i t e s c h i s t and s i l v e r y s e r i c i t e - q u a r t z i t e , c o n t a i n exposures of c l e a r l y r e c o g n i z e a b l e d a c i t i c and a n d e s i t i c v o l c a n i c b r e c c i a . S t r u c t u r e : The rocks of the t r a c h y t e s u i t e e x h i b i t b r e c c i a t i o n , c a t a c l a s i s and m y l o n i t i z a t i o n s t r u c t u r e s . The f o l i a t i o n i n the rocks s t r i k e s n o r t h - e a s t e r l y with a 300 d i p to the northwest. The m i n e r a l i z e d zones are deformed and are near to s e v e r a l f a u l t s and t h r u s t s . M i n e r a l i z a t i o n : The two main m i n e r a l i z e d zones present at Rexspar are: 1) an uranium r i c h zone c o n f i n e d to t u f f a c e o u s and a r g i l l i t i c lenses c o n t a i n i n g abundant p y r i t e a s s o c i a t e d with aggregates of uranium bearing f l u o r p h l o g o p i t e . The lenses are d i s c o n t i n u o u s , average 20cm i n t h i c k n e s s , and are conformable with the s c h i s t o s i t y of the host t r a c h y t e . 2) a f l u o r i t e zone, barren of both thorium and uranium, i s m i n e r a l i z e d with c e l e s t i t e , p y r i t e , t r a c e of galena and molybdenite. The m i n e r a l i z a t i o n at Rexspar has been i n t e r p r e t e d by Preto (1978, i n BCDM Geology) as r e s u l t i n g from d e p o s i t i o n from a l a t e stage d e u t e r i c v o l a t i l e r i c h f l u i d evolved from the h i g h l y d i f f e r e n t i a t e d i n t r u s i v e - e x t r u s i v e igneous s u i t e . However, because C02 a p p a r e n t l y played an important r o l e i n the t r a n s p o r t and d e p o s i t i o n of uranium a s s o c i a t e d with hydrothermal s o l u t i o n s (Morton, 1978), then the uranium and thorium m i n e r a l i z a t i o n could be syngenetic with the t r a c h y t e u n i t . 1 42 Sample d e s c r i p t i o n : No samples were c o l l e c t e d from the Rexspar d e p o s i t by the w r i t e r . The data r e f e r r e d to here came from analyses by the G e o l o g i c a l Survey of Canada (sample number G79SA-001. References: GSC paper 78-1B, pp. 137-140. BCDM Geology i n BC 1977-1981, pp. 44-56 CIM B u l l . , 71, 1978, pp. 82. MORTON, R.D., AUBUT, A., GANDHI, S.S. 1978. Rexspar Deposit. G e o l o g i c a l Survey of Canada, Current Research, paper 78-1B, pp. 137-140. 143 MT McCLENNAN AREA D e p o s i t names: Red Top , Mt McClennan, S u n r i s e (Naomi). A l s o known as : Mimsic C la ims M i n f i l e number: 082M-044, 046 M i n e r a l Inventory number: 82M12-PB1 Map numbers: 531, 539, 541; L a t . 51.64QN L o n g . 119.78ow L o c a t i o n : T h i s area comprises three o l d p r o s p e c t s near the summit of the McClennan Mountain l o c a t e d about 7.5km n o r t h e a s t of B i r c h I s l a n d . A l l the showings are a c c e s s i b l e v i a f o r e s t r y r o a d s . Host Rock: The m i n e r a l i z e d o c c u r r e n c e s of the Mt McClennan area are hos ted by g r e e n s c h i s t and by c a l c a r e o u s c h l o r i t i c and g r a p h i t i c s c h i s t i n t e r c a l a t e d w i t h minor q u a r t z i t e s i l i c e o u s s c h i s t and carbonate (EBQ). G r a n i t i c rocks c rop out about 2km nor th of the showings ; the c o n t a c t between the i n t r u s i o n and the s c h i s t s i s marked by the development of h o r n f e l s i c rocks and by skarn zones i n c a r b o n a t e - r i c h h o r i z o n s . Lamprophyre dykes o c c u r i n the western end of the a r e a . S t r u c t u r e : Rocks i n the v i c i n i t y of McClennan