UBC Theses and Dissertations

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UBC Theses and Dissertations

Geology of the Topley intrusives in the Endako area British Columbia Bright, Edward Gordon 1967

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G E O L O G Y O F T H E T O P L E Y I N T R U S I V E S I N T H E E N D A K O A R E A B R I T I S H C O L U M B I A b y E D W A R D G O R D O N B R I G H T B . S c , M c M a s t e r U n i v e r s i t y , O n t a r i o , 1964 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 L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n the D e p a r t m e n t of G E O L O G Y We accept t h i s t h e s i s as c o n f o r m i n g to the r e q u i r e d s t a n d a r d T H E 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 A p r i l , 1967 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, 1 agree t h a t the L i b r a r y s h a l l make i t f r e e l y avai1ab1e f o r r e f e r e n c e and study I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s I t i s understood t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n Department of The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada i A B S T R A C T G r a n i t i c r o c k s of the T o p l e y i n t r u s i v e s u n d e r l y i n g 100 s q u a r e m i l e s , c e n t e r e d a r o u n d E n d a k o , n o r t h c e n t r a l B r i t i s h C o l u m b i a , f o r m p a r t of a c o m p o s i t e b o d y w h i c h l i e s i n a n o r t h w e s t t r e n d i n g b e l t of g r a n i t i c p lutons extending f r o m B a b i n e L a k e to Q u e s n e l , a d i s t a n c e of 180 m i l e s . R o c k s of the T o p l e y c o m p l e x i n the E n d a k o a r e a have i n t r u d e d v o l c a n i c r o c k s of the T a k l a G r o u p ( U p p e r T r i a s s i c to J u r a s s i c ) and a r e u n c o n f o r m a b l y o v e r l a i n b y f l a t - l y i n g T e r t i a r y v o l c a n i c f l o w s . T h e s e i n t r u s i o n s a r e p r o b a b l y of L o w e r J u r a s s i c to L o w e r C r e t a c e o u s age. The g r a n i t i c r o c k s , r a n g i n g f r o m d i o r i t e to a l a s k i t e f o r m s i x l a r g e s e p a r a t e l y e m p l a c e d and s h a r p l y bounded i n t r u s i v e b o d i e s . The deve lopment of the T o p l e y c o m p l e x can be d i v i d e d c h r o n o l o g i c a l l y , f r o m o l d e s t to youngest , into f ive m a j o r s tages: (I) the S i m o n B a y ( d i o r i t e ) c o m p l e x ; (II) the Endako q u a r t z m o n z o n i t e w h i c h i s the h o s t r o c k of the Endako m o l y b d e n u m deposi t , and the F r a n c o i s g r a n i t e ; (III) the Glennanan c o m p l e x ; (IV) the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e ; and (V) the S t e l l a k o q u a r t z m o n z o n i t e . i i The Glennanan c o m p l e x , w h i c h i s the bes t exposed and m o s t i n t e n s e l y s tudied i n t r u s i v e , c o n s i s t s of two l a r g e a s y m m e t r i c a l l y zoned bodies and a s m a l l s tock of p o r p h y r i t i c q u a r t z m o n z o n i t e . The l a r g e r zoned body n e a r the town of Endako h a s : (1) a w e s t e r n zone of p o r p h y r i t i c g r a n i t e ; (2) an i n t e r m e d i a t e zone of p o r p h y r i t i c q u a r t z m o n z o n i t e ; and (3) an e a s t e r n zone of p o r p h y r i t i c g r a n o d i o r i t e . A g r a n o d i o r i t e zone i s absent i n the a s y m m e t r i c a l l y zoned N i t h i M o u n t a i n i n t r u s i v e b o d y . A l l i n t e r n a l contact a r e g r a d a t i o n a l and a l l r o c k zones conta in l a r g e r e c t a n g u l a r p e r t h i t e m e g a c r y s t s w h i c h enc lose o r i e n t e d c r y s t a l s of p l a g i o c l a s e and other m i n e r a l s . T h e deve lopment of the r o c k zones c a n be accounted f o r b y d i f f e r e n t i a t i o n of a h o r n b l e n d e - b i o t i t e g r a n o d i o r i t e m a g m a at depth and s u c c e s s i v e i n t r u s i o n of f i r s t g r a n i t e , then q u a r t z m o n z o n i t e and f i n a l l y g r a n o d i o r i t e . T o p l e y stages II to V r e p r e s e n t a cont inuous p e r i o d of e p i z o n a l i n t r u s i o n f o l l o w i n g the e m p l a c e m e n t of the m o r e deep seated ( m e s o z o n a l ? ) S i m o n B a y c o m p l e x . N o r t h w e s t e r l y and n o r t h e a s t e r l y t r e n d i n g f r a c t u r e zones c o n t r o l l e d the s t r u c t u r a l e v o l u t i o n of the T o p l e y c o m p l e x i n the m a p a r e a . i i i T A B L E O F C O N T E N T S P a g e I N T R O D U C T I O N 1 S C O P E O F I N V E S T I G A T I O N 1 L O C A T I O N A N D A C C E S S I B I L I T Y 1 P H Y S I O G R A P H Y 2 A C K N O W L E D G E M E N T S 4 G E N E R A L G E O L O G Y 5 M E T H O D S O F I N V E S T I G A T I O N 8 D E T E R M I N A T I O N O F T H E A L K A L I F E L D S P A R C O M P O S I T I O N 10 C H E M I C A L A N A L Y S I S 12 T A K L A G R O U P 12 D I S T R I B U T I O N A N D P E T R O G R A P H Y 13 S T R U C T U R E A N D A G E R E L A T I O N S H I P S 13 M E N A R D Q U A R T Z L A T I T E P O R P H Y R Y R S T O C K 15 D I S T R I B U T I O N A N D P E T R O G R A P H Y 15 S T R U C T U R E 15 T O P L E Y S T A G E I 17 T H E S I M O N B A Y C O M P L E X 17 F I E L D R E L A T I O N S H I P S 17 P E T R O G R A P H Y 18 i v P a g e S T R U C T U R E 20 E N V I R O N M E N T O F E M P L A C E M E N T 23 T O P L E Y S T A G E II 24 E N D A K O H O R N B L E N D E - B I O T I T E Q U A R T Z M O N Z O N I T E 24 F I E L D R E L A T I O N S H I P S 24 P E T R O G R A P H Y 25 S T R U C T U R E 32 T H E E N D A K O M O L Y B D E N U M D E P O S I T 3 5 S T R U C T U R E A N D M E T A L L I C M I N E R A L S 35 R O C K A L T E R A T I O N 36 F R A N C O I S H O R N B L E N D E - B I O T I T E G R A N I T E 37 F I E L D R E L A T I O N S H I P S 37 P E T R O G R A P H Y 37 S T R U C T U R E 42 R E L A T I O N B E T W E E N E N D A K O A N D F R A N C O I S I N T R U S I V E S 42 M O D E A N D E N V I R O N M E N T O F E M P L A C E M E N T O F T H E I N T R U S I V E S O F T O P L E Y S T A G E II 45 T O P L E Y S T A G E III 46 T H E G L E N N A N A N C O M P L E X 46 G E N E R A L D E S C R I P T I O N 46 P E T R O G R A P H Y 51 P o r p h y r i t i c H o r n b l e n d e - B i o t i t e G r a n i t e 51 G l o m e r o p o r p h y r i t i c F a c i e s of G r a n i t e 56 P o r p h y r i t i c H o r n b l e n d e - B i o t i t e Q u a r t z M o n z o n i t e 60 V P a g e P o r p h y r i t i c H o r n b l e n d e - B i o t i t e G r a n o d i o r i t e 65 D I S C U S S I O N O F T H E C H E M I C A L C O M P O S I T I O N A N D V A R I A T I O N 7 3 S T R U C T U R E 75 E N V I R O N M E N T O F E M P L A C E M E N T 77 O R I G I N O F P A R E N T M A G M A 78 D I F F E R E N T I A T I O N 80 T O P L E Y S T A G E I V 85 T H E C A S E Y B I O T I T E Q U A R T Z M O N Z O N I T E A L A S K I T E 85 F I E L D R E L A T I O N S H I P S 85 P E T R O G R A P H Y 86 S T R U C T U R E 91 E N V I R O N M E N T O F E M P L A C E M E N T 91 T O P L E Y S T A G E V 93 T H E S T E L L A K O H O R N B L E N D E - B I O T I T E M O N Z O N I T E 93 F I E L D R E L A T I O N S H I P S 93 P E T R O G R A P H Y 94 S T R U C T U R E 97 E N V I R O N M E N T O F E M P L A C E M E N T 98 T H E P O N D Q U A R T Z M O N Z O N I T E P L U G 99 T H E F R A S E R Q U A R T Z M O N Z O N I T E S T O C K 100 E N D A K O G R O U P O F V O L C A N I C S 102 S U M M A R Y A N D C O N C L U S I O N S 103 B I B L I O G R A P H Y 109 C o m p o s i t i o n of P u r i f i e d C r y p l o p e r t h i t e s ( V i s i b l e A l b i t e P a r t of P e r t h i t e Removed) of the T o p l e y I n t r u s i v e R o c k T y p e s as D e t e r m i n e d b y X - r a y a n a l y s i s M o d e s of the S i m o n B a y C o m p l e x , N o r t h of the Endako R i v e r ( A r m s t r o n g , 1949) Modes of the S i m o n B a y C o m p l e x , South of the Endako R i v e r M o d a l A n a l y s e s of the Endako I n t r u s i v e M o d a l A n a l y s e s of the F r a n c o i s I n t r u s i v e M o d a l A n a l y s e s of the Glennanan C o m p l e x R e c a l c u l a t e d M o d a l A n a l y s e s of the G l e n n a n a C o m p l e x C a l c u l a t e d C h e m i c a l A n a l y s i s of the Glennanan C o m p l e x f r o m M o d a l A n a l y s e s ( T a b l e VII) M o d a l A n a l y s e s of the C a s e y I n t r u s i v e M o d a l A n a l y s e s of the r o c k s of the S t e l l a k I n t r u s i v e I L L U S T R A T I O N S v i 1 M A P G e o l o g i c a l m a p of the E n d a k o A r e a B r i t i s h C o l u m b i a i n f o l d e r F i g u r e 1 7. R e g i o n a l d i s t r i b u t i o n of T o p l e y L n t r u s i v e s and l o c a t i o n of the Endako m a p a r e a Sketch m a p of L i n e a m e n t s n e a r the Endako o r e b o d y f r o m an a i r photograph ( C a r r , 1965) The M o d a l Q : A b : O r r a t i o s of the Endako q u a r t z m o n z o n i t e (O) and the F r a n c o i s g r a n i t e ( X ), c a l c u l a t e d f r o m T a b l e s I V and V The M o d a l Q : A b : O r r a t i o s of the Glennanan c o m p l e x , c a l c u l a t e d f r o m T a b l e V I S i m p l e s k e t c h showing s t r u c t u r a l o r i e n t a t i o n and z o n a l a r r a n g e m e n t of p l a g i o c l a s e ( P ) , h o r n b l e n d e (Hb), B i o t i t e (B) , q u a r t z (Q), sphene (S) and magnet i te i n m i c r o c l i n e m e g a c r y s t f r o m the g l o m e r o p o r p h y r i t i c f a c i e s of the Glennanan gran i te r o c k zone V a r i a t i o n d i a g r a m c o m p a r i n g the c u r v e s of the p r i n c i p l e ox ides of the Glennanan r o c k types (X) c a l c u l a t e d f r o m T a b l e VIII , w i t h those of 27 p i t chs tones and p e r l i t e s and 4 t r a c h y l i t e s (O) ( B o w e n , 1928, f i g . 38, p . 127) V a r i a t i o n d i a g r a m f o r the Glenannan c o m p l e x f r o m ( l ) g r a n o d i o r i t e , (2) q u a r t z m o n z o n i t e , to (3) gran i te p l o t t e d on the N a - C a - K ox ide t e r n a r y d i a g r a m ( c a l c u l a t e d f r o m T a b l e VIII) V a r i a t i o n d i a g r a m f o r the Glennanan c o m p l e x f r o m (1) g r a n o d i o r i t e , (2) q u a r t z m o n z o n i t e , to (3) gran i te p l o t t e d on the a l k - F e " + F e " - M g t e r n a r y d i a g r a m ( c a l c u l a t e d f r o m T a b l e VIII) P a g e 3 34 44 50 58 70 71 72 9 D i a g r a m a t i c s k e t c h showing a h y p o t h e t i c a l development of r o c k zones of the Glennanan C o m p l e x 82 F i g u r e 1; T e x t u r e of m e d i u m - g r a i n e d S i m o n B a y D i o l i t e , (P) p l a g i o c l a s e , (Q) q u a r t z , (B) b i o t i t e (x3 5, c r o s s e d n i c o l s ) F i g u r e 2; A n h e d r a l p o i k i l i t i c h o r n b l e n d e (Hb) and b io t i t e (B) i n t e r s t i t i a l to p l a g i o - c l a s e (P) i n S i m o n B a y d i o r i t e (x35, p l a i n l i g h t F i g u r e 1: P a t c h p e r t h i t i c i n t e r growths (P) i n the m i c r o c l i n e (M) of the E n d a k o q u a r t z m o n z o n i t e (x95, c r o s s e d n i c o l s ) F i g u r e 2: R e l i c p l a g i o c l a s e (P) g r a i n s i n m i c r o p e r t h i t e ( M ) . R o c k type i s Endako q u a r t z m o n z o n i t e (x45, c r o s s e d n i c o l s ) F i g u r e 1: M i c r o c l i n e conta in ing o r i e n t e d l a m e l l a e of e x s o l v e d a l b i t e . N o t e the s t r o n g u n d u l a t o r y a n h e d r a l q u a r t z of the Endako q u a r t z m o n z o n i t e (x35, c r o s s e d n i c o l s ) F i g u r e 2: S u b g r a p h i c habi t of q u a r t z (Q) and m i c r o c l i n e (M) i n the f i n e - g r a i n e d Endako q u a r t z m o n z o n i t e . N o t e p l a g i o c l a s e (P) i n c l u s i o n s i n q u a r t z (x90, c r o s s e d n i c o l s ) F i g u r e 1: I n t e r l o c k i n g r e l a t i o n of a n h e d r a l b i o t i t e (B) , q u a r t z (Q) p l a g i o c l a s e (P) and m i c r o c l i n e (M) i n the c o a r s e - g r a i n e d Endako q u a r t z m o n z o n i t e (x35, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of the f i n e - g r a i n e d Endako i n t r u s i v e near the contact w i t h the F r a n c o i s gran i te (xlOO, c r o s s e d n i c o l s ) F i g u r e 1: T e x t u r e of the F r a n c o i s gran i te n e a r c h i l l e d contact . (x lOO, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of the F r a n c o i s g r a n i t e i n c e n t r a l r e g i o n s of the i n t r u s i v e . Note the i n t e r - l o c k i n g g r a i n s of m i c r o c l i n e ( M ) , p l a g i o c l a s e (P) and q u a r t z fQ) , (x35, c r o s s e d n i c o l s ) F i g u r e 1: M i c r o p e r t h i t e r e p l a c i n g p l a g i o c l a s e (P) i n the Glennanan g r a n i t e . N o t e e u h e d r a l q u a r t z (Q) i n m i c r o p e r t h i t e (M) (xlOO, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of the Glennanan g r a n i t e n e a r c h i l l e d m a r g i n s . M i c r o p e r t h i t e (M) i s p a r t l y m a n t l e d h y p l a g i o c l a s e (P) , (x95, c r o s s e d n i c o l s ) F i g u r e 1: P o i k i o l i t i c m i c r o p e r t h i t e (M) c o n t a i n i n g s u b h e d r a l p l a g i o c l a s e (P) and e u h e d r a l quar ts (Q) c r y s t a l s (x35, c r o s s e d n i c o l s ) i n the Glennanan gran i te F i g u r e 2: F i n e l y g r a n u l a r q u a r t z (Q), m i c r o - c l i n e ( M ) , p l a g i o c l a s e (P) and b i o t i t e (B) i n c o a r s e - g r a i n e d g r o u n d m a s s of Glennanan gran i te (xlOO, c r o s s e d n i c o l s ) F i g u r e 1: O r i e n t e d i n c l u s i o n s of p l a g i o c l a s e (P) sphene (S) and unor iented e u h e d r a l q u a r t z (Q) i n p e r t h i t e m e g a c r y s t of Glennanan g l o m e r - o p o r p h y r i t i c gran i te (x45, c r o s s e d n i c o l s ) F i g u r e 2: Contac t between p e r t h i t e m e g a c r y s t and g r o u n d m a s s i n g l o m e r o p o r p h y r i t i c g r a n i t e . N o t e a n h e d r a l m i c r o c l i n e (M) and r o u n d q u a r t z (Q) g r a i n s n e a r edge of m e g a c r y s t (x45, c r o s s e d n i c o l s ) F i g u r e 1: Z o n a l p a t t e r n of a n h e d r a l q u a r t z o v e r g r o w t h s on e u h e d r a l q u a r t z c r y s t a l s i n m i c r o p e r t h i t e of the Glennanan q u a r t z m o n - zoni te (x3 5, c r o s s e d n i c o l s ) ' F i g u r e 2: e u h e d r a l q u a r t z (Q) c r y s t a l s w i t h a n h e d r a l o v e r g r o w t h s , i n the m i c r o c l i n e (M) of the Glennanan q u a r t z m o n z o n i t e (x450, c r o s s e d n i c o l s ) F i g u r e 1: E u h e d r a l q u a r t z c r y s t a l s i n m i c r o - p e r t h i t e and zoned p l a g i o c l a s e i n the Glennanan q u a r t z m o n z o n i t e (x35, c r o s s e d n i c o l s ) F i g u r e 2: I n t e r s t i t i a l habi t of q u a r t z (Q) and m i c r o c l i n e (M) i n the Glennanan g r a n o d i o r i t e (x lOO, c r o s s e d n i c o l s ) F i g u r e 1: E u h e d r a l sphene a s s o c i a t e d w i t h m a f i c m i n e r a l s i n Glennanan g r a n o d i o r i t e (x35, p l a i n l ight) F i g u r e 2: S u b h e d r a l h o r n b l e n d e (Hb) and b i o t i t e (B) i n Glennanan g r a n o d i o r i t e (x35, p l a i n l ight ) F i g u r e 1: A n h e d r a l and e u h e d r a l q u a r t z (Q) c r y s t a l s i n m i c r o c l i n e (M) w h i c h i s i n t e r s t i t i a l to p l a g i o c l a s e (P) i n the c h i l l e d zone of the C a s e y a l a s k i t e (xlOO, c r o s s e d n i c o l s ) F i g u r e 2: M i c r o c l i n e (M) i n t e r s t i t i a l to p l a g i o - c l a s e (P) and s u b h e d r a l to a n h e d r a l q u a r t z (Q) i n the c e n t r a l zone of the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e (x35, c r o s s e d n i c o l s ) F i g u r e 1: S a u s s u r i t i z e d s u b h e d r a l p l a g i o c l a s e (P) w i t h i n t e r s t i t i a l q u a r t z (Q) and m i c r o p e r t h i t e (M) i n the S te l lako q u a r t z m o n z o n i t e (xlOO, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of S te l l ako q u a r t z m o n z o n i t e Note a n h e d r a l b i o t i t e (B) and s u b h e d r a l p l a g i o - c l a s e (P) i n m i c r o p e r t h i t e ( M ) , (x35, c r o s s e d n i c o l s ) I N T R O D U C T I O N S C O P E O F I N V E S T I G A T I O N T h i s t h e s i s i s c o n c e r n e d w i t h the g e o l o g i c a l h i s t o r y of the T o p l e y b a t h o l i t h of B r i t i s h C o l u m b i a . The p a p e r i s a s tudy of the d i s t r i b u t i o n , p e t r o l o g y , m i n e r a l o g y and s t r u c t u r e of the v a r i o u s i n t r u s i v e p h a s e s . A s h o r t account of the a l t e r a t i o n and s u l f i d e m i n e r a l i z a t i o n at the Endako m i n e i s a lso i n c l u d e d . The v a r i o u s phases of the T o p l e y are shown on the a c c o m p a n y i n g g e o l o g i c a l m a p ( in f o l d e r ) . L O C A T I O N A N D A C C E S S I B I L I T Y The m a p a r e a l i e s 100 m i l e s wes t of P r i n c e G e o r g e , B r i t i s h C o l u m b i a . The town of E n d a k o , w h i c h i s s i tua ted on H i g h w a y 16 and on a b r a n c h l i n e of the C N . R . i s c e n t r a l l y l o c a t e d i n the a r e a . The Endako o p e n - p i t m o l y b d e n u m m i n e i s s i x m i l e s southwest of the town. The a r e a i s r e a d i l y a c c e s s i b l e b y three m a i n g r a v e l roads w h i c h connect H i g h w a y 16 w i t h the m i n e and m a n y r e s o r t s and p r i v a t e cottages along the n o r t h s h o r e of F r a n c o i s L a k e . N u m e r o u s s e c o n d a r y 2 roads w h i c h often r e q u i r e a f o u r - w h e e l dri\e v e h i c l e , t r a v e r s e the a r e a . P H Y S I O G R A P H Y The F r a n c o i s L a k e r e g i o n l i e s on the s o u t h e r n edge of the Nechako P l a t e a u p h y s i o g r a p h i c uni t , due east of the s o u t h e r n extent of the N e c h a k o P l a i n . "In the p l a t e a u p r o p e r , the v a l l e y s a r e b r o a d and the d i v i d e s are r o u n d e d h i l l s that r i s e 1500 to 2 500 feet above the v a l l e y f l o o r s ' 1 ( A r m s t r o n g , 1949)- The 100 s q u a r e m i l e m a p a r e a has i t s l e a s t and greates t e leva t ions at F r a n c o i s L a k e (2,197 feet) and N i t h i M o u n t a i n (4, 435 feet) r e s p e c t i v e l y . The p r o p o r t i o n of b e d r o c k exposed i n the a r e a i s e s t i m a t e d at about t h r e e p e r c e n t . G l a c i a l t i l l and f l u v i o - g l a c i a l g r a v e l s r e a c h t h i c k n e s s i n e x c e s s of 20 feet on the h i g h e r g r o u n d and p r o b a b l y m u c h g r e a t e r t h i c k n e s s i n the m a j o r v a l l e y s . D u r i n g the m a x i m u m deve lopment of the C o r d i l l e r a n g l a c i e r , the m o u n t - i c e - f i e l d s f l o w e d out onto the l o w - l y i n g N e c h a k o P l a t e a u and P l a i n . H e r e the l a r g e v a l l e y g l a c i e r s c o a l e s c e d and m o v e d i n a g e n e r a l l y e a s t e r l y and n o r t h e a s t e r l y d i r e c t i o n . The l a s t advance of the i c e was f o l l o w e d b y s tagnat ion, decay of the i c e - s h e e t s and the development of g l a c i a l l a k e s . " F r a n c o i s L a k e was d a m m e d b y s t a g - nant i c e at the southern foot of N i t h i M o u n t a i n and e m p t i e d into F r a s e r L a k e t h r o u g h a r o c k - c u t canyon i n i t s p r e s e n t s p i l l w a y , the S te l l ako R i v e r " ( C a r r , |<Us). A - l f . R G . S . C . M A P 9 3 2 A ( 2 n d t d . ) 4 A C K N O W L E D G E M E N T S The author i s indebted to D r . K . C . M c T a g g a r t , of the U n i v e r s i t y of B r i t i s h C o l u m b i a , who ac ted as s u p e r v i s o r f o r t h i s t h e s i s and o f f e r e d a d v i c e and e n c o u r a g e m e n t d u r i n g the p r e p a r a t i o n of th i s m a n u s c r i p t . A p p r e c i a t i o n i s a lso e x p r e s s e d to D r s . W . H . Whi te and A . J . S i n c l a i r of the U n i v e r s i t y of B r i t i s h C o l u m b i a , for t h e i r h e l p and guidance . S p e c i a l thanks are due to D r . M . J . C a r r of the 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 of M i n e s , who s u p e r v i s e d the author i n the c o u r s e of the f i e l d w o r k on w h i c h this t h e s i s i s b a s e d . H e k i n d l y a l l o w e d the author to use the government g e o l o g i c a l m a p s of the Endako a r e a as w e l l as a l a r g e c o l l e c t i o n of s p e c i m e n s and t h i n - s e c t i o n s . 