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UBC Theses and Dissertations

Geologic setting and petrology of the Proterozoic Ogilvie Mountains breccia of the Coal Creek inlier,… Lane, Robert Andrew 1990

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GEOLOGIC SETTING AND PETROLOGY OF THE PROTEROZOIC OGILVIE MOUNTAIN BRECCIAS OF THE COAL CREEK INLIER, SOUTHERN OGILVIE MOUNTAINS, YUKON TERRITORY b y ROBERT ANDREW LANE B . S c , 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 , 1984 A T H E S I S SUBMITTED I N P A R T I A L F U L F I L L M E N T OF T H E REQUIREMENTS FOR THE DEGREE OF MASTER OF S C I E N C E i n T H E F A C U L T Y OF GRADUATE S T U D I E S D e p a r t m e n t o f G e o l o g i c a l S c i e n c e s We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y OF B R I T I S H COLUMBIA M a r c h , 1990 © ROBERT ANDREW L A N E , 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) FRONTISPIECE: V i e w l o o k i n g e a s t a t r e s i s t a n t e x p o s u r e o f b u f f w e a t h e r i n g O g i l v i e M o u n t a i n s b r e c c i a (OMB), l o c a t e d j u s t e a s t o f t h e DONUT b r e c c i a l o c a l i t y , i n c o n t a c t w i t h g r e y w e a t h e r i n g Q u a r t e t G r o u p . ABSTRACT O g i l v i e M o u n t a i n s b r e c c i a (OMB) i s i n E a r l y (?) t o L a t e P r o t e r o z o i c r o c k s o f t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , Y u k o n T e r r i t o r y . H o s t r o c k s a r e t h e W e r n e c k e S u p e r g r o u p ( F a i r c h i l d L a k e , Q u a r t e t a n d G i l l e s p i e L a k e g r o u p s ) a n d l o w e r F i f t e e n m i l e g r o u p . D i s t r i b u t i o n a n d 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 o f t h e b r e c c i a w e r e d e l i n e a t e d b y r e g i o n a l m a p p i n g . OMB was c l a s s i f i e d b y c l a s t t y p e a n d m a t r i x c o m p o s i t i o n . O g i l v i e M o u n t a i n s b r e c c i a c r o p s o u t d i s c o n t i n u o u s l y a l o n g two e a s t - t r e n d i n g b e l t s c a l l e d t h e N o r t h e r n B r e c c i a B e l t (NBB) a n d t h e S o u t h e r n B r e c c i a B e l t ( S B B ) . T h e NBB e x t e n d s a c r o s s a p p r o x i m a t e l y 40 km o f t h e map a r e a , a n d t h e SBB i s a b o u t 15 km l o n g . I n d i v i d u a l b o d i e s o f OMB v a r y f r o m d y k e - a n d s i l l - l i k e t o p o d - l i k e . T h e b r e c c i a b e l t s e a c h c o i n c i d e w i t h a r e g i o n a l s t r u c t u r e . T h e NBB c o i n c i d e s w i t h a n o r t h s i d e down r e v e r s e f a u l t — a n i n f e r r e d r u p t u r e d a n t i c l i n e — c a l l e d t h e M o n s t e r f a u l t . T h e SBB c o i n c i d e s w i t h a n o r t h s i d e down f a u l t c a l l e d t h e F i f t e e n m i l e f a u l t . T h e s e f a u l t s , a t l e a s t i n p a r t , g u i d e d a s c e n d i n g b r e c c i a . T h e a g e o f OMB i s c o n s t r a i n e d b y f i e l d r e l a t i o n s h i p s a n d g a l e n a l e a d i s o t o p e d a t a . I t i s y o u n g e r t h a n t h e G i l l e s p i e L a k e G r o u p , a n d i s a t l e a s t a s o l d a s t h e l o w e r F i f t e e n m i l e g r o u p b e c a u s e i t i n t r u d e s b o t h o f t h e s e u n i t s . A g a l e n a l e a d i s o t o p e m o d e l age f o r t h e H a r t R i v e r s t r a t i f o r m m a s s i v e s u l p h i d e d e p o s i t t h a t i s i n G i l l e s p i e i v L a k e G r o u p r o c k s i s 1 . 4 5 G a . G a l e n a f r o m v e i n l e t s c u t t i n g a d y k e t h a t c u t s OMB i n l o w e r F i f t e e n m i l e g r o u p r o c k s i s 0 . 9 0 G a i n a g e . T h e r e f o r e t h e a g e o f OMB f o r m a t i o n i s b e t w e e n 1 . 4 5 a n d 0 . 9 0 G a . O g i l v i e M o u n t a i n s b r e c c i a (OMB) h a s b e e n c l a s s i f i e d i n t o m o n o l i t h i c ( o l i g o m i c t i c ) a n d h e t e r o l i t h i c ( p o l y m i c t i c ) l i t h o l o g i e s . T h e s e h a v e b e e n f u r t h e r d i v i d e d b y m a j o r m a t r i x c o m p o n e n t s — e n d members a r e c a r b o n a t e - r i c h , h e m a t i t e -r i c h a n d c h l o r i t e - r i c h . M o n o l i t h i c b r e c c i a s w i t h c a r b o n a t e m a t r i c e s d o m i n a t e t h e N B B . H e t e r o l i t h i c b r e c c i a s a r e a b u n d a n t l o c a l l y i n t h e N B B , b u t a r e p r e v a l e n t i n t h e S B B . F r a g m e n t s w e r e d e r i v e d m a i n l y f r o m t h e W e r n e c k e S u p e r g r o u p . I n t h e SBB f r a g m e n t s f r o m t h e l o w e r F i f t e e n m i l e g r o u p a r e p r e s e n t . Uncommon m a f i c i g n e o u s f r a g m e n t s w e r e f r o m l o c a l d y k e s . OMB a r e g e n e r a l l y f r a g m e n t d o m i n a t e d . R e c o g n i z e d f r a g m e n t s a r e u p t o s e v e r a l 10s o f m e t r e s a c r o s s a n d g r a d e i n t o m a t r i x s i z e d g r a i n s . H y d r o t h e r m a l a l t e r a t i o n h a s l o c a l l y o v e r p r i n t e d OMB a n d i n t r o d u c e d s i l i c a , h e m a t i t e a n d s u l p h i d e m i n e r a l s . T h i s m i n e r a l i z a t i o n h a s r e c e i v e d l i m i t e d a t t e n t i o n f r o m t h e m i n e r a l e x p l o r a t i o n i n d u s t r y . R a r e e a r t h e l e m e n t c h e m i s t r y r e f l e c t s a l a c k o f m a n t l e o r d e e p - s e a t e d i g n e o u s p r o c e s s i n t h e f o r m a t i o n o f OMB. H o w e v e r , t h i s may b e o n l y a n a p p a r e n t l a c k b e c a u s e f l o o d i n g b y a l a r g e v o l u m e o f s e d i m e n t a r y m a t e r i a l c o u l d o b s c u r e a R E E p a t t e r n i n d i c a t i v e o f a n o t h e r s o u r c e . T h e g e n e s i s o f OMB i s s i g n i f i c a n t l y s i m i l a r t o m o d e r n mud d i a p i r s . I t i s p r o p o s e d t h a t OMB o r i g i n a t e d f r o m V p r e s s u r i z e d , u n d e r c o n s o l i d a t e d f i n e g r a i n e d l i m e y s e d i m e n t s ( F a i r c h i l d L a k e G r o u p ) . T h e s e w e r e t r a p p e d b e l o w a n d l o a d e d b y t u r b i d i t e s ( Q u a r t e t G r o u p ) a n d y o u n g e r u n i t s . T e c t o n i c s a n d t h e i n i t i a t i o n o f m a j o r f a u l t s a p p a r e n t l y t r i g g e r e d movement o f t h e p r e s s u r i z e d f l u i d - r i c h m e d i u m . T h e r e s u l t i n g b o d i e s o f b r e c c i a a r e s i l l - l i k e a n d d i a p i r - l i k e s e d i m e n t a r y i n t r u s i o n s . F l u i d - r i c h p h a s e s may h a v e c a u s e d h y d r o f r a c t u r i n g ( b r i t t l e f a i l u r e ) o f t h e s u r r o u n d i n g r o c k s ( e s p e c i a l l y i n t h e h a n g i n g w a l l ) . B r e c c i a i n t r u s i o n w o u l d h a v e i n c r e a s e d t h e w i d t h o f t h e p a s s a g e way w h i l e e n c o r p o r a t i n g m o r e f r a g m e n t s . I r o n - a n d o x y g e n - r i c h h y d r o t h e r m a l f l u i d s a p p a r e n t l y w e r e a s s o c i a t e d w i t h t h e d i a p i r i s m . P r e s u m a b l y t h e s e f l u i d s a r e r e s p o n s i b l e f o r t h e h i g h c o n t e n t s o f h e m a t i t e a n d i r o n c a r b o n a t e i n f r a g m e n t s , a n d e s p e c i a l l y , i n t h e m a t r i x o f t h e b r e c c i a s . E x h a l a t i o n o f t h e s e f l u i d s may h a v e f o r m e d t h e s e d i m e n t a r y i r o n f o r m a t i o n s t h a t a r e s p a t i a l l y a s s o c i a t e d w i t h t h e b r e c c i a s . v i T A B L E O F C O N T E N T S P a g e T I T L E PAGE i F R O N T I S P I E C E i i A B S T R A C T i i i T A B L E OF CONTENTS v i L I S T OF T A B L E S v i i i L I S T OF F I G U R E S i x L I S T OF P L A T E S x i L I S T OF MAPS X V i i i ACKNOWLEDGEMENTS x i x 1.0 I N T R O D U C T I O N 1 1 . 1 G E N E R A L STATEMENT 1 1 .2 L O C A T I O N AND A C C E S S 4 1 .3 P R E V I O U S WORK 5 1.4 S C O P E OF T H E S I S 6 2.0 R E G I O N A L GEOLOGY 8 2 . 1 R E G I O N A L S E T T I N G AND T E C T O N I C E V O L U T I O N 8 2 . 2 S T R A T I G R A P H I C SUMMMARY AND R E G I O N A L C O R R E L A T I O N 13 2 . 3 GEOLOGY OF T H E COAL C R E E K I N L I E R 16 2 . 3 . 1 I n t r o d u c t i o n 16 2 . 3 . 2 S t r a t i f i e d R o c k s 19 2 . 3 . 2 . 1 W e r n e c k e S u p e r g r o u p 19 2 . 3 . 2 . 2 F i f t e e n m i l e A s s e m b l a g e 3 0 2 . 3 . 2 . 3 H a r p e r G r o u p 31 2 .3 .2.4 P a l e o z o i c R o c k s 32 2 . 3 . 3 C r o s s - C u t t i n g R o c k s 34 2 . 3 . 3 . 1 M a f i c d y k e s 34 2 . 3 . 3 . 2 O g i l v i e M o u n t a i n s B r e c c i a 37 2.4 S T R U C T U R A L GEOLOGY 41 2.4 . 1 I n t r o d u c t i o n 41 2.4 .2 S t r u c t u r a l D a t a a n d I n t e r p r e t a t i o n 42 3.0 D E T A I L E D GEOLOGY O F T H E O G I L V I E MOUNTAINS B R E C C I A . . . 5 1 3 . 1 G E N E R A L D E S C R I P T I O N AND C L A S S I F I C A T I O N 51 3 . 1 . 1 D i s t r i b u t i o n a n d F o r m 51 3 . 1 . 2 C o n t a c t R e l a t i o n s 53 3 . 1 . 3 A l t e r a t i o n 55 3.1.4 T e x t u r a l V a r i e t i e s 60 3 . 1 . 5 C l a s s i f i c a t i o n 64 3 . 2 PETROGRAPHY 65 3 . 2 . 1 M o n o l i t h i c O g i l v i e M o u n t a i n s B r e c c i a . . . . 6 7 3 . 2 . 1 . 1 M o n o l i t h i c F a i r c h i l d L a k e G r o u p OMB 67 3 . 2 . 1 . 2 M o n o l i t h i c Q u a r t e t G r o u p OMB . . . 80 3 . 2 . 1 . 3 M o n o l i t h i c G i l l e s p i e L a k e G r o u p OMB 82 v i i Page 3 . 2 . 2 H e t e r o l i t h i c O g i l v i e M o u n t a i n s B r e c c i a . . 8 4 3 . 2 . 2 . 1 H e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x OMB 84 3 . 2 . 2 . 2 H e t e r o l i t h i c h e m a t i t e - r i c h m a t r i x OMB 95 3 . 2 . 2 . 3 H e t e r o l i t h i c c h l o r i t e - r i c h m a t r i x OMB 105 3 . 3 OTHER B R E C C I A BODIES I N T H E C O A L C R E E K I N L I E R . . 1 0 9 4.0 PETROCHEMISTRY 117 4 . 1 INTRODUCTION 117 4 . 2 S A M P L I N G AND A N A L Y T I C A L METHODS 118 4 . 3 MAJOR AND MINOR ELEMENT O X I D E AND T R A C E E L E M E N T CHEMISTRY 119 4 . 3 . 1 M a j o r E l e m e n t C h e m i s t r y 119 4 . 3 . 2 M i n o r a n d T r a c e E l e m e n t s 121 4 . 4 R A R E E A R T H ELEMENT CHEMISTRY OF T H E O G I L V I E MOUNTAINS B R E C C I A 122 4 . 4 . 1 D a t a P r e s e n t a t i o n 125 4 . 4 . 2 D a t a A n a l y s i s 133 4 . 4 . 3 I n t e r p r e t a t i o n o f D a t a 135 5 .0 ORIGIN OF THE OGILVIE MOUNTAINS BRECCIA OF THE COAL CREEK I N L I E R 137 5 . 1 WORLD EXAMPLES OF B R E C C I A S I M I L A R TO O G I L V I E MOUNTAINS B R E C C I A 137 5 . 2 ORIGINS PROPOSED BY OTHERS FOR O G I L V I E MOUNTAINS B R E C C I A 139 5 . 3 G E O L O G I C A L CONSTRAINTS ON G E N E S I S OF T H E O G I L V I E MOUNTAINS B R E C C I A 142 5 . 4 G E N E T I C MODEL PROPOSED FOR T H E O G I L V I E MOUNTAINS B R E C C I A 145 R E F E R E N C E S 153 AP P ENDI X A : METALLOGENY OF T H E C O A L C R E E K I N L I E R 163 AP P ENDI X B : POTASSIUM-ARGON P R E P A R A T I O N AND A N A L Y T I C A L PROCEDURES 178 APPENDIX C : S P E C I F I C R E F E R E N C E S USED TO CONSTRUCT F I G U R E 2 . 1 182 APPENDIX D : SUMMARY OF O G I L V I E MOUNTAINS B R E C C I A I N T H I N S E C T I O N 183 AP P ENDI X E : G E O C H E M I C A L TECHNIQUES AND R E S U L T S 185 AP P ENDI X F : T H E DEVELOPMENT OF RARE E A R T H E L E M E N T CHEMISTRY AND I T S G E O L O G I C A L A P P L I C A T I O N S . . . 2 0 8 APP ENDI X G : A REVIEW OF WORLD WIDE P R O T E R O Z O I C B R E C C I A S FROM T H E L I T E R A T U R E 212 v i i i LIST OF TABLES P a g e Table 2.1 S t r a t i g r a p h i c u n i t s a n d t e c t o n i c e v e n t s o f t h e C o a l C r e e k I n l i e r ( a d a p t e d f r o m R o o t s (1987) a n d T h o m p s o n a n d R o o t s ( 1 9 8 2 ) ) 10 TABLE 3.1 A b r i e f d e s c r i p t i o n o f b r e c c i a l o c a l i t i e s e x a m i n e d i n d e t a i l (Map l ) i n t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 54 TABLE 3.2. C l a s s i f i c a t i o n scheme u s e d t o c h a r a c t e r i z e O g i l v i e M o u n t a i n s b r e c c i a o f t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 65 Table 4 .1 R a r e e a r t h e l e m e n t a b u n d a n c e s i n c h o n d r i t i c m e t e o r i t e s ( W a k i t a e t a l . , 1 9 7 1 ; i n B o y n t o n , 1 9 8 4 ) , u s e d t o n o r m a l i z e t h e raw s a m p l e d a t a ( T a b l e E . 6 ) , a n d t h e N o r t h A m e r i c a n s h a l e s c o m p o s i t e ( N A S C ; H a s k i n e t a l . . 1968) 128 Table 4.2 C h o n d r i t e n o r m a l i z e d R E E d a t a f o r 17 r o c k s f r o m t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y . T h e d u p l i c a t e a n a l y s e s f o r f o u r s a m p l e s , p r e s e n t e d i n T a b l e E . 6 , w e r e a v e r a g e d p r i o r t o n o r m a l i z i n g . N o r m a l i z i n g s t a n d a r d s a r e i n T a b l e 4 . 1 129 Table 4.3 D e s c r i p t i o n o f a n o m a l o u s R E E p a t t e r n s i n s a m p l e s o f b r e c c i a s f r o m t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 136 Table 5.1 A c o m p a r i s o n o f t h e c h a r a c t e r i s t i c s o f P r o t e r o z o i c b r e c c i a d e p o s i t s f r o m t h e O g i l v i e a n d W e r n e c k e M o u n t a i n s t o O l y m p i c Dam a n d M t . P a i n t e r , A u s t r a l i a , a n d t o E a s t A r m o f G r e a t S l a v e L a k e a n d B a t h u r s t I n l e t 140 LIST OF FIGURES P a g e Figure 1.1 Map o f Y u k o n T e r r i t o r y a n d w e s t e r n N o r t h w e s t T e r r i t o r i e s s h o w i n g t h e d i s t r i b u t i o n o f P r o t e r o z o i c r o c k s a n d t h e p o s i t i o n o f t h e f i e l d a r e a w i t h r e s p e c t t o m a j o r p h y s i o g r a p h i c d i v i s i o n s , m a j o r h i g h w a y s a n d t o w n s 2 Figure 2.1 R e g i o n a l s t r a t i g r a p h i c c o r r e l a t i o n c h a r t f o r P r o t e r o z o i c a n d o v e r l y i n g P a l e o z o i c r o c k s o f t h e N o r t h e r n C o r d i l l e r a a n d t h e P u r c e l l M o u n t a i n s , s o u t h e a s t e r n B . C 12 Figure 2.2 G e o l o g y o f t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 18 Figure 2.3 S t e r e o n e t p l o t s o f s t r u c t u r a l d a t a f o r : (a) d o m a i n 1, (b) d o m a i n 2 , (c) d o m a i n 3 , a n d (d) d o m a i n 4 , C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 46 Figure 2 .4 S c h e m a t i c r e p r e s e n t a t i o n o f t h e d e v e l o p m e n t o f s t r u c t u r e s t h a t a r e r e l a t e d t o b r e c c i a f o r m a t i o n . T o p : F o l d i n g a n d f a u l t i n g d u r i n g P r o t e r o z o i c c o m p r e s s i o n . B o t t o m : D e f o r m a t i o n b y f a u l t s a l o n g w h i c h e m p l a c e m e n t o f t h e O g i l v i e M o u n t a i n s b r e c c i a ( shown a s t r i a n g l e s ) was c o n c e n t r a t e d . F L G = F a i r c h i l d L a k e G r o u p ; QG = Q u a r t e t G r o u p ; G L G = G i l l e s p i e L a k e G r o u p ; a n d t h e s t i p p l e d p a t t e r n i s t h e l o w e r F i f t e e n m i l e g r o u p . D a s h e d w i g g l y l i n e i n F L G i s a z o n e o f d e t a c h m e n t 50 Figure 3.1 P o s i t i o n o f O g i l v i e M o u n t a i n s b r e c c i a l o c a l i t i e s t h a t w e r e i n v e s t i g a t e d a n d a r e d i s c u s s e d i n t h e t e x t 52 Figure 4 .1a T e r n a r y p l o t o f L a - T h - S c . D a t a f r o m s a m p l e s u i t e 3 a r e p l o t t e d ; s y m b o l c o d e s a r e l i s t e d o n t h e f o l l o w i n g p a g e . UC = u p p e r c r u s t ; T C = b u l k c o n t i n e n t a l c r u s t ; OC = o c e a n i c c r u s t ( f r o m T a y l o r a n d M c L e n n a n , 1 9 8 5 ) . D a s h e d l i n e r e p r e s e n t s f i e l d o f 40 s h a l e a n a l y s e s ( f r o m T a y l o r a n d M c L e n n a n , 1985) 123 Figure 4 .1b L i s t o f s y m b o l s a n d t h e i r c o r r e s p o n d i n g s a m p l e n u m b e r s a n d l i t h o l o g i c name f o r t h e L a - T h - S c d i a g r a m o n F i g u r e 4 . 1 a 12 4 X p a g e Figure 4.2 C h o n d r i t e n o r m a l i z e d R E E p l o t o f some h o s t s e d i m e n t a r y r o c k s a n d m o n o l i t h i c b r e c c i a s f r o m t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t -c e n t r a l Y u k o n T e r r i t o r y 130 Figure 4.3 C h o n d r i t e n o r m a l i z e d R E E p l o t o f some m o n o l i t h i c b r e c c i a s a n d h e t e r o l i t h i c b r e c c i a s f r o m t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t -c e n t r a l Y u k o n T e r r i t o r y . 131 Figure 4.4 C h o n d r i t e n o r m a l i z e d R E E p l o t o f h e t e r o l i t h i c b r e c c i a s , b r e c c i a m a t r i x c o n c e n t r a t e s , a c a r b o n a t i t e ( ? ) d y k e , a n d a b a n d e d i r o n f o r m a t i o n f r o m t h e C o a l C r e e k I n l i e r , s o u t h e r n O g i l v i e M o u n t a i n s , w e s t - c e n t r a l Y u k o n T e r r i t o r y 132 Figure 5.1 C o m p a r i s o n o f ( t o p ) s e i s m i c r e f l e c t i o n s e c t i o n a c r o s s a mud d i a p i r f i e l d f r o m B a r b a d o s ( a f t e r B r o w n a n d W e s t b r o o k , 1988) a n d ( b o t t o m ) p r o p o s e d m o d e l f o r f o r m a t i o n o f O g i l v i e M o u n t a i n s b r e c c i a ( O M B ) . N o t e p a r t i c u l a r l y t h e c o m p a r a b l e s c a l e s , t h e i m b r i c a t e f a u l t i n g a n d t h e a s s o c i a t e d g e n t l e f o l d i n g . I n t h e OMB m o d e l t h e z o n e o f h i g h f l u i d p r e s s u r e w o u l d h a v e b e e n t h e F L G s i l t y c a r b o n a t e a n d muddy s e d i m e n t . T h e s e p r e s s u r e s w e r e i n d u c e d b y d e p o s i t i o n o f Q u a r t e t G r o u p t u r b i d i t e s . T h e M o n s t e r a n d F i f t e e n m i l e f a u l t s l o c a l i z e d e m p l a c e m e n t a n d f o r m a t i o n o f OMB. F L G = F a i r c h i l d L a k e G r o u p ; QG = Q u a r t e t G r o u p ; G L G = G i l l e s p i e L a k e G r o u p ; a n d 15G = l o w e r F i f t e e n m i l e g r o u p . SBB = S o u t h e r n B r e c c i a B e l t a n d NBB = N o r t h e r n B r e c c i a B e l t 149 x i LIST OF PLATES P a g e Plate 2.1 O u t c r o p o f r i b b e d w e a t h e r i n g p l a t y d o l o m i t i c s i l t s t o n e a n d d o l o m i t i c l i m e s t o n e o f F a i r c h i l d L a k e G r o u p ( u n i t 1 A ; l o c a t e d a b o u t 1 km n o r t h o f t h e BEEHIVE l o c a l i t y ) . P e n f o r s c a l e 22 Plate 2.2 P l a t y w e a t h e r i n g , d o l o m i t i c s i l t s t o n e -d o l o m i t i c l i m e s t o n e w i t h d i s t i n c t i v e c h l o r i t e p a r t i n g s o f t h e F a i r c h i l d L a k e G r o u p ( u n i t 1 A ; s a m p l e B L 9 - 2 2 ) 23 Plate 2.3 P i n k t o b u f f w e a t h e r i n g s i l t y d o l o s t o n e ( u n i t I B ; s a m p l e B L 8 7 - 3 ) o f F a i r c h i l d L a k e G r o u p i s b e s t e x p o s e d i n t h e N o r t h e r n B r e c c i a B e l t a r e a , e s p e c i a l l y n o r t h a n d w e s t o f t h e BEEHIVE. W e a t h e r -r e s i s t a n t f e a t u r e s , m o s t l i k e l y c a s t s o f g y p s u m o r a n h y d r i t e , o c c u r o n l y l o c a l l y 24 Plate 2 .4 I n t e r b e d d e d , f i n e g r a i n e d q u a r t z i t e a n d d o l o m i t e ( u n i t I B ; s a m p l e B L 4 - 7 ) o f F a i r c h i l d L a k e G r o u p f r o m t h e LALA l o c a l i t y 26 Plate 2.5 P r o m i n e n t e x p o s u r e o f g r e y - b r o w n w e a t h e r i n g t u r b i d i t e s e q u e n c e , i n t e r b e d d e d f i n e g r a i n e d s a n d s t o n e a n d a r g i l l i t e , ( u n i t 2) o f Q u a r t e t G r o u p . T h i s t y p i c a l e x p o s u r e i s l o c a t e d a b o u t 5 km n o r t h o f t h e BEEHIVE. . 27 Plate 2.6 C l o s e u p o f c r o s s b e d d i n g i n s a n d s t o n e o f t u r b i d i t e i n Q u a r t e t G r o u p ( u n i t 2 ; s a m p l e B L 8 7 - 6 1 l o c a t e d a b o u t 5 km n o r t h o f t h e BEEHIVE) 29 Plate 2.7 C o l u m n a r s t r o m a t o l i t e s (Conophyton) i n G i l l e s p i e L a k e G r o u p d o l o s t o n e ( u n i t 3A) l o c a t e d a p p r o x i m a t e l y 4 . 5 km w e s t o f LALA l o c a l i t y 33 Plate 2.8 O u t c r o p o f m a r o o n c o n g l o m e r a t e o f S l a t s C r e e k G r o u p ( u n i t 6) f r o m n o r t h e a s t e r n c o r n e r o f f i e l d a r e a (Map 1) 33 Plate 2.9 W e a t h e r e d s u r f a c e a n d c u t p o l i s h e d s u r f a c e ( l e f t , wet ) o f h e m a t i t e s t a i n e d , a m y g d a l o i d a l d i a b a s e d y k e ( s a m p l e B L 3 7 - 1 9 ) f r o m n o r t h w e s t c o r n e r o f f i e l d a r e a (Map 1) 36 xi i p a g e Plate 2.10 R u g g e d e x p o s u r e o f p i n k w e a t h e r i n g h e t e r o l i t h i c b r e c c i a , l o o k i n g e a s t , e a s t o f DONUT l o c a l i t y (Map 1 ) . B r e c c i a i s d i s c o r d a n t w i t h Q u a r t e t G r o u p r o c k s ( b l a c k i n f o r e g r o u n d ) . C o n t a c t ( d a s h e d l i n e ) r u n s f r o m l o w e r r i g h t t o m i d d l e l e f t e d g e o f p h o t o 38 Plate 2.11 P h o t o g r a p h o f Q u a r t e t G r o u p ( u n i t 2) t u r b i d i t e s s h o w i n g t h e r e l a t i o n s h i p b e t w e e n b e d d i n g a n d a x i a l p l a n e r c l e a v a g e . F i n e g r a i n e d s a n d s t o n e l a y e r s d e f i n e b e d d i n g t h a t d i p s m o d e r a t e l y t o t h e s o u t h . A r g i l l i t e shows s t e e p l y s o u t h d i p p i n g a x i a l p l a n e r c l e a v a g e . T h i s c l e a v a g e s t e e p e r t h a n b e d d i n g r e l a t i o n s h i p i n d i c a t e s t h a t b e d d i n g i s n o t o v e r t u r n e d . O u t c r o p i s l o c a t e d a b o u t 3 km s o u t h e a s t o f LALA l o c a l i t y (Map 1) 43 P late 3.1 F a i r c h i l d L a k e G r o u p d o l o s t o n e ( u n i t I B ; s a m p l e B L 5 - 8 l o c a t e d i n t h e n o r t h e a s t c o r n e r o f t h e f i e l d a r e a ) s h o w i n g t y p i c a l h e m a t i t i c a l t e r a t i o n 58 Plate 3.2 H y d r o t h e r m a l l y a l t e r e d b r e c c i a f r o m t h e LALA m i n e r a l p r o s p e c t (Map 1) d i s p l a y i n g c o c k a d e t e x t u r e ( r h y t h m i c a l l y p r e c i p i t a t e d q u a r t z a n d h e m a t i t e : s a m p l e B L 4 0 - 1 1 , u p p e r l e f t ) , c a r b o n a t e - q u a r t z - s e r i c i t e a l t e r a t i o n ( s a m p l e B L 4 0 - 2 7 , u p p e r r i g h t ) a n d i n t e n s e s i l i c i f i c a t i o n ( s a m p l e B L 4 0 - 2 9 , b o t t o m ) 59 Plate 3.3 H e m a t i t i c h e t e r o l i t h i c c h l o r i t e - r i c h m a t r i x b r e c c i a ( u n i t B H c l ; s a m p l e B L 5 0 - 2 l o c a t e d i n c e n t r a l p a r t o f S o u t h e r n B r e c c i a B e l t ; Map 2) d i s p l a y i n g d e l i c a t e . l a m i n a t i o n s . N o t e v a r y i n g d e g r e e s o f h e m a t i t e r e p l a c e m e n t o f f r a g m e n t s ( n e a r t o p a n d r i g h t s i d e ) t h a t i n d i c a t e h e m a t i t i z a t i o n was s e c o n d a r y 61 Plate 3.4 H e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x b r e c c i a ( u n i t B H c b ; s a m p l e B L 3 4 - 5 l o c a t e d o n r i d g e a b o u t 1 . 5 km s o u t h e a s t o f LALA l o c a l i t y ) s h o w i n g w e l l - d e f i n e d l a y e r i n g a n d t e x t u r e s s u c h a s w e a k l y d e f i n e d g r a d e d b e d d i n g o f p o s s i b l e s e d i m e n t a r y o r i g i n 62 Plate 3.5 M o n o l i t h i c b r e c c i a ( u n i t BM1; s a m p l e B L 3 2 - 5 l o c a t e d o n r i d g e a b o u t 1 . 5 km s o u t h o f LALA l o c a l i t y ) s h o w i n g s u b r o u n d e d p i n k q u a r t z i t e f r a g m e n t s i n a d e n s e m a t r i x o f p r e d o m i n a n t l y c h l o r i t e . T h e c h a o t i c j u m b l e d t e x t u r e i s common t o m o s t b r e c c i a 63 x i i i p a g e Plate 3.6 E x p o s u r e o f h e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x b r e c c i a ( u n i t B H c b ) , l o c a t e d a b o u t 2 km w e s t o f t h e BEEHIVE l o c a l i t y , d i s p l a y i n g a n g u l a r b l o c k o f b e d d e d d o l o s t o n e 0 . 8 m i n l e n g t h ( m i d d l e r i g h t ) , s m a l l e r a n g u l a r b l o c k s o f a r g i l l i t e ( l o w e r l e f t ) , a n d a b u n d a n t s u b r o u n d e d f r a g m e n t s o f s e v e r a l v a r i e t i e s 68 Plate 3.7 V i e w o f t h e SLAB l o o k i n g w e s t . T h e s h a r p c o n t a c t b e t w e e n o v e r l y i n g OMB ( b u f f ) a n d Q u a r t e t G r o u p ( g r e y ) i s t h e M o n s t e r f a u l t . T r u n c a t i o n o f b e d d i n g i n Q u a r t e t G r o u p r o c k s i s v i s i b l e a t r i g h t s k y l i n e 71 Plate 3.8 M o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM1; s a m p l e B L 2 6 - 2 l o c a t e d a b o u t 3 km e a s t o f LALA l o c a l i t y ) 72 Plate 3.9 P h o t o m i c r o g r a p h o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM3; t h i n s e c t i o n B L 1 6 - 2 ) s h o w i n g s u b r o u n d e d q u a r t z i t e f r a g m e n t s ( s e v e r a l a r e o u t l i n e d b y a d a s h e d l i n e ) i n a c a r b o n a t e m a t r i x . N o t e g r o w t h z o n e d d o l o m i t e g r a i n a n d o t h e r d o l o m i t e r h o m b s — e v i d e n c e o f r e c r y s t a l l i z a t i o n 73 Plate 3.10 P h o t o g r a p h o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t B M 1 ) . A l a r g e b l o c k o f s e m i -p l a s t i c a l l y d e f o r m e d F a i r c h i l d L a k e G r o u p d o l o m i t i c s i l t s t o n e ( u p p e r m i d d l e ) a n d t h e c e n t i m e t r e s i z e d a n g u l a r f r a g m e n t s i n a h e m a t i z e d c a r b o n a t e m a t r i x ( l o w e r m i d d l e ) a r e d i s p l a y e d . T h e o u t c r o p i s l o c a t e d o n t h e w e s t r i d g e o f t h e DONUT. P e n c i l f o r s c a l e 76 Plate 3.11 C u t a n d p o l i s h e d s u r f a c e o f c r a c k l e b r e c c i a v a r i e t y o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM1; s a m p l e B L 1 8 - 1 0 l o c a t e d a p p r o x i m a t e l y 6 km w e s t - s o u t h w e s t o f t h e BEEHIVE l o c a l i t y ) f r o m m a r g i n o f b r e c c i a b o d y . C o n t o r t e d b e d d i n g a n d c l e a r r o t a t i o n o f some f r a g m e n t s a r e c o n s p i c u o u s 77 Plate 3.12 C u t a n d p o l i s h e d (wet) s u r f a c e o f c h a n n e l w a y b r e c c i a v a r i e t y o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM1: s a m p l e TW208 l o c a t e d o n r i d g e a b o u t 1 . 7 5 km s o u t h e a s t o f LALA l o c a l i t y ) . F r a g m e n t s a r e q u a r t z i t e i n a q u a r t z - a n d c h l o r i t e - r i c h m a t r i x 78 Plate 3.13 C r a c k l e b r e c c i a v a r i e t y o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM1 l o c a t e d 1 . 5 km s o u t h e a s t o f LALA l o c a l i t y ) f r o m m a r g i n o f b r e c c i a b o d y . F a i r c h i l d L a k e G r o u p a t t h i s p o i n t i s m a i n l y d o l o s t o n e w i t h s i l t s t o n e i n t e r b e d s 79 j c i v p a g e Plate 3.14 M o n o l i t h i c Q u a r t e t G r o u p b r e c c i a ( u n i t BM2: s a m p l e B L 1 1 - 7 ; LALA l o c a l i t y , Map 1) f r o m L a l a m i n e r a l p r o s p e c t . Some f r a g m e n t s a r e b r e c c i a ( a n g u l a r b l a c k a r g i l l i t e f r a g m e n t s i n a p a l e g r e y m a t r i x ) ; o t h e r s a r e b l a c k a r g i l l i t e . C h a l c o p y r i t e ( y e l l o w m i n e r a l ; c e n t r e o f p h o t o g r a p h ) a n d p y r i t e a r e d i s s e m i n a t e d t h r o u g h o u t . . . . 8 1 P la te 3.15 a: P h o t o g r a p h o f c u t a n d p o l i s h e d s l a b o f h e m a t i t i c m o n o l i t h i c G i l l e s p i e L a k e G r o u p b r e c c i a ( u n i t B M 3 ; s a m p l e B L 8 7 - 7 ) f r o m t h e c o n t a c t b e t w e e n G i l l e s p i e L a k e G r o u p d o l o s t o n e a n d OMB o n t h e n o r t h e r n e d g e o f t h e DONUT j Map 1 ) . b : M i c r o p h o t o g r a p h o f m o n o l i t h i c G i l l e s p i e L a k e G r o u p b r e c c i a ( u n i t BM3; t h i n s e c t i o n B L 8 7 - 7 ; f r o m DONUT l o c a l i t y ) s h o w i n g s u b a n g u l a r f i n e g r a i n e d d o l o s t o n e f r a g m e n t s i n a c o a r s e g r a i n e d d o l o m i t e c e m e n t . M i n o r h e m a t i t e p a r t i a l l y r i m s some f r a g m e n t s 83 Plate 3.16 L o c a t i o n o f b r e c c i a s i l l i s m a r k e d b y a d a s h e d l i n e i n t h i s v i e w o f t h e "BEEHIVE" (Map 1) l o o k i n g w e s t . N o t e a l s o t h e b a n d o f b r e c c i a ( a r r o w ) h o s t e d i n Q u a r t e t G r o u p s e d i m e n t s o n f l a n k o f m o u n t a i n t o t h e l e f t o f t h e BEEHIVE 86 Plate 3.17 C u t a n d p o l i s h e d s u r f a c e o f h a n d s a m p l e f r o m h e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x b r e c c i a ( u n i t B H c b ; s a m p l e B L 1 0 - 1 4 ) f r o m t h e BEEHIVE b r e c c i a s i l l . N o t e g e n e r a l l y a n g u l a r o u t l i n e o f f r a g m e n t s a n d c h a o t i c o r i e n t a t i o n . F r a g m e n t s a r e : h e m a t i t e a l t e r e d d i a b a s e ( d ) , q u a r t z i t e ( q ) , a r g i l l i t e ( a ) , d o l o s t o n e (o) , a n d s i l t s t o n e (s) 87 Plate 3.18 C u t s u r f a c e o f h a n d s a m p l e f r o m h e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x b r e c c i a ( u n i t B H c b ; s a m p l e B L 8 7 - 7 0 ) f r o m t h e e x p o s u r e o f b r e c c i a t o t h e s o u t h ( t o t h e l e f t o f BEEHIVE i n P l a t e 3 . 1 6 ) o f t h e BEEHIVE. F r a g m e n t s a r e : d i a b a s e ( d ) , q u a r t z i t e ( q ) , a r g i l l i t e ( a ) , d o l o s t o n e (o) , a n d s i l t s t o n e (s) 89 Plate 3.19 C r o s s c u t t i n g n a t u r e o f d y k e - l i k e b r e c c i a b o d y ( o u t l i n e d b y a d a s h e d l i n e ) i s shown i n t h i s v i e w o f t h e SLAB l o c a l i t y (Map 1) l o o k i n g e a s t 90 Plate 3.20 DONUT l o c a l i t y (Map 1) l o o k i n g n o r t h - e a s t a t s t e e p l y d i p p i n g c o n t a c t , i n f o r e g r o u n d , b e t w e e n o r a n g e w e a t h e r i n g d o l o s t o n e o f G i l l e s p i e L a k e G r o u p ( u n i t 3 A , r i g h t a n d f a r l e f t ) a n d m a r o o n h e t e r o l i t h i c b r e c c i a ( u n i t B H c b , c e n t r e ) 92 XV page Plate 3.21 DONUT l o c a l i t y (Map 1) looking west from the middle of the complex. Note i r r e g u l a r and i n t e r f i n g e r i n g contact between b r e c c i a (tan, above) and Quartet Group (grey, below) 93 Plate 3.22 Outcrop of h e t e r o l i t h i c carbonate -r ich matrix OMB from the northwest part of the DONUT l o c a l i t y (Map 1) . Angular fragments cons i s t of do lomit ic s i l t s t o n e of uppermost Quartet Group and pale green s i l t s t o n e , pink s i l t y dolostone and jasper of the F a i r c h i l d Lake Group. Mafic dyke fragments are r a r e . Hammer for scale 94 Plate 3.23 Photomicrograph of core of mafic igneous fragment from sample BL35-4 (unit BHcb). Broad, green c h l o r i t e l a ths formed a f ter Fe-Mg s i l i c a t e s . Hexagonal opaque c r y s t a l s are p y r i t e 97 Plate 3.24 Prominent craggy exposure of h e t e r o l i t h i c brecc ia on east fac ing f lank of DONUT l o c a l i t y (Map 1) . SLAB l o c a l i t y (Map l) i s i n the background across the v a l l e y . Note the moderate south d ipping contact (shown by a dashed l ine) between b r e c c i a (upper r ight) and underly ing Quartet Group c l a s t i c rocks 98 Plate 3.25 H e t e r o l i t h i c hemat i te -r ich-matr ix brecc ia (unit BHh; sample BL43-7) from western edge of Southern Brecc ia Be l t (Map 1). Note p l a s t i c a l l y deformed c l a s t s and crudely defined l a y e r i n g . Clas t s are: dolostone (o), quartz i t e (q), mudstone (m), coarse grained sandstone or g r i t (g), and specular hematite (h) 99 Plate 3.26 H e t e r o l i t h i c hemat i te -r ich matrix brecc ia (unit BHh; sample BL48-3) from the (POD l o c a l i t y ; Map 1), Southern Brecc ia B e l t . Fragments are: limestone (1), hematite a l t e r e d diabase (d), q u a r t z i t e (q), a r g i l l i t e (a), dolostone (o), s i l t s t o n e (s) , mudstone (m), and jasper ( j ) . Fine grained matrix cons is t s of s p e c u l a r i t e , hematite stained carbonate and subordinate quartz 100 Plate 3.27 Hemati te-r ich matrix b r e c c i a (unit BHh; sample BL24-12) from the southeast fac ing f lank of the r idge 2 km southwest of LALA mineral showing (Map 1) , Northern Brecc ia B e l t . Note d e l i c a t e laminations of specu lar i t e 102 page Plate 3.28 Photomicrograph of h e t e r o l i t h i c hematite-r i c h matrix b r e c c i a (unit BHh; sample BL43-7) of broken c r y s t a l s of quartz (q), dolomite (d), and hematite (opaque blades) i n f ine grained matrix. Note deformation lamellae and ghost zoning, out l ined by hematite dust and f l u i d i n c l u s i o n s , i n l arges t quartz g r a i n . The broken end of t h i s c r y s t a l and sca l loped edges of other c r y s t a l s a t t e s t to comminution during emplacement of t h i s rock v i a a gaseous f l u i d . Fine grained matrix cons i s t s of muscovite, carbonate, hematite and quartz 103 Plate 3.29 Photomicrograph of h e t e r o l i t h i c hematite-r i c h matrix b r e c c i a (sample BL24-12) from area north of LALA l o c a l i t y . Note growth zones, defined by f l u i d i n c l u s i o n s , and undulose ex t inc t ion i n large quartz c r y s t a l (centre of photograph). Opaques grains are hematite; high b i r e f r i n g e n t minerals are carbonate. Fine grained matrix i s hematite, c h l o r i t e and c lay 104 Plate 3.30 Two examples of h e t e r o l i t h i c c h l o r i t e - r i c h matrix b r e c c i a (unit BHcl ; sample BL35-5, above, from r idge top about 1.5 km southeast of the LALA l o c a l i t y , and sample BL3-25, below, about 2.5 km east-southeast of LALA l o c a l i t y ) . Fragments are: quar tz i t e (q), s i l t y dolostone (o), mudstone (m) and mafic dyke (d). Fine grained matrix i s c h l o r i t e and subordinate dolomite 107 Plate 3.31 Photomicrograph of h e t e r o l i t h i c c h l o r i t e -r i c h matrix b r e c c i a (unit BHcl; t h i n sect ion of sample BL30-6 from elongate b r e c c i a body south of LALA mineral showing). Subrounded fragments of quar tz i t e are cemented by c h l o r i t e , carbonate and rock f l o u r 108 Plate 3.32 Photomicrograph of coarse c r y s t a l l i n e (metasomatic) microc l ine and quartz fragment from a h e t e r o l i t h i c c h l o r i t e - r i c h - m a t r i x brecc ia (unit BHcl ; t h i n sec t ion of sample BL50-2 from middle of Southern Breccia B e l t ) . Large ragged, p o i k i l i t i c c h l o r i t e l a t h and subhedral high b i r e f r i n g e n t dolomite are l a t e r forming minera ls . A dashed l i n e separates the f ine grained matrix ( le f t ) from the c l a s t 110 Plate 3.33 Photomicrograph of h e t e r o l i t h i c c h l o r i t e -r i ch -matr ix b r e c c i a (unit BHcl; sample BL3-25). Subrounded s i l t y dolostone fragment i s hosted i n a bimodal matrix comprised of l arger quartz and carbonate gra ins set i n a f ine grained mosaic of c h l o r i t e and hematite I l l xv i i page P la te 3.34 Quartz-hematite brecc ia from Pettet mineral showing, located about 1 km southwest of the BEEHIVE l o c a l i t y 114 P la te 3.35 Intraformational G i l l e s p i e Lake Group b r e c c i a (unit 3A) from outcrop on north bank of Beehive creek due north of LALA l o c a l i t y . This b r e c c i a forms a discontinuous zone near the base of u n i t 3A 115 x v i i i LIST OF MAPS Map l Geology of the O g i l v i e Mountains b r e c c i a , Coal Creek I n l i e r , southern O g i l v i e Mountains, C L o I L west-central Yukon T e r r i t o r y i n pocket Map 2 Sample Locations i n pocket Sp C o ACKNOWLEDGEMENTS Thi s study was supported by the Geolog ica l Survey of Canada ( C o r d i l l e r a n Divis ion) under the d i r e c t i o n of Dr. Bob Thompson and i s part of the Dawson p r o j e c t . I am indebted to him for prov id ing the opportunity to work i n the O g i l v i e Mountains and for introducing the Proterozoic geology of the Coal Creek I n l i e r . I a lso thank him for reviews of parts of t h i s t h e s i s . A d d i t i o n a l f i n a n c i a l support was provided by an A r c t i c and Alp ine Research Grant and by an NSERC Grant to Dr. C o l i n Godwin at The Univers i ty of B r i t i s h Columbia. I a l so thank my thes i s supervisor , Dr. C o l i n Godwin. His t i r e l e s s e d i t i n g of numerous draf t s of the manuscript, suggestions for i t s improvement, and the inconceivably low in teres t loan of a portable personal computer, i s appreciated. Other he lp fu l advisors at the u n i v e r s i t y inc lude: Dr. W.R. Danner, who reviewed the manuscript, Dr. J . K . R u s s e l l who reviewed the petrochemistry sect ion and provided use fu l comments, Dr. R. Chase who edited the rare earth element chemistry sect ion and Dr. A . J . S i n c l a i r who c r i t i q u e d the lead isotope sec t ion . I would a l so l i k e to acknowledge a number of people at The U n i v e r s i t y of B r i t i s h Columbia whose ass istance and d iscuss ions during d i f f e r e n t parts of t h i s projec t were b e n e f i c i a l . Janet Gabites provided exce l lent i n s t r u c t i o n during galena lead isotope analyses. Di ta Runkle provided guidance through potassium analyses and Joe Harakal performed argon analyses. Gord Hodge provided expert d r a f t i n g and photography s k i l l s and made numerous improvements to the f igures and maps i n t h i s thes i s . Yvonne Douma provided countless t h i n and pol i shed t h i n sect ions . Brian Cranston, Ray Rodway and Doug Poulson kept the rock machinery, microscopes and photographic equipment w e l l -tuned. I would a lso l i k e to thank those people at The U n i v e r s i t y of B r i t i s h Columbia not d i r e c t l y involved with t h i s p r o j e c t , but who were enjoyable companions. Dr. C h a r l i e Roots, Geologica l Survey of Canada ( C o r d i l l e r a n D i v i s i o n ) , spent time d i scuss ing many aspects of the t h e s i s . His c r i t i c a l review of parts of the manuscript and t imely encouragement helped immeasurably. Dr. Murray Hitzman of Chevron Minerals L t d . a lso provided s t imulat ing d i scuss ion and REE analyses of the brecc ia s . Cra ig Boyle , formerly of Newmont Explorat ion of Canada L t d . provided 30 element ICP analyses of the brecc ias . Doug Eaton, of Archer , Cathro and Associates provided valuable d i scuss ion of Wernecke-type brecc ia deposits and made a v a i l a b l e a p r i v a t e company report on mineral occurrences i n the Coal Creek I n l i e r . Randy M c G i l l i v r a y , Dennis Burne and Kevin May provided capable and amiable assistance i n the f i e l d . F i n a l l y I would e spec ia l l y l i k e to thank my wife, Wendy, f or her patience and understanding and c h i l d rear ing throughout the course of t h i s p r o j e c t . 