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The alteration and mineralization of the poplar copper-molybdenum porphyry deposit West-Central British.. 1979

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THE ALTERATION AND MINERALIZATION OF THE POPLAR COPPER-MOLYBDENUM PORPHYRY DEPOSIT WEST-CENTRAL BRITISH COLUMBIA by PETER MORRIS MESARD B.S. (Magna cum laude) F o r t Lewis C o l l e g e A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF - MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department o f G e o l o g i c a l Sciences We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA December 197 9 (c) Peter M o r r i s Mesard, 1979 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. I further agree that permission for extensive copying of th is thes is for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of this thes i s for f inanc ia l gain sha l l not be allowed without my written permission. Depa rtment The Univers i ty of B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 V i e w o f t h e s t u d y a r e a t a k e n f r o m t h e w e s t . T a g e t o c h l a i n L a k e i s s e e n on t h e r i g h t , a n d t h e a c c e s s r o a d t o t h e p r o p e r t y i s o n t h e l e f t . The c e n t e r o f t h e d e p o s i t i s s i t u a t e d u n d e r t h e s t a n d o f f i r t r e e s i n t h e f o r g r o u n d . ABSTRACT The Poplar copper-molybdenum porphyry d e p o s i t , l o c a t e d 270 km west of P r i n c e George, i s centered i n a l a t e Upper Cretaceous d i f f e r e n t i a t e d c a l c - a l k a l i n e s t o c k , which i n t r u d e d Lower and Upper Cretaceous sedimentary rocks . The stock i s capped by l a t e Upper Cretaceous v o l c a n i c flow r o c k s . The lower Cretaceous Skeena Group c o n s i s t s of i n t e r m e d i a t e t u f f , s i l t s t o n e , and interbedded sandstone, which s t e e p l y d i p to the south. T h i s u n i t i s unconformably o v e r l a i n by a moderately s o r t e d p o l y l i t h i c pebble conglomerate belonging t o the Upper Cretaceous Kasalka Group. The P o p l a r Stock, which hosts m i n e r a l i z a t i o n , i n c l u d e s a border phase of hornblende quartz monzodiorite porphyry which grades i n to a c e n t r a l b i o t i t e quartz monzonite porphyry. The stock i s i n t r u d e d by s e v e r a l post-ore dyke u n i t s , which i n c l u d e p o r p h y r i t i c d a c i t e , p o r p h y r i t i c r h y o l i t e , f e l s i t e , and a n d e s i t e . Ootsa Lake p o r p h y r i t i c v o l c a n i c flow r o c k s o v e r l y the d e p o s i t , and are d a c i t e i n composition. Pre-ore, and post-ore rock u n i t s have been K-Ar dated, and are w i t h i n a n a l y t i c a l e r r o r of each o t h e r , having a mean age of 74.8 ± 2 . 6 Ma. The dep o s i t i s covered e x t e n s i v e l y with g l a c i a l t i l l and a l l u v i a l sediments. Therefore the m a j o r i t y of g e o l o g i c i n f o r m a t i o n was obtained from l o g g i n g the d r i l l core from 34 diamond d r i l l h o l e s , twelve of which were logged i n d e t a i l using a computer compatible l o g g i n g format. I n f o r m a t i o n logged i n t h i s manner was used i n s t a t i s t i c a l s t u d i e s , and f o r producing computer generated graphic l o g s and p l o t s of v a r i o u s g e o l o g i c parameters, along two c r o s s - s e c t i o n s through the d e p o s i t . A l t e r a t i o n zoning at the Poplar porphyry c o n s i s t s of a 600 m by 500 m p o t a s s i c a l t e r a t i o n annulus which surrounds a 300 m by 150 m a r g i l l i c a l t e r a t i o n core. These are enclosed by 750 m wide p h y l l i c a l t e r a t i o n zone, which i s i t s e l f bordered by a low i n t e n s i t y p r o p y l i t i c a l t e r a t i o n zone. P h y l l i c a l t e r a t i o n i s de f i n e d by the occurence of s e r i c i t e , and i s the most abundant type of a l t e r a t i o n p r e s e n t . P o t a s s i c a l t e r a t i o n , r e c o g n i z e d by the occurence cf secondary K - f e l d s p a r and/or secondary b i o t i t e , i s most c l o s e l y a s s o c i a t e d with c h a l c o p y r i t e and molybdenite. At l e a s t two episodes of a l t e r a t i o n are r e c o g n i z e d at the Poplar porphyry. The f i r s t was contemporaneous with m i n e r a l i z a t i o n , f o l l o w i n g 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 the Poplar Stock. T h i s episode c o n s i s t e d of p o t a s s i c a l t e r a t i o n i n the ce n t e r of the d e p o s i t , which surrounded a 'low grade 1 core, and graded out t o p h y l l i c and p r o p y l i t i c a l t e r a t i o n f a c i e s at the p e r i p h e r y . The second a l t e r a t i o n event took place a f t e r the i n t r u s i o n of the post-ore dykes and c o n s i s t e d mainly of h y d r o l y t i c a l t e r a t i o n of p r e - e x i s t i n g a l t e r a t i o n zones which were adjacent to more permeable c e n t e r s , such as f a u l t s , c o n t a c t s , and h i g h l y j o i n t e d a r e a s . T h i s a l t e r a t i o n event i s r e s p o n s i b l e f o r the anomalous c e n t r a l a r g i l l i c zone, and the a l t e r a t i o n of dykes, i n a d d i t i o n t o probably i n t e n s i f y i n g and widening the p h y l l i c a l t e r a t i o n halo surrounding the d e p o s i t . C h a l c o p y r i t e and molybdenite were de p o s i t e d i n the p o t a s s i c zone at approximately 375° C and l e s s than 250 bars, with r e l a t i v e l y low oxygen, and r e l a t i v e l y high s u l f e r , a c t i v i t i e s and moderate pH. As the p o t a s s i c a l t e r a t i o n zone was invaded by more a c i d i c s o l u t i o n s f e l d s p a r s were a l t e r e d s e r i c i t e and c l a y , and c h a l c o p y r i t e was destroyed to form p y r i t e and hematite. Copper was removed from the system. S t a t i s t i c a l s t u d i e s i n c l u d e u n i v a r i a n t one-way and two-way c o r r e l a t i o n m a t r i c e s , and m u l t i v a r i a n t r e g r e s s i o n a n a l y s i s . S t a t i s t i c a l c o r r e l a t i o n s g e n e r a l l y support e m p i r i c a l c o r r e l a t i o n s made i n the f i e l d . These i n c l u d e p o s i t i v e c o r r e l a t i o n s between var i o u s p o t a s s i c a l t e r a t i o n f a c i e s m i n e r a l s , and these minerals and c h a l c o p y r i t e and molybdenite. M u l t i v a r i a n t r e g r e s s i o n a n a l y s i s was used to determine which a l t e r a t i o n minerals were best s u i t e d f o r i n d i c a t i n g c h a l c o p y r i t e and molybdenite. These minerals are q u a r t z , b i o t i t e , magnetite, s e r i c i t e , K - f e l d s p a r , and p y r i t e . Large e r r o r l i m i t s and poor c o r r e l a t i o n s t a t i s t i c s i n the r e s u l t s from these s t u d i e s are a t t r i b u t e d to d e v i a t i o n s from normal d i s t r i b u t i o n s f o r a l l m i n e r a l s . A p o s s i b l e cause of t h i s may have been the m u l t i s t a g e a l t e r a t i o n events t h a t the d e p o s i t has undergone V ACKNOWLEDGMENTS There are numerous i n d i v i d u a l s who o f f e r e d support, d i s c u s s i o n , and advice during the course of t h i s study. Dr. C. I . Godwin f i r s t suggested the study, f i n a n c i a l l y supported i t , and was a source of a d v i c e , i d e a s , and enthusiasm, from the beginning. Dr. A. S i n c l a i r v i s i t e d me i n the f i e l d , and c l e a r e d up many misconceptions d e a l i n g with s t a t i s t i c s . Dr. 1 . Brown was very h e l p f u l i n d i s c u s s i n g concepts and i d e a s , and provoking much thought about hydrothermal geochemistry. A grant from the B r i t i s h Columbia M i n i s t r y o f Mines supported many of the f i e l d expenses. Dr. N. C. C a r t e r , i n p a r t i c u l a r was very helpful;. B. Bowen, of Utah Mines L t d . , p a r t i c i p a t e d i n a number of d i s c u s s i o n s and pro v i d e d company i n f o r m a t i o n d e a l i n g with the d e p o s i t . Mr. E. Montgomery helped i n l o g i s t i c s and i n o f f e r i n g t e c h n i c a l advice about draughting and photography. I owe a great d e a l t o Ms. Linda Mah who typed both the rough d r a f t , and d i d a n i c e job of t y p i n g the f i n a l copy i n t o the computer. Mr. and Mrs. M i l e s S h e l f o r d , of F r a n c o i s Lake, B r i t i s h Columbia, were most generous, and were sources of encouragement during the f i e l d p o r t i o n of t h i s study. F i n a l l y , Ms. R. Wegner was very h e l p f u l i n preparing the f i g u r e s , p l a t e s , and c a p t i o n s f o r the f i n a l d r a f t , and f o r demonstrating r a r e good humour during the f i n a l s tages of the w r i t i n g o f t h i s t h e s i s . v i TABLE OF CONTENTS FRONTISPIECE - i i ABSTRACT . . . i i i ACKNOWLEDGMENTS , . . . . V TABLE OF CONTENTS . . . v i LIST OF FIGURES X LIST OF PLATES x i i LIST OF TAELES xiv LIST OF MAPS XV CHAPTER I : INTRODUCTION 1 1.1 L o c a t i o n 1 1.2 Access 2 1.3 P h y s i o g r a p h i c S e t t i n g 3 1.4 H i s t o r y And Development ............................ 5 1.5 Scope Of Study .... , 7 CHAPTER I I REGIONAL GEOLOGIC SETTING 9 2.1 R e g i o n a l T e c t o n i c S e t t i n g .......................... 9 2.2 Re g i o n a l Geology ......................, 11 v i i CHAPTER I I I GEOLOGY OI THE POPLAR PORPHYRY DEPOSIT ........ 15 3.1 General Statement .................................. 15 3.2 P o p l a r l o g 16 3.3 G e o l o g i c Maps And C r o s s - s e c t i o n s ................... 19 . 3. a Rock U n i t s 24 3.4.1 Overview 24 3.4.2 P r e - I n t r u s i v e Bocks ........................... 25 3.4.2.1 Skeena Group . 25 3.4.2.2 Kasalka Group 27 3.4.2.3 C o r r e l a t i o n Of P r e - I n t r u s i v e Rock Un i t s .. 29 3.4.3 M i n e r a l i z e d I n t r u s i v e Rocks ..................... 30 3.4.3.1 General Statement ........................ 30 3.4.3.2 Hornblende Quartz Monzodiorite ........... 31 3.4.3.3 B i o t i t e Quartz Monzonite ................. 34 3.4.4 Post-Ore Dykes 39 3.4.4.1 General Statement 39 3.4.4.2 P o r p h y r i t i c D a c i t e Dykes 39 3 .4 .4 .3 F e l s i t e Dykes 42 3.4.4.4 P o r p h y r i t i c R h y o l i t e Dykes 42 3.4.4.5 Andesite Dykes .. 44 3.4.5 E x t r u s i v e Rocks 44 3.4.5.1 Ootsa Lake Group 44 3.4.5.2 C o r r e l a t i o n Of E x t r u s i v e Rocks 47 3.5 K-Ar Age Determinations ............................ 47 3.6 Comparison Of The Poplar Porphyry To Other Porphyry Deposits Of West-Central B r i t i s h Columbia 48 3.7 S t r u c t u r e ........................................... 51 CHAPTER IV MINERALIZATION AND ALTERATION OF THE POPLAR v i i i PORPHYRY DEPOSIT 54 4.1 General Statement .................................. 54 4.2 D i s t r i b u t i o n Of 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 Zones At The P o p l a r Porphyry 58 4.3 S u l f i d e Mineralogy ................................. 64 4.3.1 C h a l c o p y r i t e 64 4.3.2 Molybdenite 67 4.3.3 B o r n i t e .. 70 4.3.4 C o v e l l i t e 71 4.3.5 T e t r a h e d r i t e 71 4.4 A l t e r a t i o n Mineralogy ............................... 72 4.4.1 P o t a s s i c A l t e r a t i o n ........................... 72 4.4.2 P h y l l i c A l t e r a t i o n 84 4.4.3 A r g i l l i c A l t e r a t i o n 94 4.4.4 P r o p y l i t i c A l t e r a t i o n 97 4.4.5 Secondary A l t e r a t i o n .......................... 99 4.5 Chemical Aspects Of 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 Zoning 101 4.5.1 General Statement 101 4.5.2 D i s c u s s i o n ..................................... 101 4.6 Environment Of Ore D e p o s i t i o n ...................... 112 4.7 E v o l u t i o n Of 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 Zoning At The Po p l a r Porphyry ...................... . . 1 1 5 CHAPTER V GEOSTATISTICS OF THE POPLAR PORPHYRY 117 5.1 General Statment 117 5.2 C o r r e l a t i o n s Eetween V a r i a b l e s ..................... 119 5.2.1 Two-Way C o r r e l a t i o n Matrix 119 5.2-2 One-way C o r r e l a t i o n M a t r i x 126 i x 5.3 M u l t i v a r i a n t A n a l y s i s 128 5.3.1 General Statement 128 5.3.2 M u l t i v a r i a n t Equation For C h a l c o p y r i t e And Molybdenite 130 5.3.3 E s t i m a t i o n Of E r r o r In M u l t i v a r i a n t Equations 132 5.4 Summary Of G e o s t a t i s t i c s 134 CHAPTER VI CONCLUSIONS 136 BIBLIOGRAPHY - . 139 APPENDIX A A n a l y t i c a l Data 152 APPENDIX B P o p l a r l o g 155 APPENDIX C Computer Programs Used In T h i s Study ............174 APPENDIX D Thin S e c t i o n D e s c r i p t i o n s .178 X LIST OF FIGURES Fi g u r e 1.1 L o c a t i o n Of The Poplar Porphyry ................ 2 Fi g u r e 1.2 Major P h y s i o g r a p h i c S u b d i v i s i o n s .......4 F i g u r e 2.1 Regional T e c t o n i c S e t t i n g ......................10 Fi g u r e 3.1 T y p i c a l Zonations In Porphyry Deposits .........17 Fi g u r e 3.2 Geology Of The C e n t r a l P o r t i o n Of The Study Area ,20 F i g u r e 3.3 Computer Generated C r o s s - s e c t i o n Of Geology Along Line A-A ......................................... 22 Fi g u r e 3.4 Computer Generated C r o s s - s e c t i c n Of Geology Along L i n e B-B* .23 Fi g u r e 3.5 Supplmentary C r o s s - s e c t i o n Along C-C*..Back Pocket Fig u r e 3.6 Supplmentary C r o s s - s e c t i o n Along D-D*..Back Pocket Figure 3.7 Supplmentary C r o s s - s e c t i o n Along E-E*..Back Pocket F i g u r e 3.8 Supplmentary C r o s s - s e c t i o n Along F-F (..Back Pocket F i g u r e 3.9 Ternary Diagram Showing The Compositional F i e l d s Of The Nanika And B u l k l e y I n t r u s i o n s ................... 50 Fi g u r e 3.10 A e r i a l Phcto Lineaments In The Study Area .....52 Fi g u r e 4.1 Computer Generated C r o s s - s e c t i c n Showing 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 Along Line A-A1 ........... 60 Fi g u r e 4.2 Computer Generated C r o s s - s e c t i o n Showing 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 Along Line B-B* ........... 61 Fi g u r e 4.3 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 Of The C e n t r a l P o r t i o n Of The Study Area ........................62 F i g u r e 4.4 Bar Graph For C h a l c o p y r i t e ..................... 65 Fi g u r e 4.5 Bar Graph For Molybdenite ......................68 x i F i g u r e 4.6 Graphic Log Of P o t a s s i c A l t e r a t i o n In D r i l l Core 74 F i g u r e 4.7 Bar Graph For K - f e l d s p a r ....................... 78 Figu r e 4.8 Bar Graph For B i o t i t e 80 Fi g u r e 4.9 Graphic Log Of P h y l l i c A l t e r a t i o n In D r i l l Core 85 F i g u r e 4.10 Bar Graph For S e r i c i t e ........................ 87 F i g u r e 4.11 Bar Graph For Quartz .......91 F i g u r e 4.12 Bar Graph For P y r i t e .......................... 93 F i g u r e 4.13 Bar Graph For Clay «... ....96 F i g u r e 4.14 U n i v a r i a n t S t a b i l i t y R e l a t i o n s h i p s In The System A1 Z0 3 - (K 20-Na 20)-Si0 2-H 20 104 Fi g u r e 4.15 Schematic Diagram Of F l u i d P a t h l i n e s Adjacent To A C o o l i n g I n t r u s i o n .106 F i g u r e 4.16 Log A(S 2 ) - v s - L o g A(0 2) Diagram For The System Cu-Fe-0 -S .......................113 Figure 5.1 P o s i t i v e C o r r e l a t i o n C l u s t e r Based On A l t e r a t i o n F a c i e s 123 Figu r e 5.2 Ranked I n t e n s i t y Of C h a l c o p y r i t e Verse Log Percent C h a l c o p y r i t e ................................... 134 Figu r e B.1 P o p l a r l o g Coding Form Used In The F i e l d ........157 Figu r e B.2 Model Of A l t e r a t i o n F a c i e s In Porphyry Deposits 170 Figu r e B.3 Model Of Mi n e r a l F a c i e s In Porphyry Deposits ...173 LIST OF PLATES P l a t e 3.1 Skeena Group Rocks .............................. 26 P l a t e 3.2 Kasalka Group Conglomerate ...28 P l a t e 3.3 Hornblende Quartz Monzodiorite .33 P l a t e 3.4 B i o t i t e Quartz Mcnzonite ........................36 P l a t e 3.5 I n t r u s i v e B r e c c i a ............................... 38 P l a t e 3.6 P o r p h y r i t i c Dacite Dykes ........................ 40 P l a t e 3.7 P o r p h y r i t i c R h y o l i t e ............................ 43 P l a t e 3.8 Ootsa Lake Group V o l c a n i c Flow Rocks 46 P l a t e 4.1 Photomicrograph Of C h a l c o p y r i t e And Magnetite ...67 P l a t e 4.2 Photomicrograph Of Molybdenite Selvage ........... 70 P l a t e 4.3 Photomicrograph Of Intergrown B o r n i t e And C h a l c o p y r i t e ...........................................71 P l a t e 4.4 Example Of P o t a s s i c A l t e r a t i o n .................. 73 P l a t e 4.5 Example Of Potassium F e l d s p a r Envelopes .........75 P l a t e 4.6 K - f e l d s p a r A l t e r a t i o n Of P l a g i o c l a s e Phenocrysts ,76 P l a t e 4.7 Secondary B i o t i t e A l t e r a t i o n .79 Pla t e 4.8 Photomicrograph Of Secondary B i o t i t e . R e p l a c i n g Primary B i o t i t e ...81 P l a t e 4.9 Phototmicrograph Of C o e x i s t i n g C h a l c o p y r i t e And Magnetite 82 P l a t e 4.10 S e r i c i t e Envelopes Around V e i n l e t s And F r a c t u r e s ,. ........................................ .............84 P l a t e 4.11 Examples Of P h y l l i c A l t e r a t i o n ...88 P l a t e 4.12 Photomicrograph Showing S e l e c t i v e A l t e r a t i o n Of Zoned P l a g i o c l a s e 89 x i i i P l a t e 4.13 Example Of A r g i l l i c A l t e r a t i o n .,.97 P l a t e 4.14 Photomicrograph Of P r o p y l i t i c A l t e r a t i o n . . . . . . . 9 9 x i v LIST OF TABLES Table 2.1 Major V o l c a n i c And Sedimentary Bock U n i t s Of West-Central B r i t i s h Columbia . . . . . . . . . . . . . . . . a . . . . . . . . . 12 Table 2.2 Major P l u t o n i c Bock U n i t s Of West-Central B r i t i s h Columbia ........................... ... .................. 13 Table 4.1 A l t e r a t i o n And Ore M i n e r a l s Becorded At The Poplar Porphyry 56 Table 4.2 A l t e r a t i o n F a c i e s At The Poplar Porphyry ........58 Table 5.1 F i f t e e n Hydrothermal Mi n e r a l s Used In S t a t i s t i c a l A n a l y s i s ....120 Table 5.2 Two-Way C o r r e l a t i o n Matrix .................122 Table 5.3 M i n e r a l C o r r e l a t i o n s Based On A l t e r a t i o n F a c i e s .125 Table 5.4 One-Way C o r r e l a t i o n Matrix ...127 Table B.1 Comment Codes Used On P o p l a r l o g .................158 T a i l e B.2 F i r s t Type M o d i f i e r Used With P o p l a r l o g .........160 Table B.3 Second Type M o d i f i e r Used With P o p l a r l o g 162 Table B.4 S i l i c a t e Carbonate And S u l f a t e A l t e r a t i o n M i n e r a l s ..................166 Table B.5 Mode And Degree Of 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 167 Table B.6 One L e t t e r Codes For Estimated Volume Percent Of M i n e r a l s ,..................168 Table B.7 C h e c k l i s t Of A l t e r a t i o n M i n e r a l Abundances ...... 169 Table B.8 S u l f i d e And Oxide M i n e r a l s 171 Table B.9 C h e c k l i s t Of S u l f i d e And Oxide Abundances ....... 172 XV MAPS MAP A Back Pocket MAP B .......Back Pocket 1 CHAPTER I INTRODUCTION 1.1 L o c a t i o n The Poplar copper-molybdenum porphyry d e p o s i t , centered near 54<>01«N, 126°58» W (N.T.S. 93L/3E; 93E/15W), i s l o c a t e d i n w e s t - c e n t r a l B r i t i s h Columbia approximately 270 km west of Pr i n c e George and 50 km south-southwest of Houston, i n the Omineca Mining D i v i s i o n ( F i g . 1.1). The d e p o s i t i s s i t u a t e d near the ce n t r e of the no r t h e a s t shore of T a g e t o c h l a i n ( l o c a l name Poplar) Lake. 1 .2 Access Access t o the Poplar porphyry by motor v e h i c l e i s made from Highway 16, one km west cf Houston, v i a the Morice River, Owen Lake, and Tahtsa Reach f o r e s t access roads t o the southeast end of T a g e t o c h l a i n Lake. A po o r l y developed d i r t road p a r a l l e l s the n o r t h - e a s t shore c f the l a k e and termin a t e s at a core shack and abandoned d r i l l camp on the p r o p e r t y . The t o t a l d i s t a n c e from Houston i s 80 km. Access t o the dep o s i t can a l s o be made by h e l i c o p t e r from a h e l i c o p t e r base i n Smithers o r by f l o a t plane which can l a n d on T a g e t o c h l a i n Lake, adjacent t o the property. 2 F i g u r e 1.1: L o c a t i o n o f t h e P o p l a r p o r p h y r y d e p o s i t ; w e s t - c e n t r a l B r i t i s h C o l u m b i a . 