5 G E N E R A L G E O L O G Y The T o p l e y plutons of B r i t i s h C o l u m b i a are r e p r e s e n t e d b y a dozen or m o r e phases of g r a n i t i c r o c k that m a k e up s e v e r a l c o m p o s i t e b o d i e s . O n the F o r t St. J a m e s m a p sheet ( A r m s t r o n g J . E . , 1949) 600 s q u a r e m i l e s of the s o u t h e r n p a r t of the a r e a a r e shown as u n d e r - l a i n b y T o p l e y o r s i m i l a r i n t r u s i v e s (see d i s t r i b u t i o n m a p , f i g . I) The T o p l e y r o c k s extend d i s c o n t i n u o u s l y f r o m B a b i n e L a k e to Q u e s n e l , a d is tance of about 180 m i l e s a long a n o r t h w e s t e r l y t r e n d . T h e y a r e shown i n t r u d i n g r o c k s of the C a c h e C r e e k G r o u p ( L o w e r P e n n s y l v a n i a n to U p p e r P e r m i a n ) , the T a k l a G r o u p (Upper T r i a s s i c to J u r a s s i c ) and as p a r t l y o v e r l a i n b y s t r a t a of the H a z e l t o n ( J u r a s s i c to L o w e r C r e t a c e o u s ) and younger g r o u p s . A r m s t r o n g (1949) was u n c e r t a i n about the contact r e l a t i o n between the T o p l e y p l u t o n i c r o c k s and the v o l c a n i c r o c k s of the T a k l a G r o u P > but c o n c l u d e d "the T o p l e y i n t r u s i o n s a r e p r o b a b l y of p r e - L o w e r C r e t a c e o u s age and a r e p o s s i b l y of p o s t M i d d l e P e r m i a n , p r e - U p p e r T r i a s s i c age" . R a d i o m e t r i c dates on b io t i t es f r o m the l a r g e T o p l e y i n t r u s i v e s (except the S i m o n B a y C o m p l e x ) i n the Endako A r e a of B r i t i s h C o l u m b i a (White , W . H . , 1966, 1967) group a r o u n d a date of 140 m i l l i o n y e a r s . ( M i d d l e J u r a s s i c ) . * W h i t e , W . H . , 1966, p e r s o n a l c o m m u n i c a t i o n 6 S i x l a r g e plutons and two m i n o r i n t r u s i v e s tocks c o m p r i s e a p p r o x i m a t e l y 90 p e r c e n t of the b e d r o c k i n the t h e s i s a r e a . A s m a l l a r e a of m e t a v o l c a n i c r o c k s a s s i g n e d to the T a k l a G r o u p ( A r m s t r o n g , 1949) o c c u r on the s o u t h - w e s t e r n edge of the T o p l e y c o m p l e x . A t the southwest m a r g i n of the m a p , the e a s t e r n edge of a l a r g e a r e a of f la t l y i n g l a v a f l o w s , of the Endako G r o u p ( O l i g i o c e n e or Eocene) , u n c o n - f o r m a b l y o v e r l y the T o p l e y r o c k s . O b s e r v a t i o n b y the author of the u n c o n f o r m i t y n e a r D r y W i l l i a m ' s L a k e , east of the m a p a r e a , d i s c l o s e d a deeply (up to 10 feet) w e a t h e r e d g r a n i t e s u r f a c e . I s o l a t e d o c c u r r e n c e s of the Endako G r o u p a r e a l so to be found i n the n o r t h - e a s t and s o u t h - east c o r n e r s of thearea. The g r a n i t i c r o c k s range f r o m d i o r i t e to a l a s k i t e . T h r e e q u a r t e r s of the a r e a , h o w e v e r , i s u n d e r l a i n b y q u a r t z m o n z o n i t e and g r a n d d i o r i t e . The d i v i s i o n s between g r a n o d i o r i t e , q u a r t z m o n z o n i t e and gran i te a r e made at the a r b i t r a r y b o u n d a r y r a t i o s of s o d i c o l i g i o c l a s e to t o t a l f e l d s p a r of, 1:3 and 2:3 r e s p e c t i v e l y . The d i v i s i o n between q u a r t z d i o r i t e and g r a n o d i o r i t e i s b a s e d on the anor th i te content of the p l a g i o - c l a s e , A n „ . to A n _ o J and A n , , to A n _ _ , r e s p e c t i v e l y . 3 0 50 10 29 E a c h p l u t o n tends to be l i t h o l o g i c a l l y homogeneous except for the zoned Glennanan c o m p l e x and the S i m o n B a y c o m p l e x . Contacts between the T o p l e y plutons a r e s e l d o m o b s e r v e d but l u c k i l y m o s t phases m a i n t a i n d i s t i n c t fea tures of t ex ture o r c o m p o s i t i o n on e i t h e r s ide of the contact zone. D i s t i n c t c r o s s - c u t t i n g r e l a t i o n s h i p s are shown o n l y b y the C a s e y and S te l lako q u a r t z m o n z o n i t e s (see g e o l o g i c a l m a p i n f o l d e r at b a c k ) . The deve lopment of th i s b a t h o l i t h i c c o m p l e x i n the Endako A r e a can be s u b d i v i d e d into f ive m a j o r stages of igneous a c t i v i t y . T h e s e stages a r e o u t l i n e d c h r o n o l o g i c a l l y f r o m o ldes t to youngest as f o l l o w s S T A G E I (1) S i m o n B a y c o m p l e x S T A G E II (1) Endako q u a r t z m o n z o n i t e (2) F r a n c o i s gran i te S T A G E III (1) Glennanan p o r p h y r i t i c g r a n i t e - q u a r t z m o n z o n i t e - grano dio r i t e c o m p l e x S T A G E I V (1) C a s e y q u a r t z m o n z o n i t e - a l a s k i t e S T A G E V ( 1 ) S te l lako q u a r t z m o n z o n i t e (2) F r a s e r and P o n d q u a r t z m o n z o n i t e The age of m i n o r i n t r u s i o n s of apl i te , dac i te , andesi te , d iabase q u a r t z m o n z o n i t e , and q u a r t z d i o r i t e w i t h r e s p e c t to the v a r i o u s stag? i s unknown. 8 M E T H O D S O F I N V E S T I G A T I O N F i e l d w o r k was done d u r i n g the s u m m e r of 1965, when the author was e m p l o y e d b y the 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 of M i n e s and P e t r o l e u m R e s o u r c e s . A d e t a i l e d b e d r o c k m a p of the a r e a south of the Endako R i v e r (see m a p i n pocket) was p r e p a r e d on a s c a l e , one i n c h to one m i l e . The author was p r o v i d e d w i t h h a n d s p e c i m e n s and d e t a i l e d i n f o r m a t i o n on the f i e l d r e l a t i o n s h i p s of the r o c k s n o r t h of the r i v e r , b y M . J . C a r r of the 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 of M i n e s . The a r e a c o v e r e d b y th is m a p i s a p p r o x i m a t e l y 100 s q u a r e m i l e s. L a b o r a t o r y s tudies i n c l u d e d the e x a m i n a t i o n of 48 t h i n - s e c t i o n s chosen as r e p r e s e n t a t i v e of the T o p l e y i n t r u s i v e s . F o r v e r y p o r p h y r i t i c s p e c i m e n s , two or m o r e t h i n sec t ions w e r e m a d e . T h e i r c o m p l e m e n t a r y hand s p e c i m e n s w e r e c h e c k e d f o r u n i f o r m i t y of t e x t u r e and c o m p o s i t i o n . The a p p r o x i m a t e m o d a l c o m p o s i t i o n s of the T o p l e y i n t r u s i v e s was c a l c u l a t e d f o r 29 s p e c i m e n s . B e c a u s e of the c o a r s e - g r a i n e d n a t u r e of s o m e of these i n t r u s i v e s , p a r t i c u l a r l y the Glennanan and E n d a k o , a p o i n t - c o u n t t h i n - s e c t i o n a n a l y s i s gave v e r y e r r o n e o u s r e s u l t s f o r the a l k a l i f e l d s p a r and m a f i c m i n e r a l content. In s u c h cases the modes of the m a j o r m i n e r a l s , 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 and q u a r t z w e r e c a l c u - l a t e d f r o m p o i n t - c o u n t s on p o l i s h e d hand s p e c i m e n s . The r o c k sec t ions 9 w e r e s t a i n e d w i t h c o b a l t i - n i t r a t e p r i o r to e x a m i n a t i o n . T h e p o i n t - count was p e r f o r m e d u s i n g g r i d s of v a r i o u s s i z e s d r a w n on g lass p l a t e s . The s p a c i n g of the g r i d l i n e s was d e t e r m i n e d b y the l a r g e s t g r a i n d i a m e t e r w i t h i n the hand s p e c i m e n under i n v e s t i g a t i o n . Wh en the h a n d - s p e c i m e n conta ined u n u s u a l l y l a r g e p h e n o c r y s t s ( a l a k l i f e l d s p a r ) , a g r i d s p a c i n g between the l a r g e s t g r a i n d i a m e t e r i n the g r o u n d m a s s and the p h e n o c r y s t s was u s e d . P e r t h i t i c i n t e g r o w t h s are v i s i b l e i n the f e l d - s p a r s conta ined i n the E n d a k o , F r a n c o i s and Glennanan i n t r u s i r e s . T h e r e was c o n s i d e r a b l e d i f f i c u l t y i n count ing th is m i n e r a l phase s e p a r - a te ly f r o m the host potash f e l d s p a r d u r i n g the p o i n t - c o u n t b e c a u s e : (1) t h e i r d i a m e t e r was s o m e t i m e s l e s s than the d i a m e t e r of the g r i d l i n e s ; and (2) s t r o n g s t a i n i n g of the a l k a l i f e l d s p a r b y c o b a l t i - n i t r a t e m a s k e d t h e i r p r e s e n c e . The modes of 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 and q u a r t z so obta ined w e r e then c o m b i n e d w i t h the m o d e s of the m a f i c m i n e r a l s and a c c e s s o r i e s f r o m t h i n - s e c t i o n p o i n t - c o u n t s i n c a l c u l c a t i n g the f i n a l mode of the whole r o c k . It was n e c e s s a r y d u r i n g th i s f i n a l c a l c u l a t i o n to i n c l u d e i n the f i n a l mode of the p l a g i o c l a s e the a p p r o x i m a t e amount of e x s o l v e d p l a g i o c l a s e i n the potash f e l d s p a r . The p r o p o r t i o n of e x s o l v e d p l a g i o c l a s e i n the m i c r o c l i n e of the Endako o r Glennanan i n t r u s i v e s v a r i e s f r o m 2 to 10 p e r c e n t w i t h i n a s ing le t h i n s e c t i o n . The p r e s e n c e of s m a l l i r r e g u l a r r e l i c t p r i m a r y p l a g i o c l a s e g r a i n s i n the p e r t h i t e caused a d d i t i o n a l d i s c r e p a n c i e s i n the m o d e s . The e r r o r 10 i n c a l c u l a t i n g the m o d e of m i c r o c l i n e c o u l d be as h i g h as 10 p e r c e n t i n the c o a r s e - g r a i n e d r o c k s of the Glennanan c o m p l e x w h i c h conta in e x c e p t i o n a l l y l a r g e p h e n o c r y s t s of p e r t h i t e . D E T E R M I N A T I O N O F T H E A L K A L I F E L D S P A R C O M - P O S I T I O N The c o m p o s i t i o n of c r y p t o p e r t h i t e s for the T o p l e y i n t r u s i v e s (see T a b l e I) was d e t e r m i n e d w i t h a P h i l l i p s 1963 m o d e l X - r a y d i f f r a c t o m e t e r w i t h a g o n i o m e t e r h e a d . T h i s m e t h o d i n v o l v e s the m e a s u r e m e n t of the angle between a k n o w n s t a n d a r d peak £ (101) r e f l e c t i o n of K B r O ^ 3 and the peak of the (201) r e f l e c t i o n of a l k a l i f e l d s p a r . The d i f f e r e n c e , A 2 Q = [ 29 (201) O r - 20 ( l O l ) K B r O j i s d i r e c t l y p r o p o r t i o n a l to the o r t h o e l a s e content. P a r s o n s (1965) p l o t t e d the A 2Q~ f o r 15 f e l d s p a r s f r o m f e l d s p a t h i c syeni te i n t r u s i o n s i n S c o t l a n d and found that they f e l l between the A 20 s t a n d a r d c u r v e s of the m i c r o c l i n e - l o w a lb i te s e r i e s ( O r v i l l e , I960 and S m i t h , 1956) and the s a n i dine - h i g h a lbi te s e r i e s ( O r v i l l e , 1963). The A 20 f o r the a l k a l i f e l d s p a r s i n th is s tudy w e r e p l o t t e d between these two p a r a l l e l p l o t s somewhat c l o s e r to the m i c r o c l i n e - l o w a lb i te l i n e w h i c h i s c h a r a c t e r i s t i c of the p l u t o n i c r o c k e n v i r o n m e n t ( S e l l m e r , 1966). N i n e s p e c i m e n s of penthite (Table I), w e r e p u r i f i e d f i r s t b y m a g n e t i c s e p a r a t i o n w i t h the F r a n z I s o d y n a m i c S e p a r a t o r and then each n o n - m a g n e t i c concentrate was p a s s e d t h r o u g h a s o l u t i o n of b r o m o - f o r m - m e t h y l h y d r a t e ( s p e c i f i c g r a v i t y 2.57 g m / c c ) . A l k a l i f e l d s p a r 11 f loats i n th is s o l u t i o n w h e r e a s p l a g i o c l a s e , q u a r t z and the n o n - m a g n e t i c a c c e s s o r i e s s i n k . The p u r i f i e d a l k a l i f e l d s p a r was heated i n an e l e c t r i c f u r n a c e at 920+ 20 degrees c e n t i g r a d e for 24 h o u r s to h o m o g e n i z e l o w a l b i t e - m i c r o c l i n e c r y p t o p e r t h i t e . The heated a l k a l i f e l d s p a r was m i x e d w i t h K B r O ^ (2:1 ra t io ) and m o u n t e d on a g lass s l i d e w i t h n a i l p o l i s h . T h i s m i x t u r e was then scanned o v e r a range of 20 = 19-60 degrees to 20 = 22. 20 degrees w i t h the X - r a y d i f f r a c t o m e t e r . It was a s s u m e d that a l l a lbi te was r e m o v e d d u r i n g the p u r i f i c a t i o n except the v e r y f ine c r y p t o p e r t h i f i c i n t e r g r o w t h s of a lb i te i n the m i c r o c l i n e . The author f o l l o w e d S e l m e r ' s (1966) d e t a i l e d out l ine of the o r i g i n a l p r o c e d u r e put f o r w a r d b y P h a i r and F i s h e r (1962). S e l l m a r (1966) u s i n g the s a m e equipment as the author i n th is s tudy c o n c l u d e d that the a c c u r a c y of h i s r e s u l t s was i n the o r d e r of + 5 p e r c e n t of O r . T A B L E I C O M P O S I T I O N O F P U R I F I E D C R Y P T O P E TIT H I T E S ( V I S I B L E A L B I T E P A R T O F P E R T H I T E R E M O V E D ) O F T H E T O P L E Y I N T R U S I V E R O C K T Y P E S A S D E T E R M I N E D B Y X - R A Y A N A L Y S I S R o c k Type W e i g h t % of O r (by X - R a y ) F i n e - g r a i n e d Endako q u a r t z m o n z o n i t e C o a r s e - g r a i n e d Endako q u a r t z m o n z o n i t e F i n e - g r a i n e d F r a n c o i s gran i te Glennanan g l o m e r o p o r p h y r i t i c f a c i e s at D r y W i l l i a m s L a k e 100 82 100 Glennanan gran i te 92 Glennanan g l u m e r o p o r p h y r i t i c f a c i e s on N i t h i M o u n t a i n 95 90 Glennanan q u a r t z m o n z o n i t e 88 Glennanan q u a r t z m o n z o n i t e 85 C a s e y a l a s k i t e 82 A p l i t e d ike cut t ing Glennanan grani te 85 12 C H E M I C A L A N A L Y S I S O F T H E T O P L E Y I N T R U S I V E S C A L C U L A T E D F R O M M O D A L A N A L Y S I S D r . A . J . S i n c l a i r of the ' D e p a r t m e n t of G e o l o g y , U n i v e r s i t y of B r i t i s h C o l u m b i a has adapted f o r the U . B . C . c o m p u t e r a p r o g r a m that p r o v i d e s an a p p r o x i m a t e l y c h e m i c a l c o m p o s i t i o n of a r o c k f r o m i t s m o d a l a n a l y s i s . The r e s u l t s obta ined f r o m t h i n - s e c t i o n and hand s p e c i m e n p o i n t - c o u n t s (see page 8 ) w e r e d i v i d e d into the f o l l o w i n g c o m p o n e n t s : o r t h o c l a s e , a lb i te , anor th i te , q u a r t z , b i o t i t e , h o r n b l e n d e , and the v a r i o u s a c c e s s o r y m i n e r a l s . The p r o p o r t i o n of a lb i te to anor th i te was c a l c u l a t e d f r o m the O r content of the c r y p t o p e r t h i t i c m i c r o c l i n e and the average A b : A n r a t i o s of the p l a g i o c l a s e i n the r o c k type . A c o m p o s i t i o n m o s t r e p r e s e n t a t i v e of the h o r n b l e n d e and b i o t i t e i n the r o c k type under e x a m i n a t i o n was chosen f r o m s t a n d a r d c h e m i c a l ana lyses w h i c h h a d b e e n adapted into the c o m p u t e r p r o g r a m . 13 T A K L A G R O U P D I S T R I B U T I O N A N D P E T R O G R A P H Y V o l c a n i c r o c k s a s s i g n e d to the T a k l a group ( A r m s t r o n g , 1949) a r e r e s t r i c t e d to a s i n g l e l o c a l i t y on the n o r t h s h o r e of F r a n c o i s L a k e , 3 m i l e s southwest of the Endako m i n e . T h e y c o v e r an a r e a of a p p r o x i m a t e l y t h r e e - q u a r t e r s of a s q u a r e m i l e , on the s o u t h e r n edge of the T o p l e y i n t r u s i o n s . The r o c k s a r e p o r p h y r i t i c dac i tes and q u a r t z l a t i t e f l o w s , tuf fs and b r e c c i a s . P h e n o c r y s t s of q u a r t z , b i o t i t e , white or p i n k p l a g i o - c l a s e o r o c c a s i o n a l l y p i n k p o t a s h f e l d s p a r o c c u r i n a g r e y - g r e e n to p u r p l e a p h a n i t i c m a t r i x . The r o c k s a r e f r a c t u r e d and h y d r o t h e r m a l l y a l t e r e d w i t h the p r o d u c t i o n of epidote , c h l o r i t e , p y r i t e , s p e c u l a r i t e and p o s s i b l y t o u r m a l i n e ( C a r r , 1965). S T R U C T U R E A N D A G E R E L A T I O N S H I P S The contact of the T a k l a r o c k s w i t h the F r a n c o i s g r a n i t e was not o b s e r v e d . The att i tude of the v o l c a n i c r o c k s i s a l so unknown. T h e y a r e f r a c t u r e d and h y d r o t h e r m a l l y a l t e r e d , but contact m e t a m o r p h i c affects a r e absent . To the wes t , the T a k l a r o c k s a r e o v e r l a i n b y a t h i c k 14 sequence of r e l a t i v e l y f l a t - l y i n g t e r t i a r y v o l c a n i c s of the Endako G r o u p . O n the F o r t St. J a m e s M a p Sheet ( A r m s t r o n g , 1949) the T o p l e y i n t r u s i v e s a r e shown i n t r u d i n g r o c k s of the T a k l a G r o u p ( U p p e r T r i a s s i c o r J u r a s s i c ) . In the t h e s i s a r e a , the T a k l a v o l c a n i c s a r e cut b y a 10 foot m e d i u m - g r a i n e d p i n k q u a r t z m o n z o n i t e p o r p h y r y r d i k e and the M e n a r d q u a r t z l a i t i t e p o r p h y r y s tock . The q u a r t z m o n z o n i t e dike i s p r o b a b l y r e l a t e d to one of the T o p l e y i n t r u s i v e s . 15 T H E M E N A R D Q U A R T Z L A T I T E P O R P H Y R Y S T O C K D I S T R I B U T I O N A N D P E T R O G R A P H Y A s m a l l s tock or p l u g w h i c h i n t r u d e s the T a k l a v o l c a n i c s , u n d e r l i e s an a r e a of about 100 a c r e s on the n o r t h s h o r e of F r a n c o i s L a k e , n e a r M e n a r d ' s r e s o r t . The r o c k i s a r e d o r p u r p l e q u a r t z l a t i t e p o r p h y r y . P e h n o c r y s t s c o m p r i s e up to 40 p e r c e n t of th i s aphani t i c r o c k . In o r d e r of abundance the p h e n o c r y s t s a r e p l a g i o c l a s e , b i o t i t e , q u a r t z , augite and h o r n b l e n d e ( C a r r , 1965). S u b h e d r a l p l a g i o c l a s e p h e n o c r y s t s a r e whi te o r f l e s h c o l o r e d . B i o t i t e f o r m s c h l o r i t i z e d p l a t e s or t h i c k books 1/2 c m . l o n g . Q u a r t z p h e n o c r y s t s a r e r o u n d o r k i d n e y shaped and augite and h o r n b l e n d e f o r m l o n g b l a c k p r i s m s . In t h i n s e c t i o n the aphani t i c m a t r i x i s c o m p o s e d of a g r a n u - l a r m i x t u r e of about 35% q u a r t z and 65% potash f e l d s p a r w i t h m i n o r patches of c h l o r i t e and epidote . S T R U C T U R E The i n t r u s i v e seems to be a s m a l l s tock e m p l a c e d i n the T a k l a v o l c a n i c s under n e a r - s u r f a c e c o n d i t i o n s . The contact w i t h the v o l c a n i c s was not o b s e r v e d . The stock i s cut b y a l t e r e d p o r p h y r i t i c r h y o l i t e , 16 q u a r t z l a t i t e d i kes and a m e d i u m g r a i n e d q u a r t z m o n z o n i t e p o r p h y r y dike w h i c h a lso cuts the T a k l a v o l c a n i c s . The n o r t h w e s t e r l y t r e n d of these d ikes i s the s a m e as that of m i n o r i n t r u s i o n s i n the o l d e r v o l c a n i c s . The s i m i l a r i t y of the m e d i u m - g r a i n e d q u a r t z m o n z o n i t e p o r p h y r y dike w i t h the r o c k types of the T o p l e y i n t r u s i v e s suggests a p r e - T o p l e y age for t h i s s tock and hence f o r the T a k l a v o l c a n i c r o c k s as w e l l . T O P L E Y S T A G E I T H E S I M O N B A Y C O M P L E X F I E L D R E L A T I O N S H I P S R e g i o n a l l y , the S i m o n B a y c o m p l e x f o r m s a w i d e b e l t of h y b r i d g n e i s s , a m p h i b o l i t e , f o l i a t e d d i o r i t e and q u a r t z d i o r i t e and m i n o r l e n s e s of gabbro , w h i c h extends f r o m Stuart L a k e (see f i g . 1) s o u t h - e a s t e r l y b e y o n d N i t h i M o u n t a i n . The n o r t h e a s t e r n and e a s t e r n m a r g i n of the T o p l e y c o m p l e x a r e bounded b y t h i s c o m p l e x to the n o r t h w e s t b e y o n d the m a p a r e a . T h i s t r e n d i s not too apparent i n the m a p a r e a i t s e l f b e c a u s e the S i m o n B a y c o m p l e x i s i n t r u d e d b y the Glennanan, C a s e y and S te l lako p l u t o n s . The S i m o n B a y c o m p l e x enters the m a p a r e a i n the n o r t h e a s t n e a r F r a s e r L a k e , w h e r e i t u n d e r l i e s an a r e a of a p p r o x i m a t e l y eight s q u a r e m i l e s . The c e n t r a l p a r t of t h i s a r e a i s o v e r l a i n b y v o l c a n i c r o c k s of the Endako G r o u p . I s o l a t e d e x p o s u r e s of d i o r i t e a r e to be found a lso on the f l a n k s of N i t h i M o u n t a i n south of the Endako R i v e r . The c o n t i n u i t y of these e x p o s u r e s i s i n t e r r u p t e d b y g r e a t expanses of d r i f t and a r e a s of younger i n t r u s i v e s . P E T R O G R A P H Y T h e t y p i c a l r o c k types of the S i m o n B a y c o m p l e x , n o r t h of the Endako R i v e r , a r e g r e e n , f ine to m e d i u m - g r a i n e d f o l i a t e d b i o t i t e - h o r n b l e n d e d i o r i t e w i t h m i n o r l e n s e s of d a r k g r e e n gabbro and l o c a l a r e a s of a l t e r n a t i n g d i o r i t e gne iss and a m p h i b o l i t e . The m o d e of these r o c k s i s shown i n tab le II, ( A r m s t r o n g , 1949). The author d i d not m a p the a r e a n o r t h of the E n d a k o R i v e r but h a n d s p e c i m e n s of these r o c k s and i n f o r m a t i o n r e g a r d i n g t h e i r f i e l d r e l a t i o n s h i p s w e r e p r o v i d e d b y M . J . C a r r ( 1 9 6 5 ) . T A B L E II M O D E S O F T H E S I M O N B A Y C O M P L E X , N O R T H O F T H E E N D A K O R I V E R ( A R M S T R O N G , 1949) G a b b r o D i o r i t e D i o r i t e P l a g i o c l a s e 69. 1 62 .5 4 0 . 8 A u g i t e 29. 1 B i o t i t e 33 .3 6 .1 H o r n b l e n d e - 2 . 2 49-7 Q u a r t z ~ t r 1.0 M a g n e t i t e 1.5 2 . 5 The t y p i c a l r o c k types of the S i m o n B a y c o m p l e x , south of the Endako R i v e r a r e b i o t i t e - h o r n b l e n d e d i o r i t e and l o c a l a r e a s of 19 g r a n o d i o r i t e n e a r the contact w i t h the younger S te l lako q u a r t z m o n z o n i t e . A p r i m a r y f o l i a t i o n i s shown b y a s u b p a r a l l e l o r i e n t a t i o n of the b i o t i t e and h o r n b l e n d e . The t r e n d and a l i g n m e n t of m a f i c s w i t h i n l o c a l a r e a s of gneiss and a m p h i b o l i t e p a r a l l e l the f o l i a t i o n of the d i o r i t e . D a r k f i n e - g r a i n e d a n g u l a r o r l e n t i c u l a r i n c l u s i o n s of a m p h i b o l i t e a r e c o m m o n . T A B L E H I M O D E S O F T H E S I M O N B A Y C O M P L E X , S O U T H O F T H E E N D A K O R I V E R 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 Q u a r t z B i o t i t e H a r t m a n ' s H i l l M o u s e P o i n t M u d h o l e D i o r i t e G r a n o d i - L a k e Gran« o r i t e o d i o r i t e t r a c e 9-6 15 .8 59 .5 6 3 . 4 54 .8 4 . 0 6 .2 12 .2 2 .1 3 .1 9 . 5 H o r n b l e n d e 31 .1 15.0 5 .2 M a g n e t i t e 2 . 2 3 .0 2 . 