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UBC Theses and Dissertations

Petrogenetic study of the Guichon Creek Batholith, B.C. Westerman, Christopher John 1970

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A P E T R O G E N E T I C STUDY G F T H E GUICHON CREEK B A T H O L I T H , B . C . b y C h r i s t o p h e r J . W e s t e r m a n B . S c . U n i v e r s i t y o f L o n d o n , 1967 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF 1 THE R E Q U I R E M E N T S FOR THE DEGREE OF MASTER OF S C I E N C E i n t h e D e p a r t m e n t o f GEOLOGY We a c c e p t t h i s t h e s i s a s 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 U N I V E R S I T Y OF B R I T I S H COLUMBIA A p r i l , 1970 In presenting this thesis in partial fulfilment of the requirements f o r 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 tha permission for extensive copying of this thesis f o r scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis f o r financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada Date f^tJP lf7& ABSTRACT The G u i c h o n C r e e k b a t h o l i t h i s e x p o s e d a p p r o x i m a t e l y 2 0 0 m i l e s N . E . o f V a n c o u v e r , B . C . a n d i s a z o n e d ' g r a n i t i c 1 p l u t o n o f L o w e r J u r a s s i c a g e ( 1 9 8 - 8 m y ) . The b a t h o l i t h c o n s i s t s o f s e v e n m a j o r i n t r u s i v e p h a s e s . Tho p r e d o m i n a n t r o c k t y p o i s g r a n o d i o r i t e w i t h l e s s o r a m o u n t s o f q u a r t z d i o r i t e a n d q u a r t z m o n z o n i t e . S t u d y o f r o c k a n d m i n e r a l c o m p o s i t i o n s h a s r e v e a l e d a g r a d u a l v a r i a t i o n i n t h e r e l a t i v e p r o p o r t i o n s o f m i n e r a l p h a s e s a s c r y s t a l l i s a t i o n o f t h e b a t h o l i t h p r o c e e d e d . T h o c h e m i c a l c o m p o s i t i o n s , h o w e v e r , o f t h e i n d i v i d u a l m i n e r a l p h a s e s show v e r y l i t t l e c h a n g e . T h e r e l a t i v e r o l e s o f a s s i m i l a t i o n a n d magma c o n v e c t i o n i n p r o d u c i n g c o m p o s i t i o n a l v a r i a t i o n s i n t h e e a r l y p h a s e s o f t h e b a t h o l i t h a r e d i s c u s s e d . A l k a l i f e l d s p a r s a r e m i c r o p e r t h i t i c w i t h b u l k c o m p o s i t i o n s i n t h e r a n g e 7 1 - 8 6 Wt% Or a n d t h e c o m p o s i t i o n s o f t h e p o r t h i t i c c o m p o n e n t s a p p r o a c h p u r e e n d m e m b e r s . The p o t a s s i c p h a s e s o f t h e p e r t h i t e s h a v e s t r u c t u r a l s t a t e s e q u i v a l e n t t o t h a t o f o r t h o c l a s e . The p l a g i o c l a s e f e l d s p a r s a r c o l i g o c l a s e s w i t h l o w t o i n t e r m e d i a t e s t r u c t u r a l s t a t e s . P l a g i o c l a s e f r o m t h e e a r l y p h a s e s o f t h e b a t h o l i t h ( H y b r i d a n d H i g h l a n d V a l l e y p h a s e s ) show n o r m a l z o n i n g w h e r e a s t h o s e f r o m t h o l a t e r phases ( B e t h l e h e m a n d B e t h s a i d a ) show o s c i l l a t o r y z o n i n g . B i o t i t e s f r o m t h o m a j o r p h a s e s o f t h e b a t h o l i t h h a v e p r o g r e s s i v e l y l o w e r F e / ( F c + M g ) r a t i o s w i t h p r o g r e s s i v e l y i n c r e a s i n g s i l i c a c o n t e n t o f t h e h o s t r o c k s . P l a g i o c l a s e c r y s t a l l i z e d e a r l y i n t h e o l d e r p h a s e s o f t h e b a t h o l i t h w h e r e a s q u a r t z was t h o e a r l y m i n e r a l t o c r y s t a l l i z e f r o m t h e y o u n g e r m a j o r p h a s e s . E v i d e n c e s u g g e s t s t h a t magma c o n v e c t o d d u r i n g c r y s t a l l i s a t i o n o f t h e o l d e r p h a s e s o f t h e b a t h o l i t h b u t t h a t t h o y o u n g e r p h a s e s c r y s t a l l i s e d f r o m a s t a t i o n a r y magma. C o m p a r i s o n s w i t h e x p e r i m e n t a l s y s t e m s s u g g e s t t h a t t h e e a r l y magma c r y s t a l l i s e d u n d e r c o n d i t i o n s o f r e l a t i v e l y l o w t o t a l p r e s s u r e s i n t h e o r d e r o f 1 o r 2 k b b u t t h a t t h e l a t e r p h a s e s may h a v e b e e n s u b j e c t e d t o t o t a l p r e s s u r e s i n t h e o r d e r o f 1+ o r 5 k b d u r i n g c r y s t a l l i s a t i o n . T h i s i n c r e a s e i n t o t a l p r e s s u r e s was m o s t p r o b a b l y duo t o i n c r e a s i n g v o l a t i l e p r e s s u r e s d u r i n g c r y s t a l l i s a t i o n . i v L I S T OF CONTENTS P A G E I I n t r o d u c t i o n 1 I I G e o l o g i c s e t t i n g o f t h e b a t h o l i t h 5 I I I The A l k a l i f e l d s p a r s a . Mode o f o c c u r r e n c e 9 b . M e t h o d o f s t u d y 9 c . C o m p o s i t i o n s o f t h e N a t u r a l A l k a l i F e l d s p a r s 15 d . S t r u c t u r a l s t a t e s o f t h e N a t u r a l A l k a l i F e l d s p a r s 17 e . B u l k c o m p o s i t i o n s o f t h e h o m o g e n i s e d a l k a l i f e l d s p a r s 25 I V The P l a g i o c l a s e F e l d s p a r s a . Mode o f o c c u r r e n c e 27 b , P l a g i o c l a s e C o m p o s i t i o n s a n d Z o n i n g . . . . 27 V T h e B i o t i t e , s a . Mode o f O c c u r r e n c e -^2 b . M e t h o d o f S t u d y UU c . D i s c u s s i o n o f R e s u l t s ^6 V I M o d a l A n a l y s e s a n d C a l c u l a t e d C h e m i c a l C o m p o s i t i o n s 56 V I I G e o l o g i c a l e v o l u t i o n o f t h e b a t h o l i t h 72 V I I I Summary a n d C o n c l u s i o n s 83 V PAGE R e f e r e n c e s C i t e d . . . 90 A p p e n d i x 1. P e t r o g r a p h i c d e s c r i p t i o n s 95 2. M o d a l a n a l y s e s a n d c a l c u l a t e d c h e m i c a l c o m p o s i t i o n s 102 3 . B i o t i t e 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 - e x p e r i m e n t a l p r o c e d u r e s ; 110 v i L I S T OF T A B L E S T A B L E P A G E I . P h a s e s a n d v a r i e t i e s o f i n t r u s i v e r o c k k I I . U n i t c e l l p a r a m e t e r s o f K r i c h p h a s e s i n a l k a l i f e l d s p a r s 11 I I I . C o m p o s i t i o n s o f t h e p e r t h i t i c p h a s e s o f t h e a l k a l i f e l d s p a r s , a n d d a t a p l o t t e d i n F i g . 5 . 13 I V . U n i t c e l l p a r a m e t e r s f o r h o m o g e n i s e d a l k a l i f e l d s p a r s . Ik V . R e l a t i o n b e t w e e n e s t i m a t e d b u l k c o m p o s i t i o n a n d d e g r e e o f a n o m o l y f o r c o m p u t e r r e f i n e d a l k a l i f e l d s p a r s 19 V I . ° 2 9 v a l u e s f o r 201 r e f l e c t i o n s ( C u K ^ ) a n d e s t i m a t e d b u l k c o m p o s i t i o n s o f h o m o g e n i s e d a l k a l i f e l d s p a r s f r o m t h e G u i c h o n C r e e k b a t h o l i t h 26 V I I . T a b l e o f p l a g i o c l a s e c o m p o s i t i o n s 28 V I I I . O b s e r v e d X - r a y i n t e n s i t y r a t i o I ^ j ^ : f o r 3 b i o t i t e s a m p l e s a s a f u n c t i o n o f s a m p l e p r e p a r a t i o n k5 I X . R e s u l t s o f p a r t i a l 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 b i o t i t e s f r o m t h e G u i c h o n C r e e k b a t h o l i t h k'd X . C r i t e r i a , s u g g e s t e d b y B u d c d n g t o n (1959) a s i n d i c a t i v e o f m e s o z o n a l i n t r u s i o n w h i c h a r e p r e s e n t i n t h e G u i c h o n C r e e k b a t h o l i t h 80 X I . E l e c t i ' o n m i c r o p r o b e a n a l y s e s o f b i o t i t e s t a n d a r d s . D a t a u s e d i n c o n s t r u c t i o n o f F i g . 17 115 v i i LIST OF FIGURES FIGURE PAGE 1. Geology of the Guichon Creek b a t h o l i t h .... 3 2. Sample l o c a t i o n map 8 3 - O r t h o c l a s e content of a l k a l i f e l d s p a r s p l o t t e d as a f u n c t i o n o f the a c e l l _ dimension, u n i t c e l l volume and 2 0 2 0 1 CuKoi . S i m p l i f i e d from Wright and Stewart ( i960) and Wright ( 1 9 6 8 ) 16 4 . R e f i n e d c e l l parameters f o r a l k a l i f e l d s p a r s from the Guichon Creek b a t h o l i t h p l o t t e d on a b - £ p l o t , s i m p l i f i e d from Wright and Stewart ( i960) 1 8 5 . A l k a l i f e l d s p a r s from the Guichon Creek b a t h o l i t h p l o t t e d on a 0 6 0 - 2 0 4 (°20 CuK «* ) p l o t , s i m p l i f i e d from Wright ( 1 9 6 8 ) 1 8 6 . X-ray d i f f r a c t i o n p a t t e r n f o r sample 3 1 . i n the r e g i o n of 30°29 CuK * 2 2 7 . Modal f e l d s p a r c o n s t i t u e n t s o f the Guichon Creek b a t h o l i t h samples r e c a l c u l a t e d t o 1 0 0 % An+Ab+Or 3 3 8 . P l a g i o c l a s e z o n i n g schemes 36 9. C o m p o s i t i o n s of p l a g i o c l a s e s i n e q u i l i b r i u m v/ith g r a n i t i c m e l t s as a f u n c t i o n o f temperature at 2 k b water p r e s s u r e (From P i w i n s k i , 1 9 6 8 , p. 5 6 0 ) 4 0 1 0 . R e l a t i o n between abundance o f b i o t i t e and s i l i c a c o n t ent o f hos t .rock 4 3 1 1 . B i o t i t e c o m p o s i t i o n s as a f u n c t i o n of the s i l i c a c o n t ent of t h e host r o c k 47 1 2 . S t a b i l i t y o f b i o t i t e s as a f u n c t i o n o f f 0 £ and temperature at 2 0 7 0 b a r s t o t a l p r e s s u r e (From Wones and E u g s t e r , 1 9 6 5 ) . . . . 50 v i i i FIGURE PAGE 1 3 a . P l o t of modal q u a r t z - o r t h o c l a s e - a l b i t e -a n o r t h i t e f o r the Guichon Creek b a t h o l i t h samples 3 5 b. Schematic phase diagram f o r the t e r n a r y system Qz-Or-Ab-An a t 1 k i l o b a r water vapour p r e s s u r e 55 1^1-. C a l c u l a t e d component o x i d e s p l o t t e d as a f u n c t i o n o f s i l i c a c ontent f o r the Guichon Creek b a t h o l i t h samples 6 ^ , 6 5 1 5 . Chemical c o m p o s i t i o n s of proposed Guichon Creek b a t h o l i t h p r i m a r y nagma, ' c o n t a n i n a t e d ' Guichon r o c k s and N i c o l a Group e x t r u s i v e r o c k s 6 8 16. Summary o f c o m p o s i t i o n a l v a r i a t i o n s i n the Guichon Creek b a t h o l i t h 82 1 7 . M i c r o p r o b e a n a l y s e s . T o t a l counts observed as a f u n c t i o n of c o m p o s i t i o n f o r b i o t i t e s t a n d a r d s 11^ i x L I S T OF P L A T E S P L A T E P A G E 1 . P a r t i a l l y r e s o r b e d p l a g i o c l a s e e n c l o s e d w i t h i n p o i k i l i t i c a l k a l i f e l d s p a r . S a m p l e #11 . C h a t a w a y v a r i e t y . C r o s s e d n i c o l s , x 3 0 * 3 1 2 . P a r t i a l l y r e s o r b e d p l a g i o c l a s e e n c l o s e d w i t h i n p o i k i l i t i c a l k a l i f e l d s p a r . S a m p l e # 1 0 . C h a t a w a y v a r i e t y . C r o s s e d n i c o l s , x 3 0 3 1 3 . P a r t i a l l y r e s o r b e d , o s c i l l a t o r y z o n e d p l a g i o c l a s e e n c l o s e d i n p o i k i l i t i c , p e r t h i t i c a l k a l i f e l d s p a r . N o t e t h e a l b i t i c r i m t o t h e p l a g i o c l a s e . S a m p l e # 2 5 , B e t h l e h e m p h a s e . C r o s s e d n i c o l s , x 3 0 . 3 5 k. O s c i l l a t o r y z o n i n g i n p l a g i o c l a s e . S a m p l e # 34» B e t h s a i d a p h a s e . C r o s s e d n i c o l s , x 3 0 3 5 5 . S a m p l e f r o m a c h i l l e d B e t h s a i d a d y k e f r o m e a s t o f t h e B e t h l e h e m C o p p e r p r o p e r t y . N o t e p r e s e n c e o f s u b h e d r a l - e u h e d r a l p h e n o c r y s t s o f q u a r t z a n d e u h e d r a l p o i k i l i t i c b i o t i t e . S c a l e i n c e n t i m e t r e s . . 62 X ACKNOWLEDGEMENTS The a u t h o r w i s h e s t o e x p r e s s h i s t h a n k s t o D r s . K . C . M c T a g g a r t , E . P . M e a g h e r and u r . A . Gower who a c t e d a s t h e s i s s u p e r v i s o r s . T h a n k s a r e a l s o d u e t o D r . K . E . N o r t h c o t e o f t h e B r i t i s h C o l u m b i a D e p a r t m e n t o f M i n e s and P e t r o l e u m R e s o u r c e s who s u p p l i e d a l l t h e s a m p l e s u s e d , t o D r . J . H . Y . R i m s a i t e o f t h e G e o l o g i c a l S u r v e y o f C a n a d a who s u p p l i e d c h e m i c a l l y a n a l y s e d b i o t i t e s a n d t o M . O s a t e n k o o f C o m i n c o L t d . , G e o l o g i c a l R e s e a r c h d i v i s i o n who p r o v i d e d c h e m i c a l a n a l y s e s o f t h e b i o t i t e s t a n d a r d s s u p p l i e d b y D r . J . A . G o w e r . 1 I Introduction The Guichon Creek batholith crops out over an area of approximately if00 sq. miles near to and southeast of the town of Ashcroft in the Interior Plateau of British Columbia. The batholith i s of considerable scientific and economic interest. The Bethlehem Copper and Craigmont Mines, and several potential mines such as Lornex and Valley Copper occur within or adjacent to the batholith. Early geological mapping of the eastern half of the Guichon Creek batholith, at a scale of if miles to 1 inch, was completed by W.E. Cockfield ( 1 9 i f 7 ) , and of the western half by S. Duffell and K.C. McTaggart ( 1 9 5 2 ) . Several detailed reports of parts of the batholith have been prepared by J.M. Carr ( 1 9 5 9 - 1 9 6 3 ) and the geology of mineral deposits associated with the batholith has been described by W.H. White, R.M. Thompson and K.C. McTaggart ( 1 9 5 7 ) . Radiometric K/Ar age determinations from the batholith have been published by Baadsgard et al ( 1 9 6 1 ) , Dirom ( 1 9 6 5 ) , Wanless et al ( 1 9 6 5 , 1 9 6 7 ) , White et al ( 1 9 6 7 ) , and Northcote ( 1 9 6 8 , 1 9 6 9 ) . Christmas et al ( 1 9 6 9 ) have studied the rubidium/strontium, sulphur and oxygen isotopic composition of samples from the batholith and the 2 associated Craigmont ore body. Previous work on the batholith culminated in a detailed geologic and geochronologic study by Northcote (1969). Northcote mapped seven separate intrusive phases of the batholith, described them, and explained the differences between them as due to the combined action of assimilation and magmatic differentiation. In addition Northcote proposed that a change from mesozonal to epizonal environments occurred during emplacement of the pluton. The present work was undertaken as an attempt to further describe the mineralogy of the various phases and the mechanisms involved in the emplacement of the batholith. It was hoped that the differentiation occurring within the pluton would be reflected in the changing compositions of feldspars and biotites which occur throughout the batholith. In addition i t was hoped that study of the variation in the structural states of the al k a l i feldspars would help in determining the history of crystallisation and changes in the environment of emplacement of the batholith. A l l of the samples used in the present investigation were collected by Dr.. K..E. Northcote during the preparation of his Ph.D thesis (University of British Columbia) in the summers of 1963 and 196^. TABLE I Phases and Varieties of Intrusive Rocks (from Northcote 1969) Relatively Old ( 1 ) Hybrid phase - quartz diorite, granodiorite ( 2 ) Highland Valley phase (2G) Guichon variety - quartz diorite, granodiorite ( 2 C ) Chataway variety - granodiorite, quartz monzonite ( 2 L R ) LeRoy granodiorite - granodiorite, quartz monzonite Intermediate Age ( 3 ) Gump Lake phase - granodiorite, quartz monzonite (4) Bethlehem phase - granodiorite, quartz monzonite (5) Witches Brook phase Variety A - granodiorite Variety B - granodiorite Variety C - granodiorite, quartz monzonite, granite Bethlehem porphyries Relatively Young (6) Bethsaida phase - quartz monzonite. granodi. or? t^ ( 7 ) Gnawed Mountain porphyries, younger Bethlehem porphyries and associated intrusive breccias Leucocratic dykes and irregular-shaped bodies 5 1 1 G e o l o g i c a l S e t t i n g o f t h e B a t h o l i t h The g e n e r a l g e o l o g y o f t h e G u i c h o n C r e e k b a t h o l i t h h a s b e e n d e s c r i b e d b y N o r t h c o t e ( 1968, 1969) a n d o n l y a b r i e f summary w i l l be g i v e n h e r e . The b a t h o l i t h i s a s e m i c o n c o r d a n t , z o n e d , ' g r a n i t i c ' p l u t o n c o n s i s t i n g o f s e v e r a l i n t r u s i v e p h a s e s a r r a n g e d i n a r o u g h l y c o n c e n t r i c p a t t e r n . T h e b a t h o l i t h i c r o c k s i n t r u d e s e d i m e n t a r y r o c k s o f t h e C a c h e C r e e k G r o u p ( P e r m i a n ) a n d N i c o l a G r o u p ( K a r n i a n s t a g e : U p p e r T r i a s s i c ) c a u s i n g l o c a l c o n t a c t m e t a m o r p h i s m t o a l b i t e -e p i d o t e o r h o r n b l e n d e h o r n f e l s f a c i e s . The b a t h o l i t h i s o v e r l a i n u n c o n f o r m a b l y b y M i d d l e a n d U p p e r J u r a s s i c s e d i m e n t s a n d L o w e r C r e t a c e o u s a n d T e r t i a r y v o l c a n i c a n d s e d i m e n t a r y r o c k s . T h e r e i s no e v i d e n c e o f a n y s i g n i f i c a n t m e t a m o r p h i c a c t i v i t y o c c u r r i n g i n t h e r e g i o n a f t e r e m p l a c e m e n t o f t h e b a t h o l i t h . P u b l i s h e d r a d i o m e t r i c a g e d e t e r m i n a t i o n s o f r o c k s f r o m t h e b a t h o l i t h g i v e a n a v e r a g e a g e o f a p p r o x i m a t e l y 198 my. ( D i r o m , 1965; W a n l e s s e t a l 1 9 6 5 , 1967; W h i t e e t a l 1967; N o r t h c o t e 1969; C h r i s t m a s e t a l , 1 9 6 9 ) . N o r t h c o t e h a s d i v i d e d t h e b a t h o l i t h i n t o s e v e n m a j o r p h a s e s ( T a b l e I , F i g . 1) p r i m a r i l y o n f i e l d r e l a t i o n s h i p s a n d t e x t u r a l v a r i a t i o n s . M o s t o f t h e b a t h o l i t h i s c o m p o s e d o f g r a n o d i o r i t e , w i t h l e s s e r 6 a m o u n t s o f q u a r t z d i o r i t e , q u a r t z m o n z o n i t e a n d w i t h m i n o r g r a n i t e . I n a g e n e r a l way t h e o l d e r p h a s e s t e n d t o be. b a s i c , t h e y o u n g e r p h a s e s t o be a c i d i c . N o r t h c o t e h a s s u g g e s t e d t h a t t h e G u i c h o n v a r i e t y g r a n o d i o r i t e may a p p r o x i m a t e t h e c o m p o s i t i o n o f t h e o r i g i n a l magma a n d t h a t t h e m o r e b a s i c r o c k s may be t h e r e s u l t o f c o n t a m i n a t i o n , t h e more a c i d i c r o c k s t h e r e s u l t o f d i f f e r e n t i a t i o n o f t h i s magma. The r o u g h l y c o n c e n t r i c p a t t e r n o f t h e m a j o r p h a s e s o f t h e b a t h o l i t h i s d i s r u p t e d b y t h r e e o f t h e m i n o r p h a s e s . The Gump L a k e p h a s e o c c u r s a s a s e r n i p e r i p h e r a l b o d y o n t h e e a s t e r n m a r g i n o f t h e b a t h o l i t h , t h e L e R o y a n d W i t c h e s B r o o k p h a s e s o c c u r a s i r r e g u l a r d y k e - l i k e b o d i e s w i t h i n o l d e r p h a s e s . C o n t a c t s b e t w e e n p h a s e s r a n g e f r o m s h a r p l y i n t r u s i v e t o b r o a d l y g r a d a t i o n a l a n d a s i n g l e c o n t a c t may v a r y i n n a t u r e a l o n g i t s l e n g t h . C h i l l e d c o n t a c t s b e t w e e n p h a s e s a r e e x t r e m e l y r a r e a n d f o r t h i s r e a s o n N o r t h c o t e c o n s i d e r s t h a t a l l . , p h a s e s w e r e h o t a t a p p r o x i m a t e l y t h e same t i m e , i n f e r r i n g o n l y a s h o r t t i m e i n t e r v a l b e t w e e n i n t r u s i v e p u l s e s . T h e m a j o r p h a s e s o f t h e b a t h o l i t h h a v e a c o a r s e - g r a i n e d , h y p i d i a m o r p h i c t e x t u r e , a n d o n l y t h e y o u n g e s t , m i n o r p h a s e s i n c l u d e p o r p h y r i t i c r o c k s . The H y b r i d , H i g h l a n d V a l l e y , W i t c h e s B r o o k a n d p a r t s o f t h e B e t h l e h e m p h a s e s 7 a l l e x h i b i t , t o v a r y i n g degrees, alignment of p l a g i o c l a s e c r y s t a l s . In a d d i t i o n a rough f o l i a t i o n o f m a f i c m i n e r a l s i s p r e s e n t , l o c a l l y , w i t h i n the Guichon v a r i e t y . On the b a s i s of t e x t u r a l e v i d e n c e , N o r t h c o t e (1969) has suggested t h a t the e a r l y phases o f t h e b a t h o l i t h were emplaced under mesozonal c o n d i t i o n s and t h a t p r o g r e s s i v e e r o s i o n o f the cover r o c k s e s t a b l i s h e d e p i z o n a l c o n d i t i o n s d u r i n g emplacement o f the l a t e r phases. — c O n \ N 1 \ Fig. 2 . Sample location map. / I "A A \ ) / / / 5 / \ \ L V I 7 \ / ^ J l S'jli/ B / / \ - V -/ / \ / / 2 2 \ \ V 30\\ • H / *,y .A \ \ \ \ \ \ \ \ A 23 V \ \ 24 \ 1 6 ^ 2 7 \ j/\ \ • 20 33 )W —t w II II w \ ^ A r\'21 35 / / / // \ f N\ \ I K-28 ^•17 •29 9 I I I The A l k a l i F e l d s p a r s a ) Mode o f O c c u r r e n c e The r o c k s i n v e s t i g a t e d c o n t a i n b e t w e e n 1% a n d 2 0 % a l k a l i f e l d s p a r , m o s t o f w h i c h i s e i t h e r i n t e r s t i t i a l o r p o i k i l i t i c , e n c l o s i n g p l a g i o c l a s e , q u a r t z , h o r n b l e n d e a n d b i o t i t e . A s a g e n e r a l r u l e f i n e - g r a i n e d r o c k s c o n t a i n i n t e r s t i t i a l a l k a l i f e l d s p a r w h e r e a s i n c o a r s e g r a i n e d r o c k s i t i s p o i k i l i t i c . A l l t h e s a m p l e s i n v e s t i g a t e d a r e e i t h e r m i c r o p e r t h i t e o r c r y p t o p e r t h i t e i n w h i c h t h e s u b o r d i n a t e , a l b i t e - r i c h p h a s e o c c u r s a s e x t r e m e l y t h i n s t r i n g l e t s . ( c . f . A i l i n g , 1 9 3 8 , p . 