Mountain are h i g h l y f o l i a t e d and are f o l d e d around a s t r o n g e a s t e r l y t r e n d i n g open a n t i f o r m p l u n g i n g 1 5 O E . The south l imb of the a n t i f o r m has been d i s l o c a t e d by f a u l t i n g and g r a n i t i c i n t r u s i o n . M i n e r a l i z a t i o n : Pb-Zn-Ag and Cu o c c u r r e n c e s are widespread i n the a r e a , the three o l d workings sampled f o r the present s tudy a r e : 1) the e a s t e r n area t h a t compri sed the o l d S u n r i s e group and Naomi c l a i m s . The m i n e r a l i z a t i o n c o n s i s t s of p y r r h o t i t e and p y r i t e wi th ga lena and s p h a l e r i t e o c c u r i n g i n q u a r t z i t i c rocks as l e n t i c u l a r sheets t r a c e a b l e on sur face over a d i s t a n c e of 125m a long s t r i k e . The sheets va ry i n t h i c k n e s s from .3 to 1.2m and are not t o t a l l y conformable w i t h the e n c l o s i n g h o s t . 2) the c e n t r a l area hos t s the MT McClennan (Snow) showing. T h i s showing c o n t a i n s mass ive and semi-mass ive h e a v i l y o x i d i z e d p y r i t e wi th g a l e n a , s p h a l e r i t e and minor amounts of c h a l c o p y r i t e i n impure l imy h o r i z o n s . The s u l p h i d e r i c h l a y e r s are up to 50cm t h i c k and p a r a l l e l the s c h i s t o s i t y and c o m p o s i t i o n a l l a y e r i n g of the s c h i s t s . A magnet i te b e a r i n g skarn i s deve loped below an ad j acent prominent bed of c r y s t a l l i n e l i m e s t o n e . 144 3) the western area hosts the Red Top showing which c o n s i s t s of galena and s p h a l e r i t e a s s o c i a t e d with s i l i c i f i e d p y r i t i c zones o c c u r i n g along bedding i n limestone. C h a l c o p y r i t e f i l l s many g a s h - l i k e openings. The su l p h i d e s have an e r r a t i c d i s t r i b u t i o n along s t r i k e , o c c u r i n g i n blows and seams. Nevertheless they are stratabound to a d e f i n i t e s t r a t i g r a p h i c h o r i z o n composed of ca l c a r e o u s quartz s e r i c i t e s c h i s t adjacent to an ho r i z o n t h a t v a r i e s from skarn to c l e a r c r y s t a l l i n e limestone. In g e n e r a l these m i n e r a l i z e d bodies appear to occur as d i s c o n t i n u o u s lenses (more or l e s s conformable with the s c h i s t o s i t y ) or as e r r a t i c s w e l l i n g s formed by limestone replacement and/or skarn development due to metasomatism probably r e l a t e d to the i n t r u s i o n of the Raft b a t h o l i t h . Samples d e s c r i p t i o n : 1) e a s t e r n area ( S u n r i s e ) : F i n e g r a i n e d h i g h l y a l t e r e d sample c o n t a i n i n g s p h a l e r i t e and galena a s s o c i a t e d with abundant p y r i t e . 2) c e n t r a l area (Mt McClennan): Coarse and f i n e g r a i n e d galena from d i s s e m i n a t i o n s from an a l t e r e d limy h o r i z o n . 3) western area (Red Top): Seams of f i n e g r a i n e d s u l p h i d e s disseminated i n c h l o r i t i c s c h i s t . References: BCDM ASS. RPT. 6931, 6603, 5813, 436. BCDM Geology i n BC 1977-81, pp. 44-56. 145 VAVENBY: Map number: 042; Lat. 51.58ON Long. 119.75ow Description: Quartz vein containing narrow sulphides seam (5cm wide) cut throught the Tshinakin Limestone (EBGt). The vein i s mineralized with galena and contains abundant c a l c i t e material. A syenite dyke occurs in the v i c i n i t y of the mineralized vein. References: Paul Schiarizza, pers. comm., 1985. PS-75-185: Map number: 04 8; Lat. 5 1 . 