5 In t h i n - s e c t i o n the d i o r i t e c o n s i s t s of abundant s u b h e d r a l p l a g i o c l a s e , s u b h e d r a l to a n h e d r a l dark b r o w n b i o t i t e and g r e e n h o r n - b lende w i t h m i n o r i n t e r s t i t i a l q u a r t z and o c c a s i o n a l l y s m a l l patches 20 of i n t e r s t i t i a l m i c r o p e r t h i t e . M o s t p l a g i o c l a s e i s andes ine ( A n to A n ) hut i t r a n g e s f r o m s o d i c o l i g i o c l a s e to l a b r a d o r i t e . The 3 o p l a g i o c l a s e d i s p l a y s n o r m a l zoning but i s f a i n t l y o s c i l l a t o r y zoned i n the g r a n o d i o r i t e at M u d h o l e L a k e . M y r m e k i t e o c c u r s a l o n g s o m e contacts be tween p l a g i o c l a s e and m i c r o p e r t h i t e i n the g r a n o d i o r i t e . I n t e r s t i t i a l m i c r o p e r t h i t e p o r k i l i t i c a l l y e n c l o s e s i n c l u s i o n s of p l a g i o - c l a s e , h o r n b l e n d e , b i o t i t e o r o c c a s i o n a l l y q u a r t z . G r e e n h o r n b l e n d e o c c u r s as p r i s m a t i c c r y s t a l s o r r a g g e d l y t e r m i n a t e d g r a i n s c o n t a i n i n g i n c l u s i o n s of q u a r t z , m a g n e t i t e , apat i te o r o c c a s i o n a l l y p l a g i o c l a s e . P o i k i l i t i c b r o w n - r e d d i s h b r o w n b i o t i t e f o r m s d i s c r e t e c r y s t a l s or aggregates and i n t e r g r o w t h s w i t h h o r n - b l e n d e . A c c e s s o r i e s i n c l u d e apat i te , m a g n e t i t e , sphene and p y r i t e . The r o c k s of the S i m o n B a y c o m p l e x , i n g e n e r a l a r e s t r o n g l y s h e a r e d and a l t e r e d w i t h the p r o d u c t i o n of a c t i n a l i t e , c h l o r i t e , epidote , l e u c o x e n e , p y r i t e and i r o n o x i d e s . S T R U C T U R E The contact of the S i m o n B a y c o m p l e x w i t h the o l d e r c o u n t r y r o c k l i e s b e y o n d the m a p a r e a and was not o b s e r v e d b y the author . F o l i a t i o n i s v i s i b l e i n the S i m o n B a y d i o r i t e as p a r a l l e l a r r a n g e m e n t of b i o t i t e f l a k e s , p r i s m a t i c h o r n b l e n d e , m a f i c c lots and i n c l u s i o n s . Its a s s o c i a t i o n w i t h the i n t e r l o c k i n g t e x t u r e of the f e l d s p a r and q u a r t z P L A T E I T e x t u r e of m e d i u m - g r a i n e d S i m o n B a y d i o r i t e , (P) p l a g i o c l a s e , (Q) Q u a r t z , (B) B i o t i t e . (X35, c r o s s e d n i c o l s ) A n h e d r a l p o i k i l i t i c h o r n b l e n d e (Hb) and b i o t i t e (B I n t e r s t i t i a l to p l a g i o c l a s e (P) i n S i m o n B a y d i o r i t (X35, p l a i n l i g h t ) . suggests a p r i m a r y o r i g i n i n s h e a r e d and u n s h e a r e d e x p o s u r e s . The l o c a l a r e a s of g n e i s s , a m p h i b o l i t e and gabbro , p a r t i c u l a r l y n o r t h of the Endako R i v e r , whose t r e n d g e n e r a l l y c o n f o r m s to the f o l i a t i o n , suggests the p o s s i b i l i t y of an i n h e r i t e d f o l i a t i o n due to g r a n i t i z a t i o n of the c o u n t r y r o c k . W h e r e the S i m o n B a y c o m p l e x has b e e n cut b y the S te l lako q u a r t z m o n z o n i t e , the w a l l r o c k s have b e e n sub jec ted to p o t a s h m e t a s o m a t i s m . The f o l i a t i o n of the S i m o n B a y c o m p l e x i n g e n e r a l c o n f o r m s to the r e g i o n a l n o r t h w e s t t r e n d of the b e l t of T o p l e y i n t r u s i o n s ( f i g . 1). N e a r A l f L a k e , D e s e r t e r L a k e and N o r t h w a r d b e y o n d the m a p b o u n d a r y , the f o l i a t i o n i s s t e e p l y i n c l i n e d and s t r i k e s n o r t h w e s t e r l y , w e s t e r l y and n o r t h e a s t e r l y . T h r e e m i l e s to the east of A l f L a k e at S i m o n B a y , the f o l i a t i o n changes to an e a s t - w e s t d i r e c t i o n but south of F r a s e r L a k e , the t r e n d swings b a c k to the n o r t h - n o r t h e a s t . T h i s t r e n d i s m a i n t a i n e d i n the i s o l a t e d e x p o s u r e s of the c o m p l e x as f a r south as N i t h i M o u n t a i n , w h e r e i t aga i n swings to an e a s t e r l y d i r e c t i o n , southwest of M a r y L a k e . The v a r i a t i o n of the f o l i a t i o n d i r e c t i o n , south of the Endako R i v e r m a y p o s s i b l y be the r e s u l t of the s h i f t i n g of l a r g e b l o c k s of S i m o n B a y d i o r i t e d u r i n g the e m p l a c e m e n t of the i n t r u s i v e s of stage II to I V . T h i s f o l i a t i o n does not appear to be the r e s u l t of s h e a r i n g i n these a r e a s . E N V I R O N M E N T O F E M P L A C E M E N T A m e s o z o n a l depth of e m p l a c e m e n t i s i n d i c a t e d b y ; (1) the p r i m a r y f o l i a t i o n of the S i m o n B a y d i o r i t e ; (2) a l i g n m e n t of s c r e e n s of a m p h i b o l i t e , gneiss and gabbro ; and (3) the g e n e r a l t r e n d of the S i m o n B a y c o m p l e x n o r t h of the Endako R i v e r w h i c h c o n f o r m s to the r e g i o n a l t r e n d of the T o p l e y p l u t o n s . The ev idence , h o w e v e r , i s i n c o n c l u s i v e and does not r u l e out a m o r e deep seated e n v i r o n m e n t of e m p l a c e m e n t or p o s s i b l y an o r i g i n b y g r a n i t i z a t i o n i n s i t u . 24 T O P L E Y S T A G E II E N D A K O H O R N B L E N D E - B I O T I T E Q U A R T Z M O N Z O N I T E F I E L D R E L A T I O N S H I P S T h e Endako q u a r t z m o n z o n i t e f o r m s a r e g u l a r b e l t a v e r a g i n g t h r e e m i l e s w i d e , w h i c h extends f r o m the S t e l l a k o R i v e r , w e s t - n o r t h - w e s t w a r d f o r at l e a s t n ine m i l e s . T h i s i n t r u s i v e , w h i c h conta ins the Endako m o l y b d e n u m depos i t , i s bounded on the south b y the younger F r a n c o i s g r a n i t e and o n the n o r t h b y the younger C a s e y q u a r t z m o n - zoni te and i n p a r t b y the Glennanan g r a n i t e . The s o u t h e a s t e r n e x t e n s i o n of t h i s b e l t m a y be t r u n c a t e d b y the S t e l l a k o q u a r t z m o n z o n i t e , east o f the S te l lako R i v e r s i n c e i t does not r e a p p e a r i n the m a p a r e a . T o the n o r t h w e s t , the Endako q u a r t z m o n z o n i t e i s c o v e r e d b y s e d i m e n t s of the E n d a k o R i v e r f l o o d p l a i n . Thecontac t of the E n d a k o q u a r t z m o n z o n i t e w i t h m o s t of the o ther p lutons i n the E n d a k o a r e a , was not seen bvjtthe abruptness of the t e x t u r a l and m i n e r a l o g i c a l changes f r o m one to the o ther , a ids i n d e t e r m i n i n g i t s p o s i t i o n . X e n o l i t h s of f ine g r a i n e d dark g r e y q u a r t z d i o r i t e , r i c h i n b i o t i t e , a r e abundant p a r t i c u l a r l y a long the S te l lako R i v e r . T h e y o c c u r as r o u n d e d r e s o r b e d bodies and i r r e g u l a r m a f i c c lots r a n g i n g i n s i z e f r o m 1 to 4 c m . o r , l e s s c o m m o n l y , a s l e n t i c u l a r f r a g m e n t s one foot 25 or m o r e i n l ength n e a r the S te l l ako R i v e r . P E T R O G R A P H Y The t y p i c a l r o c k of the E n d a k o i n t r u s i v e i s a p i n k i s h - g r e y m e d i u m - g r a i n e d h y p i d i o m o r p h i c g r a n u l a r o r o c c a s i o n a l l y s u b p o r p h y r i t i c h o r n b l e n d e . - b i o t i t e q u a r t z m o n z o n i t e . A r e a s i n the n o r t h e a s t e r n p a r t of the i n t r u s i v e w h e r e i t i s i n t r u d e d b y the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e a r e g r a n i t e . T h i s v e r y g r a d i t i o n a l v a r i a t i o n i s a f u n c t i o n of i n c r e a s i n g p o t a s h f e l d s p a r a lone . S u b h e d r a l r e d p e r t h i t i c f e l d s p a r c r y s t a l s w h i c h m a y exceed lengths of 1 c. m . i n the g r a n i t e , i m p a r t a s u b p o r p h y r i t i c t e x t u r e to the r o c k . W i t h d e c r e a s i n g s i z e and content of p e r t h i t e , the Endako i n t r u s i v e i s an e q u i g r a n u l a r q u a r t z m o n z o n i t e i n w h i c h a few p h e n o c r y s t s of p lagiofc lase , q u a r t z and p e r t h i t e c a n s t i l l be found. The l a c k of e x p o s u r e s p r e v e n t e d the d r a w i n g of b o u n d a r i e s between these v a r i a t i o n s . P e r t h i t e , q u a r t z , b i o t i t e and h o r n b l e n d e a r e i n t e r s t i t i a l to p l a g i o c l a s e . B i o t i t e f o r m s h e x a g o n a l b o o k s , t h i n p la tes and i r r e g u l a r c l u s t e r s . H o r n b l e n d e o c c u r s as a n h e d r a l to p r i s m a t i c g r a i n s or aggregates w i t h b i o t i t e . The modes of the r o c k s of the Endako i n t r u s i v e a r e shown i n T a b l e I V . In t h i n - s e c t i o n , the l a r g e r g r a i n s of m i c r o c l i n e m i c r o p e r t h i t e have a g e n e r a l e n h e d r a l f o r m though t h e i r b o u n d a r i e s a r e i r r e g u l a r T A B L E I V M O D A L A N A L Y S E S O F T H E E N D A K O I N T R U S I V E E G B - 4 E G B - 8 5 E G B - 1 4 E N - 1 7 4 E G B - 1 1 E N - 1 7 5 E N - S T E L L A E N - 5 E N - 1 7 3 M i c r o l i n e 54. 9 P l a g i o c l a s e * 25 .9 Q u a r t z 14. 5 B i o t i t e 2. 2 H o r n b l e n d e 1. 3 Magnet i te 0. 5 Sphene ' 0 .8 A p a t i t e t r . 51. 1 31. 1 14. 3 1. 0 0. 4 1. 0 t r . t r . 50. 1 28. 4 14. 7 3. 0 2. 0 1. 2 t r . t r . 40. 8 36. 4 16.6 4. 0 1.0 1.8 1. 3 t r . 43.3 28.6 21. 6 2. 5 0. 8 0. 6 0.5 t r . 45 . 9 26. 6 17. 7 3. 5 2. 0 1. 5 1.2 t r . 46. 9 4 . 6 40. 3 7. 1 0. 5 1. 0 t r . t r . 43 . 0 18. 0 32. 0 4. 0 1. 0 1. 0 t r . t r . 34. 7 41 . 9 15. 4 4 . 5 2. 0 1. 0 0. 5 t r . C o m p o s i t i o n of p l a g i o c l a s e i s A n ^ g to A n C o m p o s i t i o n of c r y p t o p e r t h i t e m i c r o c l i n e i s O r g g P L A T E II 27 F i g u r e 2: R e l i c p l a g i o c l a s e (P) g r a i n s i n m i c r o p e r t h i t e (M) R o c k types i s E n d a k o q u a r t z m o n z o n i t e . ( x 4 5 , c r o s s e d n i c o l s ) 28 and p o i k i l i t i c a l l y enc lose a l l the other m i n e r a l s . M o r e c o m m o n l y , m i c r o c l i n e f o r m s a n h e d r a l p o i k i o l i t i c g r a i n s i n t e r s t i t i a l to p l a g i o - c l a s e (plate II, f i g . 2). M i c r o p e r t h i t i c t e x t u r e s that range f r o m f ine f i l m s to i r r e g u l a r n e t w o r k s of s t r i n g e r s and v e i n s ( b r a i d per th i te ) and c o a r s e i r r e g u l a r patches ( E m m o n s , 1953) m a y b e o b s e r v e d w i t h i n a s i n g l e g r a i n of m i c r o c l i n e . T h e n p l a g i o c l a s e l a m e l l a e (plate III, f i g . 1) the l e a s t abundant f o r m of p e r t h i t e a r e o r i e n t e d p a r a l l e l to the (010) c leavage d i r e c t i o n i n the m i c r o c l i n e ; o r i e n t a t i o n s i n the (001) c leavage d i r e c t i o n a r e l e s s c o m m o n . P l a g i o c l a s e i n v e i n p e r t h i t e (plate III, f i g . -2) o c c u r s as l o n g n a r r o w b r a n c h i n g s t r i n g e r s w h i c h o v e r l a p i n p a r t but g e n e r a l l y a r e e longated i n the same d i r e c t i o n as f i l m p e r t h i t e . The g r a d a t i o n a l na ture of the r e g u l a r l y o r i e n t e d f i l m and b r a i d p e r t h i t i c i n t e r g r o w t h s suggests an e x s o l u t i o n o r i g i n . P l a g i o - c l a s e i n v e r y c o a r s e v e i n s a n d i r r e g u l a r patches (plate II, f i g . 1) i s d i s t r i b u t e d e q u a l l y throughout the host m i c r o c l i n e and c r o s s - c u t s the o r i e n t e d s t r i n g e r s and l a m e l l a e . T h e s e f o r m s of p e r t h i t e a r e l o c a l l y c o n t r o l l e d b y the s t r u c t u r e of the hos t . The patches and ve ins are c o a r s e enough i n p l a c e s to show p o l y s y n t h e t i c t w i n n i n g , h o w e v e r , the i n d i v i d u a l t w i n l a m e l l a e can not be t r a c e d f r o m one a r e a to the i m m e d i a t e l y adjacent one. A r e p l a c e m e n t o r i g i n f o r the c o a r s e v e i n and p a t c h p e r t h i t e i s i n d i c a t e d , thoughtthey m a y have been c o n t r o l l e d p a r t l y b y e a r l y e x s o l u t i o n p e r t h i t e . P L A T E III M i c r o c l i n e c o n t a i n i n g o r i e n t e d l a m e l l a e of e x s o l v e d a l b i t e . Note the s t r o n g u n d u l a t o r y a n h e d r a l q u a r t z of E n d a k o q u a r t z m o n z o n i t e (x35, c r o s s e d n i c o l s ) Subgraphic habit of q u a r t z (A) and m i c r o c l i n e (M) i n the f i n e - g r a i n e d E n d a k o q u a r t z m o n z o m t Note p l a g i o c l a s e (P) i n c l u s i o n s i n q u a r t z . (x90, c r o s s e d n i c o l s ) 30 E u h e d r a l to s u b h e d r a l n o r m a l l y zoned p l a g i o c l a s e ranges i n c o m p o s i t i o n f r o m A n ^ g to An^^. Some l a r g e g r a i n s show o s c i l l a t o r y zoning i n the c o r e a r e a s but r e v e r t to a n o r m a l t r e n d near the r i m s . C o r r o d e d p l a g i o c l a s e b o r d e r s and m y r m e k i t e are abundant a long the contacts b e t w e e n m i c r o c l i n e and p l a g i o c l a s e (plate I V , f i g . Z) . C l u s t e r s of s m a l l v e r y i r r e g u l a r g r a i n s of p l a g i o c l a s e i n m i c r o c l i n e (plate II, f i g . Z) a r e the r e s u l t of t h e i r advanced r e p l a c e m e n t b y the hos t . In the c o a r s e - g r a i n e d Endako q u a r t z m o n z o n i t e , q u a r t z o c c u r s as i r r e g u l a r , i n t e r s t i t i a l g r a i n s w i t h s t r o n g u n d u l a t o r y e x t i n c t i o n (plate III, f i g . 1). Q u a r t z i n the f i n e r - g r a i n e d r o c k s b o r d e r i n g on the c h i l l e d zone of the F r a n c o i s gran i te o c c u r s as i n t e r s t i t i a l g r a i n s w h i c h i n p l a c e s a r e g r a p h i c a l l y i n t e r g r o w n w i t h m i c r o c l i n e m i c r o p e r t h i t e (plate III, f i g . Z). Q u a r t z enc lose p l a g i o c l a s e , b i o t i t e , h o r n b l e n d e and a c c e s s o r y m i n e r a l s . F i n e l y g r a n u l a r q u a r t z and f e l d s p a r have been i n t r o d u c e d a long f r a c t u r e s and g r a i n b o u n d a r i e s of the p r i m a r y m i n e r a l s , i n s p e c i m e n s e x a m i n e d n e a r the Endako o r e body . P o i k i o l i t i c r a g g e d laths or s u b h e d r a l g r a i n s of b i o t i t e e n c l o se g r a i n s of s p h e r e , apati te magnet i te and b r o w n h o r n b l e n d e . B i o t i t e f o r m s r i m s a r o u n d and i n t e r growths w i t h h o r n b l e n d e and has the f o l l o w i n g p l e o c h r o i c s c h e m e : X , pa le g r e e n ; Y g r e e n i s h b r o w n ; Z , m e d i u m b r o w n . C l u s t e r s of s t r a w y e l l o w to p a l e g r e e n b i o t i t e , c a l c i t e and epidote a r e s e c o n d a r y after h o r n b l e n d e . P L A T E IV I n t e r l o c k i n g r e l a t i o n of a n h e d r a l b io t i t e (B) q u a r t z (Q) p l a g i o c l a s e (P) and m i c r o c l i n e (M) i n the c o a r s e - g r a i n e d E n d a k o q u a r t z m o n z o n i t e (x35, c r o s s e d n i c o l s ) T e x t u r e of the f ine g r a i n e d Endako i n t r u s i v e near the contact w i t h the F r a n c o i s g r a n i t e . (x lOO, c r o s s e d n i c o l s ) 32 Sphene, magnet i te and apati te a r e the m o s t abundant a c c e s s o r i e s i n th i s r o c k . Sphene f o r m s r h o m b i c c r y s t a l s and aggregates w i t h m a g n e t i t e , apatite and b i o t i t e . I l l m e n i t e o c c u r s as i n c l u s i o n s i n sphene, i n t e r g r o w t h s w i t h magnet i t e o r as d a r k r e d d i s h b r o w n s k e l e t a l c r y s t a l s . A p a t i t e f o r m s e u h e d r a l c r y s t a l s and c l u s t e r s of s m a l l c r y s t a l s of r u t i l e and p y r i t e a r e p r e s e n t . P y r i t e i s m o s t l i k e l y the r e s u l t of d e u t e r i c or h y d r o t h e r m a l a l t e r a t i o n . O u t s i d e of the i m m e d i a t e E n d a k o m i n e a r e a , the a l t e r a t i o n f o r the m o s t p a r t i s r e s t r i c t e d to the m a f i c m i n e r a l s of the E n d a k o q u a r t z m o n z o n i t e . In s t r o n g l y s h e a r e d and f r a c t u r e d e x p o s u r e s : (1) h o r n b l e n d e i s c h l o r i t i z e d ; (2) sphene i s a l t e r e d to f i n e r g r a n u l a r l e u c o x e n e ; and (3) i n t e r g r o w t h s of c h l o r i t e , s e r i c i t e , c a l c i t e and i r o n o r e f o r m p s u e d o m o r p h s a f ter b i o t i t e . P l a g i o c l a s e i s s t r o n g l y s a u s s u r i t i z e d and m i c r o c l i n e i s c h a r g e d w i t h k a o l i n i t e ( ? ) . S T R U C T U R E E v i d e n c e of w i d e s p r e a d f a u l t i n g w h i c h d i d not p r o d u c e r e c o g - n i z a b l e of fsets i s seen i n the s h e a r e d , f r a c t u r e d and a l t e r e d na ture of m a n y o u t c r o p s , p a r t i c u l a r l y near the E n d a k o m i n e . K n o w n f a u l t s , s h e a r s , d ikes and contacts c o i n c i d e c l o s e l y w i t h w e s t - n o r t h w e s t and nor theas t l i n e a m e n t s (see m a p i n f o l d e r ) . F r o m a i r p h o t o g r a p h s , a n e t w o r k of c l o s e l y s p a c e d m a j o r l i n e a r s c a n be d i s c e r n e d ( f i g . 2) i n the i m m e d i a t e m i n e a r e a . S ince some of these l i n e a r s do c o r r e s p o n d to f a u l t s , s h e a r s and d i k e s , m a n y of the o thers m a y a lso m a r k s u c h f e a t u r e s . The n o r t h e a s t e r l y l i n e a m e n t s appear to of fset the w e s t - n o r t h w e s t e r l y set w h i c h p a r a l l e l the contacts of the Endako i n t r u s i v e . G e o l o g i c a l m a p p i n g w i t h i n the Endako o r e body ( K i m u r a , 19.66) d i s c l o s e s the s a m e s t r u c t u r a l p a t t e r n i n p l a c e s , but not of the s a m e o r d e r of m a g n i t u d e . T h e s e m a j o r s t r u c t u r a l e lements are e a s i l y t r a c e a b l e on a i r photographs o v e r l a r g e d is tances w i t h i n the Endako and F r a n c o i s i n t r u s i v e s but a r e often vague or undetectable when sought i n the younger i n t r u s i o n s . D i s c o r d a n t p lutons and d ikes do h o w e v e r m a r k t h e i r p r e s e n c e i n the younger p l u t o n s . The contacts of the E n d a k o q u a r t z m o n z o n i t e w i t h the o l d e r S i m o n B a y c o m p l e x o r m o s t of the younger i n t r u s i v e s w e r e not o b s e r v e d b y the author . The c h i l l e d m a r g i n of the C a s e y q u a r t z m o n z o n i t e was o b s e r v e d adjacent to un c o n t a m i n a t e d s h e a r e d Endako q u a r t z m o n z o n i t e i m m e d i a t e l y south of h i g h w a y 16. The Endako i n t r u s i v e p r o g r e s s i v e l y d e c r e a s e s i n g r a i n s i z e t o w a r d s the c h i l l e d contact of the younger F r a n c o i s g r a n i t e , southwest of the Endako m i n e . A weak n o r t h e r l y p l a n a r o r i e n t a t i o n of the xeno l i ths was o b s e r v e d a long p a r t s of the S te l lako R i v e r . The ex tens ion of the Endako i n t r u s i v e to the southeast m a y cut the e a s t - w e s t fol iat ion, of the S i m o n B a y c o m p l e x on N i t h i M o u n t a i n .  35 E N D A K O M O L Y B D E N U M D E P O S I T S T R U C T U R E A N D M E T A L L I C M I N E R A L S The E n d a k o o r e depos i t o c c u r s w h o l l y w i t h i n the Endako i n t r u s i v e n e a r the j u n c t i o n of a c l o s e n e t w o r k of w e s t - n o r t h w e s t e r l y and n o r t h e a s t e r l y t r e n d i n g faul ts and l i n e a m e n t s . T h i s a r e a has been p a r t i c u l a r l y s u s c e p t i b l e to in tense and continuous f r a c t u r i n g and l o c a l b l o c k f a u l t i n g . In the m i n e a r e a the Endako q u a r t z m o n z o n i t e has been i n t r u d e d b y p r e - m i n e r a l a p l i t e , p o r p h y r i t i c gran i te d ikes and b r o w n to p ink q u a r t z f e l d s p a r p r o p h y r y dikes as w e l l as p o s t - m i n e r a l l a m p r o p h y r e and diabase d i k e s . The b r o w n p o r p h y r y dikes a r e not found e l s e w h e r e i n the m a p a r e a . The o r e b o d y s t r i k e s S 6 0 ° E , dips 2 0 ° to 5 0 ° south, and m e a s u r e s 5, 500 feet l o n g b y 1, 200 feet wide ( K i m u r a , 1966). M a r g i n s are a r b i t r a r i l y d e t e r m i n e d b y a s s a y cutof fs . M o l y b d e n i t e and p y r i t e a r e the m a j o r m e t a l l i c m i n e r a l s w i t h m i n o r amounts of h e m a t i t e and magnet i t e and t r a c e amounts of c h a l c o p y r i t e . M i n e r a l i z a t i o n i s of two t y p e s . The m o s t p r o m i n e n t m i n e r a l i z a t i o n i s a s e r i e s of q u a r t z - m o l y b d e n i t e v e i n s , continuous over s e v e r a l h u n d r e d feet and r a n g i n g i n widths f r o m a few inches to as m u c h as f ive feet. T h e s e p a r a l l e l v e i n s m o s t l y s t r i k e east and n o r t h of east and dip s o u t h w a r d at 45 d e g r e e s . The second type of m i n e r a l i z a t i o n c o n s i s t s of a s t o c k w o r k of n a r r o w q u a r t z - m o l y b d e n i t e v e i n s and f r a c t u r e f i l l i n g s adjacent to and s u r r o u n d i n g the m a i n v e i n n e t w o r k . A p y r i t e ha lo conta in ing n a r r o w b a r r e n q u a r t z f r a c t u r e f i l l i n g s i s r e p o r t e d on the south s ide of the o r e b o d y . The m i n e geo log is t s ( K i m u r a , 1966) have d e t e r m i n e d t h r e e d i s t i n c t phases of h y d r o t h e r m a l a l t e r a t i o n i n the o r e zone: R O C K A L T E R A T I O N (a) the deve lopment of p o t a s h f e l d s p a r and s e c o n d a r y b i o t i t e envelope adjacent to the ve ins and f r a c t u r e s . (b) a second, l e s s c o m m o n m i x t u r e of f ine q u a r t z , s e r i c i t e and p y r i t e adjacent to v e i n s and f r a c t u r e s . (c) a p e r v a s i v e k a o l i n i z a t i o n of the host r o c k i n s e v e r a l degrees of i n t e n s i t y . In the m o s t in tense phase , p o t a s h f e l d s p a r s ta r t s to b r e a k down to k a o l i n i t e , b i o t i t e i s c h l o r i t i z e d and p l a g i o c l a s e i s c o m p l e t e l y b r o k e n down to a g r e a s y g r e e n i s h m i x t u r e of c l a y m i n e r a l s . Some s e c o n d a r y b l a c k b i o t i t e i s a l so p r o d u c e d at t h i s s tage. 37 F R A N C O I S H O R N B L E N D E - B I O T I T E G R A N I T E F I E L D R E L A T I O N S H I P S The F r a n c o i s g r a n i t e o c c u r s as a r e g u l a r b o d y w h i c h t r e n d s n o r t h w e s t e r l y and has a l ength i n the m a p a r e a of 6 1/2 m i l e s and a w i d t h of 1 3/4 m i l e s . F l a t l y i n g v o l c a n i c s of the Endako G r o u p o v e r l i e the F r a n c o i s i n t r u s i v e a long i t s s o u t h w e s t e r n m a r g i n . P E T R O G R A P H Y The t y p i c a l r o c k type of the F r a n c o i s i n t r u s i v e i s a r e d , m e d i u m - g r a i n e d h y p i d i o m o r p h i c g r a n u l a r h o r n b l e n d e - b i o t i t e g r a n i t e w i t h a p o r p h y r i t i c c h i l l e d b o r d e r f a c i e s at the contact w i t h the Endako i n t r u s i v e . In p l a c e s the r o c k i s a q u a r t z m o n z o n i t e . A g r a n o p h y r i c t e x t u r e o c c u r s i n the c h i l l e d m a r g i n s and f i n e - g r a i n e d r o c k s . In the m e d i u m - g r a i n e d c e n t r a l r e g i o n s , p e r t h i t e and q u a r t z a r e i n t e r s t i - t i a l to p l a g i o c l a s e . P l a g i o c l a s e p h e n o c r y s t s r e a c h lengths of 7 m . m . i n the c h i l l e d m a r g i n s . A l l m i n e r a l s of the F r a n c o i s g r a n i t e show v a r i o u s stages of d e u t e r i c o r h y d r other m a i a l t e r a t i o n . N e a r the b o r d e r s of the i n t r u s i v e , p l a g i o c l a s e i s t h o r o u g h l y s a u s s u r i t i z e d , p e r t h i t e i s c h a r g e d w i t h a d r u s y g r e y m i n e r a l ( k a o l i n i t e ? ) and m i n o r s e r i c i t e , and b io t i t e i s P L A T E V T e x t u r e of the F r a n c o i s gran i te near c h i l l e d contact (xlOO, c r o s s e d n i c o l s ) T e x t u r e of the F r a n c o i s grani te i n c e n t r a l r e g i o n s of the i n t r u s i v e . Note the i n t e r l o c k i n g g r a i n s of m i c r o c l i n e (m), p l a g i o c l a s e (p) and q u a r t z (a) (x35, c r o s s e d n i c o l s ) T A B L E V M O D A L A N A L Y S E S O F T H E F R A N C O I S I N T R U S I V E G r a n i t e Q u a r t z M o n z o n i t e E N - 1 9 0 E M - 1 9 3 E N - 1 9 1 E N - 1 9 4 E N - 1 9 2 M i c r o c l i n e 4 8 . 