1 ^ 2 ) . W h e r e v e r p o i k i l i t i c a l k a l i f e l d s p a r i s i n c o n t a c t w i t h p l a g i o c l a s e t h e a l k a l i f e l d s p a r e i t h e r f o r m s e m b a y m e n t s i n t h e p l a g i o c l a s e , o r m y r m e k i t i c i n t e r g r o w t h s a r e p r e s e n t w i t h i n t h e p l a g i o c l a s e m a r g i n a l r e g i o n s . The s i g n i f i c a n c e o f t h e s e f e a t u r e s i n d i s c u s s e d i n c h a p t e r I V . b ) M e t h o d o f S t u d y A l k a l i F e l d s p a r s w e r e s e p a r a t e d f r o m t h e 8 0 - 1 2 0 m e s h f r a c t i o n o f t h e c r u s h e d a n d s i e v e d r o c k u s i n g a c o m b i n a t i o n o f e l e c t r o m a g n e t i c a n d h e a v y - l i q u i d m e t h o d s . M a g n e t i t e a n d o t h e r s t r o n g l y m a g n e t i c m i n e r a l s w e r e f i r s t r e m o v e d f r o m t h e s i z e f r a c t i o n w i t h a h a n d m a g n e t . The r e m a i n i n g m a t e r i a l was t h e n p a s s e d t h r o u g h a F r a n z 10 e l e c t r o m a g n e t i c s e p a r a t e r s et at maximum amperage, to remove mafic m i n e r a l s and any h e a v i l y a l t e r e d f e l d s p a r . The r e m a i n i n g f r a c t i o n v/as then p r o c e s s e d by s e p a r a t i o n i n bromoform d i l u t e d w i t h acetone t o a s p e c i f i c g r a v i t y such t h a t a q u a r t z c r y s t a l sank and an o r t h o c l a s e c r y s t a l f l o a t e d i n the m i x t u r e . The " f l o a t " f r a c t i o n from t h i s f i n a l s e p a r a t i o n c o n s i s t s o f a l k a l i f e l d s p a r w i t h v e r y minor amounts o f a d h e r i n g q u a r t z . The " s i n k " f r a c t i o n s c o n s i s t m a i n l y o f d i s c r e t e q u a r t z and p l a g i o c l a s e g r a i n s w i t h minor but v a r i a b l e amounts o f composite g r a i n s and o c c a s i o n a l non-magnetic m a f i c m i n e r a l s . Smear mounts were made of each sample and t h r e e X-ray d i f f r a c t o m e t e r p a t t e r n s were r u n f o r each u s i n g CaF 2 (a = 5.4631 - .0006&) as an i n t e r n a l s t a n d a r d . The r u n s v/ere made u s i n g N i f i l t e r e d Cu r a d i a t i o n from a 29 an g l e o f 58° t o 19°, at a scan speed o f -}°/m±n. and c h a r t speed of 2cm/min. For t w e l v e o f the samples a l l peaks p r e s e n t were measured and i n d e x e d u s i n g the t a b l e s g i v e n by Wright and Stewart (1968). U n i t c e l l parameters (Table I I ) f o r the K - r i c h phase i n these samples have been c a l c u l a t e d u s i n g the ' v a r i a b l e - i n d e x i n g ' computer program developed by Evans, Appleman and Handwerker (1963) of the U.S.G.S. rp J - T V J p TpJIT C E L T . 1 0 APAMETE 'RS OP K P J C P I PF ' - 'SE I>7 j i L K * T , I ^"^LDS^/'^S J3a-ple ./ i Phase Or 0 a(A) h(A) 0 c(A) cx y 8 _V(A) 3 No. of lines used I Std. 1 r) r> Q y» I (°29) 1 op 0 + 8 . 5 8 l - . 0 0 3 12.984 . 0 0 3 7 . 2 0 5 . 0 0 1 90° 116 ~ 2 . 5 5 ' 1 . 4 5 1 90° ' 721 .13 xo 18 .017 4 1 Q? • n +8.575 - . 0 0 2 12.994 . 0 0 2 7 . 2 0 1 . 0 0 1 90° 1 1 6 ° 1 .59 ' 1.02» 90° 721 .06 1 p 15 . 009 6 2G 91. 5 H 3.576 - . 00/-I-1 2 . 9 8 5 . 0 0 3 7 . 2 0 3 .001 90° 116° P ? 7 l ••— • ' — _ / 1.29 ' 90° 7 P O 70 ' . ^ 3 1 13 . 0 1 3 12 2C 91. 5 . 8 . 5 7 3 - .004 1 2 . 9 8 7 . 0 0 3 7 . 2 0 4 . 0 0 2 90° 116° 1 . 0 8 ' 1.58' 90° 7 P O qo .36 15 j.016 • 13 " 2C 92. o .3.577 - . 0 0 5 12.988 . 0 0 4 7 . 2 0 3 . 0 0 2 90° 116° 2.49' 1 . 7 0 ' 90° 7 2 1 . 0 2 .42 14 .017 17 2LE 38. , 8 . 5 5 5 - .007 12.989 "!6o5 7 . 2 0 3 . 0 0 2 90° 116° 3.29' 2 . 0 5 ' 90° 7 1 9 . 6 0 .60 13 . 0 2 3 ] _ 0 OP > — . n. , 8 . 5 8 0 - . 0 0 5 12.935 .004 7.206 . 0 0 2 on 0 116° 3 . 0 4 ' 1 OR I -i- • > w 90° 721.13 .45 12 . 0 1 3 22 /,. 96. O 17 0 1, - . 0 0 3 12.938 .002 7.206 . 0 0 1 90° 116° X • ' !-u r> ••"^ r7 i •-• • —* / COO- 721.97 0 7 • •-• 14 0 1 0 . UL'^ 23 93. o Q r.nO I m QQ X 12.992 . 003 7.204 . 0 0 1 9 0 0 116° 0.16' 1.45* O O 0 721.57 .27 17 O " ! ^ . vj J_ C 27 5 90. 0 r r i _ o o p 12.990 . 0 0 2 7.206 ' ."001 90° 116° 0 . 2 2 ' O H^.\ 90° 720.46 .16 13 0 0 0 PQ 5 89. o , 8 . 5 6 2 - .004 12.930 . 0 0 3 7.203 . 0 0 2 2 2 Q ' r*10 ^  7 1 0 ^ 0 . 4 0 1 0 . 013 33 '6 OP f CT. 0 c O - i - . 0 0 3 10 nP.c; . 003 7 .204 . 0 0 1 90° 116° 1 .35 ' 1 .36 ' 0 O ° noi x o .28 1 . 014 12 I n p u t f o r t h e c a l c u l a t i o n s was r e s t r i c t e d t o t h o s e r e f l e c t i o n s t h a t c o u l d be u n i q u e l y i n d e x e d a n d w h i c h s h o w e d a t o t a l d e v i a t i o n o f l e s s t h a t 0 . 0 1 5 ° 20 f r o m t h r e e d i f f r a c t o m e t e r p a t t e r n s . F o l l o w i n g t h e p r e c e d e n t o f W r i g h t a n d S t e w a r t (1968) t h e m a j o r i t y o f t h e p e a k s h a v e b e e n m e a s u r e d a s c l o s e a s p o s s i b l e t o t h e maximum p e a k h e i g h t . H o w e v e r , i n u n c e r t a i n o r a m b i g u o u s c a s e s , p e a k s w e r e m e a s u r e d a t t h e 2/3 p e a k h e i g h t p o s i t i o n . F o r t h e r e m a i n i n g s a m p l e s t h e p o s i t i o n s o f t h e 060, 2 0 4 , a n d 201 r e f l e c t i o n s f o r t h e K - r i c h p h a s e , a n d t h e 201 r e f l e c t i o n f o r t h e N a - r i c h p h a s e , ' h a v e b e e n m e a s u r e d . ( T a b l e I I I ) . A l l t h e s a m p l e s i n v e s t i g a t e d c o n t a i n b o t h a K - r i c h , a n d a n N a - r i c h p h a s e a n d h e n c e t h e r e i s t h e c h a n c e o f m u t u a l i n t e r f e r e n c e f o r some o f t h e r e f l e c t i o n s . I n m o s t o f t h e s a m p l e s , h o w e v e r , t h e N a - r i c h p h a s e v/as g r e a t l y s u b o r d i n a t e - a s e s t i m a t e d f r o m t h e (201) a n d (002) r e f l e c t i o n i n t e n s i t i e s - a n d h e n c e i n t e r f e r e n c e e f f e c t s a r e m i n i m a l . None o f t h e s a m p l e s e x h i b i t e d a s u f f i c i e n t n u m b e r o f c h a r a c t e r i s t i c r e f l e c t i o n s , f o r t h e N a - r i c h p h a s e , t o a l l o w c a l c u l a t i o n o f t h e u n i t c e l l p a r a m e t e r s . I n o r d e r t o e s t i m a t e t h e b u l k c o m p o s i t i o n o f t h e a l k a l i f e l d s p a r s e p a r a t e s , e a c h s a m p l e was h e a t e d i n a s i l i c a - g l a s s t u b e a t 990°C f o r t h r e e d a y s . A t t h e e n d 13 TABLE I I I Potass i c Phase So die' Phase Sample Phase Est. Or degrees 20 Est. Ab degrees 2Q # Wt% 201 060 204 Wt% 201 1 1 89.0 21 .034 2 1 . 88.5 21 .039 41.714 50.612 99.5 22.041 3 1 90.0 21 .014 41 .705 50.669 98.0 22 .018 j 4 1 89.0 21 .030 41.661 50.706 95-5 21.985 5 2G 91.5 20 .996 41 .709 50.692 99.0 22 .037 6 2G 89.0 21 .034 41.687 50.673 97.0 21.998 • 7 2G 88.0 21 .037 41 .696 50.641 8 2G 2 a l k a l i f e l d s p a r s present 9 2C 89.0 21 .029 41.676 50.659 97.0 22 .001 10 2C 91.0 21.009 41.686 50.644 97.0 21.999 11 2C 89.0 21.026 41.701 50.667 98.0 22 .019 12 2C 88.0 21 .038 41 .701 50.673 50.677 13 2C 89.5 21 .019 41.674 97.5 22 .014 14 2LR 85.5 21.064 41.679 50.624 15 2LR 86.5 21 .052 41 .684 50.677 98.5 22 .029 16 2LR 85.0 21 .071 41.681 50.684 17 2LR 86.0 21 .058 41 .683 50.636 18 2LR 89.0 89.0 21.026 41 .693 50.657 19 3 21 .035 41.687 50.656 99.0 22 .035 20 3 87.5 21.046 41.681 50.629 21 3 89.5 21 .021 41.684 50.647 .98.5 22.029 22 4 91.0 21.004 41.686 50.646 98.0 22.020 23 4 89.5 21 .024 41.676 50.668 97.5 22 .015 24 4 89.0 2 a l k a l i f e l d s p a r s present 25 4 21 .029 41.654 50.682 26 5 89.5 21.024 41.672 50.664 27 5 86.5 21 .055 41.679 50.652 97.5 22.014 28 5 86.0 21.061 41.729 50.639 96.0 21.976 29 5 85-5 21.067 41.708 50.634 98.5 22.027 30 5 87.5 21.046 41.676 50.672 31 5 91 .5 20 .996 41.766 50.582 100.0 22 .059 32 6 89.5 21 .021 41.681 50.654 33 6 90.51 21.011 41.681 50.642 100.0 22 .051 34 6 89.5 21 .021 41.698 50.672 35 6 88.5 21 .039 41.684 50.662 TABLE IV UNIT CELL PARAMETERS FOR HOMOGENISED ALKALI FELDSPARS Unit C e l l Parameters No. of l i n e s used Std. Sample If- Phase V/t% Or a (A) b(A) c(A) P 0 -z V ( A K e r r o r (°2G) 1 3 Homogenised 2C 8 3 . 0 8 . 5 4 0 - . 0 0 4 1 2 . 9 9 6 . 0 0 3 7 . 2 0 0 . 0 0 1 90° 1 1 5 ° 58.79' 1 . 7 5 ' 90° 718.41 . ^6 16 . 0 1 7 ?-9 Homogenised 5 7 3 . 5 8 . 5 1 3 - .006 12.976 . 0 0 4 7.199 . 0 0 2 9 0 ° 116° 0 . 1 3 ' 1 . 7 1 ' 9 0 ° 71':-. 8 5 . 5 3 1 1 , . 0 1 7 h-1 -p-15 of t h i s period most samples showed only a single (201) r e f l e c t i o n on diffractorceter patterns, i n d i c a t i n g that homogenisa.tion was complete * Any samples exhibiting more than one (201) r e f l e c t i o n were returned for further heating u n t i l no further change i n the position of the 201 r e f l e c t i o n ( s ) was recorded. Unit c e l l parameters were determined for tv;o of the homogenised samples using CaF2 as an in t e r n a l standard,(Table IV) and the position of the 201 r e f l e c t i o n was measured for the remainder (Table VI) using KBrO-^  (101 r e f l e c t i o n at 20.215°29 CuK ^ ) as an i n t e r n a l standard. c) Compositions of the Natural Feldspars Wright and Stewart ( I 9 6 8 ) have shown that the a c e l l dimension, unit c e l l volume, and the position of the 201 X-ray r e f l e c t i o n of a l k a l i feldspars show a direct correlation with composition which i s independent of the structural state of the material. (Fig. 3). Thus, for those samples for which unit c e l l dimensions have been refined, the compositions of the K-rich phase have been estimated from the unit c e l l volume (Table II). Compositions for the remaining samples have been estimated from a knowledge of the position of the 201 r e f l e c t i o n . (Table VI). Table V compares compositions estimated from unit T 1 1 1 1 1 1 r 6 6 0 1 1 1 1 1 1— — I 1 1 L I i i 1 1 1 1 1 1 r I i i i i i i i i i i Ab 20 4 0 6 0 8 0 Or W e i g h t % Or F i g . 3 O r t h o c l a s e content of a l k a l i f e l d s p a r s p l o t t e d as a f u n c t i o n of t h e _ a c e l l d i m e nsion, u n i t c e l l volume and °28 201 CuK«. . S i m p l i f i e d from Wright and Stewart (1968) and Wright * ( 1 9 6 8 ) . 17 c e l l volumes, a c e l l d imensions and 201 X-ray d i f f r a c t i o n r e f l e c t i o n s f o r the t w e l v e ' r e f i n e d ' a l k a l i , f e l d s p a r s . In g e n e r a l the e s t i m a t e s o b t a i n e d from t h e s e t h r e e parameters agree w i t h i n the -2% a c c u r a c y c l a i m e d f o r t h e methods by Wright and Stewart (1968). The samples i n v e s t i g a t e d comprise K - r i c h phases whose c o m p o s i t i o n s v a r y from 87 t o 92 Wt% Or, and Na r i c h phases w i t h c o m p o s i t i o n s between 95 and 100 V!t% Ab. Because the e r r o r i n measurement o f c o m p o s i t i o n i s a p p r o x i m a t e l y - 2Wt% Or i t can be s t a t e d t h a t t h e a l k a l i f e l d s p a r s throughout the p l u t o n have reached a p p r o x i m a t e l y the same stage of p e r t h i t i c unmixing. A l t h o u g h none o f the samples e x h i b i t any o p t i c a l e v i d e n c e of c o m p o s i t i o n a l z o n i n g the 201 d i f f r a c t i o n peaks f o r the K - r i c h phase i n s e v e r a l samples are v e r y s l i g h t l y skewed towards h i g h e r Or Wt% v a l u e s , t h u s s u g g e s t i n g t h a t s l i g h t z o n i n g may i n f a c t be p r e s e n t . d) S t r u c t u r a l S t a t e s o f the N a t u r a l A l k a l i F e l d s p a r s The s t r u c t u r a l s t a t e s o f the K - r i c h phases o f the n a t u r a l p e r t h i t e s have been e s t i m a t e d from a knowledge of the b and _c c e l l d i m e n s i o n s , or from the p o s i t i o n o f the (060) and (20Z+) X-ray d i f f r a c t i o n r e f l e c t i o n s . F i g u r e L\. ( s i m p l i f i e d from Wright and S t e w a r t ) shows d a t a 18 I i i i i 1 — i r ~ — i 1 — r 12.80 12.84 12.88 12.32 12.96 13.00 b. A F ig . 4: Refined cell parameters for alkali feldspars from the Guichon Creek batholith plotted on a b-c plot simplified from Wright a Stewart (1968) . Dashed lines represent contours for the a_ cel l d imension. Fig. 5'. Alkali feldspars from the Guichon Creek batholith plotted on a 0 6 0 - 2 0 4 plot simplified from Wright ( 1 9 6 8 ) . Dashed lines represent contours for 2 9 201 . R e l a t i o n between e s t i m a t e d b u l k c o m p o s i t i o n s and degree of anomoly f o r computer r e f i n e d a l k a l i f e l d s p a r Sample V(X)3 a ( C a l c ) ( A ) a ( e s t ) ( A ) Anomoly 201 obs. Co m p o s i t i o n V/t% Or E s t i m a t e d from V~ . a ( C a l c ) a ( e s t ) 201 obs. 33 6 1 3 1 9 12 2 9 2 3 2 2 '4 17 2 7 7 2 1 . 3 2 7 2 0 . 7 9 7 2 1 . 1 8 7 2 1 . 0 2 7 2 1 . 1 3 7 2 0 . 9 0 7 1 9 . 7 9 7 2 1 . 5 7 7 2 1 . 9 7 7 2 1 . 0 6 719.60 720./.;.6 8 . 5 7 6 o . > o ± 8 . 5 7 7 8 . 5 3 0 8 . 5 7 3 8 . 5 6 2 8 . 5 7 8 8 . 5 8 4 8 . 5 7 5 8 . 5 5 5 8.56/+ o c o 0.5o 8 . 5 7 5 8 . 5 8 8 . 5 9 8 .60 8 . 5 9 8 . 5 9 8 . 6 1 8 . 6 2 8 . 6 2 3 . 6 1 8 . 6 2 , 0 1 2 , 0 2 , 0 2 , 0 3 0 . 0 3 2 . 0 3 8 . 0/45 . 0 6 0 . 0 6 0 21.011 21.03.'+ 2 1 . 0 1 4 21.019 2 1 . 0 3 5 2 1 . 0 3 8 21.067 21.02/f 21.004 2 1 . 0 3 0 21.058 21.035 9 2 . 5 91 . .5 9 2 . 0 9 2 . 0 9 1 . 5 3 9 . 0 9 3 - 0 O r , 5 9 2 . 0 P P ^ or> q 94 9 3 9 4 -9 3 9/4 92 90 9 3 9 4 O O o n 9/4 9 1 94 96 00 96 96 9 9 100 100 9 5 100 on q .0 PQ o n n 8 9 . 5 8 9 . 0 8 8 . 0 . 5 8 9 . 5 01 n P o n o . •-' O D . J or c ; Q " 20 f o r t h e 12 " r e f i n e d " s a m p l e s p l o t t e d o n a b v s . _c d i a g r a m . S i m i l a r l y F i g u r e 5 i s a °20 (060) v s . °20(2O4) p l o t o f d a t a f o r a l l t h e s a m p l e s i n v e s t i g a t e d . When t h e b a n d _c c e l l d i m e n s i o n s f o r a n y s a m p l e a r e p l o t t e d o n F i g . 1+ t h e a c e l l d i m e n s i o n may be e s t i m a t e d f r o m t h e c r o s s c o n t o u r s . F o r a p p r o x i m a t e l y h a l f o f t h e s a m p l e s i n v e s t i g a t e d t h e v a l u e f o r a s o e s t i m a t e d d o e s n o t a g r e e w i t h t h e a v a l u e c a l c u l a t e d f r o m t h e c e l l r e f i n e m e n t . W r i g h t a n d S t e w a r t (1968) h a v e d e s c r i b e d a l k a l i f e l d s p a r s i n w h i c h a ' c a l c u l a t e d ' d i f f e r s f r o m a ' e s t i m a t e d ' b y m o r e t h a n .02 A a s h a v i n g ' a n o m o l o u s ' c e l l d i m e n s i o n s . T h e y s u g g e s t t h a t i n s u c h c a s e s t h e c o m p o s i t i o n o f t h e s a m p l e may be e s t i m a t e d f r o m t h e c e l l v o l u m e , o n t h e p r e m i s e t h a t t h e a t o m s w i l l o c c u p y t h e same v o l u m e r e g a r d l e s s o f t h e c o n f i g u r a t i o n o f t h e u n i t c e l l . F u r t h e r m o r e , t h e y s t a t e t h a t t h e s a m p l e may be d e f i n e d i n t e r m s o f a n ' a p p a r e n t ' s t r u c t u r a l s t a t e . T a b l e V l i s t s c e l l v o l u m e s , a n d c a l c u l a t e d a n d e s t i m a t e d a c e l l p a r a m e t e r s f o r t h e ' c o m p u t e r r e f i n e d ' s a m p l e s i n v e s t i g a t e d . The p r e s e n t s t u d y a g r e e s w i t h W r i g h t a n d S t e w a r t ' s o b s e r v a t i o n s t h a t i n a l l a n o m o l o u s s a m p l e s t h e a c a l c u l a t e d v a l u e s a r e l o w e r t h a n t h e a e s t i m a t e d v a l u e s . H o w e v e r , T i l l i n g (1968) h a s r e p o r t e d s a m p l e s i n w h i c h t h e r e v e r s e h o l d s t r u e . T h e a n o m a l o u s c o n d i t i o n e x h i b i t e d b y s u c h a l k a l i f e l d s p a r s w o u l d a p p e a r t o be r e l a t e d t o t h e i r p e r t h i t i c n a t u r e a n d may be due t o s t r a i n s i m p o s e d o n t h e s t r u c t u r e d u r i n g p e r t h i t i c u n m i x i n g . The G u i c h o t h o l i t h a l k a l i f e l d s p a r s p l o t t e d o n F i g u r e s i+ a n d 5 l i e w i t h i n t h e o r t h o c l a s e f i e l d b e t w e e n t h e o r t h o c l a s e P 5 0 - 5 6 F o f W r i g h t a n d S t e w a r t (1968) a n d t h e maximum m i c r o c l i n e o f O r v i l l e (1967). The o n l y e x c e p t i o n t o t h i s i s s a m p l e #31 w h i c h p l o t s o n F i g . 5 w i t h i n t h e i n t e r m e d i a t e m i c r o c l i n e f i e l d . T h e s a m p l e i s f r o m a s m a l l i n t r u s i v e m a s s o n t h e w e s t e r n m a r g i n o f t h e b a t h o l i t h , a n d h a s b e e n t e n t a t i v e l y c o r r e l a t e d w i t h t h e W i t c h e s B r o o k p h a s e . T h e r o c k c o n t a i n s 26 v o l % o f m e d i u t o c o a r s e g r a i n e d m i c r o p e r t h i t i c a l k a l i f e l d s p a r w h i c h h a s a s u b h e d r a l h a b i t , a n d a b u l k c o m p o s i t i o n o f 6^Wt?& O r . I n a d d i t i o n , t h e r o c k , c o n t a i n s 76 Wt% Si02 a n d a p p e a r s t o be t h e m o s t h i g h l y d i f f e r e n t i a t e d o f t h e s a m p l e s s t u d i e d . T h e X - r a y d i f f r a c t o m e t e r p a t t e r n f o r t h i s s a m p l e c o n t a i n s no w e l l d e f i n e d 131 o r 131 r e f l e c t i o n s f o r t h e p o t a s i u m r i c h p h a s e . T h e r e f l e c t i o n s i n t h e r e g i o n b e t w e e n 29.25° a n d 30.50° 20 C u K * a r e i l l u s t r a t e d i n F i g . 6 . . The h i g h e r i n t e n s i t y r e f l e c t i o n w i t h c e n t r e o f s y m r n e t t r y a t a p p r o x i m a t e l y 30.1° 20 C u K * i s m o s t p r o b a b l y a c o m p o s i t e r e f l e c t i o n 22 F i g . 6 X - r a y d i f f r a c t i o n p a t t e r n f o r s a m p l e 31 i n t h e r e g i o n o f 30° 2 0 CuK<* A l s o shown a r e t h e r a n g e s o f p o t a s s i c a n d s o d i c a l k a l i f e l d s p a r r e f l e c t i o n s w h i c h may a p p e a r i n t h i s r e g i o n . ( F r o m W r i g h t a n d S t e w a r t , 1968) 23 c a u s e d b y t h e i n f e r e n c e o f t h e 131 a l b i t e r e f l e c t i o n a n d . a 131 m i c r o c l i n e r e f l e c t i o n . The v e r y b r o a d r e f l e c t i o n e x t e n d i n g f r o m a p p r o x i m a t e l y 2 9 - 5 ° t o 2 9 . 9 ° 2© CuKot p r o b a b l y r e p r e s e n t s a 131 r e f l e c t i o n f r o m a t r i c l i n i c p o t a s s i u m r i c h p h a s e a n d t h e r e i s a d i s t i n c t p o s s i b i l i t y t h a t a 131 r e f l e c t i o n f r o m a m o n o c l i n i c p o t a s s i u m p h a s e may a l s o be r e p r e s e n t e d h e r e . T h i s w o u l d i n d i c a t e t h a t t h e p o t a s s i u m r i c h p h a s e o f t h e p e r t h i t e i s p r e s e n t i n a w i d e r a n g e o f s t r u c t u r a l s t a t e s . I n c o n t r a s t t h e 060 a n d 204 r e f l e c t i o n s f r o m t h e p o t a s s i u m r i c h p h a s e i n t h i s s a m p l e a r e r e l a t i v e l y s h a r p a n d w e l l d e f i n e d . S m i t h a n d M a c k e n z i e (1961) h a v e s u g g e s t e d f r o m t h e o r e t i c a l c o n s i d e r a t i o n s t h a t a s t h e S i - A l o r d e r o f a p e r t h i t i c a l k a l i f e l d s p a r i n c r e a s e s , s o s h o u l d t h e p u r i t y o f t h e p e r t h i t i c c o m p o n e n t s . T i l l i n g (1968) h a s o b s e r v e d a g e n e r a l i n c r e a s e i n ' t r i c l i n i c i t y ' w i t h i n c r e a s i n g l y a l b i t i c b u l k c o m p o s i t i o n s o f - o e r t h i t i c a l k a l i f e l d s p a r s f r o m t h e R a d e r C r e e k P l u t o n , B o u l d e r B a t h o l i t h , M o n t a n a . The c o m p o s i t i o n s o f t h e p e r t h i t i c c o m p o n e n t s i n s a m p l e #31 a p p r o a c h c l o s e l y t h e p u r e e n d member c o m p o s i t i o n s a n d a r e v e r y s i m i l a r t o t h e o t h e r s a m p l e s . f r o m t h e G u i c h o n C r e e k b a t h o l i t h . S a m p l e #31 i s u n i q u e h o w e v e r , b e c a u s e i t i s c o n s i d e r a b l y m o r e o r d e r e d w i t h r e s p e c t t o A l a n d S i , a n d h a s a more s o d i c b u l k c o m p o s i t i o n t h a n t h o o t h e r s a m p l e s . T h u s a g r e a t e r d e g r e e o f p e r t h i t i c u n m i x i n g m u s t h a v e t a k e n p l a c e i n s a m p l e # 3 1 , a n d t h e c o n s e q u e n t l y g r e a t e r a m o u n t o f d i f f u s i o n o f An a n d K i o n s may h a v e a l l o w e d a h i g h e r d e g r e e o f S i - A l o r d e r i n g t o t a k e p l a c e . T h u s , v / i t h a s i n g l e e x c e p t i o n , t h e a l k a l i f e l d s p a r s f r o m t h e G u i c h o n b a t h o l i t h a r e o r t h o c l a s e e x h i b i t i n g a p p r o x i m a t e l y e q u i v a l e n t ' a p p a r e n t ' s t r u c t u r a l s t a t e s . The s l i g h t s c a t t e r o f d a t a p o i n t s o n F i g s , k a n d 5 m o s t p r o b a b l y r e f l e c t s , i n l a r g e p a r t , e x p e r i m e n t a l e r r o r s £.nd t h e a n o m a l o u s n a t u r e o f many o f t h e s a m p l e s . The e q u i v a l e n c e i n ' a p p a r e n t ' s t r u c t u r a l s t a t e o f t h e a l k a l i f e l d s p a r s d o e s n o t n e c e s s a r i l y m e a n , h o w e v e r , t h a t t h e t e m p e r a t u r e o f t h e i r o r i g i n a l c r y s t a l l i s a t i o n d i d n o t v a r y . The r e l a t i v e s t r u c t u r a l s t a t e o f a m o n o c l i n i c a l k a l i f e l d s p a r i s d e p e n d e n t o n t h e d e g r e e o f A l / S i o r d e r i n g o v e r t h o n o n e q u i v a l e n t T^ a n d t c t r a h c d r a l s i t e s . The o r d e r i n g i s a c h i e v e d b y d i f f u s i o n , i n t h e s o l i d s t a t e , o f A l i n t o t h o m o r e f a v o u r a b l e T^ s i t e s , a n d t h o c o o l i n g h i s t o r y o f t h e m a t e r i a l w i l l d e t e r m i n e 25 t h e a m o u n t o f t i m e d u r i n g w h i c h d i f f u s i o n may t a k e p l a c e . T h e r e f o r e b o t h t h e i n i t i a l c r y s t a l l i s a t i o n t e m p e r a t u r e a n d t h e c o o l i n g h i s t o r y o f t h e h o s t r o c k w i l l a f f e c t t h e f i n a l , r e l a t i v e s t r u c t u r a l s t a t e o f a n a l k a l i f e l d s p a r . e ) B u l k C o m p o s i t i o n s o f t h e H o m o g e n i s e d A l k a l i F e l d s p a r T a b l e V I g i v e s o b s e r v e d °2©(201) f o r t h e h o m o g e n i s e d s a m p l e s a n d t h e c o r r e s p o n d i n g e s t i m a t e d b u l k c o m p o s i t i o n s i n Wt% O r . A s may be s e e n a l k a l i f e l d s p a r b u l k c o m p o s i t i o n s a r e g e n e r a l l y i n t h e r a n g e 71 t o 86 Wt% w i t h t h e e x c e p t i o n o f t w o s a m p l e s f r o m t h e P i t c h e s B r o o k P h a s e w h i c h h a v e b u l k c o m p o s i t i o n s o f 65 Wt% Or a n d 65 Wt% O r . T h e r e s e e m s t o be no r e g u l a r v a r i a t i o n o f t h e a l k a l i f e l d s p a r b u l k c o m p o s i t i o n s f r o m one p h a s e o f t h e b a t h o l i t h t o a n o t h e r , n o r i s t h e r e a n y c o r r e l a t i o n w i t h t h e c o m p o n e n t o x i d e c o n t e n t s o f t h e r o c k s a m p l e s a s d e r i v e d f r o m c h e m i c a l e s t i m a t e s , ( s e e A p p e n d i x 2) 2 6 TABLE V I 20 v a l u e s f o r 201 r e f l e c t i o n s . (CuK«radiation) and e s t i m a t e d b u l k c o m p o s i t i o n o f homogenised a l k o . l i f e l d s p a r s from the Guichon Crook b a t h o l i t h Sample # Phase °20(2O1)* ° 2 0 Spread from 3 t r a c e s """Estimated Wt% Or. 1 1 2 1 . 1 1 3 . 0 0 5 8 1 . 5 ? 1 2 1 . 1 2 4 . 0 1 3 8 0 . 0 3 1 21.116 . 0 0 3 8 1 . 4 1 2 1 . 1 1 1 . 0 0 3 8 2 . 5 2G 21.216 . 0 0 3 72 6 2G 2 1 . 1 4 6 . 0 0 8 7 9 . 7 2G 2 1 . 0 8 9 . 0 0 2 8 4 . 8 2G 2 1 . 1 6 9 . 0 0 5 76. 9 2C 2 1 . 2 1 3 . 0 0 5 7 2 . • 8 0 . 5 10 2C 2 1 . 1 1 9 . 0 1 3 11 2C 2 1 . 1 2 0 . 0 0 5 8 0 . 5 12 2C 2 1 . 0 8 2 . 0 1 5 3 4 . 13 2C 2 1 . 1 1 6 . 0 1 0 8 1 . 14 2LR 2 1 . 1 3 1 . 0 1 0 7 9 . 5 15 2LR 2 1 . 1 2 3 . 0 0 5 8 0 . 16 . 2LR 2 1 . 1 4 1 . 0 0 5 7 9 . 17 2LR 2 1 . 1 3 2 . 0 0 8 7 9 . 5 13 2LR 21.164 . 0 0 8 77. 19 3 2 1 . 2 0 0 . 0 1 0 7 3 - 5 2 0 3 2 1 . 0 9 6 . 0 0 3 8 2 . 5 2 1 3 2 1 . 1 8 4 . 