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Petrology, geochronometry and economic geology : the Zeta tin-silver prospect, Arsenic Ridge, west-central… Abercrombie, Shirley May 1990

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PETROLOGY, GEOCHRONOMETRY AND ECONOMIC GEOLOGY: THE ZETA TIN-SILVER PROSPECT, ARSENIC RIDGE, WEST-CENTRAL YUKON (115P/14 and 116A/03) By S h i r l e y May Abercrombie B.Sc.(Honours), U n i v e r s i t y o f Western O n t a r i o , 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE - i n THE FACULTY OF GRADUATE STUDIES (Department o f G e o l o g i c a l S c i e n c e s ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA FEBRUARY 1 9 9 0 ( f ) S h i r l e y May Abercrombie, 1989 §8 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of C pnlac^ca) The University of British Columbia Vancouver, Canada Date H Q - ^ K a?, m o  DE-6 (2/88) ABSTRACT A r s e n i c Ridge i s l o c a t e d i n the n o r t h w e s t e r n p a r t o f the L o s t Horses b a t h o l i t h , S y e n i t e Range, Yukon T e r r i t o r y . T h i s a r e a i s w i t h i n t h e Omineca C r y s t a l l i n e B e l t of the Canadian C o r d i l l e r a . N o r t h American m i o g e o c l i n a l r o c k s o f the upper P r e c a m b r i a n t o Lower Cambrian G r i t U n i t were n o r t h w a r d l y t h r u s t onto O r d o v i c i a n t o S i l u r i a n Road R i v e r F o r m a t i o n d u r i n g t h e L a t e T r i a s s i c t o E a r l y J u r a s s i c a r c -c o n t i n e n t c o l l i s i o n . S m a l l mid-Cretaceous (83 t o 100 Ma, K-Ar on b i o t i t e ) , e p i z o n a l f e l s i c i n t r u s i o n s were emplaced i n r a d i o g e n i c S r - e n r i c h e d metasedimentary r o c k s o f t h e a n c i e n t c o n t i n e n t a l margin ( p e r i c r a t o n i c s e d i m e n t a r y p r i s m ) . The mid-Cretaceous ( s y e n i t e phase, 87+3 Ma, K-Ar on b i o t i t e ; g r a n i t e phase, 95+3 Ma, K-Ar on b i o t i t e ) L o s t Horses b a t h o l i t h i s a c i r c u l a r , S-type, composite p l u t o n w i t h i n the Selwyn B a s i n . The Selwyn B a s i n i s an e p i c o n t i n e n t a l t r o u g h p a r t i a l l y bounded on the west by t h e C a s s i a r P l a t f o r m and on t h e e a s t and n o r t h e a s t by c a r b o n a t e r o c k s o f t h e MacKenzie P l a t f o r m . S-type p l u t o n s a re a p r o d u c t o f Hercynotype a r c - c o n t i n e n t a l c o l l i s i o n a l t e c t o n i c s . i i The zoned i n t r u s i v e r o c k s a l o n g A r s e n i c R i d g e , from c o r e t o r i m , have been c l a s s i f i e d as t o u r m a l i n e o r b i c u l a r g r a n i t e , g r a n i t e , q u a r t z s y e n i t e and s y e n i t e . With i n c r e a s i n g SiC-2 : (1) the major e l e m e n t s - - A l 2 O 3 , FeO, MgO, CaO, T i 0 2 , MnO and P2 0 s - - t e n d t o d e c r e a s e , ( 2 ) t r a c e e l e m e n t s - - Z r , V, S r , N i , and Ba--are c h a r a c t e r i z e d by extreme d e p l e t i o n s , and ( 3 ) the t r a c e element, Rb, i s s l i g h t l y e n r i c h e d . The s y e n i t e i s a l k a l i n e whereas th e q u a r t z s y e n i t e , g r a n i t e , g r a n i t e dyke, and t o u r m a l i n e o r b i c u l a r g r a n i t e a r e s u b - a l k a l i n e . Magmatic d i f f e r e n t i a t i o n o f t h e p l u t o n i s demonstrated by a d e c r e a s i n g t r e n d o f ( N a 2 0 + K 2 O ) and T i 0 2 w i t h i n c r e a s i n g S i 0 2 , and by an i n c r e a s i n g Rb c o n t e n t w i t h a d e c r e a s e i n Ba and S r . The e s t i m a t e d p a r t i a l p r e s s u r e of water d u r i n g f o r m a t i o n of t h e L o s t Horses g r a n i t e m e l t i s b r o a d l y e s t i m a t e d as >10 k b a r . E l e c t r o n m i c r o p r o b e t r a v e r s e s a c r o s s o r t h o c l a s e megacryst c o r e s and r i m s i d e n t i f i e d a c o n c e n t r a t i o n o f a l b i t e l a m e l l a e i n t h e r i m and barium, s t r o n t i u m and c a l c i t e r i c h c o r e s . The l a t t e r i s i n d i c a t i v e o f a m e l t u n d e r g o i n g p r o g r e s s i v e d e p l e t i o n o f barium by f r a c t i o n a l c r y s t a l l i z a t i o n . i i i The age of the b a t h o l i t h i s e a r l y L a t e C r e t a c e o u s , a p p r o x i m a t e l y 97 Ma. T h i s was d e t e r m i n e d from e a r l y L a t e C r e t a c e o u s d a t e s o f 95+3 Ma from K-Ar on b i o t i t e and 88+4 Ma from K-Ar on a h o r n b l e n d e , and a l a t e E a r l y C r e t a c e o u s date of 101+6 Ma from a whole r o c k - m i n e r a l ( b i o t i t e , h o r n b l e n d e , t o t a l f e l d s p a r ) Rb-Sr i s o c h r o n . I n i t i a l s t r o n t i u m r a t i o s f o r t h e g r a n i t i c r o c k s a l o n g A r s e n i c Ridge a r e about 0.712 s u g g e s t i n g t h a t r a d i o g e n i c s t r o n t i u m was d e r i v e d m a i n l y from m e l t i n g and/or a s s i m i l a t i o n of o l d s i a l i c c r u s t d u r i n g magma g e n e s i s . The model Rb-Sr age, TUR, f o r t h e g r a n i t i c r o c k s on A r s e n i c Ridge i s 238 Ma. T h i s i n d i c a t e s t h a t a d o m i n a n t l y upper mantle s o u r c e i s u n l i k e l y . Pb-Pb i s o t o p e r a t i o s f o r the zoned p l u t o n i c r o c k s , the s u r r o u n d i n g sediments and the o r e m i n e r a l s e p a r a t e s p l o t between t h e p e r i c r a t o n i c and B l u e b e l l c u r v e s (from 0 Ma t o 140 Ma m i x i n g l i n e s ) i n d i c a t i n g t h a t t h e l e a d i s a mix of upper c r u s t and lower c r u s t s o u r c e s . Lead s u l p h i d e a n a l y s e s from t h e Z e t a p r o s p e c t , Tombstone Range and t h e Keno-Galena H i l l a r e a s a r e i n d i s t i n g u i s h a b l e from t h e f e l d s p a r r o c k l e a d . T h i s shows t h a t t h e l e a d s o u r c e f o r t h e s e v e i n i v deposits i s the surrounding plutons and not the surrounding sedimentary rocks. The least radiogenic lead has a model age of about 100 Ma. Nd/Sm and Nd analyses indicate that Arsenic Ridge g r a n i t i c rocks were derived from, or assimilated, old cru s t a l rocks whose Sm/Nd had been lowered at the time of separation from CHUR. Nd rati o s for the granite and the feldspar megacrysts are a l l very close to 0.51210. The model Sm-Nd age, TDH , for a granite along Arsenic Ridge i s 1.26 Ga. Approximate percentages of continental crust and mantle incorporated in the melt were calculated. If the contamination i s upper c r u s t a l in o r i g i n then there was a maximum of 30% mantle incorporated i n the melt. No mantle component i s needed i f the contamination source i s lower crust. However, since granite 1 4 7Sm/ 1 4 4Nd rati o s are close to the average continental crust r a t i o , the o r i g i n i s upper crust with a small mantle component. 1 4 3 N d / 1 4 4 N d and 8 7 S r / 8 6 S r r a t i o s for the g r a n i t i c rocks from the Lost Horses batholith plot in the Phanerozoic quadrant of Faure (1986) and are sim i l a r to values from the Sierra Nevada batholith. Epsilon values of Nd and Sr v suggest the g r a n i t e i s S-type which agrees w i t h the f i e l d , p e t r o g r a p h i c and c h e m i c a l e v i d e n c e . The g r a n i t e p l o t s w i t h i n the f i e l d f o r m i o g e o c l i n e s as d e t e r m i n e d by Farmer and DePaolo (1983 ). The Zeta t i n - s i l v e r g r e i s e n v e i n p r o s p e c t s l i e i n b o t h the O r d o v i c i a n - S i l u r i a n metasediments of t h e Road R i v e r Group a t the n o r t h e a s t e r n c o n t a c t , and i n the zoned, mid-Cretaceous L o s t Horses b a t h o l i t h . M i n e r a l i z a t i o n on the p r o p e r t y o c c u r s i n two forms: (1) c a s s i t e r i t e b e a r i n g g r e i s e n v e i n s i n h o r n f e l s e d q u a r t z i t e , and (2) g r e i s e n v e i n s ( s u l p h i d e and q u a r t z w i t h minor t o u r m a l i n e , and t o u r m a l i n e and q u a r t z w i t h minor s u l p h i d e i n g r a n i t i c r o c k s ) . K-Ar m u s c o v i t e d a t i n g of t h e s e r i c i t i c c a s s i t e r i t e g r e i s e n (87.0+3.0 Ma), i n d i s t i n g u i s h a b l e from th e K-Ar b i o t i t e d a t e f o r t h e s y e n i t e phase o f the b a t h o l i t h (86.8+2.7 Ma), e s t a b l i s h e s a g e n e t i c r e l a t i o n s h i p between th e two. The f o l l o w i n g f o u r - s t a g e model d e s c r i b e s the e v o l u t i o n o f t h e L o s t Horses b a t h o l i t h : s t a g e 1, i n i t i a l m e l t i n g , s t a g e I I , m e l t a c c u m u l a t i o n s and a s s i m i l a t i o n , s t a g e I I I , d i a p i r i c r i s e and c h e m i c a l d i f f e r e n t i a t i o n ( f r a c t i o n a l c r y s t a l l i z a t i o n ) , and s t a g e IV, magmatic h y d r o t h e r m a l . T h i s v i l a s t s t a g e g e n e r a t e d t i n - s i l v e r v e i n and g r e i s e n m i n e r a l i z a t i o n . The s o u r c e f o r t h i s l i t h o p h i l e m i n e r a l i z a t i o n and a s s o c i a t e d S-type g r a n i t i c r o c k i s d o m i n a n t l y from a s i a l i c c l a s t i c wedge w i t h upper c r u s t a l g e o c h e m i c a l c h a r a c t e r i s t i c s . v i i TABLE OF CONTENTS Page COPY AND REFERENCE PERMISSION i ABSTRACT i i TABLE OF CONTENTS v i i x LIST OF FIGURES x i LIST OF TABLES x v i i LIST OF PLATES x i x LIST OF APPENDICES x x i i i ACKNOWLEDGEMENTS X X V 1 INTRODUCTION 1 1.1 SCOPE OF THESIS 2 2 REGIONAL GEOLOGY 3 2.1 REGIONAL GEOLOGY 3 3 LOCAL GEOLOGY 9 3.1 INTRODUCTION 9 3.2 D e s c r i p t i o n o f U n i t s 9 3.2.1 Sedimentary Rocks 9 3.2.2 I n t r u s i v e Rocks 16 3.2.2.1 Magmatic E p i d o t e 36 v i i i Page 3.2.3 Dyke Rocks 37 3.3 CHEMICAL PETROLOGY 40 3.3.1 I n t r o d u c t i o n 40 3.3.2 Chemical V a r i a t i o n W i t h i n the Rocks o f A r s e n i c Ridge 41 3.3.3 Pearce Element R a t i o s o f Whole Rock Samples 54 3.3.4 Probe a n a l y s e s 60 3.4 MINERALIZATION AND ALTERATION 71 4 ISOTOPIC STUDIES 85 4.1 INTRODUCTION 85 4.2 K-AR DATING 87 4.2.1 I n t r o d u c t i o n 87 4.2.2 Method of A n a l y s i s 87 4.2.3 R e s u l t s 90 4.2.4 I n t e r p r e t a t i o n 91 4.3 RB-SR GEOCHRONOMETRY 91 4.3.1 I n t r o d u c t i o n 91 4.3.2 Method o f A n a l y s i s 92 4.3.3 R e s u l t s 92 4.3.4 I n t e r p r e t a t i o n 93 i x Page 4.4 PB-PB SYTEMATICS 106 4.4.1 I n t r o d u c t i o n 106 4.4.2 Method of A n a l y s i s 106 4.4.3 R e s u l t s 107 4.4.4 I n t e r p r e t a t i o n 110 4.5 ND-SM ANALYSES 120 4.5.1 I n t r o d u c t i o n 120 4.5.2 Method o f A n a l y s i s 120 4.5.3 R e s u l t s 121 4.5.4 I n t e r p r e t a t i o n 121 5 CONCLUSIONS 126 5.1 GEOLOGIC SETTING OF ARSENIC RIDGE 126 5.2 THE GRANITIC UNITS 128 5.3 DATING 131 5.4 ORIGIN OF GRANITIC ROCKS 134 5.5 ZETA MINERALIZATION 144 5.6 MODEL OF MAGMA EVOLUTION AND MINERALIZATION 146 6 REFERENCES CITED 151 x LIST OF FIGURES Page Figure 2.1: Regional geology of the Syenite Range area showing the location of Arsenic Ridge with respect to Lost Horses batholith, west-central Yukon (from Bostock, 1964 and Green, 1972). Inset shows study area to be within the Selwyn Basin. 4 Figure 3.1: Local geology and sample location map of the Zeta Property, Lost Horses batholith, west-central Yukon. in pocket Figure 3.2: Generalized l o c a l geology and sample location map of the Zeta Property, Lost Horses batholith, west-central Yukon (from Fig. 3.1). 10 Figure 3.3: Quartz - orthoclase - a l b i t e triangular plot of normative and modal composition (Appendix A; Table 3.1) of major units from Arsenic Ridge, Lost Horses batholith, Yukon. 42 x i F i g u r e 3.4: Major element o x i d e c o n t e n t p l o t t e d v e r s u s S i 0 2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 3.5: Trace element o x i d e c o n t e n t p l o t t e d v e r s u s S i 0 2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 3.6: Na2 0 + K2O and CaO c o n t e n t p l o t t e d v e r s u s S i 0 2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 3.7: T i 0 2 c o n t e n t p l o t t e d v e r s u s SiC-2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 3.8: Barium - r u b i d i u m - s t r o n t i u m t r i a n g u l a r p l o t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Figure 3.9: Quartz - orthoclase - a l b i t e triangular plot (data from Table 3.1) for major units on Arsenic Ridge, Lost Horses batholith, Yukon. Figures 3.10: Rb/Y versus distance from batholith margin (data from Table 3.1 and 3.2) for major rock units on Arsenic Ridge, Lost Horses batholith, Yukon. Figure 3.11: Ni/Y versus distance from batholith margin data from Table 3.1 and 3.2) for major rock units on Arsenic Ridge, Lost Horses batholith, Yukon. Figure 3.12a-d: Selected major and trace element contents plotted verus SiOz contents (data from Table 3.2) from four microprobe traverses across K-feldspar megacrysts from granite, Arsenic Ridge, Lost Horses batholith, Yukon. F i g u r e 4.1: 8 7 Sr/ 8<5Sr v e r s u s 8 7 R b / 8 6 S r p l o t o f whole r o c k s and m i n e r a l s e p a r a t e s ( d a t a used from T a b l e 4.3) from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 4.2: 8 7 S r / 8 6 S r v e r s u s 8 7 R b / 8 6 S r p l o t o f K-f e l d s p a r c o r e (n=5) and r i m (n=5) a n a l y s e s from a m e g a c r y s t i c g r a n i t e ( d a t a from T a b l e 4.3) A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 4.3: 2ospb/2 0 4pb v e r s u s 2 0 6 P b / 2 0 4 P b and 2o?pb/20 4pb v e r s u s 2ospb/20 4pb p l o t s o f whole r o c k samples, average K - f e l s p a r c o r e s (n=5), average K - f e l d s p a r r i m s (n=5), hornblende s e p a r a t e (n=l) and b i o t i t e s e p a r a t e ( n = l ; d a t a a r e i n T a b l e 4.4) from t h e major u n i t s on A r s e n i c R i d g e , Yukon. x i v F i g u r e 4.4 2 ° 8 P b / 2 0 4 P b v e r s u s 2oepb/20 4pb and 207 Pb/ 2 04 Pb v e r s u s 2 0 6 pb/2 0 4 pt, p l o t s o f K-f e l d s p a r c o r e s and r i m s ( d a t a used from T a b l e 4.4) from a m e g a c r y s t i c g r a n i t e on A r s e n i c R i d g e , Yukon and s u l p h i d e a n a l y s e s ( d a t a from T a b l e 4.5) from Z e t a , Tombstone and Galena H i l l a r e a s , Selwyn B a s i n , Yukon. F i g u r e 5.1: 1 4 3 N d / 1 4 4 N d v e r s u s 8 7 S R / 8 6 S R p i o t of p r e s e n t day i s o t o p i c r a t i o s of g r a n i t i c r o c k s of the c o n t i n e n t a l c r u s t from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. F i g u r e 5.2: I n i t i a l end v e r s u s esr p l o t of I - and S-type g r a n i t e s from s o u t h e a s t e r n A u s t r a l i a . Data from M c C u l l o c h and C h a p p e l l (1982) and Ta b l e 4.6. M i x i n g l i n e components from F a u r e , (1986). xv F i g u r e 5.3: I n i t i a l eu& v e r s u s esr p l o t i n d i c a t i n g t h e i s l a n d a r c , e u g e o c l i n e , m i o g e o c l i n e and c r a t o n f i e l d s of G r e a t B a s i n , o f the w e s t e r n U n i t e d S t a t e s , g r a n i t i c r o c k s . F i g u r e 5.4: Schematic d r a w i n g of t h e f o u r s t a g e s o f f o r m a t i o n f o r t h e L o s t Horses b a t h o l i t h , Yukon. x v i LIST OF TABLES T a b l e 3.1: Major and t r a c e element d a t a w i t h n o r m a t i v e and modal m i n e r a l o g y from major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. T a b l e 3.2: E x a m i n a t i o n o f c o n s e r v e d elements u s i n g t r a c e elements r a t i o e d t o Y f o r major g r a n i t i c r o c k s (dykes e x c l u d e d ) from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. T a b l e 3.3: Major o x i d e element a n a l y s e s f o r f o u r m i c r o p r o b e t r a v e r s e s a c r o s s an o r t h o c l a s e megacryst from a g r a n i t e (sample SA48, F i g s . 3.1, 3.2) on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. T a b l e 4.1: Samples and methods of a n a l y s i s f o r major r o c k u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. x v i i T a b l e 4.2: A n a l y t i c a l d a t a f o r C r e t a c e o u s K-Ar d a t e s from the S y e n i t e Range and s u r r o u n d i n g a r e a , w e s t - c e n t r a l Yukon. T a b l e 4.3: Rubidium and s t r o n t i u m i s o t o p e d a t a f o r the major r o c k u n i t s a l o n g A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. T a b l e 4.4: Rock l e a d - i s o t o p e a n a l y s e s from sediments and g r a n i t i c r o c k s a l o n g A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. T a b l e 4.5: Lead i s o t o p e a n a l y s e s on s u l p h i d e s from Z e t a , Tombstone and Galena H i l l a r e a s , Selwyn B a s i n , Yukon. T a b l e 4.6: Measured and i n i t i a l r a t i o s o f Nd and Sm on a g r a n i t e (SA48) and 3 p a i r s of K-f e l d s p a r megacryst c o r e s and r i m s from A r s e n i c Ridge, L o s t Horses b a t h o l i t h , Yukon. x v i i i LIST OF PLATES P l a t e 2.1: L o o k i n g n o r t h e a s t a l o n g A r s e n i c R i d g e , L o s t Horses b a t h o l i t h a r e a , Yukon. P l a t e 3.1: Coarse g r a i n e d e q u i g r a n u l a r s y e n i t e ( F i g s . 3.1, 3.2: u n i t 2 a ) , L o s t Horses b a t h o l i t h , Yukon. P l a t e 3.2: M e g a c r y s t i c s y e n i t e ( F i g s . 3.1, 3.2: u n i t 2 a ) , L o s t Horses b a t h o l i t h , Yukon. P l a t e 3.3: K - f e l d s p a r megacryst from a s y e n i t e on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon e x h i b i t i n g g r a n o p h y r i c t e x t u r e . P l a t e 3.4: P l a g i o c l a s e o r i e n t e d p a r a l l e l t o t h e l o n g a x i s o f a s y e n i t e h o s t e d a K - f e l d s p r megacryst, A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. P l a t e 3.5: M a t r i x a u g i t e b e i n g r e p l a c e d by h o r n b l e n d e , U n i t 2a, ( s y e n i t e ) , A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. x i x Plate 3.6: Pyroxene exsolution within a syenite, Arsenic Ridge, Lost Horses batholith, Yukon Plate 3.7: Magmatic epidote within a syenite, Arsenic Ridge, Lost Horses batholith, Yukon. Plate 3.8: Matrix plagioclase from a syenite on Arsenic Ridge Ridge, Lost Horses batholith,. Yukon exhibiting growth zoning. Plate 3.9: "Tourmaline orbicular granite" (Figs 3.1, 3.2: unit 2d), Lost Horses batholith, Yukon. Plate 3.10: Zoned K-feldspar megacryst from a granite along Arsenic Ridge, Lost Horses batholith, Yukon. Plate 3.11: Microprobe traverses across K-feldspar megacryst A from granite (Figs. 12a-d, sample SA48) Lost Horses batholith, Yukon. xx P l a t e 3.12: M i c r o p r o b e t r a v e r s e s a c r o s s K-f e l d s p a r megacryst B from g r a n i t e ( F i g s . 12a-d, sample SA48) L o s t Horses b a t h o l i t h , Yukon. P l a t e 3.13: C a s s i t e r i t e (CS) from Trench 1983-3, Zeta showing, w e s t - c e n t r a l Yukon, o c c u r as d a r k e r b l e b s w i t h i n b l a c k t o u r m a l i n e v e i n l e t s t h a t form up t o 0.5% of t h e r o c k . P l a t e 3.14: Envelopes around t o u r m a l i n e v e i n s , from Trench 1983-1, Zeta showing, west-c e n t r a l Yukon, c o n s i s t of m o d e r a t e l y t o s t r o n g l y t o u r m a l i n i z e d , k a o l i n i z e d and l i m o n i t i z e d s y e n i t e . P l a t e 3.15: The C i r q u e v e i n ( F i g s . 3 1, 3.2), Zeta p r o s p e c t , w e s t - c e n t r a l Yukon, i s a zoned q u a r t z - s u l p h i d e v e i n c o n t a i n i n g about 65% p y r i t e ( P Y ) , 5% a r s e n o p y r i t e ( A S ) , 25% t o u r m a l i n e (TO) and 5% a l t e r e d f e l d s p a r s . xx i Plate 3.16: The Low Fog vein (Figs. 3.1, 3.2), Zeta prospect, west-central Yukon, t y p i c a l l y contains sphalerite (SL) and pyrite (PY) surrounded by stannite (SN) and jamesonite (JM). Plate 3.17: Polished section from the Main Zone (Figs. 3.1, 3.2: 1983-1 Trench), Zeta prospect, west-central Yukon, shows sphalerite (SL) i n a quartz gangue containing inclusions of stannite (SN), jamesonite (JM), and chalcopyrite (CP). Plate 3.18: Cross section of the Gash vein (Figs. 3.1, 3.2), Zeta prospect, west-central Yukon, shows a symmetrical a l t e r a t i o n envelope on the central tourmaline-quartz low sulphide vein. x x i i LIST OF APPENDICES Appendix A: T h i n s e c t i o n d e s c r i p t i o n s and p o i n t c o u n t i n g d a t a f o r g r a n i t i c r o c k s from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Appendix B: M i c r o p r o b e s e t u p f o r probe t r a v e r s e s a c r o s s a K - f e l d s p a r megacryst from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Appendix C: Sample p r e p a r a t i o n p r o c e d u r e s f o r a n a l y s e s of s e d i m e n t a r y and g r a n i t i c r o c k s from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Appendix D: The U n i v e r s i t y of B r i t i s h Columbia Geochronometry Lab p r o c e d u r e s and e r r o r c a l c u l a t i o n s f o r K-Ar, Rb-Sr and Sm-Nd a n a l y s e s . x x i i i Appendix E: Programs f o r c o r r e c t i n g raw l e a d i s o t o p e d a t a f o r s e d i m e n t a r y and g r a n i t i c r o c k s a l o n g A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. x x i v ACKNOWLEDGMENTS I thank C o l i n Godwin f o r h i s guidance i n s u p e r v i s i o n of t h i s t h e s i s . J . B i c z o k and B. Mercer o f Noranda E x p l o r a t i o n Company L i m i t e d , W h i t e h o r s e and Vancouver o f f i c e s r e s p e c t i v e l y , p r o v i d e d f i e l d s u p p o r t , c o s t s o f t h e s i s p r e p a r a t i o n and i n f o r m a t i o n on t h e Zeta p r o p e r t y . R.L. Armstrong g u i d e d t h e Rb-Sr and Sm-Nd i s o t o p e a n a l y s e s ; h i s h e l p was i n v a l u a b l e and a p p r e c i a t e d . F u n d i n g of some a n a l y s e s and some t r a n s p o r t a t i o n by the E x p l o r a t i o n and G e o l o g i c a l S e r v i c e s D i v i s i o n of DIAND i s a p p r e c i a t e d . A d d i t i o n a l s u p p o r t was o b t a i n e d from The U n i v e r s i t y of B r i t i s h Columbia, and NSERC g r a n t s t o R.L. Armstrong and t o C.I. Godwin. F i e l d a s s i s t a n c e by John Nash was h e l p f u l . S u g g e s t i o n s from Diane Emond, Department of I n d i a n and N o r t h e r n Development, W h i t e h o r s e , and D, S i n c l a i r , G e o l o g i c a l Survey of Canada, Ottawa were u s e f u l . Bob Cann r e v i e w e d t h i s t h e s i s . D. Reddy, R.L. Armstrong and Stanya Horsky h e l p e d i n the o r g a n i z a t i o n of t h e X-ray f l u o r e s c e n c e a n a l y s e s . I am g r a t e f u l t o J a n e t G a b i t e s , D i t a R u n k l e , Anne Andrew, John K n i g h t and Joe H a r a k a l f o r t h e i r e x p e r t i s e i n v a r y i n g XXV a s p e c t s o f sample a n a l y s e s . I a l s o thank s t a f f , t e c h n i c i a n s and f e l l o w g r a d u a t e s t u d e n t s i n the Department o f G e o l o g i c a l S c i e n c e s . Many thanks t o my coworkers a t Canamax Resources K e t z a R i v e r Mine, e s p e c i a l l y R. McCombe, D. Bergen, W. B r i l l , who encouraged and s u p p o r t e d t h e c o m p l e t i o n of t h i s t h e s i s . M. Burke, B. Hardy and D. Opper c a p a b l y l o o k e d a f t e r t h e geol o g y department d u r i n g my absence. I n v a l u a b l e computer a s s i s t a n c e w h i l e a t the m i n e s i t e was p r o v i d e d by B. S t . Amand, A. H a r t n o l l and I . Magagi. xxv i CHAPTER 1 INTRODUCTION The Lost Horses batholith and the Zeta t i n - s i l v e r prospect i s approximately 105 km east of Dawson City, west-central Yukon T e r r i t o r y (Fig. 2.1). This area, centered near 63°59*N, 137°20*W (NTS: 115P/14, 116A/03), l i e s within the Syenite Range. Vein and greisen mineralization on the Zeta property, owned by Noranda Exploration Company Limited, Toronto, l i e s along the northern contact of the Cretaceous Lost Horses batholith, mainly within Ordovician - S i l u r i a n c l a s t i c and chemical metasediments of the Road River Group (Plate 2.1). S i g n i f i c a n t arsenic values i n s i l t obtained from a single stream draining the northern margin of the intrusion prompted the o r i g i n a l staking by Noranda in 1980 (Jago, 1982; Biczok, 1983). Detailed mapping, trenching and s o i l sampling resulted i n the discovery of greisen (as defined by Shcherba, 1970). Tin and s i l v e r mineralization, associated with greisenized c a s s i t e r i t e - bearing veins and v e i n l e t s , has been found on the property. 1 1.1 SCOPE OF THESIS T i n m i n e r a l i z a t i o n t h r o u g h o u t t h e w o r l d i s u s u a l l y a s s o c i a t e d w i t h g r a n i t e . At the Z e t a p r o p e r t y i t has formed w i t h i n and a d j a c e n t t o a zoned m e g a c r y s t i c b a t h o l i t h t h a t i s m a i n l y s y e n i t e i n c o m p o s i t i o n . In o r d e r t o u n d e r s t a n d t h e g e n e s i s of t h e s y e n i t e — a s r e l a t e d t o t i n - s i l v e r m e t a l l o g e n y and z o n i n g from s y e n i t e , t h r o u g h q u a r t z s y e n i t e , t o a g r a n i t e c o r e — d e t a i l e d p e t r o l o g i c and i s o t o p i c s t u d i e s were und e r t a k e n a l o n g A r s e n i c Ridge ( F i g . 2.1). T h i s r i d g e t r a v e r s e s about o n e - h a l f o f the L o s t Horses b a t h o l i t h e x t e n d i n g from t h e n o r t h w e s t e r n edge of the b a t h o l i t h t o the c o r e . Rb-Sr, Pb-Pb and Nd-Sm r a d i o g e n i c i s o t o p e s t u d i e s , c o n c e n t r a t e d on the g r a n i t e and on i t s zoned K - f e l d s p a r m e g a c r y s t s , were t o h e l p i l l u c i d a t e the g e n e s i s of t h e b a t h o l i t h and the s i g n i f i c a n c e of i t s g e n e s i s t o m e t a l l o g e n y . 2 CHAPTER 2 REGIONAL GEOLOGY 2.1 REGIONAL GEOLOGY The S y e n i t e Range l i e s w i t h i n the Selwyn B a s i n of the Canadian C o r d i l l e r a ( F i g . 2.1). The Selwyn B a s i n i s an e p i c o n t i n e n t a l t r o u g h p a r t i a l l y bounded on t h e west (seaward) by t h e C a s s i a r P l a t f o r m and on the e a s t and n o r t h e a s t by c a r b o n a t e r o c k s of the Mackenzie P l a t f o r m . I t r e p r e s e n t s a weakly metamorphosed L a t e P r e c a m b r i a n t o T r i a s s i c m i o g e o c l i n a l t r a n s i t i o n from s h a l l o w water l i m e s t o n e , d o l o s t o n e and sandstone i n t h e e a s t t o t u r b i d i t i c s a ndstone, deep water l i m e s t o n e , s h a l e and c h e r t i n t h e west (Anderson, 1988). The Selwyn B a s i n i s e l o n g a t e , t r e n d s n o r t h w e s t and i s p a r a l l e l t o the T i n t i n a F a u l t . R i g h t hand movement of a p p r o x i m a t e l y 450 km d u r i n g upper C r e t a c e o u s t o T e r t i a r y time c h a r a c t e r i z e the T i n t i n a F a u l t ( R o d d i c k , 1967; Templeman-Kluit, 1979; G a b r i e l s e , 1985). The L o s t Horses b a t h o l i t h i s a p p r o x i m a t e l y 30 k i l o m e t e r s n o r t h e a s t o f t h e T i n t i n a F a u l t ( F i g . 2.1). The C r e t a c e o u s L o s t Horses b a t h o l i t h ( F i g . 2.1), i s a c i r c u l a r (8.5 km d i a m e t e r ) composite p l u t o n w i t h a s m a l l 3 F i g u r e 2.1: R e g i o n a l geology of the S y e n i t e Range a r e a showing the l o c a t i o n of A r s e n i c Ridge w i t h r e s p e c t t o L o s t Horses b a t h o l i t h , w e s t - c e n t r a l Yukon (from B o s t o c k , 1964 and Green, 1972). I n s e t shows s t u d y a r e a t o be w i t h i n the Selwyn B a s i n . U n i t s a re as f o l l o w s : U n i t 1 - Precambrian t o O r d o v i c i a n s c h i s t , q u a r t z i t e , p h y l l i t e and l i m e s t o n e ; U n i t 2 - O r d o v i c i a n t o Devonian q u a r t z i t e , s l a t e , p h y l l i t e , l i m e s t o n e and c o n g l o m e r a t e ; U n i t 3 - J u r a s s i c t o C r e t a c e o u s - gabbro, p e r i d o t i t e , s e r p e n t i n i t e and d i o r i t e ; U n i t 4 - J u r a s s i c t o C r e t a c e o u s s y e n i t e and m o n z o n i t e ; U n i t 5 - J u r a s s i c t o C r e t a c e o u s g r a n i t e , g r a n o d i o r i t e and q u a r t z monzonite; and, U n i t 6 - T e r t i a r y and l a t e r u n c o n s o l i d a t e d g l a c i a l and a l l u v i a l d e p o s i t s . core (2.8 km in diameter) of granite surrounded by a coarse, megacrystic syenite. The syenite phase of t h i s batholith has been dated at early Late Cretaceous, .87+3 Ma (K-Ar b i o t i t e ; Table 4.2; Christopher, 1973), whereas, the granite has been dated at 95+3 Ma (K-Ar, b i o t i t e ) . (Other dates in Table 4.2 are: K-Ar, hornblende, 88+4 Ma; and, Rb-Sr, 101+6 Ma.) The batholith intrudes Paleozoic quartzites, coarse e l a s t i c s , black to gray cherts, and s i l t s t o n e s and greywackes of the Road River Group (Bostock, 1964; Green, 1972; Thompson and Roots, 1982; Plate 2.1). These sediments might include part of the Devonian "Black C l a s t i c Unit"; no firm f o s s i l evidence has been found. These Paleozoic sediments were deposited in an elongate, possibly f a u l t -bounded, basin that trends north-northeast and was broadly folded about an easterly trending axis (Thompson and Roots, 1982). Local basins are suggested by the occurrence of stratiform barite and thick units of coarse chert-pebble conglomerate. The Zeta t i n - s i l v e r prospect occurs i n sedimentary rocks less than 180 metres from t h e i r contact with syenite of the northwestern edge of the Lost Horses batholith. 5 P l a t e 2.1 L o o k i n g n o r t h e a s t a l o n g A r s e n i c Ridge, L o s t Horses b a t h o l i t h a r e a , Yukon. Trench i n c e n t r e of p i c t u r e marks the approximate c o n t a c t between Road R i v e r Group t o the n o r t h , and s y e n i t e of the L o s t Horses b a t h o l i t h t o the s o u t h . 6 The Tombstone b a t h o l i t h l i e s a p p r o x i m a t e l y 7 5 k i l o m e t e r s n o r t h w e s t o f the L o s t Horses b a t h o l i t h ( F i g . 2.1). I t i s a s u b c i r c u l a r composite i n t r u s i o n c o n s i s t i n g of d o m i n a n t l y m i a s k i t i c a l k a l i s y e n i t e ( n o r d m a r k i t e ) . The s o u t h e r n b o r d e r u n i t i s p s e u d o l e u c i t e t i n g u a i t e , and the c o r e and m a r g i n a l d i k e b o d i e s c o n s i s t of monzonite, q u a r t z monzonite and g r a n i t e (Olade and G o o d f e l l o w , 1978). The c o n t a c t between th e t i n g u a i t e and s y e n i t e i n t h e s o u t h e r n p a r t o f the b a t h o l i t h i s s h a r p and i n t r u s i v e , whereas t h a t between the s y e n i t e and monzonite i s g r a d a t i o n a l (Tempelman-K l u i t , 1969). The l e a d - z i n c - s i l v e r v e i n s o f the Keno H i l l - Galena H i l l (Keno H i l l on Yukon i n s e t ) a r e a s l i e a p p r o x i m a t e l y 80 k i l o m e t r e s s o u t h e a s t o f t h e L o s t Horses b a t h o l i t h ( F i g . 2.1). J u r a s s i c and Lower C r e t a c e o u s s e d i m e n t a r y r o c k s , c o n s i s t i n g o f b l a c k s l a t e and p h y l l i t i c s l a t e (Lower S c h i s t ) , and m a s s i v e , M i s s i s s i p p i a n , g r e y , t h i c k - b e d d e d o r t h o q u a r t z i t e (Keno H i l l q u a r t z i t e ) u n d e r l i e t h e Keno H i l l - Galena H i l l a r e a (Lynch, 1989; Tempelman-Kluit, 1970; B o y l e , 1965). They d i p t o t h e s o u t h e a s t . Conformable l e n s e s and s i l l s o f g r e e n s t o n e o c c u r i n t h e lower s c h i s t and 7 c e n t r a l q u a r t z i t e f o r m a t i o n s , and a few q u a r t z - f e l d s p a r p o r p h y r y s i l l s a r e p r e s e n t l o c a l l y i n both of the f o r m a t i o n s . M i d - C r e t a c e o u s g r a n i t e s t o c k s , r a n g i n g i n c o m p o s i t i o n from g r a n i t e t o q u a r t z d i o r i t e , o u t c r o p n o r t h e a s t and s o u t h e a s t of t h e main m i n e r a l b e l t . Two p r i n c i p a l f a u l t systems o c c u r i n t h e a r e a : n o r t h e a s t -s t r i k i n g v e i n f a u l t s , w h i c h t o g e t h e r w i t h numerous s u b s i d i a r i e s c o n t a i n s a l l t h e ore b o d i e s , and n o r t h -n o r t h e a s t t o n o r t h w e s t - t r e n d i n g f a u l t s t h a t c u t t h e o r e b o d i e s and a r e b a r r e n (Lynch, 1986; B o y l e , 1965). 8 CHAPTER 3 LOCAL GEOLOGY 3.1 INTRODUCTION The p r o p e r t y was mapped by the w r i t e r d u r i n g J u l y and August 1985. D e t a i l e d g e o l o g y , p r e s e n t e d i n F i g u r e 3.1 ( i n p o c k e t ) , i s p r e s e n t e d below. I s o t o p i c s t u d i e s f o l l o w i n Cha p t e r 4. 3.2 DESCRIPTION OF UNITS 3.2.1 Sedimentary Rocks F i n e t o c o a r s e g r a i n e d c l a s t i c and c h e m i c a l metasediments, a d j a c e n t t o and n o r t h w e s t of t h e L o s t Horses b a t h o l i t h , s t r i k e about 100° and d i p 80° n o r t h , and h o s t the Zeta p r o p e r t y ( F i g . 3.1). These O r d o v i c i a n - S i l u r i a n metasediments, from t h e c o n t a c t outwards t o t h e n o r t h ( F i g s . 3.1, 3.2) a r e : q u a r t z i t e and c o a r s e e l a s t i c s ( u n i t l a ) , g r a y c h e r t ( l b ) , b l a c k c h e r t w i t h s h a l e ( l c ) , l a m i n a t e d b a r i t e ( I d ) , and sandy s i l t s t o n e t o s i l i c e o u s s i l t s t o n e ( l e ) . U n i t l a , compact, l o c a l l y r u s t y , p a l e t o da r k , f i n e t o c o a r s e g r a i n e d q u a r t z i t e can be t r a c e d f o r s e v e r a l 9 F i g u r e 3.2: G e n e r a l i z e d l o c a l g e o l o g y and sample l o c a t i o n map o f the Zeta P r o p e r t y , L o s t Horses b a t h o l i t h , w e s t - c e n t r a l Yukon (from F i g . 3.1). U n i t s ( s e c t i o n 3.2)are as f o l l o w s : U n i t l a - q u a r t z i t e ; U n i t l b - p a l e g r a y c h e r t ; U n i t l c - b l a c k c a r b o n a c e o u s and grey c h e r t w i t h s h a l e ; U n i t I d - f i n e l y bedded s i l t s t o n e ; U n i t 2a - s y e n i t e ; U n i t 2b - q u a r t z s y e n i t e ; U n i t 2c - m e g a c r y s t i c g r a n i t e ; U n i t 2d -t o u r m a l i n e o r b i c u l a r g r a n i t e ; U n i t 3a - q u a r t z f e l d s p a r p o r p h y r y d i k e ; U n i t 3b - g r a n i t e d i k e ; U n i t 3c - l a m p r o p h y r e d i k e . Sample codes a r e as i n F i g u r e 3.1. k i l o m e t e r s a l o n g s t r i k e t o t h e e a s t and west. Bedding t h i c k n e s s e s a r e g e n e r a l l y l e s s than 20 cm. The u n i t , about 150 m i n t h i c k n e s s , i s h o r n f e l s e d . R e d d i s h brown c a s s i t e r i t e , v i s i b l e i n o u t c r o p , o c c u r s l o c a l l y i n s h e e t e d m i c r o v e i n s o f q u a r t z . The q u a r t z i t e i s composed of 53% q u a r t z , 36% s e r i c i t e , 5% m u s c o v i t e , 4% b i o t i t e and 2% opaques (Appendix A, T a b l e 3.1). A n h e d r a l q u a r t z , s e r i c i t e and opaques form a v e r y f i n e g r a i n e d groundmass (90%) a v e r a g i n g 0.08 mm i n d i a m e t e r . I s o t o p i c d a t e s from m u s c o v i t e i n t h i s q u a r t z i t e a r e d i s c u s s e d i n Chapter 4. T h i s q u a r t z i t e u n i t i s t y p i c a l l y i n t e r b e d d e d w i t h c o a r s e e l a s t i c s , t a n and gray l i m e s t o n e , l a m i n a t e d greywacke and sandy s i l t s t o n e . The c o a r s e e l a s t i c s a r e medium t o c o a r s e g r a i n e d p e b b l y q u a r t z i t e t o p e b b l y greywacke. L o c a l l y m a t r i x - s u p p o r t e d c h e r t p e b b l e conglomerate o c c u r s . The t a n and g r a y l i m e s t o n e i s f i n e g r a i n e d and b r e c c i a t e d . The bands a r e marked by a l t e r n a t i n g l a y e r s o f d a r k g r a y and t a n l i m e s t o n e . I n t h i n s e c t i o n (Appendix A ) , c o a r s e r g r a i n e d c a r b o n a t e averages l e s s t h a n 0.05 mm a c r o s s . 11 TABLE 3.1: Ha j o t and t r a c e e l e i e n t d a t a w i t h n o r s a t i v e and i c d a l l i n e t a l o g y f r o g n a j o r u n i t s a l o n g A r s e n i c R i d ge, L o s t Horses b a t h o l i t h , l u k o n . SAMPLE SA06 SAI1 SA18 SA24 SA33 SA38 Rock Grywcke Syenite AH. lo-Orb Syenite Syenite Type Otite Granite SA39 SA41 SA42 SA45 SA48 SA50 SA90 Granite OU Oil To-rich To-rich Syenite lo-Orb Dyke Syenite Syenite Granite granite Granite MAJOR ELEMENTS Ut. \)' Si02 67.67 62.12 73.06 70.39 60.07 60.23 76.06 64.96 67.64 68.04 67.12 60.92 78.04 A1203 16.25 18.26 16.62 14.85 16.01 15.05 12.99 15.99 15.84 15.44 15.81 17.07 13.58 FeO 8.98 4.48 3.39 9.81 5.39 6.33 1.63 4.07 3.61 3.73 3.55 5.26 0.45 MgO 1.92 0.53 1.01 0.51 2.92 3.69 0.00 1.54 0.64 0.90 1.06 1.34 0.00 CaO 2.71 1.95 0.43 2.21 4.25 5.16 1.15 3.48 2.64 2.49 2.75 3.36 1.34 Na20 1.09 3.46 0.17 0.B1 2.48 2.00 2.45 2.60 2.B5 2.78 2.62 3.21 0.40 K20 0.21 8.44 4.33 1.04 7.75 6.17 5.58 6.45 6.16 5.87 6.35 7.83 6.09 Ti02 1.08 0.49 0.89 0.27 0.63 0.85 0.11 0.56 0.40 0.50 0.46 0.52 0.07 MnO 0.0< 0.09 0.01 0.06 0.11 0.12 0.00 0.08 0.07 0.08 0.08 0.13 0.00 P20S 0.05 0.15 0.09 0.03 0.37 0.42 0.04 0.25 0.16 0.18 0.20 0.30 0.02 Noraalized 100.01 99.98 100.01 100.00 99.98 100.02 100.01 99.99 100.01 100.00 100.01 100.00 100.00 total' 101 \ 1.06 1.43 3.51 2.76 0.88 0.87 0.26 0.68 0.36 0.90 0.91 0.46 2.82 TRACE ELENENTS(ppi)* Ba 207 1401 4466 51 2481 2055 297 1791 1627 1422 1608 1957 379 Cr 12B 20 92 304 112 101 27 157 45 34 198 48 204 Kb 23 40 20 7 22 28 28 31 35 39 33 . 25 "7 Ni 33 12 22 7 16 15 1 11 16 14 7 16 4 Bb(P -47(9.3]' 407(389]' 1781240]! 079(70.3]' 323(343]' 308(314]' 445(444]' 338(361]' 328(384]' 346(354)' 373(392]' 331(319]' 503| Sr(P 183[14B]' 691|643]' 062[76]J 305(256]' 87B|937]' 733(782]' 178(183]' 691(724]' 689(727)' 595(654)' 631(655]' 796(823]' 122[ ¥ 183 47 210 20 139 161 9 94 64 71 76 90 6 y 33 28 26 9 27 26 15 24 26 27 27 28 14 it 234 714 203 88 394 304 103 266 239 279 260 702 8B NORMATIVE (nt.»)< Orthoclase 49.88 6.15 45.81 36.47 32.9B 38.12 36.41 34.69 37.53 46.57 35.99 Albite 29.28 6.85 20.98 16.92 20.73 22.00 24.12 23.52 22.17 27.16 3.38 Anorthite 8.69 10.77 9.66 13.86 5.44 12.91 12.05 11.18 12.34 8.89 6.52 Quartz 4.33 54.00 4.55 10.52 37.78 16.03 20.67 22.61 20.06 3.97 49.52 Orthopyroxene 3.11 6.27 5.94 8.04 0.70 4.22 3.02 3.60 5.95 3.26 0.14 Oiopside 7.20 7.16 2.19 4.75 3.94 Corundui 0.24 9.45 0.92 0.07 0.42 0.10 Magnetite 3.38 7.39 4.06 4.77 1.23 3.07 2.73 2.81 2.68 3.97 0.33 IUenite 0.93 0.51 1.20 1.61 0.21 1.06 0.76 0.95 0.87 0.99 0.13 Apatite 0.36 0.07 0.88 0.99 0.09 0.59 0.38 0.43 0.47 0.71 0.05 Total 100.20 100.47 100.27 100.35 100.09 100.20 100.20 100.21 100.19 100.27 100.01 TABLE 3.1 (continued).  SAMPLE SAO& SMI SA18 SA24 SA33 SA38 SAJ9 SA4I SA42 S»4S SA4S SA50 SA90 Rock Grywcke Syenite Alt. To-Drb Syenite Syenite Granite Qtz Otz To-rich To-rich Syenite To-Orb Type Otzte Granite Dyke Syenite Syenite Granite Granite Granite tlODAl (vol.*) Orthoclase Plagioclse Altered Feldspar Quartz 45.0 Hornblende Biotite 40.0 Augite Orthopyroxene lourwaline 3.0 Buscovite Sericite Opaques 2.0 Sphene Epidote Apatite Calcite 63.3 36.2 57.6 13.8 52.0 (1.0 10.6 5.0 (1.0 7.B 5.B 4.4 5.0 0.5 35.0 3.0 (1.0 (1.0 (1.0 (1.0 (1.0 52.1 8.8 36.0 3.1 47.5 20.9 12.5 12.3 5.8 1.0 52.6 22.3 2.8 15.6 6.7 53.8 15.6 1B.0 6.0 5.3 1.3 60.1 18.3 3.3 3.5 59.1 30.9 7.0 3.0 (1.0 (1.0 (1.0 (1.0 tr (1.0 <1.0 (1.0 (1.0 (1.0 (1.0 (1.0 1 The «ajor eleients were analyzed at the Oepartient of Geological Sciences using a Philips PH 1410 XRF. The data were reduced using the TurboPascal prograi "XRF3" written by J.K. Russel and U. Thirugnanai, 1988. ! The trace eleient data were averaged fron two separate sets ol analyses lade bythe Oepartient of Oceanography on an automated Philips PH 1400. Nb, Rb, Sr, r and Zr Here in excellent agreement between the two runs, whereas Ba, Cr and Hi were only fair, and V was poor in reproducibility. 