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Geology of the Boss Mountain Mine, British Columbia Soregaroli, Arthur Earl 1968

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GEOLOGY OF THE BOSS MOUNTAIN MINE, BRITISH COLUMBIA by ARTHUR EARL SOREGAROLI B . S c . , Iowa S t a t e U n i v e r s i t y , 1 9 5 9 M . S c . , U n i v e r s i t y o f Idaho, 1 9 6 1 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Geology We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s tandard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1 9 6 8 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Br i t ish 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 represen-tatives. 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 Br i t ish Columbia Vancouver 8, Canada V ( i ) ABSTRACT D e t a i l e d i n v e s t i g a t i o n of the Boss Mountain molybdenite deposits,, which are on the northeast slope of Takomkane Mountain approximately 35 miles north-northeast of 100 Mile House, B r i t i s h Columbia, was undertaken to determine the o r i g i n of the d e p o s i t s , c o n t r o l s of m i n e r a l i z a t i o n , e f f e c t s of mineral-i z a t i o n on the host rock, o r i g i n of the b r e c c i a bodies, and the r e l a t i o n s h i p of these fe a t u r e s to the Boss Mountain Stock. The d e p o s i t s occur i n g r a n o d i o r i t e and p o r p h y r i t i c b i o -t i t e g r a n o d i o r i t e phases of the composite Takomkane B a t h o l i t h near an e p i z o n a l Cretaceous quartz monzonite porphyry body, the Boss Mountain Stock. Molybdenite occurs i n economic concentrations i n two c l a s s e s of d e p o s i t s : 1) B r e c c i a De-p o s i t s , which i n c l u d e f r a c t u r e zones, and 2 ) Vein Deposits, which include both s i n g l e and m u l t i p l e systems. The sequence of ore formation, which i n c l u d e s r h y o l i t e porphyry and r h y o l i t e dyke emplacement, b r e c c i a formation, f r a c t u r e development, m i n e r a l i z a t i o n , and a l t e r a t i o n , i s d i -r e c t l y r e l a t e d to the o s c i l l a t o r y emplacement of the Boss Mountain Stock. The Boss B r e c c i a s , i n c l u d i n g Phase I B r e c c i a , Quartz B r e c c i a , and Phase I I I B r e c c i a , were formed by p u l s a t i n g mag-mat i c a c t i v i t y a c t i n g on an i r r e g u l a r i t y on the side of the magma chamber (Boss Mountain S t o c k ) . The rock above t h i s i r -r e g u l a r i t y was f r a c t u r e d by magmatic advances. Withdrawal of ( i i ) magmatic pressure permitted c o l l a p s e of the o v e r l y i n g f r a c t u r -ed rock forming b r e c c i a bodies. R h y o l i t e porphyry dykes, apophyses of the Boss Mountain Stock, preceded and accompanied Phase I B r e c c i a formation. N o n - p o r p h y r i t i c r h y o l i t e dykes cut Phase I B r e c c i a and have been engulfed by l a t e r b r e c c i a phases. Four stages of rock a l t e r a t i o n g e n e t i c a l l y r e l a t e d to the d e p o s i t s , i n c l u d i n g ( i n c h r o n o l o g i c a l o r d e r ) : Stage 1, garnet-hornblende Stage 2 , b i o t i t e ; Stage 3 , m i c r o p e r t h i t e - c h l o r i t e -s e r i c i t e ; and. Stage k, c h l o r i t e - t a l c , have been i d e n t i f i e d and d e l i n e a t e d . Stage 1 formed i n mylonite zones around the Boss Mountain Stock, Stages 2 and 3 around centres of m i n e r a l -i z a t i o n and Stage H- occurs i n and near shear zones. F i v e periods of f r a c t u r e development, each of which con-t a i n s quartz ve i n s of unique mineralogy and c h a r a c t e r i s t i c s , were i n t e r s p e r s e d w i t h b r e c c i a formation, a l t e r a t i o n and m i n e r a l i z a t i o n . M i n e r a l i z a t i o n accompanied b r e c c i a formation and. f r a c t u r e development. Molybdenite was introduced, d u r i n g three sep-ara t e periods of m i n e r a l i z a t i o n , two of which were separated by a barren stage t h a t produced a complex mineral assemblage. P y r i t e accompanies a l l stages of m i n e r a l i z a t i o n . P l e i s t o c e n e (?) a l k a l i b a s a l t dykes r e l a t e d t o Takomkane Volcano, which forms the twin summits of Takomkane Mountain, ( i i i ) cut a l l rocks and ore s t r u c t u r e s . The v o l c a n i c rocks of the volcano contain x e n o l i t h s of g r a n o d i o r i t e , g l a s s y black a u g i t and p e r i d o t i t e . ( i v ) TABLE 0? CONTENTS Page ABSTRACT ' ( i ) I. INTRODUCTION 1 LOCATION AND ACCESS 1 SCOPE OF PRESENT WORK 1 PHYSICAL FEATURES 2 ACKNOWLEDGMENTS 3 I I . PETROLOGY OF THE MINE AREA 5 HYPERSTHEME GABBRO • 6 TAKOMKANE BATHOLITH . 1 2 S y e n o d i o r i t e 1 3 G r a n o d i o r i t e 1 5 Age 18 P o r p h y r i n i c B i o t i t e G r a n o d i o r i t e 18 ANDESITE PORPHYRY AND ANDESITE 2 1 PEGMATITE 2 3 BOSS MOUNTAIN STOCK 2 6 Outer C h i l l Zone 28 Inner C h i l l Zone ' 2 8 Quartz Mcnzonite Porphyry 3 2 Rhyolit.e Porphyry and -Rhyollte Jk Environment of Emplacement 3 9 BOSS BRECCIAS kl Phase I B r e c c i a 1^ Quartz B r e c c i a k$ Phase I I I B r e c c i a 5 0 TIME OF INTRUSION OF RHYOLITE PORPHYRY AND RHYOLITE 5 2 TAKOMKANE VOLCANIC ROCKS 5 3 A l k a l i B a s a l t 5 7 X e n o l i t h s 6 0 P e r i d o t i t e 61 Mineralogy 6 2 O l i v i n e 6 2 Chromian Diopside 6k E n s t a t i t e 6 ? S p i n e l 6 ? O r i g i n of X e n o l i t h s 6 8 I I I . STRUCTURE 7 2 GENERAL STRUCTURE 7 2 F a u l t s 7 2 Molybdenite Creek F a u l t 7 2 Post-Mineral F a u l t s 7 3 J o i n t s 7 5 ( v ) Page LOCAL STRUCTURE 7 5 Garnet-Hornblende V e i n l e t s 7 7 Ore Fractures - 504-5 Level 80 Group 1 Fractures . 8 3 Group 2 Fractures 8 5 Group 3 Fractures 8 5 Group 4 Fractures 8 7 Group 5 Fractures 8 9 Post-Ore Fractures - 5045 Level 9 2 Group 6 Fractures 9 2 Group 7 and. 8 Fractures 9 5 GENETIC IMPLICATIONS OF FRACTURE PATTERNS 9 6 IV. ROCK ALTERATION 99 ALTERATION UNRELATED TO ORE DEPOSITION 9 9 P r o p y l i t i c A l t e r a t i o n 9 9 Z e o l i t e - C a l c i t e - C l a y Assemblage 1 0 0 ALTERATION GENETICALLY RELATED TO ORE DEPOSITION 1 0 3 Stage 1 : Garnet-hornblende . 1 0 3 Stage 2 : B i o t i t e 1 0 6 Stage 3- M i c r o o e r t h i t e - C h l o r i t e - S e r i c i t e 1 1 5 Stage 4 : C h l o r i t e - T a l c 1 2 2 V. ORE DEPOSITS 124 HISTORY AND MINE DEVELOPMENT 124 FORM OF MINERAL DEPOSITS 1 2 7 CHARACTER OF MINERALIZATION 1 3 2 MINERALOGY 1 3 5 Nonmetallic Minerals 137 B i o t i t e 1 3 7 C a l c i t e - 138 C h l o r i t e 1 3 8 F l u o r i t e I 3 8 M i c r o p e r t h i t e 1 3 9 Quartz 139 S e r i c i t e 1 3 9 M e t a l l i c Minerals 1 3 9 P y r i t e 1.42 Molybdenite 144 R u t l i e 145 Magnetite 145 C h a l c o p y r i t e 147 S p h a l e r i t e • 149 S c h e e l i t e - P o w e l l i t e 149 A i k i n i t e . 1 5 0 B i s m u t h i n i t e 1 5 1 P y r o l u s i t e 1 5 1 Specular Hematite 1 5 2 T e t r a h e d r i t e 1 5 2 Anatase 1 5 3 ( v i ) Page Products of Weathering 1 5 3 Limonite 1 5 ^ 'Ferrimolybdite 1 5 ^ Manganese Oxide 1 5 5 J a r o s i t e 1 5 5 P o w e l l i t e 1 5 5 Leucoxene 1 5 6 Hematite 1 5 6 Malachite 1 5 7 Paraecenesis 1 5 7 CLASSIFICATION 1 5 7 AGE OF THE DEPOSITS 1 6 0 V I . GENESIS OF THE ORES I 6 3 ORIGIN OF THE BOSS BRECCIAS 1 6 3 SEQUENCE OF ORE FORMATION 1 7 5 SELECTED BIBLIOGRAPHY 1 7 9 APPENDIX 1 : CONTOURED EQUAL-AREA PROJECTIONS OP FRACTURES: 5 0 ^ 5 LEVEL 189 ( v i i ) ILLUSTRATIONS MAPS Map: 1. Geology of the Boss Mountain Mine Area In pocket 2 . Surface Geology: Boss Mountain Mine In pocket 3 . A l t e r a t i o n D i s t r i b u t i o n In pocket PLATES P l a t e : Page 2 . 1 . Photomicrograph (crossed n i c o l s ) of a n t i - 1 1 p e r t h i t e zone, i n p l a g i o c l a s e of hypersthene gabbro. 2 . 2 . Contact between c h i l l e d margin (granophyre) 2 9 of the Boss Mountain Stock ( l e f t ) and the g r a n o d i o r i t e phase of the Takomkane Bath-o l i t h ( r i g h t ) . (Scale i s i n i n c h e s ) . 2 . 3 . Photomicrograph (crossed n i c o l s ) of contact 2 9 between c h i l l e d , margin (granophyre) of Boss Mountain Stock ( l e f t ) and g r a n o d i o r i t e phase of the Takomkane B a t h o l i t h ( r i g h t ) . 2.k, Photomicrograph (crossed n i c o l s ) of grano- . 3 1 phyre from the outer c h i l l zone of the Boss Mountain Stock. 2 . 5 - Photomicrograph (crossed n i c o l s ) of sub- 3 1 granophyric t e x t u r e of the groundmass of r h y o l i t e porphyry dyke, 2 . 6 . Photomicrograph (crossed n i c o l s ) of quartz ' 3 8 phenocryst i n r h y o l i t e porphyry dyke. 2 . 7 . Photomicrograph (crossed, n i c o l s ) of embayed 3 8 quartz phenocryst i n quartz inonzonite por-phyry (Boss Mountain S t o c k ) . 2 . 8 . Phase I B r e c c i a . Angular fragments of _ grano- kk d i o r i t e , group 1 quartz v e i n (q) and. garnet-hornblende v e i n l e t (g) i n comminuted matrix ( b l a c k ) . (Scale i s i n i n c h e s ) , 2 . 9 . Phase I B r e c c i a . Angular fragments of grano- kk d i o r i t e and r h y o l i t e porphyry ( r ) i n com-minuted matrix (grey). (Scale i s i n i n c h e s ) . ( v i i i ) Page 2 . 1 0 . Quartz B r e c c i a . Fragments 'of g r a n o d i o r i t e 4 7 and a l t e r e d andesite dyke (black) i n quartz matrix (white). .Molybdenite forms dark-coloured rims on the fragments. (Scale i s i n inches ). 2 . 1 1 . Phase I I I B r e c c i a . Angular t o rounded f r a g - 4 7 merits of g r a n o d i o r i t e , quartz (white) and a l t e r e d andesite dyke (black) i n comminuted matrix (grey). (Scale i s i n in c h e s ) . 2 . 1 2 . Photomicrograph (plane p o l a r i z e d l i g h t ) of 7 0 a l k a l i bass.lt w i t h p e r i d o t i t e i n c l u s i o n s . S p i n e l (s) g r a i n s have dark rims at contact w i t h a l k a l i b a s a l t , ( o l i v i n e ( o ) ; chromian d i o p s i d e ( d ) ) . 2 . 1 3 - Photomicrograph (plane p o l a r i z e d l i g h t ) of 7 0 s p i n e l g r a i n ( c e n t r e ; b l a c k ) i n a l k a l i b a s a l t . Note the a l k a l i b a s a l t adjacent to the g r a i n Is impoverished, i n magnetite (small b l a c k g r a i n s ) . 4 . 1 . M y l o n i t i z e d g r a n o d i o r i t e c o n t a i n i n g v e i n l e t s 1 0 5 of garnet (grey) w i t h hornblende selvedges ( b l a c k ) . (Scale i s i n in c h e s ) . 4 . 2 . Photomicrograph (crossed n i c o l s ) of hydro- 1 1 2 thermal b i o t i t e which has p a r t l y replaced magmatic b i o t i t e . 4 . 3 . Photomicrograph (plane polarized, l i g h t ) of 1 1 2 pseudomorphic hydrothermal b i o t i t e which has replaced magmatic hornblende. 4 . 4 . Photomicrograph (plane p o l a r i z e d l i g h t ) of 1 1 9 c h l o r i t i z e d b i o t i t e w i t h r u t i l e i n c l u s i o n s ( b l a c k ) . 4 . 5 . Photomicrograph (plane polarized, l i g h t ) of 1 1 9 hydrothermal b i o t i t e cut by molybdenite , ( b l a c k ) . 4 . 6 . Photomicrograph (plane p o l a r i z e d l i g h t ) of 1 2 1 r u t i l e (black) i n quartz near c h l o r i t e (grey). 4 . 7 . Photomicrograph (plane polarized, l i g h t ) of 1 2 1 r u t i l e (black) i n e p i g e n e t i c c h l o r i t e . ( i x ) 5 . 1 . 5 . 2 . 5 . 3 . 5 . 4 . 5 . 5 . 5 . 6 . F i g u r e : "2.1 . 2 . 2 . 2 . 3 . 2 . 4 . 2 . 5 . Fracture Ore. Angular fragments of grano-d i o r i t e and a l t e r e d andesite dyke (black) i n molybdenite matrix ( g r e y ) . (Scale i s i n in c h e s ) . F r acture Ore. Angular fragments of grano--d i o r l t e and quartz (white) i n molybdenite matrix (grey). (Scale i s i n i n c h e s ) . Group I quartz v e i n cut by molybdenite v e i n -l e t s (mo) and a quartz-magnetite v e i n l e t (m). Note the sugary t e x t u r e of the quartz v e i n and the weak a l t e r a t i o n (a) of the grano-d i o r i t e adjacent to the vein,, (Scale i s i n in c h e s ) . Banded group 5 quartz v e i n w i t h c h a r a c t e r -i s t i c f r a c t u r e s normal to the v e i n w a l l s . ' Grey bands are molybdenite. (Scale i s i n in c h e s ) . Coarsely c r y s t a l l i n e molybdenite from the High-Grade Vein. Black fragment i s a l t e r e d andesite host rock, ' (Scale i s i n i n c h e s ) . C h a r a c t e r i s t i c t e x t u r e of co a r s e l y c r y s t a l -l i n e molybdenite i n the High-Grade Vein. (Scale i s i n i n c h e s ) . FIGURES Loc a t i o n of area of study showing area underlain, by the Takomkane B a t h o l i t h . Composition of p l u t o n i c rocks i n the Boss Mountain area. Equal-area p r o j e c t i o n (lower hemisphere) of poles t o 74 andesite and andesite porphyry dykes. Equal-area p r o j e c t i o n (lower hemisphere) of poles to 47 pegmatite dykes. Equal-area p r o j e c t i o n (lower hemisphere) of poles to 18 r h y o l i t e porphyry and r h y o l i t e dykes. Page 2 . 6 . Sketches of contacts between Quartz B r e c c i a 4 9 dykes and g r a n o d i o r i t e on the 5 0 4 5 l e v e l . 2 . 7 . Centres of T e r t i a r y and Recent volcanisra i n 5 4 the Cariboo r e g i o n . 2.8. Equal-area p r o j e c t i o n (lower hemisphere) of . 5 6 poles to 3 9 a l k a l i b a s a l t dykes. 2 . 9 . Compositions of 3 3 p e r i d o t i t e i n c l u s i o n s 6 5 from the Takomkane v o l c a n i c rocks ( s p i n e l excluded). 2 . 1 0 . Compositions of o l i v i n e s from the Takomkane 6 6 v o l c a n i c rocks. 2 . 1 1 . Compositions of s p i n e l s from p e r i d o t i t e in™ 6 9 e l u s i o n s i n the Takomkane v o l c a n i c rocks. • 3 . 1 . Equal-area p r o j e c t i o n (lower hemis'phere) of 7 6 poles t o 3 2 1 j o i n t s on Takomkane Mountain, 3.2. I d e a l i z e d plan of part of the 5 0 4 5 l e v e l ? 8 showing a t t i t u d e s of garnet-hornblende v e i n l e t s and t h e i r r e l a t i o n s h i p to the Boss Mountain Stock. 3 . 3 . Equal-area p r o j e c t i o n s (lower hemisphere) of 7 9 poles to garnet-hornblende v e i n l e t s ( 5 0 4 5 l e v e l ) . 3 . 4 . - Stereographic p r o j e c t i o n s (lower hemisphere) 82 of group 1 f r a c t u r e s i n d i f f e r e n t areas of the 5 0 4 5 l e v e l . 3 . 5 , Sterographic p r o j e c t i o n s (lower hemisphere) 84 of group 2 f r a c t u r e s i n d i f f e r e n t areas of t h e " 5 0 4 5 l e v e l . 3.6. Stereographic p r o j e c t i o n s (lower hemisphere) 86 of group 3 f r a c t u r e s i n d i f f e r e n t areas of the 5 0 4 5 l e v e l . 3.7. Stereographic p r o j e c t i o n s (lower hemisphere) 88 of group 4 f r a c t u r e s i n d i f f e r e n t areas of . t h e " 5 0 4 5 l e v e l . 3.8. Stereographic p r o j e c t i o n s (lower hemisphere) 9 0 of group 5 f r a c t u r e s i n d i f f e r e n t areas of the 5 0 4 5 l e v e l . (xi.) Page 3 . 9 . Stress elements of group 5 quartz v e i n s . 9 1 3 . 1 0 . Stereographic p r o j e c t i o n s (lower hemisphere) 9 3 of group 6 f r a c t u r e s in. d i f f e r e n t areas of t h e " 5 0 4 5 l e v e l . 3 . 1 1 . Stereographic p r o j e c t i o n s (lower hemisphere) 9k of groups 7 and. 8 f r a c t u r e s i n d i f f e r e n t areas 'of the 5 0 4 5 l e v e l . 3 . 1 2 . Formation of f r a c t u r e s . • . 9 8 4 . 1 . Composition of 14 garnets; Boss Mountain 1 0 7 Mine. 4 . 2 . Mineral v a r i a t i o n s i n altered, andesite and 114 andesite porphyry dykes i n r e l a t i o n to i n -c r e a s i n g b i o t i t e content. 5 . 1 . Level plans of part of the Boss Mountain 129 molybdenite d e p o s i t s . 5 . 2 . T y p i c a l c r o s s - s e c t i o n s of the Boss Mountain 1 3 1 molybdenite d e p o s i t s ( l o o k i n g g r i d north -M 3 5 ° W ) . 5 . 3 . L o n g i t u d i n a l s e c t i o n (projected. t o ' 5 0 0 0 E 1 3 3 g r i d l i n e ) through part of the Boss Mountain molybdenite depo s i t s ( l o o k i n g west). 5 . 4 . Published potassium-argon dates of molyb- 1 6 2 d.enum-bearing and related, rocks i n east-c e n t r a l B r i t i s h Columbia. 6 . 1 . Formation of b r e c c i a bod,ies. 1 7 2 6 . 2 . Plan and s e c t i o n i l l u s t r a t i n g the r e l a t i o n - 174 s h i p between the Boss B r e c c i a s and. the Boss Mountain Stock. 1 . 1 . Contoured equal-area p r o j e c t i o n s (lower 1 9 0 hemisphere) of poles to f r a c t u r e s i n Area A; 5 0 4 5 l e v e l , I . ' 2 . Contoured equal-area p r o j e c t i o n s (lower 191 hemisphere) of poles to f r a c t u r e s i n Area B; 5 0 4 5 l e v e l . ( x i i ) Page 1 . 3 . Contoured equal-area p r o j e c t i o n s (lower 192 hemisphere) of poles to f r a c t u r e s i n Area C; 5045 l e v e l . 1 . 4 . Contoured equal-area p r o j e c t i o n s (lower 193 hemisphere) of poles t o f r a c t u r e s i n Area D; 5045 l e v e l . i . 5 » "Contoured equal-area p r o j e c t i o n s (lower 194 hemisphere) of poles t o f r a c t u r e s in . Area E; 5045 l e v e l . 1 . 6 . Contoured equal-area p r o j e c t i o n s (lower 195 hemisphere) of poles to f r a c t u r e s i n Area F; 5045 l e v e l (continued). . 1 .7 . Contoured equal-area p r o j e c t i o n s (lower 196 hemisphere) of pol.es to f r a c t u r e s i n Area F: 5045 l e v e l (continued from Figure 1 . 6 ) . 1 . 8 . Contoured equal-area diagrams (lower hemis- 197 phere) of poles to f r a c t u r e s i n Area G; 5045 l e v e l (continued). 1 . 9 . Contoured equal-area p r o j e c t i o n s (lower 198 hemisphere) of poles to f r a c t u r e s i n Area G; 5045 l e v e l (continued from Figure 1 . 7 . ) . 1 . 1 0 . Contoured equal-area p r o j e c t i o n s (lower 199 hemisphere)' of poles t o f r a c t u r e s i n Area H; 5045 l e v e l . TABLES Table: 2 . 1 . Table of Formations; Boss Mountain. Mine area. 8 2 . 2 . Modes of hypersthene gabbros from the Boss 9 Mountain Mine area. 2 . 3 . Modes of rocks from the Takomkane B a t h o l i t h . 16 2 . 4 . Modes of t y p i c a l pegmatite dykes from the 24 Boss Mountain Mine area. 2 . 5 . Modes of rocks from the Boss Mountain Stock. 27 ( x i l i ) Page 2 . 6 . Modes of r h y o l i t e porphyry and r h y o l i t e 37 dykes from the Boss Mountain Mine area. 2 . 7 . Modes of a l k a l i b a s a l t dykes. 58 2 . 8 . Modes of p e r i d o t i t e i n c l u s i o n s from the 63 Takomkane v o l c a n i c rocks. 2 . 9 . Composition of o l i v i n e s from p e r i d o t i t e i n - 64 e l u s i o n s and groundmass of the Takomkane .volcanic rocks, 2 . 1 0 . C e l l edge and s p e c i f i c g r a v i t y measure- 71 ments of s p i n e l s from p e r i d o t i t e i n c l u s i o n s i n the Takomkane v o l c a n i c rocks. 3 . 1 . C h r o n o l o g i c a l chart of f r a c t u r e s on the 5045 81 l e v e l ; Boss Mountain mine. 3 . 2 . Group 5 f r a c t u r e s ; a t t i t u d e s Of s t r e s s 92 elements. 4 . 1 . Mod.es of andesite and andesite porphyry dykes 115 and t h e i r a l t e r e d e q u i v a l e n t s ; Boss Mountain mine area. 4 . 2 . Comparison of c h l o r i t e s produced dur i n g 118 Stage 3 a l t e r a t i o n . 5 . 1 , Nonmetallic minerals of the Boss Mountain 1 3 7 molybdenite d e p o s i t s , 5 . 2 , Mineralogy and character of quartz v e i n s . 140 5 . 3 . M e t a l l i c minerals of the Boss Mountain 142 molybdenite d e p o s i t s . 5 . 4 . Semi - q u a n t i t a t i v e spectrographic analyses 150 of s c h e e l i t e . ' 5 . 5 . Secondary minerals of the Boss Mountain 154 molybdenite d e p o s i t s , 5 . 6 . Paragenetic sequence of minerals g e n e t i c a l l y I 5 8 r e l a t e d to the Boss Mountain molybdenite d.eposits. 6 . 1 . C h r o n o l o g i c a l chart of phenomena r e l a t e d to 177 ore format1on. 1 I . INTRODUCTION LOCATION AND ACCESS The Boss Mountain Mine i s on the northeast slope of Takom-kane Mountain ( B i g Timothy Moxintain) at longitude 1 2 0 ° 5 6 ' , l a t i t u d e 5 2 ° 0 6 s (Figure 2 . 1 ) , Access t o the mine and towns!te i s from 1 0 0-Mile Rouse by approximately 60 miles of good road, the f i r s t 18 miles of which are hard-surfaced. The molybdenum de p o s i t s which are i n a cirque a t the head of Molybdenite Creek outcrop between 5-+00 and 5700 feet- e l e v a t i o n . The m i l l s i t e and a d i t l e v e l are one mile east of the d e p o s i t s at e l e v a t i o n 5045 f e e t . The townsite at Hendrix Lake i s s i x miles east of the mine at e l e v a t i o n 2000 f e e t . SCOPE OF PRESENT WORK De t a i l e d i n v e s t i g a t i o n of the Boss Mountain molybdenum d e p o s i t s and the surrounding area was undertaken to determine the o r i g i n of the molybdenite d e p o s i t s , the c o n t r o l s of mi n e r a l -i z a t i o n , the e f f e c t s of m i n e r a l i z a t i o n on the host rock, the o r i g i n of the b r e c c i a bodies, and the r e l a t i o n s h i p o f " m i n e r a l -i z a t i o n to the Boss Mountain Stock. Creologic data were c o l l e c t e d d u r i n g the 1963 and 1964 f i e l d seasons and. durin g numerous b r i e f v i s i t s to the area i n 1965 , 1966 and. 1967 . The immediate area of the mine was mapped on the surface and i n the underground workings at 1 i n c h to 30 f e e t . An area w i t h i n a 3000 f o o t r a d i u s of the mine was mapped at 1 i n c h to 100 f e e t . Both maps were combined i n t o Map 2 ( i n pocket; 1 i n c h to 200 f e e t ) f o r t h i s r e p o r t . Mapping at 1 i n c h to 1000 f e e t covered an area three miles wide and s i x miles long, h a l f of which i s shown on • Map 1 ( i n pocket). Many reconnaissance t r i p s were made i n t o surrounding areas to gain f a m i l i a r i t y w i t h rocks outside the area of study. Low-level a e r i a l photographs (1 inch to 1000 feet) g r e a t l y f a c i l i t a t e d f i e l d mapping. PHYSICAL FEATURES Takomkane Mountain, which marks the western boundary of the Quesnel Highland, r i s e s about 2000 f e e t above the Eraser Plateau. The Quesnel Highland, a h i g h l y d i s s e c t e d part of the I n t e r i o r P l a t e a u , i s the t r a n s i t i o n zone between the Fraser Plateau on the west and the Cariboo Mountains on the east. The summits of most mountains i n the Quesnel Highland, i n c l u d i n g Takomkane Mountain, have been rounded by a P l e i s t o c e n e i c e sheet and then had t h e i r f e atures sharpened by the development of cirques "....on the northern and northeastern sides d u r i n g the l a t e stage of g l a c -i a t i o n . " ( Holland, 1964 , 'p. 7 3 ) . Molybdenite Creek and other streams north of the mine d r a i n northward i n t o the H o r s e f l y R i v e r , a t r i b u t a r y of the'Quesnel River-Quesnel Lake drainage. Boss Creek and Hend.rix Creek flow southward to Canim Lake and then i n t o the Clearwater-North Thompson drainages. Both the Quesnel and Thompson r i v e r s are 3 t r i b u t a r i e s of the Fraser R i v e r . Bedrock i s poorly exposed i n most areas l e s s than 6000 f e e t i n e l e v a t i o n , but la r g e areas are e x t e n s i v e l y exposed i n cirque w a l l s above t h i s e l e v a t i o n . The r o l l i n g summit of Takomkane Mountain i s l o c a l l y covered w i t h t h i n veneer of g l a c i a l d e p o s i t s and swamps. Thick growths of tre e s and low brush cover most areas below t i m b e r l i n e , except the v a l l e y s of Boss Creek and Molybdenite Creek which contain extensive swamps. ACKNOWLEDGMENTS The author i s indebted to a l l i n d i v i d u a l s who provided a s s i s t a n c e and encouragement during the c o l l e c t i o n of data and prep a r a t i o n of t h i s t h e s i s . S p e c i a l r e c o g n i t i o n i s due Mr. C. C. Sheng, formerly of Noranda E x p l o r a t i o n Company, Li m i t e d who did the p r e l i m i n a r y g e o l o g i c a l work a f t e r a q u i s i t i o n of the prop-e r t y by Noranda and. thanks are a l s o extended to many other mem-bers of the Noranda o r g a n i z a t i o n . The author i s g r a t e f u l to Professor W. H. White, Department of Geology, Univei-sity of B r i t i s h Columbia, f o r h i s guidance du r i n g the w r i t i n g of t h i s t h e s i s . S p e c i a l thanks are due Pro-f e s s o r s R. M. Thompson, J . V. Ross, and K. C. McTaggart f o r t h e i r a s s i s t a n c e and d i s c u s s i o n s concerning s p e c i f i c s e c t i o n s . Noranda E x p l o r a t i o n Company, L i m i t e d , generously defrayed most of the costs and provided other s e r v i c e s . Hand specimen photographs were taken by Gordon Coots. F i n a l l y , the author 4 acknowledges the N a t i o n a l Research C o u n c i l f o r h i s s t u d e n t s h i p , which was he ld a t the U n i v e r i s l t y o f B r i t i s h Co lumbia from September 1964 t o May 1965 . 5 I I . PETROLOGY OF THE MINE AREA The Boss Mountain molybdenite d e p o s i t s occur i n granodi-o r i t e and porp.hyritic g r a n o d i o r i t e phases of a composite batho-l i t h , the Takomkane b a t h o l i t h , that crops out s p o r a d i c a l l y over an area of more than 500 square miles i n e a s t - c e n t r a l B r i t i s h Columbia (Figure 2 . 1 ) . The b a t h o l i t h cuts T r i a s s i c v o l c a n i c and sedimentary rocks that probably are c o r r e l a t i v e s of the N i c o l a Group. A l l other rocks i n the map area are younger than the bath-o l i t h (Table 2 . 1 ) , Andesite and pegmatite dykes cut a l l phases of the b a t h o l i t h but are o l d e r than molybdenum m i n e r a l i z a t i o n . A complex composed of r h y o l i t e porphyry and r h y o l i t e dykes, three phases of b r e c c i a s (Boss B r e c c i a s ) , and the Boss Mountain Stock i s found only i n the v i c i n i t y of the mine. A l l rocks i n the map area are cut by dykes of a l k a l i b a s a l t which are related, to the Takomkane Volcano. The northeast side of the v o l c a n i c cone has been removed by e r o s i o n , but the r e -maining part i s about 2 , 0 0 0 f e e t i n diameter. A l k a l i b a s a l t and agglomerate which form the cone c o n t a i n abundant i n c l u s i o n s of p e r i d o t i t e , a u g i t e , and g r a n o d i o r i t e . The age of the volcano i s u n c e r t a i n , but i t appears to have been subject to a l p i n e g l a c i a -t i o n and i n t h i s r e p o r t the age i s considered t o be P l e i s t o c e n e . Boss Creek and the lower part of Molybdenite Creek v a l l e y s occupy a northwesterly t r e n d i n g lineament that i s probably the 6 t r a c e o f a f a u l t or f a u l t zone . H e n d r i x Creek v a l l e y , eas t of the map a r e a , o c c u p i e s a d e e p e r , p a r a l l e l l i n e a m e n t . G l a c i a l and s tream d e p o s i t s cover much of map a r e a , e s p e c -i a l l y the lower l e v e l s . The s u r f i c i a l d e p o s i t s have not r e -c e i v e d d e t a i l e d s t u d y , and w i l l not be d e s c r i b e d . HYPERSTHENE GABBRO Rounded x e n o l i t h s of hypers thene gabbro occur throughout the mapped p a r t of the Takomkane B a t h o l i t h . The l a r g e s t xeno-l i t h , which c r o p s out on the west s lope o f the mountain (Map 1 ) , exceeds 1 , 0 0 0 f e e t i n d i a m e t e r and i s c r u d e l y e l l i p t i c a l i n p l a n . The c o n t a c t w i t h the e n c l o s i n g s y e n o d i o r i t e i s s h a r p , w i t h apo-physes of s y e n o d i o r i t e e x t e n d i n g s e v e r a l f e e t i n t o hypers thene g a b b r o . The e n c l o s i n g r o c k c o n t a i n s abundant s m a l l ( s i x i n c h e s t o t h r e e f e e t i n l e n g t h ) , t a b u l a r i n c l u s i o n s w i t h h i g h l y rounded c o r n e r s c l o s e t o the l a r g e x e n o l i t h , but these become fewer and d i m i n i s h t o l e s s than one p e r c e n t over a d i s t a n c e o f 15 t o 20 f e e t . Most x e n o l i t h s of h y p e r s t h e n e gabbro i n o t h e r p a r t s of the b a t h o l i t h , e s p e c i a l l y i n the g r a n o d i o r i t e phase-, c o n t a i n more o r t h o c l a s e than t h i s l a r g e x e n o l i t h , p r o b a b l y the r e s u l t of metasomatism by the magma from which the e n c l o s i n g r o c k s c r y s t a l -l i z e d . W i t h i n the mine a r e a the x e n o l i t h s were, s u b j e c t e d to v a r y i n g degrees of h y d r o t h e r m a l a l t e r a t i o n and have undergone the same changes as o t h e r r o c k s . . B i o t i t i z a t i o n has been ex-treme i n some x e n o l i t h s . In hand specimen medium-to coarse-grained hypersthene gab-bro i s dark grey to brownish grey. Minerals i d e n t i f i e d i n t h i n s e c t i o n i n c l u d e a n t i p e r t h i t i c p l a g i o c l a s e , a u g i t e , hypersthene, o r t h o c l a s e , and b i o t i t e . Minor q u a n t i t i e s of hornblende, quartz a p a t i t e , c h l o r i t e , s e r i c i t e , sphene, serpentine, p y r i t e , magnet-i t e t l l m e n i t e and carbonate comprise the remainder of the rock. The modes of four specimens of hypersthene gabbro, determined by p o i n t - c o u n t i n g t h i n sections,, are l i s t e d i n Table 2 . 2 . Subhedral a n t i p e r t h i t i c p l a g i o c l a s e forms the framework of the i n t e r g r a n u l a r t e x t u r e of the rock. The s u b p a r a l l e l l a t h s of p l a g i o c l a s e are weakly zoned ( o s c i l l a t o r y ) w i t h compositional v a r i a t i o n s from An, t o An Many l a t h s are bent. * U 55 A n t i p e r t h i t e i s c h a r a c t e r i s t i c of the hypersthene gabbros. Rectangular blebs of o r t h o c l a s e , are confined t o i l l - d e f i n e d composition zones ( P l a t e 2 . 3 ) i n the e n c l o s i n g p l a g i o c l a s e . At high temperatures (independent of pressure) the p l a g i o -c l a s e s t r u c t u r e i s capable of i n c o r p o r a t i n g l a r g e amounts of potassium. During the c o o l i n g of the p l a g i o c l a s e the potassium phase may exsolve as d i s c r e t e bodies of o r t h o c l a s e or may be r e t a i n e d i n an apparently homogeneous p l a g i o c l a s e . Sen (1959) pointed out that r e h e a t i n g or shearing of p l a g i o c l a s e w i t h po-tassium i n s o l i d s o l u t i o n can cause e x s o l u t i o n of o r t h o c l a s e . Reheating of the hypersthene gabbro by the Takomkane B a t h o l i t h probably caused the development of a n i t p e r t h i t e i n these rocks. R e s t r i c t i o n of orthoclase to s p e c i f i c zones i s probably due to 8 ERA PERIOD OF EPOCH NAME LITHOLOGY Recent P l e i s t o c e n e Stream Sediments and G l a c i a l de-p o s i t s CENOZOIG unconformity P l e i s t o c e n e ( ? ) Takomkane V o l -cano and r e l a t -ed dykes A l k a l i b a s a l t unconformable and i n t r u s i v e Cretaceous Boss Mountain Stock and r e " l a t e d dykes Boss B r e c c i a s Quartz monzonite porphyry Phase I I I B r e c c i a ; comminuted matrix w i t h b i o t i t e Q u artz-Breccia; quartz matrix R h y o l i t e dykes Phase I B r e c c i a ; comminuted matrix R h y o l i t e porphyry dykes i n t r u s i v e i n t o b a t h o l i t h • pegmatite dykes MESOZOIC i n t r u s i v e i n t r u s i v e Andesite and andesite porphyry dykes J u r a s s i c Takomkane B a t h o l i t h i n t r u s i v e P o r p h y r i t i c grano-d i o r i t e G r a n o d i o r i t e S y e n o d i o r i t e - D i o r -i t e Hypersthene gabbro Table 2 . 