@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Earth, Ocean and Atmospheric Sciences, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Bright, Edward Gordon"@en ; dcterms:issued "2012-03-22T21:23:02Z"@en, "1967"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """Granitic rocks of the Topley intrusives underlying 100 square miles, centered around Endako, north central British Columbia, form part of a composite body which lies in a northwest trending belt of granitic plutons extending from Babine Lake to Quesnel, a distance of 180 miles. Rocks of the Topley complex in the Endako area have intruded volcanic rocks of the Takla Group (Upper Triassic to Jurassic) and are unconformably overlain by flat-lying Tertiary volcanic flows. These intrusions are probably of Lower Jurassic to Lower Cretaceous age. The granitic rocks, ranging from diorite to alaskite form six large separately emplaced and sharply bounded intrusive bodies. The development of the Topley complex can be divided chronologically, from oldest to youngest, into five major stages: (I) the Simon Bay (diorite) complex; (II) the Endako quartz monzonite which is the host rock of the Endako molybdenum deposit, and the Franco is granite; (III) the Glennanan complex; (IV) the Casey quartz monzonite-alaskite; and (V) the Stellako quartz monzonite. The Glennanan complex, which is the best exposed and most intensely studied intrusive, consists of two large asymmetrically zoned bodies and a small stock of porphyritic quartz monzonite. The larger zoned body near the town of Endako has: (1) a western zone of porphyritic granite; (2) an intermediate zone of porphyritic quartz monzonite; and (3) an eastern zone of porphyritic granodiorite. A granodiorite zone is absent in the asymmetrically zoned Nithi Mountain intrusive body. All internal contact are gradational and all rock zones contain large rectangular perthite megacrysts which enclose oriented crystals of plagioclase and other minerals. The development of the rock zones can be accounted for by differentiation of a hornblende-biotite granodiorite magma at depth and successive intrusion of first granite, then quartz monzonite and finally granodiorite. Topley stages II to V represent a continuous period of epizonal intrusion following the emplacement of the more deep seated (mesozonal?) Simon Bay complex. Northwesterly and northeasterly trending fracture zones controlled the structural evolution of the Topley complex in the map area."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/41714?expand=metadata"@en ; skos:note "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 , | 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 . c^ 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'.,^ .^. 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' "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0053529"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Geological Sciences"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Geology of the Topley intrusives in the Endako area British Columbia"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/41714"@en .