0 1 3 7 5 -2 2 4 2 1 . 1 9 7 . 0 0 5 7 3 . 5 2 3 4 2 1 . 1 4 4 . 0 1 3 7 8 . 5 2 4 2 1 . 2 4 1 . 0 1 0 7 0 . 2 5 4 2 1 . 1 3 9 . 0 0 3 7 9 . 2 6 5 2 1 . 1 2 5 . 0 0 5 8 0 . 2 7 5 2 1 . 2 9 3 . 0 0 8 6 5 . 5 2 8 5 2 1 . 1 5 0 .006 7 8 . 2 9 • 5 2 1 . 2 0 4 . 0 0 3 7 3 . 0 3 0 5 21.166 . 0 0 8 7 6 . 5 3 1 5 2 1 . 3 1 9 . 0 0 3 6 3 . 32 6 2 1 . 1 5 2 • . 0 0 3 7 8 . 3 3 6 2 1 . 2 3 1 . 0 0 7 7 1 . 3k 6 2 1 . 1 7 9 . 0 0 8 7 4 . 5 3 5 6 2 1 . 0 7 0 . 0 0 5 8 5 . *°29 (201) v a l u e s a r c averages o f 3 d i f f r a c t o m e t c r t r a c e s + Accuracy e s t i m a t e d a t - 2 Wt% Or. 27 I V P l a g i o c l a s e F eMjsjDjar_s a ) Mode o f O c c u r r e n c e P l a g i o c l a s e o c c u r s a s s u b h e d r a l o r e u h e d r a l c r y s t a l s i n a l l p h a s e s o f t h e b a t h o l i t h , a n d h a s a n e x t r e m e l y v a r i a b l e g r a i n s i z e r a n g i n g f r o m 4 m m t o l e s s t h a n 0 . 5 m m . A l b i t e o r c o m b i n e d a l b i t e - c a r l s b a d t w i n n i n g i s u b i q u i t o u s b u t p e r i c l i n e t w i n n i n g i s s c a r c e . N o r m a l a n d o s c i l l a t o r y z o n i n g a r e common a n d p a t c h y z o n i n g i s f r e q u e n t l y p r e s e n t . Z o n i n g i s d i s c u s s e d more f u l l y i n t h e f o l l o w i n g s e c t i o n . H o r n b l e n d e , m a g n e t i t e a n d b i o t i t e i n c l u s i o n s a r e common, w i t h b i o t i t e s h o w i n g a s l i g h t t e n d e n c y t o be r e s t r i c t e d t o r i m r e g i o n s . I n t h e H y b r i d p h a s e , a n d l e s s c o m m o n l y i n t h e H i g h l a n d V a l l e y p h a s e , p y r o x e n e a l s o a p p e a r s a s a n i n c l u s i o n a n d t e n d s t o be r e s t r i c t e d t o c o r e r e g i o n s . I n t e n s e a l t e r a t i o n t o a f i n e - g r a i n e d c o l o r l e s s m i c a i s e s p e c i a l l y common i n t h e H y b r i d p h a s e a n d some a l t e r a t i o n o c c u r s i n p l a g i o c l a s e c o r e r e g i o n s o f a l m o s t a l l t h e s a m p l e s s t u d i e s . b ) P l a g i o c l a s e C o m p o s i t i o n s a n d Z o n i n g P l a g i o c l a s e c o m p o s i t i o n s h a v e b e e n m e a s u r e d i n t h i n - s e c t i o n u s i n g t h e p e r p e n d i c u l a r t o ' a ' m e t h o d a n d a 4 - a x i s u n i v e r s a l s t a g e . U n i v e r s a l s t a g e m e a s u r e m e n t s o f 2 V z i n d i c a t e t h a t t h e s t r u c t u r a l s t a t e s o f t h e p l a g i o c l a s e s v a r y f r o m l o w t o i n t e r m e d i a t e . B e c a u s e 2 8 P l a g i o c l a s e c o m p o s i t i o n s - see t e x t f o r e x p l a n a t i o n Bulk composition Sample # Phase Wt% An Wt % An Core Main Rim Rim c o n t a c t w i t h O p t i c a l X-Ray A l k a l i f e l d s p a r JL 1 47 36 36 4 3 44.0 2 1 3 5 2 8 heavy a l t e r a t i o n 3 2 • 2 3 . 5 3 1 3 0 2 6 ?12heavy a l t e r a t i o n 30 , 3 0 . 5 4 1 3 8 2 7 20 3 5 , 3 5 . 5 5 2G 36 2 7 none observed 31 2 5 . 5 6 2G 3 8 2 5 24 3 4 3 5 . 5 7 2G 3 8 2 7 20 3 2 . 2 8 8 2G 4 8 20 zero 30 . 24 • 0 9 2C 3 8 20 20 3 3 36 10 2C 36 20 z e r o 3 3 ' 3 3 11 2C 36 2 6 2 6 3 3 3 3 12 2C 32 32 3 2 32 2 5 . 0 14 2LR 4 5 2 5 m y r m e k i t i c 3 9 3 2 . 0 1 5 2LR 41 24 24 3 3 32.0 16 2LR 3 9 2 5 20 3 3 3 3 17 2LR 3 1 20 20 2 8 2 7 . 5 1 8 2LR 3 2 20 20 2 8 3 1 - 5 1 9 3 3 3 20 zero 50 2 9 . 0 20 3 3 2 20 zero 2 7 do . ) 21 3 2 7 20 zero 2 9 29.0 22 4 36 3 8 18 18 3 1 3 2 . 0 2 3 4 20 z e r o 2 8 2 7 . 5 24 4 38 20 zero 2 8 2 9 . 5 2 5 4 38 20 zero 3 0 3 1 . 5 2 6 5 4 8 20 zero 3 5 2 6 . 5 27 5 36 20 z e r o 2 8 2 7 . 5 2 8 . 5 2 9 20 zero 27 2 6 . 5 2 9 5 3 3 20 zero 2 8 2 8 . 0 30 5 40 20 z e r o 27 23.0 3 1 5 24 7 7 or zero 12 11.0 32 6 3 8 20 zero 2 8 2 8 . 5 I 3 3 6 32 20 20 2 8 1 2 7 . 5 3 4 6 3 4 20 zero 3 0 2 9 - 5 ! 3 5 i 6 2 3 16 zero 24 2 3 . 5 29 the p l a g i o c l a s e e x h i b i t c o n s i d e r a b l e c o m p o s i t i o n a l z o n i n g i t i s r a t h e r d i f f i c u l t to e s t i m a t e b u l k c o m p o s i t i o n s . Because o f t h i s d i f f i c u l t y X-ray d i f f r a c t o m e t e r p a t t e r n s v/ere o b t a i n e d f o r a l l the samples, w i t h s i x o s c i l l a t i o n s b e i n g made i n the range 29° to 33° 29 u s i n g C u K ^ r a d i a t i o n . The s e p a r a t i o n of the (131) and (131) peaks was measured and the average v a l u e f o r each sample compared t o the ' l o w ' . p l a g i o c l a s e curve o f Smith ( 1 9 5 6 ) . For 75% of the samples i n v e s t i g a t e d the average c o m p o s i t i o n from the d i f f r a c t o m e t e r method agrees t o w i t h i n 2 Wt% An w i t h the average v a l u e e s t i m a t e d by o p t i c a l e x a m i n a t i o n . For the r e m a i n i n g samples the d i f f r a c t o m e t e r averages are lower i n An content and a l l these samples' c o n t a i n p l a g i o c l a s e s w i t h s t r o n g l y s e r i c i t i s e d core r e g i o n s . In such cases the average or b u l k c o m p o s i t i o n f i n a l l y a c c e p t e d was t h a t o b t a i n e d by o p t i c a l e x a m i n a t i o n . Table V I I l i s t s c o m p o s i t i o n a l ranges and o p t i c a l and X-ray d i f f r a c t o m e t e r e s t i m a t e s of average p l a g i o c l a s e c o m p o s i t i o n s . In g e n e r a l , core c o m p o s i t i o n s are i n the range An3§ t o An£8 a n d i t i s o n l y i n the Witches Brook phase t h a t t h i s range i s exceeded - An 32 t o An^Q. P l a g i o c l a s e s from the H y b r i d phase and from the Guichon v a r i e t y o f the H i g h l a n d V a l l e y phase have r i m c o m p o s i t i o n s a v e r a g i n g 30 A r ^ y w h i l s t a l l t h e o t h e r s a m p l e s i n v e s t i g a t e d h a v e r i m c o m p o s i t i o n s o f a p p r o x i m a t e l y Anp . Many o f t h e s a m p l e s e x h i b i t p o i k i l i t i c a l k a l i f e l d s p a r i n c o n t a c t w i t h s u b h e c l r a l - e u h e d r a l p l a g i o c l a s e . I n s u c h c a s e s t h e a l k a l i f e l d s p a r c o m m o n l y o c c u p i e s e m b a y m e n t s i n t o t h e p l a g i o c l a s e , ( p l e . t c j l a n d 2 ) w h i c h s u g g e s t s t h a t r e s o r p t i o n o f p l a g i o c l a s e was t a k i n g p l a c e d u r i n g t h e f i n a l s t a g e s o f c r y s t a l l i s a t i o n i n t h e s e s a m p l e s . F u r t h e r m o r e , a v e r y t h i n r i m o f a l b i t e o c c u r s w i t h i n t h e p l a g i o c l a s e , p a r a l l e l i n g t h e r e s o r b e d o u t l i n e o f t h e c r y s t a l . ( P l a t e 3) Two a l t e r n a t i v e h y p o t h e s e s may be p u t f o r w a r d t o a c c o u n t f o r t h e p r e s e n c e o f t h e s e a l b i t e r i m s : ( i ) I t i s p o s s i b l e t h a t , d u r i n g r e s o r p t i o n o f t h e p l a g i o c l a s e , c a l c i u m may h a v e b e e n d i f f u s i n g o u t o f t h e p l a g i o c l a s e r i m m o r e r a p i d l y t h a n s o d i u m . L a t e s t a g e m a g m a t i c l i q u i d i n g r a n i t i c r o c k s i s c o m m o n l y b e l i e v e d t o be e n r i c h e d i n s o d i u m a n d p o t a s s i u m r e l a t i v e t o c a l c i u m . T h e r e f o r e t h e c o m p o s i t i o n g r a d i e n t b e t w e e n l a t e m a g m a t i c l i q u i d a n d p l a g i o c l a s e c r y s t a l s w o u l d be g r e a t e r f o r c a l c i u m t h a n f o r s o d i u m , a n d h e n c e more r a p i d d i f f u s i o n o f t h e c a l c i u m r i c h c o m p o n e n t o u t o f t h e p l a g i o c l a s e i s t o be e x p e c t e d . The a l b i t e r i m s a p p e a r t o h a v e d i f f u s e i n n e r e d g e s , w h i c h may s u p p o r t t h e d i f f u s i o n h y p o t h e s i s . 31 P l a t e 1 P a r t i a l l y r e s o r b e d p l a g i o c l a s e e n c l o s e d w i t h i n p o i k i l i t i c a l k a l i f e l d s p a r . S a m p l e #11. C h a t a w a y v a r i e t y . C r o s s e d n i c o l s , x 30. 32 H o w e v e r , t h e t h i n n e s s o f t h e r i m s p r e v e n t s a c l o s f e s t u d y o f t h i s f e a t u r e . ( i i ) Bowen a n d T u t t i e 1958 h a v e s u g g e s t e d t h a t a l b i t e r i m s o n o r t h o c l a s c - r i c h a l k a l i f e l d s p a r s may be t h e r e s u l t o f d i f f u s i o n o f t h e a l b i t e c o m p o n e n t t o c r y s t a l m a r g i n s d u r i n g p e r t h i t i c u n m i x i n g . T h i s d o e s n o t scorn t o be a v e r y l i k e l y e x p l a n a t i o n i n t h o p r e s e n t s a m p l e s , h o w e v e r , b e c a u s e o f t h e r e l a t i v e l y f i n e s c a l e o f t h e a s s o c i a t e d p e r t h i t i c l a m e l l a e . I n a d d i t i o n , t h e a l b i t e r i m s a r e o p t i c a l l y c o n t i n u o u s w i t h t h e p l a g i o c l a s e r a t h e r t h a n w i t h t h e a l k a l i f e l d s p a r s . L a t e s t a g e r e s o r p t i o n o f p l a g i o c l a s e h a s b e e n e x p l a i n e d b y T u t t l e a n d Bowen (1958) w i t h r e f e r e n c e t o t h e s y s t e m N a A l S i ^ O g - K A l S i ^ O g - C a A l 2 S i 2 0 g . I n F i g . 7 t h e l i n e ABC r e p r e s e n t s t h e l i m i t o f f e l d s p a r s o l i d s o l u t i o n i n t h i s s y s t e m a n d t h e l i n e DBF i s a s i n g l e f i e l d b o u n d a r y c o r r e s p o n d i n g t o l i q u i d c o m p o s i t i o n s w h i c h a r e i n e q u i l i b r i u m w i t h two f e l d s p a r s a t 1 k b w a t e r v a p o u r p r e s s u r e ( J a m e s a n d H a m i l t o n 1969). S t r o n g l y f r a c t i o n a t e d l i q u i d s w h i c h c r y s t a l l i s e d p l a g i o c l a s e a t a n e a r l y s t a g e may e v e n t u a l l y e n t e r t h e f i e l d B E F , a t w h i c h t i m e p l a g i o c l a s e r e s o r p t i o n a n d r e p l a c e m e n t b y a l k a l i f e l d s p a r may t a k e p l a c e . S a m p l e #31 r e p r e s e n t s a h i g h l y f r a c t i o n a t e d m a g m a t i c l i q u i d w h i c h i n i t i a l l y c r y s t a l l i s e d H y b r i d , H i g h l a n d v a l l e y and L e r o y p h a s e s a m p l e s . B e t h l e h e m , W i t c h e s b r o o k a n d B e t h s a i d a p h a s e s a m p l e s c, G u m p l a k e p h a s e s a m p l e s . Ano rt h i t e A l b i t e O r t h o c l a s e F i g . 7 . M o d a l f e l d s p a r c o n s t i t u e n t s of the G u i c h o n C r e e k b a t h o l i t h s a m p l e s r e c a l c u l a t e d t o 100% An + A b + O r . A B C r e p r e s e n t s t h e l i m i t o f t e r n a r y s o l i d s o l u t i o n i n n a t u r a l f e l d s p a r s . D E F i s t h e b o u n d a r y c u r v e s e p a r a t i n g t h e f i e l d s of p l a g i o c l a s e a n d a l k a l i f e I d s p a r . 3k p l a g i o c l a s e f e l d s p a r An22« T h i s p l a g i o c l a s e r a p i d l y became, o u t o f e q u i l i b r i u m w i t h t h e m a g m a t i c l i q u i d a n d was c o n s e q u e n t l y p a r t i a l l y r e s o r b e d a n d r e p l a c e d b y a n a l k a l i f e l d s p a r O r - ^ . T h u s #31 c o n s i s t s o f a n • e q u i g r a n u l a r m o s a i c o f q u a r t z , a l k a l i f e l d s p a r a n d c r y s t a l s w i t h p a r t i a l l y r e s o r b e d p l a g i o c l a s e c o r e s a n d a l k a l i f e l d s p a r m a n t l e s . A l t h o u g h p l a g i o c l a s e c o m p o s i t i o n s show v e r y l i t t l e v a r i a t i o n t h r o u g h o u t t h e b a t h o l i t h , t h e n a t u r e o f t h e z o n a t i o n i s s i g n i f i c a n t a n d d i v i d e s t h e p h a s e s i n t o t w o m a j o r g r o u p s . T h u s p l a g i o c l a s e s f r o m t h e H y b r i d a n d H i g h l a n d V a l l e y p h a s e s e x h i b i t o n l y n o r m a l z o n i n g w i t h s u p e r i m p o s e d p a t c h y z o n i n g , w h i l s t t h o s e f r o m t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s h a v e d e l i c a t e l y o s c i l l a t o r y z o n e d c o r e s a n d n o r m a l l y z o n e d r i m s . The c h a n g e f r o m c o r e t o r i m r e g i o n s i s i n a l l c a s e s g r a d a t i o n a l t h r o u g h p r o g r e s s i v e n o r m a l z o n i n g . P l a g i o c l a s e s f r o m t h e Gump L a k e p h a s e e x h i b i t a z o n i n g scheme i n t e r m e d i a t e b e t w e e n t h e t w o p r e v i o u s l y d e s c r i b e d , i n t h a t c o r e s may h a v e t h r e e o r f o u r v e r y b r o a d o s c i l l a t o r y z o n e s f o l l o w e d c o n t i n u o u s l y b y a n o r m a l l y z o n e d r i m . S a m p l e s f r o m N o r t h c o t e ' s W i t c h e s B r o o k p h a s e may e x h i b i t e i t h e r o r b o t h o f t h e s c h e m e s , s u g g e s t i n g t h a t some o f t h e s e s a m p l e s a r e r e l a t e d t o t h e H i g h l a n d 35 P l a t e 3 P a r t i a l l y r e s o r b e d , - o s c i l l a t o r y z o n e d p l a g i o c l a s e e n c l o s e d w i t h i n p o i k i l i t i c , p e r t h i t i c a l k a l i f e l d s n a r . N o t e t h e a l b i t i c r i m t o the p l a g i o c l a s e . S a m p l e #2$, B e t h l e h e m p h a s e . C r o s s e d n i c o l s , x 30. P l a t e if O s c i l l a t o r y z o n i n g i n p l a g i o c l a s e . C a m p l e #3%. B e t h s a i d a p h a s e . C r o s s e d n i c o l s , x 3 0 . F ig . 8 P lag ioc lase zoning s c h e m e s . 36 O 0-5 I'O I i 1 Millimetres V a l l e y p h a s e a n d o t h e r s t o t h e B e t h l e h e m p h a s e . F i g . 8 i l l u s t r a t e s t h e n a t u r e o f t h e z o n i n g s c h e m e s . S a m p l e #27 i s p a r t i c u l a r l y i n t e r e s t i n g i n t h a t i t d i s p l a y s a h o m o g e n o u s c o r e ( A n - ^ ) s i m i l a r t o s a m p l e s f r o m t h e H i g h l a n d V a l l e y p h a s e , w h i c h t e r m i n a t e s i n a n a b s o r p t i o n r i n d a n d i s f o l l o w e d b y a more b a s i c o s c i l l a t o r y z o n e d i n n e r r i m A n ^ g g i v i n g way t o a n o r m a l l y z o n e d o u t e r r i m (An^7_2Q), a c h a r a c t e r i s t i c o f t h e B e t h l e h e m a n d l a t e r p h a s e s . N o r m a l z o n i n g i n p l a g i o c l a s e c r y s t a l s i s g e n e r a l l y b e l i e v e d t o r e s u l t f r o n n o n - r e a c t i o n b e t w e e n c r y s t a l s i n t h e a n o r t h i t e - a l b i t e s o l i d s o l u t i o n s e r i e s a n d magma d u r i n g c r y s t a l l i s a t i o n i n r e s p o n s e t o f a l l i n g t e m p e r a t u r S u c h l a c k o f r e a c t i o n w o u l d seem l i k e l y f o r p l a g i o c l a s e s o f t h e H y b r i d a n d H i g h l a n d V a l l e y p h a s e s w h i c h a r e b e l i e v e d t o h a v e c r y s t a l l i s e d u n d e r c o n d i t i o n s o f c o n v e c t i v e magma f l o w . C o n v e r s e l y t h e m e c h a n i s m s l e a d i n g t o t h e d e v e l o p m e n t o f d e l i c a t e o s c i l l a t o r y z o n i n g i n p l a g i o c l a s e s a r e i m p e r f e c t l y k n o w n . V a n c e (1957) h a s d i s c u s s e d t h e v a r i o u s t h e o r i e s . B a s i c a l l y t h e t h e o r i e s c a n be d i v i d e d b e t w e e n t h o s e t h a t i n v o k e r e p e a t e d v a r i a t i o n s o f t e m p e r a t u r e , p r e s s u r e a n d / o r p a r t i a l v o l a t i l e p r e s s u r e o r r e q u i r e r e p e a t e d r e l a t i v e movement o f c r y s t a l a n d magma, a n d t h o s e b a s e d o n t h e d i f f u s i o n s u p e r s a t u r a t i o n t h e o r y o f H a r l o f f (192?) a s e x p a n d e d b y H i l l s (1936) a n d B o t t i n g a e t a l ( 1 9 6 6 ) . The l a t t e r a u t h o r s r e l a t e t h e d e g r e e o f s u p e r s a t u r a t i o n i n t h e magma i m m e d i a t e l y a d j a c e n t t o t h e c r y s t a l - l i q u i d i n t e r f a c e t o t h e m e c h a n i s m o f n u c l e a t i o n a n d t h e g e o m e t r i c c o n f i g u r a t i o n o f t h a t i n t e r f a c e . The p r e s e n c e o f a s u p e r s a t u r a t e d l a y e r i m m e d i a t e l y a d j a c e n t t o t h e i n t e r f a c e o f o s c i l l a t o r y z o n e d b y t o w n i t e c r y s t a l s s e t i n t h e g l a s s y m a t r i x o f a n o c e a n i c b a s a l t h a s b e e n p r o v e n b y B o t t i n g a e t a l u s i n g a n e l e c t r o n m i c r o p r o b e a n a l y s e r . The t h e o r y r e q u i r e s t h a t t h e r e be no r e l a t i v e movement b e t w e e n g r o w i n g p l a g i o c l a s e c r y s t a l s a n d t h e b o u n d a r y l a y e r i n t h e magma i m m e d i a t e l y a d j a c e n t t o t h e i n t e r f a c e . M o s t o f t h e o s c i l l a t o r y z o n i n g o b s e r v e d i n p l a g i o c l a s e s f r o m t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s i s o f t h e r e g u l a r , d e l i c a t e t y p e . I f t h i s t y p e o f z o n i n g v/ere due t o v a r i a t i o n s o f t e m p e r a t u r e o r p r e s s u r e w i t h i n t h e magma c h a m b e r i t w o u l d r e q u i r e t h a t t h e s e v a r i a t i o n s be e x t r e m e l y r e g u l a r i n b o t h t i m i n g a n d d e g r e e . F o r t h i s r e a s o n t h e m o d i f i e d d i f f u s i o n - s u p e r s a t u r a t i o n t h e o r y i s c o n s i d e r e d b y t h e p r e s e n t a u t h o r t o be t h e m o s t v i a b l e e x p l a n a t i o n c u r r e n t l y a v a i l a b l e f o r t h e p r e s e n c e o f r e g u l a r d e l i c a t e o s c i l l a t o r y z o n i n g i n i g n e o u s p l a g i o c l a s e Some o f t h e B e t h l e h e m p h a s e p l a g i o c l a s e c r y s t a l s d o , 39 h o w e v e r , c o n t a i n one o r t w o s l i g h t l y w i d e r z o n e s t h a t h a v e i r r e g u l a r o u t l i n e s . I t i s p o s s i b l e t h a t t h e s e z o n e s may r e p r e s e n t v a r i a t i o n s i n v o l a t i l e p r e s s u r e s a c c o m p a n y i n g i n t r u s i o n o f W i t c h e s B r o o k d y k e p h a s e . V a n c e ( 1 9 5 7 ) h a s d i s c u s s e d t h e o r i g i n o f n o r m a l l y z o n e d r i m s s u c c e e d i n g o s c i l l a t o r y z o n e d c o r e s i n p l a g i o c l a s e c r y s t a l s . Ho h a s s u g g e s t e d t h a t t h e a t t a i n m e n t o f v o l a t i l e s a t u r a t i o n w i t h c o n s e q u e n t r e s u r g e n t b o i l i n g may be s u f f i c i e n t t o p r e v e n t t h e o p e r a t i o n o f t h e d i f f u s i o n - s u p e r s a t u r a t i o n p r o c e s s a n d g r o w t h o f o s c i l l a t o r y z o n e d p l a g i o c l a s e , t h u s c a u s i n g t h e d e p o s i t i o n o f n o r m a l l y z o n e d r i m s . P i w i n s k i ( 1 9 6 8 ) h a s c a r r i e d o u t m e l t i n g e x p e r i m e n t s o n g r a n o d i o r i t e s a m p l e s f r o m t h e S i e r r a N e v a d a b a t h o l i t h a n d h a d d e t e r m i n e d c o m p o s i t i o n s o f f e l d s p a r s c o e x i s t i n g w i t h t h e m e l t a t v a r i o u s t e m p e r a t u r e s . ( F i g . 9 ) T h i s s t u d y h a s s h o w n t h a t i n t h e w a t e r s a t u r a t e d s y s t e m , t h e p l a g i o c l a s e c o m p o s i t i o n c o e x i s t i n g w i t h t h e m e l t c h a n g e s r a p i d l y w i t h i n i t i a l s l i g h t i n c r e a s e i n t e m p e r a t u r e . F u r t h e r i n c r e a s e s i n t e m p e r a t u r e c a u s e t h e r a t e o f c h a n g e o f p l a g i o c l a s e c o m p o s i t i o n t o d e c r e a s e m a r k e d l y . The o n s e t o f r a p i d l y c h a n g i n g p l a g i o c l a s e e q u i l i b r i u m c o m p o s i t i o n s d u r i n g c r y s t a l l i s a t i o n w o u l d p r o b a b l y t e n d t o t e r m i n a t e t h e e f f e c t i v e n e s s o f a n y s l o w d i f f u s i o n p r o c e s s l i k e l y t o 40 l 1 1 1 1 1 1 r subsolidus —I 1 1 I i i • | 20 40 60 80 Weight % An . F i g . 9 C o m p o s i t i o n s o f p l a g i o c l a s e s i n e q u i l i b r i u m w i t h g r a n i t i c m e l t s a s -a f u n c t i o n o f t e m p e r a t u r e a t 2 k b w a t e r p r e s s u r e . ( A f t e r P i w i n s k i , 1968, p.560) 4 1 c a u s e o s c i l l a t o r y z o n i n g , t h u s c a u s i n g t h e p r e c i p i t a t i o n o f n o r m a l l y z o n e d p l a g i o c l a s e . T e x t u r a l e v i d e n c e s u g g e s t s t h a t t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s c r y s t a l l i s e d u n d e r c o n d i t i o n s o f h i g h e r v o l a t i l e p r e s s u r e s t h a n h a d p r e v i o u s l y e x i s t e d . P i w i n s k i ' s e x p e r i m e n t a l d a t a a r e t h e r e f o r e p r o b a b l y a p p l i c a b l e t o p l a g i o c l a s e c r y s t a l l i s a t i o n i n t h o s e p h a s e s a n d t h e h y p o t h e s i s b a s e d o n h i s s t u d y i s p r e s e n t e d a s a n a l t e r n a t i v e t o V a n c e ' s s u g g e s t i o n . The u n i q u e p l a g i o c l a s e z o n i n g s c h e m e p r e s e n t i n t w o o f t h e W i t c h e s B r o o k p h a s e s a m p l e s , (#27 a n d #26) i s n o t e a s i l y e x p l a i n e d . T h e p a r t i a l l y r e s o r b e d , n o r m a l l y z o n e d c o r e s o f t h e s e p l a g i o c l a s e s s u g g e s t a f f i n i t i e s t o t h e H i g h l a n d V a l l e y p h a s e , w h i l s t t h o o u t e r z o n i n g s c h e m e s a r e i d e n t i c a l t o t h o s e p r e s e n t i n B e t h l e h e m p h a s e p l a g i o c l a s e s . N o r t h c o t e (1969) h a s s u g g e s t e d t h a t t h e W i t c h e s B r o o k p h a s e may be a d y k e p h a s e a s s o c i a t e d w i t h t h e m a j o r B e t h l e h e m p h a s e . I f s u c h i s t h e c a s e t h e n t h e r e s o r b e d p l a g i o c l a s e c o r e s o f s a m p l e s #27 a n d #26 may be x e n o c r y s t s o f e a r l i e r p h a s e s w h i c h w e r e m a n t l e d b y t y p i c a l B e t h l e h e m p h a s e m a t e r i a l , p r i o r t o b e i n g i n t r u d e d a s d y k e s o f t h e W i t c h e s B r o o k t y p e . The l a c k o f s u c h x e n o c r y s t s w i t h i n t h e m a j o r B e t h l e h e m p h a s e r o c k s may be due t o t h e , f a c t t h a t more c o m p l e t e a s s i m i l a t i o n w a s p o s s i b l e d e e p e r w i t h i n t h e m a i n c h a m b e r . 