1 . TABLE OF FORMATIONS: BOSS MOUNTAIN MINE AREA 9 o r i g i n a l compositional zoning i n the p l a g i o c l a s e . Sen ( 1959) observed that the orthoclase of a n t i p e r t h i t e s which he be l i e v e d to be magmatic i n o r i g i n i s i n o p t i c a l o r i e n t a t i o n w i t h ortho-. c l a s e g r a i n s adjacent to the a n t i p e r t h i t e . Where orthoclase i s observed i n contact w i t h a n t i p e r t h i t e g r a i n s i n the hypersthene gabbro of Takomkane Mountain, the o p t i c a l o r i e n t a t i o n s of the ortho c l a s e are not p a r a l l e l to the orthoclase w i t h i n the a n t i -p e r t h i t e . I f t h i s c r i t e r i o n i s v a l i d , the Takomkane Mountain a n t i p e r t h i t e s are not magmatic and have formed d u r i n g reheating of the x e n o l i t h s . • Plagioclase (Antiperthitic) Orthoclase Quartz Hypersthene Augite Hornblende Biotite Apatite Sphene Magnetite Specimen An 7 - 7 . 2 - 1 68 41^50 10 X 3 14 X 3 X - X 7 - 1 4 . 2 - 1 73 52-53 3 - 3 16 - 5 X - X 9 - 3 . 1 ( a l t e r e d ) 63 40 -55 12 - X X X 25 X X X 9 - 4 . 1 75 51-55 3 •v 7 11 X 4 X - X x Minor - Absent Table 2 , 2 . Modes of hypersthene gabbros from the Boss Moun-t a i n Mine area. Stubby, r a t h e r equant, c o l o u r l e s s to l i g h t green augite g r a i n s r a r e l y are rimmed by green hornblende. Fresh hypers-10 thene g r a i n s e x h i b i t weak, l i g h t p i n k t o c o l o u r l e s s p l e o c h r o i s m . Dark brown b i o t i t e , p r o b a b l y of d e u t e r i c o r i g i n , o c c u r s as r a d i a t i n g c l u s t e r s of s u b h e d r a l c r y s t a l s a d j a c e n t to magnet i t e g r a i n s . The o r i g i n of the hypers thene gabbro i s no t known. S e v e r a l p o s s i b l e a l t e r n a t i v e o r i g i n s can be p o s t u l a t e d , but t h e r e i s a l a c k of c o n c l u s i v e ev idence to any s i n g l e mechanism. The gabbros may be: 1) p r i m a r y igneous r o c k s , 2) contam-i n a t e d magmatic r o c k s , or 3) metasomat ic r o c k s . I f the h y p e r s t h e n e gabbro i s a p r i m a r y igneous r o c k , the prob lem a r i s e s whether i t i s an e a r l y phase of the Takomkane B a t h o l i t h or a r o c k from a s e p a r a t e and u n r e l a t e d i n t r u s i v e e v e n t . P o o r l y - e x p o s e d r o c k s eas t of Boss C r e e k , which are i n c o n -t a c t w i t h N i c o l a Group v o l c a n i c r o c k s suggest an o r i g i n by c o n t a m i n a t i o n of a p r i m a r y magma. These r o c k s , which c o n s i s t o f d i o r l t e , g a b b r o , hornb lende g a b b r o , a n o r t h o s i t e , and h y p e r s -thene gabbro appear t o grade i n t o p y r o x e n i t e near the c o n t a c t w i t h the v o l c a n i c r o c k s . C o n t a m i n a t i o n of a s y e n o d i o r l t e - g r a n o -d i o r i t e magma by i n c o r p o r a t i o n of a n d e s i t i c v o l c a n i c r o c k a l o n g the c o n t a c t s might p o s s i b l y produce such a sequence of g a b b r o i c r o c k s . I n h e r e n t f e a t u r e s oppos ing t h i s mode of o r i g i n i n c l u d e : 1) the h i g h t emperatures n e c e s s a r y to a s s i m i l a t e l a r g e q u a n t i -t i e s of and.es i tes p r o b a b l y c o u l d not be. o b t a i n e d from the p a r e n t -11 P l a t e 2 . 1 . Photomicrograph (crossed n i c o l s ) of a n t i p e r t h i t e (a) zone i n p l a g i o c l a s e of hypersthene gabbro. 12 a l magma, 2) the presence of a n o r t h o s i t e s , 3) the l a c k of p a r t l y a s s i m i l a t e d blocks of andesi t e , and 4) andesite i s not b a s i c enough to make gabbro from a s y e n o d i o r i t e - g r a n o d i o r i t e melt. The f i n a l p o s s i b l e o r i g i n of the hypersthene gabbro and r e -l a t e d rocks i s that they were formed through metasomatism of N i c o l a v o l c a n i c rocks by the i n t r u d i n g magma. Hornblende and au g i t e - d i o p s i d e h o r n f e l s i n g of the N i c o l a andesites l o c a l l y i s extreme and rocks of almost 100 percent pyroxene are r e l a t i v e l y common. Further s p e c u l a t i o n on t h i s subject i s not p o s s i b l e without much more d e t a i l e d study, both, i n the f i e l d and. i n the l a b o r a t o r y . TAKOMKANE -BATHOLITH Most of the rocks which crop out on Takomkane Mountain are part of a composite b a t h o l i t h which has not received an o f f i c i a l name. Campbell (personal communication, 1965) ^ a s suggested the name TAKOMKANE BATHOLITH f o r these rocks and f o r ease of r e f e r -ence h i s suggestion w i l l be followed. The area u n d e r l a i n by the b a t h o l i t h i s shown i n Figure 2.1. Three phases of the Takomkane B a t h o l i t h , which have been recognized and are described. i n t h i s r e p o r t , are 1) a syenodi-o r i t e phase, 2) a g r a n o d i o r i t e phase, and 3) a p o r p h y r i t i c b i o -t i t e g r a n o d i o r i t e phase. Gradations between adjacent phases can be found. The w r i t e r does not know whether these phases are present or abundant i n the main part of the b a t h o l i t h , but 13 Campbell ( 1 9 6 1 , 1 9 6 3 , and 1966) has mapped most of the b a t h o l i t h as predominantly g r a n o d i o r i t e . S y e n o d i o r i t e S y e n o d i o r i t e i s confined to the western and northeastern part of the map area (Map 1 ) . Contacts between the s y e n o d i o r i t e phase and the g r a n o d i o r i t e phase are t r a n s i t i o n a l through a zone that ranges from a few tens of fe e t t o more than 200 f e e t . In hand specimens the s y e n o d i o r i t e i s c h a r a c t e r i z e d by black hornblende c r y s t a l s set i n a grey matrix of p l a g i o c l a s e and o r t h -oclase. The rock i s g e n e r a l l y massive, but l o c a l l y , e s p e c i a l l y i n more b a s i c members, the mafic minerals are crudely a l i g n e d . P o i k i l i t i c o r t h o c l a s e grains are conspicuous as they are i n a l l the b a t h o l i t h i c rocks. The hypidiomorphic granular t e x t u r e of the s y e n o d i o r i t e l o c a l l y grades i n t o an i n t e r g r a n u l a r t e x t u r e . Minerals i d e n t -i f i e d i n t h i n s e c t i o n i n c l u d e ; p l a g i o c l a s e , o r t h o c l a s e , horn-blende, a u g i t e , b i o t i t e , q u a r t z , and minor q u a n t i t i e s of a p a t i t e , sphene, magnetite,. pyri,te, epidote, c h l o r i t e , and s e r i c i t e , The modes of two specimens of s y e n o d i o r i t e determined by point counts of t h i n s e c t i o n s are shown i n Table 2 , 3 (see a l s o Figure 2 . 2 ) . . Zoned (normal) p l a g i o c l a s e l a t h s range i n composition from cores of An^^ to rims of A n ^ . Bent l a t h s of p l a g i o c l a s e occur w i t h i n the contact zones w i t h other phases, but were, not ob-1 4 Figure 2 .1 . Locat ion of area of study showing surface d i s t r i b u t i o n of Takomkane B a t h o l i t h . 15 served elsewhere i n the s y e n o d i o r i t e . S e r i c i t e and/or epidote have replaced a small part of a l l p l a g i o c l a s e g r a i n s . P o i k i l i t i c o r t h o c l a s e , which encloses p l a g i o c l a s e , typ-i c a l l y i s p e r t h i t i c adjacent t o p l a g i o c l a s e g r a i n s . Orthoclase-quartz boundaries are micrographic. Hornblende, which i s the predominant mafic mineral i n the rock, contains remnant patches of aug i t e . Augite l o c a l l y i s as abundant as hornblende. B i o t i t e i s common and i n some areas i s more abundant than a u g i t e , e s p e c i a l l y near g r a n o d i o r i t e phases. Rounded x e n o l i t h s of hypersthene gabbro up to one foot i n diameter are common throughout the s y e n o d i o r i t e . Dykes of and-e s i t e porphyry and andesit e , pegmatite, and a l k a l i b a s a l t cut th e . s y e n o d i o r i t e phase of the b a t h o l i t h . G r a n o d i o r i t e Medium-to coarse-grained g r a n o d i o r i t e crops out over much of Takomkane Mountain. . The rock grades i n t o s y e n o d i o r i t e toward the west and the northeast. The eastern contact was not ob-served. In hand specimen black to greenish-black hornblende and b i o t i t e are set i n a white t o l i g h t - g r e y groundmass of p l a g i o -c l a s e , o r t h o c l a s e , and quartz. The rock g e n e r a l l y i s f r e s h but l o c a l l y the f e l d s p a r s are chalky on the surface and i r o n l i b e r -ated from the mafic minerals d u r i n g surface weathering coats some of the rock w i t h a t h i n , l i g h t brown l i m o n i t e s t a i n . 16 Takomkane B a t h o l i t h Plagioclase • Orthoclase 1 Quartz 1 1 Biotite - . Hornblende -Augite Apatite Sphene J Epidote Chlorite Carbonate Sericite G r a n o d i o r i t e Phase N o . * Sample a! i° An 1 6-26.2 6o 38-48 10 1.4 2 12 - X X X 2 — X 2 7-10.3-1 60 36-44 12 15 5 10 1 X X X - X 3 7-12.1-1 55 38-42 15 10 3 17 1 X X X X - X 4 7-12.14-1 5? 33-42 14 12 6 11 - X X X X - X 5 8 - 2 . i l 58 39-45 13 17 4 9 - X X X X - X 6 ' 8-31 .2 54 35-44 !9 13 10 3 - X X X X X X 7 36 50 38-41 8 12 8 15 - X X X X X X 8 BS-6 50 35-41 6 18 20 - - X X X 2 X X 9 BS-19 56 35-42 18 11 6 7 - X X X X X X 10 BS-24 52' 35-40 12 13 10 8 - X X X - X 11 8-3.3 54 38-50 9 7 6 7 3 *v X X X - X 12 8-6.3 47 35-43 17 6 10 15 14 X X X X - X P o r p h y r i t i c B i o t i t e G r a n o d i o r i t e Phase 13 6 - 2 7 . 1 ' 58 24-39 18 10 - 12 - X X X X X X 14 6-27.2 .55 28-34 17 17 - 10 - X X X X X X 15 7-7 .3-1 61 22-40 25 12 1 - - X X X X - X 16 8-28.2 44 23 -37 15 25 16 - X X X - - X S y e n o d i o r l t e Phase 17 7-14.3-1 61 41-51 11 2 5 16 3 X - X X - X 18 6 -25 . 1 60 48-50 10 JL 4 12 11 X - X X - X x Minor - Absent * See Figure 2 . 2 Table 2 . 3 . Modes of rocks from Takomkane B a t h o l i t h . 17 The modes of s e v e r a l specimens of the rock, as determined from p o i n t counts of t h i n s e c t i o n s are shox^n i n Table 2.3. Euhedral to subhedral c r y s t a l s of zoned p l a g i o c l a s e range i n composition from An-^^(rims) to A n ^ C c o r e s ) . The o r t h o c l a s e content, which v a r i e s considerably ' ( 6 - 1 9 $ ) , c o n s i s t s of both l a r g e p o i k i l i t i c g r a i n s and smaller n o n p o i k i l -i t i c i n t e r s t i t i a l g r a i n s . P o i k i l i t i c m i c r o p e r t h i t e g r a i n s en-c l o s e euhedral g r a i n s of p l a g i o c l a s e . Quartz content ranges between 10 and 18 percent and de-creases through the contact zone to l e s s than one percent i n the s y e n o d i o r i t e . Hornblende i s the predominant mafic m i n e r a l , comprising 5 to 7 percent of the rock. Augite remnants w i t h i n the hornblende are g e n e r a l l y r a r e but are common near the t r a n s i t i o n zone between the g r a n o d i o r i t e and s y e n o d i o r i t e phases. Brown b i o t i t e forms l a r g e (up t o 10 mm., i n length) ragged c r y s t a l s t h a t seldom comprise more than 4 percent of the rock. In specimen BS - 6 (number 8, Table 2.3) the I n t r o d u c t i o n of hydrothermal b i o t i t e has raised, the t o t a l b i o t i t e content to 20 percent. The g r a n o d i o r i t e phase of. the Takomkane B a t h o l i t h i s cut by' s e v e r a l other rock u n i t s . P o r p h y r i t i c b i o t i t e g r a n o d i o r i t e , a younger phase of the b a t h o l i t h , cuts the g r a n o d i o r i t e i n the mine area' (Map 2). The g r a n o d i o r i t e a l s o i s cut by v a r i o u s dykes, the Boss Breccias,: and the Boss Mountain quartz..monzonite stock. 18 X e n o l i t h s of h y p e r s t h e n e gabbro a r e numerous w i t h i n t h e grano-d i o r i t e . Ag_e A s i n g l e K/Ar age from t h e g r a n o d i o r i t e phase was d e t e r -mined as 187- m.y. by t h e G e o l o g i c a l Survey of Canada (Leech e t a l , 1 9 6 3 ) . The sample was t a k e n by Campbell 1800 f e e t e a s t -s o u t h e a s t of Takomkane V o l c a n o and w e l l beyond t h e i n f l u e n c e of the molybdenum d e p o s i t s . T h i s age would p l a c e t h e c r y s t a l l i z -a t i o n of the g r a n o d i o r i t e phase of the b a t h o l i t h i n t h e e a r l y J u r a s s i c (White e t a l , 1 9 6 7 ) . G e o l o g i c e v i d e n c e , which c o n s i s t s o f an i n t r u s i v e r e l a t i o n s h i p of the. b a t h o l i t h w i t h Upper T r i -a s s i c N i c o l a Group r o c k s , i s c o n s i s t e n t w i t h t h i s K/Ar age. P o r p h y r i t i c B i o t i t e G r a n o d i o r i t e A s t o c k and s e v e r a l dykes of p o r p h y r i t i c b i o t i t e g r a n o-d i o r i t e , w hich a r e exposed on the s u r f a c e and i n t h e underground w o r k i n g s a t Boss Mountain M i n e s have i n t r u d e d t h e g r a n o d i o r i t e phase of t h e b a t h o l i t h . . P o r p h y r i t i c b i o t i t e g r a n o d i o r i t e c r o p s out nea r the Boss B r e c c i a s as an e l o n g a t e , n e a r l y e l l i p t i c a l body measuring 800 f e e t l o n g and 400 f e e t wide. The s t o c k t r e n d s N 2 5 ° E and, as i n t e r p r e t e d from s u b s u r f a c e i n t e r s e c t i o n s the c o n t a c t s appear t o be n e a r l y v e r t i c a l . P l a g i o c l a s e and b i o t i t e • p h e n o c r y s t s a r e s e t i n a medium-19 Figure 2.2. Composition of pl u t o n i c rocks from the Boss Mountain area. Numbers re f e r to Tables 2.3 and 2 . 6 . (Diagram after Johannsen, 1931). 20 g r a i n e d groundmass of i n t e r l o c k i n g q u a r t z and o r t h o c l a s e . Sphene , a p a t i t e , and z i r c o n a r e t h e a c c e s s o r y m i n e r a l s and c h l o r i t e , r u t i l e , e p i d o t e , s e r i c i t e , p y r i t e and l i m o n i t e are a l t e r a t i o n p r o d u c t s . The modes of t y p i c a l p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e s a r e shown i n T a b l e 2 .3 (numbers 13 t h rou gh 1 6 ) . E u h e d r a l p l a g i o c l a s e p h e n o c r y s t s (8-15 mm. i n l e n g t h ) d i s -p l a y o s c i l l a t o r y z o n i n g . The a n o r t h i t e c o n t e n t i n c r e a s e s and t h e n d e c r e a s e s from the core to the r i m . C o m b i n a t i o n t w i n n i n g i s a common f e a t u r e o f the p l a g i o c l a s e p h e n o c r y s t s . S e r i c i t e has p r e f e r e n t i a l l y r e p l a c e d c e r t a i n zones i n the p l a g i o c l a s e . O r t h o c l a s e i s p e r t h i t i c and r a r e l y forms s u b g r a p h i c i n t e r -growths a l o n g c o n t a c t s w i t h q u a r t z g r a i n s . The g r a i n b o u n d a r i e s o f o r t h o c l a s e and q u a r t z a r e i n t e r l o c k i n g . Brown magmatic b i o t i t e i s , f o r the most p a r t , r e p l a c e d by mosaic masses o f h y d r o t h e r m a l b i o t i t e . . C h l o r i t e l o c a l l y has r e p l a c e d much of the b i o t i t e . Medium-to f i n e - g r a i n e d p o r p h y r i t i c dykes c o r r e l a t i v e w i t h the p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e were i n t e r s e c t e d i n the underground w o r k i n g s . The dykes c o n t a i n b i o t i t e , p l a g i o c l a s e , and o r t h o c l a s e p h e n o c r y s t s i n a g r e y m a t r i x o f q u a r t z and o r t h o -c l a s e . The p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e body grades i n t o g r a n o d i o r i t e over a d i s t a n c e of a few tens of f e e t . P o r p h y r i t i c b i o t i t e g r a n o d i o r i t e dykes c u t the g r a n o d i o r i t e and are c o n -21 s i d e r e d as the l a s t phase of the b a t h o l i t h t o c r y s t a l l i z e . The Boss B r e c c i a s and s e v e r a l o ther r o c k u n i t s cut the p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e . ANDESITE PORPHYRY AND ANDESITE Dykes of a n d e s i t e and. a n d e s i t e p o r p h y r y and t h e i r a l t e r e d e q u i v a l e n t s o u t c r o p s p o r a d i c a l l y throughout the map a r e a . There a r e two s e t s of d y k e s . The most prominent set s t r i k e s n o r t h 20 to. 45 degrees west w i t h d i p s r a n g i n g from 70 degrees eas t to 70 degrees west . Most of these dykes are v e r t i c a l . The second set, which i s s u b o r d i n a t e i n number but impor tant from an economic v i e w p o i n t , s t r i k e s n o r t h 60 to 72 degrees eas t and d i p s 40 to 80 d e g r e e s ' n o r t h w e s t . Widths range from s i x i n c h e s t o about t en f e e t , but most dykes a r e between two and f o u r f e e t wide . The v e r t i c a l ex tent of some a n d e s i t e dykes exceeds 450 f e e t w i t h o u t v i s i b l e change i n t r e n d or c h a r a c t e r . Most dykes are ex-posed f o r o n l y a few tens of f e e t , but some have been t r a c e d f o r 100 f e e t or more and o t h e r s have been p r o j e c t e d by d r i l l ho l e i n t e r s e c t i o n s f o r l e n g t h s exceed ing 1 ,000 f e e t . P h e n o c r y s t s of hornblende and l e s s abundant p l a g i o c l a s e l i e i n a d a r k grey groundmass. The t e x t u r e ranges from i n t e r -g r a n u l a r to t r a c h y t i c w i t h g lomerophyri 'c hornblende i n p o r p h y -r i t i c v a r i e t i e s . P h e n o c r y s t s of hornblende and p l a g i o c l a s e com-p r i s e 18 t o 20 p e r c e n t of the dykes and p l a g i o c l a s e forms the b u l k of the groundmass. The modes f a l l w i t h i n the f o l l o w i n g 22 s EZ2 10-15% Figure 2.3. Equal-area p r o j e c t i o n (lower hemisphere) of poles to 74 andesite and andesite porphyry dykes. 23 l i m i t s : hornblende 1 5 - 2 0 $ , b i o t i t e 0 - 2 $ , p l a g i o c l a s e 78-81$, and minor amounts of q u a r t z , a p a t i t e , z i r c o n , c h l o r i t e , epidote, s e r i c i t e , carbonate, p y r i t e , and. magnetite. Hornblende i s s t r o n g l y p l e o c h r o i c (green to l i g h t brown) and i n d i v i d u a l c r y s t a l s a t t a i n a maximum le n g t h of 20 mm. Phenocrysts commonly are twinned and show marked zoning. Horn-blende l o c a l l y has been replaced, by mosaics of epidote. P l a g i o c l a s e phenocrysts a t t a i n a maximum length of f i v e mm., but average two mm. Phenocrysts are zoned (normal) with rims of A n ^ a n (3- cores of A n^^. Groundmass p l a g i o c l a s e , which comprises up t o 75 percent of the rock, has a composition of An 4 3 - 4 5 . Carbonate, s e r i c i t e , and/or c l a y minerals l o c a l l y have replaced p l a g i o c l a s e . B i o t i t e has replaced hornblende, e s p e c i a l l y on the rims of the hornblende g r a i n s . C h l o r i t e replaced b i o t i t e and horn-blend e. PEGMATITE Pegmatite dykes crop out i n the b a t h o l i t h i c rocks through-out the map area. Some dykes are sinuous w i t h h i g h l y i r r e g u l a r t h i c k n e s s e s . The maximum observed, thickness i s 14 inches and the average thickness i s about 5 inches. The g r a i n s i z e of the major m i n e r a l s , which'ranges from 5 mm. t o 80 mm., g e n e r a l l y averages 20 to 40 mm. Accessory min-e r a l s seldom exceed 10 mm, i n length. 24 03 u to 03 05 OS -— 03 Ph rH +5 CQ O H •H N T5 O -P 03 -P P rH •H «H 03 u 03 bO -P £ <M $ o 1 rH O Ph cts P h CQ to P e r t h i t e A 41 4 •3 '-' 12-16 - X X G r a p h i c B 78 12 0-7 X X X A . Dykes l e s s than s i x i n c h e s i n t h i c k n e s s . B . Dykes g r e a t e r than s i x i n c h e s i n t h i c k n e s s . T a b l e 2 . 4 . Modes of t y p i c a l pegmat i te dykes from Boss Mounta in a r e a . The dykes f a l l i n t o two b r o a d c a t e g o r i e s . Dykes l e s s than s i x i n c h e s i n t h i c k n e s s a r e composed of q u a r t z , p e r t h i t e , b l a c k t o u r m a l i n e , sphene, and magnet i t e ( T a b l e 2 . 4 , A ) . Dykes g r e a t e r t h a n s i x i n c h e s i n t h i c k n e s s c o n t a i n g r a p h i c q u a r t z and p o t a s h f e l d s p a r , p l a g i o c l a s e and a c h l o r i t i z e d p h y l l o s i l i c a t e ( b i o t i t e ? ) , as w e l l as t o u r m a l i n e , sphene, and magnet i te ( T a b l e 2 . 4 , B ) . Many pegmat i t e dykes a r e cut- by narrow e p i d o t e v e i n l e t s . Modal d e t e r m i n a t i o n s were made on hand specimens u s i n g a 2 mm., t r a n s p a r e n t g r i d . A c l o s e r e l a t i o n s h i p e x i s t s , between pegmat i t e dyke o r i e n -t a t i o n and g e o g r a p h i c l o c a t i o n on Takomkane M o u n t a i n . The most prominent s t r i k e i s n o r t h 40 to 70 degrees west w i t h d i p s o f 25 i Northwest A r ea 0 > 5,% m i-5% Figure 2 . 4 . Equal-area p r o j e c t i o n (lower hemisphere) of poles to 47 pegmatite dykes, (The labels r e f e r to parts of the map area). 26 40 t o 80 degrees northward (Figure 2 . 4 ) . Dykes of t h i s o r i e n -t a t i o n crop out only i n the northwest part of the map area and occupy p r e - e x i s t i n g (or p o s s i b l y contemporaneous), j o i n t s . Each pegmatite dyke symbol i n t h i s area of the map represents 10 dykes. J o i n t s of t h i s o r i e n t a t i o n a l s o are found only i n the northwest p o r t i o n of the map area. The dykes range from one inch t o four inches i n thic k n e s s and can be traced f o r s e v e r a l tens of f e e t along t h e i r s t r i k e . In the w e s t - c e n t r a l part of the map area the pegmatite dykes which are few i n number s t r i k e north 45 to 80 degrees east and d i p 10 to 45 degrees south. The dykes are more i r -r e g u l a r i n shape and s i z e than the northwest-trending dykes. Thickness ranges from a minimum of 3 inches t o a maximum of 14 inches. The l a c k of observed j o i n t s of t h i s o r i e n t a t i o n may e x p l a i n the i r r e g u l a r form of the dykes i n t h i s s p e c i f i c area. BOSS MOUNTAIN STOCK The Boss Mountain Stock i s a body of quartz monzonite and quartz monzonite porphyry which intruded the g r a n o d i o r i t e phase of the Takomkane B a t h o l i t h . The f u l l a r e a l extent of the stock i s unknown. However, work done to date i n d i c a t e s a minimum east-west surface diameter of 2 , 5 0 0 f e e t . Because outcrop i s poor i n the area u n d e r l a i n by the stock, i n f o r m a t i o n concerning the petrography and other f e a t u r e s of the stock has been o b t a i n -ed from underground exposures, and the surface contact i s , i n 2 7 p a r t , p r o j e c t e d from underground i n f o r m a t i o n . Specimens from d i f f e r e n t p a rts of the Boss Mountain Stock appear q u i t e d i f f e r e n t i n hand specimen, but the modes are n e a r l y the same. The d i f f e r e n c e s i n appearance are caused by v a r i a b l e degrees of s e r i c i t i z a t i o n and minor d i f f e r e n c e s i n g r a i n s i z e . Boss Mountain Stock Plagioclase i | . Orthoclase j Quartz j Biotite 1 1 1 Hornblende j -p •H 4-5 al Pi < ! Zircon j Sericite j Chlorite | Epidote | j Carbonate j ! Rutile No. Sample No. % An | . Orthoclase j Quartz j Biotite 1 1 1 Hornblende j ! Zircon j Sericite j Chlorite | Epidote | j Carbonate j ! Rutile 2 0 3 2 2 7 3 0 •1 — X X 1 0 X X -X X 2 1 5 9 3 3 7 - 1 3 3 7 2 0 i - X X 9 X - X X 2 2 5 9 + 1 0 3 2 1 0 - 1 6 3 4 24 • - - X X 9 X X X X 2 3 1 0 - 2 7 . 1 0 3 5 3 - 1 6 2 9 3 4 X - X X 2 - X X 24 1 0 - 2 8 . 9 3 4 6-16 3 0 3 3 2 - X X X X - X X 2 5 8 - 9 . 4 3 5 4 - 1 4 3 1 3 2 - - X X 1 X - X X 26 3 7 a ( o u t e r 1 - 6 7 3 2 X X X X - - - - -c h i l l * zone) 2 7 3 7 t > ( inner 2 1 3 - 1 6 4 3 3 5 - X X X X X X X X c h i l l zone) 2 8 3 ? 2 9 1 1 - 1 8 3 0 3 3 5 - X X X 2 X X X x Minor See Figure 2 . 2 Table 2 . 5 . Modes of rocks from the Boss Mountain Stock. In a l l parts of the stock, except i n a narrow part of i t s c h i l l e d c o n t a c t , subhedral p l a g i o c l a s e , o r t h o c l a s e , and quartz phenocrysts c h a r a c t e r i z e the rock. P y r i t e i s ubiq u i t o u s . 28 As observed i n the subsurface workings the east contact of the Boss Mountain Stock w i t h the g r a n o d i o r i t e phase of the b a t h o l i t h i s sharp and w e l l - d e f i n e d ( P l a t e 2 . 2 and 2 . 3 ) and d i p s 45 t o 60 degrees to the east. Outer C h i l l Zone The stock shows a c h i l l e d zone s i x to eight f e e t wide. The outer four t o s i x inches of t h i s c h i l l zone are composed almost e n t i r e l y of graphic intergrowths of quartz and o r t h o c l a s e ( P l a t e s 2 . 3 and 2 . 4 ) w i t h very minor q u a n t i t i e s of b i o t i t e (now a l t e r e d to c h l o r i t e ) , p l a g i o c l a s e , hornblende, a p a t i t e and z i r -con. The mode of the rocks i n the outer c h i l l zone i s shown i n Figure 2 , 2 and Table 2 . 5 (number 2 6 ) . The rock (granophyre) i n the outer c h i l l zone i s f r e s h and the graphic intergrowth i s e a s i l y recognized w i t h a hand l e n s . The outer c h i l l zone grades r a p i d l y i n t o p o r p h y r i t i c g r a n i t e w i t h a f i n e - t o medium-grained groundmass, the inner c h i l l zone. The'pinkish outer c h i l l zone c o n t r a s t s w i t h the greenish to grey-green inner c h i l l zone. Inner C h i l l Zone The inner c h i l l zone i s c h a r a c t e r i z e d by subhedral quartz phenocrysts, and subhedral p l a g i o c l a s e c r y s t a l s set i n a ground-mass of a p l i t i c to granophyric quartz and o r t h o c l a s e w i t h a l i t t l e i n t e r s t i t i a l p l a g i o c l a s e . The t e x t u r e of the groundmass of t h i s phase of the stock i s i d e n t i c a l t o the t e x t u r e of the 29 2 [ B E I S I C G D C a a 3 2 0 9 4 P 4 n I I M I M I I H m i n i w m i j P " 0 2 8 1 9 ! 1 P l a t e 2 . 2 Contact between c h i l l e d margin (granophyre) of Boss Mountain Stock ( l e f t ) and g r a n o d i o r i t e phase of Takomkane B a t h o l i t h . ( r i g h t ) , (Scale i s i n inches.) P l a t e 2 . 3 . Photomicrograph (crossed n l c o l s ) of contact between c h i l l e d margin (granophyre) of Boss Mountain Stock ( l e f t ) and f t r a n o d i o r i t e phase of the Takomkane B a t h o l i t h ( r i g h t ) . 30 r h y o l i t e porphyry dykes. The mode of a rock from the inner c h i l l zone i s g r a n i t e i n composition and i s shown i n Figure 2 . 2 and Table 2 . 5 (number 2 ? ) . The mode i s almost i d e n t i c a l t o the modes of the r h y o l i t e porphyry dykes (Table 2 . 6 ) . Glassy, c l e a r hexagonal quartz phenocrysts are p a r t l y embayed. E x t i n c t i o n g e n e r a l l y i s uniform, but i s o l a t e d pheno-c r y s t s e x h i b i t weak undulatory e x t i n c t i o n . The quartz- pheno-c r y s t s measure up t o 6 mm. i n diameter and. average 2 mm. Small phenocrysts are more n e a r l y euhedral than are l a r g e r ones. S e r i c i t i z e d , r a t h e r ragged, p l a g i o c l a s e phenocrysts are normally zoned w i t h cores of An^g and narrow rims of An^_g. Anhedral groundmass p l a g i o c l a s e , which i s l e s s a l t e r e d than the phenocrysts, has a composition of &nio-\2' P l a S l o c J - a s e phenocrysts are up to 7 mm, i n le n g t h and average about 3 m m » » whereas the groundmass p l a g i o c l a s e seldom exceeds 0 . 3 mm. i n len g t h . Orthoclase, which i s confined to the groundmass of the c h i l l e d rock, occurs as granophyric to a p l i t i c intergrowths w i t h q uartz. B i o t i t e has been h i g h l y a l t e r e d to very l i g h t green, weakly p l e o c h r o i c c r y s t a l s of c h l o r i t e w i t h r u t i l e i n -c l u s i o n s . Accessory and a l t e r a t i o n minerals observed i n t h i n s e c t i o n s are: z i r c o n , a p a t i t e , c h l o r i t e (xvith- r u t i l e i n c l u s i o n s ) , c a r -bonate., epidote, and. p y r i t e . Some z i r c o n c r y s t a l s have t h i n overgrowths. 31 P l a t e 2 . 5 . Photomicrograph (crossed n i c o l s ) of sub-granophyric text u r e of the groundmass of r h y o l i t e porphyry dyke. • • 3 2 Quartz Monzonite Porphyry Medium to coarse-grained quartz monzonite porphyry com-p r i s e s the bulk of the Boss Mountain Stock. The core (?) of the stock, where f r a c t u r i n g i s widely spaced, i s composed of f r e s h , orange-coloured quartz monzonite.porphyry. The orange colour i s imparted by f e l d s p a r phenocrysts and groundmass. Bot' p l a g i o c l a s e and orthoclase are shades of orange, Phenocrysts of subhedral q u a r t z , p l a g i o c l a s e and o r t h o c l a s set i n a groundmass of quartz and orthoclase c h a r a c t e r i z e the porphyry. The t e x t u r e i s p c r p h y r i t i c w i t h an . hypidiomorphic granular groundmass. The p l a g i o c l a s e - o r t h o c l a s e r a t i o of the phenocrysts ( 1 0 : 1 ) c o n t r a s t s w i t h the r a t i o i n the groundmass ( 1 : 3 0 ) . Primary minerals i n c l u d e : p l a g i o c l a s e , o r t h o c l a s e , q u a r t z , b i o t i t e . , and minor q u a n t i t i e s of hornblende, z i r c o n , . and a p a t i t e . Secondary m i n e r a l s , i n order of decreasing quan-t i t y , c o n s i s t of: s e r i c i t e , carbonate, p y r i t e , c h l o r i t e , r u -t i l e , epidote, and z e o l i t e . The modes of seven specimens of quartz monzonite porphyry are shown i n Table 2 . 5 and i n Figure 2 . 2 (numbers 2 0 , 21, 2 2 , 2 3 , 24, 25 and 2 8 ) . Subhedral to euhedral quartz phenocrysts have a t t a i n e d a maximum diameter of 1? mm. Small phenocrysts ( l e s s than 10 mm. .generally are n e a r l y euhedral w i t h well-developed c r y s t a l faces but phenocrysts l a r g e r than 10 mm. i n diameter are subhedral w i t h h i g h l y embayed c r y s t a l faces. 33 O l i g o c l a s e (An^Q^g) phenocrysts w i t h very weakly-zoned rims of An^_g e x h i b i t v a r y i n g degrees of s e r i c i t e replacement. The phenocrysts range from 3 to 14 mm. i n length but most measure between 4 and 8 mm. The colour of the p l a g i o c l a s e changes from orange i n the f r e s h rock t o greenish grey i n i n -tensely- s e r i c i t i z e d . rocks. Fresh p l a g i o c l a s e contains i r r e g u l a r dark r e d d i s h patches. Cause of the orange c o l o u r a t i o n i s not known. Subhedral orthoclase phenocrysts, which are l i g h t orange i n colour range from 8 t o 23 mm. i n l e n g t h . Most c r y s t a l s are f r e s h . Anhedral orthoclase i n the groundmass seldom exceeds 2 mm. i n diameter. Mafic minerals are subordinate to other s i l i c a t e s i n the rock. B i o t i t e .