5 8 O N Long. 119.75ow Desciption: Galena and sphalerite occur in a narrow quartz vein cutting the Tshinakin Limestone, 4km east of the f o s s i l occurrence near Vavenby. References: Paul Schiarizza, pers. comm., 1985. SONJA: Also known as: LSD, Valentine. Minf i l e number: 092P-049 Map number: 044; Lat. 51.590N Long. 120.0low Location: This small mineralized showing occurs on the south bank of the North Thompson River, 1km east of the Clearwater railway station. Description: Discontinuous s i l i c i f i e d lenses or veins carry c r y s t a l l i n e galena and anglesite. The mineralized masses occur within a quartz s e r i c i t i c schist wedge of the Eagle Bay Formation close to the contact with the Fennell Formation. The mineralization appears to follow the east side of a major dyke (3.5 to 13m wide) which cuts the rocks of the Eagle Bay formation. References: BCDM EXPL. in BC 1976, p. E132. BCDM GEM 1969, p. 230. 1 46 BIRCH ISLAND: M i n f i l e number: 082M-023 Mi n e r a l Inventory number: 82M12-PB2 Map Number: 040; L a t . 5 1 . 5 6 O N Long. 119.90OW Pro d u c t i o n as l i s t e d i n M i n f i l e : 14 tonnes of ore (1926): 6,566 g Ag 3,362 kg Pb L o c a t i o n : The o l d workings are l o c a t e d along Foghorn Creek road south of B i r c h I s l a n d . D e s c r i p t i o n : E r a t i c galena m i n e r a l i z a t i o n occurs i n a f i s s u r e v e i n c u t t i n g through a q u a r t z i t i c member of the f e l s i c u n i t (EBA). The f i s s u r e , s t r i k i n g north and d i p p i n g s t e e p l y west, i s bordered by a zone i n which p y r i t e , s i d e r i t e and c a l c i t e are l o c a l l y abundant. The presence of manganese ore was a l s o r e p o r t e d from t h i s area (1931). References: BCDM MMAR 1931, p. 107. BCDM MMAR 1929, p. C22 4. TINDAL: Map number: 043; L a t . 51 . 6 0 O N Long. 119.78ow D e s c r i p t i o n : Galena was c o l l e c t e d i n an o l d a d i t from a quartz v e i n c u t t i n g quartz s e r i c i t e s c h i s t of the Eagle Bay Formation. References: none a v a i l a b l e 1 47 APPENDIX B LABORATORY PROCEDURES FOR GALENA LEAD ISOTOPE ANALYSIS B.1 GALENA LEAD SAMPLE PREPARATION Galena c r y s t a l s s e l e c t e d from rock or ore samples are s t o r e d i n p l a s t i c v i a l s . Approximately 10 mg of g r a i n s of c l e a n galena are p i c k e d out, using a needle and a b i n o c u l a r microscope, and put i n t o a d i s p o s a b l e 10 ml polypropylene beaker. A cl e a n g l a s s beaker (10 ml) i s weighed, then the galena g r a i n s are emptied i n t o the g l a s s beaker and the c o n t a i n e r i s reweighed. The weight of the sample i n d i c a t e s the amount of water t h a t must be added to the lead c h l o r i d e c r y s t a l s p r i o r to l o a d i n g . Approximately 8 ml 2N HCl i s added to the sample i n the g l a s s beaker, which i s then l e f t o v e r n i g h t on a h o t p l a t e . The lea d s u l p h i d e i s converted to le a d c h l o r i d e with the p r o d u c t i o n of hydrogen s u l p h i d e . The dry PbCl2 c r y s t a l s are r i n s e d i n 4N HCl three times. Most of the i m p u r i t i e s are r e a d i l y d i s s o l v e d i n 4N HCl, but PbCl2 i s l e a s t s o l u b l e at t h i s n o r m a l i t y . Cleaned le a d c h l o r i d e c r y s t a l s are d r i e d by r e t u r n i n g the beaker to the h o t p l a t e f o r a few minutes. A s o l u t i o n c o n t a i n i n g 1 ug Pb per 2 u l aqueous s o l u t i o n i s prepared by adding a c a l c u l a t e d amount of quartz d i s t i l l e d water a l l o w i n g f o r the l o s s of 30% of