4 2 V B i o t i t e s a ) Mode o f O c c u r r e n c e B i o t i t e i s p r e s e n t i n a l l o f t h e s a m p l e s s t u d i e d f r o m t h e b a t h o l i t h . The a m o u n t o f b i o t i t e t e n d s t o d e c r e a s e w i t h i n c r e a s i n g s i l i c a c o n t e n t o f t h e h o s t r o c k ( F i g 10). I n r o c k s w i t h l e s s t h a n 65 Wt% Si0 2 c o n t e n t b i o t i t e i s a c c o m p a n i e d b y b o t h p y r o x e n e a n d h o r n b l e n d e . B i o t i t e a n d h o r n b l e n d e o c c u r i n a p p r o x i m a t e l y e q u a l a m o u n t s i n t h o s e r o c k s w i t h Si0 2 c o n t e n t s b e t w e e n 65 Wt% a n d 70 Wt%, a n d b i o t i t e i s t h e d o m i n a n t m a f i c m i n e r a l i n more s i l i c e o u s r o c k s . I n r o c k s c o n t a i n i n g g r e a t e r t h a n 75 Wt% S i O p b i o t i t e i s t h e o n l y f e r r o m a g n e s i a n s i l i c a t e p r e s e n t . I n a d d i t i o n , q u a r t z , p l a g i o c l a s e , a l k a l i f e l d s p a r a n d m a g n e t i t e a r c p r e s e n t i n a l l t h e s a m p l e s b u t m u s c o v i t e i s e n t i r e l y a b s e n t . B i o t i t e g e n e r a l l y o c c u r s a s r a g g e d , s u b h e d r a l t o e u h e d r a l c r y s t a l s a n d e x h i b i t s a w i d e r a n g e i n g r a i n s i z e . Some o f t h e c o a r s e - g r a i n e d s a m p l e s c o n t a i n l a r g e , e u h e d r a l , p o i k i l i t i c b i o t i t e s w i t h p l a g i o c l a s e , q u a r t z a n d m a g n e t i t e o c c u r r i n g c o m m o n l y a s i n c l u s i o n s . O n l y i n t h e H y b r i d p h a s e d o e s b i o t i t e e x h i b i t a t e n d e n c y t o r i m o r r e p l a c e p y r o x e n e a n d h o r n b l e n d e , i n a l l o t h e r p h a s e s b i o t i t e a n d h o r n b l e n d e c o e x i s t w i t h o u t r e p l a c e m e n t . F i g . 1 0 . R e l a t i o n b e t w e e n a b u n d a n c e and s i l i c a c o n t e n t of h o s t r o c k . of b i o t 44 The type of i n c l u s i o n s p r e s e n t i n a l l o f the b i o t i t e s suggest t h a t b i o t i t e s t a r t e d t o c r y s t a l l i s e d u r i n g the s i m u l t a n e o u s c r y s t a l l i s a t i o n of p l a g i o c l a s e and q u a r t z , but p r i o r t o the s e p a r a t i o n of a l k a l i f e l d s p a r . C h l o r i t i c a l t e r a t i o n o f b i o t i t e s i s i n s i g n i f i c a n t i n the m a j o r i t y of the samples but up t o about 50% c h l o r i t i s a t i o n o c c u r s i n a fev; samples. b) Method of Study B i o t i t e micas e x h i b i t a. l a r g e range of p o s s i b l e c h e m i c a l s u b s t i t u t i o n s w i t h i n the c r y s t a l s t r u c t u r e . 3+ U+ Thus A l ^ may r e p l a c e S i i n the t e t r a h e d r a l l a y e r , Ca, Na, Ba, Rb e t c may s u b s t i t u t e as i n t c r l a y e r c a t i o n s i n p l a c e of K., and OH a n i o n s may be r e p l a c e d by CI™ or F . The most p e t r o g e n e t i c a l l y i m p o r t a n t s u b s t i t u t i o n s however occur i n the o c t a h e d r a l l a y e r where Mg^ + may be 2+ 3+ 3+ 3+ 2+ r e p l a c e d by Fe , Fe^ , A l v , T i ^ and Mn . D i f f e r e n c e s i n p h y s i c a l p r o p e r t i e s of the b i o t i t e s a r c caused by the wide range of p o s s i b l e c h e m i c a l s u b s t i t u t i o n . I t i s not s u r p r i s i n g t h e r e f o r e t h a t a t t e m p t s to c o r r e l a t e changes i n p h y s i c a l p r o p e r t i e s w i t h the v a r i a t i o n i n c o n c e n t r a t i o n of a s i n g l e element or s i m p l e element r a t i o have been l a r g e l y u n s u c c e s s f u l . ( c . f . R i m s a i t e 1967). The p r e s e n t a u t h o r has attempted t o make e s t i m a t e s 45 of the percentage of t o t a l o c t a h e d r a l i r o n group met a l s p r e s e n t i n b i o t i t e s from the Guichon B a t h o l i t h u s i n g Gower's (1957) X-ray d i f f r a c t o m e t e r method. The r e s u l t s have shown t h a t v a r i a t i o n i n the degree of p r e f e r r e d o r i e n t a t i o n o f the sample may i n t r o d u c e as much as 10% v a r i a t i o n i n the e s t i m a t e d percentage o f t o t a l o c t a h e d r a l i r o n group m e t a l s , (Table V I I I ) when i n t e n s i t y r a t i o s IQQ^/IQQ^ are r e l a t e d t o R i m s a i t e ' s F i g 11 (1957 p.3 7 ) . The study was t h u s d i s c o n t i n u e d i n f a v o u r of more d i r e c t c h e m i c a l a n a l y s i s . Sample # Sample Pr e p a r a t i o n T 0 0 4 x 0 0 5 % Fo o c t . A . l A.2 Coar F i n e se g r i n d g r i n d - s l u r r y mount - s l u r r y mount . 6 8 4 .570 28 22 B . l B . 2 B . 3 B . 4 F i n e F i n e F i n e F i n e g r i n d g r i n d g r i n d g r i n d - s l u r r y mount - s l u r r y mount - c e n t r i f u g e d - c e n t r i f u g e d .661 .937 . 8 4 8 .822 27 40 36 35 C . l C .2 F i n e F i n e g r i n d g r i n d - s l u r r y mount - s l u r r y mount .827 .741 35 31 Table V I I I Observed i n t e n s i t y r a t i o IQQT| f o r 3 b i o t i t e samples as a f u n c t i o n o f sample p r e p a r a t i o n Any form o f s t a n d a r d c h e m i c a l a n a l y s i s t e c h n i q u e o f m i n e r a l c o n c e n t r a t e s s u f f e r s from the f a c t t h a t i t i s sometimes i m p o s s i b l e t o o b t a i n a c o m p l e t e l y pure sample. In a n a l y s i s of b i o t i t e c o n c e n t r a t e s , a d m i x t u r e s of i r o n 46 o x i d e , c h l o r i t e , amphibolc and i n c l u s i o n s o f z i r c o n , sphene, r u t i l e , a p a t i t e and q u a r t z may i n t r o d u c e l a r g e and unknown e r r o r s . For t h i s r e a s o n , the e l e c t r o n -m i c r o p r o b c has been used f o r p a r t i a l a n a l y s e s o f the b i o t i t e s from the Guichon b a t h o l i t h . The use o f t h i s i n s t r u m e n t has the added advantage t h a t o n l y s m a l l amounts of the sample a r c r e q u i r e d . B i o t i t e m i n e r a l c o n c e n t r a t e s f o r a p p r o x i m a t e l y h a l f o f t h e samples s t u d i e d had a l r e a d y been produced by K.E. N o r t h c o t e f o r use i n K/Ar age d e t e r m i n a t i o n s . The p r e s e n t a u t h o r i s g r a t e f u l t o Dr. N o r t h c o t e and t o Dr. W.H. White f o r p e r m i s s i o n t o use t h e s e c o n c e n t r a t e s i n the p r e s e n t s t u d y . B i o t i t e s from the r e m a i n i n g samples were c o n c e n t r a t e d by s i e v i n g of crushed r o c k f o l l o w e d by hand p i c k i n g of the +40 mesh f r a c t i o n . D e t a i l s o f the e x p e r i m e n t a l t e c h n i q u e s employed i n the e l e c t r o n microprobe a n a l y s e s and a d i s c u s s i o n o f the e r r o r s i n v o l v e d i n the method a r e p r e s e n t e d i n Appendix 3. °) D i s c u s s i o n o f R e s u l t s The r e s u l t s o f the- p a r t i a l a n a l y s e s of 14 b i o t i t e samples from the Guichon b a t h o l i t h are g i v e n i n Table IX. R e s u l t s are g i v e n i n terms of Wt% Mg and Fe s i n c e i t i s not p o s s i b l e t o d i s t i n g u i s h v a r i o u s v a l e n c e s t a t e s w i t h the e l e c t r o n microprobe. For t h i s r e a s o n the r e s u l t s f o r hi F i g .11: s i l i c a B i o t i t e c o m p o s i t i o n s as a f u n c t i o n of the c o n t e n t of t h e host r o c k . ample Wt% Mg m i c r o p r o b o 31 14 19 20 6 2 23 4 29 15 9 34 34 (Dup) 11 35 6 . 0 7 . 8 8 . 1 8 . 6 8 . 6 9 . 1 9 . 2 9 . 3 9 . 4 9 . 4 9 . 4 9 . 5 9 . 7 1 0 . 0 1 0 . 0 Fe m i c r o p r o b e 1 9 . 5 15-5 1 5 . 1 1 5 - 3 1 4 . 8 16 .0 1 3 . 0 1 3 . 3 12.6 1 3 . 3 1 2 . 9 1 2 . 4 1 2 . 2 1 3 . 0 1 3 . 3 c r F e Wt% . 2 5 . 10 . 2 0 . 2 5 . 7 0 . 4 0 . 3 0 . 10 . 2 0 . 0 5 . 10 . 2 0 . 2 5 . 10 . 10 T a b l e I X R e s u l t s o f p a r t i a l e l e c t r o n - m i c r o p r o b o a n a l y s i s o f b i o t i t e s f r o m t h e G u i c h o n C r e e k b a t h o l i t h . cr ( o n e s t a n d a r d d e v i a t i o n ) i s a f u n c t i o n o f s a m p l e i n h o m o g e n e i t y , s u r f a c e r o u g h n e s s a n d t h e s t a t i s t i c a l v a r i a t i o n o f X - r a y g e n e r a t i o n , ( s e e A p p e n d i x 3) k9 i r o n m u s t be r e g a r d e d a s t o t a l i r o n ( F e + F e ^ ) . R e l a t i v e e r r o r s i n a n a l y s e s ; t a k i n g i n t o a c c o u n t e x p e r i m e n t a l e r r o r s , t h e s t a t i s t i c a l v a r i a t i o n i n X - r a y g e n e r a t i o n , a n d s a m p l e i n h o m o g e n e i t y : a r e e s t i m a t e d a s - 0 . 3 5 Wt% Mg a n d - 0 . 2 5 Wt% F e . No r e g u l a r c o m p o s i t i o n a l z o n i n g was o b s e r v e d i n a n y o f t h e s a m p l e s s t u d i e d . T h e r e i s a r e g u l a r v a r i a t i o n i n t h e i r o n a n d m a g n e s i u m c o n t e n t s o f t h e b i o t i t e s w i t h i n c r e a s i n g a c i d i t y o f t h e h o s t r o c k . T h u s f o r t h e h o r n b l e n d e -b e a r i n g s a m p l e s t h e r e i s a d e c r e a s e i n t h e Fe/(Fo + Mg) r a t i o o f t h e b i o t i t e s w i t h i n c r e a s i n g c o n t e n t o f SIO^ i n t h e h o s t r o c k ( F i g 11). T h i s t r e n d i s r e v e r s e d i n t h o s e s a m p l e s t h a t c o n t a i n b i o t i t e a s t h e o n l y f o r r o -m a g n e s i a n s i l i c a t e m i n e r a l , i . e . t h o s e r o c k s c o n t a i n i n g g r e a t e r t h a n 73 Wt% S i 0 2 > T h e o b s e r v e d b i o t i t e c o m p o s i t i o n a l t r e n d s a r e r e m a r k a b l y s i m i l a r t o t h o s e t h a t e x i s t w i t h i n t h e B e n N e v i s , S c o t l a n d , i n g c o u s c o m p l e x ; a s r e p o r t e d b y H a s l a m (1968). F u r t h e r m o r e , i n t h e B e n N e v i s c o m p l e x , t h e h o r n b l e n d e s a n d c l i n o p y r o x e n e s e x h i b i t c o m p o s i t i o n a l v a r i a t i o n s t h a t a r e e x a c t l y a n a l o g o u s t o t h o s e o f t h e c o e x i s t i n g b i o t i t e s . H a s l a m h a s e m p h a s i s e d t h a t t h i s o b s e r v e d t r e n d o f d e c r e a s i n g F e / ( F c + Mg) r a t i o s i n f e r r o m a g n e s i a n s i l i c a t e s w i t h i n c r e a s i n g d i f f e r e n t i a t i o n o f t h e h o s t r o c k i s t h e r e v e r s e o f w h a t m i g h t be s u g g e s t e d F i g . 1 2 S t a b i l i t y o f b i o t i t e s a s a f u n c t i o n o f fOp a n d t e m p e r a t u r e a t 2070 b a r s t o t a l p r e s s u r e . S u b h o r i z o n t a l l i n e s r e p r e s e n t c o n t o u r s o f c o n s t a n t 100 F e / ( F e + M g ) v a l u e s . A r r o w s l a b e l l e d I a n d I I r e p r e s e n t o x i d i s i n g a n d r e d u c i n g t r e n d s i n c r y s t a l l i s i n g magmas. D i a g r a m f r o m Wones a n d E u g s t e r , (1965) 51 b y t h e r e s u l t s o f e x p e r i m e n t a l s t u d i e s o f s y n t h e t i c s y s t e m s . The f a c t o r s w h i c h may c o n t r i b u t e t o t h i s r e v e r s a l i n c l u d e t h e p a r t i a l p r e s s u r e s o f o x y g e n a n d w a t e r a n d t h e t o t a l p r e s s u r e s o p e r a t i v e , a n d t h o p h a s e a s s e m b l a g e s p r e s e n t . Wones a n d E u g s t e r ( 1 9 6 5 ) h a v e s t u d i e d t h e c o m p o s i t i o n a l v a r i a t i o n o f s y n t h e t i c b i o t i t e s c r y s t a l l i s e d a t v a r i a b l e o x y g e n f u g a c i t i e s . F i g 12 i s a r e p r o d u c t i o n o f Wones a n d E u g s t e r ' s F i g 1 3 (1965> p . 1 2 5 4 ) a n d s h o w s t h e s t a b i l i t y o f b i o t i t e s a s a f u n c t i o n o f f 0 2 a n d t e m p e r a t u r e a t a t o t a l p r e s s u r e o f 2 0 7 0 b a r s . T h i s d i a g r a m r e p r e s e n t s u n u s u a l b u l k c o m p o s i t i o n s b e c a u s e b i o t i t e s a r e much m o r e c o m m o n l y a s s o c i a t e d w i t h a m p h i b o l e s a n d p y r o x e n e s t h a n w i t h o l i v i n e s . Wones a n d E u g s t e r e m p h a s i s e t h e f a c t t h a t e x t r a p o l a t i o n s f r o m F i g . 12 t o a s s e m b l a g e s c o n t a i n i n g b i o t i t e a n d a m p h i b o l o i p y r o x e n e a r e u n r e l i a b l e . The t w o t r e n d l i n e s l a b e l l e d I a n d I I o n F i g 12 r e p r e s e n t t h e c h a n g i n g c o n d i t i o n s e x p e c t e d d u r i n g h y p o t h e t i c a l c r y s t a l l i s a t i o n o f t w o magmas. T r e n d I r e p r e s e n t s a magma w h i c h , d u r i n g c r y s t a l l i s a t i o n a n d c o o l i n g , b e c o m e s s a t u r a t e d i n K^O, r e a c t s w i t h t h a t c o m p o n e n t , a n d l o s e s h y d r o g e n t o t h e e n v i r o n m e n t . U n d e r s u c h c o n d i t i o n s b i o t i t e c o m p o s i t i o n s w i l l r e m a i n e s s e n t i a l l y c o n s t a n t . T r e n d I I r e p r e s e n t s 52 a magma t h a t i s ' b u f f e r e d ' b y t h e m i n e r a l a s s e m b l a g e t h a t i t c o n t a i n s . T h u s w i t h f a l l i n g t e m p e r a t u r e , f C ^ a l s o d e c r e a s e s a n d b i o t i t e c o m p o s i t i o n s w i l l become c o n s e c u t i v e l y more i r o n r i c h . E v i d e n c e w i l l be p r e s e n t e d i n C h a p t e r V I w h i c h s u g g e s t s t h a t c r y s t a l l i s a t i o n o f t h e G u i c h o n b a t h o l i t h o c c u r r e d u n d e r c o n d i t i o n s o f p r o g r e s s i v e l y i n c r e a s i n g v o l a t i l e p r e s s u r e s . I n s u c h a c a s e t h e p o s s i b i l i t y e x i s t s t h a t o x y g e n f u g a c i t i e s may a l s o h a v e b e e n i n c r e a s i n g due t o r e a c t i o n b e t w e e n w a t e r a n d magma a n d t h e l o s s o f h y d r o g e n t o t h e e n v i r o n m e n t . T h i s w o u l d e x p l a i n t h e o b s e r v e d s l i g h t p r o g r e s s i v e d e c r e a s e s i n F e / F e + K g r a t i o s i n b i o t i t e s w i t h p r o g r e s s i v e c o n s o l i d a t i o n o f t h e magma. The r e v e r s a l o f t h o t r e n d t h a t o c c u r s a t 73 Virt% S i O ^ o f t h e h o s t r o c k i n F i g 11 a l s o c o r r e s p o n d s t o a c h a n g e i n t h e m i n e r a l a s s e m b l a g e p r e s e n t , w h e r e b i o t i t e b e c o m e s t h o o n l y f e r r o m a g n e s i a n s i l i c a t e p r e s e n t . I t i s p o s s i b l e t h a t t h e new m i n e r a l a s s e m b l a g e may h a v e a ' b u f f e r i n g ' e f f e c t o n t h e p r e v a i l i n g o x y g e n f u g a c i t i e s - a n e f f e c t t h a t was n o t p r e s e n t w i t h t h e p r e v i o u s l y e x i s t i n g m i n e r a l a s s e m b l a g e . I f t h i s i s c o r r e c t t h e n t h e o x y g e n f u g a c i t y w o u l d d e c r e a s e w i t h d e c r e a s i n g t e m p e r a t u r e a n d t h e o b s e r v e d r a p i d i n c r e a s e i n t h e F e / F e + Mg r a t i o i n b i o t i t e s w o u l d 53 be produced. I t i s t h e r e f o r e suggested t h a t the m i n e r a l assemblage and the p a r t i a l p r e s s u r e s of v o l a t i l e s t h a t e x i s t e d d u r i n g c r y s t a l l i s a t i o n o f t h a t assemblage may bot h have had an e f f e c t on the c o m p o s i t i o n of the b i o t i t e s c r y s t a l l i s i n g from the magma. Tho d i s c u s s i o n o f b i o t i t e c r y s t a l l i s a t i o n i n the Guichon b a t h o l i t h has, of n e c e s s i t y , been p u r e l y q u a l i t a t i v e . Wones and S u g s t o r (1965) have p u b l i s h e d d a t a t h a t a l l o w q u a n t i t a t i v e e s t i m a t e s t o be made o f the independent i n t e n s i v e parameters, t e m p e r a t u r e , f u g a c i t y of HpO, and. f u g a c i t y o f oxygen, which were o p e r a t i v e d u r i n g c r y s t a l l i s a t i o n o f the assemblage b i o t i t e + s a n i d i n e + m a g n e t i t e . The common assemblages p r e s e n t i n the Guichon b a t h o l i t h samples, however, i n c l u d e h o r n b l e n d e , p l a g i o c l a s e , q u a r t z - c l i n o p y r o x e n e , p y r i t e or o t h e r s u l p h i d e s , sphene a p a t i t e and z i r c o n , i n a d d i t i o n t o b i o t i t e , a l k a l i f e l d s p a r and ma g n e t i t e . Furthermore i n any c a l c a l a t i o n of the i n t e n s i v e v a r i a b l e s o p e r a t i v e d u r i n g c r y s t a l l i s a t i o n , t he a c t i v i t y o f the KFe^AlSi^O-^Q(OH) component i s a c r i t i c a l f a c t o r . The d a t a p r e s e n t l y a v a i l a b l e f o r the Guichon b a t h o l i t h b i o t i t e s does not a l l o w an e s t i m a t e o f t h i s parameter because of the l a c k of any q u a n t i t a t i v e d a t a on the 3+ 2+ Fe-' /Fe r a t i o i n the b i o t i t e s . The e v a l u a t i o n o f t h i s r a t i o b y s t a n d a r d wet c h e m i c a l a n a l y s i s s u f f e r s f r o m i n a c u r a c i e s t h a t a r e due t o t h e p r e s e n c e o f m a g n e t i t e a n d / o r c h l o r i t e a s i n c l u s i o n s i n t h e b i o t i t e . A n o r t h U e H y b r i d , H l g h j o n d v a l l e y a n d L e r o y p h a s e s a m p l e s . B e t h l e h e m , W l t c h a s B r o o k , a n d B e t h s a l d a p h a s e s a m p l e * G u m p L o k t p h a s e s a m p l e s . . A n o r t h i t e A l b i t e O r t h o c l o s e A l b i t e Orthoclase Fig. 13 o: Plot of modal quartz — or thoc lase -a lb i te -anorth i te for the Guichon Creek batholith samples. A—B is the trend line for the samples in three dimensions. C—D is a projection of A - B onto the base of the tetrahedron from the anorthite c o r n e r . Fig. 13b : Schemat ic phase diagram for the quote/nary system Q z ^ O r . - A b . - A n . at I k i lobar water vapour pre s s u re . vn 56 V I M o d a l A n a l y s e s a n d C a l c u l a t e d C h e m i c a l C o m p o s i t i o n s M o d a l a n a l y s e s f o r a p p r o x i m a t e l y h a l f o f t h e s a m p l e s i n v e s t i g a t e d h a v e b e e n r e p o r t e d b y N o r t h c o t e ( 1 9 6 9 ) . F o r t h e r e m a i n d e r o f t h e s a m p l e s m o d a l a n a l y s e s w e r e c a r r i e d o u t o n s t a n d a r d t h i n s e c t i o n s u s i n g a t r a v e r s i n g p o i n t c o u n t m i c r o s c o p e s t a g e . F o r c o a r s e - g r a i n e d s a m p l e s 500 p o i n t s w o r e c o u n t e d i n e a c h t h i n s e c t i o n w i t h a p o i n t s p a c i n g o f 1mm, f i n e - g r a i n e d s a m p l e s w e r e a n a l y s e d w i t h a p o i n t s p a c i n g o f -g-mm a n d 1000 p o i n t s v/ere c o u n t e d . M o d a l a n a l y s e s a r e p r e s e n t e d i n A p p e n d i x 2 . F i g 13a s h o w s t h e m i n e r a l o g i c a l v a r i a t i o n w i t h i n t h e p l u t o n e x p r e s s e d i n t e r m s o f m o d a l q u a r t z , o r t h o c l a s e , a l b i t e a n d a n o r t h i t e r e c a l c u l a t e d t o 100 Wt%. W i t h i n t h e ' g r a n o d i o r i t e * t e t r a h e d r o n o f F i g 13a t h e s a m p l e s , w i t h t h e e x c e p t i o n o f t h o s e f r o m t h e Gump L a k e p h a s e , a l l l i e o n t h e p l a n e ABCD w h i c h i n t e r s e c t s t h o Q, O r , Ab b a s e o f t h e t e t r a h e d r o n i n l i n e CD. The l i n e A B d e s c r i b e s t h e t r e n d ' o f t h e g r a d u a l l y d i f f e r e n t i a t i n g magma t o w a r d s i n c r e a s i n g q u a r t z a n d o r t h o c l a s e c o n t e n t s , d e c r e a s i n g p l a g i o c l a s e c o m p o n e n t s a n d c o n c o m i t a n t i n c r e a s e i n t h o A b / A n r a t i o . F i g 13b i s a h y p o t h e t i c a l p h a s e d i a g r a m o f t h e g r a n o d i o r i t e s y s t e m b a s e d p a r t l y o n 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 s o f t h e t e r n a r y s y s t e m s t h a t c o n s t i t u t e t h e 57 faces of the tetrahedron. Phase r e l a t i o n s i n the system Ab-Or-Q have been studied at water vapour pressures from 0 . 5 to 10Kb by Tut t i c and Bowen (1958) and Luth, Jahns and T u t t l e (1964). Yodcr 0-967) i n v e s t i g a t e d ternary compositions i n the system Ab-An-Q at 5 kb water vapour pressure. Tho binary system An-Q has been studied at atmospheric pressure by Schairer and Bowen ( 1 9 4 7 ) and at l k b Ph^O by Stewart (1967). P r e l i m i n a r y data on the system An-Ab-Or have been published by Franco and Schairer ( 1951)> Yoder, Stewart and Smith ( 1 9 5 7 ) and James and Hamilton ( 1 9 6 9 ) . S i m i l a r l y experimental r e s u l t s i n the system An-Ab-Or-Q-^O have been published by Von. Pla t e n ( 1 9 6 5 ) and by James and Hamilton (1969). The curved surface abed w i t h i n the tetrahedron of F i g 13b separates regions of compositions f i r s t c r y s t a l l i s i n g f e l d s j j a r , from those f i r s t c r y s t a l l i s i n g quartz. Compositions l y i n g on t h i s plane w i l l be i n e q u i l i b r i u m with both of tho minerals whose regions i t separates. Tho plane defg s i m i l a r l y separates tho two felds p a r regions; above t h i s plane p l a g i o c l a s e i s the primary phase, and below i t a l k a l i f e ldspar i s the primary phase. The tv/o surfaces i n t e r s e c t to form a l i n e along which l i q u i d s are i n e q u i l i b r i u m with p l a g i o c l a s e + a l k a l i feldspar + s i l i c 61 Vci.pOU.3T • The sequence of rock compositions from tho Hybrid 58 p h a s e , t h r o u g h t h e H i g h l a n d V a l l e y p h a s e t o t h e L e R o y g r a n o d i o r i t e o c c u p y s u c c e s s i v e l y more d i f f e r e n t i a t e d p o s i t i o n s a l o n g t h e t r e n d A - B i n F i g 13 . T e x t u r a l e v i d e n c e f r o m t h e s e r o c k s i n d i c a t e s t h a t p l a g i o c l a s e was t h e f i r s t f e l s i c m i n e r a l t o c r y s t a l l i s e a n d t h a t i t was f o l l o w e d a t a much l a t e r s t a g e b y q u a r t z , a n d f i n a l l y b y a l k a l i f e l d s p a r w h i c h i s c o n s p i c u o u s l y i n t e r s t i t i a l o r p o i k i l i t i c . T h i s i s e x a c t l y t h e s e q u e n c e o f f e l s i c c r y s t a l l i s a t i o n t h a t w o u l d be p r e d i c t e d b y F i g 13. R o c k c o m p o s i t i o n s f r o m t h o Gump L a k e p h a s e do n o t l i e o n t h e g e n e r a l t r e n d s u r f a c e ABCD i n F i g 13 b u t a r e d i s p l a c e d t o w a r d s t h e q u a r t z c o r n e r o f t h e t e t r a h e d r o n . N o r t h c o t e (1969) h a s s u g g e s t e d t h a t t h e Gump L a k e p h a s e may n o t be r e l a t e d g e n e t i c a l l y t o t h e r e s t o f t h o G u i c h o n b a t h o l i t h a n d t h a t i t may be a n o f f s h o o t o f t h e c e n t r a l N i c o l a b a t h o l i t h w h i c h l i e s t o t h e e a s t . The r e l a t i o n s s h o w n i n F i g 13 t e n d t o s u p p o r t N o r t h c o t e ' s s u g g e s t i o n . P l a g i o c l a s e a n d q u a r t z c r y s t a l s i n t h e Gump L a k e p h a s e t e n d t o be c q u i d i m o n s i o n a l s u g g e s t i n g t h a t t h e y p e r h a p s c r y s t a l l i s e d a l m o s t s i m u l t a n e o u s l y , w h i l s t a l k a l i f e l d s p a r i s c i t h e r i n s t i t i a l o r p o i k i l i t i c . The Gump L a k e s a m p l e s p l o t o n F i g 13b a p p r o x i m a t e l y o n t h e p l a g i o c l a s e - q u a r t z s u r f a c e some way a b o v e t