1.0 INTRODUCTION 1.1 GENERAL STATEMENT Enigmatic b r e c c i a complexes are exposed i n the Coal Creek I n l i e r , an oval-shaped, east - trending eros iona l window located i n the southern O g i l v i e Mountains, west -central Yukon T e r r i t o r y (Figure 1) . The b r e c c i a complexes are d i s t r i b u t e d along two d i s t i n c t northeast trending be l t s that are about 40 and 15 km long, r e s p e c t i v e l y . Brecc ias wi th in these be l t s are c a l l e d the O g i l v i e Mountains b r e c c i a (OMB). Proterozoic she l f assemblages of the Middle Proterozo ic Wernecke Supergroup and lower Fi f teenmile group host these brecc ias . These s t r a t a make up part of a discontinuous east trending b e l t of Proterozoic sediments that extends eastward from e a s t - c e n t r a l Alaska through the O g i l v i e and Wernecke Mountains in to the Mackenzie Mountains, Northwest T e r r i t o r i e s . The occurrence of Proterozoic rocks i n the southern O g i l v i e Mountains was o r i g i n a l l y c a l l e d "Coal Creek Dome" by Green (1972). "Coal Creek I n l i e r " , as suggested by Roots (1987), i s adopted here because the exposure resu l ted from 2 COAL CREEK DOME INLIER DETAIL 140° W (J) Alaska Highway j _j Sequence A § Klondike Highway | | Sequence B Dempster Highway J _ J S E Q U E N C E C Figure 1.1 Map of Yukon Territory and western Northwest Territories showing the distribution of Proterozoic rocks (adapted from Young et a l . . 1979) and the position of the f i e l d areas (Map 1; inset) with respect to major physiographic divisions (Tempelman-Kluit, 1979), major highways and towns. Sequence A includes the Wernecke Supergroup; sequence B consists Fifteenmile assemblage, Pinguicula Group and Mackenzie Mountains Supergroup; and Sequence c i s made up of Windermere Supergroup and i t s equivalents. The f i e l d areas follow the Northern Breccia Belt and the Southern Breccia Belt. 3 t h e e r o s i o n o f s t r u c t u r a l l y s h o r t e n e d a n d t h i c k e n e d s h e l f s t r a t a (Thompson a n d R o o t s , 1982) r a t h e r t h a n b y u p w a r d a r c h i n g o f t h e b a s e m e n t a s t h e t e r m "dome" s u g g e s t s . T h e W e r n e c k e - t y p e b r e c c i a s i n t h e W e r n e c k e M o u n t a i n s , c e n t e r e d a b o u t 300 km e a s t o f t h e C o a l C r e e k I n l i e r , a p p a r e n t l y a r e s i m i l a r t o t h e O g i l v i e M o u n t a i n s b r e c c i a . T h e W e r n e c k e - t y p e b r e c c i a s h a v e b e e n i n v e s t i g a t e d a n d d e s c r i b e d i n d e t a i l ( A r c h e r e t a l . , 1986 ; A r c h e r a n d S c h m i d t , 1 9 7 8 ; B e l l , 1 9 7 8 , 1 9 8 2 , 1 9 8 6 ; B e l l a n d D e l a n e y , 1 9 7 7 ; D e l a n e y , 1 9 8 1 ; E a t o n , p e r s . c o m m . , 1 9 8 8 ; L a z n i c k a a n d E d w a r d s , 1 9 7 9 ; T h o m p s o n a n d R o o t s , 1 9 8 2 ) . T h e y h a v e b e e n c o m p a r e d f a v o r a b l y b y B e l l ( 1 9 8 6 , 1987) w i t h b r e c c i a s t h a t h o s t t h e w o r l d c l a s s O l y m p i c Dam g o l d - c o p p e r - u r a n i u m d e p o s i t n o r t h o f A d e l a i d e , A u s t r a l i a . P r o t e r o z o i c b r e c c i a c o m p l e x e s o f a s i m i l a r n a t u r e a l s o h a v e b e e n r e p o r t e d f r o m t h e v i c i n i t y o f t h e E a s t A r m o f G r e a t S l a v e L a k e ( R e i n h a r d t , 1972) a n d f r o m t h e B a t h u r s t I n l e t a r e a ( C e c i l e a n d C a m p b e l l , 1 9 7 7 ) , N o r t h w e s t T e r r i t o r i e s . T h e W e r n e c k e M o u n t a i n b r e c c i a s o c c u r i n s t r u c t u r a l l y c o m p l e x z o n e s a n d h a v e b e e n m o d e r a t e l y t o i n t e n s e l y a l t e r e d ( E a t o n , p e r s . c o m m . , 1 9 8 8 ) . T h e y p o t e n t i a l l y h o s t e c o n o m i c d e p o s i t s o f g o l d , c o p p e r , c o b a l t a n d u r a n i u m . I n c o n t r a s t , t h e C o a l C r e e k I n l i e r i s r e l a t i v e l y u n c o m p l i c a t e d b y s t r u c t u r e a n d l i t t l e a l t e r e d . E x p l o r a t i o n , a l b e i t l i m i t e d t o d a t e , h a s y e t t o d i s c o v e r a n y m i n e r a l i z a t i o n o f m a j o r It i n t e r e s t . Some b r e c c i a textures i n the O g i l v i e Mountains brecc ia resemble g lacio-marine brecc ias of the much younger Rapitan Group (Yeo, 1981) i n the Mackenzie and Wernecke Mountains to the east . The brecc ia complexes l o c a l l y are hemat i te -r ich . In some respects they are s i m i l a r to Algoma-type banded i r o n formations. Only minor base and precious metal occurrences are hosted by the brecc ia complexes of the Wernecke and O g i l v i e Mountains. I f the corre la t ions to .Olympic Dam, A u s t r a l i a are r e a l and j u s t i f i e d they may have economic p o t e n t i a l . Consequently, inves t iga t ion of these r e l a t i v e l y undeformed and unaltered brecc ias i n the O g i l v i e Mountains was designed to e luc idate types, sources and mechanism of formation of these major bodies of b r e c c i a . 1.2 LOCATION AND ACCESS The Coal Creek I n l i e r i s wi th in the Omineca Belt (Wheeler and Gabr ie l se , 1972; Monger et a l . , 1972) and i s about 55 km north of T i n t i n a Trench. I t i s i n the western port ion of the southern O g i l v i e Mountains, Yukon T e r r i t o r y . The study area (Figure 1.1) cons is t s of two east - trending be l t s that cover 170 square ki lometres . The norther ly band, centered near 6 4 ° 5 1 / north and 1 3 9 ° 3 0 / west, i s greater than 5 4 0 km i n length, and of v a r i a b l e width up to 3 km. The southerly band, centered approximately at 6 4 ° 4 5 / north and 1 3 9 ° 1 9 / west, i s 15 km long and about 10 m to 100 m wide. The area covers port ions of the fo l lowing 1:50,000 scale map sheets (NTS): 116B/11, 116B/12 and 116B/14. This region of the Yukon T e r r i t o r y , along with parts of Alaska , were unglaciated during the Pleistocene (Bostock, 1946, 1961). The topography thus formed by subaer ia l eros ion . The unglaciated area i s composed of long r idges of low to moderate r e l i e f . In the f i e l d area a l t i t u d e s range from about 975 m to over 1950 m. Outcrop, discontinuous but abundant on the crests and f lanks of steep-sided r idges , i s uncommon i n v a l l e y bottoms. Access to the area was by h e l i c o p t e r s tat ioned, for the f i r s t h a l f of the summer of 1986, from a base camp located j u s t o f f the Dempster highway 60 km north-east of the f i e l d area. During the second h a l f of the summer of 198 6 and during J u l y of 1987 the h e l i c o p t e r was based i n Dawson C i t y , about 85 km south of the f i e l d area. 1.3 PREVIOUS WORK The e a r l i e s t recorded observations i n the area studied were made i n 1887 by O g i l v i e (1913) who led a party that surveyed the Alaska - Yukon T e r r i t o r y border. In 1910-1912 6 Cairnes (1914) mapped a 12 km wide transect along t h i s boundary and formulated a pre l iminary geologic framework. Reconnaissance mapping i n the region was f i r s t formally c a r r i e d out by the Geological Survey of Canada i n the summer of 1961 by Green and Roddick who completed three contiguous 1:250,000 sca le map sheets: Dawson, Larson Creek and Nash Creek (Green and Roddick, 1962; Green, 1972). A l l subsequent geologis ts have used t h e i r work as a base. More recent ly , 1:50,000 sca le mapping of the Dawson map area by R . I . Thompson and C R . Roots of the Geologica l Survey of Canada has been done. This work i s scheduled to come out as an Open,Fi le Report i n 1990. Ph.D. theses by Mercier (1985), Roots (1987), and Mustard (1990) provide more d e t a i l e d descr ipt ions of some s p e c i f i c areas. 1.4 SCOPE OF THESIS This thes i s invest igates the nature of enigmatic brecc ia complexes that crop out i n Coal Creek I n l i e r of the O g i l v i e Mountains, Yukon T e r r i t o r y . I t includes: (i) a map showing t h e i r l i t h o l o g i c d i s t r i b u t i o n , ( i i ) de scr ip t ion and i n t e r p r e t a t i o n of t h e i r contacts , ( i i i ) t h e i r minera log ica l and chemical c h a r a c t e r i s t i c s , and (iv) analys i s of genetic models that describe modes of b r e c c i a formation. Assessments and b r i e f descr ip t ions of mineral 7 occurrences are appended i n sections descr ib ing galena lead isotopes i n the Coal Creek I n l i e r . Two regions of known brecc ia crop out across port ions of three 1:50,000 map sheets (NTS: 116B/11, 116B/12 and 116/14). These were invest igated during the f i e l d season of 1986. Add i t i ona l mapping was c a r r i e d out during J u l y of 1987. 2.0 REGIONAL GEOLOGY 2.1 REGIONAL SETTING AND TECTONIC EVOLUTION The northern extension of the Rocky Mountain Fold and Thrust Be l t forms a broad arc across c e n t r a l Yukon T e r r i t o r y . I t contains a t h i c k sedimentary sequence that was deposited on the passive cont inental margin of North America between Middle Proterozoic and Permian time (Price , 1964) . During the Middle to Late Proterozoic shallow water carbonate s t r a t a dominated the region. These are the oldest known rocks of the northern C o r d i l l e r a (Gabrie lse , 1967). They are preserved i n several s t r u c t u r a l i n l i e r s surrounded by Paleozoic Selwyn Basin and Mackenzie Platform s t r a t a (Figure 1.1). In the southern part of the southern O g i l v i e Mountains, Selwyn Basin s t r a t a i s underla in by the Hyland Group (Gordy, i n press) of the Windermere Supergroup. Unnamed Cambro-Ordovician vo lcan ic s and Ordovician to Devonian Road River Formation o v e r l i e the c l a s t i c and carbonate rocks of the 9 Hyland Group. The northern part of the southern O g i l v i e Mountains cons i s t of two l a t e r a l l y extensive, dominantly platform carbonate assemblages: (1) Wernecke Supergroup, that i s o v e r l a i n unconformably by the (2) Fi f teenmile assemblage. These are dominated by shallow water carbonate rocks of Middle to Late Proterozoic age. Strat igraphy and tec ton ic events i n the h i s t o r y of the Coal Creek I n l i e r i s out l ined i n Table 2 .1 . Thick mid-Proterozoic sect ions of shallow water, f ine grained c l a s t i c and carbonate rocks that const i tute the Wernecke Supergroup (Delaney, 1981) accumulated on the s table cont inenta l platform of western North America. During subsequent compression, a pervasive cleavage developed i n Wernecke Supergroup rocks (Mercier, 1987). In the O g i l v i e and Wernecke Mountains, arg i l laceous rocks were weakly r e g i o n a l l y metamorphosed to lower greenshist grade (Gabrie lse , 1967). U p l i f t and erosion of these uni ts produced a marked eros ional unconformity at the base of the Fi f teenmi le assemblage (informal des ignat ion; Thompson, pers . comm., 1988). This per iod of t ec ton ic i n s t a b i l i t y , termed the Fi f teenmi le Orogeny by Mercer (1989) for the southern O g i l v i e Mountains region, occurred at about the same time as the Racklan Orogeny (Gabrie lse , 1967; Eisbacher, 1978) or Racklan Tectonic Event (Thompson, pers . 10 Table 2.1 Str a t i g r a p h i c units and t e c t o n i c events of the Coal Creek I n l i e r (adapted from Roots (1987) and Thompson and Roots (1982)). AGE UNIT MAP UNIT 1 LITHOLOGY Ea r l y Ordovician Road River Group 8 R to Devonian (165 m) -black shale, chert Transgressive E a r l y Cambrian "CDb" formation 7 C to Devonian (>250 m) -thick bedded, pale grey dolostone Conformable; l o c a l angular unconformity Sl a t s creek group 6 S Early Cambrian (>30 m) -white dolostone, purple mudstone, conglomerate pale green a r g i l l i t e and sandstone Contact r e l a t i o n s unknown-possible l a t e r a l equivalent to Harper Group (?) HARPER GROUP Late Proterozoic Upper Harper group Hu (0-450 m) Mount Harper Volcanic Hv complex (0-1500 m) Lower Harper group HI (0-1100 m) -conglomerate, shale s i l t s t o n e , mudstone -basalt flows, breccia, and minor r h y o l i t e -conglomerate, pebbly sandstone, mudstone Hayhook Tectonic Event: disconformable; l o c a l l o c a l l y gradational angular unconformity; FIFTEENMILE ASSEMBLAGE Middle to Upper Fifteenmile 5 Fu Late Proterozoic group (2500 m) Lower Fifteenmile 4C F l group (1500 m) 4B -grey f i n e l y laminated dolomitic limestone and dolostone -upper member: mudstone, s t r o m a t o l i t i c limestone, and quartz sandstone middle member: dolostone Fifteenmile (Racklan) Tectonic Event: angular unconformity; l o c a l l y conformable WERNECKE SUPERGROUP Earl y to GILLESPIE LAKE GROUP 3B Wg Middle Proterozoic (3500 m) 3A -upper member: buff-weathering dolostone lower member: orange weathering dolostone Conformable: l o c a l angular unconformity QUARTET GROUP 2 Wq (>2250 m) -grey sandstone, mudstone and black a r g i l l i t e Angular unconformity; l o c a l l y disconformable FAIRCHILD LAKE GROUP IB Wf (>650 m) 1A -pink-weathering s i l t y dolostone, mudstone and quartzite greenish-grey to purple dolomitic s i l t s t o n e and dolomitic limestone 1 Numbers are units used on Map 1 ( i n pocket); l e t t e r s designate un i t s used on Figure 2.1 comm., 1988). In the O g i l v i e Mountains, f o l d i n g accompanied by cleavage development, was followed by syndeposi t ional growth f a u l t i n g associated with the i n i t i a t i o n of F i f teenmi le assemblage depos i t ion (Thompson, pers . comm., 1987). The Upper Fi f teenmile group cons is ts of several ki lometers of shallow water she l f dolostone that over l i e s Lower Fi f teenmile group rocks conformably. The Hayhook Orogeny (Eisbacher, 1981; D e v l i n , 1988), a 750 Ma extensional event followed the depos i t ion of the upper Fi f teenmile group. In the southern O g i l v i e Mountains i t i s c a l l e d the Harper r i f t event (Roots, 1987). This event resu l ted i n u p l i f t , erosion and the subsequent development of a s i g n i f i c a n t angular unconformity at the base of the over ly ing r i f t assemblage that c a l l e d the Harper group (Roots, 1987, 1982). In l o c a l i t i e s south of Coal Creek I n l i e r , the Dawson Faul t (Figure 2.1) p h y s i c a l l y separates upper Fi f teenmi le group from the Harper group. C l a s t i c sediments and vo lcanics of the Harper group are the youngest Proterozoic rocks preserved i n the Coal Creek I n l i e r . Basal e l a s t i c s of the Harper group were deposited in to a northwest-trending h a l f graben. Cambrian (and older?) coarse e l a s t i c s and carbonates of the S la t s Creek group and over ly ing Cambrian to Devonian carbonates of the "CDb" formation (Norris and Hopkins, 1977) 12 Figure 2.1 Regional s t r a t i g r a p h i c c o r r e l a t i o n chart for Proterozoic and over ly ing Paleozoic rocks of the Northern C o r d i l l e r a and the P u r c e l l Mountains, south eastern B . C . Adapted from Eisbacher (1981) and Roots (1987). A d d i t i o n a l references (superscripted numbers) are i n Appendix C. HE = Hayhook tectonic event; RE = Rackla tectonic event. Dykes and s i l l s i n the Mackenzie Mountains were emplaced at approximately 770 Ma (Armstrong et a l . . 1982). r e s t unconformably on Proterozoic s t ra ta and represent a re turn to s table she l f condi t ions . The en t i re Proterozo ic and Phanerozoic successions were folded and fau l ted during Mesozoic thrus t ing (Thompson and Roots, 1982) when a complex v o l c a n i c - p lu ton ic arc was welded to the cont inenta l margin (Templeman-Kluit, 1979). Remnants of t h i s arc comprise the Yukon Tanana Terrane (Templeman-Kluit, 1979) that l i e s to the southwest of Selwyn basin and T i n t i n a F a u l t . 2.2 STRATIGRAPHIC SUMMARY AND REGIONAL CORRELATION The fo l lowing summary i s de ta i l ed i n the c o r r e l a t i o n chart of Figure 2.1. Figure 1.1 shows the d i s t r i b u t i o n of Proterozo ic rocks across the northern C o r d i l l e r a . S i m i l a r i t y between Wernecke Supergroup rocks and the B e l t - P u r c e l l Supergroup of southeastern B r i t i s h Columbia, southwestern Alber ta and adjo in ing Montana was noted by Cairnes (1914) and Mert ie (1937); s t r a t i g r a p h i c c o r r e l a t i o n i s supported by more recent studies (Gabrielse , 1967; Young, 1978; Young et a l . . 1979) of Wernecke and B e l t - P u r c e l l Supergroup s t r a t a with the lower part of the T i n d i r Group i n e a s t - c e n t r a l Alaska . Subsequently, Young (1982) has argued that the Lower T i n d i r Group i s Late Proterozoic and i s a s t r a t i g r a p h i c equivalent of the Pinguicula Group i n the Wernecke Mountains and therefore not c o r r e l a t i v e with the Wernecke Supergroup. The c o r r e l a t i o n of P inguicula Group (Eisbacher, 1981) with the Mackenzie Mountains Supergroup i n the Mackenzie Mountains i s t e n t a t i v e l y supported by Young et  a l . (1979) and Eisbacher (1981), but disputed by Aitken (1986). Conclusive evidence i s , however, l ack ing (Gabrielse and Campbell, i n pres s ) . F i f teenmi le assemblage rests unconformably on Wernecke Supergroup s t r a t a . I t occurs at the same s t r a t i g r a p h i c horizon as does the Pinguicula Group i n the Wernecke Mountains, and appears to be a time s t r a t i g r a p h i c equivalent (Thompson, pers . comm., 1987). The age of the Bel t - P u r c e l l Supergroup i n the southern C o r d i l l e r a i s known only approximately. Preserved basal sect ions that o v e r l i e c r y s t a l l i n e basement have a minimum age of more than 1.6 Ga (Burwash, Baagsgaard and Peterman, 1962). In the northwestern part of the Canadian Sh ie ld a per iod of widespread mafic igneous a c t i v i t y occurred at about 1.2 Ga (Stockwell et a l . . 1970). This s i g n i f i e s an important period of c r u s t a l extension (Young et a l . . 1979) . Proterozo ic s trat igraphy of the northern C o r d i l l e r a were grouped in to three major d i v i s i o n s , Sequence A, Sequence B and Sequence C, separated from each other by a reg ional unconformity (Young et a l . . 1979). Sequence A includes the Wernecke Supergroup; Sequence B consis ts of the Pinguicu la Group and Mackenzie Mountains Supergroup; and Sequence C i s made up of the Ekwi Supergroup and Rapitan Group (or Windermere Supergroup; Eisbacher, 1981). Be l t -P u r c e l l rocks are therefore equivalent to sequences A and B. Sequence C corre la tes with the Windermere Supergroup of southeastern B r i t i s h Columbia. The o ldest rocks exposed i n the core of the Coal Creek I n l i e r are corre la ted with the Middle Proterozoic Wernecke Supergroup of the Wernecke Mountains. They are c o r r e l a t i v e on the bas i s of equivalent s t r a t i g r a p h i c p o s i t i o n , l i t h o l o g i c s i m i l a r i t y (Delaney, 1981, 1985) and the presence of b r e c c i a s . This s trat igraphy forms an e s s e n t i a l l y continuous outcrop be l t from the Southern O g i l v i e Mountains in to the Wernecke Mountains. The age of the Mackenzie Mountains Supergroup has been es tabl i shed between 1.2 Ga and 770 Ma (Rb-Sr radiometric ages from Barager i n Wanless and Loveridge, 1972, and Armstrong et a l . . 1981; Gabrie l se and Campbell, 1990). In t u r n , radiometr ic age data and l i t h o l o g i c s i m i l a r i t i e s support the c o r r e l a t i o n of the Mackenzie Mountains Supergroup with upper B e l t - P u r c e l l Supergroup (Missoula Group) rocks (Young et a l . . 1978). Harper group basal e l a s t i c s i n the southern O g i l v i e Mountains represent the onset of Windermere sedimentation. 16 Poss ib le c o r r e l a t i v e s of the Harper r i f t assemblage are the upper T i n d i r Group (Young, 1982), the Coates Lake Group (Jefferson and P a r r i s h , 1989), and part of the Rapitan Group (Eisbacher, 1981). Uppermost Harper group may be c o r r e l a t i v e with the Hyland Group of the Mackenzie Mountains. "CDb" formation unconformably o v e r l i e s a l l o lder rocks of the Coal Creek I n l i e r . I t was deposited on a shallow platform that extended from eas t - cen tra l Alaska (Jones Ridge Formation) eastward into the Mackenzie Mountains, Northwest T e r r i t o r i e s . South of the platform was the Selwyn Basin , that contained an o f f s h e l f succession cons i s t ing of the Road River Formation. This i s a prevalent un i t forming recess ive outcrops that can be traced from the O g i l v i e Mountains eastward to the Mackenzie Mountains. "CDb" formation i s i n part a t i m e - s t r a t i g r a p h i c equivalent to the Road River Formation. 2.3 GEOLOGY OF COAL CREEK INLIER 2.3.1 Introduct ion Coal Creek I n l i e r contains three Proterozoic successions (Figures 2.1 and 2.2, and Table 2 .1) . From oldest to youngest they are: Wernecke Supergroup, F i f teenmi le assemblage (informal) and Harper group ( informal) . Each succession general ly forms east trending be l t s across the i n l i e r . The geology of the Coal Creek I n l i e r i s shown i n Figure 2.2. Wernecke Supergroup consis ts of three p a r t s . In ascending order they are: F a i r c h i l d Lake Group, Quartet Group, and G i l l e s p i e Lake Group (Table 2 .1 ) . The Fi f teenmile assemblage i s d iv ided into the lower Fi f teenmile group and the upper Fi f teenmile group. The Harper group consis ts of three d i v i s i o n s . In ascending order , they are: Lower Harper group, Mount Harper v o l c a n i c complex, and Upper Harper group. O g i l v i e Mountains brecc ia (OMB) contact a l l d i v i s i o n s of the Wernecke Supergroup and the lower Fi f teenmi le group. They are s p a t i a l l y associated with mafic dykes, and crop out along two east trending be l t s c a l l e d : (i) the Northern Breccia B e l t , and ( i i ) the Southern Brecc ia B e l t . The Northern Brecc ia Be l t coincides with a s teeply south dipping reverse f a u l t c a l l e d the Monster f a u l t . The Southern Brecc ia Be l t co inc ides with a steeply d ipping nor th - s ide -down f a u l t c a l l e d the Fif teenmile f a u l t . Th i s f a u l t juxtaposes lower Fi f teenmile group against Quartet Group. E a r l y Paleozoic S la t s Creek group ( F r i t z , 1980), "CDb" formation, and i t s o f f - s h e l f c o r r e l a t i v e the Road River Formation unconformably o v e r l i e the Proterozo ic rocks . 1 3 9 ° 30 ' I 1 3 9 ° I V - l - ' A ^ ^ : - - ^ -----, - - - - - - W i s w, ^six^--^ T 6 4 ° -50'N 65 ^/ 40 6 4 ' 50'N 40 S > ^ , -40 \ 2 0 s ) H U \ . Fu 15, ~~3°. >J7 „w< i£s*jr-'' F u ,...--20 / "r~^~-~)t^Q< Kilometres 6 4 » -40'N 6 4 ' 40'N 1 140" 30 ' O R D O V I C I A N to DEVONIAN | R | Road River Group EARLY C A M B R I A N to DEVONIAN [ C | CDb Formation | S | Slats Creek Group LATE P R O T E R O Z O I C to EARLY C A M B R I A N Harper Group — i — 1 4 0 ° MIDDLE to LATE PROTEROZOIC Fifteenmile Assemblage Hu | Upper Harper Group Hv | Mt. Harper Volcanic Complex HI I Lower Harper Group | Fu | Upper Fifteenmile Group [ F| | Lower Fifteenmile Group | | Ogilvie Mtn. breccias EARLY? to MIDDLE PROTEROZOIC Wernecke Supergroup | W g | Gillespie Lake Group | W q | Quartet Group I Wf I Fairchild Lake Group SYMBOLS y y Bedding (inclined, vertical) - — C o n t a c t s (known, approx., assumed) , j - r- Faults (ball denotes side down) ..< >- Thrust fault (teeth on upper plate) FIGURE 2.2 Figure 2.2 Geology of the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-cen tra l Yukon T e r r i t o r y . (See Map 1, i n pocket, for d e t a i l . ) 19 T h e i r contact out l ines the Coal Creek I n l i e r . 2.3.2 S t r a t i f i e d Rocks 2 .3 .2 .1 Wernecke Supergroup Wernecke Supergroup i n the Coal Creek I n l i e r , southern O g i l v i e Mountains consis ts of three mappable u n i t s . The base of the Wernecke Supergroup i s not exposed; therefore t o t a l th ickness i s not known. The o ldest un i t i s t e n t a t i v e l y corre la t ed with the F a i r c h i l d Lake Group (Delaney, 1981) because i t underl ies Quartet Group rocks and i t s l i t h o l o g i e s ( s i l t y dolomite, do lomit ic s i l t s t o n e , mudstone and quartz i te ) are s i m i l a r to those reported i n the type area—the Wernecke Mountains. In the Wernecke Mountains, Delaney (1985) reported a minimum thickness of 4 km for the F a i r c h i l d Lake Group. Quartet Group i n the Coal Creek I n l i e r , cons is ts of interbedded f ine grained grey sandstone to s i l t s t o n e and black a r g i l l i t e . I t forms a d i s t i n c t i v e l y d u l l succession approximately 3.5 km th i ck (thickness estimate from cross -sect ions; see Map 1). Quartet Group i n the Wernecke Mountains type area i s at l eas t 5 km t h i c k (Delaney, 1981) and represents a t u r b i d i t e succession (Delaney, 1981; 1985). G i l l e s p i e Lake Group i n the Coal Creek I n l i e r i s a 20 t h i c k succession of predominantly and c h a r a c t e r i s t i c a l l y orange weathering dolostone. I t i s about 3 km t h i c k (thickness estimate from cross - sec t ions ; see Map 1). The thickness of the G i l l e s p i e Lake Group i n the Wernecke Mountains i s greater than 4 km (Delaney, 1981, 1985). Aggregate thickness for the Quartet and G i l l e s p i e Lake groups, estimated from cross-sect ions of the f i e l d area (Map 1), i s about 6.5 km. This i s considerably l e ss than the more than 9 km reported by Delaney (1981; 1985) for the combined thickness of Quartet Group (5 km). This may represent a reg ional westward th inning of the succession. A l t e r n a t i v e l y , s t r u c t u r a l thickening of Quartet and G i l l e s p i e Lake group s t r a t a i n the Wernecke Mountains may have occurred. Recent mapping i n the southern Wernecke Mountains i d e n t i f i e d thrust fau l t s that repeated sect ions of G i l l e s p i e Lake Group s trat igraphy (Mustard et a l . , 1990) . F a i r c h i l d Lake Group (Units l a and l b ; Map 1) The base of the F a i r c h i l d Lake Group i s not exposed and not a l l of the informal subdivis ions reported by Delaney (1981) for the Wernecke Mountains were observed. F a i r c h i l d Lake Group rocks crop out discont inuously along the south s ide or "hanging wal l" of the Monster f a u l t and are int imate ly associated with OMB (Map 1) . U n i t l a i s t h e l o w e s t e x p o s e d u n i t o f t h e W e r n e c k e S u p e r g r o u p i n t h e C o a l C r e e k I n l i e r . I t c o n s i s t s o f d o l o m i t i c s i l t s t o n e a n d d o l o m i t i c l i m e s t o n e t h a t h a s a d i s t i n c t i v e l y r i b b e d w e a t h e r i n g p r o f i l e ( P l a t e 2 . 1 ) . S t r o m a t o l i t e s o c c u r l o c a l l y i n a n o t h e r w i s e p l a t y g r e e n i s h -g r e y t o p u r p l e s u c c e s s i o n . T h e p l a t y l i m e s t o n e c h a n g e s c o m p o s i t i o n t o w a r d t h e e a s t - s o u t h e a s t t o a p a l e g r e y d o l o m i t i c l i m e s t o n e w i t h d i s t i n c t i v e c h l o r i t e p a r t i n g s ( P l a t e 2 . 2 ) . U n i t l a g e n e r a l l y d i p s t o t h e n o r t h , i s l o c a l l y d i s r u p t e d , h a s s t r a t i g r a p h i c c o n t i n u i t y a l o n g s t r i k e , a n d i s 500 t o 600 m t h i c k . U n i t l b o v e r l i e s U n i t l a w i t h a p p a r e n t c o n f o r m i t y . I t i s a r e s i s t a n t p i n k t o g r e y s i l t y d o l o m i t e ( P l a t e 2 . 3 ) a n d d o l o m i t i c m u d s t o n e t h a t w e a t h e r s p i n k t o b r o w n . O c c a s i o n a l b e d s o f g r e y t o p u r p l e q u a r t z i t e a n d j a s p i l l i t e a r e a l s o p r e s e n t . U n i t l b i s l a m i n a t e d a n d medium t o t h i c k b e d d e d . A t t h e e a s t e n d o f t h e i n l i e r , m e a s u r e d s e c t i o n s t h i c k e r t h a n 100 m e t r e s c o n s i s t o f i n t e r b e d d e d q u a r t z i t e a n d d o l o s t o n e ( P l a t e 2 . 4 ) , q u a r t z i t e a n d m u d s t o n e , a n d m u d s t o n e a n d d o l o s t o n e . T h e r a t i o o f q u a r t z i t e t o d o l o m i t e i n t h e i n t e r b e d d e d q u a r t z i t e a n d d o l o s t o n e u n i t v a r i e s r a p i d l y (5 t o 15 m) a l o n g a n d a c r o s s s t r i k e . A s t h e q u a r t z i t e c o n t e n t i n c r e a s e s , b e d d i n g d i s a p p e a r s a n d t h e s u c c e s s i o n b e c o m e s m a s s i v e . T h i s f i e l d e v i d e n c e s u g g e s t s t h a t t h e q u a r t z i t e Plate 2.1 Outcrop of ribbed weathering platy dolomitic s i l t s t o n e and dolomitic limestone of F a i r c h i l d Lake Group (unit 1A; located about 1 km north of the BEEHIVE l o c a l i t y ) . Pen for scale. 3^ Plate 2.2 Platy weathering, dolomitic siltstone-dolomitic limestone with d i s t i n c t i v e c h l o r i t e partings of the F a i r c h i l d Lake Group (unit 1A; sample BL9-22). 2k Plate 2.3 P i n k t o b u f f w e a t h e r i n g s i l t y d o l o s t o n e ( u n i t I B ; s a m p l e B L 8 7 - 3 ) o f F a i r c h i l d L a k e G r o u p i s b e s t e x p o s e d i n t h e N o r t h e r n B r e c c i a B e l t a r e a , e s p e c i a l l y n o r t h a n d w e s t o f t h e BEEHIVE. W e a t h e r - r e s i s t a n t f e a t u r e s , m o s t l i k e l y c a s t s o f g y p s u m o r a n h y d r i t e , o c c u r o n l y l o c a l l y . may be r e c r y s t a l l i z e d j a s p e r o i d — o r i g i n a l l y f ine grained s i l i c a replacement of l imestone—petrographic examination of samples was inconc lus ive . S t r a t i g r a p h i c cont inu i ty of Unit lb i s d i srupted by i r r e g u l a r zones of b r e c c i a t i o n . Bedding wi th in i n d i v i d u a l segments i s i n t e r n a l l y coherent but d i f f e r s from nearby ones. This suggests the un i t has been broken apart by the b r e c c i a t i o n process . Widespread development of O g i l v i e Mountains b r e c c i a coincides with t h i s s t r a t i g r a p h i c l e v e l . Quartet Group (Unit 2; Map 1) Quartet Group, Uni t 2, over l i e s the F a i r c h i l d Lake Group with angular discordance i n some areas and disconformably i n others . I t i s a monotonous, grey to brown weathering, medium to t h i c k bedded f ine grained succession of sandstone, s i l t s t o n e , dolomit ic s i l t s t o n e and mudstone. L o c a l l y there are rare quartz i t e pebble and cobble conglomerate. In the Wernecke Mountains Delaney (1981) d iv ided the succession into two uni ts of informal des ignat ion. For the purpose of t h i s study the Quartet Group was not subdivided. The dominant Quartet Group l i t h o l o g y i n the study area i s interbedded f ine grained sandstone, s i l t s t o n e and p h y l l i t i c a r g i l l i t e (Plate 2 .5) . Beds of laminated and P l a t e 2.4 I n t e r b e d d e d , f i n e g r a i n e d q u a r t z i t e a n d d o l o m i t e ( u n i t I B ; s a m p l e BL4-7) o f F a i r c h i l d L a k e G r o u p f r o m t h e LALA l o c a l i t y . Plate 2.5 P r o m i n a n t e x p o s u r e o f g r e y - b r o w n w e a t h e r i n g t u r b i d i t e s e q u e n c e , i n t e r b e d d e d f i n e g r a i n e d s a n d s t o n e a n d a r g i l l i t e , ( u n i t 2) o f Q u a r t e t G r o u p . T h i s t y p i c a l e x p o s u r e i s l o c a t e d a b o u t 5 km n o r t h o f t h e BEEHIVE. cross- laminated sandstone and s i l t s t o n e , t y p i c a l l y 3 0 cm t h i c k , are separated by t h i n layers of a r g i l l i t e that mark the top of each composite t u r b i d i t e (cf . Bouma, 1962) . L o c a l l y , w i th in t h i s succession, there are t h i c k pale red and green c l a y - r i c h beds. Sedimentary features displayed by t h i s u n i t inc lude: slump textures , interference r i p p l e marks and trough cross-beds (Plate 2 .6) . At the top of the succession are t h i n interbeds of rusty weathering dolomite; t h e i r presence marks the t r a n s i t i o n in to the over ly ing platform carbonate sequence. G i l l e s p i e Lake Group (Unit 3a and 3b; Map 1) G i l l e s p i e Lake Group conformably o v e r l i e s the Quartet Group i n the northern part of the Coal Creek I n l i e r . The contact i s t r a n s i t i o n a l (Thompson and Roots, 1982). In the type area i n the Wernecke Mountains, Delaney (1981) noted a t r a n s i t i o n a l r e l a t i o n s h i p between G i l l e s p i e Lake and Quartet group rocks . He subdivided the G i l l e s p i e Lake Group into seven informal u n i t s . In the Coal Creek I n l i e r two uni ts are recognized: a basal un i t (Unit 3a) cons i s t ing of orange weathering grey dolostone, and an upper un i t (Unit 3b) made of grey to buff weathering s i l t y dolostone. The basal un i t i s laminated suggesting i t accumulated i n quiet water below a wave base, poss ib ly as a l g a l accumulations. Intraformational brecc ia (see sec t ion 3.3 for d e t a i l e d descr ipt ion) occurs l o c a l l y near the base of Uni t 3a. The 9^ Plate 2.6 Close up of crossbedding i n sandstone of t u r b i d i t e i n Quartet Group (unit 2; sample BL87-61 located about 5 km north of the BEEHIVE) . upper u n i t contains colonies of the d i s t i n c t i v e , columnar s tromato l i t e Conophvton (cf. Donaldson, 1976) that are 5 to 10 cm i n diameter (Plate 2.7) and 10 to 15 cm t a l l . 