1 Analyses, performed separately by XRF in the Oepartient of Geological Sciences for Rb-Sr geochronoietry, are also reported in Table 4.2. ' CIPH noris and cation noris were calculated using 08CATN0RH prcgrai written by R.l. Arastrong. C o l l o f o r m t e x t u r e i s v i s i b l e . O r g a n i c s t r u c t u r e s , p o s s i b l y o o i d s , were found l o c a l l y . The b r e c c i a i s composed o f v e r y f i n e g r a i n e d a n g u l a r fragments of c a r b o n a t e ( w i t h t r a c e s of b i o t i t e ) up t o 4.0 mm i n d i a m e t e r (Appendix A ) . Ten p e r c e n t of t h e fragments c o n t a i n 5% a n h e d r a l q u a r t z and 1% m u s c o v i t e a v e r a g i n g 0.1 mm i n d i a m e t e r . L o c a l l y c o a r s e c a l c i t e ( g r a i n s a v e r a g i n g 2.0 mm i n d i a m e t e r ) i n f i l l s v o i d s . Fragments are c u t by c a l c i t e v e i n l e t s a v e r a g i n g 0.1 mm i n w i d t h . The l a m i n a t e d graywacke i s f i n e g r a i n e d , dark gray and has a p a l e orange weathered s u r f a c e . The graywacke i s l o c a l l y i n t e r b e d d e d w i t h b l a c k c h e r t and i s composed of 45% q u a r t z , 40% b i o t i t e , 3% t o u r m a l i n e and 2% opaques (Appendix A, T a b l e 3.1). The m a t r i x i s composed of a n h e d r a l q u a r t z a v e r a g i n g 0.05 mm i n d i a m e t e r , and a f i n e g r a i n e d m i x t u r e of c h l o r i t e , c l a y and b i o t i t e . I s o t o p i c r a t i o s and d a t e s from t h i s graywacke a r e d i s c u s s e d i n Chaper 4. Q u a r t z v e i n s c u t b o t h q u a r t z i t e and greywacke. Coarse g r a i n e d v e i n s c o n t a i n i n g a n h e d r a l q u a r t z (up t o 0.6 mm i n d i a m e t e r , 0.4 mm a v e r a g e ) , m u s c o v i t e (about 0.3 mm i n d i a m e t e r ) and b i o t i t e ( a v e r a g i n g 0.3 mm i n d i a m e t e r ) 14 t r a v e r s e the q u a r t z i t e . C a s s i t e r i t e , v i s i b l e i n o u t c r o p , o c c u r s i n q u a r t z v e i n s t h a t average 2.0 mm i n w i d t h . T o u r m a l i n e o c c u r s l o c a l l y w i t h b i o t i t e . Opaques a v e r a g i n g 0.05 mm i n d i a m e t e r o c c u r w i t h i n b i o t i t e and q u a r t z . V e i n s a r e d e s c r i b e d i n d e t a i l i n t h e m i n e r a l i z a t i o n and a l t e r a t i o n s e c t i o n ( s e c t i o n 3.4). U n i t l b , p a l e g r e y f r a c t u r e d c h e r t , o c c u r s i n subcrop. I t s c o m p o s i t i o n and c o l o u r i s s i m i l a r t o c l a s t s found i n the c h e r t p e b b l e c o n g l o m e r a t e . Grey c h e r t beds, i n t e r b e d d e d w i t h b l a c k c h e r t , average 5 cm i n t h i c k n e s s . I n t h i n s e c t i o n (Appendix A; F i g s . 3.1, 3.2), t h e c h e r t i s a l t e r e d t o a f i n e g r a i n e d m i x t u r e o f q u a r t z , b i o t i t e and c h l o r i t e . T h i s u n i t , about 5 m t h i c k , i s o v e r l a i n by t h e b l a c k c h e r t o f u n i t l c . U n i t l c , b l a c k carbonacepus and g r e y . c h e r t w i t h s h a l e , o c c u r s as beds 1 t o 4 m i n t h i c k n e s s ; the u n i t i s about 15 m t h i c k . I n t e r b e d s up t o 5 cm t h i c k o f l a m i n a t e d c h e r t y s h a l e and s h a l e a r e common. The b l a c k s h a l e i s almost opaque i n t h i n s e c t i o n (Appendix A; F i g s . 3.1, 3.2). Quartz v e i n s c u t t i n g t h i s u n i t (about 5% of i t ) range from minute t o 0.4 15 mm i n w i d t h . Quartz g r a i n s v a r y from 0.05 t o 0.1 mm i n d i a m e t e r . U n i t I d , p a l e , p r a n g e - w e a t h e r i n g , f i n e l y i n t e r l a m i n a t e d w h i t e s i l i c e o u s b a r i t e , i s 3 m t h i c k . U n i t l e , a r u s t y weathering,, f i s s i l e and f i n e l y bedded s i l t s t o n e , i s about 800 m t h i c k . I t i s t i g h t l y f o l d e d c l o s e t o t h e i n t r u s i v e c o n t a c t . 3.2.2 I n t r u s i v e Rocks U n i t 2a, c o a r s e g r a i n e d , e q u i g r a n u l a r ( P l a t e 3,1) and m e g a c r y s t i c ( P l a t e 3.2) s y e n i t e , forms th e o u t e r 5.7 km wide margin of t h e b a t h o l i t h ( F i g s . 3.1, 3.2). T y p i c a l l y the s y e n i t e i s composed of 70% K - f e l d s p a r , 20% hornblende and 10% b i o t i t e ; p l a g i o c l a s e and q u a r t z o c c u r i n amounts l e s s than 10%. In t h e m e g a c r y s t i c phase ( P l a t e 3.2) K - f e l d s p a r c r y s t a l s g e n e r a l l y average 3 cm i n l e n g t h and comprise 65% of t h e r o c k ; zoned megacrysts 7 cm i n d i a m e t e r have been found about 2.5 km from t h e o u t e r c o n t a c t o f t h e b a t h o l i t h . Hornblende l a t h s a r e up t o 8 mm l o n g and b i o t i t e books a r e 16 P l a t e 3 . 1 Coarse g r a i n e d e q u i g r a n u l a r s y e n i t e ( F i g s . 3 . 1 , 3.2: u n i t 2 a ) , L o s t Horses b a t h o l i t h , Yukon. T h i s sample, from near the s y e n i t e - s e d i m e n t a r y r o c k c o n t a c t c o n s i s t s of K - f e l d s p a r , h o r n b l e n d e , b i o t i t e and minor p l a g i o c l a s e . 17 P l a t e 3.2 Megacrystic s y e n i t e ( F i g s . 3.1, 3.2: u n i t 2a), Lost Horses b a t h o l i t h , Yukon. This sample from the centre of u n i t 2a i n Figure 3.1, has K-feldspar phenocrysts up to 8 cm long. O v e r a l l m i n e r a l o g i c a l composition i s s i m i l a r to that of the coarse grained s y e n i t e ( P l a t e 3.1). 18 up t o 8 mm i n d i a m e t e r . F e l d s p a r c r y s t a l s a t the c o n t a c t , up t o 2 cm i n l e n g t h , a r e randomly o r i e n t e d . About 0.5 km from the c o n t a c t K - f e l d s p a r megacrysts a r e t y p i c a l l y a l i g n e d , s t r i k i n g a p p r o x i m a t e l y 140° and d i p p i n g 70° s o u t h - -t h e y a r e not a l i g n e d p a r a l l e l t o t h e c o n t a c t ( F i g s . 3.1, 3.2). Rusty w e a t h e r i n g q u a r t z - c h l o r i t e x e n o l i t h s , up t o 10 cm i n d i a m e t e r , a r e common c l o s e t o the sediment c o n t a c t where they form about 1% o f the volume of t h e s y e n i t e . The s y e n i t e i n t h i n s e c t i o n (Appendix A) i s composed of 57% o r t h o c l a s e , 12% p l a g i o c l a s e , 15% h o r n b l e n d e , 8% b i o t i t e , 4% a u g i t e , 2% o r t h o p y r o x e n e , 2% q u a r t z and t r a c e amounts of e p i d o t e , a p a t i t e , sphene, opaques, c a l c i t e and r u t i l e ( T a b l e 3.1). ( O p t i c a l p r o p e r t i e s o f the o r t h o p y r o x e n e i n c l u d e : low b i r e f r i n g e n c e , h i g h p o s i t i v e 2V, and t h e p r e s ence of e x s o l u t i o n l a m e l l a e . ) O r t h o c l a s e o c c u r s as megacrysts (30 t o 95% of t o t a l o r t h o c l a s e , average 93%) up t o 4.5 cm i n d i a m e t e r , and as c o a r s e g r a i n s 3.5 mm i n d i a m e t e r w i t h i n the m a t r i x (5 t o 70% o f t o t a l o r t h o c l a s e , average 7%). A l l o f t h e above m i n e r a l s , w i t h t h e e x c e p t i o n o f c a l c i t e , a r e found as i n c l u s i o n s w i t h i n o r t h o c l a s e . M e g a c r y s t s e x h i b i t g r a n o p h y r i c t e x t u r e ( P l a t e 3.3). S e r i c i t e a l t e r a t i o n o c c u r s 19 P l a t e 3.3 K - f e l d s p a r megacryst from a s y e n i t e on A r s e n i c Ridge, L o s t Horses b a t h o l i t h , Yukon e x h i b i t i n g g r a n o p h y r i c t e x t u r e ( K - f e l d s p a r and q u a r t z ) . P l a n e p o l a r i z e d l i g h t . F i e l d of view c o v e r e d by photograph i s 2 mm. 20 on f r a c t u r e p l a n e s and c l e a v a g e t r a c e s . P l a g i o c l a s e c o m p o s i t i o n ( d e t e r m i n e d by the M i c h e l Levy method on a l b i t e o r combined a l b i t e - C a r l s b a d t w i n s ) i s a n d e s i n e (An2 4-An4 8; one sample was l a b r a d o r i t e , Ans4 ). P l a g i o c l a s e g r a i n s range up t o 7 mm i n d i a m e t e r but average 1.3 mm. P l a g i o c l a s e w i t h i n t h e o r t h o c l a s e megacrysts i s more sodium r i c h ( a l b i t e ) than the m a t r i x and i s o r i e n t e d p a r a l l e l t o t h e l o n g a x i s of t h e megacrysts ( P l a t e 3.4). A n d e s i n e c o n t a i n s opaques, h o r n b l e n d e , q u a r t z , a p a t i t e , c a l c i t e and b i o t i t e . S e r i c i t e a l t e r a t i o n , from 5-90%, f o l l o w s c l e a v a g e t r a c e s and f r a c t u r e p l a n e s . Green h o r n b l e n d e ( m a t r i x ) ranges up t o 4.0 mm and averages 1.25 mm i n l e n g t h . A u g i t e , b i o t i t e , sphene, a p a t i t e , opaques, e p i d o t e , p l a g i o c l a s e and o r t h o p y r o x e n e o c c u r w i t h i n h o r n b l e n d e . Hornblende and b i o t i t e a r e l o c a l l y c h l o r i t i z e d . Brown b i o t i t e i n the m a t r i x , up t o 4.0 mm and a v e r a g i n g 1.2 mm i n d i a m e t e r , h o s t s z i r c o n s , a p a t i t e , opaques, r u t i l e , p l a g i o c l a s e , a u g i t e , h o r n b l e n d e , e p i d o t e , sphene and o r t h o p y r o x e n e . A u g i t e , up t o 6.0 mm and a v e r a g i n g 1.0 mm i n d i a m e t e r , h o s t s b i o t i t e , opaques, a p a t i t e , o r t h o c l a s e , h o r n b l e n d e and e p i d o t e . Both a u g i t e and o r t h o p y r o x e n e a r e r e p l a c e d by h o r n b l e n d e , and a r e found 21 ate 3 .4 P l a g i o c l a s e o r i e n t e d p a r a l l e l to the long a x i s of a sye n i t e hosted K-f e l d s p a r megacryst, Arsenic Ridge, Lost Horses b a t h o l i t h , Yukon. Crossed p o l a r s . F i e l d of view covered by photograph i s 3.5 mm. 22 as remnant c o r e s w i t h i n h o r nblende ( P l a t e 3.5). Orthopyroxene g r a i n s , up t o 4.0 mm but a v e r a g i n g 1.2 mm i n d i a m e t e r , c o n t a i n a p a t i t e , b i o t i t e , h o r n b l e n d e and opaques. P l a t e 3.6 shows pyroxene e x s o l u t i o n . Q u a r t z i s a n h e d r a l , up t o 2.0 mm i n d i a m e t e r (averages 0.7 5 mm), and o c c u r s w i t h i n o r t h o c l a s e and h o r n b l e n d e . E p i d o t e ranges up t o 1.0 mm i n d i a m e t e r and averages 0.5 mm ( P l a t e 3.7). I t i s a s s o c i a t e d w i t h m a f i c m i n e r a l s and i s p r e s e n t w i t h i n h o r n b l e n d e , o r t h o c l a s e , b i o t i t e and a u g i t e . Because t h e e p i d o t e w i t h i n t h e s y e n i t e i s e u h e d r a l , not o f t e n a s s o c i a t e d w i t h m a f i c m i n e r a l s and u n a l t e r e d , i t may be magmatic i n o r i g i n . A p a t i t e and opaques a r e e u h e d r a l , average 0.05 mm i n d i a m e t e r , and o c c u r w i t h a l l o f t h e major m i n e r a l s . E u h e d r a l sphene averages 0.1 mm i n d i a m e t e r and i s found w i t h i n h o r n b l e n d e . C a l c i t e o c c u r s w i t h i n t h e m a t r i x where i t averages 0.7 5 mm i n d i a m e t e r ; i t a l s o o c c u r s i n v e i n l e t s . R u t i l e n e e d l e s , up t o 1.0 mm i n l e n g t h , were found w i t h i n h o r n b l e n d e , o r t h o c l a s e and b i o t i t e . I s o t o p i c r a t i o s and d a t e s from t h i s s y e n i t e a r e d i s c u s s e d i n Chapter 4. D r i l l c o r e i n t e r s e c t i o n s d e f i n e a v a r i a b l y a l t e r e d medium-grained b i o t i t e s y e n i t e dyke (Jago, 1984). T h i s 23 P l a t e 3.5 M a t r i x a u g i t e ( l i g h t gray) b e i n g r e p l a c e d by hornblende ( g r e e n ) , U n i t 2a, ( s y e n i t e ) , A r s e n i c R idge, L o s t Horses b a t h o l i t h , Yukon. Pl a n e p o l a r i z e d l i g h t . F i e l d of view c o v e r e d by photograph i s 3.5 mm. 24 t e 3.6 Pyroxene e x s o l u t i o n w i t h i n a s y e n i t e , A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. L i n e s w i t h i n the pyroxenes r e p r e s e n t a u g i t e l a m e l l a e w i t h i n o r t h o p y r o x e n e . Pyroxenes a r e w i t h i n a K - f e l d s p a r megacryst. C r o s s e d p o l a r s . F i e l d of view c o v e r e d by photograph i s 3.5 mm. 25 P l a t e 3.7 Magmatic e p i d o t e w i t h i n a s y e n i t e , A r s e n i c R idge, L o s t Horses b a t h o l i t h , Yukon. Note th e e u h e d r a l n a t u r e and t y p i c a l b i r e f r i n g e n c e c o l o u r s of the e p i d o t e . C r o s s e d p o l a r s . F i e l d of view c o v e r e d by photograph i s 2.1 mm. 26 unit, although not defined at the surface, may be part of unit 2a. Within the intrusions the dyke i s medium grained with b i o t i t e c r y s t a l s up to 1 cm i n diameter. However, within the metasediments t h i s unit i s very fine grained, but s t i l l b i o t i t e r i c h (up to 30%). The dyke i s t y p i c a l l y k a o l i n i t i z e d and hematitized. Splays in these dykes are common. Adjacent metasediments are altered to clay. Units 2b, 2c and 2d form a c e n t r a l l y zoned core of quartz syenite and granite that i s approximately 2.8 km i n diameter. Progressively towards the core, units comprise quartz syenite (unit 2b), granite (unit 2c), and "tourmaline orbicular" granite (unit 2d). Contacts between the quartz syenite and granite are gradational, whereas contacts between the "tourmaline orbicular" granite and the granite are sharp (Figs. 3.1 and 3.2). Unit 2b,coarse grained megacrystic quartz syenite, contains up to 15% smokey brown quartz (2 mm i n diameter), 60% K-feldspar (2 cm i n diameter), 10% plagioclase (2.5 mm in diameter), 10% hornblende (2 mm in diameter) and 5% b i o t i t e (1 mm i n diameter). Megacrysts i n an equigranular matrix comprise 45% of t h i s unit. 27 P e t r o g r a p h i c a l l y (Appendix A ) , the q u a r t z s y e n i t e c o n t a i n s 51% o r t h o c l a s e , 18% p l a g i o c l a s e , 12% q u a r t z , 13% h o r n b l e n d e , 6% b i o t i t e and t r a c e amounts of o r t h o p y r o x e n e , a u g i t e , sphene, opaques, a p a t i t e and e p i d o t e ( T a b l e 3.1, F i g . 3.3). O r t h o c l a s e o c c u r s as megacrysts (85%) up t o 3.5 cm i n d i a m e t e r ; w i t h i n t h e m a t r i x o r t h o c l a s e c r y s t a l s c o m p r i s e 15%. The o r t h o c l a s e megacrysts e x h i b i t g r a n o p h y r i c t e x t u r e and h o s t i n o r d e r o f abundance, t r a c e amounts of p l a g i o c l a s e , b i o t i t e , h o r n b l e n d e , a u g i t e , q u a r t z , o r t h o p y r o x e n e and opaques. Cleavage t r a c e s and f r a c t u r e p l a n e s a r e s e r i c i t i z e d . P l a g i o c l a s e i s a n d e s i n e (An3 5 -A n s o ) . M a t r i x p l a g i o c l a s e e x h i b i t s c o n c e n t r i c growth z o n i n g ( P l a t e 3.8), ranges up t o 4.5 mm i n d i a m e t e r (average 1.7 mm), and c o n t a i n s opaques, h o r n b l e n d e , b i o t i t e and a p a t i t e . P l a g i o c l a s e w i t h i n t h e o r t h o c l a s e megacrysts i s e n r i c h e d i n sodium ( a l b i t e c o m p o s i t i o n ) and i s a l i g n e d p a r a l l e l t o t h e l o n g d i r e c t i o n o f t h e m e g a c r y s t s . S e r i c i t e a l t e r a t i o n ( 5 -80%) i s c o n c e n t r a t e d a l o n g f r a c t u r e p l a n e s and c l e a v a g e t r a c e s . A n h e d r a l q u a r t z , r a n g i n g up t o 3.0 mm i n d i a m e t e r 28 P l a t e 3.8 M a t r i x p l a g i o c l a s e from a s y e n i t e on A r s e n i c Ridge Ridge, L o s t Horses b a t h o l i t h , Yukon e x h i b i t i n g growth z o n i n g . C r o s s e d p o l a r s . F i e l d of view c o v e r e d by photograph i s 3.5 mm. 29 (average 1.3 mm), c o n t a i n s b i o t i t e , p l a g i o c l a s e , h o r n blende and opaques. Hornblende, up t o 3.5 mm i n l e n g t h (average 1.2 mm), c o n t a i n s remnant a u g i t e and o r t h o p y r o x e n e , opaques, b i o t i t e , a p a t i t e , sphene and q u a r t z . About 10% of the h o r n b l e n d e and b i o t i t e i s a l t e r e d t o c h l o r i t e . B i o t i t e c o n t a i n s opaques, a p a t i t e , p l a g i o c l a s e , sphene, z i r c o n and q u a r t z , and ranges up t o 1.5 mm i n d i a m e t e r (average 0.8 mm). A u g i t e and o r t h o p y r o x e n e a r e p r e s e n t as a few remnant c o r e s w i t h r i m s r e p l a c e d by h o r n b l e n d e . A u g i t e averages 1.0 mm i n d i a m e t e r and c o n t a i n s opaques, a p a t i t e , b i o t i t e and h o r n b l e n d e . Orthopyroxene averages 0.5 mm i n d i a m e t e r and c o n t a i n s b i o t i t e , h o r n blende and opaques. Sphene averages 0.5 mm i n d i a m e t e r and i s i n c o n t a c t w i t h t h e m a f i c m i n e r a l s . Opaques, a p a t i t e and e p i d o t e average 0.05 mm i n d i a m e t e r . The h a b i t of t h e e p i d o t e i n t h i s u n i t i s t h e same as i n s y e n i t e ( u n i t 2a, above). Opaques o c c u r as i n c l u s i o n s w i t h i n a l l major m i n e r a l s . A p a t i t e and e p i d o t e o c c u r w i t h i n h o r n b l e n d e , p l a g i o c l a s e , o r t h o c l a s e and b i o t i t e . I s o t o p i c r a t i o s and d a t e s from t h i s q u a r t z s y e n i t e a r e d i s c u s s e d i n Chapter 4. 30 U n i t 2c, m e g a c r y s t i c g r a n i t e , i s marked by an i n c r e a s e i n q u a r t z t o about 25%. The c o n t a c t t h e r e f o r e i s somewhat a r b i t r a r i l y drawn on F i g u r e s 3.1 and 3.2. Towards the margin of t h e b a t h o l i t h t h e q u a r t z c o n t e n t g r a d u a l l y d e c r e a s e s over s e v e r a l hundred meters. Hornblende i s more abundant than b i o t i t e . O r i e n t e d K - f e l d s p a r m e g a c r y s t s , up t o 8 cm a c r o s s , a r e zoned, l o c a l l y have a l b i t i c r i m s , and commonly a r e a l i g n e d . M i n o r t o u r m a l i n e (up t o 8% of t h e u n i t ) i n the g r a n i t e i s most p r e v a l e n t a d j a c e n t t o the t o u r m a l i n e p a t c h g r a n i t e ( u n i t 2d, below) where i t o c c u r s e i t h e r i n t e r s t i t i a l l y o r as 3 mm wide v e i n l e t s . The g r a n i t e , as seen i n t h i n s e c t i o n (Appendix A ) , c o n t a i n s 50% o r t h o c l a s e , 20% q u a r t z , 14% p l a g i o c l a s e , 7% h o r n b l e n d e , 4% b i o t i t e , 5% t o u r m a l i n e a n d ' t r a c e s o f a u g i t e , sphene, a p a t i t e , opaques and c a l c i t e . 90% of t h e o r t h o c l a s e o c c u r s as megacrysts up t o 1.8 cm i n d i a m e t e r (2.0 mm a v e r a g e ) ; t h e m a t r i x o r t h o c l a s e averages 2.0 mm i n d i a m e t e r . I t e x h i b i t s g r a n o p h y r i c t e x t u r e and c o n t a i n s a l l of the m i n e r a l s above. F r a c t u r e p l a n e s and c l e a v a g e t r a c e s a r e s e r i c i t i z e d . Q u a r t z i s a n h e d r a l , ranges up t o 4.0 mm i n d i a m e t e r (1.0 mm average) and c o n t a i n s i n c l u s i o n s o f 31 b i o t i t e , h o r n b lende and a p a t i t e . P l a g i o c l a s e c o m p o s i t i o n i s a n d e s i n e (An36-4s). I t ranges up t o 4.0 mm i n d i a m e t e r (averages 2.0 mm), e x h i b i t s normal and r e v e r s e d z o n i n g , and c o n t a i n s b i o t i t e . P l a g i o c l a s e w i t h i n o r t h o c l a s e megacrysts i s sodium r i c h ( a l b i t i c ) and g e n e r a l l y a l i g n e d p a r a l l e l t o t h e l o n g a x i s of t h e megacryst. Cleavage t r a c e s and f r a c t u r e p l a n e s a r e s e r i c i t i z e d . Green h o r n b l e n d e ranges up t o 4.0 mm i n d i a m e t e r (average 1.5 mm) and c o n t a i n s q u a r t z , b i o t i t e and a l l o f t h e u s u a l t r a c e m i n e r a l s . Brown b i o t i t e , up t o 2.0 mm i n d i a m e t e r and a v e r a g i n g 1.0 mm, c o n t a i n s q u a r t z , z i r c o n , opaques and a p a t i t e . Hornblende and b i o t i t e a r e s l i g h t l y c h l o r i t i z e d . T o u r m a l i n e o c c u r s w i t h q u a r t z i n v e i n s and p a t c h e s up t o 3.0 mm wide. A few remnant c o r e s of a u g i t e a r e r e p l a c e d by h o r n b l e n d e . A u g i t e averages 1.0 mm i n d i a m e t e r and c o n t a i n s i n c l u s i o n s o f b i o t i t e , q u a r t z , h o r n b l e n d e and a p a t i t e . Sphene averages 0.3 mm i n d i a m e t e r and i s a s s o c i a t e d w i t h m a f i c m i n e r a l s . A p a t i t e and opaque g r a i n s a r e e u h e d r a l , average 0.0 5 mm i n d i a m e t e r , and o c c u r w i t h i n o r t h o c l a s e , b i o t i t e , h o r n b l e n d e and q u a r t z . C a l c i t e o c c u r s w i t h i n t h e m a t r i x . I s o t o p i c r a t i o s and d a t e s f o r t h i s g r a n i t e a r e d i s c u s s e d i n Chapter 4. 32 U n i t 2d, t o u r m a l i n e o r b i c u l a r g r a n i t e , i s medium g r a i n e d and c o n t a i n s 49% K - f e l d s p a r (1 cm i n d i a m e t e r ) , 15% p l a g i o c l a s e , 30% q u a r t z (3 mm i n d i a m e t e r ) , 2% t o u r m a l i n e , and 4% opaques and m u s c o v i t e . T ourmaline i s c o n c e n t r a t e d i n l a r g e o v a l zoned o r b i c u l e s up t o 25 cm a c r o s s ( P l a t e 3.9). These o r b i c u l e s c o n s i s t o f 25% t o u r m a l i n e , 30% s e r i c i t i z e d p l a g i o c l a s e , 40% q u a r t z , and t r a c e s of green " f l u o r i t e , p y r i t e and c h a l c o p y r i t e . The t o u r m a l i n e o r b i c u l e s c o n s i s t of s e v e r a l m i n e r a l i z e d zones ( P l a t e 3.9). From h o s t g r a n i t e i n w a r d s , t h e s e zones c o n s i s t o f : (1) a l e u c o c r a t i c h a l o o f b i o t i t e - f r e e g r a n i t e , 1 t o 2 cm wide, (2) a d a r k o u t e r zone 1 t o 5 cm wide t h a t c o n s i s t s m a i n l y of q u a r t z and t o u r m a l i n e , and (3) a l e u c o c r a t i c c o r e zone w i t h a r a d i u s of 1 t o 2 cm t h a t c o n s i s t s of q u a r t z , K - f e l d s p a r , a l b i t e and t o u r m a l i n e . The g r a n i t e h o s t i n g t h e o r b i c u l e s i s composed, as seen i n t h i n s e c t i o n (Appendix A ) , o f : 61% e q u i g r a n u l a r a l t e r e d f e l d s p a r , 36% q u a r t z , 5% t o u r m a l i n e and 2% m u s c o v i t e , w i t h t r a c e s o f b i o t i t e and opaques. F e l d s p a r , up t o 4.5 mm i n d i a m e t e r , but a v e r a g i n g 1.7 mm, i s s e r i c i t e - q u a r t z , 33 P l a t e 3.9 "Tourmaline p a t c h " g r a n i t e ( F i g s 3.1, 3.2: u n i t 2d), L o s t Horses b a t h o l i t h , Yukon. The t o u r m a l i n e o r b i c u l e s , up t o 25 cm i n d i a m e t e r , comprise 25% of the r o c k o v e r a l l and c o n t a i n 60% t o u r m a l i n e , 30% s e r i c i t i z e d p l a g i o c l a s e , 10% q u a r t z and t r a c e s of f l u o r i t e , p y r i t e and c h a l c o p y r i t e . 34 t o u r m a l i n e , c l a y and c h l o r i t e a l t e r e d (50-100%) e s p e c i a l l y a l o n g c l e a v a g e t r a c e s and f r a c t u r e s . Q uartz i s a n h e d r a l , ranges up t o 3.0 mm i n d i a m e t e r but averages 1.3 mm, and c o n t a i n s i n c l u s i o n s of a l t e r e d f e l d s p a r . T o u r m a l i n e i s e u h e d r a l , b l u e i n c o l o u r , up t o 2.0 mm i n l e n g t h (average 1.0 mm), and c o n t a i n s q u a r t z and a l t e r e d f e l d s p a r . E u h e d r a l m u s c o v i t e o c c u r s as r o s e t t e s up t o 1.5 mm i n d i a m e t e r w i t h i n q u a r t z and f e l d s p a r and i n t h e m a t r i x . B i o t i t e and opaques ar e v e r y f i n e g r a i n e d and a r e p r e s e n t i n the f e l d s p a r s . T e x t u r a l e v i d e n c e i n d i c a t e s t h a t some of the t o u r m a l i n e i n the o r b i c u l e s formed d i r e c t l y from B - r i c h f l u i d s and some by replacement of K - f e l d s p a r . The q u a r t z t o u r m a l i n e o r b i c u l e s p r o b a b l y formed from B-r i c h aqueous magmatic f l u i d s w hich were t r a p p e d near the upper zone of the p l u t o n (cf...... S i n c l a i r and R i c h a r d s o n , 1986). E x p e r i m e n t a l s t u d i e s show t h a t t h e a d d i t i o n of boron d e p r e s s e s t h e s o l u d u s of H 2 0 - s a t u r a t e d g r a n i t i c m e l t s so t h a t an aqueous magmatic phase can c o e x i s t w i t h such m e l t s a t t e m p e r a t u r e s s i g n i f i c a n t l y lower than f o r B - f r e e m e l t s ( C h o r l t o n and M a r t i n , 1978). S e p a r a t i o n of B - r i c h f l u i d s t h a t formed t h e q u a r t z - t o u r m a l i n e o r b i c u l e s may have 35 o c c u r r e d d u r i n g t h e l a s t s t a g e s i n t h e e v o l u t i o n of t h e L o s t Horses g r a n i t e magma. I s o t o p e r a t i o s and d a t e s f o r t h i s t o u r m a l i n e o r b i c u l e g r a n i t e a r e d i s c u s s e d i n Chapter 4. A s s o c i a t e d w i t h the t o u r m a l i n e o r b i c u l a r g r a n i t e i s a f i n e g r a i n e d , brown s p o t t e d g r a n i t e of s i m i l a r c o m p o s i t i o n t h a t i s composed of 55% f e l d s p a r , 40% q u a r t z and 4% t o u r m a l i n e . T h i s l a t t e r u n i t by i t s d i s t r i b u t i o n appears t o be a c h i l l e d c o n t a c t phase of the o r b i c u l a r g r a n i t e a d j a c e n t t o t h e g r a n i t e (Jago, 1984). 3.2.2.1 Magmatic E p i d o t e Magmatic e p i d o t e was t e n t a t i v e l y i d e n t i f i e d i n s y e n i t e ( u n i t 2a) and q u a r t z s y e n i t e ( u n i t 2b) on the b a s i s o f i t s e u h e d r a l h a b i t , and n o n - a s s o c i a t i o n w i t h m a f i c m i n e r a l s . The p r e s e n c e of magmatic e p i d o t e i n d i c a t e s t h a t the p l u t o n c r y s t a l l i z e d under l i t h o s t a t i c p r e s s u r e s o f a t l e a s t 6 k b a r , and most l i k e l y not l e s s t h a n 8 k b a r o r 25-30 km depth (Zen and Hammarstrom, 1984). C o n s t r a i n t s on t h e c r u s t a l h i s t o r y a r e as f o l l o w s : t h e c r u s t a l t h i c k n e s s a t t h a t time must have been 55-75 km, comparable t o t h e c e n t r a l Andes; the t e m p e r a t u r e of t h e h o s t c o u n t r y r o c k c o u l d not have been 36 more than about 800°C, y i e l d i n g an upper l i m i t t o t h e p a l e o t h e r m a l g r a d i e n t of about 20°C/km ( i t may be c l o s e r t o 12°C/km); t h u s , the m i n i m a l r a t e of r e g i o n a l u p l i f t i s on the o r d e r of 1 mm/yr ( c f . Zen, 1985). 3.2.3 Dyke Rocks U n i t 3a, a w h i t e t o p i n k , r e c e s s i v e w e a t h e r i n g / q u a r t z f e l d s p a r p o r p h y r y d i k e ( F i g s . 3.1, 3.2), i s 30 m i n w i d t h and c r o s s e s A r s e n i c Ridge ( F i g s . 3.1, 3.2) p a r a l l e l t o t h e s e d i m e n t a r y i n t r u s i v e c o n t a c t . P h e n o c r y s t s , 35% o f t h e dyke, a r e s u p p o r t e d by a f i n e g r a i n e d m a t r i x . The p h e n o c r y s t s a r e 7 5% a n h e d r a l q u a r t z up t o 8 mm i n d i a m e t e r , and 25% a l t e r e d f e l d s p a r up t o 4 mm i n d i a m e t e r . O v e r a l l , as d e t e r m i n e d i n t h i n s e c t i o n (Appendix A ) , t h e q u a r t z f e l d s p a r p o r p h y r y d i k e c o n t a i n s 41% q u a r t z , 27% a l t e r e d f e l d s p a r , 20% s e r i c i t e , 7% m u s c o v i t e , 5% a l t e r e d m a f i c s and a t r a c e o f sphene. F e l d s p a r p h e n o c r y s t s a r e a l t e r e d t o c l a y and s e r i c i t e on f r a c t u r e p l a n e s and c l e a v a g e t r a c e s . A l t e r e d remnant f r a g m e n t s , p r e v i o u s l y m a f i c , a r e a n g u l a r and average 0.5 mm i n d i a m e t e r . The m a t r i x i s composed of f i n e g r a i n e d a n h e d r a l q u a r t z and a l t e r e d f e l d s p a r . Very f i n e g r a i n e d s e r i c i t e - q u a r t z has c o m p l e t e l y a l t e r e d the 37 f e l d s p a r s . S e r i c i t e i s up t o 1.0 mm i n d i a m e t e r (average 0.3 mm) and i s a s s o c i a t e d w i t h minor c l a y a l o n g c l e a v a g e p l a n e s . R u t i l e o c c u r s as n e e d l e s w i t h i n a l l o r i g i n a l m i n e r a l s . T o u r m a l i n e a g g r e g a t e s up t o 3 mm i n d i a m e t e r , and p y r i t e cubes (1%) up t o 1.5 cm i n d i a m e t e r , o c c u r l o c a l l y . U n i t 3b, f i n e t o medium g r a i n e d g r a n i t e d i k e s ( F i g s . 3.1, 3.2), up t o 1 m i n w i d t h , o c c u r a l o n g A r s e n i c Ridge. The d i k e s c o n t a i n 55% f e l d s p a r (1 mm i n l e n g t h ) , 30% a n h e d r a l q u a r t z (1 mm i n d i a m e t e r ) , 3% b i o t i t e , 2% p y r r h o t i t e , and 5% t o u r m a l i n e as r o s e t t e s , n e e d l e s and s p l a y s up t o 2 cm a c r o s s . I n t h i n s e c t i o n (Appendix A ) , the g r a n i t e d i k e s c o n t a i n 52% o r t h o c l a s e , 38% q u a r t z , 8% p l a g i o c l a s e , 2% b i o t i t e and t r a c e s of a p a t i t e and sphene ( T a b l e 3.1, F i g . 3 . 3 ) . O r t h o c l a s e ranges up t o 4.0 mm i n d i a m e t e r (1.3 mm average) and c o n t a i n s i n c l u s i o n s of b i o t i t e , q u a r t z , a p a t i t e and r u t i l e . I t i s s e r c i t i z e d on c l e a v a g e t r a c e s and f r a c t u r e p l a n e s . Q u a r t z i s i r r e g u l a r l y , shaped, up t o 3.0 mm i n d i a m e t e r (average 0.8 mm) and c o n t a i n s b i o t i t e and r u t i l e n e e d l e s . P l a g i o c l a s e c o m p o s i t i o n i s a n d e s i n e (An24). I t i s up t o 3.5 mm i n d i a m e t e r (average 0.5 mm), and i s s e r c i t e a l t e r e d on 38 c l e a v a g e t r a c e s and f r a c t u r e p l a n e s ; i t h o s t s t r a c e amounts of b i o t i t e . P l a g i o c l a s e i s r e v e r s e l y zoned ( a l b i t e c o r e s and o l i g o c l a s e r i m s ) . B i o t i t e , up t o 2.5 mm i n d i a m e t e r (average 0.75 mm), i s c h l o r i t i z e d . A p a t i t e and sphene a r e e u h e d r a l , average 0.05 mm i n d i a m e t e r and o c c u r w i t h i n t h e o r t h o c l a s e . I s o t o p i c r a t i o s and ages a r e d i s c u s s e d i n Chapter 4. U n i t 3c, b i o t i t e lamprpphyre dyke ( F i g s . 3.1, 3.2), c o n t a i n s 5% b i o t i t e p h e n o c r y s t s up t o 1.5 cm i n d i a m e t e r i n a gray t o d a r k g r a y , f i n e g r a i n e d m a t r i x . In t h i n s e c t i o n (Appendix A ) , the lamprophyre dyke i s a l t e r e d and c o n t a i n s 5% b i o t i t e , 45% q u a r t z , 35% f i n e g r a i n e d a l t e r e d m i n e r a l m a t r i x and 15% opaques. B i o t i t e p h e n o c r y s t s a r e c h l o r i t e a l t e r e d . Q uartz i s f i n e g r a i n e d (average 0.05 mm i n d i a m e t e r ) and o c c u r s o n l y i n t h e m a t r i x . The f i n e g r a i n e d a l t e r e d m a t r i x c o n s i s t s m a i n l y o f c a l c i t e , s e r i c i t e , c h l o r i t e and b i o t i t e . D i s s e m i n a t e d opaques range up t o 0.1 mm i n d i a m e t e r (average 0.05 mm). T r a c e s of d i s s e m i n a t e d c h a l c o p y r i t e , v i s i b l e i n o u t c r o p , o c c u r w i t h i n t h i s dyke. 39 3.3 CHEMICAL PETROLOGY 3.3.1 I n t r o d u c t i o n Major and t r a c e element d a t a f o r 13 samples were de t e r m i n e d by X-ray f l u o r e s c e n c e i n f a c i l i t i e s a t The U n i v e r s i t y of B r i t i s h Columbia. The t e n major elements were a n a l y z e d a t t h e Department o f G e o l o g i c a l S c i e n c e s u s i n g a P h i l i p s PW 1410 w i t h a Mo tube f o r Mn and a Cr tube f o r Fe, T i , Ca, K, S i , A l , P, Mg and Na. The d a t a were reduced u s i n g the T u r b o P a s c a l program "XRF3*1 w r i t t e n by J.K. R u s s e l and U. Thirugnanam, 1988. CIPW norms and c a t i o n norms were c a l c u l a t e d u s i n g OBCATNORM program w r i t t e n by R.L. Armstrong. The t r a c e element d a t a were averaged from two s e p a r a t e s e t s of a n a l y s e s made by t h e Department of Oceanography on an automated P h i l i p s PW 1400. Nb, Rb, S r , Y and Zr were i n e x c e l l e n t agreement between t h e two r u n s , whereas Ba, Cr and N i were o n l y f a i r , and V was poor i n r e p r o d u c i b i l i t y . Sample l o c a t i o n s a r e shown on F i g u r e s 3.1 and 3.2. Major and minor element d a t a f o r t h e r o c k s a l o n g A r s e n i c Ridge a r e i n Ta b l e 3.1. 40 Normative and modal d a t a (from Appendix A and T a b l e 3.1) f o r 24 r o c k samples a r e p l o t t e d on a QZ-OR-AB t e r n a r y p l o t ( F i g . 3.3). The samples p l o t i n the f o l l o w i n g f i e l d s a f t e r S t r e i k e i s e n (1976): s y e n i t e (n = 1 1 ) , q u a r t z s y e n i t e (n = 4 ) , g r a n i t e (n = 8) and q u a r t z - r i c h g r a n i t o i d f i e l d (n = 1 ) . However, t h e q u a r t z - r i c h g r a n i t o i d sample i s v e r y a l t e r e d and t h e r e f o r e t h e r e s u l t i s u n r e l i a b l e . 3.3.2 Chemical V a r i a t i o n s W i t h i n Igneous Rocks of A r s e n i c Ridge M a j o r and minor elements f o r 11 s y e n i t e t h r o u g h g r a n i t e samples a l o n g w i t h modal and n o r m a t i v e abundances a r e p r e s e n t e d i n T a b l e 3.1. Weight p e r c e n t S i 0 2 v a r i e s from 60.1 ( s y e n i t e ) t o 78.0 ( t o u r m a l i n e o r b i c u l e g r a n i t e ) . Weight p e r c e n t major elements p l o t t e d v e r s u s S i 0 2 ( F i g . 3.4) d i s p l a y f a i r l y c o n t i n u o u s v a r i a t i o n s . As S i 0 2 i n c r e a s e s , a l l major o x i d e s ( A I 2 O 3, FeO, MgO, CaO, T i 0 2 , MnO and P 2 O 5 ) d e c r e a s e ; K2O remains a p p r o x i m a t e l y c o n s t a n t and Na2 0 d e c r e a s e s s l i g h t l y . The t o u r m a l i n e p a t c h g r a n i t e ( S i 0 2 = 78.1 wt%) c o n t a i n s e l e v a t e d T i 0 2 and FeO v a l u e s and low Na2 0 v a l u e s . T h i s r e f l e c t s t h e 5% i r o n - r i c h s c h o r l i t e t o u r m a l i n e 41 QZ F i g u r e 3.3: Q u a r t z - o r t h o c l a s e - a l b i t e t r i a n g u l a r p l o t of n o r m a t i v e and modal c o m p o s i t i o n (Appendix A; T a b l e 3.1) o f major u n i t s from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Normative v a l u e s a r e p l o t t e d as c l o s e d symbols; modal c o m p o s i t i o n s a r e p l o t t e d as open symbols. F i e l d o c c u r e n c e d i s t r i b u t i o n i s coded: • = g r a n i t e ; • = q u a r t z s y e n i t e ; 4 = s y e n i t e ; A = g r a n i t e dyke; * = a l t e r e d ( s i l i c i f i e d ? ) t o u r m a l i n e o r b i c u l a r g r a n i t e . F i e l d s and c l a s s i f i c a t i o n c r i t e r i a a r e from S t r e i k e i s e n (1975) where: QZ = q u a r t z ( 1 0 0 % ) ; OR = a l k a l i f e l d s p a r ( o r t h o c l a s e , A l b i t e Ano- 5 ) ; and, AB = p l a g i o c l a s e Ano5 - I o o . 42 0 . 4 0 . 2 o . a O S 0 . 4 0 2 0 in •a X O 4 . 0 2 . o 0 . 0 4 O 2 . 0 0 0 t e o l e . o 14. o 12 o -• • • * A - O — I* Mn 0 « • • • - • -Ti o, t -• • • • -A • K, 0 - • -• • A 0 Na t c • • • • A -1 0 > Ca 0 -• • \ i Mg 0 t • • • * -t Fe 0 • > • » o _ • A • A l , 0 * • • # • -• -_j L_ J, 1 I A a 1 1 O 10 0 . 0 8 O 7 . 0 S O J O l . O 3 . 0 1.0 so 0 0 4 0 2 0 0 0 6 0 . 0 6 2 0 S 4 . 0 S S . O 6 8 . 0 T O . O 7 2 . 0 7 4 . 0 7 S . O 7 8 . 0 Si 0 2 (wt. %) F i g u r e 3.4: M a j o r element o x i d e c o n t e n t p l o t t e d v e r s u s Si02 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols used a r e : • = s y e n i t e (n=4); • q u a r t z s y e n i t e (n=2);«= g r a n i t e s (n=3); t o u r m a l i n e o r b i c u l a r g r a n i t e ( n = l ) ; • = g r a n i t i c dyke ( n = l ) ; and, x = a l t e r e d t o u r m a l i n e o r b i c u l a r g r a n i t e ( n = l ) . 43 i n t h e r o c k . T r a c e s o f a p a t i t e and sphene may account f o r the h i g h P2O5 and T i 0 2 v a l u e s i n t h e s y e n i t e . Decreases i n FeO, MgO and T i 0 2 c o n t e n t c o r r e s p o n d w i t h d e c r e a s i n g abundances of f e r r o m a g n e s i a n s i l i c a t e s i n more d i f f e r e n t i a t e d r o c k s . Trace element c o n t e n t a g a i n s t S i 0 2 c o n t e n t i s p l o t t e d i n F i g u r e 3.5. T r a c e element v a r i a t i o n s w i t h i n c r e a s i n g S i 0 2 i s c h a r a c t e r i z e d b oth by extreme d e p l e t i o n s and by moderate e n r i c h m e n t s . Z r , V, S r , N i and Ba c o n c e n t r a t i o n s d e c r e a s e s t r o n g l y (>5 t i m e s ) from s y e n i t e t o g r a n i t e s . Y and Nb d e c r e a s e s l i g h t l y (2-3 t i m e s ) . Rb i n c r e a s e s almost t w o - f o l d from s y e n i t e t o g r a n i t e ; Cr v a r i a t i o n i s not s y s t e m a t i c . Ba shows a p o s i t i v e c o r r e l a t i o n w i t h S r , and t h e y b o t h d e c r e a s e w i t h t h e i n c r e a s e i n Rb. G e n e r a l l y h i g h e r Zr v a l u e s a r e o b s e r v e d i n t h e s y e n i t e s t h a n i n the S i 0 2 - r i c h phases, such as the t o u r m a l i n e o r b i c u l e g r a n i t e . T h i s may r e f l e c t a r e l a t i v e abundance o f a c c e s s o r y z i r c o n i n t h e e a r l y c r y s t a l l i z i n g f r a c t i o n o f t h e magma. A l k a l i n e . . v e r s u s s u b a l k a l i n e c h a r a c t e r i s t i c s of t h e major u n i t s were examined on t h e (Na2 0 + K 2 O ) v e r s u s S i 0 2 44 • • • Z r 9 0 0 3 0 0 • " • Sr 9 0 0 9 0 0 Rb E a. a. 3 9 0 2 9 0 o Ni « Nb 8a 2 0 0 0 I 8 0 0 • l O O O -S O O • C r 6 0 . 0 6 2 . 0 6 4 O 6 6 0 6 8 . 0 7 0 . 0 7 2 . 0 7 4 0 7 6 O 7 6 0 SI 0 2 (wt. %) F i g u r e 3.5: Trac e element o x i d e c o n t e n t p l o t t e d v e r s u s SiC-2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.4. 45 diagram i n F i g u r e 3.6. T h i s f i g u r e i n d i c a t e s t h a t t h e s y e n i t e s a re a l k a l i n e whereas t h e q u a r t z s y e n i t e s , g r a n i t e s , g r a n i t e dykes and t o u r m a l i n e p a t c h g r a n i t e s a r e sub-a l k a l i n e . T i n g u a i t e ( p h o n o l i t e ) , s y e n i t e , monzonite, and g r a n i t e c h e m i s t r y from t h e Tombstone M o u n t a i n s , Yukon (Olade and G o o d f e l l o w , 1978), i s p l o t t e d f o r comparison. The Tombstone Mountains a r e about 75 km w e s t - n o r t h w e s t o f A r s e n i c Ridge. T h i s d e c r e a s i n g t r e n d i n ( N a 2 0 + K 2 O ) : S i 0 2 r e f l e c t s magmatic e v o l u t i o n . C o n c o m i t t a n t l y , CaO (wt%) d e c r e a s e s w i t h d i f f e r e n t i a t i o n ( F i g . 3.6). The s w i t c h from a l k a l i n e t o s u b a l k a l i n e i s s i m i l a r i n the nearby Tombstone a r e a , where t h e t i n g u a i t e and s y e n i t e a r e a l k a l i n e , but t h e monzonite and g r a n i t e a r e s u b a l k a l i n e ( F i g . 3.6). S i l i c a and t i t a n i a v e r s u s . s i l i c a commonly a r e used t o m o n i t o r f r a c t i o n a t i o n i n igneous s u i t e s ( R i c h a r d s o n , 1988). F i g u r e 3.7 shows t h a t i n t h e g r a n i t e r o c k s on A r s e n i c R i d g e , s i l i c a has i n c r e a s e d and t i t a n i a has d e c r e a s e d w i t h p r o g r e s s i v e magmatic f r a c t i o n a t i o n as i n d i c a t e d by i n c r e a s i n g S i 0 2 . T i t a n i a d e c r e a s e s from 0.85% t o 0.07%. 46 3 S . O 3 8 . 0 6 0 . 0 6 2 0 6 4 O 6 6 . 0 6 8 . 0 7 0 . 0 7 2 . 0 7 4 O 7 6 . 0 7 8 O S O . O B Z . O Si 0-, (wt. %) F i g u r e 3.6: Na2 0 + K2O and CaO c o n t e n t p l o t t e d v e r s u s S i 0 2 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.4. Data f o r t h e a l k a l i n e v e r s u s s u b a l k a l i n e l i n e i s from I r v i n e and B a r a g a r (1971). V a l u e s f o r t h e Tombstone b a t h o l i t h (dashed l i n e s e n c l o s i n g f i e l d s o f s m a l l d o t s ) a r e from Olade and G o o d f e l l o w (1978). 0.9 V ft _1_ _1_ _ l _ 5 8 . 0 6 0 0 6 2 . 0 6 4 . 0 6 6 . 0 6 8 . 0 7 0 . 0 7 2 . 0 7 4 . 0 7 6 . 0 7 8 . 0 8 0 . 0 Si 0 2 (wt. %) F i g u r e 3.7: Ti02 c o n t e n t p l o t t e d v e r s u s Si02 c o n t e n t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.4. 48 Sphene and b i o t i t e a r e the most i m p o r t a n t m i n e r a l o g i c a l h o s t s of t i t a n i a . T i t a n i a , t h e r e f o r e appears t o have been s t e a d i l y d e p l e t e d d u r i n g t h e e v o l u t i o n : s y e n i t e t o q u a r t z s y e n i t e t o g r a n i t e . The g r a n i t e dyke and t o u r m a l i n e o r b i c u l e g r a n i t e r e p r e s e n t the most d i f f e r e n t i a t e d g r a n i t i c u n i t s because t h e y c o n t a i n the l o w e s t t i t a n i a v a l u e s . E x c l u d i n g t h e a n a l y s i s of a l t e r e d g r a n i t e , t h e r e i s a l a r g e gap i n t h e t i t a n i a sequence (from 0.38% t o 0.13%) between the s y e n i t e -g r a n i t e and t o u r m a l i n e o r b i c u l a r g r a n i t e and t o u r m a l i n e o r b i c u l a r g r a n i t e . T h i s i n d i c a t e s t h a t t h e t o u r m a l i n e o r b i c u l e g r a n i t e (and the g r a n i t e dyke) formed s e p a r a t e l y ; t h e y a r e younger on t h e b a s i s o f c r o s s - c u t t i n g r e l a t i o n s h i p s . Rb, Sr and Ba t e r n a r y diagram, F i g u r e 3.8, w i t h a n a l y s e s ( T a b l e 3.1) from A r s e n i c R i d g e , d i s p l a y s two groups. The f i r s t c o n t a i n s s y e n i t e , q u a r t z s y e n i t e and g r a n i t e . The second c o n t a i n s t h e g r a n i t e dyke and t h e t o u r m a l i n e o r b i c u l e g r a n i t e . G e n e r a l l y , Rb, Ba and S r c o n c e n t r a t i o n a r e c o n t r o l l e d by p r o c e s s e s o f c r y s t a l 49 Ba 8 0 6 0 4 0 2 0 F i g u r e 3.8: Barium - r u b i d i u m - s t r o n t i u m t r i a n g u l a r p l o t ( d a t a from T a b l e 3.1) f o r major u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.4. 