0 39 .4 4 6 . 0 35 .7 33 .7 P l a g i o c l a s e * 9-8 18.8 16.0 31 .0 28 .8 Q u a r t z 29-8 32 .0 32 .0 2 5 . 3 29-9 B i o t i t e 8 .7 2 . 5 5 .0 6 .2 5 . 4 H o r n b l e n d e 2 . 4 1.0 t r . 1.5 0 .7 M a g n e t i t e 1.2 0 .5 1.0 1.0 1.2 Sphene t r . t r . t r . t r . t r . ^ C o m p o s i t i o n of p l a g i o c l a s e a v e r a g e s A n . c o m p l e t e l y c h l o r i t i z e d and s t a i n e d b y l i m o n i t e . A g g r e g a t e s of b l e a c h e d b i o t i t e a r e s e c o n d a r y after l o n g n e e d l e - s h a p e d h o r n b l e n d e c r y s t a l s . S m a l l amounts of r e l a t i v e l y f r e s h h o r n b l e n d e can be found i n the c e n t r a l a r e a s of the i n t r u s i o n . S m a l l m i a r o l i t i c e a v i t i e s c o n t a i n i n g e u h e d r a l q u a r t z and p o t a s h a r e s c a r c e . The m o d a l c o m p o s i t i o n s of the F r a n c o i s i n t r u s i v e a r e shown i n T a b l e V . In t h i n - s e c t i o n , m i c r o c l i n e m i c r o p e r t h i t e i s g r a p h i c a l l y i n t e r - g r o w n w i t h q u a r t z i n the c h i l l e d m a r g i n s and f i n e - g r a i n e d r o c k s of the F r a n c o i s g r a n i t e . In the m e d i u m - g r a i n e d i n t e r i o r of the i n t r u s i v e m i c r o p e r t h i t e and q u a r t z a r e i n t e r s t i t i a l to p l a g i o c l a s e (plate V . f i g . 2) A g r a n o p h y r i c t e x t u r e o c c u r s l o c a l l y . M i c r o p e r t h i t e p o i k i o l i t i c a l l y e n c l o s e s a l l m i n e r a l s i n the c o a r s e - g r a i n e d r o c k s and p l a g i o c l a s e f o r m s o r i e n t e d l a m e l l a e , s t r i n g e r s , v e i n s and i r r e g u l a r patches t h r o u g h - out the host m i c r o c l i n e . M i c r o p e r t h i t e , i f p r e s e n t i n the c h i l l e d b o r d e r f a c i e s of the F r a n c o i s g r a n i t e , o c c u r s l a r g e l y as s p a r s e o r i e n t e d l a m e l l a e and s t r i n g e r s i n the m i c r o c l i n e . R e p l a c e m e n t of p l a g i o c l a s e b y m i c r o c l i n e i s l e s s abundant i n the b o r d e r zones than i n the i n t e r i o r reg ions of the i n t r u s i v e . S u b h e d r a l p l a g i o c l a s e , the e a r l i e s t f o r m i n g m i n e r a l , o c c u r s as p h e n o c r y s t s i n and n e a r the c h i l l e d m a r g i n s . E l s e w h e r e i t i s n e a r l y e q u i d i m e n s i o n a l w i t h m i c r o p e r t h i t e and q u a r t z . The c o m p o s i t i o n ranges f r o m A n 0 to A n 0 0 ; zoning i s n o r m a l and l e s s c o m m o n l y o s c i l l a t o r y . 41 S t r o n g l y d e f o r m e d t w i n l a m e l l a e a s s o c i a t e d w i t h m a r k e d u n d u l a t o r y q u a r t z and bent and b r o k e n b i o t i t e c a n be o b s e r v e d i n sec t ions t a k e n a long the b o r d e r s of the p l u t o n . The c o r e r e g i o n s of m o s t p l a g i o c l a s e c r y s t a l s a r e c r o w d e d w i t h s a u s s u r i t i c and s e r i c i t i c i n c l u s i o n s . "With in tense a l t e r a t i o n the s o d i c r i m s a r e s e r i c i t i z e d ; epidote , c a l c i t e and g r a n u l a r i r o n o r e a r e e a s i l y i d e n t i f i a b l e i n the p l a g i o c l a s e c o r e s and m i c r o c l i n e i s c h a r g e d w i t h s e r i c i t e and k a o l i n i t e ( ? ) . The m a f i c m i n e r a l s of the F r a n c o i s gran i te c o n s i s t of pa le b r o w n i n t e r g r a n u l a r b io t i t e and subordinate a n h e d r a l p a l e green h o r n - b l e n d e . Ragged la ths of p o i k i l i t i c b i o t i t e conta in i n c l u s i o n s of a l l the m i n e r a l s except m i c r o c l i n e . B i o t i t e has the f o l l o w i n g p l e o c h r o i c s c h e m e ; X , pa le b r o w n ; Y , l i g h t g r e e n ; Z , d a r k g r e e n . In the m e d i u m g r a i n e d i n t e r i o r of the i n t r u s i v e , b r o w n b i o t i t e i s p a r t l y a l t e r e d to c h l o r i t e and f ine g r a n u l a r sphene and s e c o n d a r y s t r a w y e l l o w to p a l e g r e e n b i o t i t e i s i n t e r g r o w n w i t h h o r n b l e n d e . In the b o r d e r a r e a s of the i n t r u s i v e , b r o w n b i o t i t e i s c o m p l e t e l y a l t e r e d to a m i x t u r e of c h l o r i t e and l i m o n i t e and a l l h o r n b l e n d e has been r e p l a c e d b y a m i x t u r e of c h l o r i t i z e d s e c o n d a r y b i o t i t e , c a l c i t e and epidote . A c c e s s o r i e s i n c l u d e r h o m b i c sphene, e u h e r a l apati te , magnet i te , and p y r i t e . I r r e g u l a r m a s s e s of l eucoxene and l i m o n i t e a r e a l t e r a t i o n p r o d u c t s of sphene and p y r i t e r e s p e c t i v e l y . 42 S T R U C T U R E The F r a n c o i s g r a n i t e i s i n t r u s i v e into the f i n e r - g r a i n e d s o u t h - w e s t e r n edge of the c o a r s e - g r a i n e d E n d a k o q u a r t z m o n z o n i t e . A s h a r p contact can be d r a w n between t h e m . A c h i l l e d contact was o b s e r v e d i n the c o r e of a d r i l l - h o l e l o c a t e d one m i l e due west of the Endako m i n e . Two h u n d r e d feet n o r t h of F r a n c o i s L a k e , the p o r p h y r i t i c c h i l l e d m a r g i n a l zone i n w h i c h the g r o u n d m a s s m i n e r a l s average 1 1 / 2 m . m . i n s i z e i s e x p o s e d . T h i s t e x t u r e was o b s e r v e d o v e r a w i d t h of a p p r o x i - m a t e l y 70 feet . The F r a n c o i s seems to have an i n t r u s i v e r e l a t i o n s h i p w i t h the T a k l a v o l c a n i c s . T o w a r d s th is contact , the m e d i u m - g r a i n e d g r a n i t e d e c r e a s e s i n g r a i n s i z e and i n p l a c e s a s s u m e s a p o r p h y i t i c c h a r a c t e r . T h e r e i s no evidence that these v o l c a n i c s w e r e a f fec ted b y contact m e t a m o r p h i s m . The i n t r u s i o n i t s e l f i s not f o l i a t e d and contains s m a l l p a r t l y a s s i m i l a t e d i n c l u s i o n s of a type m o r e often seen i n the Endako q u a r t z m o n z o n i t e . Two dominant att itudes of shears and dikes a r e N40 W to N60 W and N20 E to N60 E w i t h steep dips to the west , southwest and n o r t h e a s t . R E L A T I O N S H I P B E T W E E N T H E E N D A K O A N D F R A N C O I S I N T R U S I V E S : The Endako q u a r t z m o n z o n i t e w h i c h i s i n t r u d e d b y the F r a n c o i s 43 g r a n i t e shows s i m i l a r i t i e s i n t e x t u r e and const i tuents to the l a t t e r when e x a m i n e d i n t h i n - s e c t i o n . The s u b g r a p h i c r e l a t i o n of q u a r t z and m i c r o p e r t h i t e i n the f i n e - g r a i n e d Endako q u a r t z m o n z o n i t e i s c o m p a r a b l e to the g r a p h i c habi t of q u a r t z and m i c r o p e r t h i t e i n the F r a n c o i s g r a n i t e . Q u a r t z i s i n t e r s t i t i a l i n m o s t of the Endako i n t r u s i v e and the c e n t r a l r e g i o n s of the F r a n c o i s g r a n i t e . T h e i r p l a g i o c l a s e s have n o r m a l zoning but the c o m p o s i t i o n i n the F r a n c o i s i s m o r e c a l c i c . B r o w n b i o t i t e and s e c o n d a r y s t r a w y e l l o w b i o t i t e after h o r n b l e n d e are p r e s e n t i n both i n t r u s i v e s and t h e i r x e n o l i t h s are of the s a m e t y p e . T h e s e s i m i l a r i t i e s suggest a c o m m o n s o u r c e and e n v i r o n m e n t of e m - p l a c e m e n t f o r the Endako q u a r t z m o n z o n i t e and the F r a n c o i s g r a n i t e . F i g u r e 3 shows the p lo t of the m o d a l c o m p o s i t i o n s of these two i n t r u s i v e s on the A b - S i O ^ - O r t e r n a r y d i a g r a m . In g e n e r a l they p l o t i n two separa te a r e a s but two p lo t s of the Endako q u a r t z m o n z o n i t e do o v e r - l a p the F r a n c o i s gran i te f i e l d .  45 M O D E A N D E N V I R O N M E N T O F E M P L A C E M E N T O F T H E I N T R U S I V E S O F T O P L E Y S T A G E II: The absence of f o l i a t i o n i n the F r a n c o i s g r a n i t e and the Endako q u a r t z m o n z o n i t e except f o r a weak a l i g n m e n t of i n c l u s i o n s i n the E n d a k o i n t r u s i v e a l o n g the S te l lako R i v e r suggests that these m a g m a s w e r e l a r g e l y l i q u i d when e m p l a c e d . The r a n d o m o r i e n t a t i o n of p l a g i o - c l a s e p h e n o c r y s t s i n the c h i l l e d m a r g i n s of the F r a n c o i s g r a n i t e suppor ts th is a s s u m p t i o n . T h e F r a n c o i s i n t r u s i v e m a y r e p r e s e n t a second g e n e r a t i o n of m a g m a f r o m the same s o u r c e as the Endako o r p o s s i b l e a l a t e r i n j e c t i o n of m o r e a l k a l i - r i c h m a t e r i a l f r o m a s ing le d i f f e r e n t i a t i n g m a g m a at depth. A n e p i z o n a l depth of e m p l a c e m e n t f o r the Endako q u a r t z m o n z o n i t e and the F r a n c o i s gran i te i s i n d i c a t e d b y : (1) the absence of f o l i a t i o n i n both i n t r u s i v e s ; (2) the p o r p h y r i t i c c h i l l e d m a r g i n and the p r e s e n c e of m a r i o l i t i c c a v i t i e s i n the F r a n c o i s g r a n i t e ; (3) the g r a n o - p h y r i c t ex ture i n the F r a n c o i s grani te and a w e a k e r deve loped s i m i l a r t ex ture i n the f i n e - g r a i n e d r o c k s of the Endako q u a r t z m o n z o n i t e , and (4) the c o n f o r m i t y of t h e i r contacts to each other and to the r e g i o n a l n o r t h w e s t t r e n d of the S i m o n B a y c o m p l e d near and b e y o n d the n o r t h e r n m a r g i n s of the m a p a r e a . T h i s i s m o r e c o m m o n l y a c h a r a c t e r i s t i c of m e so zona l plutons (Buddington, 1959). 46 T O P L E Y S T A G E III T H E G L E N N A N A N C O M P L E X G E N E R A L D E S C R I P T I O N The Glennanan c o m p l e x u n d e r l i e s about 30 square m i l e s of the m a p a r e a (see m a p i n f o l d e r ) . T h i s i s o n l y a s m a l l p a r t of a l a r g e c o m p o s i t e b o d y w h i c h extends eight m i l e s or m o r e n o r t h w e s t b e y o n d the b o u n d a r i e s of the t h e s i s a r e a . R e g i o n a l m a p p i n g of th i s a r e a b y the 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 of M i n e s ( C a r r , 1965) d i s - c l o s e d l a r g e a r e a s of Glennanan (des ignated T a t i n , Tdtan , R e x and T r i a n g l e L a k e i n t r u s i v e s , F i g u r e 22, page 144A, L o d e M e t a l s i n B r i t i s h C o l u m b i a , 1965) p o r p h y r i t i c q u a r t z m o n z o n i t e and g r a n o d i o r i t e w i t h l i t t l e o r no g r a n i t e . In contras t , the r o c k s of the Glennanan c o m p l e x i n the m a p a r e a a r e p r e d o m i n a n t l y p o r p h y r i t i c gran i te and q u a r t z m o n z o n i t e . The Glennanan i n t r u s i v e f o r m s t h r e e separate bodies i n the m a p a r e a . The l a r g e s t body, c e n t e r e d a r o u n d the town of E n d a k o , i s the a s y m m e t r i c a l l y zoned southeas tern p a r t of the m a i n Glennanan p luton w h i c h t r e n d s n o r t h - n o r t h w e s t far b e y o n d the m a p a r e a . The e a s t - w e s t t r e n d i n g Endako R i v e r f l o o d p l a i n d i v i d e s th i s body into two s e g m e n t s . I m m e d i a t e l y south of the r i v e r , c o a r s e - g r a i n e d p o r p h y r i t i c r r a n i t e f o r m s the m a r g i n a l zone a r o u n d the w e s t e r n and southwestern b o r d e r s of the i n t r u s i v e . A p o r p h y r i t i c c h i l l e d zone was o b s e r v e d 1/4 m i l e east of C a s e y L a k e . The g r a n i t e zone grades into a c o a r s e - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e q u a r t z m o n z o n i t e . I m m e d i a t e l y n o r t h of the Endako R i v e r , m e d i u m g r a i n e d p o r p h y r i t i c q u a r t z m o n z o n i t e f o r m s a n a r r o w segment a r o u n d the exposed w e s t e r n edge of the Glennanan c o m p l e x . T h i s segment , w h i c h seems to be g r a d a - t i o n a l w i t h the q u a r t z m o n z o n i t e south of the r i v e r , grades e a s t w a r d into a b r o a d zone of p o r p h y r i t i c g r a n o d i o r i t e . A b o d y of a p l i t e l i e s a l o n g the w e s t e r n e x p o s e d edge of the p o r p h y r i t i c q u a r t z m o n z o n i t e to the w e s t . The p o r p h y r i t i c g r a n o d i o r i t e i s b o r d e r e d on the east i n the m a p a r e a and the n o r t h e a s t b e y o n d i t , b y the o l d e r S i m o n B a y ( d i o r i t e ) c o m p l e x . The s e c o n d Glennanan i n t r u s i v e body o c c u r s eight m i l e s s o u t h - east of the t o w n of E n d a k o . It f o r m s an a s y m m e t r i c a l l y zoned c r e s c e n t shaped body, f i v e m i l e s l o n g and one m i l e w i d e a long the wes t f lank of N i t h i M o u n t a i n . A b a n d of p o r p h y r i t i c gran i te l i e s a long the w e s t e r n m a r g i n of th i s i n t r u s i v e . G r a d a t i o n a l l y bounded bodies of g l o m e r o - p o r p h y r i t i c g r a n i t e , up to 50 feet i n l ength , a r e exposed a long the c h i l l e d b o r d e r s of the Glennanan grani te on N i t h i M o u n t a i n . S i m i l a r zones a r e found at A l f L a k e and near D r y W i l l i a m ' s L a k e jus t b e y o n d the e a s t e r n m a r g i n of the imap a r e a . In a l l t h r e e p l a c e s , the adjacent c o u n t r y r o c k i s the S i m o n B a y . d i o r i t e . J It i s p r o b a b l e that s i m i l a r i r r e g u l a r l e n s e s of g l o m e r o p o r p h y r i t i c grani te o c c u r ' i n t e r m i t t e n t l y 48 a long other p a r t s of the c h i l l e d m a r g i n s of the g r a n i t e . The g r a n i t e zone grades into a p o r p h y r i t i c q u a r t z m o n z o n i t e . A s m a l l e x p o s u r e of p o r p h y r i t i c q u a r t z m o n z o n i t e , c o v e r i n g an a r e a of about 1/2 s q u a r e m i l e , o c c u r s on the e a s t e r n f lank of N i t h i M o u n t a i n , south of the F o s t e r L a k e s . T h i s was p o s s i b l y p a r t of the l a r g e r b o d y on the wes t f lank of N i t h i M o u n t a i n but has been i s o l a t e d f r o m i t b y the i n t r u s i o n of the younger C a s e y q u a r t z m o n z o n i t e - a l a s k i t e . P o r p h y r i t i c q u a r t z m o n z o n i t e f o r m s a t h i r d i n t r u s i v e b o d y one m i l e l o n g and 1 /2 m i l e w i d e n e a r A l f L a k e n o r t h of the Endako R i v e r . M o d e s of each r o c k type a r e shown i n T a b l e V I . The a v e r a g e d e n s i t i e s of the p o r p h y r i t i c g r a n o d i o r i t e , q u a r t z m o n z o n i t e and g r a n i t e a r e 2. 73, 2. 68 and 2. 64 g m / c c r e s p e c t i v e l y . M i n o r i n t r u s i o n s i n c l u d e a p l i t e s , p o r p h y r i t i c dac i te , l a t i t e and r h y o l i t e d ikes as w e l l as f ine g r a i n e d q u a r t z m o n z o n i t e , q u a r t z d i o r i t e and diabase d i k e s . T h e i r dominant t r e n d s a r e n o r t h w e s t and n o r t h to n o r t h e a s t . 49 T A B L E V I M O D A L A N A L Y S E S O F T H E G L E N N A N A N C O M P L E X G R A N I T E 1 E G B - 1 * E G B - 2 E G B - 1 6 9 E N - 171 E N - 1 6 8 1 M i c r o c l i n e 70. 1 55 . 0 55 .5 55 . 8 5 1 . 9 P l a g i o c l a s e 2 11. 2 25 . 0 14. 3 25 . 3 25. 0 Q u a r t z 17. 1 20 . 0 27 .7 17. 2 17. 7 B i o t i t e 1.0 2 . 0 2. 3 1. 6 2 .8 H o r n b l e n d e 0. 3 1. 0 0 .5 0. 7 1.3 M a g n e t i t e 0 .4 0. 5 0. 6 1. 5 1.0 Sphene 0. 5 t r . t r . 0. 4 0 .8 A p a t i t e t r . t r . t r . t r . 0. 3 * - c h i l l e d m a r g i n (2) p l a g i o c l a s e r a r Q U A R T Z M O N Z O N I T E r a n g e s f r o m A n to An- ,g G R A N O D I O R I T E E G B - 8 E N -170 E G B - 1 2 E G B - 1 6 E G B ' M i c r o c l i n e ' ' ' 4 1 . 4 4 6 . 5 4 2 . 0 23 .9 2 1 . 1 P l a g i o c l a s e 2 35 .5 32 . 6 30 . 0 4 2 . 9 4 7 . 7 Q u a r t z 14 .7 16. 3 26. 0 2 1 . 0 17.5 B i o t i t e 3 .5 3 . 0 2 . 0 4 . 5 5 .6 H o r n b l e n d e 1.8 1. 2 1.0 2 .2 5 .5 M a g n e t i t e 1.2 1. 0 t r . 2 .2 3 .4 Sphene 1.4 0. 5 t r . 1.6 1.2 A p a t i t e 0 .3 t r . t r . t r . t r . (1) The c o m p o s i t i o n of the a l k a l i f e l d s p a r r a n g e d f r o m O r . to Orgr i n the g r a n i t e and O r g g to O r g g i n the q u a r t z m o n z o n i t e aha g r a n o d i o r i t e (see T a b l e I) (2) P l a g i o c l a s e ranges f r o m A n 2 2 to A n 3 4 i n q u a r t z m o n z o n i t e and g r a n o d i o r i t e . 50 Figure 4» The nodal Q:AbjQr r-tios of the Olennrn^n coupler, calculated froa Ifiblo VI. 51 P E T R O G R A P H Y P o r p h y r i t i c H o r n b l e n d e - B i o t i t e G r a n i t e P i n k to g r e y , v e r y c o a r s e - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e g r a n i t e f o r m s a c r e s c e n t i c m a r g i n a l z o n i n g r a n g i n g f r o m 2, 500 feet to 5, 000 feet w i d e a r o u n d the w e s t e r n and s o u t h w e s t e r n s ide of the m a i n i n t r u s i v e b o d y . P o r p h y r i t i c g r a n i t e f o r m s a b o r d e r zone, r a n g i n g f r o m 1000 to 4000 feet w i d e a long the w e s t e r n s ide of the N i t h i M o u n t a i n i n t r u s i v e b o d y . The g r a n i t e grades into c o a r s e - g r a i n e d p r o p h y r i t i c h o r n b l e n d e - b i o t i t e q u a r t z m o n z o n i t e . P i n k to p a l e orange p e r t h i t i c m i c r o c l i n e f o r m s r e c t a n g u l a r c r y s t a l s , r a n g i n g i n l ength f r o m 1 to 4 c m . , i n the c h i l l e d b o r d e r s and i n t e r i o r r e g i o n s of the g r a n i t e zone. A r o u g h z o n a l a r r a n g e m e n t of q u a r t z , b i o t i t e , h o r n - b lende , sphene, magnet i t e and t a b u l a r p l a g i o c l a s e i s d i s p l a y e d , p a r t i c u l a r l y i n the l a r g e r p h e n o c r y s t s ( m e g a c r y s t s ) . P l a g i o c l a s e f o r m s s u b h e d r a l whi te c r y s t a l s , g e n e r a l l y subordinate i n s i z e to p e r t h i t e , but o c c a s i o n a l l y o c c u r s as p h e n o c r y s t s 1 c m . l o n g . C r y s t a l faces can be seen on q u a r t z g r a i n s throughout the g r o u n d m a s s . Q u a r t z i n d i s c r e t e g r a i n s or c l u s t e r s i s i n t e r s t i t i a l to p l a g i o c l a s e and p e r t h i t e m e g a c r y s t s . B i o t i t e f o r m s t h i c k hexagona l books o r p l a t y aggregates . Subordinate h o r n b l e n d e i s i n c o n s p i c u o u s i n the c h i l l e d b o r d e r f a c i e s of the g r a n i t e . P e r t h i t e m e g a c r y s t s a r e c o n c e n t r a t e d i n l o c a l a reas of g l o m e r o - p o r p h y r i t i c g r a n i t e a long the b o r d e r s of the g r a n i t e zone. The r e l a t i v e c o a r s e - g r a i n s i z e of s u b h e d r a l p e r t h i t e , i n the c o a r s e - g r a i n e d g r o u n d - m a s s , g i v e the r o c k a p o r p h y r i t i c t ex ture even w h e r e p e r t h i t e m e g a - c r y s t s a r e s c a r c e o r absent . A weak p l a n a r o r i e n t a t i o n of the m e g a c r y s t s i s p e r c e p t i b l e n e a r the m a r g i n of the gran i te and i n the g l o m e r o p o r p h y r i t i c f a c i e s . I n c l u s i o n s a r e absent i n the o b s e r v e d c h i l l e d m a r g i n a l zones but s m a l l , i r r e g u l a r i n c l u s i o n s of q u a r t z m o n z o n i t e or q u a r t z d i o r i t e and i r r e g u l a r m a f i c c lots w e r e o b s e r v e d i n the c o a r s e - g r a i n e d r o c k s . In t h i n s e c t i o n , m i c r o c l i n e m i c r o p e r t h i t e i n the c o a r s e - g r a i n e d g r o u n d m a s s o c c u r s i n two f o r m s : (1) s u b h e d r a l g r a i n s whose m a r g i n s p o i k i o l i t i c a l l y e n c l o s e a l l m i n e r a l s i n the r o c k ; and (2) s m a l l equant o r a n h e d r a l i n t e r s t i t i a l g r a i n s (plate VII , f i g . 