h e p l a g i o c l a s e - q u a r t z - o r t h o c l a s e e q u i l i b r i u m l i n e , 59 w h i c h s u p p o r t s t h e p r o p o s e d c r y s t a l l i s a t i o n s e q u e n c e . The s a m p l e s f r o m t h e B e t h l e h e m a n d B c t h s a i d a p h a s e s p l o t o n F i g 13 i n a p o s i t i o n t h a t l i e s w i t h i n t h e g e n e r a l t r e n d a n d i s n o t r a d i c a l l y d i f f e r e n t f r o m t h a t o f t h e H i g h l a n d V a l l e y p h a s e , b u t w h i c h i n d i c a t e s a s l i g h t e n r i c h m e n t i n a l b i t e . L e R o y g r a n o d i o r i t e s a m p l e s p l o t o n F i g 13 i n a p o s i t i o n w h i c h i n d i c a t e s t h a t t h e y a r e m o r e d i f f e r e n t i a t e d t h a n t h e b u l k o f t h e B e t h l e h e m a n d B c t h s a i d a p h a s e s a m p l e s . . T h i s t e n d s t o c o n f i r m N o r t h c o t e ' s (1969) s u g g e s t i o n t h a t t h e L e R o y g r a n o d i o r i t e d y k e p h a s e f o r m e d i n r e s p o n s e t o l o c a l d i f f e r e n t i a t i o n i n c u p o l a s , w h i l s t t h e b u l k o f t h e B e t h l e h e m a n d B c t h s a i d a p h a s e s l a t e r c r y s t a l l i s e d w i t h i n t h e m a i n magma c h a m b e r . The W i t c h e s B r o o k p h a s e - w h i c h h a s b e e n t e n t a t i v e l y c o r r e l a t e d w i t h t h e B e t h l e h e m p h a s e b y N o r t h c o t e (1969) - e x h i b i t s t h e w i d e s t r a n g e o f c o m p o s i t i o n o n F i g 13. A d i s t i n c t i o n h a s a l r e a d y b e e n made ( C h a p . I V ) b e t w e e n t h o s e s a m p l e s c o n t a i n i n g o n l y n o r m a l l y z o n e d p l a g i o c l a s e a n d t h o s e c o n t a i n i n g o s c i l l a t o r y z o n e d p l a g i o c l a s e , a n d t h i s d i s t i n c t i o n i s c o n f i r m e d b y F i g 13 . The t w o s a m p l e s c o n t a i n i n g o s c i l l a t o r y z o n e d p l a g i o c l a s e s - a d i s t i n c t i v e f e a t u r e o f t h e B e t h l e h e m p h a s e - h a v e c o m p o s i t i o n s t h a t a r c e s s e n t i a l l y t h e same a s t h o s e o f t h e B e t h l e h e m p h a s e . The t h r e e s a m p l e s w i t h o n l y n o r m a l l y z o n e d p l a g i o c l a s e s 60 h a v e c o m p o s i t i o n s c o r r e s p o n d i n g t o t h o s e o f t h e m o s t h i g h l y d i f f e r e n t i a t e d L e R o y g r a n o d i o r i t e . I t i s s u g g e s t e d t h e r e f o r e t h a t t h e W i t c h e s B r o o k d y k e - l i k e p h a s e o f N o r t h c o t e (1969) i n f a c t r e p r e s e n t s t w o s e p a r a t e p h a s e s . The f i r s t o f t h e s e i s a s s o c i a t e d w i t h t h e more d i f f e r e n t i a t e d l a t e c o m p o n e n t s o f t h e e a r l y p h a s e s o f t h e b a t h o l i t h , a n d t h o s e c o n d i s a s s o c i a t e d w i t h t h e l a t e r , l e s s d i f f e r e n t i a t e d B e t h l e h e m p h a s e . B o t h o f t h e s e g r o u p s e x h i b i t e a r l y e u h e d r a l p l a g i o c l a s e ; l a t e r a n h c d r a l q u a r t z a n d f i n a l a n h e d r a l , i n t e r s t i t i a l a l k a l i f e l d s p a r . T h e S p a t s u m q u a r t z m o n z o n i t e s a m p l e #31> w h i c h N o r t h c o t e h a s t e n t a t i v e l y e q u a t e d w i t h t h e W i t c h e s B r o o k p h a s e , i s t h e m o s t h i g h l y d i f f e r e n t i a t e d s a m p l e s t u d i e d . The r o c k c o n t a i n s r o u g h l y e q u i d i m e n s i o n a l s u b h e d r a l q u a r t z , p l a g i o c l a s e a n d a l k a l i f e l d s p a r i n t h e p r o p o r t i o n s 41:30:26 v o l %, s u g g e s t i n g t h a t c r y s t a l l i s a t i o n o f t h o s e t h r e e m i n e r a l s was a l m o s t s i m u l t a n e o u s . The p o s i t i o n o f t h i s s a m p l e o n F i g 13 i n d i c a t e s t h a t i t l i e s v e r y c l o s e t o t h e h y p o t h e t i c a l u n i v a r i a n t c u r v e . D u r i n g c r y s t a l l i s a t i o n o f t h o B e t h l e h e m p h a s e a c h a n g e i n t h e o r d e r o f f o r m a t i o n o f t h e f e l s i c m i n e r a l s o c c u r r e d . E a r l y ( o u t e r ) B e t h l e h e m p h a s e s a m p l e s c o n t a i n l a r g e e u h e d r a l p l a g i o c l a s e c r y s t a l s , some o f w h i c h e x h i b i t 61 a p r e f o r o d o r i e n t a t i o n , s e t i n a f i n e r g r a i n e d m o s a i c o f p l a g i o c l a s e , q u a r t z a n d a l k a l i f e l d s p a r . T h i s i n d i c a t e s e a r l y p l a g i o c l a s e c r y s t a l l i s a t i o n . T h e l a t e r ( i n n e r ) B e t h l e h e m p h a s e a n d t h e B e t h s a i d a pha.se c o n t a i n l a r g o , s u b h c d r a l , f r a c t u r e d q u a r t z c r y s t a l s v / h i c h a p p e a r t o be s l i g h t l y r e s o r b e d p h e n o c r y s t s . T h i s i s c o n f i r m e d b y t h e t e x t u r a l e v i d e n c e e x h i b i t e d b y a d y k o o f B e t h s a i d a g r a n o d i o r i t e t h a t c u t s G u i c h o n p h a s e r o c k s o a s t o f t h e B e t h l e h e m C o p p e r p r o p e r t y ( W h i t e e t a l 1956). T h i s d y k e c o n t a i n s l a r g e e u h e d r a l t o s u b h e d r a l q u a r t z p h e n o c r y s t s s e t i n a f i n e r g r a i n e d m a t r i x o f q u a r t z a n d f e l d s p a r ( s e e P h o t o 5 ) . T h u s i t w o u l d a p p e a r t h a t t h e l a t e r p o r t i o n s o f t h e B e t h l e h e m p h a s e a n d t h e B e t h s a i d a p h a s e b e g a n c r y s t a l l i s a t i o n f r o m w i t h i n t h e q u a r t z f i e l d o f t h e ' g r a n o d i o r i t e t e t r a h e d r o n ' . T h e e s s e n t i a l s i m i l a r i t y o f t h e c o m p o s i t i o n s o f t h e H i g h l a n d V a l l e y p h a s e a n d t h e B e t h l c h e m / B c t h s a i d a p h a s e s h a s a l r e a d y b e e n n o t e d . T h u s p r o g r e s s i v e s i l i c a e n r i c h m e n t duo t o d i f f e r e n t i a t i o n c a n n o t be c a l l e d u p o n t o e x p l a i n t h e p r e s e n c e o f q u a r t z p h e n o c r y s t s i n t h e l a t e r p h a s e s . T u t t l e a n d Bowen (1958) a n d o t h e r s h a v e s h o w n e x p e r i m e n t a l l y t h a t p r o g r e s s i v e i n c r e a s e s i n PIL,0 w i l l c a u s e p r o g r e s s i v e i n c r e a s e s i n t h e s i z e o f t h e q u a r t z f i e l d i n t h e s y s t e m A b - O r - Q z - H n i t i s s u g g e s t e d t h e r e f o r e t h a t t h e 62 P l a t e 5 S a m p l e f r o m a c h i l l e d B e t h s a i d a d y k e f r o m e a s t o f t h e B e t h l e h e m C o p p e r p r o p e r t y . N o t e p r e s e n c e o f s u b h e d r a l - e u h e d r a l p h e n o c r y s t s o f q u a r t z a n d e u h e d r a l p o i k i l i t i c b i o t i t e . S c a l e i n c e n t i m e t r e s . 6 3 B e t h l e h e m a n d B e t h s a i d a s a m p l e s c o n t a i n i n g e a r l y q u a r t z p h e n o c r y s t s may h a v e c r y s t a l l i s e d u n d e r c o n d i t i o n s o f c o n s i d e r a b l y h i g h e r v o l a t i l e p r e s s u r e s t h a n h a d p r e v i o u s l y e x i s t e d . E x p e r i m e n t a l w o r k i n s y n t h e t i c s y s t e m s d o n e b y o t h e r i n v e s t i g a t o r s w o u l d seem t o i n d i c a t e t h a t t h e p r e s e n c e o f q u a r t z o n t h e l i q u i d u s i n t h e ' g r a n o d i o r i t e ' s y s t e m may r e q u i r e t o t a l p r e s s u r e s i n t h e o r d e r o f k o r 5 k b ( I t m u s t be e m p h a s i s e d h o w e v e r t h a t t h i s r e p r e s e n t s a t b e s t a n ' i n s p i r e d ' e s t i m a t e ) . N o r t h c o t e (1969) h a s s u g g e s t e d t h a t t h e B e t h s a i d a p h a s e c r y s t a l l i s e d i n a n e p i z o n a l e n v i r o n m e n t , t h u s i m p l y i n g , a t m o s t , 6 t o 8 km o f c o v e r w h i c h w o u l d p r o d u c e a ' l o a d ' p r e s s u r e i n t h e o r d e r o f 1 .5 t o 2 k b . I f t h e a b o v e e s t i m a t e s a r c c o r r e c t , i t f o l l o w s t h a t t h e v o l a t i l e p r e s s u r e s e x i s t i n g d u r i n g c r y s t a l l i s a t i o n o f t h e B e t h s a i d a p h a s e m u s t h a v e b e e n i n t h e o r d e r o f 2. t o 3 - 5 k b . F u r t h e r m o r e t h e r e i s c o n s i d e r a b l e e v i d e n c e t h a t c o n d i t i o n s o f h i g h v o l a t i l e p r e s s u r e s e x i s t e d d u r i n g t h e f o r m a t i o n o f many o f t h e s m a l l , l a t e i g n e o u s b o d i e s t h a t o r e b e l i e v e d r e l a t e d t o t h e B e t h l e h e m o r / a n d B e t h s a i d a p h a s e s . W h i t e e t a l ( 1 9 5 6 ) , f o r i n s t a n c e , e x p l a i n t h o p r e s e n c e o f n u m e r o u s b r e c c i a p i p e s o n t h e B e t h l e h e m C o p p e r p r o p e r t y o n t h e b a s i s o f s u b v o l c a n i c e x p l o s i o n s due t o i n c r e a s i n g v o l a t i l e p r e s s u r e s . C h e m i c a l e s t i m a t e s f o r t h e s a m p l e s h a v e b e e n c a l c u l a t e d 64 4 r Wt % K 2 0 Wt % Na 2 0 6 r 5 4 3 2 - O -o J I I I 8 7 h wt % CaO 80 Wt % S iO -F i g . 14 C a l c u l a t e d c o m p o n e n t o x i d e s a s a f u n c t i o n o f s i l i c a c o n t e n t f o r t h e G u i c h o n C r e e k b a t h o l i t h s a m p l e s . H y b r i d a n d H i g h l a n d V a l l e y p h a s e s Gump L a k e p h a s e B e t h l e h e m , W i t c h e s B r o o k a n d B e t h s a i d a p h a s e s 6 6 u s i n g the computer program of D i e t r i c h and Shoohan (1964) m o d i f i e d f o r use on the U n i v e r s i t y o f B r i t i s h Columbia, I.B.M. 360 computer. The program a s s i g n s average c h e m i c a l parameters t o the m i n e r a l s p r e s e n t i n the mode and c o n v e r t s these t o c h e m i c a l e s t i m a t e s f o r the r o c k sample. Input i s i n the form o f m i n e r a l volume p e r c e n t a g e s and output i s p r e s e n t e d as m i n e r a l weight p e r c e n t a g e s and component o x i d e weight p e r c e n t a g e s . Orthocle.se, a l b i t e and a n o r t h i t c a re t r e a t e d as s e p a r a t e m i n e r a l c o n s t i t u e n t s , and t h e r e f o r e the d a t a o f T a b l e s VI and V I I was u t i l i s e d f o r program i n p u t . B i o t i t e , hornblende and a u g i t e a n a l y s e s used were thos e from 'average 5 g r a n o d i o r i t i c r o c k s as r e p o r t e d i n r e c e n t l i t e r a t u r e , and a l l opaque m i n e r a l s v/ere t r e a t e d as m a g n e t i t e . Chemical e s t i m a t e s are p r e s e n t e d i n Appendix 2 and s i l i c a v a r i a t i o n diagrams f o r the component o x i d e s are p r e s e n t e d as F i g 14. The diagrams emphasise the r e s t r i c t e d range of c o m p o s i t i o n a l v a r i a t i o n w i t h i n the b a t h o l i t h , and a l s o the o v e r l a p p i n g n a t u r e o f the c o m p o s i t i o n a l ranges of the v a r i o u s phases. The r a t h e r wide v e r t i c a l s c a t t e r i n g o f d a t a p o i n t s on the v a r i a t i o n diagrams i s to be expected and i s p a r t l y due to the e r r o r s i n h e r e n t i n modal a n a l y s e s . F i g 14 shows t h a t the sequence H y b r i d - G u i c h o n -Chataway-Leltoy phases d i s p l a y s a p r o g r e s s i v e d i s p l a c e m e n t 67 t o w a r d s more s i l i c a r i c h c o m p o s i t i o n s , w h i c h i s p r o b a b l y l a r g e l y t h e r e s u l t o f c o n t i n u i n g d i f f e r e n t i a t i o n . The l a t e r p h a s e s B e t h l e h e m , W i t c h e s B r o o k a n d B e t h s a i d a b e l o n g t o t h e i n t e r m e d i a t e members o f t h e s c r i e s a n d v e r y l i t t l e d i s c r i m i n a t i o n c a n be made b e t w e e n t h e m o n t h o b a s i s o f t h e c h e m i c a l e s t i m a t e s . The m o s t a c i d i c s a m p l e a n a l y s e d comes f r o m a s m a l l i s o l a t e d b o d y a t t h e w e s t e r n m a r g i n o f t h e b a t h o l i t h w h i c h N o r t h c o t e h a s c a l l e d t h e S p a t sum Q u a r t z M o n z o n i t e , a n d w h i c h he e q u a t e s w i t h t h e W i t c h e s B r o o k p h a s e . I t h a s b e e n s u g g e s t e d b y N o r t h c o t e t h a t t h e G u i c h o n p h a s e a p p r o x i m a t e s t h e c o m p o s i t i o n o f t h e o r i g i n a l magma a n d t h a t t h e m o r e b a s i c m e m b e r s o f t h e p l u t o n may be t h o r e s u l t o f a s s i m i l a t i o n o f c o u n t r y r o c k d u r i n g i n t r u s i o n . The p r e s e n c e o f a x c n o l i t h - r i c h z o n e e x t e n d i n g f o r s e v e r a l h u n d r e d f e e t i n w a r d s f r o m t h e o u t e r m a r g i n s o f t h e H y b r i d p h a s e c e r t a i n l y t e n d s t o s u p p o r t t h i s s u g g e s t i o n . An a t t e m p t ha.s b e e n made t o c o n s t r u c t a n ' a d d i t i o n ' d i a g r a m ( c . f . Bowen 1928, p .76) t o t e s t t h e a s s i m i l a t i o n h y p o t h e s i s . The a v e r a g e c o m p o s i t i o n o f t h e r o c k s i n t r u d e d b y t h e b a t h o l i t h i s a p a r t i c u l a r l y d i f f i c u l t p a r a m e t e r t o e s t i m a t e . T h e P e r m i a n C a c h e C r e e k G r o u p a d j a c e n t t o t h e p r e s e n t b a t h o l i t h c o n t a c t i s c o m p o s e d p r e d o m i n a n t l y o f a n d e s i t i c g r e e n s t o n e s w i t h s u b o r d i n a t e 68 F i g . 15 C h e m i c a l c o m p o s i t i o n s o f p r o p o s e d G u i c h o n b a t h o l i t h p r i m a r y magma ( ' a v e r a g e ' G u i c h o n ) , ' c o n t a m i n a t e d ' G u i c h o n r o c k s a n d N i c o l a G r o u p e x t r u s i v e r o c k s . N i c o l a a n a l y s e s a r e f r o m S c h a u (1968) a n d r e l a t e t o h i s p r o p o s e d ' A ' a n d ' P ' t y p e e x t r u s i v e c y c l e s . 69 a r g i l l i t c and chert. The Upper T r i a s s i c N i c o l a group i s predominantly a n d e s i t i c or b a s a l t i c v o l c a n i c rocks with minor limestone, a r g i l l i t c , q u a r t z i t e , groywacko and arkoso. ( C o c k f i c l d , 1947, D u f f e l and McTaggart, 1951). Schau (1969) has presented chemical analyses of vo l c a n i c rocks from tho N i c o l a group. An average composition f o r tho N i c o l a v o l c a n i c group taken from Schau's data, has been p l o t t e d on F i g 15 along with tho e s t a b l i s h e d trends of chemical v a r i a t i o n for the Guichon b a t h o l i t h samples. I t i s obvious that the 'average' N i c o l a v o l c a n i c , supposedly contaminated Guichon samples and tho proposed Guichon magma, compositions do not l i e on s t r a i g h t l i n e trends. The absence of such trends would tend to i n d i c a t e that a s s i m i l a t i o n has not been a major f a c t o r i n producing chemical v a r i a t i o n through the b a t h o l i t h . I t must be emphasised however that the v a r i a b l e amounts of sedimentary rock present i n both the N i c o l a and Cache Creek groups may p o s s i b l y have a s i g n i f i c a n t e f f e c t on the composition of tho assumed contaminating m a t e r i a l . Bowen (1928) has emphasised that i n order to melt basic m a t e r i a l added to a more a c i d i c magma considerable amounts of superheat would be necessary to prevent r a p i d c r y s t a l l i s a t i o n of tho magma. The presence of p r e f e r e n t i a l l y oriented p l a g i o c l a s e c r y s t a l s i n 70 most of the H y b r i d r o c k s s u g g e s t s t h a t the magma had reached l i q u i d u s c o n d i t i o n s p r i o r t o i n t r u s t i o n and hence d i d not have any a p p r e c i a b l e amount o f superheat. Thus m e l t i n g o f any a s s i m i l a t e d m a t e r i a l i s u n l i k e l y t o have o c c u r r e d . Bowen (1928) has suggested, however, t h a t c o n v e r s i o n o f more b a s i c m a t e r i a l i n t o c o n s t i t u e n t s t h a t a r c i n e q u i l i b r i u m w i t h t h e a c i d magma may take p l a c e w i t h o u t m o l t i n g . N o r t h c o t e (1969) has r e p o r t e d x c n o l i t h s w i t h i n the H y b r i d phase which d i s p l a y a marked v a r i a t i o n i n degree o f a s s i m i l a t i o n . Some x c n o l i t h s have sharp a n g u l a r o u t l i n e s w h i l s t o t h e r s are reduced t o i n d i s t i n c t c l u s t e r s of m a f i c m i n e r a l s . T h i s suggests t h a t the more a c i d i c components of the x c n o l i t h s may have been more e a s i l y c o n v e r t e d i n t o c o n s t i t u e n t s i n e q u i l i b r i u m w i t h the magma than the more b a s i c components. I f such i s the case i t would e x p l a i n the l a c k o f agreement between the evidence from the f i e l d and t h a t from the ' a d d i t i o n ' diagram of F i g 1 5 . An a l t e r n a t i v e h y p o t h e s i s f o r the o r i g i n of the more b a s i c r o c k s i s t h a t they a r c the d i r e c t r e s u l t o f magmatic d i f f e r e n t i a t i o n . The f o l i a t e d n a t u r e o f the o a r l y phases of the b a t h o l i t h s u g gests t h a t t i c f l o w has o c c u r r e d , p o s s i b l y as a r e s u l t o f n a t u r a l c o n v e c t i o n w i t h i n the magma chamber. I f c o n v o c t i v c f l o w d i d take p l a c e d u r i n g 71 i n t r u s i o n t h e r e e x i s t s t h e p o s s i b i l i t y t h a t e a r l y formed, c r y s t a l s - p r e d o m i n a n t l y o l i g o c l a s e a n d p y r o x e n e -may become a t t a c h e d t o t h e r o o f o r w a l l s o f t h e magma c h a m b e r , t h u s s u c c e s s i v e l y e n r i c h i n g t h e magma i n more-a c i d i c c o m p o n e n t s . I n a l l p r o b a b i l i t y m a g m a t i c d i f f e r e n t i a t i o n a n d s u b o r d i n a t e a s s i m i l a t i v e a c t i o n h a v e c o m b i n e d t o p r o d u c e t h e r a n g e o f c o m p o s i t i o n s e x h i b i t e d b y t h e e a r l i e r p h a s e s o f t h e b a t h o l i t h . T h o r e t u r n t o t h e c h e m i c a l l y i n t e r m e d i a t e members o f t h e s e r i e s e x h i b i t e d b y t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s when c o m b i n e d w i t h t h e e v i d e n c e o f p l a g i o c l a s e z o n a t i o n s c h e m e s - a s d i s c u s s e d o n p a g e 3k - s u g g e s t s t h a t a r e n e w e d i n t r u s i o n o f t h e magma o c c u r r e d p r i o r t o c o n s o l i d a t i o n o f t h e B e t h l e h e m p h a s e . T e x t u r a l i n f o r m a t i o n s u g g e s t s t h a t t h e b u l k o f t h i s magma c r y s t a l l i s e d u n d e r f a i r l y q u i e s c e n t c o n d i t i o n s . I t seems l i k e l y , t h e r e f o r e , t h a t t h e r a n g e o f c h e m i c a l c o m p o s i t i o n s e x h i b i t e d b y t h e s e p h a s e s i s l a r g e l y t h e r e s u l t o f l o c a l h e t e r o g e n i c s c a u s e d b y i n c o m p l e t e m i x i n g o f magma. The c o m p o s i t i o n a l r a n g e s may a l s o be p a r t l y due t o e r r o r s i n t h e m o d a l a n a l y s e s f r o m w h i c h c h e m i c a l e s t i m a t e s w e r e c a l c u l a t e d . 72 V I I G e o l o g i c a l E v o l u t i o n o f tho B a t h o l i t h Tho h i s t o r y o f emplacement of the Guichon Creek b a t h o l i t h has p r e v i o u s l y been d i s c u s s e d by N o r t h c o t e ( 1 9 6 9 ) and the f o l l o w i n g i n t e r p r e t a t i o n i s l a r g e l y an e x t e n s i o n o f N o r t h c o t e ' s i d e a s . The o n l y s i g n i f i c a n t d i f f e r e n c e between the two schemes i s t h a t the p r e s e n t work s u g g e s t s t h a t c o n v e c t i v o magma f l o w has been l a r g e l y r e s p o n s i b l e f o r the t e x t u r a l and c o m p o s i t i o n a l d i f f e r e n c e between s u c c e s s i v e phases. The p o s s i b i l i t i e s o f magma c o n v e c t i o n have been d i s c u s s e d by Grout ( 1 9 1 8 ) , Knopoff ( 1 9 6 4 ) , Shaw ( 1 9 6 5 ) and B a r t l e t t ( 1 9 6 9 ) , and thes e a u t h o r s have c o n c l u d e d t h a t c o n v e c t i o n may c o n s t i t u t e a s i g n i f i c a n t p h y s i c a l f a c t o r d u r i n g the c r y s t a l l i s a t i o n o f g r a n i t i c magmas. Shaw ( 1 9 6 5 ) a l s o s u g g e s t s t h a t p o c k e t s o f s t r o n g l y d i f f e r e n t i a t e d l i q u i d may develop c l o s e t o the top of a magma chamber due t o the a c t i o n of l o c a l h i g h l e v e l c o n v e c t i v e v o r t i c e s . Very l i t t l e i s known c o n c e r n i n g the u l t i m a t e o r i g i n o f the ma.gma t h a t c r y s t a l l i s e d t o form the Guichon Creek b a t h o l i t h . C h r i s t m a s et a l ( 1 9 6 9 ) have i n v e s t i g a t e d the s t r o n t i u m i s o t o p i c c o m p o s i t i o n o f r o c k s from the b a t h o l i t h and from the Craigmont mine. They r e p o r t an i n i t i a l Sr V S r r a t i o f o r the Craigmont i s o c h r o n o f 0 . 