3 1.3 P h y s i o g r a p h i c S e t t i n g The study area l i e s w i t h i n the I n t e r i o r P l a t e a u , approximately 20 km east of i t s boundary with the Coast Mountains. Major ph y s i o g r a p h i c s u b d i v i s i o n s o f w e s t - c e n t r a l B.C. are shown i n F i g u r e 1.2 ( a f t e r C a r t e r , 1974; and H o l l a n d , 1S78). The d e p o s i t i s l o c a t e d i n the w e s t - c e n t r a l p o r t i o n of the Nechako P l a t e a u , an area of low r e l i e f t h a t i s l a r g e l y u n d i s s e c t e d by e r o s i o n (Holland, 1964}; e l e v a t i o n g e n e r a l l y ranges frcm 1225 m to 1530 m. T h i s p o r t i o n of the p l a t e a u forms a r e e n t r a n t i n t o the Hazelton Mountains and i s bounded to the north and west by the Bulkley Ranges, and t o the south by the l a h t s a Ranges. Intense g l a c i a t i o n i n the area has r e s u l t e d i n the development of many s u b p a r a l l e l , n o r t h e a s t t r e n d i n g l i n e a r l a k e s (e.g. Morice, Nanika, and W h i t e s a i l Lakes). T h i s o r i e n t a t i o n i n d i c a t e s a n o r t h e a s t t c eastward movement of advancing i c e that o r i g i n a t e d from higher e l e v a t i o n s i n the Coast Range t o the west ( D u f f e l l , 1959). T a g e t o c h l a i n Lake, however, tren d s almost normal t o t h i s d i r e c t i o n and evidence presented i n S e c t i o n 3.7 suggests a s t r u c t u r a l l y c o n t r o l l e d o r i g i n f o r the lake and adjacent v a l l e y . D u f f e l l (1959) e s t i m a t e s t h a t the g l a c i a l i c e had a minimum t h i c k n e s s cf 1345 m because a l l peaks i n the area were covered ty i c e . R 10 to 25 km wide physiographic " t r a n s i t i o n zone" l i e s F i g u r e 1.2: M a j o r p h y s i o g r a p h i c s u b d i v i s i o n s o f w e s t - c e n t r a l B r i t i s h C o l u m b i a ( a f t e r C a r t e r , 1974; a n d H o l l a n d , 1978). 5 b e t w e e n t h e N e c h a k o F l a t e a u a n d t h e C o a s t R a n g e s ( D u f f e l l , 1 9 5 9 ) , a n d i s c h a r a c t e r i z e d b y s m a l l m o u n t a i n r a n g e s ( e . g . S i t o l a , T a h t s a , a n d flhitesail R a n g e s ) t r e n d i n g n o r t h e a s t t o e a s t , n o r m a l t o t h e r e g i o n a l n o r t h w e s t t r e n d o f t h e C a n a d i a n C o r d i l l e r a . L o c a l l y , t h e d e p o s i t i s s i t u a t e d i n a n o r t h w e s t t r e n d i n g v a l l e y w h i c h p a r a l l e l s T a g e t o c h l a i n L a k e . T h e a r e a i s c h a r a c t e r i z e d b y m o d e r a t e l y r o l l i n g t o p o g r a p h y w h i c h r a n g e s i n e l e v a t i o n f r o m 8 4 0 m a t l a k e l e v e l t o 1 1 1 0 m a t t h e w e s t e r n p o r t i o n o f t h e s t u d y a r e a , a n d r i s e s t o 1 6 2 6 m o n P o p l a r M o u n t a i n , 6 . 5 km t o t h e n o r t h e a s t . Two s m a l l s t r e a m s , C a n y o n C r e e k a n d E a s t C r e e k , c r e s s t h e a r e a a n d f l o w i n t o T a g e t o c h l a i n L a k e . L o c a l e r o s i o n a l r e l i e f v a r i e s f r o m l e s s t h a n 1 m t o o v e r 10 m, l o c a l l y f o r m i n g s t e e p c l i f f s . V e g e t a t i o n i n c l u d e s g r a s s e s , w i l d f l o w e r s , a n d s t a n d s o f a s p e n , s p r u c e , a n d p i n e t r e e s . O p e n m e a d o w s c o m p r i s e r o u g h l y 60 p e r c e n t o f t h e l a n d a r e a , a n d a r e u t i l i z e d b y l o c a l r a n c h e r s f o r c a t t l e g r a z i n g . A v e r a g e a n n u a l p r e c i p i t a t i o n a v e r a g e s 7 5 t o 100 c m , b u t t h i s s t u d y w a s c a r r i e d o u t d u r i n g 1 9 7 8 , a n u n u s u a l l y d r y a n d warm f i e l d s e a s o n m a r k e d b y o n l y e i g h t d a y s o f i n c l e m e n t w e a t h e r . 1.4 H i s t o r y a n d D e v e l o p , p e n t E v i d e n c e o f s t a k i n g a n d l i m i t e d a s s e s s m e n t w o r k p r i o r t o 1 9 7 0 was d i s c o v e r e d i n C a n y c n C r e e k d u r i n g t h e c o u r s e o f f i e l d m a p p i n g . H o w e v e r , n o t h i n g was f o u n d t o i d e n t i f y t h e f o r m e r d e v e l o p e r s . 6 The most recent h i s t o r y and development o f the p r o p e r t y began i n the f a l l of 1970 with the i n i t i a l s t a k i n g of s i x claims by F. Onuchi and C. C r i t c h l o w ( p r o s p e c t o r s under c o n t r a c t t o E l Paso Mining and M i l l i n g Co. L t d . ) , f o l l o w i n g the d i s c o v e r y of geochemical anomalies i n s i l t and s o i l samples. During the summer of 1971 a d d i t i o n a l s o i l geochemical surveys l e d t o the stak i n g of 36 a d d i t i o n a l c l a i m s , which were recorded by F. Onuchi and M. Callaghan ( C r i t c h l o w , pers. comm., 1978). That f a l l H. Jones of E l Paso Mining and M i l l i n g Co. L t d . commenced l i m i t e d g e o l o g i c mapping and extensive s o i l geochemical surveys (Jones, 1972). Copper and s i l v e r anomalies d i s c o v e r e d by these surveys were i n v e s t i g a t e d i n the s p r i n g f o r 1972 by the excavation of four trenches. Based on the d i s c o u r a g i n g r e s u l t s from these i n v e s t i g a t i o n s E l Paso Mining and M i l l i n g Co. Ltd . t r a n s f e r r e d a l l claims on the property t o the o r i g i n a l p r o s p e c t o r s i n March of 1973 (Jones, 1972; and C r i t c h l o w , pers. comm., 1$78). C r i t c h l o w brought A. Schmidt of Hudson Bay O i l and Gas Co. L t d . i n t c examine the area d u r i n g the summer of 1973 and a d d i t i o n a l c l a i m s were staked t h a t f a l l ( C r i t c h l o w , pers. comm., 1S78). Most of the claims were restaked by C r i t c h l o w during June of 1974, a f t e r many had lap s e d . In August he d r i l l e d a h o l e near the south end of Canyon Creek and di s c o v e r e d "encouraging m i n e r a l i z a t i o n " (Critchlow, pers. comm., 1978). T. Sc h r o e t e r , Resident G e o l o g i s t at Smithers f o r the B r i t i s h Columbia M i n i s t r y of Mines, i n v e s t i g a t e d the f i n d and f o l l o w i n g h i s suggestion the 7 property was o f f e r e d to s e v e r a l mining companies. The p r o p e r t y was optioned by Utah Mines L t d . on October 2, 1974. E x p l o r a t i o n and development of the property commenced i n the f a l l of 1^74; work i n c l u d e d induced p o l a r i z a t i o n and ground- magnetic g e o p h y s i c a l surveys and the d r i l l i n g of fo u r BQ s i z e d diamond d r i l l h o l e s , t o t a l l i n g 937 m (Schmidt, 1975; W i t h e r l y , 1S75) . Between 1S75 and 1977 a d d i t i o n a l e x p l o r a t i o n and development i n c l u d e d geologic mapping, s o i l and s i l t geochemical surveys, g e o p h y s i c a l surveys, and the d r i l l i n g of 36 NQ s i z e d diamond d r i l l h o l e s , t o t a l l i n g 7344 m i n depth. 1.5 Scope of Study Nine weeks were spent on the pr o p e r t y , d u r i n g the course of t h i s study, examining and irapping the s u r f i c i a l geology and lo g g i n g the subsurface geology from d r i l l core from 34 diamond d r i l l h o l e s . P a r t i c u l a r a t t e n t i o n was paid to l o g g i n g the core along two c r o s s - s e c t i o n s through the deposit (Map ft : S e c t i o n s A-A' and B- B'). D e t a i l e d l o g g i n g i n v o l v e d the use of a computer compatible data format, which was adopted to a i d i n s t a t i s t i c a l s t u d i e s 8 i n v o l v i n g a l a r g e number of g e o l o g i c v a r i a b l e s and to f a c i l i t a t e computer p l o t t i n g of d r i l l hole i n f o r m a t i o n . Wore d e t a i l e d d e s c r i p t i o n s cf t h i s l o g g i n g format are given i n Chapter I I I and Appendix E. 9 CHAPTER II REGIONAI GEOLOGTC SETTING 2 . 1 J R i o j i a l _ T _ § c t o n i c S e t t l n c j R e g i o n a l t e c t o n i c e l e m e n t s o f w e s t - c e n t r a l B r i t i s h C o l u m b i a a r e s h e w n i n F i g u r e 2 . 1 ; i n c l u d e d a r e t h e C o a s t G e a n t i c l i n e , t h e H a z e l t o n T r o u g h , t h e N e c h a k o T r o u g h a n d B o w s e r B a s i n , t h e S k e e n a A r c h a n d t i e P i n c h i G e a n t i c l i n e . T h e P o p l a r p o r p h y r y d e p o s i t i s s i t u a t e d o n t h e s o u t h e r n f l a n k o f t h e S k e e n a A r c h , w h i c h w a s a n o r t h e a s t t o e a s t e r l y t r e n d i n g p o s i t i v e f e a t u r e f r c m l o w e r M i d d l e J u r a s s i c t o U p p e r J u r a s s i c ( T i p p e r a n d R i c h a r d s , 1 9 7 6 ) . W h i t e ( 1 9 5 9 ) f i r s t r e c o g n i z e d t h e S k e e n a A r c h a s a s a l i e n t i n t h e n o r t h w e s t t r e n d i n g f o l d s o f t h e C o r d i l l e r a . T h e c r e s t o f t h e a r c h i s m a r k e d b y a c o n c e n t r a t i o n o f s m a l l s t o c k s a n d b a t h o l i t h s ( C a r t e r , 1 9 7 4 ) . V a r i o u s o r i g i n s f o r t h e S k e e n a A r c h h a v e b e e n p r o p o s e d , i n c l u d i n g : ( 1 ) a r e a c t i v a t e d P r e c a m b r i a n b a s e m e n t f e a t u r e ( C a r t e r , 1 9 7 4 ) ; ( 2 ) a J u r a s s i c v o l c a n i c a r c , p o s s i b l y c o n t r o l l e d b y b a s e m e n t f e a t u r e s ( E i s b a c h e r , 1 9 7 7 ) a n d ; ( 3 ) a n i n t e r a r c h i g h f o r m e d s y n c h r o n o u s l y w i t h a n d e s i t i c v c l c a n i s m ( M o n g e r , e t a l . , 1 9 7 2 ) . T h e S k e e n a A r c h s e p a r a t e s t h e B o w s e r E a s i n t o t h e n o r t h , f r c m t h e N e c h a k o T r o u g h t o t h e s o u t h . T h e s e b a s i n s a r e i n t e r p r e t e d a s i n t r a - c o n t i n e n t a l s u c c e s s o r b a s i n s f i l l e d w i t h F i g u r e 2.1: R e g i o n a l t e c t o n i c s e t t i n g o f t h e P o p l a r p o r p h y r y i n w e s t - c e n t r a l B r i t i s h C o l u m b i a . 11 M i d d l e t o O p p e r J u r a s s i c f l y s c h a n d d e l t a i c d e p o s i t s d e r i v e d f r o m t w o p a l e o - t o p o g r a p h i c h i g h s ; t h e P i n c h i G e a n t i c l i n e a n d t h e S k e e n a ftrch ( E i s t a c h e r , 1 9 7 7 ; C a r t e r , 1 9 7 4 ; a n d T i p p e r a n d R i c h a r d s , 1 9 7 6 ) . 2 . 2 R e g i o n a l . G e c l o g y T h e P o p l a r p o r p h y r y d e p o s i t i s s i t u a t e d w i t h i n t h e I n t e r m o n t a n e B e l t i n w e s t - c e n t r a l E r i t i s h C o l u m b i a , a p p r o x i m a t e l y 30 km e a s t o f t h e b o u n d a r y w i t h t h e C o a s t C r y s t a l l i n e C o m p l e x . S t r a t i f i e d v o l c a n i c a n d s e d i m e n t a r y r o c k s , r a n g i n g i n a g e f r o m l o w e r M e s o z o i c t o P a l e o c e n e ( T i p p e r a n d R i c h a r d s , 1 9 7 6 b ) u n d e r l i e t h e I n t e r m o n t a n e B e l t o f w e s t - c e n t r a l E r i t i s h C c l u m t i a . M a j o r g e o l o g i c f o r m a t i o n s o f t h i s r e g i o n a r e c o m p i l e d a n d s u m m a r i z e d i n T a b l e s 2.1 a n d 2 . 2 ( a f t e r D u f f e l l , 1 9 5 9 ; C a r t e r 1 9 7 4 ; M a c l n t y r e , 1 9 7 6 ; T i p p e r a n d R i c h a r d s , 1 9 7 6 b ; a n d flocdsworth, 1 9 7 9 ) . T h e C o a s t C r y s t a l l i n e C o m p l e x o f w e s t - c e n t r a l B r i t i s h C o l u m b i a i s u n d e r l a i n b y a c e n t r a l g n e i s s c o m p l e x c o m p o s e d o f b a n d e d a m p h i b c l i t e g n e i s s e s , p l u t o n i c r o c k s a n d m i n o r s c h i s t s , a n d s k a r n a n d m a r b l e ( W o o d s w o r t h , 1 9 7 9 ) . T h i s c o m p l e x i s i n p a r t d e r i v e d f r o m m i g t r a t i z a t i o n o f t h e P a l e o z o i c G a m s b y G r o u p , w h i c h c o n s i s t s o f f e l s i c a n d m a f i c t u f f , e p i c l a s t i c v o l c a n i c r o c k s , a n d l i m e s t o n e a n d a s s o c i a t e d s k a r n . T h e r o c k s o f t h i s g r o u p h a v e a l l b e e n m e t a m o r p h o s e d t o a t l e a s t t h e g r e e n s c h i s t f a c i e s ( W o o d s w o r t h , 1 9 7 9 ) . Many s a t e l l i t e s o f t h e C o a s t TABLE 2.1 VOLCANIC AND SEDIMENTARY STRATIGRAPHY OF WEST-CENTRAL BRITISH COLUMBIA Epoch Oligocene or l a t e r L a t e s t Upper Cretaceous to Oligocene Upper Cretaceous to Paleogene E a r l y Upper Cretaceous Lower Cretaceous Lower to Middle J u r a s s i c Group Endako unconformity Ootsa Lake Sustut Formation R e f unconformity Kasalka unconformity Skeena unconformity Hazelton Brothers Peak Local unconformity Tango Creek Swing Peak Mt. Baptiste Smithers N i l k i t w a Telkwa Upper T r i a s s i c Takla D e s c r i p t i o n F l a t l y i n g b a s a l t i c flows and r e l a t e d t u f f s and b r e c c i a Mainly a c i d i c flows with minor b a s a l t , andesite, t u f f , b r e c c i a , and rare (basal) conglomerate A c i d i c a s h - f a l l t u f f s and t h i c k conglomerate bodies Feldspathic to chert-pebble-bearing a r e n i t e s , mudstone and p o l y m i c t i c conglomerate Thick succession of flows and coarse c l a s t i c rocks (lahars) Rhyolite, subordinate a n d e s i t i c p y r o c l a s t i c and flow rocks, and b a s a l pebble conglomerate Greywacke, sandstone, shale, conglom- erate, minor to major c o a l seams, and b a s a l t i c to r h y o l i t i c b r e c c i a , t u f f s , and flows Greywacke, l i t h i c sandstone, s i l t - stone, shale, t u f f , v o l c a n i c b r e c c i a , pebble conglomerate, and s i l t y limestone Interbedded shale, greywacke, andesite to r h y o l i t e t u f f and b r e c c i a , minor limestone C l a s t i c , p y r o c l a s t i c , and flow rocks B a s a l t i c to a n d e s i t i c v o l c a n i c rocks p e l i t i c sedimentary rocks, minor carbonate rocks +References: 1) Tipper and Richards(1976); 2) Maclntyre(1976); 3) Duffell(1959); 4) Carter(1976); 5) Eisbacher(1974) to TABLE 2.2 INTRUSIVE ROCKS OF WEST-CENTRAL BRITISH COLUMBIA Age(Ma) 47-54 49-53 49-55 47-56 43-51 7 0-84 104* 133-155 173-206 Epoch Eocene Eocene Eocene Eocene Middle Eocene Upper Cretaceous to T e r t i a r y Upper Cretaceous Upper Cretaceous Upper J u r a s s i c to Lower Cretaceous Middle to Upper J u r a s s i c Upper T r i a s s i c to Lower J u r a s s i c I n trusive Suite A l i c e Arm Goosly Lake Babine Nanika Coast C r y s t a l l i n e Complex Intrusions Mt. Bolom Bulkley Kasalka K i t s a u l t Francois Lake Topley Ref' 4 4 4 4 4 5 4 5 4,5 4,5 D e s c r i p t i o n Small stocks of quartz monzonite porphyry which host major molybdenum deposits, i n c l u d i n g B.C. moly P o r p h y r i t i c gabbro and synenomonzonite, representing centers of volcanism(?) Small plugs, dykes, and dyke swarms of f i n e grained b i o t i t e f e l d spar porphyry ranging from g r a n o d i o r i t e to quartz d i o r i t e Small plutons of quartz monzonite to granite; hosts major copper-molybdenum deposits Quartz d i o r i t e , g r a n o d i o r i t e , quartz monzonite; forms s a t e l l i t i c stocks east of, and marginal to, a c e n t r a l migmatitic gneiss P o r p h y r i t i c biotite-hornblende granophyre Stocks and small b a t h o l i t h s of p o r p h y r i t i c g r a n o d i o r i t e and quartz monzonite; hosts copper-molybdenum and molybdenum-tungsten deposits P o r p h y r i t i c l a t i t e - a n d e s i t e , p o r p h y r i t i c d a c i t e , d i o r i t e Quartz d i o r i t e , augite porphyry p o r p h y r i t i c andesite, d a c i t e P o r p h y r i t i c quartz monzonite, d i o r i t e , quartz d i o r i t e , and g r a n o d i o r i t e i n t r u s i o n s nf b a t h o l i t deposit o b a t h o l i t h i c s i z e ; Hosts Endako molybdenum Quartz d i o r i t e to quartz monzonite; occupies core of Skeena Arch References: 1) Tipper and Richards( * Maclntyre determined t h i s K-Ar date ceous age f o r t h i s s u i t e . 1976); 2) Maclntyre(1976); 3) D u f f e l l ( 1 9 5 9 ) ; 4) Carter (1976); 5) Eisbacher(1974) i s incompatible with other geologic c o n s t r a i n t s and suggests an Upper Creta- 14 C r y s t a l l i n e C o m p l e x f o r c i b l y o f t h e I n t e r m o n t a n e E e l t a n d b y u l t r a m e t a m o r p h i s m c f t h e c 1 9 7 0 ; a n d C a r t e r , 1 S 7 4 ) . i n t r u d e s t r a t i f i e d M e s o z o i c r o c k s a r e t h o u g h t t c h a v e b e e n g e n e r a t e d e n t r a l g n e i s s c o m p l e x ( H u t c h i n s o n , C a r t e r ( 1 9 7 4 ; a n d 1 S 7 6 ) h a s d e f i n e d f c u r i n t r u s i v e r o c k s u i t e s , i n w e s t - c e n t r a l E r i t i s h C o l u m b i a , w h i c h h o s t c o p p e r o n l y , c o p p e r - m o l y b d e n u m , a n d m o l y b d e n u m o n l y m i n e r a l i z a t i o n . T h e i n d i v i d u a l s u i t e s a r e c h a r a c t e r i z e d a n d d i s t i n g u i s h e d f r o m o n e a n o t h e r b y d i f f e r e n c e s i n a g e , t y p e o f m i n e r a l i z a t i o n , h o s t r o c k c o m p o s i t i o n , a n d l o c a t i o n ( C a r t e r , 1 9 7 4 , a n d 1 9 7 6 ) . T h e s e t t i n g o f t h e P o p l a r p o r p h y r y w i t h r e s p e c t t o C a r t e r ' s c l a s s i f i c a t i o n s c h e m e i s d i s c u s s e d i n S e c t i o n 3 . 6 . 15 C H A P T E R I I I G E O L O G Y O I T H E P O P L A R P O R P H Y R Y D E P O S I T 3. 1 GENERAL STATEMENT P r i o r t o t h e i n i t i a t i o n o f f i e l d w o r k i t was k n o w n t h a t t h e m a j o r i t y o f g e o l o g i c a l i n f o r m a t i o n w o u l d h a v e t o b e o b t a i n e d f r c m d r i l l c o r e . I t f u r t h e r was d e c i d e d t h a t d e t a i l e d l o g g i n g o f c o r e f r c m t w o c r o s s - s e c t i o n s t h r o u g h t h e p r e v i o u s l y d e f i n e d c e n t e r o f t h e d e p o s i t w c u l d f o r m t h e m a j o r p o r t i o n o f t h e s t u d y . D r i l l c o r e f r o m o t h e r h o l e s w o u l d b e l o g g e d i n l e s s d e t a i l t o f a c i l i t a t e e x t r a p o l a t i o n o f g e o l o g i c f e a t u r e s i n t h r e e d i m e n s i o n s . D u r i n g t h e c o u r s e o f f i e l d s t u d y c o r e f r o m 12 h o l e s t o t a l l i n g 2 6 4 3 m was l o g g e d i n d e t a i l , a n d c o r e f r o m 22 o t h e r s t o t a l l i n g 6 6 5 7 m w a s l o g g e d i n l e s s d e t a i l . E m p h a s i s o n i n f o r m a t i o n f r o m d r i l l c o r e m a d e i t d e s i r a b l e t o l e g t h e c o r e i n s u c h a m a n n e r t h a t t h e d a t a o b t a i n e d w o u l d be q u a n t i t a t i v e a n d t h e r e f o r e v a l i d f o r s t a t i s t i c a l a n a l y s e s . T h i s r e q u i r e d t h a t t h e m e a s u r e m e n t s a n d m e t h o d s u s e d t o l o g t h e c o r e a n d r e c o r d t h e d a t a t e a s c o n s i s t e n t a n d a c c u r a t e a s p o s s i b l e . A t t h e s a m e t i m e t h e m e t h o d s h a d t o b e f l e x i b l e e n o u g h t o a c c o m o d a t e a n y o b s e r v e d g e o l o g i c f e a t u r e t h a t was c o n s i d e r e d p e r t i n e n t . I n a d d i t i o n i t w a s d e s i r e d t h a t t h e i n f o r m a t i o n b e a m e n a b l e t c c o m p u t e r p r o c e s s i n g . 16 A l o g g i n g format t h e r e f o r e was designed by modifying previous computer compatible l o g g i n g formats ( c . f . Blanchet and Godwin, 1972; Godwin, et a l . , 1977; and W i l t o n , 1978), and i s r e f e r r e d t c as " P o p l a r l o g " . 3.2 P o p l a r l o g P o p l a r l o g i s the name given to a 80 column d r i l l core l o g g i n g format, designed t c be compatible with the 80 columns of a standard computer ca r d . Appendix B c o n t a i n s a blank P o p l a r l o g coding format and a d e t a i l e d d e s c r i p t i o n of i t s use. Also i n Appendix E are t a b l e s with the meaning of symbols and codes that were used i n f i l l i n g cut the form. The m a j o r i t y of these symbols and codes as well as the diagrams cn which they are based, are taken from Godwin (1976), Elanchet and Godwin (1972) and Godwin, et a l . (1977). P o p l a r l o g was designed using the Lowell and G u i l b e r t (1970) model of a ' t y p i c a l ' porphyry d e p o s i t as a b a s i s , a s i m p l i f i e d v e r s i o n of which i s shown i n F i g u r e 3.1. The major c h a r a c t e r i s t i c of t h i s model i n c l u d e : (1) c o n c e n t r i c s h e l l s of 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 centered around a p o r p h y r i t i c c a l c - a l k a l i n e s t o c k , (2) occurrence cf c h a r a c t e r i s t i c minerals and/or mineral assemblages cf 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 i n each 17 Vns C H L O R I - P O T A S S I C MODEL OF ALTERATION ZONATION Vns MODEL OF MINERALIZATION P R O P Y L I T I C c h l o r i t e , t p i d o l « , o l b i t « , e o r b o n o t i A R G I L L I C c l o y i , q u o r t l P H Y L L I C t f r i c l t * , q u a r t z , p y r l t t P O T A S S I C K - f « l d » p o r , b i o t i t e C H L O R I- P O T A S S I C c h i o r i t • , K- f t l d i por , » « r i c i t • V n i V t i MVI vtini v t i n l e t t mi Cr 0 v «in I e tt Ont d i t s t m i n o t l o n t (after Lowel l and Guilbert, 1970) Figure 3.1: (a) Typical zonation of a l t e r a t i o n facies i n a porphy- ry deposit; (b) model for "modes" of occurrence of a l t e r a t i o n and economic minerals i n a porphyry deposit. These models formed the basis for the development of Poplarlog. 