the sample due to n o n - d i s s o l u t i o n of some of the galena and l o s s of lea d c h l o r i d e d u r i n g r i n s i n g . B.2 PREPARATION AND LOADING OF FILAMENTS Pre-cleaned rhenium r i b b o n 1.5 cm long i s spot-welded to s i n g l e f i l a m e n t p o s t s . A m i c r o p i p e t t e with d i s p o s a b l e t i p s i s used to load 2 u l of sample onto each f i l a m e n t , using a new t i p f o r each sample. Samples are d r i e d at 1 Amp. 4 u l of s i l i c a g e l - p h o s p h o r i c a c i d s o l u t i o n i s loaded on top of the dry sample. T h i s i s l e f t to dry at 1.1 Amp, then the c u r r e n t i s g r a d u a l l y i n c r e a s e d u n t i l the load d i s s o l v e s and r e p r e c i p i t a t e s . When r e c r y s t a l l i z a t i o n i s complete, the c u r r e n t i s slowly i n c r e a s e d u n t i l white smoke i s given o f f and the loa d turns white. The cu r r e n t can then be turned up to 2 Amps or higher to allow the load to glow g e n t l y f o r a few seconds, then o f f . B.3 MASS SPECTROMETRIC PROCEDURES A l l the r e p o r t e d analyses were done by F r a n c o i s e Goutier i n the Geochronology Laboratory at the U n i v e r s i t y of B r i t i s h Columbia using a VG Isotopes Isomass 54R mass spectrometer l i n k e d to a HP-85 microcomputer. 1 48 Samples were loaded i n t o the mass spectrometer, s i x at a time, and heated to 11500-12500. The i s o t o p i c composition i s measured using 'UBCGPB1 programs. Due to the u n c e r t a i n i t y i n measuring 204pb peak, t h i s program measured the 204pb/207pb r a t i o twice as o f t e n as the other two r a t i o s , improving the s t a t i s t i c s on the r a t i o . Raw data i s converted to the 206pb/204pb, 207pb/204pb and 208pb/204pb r a t i o s , then normalized to absolute values using c o r r e c t i o n f a c t o r s determined by repeated analyses of the Broken H i l l Standard (Table 3.1). Each a n a l y s i s i s r e p o r t e d with an a s s o c i a t e d e r r o r based on a combination of the f r a c t i o n a t i o n v a r i a t i o n between runs, the u n c e r t a i n i t y i n mass f r a c t i o n a t i o n f a c t o r s , and w i t h i n - r u n p r e c i s i o n . References: Andrew, A. Ph.D T h e s i s i n p r e p a r a t i o n , U n i v e r s i t y of B r i t i s h Columbia. 149 A P P E N D I X C Adams Plateau: Lead Sample No Deposit/Sample Name 30504-001 ENARGITE 30504-00102 ENARGITE 30504- AVG ENARGITE N=2 30504/00101 ENARGITE 30505- 002 FOGHORN (SAMPLE 011) 30505-00201 FOGHORN (SAMPLE Oi l ) 30505-003 FOGHORN (VEIN 007) 30505-003D1 FOGHORN (VEIN 007) 30505-AVG2 FOGHORN N=2 (SAMPLE 011) 30505-AVG3 FOGHORN N=2 (VEIN 007) 30505- AVG FOGHORN N=4 30505/001 FOGHORN (SAMPLE 007) 30505/001D1 FOGHORN (SAMPLE 007) 30506- 001 AGATE BAY 30506-00101 AGATE SAY 30506-00102 AGATE BAY 30506- AVG AGATE 5AY N=3 30505/001 D3 AGATE BAY 30507- 001 BECA (TDM) 30507-00101 BECA (TQM) 30507-001D2 BECA (TOM) 30507- AVG BECA N=3 30507/00103 BECA (TOM) 30508- 001 BIRK CREEK (SECTION X DUMP) 30508-00101 BIRK CREEK (SECTION X DUMP) 30508-002 BIRK CREEK (SECTION X) 3050B-002D1 BIRK CREEK (5ECTI0N X ) 30508-00301 BIRK CREEK (SECTION 012) 30506-004 BIRK CREEK (VEIN SECT. 012) 30508-00401 BIRK CREEK (VEIN SEC.012) 30506-0C5 BIRK CREEK (NEAR BRIDGE) 30508-506 BIRK CREEK (G79BA-001 ) 30508-50601 BIRK CREEK (G79BA-002) 30508-AVG1 BIRK CREEK N=2 (SECT. DUMP) 30508-AUG2 BIRK CREEK N=2 (SECT . X ) 3050B-AVG4 BIRK CREEK N=2 (SECT. X ) 30508-AUG6 BIRK CREEK (G79BA-AVG) 30508-AVG BIRK CREEK N=10 30508/003 BIRK CREEK (SECTION 012) 3050S-SO1 BROKEN RIOGE (G79BN-001) 30511-001 HOMESTAKE 30511-002 HOMESTAKE 30511-002D1 HOMESTAKE 30511-502 HOMESTAKE (KAMAO 70) 30511-501 HOMESTAKE (361-G79H0-001) 30511-AVG2 HOMESTAKE N=2 30511-AVG HOMESTAKE N=5 30511/OOl D1 HOMESTAKE 30513-001 FORTUNA 30513-00101 FORTUNA 30513-AVG FORTUNA N=2 30515-001 REA GOLD (MASS. SULPH.HORZ .) 