2.) P e r t h i t e m e g a - c r y s t s have a g e n e r a l e u h e d r a l f o r m but t h e i r b o u n d a r i e s a r e v e r y i r r e g u l a r and p a r t l y or w h o l l y enc lo se m i n e r a l s of the m a t r i x (plate VII , f i g . 1.) . The m e g a c r y s t s d i s p l a y c a r l s b a d o r di f fuse to s h a r p g r i d t w i n n i n g . M i c r o p e r t h i t i c t e x t u r e s , that range f r o m f ine f i l m s to ve ins o r n e t w o r k s of v e i n s and i r r e g u l a r patches , d i s p l a y c r o s s - cut t ing r e l a t i o n s h i p s , i n the host m i c r o c l i n e . P l a g i o c l a s e i n f ine s t r i n g e r s and l a m e l l a e w h i c h a r e o r i e n t e d p a r a l l e l to the c leavage d i r e c t i o n s of the m e g a c r y s t s p r o b a b l y h a d an e x s o l u t i o n o r i g i n . The m e g a c r y s t s conta in abundant i n c l u s i o n s of m a i n l y p l a g i o c l a s e but b i o t i t e , h o r n b l e n d e , q u a r t z , magnet i te and sphene a r e a l so p r e s e n t . The t a b u l a r shaped c r y s t a l s a r e o r i e n t e d w i t h t h e i r longes t d i r e c t i o n p a r a l l e l to the (010), (001) and (110) p lanes of the m i c r o c l i n e ( f i g . 5) T h e i r s t r i k i n g s t r u c t u r a l o r i e n t a t i o n and z o n a l a r r a n g e m e n t i n the m e g a c r y s t s i s m o r e f u l l y d e s c r i b e d l a t e r i n the d i s c u s s i o n of the g l o m - e r o p o r p h y r i t i c f a c i e s of the g r a n i t e . S u b h e d r a l p l a g i o c l a s e d i s p l a y s o s c i l l a t o r y z o n i n g and c o m b i n - a t ion t w i n n i n g . P l a g i o c l a s e i s s t r o n g l y r e p l a c e d b y m i c r o c l i n e (plate V I , f i g . 1. ) and m y r m e k i t e o c c u r s a long m o s t contacts between t h e m In the c h i l l e d m a r g i n , p l a g i o c l a s e f o r m s m a n t l e s a long p a r t s of the l a r g e r a n h e d r a l m i c r o c l i n e w h i c h e x t i n g u i s h s i m i l t a n e o u s l y g r a i n s (plate V I , f i g . 2) P l a g i o c l a s e ranges i n c o m p o s i t i o n f r o m A n to 2 o A n , i n the c o r e s to An„ , to A n „ at the edges . Q u a r t z o c c u r s i n 24 26 22 6 t h r e e f o r m s : (1) i r r e g u l a r l a r g e aggregates c o m p o s e d of a n h e d r a l and s u b h e d r a l c r y s t a l s , i n the c h i l l e d m a r g i n s ; (2) e u h e d r a l , u n s t r a i n e d c r y s t a l s that a r e i n c l u d e d i n g r o u n d m a s s m i c r o c l i n e , the m a r g i n s of p e r t h i t e m e g a c r y s t s (plates V I , VI I , f i g s 1, 1 respec t ive ly ) ; ' and (3) i r r e g u l a r , i n t e r s t i t i a l f r a c t u r e d g r a i n s , w i t h u n d u l a t o r y e x t i n c t i o n w h i c h c o m m o n l y f o r m o v e r g r o w t h s on the e a r l i e r e u h e d r a l f o r m . M a f i c m i n e r a l s a r e b i o t i t e and m i n o r h o r n b l e n d e . B i o t i t e p o i k i o l i t i c a l l y enc loses apati te , sphene, magnet i te and hornblende and has the f o l l o w i n g p l e o c h r o i c s c h e m e : X , y e l l o w i s h b r o w n ; Y , dark b r o w n ; P L A T E V I 5 4 f F i g u r e 1: M i c r o p e r t h i t e r e p l a c i n g p l a g i o c l a s e (P) i n the G l e n n a n a n g r a n i t e . Note e u h e d r a l q u a r t z (Q) i n m i c r o p h e r t h i t e ( M ) . (x lOO, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of G l e n n a n a n g r a n i t e n e a r c h i l l e d m a r g i n s . M i c r o p e r t h i t e (M) is partly- m a n t l e d by p l a g i o c l a s e (P) (x95, c r o s s e d n i c o l s ) P L A T E V I I 55 F i g u r e 1 : P o i k i l i t i c m i c r o p e r t h i t e (M) conta in ing sub- h e d r a l p l a g i o c l a s e (P) and e u h e d r a l q u a r t z (Q) c r y s t a l s . (x35, c r o s s e d n i c o l s ) i n the G l e n n a n a n g r a n i t e . 56 Z , g r e e n i s h b r o w n . It f o r m s h e x a g o n a l p l a t e s , r a g g e d laths i n t e r - g r o w n w i t h g r e e n h o r n b l e n d e and i r r e g u l a r c l u s t e r s w i t h h o r n b l e n d e i n the g r o u n d m a s s . F i n e l y g r a n u l a r m i c r o c l i n e , q u a r t z , p l a g i o c l a s e and m a f i c m i n e r a l s r a n g i n g i n s i z e f r o m 1 m . m . to 0. 3 m . m . f o r m i r r e g u l a r pockets i n the c o a r s e r g r a i n e d g r o u n d m a s s (plate VII , f i g . 2} and n a r r o w zones a long the g r a i n b o u n d a r i e s of the m e g a c r y s t s throughout the g r a n i t e . A t the m o s t , t h i s f e a t u r e const i tutes between 1 and 2 p e r c e n t of the r o c k and i n d i c a t e s a l a te stage of r a p i d c o o l i n g af ter m o s t of the m a g m a h a d c r y s t a l l i z e d . T h i s fea ture was not o b s e r v e d i n the p o r p h y r i t i c q u a r t z m o n z o n i t e o r g r a n o d i o r i t e . R h o m b i c sphene, e u h e d r a l apat i te and magnet i t e a r e v e r y c o m m o n a c c e s s o r y m i n e r a l s i n the g r a n i t e . A l l a n i t e i s p r e s e n t i n s m a l l q u a n t i t i e s . G l o m e r o p o r p h y r i t i c F a c i e s of G r a n i t e L o c a l a r e a s of h o r n b l e n d e - b i o t i t e g r a n i t e c o m p o s e d of 25 to 75 p e r c e n t p e r t h i t e m e g a c r y s t s o c c u r a long the c h i l l e d m a r g i n s of the g r a n i t e . The c r u d e a l i g n m e n t of p e r t h i t e c r y s t a l s , the l a r g e s t of w h i c h m e a s u r e d 4 c m . l o n g and 1. 5 c m . w i d e , g ive the r o c k a weak f o l i a t i o n . In the f i n e - t o m e d i u m - g r a i n e d groundmass , p e r t h i t e , q u a r t z , p l a g i o c l a s e , b i o t i t e and h o r n b l e n d e a r e i n t e r s t i t i a l to the p e r t h i t e m e g a c r y s t s and a few l a r g e aggregates of q u a r t z . 57 In t h i n - s e c t i o n , the m a r g i n s of the m i c r o c l i n e m e g a c r y s t s extend i r r e g u l a r l y into the a l l o t r i o m o r p h i c g r a n u l a r g r o u n d m a s s . E u h e d r a l to s u b h e d r a l p l a g i o c l a s e , b i o t i t e , hornb lende and sphene a r e o r i e n t e d on the (010), (001) and (110) p lanes of the m i c r o c l i n e ( f i g . 5. and p la te VIII , f i g . 1). The (100) face of p l a g i o c l a s e has a s t r o n g p r e f e r e n c e for o r i e n t a t i o n on the (100) face of m i c r o c l i n e . The o r i e n - t a t i o n of q u a r t z , magnet i te or the o c c a s i o n a l c r y s t a l of apati te does not appear to have been c o n t r o l l e d b y the s t r u c t u r e of the m i c r o c l i n e . Q u a r t z o c c u r s i n two f o r m s : (1) r o u n d e d or a n h e d r a l g r a i n s o r i r r e g u l a r m a n t l e s p a r t i a l l y r i m m i n g p l a g i o c l a s e , b i o t i t e , h o r n b l e n d e , o r sphene i n the c e n t r a l a r e a s of the m e g a c r y s t s ; and (2) e u h e d r a l to s u b h e d r a l g r a i n s a long the m a r g i n s of the m e g a c r y s t s (plate VIII f i g . 2). The i n c l u s i o n s a l s o d i s p l a y a z o n a l a r r a n g e m e n t i n the m e g a - c r y s t s . W i t h the e x c e p t i o n of biotite a l l m i n e r a l s a r e found i n o r n e a r the c o r e r e g i o n s . B i o t i t e occurs i n the o u t e r m o s t zones of the m e g a - c r y s t s ( f i g . 5) w h e r e the h i g h e s t c o n c e n t r a t i o n of i n c l u s i o n s a r e found. I n c l u s i o n s i n the c o r e s a r e not as s t r o n g l y o r i e n t e d as those i n the p e r i s p h e r a l zones of the m e g a c r y s t s . H e r e , p l a g i o c l a s e f o r m s e u h e d r a l to s u b h e d r a l g r a i n s r a n g i n g i n s i z e f r o m 0. 6 m . m . to 0. 1 m . m . , w h e r e a s the l a r g e r gra ins i n the ..outer zones a r e e m b a y e d b y the m i c r o c l i n e . P l a g i o c l a s e i n c l u s i o n s have b r o a d c a l c i c c o r e s w i t h t h i n s o d i c m a r g i n s . M o s t g r a i n s d i s p l a y n o r m a l zoning and p o l y s y n t h e t i c 58 0 1 2 Figure 5. Structur? 1 orient?tion and zonal ?r?''nge- 'pent of p l a g i o c l a s e ( p ) , b i o t i t e (b), horn- blende (hbj and. .sphene ( s ) , and unoriented quartz ( o ) »nd magnetite (nig) in. a p e r t h i t e megacryst from the glomeroporphyriti© f a c i e s of the Glennanan g r a n i t e . P L A T E VIII 59 F i g u r e 1 : O r i e n t e d i n c l u s i o n s of p l a g i o c l a s e ( P ) , sphene (S) and u n o r i e n t e d e u h e d r a l q u a r t z (Q) i n p e r t h i t e m e g a c r y s t of Glennanan g l o m e r o - p o r p h y r i t i c g r a n i t e (x45, c r o s s e d n i c o l s ) F i g u r e 2: Contac t zone between per th i te m e g a c r y s t and g r o u n d m a s s i n g l o m e r o p h y r i t i c g r a n i t e . Note a n h e d r a l m i c r o c l i n e (M) and r o u n d q u a r t z (Q) g r a i n s near edge of per th i te m e g a c r y s t (x45, c r o s s e d n i c o l s ) t w i n n i n g . The c o m p o s i t i o n of nine o r i e n t e d p l a g i o c l a s e g r a i n s f r o m a s i n g l e p e r t h i t e m e g a c r y s t was d e t e r m i n e d u s i n g the a - n o r m a l m e t h o d and a p p r o p r i a t e c u r v e s f r o m D e e r , H o w i e and Z u s s m a n (1963). The c o m p o s i t i o n s showed a p r o g r e s s i v e change f r o m the i n t e r i o r to the m a r g i n s of the m i c r o c l i n e m e g a c r y s t ( f i g . 5) o f A n , A n to A n Jo 34 29 r e s p e c t i v e l y . A t the m a r g i n s of the m e g a c r y s t s , v e r y c o a r s e - g r a i n e d m y r m e k i t e o c c u r s a l o n g the contacts w i t h p l a g i o c l a s e . I n t e r s p e r s e d w i t h zones of m y r m e k i t e a r e a r e a s of m i c r o p e g m a t i t e . In the g r o u n d - m a s s p r o p e r , m y r m e k i t e i s abundant but m i c r o p e g m a t i t e i s s c a r c e . The c o m p o s i t i o n of the g r o u n d m a s s p l a g i o c l a s e a v e r a g e s A n but 2o m a y range as h i g h as A n or as l o w as A n . O s c i l l a t o r y zoning 32 25 w i t h a s t r o n g n o r m a l t r e n d n e a r the edges i f c o m m o n . P o i k i l i t i c m i c r o p e r t h i t i c m i c r o c l i n e c o m p r i s e s about 20 p e r c e n t of the g r o u n d m a s s It f o r m s i n t e r s t i t i a l g r a i n s o r , l e s s c o m m o n l y , s m a l l equant g r a i n s (plate VIII , f i g . 2). Q u a r t z f o r m s e u h e d r a l o r , m o r e c o m m o n l y , i r r e g u l a r i n t e r s t i t i a l g r a i n s . The m a f i c m i n e r a l s o c c u r i n the s a m e m a n n e r as i n the p o r p h y r i t i c g r a n i t e . P o r p h y r i t i c H o r n b l e n d e - B i o t i t e Q u a r t z M o n z o n i t e C o a r s e - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e q u a r t z m o n z o n i t e f o r m s : (1) a p l u g n e a r A l f L a k e ; (2) the e a s t e r n zone of the N i t h i M o u n t a i n i n t r u s i v e body; and (3) the i n t e r m e d i a t e zone be tween p o r p h y r i t i c g r a n i t e and g r a n o d i o r i t e a long the Endako R i v e r f l o o d p l a i n . The b o u n d a r y between each r o c k zone i s a r b i t r a r i l y b a s e d on t h e i r p l a g i o c l a s e to t o t a l f e l d s p a r r a t i o . P e r t h i t e m e g a c r y s t s , c o n t a i n i n g i n c l u s i o n s of p l a g i o c l a s e , b i o t i t e and h o r n b l e n d e , c o m p r i s e l e s s than 10 p e r c e n t , but u s u a l l y m o r e than 5 p e r c e n t , of the q u a r t z m o n z o n i t e and a r e m u c h s m a l l e r than those of the g r a n i t e zone. D a r k g r e e n t a b u l a r o r p r i s m a t i c h o r n b l e n d e c o m p r i s e s be tween 3 and 4 p e r c e n t of the r o c k , but r e a c h e s a m a x i m u m of about 8 p e r c e n t i n the A l f - L a k e s tock . T h e r e i s a c r u d e a l i g n m e n t of p e r t h i t e m e g a c r y s t s and p r i s m a t i c h o r n b l e n d e n e a r A l f L a k e . X e n o l i t h s a r e m o r e abundant i n the m e d i u m - g r a i n e d q u a r t z m o n z o n i t e , n o r t h of the town of E n d a k o , than i n the c o a s r e - g r a i n e d q u a r t z m o n z o n i t e o r g r a n i t e south of the Endako R i v e r and on N i t h i M o u n t a i n . In t h i n - s e c t i o n , r e l a t i v e l y l a r g e g r a i n s of p o i k i o l i t i c m i c r o c l i n e m i c r o p e r t h i t e are l a r g e l y i n t e r s t i t i a l to p l a g i o c l a s e but some s m a l l , equant, s h a r p l y t w i n n e d g r a i n s of m i c r o c l i n e w e r e o b s e r v e d i n s o m e s p e c i m e n s . T h e y o c c u r as d i s c r e t e g r a i n s i n m i c r o p e r t h i t e w i t h e u h e d r a l q u a r t z c r y s t a l o r i n t e r l o c k i n g g r a i n s w i t h p l a g i o c l a s e and a n h e d r a l q u a r t z . C o r r o s i o n of p l a g i o c l a s e b y m i c r o c l i n e and m y r m e k i t e are not as p r o m i n e n t i n the q u a r t z m o n z o n i t e as i n the g r a n i t e zone. E u h e d r a l to s u b h e d r a l o s c i l l a t o r y zoned p l a g i o c l a s e (plate X , f i g . 1) v a r i e s i n c o m p o s i t i o n f r o m A n ^ A to A n . The c o r e s of some g r a i n s P L A T E I X Z o n a l p a t t e r n of a n h e d r a l q u a r t z o v e r g r o w t h s on e u h e d r a l q u a r t z c r y s t a l s i n the m i c r o p e r t h i t of the Glennanan q u a r t z m o n z o n i t e . (x35, c r o s s e d n i c o l s ) E u h e d r a l q u a r t z (Q) c r y s t a l s w i t h a n h e d r a l o v e r g r o w t h s , i n the m i c r o c l i n e (M) of the Glennanan q u a r t z m o n z o n i t e . (x450, c r o s s e d n i c o l s ) P L A T E X E u h e d r a l q u a r t z c r y s t a l s i n m i c r o p e r t h i t e and zoned p l a g i o c l a s e i n the Glennanan q u a r t z m o n z o n i t e , (x35, c r o s s e d n i c o l s ) I n t e r s t i t i a l habi t of q u a r t z (Q) and m i c r o c l i n e (M) i n the Glennanan g r a n o d i o r i t e , (xlOO, c r o s s e d n i c o l s ) 64 a r e s a u s s u r i t i z e d and conta in i n c l u s i o n s of p r i s m o t i c h o r n b l e n d e , a n h e d r a l to r o u n d e d q u a r t z and t a b u l a r b i o t i t e . Q u a r t z , l i k e i n the g r a n i t e zone o c c u r s i n t h r e e f o r m s : (1) e u h e d r a l c r y s t a l s e n c l o s e d i n m i c r o c l i n e m i c r o p e r t h i t e (plate X , f i g . 1) or i n t e r l o c k i n g g r a i n s i n the g r o u n d m a s s ; (2) i r r e g u l a r , i n t e r - s t i t i a l g r a i n s w h i c h c o m m o n l y f o r m o v e r g r o w t h s on the e u h e d r a l f o r m ; and (3) an a s s o c i a t i o n of e u h e d r a l q u a r t z g r a i n s and g r a p h i c q u a r t z i n m i c r o c l i n e (plate I X , f i g . 1). A c l o s e e x a m i n a t i o n of these q u a r t z i n t e r g r o w t h s d i s c l o s e d that they a r e e u h e d r a l q u a r t z c r y s t a l s , 0 .05 m . m . and l e s s i n s i z e w h i c h have b e e n o v e r g r o w n w i t h a n h e d r a l q u a r t z . The o p t i c a l o r i e n t a t i o n of these i n t e r g r o w t h s i s d e t e r m i n e d b y the e n c l o s e d e u h e d r a l c r y s t a l o r c r y s t a l s . Some q u a r t z i n t e r g r o w t h s do not conta in e u h e d r a l q u a r t z n u c l e i and t h e i r o p t i c a l o r i e n t a t i o n appears to have been c o n t r o l l e d b y the host m i c r o c l i n e . The e u h e d r a l f o r m of the q u a r t z and the equant g r a i n s of m i c r o c l i n e i n the m i c r o p e r t h i t e suggests to the author that they f o r m e d i n a m a g m a w i t h l i t t l e i n t e r - f e r e n c e f r o m adjacent c r y s t a l s . I n t e r s t i t i a l b r o w n b i o t i t e and g r e e n hornblende c o m p r i s e as m u c h as 10 p e r c e n t of the r o c k . Sphene and magnet i te a r e m o r e a b u n - dant than i n the g r a n i t e zone. 65 P o r p h y r i t i c H o r n b l e n d e - B i o t i t e G r a n o d i o r i t e P i n k i s h - g r e y m e d i u m - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e g r a n o d i o r i t e o c c u r s o n l y n o r t h of the Endako R i v e r but cont inues eight m i l e s o r m o r e n o r t h w e s t b e y o n d the m a p a r e a . It c o v e r s an a r e a of a p p r o x i m a t e l y f ive square m i l e s and i s g r a d a t i o n a l to a n a r r o w zone of m e d i u m - g r a i n e d q u a r t z m o n z o n i t e a long the w e s t e r n edge. The g r a n o d i o r i t e seems to be g r a d a t i o n a l w i t h the q u a r t z m o n z o n i t e i m m e d i - a t e l y south of the Endako R i v e r . The g r a n o d i o r i t e contains i n p l a c e s be tween 1 and 5 p e r c e n t p e r t h i t e m e g a c r y s t s w h i c h a r e m o s t l y 1 or 2 c m . l o n g . P h e n o c r y s t s of p l a g i o c l a s e and hornblende or o c c a s i o n a l l y l a r g e q u a r t z aggregates m a y b e found a s s o c i a t e d w i t h m e g a c r y s t s i n l o c a l pods and c l u s t e r s n e a r the e a s t e r n edge of the g r a n o d i o r i t e . A n i n d i s t i n c t f o l i a t i o n m a r k e d b y the p r e f e r r e d a l i g n m e n t of i n c l u s i o n s and e longated aggregates of h o r n b l e n d e and b i o t i t e b e c o m e s m o r e apparent n e a r the contact w i t h the S i m o n B a y d i o r i t e . In the e a s t e r n - m o s t e x p o s u r e of the g r a n o d i o r i t e i n the m a p a r e a and to the n o r t h b e y o n d i t s b o u n d a r i e s , l o c a l pods and c l u s t e r s of p e r t h i t e p h e n o c r y s t s together w i t h s w a r m s of q u a r t z d i o r i t e i n c l u s i o n s , g ive the r o c k a weak f o l i a t i o n . In t h i n - s e c t i o n , s u b h e d r a l p l a g i o c l a s e d i s p l a y s s t r o n g o s c i l l a t o r y zoning w i t h s a u s s u r i t i z e d c o r e s i n w h i c h epidote, c a l c i t e and s e r i c i t e a r e e a s i l y i d e n t i f i a b l e . The average s i z e i s 4 m . m . b y 2 m . m , but P L A T E X I S u b h e d r a l hornblende (Hb) and b io t i t e (B) i n Glennanan g r a n o d i o r i t e , (x35, p l a i n l ight) o c c a s i o n a l l y p h e n o c r y s t s 1 c m . l o n g a r e found. The c o m p o s i t i o n ranges f r o m A n to A n i n the c o r e to A n o r m o r e sodic on the 3 4 ZO 2 4 r i m s . I n c l u s i o n s of hornblende b i o t i t e and a n h e d r a l q u a r t z a r e p r e s e n t . M i c r o c l i n e m i c r o p e r t h i t e and q u a r t z a r e i n t e r s t i t i a l to p l a g i o c l a s e (plate X , f i g . 2 ) . A few s m a l l e u h e d r a l c r y s t a l s of q u a r t z a r e p r e s e n t i n the t r a n s i t i o n zone between q u a r t z m o n z o n i t e and grano d i o r i t e . M y r m e k i t e i s s c a r c e a long the contacts be tween p l a g i o c l a s e and m i c r o c l i n e and p o i k i o l i t i c b r o w n b i o t i t e and g r e e n h o r n b l e n d e a r e i n t e r s t i t i a l to p l a g i o c l a s e . H o r n b l e n d e f o r m s p r i s m a t i c or a n h e d r a l g r a i n s or aggregates , i n t e r g r o w n w i t h b i o t i t e (plate X I , f i g . 2 ) . H o r n b lende has the f o l l o w i n g p l e o c h r o i c s c h e m e : X , pa le green ; Y , dark g r e e n ; Z , g r e e n i s h b r o w n . C h l o r i t e and s e r i c i t e a r e the c o m m o n a l t e r a t i o n p r o d u c t s of b i o t i t e but h o r n b l e n d e i s r e l a t i v e l y f r e s h - l o o k i n Sphene i s r e l a t i v e l y abundant but apatite i s l e s s so than i n the other r o c k types of the i n t r u s i v e . Sphene f o r m s v e r y l a r g e r h o m b i c c r y s t a l s (plate X I , f i g . 1) up to 2 . m . m . l o n g . M a g n e t i t e , b e s i d e s f o r m i n g i n t e r l o c k i n g gra ins w i t h the other a c c e s s o r i e s i n the g r o u n d - m a s s , c o m m o n l y f o r m s i n c l u s i o n s i n or i n t e r g r o w t h s w i t h sphene. T A B L E V I I R E C A L C U L A T E D M O D A L A N A L Y S E S O F T H E G L E N N A N A N C O M P L E X (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) M i c r o c l i n e 62 .8 50 .5 4 6 . 6 4 5 . 2 36 .1 5 0 . 5 23 .9 20 .8 17 .9 4 2 . 7 3 2 . 7 3 8 . 3 A l b i t e * 14.4 19 .3 15.6 18 .2 29 .5 19. 3 33 .9 3 5 . 9 37. 7 3 8 . 0 2 9 . 9 28 .1 A n o r t h i t e * 2 . 7 5 . 0 3 . 8 5 . 2 9 . 6 5 . 0 10 .7 10 .8 11.1 1 0 . 7 9 .3 9 .1 Q u a r t z 17.2 18.9 30 .3 17.6 14.4 18.9 15.5 21 .5 16.9 7 .0 19 .3 12 .7 B i o t i t e 1.1 2 .4 2 .3 7 .2 3 .9 2 .4 6 .2 4 . 5 5 . 6 0 .7 2 .9 7 .3 Hornblende 0 .2 1.8 0 .2 3 .4 2 .1 1.8 4 . 4 2 .2 5 . 5 0 .5 2 .3 0 .8 Magnet i te 0.8 1.3 0 .8 1.9 2 .8 1.3 3 .6 2 .2 3 .4 0 .4 2 .4 0 .7 Sphene 0.4 0 .5 0 .4 1.0 1.8 0 .5 1.4 1.6 1.3 - - - 0 .9 * A v e r a g e v a l u e s of An24 and O r a o f o r the p l a g i o c l a s e and a l k a l i f e l d s p a r s r e s p e c t i v e l y , w e r e u s e d to r e c a l c u l a t e the a lb i te and anor th i te separa te ly , f o r the c a l c u l a t i o n of the c h e m i c a l a n a l y s i s of these r o c k s . ĉ CO T A B L E VIII C A L C U L A T E D C H E M I C A L A N A L Y S I S O F T H E G L E N N A N A N C O M P L E X F R O M M O D A L A N A L Y S E S ( T A B L E VII) S a m p l e N o . s i o 2 A 1 2 ° 3 F e 2 0 3 FeO MgO CaO N a 2 0 K 2 0 TiO 2 (1) E G B - 1 69 .6 15 .5 0 .59 0 .48 0.17 0 .82 1.70 10. 