(generally bleached or a l t e r e d to c h l o r i t e ) and/ or hornblende r a r e l y are observed i n t h i n s e c t i o n . S e r i c i t i z a t i o n of the quartz monzonite porphyry ranges from weak to intense and has p r e f e r e n t i a l l y a f f e c t e d p l a g i o -c l a s e . Phenocrysts of orthoclase have escaped s e r i c i t i z a t i o n , except i n the most i n t e n s e l y a l t e r e d rocks. Orthoclase i n the groundmass has been s e r i c i t i z e d . The l i g h t orange colour of the or t h o c l a s e phenocrysts becomes more creamy with i n c r e a s i n g ser-i c i t i z a t i o n of the o r t h o c l a s e , S e r i c i t i z a t i o n has imparted a sugary, greasy appearance to the rock. C h l o r i t e i s present i n a l l samples. Between crossed n i c -o l s the c h l o r i t e i s an anomalous chocolate brown colour. Red, 3k amber, green, or black r u t i l e i n c l u s i o n s occur i n both c h l o r i t e and i n s e r i c i t e . Most c h l o r i t e i s i n t e r s t i t i a l and i s be l i e v e d to be of hydrothermal o r i g i n . Ubiquitous p y r i t e forms up to 11 percent of the rock. Throughout the quartz monzonite porphyry, widely-spaced' m i a r o l i t i c c a v i t i e s , o r i g i n a l l y bordered by euhedral c r y s t a l s of quartz and o r t h o c l a s e , have been f i l l e d w ith s e r i c i t e , c h a l -c o p y r i t e , and carbonate. A p a t i t e rods occur w i t h i n quartz c r y s -t a l s . The c a v i t i e s , which g e n e r a l l y are small ( 3 - 5 iron, i n length) and I r r e g u l a r , o b t a i n a maximum length of 25 mm. R h y o l i t e Porphyry and R h y o l i t e R h y o l i t e porphyry and r h y o l i t e dykes, which occur only near the molybdenite d e p o s i t s , are apophyses of the Boss Mount-a i n Stock.. Dykes range i n th i c k n e s s from 6 inches to 12 f e e t . Some have been projected along s t r i k e from i n t e r m i t t e n t out-crop and d r i l l hole i n t e r s e c t i o n s f o r more than 1 , 0 0 0 f e e t . V e r t i c a l p r o j e c t i o n s from subsurface workings, d r i l l hole i n -t e r s e c t i o n s , and surface outcrop exceed 500 f e e t . Most of the dykes s t r i k e n orth 35 to 50 degrees west w i t h n e a r - v e r t i c a l d i p s (Figure 2 „ 5 ) . The dyke-rock g e n e r a l l y i s p o r p h y r i t i c w i t h phenocrysts of c o l o u r l e s s euhedral q u a r t z , white subhedral p l a g i o c l a s e , and l i g h t p i n k i s h t a n , euhedral o r t h o c l a s e set i n a l i g h t tan t o grey, a p h a n i t i c matrix. N o n - p o r p h y r i t i c v a r i e t i e s are l e s s 35 E3 1-14% >i5% Figure 2.5. Equal-area p r o j e c t i o n (Lower hemisphere) of poles to 18 r h y o l i t e porphyry and r h y o l i t e dykes. 36 common, but are i d e n t i c a l i n colour ( l i g h t tan t o grey) to the p o r p h y r i t i c dykes. Some a p h a n i t i c grey dykes are almost cherty i n appearance. Phenocrysts a t t a i n a maximum l e n g t h of ? mm. and comprise up to 25 percent of the rock. The r h y o l i t e general-l y i s h i g h l y f r a c t u r e d w i t h quartz-molybdenite v e i n l e t s , y e llow muscovite, or brown s t i l b i t e c o a t i n g most of the f r a c t u r e s . T y p i c a l r h y o l i t e porphyry c o n s i s t s of 20 t o 25 percent phenocrysts of q u a r t z , m i c r o p e r t h i t e , and p l a g i o c l a s e i n a r a t i o of n e a r l y 1:2:3 set i n a granophyric ( P l a t e 2.4) to a p l i t i c groundmass. The groundmass, which comprises 75 to 80 percent ; of the.rock, c o n s i s t s of q u a r t z , o r t h o c l a s e , and p l a g i o c l a s e i n a r a t i o of 3'3:1. B i o t i t e , hornblende, s e r i c i t e , a p a t i t e , z i r c o n , c h l o r i t e , r u t i l e , magnetite, p y r i t e , carbonate and molyb-den i t e form a very minor part of the groundmass. The modes of f i v e r h y o l i t e porphyry and r h y o l i t e dykes are shown i n Table 2.6. Subhedral p l a g i o c l a s e phenocrysts w i t h corroded, edges and anhedral c r y s t a l s i n the groundmass have a composition of An 7-10. S e r i c i t e a l t e r a t i o n of the p l a g i o c l a s e ranges from weak to extreme. The phenocrysts have the same p h y s i c a l appearance and almost the same composition as p l a g i o c l a s e phenocrysts i n the Boss Mountain Stock. Euhedral m i c r o p e r t h i t i c o r thoclase phenocrysts comprise up to 10 percent of the rock. The e x s o l -ved p l a g i o c l a s e l o c a l l y i s l a r g e enough to a l l o w determination of the a n o r t h i t e content (An 10-12).-37 Specimen Quartz ! Orthoclase (Microperthitic) Plagioclase | Biotite 1 1 Hornblende j Apatite 1 1 j Zircon j | Magnetite j Molybdenite i Chlorite | Rutile j j Sericite Pyrite ' j Carbonate Quartz ! Orthoclase (Microperthitic) % An | Biotite 1 1 Hornblende j Apatite 1 1 j Zircon j | Magnetite j Molybdenite i Chlorite | Rutile j j Sericite Pyrite ' j Carbonate •91 (P) 5 8 12 8-10 (G) 30 34 11 8 X - X X X — X — X X X 9 1 - 3 0 (P) 4 7 10 10 (G) 35 35 9 7 X - X X X X X X X X • — BS-17 (P) 3 5 12 9-10 (G) 32 36 12 9 - X X X X - - — X X X 8-41 (P) 7 8 8 7-8 (G) 36 32 9 7 X - "V A X X — - — X — — BS-26 40 46 15 7-9 - X X X •- X X X X P Phenocrysts G Groundmass x Minor - Absent Table 2 . 6 Modes of r h y o l i t e porphyry and r h y o l i t e dykes from the Boss Mountain mine area. Quartz occurs as euhedral weakly embayed phenocrysts ( P l a t e 2.6) -and i n the groundmass as granophyric and subgrano-phyric intergrowths w i t h o r t h o c l a s e . The t o t a l quartz content of the dykes i s 35-42 percent. The quartz phenocrysts c l o s e l y resemble the small phenocrysts i n the Boss Mountain Stock. Pale brown hydrothermal b i o t i t e forms up to 2 percent of the r h y o l i t e porphyries. B i o t i t e l o c a l l y has' been bleached a l -most c o l o u r l e s s and contains i n c l u s i o n s of r e t i c u l a t e d r u t i l e . 38 P l a t e 2.6, Photomicrograph (crossed n i c o l s ) of quartz phenocryst i n r h y o l i t e porphyry dyke. 1 cm. P l a t e 2.7. Photomicrograph (crossed n i c o l s ) of embayed quartz phenocryst i n quartz monzonite porphyry. 39 R h y o l i t e porphyry dykes cut the b a t h o l i t h i c rocks and and-e s i t e dykes, and n o n p o r p h y r i t i c r h y o l i t e dykes cut the Phase I B r e c c i a (described i n l a t e r s e c t i o n ) . The dykes are considered to be r e l a t e d t o the Boss Mountain Stock, A genetic r e l a t i o n between these two rock u n i t s i s suggested by 1) the i d e n t i c a l composition and texture of the inner c h i l l zone of the Boss Mountain Stock and of the dykes, 2) character and composition of the p l a g i o c l a s e , 3) character of the quartz phenocrysts, 4) z i r c o n , which i s the common accessory mineral i n both u n i t s , and 5) geographic proximity. G r a i n s i z e i s the only v i s i b l e d i f f e r e n c e i n these two rocks. Environment of Emplacement • General conclusions concerning the environment of emplace-ment of the Bess Mountain Stock can be drawn by comparing the c h a r a c t e r i s t i c features w i t h Buddington's c l a s s i f i c a t i o n of plutons ( 1 9 5 9 ) . Many of the c r i t e r i a d i a g n o s t i c of e p i z o n a l plutons are c h a r a c t e r i s t i c of the Boss Mountain Stock. The f e a t u r e s of the Boss Mountain Stock, which have been d e s c r i b e d , and are c h a r a c t e r i s t i c of- e p i z o n a l p l u t o n s , are itemized below:; 1 ) a l a r g e l y or wholly d i s c o r d a n t r e l a t i o n to the surround-rocks. 2) c h i l l e d margins w i t h sharp contact. 3) granophyric bord.ers. Granophyre, i n g e n e r a l , occurs e x c l u s i v e l y i n the epizone. 40 4) g e n e t i c a l l y r e l a t e d porphyry dykes. 5) no f o l i a t i o n ; some may have primary l i n e a r s t r u c t u r e . 6) m i a r o l i t i c c a v i t i e s . 7) associated b r e c c i a s w i t h the smaller plutons. 8) no contact metamorphism adjacent to p o r p h y r i t i c v a r i e t i e s . Some feat u r e s d i a g n o s t i c of e p i z o n a l plutons are l a c k i n g or were not observed at Boss Mountain. These fea t u r e s are l i s t e d below, 1) E p i z o n a l plutons g e n e r a l l y c o n t a i n roof, pendants. (Roof pendants may have been removed by e r o s i o n ; or may be present, but not observed because of the l a c k of exposures.) 2) V o l c a n i c rocks of the same composition, as the pluton are o f t e n present, except i n plutons from the deeper part of the epizone. 3) Lamprophyre dykes g e n e r a l l y are ass o c i a t e d w i t h e p i -zonal plutons. In summary, the observed features of the Boss Mountain Stock are d i a g n o s t i c of e p i z o n a l plutons. The l a c k of some featu r e s i s to be expected and the examples c i t e d by Buddington (1959) do not contain a l l f e a t u r e s d i a g n o s t i c of e p i z o n a l p l u -tons. However, the l a c k of c e r t a i n f e a t u r e s i s . unimportant i n the c l a s s i f i c a t i o n of the p l u t o n , the important f a c t i s that the Boss Mountain Stock does not contain f e a t u r e s d i a g n o s t i c of plutons emplaced i n the mesozone or catazone. 41 BOSS BRECCIAS B r e c c i a s are g e o l o g i c a l l y i n t e r e s t i n g and economically important fe a t u r e s of the Boss Mountain mine and are r e f e r r e d to c o l l e c t i v e l y as the "Boss B r e c c i a s " . Three phases have been recognized: Phase I has a comminuted grey matrix; Quartz B r e c c i a (Phase I I ) has a quartz matrix; and Phase I I I has a comminuted brown matrix. Only the modes of occurrence and petrography of these b r e c c i a phases w i l l be described i n t h i s s e c t i o n ; t h e i r genesis and r e l a t i o n s to orebodies w i l l be d e a l t w i t h i n Chap-t e r s 4 and 5 . Phase I B r e c c i a Phase I B r e c c i a crops out as three apparently unconnected bodies near the molybdenite d e p o s i t s (Map 2). Boundaries of the b r e c c i a bodies are based on exposures and diamond d r i l l i n t e r -s e c t i o n s and are somewhat c o n j e c t u r a l because of the paucity of outcrop. Contacts betx\-een Phase I B r e c c i a and older rocks are sharp to i n d i s t i n c t . The b r e c c i a grades p r o g r e s s i v e l y i n t o f r a c t u r e d g r a n o d i o r i t e w i t h l i t t l e matrix and then i n t o massive g r a n o d i o r i t e . Three bodies of Phase I B r e c c i a were found during the course of mapping the ore d e p o s i t s . The l a r g e s t body i s adjacent to the b r e c c i a ore zones (described i n a l a t e r s e c t i o n ) and extends i n a w e sterly d i r e c t i o n f o r more than 1000 f e e t (Map 2). The west end of the b r e c c i a has amoeboid p r o j e c t i o n s i n t o the grano-42 d i o r l t e , but elsewhere the contacts are r e g u l a r . A second body of Phase I B r e c c i a l i e s about 400 f e e t south of the Phase I B r e c c i a body described above and the two bodies are separated by an area of g r a n o d i o r i t e and p o r p h y r i t i c b i o -t i t e g r a n o d i o r i t e . The body t r e n d s . g e n e r a l l y northwesterly f o r 500 f e e t , widens to the southeast, and. terminates w i t h amoeboid p r o j e c t i o n s i n g r a n o d i o r i t e . The third, exposed, body of Phase I B r e c c i a , which l i e s about 1000 f e e t n o r t h of the l a r g e s t Phase I B r e c c i a body, i s exposed i n a,few s c a t t e r e d outcrops over an area 120 f e e t long and 50 f e e t wide. The s i z e and shape of t h i s body i s unknown. Phase I B r e c c i a c o n s i s t s mainly of fragments of granod I. or-i t e i n grey t o black matrix ( P l a t e s 2 . 8 and 2 . 9 ) . R h y o l i t e porphyry, andesite porphyry, and/or sugary quartz v e i n fragments g e n e r a l l y are subordinate i n quantity t o g r a n o d i o r i t e and com-p r i s e l e s s than 5 percent of the fragments. The comminuted ma-t r i x has been r e c r y s t a l l i z e d in. some areas and r e c o g n i t i o n i n hand specimen i s d i f f i c u l t . Zones and. " v e i n l e t s " of broken p l a g i o c l a s e and hornblende c r y s t a l s are the major i n d i c a t o r s of r e c r y s t a l l i z e d areas. Isolated, dyke . fragments i n otherwise homogeneous g r a n o d i o r i t e a l s o provide clues to areas of r e c r y s -t a l l i z e d matrix. The angular to subrounded fragments range i n s i z e from microscopic to s e v e r a l f e e t i n diameter. Predominant range of *3 s i z e i s from two t o ten inches. Fragment edges g e n e r a l l y are sharp and d i s t i n c t , although i n places fragment boundaries seem i r r e g u l a r and i l l - d e f i n e d ( p o s s i b l y where the surface observed i s n e a r l y p a r a l l e l t o the fragment-matrix i n t e r f a c e ) . L o c a l l y , and even over d i s t a n c e s of more than 100 f e e t , the p r o p o r t i o n of matrix i n the Phase I B r e c c i a may reach 40 percent, but on the whole i s about 10 percent. Microscopic examination r e v e a l s t h a t the matrix i s composed of f i n e - g r a i n e d (.01 t o 1.5 mm.) fragments of q u a r t z , o r t h o c l a s e , p l a g i o c l a s e , hornblende, b i o t i t e , a p a t i t e and sphene. Angular g r a i n s of o r t h o c l a s e , p l a g i o c l a s e and a p a t i t e were observed w i t h i n g r a i n s of homogeneous, u n s t r a i n e d , r e c r y s t a l l i z e d q u a r t z . Quartz i n rock fragments has strong undulatory e x t i n c t i o n . In r e s t r i c t e d areas of the Phase I B r e c c i a the fragments are cemented by non-granulated, r h y o l i t e porphyry. Such areas have a maximum l e n g t h of 40 f e e t (Map 2) and g e n e r a l l y are somewhat elongate i n p l a n . Minute subhedral g r a i n s of l i g h t brown b i o t i t e are l o c a l l y disseminated among the other minerals of the matrix and a l s o occur In v e i n l e t s ' and as selvedges on r e c r y s t a l l i z e d quartz and o r t h o c l a s e . E v i d e n t a l l y such b i o t i t e i s younger than Phase I B r e c c i a . Phase I B r e c c i a , which contains fragments of g r a n o d i o r i t e , p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e , andesite porphyry, r h y o l i t e P l a t e 2.8. Phase I B r e c c i a . A n g u l a r fragments of g r a n o d i -o r i t e , group 1 q u a r t z v e i n ( q ) , and g a r n e t -hornblende v e i n l e t (g) i n comminuted m a t r i x ( b l a c k ) . ( S c a l e i s i n i n c h e s ) . P l a t e 2.9. Phase I B r e c c i a . A n g u l a r fragments of g r a n o d i o r i t e and r h y o l i t e p o r p h y r y ( r ) i n comminuted m a t r i x ( g r e y ) . ( S c a l e i s i n i n c h e s . ) porphyry, garnet v e i n l e t s , and sugary quartz v e i n s , must be younger than a l l such rock u n i t s . I n t r u s i o n of r h y o l i t e dykes and formation of Phase I B r e c c i a probably are oogenetic processes. The Phase I B r e c c i a cuts r h y o l i t e porphyry dykes and dyke fragments are common w i t h i n the b r e c c i a . I r r e g u l a r bodies of r h y o l i t e porphyry l o c a l l y form part of the matrix .of the Phase I B r e c c i a (Map 2). F i n a l -l y , n o n p o r p h y r i t i c r h y o l i t e dykes cut the Phase I B r e c c i a and. occur as fragments i n the l a t e r b r e c c i a phases. In summary, dyke emplacement commenced before and continued d u r i n g and a f t e formation of the Phase I B r e c c i a , but ceased, before formation of Quartz B r e c c i a . . Quartz B r e c c i a During a second phase of b r e c c i a formation, quartz was introduced as matrix between rock fragments. Quartz matrix c h a r a c t e r i z e s the b r e c c i a and has given r i s e to the term "Quartz B r e c c i a " . Quartz B r e c c i a bodies are w e l l - d e f i n e d , s t e e p l y plunging l e n t i c u l a r or p i p e - l i k e bodies. The l a r g e s t of these, part of.the Main B r e c c i a Zone (Map 2 ) , i s somewhat l e n t i c u l a r i n surface p l a n . The zone trends north 35 degrees west, plunges s t e e p l y northwestwards, and dips 75 to 90 degrees eastward f o r the f i r s t 500 v e r t i c a l f e e t . The north end and the southwest side of the b r e c c i a have been modified by l a t e r b r e c c i a t i o n and 46 the o r i g i n a l contacts were destroyed. Surface exposure of the Main B r e c c i a Zone i s 500 f e e t long and at the maximum i s 150 f e e t wide. The c o n f i g u r a t i o n of the body i s w e l l - d e f i n e d by underground workings and diamond d r i l l holes down t o the 5 0 4 5-foot l e v e l . Below t h i s l e v e l , a few d r i l l holes have defined the western contact, but not the east-ern contact. The d i p of the western contact remains r e l a t i v e l y constant as' f a r as i t has been t r a c e d . The South B r e c c i a Zone i s an e l l i p s o i d a l area of p o o r l y -developed quartz b r e c c i a which l i e s 220 f e e t south 35 degrees east of the Main B r e c c i a Zone. The zone s t r i k e s north 55 de^ grees west on surface with a l e n g t h of 250 f e e t and a width ranging from 90 to 110 f e e t . The degree of b r e c c i a t i o n i n -creases' w i t h i n c r e a s i n g depth. , Smaller bodies of Quartz B r e c c i a cut the Phase I B r e c c i a . The smaller bodies are e l l i p t i c a l i n plan and range from 10 to 35 f e e t along the maximum diameter. B r i l l hole i n t e r s e c t i o n s confirm a v e r t i c a l to n e a r - v e r t i c a l plunge to the pipes. D i s -t r i b u t i o n of the smaller pipes i s e r r a t i c and does not appear to f o l l o w any obvious c o n t r o l s . Most contacts of the quartz b r e c c i a w i t h the g r a n o d i o r i t e are t r a n s i t i o n a l ; some are sharp. T r a n s i t i o n a l contacts grade from Quartz B r e c c i a to quartz stockwork w i t h nonrotated. f r a g -ments and. then i n t o massive g r a n o d i o r i t e w i t h widely separated 47 P l a t e 2.10. Quartz B r e c c i a . Fragments of g r a n o d i o r i t e and a l t e r e d andesite dyke (black) i n quartz matrix (white). Molybdenite forms the dark-coloured rims on the fragments. (Scale i s i n inches.) P l a t e 2.11. Phase I I I B r e c c i a . Angular to rounded fragments of g r a n o d i o r i t e , quartz ( w h i t e ) , and a l t e r e d ande-s i t e dyke (black) i n comminuted matrix ( g r e y ) . (Scale i s i n inches.) 48 quartz v e i n s . Sharp contacts are r e s t r i c t e d to d y k e - l i k e bodies of Quartz B r e c c i a . Adjacent to sharp contacts the r e l a t i v e move-ment of the fragment's i n the b r e c c i a has been a s c e r t a i n e d . Along some contacts the g r a n o d i o r i t e fragments can be recon-s t r u c t e d l i k e pieces of -a jigsaw puzzle (Figure 2.6). In a l l cases where fragments'were r e c o n s t r u c t e d to o r i g i n a l p o s i t i o n s w i t h the w a l l - r o c k , the fragments showed a movement downward from t h e i r p o i n t of o r i g i n . This f e a t u r e i s important i n any i n t e r p r e t a t i o n of the o r i g i n of the b r e c c i a s . Most fragments are g r a n o d i o r i t e , but p o r p h y r i t i c b i o t i t e g r a n o d i o r i t e , andesite porphyry and andesite dykes, garnet v e i n -l e t s , e a r l y quartz v e i n s , r h y o l i t e porphyry dyke, and Phase I B r e c c i a fragments are present and l o c a l l y are abundant. Fragments range i n s i z e from a f r a c t i o n of an inch to f i v e f e e t , but most range.from one inch t o one foot i n length. Abrasion between h i g h l y angular fragments has been n e g l i g i b l e , and some fragments have r e t a i n e d needlesharp p o i n t s . Adjacent fragments i n the Quartz B r e c c i a are r a r e l y i n contact w i t h each other and appear to " f l o a t " i n a white quartz matrix ( P l a t e 2.10). .In d r i l l core the d i f f e r e n t i a t i o n between Quartz B r e c c i a and quartz stockwork i s extremely d i f f i c u l t . In t h i n s e c t i o n the contact between matrix and fragments g e n e r a l l y ..is sharp. M i c r o p e r t h i t e occurs e x c l u s i v e l y along the Figure 2.6. Sketches of contacts between Ouartz Breccia dykes and granodiorite on the 5045 level. s 50 edges of the quartz matrix and has replaced adjacent parts of rock fragments. The a l k a l i f e l d s p a r i n the g r a n o d i o r i t e f r a g -ments a l s o i s m i c r o p e r t h i t i c and i n t h i n s e c t i o n c l o s e l y resem-b l e s metasomatic m i c r o p e r t h i t e , except f o r the p o i k i l i t i c h a b i t of the magmatic v a r i e t y . Quartz B r e c c i a i s cut by Phase I I I B r e c c i a , c h l o r i t e v e i n -l e t s , quartz v e i n s , a l k a l i b a s a l t dykes, and c a l c i t e - z e o l i t e v e i n l e t s . Phase I I I B r e c c i a . The main body of Phase I I I B r e c c i a formed vii t h i n and along the southwest side of the p r e - e x i s t i n g Quartz B r e c c i a . The b r e c c i a i s a somewhat e l l i p t i c a l - b o d . y which extends through a known v e r t i c a l range greater than 600 f e e t . The top of the. Phase III. B r e c c i a body i n the Main B r e c c i a Zone does not reach the surface. The body i s 50 to 100 f e e t wide and. 150 to 300 f e e t long. In'hand, specimen, Phase I I I B r e c c i a i s composed of angular to well-rounded fragments i n grey to l i g h t brown matrix. The matrix g e n e r a l l y i s somewhat porous and. contains v i s i b l e creamy to salmon-coloured orthoclase c r y s t a l s , secondary z e o l i t e s , and disseminated molybdenite. The s i l i c e o u s matrix appears somewhat sugary when viewed with a hand. l e n s . Much of the s i l i c a was probably derived from comminution of the quartz, matrix•of the Quartz B r e c c i a , 51 Angular fragments of Quartz B r e c c i a occur at the borders of the Phase I I I B r e c c i a zones. However, w i t h i n a foot or two of the contact the fragments of Quartz B r e c c i a w i t h i n the Phase I I I B r e c c i a become well-rounded. P l a t e 2.11 shows a t y p i c a l sample of Phase I I I B r e c c i a c o n t a i n i n g well-rounded and angular fragments of q u a r t z , g r a n o d i o r i t e , and a l t e r e d andesite dyke. Contacts between matrix and fragments g e n e r a l l y are sharp. The p r o p o r t i o n of martix i n Phase I I I B r e c c i a may exceed ?0 percent of the rock over areas 30 f e e t or more i n diameter„ but g e n e r a l -l y averages 20 t o 30 percent. Petrographic study of the matrix of the Phase I I I B r e c c i a r e v e a l s that the sugary t e x t u r e i s due i n part to rounded g r a i n s of quartz i n a f i n e r - g r a i n e d , more highly-comminuted groundmass. Quartz fragments show undulatory e x t i n c t i o n . Fine-grained sub-he d r a l b i o t i t e c r y s t a l s and golden brown s t l l b i t e impart the l i g h t brown colour to the matrix. S t i l b i t e has replaced f r a g -ments of p l a g i o c l a s e . Creamy t o salmon-coloured hydrothermal or t h o c l a s e Is m i c r o p e r t h i t i c - and has replaced fragments of p l a g i o c l a s e and o r t h o c l a s e i n the matrix and i n the g r a n d i o r i t e fragments. B i o t i t e and euhedral molybdenite c r y s t a l s , which are d i s -t r i b u t e d uniformly throughout the matrix of the Phase I I I B r e c c i a , have p a r t l y replaced fragments of g r a n o d i o r i t e . A l t e r a t i o n of dyke and g r a n o d i o r i t e fragments has been 52 more intense i n the Phase I I I B r e c c i a than i n other b r e c c i a phases. Some g r a n o d i o r i t e fragments have been a l t e r e d to earthy, white, s e r i c i t e and c l a y 'minerals with light.brown ovoid.s comprised of many, small hydrothermal b i o t i t e c r y s t a l s . Other fragments which have not been a l t e r e d to cl a y minerals l o c a l l y have been replaced by creamy to salmon-coloured orthoclase ac-companied by c h l o r i t i z a t i o n of the mafic minerals, o Phase I I I B r e c c i a and Phase I B r e c c i a are s i m i l a r i n ap-pearance except f o r the f o l l o w i n g d i s t i n g u i s h i n g f e a t u r e s : 1. The abundance of rounded fragments i n the Phase I I I B r e c c i a d i s t i n g u i s h e s i t from the Phase I B r e c c i a which i s comprised of.angular fragments. 2. Fragments of Quartz B r e c c i a , which i s younger than the Phase I B r e c c i a , c l e a r l y i d e n t i f i e s the Phase I I I B r e c c i a . 3. Disseminated b i o t i t e and molybdenite d i s t i n g u i s h the matrix of the Phase I I I B r e c c i a from the barren (except f o r b i o t i t e s t r i n g e r s i n f r a c t u r e s ) matrix of the Phase I B r e c c i a . TIME OF INTRUSION OF RHYOLITE PORPHYRY AND RHYOLITE DYKES I n t r u s i o n of r h y o l i t e porphyry and r h y o l i t e dykes, which are apophyses of the Boss Mountain Stock, accompanied formation of Phase I B r e c c i a . R h y o l i t e porphyry dyke fragments occur i n the Phase I B r e c c i a and l o c a l l y r h y o l i t e porphyry comprises the matrix of t h i s b r e c c i a , N onporphyritic r h y o l i t e dykes cut the Phase I B r e c c i a , but occur as fragments i n l a t e r b r e c c i a phases. In summary, i n t r u s i o n of r h y o l i t e prophyry (and. r h y o l i t e ) dykes 53 and f o r m a t i o n of Phase I B r e c c i a are contemporaneous p r o c e s s e s r e l a t e d to emplacement of the Boss Mountain S t o c k . TAKOMKANE VOLCANIC ROCKS The Takomkane v o l c a n i c r o c k s , p a r t of which forms the tw in summits of Takomkane M o u n t a i n , are the youngest r o c k s i n the map a r e a . The v o l c a n i c r o c k s , which r i s e about 250 f e e t above the s u r r o u n d i n g p l a t e a u - l i k e u p l a n d , a r e p a r t o f a v o l c a n i c cone , one o f s e v e r a l e x t i n c t v o l c a n i c c e n t r e s i n the C a r i b o o r e g i o n ( F i g u r e 2 . 7 ) . L a v a breached the wes tern s i d e of the cone and f lowed down a g e n t l e d e p r e s s i o n f o r m i n g a t o n g u e - l i k e f low some 2500 f e e t l o n g and about 15 f e e t t h i c k a t i t s o u t e r e x t r e m i t y . The n o r t h e a s t e r n edge of the cone was removed by an a l p i n e g l a -c i e r r e s u l t i n g i n a 3 0 - t o 8 0 - f o o t e scarpment . The p a r t of the cone t h a t has escaped e r o s i o n measures 3000 f e e t ( n o r t h - s o u t h ) by 2000 f e e t ( e a s t - w e s t ) . Most s treams d r a i n i n g the a r e a , ex-cept T e n - M i l e Creek, , c o n t a i n l i t t l e f l o a t d e r i v e d from the v o l c a n o . G l a c i a l d e p o s i t s c o n t a i n s p o r a d i c a l l y d i s t r i b u t e d rounded b o u l d e r s and c o b b l e s o f a l k a l i b a s a l t , presumably d e -r i v e d from Takomkane. V o l c a n o . U n c o n s o l i d a t e d v o l c a n i c e j e c t a r a n g i n g i n s i z e from ash to b l o c k s as l a r g e as 3 f e e t i n d i a m e t e r form most o f the cone . E x c e p t f o r the tongue of l a v a west of the cone,, f lows and a g -g l o m e r a t e are most abundant n e a r the eas t edge of the cone . V o l c a n i c bombs and bomb f r a g m e n t s , some w i t h n u c l e i ! of 54 55 p e r i d o t i t e or a l k a l i b a s a l t , are abundant. Most contacts are concealed by r u b b l e , except on the south edge of the cone where a small r i l l has exposed the contact w i t h the u n d e r l y i n g g r a n o d i o r i t e . Heinecke ( 1 9 2 0 , p.83) described the contact at the base of the northeast escarpment as f o l l o w s : "On the northeast and steeper side of the h i l l s . . . , t h e a c t u a l contact between the g r a n i t e and the l a v a i s exposed at the foot of the h i l l , where i t s t r i k e s north 10 degrees east and d i p s 60 degrees to the west. The g r a n i t e i s shattered and o x i d i z e d and the l a v a i s dense at the contact." X e n o l i t h s of p e r i d o t i t e , g l a s s y black a u g i t e , and granodi-o r i t e , which occur throughout the flows and e j e c t a , are espec-i a l l y numerous i n the eastern exposures. Dykes r e l a t e d to the volcano r a r e l y are seen i n outcrop because of t h e i r high s u s c e p t i b i l i t y to weathering, but they are numerous i n the underground workings of the mine. The dykes occupy two sets of v e r t i c a l post-mineral f r a c t u r e s which s t r i k e n orth 10 t o 25 degrees east and north 50 to 60 degrees east (Figure 2 . 8 ) , Some lineaments may r e f l e c t weathered a l -k a l i b a s a l t dykes. Columnar j o i n t s are well-developed i n most dykes, but those without j o i n t s c o n t a i n abundant elongated, v e s i c l e s and c e n t r a l v e s i c l e pipes l i n e d w i t h c l u s t e r s of s t i l -b i t e c r y s t a l s . Dark greenish black g l a s s c h a r a c t e r i z e s the c h i l l e d margins of a l l dykes. Dykes range i n thickness from 6 inches to 30 f e e t , but-few exceed 3 f e e t . A s u b h o r i z o n t a l t r a i n of g r a n o d i o r i t e boulders l i e s about Figure 2.8. Equal-area p r o j e c t i o n (lower hemisphere) of poles to 39 a l k a l i basalt dykes. 57 75 f e e t below the summit of the south r i d g e of the cone. Boulders of g r a n o d i o r i t e are sc a t t e r e d over the cone below t h i s l e v e l , but not above i t . Other g r a n o d i o r i t e fragments that have been r a f t e d i n t o place by v o l c a n i c a c t i o n are coated w i t h a t h i n r i n d of c h i l l e d a l k a l i b a s a l t . The boulders i n and near the boulder t r a i n are not coated with an a l k a l i b a s a l t r i n d , and probably were deposited along the edge of a g l a c i e r . The v o l c a n i c rocks l i e upon a g l a c i a t e d surface (Suther-land-Brown, 1957) and have been eroded by g l a c i a l a c t i o n as shown.by the abundance of g l a c i a l e r r a t i c s on the cone, the boulders der i v e d from the cone i n g l a c i a l d e p o s i t s , and the r e -moval of the northeast part of the cone by an a l p i n e g l a c i e r . Sutherland-Brown (1957) concluded from t h i s evidence t h a t : "....The mountain has obviously been g l a c i a t e d before the cone was b u i l t , and. the presence of e r r a t i c boulders and minor s c u l p t u r i n g of the cone i n d i c a t e that i t was a l s o g l a c i a t e d a f t e r . A l l f a c t s i n d i c a t e that the cone and flows were formed l a t e i n the P l e i s t o c e n e epoch." A l k a l i B a s a l t Rocks from a l k a l i b a s a l t dykes and flows e x h i b i t some d i f f e r e n c e s . Dyke-rocks g e n e r a l l y are more co a r s e l y c r y s t a l -l i n e than flow-rocks and f o r t h i s reason they have re c e i v e d more i n t e n s i v e i n v e s t i g a t i o n . Dykes are dark o l i v e green to green-i s h b l a c k , x«rhereas lavas are red-brown to blac k . ' Few minerals can be i d e n t i f i e d i n :hand specimen, except i n x e n o l i t h s , which occur only i n lavas and e i e c t a . 58 Weakly p o r p h y r i t i c a l k a l i b a s a l t dykes contain glomero-p h y r i c patches of augite c r y s t a l s set i n an i n t e r g r a n u l a r to h y a l o p h i t i c groundmass of p l a g i o c l a s e , o r t h o c l a s e , b i o t i t e , o l i v i n e ( ? ) , g l a s s , a p a t i t e , magnetite, and an u n i d e n t i f i e d mineral. The modes of three specimens of a l k a l i b a s a l t dyke determined by point counts of t h i n s e c t i o n s are l i s t e d i n Ta-bl e 2 . 