50 f r a c t i o n a t i o n . Ba and S r de c r e a s e s c o n c o m i t t e n t l y w i t h Ca i n d i c a t i n g i n c o r p o r a t i o n i n t o r e l a t i v e l y e a r l y p l a g i o c l a s e . Rb i n c r e a s e s i n r e s i d u a l f l u i d s f o l l o w i n g p o t a s s i u m i n c o r p o r a t e d i n t o l a t e r o r t h o c l a s e . Thus t h e s e p a r a t i o n i n the d a t a s u g g e s t s a g r e a t e r degree o f f r a c t i o n a t i o n not o n l y i n t h e t o u r m a l i n e b r b i c u l e g r a n i t e o v e r the s y e n i t e but a l s o i n t h e t o u r m a l i n e o r b i c u l e g r a n i t e o v er t h e g r a n i t e . The t o u r m a l i n e o r b i c u l e g r a n i t e and dyke a r e p r o b a b l y younger phases w i t h a d i s t i n c t l y d i f f e r e n t e v o l u t i o n from t h a t o f the s y e n i t e , q u a r t z s y e n i t e o r g r a n i t e (see t i t a n i a above). Normative a l b i t e , q u a r t z and o r t h o c l a s e t e r n a r y diagram, F i g u r e 3.9, i s p l o t t e d u s i n g t h e a n a l y s e s f o r r o c k s a l o n g A r s e n i c R i dge l i s t e d i n Ta b l e 3.1. These p l o t s a r e used t o e s t i m a t e p a r t i a l p r e s s u r e o f water d u r i n g f o r m a t i o n o f low c a l c i u m , e x p e r i m e n t a l , g r a n i t e m e l t s ( T u t t l e and Bowen, 1958 and L u t h e t a l . 1964). Data p o i n t s f o r g r a n i t e i n d i c a t e t h a t the p l u t o n c r y s t a l l i z e d a t a water p r e s s u r e (PH2O) near t o but g r e a t e r t h a n 10 kb. The g r a n i t e dyke p l o t s c l o s e t o the PH20 = 0.5 kb minimum. The t o u r m a l i n e o r b i c u l e g r a n i t e p l o t s markedly 51 QZ F i g u r e 3.9: Q u a r t z - o r t h o c l a s e - a l b i t e t r i a n g u l a r p l o t ( d a t a from T a b l e 3.1) f o r g r a n i t e s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.4. Dashed l i n e s a r e w a t e r s a t u r a t e d minima a t i n d i c a t e d p r e s s u r e s ( T u t t l e and Bowen, 1958; L u t h e t a l ; 1964) . 52 below the 0.5 kb minima s u g g e s t i n g t h a t t h i s diagram i s not a p p r o p r i a t e f o r t o u r m a l i n e b e a r i n g g r a n i t e . F l u o r i n e , and perhaps boron, would a f f e c t the s o l i d u s s t r o n g l y . C l a s s i f i c a t i o n of g r a n i t i c r o c k s - - o n t h e b a s i s o f f i e l d , p e t r o g r a p h i c and a n a l y t i c a l c r i t e r i a — a s I - t y p e , S-t y p e and A-type p l u t o n s i s o u t l i n e d i n Anderson (1988) and C h a p p e l l and White, (1974). The L o s t Horses b a t h o l i t h appears t o be an S-type o r Hercynotype p l u t o n by s a t i f y i n g the f o l l o w i n g c r i t e r i a : (1) the b a t h o l i t h o c c u r s i n a p o s t -t e c t o n i c environment; (2) t i n 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 w i t h the b a t h o l i t h ; (3) t h e p l u t o n i s s i m p l y i n t r u d e d , a p p a r e n t l y d i a p i r i c a l l y emplaced and raetasomatically o v e r p r i n t e d ; (4) t h e b a t h o l i t h i s c o m p o s i t i o n a l l y r e s t r i c t e d t o p r e d o m i n a n t l y s y e n i t e , q u a r t z s y e n i t e and g r a n i t e ; (5) g r a d a t i o n a l c o n t a c t s o c c u r between th e major u n i t s : s y e n i t e , q u a r t z s y e n i t e and g r a n i t e ; whereas t h e g r a n i t e and t o u r m a l i n e o r b i c u l e g r a n i t e c o n t a c t i s s h a r p ; (6) l a t e dykes of g r a n i t e o r a p l i t e c o m p o s i t i o n o c c u r w i t h i n t h e p l u t o n ; (7) g r a n i t i c r o c k s have t e x t u r e s t h a t v a r y from m e g a c r y s t i c i n t h e r i m t o e q u i g r a n u l a r i n the c o r e ; (8) b i o t i t e i s c h a r a c t e r i s t i c a l l y p a l e y e l l o w t o r u s t y brown i n 53 p l e o c h r o i s m , and commonly c o n t a i n s z i r c o n s ; (9) a c c e s s o r y m i n e r a l s i n c l u d e i l m e n i t e , z i r c o n , a p a t i t e , t o u r m a l i n e and m u s c o v i t e ; (10) g r a n i t e phases have s i l i c a c o n t e n t s t h a t average >70 wt%; (11) the p l u t o n has r o c k s w i t h molar Al2 0 3 /(CaO + Na2 0 + K 2 0 ) > 1.1 t h a t i s t y p i c a l l y p e r a l u m i n o u s ; (12) t h e b a t h o l i t h has a K2O c o n t e n t t h a t i s g r e a t e r than Na2 0; (13) t h e p l u t o n has a r e l a t i v e l y low TiC>2 c o n t e n t ; and (14) a l l a n a l y s e s of g r a n i t i c u n i t s (whole r o c k o r m i n e r a l s e p a r a t e s ) e s t a b l i s h i n i t i a l 8 7 S r / 8 6 S r r a t i o s g r e a t e r than 0.708. 3.3.3 P e a r ce R a t i o s o f Whole Rock Samples The s y e n i t e , q u a r t z s y e n i t e and g r a n i t e u n i t s a l o n g A r s e n i c Ridge appear t o be g r a d a t i o n a l w i t h one a n o t h e r ( F i g . 3.2). Pearce element r a t i o diagrams f o r t r a c e elements i n t h e s e u n i t s were e x p l o r e d i n e x a m i n i n g t h e i r i n t e r r e l a t i o n s h i p . P e a r c e element r a t i o diagrams a r e X - Y p l o t s . R a t i o s a l o n g t h e axes a r e chosen such t h a t t h e s l o p e of l i n e s d e f i n e d can be used t o i d e n t i f y m i n e r a l s removed by f r a c t i o n a t i o n . The denominator of t h e r a t i o s must be a 54 c o n s e r v e d c o n s t i t u e n t — o n e t h a t does not t a k e p a r t i n p h y s i c a l - c h e m i c a l p r o c e s s b e i n g d e s c r i b e d ( R u s s e l l and N i c h o l l s , 1988). One t e s t of whether o r not an element or r a t i o i s c o n s e r v e d i s t o d e t e r m i n e , by F - t e s t s t a t i s t i c , i f the v a r i a n c e i n t h e t r a c e element d a t a f o r t h e d a t a ( S D 2 ) , g r a n i t i c r o c k s i n t h i s c a s e , i s s i g n i f i c a n t l y d i f f e r e n t from t h e v a r i a n c e e x p e c t e d from the a n a l y t i c a l u n c e r t a i n t y ( S A 2 ) . I f SD 2 i s s i g n i f i c a n t l y l e s s t h a n SA 2 then t h e e l e m e n t ( s ) examined a r e p r o b a b l y c o n s e r v e d , and t h i s means t h e y c o u l d be comagmatic. On t h e o t h e r hand, i f SD 2 i s s i g n i f i c a n t l y g r e a t e r than SA 2 then t h e elements p r o b a b l y a r e not c o n s e r v e d and may not be comagmatic. Trace element d a t a i n whole r o c k samples f o r s y e n i t e (n=3), q u a r t z s y e n i t e (n=2), and g r a n i t e (n=2) from A r s e n i c Ridge were examined f o r e x i s t e n c e o f c o n s e r v e d elements. Y t t r i u m (Y) was chosen f o r t h e denominator o f t h e r a t i o s because i t u s u a l l y i s not s e l e c t i v e l y i n c o r p o r a t e d i n t o m i n e r a l phases o b s e r v e d i n t h e s e r o c k s . T a b l e 3.2 p r e s e n t s t h i s d a t a . ( F - t e s t s t a t i s t i c was e v a l u a t e d a t = 0.05, o r 55 TABLE 3.2: E i a i i n a t i o n o f conserved e l e i e n t s u s i n g t r a c e e l e t e n t s r a t i o e d t o I f o r l a j o r g r a n i t i c r o c k s (dykes e x c l u d e d ) from A r s e n i c l i d g e , L o s t E:rses. b a t h o l i t h , !.!. TRACE SA11 SA33 SA38 SA41 SA42 SA45 SA48 SA50 Mean STO SM STD'/SA! Results' ELEMENT Syenite Syenite Syenite OU ill Granite Granite Syenite (pm) Syenite Syenite 6a/T 50.036 91.889 79.039 74.625 62.577 52.66? 59.556 69.893 67.535 15.101 5.109 8.738 Ha Cr/Y 0.714 4.148 3.835 6.542 1.731 1.259 7.333 1.714 3.416 2.667 0.344 60.053 Ha Nb/t 1.429 0.815 1.077 1.292 1.346 1.444 1.222 0.893 1.190 0.255 0.089 8.147 Ha Ni/Y 0.429 0.593 0.577 0.453 0.615 0.519 0.259 0.571 0.503 0.126 0.155 0.666 HO Rb/T 14.536 11.963 11.846 14.083 12.615 12.BIS 13.815 11.821 12.937 1.153 0.973 1.406 Ho Sr/T 24.679 32.519 28.192 28.792 26.500 22.037 23.370 28.429 26.B14 3.621 2.016 3.227 Ha v/y 1.679 5.14B 6.192 3.917 2.462 2.630 2.815 3.214 3.507 1.608 0.373 18.548 Ha I'll 25.500 14.593 11.692 11.083 9.192 10.333 9.630 25.071 14.637 7.244 1.139 40.465 Ha ' Ho : So1 < S»' coiagiatic; Ha : So2 > Si ! coaagiatic 1.8.) R a t i o s w i t h Ba, C r , Nb, S r , V and Zr have v a r i a n c e s i n the d a t a g r e a t e r than t h e v a r i a n c e due t o a n a l y t i c a l u n c e r t a i n t y and, t h e r e f o r e , may not be c o n s e r v e d . Rb and N i r a t i o s have F - t e s t s t a t i s t i c s l e s s than 1.8 and may be co n s e r v e d . However, Rb/Y r a t i o s , p l o t t e d i n F i g u r e 3.10, appear t o i n c r e a s e s y s t e m a t i c a l l y from b a t h o l i t h r i m ( s y e n i t e ) toward the c o r e ( g r a n i t e ) . T h i s s u g g e s t s a comagmatic r e l a t i o n s h i p w i t h v a r i a t i o n s due t o some p r o c e s s such as d i f f e r e n t i a t i o n . I t a l s o i n d i c a t e s t h a t Rb i s not c o n s t a n t and not c o n s e r v e d as i n d i c a t e d above. Ni/Y r a t i o s a r e c o n s i s t a n t ( w i t h i n a n a l y t i c a l u n c e r t a i n t y ) from r i m t o c o r e ( F i g . 3.11) s u g g e s t i n g t h a t b o t h N i and Y may be co n s e r v e d . However, N i c o n c e n t r a t i o n s a r e t o o s m a l l t o have c o n f i d e n c e i n them. As t h e r e i s no independent means o f e v a l u a t i n g whether t h e A r s e n i c Ridge r o c k s c o n t a i n a c o n s e r v e d c o n s t i t u e n t , f u r t h e r a n a l y s i s w i t h Pearce Element r a t i o s i s p r e c l u d e d . 57 15.0 r-14 .0 R b Y 13.0 I2 .0 II.O -IO.O -TO ORB GRAN -GRAN •QZ SYEN J L i S YEN C O R E DISTANCE FROM MARGIN R I M F i g u r e s 3.10: Rb/Y and K2 0 / S i 0 2 v e r s u s d i s t a n c e from margin ( d a t a from T a b l e 3.1 and 3.2) f o r major r o c k u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols used a r e : • = s y e n i t e (n=4); • = q u a r t z s y e n i t e ; and, •= g r a n i t e s . S o l i d l i n e j o i n s K 2 0 / S i 0 2 d a t a p o i n t s . D i s t a n c e from b a t h o l i t h r i m t o c o r e a l o n g A r s e n i c R i dge i s about 2.1 km. Mapped l i t h o l o g i c c o n t a c t s a r e p l o t t e d f o r r e f e r e n c e . 58 0 . 7 0 0 l i Y 0 . 6 0 0 0 . 5 0 0 -0 . 4 0 0 -0 . 3 0 0 -TO ORB GRAN -GRAN -QZ SYEN 0 . 2 0 0 I ' I SYEN CORE DISTANCE FROM MARGIN RIM F i g u r e 3.11: Ni/Y v e r s u s d i s t a n c e from b a t h o l i t h m a r g i n ( d a t a from T a b l e 3.1 and 3.2) f o r major r o c k u n i t s on A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Symbols a r e as i n F i g u r e 3.10. D i s t a n c e from b a t h o l i t h r i m t o c o r e a l o n g A r s e n i c R i dge i s about 2.1 km. Mapped l i t h o l o g i c c o n t a c t s a r e p l o t t e d f o r r e f e r e n c e . 59 3.3.4 Probe A n a l y s i s o f K - f e l d s p a r i n G r a n i t e ( U n i t 2C) K - f e l d s p a r megacrysts w i t h i n t h e g r a n i t e from A r s e n i c Ridge ( F i g s . 3.1, 3.2) range up t o 3.0 cm i n d i a m e t e r and a r e commonly zoned (a narrow p a l e p i n k r i m surrounds a gray c o r e ; P l a t e 3.10). Two c r y s t a l s from t h i s g r a n i t e were a n a l y z e d t o d e t e r m i n e major o x i d e v a r i a t i o n s from c r y s t a l c o r e t o r i m . A l l samples were ru n on a Cameca SX-50 e l e c t r o n m i c r o p r o b e a t t h e The U n i v e r s i t y of B r i t i s h Columbia. M i c r o p r o b e s e t u p and s t a n d a r d s , and t h e method used f o r c o r r e c t i n g s t r o n t i u m v a l u e s a r e i n Appendix B ( T a b l e B . l ) . F e l d s p a r c r y s t a l s e c t i o n s were p r e p a r e d u s i n g the method o u t l i n e d i n Appendix C. The major element e l e c t r o n m i c r o p r o b e a n a l y s i s o f the K - f e l d s p a r megacrysts from A r s e n i c Ridge a r e l i s t e d i n T a b l e B.2, Appendix B. Data from t h e f o u r t r a v e r s e s ( P l a t e s 3.11 and 3.12) have been a r r a n g e d i n t o c o r e and r i m c a t e g o r i e s w i t h averages and s t a n d a r d d e v i a t i o n s ( T a b l e 3.3). A n a l y s e s of q u a r t z and a l b i t e i n c l u s i o n s i n the K - f e l d s p a r s have been removed. 60 P l a t e 3.10 Zoned K - f e l d s p a r megacryst from a g r a n i t e a l o n g A r s e n i c Ridge, L o s t Horses b a t h o l i t h , Yukon. K - f e l d s p a r c o r e i s gray and the r i m i s p a l e p i n k . F i e l d of view c o v e r e d by the photograph i s 15 cm. 61 P l a t e 3.11: Microprobe traverses across K-f e l d s p a r megacryst (A) from g r a n i t e (Figs . 12a-d, sample SA48) Lost Horses b a t h o l i t h , Yukon. Lines i n d i c a t e traverses (Tables 3.3 and B.2) from core to rim. Megacryst A has two t r a v e r s e s : 1) from North to South, points 1-21; 2) from East to West, points 22-42. F i e l d of view covered by the photograph i s 4.5 mm. P l a t e 3.12: Microprobe traverses across K-f e l d s p a r megacryst (B) from g r a n i t e ( F i g s . 12a-d, sample SA48) Lost Horses b a t h o l i t h , Yukon. Lines i n d i c a t e traverses (Tables 3.3 and B.2) from rim to core. Megacryst B has two t r a v e r s e s : 1) Northeast to Southwest, points 43-71; 2) Northwest to Southeast, p o i n t s 72-91. F i e l d of view covered by photographs i s 4.5 mm. 62 T A B L E 3 . 3 M a j o r o x i d e e l e m e n t a n a l y s e s f o r f o u r m i c r o p r o b e t r a v e r s e s a c r o s s a n o r t h o c l a s e m e g a c r y s t f r o m a g r a n i t e o n A r s e n i c R i d g e , L o s t H o r s e s b a t h o l i t h , Y u k o n . Q u a r t z , a l b i t e a n d b i o t i t e a n a l y s e s h a v e b e e n d e l e t e d . P o i n t S i 0 2 A l ?0z C, aO S r O B a .0 N a ? 0 K2O T o t a l CORE T r a v e r s e 1 1 6 9 . . 1 2 2 0 . 2 0 0 . 0 9 0 . . 12 0 . 5 9 1 . . 4 1 8 . 7 2 1 0 0 . 6 0 2 6 5 . 9 0 19 . 3 1 0 . 1 4 0 . . 2 0 0 . 7 6 1 . 5 2 1 3 . 8 0 1 0 1 . 9 7 3 6 6 . 7 6 19 . 8 5 0 . 51 0 . . 1 5 0 . 7 4 2 . . 6 6 1 0 . 6 2 1 0 1 . 6 4 4 6 7 . . 1 4 1 9 . 6 5 0 . 4 2 0 . . 18 0 . 7 4 2 . 7 6 1 0 . 9 6 1 0 2 . 1 8 5 6 6 . . 5 8 1 9 . 7 0 0 . 3 7 0 . . 16 0 . 5 9 2 . . 8 7 11 . 0 3 1 0 1 . 6 3 6 6 5 . 6 1 1 9 . 3 9 0 . 6 5 0 . . 16 0 . 5 3 2 . 8 5 11 . 8 0 1 0 1 . 3 2 7 6 7 . 4 5 1 9 . 5 4 0 . 1 6 0 . . 1 9 0 . 7 9 2 . 4 1 11 . 5 8 1 0 2 . 4 7 8 6 7 . 3 8 19 . 5 9 0 . 4 4 0 . . 1 5 0 . 4 5 3 . 2 1 9 . 9 0 1 0 1 . 4 6 9 6 7 . . 6 2 1 9 . 3 6 0 . 1 6 0 . . 1 2 0 . 3 6 3 . . 7 4 1 0 . 8 9 1 0 2 . 6 0 1 0 6 6 . . 7 9 1 9 . 7 3 0 . 31 0 . . 14 0 . 4 3 1 . 9 1 1 2 . 1 8 1 0 1 . 8 3 11 6 7 . . 3 1 1 9 . 4 9 0 . 1 5 0 . . 1 7 0 . 5 9 2 . . 2 9 11 . 6 9 1 0 2 . 0 4 12 6 6 . . 5 0 1 9 . 3 3 0 . 17 0 . . 1 5 0 . 6 0 1 . 7 3 1 3 . . 1 7 1 0 1 . 9 8 T r a v e r s e 2 2 2 6 6 . . 5 0 1 9 . 6 3 0 . 2 8 0 . . 2 0 0 . 8 1 2 . . 6 9 11 . 5 2 1 0 1 . 9 6 2 3 6 6 . . 5 7 1 9 . 1 6 0 . 17 0 . . 1 8 0 . 7 3 ~> . 1 4 1 3 . 0 2 1 0 2 . 3 6 2 4 6 6 . . 1 7 1 9 . 4 4 0 . 4 3 0 . . 1 6 0 . 7 7 2 . . 0 7 1 2 . 7 5 1 0 2 . 1 2 2 5 6 6 . . 8 4 19 . 7 2 0 . 4 0 0 . . 1 5 0 . 8 7 2 . . 9 8 11 . . 2 5 1 0 2 . 5 6 2 6 6 7 . . 4 2 1 9 . 4 5 0 . 2 0 0 . . 1 8 0 . 7 9 2 . . 5 3 11 . 8 8 1 0 2 . 8 1 2 7 6 6 . . 2 5 2 0 . 0 4 0 . 9 1 0 . . 15 0 . 7 3 2 . . 6 3 1 0 . 6 4 l O l . 6 9 2 8 6 7 . . 1 4 1 9 . 1 9 0 . 0 7 0 . . 1 3 0 . 6 4 2 . . 5 6 1 2 . 7 2 1 0 2 . 7 8 3 0 6 7 . . 3 9 19 . 3 7 0 . 1 9 0 . . 1 3 0 . 5 1 2 . . 2 4 11 . . 8 8 1 0 2 . 0 6 3 1 6 7 . . 1 1 1 9 . 3 2 0 . 1 3 0 . . 1 3 0 . 5 2 2 . . 3 0 1 2 . 2 4 1 0 2 . 0 9 3 2 6 6 . . 1 8 1 9 . 4 5 0 . 3 7 0 . . 2 0 0 . 7 8 2 . . 2 3 1 1 . . 1 3 1 0 0 . 6 6 3 3 6 6 . . 2 5 1 9 . 7 8 0 . 5 3 0 . . 1 6 0 . 7 8 2 . . 3 5 1 0 . 6 6 1 0 0 . 8 3 3 4 6 7 . . 2 7 1 8 . 8 8 0 . 0 1 0 . OS 0 . 6 5 1 . 4 6 1 3 . 6 9 1 0 2 . 3 5 3 5 6 6 . . 9 7 1 9 . 5 8 0 . 4 3 0 . . 1 5 0 . 6 7 2 . . 8 7 11 . 0 6 1 0 2 . 0 7 3 6 6 7 . . 1 2 1 9 . 4 8 0 . 4 8 0 . 1 5 0 . 4 0 2 . 5 5 11 . 1 3 1 0 1 . 6 5 3 7 6 6 . . 2 8 1 9 . 0 2 0 . 11 0 . . 14 0 . 5 0 1 . 8 9 1 3 . 5 0 1 0 1 . 7 9 . T r a v e r s e 3 5 2 6 4 . . 4 9 1 8 . 8 3 0 . 0 7 0 . . 1 8 0 . 6 5 0 . . 9 5 14 . 9 0 1 0 0 . 4 0 5 3 6 6 . . 6 9 1 8 . 9 8 0 . 0 6 0 . . 10 0 . 5 4 1 , . 8 3 1 3 . 8 6 1 0 2 . 4 1 5 5 6 6 . . 0 6 1 9 . 0 3 0 . 1 0 0 . 1 2 0 . 7 0 1 . 3 7 1 3 . 9 7 1 0 1 . 6 9 5 6 6 6 . . 0 2 1 9 . 0 7 0 . 0 9 0 . . 1 3 0 . 6 9 1. . 7 0 1 3 . 8 9 1 0 1 . 8 9 5 7 6 5 . . 9 9 1 9 . 0 8 0 . 1 1 0 . . 1 5 0 . 8 4 1 . 5 2 1 3 . 5 4 1 0 1 . 5 7 5 8 6 6 . . 5 8 1 9 . 6 0 0 . 1 4 0 . 17 0 . 9 7 2 . . 3 0 11 . 6 6 1 0 1 . 7 5 5 9 6 6 . . 0 5 1 9 . 0 5 0 . 3 3 0 . 1 8 0 . 8 5 2 . . 9 4 11 . 5 9 1 0 1 . 7 4 6 0 6 6 . . 6 9 1 9 . 7 7 0 . 5 0 0 . . 1 4 0 . 8 4 2 . . 3 2 1 0 . 7 5 1 0 1 . 3 3 6 1 6 6 . . 8 2 1 9 . 6 1 0 . 3 7 0 . 1 9 0 . 8 4 2 . . 5 8 11 . 3 2 1 0 2 . 0 1 6 2 6 6 . . 5 1 1 9 . 6 2 0 . 6 0 0 . . 1 7 0 . 7 5 2 . . 6 3 1 0 . 8 2 1 0 1 . 4 3 6 3 6 6 . . 9 4 1 9 . 5 1 0 . 5 2 0 . 16 0 . 6 2 2 . . 6 4 1 1 . 6 1 1 0 2 . 3 4 6 4 6 6 . . 9 6 1 9 . 4 4 0 . 1 7 0 . . 1 7 0 . 5 6 1. . 7 9 1 2 . 7 4 1 0 2 . 1 8 6 5 6 6 . . 4 7 1 9 . 2 6 0 . 1 1 0 . 1 3 0 . 4 9 1 . 6 2 1 3 . 3 0 1 0 1 . 7 3 6 6 6 6 . . 6 3 1 8 . 9 1 0 . 0 8 0 . . 1 3 0 . 5 1 1 , . 8 4 14 . 0 8 1 0 2 . 5 0 6 7 6 6 . . 9 6 1 9 . 7 4 0 . 5 8 0 . . 1 9 0 . 7 0 2 . . 7 3 1 0 . 4 2 1 0 1 . 6 6 6 8 6 6 . . 7 1 1 9 . 6 2 0 . 3 6 0 . . 2 3 0 . 8 0 2 . . 3 7 1 0 . 9 3 1 0 1 . 3 6 6 9 6 6 . . 4 1 1 9 . 7 2 0 . 7 0 0 . 1 9 0 . 6 8 2 . . 5 8 1 0 . 4 9 1 0 1 . 1 1 7 0 6 5 . . 5 4 19 . 4 6 0 . 3 6 0 . . 2 4 0 . 8 4 1 . 8 8 1 2 . 4 5 1 0 1 . 1 1 7 1 6 6 . . 5 9 19 . 8 1 0 . 4 6 0 . 1 8 0 . 7 9 3 . . 0 8 1 0 . 7 5 1 0 2 . 0 0 1 ABLE 3 . 3 ( c o n t i n u e d ) P o i n t S1O2 AI2O3 C a O S r O EsaO N a ? 0 K z O T o t a l C O R E T r a v e r s e 4 7 9 6 6 . . 6 2 1 9 . . 6 2 0 . . 3 7 0 . . 17 0 . . 7 4 2 . . 5 0 1 1 . . 0 4 1 0 1 . 4 0 8 0 6 7 . 4 2 1 9 . 6 3 0 . 3 5 0 . 1 8 0 . 7 8 2 , . 0 4 1 2 . 0 3 1 0 2 . 7 7 8 1 6 6 , . 8 6 1 9 . . 8 0 0 . 4 2 0 . . 1 6 0 . . 7 6 2 . 3 4 1 1 . . 4 5 1 0 2 . 1 3 8 2 6 6 . 6 5 1 9 • 7 8 0 . 4 1 0 . 1 8 0 . 8 0 2 . . 2 3 . 11 . 3 4 1 0 1 . 7 1 8 3 6 6 . 5 1 1 9 . . 7 9 0 . 7 0 0 . 1 7 0 . . 8 3 2 . . 8 2 1 0 . . 1 3 1 0 1 . . 2 9 8 4 6 7 . 2 3 1 9 . 7 5 0 . 4 2 0 . 1 7 0 . 8 3 2 . 3 7 1 1 . 9 0 1 0 3 . 0 0 8 5 6 7 . 1 8 1 9 . . 5 2 0 . 2 5 0 . . 2 2 0 . 9 4 2 . . 4 9 1 2 . . 0 5 1 0 2 . . 9 9 8 6 6 7 . 4 2 2 0 . . 3 2 0 . 9 8 0 . 1 3 0 . . 5 4 3 . . 0 1 8 . 0 9 1 0 0 . 8 3 8 7 6 7 . . 3 5 1 9 . . 6 0 0 . . 2 2 0 . . 2 4 0 . . 8 9 2 . . 6 3 1 1 . . 4 5 1 0 2 . 7 3 8 8 6 7 . . 14 1 9 . . 9 0 0 . 3 4 0 . . 2 2 0 . . 9 9 2 . . 3 2 1 0 . 5 7 1 0 1 . 8 1 8 9 6 7 . . 1 9 1 9 . . 7 5 0 . . 5 3 0 . . 2 1 0 . . 8 3 2 . . 7 2 1 0 . . 7 3 1 0 2 . . 3 0 9 0 6 4 . . 9 2 2 0 . . 1 8 1. . 2 6 0 . . 1 8 0 . . 6 9 3 . . 2 6 1 0 . . 0 0 1 0 0 . 8 2 9 1 6 4 . . 0 3 1 9 . . 2 0 0 . . 2 2 0 . . 2 0 1 . . 3 0 1 . 4 8 1 4 . . 2 0 1 0 0 . 9 6 C O R E A V E R A G E 6 6 . . 6 7 1 9 . . 5 2 0 . . 3 5 0 . . 1 7 0 . . 71 2 . . 3 3 11 . . 7 5 1 0 1 . . 8 4 C O R E S T D O E V 0 . . 7 7 0 . . 3 2 0 . . 2 4 0 . . 0 3 0 . . 1 6 0 . . 5 4 1 . 3 6 0 61 N 5 9 5 9 5 9 5 9 5 9 5 9 5 9 5 9 R I M T r a v e r s e 1 1 3 6 6 . . 9 5 1 8 . 9 7 0 . . 0 2 0 . . 0 6 0 . . 4 9 1 . 4 9 1 3 . 7 8 1 0 2 . 0 9 14 6 7 . . 0 5 1 8 . . 9 2 0 . . 0 8 0 . . 0 8 0 . . 4 4 2 . . 3 7 1 2 . . 6 4 1 0 1 . 9 2 16 6 8 . . 3 9 1 9 . . 4 3 0 . . 1 9 0 . , 1 0 0 . . 3 2 3 . 7 2 9 . . 9 3 1 0 2 . . 4 3 17 6 5 . . 6 8 1 9 . . 2 9 0 . . 1 1 0 . . 11 0 . . 4 5 1 . 9 7 1 3 . . 1 5 1 0 1 . 0 9 1 8 6 6 . . 9 9 1 9 . . 2 5 0 . . 0 8 0 . 0 8 0 . . 3 5 1 . 4 8 1 3 . . 0 4 1 0 1 . . 6 1 19 6 7 . . 8 6 1 9 . . 3 4 0 . . 1 3 0 . . 0 6 0 . . 2 2 2 . . 2 4 11 . 8 8 1 0 2 . 0 8 2 1 6 7 . . 4 2 1 9 . . 0 1 0 . . 0 4 0 . . 0 3 0 . . 0 4 1 . 7 5 1 3 . . 1 7 1 0 1 . . 7 8 T r a v e r s e 2 3 8 6 7 . . 3 4 1 8 . . 8 9 0 . . 0 9 0 . . 0 9 0 . . 2 4 1 . 8 2 1 3 . . 8 0 1 0 2 . 6 0 3 9 6 7 . . 5 0 1 9 . . 0 1 0 . . 0 7 0 . . 0 9 0 . . 2 4 1 . 8 8 1 3 . 1 5 1 0 2 . 2 8 4 1 6 7 . . 5 3 1 9 . . 0 9 0 . . 1 2 0 . . 1 1 0 . . 4 9 1 . 3 4 1 3 . . 8 5 1 0 2 . . 8 8 4 2 6 6 . . 7 7 1 8 . . 9 8 0 . . 0 6 0 . . 0 5 0 . 1 9 1 . 7 4 1 3 . 8 9 1 0 2 . 0 2 T r a v e r s e 3 4 6 6 6 . . 8 5 1 9 . 0 3 0 . . 1 1 0 . . 0 7 0 . . 4 0 1 . 8 3 1 3 . . 6 1 1 0 2 . . 2 4 4 7 6 6 . . 1 6 1 8 . . 9 6 0 . . 11 0 . . 1 1 0 . . 3 0 1 . 6 7 14 . . 4 3 1 0 2 . 0 7 4 8 6 6 . . 3 0 1 8 . . 9 1 0 . . 0 8 0 . . 1 1 0 . . 3 6 1 . 3 6 1 4 . . 8 6 1 0 2 . . 3 2 5 0 6 6 . . 4 3 1 8 . . 7 8 0 . . 0 7 0 . . 0 9 0 . . 3 6 1 . 1 9 14 . . 9 1 1 0 2 . 1 7 T r a v e r s e 4 7 5 6 5 . . 4 1 1 8 . . 9 4 0 . . 0 6 0 . . 0 8 0 . . 4 9 1 . 8 5 1 4 . . 3 2 1 0 1 . . 4 8 7 7 6 6 . 9 3 1 9 . . 1 0 0 . . 0 4 0 . 0 8 0 . 1 8 1 . 0 8 1 5 . . 1 1 1 0 2 . 8 6 7 8 6 5 . . 9 1 1 9 . . 6 8 0 . . 4 2 0 . . 2 0 0 . . 7 0 2 . . 5 9 1 1 . . 4 5 1 0 1 . . 2 9 R I M A V E R A G E 6t>. 8 6 1 9 . 0 9 0 . 1 0 0 . 0 9 0 . 3 5 1 . 8 5 1 3 . 3 9 1 0 2 . 0 7 R I M S T D D E V 0 . 7 5 0 . 2 2 0 . 0 9 0 . 0 3 0 . 1 5 0 . 5 9 1 . 2 7 0 . 4 8 N 1 8 1 8 1 8 1 8 1 8 1 8 1 8 I B Major o x i d e p r o f i l e s a r e shown i n F i g u r e s 3.12a-d. C o n c e n t r a t i o n s o f SiC-2 and AI2O3 remain c o n s t a n t from c o r e t o r i m . Na2 0 and K2O a r e r e l a t i v e l y c o n s t a n t from c o r e t o r i m . However, c o n c u r r e n t d e c r e a s e s i n p o t a s s i u m and barium w i t h i n c r e a s e s i n sodium i n d i c a t e t h e p r e s e n c e of a l b i t e l a m e l l a e . A l b i t e l a m e l l a e were o b s e r v e d i n o r t h o c l a s e megacrysts i n t h i n s e c t i o n (Appendix A ) . On average, a l b i t e i s more abundant i n t h e r i m than i n t h e c o r e . The a r i t h m e t i c a v e r a g e s , +1 s t a n d a r d d e v i a t i o n , f o r c o r e and r i m were c a l c u l a t e d a f t e r s u b d i v i s i o n i n t o t h e s e c a t e g o r i e s based on v i s u a l e x a m i n a t i o n o f P l a t e s 3.11 and 3.12. CaO ( c o r e 0.35+0.24, r i m 0.10+0.09 w t . % ) , SrO ( c o r e 0.17+0.03, r i m 0.09+0.03 w t . % ) , and BaO ( c o r e 0.71+0.16, r i m 0.35+0.15 wt.%) d e c r e a s e from c r y s t a l c o r e t o r i m . K u r y v i a l (1976) and K e r r i c k (1969) have r e p o r t e d z o n a t i o n of Ba i n a l k a l i f e l d s p a r s o f p o r p h y r i t i c q u a r t z monzonites. They c o n c l u d e d t h a t a l k a l i f e l d s p a r s w i t h h i g h c o n c e n t r a t i o n s o f Ba i n the c e n t e r s and low Ba c o n c e n t r a t i o n i n t h e r i m s r e p r e s e n t c r y s t a l l i z a t i o n from a m e l t u n d e r g o i n g p r o g r e s s i v e d e p l e t i o n of barium. In t h e same way c a l c i u m and g e o c h e m i c a l l y 65 F i g u r e 3.12a-d: S e l e c t e d major and t r a c e element c o n t e n t s p l o t t e d v e r s u s Si02 c o n t e n t s ( d a t a from Table 3.2) from f o u r m i c roprobe t r a v e r s e s a c r o s s K - f e l d s p a r megacrysts from g r a n i t e , A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. Dashed l i n e s r e p r e s e n t the c o r e t o r i m c o n t a c t as d e t e r m i n e d from measurement on P l a t e s 3.4 and 3.5. D o t t e d and dashed l i n e s i n d i c a t e a l b i t e a n a l y s e s . Core and r i m averages a r e p l o t t e d f o r r e f e r e n c e . 66 0600 0.200 K , 0 E cr C • < No, O ] ' ' : - Ba 0 . • ' . • • • • { . . . • • • Sr 0 . . Co 0 $ . ; o u Rim 0 t • a . • • A I . O , • • . • SI 0 , 2 0 0 0 4 0 0 0 6 0 0 0 - . U - . 1—. J L . . — l . • 0 0 0 • • 10000 1 2 3 4 3 6 7 6 9 (O II 12 13 14 13 16 17 18 19 2 0 21 Data Points on a Line Traverse 67 K t O • < 3 I Core Rim • Q I • • • N o . O I . • B a O • • -J . ' • • • • Sr O {• " C a O c < 1 5 . S . * . c « E ac 0 1 ? ' -• t A I 2 O s SI O , • • 1000 4000 WOO i \ • 000 3 i 1 1 1 1 1—i . — ; — i — ll 25 24 2 5 26 27 2 1 29 3 0 51 3 2 13 34 39 36 57 36 39 4 0 41 42 D a t a Points on a L i n e T r a v e r s e 68 16 O 14.0 U 0 10.0 oaoo 0.400 O 400 66 O K , O • • • f - : • • • ' • . - " ' I ' ' - . . . • • y N a . O • r B a 0 r a D a 3 ( o • E D t • • S r O • I" • C o 0 a < 0 o J < Co,, 1 • * e D t \ : r • • • • • • " Si O, I O N *000 1 1— . — U i ,1 •000 . •• 1 • 1 1000 too 0 t i o o o . — J . L 5.0 O.IOO 20.0 i » . o n 1 ' I i  li I I . i I I 71 70 69 61 67 66 6 5 64 6 3 62 II 6 0 » 51 57 56 55 54 5 ] 5 2 51 50 49 46 47 46 4 5 44 Data Points on a Line Traverse 69 No, O K . O Ba O S r O . Ca O * A l , O, 1. 1 0 0 0 0 , SI O, 01 0 O 6 0 6 8 6 7 8 6 6 6 8 4 6 3 8 2 81 8O 79 7 8 7 6 7 3 7 4 7 3 7 2 Data Points on a Line Traverse 70 s i m i l a r s t r o n t i u m become l e s s c r y s t a l l i z a t i o n sequences. abundant f o l l o w i n g normal 3.4 MINERALIZATION AND ALTERATION M i n e r a l i z a t i o n on t h e Zeta P r o p e r t y o c c u r s i n two forms: (1) c a s s i t e r i t e g r e i s e n i n h o r n f e l s e d q u a r t z i t e , and (2) g r e i s e n v e i n s . Most m i n e r a l i z e d zones t r e n d about 070°, p a r a l l e l t o the s t r o n g e s t j o i n t s e t i n t h e b a t h o l i t h . G r e i s e n i n h p r n f e l s i s marked by r e d d i s h - brown c a s s i t e r i t e , l o c a l l y up t o 0.5% of t h e r o c k , t h a t i s found as g r a i n s up t o 3 mm i n d i a m e t e r w i t h i n t h e s e r i c i t i z e d q u a r t z i t e ( P l a t e 3.13). M i n e r a l i z e d f r a c t u r e s u r f a c e s t r e n d a p p r o x i m a t e l y 120° w i t h a s t e e p n o r t h e r l y d i p . K-Ar whole r o c k d a t i n g ( T a b l e 4.2) o f t h i s s e r i c i t i c g r e i s e n m i n e r a l i z a t i o n g i v e s e a r l y L a t e C r e t a c e o u s , 87+3 Ma, which i s i n d i s t i n g u i s h a b l e from th e K-Ar b i o t i t e d a t e f o r t h e s y e n i t e o f 87+3 Ma ( s e c t i o n 4.2). H o r n f e l s e d q u a r t z i t e , c o n t a i n i n g 3% p y r i t e , e xtends about 100 m outwards from the 71 P l a t e 3.13 C a s s i t e r i t e (CS) from Trench 1983-3, Zeta showing, w e s t - c e n t r a l Yukon, occur as darker blebs w i t h i n black tourmaline v e i n l e t s that form up to 0.5% of the rock. V e i n l e t s mainly f o l l o w n e a r l y v e r t i c a l northwest-southeast tre n d i n g f r a c t u r e s w i t h i n the 1983-3 Trench ( F i g s . 3.1, 3.2). 72 s y e n i t e c o n t a c t . W i t h i n t h i s h o r n f e l s c a s s i t e r i t e b l e b s i n q u a r t z v e i n subcrop a r e common. G r e i s e n v e i n s a r e o f two t y p e s : (1) s u l p h i d e - r i c h q u a r t z v e i n s w i t h minor t o u r m a l i n e , and (2) t o u r m a l i n e - r i c h q u a r t z v e i n s w i t h minor s u l p h i d e s . Both t y p e s of v e i n c u t thr o u g h the s e d i m e n t a r y r o c k - s y e n i t e c o n t a c t ( F i g . 2.1). S u l p h i d e r i c h q u a r t z v e i n s , r e p r e s e n t e d by t h e Low Fog showing and the C i r q u e showing ( F i g s . 3.1, 3.2), p a r a l l e l major j o i n t i n g t h a t d i p s n e a r l y v e r t i c a l l y and t r e n d s 060° t o 090°. S e v e r a l s u b - p a r a l l e l , narrow (15 m), but l a t e r a l l y e x t e n s i v e (>500 m l o n g ) shear zones, c o n t a i n d i s c o n t i n u o u s l y m i n e r a l i z e d q u a r t z - s u l p h i d e - k a o l i n i t e - l i m o n i t e v e i n s . I n d i v i d u a l v e i n s a r e narrow (30 cm w i d e ) , and a r e t y p i c a l l y s p l a y e d and s e p a r a t e d from o t h e r p a r a l l e l v e i n s by l e s s than two t o t h r e e metres o f b a r r e n h o s t r o c k . The f o l l o w i n g s u l p h i d e m i n e r a l s , i n approximate o r d e r of abundance, a r e p r e s e n t i n t h e s e v e i n s : 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 , s t a n n i t e , c h a l c o p y r i t e , j a m e s o n i t e , c a s s i t e r i t e and c o v e l l i t e . V e i n s a r e o f t e n zoned w i t h a r s e n o p y r i t e - r i c h m a r g i n s , and q u a r t z - and j a m e s o n i t e - r i c h c o r e s . A l t e r a t i o n 73 e n v e l o p e s around t h e s e v e i n s form up t o 80% o f the t o t a l w i d t h of the showings. A l t e r a t i o n e n v e l o p e s of q u a r t z + t o u r m a l i n e + s u l p h i d e a r e 5 t o 10 t i m e s w i d e r than the v e i n , and c o n s i s t of p a r a l l e l zones of m o d e r a t e l y t o c o m p l e t e l y k a o l i n i t i z e d and s t r o n g l y l i m o n i t e (+ h e m a t i t e ) s t a i n e d i n t r u s i v e r o c k . A l t e r a t i o n a d j a c e n t t o v e i n s i s i n t e n s e , f o r m i n g a m a s s i v e , l o c a l l y banded and porous zone of k a o l i n i t e . G r a d a t i o n a l l y outwards from the v e i n , k a o l i n i z a t i o n d e c r e a s e s i n i n t e n s i t y and igneous t e x t u r e s a r e sometimes p r e s e r v e d . T o u r m a l i n e r o s e t t e s w i t h i n k a o l i n i z e d s y e n i t e o c c u r i n the Main Zone a t Trench 83-3 ( P l a t e 3.14). B i o t i t e , f o l l o w e d by h o r n b l e n d e , p r o g r e s s i v e l y becomes more common as r e l a t i v e l y u n a l t e r e d i n t r u s i v e i s approached. L i m o n i t i z a t i o n and c h l o r i t i z a t i o n a r e t h e outermost a l t e r a t i o n f e a t u r e s o f t h e s e v e i n s . W i t h i n t h e v e i n s , two massive t o u r m a l i n e - r i c h s e c t i o n s a r e o f t e n s h a r p l y s e p a r a t e d by a narrow c l a y - r i c h s e c t i o n . The l a t t e r c o u l d be a d i s t i n c t i v e t y p e o f v e i n m a t e r i a l but p r o b a b l y i s i n t e n s e l y a l t e r e d w a l l r o c k . 74 P l a t e 3.14 Envelopes around tourmaline ve i n s , from Trench 1983-1, Zeta showing, west-central Yukon, c o n s i s t of moderately to s t r o n g l y t o u r m a l i n i z e d , k a o l i n i z e d and l i m o n i t i z e d s y e n i t e . Tourmaline r o s e t t e s , up to 2 cm i n diameter, form 20% of the a l t e r e d rocks. Pale areas are k a o l i n i t e r i c h . 75 S u r f a c e samples from the C i r q u e ( P l a t e 3.15) and t h e Low Fog ( P l a t e 3.16) showings ( F i g s . 3.1, 3.2) c o n t a i n 10 t o 65% s u l p h i d e m i n e r a l s ( p y r i t e 10-75%, a r s e n o p y r i t e 5-30%, s p h a l e r i t e 2%, and minor s t a n n i t e and j a m e s o n i t e ) , w i t h 50-74% q u a r t z , 1-30% t o u r m a l i n e , and minor a l t e r e d f e l d s p a r . The C i r q u e v e i n , 1.4 m i n w i d t h , i s c h a r a c t e r i z e d by abundant p y r i t e and t o u r m a l i n e w i t h minor a r s e n o p y r i t e and a l t e r e d f e l d s p a r s . By comparison, t h e Low Fog v e i n i s o n l y 0.7 m wide and i s r e l a t i v e l y a r s e n o p y r i t e - and q u a r t z - r i c h w i t h o n l y minor t o u r m a l i n e and p y r i t e . Both showings c o n t a i n comb t e x t u r e d q u a r t z i n d i c a t i n g open space f i l l i n g . P a r a g e n e s i s of t h e s u l p h i d e - r i c h q u a r t z v e i n s , from o l d e s t t o youngest m i n e r a l s , i s : e a r l y q u a r t z and e a r l y t o u r m a l i n e , c a s s i t e r i t e w i t h c h a l c o p y r i t e and s p h a l e r i t e ( w i t h e x s o l v e d s t a n n i t e ) , p y r i t e and a r s e n o p y r i t e , i n t e r m e d i a t e t o u r m a l i n e , l a t e t o u r m a l i n e , j a m e s o n i t e , f r a c t u r i n g and c a t a c l a s i s w i t h r e m o b i l i z a t i o n of j a m e s o n i t e i n t o f r a c t u r e s i n e a r l i e r s p h a l e r i t e , c r y s t a l l i z a t i o n of e u h e d r a l q u a r t z , l a t e p y r i t e and a r s e n o p y r i t e , and a f i n a l s t a g e of t o u r m a l i n e w i t h q u a r t z . Supergene a l t e r a t i o n produced l o c a l c o v e l l i t e . 76 P l a t e 3.15 The C i r q u e v e i n ( F i g s . 3 1, 3.2), Zeta p r o s p e c t , w e s t - c e n t r a l Yukon, i s a zoned q u a r t z - s u l p h i d e v e i n c o n t a i n i n g about 65% p y r i t e ( P Y ) , 5% a r s e n o p y r i t e (AS), 25% t o u r m a l i n e (TO) and 5% a l t e r e d f e l d s p a r s . F i e l d of view i n the photograph i s 2.4 mm. 77 P l a t e 3.16 The Low Fog v e i n ( F i g s . 3.1, 3.2), Zeta p r o s p e c t , w e s t - c e n t r a l Yukon, t y p i c a l l y c o n t a i n s s p h a l e r i t e (SL) and p y r i t e (PY) surrounded by s t a n n i t e (SN) and j a m e s o n i t e (JM). S p h a l e r i t e c o n t a i n s s m a l l e x s o l u t i o n b l e b s of c h a l c o p y r i t e and s t a n n i t e i n e m u l s i o n t e x t u r e . Note t h a t r e c r y s t a l l i z e d p y r i t e (PY) c o n t a i n s b l e b s of s t a n n i t e . F i e l d of view c o v e r e d by photograph i s 2.4 mm. 78 Assuming c o n s i s t e n t m i n e r a l o g y t h r o u g h o u t t h e Zeta p r o p e r t y , e s t i m a t e s o f t h e temperature of emplacement f o r the s u l p h i d e s a r e from 363° + 50°C (as d e f i n e d by the Fe-As-S system) t o 860°C as i n d i c a t e d by the Cu-Fe-Sn-S system ( B a r t o n , 1969; Lee, 1972; Ri b b e , 1974; C l a r k e , 1960). T h i s upper temperature l i m i t i s u n r e a l i s t i c because i t i s h i g h e r t h a n t h a t of most g r a n i t i c m e l t s . O t h e r w i s e the l i m i t s a r e w i t h i n t h o s e proposed by Shcherba (1970) who su g g e s t e d t h a t g r e i s e n i z a t i o n o c c u r s between 470°C t o 360°C. T o u r m a l i n e r i c h q u a r t z y e i n s v e i n s a r e c h a r a c t e r i s t i c o f t h e Main Zone and t h e Gash showing ( F i g s . 3.1, 3.2). These v e i n s a r e l e s s t h a n 80 m l o n g , but t o u r m a l i n e as j o i n t f i l l i n g s may ext e n d over 175 m. V e i n s range i n w i d t h from 1.5 m t o s e v e r a l c e n t i m e t r e s ; i n d r i l l c o r e s e m i - c o n t i n u o u s v e i n s up t o 3 m wide were obs e r v e d . T o u r m a l i n e , t h e major gangue m i n e r a l , c o n s i s t s of t h r e e g e n e r a t i o n s : (1) e a r l y r a d i a l a g g r e g a t e s o f c o a r s e b l a c k t o u r m a l i n e r e p l a c e d by (2) i n t e r m e d i a t e r a d i a l a g g r e g a t e s of b l u e - g r e e n t o u r m a l i n e , and f o l l o w e d by (3) l a t e v e i n l e t s o f p a l e brown t o u r m a l i n e . The e a r l y t o u r m a l i n e i s p a l e y e l l o w i s h green i n t h i n s e c t i o n and forms p a t c h e s of e x t r e m e l y f i n e g r a i n e d a g g r e g a t e s o f equant 79 t o p r i s m a t i c c r y s t a l s (0.03 mm i n d i a m e t e r ) w i t h c o a r s e r p r i s m a t i c g r a i n s toward th e b o r d e r s of t h e p a t c h e s . I n t e r m e d i a t e t o u r m a l i n e c o n s i s t s of r a d i a t i n g a g g r e g a t e s of e l o n g a t e p r i s m a t i c c r y s t a l s up t o 2 mm i n l e n g t h ; c o l o u r s i n t h i n s e c t i o n v a r y w i d e l y , t h e l a t e brown t o u r m a l i n e i s b l u e i n t h i n s e c t i o n and forms v e i n l e t s t h a t c u t e a r l i e r p a t c h e s of b l a c k t o u r m a l i n e . M i n o r t o t r a c e amounts of f i n e g r a i n e d a r s e n o p y r i t e , p y r i t e , j a m e s o n i t e and b o u l a n g e r i t e o c c u r a t t h e margins of the v e i n s . D r i l l i n g i n d i c a t e s t h a t t h e p e r c e n t a g e of s u l p h i d e s might i n c r e a s e w i t h depth (Jago, 1984). The k a o l i n i t e - s e r i c i t e a l t e r a t i o n e n v elope i s up t o 10 t i m e s the w i d t h o f t h e v e i n . The Main zone ( F i g s . 3.1, 3.2; P l a t e 3.17), 1.0-3.0 m wide, i s exposed on s u r f a c e i n t h e 1983-1 Trench, and has been i n t e r s e c t e d i n d r i l l c o r e over a l a t e r a l d i s t a n c e o f 150 m, a v e r t i c a l d i s t a n c e o f 100 m, and i s open a t depth. 1988 d r i l l i n d i c a t e d r e s e r v e s a r e 98,248 tonnes a t 557 g/t (Yukon E x p l o r a t i o n , 1988, p.220). The zone i n t e r s e c t s the sediment c o n t a c t a t 60° i n p l a n v i e w and c o n t a i n s between one and t h r e e p a r a l l e l t o u r m a l i n e , and t o u r m a l i n e - q u a r t z + c l a y + s u l p h i d e g r e i s e n v e i n s , which a l t h o u g h 80 P l a t e 3.17 P o l i s h e d s e c t i o n from the Main Zone (F i g s . 3.1, 3.2: 1983-1 Trench), Zeta prospect, w e s t - c e n t r a l Yukon, shows s p h a l e r i t e (SL) i n a quartz gangue co n t a i n i n g i n c l u s i o n s of s t a n n i t e (SN), jamesonite (JM), and c h a l c o p y r i t e (CP). F i e l d of view i n the photograph i s 1.2 mm. 81 m i n e r a l o g i c a l l y complex, c o n t a i n e r r a t i c a l l y d i s t r i b u t e d m i n e r a l s c o n t a i n i n g s i l v e r , antimony and t i n . The v e i n has been h e a v i l y o x i d i z e d w i t h i n 40 m o f the p r e s e n t s u r f a c e . Deeper l e v e l s o f t h e v e i n , w h i c h presumably have not been l e a c h e d , c o n t a i n h i g h e r s i l v e r grades a s s o c i a t e d w i t h l e a d and antimony v a l u e s . T i n m i n e r a l i z a t i o n averages 0.1%, but v a l u e s as h i g h as 0.6% have been o b t a i n e d from s u r f a c e samples of v e i n f l o a t . The Gash zone ( F i g s . 3.1, 3.2), marked by t o u r m a l i n e and i n t e r m i t t e n t r a r e s u l p h i d e v e i n s , f o l l o w s a c u r v e d shear t h a t t r e n d s from n o r t h e a s t t o southwest. The zone about 2 m i n w i d t h , c o n t a i n s t h i n l y spaced, v e r y narrow s u b - p a r a l l e l t o u r m a l i n e v e i n l e t s a l o n g j o i n t s . The c e n t r a l 1 m wide c o r e c o n s i s t s m a i n l y o f q u a r t z and c l a y w i t h minor a r s e n o p y r i t e and p y r i t e . The v e i n i s e n c l o s e d by a 1.0 m wide s y m m e t r i c a l a l t e r a t i o n envelope ( P l a t e 3.18). Near th e v e i n , k a o l i n i z a t i o n and l i m o n i t i z a t i o n a r e i n t e n s e , but t h i s a l t e r a t i o n d i m i n i s h e s outward o v e r 0.5 m. P o o r l y t e r m i n a t e d q u a r t z c r y s t a l s i n the~ c o r e of t h e v e i n , t h e c o l l o f o r m n a t u r e o f t o u r m a l i n e r i c h m i n e r a l i z a t i o n , and the symmetry 82 P l a t e 3.18 Cross s e c t i o n of the Gash v e i n ( F i g s . 3.1, 3.2), Zeta p r o s p e c t , west-c e n t r a l Yukon, shows a s y m m e t r i c a l a l t e r a t i o n envelope on the c e n t r a l t o u r m a l i n e - q u a r t z low s u l p h i d e v e i n . Assemblages, t o t a l l i n g 1 m i n w i d t h , from u n a l t e r e d s y e n i t e inwards i n c l u d e s : (1) q u a r t z >> t o u r m a l i n e + c l a y ; (2) t o u r m a l i n e > q u a r t z , q u a r t z + c l a y w i t h minor t o u r m a l i n e ; (3) q u a r t z >> t o u r m a l i n e , and (4) a c o l l o f o r m t o u r m a l i n e c o r e . 83 of v e i n m i n e r a l o g i e s s u g g e s t s t h a t m u l t i p l e e p i s o d e s of m i n e r a l d e p o s i t i o n i n open spaces o c c u r r e d . 84 CHAPTER 4 ISOTOPIC STUDIES 4.1 INTRODUCTION T i n - s i l v e r m i n e r a l i z a t i o n on the Zeta p r o p e r t y , u n l i k e most t i n m i n e r a l i z a t i o n t hroughout the w o r l d , i s a s s o c i a t e d w i t h g r a n i t e p l u t o n s and appears t o be r e l a t e d t o s y e n i t e . Because s y e n i t e r e l a t e d t i n m i n e r a l i z a t i o n i s u n u s u a l , i s o t o p e s and geo c h r o n o l o g y were u t i l i z e d t o de t e r m i n e t h e age and o r i g i n of t h e zoned i n t r u s i v e r o c k s . Samples were s e l e c t e d from t h e c o u n t r y r o c k s , s y e n i t e s , q u a r t z s y e n i t e s , g r a n i t e s , t o u r m a l i n e o r b i c u l a r g r a n i t e , g r a n i t e dykes ( F i g s . 3.1, 3.2), and c o r e s and r i m s o f o r t h o c l a s e megacrysts i n g r a n i t e . These were a n a l y z e d ( T a b l e 4.1) f o r K-Ar d a t i n g ( s e c t i o n 4.2), Rb-Sr ( s e c t i o n 4.3), Pb-Pb ( s e c t i o n 4.4) and Sm-Nd ( s e c t i o n 4.5). 85 TABLE 4.1: Samples and methods of analyses for major rock units on Arsenic Ridge, Lost Horses batholith, Yukon. Sample locations are shown in Figure 3.1 and details of analytical methods are in Appendix C. I s o t o p e A n a l y s i s Sample Rock L a t i t u d e L o n g i t u d e K-Ar Rb-Sr Pb-Pb Sm-Nd Number Name Whole Rock SA06 Greywacke 63. . 98° N SA1 1 S y e n i te 63. .99CN SA18 A l t Quar t z i te 63 . 98° N SA24 TO Orb G r a n i t e 1 63 . ,95°N SA33 S y e n i te 63 . ,97°N SA38 S y e n i te 63. .96°N SA39 G r a n i te Dyke 63. ,96°N SA41 Quartz S y e n i t e 63 . 95^N SA42 Qu a r t z S y e n i t e 63. ,95°N SA45 G r a n i t e (TO)* 63 .9S°N SA48 G r a n i t e (TO)* 63. .95°N SA50 S y e n i te 63 . 