18 p a r t i c u l a r s h e l l , and (3) c o n c e r t r i c v a r i a t i o n i n the s t y l e of occurrence of 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 , frcm disseminated and p e r v a s i v e at the center grading t c v e i n s at the p e r i p h e r y cf the d e p o s i t . Every porphyry d e p o s i t , however, i s urique, t h e r e f o r e the ceding f c r i t a t has been designed to accomodate d e v i a t i o n s from the t y p i c a l d e p o s i t . V a r i a b l e s thought t c be the most v a l u a b l e i n d e s c r i b i n g the E c p l a r porphyry d e p o s i t i n c l u d e : (1) p o s i t i o n cf a d e s c r i b e d i n t e r v a l cf cere i n x,y,z space , (2) 2cne cf enrichoent ( i . e. hypegene, supergene, oxid e , supergene s u l f i d e ) , (3) o r i g i n a l ( p r e - a l t e r a t i c n ) reck type; with d e s c r i p t i v e and g u a l i f y i r g l a t e l s to record d i f f e r e n c e s i n t e x t u r e and cr mineralogy which could l a t e r te used as c r i t e r i a t c fern s u b d i v i s i o n s cf reck u n i t s . (4) unusual or s p e c i f i c t e x t u r a l f e a t u r e s present i n the c e r e , and (5) s u l f i d e , oxide and s i l i c a t e a l t e r a t i o n and economic 19 u i n e i a l s present; t h e i r s t y l e cr "mode" c f o c c u r r e n c e , i n t e r s i t y , ard p o s i t i o n w i t h i n the L o w e l l and G u i l r e r t (1S70) model. Ihree iieter depth i n t e r v a l s (roughly equal to two f i v e f o o t core tcx lengths) were used to d e s c r i b e the c o r e . However, i n a f e * holes the nature cf the cere was extremely homogenous and a 6 in (20 f t ) i n t e r v a l *as used to expedite l o g g i n g . Shorter i n t e r v a l s viere used when afcrupt changes i n the nature of the core were c r s e r v e d . 3.2 Geological,Map and C r e s s - s e c t i o n s fciap fi (1:2500 c r 1 cm = 25 m) shews the geology cf the I c p l a r pciphyry d e p e s i t . The sap area, approximately 1800 m north-south ard 2100 n east-west, encompasses an area of 3.8 km 2. E r i l l h o l e s legged i r d e t a i l ( i . e., 3 m i n t e r v a l s ) are shewn as c l c s e d c i r c l e s , these logged i n l e s s d e t a i l are shown as open c i r c l e s . Figure 3.2 i s a map of the c e n t r a l p o r t i o n of the d e p o s i t . C r o s s - s e c t i c n s A-A' and B-E * are through these holes logged i n d e t a i l . C r c s s - s e c t i c n A-A* trends east-west through e i g h t h o l e s , and i s 1500 ir long; s e c t i o n E-E * t r e n d s 035° azimuth and i n c l u d e s four h o l e s , ever a d i s t a n c e of 625 m. The geology of these s e c t i o n s , tasec cn computer c l e f s cf d r i l l hole i n f o r m a t i o n are sho«n i n F i g u r e s 3.3 and 3.4. These s e c t i o n s ;20 s s s s s vS.S W >9 -\ 3b / \ \ v \ \ \ ~ s / o-l-~—,2-V\ 1 14 o 28 / A - ©^6-0.- \ s . s 5 — " \ \ \ \ V 3b N 4b xx. / \ / / F i g u r e 3 . 2 : G e o l o g y o f t h e c e n t r a l p o r t i o n o f t h e s t u d y a r e a ( l e g e n d i d e n t i c a l w i t h M a p A ) , s c a l e = 1 : 5 0 0 0 . R o c k u n i t s a r e : ( 1 ) S k e e n a G r o u p ; ( 2 ) K a s a l k a . G r o u p ; ( 3 a ) h o r n b l e n d e q u a r t z raon- z o d i o r i t e , ( 3 b ) b i o t i t e q u a r t z m o n z o n i t e ; ( 4 a ) p o r p h y r i t i c d a - c i t e , ( 4 b ) f e l s i t e ; ( 5 ) p o r p h y r i t i c r h y o l i t e ; ( 6 ) a n d e s i t e ; ( 7 ) O o t s a L a k e G r o u p . 21 F i g u r e s 3 .3 and 3 . 4 : Computer g e n e r a t e d c r o s s - s e c t i o n s o f g e o l o - gy a l o n g l i n e s A-A' and B-B' on Map A, r e s p e c t i v e l y . LEGEND FOR COMPUTER GENERATED CROSS-SECTIONS OF THE POPLAR PORPHYRY Geology Rockunit Andesite Rhyolite dyke F e l s i t e dyke Dacite dyke Bi o t i t e quartz monzonite porphyry - intrusive breccia Skeena Group Interval of core which could not be identified i n the f i e l d ; usu- a l l y due to intense alteration. CROSS-SECTION SYMBOLS : ground surface overburden-bedrock contact -.—1 : — ' : geologic contact A , A/ ' W a A/ A. a\> fault, or faulted contact Tl 28 top of d r i l l hole 28, on cross- section 1 Symbol o o • ® 616.35 642.75 663.15 I L I i i ELEVATION ABOVE SEA LEVEL (METRES) 635.55 721.94 748.34 774.74 801.14 827.54 853.34 880.34 _ l I I I I I I I I I I I l i l l 306.74 333.14 _J L_ cr %/•» fcO V/"» NJ"> A ^ OJ OJ cr ~D i — .O T —1 Q " i I 1 i 1—=» k U ro •CD ro m Q 1 1 o CD -< ID i— i o CD i— \ i i — i m —i i—» 04 CJO ro OJ ID GODC PLOT# 01637120. C3_ „ ^ ^ t<B RO„ ELEVRTION flBByE SER LEVEL (METRES) ; 616.35 632.75 669.15 695.55 721.94 738.34 774.74 801.14 827.54 853.94 890.34 906.74 933 — J 1 1 1 1 1 1 1 I - J I I I i i i i i i i I I I | \ cn. — i CD O cn a) cu' NJ / / / / CT \ \ \ \ cn C O " Jx cn Q - ;o • L C J ~ J to-ol rnw_ X I m p r " o f — K D VK«/» ^ VIS V A Q VA,y> * VA VA i n V A VA vA sA VA CM <A VA Q 3 c a m - cu. co oi *A V \ K IA I f t ^ ^ ^ ^ ^ ^ W V N ^ V ) VnVt V A V » V \ V \ V \ V ^ \ r t V \ Vf> l A V* VA VA \A V \ V > V A V > V » V \ W A v«\ A A VA sA vA \A\T» . NJ CM cr ^ 1 S V, ^ V V V " £ * ^ V A cr VA Vs \ A V CO 5 - cn fO cn Ol Ol a- CD cn cn" cn g " cn cn o- NJ 2 4 are p l o t t e d at a s c a l e cf 1:1320 (1 cm=13.2 m) , which i s the s m a l l e s t s i z e that p l o t t i n g c c u l d te dene while r e t a i n i n g adequate r e s o l u t i o n letween i n t e r v a l s . Supplementary c r e s s - s e c t i o n s C - C , r - C , I-E* and F-F' ( F i g s . 2.5, 2.6, 3.7,and 2.8) are based on d r i l l h o l e s logged i n l e s s d e t a i l . These s e c t i o n s trend east-west with lengths cf SOC ir, 70C m, 400 m, and SCO m r e s p e c t i v e l y , and are drawn at a s c a l e cf 1:2500, c c n p s t i t l e with Map A. 2. ii Jock_Uj3its 2.4.1 C v e r v i e v> The E c p l a r ccpper-ttclybdenum porphyry d e p o s i t i s centered i n a l a t e Cpper Cretaceous c o i p c s i t i c n a l l y zoned p o r p h y r i t i c c a l c - a l k a l i n e stock which has i n t r u d e d upper Mesczcic v c l c a n i c l a s t i c ard e p i c l a s t i c s e d i n e n t a i y recks. 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 were synchronous with emplacement and t h e r e f o r e the deposit i s c o n s i d e r e d tc te paramagmatic ( a f t e r White, et a l . , 1S6£). The deposit i s cut ty s e v e r a l post-<-mineralization dykes ard i s capped t ] f e l s i c v o l c a n i c flew r e c k s . 25 3 . 4 . 2 Ire-Jn t i i v e _ | c c k g 3 . 4 . 2 . 1 i i i € E j _ 6 t c u j Skeena Group recks (Unit 1) c o n s i s t cf t h i n l y tedded dark grey to l i g h t t a r green c r y s t a l and l a p i l l i (aquagene?) t u f f and s i l t s t o n e , and t h e i r contact metamorphosed e q u i v a l e n t s , with l o c a l l y i n t e r t e d d e d rcedium grained sandstone l e n s e s up to one meter t h i c k ( E l a t e 3 . 1 ) . The u n i t forms an east-west t r e n d i n g t e l t through the study area (Map S ) , ranging frcm 60 t c 725 m wide. Bedding i s d e f i n e d ty sharp changes i n e c l o u r and t e x t u r e , with p l a n a r t u t l o c a l l y u n d u l a t i n g tedding s u r f a c e s t h a t d i p between 5 5 ° and 8 0 ° to the southeast. Upper and lewer c o n t a c t s cf t h i s u n i t are covered so t h a t i t s t c t a l t h i c k n e s s i s unknewn, but assuming an average dip cf 7 C ° ard a rcn-repeated s e c t i o n , there i s a maxiffium 845 to cf s t r a t i g r a p n i c s e c t i o n p r e s e n t . Tuffaceous rocks are h i g h l y s i l i c e o u s . C r y s t a l t u f f c o n s i s t s cf t r c k e n guartz c r y s t a l s ranging i n s i z e frcm 0.1 t c 0.25 rrm i n a c h l c r i t i c matrix. C l c t s of c h l o r i t e , c l a y , and s p h e r u l i t i c guartz are p r o t a b l y pseudomorphic a f t e r hornblende and b i o t i t e . l i t h i c l a p i l l i range f r c n 4 nm t c 3 cm i n s i z e . Most rocks c f t h i s u n i t have undergone v a r y i n g degrees of 26 P l a t e 3.1: S k e e n a Group r o c k s ( U n i t 1, l e f t to r i g h t ) :_ (a) s i l i - c e o u s a s h t u f f , i r o n s t a i n i n g f r o m w e a t h e r e d p y r i t e v e i n l e t s ; (b) t h i n l y b e d d e d s i l t s t o n e , l i g h t e r p a t c h e s a r e l e n s e s o f c o a r - s e r m a t e r i a l ? (c) c r y s t a l t u f f . S c a l e i s i n c e n t i m e t e r s . 27 c o n t a c t Betamerphisa and/or hydrothermal a l t e r a t i o n . E i f f e r e n c e s i n p e r m e a b i l i t y between sandstone l e n s e s and the t u f f probably account f o r an apparent s t r a t i g r a p h i c c o n t r o l to hydrothermal a l t e r a t i o n . Sandstone i s i n t e n s e l y a l t e r e d , but adjacent t u f f teds are net. 3.1.2.2 K a s a l k G r o u p Kasalka Group recks (Dnit 2) are found i n a 300 m by 500 m s a l i e n t cf p r e - i n t r u s i v e recks i n the southeast p o r t i o n of the study area (hap A). This u n i t , composed of r e d d i s h brown weathering p c l y l i t h i c conglomerate, l i e s unconformably over Skeena Group r o c k s . Ihe contact i s nowhere exposed and bedding i n the conglomerate i s undeterminable; however, c u t c r c p s of the Kasalka and Skeena Groups are found l e s s than 10 m apart and n e i t h e r u n i t grades towards the c o n t a c t , t h e r e f o r e the c o n t a c t appears to be sharp. Ihe conglomerate (Plate 3.2) c o n s i s t s of 85 percent rounded to sutangular c l a s t s of f e l s i c to i n t e r m e d i a t e t u f f , and a n d e s i t e , g u a r t z , and banded c h e r t . L i t h i c c l a s t s are the most abundant and l a r g e s t , ranging from one to f i v e cm i n diameter. Quartz c l a s t s are mere rounded and are 0.25 t o one cm i n diameter. Barker t u f f fragments appear i d e n t i c a l to some of the Skeena Group r e c k s . The matrix c o n s i s t s cf l e s s than two mm g r a i n s o f c h e r t and guartz. The rock i s cemented by s i l i c a , p y r i t e , s p e c u l a r and earthy hematite, and l i m o n i t e . 28 P l a t e 3.2: K a s a l k a Group c o n g l o m e r a t e ( U n i t 2 ) . C l a s t s shown c o s i s t o f r h y o l i t i c (?) and i n t e r m e d i a t e t u f f s , a n d q u a r t z . S c a l e i s m a r k e d i n c e n t i m e t e r s . 29 3- <4. 2. 3 C o r r e l a t i o n cf P r e - I n t r usive Bock U n i t s Tipper and E i c h a r d s (1967a) have d e s c r i b e d the upper p o r t i o n of the Hazeltcn Greup as i n c l u d i n g an assemblage of greywacke, l i t h i c sandstone, s i l t s t o n e , t u f f a c e o u s s h a l e , t u f f , v o l c a n i c b r e c c i a and a poorly s o r t e d pebble conglomerate. T h i s u n i t was thought by Bcwen (1974, 1975, and 1976), and Mesard et a l . (1979) to u n d e r l i e the study area (Map A). However, with i n f o r m a t i o n obtained from recent r e g i o n a l mapping to the immediate south and southeast of T a g e t o c h l a i n Lake by Woodsworth (1979, and pers. comm. 1978) the lower v o l c a n i c l a s t i c and e p i c l a s t i c u n i t (Unit 1) i s a s s i g n e d here to the Lower Cretaceous Skeena Group. The Skeena Group nas been d e s c r i b e d by T i p p e r and fiichards (1976a) to c o n s i s t of greywacke, sandstone, s h a l e , conglomerate and v o l c a n i c s t r a t a (Table 2.1). The upper conglomerate u n i t (Unit 2) i s now assigned to the b a s a l p o r t i o n of the Upper Cretaceous Kasalka Group, which has been d e f i n e d by Maclntyre (1976) i n the Tahtsa Lake area, approximately 30 km south c f T a g e t o c h l a i n Lake. Maclntyre (1S76) d e s c r i b e d t h i s u n i t as a p o o r l y s o r t e d pebble conglomerate c o n t a i n i n g rounded to subangular c l a s t s of o x i d i z e d Hazelton and Skeena Group rocks i n a sandy matrix cemented with i r o n oxide and s i l i c a . The occurrence of the Kasalka Group conglomerate i n the study area i s the f u r t h e s t l o c a t i o n n o r t h of Tahtsa Lake t h a t t h i s u n i t has been observed. 30 3.4-3 M i n e r a l i z e d I n t r u s i v e Bocks 3.4.3.1 General Statement P r i o r to the present study a number of p o r p h y r i t i c i n t r u s i v e r o c k s , r e l a t e d t c 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 , were i d e n t i f i e d by Utah Mines Ltd. g e o l o g i s t s (Bowen, 1975, 1976 and p e r s . comm. 1S78). However, through the d e t a i l e d l o g g i n g of core d u r i n g the course of t h i s study, i t i s concluded t h a t the t e x t u r a l and m i n e r a l o g i c a l d i f f e r e n c e s p r e v i o u s l y a t t r i b u t e d to d i f f e r e n t i n t r u s i v e rocks are mainly due to the v a r y i n g e f f e c t s of hydrothermal a l t e r a t i o n . The m a j o r i t y of 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 at the Poplar porphyry d e p o s i t occurs within a l a t e Upper Cretaceous guartz monzcdiorite t c guartz mcnzonite stock (Units 3a and 3b). Older rocks a l s o host s u l f i d e m i n e r a l i z a t i o n ; younger rocks are barren except f o r r a r e occurrences of p y r i t e . . T h e r e f o r e the major m i n e r a l i z a t i o n - a l t e r a t i o n event i s g e n e t i c a l l y r e l a t e d to t h i s i n t r u s i v e stock. Hornblende guartz monzodiorite (Unit 3a) , although mapped as a separate u n i t , i s probably a h y b r i d border phase of the b i o t i t e guartz monzonite porphyry s t o c k (Unit 3b). Widespread and v a r i a b l e a l t e r a t i o n of a l l rock u n i t s (except Ootsa Lake Group v o l c a n i c rocks, u n i t 7) makes hand specimen and t h i n s e c t i o n examination d i f f i c u l t . . Commonly, only pseudomorphs a f t e r p l a g i o c l a s e and mafic minerals are a v a i l a b l e 3 1 f o r the i n t e r p r e t a t i o n of o r i g i n a l t e x t u r e and t o estimate o r i g i n a l mineral abundances. Groundmass minerals were o f t e n t o t a l l y o b l i t e r a t e d . Ambiguous r e l a t i o n s h i p s between a l t e r a t i o n minerals compounded these d i f f i c u l t i e s . Hock d e s c r i p t i o n s which f o l l o w ignore a l t e r a t i o n e f f e c t s and are based on samples which have undergone the l e a s t amount of a l t e r a t i o n . Bock names are taken from the c l a s s i f i c a t i o n of S t r e c k e i s e n (1967) and the I n t e r n a t i o n a l Onion of G e o l o g i c a l S c i e n c e s , I.U.G.S. (1973). 3.4.3.2 Hornblende Quartz Monzodiorite Hornblende guartz monzodiorite (Unit 3a) i s found at the s u r f a c e i n both the southern and western p o r t i o n s of the study area (Map A). The southern occurrence i s bounded on the south by T a g e t o c h l a i n Lake, and i s found i n i n t r u s i v e c o n t a c t with Kasalka Group rocks (Unit 2) to the n o r t h . The western occurrence forms a north-south t r e n d i n g outcrop p a t t e r n which i s i n g r a d a t i o n a l c o n t a c t with the b i o t i t e guartz monzonite porphyry (Unit 3b) to the e a s t , and i n presumed i n t r u s i v e c o n t a c t (?) with Skeena Group rocks (Unit 1) to the west. However, t h i s western c o n t a c t i s covered by Ootsa Lake Group v o l c a n i c r o c k s , (Unit 7) and t h e r e f o r e the exact nature of the c o n t a c t i s unknown. F r e s h h o r n b l e n d e g u a r t z m o n z o d i o r i t e , i n hand sample, i s 32 pale t o dark grey and weathers pale tan t o brown. The rock i s p o r p h y r i t i c , with p l a g i o c l a s e and hornblende phenocrysts ranging i n long dimension frcm one to e i g h t mm and from one to 20 mm, r e s p e c t i v e l y . Phenocryst packing v a r i e s from 10 to 80 percent, and phenocryst s i z e v a r i e s i n v e r s e l y with abundance (Plate 3.3 ). The grcundmass i s a p h a n i t i c t o m i c r o c r y s t a l l i n e and ranges from l i g b t t o dark grey i n c o l o u r . Thin s e c t i o n s of t h i s u n i t show i t t o be composed of f i v e to 20 percent euhedral to subhedral hornblende with an average l e n g t h of 1.5 mm and a range of 0.1 mm to 20 mm. S e r i a t e euhedral to s u b h e d r a l p l a g i o c l a s e c r y s t a l s r a n g i n g i n s i z e from 0.01 to e i g h t mm, comprise from 10 to 70 percent of the rock. P l a g i o c l a s e (about An33) i s commonly g l o m e r o p o r p h y r i t i c and zoned, and l o c a l l y c o n t a i n s i n c l u s i o n s of quartz and z i r c o n . Quartz, ranqing from one to 10 percent, occurs as resorbed 0. 1 to one mm subhedral c r y s t a l s and anhedral i n f i l l i n g s between p l a g i o c l a s e c r y s t a l s i n the groundmass. O r t h o c l a s e comprises about 15 percent of the rock, o c c u r r i n g as clouded e q u i g r a n u l a r anhedral c r y s t a l s i n the groundmass. Magnetite comprises approximately f i v e percent of the rock, o c c u r r i n g as d i s c r e t e g r a i n s i n the groundmass or as i n c l u s i o n s i n hornblende c r y s t a l s . E u hedral books of primary o i o t i t e , one to two mm across, range frcm l e s s than one to f i v e percent of the rock and are l e s s abundant than hornblende. 33 P l a t e 3 . 3 : T e x t u r a l v a r i a t i o n s w i t h i n t h e h o r n b l e n d e q u a r t z mon- z o d i o r i t e ( U n i t 3 a ) . The s a m p l e on t h e l e f t c o n t a i n s m i n o r c h a l - c o p y r i t e , t h e o t h e r s a r e b a r r e n . 34 Whole rock major element analyses and C-I.P.W. norms of t h i s u n i t i s l i s t e d i n Table A. 2 (Appendix A). These data w i l l be d i s c u s s e d i n more d e t a i l i n S e c t i o n 3.6. A K-Ar model age of 76.2 ± 2.7 Ma was determined from a hornblende separate from t h i s u n i t (Table A.1 i n Appendix A). This age i s not s t a t i s t i c a l l y d i s t i n g u i s h a b l e from that of the b i o t i t e guartz monzonite porphyry, d i s c u s s e d below. T h i s i s a major c r i t e r i o n f o r i n t e r p r e t i n g the g e n e t i c r e l a t i o n s h i p between these two u n i t s ( S e c t i o n 3 . 5 ) . 3.4.3.3 B i o t i t e puartz Monzonite Porphyry B i o t i t e guartz monzonite porphyry (Unit 3b) u n d e r l i e s the n o r t h e a s t g u a r t e r of the study area (Map A), and comprises the most abundant rock type i n the c r o s s - s e c t i o n s (Fi g s . 3.3, 3.4, 3.5, 3.6, 3.7,and 3 . 8 ) . T h i s u n i t i s bordered to the south and e a s t by Skeena Group rocks; t o the west i t i s i n g r a d a t i o n a l c o n t a c t with the hornblende d i o r i t e . Boundaries to the n o r t h and n o r t h e a s t have not been mapped. Contacts between the b i o t i t e guartz monzonite and Skeena Group rocks g e n e r a l l y are i n t r u s i v e but l o c a l l y are f a u l t e d forming s t e e p l y sheared i n l i e r s of Skeena Group rocks w i t h i n the i n t r u s i o n ( F i g s . 3.3 and 3.4). Rocks on both s i d e s of t h i s c o n t a c t have g e n e r a l l y teen a l t e r e d to such an extent that the o r i g i n a l t e x t u r e i s t o t a l l y o b l i t e r a t e d which makes 35 i d e n t i f i c a t i o n of the rock type d i f f i c u l t . T h i s i n t e n s e a l t e r a t i o n i s due to abundant f r a c t u r e s and v e i n s near the c o n t a c t and the e f f e c t these f r a c t u r e s had on the l o c a l i z a t i o n of hydrothermal f l u i d s . Contacts with the hornblende q u a r t z monzcdiorite are g r a d a t i o n a l and are nowhere observed i n outcrop. The c o n t a c t i s a r b i t r a r i l y d e f i n e d by a 1:1 hornblende to b i o t i t e r a t i o . B i o t i t e q uartz monzonite porphyry i s l i g h t grey to black when f r e s h , and weathers r e d d i s h crown (Plate 3.4). One to seven mm euhedral b i o t i t e phenocrysts are d i a g n o s t i c , comprising t h r e e t o 15 percent of the rock. Euhedral to subhedral p l a g i o c l a s e phenocrysts range from two to e i g h t mm a c r o s s and comprise f i v e to 80 percent of the rock. Size and packing of p l a g i o c l a s e phenocrysts i s v a r i a b l e , even over s h o r t d i s t a n c e s , and has a profound e f f e c t on the i n t e n s i t y and type of a l t e r a t i o n present (discussed f u r t h e r i n s e c t i o n 4.4 . 