7 . Euhedral l a t h s of p l a g i o c l a s e up to 1 mm, long range i n composition from A n ^ t o A n 6 0 * ^ e c o r e s °^ m o s t c r y s t a l s are weakly a l t e r e d to s e r i c i t e but there i s l i t t l e v i s i b l e zoning. P l a g i o c l a s e was not i d e n t i f i e d i n rocks w i t h high g l a s s content. Lavas c o n t a i n m i c r o l i t e s and small ( 0 . 2 mm.) c r y s t a l s of p l a g -i o c l a s e w i t h compositions of An^g_gQ. Smal l , rounded gr a i n s of ort h o c l a s e occur i n the groundmass. 0) -. — to a to 0) rH cd 4-i O rH C.) Q) fH c <D o O C 4^> P 4J % P o -p •H to • H 0) O •H fef.i •C • H > 4^ to -P c rH «5 4-3 60 •H O a cS bp O t—1 >H rH rH Pi <s c fl) o < o PQ < N Specimen % An 5 - 2 5 . 1 65 ~"58^60 # 25 2 3 3 2 L 5 - 1 9 . 4 - - - 26 4 66 * 1 1 2 1 0 - 2 7 . 1 1 70 53-60 21 ? 4 . 3 . 2 *• -- absent * minor ? p o s s i b l e Table 2 . 7 . Modes of a l k a l i b a s a l t dykes. 59 Augite occurs as c o l o u r l e s s to l i g h t green euhedral c r y s -tals up to 0.1 mm. long i n the groundmass and i n glomerophyric patches up to 1 mm. i n diameter.' Serpentine and carbonate pseudomorphs of what probably were euhedral o l i v i n e c r y s t a l s are s p o r a d i c a l l y s c a t t e r e d through the rocks. Anhedral xenocrysts of o l i v i n e are widely d i s t r i b u t e d through a l l l a v a s , but are not found i n dykes, Euhedral to subhedral p l a t e s of red-brown t o l i g h t brown b i o t i t e , which comprise up to 4 percent of some r o c k s , occur as uniformly d i s t r i b u t e d small (up t o 0,2 mm.) p l a t e s between aug-i t e and. p l a g i o c l a s e g r a i n s . Brown g l a s s , which g e n e r a l l y i s weakly a l t e r e d , comprises up to 66 percent of some dykes. Lavas and dykes g e n e r a l l y con-t a i n l i t t l e g l a s s , except near t h e i r margins. The groundmass of a l l rocks contain v a r i a b l e q u a n t i t i e s of an u n i d e n t i f i e d c o l o u r l e s s mineral which has low b i r e f r i n -gence and an index of r e f r a c t i o n l e s s than balsam. The mineral was too small and too crowded with other minerals to permit i d e n t i f i c a t i o n , but i t may be a f e l d s p a t h o i d , .orthoclase, or p o s s i b l y a z e o l i t e . A p a t i t e and magnetite are ubiquitous i n the a l k a l i b a s a l t s . S t i l b i t e occurs i n v e s i c l e s and. f i l l s f r a c t u r e s i n the rocks. L e u c i t e was i d e n t i f i e d , w i t h an X-ray powder photograph, but was not observed, i n t h i n s e c t i o n . Peach ( I 9 6 3 , P.6) i d e n t i f i e d 6o l e u c i t e as a major mineral i n some rocks from Takomkane volcano and s t a t e s , "the l a v a . . , , i n places approaches l e u c i t i t e i n comp-o s i t i o n . " Such rocks have.not been i d e n t i f i e d d u r i n g t h i s b r i e f i n v e s t i g a t i o n of these v o l c a n i c rocks. XENOLITHS Three kinds of x e n o l i t h s , excluding cognate x e n o l i t h s of a l k a l i b a s a l t , are widespread in. the Takomkane v o l c a n i c rocks. They l o c a l l y c o n s t i t u t e up to 25 percent of the lavas i n the eastern exposures, but average l e s s than 1 percent, P e r i d o t i t e x e n o l i t h s are most abundant, followed by g r a n o d i o r i t e , and then g l a s s y black augite. G r a n o d i o r i t e and augite x e n o l i t h s , which have not been studied i n d e t a i l , are b r i e f l y d.escribed below. G r a n o d i o r i t e x e n o l i t h s show various degrees of d i g e s t i o n and a l t e r a t i o n by the e n c l o s i n g a l k a l i b a s a l t . Primary mafic minerals i n grano-d i o r i t e ( b i o t i t e and hornblende) were most, s u s c e p t i b l e to a l t e r -a t i o n . In some x e n o l i t h s s i t e s p r e v i o u s l y occupied, by primary • mafic minerals are open vugs l i n e d w i t h a c i c u l a r green or brown-c r y s t a l s of pyroxene (?)." P l a g i o c l a s e g r a i n s have been r e c r y s -tallized. along t h e i r borders to r a d i a t i n g groups of c r y s t a l s w i t h r e f r a c t i v e i n d i c e s l e s s than balsam. Orthoclase has been s i m i l a r l y a f f e c t e d , but quartz r a r e l y has been v i s i b l y a l t e r e d . Rounded., gl a s s y black augite c r y s t a l s (xenocrysts) range from 5 to 47 mm. i n diameter. Cleavage i s seldom d i s c e r n a b l e 61 i n hand specimens. Most xenocrysts have subconchoidal f r a c t u r e and are e a s i l y mistaken f o r v o l c a n i c g l a s s . Thin s e c t i o n ex-amination of one small (10 mm.) xenocryst was used to i d e n t i f y the mineral as a u g i t e . P e r i d o t i t e I n c l u s i o n s of p e r i d o t i t e , which show a wide d i v e r s i t y i n composition, are s p o r a d i c a l l y d i s t r i b u t e d throughout the Tak- • omkane v o l c a n i c r o c k s . They are e s p e c i a l l y abundant on the east edge of the cone where they comprise from 1 to 25 percent of the l a v a s . Most a l k a l i b a s a l t dykes do not c o n t a i n p e r i d o t i t e i n c l u s i o n s . The average s i z e range of the p e r i d o t i t e i n c l u s i o n s i s from 2 t o 6 inches,, but the t o t a l range i s from xenocrysts of microscopic s i z e t o c r y s t a l aggregates 20 inches i n diameter. Most i n c l u s i o n s are rottnded, but some have subrounded. shapes.. The i n c l u s i o n s p r o g r e s s i v e l y decrease i n s i z e and abundance w i t h i n c r e a s i n g d i s t a n c e from the eastern edge of the cone. The mineral composition of the p e r i d o t i t e s c o n s i s t s of v a r i a b l e q u a n t i t i e s of o l i v i n e , c linopyroxene, orthopyroxene, and s p i n e l . In a world-wide survey of p e r i d o t i t e i n c l u s i o n s , Ross et. a l ( 1 9 5 4 ) showed the clinopyroxenes of p e r i d o t i t e i n -c l u s i o n s are chromian diopsi.de and the orthopyroxenes are. en-s t a t i t e . In the present study, modal analyses of 30 p e r i d o -tite i n c l u s i o n s were determined by p o i n t counting hand specimens 62 using a transparent g r i d (2 mm. spacing). Three modal analyses were made by po i n t counts of t h i n s e c t i o n s . The coarse-grained t e x t u r e and the coarse l a y e r i n g Tendered point counts of t h i n s e c t i o n s of d o u b t f u l value. The modes of these 33 specimens are l i s t e d i n Table 2 . 8 and the corresponding r a t i o s of o l i v i n e , chromian d i o p s i d e , and e n s t a t i t e are p l o t t e d i n Figure 2 . 9 . Most i n c l u s i o n s contain more than 50 percent o l i v i n e and some specimens c o n t a i n predominantly chromian d i o p s i d e , but few spec-imens contain e n s t a t i t e as the dominant mineral. Layering i n most i n c l u s i o n s i s s u b t l e , g e n e r a l l y being expressed as t h i n discontinuous bands of chromian d i o p s i d e . Other i n c l u s i o n s have coarse a l t e r n a t i n g l a y e r s of d i f f e r e n t composition. Mineralogy O l i v i n e , chromian d i o p s i d e . e n s t a t i t e , and s p i n e l comp-r i s e the mineral c o n s t i t u e n t s of a l l observed p e r i d o t i t e i n -c l u s i o n s , P l a g i o c l a s e , a minor c o n s t i t u e n t of p e r i d o t i t e i n c l u s i o n s throughout the world (Ross et a l , 195^)» was reported by Reinecke ( 1920) as a minor c o n s t i t u e n t of some p e r i d o t i t e s from the Takomkane l a v a s , but i t was not observed i n t h i s i n -v e s t i g a t i o n . O l i v i n e - O l i v i n e , the most abundant mineral i n the p e r i d o t i t e i n c l u s i o n s (Figure 2 . 9 ) . a l s o occurs as xenocrysts i n the a l k a l i 63 No. Specimen O l i v i n e Chromian Di opside E n s t a t i t e S p i n e l 1 7-14.8-1 0 98 . 0 2 2 9-4 .5 (a) 93 4 2 1 3 (b) 82 10 6 2 4 7-17.9 0 65 30 5 5 no number 15 79 6 0 6 7-12.8-1 13 86 1 0 7 7-17.8 70 16 13 1 8 7-17.11 66 14 19 1 9 no number 96 2 0 2 10 no number 72 7 20 1 11 7 -15 . 2 (a) 53 18 29 t r 12 (b) 59 22 17 1 13 (c) 70 7 22 1 14 (d) 61 29 10 t r 15 (e) 77 22 1 0 . 16 ( f ) 75 8 16 1 17 (g) 67 4 28 1 18 (h) 94 3 ? t r 19 ( i ) 70 17 13 t r 20 U ) 74 ' 11 15 t r 21 (k) 63 29 8 t r 22 (1) 67 5 28 0 23 (m) 20 54 26 0 24 (n) 53 • 19 28 t r 25 7 -15 . 3 (a) 68 14 18 t r 26 (b) 65 8 27 t r 27 (c) 67 17 16 t r 28 7 - 1 5 . 2 . 83 7 10 t r 29 7-17.10 66 16 18 t r 30 no number 2 97 0 t r 31 A* 0 40 50 10 32 B* 70 12 15 3 33 C* 11 84 4 1 Thin s e c t i o n modes. Table 2 . 8 . Modes of p e r i d o t i t e i n c l u s i o n s from the Takomkane v o l c a n i c rocks. b a s a l t s . The anhedral, equidimensional, transparent, l i g h t green o l i v i n e g r a i n s range i n s i z e from 1 mm. to 10 mm. Broad twin planes were observed i n some o l i v i n e g r a i n s . A l t e r e d o l i v i n e g r a i n s , which are red i n hand specimen, contain b r i g h t 64 red t h r e a d - l i k e f i l a m e n t s p e n e t r a t i n g the g r a i n s near t h e i r borders. O l i v i n e g r a i n s were e x t r a c t e d from i n c l u s i o n s and from the groundmass f o r de t e r m i n a t i o n of composition using the X-ray powder photograph method described by Jambor and Smith ( I 9 6 3 ) . The o l i v i n e s from the Takomkane v o l c a n i c rocks have composi-t i o n s ranging from Fog^. ^  to Fog^ ^  (Table 2 . 9 and Figure 2 . 1 0 ) . N o n - f i l t e r e d i r o n r a d i a t i o n was used f o r a l l determin-• a t i o n s , except number 12 i n which n i c k e l o x i d e - f i l t e r e d copper r a d i a t i o n was used. A l l f i l m s were co r r e c t e d f o r shrinkage. UBC % Fo Number . Specimen Film No. (calculated) 1 6 - 2 3 . 2 fgrouhdmass) 4937 8 9 . 9 1 2 7-10.1 4805 85.14 3 7 -12 .2-1 (groundmass) 4943 89.52 4 7 - 1 5 . 7 4803 8 7 . 9 3 5 7-15.10 4804 8 7 . 5 3 6 7-17.7 4819 88.09 7 7-17.11 4820 88.09 8 9 * 4 . 5 (groundmass) 4938 8 9 . 9 1 9 9 - 4 . 6 (groundmass) 4939 8 9 . 5 2 10 9 - 4 . 8 (groundmass) 4940 85.14 11 no number 4807 88.09 12 #4AS 4290 88.09 Table 2 . 9 . Composition of o l i v i n e s from p e r i d o t i t e I n c l u s i o n s and. groundmass of Takomkane v o l c a n i c r o c k s . Chromian Diopside - Chromian d i o p s i d e occurs as emerald-green ,-equidlmensional t o lath-shaped gr a i n s ranging i n s i z e from 1 t o 60 mm. Weathered specimens are d u l l o l i v e green. The chrom-i a n d i o p s i d e content of the i n c l u s i o n s ranges from 2 t o 98 per-cent, but most i n c l u s i o n s c o ntain l e s s than 30 percent. Spectre-65 01 28 •15 .21 20 J6 JO I? '32 '13 27. JC 2 5 2& 26 17-• 14 .|2 24« ,23 •33 1/30 Di Figure 2.9, 50 31 Composition of 33 p e r i d o t i t e i n c l u s i o n s from Takomkane volcanic rocks (sp i n e l excluded). o Mol. percent Forsterite H o O o r> 3 TJ Cfl o • CO rr *-». o H* 3 W 03 O r« >-fi C'J g o r~* <" <"? (-•• ft) D m cn f» r » i 3 M cr O o rr ^ =r w 3 r-3 rr P' b -» 3 i—• vD 3 O o CO - - < • o r> B) 3^ H * N 5 o o O n ON 67 g r a p h i c a n a l y s e s conf i rmed the presence of chromium (IT. B . C . #1-18). In t h i n s e c t i o n chromian d i o p s i d e i s green i n p lane p o l a r i z e d l i g h t and e x h i b i t s w e l l - d e v e l o p e d c l e a v a g e . Some g r a i n s , e s p e c i a l l y those l a r g e r than 20 mm. have d i a l l a g e p a r t -i n g ( 1 0 0 ) . E n s t a t i t e - E n s t a t i t e o c c u r s as t r a n s l u c e n t , e q u i d i m e n s i o n a l g r a i n s up t o 10 mm. i n d i a m e t e r . C o l o u r i n hand specimen ranges from h o n e y - y e l l o w (number 31) t o brown or g r e e n i s h brown. S m a l l e x s o l u t i o n l a m e l l a e of c l i n o p y r o x e n e were observed i n some e n -s t a t i t e g r a i n s . S p i n e l - S p i n e l s , which comprise l e s s than 2 p e r c e n t of most i n c l u s i o n s , a r e c o l o u r l e s s t o b l a c k i n hand spec imen. Most are a n h e d r a l , except o c c a s i o n a l b l a c k , s u b m e t a l l i c g r a i n s t h a t have s u b h e d r a l f o r m . S p i n e l s a r e c o l o u r l e s s t o t a n i n p l a n e p o l a r i z e d l i g h t . Broitfn t o b l a c k r i m s occur on s p i n e l s i n c o n t a c t w i t h a l k a l i b a s a l t ( P l a t e 2 . 1 2 ) . S p i n e l x e n o c r y s t s e x h i b i t v a r i o u s degrees of r i m deve lopment . Some x e n o c r y s t s are e n t i r e l y b l a c k , o t h e r s have o n l y a narrow b l a c k r i m . A l k a l i b a s a l t a d j a c e n t to such rimmed s p i n e l g r a i n s i s i m p o v e r i s h e d i n magnet i t e c r e a t i n g a l i g h t - c o l o u r e d h a l o around the g r a i n s ( P l a t e 2 . 1 3 ) . These b l a c k r i m s may be caused by i r o n r e p l a c i n g magnesium i n the s p i n e l s t r u c t u r e . The l i b e r a t e d magnesium c o u l d t h e n be i n c o r p o r a t e d 68 i n the pyroxenes or b i o t i t e d u r i n g c r y s t a l l i z a t i o n of the l a v a s . The exchange of i r o n f o r magnesium i n . t h e s p i n e l would r e s u l t i n an increased s p e c i f i c g r a v i t y without much increase i n c e l l edge. S p e c i f i c g r a v i t y and c e l l edge were measured on 11 s p i n e l g r a i n s . C e l l edges were measured from X-ray powder photographs corre c t e d f o r f i l m shrinkage. N o n - f i l t e r e d i r o n r a d i a t i o n was used on a l l samples, except number 11 which u t i l i z e d n i c k e l o x i d e - f i l t e r e d copper r a d i a t i o n . Two s p e c i f i c g r a v i t y determinations were made on each s p i n e l using a Berman Balance and the average of these two readings i s given i n Table 2 . 1 0 . The r e s u l t s of s p e c i f i c g r a v i t y and c e l l edge determinations are p l o t t e d on the compo-s i t i o n diagram of Deer et a l (1964, v o l . 5, P . 6 1 ) and are shown i n Figure 2 . 1 1 . Compositions are grouped near the s p i n e l (MgAlgO^) corner of the diagram. One b l a c k s p i n e l w i t h metal-l i c l u s t r e (number 5) has a composition near t h a t of h e r c y n i t e (FeAlgO^) suggesting t h a t i r o n has replaced the o r i g i n a l mag-nesium i n the s p i n e l . O r i g i n of X e n o l i t h s Many d i s c u s s i o n s of the o r i g i n of p e r i d o t i t e x e n o l i t h s i n v o l c a n i c rocks are found i n the l i t e r a t u r e (Ross et a l , 1 9 5 4 ; B r o t h e r s , I 9 6 0 ; W i l s h i r e and Bi n n s , I 9 6 I ; Talbot et a l , 1 9 6 3 ; Jackson, I 9 6 6 ) . The two most commonly accepted t h e o r i e s of o r i g i n are: 1) the x e n o l i t h s are d e r i v e d from c r y s t a l cumulates . of the host r o c k s ; or 2) they are pieces of the mantle that have 6 9 1 cm. P l a t e 2.12. Photomicrograph (plane p o l a r i z e d l i g h t ) of a l k a l i b a s a l t with p e r i d o t i t e x e n o l i t h s . S p i n e l (s) grains have dark rims at contact w i t h a l k a l i b a s a l t . ( o l i v i n e , o: chromian d i o p s i d e , d) P l a t e 2,13, Photomicrograph (plane p o l a r i z e d l i g h t ) of a s p i n e l (centre) g r a i n i n a l k a l i b a s a l t . Note the a l k a l i b a s a l t adjacent to the s p i n e l i s impoverished i n magnetite near the s p i n e l g r a i n . 71 UBC C e l l Edge S p e c i f i c Number Specimen F i l m No. (measured) G r a v i t y 1 7 - 1 5 . 8 ' 4 9 1 0 8.182 4 . 0 9 2 7 - 1 7 . 1 0 4 8 1 2 8 . 1 4 3,79 3 7 - 2 7 . 3 4 8 0 2 8 . 1 0 3.59 4 9-4.6 4966 8 . 1 8 4 . 0 2 5 # 2 A E S 4814 8 . 1 4 4.33 6 #3AES 4 8 0 8 8 . 2 4 4.35 7 #1RMT 4 9 6 5 8 . 1 4 3.74 8 # 2 R M T 4 9 7 2 8.18 4 . 1 3 9 #3RMT 4 9 7 8 • 8 . 1 5 3 .90 1 0 # 4 R M T 4 9 7 6 8 . 1 5 3 . 7 6 1 1 no number 4 0 7 2 8 . 1 6 3 . 8 0 (Numbers 7» 8 , 9? and 1 0 from samples c o l l e c t e d by R. M. Thompson) Table 2 . 1 0 . C e l l edge and s p e c i f i c g r a v i t y measurements of s p i n e l s from p e r i d o t i t e x e n o l i t h s i n Takomkane v o l c a n i c rocks. been brought to the surface along v o l c a n i c conduits. The f o l l o w i n g f e a t u r e s of p e r i d o t i t e x e n o l i t h s can be explained by e i t h e r theory of o r i g i n . P e r i d o t i t e x e n o l i t h s : 1. are world-wide i n occurrence. 2 . occur almost e x c l u s i v e l y i n a l k a l i basalts., 3. have i d e n t i c a l mineralogy throughout the world. 4. are laye r e d . D e t a i l e d i n v e s t i g a t i o n of one or more of these features has l e d v a r i o u s authors to opposing c o n c l u s i o n s . I t i s , beyond the scope of the present study t o t r y to r e s o l v e the o r i g i n of p e r i d o t i t e x e n o l i t h s through an exhaustive l i t e r a t u r e survey. The data from t h i s p r e l i m i n a r y study of the Takomkane v o l c a n i c rocks and associated p e r i d o t i t e x e n o l i t h s agrees w i t h published data, but are not adequate to e x p l a i n t h e i r o r i g i n . 72 I I I . STRUCTURE S t r u c t u r a l f eatures of the Boss Mountain Mine area i n -clude j o i n t s and f a u l t s , as w e l l as a myriad of quartz v e i n s . Some of these f e a t u r e s are of d i f f e r e n t ages and. older s t r u c -tures may be g r e a t l y d i s l o c a t e d or otherwise concealed by young-er s t r u c t u r e s . Those features unrelated t o ore d e p o s i t i o n are described under the s e c t i o n on General S t r u c t u r e and those r e -l a t e d to ore d e p o s i t i o n under Local S t r u c t u r e . GENERAL STRUCTURE Fa u l t s A l l f a u l t s i n the area surrounding the Boss Mountain Mine can be grouped, i n t o f i v e sets based on a t t i t u d e . Most f a u l t s are of post-minferal age. Molybdenite Creek^Fault The broad v a l l e y s of Boss Creek and Molybdenite Creek form a continuous lineament t r e n d i n g north 35 to 40 degrees west which i s i n f e r r e d as the trace of a f a u l t , the Molybdenite Creek Fault (Map 1), I t cuts the Takomkane B a t h o l i t h w i t h i n the map area and continues through N i c o l a Group v o l c a n i c rocks to the north (personal o b s e r v a t i o n ) . In the map area there are no marker u n i t s that can be used to measure displacement. From i t s topographic expression the f a u l t i s b e l i e v e d to have a steep d i p . Although the age of the Molybdenite Creek f a u l t i s unknown 73 . - . • i t probably i s one of the oldest f r a c t u r e s i n the area, A f a u l t along Ten - r M i l e Creek causes a r i g h t - l a t e r a l s e p a r a t i o n of the Molybdenite Creek f a u l t ' o f the order of 1000 f e e t . P o s t - M i n e r a l F a u l t s Four sets of post-mineral f a u l t s have been recognized on Takomkane Mountain. The abundance of outcrop near the summit of the mountain has permitted establishment of the f o l l o w i n g c h r o n o l o g i c a l sequence of post-mineral f a u l t s ( o l d e s t to young-e s t ) : ( 1 ) s t r i k e s n orth 60 degrees west w i t h a v e r t i c a l d i p , ( 2 ) s t r i k e s n o r t h 50 to 58 degrees east w i t h a v e r t i c a l d i p , ( 3 ) s t r i k e s n o r t h 10 to 30 degrees east w i t h a v e r t i c a l d i p , and ( 4 ) s t r i k e s n o r t h 70 degrees east t o south 80 degrees east w i t h d i p s from 69. degrees south t o v e r t i c a l . The f a u l t s are expressed by pronounced lineaments, some of which extend f o r thousands of f e e t . For the most p a r t , these f a u l t s have had l i t t l e v i s i b l e e f f e c t on adjacent rocks,• a l -though shear f r a c t u r e s have developed p a r a l l e l t o some f a u l t s . Most: f a u l t surfaces are obscured by debris., but where v i s i b l e , as i n c i r q u e w a l l s , the a d j o i n i n g rock i s i n t i m a t e l y f r a c t u r e d w i t h many slackensided surfaces.. F a u l t s t h a t s t r i k e n o r t h 60 degrees west are w e l l developed i n the northwestern and i n the southern part of the map area, but are weak or absent i n the c e n t r a l p a r t . These f a u l t s are 74 cut by s i n i s t r a l f a u l t s s t r i k i n g north 50 to 58 degrees east. F a u l t s s t r i k i n g north 50 t o 58 degrees east are the most abundant post-mineral f a u l t s i n the map area. Numerous j o i n t s (shear f r a c t u r e s ) p a r a l l e l f a u l t s of t h i s set. A t h i r d set of post-mineral f a u l t s , which s t r i k e s north 10 to 30 degrees east with v e r t i c a l d i p s , cuts the north 50 to 58 degree east f a u l t s , F a u l t s of t h i s age are seldom detected i n surface exposures, but are prominent i n the mine workings. F a u l t s of the youngest set s t r i k e from north 70 degrees east to south 80 degrees east and d i p from 69 degrees south t o v e r t i c a l . These e a s t e r l y s t r i k i n g f a u l t s cut a l l others i n the map area and form the most prominent and most continuous lineaments. The most prominent of these f a u l t s i s the Ten-Mile Creek F a u l t whitsh extends across the e n t i r e map area and o f f s e t the Molybdenite Creek Fault.' Evidence of displacement i s based upon the separation of two r i d g e s east of Molybdenite and. Boss Creeks. The break between these r i d g e s c o i n c i d e s w i t h the probable t r a c e of the Ten-Mine Creek F a u l t , J o i n t s are mod-e r a t e l y well-developed adjacent to Ten-Mile Creek F a u l t . A l l post-mineral f a u l t s are older than the Takomkane Volcano, but only f a u l t s s t r i k i n g north 50 t o 58 degrees east and north 10 t o 30 degrees east commonly contain b a s a l t dykes. 75 J o i n t s S e v e r a l prominent j o i n t s e t s , which e x h i b i t a s t r i k i n g c o n t r o l of topography, cut the rocks i n the map area. Figure 3.1 i s an equal-area p r o j e c t i o n (lower hemisphere) of poles t o j o i n t s . Three of these j o i n t sets are found i n almost a l l ex-posures, although the degree of development i s not always equal. These j o i n t s , marked 1, 2, and 3 i n Figure 3.1t have the f o l -l owing average a t t i t u d e s : (1) s t r i k e s n o r t h 42 degrees west and d i p s 42 degrees south, (2) s t r i k e s n o r t h 45 degrees west and d i p s 48 degrees n o r t h , and ( 3 ) s t r i k e s north 41 degrees west and d i p s v e r t i c a l l y . The f i r s t set i s most abundant. The s t r i k e of j o i n t set 2 (N45°W) i s more w e s t e r l y (N58°W) w i t h steeper d i p s (60°N) i n the north p a r t of the map area (Figure 3.1» number 2a). Superimposed on. j o i n t s e t s 1, 2, and 3 i s another set s t r i k i n g n o r t h 56 degrees east w i t h d i p s t h a t are predominantly v e r t i c a l but range from 60 degrees south to 70 degrees n o r t h (Figure 3.-1. number 4 ) . This j o i n t set p a r a l l e l s post-mineral f a u l t s . Other j o i n t sets are l o c a l i n d i s t r i b u t i o n and g e n e r a l l y p a r a l l e l f a u l t s . LOCAL STRUCTURE Loca l s t r u c t u r e s i n c l u d e garnet-hornblende v e i n l e t s , which occupy narrow mylonite zones, q u a r t z - f i l l e d f r a c t u r e s and 76 E3 I -5% B5-10% Effl 10-15% Figure 3.1. Equal-area p r o j e c t i o n (lower hemisphere) of poles to 321 j o i n t s on Takomkane Mountain. 77 u n f i l l e d f r a c t u r e s . The f r a c t u r e s , both q u a r t z - f i l l e d and barren, have been studied i n d e t a i l on the 5045 l e v e l of the mine which provides s e v e r a l thousand f e e t of continuous 3 -dimensional exposure through a l l known g e o l o g i c a l f e a t u r e s , ex-cept the Takomkane volcano. Sublevels are r e s t r i c t e d to ore-bearing areas and are u s e f u l f o r comparative purposes. Surface exposures are too few and discontinuous to provide data as mean-i n g f u l as that obtained on the 5 0 4 5 l e v e l . Garnet-Hornblende V e i n l e t s Along the 5045 main haulage l e v e l , both east and west of the Boss Mountain Stock,, g r a n o d i o r i t e and andesite dykes are cut by numerous garnet-hornblende v e i n l e t s . These occupy nar-row mylonite zones which are i n t e r p r e t e d as shear f r a c t u r e s . A t t i t u d e s of 1 2 3 v e i n l e t s east of the stock and of 48 v e i n l e t s west of the stock are shown on stereograms i n Figure 3.3. Three sets of f r a c t u r e s that seem to be present i n each area have average a t t i t u d e s summarized as f o l l o w s : East of Boss Mountain Stock West of Boss Mountain Stock 1 . s t r i k e "N58°Wr d i p v e r t i c a l 1. s t r i k e N72 UE; d i p " ' v e r t i c a l 2 . s t r i k e N12°W; d i p 7 1 ° E 2 . s t r i k e N20°E; d i p v e r t i c a l 3 . s t r i k e . N68°E; d i p 6 3 ° S 3 . s t r i k e N34°W; d i p v e r t i c a l changing to s t r i k e N56°Ej d i p v e r t i c a l Sets 1 and 2 are i n t e r p r e t e d as conjugate shears so oriented, that the b i s e c t r i x of the acute angle i s roughly normal to the surface of the Boss Mountain Stock i n each area. Set 3 , roughly ce-nsure 3.2. Idealized plan of part of the 5045 l e v e l showing att i t u d e s of garnet-hornblende v e i n l e t s and t h e i r r e l a t i o n s h i p to the Boss Mountain Stock. 79 West of Boss Mountain Stock «8 points) Figure 3.3. Equal-area projections (lower hemisphere) of poles to garnet -hornblende velnlcts(5D45 level). 80 p a r a l l e l to the surface of the stock i n each area, i s i n t e r p r e t e d as a c o n c e n t r i c shear. This a n a l y s i s of the f r a c t u r e p a t t e r n i s j u s t i f i e d by f i e l d observations. Fractures of sets 1 and 2 cross without o f f s e t , whereas f r a c t u r e s of set 3 are cut by those of sets 1 and 2. Figure 3.2 i s an i d e a l i z e d r e p r e s e n t a t i o n of the r e l a t i o n of these f r a c t u r e sets to. the Boss Mountain Stock. When the stock was intruded the w a l l - r o c k was d i s r u p t e d f i r s t by shearing p a r a l l e l to the contact and l a t e r by conjugate shears so oriented. that the a x i s of maximum s t r e s s was normal to the contact. Ore Fractures - 5 0 ^ 5 Level A d e t a i l e d a n a l y s i s of both barren and m i n e r a l i z e d f r a c -tures i n the underground workings was made i n an e f f o r t to help e x p l a i n the genesis of the Boss B r e c c i a s and. ore d e p o s i t s . The eig h t groups of f r a c t u r e s i d e n t i f i e d i n t h i s study i n c l u d e pre-m i n e r a l , contemporaneous and post-mineral f r a c t u r e s . Recognition and c o r r e l a t i o n of f r a c t u r e s of a given age i s dependent upon c r o s s - c u t t i n g r e l a t i o n s , a t t i t u d e s of f r a c t u r e s , and upon the character and mineralogy of quartz veins which f i l l most of the f r a c t u r e s . In most cases the character and miner-alogy of the quartz veins i s the only r e l i a b l e • feature f o r cor-r e l a t i o n i n d i f f e r e n t areas of the mine. The underground workings of the 5 0 ^ 5 l e v e l were divided, i n t o eight areas based upon p r o x i m i t y to geo l o g i c features such as the Fracture A t t i t u d e Area Character Genetic a f f i n i t y 8 N5°W to N10°E; 9 0 ° a l l Barren; c a l c i t e - z e o l i t e P o s t - m i neral: Unknown 7 N 5 0 - 6 0°E; 90° a l l Barren; c a l c i t e - z e o l i t e P o s t - m i neral: Unknown 6 N?8-82°E; 40-48°N a l l Barren; c h l o r i t i z e d P o st-mineral: Unknown 5 N70-7^°W; 20--30°S N19°E; 20°N N47°E; 30°S N5°E; 20-35°S N75-80°E; 40-45°N N75°E; 30°N N48°W; 20°S C,D,E D,G E F G H . 'K Quartz-molybdenite v e i n s . Reduction of pressure at depth - High-Grade Vein and S t r i n g e r Zones. 4 E a r l y : N5°W; 50 OS N45°E; 20°S N'30°E; 4 5 0 S Late: N12-20°E; 6 6 - 6 8°S N30°E; 15°N Composite: N20-30OW; 18°S N10°Wj 15-25°S N60°E; 40-70°N A C E A,3,C C D F.G G Quartz v e i n s , (composite) Complex mineralogy. End of Phase I I I Brec-c i a formation and c r y s t a l l i z a t i o n of the Boss Mountain Stock. 3 N40-45°E; 30°S N50-70°E; 60-65°S F D,G Quartz-molybdenite v e i n s Phase I I I B r e c c i a 2 N28-43°W; 75N to 9 0 c C,G H Quartz ve i n s i n some Quartz B r e c c i a i ( o l d e s t ) N40-60°E; 90° A l l * Quartz veins i n some Unknown (* except B) Table J.l. C h r o n o l o g i c a l chart of f r a c t u r e s on the 504-5 l e v e l ; Boss Mountain Mine. CO 1 •  Figure 3.4. Stereographic projections (lov;er hemisphere) of group 1 f r a c t u r e s i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix I for contoured equal-area p r o j e c t i o n s ) ; 8 3 Boss B r e c c i a s and the Boss Mountain Stock, These areas have been designated A, B, C, D, E, P, G, and H on the accompanying, f i g u r e s . Few f r a c t u r e s , e s p e c i a l l y those f i l l e d , w i t h quartz v e i n s , show evidence of movement. ' Apparent, displacement, where v i s i b l e , seldom exceeds one f o o t . Some f r a c t u r e s of each age o f f s e t older f r a c t u r e s , dykes, etc. and some fracture' surfaces a r e . s l i c k e n -sided.. Table 3 . 1 i s a summary of the r e l a t i v e age, o r i e n t a t i o n , c h a r a c t e r , and p o s s i b l e genetic s i g n i f i c a n c e of a l l f r a c t u r e s e t s , which are discussed i n d i v i d u a l l y below. Equal-area stereograms (lower hemisphere) from which the f o l l o w i n g a t - . t i t u d e s were derived are shown i n Appendix I. G r o u p ! Fractures Group 1 f r a c t u r e s , the o l d e s t recognized group, occur throughout the mine area, except in. the Boss B r e c c i a s and. the Boss Mountain Stock (Figure 3 . 4 ) . A t t i t u d e s of the fractures,-which are s u r p r i s i n g l y 'consistent, range, from north kO to 6 0 degrees east and a l l d i p v e r t i c a l l y or very n e a r l y so. A f t e r quartz was deposited i n the f r a c t u r e s they were sheared, g i v i n g the quartz veins a sugary appearance wi t h weakly banded s t r u c -t u r e p a r a l l e l to the f r a c t u r e s . Near the Main B r e c c i a Zone, i n area C, molybdenite was added to the veins at some l a t e r time. P y r i t e i s disseminated, through the v e i n s . Boss Breccias \\*\ Boss Mountain Stock | 1 Takomkane Batholith • N I Figure 3.5. Stereographic pr o j e c t i o n s (lower hemisphere) of group 2 fractures i n d i f f e r e n t areas of the .5045 l e v e l (see Appendix I for contoured equal-area p r o j e c t i o n s ) . 