7 0 .20 (2) E N - 1 7 1 68 .6 16.1 1. 16 0 .83 0 .31 1.48 2 .75 8 .44 0. 21 (3) E G B - 1 8 73 .8 13.3 0 .64 0 .70 0 .27 0.98 1.85 8. 07 0. 23 (4) E G B - 3 66. 1 15. 1 1.71 2 .21 1.48 1.92 2 . 19 8. 25 0 .65 (5) E G B - 8 65 .1 16 .6 1.81 1. 61 0 .87 2 . 9 1 3 .50 6 .42 0 .86 (6) E G B - 1 7 2 68 .9 15.3 1. 12 1. 02 0 .66 1.39 2 .30 8 .75 0 .29 (7) E G B - 1 5 63 .6 16 .2 2. 90 2 .64 1.64 3 .23 4 . 04 4 . 5 7 0.78 (8) E G B - 1 6 67 .6 15.6 1. 78 1. 74 0 .95 3 . 05 4 . 2 7 3 .90 0.81 (9) E G B -17 64 .2 15.9 2 .80 2. 54 1.84 3 .52 4 . 4 8 3 .49 0.71 (10) E G B - 5 * 65 .9 19 .2 0. 31 0. 28 0. 18 2 .21 4 . 4 9 7. 28 - - (11) E G B - 6 * 67 .3 15.8 1.83 1.46 0 .82 2 .60 3 .54 5 . 77 0 .47 (12) E G B - 9 * 6 5 . 0 17. 2 0 .94 1.85 1.34 2 .41 3 .59 7. 13 0 .52  CaQ* v 72 Figure e. V' r i ^ t i u i diagm f o r the Glennen-n complex i r o n {">.) g r a n o d i o r i t e , (2) quartz wonaonite to (3) granite, (cklcul~ted from ?a ble 7171). 73 D I S C U S S I O N O F T H E V A R I A T I O N D I A G R A M S F O R T H E G L E N N A N A N C O M P L E X : The p e r c e n t a g e of the p r i n c i p l e ox ides of the Glennanan r o c k s f r o m T a b l e VIII have been p lo t ted w i t h the v a r i a t i o n d i a g r a m s of p i t c h s t o n e s and p e r l i t e s , ( f i g . 38) B o w e n , 1928, page 1Z7 i n f i g u r e 6, T h e s e s t a n d a r d c u r v e s r e p r e s e n t an unquest ionable m a g m a t i c v a r i a t i o n . The a r e a s des ignated A and A ^ r e p r e s e n t a l a r g e group of g r a n i t e s , h i g h i n SiO and r a t h e r l o w i n both a l k a l i s ; B and B a r e g r a n i t e s h i g h i n K^O and v e r y l o w i n N a ^ O ; C and C^ a r e g r a n i t e s w i t h e x t r e m e l y h i g h K 0 and but l i t t l e N a 0; and D and D a r e a group 2 2 1 of s i l i c e o u s g r a n i t e s v e r y h i g h i n soda w i t h potash n e a r l y l a c k i n g ( B o w e n , 1928). T h e r e a r e no c o r r e s p o n d i n g r o c k s among p i t chs tones and p e r l i t e s i n these des ignated areas except i n the case of B and B ^ . R h y o l i t i c o b s i d i a n s whose c o m p o s i t i o n s a r e analogous to the c r y s t a l l i n e igneous r o c k s do not p l o t i n these c i r c l e d areas ( B o w e n , 1928). The fact that c r y s t a l l i n e r o c k s i n c l u d e c o m p o s i t i o n s u n m a t c h e d i n g l a s s y r o c k s suggest an o r i g i n of r o c k s i n these c i r c l e d areas b y c r y s t a l a c c u m u l a t i o n (Bowen, 1928) or some other s e c o n d a r y p r o c e s s of d i ff e r ent i a t i o n . The s t r i k i n g fea ture of the v a r i a t i o n i n the Glennanan r o c k s i s the h i g h v a l u e of the K 0 and the l o w value of N a 0. The A 1 2 0 . Fe^O^+FeO, MgO and CaO of the Glennanan c o m p l e x p a r a l l e l the c o m - 74 p o s i t i o n a l v a r i a t i o n i n the g l a s s y r o c k s , F i g . 6 but the t r e n d of the a l k a l i s depar ts at a SiO„ content of 65 p e r c e n t and m o v e s into the f i e l d ( C and C^) of p o t a s h r i c h g r a n i t e s . O v e r a SiO range of 65 to 71 p e r c e n t , the K 0 va lue v a r i e s f r o m 3. 5 to 8 .8 and N a 0 v a r i e s f r o m 3. 5 to 1.7 p e r c e n t . A K^O value of 10. 1 was obta ined f r o m the c h i l l e d zone of the g r a n i t e . R y o l i t i c o b s i d i a n s , the aphani t i c e q u i - va lents of g r a n i t i c r o c k s c l u s t e r a r o u n d a K^O value of 4 . 5 p e r c e n t and a Na^O content of about 4 p e r c e n t . A n e r r o r of 10 p e r c e n t was a s s u m e d p o s s i b l e (Page )o ) i n the m o d a l a n a l y s i s of the p o t a s h feldspar i n the c o a r s e g r a i n e d p o r - p h y r i t i c g r a n i t e . F r o m the c a l c u l a t e d c h e m i c a l a n a l y s i s of the Glennanan s p e c i m e n s E G B - 1 8 a and E n - 1 7 1 ( T a b l e s VII , VIII) whose b i o t i t e content i s 1. 8 and 1. 6 r e s p e c t i v e l y the v a r i a t i o n i n the K^O v a l u e of the r o c k i n r e s p o n s e to the changing mode of m i c r o c l i n e can be a p p r o x i m a t e d . A 10 p e r c e n t e r r o r i n the mode of m i c r o c l i n e f o r E G B - 1 8 , w o u l d r e s u l t i n a 7 p e r c e n t e r r o r i n the K^O va lue o r a d e c r e a s e f r o m a K 0 v a l u e of 8. 04 to 7. 48 p e r c e n t . The average K 0 va lue i n the 2 2 Glennanan granite i s 8 .4 p e r c e n t . If the c o r r e c t va lue of the potash content i n the c h i l l e d zone of the g r a n i t e i s n e a r th i s average va lue r a t h e r than the c a l c u l a t e d v a l u e of 10. 1 ( sp . E G B - 1 ) p e r c e n t , an e r r o r of a p p r o x i m a t e l y 40 p e r c e n t i n the m o d a l a n a l y s i s of m i c r o c l i n e w o u l d have h a d to be m a d e . T h i s does not s e e m v e r y l i k e l y . 75 The author conc ludes that a v a r i a t i o n ( f i g . 6) i n the K^O va lue of the Glennanan c o m p l e x o v e r a SiO^ content of 64 to 73 p e r c e n t , f r o m 3. 5 to 8 p e r c e n t i s a c l o s e a p p r o x i m a t i o n and the v a r i a t i o n i s t o w a r d a r e a C ^ or p o s s i b l y B ^ , r e p r e s e n t a t i v e of gran i tes r i c h i n p o t a s h and l o w i n soda . The s m o o t h v a r i a t i o n c r u v e s of c e r t a i n ox ides of the r o c k zones i n the Glennanan c o m p l e x , f i g s . 7 and 8 a r e compatab le w i t h t h e i r f o r m a t i o n b y d i f f e r e n t i a t i o n of a p a r e n t g r a n o d i o r i t e m a g m a . S T R U C T U R E The Glennanan i n t r u s i v e c o m p l e x o c c u r s as t h r e e separate bodies i n the m a p a r e a : (1) an a s y m m e t r i c a l l y zoned b o d y of p o r p h y r i t i c g r a n i t e - q u a r t z m o n z o n i t e - and g r a n o d i o r i t e b o r d e r i n g on the Endako R i v e r ; (2) an a s y m m e t r i c a l l y zoned body of p o r p h y r i t i c g r a n i t e - a n d q u a r t z m o n z o n i t e on N i t h i M o u n t a i n ; and (3) a s m a l l s tock of p o r p h y r i t i c q u a r t z m o n z o n i t e a r o u n d A l f L a k e . P e r t h i t e m e g a c r y s t s a r e p r e s e n t i n a l l r o c k zones but a r e l a r g e r and m o r e abundant i n the g r a n i t e zone. The l a r g e r i n t r u s i v e body, spanning the Endako R i v e r , i s the s o u t h - e a s t e r n e x t e n s i o n of the m a i n Glennanan p luton w h i c h extends i n a n o r t h - n o r t h w e s t d i r e c t i o n , 8 m i l e s o r m o r e beyond the map a r e a . A l l contacts between the r o c k zones of the c o m p l e x a r e g r a d a t i o n a l o v e r w i d e a r e a s . The t r e n d of the r o c k zones of the l a r g e r body c o n f o r m s 76 to the g e n e r a l n o r t h - n o r t h w e s t t r e n d of the m a i n p luton , w h e r e a s the r o c k zones on N i t h i M o u n t a i n t r e n d i n a m o r e n o r t h e r l y d i r e c t i o n . A weak f o l i a t i o n , c h a r a c t e r i s t i c of e p i z o n a l i n t r u s i v e s (Buddington , 1959) i s m a r k e d b y : (1) the p r e f e r r e d o r i e n t a t i o n of p e r t h i t e m e g a c r y s t s a long the c h i l l e d m a r g i n s of the gran i te zone; and (2) p r e f e r r e d a l i g n m e n t of m a f i c m i n e r a l s , c l u s t e r s of p e r t h i t e m e g a c r y s t s and x e n o l i t h s n e a r the contact of the g r a n o d i o r i t e , p a r t i c u l a r l y n o r t h of the m a p a r e a ( C a r r , 1965), w i t h the S i m o n B a y d i o r i t e . The c o n f o r m i t y of these fea tures w i t h the w a l l r o c k suggests that the f o l i a t i o n i s a p r i m a r y f low s t r u c t u r e . The f o l i a t i o n dips s t e e p l y and s t r i k e s between west and nor thwes t i n the gran i te zone and n o r t h and n o r t h w e s t e r l y i n the g r a n o d i o r i t e . F o l i a t i o n i n the q u a r t z m o n z o n i t e and throughout m o s t of the grani te and g r a n o d i o r i t e zones i s i n d i s t i n c t o r absent . The l a c k of exposures p r e v e n t e d d i r e c t o b s e r v a t i o n of the contacts of the Glennanan i n t r u s i v e b o d i e s w i t h the c o u n t r y r o c k and the o r d e r of e m p l a c e m e n t of the Glennanan r o c k zones i s not k n o w n . The p o r p h y r i t i c c h i l l e d m a r g i n of the gran i te zone, d i a g n o s t i c feature of the epizone (Buddington, 1959) i s exposed 1/4 m i l e due east of C a s e y L a k e . H e r e , the c h i l l e d zone of the grani te i s exposed o v e r a w i d t h of a p p r o x i m a t e l y 50 feet and i s s e p a r a t e d f r o m the c h i l l e d m a r g i n of the C a s e y i n t r u s i v e to the west b y about 60 feet of o v e r b u r d e n . 77 N o r t h of C asey L a k e , the contact between the Glennanan g r a n i t e and the Endako q u a r t z m o n z o n i t e i s h i d d e n but seems to have been c o n t r o l l e d b y a n o r t h - n o r t h w e s t f r a c t u r e zone t h r o u g h C a s e y L a k e . A 30 to 50 foot w i d e d a r k g r e y p o r p h y r i t i c l a t i t e d ike , w h i c h cuts the E n d a k o , C a s e y and the Glennanan i n t r u s i v e s , has been i n t r u d e d along this zone (see m a p i n f o l d e r ) . O n the w e s t f lank of N i t h i M o u n t a i n the u n c o n t a m i n a t e d p o r p h y r i t i c c h i l l e d m a r g i n of the g r a n i t e and m e d i u m - g r a i n e d f o l i a t e d S i m o n B a y d i o r i t e are exposed about 100 feet f r o m each o t h e r . The nature of the contact of the Glennanan q u a r t z m o n z o n i t e zones , n o r t h of the E n d a k o R i v e r and on N i t h i M o u n t a i n , w i t h the o l d e r p lutons i s not k n o w n . The e a s t e r n m o s t e x p o s u r e of the p o r p h y r i t i c g r a n o d i o r i t e i s f o l i a t e d and c o n t a m i n a t e d b y i n c l u s i o n of the S i m o n B a y d i o r i t e c o m p l e x . E N V I R O N M E N T O F E M P L A C E M E N T That the i n t r u s i v e bodies of the Glennanan C o m p l e x w e r e e m p l a c e d i n the epizone (Buddington, 1959) i s suggested b y : (1) w e a k l y deve loped f l o w s t r u c t u r e s a long the m a r g i n s of the gran i te and g r a n o d i o r i t e adjacent to the o l d e r S i m o n B a y C o m p l e x ; (2) s h a r p l y bounded p o r p h y r i t i c c h i l l e d m a r g i n s of the gran i te w h i c h a r e g r a d a t i o n a l i n w a r d to c o a r s e - g r a i n e d p o r p h y r i t i c g r a n i t e - q u a r t z m o n z o n i t e - a n d g r a n o d i o r i t e ; and (3) g r a n o p h y r i c t e x t u r e i n the g l o m e r o p o r p h y r i t i c f ac ies of the grani te and i n the p o r p h y r i t i c q u a r t z m o n z o n i t e . O R I G I N O F T H E P A R E N T M A G M A The u n c o n t a m i n a t e d p o r p h y r i t i c c h i l l e d m a r g i n s of the Glennanan g r a n i t e d i s q u a l i f i e s g r a n i t i z a t i o n as a m o d e of o r i g i n f o r the c o m p l e x . The v a r i a t i o n t r e n d s of the p r i n c i p l e ox ides of the Glennanan r o c k types ( f i g . 6) l e n d support to a m a g m a t i c o r i g i n f o r these r o c k s . The c o m p o s i t i o n of the m a i n r o c k zones v a r i e s s y s t e m a t i c a l l y f r o m the c h i l l e d m a r g i n of the g r a n i t e zone to the g r a n o d i o r i t e zone ( T a b l e V I ) . The c o m p o s i t i o n a l t r e n d s e s t a b l i s h e d i n the t e r n a r y d i a g r a m s , F i g . 7 and 8, a r e c o m p a t a b l e w i t h the f o r m a t i o n of the p l u t o n b y d i f f e r e n t i a t i o n of a p a r e n t g r a n o d i o r i t e m a g m a . A m a g m a t i c o r i g i n of the p e r t h i t e m e g a c r y s t s of the g l o m e r o - p o r p h y r i t i c f a c i e s of the gran i te i s s t r o n g l y i n d i c a t e d f r o m the f o l l o w i n e v i d e n c e : (1) z o n a l d i s t r i b u t i o n of e u h e d r a l and a n h e d r a l i n c l u s i o n s (2) s y s t e m a t i c i n c r e a s e i n a lb i te content of p l a g i o c l a s e i n c l u s i o n s w i t h i n c r e a s i n g d is tance f r o m the centre of the p e r t h i t e m e g a c r y s t s (3) the s t r u c t u r a l and o p t i c a l o r i e n t a t i o n s of the i n c l u s i o n s , p a r t i c u l a r l y the p l a g i o c l a s e w i t h the hos t p e r t h i t e ( H i b b a r d M . J . , 1965) The p r e s e n c e of p e r t h i t e m e g a c r y s t s and l a r g e aggregates of q u a r t z i n the c h i l l e d b o r d e r s as w e l l as i n t e r i o r zones of the G l e n - nanan c o m p l e x i n d i c a t e s a v e r y e a r l y stage of c r y s t a l l i z a t i o n f o r these 79 c o n s t i t u e n t s . S ince t h e r e a r e p l a g i o c l a s e c r y s t a l s i n the c o r e of the p e r t h i t e m e g a c r y s t s , p l a g i o c l a s e w i t h a c o m p o s i t i o n about A n ^ g 2 m u s t have b e e n the f i r s t f e l d s p a r phase to c r y s t a l l i z e . The amount of p l a g i o c l a s e that f o r m e d ' b e f o r e the appearance of a l k a l i f e l d s p a r m u s t have been s m a l l . In g e n e r a l , 75 p e r c e n t o r m o r e of the i n c l u s i o n s of p l a g i o c l a s e are c o n c e n t r a t e d i n the outer r e g i o n s of the m e g a c r y s t s . The q u a r t z , h o r n b l e n d e , sphene and magnet i t e i n c l u s i o n s i n the c o r e a reas i n d i c a t e that they a l so j o i n e d p l a g i o c l a s e at a v e r y e a r l y stage of c r y s t a l l i z a t i o n . B i o t i t e f o r m e d l a t e r than h o r n b l e n d e . H i b b a r d (pg . 254, 1965) states "the o r i e n t a t i o n of the p l a g i o - c l a s e c r y s t a l s p a r a l l e l to r a t i o n a l c r y s t a l l o g r a p h i c p lanes of the p h e n o c r y s t s i s e x p l a i n e d m o s t l o g i c a l l y as a continuous p r o c e s s of a t tachment and i n c o r p o r a t i o n of s m a l l p l a g i o c l a s e c r y s t a l s on the e u h e d r a l s u r f a c e s of g r o w i n g a l k a l i f e l d s p a r c r y s t a l s . T h i s means that c r y s t a l s of p l a g i o c l a s e and a l k a l i f e l d s p a r w e r e suspended i n a m e l t and that the m e l t was s u f f i c i e n t l y m o b i l e to a l l o w these g r o w i n g c r y s t a l s to c o m e into contact . T u r b u l e n c e r e l a t e d to m a g m a t i c f low i s p r o b a b l y r e s p o n s i b l e for the m o t i o n r e q u i r e d b y th is h y p o t h e s i s . " P e r t h i t e m e g a c r y s t s w h i c h conta in o r i e n t e d and n o n - o r i e n t e d i n c l u s i o n s i n the other r o c k zones of the Glennanan c o m p l e x p r o b a b l y deve loped i n the same m a n n e r as the m e g a c r y s t s i n the g l o m e r o - p o r p h y r i t i c f a c i e s of the g r a n i t e zone. The e u h e d r a l f o r m of q u a r t z and the equant g r a i n s of m i c r o c l i n e i n the i n t e r s t i t i a l m i c r o p e r t h i t e 80 of the Glennanan p o r p h y r i t i c gran i te and q u a r t z m o n z o n i t e suggests that they f o r m e d i n a m a g m a w i t h l i t t l e i n t e r f e r e n c e f r o m adjacent c r y s t a l s . T h e s e f e a t u r e s , together w i t h the g e n e r a l l a c k of f l o w s t r u c t u r e s i n a l l r o c k zones , suggests that the m a g m a was e m p l a c e d i n a h i g h l y f l u i d s tate . D I F F E R E N T I A T I O N A l t h o u g h the a s y m m e t r i c a l p a t t e r n of the Glennanan i n t r u s i v e s suggests i n t r u s i o n of t h r e e independent m a g m a s , the u n i v e r s a l i t y of the p e r t h i t e m e g a c r y s t s and the g r a d a t i o n a l contacts be tween the r o c k zones d i s q u a l i f i e s th i s h y p o t h e s i s . D i f f e r e n t i a t i o n of a s i n g l e m a g m a i n s i t u to f o r m a p o r p h y r i t i c g r a n i t e zone a long the w e s t e r n s i d e , an i n t e r m e d i a t e zone of p o r p h y r i t i c q u a r t z m o n z o n i t e , and an e a s t e r n zone of p o r p h y r i t i c g r a n o d i o r i t e , n o r t h of the Endako R i v e r i s not v e r y l i k e l y because of the r e l a t i v e i m m o b i l i t y of c r y s t a l s i n v i s c o u s g r a n i t e m e l t s . D i f f e r e n t i a t i o n i n p l a c e m a y have a r i s e n as a r e s u l t of c o n t a m i n a t i o n of a g r a n i t i c m a g m a b y m o r e b a s i c w a l l r o c k m a t e r i a l . The gran i te zone i f e m p l a c e d a long the e a s t e r n contact of the p l u t o n m a y have been m o d i f i e d to a g r a n o d i o r i t e b y a s s i m i l a t i o n of the S i m o n B a y d i o r i t e n o r t h of the Endako R i v e r . The g r a n i t e zone on the southwest s ide of"this body i s u n c o n t a m i n a t e d but th is m i g h t be expected s ince the c o u n t r y r o c k , the Endako q u a r t z 81 m o n z o n i t e i s c h e m i c a l l y s i m i l a r to the i n t r u d i n g p h a s e . H o w e v e r , the u n c o n t a m i n a t e d p o r p h y r i t i c g r a n i t e contact w i t h the S i m o n B a y d i o r i t e on N i t h i M o u n t a i n i n d i c a t e s a m i n o r r o l e of w a l l r o c k a s s i m i l a t i o n i n the f o r m a t i o n of the Glennanan c o m p l e x i n the m a p a r e a . The author conc ludes that the c o m p o s i t i o n a l v a r i a t i o n i s the r e s u l t of d i f f e r e n t i a t i o n of a s ing le m a g m a at depth. A homogeneous m a g m a of i n t e r m e d i a t e c o m p o s i t i o n t h r o u g h some m e c h a n i s m of d i f f e r e n t i a t i o n at depth, m i g h t y i e l d a heterogeneous body of m a g m a m o r e a l k a l i - r i c h i n the upper r e g i o n s . The c o n c e n t r a t i o n of p e r t h i t e m e g a c r y s t s i n the g r a n i t e zone suggests the p o s s i b i l i t y that t h i s f r a c t i o n a t i o n m i g h t have o c c u r r e d i n r e s p o n s e to the g r a v i t a t i o n a l r i s i n g of these c r y s t a l s i n a denser l i q u i d . The e f fec t iveness of s u c h a p r o c e s s i n the d i f f e r e n t i a t i o n of v i s c o u s g r a n i t i c m e l t s i s l e s s w i d e l y accepted than i s the d o w n w a r d c o n c e n t r a t i o n of h e a v y m i n e r a l s i n b a s i c m a g m a s ( T u r n e r and V e r h o o g e n , I960, p g . 84). A m e c h a n i s m w h e r e b y a l k a l i s m a y be c o n c e n t r a t e d i n the upper r e g i o n s of the m a g m a has been suggested b y K e n n e d y , 1955, " W a t e r w i l l d i f fuse and d i s t r i b u t e i t s e l f i n a m a g m a so that the c h e m i c a l p o t e n t i a l of w a t e r i s the s a m e throughout the m a g m a c h a m b e r . B y this m e c h a n i s m water tends to be c o n c e n t r a t e d i n the m a g m a c h a m b e r i n the reg ions of l o w e s t p r e s s u r e s and t e m p e r a t u r e s . A l k a l i s and c e r t a i n m e t a l s w i l l c o - o r d i n a t e w i t h water and, s i m i l a r l y be c o n c e n t r a t e d i n the r e g i o n s of l o w e s t p r e s s u r e and t e m p e r a t u r e . " 82 Figure 9d LEGEND porphyritic grarodiorite Porphyritic quartz mon zonite Porphyritic granite present erosional level Figure 9» Diagrammatic sketch showing a h y p o t h e t i c a l deve] opnent of rock zones of the Glennanan Complex. 83 A n h y p o t h e t i c a l sequence of events that i s p r o p o s e d to e x p l a i n the deve lopment of the a s y m m e t r i c a l r o c k zones i n the Glennanan i n t r u s i v e b o d i e s i s i l l u s t r a t e d d i a g r a m a t i c a l l y i n F i g u r e 9. Ln f i g u r e 9a, l a r g e p o t a s h f e l d s p a r s c r y s t a l l i z e d f r o m the a l k a l i - r i c h m a g m a f o r m e d at the top of the m a g m a c h a m b e r . The cont inuous r e m o v a l and i n c o r p o r a t i o n i n the g r o w i n g p o t a s h f e l d s p a r s of other c r y s t a l phases f o r m i n g i n the m a g m a , c o n t r i b u t e d to the p r o c e s s e f fec t ing d i f f e r e n t i a t i o n , that i s , d i f f u s i o n of v o l a t i l e s and a l k a l i s . D u r i n g the f i r s t stage of i n t r u s i o n ( f i g . 9b) the u p p e r p a r t of the m a g m a , c h a r g e d w i t h these potash f e l d s p a r m e g a c r y s t s , was d r a w n off to f o r m the outer c o a r s e - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e g r a n i t e . The steep d i p p i n g att i tude of the o b s e r v e d f l o w s t r u c t u r e s a long the b o r d e r s of the i n t r u s i v e i n d i c a t e s that v e r t i c a l m o v e m e n t was p r o m i n e n t and that the p luton i s p r o b a b l y not d o m e d at the p r e s e n t e r o s i o n a l l e v e l . In p l a c e s a long the r a p i d l y c o o l i n g m a r g i n s of the g r a n i t e zone, p o t a s h f e l d s p a r m e g a c r y s t s w e r e a l i g n e d p a r a l l e l to the steep f l o w d i r e c t i o n b y the u p w a r d and o u t w a r d f o r c e of the i n t r u d i n g m a g m a . A t other l o c i , pockets of m a g m a s a t u r a t e d w i t h m e g a c r y s t s w e r e swept off and c a r r i e d up as uni ts to p r o d u c e the g l o m e r o p o r p h y r i t i c g r a n i t e a long the c h i l l e d m a r g i n s . The v e r y c o a r s e - g r a i n e d tex ture of the p o r p h y r i t i c grani te zone over m o s t of i t s w i d t h i n d i c a t e s that except for a long the m a r g i n s , the m a g m a c o o l e d v e r y s l o w l y . C r y s t a l l i z a t i o n i n w a r d s , p o s s i b l y t o w a r d s a q u a r t z m o n z o n i t e c o m - p o s i t i o n , was p r o b a b l y s t i l l t a k i n g p l a c e when the q u a r t z m o n z o n i t e f r a c t i o n of the m a g m a was d r a w n off and i n t r u d e d into the e a s t e r n edge of the gran i te zone ( f i g . 