7 0 3 7 which f a l l s w i t h i n the range of v a l u e s from r e c e n t 75 b a s a l t s (0.703-0.706). T h e y c o n c l u d e t h e r e f o r e " . . . t h a t t h e o r e m i n e r a l s a n d K - f c l d s p a r g a n g u e d i d n o t o r i g i n a t e b y f u s i o n o f a n c i e n t s i a l i c b a s e m e n t o r C a c h e C r e e k o r N i c o l a r o c k s , b u t m u s t h a v e d e v e l o p e d i n O n or a n e n v i r o n m e n t w i t h l o w S r / S r ° r a t i o s s i m i l a r t o r e c e n t b a s a l t . S u c h a s o u r c e c o u l d bo c i t h e r r e a b s o r b e d o c e a n i c c r u s t ( W i l s o n 1968), t h o u p p e r m a n t l e o r a b a s i c l a y e r i n t h e l o w e r p a r t o f t h o c r u s t . . . . " . T h e y f u r t h e r i m p l y t h a t t h e magma w h i c h f o r m e d t h e G u i c h o n b a t h o l i t h d e v e l o p e d i n a s i m i l a r e n v i r o n m e n t . I n i t i a l r i s e o f e a r l y magma v/as p o s s i b l y duo t o g r a v i t a t i o n a l i n s t a b i l i t y o f t h e l e s s d e n s e magma i n r e l a t i o n t o t h e r o c k s p r e s e n t a t t h o p l a c e o f f o r m a t i o n . I n t r u s i o n o f t h e e a r l y g r a n i t i c magma was p r o b a b l y c o n t r o l l e d b y t h e d o m i n a n t l y NW-SE s t r i k e o f t h e c o u n t r y r o c k s a n d may h a v e b e e n i n p a r t a c c o m p l i s h e d b y m a g m a t i c s t o p p i n g , a s e v i d e n c e d b y t h e x e n o l i t h s p r e s e n t i n t h e o u t e r p h a s e s o f t h e b a t h o l i t h . A l t h o u g h t h o t e m p e r a t u r e o f t h e e a r l y magma a t t h e t i m e o f e m p l a c e m e n t n e e d n o t h a v e b e e n v e r y h i g h , t h e t e m p e r a t u r e d i f f e r e n c e b e t w e e n magma a n d c o u n t r y r o c k w o u l d p r o b a b l y h a v e b e e n c o n s i d e r a b l e . I n s u c h c a s e s c o n d u c t i o n o f h e a t i n t o t h e w a l l r o c k s a t t h o m a r g i n o f t h o i n t r u s i o n may w e l l h a v e l e d t o a t e m p e r a t u r e d i f f e r e n t i a l w i t h i n t h e c h a m b e r w h i c h c o u l d n o t be 74 s a t i s f i e d by c o n d u c t i o n o f t h e r m a l e n e r g y t h r o u g h t h e magma. T h i s i n t u r n w o u l d p r e c i p i t a t e magma c o n v e c t i o n . A c o m b i n a t i o n o f i n t r u s i v e f l o w a n d m a g m a t i c c o n v e c t i o n w o u l d a c c o u n t f o r t h e f o l i a t i o n o f p l a g i o c l a s e c r y s t a l s o b s e r v e d i n t h e o u t e r p h a s e s o f t h e b a t h o l i t h . R e l a t i v e movement o f magma a n d c r y s t a l l i s i n g p l a g i o c l a . s e , a s m i g h t be e x p e c t e d t o o c c u r d u r i n g m a g m a t i c c o n v e c t i o n , w o u l d a l s o e x p l a i n t h o n o r m a l z o n i n g e x h i b i t e d b y p l a g i o c l a s e s f r o m H y b r i d a n d H i g h l a n d V a l l e y p h a s e s . P o s s i b l e c o n c e n t r a t i o n o f e a r l y f o r m e d m i n e r a l p h a s e s - p r i m a r i l y p l a g i o c l a s e a n d p y r o x e n e - a t t h e p e r i p h e r y o f t h e magma c h a m b e r , c o m b i n e d w i t h l o c a l a s s i m i l a t i o n o f c o u n t r y r o c k a n d a p r o g r e s s i v e i n w a r d s s o l i d i f i c a t i o n , p r o b a b l y l e d t o a g r a d u a l e n r i c h m e n t o f t h e r e m a i n i n g magma i n a c i d i c c o m p o n e n t s . I n t h i s m a n n e r t h e o b s e r v e d g r a d u a l c h a n g e i n r o c k c o m p o s i t i o n d u r i n g c r y s t a l l i s a t i o n o f t h e H y b r i d a n d H i g h l a n d V a l l e y p h a s e s may h a v e b e e n a c c o m p l i s h e d . T h e o b s e r v e d f o l i a t i o n o f b o t h p l a g i o c l a s e a n d m a f i c m i n e r a l s i n a l a r g e p a r t o f t h e G u i c h o n V a r i e t y , i n a d d i t i o n t o i t s i n t r u s i v e n a t u r e i n t o t h e H y b r i d p h a s e , s u g g e s t e d t o N o r t h c o t e t h a t a m a g m a t i c p u l s e m u s t h a v e o c c u r r e d d u r i n g c r y s t a l l i s a t i o n o f t h e H i g h l a n d V a l l e y p h a s e . T h i s i n t r u s i v e movement m u s t h a v e o c c u r r e d w h e n 75 c r y s t a l l i s a t i o n of the Guichon variety was f a i r l y well advanced, and movement would have taken the form of flowage of a largely c r y s t a l l i n e mush. The conditions of c r y s t a l l i s a t i o n of the Chataway variety must have been very similar to those existing during c r y s t a l l i s a t i o n of the Hybrid phase. The only observable differences between these two units are that the Chatav/ay variety c r y s t a l l i s e d from a more acidic magma and that assimilation was largely inoperative. The continuing trend of d i f f e r e n t i a t i o n i s exhibited by tho LeRoy granodiorite phase. The dyke l i k e nature of th i s phase has been ascribed by Northcote to l o c a l increases i n v o l a t i l e pressures possibly within cupolas at the roof of the magma chamber, which exceeded confining pressure and strength of overlying rock, causing fracturing i n cooler c r y s t a l l i n e phases. The Gump Lake phase does not appear to be d i r e c t l y related to the other phases of the Guichon batholith. As explained i n Chapter VI, i t i s suggested that tho Gump Lake phase may bo an offshoot of the Nicola Batholith which outcrops to tho east. Because of tho r e l a t i v e l y small size of the Gump Lake phase, and i t s intrusion into rocks already heated by previous phases, i t i s probable that conductive heat transfer through the 76 magma was able to keep pace with r e l a t i v e l y slow heat loss to the surrounding rocks and hence magma convection never developed. Such conditions would explain the lack of f o l i a t i o n and the coarse-grained, oquigranular nature of t h i s phase. Textural evidence suggests that plagioclase and quartz c r y s t a l l i s e d e s s e n t i a l l y simultaneously from the Gump Lake magma. The return to more intermediate bulk compositions and the complete change i n the nature of plagioclase zoning schemes exhibited by the Bethlehem and Bethsaida phases indicate, a renewed i n f l u x of magma into the area. Tho composition of t h i s magma was more basic than that which c r y s t a l l i s e d the LeRoy granodiorite and yet more aci d i c than the bulk composition of the e a r l i e r magma. The emplacement of the la t e r magma was probably governed larg e l y by zones of weakness o r i g i n a l l y created by the ea r l i e r magma, and the processes involved are believed to have included at least minor remelting of Highland Valley phase rocks. Remelting i s suggested by plagioclase zoning schemes (discussed e a r l i e r , p. 41) i n Witches Brook phase rocks, "which Northcote believes to be an associated dyke phase of the Bethlehem phase. In view of the close compositional s i m i l a r i t y between Highland Valley and 77 B e t h l e h e m p h a s e r o c k s t h e p r o b l e m s o f a s s i m i l a t i o n seem n o t t o be i n s u r m o u n t a b l e . The i n t r u s i o n o f t h e l a t e r magma i n t o b a t h o l i t h i c r o c k s t h a t w e r e p r o b a b l y a l r e a d y a t e l e v a t e d t e m p e r a t u r e s may h a v e p r e c l u d e d t h e f o r m a t i o n o f a n y s i g n i f i c a n t t e m p e r a t u r e g r a d i e n t , a n d h e n c e raagmatic c o n v e c t i o n , i n a l l p r o b a b i l i t y , d i d n o t o c c u r . I f t h o p r e s e n c e o f d e l i c a t e o s c i l l a t o r y z o n i n g i n p l a g i o c l a s e f e l d s p a r s i s due t o t h e p r o c e s s e x p o u n d e d b y t h e d i f f u s i o n - s u p o r s a t u r a t i o n t h e o r y o f H a r l o f f ( 1 9 2 7 ) a n d l a t e r w o r k e r s , t h e n t h e c r y s t a l l i s a t i o n o f t h e B e t h l e h e m a n d l a t e r p h a s e s m u s t h a v e t a k e n p l a c e u n d e r v e r y q u i e s c e n t c o n d i t i o n s . A n a p p a r e n t c o n t r a d i c t i o n t o t h i s , h o w e v e r , i s t h e p r e s e n c e o f a n i m p e r f e c t p l a g i o c l a s e p r e f e r r e d o r i e n t a t i o n i n t h e o u t e r p a r t s o f t h o B e t h l e h e m p h a s e . L o c a l c o n v e c t i o n a n d / o r i n t r u s i v e f l o w may h a v e o c c u r r e d a t t h e p e r i p h e r y o f t h e magma c h a m b e r d u r i n g e a r l y c r y s t a l l i s a t i o n c a u s i n g o r i e n t a t i o n o f p l a g i o c l a s e c r y s t a l s . I f s u c h f l o w o c c u r r e d d u r i n g e a r l y s t a g e s o f p l a g i o c l a s e c r y s t a l l i s a t i o n i t i s j u s t c o n c e i v a b l e t h a t t h o v i s c o s i t y o f t h e magma p r e v e n t e d r e l a t i v e c r y s t a l - l i q u i d b o u n d a r y l a y e r movement a n d o s c i l l a t o r y z o n i n g c o n t i n u e d u n i n t e r r u p t e d . D u r i n g c o n s o l i d a t i o n o f t h e B e t h l e h e m p h a s e t h e v o l a t i l e p r e s s u r e s w i t h i n t h e magma c h a m b e r m u s t h a v e r i s e n no .'° c o n s i d e r a b l y t h u s p e r m i t t i n g t h e i n i t i a l c r y s t a l l i s a t i o n o f q u a r t z r a t h e r t h a n p l a g i o c l a s e . On t h e b a s i s o f t e x t u r a l a n d f i e l d e v i d e n c e , N o r t h c o t e (1969) h a s s u g g e s t e d t h a t t h e e a r l y p h a s e s o f t h o b a t h o l i t h w e r e d i s p l a c e d u n d e r m c s o z o n a l c o n d i t i o n s , and. t h a t p r o g r e s s i v e e r o s i o n o f t h e c o v e r r o c k s e s t a b l i s h e d e p i z o n a l c o n d i t i o n s b e f o r e e m p l a c e m e n t o f t h e l a t e r p h a s e s . The p o s s i b i l i t y e x i s t s t h a t a r e l a t i v e l y l o n g t i m e i n t e r v a l s e p a r a t e d t h e e m p l a c e m e n t o f e a r l y a n d l a t e p h a s e s o f t h o b a t h o l i t h . The n a t u r e o f t h e c o n t a c t s b e t w e e n B e t h l e h e m a n d H i g h l a n d V a l l e y p h a s e s ~ w h i c h v a r y f r o m s h a r p l y i n t r u s i v e t o g r a d a t i o n a l - s u g g e s t s t o t h e p r e s e n t a u t h o r , h o w e v e r , t h a t t h o t w o p h a s e s w e r e s e p a r a t e d b y a r e l a t i v e l y s h o r t t i m e i n t e r v a l . N o r t h c o t e a l s o h a s s u g g e s t e d t h a t t h e e m p l a c e m e n t a n d c r y s t a l l i s a t i o n o f t h e e a r l y p h a s e s may h a v e o c c u p i e d o n l y f o u r m i l l i o n y e a r s . The p r e s e n t a u t h o r h a s a r g u o d t h a t t h o i n t r u s i o n o f t h e l a t e r magma i n t o r o c k s t h a t w e r e p r o b a b l y a l r e a d y a t e l e v a t e d t e m p e r a t u r e s p r e v e n t e d c o n v o c t i v c f l o w a n d h e n c e t h e l a t e r p h a s e s c r y s t a l l i s e d u n d e r e s s e n t i a l l y q u i e s c e n t c o n d i t i o n s i n t h e p r e s e n c e o f h i g h v o l a t i l e -p r e s s u r e s . T h u s t h o c h a n g e i n t e x t u r a l f e a t u r e s f r o m e a r l y t o l a t e p h a s e s may p o s s i b l y be e x p l a i n e d b y v a r i a t i o n i n p h y s i c a l p a r a m e t e r s o t h e r t h a n t h o s e '79 c o n t r o l l e d b y d e p t h o f i n t r u s i o n . The m i n e r a l o g i c a l v a r i a t i o n s p r e s e n t e d i n t h e p r e s e n t t h e s i s c o n t a i n no e v i d e n c e t o s u p p o r t a n y g r e a t c h a n g e s i n d e p t h o c c u r r i n g d u r i n g c r y s t a l l i s a t i o n o f t h e m a i n p h a s e s o f t h e b a t h o l i t h . T h e p r e s e n c e o f l o c a l b r e c c i a p i p e s , within t h e G u i c h o n b a t h o l i t h , c e r t a i n l y s u g g e s t s t h a t t h e v e r y l a t e s t a g e i g n e o u s a c t i v i t y t o o k p l a c e u n d e r e p i z o n a l t y p e c o n d i t i o n s . I s i t p o s s i b l e t h a t t h e e n t i r e b a t h o l i t h c r y s t a l l i s e d u n d e r o p i z o n a l c o n d i t i o n s ? N o r t h c o t e h a s l i s t e d c r i t e r i a p r e s e n t w i t h i n t h o o l d e r p h a s e s o f t h e b a t h o l i t h w h i c h -a c c o r d i n g t o B u d d i n g t o n (1959) - w o u l d s u g g e s t m c s o z o n a l c r y s t a l l i s a t i o n ( s e c T a b l e X ) . The p r e s e n c e o f a l l t h e s e f e a t u r e s w i t h i n a n e p i z o n a l e n v i r o n m e n t c o u l d be a d a q u a . t e l y e x p l a i n e d i f c o n v e c t i o n was a c t i v e w i t h i n t h e magma c h a m b e r , t h u s c a u s i n g a c o n t i n u i n g , r e l a t i v e l y r a p i d t r a n s f e r o f h e a t t o t h e c h a m b e r m a r g i n s . T h i s c o u l d a c c o u n t f o r t h e p r e s e n c e o f c o m p l e x e m p l a c e m e n t r e l a t i o n s h i p s t o c o u n t r y r o c k , c o n t a c t m o t a m o r p h i s m o f e p i d o t e - a m p h i b o l i t c g r a d e a n d p a r t i a l a s s i m i l a t i o n o f c o u n t r y r o c k . The p r e s e n c e o f p r e f e r e n t i a l l y o r i e n t e d p l a g i o c l a s e c r y s t a l s w i t h i n t h e o l d e r p h a s e s o f t h e b a t h o l i t h may be e v i d e n c e t h a t c o n v e c t i o n w a s o c c u r r i n g d u r i n g t h e i r c r y s t a l l i s a t i o n . I f s u c h i s t h e c a s e t h e n t h e a p p a r e n t c h a n g e f r o m m e s o z o n a l t o o p i z o n a l c o n d i t i o n s 80 T A B L E X C r i t e r i a , s u g g e s t e d b y B u d d i n g t o n ( 1 9 5 9 ) a s i n d i c a t i v e o f m e s o z o n a l i n t r u s i o n , w h i c h a r e p r e s e n t i n t h e G u i c h o n C r e e k b a t h o l i t h ( F r o m N o r t h c o t e j 1 9 6 8 ) a ) D e g r e e o f m e t a m o r p h i s r a o f c o u n t r y r o c k s n o t m o r e i n t e n s e t h a n g r e e n - s c h i s t a n d e p i d o t e - a m p h i b o l i t e f a c i e s ( 4 0 0 - 5 0 0 ° ) . b ) C o m p l e x e m p l a c e m e n t r e l a t i o n s h i p s t o c o u n t r y r o c k ; i n p a r t d i s c o r d a n t , i n p a r t c o n c o r d a n t . L o c a l r e p l a c e m e n t . c ) P l a n a r f o l i a t i o n i s o f t e n w e l l d e v e l o p e d , e s p e c i a l l y i n o u t e r p o r t i o n s o f t h e p l u t o n , b u t i s c o m m o n l y l o c a l , e l u s i v e o r m i s s i n g i n t h e c o r e . d ) Y o u n g e r u n i t s may c r o s s c u t f o l i a t i o n o f o l d e r u n i t s , o r t h e s t r u c t u r e may l o c a l l y b e i n d e p e n d e n t o f b o u n d a r y u n i t s w i t h i n a c o m p o s i t e p l u t o n . e ) A s s i m i l a t i o n may be s i g n i f i c a n t i n b o r d e r o r r o o f z o n e s , f ) E m p l a c e m e n t b y r e c o n s t i t u t i o n a n d r e p l a c e m e n t i s c o m m o n l y a b s e n t o r s u b o r d i n a t e . g ) C h i l l b o r d e r f a c i e s , i n t h e s e n s e o f a p h a n i t i c t e x t u r e , a r e a b s e n t . ( P r e s e n t i n t h e y o u n g e s t p h a s e s o f t h e G u i c h o n b a t h o l i t h ) . h ) M i g m a t i t e s a r e a b s e n t o r s u b o r d i n a t e . i ) P e g m a t i t e s a n d a p l i t e s common e s p e c i a l l y i n t h e b o r d e r z o n e s . T h e y may h a v e a r a d i a l f a b r i c . j ) M i a r o l i t i c s t r u c t u r e i s a b s e n t . k ) C o n t a c t m e t a m o r p h i c a u r e o l e s may be w e l l d e v e l o p e d . s u g g e s t e d b y N o r t h c o t e may n o t bo r e a l a n d t h e e r o s i o n o f s e v e r a l t h o u s a n d s o f f e e t o f L o w e r J u r a s s i c s e d i m e n t s d u r i n g t h e e m p l a c e m e n t o f t h e b a t h o l i t h may n o t be n e c e s s a r y . The p r e s e n t a u t h o r w o u l d s u g g e s t t h e r e f o r e t h a t d u r i n g c r y s t a l l i s a t i o n o f t h e b a t h o l i t h t h o l e v e l o f e m p l a c e m e n t o f t h e b a t h o l i t h , i . e . t h e d e p t h o f c o v e r , may h a v e c h a n g e d b y a s l i t t l e a s two k i l o m e t r e s . I t h a s a l r e a d y b e e n s t a t e d t h a t c r y s t a l l i s a t i o n o f t h e b u l k o f t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s i s b e l i e v e d t o h a v e o c c u r r e d u n d e r e s s e n t i a l l y q u i e s c e n t c o n d i t i o n s . The s l o w c o o l i n g o f t h e magma u n d e r s u c h c o n d i t i o n s n a t u r a l l y l e d t o t h e c r y s t a l l i s a t i o n o f t h e c o a r s e g r a i n e d , e v e n t e x t u r e d B e t h s a i d a p h a s e . T c x t u r a l e v i d e n c e s u g g e s t s t h a t t h e B e t h s a i d a p h a s e c r y s t a l l i s e d u n d e r c o n d i t i o n s o f h i g h . v o l a t i l e p r e s s u r e s . T h e c o n t i n u i n g e n r i c h m e n t o f t h e magma i n v o l a t i l o s a n d c o n s e q u e n t i n c r e a s e s i n v o l a t i l e p r e s s u r e s p r o b a b l y e v e n t u a l l y r e s u l t e d i n l o c a l f r a c t u r i n g o f t h o w a l l s o f t h e magma c h a m b e r . L o c a l f r a c t u r i n g was a c c o m p a n i e d b y e m p l a c e m e n t o f p o r p h y r y d y k e s w a r m s , p i p e b r e c c i a s ' a n d p o s s i b l y t h e Gnawed M o u n t a i n P o r p h y r i e s . L o c a l e m p l a c e m e n t o f B e t h s a i d a . p h a s e d y k e s i n t o o l d e r p h a s e s a l s o o c c u r r e d a t t h i s t i m e . C o p p e r - r i c h m i n e r a l d e p o s i t s s u c h a s B e t h l e h e m , T r o j a n , K r a i n , O . K . a n d L o r n e x a c c o m p a n i e d t h i s f i n a l i g n e o u s a c t i v i t y . S A M P L E N U M B E R . 2 4 6 8 10 12 14 16 18 2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 . 8 0 1 1 1 1 . 1 1 1 1 . 1 1 1 1 1 | 1 1 1 1 l| I 1 1 1 1 1 1 | 1 1 1 1 1 1 | 1 1 1 1 • Fe/Fe+Mg 1 | 1 1 ] ! Biotite • 1 1 1 * • 1 ' i i . 6 0 — • 1 * 1 • • 1 © i • i « • 9 0 | j 1 1 \ 1 Or. W t . % * 1 * 1 1 . i i ° A l k a l i 8 0 F e l d s p p r . . • ' • 1 • • • .1 • 1 • • r i • i • • • i • • • 7 0 * I * 1 1 1 • i . • 6 0 1 1 1 i • 1 1 1 i 4 0 - | [ i i i A n . W t . % 3 0 • • • * • • • * • 1 * * 1 • • • 1 i * 1 * • 1 • . • • • • — 1 * • Plagioclase 2 Q 1 1 i ! i • i 10 Z o n i n g -N o r m a l i i i i Normal -+• Oscillatory I 1 i Normal 1 | j Normal + ~ 1 ' I Oscillatory 8 0 -! ! 1 1 • • 1 • 1 * 1 1 •1 1 • Si 0 2 - W t . % 7 0 « J • 1 1 * 1 * • . • • 1 • 1 . ' R o c k 6 Q - • • • • t i l l • • 1 j • 1 1 1 1 1 1 1 1 1 1 ' 1 1 1 1 1 l' 1 1 1 1 1 1 1 1 1 l 1 1 ! i ' i i i i Intrusive HYBRID Guichon i Chataway i Leroy I 1 GUMP |BETHLEHEM] WITCHES 1 BETHSAIDA ' 1 phase. 1 ' HIGHLAND V A L L E Y | LAKE 1 J BROOK ! i Fin I fi * R n m m n r u r> f r o m n n e i t i o n o l u n r i n t i n n s in the G u i c h o n C r e e k b a t h o l i t h 83 V I I i Summary a n d C o n c l u s i o n s The p r e s e n t s t u d y h a s b e e n c o n c e r n e d w i t h t h e c h a n g i n g m i n e r a l o g i c a l c o m p o s i t i o n o f t h e r o c k s p r o d u c e d d u r i n g c r y s t a l l i s a t i o n o f t h e G u i c h o n C r e e k b a t h o l i t h . The s t u d y h a s s h o w n t h a t , i n g e n e r a l , t h e r e v/as a s l o w p r o g r e s s i v e c h a n g e i n t h e r e l a t i v e p r o p o r t i o n s o f v a r i o u s m i n e r a l p h a s e s p r e s e n t i n t h e r o c k s a s c r y s t a l l i s a t i o n o f t h e b a t h o l i t h p r o c e e d e d . Tho c h e m i c a l c o m p o s i t i o n s o f t h e i n d i v i d u a l m i n e r a l p h a s e s , h o w e v e r , show v e r y l i t t l e c h a n g e w i t h d e c r e a s i n g r e l a t i v e a g e o f t h e h o s t r o c k . ( F i g 16). A l k a l i f e l d s p a r s t h r o u g h o u t t h e b a t h o l i t h a r c m i c r o p c r t h i t i c a n d t h e p o t a s s i u m r i c h p h a s e s o f t h e s e h a v e s t r u c t u r a l s t a t e s e q u i v a l e n t t o t h a t o f o r t h o c l a s e . The t w o u n m i x e d p h a s e s o f t h e a l k a l i f e l d s p a r a r e a l m o s t p u r e o r t h o c l a s e a n d p u r e a l b i t e r e s p e c t i v e l y . The b u l k c o m p o s i t i o n s o f a r t i f i c i a l l y h o m o g e n i s e d a l k a l i f e l d s p a r s f r o m t h o b a t h o l i t h r a n g e f r o m 71 t o 86 Wt% O r . T h e r e i s a s e e m i n g l y r a n d o m v a r i a t i o n o f b u l k c o m p o s i t i o n s a n d s t r u c t u r a l s t a t e s o f t h e a l k a l i f e l d s p a r s f r o m t h e v a r i o u s p h a s e s o f t h e b a t h o l i t h . P l a g i o c l a s e f e l d s p a r s f r o m t h e b a t h o l i t h a r e o f l o w o r i n t e r m e d i a t e s t r u c t u r a l s t a t e s . P l a g i o c l a s e f r o m t h e H y b r i d a n d H i g h l a n d V a l l e y p h a s e s show n o r m a l z o n i n g v / i t h 34 c o r e s An^3_32 a n ^ r i r n s ^^Q-ZO' ^ u m P L a k e p h a s e c a r r i e s o s c i l l a t o r y z o n e d p l a g i o c l a s e s w i t h c o r e s A n ^ a n d r i m s An2Q. P l a g i o c l a s e s f r o m t h e B e t h l e h e m a n d B e t h s a i d a p h a s e s e x h i b i t o s c i l l a t o r y z o n i n g w i t h c o r e s A n ^ g 23 a n c * r i m s A n 2 Q . The W i t c h e s B r o o k p h a s e may c o n t a i n p l a g i o c l a s e s s i m i l a r t o t h o s e o f c i t h e r t h o H i g h l a n d V a l l e y o r t h e B e t h l e h e m p h a s e . I n many o f t h o s a m p l e s s t u d i e d p a r t i a l r e s o r p t i o n o f p l a g i o c l a s e o c c u r s a t p l a g i o c l a s e - a l k a l i f e l d s p a r g r a i n b o u n d a r i e s . T h e r e i s a n a p p r o x i m a t e c o r r e l a t i o n b e t w e e n t h e s i l i c a c o n t e n t o f a n y r o c k a n d t h o c o n c e n t r a t i o n o f b i o t i t e t h a t i t c o n t a i n s . W i t h i n t h e m a j o r p h a s e s o f t h o b a t h o l i t h t h e r e i s a l s o a s l i g h t r e g u l a r d e c r e a s e i n t h o F c / F e + Mg r a t i o o f t h o b i o t i t e w i t h i n c r e a s i n g s i l i c a c o n t e n t o f t h e h o s t r o c k i n w h i c h i t i s f o u n d . Tho F o / F c + Mg r a t i o i n b i o t i t e s a l s o a p p e a r s t o bo a f f e c t e d b y t h e p r e s e n c e o f a n y o t h e r f e r r o m a g n e s i a n s i l i c a t e s . T h u s i n t h o s e r o c k s c o n t a i n i n g more t h a n 73 Wt% S i 0 2 b i o t i t e i s t h e o n l y f e r r o m a g n e s i a n s i l i c a t e p r e s e n t , a n d t h o F e / F e + Mg r a t i o s i n t h e s e b i o t i t e s i n c r e a s e s r a p i d l y w i t h f u r t h e r i n c r e a s e s i n t h e s i l i c a c o n t e n t o f . t h e h o s t r o c k s . S u c h c o n d i t i o n s a r c f o u n d o n l y i n t h e s a m p l e s f r o m t h o Gump L a k e p h a s e - w h i c h may n o t be g e n e t i c a l l y r e l a t e d t o t h e r e s t o f t h e G u i c h o n C r e e k •OP b a t h o l i t h - a n d f r o m t h e S p a t sum q u a r t z - m o n z o n i t e w h i c h i s b e l i e v e d t o bo a l a t e s t a g e d i f f e r e n t i a t e o f t h e b a t h o l i t h . The v a r i a t i o n s i n F c / F c + Mg r a t i o s i n b i o t i t e s may be p r o d u c e d b y v a r i a b l e f u g a c i t i c s o f o x y g o n w h i c h i n t u r n may bo c o n t r o l l e d b y t h e p r e s e n c e o r a b s e n c e o f o t h e r f e r r o m a g n e s i a n s i l i c a t e p h a s e s . The v a r i a b l e t e x t u r e s a n d c o m p o s i t i o n s p r e s e n t i n t h e G u i c h o n C r e e k b a t h o l i t h a r e t h o p r o d u c t s o f c r y s t a l l i s a t i o n o f magma u n d e r v a r y i n g p h y s i c a l c o n d i t i o n s . T h o s e c o n d i t i o n s i n c l u d e d a s s i m i l a t i v e r e a c t i o n w i t h c o u n t r y r o c k s , m a g m a t i c c o n v e c t i o n a n d d i f f e r e n t i a t i o n a n d v a r y i n g v o l a t i l e a n d o x y g e n p r e s s u r e s . Two d i s t i n c t i v e e v e n t s i n t h e c r y s t a l l i s a t i o n h i s t o r y c a n bo d i s c e r n e d f r o m t h e m i n o r a l o g i c a l s t u d y . 