2 .3.2.2 Fi f teenmile Assemblage Fi f teenmi le assemblage unconformably o v e r l i e s Wernecke Supergroup rocks. I t cons i s t s of two l i t h o l o g i c a l l y d i s t i n c t successions: the lower Fif teenmile group, composed p r i m a r i l y of c l a s t i c rocks with minor dolostone; and the upper Fi f teenmile group, cons i s t ing of shallow water p lat formal dolostone. Lower Fi f teenmile Group (Units 4a, 4b and 4c; Map 1) Lower Fi f teenmile group i s informal ly d iv ided into lower, middle, and upper members. Contacts between members are gradat iona l . The middle and upper members are , i n p a r t , t i m e - s t r a t i g r a p h i c equivalents (Roots, pers . comm., 1988). Only the lower member (Unit 4a) crops out i n the f i e l d area. I t i s composed dominantly of b lack, f ine grained to medium grained sandstone, shale and black limestone; grey dolostone o l i s t o l i t h s , tens of metres i n diameter, are an outstanding feature . Uni t 4a forms an east - trending outcrop b e l t across the centre of the Coal Creek I n l i e r (Map 1). I t i s approximately 1,500 m t h i c k . The middle (Unit 4b) and upper (Unit 4c) members, crop out south of the f i e l d area . Uni t 31 4b cons i s t s mainly of t h i c k bedded dolostone and dolostone b r e c c i a . Uni t 4c cons is ts of mudstone, s t r o m a t o l i t i c limestone and quartz sandstone. Upper Fi f teenmile Group (Unit 5; Map 1) Upper Fi f teenmile group cons i s t s of massive, pale grey, craggy weathering sugary dolostone (Thompson and Roots, 1982) . There are occasional t h i n bands of black shale . In l o c a l i t i e s north and east of Mount Harper, conglomerate dominated by c l a s t s of upper F i f teenmi le group grades upward in to basal conglomerates of Harper group (Roots, 1988; Mustard, 1990). However, the contact between the upper Fi f teenmi le and Harper groups i s genera l ly an angular unconformity, upper Fi f teenmi le group rocks do not crop out i n the f i e l d area. 2 .3 .2 .3 Harper Group (Units HI, Hv and Hu; Figure 2.2) Harper group cons is ts of c l a s t i c and vo lcan ic rocks that disconformably overly upper Fi f teenmile group and res t unconformably on older un i t s i n the southern part of the i n l i e r . I t i s d iv ided into two c l a s t i c successions c a l l e d the lower Harper group and upper Harper group. A middle member i s c a l l e d the Mount Harper vo l can ic complex (MHVC). MHVC i s a bimodal su i te of p r i m a r i l y t h o l e i i t i c basa l t and minor f e l s i c flows and dykes (Roots, 1987). I t i s conformable with the underlying Lower Harper group. The Upper Harper group has been interpreted by Mustard (pers. comm., 1987) to have formed i n a hal f -graben during depos i t ion of the Windermere Supergroup (Roots, 1987). Harper group rocks crop out south and east of the map area (see Figure 2 .2) . 2 .3 .2 .4 Paleozoic Rocks S l a t s Creek Group (Unit 6; Map 1) S l a t s Creek group (Unit 6) i s exposed beneath dolostone of the CDb formation i n the north and east parts of the Coal Creek I n l i e r . I t i s made up of pale grey weathering dolostone, purple graded conglomerates and pale green a r g i l l a c e o u s sandstone (Plate 2 .8) . The s t r a t i g r a p h i c p o s i t i o n i s s i m i l a r to that of the uppermost Harper Group (along the west and south sides of the i n l i e r ) , but S la t s Creek group i s Lower Cambrian ( F r i t z , 1980). CDb Formation (Unit 7; Map 1) CDb formation (informal des ignat ion; N o r r i s , 1982) cons is ts of t h i c k bedded, pale grey weathering c r y s t a l l i n e dolostone of Cambrian to Devonian age. I t disconformably over l i e s S l a t s Creek group and o lder Proterozoic uni t s around the margin of the Coal Creek I n l i e r . I t a lso forms Plate 2.7 Columnar stromatol i tes (Conophyton) i n G i l l e s p i e Lake Group dolostone (unit 3 A ) located approximately 4 . 5 km west of LALA l o c a l i t y . Plate 2.8 Outcrop of maroon conglomerate of S la t s Creek Group (unit 6) from northeastern corner of f i e l d area (Map i s o l a t e d caps on r idge tops i n the eastern part of the f i e l d area (Map 1). Road River Group (Unit 8; Map 1) Road River Group (Unit 8) consis ts of Ordovic ian to Devonian black, carbonaceous shale that forms a transgress ive sequence over the CDb formation (Unit 7 ) . I t outcrops i n the northern part of Map 1. 2.3.3 Cross - cu t t ing Rocks 2 .3 .3 .1 Mafic Dykes Numerous dark green to brown weathering dykes of diabase intrude Wernecke Supergroup s t r a t a . The dykes general ly are 1 to 5 m t h i c k and are dominantly east or north-northwest trending and steeply d ipping . Where they cut Quartet Group rocks , dykes are d i f f i c u l t to observe because of t h e i r s i m i l a r weathering c h a r a c t e r i s t i c s i n outcrop. However, the dykes are d i s t i n c t where they cut F a i r c h i l d Lake Group and G i l l e s p i e Lake Group dolostones. This i s because of t h e i r contrast ing dark green weathering and greater res i s tance to eros ion . A l t e r a t i o n zones adjacent to the dykes are t h i n and weakly developed i n the F a i r c h i l d Lake Group; i n the G i l l e s p i e Lake Group they are bounded by bleached zones up to several metres wide. The 35 dykes are moderately to s trongly fractured and l o c a l l y b r e c c i a t e d . Fractures and j o i n t s are commonly l i n e d with specular hematite, and less commonly, cha lcopyr i t e . Cros s - cu t t ing s t r a t i g r a p h i c re la t ionsh ips ind ica te that the dykes are of several ages. Angular fragments of diabase occur l o c a l l y i n the OMB bodies . Dykes of s i m i l a r diabase a l so cut OMB complexes i n several l o c a l i t i e s and form extensions along the trend of l i n e a r OMB bodies. The ages of these dykes are constrained by several fac tors : (i) they crosscut and therefore postdate the Wernecke Supergroup; ( i i ) they were intruded both before and a f ter brecc ia formation; ( i i i ) they predate (are truncated by) depos i t ion of upper Fi f teenmile group, "CDb" Formation and S la t s Creek Group; and (iv) a galena lead isotope date (Appendix A: Showing-10190) of associated mineralization—presumably about the same age as the dykes—is about 0.9 Ga. These mafic in trus ions are medium to dark green and are genera l ly medium to coarse grained. In several l o c a l i t i e s , where dykes come into contact with brecc ia bodies, the dykes are amygdaloidal or poss ib ly v a r i o l i t i c (Figure 2 .9) . This texture may have resul ted from: (i) the exsolut ion of v o l a t i l e s by the magma c lose to the surface (Best, 1982) or ( i i ) the presence of immiscible l i q u i d blebs . Specimens from the v i c i n i t y of OMB bodies d i sp lay i r r e g u l a r pink to red s ta ined blotches i n d i c a t i v e of hematization associated 36 Plate 2.9 W e a t h e r e d s u r f a c e a n d c u t p o l i s h e d s u r f a c e ( l e f t , wet ) o f h e m a t i t e s t a i n e d , a m y g d a l o i d a l d i a b a s e d y k e ( s a m p l e B L 3 7 - 1 9 ) f r o m n o r t h w e s t c o r n e r o f f i e l d a r e a (Map 1 ) . with the b r e c c i a s . Thin sections of 12 d i f f e r e n t dykes were studied to determine i f they were su i tab le for dat ing . A l l but two were pervas ive ly c h l o r i t e - a l t e r e d ; amphiboles i n the two remaining samples were a c t i n o l i t e (a mineral unsuitable for K-Ar dating) intergrown with appreciable amounts of c h l o r i t e . P lag ioc lase i s almost e n t i r e l y s a u s u r i t i z e d . Euhedral i r o n oxides, l i k e l y magnetite, replace intergrown a c t i n o l i t e and c h l o r i t e . 2.3.3.2 O g i l v i e Mountains brecc ia (OMB) O g i l v i e Mountains brecc ia (OMB; P late 2.10) i s a s i g n i f i c a n t and mappable u n i t . I t crops out discont inuously along two eas t - trending b e l t s . The Northern Brecc ia Bel t i n the northern part of the f i e l d area (Map 1) i s about 35 kilometers i n length . The Southern Brecc ia Be l t i n the southern par t of the f i e l d area i s approximately 15 km long. The l i n e a r d i s t r i b u t i o n of these fragmental rocks (Map 1 ) coincides with prominent s tructures in formal ly c a l l e d the Monster f a u l t (northern part of Map 1), and the Fif teenmile f a u l t (southern part of Map 1). Breccias both intrude and cross -cut the f a u l t s . The breccias therefore are probably contemporaneous, but may be younger than these s tructures . O g i l v i e Mountains brecc ia are exposed at d i f f e r e n t s t r a t i g r a p h i c l e v e l s : (i) within F a i r c h i l d Lake Group s t r a t a , ( i i ) at the F a i r c h i l d Lake Group - Quartet Group Plate 2.10 R u g g e d e x p o s u r e o f p i n k w e a t h e r i n g h e t e r o l i t h i c b r e c c i a , l o o k i n g e a s t , e a s t o f DONUT l o c a l i t y (Map 1) . B r e c c i a i s d i s c o r d a n t w i t h Q u a r t e t G r o u p r o c k s ( b l a c k i n f o r e g r o u n d ) . C o n t a c t ( d a s h e d l i n e ) r u n s f r o m l o w e r r i g h t t o m i d d l e l e f t e d g e o f p h o t o . contact , ( i i i ) at the top of the Quartet Group near the Quartet Group - G i l l e s p i e Lake Group contact , and (iv) w i th in lower Fi f teenmile group rocks . Brecc ia bodies are both conformable and discordant with respect to bedding. Conformable brecc ia bodies or brecc ia s i l l s general ly d i sp lay gradat ional contacts . Discordant brecc ias commonly exh ib i t s teeply dipping to v e r t i c a l contacts , are l o c a l l y associated with diabase dykes, and are sometimes p a r a l l e l to and may occupy f a u l t s . The brecc ia bodies vary i n composition. This i s r e f l e c t e d i n the o v e r a l l co lour of outcrops. Cream-coloured brecc ias have a carbonate-r ich matrix with commonly subrounded c l a s t s of green a r g i l l i t e and pink s i l t y dolostone. Hemati te-r ich matrix brecc ias are commonly red to maroon. Breccias with a c h l o r i t e - r i c h matrix are dark green and commonly include mafic i n t r u s i v e rock fragments. In places t h i s brecc ia i s mottled from abundant pink c l a s t s . Brecc ia fragments are genera l ly from F a i r c h i l d Lake Group. They are common sub-angular and probably have not t r a v e l l e d far from t h e i r source. However, brecc ia fragments derived from Quartet Group, G i l l e s p i e Lake Group and Lower Fi f teenmi le group are common l o c a l l y . A lack of s i g n i f i c a n t fragment r o t a t i o n , i n some instances , indicates that the brecc ias are represented commonly by crackled country rock. The absolute age of the O g i l v i e Mountains brecc ia i s not known. However, s t r a t i g r a p h i c re la t ionsh ips constra in OMB to be post-Wernecke Supergroup and approximately syn-lower Fi f teenmi le group i n age (see galena lead data below). The upper extent of the brecc ias i s i n rocks affected by the Racklan Tectonic Event (lower Fi f teenmile group). A study of Proterozoic hosted, galena-bearing mineral occurrences that occur i n and around the Coal Creek I n l i e r (Appendix A) have helped to constra in the age of OMB emplacement. The Hart River s t r a t i f o r m volcanigenic massive sulphide depos i t , located about 150 km east of the Coal Creek I n l i e r , i s hosted i n G i l l e s p i e Lake Group a r g i l l i t e s . I t has a galena lead isotope model age of about 1.35 to 1.4 5 Ga. This date therefore i s the age of part of the G i l l e s p i e Lake Group. In add i t ion , the Tart Pb-Zn brecc ia prospect i s hosted i n G i l l e s p i e Lake Group dolostone. I t has a galena lead model age of about 1.3 Ga; although i t might be epigenet ic , a syngenetic o r i g i n would give an upper age estimate for the G i l l e s p i e Lake Group. Therefore the OMB that cross -cuts G i l l e s p i e Lake Group i s younger than 1.45 G a — i t might be younger than 1.3 Ga. Galena from c a l c i t e v e i n l e t s i n an a l t ered mafic dyke that cross -cuts OMB that i s hosted i n Lower Fi f teenmile group was dated at about 0.9 Ga. This provides a minimum age for the emplacement of OMB. Two samples of c h l o r i t e - r i c h matrix were dated using K-Ar whole rock methods (Appendix B) . However, no relevant age information was produced. Both are apparently reset ages: one age (360 Ma) happens to co inc ide with a Devono-M i s s i s s i p p i a n metallogenic event that was extensive throughout the northern Canadian C o r d i l l e r a . Chapter 3 describes the O g i l v i e Mountains b r e c c i a i n d e t a i l . A c l a s s i f i c a t i o n scheme, that d iv ides the brecc ias into monol i thic and h e t e r o l i t h i c v a r i e t i e s , i s introduced. Petrochemistry of O g i l v i e Mountains b r e c c i a follows i n Chapter 4. 2.4 STRUCTURAL GEOLOGY 2.4.1 Introduct ion The t h i c k Proterozoic succession of Wernecke Supergroup carbonate and c l a s t i c sedimentary rocks i n the Coal Creek I n l i e r have been deformed, probably at several t imes. The Northern Brecc ia Be l t d iv ides Map 1 in to northern and southern parts with opposing bedding a t t i t u d e s . North of the Northern Brecc ia Bel t beds dip moderately north; south of the Northern Brecc ia Bel t beds dip moderately south. However, a t t i tudes adjacent to the Northern Brecc ia Belt are i r r e g u l a r i n s t r i k e and d i p . Thus, the elongate eastern trend of the Northern Brecc ia Bel t coincides with both: (i) an a x i a l t race of an a n t i c l i n e , and ( i i ) a zone of f a u l t i n g that resu l ted i n reg ional r o t a t i o n of large segments north and south of the Northern Brecc ia B e l t . Steep, east-trending a x i a l plane f o l i a t i o n supports the presence of an a n t i c l i n e , but imbricate reverse f a u l t i n g along the Northern Brecc ia Be l t (see cross - sec t ions , Map 1) ind ica te that f a u l t i n g has an important r o l e a l so . Several hundred s t r u c t u r a l a t t i tudes of bedding and f o l i a t i o n were measured over Map 1 ( in pocket) . Add i t i ona l s t r u c t u r a l f i e l d data were obtained from R . I . Thompson and C R . Roots of the Geolog ica l Survey of Canada, and E . Mercer (1986) who performed reg ional mapping both i n and around the f i e l d area. These data have been compiled in to four p_i diagrams. Each represent a s t r u c t u r a l domain (Figures 2.3a through 2.3b). One domain i s north of NBB; three domains are south of the NBB. Interpretat ion of the s t r u c t u r a l data fol lows. 2.4.2 S t r u c t u r a l Data and Interpretat ion Sedimentary bedding i s general ly wel l defined i n most major un i t s i n the Coal Creek I n l i e r . However, F a i r c h i l d Lake Group rocks show abrupt changes between areas of consistent bedding. These sudden changes suggest that large blocks of s t r a t a have been rotated with respect to each P l a t e 2 .11 P h o t o g r a p h o f Q u a r t e t G r o u p ( u n i t 2) t u r b i d i t e s s h o w i n g t h e r e l a t i o n s h i p b e t w e e n b e d d i n g a n d a x i a l p l a n e r c l e a v a g e . F i n e g r a i n e d s a n d s t o n e l a y e r s d e f i n e b e d d i n g t h a t d i p s m o d e r a t e l y t o t h e s o u t h . A r g i l l i t e shows s t e e p l y s o u t h d i p p i n g a x i a l p l a n e r c l e a v a g e . T h i s c l e a v a g e s t e e p e r t h a n b e d d i n g r e l a t i o n s h i p i n d i c a t e s t h a t b e d d i n g i s n o t o v e r t u r n e d . O u t c r o p i s l o c a t e d a b o u t 3 km s o u t h e a s t o f LALA l o c a l i t y (Map 1 ) . other. Therefore the i n t e r n a l s t r u c t u r a l complexity exhib i ted by the F a i r c h i l d Lake Group, and i t s c lose s p a t i a l a s soc ia t ion with O g i l v i e Mountains b r e c c i a , p r o h i b i t i t s i n t e r p r e t a t i o n using s t r u c t u r a l (bedding and f o l i a t i o n ) data . The unconformity that occurs between F a i r c h i l d Lake Group and over ly ing Quartet Group may r e f l e c t an event that predates the Racklan Tectonic Event. Above t h i s unconformity, Quartet , G i l l e s p i e Lake and lower Fi f teenmile group rocks have been separated into the fol lowing four s t r u c t u r a l domains: (1) Domain 1 (Figure 2.3a) covers Quartet and G i l l e s p i e Lake Group rocks that occur north of the Northern Brecc ia B e l t . (2) Domain 2 (Figure 2.3b) i s occupied by Quartet and G i l l e s p i e Lake Group rocks that l i e south of Northern Brecc ia Be l t and north of lower Fi f teenmi le group s t r a t a . (3) Domain 3 (Figure 2.3c) occurs south of domain 2 and covers lower Fi f teenmile group rocks north of the Southern Brecc ia B e l t . (4) Domain 4 (Figure 2.3d) includes the area of Quartet and G i l l e s p i e Lake Group rocks that occur south of the Southern Brecc ia B e l t . Figure 2.3a, the p_i diagram of domain 1, includes 72 bedding and 15 f o l i a t i o n measurements. Poles to bedding and f o l i a t i o n define e a s t - s t r i k i n g bedding and f o l i a t i o n with dips to both the north and south. Younging d i r e c t i o n s i n Quartet Group are cons i s tent ly tops up. C r i t e r i a observed i n Quartet Group rocks include: r i p p l e marks with trough cross-beds, graded f ine grained sandstone laminae, load casts and rare slump features. S t r a t i g r a p h i c tops i n G i l l e s p i e Lake Group rocks are a lso cons i s t ent ly tops up. C r i t e r i a inc lude morphology of columnar s tromato l i tes , which l o c a l l y are abundant i n some sect ions of dolostone. P lo t ted data for s t r u c t u r a l domains 2, 3 and 4 are shown i n Figures 2.3b, 2.3c and 2.3d, re spec t ive ly . In domain 2 (Figure 2.3b) poles to bedding define shallowly eastern plunging, general ly e a s t - s t r i k i n g f o l d s . A x i a l planes d ip s teeply south-southeast. The ]3i diagram for domain 3 (Figure 2.3c) r e f l e c t s open east trending folds of almost no plunge. The data from domain 4 (Figure 2.3d) shows an east trend to bedding and f o l i a t i o n . Most beds d ip southerly but f o l i a t i o n i s h ighly v a r i a b l e suggesting e i ther more than one per iod of deformation or chaot ic d i s rupt ion to the dips i n a north-south sense. Minor fo lds i n Quartet Group interbedded a r g i l l i t e -sandstone sequences, l o c a l l y accompanied by well-developed a x i a l p lanar cleavage, define a reg ional scale east - trending a n t i c l i n e . The a x i a l trace of the f o l d i s located along the occurrence of b r e c c i a and F a i r c h i l d Lake Group rocks that are eas t - trending and crop out between the opposing dips i n s t r u c t u r a l domains 1 and 2. Domain 1 comprises north (a) domain 1 (b) domain 2 Figure 2.3 Stereonet p lo ts of s t r u c t u r a l data for (a) domain 1, (b) domain 2, (c) domain 3, and (d) domain 4. The stereonets depict poles to bedding (x's) and poles to a x i a l planar cleavage ( t r iang le s ) . Figure 2.3 Continued dipping s trata—the north limb of the a n t i c l i n e which def ines an east - trending f o l d axis that l i e s to the south. Domain 2 comprises south-dipping s t r a t a , or the south limb of the a n t i c l i n e that define an east - trending fo ld axis that l i e s to the north . The v a r i a t i o n i n dips of a x i a l p lanar cleavage could be re la ted to l o c a l r o t a t i o n of blocks wi th in each s t r u c t u r a l domain. Lower Fi f teenmile group rocks above the unconformity show s i m i l a r s t r u c t u r a l poles to the G i l l e s p i e Lake Group below, i n d i c a t i n g that no deformation occurred between depos i t ion of these two u n i t s . Therefore domains 2 and 3 are grouped together. The Southern Breccia Be l t i s s i tuated along a major reg iona l s t ructure (the Fi f teenmile fault ) and d iv ides domains 3 and 4. Domain 4 i s s i m i l a r to domain 2 and represents the south limb of the reg ional a n t i c l i n e . This ind icates that the fau l t between them i s p lanar . There i s l i t t l e evidence to suggest the s t y l e of f a u l t i n g , but the north s ide i s down based on s t r a t i g r a p h i c r e l a t i o n s h i p s . S t r u c t u r a l data, above, s trongly supports the presence of an a n t i c l i n a l axis that i s approximately co incident with the elongate east-west trend of the Northern Brecc ia B e l t . However, constra ints imposed by mapping (Map 1) define f a u l t s (the Fi f teenmile and Monster faults ) that are more r e a d i l y understood i n cros s - s ec t ion . (Note i n Map 1 the f a u l t - b r e c c i a assoc ia t ion , and the repeated occurrence of F a i r c h i l d Lake Group along the trend of the Northern Breccia Be l t and Monster f a u l t . ) The Fi f teenmi le and Monster fau l t s l i k e l y had t h e i r soles i n F a i r c h i l d Lake Group—a un i t that , at the time of f a u l t i n g , was probably only semi-consolidated (see sect ions 5.3 and 5.4) . Faul t s acted as guides for much of the b r e c c i a emplacement. The r e l a t i o n s h i p s of fo ld ing and f a u l t i n g are shown d iagramat ica l ly i n Figure 2.4. This model ind icates that the u n i t most l i k e l y responsible for decollement i s the F a i r c h i l d Lake Group. Major imbricate , reverse fau l t s mark the North and South Breccia Be l t s and imply a compressional regime at the time of brecc ia emplacement. 50 basement Figure 2.4 Schematic representation of the development of structures that are related to breccia formation. Top: Folding and faulting during Proterozoic compression. Bottom: Deformation by faults along which emplacement of the Ogilvie Mountain breccia (shown as triangles) was concentrated. FLG = Fairchild Lake Group; QG = Quartet Group; GLG = Gillespie Lake Group; and the stipled pattern is the lower Fifteenmile group. Dashed wiggley line in FLG is a zone of detachment. 3.0 DETAILED GEOLOGY OF THE OGILVIE MOUNTAINS BRECCIA 3.1 GENERAL DESCRIPTION AND CLASSIFICATION 3.1.1 D i s t r i b u t i o n and Form The O g i l v i e Mountains brecc ia (OMB) of the Coal Creek I n l i e r are exposed discont inuously along two east trending b e l t s , namely the Northern Brecc ia Bel t and the Southern Brecc ia Be l t (see sec t ion 2 .3 .2 .2 ) . The t o t a l area of exposed b r e c c i a on Map 1 ( in pocket) i s 55 square km: i t accounts for about seven percent of the t o t a l map area of 770 square km. Ind iv idua l OMB bodies vary i n s i z e and extent. Widths of brecc ia at surface range from 2 m to more than 1,000 m. The Northern Brecc ia Be l t (NBB) coincides with the Monster f a u l t (Map 1), a steep to moderately south dipping reverse f a u l t . In the eastern h a l f of the NBB the brecc ias occur wi th in the only large exposure of F a i r c h i l d Lake Group i n the southern O g i l v i e Mountains. In the western part of t h i s b e l t they occur near and along the contacts between Quartet Group and G i l l e s p i e Lake Group rocks , or wholly ) 3 9 « 3 0 ' S 3 8 " 3 0 ' W S4° 4 0 ' N ti v. 1 \ \ Wq X V ) S O ' N "Vs-' K TOD A >'V;r _ -/ V /* V / / * . . t- V 4 0 ' N VV(J 1 4 0 ' 3 0 ' 1 O R U O V I C I A N to DEVONIAN [ R I R o a d River G r o u p EARLY CAMBRIAN to DEVONIAN C D b Form&Uon \s" j S l a t s C r e e k G r o u p L A T E P R O T E R O Z O I C to EARIV C A M B R I A N H a r p e r G r o u p [ Hu j Upper Harper G r o u p | Hv~? Mi. Harper V o l c a n i c C o m p l e x | HI i Lower Harper Q r o u p MIDDLE to EA EE E K O ' U R O Z O I C Fi f teenmile A s s e m b l a g e I Eu | Upper FiSteanmile Group Lower Fifteenmile Group EASslYr to MIDDLE PRO' l i 'ROZO! ' . . W e r n e c k e S u p e r g r o u p i vV(j| Giliespie Lake Group •-. W n i Ouartnt Group ' ' f r :WA take Group OgHvte Mtn. b r e c c i a s S Y M B O L S Bedding (inclined, vertical) Contact.'5 ' . k n o w n , a p p r o * . , a s s u m o d ) Faults (ban denotes side down} Thrust fault {teeth on upper plaro) Figure 3.1 Pos i t ion of O g i l v i e Mountain brecc ia l o c a l i t i e s that are discussed i n the t ext . ro with in rocks of the Quartet Group. Contrast ing bedding a t t i tudes i n Quartet s t r a t a on e i t h e r s ide of the brecc ia suggest that the f a u l t i n g i s co inc ident with the l oca t ion of the b r e c c i a . The thickness of the b r e c c i a bodies var ie s considerably ranging from occurrences l e ss than 2 metres wide to large exposures over a ki lometre across . The Southern Brecc ia Be l t co inc ides with the F i f teenmi le f a u l t (Map 1), a s u b - v e r t i c a l north s ide down f a u l t . I t juxtaposes Quartet Group c l a s t i c sediments (on the south) against carbonate and c l a s t i c sediments of the lower F i f teenmi le group to the north . From east to west the t h i n d y k e - l i k e form of the b r e c c i a , vary ing from 10 to 200 m wide, changes to e l l i p t i c a l bodies that range from 50 to 2,000 m i n diameter. Iso lated pods of OMB occur so l e ly wi th in Quartet Group and lower Fi f teenmi le group s t ra ta (Map 1) . S ix l o c a l i t i e s along the trend of the brecc ias were inves t igated i n d e t a i l . These areas are l i s t e d i n Table 3.1 and l a b e l l e d on Map 1. 3.1.2 Contact Relat ions Contacts between brecc ia and host rock mater ia l are e i t h e r sharp or gradat iona l . Brecc ia bodies that d i sp lay gradat ional contacts have a core of well-mixed TABLE 3.1 A b r i e f d e s c r i p t i o n of b r e c c i a l o c a l i t i e s examined i n d e t a i l (Map 1) i n the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . BRECCIA LOCALITY DESCRIPTION DONUT SLAB BEEHIVE LALA DYKE POD c i r c u l a r brecc ia body, about 3 km wide, flanked by G i l l e s p i e Lake and Quartet Group, and cored by Quartet Group. south-dipping brecc ia body, up to 1.5 km i n maximum dimension, that contains massive blocks of Quartet Group and truncates Quartet Group. conformable wedge of b r e c c i a , 60 m t h i c k , with gradat ional contacts of fractured F a i r c h i l d Lake Group. complex area of approximately 45 ha cons i s t ing of i r r e g u l a r l y shaped b r e c c i a bodies accompanied by hydrothermal a l t e r a t i o n and s i g n i f i c a n t copper m i n e r a l i z a t i o n . t h i n and discontinuous, snake- l ike body of b r e c c i a , 15 km long and averaging about 75 m i n width, that occupies a f a u l t between Quartet Group and lower Fi f teenmi le group. h a l f km wide, tadpole-shaped b r e c c i a body encapsulated i n Quartet Group rocks . h e t e r o l i t h i c b r e c c i a , and or margin of weakly to moderately a l t ered monol i th ic brecc ia which grades outward into to crackled rock. The matrix to fragment r a t i o and the degree of r o t a t i o n of fragments decreases toward the margin of the b r e c c i a . The width of the zone appears to depend on the host l i t h o l o g y and i t s tendency to f rac ture : F a i r c h i l d Lake Group rocks are p a r t i c u l a r l y suscept ib le to "crackl ing", i n part because of a competency contrast between dolomite and a r g i l l i t e l a y e r s . Sharp or abrupt contacts are more common than gradat ional contacts . This i s e s p e c i a l l y true where the b r e c c i a bodies are elongate or d y k e - l i k e . Sharp-walled contacts are in terpreted to be e i ther i n t r u s i v e or faul ted Host rock i s commonly moderately fractured wi th in tens of metres of the contact , and fractures are minera l i zed with i r o n carbonate, quartz or hematite. In several l o c a l i t i e s s t r a t a have been warped or dragged upwards to s teeply dipping a t t i tudes , apparently by i n j e c t i o n of the b r e c c i a . 3.1.3 A l t e r a t i o n Several types of a l t e r a t i o n are associated with the O g i l v i e Mountains b r e c c i a : hemat i t i zat ion , carbonat iza t ion c h l o r i t i z a t i o n and s i l i c i f i c a t i o n . These four s t y l e s of a l t e r a t i o n v a r i a b l y a f fec t the brecc ias and t h e i r host rocks . Weak to moderate host rock a l t e r a t i o n i s t y p i c a l . I t i s general ly more extensive than the l e ss common and l i m i t e d zones of intense a l t e r a t i o n . A l b i t i z a t i o n was not observed i n the f i e l d area. O g i l v i e Mountains brecc ia and host rock contact zones general ly are weak to moderately hematite a l t e r e d . The brecc ias are commonly and c h a r a c t e r i s t i c a l l y hematized. This a l t e r a t i o n v a r i e s from pale pink to b lood-red stained carbonate matrix to l o c a l massive s p e c u l a r i t e . These b r e c c i a bodies commonly form res i s tan t craggy towers and pinnacles that can be recognized from a distance by t h e i r pink to maroon co lour . F a i r c h i l d Lake Group rocks are , i n general , r e g i o n a l l y weakly hemat i t i c . However, adjacent to b r e c c i a bodies the degree of hemat i t i za t ion i s commonly more intense . The permeable beds are stained to deep reds and maroons (Plate 3 .1) , and contain l o c a l jasper . The more intense ly a l t e r e d zones are a few tens of metres across and are t y p i c a l l y accompanied by fractures that have been healed with blood-red carbonate and s p e c u l a r i t e . Quartet Group rocks i n contact with b r e c c i a bodies are general ly only weakly a l t e r e d , d i s p l a y i n g minor d i sco lourat ion to pale greys, greens and reds . However i n some cases wal lrock i s pervas ive ly hematized to a deep red , and red earthy hematite dust i s disseminated throughout the host rock. G i l l e s p i e Lake Group dolostone d i sp lays minor hematit ic s t a i n i n g , but t y p i c a l l y shows l i t t l e a l t e r a t i o n . Bedding at contact margins i s commonly d isrupted to densely f rac tured . Veins and frac ture f i l l i n g s near the contact cons i s t of brown i r o n carbonate that i s general ly devoid of specular hematite. Carbonate a l t e r a t i o n i s common throughout the O g i l v i e Mountains b r e c c i a . Most not i ceab ly , i t occurs as ferruginous dolomite with rhombs 1 to 3 mm i n diameter that replace the primary mineralogy of c l a s t s and o r i g i n a l matrix const i tuents . Carbonat izat ion of host rocks i s not conspicuous because of t h e i r primary carbonate mineralogy. However, t h i n sect ions of b r e c c i a from the contact zones show carbonate rep lac ing f ine grained groundmass. Carbonate overgrowths on o r i g i n a l grains are a lso common. C h l o r i t e occurs as medium to coarse grained p la ty masses and i s o l a t e d elongate la ths i n the matrix of the b r e c c i a s , sometimes accounting for 80% of the matrix at hand sample s c a l e . Although deemed an a l t e r a t i o n mineral , no precursor minera l , such as b i o t i t e , was observed i n any of the b r e c c i a specimens. C h l o r i t e i s a lso abundant i n a l t e r e d mafic dykes, where i t formed a f t e r Fe-Mg s i l i c a t e s as a r e s u l t of lower greenshist grade metamorphism. S i l i c i f i c a t i o n i n OMB i s l o c a l l y intense and replaces s i l t y to sandy do lomite -r i ch sedimentary fragments. Textura l features common to s i l i c i f i e d brecc ias include c louding of fragment-matrix boundaries and general bleaching of the a l t e r e d rock. Limi ted quartz + hematite stockwork zones occur l o c a l l y i n moderately to densely b r i t t l e fractured Quartet sediments at b r e c c i a margins. Weak s i l i c i f i c a t i o n i s shown by s i l i c a replacement of the more permeable layers i n interbedded a r g i l l i t e - s i l t s t o n e u n i t s . The LALA l o c a l i t y (Map 1), an area of some mineral explorat ion a c t i v i t y i n the 1970s, has s i l i c i f i e d fragments and exh ib i t s features of open space f i l l i n g , such as cockade and cockscomb textures (Plate 3 .2) . S e r i c i t i z a t i o n i s general ly present i n minor amounts. Later 58 Plate 3.1 F a i r c h i l d Lake Group dolostone (unit IB; sample BL5-8 located i n the northeast corner of the f i e l d area) showing t y p i c a l hematit ic a l t e r a t i o n . 59 Plate 3.2 Hydrothermally a l t ered brecc ia from the LALA mineral prospect (Map 1) d i sp lay ing cockade texture (rythmical ly p r e c i p i t a t e d quartz and hematite: sample B L 4 0 -11, upper l e f t ) , carbonate -quartz - ser i c i t e a l t e r a t i o n (sample BL40-27, upper r ight) and intense s i l i c i f i c a t i o n (sample BL40-29, bottom). carbonate has f i l l e d the remaining c a v i t i e s . Disseminated and l a t e stage vein-hosted sulphide m i n e r a l i z a t i o n , c o n s i s t i n g of p y r i t e , cha lcopyr i te and born i t e , i s present l o c a l l y i n amounts l e ss than 1%. 3.1.4 Textural V a r i e t i e s O g i l v i e Mountains brecc ia are general ly matr ix-supported, but both matr ix- and fragment-supported v a r i e t i e s are common and general ly occur i n the same outcrop. Fragments make up 30 to 80% of the rock. Roundness of fragments range widely from angular to rounded, but i s genera l ly subangular to subrounded. Shapes range from p la tes and blocks with sharp edges to wel l rounded s p h e r i c a l c l a s t s . Rare fragments form wavy, i r r e g u l a r shapes with serrate terminat ions . Fragments range i n s i ze from less than 1 cm to greater than 5 m. On fresh surfaces OMB i s commonly mottled pink and green, or maroon to purple i n co lour . Weathered surfaces of outcrops, usua l ly pink to maroon and rusty brown, are knobby and p i t t e d due to the contrast between weather-res is tant fragments and recess ive weathering matrix. D e l i c a t e l y laminated (Plate 3.3) and coarse grained c l a s t i c - l o o k i n g layered textures (Plate 3.4) are common l o c a l l y , but a chaot ic jumble of mixed c l a s t s (Plate 3.5) i s the norm. 61 Plate 3.3 Hematitic h e t e r o l i t h i c c h l o r i t e - r i c h matrix brecc ia (unit BHcl; sample BL50-2 located i n centra l part of Southern Brecc ia Be l t ; Map 2) d i s p l a y i n g de l i ca te laminations . Note varying degrees of hematite replacement of fragments (near top and r i g h t side) that indicate hemat i t izat ion was secondary. 0 2 P l a t e 3 .4 H e t e r o l i t h i c carbonate-r ich matrix brecc ia (unit BHcb; sample BL34 -5 located on r idge about 1 .5 km southeast of LALA l o c a l i t y ) showing wel l -def ined layer ing and textures such as weakly defined graded bedding of poss ib le sedimentary o r i g i n . Plate 3.5 Monol i th ic brecc ia (unit BM1; sample BL32-5 located on r idge about 1.5 km south of LALA l o c a l i t y ) showing subrounded pink quartz i t e fragments i n a dense matrix of predominantly c h l o r i t e . The chaot ic jumbled texture i s common to most b r e c c i a . Each of the three u n i t s of the Wernecke Supergroup are represented as fragments i n the brecc ias , but F a i r c h i l d Lake Group l i t h o l o g i e s are the most common. Rare fragments der ived from the lower Fi f teenmi le group occur l o c a l l y i n the Southern Brecc ia B e l t . Minor mafic igneous fragments are l i k e l y derived from diabase dykes that crop out nearby. 3.1.5 C l a s s i f i c a t i o n O g i l v i e Mountains breccia (OMB) were d iv ided into two groups i n the f i e l d : (1) m o n o l i t h i c— ( i . e . o l igomic t i c ) brecc ia fragments are of one l i t h o l o g y , and (2) h e t e r o l i t h i c — ( i . e . polymict ic) brecc ia fragments are of many l i t h o l o g i e s . These terms are commonly used for descr ib ing brecc ias and are consis tent with the terminology presented by Laznicka (1989) . Both the monol i thic and h e t e r o l i t h i c b r e c c i a groups were d iv ided into three sub-units based on fragment l i t h o l o g i e s and type of matrix . A l t e r a t i o n complicates the i d e n t i f i c a t i o n and c l a s s i f i c a t i o n of these b r e c c i a s . S p e c i f i c a l l y , s i l i c a f looding and pervasive hemat i t i za t ion a l t e r the o r i g i n a l textures and mineralogy of the fragments that would otherwise enable them to be more e a s i l y i d e n t i f i e d . Table 3.2 summarizes the c l a s s i f i c a t i o n scheme used. The fo l lowing sect ion describes the c h a r a c t e r i s t i c s of some of the brecc ia bodies, w i th in the l a b e l l e d areas on Map 1. TABLE 3 .2 . C l a s s i f i c a t i o n scheme used to character ize O g i l v i e Mountains brecc ia of the Coal Creek I n l i e r , southern O g i l v i e Mountains, west -central Yukon T e r r i t o r y . Brecc ia v a r i e t y Fragment l i t h o l o g y 3 GLG Dominant matrix component carb c h l r hem s i l Mono l i th i c H e t e r o l i t h i c QG FLG mixture of GLG+QG+FLG +FMG 1. Abbreviat ions are as fol lows: GLG = G i l l e s p i e Lake Group; QG = Quartet Group; FLG = F a i r c h i l d Lake Group; FMG = F i f teenmi le Group; carb = mainly dolomite and ferruginous dolomite; c h l r = c h l o r i t e ; hem = specu lar i t e and red opaque hematite "dust"; s i l = quartz . 