97°N SA90 TO Orb G r a n i t e 1 63. .95°N M i n e r a l S e p a r a t e s SA48BI B i o t i te SA48H6 Ho r n b l e n d e SA48TF T o t a l F e l d s p a r SA48B C o r e K - F e l d s p a r SA48B Rim K - F e l d s p a r SA48C Core K - F e l d s p a r SA48C Rim K - F e l d s p a r SA48D C o r e K - F e l d s p a r SA480 Rim K - F e l d s p a r SA48E C o r e K - F e l d s p a r 3A48E Rim K - F e l d s p a r SA48F Core K - F e l d s p a r SA48F Rim K - F e l d s p a r SA48 C&R3 K - F e l d s p a r SA48 C&R3 K - F e l d s p a r 137.29°W X X 137.34°W X X 137.29°W X X X 137.32°W X X 137.30°W X X 137.31°W X X 137.31°W X X 137.31°W X X 137.31°W X X 137.31°W X X 137.32°W X X X 137.30°W X X 137.32°W X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 1 TO Orb G r a n i t e - T o u r m a l i n e O r b i c u l e G r a n i t e . 2 (TO) = T o u r m a l i n i z e d . 3 C&R - Core and Rim. 86 4.2 K-AR DATING 4.2.1 I n t r o d u c t i o n K-Ar methods were used t o date t h e L o s t Horses b a t h o l i t h , and t o r e l a t e t h e t i n - g r e i s e n m i n e r a l i z a t i o n t o t h e i n t r u s i o n . Three samples were a n a l y z e d ( T a b l e s 4.1, 4.2): a hornblende s e p a r a t e and a b i o t i t e s e p a r a t e from t h e g r a n i t e (sample SA48), and a m u s c o v i t e a l t e r e d q u a r t z i t e w i t h v e i n s b e a r i n g t r a c e c a s s i t e r i t e . B i o t i t e , m u s c o v i t e and whole r o c k K-Ar a n a l y s e s f o r q u a r t z monzonites, s y e n i t e s and s c h i s t s from s u r r o u n d i n g a r e a s (Moose Creek, S t e w a r t C r o s s i n g , S c h e e l i t e Dome and t h e S y e n i t e Range) a r e l i s t e d i n T a b l e 4.2 f o r r e f e r e n c e . 4.2.2 Method of A n a l y s i s A n a l y t i c a l d e t a i l i s a v a i l a b l e i n Appendix D ( w r i t t e n communication from R.L. Armstrong f o r t h e Geochronometry 87 TABLE 4.2: A n a l y t i c a l data f o r Cretaceous K-Ar dates' f r o i the Syenite Range and surrounding area, v e s t - c e n t r a l Tukon T e r r i t o r y . S a i p l e Ho. Material Location Unit 4 p f l r [ r a d ) c 4 0 A r ( t o t a l ) 4 0 A r ( r a d ) c (10-6S1P/S Dale ("a)' lite' SA18* Whole rock Ars e n i c Ridge Zeta g r e i s e n t a t . 63.98»N long. 137.29°W Unit l a : q u a r t z i t e 3.34.0.00 11.562 87.0*3.0 l a t e Cretaceous SA 4B* B i o t i t e Arsenic Ridge, 7eta l a t . 63.95'N Long. 137.32'H Unit 2c: gran i t e 5.80)0.04 0.951 21.962 94.9*3.3 l a t e Cretaceous SA4B> Hornblende Arsenic Ridge, Zeta Lat. 63.95°N Long. 1J7.30°H Unit 2C: g r a n i t e 1.41*0.04 0.905 4.935 88.0*3.8 Late Cretaceous 6SC65-50' B i o t i t e Moose Creek l a t . 63.50" long. 136.95'H Quart! l o n z o n i t e 7.27 0.68 87.0*3.5 Late Cretaceous GSC70-47' Muscovite Steuart Crossing Lat. 64.23°H Long. 129.48°N S c h i s t 0.91 69.0M.O l a t e Cretaceous GSC81-40" B i o t i t e S c h e e l i t e Doie l a t . 63.75»N long. 136.25°* Quart! aonronite 6.26 0.836 99.3*1.9 Ea r l y Cretaceous GS101' B i o t i t e S c h e e l i t e Doae Lat. 63.80°N Long. 136.28'N Quartz tonzonite 6.75*0.01 0.907 24.317 90.4*2.9 Late Cretaceous TABLE 4.2 (continued) S a i p l e No. Ma t e r i a l Location Unit 40flr t r a d l f 4 0 A r ( t o t a l ) 40ftr(rad) c (10-6STr7< Date (Ma)' Tine' PC16' B i o t i t e PC17J B i o t i t e Syenite Range t a t . 63.98°N Long. 137.32°» Syenite Syenite Range t a t . 63.96°N Long. 137.37°* Quartz l o n z o n i t e 6.92*0.03 7.10*0.03 0.94 0.96 23.91 25.76 B6.Bt2.7 Late Cretaceous 91.0f2.7 Late Cretaceous • Dates are a l l standardized to constants (Steiger and Jager, 1977):Ae 1 0- 5 8 1*! 0"" y e a r " 1 , Ap=4.960x10"" y e a r - 1 , , SK/K:1.167x10"' a t o i r a t i o . Dates have e s t i i a t e d one s i g i a e r r o r s . • One half of d i f f e r e n c e betaeen d u p l i c a t e analyses. < 40Ar(rad) i s radiogenic. T i i e d e s i g n a t i o n i s a f t e r Barland et a l . (1989). * S a i p l e s i t e f o r SA1B and SA48 i s on Figures 3.1 and 3.2. This a n a l y s i s aas done i n the Geochronology Laboratory, Department of Geolo g i c a l Sciences, U.8.C. Mineral separates and p o t a s s i u i analyses aere by K. Scott and D. Runkle; Argon analyses aere by 1. Harakal. ' A n a l y s i s f r o i Kanless e t _ a l . (1967); *»Ar/<n : 0.0051. « Analyses f r o i Hanless et_.aL (1972); "Ar/<«K : 0.0040. » A n a l y s i s f r o i Stephens e t j L (1982); <«Ar/«U : 0.00593. ' A n a l y s i s fro» Kuran et al... (1982). ' A n a l y s i s f r o i Christopher (1973). Apatite f r o i PC16 y i e l d e d a f i s s i o n track date of 76tBfla. L a b o r a t o r y , a t The U n i v e r s i t y of B r i t i s h Columbia , March 1989). P o t a s s i u m i s d e t e r m i n e d i n d u p l i c a t e by atomic a b s o r p t i o n u s i n g a T e c h t r o n AA4 s p e c t r o p h o t o m e t e r on d i l u t e s u l p h a t e s o l u t i o n s b u f f e r e d by Na and L i n i t r a t e s . Argon i s determined' by i s o t o p e d i l u t i o n u s i n g an AE1 MS-10 mass s p e c t r o m e t e r w i t h Carey Model 10 v i b r a t i n g r e e d e l e c t r o m e t e r , a h i g h p u r i t y 3 8 A r s p i k e , and c o n v e n t i o n a l gas e x t r a c t i o n and p u r i f i c a t i o n p r o c e d u r e s as d e s c r i b e d by White and o t h e r s (1967). 4.2.3 R e s u l t s A n a l y t i c a l d a t a f o r K-Ar d a t e s from t h e S y e n i t e Range and s u r r o u n d i n g a r e a s a r e c o m p i l e d i n T a b l e 4.2. Samples from t h e Zet a p r o p e r t y , i n c l u d i n g t h e a l t e r e d q u a r t z i t e and b i o t i t e and ho r n b l e n d e s e p a r a t e s , a r e e a r l y L a t e C r e t a c e o u s i n age. The dat e f o r t h e a l t e r e d q u a r t z i t e i s 87.0+3.0 Ma, the b i o t i t e s e p a r a t e i s 94.9+3.3 Ma and t h e h o r n b l e n d e s e p a r a t e i s 88.0+3.8 Ma. The a l t e r e d q u a r t z i t e c o n t a i n s 5% m u s c o v i t e f l a k e s up t o 5.0 mm i n d i a m e t e r t h a t i s both p e r v a s i v e and a s s o c i a t e d w i t h c a s s i t e r i t e b l e b s i n q u a r t z 90 v e i n s . Dates from t h e s u r r o u n d i n g r e g i o n range from Early-C r e t a c e o u s t o L a t e C r e t a c e o u s (99.3+3.7 Ma t o 69.0+2.0) Ma. 4.2.4 I n t e r p r e t a t i o n The L o s t Horses b a t h o l i t h , d a t e d by t h e p o t a s s i u m argon method, i s L a t e C r e t a c e o u s ( b i o t i t e SA48, 94.9+3.0 Ma; horn b l e n d e SA48, 88.0+4.0). T i n - g r e i s e n m i n e r a l i z a t i o n ( m u s c o v i t e from sample SA18 WR) a l s o d a t e s as L a t e C r e t a c e o u s (87+3 Ma). The age of m i n e r a l i z a t i o n , i n d i s t i n g u i s h a b l e from t h e age o f the i n t r u s i v e , s u g g e s t s a g e n e t i c r e l a t i o n s h i p t o t h e s p a t i a l l y a d j a c e n t s y e n i t e . 4.3 RB-SR GEOCHRONOMETRY 4.3.1 I n t r o d u c t i o n Rb-Sr was used t o date the b a t h o l i t h and t o dete r m i n e some o f t h e geo c h e m i c a l c h a r a c t e r i s t i c s r e l e v a n t t o the o r i g i n of t h e b a t h o l i t h . P o t a s s i u m f e l d s p a r megacrysts were 91 a n a l y z e d t o i n v e s t i g a t e e q u i l i b r i u m between t h e c o r e s and r i m s , and between megacrysts and whole r o c k . 4.3.2 Method o f A n a l y s i s Sr i s o t o p i c measurements were made on a Vacuum-G e n e r a t o r s Isomass 54R mass s p e c t r o m e t e r automated w i t h a H e w l e t t - P a c k a r d HP-85 computer. Sample p r e p a r a t i o n , n o r m a l i z a t i o n r a t i o s , s t a n d a r d s and p r e c i s i o n s a re d e s c r i b e d i n Appendix C and Appendix D. A l l a n a l y s e s were r u n i n the Geochronometry L a b o r a t o r y of The U n i v e r s i t y of B r i t i s h Columbia. 4.3.3 R e s u l t s A t o t a l o f 13 whole r o c k s ( i n c l u d i n g s e d i m e n t a r y r o c k s , s y e n i t e s , q u a r t z s y e n i t e s , g r a n i t e s and g r a n i t e d y k e s ) , t h r e e m i n e r a l s e p a r a t e s ( b i o t i t e , h o r n b l e n d e and t o t a l f e l d s p a r ) , and f i v e p a i r s of K - f e l d s p a r c o r e s and r i m s were a n a l y z e d f o r Rb-Sr. Sample l o c a t i o n s a l o n g A r s e n i c Ridge 92 a r e shown i n F i g u r e s 3.1 and 3.2; t h e r e s u l t s a r e l i s t e d i n T a b l e 4.3. 8 7 S r / 8 6 Sr v e r s u s 8 7 Rb/ 8 6 Sr v a l u e s f o r a l l of t h e whole r o c k and m i n e r a l samples a r e p l o t t e d i n F i g u r e 4.1. Two t o u r m a l i n e o r b i c u l e g r a n i t e samples (SA24 and SA90) were a n a l y z e d . SA24 i s h i g h l y a l t e r e d (Appendix A) and p r o b a b l y i s n ot r e l i a b l e . Combined c o r e and r i m 8 7 S r / 8 6 S r r a t i o s , a p proximate t h e average of t h e c o r e s and r i m s . I n i t i a l r a t i o s f o r the i n d i v i d u a l r o c k and m i n e r a l samples were c a l c u l a t e d u s i n g a r o c k age of 95 Ma as d e t e r m i n e d from K-Ar a n a l y s i s ( T a b l e 4.2; b i o t i t e sample SA48). A l l i s o c h r o n s were c a l c u l a t e d u s i n g t h e r e g r e s s i o n f i t d e s c r i b e d by York (1967 ). 4.3.4 I n t e r p r e t a t i o n E l e v e n g r a n i t i c whole r o c k samples ( T a b l e 4.3) form the b a s i s of the Rb-Sr e r r o r c h r o n p l o t t e d on F i g u r e 4.1. From t h e s e a l a t e E a r l y C r e t a c e o u s d a t e , 101+12 Ma, and an 93 TABLE (.3: B o D i d i u i and strontium c o n c e n t r a t i o n s and s t r o n t i u i isotope data f o r tbe najor rock u n i t s along A r s e n i c Ridge, l o s t Sotses b a t h o l i t h , Tukoa. Metnod of analyses was by iso t o p e d i l u t i o n . S a i p i e l o c a t i o n are shorn on Figure 3.1. SAMPLE NUMBER ROCK . DESCRIPTION (Unit No.) XSiQ2 Sr p p i Rb p p i «!Rb/»'Sr ID(XRF) " S r / " S r * ' S r / « S r E r r o r ' At 95 Ma 87Sr/86Si *KLE_ ROCK .SAMPLES SA06HR Greyaacke ( l a ) 67.67 0.21 148 9.3 0.162(0.083) 0.72687 0.0001! 0.72662 SAHMR Syenite (2a) 62.12 8.44 643 389 1.752(1.744) 0.71529 0.00009 0.71292 SA18HR A l t . Q u a r t z i t e ( l a ) 73.06 4.33 76 240 9.17(8.831) 0.74759 0.00006 0.73520 SA24HR To-Orb Granite ( 2 d ) ! 70.39 1.04 256 70.3 . 0.795(0.811) 0.71322 0.00002 0.71214 SA33UR Syenite (2a) 60.07 7.75 937 343 1.060(1.086) 0.71440 0.00008 0.71296 SA38UR Syenite (2a) 60.23 6.17 782 314 1.163(1.245) 0.71383 0.00003 0.71225 SA39UR Granite Oyke (3b) 76.06 5.58 183 444 7.03(7.444) 0.72315 0.00011 0.71363 SA41NR Quartz Syenite (2b) 64.96 6.45 724 361 1.444(1.451) 0.71371 0.00005 0.71134 SA42MR Quartz Syenite (2b) 67.64 6.16 727 384 1.529(1.409) 0.71325 0.00005 0.71118 SA45NR Granite K i t h l o ( 2 c F 68.04 5.87 654 354 1.567(1.708) 0.713B7 0.00004 0.71175 SA48HR Granite a i t h l o ( 2 c ) 2 67.12 6.35 655 392 1.733(1.754) 0.71391 0.00008 0.71156 SA50NR Syenite (2a) 60.92 7.BB 823 319 1.122(1.239) 0.71466 0.00006 0.71316 SA90HR To-Orb Granite (2d)' 7B.04 6.09 117 475 11.77(12.375) 0.72785 0.00009 0.71192 MINERAL SEPARATES FROM SAMPLE SA48 Unit 2d Granite SA48B1 B i o t i t e 5.80 ! 5B.3 1030 51.54 0.769 0.002 NA> SA4BHB Hornblende 1.41' 153 21B 4.127 0.71697 0.00004 0.71138 SA48TF Total Feldspar 835 460 1.595 0.71382 0.00006 0.71166 SA4BB Core K-feldspar 1420 443 0.903 0.71311 0.00006 0.71189 SA466 R i l K-feldspar 983 542 1.598 0.71384 0.00006 0.71168 SA48C Core K-feldspar 1301 439 0.978 0.71306 0.00006 0.71174 SA4BC R i l K-Feldspar 962 535 1.612 0.71375 0.00006 0.71157 SA4BD Core K-feldspar 13B2 467 0.978 0.71323 0.00006 0.71190 TABLE 4.3 (continued) SAMPLE NUMBER ROCK DESCRIPTION (Unit No.) U i 0 2 U i O Sr ppi Rb p p i " R b / » » S r ID(XRF) i'Sr/«Sr " S r / a ' S r Erro r * At 95 Ma 87Sr/86Si SA48D Ria K-Feldspar 1062 611 1.666 0.71388 0.00008 0.71162 SA48E Core K-Feldspar 1405 468 0.964 0.71324 0.00009 0.71193 SA46E Ria K-Feldspar 1036 574 1.604 0.71390 0.00007 0.71173 SA48F Core K-Feldspar 1374 440 0.928 0.71319 0.00009 0.71193 SA48F R i i K-Feldspar 969 578 1.729 0.71398 0.00007 0.71164 SA4B CIR K-Feldspar 1259 507 1.168 0.71341 0.00003 0.71183 SA48 CSR K-Feldspar 1207 503 1.206 0.71345 0.00006 0.71182 SA48 K-F Core average (n=5) 1376 451 0.950 0.71315 0.00003 0.71186 SA48 K-F R i i average (n:5) 1002 568 1.641 0.71386 0.00003 0.71164 SA48 K-F Megacryst average ( n U 2 ) 1197 509 1.277 0.71350 ' Measured r a t i o s have been n o n a l i t e d to a , 6 S r / 1 8 S r r a t i o of 0.1194 and adjusted so that the National Bureau of Standards standard SrC0:(SRM 987) g i v e s a >'Sr/"Sr r a t i o of 0.71019)0.00002 and the E i i e r and Aiend Sr standard a r a t i o of 0.70800*0.00002. The p r e c i s i o n of a s i n g l e " ' S r / e ' S r r a t i o i s n o r i a l l y < 0.0001 (one s i g i a ) . Any exceptions are noted. 1 B i o t i t e analyses not good enough f o r an i n i t i a l Sr c a l c u l a t i o n . 1 To : T o u r i a l i n e 1 Value represents percent K. Figure 4.1: 8 7 S r / 8 6 Sr versus 87 Rb/ 8<3Sr p l o t of whole rocks and mineral separates (data used from Table 4.3) from Arsenic Ridge, Lost Horses b a t h o l i t h , Yukon. Symbols used are: • = sedimentary rocks; •% = sy e n i t e ; • = quartz s y e n i t e ; • = g r a n i t e ; O = tourmaline o r i b i c u l a r g r a n i t e ; A = g r a n i t e dyke; + = hornblende; x = b i o t i t e ; and, * = t o t a l f e l d s p a r . 96 97 i n i t i a l r a t i o of 0.7121 was c a l c u l a t e d . I f the g r a n i t i c dyke i s removed from t h i s sample s u i t e (n = 1 0 ) , t h e r e c a l c u l a t e d i s o c h r o n i s e a r l y L a t e C r e t a c e o u s , 93+5 Ma, w i t h an i n i t i a l r a t i o of 0.7122 ( F i g . 4.1). The SA48 Rb-Sr i s o c h r o n ( T a b l e 4.3)—composed of a whole r o c k , b i o t i t e s e p a r a t e , h o r n b l e n d e s e p a r a t e and a t o t a l f e l d s p a r s e p a r a t e — d e f i n e s a l a t e E a r l y C r e t a c e o u s d a t e , 101+6 Ma, and an i n i t i a l r a t i o of 0.7114. T h i s Rb-Sr whole r o c k m i n e r a l i s o c h r o n c l o s e l y a p p r o x i m a t e s t h e age o f t h e p l u t o n i c s u i t e , and i s p l o t t e d f o r comparison on F i g u r e s 4.1 and 4.2. Twelve c o r e s , r i m s , and c o r e and r i m samples ( T a b l e 4.3) form t h e b a s i s o f t h e Rb-Sr K - f e l d s p a r megacryst i s o c h r o n ( F i g . 4.2). T h i s y i e l d e d a d a t e o f L a t e C r e t a c e o u s , 71+4 Ma, and an i n i t i a l r a t i o of 0.7122. 8 7 S r / 8 6 S r r a t i o s , c a l c u l a t e d a t 95 Ma, f o r t h e s e d i m e n t s , s y e n i t e s , q u a r t z s y e n i t e s , g r a n i t e s , t o u r m a l i n e o r b i c u l a r g r a n i t e , g r a n i t e dyke, m i n e r a l s e p a r a t e s , and K-f e l d s p a r c o r e s and r i m s a r e i n T a b l e 4.3. A l l such i n i t i a l 98 Figure 4 . 2 : 8 7 S r / 8 6 S r versus 8 7 R t , / s 6 S r p l o t of K-feldspar core (n=5) and rim (n=5) analyses from a megacrystic g r a n i t e (data from Table 4 . 3 ) Arsenic Ridge, Lost Horses b a t h o l i t h , Yukon. Symbols used are: • = K-feldspar cores; and o= K-feldspar rims; A = K-feldspar cores and rims; and x= megacryst average; • = g r a n i t e whole rock; and, * = t o t a l f e l d s p a r separate. 99 100 8 7 S r / 8 6 S r r a t i o s of the g r a n i t i c r o c k s l i e i n the f i e l d w i t h i n i t i a l 8 7 S r / 8 6 S r > 0.706, which r e p r e s e n t s s t r o n t i u m e v o l u t i o n i n t h e upper mantle (Fau r e , 1977). T h i s i m p l i e s t h a t : (1) t h e s t r o n t i u m was d e r i v e d from o l d c r u s t a l r o c k s of s i a l i c c o m p o s i t i o n t h a t a r e e n r i c h e d i n r a d i o g e n i c 8 7 S r because of t h e i r age and h i g h Rb/Sr r a t i o ; and/or (2) some of t h e s t r o n t i u m o r i g i n a t e d from a s o u r c e i n t h e upper m a n t l e , but i t s i s o t o p i c c o m p o s i t i o n was s i g n i f i c a n t l y m o d i f i e d by a d d i t i o n o f f o r e i g n r a d i o g e n i c 8 7 S r . The average i n i t i a l 8 7 S r / 8 6 S r and average p r e s e n t day 8 7 R b / 8 6 S r r a t i o s f o r t h e g r a n i t i c r o c k s a l o n g A r s e n i c Ridge a r e 0.71226 and 2.815, r e s p e c t i v e l y . U s i n g t h e s e average r a t i o s and the f o l l o w i n g e q u a t i o n s (DePaolo, 1981a; DePaolo, 1981b; Farmer and DePaolo, 1983) a model Rb-Sr age (UR) of the s o u r c e r o c k from which the magma was g e n e r a t e d can be c a l c u l a t e d . The Rb-Sr age, TOR, r e p r e s e n t t h e time when a r o c k sample would have had esr=0 (DePaolo and Wasserburg, 1979a). The CUR o f the model d e p l e t e d mantle i s g i v e n by: c s r U R ( T ) = -0.65T 2 + 8T - 23 (1) 101 where T i s i n AE (10 9 y r . ) . The e s r of a r o c k sample a t a time T i n the p a s t i s g i v e n by: e s r ( T ) = e s r ( O ) - f R b / S r Q s r T (2) where e s r ( O ) i s the measured v a l u e , Q s r = 16.67, and f R b / s r i s t h e Sr/Rb enrichment f a c t o r , d e f i n e d as: f R b / S r = (87Rb/86SrROCK/0.0827 ) - 1 (3) The TUR model age i s o b t a i n e d by e q u a t i n g (1) and ( 2 ) , t h a t i s , s o l v i n g f o r T t o s a t i s f y : € s r R o c K ( T ) - e s r U R ( T ) (4) Thus, t h e model Rb-Sr age, TOR, f o r t h e g r a n i t i c r o c k s on A r s e n i c Ridge i s 238 Ma. However, f o r s t r o n t i u m s y s t e m a t i c s e q u a t i o n (1) i s not w e l l c o n s t r a i n e d . I t r e p r e s e n t s a w o r k i n g model based on t h e Nd e q u a t i o n (see s e c t i o n 4.5.4). The v a l i d i t y of the Rb-Sr model age depends on t h e assumption t h a t t h e Rb-Sr r a t i o o f t h e r o c k was not a l t e r e d by g e o l o g i c p r o c e s s e s (metamorphism, e r o s i o n and r e d e p o s i t o n ) i n t h e c r u s t . S t r o n t i u m model ages a r e u s u a l l y younger t h a n ages o b t a i n e d from Sm/Nd r a t i o s (see s e c t i o n 4.5.4) because t h e former a r e a f f e c t e d markedly by t h e s e 102 p r o c e s s e s . A s o u r c e age o f 286 Ma i s u n r e a l i s t i c a l l y young, and much younger t h a n t h e Sm-Nd c a l c u l a t i o n (see s e c t i o n 4.5.4) of 1.26 Ga. The s y e n i t e , q u a r t z s y e n i t e s and g r a n i t e s a l o n g A r s e n i c Ridge ( F i g s . 3.1, 3.2) c o n t a i n zoned ( p i n k c o r e and gr a y r i m , P l a t e 3.10) o r t h o c l a s e megacrysts (sample SA48), up t o 6 cm i n l e n g t h . F i v e s e t s of c o r e and rim s were s e p a r a t e d and a n a l y s e d f o r Rb-Sr r a t i o s u s i n g the methods d e s c r i b e d i n Appendix C. R e s u l t s a r e t a b u l a t e d i n T a b l e 4.3 and p l o t t e d on F i g u r e 4.2. The p o t a s s i u m f e l d s p a r megacryst c o r e s and ri m s p l o t a d j a c e n t t o and l e f t o f the whole r o c k (SA48) i s o c h r o n ( F i g . 4.2), and form an apparent i s o c h r o n of l e s s e r s l o p e . T h i s apparent i s o c h r o n f o r t h e K - f e l d s p a r c o r e s and ri m s g i v e s a 72 Ma d a t e and a 0.7122 i n i t i a l r a t i o . T h i s s u g g e s t s t h a t t h e megacrysts a r e markedly younger than the whole r o c k , which i s u n r e a l i s t i c . The f o l l o w i n g summarizes Rb-Sr i n f o r m a t i o n o b t a i n e d from t h e c o r e - r i m d a t a : (1) The K - f e l d s p a r c o r e s a r e not i n e q u i l i b r i u m w i t h t h e whole r o c k as d e f i n e d by t h e whole r o c k - m i n e r a l i s o c h r o n . 103 (2) The K - f e l d s p a r r i m s approximate e q u i l i b r i u m w i t h t h e whole r o c k s as d e f i n e by t h e whole r o c k - m i n e r a l i s o c h r o n . (3) The K - f e l d s p a r c o r e s by geometry a r e o l d e r t h a n t h e r i m . I f the i n i t i a l r a t i o of t h e whole r o c k -m i n e r a l i s o c h r o n (0.7114) i s used t o d e t e r m i n e t h e apparent age of an i s o c h r o n though th e c l u s t e r of c o r e a n a l y s e s , t h e c o r e i s about 6 Ma o l d e r than the r i m . (4) I n i t i a l r a t i o of t h e K - f e l d s p a r c o r e i s 0.7119 (T a b l e 4.3), i f t h e age o f the c o r e i s assumed t o be e q u i v a l e n t t o the age of t h e o v e r a l l r o c k , namely 95 Ma. (5) I n i t i a l r a t i o s o f t h e K - f e l d s p a r r i m s i s 0.7116 (T a b l e 4.3), assuming an age o f 9 5 Ma. T h i s i s a p p r o x i m a t e l y t h e same but s l i g h t l y h i g h e r t h a n t h e whole r o c k - m i n e r a l i s o c h r o n i n i t i a l r a t i o o f 0.7114. The K - f e l d s p a r m e gacrysts grew i n a m e l t o f c h a n g i n g c o m p o s i t i o n . S c h u l e r and S t e i g e r (1978) obse r v e d p h e n o c r y s t d i s e q u i l i b r i u m and i n t e r p r e t e d i t as e v i d e n c e o f p r o g r e s s i v e c o n t a m i n a t i o n d u r i n g c r y s t a l l i z a t i o n ( c f . Godwin e t a l . , 104 1980). The c o r e s c r y s t a l l i z e d from a more p r i m i t i v e magma whereas t h e r i m grew d u r i n g o r a f t e r t h e s o l i d i f i c a t i o n of the m a t r i x . Sedimentary r o c k s s u r r o u n d i n g A r s e n i c R idge gave 8 7 S r / 8 6 S r v a l u e s a t 95 Ma o f 0.7266 and 0.7352 ( T a b l e 4.3). Such s e d i m e n t a r y r o c k s , o r upper c r u s t a l e q u i v a l e n t s , c o u l d have p r o v i d e d a 8 7 S r - e n r i c h e d contaminant because they a r e e n r i c h e d i n 8 7 S r r e l a t i v e t o the b a t h o l i t h . A r r i e n s e t al..., (1966) and Brooks (1966) n o t e d i n g r a n i t i c r o c k s open system b e h a v i o r where t h e m i n e r a l phases had a c o n s i s t e n t p a t t e r n of l o s s of r a d i o g e n i c S r from K - f e l d s p a r and g a i n by p l a g i o c l a s e . I s o t o p i c r e d i s t r i b u t i o n o f t h i s t y p e o f r a d i o g e n i c s t r o n t i u m might be r e f l e c t e d i n t h e K - f e l d s p a r megacrysts on A r s e n i c R i d g e . S p e c i f i c a l l y , K - f e l d s p a r c o r e - r i m d a t a i s c o m p a t i b l e w i t h p r e f e r e n t i a l l o s s o f r a d i o g e n i c s t r o n t i u m from t h e r i m s . 105 4.4 PB-PB SYSTEMATICS 4.4.1 I n t r o d u c t i o n The Pb-Pb system was used t o i n v e s t i g a t e : (1) the i s o t o p i c s i g n a t u r e of t h e L o s t Horses b a t h o l i t h , (2) t h e r e l a t i o n s h i p of t h e b a t h o l i t h t o the s u r r o u n d i n g s e d i m e n t s , and (3) i s o t o p i c v a r i a t i o n s among the s y e n i t e , q u a r t z s y e n i t e , g r a n i t e and t o u r m a l i n e o r b i c u l a r g r a n i t e . P o t a s s i u m f e l d s p a r c o r e s and r i m s from a g r a n i t e were a l s o a n a l y z e d t o h e l p d e t e r m i n e the l e a d s o u r c e f o r t h e magma from which t h e y were formed. A j a m e s o n i t e sample from th e Z e t a p r o s p e c t (Low Fog showing) was compared t o g a l e n a b e a r i n g v e i n d e p o s i t s i n the r e g i o n (Tombstone Mountains and Keno H i l l ) , and a l s o t o whole r o c k l e a d r e s u l t s . 4.4.2 Method of A n a l y s i s Samples were p r e p a r e d u s i n g t h e method o u t l i n e d i n Appendix C. Pb i s o t o p i c measurements were made on a Vacuum-G e n e r a t o r s Isomass 54R mass s p e c t r o m e t e r automated w i t h a 106 H e w l e t t - P a c k a r d HP-85 computer. A l l samples were r u n a t the Geochronometry L a b o r a t o r y , The U n i v e r s i t y of B r i t i s h Columbia. Raw d a t a were c o r r e c t e d u s i n g t h e WRPBIC, WRPBID, BLANKSUB, MUCALC and T1C0RR programs l i s t e d i n Appendix E. Two n o n - s p i k e d and two s p i k e d b l a n k s were r u n . W i t h i n - r u n e r r o r was de t e r m i n e d by r e p e a t e d a n a l y s i s of Broken H i l l s t a n d a r d #1. At 1 sigma i t i s about 0.01%. A l l l e a d a n a l y s e s a r e l i s t e d i n T a b l e E . l , Appendix E. Uranium v a l u e s were a n a l y s e d by Acme Geochemical L a b o r a t o r y , Vancouver, B.C u s i n g an ICP mass s p e c t r o m e t e r . 4.4.3 R e s u l t s A t o t a l of 13 whole r o c k s ( i n c l u d i n g s e d i m e n t a r y r o c k s , s y e n i t e s , q u a r t z s y e n i t e s , g r a n i t e s and g r a n i t e d y k e s ) , 3 m i n e r a l s e p a r a t e s ( b i o t i t e , h o r n b l e n d e and t o t a l f e l d s p a r ) , 5 s e t s o f o r t h o c l a s e c o r e s and r i m s , and 1 j a m e s o n i t e sample from A r s e n i c Ridge ( F i g s . 3.1, 3.2) were a n a l y z e d . The r e s u l t s a r e l i s t e d i n T a b l e 4.4. Lead i s o t o p e d a t a a r e p l o t t e d on the 2 ° 7 P b / 2 0 4 P b v e r s u s 20 6pb/20 4pb p i Q t and t h e 107 TABLE (,.(: Lead-isotope analyses f o r sediaents and g r a n i t i c rocks along Arsenic Ridge, Lost Horses b a t h o l i t h , Yukon. Sauple s i t e s are shown on Figure 1.1. BLANK CORRECTED* TIME CORRECTED1 SAMPLE ARLS1 MAT P8206/4 P66/4 P8207/4 P87/4 P8208/4 P8S/4 P8206/4 PB6/4 PB207/4 PB7/4 CODE ARAL ABS*/- ABSt/- ABSt/- ABS»/- A8St/ SA06WR SA HR 19.110 0.000 15.660 0.000 39.001 0.001 19.103 0.001 15.660 0.000 SA06HR SA HR 19.110 0.000 15.660 0.000 39.001 0.001 19.105 0.001 15.660 0.000 SA06NR-AVG [19.110] [0.000] [15.660] [0.000] [39.001] [0.001] [19.104] [0.001] [15.660] [0.000] SALIWR SA tJR 19.532 0.001 15.710 0.000 39.441 0.002 SA11HR SA m 19.475 0.003 15.683 0.000 39.376 0.026 SA11HR-AVG [19.504] [0.002] [15.697] [0.000] [39.409] [.014] SA18WR SA HR 19.183 0.006 15.752 0.001 39.551 0.082 19.129 0.008 15.749 0.001 SftiawR JG HR 19.173 0.001 15.692 0.000 39.219 0.003 19.119 0.006 15.689 0.000 SA18HR-AVG [19.178] [0.0031 [15.722] [0.001) [39.385) [0.043] [19.124] [.007] [15.719] [0.001] SA24HR SA HR 20.240 0.005 15.701 0.001 39.222 0.055 20.054 0.021 15.692 0.001 SA24HR JG KR 20.242 0.001 15.706 0.000 39.212 0.003 20.057 0.020 15.697 0.001 SA24HR-AVS [20.241] [0.003] [15.704] [0.001] [39.217] [0.029] [20.056] [0.021] [15.695] [0.001] SAJ1WR SA MR 19.136 0.002 15.630 0.000 39.080 0.006 SA33HR SA HR 19.155 0.002 15.660 0.000 39.142 0.007 SA33HR-AVG [19.146] [0.002] [15.645] [0.000] [39.111] [0.007] SA3BMR SA HR 19.544 0.001 15.688 0.003 39.340 0.001 SA39HR SA HR 20.493 0.002 15.720 0.019 39.385 0.008 19.081 0.050 15.652 0.020 SA41HR SA HR 19.578 0.001 15.684 0.006 39.380 0.003 19.279 0.011 15.670 0.006 SA42MR SA HR 19.571 0.001 15.685 0.005 39.307 0.002 SA4SHR SA MR 19.667 0.001 15.700 0.000 39.433 0.001 SA45WR SA HR 19.667 0.001 15.700 0.000 39.433 0.001 SA4SHR-AVG [19.667) [0.001] [15.700] [0.000] [39.433) [0.001] SA4BUR SA HR 19.609 0.001 15.693 0.000 39.362 0.002 19.477 0.014 15.687 0.001 SA48HR SA HR 19.609 0.001 15.693 0.000 39.362 0.002 19.510 0.011 15.686 0.000 SA48HR-AVS [19.609] (0.001) [15.693] 0.000 [39.362] (0.002] [19.494] [0.013] [15.683] [0.001] SA50HR SA NR 19.372 0.001 15.708 0.000 39.276 0.002 SA50HR SA HR 19.403 0.001 15.689 0.000 39.253 0.001 SA50HR-AVG [19.388] [0.001] [15.699] 10.000) (39.265) [0.002] SA90MR SA HR 20.240 0.001 15.707 0.008 39.243 0.003 19.982 0.009 15.695 0.008 SA48HB SA H6 20.998 0.001 15.794 0.000 41.750 0.002 20.128 0.060 15.752 0.003 SA4BHB SA H8 21.193 0.001 15.785 0.000 41.879 0.002 20.303 0.061 15.742 0.003 SA4BHB-AVG [21.096] [0.001] [15.790] [0.000] [41.815] [0.002] [20.216) [0.061] [15.747] [0.003] SA48BI SA 81 21.110 0.002 15.760 0.000 40.284 0.014 20.737 0.036 15.742 0.002 SA488I JG 81 21.100 0.001 15.761 0.000 40.256 0.002 20.730 0.036 15.743 0.002 SA48BI-AVS [21.105) [0.0021 (15.761) [0.000] [40.270] [0.08] (20.734) [0.036] [15.743] [0.002] !A31E 4.4 Icc :t itu6d) BLAH* CORRECTED; HUE CORRECTED1 o SAMPLE AMLST MAT P8206/4 P86/4 P8207/4 P87/4 PB20S/4 PB8/4 P8206/4 PB6/4 P8J07/4 PB7/4 CODE ANAL A8S*/- ABSt/- ABSt/- A6S*/- ABS»/ SA4STF SA TF (19.281) (0.001) (15.674) (0.000) (39.098) (0.001) SA468C SA KF 19.153 0.001 15.684 0.002 39.046 0.001 19.135 0.009 15.633 0.002 SA438R SA KF 19.188 0.001 15.673 0.006 39.040 0.003 19.172 0.008 15.672 0.006 SA43CC SA KF 19.241 0.001 15.732 0.001 39.206 0.001 19.134 0.009 15.652 0.001 SA4SCR SA KF (19.152) (0.001) (15.653) (0.000) (33.966) (0.001) SA430C SA KF 19.176 0.001 15.674 0.003 39.022 0.002 19.143 0.002 15.672 0.003 SA4SDR SA KF 19.165 0.000 15.670 0.001 39.042 0.000 19.084 0.005 15.665 0.001 SA48EC SA KF (19.154) (0.00!) (15.644) (0.000) (39.967) (0.002) SA4SER SA KF (19.228) (0:001) (15.680) (0.000) (39.103) (0.001) SA.3FC SA KF (19.194) (0.001) (15.667) (0.000) (33.026) (0.001) SA48FR SA KF (19.177) (0.001) (15.654) (0.000) (38.932) . (0.001) SA48C»R SA KF (19.162) (0.001) (15.675) (0.000) (39.045) (0.001) SA48 CORE AVERAGE (19.184) [15.680) (39.053) SA48 RIM AVERAGE (19.186) (15.660) (39.027) : M a t e r i a l analysed i s as f o l l o w s : KR:Mhole Rock; HB:Hornbiende Separate; 8 I : 8 i o t i t e Separate; T F : I c t a i Feldspar; -.KF:K-Feldspar Core or Rin; C+R-K-Feldspar Core and R i l . ' Blank analyses and program used i n c o r r e c t i o n I8LANKSU8) are i n Appendix E (Tables E . l and E.2). () Denote that analyses were not blank c o r r e c t e d because c o r r e c t i o n s «ere i n s i g n i f i c a n t . ' Data was :i«e c o r r e c t e d to 95 ha using p r o g r a i 11C0RR de s c r i o e d i n Appendix E. oapb/2 0 4 p b v e r s u s 2 0 6 P b / 2 0 4 P b p l o t i n F i g u r e 4.3. Some samples were r e p e a t e d f o r b e t t e r p r e c i s i o n ; r e s u l t s were averaged as noted i n T a b l e 4.4. Samples w i t h t i e l i n e s l i n k t ime c o r r e c t e d r a t i o s w i t h a c t u a l r a t i o s ( F i g . 4.3). A l l l e a d d a t a were c o r r e c t e d u s i n g the K-Ar date of 95 Ma ( b i o t i t e from sample SA48; 94.9 + 3.3 Ma; T a b l e 4.4). 4.4.4 I n t e r p r e t a t i o n F i g u r e 4.3 shows v a r i a t i o n s i n 2 ° 6 P b / 2 0 4 P b from s e d i m e n t a r y r o c k s near t h e s y e n i t e c o n t a c t and i n g r a n i t i c r o c k s and m i n e r a l s e p a r a t e s from the same. Hornblende and b i o t i t e m i n e r a l s e p a r a t e s a r e t h e most r a d i o g e n i c and p o t a s s i u m f e l d s p a r c o r e s and r i m s a r e the l e a s t r a d i o g e n i c . Hornblende and b i o t i t e a p p a r e n t l y have h i g h t h o r i u m c o n t e n t s because t h e y a r e n o t a b l y e n r i c h e d i n 2 0 8 p}0/2 0 4 p}0. An a l t e r e d q u a r t z i t e (SA18) i s e n r i c h e d i n 2 0 7 P b / 2 0 4 P b , but t h e greywacke sample c o n t a i n s on average 1,500 p a r t s p e r m i l l i o n l e a d (Appendix E, T a b l e E . l ) . T h e r e f o r e , t h e s e sediments have p r o b a b l y been m i n e r a l i z e d and a r e not 110 F i g u r e 4.3: 2 0 8 Pb/ 2 0 4 Pb v e r s u s 2 0 6 P b/2 0 4 pt ) a n d 2 0 7 P b / 2 0 4 P b v e r s u s 20 6 Pb/20 4 P b p l o t s of whole r o c k samples, average K - f e l d s p a r c o r e s (n=5), average K - f e l d s p a r r i m s (n=5), h o r n b l e n d e s e p a r a t e (n=l) and b i o t i t e s e p a r a t e ( n = l ; d a t a a r e i n T a b l e 4.4) from the major u n i t s on A r s e n i c R i d g e , Yukon. Symbols a r e as f o l l o w s : A = whole r o c k s : • = K - f e l d s p a r c o r e ; • = K-f e l d s p a r r i m ; + = hornblende s e p a r a t e ; x = b i o t i t e s e p a r a t e ; • = j a m e s o n i t e ; and, BB = B l u e b e l l growth c u r v e ; PC = p e r i c r a t o n i c growth c u r v e . I n i t i a l v a l u e s (open symbols) c a l c u l a t e d f o r an average age of 95 Ma are c o n n e c t e d t o the p r e s e n t v a l u e s ( s o l i d s y m b o l s ) . I l l 3 9 6 | -XI Q. CM \ XI ° - 3 9 . 2 | O O (M 3 9 0 | matt frac'lomotion ma at trodonatiom OOI % 1 8 . 0 1 9 5 2 0 . 0 2 0 6 Pb / 2 0 4 Pb 2 1.0 r e p r e s e n t a t i v e o f the h o s t sediments. T h i s i s s u p p o r t e d f u r t h e r by the s i m i l a r i t y i n l e a d i s o t o p e s between the s e d i m e n t a r y r o c k s and t h e j a m e s o n i t e ( T a b l e s 4.4, 4.5). A l l g r a n i t i c r o c k s and m i n e r a l s e p a r a t e s p l o t below t h e s h a l e c u r v e (Godwin and S i n c l a i r , 1982) and t h e p e r i c r a t o n i c c u r v e ( F i g . 4.3; G o u t i e r , 1986 and Godwin e t a l , . , 1988). They a l s o p l o t above the B l u e b e l l c u r v e (Andrew e t a l . , 1984). The s h a l e and p e r i c r a t o n i c c u r v e s a r e r e f e r e n c e c u r v e s f o r the growth o f l e a d i n upper c o n t i n e n t a l and upper c r u s t a l environments i n t h e Canadian C o r d i l l e r a . The B l u e b e l l c u r v e i s thought t o r e p r e s e n t e v o l u t i o n o f l e a d i n a lower c r u s t a l ( w i t h p o s s i b l y some upper mantle component) environment (Andrew, 1982; Andrew e t a l . , 1984). The g r a n i t i c r o c k s o f A r s e n i c Ridge p l o t between t h e s e c u r v e s i n d i c a t i n g t h e l e a d i s a m i x t u r e from upper c r u s t and lower c r u s t and/or upper mantle s o u r c e s . Because t h e d a t a i s r e l a t i v e l y c l o s e t o the p e r i c r a t o n i c c u r v e , i t s u g g e s t s t h a t the l e a d s o u r c e i s p r e d o m i n a n t l y upper c r u s t a l w i t h a minor l o w e r c r u s t and/or upper mantle l e a d component. P o i n t s i n b i l l i o n y e a r s (Ga) a r e p l o t t e d a l o n g the p e r i c r a t o n i c and B l u e b e l l c u r v e s . A c r u d e age d e t e r m i n a t i o n 113 f o r t h e b a t h o l i t h i s p r o v i d e d by the g r i d o f m i x i n g l i n e s formed by j o i n i n g p o i n t s on the two c u r v e s of l i k e ages. The l e a s t r a d i o g e n i c Pb has a model age of about 100 Ma. P o t a s s i u m - f e l d s p a r megacryst c o r e s and r i m s from a g r a n i t e on A r s e n i c Ridge and s u l p h i d e samples from t h e Z e t a P r o s p e c t , Tombstone Mountains and Keno-Galena H i l l a r e a s , Yukon, a r e p l o t t e d on a 2 0 7 P b / 2 0 4 P b v e r s u s 2 0 6 P b / 2 0 4 P b p l o t , and on a 2 0 « P b / 2 0 4 P b v e r s u s 2 0 6 P b / 2 0 4 P b p l o t ( F i g . 4.4). Lead v a l u e s f o r the K - f e l d s p a r megacryst c o r e s and r i m s a r e almost i d e n t i c a l ( T a b l e 4.4). R a t i o s a r e as f o l l o w s : (1) average c o r e (n = 5) 2 0 6 P b / 2 0 4 P b i s 19.184 and t h e r i m (n = 5) i s 19.186, (2) average c o r e (n = 5) 2 0 7 P b / 2 0 4 P b i s 15.680 and t h e r i m (n = 5) i s 15.660, and (3) average c o r e (n = 5) 2 o a p b / 2 0 4 P b i s 3 9 . 0 5 3 and t h e r i m (n = 5) i s 39.027. The c o r e s c o u l d be s l i g h t l y more r a d i o g e n i c t h a n t h e r i m s . One c o r e sample (SA48CC) appears t o be e n r i c h e d i n 2 0 7 P b / 2 0 4 P b , but t h i s a n a l y s i s more l i k e l y r e f l e c t s a n a l y t i c a l s c a t t e r . A l l K - f e l d s p a r c o r e s and r i m s p l o t below th e p e r i c r a t o n i c c u r v e and above th e B l u e b e l l c u r v e s u g g e s t i n g an upper 114 F i g u r e 4.4: 2 0 8 P b / 2 0 4 P b v e r s u s 2 0 6 P b / 2 0 4 P b and 2 o ? P b / 2 0 4 P b v e r s u s 20 6pb/2 04pb p l o t s o f K-f e l d s p a r c o r e s and r i m s ( d a t a used from Ta b l e 4.4) from a m e g a c r y s t i c g r a n i t e on A r s e n i c R i d g e , Yukon and s u l p h i d e a n a l y s e s ( d a t a from T a b l e 4.5) from Z e t a , Tombstone and Galena H i l l a r e a s , Selwyn B a s i n , Yukon. Symbols used a r e : •= K - f e l d s p a r c o r e ; and O = K - f e l d s p a r r i m ; • = Zeta p r o s p e c t ; • =Keno H i l l ; • =Tombstone a r e a ; • = average K - f e l d s p a r c o r e ; 9 = average K - f e l d s p a r r i m ; and, PC = P e r i c r a t o n i c growth c u r v e . M i x i n g l i n e s t i e d t o B l u e b e l l Curve (not shown). 115 116 c r u s t a l l e a d s o u r c e w i t h a s m a l l lower c r u s t and/or mantle component. S y e n i t e Range ( F i g . 2.1) i s g e o g r a p h i c a l l y c l o s e t o t h e Tombstone and Keno-Galena H i l l a r e a s , 75 km t o t h e n o r t h -n o r t h w e s t and 80 km t o t h e e a s t - n o r t h e a s t , r e s p e c t i v e l y . Lead i s o t o p e a n a l y s e s on g a l e n a from t h e s e a r e a s and a j a m e s o n i t e sample from t h e Z e t a p r o s p e c t (Low Fog showing, F i g . 3.2) a r e l i s t e d i n T a b l e 4.5 and p l o t t e d on F i g u r e 4.4. The j a m e s o n i t e and g a l e n a samples o v e r l a p o r p l o t w i t h i n t h e same f i e l d . The average Tombstone Mountain d a t a i s s l i g h t l y more r a d i o g e n i c than t h a t o f the Zeta and t h e Keno - Galena H i l l a r e a s . The s u l p h i d e d a t a are c o n s i s t a n t w i t h the K-f e l d s p a r d a t a , i n t h a t t h e y p l o t below the p e r i c r a t o n i c c u r v e and above the B l u e b e l l c u r v e . T h i s a l s o s u p p o r t s an upper c r u s t a l l e a d s o u r c e w i t h a s m a l l . l o w e r c r u s t and/or mantle component. Lead i s o t o p e d a t a from the s u l p h i d e and t h e c o r e s and r i m s o f the K - f e l d s p a r megacrysts o v e r l a p ( F i g . 4.4). I t appears t h a t t h e s o u r c e o f l e a d f o r t h e Keno H i l l and Tombstone d e p o s i t s i s t h e s u r r o u n d i n g p l u t o n s and not t h e 117 TABIE I . S . Lead i s o t o p e a n a l y s e s on s u l p h i d e f r o i Z e t a , Tombstone and G a l e n a H i l l a r e a s , Selwyn B a s i n , Yukon T e r r i t o r y . Data a r e f r o m G o d v i n , G a b i t e s and Andrew (1988) and Godwin, S i n c l a i r and Eyan { 1 9 8 2 ) . S a s p l e No. D e p o s i t Nate Lat» North Long" Nest Win. 2 0 S p b / 2 H p D 20)p(,/2O(pb 20IJ>b/J0«pb UI1) .ERQSPECT SA-JAH 2et a P r o s p e c t 63.96 137 33 JA 19 132 15.664 39.027 TOMBSTONE AREA 10071-001 S p o t t e d lam 64.37 13B 70 GL 19 217 15.5B2 39.064 10076-001 Tonbstone 1 (Grave) 64.40 138 69 GL 19 330 15.701 39.253 10076-002 T o i b s t o n e II ( S u b t r a c t ) 64.40 138 66 GL 19 056 15.667 38.913 10076-003 T o i b s t o n e I I I (Robert S e r v i c e ) 64.39 138 64 GL 19 484 15.707 39.599 AVERAGE (K:<) Gl 19 272 15.689 39.207 STANDARD DEVIATION (N:4) 0 180 0.018 0.296 KENO - GALENA HILL AREAS 10086-AVG1 H e c t o r - C a l u i e t (n=2) 63.92 135 39 GL 19 117 15.678 39.077 10086-AVG2 E l s a ( n:J) 63.91 135 46 GL 19 146 15.662 39.155 10086-AVG3 S i l v e r King (n;3) 63.90 135 57 Gl 19 154 15.673 39.323 10086-006 Paddy 63.9A 135 AA GL 19 039 15.706 3B.973 10086-009 Ruby 63.91 135 43 GL 19 112 15.649 38.997 10086-011 Berai n g h a a P i t 63.91 135 43 GL 19 133 15.713 39.368 10086-AV64 Husky (n:4) 63.92 135 48 GL 19 134 15.647 39.150 10086-AVG5 Keno (n:3) 63.94 135 94 GL 19 170 15.665 39.223 10086-018 Stone 63.96 135 23 GL 19 180 15.656 39.253 10086-019 la d u e 63.96 135 28 GL 19 321 15.676 39.373 10086-020 Shaarock 63.94 135 24 GL 19 235 15.685 39.454 AVERAGE ( K : l l ) GL 19 158 15.674 39.203 STANDARD DEVIATION ( I C U ) 0 072 0.021 0.144 s h a l e s . I f the s h a l e s were the s o u r c e f o r t h e l e a d then t h e g a l e n a a n a l y s e s would p l o t on or v e r y c l o s e t o t h e p e r i c r a t o n i c c u r v e . The age of m i n e r a l i z a t i o n i n the Keno H i l l - G a l e n a H i l l a r e a i s about 100 Ma based on K-Ar d a t i n g of m u s c o v i t e by S i n c l a i r e t a l . (1980) and Lynch (1989). Both S i n c l a i r e t a l , (1980) and Lynch (1989a, 1989b) i n d i c a t e d t h a t v e i n m i n e r a l i z a t i o n i s r e l a t e d t o a c i r c u l a t i n g h y d r o t h e r m a l system d r i v e n by t h e r m a l energy from g r a n i t i c i n t r u s i o n s . A l t h o u g h t h e i r d a t a d e f i n e t h e age o f m i n e r a l i z a t i o n t o be c o i n c i d e n t w i t h age of t h e i n t r u s i o n s , t h e y do not c o n s t r a i n t h e s o u r c e o f the l e a d - - i t c o u l d be from t h e s u r r o u n d i n g s e d i m e n t a r y r o c k s and/or t h e i n t r u s i v e s t h e m s e l v e s . Lynch (1989a, 1989b) f a v o u r s an o r i g i n d i r e c t l y from s u r r o u n d i n g Keno H i l l q u a r t z i t e . He d e t e r m i n e d t h a t t h e m i n e r a l o g i c a l zones a r e s p a t i a l l y r e l a t e d t o t h e Mayo Lake p l u t o n , but t h a t the h y d r o t h e r m a l v e i n s b e g i n o u t s i d e b o t h t h e p l u t o n and i t s c o n t a c t metamorphic a u r e o l e . As a r e s u l t , t h e p l u t o n remains p r e d o m i n a n t l y u n a l t e r e d and no m a t e r i a l i n p u t from t h e p l u t o n t o t h e v e i n system i s a p p a r e n t . T h i s work, 119 however, i d e n t i f i e s t he p l u t o n s as t h e major s o u r c e f o r the l e a d m i n e r a l i z a t i o n . 4.5. SM-ND SYSTEMATICS 4.5.1 I n t r o d u c t i o n Sm-Nd a n a l y s e s p r o v i d e an i s o t o p i c s i g n a t u r e f o r t h e g r a n i t e o f the L o s t Horses b a t h o l i t h and t h e c o r e s and r i m s of i t s K - f e l d s p a r m e g a c r y s t s . These p r o v i d e a d d i t i o n a l i n f o r m a t i o n on the so u r c e of t h e magma. 