2 ) . Hornblende phenocrysts form up to e i g h t percent of the r o c k . The a p h a n i t i c groundmass i s dark t o pale grey to pink. E x o t i c fragments of Skeena Group (?) rocks ranging from one to 10 cm across were l o c a l l y observed. M i c r o s c o p i c a l l y , the p o r p h y r i t i c t e x t u r e v a r i e s from h i a t a l t o s e r i a t e . Rare f r e s h p l a g i o c l a s e (about fin35) has normal and o s c i l l a t o r y zoning and i s l o c a l l y g l o m e r o p o r p h y r i t i c . The groundmass i s composed of 0.05 t o 0.5 mm e q u i d i m e n s i o n a l 36 P l a t e 3 .4 : B i o t i t e quarts m o n z o n i t e p o r p h y r y ( U n i t 3b). T h i s shows t h e c o m p o s i t i o n a l and t e x t u r a l v a r i a t i o n w i t h i n t h e u n i t . P l a g i o c l a s e a b u n d a n c e and i t s s u s c e p t i b i l i t y t o a l t e r a t i o n h a d t h e m o s t e f f e c t on t h e v a r i a t i o n i n a p p e a r a n c e . P l a g i o c l a s e abun- d a n c e and i n t e n s i t y o f a l t e r a t i o n i n c r e a s e s f r o m l e f t t o r i g h t . 37 anhedral o r t h o c l a s e and quartz, comprising 10 to 15 percent and 10 to 20 percent of the rock, r e s p e c t i v e l y . O r t h o c l a s e forms l o c a l myrmekitic t e x t u r e s with guartz or p l a g i o c l a s e . Magnetite i s commonly present as minute d i s s e m i n a t i o n s . Minor euhedral to subhedral a p a t i t e i s a l s o observed. B i o t i t e g u a r t z monzonite porphyry very l o c a l l y c o n s i s t s of an i n t r u s i v e b r e c c i a (Plate 3.5). The b r e c c i a c o n s i s t s of fragments of b i o t i t e porphyry and Kasalka Group(?) rocks which comprise 40 t o 80 percent of the rock. Fragments are angular to subrounded, vary i n s i z e from 0.5 to 5 cm a c r o s s and are r o t a t e d and g e n e r a l l y matrix supported. The matrix i s b l a c k t o grey and v a r i e s from a p h a n i t i c t o p o r p h y r i t i c with one to e i g h t mm zoned and g l o m e r o p o r p h y r i t i c p l a g i o c l a s e phenocrysts and one to two mm b i o t i t e phenocrysts. The groundmass of the matrix i s composed of 25 percent 0.05 to 1.5 mm euhedral t o subhedral b i o t i t e , and 50 percent subhedral to anhedral p l a g i o c l a s e 0.05 to one mm i n l e n g t h . The remainder c o n s i s t s of f i n e g r a i n e d q u a r t z , o r t h o c l a s e , magnetite and a p a t i t e . Normative m i n e r a l abundances f o r the b i o t i t e guartz monzonite porphyry are l i s t e d i n Table A.2 (in Appendix A). Two concordant l a t e Upper Cretaceous K-Ar model ages f o r t h i s u n i t , have been determined from b i o t i t e s e p a rates to be 76.9 ± 2.3 Ma and 73.7 ± 2.5 Ma (Table A.1 i n Appendix A). 38 C M P l a t e 3.5: I n t r u s i v e b r e c c i a p h a s e of t h e b i o t i t e q u a r t z monzo- n i t e ( U n i t 3b) . The c l a s t s c o n s i s t o f b o t h f r a g m e n t s o f t h e p o r - p h y r i t i c p h a s e o f U n i t 3b, and o f K a s a l k a G r o u p r o c k s ( U n i t 2 ) . The m a t r i x c o n s i s t s o f 25% b i o t i t e . C h a l c o p y r i t e v e i n l e t r u n s v e r t i c a l l y t h r o u g h t h e s a m p l e one c e n t i m e t e r f r o m t h e l e f t e d g e . 39 3.4.4 Post^Ore Dykes 3.4.4. 1 General Statement S e v e r a l north to northwest t r e n d i n g dykes i n t r u d e a l l p r e v i o u s l y d e s c r i b e d rock u n i t s (Map A and F i g . 3.2). The dykes do not c o n t a i n any s u l f i d e s but are g e n e r a l l y a l t e r e d , e s p e c i a l l y at t h e i r c o n t a c t s . T h i s s t r o n g l y i n d i c a t e s a second p o s t - m i n e r a l i z a t i o n a l t e r a t i o n event, and w i l l be d i s c u s s e d i n more d e t a i l i n S e c t i o n 4.4.5. There are four l i t h o l o g i c a l l y d i s t i n c t dyke u n i t s ; from o l d e s t t o youngest these are: p o r p h y r i t i c r h y o d a c i t e , f e l s i t e , p o r p h y r i t i c r h y o l i t e , and a n d e s i t e . R e l a t i v e ages are d e f i n e d by c r o s s - c u t t i n g r e l a t i o n s h i p s . 3.4.4.2 P o r p h y r i t i c Dacite Dykes P o r p h y r i t i c d a c i t e (Unit 4a) occurs i n f a u l t e d and i n t r u s i v e c o n t a c t with a l l other rock u n i t s except Kasalka Group rocks . The u n i t i s found i n three separate areas (Map A): (1) j u s t east of the c o n t a c t between Ootsa Lake Group v o l c a n i c rocks and the hornblende d i o r i t e , i n the western p o r t i o n of the study area, (2) i n c o n t a c t with a p o r p h y r i t i c r h y o l i t e dyke (Unit 5 ) , where both dyke u n i t s i n t r u d e m i n e r a l i z e d b i o t i t e porphyry i n the c e n t e r of the study area, and (3) as one of many dyke u n i t s which occur between the b i o t i t e q uartz monzonite porphyry and Skeena Group rocks i n the eastern p o r t i o n of Map A . P o r p h y r i t i c d a c i t e (Plate 3.6) i s c h a r a c t e r i s t i c a l l y red to 40 P l a t e 3.6: P o r p h y r i t i c d a c i t e ( U n i t 4 a ) . The d r i l l c o r e s a m p l e o n t h e l e f t shows p i l o t a x i t i c t e x t u r e and c o n t a i n s x e n o l i t h s . The m i d d l e s a m p l e i s a q u a r t z l a t i t e - a n d e s i t e f r o m o u t c r o p a nd i s c o r r e l a t e d w i t h t h e d a c i t e . The s a m p l e on t h e r i g h t shows t h e u n i t as i t was m o s t commonly o b s e r v e d , w i t h b i o t i t e p h e n o c r y s t s . 41 purple i n c o l o u r , with a f i n e g r a i n e d p i l o t a x i t i c t e x t u r e . Amygdules, one to 20 mm a c r o s s c o n t a i n quartz and c a l c i t e . Bounded quartz "eyes" are l o c a l l y observed. Fine to medium qra i n e d euhedral p l a q i o c l a s e , b i o t i t e , and hornblende phenocrysts comprise up to 25, 10 and f i v e p ercent of the rock r e s p e c t i v e l y . Zoned and g l o m e r o p o r p h y r i t i c p l a g i o c l a s e (about An28) ranges from one t o 10 mm a c r o s s and have been p a r t i a l l y r e s o r b e d . B i o t i t e i s one to f i v e mm i n diameter. Hornblende i s one to f i v e mm i n l e n g t h and has g e n e r a l l y been a l t e r e d t o c h l o r i t e . The groundmass of the p o r p h y r i t i c d a c i t e c o n s i s t s of mostly 0.1 ram l a t h s of p l a g i o c l a s e with l e s s e r anhedral g r a i n s of q uartz and o r t h o c l a s e . F i n e g r a i n e d a p a t i t e i s an accessory mineral. Whole rock analyses of two samples o f t h i s u n i t are presented i n Table A.2; one sample i s from outcrop, the other from d r i l l c o r e . The former i s c l a s s i f i e d as a quartz l a t i t e - a ndesite and the l a t t e r as a d a c i t e ( a f t e r S t r e c h e n i s e n , 1967). T i e term p o r p h y r i t i c d a c i t e i s p r e f e r r e d as a f i e l d name, and i s used here to d e s c r i b e both rock types. One K-rAr model age of 72.2 ± 3.0 Ma has been determined f o r t h i s u n i t from a b i o t i t e separate taken frcm d r i l l core (Table A.2 i n Appendix A). T h i s date i s important because i t p l a c e s an upper l i m i t on the age of the m i n e r a l i z i n g event at the Poplar porphyry. F i e l d evidence, i n c l u d i n g c h i l l e d c o n t a c t s and 42 p a u c i t y of s u l f i d e m i n e r a l i z a t i o n , a l s o i n d i c a t e s t h a t t h i s u n i t i s younger than the m i n e r a l i z i n g event which accompanied the i n t r u s i o n of the b i o t i t e quartz monzodiorite porphyry. 3.4.4.3 F e l s i t e Dykes L i g h t pink to tan a p h a n i t i c dykes (Unit 4b) l e s s than two meters t h i c k were noted i n d r i l l core . This u n i t resembles c h i l l e d p o r t i o n s of the p o r p h y r i t i c d a c i t e dyke and i s probably e q u i v a l e n t to i t . However, l o c a l l y t h i s u n i t may'be the c h i l l e d e q u i v a l e n t to the p o r p h y r i t i c r h y o l i t e . 3.4.4.4 P o r p h y r i t i c Bhyolite, Dykes Steep l y d i p p i n q p o r p h y r i t i c "quartz eye" r h y o l i t e dykes (Unit 5) are the most abundant type of dyke rock i n the study area (Map A.), and are found i n f a u l t e d or i n t r u s i v e c o n t a c t with a l l other rock u n i t s except the Kasalka Group. Contacts with the p o r p h y r i t i c r h y b d a c i t e are q e n e r a l l y c h i l l e d , but are l o c a l l y g r a d a t i o n a l . Dykes o f t h i s u n i t g e n e r a l l y trend n o r t h w e s t e r l y and are co n c e n t r a t e d i n areas marked by a e r i a l - photograph lineaments which probably r e f l e c t f a u l t zones. P o r p h y r i t i c r h y o l i t e (Plate 3.7) i s c h a r a c t e r i s t i c a l l y white to tan with d i s t i n c t i v e one t o f i v e mm embayed q u a r t z phenocrysts ("eyes") comprising 10 percent of the rock. C h l o r i t i z e d b i o t i t e patches, one to f i v e mm a c r o s s are l o c a l l y observed; one to two mm a r g i l l i z e d p l a g i o c l a s e phenocyrsts are rare,. The a p h a n i t i c groundmass c o n s i s t s of 0.05 t o 0.2 mm eguidimensional 43 P l a t e 3 . 7 : P o r p h y r i t i c r h y o l i t e ( U n i t 5 ) . E m b a y e d q u a r t z " e y e s " a r e t h e m o s t d i s t i n c t i v e f e a t u r e o f t h i s u n i t . G r e e n i s h s p o t s a r e c h l o r i t e p a t c h e s a f t e r b i o t i t e . T h e s a m p l e o n t h e r i g h t h a s b e e n s t a i n e d t o s h o w K - f e l d s p a r i n t h e g r o u n d m a s s . 44 e g u i g r a n u l a r guartz and o r t h o c l a s e . 3.4.4.5 Andesite Dykes Dark grey a n d e s i t e dykes (Unit 6) were i n t e r s e c t e d i n a few d r i l l h o l e s . T h i s u n i t i s h i g h l y magnetic and c o n s i s t s of two percent a l t e r e d , subhedral p l a g i o c l a s e and g u a r t z phenocrysts 0.5 t o 1.0 mm i n diameter. The e g u i g r a n u l a r groundmass c o n s i s t s of 95 percent subhedral p l a g i o c l a s e and three percent anhedral q u a r t z , 0.1 t o 0.2 mm i n diameter. L o c a l l y the t e x t u r e i s amygdaloidal and p i l o t a x i t i c . A few 0.5 mm pseudomorphs of c h l o r i t e a f t e r hornblende (?) are a l s o observed. 3.4.5 E x t r u s i v e Bocks ——————— i. , y. • 3.4.5.1 Ootsa Lake Group Ootsa Lake Group v o l c a n i c flow r o c k s (Unit 7) cap the h i l l immediately west of the d e p o s i t (Map A). From a e r i a l photographs the lower c o n t a c t of t h i s u n i t , both near the d e p o s i t and on h i l l s 1.5 km north and northwest of the map area, l i e at approximately the same e l e v a t i o n ; t h e r e f o r e , the lower c o n t a c t of t h i s u n i t i s h o r i z o n t a l . Although the contact i s obscured i n the study area the f l a t a t t i t u d e r e q u i r e s an unconformable c o n t a c t with u n d e r l y i n g u n i t s . Ootsa Lake Group v o l c a n i c s a l s o crop out t o p o g r a p h i c a l l y much lower, i n Canyon Creek (Map A), and probably were emplaced by b l o c k f a u l t i n g (see S e c t i o n 3.7)•. 45 These rocks have not been dated i s o t o p i c a l l y , but are post- i n t r u s i v e s i n c e they o v e r l i e and are not d i s p l a c e d by the major east-west t r e n d i n g f a u l t which c r o s s - c u t s the d e p o s i t i n Map A, yet protrudes from both s i d e s of v o l c a n i c cover on a e r i a l photographs. Outcrop of Ootsa Group rocks i s c h a r a c t e r i z e d by s u b p a r a l l e l cleavage t h a t produces p l a t e y rubble which i s pink, grey, or brown i n c o l o u r ( P l a t e 3.8). The rock i s p o r p h y r i t i c , with l a t e r a l v a r i a t i o n s i n phenocryst s i z e ; phenocrysts of coarse g r a i n e d p l a g i o c l a s e and hornblende occur i n the southwest, but become f i n e r g r a i n e d and impart a p i l o t a x i t i c t e x t u r e t o the rock i n the northwest p o r t i o n of Map A. M i n e r a l content c o n s i s t s of 15 to 25 percent s e r i a t e p l a g i o c l a s e phenocrysts ranging from 0 . 5 t o f i v e mm i n l o n g dimesion, and up to 10 percent hornblende phenocrysts ranging from one to f i v e mm i n l e n g t h . P l a g i o c l a s e phenocrysts l o c a l l y are pink due t o i n c l u s i o n s of hematite, and can resemble o r t h o c l a s e . The groundmass c o n s i s t s of 0 . 1 to 0 . 3 mm p l a g i o c l a s e l a t h s and s l i g h t l y l a r g e r and l e s s abundant subhedral to anhedral quartz and anhedral o r t h o c l a s e . Minor a p a t i t e i s a l s o observed. A whole rock a n a l y s i s from a coarse grained p o r p h y r i t i c 46 P l a t e 3.8: O o t s a L a k e G r o u p v o l c a n i c f l o w r o c k s ( U n i t 7 ) . The c o a r s e g r a i n e d p o r p h y r i t i c s a m p l e on t h e l e f t comes f r o m t h e s o u t h w e s t e r n p o r t i o n o f Map A. The m i d d l e s a m p l e shows p i l o t a x i - t i c t e x t u r e , a nd comes f r o m Canyon C r e e k . The s a m p l e on t h e r i g h t comes f r o m t h e n o r t h w e s t , and shows p i l o t a x i t i c t e x t u r e , as i n - d i c a t e d b y f i n e g r a i n e d c h l o r i t i z e d h o r n b l e n d e p h e n o c r y s t s . 47 flow rock from t h i s u n i t i s presented i n Table A.2 (Appendix A). The rock i s c l a s s i f i e d as a d a c i t e ( a f t e r S t r e c h e i s o n , 1967). To the w r i t e r ' s knowledge there are at present no published data on the c h e m i c a l composition of Ootsa Lake Group rocks. T h e r e f o r e , no comparison can be made between " t y p i c a l " Ootsa Lake Group rocks and the v o l c a n i c flow rocks found i n the study area. 3.4.5.2 C o r r e l a t i o n of E x t r u s i v e Bocks D u f f e l l (1959) d e s c r i b e d Ootsa Lake Group v o l c a n i c rocks as c o n s i s t i n g of "... mainly a c i d flows with minor amounts of b a s a l t , a n d e s i t e , t u f f , b r e c c i a , and r a r e conglomerate...." (Table 2.1). T i p p e r and E i c h a r d s (1967a, and 1976b) have mapped Upper Cretaceous v o l c a n i c r o c k s i n the T a g e t o c h l a i n Lake area as belonging to both the Endako and Ootsa Lake Groups (Table 2. 1) . A f t e r examining the v o l c a n i c flow rocks i n the study area (Map A), E i c h a r d s (pers. . comm. , 1978) b e l i e v e d them to belong to the Ootsa Lake Group. 3.5 K-Ar Age Determinations Four K-Ar model ages were obtained at the P o p l a r porphyry (Table A.1, Appendix A): two from b i o t i t e s e p a rates of the b i o t i t e q uartz monzonite porphyry (Unit 3b), one from a b i o t i t e separate of the d a c i t e (Unit 4a), and a hornblende separate from the hornblende quartz monzodiorite (Unit 3a). A l l aqes are i n d i s t i n g u i s h a b l e from each other w i t h i n a n a l y t i c a l e r r o r l i m i t s . The mean age of these dates i s 74.8 ± 2 . 6 Ma. 48 Because the age obtained from the p o s t - m i n e r a l i z a t i o n d a c i t e dyke i s e s s e n t i a l l y the same as f o r m i n e r a l i z e d rock u n i t s , the age of the m i n e r a l i z i n g event can be c o n s i d e r e d g e o l o g i c a l l y synchronous with the i n t r u s i o n of the b i o t i t e quartz monzonite porphyry stock. White, et a l (1968) have used the term "paramagmatic" to d e s c r i b e d e p o s i t s which are e p i g e n e t i c and can be shown by g e o l o g i c a l and/or r a d i o m e t r i c evidence to be an i n t e g r a l f e a t u r e of a magmatic event. 3.6 Comparison of the Poplar Porphyry to Other Porphyry Deposits of West-Central B r i t i s h Columbia. There are a number of porphyry d e p o s i t s l o c a t e d i n west^ c e n t r a l B r i t i s h Columbia ( C h r i s t o p h e r and C a r t e r , 1976)". C a r t e r (1974, and 1976) has separated the i n t r u s i v e rocks which host these d e p o s i t s i n t o f c u r i n t r u s i v e rock s u i t e s . Each s u i t e i s unique i n one or more of the f o l l o w i n g : geographic d i s t r i b u t i o n , type of contained m i n e r a l i z a t i o n , host rock composition, and K- Ar model age f o r i n t r u s i o n . > These f o u r i n t r u s i v e rock s u i t e s form crude north-south t r e n d i n g b e l t s . These b e l t s c o n s i s t of the f o l l o w i n g : the molybdenum bearing A l i c e Arm i n t r u s i o n s of Eocene age, on the west; copper and molybdenum b e a r i n g i n t r u s i o n s of the Upper Cretaceous B u l k l e y i n t r u s i o n s and Eocene Nanika i n t r u s i o n s , i n the c e n t e r ; and copper bearing Babine i n t r u s i o n s of Eocene age, to the east. 49 Based on geographic l o c a t i o n and type of contained m i n e r a l i z a t i o n , the Poplar Porphyry d e p o s i t cannot belong to e i t h e r the A l i c e Arm or the Babine i n t r u s i v e s u i t e s . However, i n t r u s i o n s of both the B u l k l e y and Nanika s u i t e s host copper- molybdenum porphyry d e p o s i t s , and both types are known to occur w i t h i n 5 0 km of the Poplar porphyry. The h u c k l e b e r r y , Ox Lake, Nadina , and Duck Lake i n t r u s i o n s are members of the former, and the Lucky Ship, Berg, Nadina Mountain, Goosley, and Morice Lake i n t r u s i o n s belong to the l a t t e r . The Nanika i n t r u s i v e s u i t e , however, i s Eocene i n age, and the B u l k l e y i n t r u s i o n s are Upper Cretaceous. A comparison between these ages and those obtained from the P o p l a r porphyry (Table A.1, Appendix A; and S e c t i o n 3 . 5 ) i n d i c a t e s t h a t a l l dated rock u n i t s at the Poplar porphyry were i n t r u d e d during the B u l k l e y i n t r u s i v e event. F u r t h e r support of t h i s c l a s s i f i c a t i o n i s presented i n Fi g u r e 3.9, which shows the normative c o m p o s i t i o n a l f i e l d s of the B u l k l e y and Nanika i n t r u s i o n s p l o t t e d on a t e r n a r y g 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 diagram taken from C a r t e r (1974, and 1976). A l s o shown on F i g u r e 3.9 are the normative compositions of the hornblende quartz monzodiorite porphyry (Unit 3a) and the b i o t i t e quartz monzonite porphyry (Unit 3b). Hornblende quartz monzodiorite l i e s w i t h i n the B u l k l e y c o m p o s i t i o n a l f i e l d and the b i o t i t e quartz monzonite porphyry l i e s on the boundary of t h i s f i e l d . The l a t t e r i s more potassium r i c h than most B u l k l e y r o c k s but i s l e s s s i l i c e o u s than the Nanika c o m p o s i t i o n a l f i e l d . 50 QZ F i g u r e 3.9: O r t h o c l a s e - P l a g i o c l a s e - O u a r t z t e r n a r y diagram show- i n g the c o m p o s i t i o n a l f i e l d s o f the Nanika (N) i n t r u s i o n s , and the B u l k l e y (B) i n t r u s i o n s ( a f t e r C a r t e r , 1974, and 1976). Square i s whole rock a n a l y s i s o f hornblende q u a r t z m o n z o d i o r i t e , and c i r c l e i s whole rock a n a l y s i s o f q u a r t z monzonite from the P o p l a r porphyry. 51 From these c r i t e r i a ( g eographical l o c a t i o n , contained m i n e r a l i z a t i o n , K-Ar model age, and host rock composition) the Poplar porphyry i s c l a s s i f i e d here as a B u l k l e y i n t r u s i o n . . 3. 7 S t r u c t u r e E e g i o n a l l y , the study area (Map A) l i e s j u s t east of an area r e f e r r e d to as a " T r a n s i t i o n Zone" between the Intermontane and Coast C r y s t a l l i n e t e c t o n i c b e l t s (Woodsworth, 1979; and D u f f e l l , 1959). The area surrounding Tahtsa (and probably T a g e t o c h l a i n Lake) has been d e s c r i b e d by Maclntyre (1976) as c o n t a i n i n g major s t r u c t u r a l elements i n c l u d i n g "... high angle normal and r e v e r s e f a u l t s , which bound u p l i f t e d , down f a u l t e d , and t i l t e d b l o c k s " . Woodsworth (1979, and pers..comm., 1979) i d e n t i f i e d major low angle t h r u s t f a u l t s , southwest of the study area, with probable northeast movement -a d i r e c t i o n normal to the t r e n d of the Coast C r y s t a l l i n e Complex. The dominant s t r u c t u r a l t r e n d i n the study area i s north-northwest, which p a r a l l e l s t h e t r e n d of the e a s t e r n margin of the Coast C r y s t a l l i n e Complex; the u p l i f t of which most l i k e l y dominated the s t r u c t u r a l regime i n the area (Maclntyre, 1976). Due to a p a u c i t y of outcrop i n the study area f a u l t s c o u l d be i d e n t i f i e d only i n canyons and t r a c e s were e x t r a p o l a t e d from d r i l l core i n f o r m a t i o n . A e r i a l photograph i n t e r p r e t a t i o n was used t o d e f i n e l a r g e r s t r u c t u r e s ( F i g . 