'The f i r s t m a j o r e v e n t p r o d u c e d t h o H y b r i d , H i g h l a n d V a l l e y a n d L e R o y p h a s e s o f t h e b a t h o l i t h , t h e s e c o n d m a j o r e v e n t p r o d u c e d t h e B e t h l e h e m , W i t c h e s Brook, a n d B e t h s a i d a p h a s e s a n d t h e m i n o r l a t e s t a g e p o r p h y r y s a n d b r e c c i a s a s s o c i a t e d w i t h t h e m . T h e Gump L a k e p h a s e was i n t r u d e d a t some t i m e b e t w e e n t h o two m a j o r e v e n t s o u t l i n e d a b o v e b u t i t s g e n e t i c r e l a t i o n s h i p t o t h e r e s t o f t h o b a t h o l i t h i s i n d o u b t . I t a p p e a r s f r o m a n a l y s i s o f m o d a l s a l i c c o n s t i t u e n t s t h a t t h e Gump L a k e p h a s e i s n o t d i r e c t l y r e l a t e d t o t h e o t h e r p h a s e s o f t h e G u i c h o n b a t h o l i t h a n d i t may p o s s i b l y bo g e n e t i c a l l y l i n k e d t o t h e N i c o l a b a t h o l i t h w h i c h o u t c r o p s 86 t o t h e o a s t . T h e r e i s a d e f i n i t e c h e m i c a l a n d m i n e r a l o g i c a l c h a n g e i n t h e n a t u r e o f t h e b a t h o l i t h ! c r o c k s w i t h d e c r e a s i n g r e l a t i v e a g o o f i n t r u s i o n . The e a r l y m a g m a t i c e v e n t was p r o b a b l y a c c o m p a n i e d b y a t l e a s t m i n o r a s s i m i l a t i v e a c t i o n a n d c o n v e c t i v e f l o w o f t h e magma. T h e s e c o n d i t i o n s p r o d u c e d t h e x c n o l i t h r i c h m a r g i n t o t h e b a t h o l i t h , t h e p r e f e r r e d o r i e n t a t i o n o f n o r m a l z o n e d p l a g i o c l a s e p h e n o c r y s t s i n t h e e a r l y p h a s e s a n d p r o g r e s s i v e l y l e s s b a s i c b u l k , c o m p o s i t i o n s t h r o u g h t h o H y b r i d a n d H i g h l a n d V a l l e y p h a s e s . Tho L c R o y g r a n o d i o r i t e was c m p l a c o d a s a d y k e p h a s e p o s s i b l y a s a r e s u l t o f l o c a l l y h i g h v o l a t i l e p r e s s u r e s e x i s t i n g i n c u p o l a s a t t h e b a t h o l i t h m a r g i n . T h e m o r e h i g h l y d i f f e r e n t i a t e d n a t u r e o f t h e L c R o y g r a n o d i o r i t e i s c o m p a t i b l e w i t h s u c h a n o r i g i n . The s e q u e n c e o f c r y s t a l l i s a t i o n o f t h e s a l i c m i n e r a l p h a s e s d u r i n g t h e e a r l y m a g m a t i c e v e n t w a s : p l a g i o c l a s e , q u a r t z , a l k a l i f e l d s p a r ; a n d t h e m a f i c m i n e r a l p h a s e s c r y s t a l l i s e d i n t h e s e q u e n c e : p y r o x e n e ( n o t c o m m o n ) , h o r n b l e n d e , b i o t i t e . The p r e s e n c e o f p y r o x e n e i n c l u s i o n s i n p l a g i o c l a s e c o r e s s u g g e s t s t h a t p y r o x e n e was t h o f i r s t m a j o r m i n e r a l p h a s e t o s e p a r a t e i n p y r o x e n e b e a r i n g r o c k s . T h o l a c k o f m a f i c i n c l u s i o n s i n p l a g i o c l a s e c o r e s i n r o c k s d e v o i d o f p y r o x e n e s u g g e s t s t h a t h o r n b l e n d e a n d b i o t i t e c r y s t a l l i s e d a f t e r t h e f i r s t s e p a r a t i o n o f p l a g i o c l a s e i n 87 these- r o c k s . The l a t e r m a g m a t i c e v e n t i s m o s t p r o b a b l y d i r e c t l y , g e n e t i c a l l y r e l a t e d t o t h e e a r l i e r m a g m a t i c e v e n t a n d r e c o r d s a s l i g h t r e n e w e d i n t r u s i v e m o v e m e n t . T h i s magma c r y s t a l l i s e d u n d e r q u i e s c e n t c o n d i t i o n s a n d t h u s v e r y l i t t l e d i f f e r e n t i a t i o n t o o k p l a c e . The l a c k o f c o n v o c t i v c f l o w i n t h i s magma was p r o b a b l y due t o i t s e m p l a c e m e n t i n t o h o t , c o n s o l i d a t e d r o c k s o f t h o e a r l i e r e v e n t a n d f o r t h i s r e a s o n a l s o t h e l a t e r magma c r y s t a l l i s e d t o a m u c h c o a r s e r g r a i n s i z e . The c o n d i t i o n s o f e m p l a c e m e n t o f t h o W i t c h e s B r o o k p h a s e w e r e v e r y s i m i l a r t o t h o s e o f t h e L e R o y g r a n o d i o r i t e o f t h e e a r l y m a g m a t i c - e v e n t . P l a g i o c l a s e z o n i n g s c h e m e s a n d b u l k c o m p o s i t i o n d a t a s u g g e s t t h a t some s a m p l e s o r i g i n a l l y d e s c r i b e d b y ' N o r t h c o t e ( 1 9 6 9 ) a s b e l o n g i n g t o t h o W i t c h e s B r o o k p h a s e may i n f a c t b e l o n g t o t h e L e R o y g r a n o d i o r i t e - p h a s e . D u r i n g c r y s t a l l i s a t i o n o f t h e l a t e r magma a c h a n g e i n t h e o r d e r o f c r y s t a l l i s a t i o n o f t h e s a l i c m i n e r a l p h a s e s o c c u r r e d . T h u s i n i t i a l s e p a r a t i o n o f p l a g i o c l a s e i n t h e o u t e r B e t h l e h e m p h a s e was r e p l a c e d b y i n i t i a l s e p a r a t i o n o f q u a r t z i n t h e B e t h s a i d a p h a s e . T h i s c h a n g e was m o s t p r o b a b l y d u e t o a n i n c r e a s e i n t h e v o l a t i l e p r e s s u r e s . I f r e s u l t s f r o m s y n t h e t i c 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 s c a n be d i r e c t l y a p p l i e d t o t h o p r e s e n t c a s e i t s u g g e s t s t h a t t o t a l p r e s s u r e s i n t h e o r d e r o f k k i l o b a r s e x i s t e d d u r i n g c r y s t a l l i s a t i o n o f t h e B e t h s a i d a p h a s e . The o b s e r v e d g r a d u a l d e c r e a s e i n F e / F e + Mg r a t i o s i n b i o t i t e s i n r o c k s o f b o t h t h e e a r l i e r a n d l a t e r m a g m a t i c e v e n t s s u g g e s t s t h a t t h e f u g a c i t y o f o x y g e n was a l s o i n c r e a s i n g g r a d u a l l y d u r i n g c o n s o l i d a t i o n o f t h o m a j o r p h a s e s o f t h e b a t h o l i t h . The c o n t i n u e d b u i l d u p o f v o l a t i l e p r e s s u r e s w i t h i n t h e magma c h a m b e r e v e n t u a l l y i l e d t o l o c a l f r a c t u r i n g o f t h o c h a m b e r m a r g i n s a n d t h e f o r m a t i o n o f p r o p h y r y d y k e s , p i p e b r e c c i a s a n d l o c a l e c o n o m i c m i n e r a l d e p o s i t s . N o r t h c o t e (1969) h a s s u g g e s t e d t h a t a c h a n g e f r o m m e s o z o n a l t o e p i z o n a l e m p l a c e m e n t e n v i r o n m e n t s o c c u r r e d d u r i n g c o n s o l i d a t i o n o f t h e b a t h o l i t h . Due t o t h e l a c k o f a n y e v i d e n c e t o s u g g e s t t h a t s u c c e s s i v e p h a s e s p e n e t r a t e d c n masse ' i n t o s u c c e s s i v e l y h i g h e r r e g i o n s o f t h o c r u s t N o r t h c o t e h a s s u g g e s t e d t h a t f r o m 5000 f t t o 15000 f t o f L o w e r J u r a s s i c s e d i m e n t s w o r e e r o d e d f r o m t h e r o o f o f t h o b a t h o l i t h d u r i n g i t s e m p l a c e m e n t . The m i n e r a l o g i c a l d a t a c o l l e c t e d i n t h e p r e s e n t t h e s i s c o n t a i n s no e v i d e n c e t o s u p p o r t a n y g r e a t c h a n g e s i n d e p t h o c c u r r i n g d u r i n g c r y s t a l l i s a t i o n o f t h e m a i n p h a s e s o f t h e b a t h o l i t h . The p r e s e n t a u t h o r w o u l d s u g g o t h e r e f o r e t h a t t h e p h y s i c a l c h a r a c t e r i s t i c s o f t h e b a t h o l i t h t h a t s u g g e s t m e s o z o n a l e m p l a c e m e n t may p e r h a p s be d u e t o a c o m b i n a t i o n o f e p i z o n a l e m p l a c c m o n a n d t h e a c t i o n o f c o n v e c t i o n w i t h i n t h e magma c h a m b e r . I f s u c h i s t h e c a s e t h o d e p t h o f e m p l a c e m e n t may h a v e c h a n g e d b y a s l i t t l e a s 2 km d u r i n g t h e e n t i r e c r y s t a l l i s a t i o n h i s t o r y o f t h e b a t h o l i t h . 90 R E F E R E N C E S C I T E D A i l i n g , H . L ; 1 9 3 8 : P l u t o n i c p e r t h i t e s : J o u r . G e o l . , v . 4 6 , p . 1 4 2 . B a a d s g a r d , H . , F o l i n s b c e , R . E . a n d L i p s o n , J . I 9 6 I : P o t a s s i u m - A r g o n d a t e s o f B i o t i t e s f r o m C o r d i l l e r a n G r a n i t e s : G e o l . S o c . A m . , B u l l . , v . 7 2 , p p . 6 8 9 - 7 0 2 . B a r t l e t t , R . W . ; 1 9 6 9 : Magma C o n v e c t i o n , T e m p e r a t u r e D i s t r i b u t i o n a n d D i f f e r e n t i a t i o n : Am. J o u r . S c i . , v . 2 6 7 , p p . 1 0 6 7 - 1 0 8 2 . B o t t i n g a , Y . ; K u d o , A . , a n d W e i l l , D . , 1 9 6 6 : Some o b s e r v a t i o n s o n o s c i l l a t o r y z o n i n g a n d c r y s t a l l i s a t i o n o f m a g m a t i c p l a g i o c l a s e s : A m e r . M i n , v . 5 1 , p p . 7 9 2 - 8 0 6 . B o w e n , N . L . ; 1 9 2 8 : The e v o l u t i o n o f t h e i g n e o u s r o c k s : D o v e r P u b . I n c . B r o w n , B . E . ; 1 9 6 2 : A l u m i n u m d i s t r i b u t i o n i n a n i g n e o u s maximum m i c r o c l i n e a n d t h e s a n i d i n e m i c r o c l i n e s e r i e s : N o r s k . G e o l . T i d s s k r . , v.kZ, p p . 2 5 - 5 6 . B u d d i n g t o n , A . 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S a m p l e n u m b e r s g i v e n i n b r a . c k . e t s r e l a t e t o t h e o r i g i n a l f i e l d s a m p l e n u m b e r u s e d b y K.E. N o r t h c o t e who c o l l e c t e d a l l t h e s a m p l e s u s e d i n t h i s s t u d y . G r a i n s i z e s a r c g i v e n i n t e r m s o f t h e g r e a t e s t d i m e n s i o n . H Y B R I D P H A S E 1. (K64-59A) Q u a r t z D i o r i t c M e d i u m g r a i n e d , e q u i g r a n u l a r , m a r k e d p r e f e r r e d o r i e n t a t i o n o f p l a g i o c l a s e . P l a g i o c l a s e s u b h c d r a l -e u h e d r a l , w i d e r a n g e i n g r a i n s i z e f r o m 2.5mm - 0 . 5 m m . , v e r y w e a k n o r m a l z o n i n g , s t r o n g s e r i c i t i c a l t e r a t i o n . O r t h o c l a s e p e r t h i t i c , i n t e r s t i t i a l o r p o i k i l i t i c a l l y e n c l o s i n g a l l o t h e r m i n e r a l s . Q u a r t z a n h e d r a l , i n t e r s t i t i a l . M a . f i c s a r e r a g g e d , a n h e d r a l a n d r e l a t i v e l y f r e s h . C l i n o p y r o x e n e i s s u b h c d r a l a n d o f a p p r o x . 1 mm g r a i n s i z e . . H o r n b l e n d e s h a v e c o r e s o f s t r o n g l y a l t e r e d c l i n o p y r o x e n e a n d c o n t a i n i n c l u s i o n s o f p l a g i o c l a s e , m a g n e t i t e a n d q u a r t z . B i o t i t e i s p a r t l y p o i k i l i t i c , e n c l o s i n g h o r n b l e n d e , q u a r t z , p l a g i o c l a s e a n d o p a q u e s . M y r m c k i t c p r e s e n t a t some p l a g i o c l a s e •-• o r t h o c l a s e g r a i n b o u n d a r i e s , i f a b s e n t p l a g i o c l a s e h a s a l b i t i c r i m a n d i s p a r t i a l l y r e s o r b e d . 2 . (K64-49A) Q u a r t z D i o r i t c V e r y s i m i l a r t o s a m p l e #1 e x c e p t f o r p r e s e n c e o f t r a c e s o f m i c r o c l i n e t w i n n i n g i n t h o a l k a l i f e l d s p a r . C l i n o p y r o x e n e o c c u r s o n l y a s c o r e s t o h o r n b l e n d e . 3 - (K64 - 1 3 ) Q u a r t z D i o r i t e V e r y s i m i l a r t o s a m p l e #1 e x c e p t t h a t c l i n o p y r o x e n e o c c u r s o n l y a s c o r e s t o h o r n b l e n d e . 4 . (k64-156A) G r a n o d i o r i t e F i n e - m e d i u m g r a i n e d , e q u i g r a n u l a r , m a r k e d p r e f e r r e d o r i e n t a t i o n o f p l a g i o c l a s e . P l a g i o c l a s e s u b h c d r a l , g r a i n s i z e 2mm, f r e s h , n o r m a l z o n i n g . Q u a r t z a n h e d r a l , i n t e r s t i t i a l . O r t h o c l a s e i n t e r s t i t i a l , v e r y few p l a g i o c l a s e i n c l u s i o n s ( s t r o n g l y r e s o r b e d ) , some m y r m e k i t i c 96 i n t e r g r o w t h s . C l i n o p y r o x e n e r a g g e d , s u b h e d r a l w i t h p l a g i o c l a s e i n c l u s i o n s . - B i o t i t e m a r k e d l y i n t e r s t i t i a l p o i k i l i t i c f o r m i n g g r a i n s w i t h m a x . s i z e 3mm. H I G H L A N D V A L L E Y P H A S E Gui_c h_on_ _ V a r i _cty_ 5 . (K63-196 - I ) C o n t a m i n a t e d ? Q u a r t z D i o r i t e M e d i u m - c o a r s e g r a i n e d g r a n u l a r t e x t u r e , m a r k e d p l a g i o c l a s e p r e f e r r e d o r i e n t a t i o n , m a f i c m i n e r a l s t e n d t o f o r m c l u s t e r s . P l a g i o c l a s e s u b h e d r a l - e u h e d r a l , n o r m a l z o n i n g , m a r k e d a l t e r a t i o n . Q u a r t z a n d o r t h o c l a s o i n t e r s t i t i a l . A l l m a f i c s e x t r e m e l y r a g g e d . C l i n o p y r o x e n e r i m m e d b y h o r n b l e n d e a n d v a r i a b l y r e p l a c e d b y s i e v e t e x t u r e h o r n b l e n d e . B i o t i t e p o i k i l i t i c e n c l o s i n g p l a g i o c l a s e , q u a r t z , m a f i c s a n d s p h e n e , e x t e n s i v e a l t e r a t i o n t o c h l o r i d e . 6 . (K63-71A) Q u a r t z D i o r i t e M e d i u m g r a i n e d , c q u i g r a n u l a r , p r e f e r r e d o r i e n t a t i o n o f l a r g e r p l a g i o c l a s e c r y s t a l s . P l a g i o c l a s e i s s u b h e d r a l -e u h e d r a l , e x h i b i t s weak n o r m a l z o n i n g , c o n s i d e r a b l e s e r i c i t i c a l t e r a t i o n a n d p a r t i a l r e s o r p t i o n w h e r e i t i s i n c o n t a c t w i t h a l k a l i f e l d s p a r . P l a g i o c l a s e g r a i n s i z e r a n g e s f r o m 3mm t o ,5mm. Q u a r t z i s i n t e r s t i t i a l t o p l a . g i o c l a s e , a n h e d r a l a n d e x h i b i t s s t r o n g e x t i n c t i o n m o s a i c s . O r t h o c l a s e i s a n h e d r a l , p o i k i l i t i c o r i n t e r s t i t i a l e n c l o s i n g p l a g i o c l a s e a n d h o r n b l e n d e . H o r n b l e n d e i s r a g g e d b u t s u b h c d r a . l , o f t e n h a s c o r e s o f c l i n o p y r o x e n e a n d t e n d s t o f o r m c l u s t e r s o f g r a i n s . B i o t i t e i s r a g g e d a n d g e n e r a l l y a n h e d r a l w i t h s t r o n g c h l o r i t i c a l t e r a t i o n a n d q u a r t z s t r i n g e r s a r e p r e s e n t a , l o n g t h o c l e a v a g e . B i o t i t e g e n e r a l l y a b o u t 1mm b u t may be p o i k i l i t i c u p t o 3mm. Opaque m i n e r a l s show a s t r o n g a s s o c i a t i o n w i t h b i o t i t e a n d h o r n b l e n d e . 7. ( K 63-104- I ) G r a n o d i o r i t e M e d i u m - c o a r s e g r a i n e d c q u i g r a n u l a r . P l a g i o c l a s e c u h o d r a l - s u b h o d r a l , 4mm-0.4mm, s l i g h t a l t e r a t i o n a n d n o r m a l z o n i n g , p a r t i a l r e s o r p t i o n when i n c o n t a c t w i t h o r t h o c l a s o . Q u a r t z a n h e d r a l e q u a n t g r a i n s , 0.3mm. O r t h o c l a s e p e r t h i t i c , f r e s h , i n t e r s t i t i a l o r p o i k i l i t i c u p t o 5mm. H o r n b l e n d e s u b h e d r a l , p o i k i l i t i c e n c l o s i n g q u a r t z , p l a g i o c l a s e a n d o p a q u e s , u p t o 3mm. B i o t i t e 97 r a g g e d , p o i k i l i t i c e n c l o s i n g q u a r t z p l a g i o c l a s e a n d o p a q u e s , a p p r o x . 15% c h l o r i t i c a l t e r a t i o n . 8 . (K64-207) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #6. O r t h o c l a s e i s m a r k e d l y i n t e r s t i t i a l , p y r o x e n e i s a b s e n t a n d m i c r o g r a p h i c i n t e r g r o w t h s o f q u a r t z a n d o r t h o c l a s e a r c common. Chataway Variety 9 . (K.64-H6a-I) Q u a r t z D i o r i t c Medium-coarse g r a i n e d e q u i g r a n u l a r . P l a g i o c l a s e e x h i b i t s a r o u g h p r e f e r r e d o r i e n t a t i o n , i s e u h e d r a l -s u b h o d r a l , 4mm - 0 . 5 m m , s l i g h t a l t e r a t i o n , n o r m a l z o n i n g , p a r t i a l r e s o r p t i o n w h e r e i n c o n t a c t w i t h o r t h o c l a s e . Q u a r t z i s a n h e d r a l , i n t e r s t i t i a l t o p l a g i o c l a s e a n d h a s s t r o n g e x t i n c t i o n m o s a i c s . O r t h o c l a s e i s p o i k i l i t i c u p t o 3mm, a n h e d r a l a n d e n c l o s e s p l a g i o c l a s e , q u a r t z a n d h o r n b l e n d e . M y r m o k i t e i s p r e s e n t a t some o r t h o c l a s c -p l a g i o c l a s e j u n c t i o n s . H o r n b l e n d e i s s u b h c d r a l u p t o 2 .5mm, f r e s h a n d h a s q u a r t z , p l a g i o c l a s e a n d o p a q u e i n c l u s i o n s . B i o t i t e i s r a g g e d , s u b h c d r a l , w i t h q u a r t z a n d o p a q u e i n c l u s i o n s a n d i s a p p r o x . 5% c h l o r i t i s e d . S p h e n e i s s u b h c d r a l . 10. (K .64-48-I) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #9 e x c e p t f o r s l i g h t l y c o a r s e r g r a i n s i z e . O r t h o c l a s e p o i k i l i t i c u p t o 5mm. H o r n b l e n d e s t r o n g l y p o i k i l i t i c . B i o t i t e f r e s h . M y r m o k i t e a b s e n t . 1 1 . (K64-144) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #9- B i o t i t e a p p r o x . 2% c h l o r i t i s e d . 12. (K64-145) Q u a r t z D i o r i t c * V e r y s i m i l a r t o s a m p l e #9. M y r m o k i t e a b s e n t . B i o t i t e a p p r o x . 3 0 % c h l o r i t i s e d . L e R o y V a r i e t y 14. (K63~209a-I) G r a n o d i o r i t e M e d i u m - f i n e g r a i n e d , e q u i g r a n u l a r , a v e r a g e g r a i n s i z e a p p r o x . 1 . 5 m m , r o u g h p r e f e r r e d o r i e n t a t i o n o f p l a g i o c l a s e . P l a g i o c l a s e s u b h e d r a l - e u h e d r a l , w i d e r a n g e i n g r a i n s i z e 5mm - 0 . 5 m m , n o r m a l z o n i n g , m o d e r a t e l y f r e s h , p a r t i a l r e s o r p t i o n when i n c o n t a c t w i t h o r t h o c l o . s e , i n c l u s i o n s o f o p a q u e s a n d s p h e n o . Q u a r t z may o c c u r a s 1) l a r g e r ( . 7 m m ) , p o i k i l i t i c a n h e d r a l g r a i n s w i t h p l a g i o c l a s e i n c l u s i o n s a n d m o s a i c e x t i n c t i o n , o r 2) a s s m a l l e r (.2mm) r o u n d e d o q u a n t g r a i n s w h i c h a r e p a r t i c u l a r l y common a s i n c l u s i o n s i n o r t h o c l a s e . O r t h o c l a s e i s a n h e d r a l i n t e r s t i t i a l a n d p o i k i l i t i c e n c l o s i n g p l a g i o c l a s e , q u a r t z , h o r n b l e n d e a n d o p a q u e s . H o r n b l e n d e i s r a g g e d , s u b h e d r a l , u p t o 3mm, p o i k i l i t i c , e n c l o s i n g q u a r t z , s p h e n o a n d o p a q u e s . B i o t i t e i s r a g g e d , a n h e d r a l , u p t o 1mm, s e m i - p o i k i l i t i c e n c l o s i n g q u a r t z a n d o p a q u e s . 1 5 - ( K 6 3 ~ 2 1 0 a - I ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #14. 1 6 . (K63 - I 8 5 a-I) G r a n o d i o r i t e • V e r y s i m i l a r t o s a m p l e #14. 17 . (.K64-101) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #14 . 1 8 . (K63-37) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #14. GUMP L A K E P H A S E 1 9 . (K64 - 9 8 - I ) G r a n o d i o r i t e C o a r s e - g r a i n e d w e a k l y p o r p h y r i t i c . Q u a r t z i s c o a r s e g r a i n e d , a n h e d r a l a n d e i t h e r i n t e r s t i t i a l o r f o r m i n g c o m p o s i t e ? f r a c t u r e d c r y s t a l s , m o s a i c e x t i n c t i o n a n d o c c a s s i o n a l p l a g i o c l a s e i n c l u s i o n s . P l a g i o c l a s e i s e u h e d r a l o r s u b h e d r a l w i t h g r a i n s i z e 5mm t o Irnm, s l i g h t a l t e r a t i o n , w e a k o s c i l l a t o r y a n d n o r m a l z o n i n g w i t h a l b i t i c r i m s common. S e v e r e r e s o r p t i o n o f p l a g i o c l a s e when i n c o n t a c t w i t h o r t h o c l a s e , a l s o some m y r m o k i t o p r e s e n t . O r t h o c l a s e i s p e r t h i t i c , a n h e d r a l , i n t e r s t i t i a l o r c o a r s e p o i k i l i t i c , e n c l o s i n g p l a g i o c l a s e a n d q u a r t z . B i o t i t e i s f r e s h , r a g g e d , a n h e d r a l , w e a k l y p o i k i l i t i c 99 e n c l o s i n g p l a g i o c l a s e a n d q u a r t z , a n d t e n d s t o f o r m c l u s t e r s a s s o c i a t e d w i t h a c c e s s o r y o p a q u e s . 2 0 . ( K 6 4 - 8 8 ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #19 e x c e p t f o r a p p r o x . 10% c h l o r i t i s a t i o n o f b i o t i t e . 2 1 . ( K 6 4 - 9 8 ) Q u a r t z M o n z o n i t e V e r y s i m i l a r t o s a m p l e #19. B E T H L E H E M P H A S E 2 2 . (K63 - H 5 ) G r a n o d i o r i t e C o a r s e g r a i n e d , w e a k l y p o r p h y r i t i c . P l a g i o c l a s e s u b h c d r a l , l a r g e r c r y s t a l s e x h i b i t r o u g h p r e f e r r e d o r i e n t a t i o n , w e a k o s c i l l a t o r y z o n i n g w i t h v a r i a b l e a l t e r a t i o n o f z o n e s . Q u a r t z a n h e d r a l , i n t e r s t i t i a l t o p l a g i o c l a s e , m o s a i c e x t i n c t i o n common. H o r n b l e n d e a n d b i o t i t e b o t h r . g g c d , s u b h c d r a l , p o i k i l i t i c e n c l o s i n g p l a g i o c l a s e a n d q u a r t z . O r t h o c l a s e p e r t h i t i c , a n h e d r a l i n t e r s t i t i a l o r p o i k i l i t i c , s l i g h t a l t e r a t i o n . 2 3 . ( K 6 4 - 1 8 6 A ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #22. Zh. ( K 6 3 - 1 8 2 ) G r a n o d i o r i t e C o a r s e - g r a i n e d w e a k l y p o r p h y r i t i c . Q u a r t z may be 1 ) s u b h c d r a l , c o a r s e f r a c t u r e d c r y s t a l s , o f t e n c o m p o s i t e , o r 2 ) i n t e r s t i t i a l a n h e d r a l g r a i n s . P l a g i o c l a s e i s e u h e d r a l , 5mm - 0 . 5 m m , e x h i b i t s o s c i l l a t o r y / n o r m a l z o n i n g a n d i s v a r i a b l y a l t e r e d . I n c l u s i o n s o f h o r n b l e n d e a n d q u a r t z . a r e common a n d p a r t i a l r e s o r p t i o n h a s o c c u r r e d when i n c o n t a c t w i t h o r t h o c l a s e . O r t h o c l a s e i s p e r t h i t i c a n h e d r a l , i n t e r s t i t i a l o r w e a k l y p o i k i l i t i c , i n c l u s i o n s o f p l a g i o c l a s e , h o r n b l e n d e , s p h e n e a n d o p a q u e s . Some s m a l l e r i n t e r s t i t i a l g r a i n s e x h i b i t m i c r o c l i n e t y p e g r i d t w i n n i n g a n d t h i s a l s o o c c u r s a t e d g e s o f some p o i k i l i t i c g r a i n s . B i o t i t e a n d h o r n b l e n d e r a g g e d , s u b h c d r a l w i t h s l i g h t c h l o r i t i c a l t e r a t i o n a t e d g e s . 2 5 . ( K 6 3 - 3 9 ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #2.1+ e x c e p t f o r l a c k o f 1 0 0 m i c r o c l i n e t y p o g r i d twinning i n t h e a l k a l i f e l d s p a r a n d p r e s e n c e o f h o r n b l e n d e o n l y a s i n c l u s i o n s i n s a l i c c o n s t i t u e n t s . W I T C H E S BROOK P H A S E 2 6 . ( K 6 3 - 1 7 D G r a n o d i o r i t e M e d i u m - g r a i n e d , w e a k l y p o r p h y r i t i c . P l a g i o c l a s e v a r i a b l e g r a i n s i z e 5mm - 0 . 