4.5.2 Method of A n a l y s i s Samples were p r e p a r e d u s i n g t h e methods o u t l i n e d i n Appendix C, f o l l o w e d by a d d i t i o n a l a n a l y s e s as o u t l i n e d i n Appendix D. Sm and Nd i s o t o p i c measurements were made on a Vacuum G e n e r a t o r s Isomass 54R mass s p e c t r o m e t e r automated w i t h a H e w l e t t - P a c k a r d HP-85 computer. A l l samples were r u n i n the Geochronometry L a b o r a t o r y a t The U n i v e r s i t y o f 120 B r i t i s h Columbia. I n i t i a l c h e m i s t r y was unde r t a k e n by the a u t h o r ; f i n a l s t e p s and mass s p e c t r o m e t r y were completed by D. Ru n k l e , A. Andrew and R.L. Armstrong. 4.5.3 R e s u l t s One g r a n i t e whole r o c k , and f o u r p a i r s of p o t a s s i u m f e l d s p a r c o r e s and r i m s from t h e same g r a n i t e on A r s e n i c Ridge ( F i g s . 3.1, 3.2), were a n a l y z e d . The r e s u l t s a r e l i s t e d i n Ta b l e 4.6. 1 4 3 N d / 1 4 4 N d r a t i o s f o r t h e g r a n i t e and the average o r t h o c l a s e c o r e s and r i m s show l i t t l e v a r i a t i o n ; a l l a r e v e r y c l o s e t o 0.51210. 4.5.4 I n t e r p r e t a t i o n DePaolo and Wasserburg (1976a) i n t r o d u c e d t h e " e p s i l o n parameter", which e x p r e s s e s t h e d i f f e r e n c e between t h e i n i t i a l 1 4 3 N d / 1 4 4 N d r a t i o of a s u i t e of r o c k s and t h e c o r r e s p o n d i n g v a l u e o f t h i s r a t i o i n CHUR a t the time of c r y s t a l l i z a t i o n o f t h e r o c k s . (CHUR sta n d s f o r " c h o n d r i t i c 121 TAEL5 (.6: J.rsemc Ridge neodyaiuu and sa s a r i u a isotope data for a g r a t u t a and K-csidspar core and r i i s f r o : , Lost Horses b a t h o l i t h , Yu'tcn. S a i p l e l o c a t i o n s are shown u Figure 3.1. SAMPLE NUMBER ROCK DESCRIPTION S i pp« S i PCI ljT Error Nd ppi Nd ppa I j r E r r o r >«'S«/'"Nd ' « > S i / " 4 N d l J T E r r o r '«N.d/'"Nd >«Nd/'«''«d I j r E r r o r I n i t i a l ($95 Ha) >«Nd/'««Nd SA48WR Granite 7.92 0.003 48.05 0.090 0.0996 0.0002 0.51210 0.000025 0.51204 SA48C Core K-feldspar 0.846 0.0003 5.48 0.003 0.0932 0.0001 0.51204 0.000014 0.51198 SA48C Rio K-feldspar 0.734 0.0004 5.38 0.010 0.0824 0.0001 0.51203 0.000027 0.51198 SA48D Core K-feldspar 0.529 0.0002 3.64 0.004 0.0879 0.0001 0.51206 0.00001? 0.51201 SA48D R i l K-feldspar 0.981 0.001 5.73 0.003 0.1035 0.0001 0.51193 0.000029 0.51187 SA488SE Core ( c o i p o s i t e ) SA488SE R i ( ( c o i o o s i t e ) 0.51213 0.51215 0.00009 0.00007 Average (Weighted) K-feldspar Core Average (Weighted) K-feldspar Rin 0.51205 0.51200 0.00001 0.00002 u n i f o r m r e s e r v o i r " and t h i s model assumes t h a t t e r r e s t r i a l Nd has e v o l v e d i n a u n i f o r m r e s e r v o i r whose Sm/Nd r a t i o i s eq u a l t o t h a t of c h o n d r i t i c m e t e o r i t e s . ) The i n i t i a l e p s i l o n v a l u e f o r t h e g r a n i t e from A r s e n i c Ridge i s -10.49. A n e g a t i v e e p s i l o n v a l u e i n d i c a t e s t h a t the r o c k s were d e r i v e d from s o u r c e s t h a t had a lower Sm/Nd r a t i o than t h e c h o n d r i t i c r e s e r v o i r ( F a u r e , 1986). T h i s a l s o means t h a t such r o c k s were d e r i v e d from, o r a s s i m i l a t e d , o l d c r u s t a l r o c k s whose Sm/Nd had been lo w e r e d a t the time of s e p a r a t i o n from CHUR. TDM ( d e p l e t e d m antle) ages p r o v i d e a s e l f - c o n s i s t e n t , e m p i r i c a l model f o r e v a l u a t i n g t h e f o r m a t i o n t i m e s of c o n t i n e n t a l c r u s t (DePaolo, 1981a, DePaolo, 1981b, Farmer and DePaolo, 1983). The model Sm-Nd age TDM r e p r e s e n t s the tim e when a r o c k sample would have had t h e same v a l u e of eHd as t h e d e p l e t e d upper mantle. The ewa of t h e model d e p l e t e d namtle i s g i v e n by: S H d D M ( T ) = 0.25T 2 - 3T + 8.5 (5) where T i s i n AE ( 1 0 9 y r s . ) . The e M d of a r o c k sample a t a time T i n t h e p a s t i s g i v e n by: 123 e H d R O C K ( T ) = € H d R O C K ( 0 ) - f S m / H d Q N d T (6) where e N d ( O ) i s the measured v a l u e , C j N d = 25-1 A E - i , and f s B i / K d i s t h e Sm/Nd enrichment f a c t o r , d e f i n e d as: f s m / H d = ( 1* 7Sm/ 1**NdRocK/0.1967) - 1 (7) The TDM model age i s o b t a i n e d by e q u a t i n g (5) and ( 6 ) , t h a t i s , s o l v i n g f o r T t o s a t i s f y : e N d R O C K ( T ) _ € H d D M ( T ) (8) The model Sm-Nd age TDM f o r a g r a n i t e (SA48; T a b l e 4.6) from A r s e n i c Ridge i s 1.26 b i l l i o n y e a r s . T h i s d a t a has g e o l o g i c a l s i g n i f i c a n c e o n l y when t h e Sm/Nd r a t i o of the da t e d r o c k d i d not change s i n c e t h e time of s e p a r a t i o n of Nd from the c h o n d r i t e r e s e r v o i r . T h i s c o n d i t i o n i s s a t i s f i e d b e t t e r by Sm and Nd than by Rb and S r (see s e c t i o n 4.3.4). T h i s i s because the ge o c h e m i c a l p r o p e r t i e s of t h e r a r e e a r t h s a r e much more s i m i l a r than th o s e o f t h e a l k a l i m e t a l s and t h e a l k a l i n e e a r t h s . However, t h e age o f the so u r c e i s c l o s e r t o 2.2 Ga (Erdmer and Baadsgaard, 1987). Thus, t h e model age f o r TDM i s not a p p r o p r i a t e , and t h e so u r c e f o r t h e g r a n i t i c r o c k s does n o t appear t o be d e p l e t e d mantle. 124 Approximate p e r c e n t a g e s o f c o n t i n e n t a l c r u s t and mantle m a t e r i a l i n c o r p o r a t e d i n t o t he mel t can be c a l c u l a t e d f o r the r o c k s a l o n g A r s e n i c Ridge ( a t 95 Ma) by u s i n g e s d R 0 C K , e n d D M , and ewd c c v a l u e s . A t 95 Ma t h e e i i d R 0 C K = -9.32 and the € N d D H = +8.22. The v a l u e s of upper and lower c o n t i n e n t a l c r u s t were c a l c u l a t e d u s i n g t h e f o l l o w i n g : 1 4 7Sm/ 1 4*NdRocK = 0.115 f o r upper c r u s t ; 1 4 7 Sm/ 1 4 4NdaocK = 0.15 f o r lower c r u s t , and t h e c o n t i n e n t a l c r u s t age i s 2 Ga. The € N d v a l u e f o r upper c r u s t i s -16.61 and t h e v a l u e f o r lower c r u s t i s -7.86. I f t h e upper c r u s t i s the sour c e of c o n t a m i n a t i o n , then t h e r e i s a maximum of 30% mantle i n c o r p o r a t e d i n t h e mel t a t t h e time o f f o r m a t i o n . I f t h e lower c r u s t i s the s o u r c e o f t h e c o n t a m i n a t i o n t h e r e i s no mantle component. The 1 4 7 S m / 1 4 4 N d r a t i o f o r t h e g r a n i t e from A r s e n i c Ridge i s 0.0966 ( T a b l e 4.6). T h i s i s v e r y c l o s e t o t h e average c o n t i n e n t a l c r u s t v a l u e o f 0.100 f o r t h e g r a n i t i c r o c k s . Neodymium and s t r o n t i u m i n i t a l r a t i o s . a n d e p s i l o n v a l u e s a r e p l o t t e d and d i s c u s s e d i n s e c t i o n 4.6. 125 CHAPTER 5 CONCLUSIONS 5.1 GEOLOGIC SETTING OF ARSENIC RIDGE A r s e n i c Ridge i n t h e n o r t h w e s t e r n p a r t of the S y e n i t e Range l i e s w i t h i n the Omineca C r y s t a l l i n e B e l t of the Canadian C o r d i l l e r a . N o r t h American m i o g e o c l i n a l r o c k s o f the upper P r e c a m b r i a n t o Lower Cambrian G r i t U n i t were n o r t h w a r d l y t h r u s t onto O r d o v i c i a n t o S i l u r i a n Road R i v e r F o r m a t i o n d u r i n g t h e L a t e T r i a s s i c t o E a r l y J u r a s s i c a r c -c o n t i n e n t c o l l i s i o n ( B o s t o c k , 1947 and 1964; Templeman-K l u i t , 1979; E i s b a c h e r , 1981; Monger e t a l . , 1982; F r i t z e t a l . , 1983). S m a l l e p i z o n a l f e l s i c i n t r u s i o n s o f mid-Cretaceous age (83 t o 108 Ma; b i o t i t e , K-Ar, Stevens e t a l , , 1982) were emplaced i n the metasedimentary r o c k s o f t h e Omineca C r y s t a l l i n e B e l t . These metasedimentary r o c k s r e p r e s e n t t h e a n c i e n t c o n t i n e n t a l margin. T h i s margin, a p e r i c r a t o n i c s e d i m e n t a r y p r i s m , has d e f i n i t e upper c r u s t a l c h a r a c t e r i s t i c s . Igneous r o c k s from t h e e a s t e r n Yukon have h i g h i n i t i a l Sr ( g e n e r a l l y o v er 0.71; Kuran, 1982; S i n c l a i r e t a l . , 1986) r e f l e c t i n g the a d d i t i o n o f r a d i o g e n i c Sr from 126 t h e P r e c a m b r i a n c r u s t . F i e l d r e l a t i o n s and r e g i o n a l geology show t h a t t h e p l u t o n s were emplaced a t a h i g h l e v e l i n Pr e c a m b r i a n t o P a l e o z o i c s i a l i c c r u s t a l r o c k s i n a m o s t l y p o s t - k i n e m a t i c t e c t o n i c s e t t i n g a f t e r a p e r i o d of major d e f o r m a t i o n r e l a t e d t o a r c - c o n t e n e n t a l c o l l i s i o n (Emond, 1989). The mid-Cretaceous ( s y e n i t e phase, 87+3 Ma, K-Ar, b i o t i t e , C h r i s t o p h e r , 1973; g r a n i t e phase, 95+3 Ma, K-Ar, b i o t i t e , t h i s s t u d y ) L o s t Horses b a t h o l i t h i s a c i r c u l a r , S-t y p e , composite p l u t o n w i t h i n the Selwyn B a s i n of Yukon. S-typ e p l u t o n s a r e a p r o d u c t o f Hercynotype a r c - c o n t i n e n t a l c o l l i s i o n a l t e c t o n i c s ( P i t c h e r , 1982). The Selwyn B a s i n i s an e p i c o n t i n e n t a l t r o u g h p a r t i a l l y bounded on t h e west by the C a s s i a r P l a t f o r m and on t h e e a s t and n o r t h e a s t by c a r b o n a t e r o c k s of t h e Mackenzie P l a t f o r m . Weakly metamorphosed l a t e P r e c a m b r i a n t o T r i a s s i c m i o g e o c l i n a l s h a l l o w water l i m e s t o n e , d o l o s t o n e and sandstone a re c h a r a c t e r i s t i c on t h e e a s t ; t u r b i d i t i c s a n d s t one, deep water l i m e s t o n e , s h a l e and c h e r t predominate i n t h e west. The L a t e C r e t a c e o u s T i n t i n a F a u l t , p a r a l l e l s t h e s o u t h w e s t e r n margin o f Selwyn B a s i n . The L o s t Horses b a t h o l i t h , 127 a p p r o x i m a t e l y 30 km n o r t h e a s t of t h e T i n t i n a F a u l t o c c u r s near the n o r t h w e s t e r n edge of the Selwyn B a s i n . 5.2 THE GRANITIC UNITS The g r a n i t i c r o c k s a l o n g A r s e n i c R i d g e , from t h e r i m t o t h e c o r e , have been c l a s s i f i e d f o l l o w i n g S t r e c k e i s e n (1975) as s y e n i t e , q u a r t z s y e n i t e , g r a n i t e and t o u r m a l i n e o r b i c u l e g r a n i t e . Major elements ( A I 2 O 3, FeO, MgO, CaO, T i 0 2 , MnO and P 2 O 5) d e c r e a s e as S i 0 2 i n c r e a s e s from the s y e n i t e r i m t o t o u r m a l i n e o r b i c u l a r g r a n i t e c o r e . K2O remains a p p r o x i m a t e l y c o n s t a n t and Na2 0 d e c r e a s e s s l i g h t l y . T r a c e element v a r i a t i o n s w i t h i n c r e a s i n g S i 0 2 i s c h a r a c t e r i z e d by i n t e n s e d e p l e t i o n s ( Z r , V, S r , N i and Ba) and by l e s s i n t e n s e e n r i c h m e n t s (Rb). Y and Nb d e c r e a s e o n l y s l i g h t l y ; v a r i a t i o n i n minor Cr c o n t e n t i s e r r a t i c . The s y e n i t e s a r e a l k a l i n e whereas th e q u a r t z s y e n i t e s , g r a n i t e s , g r a n i t e dykes and t o u r m a l i n e p a t c h g r a n i t e s a r e s u b - a l k a l i n e . The e s t i m a t e d p a r t i a l p r e s s u r e of water d u r i n g t h e f o r m a t i o n of L o s t Horses g r a n i t e m e l t s i s b r o a d l y e s t i m a t e d as 10 k b a r s . 128 P r o g r e s s i v e magmatic d i f f e r e n t i a t i o n o f t h e p l u t o n r i m t o c o r e i s demonstrated by a d e c r e a s i n g t r e n d i n (Na2 0 + K2O) and t i t a n i a w i t h i n c r e a s i n g s i l i c a , and i n c r e a s i n g Rb w i t h a d e c r e a s e i n Ba and S r . Two groups a r e apparent: (1) s y e n i t e , q u a r t z s y e n i t e and g r a n i t e . (NazO + K2O) and t i t a n i a v a l u e s a r e the g r e a t e s t i n t h e s y e n i t e ( r i m ) and p r o g r e s s i v e l y d e c r e a s e t h r o u g h the q u a r t z s y e n i t e t o t h e g r a n i t e ( c o r e ) w i t h i n c r e a s i n g s i l i c a . Ba i s h i g h , Sr i s c o n s t a n t and Rb i s h i g h i n t h i s group. (2) t o u r m a l i n e o r b i c u l a r g r a n i t e and t h e g r a n i t e d i k e . These r o c k s c o n t a i n low (NazO + K2O) and t i t a n i a v a l u e s . Rb i s h i g h , Sr i s c o n s t a n t and Ba has d e c r e a s e d . E l e v a t e d Rb v a l u e s , r e l a t i v e t o group 1, ar e s i g n i f i c a n t because d u r i n g f r a c t i o n a l c r y s t a l l i z a t i o n Ba and Sr d e c r e a s e w h i l e Rb i n c r e a s e s i n t h e r e s i d u a l f l u i d . T h e r e f o r e , i t appears t h a t group 1 ( s y e n i t e , q u a r t z s y e n i t e and g r a n i t e ) d i f f e r e n t i a t e d from the magma e a r l i e r and 129 s e p a r a t e l y from group 2 ( t o u r m a l i n e o r b i c u l a r g r a n i t e and the g r a n i t e d i k e ) . T race element d a t a f o r the s y e n i t e , q u a r t z s y e n i t e and g r a n i t e whole r o c k s a l o n g A r s e n i c Ridge were examined t o d e t e r m i n e c o n s e r v e d elements. Y v a l u e s a r e r e l a t i v e l y c o n s t a n t from b a t h o l i t h c o r e t o r i m and a l l t r a c e element d a t a was r a t i o e d t o t h i s element. Conserved elements, however, were not u n e q u i v i c a l l y i d e n t i f i e d and Pearce element p l o t s were not pursued f u r t h e r . However, Rb/Y r a t i o s , appear t o s y s t e m a t i c a l l y i n c r e a s e from b a t h o l i t h r i m towards the c o r e . K2 0/Si02 r a t i o s i n c r e a s e from r i m t o c o r e r e f l e c t i n g a change from s y e n i t e t o g r a n i t e , and i n c r e a s i n g abundances of K - f e l d s p a r m e gacrysts. E l e c t r o n m i c r o p r o b e t r a v e r s e s a c r o s s o r t h o c l a s e m egacrysts from c o r e t o r i m i d e n t i f i e d : (1) a c o n c e n t r a t i o n of a l b i t e l a m e l l a e i n t h e r i m s , and (2) barium, s t r o n t i u m and c a l c i u m r i c h c o r e s . The l a t t e r i n d i c a t e a melt p r o g r e s s i v e l y d e p l e t e d i n barium ( M i c h a e l s , 1986). 130 5.3 DATING A ho r n b l e n d e s e p a r a t e and a b i o t i t e s e p a r a t e were a n a l y z e d by the K-Ar method of d a t i n g and r e t u r n e d d a t e s of 88+4 Ma and 95+3 Ma, r e s p e c t i v e l y . A Rb-Sr i s o c h r o n composed o f a whole r o c k , b i o t i t e s e p a r a t e , h o r nblende s e p a r a t e , and a t o t a l f e l d s p a r s e p a r a t e y i e l d e d a l a t e E a r l y C r e t a c e o u s date of 101+6 Ma. I n i t i a l S r r a t i o s f o r t h e sed i m e n t s , s y e n i t e s , q u a r t z s y e n i t e s , g r a n i t e s , t o u r m a l i n e o r b i c u l a r g r a n i t e , g r a n i t e dykes, m i n e r a l s e p a r a t e s and K-f e l d s p a r c o r e s and r i m s a r e a l l above 0.711. T h i s s u g g e s t s t h a t s t r o n t i u m was d e r i v e d m a i n l y from m e l t i n g and/or a s s i m i l a t i o n o f o l d s i a l i c c r u s t d u r i n g magma g e n e s i s . The s y e n i t e , q u a r t z s y e n i t e and g r a n i t e a l o n g A r s e n i c R i dge c o n t a i n zoned ( p i n k c o r e and gray r i m ) o r t h o c l a s e m e g acrysts. An i s o c h r o n f o r the K - f e l d s p a r c o r e s (n = 5) and r i m s (n = 5) g i v e s a 72 Ma d a t e . The K - f e l d s p a r c o r e s a r e not i n e q u i l i b r i u m w i t h the K - f e l d s p a r r i m s and the whole r o c k . The K - f e l d s p a r r i m s , t o t a l f e l d s p a r s e p a r a t e and t h e g r a n i t e whole r o c k p l o t t o t h e l e f t o f and above t h e SA48 i s o c h r o n . The K - f e l d s p a r c o r e s p l o t t o t h e l e f t of t h e 131 i s o c h r o n ( F i g . 4.2). The f o l l o w i n g d e f i n e t h e c o r e - r i m d a t a : (1) The K - f e l d s p a r c o r e s a r e not i n e q u i l i b r i u m w i t h t h e whole r o c k d e f i n e d by the w h o l e - r o c k m i n e r a l i s o c h r o n . (2) The K - f e l d s p a r r i m s approximate e q u i l i b r i u m w i t h the whole r o c k s as d e f i n e by the w h o l e - r o c k m i n e r a l i s o c h r o n . (3) The K - f e l d s p a r c o r e s by geometry a r e o l d e r than the r i m . I f the i n i t i a l r a t i o of t h e w h o l e - r o c k m i n e r a l i s o c h r o n (0.7114) i s used t o d e t e r m i n e t h e apparent age of an i s o c h r o n though the c l u s t e r o f c o r e a n a l y s e s , t h e c o r e i s about 6 Ma o l d e r t h a n t h e r i m . (4) I n i t i a l r a t i o o f t h e K - f e l d s p a r c o r e i s 0.7119 ( T a b l e 4.3), i f t h e age of t h e c o r e i s assumed t o be e q u i v a l e n t t o t h e age of t h e o v e r a l l r o c k , namely 95 Ma. (5) I n i t i a l r a t i o s o f t h e K - f e l d s p a r r i m s i s 0.7116 (T a b l e 4.3), assuming an age o f 9 5 Ma. T h i s i s 132 s l i g h t l y h i g h e r t h a n the w h o l e - r o c k m i n e r a l i s o c h r o n i n i t i a l r a t i o of 0.7114. The K - f e l d s p a r megacrysts grew i n a m e l t of c h a n g i n g c o m p o s i t i o n . S c h u l e r and S t e i g e r (1978) o b s e r v e d p h e n o c r y s t d i s e q u i l i b r i u m and i n t e r p r e t e d i t as e v i d e n c e of p r o g r e s s i v e c o n t a m i n a t i o n d u r i n g c r y s t a l l i z a t i o n . Sedimentary r o c k s s u r r o u n d i n g A r s e n i c R idge c o u l d have p r o v i d e d a 8 7 S r -e n r i c h e d contaminant because they a r e e n r i c h e d i n 8 7 S r r e l a t i v e t o the b a t h o l i t h . A r r i e n s e t a l . , (1966) n o t e d i n g r a n i t i c r o c k s open system b e h a v i o r where t h e m i n e r a l phases had a c o n s i s t e n t p a t t e r n o f l o s s o f r a d i o g e n i c S r from K-f e l d s p a r and g a i n by p l a g i o c l a s e . I s o t o p i c r e d i s t r i b u t i o n of t h i s t y pe of r a d i o g e n i c s t r o n t i u m might be r e f l e c t e d i n the K - f e l d s p a r megacrysts on A r s e n i c R i dge. S p e c i f i c a l l y , K - f e l d s p a r c o r e - r i m d a t a i s c o m p a t i b l e w i t h p r e f e r e n t i a l l o s s o f r a d i o g e n i c s t r o n t i u m from t h e r i m s . The model Rb-Sr age, TOR, f o r t h e g r a n i t e on A r s e n i c Ridge i s 238 Ma. T h i s d a t e i n d i c a t e s t h a t a d o m i n a n t l y upper mantle s o u r c e i s u n l i k e l y . 133 Pb from the g r a n i t i c r o c k s on A r s e n i c Ridge ( T a b l e 4.4, F i g . 4.3) p l o t s below t h e p e r i c r a t o n i c c u r v e and above the B l u e b e l l c u r v e (Andrews e t a l . , 1984). M i x i n g l i n e s from th e p e r i c r a t o n i c and B l u e b e l l c u r v e s do not t i g h t l y c o n s t r a i n the age o f t h e L o s t Horses b a t h o l i t h o r s u l p h i d e s , but a r e c o m p a t i b l e w i t h t h e i r M esozoic age. Nd-Sm a n a l y s e s of a g r a n i t e and f o u r p a i r s of o r t h o c l a s e c o r e s and r i m s i n d i c a t e t h a t t h e g r a n i t e was d e r i v e d from, o r a s s i m i l a t e d , o l d c r u s t a l r o c k s whose Sm/Nd had been lowered a t t h e time o f s e p a r a t i o n o f t h e magma. P r e s e n t day 1 4 3 N d / * 4 4 N d and 8 7 S r / 8 6 S r r a t i o s of the g r a n i t e r o c k whole r o c k from A r s e n i c Ridge a r e s i m i l a r t o t h e S i e r r a Nevada b a t h o l i t h s and p l o t low i n the P h a n e r o z o i c f i e l d as d e f i n e d by Faure (1986). 5.4 ORIGIN OF GRANITIC ROCKS The g r a n i t i c r o c k s a l o n g A r s e n i c Ridge--as de t e r m i n e d by Rb-Sr, Pb-Pb and Sm-Nd r a d i o g e n i c i s o t o p e a n a l y s e s - - a r e thought t o have o r i g i n a t e d from c o n t i n e n t a l c r u s t as a r e s u l t of Hercynotype a r c - c o n t i n e n t c o l l i s i o n t e c t o n i c s . 134 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 s f o r g r a n i t i c r o c k s from A r s e n i c Ridge range from 0.7112 t o 0.71363 (T a b l e 4.3) i n d i c a t i n g t h e i r s o u r c e magmas c o n t a i n e d s i g n i f i c a n t p o r t i o n s of o l d s i a l i c m a t e r i a l . T h i s f o l l o w s Armstrong e t a l , (1977) and Faure and P o w e l l (1972). They c o n c l u d e d t h a t i n i t i a l r a t i o s g r e a t e r t h a n 0.706 r e p r e s e n t m e l t i n g and/or a s s i m i l a t i o n d u r i n g magma g e n e s i s o f o l d s i a l i c c r u s t . Lead i s o t o p e d a t a ( T a b l e 4.4; F i g . 4.3) p l o t s between the p e r i c r a t o n i c c u r v e , a c u r v e f o r t h e growth o f l e a d i n upper c r u s t a l environments i n the Canadian C o r d i l l e r a , and the B l u e b e l l c u r v e , which r e p r e s e n t s t h e e v o l u t i o n o f l e a d i n a lower c r u s t a l o r upper mantle environment of t h e Canadian C o r d i l l e r a (Godwin and S i n c l a i r , 1982; Andrew e t a l . , 1984). M e g a c r y s t i c K - f e l d s p a r c o r e and r i m a n a l y s e s a r e i n d i s t i n g u i s h a b l e from each o t h e r , and a l s o i n d i c a t e t h i s l e a d s o u r c e . Lead s u l p h i d e a n a l y s e s from t h e Zeta P r o s p e c t , Tombstone Range and t h e Keno-Galena H i l l a r e a s a r e i n d i s t i n g u i s h a b l e from the f e l d s p a r l e a d o f t h e g r a n i t e on A r s e n i c R i d g e . T h i s s t r o n g l y s u g g e s t s t h a t t h e l e a d s o u r c e f o r t h e s e v e i n s a r e the p l u t o n s and not t h e i n t r u d e d s e d i m e n t a r y r o c k s . A l l d a t a f o r s u l p h i d e and K - f e l d s p a r a r e 135 c l o s e r t o the p e r i c r a t o n i c c u r v e than t h e B l u e b e l l c u r v e . T h e r e f o r e the magma t h a t formed the b a t h o l i t h p r o b a b l y was ge n e r a t e d i n an upper c r u s t a l environment w i t h a minor lower c r u s t and/or mantle component. Nd i s o t o p e s i n d i c a t e t h a t the g r a n i t i c r o c k s were d e r i v e d from, o r a s s i m i l a t e d o l d c r u s t a l r o c k s whose i n i t i a l Sm/Nd r a t i o had been lo w e r e d a t t h e time of s e p a r a t i o n . The model Sm-Nd age TDM, r e p r e s e n t i n g t h e time when a r o c k sample would have had t h e same v a l u e o f SN<I as t h e d e p l e t e d upper mantle, f o r a g r a n i t e (SA48) from A r s e n i c Ridge i s 1.26 Ga. T h i s i s younger than t h e p r o b a b l e 2.2 Ga age of the s o u r c e and i n d i c a t e s a more complex model f o r i t s o r i g i n . Approximate p e r c e n t a g e s o f c o n t i n e n t a l c r u s t and mantle i n c o r p o r a t e d i n the mel t were c a l c u l a t e d f o r the g r a n i t e a l o n g A r s e n i c Ridge. A s o u r c e age o f 2.0 Ga was used (cf.... Erdmer and Baadsgaard, 1987). I f t h e s o u r c e o f the c o n t a m i n a t i o n i s the upper c r u s t , t h e n t h e r e was a maximum o f 30% mantle i n c o r p o r a t e d i n t h e m e l t . I f the lower c r u s t i s t he s o u r c e o f c o n t a m i n a t i o n no mantle component i s needed. However, because the g r a n i t e 1 4 7 S m / 1 4 4 N d r a t i o i s 136 v e r y c l o s e t o the average c o n t i n e n t a l c r u s t r a t i o , t h e o r i g i n appears t o be upper c r u s t a l w i t h a s m a l l mantle component. P r e s e n t day 1 4 3 N d / 1 4 4 N d and 8 7 S r / 8 6 S r r a t i o s o f g r a n i t i c r o c k s of P h a n e r o z o i c and Pr e c a m b r i a n age s c a t t e r w i d e l y i n F i g u r e 5.1, but a r e c o n c e n t r a t e d p r i m a r i l y i n quadrant IV. Rocks of P h a n e r o z o i c age l i e w i t h i n a band a t the t o p of quadrant IV ( 1 4 3 N d / l 4 4 N d > 0.5118) whereas Pre c a m b r i a n g r a n i t i c r o c k s occupy t h e lower p o r t i o n o f t h e diagram. The whole r o c k g r a n i t e sample from A r s e n i c Ridge p l o t s low i n t h e P h a n e r o z o i c quadrant i n an a r e a a l s o r e p r e s e n t a t i v e o f p a r t of t h e S i e r r a Nevada b a t h o l i t h . The 8 7 S r / 8 6 S r r a t i o s show g r e a t e r v a r i a t i o n than t h e 1 4 3 N d / 1 4 4 N d r a t i o s because 8 7 R b decays more r a p i d l y than 1 4 7Sm, and t h e Rb/Sr r a t i o s o f g r a n i t i c r o c k s a r e somewhat h i g h e r and much more v a r i a b l e than t h e i r Sm/Nd r a t i o s ( F a u r e , 1986). 137 O 7 0 0 0 0 0 . 7 0 5 0 0 0 . 7 1 0 0 0 0 . 7 I 3 O 0 0 . 7 2 0 0 0 0 . 7 2 5 0 0 0 . 7 3 0 0 0 87 S r / 8 6 Sr F i g u r e 5.1: 1 4 3 N d / 1 4 4 N d v e r s u s 8 7 S r / 8 6 S r p l o t of p r e s e n t day i s o t o p i c r a t i o s of g r a n i t i c r o c k s of the c o n t i n e n t a l c r u s t from A r s e n i c R i dge, L o s t Horses b a t h o l i t h , Yukon. Symbols used a r e : • = g r a n i t e whole r o c k ; • = average K - f e l d s p a r megacryst c o r e , and o = average K - f e l d s p a r megacryst r i m . P r e c a m b r i a n and P h a n e r o z o i c time l i n e s a r e p l o t t e d f o r r e f e r e n c e . Data from F a u r e , 1986, T a b l e 4.3 and 4.6. F i g u r e 5.2 shows e p s i l o n v a l u e s o f Nd and Sr ( c a l c u l a t e d from i n i t i a l 1 4 3 N d / 1 4 4 N d and 8 7 S r / 8 6 S r r a t i o s ) from known I - and S-type g r a n i t e s from s o u t h e a s t e r n A u s t r a l i a ( M c C u l l o c h and C h a p p e l l , 1982). A u s t r a l i a n S-type g r a n i t e s have a r e l a t i v e l y r e s t r i c t e d range i n CNd v a l u e s from -6.1 t o -9.8, but have a l a r g e range i n i n i t i a l 8 7 S r / 8 6 S r of from 0.7094 t o 0.7184. I - t y p e s have v a r i a b l e e p s i l o n Nd r a n g i n g from +0.4 t o -8.9, and a more l i m i t e d range i n i n i t i a l 8 7 S r / 8 6 S r of from 0.70453 t o 0.7119. The f i e l d s o v e r l a p a t i n i t i a l 8 7 S r / 8 6 S r v a l u e s of 0.710-0.712. The g r a n i t e sample from A r s e n i c Ridge p l o t s below the I - and S-type f i e l d s ( € H d = -10.49, e s r = +101.79) o u t l i n e d by M c C u l l o c h and C h a p p e l l (1982), and t h e r e f o r e does not c l e a r l y b e l o n g t o e i t h e r g r a n i t e t y p e . A l t h o u g h t h e esr v a l u e p l o t s w i t h i n t h e o v e r l a p zone as d e s c r i b e d above, the € N d v a l u e i s v e r y n e g a t i v e and t h e g r a n i t e c o u l d be c l a s s i f i e d as S-type on t h i s b a s i s a l o n e . T h i s i n t e r p r e t a t i o n agrees w i t h t h e f i e l d , p e t r o g r a p h i c and c h e m i c a l e v i d e n c e d i s c u s s e d i n s e c t i o n 3.3.2. A m i x i n g l i n e composed of a c r u s t a l component (end = -9.0, Nd = 28.0 ppm, e s r = 227.2, Sr = 140 ppm), and mantle component ( e N d = 139 z MANTL E COMPONENT \ 1 I I 1 1 V.O.2 -/ \ \ I - T Y P E \ \ / ~ > CRUSTAL. • s ^ ^ ^ < / | COMPONENT ~* _ . _ ^ 7 S - T Y P E 1 1 1 1 -50 0 +50 +IOO +150 + 200 +250 £ U R < S r > F i g u r e 5.2: I n i t i a l end v e r s u s esr p l o t o f I - and S-type g r a n i t e s from s o u t h e a s t e r n A u s t r a l i a . Data from M c C u l l o c h and C h a p p e l l (1982) and T a b l e 4.6. M i x i n g l i n e components from F a u r e , (1986). Symbols used a r e : + = g r a n i t e from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. +6.0, Nd = 14.0 ppm, e s r = -14.20, Sr = 470 ppm) has been p l o t t e d on F i g u r e 5.2 (Faur e , 1986). Both I - t y p e ( i g n e o u s ) and S-type ( s e d i m e n t a r y ) g r a n i t i c r o c k s f i t t h e same m i x i n g l i n e i n d i c a t i n g b oth a r e m i x t u r e s of two components, one " d e p l e t e d " mantle and t h e o t h e r c o n t i n e n t a l c r u s t . T h e r e f o r e i t i s p o s s i b l e t h a t S-type g r a n i t e s c o u l d c o n t a i n a mantle component o f up t o 35%. The i s l a n d a r c s , e u g e o c l i n e , c r a t o n and m i o g e o c l i n e f i e l d s f o r t h e n o r t h e r n G r e a t B a s i n o f t h e w e s t e r n U n i t e d S t a t e s , as de t e r m i n e d by Farmer and DePaolo, (1983), a r e i l l u s t r a t e d i n F i g u r e 5.3. A g r a n i t e sample from A r s e n i c Ridge p l o t s w i t h i n t h e f i e l d f o r the m i o g e o c l i n e . T h i s f i e l d i s c h a r a c t e r i z e d by e x t r e m e l y v a r i a b l e (+78 t o +466) e s r v a l u e s and a f a i r l y narrow range o f h i g h l y n e g a t i v e S N d v a l u e s (-16 t o - 1 9 ) . H i g h l y n e g a t i v e C N d v a l u e s suggest t h a t most of t h e m i o g e o c l i n e g r a n i t e s a r e e s s e n t i a l l y c r u s t a l m e l t s , w i t h no s i g n i f i c a n t m a n t l e - d e r i v e d component. The g r a n i t e from A r s e n i c Ridge i s p e r a l u m i n o u s . However, i t s e n d v a l u e i s not as n e g a t i v e and i t s e s r v a l u e i s not as p o s i t i v e as the G r e a t B a s i n g r a n i t e s . The L o s t Horses b a t h o l i t h has been i n t r u d e d i n t o the Selwyn B a s i n ( s e c t i o n 141 F i g u r e 5.3: end v e r s u s e s r p l o t i n d i c a t i n g t h e i s l a n d a r c , e u g e o c l i n e , m i o g e o c l i n e and c r a t o n f i e l d s of G r e a t B a s i n , w e s t e r n U n i t e d S t a t e s , g r a n i t i c r o c k s . Data from Farmer and DePaolo, (1983) and Table 4.6. Symbols used a r e : • = g r a n i t e from A r s e n i c R i d g e , L o s t Horses b a t h o l i t h , Yukon. 2.1; F i g . 2.1), a t h i c k m i o g e o s y n c l i n a l sequence of s e d i m e n t a r y r o c k s . S t r o n t i u m r a t i o s a t 95 Ma f o r the P a l e o z o i c s e d i m e n t a r y r o c k s s u r r o u n d i n g the L o s t Horses b a t h o l i t h were f o r graywacke, 0.7266, and f o r a l t e r e d q u a r t z i t e , 0.7352. These r a t i o s a r e g r e a t e r than t h o s e f o r t h e g r a n i t e (0.7116). T h i s c o u l d account f o r h i g h esr v a l u e s i n t h e g r a n i t i c r o c k s , and would s u p p o r t a s s i m i l a t i o n of s e d i m e n t a r y r o c k by t h e g r a n i t i c magma. F i e l d , p e t r o g r a p h i c and c h e m i c a l c r i t e r i a c l a s s i f y the p l u t o n s as S-type. C r i t e r i a f o r S-type p l u t o n s i n c l u d e : (1) the b a t h o l i t h o c c u r s i n a p o s t t e c t o n i c environment; (2) the o c c u r r e n c e of Sn-Ag m i n e r a l i z a t i o n ; (3) i n t r u s i o n of p l u t o n s t h a t a r e d i a p i r i c a l l y emplaced and m e t a s o m a t i c a l l y o v e r p r i n t e d ; (4) c o m p o s i t i o n a l l y r e s t r i c t e d p l u t o n s - -p r e d o m i n a n t l y s y e n i t e , q u a r t z s y e n i t e and g r a n i t e — w i t h g r a d a t i o n a l c o n t a c t s ; (5) g r a d i t i o n a l c o n t a c t s o c c u r between u n i t s ; (6) l a t e dykes a r e g r a n i t e i n c o m p o s i t i o n ; (7) g r a n i t i c r o c k s have t e x t u r e s t h a t range from m e g a c r y s t i c i n t h e r i m t o e q u i g r a n u l a r i n the c o r e ; (8) b i o t i t e i s c h a r a c t e r i s t i c a l l y p a l e y e l l o w t o r u s t y brown i n p l e o c h r o i s m and commonly c o n t a i n s z i r c o n s ; (9) a c c e s s o r y m i n e r a l s 143 i n c l u d e i l m e n i t e , z i r c o n s , a p a t i t e , t o u r m a l i n e and m u s c o v i t e ; (10) s i l i c a c o n t e n t averages >70%; (11) molar A l 2 03/(Cao + Na2 0 + K2O) >1.1 i s t y p i c a l l y p e r a l u m i n o u s ; (12) K2O i s g r e a t e r than N a 2 0 ; (13) T i 0 2 i s r e l a t i v e l y low; and (14) i n i t i a l 8 7 S r / 8 6 S r r a t i o s a r e g r e a t e r than 0.708. 5.5 ZETA MINERALIZATION The Zeta t i n - s i l v e r p r o s p e c t l i e s p a r t l y i n O r d o v i c i a n - Devonian c l a s t i c and c h e m i c a l metasediments of the Road R i v e r Group a t t h e n o r t h e a s t e r n c o n t a c t o f t h e zoned mid-C r e t a c e o u s L o s t Horses b a t h o l i t h . M i n e r a l i z a t i o n on t h e p r o p e r t y o c c u r s i n two forms: (1) c a s s i t e r i t e g r e i s e n i n h o r n f e l s e d q u a r t z i t e , and (2) g r e i s e n v e i n s w i t h i n the g r a n i t i c r o c k s . K-Ar d a t i n g of the s e r i c i t i c c a s s i t e r i t e g r e i s e n (87.0+3.0 Ma), i n d i s t i n g u i s h a b l e from th e date f o r t h e s y e n i t e phase of t h e b a t h o l i t h (86.8+2.7 Ma), e s t a b l i s h e s a g e n e t i c r e l a t i o n s h i p between th e two. S u l p h i d e - q u a r t z v e i n s w i t h minor t o u r m a l i n e , and t o u r m a l i n e q u a r t z v e i n s w i t h minor s u l p h i d e comprise th e g r e i s e n v e i n s . The s u l p h i d e - q u a r t z v e i n s w i t h minor 144 s u l p h i d e (Low Fog and C i r q u e showings) a r e v e r y narrow and o f t e n zoned. M i n e r a l i z a t i o n f o l l o w s f a u l t s and j o i n t s . S u l p h i d e m i n e r a l s i n c l u d e : 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 , s t a n n i t e , c h a l c o p y r i t e , j a m e s o n i t e , c a s s i t e r i t e and c o v e l l i t e . A l t e r a t i o n e nvelopes of q u a r t z + t o u r m a l i n e + s u l p h i d e a r e 5 t o 10 t i m e s w i d e r than the v e i n , and c o n s i s t o f p a r a l l e l zones of m o d e r a t e l y t o competely k a o l i n i z e d and s t r o n g l y l i m o n i t e ( t h e m a t i t e ) s t a i n e d i n t r u s i v e r o c k . S u l p h i d e emplacement t e m p e r a t u r e s , c r u d e l y e s t i m a t e d from s u l p h i d e phase diagrams, a r e w i t h i n the temperature l i m i t s l i k e l y f o r g r e i s e n i z a t i o n (360 t o 470°C as d e t e r m i n e d by Scherba, 1970). Tou r m a l i n e q u a r t z v e i n s w i t h minor s u l p h i d e (Main Zone and Gash Showing) range i n w i d t h from 1.5 m t o s e v e r a l c e n t i m e t e r s and a r e up t o 80 m i n l e n g t h . They c o n t a i n s t h r e e g e n e r a t i o n s o f t o u r m a l i n e . M i n o r t o t r a c e amounts o f f i n e g r a i n e d a r s e n o p y r i t e , p y r i t e , j a m e s o n i t e and b o u l a n g e r i t e o c c u r a t t h e v e i n margins. The k a o l i n i t e -s e r i c i t e a l t e r a t i o n e n velope i s up t o 10 t i m e s t h e w i d t h of the v e i n . Open spaced f i l l i n g t e x t u r e s a r e p r e s e n t i n both v e i n t y p e s . 145 The s y e n i t e s a l o n g A r s e n i c Ridge a r e as l i t h o p h i l e as the g r a n i t e s and p o t e n t i a l l y as t i n p r o d u c t i v e as the g r a n i t e s . S y e n i t e s i n n o r t h w e s t e r n N i g e r i a a r e a l s o a s s o c i a t e d w i t h t i n m i n e r a l i z a t i o n (Egbuniwe e t a l . . , 1985). These A f r i c a n p l u t o n s a r e thought t o have o r i g i n a t e d a t d e s t r u c t i v e p l a t e margins and a r e examples o f p e r a l k a l i n e magmatism a s s o c i a t e d w i t h s u b d u c t i o n a t the West A f r i c a n c r a t o n margin some 300 km t o the west (Egbuniwe e t . a l . , 1985). 5.6 , MODEL OF MAGMA EVOLUTION AND MINERALIZATION A f o u r s t a g e g e n e r a l i z e d g r a n i t e magma e v o l u t i o n of the L o s t Horses b a t h o l i t h i s proposed i n F i g u r e 5.4 and f o l l o w s many f e a t u r e s o f Farmer and DePaolo (1983). "Stage I " i s i n i t i a l m e l t i n g of g r a n i t i c melt from a s i a l i c c l a s t i c wedge of d o m i n a n t l y upper c r u s t a l o r i g i n . A minor lower c r u s t a l and/or mantle component i n d i c a t e s a 146 S T A G E I S T A G E II S T A G E III S T A G E IV » r . T . « n ASSIMILATION CRYSTAL FRACTIONATION HYDROTHERMAL INITIAL MELTING OF UPPER CRUST AND DIAPIRIC RISE Sn Ag GREISSENIZATION • E o - 5 0 — 7 5 — S u r f a c e S i a l i c C l a s t i c W e d g e B a s a l C r u s t M a n t l e ^ v . Intargronular 5° o • « ° l *J 11,11 ^2 — A • I I I I I I I I I I I I I I F i g u r e 5.4: Schematic drawing of the f o u r s t a g e s o f f o r m a t i o n of t h e L o s t Horses b a t h o l i t h , Yukon. Symbols used a r e as f o l l o w s : SCW(UC) = s i a l i c c l a s t i c wedge w i t h upper c r u s t a l c h e m i s t r y ; BC(LC) = b a s a l c r u s t w i t h lower c r u s t a l c h e m i s t r y ; £ = s u b d u c t i o n g e n e r a t e d ; M = mantle; e 3 3 = magma; *• = a s s i m i l a t i o n ; 4- = c r y s t a l f r a c t i o n a t i o n ; t -d i a p i r i c r i s e ; xx = g r a n - s y e n ; +•+ = t o - o r b - g r a n ; 1 = unknown; 2 = s y e n i t e ; 3 = q u a r t z s y e n i t e ; 4 = g r a n i t e ; 5 = t o u r m a l i n e o r b i c u l a r g r a n i t e ; 6 = g r e i s e n v e i n s (Sn-Ag); and, # = h o r n f e l s . p o o r l y d e v e l o p e d b a s a l c r u s t . M e l t i n g began i n t h e mid-Cre t a c e o u s w i t h s u b d u c t i o n a g a i n s t a n c e s t r a l N o r t h America. The i s o t o p i c c o m p o s i t i o n ( S r , 0, Pb and Nd) of the p a r e n t a l magma i s assumed t o be i d e n t i c a l t o t h a t of t h e magma s o u r c e . But t h e b u l k and t r a c e element c o m p o s i t i o n o f the i n i t i a l magma depends on t h e so u r c e m i n e r a l o g y and t h e p r e s s u r e , t e m p e r a t u r e and e x t e n t of m e l t i n g . The l e a d i s o t o p e d a t a p l o t s j u s t below the p e r i c r a t o n i c c u r v e ( s e c t i o n 4 . 4 . 4 ) i n d i c a t i n g a minor lower c r u s t and/or mantle component. "Stage I I " c o m p r i s e s m e l t a c c u m u l a t i o n and a s s i m i l a t i o n . F o r t h e L o s t Horses b a t h o l i t h , upper c r u s t a l m a t e r i a l was a s s i m i l a t e d i n t o t h e m e l t . T h i s upper c r u s t a l component i s i n d i c a t e d by: i n i t i a l S r r a t i o s g r e a t e r than 0.706 ( s e c t i o n 4 . 3 . 4 ) , l e a d i s o t o p e r a t i o s c l o s e t o the p e r i c r a t o n i c c u r v e ( s e c t i o n 4 . 4 . 4 ) , and, S-type g r a n i t e c h a r a c t e r i s t i c s ( s e c t i o n 3.3.2) i n c l u d i n g enrichment o f l i t h o p h i l e e l e ments. Nd i s o t o p e r a t i o s f o r t h e basement and o v e r l y i n g s e d i m e n t a r y r o c k s a r e s i m i l a r making i t d i f f i c u l t t o a s s e s s 1 4 8 Stage 2 e v o l u t i o n f o r m i o g e o c l i n a l magmas. On a 1 4 3 N d / 1 4 4 N d v e r s u s 8 7 S r / 8 6 S r p l o t (Faure, 1986), t h e g r a n i t e from the L o s t Horses b a t h o l i t h l i e s between the upper and lower c r u s t m i x i n g l i n e s . Because i t i s c l o s e r t o the upper c r u s t a l m i x i n g l i n e i t appears t o su p p o r t Stage 2 a s s i m i l a t i o n of upper c r u s t a l m a t e r i a l . The v a r i a b i l i t y of Gre a t B a s i n m i o g e o c l i n a l g r a n i t e s i n t h e eNd, and p a r t i c u l a r l y i n t h e € S r v a l u e s ( F i g . 5.3; as d i s c u s s e d above), may i n p a r t be due t o v a r i a t i o n s i n t h e amount o f p e l i t i c s e d i m e n t a r y r o c k a s s i m i l a t e d d u r i n g s t a g e 2 m i x i n g r a t h e r t h a n s o l e l y t o i s o t o p i c h e t e r o g e n e i t y i n the basement. The b u l k of a s s i m i l a t i o n o c c u r e d a t deep c r u s t a l l e v e l s where t h e w a l l r o c k i s h o t , where c r y s t a l l i z i n g m i n e r a l s have t h e h i g h e s t h e a t s o f f u s i o n , where t h e magma r i s e s s l o w l y , and where s t o p e d b l o c k s and r e s t i t i c m i n e r a l s (Chappel e t al...., 1987) s i n k s l o w l y . A s s i m i l a t i o n tends t o d i m i n i s h as t h e magma r i s e s i n t o c o o l e r c o u n t r y r o c k s a t s h a l l o w e r l e v e l s and as d i f f e r e n t i a t i o n p r oceeds (DePaolo, 1981). F r a c t i o n a l c r y s t a l l i z a t i o n p r o b a b l y accompanies a s s i m i l a t i o n . 149 "Stage I I I . " d e s c r i b e s d i a p i r i c r i s e and c h e m i c a l d i f f e r e n t i a t i o n ( f r a c t i o n a l c r y s t a l l i z a t i o n ) of the p l u t o n . A f t e r t h e d i a p i r c o a l e s c e d , i t had s h a r p b o u n d a r i e s . Because of the reduced s u r f a c e t o volume r a t i o , o n l y minor c o n t a m i n a t i o n from t h e s u r r o u n d i n g c o u n t r y r o c k s was l i k e l y . X e n o l i t h s a r e p r o b a b l y o n l y a minor so u r c e of c o u n t r y r o c k c o n t a m i n a t i o n because S-type g r a n i t e s a r e x e n o l i t h poor ( x e n o l i t h s c o mprise 1% o f the t o t a l volume of the s y e n i t e c l o s e t o the s e d i m e n t - s y e n i t e c o n t a c t a l o n g A r s e n i c R i d g e ) . "Stage IV" i s magmatic h y d r o t h e r m a l . I t i s i n d i c a t e d by an o r b i c u l a r phase, and a l t e r a t i o n h a l o s and m i n e r a l i z a t i o n . T h i s s t a g e i s a s s o c i a t e d w i t h f i n a l c r y s t a l l i z a t i o n o f the magma. These l a t e s t a g e e f f e c t s a r e e x h i b i t e d as: (1) a t o u r m a l i n e o r b i c u l a r g r a n i t e phase, and (2) Sn-Ag g r e i s s e n v e i n s i n h o r n f e l s and s y e n i t e . 