3.2 PETROGRAPHY Greater than 99% of a l l fragments have been derived from the Wernecke Supergroup. The other <1% cons i s t s of mafic igneous fragments, quartz and carbonate ve in m a t e r i a l , lower F i f teenmi le group sediments and specu lar i t e aggregates. The brecc ias are commonly fragment supported. Fragments are dominantly subangular to subrounded, range i n s i ze from <1 cm to rare fragments l a r g e r than 20 by 50 m. Average s i z e i s i n the 1 to 2 cm diameter range. Observed textures inc lude: c l a s t alignment, f o l i a t i o n , banding or l a y e r i n g , chaot ic from jumbled mixtures of fragment types, m i l l e d or abraded fragment margins, and crackled fragments. Matr ix i s composed of f i n e l y fragmented mater ia l that i s l o c a l l y gradat ional i n s i ze with fragments. The proport ion of matrix var ies appreciably over distances of l ess than two metres. Colour of the matrix covers a wide spectrum from pale greens, pinks and browns to dark greens, reds and greys . Where matrix i s wel l developed i t i s general ly darker than fragments. A l t e r n a t i v e l y , the matrix component of some brecc ias ( e spec ia l ly carbonate-r ich breccias) i s sparse and less obvious. Dominant a l t e r a t i o n minerals cons i s t of carbonate, i r o n carbonate, c h l o r i t e and hematite. Carbonate a l t e r a t i o n i s widespread as i s hemat i t i za t ion . C h l o r i t i z a t i o n occurs most commonly i n mafic dykes cu t t ing b r e c c i a s , where i t has almost e n t i r e l y replaced o r i g i n a l mafic g r a i n s . On the margins of the dykes, r a d i a t i n g sprays of c h l o r i t e has formed at the expense of a l l other const i tuents . Local s i l i c i f i c a t i o n i s moderate to intense and i s commonly associated with weak s e r i c i t i c a l t e r a t i o n . Mapped features of the brecc ia included: (i) proport ion of fragments vs . matrix , ( i i ) proport ion of each fragment type, ( i i i ) fragment s i z e : average and range, (iv) roundness and s p h e r i c i t y , (v) percent of each matrix type, (vi) textures , and (v i i ) a l t e r a t i o n . 3.2.1 Monol i th ic O g i l v i e Mountains Brecc ia Monol i th ic OMB were subdivided based on t h e i r fragment l i t h o l o g y . Four fragment v a r i e t i e s were observed: (i) F a i r c h i l d Lake Group, ( i i ) Quartet Group, and ( i i i ) G i l l e s p i e Lake Group, and (iv) lower Fi f teenmi le group. Fragments from the lower Fi f teenmile group rocks were rare— only one such occurrence was observed. Composition of the matrix was not used to c l a s s i f y monol i thic b r e c c i a s , but was noted and i s discussed below. 3 .2 .1 .1 Monol i th ic F a i r c h i l d Lake Group O g i l v i e Mountains Brecc ia (unit Bj^i) Monol i th ic F a i r c h i l d Lake Group OMB (B^i) , with fragments der ived e n t i r e l y from F a i r c h i l d Lake Group l i t h o l o g i e s , are the most common brecc ia i n the f i e l d area. The best exposures, out l ined below, occur on r idge tops where outcrops form blocky, hummocky zones that l o c a l l y include sp ires up to 2 m high . The weathered surface of 68 Plate 3.6 Exposure of h e t e r o l i t h i c carbonate-r ich matrix b r e c c i a (unit BHcb), located about 2 km west of the BEEHIVE l o c a l i t y , d i sp lay ing angular block of bedded dolostone 0.8 m i n length (middle r i g h t ) , smaller angular blocks of a r g i l l i t e (lower l e f t ) , and abundant subrounded fragments of s e v e r a l v a r i e t i e s . outcrops, commonly knobby and p i t t e d , d i sp lay the general ly chaot ic nature of the rock (Plate 3 .6) . T y p i c a l l y the brecc ias are mottled pink or buff to rusty brown or , l ess commonly, pale green. A l l l i t h o l o g i e s of F a i r c h i l d Lake Group are represented i n the b r e c c i a s , but the dominant fragment type i s pink-weathering s i l t y dolostone. Fragment s i z e ranges widely from greater than 3 m to less than 0.5 cm, but dominantly about 3 cm. Matrix i s t y p i c a l l y carbonate (dolomite and minor i r o n carbonate) with minor specular hematite, c h l o r i t e and crushed rock m a t e r i a l . The s i z e and shape of fragments v a r i e s according to the c h a r a c t e r i s t i c s of the rocks from which they o r i g i n a t e d . For instance , t h i n l y bedded, b r i t t l e layers fractured e a s i l y and formed p l a t y sharp-cornered b r e c c i a fragments. Uni t BMI has two t e x t u r a l end members, they are: (i) d i srupted or block brecc ia with r e s t r i c t e d , general ly small pod- and dyke - l ike zones that have v e r t i c a l expression (channelway b r e c c i a ; c f . Delaney, 1981), and ( i i ) crack le b r e c c i a , that forms on the margins of the more intense ly brecc ia ted and mixed zones. Disrupted or block b r e c c i a i s exposed i n the northwestern part of the map area (Map 1) on the prominant s u b - c i r c u l a r ridges i n the SLAB and DONUT l o c a l i t i e s and on the r idge northwest of the BEEHIVE (Map 1, Figure 3 .1) . The main b r e c c i a mass at the SLAB l o c a l i t y i s a tablet-shaped sec t ion that has developed on the hanging wal l of the Monster f a u l t . I t truncates north-d ipping s t r a t a of the Quartet Group (Plate 3 .7) . The southern margin of t h i s b r e c c i a body i s o v e r l a i n by south-dipping Quartet Group rocks . The bulk of the brecc ia cons is t s of blocks of p ink-to brown-weathering s i l t y dolostone whose boundaries commonly are i n d i s t i n g u i s h a b l e . However, the chaot ic nature of s t r i k e and d ip of t h i s un i t over short distances ( in the range of 5-10 m) d i sc loses i t s d isrupted nature. Where edges of i n d i v i d u a l brecc ia blocks are evident, matrix i s not we l l developed; i t consists genera l ly of dolomit ic rock f l o u r , minor white c a l c i t e carbonate and subrounded fragments of sedimentary rock l ess than 2 cm i n diameter (Plate 3 .8 ) . In t h i n sec t ion , specimen BL16-2 d i sp lays a matrix inc lud ing 90-95% subhedral dolomite that cements angular to subangular fragments of s i l t y dolostone (Plate 3 .9) . Minor quartz and hematite, and traces of muscovite and c h l o r i t e make up the remaining 5-10%. Loca l zones of brecc ia are c a l l e d conduit b r e c c i a . These are r e l a t i v e l y m a t r i x - r i c h and normally contain fragments 5 to 20 cm across (although blocks greater than 3 metres i n length do occur) . These brecc ia bodies crosscut the block b r e c c i a . The exposures are commonly no larger than 10 m across , are bounded by zones of d isrupted block Plate 3.7 View of the SLAB looking west. The sharp contact between over ly ing OMB (buff) and Quartet Group (grey) i s the Monster f a u l t . Truncation of bedding i n Quartet Group rocks i s v i s i b l e at r i g h t sky l ine . 72 Plate 3 .8 M o n o l i t h i c F a i r c h i l d Lake Group b r e c c i a ( u n i t BM1; sample BL26-2 l o c a t e d about 3 km e a s t o f LALA l o c a l i t y ) . P l a t e 3 . 9 P h o t o m i c r o g r a p h o f m o n o l i t h i c F a i r c h i l d L a k e G r o u p b r e c c i a ( u n i t BM3; t h i n s e c t i o n B L 1 6 - 2 ) s h o w i n g s u b r o u n d e d q u a r t z i t e f r a g m e n t s ( s e v e r a l a r e o u t l i n e d b y d a s h e d l i n e ) i n a c a r b o n a t e m a t r i x . N o t e g r o w t h z o n e d d o l o m i t e g r a i n a n d o t h e r d o l o m i t e r h o m b s — e v i d e n c e o f r e c r y s t a l l i z a t i o n . b r e c c i a , and occur as weather-res is tant jagged knobs on r idge c r e s t s . Prominant exposures are located i n the centre of the northern brecc ia band (Map 1 and Figure 3.1) north of the BEEHIVE) . Conduit brecc ia c h a r a c t e r i s t i c a l l y d i sp lays a w e l l -mixed or "churned" texture where fragments have been rotated and s t r a t i g r a p h i c a l l y mixed. The angular and sub-angular to sub-rounded fragments are set i n a matrix t y p i c a l l y c o n s i s t i n g of pink, pervas ive ly hematized dolomite (Plates 3.10 and 3.11) . Minor matrix components cons i s t of i r o n carbonate, c h l o r i t e , hematite and quartz . However, hydrothermal a l t e r a t i o n can s i g n i f i c a n t l y mask the o r i g i n a l character of the rock (Plate 3.12). In rare cases hematite and/or c h l o r i t e comprise most of the matrix. These rocks l o c a l l y d i sp lay weak to s trongly developed a l igned textures . These textures can be defined by the s u b p a r a l l e l arrangement of p la ty hematite blades and c h l o r i t e l a ths up to several mi l l imeters i n length. Dolomite rhombs up to 2 mm across , are minor, but occur disseminated throughout the matrix where they are l o c a l l y concentrated on fragment boundaries. Matr ix usua l ly accounts for 25 to 35% of the rock, and genera l ly contains a mixture of minerals : carbonate i s most abundant and t y p i c a l l y accounts for between about 25 and 60%, quartz accounts for 15-40% and c h l o r i t e makes up 5-15%. Blades of hematite (<1-10%), i r r e g u l a r patches of c lay (trace to about 5%), f ine grained muscovite i n trace amounts and fragments l e ss than 1 mm i n diameter comprise the remainder of the matrix . Matr ix supported v a r i e t i e s are uncommon, but may resemble coarse grained c l a s t i c sedimentary rocks . Subangular to subrounded, commonly gravel s i zed c l a s t s , are set i n a matrix c o n s i s t i n g of broken grains of quartz and fe ldspar , i r r e g u l a r patches of carbonate and c l a y , r a d i a t i n g masses of c h l o r i t e , randomly oriented blades of hematite that rim l a r g e r g r a i n s , and minor f ine grained f lakes of muscovite. C h l o r i t e and carbonate contain numerous inc lus ions and appear to replace quartz . Crackle b r e c c i a forms along the margins of some brecc ia bodies . A good exposure of t h i s b r e c c i a occurs on the southern margin of the i r r e g u l a r l y shaped body that crops out on the r idges south of the o ld LALA l o c a l i t y (Map 1) . At t h i s l o c a l i t y crack le brecc ia (Plate 3.13) cons is ts of p l a t y , angular grey to pale green fragments of s i l t s t o n e set i n a pink matrix of dolomite. The arrangement of p la ty fragments, from 1 to 10 cm across and 0.5 to 3 cm t h i c k , define a weak l a y e r i n g that becomes more pronounced away from the centre of the brecc ia body. Outer margins of the crackle b r e c c i a grade into coherent, interbedded s i l t s t o n e Plate 3.10 Photograph of monolithic F a i r c h i l d Lake Group brecc ia (unit BM1). A large block of s e m i - p l a s t i c a l l y deformed F a i r c h i l d Lake Group dolomit ic s i l t s t o n e (upper middle) and the centimetre s ized angular fragments i n a hematized carbonate matrix (lower middle) are d i sp layed . The outcrop i s located on the west r idge of the DONUT. Penc i l for sca le . Plate 3 .11 Cut and pol i shed surface of crackle brecc ia v a r i e t y of monol i thic F a i r c h i l d Lake Group brecc ia (unit BM1; sample BL18-10 located approximately 6 km west-southwest of the BEEHIVE l o c a l i t y ) from margin of brecc ia body. Contorted bedding and c l e a r ro ta t ion of some fragments are conspicuous. -3 Plate 3.12 Cut and pol ished (wet) surface of channelway b r e c c i a v a r i e t y of monol i thic F a i r c h i l d Lake Group brecc ia (unit BM1: sample TW208 located on r idge about 1.75 km southeast of LALA l o c a l i t y ) . Fragments are quartz i t e i n a quartz - and c h l o r i t e - r i c h matrix . Plate 3.13 Crackle brecc ia v a r i e t y of monol i thic F a i r c h i l d Lake Group brecc ia (unit BM1 located 1.5 km southeast of LALA l o c a l i t y ) from margin of b r e c c i a body. F a i r c h i l d Lake Group at t h i s point i s mainly dolostone with s i l t s t o n e interbeds. and dolostone. There has been l i t t l e or no add i t i on of mater ia l i n the formation of t h i s b r e c c i a . The matrix cons is t s of remobi l ized carbonate derived from the carbonate-r ich l a y e r s . 3 .2.1.2 Monol i th i c Quartet Group O g i l v i e Mountains Brecc ia (unit Bj^) Monol i th ic Quartet Group OMB (BM2) i s uncommon. I t i s l i m i t e d to fau l ted contacts between s t r a t i f i e d Quartet Group and e i t h e r h e t e r o l i t h i c b r e c c i a or F a i r c h i l d Lake Group or G i l l e s p i e Lake Group s t r a t a . I t occurs only i n the northern part of Map 1. Outcrops are pale to dark grey. Fragments are t y p i c a l l y angular to sub-angular and range from 0.5 cm to 8 cm i n length . Most occurrences contain appreciable amounts of secondary white s i l i c a as i n t r i c a t e stockworks or fracture f i l l i n g s . An exce l lent exposure of monol i thic Quartet b r e c c i a occurs on the north bank of "Beehive" creek about 200 m west of the LALA prospect (Figure 3 .1 , Map 1). This exposure, about 2 m high and 20 m long, i s notable because severa l stages of b r e c c i a t i o n are recognized i n hand sample (Plate 3.14; sample BL-11-7) . Fresh- looking angular black p h y l l i t i c a r g i l l i t e fragments several centimetres i n diameter occur next to pale grey, bleached, s i l i c a flooded composite fragments. The l a t t e r phase of b r e c c i a t i o n i s marked by the add i t i on of abundant quartz , carbonate and minor sulphides . These minerals are l i k e l y part of the 8l Plate 3.14 Monol i th ic Quartet Group brecc ia (unit BM2: sample BL11-7; LALA l o c a l i t y , Map 1) from La la mineral prospect . Some fragments are brecc ia (angular black a r g i l l i t e fragments i n a pale grey matr ix) ; others are black a r g i l l i t e . Chalcopyri te (yellow mineral ; centre of photograph) and p y r i t e are disseminated throughout. hydro-thermal a l t e r a t i o n event r e l a t e d to the nearby LALA mineral prospect (Map 1). Mult i s tage b r e c c i a t i o n i s defined by fragments that are made up of fragments. 3 .2 .1 .3 Monol i th ic G i l l e s p i e Lake Group O g i l v i e Mountains Brecc ia (unit Bjfl3) Monol i th ic G i l l e s p i e Lake Group OMB are r a r e . Only a s ing l e example i s known. I t occurs i n the northwest corner of Map 1 on the northern margin of the DONUT l o c a l i t y (Figure 3 .1 , Mapl) . The fragment supported brecc ia cons i s t s of angular fragments of f ine gra ined, pale grey dolostone (unit 3a) up to several metres i n diameter. Weakly fractured G i l l e s p i e Lake Group rocks grade into intense ly f rac tured and brecc iated vers ions adjacent to h e t e r o l i t h i c b r e c c i a . The contact between the brecc ias i s wel l exposed near and on a north-trending r i d g e . The s u b - v e r t i c a l contact i s sharp; i t i s l i k e l y a f a u l t . In t h i n sect ion angular fragments of very f ine grained dolostone are cemented by coarse grained (up to 7 mm across ) , anhedral to subhedral, intergrown dolomite or i r o n carbonate and quartz (Plate 3.15). Rare f ine grained sprays of c h l o r i t e and anhedral opaques, l i k e l y hematite, are accessor ies . Fragments are commonly rimmed by a t h i n veneer of l imon i t e . Commonly exhibi ted d i l a t i o n a l textures ind ica te that some of the brecc ias formed by i n j e c t i o n of CENTIMETRE Plate 3.15 a: P h o t o g r a p h o f c u t a n d p o l i s h e d s l a b o f h e m a t i t i c m o n o l i t h i c G i l l e s p i e L a k e G r o u p b r e c c i a ( u n i t BM3; s a m p l e B L 8 7 - 7 ) f r o m t h e c o n t a c t b e t w e e n G i l l e s p i e Lake G r o u p d o l o s t o n e a n d OMB o n t h e n o r t h e r n e d g e o f t h e DONUT', Map 1) . b: P h o t o m i c r o g r a p h o f m o n o l i t h i c G i l l e s p i e Lake Group breccia (unit BM3; t h i n section B L 8 7 - 7 ; from DONUT l o c a l i t y ) s h o w i n g s u b a n g u l a r f i n e g r a i n e d d o l o s t o n e f r a g m e n t s i n a c o a r s e g r a i n e d d o l o m i t e c e m e n t . M i n o r h e m a t i t e p a r t i a l l y r i m s some f r a g m e n t s . carbonate- and q u a r t z - r i c h mater ia l . 3.2.2 H e t e r o l i t h i c O g i l v i e Mountains b r e c c i a Fragments i n h e t e r o l i t h i c OMB are der ived from the lowermost s t r a t i g r a p h i c package of the Coal Creek I n l i e r . The sources, i n order of most common fragment type, are: F a i r c h i l d Lake Group, Quartet Group, G i l l e s p i e Lake Group, lower Fi f teenmile group, and mafic igneous mater ia l from associated diabase dykes. L i t h o l o g i c heterogeneity of the brecc ias r e f l e c t s , for the most par t , the d i v e r s i t y of t h i n l y interbedded uni t s wi th in the F a i r c h i l d Lake and Quartet Groups. L o c a l l y intense a l t e r a t i o n or metasomatism has caused d i f f e r e n t fragment types to resemble one another so that the b r e c c i a appears to be monol i th ic . H e t e r o l i t h i c O g i l v i e Mountains b r e c c i a have been subdivided on the bas is of major matrix components i n t o , i n order of abundance: (i) carbonate -r ich , ( i i ) hemat i t e -r i ch , and ( i i i ) c h l o r i t e - r i c h end members. These types are d e t a i l e d below. 3 .2 .2 .1 H e t e r o l i t h i c carbonate-r ich matrix O g i l v i e Mountains brecc ia (unit Bfjcb) H e t e r o l i t h i c carbonate-r ich matrix O g i l v i e Mountains brecc ia (Bjjcb) occurs most prominently at the BEEHIVE (Figure 3 .1 , Map 1 and Plate 3.16), a 170 m high h i l l of p a r t l y rubble-covered outcrop. I t i s s i tuated i n the western end of the broad, U-shaped, informal ly named "Beehive" v a l l e y . I t cons i s t s of well-bedded and t h i n l y bedded pink, s i l t y dolostone and green a r g i l l i t e , g r i t t y do lomit ic sandstone, and brown weathering dolostone. A h e t e r o l i t h i c b r e c c i a s i l l , 60 m i n true thickness , dips shal lowly and cuts through the h i l l about halfway up. The contacts at the margins of the brecc ia s i l l are gradat ional with the host rock: the core of h e t e r o l i t h i c b r e c c i a grades outward to monol i thic zones at the margin and into crack led , in tense ly fractured host rock. Fracture i n t e n s i t y decreases away from the margin. The lower contact of the b r e c c i a s i l l i s marked by a pale green intense ly c h l o r i t i z e d mafic dyke. This dyke d i sp lays porphyroblasts of p y r i t e and zoned amygdules with t h i c k s i d e r i t e or ankerite rims and c a l c i t e cores . Fine grains of bladed specular hematite are minor. This brown-green mottled b r e c c i a contains Quartet Group, F a i r c h i l d Lake Group and mafic igneous fragments (Plate 3.17; sample BL10-14). Subangular fragments average about 2 cm i n diameter, but rare large fragments range up to 4 m across . The matrix cons i s t s dominantly of dolomite with accessory c h l o r i t e and hematite. A small lens-shaped exposure of b r e c c i a , 180 m by 30 m crops out 400 m south of the BEEHIVE. I t occurs as an i s o l a t e d lense-shaped body hosted i n Quartet Group rocks Plate 3.16 . Locat ion of b r e c c i a s i l l i s marked by a dashed l i n e i n t h i s view of the "BEEHIVE" (Map 1) looking west. Note a l so the lens of brecc ia (arrow) hosted i n Quartet Group sediments on f lank of mountain to the l e f t of the BEEHIVE. CENTIMETRE Plate 3.17 Cut and p o l i s h e d s u r f a c e o f hand sample from h e t e r o l i t h i c c a r b o n a t e - r i c h m a t r i x b r e c c i a ( u n i t BHcb; sample BL10-14) from the BEEHIVE b r e c c i a s i l l . Note g e n e r a l l y a n g u l a r o u t l i n e o f fragments and c h a o t i c o r i e n t a t i o n . Fragments a r e : h e m a t i t e a l t e r e d d i a b a s e (d ) , q u a r t z i t e (q ) , a r g i l l i t e ( a ) , d o l o s t o n e (o ) , and s i l t s t o n e (s) . and, when viewed from a d is tance , i s i d e n t i f i e d by i t s buf f -weathering that contrasts with the dark grey Quartet Group rocks (see P late 3.16). In hand sample the orangey-pink matrix i s studded with fragments of bleached s i l t y dolostone, pale green and black a r g i l l i t e , white and green s i l i c e o u s m a t e r i a l , and pale green mafic igneous rock (Plate 3.18). The SLAB l o c a l i t y (Figure 3.1 and Map 1) has two exce l lent exposures of variegated h e t e r o l i t h i c b r e c c i a bodies that cut a host of Monol i th ic F a i r c h i l d Lake Group OMB (BJJI) • One exposure i s an eas t - trending , t h i n elongate body of b r e c c i a . I t fol lows the trace of the Monster f a u l t that d iv ides north-d ipping Quartet Group sedimentary rocks on the north from monol i thic F a i r c h i l d Lake Group OMB (Bjiji) to the south. The other i s a north-trending zone that pinches out to the north as i t cuts across and through Quartet Group rocks (Plates 3.19). The l a t t e r brecc ia body apparently squeezed between sect ions (mega blocks ?) of Quartet Group a r g i l l i t e s . I t has c l a s t s that are dominantly subrounded to subangular pink dolostone, and interbedded a r g i l l i t e and dolostone up to 40 cm i n diameter. Angular to subangular b lack a r g i l l i t e fragments up to 75 cm i n length are abundant. White sparry c a l c i t e c r y s t a l s and blebs of specular hematite are common as matrix const i tuents . Pock-marked weathered surfaces ind icate so lu t ion of coarse-grained (0.5 to 2 mm) carbonate c r y s t a l s . Carbonate also 89 Plate 3.18 Cut surface of hand sample from h e t e r o l i t h i c carbonate-r ich matrix brecc ia (unit BHcb; sample BL87-70) from the exposure of brecc ia to the south (to the l e f t of Beehive i n Plate 3.16) of the BEEHIVE. Fragments are: diabase (d), quar tz i t e (q), a r g i l l i t e (a), dolostone (o), and s i l t s t o n e (s) . Plate 3.19 Crosscutting nature of dyke-like breccia body (shown i n sketch above) i s shown i n t h i s view of the SLAB l o c a l i t y (Map l , looking east). rims c l a s t s . The DONUT area (Figure 3.1 and Map 1) i s another example l o c a l i t y for the carbonate-r ich matrix brecc ia (BHcb)• A t t h i s l o c a l i t y the gradat iona l , brecc iated contact between brecc ia and G i l l e s p i e Lake Group on the north-northeast s ide of the DONUT i s we l l exposed (Plate 3.20). Bedding i s steeply truncated; s t r a t a adjacent to the contact has been ruptured into rotated blocks 3-5 m across . On the northwest s ide of the DONUT subver t i ca l c r o s s - c u t t i n g contacts between Quartet Group and OMB are we l l d isplayed (Plate 3 .21) . There, h e t e r o l i t h i c carbonate-r ich matrix OMB inc ludes fragments from F a i r c h i l d Lake Group and uppermost Quartet Group (Plate 3.22). In t h i n sec t ion medium to coarse grained anhedral , commonly p o i k i l i t i c , (iron) carbonate, or dolomite, comprises from 45 to 70% the matrix . Anhedral to subhedral quartz , 0.1 to 2.4 mm i n diameter, account for between 15 and 35% of the matrix . Weakly developed foam texture i s evidence of r e c r y s t a l l i z a t i o n . Rare quartz grains exh ib i t mul t ip l e stages of quartz overgrowth. L i t h i c fragments (comminuted sedimentary rock) , l e s s than approximately 1 mm i n diameter, are c l a s s i f i e d as matrix and make up to 10% i t . Opaques cons i s t mainly of bladed hematite (ranging from trace amounts to 8%), that rims fragments; rare p y r i t e and l imoni te a l so occurs . C h l o r i t e i s present i n minor amounts. P l a t e 3.20 DONUT l o c a l i t y (Map 1) looking north-east at steeply dipping contact, i n foreground, between orange weathering dolostone of G i l l e s p i e Lake Group (unit 3A, r i g h t and far l e f t ) and maroon h e t e r o l i t h i c breccia (unit BHcb, centre). Plate 3.21 DONUT l o c a l i t y (Map 1 ) looking west from the middle of the complex. I r r e g u l a r and i n t e r f i n g e r i n g contact between brecc ia (buff, above) and Quartet Group (grey, below) i s shown i n sketch above. oh Plate 3.22 Outcrop of h e t e r o l i t h i c carbonate-r ich matrix OMB from the northwest part of the DONUT l o c a l i t y (Map 1). Angular fragments cons i s t of do lomit ic s i l t s t o n e of uppermost Quartet Group and pale green s i l t s t o n e , pink s i l t y dolostone and jasper of the F a i r c h i l d Lake Group. Mafic dyke fragments are r a r e . Hammer for sca le . Accessory components of the matrix , that occur i n trace amounts, are a c t i n o l i t e / t r e m o l i t e and epidote . Specimen BL35-4 contains severa l subrounded to rounded fragments of s trongly carbonate a l t e r e d igneous i n t r u s i v e rock. The cores of these fragments cons i s t of a coarse grained mesh of a c t i n o l i t e / t r e m o l i t e , carbonate, c h l o r i t e and quartz 0.2 to 2 mm i n length (Plate 3.23). Masses of rusty i r o n oxide and coarse grained i r o n carbonate comprise the a l t e r e d rims, which are t y p i c a l l y 1 to 3 mm wide. Common p y r i t e euhedra range i n s i z e from 0.6 to 1.7 mm. 3 .2 .2 .2 H e t e r o l i t h i c hemat i t e -r i ch matrix O g i l v i e Mountains Brecc ia (unit Buh) H e t e r o l i t h i c hemat i te -r ich matrix OMB (Bah) are r e l a t i v e l y common, but exposures are l i m i t e d i n extent. Outcrops have been observed mainly on r idge cres ts where they form prominent, often jagged, craggy towers (Plate 3.24). Good exposures occur i n the Southern Brecc ia Be l t at the eastern-most edge of the DYKE l o c a l i t y (Map 1), and at the tadpole shaped brecc ia body (POD l o c a l i t y ; Figure 3.1 and Map 1) located i n the middle of the southern part of SBB. One occurrence at the former l o c a l i t y i s a narrow, dyke - l ike exposure of h e t e r o l i t h i c b r e c c i a of l a r g e l y hemat i te -r i ch matrix b r e c c i a . Layering i n t h i s brecc ia dips 75 degrees to the south and i s weakly defined by the o r i e n t a t i o n of elongate c l a s t s and whispy discontinuous laminae of specular hematite (Plate 3.25). These brecc ias are matrix supported. Fragments, subangular to subrounded, are l o c a l l y p l a s t i c a l l y deformed and range up to 8 cm i n diameter. Fragment l i t h o l o g i e s cons i s t of grey to black laminated a r g i l l i t e , pink s i l t y dolostone, white to purple q u a r t z i t e , "bal l s" of specular hematite and uncommon jasper . Hematite, both specular and earthy v a r i e t i e s , i s the dominant matrix const i tuent . Less common matrix components include dolomite, c h l o r i t e , quartz and comminuted host rock. H e t e r o l i t h i c hemat i te -r ich matrix b r e c c i a a lso occurs at the " t a i l end" of the POD l o c a l i t y (Figure 3.1 and Map 1) . This b r e c c i a body appears to be genera l ly weakly zoned from c h l o r i t e - r i c h i n the east to hemat i te -r ich i n the west. The contact between the zones i s not wel l exposed and i s assumed to be i r r e g u l a r and t r a n s i t i o n a l . However the " t a i l " end i s made up dominantly of hemat i te -r ich matrix brecc ia that i s purple-maroon to pink i n outcrop. The brecc ia includes subrounded c l a s t s averaging about 4 mm i n diameter that cons i s t of grey dolomite, dark grey to black a r g i l l i t e , red mudstone, pink s i l t y dolomite and aggregates of specular hematite. These c l a s t s are set i n a matrix of s p e c u l a r i t e , minor carbonate, quartz and c h l o r i t e (Plate 3.26). Layering i s absent. Contacts between brecc ia and host rock, where wel l exposed, are sharp and s u b v e r t i c a l . 97 Plate 3.23 Photomicrograph of core of mafic igneous fragment from sample BL35-4 (unit BHcb). Broad, green c h l o r i t e la ths formed a f ter Fe-Mg s i l i c a t e s . Hexagonal opaque c r y s t a l s are p y r i t e . 98 Plate 3.24 Prominant craggy exposure of h e t e r o l i t h i c b r e c c i a on east facing f lank of DONUT l o c a l i t y (Map 1) . SLAB l o c a l i t y (Map 1) i s i n background across the v a l l e y . The south dipping contact (shown i n sketch above) between b r e c c i a (upper r ight) and underly ing Quartet Group c l a s t i c rocks. 99 Plate 3.25 H e t e r o l i t h i c hemat i te-r ich-matr ix brecc ia (unit BHh; sample BL43-7) from western edge of Southern Brecc ia Be l t (Map 1). Note p l a s t i c a l l y deformed c l a s t s and crudely defined l a y e r i n g . Clasts are: dolostone (o), quar tz i t e (q), mudstone (m), coarse grained sandstone or g r i t (g), and specular hematite (h). 100 Plate 3.26 H e t e r o l i t h i c hemat i te -r ich matrix brecc ia (unit BHh; sample BL48-3) from the (POD l o c a l i t y ; Map 1), Southern Breccia B e l t . Fragments are: limestone (1), hematite a l t ered diabase (d), quartz i t e (q), a r g i l l i t e (a), dolostone (o) , s i l t s t o n e (s) , mudstone (m), and jasper ( j ) . Fine grained matrix comprises specu lar i t e , hematite stained carbonate and subordinate quartz . Hemat i te -r ich matrix OMB a lso occur at the Northern Brecc ia Be l t north of the LALA l o c a l i t y (Figure 3.1 and Map 1) . Numerous outcrops of brecc ia are cut by a 3 m wide west-trending diabase dyke on the south fac ing slope of the r idge . These c h a r a c t e r i s t i c a l l y layered fragmental rocks are between 50 and 75% hematite (Plate 3.27). Fragments make up to about 60% of the rock and are derived from F a i r c h i l d Lake Group and Quartet Group rocks . Rocks from t h i s occurrence may be sedimentary i ron formation. Matrices of these rocks are character ized i n t h i n sect ion by t h i c k to t h i n tabular plates and elongate laths of hematite up to 4 mm long that t y p i c a l l y comprises between 25 and 75% of the rock. Lesser matrix components cons i s t of: subhedral quartz (0.03 mm to 1.4 mm i n diameter; 20-45%); p o i k i l i t i c anhedral patches, and less common euhedral rhombs of i r o n carbonate (10-25%) up to 5 mm across; minor c h l o r i t e , c lay and small l i t h i c fragments; traces of potassium fe ldspar and f ine grained euhedral tourmaline; l o c a l s e r i c i t e ; and rare p y r i t e and cha l copyr i t e . Quartz overgrowths on quartz and carbonate overgrowths on carbonate grains are common. Poorly developed foam texture i n some fragments and growth of euhedral c r y s t a l s are evidence of r e c r y s t a l l i z a t i o n (Plates 3.28 and 3.29). The fragments i n these rocks are genera l ly rimmed with hematite or coarse grained carbonate. Microscopic layer ing i s defined by d i scre te bands of a l igned hematite blades. Aggregates of 102 Plate 3.27 Hemati te-r ich matrix brecc ia (unit BHh; sample BL24-12) from southeast fac ing f lank of r idge about 2 km southwest of LALA mineral showing (Map 1), Northern Brecc ia B e l t . Note de l i ca t e laminations of s p e c u l a r i t e . Plate 3.28 Photomicrograph of h e t e r o l i t h i c hemat i te -r ich matrix brecc ia (unit BHh; sample B L 4 3 - 7 ) of broken c r y s t a l s of quartz (q), dolomite (d), and hematite (opaque blades) i n f ine grained matrix. Note deformation lamellae and ghost zoning, out l ined by hematite dust and f l u i d i n c l u s i o n s , i n larges t quartz g r a i n . The broken end of t h i s c r y s t a l and scal loped edges of other c r y s t a l s a t t e s t to comminution during emplacement of t h i s rock v i a a gaseous f l u i d . Fine grained matrix consists of muscovite, carbonate, hematite and quartz . 10k Plate 3.29 Photomicrograph of h e t e r o l i t h i c hemat i te -r ich matrix b r e c c i a (sample BL24-12) from area north of LALA l o c a l i t y . Note growth zones, defined by f l u i d inc lus ions , and undulose ex t inc t ion i n large quartz c r y s t a l (centre of photograph). Opaques grains are hematite; high b i r e f r i n g e n t minerals are carbonate. Fine grained matrix i s hematite, c h l o r i t e and c l a y . f ine to medium grained specu lar i t e a lso form rare subrounded c l a s t s . A l l fragments are of sedimentary rocks that are often s trongly hematized. 3 .2.2.3 H e t e r o l i t h i c c h l o r i t e - r i c h matrix O g i l v i e Mountains Brecc ia (unit BH CI) H e t e r o l i t h i c c h l o r i t e - r i c h matrix OMB (BH CI ; P late 3.30) are common l o c a l l y , but exposures are genera l ly smal l . Several exposures of t h i s brecc ia occur i n a band that trends across two r idges to the south and east of the LALA prospect (Figure 3.1 and Map 1). The s t r i k e length of t h i s elongate zone i s more than 4 km, and i t v a r i e s i n width from 50 to 300 metres. I t occurs at the contact between F a i r c h i l d Lake Group rocks to the north and Quartet Group rocks to the south. The southern contact of the brecc ia body i s exposed where i t crosses two prominent r idges . Here the contacts appear to be steep and sharp. Fragments, general ly subrounded, vary i n l i t h o l o g y , but cons i s t mostly of pink quartz i t e and s i l t y dolostone from the F a i r c h i l d Lake Group. Other fragment types include dark grey to purple s i l i c e o u s a r g i l l i t e (Quartet Group), banded pink chert , and quartz-carbonate ve in m a t e r i a l . Mafic igneous fragments are rare and G i l l e s p i e Lake Group fragments are absent. Fragments, i n t h i n s ec t ion , commonly cons is t s of r e c r y s t a l l i z e d quartz and carbonate of various g r a i n s i zes ; quartz overgrowths are abundant. Carbonate, c lay and f ine grained anhedral hematite i s disseminated throughout the pink fragments. C h l o r i t e , minor carbonate and rare specu lar i t e cements the fragments. Micro fractures i n fragments are healed with c h l o r i t e and l e s ser white to pink quartz and carbonate. Hematite, a common accessory mineral i n the matrix component of the b r e c c i a , occurs i n amounts from trace up to 3%. Specular hematite i s commonly disseminated throughout the fragments. C h l o r i t e , as seen i n t h i n sect ion (Plate 3.31), occurs as f ine to medium grained r a d i a t i n g masses and l ess commonly as coarse grained (2-3 mm) l a t h s . I t makes up between 35 and 70% of the matrix . Carbonate, i r o n carbonate and hematite, s i l i c a , and l o c a l l y as much as 2% s e r i c i t e comprise the remainder of the matrix . S e r i c i t e - b e a r i n g brecc ias are cross -cut by pos t -brecc ia sulphide-bearing quartz-carbonate ve ins . C h l o r i t e - r i c h matrix brecc ias are also present i n the Southern Brecc ia B e l t . Sample BL50-2 (see Plate 3.3) i s a f i n e l y layered, matrix supported example that contains rare rounded fragments of pink spotted rock. These fragments 107 Plate 3.30 Two examples of h e t e r o l i t h i c c h l o r i t e - r i c h -matrix brecc ia (unit BHcl; sample BL35-5, above, from r idge top about 1.5 km southeast of the LALA l o c a l i t y , and sample BL3-25, below, about 2.5 km east-southeast of LALA l o c a l i t y ) . Fragments are: quartz i t e (q), s i l t y dolostone (o), mudstone (m) and mafic dyke (d). Fine grained matrix i s c h l o r i t e and subordinate dolomite. 