9 c). T h i s n e w l y i n t r u d e d m a g m a m i x e d c o m p l e t e l y w i t h the g r a n i t e a long t h e i r contacts to f o r m the c o a r s e - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e q u a r t z m o n z o n i t e i n t e r m e d i a t e zone. Some p o t a s h f e l d s p a r m e g a c r y s t s w e r e p r o b a b l y s t i l l a v a i l a b l e i n the m a g m a c h a m b e r to be d r a w n off d u r i n g this s tage . Pn the s a m e m a n n e r as the p r e c e d i n g s tages , the r e m a i n d e r of the d i f f e r e n t i a t e d m a g m a was d r a w n off and i n t r u d e d into the e a s t e r n edge of the p o r p h y r i t i c q u a r t z m o n z o n i t e ( f i g . 9d) to p r o d u c e the m e d i u m - g r a i n e d p o r p h y r i t i c h o r n b l e n d e - b i o t i t e g r a n o d i o r i t e zone, n o r t h of the Endako R i v e r . If at th is stage, the m a g m a h a d been c o m p l e t e l y depleated of m e g a c r y s t s , i t m a y have been p o s s i b l e f o r the g r a n o d i o r i t e to capture some m e g a c r y s t s f r o m the c r y s t a l l i z i n g p o r p h y r i t i c q u a r t z m o n z o n i t e zone. W a l l r o c k c o n t a m i n a t i o n i s a m i n o r effect a long the e a s t e r n contact of the g r a n o d i o r i t e zone and does not appear to have h a d an effect on the o v e r a l l development of the r o c k zones i n the m a p a r e a . T O P L E Y S T A G E I V C A S E Y B I O T I T E Q U A R T Z M O N Z O N I T E - A L A S K I T E F I E L D R E L A T I O N S H I P S The m a j o r center of i n t r u s i o n of the C a s e y q u a r t z m o n z o n i t e i s n o r t h of S a v o r y L a k e , jus t beyond the n o r t h w e s t e r n m a r g i n s of the m a p a r e a (see C a r r , 1965). R a d i a t i n g f r o m th is m a i n i n t r u s i v e b o d y a r e a s e r i e s of v e r y l a r g e f i n e - t o - m e d i u m - g r a i n e d dikes w h i c h extend f o r m i l e s a c r o s s the r e g i o n a l t r e n d of the o l d e r i n t r u s i v e s of the T o p l e y c o m p l e x . I s o l a t e d s tocks and d i k e s , c o n s i d e r a b l e d i s t a n c e s f r o m th is center , a r e p o s s i b l y r e l a t e d to other centers of i n t r u s i o n w h i c h d i d not b r e a c h the p r e s e n t e r o s i o n a l s u r f a c e of the t h e s i s a r e a . Such a s a t e l l i t e d i k e , a v e r a g i n g one m i l e i n w i d t h , enters the m a p a r e a south of S a v o r y L a k e and continues e a s t - s o u t h e a s t a d i s t a n c e of 11 m i l e s to the S te l lako R i v e r . A s h a r p l y bounded stock of C a s e y q u a r t z m o n z o n i t e - a l a s k i t e u n d e r l i e s an a r e a of a p p r o x i m a t e l y 12 squar m i l e s on the east f lank of N i t h i M o u n t a i n . S m a l l i s o l a t e d e x p o s u r e s o c c u r a long the n o r t h e r n edge of the m a p a r e a and p r o b a b l y r e p r e s e n t the s o u t h e r n ex tens ion of l a r g e r s a t e l l i t e dikes of the m a i n p l u t o n . 86 S u b s i d u a r y dikes and apl i tes o c c u p y f r a c t u r e s r a n g i n g i n w i d t h f r o m one i n c h to 500 feet, a long the m a i n contac ts . P E T R O G R A P H Y S p e c i m e n s t a k e n f r o m the m a i n C a s e y i n t r u s i o n n o r t h of the m a p a r e a , a r e p i n k 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 to s u b - p o r p h y r i t i c b i o t i t e q u a r t z m o n z o n i t e s . H o r n b l e n d e i s not p r e s e n t . The a v e r a g e g r a i n s i z e i s 8 m . m . but p e r t h i t e and q u a r t z m a y r e a c h d i a m e t e r s of 1. 5 c m . i n p l a c e s . A p o r p h y r i t i c t e x t u r e i s g e n e r a l l y i n c o n s p i c u o u s b e c a u s e of the i r r e g u l a r i t y of the g r a i n m a r g i n s . B i o t i t e c o m p r i s e s be tween 2 and 4 p e r c e n t of the r o c k . M i a r o l i t i c c a v i t i e s and pods of p e g m a t i t e a r e m o r e abundant than i n the s a t e l l i t i c i n t r u s i o n s i n the t h e s i s a r e a . A p o r p h y r i t i c c h i l l e d f a c i e s was o b s e r v e d n e a r O w l L a k e , 5 m i l e s n o r t h of S a v o r y L a k e . The C a s e y i n t r u s i o n s i n the m a p a r e a have v e r y b r o a d b o r d e r zones , c o m p o s e d of f i n e - g r a i n e d ( a v e r a g i n g 2 m . m . i n s i z e ) p o r p h y r i t i c l e u c o c r a t i c g r a n i t e and q u a r t z m o n z o n i t e ( c o l l e c t i v e l y r e f e r r e d to as a l a s k i t e ) . T h i s m a r g i n a l f a c i e s i s g r a d a t i o n a l into a c e n t r a l r e g i o n c o n s i s t i n g of m e d i u m - g r a i n e d ( a v e r a g i n g 5 m . m . i n d i a m e t e r ) p o r p h y r i t i c b io t i t e q u a r t z m o n z o n i t e . In the f i n e - t o m e d i u m - g r a i n e d r o c k s , b i o t i t e m a y exceed 1 p e r c e n t and q u a r t z o r o c c a s i o n a l l y p o t a s h f e l d s p a r m a y f o r m p h e n o c r y s t s . A s h a r p l y 87 bounded c h i l l e d zone r a n g i n g i n w i d t h f r o m one foot to 50 feet was o b s e r v e d n e a r S a v o r y L a k e south of h i g h w a y 16, and due east of C a s e y L a k e r e s p e c t i v e l y . Q u a r t z p h e n o c r y s t s , 1 to 2 m . m . i n d i a m e t e r are c o n s p i c u o u s i n the v e r y f ine g r a n u l a r g r o u n d m a s s . The r o c k s i n and n e a r the m a r g i n s c a r r y o n l y t r a c e s of b i o t i t e and tend to be r i c h i n p o t a s h f e l d s p a r . M i a r o l i t i c c a v i t i e s , l e n s e s of p e g m a t i t e and pods of b i o t i t e a r e found i n the N i t h i M o u n t a i n s tock . The modes of these r o c k s i s shown i n T a b l e I X T A B L E I X M o d a l A n a l y s e s of the C a s e y I n t r u s i v e G r a n i t e Q u a r t z M o n z o n i t e E N - 1 8 4 E N - 2 0 2 E N - 1 8 5 E N - 1 8 6 M i c r o c l i n e 1 52 .0 4 5 . 3 4 0 . 0 30 .0 2 P l a g i o c l a s e 11.0 20 .1 25 .0 30 .0 Q u a r t z 37 .0 33 .1 33 .0 36.0 B i o t i t e t r . 1.5 1.0 3 .0 M u s c o v i t e t r . - t r . M a g n e t i t e t r . t r . t r . 1.0 *~ M i c r o c l i n e c o m p o s i t i o n i s O r g 2 2 - P l a g i o c l a s e c o m p o s i t i o n i s A n 88 In t h i n s e c t i o n , the m a i n t e x t u r a l d i f f e r e n c e between the f ine and c o a r s e - g r a i n e d r o c k s of the C a s e y i n t r u s i v e , i s the h a b i t of q u a r t z . In the f i n e - g r a i n and c h i l l e d m a r g i n s of the i n t r u s i v e , e u h e d r a l s i x s i d e d c r y s t a l s or r o u n d e d s u b h e d r a l g r a i n s f o r m i n c l u s i o n s i n p l a g i o c l a s e and m i c r o c l i n e (plate XI I , f i g . 1) as w e l l as i n t e r l o c k i n g c r y s t a l s i n the g r o u n d m a s s . Q u a r t z a l so o c c u r s as a n h e d r a l i n t e r s t i t i a l g r a i n s w h i c h e m b a y p l a g i o c l a s e and m i c r o c l i n e i n the f i n e - g r a i n e d r o c k s . W i t h i n c r e a s i n g g r a i n s i z e , the C a s e y i n t r u s i v e shows a l e s s g r a n u l a r , m o r e i n t e r s t i t i a l t ex ture w i t h r e s p e c t to q u a r t z and f e l d s p a r . E u h e d r a l to s u b h e d r a l q u a r t z c r y s t a l s a r e p r e s e n t i n some of the c o a r s e - g r a i n e d r o c k s of the c e n t r a l zone of the C a s e y q u a r t z m o n z o n i t e . P o i k i l i t i c p e r t h i t i c m i c r o c l i n e f o r m s i n t e r s t i t i a l g r a i n s or o c c a s i o n a l l y p h e n o c r y s t s w i t h v e r y i r r e g u l a r m a r g i n s . E x s o l v e d p l a g i o c l a s e c o m p r i s e s about 1 p e r cent of the m i c r o c l i n e i n the f i n e - g r a i n e d r o c k s and 3 to 4 p e r c e n t i n the c o a r s e - g r a i n e d q u a r t z m o n z o n i t e . E m b a y m e n t of p l a g i o c l a s e b y m i c r o p e r t h i t e and s e g r e g a t i o n of e x s o l v e d a lb i te t o w a r d s the g r a i n m a r g i n s of the host a r e m o r e p r e v a l e n t i n the c o a r s e - g r a i n e d r o c k s . P l a g i o c l a s e f o r m s s u b h e d r a l c r y s t a l s w i t h b r o a d s a u s s u r i t i c and s e r i c i t i c c o r e s and t h i n u n a l t e r e d m a r g i n s . The average c o m p o s i t i o n i s o l i g i o c l a s e ( A n ). O s c i l l a t o r y zoning i s absent i n the f i n e - g r a i n e d 89 P L A T E XI I F i g u r e 1: A n h e d r a l and e u h e d r a l q u a r t z (Q) c r y s t a l s i n m i c r o c l i n e (M) w h i c h i s i n t e r s t i t i a l to the p l a g i o c l a s e (P) i n the c h i l l e d zone of the C a s e y a l a s k i t e (xlOO, c r o s s e d n i c o l s ) go r o c k s and w e a k l y deve loped i n the c o a r s e - g r a i n e d . G r e e n b i o t i t e ranges f r o m t r a c e amounts i n the a l a s k i t e , 1-2 p e r c e n t i n the f i n e - m e d i u m - g r a i n e d a r e a s of the dike and stock, to 3 to 5 p e r c e n t i n the m a i n body, n o r t h of S a v o r y L a k e . The p l e o c h r o i c s c h e m e of b i o t i t e i s as f o l l o w s : x, m e d i u m g r e e n ; Y , d a r k g r e e n ; Z , p a l e apple g r e e n . The t e x t u r e v a r i e s f r o m i n t e r s t i t i a l w i s p s and r a g g e d la ths to t a b u l a r i n t e r l o c k i n g g r a i n s . M u s c o v i t e o c c u r s i n a l a s k i t i c a r e a s of the C a s e y i n t r u s i v e . In p l a c e s a long the m a r g i n s , i t c o m p r i s e s as m u c h of the r o c k s as does b i o t i t e . It f o r m s i n t e r g r a n u l a r la ths and w i s p s w i t h b i o t i t e , i n t e r g r o w t h s w i t h and o c c a s i o n a l l y wide r i m s on b i o t i t e g r a i n s . The contact be tween the r i m m u s c o v i t e and c o r e b i o t i t e i s v e r y s h a r p and the m u s c o v i t e r e p r o d u c e s the shape of the e n c l o s e d b i o t i t e g r a i n . The m u s c o v i t e i s f r e s h - l o o k i n g c o m p a r e d to the c h l o r i t i z e d b i o t i t e . A c c e s s o r y m i n e r a l s , apat i te , sphene, magnet i te and a l l a n i t e f o r m i n t e r l o c k i n g g r a i n s i n the g r o u n d m a s s and i n c l u s i o n s i n b i o t i t e and m i c r o p e r t h i t e . A l o n g the m a r g i n s of the C a s e y i n t r u s i v e , some effects of s t r a i n and c r u s h i n g a r e shown b y s t r o n g l y undulose q u a r t z , bent and b r o k e n p l a g i o c l a s e t w i n l a m e l l a e and d e f o r m e d m i c a s . S i m i l a r f ea tures w e r e o b s e r v e d i n some s p e c i m e n s taken f r o m the c e n t r a l a reas of the i n t r u s i v e . 91 S T R U C T U R E The e m p l a c e m e n t of the C a s e y i n t r u s i o n s i n the m a p a r e a has b e e n s t r o n g l y c o n t r o l l e d b y a set of w e s t - n o r t h w e s t e r l y and n o r t h - e a s t e r l y t r e n d i n g f r a c t u r e zones . T h i s d i s c o r d a n t i n t r u s i v e i s s h a r p l y bounded against the o l d e r i n t r u s i v e s of the T o p l e y c o m p l e x . W e s t of C a s e y L a k e , the i n t r u s i v e i s conf ined to the Endako q u a r t z m o n z o n i t e but to the east i t was e m p l a c e d a long the contact between the Glennanan c o m p l e x and the Endako p l u t o n . O n N i t h i M o u n t a i n , i t has i n t r u d e d the c e n t r a l a r e a of what was p r o b a b l y once one continuous body of the Glennanan c o m p l e x . Contac ts w i t h the o l d e r uni ts of the b a t h o l i t h a r e c h i l l e d and show no ev idence of the exchange of m a t e r i a l w i t h the w a l l r o c k s . X e n o l i t h s are absent and the r o c k l a c k s a d i r e c t i o n a l f a b r i c . A l o n g the S te l l ako R i v e r the C a s e y i n t r u s i v e i s s h a r p l y t r u n c a t e d b y the younger S t e l l a k o q u a r t z m o n z o n i t e . E N V I R O N M E N T O F E M P L A C E M E N T A n e p i z o n a l depth of e m p l a c e m e n t for the C a s e y i n t r u s i v e s i s s t r o n g l y i n d i c a t e d b y the f o l l o w i n g : (1) the s h a r p l y bounded p o p h y r i t i c c h i l l e d m a r g i n s (2) the l a c k of a f o l i a t i o n and x e n o l i t h s (3) the absence of b r e c c i a t i o n a long the contacts (4) the p r e s e n c e of m i c r o l i t i c c a v i t i e s and pods of c o a r s e g r a i n e d potash f e l d s p a r , q u a r t z and h e x a - gonal b i o t i t e b o o k s . The C a s e y q u a r t z m o n z o n i t e - a l a s k i t e was p r o b a b l y e m p l a c e d a long w i d e f r a c t u r e zones b y f o r c e f u l i n j e c t i o n of a h i g h l y f l u i d m a g m a . 93 T O P L E Y S T A G E V S T E L L A K O H O R N B L E N D E - B I O T I T E Q U A R T Z M O N Z O N I T E F I E L D R E L A T I O N S H I P S R o c k s of the S te l lako i n t r u s i v e a r e r e s t r i c t e d to the e a s t e r n p a r t of the m a p a r e a be tween the S te l lako R i v e r and the west f lank of N i t h i M o u n t a i n . T h e s e e x p o s u r e s , g e n e r a l l y c o v e r i n g l e s s than 1 s q u a r e m i l e , a r e s e p a r a t e d b y w i d e areas of r e c e n t s e d i m e n t s . S m a l l e r e x p o s u r e s o c c u r on an i s l a n d and the wes t s i d e of a p e n i n s u l a i n F r a s e r L a k e . F r e s h - l o o k i n g p o r p h y r i t i c h o r n b l e n d e q u a r t z d i o r i t e d i k e s , s t r i k i n g n o r t h e a s t e r l y , cut the Endako q u a r t z m o n z o n i t e n e a r the j u n c t i o n of the Glennanan and M i n e roads and a long the r i v e r n o r t h of P o n d L a k e . S i m i l a r d ikes cut the Glennanan g r a n i t e west of the s m a l l l a k e on the Glennanan r o a d , the q u a r t z m o n z o n i t e n e a r A l f L a k e and the S i m o n B a y d i o r i t e at M o u s e P o i n t on F r a s e r L a k e . On the p e n i n s u l a i n F r a s e r L a k e , the S i m o n B a y c o m p l e x i s a lso cut b y f i n e - g r a i n e d p o r p h y r i t i c q u a r t z d i o r i t e and q u a r t z m o n z o n i t e d ikes w h i c h a r e offshoots of the S te l lako q u a r t z m o n z o n i t e i n t r u s i v e i m m e d i a t e l y to the south. 94 P E T R O G R A P H Y The r o c k i s a f i n e - t o m e d i u m - g r a i n e d g r e y - p i n k h o r n b l e n d e b i o t i t e q u a r t z m o n z o n i t e . G r a n o d i o r i t e o c c u r s i n p l a c e s n e a r the contacts w i t h the o l d e r i n t r u s i v e s . The a p p r o x i m a t e m o d a l c o m p o s i t i o n of s e v e r a l r e p r e s e n t a t i v e types i s g i v e n i n Tab le X . T A B L E X M o d a l A n a l y s e s of the r o c k s of the S te l l ako I n t r u s i v e Q u a r t z M o n z o n i t e G r a n o d i o r i t e M u d h o l e L a k e Shotgun C r e e k L o w e r S te l l ako U p p e r * S t e l l a k o R i v e r R i v e r 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 Q u a r t z B i o t i t e H o r n b l e n d e 38. 0 20. 0 32. 0 5. 0 3. 0 20. 0 37. 0 35.0 6.0 2. 0 25. 0 45. 0 20. 0 8. 0 14. 0 55. 0 23. 0 4. 0 2. 0 1 - p l a g i o c l a s e c o m p o s i t i o n ranges - ^ 2 4 T O A N 3 4 C a r r , 1965 95 P L A T E XIII F i g u r e 1: S a u s s u r i t i z e d s u b h e d r a l p l a g i o c l a s e (P) w i t h i n t e r s t i t i a l q u a r t z (Q), and m i c r o - p e r t h i t e (M) i n the S te l lako q u a r t z m o n - zoni te . (xlOO, c r o s s e d n i c o l s ) F i g u r e 2: T e x t u r e of S te l lako q u a r t z m o n z o n i t e . Note a n h e d r a l b i o t i t e (B) , and s u b h e d r a l p l a g i o c l a s e (P) i n m i c r o p e r t h i t e (M) ( x 3 5 , c r o s s e d n i c o l s ) 96 The t e x t u r e of the S te l lako i n t r u s i v e i s e q u i g r a n u l a r a long the S te l l ako R i v e r and west of Seas L a k e but p o r p h y r i t i c at M u d h o l e L a k e and on the west f lank of N i t h i M o u n t a i n . H e r e , potash f e l d s p a r p h e n o c r y s t s range i n s i z e f r o m 1 /2 to 1 c m . l o n g . Q u a r t z and p o t a s h f e l d s p a r i n the g r o u n d m a s s a r e i n t e r s t i t i a l to p l a g i o c l a s e . B i o t i t e exceeds h o r n b l e n d e and together they c o m p r i s e between 4 and 8 p e r c e n t of the r o c k . P r i s m a t i c hornblende o r s t r e a k s and elongated m a f i c c lo ts i n the m a t r i x g ive the r o c k a weak l i n e a r e lement . N e a r the contacts of the S te l lako i n t r u s i v e the g e n e r a l l y i n d i s t i n c t f o l i a t i o n i s accentuated i n p l a c e s b y m a f i c r i c h l e n s e s and bands w h i c h give the r o c k a g n e i s s i c t e x t u r e . In t h i n - s e c t i o n , e u h e d r a l to s u b h e d r a l p l a g i o c l a s e i s n o r m a l l y zoned n e a r the S t e l l a k o River'.<but zoning i§ fa int or absent at M u d h o l e L a k e . The c o r e s have a c o m p o s i t i o n of A n to A n and the p e r i p h e r a l 30 34 zone v a r i e s be tween A m , 4 *° '^'ZO' M y r m e k i t e i s not c o m m o n . I n t e r s t i t i a l m i c r o p e r t h i t e , p o i k i o l i t i c a l l y enc loses q u a r t z , b i o t i t e , h o r n b l e n d e and p l a g i o c l a s e , and l o c a l l y embays these m i n e r a l s . U n d u l a t o r y , i n t e r s t i t i a l q u a r t z contains i n c l u s i o n s of apati te , magnet i te o r o c c a s i o n a l l y b i o t i t e and h o r n b l e n d e . B i o t i t e of the b r o w n v a r i e t y o c c u r s as s u b h e d r a l g r a i n s , r a g g e d la ths o r i n t e r g r o w t h s and c l u s t e r s w i t h h o r n b l e n d e . G r e e n hornblende c o m m o n l y f o r m s p r i s m a t i c g r a i n s . The a c c e s s o r y m i n e r a l s magnet i te , sphene, apati te and p y r i t e f o r m i n t e r s t i t i a l g r a i n s i n the groundmass o r i n c l u s i o n s i n b i o t i t e , h o r n b l e n d e , m i c r o p e r t h i t e o r o c c a s i o n a l l y p l a g i o c l a s e . 97 S T R U C T U R E The Ste l lako i n t r u s i v e cuts the Endako q u a r t z m o n z o n i t e and s h a r p l y t r u n c a t e s the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e a long the S te l lako R i v e r . H e r e , f i n e - g r a i n e d S te l l ako g r a n o d i o r i t e gneiss w i t h m i n o r l e n s e s of a m p h i b o l i t e , f o r m s a 40 foot wide m a r g i n a l zone aga ins t the C a s e y i n t r u s i v e . B a n d s of gne i ss , l e n s e s of a m p h i - b o l i t e and the m a f i c m i n e r a l s a r e a l i g n e d p a r a l l e l to the n o r t h e a s t e r l y contact w i t h the C a s e y i n t r u s i v e and appear to dip s t e e p l y to the w e s t . A t a d i s t a n c e of 20 to 30 feet east of the r i v e r , the f o l i a t i o n of the S te l l ako g r a n o d i o r i t e i s i n d i s t i n c t and the r o c k i s m e d i u m - g r a i n . The t o t a l w i d t h of the f i n e - g r a i n e d c h i l l e d zone i s a p p r o x i m a t e l y 75 feet . The contact of the S te l lako i n t r u s i v e w i t h the Endako q u a r t z m o n z o n i t e i s h i d d e n . O n the l a r g e p e n i n s u l a at the west end of F r a s e r L a k e , the contact w i t h the S i m o n B a y d i o r i t e i s c r o w d e d w i t h angular to subrounded f r a g m e n t s of a m p h i b o l i t e and q u a r t z d i o r i t e ( C a r r , 1965) O n the west s ide of H a r t m a n ' s H i l l , S i m o n B a y d i o r i t e has been potash m e t a s o m a t i z e d b y the i n t r u d i n g S te l lako q u a r t z m o n z o n i t e . T h i s has r e s u l t e d i n a t r a n s i t i o n zone a p p r o x i m a t e l y 200 feet w i d e c o m p o s e d of S te l lako g r a n o d i o r i t e and S i m o n B a y s y e n o d i o r i t e between the t y p i c a l r o c k types of these two i n t r u s i v e s . A p l i t e d ikes and segregat ions of hornblende and potash f e l d s p a r are c o m m o n i n th i s t r a n s i t i o n zone. P o t a s h m e t a s o m a t i s m was o b s e r v e d i n the S i m o n B a y d i o r i t e adjacent 98 to the S te l lako i n t r u s i v e near M a r y and M u d h o l e L a k e s . The f o l i a t i o n of the S te l l ako i n t r u s i v e i n these t r a n s i t i o n zones , p a r a l l e l s that o b s e r v e d i n the o l d e r d i o r i t e . E N V I R O N M E N T O F E M P L A C E M E N T A n upper m e s o z o n a l to l o w e r e p i z o n a l depth of e m p l a c e m e n t i s i n d i c a t e d b y : (1) c h i l l e d and u n c h i l l e d contacts ; (2) f o l i a t e d m a r g i n s and l o c a l zones of gneiss near the b o r d e r s w h i c h c o n f o r m to the t r e n d of the w a l l r o c k ; (3) the sharp t r u n c a t i o n of the C a s e y q u a r t z m o n z o n i t e a long the S te l l ako R i v e r ; and (4) b r e c c i a t e d contacts and f e l d s p a t h i z a t i o n of the S i m o n B a y w a l l r o c k s . E m p l a c e m e n t was p r o b a b l y a c c o m p l i s h e d b y f o r c e f u l i n t r u s i o n w i t h l o c a l s toping , w a l l r o c k a s s i m i l a t i o n and m e t a s o m a t i s m . 99 P O N D Q U A R T Z M O N Z O N I T E P L U G T h i s r o c k i s expo sed i n a s i n g l e outcrop near the t a i l i n g s - p o n d d a m n o r t h of the Endako m i n e . It i s a p i n k i s h - g r e y , f r e s h l o o k i n g , 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 h o r n b l e n d e - b i o t i t e q u a r t z m o n z o n i t e . In t h i n s e c t i o n the t ex ture i s l a r g e l y h y p i d i o m o r p h i c g r a n u l a r w i t h an average g r a i n s i z e of 2. 