150 6. REFERENCES CITED Anderson, R.G., 1988. An o v e r v i e w of some Mesozoic and T e r t i a r y p l u t o n i c s u i t e s and t h e i r a s s o c i a t e d m i n e r a l i z a t i o n i n t h e n o r t h e n Canadian C o r d i l l e r a . I n Recent advances i n the ge o l o g y of g r a n i t e - r e l a t e d m i n e r a l d e p o s i t s , pp. 96-113, R.P. T a y l o r and D.F. S t r o n g , e d i t o r s . Canadian I n s t i t u t e o f M i n i n g and M e t a l l u r g y S p e c i a l Volume 39., 445p. Andrew, A., 1982. A l e a d i s o t o p e s t u d y of s e l e c t e d p r e c i o u s m e t a l d e p o s i t s i n B r i t i s h Columbia. U n i v e r s i t y of B r i t i s h Columbia, Vancouver, U n p u b l i s h e d M.Sc. t h e s i s , 97p. Andrew, A., C.I. Godwin, and A . J . S i n c l a i r , 1984. M i x i n g l i n e i s o c h r o n s : a new i n t e r p r e t a t i o n of g a l e n a l e a d i s o t o p e d a t a from s o u t h e a s t e r n B r i t i s h Columbia. Economic Geology, volume 79, pp. 919-932. Armstrong, R.L., W.H. Taubeneck, and P.O. H a l e s , 1977. Rb-Sr and K-Ar geochronometry of Meso z o i c g r a n i t i c r o c k s and t h e i r S r i s o t o p i c c o m p o s i t i o n , Oregon, Washington, and Idaho. G e o l o g i c a l S o c i e t y o f Ameri c a B u l l e t i n , volume 88, pp. 397-411. A r r i e n s , P.A., C. Br o o k s , V.M. B o f i n g e r , and W. Compston, 1966. The d i s c o r d a n c e o f m i n e r a l ages i n g r a n i t i c r o c k s r e s u l t i n g from t h e r e d i s t r i b u t i o n of r u b i d i u m and s t r o n t i u m . J o u r n a l o f G e o p h y s i c a l R e s e a r c h , volume 71, number 20, pp. 4981-4994. B a r t o n , P.B., 1969. Thermochemical Study o f the System Fe-As-S. Geochimica Cosmochimica A c t a , volume 33, pp. 841-857. B i c z o k , J . L . , 1983. Omega 1-32 C l a i m s , E x p l o r a t i o n Report No. 1, Geology, G e o c h e m i s t r y and G e o p h y s i c s , 1983. Noranda E x p l o r a t i o n Company L t d . , assessment r e p o r t , pp. 11-17. 151 B o s t o c k , H. S., 1947. Mayo, Yukon T e r r i t o r y ; G e o l o g i c a l Survey of Canada, Map 890A. B o s t o c k , H.S., 1964. Geology McQueston Map-Area, Yukon T e r r i t o r y . G e o l o g i c a l Survey of Canada, Map 1143A. B o y l e , R.W., 1965. Geology, g e o c h e m i s t r y and o r i g i n of the l e a d - z i n c - s i l v e r d e p o s i t s of t h e K e n o - H i l l - G a l e n a H i l l a r e a , Yukon T e r r i t o r y . G e o l o g i c a l Survey of Canada, B u l l e t i n 111, 302p. B r o o k s , C , 1966. The e f f e c t of m i n e r a l age d i s c o r d a n c e i s on t o t a l - r o c k Rb-Sr i s o c h r o n s o f the Heemskirk g r a n i t e , Western Tasmania. J o u r n a l of G e o p h y s i c a l R e s e a r c h , volume 71, number 22, pp. 5447-5458. C h a p p e l l , B.W. and A.J.R. White, 1974. Two c o n t r a s t i n g g r a n i t e t y p e s . P a c i f i c Geology, volume 8, pp. 173-174. C h a p p e l l , B.W., A.J.R. White, and D. Wyborn, 1987. The importance of r e s i d u a l s o u r c e m a t e r i a l ( r e s t i t e ) i n g r a n i t e p e t r o g e n e s i s . J o u r n a l of P e t r o l o g y , volume 28, pp. 1111-1138. C h o r l t o n , L.B. and R.F. M a r t i n , 1978. The e f f e c t of boron on the g r a n i t e s o l i d u s . Canadian M i n e r a l o g i s t , volume 16, pp. 239-244. C h r i s t o p h e r , P e t e r A l l e n , 1973. A p p l i c a t i o n of K-Ar and F i s s i o n - T r a c k D a t i n g t o the M e t a l l o g e n y o f P o r p h y r y and R e l a t e d M i n e r a l D e p o s i t s i n t h e Canadian C o r d i l l e r a . U n i v e r s i t y of B r i t i s h Columbia, Vancouver, U n p u b l i s h e d Ph.D. T h e s i s , 161p. C l a r k e , L.A., 1960. The Fe-As-S System; Phase R e l a t i o n s and A p p l i c a t i o n s . Economic Geology, volume 55, pp. 1345-1381. DePaolo, D.J. and G.J. Wasserburg, 1976a. Nd i s o t o p i c v a r i a t i o n s and p e t r o g e n e t i c models. G e o p h y s i c a l R e s e a r c h L e t t e r s , volume 3, pp. 249-252. 152 DePaolo, D.J., 1981a. A neodymium and s t r o n t i u m i s o t o p i c s t u d y of t h e Mesozoic c a l c - a l k a l i n e g r a n i t i c b a t h o l i t h s of t h e S i e r r a Nevada and P e n i n s u l a r Ranges, C a l i f o r n i a . J o u r n a l o f G e o p h y i c a l R e s e a r c h , volume 86, pp. 10470-10488. DePaolo, D. J . , 1981b. Neodymium i s o t o p e s i n the C o l o r a d o F r o n t Range and c r u s t - m a n t l e e v o l u t i o n i n t h e P r o t e r o z o i c . N a t u r e , volume 291, pp. 193-196. Egbuniwe, I.G., W.R. F i t c h e s , M. B e n t l e y and N.J. S n e l l i n g , 1985. L a t e Pan A f r i c a n s y e n i t e - g r a n i t e p l u t o n s i n NW N i g e r i a . J o u r n a l o f A f r i c a n E a r t h S c i e n c e s , volume 3, number. 4, pp. 427-435. E i s b a c h e r , G.H., 1981. Sedimentary t e c t o n i c s and g l a c i a l r e c o r d i n the Windemere Supergroup, MacKenzie Mountains, n o r t h w e s t e r n Canada. G e o l o g i c a l Survey of Canada, Paper 80-27. Emond, D., 1989. P l u t o n i c r o c k s of the McQueston a r e a , c e n t r a l Yukon T e r r i t o r y . U n p u b l i s h e d r e p o r t . Erdmer, P. and H. Baadsgaard, 1987. 2.2 Ga age o f z i r c o n s i n t h r e e o c c u r r e n c e o f Upper P r o t e r o z o i c c l a s t i c r o c k s of t h e n o r t h e r n C a s s i a r T e r r a n e , Yukon and B r i t i s h C olumbia. Canadian J o u r n a l of E a r t h S c i e n c e s , volume 24, pp. 1919-1924. Farmer, G.L. and D.J. DePaolo, 1983. O r i g i n o f Mesozoic and T e r t i a r y g r a n i t e i n t h e w e s t e r n U n i t e d S t a t e s and i m p l i c a t i o n s f o r p r e - M e s o z o i c c r u s t a l s t r u c t u r e . 1. Nd and S r i s o t o p i c s t u d i e s i n the g e o c l i n e of the N o r t h e r n G r e a t B a s i n . J o u r n a l o f G e o p h y s i c a l R e s e a r c h , volume 88, pp. 3379-3401. Fa u r e , G., and J.L. P o w e l l , 1972. S t r o n t i u m I s o t o p e Geology. S p r i n g e r V e r l a g , 188p. Faur e , G., 1977. P r i n c i p l e s of I s o t o p e Geology. John W i l e y and Sons, New York, 464pp. 153 F a u r e , G., 1986. P r i n c i p l e s of I s o t o p e Geology. John W i l e y and Sons, New York, 589p. F r i t z , W.H., G. M. Narbonne, and S.P. Gordey, 1983. S t r a t a and t r a c e f o s s i l s near the Precambrian-Cambrian boundary, MacKenzie, Selwyn and Wernecke Mountains, Yukon and Northwest T e r r i t o r i e s . In C u r r e n t R e s e a r c h , P a r t B, G e o l o g i c a l Survey of Canada, Paper 83-1B, pp. 365-375. G a b r i e l s e , H., 1985. Major d e x t r a l d i s p l a c e m e n t s a l o n g the N o r t h e r n Rocky Mountain Trench and r e l a t e d l i n e a m e n t s i n n o r t h c e n t r a l B r i t i s h Columbia. G e o l o g i c a l S o c i e t y o f America B u l l e t i n , pp. 1-14. Godwin, C.I., R.L. Armstrong and K.M. Thompson, 1980. Geology, K-Ar and Rb-Sr d a t i n g o f t h e C l e a t u n g s t e n s k a r n p r o p e r t y , Selwyn Mountains, Yukon T e r r i t o r y . Canadian I n s t i t u t e M i n i n g and M e t a l l u r g y B u l l e t i n , volume 75, number 821, pp. 90-93. Godwin, C . I . , J.E. G a b i t e s and A. Andrew, 1988. L e a d t a b l e : a g a l e n a l e a d i s o t o p e d a t a base f o r t h e Canadian C o r d i l l e r a . B.C. M i n i s t r y of Energy, Mines and P e t r o l e u m R e s o u r c e s , G e o l o i c a l Survey Branch, Paper 1988-4, 188p. Godwin, C.I., and A . J . S i n c l a i r , 1982. Average l e a d i s o t o p e growth c u r v e s f o r s h a l e - h o s t e d z i n c - l e a d d e p o s i t s , Canadian C o r d i l l e r a . Economic Geology, volume 7, pp. 675-690. G o u t i e r , F.M., 1986. Galena l e a d i s o t o p e s t u d y o f m i n e r a l d e p o s i t s i n the E a g l e Bay f o r m a t i o n , s o u t h e a s t e r n B r i t i s h Columbia. U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, U n p u b l i s h e d M.Sc. t h e s i s , 153p. Green, L.H., 1972. Geology of Nash Creek, L a r s o n Creek and Dawson map a r e a s , Yukon T e r r i t o r y (106D, 116A, 116B and 1 1 6 C ( E l / 2 ) ) , O p e r a t i o n O g i l v i e . G e o l o g i c a l Survey of Canada, Memoir 364, 157p. 154 H a r l a n d , W.B., R.L Armstrong, A.V. Cox, L.E. C r a i g , A.G. S m i t h , and D.G., 1989. A G e o l o g i c Time S c a l e 1989. Cambridge U n i v e r s i t y P r e s s . Jago, B., 1982. Yukon Uranium P r o j e c t on E x p l o r a t i o n . Mattagami Lake E x p l o r a t i o n Ltd./Noranda E x p l o r a t i o n Co., L t d . , i n t e r n a l company r e p o r t , pp. 99-10 5. Jago, B., 1984. The Z e t a 1984 E x p l o r a t i o n R e p o r t . Geology, G e o c h e m i s t r y , G e o p h y s i c s , T r e n c h i n g and Diamond D r i l l i n g . Z eta 1-84 C l a i m s . Noranda E x p l o r a t i o n Co., L t d . , i n t e r n a l company r e p o r t , 93p. K e r r i c k D.M., 1969. K - f e l d s p a r megacrysts from a p o r p h y r i t i c q u a r t z monzonite c e n t r a l S i e r r a Nevada, C a l i f o r n i a . The American M i n e r a l o g i s t , volume 54, pp. 839-849. Kuran, V.M., C.I. Godwin and R.L. Armstrong, 1982. Geology and Geochronometry of t h e S c h e e l i t e Dome Tungsten-B e a r i n g Skarn P r o p e r t y , Yukon T e r r i t o r y . Canadian I n s t i t u t e of M i n i n g and M e t a l l u r g y B u l l e t i n , volume 75, number 838, pp. .137-142. K u r y v i a l , R.J., 1976. Element p a r t i t i o n i n g i n a l k a l i f e l d s p a r from t h r e e i n t r u s i v e b o d i e s of t h e c e n t r a l Wasatch Range, Utah. G e o l o g i c a l S o c i e t y of America B u l l e t i n , volume 87, pp. 657-660. Lee, J.T., 1972. E x p e r i m e n t a l I n v e s t i g a t i o n on S t a n n i t e -S p h a l e r i t e S o l i d S o l u t i o n S e r i e s . Neues J a h r b u c h f u r M i n e r a l o g i e . M o n a t s h e f t e , volume 24, pp. 556-559. L u t h , W.C., R.H. Johns and O.F. T u t t l e , 1964. The g r a n i t e system a t p r e s s u r e s o f 4-10 Kb. J o u r n a l of G e o p h y s i c a l R e s e a r c h , volume 69, pp. 759-773. Lynch, J.V.G., 1986. M i n e r a l z o n i n g i n t h e Keno H i l l s i l v e r - l e a d - z i n c m i n i n g d i s t r i c t , Yukon. I n Yukon Geology, volume 1, E x p l o r a t i o n and G e o l o g i c a l S e r v i c e s D i v i s i o n , Yukon, I n d i a n and N o r t h e r n A f f a i r s Canada, pp. 89-97. 155 Lynch, J.V.G., 1989a. Hydrothermal z o n i n g i n the K e n o - H i l l Ag-Pb-Zn v e i n system, Yukon: a Study i n s t r u c t u r a l g e o l o g y , m i n e r a l o g y , f l u i d i n c l u s i o n s , and s t a b l e i s o t o p e g e o c h e m i s t r y . U n i v e r s i t y of A l b e r t a , Edmonton, U n p u b l i s h e d Ph.D. t h e s i s , 218p. Lynch, J.V.G., 1989b. L a r g e - s c a l e h y d r o t h e r m a l z o n i n g r e f l e c t e d i n the t e t r a h e d r i t e - f r e i b e r g i t e s o l i d s o l u t i o n , Keno H i l l Ag-Pb-Zn d i s t r i c t , Yukon. Canadian M i n e r a l o g i s t , volume 27, pp. 383-400. M c C u l l o c h , M.T. and B.W. C h a p p e l l , 1982. Nd i s o t o p i c c h a r a c t e r i s t i c s o f S- and I - t y p e g r a n i t e s . E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , volume 58, pp. 51-64. M i c h a e l s , P., 1984. C h e m i c a l d i f f e r e n t i a t i o n of the C o r d i l l e r a P a i n e g r a n i t e , S o u t h e r n C h i l e ( i n s i t u . ) f r a c t i o n a l c r y s t a l l i z a t i o n . C o n t r i b u t i o n s t o M i n e r a l o g y and P e t r o l o g y , volume 87, 179-195. Monger, J.W.H., R.A. P r i c e , and D.J. Tempelman-Kluit, 1982. T e c t o n i c a c c r e t i o n and t h e o r i g i n o f two major metamorphic and p l u t o n i c w e l t s i n t h e Canadian C o r d i l l e r a . Geology, volume 10, pp. 70-75. Olade, M.A. and W.D. G o o d f e l l o w , 1978. L i t h o g e o c h e m i s t r y and h y d r o g e o c h e m i s t r y o f uranium and a s s o c i a t e d elements i n the Tombstone B a t h o l i t h , Yukon, Canada. In Geochemical E x p l o r a t i o n 1988. P r o c e e d i n g s o f the 7th I n t e r n a t i o n a l Geochemical Symposium, pp. 407-428, J.R. W a t t e r s o n and T.K. Theobold, e d i t o r s . Golden, C o l o r a d o , A s s o c i a t i o n o f E x p l o r a t i o n Geochemists. P i t c h e r , W.S., 1982. G r a n i t e t ype and t e c t o n i c environment. I n Mountain B u i l d i n g P r o c e s s e s , pp.19-40, K.J. Hsu, e d i t o r . Academic P r e s s , London. R i b b e , P.H., 1974 ( E d i t o r ) . S u l p h i d e M i n e r a l o g y . M i n e r a l o g i c a l S o c i e t y of America S h o r t Course Notes. Volume 1, S o u t h e r n P r i n t i n g Company, B l a c k s b u r g , V i r g i n i a . November 1974, l l l p . 156 R i c h a r d s o n , J.M., 1988. F i e l d and t e x t u r a l r e l a t i o n s h i p of a l t e r a t i o n and g r e i s e n - h o s t e d m i n e r a l i z a t i o n a t the E a s t K e m p t v i l l e t i n d e p o s i t , D a v i s Lake Complex, southwest Nova S c o t i a . I n Recent advances i n the g e o l o g y of g r a n i t e - r e l a t e d m i n e r a l d e p o s i t s , pp. 265-279, R.P. T a y l o r and D.F. S t r o n g , e d i t o r s . Canadian I n s t i t u t e of M i n i n g and M e t a l l u r g y S p e c i a l Volume 39, 445p. Roddick, J.A., 1967. T i n t i n a t r e n c h . J o u r n a l of Geology, volume 75, pp. 23-33. R u s s e l , J.K. and J . N i c h o l l s , 1988. A n a l y s e s of p e t r o l o g i c hypotheses w i t h Pearce element r a t i o s . C o n t r i b u t i o n s t o M i n e r a l o g y and P e t r o l o g y , volume 99, pp. 25-35. S c h u l e r , C , and R.H. S t e i g e r , 1978. On t h e g e n e s i s of f e l d s p a r megacrysts i n g r a n i t e s ; an Rb-Sr i s o t o p i c s t u d y . F o u r t h I n t e r n a t i o n a l C o n f e r e n c e , Geochronblogy, Cosmochronoloy, I s o t o p e Geology, 1978, R.E. Zartman, e d i t o r . U.S. G e o l o g i c a l Survey, Open F i l e R eport 78-701, pp. 386-387. Shcherba, G.N., 1970. G r e i s e n s . I n t e r n a t i o n a l Geology Review, volume 12, number 2, pp. 114-150, 239-259. S i n c l a i r , A . J . , O.J. T e s s a r i , and J.E. H a r a k a l , 1980. Age o f Ag-Pb-Zn m i n e r a l i z a t i o n , K e n o - H i l l - G a l e n a H i l l a r e a , Yukon T e r r i t o r y . Canadian J o u r n a l of E a r t h S c i e n c e s , volume 17, pp. 1100-1103. S i n c l a i r , W.D. and J.M. R i c h a r d s o n , 1986. Q u a r t z - t o u r m a l i n e o r b i c u l e s i n the S e a g u l l B a t h o l i t h , Yukon T e r r i t o r y : M i n e r a l o g y , g e o c h e m i s t r y and r e l a t i o n s h i p t o t i n m i n e r a l i z a t i o n . U n p u b l i s h e d r e p o r t . S t e i g e r , R.H. , and E. J a g e r , 1977. Subcommission on Geochronology: C o n v e n t i o n on t h e Use o f Decay C o n s t a n t s i n Geo- and Cosmoschronology. E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , volume 36, pp. 359-362. 157 S t e v e n s , R.D., R.N. D e l a b i o and G.R. Lachance, 1982. Age D e t e r m i n a t i o n s and G e o l o g i c a l S t u d i e s , K-Ar I s o t o p i c Ages, Report 16. G e o l o g i c a l Survey o f Canada, Paper 82-2, 56p. S t r e c k e i s e n , A.L., 1976. To each p l u t o n i c r o c k i t s p r o p e r name. E a r t h S c i e n c e Reviews., volume 12, pp. 1-33. Tempelman-Kluit, D.J., 1969. A r e - e x a m i n a t i o n of p s e u d o l u c i t e from S p o t t e d Fawn Creek, w e s t - c e n t r a l Yukon. Canadian J o u r n a l of E a r t h S c i e n c e s , volume 6, pp. 55-62. Tempelman-Kluit, D.J., 1970. S t r a t i g r a p h y and s t r u c t u r e of t h e "Keno H i l l Q u a r t z i t e " i n Tombstone R i v e r - U p p e r K l o n d i k e R i v e r map a r e a s , Yukon T e r r i t o r y (116 b/7,B/8). G e o l o g i c a l Survey of Canada B u l l e t i n 180, 102p. Tempelman-Kluit, D.J., 1979. T r a n s p o r t e d c a t a c l a s i t e , o p h i o l i t e and g r a n o d i o r i t e i n Yukon: E v i d e n c e of a r c -c o n t i n e n t a l c o l l i s i o n . G e o l o g i c a l Survey of Canada, Paper 79-14, 27p. Thompson, R.I. and C.F. R o o ts, 1982. O g i l v i e M o untains; P a r t A: A New R e g i o n a l Mapping Program, P a r t B: V o l c a n i c r o c k s i n n o r t h - c e n t r a l Dawson map a r e a . . In " C u r r e n t R e s e a r c h , P a r t A." G e o l o g i c a l Survey of Canada, Paper 82-1A, pp. 403-414. T u t t l e , O.F., and N.L. Bowen, 1958. O r i g i n o f g r a n i t e i n t h e l i g h t o f e x p e r i m e n t a l s t u d i e s i n t h e system NaAlSi3 0a-KAlSi3 0 8 - S i 0 2 - H 2 O . G e o l o g i c a l S o c i e t y of A m e r i c a , Memoir 74, 153p. Wanless, R.K., R.D. S t e v e n s , G.R. Lachance, and C M . Edmonds, 1967. Age D e t e r m i n a t i o n s and G e o l o g i c a l S t u d i e s , K-Ar I s o t o p i c Ages, Re p o r t 7. G e o l o g i c a l Survey of Canada, Paper 66-17, 120p. 158 Wanless, R.K., R.D. S t e v e n s , G.R. Lachance, and R.N. D e l a b i o , 1970. Age D e t e r m i n a t i o n s and G e o l o g i c a l S t u d i e s , K-Ar I s o t o p i c Ages, Report 10. G e o l o g i c a l Survey of Canada, Paper 71-2, 96p. White, W.H., G.P. E r i c k s o n , K.E. N o r t h c o t e , G.E. D i r o n , and J.E. H a r a k a l , 1967. I s o t o p i c d a t i n g of the Guichon B a t h o l i t h , B r i t i s h Columbia. Canadian J o u r n a l o f E a r t h S c i e n c e s , volume 4, pp. 677-690. York, D. , 1967. The b e s t i s o c h r o n . E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , volume 2, pp. 479-482. Zen, E., and J.M. Hammarstrom, 1984. Magmatic e p i d o t e and i t s p e t r o l o g i c s i g n i f i c a n c e . Geology, volume 12, pp. 515-518. Zen, E., 1985. I m p l i c a t i o n s o f magmatic e p i d o t e - b e a r i n g p l u t o n s on c r u s t a l e v o l u t i o n i n the a c c r e t e d t e r r a i n e s o f n o r t h w e s t e r n N o r t h A merica. Geology, volume 13, pp. 266-269. 159 APPENDIX A 160 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 01 LOCATION: Figure 3.1 ROCK NAME: Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 70% K-feldspar, 25% hornblende and 5% b i o t i t e . K-feldspar megacrysts are gray in colour and average 2.5 x 0.5 cm in size. Megacrysts are uniform in size. Hornblende and b i o t i t e make up the matrix with hornblende up to 0.5 cm in diameter and b i o t i t e up to 0.25 cm in diameter. K-feldspar megacrysts are not aligned. Weathered outcrop has a white coloration. Quartz and plagioclase is not v i s i b l e . DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.l Modal mineralogy for sample SA 01. Mineral/ Material % Method2 Comments (+S>1 Megacrys t Matrix Orthoclase (Orth) Plagioclase (Plag) 75 25 68 (4.0) 9 . 5 (2.5) V V PC PC Hornblende 12.5 PC (Hnblde) (2.9) Biotite 3 . 5 PC (Bi) (1.6) Augite 6.5 PC (Aug) (2.1) Epidote tr PC (Ep) Apatite tr PC (Apat) Sphene tr PC (Sph) Rutile tr PC ( Rut) Opaques tr PC (Opa) Quartz tr PC (Qtz) Occurs as: (1) megacrysts(85%) (2) matrix (15%) - size range: 1.0 mm - 2.0 cm - granophyric texture - contains plag, qtz, apat, bi and op - s e r i c i t e on fractures and cleavage planes - An3 5 , andes ine - up to 2.0 mm, average 1.0 mm - aligned p a r a l l e l to the long direction of K-feldspar -contains op and hnblde - s e r i c i t e on fractures and cleavage planes -up to 3.0 mm, averages 1.0 mm -contains aug, b i , sph and apat -up to 2.5 mm, averages 1.0 mm -contains zircons, apat and op -up to 2 mm, averages 1.0 mm -as cores within hornblende -contains b i , op and apat -up to 1.0 mm diameter -associated with mafics -up to 0.5 mm, avg 0.05 mm -euhedral within hnblde, orth -averages 0.1 mm -within hornblende -needles up to 1.0 mm, -within hnblde, orth and bi -up to 0.1 mm in diameter -within bi and hnblde -up to 0.5 mm diameter -within orth, and as matrix 1 S, standard deviation, is calculated for point count data using: 200 /P(1-P). ^ n 2 V = visual estimate using percent charts; PC = point counting. 161 APPENDIX A THIN SECTION DESCRIPTION ROCK NUMBER: SA 02 LOCATION: Figure 3.1 ROCK NAME: Quartz Feldspar Porphyry HAND SAMPLE DESCRIPTION: Quartz feldspar porphyry with 25% feldspar and 10% quartz phenocrysts and 65% matrix. Quartz i s anhedral, brown in colour and up to 8 mm in diameter. Feldspar i s subhedral, tan coloured and up to 4 mm in diameter. Fine grained quartz and feldspar comprise the matrix. Pyrite cubes are up to 1.5 cm in diameter (average 1.5 mm) and are present in trace amounts. Tourmaline patches (3 mm in diameter) were found l o c a l l y . DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.2 Modal mineralogy for sample SA 02. M ineral/ % Method2 Comments Material <+S)i Phenocryst 35 V Matrix 65 V Quartz 41 V Occurs as:(1)phenocrysts(90%) (2) matrix (10%) - phenocrysts range up to 3.5 mm in diameter, averages 0.5mm - fine grained groundmass - anhedral, interlocking grains Orthoclase 27 V Occurs as: (1) phenocrysts (2) matrix - phenocrysts range up to 3.5 mm in diameter, averages 1.0 mm - fine grained groundmass - s e r i c i t e altered on fractures and cleavage planes Muscovite 7 V - up to 1 mm in diameter, averages 0.25 mm - altered by clays along cleavage planes S e r i c i te 20 V - fine grained - completely altered feldspars Altered Mafics 5 V - remnant angular phenocrysts - phenocrysts averages 0.5 mm in diameter Rutile tr V - as needles within a l l minerals S, standard deviation• is calculated for point count data using: 200^/P(1-P)• V = visual estimate using percent charts; PC = point counting 162 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 03 LOCATION: Figure 3.1 ROCK NAME: Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 80% K-feldspar, 15% hornblende, 5% b i o t i t e . K-feldspar megacrysts are gray and average 2.5 x 0.5 cm in size. Hornblende and b i o t i t e form the matrix and are up to 0.5 cm in diameter. Weathered surface is white and mafics are l o c a l l y rusty. No alignment of K-feldspars, and no megascopic plagioclase or quartz was noted. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.3 Modal mineralogy for sample SA 03. Mineral/ Material % (+S)1 Method2 Comments Megacryst 80 V Matrix 20 V Orthoclase 65 .7 PC Occurs as: (1) megacrysts(95%) (Orth) (4 .0) (2) matrix(5%) - size range: 1.5 mm - 2.0 mm - granophyre texture - contains plag, hnblde, b i , qtz and apat Plagioclase 11 .4 PC - Anal, andesine (Plag) (2 .7) - up to 4.0 mm in length, avg 1 . 0mm - s e r i c i t e altered on fractures and cleavage planes Hornblende 15 .4 PC - up to 3.0 mm in diameter, (Hnblde) (3 . 1 ) averages 1.0 mm - contains cores of aug, apat, opa and bi - altered by chlo r i t e Biotite 5 . 4 PC - up to 3.0 mm in length, (Bi ) ( I .9) averages 0.75 mm - contains zircons, opa and rut Augi te 2. 1 PC - averages 0.5 mm in diameter (Aug) ( 1 .2) - as cores within hornblende, almost a l l being replaced by hornblende Opaques tr PC - averages 0.05 mm diameter (Opa) - found as inclusions within a l l above minerals except apatite Apat i te tr PC - averages 0.05 mm in diameter (Apat) - found as euhedral inclusions within a l l above minerals except opaques Quartz tr PC - averages 0.5 mm in diameter (Qtz) - found within orthoclase and as matrix 1 S, standard deviation• is calculated for point count data using: 200^/P( l^ p i • 2 V = visual estimate using percent charts; PC = point counting. 163 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 04 LOCATION: Figure 3.1 ROCK NAME: Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 60% K-feldspar, 10% plagioclase, 20% hornblende and 10% b i o t i t e . K-feldspar megacryststs are blue-gray in colour and up to 4 cm in length. Plagioclase (white, average 2 mm), hornblende (dark green, average 2.0 mm) and b i o t i t e flakes (up to 8.0 mm in diameter) form the matrix. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.4 Modal mineralogy for sample SA 04. Mineral/ % Method2 Comments Material ( +S> l Megacrysts 75 V Matrix 25 V Orthoclase 62.1 PC Occurs as: (1) megacrysts(90%) (Orth) (5.7) (2) matrix(10%) - size range: 0.5 mm - 1.0 cm - granophyric texture - contains qtz, hnblde, bi , plag and ep - s e r i c i t e on fractures and cleavage planes Plagioclase 10.3 PC - An2 4 , andesine (Plag) (3.6) - up to 4.5 mm in length, averages 1.75 mm - contains hnblde - within orth and bi - altered by s e r i c i t e on cleavage traces and fracture planes Quartz 1 . 7 PC - anhedral phenocrysts average (Qtz) (4.4) 1.0 mm in diameter - within matrix and orth Hornblende 19.0 PC -up to 3.5 mm in diameter, (Hnblde) (4.6) averages 1.5 mm - contains cores of aug, opa, apa, b i , ep and plag - ch l o r i t e altered Bio t i t e 5.9 PC - up to 7.5 mm in length, (Bi) (4.0) averages 1.0 mm - contains zircons, plag, apa, aug and apa Augite 1.0 PC - up to 3.5 mm in length, (Aug) (3.4) averages 0.5 mm - as cores in hnblde, being replaced by hnblde - contains opaques Opaques <1 PC - averages 0.05 mm in diameter (Opa) - as inclusions within a l l minerals except apatite Epidote < 1 PC - up to 0.5 mm in diameter (Epi) - within hnblde and orth - euhedral, unaltered Apatite <1 PC - averages 0.05 mm in diameter (Apa) - as inclusions within a l l minerals except apatite Orthopyroxene <1 PC - averages 0.5 mm in diameter (Opx) - as cores within hornblende 1 S, standard deviation, is calculated for point count data using: 200/ P( l-F) . 2 V = visual estimate using percent charts; PC = point count ing 164 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 06 LOCATION: Figure 3.1 ROCK NAME: Greywacke HAND SPECIMEN DESCRIPTION: Dark gray, fine grained graywacke. Weathered surface are pale orange. Contains 2 mm wide quartz veins with traces of c a s s i t e r i t e . Locally interlayered with black chert. Matrix is a fine grained mix of chl o r i t e , b i o t i t e and quartz. Veins are composed of 0.5 mm diameter b i o t i t e and quartz. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A. 5 Modal mineralogy for sample SA06. Mineral/ % Method1 Comments Material Quartz Bioti te Tourmaline Opaques 45 40 anhedral fine grained matrix 0.05 mm average in veins up to 0.5 mm in diameter anhedral, up to 1.0 mm in diameter greatest percentage in fine grained matrix with quartz and clay as needles up to 0.1 mm in diameter occurs in one patch mixed with b i o t i t e averages 0.05 mm in diameter within b i o t i t e and quartz V = visual estimate using percent charts; PC = point counting. 165 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 07 LOCATION: Figure 3.1 ROCK NAME: Gray Chert HAND SPECIMEN DESCRIPTION: Gray, fine grained chert interlayered with black chert. Interlayers average 5.0 cm in width. Weathered surfaces are gray. Chert i s very fine grained and altered to quartz, b i o t i t e and ch l o r i t e . Veins contain quartz, epidote, muscovite and plagioclase. 10% of the specimen is veins. DESCRIPTION BY: SMA DATE: JULY 1985 166 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 08 LOCATION: Figure 3.1 ROCK NAME: Black Shale HAND SPECIMEN DESCRIPTION: Fine grained bLack shale that is l o c a l l y carbonaceous. Weathered surfaces are black. Specimen is almost opaque in thin section, but contains quartz grains from 0.05 mm to 0.1 mm in diameter. Quartz veins range from minute to 0.4 mm in width. DESCRIPTION BY: SMA DATE: JULY 1985 167 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 10 LOCATION: Figure 3.1 ROCK NAME: Altered Lamprophyre Dyke HAND SPECIMEN DESCRIPTION: Dark green lamphrophyre with b i o t i t e phenocrysts, up to 1.5 cm in diameter, and a fine grained matrix. Minor disseminated chalcopyrite occurs. Weathered rinds are reddish brown. DESCRIPTION BY : SMA DATE: JULY 1985 TABLE A.8 Modal mineralogy for sample SA 10. Mineral/ % Method1 Comments Material Phenocrysts 5 V Matrix 95 V Biotite 5 V - up to 1.5 mm in diameter - chlorite altered Quartz 45 V - fine grained - averages 0.05 mm in diameter Alteration 35 V - fine grained mix of c a l c i t e , s e r i c i t e , c h l o r i t e and bi o t i t e Opaques 15 V - up to 0.1 mm in diameter, averages 0.05mm 1 V = visual es t imate using percent charts; PC = point counting. 168 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 13 ROCK NAME: Syenite LOCATION: Figure 3.1 HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 75% K-feldspar, 20% hornblende and 5% b i o t i t e . K-feldspar megacrysts are gray and up to 3.0 cm in diameter. Hornblende and bi o t i t e form the matrix and average 0.4 mm in diameter. Phenocrysts are not aligned. Weathered surfaces are gray. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.9 Modal mineralogy for sample SA 13. Mineral/ % Method2 Comments Material (+S'1 Megacrysts Matr ix Orthoclase (Orth) Plagioclase (Plag) Quartz (Qtz) Hornblende (Hnblde) Augi te (Aug) Bioti t e (Bi) Epidote (Epi) Sphene (Sph) Apat i te ( Apa) Opaques (Opa) 80 20 66.3 (6.1) 7 . 1 (3.3) 1 . 1 (3.3) 15.5 (4.7) 5.5 (3.5) 4 . 5 (2.7) <1 < 1 <1 < 1 PC Occurs as: (1) megacrysts(95%) (2) matrix(5%) - size range: 1.5 mm - 2.0 cm - contains plag, b i , hnblde, qtz, opa and aug - granophyric texture - s e r i c i t e altered on cleavage planes and fractures - hematized feldspars PC - too heavily altered to get an accurate composi t ion -up to 0.45 mm in diameter, averages 0.15 mm - contains hnblde and opa - s e r i c i t e altered along cleavage planes and f ractures PC - averages 1.5 mm in diameter - anhedral, i n f i l l i n g spaces - within orth and as matrix PC - up to 3.5 mm in diameter, averages 1.0 mm - contains aug core, apa, opa and bi PC - up to 3.0 mm in diameter, averages 1.0 mm - as cores in hnblde - contains opa and apa - altered by hornblende PC - up to 4.0 mm in length, averages 1.0 mm - contains opa and hnblde PC - averages 0.5 mm in diameter - associated with hnblde PC - averages 1.0 mm in diarater - associated with hnblde PC - averages 0.05 mm in diameter - within orth, plag, qtz, hnblde and aug PC - averages 0.05 mm in diameter - within orth, plag, qtz, hnblde and aug 1 S, standard deviation, is calculated for point count data using: 200^/ELIZEI-2 V = visual estimate using percent charts; PC = point counting. 169 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 15 LOCATION: Figure 3.1 ROCK NAME: Limestone HAND SPECIMEN DESCRIPTION: Very fine grained limestone!100% c a l c i t e ) with interlocking grains, contains organic structures, possibly ooids. Two obvious textures occur: (1) Banded or colloform structures marked by alternating layers of dark gray coarser grained c a l c i t e , 0.1 mm in diameter, interlayered with tan fine grained carbonate less than 0.1 mm in diameter. (2) Brecciated limestone, composed of very fine grained carbonate fragments up to 4.0 mm in diameter, i s predominantly carbonate but 10% of the fragments contains 5% anhedral quartz and 1% muscovite (0.1 mm in diameter). Matrix to the fragments is coarse grained carbonate. Average grain size is 0.1 mm diameter. Locally coarse c a l c i t e , averaging 2.0 mm in diameter, i n f i l l s voids. There are traces of b i o t i t e in the fragments. The specimen is broken by narrow c a l c i t e veins averaging 0.1 mm across. DESCRIPTION BY: SMA DATE: JULY 1985 170 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 18 LOCATION: Figure 3.1 ROCK NAME: Quartzite HAND SPECIMEN DESCRIPTION: Medium grained quartzite with a brown weathered surface. Muscovite (5%) is up to 5.0 mm in diameter. Cassiterite, up to 2.0 mm in diameter, i s found along fractures. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.11 Modal mineralogy for sample SA 18. X Method1 Comments Mineral / Material 52 V - average 0.075 mm in diameter - coarser quartz in veins, that average 0.2 mm across 5 V - up to 0.5 mm in diameter - predominantly within veins but .also within quartzite 35 V - very fine grained 5 V - up to 0.6 mm in length - predominantly within veins - contains quartz 3 V - averages 0.05 mm in diameter - disseminated in matrix - subhedral and anhedral - within quartz, muscovite and seric i te Veins are composed of quartz, muscovite and opaques. Quartzite is a fine grained mix of quartz and muscovite. Quartz Muscovite Ser i c i t e Biotite Opaques V = visual estimate using percent chart; PC counting. point 171 APPENDIX. A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 20 LOCATION: Figure 3.1 ROCK NAME: Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 60% K-feldspar, 10% plagioclase, 25% hornblende and 5% b i o t i t e . K-feldspar megacrysts are gray and average 2.5 x 0.5 mm in size. Megacrysts are uniform in size. Hornblende, b i o t i t e and plagioclase form the matrix and average 2.0 mm in diameter. Weathered outcrop is white. Quartz is not v i s i b l e in hand specimen. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.12 Modal mineralogy for sample SA 20. Mineral/ % Method2 Comments M i nera1 (+S)» Megacrysts 85 V Matrix 15 V Orthoclase 62 PC Occurs as: (1) megacrysts(95%) (Orth) (6.0) (2) matrix(5%) - size range: 0.5 mm - 2.5 cm - granophyric texture - contains plag, b i , hnblde, opa and apa - s e r i c i t e on fractures and cleavage planes Plagioclase 14.7 PC - Ans4, labradorite (Plag) (4.4) - up to 7.0 mm in diameter, averages 1.0 mm - contains opa and hnblde - plagioclase within orthoclase aligned p a r a l l e l to the long axis of the orthoclase crystal - s e r i c i t e on fractures and cleavage planes Quartz 0.5 PC - averages 0.3 mm in diameter (Qtz) (2.3) - occurs within orthoclase and matrix Hornblende 8. 1 PC - up to 3.5 mm diameter, (Hnblde) (3.4) averages 1.00 mm - contains opa, apa, aug cores, bi and epi Augi te 8 . 1 PC - up to 3.0 mm in diameter, (Aug) (3.4) averages 1.00 mm - within hnblde as cores - altered by hornblende - contains opa and apa Biot i t e 6.6 PC - up to 3.5 mm in diameter, (Bi) (3.1) averages 1.5 mm - contains plag, opa and apa - altered by chlo r i t e along cleavage planes Epidote < 1 PC - averages 0.1 mm diameter (Epi ) - within hornblende Apat i te < 1 PC - averages 0.05 mm in diameter (Apa) - within orth, plag, qtz, hnblde, aug and bi Opaques <1 PC - averages 0.05 mm in diameter (Opa) - within orth, plag, qtz, hnblde, aug and bi Sphene <1 PC - averages 0.1 mm in diameter (Sph) - within hornblende 1 S, standard deviation, is calculated for point count data using: 200/ P(1-P1. 2 V = visual estimate using percent charts; PC = point counting. 172 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 22 LOCATION: Figure 3.1 ROCK NAME: BIOTITE DYKE HAND SPECIMEN DESCRIPTION: Medium grained dyke with 45% K-feldspar, 40% quartz, 5% bio t i t e and trace plagioclase. Darker patches, up to 5 mm in diameter and 20% of the rock, have a greater percentage of b i o t i t e . DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.13 Modal mineralogy for sample SA 22. Mineral/ % Method2 Comments Material (+S ) l Quartz 44 PC - up to 2.0 mm in diameter, (Qtz) (6.1) averages 0.5 mm - within orth and plag Orthoclase 45.1 PC - up to 4.0 mm in length, (Orth) (6.1) averages 1.0 mm - contains qtz, s e r i c i t e , bi - altered by s e r i c i t e on cleavage planes, cores are destroyed Plagioclase 9.4 PC - An3 5 , andesine (Plag) ' (3.6) - up to 2.5 mm in length, averages 0.35 mm - altered by s e r i c i t e on fracture planes, some cores are destroyed B i o t i t e 1.5 PC - up to 0.75 mm in length, (Bi ) (4.0) averages 0.5 mm - altered by ch l o r i t e - contains opaques Sphene <1 PC - up to 0.5 mm in diameter, (Sph) averages 0.1 mm - associated with b i o t i t e Epidote < 1 PC - averages 0.1 mm (Epi) - within feldspars Opaques < 1 PC - averages 0.05 mm in diameter (Opa) - within b i , qtz, orth and plag 1 S, standard deviation. is calculated for point count data using: 200^/ P( l - ~ . 2 V = visual estimate using percent charts; PC = point counting. 173 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 24 LOCATION: Figure 3.1 ROCK NAME: Tourmaline Orbicular Granite HAND SPECIMEN DESCRIPTION: Contains 45% gray K-feldspar, 30% brown quartz and 25% brown plagioclase. Minerals are equigranular and average 2.0 mm in diameter. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A. 14 Modal mineralogy for sample SA 24. Mineral/ % Method2 Comments Material (ts) i Altered 63.3 PC - up to 4.5 mm in diameter, Feldspar (5.9) averages 2.0 mm - phenocrysts are t o t a l l y to 75% altered. - remnant Carlsbad twinning l o c a l l y is v i s i b l e Quartz 36.2 (5.9) PC - up to 2.5 mm in diameter, averages 1.5 mm - anhedral Muscovi te 0.5 (2.3) PC - up to 1.5 mm in diameter - radiating crystals - within matrix, but also within quartz and feldspar B i o t i t e < 1 PC - very fine grained masses - predominantly within altered feldspar Opaques <1 PC - averages 0.05 mm in diameter - within feldspars and opaques S, standard deviation, is calculated for point count data using: 200^/P(1-P). V = visual estimate using percent charts; PC = point count ing. 174 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 28 LOCATION: Figure 3.1 ROCK NAME: Quartzite HAND SPECIMEN DESCRIPTION: Fine grained, altered quartzite with muscovite on fractures and veins. Weathered surfaces are tan. Cassiterite, up to 3.0 mm in diameter and disseminated along fractures, is present in the specimen. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A. 15 Modal mineralogy for sample SA 28. Mineral/ % Method2 Comments Material L t s ) 1 Quartz 54 V Occurs as (1) with s e r i c i t e in a very fine grained mass (90%) avg 0.05 mm diameter (2) in veins (10%) up to 0.6 mm in diameter, averages 0.4 mm - anhedral Sericite 37 V - very fine grained mix with quartz, averages 0.05 mm diameter - with fine grained c h l o r i t e Muscovite. 5 V - averages 0.3 mm in diameter - occurs predominantly in veins - contains quartz Biotite 2 V - averages 0.3 mm in diameter - occurs predominantly in veins - contains quartz Opaques 2 V - averages 0.05 mm in diameter - within quartz, s e r i c i t e , muscovite and b i o t i t e S, standard deviation, i s calculated for point count data using zooyrnTp). V = visual estimate using percent charts; PC = point counting. 175 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 32 LOCATION: Figure 3 . 1 ROCK NAME: Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 75% K-feldspar, 5% plagioclase, 15% hornblende and 5% b i o t i t e . K-feldspar occurs as gray megacrysts up to 3.0 cm in diameter. Plagioclase, hornblende and bioite form the matrix which averages 5.0 mm in diameter. No alignment of the megacrysts was noted. Weathered surfaces are gray. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.16 Modal mineralogy for sample SA 32. M i nera1/ Material % Method2 Comments (+S)i Megacrysts Matri x Orthoclase (Orth) Plag ioclase (Plag) Quartz (Qtz) Hornblende (Hnblde) Biotite (Bi ) Sphene (Sph) Apat i te (Apa) Calcite (Calc) Opaques (Opa) 75 25 63 . 7 (4. i ; 8.5 (2.4) 2 . 7 (1.4) 16 . 1 (3.2) 8 . 2 (2.4) 0.8 (4.2) < 1 < 1 tr V V PC PC PC PC PC PC PC PC PC Occurs as: (1) megacrysts(95%) (2) matrix(5%) - size range: 0.5 mm - 2.0 cm - granophyric texture - contains plag, sph, b i , hnblde; opa, apa and qtz - s e r i c i t e alteration is on fractures and cleavage traces - An4 8 , andesine - up to 4.0 mm in length, averages 1.0 mm - contains opa - s e r i c i t e altered on cleavage planes and fractures ( from 5-90%) - exhibits growth zoning - megacrysts are aligned - up to 2.0 mm in diameter, averages 1.0 mm - within hnblde and orth - up to 2.5 mm in diameter, averages 1.0 mm - contains bi, sph, apa and a few r e l i c augite cores - up to 1.5 mm in diameter, averages 0.75 mm - contains apa, opa and hnblde - up to 0.2 mm in diameter, averages 0.05 mm - associated with bi, and hnblde - as inclusions within hnblde - contains hnblde - averages 0.05 mm in diameter - within orth, plag, qtz, hnblde and bi - averages 0.75 mm in diameter - as veinlets and crystal open space f i l l i n g s - averages 0.05 mm in diameter - as inclusions within a l l minerals except sph, apa and calc. 1 S, stundard deviation, i s calculated for point count data using: 2 0 0 J V i 1~) • 2 V = visual estimate using percent charts; PC = point counting. 