3,^10). . Outcrop d i s t r i b u t i o n , the d i l a t i o n a l nature of dykes, the orthogonal nature of drainage p a t t e r n s , and the alignment of these pattens 5 2 53 with major a e r i a l photograph lineaments a l s o were used to t e n t a t i v e l y i d e n t i f y f a u l t s i n the study area. . The r e g i o n a l l y d i s c o r d a n t t r e n d of T a g e t o c h l a i n Lake a l s o i s l i k e l y due to s t r u c t u r a l c o n t r o l , as can be seen i n F i g u r e 3.10 (Woodsworth, per s . comm. 1979; and Tipper and Hichards 1976a). J o i n t i n g , although common i n d r i l l c o r e , i s observed i n outcrop only i n Canyon Creek and East Creek canyons. J o i n t s e t s are spaced from centimeters t o meters apart, forming a blocky to p a r a l l e l p a t t e r n i n Canyon Creek. L o c a l l y abundant, one to f i v e cm, q u a r t z - p y r i t e v e i n s i n Canyon Creek p a r a l l e l the dominant nort h to n o r t h w e s t e r l y t r e n d of j o i n t i n g . T h i s i n d i c a t e s the importance of j o i n t i n g f o r l o c a l i z a t i o n of hydrothermal s o l u t i o n s during m i n e r a l i z a t i o n of the Poplar porphyry, and i s evidence f o r d i r e c t i o n a l p e r m e a b i l i t y of these s o l u t i o n s (discussed i n S e c t i o n 4.5). 54 CHAPTER IV MINERALIZATION AND ALTERATION OF THE POPLAR PORPHYRY DEPOSIT 4.1 General Statement The major problem i n d e c i p h e r i n g and i n t e r p r e t i n g the geology of the P o p l a r porphyry d e p o s i t was d i s t i n g u i s h i n g the t e x t u r a l and m i n e r a l o g i c a l changes i n the rock due to v a r i a t i o n s w i t h i n the o r i g i n a l rock from those changes due t o the e f f e c t s of hydrothermal and supergene a l t e r a t i o n . E a r l y i n the course of f i e l d study i t was determined t h a t the m a j o r i t y of v a r i a t i o n s i n the appearance of the core was due to widespread a l t e r a t i o n which v a r i e d i n type, i n t e n s i t y , and mode of occurrence r a t h e r than d i f f e r e n c e s i n the o r i g i n a l rock type. The e f f e c t o f t h i s v a r i a t i o n i s most d i s c e r n i b l e i n the b i o t i t e porphyry (Plate 3.4). To d e f i n e 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 z o ning at the Poplar porphyry the mode of occurrence (degree of d i s p e r s i o n , e. g. v e i n s , patches, envelopes, or pervasive) and i n t e n s i t y (on ranked s c a l e of abundance from n i l = 0 to most i n t e n s e = 9; see Appendix B) of twelve s i l i c a t e , c arbonate, s u l f a t e , oxide, and s u l f i d e a l t e r a t i o n m i n e r a l s , and f o u r s u l f i d e ore minerals were recorded f o r each 3 m depth i n t e r v a l (Table 4.1). The " i n t e n s i t y " of a p a r t i c u l a r m i n e r a l i s used here t o mean the v o l u m e t r i c abundance of the m i n e r a l , and i m p l i e s no c o n n o t a t i o n to the p h y s i c a l c o n d i t i o n s ( i . e. pressure-^temperature) of the mineral's formation. Separate s c a l e s were used t o rank the 55 i n t e n s i t y of d i f f e r e n t mineral groups. S i l i c a t e , carbonate, and s u l f a t e minerals were ranked on one s c a l e , and s u l f i d e and oxide minerals ranked using another s c a l e (Table B.6, Appendix B). Separate s c a l e s were used because the former group of minerals g e n e r a l l y occurred i n g r e a t e r abundance than the l a t t e r , and to maintain r e s o l u t i o n between d i f f e r e n c e s i n i n t e n s i t y i n the s u l f i d e - o x i d e group s m a l l e r i n t e r v a l s were used t o rank t h e i r i n t e n s i t y . For example, a 3 m i n t e r v a l of core which c o n t a i n e d 1235 c h a l c o p y r i t e and 12% K - f e l d s p a r would be d e s c r i b e d as being "Very High" i n c h a l c o p y r i t e and given a rank of 8 while the K- f e l d s p a r would be d e s c r i b e d as " F a i r " and given a rank of 3. The occurrence and r e l a t i v e abundances of these m i n e r a l s , i n every i n t e r v a l of core, was compared to a " c h e c k l i s t " of those abundances expected i n any one of nine p a r t i c u l a r hypogene 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 f a c i e s i n the L o w e l l and G u i l b e r t (1970) model, as modified by Blanchet and Godwin (1976) (See Tables B.7, and B.9 i n Appendix B). A major problem encountered by using t h i s approach was t h a t two or more min e r a l s , c h a r a c t e r i s t i c of separate and mutally e x c l u s i v e a l t e r a t i o n zones, a c c o r d i n g to the " c h e c k l i s t " , were commonly observed i n a s i n g l e i n t e r v a l of c o r e . 56 T&BLE 4,1 A l t e r a t i o n And Ore M i n e r a l s Recorded At The Poplar Porphyry Using P o p l a r l o g A l t e r a t i o n M i n e r a l s Ore M i n e r a l s Quartz C h a l c o p y r i t e K - f e l d s p a r B o r n i t e B i o t i t e C h a l c o p y r i t e S e r i c i t e (muscovite) Molybdenite C h l o r i t e C l a y Epidote Carbonate Anhydrite-gypsum P y r i t e Hematite Magnetite T h i s problem reduced the e f f e c t i v e n e s s of the " c h e c k l i s t " method of d e f i n i n g a l t e r a t i o n zones. Examples of c o n f l i c t i n g m i n e r a l assemblages which may be found i n a p a r t i c u l a r i n t e r v a l i n c l u d e : ( 1 ) v e i n minerals may be i n c o m p a t i b l e with p e r v a s i v e a l t e r a t i o n , (2) supergene mineral assemblages may be superimposed on hypogene assemblages, (3) incomplete a l t e r a t i o n r e a c t i o n s are r e p r e s e n t e d , (4) metastable m i n e r a l assemblages may occur, and (5) assemblages represent m u l t i p l e a l t e r a t i o n events. 57 There were, however, d e f i n i t e but more g e n e r a l mineral a s s o c i a t i o n s , observed at v a r i o u s i n t e r v a l s of occurrence i n d r i l l c o r e , t h a t p a r a l l e l the Lowell and G u i l b e r t (1970), Blanchet and Godwin (1972) , and Godwin (1976) 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 zones.„ These zones are d e f i n e d here as the p o t a s s i c , p h y l l i c , a r g i l l i c , and p r o p y l i t i c f a c i e s of a l t e r a t i o n , and the c h a l c o p y r i t e - m o l y b d e n i t e zone of m i n e r a l i z a t i o n . T h i s c l a s s i f i c a t i o n has no g e n e t i c c o n n o t a t i o n and r e f e r s only to the occurrence of the d i a g n o s t i c mineral(s) d e f i n e d f o r each f a c i e s . Each zone i s c h a r a c t e r i z e d by a d i a g n o s t i c m i n e r a l , or m i n e r a l s , which d e f i n e a p a r t i c u l a r f a c i e s ; a s s o c i a t e d minerals are a l s o commonly present, but are not c o n s i d e r e d d i a g n o s t i c s i n c e they occur i n more than one f a c i e s (Table 4 . 2 ) . 58 TABLE 4.2 ALTERATION FACIES AT THE POPLAR PORPHYRY DEPOSIT, AND THEIR DIAGNOSTIC AND ASSOCIATED MINERALOGY. IN ORDER OF DECREASING ALTERATION GRACE. Mineralogy F a c i e s ( u n d e r l i n e d minerals are d i a g n o s t i c ) P o t a s s i c K - f e l d s p a r . b i o t i t e . magnetite, guartz carbonate P h y l l i c s e r i c i t e . g u a r t z , p y r i t e , carbonate, hematite, gypsum A r g i l l i c c l a y , carbonate, g u a r t z , gypsum P r o p y l i t i c e p i d o t e , c h l o r i t e , carbonate 4.2 D i s t r i b u t i o n Of 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 , Zones At The Poplar,, Porphyry The d i s t r i b u t i o n of 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 zones at the Poplar porphyry i s shown i n plan on Map B and Figure 4.3, and i n c r o s s - s e c t i o n along l i n e s A-A» and B-B• on F i g u r e s 4.1 and 4.2, r e s p e c t i v e l y . 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 zones are d e f i n e d by p l o t t i n g the abundances of i n d i v i d u a l d i a g n o s t i c m i n e r a l s , from d r i l l hole data, on computer generated c r o s s - s e c t i o n s . I n t e r v a l s t h a t are above background l e v e l s of ranked abundance were used t o determine the d i s t r i b u t i o n of a p a r t i c u l a r f a c i e s . , Because some p h y l l i c a l t e r a t i o n was recorded 59 . F i g u r e s 4.1 and 4.2: Computer generated c r o s s - s e c t i o n s o f 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 a l o n g l i n e s A-A 1 and 3-B\ r e s p e c t i v e l y LEGEND FOR COMPUTER GENERATED CROSS-SECTIONS OF THE POPLAR PORPHYRY C h a l c o p y r i t e Abundance Volume Percent 0 0.25%(trace) < 0.25% 0.25-0.5% 0.5-1.0% 16.0% Ranked Intensity Symbol 0 - 1 a 2 S 3 Y 4 6 1.0-2.0% 5 * ' E 2.0-4.0% 6 n 7 e 4.0-8.0% 7 R ."• X 8.0-16.0% s 9 • v CROSS-SECTION SYMBOLS ground surface overburden-bedrock contact geologic contact A, A/ "V A, A, A/ A/A, l\j fault, or faulted contact Yl 28 t oP o f d r i 1 1 hole 28, on cross section 1 EL^/HUON ABOVE SEA LEVAL (METFRS) _ n n e „ _ 616.35 642.75 663.15 695.55 ^21.94 748.34 774.74 801.14 827.54 853.94 880.34 906.74 933.14 ~ ' ' » _ J I I I I I I I I I I I I I I I I I fO O o ro M ru ID CO LO O co LO to (O CO CO Lo' to LO CO « CD CD 6 Ln' CO LO io" CD & o Lo' CD cn cn CO cn to cn cn to Ln" (Jl to cn • to cn ro ro Lo" «o cn 3 cn o 3̂ ro t o " CO m —Icn !±-LO CD co r--o gg <4f X - I ™ " cog —ico t—I is- 1 £ CO Lo' cn co ro C O X ) m o CO m a rn co o — < DO O m m I r n a co X ) ~n C D i — i O to cn cn Ln* cn CO to to cn ro-© CO ro-o cn ro-o ro-o to •o Ln' ro-ro co • . CO XI n ZD :z: a ZD x Gl m •D ! ZD O ZD "D ZT m x i ZD o Lo" ro- t — a — i CO - J ' ro- M o co ro co • . cn co ro - U cn io' co ro- H ro Lo' ro- LO o CO LO ro -co co ro • co CD cn co ro- <o io" ro ro 4» CO ro ro" 6 ro O K ..i i y 1111111111 II!! 11111111111111 III i y 111111111111111111 C O ro CO ON •o C O rs CM •II 11 1111111111111111 i P*?03"! I I P I I I I I I III I I I I O . l . v •2K 5 prm 4 23 5? 4 2TK X A X 3 P N Kl 4JU / / / II I' 1 , 1 " LJ v N V ^ v v \ \ \ , \ \ \ \ \ V V; ^ \ \ \ \ \ \ \ . \ \ . \ . \ . ^ ^ \ \ \ \ \ v v ^ ^ \ \ \ X to fN MI in r 111111111111111111111111111 ii iii! 11 III 11 III 1111 CO i i 1— i i 1 1 1 1 — i 1 1 1 1 1 1 1 r~ t>e*088 t«es& bS'Lze -brioe trwx W&L WIZL ss'ssg si'699 tS3̂ 13W) "13A3~1 B3S 3r\Q8ti N0I18A3~]3 '221Z.£910 #101d 3Q03 62 F i g u r e 4 . 3 : 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 o f the c e n t r a l p o r t i o n of the P o p l a r porphyry d e p o s i t (see Map B f o r more d e t a i l ; l e - gend i d e n t i c a l w i t h Map B). Scale= 1:5000. H o r i z o n t a l l i n e s = c h a l c o p y r i t e zone (C) ; v e r t i c a l l i n e s = molybdenite zone (M) ; r i g h t s l o p i n g l i n e s = b i o t i t e zone (B); l e f t s l o p i n g l i n e s = K- f e l d s p a r zone (K); ph= p h y l l i c zone; a= a r g i l l i c zone; pr= p r o - p y l i t i c zone. 63 i n almost every i n t e r v a l of c o r e , p o t a s s i c a l t e r a t i o n was given p r i o r i t y when both f a c i e s were present i n an i n t e r v a l of core. Zoning so d e f i n e d avoids the complexity, noted i n Secton 4. 1, caused when d i a g n o s t i c minerals of more than one f a c i e s occur together i n the same i n t e r v a l of c o r e . Zoning i s shown on Map A to c o n s i s t of a 600 m by 500 m r i n g of p o t a s s i c a l t e r a t i o n a s s o c i a t e d with c h a l c o p y r i t e and molybdenite m i n e r a l i z a t i o n . The p o t a s s i c annulus surrounds a 300 m by 150 m c e n t r a l core c o n s i s t i n g mostly of p h y l l i c and a r g i l l i c a l t e r a t i o n . A 750 m wide east-west t r e n d i n g p e r i p h e r a l zone, c o n s i s t i n g l a r g e l y of p h y l l i c a l t e r a t i o n a t depth and p h y l l i c and a r g i l l i c a l t e r a t i o n near the s u r f a c e , encompasses the p o t a s s i c a l t e r a t i o n zone. Fresh rocks are l o c a l l y observed w i t h i n t h i s p e r i p h e r a l zone; however, most have undergone a r g i l l i c to p h y l l i c a l t e r a t i o n . Outside the p e r i p h e r a l zone, rocks are g e n e r a l l y f r e s h but l o c a l l y p r o p y l i t i z e d . A p o r t i o n of the p o t a s s i c a l t e r a t i o n annulus i s t r u n c a t e d by an east-west t r e n d i n g f a u l t (Map A). The o f f s e t p o r t i o n was not i n t e r s e c t e d n o r t h of the f a u l t by any d r i l l h o l e . T h e r e f o r e , i t s l o c a t i o n i s unknown, and o f f s e t along the f a u l t i s undetermined. T h i s z o n a t i o n i s a t y p i c a l f o r porphyry d e p o s i t s i n g e n e r a l ( F i g . 3.1). Since the P o p l a r porphyry c o n s i s t s of an a r g i l l i c core which i s lower i n ' a l t e r a t i o n grade* than the p o t a s s i c annulus which surrounds i t , a second a l t e r a t i o n event l i k e l y 64 took p l a c e . T h i s i s d i s c u s s e d i n more d e t a i l i n S e c t i o n 4.4.5. 4.3 S u l f i d e Mineralogy C h a l c o p y r i t e and l e s s e r molybdenite are the most abundant economic minerals present at the P o p l a r porphyry. B o r n i t e , c o v e l l i t e , and t e t r a b e d r i t e are minor and seldom observed i n hand samples. Traces of c h a l c o c i t e , s p h a l e r i t e and galena were a l s o observed. 4.3.1 C h a l c o p y r i t e C h a l c o p y r i t e at the Poplar porphyry i s a s s o c i a t e d with the p o t a s s i c zone, encompassing the c e n t r a l low grade core ( F i g s . 4. 1, 4.2,and 4.3,; and Map B). High grade c h a l c o p y r i t e zones a l s o occur i n h o l e s 34 and 39, and are thought by Bowen (pers. comm. 1978) to be p a r t of a deeper or separate ore body. C h a l c o p y r i t e commonly occurs as 0.5 t o 3 mm rounded to s t e l l a t e d d i s s e m i n a t i o n s , and i s l e s s abundant as veins and v e i n l e t s , which may a l s o c o n t a i n quartz ( F i g . . 4 . 4 ) . Numerous i n t e r v a l s hosted c h a l c o p y r i t e i n s e v e r a l separate modes o f occurrence ( i . e., as v e i n s and d i s s e m i n a t i o n s , or as patches and v e i n s , e t c . ) . &s observed i n p o l i s h e d s e c t i o n , d i s s e m i n a t i o n s of c h a l c o p y r i t e are g e n e r a l l y the r e s u l t of d i l a t i o n or 1 6 0 H 16CH 1 4 0 - 4 1 4 0 H 1 2 0 H 1 2 0 H 1 0 0 1 0 0 8 0 - 80H o c ca cr 6 0 H ^ 40H 6 0 H 4 0 - 2CH 2 0 - 1 6 7 8 1 2 3 7 8 C H A L C O P Y R I T E intensity C H A L C O P Y R I T E m o d e F i g u r e 4.4: Bar graphs o f the ranked i n t e n s i t y o f c h a l c o p y r i t e , and i t s mode"of"occurrence r e c o r d e d f o r each 3m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s from 1= t r a c e to 9= extreme; mod i n c r e a s e s from 1= v e i n s to 9= d i s s e m i n a t e d (see Appendix B f o r more d e t a i l ) . 66 i n t e r s e c t i o n s of m i c r o v e i n l e t s , and l e s s commonly as i s o l a t e d g r a i n s , commonly i n a l t e r e d mafic minerals (Plate 4.1). C h a l c o p y r i t e occurs with disseminated p y r i t e g r a i n s , and occurs as 0.01 to 0.05 mm i n c l u s i o n s i n magnetite. During the course of f i e l d work a strong p o s i t i v e e m p i r i c a l r e l a t i o n s h i p between- the abundance of c h a l c o p y r i t e m i n e r a l i z a t i o n and of b i o t i t e and K - f e l d s p a r a l t e r a t i o n was observed. T h i s r e l a t i o n s h i p was e s p e c i a l l y d i s c e r n i b l e where a l t e r a t i o n f a c i e s changed over s h o r t i n t e r v a l s . . S t a t i s t i c a l s t u d i e s (Chapter V) emphasize these r e l a t i o n s h i p s , a l l of which have been d e s c r i b e d i n the l i t e r a t u r e (Norton, 1972; Creasey, 1966; and Carson and Jamb-or, 1977). 4.3.2 Molybdenite I t i s d i f f i c u l t to estimate molybdenite i n t e n s i t y i n hand sample because of i t s g e n e r a l l y low abundance. However, a d e f i n i t e s p a t i a l z o n a t i o n of molybdenite i s shown i n S e c t i o n s A" A' and B-B" (F i g s . 4.1, 4.2, and 4.3; and Map B). Molybdenite, l i k e c h a l c o p y r i t e , i s s p a t i a l l y a s s o c i a t e d with p o t a s s i c a l t e r a t i o n m i n e r a l s , but a l s o has a s t r o n g e m p i r i c a l c o r r e l a t i o n with quartz v e i n s . Molybdenite i s l a r g e l y r e s t r i c t e d t o guartz veins ( F i g . 4.5), and i s commonly e i t h e r "ribboned" (see Wallace, e t a l . , 1978), which c o n s i s t s of a l t e r n a t i n g l a y e r s of guartz and 67 P l a t e 4 . 1 : P h o t o m i c r o g r a p h (30 X) s h o w i n g a n h e d r a l g r a i n s o f d i s s e m i n a t e d c h a l c o p y r i t e ( y e l l o w ) w i t h v e r y s m a l l s p o t s o f mag- n e t i t e ( w h i t e ) l o c a t e d on t h e s i t e o f a c h l o r i t i z e d (?) b i o t i t e p h e n o c r y s t . 160 H 1 4 0 H 210 H p o - i s o n 100- 1 5 0 H 8 0 H >> o c « 60H 1 2 0 - 90- 40- 60H 2 0 H 3 0 H 1 2 3 4 5 6 7 8 9 M O L Y B D E N I T E intensity 1 2 3 4 5 6 7 8 9 M O L Y B D E N I T E m o d e F i g u r e 4 . 5 : B a r g r a p h s o f t h e r a n k e d i n t e n s i t y o f m o l y b d e n i t e , a n d i t s m o d e o f o c c u r r e n c e , c o r d e d f o r e a c h 3 m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s f r o m 1 = t r a c e t o 9 = e x t r e m e ; m o d e c r e a s e s f r o m 1 = v e i n s t o 9 = d i s s e m i n a t e d ( s e e A p p e n d i x B f o r m o r e d e t a i l ) . 69 coarse g r a i n e d molybdenite, or occurs i n a dark coloured mixture of guartz and very f i n e grained molybdenite ( P l a t e 4 .2 ) . 4.3.3 B o r n i t e B o r n i t e , only r a r e l y observed i n d r i l l c o r e , occurs as f i n e g r a i n e d d i s s e m i n a t i o n s , a s s o c i a t e d with c h a l c o p y r i t e and l o c a l l y with s p e c u l a r hematite. I t occurs i n p o l i s h e d s e c t i o n as rims around t e t r a h e d r i t e i n c l u s i o n s i n c h a l c o p y r i t e and between c h a l c o p y r i t e and hematite g r a i n s ( P l a t e 4 . 3 ) . . 4-3.4 C o v e l l i t e C h a l c o p y r i t e and b o r n i t e ae observed i n d r i l l core to be very l o c a l l y t a r n i s h e d with a blue t o purple i r i d e s c e n t c o a t i n g of c o v e l l i t e . In p o l i s h e d s e c t i o n c o v e l l i t e i s i n c o n t a c t with c h a l c o p y r i t e along g r a i n boundaries and f r a c t u r e s . 4.3.5 T e t r a h e d r i t e T e t r a h e d r i t e was i d e n t i f i e d only once i n a hand sample of d r i l l c o r e . However, i n p o l i s h e d s e c t i o n t e t r a h e d r i t e appears to be more widespread. I t i s found as borders on, and i n c l u s i o n s i n , c h a l c o p y r i t e ( P l a t e 4.3). The presence of t e t r a h e d r i t e i n d i c a t e s t h a t s i l v e r might be a r e c o v e r a b l e by- product at the P o p l a r porphyry. 70 P l a t e 4.2: P h o t o m i c r o g r a p h (30 X) o f a molybdenite s e l v a g e i n a q u a r t z v e i n ; t h e edge o f a m o l y b d e n i t e v e i n i n t h e l o w e r l e f t c o r - n e r . 