30515-002 REA GOLD (VEIN) Isotope Data Mt Anl Qual Pb6/4 J6/4 Pb7/4 J7:4 GL FG GOOO 19.101 0.01 15.692 0.01 GL FG GOOO 19.090 0.03 15.688 0.03 GL FG GOOO 19.096 0.02 15.690 0.02 GL FG FAIR 19.079 0.06 15.664 0.04 GL FG GOOD 19.190 0.03 15.708 0.03 GL FG GOOO 19.202 0.03 15.693 0.03 GL FG GOOD 19.225 0.04 15.713 0.03 GL FG FAIR 19.213 0.12 15.728 0.12 GL FG GOOD 19.196 0.03 15.701 0.03 GL FG GO/FR 19.219 0.08 1 5.721 0.08 GL FG GD/FR 19.20B 0.05 15.711 0.05 GL FG POOR 18.915 0.41 15.516 0.41 GL FC FAIR 19.073 0.21 15.680 0.20 GL FG GOOD 19.148 0.02 15.703 0.02 GL FG FAIR 19.148 0.05 15.705 0.02 GL FG FAIR 19.134 0.05 15.695 0.05 GL FG FAIR 19.143 0.04 15.701 0.03 GL FG FAIR 19.033 0.06 15.633 0.06 GL FG GOOD 19.334 0.02 15.668 0.02 GL FG GOOO 19.344 0.02 1 5.6B7 0.01 GL FG FAIR 19.339 0.01 15.684 0.01 GL FG GO/FR 19.339 0.02 15.660 0.02 GL FG POOR 19.322 0.03 15.703 0.03 CL FG GODD 18.948 0.02 15.718 0.02 GL FG FAIR 18.947 0.08 15.741 0.08 GL FG GOOD 18.904 0.03 15.71C 2.01 GL FG GOOD 18.882 0.03 15.599 0.03 GL FG POOR 19.026 0.39 15.798 0.39 GL FG GODD 18.896 0.02 15.705 0.01 GL FD POOR 18.949 0.14 15.741 0.05 GL FG GOOD 18.eQ3 0.01 15.721 0.01 GL BR FAIR 18.878 0.06 15.708 0.13 GL BR FAIR 1B.669 0.08 15.722 0.16 GL FG GD/FR 18.948 0.05 15.730 0.05 GL FG GOOD 18.893 0.03 15.705 0.02 GL FG GD/PR 18.923 0.08 15.723 0.03 GL BR FAIR IB.874 0.07 15.715 0.08 GL G/R GD/FR 18.907 0.06 1 5.716 0.05 GL FG FAIR 18.901 0.02 15.691 0.01 GL BR FAIR 19.249 0.08 15.697 0.11 GL FG FAIR 18.776 0.05 15.696 0.05 GL FG FAIR 18.8B7 0.05 15.693 0.05 GL FG GOOD 18.900 0.04 15.705 0.02 GL GSC FAIR 18.827 0.00 15.719 0.00 GL GSC FAIR 18.878 0.08 15.687 0.17 GL FG FAIR 18.894 0.05 15.699 0.03 GL FR/GO 18.854 0.06 15.700 0.10 GL FG POOR 18.B69 0.19 15.770 0.19 GL FG GOOO 19.118 0.02 15.716 0.01 GL FG GOOD 19.132 0.02 15.726 0.02 GL FG GOOO 19.125 0.02 15.721 0.02 GL FG FAIR 18.859 0.04 15.709 0.04 GL FG GOOD 18.852 0.01 15.6B0 0.01 1 50 Pb8/4 US/4 Pb6/7 *6/7 Pb6/B H6/8 38.993 0.02 1.21720 0.01 0.489849 0.01 38.981 0.03 1.216B7 0.00 0.489732 O.OO 38.987 0.05 1.21704 0.01 0.489791 0.01 3B.875 0.07 1.21799 0.04 0.490772 0.04 39.140 0.04 1.22164 0.01 0.490291 0.02 39.077 0.03 1.22356 0.01 0.491389 0.01 39.146 0.05 1.22355 0.03 0.491108 0.03 39.189 0.12 1.22156 0.01 0.490262 0.01 39.109 0.03 1.22260 0.01 0.490840 0.02 39.168 0.08 1.22260 0.02 0.490685 0.02 39.138 0.06 1.22258 0.02 0.490763 0.02 38.537 0.42 1.21908 0.07 0.490829 0.08 38.959 0.21 1.21643 0.05 0.489572 0.04 38.927 0.04 1.21938 0.01 0.491889 0.04 3B.916 0.10 1 .21916 0.05 0.492018 0.08 3B.8B5 0.05 1 .21912 0.01 0.492084 0.01 38.909 0.06 1.21922 0.02 0.491997 0.04 38.581 0.06 1.21749 0.02 0.492044 0.02 38.979 0.02 1.23393 0.01 0.496001 0.01 39.042 0.02 1.23317 0.01 0.495474 0.01 39.026 0.01 1.23300 0.01 0.495531 0.00 39.016 0.02 1.23338 0.01 0.495669 0.01 39.056 0.03 1.23049 0.01 0.494725 0.02 38.661 0.03 1 .2054 B 0.01 0.487575 0.01 38.e56 0.08 1.20368 0.01 0.487617 0.01 38.791 0.03 1.20328 0.03 0.487321 0.01 38.751 0.03 1.20275 0.01 0.487256 0.01 39.027 0.39 1.20433 0.01 0.487514 0.02 3B.755 0.02 1 .20319 0.02 0.487565 0.01 36.987 0.16 1.20384 0.13 0.486037 0.07 38.829 0.01 1.20174 0.01 0.486577 0.00 38.B93 0.18 1.20182 0.00 0.486224 0.00 38.834 0.18 1.20018 0.00 0.486737 0.00 38.859 0.05 1.20458 0.01 0.487448 0.01 38.771 0.03 1.20302 0.02 