176 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 33 LOCATION: F i g u r e 3.1 ROCK NAME: S y e n i t e HAND SPECIMEN DESCRIPTION: Co a r s e g r a i n e d s y e n i t e w i t h 7056 K - f e l d s p a r , 5% p l a g i o c l a s e , 20% h o r n b l e n d e and 5% b i o t i t e . K - f e l d s p a r m e g a c r y s t s a r e g r a y and up t o 4.0 mm i n d i a m e t e r . P l a g i o c l a s e , h o r n b l e n d e and b i o t i t e c o m p r i s e t he m a t r i x w i t h an a v e r a g e d i a m e t e r of 3.0 mm i n d i a m e t e r . K - f e l d s p a r c r y s t a l s a r e a l i g n e d . DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.17 Modal m i n e r a l o g y f o r sample SA 33. M i n e r a l / X Method 2 Comments M a t e r i a l (+S)» M e g a c r y s t s 75 V M a t r i x 25 V O r t h o c l a s e 57 . 6 PC O c c u r s a s : ( I ) m e g a c r y s t s ( 9 5 % ) ( O r t h ) ( 5 . 7) (2) m a t r i x ( 5 % ) - s i z e r a n ge: 2.0 mm - 2.2 cm - c o n t a i n s p l a g , b i , h n b l d e , apa, opa, aug and e p i - c o n t a i n s s e r i c i t e on f r a c t u r e s and c l e a v a g e p l a n e s P l a g i o c l a s e 13. 8 PC - An4 8, andes i ne ( P l a g ) ( 3 . 9) - up t o 4.0 mm i n l e n g t h , a v e r a g e s 2.0 mm - c o n t a i n s h n b l d e and opa - s e r i c i t e a l t e r e d on f r a c t u r e s and c l e a v a g e p l a n e s ( 5 - 8 0 % a l t e r a t i o n ) - e x h i b i t s growth z o n i n g H o r n b l e n d e 10. 6 PC - up t o 3.0 mm i n d i a m e t e r , (Hnblde) ( 3 . 5) a v e r a g e s 1.5 mm - c o n t a i n opa, apa, b i , aug, opx c o r e s , sph and e p i B i o t i t e 7.8 PC - up t o 3.0 mm i n d i a m e t e r , ( B i ) ( 3 . 1) a v e r a g e s 1.5 mm - c o n t a i n s e p i , sph, apa opa, p l a g , z i r c o n s , aug and opx - a l t e r e d by c h l o r i t e Aug i t e 5.8 PC - up t o 2.5 mm i n d i a m e t e r , (Aug) ( 2 . 7) a v e r a g e s 1.0 mm - as c o r e s w i t h i n h n b l d e and i n o r t h - p a r t l y r e p l a c e d by h n b l d e - c o n t a i n s b i , opa and h n b l d e O r t h o p y r o x e n e 4 . 4 PC - a v e r a g e s 1.5 mm i n d i a m e t e r (Opx) ( 2 . 3) - o c c u r s as c o r e s w i t h i n h n b l d e and r e l a t i v e l y u n a l t e r e d i n the m a t r i x - c o n t a i n s apa, b i , h n b l d e , and opa Q u a r t z < 1 PC - a v e r a g e s 0.1 mm i n d i a m e t e r ( Q t z ) - a n h e d r a l , open space f i l l i n g Sphene <1 PC - a v e r a g e s 0.05 mm i n d i a m e t e r (Sph) - a s s o c i a t e d w i t h h n b l d e and V\ i D 1 - o c c u r s w i t h i n h n b l d e E p i d o t e < 1 PC - a v e r a g e s 0.1 mm i n d i a m e t e r ( E p i ) - o c c u r s w i t h i n b i and o r t h , - c o n t a i n s apa - a s s o c i a t e d w i t h aug, opx, and h n b l d e Opaques < 1 PC - a v e r a g e s 0.05 mm i n d i a m e t e r (Opa) - w i t h i n o r t h , p l a g , h n b l d e , b i , aug and opx Apat i t e < 1 PC - a v e r a g e s 0.05 mm i n d i a m e t e r (Apa) - o c c u r s w i t h i n o r t h , p l a g , h n b l d e , b i , aug and opx S, s t a n d a r d d e v i a t i o n , i s c a l c u l a t e d f o r p o i n t c o u n t d a t a u s i n g : 200/p(1-PT. V = v i s u a l e s t i m a t e u s i n g p e r c e n t c h a r t s ; PC = p o i n t c o u n t i n g . 177 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 34 ROCK NAME: Syenite LOCATION: Figure 3.1 HAND SPECIMEN DESCRIPTION: Syenite with 50X K-feldspar, 30X hornblende and 25X biotite. K-feldspar megacrysts are gray and up to I.5 cm in diameter. Hornblende, biotite, plagioclase and orthoclase comprise the matrix and are up to 2.0 mm in diameter. Weathered surfaces have a red to brown-gray rind. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.18 Modal mineralogy for sample SA 34. Mineral/ Method2 Comments Material (+S)1 Megacryst 60 V Matrix 40 V Orthoclase 46 . 3 PC Occurs as: (1) megacrysts(30X) (Orth) (5 .8) (2) matrix!70%) - size range: 1.5 ram - 4.5 mm - granophyric texture - contains plag, hnblde, bi aug, opx, apa, opa and sph - sericite on fractures and cleavage planes Plagioclase 17 .0 PC - Ante, andesine (Plag) (4 .4) - up to 4.0 mm in diameter, averages 1.5 mm - contains opa, apa and calc - sericite on fractures and cleavage planes Quartz 3. 1 PC - up to 0.8 mm in diameter, (Qtz) (2 .0) averages 0.4 mm - f i l l s open spaces Hornblende 10 . 9 PC - up to 3.5 mm in length, (Hnblde) (3 .6) averages 1.5 mm - contains aug, opx cores, opa, apa, bi and sph - altered by chlorite Biotite 13 .3 PC - up to 3.0 mm in diameter, (Bi) (4 .0) averages 2.0 mm - contains opa, hnblde, aug and apa - altered by chlorite Augite 5 . 1 PC - up to 6.0 mm in diameter, (Aug) (2 .6) averages 2.0 mm - contains apa, bi, hnblde, opa and epi - pyroxene exsolution - altered by hornblende Orthopyroxene 4 . 3 PC - up to 4.0 mm in diameter, (Opx) (2 .4) averages 1.5 mm - contains opa, apa, hnblde, and bi Apatite <1 PC - averages 0.05 mm in diameter (Apa) - occurs within a l l minerals Epidote < 1 PC - averages 0.1 mm in diameter (Epi) - within aug - associated with mafics Sphene <1 PC - averages 0.2 mm in diameter (Sph) - irregular shaped - associated with mafics Opaques <1 PC - averages 0.05 mm in diameter (Opa) - within orth, plag, qtz, hnblde, bi, aug and opx S, standard deviation. is calculated for point count data using: 2 0 0 y P(1-P)• V = visual estimate using percent charts; PC = point counting. 178 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 37 ROCK NAME: Granite Dyke 10CATION: Figure 3.1 HAND SPECIMEN DESCRIPTION: Granitic dyke with 50% K-feldspar, 5% plagioclase, 40% quartz and 5% b i o t i t e . Dike is equigranular, average grain size is 2.0 mm in diameter. Contains traces of tourmaline as disseminations and patches. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A. 19 Modal mineralogy for sample SA37, Mineral/ Material % Method2 Comment (+S)i Orthoclase (Orth) Quartz (Qtz) Plagioclase (Plag) 51.3 (5.5) 40.3 (5.4) 6.9 (2.i PC PC PC Bioti te ( Bi ) Apati te (Apa) 1 . 5 (4.5) <1 PC PC up to 3.0 mm in diameter, averages 1.0 mm contains bi, qtz, apa, and r u t i l e s e r i c i t e altered along cleavage planes and fractures up to 3.0 mm in diameter, averages 1.0 mm anhedral, very irregular, interlocking grains contains r u t i l e needles and bi An24, oligoclase; poorly developed twinning up to 1.0 mm in diameter, averages 0.3 mm contains minor amounts of bi s e r i c i t e altered on fractures and cleavage planes up to 2.5 mm in diameter, averages 1.0 mm chl o r i t e altered within orth and qtz averages 0.05 mm in diameter within orth and bi 1 S, standard deviation, is calculated for point count data using: 2 0 0 J P l 1~) • 2 V = visual estimated using percent charts; PC = point counting. 179 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 39 LOCATION: Figure 3.1 ROCK NAME: Granite Dyke HAND SPECIMEN DESCRIPTION: Granitic or ap l i t e dyke with 50% K-feldspar, 10% plagioclase, 30% quartz, 10% hornblende and 1% b i o t i t e . The dyke is equigranular with an average grain size of 2.0 mm. Also present are traces of tourmaline, as 2.0 cm diameter patches, and disseminated pyrrhotite up to 8.0 mm in d iameter. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A. 20 Modal mineralogy for sample SA 39. Mineral/ % Method2 Comments Material (+S)l Orthoclase 52. 1 PC - up to 4.0 mm in diameter, (Orth) (5.4) averages 1.5 mm - contains bi and qtz - s e r i c i t e on fractures and cleavage traces Quartz 36 .0 PC - up to 1.5 mm in diameter, (Qtz) (5.2) averages 0.5 mm - anhedral, very irregular shaped - contains bi o t i t e Plagioclase 8 . 8 PC - An24, andesine (Plag) (3.1) - up to 3.5 mm in diameter, averages 0.75 mm - reverse zoning with a l b i t e cores and oligoclase rims - plag exhibits growth zoning Biotite 3 . 1 PC - up to 2.0 mm in diameter, (Bi) (1.9) averages 0.5 mm - within qtz and orth - c h l o r i t e altered Apat i te < 1 PC - averages 0.05 mm in diameter (Apa) - within orthoclase Sphene < 1 PC - averages 0.05 mm in diameter (Sph) - within orth 1 S, standard deviation, i s calculated for point count data using: 200/ P( 1-P~) • 2 V = visual estimate using percent charts; PC = point counting. ±80 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 40 LOCATION: Figure 3.1 ROCK NAME: Quartz Syenite HAND SPECIMEN DESCRIPTION: Quartz syenite with 55% K-feldspar, 15% plagioclase, 10% quartz, 15% hornblende and 5% biotite. K-feldspar megacrysts are gray up to 4.0 cm in length. Plagioclase, quartz, hornblende and biotite form the matrix that averages 2.0 mm in diameter. Weathered outcrop surfaces are gray. DESCRIPTION BY: SUA DATE: JULY 1985 TABLE A.21 Modal mineralogy for sample SA 40. Mineral/ % Method2 Comment Material (+S)1 Megacryst Matr ix Orthoclase 58.1 (Orth) (5.6) Plagioclase 13.7 (Plag) (3.9) Quartz (Qtz) Biotite (Bi) Aug i te (Aug) Sphene (Sph) Opaques (Opa) Apat i te (Apa) • Epidote (Epi) 8.6 (3.2) Hornblende 12.0 (Hnblde) (3.7) 6 . 4 (2.8) 1 . 2 (3.9) Orthopyroxene <1 (Opx) < 1 < 1 < 1 < 1 PC Occurs as: (1) megacrysts(90%) (2) matrix(10%) - size range: 2.0 mm - 3.5 cm - granophyric texture - contains plag, bi, hnblde, aug, qtz and opx - sericite altered on fractures and cleavage pianes PC - A n 5 0 , andesine - up to 4.5 mm in diameter, averages 2.0 mm - contains opa, hnblde and bi - sericite altered on cleavage planes and fractures (5-80% altered) PC - up to 2.5 mm in diameter, averages 1.5 mm - contains bi, plag, hnblde, and opa - anhedral PC - up to 3.5 mm in diameter, averages 1.5 mm - contains remnant aug and opx cores, opa, bi and apa - chlorite alteration PC - up to 1.5 mm in diameter, averages 1.0 mm - contains opa, apa plag and sph - wi thin hnblde - some chlorite alteration PC - up to 2.0 mm in diameter, averages 1.0 mm - within hnblde and replaced by hnblde - contains opa, apa, bi, and hnblde PC - averages 0.5 mm in diameter - core within hnblde; also replaced by hnblde PC - up to 1.5 mm in diameter, averages 0.5 mm - associated with hnblde and b i - within hnblde - contains epi PC - averages 0.5 mm in diameter - within orth, plag, qtz, hnblde, bi and aug PC - averages 0.05 mm in diameter - within hnblde Pc - averages 0.5 mm in diameter - associated with hnblde and bi - within bi S, s t a n d a r d d e v i a t i o n , i s c a l c u l a t e d f o r p o i n t c o u n t d a t a u s i n g : 200Jfl l - T ) • V = v i s u a l e s t i m a t e u s i n g p e r c e n t c h a r t s ; PC = p o i n t c o u n t i n g . 1 8 1 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 42 LOCATION: Figure 3.1 ROCK NAME: Quartz Syenite HAND SPECIMEN DESCRIPTION: Quartz syenite with 55% K-feldspar, 10% plagioclase, 15% quartz, 20% hornblende and a trace of b i o t i t e . K-feldspar occurs as: (a) predominantly zoned megacrysts (80%) up to 2.0 cm in diameter, and (b) matrix (20%) up to 2.0 mm in diameter. Quartz, plagioclase and mafics form the matrix that averages 3.0 mm in diameter. Hornblende and bio t i t e disseminations occur within the megacrysts. Weathered surfaces are gray. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.22 Modal mineralogy for sample SA 42. Mineral/ % Method2 Comments Material (+S)1 Megacrys ts 45 V Matrix 55 V Orthoclase 47 . 5 PC Occurs as: (1) megacrysts(85%) (Orth) (4. 8) (2) matrix)15%) - size range: 2.5 mm - 1.0 cm - granophyric texture - contains qtz, hnblde, b i , plag and opa - s e r i c i t e altered on cleavage traces and fractures Plagioclase 20. 9 PC - An4 5 , andesine (Plag) (3. 9) - up to 3.5 mm in length, averages 1.5 mm - contains opa, hnblde and apa - s e r i c i t e altered on cleavage planes and fractures - exhibits concentric growth zoning Quartz 12 . 5 PC - up to 3 . 0 mm in diameter, (Qtz ) (3. 2) averages 1.0 mm - contains opa, bi and hnblde - anhedral Hornblende 12 . 3 PC - up to 2.0 mm in diameter, (llnbl de ) (3. 2) averages 1.0 mm - contains opx, opa, b i , sph and apa - few cores of r e l i c opx occur - altered by chlo r i t e B i o t i t e 5 . 8 PC - up to 1.5 mm in diameter, (Bi) (2. 3) averages 0.75 mm - contain zircons opa, apa, and qtz Orthopyroxene 1 .0 1 PC - averages 1.5 mm in diameter (Opx) (4. 1 ) - replaced by hnblde - contains bi, hnblde and opa Sphene <1 PC - averages 0.05 mm in diameter (Sph) - within hnblde and bi Opaques < 1 PC - averages 0.05 mm in diameter (Opa) - within orth, plag, qtz, hnblde, bi and opx Apat i te < 1 PC - averages 0.05 mm in diameter (Apa) - within plag, bi and hnblde Epidote tr PC - averages 0.05 mm in diameter ( Epi ) - within orth and hnblde S, s t a n d a r d d e v i a t i o n , i s c a l c u l a t e d f o r p o i n t c o u n t d a t a u s i n g : 200/PI1-FT• J n V = v i s u a l e s t i m a t e u s i n g p e r c e n t c h a r t s ; PC = p o i n t c o u n t i n g . 182 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 43 ROCK NAME: Quartz Syenite LOCATION: Figure 3.1 HAND SPECIMEN DESCRIPTION: Quartz syenite with 50% K-feldspar, 20% quartz, 15% plagioclase and 15% hornblende. K-feldspar occurs as: (a) zoned megacrysts (90%) up to 3.0 cm in length, and (b) matrix (10%) up to 2.0 mm in diameter. Quartz, plagioclase and hornblende form the matrix with an average diameter of 2.0 ram. Feldspars are aligned north-south. Weathered surfaces are gray. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.23 Modal mineralogy for sample SA 43. Mineral/ % Method2 Comments Material ( +.S ) 1 Megacryst 45 V Matrix 55 V Orthoclase 53 . 1 PC Occurs as: (1) megacrysts(80%) (Orth) (5 .0) (2) matrix(20%) - size range: 1.5 mm - 2.0 cm - myrmekitic intergrowth of plag, qtz and orth - contains inclusions of plag, b i , hnblde, qtz, opx, and opa - s e r i c i t e altered on fractures and cleavage planes Plagioclase 18 .6 PC - An3 5 , andesine (Plag) (3 .9) - up to 4.0 mm in length, averages 1.5 mm - contains bi and opa - exhibits concentric growth zoning - plag aligned p a r a l l e l to the long direction of the orthoclase cr y s t a l - s e r i c i t e altered (5-80%) on cleavage planes and fractures Quartz 10 .0 PC - up to 3.0 ram in diameter, (Qtz) (3 .0) averages 1.5 mm - anhedral - contains bi and opa Hornblende 11 .2 PC - up to 3.5 mm in diameter, (Hnblde) (3 • 2) averages 1.0 mm - contains b i , opa, sph and qtz - c h l o r i t e altered B i o t i t e 7 . 1 PC - up to 1.5 mm in diameter, (Bi) (2 .6) averages 0.75 mm - contains zircons, opa and qtz - c h l o r i t e altered Sphene < 1 PC - averages 0.5 mm in diameter (Sph) - within hornblende Orthopyroxene <1 PC - averages 0.5 mm in diameter /Opx) - a few r e l i c cores are l e f t in hnblde - contains hnblde Opaques <1 PC - averages 0.05 mm in diameter (Opa) occurs within orth, plag, qtz, hnblde, b i , sph and opa 1 S, standard deviation. ia calculated for point count data using: 200/P( 1-P~) . J n V = visual estimate using percent charts; PC counting. 183 point APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 44 LOCATION: Figure 3.1 ROCK NAME: Granite HAND SPECIMEN DESCRIPTION: Quartz syenite with 60% K-feldspar, 20% quartz, 10% plagioclase, 10% hornblende and traces of b i o t i t e . K-feldspar megacrysts are gray and up to 6.0 x 20 mm. Quartz (brown, up to 3.0 mm in diameter), plagioclase (white, averages 2.0 mm in diameter), hornblende (dark green, up to 8.0 mm in diameter) and b i o t i t e (averages 1.0 mm in diameter) form the matrix. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.24 Modal mineralogy for sample SA 44. Mineral/ % Method2 Comments Material (+S)i Megacryst 45 V Matrix 55 V Orthoclase 57 .9 PC Occurs as: (1) megacrysts(90%) (Orth) (5 .3) (2) matrix!10%) - size range: 2.0 mm - 1.8 cm - granophyric texture - contains plag, b i , hnblde, qtz and opa - s e r i c i t e altered on fractures and cleavage planes Quartz 18 .4 PC - up to 3.0 mm in diameter, (Qtz) (4 .2) averages 1.0 mm - anhedral - contains b i , hnblde and apa Plagioclase 12 . 1 PC - An22, oligoclase (Plag) (3 .5) - up to 3.5 mm in length, averages 2.0 mm -exhibits growth and reversed zoning - contains bi - s e r c i c i t e altered (5-80%) on cleavage planes and f ractures Hornblende 8. 4 PC - up to 3.5 mm in diameter, (Hnblde ) (3 .0) averages 1.5 mm - contains qtz, bi, sph and apa - c h l o r i t e altered Biotite 3 . 2 PC - up to 2.0 mm in diameter, (Bi ) ( 1 .9) averages 1.0 mm - contains qtz and zircons - ch l o r i t e altered Sphene < 1 PC - averages 0.1 mm in diameter (Sph) - within hnblde Apatite. < 1 PC - averages 0.05 mm in diameter (Apa) - within orth, hnblde and qtz Opaques <1 PC - averages 0.05 mm in diameter (Opa) - within orthoclase S, standard deviation, is calculated for point count data using 200 /P(1-P). v n V = visual estimate using percent charts; PC = point counting. 184 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 45 ROCK NAME: Granite LOCATION: Figure 3.1 HAND SPECIMEN DESCRIPTION: Granite with 50% K-feldspar, 20% quartz, 10% plagioclase and 20% hornblende with a trace of b i o t i t e . K-feldspar megacrysts (80%) are zoned, up to 2.5 cm in diameter and unaligned. K-feldspar in the matrix are up to 3.0 mm in diameter. Plagioclase (white), quartz (brown), hornblende and bi o t i t e form the matrix and average 4.0 mm in diameter. Biot i t e books up to 8.0 mm in diameter occur and are l o c a l l y prominant. Weathered surfaces are gray. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.25 Modal mineralogy for sample SA 45. M ineral/ Material (+S)i Method2 Comments Megacrys ts Matrix Orthoclase (Orth) 45 55 52.6 (5.9) V V PC Plagioclase (Plag) Quartz (Qtz) llornb] ende (Hnblde) Biotite (Bi ) Sphene (Sph) Apat i te (Apa) Opaques (Opa) 22 . 3 (4.9) 2 . 8 (1.9) 15.6 (4.3) 6 . 7 (2.9) <1 < 1 <1 PC PC PC PC PC PC PC Occurs as: ( 1 ) megacrysts(85%) (2) matrix!15%) - size range: 2.0 mm - 1.5 cm - granophyric texture - contains plag, qtz, b i , hnblde and opa - s e r i c i t e altered on cleavage planes and fractures - A n 4 5 , andesine - up to 4.0 mm in length, averages 1.5 mm - exhibit growth zoning and myrmekitic texture - contains bi - averages 1.5 mm in diameter - anhedral - contains bi - up to 3.5 mm in diameter, averages 1;5 mm - contains bi, qtz, sph, opa, and one altered enstatite core - ch l o r i t e altered - up to 2.0 mm in diameter, averages 1.0 mm - contains zircons, opa and apa - up to 1.0 mm in diameter - in matrix associated with hnblde - averages 0.05 mm in diameter - euhedral - within orth and bi - averages 0.05 mm in diameter - occurs within orth, bi and hnblde 1 S, standard deviation• is calculated for point count data using: 20^/P( 1-P~) • V = visual estimate using percent charts; counting. 185 PC point APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 46 LOCATION: Figure 3.1 ROCK NAME: Granite HAND SPECIMEN DESCRIPTION: Granite with 55% K-feldspar, 20% quartz, 10% plagioclase, 15% hornblende, 15% tourmaline and trace b i o t i t e . K-feldspar megacrysts are zoned, up to 2.5 cm in diameter, and unaligned. Quartz, plagioclase, hornblende and b i o t i t e comprise the matrix and average 3.0 mm in diameter. B i o t i t e occurs in trace amounts in the matrix. Tourmaline occurs as veins up to 3.0 mm in width. A bleached envelope marks the vein. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.26 Modal mineralogy for sample SA 46. Mineral/ % Method2 Comments Material ( +.S)1 Megacrysts 40 V Matrix 60 V Orthoclase 41 .9 PC Occurs as: (1) megacrysts(95%) (Orth) (5 .7) (2) matrix(5%) - size range: 3.0 mm - 1.5 cm - contains plag, qtz,^bi, hnblde, and opa - s e r i c i t e altered on cleavage planes and fractures Plagioclase 18 . 1 PC - Ana2, andesine (Plag) (4 .5) - up to 4.0 mm in diameter, averages 2.0 mm - contains bi - s e r i c i t e altered (5-100%) on fractures and cleavage planes - muscovite alteration Quartz 25 .2 PC - averages 1.0 mm in diameter (Qtz ) (5 .0) - anhedral - contains bi Hornblende 5 . 4 PC - up to 3.5 mm in diameter, (Hnblde) (2 .6) averages 1.5 mm - contains b i , qtz, sph and trace c a l c i t e - chlorite altered Tourmaline 5 . 4 PC - occurs within a vein as (Tour) (2 .6) radiating crystals - vein contains qtz and to Biotite 4 . 0 PC - up to 2.0 mm in diameter, (Bi ) (2 .3) averages 0.75 mm - contains zircons and qtz - chlorite altered Sphene <1 PC - averages 0.3 mm in diameter (Sph) - associated with hnblde Opaques < 1 PC - averages 0.1 mm in diameter (Opa) - occurs within orth, hnblde and bi Apatite <1 PC - averages 0.05 mm in diameter (Apa) - occurs within qtz and orth S, standard deviation, is calculated for point count data using: 200/P( 1-P~ • V = visual estimate using percent charts; PC = point counting. . _ , APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 48 LOCATION: ROCK NAME: Megacrystic Granite Figure 3.1 HAND SPECIMEN DESCRIPTION: Megacrystic granite with 65% K-feldspar, 10% plagioclase, 20% quartz, 15% hornblende, trace b i o t i t e and tourmaline. K-feldspar megacrysts are zoned (pale pink rim and gray core), up to 2.0 cm in diameter and are unaligned. Quartz, plagioclase and mafics comprise the matrix and average 3.0 mm in diameter. Tourmaline occurs as small patches in the matrix. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.27 Modal mineralogy for sample SA 48. Mineral/ % Method2 Comments Material ( + S ) l Megacryst 40 V Matrix 60 V Orthoclase 53 .8 PC Occurs as: (1) megacrysts(90%) (Orth) (5 .8) (2) matrix (10%) - size range: 0.4mra - 1. 5 cm - contains plag, hnblde, aug, bi, qtz, ep and sph - s e r i c i t e on fracture planes and cleavage traces Plagioclase 15 .6 PC - An3 6 , andes ine (Plag) (4 .7) - up to 4.0 mm, average 2 . 5 cm - aligned p a r a l l e l to the long direction of K-feldspar - contains hnblde, bi and qtz - s e r i c i t e on fracture planes and cleavage traces - concentric growth zoning Quartz 18 .0 PC - up to 4.0 mm, average 1 . 0mm (Qtz) (4 .5) - occurs within a l l minerals as inclusions. - contains bioite - part of the matrix Hornblende 6 . 0 PC - up to 4.0 mm, average 1.5 mm (Hnblde) (2 .7) - contains b i , sph, qtz and calc - replaces augite - chlorite altered B i o t i t e 5 . 3 PC - up to 2.0 mm, average 1.0 mm (Bi ) (2 .5) - contains opa, qtz and zircons - chlorite altered Augite 1 . 3 PC - up to 4.5 mm, average 1.0 mm (Aug) (3 .9) - contains b i , qtz, sph and hnblde - l o c a l l y replaced by hornblende Sphene < 1 PC - up to 1.0 mm, average 0.5 mm (Sph) - associated with hnblde and bi - contains hnblde Opaques < 1 PC - averages 0.01 mm (Opa) - within a l l major minerals Calci te tr PC - averages 0.05 mm in diameter (Calc) - occurs as phenocrysts in the matrix 1 S, standard deviation. i s calculated for point count data using: 200 /PI1-P)• 2 V = visual estimate using percent charts; PC = point counting. 187 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 50 LOCATION: Figure 3.1 ROCK NAME: Coarse Grained Syenite HAND SPECIMEN DESCRIPTION: Coarse grained syenite with 75% K-feldspar, 20% hornblende and 5% b i o t i t e . K-feldspar megacrysts are up to 4.0 cm in length and are gray. Hornblende and b i o t i t e form the matrix and average 4.0 mm in diameter. Weathered surfaces are gray. Outcrops contain up to 5% xenoliths of chlorite schist. DESCRIPTION BY: SMA DATE: JULY 1985 TABLE A.28 Modal mineralogy for sample SA 50. Mineral/ % Method2 Comments Material ( t . s ) 1 Megacrysts 75 V Matrix 25 V Orthoclase 60 . 1 PC Occurs as: (1) megacrysts(95%) (Orth) (5 .55) (2) matrix(5%) - size range: 3.5 mm - 2.0 cm - granophyric texture - contains qtz, plag, b i , hnblde, apa, aug and opa - s e r i c i t e altered on fractures and cleavage planes Plag ioclase 14 .8 PC - Anas, andesine (Plag) (4 .03) - up to 4.5 mm in length, averages 2.0 mm - aligned p a r a l l e l to K-feldspar long axis - contains opa, bi and hnblde Hornblende 18 . 3 PC - up to 4.0 mm in length, (Hnblde ) (4 .39) averages 1.5 mm - contains sph, b i , aug cores, opa and apa - ch l o r i t e altered Augite 3 . 5 PC - up to 3.0 mm in length, (Aug) (2 • 1) averages 1.0 mm - contains hnblde, b i , apa and opa - within hnblde as remnant cores; replaced by hnblde Bioti t e 3 . 3 PC - up to 3.0 mm in length, (Bi) (2 .0) averages 1.0 mm - contains zircons, opa, hnblde, aug and apa - chl o r i t e altered Opaques < 1 PC - averages 0.05 mm in diameter (Opa) - occurs within orth, plag, hnblde, aug and bi Sphene <1 PC - averages 0.1 mm in diameter (Sph) - occurs within hnblde Apati te < 1 Pc - averages 0.05 mm in diameter (Apa) - occurs within orth, hnblde, bi and aug S, standard deviation, is calculated for point count data using: 200Jp( 1-p") • V = visual estimate using percent charts; PC = point count ing 188 APPENDIX A THIN SECTION DESCRIPTION SAMPLE NUMBER: SA 90 LOCATION: Figure 3.1 ROCK NAME: Tourmaline Orbicule Granite HAND SPECIMEN DESCRIPTION: Tourmaline orbicule granite contains 5% tourmaline orbicules up to 15 cm in diameter. Orbicules are 9594 radiating tourmaline with minor amounts of altered plagioclase, quartz and sulphides. The granite hosting the orbicules is composed of equigranular quartz (30%), K-feldspar (45%) and plagioclase (25%). Mafics are present in trace amounts. Matrix is tan and averages 3.0 mm in diameter. DESCRIPTION BY : SMA DATE: JULY 1985 TABLE A.29 Modal mineralogy for sample SA 90. Mineral/ % Method2 Comments Material ( +S) I Altered 62.1 PC - up to 3.5 mm in diameter, feldspar (3.72) averages 1.5 mm - contains inclusions of muse, qtz and tourm - altered by: s e r i c i t e and ca l c i t e on cleavage planes Quartz 30.9 PC - up to 3.0 mm in diameter, (Qtz) (3.43) averages 1.0 mm - anhedral - contains altered feldspar Tourmaline 4.0 PC - up to 2.0 mm in diameter, (Tour) ( 1 .46) averages 1.0 mm - contains qtz and altered feldspar - euhedral Muscovite 3.0 PC - up to 0.75 mm in diameter (Mus) - associated with feldspar S, standard deviation, is calculated for point count data using: 200/P(1-P)• •J n V = visual estimate using percent charts; PC = point counting. 189 APPENDIX B 190 APPENDIX B TABLE B . l : MICROPROBE SETUP M a t e r i a l : O r t h o c l a s e Megacryst KV: 15 C u r r e n t : 20nA X t a l : Spec 1 (HP): L i F Spec 2 ( L P ) : TAP Spec 3 (HP): PET Spec 4 (LP) : TAP Element L i n e S t d Name Std # Spec X t a l P o s i t +Bkg -Bkg/ D i f / Time Theor ( h i g h ) S l o p e I n t sec S i 0 2 K S a n i d i n e F423 3 PET 81448 + 800 + 800 I n t 10 A I 2 O 3 K S a n i d i n e F423 2 TAP 32460 + 1000 + 1000 I n t 10 CaO K A n o r t h o c l a s e F365 3 PET 38387 + 600 + 600 I n t 10 SrO L S t r o n t i a n i t e C23 4 TAP 26687 + 2226 + 2226 I n t 10 BaO L B a r i t e E16 1 LIF 68948 + 800 + 800 I n t 10 NaO K A n o r t h o c l a s e F365 2 TAP 46346 + 700 + 700 I n t 10 K2O K S a n i d i n e F423 3 PET 42750 + 600 + 600 I n t 10 Comments: A n a l y z e d w i t h beam w i d t h 3.5x3.5 R a s t o r 'ABLE B.2: Major e l e i e n t o i i d e analyses of four e l e c t i o n l i c r o p r o b e traverses across a K-feldspar l e g a c r y s t f r o i i a g r a n i t e on it s e n i c Sidge, Lost Sorses b a t h o l i t h , tuton. (robe t r a v e r s e s are shown on Plates 3.10 and 3.11. POINTS FEATURE SiO; A b O j CaO Sr0> BaO ha?0 K;0 TOTAL A8 OR AN Core 69 12 20 20 0 09 0.12 0 59 1 41 8 72 100 60 19 57 79 73 0.69 Core 65 90 19 31 0 14 0.21 0 76 1 52 13 80 101 97 14 21 85 05 0.74 Core 66 76 19 85 0 51 0.15 0 74 2 66 10 62 101 64 26 82 70 35 2.83 Core 67 14 19 51 0 42 0.18 0 74 2 76 10 96 102 18 27 04 70 70 2.26 Core 66 57 19 70 0 37 0.16 0 59 2 B7 11 03 101 63 27 77 70 26 1.97 Core 65 61 19 39 0 65 0.16 0 53 2 85 11 80 101 32 25 99 70 75 3.26 Core 67 45 19 54 0 16 0.19 • 0 79 2 41 11 58 102 47 23 81 75 30 0.89 Core 67 38 19 59 0 44 0.15 0 45 3 21 9 90 101 46 32 22 65 36 2.41 Core 67 62 19 36 0 16 0.12 0 36 3 74 10 89 102 60 34 00 65 18 0.82 Core 66 79 19 73 0 31 0.14 0 43 1 91 12 IB 101 83 18 91 79 39 1.70 Core 67 31 19 49 0 15 0.17 0 59 2 29 11 69 102 04 22 38 76 42 0.80 Core 66 50 19 33 0 17 0.15 0 60 1 73 13 17 101 98 16 50 82 60 0.90 Rii 66 95 18 97 0 02 0.06 0 44 1 49 13 7B 102 09 14 06 85 83 0.11 Rii 67 05 18 92 0 08 0.08 0 44 2 37 12 64 101 92 22 06 77 55 0.39 A l b i t e 68 03 19 43 0 15 0.11 0 45 4 46 9 20 102 IB 42 06 57 13 0.80 Rii 68 39 19 43 0 19 0.10 0 32 3 72 9 93 102 43 35 93 63 07 1.00 Rii 65 68 19 29 0 11 0.11 0 45 1 97 13 15 101 09 18 41 81 00 0.58 Rii 66 99 19 25 0 08 0.08 0 35 1 48 13 04 101 61 14 62 84 92 0.46 Rii 67 86 19 34 0 13 0.06 0 22 2 24 11 B8 102 08 22 08 77 21 0.72 Quart; 99 39 0 03 0 01 -0.02 0 01 0 00 0 00 99 93 36 18 18 92 44.90 Rii 67 42 19 01 0 04 0.03 0 04 1 75 13 17 101 79 16 75 83 06 0.19 Core 66 50 19 63 0 28 0.20 0 81 2 69 11 52 101 96 25 83 72 71 1.46 Core 66 57 19 16 0 17 0.18 0 78 2 14 13 02 102 36 19 B2 79 30 0.87 Core 66 17 19 44 0 43 0.16 0 77 2 07 12 75 102 12 19 32 7B 46 2.22 Core 66 84 19 72 0 40 0.15 0 87 2 98 11 25 102 56 28 08 69 84 2.08 Core 67 42 19 45 0 20 0.18 0 79 2 53 11 88 102 81 24 20 74 72 1.08 Core 66 25 20 04 0 91 0.15 0 73 2 63 10 64 101 69 25 94 69 08 4.98 Core 67 14 19 19 0 07 0.13 0 64 2 56 12 72 102 78 23 33 76 33 0.34 A l b i t e 64 61 21 62 2 78 0.15 0 57 4 08 7 27 101 41 39 25 45 96 14.79 Core 67 39 19 37 0 19 0.13 0 51 2 24 11 88 102 06 22 04 76 93 1.04 Core 67 11 19 32 0 13 0.13 0 52 2 30 12 24 102 09 22 05 . 77 27 0.68 Core 66 18 19 45 0 37 0.20 0 78 2 23 11 13 100 66 22 83 75 05 2.12 Core 66 25 19 78 0 53 0.16 0 78 2 35 10 66 100 83 24 30 72 65 3.04 Core 67 27 18 89 0 01 0.05 0 65 1 46 13 69 102 35 13 93 86 02 0.05 Core 66 97 19 58 0 43 0.15 0 67 2 87 11 06 102 07 27 61 70 11 2.28 Core 67 12 19 45 0 48 0.15 0 40 2 55 11 13 101 65 25 14 72 25 2.61 Core 66 28 19 02 0 11 0.14 0 50 1 89 13 50 101 79 17 46 81 98 0.57 Rii 67 34 13 89 0 09 0.09 0 24 1 82 13 80 102 60 16 63 82 92 0.45 Rii 67 50 19 01 0 07 0.09 0 24 1 B8 13 15 102 28 17 82 81 84 0.34 A l b i t e 68 89 19 01 0 14 0.12 0 31 . 4 82 8 21 101 84 46 79 52 46 0.75 Rii 67 53 19 09 0 12 0.11 0 49 1 34 13 85 102 88 12 73 86 61 0.65 Rii 66 77 18 98 0 06 0.05 0 19 1 74 13 89 102 02 15 96 83 72 0.32 Quart: 99 24 0 03 0 01 -0.01 0 00 0 00 0 00 99 78 8 55 20 71 70.74 B i o t i t e ? 35 39 11 68 0 01 O.00 0 00 0 07 10 13 57 47 1 08 98 84 0.08 B i o t i t e ? 35 15 11 87 0 01 0.00 0 08 0 10 9 98 57 36 1 54 98 35 0.11 Rii 66 85 19 03 0 11 0.07 0 40 1 83 13 61 102 24 16 90 82 54 0.56 Rii 66 16 18 96 0 11 0.11 0 30 1 67 14 43 102 07 14 90 84 54 0.56 Table B.2 (continued) POINTS FEATURE SiO? Al?0j CaO SrO 1 BaO Na;0 K?0 TOTAt AB OR AN 48 R i l 66 .30 18 .91 0 .08 0, .11 0 .36 1 .36 14.86 102. .32 12. 14 87 .46 0.39 49 A l b i t e 66 .84 18, .99 0 .02 0, .06 0 .50 2 .29 12.51 101. .55 21. 74 78. .16 0.10 50 R i l 66 .43 18 .78 0 .07 0 .09 0 .36 1 .19 14.91 102. .17 10. ,79 88. .86 0.35 51 A l b i t e 66 .67 19, .16 0 .22 0, .17 0. .45 2 .26 12.56 101 .81 21 .21 77 .67 1.12 52 Core 64 .49 18. .83 0 .07 0, .18 0, .65 0 .95 14.90 100. .40 8. 77 90 .87 0.36 52 Core 66 .69 18, ,98 0 .06 0 .10 0, .54 1 .83 13.86 102 .41 16 .68 83 .03 0.29 54 A l b i t e 66 .52 20, .06 0 .79 0. .14 0, .65 3 .18 10.38 102 .06 30 .42 65 .40 4.18 55 Core 66. .06 19, .03 0 .10 0 .12 0 .70 1 .37 13.97 101 .69 12 .90 86 .58 0.52 56 Core 66. .02 19, .07 0 .09 0, .13 0, .69 1 .70 13.89 101 .89 15 .61 83 .94 0.45 57 Core 65. ,99 19, .08 0 .11 0. .15 0. 84 1 .52 13.54 101. .57 14 .49 84 .91 0.60 58 Core 66. ,5B 19. 60 0 .14 0, .17 0. .97 2. .30 11.66 101 .75 22 .90 76 .33 0.76 59 Core 66. ,05 19. ,05 0 .33 0. 18 0. .85 2 .94 11.59 101. .74 27 .38 70 .90 1.72 60 Core 66. .69 19. 77 0, .50 0. 14 0. 84 2, .32 10.75 101 .33 23 .96 73 .17 2.87 61 Core 66. ,82 . 19. .61 0 .37 0. .19 0. 84 2, .58 11.32 102. .01 24. .84 73 .17 1.99 62 Core 66. .51 ' 19. .62 0, .60 0. .17 0. .75 2, .63 10.82 101. ,43 26. .05 70 .67 3.28 63 Core 66. .94 19. 51 0, .52 0. .16 0 .62 2 .64 11.61 102, .34 24 .99 72 .31 2.70 64 Core 66. .96 19. .44 0 .17 0, .17 0, .56 1 .79 12.74 102. 18 17. 40 81 .70 0.90 65 Core 66. .47 19. ,26 0 .11 0. 13 0. .49 1, .62 13.30 101. 73 15. 55 83. .86 0.59 66 Core 66. .63 18. .91 0. .08 0. 13 0. .51 1, .84 14.08 102. .50 16. 48 83. 15 0.37 67 Core 66. .96 19. ,74 0 .58 0. 19 0. 70 2 .73 10.42 101. .66 27. .59 69. 19 3.22 68 Core 66. .71 19. .62 0. .36 0. .23 0. SO 2, .37 10.93 101. .36 24. ,37 73. .68 2.05 69 Core 66. .41 19. 72 0, .70 0, .19 0. .68 2, .58 10.49 101. 11 26. 15 69. .95 3.91 70 Core 65. .54 19. .46 0, .36 0. 24 0. .84 1 .88 12.45 101. .11 18. ,33 79. .73 1.95 71 Core 66. 59 19. 81 0, .46 0. .18 0. 79 3, .08 10.75 102. .00 29, ,58 67. .99 2.43 72 B i o t i t e ? 34. ,89 11. 89 0, .01 0. .00 0. .00 0, .09 9.98 57 .03 1. 3S 98. .56 0.06 73 B i o t i t e ? 31. .78 12. 30 2, .47 0. .00 0. .00 0. .10 0.70 47 .50 4. 97 23 .93 71.10 74 A l b i t e 67. ,87 19. 45 0 .10 0, .06 0. .32 4. .09 9.71 101. .94 38, .80 60 .68 0.52 75 R i l 65. ,41 18. ,94 0. .06 0, .08 0. 49 1. .85 14.32 101. .48 16 ,3B 83 .34 0.28 76 R i i 50. ,12 18. ,49 0. .74 0. .04 0. .28 2. .07 6.91 78 .91 29. ,40 64 .76 5.84 77 R i l 66. ,93 19. 10 0. .04 0, .08 0. 18 1. .08 15.11 102. 86 9. ,78 90 .05 0.18 78 R i l 65. .91 19, ,68 0. .42 0. .20 0, .70 2, ,59 11.45 101. 29 25. .04 72. .72 2.23 79 Core 66. .62 19. .62 0. .37 0, .17 0. .74 2, .50 11.04 101. 40 25. .08 72. .87 2.05 80 Core 67. 42 19. 63 0 .35 0. 18 0. .78 2, .04 12.03 102. 77 20. 07 78. .02 1.91 81 Core 66. .86 19. ,80 0. ,42 0, .16 0. .76 2. .34 11.45 102. 13 23. .15 74. .53 2.32 82 Core 66. .65 19. ,78 0. .41 0. .18 0. .80 2, .23 11.34 101. .71 22. .48 75. .25 2.27 83 Core 66. .51 19. ,79 0. .70 0. .17 0. .83 2, 82 10.13 101. .29 2B. .54 67. .55 3.91 84 Core 67, ,23 19. ,75 0 .42 0. .17 0. .83 2, .37 11.90 103. .00 22. .69 75. .06 2.25 85 Core .18 19. ,52 0. .25 0, .22 0. .94 2, .49 12.05 102. .99 23. .56 75. .13 1.30 86 Core 67, ,42 20. ,32 0. .98 0. .13 0 .54 3, .01 8.09 100. 83 33. .91 59. .97 6.12 87 Core 67 .35 19. .60 0 .22 0, .24 0, .89 2, .63 11.45 102. 73 25. .60 73. .20 1.20 88 Core 67, .14 19. ,90 0. .34 0, ,22 0. .99 2, .32 10.57 101, .81 24. .55 73. .49 1.96 89 Core 67 ,19 19. ,75 0 .53 0, .21 0, .83 2. .72 10.73 102, .30 27 .01 70. .08 2.91 90 Core 64, .92 20. .18 1 .26 0. .18 0, .69 3, .26 10.00 100. .82 30. .94 62 .46 6.60 91 Core 64. ,03 19. ,20 0, .22 0. .20 1 .30 1 .48 14.20 100, 96 13 .52 85 .37 1.11 1 S t r o n t i u i data c o r r e c t e d using the f o l l o n i n g f o r i u l a : Total SrO : Measured SrO - (0.10051lxSiO; »t»). APPENDIX C 194 APPENDIX C LABORATORY PROCEDURES FOR STRONTIUM, RUBIDIUM AND ROCK LEAD ISOTOPE ANALYSES C . l . l WHOLE ROCK SAMPLE PREPARATION Rock samples were broken u s i n g a h y d r a u l i c r o c k -s p l i t t e r u n t i l t h e y were of s u i t a b l e s i z e f o r c r u s h i n g (7 t o 8 cm d i a m e t e r ) . Weathered o u t e r s u r f a c e s were d i s c a r d e d . The r o c k c h i p s were c r u s h e d w i t h a j a w - c r u s h e r and then ground u s i n g a t u n g s t e n c a r b i d e r i n g m i l l (5 m i n u t e s ) u n t i l t he powder d i d not f e e l g r i t t y . The m i l l was c l e a n e d between samples u s i n g d i s t i l l e d w a ter and compressed a i r . The f i r s t l o a d of r o c k powder was d i s c a r d e d ; the second and subsequent l o a d s were saved f o r a n a l y s i s . C.1.2 ZONED FELDSPAR SAMPLE PREPARATION A b l o c k o f r o c k e n c l o s i n g a f e l d s p a r c r y s t a l , a p p r o x i m a t e l y 3 cm i n d i a m e t e r and w i t h d i s t i n c t z o n i n g , was c u t u s i n g a l a r g e diamond r o c k saw. T h i s b l o c k was trimmed w i t h t h i s saw t o about 2 cm by 3 cm; c a r e was t a k e n not t o c u t t h e c r y s t a l . The r e s u l t i n g b l o c k and c o n t a i n e d c r y s t a l 195 was then c u t i n t o a s e r i e s of w a f e r - t h i n s l i c e s u s i n g an o i l - b a t h Micromet saw. A new saw b l a d e was used f o r t h e s e samples t o a v o i d c o n t a m i n a t i o n from e a r l i e r c u t s u l p h i d e samples. C r y s t a l s l i c e s were washed w i t h soap and w a t e r , and r i n s e d w i t h d i s t i l l e d w ater. Excess c o u n t r y r o c k s u r r o u d i n g t h e c r y s t a l was removed by sna p p i n g t h e wa f e r s w i t h t h e a s s i s t a n c e o f a s t a n d a r d r a z o r b l a d e . The c r y s t a l was d i v i d e d i n t o c o r e and r i m p o r t i o n s w i t h t h e a i d of a r a z o r b l a d e and a b i n o c u l a r m i c r o s c o p e . Cores were d i s t i n g u i s h e d from r i m s by t h e i r p a l e r p i n k c o l o u r . Core and r i m c h i p s were s t o r e d s e p a r a t e l y i n c l e a n e d g l a s s b o t t l e s . C h i p s were hand c r u s h e d w i t h an agate m o r t a r and p e s t l e . The mortar and p e s t l e were c l e a n e d a f t e r e v e r y sample w i t h compressed a i r and acetone. C.2 BIOTITE AND HORNBLENDE SEPARATION FROM WHOLE ROCK AND ZONED FELDSPAR SAMPLES The m a j o r i t y o f t h e b i o t i t e and ho r n b l e n d e were removed w i t h heavy l i q u i d s e p a r a t i o n . Samples were put t h r o u g h bromoform (S.G.= 2.35) t w i c e and a v i s u a l e s t i m a t e o f t h e r e m a i n i n g b i o t i t e and hor n b l e n d e was r e c o r d e d . Most o f t h e r e m a i n i n g b i o t i t e and hor n b l e n d e i n t h e sample was s e p a r a t e d 196 u s i n g the F r a n t z i s o d y n a m i c s e p a r a t o r . Ramp f e e d was 50, c o n t a i n e r f e e d was 29, magnetic a n g l e was s e t a t 14°, and the c u r r e n t was 0.7 amps. Samples were f e d th r o u g h t h r e e t i m e s a t a low speed t o remove as much m a f i c m i n e r a l as p o s s i b l e . Remaining b i o t i t e and hornblende c o n t e n t was r e c o r d e d . Samples were then ground f o r 15 minutes on a m e c h a n i c a l agate m o r t a r ( p r e v i o u s l y washed and c l e a n e d w i t h acetone. C.3 METHOD FOR SIMULTANEOUSLY DETERMINING LEAD, STRONTIUM, RUBIDIUM, NEODYMIUM AND SAMARIUM ISOTOPE COMPOSITION C.3.1 Sample D i s s o l u t i o n 1. 0.300 gm o f m i n e r a l s e p a r a t e o r whole r o c k powder was weighed out on a t o p - l o a d i n g M e t t l e r b a l a n c e i n t o l a r g e t e f l o n bombs o f K r o g h - d e s i g n . Beaker h o l d e r numbers, beaker l e t t e r s ( i m p r e s s e d on t h e s i d e o f t h e b e a k e r ) , and sample number were r e c o r d e d i n a l a b book. Because the c o r e and r i m powders, were of l i m i t e d s u p p l y , 0.300 g were u s e d - - t h i s i s l e s s than t h e s t a n d a r d amount u s u a l l y used (0.60 g ) . 2. In a fume hood, 2 ml of HF and 10 drops of 2B 12.5N HNO3 were s l o w l y added t o 0.300 g of r o c k powder. T h i s was 197 d r i e d on a hot p l a t e a t a p p r o x i m a t e l y 100°C. A f e r c o o l i n g , a d d i t i o n of HF was r e p e a t e d and the bomb was assembled. The bombs were cooked i n t h e oven a t 190°C f o r 24 hours t o i n s u r e d i s s o l u t i o n of a c c e s s o r y phases. The oven was t u r n e d o f f ; as t h e bombs c o o l e d , the l i d s were screwed down ( a p p r o x i m a t e l y e v e r y o n e - h a l f h o u r ) . When c o o l (so one c o u l d h a ndle w i t h o u t g l o v e s ) , they were t r a n s f e r e d t o 10 ml S a v i l l e x b e a k e r s . The s o l u t i o n was e v a p o r a t e d a t a p p r o x i m a t e l y 100°C t o d r y n e s s i n a l a m i n a r - f l o w hood. 5 ml of 6N HC1 and 10 drops of 2B 12.5 HNO3 were added and t h e sample was d r i e d . T h i s was r e p e a t e d . 5 ml o f 3N HC1 (enough t o c o v e r the bottom of the beaker) was added t o r e -d i s s o l v e t h e sample. The sample was then r e a d y f o r t r a n s f e r t o t h e i o n exchange columns. I f the sample was run i m m e d i a t e l y through t h e columns, a l i d was put on a f t e r removal from the hot p l a t e t o i n h i b i t e v a p o r a t i o n . The samples g e n e r a l l y were a l l o w e d t o s i t o v e r n i g h t t o ensure good d i s s o l u t i o n . C.3.2 ION EXCHANGE COLUMNS Lead, s t r o n t i u m and REE s e p a r a t i o n t o o k a p p r o x i m a t e l y 9 hours u s i n g t h e i o n exchange columns because t h r e e elements 198 were t a k e n o f f i n sequence. Columns used were about 100 cm l o n g and h e l d 100 ml. The n i g h t b e f o r e ( a f t e r .7 p.m. o r r e s i n c o u l d have d r i e d ) t h e ru b b e r s t o p p e r s were p u l l e d o f f the columns t o a l l o w them t o d r a i n . 30 a c i d c l e a n e d t e f l o n b e akers and 30 spaces on a hot p l a t e were needed d u r i n g t h i s column s e p a r a t i o n p r o c e d u r e . The f o l l o w i n g n o t e s e x p l a i n s p e c i f i c d e t a i l s : 1. R e s e r v o i r s were r i n s e d w i t h 5 ml o f 3N HCL, from a s q u i r t b o t t l e (columns were r o t a t e d w h i l e a c i d was added). Columns were a l l o w e d t o d r a i n , and t h e n the washing was r e p e a t e d . A l l r e s i n was f l u s h e d out of the r e s e r v o i r i n t o t h e column. 2, W h i l e columns were d r a i n i n g , 10 numbered and a c i d -c l e a n e d p l a s t i c c e n t r i f u g e tubes ( l a b e l l e d w i t h an i n s o l u b l e marker) were p l a c e d i n n u m e r i c a l o r d e r i n two r a c k s . Samples, soaked i n 3N HC1, were t r a n s f e r r e d t o t h e s e c e n t r i f u g e t u b e s . Beakers and t h e s i d e s o f tubes were r i n s e d w i t h s m a l l amounts of 3N HC1 t o i n s u r e t h a t a l l o f t h e sample was a t t h e bottom o f t h e tube. They were not a l l o w e d t o end up more than o n e - t h i r d f u l l . Beaker numbers were checked a g a i n s t h o l d e r and tube numbers. C e n t r i f u g i n g f o r about 2 minutes a t a s e t t i n g of 6 ( t u b e s had t o be 199 balanced in the centrifuge) was s u f f i c i e n t to separate l i q u i d s from s o l i d s . 