71 P l a t e 4.3: P h o t o m i c r o g r a p h (12 5 X) s h o w i n g i n t e r g r o w n b o r n i t e ( v i o l e t ) and c h a l c o p y r i t e ( y e l l o w ) d i s s e m i n a t i o n w i t h s m a l l r i m o f t e t r a h e d r i t e on t h e u p p e r r i g h t edge. 72 4.4 A l t e r a t i o n Mineralogy 4.4.1 P o t a s s i c A l t e r a t i o n Numerous names and m i n e r a l o g i c a l d e f i n i t i o n s have been given f o r the p o t a s s i c a l t e r a t i o n assemblages found i n porphyry d e p o s i t s throughout the world (g. v. Creasey,,1959 and 1966; Burnham, 1962; L o w e l l and G u i l b e r t 1970; Rose, 1972; and Gustafson and Hunt, 1S75). Based on chemical e q u i l i b r i a s t u d i e s by Hemley (1959) and Hemley and Jones (1964), Jambor and Beaulne (1978) have d e f i n e d p o t a s s i c a l t e r a t i o n a t the Highland V a l l e y , B r i t i s h Columbia, as c o n s i s t i n g of secondary K - f e l d s p a r and/or secondary b i o t i t e , e x c l u s i v e of a l l minerals c o n s i d e r e d e s s e n t i a l c o n s t i t u e n t s of other a l t e r a t i o n f a c i e s ( i . e., s e r i c i t e , and k a o l i n i t e ) . The assemblages K - f e l d s p a r ± b i o t i t e , and b i o t i t e ± K- f e l d s p a r are observed i n the f i e l d to be a s s o c i a t e d c l o s e l y with c h a l c o p y r i t e and l e s s e r molybdenite. Other m i n e r a l s commonly observed i n t h i s f a c i e s are magnetite, carbonate (mainly c a l c i t e ) and quartz (Plate 4.4). A t y p i c a l i n t e r v a l of p o t a s s i c a l t e r a t i o n i n d r i l l core i s shown g r a p h i c a l l y i n F i g u r e 4.6, which i s a bar graph of mineral abundances recorded f o r each 3 m i n t e r v a l of d r i l l c ore. Salmon pink o r t h o c l a s e i s the only potassium f e l d s p a r observed i n the d e p o s i t ( P l a t e s 4.5, and 4.6)., The m a j o r i t y of secondary K - f e l d s p a r occurs as envelopes around veins of q u a r t z , 73 P l a t e 4.4: E x a m p l e of p o t a s s i c a l t e r a t i o n . M a g n e t i t e v e i n i s s u r - r o u n d e d b y a K - f e l d s p a r e n v e l o p e w h i c h g r a d e s o u t t o p e r v a s i v e s e c o n d a r y b i o t i t e . A l a t e r c h a l c o p y r i t e v e i n c a n be s e e n o f f s e t t - i n g t h e m a g n e t i t e v e i n . B 1 3? rvi ht>Ji K - S P A P R TOT T Tp M U S C O V I T E C L A Y C A R B O N A T E A N H Y D R I T E P Y P I T E C H A L C O P Y M O L Y B D E N I T E 74 ~? ?„ 30 AO *0 fO T0 11<"» ! ?0 ! 3" 1 A l I AO 1 fcO 1 70 ! 90 1 PO ~510" 710 ?30 741 _? 51 7r>0 770 ? 00 7^0 IPO ~VO0~ 310 316 ? 71 ' 3 n 3 fti 170 3 <?0 7 Q-1 A n o " 6 1 0 ' A ?1 ift n i t O A 50 A57 4 70 4 RO 4 1 1 5 00 r jo H H M f ' M H H t l O i M U M H n 0 N M M u n ^ *j M U M H D M ~ " MM H O 5 M M. u u n o •.( M M M O ' M H H i r " M H!l'-»ni MM U H - 3 w U M W O O n M M H n s M U M M ° " M l i M u r ' S ij~ D X P C V * p yon v y P H p n q p p ^ P " ri r p M p o i i c " P ' j p n i i c T n r r n r p n n p n c D n p * 1 q c f > n p i » H P] p r " » c Pl_ P P ^ F n-ipD n c P ' I P f oc n v p n n F P ' J pn ; t F ~ P M P P R P D *j P o n p D * J P O (\ c P R P H F F L F ' l c o^pprycr- p 7 pp o r p o p p q p p n p p R P nnpof^F ** * ** * ***** ***** ***** ***** ***** •-#**— * * * * * * * * * * * * * * * * *. * * * * ** "•****" ** #* ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** ** ** * + * * * * * * "~* "* * * ** ** * * * * " * * * * " * * * ** * T * * * * * * * * ** **** * * * * * * * * * * * * * * * * * * * * * * * * ********* '"*** **• *** ** * * + * ******** * '" ******** *"' * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** ** ** * » - * * * * * * * * * * * *•* * * ""**•'** * * * * * * * * * * * * *•/.- * ** ** ** ** ** * * ** ** * * **** ** * * **** ** * * **** ** * * * * * * ' ** * * * * ***** **** ** * * * ** ***** **** ** * * * * ** ** ** * * * * *• ** ** * ** • +** *** ** * * *** *** ** * * + * ** ** * * * ** ** ** * * * * ** * **** *•• * * * *** **** *•« ***** **** * * * ***** • **** **' * ********* **** **** *** ** *•* ***** **** • *** **** *** ** *** ******* **** ** ** * ******* *+** ** ** * ******* ** ** ** ** ** ******* ** ** ** ~ ** ******** *** *** * * *** ******** *** ** * * * * ** ****** ** ** ** * ****** ** ** ** *** * ***** ** ** ** *** ******* ** ** ** *•* ******* ** ****** • * ** ** *** * **« ** ****** * ** ***** ** ******. * ** *** ** ** ***** * * ** ** * ****** ****** ** " * ****** * ***** ** * ****** '*•*** **** *** * ****** ***** * *** ***** *•** ******** * *** *** **» * • * ******** «*** * + * ** * * ** ****** ** + *'-**' * ****** ** * ** * ****** • * ** * ** ***** * * * * ** * * ** * ** ***** * ***** **** ** ** ** ****** **** *.* ** ** ****** ** * * ** ****** * ** ***** ****** ***** ** **** ** *** * * ***** ** **** ** ***** ******* ** *** ** ******* ** *** ** ****** ******* ** ** ** •* ****** ******* ** ** *** * F i g u r e 4.6: G r a p h i c l o g o f m i n e r a l i n t e n s i t y ( f r o m z e r o t o n i n e s t a r s ) f o r a l l m i n e r a l s r e c o r - d e d on P o p l a r l o g . T h i s i n t e r v a l i s f r o m d r i l l h o l e 24 and r e p r e s e n t s a t y p i c a l i n t e r v a l o f p o t a s s i c a l t e r a t i o n ( i . e. K - f e l d s p a r , and b i o t i t e ) . - j 75 1 W 1 w iff J 0 1 i 2 4 6 8 I l I 1 10 12 14 1 j C M P l a t e 4.5: E x a m p l e s of p o t a s s i u m f e l d s p a r e n v e l o p e s ( l e f t to r i g h t ) . K - f e l d s p a r s u r r o u n d s a q u a r t z v e i n and g r a d e s o u t i n t o a g r e e n s e r i c i t e e n v e l o p e ; K - f e l d s p a r e n v e l o p e s u r r o u n d i n g a q u a r t z - c h a l c o p y r i t e v e i n i s d e v e l o p e d i n p r e v i o u s p e r v a s i v e s e c o n d a r y b i o t i t e a l t e r a t i o n ; and a s i m i l a r s a m p l e t o t h e m i d d l e o n e , w h i c h h a s b e e n s t a i n e d t o show t h e n a t u r e o f t h e K - f e l d s p a r ( y e l l o w ) a l t e r a t i o n . P l a g i o c l a s e i s w h i t e . 76 r 4 P l a t e 4.6: K - f e l d s p a r a l t e r a t i o n o f p l a g i o c l a s e p h e n o c r y s t s i n an e n v e l o p e s u r r o u n d i n g a q u a r t z - c h a l c o p y r i t e v e i n . S c a l e i s i n c e n - t i m e t e r . 77 c h a l c o p y r i t e a n d c a r b o n a t e , a n d a s c o m b i n a t i o n s o f v e i n s a n d p e r v a s i v e o c c u r r e n c e s ( F i g . 4.7). T h e r e i s n o e m p i r i c a l c o r r e l a t i o n b e t w e e n v e i n m a t e r i a l o r w i d t h , a n d w i d t h o f t h e a s s o c i a t e d e n v e l o p e . O n e mm t o f i v e cm e n v e l o p e s a r e w e l l d e f i n e d i n i n t e r v a l s w h i c h a l s o c o n t a i n p e r v a s i v e s e c o n d a r y b i o t i t e . P e r v a s i v e s e c o n d a r y b i o t i t e i m p a r t s a d u s t y b r o w n t o j e t b l a c k c o l o u r t o t h e r o c k , d e p e n d i n g o n t h e i n t e n s i t y o f b i o t i t e a l t e r a t i o n ( P l a t e 4.7); e n v e l o p e s a n d p a t c h e s a r e o b s e r v e d l e s s o f t e n ( F i g . 4 . 8 ) . I n g e n e r a l , b i o t i t e i s m o s t a b u n d a n t i n i n t e v a l s o f l o w v e i n a n d f r a c t u r e d e n s i t i e s . . B i o t i t e p a t c h e s , l o c a l 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 d i s s e m i n a t i o n s , c o n s i s t o f o n e t o t h r e e cm w i d e s p o t s , p s e u d o m o r p h i c a f t e r m a f i c x e n o l i t h s . P e r v a s i v e b i o t i t e o c c u r s a s 0 . 0 5 mm t o 0 . 2 mm s u b h e d r a l t o a n h e d r a l p s e u d o m o r p h s a f t e r p r i m a r y b i o t i t e a n d h o r n b l e n d e ( P l a t e 4 . 8 ) . O p a q u e m i n e r a l s ( p y r i t e , c h a l c o p y r i t e , m a g n e t i t e , e t c . ) a r e c o m m o n l y a s s o c i a t e d w i t h t h e l a t t e r t y p e o f o c c u r r e n c e . M a g n e t i t e i s m o s t c o m m o n l y o b s e r v e d a s 0.1 t o 2 mm e u h e d r a l t o s u b h e d r a l d i s s e m i n a t e d g r a i n s a n d i n r a r e q u a r t z - m a g n e t i t e ± p y r i t e ± c h a l c o p y r i t e ± h e m a t i t e v e i n s . M a g n e t i t e i s 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 , i n b o t h d i s s e m i n a t i o n s a n d v e i n s ( P l a t e 4 . 9 ) . M a g n e t i t e a n d h e m a t i t e a r e b o t h f o u n d a s i n t e r g r o w t h s o r p s e u d o m o r p h s a f t e r p r i m a r y m a f i c m i n e r a l s a n d 8 0 n 7CH 60H 5 0 - 4 0 >, 3 0 - 1 o c a> => 2 0 H cr a> >- "~ ioH 160H 140H 120H 100- 8 0 H 6 0 - 4 0 - 2 0 " 3 4 5 6 7 8 9 3 4 5 6 7 8 K - F E L D S P A R intensity K - F E L D S P A R - m o d e Figure 4.7: Bar graphs of the ranked i n t e n s i t y of K-feldspar, and i t s mode of occurrence, r e- corded for each 3m i n t e r v a l of core. Intensity increases from 1= trace to 9= extreme; mode in- creases from 1= veins to 9= disseminated (see Appendix B for more d e t a i l ) . 00 7 9 P l a t e 4 . 7 : D u s t y d a r k b r o w n s e c o n d a r y b i o t i t e near t h e b o t t o m o f t h e s a m p l e i s o v e r p r i n t e d by a K - f e l d s p a r e n v e l o p e ( m i d d l e o f s a m p l e ) a d j a c e n t t o a s p l i t m o l y b d e n i t e v e i n ( m e t a l l i c g r e y i n u p p e r p o r t i o n o f s a m p l e ) . 40-1 80 H 35 H 70H 30H 60H 25H 5 C H >» CJ c <u cr 2 OH 1 5 H 40H 30' 10- 20H 10- 7 8 9 7 8 9 B I O T I T E i n tens i ty B I O T I T E m o d e F i g u r e 4.8: B a r g r a p h s o f t h e r a n k e d i n t e n s i t y o f b i o t i t e , a n d i t s mode o f o c c u r r e n c e , r e c o r - d e d f o r e a c h 3m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s f r o m 1= t r a c e t o 9= e x t r e m e ; mode i n - c r e a s e s f r o m 1= v e i n s t o 9= d i s s e m i n a t e d ( s e e A p p e n d i x B f o r more d e t a i l ) . 00 o 81 P l a t e 4.8: P h o t o m i c r o g r a p h (12 5 X) s h o w i n g d a r k i r r e g u l a r g r a i n s o f s e c o n d a r y b i o t i t e r e p l a c i n g p r i m a r y b i o t i t e p h e n o c r y s t . Opaque g r a i n s a r e m a g n e t i t e ( ? ) . 82 P l a t e 4.9: P h o t o m i c r o g r a p h (30 X) s h o w i n g i r r e g u l a r d i s s e m i n a - t i o n s o f c h a l c o p y r i t e ( y e l l o w ) and m a g n e t i t e ( w h i t e ) . 83 a s s o c i a t e d with secondary b i o t i t e . P o t a s s i c a l t e r a t i o n , was i n g e n e r a l the e a r l i e s t a l t e r a t i o n event at the Poplar porphyry. T h i s i s d i s c e r n i b l e where the d i a g n o s t i c mineral (s) of more than one a l t e r a t i o n f a c i e s are observed together. C r o s s - c u t t i n g r e l a t i o n s h i p s of veins and envelopes and replacement t e x t u r e s (S e c t i o n 4.4.2) i n d i c a t e t h a t p h y l l i c and a r g i l l i c f a c i e s are superimposed on rocks t h a t have undergone pr e v i o u s p o t a s s i c a l t e r a t i o n (Plate 4.10). L o c a l l y , however, p o t a s s i c and p h y l l i c a l t e r a t i o n are synchronous ( i . e., a guartz v e i n with a K - f e l d s p a r envelope grading i n t o a s e r i c i t e envelope; P l a t e 4.5). 4.4.2 P h y l l i c a l t e r a t i o n P h y l l i c a l t e r a t i o n i s the most abundant a l t e r a t i o n f a c i e s observed at the Poplar porphyry d e p o s i t (Map B; and F i g s . 4.1, 4.2, and 4.3); a f f e c t i n g t o some e x t e n t , almost every i n t e r v a l of c o r e . S e r i c i t e , p y r i t e and guartz are the most commonly observed mineral cf t h i s f a c i e s ( F i g . . 4 . 9 ) ; p e r v a s i v e carbonate a l t e r a t i o n a l s o i s commonly observed i n t h i n s e c t i o n . S e r i c i t e i s i n e q u i l i b r i u m with K - f e l d s p a r or k a o l i n i t e along u n i v a r i a n t l i n e s i n temperature-pH space (Hemley and Jones, 1964). Under other than u n i v a r i a n t c o n d i t i o n s these minerals are mutually e x c l u s i v e , consequently s e r i c i t e alone i s d i a g n o s t i c of t h i s a l t e r a t i o n f a c i e s . The term s e r i c i t e i s used 84 P l a t e 4.10: G r e e n and b rown s e r i c i t e e n v e l o p e s f r o m numerous v e i n l e t s and f r a c t u r e s i m p a r t a p e r v a s i v e a l t e r a t i o n t o t h e r o c k N o t e t h a t a s m a l l p o r t i o n w h i c h had u n d e r g o n e p r e v i o u s p o t a s s i c a l t e r a t i o n r e m a i n s . C i^Mr i cpTH5nrK T ' Y ' ' c OUA°TJ K-SP4» R i n T I T P MUSCOVITE CLAY CARBONXTE ANHYORlTE PYRITE CH4LCOPV MOLYBDENITE 1 3' ^ 7n S«n «• on 7^n pp QFUp no n c y p p | n p e< F nj_ p o q p r»• I PP " r 7*11 7_v) 7 7 0 7 RO **90 o nn 0 1 0 H7T ? ?0" 940 R c 1 B"»0 P q ' i "rt 90 901 OI0 0 ? i 0 3 0 0 4 0 Q50~ 9^0 9 30 1 r no Tf 04" p M D D n p PI or»n c D i_ o r» n F 0| ppf^c P ( p p q c o nnp q F ' f-norj P F - " PI or>;»c P| Ppn.F pn pn ap P1PPP.F pnpn 'n C — P 1 P O r \ c p n p p n p o n p p n c r r o r q c D1Ri>qc P ^ P M l ! " p n o n q p on 00 q p pp PDrt C pn P P n c n p p ^ c p^pTTqP P O P f ' T F p n p n q c pn D P ^ c n n p t ' i r P»| P p q F rinop'ii! ** 4* ** ** * * *** ***** * * *** ** + * *c • * * *TV * * * * * * * • * * * * * *fr ** ** * * * * * * * * * * * * * * ** ** **** **** ** ** **** ~ * * i r * ~ * * * * * * ** * * * * * * * * * * * * * • * * * ** •* •** * * * * " * >Y * ***** ***** *****" ***** * * * * * * * * * * * * ** ** ** ** ** ** ** *•* ** •* **** **** *** *** *** *** *** ** • ** ** * * **** *** *** *** * "'•"•"** **** •*• * ***** ***** **** **** ***** ***** **** ***• * * ** * * * **** ™* *** ***** ***** * * ** **** **** **** ** ** ** * ** * ** * * * * * "*"* * * * * * * * * * * * * * * * * * * * * * * * * * * * *** *** * * ** ** » * * * ** ** * * * * * * * * * — * * * * * ~ ~ *** ** ***** *** * • *• * * * * * ~*v • ** *** *** *** *•* ** ** F i g u r e 4.9: G r a p h i c l o g o f m i n e r a l i n t e n s i t y ( f r o m z e r o t o n i n e s t a r s ) f o r a l l m i n e r a l s r e c o r - d e d o n P o p l a r l o g . T h i s i n t e r v a l i s f r o m d r i l l h o l e 32 and r e p r e s e n t s a t y p i c a l i n t e r v a l o f p h y l l i c a l t e r a t i o n . 0 0 86 here to d e s c r i b e f i n e grained secondary muscovite, a f t e r Hurlbut (1971), Jambor and Delabio (1978), and Lowell and G u i l b e r t (1970). The mineral i s i d e n t i f i e d i n hand specimen by l i g h t l y s c a t c h i n g the s u r f a c e of a sample with a needle; a r e s u l t a n t " s i e e n " i s i n d i c a t i v e of s e r i c i t e . Clay minerals on the other hand, produce a d u l l e a r t h l y s c r a t c h . I f both minerals are present d i s t i n c t i o n i s d i f f i c u l t . h b i n o c u l a r microscope f a c i l i t a t e d f i e l d i d e n t i f i c a t i o n . S e r i c i t e occurs as a p e r v a s i v e a l t e r a t i o n with l e s s commonly observed envelopes and patches (Fig. 4.10). P e r v a s i v e s e r i c i t e a l t e r a t i o n occurs; as (1) pseudomorphic replacement a f t e r b i o t i t e and hornblende phenocrysts and i s commonly a s s o c i a t e d with p y r i t e , carbonate, and c h l o r i t e ; (2) as an a l t e r a t i o n of f i n e g r a i n e d 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 i n the groundmass, which imparts a p e r v a s i v e b l e a c h i n g t o the rock, and (3) as a l i g h t green to white s e l e c t i v e a l t e r a t i o n o f p l a g i o c l a s e phenocrysts. The l a t t e r type of occurrence has the g r e a t e s t a f f e c t on the a l t e r a t i o n i n t e n s i t y recorded, s i n c e the v o l u m e t r i c i n t e n s i t y of a l t e r a t i o n i s dependent on the o r i g i n a l p l a g i o c l a s e abundance i n the rock. P l a g i o c l a s e and b i o t i t e phenocrysts and are the most s u s c e p t i b l e to p h y l l i c a l t e r a t i o n (commonly a l t e r e d i n an otherwise f r e s h rock) f o l l o w e d by p l a g i o c l a s e , b i o t i t e and K - f e l d s p a r i n the groundmass (Plate 4.11). In zoned p l a g i o c l a s e s e r i c i t e s e l e c t i v l y a l t e r s p a r t i c u l a r zones, e i t h e r s i n g u l a r l y or with a s s o c i a t e d carbonate and c l a y (Plate 4.12).. Envelopes of s e r i c i t e , q u a r t z , and 16CH 640H 140- 560 A 1 2 0 H 480 H 100H 400H 80H 320-^ >> o c. CT 0> 60- 40H 240H 160- 20- 80 H 6 7 8 9 S E R I C I T E i n t e n s i t y S E R I C J T E 6 7 8 9 m o d e F i g u r e 4 . 1 0 : B a r g r a p h s o f t h e r a n k e d i n t e n s i t y o f s e r i c i t e , a n d i t s m o d e o f o c c u r r e n c e , r e - " c o r d e d f o r e a c h 3m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s f r o m 1= t r a c e t o 9= e x t r e m e ; m o d e i n c r e a s e s f r o m 1= v e i n s t o 9= d i s s e m i n a t e d ( s e e A p p e n d i x B f o r m o r e d e t a i l ) . 88 P l a t e 4.11: T h r e e e x a m p l e s o f p h y l l i c a l t e r a t i o n . L e f t : s e r i c i t i - z a t i o n o f b i o t i t e p h e n o c r y s t s ( b r o w n , l i n o n i t e p a t c h e s ) a n d p l a - g i o c l a s e p h e n o c r y s t s ( b l e a c h e d ) ; m i d d l e : e x t r e m e p e r v a s i v e p y r i t e - s e r i c i t e - q u a r t z b l e a c h i n g . P y r i t e a n d q u a r t z v e i n l e t s c r o s s t h e s a m p l e , s e r i c i t e b l e a c h e s p l a g i o c l a s e p h e n o c r y s t s and g r o u n d m a s s ; r i g h t : s e r i c i t e e n v e l o p e a f f e c t s o n l y p l a g i o c l a s e p h e n o c r y s t s , a r o u n d a K - f e l d s p a r e n v e l o p e and q u a r t z v e i n . 89 P l a t e 4.12: P h o t o m i c r o g r a p h (30 X) shov/ing s e l e c t i v e a l t e r a t i o n o f z o n e d p l a g i o c l a s e a l o n g s p e c i f i c c o m p o s i t i o n a l z o n e s . F i n e g r a i n e d m a t e r i a l c o n s i s t s o f s e r i c i t e and c a r b o n a t e . H i g h l y b i - r e f r i n g e n t m i n e r a l a t l o v ; e r l e f t i s h o r n b l e n d e . 90 p y r i t e range i n width from l e s s than one mm up to tens o f cen t i m e t e r s . Quartz and q u a r t z - p y r i t e veins are most commonly a s s o c i a t e d with s e r i c i t e envelopes. Greenish one to 15 mm patches of s e r i c i t e , g e n e r a l l y with guartz surrounding a p y r i t e nucleus are formed from the a l t e r a t i o n of mafic phenocrysts or x e n o l i t h s . In t h i n s e c t i o n s e r i c i t e g e n e r a l l y i s l e s s abundant then had been recorded i n the f i e l d , and i s more commonly a s s o c i a t e d with c l a y and carbonate than had been thought d u r i n g core l o g g i n g . Quartz i s the most widespread and abundant a l t e r a t i o n mineral i n the d e p o s i t , and occurs at l e a s t l o c a l l y , with a l l other a l t e r a t i o n m i n e r a l s ; however, i t i s most commonly observed with s e r i c i t e and p y r i t e . Quartz i s l a r g e l y c o n f i n e d to v e i n s , combinations of veins and patches, and patches and envelopes ( F i g . 4.11). Quartz v e i n i n g i s the most important c r i t e r i o n a f f e c t i n g the d i s t r i b u t i o n and mode of occurrence of other a l t e r a t i o n m inerals; veins of quartz are commonly surrounded by K - f e l d s p a r and/or s e r i c i t e envelopes. L o c a l l y q uartz extends outwards from v e i n s t c form p e r v a s i v e l y s i l i c i f i e d rock. Quartz a l s o occurs i n ve i n s c o n t a i n i n g p y r i t e , molybdenite, c h a l c o p y r i t e and l o c a l l y s p e c u l a r i t e and magnetite. P y r i t e i s the most abundant and widespread s u l f i d e at the Poplar porphyry and i s observed i n almost a l l i n v e r v a l s of core. P y r i t e has a bimodal mode of occurrence. F i g u r e 4.12 400- 140 + 3 5CH 120H 300H 100 1 2 5 0 - >> o 80 2 0 0 - Z3 cr <x> GOH - 4 C H 150H 100- 20-i 50- 6 7 8 6 7 8 Q U A R T Z i n t e n s i t y Q U A R T Z m o d e F i g u r e 4.11: Bar graphs o f the ranked i n t e n s i t y o f q u a r t z , and i t s mode o f o c c u r r e n c e , r e ded f o r each 3m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s from 1= t r a c e to 9= extreme; mode i cre a s e s from 1= v e i n s to 9= d i s s e m i n a t e d (see Appendix B f o r more d e t a i l ) . 9Z i l l u s t r a t e s t h a t p y r i t e occurs e i t h e r as patches, and combinations of patches and v e i n s , or as di s s e m i n a t i o n s . P y r i t e i s ccmmonly observed on the s i t e s of a l t e r e d mafic minerals and l e s s commonly as patches r e p l a c i n g mafic x e n o l i t h s . P y r i t e may c o n t a i n intergrowths cf both c h a l c o p y r i t e and b o r n i t e . Specular hematite i s a s s o c i a t e d with both p h y l l i c and p o t a s s i c a l t e r a t i o n . However, because magnetite i s much more abundant i n p o t a s s i c a l t e r a t i o n , hematite i s probably an o x i d i z e d product of magnetite i n the p h y l l i c a l t e r a t i o n f a c i e s which i s observed to have been superimposed on pr e v i o u s p o t a s s i c a l t e r a t i o n . Hematite occurs as one mm d i s s e m i n a t i o n s , and with guartz and c a l c i t e i n v e i n s . C a l c i t e and l e s s e r s i d e r i t e and dolomite were observed i n d r i l l c o r e , mainly as ve i n s and v e i n l e t s and l e s s commonly as pe r v a s i v e a l t e r a t i o n of p l a g i o c l a s e phenocrysts, with c l a y and s e r i c i t e . Carbonate veins are a s s o c i a t e d with p y r i t e and minor c h a l c o p y r i t e . P e r v a s i v e c a l c i t e a l t e r a t i o n observed i n t h i n s e c t i o n i s a s s o c i a t e d with s e r i c i t e , c l a y and c h l o r i t e o c c u r r i n g as subhedral to anhedral c r y s t a l s and patches on a l t e r e d p l a g i o c l a s e and hornblende phenocrysts. Carbonate observed i n t h i n s e c t i o n shows i t to be more abundant than had o r i g i n a l l y been thought d u r i n g the f i e l d study. In p a r t i c u l a r carbonate i s s t r o n g l y a s s o c i a t e d i n t h i n s e c t i o n with s e r i c i t e and c l a y . Gypsum and l e s s e r a n h y d r i t e , i s widespread and l o c a l l y 160H 160H M O - M O - 120 H 120H 100H 100- o c Q) cr a> 80 H 60- 4 0 H 20- 80- 60- 4 0 H 20- -| 2 3 4 5 6 7 8 9 PYRITE intensity 2 3 4 5 6 7 8 9 PYRITE mode F i g u r e 4.12: Bar graphs o f the ranked i n t e n s i t y o f p y r i t e , and i t s mode o f o c c u r r e n c e , r e c o r - ded f o r each 3m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s from 1= t r a c e to 9= extreme; mode i n - cre a s e s from 1= v e i n s to 9= d i s s e m i n a t e d (see Appendix B f o r more d e t a i l ) . 