108 Plate 3.31 Photomicrograph of h e t e r o l i t h i c c h l o r i t e - r i c h matrix brecc ia (unit BHcl; t h i n sec t ion of sample BL30-6 from elongate brecc ia body south of LALA mineral showing). Subrounded fragments of quartz i t e are cemented by c h l o r i t e , carbonate and rock f l o u r . cons is t of a mosaic of intergrown microc l ine , with euhedral tourmaline as i n c l u s i o n s , and quartz with subordinate carbonate and c h l o r i t e (Plate 3.32). The matrix contains abundant la ths of c h l o r i t e that commonly replace quartz and f ine grained port ions of the matrix. The s u b p a r a l l e l alignment of whispy, c u r v i l i n e a r c h l o r i t e , hematite l a ths , and the long axes of elongate fragments i n other samples give the rock a planer f a b r i c (Plate 3.33). This f a b r i c appears to r e s u l t from flow. 3.3 OTHER BRECCIA BODIES IN THE COAL CREEK INLIER Faul t b r e c c i a (?) made up of Quartet Group mater ia l i s s i tuated along a contact between brecc iated F a i r c h i l d Lake Group and Quartet Group s t r a t a on the r idge about 1.5 km due west of the BEEHIVE (Figure 3.1 and Map 1). This occurrence i s approximately 30 m wide and 300 or more metres i n length. At t h i s l o c a l i t y there has been no apparent in troduct ion of s i l i c e o u s or carbonate -r ich mater ia l . The b r e c c i a i s green-grey or rusty brown weathering but has a grey surface when fresh . Larger fragments are tabular and p l a t y and general ly l ess than 5 cm i n length. Fragments smaller than 0.5 cm i n diameter are subrounded to wel l rounded i n d i c a t i n g that some fragment m i l l i n g occurred. The matrix cons i s t s e n t i r e l y of comminuted a r g i l l i t e . The rock i s not we l l indurated and therefore dissaggregates e a s i l y . This b r e c c i a body i s elongate and occurs on the contact between Quartet Group and 110 Plate 3.32 Photomicrograph of coarse c r y s t a l l i n e (metasomatic) microc l ine and quartz fragment from a h e t e r o l i t h i c c h l o r i t e - r i c h - m a t r i x brecc ia (unit BHcl ; t h i n sect ion of sample BL50-2 from middle of Southern Brecc ia B e l t ) . Large ragged, p o i k i l i t i c c h l o r i t e l a t h and subhedral high b i re fr ingent dolomite are l a t e r forming minerals . A dashed l i n e separates the f ine grained matrix ( le f t ) from the c l a s t . Plate 3.33 P h o t o m i c r o g r a p h o f h e t e r o l i t h i c c h l o r i t e - r i c h -m a t r i x b r e c c i a ( u n i t B H c l ; s a m p l e B L 3 - 2 5 ) . S u b r o u n d e d s i l t y d o l o s t o n e f r a g m e n t i s h o s t e d i n a b i m o d a l m a t r i x c o m p r i s e d o f l a r g e r q u a r t z a n d c a r b o n a t e g r a i n s s e t i n a f i n e g r a i n e d m o s a i c o f c h l o r i t e a n d h e m a t i t e . F a i r c h i l d Lake Group about 2.5 km west-northwest of the BEEHIVE. I t l i k e l y formed i n a f a u l t zone. Ouartz - specu lar i t e brecc ia outcrops about 800 m southeast of the BEEHIVE (Figure 3.1 and Map 1) . I t occurs as a low r e l i e f s u b - c i r c u l a r zone. Intensely hematized Quartet Group sandstones host t h i s b r e c c i a occurrence. Coarse grained trans lucent , c r y s t a l l i n e quartz and medium to coarse grained specular hematite comprise the i r r e g u l a r l y -shaped fragments (Plate 3.34). The matrix cons i s t s of hematite. P y r i t e and cha lcopyr i te , associated with hematite occur r a r e l y . Quartz-sulphide veins (Pettet mineral showing; sample l o c a t i o n BL34-17, Map 2), about 20 m south of t h i s b r e c c i a , may be gene t i ca l l y r e l a t e d . Intraformational brecc ia of the G i l l e s p i e Lake Group crops out i n several exposures along one p a r t i c u l a r s t r a t i g r a p h i c hor izon i n the northeastern part of the map area. I t occurs at the base of un i t 3a near the Quartet Group - G i l l e s p i e Lake Group contact . The best exposures are s i tuated on the north bank of "Beehive" creek about 100 m northeast of the creek exposure of monol i th ic Quartet Group b r e c c i a mentioned above. This exposure i s 150 m long and 4 m high and p a r a l l e l s the creek. To the northeast , along the trend of the outcrop, brecc ia gives way to f rac tured , wavy bedded flaggy dolostone over a distance of 12 m. Weathering of the exposed j o i n t faces has h ighl ighted the "jigsaw" or mosaic brecc ia texture of the outcrop (Plate 3.35). Pale grey, t h i n l y bedded, buff weathering dolostone with <0.5 cm interbeds of s i l t y dolostone comprise the b r e c c i a fragments. They are cemented by an orangey-brown matrix cons i s t ing of s i d e r i t e and f ine dolostone b i t s . In hand sample i t i s c l ear that fragments have not moved far with respect to surrounding fragments. Larger fragments can be reconnected with l i t t l e jockeying of i n d i v i d u a l p ieces . The presence of the small b i t s that are l e ss than 2 mm i n diameter ind ica te that minor m i l l i n g has occurred. Addi t ion of mater ia l can not be determined: the carbonate matrix most l i k e l y was derived l o c a l l y and i s s ta ined by i r o n o r i g i n a l l y present i n the host rock. The textures displayed at t h i s l o c a l i t y are s i m i l a r to those seen at the TART lead z inc prospect , (see Appendix A) v i s i t e d during J u l y of 1986. I t occurs east of the f i e l d area and i s a l so hosted i n G i l l e s p i e Lake Group dolostone. These b r e c c i a deposits could be the r e s u l t of i n s i t u b r e c c i a t i o n formed by s o l u t i o n - c o l l a p s e . However no s p e c i f i c evidence of kars t ing has been documented. Pebble dykes are rare ; two such brecc ias were discovered i n the f i e l d area. One pebble dyke outcrops at the DONUT (Figure 3.1 and Map 1; s p e c i f i c a l l y at sample Plate 3 . 3 4 Quartz-hematite brecc ia from Pettet mineral showing, located about 1 km southwest of the BEEHIVE l o c a l i t y . Plate 3.35 Intraformational G i l l e s p i e Lake Group brecc ia (unit 3A) from outcrop on north bank of Beehive creek due north of LALA l o c a l i t y . This brecc ia forms a discontinuous zone near the base of un i t 3A. l o c a t i o n BL87-21 on Map 2) where i t crosscuts the folded Quartet Group core of the brecc ia complex. The other pebble dyke occurs c u t t i n g hematite stained Quartet Group rocks that outcrop on the north facing f lank of the r idge north of the LALA mineral showing (Figure 3.1 and Map 1) . Both dykes are l i m i t e d i n extent. The larger one i s about 1.5 m i n width. Weathered outcrops are tan coloured and fresh surfaces are cream coloured. Fragments form r e s i s t a n t knobs against the recess ive weathering matrix. Rounded fragments of white quartz i t e or laminated quartz sandstone are between 2 mm and 6 cm i n diameter and comprise the only fragment types. The matrix cons is t s of almost 100% coarse gra ined, l i k e l y r e c r y s t a l l i z e d , dolomite with rare f ine grained f l ecks of white mica and anhedral opaques. Sandstone dvkelets . several cm wide but more than 10 m i n length crosscut Quartet Group sediments at the DONUT l o c a l i t y (Figure 3.1 and Map 1). They occur c lose to the pebble dyke and may be re la ted g e n e t i c a l l y . However, the sandstone dykes are truncated by one sec t ion of h e t e r o l i t h i c OMB. They therefore predate OMB formation at t h i s po in t . 4.0 PETROCHEMISTRY 4.1 INTRODUCTION Whole rock chemistry of the major s t r a t i g r a p h i c un i t s was measured and compared to published rock chemistry of the Wernecke Supergroup. Trace element concentrations and Rare earth element (REE) contents for s t r a t i f i e d host rocks provide average "background" analyses. T o t a l REE concentrat ions , normalized REE r a t i o s and normalized REE patterns of the major l i t h o s t r a t i g r a p h i c u n i t s provide a range of upper c r u s t a l values for the Coal Creek I n l i e r . The bulk chemical compositions of the brecc ias are d i c ta ted by fragment type and abundance. Consequently, quant i ta t ive i n t e r p r e t a t i o n of the major and trace element chemistry i s not pos s ib l e . Rare earth element (REE) chemistry of the O g i l v i e Mountains b r e c c i a inc lud ing rare earth element t o t a l s , normalized REE r a t i o s and normalized REE pat terns , provide a means to compare and contrast brecc ia u n i t s . Consequently REE patterns can be used to ascer ta in the o r i g i n s of the brecc ias . For example, brecc ias r e l a t e d to carbonati te emplacement normally would have d i s t i n c t REE patterns compared to those from brecc ias formed by sedimentary processes. 4.2 SAMPLING AND ANALYTICAL METHODS Representative samples of the main l i t h o l o g i e s i n the map area (Map 1) were chemical ly analyzed. A l l were c o l l e c t e d from surface outcrops. Specimens were cleaned of weathered or fracture surface m a t e r i a l . Several a n a l y t i c a l techniques (Appendix E) were used to measure major, minor, t race and REE concentrat ions. Three sample su i tes cons i s t of: the main l i t h o l o g i e s , a l l v a r i e t i e s of OMB and p a r t i c u l a r brecc ia matrix concentrates . The su i tes are representat ive of a l l regions of the area mapped. Sample loca t ions are shown on Map 2 ( in pocket) , b r i e f hand sample descr ip t ions and chemical r e s u l t s are presented i n Appendix E (Tables E . l through E . 6 ) . Sui te 1 consis ts of samples of brecc ias (15 samples), s t r a t i f i e d host rocks (6 samples) and dykes (2 samples). The Ottawa Branch of the Geo log ica l Survey of Canada measured major and minor oxide and trace element contents by X-ray fluorescence ana lys i s (XRF), and trace and rare earth element concentrations by induced coupled plasma (ICP) techniques. Sui te 2 comprises 20 samples inc lud ing brecc ias (13 samples) and s t r a t i f i e d host rocks (7 samples). This su i t e was analyzed for over 50 trace and rare earth elements by ACME A n a l y t i c a l Laboratories i n Vancouver using ICP techniques. A d d i t i o n a l l y , seven of the twenty samples were analyzed by ICP for major and minor oxides (Table E . 4 A ) . Sui te 2 represents a reconnaissance geochemical survey, done i n conjunction with Newmont Explorat ion of Canada L t d . They were interes ted i n i d e n t i f y i n g brecc ia bodies that were markedly anomalous i n copper, gold , uranium and REE. The trace element analyses (Table E.4B) by ICP are not s t r i c t l y quant i ta t ive ; therefore they are not discussed f u r t h e r . However, several anomalous samples were discovered; these were incorporated into Sui te 3 for q u a l i t a t i v e analyses . Suite 3 comprises 22 samples (18 brecc ia s , four dup l i ca te s , three s t r a t i f i e d host rocks, and one standard) . Th i s su i te was analyzed for rare earth and trace elements by instrumental neutron a c t i v a t i o n analys i s (INAA) by Bondar-Clegg & Company L t d . , North Vancouver. 4.3 MAJOR AND MINOR ELEMENT OXIDE AND TRACE ELEMENT CHEMISTRY 4.3.1 Major Element Oxides Twenty-eight samples were analyzed for major element oxides (Tables E.2 and E . 4 A ) . There are no publ ished analyses for Wernecke Supergroup rocks or OMB from the O g i l v i e Mountains. Furthermore, there are few d e t a i l e d studies of the geochemistry of s t r a t i f i e d Wernecke Supergroup rocks from elsewhere. Delaney (1985) and Goodfellow (1979) have published some analyses of Wernecke Supergroup rocks from the Wernecke Mountains; these are used below. F a i r c h i l d Lake Group and Quartet Group sediments from the Wernecke Mountains general ly are s i m i l a r chemical ly (Goodfellow, 1979; Delaney, 1985). There are two notable exceptions: s p e c i f i c a l l y , F a i r c h i l d Lake Group rocks are higher i n Ca+Mg, and lower i n Na than Quartet Group rocks . Limited analyses of F a i r c h i l d Lake Group and Quartet Group rocks from the present study support t h i s conc lus ion . A t y p i c a l Quartet Group sandstone (sample BL54-3) p l o t s i n the potass ic sandstone f i e l d of the Fe203+MgO, Na20, K2O ternary diagram. F a i r c h i l d Lake Group and G i l l e s p i e Lake Group are do lomi te -r i ch rocks although megascopically and microscop ica l l y , F a i r c h i l d Lake Group rocks contain more s i l t y to g r i t t y c l a s t i c m a t e r i a l . Chemical analyses of rocks from the two groups are reported i n Table E .4A. G i l l e s p i e Lake Group dolostone (sample BL25-5) contains less Si02 (8% vs . 33%), more MgO and CaO (45% combined vs . 28% combined) and l e s s Fe203 and K2O (2.3% and 0.5% vs . 2.6% and 3.4%) than s i l t y or sandy dolostones represented by sample BL3-7) . Chemical analyses of two do lomit i c s i l t s t o n e s of the F a i r c h i l d Lake Group (Table E . 2 ; samples BL9-2 and BL9-22) are a lso chemical ly d i s t i n c t from G i l l e s p i e Lake Group dolostone. In general , the whole rock chemical compositions r e f l e c t the d i f f e r e n t depos i t ional se t t ings of the l i t h o l o g i c un i t s that comprise the Wernecke Supergroup. 4.3.2 Minor and Trace Elements F o r t y - f i v e samples were evaluated for t h e i r minor and trace element content (Tables E.2 and E . 6 ) . Trace elements can provide information about the petrogenesis of l i t h o l o g i c u n i t s . For example, Th, Hf, Co, La and Sc are not dispersed by in terac t ions with sea water (Taylor and McLennan, 1985). Analyses of F a i r c h i l d Lake Group, Quartet Group and G i l l e s p i e Lake Group rocks are p l o t t e d i n the ternary diagram La - Sc - Th (suite 3 data) . Average upper crust (NASC; Haskin et a l . . 1968) i s p l o t t e d for reference (Figure 4 .1) . The majori ty of data p l o t w i t h i n , or c lose to , the dashed out l ine representing the composit ional spectrum of post-Archean shales (Taylor and McLennan, 1985). Anomalous samples, r e l a t i v e to upper crus t , occur as: (i) a c l u s t e r j u s t below the La apex, and ( i i ) an i s o l a t e d point o f f se t toward the Sc apex. In the case of (i) the four analyses cons i s t of two hemat i te -r ich brecc ias (samples BL24-12 and BL34-15), a carbonate-r ich matrix b r e c c i a (sample BL35-4), and an i n t r u s i v e , coarsely c r y s t a l l i n e carbonate dyke (sample MS-1I) . The l o c a t i o n of these samples r e f l e c t s the r e l a t i v e enrichment of La i n the rocks over both Th and Sc. Th i s i s p a r t i c u l a r l y apparent for sample BL35-4, which i s comprised of abundant c l a s t i c m a t e r i a l . However, the remaining three samples are r e l a t i v e l y depleted i n Th (two are below detect ion l i m i t of 0.5 ppm: these were assigned values of 0.3 ppm for p l o t t i n g purposes) and Sc. Sedimentary rock fragments are rare to absent i n the l a t t e r . 4.4 RARE EARTH ELEMENT GEOCHEMISTRY OF OGILVIE MOUNTAIN BRECCIAS Sixteen brecc ias , three separates of brecc ia matrix and three sedimentary rock samples, b r i e f l y described i n Table E . 5 , were analyzed by instrumental neutron a c t i v a t i o n ana lys i s (INAA). Concentrations of the fol lowing REEs were determined: L a , Ce, Pr , Nd, Sm, Eu, Gd, Tb, Dy, Ho, E r , Tm, Yb and L u . The r e s u l t s are presented i n Table E . 6 ; a n a l y t i c a l techniques are described i n Gibson and Jagam (1980). Detection l i m i t s for the i n d i v i d u a l REE v a r i e d from 0.1 ppm for samarium to 200 ppm for gadolinium (see Table E . 8 ) . Rare earth element concentrations below detect ion l i m i t s are reported as less than ("<") the detect ion l i m i t for that p a r t i c u l a r REE. Figure 4.1a Ternary plot of La-Th-Sc. Data from sample suite 3 are plotted; symbol codes are listed on the following page. UC = upper crust; TC = bulk continental crust; OC = oceanic crust (from Taylor and McLennan, 1985). Dashed line represents field of 40 shale analyses (from Taylor and McLennan, 1985). X BL1- 1 Quartet Group; sandstone + BL33 -1 F a i r c h i l d Lake Group; i r o n formation O MS-II carbonate dyke • BL18 -10 hemati t ic carbonate b r e c c i a matrix • TW-208A BM1; c h l o r i t e - r i c h matrix and Monol i th ic brecc ia c h l o r i t i c fragments • BL26 -2 BM1; carbonate-r ich matrix A BL34 -15 hematite-vein quartz b r e c c i a • BL54 -1 BM1; carbonate-r ich matrix 0 BL50 -6 BM4; matrix poor • BL33 -3 BM1; carbonate matrix and t r a c e sulphides Q BL46 -10 BHcl ; abundant dolostone and mudstone fragments © BL35 -4 BHcb; abundant s i l t y dolostone and quar tz i t e fragments € BL50 -2 BHcl ; abundant a r g i l l i t e and dolostone fragments 0) BL87 -70 BHcb; abundant dolostone, sandstone and mudstone fragments 7^ BL43 -7 BHh; dolostone and mudstone fragments common O BL24 -12 BHh; c l a s t poor G BL27 -6 S l a t s Creek group conglomerate D P - l Coast Mountains granod ior t i t e Figure 4.1b L i s t of symbols and t h e i r corresponding sample numbers and l i t h o l o g i c name for the La-Th-Sc diagram on Figure 4 . l a . 4.4.1 Data Presentation Numerical ana lys i s and graphica l methods are used to present and evaluate the rare earth element (REE) data. Numerical ana lys i s of REE data cons is ts mainly of: (i) comparing the sum of the 14 REEs analyzed with establ ished ranges for d i f f e r e n t rock types from the l i t e r a t u r e , and ( i i ) evaluat ing the r e l a t i v e f r a c t i o n a t i o n between REEs using chondrite normalized r a t i o s . Graphica l methods u t i l i z e p l o t s of REE, normalized to chondri te , to produce spider diagrams or REE patterns . Rare earth element t o t a l s r e f l e c t the degree of f r a c t i o n a t i o n , r e l a t i v e to pr imordia l mantle, that has taken place during the formation of a rock (Henderson, 1984). REE t o t a l s , l i s t e d i n Table E.6 and discussed below, can be compared with t y p i c a l REE t o t a l s for a number of reference mater ia ls such as c h o n d r i t i c meteorites (undif ferent iated estimates of pr imord ia l earth) , shale (average upper c r u s t ) , mid-ocean r idge basa l t (MORB), carbonat i tes (strongly f rac t ionated , R E E - r i c h carbonate rock) . This comparison i s l i m i t e d because REE t o t a l s for many rock types have ranges that overlap s i g n i f i c a n t l y . Chondrite normalized REE r a t i o s are used to express the r e l a t i v e degree of f rac t iona t ion of the REE (Henderson, 1984). The r a t i o L a / L u (Table E.5) provides one measure of the o v e r a l l s lope of the normalized REE pat tern as long as the p l o t approximates a s t r a i g h t l i n e (the higher the r a t i o the higher the degree of f r a c t i o n a t i o n and the steeper the negative s lope ) . I t a lso provides the degree of r e l a t i v e f r a c t i o n a t i o n between l i g h t (La to Sm), and heavy (Tb to Lu) REEs. S i m i l a r l y the r a t i o La/Sm and Tb/Lu (Table E.5) give r e l a t i v e degrees of f r a c t i o n a t i o n wi th in the l i g h t REE and heavy REE port ions of the REE pat tern , r e s p e c t i v e l y . These r a t i o s are usefu l for general comparison of rocks , but i n summing the data some c r i t i c a l information, such as anomalous values for s ing le elements, i s l o s t . Graphical representat ion has the a t t r i b u t e that a l l the data i s i l l u s t r a t e d and anomalous values are apparent. The normalized REE abundances are p l o t t e d vs . the REE i n order of increas ing atomic number. The curve connecting the normalized rare earth element abundances i s c a l l e d a rare earth element pat tern . Raw REE data i s normalized r e l a t i v e to a composite of 12 chondrites from Wakita et a l . (1971; i n Boynton, 1984) (Table 4 .1) . The North American shales composite (NASC; Haskin et a l . . 1968), an estimate of the REE composition of the upper c r u s t , i s shown i n Table 4 .1 . Calcu lated chondrite normalized values are shown i n Table 4.2. Normalization against c h o n d r i t i c meteorites i s the commonly accepted procedure because c h o n d r i t i c meteorites are thought to approximate p r i m o r d i a l earth REE abundances (Henderson, 1984). The REE pattern for the p r i m o r d i a l mantle i s assumed to be f l a t because REEs have not f rac t iona ted . Chondrite normalized REE patterns for a l l 18 samples are catalogued i n Figures 4.2 to 4.4. The REE content of shales are representat ive of the ear th ' s upper crust because eros ion of the continents and the sedimentary processes which deposit mater ia l i n ocean basins have an homogenizing e f f e c t . Shales are reasonably i n v a r i a b l e i n REE concentration between d i f f e r e n t source areas, and are enriched i n t o t a l and l i g h t REE r e l a t i v e to chondr i te . The ir constant nature with respect to REE concentrations provides a usefu l standard for comparison of the c r u s t a l rocks from t h i s study. Several rare earth element concentrations are below detect ion l i m i t (e.g. Pr , Gd and E r ) , and for these REE the detec t ion l i m i t s themselves were normalized. These r a t i o s , however, could be used only i n a l i m i t i n g sense. Thus, gap are created i n the REE patterns making t h e i r i n t e r p r e t a t i o n more d i f f i c u l t . For example, i n the case of sample BL33-1 (banded i r o n formation) only 3 of 9 elements are reported s that the REE pattern cons is t s of three i s o l a t e d p o i n t s . 128 Table 4 .1 Rare earth element abundances i n c h o n d r i t i c meteorites (Wakita et a l . . 1971), used to normalize the raw sample data (Table E . 6 ) , and the North American shales composite (NASC; Haskin et a l . . 1968). NASC, an estimate of the REE compostion of the upper crus t , i s p l o t t e d i n Figures 4.2, 4.3 and 4.4 for reference . Normalized abundances are i n Table 4.2. Element Name Atomic Number Chondrites (composite of 12) Shale (NASC) North America La lanthanum 57 0.34 32 Ce cerium 58 0.91 73 Pr praeseodymium 59 0.121 7.9 Nd neodymium 60 0.64 33 Pm1 promethium 61 Sm samarium 62 0.195 5.7 Eu europium 63 0.073 1.24 Gd gadolinium 64 0.26 5.2 Tb terbium 65 0.047 0.85 Dy dysprosium 66 0.30 -Ho holmium 67 0.078 1.04 Er erbium 68 0.20 3.4 Tm thulium 69 0.032 0.50 Yb ytterbium 70 0.22 3.1 Lu lutet ium 71 0.034 0.48 1: promethium, v i r t u a l l y absent i n t e r r e s t r i a l matter because of i t ' s short h a l f l i f e , i s not reported. Table 4.2 Chondrite normalized REE data for 17 rocks fro« the COBI Creek Inlier, southern Ogilvie Mountains, vest-central Yukon Territory. The duplcate analyses for four samples, presented in Table E.6, were averaged prior to normalizing. Normalizing standards are in Table 4.1. S 2 = ~==== = -======== ======= ======= ======= =======: ! ======== ======== ======== ======== ======== == = = = = = = = . . . . . . BL33-1 BL1-1 BL27-6 BL26-2 BL33-3 BL54-1 TW-208A BL50-6 BL18-10 BL35-4 BL87-70 BL24-12 BL34-15 BL43-7 BL46-10 BL50-2 MS-II La 9.4 167 177 81.9 300 51.5 30.9 151 12.6 1100 57.1 270 37.2 254 94.7 152 353 Ce 7.7 117 117 57.7 185 38.5 24.2 109 12.1 239 41.8 117 41.8 150 64.3 103 223 Pr <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 <413 Nd <15.6 68.fi 70.3 40.6 98.4 28.1 <15.6 65.6 <15.6 203 34.4 40.6 36.7 78.1 41.4 64.1 144 SIB 7.7 40.0 36.9 19.5 54.4 14.4 8.2 33.8 12.8 106 21.0 15.9 52.1 40.5 21.5 32.3 106 Eu <13.7 13.7 27.4 <13.7 27.4 <13.7 <13.7 13.7 <13.7 82.2 13.7 54.8 68.5 41.4 <13.7 27.4 41. 1 Gd <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 <770 Tb <21.3 <21.3 <21.3 <21.3 21.3 <21.3 <21.3 <21.3 <21.3 42.6 <21.3 <21.3 138 <21.3 <21.3 <21.3 63.8 Dy 3.3 16.7 13.3 8.3 20.0 6.7 3.3 16.7 6.7 25.0 16.7 <3.3 115 13.3 8.3 13.3 56.7 Ho <12.8 <12.8 <12.fi <12.8 <12.8 <12.8 <12.8 <12.8 <12.8 <12. 8 <12.8 <12. a 89.7 <12. 8 <12.8 <12.8 .25.6 Er <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 <500 Tn <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 <15.6 34.4 <15.6 <15.6 <15.6 <15.6 Yb <2.3 10.9 6.8 6.7 8.2 5.9 5.0 11.4 5.9 16.1 8.6 <2.3 32.7 8.6 6.8 9.5 10.9 Lu <2.9 11.a 5.9 5.9 8.2 5.9 5.9 11.8 5.9 11.a 8.8 <2.9 19.1 5.9 5.9 a. a 5.9 = = = ======== ======= ======= ======= ======= : 1 The 'less than* sign <<) denotes that the normalized abundance i s belo* the normalized detection U n i t (see also Appendix E). H ro 1000 q w H M Q O a 100 a, o o PH PH PH 10 -A A A A A BL27-6 Slats Creek Group conglomerate (6) + + + + + BL1-1 Quartet Group sandstone (2) • • • • • BL50-6 Monolithic breccia (BM4) o o o o o BL26-2 Monolithic breccia (BM1) •b-b-b-Crii BL54-1 Monolithic breccia (BMl) NASC UPPER CRUST o La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu R A R E E A R T H E L E M E N T F i g u r e 4 . 2 Chondrite normalized REE p lo t of some host sedimentary rocks and monol i thic breccias from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-c e n t r a l Yukon T e r r i t o r y . NASC ( so l id l ine) i s p lo t ted for reference as a t y p i c a l REE pattern of the upper crus t . 1000 w H PH Q o a PH PH W u O PH PH PH 100 10T A A A A A B L 3 3 - 3 + + + + + B L 4 3 - 7 • • • • • BL50 -2 ooooo B L 4 6 - 1 0 ftftftft* B L 8 7 - 7 0 M o n o l i t h i c b r e c c i a (BM1) H e t e r o l i t h i c b r e c c i a (BHh) b r e c c i a b r e c c i a b r e c c i a H e t e r o l i t h i c H e t e r o l i t h i c H e t e r o l i t h i c N A S C U P P E R C R U S T BHcl ) BHc l ) BHcb) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu R A R E E A R T H E L E M E N T F i g u r e 4 . 3 Chondrite normalized REE p lo t of some monol i thic brecc ias and h e t e r o l i t h i c breccias from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-cen tra l Yukon T e r r i t o r y . NASC ( so l id l ine) i s p lo t ted for reference as a t y p i c a l REE pattern of the upper crus t . La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu R A R E E A R T H E L E M E N T F i g u r e 4.4 Chondrite normalized REE plot of h e t e r o l i t h i c brecc ias , brecc ia matrix concentrates, a carbonatite(?) dyke, and a banded i r o n formation from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . These "anomalous" REE patterns are compared to the f i e l d of REE patterns from Figures 4 . 2 and 4 . 3 (patterned area) that c lose ly resemble NASC. 4.4.2 Data Analys i s T o t a l REE contents are tabulated i n Table E . 6 . A l l samples are enriched i n REEs r e l a t i v e to chondrite . Some samples are geochemically anomalous. T o t a l REE content for brecc ia samples ranges from 77 ppm to 769 ppm. Representative samples of reg iona l sedimentary uni t s range from 13 ppm to 226 ppm. The samples can be d iv ided , based on t o t a l REE content, in to one of the fol lowing three categories: (i) very low REE t o t a l (chemical p r e c i p i t a t e s ) , ( i i ) moderate REE t o t a l cons is tent with upper c r u s t a l rocks , and ( i i i ) high REE t o t a l (anomalous rocks ) . REE Ratios for La /Lu range from 2.1 and 93.2. The highest degree of f r a c t i o n a t i o n has occurred i n a h e t e r o l i t h i c brecc ia (sample BL35-4) and i s a r e s u l t of the rock being r e l a t i v e l y enriched i n L a . The lowest La /Lu value corresponds to hematite-stained carbonate matrix mater ia l (sample BL18-10). This mater ia l i s apparently not f rac t ionated . Eu/Sm values range from 0.34 to 3.45. The three hemat i te -r ich brecc ia samples have an Eu/Sm r a t i o of greater than one, whereas the sediments range from 0.34 to 0.74. Monol i th ic brecc ias range between 0.41 and 0.50, and other h e t e r o l i t h i c brecc ias ( inc luding the b r e c c i a matrix separates) range from 0.39 to 0.85. Chondrite-normalized REE patterns (Figures 4.2 to 4.4) f a l l in to two d i s t i n c t groups: (i) patterns s i m i l a r to an upper c r u s t a l s ignature (Figures 4.2 and 4.3) and ( i i ) anomalous REE patterns (Figure 4 .4) . Anomalous REE patterns were observed for the fol lowing sample rock types: (1) i n t r u s i v e coarse c r y s t a l l i n e carbonate dyke [carbonatite (?)] (sample MS-1I): REE pattern d i sp lays a somewhat i r r e g u l a r , but approximately l i n e a r negative slope (high lanthanum and low lutet ium) . The i r r e g u l a r i t i e s define a negative europium anomaly, and r e l a t i v e l y enriched terbium and dysprosium. (2) c h l o r i t e - r i c h h e t e r o l i t h i c b r e c c i a (sample BL35-4): REE pattern has a more r e g u l a r l y negative slope and a negative Ce anomaly. (3) massive hematite-quartz brecc ia (sample BL34-15): REE pattern approximates a wave with moderately concentrated l i g h t REE (enriched i n Sm) and a p o s i t i v e Eu anomaly; i t a lso i s r e l a t i v e l y enriched i n heavy REE that are h ighly f rac t ionated (steep negative s lope) . (Two hemat i te -r ich h e t e r o l i t h i c b r e c c i a s , samples BL12-24 and BL43-7, a lso d i sp lay p o s i t i v e Eu anomalies, however that i s the only s i m i l a r i t y between the REE patterns for the two rock types. (4) hematite-stained carbonate matrix (sample BL18-10): REE pattern i s r e l a t i v e l y f l a t . (5) c h l o r i t e matrix (sample 85-208A): REE pat tern i s concave upwards and i s enriched i n Yb and Lu r e l a t i v e to other heavy REEs. 4.4.3 Interpreta t ion of Data The REE patterns for most samples (Figure 4.2 and 4.3 r e f l e c t upper c r u s t a l rock chemistry and are marked by r e l a t i v e l y steep l i g h t REE frac t iona t ion compared to the heavy REE t a i l . Dips i n Eu abundances are c h a r a c t e r i s t i c of upper c r u s t a l a f f i n i t i e s (Henderson, 1984). The fo l lowing samples d i sp lay markedly anomalous features i n t h e i r REE patterns (Figure 4 .4) . These patterns are summarized i n Table 4.3. Anomalous samples are: BL33-1 (part of un i t l a , banded i r o n formation), BL18-10 (unit BHh, i r o n carbonate matrix to hematite- and carbonate-r ich-matr ix h e t e r o l i t h i c b r e c c i a ) , BL35-4 (unit BHcb, c h l o r i t e - r i c h -matrix h e t e r o l i t h i c b r e c c i a ) , BL24-12 (unit BHh, hematite-r i c h - m a t r i x h e t e r o l i t h i c b r e c c i a ) , BL34-15 (BM1, hematite-quartz -cha lcopyr i te b r e c c i a ) , and MS-1I (a uniform coarsely c r y s t a l l i n e carbonate dyke that cross-cuts F a i r c h i l d Lake Group Monol i th ic b r e c c i a ) . The general ly weak, or lack of REE enrichment i n OMB r e l a t i v e to unaltered wal lrock and s i m i l a r i t y of REE patterns and slopes to NASC, with a few exceptions, suggest Table 4.3 Descr ipt ion of anomalous REE patterns i n samples of brecc ias from the Coal Creek I n l i e r , O g i l v i e Mountains, west -central Yukon. Sample No Features of Anomalous REE Patterns BL33-1 uniformly depleted, f l a t REE pattern BL18-10 r e l a t i v e l y f l a t REE pattern BL35-4 steep negative s lope; enriched i n La and depleted i n Ce BL24-12 steep negative s lope; l i k e l y p o s i t i v e Eu anomaly BL34-15 depleted l i g h t REE end r e s u l t i n g i n a "hump" i n the middle of the pat tern MS-II enriched l i g h t REE; steep negative slope a lack of deep-seated (mantle) involvement. However brecc ias are genera l ly fragment supported and the abundance of sedimentary mater ia l would l i k e l y d i l u t e mater ia l that was added by a d i f f e r e n t (and otherwise chemical ly recognizable) process . A few samples are enriched i n t o t a l REE, have v a r i a b l e L a / L u r a t i o s , and anomalous REE patterns r e l a t i v e to upper c r u s t . These samples are e i t h e r fragment-poor brecc ias or samples of matrix mater ia l from brecc ias . The anomalous samples might ind ica te r e s t r i c t e d zones of concentrated transport and hydrothermal depos i t ion of REE. 5.0 ORIGIN OF THE OGILVIE MOUNTAINS BRECCIA OF THE COAL CREEK INLIER 5.1 WORLD EXAMPLES OF BRECCIAS SIMILAR TO OGILVIE MOUNTAINS BRECCIA (OMB) O g i l v i e Mountains brecc ia (OMB), and Wernecke Mountain or Wernecke-type b r e c c i a , are hosted i n Wernecke Supergroup rocks . Both brecc ias are s i m i l a r i n age and s t r u c t u r a l s t y l e ( B e l l , 1982), matrix and fragment composition, and a l t e r a t i o n (Abbott, 1986; Delaney, 1981). However, s i g n i f i c a n t minera l i za t ion i s known only i n the Wernecke-type brecc ias (Eaton, pers . comm., 1988). Wernecke-type breccias are s i m i l a r i n general geometry, approximate age and minor element s ignature to brecc ias of the Adeladian Province, A u s t r a l i a ( B e l l , 1982, 1986). Breccias i n the Adeladian Province host deposits i n the F l i n d e r s Ranges, A u s t r a l i a (Dalgarno and Johnson, 1965; Thomson, 1965) and the world c la s s Olympic Dam Cu-U-Au-Ag deposit (Orestes and Einuad i , 1988; Orestes et a l . . 1989). B e l l and Jef ferson (1987) and Jef ferson (1978) speculated that s i m i l a r i t i e s i n reg ional s t r a t i g r a p h i c sequence, age and poss ib ly paleomagnetic ind ica tors suggest that Proterozoic rocks i n centra l Yukon and the Adeladian Province were once adjacent. This hypothesized supercontinent may have broken up e i t h e r around 1300 or 750 600 Ma. Both she l f edges were l a t e r deformed by accret ion of i s l a n d arc and cont inental fragments—namely the C o r d i l l e r a n margin i n North America and the Great Divide Range i n Eastern A u s t r a l i a . O g i l v i e Mountains brecc ia features are s i m i l a r to thos from Middle Proterozoic brecc ia deposits on the East Arm of Great Slave Lake (Reinhardt, 1972) and near Bathurst In le t (Ceci le and Campbell, 1977), both i n the D i s t r i c t of Mackenzie, Northwest T e r r i t o r i e s . The cont inenta l margin se t t ing of these are s i m i l a r to OMB. East Arm brecc ias do, however, involve basement rocks and OMB do not. However, both brecc ias are emplaced along f a u l t s and along bedding. Textural v a r i e t i e s of brecc ia are a lso s i m i l a r . L o c a l l y Bathurst In l e t and OMB brecc ias d i s p l a y contorted fragments and d isrupted zones that poss ib ly represent semiplast ic b r e c c i a t i o n and dewatering, r e s p e c t i v e l y . Bathurst In le t and OMB brecc ias both host unusually zoned quartz and carbonate c r y s t a l s that are i d e n t i c a l i n t h i n sec t ion . These c r y s t a l s are considered by C e c i l e and Campbell (1977) to be evidence for the presence of i n t e r s t i t i a l so lut ions among the brecc ia fragments. Table 5.1 summarizes phys ica l features of these brecc ias upon which genetic 139 in terpre ta t ions have been based. Mud volcanoes and d i a p i r s of the Barbados, Caribbean (Brown and Westbrook, 1988) and Timor, eastern Indonesian (Barber et a l . . 1986) areas, share many features with OMB of the Coal Creek I n l i e r . Most s i g n i f i c a n t l y , they formed i n cont inenta l she l f se t t ings and are s i m i l a r i n s i ze and extent. Emplacement of the d i a p i r s are t e c t o n i c a l l y tr iggered and s t r u c t u r a l l y c o n t r o l l e d . A pressur ized source bed for b r i n e , and b r i t t l e and p l a s t i c fragments, i s fundamental to the generation of a mud d i a p i r . An appropriate source u n i t appears to be involved i n the OMB. Hydrothermal a l t e r a t i o n and the v a r i e t y of brecc ia textures observed i n OMB could have been generated during the formation of mud d i a p i r s . Because mud d i a p i r s breach the surface as mud volcanoes, re la ted sea- f loor sedimentary processes may have been important. S p e c i f i c a l l y , some of the i r o n formation associated with OMB might be re la ted to hydrothermal exhalat ions from mud d i a p i r s i n t h i s way. 5.2 ORIGINS PROPOSED BY OTHERS FOR OGILVIE MOUNTAINS BRECCIA (OMB) Several theor ies for the o r i g i n of the O g i l v i e Mountains b r e c c i a (OMB) have evolved. In the Coal Creek I n l i e r , Southern O g i l v i e Mountains, Mercier (1987) , observed concordant contacts i n a few locat ions , and proposed that T a b l e 5 .1 A c o m p a r i s o n o f t h e c h a r a c t e r i s t i c s o f P r o t e r o z o i c b r e c c i a d e p o s i t s f r o m t h e O g i l v i e and Wernecke M o u n t a i n s t o O l y m p i c Dam and H t . P a i n t e r , A u s t r a l i a , and t o E a s t Arm o f G r e a t S l a v e L a k e and B a t h u r s t I n l e t . C o a l C r e e k ' Wernecke ' O l y m p i c Dam' F l i n d e r s R a n g e s ' E a s t Arm o f B a t h u r s t I n l i e r Mtns . G r e a t S l a v e L a k e " I n l e t ' R e g i o n a l S e t t i n g T e c t o n i c S e t t i n g S t r u c t u r a l C o n t r o l C o n t i n e n t a l m a r g i n C o m p r e s s i o n a l r e g i m e M a j o r P r o t e r o z o i c f a u l t s C o n t i n e n t a l ma rg i n E x t e n s i o n a l r e g i m e F a u l t s A d e l a i d e G e o s y n c l i n e E x t e n s i o n a l r e g i m e D e e p - s e a t e d f r a c t u r e s A d e l a i d e G e o s y n c l i n e Orogeny ( m i l d ) F o l d a x e s , Deep f a u l t s C o n t i n e n t a l m a r g i n E x t e n s i o n a l r e g i m e D e e p - s e a t e d f r a c t u r e s C o n t i n e n t a l m a r g i n T r a n s t e n s i o n a l S i n i s t r a l s t r i k e - s l i p f a u l t s H o s t Rock and p e r i o d o f d e p o s i t i o n Wernecke SG and L o v e r F i f t e e n m i l e g r o u p > 0 . 