85 Group 1 f r a c t u r e s which cut g r a n o d i o r i t e , andesite dykes and garnets-hornblende v e i n l e t s , are i n t u r n cut by the Boss B r e c c i a s , Boss Mountain Stock and r e l a t e d dykes, together with a l l other quartz veins and a l k a l i b a s a l t dykes. Group 2 Fractures Group 2 f r a c t u r e s , which occur near but not i n the Boss B r e c c i a s (Figure 3.5, areas C, E, G. and H), s t r i k e north 28 to 50 degrees west and d i p 75 degrees north to v e r t i c a l . Some f r a c t u r e s are f i l l e d w i t h barren quartz veins that contain minor amounts of p y r i t e and m i c r o p e r t h i t e . The a t t i t u d e s of the f r a c t u r e s are s t x b p a r a l l e l to the s t r i k e of the Quartz B r e c c i a (Main B r e c c i a Zone). North of the Main B r e c c i a Zone (Figure 3.5, areas G and. H) the a t t i t u d e s of the f r a c t u r e s p a r a l l e l the Quartz B r e c c i a (north 35 degrees west, d i p 75 to 80 degrees n o r t h ) . Group 2 f r a c t u r e s -cut group 1 f r a c t u r e s , g r a n o d i o r i t e , Phase I B r e c c i a , and. andesite dykes and. are cut by l a t e r quartz v e i n s . -Gr oup_ 3-ffr a °- *f u,r e s Group 3 f r a c t u r e s are r e s t r i c t e d to areas north and west of the Phase I I I B r e c c i a , (Figure 3.6, areas D, F, and G,). The . f r a c t u r e s , which are nowhere abundant, g e n e r a l l y . a r e f i l l e d w i t h quartz-molybdenite v e i n s . £ Figure 3.6. Stereographic projections (lower hemisphere) of group 3 fractures i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix I for contoured equal-area p r o j e c t i o n s ) . 87 Group 3 f r a c t u r e s s t r i k e north 50 to 67 degrees east and d i p 60 t o 65 degrees south i n areas D and G. In area F the vein s s t r i k e n o r t h 40 to 45 degrees east and d i p JO degrees south. Reverse movement of a few inches occurs on some f r a c -t u r e s . The r e l a t i v e g e o l o g i c age of the f r a c t u r e s i s w e l l -documented. Group 3 f r a c t u r e s cut g r a n o d i o r i t e , Quartz B r e c c i a and group 1 f r a c t u r e s adjacent to Phase I I I B r e c c i a . Both group 4 and group 5 f r a c t u r e s cut group 3 f r a c t u r e s . Group 4 F r a c t u r e s Group 4 f r a c t u r e s have been observed i n most areas of the underground workings (Figure 3 . 7 ) . The a t t i t u d e s of the f r a c -t u r e s and quartz veins i n d i f f e r e n t areas of the 5045 l e v e l are l i s t e d i n Table 3.1. Quartz v e i n s i n group 4 f r a c t u r e s are com p o s i t e west of and i n the Boss B r e c c i a s (Figure 3 . 7 . areas D, E, and G), but occur as two separate sets east of the b r e c c i a s (areas A, B, and C). E a r l y stage veins c o n t a i n q u a r t z , molyb-d e n i t e , m i c r o p e r t h i t e , c h l o r i t e , p y r i t e , and r u t i l e . Late stage quartz v e i n s , which have a mineralogy s i m i l a r to e a r l y , stage quartz veins ( q u a r t z , m i c r o p e r t h i t e , c h l o r i t e , , and p y r i t e are recognized by t h e i r accessory minerals such as: a i k i n i t e , b i s m u t h i n i t e , c h a l c o p y r i t e , s p h a l e r i t e , magnetite, s c h e e l i t e , s e r i c i t e , f l u o r i t e , c a l c i t e , and anatase. Late stage quartz v e i n s i n group 4 f r a c t u r e s have been superimposed, upon and are £ Early Late Composite Figure 3.7. Stereographic projections (lower hemisphere) of group 4 fra c t u r e s i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix .1- f o r contoured equal-area p r o j e c t i o n s ) . 8 9 confined to the v e i n boundaries•of e a r l y stage quartz veins i n areas D, F, and G. In area A, B, and C e a r l y and l a t e group 4 quartz v e i n s occupy separate f r a c t u r e s e t s . Group j?.,,.FTa,£.turgs More d e t a i l has been obtained about group 5 f r a c t u r e s and t h e i r a s s o c i a t e d quartz-molybdenite veins than any others. The r i b b o n - l i k e character of the veins i s s i g n i f i c a n t to t h e i r r e c o g n i t i o n . The veins form an important part of the S t r i n g e r Zones and the High-grade Vein system. Fractures of t h i s age have not been recognized i n or east of the Boss Mountain Stock, but are prominent and abundant i n and near the Main B r e c c i a Zone where much data has been c o l l e c t e d regarding o r i e n t a t i o n s . When these data were plotted- on equal-area stereonets (Appendix I) the f o l l o w i n g f r a c t u r e sets became evident: Area A t t i t u d e of Sets S t r i k e DIE r> N?5°W 2 0 ° S D N19°E 2 0 °W N?4°W 3 0 ° s E N47°E 3 0 ° s N?5°W 3 0 °s F N18°E 2 5 ° W G . N13°E 3 0 ° w N ? 9 ° E 4 3 ° N H N48°W 2 0 °S N76°E 3 0 ° N I t i s noted that two'sets appear.in areas D, E, G, and H. Because f r a c t u r e s of these sets have mutual i n t e r s e c t i o n s i t i s concluded that they represent p a i r s of conjugate shear planes. \ 0 o Figure 3 . 8 . Stereographic pr o j e c t i o n s (lower hemisphere) of group 5 fractures i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix I f o r contoured squal^area projections) -. Figure 3.9. Stress elements of group 5 quartz veins. A: Orientation and attitudes in specific areas. B ! Stereographic projections (lower hemisphere) of stress elements (note that P(min) defines a great circle). 9 2 I f Hartman's Law that the a x i s of maximum pressure (P max) b i s e c t s the acute angle between shear planes i s accepted, then the- s t r e s s d i s t r i b u t i o n i s as shown, i n Table 3.2. Area P(max) P ( i n t ) P(min) D ' S32°E at 5 ° S ? 6 ° W at 16° N48°E at 7 4 ° E N77°E h o r i z o n t a l S17°E at 28° N14°W at 64° G N32°E at 11° N65°W- at 3 0 ° S39°E at 5 8 ° H N25°E at 5 ° N65°W at 6 ° S26°E at 82° Table 3.2 Group 5 f r a c t u r e s . O r i e n t a t i o n s of s t r e s s elements. Such a s t r e s s d i s t r i b u t i o n i s i l l u s t r a t e d by Figure 3 . 9 . From a composite stereogram p l o t of these s t r u c t u r a l elements. I t i s noted that P(max) and P ( i n t ) have random o r i e n t a t i o n but the P(min) are concentrated, i n a small- area, the centre of which l i e s i n a north 7 4 degrees east d i r e c t i o n at 83 degrees (Figure 3 . 9 . B). The genet i c i m p l i c a t i o n s of t h i s s t r e s s d i s t r i b u t i o n pattern, i s d e a l t w i t h i n a l a t e r s e c t i o n . Post-Ore Frac t u r e s — 5 0 4 5 L e v e l Group 6' F r a c t u r e s Group 6 f r a c t u r e s have been recognized i n a l l rocks,, ex-cept the Boss Mountain Stock and some co n t a i n post-mineral a l k a l i b a s a l t dykes. The- f r a c t u r e s s t r i k e n o r t h 7 8 t o 8 2 degrees east, d i p 40 t o 48 degrees n o r t h (Figure 3 . 1 0 ) and p e r s i s t over lengths exceeding 5 0 0 " feet.. ' Much shearing and intense c h l c r l t i z a t l o n has -occured along such f r a c t u r e s . \ 0 Figure 3.10. Stereographic projections (lower hemisphere) of group 6 fr a c t u r e s i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix I for contoured.equal-area: :.projectioris). Figure 3 . 1 1 . Stereographic p r o j e c t i o n s (lower hemisphere) of group 7 and group 8 f r a c t u r e s i n d i f f e r e n t areas of the 5045 l e v e l (see Appendix-I for contoured equal -area p r o j e c t i o n s ) -9 5 Wallrock adjacent to such f r a c t u r e s i s a l t e r e d t o c l a y minerals. Fractures of t h i s set are c l e a r l y post-mineral. They cut and o f f s e t quartz-molybdenite veins i n a l l ore bodies and produced d r a g - f o l d s i n the quartz of the High-Grade Vein. A l l observed displacements i n d i c a t e normal f a u l t i n g . Group 7 a l i f l Group 8 Fractures F r a c t u r e s of groups 7 and 8 (Figure 3.11), a l s o post-mineral i n age, o f f s e t a l l ore-bearing s t r u c t i i r e s and have no gene t i c r e l a t i o n s h i p t o m i n e r a l i z a t i o n . The f r a c t u r e s of. group 7 s t r i k e north 5 0 to 6 0 degrees east and d i p v e r t i c a l l y . Group 8 f r a c t u r e s , which o f f s e t group 7 f r a c t u r e s , s t r i k e n o r t h 5 degrees west to north 2 0 degrees east and. d i p v e r t i c a l -l y . ' Both sets of f r a c t u r e s contain abundant, water-bearing open spaces, f i l l e d , or p a r t l y f i l l e d w i t h c a l c i t e and z e o l i t e s . Many group ? f r a c t u r e s contain a l k a l i b a s a l t dykes. . Group 7 and 8 f r a c t u r e s are prominent outside the immediate mine area and were d.escribed. i n the s e c t i o n on General S t r u c t u r e . One set of f r a c t u r e s found, only east of the Boss Mountain Stock s t r i k e s north 3 8 degrees east and. di p s 5 5 degrees n o r t h -west. The s i g n i f i c a n c e of t h i s f r a c t u r e s e t , which does not f i t i n t o the p a t t e r n of f r a c t u r e s described above, i s unknown, 96 GENETIC IMPLICATIONS OF FRACTURE .PATTERNS The garnet-hornblende v e i n l e t s surrounding the Boss Mountain Stock occupy primary f r a c t u r e s that formed during i t s i n t r u s i o n . The co n c e n t r i c set represents adjustment of the country rock by reverse f a u l t i n g above a r i s i n g pluton as i l -l u s t r a t e d by Figure 3 .12 ; A. The conjugate sets represent l a t e r a l expansion of the pluton probably at horizons near i t s upper surface. Barren and q u a r t z - f i l l e d , f r a c t u r e s (Group 2 F r a c t u r e s ) represent adjustments by f r a c t u r i n g c l o s e l y related, i n time and space t o development of quartz b r e c c i a . The f r a c t u r e s are s u b p a r a l l e l t o a prominent j o i n t set th a t may have had some c o n t r o l on f r a c t u r e development. The p o s i t i o n , a t t i t u d e and. r e l a t i v e age of group 3 q u a r t z -molybdenite veins suggests that they were formed during Phase I I I B r e c c i a development. During the i n i t i a l stage of Phase I I I B r e c c i a development, pressure d i r e c t e d upward r e s u l t e d i n r e -verse f a u l t i n g (accompanied by quartz-molybdenite i n t r o d u c t i o n ) i n the surrounding rock (Quartz B r e c c i a and. g r a n o d i o r i t e ) i n a manner i l l u s t r a t e d , by Figure 3 .12 ; A. Group 4 f r a c t u r e s and. quartz veins probably were formed by a decrease i n the v e r t i c a l component of s t r e s s which accom-panied c r y s t a l l i z a t i o n . a n d subsidence of the outer part of the Boss Mountain Stock (Figure 3.12; B). As t h i s decrease took 97 p l a c e , f i r s t e a r l y group 4 veins formed followed by l a t e group 4 v e i n s . E a r l y group 4 veins were reopened d u r i n g l a t e group 4 development and l a t e group 4 minerals were superimposed on the e a r l i e r - f o r m e d s u i t e . Group 5 quartz-molybdenite veins occupy f r a c t u r e s that, formed as the r e s u l t of pressure r e d u c t i o n at depth i n a manner suggested by Anderson (1936) f o r the development of r i n g dykes (Figure 3 . 1 2 ; B). In t h i s f r a c t u r e system maximum s t r e s s e s (?(max)) are everywhere n e a r l y h o r i z o n t a l (see Table 3 . 2 and. Figure 3 . 9 ) . Minimum s t r e s s e s (P(min)), which are steep i n a l l areas, are concentrated around, a point which l i e s i n a north 74 degrees east d i r e c t i o n at 8 3 degrees. The maximum s t r e s s e s represent the normal Inherent c o n f i n i n g pressures of the rock which became maximized by a r e d u c t i o n i n pressure below and r e s u l t e d i n the development of f r a c t u r e s now occupied by the group 5 quartz-molybdenite v e i n s . In summary, the development of garnet-hornblende v e i n -l e t s and. quartz veins can be explained by increase or decrease i n pressures from below. The u l t i m a t e source, of t h i s pressure v a r i a t i o n , which i s a l s o r e l a t e d to b r e c c i a development, prob-ably was the Boss Mountain Stock. Figure 3.12. Formation of f r a c t u r e s . (A, f o r c e f u l i n j e c t i o n . B, withdrawal of pressure). Modified a f t e r Anderson, 1936. 99 IV. ROCK ALTERATION Rock a l t e r a t i o n i n the Boss Mountain mine area r e s u l t e d i n the appearance of many d i f f e r e n t mineral assemblages, some g e n e t i c a l l y r e l a t e d and some unrelated to ore d e p o s i t i o n . The degree of a l t e r a t i o n ranges from very weak to int e n s e . . ALTERATION UNRELATED TO ORE DEPOSITION A l t e r a t i o n u n r e l a t e d to ore d e p o s i t i o n i n c l u d e s p r o p y l i t i z a t i o n and a z e o l i t e - c a l c i t e - c l a y assemblage, P r o p y l i t i c A l t e r a t i o n Widespread p r o p y l i t i c a l t e r a t i o n g e n e r a l l y i s r e s t r i c t e d t c the p r o x i m i t y of f r a c t u r e s but l o c a l l y i s more pervasive. I r r e g u l a r , d i s c o n t i n u o u s and randomly-oriented f r a c t u r e s through-out the area c o n t a i n epldote and the a d j o i n i n g rock has been c h l o r i t i z e d and s a u s s u r i t i z e d f o r a few inches from f r a c t u r e s . Three areas of more; pervasive p r o p y l i t i c a l t e r a t i o n are i n d i c a t e d on -Map 3 . Area 1 i s no r t h of Takomkane Volcano near some o l d copper showings; area I I , west of the mine, i s the l a r g e s t and most i n t e n s e l y a l t e r e d ; and area I I I i s exposed on a bench below the cirque- w a l l s south-southwest o f the mine. In these areas epidote v e i n l e t s are two inches to one foot apart and the i n t e r v e n i n g rock i s completely or p a r t l y c h l o r -100 i t i z e d . and s a u s s u r i t i z e d . Minor amounts of p y r i t e o c c u r i n b o t h the v e i n l e t s and i n the r o c k , but may not be p a r t of the p r o p y -l i t i c a l t e r a t i o n . P y r i t e which forms a h a l o around the molyb-denum m i n e r a l i z a t i o n i s c l e a r l y superimposed upon and i s t h e r e -f o r e younger t h a n the p r o p y l i t i c a l t e r a t i o n . Z e o l i t e - C a l c i t e - C l a y Assemblage P o s t - m i n e r a l f r a c t u r e s throughout the a r e a commonly c o n t a i n f i l l i n g s and e n c r u s t a t i o n s of z e o l i t e and c a l c i t e which r e p -r e s e n t the l a s t s tage o f r o c k a l t e r a t i o n . T h i s a l t e r a t i o n , presumably r e l a t e d t o Takomkane V o l c a n o , i s t oo e r r a t i c i n d i s -t r i b u t i o n t o be shown on Map J. W i t h i n the mine the z e o l i t e -\ c a l c i t e - c l a j r assemblage o c c u r s not o n l y i n p o s t - m i n e r a l f r a c -t u r e s , b u t i s found a l s o as c r y s t a l l i n e growths i n vugs i n Phase I I I B r e c c i a and q u a r t z v e i n s and i n v e s i c l e s i n a l k a l i b a s a l t d y k e s . Four z e o l i t e s , , s t i l b i t e , c h a b a z i t e , sodium harmotome, and h e u l a n d i t e , were i d e n t i f i e d by X - r a y powder p h o t o g r a p h s . S t i l -b i t e i s the most abundant and most w idespread z e o l i t e . , Chab-a z i t e i s r e l a t i v e l y common and sodium harmotome and h e u l a n d i t e a r e r a r e . E u h e d r a l golden, y e l l o w t o g o l d e n brown; c r y s t a l s and c r y s t a l a g g r e g a t e s of s t i l b i t e l i n e open f r a c t u r e s and v u g s . I n d i v i d u a l c r y s t a l s , w h i c h - r a n g e i n l e n g t h from a f r a c t i o n of a mi l l imeter t o 10 mm, were d e p o s i t e d i n s u b - r a d i a t i n g and randomly o r i e n t e d 1 0 1 groups i n open spaces. Anhedral masses of s t i l b i t e a l s o r e p l a c e p l a g i o c l a s e i n the matrix and fragments of the Phase I I I B r e c c i a , imparting a brownish colour. Chabazite i s more r e s t r i c t e d i n d i s t r i b u t i o n than s t i l b i t e . Transparent to t r a n s l u c e n t honey-brown rhombohedra of chabazite occur i n vugs i n Phase I I I B r e c c i a and i n q u a r t z - m i e r o p e r t h i t e -p y r i t e v e i n s . S t i l b i t e g e n e r a l l y occurs w i t h c h a b a z i t e , i n places as e n c r u s t a t i o n s . Angles between rhombohedral faces of chabazite c r y s t a l s are almost 9 0 d.egrees and the c r y s t a l s appear n e a r l y c u b i c , resembling f l u o r i t e . Cleavage, v i s i b l e i n most c r y s t a l s , i s p a r a l l e l to c r y s t a l faces ( 1 0 1 1 ) . The s i z e of the chabazite rhombohedra averages 3 mm., but c r y s t a l s as l a r g e as 1 5 mm. have been found. In t h i n s e c t i o n , chabazite appears i s o t r o p i c and resembles f l u o r i t e except f o r cleavage. In plane p o l a r i z e d l i g h t chab-a z i t e i s c o l o u r l e s s to l i g h t pink and has a r e f r a c t i v e index l e s s than o r t h o c l a s e . . Chabazite r a r e l y replaced- p l a g i o c l a s e and orthoclase ( m i c r o p e r t h i t e ) i n the Phase I I I B r e c c i a . Some garnet-hornblende ve i n s c o n t a i n chabazite. Sodium harmotome was observed only i n the Boss Mountain Stock. V e i n l e t s g e n e r a l l y are l e s s than -| inch wide, but l o c a l l y s w e l l to 2 inches. Wider s e c t i o n s of the veins are vuggy and lined, w i t h white euhedral c r y s t a l s up to 5 mm, i n l e n g t h . Sodium harmotome occurs, only near a l k a l i b a s a l t dykes and development probably i s related:'to dyke i n t r u s i o n . The 102 mineral was not studied i n t h i n .section. . Co l o u r l e s s c r y s t a l s of heulandite were observed i n narrow, somewhat vuggy v e i n l e t s which cut a l k a l i b a s a l t dykes. Vuggy parts of v e i n l e t s are l i n e d with euhedral heulandite c r y s t a l s " and white c a l c i t e scalenohedra. The nea r l y equant heulandite t a b l e t s have p e r f e c t 0.1.0 cleavage,. Cleavage faces have a pea r l y l u s t r e . C r y s t a l s range i n s i z e from 0 . 0 5 row. to 0 . 5 mm. The mineral was i d e n t i f i e d by use of X-ray powder photographs. C a l c i t e occurs i n a myriad of forms, but only those as-so c i a t e d w i t h z e o l i t e s w i l l be described. Scalenohedrons, rhombohedrons, and hexagonal prisms of golden c a l c i t e were de-posite d on the w a l l s of open f r a c t u r e s . I n d i v i d u a l c r y s t a l s reach a length of k0 mm. and g e n e r a l l y are completely coated w i t h randomly oriented, aggregates of s t i l b i t e . C o l o u r l e s s hex-agonal p l a t e s , golden scalenohedrons, ..and other more complex forms were deposited upon s t i l b i t e . In any i n d i v i d u a l vug a l l c r y s t a l s of the same age have the same form. When more than one age of c a l c i t e occur together, they g e n e r a l l y d i f f e r In morph-ology. Clay minerals, which developed i n p l a g i o c a l s e and micro-p e r t h i t e only adjacent to f r a c t u r e s c o n t a i n i n g z e o l i t e s and/or c a l c i t e , probably are another product of t h i s l a s t stage of v a l t e r a t i o n . V a r i e t i e s of c l a y minerals were not i d e n t i f i e d . 1 0 3 ALTERATION GENETICALLY RELATED TO ORE DEPOSITION Four d i s t i n c t stages of hydrothermal a l t e r a t i o n can be recognized i n the Boss Mountain mine area. ( 1 ) Garnet-Hornblende ( 2 ) B i o t i t e ( 3 ) M i c r o p e r t h i t e - C h l o r i t e - S e r i c i t e (4) C h l o r i t e - T a i c The d i s t r i b u t i o n and l i m i t s of each stage, except the l a s t , are shown on Map 3 . Stage 1 : Garnet-Hornblende The garnet-hornblende mineral assemblage i s the i n i t i a l stage of a l t e r a t i o n r e l a t e d t o ore d e p o s i t i o n ' and i s important i n the i n t e r p r e t a t i o n of the genesis of the ore deposits., The assemblage occurs i n narrow v e i n l e t s which occupjr mylonite zones i n g r a n o d i o r i t e and.in andesite porphyry dykes around the Boss Mountain Stock. Garnet and hornblende have replaced the host rock i n and near the mylonite zones. D i s t r i b u t i o n of the v e i n l e t s , as shown on Map 3 (In pocket), i s based upon observations i n underground workings and i n diamond, d r i l l i n t e r s e c t i o n s . T h e . v e i n l e t s occupy a zone as much as 2500 f e e t wide around the stock. Immediately west of the stock there i s an apparent l a c k of v e i n l e t s . However, on c l o s e r ex-amination v e i n l e t s of hornblende (without garnet) were found i n narrow mylonite zones (up to | i n c h wide) which p a r a l l e l garnet-hornblende v e i n l e t s f a r t h e r west. A t t i t u d e s of the garnet-hornblende v e i n l e t s d i f f e r east and 104 west of the Boss Mountain Stock. In both areas, there are thre prominent a t t i t u d e s which correspond to.a set of conjugate shears and. a c o n c e n t r i c shear around the stock. Development of these f r a c t u r e s was discussed i n Chapter 3-Garnet-hornblende v e i n l e t s range i n t h i c k n e s s from a. f r a c -t i o n of an i n c h to s i x inches and average l e s s than one i n c h . I n d i v i d u a l v e i n l e t s can be traced along s t r i k e f o r s e v e r a l tens of f e e t . . The t h i c k n e s s v a r i e s g r e a t l y -within i n d i v i d u a l v e i n -l e t s and most v e i n l e t s grade i n t o narrower mylonite zones. T y p i c a l l y , each v e i n l e t i s c h a r a c t e r i z e d by a core of red-brown garnet bordered by a b l a c k to b l u i s h b l a c k selvedge of horn-blende and magnetite ( P l a t e 4.1). Epidote forms an important p a r t of some v e i n l e t s , but i s l a c k i n g i n others". D i s t r i b u t i o n of e p i d o t e , both are a l l y and w i t h i n i n d i v i d u a l v e i n l e t s , i s very e r r a t i c . G r a n o d i o r i t e adjacent to garnet-hornblende v e i n l e t s i s weakly m y l o n i t i z e d f o r a width up t o two inches. These myloni-t i z e d areas,- which are r e a d i l y v i s i b l e i n hand specimen, gen-e r a l l y are a l t e r e d to f i n e - g r a i n e d s e r i c i t e . Some v e i n l e t s grade l a t e r a l l y into" mylonite-zones without garnet-hornblende development. Aggregates of anhedral garnet c r y s t a l s form the cores of the v e i n l e t s . I n d i v i d u a l garnet anhedra do not exceed 0.2 mm. i n diameter.. S e v e r a l specimens of garnet were s e l e c t e d f o r 105 P l a t e 4 . 1 , M y l o n i t i z e d g r a n o d i o r i t e c o n t a i n i n g v e i n l e t s of garnet (grey) w i t h hornblende selvedges ( b l a c k ) . (Scale i s i n i n c h e s ) . 1 0 6 measurement of r e f r a c t i v e index, s p e c i f i c g r a v i t y and c e l l edge. Fourteen samples were of s u f f i c i e n t p u r i t y to measure index of r e f r a c t i o n and c e l l edge, but were too small f o r s p e c i f i c grav-i t y measurement. R e f r a c t i v e index and c e l l edge data are p l o t t e d on Winchell's diagram ( 1 9 5 8 , p . 5 9 7 ) r e s u l t i n g i n a concentration of p o i n t s near the andradite corner of the diagram (Figure 4 . 1 ) . Index of r e f r a c t i o n measurements (measured•with an Abbey refractometer) range from 1 . 8 6 9 t o 1 . 8 7 3 . C e l l edge determin-. o. a t i o n s alone ( 1 2 . 0 0 - 1 2 . 0 3 A) i n d i c a t e a garnet r i c h i n the andradite molecule. Determinations of c e l l edge were made from X-ray powder photographs corrected f o r f i l m shrinkage. Green hornblende forms a selvedge of subhedral c r y s t a l s up to 0 . 1 mm. i n l e n g t h adjacent t o the garnet core. I d e n t i f i -c a t i o n i s based on e x t e r n a l form, pleochroism, and cleavage. Disseminated euhedral magnetite accompanies the hornblende. L o c a l l y , aggregates and v e i n l e t s of anhedral magnetite cut the hornblende selvedge but l i t t l e magnetite occurs i n the garnet cores. Chabazite, which was noted near the center of the garnet core i n two t h i n s e c t i o n s , probably r e p l a c e s p l a g i o c l a s e . Stage 2 : B i o t i t e B i o t i t e i s the most widespread product of potassium meta-somatism. With the exception of the Boss Mountain Stock and the a l k a l i - b a s a l t dykes, hydrothermal b i o t i t e occurs i n a l l rocks 107 Figure 4.1. Composition of 14 garnets; Boss Mountain Mine. (Diagram modified from Wine he II, 1958, p. 597). 108 throughout the mine workings. The western l i m i t of the b i o t i t e zone has been traced on the surface approximately 1 , 0 0 0 f e e t west of the underground workings. Map 3 ( i n pocket) shows the d i s t r i b u t i o n of hydrothermal b i o t i t e as determined from under-ground workings, s c a t t e r e d outcrops, trenches, readouts, and diamond d r i l l i n t e r s e c t i o n s . L i m i t s of a l t e r a t i o n to the n o r t h -east and south could not be e s t a b l i s h e d because of the l a c k of rock exposures. The western l i m i t i s near the base of cirque w a l l s which r i s e 1 , 5 0 0 f e e t above the v a l l e y f l o o r . B i o t i t e metasomatism i s most intense i n and near the b r e c c i a s . The degree of metasomatic replacement g e n e r a l l y de-creases w i t h i n c r e a s i n g d i s t a n c e from the b r e c c i a s , except i n andesite dykes' which are i n t e n s e l y b i o t i t i z e d : everywhere w i t h -i n the b i o t i t e zone. The presence of hydrothermal b i o t i t e i n g r a n o d i o r i t e or p o r p h y r i n i c b i o t i t e g r a n o d i o r i t e has not a l t e r e d the o v e r a l l appearance of the rock, which has a f r e s h appearance i n hand specimen. Hydrothermal b i o t i t e can be r e a d i l y i d e n t i f i e d i n hand specimen w i t h the a i d of a hand l e n s . Apparently homogeneous primary mafic minerals (hornblende and b i o t i t e ) are composed of aggregates of f i n e - g r a i n e d b l a c k to green-ish, b l a c k b i o t i t e . c r y s t a l s . Weakly a l t e r e d specimens from p e r i p h e r a l areas r e q u i r e thin- s e c t i o n examination • . f o r i d e n t i f i c a t i o n of hydrothermal b i o t i t e . A c t i n o l i t e i s 1 0 9 l o c a l l y abundant w i t h the b i o t i t e i n a l t e r e d andesite dykes. The b i o t i t e i s o l i v e - g r e e n to pale brown i n plane p o l a r i z e d l i g h t . Olive-green b i o t i t e occurs as mosaic ovolds, irre g u l a r -patches, pseudomorphs and. v e i n l e t s of randomly orie n t e d c r y s t a l s and as s i n g l e c r y s t a l s i n altered, andesite dykes. Pale brown b i o t i t e occurs as s i n g l e c r y s t a l s i n the matrix of the Phase I I I B r e c c i a and as aggregates of euhedral c r y s t a l s . r e p l a c i n g an-d e s i t e dyke fragments i n Phase I I I B r e c c i a . ' I n d i v i d u a l b i o t i t e c r y s t a l s range from 0 . 1 to 0 . 5 mm. i n l e n g t h . M i c r o f r a c t u r e s and the arrangement of mafic minerals of magmatic o r i g i n determine the d i s t r i b u t i o n of hydrothermal b i o -t i t e . Ovoids of b i o t i t e c r y s t a l s g e n e r a l l y are of the same s i z e as primary mafic minerals i n the host rock (1 to 4 mm). Many pseudomorphs of hydrothermal b i o t i t e a f t e r magmatic hornblende and l e s s commonly, hydrothermal hornblende, have r e t a i n e d the e x t e r n a l morphology of the host ( P l a t e 4 . 3 ) . Replacement of magmatic b i o t i t e g e n e r a l l y r e s u l t s i n I r r e g u l a r masses, and patches of b i o t i t e c r y s t a l s , some w i t h t h i n bands, of magnetite g r a i n s o r i e n t e d p a r a l l e l to the cleavage of the o r i g i n a l mag-matic b i o t i t e . In the i n i t i a l stages of b i o t i t e metasomatism only the edges of magmatic c r y s t a l s are replaced ( P l a t e 4 . 2 ) . Rocks which c o n t a i n abundant m i c r o f r a c t u r e s have abundant hy-drothermal b i o t i t e along the f r a c t u r e s as w e l l as replacements 110 of primary mafic minerals. In some h i g h l y a l t e r e d rocks even the f e l d s p a r s have been p a r t l y a l t e r e d to b i o t i t e . I n t r o d u c t i o n of hydrothermal b i o t i t e i n t o the g r a n o d i o r i t e and other rocks r e s u l t e d In other more su b t l e changes w i t h i n the r.ocks. P l a g i o c l a s e g r a i n s contain very small amounts of s e r i c i t e where they are i n contact w i t h hydrothermal b i o t i t e but not e l s e -where i n the g r a i n . This may have been caused by d i f f u s i o n of potassium during development of hydrothermal b i o t i t e , Chlor-i t i z a t i o n of hydrothermal b i o t i t e released potash and. f u r t h e r c o n t r i b u t e d to the s e r i c i t i z a t i o n of p l a g i o c l a s e . In rocks which contain v i s i b l e c h l o r i t e , s e r i c i t i z a t i o n has imparted a chalky appearance to the p l a g i o c l a s e . The type of host rock has played an important r o l e i n the i n t e n s i t y of b i o t i t e metasomatism. Most of the above d e s c r i p -t i o n s of b i o t i t e metasomatism apply to g r a n o d i o r i t e and por-p h y r i n i c b i o t i t e g r a n o d i o r i t e because these rock types form the bulk of the a l t e r e d rock. Other, r o c k s , though of l e s s quant-i t a t i v e importance, have i n some cases been more i n t e n s e l y metasomatized. X e n o l i t h s of hypersthene gabbro were h i g h l y s e n s i t i v e to b i o t i t e a l t e r a t i o n . Some x e n o l i t h s have been so i n t e n s e l y a l -tered that t h e i r o r i g i n a l composition i s d i f f i c u l t to a s c e r t a i n except by the te x t u r e of the remaining p l a g i o c l a s e . B i o t i t e p r e f e r e n t i a l l y replaced mafic minerals; hence, d i s t r i b u t i o n of I l l primary mafic minerals i n the gabbro has l a r g e l y determined the d i s t r i b u t i o n of hydrothermal b i o t i t e . R h y o l i t e and r h y o l i t e porphyry dykes,, which c o n t a i n few mafic minerals contain l i t t l e hydrothermal b i o t i t e . Hydrothermal b i o t i t e occurs as evenly d i s t r i b u t e d euhedral g r a i n s i n the matrix of Phase I I I B r e c c i a , In c o n t r a s t hydrothermal b i o t i t e occurs i n s t r i n g e r s i n the Phase I B r e c c i a . Adjacent to such s t r i n g e r s , b i o t i t e r e p l a c e s and t r a n s e c t s f e l d s p a r s i n the matrix. The e f f e c t of b i o t i t e a l t e r a t i o n on andesite and andesite porphyry dykes and dyke fragments i n the b r e c c i a s ranges from weak, t o extreme. Table 4 .1 shows the modes of unalte r e d and a l t e r e d a ndesite and and e s i t e porphyry dykes. In weakly a l t e r e d dykes (Table 4 . 1 , number 3) b i o t i t e i s not d i s c e r n a b l e w i t h the naked eye. S e v e r a l pronounced changes occur i n andesite dykes- w i t h i n c r e a s e i n the q u a n t i t y of hydrothermal b i o t i t e . As the b i o -t i t e content i n c r e a s e s the rock becomes p r o g r e s s i v e l y more s c h i s t o s e i n appearance u n t i l the end-product i s a b i o t i t e " s c h i s t " composed almost e n t i r e l y : of b i o t i t e (Table 4 . 1 , number 1.1),.. The c o l o u r of the dykes g e n e r a l l y becomes greener w i t h i n c r e a s i n g a l t e r a t i o n and dyke fragments i n the. breccias: are dark greenish black or l i g h t brown. V e i n l e t s of b i o t i t e and/or a c t i n o l i t e a l s o occur In weakly a l t e r e d dykes. 112 P l a t e 4 . 