94 abundant i n the d e p o s i t , o c c u r i n g i n v e i n s , averaging one cm wide. Although gypsum i s widespread, and found w i t h i n the p o t a s s i c zone, i t i s most s t r o n g l y a s s o c i a t e d with p h y l l i c a l t e r a t i o n . Gypsum i s c h a r a c t e r i s t i c a l l y white t o pink and v a r i e s from a d u l l massive t r a n s l u c e n t v a r i e t y t o a r a r e c l e a r euhedral v a r i e t y , with c r y s t a l s up to f i v e cm a c r o s s . Veins of gypsum are commonly vuggy and l o c a l l y a s s o c i a t e d with quartz and c a l c i t e . P y r i t e i s a commonly a s s o c i a t e d m i n e r a l . P h y l l i c a l t e r a t i o n i s c l o s e l y a s s o c i a t e d with veins and f r a c t u r e s , and although s e r i c i t e g e n e r a l l y occurs as a p e r v a s i v e a l t e r a t i o n i t i s almost always a s s o c i a t e d with q u a r t z , gypsum or p y r i t e v e i n i n g , or barren f r a c t u r e s . . Much of pervasive s e r i c i t i c a l t e r a t i o n i s the r e s u l t of o v e r l a p p i n g envelopes. Some of the most i n t e n s e p h y l l i c a l t e r a t i o n o ccurs on both s i d e s of the c o n t a c t between b i o t i t e porphyry and Skeena Group r o c k s . 4.4.3 A r g i l l i c A l t e r a t i o n A r g i l l i c a l t e r a t i o n i s r e s t r i c t e d i n d i s t r i b u t i o n and o n l y l o c a l l y i s i n t e n s e l y developed. C l a y i s the d i a g n o s t i c m i n e r a l of t h i s f a c i e s ; however no d i s t i n c t i o n could be made i n the f i e l d between d i f f e r e n t c l a y m i n e r a l s . Carbonate and q u a r t z are a s s o c i a t e d minerals i n the a r g i l l i c f a c i e s . The most abundant and continuous occurrence of c l a y i s found i n the upper p o r t i o n of d r i l l hole 23 and i n i n t e r v a l s of extremely sheared rock i n d r i l l hole 3 (Map B). 95 Clay i s i n d e n t i f i e d i n hand sample by a t a c k i n e s s to the tongue, an a r g i l l a c e o u s odor, the l a c k of a sheen when s c r a t c h e d with a needle, and by a pock-marked appearance i n d r i l l core due to i t s removal by d r i l l i n g f l u i d s ( F i g . 4.13). P l a g i o c l a s e phenocrysts were the most s u s c e p t i b l e to a r g i l l i c a l t e r a t i o n ( P l a t e s 4.13). Clay forms extremely f i n e grained patches of low b i r e f r i n g e n c e and low r e l i e f . Limonite may l o c a l l y occur as a dark brown to opaque high r e l i e f s t a i n with c l a y minerals to form a dusty or clouded appearance i n t h i n s e c t i o n . Samples of d r i l l c o r e , s e l e c t e d from i n t e r v a l s where c l a y was recorded on P o p l a r l o g i n the f i e l d were analyzed by X-ray d i f f r a c t i o n techniques t o a s c e r t a i n the type of c l a y minerals present (c. f . Godwin, 1976). K a o l i n i t e was i d e n t i f i e d i n every sample analyzed; i l l i t e was detected i n only one sample. S e r i c i t e , b i o t i t e , and c h l o r i t e were l o c a l l y recorded i n a d d i t i o n t o k a c l i n i t e . No p y r o p h y l l i t e was d e t e c t e d . 4. 4. 4 P r o p y l i t j c , A l t e r a t i o n P r o p y l i t i c a l t e r a t i o n was never observed i n d r i l l c o r e , nor was i t obvious i n s u r f a c e samples, because of i t s low i n t e n s i t y and l i m i t e d occurrence. Epidote i s the d i a g n o s t i c mineral of t h i s f a c i e s ^ but c h l o r i t e , carbonate and a l b i t i z e d p l a g i o c l a s e are a l s o observed. 6 0 H 45- 1 2 0 H 1 0 0 H <_> c a> z> cr a> 30H 80H 60 H 15 40H 2 0 H 7 8 9 6 7 8 9 C L A Y intensity C L AY mode F i g u r e 4 . 1 3 : B a r g r a p h s o f t h e r a n k e d i n t e n s i t y o f c l a y , a n d i t s m o d e o f o c c u r r e n c e , r e c o r d e d f o r e a c h 3 m i n t e r v a l o f c o r e . I n t e n s i t y i n c r e a s e s f r o m 1 = t r a c e t o 9 = e x t r e m e ; m o d e i n c r e a s e s f r o m 1 = v e i n s t o 9 = d i s s e m i n a t e d ( s e e A p p e n d i x B f o r m o r e d e t a i l ) . P l a t e 4.13: A r g i i l i c a l t e r a t i o n f r o m t h e c e n t r a l a r g i i l i c z o n e , b l e a c h e d t o k a o l i n i t e . G r e e n i s h b i o t i t e r e m a i n s f r e s h . i n t h e b i o t i t e q u a r t z m o n z o n i t e P h e n o c r y s t s o f p l a g i o c l a s e a r e p a t c h e s a r e s e r i c i t e . N o t e t h a t 98 Epidote occurs i n hornblende phenocrysts and as 0.1 to 0.5 mm subhedral intergrowths with a l b i t i z e d p l a g i o c l a s e phenocrysts (Plate 4.14) . C h l o r i t e i s the most abundant p r o p y l i t i c a l t e r a t i o n m i n e r a l , but i t i s a l s o observed i n other f a c i e s ( i . e. a r g i l l i c ) and i s t h e r e f o r e not d i a g n o s t i c . I t occurs as i n t e r g r o w t h s i n b i o t i t e and hornblende developed p a r a l l e l to o r i g i n a l cleavage or along rims. 4. 4. 5 Secondary, A l t e r a t i o n The g e n e r a l p a u c i t y of c l a y m i n e r a l s i n d r i l l core compared to l o c a l l y moderate to h i g h abundances i n s u r f i c i a l r o c k s , and the l o c a l i z a t i o n o f c l a y i n zones of r e l a t i v e l y high p e r m e a b i l i t y near f a u l t zones suggests t h a t much a r g i l l i c a l t e r a t i o n i s secondary, and p o s s i b l y supergene, i n o r i g i n . The c l o s e s p a t i a l r e l a t i o n s h i p between t h i s c e n t r a l a r g i l l i c a l t e r a t i o n zone and the major north-northwest t r e n d i n g Canyon Creek f a u l t i s f u r t h e r evidence f o r a secondary o r i g i n t o t h i s a l t e r a t i o n due to a l o c a l l y h i g h e r p e r m e a b i l i t y . However the d i f f e r e n t i a t i o n of c l a y s d e r i v e d by supergene processes from c l a y s d e r i v e d from hypogene processes i s d i f f i c u l t (Rose, 1970; Creasy, 1966; and Godwin, 1976). The g e n e r a l l a c k of i n t e n s e a r g i l l i c a l t e r a t i o n at the p e r i p h e r y of the d e p o s i t , and i t s occurrence a t the c e n t e r , 9 9 P l a t e 4.14: P h o t o m i c r o g r a p h (30 X) o f p r o p y l i t i c a l t e r a t i o n i n t h e h o r n b l e n d e q u a r t z m o n z o d i o r i t e . H i g h l y b i r e f r i n g e n t m i n e r a l i s e p i d o t e i n a l t e r e d p l a g i o c l a s e g r a i n . G roundmass i s l a r g e l y c h l o r i t e a n d c l a y . 100 surrounded by a p o t a s s i c a l t e r a t i o n zone, i s c o n t r a r y to a l t e r a t i o n z o n a t i o n observed a t the other d e p o s i t and d e s c r i b e d i n the l i t e r a t u r e ( i . e. L o w e l l and G u i l b e r t , 1970; Drummond and Godwin, 1976; Eose, 1970; and Helgeson 1972). T h i s i s e s p e c i a l l y so, s i n c e no supergene s u l f i d e o r oxide minerals are present with the inten s e a r g i l l i c a l t e r a t i o n . T h e r e f o r e t h i s c e n t r a l a r g i l l i c a l t e r a t i o n zone was formed e i t h e r by a l a t e stage hydrothermal event which a f f e c t e d only those l o c a t i o n s adjacent to areas of higher p e r m e a b i l i t y such as the Canyon Creek f a u l t ; or from supergene processes which would have used the same permeable channels. Based only on the d i s t r i b u t i o n of a l t e r a t i o n f a c i e s which are present i n rocks which host m i n e r a l i z a t i o n at the Poplar porphyry t h i s second a l t e r a t i o n event c o u l d be e i t h e r supergene or hypogene i n o r i g i n . However, s i n c e many pos t - o r e dykes are a l s o a l t e r e d {i. e. 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 phenocrysts i n the p o r p h y r i t i c d a c i t e , and c h l o r i t i z a t i o n of b i o t i t e i n the p o r p h y r i t i c r h y o l i t e ) the s o l u t i o n s which a l t e r e d these rocks must have been r e l a t i v e l y warm and had a r e l a t i v e l y low pH. Since t r a c e s of unoxidized and u n a l t e r e d p y r i t e and c h a l c o p y r i t e are observed i n the c e n t r a l a r g i l l i c core of the deposit the second a l t e r a t i o n event was most l i k e l y not supergene i n o r i g i n , or secondary copper minerals would be expected ( i . e. c o v e l l i t e , c h a l c o c i t e , c u p r i t e , e t c . ) . Therefore t h i s a l t e r a t i o n episode i s c o n s i d e r e d to be hypogene i n nature and may i n f a c t be r e l a t e d to the i n t r u s i o n of the dykes themselves which would have l o c a l l y r a i s e d the temperature of the Popl a r Stock, or t o the o v e r l y i n g Ootsa Lake Group v o l c a n i c s , which cap the d e p o s i t . 101 4.5 Chemical Aspects of 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 Zoning 4.5.1 General Statement The three c r i t e r i a f o r determining the s t a b i l i t y of a mineral or mineral assemblage i n an agueous system are: p r e s s u r e , temperature and chemical p o t e n t i a l (or a c t i v i t y r a t i o ) of a l l components (Gibbs, 1873). In t h i s s e c t i o n the z o n a t i o n observed at the P o p l a r porphyry w i l l be d i s c u s s e d i n terms of these v a r i a b l e s . 4. 5. 2 D i s c u s s i o n The g e n e r a l i z e d chemical r e a c t i o n s which best c h a r a c t e r i z e the mineralogy of s p e c i f i c a l t e r a t i o n zones, based on m i n e r a l s observed i n hand and t h i n s e c t i o n and the d i s t r i b u t i o n of these zones, i n c l u d e : (4.1) P l a g i o c l a s e +K+ = O r t h o c l a s e • (Na«-,Ca+ + ) (4.2) Annite + Mg++ = Phlogopite + Fe++ (4.3) O r t h o c l a s e + H+ = S e r i c i t e + Quartz + K+ (4.4) P l a g i o c l a s e + H* + CC 2 + K+ = S e r i c i t e + Carbonate + Na+ + Quartz (4.5) Muscovite • H+ = K a o l i n i t e + K+ (4.6) A n o r t h i t e • H+ + CCL = K a o l i n i t e 102 + Carbonate + Quartz (4.7) A n o r t h i t e + COz * Quartz + Na+ = A l b i t e + Carbonate (4.8) Hornblende + CO^ = C h l o r i t e + Carbonate (4.9) A n o r t h i t e + H+ = Epidote + H 20 + Quartz These chemical r e a c t i o n s are g e n e r a l i z e d and are used only to help account f o r many of the m i n e r a l r e l a t i o n s h i p s observed i n hand sample and t h i n s e c t i o n . Products of the r e a c t i o n s are observable a l t e r a t i o n minerals ( i . e. carbonate and s e r i c i t e a f t e r p l a g i o c l a s e ) , and r e a c t a n t s can be i d e n t i f i e d l o c a l l y from pseudomorphs (i. e. c h l o r i t e a f t e r hornblende) , or as a remaining p a r t of a primary m i n e r a l which d i d not r e a c t (see d e t a i l e d t h i n s e c t i o n d e s c r i p t i o n s i n Appendix D). Microprobe analyses of b i o t i t e s was beyond the scope of t h i s study, however r e c t i o n s (4.2) i s probable f o r the d e p o s i t based on s t u d i e s o f b i o t i t e s frcm North America porphyry d e p o s i t s by Beane (1974). Reactions (4.1) and (4.2) occur w i t h i n the p o t a s s i c a l t e r a t i o n f a c i e s ; (4.3) and (4.4) occur w i t h i n the p h y l l i c f a c i e s ; (4.5) and (4.6) c h a r a c t e r i z e d the a r g i i l i c f a c i e s and (4.7) , (4.8) ' and (4.9) d e f i n e the p r o p y l i t i c f a c i e s ; • - 103 The r e c t i o n s (4.3) t o (4.6) and (4.9) are h y d r o l y t i c r e a c t i o n s (Hemley, 1964) , that i s , they i n v o l v e the consumption of H+ and the consequent r e l e a s e of a c a t i o n ( i i e. K +,Ca + +,Na+). Numerous authors (e. g,. Helgeson, 1970; L o w e l l and G u i i b e r t , 1970; Hemley, 1959; Hemley and Jones, 1964; and Rose, 1970), have suggested t h a t the t y p i c a l p o t a s s i c to p h y l l i c t o a r g i l l i c to p r o p y l i t i c a l t e r a t i o n observed at many porphyry d e p o s i t s are due to v a r i o u s degrees of h y d r o l y t i c a l t e r a t i o n . Helgeson (1970) has suggestd that a l t e r a t i o n p a t t e r n s at porphyry d e p o s i t s are compatible with a c i d i c s o l u t i o n s e n t e r i n g the margin of a p l u t o n and r e a c t i n g with host and country rocks, becoming l e s s a c i d i c with d i s t a n c e t r a v e l l e d inwards towards the c o r e . As the f l u i d r i s e s , due to t h e r m a l l y induced g r a v i t a t i o n a l i n s t a b i l i t y (Norton and Knight, 1977), i t c o o l s and may p r e c i p i t a t e s u l f i d e s (Helgeson, 1964), thereby r e d u c i n g s o l u t i o n pH, which promotes f u r t h e r a c i d i c a t t a c k at shallow depths producing p h y l l i c and a r g i l l i c a l t e r a t i o n zones above the d e p o s i t as w e l l as along i t s margins (Helgeson, 1970). I m p l i c i t i n t h i s and s i m i l a r models ( i . e. Norton, 1972; Norton and Knight, 1977; Norton and Knapp, 1977; V i l l a s and Norton, 1977; C a t h l e s , 1977; Cunningham, 1978) i s t h a t f l u i d flow i s f r e e and p e r m e a b i l i t y i s symmetrical and i s o t r o p i c . F i g u r e 4.14 i s a mineral s t a b i l i t y diagram a f t e r Hemley and Jones (1964), Hemley (1959), and Hemley, Meyers, and R i c h t e r 104 F i g u r e 4.14: U n i v a r i a n t s t a b i l i t y r e l a t i o n s i n t h e s y s t e m Al„0_.- ( K 2 0 , N a o 0 ) - S i O , - H 2 0 ( a f t e r H e m l e y , e t a l . , 1 9 6 0 ) . C i r c l e d n u m b e rs r e p r e s e n t c h e m i c a l e q u a t i o n s ; p o s s i b l e m e c h a n i s m s a r e d i s - • c u s s e d i n t h e t e x t , t o i n h i b i t a f l u i d f r o m e n t e r i n g t h e K a o l i n i t e S t a b i l i t y f i e l d . T o t a l p r e s s u r e = 1 k b . 105 (1961); with the ' d i r e c t i o n ' t h a t a f l u i d packet, belonging t o on the f l u i d p a t h l i n e i n F i g u r e 4.15, takes from p o t a s s i c to a r g i i l i c a l t e r a t i o n f a c i e s i n d i c a t e d by an arrow. Superimposed on the diagram are numbered r e a c t i o n s (4.3) to (4.6). k schematic diagram of a porphyry type hydrothermal system with c o n v e c t i v e path l i n e s , a f t e r Norton and Knight (1977), i s shown i n F i g u r e 4.15. Numbered r e a c t i o n s (4.3) to (4.6) are p l a c e d at a p p r o p r i a t e p o s i t i o n s along the path l i n e s t o produce the a l t e r a t i o n zoning observed a t ' t y p i c a l ' porphyry d e p o s i t s . The l a c k of hydrothermal a r g i i l i c a l t e r a t i o n at the Poplar porphyry may be due to one or more of the f o l l o w i n g reasons (F i g . 4. 14) : (1) the o r i g i n a l groundwater may not have had a s u f f i c i e n t l y low pH to b r i n g p l a g i o c l a s e or K - f e l d s p a r i n t o the k a o l i n i t e s t a b i l i t y f i e l d ; (2) i s o t r o p i c p e r m e a b i l i t y along f a u l t s and j o i n t s may have r e s t r i c t e d groundwater to c e r t a i n areas of the d e p o s i t ; and (3) the temperature of the i n t r u s i o n and surrounding r o c k s may have been high enough t o keep f e l d s p a r i n the muscovite s t a b i l i t y f i e l d ( F i g . 4. 14) f o r most of the hydrothermal event, and then a r a p i d c o o l i n g and guick c e s s a t i o n of t h e r m a l l y induced h y d r o l o g i c flow, with the m a j o r i t y of the d e p o s i t spending l i t t l e or any of i t s time i n the k a o l i n i t e s t a b i l i t y f i e l d , u n t i l the second a l t e r a t i o n event. Reactions (4.1), (4.4) and (4.7) i n v o l v e potassium and/or 106 F i g u r e 4.15: S c h e m a t i c d i a g r a m o f f l u i d p a t h l i n e s a d j a c e n t t o a h o t p o r p h y r y t y p e i n t r u s i o n ( a f t e r N o r t o n , , a n d K n i g h t , 1977) . C i r c l e d numbers r e f e r t o c h e m i c a l e q u a t i o n s r e f e r e n c e d i n t h e t e x t and F i g u r e 4.14; d o t t e d l i n e s a r e i s o t h e r m s . 107 sodium metasomatism. A l t e r n a t i v e l y (4.4), (4.6), (4.7) and (4.8) may i n v o l v e an i n c r e a s e i n f ( C 0 2 ) . . The high r e l a t i v e a l k a l i a c t i v i t y of the s o l u t i o n , i m p l i c i t i n (4.1), (4.4) and (4.7), may i n part be due to the r e l e a s e of these c a t i o n s i n t o s o l u t i o n during h y d r o l y t i c a l t e r a t i o n . Norton (1977, F i g . 4) shows t h a t depending on rock p e r m e a b i l i t y and i n i t i a l p o s i t i o n of a " f l u i d packet" with r e s p e c t to the i n t r u s i o n , some f l u i d would indeed invade the already formed p o t a s s i c zone a f t e r t r a v e l l i n g through rocks that had undergone h y d r o l y t i c a l t e r a t i o n . However, mass balance c a l c u l a t i n s by Helgeson (1970), i n d i c a t e t h a t the a c t u a l m o l a l i t y of c a t i o n s i n s o l u t i o n remains e s s e n t i a l l y constant, and t h a t the high a l k a l i a c t i v i t i e s are i n s t e a d due to a decrease of up t o two o r d e r s of magnitude of hydrogen i o n . T h i s f i n d i n g has been s u b s t a n t i a t e d by Hemley and Jones (1964) who show t h a t the s t a b i l i t y of a p a r t i c u l a r mineral i s a f u n c t i o n of the " a c t i v i t y r a t i o " ( i . e. a (Na+)/a (H+)) r a t h e r than the a c t i v i t y of a s p e c i e s alone. Therefore a l k a l i metasomatism may occur e i t h e r by a r i s e i n the a l k a l i a c t i v i t y due to c a t i o n r e l e a s e d u r i n g h y d r o l y t i c a l t e r a t i o n , or more l i k e l y , a decrease i n a(H*) i n s o l u t i o n d u r i n g t h i s a l t e r a t i o n . Another source of a l k a l i s f o r p o t a s s i c or p r o p y l i t i c a l t e r a t i o n (4.1), (4.2) and (4.7), could be the i n t r u s i v e i t s e l f . A l k a l i s , water and s i l i c a are p a r t i t i o n e d to the l a t e s t v o l a t i l e r i c h phase of a c r y s t a l l i z i n g g r a n i t i c magma (Jahns and Burnham, 1969; Hyndman, 1972; Burnham, 1967; and Carmichael, et 108 a l . , 1974). This f l u i d has been shown to make a s u b s t a n t i a l c o n t r i b u t i o n to a hydrothermal system ( T a y l o r , 1974; and F o r e s t e r and T a y l o r , 1974). F r a c t u r i n g of a c h i l l e d and impermeable b r i t t l e s h e l l which e n c l o s e s a c r y s t a l l i z i n g water s a t u r a t e d magma, e i t h e r by P(H aO) exceeding l i t h o s t a t i c p r essure p l u s t e n s i l e s t r e n g t h , or by o u t s i d e t e c t o n i c i n f l u e n c e , c o u l d i n i t i a t e b o i l i n g , and the consequent r e l e a s e of a l k a l i r i c h f l u i d s along f r a c t u r e s and m i c r o v e i n l e t s producing a l k a l i d e u t e r i c a l t e r a t i o n . B o i l i n g a l s o promotes s u l f i d e d e p o s i t i o n , s i n c e i t r a i s e s s o l u t i o n pH, and c o n c e n t r a t e s aqueous s p e c i e s ( C a t h l e s , 1977; Cunningham, 1978). P a r t i c u l a r c h a r a c t e r i s t i c s of 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 zoning at the Poplar porphyry d e p o s i t are compatible with some of these f e a t u r e s . I g n o r i n g the c e n t r a l p h y l l i c and a r g i i l i c zone (Section 4.2) because i t i s l i k l e y a secondary a l t e r a t i o n f e a t u r e (Section 4.4.5), the P o p l a r porphyry c o n s i s t s of an annular p o t a s s i c a l t e r a t i o n zone around a 'barren* core surrounded by a zone of p h y l l i c and l e s s e r a r g i i l i c a l t e r a t i o n (c. f. F i g . 