5 m . m . M i n o r amounts of i n t e r - g r a n u l a r f i n e - g r a i n e d q u a r t z and f e l d s p a r a r e p r e s e n t , but i n i n s u f f i c i e n t quant i ty to g ive the r o c k a p o r p h y r i t i c t e x t u r e . S u b - p o i k i l i t i c , i n t e r s t i t i a l m i c r o p e r t h i t e i n c l u d e s a l l m i n e r a l s . S e r i c i t i c m i c r o p e r t h i t e l o c a l l y embays p l a g i o c l a s e and q u a r t z . M y r m e k i t i c b o r d e r s a r e not c o m m o n on p l a g i o c l a s e w h i c h has s t r o n g n o r m a l zoning w i t h a weak o s c i l l a t o r y t r e n d i n the c o r e r e g i o n s . The c o m p o s i t i o n ranges f r o m A n , , to A n . V a r i a t i o n s w i t h i n i n d i v i d u a l zoned c r y s t a l s c o u l d not 16 25 be d e t e r m i n e d because of the w e a k l y developed t w i n l a m e l l a e . A n h e d r a l q u a r t z together w i t h b i o t i t e and hornblende have an i n t e r g r a n u l a r hab i t . A c c e s s o r i e s i n c l u d e sphene and magnet i t e . The e s t i m a t e d m o d a l c o m p o s i t i o n i s p e r t h i t e , 20%; p l a g i o c l a s e , 50%; q u a r t z , 35%; b i o t i t e , 3%; hornb lende , 2%; and a c c e s s o r i e s , 1%. The P o n d q u a r t z m o n z o n i t e p r o b a b l y i n t r u d e s the Endako q u a r t z 100 m o n z o n i t e . It i s not k n o w n whether this p l u g i s younger or o l d e r than the F r a s e r q u a r t z m o n z o n i t e s tock . F R A S E R Q U A R T Z M O N Z O N I T E S T O C K E x p o s u r e s of this m e d i u m g r a i n e d s u b p o r p h y r i t i c p i n k b i o t i t e - h o r n b l e n d e q u a r t z m o n z o n i t e are conf ined to two outcrops on H i g h w a y 16, n e a r the w e s t end of F r a s e r L a k e . Tn the hand s p e c i m e n , s u b h e d r a l g r e y - g r e e n p l a g i o c l a s e and p r i s m a t i c d a r k g r e e n h o r n b l e n d e f o r m p h e n o c r y s t up to 8 m . m . l o n g , i n a p i n k g r o u n d m a s s a v e r a g i n g between 1 and 3 m . m . i n g r a i n s i z e . In t h i n s e c t i o n p o i k i l i t i c m i c r o p e r t h i t e i n c l u d e s p l a g i o c l a s e , b i o t i t e and h o r n b l e n d e and i s g r a p h i c a l l y i n t e r g r o w n w i t h q u a r t z . S u b h e d r a l p l a g i o c l a s e has a c o m p o s i t i o n about A n ^ g a n d exhib 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 . P o i k i l i t i c r e d d i s h b r o w n b io t i t e and p r i s m a t i c or a n h e d r a l g r e e n h o r n b l e n d e a r e i n t e r s t i t i a l . B i o t i t e f o r m s r i m s on or i n t e r g r o w t h s w i t h h o r n b l e n d e . A c c e s s o r y m i n e r a l s are apat i te , magnet i te and sphene. The e s t i m a t e d m o d a l c o m p o s i t i o n i s p e r t h i t e , 32%; p l a g i o c l a s e , 43%; q u a r t z , 18%; b i o t i t e 2%; hornb lende , 5% and a c c e s s o r i e s 1-2%. The outcrops of the F r a s e r p o r p h y r i t i c q u a r t z m o n z o n i t e o c c u p y a p o s i t i o n i n an a r e a of c o n t r a s t i n g l o w m a g n e t i c s u s c e p t a b i l i t y ( a e r o m a g n e t i c M a p s 1589-G, H a l l e t L a k e and 1590 -G F r a s e r L a k e , 101 1963) w i t h the s u r r o u n d i n g S te l l ako q u a r t z m o n z o n i t e . Contacts w e r e not o b s e r v e d and f o l i a t i o n i s absent. The e a s t e r n o u t c r p p i s f i n e r - g r a i n e d than the other and p o s s i b l y l i e s c l o s e to the edge of the s tock . U s i n g these guides , the F r a s e r s tock w o u l d then s e e m to f o r m an e a s t - w e s t t r e n d i n g e l l i p t i c a l body a p p r o x i m a t e l y 1 /2 m i l e wide and 1 m i l e l o n g . The i n t r u s i v e p r o b a b l y i n t r u d e s the Ste l lako q u a r t z m o n z o n i t e and i t s g r a n o p h y r i c t e x t u r e i n d i c a t e s an e p i z o n a l e n v i r o n m e n t of e m p l a c e m e n t (Buddington , 1959)- E N D A K O G R O U P The Endako i n t e r m e d i a t e to b a s i c v o l c a n i c f lows u n c o n f o r m - ab ly o v e r l y 8 s q u a r e m i l e s of the T o p l e y i n t r u s i v e c o m p l e x on the n o r t h shore of F r a n c o i s L a k e , 6 square m i l e s on the n o r t h w e s t s h o r e of F r a s e r L a k e and s m a l l a r e a s southeast of N i t h i M o u n t a i n . The v o l c a n i c r o c k s a r e dark g r e e n or b r o w n a n d e s i t i c or b a s a l t i c f lows s h o w i n g a m y g d a l o i d a l , v e s i c u l a r , s c o r i a c e o u s or p o r p h y r i t i c t e x t u r e s . C h a l c e d o n i c q u a r t z , p ink to c r e a m - c o l o r e d c a l c i t e , c h l o r i t e anx z e o l i t e s f o r m the a m y g d u l e s . P h e n o c r y s t s of p l a g i o c l a s e and p y r o x e n e a r e p r o m i n e n t a long the n o r t h s h o r e of F r a n c o i s L a k e . T h e s e f l a t - l y i n g f lows a r e a s s i g n e d to the Endako G r o u p of O l i g i o c e n e or E o c e n e age. 103 S U M M A R Y A N D C O N C L U S I O N S The T o p l e y i n t r u s i v e s i n the Endako a r e a m a k e up p a r t of a c o m p o s i t e body w h i c h o c c u r s i n a n o r t h w e s t t rending be l t of g r a n i t e p lutons w h i c h extends d i s c o n t i n u o u s l y f r o m Bab ine L a k e to Q u e s n e l , a d is tance of 180 m i l e s (see F i g . 1). The F r a n c o i s i n t r u s i v e phase of the c o m p l e x i n t r u d e s v o l c a n i c r o c k s of the T a k l a G r o u p of U p p e r T r i a s s i c to J u r a s s i c age. F l a t l y i n g v o l c a n i c s of the Endako G r o u p (Eocene o r O l i g i o c e n e ) u n c o n f o r m a b l y o v e r l y the T o p l e y i n t r u s i v e s i n p a r t s of the m a p a r e a . S h e a r e d and a l t e r e d d i o r i t e w i t h m i n o r l e n s e s of a m p h i b o l i t e , gneiss and gabbro of the S i m o n B a y c o m p l e x i s the o ldes t p l u t o n i c r o c k e x p o s e d i n the m a p a r e a . The S i m o n B a y c o m p l e x , w h i c h is cut b y i n t r u s i v e s of stages III, I V and V i n the m a p a r e a , i s the s o u t h e a s t e r n ex tens ion of a d iscont inuous be l t of f o l i a t e d d i o r i t e and a m p h i b o l i t e , t r e n d i n g n o r t h w e s t e r l y a long the p e r i p h e r y of the T o p l e y i n t r u s i o n s p a r t i c u l a r l y n o r t h of the m a p a r e a ( A r m s t r o n g , 1949). The f o l i a t i o n of the S i m o n B a y c o m p l e x i n g e n e r a l c o n f o r m s to the r e g i o n a l n o r t h w e s t t r e n d of the b e l t of T o p l e y i n t r u s i o n s . The l e n s e s o r s c r e e n s of g n e i s s , a m p h i b o l i t e and gabbro w h i c h accentuate the f o l i a t i o n of the S i m o n B a y c o m p l e x p o s s i b l y r e p r e s e n t country 104 r o c k i n v a r i o u s stages of m e t a m o r p h i s m and m e t a s o m a t i s m . The f o l i a t e d d i o r i t e c o u l d be a m o r e e x t r e m e p r o d u c t of th i s same p e r i o d of g r a n i t i z a t i o n . The c h a r a c t e r of the f o l i a t i o n i n e x p o s u r e s of u n s h e a r e d d i o r i t e h o w e v e r , suggests a p r i m a r y o r i g i n p r o d u c e d d u r i n g e m p l a c e m e n t of a m a g m a . A l t h o u g h the s t r u c t u r a l ev idence i s i n c o n c l u s i v e , the author concludes that the S i m o n B a y c o m p l e x r e p r e s e n t s a m e s o z o n a l p l u t o n w h i c h was i n t r u d e d a long n o r t h w e s t zones of weakness i n the country r o c k . Stoping, m e t a s o m a t i s m and a s s i m i l a t i o n of w a l l r o c k m a t e r i a l w e r e p r o b a b l y o p e r a t i n g a long the p e r i p h e r y of the i n t r u d e d m a g m a . The i n t r u s i v e s of stage II r e p r e s e n t a r e l a t i v e l y s h a l l o w l e v e l of igneous a c t i v i t y s u p e r i m p o s e d upon the e a r l i e r m o r e deep»seated p e r i o d w h i c h f o r m e d the S i m o n B a y c o m p l e x . The c o a r s e - g r a i n e d s u b p o r p h y r i t i c Endako q u a r t z m o n z o n i t e and m e d i u m - g r a i n e d F r a n c o i s g r a n i t e , w h i c h has a p o r p h y r i t i c c h i l l e d b o r d e r zone against the f i n e - t o - m e d i u m - g r a i n e d Endako i n t r u s i v e , a r e e p i z o n a l i n t r u s i o n s . T h e y w e r e e m p l a c e d a long the s o u t h w e s t e r n edge of the g r o w i n g T o p l e y c o m p l e x under the i n f l u e n c e of a second p e r i o d of n o r t h w e s t f a u l t i n g and f r a c t u r e . T h e s e m a j o r f r a c t u r e s y s t e m s , together w i t h a l a t e r n o r t h e a s t e r l y set, have c o n t r o l l e d the s t r u c t u r a l development of the b a t h o l i t h i c c o m p l e x i n the t h e s i s a r e a . "The contacts of the Endako and F r a n c o i s i n t r u s i v e s a r e c o n f o r m a b l e to each other and the r e g i o n a l 105 n o r t h w e s t t r e n d of the S i m o n B a y c o m p l e x n e a r and b e y o n d the n o r t h e r n m a r g i n s of the m a p a r e a . The southeas tern ex tens ion of the Endako q u a r t z m o n z o n i t e , h o w e v e r , m a y cut a c r o s s the f o l i a t i o n of the o l d e r d i o r i t e on N i t h i M o u n t a i n . The absence of f o l i a t i o n i n the F r a n c o i s gran i te and Endako q u a r t z m o n z o n i t e suggests a l a r g e l y l i q u i d m o d e of t r a n s f e r f r o m depth. The F r a n c o i s i n t r u s i v e m a y r e p r e s e n t a s e c o n d genera t ion of m a g m a f r o m the same s o u r c e as the Endako i n t r u s i v e or p o s s i b l y a l a t e r i n j e c t i o n of m o r e a l k a l i - r i c h m a t e r i a l f r o m a s ing le d i f f e r e n t i a t i n g m a g m a at depth. The i n t r u s i o n s of stage II w e r e n e a r l y c o m p l e t e l y c o n s o l i d a t e d when a n e w l y f o r m e d u p s u r g e of m a g m a , the Glennanan c o m p l e x , was i n t r u d e d as : (1) a l a r g e a s y m m e t r i c a l l y zoned body of p o r p h y r i t i c g r a n i t e - q u a r t z m o n z o n i t e - a n d g r a n o d i o r i t e a long a r e g i o n a l zone of weakness between the Endako q u a r t z m o n z o n i t e and the S i m o n B a y c o m p l e x ; (2) a s m a l l e r , a s y m m e t r i c a l l y zoned body of p o r p h y r i t i c g r a n i t e - a n d q u a r t z m o n z o n i t e into the S i m o n B a y c o m p l e x on N i t h i M o u n t a o n ; and (3) a s m a l l s tock of p o r p h y r i t i c q u a r t z m o n z o n i t e into the o l d e r d i o r i t e r o c k s a r o u n d A l f L a k e . That the Glennanan i n t r u s i v e s w e r e e m p l a c e d i n a h i g h l y f l u i d state into the e p i z o n a l e n v i r o n m e n t i s i n d i c a t e d b y : (1) the steep att i tude of w e a k l y developed f low s t r u c t u r e s a long the m a r g i n s of the g r a n i t e and g r a n o d i o r i t e adjacent to the S i m o n B a y c o m p l e x ; 106 (Z) s h a r p l y bounded, u n c o n t a m i n a t e d c h i l l e d m a r g i n s i n the outer g r a n i t e zones w h i c h a r e g r a d a t i o n a l i n w a r d to c o a r s e - g r a i n e d p o r p h y r i t i c r o c k s i n the i n t e r i o r zones; (3) p e r t h i t e m e g a c r y s t s i n the c h i l l e d m a r g i n s of the gran i te zone w h i c h conta in s t r u c t u r a l l y o r i e n t e d i n c l u s i o n s ; and (4) g r a n o p h y r e i n the g r a n i t e and q u a r t z m o n z o n i t e zones . C h e m i c a l and m i n e r a l o g i c a l v a r i a t i o n of the r o c k zones a r e cons i s ten t w i t h the f o r m a t i o n of the Glennanan c o m p l e x b y d i f f e r e n t i a t i o n of a p a r e n t g r a n o d i o r i t e m a g m a . The f o l l o w i n g h y p o t h e t i c a l sequence of events i s p r o p o s e d to e x p l a i n the a s y m m e t r i c a l zon ing of these i n t r u s i o n s . D i f f e r e n t i a t i o n of a homogeneous m a g m a at depth b y d i f f u s i o n of a l k a l i s and v o l a t i l e s p r o d u c e d an a l k a l i - r i c h m a g m a n e a r the top of the m a g m a c h a m b e r . L a r g e potash f e l d s p a r s w h i c h c r y s t a l l i z e d i n th i s r e g i o n w e r e d r a w n off i n the f i r s t i n j e c t i o n of m a g m a and c o n c e n t r a t e d a long the m a r g i n s of the c r y s t a l l i z i n g gran i te zone. S u c c e s s i v e i n j e c t i o n s of q u a r t z m o n z o n i t e , and f i n a l l y g r a n o d i o r i t e , into the e a s t e r n edge of the e a r l i e r phas es w h i l e they w e r e s t i l l c r y s t a l l i z i n g f o l l o w e d q u i c k l y upon one another . C o m p l e t e m i x i n g of each i n j e c t i o n of m a g m a along the contacts p r o d u c e d wide g r a d a t i o n a l contacts between the d i f ferent r o c k zones . W a l l r o c k c o n t a m i n a t i o n d i d not affect the o v e r a l l development of these r o c k zones . The i n t r u s i o n of the Glennanan c o m p l e x subjected the e a r l i e r i n t r u s i v e s i n the m a p a r e a , p a r t i c u l a r l y the Endako q u a r t z m o n z o n i t e to in tense f r a c t u r i n g and l o c a l b l o c k f a u l t i n g . S t r o n g n o r t h e a s t f r a c t i o n zones w e r e p r o d u c e d at t h i s t i m e , w h i c h i n p l a c e s can be o b s e r v e d to of fset the e a r l i e r n o r t h w e s t e r l y set . The author pos tu la tes that w h i l e the Glennanan c o m p l e x was s t i l l c o o l i n g , a new m a g m a , w h i c h was l a t e r i n t r u d e d to f o r m the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e , was f o r m i n g at depth. A r c h i n g of the roof r o c k s i n r e s p o n s e to the u p w a r d p r e s s u r e of t h i s new m a g m a b e l o w r e s u l t e d i n a r e n e w e d v e r y s t r o n g p e r i o d of f r a c t u r i n g along the r e g i o n a l n o r t h w e s t and n o r t h e a s t zones of w e a k n e s s . The C a s e y m a g m a p e n e t r a t e d the c o u n t r y r o c k a long these m a j o r f r a c t u r e zones to f o r m the l a r g e d i s c o r d a n t dike and stock i n the map a r e a . These bodies w e r e p o s s i b l y i n t r u d e d i n advance of the m a i n a c t i v e l y s toping C a s e y q u a r t z m o n z o n i t e i n t r u s i v e w h i c h was e m p l a c e d just n o r t h of the m a p a r e a ( C a r r , 1965). That the C a s e y i n t r u s i v e s i n the m a p a r e a w e r e e m p l a c e d into the epizone b y f o r c e f u l i n j e c t i o n of a m o b i l e l a r g e l y l i q u i d m a g m a i s i n d i c a t e d b y : (1) the f i n e - g r a i n s i z e and wide c h i l l e d b o r d e r zone; (2) the l a c k of f o l i a t i o n , x e n o l i t h s and b r e c c i a t i o n a l o n g the contac ts ; and (3) the p r e s e n c e of m i a r o l i t i c c a v i t i e s . The l a s t m a j o r p e r i o d of igneous a c t i v i t y i s r e p r e s e n t e d b y the w e a k l y f o l i a t e d Ste l lako q u a r t z m o n z o n i t e i n the e a s t e r n p a r t of the m a p a r e a . Its e m p l a c e m e n t was c o n t r o l l e d i n p a r t b y n o r t h e a s t t r e n d i n g f a c t u r e zones . A n upper m e s e z o n a l to l o w e r e p i z o n a l depth of e m p l a c e m e n t i s suggested b y : (1) c h i l l e d and u n c h i l l e d m a r g i n s ; (2) g n e i s s i c zones a long the m a r g i n s w h i c h c o n f o r m to the t r e n d of 108 the w a l l r o c k s ; (3) b r e c c i a t e d contacts and f e l d s p a r t h i z a t i o n of the S i m o n B a y w a l l r o c k s ; and (4) a s h a r p d i s c o r d a n t contact a long the S t e l l a k o R i v e r w h i c h t runca tes the C a s e y q u a r t z m o n z o n i t e - a l a s k i t e . The author f a v o r s a l o w e r e p i z o n a l depth of e m p l a c e m e n t w h i c h i s c o m p a t a b l e w i t h the e a r l i e r e p i z o n a l plutons of stage III and I V and the e p i z o n a l F r a s e r q u a r t z m o n z o n i t e p l u g w h i c h p r o b a b l y i n t r u d e s the S te l l ako q u a r t z m o n z o n i t e . A g r o u p i n g of b i o t i t e r a d i o m e t r i c age dates a r o u n d 140 m i l l i o n y e a r s ( M i d d l e J u r a s s i c ) f o r the E n d a k o , Glennanan and Ste l lako i n t r u s i v e s was d e t e r m i n e d b y D r . W . H . Whi te of the Geo logy Depar tment , U n i v e r s i t y of B r i t i s h C o l u m b i a . T h e s e r e s u l t s a r e i n agreement w i t h the author ' s hypothes i s that T o p l e y stages II to V , r e p r e s e n t a r e l a t i v e l y s h o r t continuous p e r i o d of e p i z o n a l i n t r u s i o n , f o l l o w i n g the e m p l a c e m e n t of the m o r e deep seated m e s o z o n a l S i m o n B a y c o m p l e x . B e c a u s e the T o p l e y r o c k s a r e p r o b a b l y i n t r u s i v e into the T a k l a G r o u p ( U p p e r T r i a s s i c to J u r a s s i c ) , the author concludes that the i n t r u s i v e r o c k s i n the m a p a r e a a r e p r o b a b l y of L o w e r J u r a s s i c to L o w e r C r e t a c e o u s age. B I B L I O G R A P H Y A r m s t r o n g , J . E . 1949: F o r t St. J a m e s M a p - A r e a , C a s s i a r and C o a s t D i s t r i c t , B r i t i s h C o l u m b i a ; G e o l . S u r v . , Canada , M e m . 252. B o w e n , N . L . 1929: The E v o l u t a t i o n of the Igneous R o c k s ; P r i n c e t o n U n i v e r s i t y P r e s s . B u d d i n g t o n , A . F . 1939: A d i r o n d a c k igneous r o c k s and t h e i r m e t a m o r p h i s m ; M e m . G e o l . Soc. A m e r . , N o . 7. 1959: G r a n i t e E m p l a c e m e n t w i t h S p e c i a l R e f e r e n c e to N o r t h A m e r i c a ; G e o l . Soc . A m e r . , B u l l . , V . 70, p . 671-747. C a r r , M . J . 1965: The G e o l o g y of the Endako A r e a ; L o d e M e t a l s i n B r i t i s h C o l u m b i a , 1965, B . C . Dept . of M i n e s & P e t . R e s . , p . 114-138. C o m p t o n , R . R . 19 55: T r o n d h j e m i t e B a t h o l i t h n e a r B i d w e l l B a r , C a l i f o r n i a ; G e o l . Soc . A m e r . , B u l l . , V . 66, p . 9 -44 . D e e r , W . A . , H o w i e , R . A . , and Z u s s m a n , J . 1962: R o c k - F o r m i n g M i n e r a l s . 5 v o l s . L o n d o n L o n g m a n s , G r e e n and C o . L t d . E m m o n s , R . C . 1953: Se lec ted P e t r o g e n i c R e l a t i o n s h i p s of P l a g i o c l a s e ; G e o l . Soc . A m e r . , M e m . 52. H a m i l t o n , W . B. 1956: V a r i a t i o n s i n P l u t o n s of G r a n i t i c R o c k s of the Hunt ington L a k e A r e a of the S i e r r a N e v a d a , C a l i f o r n i G e o l . Soc . A m e r . B u l l . , V o l . 67, p . 1585-1598. 110 H i b b a r d , M . J . 1965: O r i g i n of Some A l k a l i F e l d s p a r P h e n o c r y s t s and t h e i r B e a r i n g on P e t r o g e n e s i s ; A m e r . J o u r n . S c i . , V o . 263, p . 245-261 . K e n n e d y , G . C . 1955: Some A s p e c t s of the R o l e of W a t e r i n R o c k M e l t s ; G e o l . Soc . A m e r . , Spec , p a p e r 62, p . 489-504. K i m u r a , E . T . and D r u m m o n d , A . D . 1966: G e o l o g y of the Endako M o l y b d e n u m Depos i t ; P r e s e n t e d at C . I. M . , B . C . Sec t ion M e e t i n g s , V i c t o r i a , B . C . O c t . 29. L a r s e n , E . S. J r . 1948: B a t h o l i t h and a s s o c i a t e d r o c k s of C o r o n a , E l s i n o r e , and San L u i s R e y Q u a d r a n g l e s , Southern C a l i f o r n i a ; M e m G e o l . Soc . A m e r . , N o . 29. P a r s o n s , I. 1965: The F e l d s p a t h i c L y e n i t e s of the L o c k A l i s h I n t r u s i o n s , A s s y n t , Sco t land ; J o u r . P e t . , V o l . 6, N o . 3, p . 365-395. N o b l e , J . A . 1952: E v a l u a t i o n of C r i t e r i a for the F o r c i b l e I n t r u s i o n of M a g m a ; J o u r . G e o l . V . 60, p . 34-57 . S c h e r m e r h o r n , L . J . G . 1956: The G r a n i t e s of T r a n scoso ( P o r t u g a l ) ; a s tudy of m i c r o c l i n a t i o n ; A m e r . J o u r . S c i . , V . 264, p . 329-340. S e l l m e r , H . W . 1966: G e o l o g y and P e t r o g e n e s i s of the Serb C r e e k I n t r u s i v e s C o m p l e x n e a r S m i t h e r s , B r i t i s h C o l u m b i a ; M . S . C . T h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a . S tevens , T . A . 1957: M e t a m o r p h i s m and the O r i g i n of G r a n i t i c R o c k s , N o r t h g a t e D i s t r i c t , C o l o r a d o ; G e o l . S u r v . P r o f , paper N o . 2 7 4 - M , p . 362. T i p p e r , H . W . 1963: Nechako R i v e r M a p - A r e a , B r i t i s h C o l u m b i a ; G e o . S u r v . Canada, M e m . 324. I l l T u r n e r , F . J . and V e r h o o g e n , J . I960 : Igneous and M e t a m o r p h i c P e t r o l o g y , Znd ed . , M c G r a w - H i l l , N e w Y o r k . T u t t l e , O . F . and B o w e n , N . L . 1958: O r i g i n of G r a n i t e i n L i g h t of E x p e r i m e n t a l S tudies ; G e o l . Soc . A m e r . , M e m . 74. C D iSAVORY 1, . • 6c \ E N D A K O \ C <̂7 ' 3 / " V A L F y '•• J L a. y 7 IN 76 » < 7 11 10 4" J ____ 5 ^ O - ^ ^ - ^ - J E n d a ^ l ^ o ^ ^ I M U D H O L E ' V V MacDonald, 1 P ^ N ; ^ Hart man's 80 8 / / / 3 / 70 / 0 FOSTERS 7 , Menard c, H A Z E L T O N AND oo' | / , , , . ;^ . *^ .v : f v>,̂ .̂. Mo 7, I \ Mo''";-. \ ^ v?u a » ' /Mb \ - A ; / G E O L O G Y O F T H E E N D A K O A R E A R I T I S H _ ^ C O L U M B I A N D E n d a k o G r o u p J J I n t e r m e d i a t e to b a s i c l a v a s HI T o p l e y P l u t o n i c R o c k s Eraser quar.t z men zoni te P a n d q uartz monzoni te Ste l lako quartz mortzonite • C a s e y quar t z m o n z o n i t e a lask i te G lennanan (6a)grani te , (6b)quar tz monzon i te , {6c ! g r a n o d i o r i t e , . ( 6 d ) a p l i t e F r a n c o i s g r a n i t e •1 I E n d a h o q u a r t z m o n z o n i t e S i m o n Bay d i o r 1 te c o mp ie x 2 I M e n a r d q u a r t z l a t l t e T a k l a G r o u p 1 I A c i d v o l c a n i c t u f f s and b r e c c i a s S Y M B O L y^/ G e o l o g i c a l c o n t a c t de f ined, assumed , g e o p h y s i c a l . O u t c r o p b o u n d a r y .D r l f t - c o v e r e d a r e a f o l i a t i o n , i n c h n e d , . v e r t i c a ; S h e a r , i n c l i n e d , v e r t i c a l - - ^ _ l ^ 3 L j l t , d e f i n e d , a s s u m e d L i n e a m e n t ^ / G r a v e l r o a d DH D i a m o n d dri l l h o l e Mo M o l y b d e n i t e o c c u r e n c e D i k€ Sea I e Imile 2 _ J I magne, t ic d e c l i n a t i o n 2 6"" 30'

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