0.487289 0.01 38.871 0.09 1.20352 0.08 0.486801 0.04 3B.863 0.18 1.20100 0.00 0.486477 0.00 38.B48 0.09 1.20304 0.05 0.486692 0.05 3B.744 0.02 1.20454 0.01 0.487849 0.01 39.253 0.13 1 .22630 0.00 0.491221 0.00 3B.574 0.05 1.19619 0.01 0.4B6742 0.01 38.681 0.06 1.20350 0.00 0.488279 0.02 3B.717 0.05 1.20341 0.04 0.488150 0.01 38.621 0.00 1.19773 0.00 0.488325 0.00 38.533 0.18 1.20343 0.12 0.490766 0.12 38.699 0.06 1.20346 0.02 0.488215 0.01 38.626 0.12 1.20085 0.07 0.486452 0.07 38.779 0.19 1.19652 0.04 0.485569 0.02 39.000 0.02 1.21643 0.01 0.490196 0.01 39.035 0.02 1.21657 0.01 0.490128 0.01 39.018 0.02 1.21650 0.01 0.490162 0.01 38.766 0.05 1.20052 0.02 0.486467 0.02 3B.687 0.02 1.2022B 0.01 0.487299 0.02 1 51 Adams Plateau: Lead Isotope Data Sample No Deposit/Sample Name 30515-002D1 REA GOLD (VEIN) 30515-003 REA GOLD (BARITE HORZ.) 30515-AVG2 REA GOLD N=2 (VEIN) 30515- AVG REA GGLD N=3 30515/00101 REA GOLD (MASS. SULPH. HORZ.) 30515/003D1 REA GOLD (BARITE HORZ.) 30516- 101 REXSPAR (G79SA-001) 30517- 001 ART 30517-001 Dl ART 30517- AVG ART N=2 30518- 001 LUCKY COON 30518-00101 LUCKY COON 30518-002 LUCKY COON (PIT 1) 3051B-AVG1 LUCKY COON N=2 30518- AVG LUCKY COON N=3 30519- 001 TUIN MOUNTAIN (FALC3.SAMPLE) 30519-00101 TWIN MOUNTAIN (FALCB.SAMPLE) 30519-501 TUIN MOUNTAIN (G79TM-001 ) 30519-AVG1 TWIN MOUNTAIN (FALCB.SAMPLE 30519-AVG TUIN MOUNTAIN N=2 30521-001 JUNE KAJUN 30521-00101 JUNE KAJUN 30521- 001D2 JUNE KAJUN 30521 -AVG JUNE KAJUN N=3 30521/101 JUNE KAJUN (G79JU-0C1) 30522- 001 9C (ZN 1) 30522-001D3 BC (ZN 1) 30522- AVG BC (ZN 1)N=2 30522/00101 3C (ZN 1) 30522/001D2 BC (ZN 1) 30523- 501 KING TUT (G79LU-001) 30524- 501 ELSIE (G79LU-002) 30525- 001 M050UIT0 KING 30525-002 MOSOUITO KING (VEIN) 30525-002D1 MOSQUITO KING (VEIN) 30525-AVG2 MOSQUITO KING N=2 (VEIN) 30525- AVG MOSQUITO KING N=2 30526- 501 PET (G79PE-001) 30527- 001 SPAR 30527-00101 SPAR 30527-002 SPAR (FLUORINE SHOWING) 30527- AVG1 SPAR N=2 30528- 001 WHITE ROCK 30528/00101 WHITE ROCK 30531-001 RED TOP 30531-002 RED TOP (TRENCH) 30531-00201 REO TOP (TRENCH) 30531-AVG2 RED TOP N=2 (TRENCH) 30531- AVG REO TOP N=2 30532- 001 FLUKE 30532-00101 FLUKE 30532- AVG FLUKE N=2 30533- 001 OR ELL 1D (RED MINERAL) Mt Anl Qual Pb6/A *6/4 Pb7/4 *.7:4 GL FG GOOD 1B.862 0.02 15.6B8 0.01 GL FG GOOD 18.893 0.03 15.706 0.03 GL FG GOOD 18.857 0.02 15.684 0.01 GL FG GOOO 18.869 0.03 15.699 0.03 GL FG POOR 18.804 0.24 15.661 0.24 GL FG POOR 18.776 0.50 15.702 0.50 GL 8R FAIR 19.177 0.10 15.911 0.20 GL FG FAIR 19.079 0.10 15.750 O.OB GL FG GOOD 19.040 0.D1 15.724 0.01 GL FG GO/FR 19.060 0.05 15.737 0.04 GL FG FAIR 19.123 0.04 15.688 0.01 GL FG GOOD 19.140 0.01 15.699 0.01 GL FG FAIR 19.163 0.10 15.696 0.01 GL FG GD/FR 19.132 0.03 15.694 0.01 GL FG GD/FR 19.142 0.07 15.694 0.01 GL FG FAIR 19.013 0.05 15.704 0.02 GL FG FAIR 19.012 0.04 15.691 0.04 GL BR FAIR 19.057 0.07 15.716 0.18 GL FG FAIR 19.013 0.05 15.69B 0.03 CL FAIR 19.035 0.06 15.707 0.10 GL FG GOOD 19.472 0.02 15.724 0.02 GL FG FAIR 19.469 0.05 15.725 0.02 GL FG FAIR 19.442 0.07 15.707 0.07 GL FG FR/GD 13.461 0.05 15.719 Q.04 GL ER FAIR 19.441 0.04 15.575 0.14 GL FG FAIR 18.294 0.01 15.552 0.01 GL FG FAIR 18.232 0.06 15.554 0.06 GL FG FAIR 18.2B8 0.03 15.553 0.03 GL FG FAIR 18.403 0.02 15.578 Q.02 GL FG POOR 18.245 0.30 15.516 0.30 GL BR FAIR 19.095 O.DB 15.6BB 0.1B GL BR FAIR 19.142 0.08 15.700 0.1B GL FG GOOD 19.075 0.01 15.692 0.01 GL FG GOOD 19.071 0.02 15.692 0.02 GL FG GOOO 19.124 0.02 15.694 0.02 GL FG GOOD 19.098 0.02 15.693 0.02 GL FG GOOO 19.090 0.02 15.693 0.02 GL BR FAIR 19.126 0.06 15.732 0.15 GL FG GOOD 19.133 0.01 15.692 0.01 GL FG GOOD 19.126 0.04 