2 . Photomicrograph (crossed n i c o l s ) of hydrothermal b i o t i t e which has p a r t l y replaced magmatic b i o t i t e . P l a t e 4 . 3 . Photomicrograph (plane p o l a r i z e d l i g h t ) of pseudo-morphic hydrothermal b i o t i t e which has replaced magmatic hornblende. 1 1 3 Figure 4 . 2 i s a p l o t of mineral v a r i a t i o n s i n andesite dykes w i t h i n c r e a s i n g " b i o t i t e content. Formation of b i o t i t e and a c t i n o l i t e rims on primary hornblende i n the dykes are the f i r s t e f f e c t s of Stage 3 a l t e r a t i o n (Table 4 . 1 , number 3 ) . Once hornblende i s completely a l t e r e d , p l a g i o c l a s e i s progres-s i v e l y r eplaced by b i o t i t e and a c t i n o l i t e . A c t i n o l i t e i n -creases at a more r a p i d r a t e than b i o t i t e u n t i l the a c t i n o l i t e content reaches about 5 5 percent of the rock. B i o t i t e then r e -places a c t i n o l i t e u n t i l the rock c o n s i s t s of e s s e n t i a l l y 1 0 0 percent b i o t i t e . Samples of a l t e r e d andesite dykes c o n t a i n i n g g r e a t e r than 9 0 percent b i o t i t e occur only as fragments i n the b r e c c i a s . Such samples may have never contained a c t i n o l i t e as a mineral, phase. A c l o s e c o r r e l a t i o n e x i s t s between the r a t i o of a c t i n o l i t e and q u a r t z . Rocks that c o n t a i n the highest percentage of a c t i n o l i t e a l s o have the highest quartz content. I t appears that p l a g i o c l a s e becomes more sodic as a c t i n -o l i t e and b i o t i t e begin to r e p l a c e i t . , A p a t i t e and z i r c o n con-t e n t of a l l samples remains constant throughout the a l t e r a t i o n process. The mineral changes o u t l i n e d above are summarized i n Table > . , 1 : and i l l u s t r a t e d ' ' by. Figure 4 . 2 . 114 100 S P E C I M E N NUMBER (see table % 6 7 8 9 10 II P E R C E N T • Plagioclase _i_Hornblende © Act ino l i te & Quartz 4 0 6 0 8 0 100 P E R C E N T H Y D R O T H E R M A L B IOTITE Figure 4.2. Mineral v a r i a t i o n s i n altered andesite and andesite porphyry dykes i n r e l a t i o n to increasing b i o t i t e content. 1 1 5 Primary A l t e r a t i o n Plagioclase Quartz Hornblende Biotite Zircon Apatite Magnetite <D CO CS rH O O •H fcO Oj rH PH Quartz Biotite Actinolite Talc Epidote Chlorite Sericite Carbonate No. Specimen % An % An 1 6-23.1 j P j 6 7 5 4 > 4 S X 1 7 - X X X — - - - - - X X X 2 8 - 6 . 2 (P) (G) 8 7 0 4 0 - 4 5 4 5 X 18 2 2 X X X - - - - - - — — — 3 1-19.2-I(P) (G) 8 7 1 3 6 - 4 2 — 1 0 — S\- X X « - - 6 5 X X - X 4 1 0 - 2 8 . 4 - - - 2 - X - 14 10-1 2 4 3 0 5 0 - X - X 5 8 - 1 1 . 2 •- - - - -. X X X 1 0 1 3 4 3 0 5 6 X -- X - X 6 1 0 - 2 7 . 1 2 - - - - •- X X X 7 1 1 8 3 5 5 0 - - - - X 7 5 0 2 - - - - X X - 1 3 1 0 2 40 4 5 - - „ X 8 - 8 - 1 . 3 - - - - -- X y •v X ' - 2 4 5 3 5 8 - X - 1 0 9 B S - 1 5 - - - X X X O .8 1 5 0 40 - - X - 3 1 0 9 - 3 . 4 - - - - - X X 2 - 2 9 6 - - - - - -1 1 1 0 - 2 7 . 1 - - • - - - X X - - - X too - - - - -P Phenocrysts G Groundmass x minor - absent Table 4 . 1 . Modes of andesite porphyry dykes and t h e i r a l t e r e d e q u i v a l e n t s ; Boss Mountain mine area. Stage 3 : M i c r o p e r t h i t e - C h l o r i t e - S e r i c i t e The Stage 3 a l t e r a t i o n assemblage g e n e r a l l y i s moderately to i n t e n s e l y developed i n Phase I I I B r e c c i a , the S t r i n g e r Zone, and the Boss Mountain Stock (Map 3 ) . Widely s c a t t e r e d occur-rences of Stage 3 a l t e r a t i o n , not shown on Map 3 , are associated 116 w i t h quartz v e i n s throughout the mine area. Creamy t o salmon-coloured m i c r o p e r t h i t e developed as sub-h e d r a l to euhedral c r y s t a l s i n the matrix and i n open vugs i n Phase I I I B r e c c i a and as anhedral g r a i n s i n b r e c c i a fragments. 'Granodiorite fragments were most s u s c e p t i b l e t o f e l d s p a t h i z a t i o n and l o c a l l y are In t e n s e l y a l t e r e d t o masses of m i c r o p e r t h i t e , c h l o r i t i z e d mafic m i n e r a l s , and s e r i c i t e , P y r i t e i s ubiquitous. Stage 3 a l t e r a t i o n i n the S t r i n g e r Zone and i n the Boss Mountain Stock i s s l i g h t l y d i f f e r e n t i n char a c t e r and i s more intense than t h a t i n the Phase I I I B r e c c i a . M i c r o p e r t h i t e , c h l o r i t e , and s e r i c i t e envelope q u a r t z - m i c r o p e r t h i t e v e i n s (Group 4 v e i n s ) f o r widths up t o seven f e e t , but g e n e r a l l y the g r a n o d i o r i t e host rock i s a l t e r e d f o r about 1.8 inches on both s i d e s of the v e i n s . C h l o r i t e formed at the expense of mafic minerals and as v u g - f i l l i n g c r y s t a l aggregates i n and near the v e i n s . S e r i c i t e occurs i n vugs and as an a l t e r a t i o n product of magmatic f e l d s p a r s . . Metasomatic m i c r o p e r t h i t e i s r e a d i l y d i s t i n g u i s h e d from mag-matic microperthite i n this area. The' creamy to salmon-coloured meta-somatic v a r i e t y c o n t r a s t s sharply w i t h the vrhite magmatic micro-p e r t h i t e In the g r a n o d i o r i t e and the orange o r t h o c l a s e of the Boss Mountain Stock. Exsolved p l a g i o c l a s e i s more i r r e g u l a r i n shape and d i s t r i b u t i o n i n metasomatic than i n magmatic micro-p e r t h i t e . Replacement of p l a g i o c l a s e i s a f e a t u r e common to 11? both m i c r o p e r t h i t e s . Much magmatic m i c r o p e r t h i t e i n grano-d i o r i t e i s p o i k i l i t i c , a f e a t u r e not shared by metasomatic m i c r o p e r t h i t e . . . I n d i v i d u a l c r y s t a l s of hydrothermal m i c r o p e r t h i t e , ranging i n s i z e from 5 t o 10 mm., formed i n vugs as euhedral, equant g r a i n s . Anhedral m i c r o p e r t h i t e ranges from 1 to 8 mm. i n diameter. V e i n l e t s of molybdenite cut metasomatic m i c r o p e r t h i t e . Minor q u a n t i t i e s of c h a l c o p y r i t e and s p h a l e r i t e occur i n parts of the Phase I I I B r e c c i a t h a t are r i c h i n metasomatic micro-p e r t h i t e . C h l o r i t e a s s o c i a t e d w i t h Stage 3 a l t e r a t i o n has e i t h e r e p i g e n e t i c or pseudomorphic form. In i t s e p i g e n e t i c form c h l o r -i t e occurs as r a d i a t i n g aggregates of subhedral c r y s t a l s i n vugs ( P l a t e 4 . 6 ) . Between crossed n i c o l s t h i s c h l o r i t e i s chocolate brown i n c o l o u r . Some, but not a l l , g r a i n s c o n t a i n i n c l u s i o n s of t r a n s l u c e n t golden brown to deep red r u t i l e c r y s t a l s ( P l a t e s 4 . 6 and 4 . 7 ) . C h l o r i t e a l s o occurs as pseudomorphs of mafic m i n e r a l s , p a r t i c u l a r l y hydrothermal b i o t i t e ( P l a t e 4 . 4 ) . In t h i n s e c t i o n the c o l o u r and h a b i t of pseudomorphic c h l o r i t e c o n t r a s t s sharply w i t h e p i g e n e t i c c h l o r i t e . The c o l o u r (crossed n i c o l s ) i s an-omalous purple to y e l l o w i s h . C h l o r i t e pseudomorphs a f t e r b i o t i t e c o n t a i n i n c l u s i o n s of very dark brown to opaque r u t i l e . Sphene occurs as minute c r y s t a l s i n c h l o r i t l z e d hornblende. Rocks 118 a f f e c t e d by Stage 3 a l t e r a t i o n c o n tain both forms of c h l o r i t e . The e p i g e n e t i c form predominates, i n the Phase I I I B r e c c i a and i n the Boss Mountain Stock and the pseudomorphic form i n the S t r i n g e r Zone. Some of the p r o p e r t i e s of the two c h l o r i t e s are compared i n Table 4.2. Epi g e n e t i c Form Pseudomorphic Form 1. As r a d i a t i n g and s i n g l e subhedral c r y s t a l s i n vugs. 2. Some, but not a l l , c o n t a i n t r a n s l u c e n t r u t i l e i n -c l u s i o n s 3.. R u t i l e not confined to c h l o r i t e s . 4. Chocolate brown(crossed n i c o l s ) . 5. L i t t l e or no e f f e c t on adjacent f e l d s p a r s . 1. Assumes form of o r i g i n a l mafic mineral. 2. Always contain opaque to weakly t r a n s l u c e n t r u t i l e or sphene i n c l u s i o n s . . 3. R u t i l e only i n c h l o r i t e . 4. Purple to y e l l o w i s h (crossed n i c o l s ) . 5. Halo of s e r i c i t e i n ad-jacent f e l d s p a r s . Table 4.2. Comparison of c h l o r i t e s produced during Stage 3 a l t e r a t i o n . F e l dspars, p a r t i c u l a r l y p l a g i o c l a s e , where i n contact w i t h c h l o r i t i z e d hydrothermal b i o t i t e contain s e r i c i t e adjacent to the contact. Such s e r i c i t e has been superimposed on s e r i c i t e a s s o c iated w i t h hydrothermal b i o t i t e development. Apparently the c h l o r i t e s t r u c t u r e could not accommodate potassium which was e x p e l l e d , forming s e r i c i t e i n the a d j o i n i n g f e l d s p a r g r a i n s . Titanium, which apparently i s l e s s mobile than potassium, remained, w i t h the c h l o r i t e , forming d i s c r e t e g r a i n s of r u t i l e or sphene. R u t i l e formed, only i n c h l o r i t i z e d hydrothermal b i o t i t e . 119 P l a t e 4 . 4 . Photomicrograph (plane p o l a r i z e d l i g h t ) of c h l o r -i t i z e d b i o t i t e w i t h r u t i l e i n c l u s i o n s ( b l a c k ) . P l a t e 4 . 5 . Photomicrograph (plane p o l a r i z e d l i g h t ) of hydro-thermal b i o t i t e cut by molybdenite ( b l a c k ) . 120 i i n d i c a t i n g the b i o t i t e probably was t i t a n i f e r o u s . Magmatic hornblende was a l s o t i t a n i f e r o u s and c h l o r i t l z e d specimens con-t a i n g r a i n s of sphene, Schwartz (1958) described the development of r u t i l e i n -c l u s i o n s during c h l o r i t i z a t i o n of b i o t i t e and concluded that r u t i l e i n c h l o r i t e i n d i c a t e s the c h l o r i t e was d e r i v e d from b i o -t i t e . This does not appear to be the s i t u a t i o n at Boss Mountain (Table 4.2). S e r i c i t e occurs as yellow to yellow-green subhedral c r y s -t a l s and c r y s t a l aggregates i n vugs and i n the groundmass of the g r a n o d i o r i t e and the Boss Mountain Stock. I t a l s o occurs i n f e l d s p a r s accompanying c h l o r i t i z a t i o n . S e r i c i t i z a t i o n shows an a f f i n i t y f o r p l a g i o c l a s e i n preference to o r t h o c l a s e . Except i n c e r t a i n weakly or moderately a l t e r e d zones, s e r i c i t i z a t i o n of the Boss Mountain Stock is extreme.. The a l -t e r a t i o n i s most intense adjacent to q u a r t z - m i c r o p e r t h i t e - p y r i t e veins (group 4 quartz v e i n s ) . R e l a t i v e proportions of q u a r t z , m i c r o p e r t h i t e and p y r i t e i n the veins vary considerably along s t r i k e and d i p . The degree of s e r i c i t i z a t i o n Of the stock i s r e a d i l y d i s -c e r n i b l e by rock c o l o u r . Weakly s e r i c i t i z e d rocks are pink to orange and appear r e l a t i v e l y f r e s h i n hand specimen, except f o r a waxy appearance of the p l a g i o c l a s e . Moderately a l t e r e d rocks are white to grey-green and contain unaltered cream-coloured 121 1 mm. Pl a t e 4 . 6 . Photomicrograph (plane p o l a r i z e d l i g h t ) of r u t i l e ( black) i n quartz near e p i g e n e t i c c h l o r i t e (grey) P l a t e 4 . 7 . Photomicrograph (plane p o l a r i z e d l i g h t ) of r u t i l e ( black) i n e p i g e n e t i c c h l o r i t e . 122 o r t h o c l a s e and glassy quartz i n a matrix of white to o l i v e green s e r i c i t e . I n t e n s e l y s e r i c i t i z e d quartz monzonite i s o l i v e green i n colour and only quartz has escaped a l t e r a t i o n , - C h l o r i t e and epidote occur i n areas of intense s e r i c i t i z a t i o n . Ubiquitous p y r i t e and minor c h a l c o p y r i t e occur throughout the stock without apparent q u a n t i t a t i v e r e l a t i o n s h i p to i n t e n s i t y of a l t e r a t i o n . Stage k: C h l o r i t e - T a l c C h l o r i t e and t a l c c h a r a c t e r i z e the Stage k a l t e r a t i o n assemblage. The assemblage i s r e s t r i c t e d to dyke-like.and v e i n -l i k e bodies f i l l i n g f r a c t u r e s which cut the Boss B r e c c i a s and surrounding rocks i n a north ? 6 to 85 degrees east d i r e c t i o n w i t h d i p s 4 5 to 6 0 degrees northward. The High-grade Vein which p a r a l l e l s t h i s f r a c t u r e s e t , has been h i g h l y sheared and a l t e r e d . Andesite dykes which were i n t e n s e l y a l t e r e d by b i o t i t e metasomatism a l s o have been e s p e c i a l l y s u s c e p t i b l e to Stage 4 a l t e r a t i o n . Most a l t e r e d andesite dykes trend north 3 0 "to 5 0 degrees west but some trend north 7 5 to 82 degrees east. East-e r l y t r e n d i n g dykes have been i n t e n s e l y a l t e r e d t o masses of c h l o r i t e and t a l c . Carbonate g e n e r a l l y accompanies a l t e r a t i o n . Stage k a l t e r a t i o n i s not shown on Map 3 because the assemblage i s r e s t r i c t e d to narrow dykes and shear zones. Northwesterly t r e n d i n g a l t e r e d andesite dykes contain much c h l o r i t e and t a l c where cut by e a s t e r l y trending f r a c t u r e s r e -l a t e d to the Stage 4 a l t e r a t i o n . 123 Patches of brown carbonate were observed i n some dykes. T a l c v e i n l e t s occur i n c a r b o n a t e - r i c h areas. In t h i n s e c t i o n the c h l o r i t e i s very pale green i n colour. Narrow fra.ctures ( l e s s than i inch) coated w i t h c h l o r i t e are common throughout the mine area and are r e l a t e d to Stage 4 a l t e r a t i o n . O r i e n t a t i o n s of these f r a c t u r e s were not measured. I r r e g u l a r v e i n - l i k e bodies of Stage '-J- a l t e r a t i o n which cut the b r e c c i a s seldom exceed f i v e inches i n t h i c k n e s s . The s c h i s t o s e character of these v e i n - l i k e bodies i s caused by shearing. Shearing r e l a t e d to .development of the a l t e r a t i o n has fold e d and f r a c t u r e d pre-e x i s t i n g group 5 quartz v e i n s . 124 V. ORE DEPOSITS HISTORY AND MINE DEVELOPMENT The f i r s t prospecting a c t i v i t y reported i n the'Takomkane Mountain area was i n 1914 when 'claims were staked on the north f l a n k of the mountain. S e v e ral m i n e r a l i z e d zones c o n t a i n i n g c h a l c o p y r i t e , p y r i t e , galena, and s p h a l e r i t e w i t h sporadic precious metal values were discovered and prospected, f o r a few years before the claims were abandoned. In 1917 , W, J . Ryan and John Foster discovered and staked molybdenite showings on the east slope of the mountain. In the f a l l of the same year s e v e r a l hundred pounds of molybdenite ore was hauled to Lac l a Hache by pack-mule. The f a t e and t o t a l amount of ore shipped, from the claims i s somewhat obscured, by h i s t o r y , but Eardley-Wilmot ( I 9 2 5 , P . 3 3 ) gives the f o l l o w i n g d e s c r i p t i o n of ore from Takomkane Mountain: " E a r l y i n 1918 , Mr. Ryan sent 7 6 I pounds of hand-picked ore to the Mines'Branch, Ottawa, from which 210 pounds of pure molybdenite was recovered, and. sold, to the Can ad. i an General E l e c t r i c Company. In a d d i t i o n 200 pounds of 75 percent ore was sold elsewhere".. Following the shipment of ore, subsequent a c t i v i t y on the claims was not recorded u n t i l 1930 when Consolidated Mining and. Smelting Company of Canada, L i m i t e d , began e x p l o r i n g the property. Several trenches were excavated, on a quartz-molybdenite v e i n system south of Molybdenite Creek and. on -a b r e c c i a zone. In 1942 the B r i t i s h Columbia Department of Mines and. Petroleum Resources took an X-ray diamond d r i l l t o the property by pack-horse and d r i l l e d a t o t a l of 1363 f e e t . Further d r i l l -ing and e x p l o r a t i o n of the b r e c c i a zone were recommended, but •the work was not performed. "In 1955 H. H. Heustls and a s s o c i a t e s cf Vancouver acquired the claims at a tax s a l e a f t e r examination and resampling of the property by W. H. White. The property was optioned to Climax. Molybdenum Company i n 1 9 5 6 . Between 1 9 5 7 and i 9 6 0 , when the option was dropped, Climax Molybdenum Company and Southwest Potash Company, L i m i t e d , completed 3 7 , 0 0 0 f e e t of diamond d r i l l -i n g ; dug s e v e r a l trenches; completed g e o l o g i c a l , geochemical, and geophysical surveys; and constructed a f a i r - w e a t h e r road s u i t a b l e f o r four-wheel d r i v e v e h i c l e s to connect w i t h a road to H o r s e f l y . In March I 9 6 I , Noranda E x p l o r a t i o n Company, L i m i t e d , optioned, the property from H. Heustis and a s s o c i a t e s . Two men were dropped, near the property by h e l i c o p t e r to r e l o g the a v a i l -able d r i l l core. When the snow melted, geological, mapping, geochemical sampling, t r e n c h i n g , and d r i l l i n g programs were i n i t i a t e d to confirm i n t e r p r e t a t i o n s based upon d r i l l core s t u d i e s . C o n s t r u c t i o n of an all-weather.road to connect the prop-e r t y w i t h the Hendrix Lake F o r e s t r y Access Road s i x miles- t o the east commenced, during the summer of I 9 6 I and was completed i n 1 9 6 2 . 126 An a d i t s i t e was s e l e c t e d approximately one mile east of the showings at the edge of a broad, r e l a t i v e l y f l a t v a l l e y which forms the head of one branch of Boss Creek. A camp was erected near t h i s s i t e and i n I 9 6 2 and I 9 6 3 a 6 0 0 0 - f o o t ex-p l o r a t i o n a d i t was d r i v e n at e l e v a t i o n 5 0 4 5 f e e t to i n t e r s e c t the Main B r e c c i a Zone. From t h i s .adit a . v e r t i c a l r a i s e was d r i v e n through the orebody to the surface and a s u b - l e v e l and second r a i s e were d r i v e n f o r sampling and d r i l l i n g purposes. Further underground e x p l o r a t i o n and sampling r e s u l t e d i n a d e c i s i o n i n l a t e I 9 6 3 to b r i n g the mine to production. The f o l l o w i n g s p r i n g c o n s t r u c t i o n of concentrating p l a n t , storage b i n s , o f f i c e b u i l d i n g s , townsite, and. other s t r u c t u r e s com-menced, and i n March, I 9 6 5 , p r o d u c t i o n was a t t a i n e d at 1 0 0 0 tons of ore per day. Underground development and e x p l o r a t i o n continued through I . 9 6 5 , 1 9 6 6 , and 1 9 6 7 and i n ' e a r l y I 9 6 8 plans were being con-sidered f o r an i n t e r n a l s haft to provide access to ore below the 5 0 4 5 l e v e l of the mine. Bulk sampling of an area of pos-s i b l e open-pit ore vras c a r r i e d on i n I 9 6 7 , but the r e s u l t s of these t e s t s have not been made p u b l i c . During nine months i n I 9 6 5 , the concentrator treated. 2 5 9 , 0 0 0 tons of ore from which 1 4 2 9 tons of concentrates con-t a i n i n g 1 , 5 8 5 , 0 0 0 pounds of molybdenum were produced (Noranda Mines, L i m i t e d , Annual Report, I 9 6 5 ) . The . f o l l o w i n g year ( I 9 6 6 ) , 127 d u r i n g the f i r s t f u l l year of production, the concentrator t r e a t e d an average of 1190 tons of ore per day w i t h a 95.8 per-cent recovery to produce 3 .069 tons of concentrates c o n t a i n i n g 3 . 5 7 6 , 0 0 0 pounds of molybdenum (Noranda Mines,. L i m i t e d , Annual Report, 1966). During I 9 6 7 , 1286 tons of ore per day were -mined and t r e a t e d with t o t a l production at. 4 6 9 , 0 0 0 tons of ore averaging 0 , 3 5 percent molybdenum. The concentrate contained 3 , 1 3 0 , 0 0 0 pounds of molybdenum. In I 9 6 7 ; "Ore reserves above the a d i t l e v e l were main-tained, at 2 , 4 7 5 , 0 0 0 tons, w i t h average grade reduced, to 0.28 percent molybdenum." (Noranda Mines, L i m i t e d , Annual Report, I 9 6 7 ) . FORM OF MINERAL DEPOSITS . The bulk of the .molybdenite ore of the Boss Mountain de-p o s i t s i s contained'within b r e c c i a bodies or v e i n systems. Ore depo s i t s g e n e r a l l y are defined, by assay boundaries. In the b r e c c i a d e p o s i t s these boimdaries are sharp and can be v i s u a l l y e s t a b l i s h e d before the. completion of assays. Ore boundaries i n v e i n systems, which r e q u i r e more d e t a i l e d a n a l y s i s , are defined by the d i s t a n c e between the vei n s and the grade of the component v e i n s . Some of the ore bodies are shown i n p l a n , c r o s s - s e c t i o n , and l o n g i t u d i n a l s e c t i o n i n Figures 5 . 1 . 5 . 2 , and 5 . 3 . The Main B r e c c i a Zone i s a crudely l e n t i c u l a r , n e a r l y v e r t i c a l body that s t r i k e s n orth 35 degrees west and-plunges s t e e p l y northwestward. The zone i s 200 to 400 f e e t l ong, 128 3 0 to more than 1 0 0 feet wide, and has been traced from the sur face to a v e r t i c a l depth exceeding 1 1 0 0 f e e t where i t termin-ates against the Boss Mountain Stock. M i n e r a l i z a t i o n bound-a r i e s of the Main B r e c c i a Zone as shown i n Figures 5 . 1 , 5 . 2 and 5 . 3 represent a grade of 0 . 4 percent molybdenum. Downward the ore zone separates i n t o two r o o t s . The northernmost root bot-toms between'elevations 5 0 4 5 f e e t and 4 9 0 0 f e e t , but the south root extends dottfnward without change to the contact w i t h the Boss Mountain Stock. For mining purposes the Fracture Ore Zone, which i s along the upper edge of the Quartz B r e c c i a , i s considered part of the Main B r e c c i a Zone; however, t h i s , zone i s s t r u c t u r a l l y d i f f e r e n t and deserves s p e c i a l d e s c r i p t i o n . The Fracture Ore Zone, a bulbous hood, that envelopes the upper edge of the Main B r e c c i a Zone, i s a body of b r e c c i a w i t h c l o s e l y spaced, unoriented f r a c t u r e s f i l l e d w i t h molybdenite and a l i t t l e quartz (Figures 5 . 1 , 5 . 2 , and 5 . 3 ) . Along i t s plunge of 4 - 5 degrees northwest-ward, t h i s body extends, from the surface downward f o r 400 f e e t . The zone a t t a i n s a maximum width of 130 feet and a h o r i z o n t a l l e n g t h of more than 3 0 0 f e e t . Four other mineralized, b r e c c i a zones are known, but have not been e x t e n s i v e l y explored. A l l are roughly v e r t i c a l , pipe-l i k e bodies, ovoid to c i r c u l a r i n plan. The l a r g e s t of these, the South B r e c c i a Zone, i s 2 5 0 f e e t long i n a d i r e c t i o n north / EZT Fracture Ore E2 Phase HL Breccia tSl Quartz Breccia I | Mineralization 5300 N 4900 W 5000 E Figure 5.1. ^JHigh-Grade Vein 5300N-42° Stringer Zone / / / 7 N ^ J U s h - C r ^ e Vein 4900N^ 5260 level 5045 level 5000 E 5C00 E Level plans of part of the lioss Mountain molybdenite deposits. 1 3 0 5 5 degrees west w i t h a maximum width of 1 1 0 f e e t . I t has been traced, by a few d r i l l holes t o a depth exceeding 1 0 0 0 f e e t and i s c u r r e n t l y being more thoroughly explored. Other b r e c c i a pipes range from 1 5 to 2 5 f e e t i n diameter and are known to p e r s i s t f o r depths exceeding 2 0 0 f e e t . Hundreds of quartz v e i n s , some of which c o n t a i n molybden-it e , and are of.economic s i g n i f i c a n c e , occur In the mine area. Most veins are narrow and somewhat i s o l a t e d and. are i n d i v i d u a l -l y of no economic i n t e r e s t , but where they occur i n s u b p a r a l l e l swarms or lodes, r e f e r r e d to as s t r i n g e r zones, they c o n s t i t u t e low-grade mineral d e p o s i t s . The most important and. best-kriown of these, the S t r i n g e r Zone, forms a f l a t - l y i n g quarter-cone, t a b u l a r i n c r o s s - s e c t i o n that s k i r t s the west side and north end of the Main B r e c c i a Zone and. the Fracture Ore Zone (Figures 5 . 1 , 5 . 2 , and 5 . 3 ) . With a th i c k n e s s ranging from 1 0 0 to 3 0 0 f e e t , t h i s zone has an arc l e n g t h i n excess of 600 f e e t and an' explored d i p l e n g t h of at l e a s t 5 0 0 f e e t . From i t s southwest end the S t r i n g e r Zone trends n o r t h e r l y and then swings e a s t e r l y around the Fracture Ore Zone, Dips i n the western part are 2 0 to 3 0 degrees to the west and In the e a s t e r l y t r e n d i n g part are 3 5 to 4 5 degrees northwestward. Because the dip^ i s low, th S t r i n g e r Zone i n t e r s e c t s the Fracture Ore Zone and the Main B r e c c i a Zone at and above the 5 1 0 0 - f o o . t e l e v a t i o n . Boundaries of the zone are determined, by the spacing and. molybdenite 132 content of the component v e i n s . West and southwest of the S t r i n g e r Zone i s another zone of s u b p a r a l l e l molybdenite-bearing quartz v e i n s which c o n s t i t u t e the West S t r i n g e r Zone. Although only p a r t l y explored, t h i s zone has a p o s s i b l e h o r i z o n t a l extension exceeding 3000 f e e t i n a general n o r t h to north 3 5 degrees west d i r e c t i o n . Dips of i n d i v i d u a l veins range from 1 5 to 3 5 degrees southwestward. Sketchy diamond d r i l l data suggest a complementary s t r i n g e r zone east of the Fracture Ore Zone. The o r i e n t a t i o n and extent of veins i n t h i s zone, the East S t r i n g e r Zone, i s not known, but they may be \ip-dip extensions of veins which form the S t r i n g e r Zone. One v e i n of economic importance, knox\m as the High-Grade V e i n , has an explored l e n g t h exceeding 400 f e e t and a width ranging from 4 to 10 f e e t . I t i s a composite v e i n that f o l l o w s a sheared and. altered, andesite dyke over most of i t s l e n g t h . The High-Grade Vein s t r i k e s n orth 76 to 80 degrees east and. d i p s 42 to 48 degrees north. Molybdenite, which i s e r r a t i c a l l y d i s -t r i b u t e d , comprises 0.X percent to a.maximum of 10 percent of the v e i n . CHARACTER OF MINERALIZATION . The character of m i n e r a l i z a t i o n i n the v a r i o u s ore zones i s g r o s s l y s i m i l a r , but d i f f e r s i n d e t a i l . A l l ore zones are com-posed of more than one stage of molybdenite m i n e r a l i z a t i o n . F r a c t u r e Ore E3 Phase II! B recc i a 03 Quartz B recc i a • (Mineral izat ion Figure 5 . 3 . Longitudinal section (projected to 5000 E g r i d l i n e ) through part of the Boss fountain molybdenite deposits (looking west). 134 Areas of s i n g l e - s t a g e molybdenite m i n e r a l i z a t i o n g e n e r a l l y are not economically s i g n i f i c a n t , except i n areas of p a r t i c u l a r l y intense pre-mineral f r a c t u r i n g . • Molybdenite deposited d u r i n g the i n i t i a l stages of mineral i z a t i o n was f i n e l y c r y s t a l l i n e (t 1 mm.) and g e n e r a l l y became p r o g r e s s i v e l y more coa r s e l y c r y s t a l l i n e with each successive stage. Molybdenite c r y s t a l s deposited i n the f i n a l stage of m i n e r a l i z a t i o n range from 5 mm. to 20 mm. i n diameter. The exception t o t h i s g e n e r a l i t y i s the m i n e r a l i z a t i o n i n the Fracture Ore Zone which contains f i n e l y c r y s t a l l i n e molybdenite that was deposited during intermediate and l a t e stages of min-e r a l i z a t i o n . . In the Main B r e c c i a Zone molybdenite occurs i n three d i f -f e r e n t modes, introduced d u r i n g two d i f f e r e n t stages of mineral i z a t i o n . Most molybdenite was introduced d u r i n g Phase I I I B r e c c i a development as part of the matrix of the b r e c c i a and a l s o along f r a c t u r e s and matrix-fragment boundaries i n the ad-jacent Quartz B r e c c i a . Group 3 quartz v e i n s , which developed d u r i n g Phase I I I B r e c c i a formation, and. group 4 quartz veins a l s o c o n t r i b u t e to part of the ore zone. Molybdenite deposited d u r i n g Phase I I I B r e c c i a development i s f i n e l y c r y s t a l l i n e , whereas molybdenite i n group 4 quartz veins i s c o a r s e l y c r y s t a l l i n e , Andesite dyke fragments and. mafic minerals i n other fragments were e s p e c i a l l y f a vorable s i t e s of molybdenite 1 3 5 d e p o s i t i o n . In a l l places molybdenite seems to occupy open spaces, such as g r a i n c o n t a c t s , vugs and f r a c t u r e s , and few replacement te x t u r e s have been observed. D e t a i l s of the m i n e r a l i z a t i o n of the South B r e c c i a Zone are scanty, but the data i n d i c a t e a s i m i l a r m i n e r a l i z a t i o n h i s t o r y . The Fracture Ore Zone, which f o r mining purposes i s con-sidered as part of the Main B r e c c i a Zone-, i s composed of two modes of molybdenite from two stages of m i n e r a l i z a t i o n . F i n e l y c r y s t a l l i n e molybdenite, which forms the matrix of the Fracture Ore ( P l a t e s 5 . 1 and 5 . 2 ) , was deposited during group k and group 5 quartz v e i n development. Molybdenite in. the accompanying quartz v e i n s , such as the High-Grade Vein, i s co a r s e l y c r y s t a l -l i n e . Molybdenite i n the High-Grade Vein System and i n the S t r i n g -er Zones i s e n t i r e l y i n quartz v e i n s , except very l o c a l l y i n the High-Grade Vein where molybdenite occurs without quartz. The S t r i n g e r Zones c o n s i s t of group 3 » group h and group 5 quartz v e i n s and commercial ore boundaries r e f l e c t the d e n s i t y of quartz v e i n s . MINERALOGY Most minerals i n the Boss Mountain'deposits were i d e n t i f i e d i n hand specimen, or i n t h i n s e c t i o n ; others required p o l i s h e d s e c t i o n and/or X-ray powder photographs f o r i d e n t i f i c a t i o n . N o n metallic, m e t a l l i c and secondary minerals are considered i n t h i s s e c t i o n . 136 m P l a t e 5 . 1 . Fracture Ore. Angular fragments of g r a n o d i o r i t e and a l t e r e d andesite dyke (black) i n molybdenite matrix (grey). (Scale i s i n i n c h e s ) . P l a t e 5 . 2 Fracture Ore. Angular fragments of g r a n o d i o r i t e and quartz (white) i n molybdenite matrix (grey). (Scale i s i n i n c h e s ) . 