9 - 1 . 6 ? Ga Wernecke SG 1 . 2 - 1 . 6 ? Ga A l k a l i c g r a n i t e 1.6 Ga A d e l a i d e S e r i e s Heysen SG W a r r i n a SG 1 . 4 - 0 . 5 5 Ga Hornby C h a n n e l FM P r o t e r o z o i c A r c h e a n g r a n i t i c g n e i s s >2. 1 Ga G o u l b u r n G roup E a r l y P r o t e r o z o i c 1 . 7 - 2 . 5 Ga A p p r o x . age o f D e p o s i t M i d d l e t o L a t e P r o t e r o z o i c L a t e P r o t e r o z o i c 1 . 4 - 1 . 5 Ga L a t e P r o t e r o z o i c t o E a r l y C a m b r i a n E a r l y P r o t e r o z o i c E a r l y P r o t e r o z o i c M i n e r a l o g y Cu , U 1 C u , Co , U U - C u - A u - A g (REE and P) Cu U, Cu U ? A l t e r a t i o n M o r p h o l o g y c a r b o n a t e h e m a t i t e q u a r t z c h l o r i t e t o u r m a l i n e s e r i c i t e c l a y k - s p a r D i s c o n t i n u o u s l i n e a r z o n e s ; i r r e g u l a r l y -shaped b o d i e s c a r b o n a t e h e m a t i t e q u a r t z c h l o r i t e k - s p a r s e r i c i t e a l b i t e c l a y D i s c o n t i n u o u s l i n e a r z o n e s ; i r r e g u l a r l y -shaped b o d i e s hematite quartz B e r i c i t e c h l o r i t e k a o l i n i t e carbonate B r e c c i a p i p e s , s t o c k v o r k s , i r r e g u l a r r e p -l a c e m e n t s , and e x h a l a t i v e s e d s r e f e r to Coats (1965) I r r e g u l a r and domal c a r b o n a t e q u a r t z s e r i c i t e c h l o r i t e v h i t e m i c a P i p e - l i k e F a u l t bounded l i n e a r z o n e s c a r b o n a t e q u a r t z c h l o r i t e t o u r m a l i n e Dykes and l a r g e c y l i n d r i c a l b o d i e s 1 = t h i s s t u d y ; 2 = L a z n i c k a and Gaboury ( 1 9 8 8 ) , B e l l (1986 , 1 9 8 2 ) , L a z n i c k a and EdwardB ( 1 9 7 9 ) ; 3 = O r e s k e s and E i n a u d i ( 1 9 8 8 ) , O r e s k e s e t a l . ( 1 9 8 9 ) ; 4 = C o a t s ( 1 9 6 5 ) , D a l g a r n o and J o h n s o n ( 1 9 6 8 ) , Lemon ( 1 9 8 5 ) , B e l l ( 1 9 8 7 ) ; 5 = R e i n h a r d t ( 1 9 7 2 ) ; 6 = C e c i l e and C a m p b e l l ( 1 9 7 7 ) . the brecc ias were sedimentary—a product of weathering and eros ion . However, h i s proposed sedimentary processes do not e f f e c t i v e l y address c r o s s - c u t t i n g re la t ionsh ips and the concentrat ion of brecc ias along reg iona l s t r u c t u r a l breaks. The l a t t e r probably represents f a u l t s that were ac t ive before and during emplacement of b r e c c i a . Although layered brecc ias and brecc ias with pre ferred alignment of elongate fragments occur i n the Coal Creek I n l i e r , they are subordinate i n volume to c r o s s - c u t t i n g brecc ia bodies. Dyke- and p i p e - l i k e exposures are not consistent with a normal sedimentary o r i g i n . The i n t e r p r e t a t i o n of Mercier (1987), furthermore, provides ne i ther an explanation for the pervasive a l t e r a t i o n d isp layed by and surrounding the b r e c c i a s , nor the occurrence of brecc ias at four s t r a t i g r a p h i c l eve l s i n the Wernecke Supergroup. Support for e i ther a g l a c i a l or a l l u v i a l o r i g i n of OMB i s meager (cf . Yeo, 1981). G l a c i a l ac t ion leaves a blanket of sand, gravel and c lay with at l eas t some c l a s t s that were not l o c a l l y derived (exot ic ) ; rounded matrix supported c l a s t s are common. Iso lated b r e c c i a - l i k e bodies with e i t h e r gradat iona l contacts or s u b - v e r t i c a l contacts are not l i k e l y to be g l a c i a l i n o r i g i n . Furthermore, s ince g l a c i a l deposits represent a t ime-horizon, the requirement of four advances of l i t h o l o g i c a l l y s i m i l a r brecc ias to expla in t h e i r occurrence at four l eve l s i n the s trat igraphy of the O g i l v i e Mountains seems u n l i k e l y . A l l u v i a l processes are s i m i l a r l y inappropr ia te . In add i t ion , such deposits are s t r a t i f i e d , commonly d i s p l a y graded beds, and thicken toward t h e i r source. Widespread exposure of OMB crosscut Wernecke Supergroup s tra t igraphy at a high angle (Thompson and Roots, 1982; Abbott, 1986). The assoc iat ion of mafic dykes with brecc ias has a l so been recognized i n these s tudies . An epigenetic o r i g i n fol lowed by l i t h i f i c a t i o n and deformation, inc lud ing extensional f a u l t i n g of the Wernecke Supergroup, was proposed by Thompson and Roots (1982). No mechanism for brecc ia generation was discussed. Numerous genetic theories have been developed for the Wernecke-type b r e c c i a s . Most of these o r i g i n s have been assumed to apply to OMB. These inc lude: steam b r e c c i a t i o n from dykes (Laznicka and Edwards, 1979), diatremes from deep-seated igneous a c t i v i t y ( B e l l , 1978; B e l l and Delaney, 1977; Archer et a l . . 1977; Archer and Schmidt, 1978), and d i a p i r i s m of e v a p o r i t i c mater ia l ( B e l l , 1986). 5.3 GEOLOGICAL CONSTRAINTS ON GENESIS OF THE OGILVIE MOUNTAINS BRECCIA (OMB) The genesis of the OMB i s constrained by the geology reported i n t h i s t h e s i s . F i e l d observations, which r e l a t e d i r e c t l y to the genesis of the OMB, and i n t e r p r e t i v e comments fol low: (1) Brecc ia bodies fol low regional eas t - trending fau l t s (> 20 km long) that are deep-seated and are appropriate conduits for the i n t r u s i o n of brecc ia and associated f l u i d s . (2) Bodies of crack le b r e c c i a , that show d i l a t i o n between (and r o t a t i o n of) angular fragments, appear to have been formed by hydrofrac tur ing . ( 3 ) Bodies of crack le brecc ia are common i n the hangingwall of brecc ia bodies . (4) Brecc ia bodies are both conformable ( s i l l - l i k e ) and c r o s s - c u t t i n g (pipe- or d y k e - l i k e ) . (5) Brecc ia fragments i n h e t e r o l i t h i c OMB are dominantly F a i r c h i l d Lake Group (the proposed source u n i t ) . (6) Rare b r e c c i a fragments of igneous rock are from c h l o r i t i z e d diabase dykes. (7) Brecc ia fragments of c r y s t a l l i n e basement do not occur and therefore , basement was probably not involved i n the development of OMB. (8) Brecc ia fragments show undeformed bedding and sedimentary textures which implies that they genera l ly resu l ted from b r i t t l e f r a c t u r i n g of sedimentary u n i t s . (9) Rare brecc ia fragments show conspicuous p l a s t i c deformation as though formed from p a r t i a l l y l i t h i f i e d sediments. (10) Brecc ia matrix cons is ts of mineral gra ins of dolomite, quartz and c lay that was most l i k e l y der ived from comminution of host sedimentary rock. (11) Brecc ia matrix genera l ly contains s i g n i f i c a n t c lay of primary or secondary o r i g i n : c h l o r i t e , quartz , c a l c i t e , hematite, muscovite, tourmaline, potassium fe ldspar (microcline) and a l b i t e are l i k e l y secondary products derived from metasomatic a l t e r a t i o n during formation of the brecc ia s . (12) Brecc ia matrix that i s c h l o r i t e - and hemat i te -r ich commonly d i sp lays t r a i n s of quartz and carbonate c r y s t a l s and small rounded wal l rock fragments that ind ica te f l u i d flow or streaming; hydrothermal f l u i d s accompanying the brecc ia could have caused the hematization and c h l o r i t i z a t i o n . (13) Brecc ia matrix has REE patterns that are genera l ly consis tent with average c r u s t a l sedimentary rocks; there i s no evidence of a deep-seated mantle source (such as a c a r b o n a t i t i c source) . (14) Sedimentary i r o n formations appear to be s p a t i a l l y associated with the OMB at several l o c a l i t i e s ; i t may have formed on the sea f l o o r from F e - r i c h exhalations associated with in trus ions of the b r e c c i a . (15) The F a i r c h i l d Lake Group un i t i s an probable source u n i t for much of the b r e c c i a because: (a) i t makes up large volumes of crack le b r e c c i a and block b r e c c i a that comprise the majori ty of OMB, (b) i t i s carbonate- and i r o n - r i c h and therefore could contr ibute these components to f l u i d s r e s u l t i n g i n carbonate- and hemat i te -r ich matrix brecc ias and associated replacement and e x h a l i t i v e i r o n formation deposi ts , (c) i t i s over la in by a t u r b i d i t i c un i t that could have been deposited r e l a t i v e l y quick ly so that high pore f l u i d pressure could have formed, and (d) although l i t h i f i e d , parts of the F a i r c h i l d Lake Group could have been p a r t l y l i t h i f i e d r e s u l t i n g i n the noted p l a s t i c a l l y deformed fragments. 5.4 GENETIC MODEL PROPOSED FOR THE OGILVIE MOUNTAINS BRECCCIA Figure 5.1 i s a genetic model for the OMB. This genet ic model i s based on f i e l d and laboratory observations (summarized i n sect ion 5 .3) . I t has been molded from i n t e r p r e t a t i o n s of Proterozoic brecc ia deposits (summarized i n sect ions 5.1 and 5.2) . The re la t ionsh ips among c l a s s i c examples from the l i t e r a t u r e support the conclusions presented here. O g i l v i e Mountains b r e c c i a are most r e a d i l y l ikened to mud d i a p i r s ac t ive i n the she l f s e t t ing (described i n Appendix G .5 ) . Major contro l s on b r e c c i a t i o n are: s t r a t i g r a p h i c l e v e l , s t r u c t u r a l weakness, a v a i l a b i l i t y of f l u i d s and a d r i v i n g mechanism. Applying t h i s model to the O g i l v i e Mountains brecc ia (OMB) the carbonate-r ich rocks of t h e F a i r c h i l d L a k e G r o u p a r e t h e s o u r c e b e d s f o r d i a p i r s a n d t h e g e n e r a t e d c a r b o n a t e - a n d c h l o r i d e - r i c h b r i n e s . T h e o v e r l y i n g s e q u e n c e o f Q u a r t e t G r o u p t u r b i d i t e s r e p r e s e n t s a r a p i d l y d e p o s i t e d l o a d t h a t s e a l e d o f f t h e F a i r c h i l d L a k e G r o u p . T h e N o r t h e r n a n d S o u t h e r n B r e c c i a B e l t s w o u l d c o r r e l a t e t o f r o n t a l i m b r i c a t e f a u l t s t h a t e x t e n d e d t o a b a s a l d e t a c h m e n t z o n e o r d e c o l l e m e n t t h a t l a y w i t h i n t h e F a i r c h i l d L a k e G r o u p . T h e p r o c e s s o f e v a p o r i t e d i a p i r i s m ( B e l l , 1986) i s n o t i n v o k e d h e r e f o r t h e g e n e r a t i o n o f OMB b e c a u s e , a p a r t f r o m r a r e g y p s u m - a n h y d r i t e c a s t s i n F a i r c h i l d L a k e G r o u p s i l t y d o l o s t o n e , no e v i d e n c e e x i s t s f o r s i g n i f i c a n t e v a p o r i t e d e p o s i t i o n i n t h e C o a l C r e e k I n l i e r . I n f a c t n o w h e r e i n t h e F a i r c h i l d L a k e G r o u p h a v e e v a p o r i t e - r i c h s t r a t a b e e n r e p o r t e d . T e x t u r e s a r e d i s s i m i l a r a l s o . M o s t e v a p o r i t e d i a p i r s a r e h i g h l y m a t r i x - d o m i n a t e d b o d i e s t h a t g r a d u a l l y make t h e i r way t o w a r d t h e s u r f a c e p a s s i v e l y b y g e n t l y d e f l e c t i n g o v e r l y i n g s t r a t a a n d f l o w i n g a r o u n d d e t a c h e d b l o c k s o f w a l l r o c k . T h e c h a o t i c t e x t u r e s o b s e r v e d i n OMB i n d i c a t e t h a t a m o r e v i o l e n t p r o c e s s t h a n e v a p o r i t e d i a p i r i s m was r e s p o n s i b l e f o r c r e a t i n g a b u n d a n t a n g u l a r f r a g m e n t s . I n a d d i t i o n , a p r o c e s s i s r e q u i r e d t o move l a r g e v o l u m e s o f h e a t e d b r i n e t h a t c o u l d b e r e s p o n s i b l e f o r c a u s i n g t h e m e t a s o m a t i c a l t e r a t i o n a s s o c i a t e d w i t h many o f t h e b r e c c i a o c c u r r e n c e s i n t h e C o a l C r e e k I n l i e r . The mud (sediment) d i a p i r model for formation of the O g i l v i e Mountains b r e c c i a i n the Coal Creek I n l i e r i s supported by: (1) an appropriate reg ional tec tonic s e t t ing ( i . e . cont inenta l margin with a rapid bui ldup of deposited t u r b i d i t e layers that could by sea l ing and loading create high pore f l u i d pressures i n the o v e r l a i n F a i c h i l d Lake Group). (2) the l i k e l y presence of imbricate reverse fau l t s (see cross - sec t ions on Map 1: i n pocket) . (3) a p l a u s i b l e source horizon i n the F a i r c h i l d Lake Group (limey, a l g a l laminated s i l t y mud) that could have been mobi l ized by high pore f l u i d pressure (1, above) along a re lease route (2, above). (4) an appropriate scale of b r e c c i a t i o n (the area of OMB occurrence i s s i m i l a r i n s i ze to that of a c t i v e l y produced mud volcanoes of the Barbados Ridge Accret ionary Complex (cf. Map 1 to f igure 2 i n Brown and Westbrook, 1988; Figure 5.1) . (5) the d i s t r i b u t i o n of elongate and i s o l a t e d brecc ia bodies i s t y p i c a l of mud d i a p i r s (cf . f igure 2 i n Brown and Westbrook, 1988; Figure 5 .1) . (6) geometric r e l a t i o n s h i p s that ind ica te r e l a t i v e l y low temperature, f o r c e f u l in trus ion that caused brecc ia to crosscut the sedimentary p i l e and de f l ec t bedding upwards. (7) d i s r u p t i o n of the country rock that decreases away from the brecc ia bodies . (8) upward transport of fragments from lower s t r a t a . F a i r c h i l d Lake Group f ine grained limey s i l t s t o n e s and mudstones were deposited on the passive margin of North America during E a r l y to Middle Proterozoic time. R e l a t i v e l y r a p i d depos i t ion of the Quartet Group t u r b i d i t e succession fol lowed. The Quartet Group t u r b i d i t e s and over ly ing G i l l e s p i e Lake Group carbonates created the load necessary to create very high pore f l u i d pressure i n the F a i r c h i l d Lake Group sediments—assuming they had not completely l i t h i f i e d . The high f l u i d pressure resu l ted from i n t e r s t i t i a l water that could not escape, l eav ing the sediments undercompacted. The high f l u i d pressure zone became a plane of detachment or basal decollement (cf. Brown and Westbrook, 1988) i n part because i t had a low shear strength due to high f l u i d pressure. F l u i d - r i c h phases were guided along t h i s decollement. The limey (and a l g a l or s t romato l i t i c ) f ine grained F a i r c h i l d Lake Group sediments were thus an appropriate source for the f l u i d - r i c h muds which were driven upwards. Pore f l u i d pressure could have been increased further by the formation of C O 2 , due to de-carbonation of limey sediments, and by the add i t i on of methane gas produced by the decomposition of organic matter (cjL. Hedberg, 1974). The development of reverse f a u l t s , whose d i s t r i b u t i o n S S B B • 4 tem , NBB N r'i fractures , r o n " , n d c«rbo«iat»-rteh ' ' s exhalation* 1 proposed high fluid pressure zone F i g u r e 5.1 Comparison of (top) s e i s m i c r e f l e c t i o n s e c t i o n across a mud d i a p i r f i e l d from Barbados ( a f t e r Brown and Uestbrook, 1988) and (bottom) proposed model f o r f o r m a t i o n of O g i l v i e Mountain b r e c c i a (OMB). Note p a r t i c u l a r l y the comparable s c a l e s , the i m b r i c a t e f a u l t i n g and the a s s o c i a t e d g e n t l e f o l d i n g . In the OMB model the zone of high f l u i d p r e s s u r e would have been the FLG s i l t y carbonate and muddy sediment. These pressures were induced by d e p o s i t i o n of Quartet Group t u r b i d i t e s . The Monster and F i f t e e n m i l e f a u l t s l o c a l i z e d emplacement and formation of OMB. FLG = F a i r c h i l d Lake Group; QG = Quartet Group; GLG = G i l l e s p i e Lake Group; and 15G = lower F i f t e e n m i l e group. SBB = Southern B r e c c i a B e l t and NBB = Northern B r e c c i a B e l t . and geometry ind ica te an assoc ia t ion with a basal decollement, were developed during depos i t ion of lower F i f teenmi le group . . This a c t i v i t y appears to have t r iggered formation of o l i s t o l i t h s i n the lower Fi f teenmile group and may have t r iggered d i a p i r i s m . Subsequent extension or d i l a t i o n or r e l a x a t i o n along major f a u l t s (co inc id ing with the end of the compressional event that resu l ted i n the development of the Monster and Fi f teenmile reverse faul ts ) could have aided the movement of pressur ized muds. These f a u l t s acted as guides to the ascending, f lu id-charged d i a p i r s . Features observed i n the f i e l d that support and embel l i sh t h i s theory include: (1) a disconformity to angular unconformity between the F a i r c h i l d Lake and Quartet groups that marks a change i n depos i t i ona l s e t t ing from r e l a t i v e l y shallow to deeper water, (2) s t r u c t u r a l breaks, in terpreted as reverse f a u l t s , that are s p a t i a l l y associated with the occurrence of OMB along the NBB and SBB; these fau l t s mirror seismic p r o f i l e s of some modern cont inenta l margins ( i . e . Barbados: Figure 5.1) , (3) hydrothermal a l t e r a t i o n that implies high f l u i d pressures leading to: (a) hangingwall monol i thic b r e c c i a , (b) f o r c e f u l emplacement of b r e c c i a , 151 (c) h e t e r o l i t h i c breccia where multiple units are cut by intruding breccia, and (d) replacement of matrix—and fragments to a lessor extent—by carbonate, hematite and c h l o r i t e . (4) temperature of the a l t e r i n g f l u i d s , i f derived at depth from within the sedimentary basin, would be i n the 50 to 200°C range (Hanor, 1979) . One p o t e n t i a l problem with t h i s model i s the time lag between deposition of the source beds and the subsequent development of mud d i a p i r s . Modern mud d i a p i r s of West Timor (Barber et a l . . 1986) have ejected blocks of T r i a s s i c and Permian sedimentary rock. Thus s t r a t a involved i n diapirism spans about 250 Ma. The age of the OMB i s not known accurately, but evidence presented above and i n Appendix A suggests that they are syn- or post-lower Fifteenmile group i n age (younger than 1200 Ma). I f the F a i r c h i l d Lake Group i s the source region then at least 250 Ma, and possibly as much as 500 Ma, passed p r i o r to the formation of the breccias. A modified mud d i a p i r model, i n which a f l u i d (gas and liquid ) i s driven by high f l u i d pressures, caused by rapid b u r i a l and sealing of underlying sediments, i s favoured here. The sediment with entrained f l u i d had the consistency of a thick s l u r r y able to transport blocks of s t r a t a . Less viscous f l u i d phases generated additional fragments by hydrofrac tur ing . Poss ib le p h y s i c a l evidence for venting of hydrothermal f l u i d s on the sea f l o o r are layered hemat i te -r ich brecc ias and i r o n formation that outcrop near the BEEHIVE l o c a l i t y . 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P h i l l i p s , W.J., 1972, Hydraul ic f r a c t u r i n g and m i n e r a l i z a t i o n . J l geo l . Soc. Lond. , v.128, p. 337-359. Piper, D.Z.,1974: Rare earth elemants i n the sedimentary c y c l e ; Chemical Geology, v . 14, p. 285-304. Price, R.A., 1964: The Precambrian P u r c e l l System i n the Rocky Mountains of southern Alber ta and B r i t i s h Columbia: Canadian Petroleum Geologists B u l l e t i n , v . 12, p. 399-426. Reesor, J.E., 1957: The Proterozoic of the C o r d i l l e r a i n southeastern B r i t i s h Columbia and southwestern A l b e r t a : Royal Society of Canada Spec ia l Pub l i ca t ion 2, p. 150-177. Reinhardt, E.W., 1972: Occurances of exot ic brecc ias i n the P e t i t o t Islands (85H/10) and Wilson Is land (85H/15) map areas, East Arm of Great Slave Lake, D i s t r i c t of Mackenzie; Geolog ica l Survey of Canada, Paper 72-25, 43 p. Reynolds, D.L., 1954: F l u i d i z a t i o n as a geologic process and i t s bearing on the problem of i n t r u s i v e gran i t e s . American Journal of Science, v . 252, p. 577-614. Roots, C.F., 1982: O g i l v i e Mountains pro jec t , Yukon; Part B: Vo lcan ic rocks i n n o r t h - c e n t r a l Dawson map-area; Geo log ica l Survey of Canada, Paper 82-1A, p. 411-414. Roots, C F . , 1987: The Regional t ec tonic s e t t ing and evo lut ion of the Late Proteozoic Mount Harper Vo lcan ic Complex, O g i l v i e Mountains, Yukon; Unpublished PhD. Thes i s , U n i v e r s i t y of C a r l t o n , Ottawa, Canada. Taylor, S.R. and McLennan, S.M., 1985: The Cont inanta l Crust : i t s composition and evo lut ion , Oxford, Blackwel l S c i e n t i f i c Pub l i ca t ions , 312 p. Tempelman-Kluit, D., 1979: Transported c a t a c l a s i t e , o p h i o l i t e and granodior i te i n Yukon: evidence of a r c -continent c o l l i s i o n ; Geologica l Survey of Canada, Paper 79-14, 27 p. Thompson, R.I., 1986: Repeated extension on the pro to -P a c i f i c margin, west-central Yukon (abst . ) : Current A c t i v i t i e s Forum 1986, Geologica l Survey of Canada, Paper 86-8, p. 11. Thompson, R.I. and Roots, C.F., 1982: O g i l v i e Mountains p r o j e c t , Yukon: Part A: a new regional mapping program; Geo log ica l Survey of Canada, Paper 82-1A, p . 405-411. Thomson, B.P., 1965: Geology and minera l i za t ion of South A u s t r a l i a ; i n Geology of A u s t r a l i a ore depos i ts , 2nd e d i t i o n , v . 1 (J . McAndrews, e d i t o r ) : 8th Com. Min . M e t a l l . Cong. A u s t r a l i a and New Zealand, p . Wakita, H., Rey, P. and Schmidt, R.A., 1971: Abundances of the 14 rare earth elements and 12 other trace elements i n Apo l lo 12 samples: f i ve igneous and one brecc ia rocks and four s o i l s ; Proc. 2nd Lunar Science Conf . , p. 1319-1329. Wanless and Loveridge, 1972: Yeo, G.M., 1981: The Late Proterozoic Rapitan g l a c i a t i o n i n the northern C o r d i l l e r a ; i n Proterozoic Basins of Canada; ed. F . H . A . Campbell, Geolog ica l Survey of Canada, Paper 81-10, p . 25-46. Yeo, G.M., Delaney, G.D., and Jefferson, C.W., 1978: Two major Proterozoic unconformit ies , northern C o r d i l l e r a : Discuss ion; Geologica l Survey of Canada, Paper 78-1B, p. 225-230. Young, G.M., Campbell, R.B. and Foulton, T.P., 1973: The Windermere Supergroup of the southeastern Canadian C o r d i l l e r a ; i n Be l t Symposium, v . 1, Department of Geology, U n i v e r s i t y of Idaho and Idaho Bureau of Mines and Geology, p. 181-203. Young, G.M.,1977: S t r a t i g r a p h i c c o r r e l a t i o n of Upper Proterozo ic rocks of northwestern Canada; Canadian Journal of Earth Sciences, v . 14, p . 1771-1787. Young, G.M., 1982: The Late Proterozo ic T i n d i r Group, east-c e n t r a l Alaska: Evolut ion of a cont inenta l margin; Geolog ica l Society of America, B u l l e t i n , v . 93, p. 759-783. Young, G.M.,Jefferson, C.W.,Delaney, G.D. and Yeo, G . M . , 1979: Middle and Late Proterozo ic evo lut ion of the northern Canadian C o r d i l l e r a and S h i e l d ; Geology, v . 7, p. 125-128. Young, G.M.,Jefferson, C.W.,Delaney, G.D. and Yeo, G.M., 1978: Upper Proterozoic s tra t igraphy of northwestern Canada and Precambrian h i s t o r y of the North American C o r d i l l e r a ; Idaho Bureau of Mines, 76.p. 163 APPENDIX A METALLOGENY OF THE COAL CREEK INLIER A . l GALENA-LEAD ISOTOPE INTERPRETATIONS OF MINERAL PROSPECTS HOSTED IN THE COAL CREEK INLIER, NORTHERN CANADIAN CORDILLERA Galena from nine prospects i n Proterozoic rocks of the Southern O g i l v i e Mountains of the Northern C o r d i l l e r a (Figure A . l and Table A . l ) were analyzed for lead isotope r a t i o s . These data have been compiled (Table A.2) to evaluate the age of m i n e r a l i z a t i o n and how they might r e l a t e to the formation of the O g i l v i e Mountain brecc ias (OMB) and re la ted t ec ton ic events. The Coal Creek I n l i e r i s wi th in the p e r i c r a t o n i c t e c t o n o - s t r a t i g r a p h i c environment of the Canadian C o r d i l l e r a . Since t h i s i s upper c r u s t a l , a l l data are evaluated r e l a t i v e to the P e r i c r a t o n i c model (Gautier, 1986; Godwin et a l . , 1988; c f . Godwin and S i n c l a i r , 1981, 1982) and the B luebe l l growth curve (Andrew et a l . . 1984). In general , the lead isotope values f a l l on or c lose to the p e r i c r a t o n i c growth curve. These data probably are dated to wi th in 50 Ma by the p e r i c r a t o n i c growth curve. Those data that p l o t below t h i s curve are probably evaluated more accurate ly using mixing l i n e s between the p e r i c r a t o n i c and B luebe l l growth curves (Andrew et a l . . 1984). Galena lead isotope c l a s s i f i c a t i o n of showings i n the Northern C o r d i l l e r a , inc lud ing some from the Coal Creek 6 4 ° -SO'N « 4 " 4 0 N i-iO^ 30' I ! 3 S c 3 0 ' i Ugly \ \ > \ I \ 1 I U T La la Tart i * i >0<i * Pettet °" T ~.T.: r Monster Dem 8hO) St'"' A "is"" j_ , ^ Seela - " ' " XV ../- * --rj 1 4 0 ° 30' ORDOVICIAN t o DEVONIAN f 39\3C" 5 10 K i lomet res | R | R o a d R i v e r G r o u p SARLY CAMBRIAN K> DEVONIAN I C ] C D b F o r m a t i o n | :> j S l a t s C r e e k G r o u p LA If: P R O T C R O Z O I C t o fARI .Y CAMBRIAN H a r p e r G r o u p I H u j Upptfr Harpor Group I Hv j Mt. Harper Volcanic Complex I I'll \ Lower Harper Group MiDOi . i : to i .ATi: P R O ' U R O Z O i ' C F i f t e e n m i l e A s s e m b l a g e ! ii-i I Upper Fiftosnmsle Group | H | Lower f i f loenmi ie Gjoitp iv.*-!:ARi.Y? i . i MIOOi.i'. PRO'ICROZOIC W e r n e c k e S u p e r g r o u p IVVgj Gilhiiipio LaKe Group [ W q j Quartet Group ! VVf I Fairchild i.aKo Group — ( - 6 4 ' SO'N 1 3 8 ° 3 0 ' « Og i l v i e M t n . b r e c c i a s S Y M B O L S Betiding (inclined, to r i i ca ! ) Con tac ts (known, apprcx . , assumed) Faults (ball denotes stoe down) Thrust fault {teeth or: upper ptuio) Mineral prospects Figure A . l Map of the Coal Creek Inlier, southern Ogilvie Mountains, west-central Yukon Territory, showing the location of Proterozoic hosted galena bearing mineral occurrences. These occurrences are discussed with respect to their galena lead isotope signatures and there implications on host rock age and age of the Ogilvie Mountain breccia. Table A.l Brief descriptions of deposits and showings, evaluated using galena lead isotope analyses, hosted by Proterozoic rocks in the Coal Creek Inlier, southern Ogilvie Mountains, west-central Yukon Territory. Deposit name Sample number NTS: Lat(N), Long(W) Host unit 2,3 Deposit type; mineralization 4 GROUP A (stars) OZ 037-AVG7 MONSTER OD 038-AVG3 188-201 116B/12W 64.75, 139.75 116B/13W: 64.82, 139.97 116B/13E: 64.84, 139.60 Gillespie Lake Group (grey dolostone) Fairchild Lake Group Quartet Group Vein, breccia Pb-Zn Breccia Zn-Pb Breccia Pb-? HART RIVER (cross) 082-AVG2 116A/10W: 64.63, 136.87 Gillespie Lake Group (argillite) Stratiform massive sulphide TART (triangle) 020-AVG8 116B/12: 64.83, 139.83 Gillespie Lake Group (grey dolostone) Breccia Zn-Cu-Pb GROUP B (boxes) UGLY 013-AVG2 SEELA 187-AVG2 showing (circle) DEM (diamond) 190-AVG2 023-001 116C/16E: 64.87, 140.03 116B/14E: 64.78, 139.10 Gillespie Lake Group Lower Fifteenmile group 116B/11W: dyke cutting breccia 64.45, 139.19 and Lower Fifteenmile group 116B/13W: Gillespie Lake Group 64.75, 139.80 Fault breccia Pb-Zn Breecia Pb-? Veins Pb Breecia Pb-? 1 Sample numbers are prefixed by the number "10". 2 Host lithologies of deposits not visited are from R.I. Thompson (unpublished open fi l e maps). 3 Refer to Table of Formations (Table 2.1) for host lithologies of those deposits visited. 4 Information regarding deposit type and mineralization is from C.I. Godwin (unpublished galena lead isotope data base). 5 Hart River deposit is in the Wernecke Mountains. 166 I n l i e r , was attempted by Godwin et a l . (1982) . The ir i n t e r p r e t a t i o n out l ined three metal logenic events (Cambrian, Devono-Miss iss ippian, and Cretaceous), none of which can be re la ted to the time of brecc ia emplacement. Consequently, the f i ve prospects reported for the Coal Creek I n l i e r i n Godwin et  a l . (1982) were resampled and reanalyzed together with four a d d i t i o n a l samples from galena-bearing mineral occurrences i n the Coal Creek I n l i e r . A b r i e f summary of each prospect appears i n Table A . l . Results from the present study su i t e , together with adjusted values from an e a r l i e r study by Godwin et a l . (1982), are shown i n Table A . 2 . A . 1 . 1 REGIONAL GEOLOGY AND PROSPECT DESCRIPTIONS Regional geology of the Coal Creek I n l i e r i s described i n Chapter 2 (see e s p e c i a l l y Table 2 .1) . A l l samples c o l l e c t e d were hosted i n Proterozoic rocks of the Coal Creek I n l i e r . Although none of the samples are from wi th in the brecc ia complexes that are the focus of t h i s thes i s work, i t i s speculated that metallogenic events might be synchronous with major c r u s t a l disturbances r e f l e c t e d by the formation of the brecc ias . Deta i l ed information does not e x i s t for the mineral prospects sampled here (Table A . l ) . The most informative source i s the p r i v a t e Yukon Mineral Inventory that was compiled by Archer , Cathro and Associates (Eaton, pers . comm., 1988). Data from t h e i r inventory i s incorporated i n Table A . l 167 and i n the galena lead data base at The U n i v e r s i t y of B r i t i s h Columbia. Data from D . I . A . N . D . publ i ca t ions has a lso been used. Major categories of deposits are carbonate hosted (4 depos i t s ) , ve in (2 deposits) and volcanogenic or sedimentary e x h a l i t i v e (1 depos i t ) , and f a u l t re la ted (2 depos i t s ) . Unfortunately , host u n i t designations i n Table A . l for the Oz mineral occurrence ( G i l l e s p i e Lake Group) does not match the i n t e r p r e t a t i o n i n Figure A . l from recent mapping (Upper Fi f teenmile group). This discrepancy cannot be resolved with ava i l ab l e information. A .1 .2 GALENA LEAD ISOTOPE ANALYSES Galena lead isotope analyses were performed at the Geochronology Laboratory, Department of Geolog ica l Sciences, The U n i v e r s i t y of B r i t i s h Columbia, by the author, J . E . Gabites or B.D. Ryan (Table A . 2 ) . Laboratory procedures used fol low those described i n Godwin et a l . (1988). Galena lead isotope r a t i o p lo t s are shown i n Figures A.2 through A . 4 . F r a c t i o n a t i o n error and 2 0 4 P b e r r o r trends are included on the l ead- l ead diagrams to f a c i l i t a t e evaluat ion of data trends . The P e r i c r a t o n i c and Bluebe l l model curves are included as references of the upper crust and lower crus t , r e spec t ive ly . The P e r i c r a t o n i c model i s app l i cab le to the area s tudied . Estimates of ages using t h i s model are within 50 Ma (cf. Godwin and S i n c l a i r , 1986). 168 Table A.2 Galena lead Isotope data for mineral occurrences in the Coal Creek Inlier, southern Ogilvie Mountains, west-central Yukon Territory. Data from the Hart River massive sulphide deposit (Godwin et a l . . 1988), Wernecke Mountains, described in the text, is also shown. Deposits are located in Figure A.l and Table A.l. Deposit Name Anal^ Normalized Lead Ratios Sample Number1 206/204 207/204 208/204 207/206 208/206 OZ 037-016 RL 16. 190 15. 404 35. 821 0. 95145 2.21261 037-048 BR 16. 275 15. 412 35. 901 0. 94696 2.20690 037-048 RL 16. 259 15. 414 35. 868 0. 94802 2.20601 037-070 RL 16. 215 15. 360 35. 731 0. 94727 2.20360 037-070D RL 16. 265 15. 420 35. 888 0. 94808 2.20646 037-071 RL 16. 277 15. 417 35. 893 0. 94717 2.20522 037-201 RL 16. 260 15. 414 35. 865 0. 94797 2.20572 037-AVG7 16. 249 15. 405 35. 852 0. 94813 2.20665 [0. 033] 3 [0. 020] [0. 060] [0. 00148] [0.00284] MONSTER 038-006 RL 16. 247 15. 426 35. 911 0. 94949 2.21025 038-015 BR 16. 265 15. 417 35. 024 0. 94785 2.15434 038-015 RL 16. 224 15. 426 35. 893 0. 95080 2.21229 038-201 RL 16. 188 15. 406 35. 818 0. 95167 2.21263 03 8-AVG3 16. 219 15. 419 35. 874 0. 95065 2.21172 [0. 030] [0. 011] [0. 050] [0. 00112] [0.00141] OD 188-201 RL 16. 263 15. 418 35. 904 0. 94809 2.20771 HART RIVER 082-001 BR 16. 520 15. 452 36. 464 0. 93535 2.20726 082-100 BR 16. 516 15. 457 36. 296 0. 93588 2.19763 082-AVG2 BR 16. 518 15. 455 36. 380 0. 93562 2.20245 [0. 002] [0. 003] [0. 084] [0. 00027] [0.00482] TART 020-001 RL 17. 022 15. 491 36. 758 0. 91007 2.15949 020-001R RL 17. 016 15. 488 36. 732 0. 91022 2.15865 020-001D RL 16. 950 15. 500 36. 681 0. 91442 2.16403 020-002 JG 16. 703 15. 481 36. 435 0. 92687 2.18139 020-002R RL 16. 696 15. 480 36. 394 0. 92719 2.17981 020-003 RL 16. 763 15. 689 36. 710 0. 93595 2.18995 020-003R RL 16. 498 15. 445 36. 139 0. 93616 2.19051 020-100 BR 16. 806 15. 447 36. 403 0. 91914 2.16607 020-AVG8 16. 807 15. 511 36. 550 0. 92298 2.17483 [0. 181] [0. 078] [0. 222] [0. 01061] [0.01323] 169 Table A.2 (continued) Deposit Name Anal'2 Normalized Lead Ratios Sample Number1 206/204 207/204 208/204 207/206 208/206 UGLY 013-002 013-002 013-002R 013-201* 013-201D* 013-AVG2 BR RL RL JG JG 17.097 17.032 17.288 16.544 16.975 17.065 [0.047] 15.543 15.510 15.616 15.044 15.468 15.527 [0.023] 36.723 36.667 36.905 35.523 35.532 36.695 [0.040] 0.90909 0.91066 0.90330 0.90937 0.91122 0.90988 2.14889 2.15280 2.13475 2.14719 2.15214 2.15085 [0.00109] [0.00275] SEELA 187-201* 187-201R 187-201D 187-AVG2 RL RL RL showing-10190 190-001 RL 190-001D RL 190-AVG2 DEM 023-001 16.805 17.081 17.072 17.077 [0.067] 17.615 17.598 17.607 [0.014] BR 18.824 15.287 15.536 15.514 15.525 [0.017] 15.579 15.574 15.577 [0.000] 15.671 36.246 36.896 36.985 36.941 [0.065] 37.523 37.491 37.507 [0.021] 38.811 0.90967 0.90955 0.90873 0.90914 [0.00069] 0.88446 0.88500 0.88473 [0.00000] 0.83248 2.15686 2.16003 2.16634 2.16319 [0.00438] 2.13020 2.13042 2.13031 [0.00000] 2.06273 3 * Sample numbers are prefixed by the number "10". Suffixes are as follows: "D" = duplicate analysis, "R" = repeat analysis, and "AVG" followed by a number defines the arithmetic average and the number of analyses used. "Anal" refers to the analyst who produced the data for each sample or sample analyzed: BR = Barry Ryan, JG = Janet Gabites, and RL = Robert Lane Standard deviation is in square brackets. The asterisk marks data excluded from cluster averages on basis of probable poor analysis. A.1 .3 RESULTS Galena lead isotope data from prospects hosted i n Proterozo ic s trat igraphy of the Coal Creek I n l i e r p l o t i n s ix separate groups or points (Figures A.2 to A . 4 ) . Averaged values , for those prospects with more than one ana lys i s , are p l o t t e d . "Groups" are made up of two or more values and "points" cons i s t of one value . GROUP A (Oz, Monster and Od) Group A p l o t s as a t i g h t c l u s t e r (Figures A.2 to A.4) on the P e r i c r a t o n i c curve and i s defined by the i so top ic s ignatures of the Oz, Monster, and Od prospects . These mineral prospects are ear ly Middle Proterozoic (about 1.6 Ga). They appear to represent the oldest deposits i n the Coal Creek I n l i e r . The host rock, therefore , i s at l eas t t h i s o l d . A l l three prospects are brecc ia and/or ve in deposits and are i n d i f f e r e n t host rocks (see Table A . l ) The 2 0 6 P b / 2 0 4 P b r a t i o s , taken o v e r a l l are s t a t i s t i c a l l y i n d i s t i n c t from each other. I f the Od occurrence, i n Quartet Group, and the Oz occurrence, i n G i l l e s p i e Lake Group are syngenetic, then the boundary between G i l l e s p i e Lake Group and Quartet Group would be at about 1.6 Ga. This i s a reasonable l o c a t i o n for t h i s boundary. I f , on the other hand, the Monster mineral occurrence i s syngenetic, then the F a i r c h i l d Lake Group would be e a r l i e s t Middle Proterozo ic . However, s ince the F a i r c h i l d 16.00 16.50 17.00 17.50 18.00 18.50 19.00 19.50 206Pb/204Pb Figure A . 