15.687 0.04 GL FG POOR 19.150 0.28 15.671 0.28 GL FG GOOD 19.130 0.03 15.690 0.03 GL FG GOOD 19.151 0.04 15.722 0.04 GL FG POOR 19.227 0.64 15.801 0.62 GL FG FAIR 19.142 0.05 15.719 0.02 GL FG GOOO 19.159 0.09 15.737 0.09 GL FG FAIR 19.136 0.07 15.710 0.00 GL FG GD/FR 19.148 0.08 15.724 0.04 GL FG GD/FR 19.146 0.06 15.721 0.04 GL FG GOOD 19.219 0.02 15.702 0.02 GL FG GOOD 19.227 0.05 15.704 0.05 GL FG GOOD 19.223 0.03 15.703 0.03 GL FG GOOD 19.362 0.02 15.715 0.02 PbB/4 JIB/4 Pb6/7 JB/7 Pb6/B %6/B 3B.742 0.03 1.20232 0.02 0.4B6872 0.03 38.823 0.03 1.20292 0.01 0.486640 0.01 3B.715 0.02 1.20232 0.02 0.487086 0.03 38.755 0.03 1.20192 0.03 0.486879 0.03 38.904 0.24 1.20066 0.03 0.483341 0.01 38.708 0.50 1.19577 0.04 0.485070 0.05 3B.9B6 0.20 1.20528 0.00 0.492734 0.00 39.185 0.11 1.21132 0.06 0.486886 0.04 39.109 0.01 1.21088 0.01 0.486848 0.00 39.147 0.06 1.21110 0.03 0.486B67 0.02 38.847 0.05 1.21B97 0.04 0.492258 0.03 36.896 0.03 1.21924 0.00 0.492096 0.02 38.958 0.10 1 .22084 0.10 0.491874 0.03 3B.872 0.04 1.21911 0.04 0.492177 0.03 3B.900 0.07 1.21968 0.06 0.492076 0.03 38.B37 0.06 1.21066 0.04 0.489554 0.02 3B.B13 0.05 1 .21166 0.01 0.489B43 0.01 38.846 0.05 1.21260 0.00 0.491415 0.00 36.825 0.06 1.21116 0.03 0.489699 0.02 38.836 0.06 1.211B8 0.03 0.490557 0.02 39.525 0.02 1.23B37 0.01 0.492647 0.01 39.513 0.05 1 .23B09 0.04 0.49271B 0.03 39.473 0.07 1.237B2 0.01 0.492534 0.01 39.504 0.05 1.23309 0.02 0.492633 0.01 39.396 0.00 1.24019 0.00 0.494320 0.00 38.309 0.01 1.17631 0.00 0.477523 0.01 38.337 0.07 1.17539 0.02 0.476B89 0.03 3B.331 0.04 1 .17S85 0.01 0.477206 0.02 36.412 0.03 1.18137 0.00 0.479100 0.01 38.243 0.30 1.17594 0.02 0.477093 0.02 38.B35 0.16 1.21718 0.00 0.492547 0.00 38.97 5 0.09 1.21925 0.00 0.491974 0.00 38.335 0.02 1.21552 0.02 0.491163 0.01 38.827 0.03 1.21532 0.01 0.491186 0.02 38.877 0.03 1.21B54 0.02 0.491907 0.01 3B.852 0.03 1 .21693 0.02 0.491547 0.02 38.846 0.03 1.2164B 0.02 0.491419 0.02 38.980 0.11 1.21575 0.00 0.491512 0.00 38.902 0.06 1.21928 0.01 0.491821 0.06 38.859 0.04 1.21926 0.01 0.492191 0.01 3B.B64 0.2B 1.22197 0.05 0.492745 0.03 38.881 0.05 1.21927 0.01 0.492006 0.03 39.048 0.04 1.21810 0.01 0.490461 0.01 39.198 0.65 1.21684 0.14 0.490511 0.15 38.938 0.06 1.217B1 0.04 0.491608 0.04 38.974 0.10 1.21748 0.01 0.491598 0.04 3B.905 0.07 1.21808 0.01 0.491880 0.01 3B.940 O.OB 1.2177B 0.01 0.491739 0.03 38.939 0.07 1.21779 0.03 0.491695 0.03 39.366 0.06 1.22398 0.01 0.488203 0.06 39.356 0.05 1.22433 0.01 0.48B550 0.02 39.361 0.05 1.22416 0.01 0.48B377 0.04 39.401 0.04 1.23213 0.01 0.491419 0.04 1 5 2 Adams P l a t e a u : L e a d I s o t o p e Data Sample No D e p o s i t / S a m p l e Name 30533-00101 OR ELL 1D (RED MINERAL) 30533-002 ORELL 1E (RED MINERAL) 30533 - AVC ORELL ID N=3 (RED MINERAL) 30534- 001 ORELL 2G (RED MINERAL) 30534-00101 ORELL 2G (RED MINERAL) 30534- AVG ORELL 2G N=2 (RED MINERAL) 30535 - 001 ORELL 3K (RED MINERAL) 30536- 001 ORELL 4N (SILVER KING,A) 30537- 001 ORELL SP 30537-001D1 ORELL 5P 30537- AVG . ORELL 5P N=2 30538- 001 UTAH PROSPECT (FORD) 30538-001D1 UTAH PROSPECT (FORD) 3O53B-O01D2 UTAH PROSPECT (FORD) 30538- 001D3 UTAH PROSPECT (FCSD) 30S3B-AVG UTAH PROSPECT N=4 30539- 001 MT McCLENNAN (X-CUTTIMG Mil'!) 30539-002 MT McCLENNAN 30539- AVG MT McCLENNAN N=2 30540- 501 BIRCH ISLAND (HL P45 KQ73-36) 30541- 001 SUNRISE 30541-002 SUNRISE 30541- AUG SUNRISE N=2 30542- 001 VAVENEY 30542-00101 VAVENEY 30542- AVG VAVEN9Y N=2 30543- 001 TINDALL (ADIT DUMP) 30544- 001 50NJA 30545- 001 SILVER K I N C - S I L V E C QUEEN 30545-00101 SILVER KING-SILVER QUEEN 30545- AVG 5ILVER KING-SILVER QUEEN N=2 30546- 001 LEEMAC 30546-00101 LEEMAC 30546- AVG LEEMAC N=2 30547- 001 ROUGE 30547-001D1 ROUGE 30547- AyG ROUGE N=2 30548- 001 P S - 3 S - 1 7 S 30548-0101 P S - 3 5 - 1 7 5 30548-AVG P S - 8 S - 1 7 5 N=2 Mt A n l D u a l P b 6 / 4 J 6 / 4 P b 7 / 4 * 7 : 4 P b 8 / 4 * 8 / 4 P b 6 / 7 5S6/7 P b 6 / 8 * 6 / 8 GL FG FAIR 19 .327 0.07 15 .682 0 .07 GL FG GOOD 1 9 . 