13? Nonmetallic Minerals Nonmetallic minerals i n the Boss Mountain d e p o s i t s include gangue and a l t e r a t i o n minerals (Table 5.1). Some minerals, such as b i o t i t e , m i c r o p e r t h i t e , s e r i c i t e , and c h l o r i t e , occur as both gangue and a l t e r a t i o n minerals. A l t e r a t i o n M i n e r a l s * Gangue Minerals A c t i n o l i t e r B i o t i t e B i o t i t e C a l c i t e C a l c i t e C h l o r i t e C h l o r i t e F l u o r i t e Clay minerals M i c r o p e r t h i t e Epidote Quartz Garnet S e r i c i t e Hornblende M i c r o p e r t h i t e S e r i c i t e T a l c Z e o l i t e s : Chabazite S t i l b i t e Heulandite Sodium Harmotome * Described i n Chapter 4, Table 5.1. Nonmetallic minerals of the Boss Mountain molybdenum d e p o s i t s . A l t e r a t i o n minerals were described i n Chapter 4, and w i l l not be repeated, Gangue minerals are described below, B i o t i t e . - - B i o t i t e , the most abundant and widespread non-m e t a l l i c mineral associated w i t h the molybdenum- d e p o s i t s , was described i n Chapter 4, The b i o t i t e occurs as a gangue mineral i n the matrix of the Phase I I I B r e c c i a and r e p l a c e s magmatic 138 hornblende and b i o t i t e i n the host rocks. C a l c i t e i - - C a l c i t e occurs i n s e v e r a l ways: 1) i n c a l c i t e -z e o l i t e v e i n s , 2) as a c o n s t i t u e n t of f a u l t gouge, 3) i n vugs and r e p l a c i n g f e l d s p a r s i n the Boss Mountain Stock, and 4 ) as a -primary mineral i n quartz v e i n s . The f i r s t three occurrences were described i n Chapter 4 . C a l c i t e i n quartz v e i n s show a wide' range of coloxir and h a b i t . Colour ranges through c o l o u r l e s s , white, pale green, and pink. Most vei n s contain l i t t l e c a l c i t e . S i n g l e subhedral rhom-bohedra completely embedded i n quartz suggest that c a l c i t e was a primary c o n s t i t u e n t of the v e i n s . Pink c a l c i t e i s foiand only i n l a t e group 4 quartz v e i n s . The curved, cleavage surfaces suggest a d o l o m i t i c composition, but X-ray powder photograph i d e n t i f i c a t i o n confirms a c a l c i t e composition. E x t e r n a l form of the c a l c i t e i s controlled, by quartz and p y r i t e c r y s t a l s . V e i n l e t s of s e r i c i t e cut the c a l c i t e . Group 5 quartz veins a l s o c o n t a i n c a l c i t e as a primary, but very minor, c o n s t i t u e n t . C h l o r i t e . - - C h l o r i t e s were.described i n considerable d e t a i l i n Chapter 4 . F l u o r i t e . --- A few small anhedral masses of f l u o r i t e , c l o s e l y a s s o c i a t e d 'with raicroperthite, were observed i n group 4 ; quartz veins and i n altered, s e c t i o n s of the Phase I I I B r e c c i a . 139 The g r a i n s , which range from 0 . 5 t o 2 mm. i n maximum d i a -meter, have dark purple cores that grade r a p i d l y outward to almost c o l o u r l e s s rims. Grains l e s s than 1 mm. i n diameter are ne a r l y c o l o u r l e s s and are e a s i l y overlooked. • Thus, f l u o r i t e may be--more common i n the d e p o s i t s than has been recognized. Ident-i f i c a t i o n was confirmed w i t h X-ray powder photographs. M i c r o p e r t h i t e . -•• See Chapter 4 . Quartz.-- Quartz, c l o s e s t a s s o c i a t e of molybdenite, occurs i n v e i n s and as matrix i n Quartz B r e c c i a . Several ages of quartz veins have been recognized i n the mine area. The s t r u c -t u r a l r e l a t i o n s of these veins were discussed i n Chapter 3 . Recognition of quartz veins from d i f f e r e n t age groups i s de-pendent upon the mineralogy, o r i e n t a t i o n of the v e i n s , and upon the character of the quartz i n the veins ( P l a t e s 5 . 3 and 5 . 4 ) . Table 5 . 2 i s a summary of the mineralogy and character of the v e i n s . S e r i c i t e . — S e r i c i t e was described i n Chapter 4 . M e t a l l i c Minerals T h i r t e e n m e t a l l i c minerals have been i d e n t i f i e d i n the Boss Mountain d e p o s i t s . The minerals represent s e v e r a l - d i f f e r e n stages of m i n e r a l i z a t i o n and some minerals appear at more than 140 Group Mineralogy Character 5 Quartz, molybdenite, p y r i t e , w h i t e ' o r t h o c l a s e ( ? ) , c a l c i t e , magn et i t e, chalc o p y r i t e. Massive to coarsely banded-many f r a c t u r e s normal to v e i n w a l l s . . Molybdenum i n i r r e g u l a r and discontinuous bands and. lenses. Tend-ency to pinch and s w e l l , ( P l a t e 5 . 4 ) ' 4 Late: q u a r t z , m i c r o p e r t h i t e , s e r i c i t e , c a l c i t e , p y r i t e , b i s m u t h i n i t e , a i k i n i t e , mag-n e t i t e , anatase, f l u o r i t e . E a r l y : q u a r t z , m i c r o p e r t h i t e , c h l o r i t e , p y r i t e , molybden-i t e , r u t i l e . Amethystine overgrowths on e a r l y quartz c r y s t a l s . M i n e r a l i z a t i o n cuts e a r l y quartz v e i n s . Vuggy v e i n s . C o l o u r l e s s q u a r t z • c r y s t a l s . M i n e r a l -i z a t i o n patchy and i r -r e g u l a r . 3 Quartz, p y r i t e , molybdenite-, m i c r o p e r t h i t e , Uniform, massive quartz w i t h i r r e g u l a r d i s t r i b u t i o n of other minerals. 2 Quartz, p y r i t e , m i c r o p e r t h i t e . Massive quartz w i t h minor p y r i t e and m i c r o p e r t h i t e . 1 Quartz, p y r i t e Sugary,, banded v e i n s . Other s u l f i d e s added l o c a l -l y during l a t e r stages of m i n e r a l i z a t i o n ( P l a t e 5 . 3 ) Table 5 . 2 . Mineralogy and character of quartz v e i n s . 141 P l a t e 5.3. Group I quartz v e i n cut by molybdenite v e i n l e t s (mo) and a quartz-magnetite v e i n l e t (m). Note the sugary t e x t u r e of the quartz v e i n and the weak a l t e r a t i o n (a) of the g r a n o d i o r i t e adjacent to the v e i n . (Scale i s i n i n c h e s ) . P l a t e 5.4. Banded group 5 quartz v e i n w i t h c h a r a c t e r i s t i c f r a c t u r e s normal to the v e i n w a l l s . Grey bands are molybdenite. (Scale i s i n i n c h e s ) . 142 one stage. Table 5.3 i s a l i s t of the m e t a l l i c minerals i n order of abundance. P y r i t e FeS.2 (most abundant) Molybdenite M 0 S 2 R u t i l e TiC-2 Magnetite Fe304 Chalcopyr.it e CuFeS2 S p h a l e r i t e ZnFeS2 S c h e e l i t e - P o w e l l i t e CaWOi|-CaMoOi|. A i k i n i t e PbCuBiS3 B i s m u t h i n i t e B12S3 P y r o l u s i t e Mn02 Specular • Hematite Fe2C>3 Te t r a h e d r i t e Cu3(Sb.,As)S3 Anatase HO 2 ( l e a s t abundant) Table 5.3. M e t a l l i c minerals of the Boss Mountain molybdenite d e p o s i t s . P y r i t e . — P y r i t e i s the most abundant and the most wide-spread mineral a s s o c i a t e d w i t h the molybdenite d e p o s i t s . I t i s a primary c o n s t i t u e n t of a l l quartz v e i n s , occurs i n q u a r t z - f r e e f r a c t u r e s , and i s disseminated through a l l rocks i n the mine area, except the a l k a l i b a s a l t s . The ore de p o s i t s are en-compassed by an extensive aureole of p y r i t e (Map 3» i n pocket) t h a t exceeds 8,000 feet i n diameter. Most p y r i t e i n quartz veins i s euhedral, the common form being the cube modified to va r y i n g degrees by p y r i t o h e d r a l and/ or octahedral forms. P y r i t e r e l a t e d to a s p e c i f i c age of quartz g e n e r a l l y e x h i b i t s the same e x t e r n a l c r y s t a l c h a r a c t e r -i s t i c s . For example, euhedral p y r i t e of e a r l y group 4 quartz 143 v e i n s i s m o d i f i e d by p y r i t o h e d r a l forms, i s d e e p l y s t r i a t e d , and has w e l l - d e v e l o p e d o c t a h e d r a l c l e a v a g e . P y r i t e i n o t h e r q u a r t z v e i n s does n o t have t h e s e c h a r a c t e r i s t i c s . The p y r i t e i n q u a r t z - f r e e f r a c t u r e s o c c u r s as t h i n f i l m s of t a b u l a r and i r r e g u l a r masses bounded by c r y s t a l f a c e s . D i s s e m i n a t e d p y r i t e assumes a wide v a r i e t y .of forms, but g e n e r a l l y o c c u r s as i r r e g u l a r a n h e d r a l p a t c h e s . These patches a t t a i n a maximum d i a m e t e r of 2 3 mm. i n the Boss Mountain S t o c k , b u t i n most o t h e r r o c k s t h e i r d i a m e t e r i s l e s s than 1 0 mm. P y r i t e d i s s e m i n a t e d t h r o u g h r h y o l i t e p o r p h y r y dykes and a n d e s i t e dykes commonly i s e u h e d r a l t o s u b h e d r a l . In t h e b a t h o l i t h i c r o c k s d i s s e m i n a t e d p y r i t e i s accompanied by s m a l l e p i d o t e g r a i n s . P y r i t e ranges i n c o l o u r from y e l l o w - w h i t e t o b r a s s - y e l l o w t o g o l d e n y e l l o w , b u t t h e r e i s no a p p a r e n t c o r r e l a t i o n between c o l o u r and o c c u r r e n c e , age or p o s i t i o n . P y r i t e from e a r l y group 4 q u a r t z v e i n s i s unique among the Boss Mountain p y r i t e s because of t h e l a r g e s i z e of the c r y s t a l s (up t o 4 i t i c h e s a l o n g the cube f a c e ) and e s p e c i a l l y because of the w e l l - d e v e l o p e d o c t a h e d r a l c l e a v a g e . I t was thought t h a t the c l e a v a g e might be caused by i m p u r i t i e s i n c o r p o r a t e d , d u r i n g c r y s t a l growth or by c h e m i c a l c o m p o s i t i o n t h a t might be ex-p r e s s e d by a v a r i a t i o n i n t h e s i z e of the c e l l edge. P o l i s h e d , s e c t i o n s of s e v e r a l s i n g l e c y r s t a l s r e v e a l e d a l a c k of impur-i t i e s t h a t could, be r e s o l v e d w i t h a m i c r o s c o p e . A s i n g l e X-ray 144 pcwder photograph of the p y r i t e gave a c e l l edge of 5 .405^ which i s i n agreement with the value of 5.40667i0O0O? reported f o r p y r i t e by Kerr et a l ( 1 9 4 5 , p.498) f o r p y r i t e from L e a d v i l l e , Colorado. Berry and Thompson ( I 9 6 2 ) r e p o r t the c e l l edge of p y r i t e as 5.419S. Much p y r i t e exposed on the surface at the Boss Mountain d e p o s i t s i s a l t e r e d t o l i m o n i t e and j a r o s i t e which have coloured the rocks r u s t y brown to yellow-brown. Mol^b^ni_t_e.— Molybdenite, the only economic mineral at Boss Mountain i s second i n abundance among m e t a l l i c minerals. P y r i t e , along w i t h the n o n m e t a l l i c minerals b i o t i t e and quartz, exceeds molybdenite i n t o t a l abundance, Three' periods of molyb-d e n i t e m i n e r a l i z a t i o n have been recognized, two or which are separated by a barren quartz v e i n phase. Generally molybdenite i n the e a r l i e s t period of m i n e r a l i z a t i o n was f i n e grained and g r a i n s i z e increased with each period of m i n e r a l i z a t i o n u n t i l the molybdenite i n the f i n a l period of m i n e r a l i z a t i o n was very coarse g r a i n e d . . . Molybdenite c h a r a c t e r i s t i c a l l y forms t h i n selvedges along the edges' of quartz veins and b r e c c i a fragments (see P l a t e 2.12, Chapter 2 ) , discontinuous bands w i t h i n some quartz veins ( P l a t e 5 . 4 ) , and l e s s commonly r o s e t t e s of coarse c r y s t a l s . Mafic minerals were favoured s i t e s of molybdenite d e p o s i t i o n . In the High-Grade Vein molybdenite c h a r a c t e r i s t i c a l l y f i l l s 145 open f r a c t u r e s i n a comb t e x t u r e . V e i n l e t s as much as four f e e t i n l e n g t h are composed of groups of molybdenite c r y s t a l s up to 20 mm. across that extend from opposing v e i n w a l l s i n t o the openings ( P l a t e s 5.5 a n d 5.6). Most openings are completely f i l l e d w i t h molybdenite, but i n some a medial opening remained th a t was f i l l e d w i t h quartz and p y r i t e . In some v e i n l e t s the medial par t contains fragments a l t e r e d w a l l rock. The v e i n l e t s , which are i n s e c u r e l y fastened t o v e i n w a l l s , are e a s i l y sep-arated from the a l t e r e d a ndesite host rock. T r a i l l ( I 9 6 3 ) reported a rhombohedral polytype of molyb-d e n i t e t h a t i s e a s i l y i d e n t i f i e d w i t h X-ray powder photographs. X-ray powder photographs of molybdenite from a l l three periods of molybdenite m i n e r a l i z a t i o n at the Boss Mountain d e p o s i t s show the molybdenite i s the common hexagonal polytype. Molybdenite i n surface exposures has been l a r g e l y a l t e r e d to f e r r i m o l y b d i t e and more r a r e l y to p c w e l l i t e . R u t i l e . — The occurrences and types of r u t i l e were de-s c r i b e d i n Chapter 4. , ' M a g n e t i t e . — Granular hydrothermal magnetite, which i s e r r a t i c a l l y d i s t r i b u t e d throughout the d e p o s i t s , g e n e r a l l y oc-curs i n and near group 4 and group 5 quartz v e i n s . Subhedral magnetite dodecahedra a s s o c i a t e d w i t h r a d i a t i n g c l u s t e r s of c h l o r i t e c r y s t a l s l i n e vugs i n group 4 veins and i n the Phase I I I B r e c c i a . 146 P l a t e 5.5. Coarsely c r y s t a l l i n e molybdenite from the High-Grade Vein. Black fragment i s a l t e r e d andesite host rock. ( S c a l e . i s i n i n c h e s ) . P l a t e 5.6. C h a r a c t e r i s t i c t e x t u r e of c o a r s e l y c r y s t a l l i n e molybdenite i n the High-Grade Vein. (Scale i s i n i n c h e s ) . 147 Magnetite appears to have c r y s t a l l i z e d contemporaneously w i t h c h a l c o p y r i t e and w i t h p y r i t e . P y r i t e of an e a r l i e r stage of m i n e r a l i z a t i o n i s cut by magnetite which i n tu r n i s cut by l a t e r stages of p y r i t e . S i m i l a r r e l a t i o n s are shown between magnetite and molybdenite. C h a l e q p y r l t e . — I r r e g u l a r masses of anhedral c h a l c o p y r i t e , which are sp a r s e l y and e r r a t i c a l l y d i s t r i b u t e d throughout the Boss Mountain d e p o s i t s , occur i n m i a r o l i t i c c a v i t i e s i n the Boss Mountain Stock, i n group 4 and group 5 quartz v e i n s , ana d i s -seminated through parts of the Phase I I I B r e c c i a zone, P y r i t e , m i c r o p e r t h i t e and c h l o r i t e are constant a s s o c i a t e s of chalco-p y r i t e . Magnetite, specular hematite, and s p h a l e r i t e are common a s s o c i a t e s and i n the Boss Mountain Stock t e t r a h e d r i t e occurs w i t h the c h a l c o p y r i t e . Widely spaced m i a r o l i t i c c a v i t i e s i n the Boss Mountain Stock, which are l i n e d w i t h euhedral quartz, m i c r o p e r t h i t e , and s e r i c i t e , have been f i l l e d w i t h c h a l c o p y r i t e . S e v e r a l samples of h i g h l y s e r i c i t i z e d rock from the stock, which were found on the waste dump, con t a i n an estimated 20 t o 50 percent t o t a l s u l f i d e s comprised of 10 to 15 parts c h a l c o p y r i t e to 1 part t e t r a h e d r i t e . The source of the samples was not found. P o l i s h -ed s e c t i o n study of the c h a l c o p y r i t e - t e t r a h e d r i t e shows that both minerals are f o r the most part f r e e of i m p u r i t i e s , except along mutual contacts where the c h a l c o p y r i t e contains rounded .1.48 blebs of t e t r a h e d r i t e . C h a l c o p y r i t e was introduced w i t h l a t e group 4 quartz veins and more r a r e l y w i t h group 5 quartz v e i n s . I t occurs as d i s -seminated g r a i n s and s t r i n g e r s i n the veins and was introduced i n t o p r e - e x i s t i n g s t r u c t u r a l or t e x t u r a l f e a t u r e s , such as quartz v e i n s , b r e c c i a s and f r a c t u r e s , during development of the l a t e group 4 and group 5 v e i n s . The c h a l c o p y r i t e i n parts of the Phase I I I B r e c c i a zones T.«ras introduced during t h i s stage of m i n e r a l i z a t i o n . P o l i s h e d s e c t i o n study of c h a l c o p y r i t e from the Boss Mountain deposits has shown that the mineral i s f r e e from ex-solved impurities-, except l o c a l l y i n samples from the Boss Mountain Stock. P y r i t e , magnetite, and molybdenite cut chalco-p y r i t e . Few'o ther minerals were observed i n contact with c h a l c o p y r i t e . Some p y r i t e from an e a r l i e r stage of mineral-i z a t i o n i s cut by c h a l c o p y r i t e . C h a l c o p y r i t e i n minute q u a n t i t i e s was found, i n s e v e r a l l o c a l i t i e s outside the molybdenite d e p o s i t s . Most noteworthy of these i s north of Takomkane Volcano i n some old. workings . where c h a l c o p y r i t e and_ p y r i t e i n quartz v e i n m a t e r i a l was found on the dump of a w a t e r - f i l l e d s h a f t , Reinecke ( 1 9 2 0 , p.9?) and Galloway (1917, p.135) described these occurences when the workings were a c c e s s i b l e . Nothing of s i g n i f i c a n c e can be added to t h e i r observations. 149 S p h a l e r i t e , — S p h a l e r i t e was observed w i t h - c h a l c o p y r i t e i n Phase I I I B r e c c i a . Aggregates of euhedral c r y s t a l s and anhedral masses of s p h a l e r i t e , which g e n e r a l l y are small ( l e s s than 2 mm,), l o c a l l y exceed 7 ram. i n diameter. I n d i v i d u a l c r y s t a l s range from 0.5 mm. to 1.5 mm. i n diameter. Large g r a i n s have a dark, i r -r i d e s c e n t t a r n i s h that imparts a black colour t o the m i n e r a l , but smaller c r y s t a l s and fragments are yellow t o l i g h t brown i n colo u r . Cleavage fragments e x h i b i t the c h a r a c t e r i s t i c resinous l u s t r e . A p o l i s h e d s e c t i o n examination d i s c l o s e d that the sphaler-i t e i s f r e e of i m p u r i t i e s . A g r a i n of dark s p h a l e r i t e and a g r a i n of yellow s p h a l e r i t e were selected, f o r c e l l edge measure-ment w i t h X-ray powder photographs. The measured, c e l l edge of . o both g r a i n s a r e * ' i d e n t i c a l (a=5.412A) and corresponds to a FeS content- of 6 mol percent (Skinner, 19&1, p.l406). Orange m i c r o p e r t h i t e and. dark green c h l o r i t e (Stage 3 a l t e r -a t i o n ) are c l o s e l y r e l a t e d to s p h a l e r i t e - c h a l c o p y r i t e occur-rences and. a l l are g e n e t i c a l l y r e l a t e d to group 4 quartz v e i n development. Scheelite-PowelJ i t e . — Late group 4 quartz veins c o n t a i n minor and i r r e g u l a r l y d i s t r i b u t e d q u a n t i t i e s of s c h e e l i t e -p o w e l l i t e . The euhedral to subhedral creamy to golden yellow c r y s t a l s range i n s i z e from 2 t o 24 mm. Fluorescence of most c r y s t a l s i s l i g h t blue ( s c h e e l i t e ) , but the outer p a r t s of some 1 5 0 c r y s t a l s f l u o r e s c e yellow ( p o w e l l i t e ) . In one l a r g e c r y s t a l the Inner core ( 1 7 mm.) f l u o r e s c e s l i g h t blue and the rim ( 5 - 7 mm.) f l u o r e s c e s yellow. The colour change i s sharp and i s marked, by a weak p h y s i c a l d i s c o n t i n u i t y i n the c r y s t a l . Other c r y s t a l s do not d i s p l a y such w e l l - d e f i n e d r e l a t i o n s between ye l l o w and l i g h t blue f l u o r e s c e n c e . Spectrographic analyses of bulk samples from the d e p o s i t s i n d i c a t e s the presence of small q u a n t i t i e s of t i n . I t was noted th a t t i n and tungsten appear to be mutually dependent. Two samples of s c h e e l i t e , the only tungsten mineral i n the d e p o s i t s , were s e l e c t e d f o r s e m i - q u a n t i t a t i v e spectrographic analyses to confirm t h i s apparent i n t e r r e l a t i o n . The analyses c l e a r l y show that s c h e e l i t e c a r r y s small q u a n t i t i e s of t i n (Table 5 . 4 ) . ' Sample 1 Sample,2 Ca VS VS VSmVery Strong W - S S SrrStrong Mo M M M^Moderate Sr M . M W.M=Weakly Moderate Sn WM WM W=Weak T i W V/ VW=Very Weak B i VW (?) VW (?) S i M M Impurity (?) Fe W W Mg W W Table 5 . 4 . S e m i - q u a n t i t a t i v e spectrographic analyses of s c h e e l i t e . A i k i n i t e . — B r i g h t , m e t a l l i c grey, subhedral t o euhedral c r y s t a l s of a i k i n i t e comprise a minute part of l a t e group 4 quartz v e i n s . The a i k i n i t e occurs as well-developed ortho-151 rhombic prisms (11.0) which e x h i b i t p e r f e c t cleavage p a r a l l e l to the b-pinacoid (010) . Terminations are r a r e . Observed c r y s t a l s , which range from 2 to 180 mm. i n l e n g t h , have a g r e y i s h black streak and are very s o f t (H=2). The measured s p e c i f i c g r a v i t y (7.09) i s comparable to Peacock's (1942, p.63) measurements of 7.0? and 7 .08. A i k i n i t e and b i s m u t h i n i t e both are found i n group 4 quartz v e i n s c l o s e l y a s s o c i a t e d w i t h s c h e e l i t e and p y r i t e , but have not been observed together. A i k i n i t e occurs only near the Main B r e c c i a Zone and b i s m u t h i n i t e was found only i n l a t e group 4 quartz veins c u t t i n g the Boss Mountain Stock. The two minerals appear to be mutually e x c l u s i v e , B i s m u t h i n i t e . - - Subhedral masses of b i s m u t h i n i t e were found i n l a t e group 4- qxiartz veins i n the Boss Mountain Stock, The m e t a l l i c grey masses have groi«i upon euhedral p y r i t e c r y s t a l s and are c l o s e l y a s s o c i a t e d w i t h s c h e e l i t e . I d e n t i f i c a t i o n of the mineral was e s t a b l i s h e d w i t h X-ray powder photographs. Because of the e r r a t i c d i s t r i b u t i o n of the m a t e r i a l and i t s small s i z e ( l e s s than 5 mm.) and q u a n t i t y , b i s m u t h i n i t e could be e a s i l y overlooked. P y r o l u s i t e . — Velvety black manganese oxide coats quartz c r y s t a l s i n some of the group 4 quartz veins on the 504-5 l e v e l of the mine. C o l o u r l e s s c a l c i t e c r y s t a l s were deposited upon the bl a c k oxide. Manganese oxide f i l m s seldom exceed. 1 5 2 0.5 mm..in t h i c k n e s s . X-ray powder photographs of the m a t e r i a l were poor but were s u f f i c i e n t t o i d e n t i f y the m a t e r i a l as pyro-l u s i t e . Genetic r e l a t i o n s h i p of the p y r o l u s i t e i s p r o b l e m a t i c a l . P y r o l u s i t e , which may be of secondary o r i g i n , i s found as t h i n f i l m s w i t h i n unoxidized quartz v e i n s on the 5 0 4 5 l e v e l . Other occurrences of secondary manganese minerals were observed! only i n surface exposures. For t h i s . r e a s o n , the p y r o l u s i t e i s b e l i e v e d to have formed d u r i n g the l a t e stages of group 4 quartz v e i n development. Specular H e m a t i t e . — Specular hematite, a r a r e mineral i n the Boss Mountain d e p o s i t s occurs i n and near group 4 quartz v e i n s and i n . Phase I I I B r e c c i a as euhedral to subhedral p l a t e s s p a t i a l l y r e l a t e d to c h a l c o p y r i t e . T r i a n g u l a r markings on the p l a t e s , . red- i n t e r n a l r e f l e c t i o n s , hardness (about 6 ) , and. brown-ish streak were the i d e n t i f y i n g p r o p e r t i e s of the m i n e r a l . P o l i s h e d s e c t i o n examination shows p l a t e s of hematite c u t t i n g anhedral g r a i n s c h a l c o p y r i t e . T e t r a h e d r i t e . - - T e t r a h e d r i t e , which was observed only i n samples, from the Boss Mountain Stock, occurs as anhedral masses i n t i m a t e l y a s s o c i a t e d w i t h c h a l c o p y r i t e . The t e t r a h e d r i t e i s g r e y i s h black w i t h a-brown st r e a k . . C e l l edge- as determined from one X-ray powder photograph i s 1 0 . 3 0 S (measured).. T e x t u r a l r e l a t i o n s suggest t h a t the t e t r a h e d r i t e and c h a l c o p y r i t e c r y s t a l -l i z e d simultaneously. C h a l c o p y r i t e r a r e l y contains rounded blebs of t e t r a h e d r i t e at mutual boundaries. T e t r a h e d r i t e was not 153 observed i n p l a c e , but was found on the waste dump. A n a t a s e . — Anatase occurs w i t h yellow s e r i c i t e which cuts group 4 quartz v e i n s . The euhedral honey-brown c r y s t a l s average 0 . 2 mm. i n diameter and have a maximum diameter of 0 . 5 mm. The b i p y r a m i d a l c r y s t a l s , which are s t r i a t e d p a r a l l e l to the base, show v a r i o u s degrees of m o d i f i c a t i o n by a second bipyramid, a prism, and b a s a l p i n a c o i d . Other m o d i f i c a t i o n s may be present, but were not recognized on the s m a l l , rough c r y s t a l s . Anatase and r u t i l e are polymorphs of Ti0£ and do not form simultaneously. Schroder ( 1 9 2 8 , p . 5 ^ ) has shown th a t anatase i s a lower temperature polymorph than i s r u t i l e . Anatase which i s g e n e t i c a l l y r e l a t e d to l a t e group 4 quartz veins may have formed at the expense of p r e - e x i s t i n g r u t i l e . Products of Weathering The minerals included i n t h i s s e c t i o n are those which formed d u r i n g weathering. Only two secondary m i n e r a l s , limon-I t e and f e r r i m o l y b d i t e , are abundant and widespread;, a l l other minerals are r a r e . Table 5 . 5 i s a l i s t of secondary minerals from the. Boss Mountain d e p o s i t s i n order of decreasing abundance (top to bottom) . 154 Limonite F e r r i m o l y b d i t e Manganese oxide hydrous i r o n oxides (most abundant) Fe2(Mo04K8H20 J a r o s i t e P o w e l l i t e Leucoxene Hematite Malachite KFe 3(S0^)2(OH)6 CaMo04 hydrous t i t a n i u m oxides (?) F e o O o Cup(0H ) p C 0 o(least abundant) Table 5 . 5 . Secondary minerals of the Boss Mountain molybdenum L i m o n i t e . — Limonite, as used here, i s a general term ap-p l i e d to brownish hydrous i r o n oxides. No attempt was made to i d e n t i f y the mineral c o n s t i t u e n t s of the l i m o n i t e . ' Limonite, the most abundant and widespread secondary min-e r a l i n the Boss Mountain d e p o s i t s f o r m e d from the o x i d a t i o n of p y r i t e , c h a l c o p y r i t e , and magnetite, as w e l l as from mafic minerals. Pervasive .limonite s t a i n was found on a l l f r a c t u r e s i n the rocks t o a depth of 40 f e e t i n the underground workings. A c t i v e water courses (open f r a c t u r e s ) ' 5 0 0 f e e t below the present ground surface contain l i m o n i t e , but the occurrence at t h i s depth i s h i g h l y r e s t r i c t e d . Many rock faces i n the underground workings, i^hich were f r e s h and. unaltered, i^nen exposed, have had l i m o n i t e deposited, on them w i t h i n two years a f t e r t h e i r exposure. Ferrimolybd i t e . — The a l t e r a t i o n of molybdenite to f e r r i -molybdite is. apparent i n most surface exposures which contain molybdenite. Fibrous, f e l t y , y e l low patches and pseudomorphs a f t e r molybdenite c h a r a c t e r i z e the f e r r i m o l y b d i t e . In many exposures much molybdenum apparently has been removed by de p o s i t s . 155 weathering. Hexagonal molds of former molybdenite c r y s t a l s i n quartz v e i n s now c o n t a i n a few a c i c u l a r c r y s t a l s of f e r r i -molybdite or are completely barren. The rocks around these areas are stained, w i t h l i m o n l t e . T i t l e y ( 1 9 6 3 , p.204) has shown tha t c o n d i t i o n s under which l i m o n i t e forms are not conducive to f e r r i m o l y b d i t e development. A c i c u l a r f e r r i m o l y b d i t e c r y s t a l s have a t t a i n e d a maximum le n g t h of 1 . 5 mm. Many occurrences are so f i n e grained that i n d i v i d u a l c r y s t a l s were not recognized. Ferrimolybd.ite i s e s s e n t i a l l y a surface feature and. was not observed more than 5 f e e t below the surface of the ground. Limonite i s the only abundant secondary mineral a t - g r e a t e r depths. Manganese oxide.-- Thin, discontinuous f i l m s and d e n d r i t i c forms of black manganese oxide are r e l a t i v e l y common on f r a c -tures i n the surface exposures .of the mine area, but are not prominent. L o c a l l y the manganese oxide has been deposited on l i m o n i t e , but r e l a t i o n to other secondary minerals could, not be-determined. Attempts to i d e n t i f y the black, oxide by use of X-ray powder photographs were u n s u c c e s s f u l . • J a r o s i t e . - - A y e l l o w i s h , earthy a l t e r a t i o n product of p y r i t e was determined as j a r o s i t e w i t h the aid. of X-ray powder photo-graphs. The mineral i s not abundant, but i s so f i n e grained and inconspicuous that i t can e a s i l y be overlooked. P o w e l l i t e . — P o w e l l i t e was- f i r s t observed i n the oxidized. 156 part of the molybdenum depos i t s when s e v e r a l samples were"ex-posed to u l t r a v i o l e t r a d i a t i o n . Under u l t r a v i o l e t r a d i a t i o n the p o w e l l i t e f l u o r e s c e s creamy yellow. P o s i t i v e i d e n t i f i c a t i o n was made with an X-ray powder photograph. Secondary p o w e l l i t e , a r a r e mineral at Boss Mountain, forms t h i n , inconspicuous, l i g h t grey to white f i l m s on. quartz and other minerals adjacent to a l t e r e d molybdenite g r a i n s . Leucoxene.-- Leucoxene i s widely d i s t r i b u t e d over Takomkane Mountain, but i t i s not an abundant mineral. The mineral occurs as a l i g h t brown to y e l l o w i s h a l t e r a t i o n product of t i t a n i u m -bearing minerals, such as r u t i l e and sphene. Sphene, the most abundant accessory mineral i n the rocks of the b a t h o l i t h , g e n e r a l l y i s f r e s h and una l t e r e d . L o c a l l y the sphene i s weakly a l t e r e d t o leucoxene. R u t i l e developed by hydrothermal s o l u t i o n s and deposited wi t h quartz veins seldom e x h i b i t s a l t e r a t i o n , but some .of the r u t i l e , e s p e c i a l l y the opaque, black v a r i e t y , i s weakly a l t e r e d t o leucoxene. C h l o r i t i z e d magmatic hornblende contains sphene which commonly i s weakly a l t e r e d to leucoxene. H e m a t i t e . — B r i g h t r e d , earthy hematite was formed as a minor a l t e r a t i o n of p y r i t e i n the underground., workings of the mine. I t occurs most oft e n i n and near altered, andesite dykes as t h i n coatings on narrow p y r i t e v e i n l e t s . When the hematite i s removed from the mine i t q u i c k l y a l t e r s to l i g h t brown l i m o n i t e . 15? M a l a c h i t e . — Malachite, a r a r e mineral i n the Boss Mountain d e p o s i t s occurs as t h i n , green c r u s t s on c h a l c o p y r i t e g r a i n s . The only malachite found i n the mine area was found i n the surface exposures of the Main B r e c c i a Zone. Several shear zones i n the surrounding areas on Takomkane Mountain c o n t a i n minute q u a n t i t i e s of malachite, e s p e c i a l l y north of the volcano. Paragenesis The paragenetic sequence of minerals g e n e t i c a l l y r e l a t e d to the' Boss Mountain molybdenite d e p o s i t s i s shown on Table 5.6. Many mine r a l s , such as p y r i t e , molybdenite, q u a r t z , m i c r o p e r t h i t e , s e r i c i t e , c h l o r i t e , and c a l c i t e , appear more than once i n the sequence and e x h i b i t c o n f l i c t i n g evidence i n a paragenetic study. The mineral r e l a t i o n s were discussed, i n foregoing sec-t i o n s . CLASSIFICATION The- most widely accepted and most e a s i l y understood c l a s -s i f i c a t i o n of ore d e p o s i t s i n use today i n North America' i s the Lindgren c l a s s i f i c a t i o n as modified by Graton (1933) and. Buddington (1935) (Park, 1964, p.213). A deposit r e q u i r e s much i n v e s t i g a t i o n , before i t can be categorized i n t o t h i s c l a s s i f i -c a t i o n . The f o l l o w i n g data from the Boss Mountain deposit bear on i t s c l a s s i f i c a t i o n . The Boss Mountain Stock, the igneous bod.y most c l o s e l y a s s o c i a t e d w i t h the molybdenite d e p o s i t , i s c l e a r l y e p i z o n a l 158 j Group 1 I Veins Phase 1 | Breccia | Quartz Breccia | Group 2 Veins Phase III | Breccia | Group 3 Veins Group Veins \ Group 5 | Veins J Group 6 i Fractures j Group 1 I Veins Phase 1 | Breccia | Quartz Breccia | Group 2 Veins Phase III | Breccia | Group 3 Veins Early Late \ Group 5 | Veins J Group 6 i Fractures N o n metallic Quartz Microperthite-S e r i c i t e C h l o r i t e B i o t i t e A c t i n o l i t e Garnet Hornblende F l u o r i t e C a l c i t e T a l c M e t a l l i c P y r i t e Molybdenite C h a l c o p y r i t e Magnetite S c h e e l i t e S p h a l e r i t e A i k i n i t e B i s m u t h i n i t e T e t r a h e d r i t e Specular Hematite R u t i l e Anatase .P y r o l u s i t e — 7 — Table 5.6, Paragenetic sequence of Minerals g e n e t i c a l l y r e l a t e d to the Boss Mountain d e p o s i t s . 