2 Galena lead isotope p lo t of 2 0 7 P b / 2 0 4 P b vs^. 2 0 6 P b / 2 0 4 P b showing the d i s t r i b u t i o n of data from Proterozoic hosted mineral occurrences i n the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Tables A . l and A.2 present b r i e f descr ipt ions and galena lead isotope data for the mineral occurrences, re spec t ive ly . Figure A . l shows t h e i r locat ions . 3 5 . 5 0 ~ \ — i — r — i — i — | — : — i — i — i — i — i — i — i — i — | — i — i — i — i — | — i — i — i — i — i — i — i — i — i — | — i — i — i — i — | 1 6 . 0 0 1 6 . 5 0 1 7 . 0 0 1 7 . 5 0 1 8 . 0 0 1 8 . 5 0 1 9 . 0 0 1 9 . 5 0 206Pb/204Pb Figure A.3 Galena lead isotope p lo t of 2 0 8 P b / 2 0 4 P b vs^ 2 0 6 P b / 2 0 4 P b showing the d i s t r i b u t i o n of data from Proterozoic hosted mineral occurrences i n the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Tables A . l and A.2 present b r i e f descr ipt ions and galena lead isotope data for the mineral occurrences, r e s p e c t i v e l y . Figure A . l shows t h e i r locat ions . 2.00 -i 0.97 0.95 0.93 0.91 0.89 0 .87 0 .85 0 .83 0.81 207Pb/206Pb F i g u r e A . 4 Galena lead isotope p lo t of 2 0 8 P b / 2 0 6 P b vs,. 2 0 7 P b / 2 0 6 P b showing the d i s t r i b u t i o n of data from Proterozoic hosted mineral occurrences i n the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Tables A . l and A.2 present b r i e f descr ipt ions and galena lead isotope data for the mineral occurrences, r e spec t ive ly . Figure A . l shows t h e i r locat ions . Lake Group i s considered to be Ear ly Proterozo ic , then the Monster mineral prospect i s more l i k e l y epigenet ic and probably formed during the same metallogenic event that made the Od and Oz mineral occurrences. Hart River Hart River s t r a t i f o r m massive s u l f i d e deposit (Morin, 1977) occurs about 150 km east of the Coal Creek I n l i e r . I t occurs i n an a r g i l l a c e o u s fac ies of the G i l l e s p i e Lake Group, the youngest member of the Wernecke Supergroup. This syngenetic deposit (Morin, 1977) has a galena lead model age of about 1.35 to 1.45 (cf . Godwin et a l . . 1988). This date i s approximately equivalent to the age of the S u l l i v a n deposit (Godwin, 1986), southeast B . C . I t a lso defines the approximate age of the youngest member of the Wernecke Supergroup. Tart The Tar t deposit has an interpreted age of about 1.3 Ga. I t i s hosted i n dolostone of the G i l l e s p i e Lake Group. I f the Tart i s co-genet ic with i t s host rock t h i s date might give an upper age for the G i l l e s p i e Lake Group. Such an age i s compatible with present ly known geology. 175 GROUP B (Ugly and Seela) Group B i s made up of two showings, the U g l y and S e e l a . These prospects occur i n brecc ias s p a t i a l l y associated with f a u l t s . The former occurs i n G i l l e s p i e Lake Group rocks and the l a t t e r occurs i n the Lower Fi f teenmile group. The in terpre ted i so top ic age i s 1.2 Ga. (The 2 0 8 P b / 2 0 4 P b r a t i o for the Seela prospect appears to be e r r a t i c ; t h i s r a t i o d i sp laces i t from the Ugly mineral occurrence on Figures A.3 and A . 4 . ) This date co inc ides with the age of the Racklan Tectonic Event (Gabrie lse , 1967; Eisbacher, 1978). I t might a l so represent the time of movement along the F i f teenmi le f a u l t with which the Seela prospect i s s p a t i a l l y assoc iated . I f the Seela showing i s syngenetic, then the 1.2 Ga date may a lso approximate the age of the lower Fi f teenmile group. The 1.2 Ga date i s probably younger than the G i l l e s p i e Lake Group. Therefore the Ugly prospect i s l i k e l y epigenet ic . Showing-10190 Showing-10190 p lo t s ju s t below the P e r i c r a t o n i c growth curve but can be modeled at about 0.9 Ga by using the mixing l i n e between the p e r i c r a t o n i c and Bluebe l l growth curves. This date coincides with the boundary between Middle Proterozo ic and Late Proterozoic (point Z i n Figures A.2 to A . 4 ) . Galena for t h i s point came from v e i n l e t s i n an a l t ered mafic dyke that cuts OMB hosted i n lower Fi f teenmi le group 176 rocks . The date therefore probably approximates the age of the mafic dyke and establ i shes a minimum age for OMB. C l e a r l y the mafic dyke fragments i n OMB are o l d e r . Dem The Dem prospect p lo t s j u s t below the P e r i c r a t o n i c growth curve i n Figure A . 2 . I t can be modeled at about 0.3 Ga (Carboniferous) . This deposit i s hosted i n lower Fi f teenmi le group and i s therefore ep igenet ic . I t i s unrelated to the OMB. A .1 .4 CONCLUSION The i n t e r p r e t a t i o n of data from the present study has y i e lded s i g n i f i c a n t l y d i f f e r e n t r e s u l t s from that of Godwin et  a l . (1982). In t h i s study data can be d iv ided into 2 groups and 4 points (Figures A.2 to A . 4 ) . A l l data are d i s t r i b u t e d along or c lose to the P e r i c r a t o n i c growth curve from about 1.6 Ga to Carboniferous time. The c l u s t e r s and points allow the dat ing of minera l i z ing events and constra in the age of the rock un i t s that host the m i n e r a l i z a t i o n . Wernecke Supergroup rocks are at l eas t as o ld as 1.56 Ga (Group A ) , are as young as about 1.35 to 1.45 Ga (Hart River) and might even be 1.30 to 1.35 Ga (Tar t ) . The age of the OMB, i f r e l a t e d to the age of the dykes, has an upper l i m i t of about 0.90 Ga (Showing-10190). The age 177 of Group B, 1.2 Ga, may define a lower l i m i t to the age of the b r e c c i a , e s p e c i a l l y s ince the brecc ias are i n lower Fi f teenmi le group. In fac t , one i m p l i c a t i o n of the galena lead isotope data i s that the Racklan Tectonic Event, which a f fec t s the lower Fi f teenmile group, may be re la ted to movement along the Fi f teenmile f a u l t . OMB occupies t h i s f a u l t ; the genet ic model (of sect ion 5.4) implies that the f a u l t and b r e c c i a are gene t i ca l l y r e l a t e d . Therefore O g i l v i e Mountains b r e c c i a , the lower Fi f teenmile group, major f a u l t i n g and the Racklan Tectonic Event might a l l be approximately equivalent i n age. Carboniferous (Dem) metallogenic events are recorded i n the Coal Creek I n l i e r . These are prominent i n the northern Canadian C o r d i l l e r a . 178 APPENDIX B POTASSIUM-ARGON PREPARATION AND ANALYTICAL PROCEDURES B . l SAMPLE PREPARATION Five samples were prepared for potassium-argon dat ing methods. The i n i t i a l stages are l i s t e d below and s p e c i f i c treatments fol low under respect ive sub-headings. (1) weathered mater ia l removed, (2) crushed to less than 0.5 cm i n a jaw crusher , (3) gr ind sample i n d i sc m i l l , and (4) s ieve sample to -40 mesh and r e t a i n the -40 mesh f r a c t i o n . Steps 3 and 4 are repeated with +40 mesh f r a c t i o n u n t i l en t i re sample passes -40 mesh. B . l . l POTASSIUM-ARGON ANALYSIS Five potassium-argon analyses were made from three c h l o r i t e - r i c h separate samples and two amphibole separate samples. Amphibole mineral separates were made from two v i s u a l l y "least a l tered" coarse-grained diabase dykes. The three c h l o r i t e - r i c h separates were from three i s o l a t e d occurances of c h l o r i t e - r i c h - m a t r i x brecc ia s . The various sample preparations are described as fo l lows. C h l o r i t e - r i c h separates (1) The -40 mesh i s hand picked for c h l o r i t e and the and the c h l o r i t e - r i c h f r a c t i o n i s re ta ined (The c h l o r i t e - p o o r f r a c t i o n i s saved as a back-up). 179 (2) Sieve each sample i n a set of "mini" nested sieves (-60 mesh on top, -80 mesh i n the middle, and -100 mesh on the botom) by hand for approximately 10 minutes. Retain the -80 +100 for further analys i s and save the -40 +60 mesh and -100 mesh as back-ups. (3) The f r a c t i o n i s passed through a magnetic column to remove any magnetic gra ins . (4) A s l i g h t l y i n c l i n e d v i b r a t i n g plane tab le i s used to further concentrate the p la ty c h l o r i t e g r a i n s . Amphibole separates (1) Sieve each sample i n a set of "mini" nested sieves (-60 mesh on top of -80 mesh ) by hand for about 10 minutes. Retain the -60 +80 mesh for further ana lys i s and save the -40 +60 mesh and -80 mesh as back-ups. (2) The f r a c t i o n i s passed through a magnetic column to remove any magnetite gra ins . (3) The f r a c t i o n i s passed through a magnetic separator several times to remove both the most magnetic and l eas t magnetic g r a i n s . This mater ia l const i tutes about 20% of the -60+80 mesh separate; i t i s d iscarded. (3) Heavy l i q u i d s (bromoform and methylene iodide) are used to further concentrate the amphibole gra ins . Potassium and ana lys i s (1) The chemical techniques used for potassium analys i s are those described i n d e t a i l i n the unpublished 180 laboratory ins t ruc t ions manual i n the Geochronology Laboratory at UBC. Potassium concentration i s determined on dupl icate samples by atomic absorption using a Techtron AA4 spectrophotometer on d i l u t e sulphate so lut ions bufered by Na and L i n i t r a t e s . (2) F ive samples (plus f i v e duplicates) were analyzed for t h e i r potassium content. Argon analys i s (1) The laboratory techniques used for argon ana lys i s are those described by White et a l . (1967). Argon i s determined by isotope d i l u t i o n using an AEI MS-10 mass spectrometer with Carey Model 10 v i b r a t i n g r e e l electrometer, high p u r i t y 3 8 A r spike and conventional gas ex trac t ion and p u r i f i c a t i o n methods. (2) Two of the i n i t i a l f i ve samples were analyzed for argon. .The p r e c i s i o n and accuracy of the age dates are the estimated a n a l y t i c a l uncer ta int i e s at one standard d e v i a t i o n . The decay constants used are those recommended by the IUGS Subcommision on Geochronology (4o K decay to 4gAr = 0.58xl0_ig yr_]_ and 40K decay to 4oCa = 4 .962X10_IQ Y r - l i S te iger and Jager , 1977). B.2 RESULTS Results are shown i n Table B . l . TABLE B.1 Analytical data for K-Ar dates from the Coal Creek I n l i e r , southern Ogilvie Mountains, west-central Yukon Territory. A l l analyses were performed at the Geochronology Laboratory, Department of Geological Sciences, The University of B r i t i s h Columbia: potassium analyses was by D. Runkle and argon analyses were by J. Harakal. Sample No. Location K * uAr (radiogenic) * uAr (radiogenic) Date (Ma) Material Unit (wt%) 4 0 A r (total) (10" 6 cnrrV1) Time 2 TW208 3.48 0.862 29.307 205+6 Uhole rock Lat. 64°53.68N +0.01 lowest Jurassic c h l o r i t e - r i c h Long. 139°09.12W matrix Unit BM1: concentrate monoclastic breccia BL30-6 Uhole rock c h l o r i t e - r i c h matrix concentrate Lat. 64°50.23N Long. 139°38.28U Unit BM1: monoclastic breccia 3.31 +0.04 0.981 51.239 360+10 Devonian-Carboniferous 1 Decay constants are from Steiger and Jager (1977): lambdae = 0.581x10"'° y r " 1 ; lambdah = 4.962x10"'" year"'; *UK/K=1.167x10"*. Errors are one standard deviation. 2 Time intervals are from Decade of North American Geology (Palmer, 1983). H Co H APPENDIX C SPECIFIC REFERENCES USED TO CONSTRUCT FIGURE 2.1 The superscr ipted numbers on Table 2.1 match the column numbers on the l e f t . F u l l l i s t i n g s are i n "REFERENCES". 1. Brabb, E . E . , 1967. 2. Churkin, M. J r . , 1973. 3. N o r r i s , D.K. and Hopkins, W.S . , 1977 4. F r i t z , W . H . , 1980 5. Roots, C . F . , 1982; 1987. 6. Thompson, R . I . and Roots, C . F . , 1982 7. Thompson, R . I . , pers . comm., 1987 8. Merc ier , E . , 1985 9. Merc ier , E . , 1987 10. C e c i l e , M . P . , 1982 11. Gordy, S . P . , i n press . 12. Young, G.M. et a l . , 1978; Young, G.M. et a l . , 1979; Eisbacher, G . H . , 1978. 13. Eisbacher , G . H . , 1981. 14. Delaney, G . D . , 1981; 1985. 15. Eisbacher , G . H . , 1976; Yeo, G . M . , 1981. 16. Je f f er son , C.W., 1978; DNAG i n press 17. Gabr ie l s e , H. et a l . , 1973. 18. A i t k e n , J . D . , 1981 19. Je f f er son , C.W., and Rue l l e , J . C . L . , 1986. 20. McMechan, M . E . and P r i c e , R . A . , 1982. 21. P r i c e , R . A . , 1964. 22. Gabr i e l s e , H . , 1972 183 APPENDIX D SUMMARY OF OGILVIE MOUNTAIN BRECCIAS IN THIN SECTION Table D . l Li thology and mineral abbreviat ions for Table D.2 Abbreviat ion Mineral Abbreviat ion Rock Name ab a l b i t e arg a r g i l l i t e ba b a r i t e cht chert cb carbonate dol dolostone c l c h l o r i t e fe f i r o n formation cy c lay i n t mafic dyke d l dolomite mds mudstone ep epidote qzt q u a r t z i t e he hematite sds sandstone ks potassium s l d s i l t y dolostone fe ldspar or do lomi t i c lm l imonite s i l t s t o n e ms muscovite met metasomatized P l p lag ioc lase sedimentary py p y r i t e rock qz quartz se s e r i c i t e t r tourmaline T A B L E D . 2 Thin sect ion suraary ot Og i lv i e Mountain breccias and s o w other breccias fro» the Coal Creek l r . l i e r , southern Og i lv i e hountains, nest-central Yukon t e r r i t o r y . U N I T ( th in sec t ion I) CLAST LIIHOLOGY qzt sds dol s l d lids chr tef int »et M O N O L I T H I C B R E C C I A S PRIMARY 6RA1NS he cb qz ks pl cy ks a l SECONDARY MINERALS ? ep d l qz cb py cy In he COMMENTS FAIRCHILD LAKE GROUP BM1 (BL3-S5) (8L6-2) (BL30-2) (H.30-6) (BL5A-1) (TMa5-J0Bfl,B) fiow texture cockaae cext'ire al igned he c l a s t supported c l a s t i c texture p o i k i l i t i c ks QUARIE7 GROUP BMi No sections 61LLEBPIE LAKE GROUP 6M3 (BL67-7B.CI X rIFitENHILE GROUP BM4 No sections H E T E R O L I T H I C B R E C C I A S r e c r y s t a l i z e d s t ra ined qz CARBOHATE-RICH-MATRIX BHcb IBL10-I4A) (BL*5-5> IBLB7-701 [BL87-7P.I vein cb,he,qz bleached s t ra ined qz HEMAT11E-RICH-HATR1X BHh (BL2V12) (H.37-I8I (6L«-7> (BU8-3I (BL67-57) he-vein qz brx a a r t i t e ? aligned c l a s t s f e l s i c igneous p o i k i l i t i c cb CHLORIIE-RICH-MATRIX BHcl (BL35-4) IBL50-2) igneous trags. flow texture H Y D R O T H E R M A L B R E C C I A S (BLte - l J ) X (8L40-27) X rec rys t a l i zed qz overgrowths P E B B L E D Y K E (BL67-21I aoioni te na t r ix 1 Li tholoqy and ninera l abbreviations are l i s t e d i n table D.1. 185 APPENDIX E GEOCHEMICAL TECHNIQUES AND RESULTS E . l GEOCHEMICAL TECHNIQUES Each major un i t was sampled for analyses of the major, trace and rare earth elements. P r i o r to shipment to the various l a b o r a t o r i e s the samples were cleaned of a l l weathered m a t e r i a l . E . l . l Sui te 1: XRF and ICP analyses Twenty-four samples were submitted to the Geologica l Survey of Canada, Minera l Resources D i v i s i o n , A n a l y t i c a l Chemistry Sect ion , X-ray Flourescence and ICP-Emmision Spectrometry l abora tor i e s i n Ottawa. Sample descr ip t ions are i n Table E . l and r e s u l t s are shown i n Table E . 2 . Major element oxides and trace elements (see Table E.2) were analyzed by XRF wavelength d i spers ive ana lys i s on fused d i s k s . FeO, H2OT, C O 2 T , C and S were analyzed by rap id chemical methods. Fe2C>3 was ca l cu la ted using Fe2C>3 = Fe2C>3T - 1.11134 * FeO (volumetric) . Detection l i m i t s f or major and trace elements, given by the laboratory , were: 0.50% for Na 2 0; 0.40% for Si02 and A 1 2 0 3 ; 0.2% for T i 0 2 , C r 2 0 3 , P 2 O 5 , S and C 0 2 ; 0.1% for Fe203, MgO and CaO; 0.05% for K 2 0 and H 2 0 ; 0.03% for FeO and 0.01% for MnO. 186 Detection l i m i t s for trace elements, provided by the laboratory, were: 30 ppm for Nb and Y; 20 ppm for Ba, Rb, Sr and Zr Results of t e s t s for p r e c i s i o n are presented i n Table E . 7 . Standards were not run therefore the accuracy of the data i s not known. ICP data for 7 trace and 2 rare earth elements were obtained 1.0 gram of sample (acid + fusion of residue) d i s so lved i n 10% HCL and d i l u t e d to 100 ml. Detection l i m i t s for t h i s set of ICP data, given by the laboratory , were: 10 ppm for Cr , Cu, La and N i ; 5 ppm for Co, V and Zn; 0.5 ppm for Be and Yb. These samples were also analyzed for se lected trace (Nb, Ba and Th) and rare earth (La and Ce) elements using ICPMS methods by X-ray Assay Laboratories Limited (XRAL), Don M i l l s , Ontar io . Detection l i m i t s are l i s t e d below, are: 1.0 ppm for Nb, Ba and La 0.5 ppm for Ce and 0.1 ppm for Th E.1 .2 Suite 2: Whole rock and 30 element ICP analyses Twenty samples were submitted to ACME A n a l y t i c a l Laboratories i n Vancouver. These analyses were provided by Newmont Exp lora t ion of Canada L t d . A l l samples were analyzed by ICP techniques for 30 elements and by ICP-MS for 26 trace and rare earth elements. Seven of these samples were a lso anlayzed for oxides plus LOI and Ba. Sample descr ip t ions are shown i n Table E.3 and r e s u l t s are tabulated i n Table E . 4 . The data i s 187 not quant i ta t ive and was meant to be used as an explorat ion guide to anomalously minera l ized brecc ia bodies. Some samples anomalous i n t h e i r rare earth element content were re-analyzed q u a n t i t a t i v e l y for REE i n Suite 3 (see sect ion E . 3 ) . For ICP ana lys i s the samples were crushed to -5 mm using a jaw crusher and then pu lver i zed to -100 mesh and s p l i t . A one-h a l f gram sample was digested with 3 ml of 3-1-2 HCL-HN03-H20 at 90oC for one hour and d i l u t e d to 10 ml with water. The leach i s near t o t a l for base metals, p a r t i a l for rock forming elements and poor for r e f r a c t o r y elements. Detection l i m i t s are as follows: 5 ppm for U, 2 ppm for As, Au, B, Ba, B i , L a , Pb, Sb, Th, V and W, 1 ppm for Cd, Co, Cu, Mn, Mo, N i , Sr and Zn, 0.1 ppm for Ag, and 0.01% for A l , Ca, Fe, K, Mg, Na, P and T i . For whole rock ICP-MS analyses 0.200 gram samples were fused with 0.60 grams of LiB02, are d isso lved and d i l u t e d i n 50 ml of 5% HNO3. Detect ion l i m i t s are 1 ppm for a l l elements except for Be which i s 10 ppm and Rb, Y, Z r , Nb, Cs and W. For whole rock ICP analyses 0.1000 gram samples were fused with 0.60 grams of LiB02 and are d isso lved i n 50 ml of 5% HNO3. Detection l i m i t s were not provided by the laboratory . E .1 .3 Suite 3: Instrumental neutron a c t i v a t i o n analyses (INAA) for rare earth elements (REE) Twenty-two samples were submitted to Bondar-Clegg and Company L t d . i n North Vancouver. Four of the samples were dupl icates and 1 was a standard. Fourteen rare earth elements 188 plus Sc, Th and U were evaluated using INAA techniques that are descr ibed i n d e t a i l i n Gibson and Jagam (1980). Sample d e s c r i p t i o n s i n Table E.5 and r e s u l t s are shown i n Table E . 6 . Atomic absorption was used to determine Co and Cu contents and XRF was used to determine Ba concentrat ion. P r e c i s i o n and accuracy of the data i s shown i n Tables E.7 and E . 8 . Re la t ive p r e c i s i o n i s var iab l e and ranges from less than 5% for Lu and Sc to 31% for Dy. Re lat ive p r e c i s i o n i s found to be e r a t i c for elements with concentrations only s l i g h t l y higher than t h e i r detect ion l i m i t s (compare Lu with Dy; Table E . 7 ) . Detect ion l i m i t s are shown i n Table E . 9 . 189 E.2 SAMPLE DESCRIPTIONS AND RESULTS Table E . l B r i e f hand sample descr ip t ions for Sample Suite 1 c o n s i s t i n g of 24 samples ( inc luding dupl icates) from the southern O g i l v i e Mountains, west -central Yukon T e r r i t o r y . These are evaluated for major and minor oxides, trace and rare earth elements. Sample locat ions are shown on Map 2 ( in pocket) . Results are tabulated i n Table E . 2 . Unit Sample No. Sample Descr ipt ion (Lat .N , Long.W) Dyke BL6-4A ( 1 3 9 ° 0 9 . 1 2 / N , 6 4 ° 5 3 . 1 0 ' W ) BL6-4B ( 1 3 9 ° 0 9 . 1 2 ' N , 6 4 ° 5 3 . 1 0 / W ) BL9-2 ( 1 3 9 ° 1 6 . 1 3 / N , 6 4 ° 5 2 . 4 6 / W ) BL9-22 ( 1 3 9 ° 1 5 . 1 3 / N , 6 4 ° 5 2 . 5 4 ' W ) BL43-10 ( 1 3 9 ° 2 4 . 9 4 / N , 6 4 ° 4 4 . 0 1 ' W ) BL2-5 ( 1 3 9 ° 0 8 . 1 8 ' N , 6 4 ° 5 3 . 3 8 ' W ) BL54-3 ( 1 3 9 ° 3 7 . 4 2 / N , 6 4 ° 5 0 . 1 3 ' W ) BL10-6 ( 1 3 9 ° 1 6 . 3 2 / N , 6 4 ° 5 1 . 5 8 ' W ) Iron formation: t h i n l y bedded white quartz , jasper , hematite and brown calcareous sandstone; trace cha lcopyr i te Iron formation: laminated hematite and f ine -gra ined b lack s i l i c e o u s sediment; trace cha lcopyr i t e and p y r i t e F a i r c h i l d Lake Group: grey weathering, brownish grey limestone; t h i n l y bedded; c h l o r i t e part ings F a i r c h i l d Lake Group: grey weathering, pale grey l imestone; t h i n l y bedded; c h l o r i t e part ings F a i r c h i l d Lake Group: maroon mudstone; crowded with rhombs (1 mm i n diameter) of dolomite Monol i th ic breccia/conglomerate: pale brown weathering, grey and brown mottled calcareous sandstone and mudstone fragments; mud matrix Quartet Group: grey weathering, dark grey f ine -gra ined sandstone Diabase: medium green, c h l o r i t i z e d and carbonatized intermediate to mafic dyke; amygdules have i ron carbonate rims and quartz cores; common p y r i t e euhedra Table E . l (continued) Unit Sample No. (Lat .N , Long.W) Sample Descr ipt ion Dyke BL47-5 ( 1 3 9 ° 1 9 . 6 4 ° 4 4 . 21'N, 73 'W) Diabase: pale grey-green carbonatized and s e r i c i t i z e d intermediate to mafic dyke; glomerocrysts of r e l i c t p lag ioc lase ; abundant c a l c i t e v e i n l e t s ; trace galena BM1 BL3-25 ( 1 3 9 ° 0 9 . 6 4 ° 5 3 . 12'N, 64'W) Monol i th ic b r e c c i a : subrounded f r a g -ments of pale grey q u a r t z i t e ; c h l o r i t e matrix BM1 BL30-6 ( 1 3 9 ° 3 8 . 6 4 ° 5 0 . 23'N, 21'W) Monol i th ic b r e c c i a : maroon dolomit ic sandstone fragments; medium-grained c h l o r i t e matrix with minor i r o n carbonate BM1 85-208A ( 1 3 9 ° 0 9 . 6 4 ° 5 3 . 12'N, 68'W) Monol i th ic b r e c c i a : c h l o r i t i c fragments i n a coarse grained c h l o r i t e matrix BM1 85-208B ( 1 3 9 ° 0 9 . 6 4 ° 5 3 . 12'N, 68'W) Monol i th ic b r e c c i a : pink s i l i c e o u s c l a s t s i n a coarse grained c h l o r i t e matrix BM2 BL33-7 ( 1 3 9 ° 0 9 . 6 4 ° 5 4 . 37'N, 93'W) Monol i th ic b r e c c i a : angular fragments of grey sandstone; i r o n carbonate matrix; 1-2% p y r i t e and trace chalcopyr i te BM4 BL50-6 ( 1 3 9 ° 1 2 . 6 4 ° 4 6 . 98'N, 02'W) Monol i th ic b r e c c i a : dark grey angular c l a s t s of laminated mudstone BHcb BL3-5 ( 1 3 9 ° 0 8 . 6 4 ° 5 3 . 55'N, 18'W) H e t e r o l i t h i c b r e c c i a : grey weathering, grey and pink mottled; c l a s t s are pink s i l t y dolostone, grey sandstone, grey mudstone; carbonate matrix; accessory c h l o r i t e ; trace hematite BHcb BL3-16 ( 1 3 9 ° 0 8 . 6 4 ° 5 3 . 84'N, 13'W) H e t e r o l i t h i c b r e c c i a : mottled grey and pink; pink and maroon mudstone, black a r g i l l i t e , grey sandstone and dolostone fragments; carbonate and c h l o r i t e matrix BHcb BL8-8 ( 1 3 9 ° 1 0 . 6 4 ° 5 3 . 89'N, 42'W) H e t e r o l i t h i c b r e c c i a : subrounded fragments of pink sandy dolostone, pink o o l i t i c l imestone, white quartz i t e and jasper; carbonate matrix 191 Table E . l (continued) Uni t Sample No. Sample Descr ip t ion (Lat .N, Long.W) BHcb BL18-10 ( 1 3 9 ° 2 3 . 6 4 ° 5 2 . 13'N, 46'W) Brecc ia matrix: red , coarse grained carbonate BHcb BL43-7 ( 1 3 9 ° 2 5 . 6 4 ° 4 4 . 25'N, 14'W) H e t e r o l i t h i c b r e c c i a : layered; c l a s t s of pink s i l t y dolostone, b lack a r g i l l i t e , grey mudstone and specular hematite masses; carbonate and hematite matrix with minor c h l o r i t e BHh BL47-11 ( 1 3 9 ° 1 9 . 6 4 ° 4 4 . 25'N, 39'W) H e t e r o l i t h i c b r e c c i a : subangular f r a g -ments of pink to maroon do lomit i c mud-stone and sandy dolostone; hematite, c h l o r i t e and carbonate matrix BHcl BL45-4 ( 1 3 9 ° 2 2 . 6 4 ° 4 4 . 61'N, 64'W) H e t e r o l i t h i c b r e c c i a : mottled pale pink and green; s i l i c i f i e d pink dolostone, white q u a r t z i t e and green mudstone fragments; f ine -gra ined c h l o r i t e - q u a r t z matrix BHcl BL47-6 ( 1 3 9 ° 1 9 . 6 4 ° 4 4 . 21'N, 73'W) H e t e r o l i t h i c b r e c c i a : white q u a r t z i t e , dark grey and green mudstone and rare pink dolostone fragments; c h l o r i t e -carbonate matrix Table E.2 Major and minor element oxides and trace elements for sample su i te 1 from Proterozo ic rocks, Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Rocks are described i n Table E . l . Sample locat ions are i n Table E . l and on Map 2 ( in pocket) . A l l analyses were by the Geolog ica l Survey of Canada, Ottawa. Sample No. BL6-4a BL6-4b BL9-2 BL9-22 BL43-10 BL2-5 XRF analyses s i o 2 (wt%) 25.4 53.0 39.5 42.6 47.0 34.4 T i 0 2 (wt%) 0.22 0.20 0.45 0.51 0.46 0.20 A 1 2 0 3 (wt%) 7.8 5.7 9.5 8.8 10.3 4.7 c r 2 o 3 (wt%) 0.01 0.01 0.00 0.00 0.00 0.00 F e 2 0 3 (wt%) 46.4 29.8 1.9 2.5 7.9 0.9 FeO (wt%) 2.0 1.0 1.4 1.9 5.4 MnO (wt%) 0.03 0. 08 0.58 0.53 0.13 0.89 MgO (wt%) 1.82 1.28 2.27 2.64 7.94 4.41 CaO (wt%) 0.38 2.05 21.14 18.32 7.28 21.49 Na 2 0 (wt%) 0.0 1.7 0.00 0.3 0.0 0.0 K 2 0 (wt%) 3.89 1.22 3.57 3.31 3.78 1.65 H 2 0T (wt%) 1.0 2.0 2.2 2.7 1.1 C0 2 T (wt%) 0.4 2.4 16.9 4.8 11.1 24.3 P2O5 (wt%) 0.29 0.27 0.20 0.20 0.13 0.08 s (wt%) 3.82 0.02 0.00 0.03 0.00 0.32 Ba (ppm) 595 293 375 1289 205 234 Nb (ppm) 0 0 0 0 0 0 Rb (ppm) 35 0 161 107 126 63 Sr (ppm) 0 0 278 346 3 48 Y (ppm) 0 0 0 0 0 0 Zr (ppm) 29 60 106 149 101 72 T o t a l (wt%) 90.5 100.7 99.1 98.3 100. 6 99.9 F e 2 0 3 T (wt%) 46.4 32 . 5 3.1 4.0 10. 0 6.9 ICP analyses- set 1 Nb (ppm) 3 3 8 8 8 3 Ba (ppm) 591 279 412 1422 188 203 La (ppm) 1 3 19 6 62 15 Ce (ppm) 2.6 5.4 37.1 11.2 107 31.0 Th (ppm) 4.2 4.2 10.4 11.1 12.9 4.2 ICP analyses- set 2 Be (ppm) 0.4 0.4 1.8 1.5 1.5 1.1 Co (ppm) 47 13 12 21 17 16 Cr (ppm) 0 0 51 51 48 44 Cu (ppm) 70000 400 15 36 17 40 La (ppm) 5 4 16 6 58 17 Ni (ppm) 9 14 32 5 33 26 V (ppm) 240 140 59 56 57 35 Yb (ppm) 0.6 0.0 1.6 1.5 1.6 0.9 Zn (ppm) 170 31 79 59 69 42 Table E.2 (continued) Sample No. BL54-3 BL10-6 BL47-5 BL3-25 BL30-6 TW208a XRF analyses SiC-2 (wt%) 67.6 39.2 41.2 61.3 62.1 54.0 TiC-2 (wt%) 0.68 1.25 1.00 0.52 0.51 0.66 A 1 2 0 3 (wt%) 17.1 11.9 14.8 12.6 11.9 14.5 C r 2 0 3 (wt%) 0.01 0.01 0.03 0.01 0.01 0.01 F e 2 o 3 (wt%) 2.1 22.2 1.4 3.3 5.8 1.7 FeO (wt%) 0.9 13.5 3.3 4.3 9.9 MnO (wt%) 0.02 0.22 0.23 0.05 0.10 0.10 MgO (wt%) 0.79 7.69 6.33 3.04 5.14 8.35 CaO (wt%) 0.28 4.81 5.49 2.79 0.77 0.33 Na 2 0 (wt%) 1.3 0.0 0.3 0.1 0.1 0.0 K 2 0 (wt%) 5.15 1.39 1.99 6.76 5.97 4.39 H 2OT (wt%) 2.5 5.12 2.5 2.9 5.5 C0 2 T (wt%) 0.3 6.8 8.1 3.5 0.9 0.0 P2O5 (wt%) 0.06 0. 09 0.08 0.12 0.12 0.19 S (wt%) 0.00 1.39 0.15 0.00 0. 00 0.00 Ba (ppm) 573 161 190 602 593 396 Nb (ppm) 0 0 0 0 0 0 Rb (ppm) 236 45 48 151 84 78 Sr (ppm) 31 0 0 38 3 0 Y (ppm) 51 6 0 0 15 0 Zr (ppm) 224 59 46 223 156 265 T o t a l (wt%) 98.9 97.0 99.8 99.1 100.7 99.1 Fe20 3 T (wt%) 3.1 22.2 16.4 6.9 10.5 12.7 ICP analyses- set 1 Nb (ppm) 143 4 3 5 7 9 Ba (ppm) 628 102 143 597 598 342 La (ppm) 19 33 3 34 4 8 Ce (ppm) 39.8 60.6 10.2 63. 8.15 16.8 Th (ppm) 23.0 1.7 0.9 12. 11.23 10.9 ICP analyses- set 2 Be (ppm) 2.8 1.1 1.2 1. 0.72 1.1 Co (ppm) 7 97 39 11 24 32 Cr (ppm) 63 50 200 56 57 58 Cu (ppm) 23 29 25 10 23 26 La (ppm) 16 50 1 32 6 8 Ni (ppm) 25 100 130 30 53 70 V (ppm) 65 300 300 70 83 120 Yb (ppm) 5 1.9 1.2 1. 2.17 0.8 Zn (ppm) 38 80 220 32 75 92 Table E.2 (continued) Sample No. TW208b BL33-7 BL50-6 BL3-5 BL3-16 BL8-8 XRF analyses S l 0 2 (wt%) 73.7 49.7 . 66.0 46.8 56.3 41.5 T i 0 2 (wt%) 0.35 1.95 0.64 0.47 0.59 0.20 A 1 2 0 3 (wt%) 9.9 13.9 14.7 8.4 14.0 3.1 C r 2 0 3 (wt%) 0.00 0.01 0.01 0.00 0.01 0.00 F e 2 0 3 (wt%) 0.5 3.1 1.2 3.4 3.4 0.9 FeO (wt%) 2.3 7.5 3.6 2.4 3.5 1.9 MnO (wt%) 0.04 0.16 0.01 0.32 0..12 0.42 MgO (wt%) 2.52 5.78 3.44 7.11 5.14 10.11 CaO (wt%) 0.60 1.50 0.61 9.56 4.91 15.43 Na 2 0 (wt%) 0.1 0.0 0.3 0.1 5.2 0.0 K 2 0 (wt%) 6.66 7.43 5.59 4.80 0.88 1.51 H 2OT (wt%) 1.5 4.2 3.7 1.5 2.8 0.7 C0 2 T (wt%) 0.8 2.1 0.8 14.5 3.7 23.5 P2O5 (wt%) 0.10 0.15 0.19 0.16 0.17 0.23 S (wt%) 0.00 0.61 0.01 0.00 0.00 0.00 Ba (ppm) 668 466 489 382 114 95 Nb (ppm) 0 0 0 0 0 0 Rb (ppm) 90 103 173 . 107 17 33 Sr (ppm) 72 0 68 63 30 80 Y (ppm) 0 13 37 0 0 0 Zr (ppm) 203 119 183 222 127 98 Tota l (wt%) 98.3 99.8 100.9 99.5 99.8 98.3 F e 2 0 3 T (wt%) 3.1 11.4 5.2 6.1 7.3 3.0 ICP analyses- set 1 Nb (ppm) 4 9 14 4 10 2 Ba (ppm) 692 454 478 414 107 78 La (ppm) 41 22 48 34 34 34 Ce (ppm) 73.0 38.3 94.1 66.0 68 61.i Th (ppm) 13.3 3.7 18.1 9.6 15 4.1 ICP analyses- set 2 Be (ppm) 0.3 0.6 4.4 1.1 1 O.i Co (ppm) 12 42 15 12 20 11 Cr (ppm) 35 33 73 42 63 31 Cu (ppm) 21 300 26 15 26 19 La (ppm) 35 16 47 32 32 32 Ni (ppm) 28 53 33 29 42 22 V (ppm) 42 420 85 49 86 35 Yb (ppm) 0.9 3.1 2.7 1.8 2.1 3 . : Zn (ppm) 58 55 68 67 95 59 195 Table E . 2 (continued) 0 Sample No. BL18-10 BL43-7 BL47-11 BL45-4 BL47-6 BLS-Sd 1 XRF analyses SiC-2 (wt%) 1.9 44.5 49.9 58.2 53.8 TiC-2 (wt%) 0.02 0.45 0.52 0.32 0.57 A 1 2 0 3 (wt%) 0.1 10.1 11.2 6.5 13.1 C r 2 0 3 (wt%) 0.00 0.01 0.00 0.00 0.01 F e 2 0 3 (wt%) 5.0 14.1 7.1 0.4 0.8 FeO (wt%) 0.7 3.1 2.3 1.9 4.8 MnO (wt%) 1.27 0.21 0.17 0.19 0.08 MgO (wt%) 18.27 5.55 6.75 5.82 6.93 CaO (wt%) 28.18 5.67 5.19 8.39 4. 32 Na 2 0 (wt%) 0.0 0.0 1.5 0.0 2.9 K 2 0 (wt%) 0.00 5.08 5.30 3.62 1.92 H 2OT (wt%) 0.2 2.1 1.9 1.0 3.3 C0 2 T (wt%) 44.2 7.6 7.4 12.8 6.2 P2O5 (wt%) 0.00 0.28 0.16 0.15 0.18 S (wt%) 0.00 0. 03 0.00 0.00 0.13 Ba (ppm) 69 1896 290 323 127 Nb (ppm) 0 3 0 0 0 Rb (ppm) 0 104 43 94 66 Sr (ppm) 51 0 41 37 96 Y (ppm) 0 0 15 0 0 Zr (ppm) 0 137 151 256 155 T o t a l (wt%) 97.0 99.0 100.6 99.5 99.1 F e 2 0 3 T (wt%) 5.8 17.6 9.7 2.5 6.1 ICP analvses- set l Nb (ppm) <1 8 6 2 7 4 Ba (ppm) 38 2120 268 321 132 420 La (ppm) 4 78 41 26 30 34 Ce (ppm) 9.7 138. 73.3 52.2 55.4 67.9 Th (ppm) 0.2 12.6 14.8 7.0 16.6 9.4 ICP analyses-•set 2 Be (ppm) 0.5 1.5 1.2 0.7 2.3 1.0 Co (ppm) 22 22 13 8 14 10 Cr (ppm) 32 41 52 28 61 35 Cu (ppm) 27 32 20 16 100 10 La (ppm) 8 73 36 26 30 28 Ni (ppm) 19 27 31 19 71 24 V (ppm) 15 86 62 30 52 49 Yb (ppm) 1.4 1.7 2.5 1.3 1.5 1.7 Zn (ppm) 55 43 65 40 62 36 1: su f f ix "d" denotes dupl icate sample; whole rock analys i s not performed on sample BL3-5d. 196 T a b l e E . 3 B r i e f hand sample descr ipt ions for Sample Sui te 2, evaluated for major and minor oxides, trace and rare earth elements, cons i s t ing of 20 samples from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Sample locat ions are shown on Map 2 ( in pocket) . Results are tabulated i n Tables E.4A and E.4B. Uni t Sample No. (Lat .N , Long.W) Sample Descr ipt ion BL3-7 ( 1 3 9 ° 0 8 . 5 5 / N , 6 4 ° 5 3 . 1 6 ' W ) F a i r c h i l d Lake Group: brown weathering pink dolostone; c a l c i t e v e i n l e t s BL4-7 ( 1 3 9 ° 0 9 . 3 1 / N , 6 4 ° 5 3 . 9 2 ' W ) F a i r c h i l d Lake Group: i n t e r l a y e r e d brown weathering buff dolomite and f ine-gra ined pale q u a r t z i t e BL11-10 ( 1 3 9 ° 1 1 . 8 2 / N , 6 4 ° 5 3 . 7 4 ' W ) BL53-4 ( 1 3 9 ° 3 6 . 9 2 / N , 6 4 ° 5 0 . 4 0 / W ) F a i r c h i l d Lake Group: densely fractured white q u a r t z i t e ; abundant carbonate v e i n l e t s ; trace cha lcopyr i te and p y r i t e Banded i r o n formation: interbedded, t h i c k l y laminated hematite and red f ine grained s i l i c a BL1-1 ( 1 3 9 ° 0 8 . 2 4 / N , 6 4 ° 5 3 . 0 9 ' W ) BL12-25 ( 1 3 9 ° 1 4 . 0 9 / N , 6 4 ° 5 3 . 7 6 / W ) Quartet Group: dark grey f ine grained sandstone; hematite v e i n l e t s Quartet Group: interbedded maroon mud-stone and f ine grained calcareous sandstone BM1 BL25-5 ( 1 3 9 ° 0 8 . 8 7 # N , 6 4 ° 5 3 . 4 2 / W ) BL33-3 ( 1 3 9 ° 1 0 . 2 8 / N , 6 4 ° 5 4 . 4 1 ' W ) G i l l e s p i e Lakes Group: tan weathering pale grey ' c r a c k l e d ' dolostone; i r o n carbonate cemented Monol i th ic "crackle brecc ia": pink dolostone; f o l i a t i o n defined by p lates of cha lcopyr i te (1-2%); white carbonate cement; trace p y r i t e BM1 BL40-11 ( 1 3 9 ° 1 0 . 4 7 ' N , 6 4 ° 5 4 . 1 4 ' W ) Monol i th ic brecc ia : pink to maroon dolostone fragments; carbonate matrix with accessory quartz; abundant s e r i c i t e BM1 BL40-27 ( 1 3 9 ° 1 0 . 7 7 ' N , 6 4 ° 5 4 . 1 8 ' W ) Monol i th ic brecc ia : weakly s i l i c i f i e d pink dolostone; open space f i l l i n g textures T a b l e E . 3 (continued) Uni t Sample : (Lat .N , NO. Long.W) Sample Descr ipt ion BM1 BL54-1 ( 1 3 9 ° 3 6 6 4 ° 5 0 .10'N, .23'W) Monol i th ic b r e c c i a : pale s i l i c e o u s dolostone fragments; carbonate matrix with minor c h l o r i t e BHcb BL3-4 ( 1 3 9 ° 0 8 6 4 ° 5 3 .55'N, .12'W) H e t e r o l i t h i c b r e c c i a : white carbonate matrix; c l a s t s are pink dolostone, grey and maroon mudstone and pale green guarz i t e ; t race cha lcopyr i te BHcb BL10-7 ( 1 3 9 ° 1 6 6 4 ° 5 1 .04'N, . 60'W) H e t e r o l i t h i c b r e c c i a : angular fragments of green and brown mudstone, grey sandstone, black a r g i l l i t e , pink dolostone, white quartz i t e and hematite s ta ined i n t r u s i v e ; carbonate matrix with minor quartz; trace specu lar i t e and p y r i t e BHcb BL39-4 ( 1 3 9 ° 1 0 6 4 ° 5 4 .03'N, .03'W) H e t e r o l i t h i c b r e c c i a : angular pink and maroon mudstone, pink dolostone and red j a s p i l l i t e fragments; fragment supported; minor white c a l c i t e matrix BHcb BL40-29 ( 1 3 9 ° 1 0 6 4 ° 5 4 .91'N, .33'W) H e t e r o l i t h i c b r e c c i a : s i l i c i f i e d ; pink dolostone and black a r g i l l i t e c l a s t s ; open space f i l l i n g textures BHcb BL45-5 ( 1 3 9 ° 2 3 6 4 ° 4 4 .25'N, .75'W) H e t e r o l i t h i c b r e c c i a : pink dolostone and black a r g i l l i t e c l a s t s ; dark grey muddy matrix; trace specu lar i t e BHcb BL49-4 ( 1 3 9 ° 1 6 6 4 ° 4 5 .45'N, .68'W) H e t e r o l i t h i c b r e c c i a : pink dolostone and green mudstone c l a s t s i n a carbonate -r ich matrix; trace c h l o r i t e and i r o n carbonate BHh BL48-3 ( 1 3 9 ° 1 8 6 4 ° 4 4 •97'N, .37'W) H e t e r o l i t h i c b r e c c i a : hematite matrix; subangular fragments of pink dolostone, grey dolostone, jasper and black a r g i l l i t e BHcl BL32-5 ( 1 3 9 ° 1 0 6 4 ° 5 3 .88'N, .24'W) H e t e r o l i t h i c b r e c c i a : c h l o r i t e with l e s sor hematite matrix; pink s i l t y dolostone and mafic i n t r u s i v e fragments 198 T a b l e E . 