5 m m , p o o r p r e f e r r e d o r i e n t a t i o n , c u h e d r a l - s u b h o d r a l , h o m o g e n o u s c o r e s , o s c i l l a t o r y z o n e d r i m s , a l t e r a t i o n p a t c h y , v a r i a b l e r e s o r p t i o n when i n c o n t a c t v / i t h o r t h o c l a s e , i n c l u s i o n s o f h o r n b l e n d e a n d m a g n e t i t e common. Q u a r t z a n h e d r a l , a p p r o x . 1mm, c q u a n t g r a i n s o r i n t e r s t i t i a l , m o s a i c e x t i n c t i o n . O r t h o c l a s e p e r t h i t i c , i n t e r s t i t i a l o r p o i k i l i t i c , a n h e d r a l u p t o 3 . 5 m m , e n c l o s e s a l l o t h e r m i n e r a l p h a s e s . B i o t i t e a n d h o r n b l e n d e r a g g e d , a n h e d r a l 0 . 5 m m , t e n d e n c y t o f o r m c l u s t e r s w i t h a c c e s s o r y s p h e n e a n d o p a q u e s . 2 7 . ( K 6 4 - 2 0 3 ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e # 2 6 . 2 8 . ( K 6 4 - 1 0 2 ) G r a n o d i o r i t e M e d i u m t o f i n e g r a i n e d . P l a g i o c l a s e s u b h c d r a l -e u h e d r a l , w e a k l y p o r p h y r i t i c , l a r g e r c r y s t a l s (3mm) e x h i b i t r o u g h p r e f e r r e d o r i e n t a t i o n , n o r m a l z o n i n g . Quartz i n t e r s t i t i a l , w e a k l y p o i k i l i t i c o r a n h e d r a l c q u a n t g r a i n s . O r t h o c l a s e i n t e r s t i t i a l o r p o i k i l i t i c , p a t c h y a l t e r a t i o n . B i o t i t e a n d h o r n b l e n d e f r e s h , a n h e d r a l , f i n e g r a i n e d ( O.p'-'-m) a n d r a g g e d , o f t e n f o r m i n g c l u s t e r s , q u a r t z i n c l u s i o n s common. S p h e n e i n t e r s t i t i a l , a n h e d r a l -s u b h c d r a l , a s s o c i a t e d w i t h m a f i c s . 2 9 . ( K 6 3 - 1 0 5 - D Q u a r t s M o n z o n i t e V e r y s i m i l a r t o s a m p l e #28 3 0 . ( K 6 3 - 8 4 ) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e #28 e x c e p t t h a t b i o t i t e i s a p p r o x . 3 0 % c h l o r i t i s e d . 3 1 . ( K 6 4 - 1 7 ) Q u a r t z M o n z o n i t e M e d i u m g r a i n e d , e q u i g r a n u l a r . P l a g i o c l a s e s u b h c d r a l 101 c o n s i d e r a b l e a l t e r a t i o n , s e v e r e r e s o r p t i o n -and a l b i t i c r i m s common, t r a c e s o f o s c i l l a t o r y z o n i n g . Q u a r t z f o r m s a n h e d r a l , c q u a n t g r a i n s w i t h m o s a i c e x t i n c t i o n , a l s o i n t e r s t i t i a l . O r t h o c l a s e p e r t h i t i c , a n h e d r a l - s u b h e d r a l , c o n s i d e r a b l e a l t e r a t i o n , p a r t l y i n t e r s t i t i a l , p a r t l y s u b h c d r a l p r i s m a t i c , f o u n d a l s o a s r i m s o f v a r i a b l e w i d t h t o p l a g i o c l a s e . B i o t i t e f i n e g r a i n e d , r a g g e d , . a n h e d r a l , a s s o c i a t e d w i t h o p a q u e m i n e r a l s . B E T H S A I D A P H A S E 3 2 . K ( 6 3 - 1 9 2 A ) G r a n o d i o r i t e 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 o r w e a k l y p o r p h y r i t i c . P l a g i o c l a s e e u h e d r a l , a v e r a g e g r a i n s i z e 3mm, c o m p o s i t e c r y s t a l s common, o s c i l l a t o r y z o n i n g , p a r t i a l r e s o r p t i o n w h e n i n c o n t a c t w i t h o r t h o c l a s e , a l b i t i c r i m s common. Q u a r t z o c c u r s a s l a r g o , s u b h c d r a l , f r a c t u r e d g r a i n s o f v a r i a b l e g r a i n s i z e , 6mm - 2mm. Some g r a p h i c i n t o r g r o w t h s o f o r t h o c l a s e a n d q u a r t z . O r t h o c l a s e p e r t h i t i c , c o a r s e , i n t e r s t i t i a l a n h e d r a l o r p o i k i l i t i c s u b h c d r a l , o c c a s s i o n a l l y p a r t i a l l y m a n t l i n g p l a g i o c l a s e . H o r n b l e n d e -o c c u r s a s a s i n g l e l a r g o , p o i k i l i t i c c r y s t a l a p p r o x . 1 . 2 c m , e n c l o s i n g p l a g i o c l a s e , q u a r t z , m a g n e t i t e a n d b i o t i t e . B i o t i t e c o a r s e , m a x . 3mm, r a g g e d , s u b h c d r a l , i n c l u s i o n s o f q u a r t z a n d p l a g i o c l a s e i n o u t e r p a r t s o f g r a i n s , a p p r o x 5% c h l o r i t i s a t i o n . A c c e s s o r y s p h e n e , o p a q u e s , a n d a p a t i t e o c c u r a s c l u s t e r s . 3 3 . (K63-238A) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e # 3 2 . H o r n b l e n d e a b s e n t . 3 4 - (K63-231) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e # 3 2 , h a s m o r e p o r p h y r i t i c t e x t u r e w i t h q u a r t z a n d p l a g i o c l a s e p h e n o c r y s t s . H o r n b l e n d e a b s e n t . B i o t i t e f r e s h , e u h e d r a l , c o a r s e -g r a i n e d a n d w e a k l y p o r p h y r i t i c . 3 5 - (K64--64) G r a n o d i o r i t e V e r y s i m i l a r t o s a m p l e # 3 2 . H o r n b l e n d e a b s e n t . 102 A p p e n d i x 2 M o d a l a n a l y s e s a n d c a l c u l a t o d c h c m i c a 1 _ c o m p o s i t i o n s I n t r u s i v e P h a s e H y b r i d S a m p l e # 1 2 3 Mode .V. -:(• P l a g i o c l a s e 60. 0 5 5 . k 5 5 . 0 5 1 . 79 A l k a l i F e l d s p a r 3 . 2 5 . 0 5 . 0 10. 8 5 Q u a r t z 1 7 . 2 1 7 . 7 20. 0 20. 9 9 B i o t i t e 6 . 0 8 . 3 8 . 0 6 . 1 8 H o r n b l e n d e 0. 4 7 . 3 10. 0 P y r o x e n e 11. 2 5 . 2 1. 0 8 . 8 0 O p a q u e 1. 8 0. 6 0. 77 1. 3 4 S p h e n o 0. 4 T r A p a t i t e 0. 5 T r 0. 0 6 Z i r c o n T r C h e m i c a l E s t i m a t e S i 0 2 60. 32 62. 2 8 6 3 . 63 6 4 . 04 AI2O3 1 7 . 12 16. 5 3 1 6 . 51 16. 11 Fc20x 3 . 02 1. 67 1. 89 2. 36 F c O 3 - 62 3 . 7k 3 . 6 9 3 . 11 MgO 2. 3 8 p 66 2. 35 2. 01 CaO 7 . 66 .6* 16 5 . 16 5 . 9 3 Na20 4 . 0 4 4 . 4 5 4 . 65 3 . 9 8 K20 0. 9 3 1. 4 3 1. 2 9 1. 9 4 HpO 0. 14 0. 3 3 0. 3 9 0. 14 P2O5 ... 0. 2 4 0. 0 3 T i 0 2 0. 55 0. 4 6 0. 4 4 0. 3 3 CaF2 - 0. 0 4 - 0. 01 M o d a l a n a l y s i s f r o m N o r t h c o t e ( 1 9 6 9 ) 103 Appendix 2 ( c o n t i n u e d ) I n t r u s i v e phase H i g h l a n d V a l l e y - Guichon V a r i e t y Sample # 5 6 7 8 Mode P l a g i o c l a s e 60. .3 60. ,8 5 2 . 2 4 9 . 9 A l k a l i F e l d s p a r 1. .1 5. ,0 11 . 6 9 . 9 Quartz 12, .9 13. • 9 2 2 . k 2 7 . 3 B i o t i t e 11. .4 7. ,1 6. 0 3 . 8 Hornblende 1. ,8 11. ,1 6. 3 6. 2 Pyroxene 7. ,0 0. ,6 0. 3 0. 2 Opo.que 4. ,2 1. • 5 1. 0 I . 0 Spheno 1. • 3 0. 2 1. 1 A p a t i t e Z i r c o n Chcmical E s t i m a t e S I 0 2 A I 2 O 3 Fozoi FeO MgO CaO Na 20 K 20 H 20 P 2 0 5 T i 0 2 CaF? 5 6 . 2 3 5 9 . 9 4 65 - 7 9 6 7 . 0 2 1 6 . 4 0 18.16 1 6 . 3 8 1 4 . 9 1 6 . 0 5 2 . 7 5 1 .87 2 . 7 9 5 . 6 9 4 . 0 1 2 . 8 2 2 . 7 8 2 . 4 1 2 . 3 3 1 .55 1.23 6.06 6 . 0 1 4.36 4 . 3 4 4.60 4 . 6 6 4 . 4 1 4 . 2 9 1.12 1 .34 2 . 1 4 1 .57 0 . 2 9 0 . 3 8 0 . 2 6 0.21 1.15 0 . 4 2 O .42 0 . 8 0 Appendix 2 ( c o n t i n u e d ) I n t r u s i v e Phase H i g h l a n d V a l l e y - Chataway Varlot Sample # Mode P l a g i o c l a s e A l k a l i F e l d s p a r Quar t z B i o t i t e Hornblende Pyroxene-Opaque Sphcne A p a t i t e Z i r c o n 9 10 11 12 61.6 A . 8 21.4 4.2 6.2 55.15 7.50 24 . 0 8 6.99 4.65 51.8 14.8 21.4 6.8 4 .8 53.2 6.8 25.2 6.8 6.6 0.6 1.2 0.94 0.22 Tr 0.4 1.0 0.4 Chemical E s t i m a t e S i 0 2 A l 2 6 3 ? c 2 0 z FeO MgO CaO NapO K p0 H 2 0 P 2 0 5 T i 0 2 CaF 2 65.26 66.13 66.21 66.34 17.51 16.67 17.16 15.89 1.25 1.75 1.04 1.89 2.15 2.73 2.39 2.99 1.30 1.38 1.38 1.62 5.60 4.52 4.24 4.46 4.87 4.48 4.41 4.40 0.98 1.64 1.58 0.22 0.26 0^26 0.29 0.87 0.44 0.32 0.55 A p p e n d i x 2 ( c o n t i n u e d ) I n t r u s i v e P h a s e H i g h l a n d V a l l e y - L e R o y V a r i e t y S a m p l e # 14 15 16 17 18 Mode -if-P l a g i o c l a s e 6 2 . 8 5 3 . 2 5 0 . 6 4 7 . 4 2 . 2 3 A l k a l i F e l d s p a r 8 . 8 1 6 . 4 1 1 . 8 16. 2 0 . 4 6 Q u a r t z 1 5 - 8 2 1 . 4 2 4 . 8 26. 2 8 . 2 2 B i o t i t e 4 . 4 4 . 2 6 . 2 6 . 3 . 9 0 H o r n b l e n d e 7 . 2 3 . 8 5 . 4 5 . 3 . 2 1 P y r o x e n e - - - -O p a q u e 0 . 6 1 . 0 1 . 2 0 . 8 9 0 . 6 3 S p h e n e 0 . 4 T r - 0 . 3 9 0 . 1 9 A p a t i t e - - - - 0 . 1 5 Z i r c o n - - - - 0 . 0 2 C J i e r a i c a l E s t i m a t e S i Op A I 2 O 3 F e p O v FeO J MgO CaO NapO K26 HpO P2°5 T1O2 C a F 2 6 2 . 5 7 . 6 5 . 4 0 6 6 . 4 8 6 8 . 11 7 0 . 4 8 1 9 . 2 2 1 8 . 1 1 16. 16 1 5 . 3 2 1 4 . 9 9 1 . 3 0 1 . 6 0 2 . 0 8 1. 6 4 1 . 1 7 2 . 3 4 1.96 2 . 8 1 2 . 51 1 . 7 1 1.46 0 . 9 3 1 . 3 9 I . 3 1 0 . 8 7 6.16 4 . 8 8 4 . 2 0 3 . 4 7 3 . 1 2 4 . 6 7 4 . 3 3 4 . 2 5 4 . 3 1 4 . 1 5 1 . 5 6 2 . 4 1 2 . 0 7 2 . 60 2.96 0 . 2 4 0.-17 0 . 2 5 0 . 2 4 0.16 - - 0 . 0 8 0 . 4 7 0 . 2 0 0 . .31 0 . 4 9 0 . 3 0 - - 0 . 0 1 1 0 6 A p p e n d i x 2 ( c o n t i n u e d ) I n t r u s i v e P h a s e Gump L a k e S a m p l e # 19 2 0 2 1 Mode * P l a g i o c l a s e 3 7 . 2 5 3 0 . 6 3 6 . 6 A l k a l i F e l d s p a r 16 . 7 7 2 2 . 4 2 3 . 4 Q u a r t z 3 9 . 1 6 3 9 . 8 3 8 . 2 B i o t i t e 5 . 2 4 4 . 8 1 . 6 H o r n b l e n d e 0 . 7 5 — P y r o x e n e - -Opaqu o 0 . 6 6 0.6 0 . 2 S p h e n e — — — A p a t i t e 0 . 0 9 - -Z i r c o n 0 . 0 9 - -C h e m i c a l E s t i m a t e S i O ; AI2D3 FopOx FoO MgO CaO N a 20 K 2 0 H 2 0 p 2 o 5 T i 0 2 C a F 2 7 4 . 5 0 76.04 76.35 1 3 . 0 9 12.22 13-56 1 . 1 4 1.06 0.34 1.63 1.47 0.47 0.66 P.53 0..17 2.47 1.86 2 . 2 5 3-59 2..83 3.73 2 . 5 0 3.66 3-02 O . 1 4 0.12 0.04 0.04 - -0.21 0 . 1 9 0.06 0.01 - — 107 A p p e n d i x 2 ( c o n t i n u e d ) I n t r u s i v e P h a s e B e t h l e h e m S a m p l e # 22 2 3 2 4 2 5 • Mode • P l a g i o c l a s e 5 9 . 4 8 5 5 . 4 5 5 3 . 3 5 0 . 8 A l k a l i F e l d s p a r 1 3 . 3 8 8 . 3 5 1 5 . 0 1 2 . 4 Q u a r t z 1 8 . 5 9 2 5 . 8 7 2 6 . 2 3 3 . 4 B i o t i t e 1.76 4 . 3 5 3 . 2 2 . 8 H o r n b l e n d e 4 . 9 5 4 . 4 8 1 . 3 0 . 6 P y r o x e n e - - - -Opaque 1.06 1 . 2 6 0 . 5 -S p h e n o 0 . 5 2 -' 0 . 4 -A p a t i t e 0 . 1 2 T r - -Z i r c o n 0 . 0 6 T r - -C h e m i c a l E s t i m a t e SiO Al?b 3 FelOx FeO MgO CaO N a 2 0 K 20 HpO p 2 o 5 TiOo CaF 2 6 5 . 3 5 67 .91 6 9 . 9 7 7 3 . 3 7 1 7 . 9 2 1 5 . 8 8 1 6 . 4 6 1 5 . 5 1 1 . 7 1 2 . 0 7 0 . 8 7 0 . 1 5 1 . 7 4 2 . 4 3 1 . 1 9 0 . 7 0 0 . 8 8 1 . 1 3 0 . 5 2 0 . 3 8 4 . 9 3 3 - 7 7 3 . 6 3 3 . 4 6 5 . 0 3 4 . 3 5 4 . 9 0 4 - 3 9 1 . 3 2 . 1 . 5 3 2 . 0 1 1.84 0 . 1 4 0 . 2 0 0 . 1 0 0 . 0 8 0 . 0 6 - - -0 . 4 1 0 . 2 4 0 . 3 5 0 . 1 2 0 . 0 1 - - -1 0 3 Appendix 2 ( c o n t i n u e d ) I n t r u s i v e Phase Witches Brook Phase Sampl c # 2 6 27 2£ 29 3 0 3 1 .ode if-P l a g i o c l a s e 53. 37 5 1 . 3 3 45. 0 40. 40 41. 0 30. 1 5 A l k a l i F e l d s p a r 11. 07 12. 66 17. 0 21. 09 20. 0 2 6 . 2 3 Quartz 2 6 . 36 2 8 . 06 28. 0 2 8 . 38 2 8 . 0 4 1 . 38 B i o t i t e 4 . 87 5 . 54 5- 0 3 . 1 1 5. 0 1 . 84 Hornblende 3 . 22 1. 87 3 . 0 4 . 50 5 . 0 Pyroxene Tr Tr Opaque 1. 06 0. 34 0. 96 0. 73 0 . 3 0 . 39 Sphcne 0. 2 6 0. 14 0. 60 1. 75 0 . 3 A p a t i t e Tr — Tr _ Z i r c o n J . X Tr -Chemical E s t i m a t e S i Op 67. 54 70. 4 1 69. 62 69. 8 0 70. 18 77. 73 A 1 2 0 3 16. 52 15- 80 1 4 . 91 14. 42 1 4 . 75 12. 17 FcpOx 1. 75 0. 78 l . 63 1. 3 1 0 . 86 0 . 55 FeO 1 3 1. 67 2. 09 1. 77 2. 0 3 0 . 58 MgO o! 9 5 0. 85 0. 95 0. 96 1 . 2 8 0 . 18 CaO 40 3 . 29 3 . 15 3 . 62 2.1 0 . 65 Na 20 4 . on •— i 4. 8 8 4. 3 3 4. 0 3 4 . 0 9 3 . 96 K 20 1. 88 1. 84 2. 59 2. 82 2 . 95 4 . 07 HpO 0. 17 0. 17 0. 1 8 0. 16 0 . 2 2 0 . 04 p 2 o 5 06 T i 0 2 0. 36 0. 3 1 0. 55 1. 10 0 . 42 0 . Appendix 2 ( c o n t i n u e d ) I n t r u s i v e Phase B c t h s a i d a Phase-Sample # 32 33 34 35 Mode P l a g i o c l a s e 5 8 . 92 57. 97 5 3 . 4 6 . 21 A l k a l i F e l d s p a r 10. 82 Ik. 55 11. 5 . 88 Quartz 19. 70 2 2 . 08 3 0 . 3 5 . 22 B i o t i t e 0 . 51 X 62 k. 11. 88 Hornblende 7. 05 0 . Ik 0 . 2 3 0 . 42 Pyroxene -Opaque 2 . 9k 1. 24 0 . 6 6 0 . 44 Sphene 0 . 23 0 . 2 6 A p a t i t e 0 . 02 0 . 18 0 . 2 6 0 . 02 Z i r c o n Tr Chemical E s t i m a t e SiO FC2O3 FeO MgO CaO Na 20 K 20 H 20 P 2 ° 5 T i 0 2 CaFo 6 4 . 2 5 6 7 . 7 9 7 0 . 9 0 7 2 . 3 4 1 6 . 5 9 1 7 . 1 3 1 5 . 7 4 1 3 . 8 4 4 . 1 6 1 .82 1 .07 0 . 7 9 2 . 8 5 1 .54 1 . 3 0 2. 54 1 . 0 2 0 . 4 0 0 . 4 5 1 . 2 0 4 . 3 4 3 . 5 2 3 . 5 9 2 . 4 3 5 . 0 9 5 . 3 5 4 . 6 7 4 . 2 8 1 .42 2 . 0 0 1 .74 1 .88 0 . 1 5 0 . 0 9 0 . 1 0 0 . 2 7 0 . 0 1 0 . 0 9 0 . 1 3 0 . 0 1 0 . 1 2 0 . 2 6 0 . 2 9 0 . 4 2 Tr 0 . 0 2 0 . 0 2 Tr 110 A p p e n d i x 3 B i o t i t e 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 1) S a m p l e S e l e c t i o n a n d P r e p a r a t i o n B i o t i t e s a m p l e s w e r e p r e p a r e d a s g r a i n m o u n t s r a t h e r t h a n a s t h i n s e c t i o n s o f r o c k s s i n c e t h i s a l l o w e d a much m o r e r e p r e s e n t a t i v e s a m p l e t o be e x a m i n e d . A p p r o x i m a t e l y h a l f o f t h e s a m p l e s u s e d w e r e o r i g i n a l l y c o n c e n t r a t e d b y K . E . N o r t h c o t e f o r u s e i n K / A r a g e d a t i n g s t u d i e s o f t h e b a t h o l i t h . The r e m a i n i n g s a m p l e s w e r e s e p a r a t e d f r o m a c r u s h e d h a n d s i z e r o c k s a m p l e b y c o m b i n e d s i e v i n g a n d h a n d p i c k i n g t e c h n i q u e s . S e v e r a l g r a i n s f r o m e a c h s a m p l e w e r e c o l d m o u n t e d i n c p o x y r e s i n c y l i n d r i c a l m o u n t s a n d p o l i s h e d . F o r 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 a p e r f e c t l y f l a t s a m p l e s u r f a c e i s r e q u i r e d i n o r d e r t o m i n i m i s e i r r e g u l a r a b s o r p t i o n e f f e c t s o n t h e X - r a y s g e n e r a t e d w i t h i n t h e s a m p l e . A p e r f e c t l y f l a t s a m p l e s u r f a c e i s e x t r e m e l y d i f f i c u l t t o a t t a i n w i t h b i o t i t e . s a m p l e s b e c a u s e o f t h e e x t r e m e l y f i n e s c a l e n a t u r e o f t h o p e r f e c t b a s a l c l e a v a g e p r e s e n t i n m i c a s . I n i t i a l h a n d p o l i s h i n g o n a g l a s s p l a t e w i t h 950 c a r b o r u n d u m g r i t w a s e m p l o y e d t o e x p o s e t h e b i o t i t e g r a i n s a t t h e s u r f a c e o f t h o e p o x y m o u n t . S e c o n d a r y p o l i s h i n g was d o n e w i t h t i n o x i d e p o w d e r o n a r o t a r y p o l i s h i n g m a c h i n e w i t h c l o t h l a p s . T h i s s e c o n d s t a g e o f t e n p r o d u c e d s a m p l e s u r f a c e s w h i c h w e r e deemed t o be s u f f i c i e n t l y w e l l p o l i s h e d . I f f u r t h e r p o l i s h i n g was n e c e s s a r y t h i s was a c h i e v e d u s i n g 1 ^ I l l a n d i yu d i a m o n d p a s t e o n a s i l k l a p r o t a r y p o l i s h i n g m a c h i n e . A l l m o u n t s w e r e c a r b o n - c o a t e d w i t h a c o a t t h i c k n e s s c o r r e s p o n d i n g t o a p u r p l o - b l u c c o l o u r o n p o l i s h e d b r a s s . ( S m i t h , 1965) 2 ) S t a n d a r d s I n o r d e r t o m i n i m i s e d i f f e r e n t i a l a b s o r p t i o n a n d f l o u r e s c e n c e e f f e c t s b e t w e e n s a m p l e s a n d s t a n d a r d s i t was d e c i d e d t h a t a n u m b e r o f c h e m i c a l l y a n a l y s e d n a t u r a l b i o t i t e s w o u l d be u s e d a s s t a n d a r d s . The a u t h o r i s p a r t i c u l a r l y g r a t e f u l t o D r . J . K . Y . R i m s a i t e o f The G e o l o g i c a l S u r v e y o f C a n a d a f o r h e r h e l p i n p r o v i d i n g t h e s t a n d a r d s p r e f i x e d R i n T a b l e X I . C h e m i c a l a n a l y s e s a n d p h y s i c a l p r o p e r t i e s f o r t h e s e s t a n d a r d s h a v e b e e n p u b l i s h e d b y D r . R i m s a i t e i n G . S . C . B u l l e t i n #149 (1967). The a u t h o r w o u l d a l s o l i k e t o t h a n k D r . J . A . Gower o f t h o G e o l o g y D e p a r t m e n t , U n i v e r s i t y o f B r i t i s h C o l u m b i a f o r p r o v i d i n g t h e s t a n d a r d s p r e f i x e d B i n T a b l e X I . P a r t i a l c h e m i c a l a n a l y s e s f o r t h e B s t a n d a r d s w e r e c a r r i e d o u t b y ' r a p i d ' , m e t h o d s b y t h e G e o l o g i c a l R e s e a r c h D e p a r t m e n t o f C o m i n c o L t d . a t T r a i l , B . C . 3) I n s t r u m o n t a t i o n a n d T e c h n i q u e The i n s t r u m e n t u s e d was a J a p o n c s e E l e c t r o n O p t i c s L a b o r a t o r i e s J x A - 3 A ( 3 1 / 4 0 ) w h i c h h a s a n o r m a l l y i n c i d e n t e l e c t r o n b e a m , a s p e c t r o m e t e r t a k e - o f f a n g l e o f 20°, a n d i s e q u i p p e d w i t h , g a s f l o w p r o p o r t i o n a l c o u n t e r s . A l l 112 a n a l y s e s were c a r r i e d out at an e l e c t r o n e x c i t a t i o n p o t e n t i a l of 2 5 k v . and sample c u r r e n t s a p p r o x i m a t e l y . . 0 8 y u A , u s i n g a spot s i z e o f a p p r o x i m a t e l y 5/tt. The e l e c t r o n beam c u r r e n t was m o n i t o r e d between each a n a l y s i s by r e t u r n i n g t o a Cadmium s t a n d a r d and c h e c k i n g t h a t the sample c u r r e n t on t h i s s t a n d a r d v/as steady. S l i g h t f l u c t u a t i o n s o f the Cadium s t a n d a r d c u r r e n t were a d j u s t e d by means o f tho condenser l e n s b i a s c o n t r o l . S i m u l t a n e o u s a n a l y s e s v/ere made f o r M g K o c and FoK <* , u s i n g a mica c r y s t a l f o r M g K o c , and a q u a r t z c r y s t a l f o r FoKoi , i n the two s p e c t r o m e t e r s . Counting response f o r FoK oc , was good, a v e r a g i n g 1 , 5 0 0 c o u n t s / s e c . f o r a sample c o n t a i n i n g 1 5 Wt% Fo. Counting response f o r M g K o c ? however, was e x t r e m e l y poor, average 3 0 c o u n t s / s e c f o r a sample c o n t a i n i n g 8 Wt% Mg. Peak t o background r a t i o s f o r an average sample were a p p r o x i m a t e l y 2 0 0 : 1 f o r FeK , and 8 : 1 f o r MgK* . Background counts v/ere found to be tho same a t 1°29 above and 1°29 below tho peak p o s i t i o n , and t h u s background counts wore t a k e n f o r a l l a n a l y s e s at 1°29 below the peak p o s i t i o n . In view of the low c o u n t i n g r a t e s f o r KgK <* , i t was n e c e s s a r y t o count f o r r e l a t i v e l y long p e r i o d s o f time at any s i n g l e s p o t . Repeated ton second a n a l y s e s of the same spot showed t h a t a f t e r a p p r o x i m a t e l y 50 sees t h e r e was a n o t a b l e decrease i n tho c o u n t i n g r a t e s f o r b o t h 113 M g K e c a n d F o K e c , p r e s u m a b l y due t o s u r f a c e c o n t a m i n a t i o n b u i l d u p . T h u s a n a l y s e s o f a s i n g l e s p o t ' w e r e c a r r i e d o u t f o r kO s e c t i m e i n t e r v a l s . I n o r d e r t o c h o c k f o r s a m p l e i n h o m o g e n c i t y 3-5 s p o t s w e r e a n a l y s e d p e r g r a i n a n d 5 g r a i n s a n a l y s e d p e r s a m p l e . I n a d d i t i o n s e v e r a l o f t h e s a m p l e s w o r e c h e c k e d f o r c o m p o s i t i o n a l z o n i n g b y m a k i n g l i n e a r t r a v e r s e s f r o m g r a i n c o r e s t o g r a i n b o u n d a r i e s . No c o m p o s i t i o n a l z o n i n g was o b s e r v e d i n a n y o f t h e s t a n d a r d s n o r i n a n y o f t h e s a m p l e s i n v e s t i g a t e d . F i g . 17 i s a p l o t o f c o m p o s i t i o n a g a i n s t t o t a l c o u n t s c o l l e c t e d p e r 40 s e e s d u r i n g a s i n g l e r u n n i n g p e r i o d f o r t h e s t a n d a r d s u s e d i n t h e p r e s e n t s t u d y . The s t a n d a r d s l i e on a v e r y s l i g h t l y c u r v e d l i n e w h i c h h a s a t e n d e n c y t o i n c r e a s e s l o p e a t h i g h e r c o u n t i n g r a t e s . Tho G u i c h o n •' b i o t i t e s a m p l e s a l l l i e w i t h i n t h e r a n g e o f s t a n d a r d s R .24 - R . l l a n d i n t h i s r a n g e t h e c o r r e l a t i o n c u r v e o f t o t a l c o u n t s c o l l e c t e d t o c o m p o s i t i o n i s e f f e c t i v e l y a s t r a i g h t l i n e . The r e l a t i v e e r r o r s i n a n a l y s i s may be g u a g e d b y i n s p e c t i o n o f F i g . 1 7 . R e l a t i v e e r r o r s i n t h e e s t i m a t e o f c o m p o s i t i o n s f o r t h e G u i c h o n b a t h o l i t h s a m p l e s a r c e s t i m a t e d a t - 0.35 Wt% Mg a n d - 0.25 Wt% F c . T h i s e s t i m a t e t a k e s i n t o a c c o u n t t h e ' f i t t i n g ' o f c o r r e l a t i o n I l k 70000-F i g . 17 M i c r o p r o b e a n a l y s e s . T o t a l c o u n t s o b s e r v e d a s a f u n c t i o n o f c o m p o s i t i o n f o r b i o t i t e s t a n d a r d s . C i r c l e s a p p r o x i m a t e o n e s t a n d a r d d e v i a t i o n o f t o t a l c o u n t s o b s e r v e d . 1 1 5 T a b i c XI Data used i n c o n s t r u c t i o n o f F i g 17 Standard # R . 3 1 R . 2 4 R .26 B . 1 2 R 1 1 R . 1 3 B . 1 6 B. 8 R. 7 B . 1 8 Wt% Mg c h e m i c a l 3 . 4 9 5 . 5 3 6 . 2 1 6 .99 8 . 6 3 8 . 8 0 11 .46 1 2 . 8 4 1 3 . 1 5 13 .69 Standard # Wt% Fo che mi c a l B . 1 8 B. 8 R. 7 B . 1 6 B . 1 2 R . l l R . 1 3 R . 2 6 R . 2 4 R . 3 1 2 . 1 2.4 4.71 6 . 8 8 . 8 3 12.57 14.49 1 6 . 8 1 1 7 . 8 8 22.42 Average T o t a l counts MgKoi ( 4 0 sees) 352 1500 1 4 6 8 1 8 3 4 2 3 8 0 2 4 8 8 3 9 4 4 4 7 1 2 4 5 1 4 5 2 2 8 Average T o t a l counts FeKot ( 4 0 sees) ^420 7612 1 4 3 6 8 1 9 4 0 8 2 5 4 3 2 3 5 5 7 6 4 3 5 8 8 5 2 1 9 2 5 0 2 4 8 7 0 5 6 0 c 1% cr counts counts Mg% 18 5 . 1 5 • -> . JL 8 0 6 . 1 . 2 7 0 4 . 7 . 1 5 50 2 . 7 • 1 2 5 160 6 . 7 . 4 112 4 . 5 . 2 5 1 7 4 4 . 4 . 2 5 1 2 4 2 . 6 . 1 5 1 4 8 3 . 3 . 2 0 46 0 . 8 .1 cr 0-counts counts Yc% 1 6 4 3 . 0 . 1 1 6 4 2 . 1 . 1 1 8 4 1 . 3 . 1 4 4 0 2 . 3 . 2 3 4 4 1 . 4 . 2 1 2 0 0 3 . 4 . 4 5 6 4 1 . 3 . 2 5 2 4 3 2 4 . 6 . 6 1 3 4 8 2 . 7 . 4 956 1 . 4 . 2 5 zr counts 1 s t a n d a r d d e v i a t i o n from the average value-o b t a i n e d from s e v e r a l spot a n a l y s e s on s e v e r a l g r a i n s from each sample c-Mg% and c-Fc% have been e s t i m a t e d from a knowledge o f counts and the c o r r e l a t i o n c u r v e s o f F i g . 14 116 c u r v e s , s a m p l e i n h o m o g o n e i t y a n d t h e s t a t i s t i c a l v a r i a t i o n o f X - r a y g e n e r a t i o n . T o t a l i n s t r u m e n t a l d r i f t was c h e c k e d b y a n a l y s e s o f s t a n d a r d s b e f o r e , d u r i n g a n d a f t e r e a c h s o t o f u n k n o w n s a m p l e s . D r i f t was f o u n d t o be l e s s t h a n one s t a n d a r d d e v i a t i o n i n t h e a c c u m u l a t e d c o u n t s f o r a l l o f t h e s t a n d a r d s e m p l o y e d . 

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