1 5 9 (Chapter 2 ) and consequently, l i t h o s t a t i c pressure would be low. B r e c c i a pipes and the dominance of open-space f i l l i n g over replacement at Boss Mountain imply a near-surface environment of low pressure. Park (196?, p.3^7) s t a t e s , "Telescoping and dumping c h a r a c t e r i z e xenothermal d e p o s i t s . " Telescoping i s the superposition' of high-and low-temperature minerals w i t h r e t e n -t i o n of re c o g n i z a b l e paragenetic sequence. Dumping, the s i m u l -taneous c r y s t a l l i z a t i o n of minerals that are not o r d i n a r i l y found together, i s the r e s u l t of sudden l o s s of temperature or pressure. Group 4 quartz veins at the Boss Mountain d e p o s i t show t e l e s c o p i n g of a low temperature mineral s u i t e upon a high temperature s u i t e . Dumping i s e x h i b i t e d i n the l a t e group 4 quartz v e i n s . Temperature l i m i t s may be i n f e r r e d from the f o l l o w i n g mineral r e l a t i o n s . 1. The presence of amethystine quartz i n l a t e group 4 quartz v e i n s i n d i c a t e s a temperature near 2 5 0 ° C ( F r o n d e l , I . 9 6 2 ) . . 2. The coexistence of s p h a l e r i t e and c h a l c o p y r i t e w i t h a l a c k of exsolved c h a l c o p y r i t e i n the s p h a l e r i t e places an upper l i m i t on c r y s t a l l i z a t i o n of t h e s e . s u l f i d e minerals a t 3 5 0 ° C (Park, 1964,, p . 2 0 0 ) . J.; Some, minerals,., such .as garnet,, hornblende, and magne-t i t e are considered to form at high temperatures (Bateman, 1 9 5 6 »• p..40). Mine r a l s such as molybdenite, b i s m u t h i n i t e , b i o t i t e , and 160 r u t i l e probably formed a t high temperatures. Stringham (1952, p.663) has shorn that b i o t i t e c r y s t a l l i z e s above 375° c l n a c i d s o l u t i o n s . ' 4. Incomplete data obtained by S i n c l a i r (personal com-munication, I 9 6 8 ) from f l u i d i n c l u s i o n s i n quartz i n d i c a t e a minimum temperature of formation between J00 and 380°C. To summarize the above data, the Boss Mountain molybdenite d e p o s i t s were formed i n a near-surface environment at tempera-tures ranging from 250°C to greater than 380°C. Deposits formed at shallow depths and at high to low temperatures, such as the Boss Mountain molybdenite d e p o s i t s , are c l a s s i f i e d as xenothermal. AGE OF THE. DEPOSITS Samples of g r a n d i o r i t e , Phase I I I B r e c c i a , and a l t e r e d andesite dyke, a l l of which c o n t a i n hydrothermal b i o t i t e , were s e l e c t e d from d i f f e r e n t areas .of the Boss Mountain Mine f o r K/Ar d a t i n g at the U n i v e r s i t y of B r i t i s h Columbia. Unaltered samples of the Boss Mountain Stock s u i t a b l e f o r d a t i n g could, not be found. The l e u c o c r a t i c nature of the r h y o l i t e porphyry and r h y o l i t e dykes rendered them u n s u i t a b l e f o r K/Ar d a t i n g . Rocks outside of the l i m i t s of hydrothermal a l t e r a t i o n (Map 3) were not analysed. Hydrothermal b i o t i t e , which was introduced during .Phase I I I B r e c c i a formation, and. the e n t i r e sequence of ore formation are 161 g e n e t i c a l l y r e l a t e d to the Boss Mountain Stock and, t h e r e f o r e , the age of the hydrothermal b i o t i t e represents the age of the Boss Mountain Stock, the Boss B r e c c i a s , and the ore d e p o s i t s . The K/Ar age of the hydrothermal b i o t i t e i n three samples i s ' . 1 0 5 - 2 m i l l i o n years (middle Cretaceous ) (White et a l , 196?) This age i s i n close agreement w i t h those obtained, by the G e o l o g i c a l Survey of Canada (Wanless et a l , 1966 and. I 9 6 ? ) from molybdenum-bearing b a t h o l i t h i c rocks i n the Clearwater-North Thompson R i v e r area (Figure 5 . 4 ) . 162 d Ceo/, Survey Canada 0 10 20 30 miles I . 1 1 1 Figure 5.4. Published potassium-argon dates of molybdenum-bearing and related rocks i n east-central B r i t i s h Columbia. 163 VI. GENESIS OF THE ORES ORIGIN OF THE BOSS BRECCIAS Various combinations of v o l c a n i c or sub-volcanic explosions and/or i n t r u s i v e a c t i v i t i e s have been used to e x p l a i n the o r i g i n of b r e c c i a pipes. Most authors recognize an associated a c i d i c magma as the source of the a c t i v i t y that r e s u l t e d i n the dev-elopment of b r e c c i a pipes. B r e c c i a s formed by v o l c a n i c explo-sions related, to more b a s i c lavas are not considered, i n the f o l l o w i n g d i s c u s s i o n s . B r e c c i a s developed by ex p l o s i v e eruptions accompanying T e r t i a r y volcanism i n Scotland have been described by T y r r e l l ( 1 9 2 8 ) , Richey ( 1 9 3 2 and 194-0) and other authors. These b r e c c i a s "....are c l e a r l y associated with r i s i n g a c i d i c magmas and are l o c a t e d along r i n g dykes" (Gates 1 9 5 9 » p . 8 0 7 ) . In 1 9 4 1 Burbank and H. CIoos independently explained the cause of b r e c c i a development and accompanying v o l c a n i c explosion by the a c t i o n of gases forced i n t o f r a c t u r e s above a r i s i n g magma. Reynolds (1954) f u r t h e r emphasized the importance of gases and applied, f l u i d i z a t i o n , the m o b i l i z a t i o n of a body of fra c t u r e d rock by the -violent a g i t a t i o n of fragments caused by the a c t i o n of gas fl o w i n g through the f r a c t u r e s , to the formation of i n -t r u s i v e b r e c c i a "pipes". Many authors have c a l l e d upon v o l c a n i c and/or sub-volcanic 164 explosions to e x p l a i n some b r e c c i a bodies r e l a t e d to mineral d e p o s i t s , e s p e c i a l l y those which r a p i d l y - d i m i n i s h i n c r o s s -s e c t i o n w i t h i n c r e a s i n g depth. B r e c c i a s a s s o c i a t e d w i t h the Bethlehem copper depo s i t s i n the Highland V a l l e y of B r i t i s h Columbia have been explained i n t h i s manner (White et a l , 1 9 5 7 ; Northcote., I 9 6 8 ) . Carr ( i 9 6 0 ) b e l i e v e d these same b r e c c i a s r e s u l t e d from explosions caused, by vapor pressure increases accompanying c h i l l i n g and r a p i d c r y s t a l l i z a t i o n of porphyry dykes. Other author (Gates, 1959; Perry, 1961; Kents, 1964) have a t t r i b u t e d such pipes to the late-magmatic phase of development, some of which c l e a r l y post-date m e t a l l i c m i n e r a l i z a t i o n (Perry I 9 6 I ) . Locke (1926) proposed that the P i l a r e s b r e c c i a pipe of Sonora,, Mexico,- was formed by m i n e r a l i z a t i o n s t o p i n g , the sub-sidence of rock fragments being a r e s u l t of the c o r r o s i v e a c t i o r of ascending hydrothermal s o l u t i o n s . A l t e r a t i o n of andesite .rock .fragments -accompanied the c o r r o s i v e a c t i o n and was f u r t h e r accentuated by a c y c l e of mineral d e p o s i t i o n . Gas-action accompanying i n t r u s i o n of a c i d i c magma has been called, upon to e x p l a i n many b r e c c i a s (Tweto, 1 9 5 1 ; Gates, 1959; P e r r y , 1 9 6 I; Kents, 1964). Such t h e o r i e s of o r i g i n do not r e q u i r e escape of gases to the surface , and thus d i f f e r from the sub-volcanic and v o l c a n i c explosion t h e o r i e s . Tweto (1951) suggested, that b r e c c i a t i o n a s s o c i a t e d with 165 the Pando s i l l s of Colorado were formed-as the r e s u l t of marginal c h i l l i n g and concomitant expulsion of gas that caused b r e c c i a t i o n ahead of an advancing magma. Gates (1959) concluded that b r e c c i a pipes i n the Shoshone Range, Nevada, were formed by o s c i l l a t o r y i n t r u s i o n of magma and described t h e i r formation as f o l l o w s : "Assume a r i s i n g cupola of magma which' i s c r y s t a l - . l i z i n g and b u i l d i n g up pressure of v o l a t i l e s and i s perhaps preceded by a vapor aureole of gas....The pres-sures of magma and gas open cracks overhead; gas rushes i n t o some of these, t e a r i n g fragments from the w a l l s •which, i n t u r n , a s s i s t i n f u r t h e r b r e c c i a t i o n by abr a s i o n , a t t r i t i o n , and wedging; magma rushes i n t o others, q u i c k l y c h i l l s and evolves more gas which b r e c c i a t e s the rocks ahead.; s t i l l others may be f i l l e d , w i t h b r e c c i a formed, by ro c k - b u r s t s . Rapid heating of'the rocks and conversion of included, water to steam may add to the fragmentation. ....Once the pressures 'have been diminished by er u p t i o n , a period of subsidence f o l l o w s , accompanied, by slumping, c o l l a p s i n g , and perhaps rock-bursting....As the magma continues to cool and. c r y s t a l l i z e , gas pressure b u i l d s up again. Another c y c l e of e r u p t i o n , b r e c c i a t i o n , and. i n t r u s i o n of magma and. gas f o l l o w s , " Perry ( I 9 6 I ) expanded upon the idea of b r e c c i a pipes dev-el o p i n g as a- r e s u l t of o s c i l l a t o r y magmatic i n t r u s i o n . He b e l i e v e s that b r e c c i a pipes form by foundering of the roof above a magma chamber caused, by decrease i n magma pressure at lo c a l i z e d , p o i n t s . He c i t e s two c r i t i c a l f eatures which r e q u i r e b r e c c i a development i n t h i s way ( p . 3 6 9 ) : 1. "....some of the.pipes show remarkable l a r g e down-ward displacement of fragments. This f a c t , combined .with the great volume increase due to b r e c c i a t i o n , c a l l s f o r removal of la r g e volumes of m a t e r i a l . " 166 2. "Second., the closed, tops of c e r t a i n pipes demonstrate th a t these l a r g e volumes;were not excavated from the top of the pipe; the inescapable conclusion i s that, withdrawal must have occurred at the bottom." Decrease i n magma pressure has been explained by d i f -f e r e n t i a l movement of magma to another part of the chamber or by withdrawal of magma during v o l c a n i c e r u p t i o n . Successive ad-vances and withdrawals of "quartz porphyry magma" produced the La Colorada pipe and i t s r e l a t e d copper-molybdenum d e p o s i t s . The importance of quartz porphyries In the sequence of b r e c c i a and. ore deposit formation are stressed by Perry ( I 9 6 I ) who summarizes Sales (1954) views on these rocks as f o l l o w s : "He considers the f i r s t break through of quartz porphyry a c r i t i c a l step i n s e t t i n g up a f o c a l point f o r d i f -f e r e n t i a t i o n of aqueous f l u i d s w i t h i n the magma. Sub-sequent c r y s t a l l i z a t i o n of the quartz porphyry closed the magma system, p e r m i t t i n g f u r t h e r segregation and con-c e n t r a t i o n of the ore f l u i d s . " In 1964 Kents published, a theory that he considers ap-p l i c a b l e to the formation of s e v e r a l d i f f e r e n t types of b r e c c i a s . Magmatic p u l s a t i o n s provide f o r c e s which cause h y d r a u l i c ramming of hydrothermal s o l u t i o n s i n t o o v e r l y i n g rocks. His theory i s as f o l l o w s : " . . . . I t i s q u i t e p o s s i b l e that hydrothermal s o l u t i o n s separated from the c o o l i n g magma during the ebbing phase of' magmatic p u l s a t i o n s ; because of, t h e i r l e s s e r d e n s i t y and v i s c o s i t y they may gather on top of a b a t h o l i t h , and form there a wet cap of • v o l a t i l e s . Such accumulated, s o l -u t i o n s w i l l be at the f o r e - f r o n t of the next magmatic onrush, to become rammed i n t o the enc l o s i n g rocks above the b a t h o l i t h , - w h i c h they may then permeate.... The s o l -u t i o n s by wedging f r a c t u r e s open, - d i v i d e or break up the enclosed rocks to fragments, and. envelope them. ...The 16? fragments may s h i f t , tumble, and become abraded, which r e s u l t s i n the formation of d i f f e r e n t types of b r e c c i a s . Kents' theory r e q u i r e s a " t i g h t cap above the hydrothermal development, to compel the s o l u t i o n s t o remain confined" (p. 1 5 5 M . During magmatic subsidence the f r a c t u r e d rocks c o l l a p s e under t h e i r own weight to form b r e c c i a s . The i n i t i a l b r e c c i a - t y p e developed i n t h i s process i n the "rupture b r e c c i a " or stock-work, which become b r e c c i a s i f they subside and are s h i f t e d . The b r e c c i a bodies of Boss Mountain which were described i n Chapter 2, can be b r i e f l y summarized as f o l l o w s : • 1 . Three phases of b r e c c i a were developed, at three d i f -f e r e n t times i n the sequence. The e a r l i e s t b r e c c i a (Phase I) has a matrix of comminuted rock w i t h l o c a l patches of r h y o l i t e porphyry. The second b r e c c i a , the Quartz B r e c c i a , has a matrix of quartz w i t h minor amounts of p y r i t e and m i c r o p e r t h i t e and. contains Phase I B r e c c i a and. r h y o l i t e dyke fragments. The Phase I I I B r e c c i a contains fragments of Quartz B r e c c i a and g r a n o d i o r i t e i n a matrix of comminuted, rock along w i t h qu a r t z , b i o t i t e , and molybdenite. A l t e r e d andesite dyke fragments occur i n a l l three b r e c c i a s . 2. Fragments i n Phase I B r e c c i a are dominantly angular; those i n Qiiartz B r e c c i a are e n t i r e l y angular; and those i n the Phase I I I B r e c c i a are angular near the contac t s , but- are dominantly round.ed throughout the remainder of the bcdy. 3 . R e l a t i v e displacement i n the Phase I B r e c c i a was prob-ably s l i g h t because fragments of r h y o l i t e porphyry dykes are crudely aligned w i t h t h e i r source i n the w a l l rock. G r a n o d i o r i t e , andesite dyke, and. quartz v e i n fragments i n Quartz B r e c c i a have a l l moved downward from t h e i r place of o r i g i n i n the w a l l rock. I n d i c a t i o n s of the . r e l a t i v e displacement of fragments w i t h i n the Phase I I I B r e c c i a were not obtained, but the a n a l y s i s of s t r u c -t u r a l f e a t u r e s (group 3 f r a c t u r e s and quartz veins) developed, during b r e c c i a formation i n d i c a t e s an upward d i r e c t i o n of s t r e s s e s . These upward-directed s t r e s s e s 168 a l s o caused intense f r a c t u r i n g along the upper edge of the Quartz B r e c c i a which was l a t e r m i n e r a l i z e d w i t h molybdenite (Fracture Ore Zone). 4. The contacts of the bre'ccias with the surrounding host rock are h i g h l y v a r i a b l e . Contacts between Phase I B r e c c i a and the w a l l rock are everywhere h i g h l y grad-a t i o n a l ; whereas the contacts-between Quartz B r e c c i a and the older rocks are abrupt t o g r a d a t i o n a l through stockwork to non-brecciated rock. Phase I I I B r e c c i a contacts w i t h Quartz B r e c c i a and g r a n o d i o r i t e are g r a d a t i o n a l over a few f e e t . Sub-volcanic explosions and. f l u i d i z a t i o n are not a p p l i c a b l e t o the o r i g i n of the Boss B r e c c i a s f o r the f o l l o w i n g reasons. There are ( i s ) : 1. no a s s o c i a t e d e x t r u s i v e rocks. 2. l i t t l e rounding of fragments, except i n the Phase I I I B r e c c i a which i s capped by o v e r l y i n g rocks and, there-f o r e , did not reach the surface. 3. no i n t r u s i v e f e a t u r e s such as i n t r u s i v e b r e c c i a dykes. A l l . b r e c c i a dykes show downward movement of fragments. 4. no evidence of any upward movement of fragments. M i n e r a l i z a t i o n s toping i s not favoured, as a mode of o r i g i n -because of the nature of the host rock, dominance of^'comminuted matrix (except i n the quartz b r e c c i a ) , and the l a c k of intense a l t e r a t i o n or replacement of the b r e c c i a fragments. Eastwood ( 1 9 6 4 , p.78). suggested that the quartz b r e c c i a s were formed by replacement of the matrix of an older b r e c c i a . The presence of angular fragments of older b r e c c i a , which show no evidence of replacement, w i t h i n the quartz b r e c c i a s 1 6 9 precludes t h i s mode of o r i g i n . The t h e o r i e s proposed by Gates (1959), Perry (1961), and Kents (1964) i n which b r e c c i a pipes are formed above columns of p u l s a t i n g a c i d i c magma are d i r e c t l y a p p l i c a b l e to the Boss B r e c c i a s . A l l three authors r e q u i r e the presence of v o l a t i l e s at the top of the column to a s s i s t i n f r a c t u r i n g the o v e r l y i n g rocks by v a r i o u s methods. Rock i s f r a c t u r e d by upward surge of magma and c o l l a p s e s i n response t o the f o r c e of g r a v i t y dtiring magmatic withdrawal. Kents (1964) has a p p l i e d d i f f e r e n t names, such as rupt u r e , subsidence, heave, kneaded, m i l l e d , late-magmatic, and burst b r e c c i a s , to b r e c c i a s w i t h d i f f e r i n g p h y s i c a l c h a r a c t e r i s t i c s and s l i g h t l y d i f f e r e n t modes of o r i g i n . The Phase I B r e c c i a and the Phase I I I B r e c c i a at Boss Mountain are "kneaded b r e c c i a s " . Kneaded b r e c c i a s are com-prised of a c h a o t i c array of angular to subangular fragments not f a r removed, from t h e i r place of o r i g i n and set i n a matrix of comminuted rock. The Quartz B r e c c i a s are "subsidence b r e c c i a s " which are characterized, by: angular fragments; downward displacement of fragments; heterogeneous fragment s i z e ; r e l a t i v e l y undisturbed contacts (stockworks) t h a t p r o g r e s s i v e l y grade i n t o completely mixed, r o c k s ; and the i n t e r s t i c e s between fragments f i l l e d w i t h hydrothermal minerals such as quartz. Subsidence b r e c c i a s are 170 formed by the " s i n k i n g of hydrothermally a f f e c t e d rocks i n response t o withdrawing of some magma" (Kents, 1 9 6 4 , p.1557) . Conclusions drawn from d e t a i l e d study of the Boss B r e c c i a s and r e l a t e d f r a c t u r e systems confirm a close genetic r e l a t i o n -s h i p w i t h the Boss Mountain Stock. I n t r u s i o n and c r y s t a l l i z a -t i o n of r h y o l i t e phorphyry magma apophyses from the Boss Mountain Stock i n i t i a t e d b r e c c i a formation at Boss Mountain. Sales ( 1954) and Perry (1961) concluded that quartz porphyry ( r h y o l i t e por-phyry) i n t r u s i o n s are the "vanguard of the m i n e r a l i z a t i o n pro-cess" a f a c t borne out i n the Boss Mountain d e p o s i t s where r h y o l i t e porphyry and r h y o l i t e magmas were intruded before, d u r i n g and.after formation of-the Phase I B r e c c i a . Most b r e c c i a pipes have formed at the. apex of a magma column (Pe r r y , I 9 6 I ; Kents, 1964), some have formed along r i n g dykes (Gates, 1 9 5 9 ) . The apex of the Boss Mountain Stock, which has been removed by e r o s i o n , does not appear to have been the locus of b r e c c i a development, m i n e r a l i z a t i o n , or a l t e r a t i o n . The locu s of such processes l i e s approximately 2000 f e e t west of the centre of the Boss Mountain Stock and r e q u i r e s s p e c i a l con-d i t i o n s f o r development. Anderson's (1936) e x p l a n a t i o n of the f r a c t u r i n g of recks by f o r c e f u l i n j e c t i o n of magma were discussed i n Chapter 3 (see Figure 3 . 1 2 ) . The a p p l i c a t i o n of h i s conclusions to an i r r e g -u l a r magma chamber might w e l l r e s u l t i n p a r t i c u l a r l y numerous 171 f r a c t u r e s l o c a l l i z e d above such an i r r e g u l a r i t y as shown i n Figure 6 . 1 , A . Subsidence of the magma column would then r e s u l t i n c o l l a p s e of the f r a c t u r e d rock, forming b r e c c i a i n that area (Figure 6 . 1 , B). Diamond d r i l l i n g e a r l y i n I 9 6 8 confirmed that the contact of the Boss Mountain Stock f l a t t e n s below the 5045 l e v e l , t e r m i n a t i n g the downward c o n t i n u a t i o n of the Boss B r e c c i a s (Figure 6 . 2 ) . The Boss Mountain Stock below the brec-c i a s i s c h i l l e d at the contact as i t i s i n the a d i t . D r i l l hole 5214 penetrated about 430 f e e t beyond the c h i l l e d contact i n t o non-chilled, quartz monzonite porphyry without v i s i b l e change i n character of the rock. The stock below the Main B r e c c i a Zone, as shown by core from diamond d r i l l hole 5216, contains l a r g e fragments of granod.iorite that have subsided, during b r e c c i a development (Figure 6 . 2 ) . D e t a i l s of the formation of the Boss B r e c c i a s are o u t l i n e d below. F l u i d emanations, e i t h e r gaseous or l i q u i d , have played an important r o l e i n b r e c c i a formation as shown by the abundance of hydrothermal minerals such as qua r t z , p y r i t e , b i o t i t e , micro-p e r t h i t e and molybdenite which accompanied, b r e c c i a formation. The importance of such emanations i n the development of f r a c t u r e s d u r i n g magmatic surges has been emphasized by s e v e r a l authors . (Gates, 1959 ; P e r ry, 1961; and. Kents, 1 9 6 4 ) . Magmatic advance f r a c t u r e d the rock above an i r r e g u l a r i t y i n the magma chamber. These f r a c t u r e s were i n i t i a l l y f i l l e d w i t h A. Magma advance and 3. Magma withdrawal and f r a c t u r i n g . foundering of f r a c t u r e d . r o o f . Figure 6.1. Formation of b r e c c i a bodies. 173 r h y o l i t e porphyry dykes. With increased pressure a l a r g e block of o v e r l y i n g rock, i n c l u d i n g the r h y o l i t e porphyry dykes, be-came i n t e n s e l y f r a c t u r e d w i t h much comminution of l a r g e r f r a g -ments. Magma of r h y o l i t e porphyry composition introduced, d u r i n g b r e c c i a formation caused r e c r y s t a l l i z a t i o n of the com-minuted matrix to such a d.egree that decrease of magmatic pres-sure ivas accompanied by l i t t l e downward movement of the, f r a g -ments. In the r e s u l t i n g Phase I B r e c c i a , fragments have not moved f a r from t h e i r place of o r i g i n although there i s abundant evidence of mixing, such as comminuted matrix and heterogeneous mixtures of fragments. A l a t e r magmatic surge produced, f r a c t u r i n g i n more confined, areas. Slow withdrawal of magmatic pressures and concomitant c o l l a p s e of the f r a c t u r e d rock accompanied by i n t r o d u c t i o n of quartz between the fragments r e s u l t e d i n b r e c c i a i n which i n -d i v i d u a l fragments seldom are i n " contact with or can be matched, w i t h adjacent fragments. The r e s u l t i n g quartz b r e c c i a s are c h a r a c t e r i z e d by angular fragments of g r a n o d i o r i t e , Phase I B r e c c i a , and dyke rocks that appear to " f l o a t " i n a matrix of quartz. These Quartz B r e c c i a bodies are c i r c u l a r , oval or l e n s o i d i n plan and form n e a r l y v e r t i c a l pipes. Collapse started, at the bottom of the f r a c t u r e d column of rock and pro-gressed upward and outward r e s u l t i n g i n a c h a o t i c mixture of fragments i n the centre of the pipes and. r e l a t i v e l y undisturbed 174 Figure 6 .2 . Plan and sect ion IIfusiratlng the relationship between the Bos s Brecc ias onri the Bos s Mountain Stock. 175 stockworks near the margins. A t h i r d upward surge of the magma column r e s u l t e d i n intense f r a c t u r i n g and comminution of the Quartz B r e c c i a i n the Main B r e c c i a Zone. The upper siu-face of t h i s Quartz B r e c c i a body was a l s o shattered but not comminuted du r i n g t h i s magmatic surge. Reduction of magmatic pressures was accompanied by c o l l a p s e of the column of f r a c t u r e d rock and by the i n t r o d u c t i o n of m a t e r i a l s which formed q u a r t z , b i o t i t e , and molybdenite i n the matrix of the b r e c c i a . This pipe of Phase I I I Breccia, i s capped by Quartz B r e c c i a . The shattered rock above the Quartz B r e c c i a , which"-was l a t e r m i n e r a l i z e d t o form the Fra c t u r e Ore Zone, d i d not c o l l a p s e completely dur i n g decrease of pressure because of the support by the un d e r l y i n g weakly f r a c t u r e d Quartz B r e c c i a . In c o n c l u s i o n , the formation of the Boss B r e c c i a s r e s u l t e d from the a c t i o n of a p u l s a t i n g magma column. An i r r e g u l a r i t y on the west side of the magma chamber r e s u l t e d i n accentuation of f r a c t u r i n g around and above the i r r e g u l a r i t y and produced, a s e r i e s of b r e c c i a bodies•of d i f f e r e n t ages and d i f f e r e n t c h a r a c t e r i s t i c s . . . Further magmatic p u l s a t i o n s produced other s t r u c t u r a l f e a t u r e s i n the same area... " SEQUENCE OF ORE FORMATION Phenomena r e l a t e d to ore formation, i n c l u d i n g igneous ac-t i v i t y , , b r e c c i a formation,- f r a c t u r e and v e i n development,. 176 a l t e r a t i o n , and m i n e r a l i z a t i o n , have been discussed i n pre-ceding s e c t i o n s . This s e c t i o n s y n t h e s i z e s a l l phenomena i n t o a c h r o n o l o g i c a l sequence as shown i n Table 6.1... Some rep-e t i t i o n of e a r l i e r conclusions i s unavoidable:. A l l phenomena i n the sequence of ore formation can be d i r e c t l y or i n d i r e c t l y c o r r e l a t e d w i t h o s c i l l a t o r y magmatic a c t i v i t y . The i n i t i a l event i n t h i s sequence was recorded by development around the Boss Mountain Stock of c o n c e n t r i c and conjugate shears new f i l l e d , w i t h garnet and hornblende. Group I quartz v e i n s , the o r i g i n of which i s unexplained, cut garnet-hornblende v e i n l e t s and are cut by a l l other f e a -o t u r e s r e l a t e d t o the sequence of ore. formation. A second magmatic surge and withdrawal was accompanied by r h y o l i t e porphyry dyke emplacement and formation of Phase I B r e c c i a . Another magmatic advance .formed f r a c t u r e s , now occupied by group 2 quartz v e i n s . With, continued magmatic advance, f o l -lowed by r e d u c t i o n of pressures accompanied by I n t r o d u c t i o n of quartz,., the Quartz B r e c c i a pipes were formed. Magmatic. surge again f r a c t u r e d the r o c k s . The e a r l i e s t f r a c t u r e s formed d u r i n g t h i s surge-were f i l l e d w i t h q u a r t z -molytdenite v e i n s . The upper'edge of the Main-Breccia Zone ( F r a c t u r e Ore Zone) was i n t e n s e l y f r a c t u r e d by t h i s upward magmatic push. Reduction of magmatic pressures r e s u l t e d i n IGNEOUS ACTIVITY BRECCIAS & ORE DEPOSITS FRAC-TURES ALTERATION 6 MINERALIZATION Crystallization of Stock Rhyolite Rhyolite Porphyry Initial Magmatic Advance High-Grade Vein Stringer Zone Phase III Breccia (Fracture Zone) Quartz Breccia Phase S Breccia 6 5 - 4 - -ea 3 2 I i 1 • 0 & e J p i " i . f r * i s r , 2 Is* N <o (S x , s s § i i 1 1 i i & Table 6.1, C h r o n o l o g i c a l chart of phenomena related, to ore formation. 178 c o l l a p s e and formation of Phase I I I B r e c c i a accompanied develop-ment of hydrothermal b i o t i t e . A f t e r Phase I I I B r e c c i a formation, f u r t h e r r e d u c t i o n i n pressure r e s u l t e d i n the development of e a r l y group 4 quartz v e i n s followed by c r y s t a l l i z a t i o n of the upper part of the Boss Mountain 'Stock. Adjustments deeper i n the stock caused develop-ment of l a t e group h quartz v e i n s , the f i r s t s t r u c t u r e s to cut the stock. This was the time of maximum potash f e l d s p a r and s e r i c i t e a l t e r a t i o n (Stage 2) as w e l l as. the time of maximum p y r i t i z a t i o n (Table 6.1). Further reductions' i n pressure from the deeper, unconsol-idated p arts of the magma chamber caused the development of f r a c t u r e s and the f i l l i n g of these f r a c t u r e s by group 5 quartz v e i n s . Molybdenite was introduced i n t o the Fracture Ore Zone at t h i s time. The f i n a l event recorded i n the sequence of ore formation was continued f r a c t u r i n g p a r a l l e l t o the High-Grade Vein accompanied by moderate to intense c h l o r i t i z a t i o n . 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Contoured equal-area projectioris (lower hemisphere) of poles to fractures in Area A; 5045 l e v e l . 191 Figure 1.2. Contoured equal-area projections(lower hemisphere) of poles.to fractures i n Area B; 5045 l e v e l . 192-Figure 1.3. Contoured equal-area projections(lower herrdsphere) of poles to fractures i n Area C; 5045 l e v e l . 193 Figure 1.4. Contoured equal-area projections (lower hemisphere) of poles to fractures i n Area D; 5045 l e v e l . 194 Figure 1.5. Contoured equal-area projections (lower hemisphere) of poles to fractures i n Area E; 5045 l e v e l . 195 1 - 5 % 6-10% >!0& Figure 1.6. Contoured equal-area projections (lower hemisphere) of poles to fractures i n Area F; 5045 l e v e l . 196 19? >5% 1-5^  198 >5% Figure 1.9. Contoured eoual-area projections (lower hemisphere) of poles to fractures i n Area C; 5045 l e v e l (continued from Figure 1.7). 199 o N O U) Boss Mountain Quartz monzonite Stock porphyry Rhyolite porphyry and rhyolite Syenodiorife Hypersthene goboro Fault Copper (defined, assumed) Lead Rock outer of Adit Joint Glacial s/r/ae Foliation 4** Road 1000 MAP I BOSS MOUNTAIN MINE AREA GEOLOGY Scale: I inch to 1000 feet Contour Interval: 200 feet A. E. Sore gar oh — 1963-66 3000feet / V V V V 7b kom kan e Vo Iconic s Boss Breccias Boss Mountain Stock Takomkane Batholith Alteration Assemblages Chlorite -Talc (Stage 4) (not shown) I^VvosJ Microp erthite - Chlorite -^ O X s X l Sericite (Stage 3) o o o o Biotite (Stage 2) P Z 7 '/A Garnet - Hornblende (Stage I) Epidote - Chlorite ( Propylitic) Zeolite - Calcite-Clay (not shown) Unrelated to f ore deposition MAP J BOSS MOUNTAIN MINE ALTERATION DISTRIBUTION 1000 Scale IOOO 2000 "ni~n: Lzr~~:j. 3000 feet ;:l I A. £. Soregaroii - 1966 

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