3. The main stopcock was opened to allow the column reservoirs to f i l l with 3N HC1. The reservoir burette, with the valve arrow pointing up, was f i l l e d to the top (where the burette pinches i n ) . When a l l the burettes were f i l l e d , the main stopcock was closed. Loading tubes were .then placed i n the columns (handled only by t h e i r exterior and not by t h e i r ends). When a l l cleaning acid soaked into the resin, the sample from the centrifuge tube was poured into the loading tube (centrifuge tube and column numbers were matched to check the correct order). Any sample s p i l l s while loading were washed or blotted. The loading tubes were removed and returned to the corresponding centrifuge tube as soon as the pouring was complete (care was taken not to touch the reservoir walls), eliminating the p o s s i b i l i t y of loading two d i f f e r e n t samples into the same column. If the loading tube touched the reservoir a kimwipe was used to blot the s p i l l , or i t was rinsed with a small amount of 3N HC1. Tygon tubing was placed on the burette t i p s and extended into the open end of the reservoir. The entire sample was allowed to soak into the re s i n BEFORE the eluting 2 0 0 a c i d was added. Meanwhile l o a d i n g tubes were c l e a n e d by r i n s i n g i n warm t a p w a t e r , f o l l o w e d by d e i o n i z e d w a t e r , and then by an a c i d b a t h i n a p e r f o r a t e d beaker. (NOTE: For the element s e p a r a t i o n p r o c e d u r e , a c i d was c o m p l e t e l y soaked i n t o the r e s i n b e f o r e a d d i t i o n a l a c i d was added. Pb, Rb, Sr and Nd-Sm samples were c o l l e c t e d a t the m i l l i l i t r e markings shown i n T a b l e C I . ) 4. Lead C o l l e c t i o n : Column t i p s were r i n s e d w i t h q u a r t z water. The c o l l e c t i o n beaker h o l d e r numbers and t e f l o n beaker i d e n t i f i c a t i o n l e t t e r ( s ) were r e c o r d e d i n t h e notebook. T e f l o n beakers were p l a c e d under t h e t i p o f t h e column on an i n v e r t e d g l a s s beaker. A c i d from the b u r e t t e s was added a few ml a t a t i m e . The r e s e r v o i r was r o t a t e d w h i l e t h e a c i d was d r i p p e d i n . A f t e r a l l o w i n g the a c i d t o soak i n , t h i s p r o c e d u r e was r e p e a t e d . A c i d t o f i l l t he column below the r e s e r v o i r was added and a l l o w e d t o soak i n . T h i s was r e p e a t e d u n t i l t h e a c i d l e v e l r e a c h e d the approximate 20 ml mark. A c i d t h a t s t a r t e d t o have a y e l l o w t i n t t o i t (around the 14 t o 16 ml mark) s i g n a l e d the p r e s e n c e of i r o n . Once a y e l l o w t i n t was o b s e r v e d the t e f l o n sample beaker was removed. ( A c c o r d i n g t o T a b l e C . l 201 to o M I'20ml 1 0 0 m l S O m l 6 0 m l 4 0 m l go m l 2 0 m l 4 0 m l 6 0 m l 8 0 m l 1 0 0 m l Ml Elutant 1 2 0 m l MO m l Table C.I l e a d i s removed b e f o r e i r o n appears; because i r o n i s d i f f i c u l t t o remove i n t h e e n s u i n g l e a d a n a l y s i s i t i s a v o i d e d ) . Beaker numbers were checked a g a i n s t column numbers t o ensure p r o p e r sample i d e n t i f i c a t i o n . T e f l o n beakers were then p l a c e d on a hot p l a t e i n a l a m i n a r fume hood a t a p p r o x i m a t e l y 100°C. G l a s s beakers were t u r n e d u p r i g h t t o c o l l e c t t h e d i s c a r d a c i d between Pb and Sr c o l l e c t i o n . A c i d was added u n t i l t h e i n i t i a l S r c o l l e c t i o n marks on a p p r o p r i a t e columns was reached. The a c i d was a l l o w e d t o soak i n . 5.Rubidium C o l l e c t i o n : Column t i p s were r i n s e d w i t h q u a r t z w a t e r . The c o l l e c t i o n beaker h o l d e r numbers and t e f l o n beaker i d e n t i f i c a t i o n l e t t e r ( s ) were r e c o r d e d i n the notebook. The t e f l o n b eakers were p l a c e d under t h e t i p of the column on an i n v e r t e d g l a s s beaker. A c i d was added t o the lower l i m i t f o r Rb on the columns and a l l o w e d t o d r a i n . The t e f l o n b eakers were removed ( c a r e was t a k e n t o a v o i d t o u c h i n g the column t i p s ) . Beaker numbers were checked a g a i n s t column numbers t o ensure p r o p e r sample i d e n t i f i c a t i o n . T e f l o n b e a k e r s were p l a c e d on a hot p l a t e i n a l a m i n a r fume hood a t a p p r o x i m a t e l y 100°C. G l a s s 203 b e a k e r s were t u r n e d u p r i g h t t o c o l l e c t the d i s c a r d a c i d between Rb and S r c o l l e c t i o n . 6 . S t r o n t i u m C o l l e c t i o n : Column t i p s were r i n s e d w i t h q u a r t z water. The c o l l e c t i o n beaker h o l d e r numbers and t e f l o n beaker i d e n t i f i c a t i o n l e t t e r ( s ) were r e c o r d e d i n the notebook. The t e f l o n b e akers were p l a c e d under the t i p of the column on an i n v e r t e d g l a s s beaker. A c i d was added t o the lower l i m i t f o r S r on the columns and a l l o w e d t o d r a i n . The t e f l o n beakers were removed ( c a r e was t a k e n t o a v o i d t o u c h i n g the column t i p s ) . Beaker numbers were checked a g a i n s t column numbers t o ensure p r o p e r sample i d e n t i f i c a t i o n w i t h column numbers. T e f l o n b eakers were p l a c e d on a hot p l a t e i n a l a m i n a r fume hood a t a p p r o x i m a t e l y 100°C. Tygon t u b i n g was removed and c l e a n e d w i t h q u a r t z w a t e r . 7.Rare E a r t h Element C o l l e c t i o n : G l a s s b eakers were t u r n e d u p r i g h t t o c o l l e c t t h e d i s c a r d a c i d . 25 ml of 6N HC1 was added t o columns 1, 2, 7 and 8, and 20 ml of 6N HC1 was added t o columns 3, 4, 5, 6, 9 and 10. T h i s a c i d was a l l o w e d t o d r a i n . The column t i p s were r i n s e d w i t h q u a r t z 204 w a t e r . The c o l l e c t i o n beaker h o l d e r numbers and t e f l o n beaker i n d e n t i f i c a t i o n l e t t e r ( s ) were r e c o r d e d i n the notebook. T e f l o n beakers were p l a c e d under t h e column t i p on an i n v e r t e d g l a s s beaker. 20 ml o f 6N HC1 was added and c o l l e c t e d i n t e f l o n b e a k e r s . A f t e r the a c i d d r a i n e d , t h e t e f l o n beakers were removed ( c a r e was t a k e n not t o t o u c h the column t i p s ) . Beaker numbers were checked a g a i n s t column numbers. The t e f l o n b eakers were p l a c e d on a hot p l a t e i n a l a m i n a r fume hood a t a p p r o x i m a t e l y 100°C. 8 . C o l u m n P r e p a r a t i o n : Once Pb, Rb, S r and REE have been c o l l e c t e d the columns were c l e a n e d . The g l a s s b e a k e r s were t u r n e d u p r i g h t and t h e l u c i t e p a n e l was i n s e r t e d t o r e s t r i c t a c i d fumes. The w a l l s and neck of the r e s e r v o i r were washed down w i t h 6N H C l - - t h e stream of the s q u i r t b o t t l e was aimed about 3 mm below t h e r i m o f t h e r e s e r v o i r neck. ( I t was s q u i r t e d s t r o n g l y so t h a t a c i d f l o w e d around the r e s e r v o i r ) . The r e s e r v o i r was r o t a t e d so t h a t a l l s i d e s were washed down. The r e s e r v o i r was f i l l e d t o a p p r o x i m a t e l y one h a l f a c e n t i m e t e r above t h e l e v e l of the l u c i t e h o l d e r . The s i g n was changed t o "6N-HC1". Columns shrank and d r a i n e d i n about 3 hours and were u s u a l l y l e f t o v e r n i g h t . 205 Columns were backwashed as f o l l o w s : (1) The l u c i t e p a n e l was removed and a s p a r e empty, t a p - w a t e r - r i n s e d beaker was a v a i l a b l e f o r each column. The a c i d from the p r e c e e d i n g s t e p was dumped i n t o the s i n k w i t h the water r u n n i n g i n both s i n k s . (2) F o r each column i n t u r n , the tygon tube from t h e q u a r t z water r e s e r v o i r (above the columns) was connected t o the column t i p . A s t i r r i n g r o d ( k e p t i n a p a r a f i l m - c o v e r e d g r a d u a t e d c y l i n d e r on t h e bench) was i n s e r t e d i n t u r n i n t o each r e s e r v o i r t o h e l p break up any lumps o f r e s i n . W i t h the w ater s t o p c o c k opened and t h e clamp removed, r e s i n was pushed up i n t o t h e r e s e r v o i r . Once the c l e a r w ater broke t o the s u r f a c e i n t h e r e s e r v o i r , t h e p i n c h c o c k clamp was r e p l a c e d i m m e d i a t e l y . The t y g o n tube was p u l l e d o f f the d r i p t i p , and an empty beaker was q u i c k l y p l a c e d under t h e column t i p . The s t i r r i n g r o d was c a r e f u l l y moved t o the n e x t column w i t h o u t t o u c h i n g t h e r e s e r v o i r r i m . When a l l of the columns were f i n i s h e d the water s t o p c o c k was c l o s e d , t h e c e n t r i f u g e tube c o v e r was r e p l a c e d on t h e t i p of t h e tygon t u b i n g , and the p i n c h c o c k was hung on the hook. The s i g n was changed t o "Q-water". 206 (3) When a l l t h e q u a r t z water had d r a i n e d , the r e s i n was r i n s e d from the r e s e r v o i r w a l l s w i t h 3N HC1. The a c i d was a l l o w e d t o soak i n and t h e p r o c e s s was r e p e a t e d s e v e r a l t i m e s . (4) 10 ml of 3N HC1 was added from the b u r e t t e s and a l l o w e d t o soak i n . T h i s r e - e q u i l i b r a t e d the r e s i n w i t h 3N a c i d . (5) Rubber s t o p p e r s were i n s e r t e d i n t o the d r i p t i p s of the columns u s i n g a s l i g h t t w i s t i n g motion w h i l e h o l d i n g onto t h e t o p s of t h e r e s e r v o i r s t o i n s u r e a good s e a l . (6) An a d d i t i o n a l 20 ml of 3N HC1 from the b u r e t t e s was added. (7) The f r o n t and t o p l u c i t e p a n e l s were r e p l a c e d and the s i g n was changed t o 3N HC1. Once the S r , Rb, Nd and Sm samples had e v a p o r a t e d t o d r y n e s s , a few drops o f HC104 were added t o t a k e up the sample; t h e n t h e samples were t r a n s f e r r e d t o t e f l o n p l a n c h e t t e s . The p l a n c h e t t e s were a r r a n g e d on t h e hot p l a t e s u r f a c e w i t h t w e e z e r s i n the same a r r a y as t h e beakers i n th e h o l d e r . Each sample was poured i n t o the a p p r o p r i a t e p l a n c h e t t e and t h e beaker was r i n s e d w i t h a few drops o f 207 HCIO4. The beaker was r e t u r n e d t o i t s p l a c e i n t h e aluminum h o l d e r . The sample was d r i e d a t 200° t o 230°C w i t h t h e lamp on. The sample was t a k e n t o complete d r y n e s s ( i . e . no a c i d drops were a l l o w e d t o remain on the s i d e of the p l a n c h e t t e ) . W h i l e the sample was d r y i n g a s e t of s m a l l p l a s t i c boxes were a r r a n g e d i n the same o r d e r as the p l a n c h e t t e s . Boxes were l a b e l l e d w i t h t h e column number, c o l l e c t i o n beaker number, element c o l l e c t e d and sample number. Beaker numbers and l a b e l s were c r o s s - c h e c k e d b e f o r e removing t h e beaker h o l d e r and the beakers t o the washing c y c l e . When the p l a n c h e t t e s were d r y t h e y were removed from the hot p l a t e and p l a c e d on a c o o l s u r f a c e f o r a minute; t h e y were then put i n s i d e the p l a s t i c boxes. The (Rb, S r ) samples were then ready t o be l o a d e d on f i l a m e n t s f o r mass s p e c t r o m e t r y o r f o r f u r t h e r p u r i f i c a t i o n s t e p s (Sm-Nd). 9. P r o c e d u r e f o r F u r t h e r P u r i f i c a t i o n of Rock Leads Once samples ( l e a d sample, s e c t i o n 4 ) , were d r y they were t a k e n up w i t h enough IN HBr t o c o v e r t h e bottom of t h e t e f l o n beaker. B e t t e r r e s u l t s were re a c h e d i f the s o l u t i o n c o u l d be l e f t f o r a few hours b e f o r e r u n n i n g t h r o u g h the 10 208 ml columns. C l e a n 10 ml columns, f i l l e d w i t h 2-3 cm of c l e a n r e s i n , were s e t up i n p l a s t i c column h o l d e r s . A f t e r a l l o w i n g t h e q u a r t z water t o d r a i n from the r e s i n the f o l l o w i n g ensued: (1) t h e f i r s t t h r e e s t e p s c l e a n e d the r e s i n and t h e columns, (2) s t e p 4 c o n d i t i o n e d the r e s i n , (3) s t e p 5 l o a d e d t h e sample, (6) the r e s u l t a n t e l u t a n t from s t e p s 6 t o 8 c o u l d have been saved f o r uranium a n a l y s i s , and (7) the e l u t a n t from t h e f i n a l s t e p 9 was saved f o r l e a d a n a l y s i s . ( A l l l i q u i d s were a l l o w e d t o d r a i n c o m p l e t e l y b e f o r e t h e next s t e p proceeded.) D e t a i l s of the 9 s t e p s a r e : Step 1: 10 ml of q u a r t z water was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 2: 10 ml of 6N HC1 was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 3: 10 ml o f q u a r t z w a t e r was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 4: 10 ml of IN HBr was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 5: The sample was added and a l l o w e d t o d r a i n . Step 6: 2 ml o f IN HBr was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d t w i c e . 209 Step 7: 10 ml of IN HBr was added and a l l o w e d t o d r a i n . Step 8: 2 ml o f 2N HC1 was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 9: L a b e l l e d t e f l o n b eakers were p l a c e d under q u a r t z water c l e a n e d t i p s . 8 ml of 6N HC1 was added and a l l o w e d t o d r a i n . The beakers were p l a c e d on a hot p l a t e a t 100°C and a l l o w e d t o d r y . The 10 ml columns were c l e a n e d u s i n g t a p w a t e r , r i n s e d i n q u a r t z water and then p l a c e d i n a c l o s e d c o n t a i n e r of 6N HC1. A f t e r t h e sample was d r y a few ml o f 2N HC1 was added and a l l o w e d t o s i t f o r a few hours. F u r t h e r l e a d s e p a r a t i o n was completed u s i n g 3 ml columns. Columns were p l a c e d i n p l a s t i c h o l d e r s and a p p r o x i m a t e l y 1 ml o f r e s i n was added and a l l o w e d t o d r a i n . The f o l l o w i n g 8 s t e p s were completed. The f i r s t 3 s t e p s c l e a n e d t h e columns and the r e s i n . Step 4 c o n d i t i o n e d t h e r e s i n . Step 5 added th e sample. Steps 6 and 7 c o u l d have been c o l l e c t e d f o r uranium a n a l y s i s . The e l u t a n t from the f i n a l s t e p was c o l l e c t e d f o r l e a d i n a c l e a n t e f l o n beaker. D e t a i l s o f the e i g h t s t e p s a r e : 210 Step 1: 2 ml of q u a r t z water was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 2: 2 ml of 6N HC1 was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 3: 2 ml o f q u a r t z water was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d . Step 4: 2 ml of 2N HC1 was added and a l l o w e d t o d r a i n . Step 5: The sample s o l u t i o n was added and a l l o w e d t o d r a i n . Step 6: A few drops of 2N HC1 was added, a l l o w e d t o d r a i n ; t h i s p r o c e s s was r e p e a t e d t w i c e . Step 7: 2 ml o f 2N HCL was added and a l l o w e d t o d r a i n . Step 8: L a b e l l e d c l e a n t e f l o n b eakers were p l a c e d under q u a r t z water r i n s e d t i p s . 2 ml o f 6N HC1 were added and a l l o w e d t o d r a i n . The beakers were p l a c e d on a hot p l a t e a t 100°C and a l l o w e d t o d r y . Once t h e sample was d r y i t was rea d y t o be l o a d e d onto f i l a m e n t s and run on the mass s p e c t r o m e t e r . 211 10. P r o c e d u r e f o r F u r t h e r P u r i f i c a t i o n o f Samarium and Neodymium The p r o c e d u r e f o r f u r t h e r p u r i f y i n g samarium and neodymium i s o u t l i n e d i n Appendix D. C.4 METHOD FOR DETERMINING ROCK LEAD, STRONTIUM, RUBIDIUM, SAMARIUM, AND NEODYMIUM ISOTOPE COMPOSITION USING THE ISOTOPE DILUTION METHOD A s p i k e was added t o the r o c k powders f o r the i s o t o p e d i l u t i o n method. I n t h i s s t u d y l e a d , s t r o n t i u m , r u b i d i u m , neodynium and samarium v a l u e s were measured and one l a r g e "super s p i k e " was used. The super s p i k e c o m p o s i t i o n i s as f o l l o w s : 2 o a p b _ 3.4937g (7.104%) i 5 0 N d / i 4 9 S m _ 6.9985g (14.231%) 8 9 S r - 17.6291g (35.847%) 8 7 R b - 21,0 578g (42.819%) T o t a l 49.7908g 100.001% 1.4 g of super s p i k e was added t o each sample. The s p i k e was weighed i n t o t h e K r o g h - d e s i g n t e f l o n bombs w i t h t h e whole r o c k o r m i n e r a l s e p a r a t e powders. I s o t o p e r a t i o s were 212 d e t e r m i n e d f o l l o w i n g t h e p r o c e d u r e s o u t l i n e i n s e c t i o n C.3.1. Samarium and neodymium p r o c e d u r e s a r e o u t l i n e d i n Appendix D. 213 APPENDIX D 214 November 20, 1989 ANALYTICAL PROCEDURES K-Ar: K is determined in duplicate by atomic absorption using a Tschtrc.n AA4 spectrophotometer on dilute sulphate solutions buffered by Na and Li nitrates. Ar is determined by isotope dilution using an AEI MS-10 mass spectrometer with Carey Model 10 vibrating reed electrometer, high purity 3 8 A r spike, and conventional gas extraction and purification procedures as described by White and others (1967). The errors reported are for range of multiple analyses for K and for estimated one standard deviation for the calculated date. Decay constants are those recommended by the IUGS Subcommission on Geochronology (Steiger and Jager, 1977). Rb-Sr. Rock samples of hand specimen size or larger from core samples, outcrops, and quarries were crushed in jaw and disc mills and then finely ground in a motor-driven agate mortar. Rb and Sr concentrations were determined by replicate analyses of pressed powder pellets using X-ray fluorescence. United States Geological Survey rock standards were used for calibration; mass absorption coefficients were obtained from Mo K-alpha Compton scattering measurements. Rb/Sr ratios have a precision of 2% (one sigma) where both concentrations exceed 50 ppm. If either concentration is below 50 ppm the ratio uncertainty is based on an uncertainty in the concentration measurement of 1 ppm. Concentrations have a precision of 5% or 1 ppm, whichever is greater. Sr isotopic composition was measured on unspiked samples prepared using standard ion exchange techniques. Sr isotopic measurements were made on a Vacuum-Generators Isomass 54R mass spectrometer automated with a Hewlett-Packard HP-85 computer Measured ratios have been normalized to a 8 6 S r / 8 8 S r ratio of 0.1194 and adjusted so that the National Bureau of Standards standard SrC0 3 (SRM 987) gives a 8 7 S r / 8 6 S r ratio of 0.71019 ± 215 November 20, 1989 0.00002 and the Eimer end Amend Sr standard a ratio of 0.70800 ± 0.00002. The precision of a single 8 7 S r / 8 6 S r ratio is normally < 0.0001 (one sigma). Any exceptions are noted. Rb-Sr dates are based on a Rb decay constant of 1.42 x 10" ' 'a ' 1 (Steiger and Jager, 1977). The regressions are calculated according to the technique of York (1967). Errors reported are one standard deviation or the standard error of the mean, unless otherwise noted. For samples with very low Sr or Rb concentrations or extremely high Rb/Sr ratios conventional isotope dilution techniques, using high purity 8 4 S r and 8 7Rb spikes, are used to obtain concentrations with a precision of 1.5$. The Rb/Sr ratio precisions, forspiked samples, will be similar to good XRF data at about 2%. Sr isotopic compositions measured on spiked samples and some mineral separates are of lower precision than usually obtained for unspiked whole rocks. Blanks for Rb and Sr are approximately 0.8 and 6 nanograms, respectively. U-Pb: Zircons are separated from finely crushed 10 to 40 kg rock samples using a wet shaking table, heavy liquids, and magnetic separator. The concentrates are washed in nitric acid or aqua regia, sized using new nylon mesh screens, split into magnetic (M) and nonmagnetic (NM) fractions, and hand picked to essentially 100$ purity as required. Concordance is sometimes improved by air abrasion techniques (Krogh, 1982). Chemical dissolution and mass spectrometry follow the procedures of Krogh (1973). Prior to 1987 we used a mixed ^ o p b - ^ U spike and the U and Pb mass spectrometry were done separately. After 1987 a mixed 205pb_233u_ 235JJ spike is used (Parrish and Krogh, 1987; Roddick and others, 1987). The dissolution is now in small-volume teflon capsules contained in a large November 20, 1989 Porr bomb (Porrish, 1987). Both U ond Pb ore now eluted into the some beaker and loaded and run together on the same Re filament with silica gel and phosphoric acid, U being run first, at somewhat lower temperature than the Pb. After 1987 a Daly collector was used to improve the quality of measurement of low-intensity 2 0 4 P b signals. U-Pb dote errors ore obtained by individually propagating all calibration ond measurement uncertainties through the entire dote calculation ond summing the individual contributions to the total variance (Nunes, 1980). The laboratory blonk has an isotopic composition: Pb 206:207:208:204 = 17.75, 15.57, 37.00, 1.00. The isotopic composition of common Pb is based on the Stocy ond Kramers (1975) common Pb growth curve. The decoy constants are those recommended by the IU6S Subcommission on Geochronology (Steiger and Jager, 1977). Concordia intercepts ore based on York (1969) regression and Ludwig (1980) error olgorithm. Errors reported for the row U-Pb doto ond final dotes and shown on concordia plots ore two sigmo (95$ confidence limits). Blanks for U ond Pb are approximately 0.03 ond 0.10 nanograms, respectively. Sm-Nd: Sample dissolution is done in Krogh (1973) teflon dissolution bombs at 200°C for 24 hours or longer, with special precautions to insure complete dissolution before ion exchonge procedures begin. Initial separation of REE is done on the same 100-200 mesh Dowex 50-X8 ion exchonge resin columns used for Sr separation with 3.0N HC1. After Sr is eluted the REE+Ba are stripped with 6N HC1. For isotope dilution onolyses o mixed 1 4 9 S m - 1 5 0 N d spike (colibroted using SPEX Sm (Sm67 lot 05781, 85.3$ Smj and Nd [ND64-1 lot 02811, 84.0$ Nd] oxides) is added before dissolution: the REE ore then further 217 November 20, 1989 purified after the initial separation by passing through the first columns again, this time loaded and eluted with 5N HC1 which gives better separation of Bo from REE (McCulloch, 1980). The dried heavy REE fraction is loaded with water on the To side filament of a double filament bead (the center filament is Re) and the mixed REE spectrum run on the moss spectrometer (Thirwall, 1982). The concentration reproducibility for successive dissolutions is only about 2$ (one sigma) but the ratios generally agree within 1$. Analyses of CIT liquid standard (provided by L. Farmer and D. J. DePaolo) indicate that the spike calibrations are accurate to within 0.1$ for Sm/Nd ratio (the numbers reported should be increased 0.1$ to give exact fit to the CIT calibration) and 1.3$ for concentration (presumably due to nonstoichiometry of the oxides used for standardization) (the numbers reported ore slightly lower than if analyzed with respect to CIT standards - Sm should be increased 1.3$, and Nd 1.2$ to give CIT agreement). For isotope composition runs Nd is separated from Sm and other elements using 2 methyl-lactic acid (2MLA) columns as described by Whitford et al. (1978). The 2MLA elutant containing Nd is baked at 150°C to volatilize water and 2MLA and loaded with water on the Ta side filament of a double filament bead (the center filament is Re). Isotope ratio measurements ( 1 4 4 Nd/ ' 4 3 Nd, corrected for 1 4 4 S m interference via '^'Sm, and , 4 6 Nd/ , 4 3 Nd) are repeated alternately until a two sigma isotope ratio precision of 20 ppm or better is obtained. Runs are aborted if the run quality deteriorates. Ratios are normalized to a , 4 6 N d / , 4 4 N d ratio of 0.7219 (O'Nions et al., 1979) and adjusted upwards 63 ppm so that analyses of the BCR-1 basalt standard give a 1 4 3 N d / 1 4 4 N d ratio of 0.512665+0.000020 (two sigma error) (a compilation of 13 values reported by other labs gives 0.512656+0.000006; BCR-1 has 218 November 20, 1989 cNd=0.00±0.05 = 0.512638±0.000025 according to Wasserburg et al., 1981). Our i.n-hcuso ,Md oxids standard gives a corrected ratio of 0.511544±0.000032. The corrected ratio for the CIT liquid Sm/Nd concentration standard is 0.511909+0.000044, compared to CIT measurements of 0.511928±0.000008 (normalized to 146Nd/ , 44Nd=0.7129) (Wasserburg et al., 1981). The La Jolla standard ( provided by G. Lugmair) gives a corrected ratio of 0.511868+0.000024 (a compilation of 9 values reported by other labs gives 0.511858±0.000009; for this standard cNd=-15.15±0.43 = 0.511861 ±0.000022 according to Wasserburg et al., 1981). The Nd oxide standard of the University of Alberta (provided by Min Sun) gives a corrected value of 0.511082 ± 0.000010, compared to a U of A value of 0.511069+0.000003 (normalized to 0.7129 and adjusted so that BCR-1=0.512656). Errors In cNd(O), cNd(T), T(DM), etc. are obtained by propagating all uncertainties in measurement through the appropriate calculation. In the case of Sm-Nd isochrons, calculated following York (1967), the error for initial Nd is calculated for the value predicted by the regression at ^ S m / 1 ^=0.1967 (CHUR value) (Fletcher and Rosman, 1982). Blanks for Sm and Nd are approximately 0.8 and 4 nanograms, respectively. REFERENCES CITED Carlson, R. W., 1980, Cmcl-mantio differentiation of the Earth and Moon: Evidence from isotopic studies for contrasting mechanisms and duration: Ph.D. thesis, University of California at San Diego, San Diego, 219 p. Fletcher, I. R. and Rosman, K. J. R., 1982, Precise determination of initial 219 November 20, 1989 from Sm-Nd isochron data: Geochimica et Cosmochimica Acta, v.46, p. 1983-1987. Krogh, T. E., 1973, A low-contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations: Geochimica et Cosmochimica Acta, v. 37, p. 485-494. Krogh, T. E., 1982, Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique: Geochimica et Cosmochimica Acta, v. 46, p. 637-649. Ludwig, K. R., 1980, Calculation of uncertainties of U-Pb isotope data: Earth and Planetary Science Letters, v. 46, p. 212-220. McCulloch, M. T., 1980, Samarium-neodymium and rubidium-strontium chronology of crustal formation: Ph.D. thesis, California Institute of Technology, Pasadena, Part 1,292 p. Nunes, P. D., 1980, The Ontario Geological Survey geochronology research program - an overview: Ontario Geological Survey Misc. Paper 92, p. 4-6. O'Nions, R. K., Carter, S. R., Evensen, N. M., and Hamilton, P. J., 1979, Geochemical and cosmochemical applications of Nd isotope analysis: Annual Review of Earth and Planetary Science, v. 7, p. 11-38. Parrish, R. R., 1987, An improved micro-capsule for zircon dissolution in U-Pb geochronology: Chemical Geology, Isotope Geoscience Section, v. 66, p. 99-102. Parrish, R. R. and Krogh, T. E., 1987, Synthesis and purification of 2 0 5 P b for U-Pb geochronology: Chemical Geology, Isotope Geoscience Section, v. 66, p. 103-110. Roddick, J. C, Loveridge, W. D., and Parrish, R. R., 1587, Precise U/Pb dating of zircon at the sub-nanogram Pb level: Chemical Geology, Isotope Geoscience Section, v. 66, p. 111 -121. Stacey, J. S. and Kramers, J. D., 1975, Approximation of terrestrial lead 220 November 20, 1989 isotope evolution by o two-stage model: Earth ond Planetary Science Letters, v. 26, p. 207-221. Steiger, R. H. ond Jager, E., 1977, Subcommission on Geochronology: Convention on the use of decoy constants in geo- and cosmochronology: Earth ond Planetary Science Letters, v. 36, p. 359-362. Thirwall, M. F., 1982, A triple-filament method for rapid ond precise analysis of rare-earth elements by isotope dilution: Chemicol Geology, v. 35, p. 155-166. Wossertjurg, G. J., Jocobsen, S. B., DePaolo, D. J., McCulloch, M. T., and Wen, T., 1981, Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions: Geochimica et Cosmochimico Acta, v.45, p. 2311-2323. White, W. H., Erickson, G. P., Northcote, K. E., Dirom, G. E., end Horakol, J. E., 1967, Isotopic doting of the Guichon Batholith, B. C: Canadian Journol of Earth Sciences, v.4, p. 677-690. Whitford, D. J., White, W. M., Hofmonn, A. W., ond James, D. E., 1978, Separation ond isotopic analysis of neodymium: Carnegie Institute of Washington Yearbook 77, p. 620-623. York, D., 1967, The best isochron: Earth ond Planetary Science Letters, v. 2, p. 479-482. York, D., 1969, Least-squares fitting of a straight line with correlated errors: Eorth ond Planetary Science Letters, v. 5, p. 320-324. 221 APPENDIX E 222 TABLE E . l : A l l l e a d I s o t o p e d a t a f o r s a i p l e s t r o a A r s e n i c R i d g e , L o s t B o r s e s b a t h o l i t h , Tulton. SAMPLE NORMOATE RUN RUNQUAL:TEMP P 8 2 0 6 : 4 PREC64 PB207:4 P874 P 8 2 0 8 : 4 P884 P 8 2 0 7 : 6 P876 P B 2 0 8 : 6 P886 NUMBER IM/DD/YY NO :BLOCKS NORM ABS+/- NORM A8S+/- NORN A B S t / - NORM . A 8 S » / - NORM A B S t / -SA06HR 12/08/87 1 good 1250 05 19 110 0 000 15 660 0 000 39 001 0 001 0 819437 0 00004 2 . 0 4 0 7 9 3 0 . 0 0 0 1 6 6 SA11HR 12/19/87 1 good 1200 07 19 532 0 001 15 710 0 000 39 441 0 002 0 804320 0 000045 2 . 0 1 9 3 0 3 0 . 0 0 0 3 2 6 'SA1IHR 0 2 / 0 8 / 8 8 1 poor 1150 10 19 475 0 003 15 683 0 000 39 376 0 026 0 805307 0 002367 2 . 0 2 1 9 2 0 0 . 0 0 5 0 7 0 SA18WR 12/08/87 1 poor 1200 02 19 183 0 006 15 752 0 001 39 551 0 082 0 821127 0 001622 2 . 0 6 1 7 2 3 0 . 0 1 0 5 1 3 SA18NR1 01/11/8B 2 f a i r 1200 09 19 173 0 001 15 692 0 000 39 219 0 003 0 818457 0 000076 2 . 0 4 5 5 0 2 0 . 0 0 0 2 4 3 SA24HR 12/09/87 1 f a i r 1200 11 20 2 4 0 ' 0 005 15 701 0 001 39 222 0 055 0 775778 0 000067 1 . 9 3 7 8 5 7 0 . 0 0 0 5 1 8 SA24HR 1 01/11/88 2 good 1200 05 20 242 0 001 15 706 0 000 39 212 0 003 0 775891 0 000096 1 . 9 3 7 1 3 9 0 . 0 0 0 2 0 7 SA33HR 12/19/87 1 f a i r 1200 07 19 136 0 002 15 630 0 000 39 080 0 006 0 816819 0 000105 2 . 0 4 2 2 4 1 0 . 0 0 0 2 5 7 SA33HR 12/27/87 poor 1200 18 19 155 0 002 15 660 0 000 39 142 0 007 0 817541 0 000139 2 . 0 4 3 4 4 2 0 . 0 0 0 3 9 6 SA38HR 12/20/87 1 good 1200 10 19 544 0 001 15 688 0 ooo 39 340 0 002 0 802710 0 000075 2 . 0 1 2 8 3 5 0 . 0 0 0 1 3 6 SA39HR 12/09/87 1 f a i r 1200 13 20 493 0 002 15 720 0 000 39 385 0 008 0 767104 0 000077 1 . 9 2 1 8 2 6 0 . 0 0 0 2 0 0 SA41HR 12/14/B7 1 good 1200 10 19 578 0 001 15 684 0 000 39 380 0 003 0 801108 0 000052 2 . 0 1 1 4 7 2 0 . 0 0 0 2 6 9 SA42HR 12/19/87 1 goad 1200 06 1? 571 0 001 15 685 0 000 39 307 0 002 0 601449 0 000034 2 . 0 0 8 4 4 1 0 . 0 0 0 2 6 0 SA45HR 12/19/87 1 good 1150 07 19 677 0 001 15 700 0 000 39 433 0 001 0 797903 0 000059 2 . 0 0 3 9 9 8 0 . 0 0 0 0 9 1 SA45HR 12/19/87 1 good 1150 07 19 677 0 001 15 700 0 000 39 433 0 001 0 797903 0 000059 2 . 0 0 3 9 9 8 0 . 0 0 0 0 9 1 SA4BHR 12/14/87 1 good 1250 07 19 609 0 001 15 693 0 000 39 362 0 002 0 800313 0 000067 2 . 0 0 7 3 6 6 0 . 0 0 0 3 2 9 SA48HR 12/14/87 1 good 1250 07 19 609 0 001 15 693 0 000 39 362 0 002 0 800313 0 000067 2 . 0 0 7 3 6 6 0 . 0 0 0 3 2 9 SflSOWR 12/27/87 1 good 1230 15 19 372 0 001 15 708 0 000 39 276 0 002 0 810839 0 000035 2 . 0 2 7 4 3 5 0 . 0 0 0 0 7 6 SA50NR 0 2 / 0 8 / 8 8 1 good 1170 08 19 403 0 001 15 689 0 000 39 253 0 001 0 808616 0 000085 2 . 0 2 3 0 3 7 0 . 0 0 0 2 1 2 SA90NR 12/14/87 1 good 1200 12 20 240 0 001 15 707 0 000 39 243 0 003 0 776034 0 000057 1 . 9 3 8 8 9 6 0 . 0 0 0 1 6 6 SA48H8 12/14/87 1 good 1200 11 20 99B 0 001 15 794 0 000 41 750 0 002 0 752164 0 000061 1 . 9 8 8 2 5 2 0 . 0 0 0 3 8 2 SA48HB 0 2 / 0 8 / 8 8 1 good 1190 08 21 193 0 001 15 785 0 000 41 879 0 002 0 744843 0 000060 1 . 9 7 6 0 7 6 0 . 0 0 0 3 4 3 SA488I 12/14/87 1 f a i r 1200 09 21 110 0 002 15 760 0 000 40 284 0 014 0 746557 0 000133 1 . 9 0 8 2 7 0 0 . 0 0 0 4 3 4 S A 4 8 B P 0 1 / 1 5 / 8 8 good 1200 09 21 100 0 001 15 761 0 000 40 256 0 002 0 746977 0 000059 1 . 9 0 7 8 8 9 0 . 0 0 0 0 9 8 SA48TF 12/14/87 1 good 1200 11 19 281 0 001 15 674 0 000 39 098 0 001 0 812942 0 000056 2.027817 0 . 0 0 0 1 1 4 SA4BBC 12/28/87 1 good 1200 07 19 153 0 001 15 684 0 000 39 046 0 001 0 818882 0 000048 2 . 0 3 8 6 1 6 0 . 0 0 0 2 6 4 SA4B8R 12/2B/87 1 good 1200 11 19 188 0 001 15 673 0 000 39 040 0 003 0 816779 0 000097 2 . 0 3 4 5 4 4 0 . 0 0 0 1 9 8 SA48CC 12/28/87 1 f a i r 1200 18 19 241 0 002 15 732 0 000 39 206 0 010 0 817613 0 000086 2 . 0 3 7 6 1 7 0 . 0 0 0 2 5 0 SA48CR 12/28/87 1 good 1200 07 19 152 0 001 15 653 0 000 38 966 0 001 0 817307 0 000082 2 . 0 3 4 4 9 2 0 . 0 0 0 1 6 1 SA4BDC 0 1 / 0 3 / 8 7 1 f a i r 1200 10 19 176 0 001 15 674 0 000 39 022 0 002 0 817375 0 000111 2 . 0 3 4 9 6 0 0 . 0 0 0 3 8 9 SA48DR 0 1 / 0 3 / 8 7 1 good 1200 08 19 185 0 000 15 670 0 000 39 042 0 000 0 B16772 0 000027 2 . 0 3 4 9 7 1 0 . 0 0 0 0 8 0 SA48EC 0 1 / 0 3 / 8 7 1 good 1200 10 19 154 0 001 15 644 0 000 38 967 0 002 0 816738 0 000065 2 . 0 3 4 3 3 0 0 . 0 0 0 2 3 1 SA48ER 0 1 / 0 3 / 8 7 1 good 1200 13 19 228 0 001 15 680 0 000 39 103 0 001 0 815504 0 000078 2 . 0 3 3 6 5 0 0 . 0 0 0 2 7 5 SA46FC 0 1 / 0 3 / 8 7 1 good 1200 07 19 194 0 001 15 667 0 000 39 026 0 001 0 816240 0 000057 2 . 0 3 3 2 3 5 0 . 0 0 0 1 0 2 SA48FR 01/03/87 1 good 1200 07 19 177 0 001 15 654 0 000 38 9 8 2 0 001 0 816303 0 000069 2 . 0 3 2 7 4 0 0 . 0 0 0 1 9 7 SA48CIR 0 1 / 0 7 / 8 8 1 good 1150 14 19 182 0 001 15 675 0 000 39 045 0 001 0 817139 0 000045 2 . 0 3 5 4 7 7 0 . 0 0 0 0 7 1 TABLE E . l ( c o n t i n u e d ) BLANK CORRECTED2 TINE CORRECTED1 5ANPLE PB 204PB P8206/4 PB6/4 PB207/4 P87/4 PB208/4 PB8/4 PB206/4 PB6/4 P8207/4 PB7/4 PPM PPH WIOIES ABS+/- •/- •/- •/- •/-SA06MR 1186.4 9 0.07658 0 . 5 19.110 0 . 0 0 0 15.660 0.000 39.001 0.001 19.103 0 . 0 0 1 15.660 0 . 0 0 0 SA06MR 1771.5 9 0.11434 0 . 3 19.110 0.000 15.660 0.000 39.001 0.001 19.105 0.001 15.660 0 . 0 0 0 SA06NA-AVG [19.110] ( 0 . 0 0 0 ] [15.660] [ 0 . 0 0 0 ] [19.103] [ 0 . 0 0 1 ] [ 1 5 . 6 6 0 ] [ 0 . 0 0 0 ] SA11NR 2 3 . 3 0.00149 19.532 0.001 15.710 0.000 39.441 0 . 0 0 2 SA11NR 2 3 . 3 0.00149 19.475 0.003 15.683 0.000 39.376 0 . 0 2 6 SA11HR-AVG (19.504) [ 0 . 0 0 2 ] [15.697] [ 0 . 0 0 0 ] [ 3 9 . 4 0 9 ] [ 0 . 0 1 4 ] SA18HR B 9 . 3 5 0.00571 3.7 19.183 0.006 15.752 0.001 39.551 0 . 0 8 2 19.129 O.0O8 15.749 0.0010 SA13NRI 8 8 . 6 5 0.00569 3 . 7 19.173 0.001 15.692 0.0000 39.219 0 . 0 0 3 19.119 0 . 0 0 6 15.689 0 . 0 0 0 3 SA18HR-AVG (19.178) (0.003) [15.722] [ 0 . 0 0 1 ] [ 3 9 . 3 8 5 ] [ 0 . 0 4 3 ] [ 1 9 . 1 2 4 ] [ 0 . 0 0 7 ] [15.719) [ 0 . 0 0 1 ] SA24NR 7 8 . 8 15 0.00499 1 2 . 5 20.240 0 . 0 0 5 15.701 0.001 39.222 0 . 0 5 5 2 0 . 0 5 4 0 . 0 2 1 15.692 0.001 SA24HR1 7 9 . 2 15 0.00502 12.5 20.242 0.001 15.706 0 . 0 0 0 39.212 0 . 0 0 3 2 0 . 0 5 7 0 . 0 2 0 15.697 0.0009 SA24NR-AVG (20.241) ( 0 . 0 0 3 ) [15.704] [0.001] [39.217] [ 0 . 0 2 9 ] [ 2 0 . 0 5 6 ] [ 0 . 0 2 1 ] [ 1 5 . 6 9 5 ] [ 0 . 0 0 1 ] SA33HR 4 8 . 0 0.O0310 19.136 0.002 15.630 0 . 0 0 0 39.080 0 . 0 0 6 SA33HR 4 8 . 2 0.00310 19.155 0.002 15.660 0 . 0 0 0 39.142 0.007 SA33HR-AVG (19.146) (0.002) [15.645] ( 0 . 0 0 0 ) [39.111] ( 0 . 0 0 7 ] SA3BHR 3 0 . 8 0.00197 19.544 O.O01 15.6B8 0.003 3 9 . 3 4 0 0 . 0 0 1 SA39NR 41.1 57 0.00259 95.1 20.493 0 . 0 0 2 15.720 0.019 3 9 . 3 8 5 0 . 0 0 8 19.081 0 . 0 5 0 15.652 0.0202 SA41HR 4 6 . 4 14 0.00296 20.1 19.578 0.001 15.684 0.006 39.380 0 . 0 0 3 19.279 0.011 15.670 0.006 SA42HR 6 6 . 8 0.00427 19.571 0.001 15.685 0.005 39.307 0 . 0 0 2 SA45WR 3 8 . 3 0.00243 19.667 0.001 15.700 0.000 3 9 . 4 3 3 0 . 0 0 1 SA45KR 3 9 . 8 0.00253 19.667 0.001 15.700 0 . 0 0 0 3 9 . 4 3 3 0.001 SA45HR-AVG [19.667) [ 0 . 0 0 1 ] [15.700] [ 0 . 0 0 0 ] [ 3 9 . 4 3 3 ] [ 0 . 0 0 1 ] SA48HR 9 5 . 5 13 0.00609 8 . 9 19.609 0.001 15.693 0 . 0 0 0 3 9 . 3 6 2 0 . 0 0 2 19.477 0.014 15.687 0.0006 SA4BHR 127.4 13 0.00813 6 . 7 19.609 0.001 15.693 0.000 39.362 0 . 0 0 2 19.510 0.011 15.688 0 . 0 0 0 SA48HR-AVG [19.609) [ 0 . 0 0 1 ] [15.693] 0 . 0 0 0 [39.362] [ 0 . 0 0 2 ] [ 1 9 . 4 9 4 ] [ 0 . 0 1 3 ] [15.688] [ 0 . 0 0 1 ] SASOMR 6 4 . 0 0.00410 19.372 0.001 15.708 0 . 0 0 0 39.276 0 . 0 0 2 SASOHR 6 3 . 7 0.00408 19.403 0.001 15.689 0.000 3 9 . 2 5 3 0 . 0 0 1 SA50NR-AVG [19.388] [ 0 . 0 0 1 ] [15.699] [ 0 . 0 0 0 ] [39.265] [ 0 . 0 0 2 ] SA90HR 5 7 . 2 15 0.00362 17.4 20.240 0.001 15.707 0.008 39.243 0 . 0 0 3 19.982 • 0 . 0 0 9 15.695 0.0080 SA4BH6 3 9 . 9 34 0.00242 5 8 . 6 20.998 0.001 15.794 0.000 41.750 0 . 0 0 2 2 0 . 1 2 8 0 . 0 6 0 15.752 0.0029 5A4BNB 3 9 . 1 34 0.00237 5 9 . 9 21.193 0.001 15.785 0 . 0 0 0 41.879 0 . 0 0 2 2 0 . 3 0 3 0 . 0 6 1 15.742 0.0030 SA48HB-AVG (21.096) ( 0 . 0 0 1 ] [15.790] [ 0 . 0 0 0 ] [41.815] [ 0 . 0 0 2 ] [ 2 0 . 2 1 6 ] [ 0 . 0 6 1 ] (15.747] [ 0 . 0 0 3 ] SA48BI 5 9 . 2 22 0.00366 25.1 21.110 0.002 15.760 o.ooo 40.284 0.014 20.737 0 . 0 3 6 15.742 0.0018 SA48BP 5 9 . 6 22 0.00368 2 4 . 9 21.100 O.001 15.761 0 . 0 0 0 40.256 0 . 0 0 2 2 0 . 7 3 0 0 . 0 3 6 15.743 0.0017 SA48BI-AVG [21.105] [ 0 . 0 0 2 ] (15.761] [ 0 . 0 0 0 ] [ 4 0 . 2 7 0 ] [ 0 . 0 8 ] ( 2 0 . 7 3 4 ] ( 0 . 0 3 6 ] [15.743] [ 0 . 0 0 2 ] ) TftSLE E.I ( c o n t i n u e d )  BLANK CORRECTED' TIME CORRECTED1 SAMPLE PB V 204PB HU P8206/4 P86/4 PB207/4 PB7/4 P8208/4 PB6/4 PB206/4 PB6/4 P8207/4 PB7/4 PPA PPN MOLES ABSt/- « / - • / - • / - • / -SA48TF 5 (19.281) (0.001) (15.674) ( 3 9 . 0 9 8 ) ( 0 . 0 0 1 ) SA48BC 5 4 . 9 0.00354 1 .2 19.153 0.001 15.684 0 . 0 0 2 39.046 0.001 19.135 0.009 15.683 0 . 0 0 2 0 SA48BR 5 8 . 8 1 0.00379 1.1 19.188 0.001 15.673 0.006 39.040 0.003 19.172 0 . 0 0 8 15.672 0 . 0 0 6 0 SA48CC 5 5 . 8 1 0.00358 1.2 19.241 0.001 15.732 0.001 39.206 0.001 19.134 0 . 0 0 9 15.652 0.0011 SA4BCR 2 (19,152) (0.001) ( 1 5 . 6 5 3 ) ( 0 . 0 0 0 ) ( 3 8 . 9 6 6 ) ( 0 . 0 0 1 ) SA4BDC 5 8 . 7 2 0.00378 2 . 2 19.176 0.001 15.674 0 . 0 0 3 39.022 0.002 19.143 0 . 0 0 2 15.672 0 . 0 0 3 0 SA4BDR 6 7 . 2 7 0.00433 6.B 19.185 0.000 15.670 0 . 0 0 1 39.042 0.000 19.084 0 . 0 0 5 15.665 0.0010 SA48EC 1 (19.154) (0.001) (15.644) ( 0 . 0 0 0 ) (39.967) ( 0 . 0 0 2 ) SA48ER 2 (19.228) (0.001) (15.680) ( 0 . 0 0 0 ) ( 3 9 . 1 0 3 ) ( 0 . 0 0 1 ) SA48FC 1 (19.194) (0.001) (15.667) ( 0 . 0 0 0 ) ( 3 9 . 0 2 6 ) (0.001) SA48FR 3 (19.177) ( 0 . 0 0 1 ) ( 1 5 . 6 5 4 ) ( 0 . 0 0 0 ) ( 3 8 . 9 8 2 ) ( 0 . 0 0 1 ) SA48CIR (19.182) ( 0 . 0 0 1 ) (15.675) ( 0 . 0 0 0 ) ( 3 9 . 0 4 5 ) ( 0 . 0 0 1 ) -SA48 CORE AVERAGE (19.184) (15.680] ( 3 9 . 0 5 3 ] SA48 RIM AVERAGE (19.186) (15.660] (39.027] " ' P b BLANK (JAN7) 0.16 0.00001 19.000 0.001 15.650 0 . 0 0 1 39.500 0.001 » > P b BLANK ( J A M ) 0 . 7 5 0.00005 19.000 0.001 15.650 0.001 39.500 0.001 ' • ' P b BLANK (JAN22) 0 . 6 5 0.00004 19.000 0.001 15.650 0.001 39.500 0.001 " ' P b BLANK (PE6S) 4.71 0 . 0 0 0 3 19.000 0.001 15.650 0.001 39.500 0.001 1 A n a l y s e s by Janet G a b i t e s . ' Blank a n a l y s e s and p r o g r a i s used i n c o r r e c t i o n (BLANKSU8) are i n Appendix E, Table E . 2 . ( ) denotes that a n a l y s e s Here not b l a n k c o r r e c t e d because c o r r e c t i o n s Here i n s i g n i f i c a n t . 1 Data H a s t i l e c o r r e c t e d to 95na u s i n g p r o g r a i (T1CORR) d e s c r i b e d i n Table E . 2 , Appendix E. 4 U r a n i u i v a l u e s a n a l y s e d by A c i e G e o c h e i i c a l L a b o r a t o r y , V a n c o u v e r , B . C . Whole rock ICP a n a l y s i s u s i n g O . l g s a i p l e f u s e d w i t h 0 . 6 g L i B O j . I t Has d i s s o l v e d and d i l u t e d n i t h 250 i l of NNOj. A n a l y s e s by ICP l a s s s p e c t r o m e t e r . APPENDIX E TABLE E.2 LEAD CORRECTION PROGRAMS INPUT DESCRIPTION OUTPUT WRPBID 20 6 p b / 2 0 4 p b + s 2 0 7 p b / 2 0 4 p b + s . 2 0 8 p b / 2 0 4 p b ± s spike weight ±0.0003g sample weight + 0.0003g raw 2 0 8 Pb/ 2 07 Pb (ID run) ± i BLANKSUB output from WRPBIC + Pb ppm + 0.1 ppm sample weight + 0.0003g amount of blank to be subtracted Spike 84-3 i s o t o p i c Pb (ppm) + s composition and u n c e r t a i n t y based concentration, mass . on e r r o r propagation f r a c t i o n a t i o n , a l l 2 0 4 P b (micromoles)+s u n c e r t a i n t i e s a s s o c i a t e d with the input data. blank composition, a l l blank c o r r e c t e d u n c e r t a i n t i e s a s s o c i a t e d 2 0 6 P b / 2 0 4 P b + s with input data. 2 0 7 P b / 2 0 4 P b + s 2 0 8 P b / 2 0 4 P b + s MUCALC U(GR) or U(NAA) + 10% divi d e d by 1.00935 2 0 4 P b micromoles + uncertainty based on 0.1 ppm t o t a l u ncertainty i n lead content U n c e r t a i n t i e s associated 2 3 8 U / 2 0 4 P b (MU) + s with input data. T1CORR 2 0 6 P b / 2 0 4 P b + s 2 0 7 P b / 2 0 4 P b + s 2 0 8 P b / 2 0 4 P b + s 2 3 8 U/.2 0 4 P b + s U n c e r t a i n t i e s a s s o c i a t e d with input data. i n i t i a l : 20 6 P b / 2 0 4 P b + s 2 0 7 P b / 2 0 4 P b + s 2 0 8 P b / 2 0 4 P b + s i = in-run p r e c i s i o n (standard e r r o r ) , s = estimated u n c e r t a i n t y based on propagation of e r r o r s (one sigma). 

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