3 5 S 0.02 15 .705 0 .02 GL FG GD/FR 19 .345 0 .04 15 .699 0.04 GL FG GOOO 19.121 0 .02 15 .705 0 .02 GL FG GOOD 19 .140 0.03 15 .722 0.02 GL FG GOOO 19.131 0.03 15 .714 0.02 GL FG FAIR 19 .354 0.05 15 .706 0.03 GL FG GOOD 19.081 0.04 15 .708 0.04 GL FG GOOD 19 .128 0.01 15 .689 0.01 GL FG FAIR 19 .128 0.05 15.694 0.05 GL FG GD/FR 19 .128 0.03 15 .692 0.03 GL FG GOOD ie.B93 0.02 15.704 0.02 GL FG GOOO 18.B64 0.07 15 .702 0 .07 GL FG GOOD 18 .875 0.01 15.691 0.01 GL FG GOOO ie.8a0 0.03 15 .695 0 . 0 3 GL FG GOOD 18 .863 0 .03 15 .698 0.03 GL FG FAIR I S . 2 4 9 0.05 15 .680 0 . 0 5 GL FG FAIR 19 .288 0 .04 15 .715 0.04 GL FG FAIR 19 .269 0 .05 15 .698 0.05 GL GSC FAIR 19 .335 0 .00 15 .820 0.00 GL FG FAIR 19 .086 0.07 15.681 0.07 GL FG GOOD 19 .123 0 .03 15.711 0.01 GL FG FR/GD 19 .105 0 .05 15 .596 0 .04 GL FG GOOD 19.127 0 .03 15 .733 0 .03 GL r G FAIR 19 .055 0 .14 15 .7C3 0 . 1 3 GL FG GD/FR 19.091 0 .08 15 .723 0 .08 GL FG GOOD 19.251 0 .02 15.714 0 .02 GL FG FAIR 19.355 0 .06 15.E91 Q.06 GL FG GOOD 19 .098 0 .07 15.631 0 .05 GL FC FAIR 19 .110 0 .06 15 .635 0 .06 GL FG GD/FR 19 .104 0 .07 15.684 Q.06 GL FG FAIR 19 .406 0 .04 15.741 6.04 GL FG GOOD 19 .375 0 .03 15 .717 0 .03 GL FG FR/GD 19.391 0 .04 15 .729 0.04 GL FG GOOD 19.267 0.01 15 .750 0.00 GL FG GOOD 19 .253 O.QO 15 .738 0.00 GL FG GOOD 19 .260 0.01 15.744 0 .00 GL FG GOOD 19 .180 0 .00 1 5.72 5 0 . 0 0 GL FG GOOD 19 .174 0.00 15.717 0.00 GL FG GOOD 19 .177 0 . 0 0 15.721 0 . 0 0 39.318 0 .07 1.23245 0.01 0 .491567 0.01 39.377 0 .03 1.23237 0.01 0 .491516 0 .02 39.360 0 .05 1.23229 0.01 0 .491493 0 . 0 2 39.044 0 .03 1.21749 0.01 0.489721 0.01 39.093 0 .04 1.21744 0 .02 0 .489604 0 . 0 3 39.069 0.04 1.21747 0 .02 0 .489663 0 . 0 2 39.383 0 .05 1.23228 0 .04 0 .491420 0 . 0 2 38 .899 0.04 1.21471 0.01 0 .490516 0.01 38.879 0.01 1.21923 0.01 0 .4919B2 0 . 0 0 3B.891 0 .05 1.21881 0 .02 0 .491834 0 .02 38.BB5 0 .03 1.21902 0 .02 0 .491908 0.01 38 .699 0 .02 1.20308 0 . 0 0 0.488201 0.01 38.696 0 .08 1.20267 0.01 0 .488007 0 . 0 3 38.659 0 .02 1.20287 0.01 0 .438240 0.01 38.651 0 .05 1.20292 0.01 0 .488468 0 . 0 5 38 .676 0.04 1.202B9 0.01 0 .488229 0 . 0 3 38 .932 0 .06 1.22757 0 .02 0 .494426 0 . 0 3 39.001 0 .06 1.22736 0.01 0 .494536 0 . 0 5 38.967 0 . 0 6 1.22747 0 .02 0.494481 0 . 0 4 39 .235 0 . 0 0 1.22200 0 .00 0.493642 0 . 0 0 38.BD6 0 .08 1 .21715 0 .03 0 .491827 0 . 0 3 3B.892 0 .04 1.21717 0 .03 0.491691 0 .02 3B.B49 0 .06 1.21716 0 .03 0 .491759 0 . 0 3 38 .889 0 .03 1 .21804 0.01 0 .491833 0.01 38 .B02 0 . 1 6 1.21344 0 .05 0 .491074 0 . 0 8 38 .846 0 .09 1.21574 0 .03 0.491454 0 . 0 5 39 .080 0 .05 1.22509 0.01 0 .492605 0 . 0 2 39.251 0 .06 1 .23353 0 . 0 0 0 .493132 0.01 38.977 0 .08 1.21789 0 .05 0.489971 0 . 0 2 38 .979 0 .06 1.21826 0.01 0.490261 0 . 0 2 38.97B 0 .07 1.21BC7 0 .03 0 .490116 0 . 0 2 39 .375 0.04 1.23287 0.02 0 .492849 0.01 39 .297 0 .04 1.23271 0.01 0 .493036 0.01 39.336 0.04 1.23279 0 .02 0 .492943 0.01 39 .172 0 .03 1.22329 0.01 0 .491845 0 . 0 3 39 .139 0 .00 1.22331 0 .00 0 .491910 0 . 0 0 39 .156 0 .02 1.22330 0.01 0 .491878 0 . 0 2 38 .696 0 .00 1 .21977 0 .00 0.492194 0 . 0 0 38 .955 0 .00 1.21997 0 .00 0 .492212 0 . 0 0 38.96 2 0 .00 '1 .21937 0 . 0 0 0 .492203 0 . 0 0

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