3 (continued) Uni t Sample ( L a t . N , NO. Long.W) Sample Descr ipt ion BHcl BL46-10 ( 1 3 9 ° 2 1 6 4 ° 4 4 .12'N, .89'W) H e t e r o l i t h i c b r e c c i a : c h l o r i t e - r i c h matrix; pink dolostone, green mudstone, jasper and minor black a r g i l l i t e fragments; trace specu lar i t e T a b l e E .4A Major and minor element oxides plus barium for seven se lected Proterozo ic rock specimens from sample su i t e 2 from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . Sample locat ions are on Map 2 ( in pocket) . Analyses, by whole rock ICP techniques, were by ACME A n a l y t i c a l Laborator ies , Vancouver. Sample No. BL3-7 BL4-7 BL53-4 BL1-1 BL12-25 BL25-5 BL48-3 SiC-2 (wt%) 33.11 45.42 57.61 52.03 48.68 8.26 51.86 T i 0 2 (wt%) 0.24 0.42 0.03 1.15 0.41 0.03 0.51 A 1 2 0 3 (wt%) 5.22 8.15 0.54 14.12 10.20 0.96 11.51 C r 2 0 3 (wt%) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 F e 2 0 3 T (wt%) 2.62 7.32 29.24 9.84 8.91 2.32 10.73 MnO (wt%) 0.29 0.26 0.15 0.26 0.43 0.55 0.17 MgO (wt%) 10.96 8.49 2.30 4.71 5.30 18.82 5.73 CaO (wt%) 16.75 9.91 4.00 6.68 7.84 6.07 4.75 Na 20 (wt%) 0.05 0.05 0.05 2.25 0.05 0.05 3.10 K 2 0 (wt%) 3.40 2 .40 0.10 2.05 4.80 0.45 1.55 P2O5 (wt%) 0.18 0.16 0.07 0.11 0.16 0.04 0.15 Ba (ppm) 392 251 23 666 1159 146 151 LOi (wt%) 27.1 17.3 5.9 6.3 13.0 42.5 9.8 T o t a l (wt%)100.01 99.94 100.00 99.64 100.01 100.09 99.90 Table E.4B Oxides, trace and rare earth elements for sample suite 2 from Proterozoic rocks, Coal Creek I n l i e r , southern Ogilvie Mountains, west-central Yukon Territory. Sample locations are on Map 2 (in pocket). A l l analyses, by ICP techniques, were by ACME Analytical Laboratories, Vancouver. Element Sample number BL3-7 BL4-7 BL11-10 BL53-4 BL1-1 BL12-25 BL25-5 BL33-3 Mo (ppm) 1 2 1 31 1 2 1 2 cu (ppm) 2 6 3508 37 81 1 14 9162 Pb (ppm) 2 2 34 5 69 4 2 2 Zn (ppm) 6 20 23 2 393 3 8 16 Ag (ppm) 0.3 0.3 0.5 0.1 0.4 0.3 0.1 0.7 Ni (ppm) 3 23 5 12 30 3 1 2 Co (ppm) .3 22 2 5 27 4 3 3 Mn (ppm) 2092 1829 1270 1128 1465 3174 3774 4808 Fe (wt%) 1.46 3.94 1.14 14.24 4.64 4.70 1.36 3 .22 As ppm) 3 4 9 3 12 5 3 2 U (ppm) 6 5 5 5 5 5 5 5 Th (ppm) 6 5 1 2 5 13 1 9 Sr (ppm) 26 16 3 5 50 30 45 18 Cd (ppm) 1 1 1 1 1 1 1 1 Sb (ppm) 2 2 2 3 4 5 5 2 Bi (ppm) 2 3 3 2 2 2 4 2 V (ppm) 4 41 3 22 194 18 3 7 Ca (wt%) 13.52 7.42 2.01 2.82 3.74 6.14 19.02 9.28 P wt%) .06 .05 .01 .02 .04 .06 .019 .05 La (ppm) 25 8 2 2 9 51 4 259 Cr (ppm) 7 15 5 3 63 15 3 5 Mg (wt%) 6.23 4.41 0.91 1.23 2.14 2.53 9.33 3.15 Ba (ppm) 56 54 17 6 263 476 51 103 T i (wt%) .01 .01 .01 .01 .15 .04 .01 .01 B (ppm) 2 2 2 2 6 7 11 2 Al (wt%) 0.16 1.41 0.04 0.14 1.96 0.54 0.08 0.22 Na (wt%) 0.05 0.05 0.01 0.02 0.14 0.04 0.03 0.05 K wt%) 0.09 0.15 0.01 0.01 0.29 0.37 0.02 0.19 W 1 1 1 2 1 2 1 1 Au [PPb) 7 2 4 3 2 2 2 3 Rare earth elements Be rppm) 10 10 10 10 10 10 10 10 Rb (ppm) 88 96 4 2 77 173 11 115 Y (ppm) 20 37 2 6 19 21 18 38 Zr 'ppm) 91 116 3 13 79 127 31 73 Nb (ppm) 12 8 5 7 10 5 5 6 Sn (ppm) 4 2 3 1 3 6 1 5 Cs (ppm) 2 2 2 2 4 6 2 2 La (ppm) 33 31 1 3 15 61 8 348 Ce (ppm) 59 55 3 5 29 86 20 497 Pr (ppm) 4 5 1 1 2 5 1 32 Nd (ppm) 32 35 1 4 10 29 11 209 Sm (ppm) 41 24 1 1 9 23 1 233 Eu (ppm) 1 1 1 1 1 1 1 6 Gd (ppm) 3 4 1 1 2 3 2 15 Tb (ppm) 1 1 1 1 1 1 1 1 Dy (ppm) 3 5 1 1 3 2 2 5 Ho (ppm) 1 1 1 1 1 1 1 1 Er (ppm) 2 3 1 1 2 2 1 2 Tm (ppm) 1 1 1 1 1 1 1 1 Yb (ppm) 3 3 1 1 3 2 1 1 LU (ppm) 1 1 1 1 1 1 1 1 Hf (ppm) 2 2 1 1 3 4 1 1 Ta (ppm) 1 1 1 1 1 1 1 1 W (ppm) 2 3 2 2 2 2 2 2 Th (ppm) 7 8 1 1 4 13 2 13 U (ppm) 2 3 1 2 1 6 1 3 Table E .4B (continued) Element Sample number BL40-11 BL40-27 BL54-1 BL3-4 BL10-7 BL39-4 BL40-29 BL45-5 MO [ppm) 2 1 1 1 1 2 1 1 CU [ppm) 50 14 1 637 13 80 120 2 Pb [ppm) 2 2 2 2 5 4 2 3 Zn [ppm) 9 3 5 16 11 33 13 11 Ag [ppm) 0.2 0.1 0.2 0.2 0.1 0.2 0.1 0.2 Ni [ppm) 2 2 18 21 2 10 7 16 Co [ppm) 2 2 3 8 6 6 6 5 Mn [ppm) 2623 2221 1081 1487 3522 3454 2723 723 Fe [wt%) 1.65 1.59 2.46 3.27 1.45 4.90 1.98 2.40 As ppm) 3 2 2 5 5 8 2 5 U [ppm) 7 5 5 6 5 5 5 5 Th [ppm) 7 1 13 8 1 3 1 10 Sr [ppm) 28 8 9 35 11 35 11 22 Cd [ppm) 1 1 1 1 1 1 1 1 Sb [ppm) 2 2 2 2 2 2 2 2 Bi [ppm) 2 2 2 2 3 2 2 2 V [ppm) 19 5 18 21 5 23 7 14 ca [wt%) 1.41 5.96 4.50 4.47 7.72 11.40 1 7.67 5.88 P wt%) .04 .06 .06 .06 .02 .03 .01 .07 La ppm) 24 3 26 6 2 9 3 14 Cr [ppm) 23 3 12 . 14 4 9 4 10 Mg [wt%) 5.47 2.29 3.05 3.18 3.52 5.44 3.50 3.37 Ba [ppm) 19 77 361 395 24 1189 9 52 T i wt%) .01 .01 .01 .01 .01 .02 .01 .01 B PPm) 2 2 2 2 2 2 2 2 Al [wt%) 0.40 0.03 1.16 1.32 0.04 0.39 0.30 0.77 Na wt%) 0.07 0.04 0.03 0.04 0.04 0.05 0.05 0.04 K wt%) 0.04 0.02 0.20 0.21 0.01 0.10 0.01 0.12 w [ppm) 1 1 1 1 1 2 1 2 AU (PPb) 1 6 1 1 4 4 2 1 Rare earth element oackaae Be [ppm) 10 10 10 10 10 10 10 10 Rb [ppm) 16 11 194 113 3 46 10 99 Y [ppm) 24 4 16 15 4 20 6 17 Zr [ppm) 75 20 166 120 10 55 10 195 Nb [ppm) 11 9 15 9 2 8 7 8 Sn (ppm) 5 1 5 6 1 5 1 2 Cs (ppm) 2 2 2 2 2 2 2 2 La (ppm) 34 4 80 25 3 25 7 31 Ce (ppm) 57 9 168 46 6 47 13 51 Pr (ppm) 5 1 13 3 1 4 1 4 Nd (ppm) 30 6 95 19 3 24 5 28 Sm (ppm) 29 1 133 15 9 35 1 33 Eu (ppm) 1 1 1 1 1 1 1 1 Gd (ppm) 3 1 5 2 1 2 1 2 Tb (ppm) 1 1 1 1 1 1 1 1 Dy (ppm) 4 1 2 2 1 2 1 2 Ho (ppm) 1 1 1 1 1 1 1 1 Er (ppm) 1 1 3 2 1 1 1 2 Tm (ppm) 1 1 1 1 1 1 1 1 Yb (ppm) 2 1 2 1 1 1 1 3 Lu (ppm) 1 1 1 1 1 1 1 1 Hf (ppm) 1 1 4 4 1 1 1 4 Ta (ppm) 1 1 1 1 1 1 1 1 W (ppm 2 2 2 2 2 2 2 2 Th (ppm) 4 1 15 11 1 4 1 9 U (ppm) 2 2 2 1 1 2 1 3 Table E.4B (continued) Element sample number BL49-4 BL48-3 BL32-5 BL46-10 Mo (ppm) 1 1 1 1 Cu [ppm) 3 11 57 3 Pb (ppm) 2 2 2 2 Zn (ppm) 10 27 24 25 Ag (ppm) 0.1 0.3 0.1 0.2 Ni (ppm) 6 18 46 25 Co (ppm) 2 6 10 11 Mn (ppm) 2049 1282 183 401 Fe wt%) 2.15 4.94 5.17 4.00 As ppm) 2 9 2 5 U rPPm) 5 5 5 5 Th 'ppm) 6 14 8 13 Sr ppm) 10 19 2 11 Cd (ppm) 1 1 1 1 Sb (ppm) 2 2 2 2 Bi (ppm) 2 2 2 2 V (ppm) 12 28 70 37 Ca (wt%) 4.98 3 .70 .41 1.61 P (wt%) .04 .05 .06 .08 La (ppm) 12 38 3 44 Cr (ppm) 8 26 38 27 Mg (wt%) 3.12 3.30 3.00 4.84 Ba (ppm) 11 72 71 277 T i (wt%) . 01 .02 .02 .02 B (ppm) 2 2 2 2 Al (ppm) 1. 00 1.36 2.31 2.53 Na (wt%) 0.03 0.05 0.02 0.01 K (wt%) 0.12 0.08 0.13 0.19 w (ppm) 2 2 1 1 AU [PPb) 4 1 1 1 Rare earth element Dackaae Be (ppm) 10 10 10 10 Rb (ppm) 84 35 59 69 Y (ppm) 8 23 6 26 Zr 'ppm) 229 142 276 177 Nb 'ppm) 8 12 13 13 Sn 'ppm) 3 7 6 2 Cs (ppm) 2 2 3 2 La (ppm) 13 41 5 54 Ce (ppm) 29 75 8 91 Pr (ppm) 2 6 1 8 Nd (ppm) 17 39 2 41 Sm (ppm) 1 22 5 37 Eu (ppm) 1 1 1 1 Gd (ppm) 1 4 1 3 Tb (ppm) 1 1 1 1 Dy (ppm) 1 4 1 2 Ho (ppm) 1 1 1 1 Er (ppm) 1 2 1 2 Tm (ppm) 1 1 1 1 Yb (ppm) 1 3 1 2 Lu (ppm) 1 1 1 1 Hf (ppm) 4 3 7 4 Ta (ppm) 1 1 1 1 w (ppm) 2 2 2 2 Th (ppm) 6 13 13 11 u (ppm) 2 3 3 3 202 Table E .5 B r i e f hand sample descr ip t ions for Sample Suite 3 from the Coal Creek I n l i e r , southern O g i l v i e Mountains, west-central Yukon T e r r i t o r y . This su i te of 22 samples ( inc luding duplicates) was evaluated for rare earth elements by instrumental neutron a c t i v a t i o n ana lys i s (INAA) Sample locat ions are shown on Map 2 ( in pocket) . Results are tabulated i n Table E . 6 . Unit Sample No. Sample Descr ipt ion (Lat .N , Long.W) 1 BL33-1 ( 1 3 9 ° 1 0 . 6 4 ° 5 4 . 47'W, 14'N) Banded i r o n formation: t h i n l y bedded to laminated jasper with minor layers of c r y s t a l l i n e carbonate and traces of malachite 2 BL1-1 ( 1 3 9 ° 0 8 . 6 4 ° 5 3 . 24'W, 09'N) Quartet Group: interbedded grey f ine grained sandstone and black a r g i l l i t e 6 BL27-6 ( 1 3 9 ° 0 8 . 6 4 ° 5 4 . 55'W, 74'N) M u l t i l i t h i c conglomerate: c l a s t s of q u a r t z i t e , dolomite, pink s i l t y dolostone, green mudstone, jasper and sp ecu lar i t e ; carbonate matrix BM1 BL26-2 ( 1 3 9 ° 0 7 . 6 4 ° 5 4 . 04 'W, 19'N) Monol i th ic b r e c c i a : pink s i l t y dolostone with rare green a r g i l l i t e c l a s t s : matrix i s carbonate BM1 BL33-3 ( 1 3 9 ° 1 0 . 6 4 ° 5 4 . 28'W, 41'N) Monol i th ic b r e c c i a : f o l i a t e d , pink s i l t y dolomite c l a s t s : 1% cha lcopyr i te BM1 BL54-1 ( 1 3 9 ° 3 6 . 6 4 ° 5 0 . 10'W, 23'N) Monol i th ic b r e c c i a : c h l o r i t e - and carbonate-r ich fragmental: pale s i l i c e o u s dolostone fragments BM1 TW208A(P) ( 1 3 9 ° 0 9 . 1 2 ' W , 6 4 ° 5 3 . 6 8 / N ) Brecc ia matrix: c h l o r i t e - r i c h separate of matrix from monol i thic b r e c c i a ; pink s i l i c i f i e d dolostone c l a s t s BM4 BL50-6(P) ( 1 3 9 ° 1 2 . 9 8 / W , 6 4 ° 4 6 . 0 2 / N ) Monol i th ic b r e c c i a : dark grey angular laminated mudstone fragments; c l a s t supported; minor carbonate matrix BHcb BL18-10(P) ( 1 3 9 ° 2 3 . 1 3 / W , 6 4 ° 5 2 . 4 6 / N ) Brecc ia matrix: red , coarse grained carbonate from h e t e r o l i t h i c brecc ia BHcb BL35-4 ( 1 3 9 ° 0 9 . 6 4 ° 5 3 . 09'W, 71'N) Layered h e t e r o l i t h i c b r e c c i a : c l a s t s are s i l i c i f i e d pink s i l t y dolostone, purple mudstone,quartzite and mafic i n t r u s i v e ; matrix i s carbonate-r ich with l e s ser c h l o r i t e and hematite 203 Table E.5 (continued) Unit Sample No. Sample Descr ipt ion (Lat .N , Long.W) BHcb BL87-70 ( 1 3 9 ° 1 6 . 6 4 ° 5 0 . 54'W, 99'N) H e t e r o l i t h i c b r e c c i a : c l a s t s are black a r g i l l i t e and gray sandstone of the Quartet Group, and pink s i l t y dolostone pale pink-orange-white s i l i c a and green a r g i l l i t e ; matrix i s dominantly buff , medium grained c r y s t a l l i n e carbonate BHh BL24-12 ( 1 3 9 ° 1 2 . 6 4 ° 5 3 . 89'W, 56'N) Massive, layered, h e t e r o l i t h i c hematite b r e c c i a : c l a s t s are mainly pink dolostone BHh BL34-15 ( 1 3 9 ° 1 7 . 6 4 ° 5 1 . l l ' W , 26'N) Hematite-quartz b r e c c i a : traces of cha lcopyr i te BHh BL43-7(P) ( 1 3 9 ° 2 5 . 2 5 ' W , 6 4 ° 4 4 . 1 4 / N ) Layered, h e t e r o l i t h i c b r e c c i a : c l a s t s of pink s i l t y dolostone, hematized g r i t t y sediments, b lack to gray a r g i l l i t e and massive hematite; matrix i s composed dominantly of carbonate and hematite with minor c h l o r i t e BHcl BL46-10 ( 1 3 9 ° 2 1 . 6 4 ° 4 4 . 12'W, 89'N) H e t e r o l i t h i c b r e c c i a : rounded c l a s t s of pink s i l t y dolostone, l i g h t green a r g i l l i t e and uncommon jasper; matrix i s c h l o r i t e - r i c h with abundant accessory carbonate and minor hematite BHcl BL50-2 ( 1 3 9 ° 1 4 . 6 4 ° 4 5 . 40'W, 78'N) H e t e r o l i t h i c b r e c c i a : fragments, general ly smaller than 1 cm, are black to marroon a r g i l l i t e , and spotted pink dolostone; wavy laminated c h l o r i t e - and hemat i te -r ich matrix; minor carbonate CARB MS-II ( 1 3 9 ° 1 8 . 6 4 ° 5 1 . 90'W, 81'N) White, massive coarse grained in t rus ive carbonate (vein) mater ia l P - l (STANDARD) Coast Mountains granodior i t e 1. Codes at end of sample are: (D) = dupl i ca te sample; (P) = pulver ized sample (whole rock (XRF) by Geolog ica l Survey of Canada). P - l (STANDARD) = standard sample provided by Dick Armstrong, Geochronology Laboratory, The U n i v e r s i t y of B r i t i s h Columbia. T a b l e E . 6 Rare earth element (REE) and trace element data for 22 samples (including duplicates) froa the Coal Creek Inlier, Ogilvie Mountains, nest-central Yukon Territory (refer to Table E.5). All values are in parts per Billion (ppm). Analyses Mere by instrumental neutron activation analysis (INAA), except where noted, and detection limits and precision of data is presented Tables E.9 and E. 10. The data is normalized to chondrite and upper crust (shale) in Table 4.1. ELEMENT' BL33-1 6L1-1 6L27-6 6L26-I 6L33-3 BL54-I TW-206A 6L50-6 SAMPLE BL18-10 NUMBER BL35-4 I II BL87-70 8L24-I2 BL34-15 I II 6L43-7 6L46-10 I II BL50-2 MS-1A P-l R a r e e a r t h e l e m e n t s ' La 3.2 56.7 60.3 21.3 34.4 102 17.5 10.5 51.3 4.3 373 376 19.4 91.9 11.7 13.6 66.2 34.6 29.8 51.7 120.0 12.5 Ce 7 106 106 40 35 168 35 22 99 11 211 224 38 106 36 40 136 63 54 94 203 24 Pr (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 (50 Nd (10 44 45 20 18 63 16 (10 42 (10 131 129 22 26 21 26 50 28 25 41 92 14 Sm 1.5 7.6 7.2 3.1 4.5 10.6 2.6 1.6 6.6 2.5 20.6 20.7 4.1 3.1 9.2 11.1 7.9 4.6 3.6 6.3 20.7 2.6 Eu (1 1 2 (1 (1 2 (1 (1 1 (1 6 6 1 4 4 6 3 (1 (1 3 (1 6d (200 (200 (200 (200 (200 (200 (230 (200 (210 (200 (200 (200 (200 (200 (1300 (2200 (200 (200 (200 (200 (200 ( 2 * Tb (1 (1 (1 (1 (1 1 (1 (1 (1 (1 2 2 (1 (1 6 7 (1 (1 (1 (1 3 . (1 Dy 1 5 4 2 3 6 2 1 5 2 6 7 5 (1 32 37 4 3 2 4 17 3 Ho (t (1 (1 (1 (1 (1 (1 (1 (1 (1 (1 (1 (1 (t 6 7 (1 (1 (1 i l (1 i l Er (100 (100 (100 (100 (100 (120 (100 (100 (100 (230 (100 (100 (100 (100 (100 (100 (100 (100 (100 (100 (100 100 Ti (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 1.1 1.0 (0.5 (0.5 (0.5 (0.5 (0.5 (0.5 Vb (0.5 2.4 1.5 1.4 1.5 1.6 1.3 1.1 2.5 1.3 3.3 3.6 1.9 (0.5 6.5 7.9 1.9 1.6 1.4 2.1 2.4 l.S Lu (0.1 0.4 0.2 0.2 0.2 0.3 0.2 0.2 0.4 0.2 0.4 0.4 0.3 (0.1 0.6 0.7 0.2 0.2 0.2 0.2 0.2 0.3 TOTAL 12.7 223.3 226.2 88.0 140.5 354.7 76.8 36.4 207.8 21.3 755.5 768.9 91.7 231.0 134.1 157.3 289.2 135.0 116.2 201.3 463.3 56.5 La/Lu 132 142 302 107 172 340 67.5 52.5 126 21.5 933 940 65 )920 19.5 19.4 431 173 149 258 600 42 La/Sa 2.1 7.3 8.4 6.9 7.6 9.6 6.3 6.6 7.6 1.7 18 16 4.7 30 1.3 1.2 11 7.5 7.6 6.2 5.6 4.5 Tb/Lu nd (2.5 (5.0 (5.0 (5.0 3.3 (5.0 (5.0 (2.5 (5.0 5.0 5.0 (3.3 nd 10 10 (5.0 (5.0 (5.0 (5.0 15 (3.3 Eu/Sm (0.67 0.13 10 (0.32 (0.22 0.19 (0.36 (0.6 0.15 (0.4 15 15 0.2 1.3 0.43 0.54 15 (0.22 (0.26 0.32 0.14 (0.36 T r a c e e l e m e n t s * Sc 1.17 13.10 13.10 5.21 6.31 7.35 14.50 16.10 15.6 14.40 21.00 20.70 11.0 1.79 0.91 1.11 9.37 10.50 10.70 11.30 0.63 i 10.70 Th 0.6 21.4 11.3 8.5 12.2 13.2 16.3 13.4 19.2 (0.5 6.1 7.9 8.7 1.6 (0.5 (0.5 12.5 12.4 15.0 16.1 (0.5 3.6 U (1 4 5 3 4 3 5 2 4 2 2 2 2 3 45 60 3 3 4 3 (1 1 Co* 9 6 21 2 2 2 3 21 9 10 12 8 17 3 4 5 10 9 11 4 (1 5 CuJ 575 24 141 3 5 5910 2 19 18 14 333 344 11 494 115 172 17 4 2 3 485 67 Ba* (20 460 6500 320 640 390 700 440 500 (20 910 940 350 (20 (20 (20 2100 750 360 640 30 660 1: I = first sample of a duplicate pair; II = second sample of a duplicate pair. 2: ( denotes less than quoted detection limit (see also Appendix E.2). 3: Atomic absorption Has used for Co and Cu analyses. ^ 4: X-ray fluorescence was used for Ba analysis. o Table E.7 Re la t ive p r e c i s i o n for Suite 1 ICP data (Table E.2) based on one r e p l i c a t e ana lys i s of sample BL3-5. Element Cone. Std . dev. Prec. (ppm) (1 sigma) (%) ICP analyses-set 1 Nb 4 0 0 Ba 417 3 7.2 La 34 0 0 Ce 67 1.0 1.5 Th 9.5 0.1 1.0 ICP ana lyses - se t 2 Be 1.1 0.1 9.0 Co 11 1 9.0 Cr 39 4 10 Cu 13 3 23 La 30 2 6.7 Ni 27 3 11 V 49 0 0 Yb 1.8 0.1 5.6 Zn 52 16 31 Table E.8 Lower detect ion l i m i t s for REE instrumental neutron a c t i v a t i o n analyses. Element Lower detect ion l i m i t La Lanthanum 0.5 Ce Cerium 5 Pr Praseodymium 50 Nd Neodymium 10 Sm Samarium 0.1 Eu Europium 1 Gd Gadolinium 200 Tb Terbium 1 Dy Dysprosium 1 Ho Holmium 1 Er Erbium 100 Tm Thulium 0.5 Yb Ytterbium 0.5 Lu Lutetium 0.1 Sc Scandium 0.05 Th Thorium 0.5 U Uranium 1 1 A l l values are i n ppm 206 T a b l e E . a R e l a t i v e p r e c i a i o n o f REE d a t a f r o m INAA ( T a b l e E . 6 ) b a s e d o n r e p l i c a t e a n a l y s e s o f f o u r s a m p l e s . L a C e Nd C o n e . ' s t d . d e v . ' P r e c . 1 C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . BL26-2 27.3 6.1 22 37 3 8.1 19 1 5.2 BL.35-4 374 2 •0.5 217 6 2.8 130 1 0.1 BL34-15 12.6 0.9 7. 1 38 2 5.3 23 3 13 BL46-10 32.2 2.4 7.4 58 5 8. 6 26 2 7.7 R e l a t i v e P r e c i s i o n 9.3 6.2 6.5 Sm E u Tb C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . BL26-2 3.8 0.7 18 N / D N /D BL35-4 20.7 0.1 0.1 6 0 0 2 0 0 BL34-15 10.1 0.9 a. 9 5 1 20 6 1 17 BL46-10 4.2 0. 4 9.5 N / D N /D R e i a t i v e P r e c i s i o n 9.1 10 a Dy Ho Tin C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . BL26-2 2 1 50 N / D N /D BL35-4 7 1 14 N / D N / D BL34-15 34 3 a. a 6 1 17 1.0 0.1 10 BL46-10 2 1 50 N/D N / D R e l a t i v e P r e c i s i o n 31 17 10 Y b L u S c C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . BL26-2 1. 4 0. 1 7.1 0.2 0 0 5.76 0 . 55 9. 5 BL35-4 3. 5 0.3 a. 6 0.4 0 0 20.85 0 . 15 0 . 1 BL34-15 7. 2 0.7 9.7 0.6 0.1 17 1.01 0 . 10 10 BL46-10 1.5 0. 1 6.7 0.2 0 0 10.60 0.10 0 . 1 R e l a t i v e P r e c i s i o n 8.0 4.3 4.9 Th U C o n e . s t d . d e v . P r e c . C o n e . s t d . d e v . P r e c . BL26-2 10. 4 1. 9 ia 3 1 33 BL35-4 a.o 0.1 1.3 2 0 0 BL34-15 N / D 52 a 15 BL46-10 13.7 1.3 9.5 3 1 33 R e l a t i v e P r e c i s i o n 9.6 20 1 C o n c e n t r a t i o n (ppm) i s t h e a v e r a g e o f t v o a n a l y s e s ; N / D - b e l o w d e t e c t i o n l i m i t . 2 S t a n d a r d d e v i a t i o n (ppm) a r e 1 e i g r o a . 3 P r e c i s i o n i s i n X Table E.10 Accuracy of REE data (INAA) based on a comparison with the geochemical standard P - l . P - l ( th is study) P - l (Erdman, 1985) s ing l e analys i s mean 1 sigma La 12.5 10.5 0. 28 Ce 24 -Nd 14 -Sm 2.8 2.7 0. 15 Eu - 0.6 0. 06 Dy 3 -Yb 1.9 1.9 0. 12 Lu 0.3 0.3 0. 0 Sc 10.7 8.7 0. 41 Th 3.6 3.7 0. 18 APPENDIX F THE DEVELOPMENT OF RARE EARTH ELEMENT CHEMISTRY AND ITS GEOLOGICAL APPLICATIONS Natural f r a c t i o n a t i o n , the concentration or deple t ion of rare earth elements (REE) i n a rock r e l a t i v e to pr imord ia l mater ia l ( chondr i t i c meteorites) , was discovered i n 1935. Since that time REE geochemical s tudies have focussed on the idea that t h i s f r a c t i o n a t i o n r e f l e c t s the h i s t o r y of the rocks i n which they are found. Rare earth elements can be used as geochemical ind ica tors of the petrogenesis of the rock and can i l l u c i d a t e some processes of formation (Graf, 1984). Several geologic processes y i e l d minerals r i c h i n rare earths . For instance: (1) Magma generated i n CO2 r i c h regions deep wi th in the upper mantle can form carbonat i tes (igneous carbonate rocks ) . Rare earth elements r e a d i l y form strong carbonate complexes i n such magmas (Muecke and Mol l er , 1988) and may be concentrated enough to form economic REE mineral deposits of which the Mountain Pass carbonat i te (Olson et a l . , 1954) i s a wel l known example. (2) G r a n i t i c magmas derived from c r u s t a l mater ia l are enriched i n REEs r e l a t i v e to t h e i r parental rock. Heavy REEs are p r e f e r e n t i a l l y incorporated into ear ly forming 209 c r y s t a l s while the l i q u i d residue and l a t e r phases (e .g . pegmatites) are enriched i n l i g h t REEs (Graf, 1977). (3) Rare earths can also be concentrated i n hydrothermal s o l u t i o n s . In contrast to magmatic mineral formation heavy REEs ra ther than l i g h t ones are p r e f e r e n t i a l l y concentrated i n the l i q u i d residue during c r y s t a l l i z a t i o n (Muecke and M o l l e r , 1988). Apart from being enriched i n heavy and/or l i g h t REEs, the processes mentioned above a lso r e s u l t i n c h a r a c t e r i s t i c REE patterns that can be d iagnost ic of the processes that formed them. The only n a t u r a l l y occurr ing n o n t r i p o s i t i v e REEs are C e 4 + (Piper , 1974) and E u 2 + (Nagasawa and Schnetz ler , 1971). Because of i t ' s d iva lent s ta te , and hence greater s i z e i n comparison to t r i v a l e n t REEs, europium r e a d i l y subst i tutes for B a 2 + i n b a r i t e and S r 2 + i n t y p i c a l c a l c i c p lag ioc lase and K- fe ldspar (Taylor and McLennan, 1985). In c e r t a i n rocks t h i s fac tor may produce r e l a t i v e europium enrichment (pos i t ive Eu anomaly) or europium deplet ion (negative Eu anomaly) with respect to the other REEs. V i r t u a l l y a l l post-Archean c l a s t i c sedimentary rocks are character ized by a negative Eu anomaly of s i m i l a r magnitude and no common sedimentary rock i s character ized by Eu enrichment (Taylor and McLennan, 1985). Cerium i s s trongly depleted i n sea water because the s table Ce ion i s C e 4 + . Chemical p r e c i p i t a t e s (sediments) that form on the ocean f l o o r have a s i g n i f i c a n t component of 210 sea water and t h i s i s r e f l e c t ed i n the REE pattern that show a r e l a t i v e deple t ion of Ce. Hydrothermal so lut ions expressed from the ocean bottom to mix with sea water p r i o r to p r e c i p i t a t i o n may a l so , depending on the degree of mixing, r e f l e c t the sea water component i n the REE pat tern . In marine carbonates, a d i s t i n c t Ce deple t ion i s common, a lso r e f l e c t i n g the Ce deplet ion i n sea water r e l a t i v e to other REEs. C l a s t i c sedimentary rocks do not share t h i s c h a r a c t e r i s t i c . Not long a f t er natural p a r t i t i o n i n g of REEs was discovered, Goldschmidt (1954) proposed that the homogenizing e f fec ts of sedimentary processes should r e s u l t i n nearly constant REE d i s t r i b u t i o n s i n sedimentary rocks . Although there are some sedimentary environments that produce rocks with a s i g n i f i c a n t v a r i a b i l i t y i n REE d i s t r i b u t i o n , REE patterns for average sediments are remarkably s i m i l a r . Haskin et a l . (1968) suggested that a composite of North American shales (NASC) was representat ive of the upper cont inenta l c r u s t . Other such composites of European Paleozoic shales (ES; Minami, 1935; i n Taylor and McLennan, 1985) and post-Archean shales from A u s t r a l i a (PAAS; Nance and Tay lor , 1976) are remarkably s i m i l a r to NASC and r e f l e c t the average REE composition of the exposed c r u s t . The REE concentrations i n q u a r t z - r i c h sedimentary rocks are t y p i c a l l y very low, because the mineral quartz harbors low amounts of REEs, but the REE pattern p a r a l l e l s that of t y p i c a l shale . Chondr i t i c meteorites have t o t a l REE concentrations that are low (several ppm) and are general ly thought to be und i f f erent ia ted (or weakly d i f f e r e n t i a t e d ) . Carbonatites , at the opposite end of the spectrum, have t o t a l REE concentrations that range up to several percent and are s trongly d i f f e r e n t i a t e d . APPENDIX G A REVIEW OF WORLD WIDE PROTEROZOIC BRECCIAS FROM THE LITERATURE G . l Wernecke-type Brecc ia Many d e t a i l s of brecc ias i n the Wernecke Mountains ( B e l l , 1986; Laznicka and Gaboury, 1986; Laznicka and Edwards, 1979) are s i m i l a r to OMB. They are described below. An i n t r u s i v e o r i g i n for the genesis of the brecc ias i s widely held ( B e l l , 1986; 1982; 1978; B e l l and Delaney, 1977; Delaney, 1985; 1981; Archer and Schmidt, 1978; Archer et  a l . . 1977; and Morin , 1976), although d e t a i l s i n t h e i r explanations d i f f e r . Some explanations have evolved over time (see for example, B e l l , 1978 vs . B e l l , 1986). Brecc ia occurrences i n the Wernecke Mountains have undergone repeated b r e c c i a t i o n , metasomatism and f a u l t i n g (Laznicka and Gaboury, 1988; Laznicka and Edwards, 1979; Laznicka, 1977). In p a r t i c u l a r the exo t i c - l ook ing fragments are a l t e r e d equivalents of l o c a l l y derived wal lrock . Two mechanisms of formation have been suggested: (1) detachment f a u l t i n g , t r iggered by basement extension (cf . documentation i n the O g i l v i e Mountains by Thompson, 1986), or (2) large , underly ing and unexposed i n t r u s i o n (Archer et a l . , 1977) supported by a general ly high Cu and Mo geochemical response over brecc ias (Archer and Schmidt, 1978). G . l . l Steam b r e c c i a t i o n from dykes Laznicka and Edwards (1979) suggested that dykes played an ac t ive r o l e i n the formation of the brecc ias . They invoked a mechanism based upon invas ion of wet, f rac tured zones by magma which reacted with water present i n rock formations to produce f lashes of steam that v i o l e n t l y bol ted toward the surface . These b l a s t s of steam brecc iated wal l rock, transported fragmented m a t e r i a l . I t a lso re su l t ed i n metasomatism and hydrothermal a l t e r a t i o n of a l l rocks i n contact with the f l u i d s . G.1.2 Intrus ive pebble-dyke or diatreme from deep-seated igneous a c t i v i t y B e l l (1978), B e l l and Delaney (1977) and Archer et a l . (1977) suggested that the cros scut t ing breccias are diatremes. They noted s i m i l a r i t i e s between the c r o s s -c u t t i n g brecc ias (psuedoconglomerates of Laznicka and Edwards, 1979) and pebble dykes associated porphyry copper deposits (Bryant, 1968; Bryner, 1961). Normal f a u l t i n g was followed by hydraul i c f r a c t u r i n g or stoping, r e s u l t i n g from ascending f l u i d s (produced from an upper mantle source); co-21k i n t r u s i o n of gabbroic mater ia l followed e a r l i e r developed avenues ( B e l l , 1978). The v a r i e t y of p l a s t i c , s emi -p las t i c and b r i t t l e features observed i n the brecc ias (Laznicka and Edwards, 1979) may have been produced by softening and d i s i n t e g r a t i o n of country rocks by f l u i d s and upward t h r u s t i n g of the brecc ias . [Conversely these features may have been formed by the piercement of u n l i t h i f i e d sediments.] These ascending hydrothermal f l u i d s could a lso create the type of a l t e r a t i o n ( i . e . a l b i t i z a t i o n , hemat i t i za t ion , s i l i c i f i c a t i o n and carbonatization) c h a r a c t e r i s t i c of the breccias and enclosing wal l rock. Archer and Schmidt (1978) in terpreted the brecc ias to have formed by gas streaming i n combination with c r u s t a l a t tenuat ion . They suggested that explosive gas release was generated by deep-seated igneous a c t i v i t y . As evidence, they c i t e d igneous c h a r a c t e r i s t i c s ( i . e . enrichments i n i r o n , copper and molybdenum, and contact a l t e r a t i o n [ inc lud ing f e l d s p a t h i z a t i o n ] ) . This was p a r t i c u l a r l y notable i n the Bonnet Plume River D i s t r i c t brecc ias that look s i m i l a r to brecc ia pipes associated with porphyry copper deposi ts (Johnson and Lowel l , 1961; Bryner, 1961). B e l l and Delaney (1977) and Archer et a l . (1977) in terpre ted the crosscut t ing brecc ias of the Wernecke Mountains as diatremes with offshoots that formed brecc ia s i l l s . Nei ther these, nor brecc ias invest igated by Laznicka and Edwards (1979) d i sp lay the c r i t e r i a assigned to t y p i c a l diatremes by Hearn (1968). G.1.3 Diapir i sm of evapor i t i c mater ia l B e l l (1986) speculated that the Wernecke-type brecc ias were emplaced by progressive i n t r u s i o n or d i a p i r i s m of lower density ( r e l a t i v e l y buoyant) e v a p o r i t i c mater ia l during deposi t ion of Quartet Group and G i l l e s p i e Lake Group. In the S la t s Creek area of the Wernecke Mountains these are l a t e r a l l y extensive and appear to fol low f a u l t splays of the Richardson Faul t A r r a y . B e l l out l ined i n d i v i d u a l brecc ia blocks i n excess of 6 km across . These presumably are too large to be mobi l ized with in a brecc ia p ipe . In t h i s model ascending evapori te d i a p i r s were channeled by major s tructures to form l a t e r a l l y extensive bodies . The evaporites were subsequently d i sso lved and the cav i ty was i n f i l l e d with wal l rock. According to t h i s model these brecc ias were der ived from s a l t - r i c h layers wi th in the F a i r c h i l d Lake Group that penetrated d i a p i r i c a l l y into over ly ing Quartet Group and lower G i l l e s p i e Lake Group s tra t igraphy . G.2 East Arm of Great Slave Lake Exot ic brecc ias from the East Arm of Great Slave Lake (Reinhardt, 1972) occur i n Archean c r y s t a l l i n e basement and the over ly ing Proterozoic sedimentary rocks . Brecc ia fragments were derived from basement and over ly ing 216 Proterozoic sedimentary rocks . The matrix comprises mainly f i n e l y comminuted sedimentary rocks; s i g n i f i c a n t amounts of f e l s i t e occur l o c a l l y . Reinhardt (1972) invoked for b r e c c i a t i o n magmatically derived gases, which suspended and transported s o l i d p a r t i c l e s , as wel l as l o c a l f e l s i t e magma. Regional f a u l t s and a nonconformity between Archean c r y s t a l l i n e basement and the over ly ing sedimentary rocks inf luenced the d i s t r i b u t i o n of the brecc ias . Hydraul ic f r a c t u r i n g could have propagated b r e c c i a t i o n l a t e r a l l y along the nonconformity. Gas streaming or f l u i d i z a t i o n (Reynolds, 1954) resu l ted i n a t t r i t i o n and reduction i n s i ze of entrained fragments with upward transport . Surface venting resu l ted i n decompression and co l lapse of v e r t i c a l conduits , and poss ib ly i n choking of columns by fragmented rock. Addi t ion of water to the permeable zone reduced in tergranular pressure and produced a s l u r r y that was squeezed upwards l i k e toothpaste. These brecc ias d i f f e r from OMB i n containing g r a n i t i c c l a s t s derived from Archean c r y s t a l l i n e basement. The bulk of the b r e c c i a , however, comprises shallow marine rocks . G.3 Bathurst I n l e t Near Bathurst I n l e t , N.W.T. Cec i l e and Campbell (1977) described dykes, 1-20 m wide, and pipes , 0.5 to 1 km across, of brecc ia composed of sedimentary c l a s t s . The c l a y - and s i l t - s i z e d matrix contains abundant m i l l i m e t r e - s i z e d euhedral growth-zoned c r y s t a l s of dolomite and quartz, and smaller tourmaline c r y s t a l s . Breccias commonly display "flowage layering", interpreted to have formed by movement of masses of semi-plastic material. Cecile and Campbell (1977) proposed that pressurized f l u i d s trapped i n the sedimentary rocks intruded overlying strata, transporting fragments upward. G.4 Adeladian Province The *Adelaidean province i n A u s t r a l i a has numerous deposits of Proterozoic breccia. They are of s p e c i a l i n t e r e s t to t h i s study because: (1) they occur i n a craton margin, (2) they cross-cut mid-Proterozoic sedimentary rocks and are approximately the same age as OMB and Wernecke-type breccia, (3) breccia fragments dominantly comprise the oldest lowest sedimentary s t r a t a that i s l o c a l l y exposed, (4) the matrix i s of clay, s i l t and sand sized material that i s carbonate-rich, (5) breccia bodies are surrounded by sedimentary rocks that display hematitic a l t e r a t i o n and l o c a l quartz-chlorite, q u a r t z - s e r i c i t e , and carbonate a l t e r a t i o n , (6) recent studies from underground exploration at the Olympic Dam deposit indicate that they are c y l i n d r i c a l , i n t r u s i v e bodies, and 218 (7) the Olympic Dam Cu-Au-U-REE b r e c c i a deposit i s the larges t copper-gold deposit i n the world. G.4 .1 F l i n d e r s Ranges The F l i n d e r s Range brecc ias (Dalgarno and Johnson, 1965; Thomson, 1965; Lemon, 1985; B e l l , 1987; Laznicka, 1988) are , i n many respects , much l i k e OMB. They comprise *he teroc las t i c brecc ias (fragments are carbonate, s i l t s t o n e , sandstone, metabasalt and gabbro i n a carbonate-r ich s i l t s t o n e matrix [Laznicka, 1988]). Evaporite d iap i r i sm i s genera l ly accepted as the genetic process responsible for brecc ias of the F l i n d e r s Ranges. Flowage of the source beds (a t h i c k sequence of t h i n bedded sandstone, s i l t s t o n e and carbonate) was f a c i l i t a t e d by water sa turat ion and by i t s confinement during sediment loading (Dalgarno and Johnson, 1965). Evidence to suggest that evaporite sequences were o r i g i n a l l y present includes: gypsum-anhydrite psuedomorphs, s a l t casts i n "source beds", and a shallow-water carbonate depos i t iona l s e t t i n g . V e r t i c a l f a u l t s , that penetrate down to e v a p o r i t i c source beds are thought to have i n i t i a t e d d i a p i r i s m (Lemon, 1985) . Subver t i ca l f a u l t s commonly cut other d i a p i r s i n the region (Thomson, 1965). U p l i f t and t i l t i n g of one f a u l t block created i n s t a b i l i t y i n the source beds and caused flow of the e v a p o r i t i c sequence upward and toward the f a u l t (Lemon, 1985). G.4.2 Olympic Dam Olympic Dam d i f f e r s from Wernecke-type brecc ias in several c r i t i c a l aspects: (i) brecc ias comprise common g r a n i t i c , as we l l as sedimentary rock fragments, and ( i i ) prominant m i n e r a l i z a t i o n occurs throughout. Brecc ia at Olympic Dam occurs as a hemati t ic b r e c c i a -dyke complex wi th in a fractured , weakly to intense ly hematized Archean grani te (Oreskes et a l . , 1989). Breccias formed as a r e s u l t of hydraul ic f r a c t u r i n g , b r e c c i a t i o n and f l u i d i z a t i o n (Oreskes and Einaudi , 1988). Previous in t erpre ta t ions described Olympic Dam brecc ias as a l l u v i a l deposits that formed along graben margins (Roberts and Hudson, 198 3) ; they were subsequently a l t ered and mineral ized by hydrothermal f l u i d s . G.5 Mud D i a p i r s and Volcanoes Mud volcanoes are the surface expression of a type of d iap i r i sm that i s associated with high pressure release of gas- and/or water-charged mud or shale (Freeman, 1968). Modern examples of mud volcanoes are confined to regions under la in by unconsolidated sediment such as c lay and shale. Abnormal pressures occur i n these sediments due to loading by over ly ing sediments. A l t e r n a t i v e l y (to the mud d i a p i r theory) , poss ib le examples of modern sub-sea f l u i d (water and or gas) escape s tructures have been i d e n t i f i e d i n regions dominated by mud volcanos where large quant i t i es of buried methane are known to be present (Brown and Westbrook, 1988). The escape of methane gas entrains c lay and connate br ines i n a s l u r r y (Hedberg, 1974). A mud (or shale) d i a p i r i s dr iven by densi ty and pressure d i s e q u i l i b r i u m . P l a s t i c deformation during ascent of gas- and water-charged mud incorporat ing blocks of more competant un i t s (Barber et a l . . 1986) cons t i tu te the b r e c c i a . Seismic r e f l e c t i o n p r o f i l e s of mud volcanoes i n modern slope basins c l e a r l y show d i a p i r s cros scu t t ing several ki lometers of s t r a t i g r a p h i c thickness (Biju-Duval et  a l . , 1982). The lack of exot ic fragments i n the brecc ia r e f l e c t s a t h i c k sequence of l i t h o l o g i c a l l y r e p e t i t i v e s t r a t a . Except for t h e i r d isrupted and discordant a t t i tudes , a b r e c c i a of large blocks i s ind i s t ingu i shab le from adjacent i n t a c t s t r a t a . Mud d i a p i r s form where underconsolidated muds are r a p i d l y bur ied , such as along cont inenta l margins and i n submarine d e l t a s . When high rates of sedimentation are combined with low permeabi l i ty , the expulsion of water cannot keep pace with increas ing overburden pressure (Hedberg, 1974). Other factors that could add s i g n i f i c a n t l y to high f l u i d pressures (Hedberg, 1974) inc lude: (i) re lease of bound water during diagenesis , such as occurs i n c lay minerals during the conversion of montmori l lonite to i l l i t e , ( i i ) change of gypsum to anhydri te , and ( i i i ) metamorphic water released during reg iona l metamorphism. Fau l t and frac ture zones l o c a l to uni t s with high f l u i d pressure would provide avenues of release that would guide the emplacement of the d i a p i r s . Ascending muds would incorporate fragments due to abrasion and hydrofractur ing of the wal l rocks . Methane and carbon dioxide generated with in the sedimentary p i l e by breakdown of organic (algal) mater ia l could a s s i s t i n the propuls ion of the muds toward the surface . Methane i s generated biochemical ly at near surface condit ions and thermochemically at .depths of several ki lometers (Hedberg, 1974). Carbon dioxide can be produced by the aqueous d i s s o l u t i o n , or decarbonation, of l imestone; i t can a lso be derived magmatically (Motyka et a l . . 1989). The main source of fragments i s b r i t t l e wa l l rocks i n the region of d i a p i r i n i t i a t i o n , or along i t s path of ascent (Laznicka, 1988). V e r t i c a l f a u l t s are points of weakness where sediments with high f l u i d pressures can escape. Densely fractured zones generate fragments that are r e a d i l y incorporated into the migrat ing mass. G.5.1 Barbados The Barbados Ridge Complex i s a subduction complex developed by sediment accre t ion (Brown and Westbrook, 1988). Sedimentary fan t u r b i d i t e s , r a p i d l y deposited on the subducting p l a t e , created high pore f l u i d pressures i n pe lag ic sequences immediately beneath the fan. The underconsolidated pe lag ic sediments are prone to m o b i l i t y . The occurrence of abundant mud d i a p i r s i s confined to t h i s area of t u r b i d i t e deposi t ion and t h e i r d i s t r i b u t i o n i s c o n t r o l l e d by imbricate thrus t s , reverse fau l t s and f o l d s . The mud d i a p i r s form elongate r idges and i so la t ed mounds. They cover over 700 square km of the surface area of the complex, a region i n excess of 300 km long and about 200 km wide. The h igh ly pressurized pe lag ic sediments are able to r e t a i n f l u i d s for a subs tant ia l per iod of time and d i a p i r i c mater ia l may take several m i l l i o n years to migrate to the surface (Brown and Weatbrook, 1988). G.5.2 Timor Timor, i n eastern Indonesia, marks where the northern margin of the A u s t r a i l i a n continent i s c o l l i d i n g with the Banda Arc (Barber et a l . . 1986). Continental margin sediments of the A u s t r a l i a n continent are being added to an imbricate wedge. This wedge of sediment became a foreland f o l d and thrus t b e l t northward. C l a y - r i c h brecc ia deposits are s i tua ted along f a u l t s . They occur as mud d i a p i r s associated with mud volcanoes. The Timor breccias were developed from shales with abnormally high pore f l u i d pressures . The Permian-Triass ic shales developed high pore pressures , i n p a r t , from overthrust ing that followed the Pl iocene c o l l i s i o n of the northwest margin of A u s t r a l i a with the Banda Arc subduction system (Barber et a l . , 1986). Other fac tors (see above) could have added to the pore f l u i d pressure . Faul ts penetrated the stacked sequence and the subsequent release of pressure caused expulsion of f l u i d s and the undercompacted f ine grained sediment. Blocks of competant u n i t s , broken up along the f a u l t , were included i n the d i a p i r as i t ascended. 

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