4.3). The high b i o t i t e abundance i n the m i n e r a l i z e d i n t r u s i v e b r e c c i a , of the b i o t i t e porphyry (S e c t i o n 3.4.3), suggests t h a t the l a s t phase of the c r y s t a l l i z i n g b i o t i t e porphyry was a l k a l i and v o l a t i l e r i c h (Section 4.4.1). Therefore the m a j o r i t y of p o t a s s i c a l t e r a t i o n i s probably pneumatolytic i n o r i g i n . 109 However, l o c a l r e v e r s a l s i n the sequence of a l t e r a t i o n ( S e c t i o n 4.4.1) suggests t h a t some p o t a s s i c a l t e r a t i o n may be d e r i v e d from l a t e r hydrogen i o n deplet e d hydrothermal s o l u t i o n s (c. f . Helgeson, 1970; and Norton, 1977; above). V i l l a s and Norton (1977), and Norton (1977) suggest t h a t p h y l l i c a l t e r a t i o n takes p l a c e s i m u l t a n e o u s l y with p o t a s s i c a l t e r a t i o n , at a lower temperature, o u t s i d e the p o t a s s i c zone. This probably took place i n h i g h l y f r a c t u r e d and permeable Skeena Group rocks (Section 3.4.2 and 3.7) during the hydrothermal event. As the i n t r u s i o n c ooled l a r g e s c a l e f r a c t u r i n g occurred due to thermal c o n t r a c t i o n . P e r m e a b i l i t y was enhanced along these f r a c t u r e s (Section 4.1 and 4.4.2) and meteoric waters flowed inward towards the c e n t r e of the d e p o s i t , h y d r o l y t i c a l l y a l t e r i n g both f r e s h rocks and those which underwent p r e v i o u s p o t a s s i c a l t e r a t i o n ( S e c t i o n 4.4.2)and produced the a l t e r a t i o n p a t t e r n s observed at the Poplar porphyry ( S e c t i o n 4.2). As the i n t r u s i o n c o o l e d , isotherms, and consequently p h y l l i c a l t e r a c t i o n c o l l a s p e d around the centre of the d e p o s i t as the lower s t a b i l i t y l i m i t of K - f e l d s p a r and p l a q i o c l a s e was reached ( F i g . 4.14; and Hemley and Jones, 1964). Those areas of the d e p o s i t which were not f r a c t u r e d , would be u n a f f e c t e d by h y d r o l y t i c a l t e r a t i o n , and t h e r e f o r e the o r i g i n a l p o t a s s i c a l t e r a t i o n minerals would remain ( S e c t i o n 4.1 and 4.4.1). The occurrence of a b r e c c i a pipe i n many porphyry d e p o s i t s i s g e n e r a l l y thought t o be an e x p r e s s i o n of an e x p l o s i v e r e l e a s e of a vapor dominated phase above a shallow c r y s t a l l i z i n g s t o c k . 110 T h i s b r e c c i a t i o n has an enormous i n f l u e n c e on the l o c a l i z a t i o n of copper and molybdenum m i n e r a l i z a t i o n (Cunningham, 1978; C a t h l e s , 1977) , and symmetrical hypogene zoning i n f l u e n c e d by the g r e a t e r p e r m e a b i l i t y (Norton, 1977). I f however, the excess pressure (P (H 20) > P ( L i t h ) + T e n s i l e Strength) i s '"tapped" by l o c a l f r a c t u r i n g events during emplacement and c o o l i n g of the s t o c k , the pressure necessary f o r the development of a b r e c c i a pipe might not m a t e r i a l i z e . Consequently the a l t e r a t i o n p a t t e r n s observed would be c o n t r o l l e d by much more d i r e c t i o n a l p e r m e a b i l i t y ( f a u l t s , f r a c t u r e s , shear zones) about the i n t r u s i o n . The l o c a l l y f a u l t e d c o n t a c t between the Poplar Stock and Skeena Group rocks (Section 3.4.3) may have aided such pressure r e l e a s e . V a r i a b l e s such as the h e a l i n g and opening of f r a c t u r e s , m u l t i p l e i n t r u s i v e events and r e g i o n a l t e c t o n i c s c o u l d f u r t h e r a f f e c t the c i r c u l a t i o n p a t t e r n s of the hydrothermal system, and consequently the a l t e r a t i o n p a t t e r n s observed. V a r i a t i o n i n the t e x t u r e ( i . e. p l a g i o c l a s e phenocryst abundance and packing, S e c t i o n 4.4.2) and bulk composition of the a l t e r e d host and country rock a l s o has a profound a f f e c t on the i n t e n s i t y of a p a r t i c u l a r a l t e r a t i o n f a c i e s . R e a c t i o n s (4.2) and (4.8) are dependent on the a c t i v i t y of f e r r o u s i r o n and the a c t i v i t y r a t i o of a(Fe++)/a(Mgt+). The o x i d a t i o n p o t e n t i a l of the system would have a major i n f l u e n c e on t h i s r a t i o s i n c e Fe+ + can be o x i d i z e d to Fe +++, while Mg has no e q u i v a l e n t t r i v a l e n t s t a t e . Also the o x i d a t i o n of Fe+ + 111 coupled with a s u l f a t e - s u l f i d e r e d u c t i o n could supply a d d i t i o n a l s u l f i d e i o n to the system. P r e c i p i t a t i o n of magnetite from s o l u t i o n would f u r t h e r tend t o favour the r i g h t hand s i d e of equation ( 4 . 2 ) . The occurrence of magnetite w i t h i n the ore zone of the P o p l a r porphyry and i t s a s s o c i a t i o n (along with c h a l c o p y r i t e ) with secondary b i o t i t e ( Section 4.4.1) i s compatible with these c h e m i c a l r e l a t i o n s h i p s . Carbonate i s an abundant a l t e r a t i o n product i n most samples of p h y l l i c and a r g i l l i c a l t e r a t i o n at the Poplar porphyry (Section 4.4 .2 and 4 . 5 . 2 , r e a c t i o n s (4.4), and (4.6), ( 4 . 8 ) ) . . Because of the c l o s e a s s o c i a t i o n of a l t e r e d p l a g i o c l a s e with c a l c i t e , the Ca++ r e l e a s e d from p l a g i o c l a s e d u r i n g h y d r o l y t i c a l t e r a t i o n i s probably the c a t i o n r e a c t a n t f o r the carbonate (Section 4.4.2) . L o c a l l y high f r a c t u r e d e n s i t y i n the host and country rocks makes the d e p o s i t l o c a l l y s u s c e p t i b l e t o a second a l t e r a t i o n event. The z o n a t i o n at the P o p l a r porphyry i n c l u d e s a c e n t r a l zone of a r g i l l i c and p h y l l i c a l t e r a t i o n which borders Canyon Creek f a u l t . T h i s zone i s e i t h e r secondary hypothermal or supergene i n o r i g i n (Section 4.4.5). In a d d i t i o n , t h i s zone occurs i n an area bounded by a p o t a s s i c a l t e r a t i o n annulus and i s s u g g e s t i v e of a "low-grade c o r e " s i m i l a r to t h a t found i n the Lowell and G u i l b e r t (1970) model, because of a n e g l i g i b l e amount of e i t h e r supergene or hypogene m i n e r a l i z a t i o n . 112 4.6 Environment of Ore D e p o s i t i o n Mineral assemblages found i n 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 zones at the P o p l a r porphyry would, by themselves, p l a c e l i t t l e c o n s t r a i n t on the a c t u a l pressures and temperatures of f o r m a t i o n and the chemical c h a r a c t e r i s t i c s of the ore f o r m i n i g s p l u t i o n s . However, work at other porphyry d e p o s i t s , with s i m i l a r p o t a s s i c zone 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 , can be used to place some l i m i t s on the environment of ore f o r m a t i o n based on f l u i d i n c l u s i o n (Roedder, 1971), s t a b l e i s o t o p e (Shepard e t a l . ,1971), and b i o t i t e geothermometry (Beane, 1974) s t u d i e s . A temperature of 375°C, and a pressure of 250 bars (approximately e q u i v i l e n t to 2.5 Km of h y d r o s t a t i c head) f o r p o t a s s i c a l t e r a t i o n and c h a l c o p y r i t e m i n e r a l i z a t i o n at the Poplar porphyry i s compatible with these s t u d i e s . C h a l c o p y r i t e i s the only copper bearing m i n e r a l observed i n the d e p o s i t , except f o r t r a c e s of b o r n i t e , c o v e l l i t e and t e t r a h e d r i t e , and i s found almost e x c l u s i v e l y i n the p o t a s s i c a l t e r a t i o n zone (Map B), a s s o c i a t e d with magnetite. F i g u r e 4.16 i s a Leg a(O z)-vs-Log a(S z ) diagram f o r the Cu-Fe-S^-0 2 system, at 250 bars and 375°C. The c h a l c o p y r i t e - m a g n e t i t e f i e l d i s shown cross - h a t c h e d . T h i s diagram i n d i c a t e s t h a t p o t a s s i c f a c i e s a l t e r a t i o n and c h a l c o p y r i t e m i n e r a l i z a t i o n occurred i n an area ranging from -34 t o -26 Log a (0 2) and from -13 t o -4 Log a ( S z ) . 113 - 1 0 H CO cr CD L U o >— X o -15H C3 O - 2 0 - 2 5 To - 2 5 - 2 0 - 1 5 - 1 0 LOG fl ( S U L F U R G R S h Figure 4.16: A Log a(S 2).-vs- Log a(0 2) diagram for the system Cu- Fe-0 2-S 2, at 375 C and 250 bars. TN= tenorite, CU= cuprite, C0= native copper, CC= chalcocite, CP= chalcopyrite, CV= c o v e l l i t e , BN= bornite, MG= magnetite, HM= hematite, P0= pyrrho t i t e , and PY= p y r i t e . The cross-hatched area i s the s t a b i l i t y f i e l d of magne- t i t e - c h a l c o p y r i t e , found i n the potassic zone of the Poplar por- phyry. Arrow indicates d i r e c t i o n of solution movement from po- t a s s i c to p h y l l i c a l t e r a t i o n f a c i e s . 114 The p h y l l i c a l t e r a t i o n assemblage c o n t a i n s no copper bearing minerals , but does c o n t a i n a p y r i t e ± hematite assemblage (Section 4„4. 2 ) . I f copper was removed from the system ( F i g - 4. 16) then p y r i t e and hematite would c o e x i s t along the j o i n d i v i d i n g t h e i r r e s p e c t i v e f i e l d s . The arrow i n F i g u r e 4.16 i n d i c a t e s the d i r e c t i o n a s o l u t i o n would move from being i n e q u i l i b r i u m with c h a l c o p y r i t e - m a g n e t i t e i n the p o t a s s i c f a c i e s to r e a c h i n g e q u i l i b r i u m with p y r i t e ± hematite i n the p h y l l i c f a c i e s ; both a(S^) and a(0 2) i n c r e a s e . I f copper was present as the s o l u t i o n changed as d e s c r i b e d above then c h a l c o c i t e + h e m a t i t e , c o v e l l i t e + p y r i t e , or c o v e l l i t e + h e m a t i t e should be p r e c i p i t a t e d as s t a b l e phases and observed i n the p h y l l i c a l t e r a t i o n zone , which they are not. T h i s suggests t h a t c h a l c o p y r i t e was removed by the same s o l u t i o n s which produced p h y l l i c a l t e r a t i o n m i n e r a l s , r a t h e r than r e a c t i n g to form another copper s u l f i d e . Equation 4.10 may i n d i c a t e a p o s s i b l e mechanism which may e x p l a i n what happened. (4.10) CuFeS 2 + 4H+ + 2C1- = C u C l " + Fe +++ + 2H ZS As the s o l u t i o n s became more a c i d i c rocks which had undergone previous p o t a s s i c a l t e r a t i o n and c o n t a i n e d K - f e l d s p a r , p l a g i o c l a s e ; and c h a l c o p y r i t e were h y d r o l y t i c a l l y attacked. K- f e l d s p a r and p l a g i o c l a s e were a l t e r e d to s e r i c i t e or c l a y ± carbonate, and c h a l c o p y r i t e was removed. The H S and Fe*++ r e l e a s e d i n r e a c t i o n 4.10 may have been r e d e p o s i t e d as p y r i t e ± 115 hematite ± c h a l c o p y r i t e ( ? ) i n the p h y l l i c a l t e r a t i o n f a c i e s . 4,. 7 E v o l u t i o n of 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 Zoning at the Poplar Porphyry In summary a model f o r the e v o l u t i o n of the Poplar porphyry d e p o s i t i n c l u d e s : A) I n t r u s i o n of a guartz monzonite stock, of the Late Cretaceous B u l k l e y i n t r u s i v e s u i t e , i n t o Lower Cretaceous marine and volcanogenic sedimentary r o c k s of the Skeena Group, with concomitant f r a c t u r i n g and f a u l t i n g of country r o c k s . , B) C h i l l i n g of an impermeable monzodiorite s h e l l around a cupola of the s t o c k i n c o n t a c t with country r o c k s . Within t h i s s h e l l a water s a t u r a t e d a l k a l i r i c h melt developes. C) L o c a l f r a c t u r i n g of the s h e l l , due to e i t h e r excess vapor pressure, or an e x t e r n a l t e c t o n i c event, i n i t i a t e s open but d i r e c t i o n a l flow between i n t r u s i v e and country rock, developing a c o n v e c t i v e hydrothermal system. P o t a s s i c a l t e r a t i o n i s formed e a r l y i n the a l t e r a t i o n sequence from l a t e stage magmatic f l u i d s , high i n a l k a l i metals (and/cr low i n H +) concomitant with d e p o s i t i o n of copper and mclybdenum s u l f i d e . F l u i d s which are i n v o l v e d i n h y d r o l y t i c a l t e r a t i o n at the periphery of 116 the ore deposit convect inwards along l o c a l i z e d fractures towards the central potassic a l t e r a t i o n zone, reacting with wall rock, r a i s i n g i t s pH and temperature along i t s path; eventually coming into equilibrium with the potassic a l t e r a t i o n f a c i e s . As the stock cools, peripheral meteroic waters t r a v e l further through previously h y d r o l y t i c a l l y altered rocks, without r a i s i n g i t s pH or temperature; subsequently the p h y l l i c and lesser a r g i i l i c a l t e r a t i o n zones collapse around the central potassic a l t e r a t i o n zone. Continuous fracturing and healing of conduits, alternately enhances and i n h i b i t s the wall rock from reacting with hydrothermal solutions, leaving some higher"alteration grade" potassic - chalcopyrite - molybdenite zones unaffected by hydrolytic a l t e r a t i o n . Seduction of stock temperature and the gradual diminution of the hydrothermal system. While the hydrothermal system was i n i t s l a s t stages numerous dykes were intruded followed by a second "lower grade" a l t e r a t i o n event which overprinted most previous a l t e r a t i o n zones that were within, or adjacent to, permeable areas ( i . e. the central a r g i i l i c a l t e r a t i o n zone). Holocene g l a c i a t i o n and removal of any cap or supergene mineralized horizons. 117 CHAPTER V GEOSTATISTICS OF THE POPLAR PORPHYRY 5.1 General Statement One o f the most valuable c h a r a c t e r i s t i c s of the P o p l a r l o g format ( S e c t i o n 3 . 1 , and Appendix B) f o r lo g g i n g d r i l l core i s th a t g e o l o g i c i n f o r m a t i o n i s amenable to s t a t i s t i c a l a n a l y s e s . Major advantages of s t a t i s t i c a l treatment of the l a r g e amount of data obtained at the Poplar porphyry i n c l u d e : the dete r m i n a t i o n of g e o l o g i c a l v a r i a b l e s which are most v a l u a b l e f o r d e s c r i b i n g s y s t e m a t i c s p a t i a l v a r i a t i o n s w i t h i n the d e p o s i t ; numerical r e s u l t s which may e i t h e r v e r i f y or a l t e r p r e v i o u s l y developed r e l a t i o n s h i p s based on f i e l d o b s e r v a t i o n s ; and to i n d i c a t e r e l a t i o n s h i p s not r e a d i l y apparent from normal f i e l d o b s e r v a t i o n . In p a r t i c u l a r , the dete r m i n a t i o n o f the type and st r e n g t h of r e l a t i o n s h i p s among c h a l c o p y r i t e , molybdenite, and a l t e r a t i o n mineral abundances can be assessed s t a t i s t i c a l l y . In t h i s chapter the r e s u l t s and i n t e r p r e t a t i o n of s t a t i s t i c a l a n a l y s e s , c o n s i s t i n g of l i n e a r c o r r e l a t i o n s , and m u l t i v a r i a n t a n a l y s i s , are presented. In a d d i t i o n to a n a l y t i c a l s t a t i s t i c a l s t u d i e s numerous computer programs have been designed t o produce graphic i l l u s t r a t i o n s of the s p a t i a l d i s t r i b u t i o n and c o r r e l a t i o n between g e o l o g i c v a r i a b l e s ( i . e. HISTLOG and CPY; Appendix C). 118 Over 1000 q u a n t i t a t i v e o b s e r v a t i o n s of 21 separate v a r i a b l e s were made during the course of d e t a i l e d l o g g i i n g of d r i l l core along c r o s s - s e c t i o n s A-A * and B-B* ( F i g . 3.3,and 3.4;and Map A). These data were reduced t o 739 ob s e r v a t i o n s by e x c l u d i n g data from unmineralized rock u n i t s such as post-ore dykes. Twenty-one v a r i a b l e s t h a t were examined i n d e t a i l are l i s t e d and d e s c r i b e d i n Appendix B; but f o r the purpose of t h i s chapter the v a r i a b l e s of most i n t e r e s t are the ranked i n t e n s i t i e s of 14 hydrothermal minerals (Table 5.1). Two computer packages, a v a i l a b l e at the Computer Science Centre a t the U n i v e r s i t y of B r i t i s h Columbia, were used i n t h i s study; TEP and MIDAS. TEP i s an acronym f o r • T r i a n g u l a r Regression Package', the major purpose of which i s r e g r e s s i o n a n a l y s i s (Le and T e n i s c i , 1978). The major s u b r o u t i n e s of TRP th a t were used, and t h e i r purpose are: INMSDC, f o r producing means, standard d e v i a t i o n s , and simple c o r r e l a t i o n c o e f f i c i e n t s ; SIMREG, f o r producing u n i v a r i a n t l i n e a r r e g r e s s i o n s ; and STPSEG, f o r m u l t i v a r i a n t r e g r e s s i o n a n a l y s i s . MIDAS, or 'Michigan I n t e r a c t i v e Data A n a l y s i s System' was used to c a l c u l a t e one-way c o r r e l a t i o n s . Each of these s u b r o u t i n e s are shown i n Appendix D as they were used i n a F o r t r a n computer programs which were w r i t t e n by the author. 119 5. 2 C o r r e l a t i o n s Between, V a r i a b l e s 5. 2. 1 Two-way C o r r e l a t i o n Matrix "Two-way" c o r r e l a t i o n s i s a term a p p l i e d when a l l o b s e r v a t i o n s have equal weight i n the c o r r e l a t i o n equation (Equation 5.1) (Le and T e n i s c i , 1978). (5.1) = "5, WL (Xi - X) (Y f - Y) ^ . H; (X; - 1 ) 2 Hi (Y; - Y ) * where: r = w; x: x" = Y Y 1/2 c o r r e l a t i o n c o e f f i c i e n t = weight of the i + K o b s e r v a t i o n = value of the i t k o b s e r v a t i o n of X sample mean of X = value of the i*'*' o b s e r v a t i o n of Y = sample mean of Y 120 TABLE 5.1 F i f t e e n Hydrothermal M i n e r a l s Osed i n S t a t i s t i c a l A n a l y s i s o f 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 a t Poplar Porphyry Deposit. ALTERATION MINERALS guartz K - f e l d s p a r b i o t i t e s e r i c i t e c h l o r i t e c l a y epidote carbonate gypsum p y r i t e hematite magnetite ORE MINERALS c h a l c o p r y i t e b o r n i t e molybdenite Table 5.2 shows the c o r r e l a t i o n matrix, and the means and standard d e v i a t i o n s of 14 economic and a l t e r a t i o n minerals observed at the Poplar porphyry. The standard d e v i a t i o n of most minerals i s as l a r g e or l a r g e r than t h e i r mean. This i s because the number zero was recorded i n the f i e l d when a p a r t i c u l a r mineral was absent i n an i n t e r v a l of core; t h e r e f o r e z e r o does no r e p r e s e n t a missing o b s e r v a t i o n , but i n s t e a d a numerical value. Except f o r q u a r t z , 121 s e r i c i t e , and p y r i t e which occur t o some extent i n most i n t e r v a l s of core, zero i s the most f r e q u e n t l y recorded value f o r any m i n e r a l , hence the standard d e v i a t i o n c a l c u l a t e d accounts f o r t h i s skewness towards zero. C o r r e l a t i o n s which d i s r e g a r d o b s e r v a t i o n s of zero i n the c o r r e l a t i o n equation (5. 1) are d i s c u s s e d i n d e t a i l i n S e c t i o n 5.2.2. C o r r e l a t i o n c o e f f i c i e n t s t h a t are s t a t i s t i c a l l y s i g n i f i c a n t have been u n d e r l i n e d i n Table 5.2 by e i t h e r a s i n g l e or double l i n e , i n d i c a t i n g s i g n i f i c a n c e a t the 99.0 percent and 99.9 percent c o n f i d e n c e l e v e l s , r e s p e c t i v e l y . Based on 739 o b s e r v a t i o n s a minimum departure from zero of 0.094 f o r the 99.0 percent c o n f i d e n c e l e v e l , and 0.127 f o r the 99.9 percent confidence l e v e l , i s r e q u i r e d f o r s i g n i f i c a n c e (Dixon and Massey, 1969). The term " s t a t i s t i c a l l y s i g n i f i c a n t " means t h a t c o r r e l a t i o n c o e f f i c i e n t s with values above those c a l c u l a t e d f o r a s p e c i f i c c o n f i d e n c e l e v e l are s i g n i f i c a n t l y d i f f e r e n t from zero ( i . e. t h e r e i s a d e f i n i t e c o r r e l a t i o n ) at the p r o b a b i l i t y of the c o n f i d e n c e l e v e l . G e o l o g i c a l l y s i g n i f i c a n t c o r r e l a t i o n s , with few e x c e p t i o n s , support c o r r e l a t i o n s based on f i e l d o b s e r v a t i o n s (Chapter IV) and are shown c l a s s i f i e d by f a c i e s i n Table 5.3. A l t e r a t i o n r e l a t i o n s h i p s d e f i n e d by these c o r r e l a t i o n groupings" aire 'not only very s i m i l a r t o those i n the f i e l d , but s t a t i s t i c a l l y s u b s t a n t i a t e the a l t e r a t i o n f a c i e s of Lowell and G u i l b e r t 7 l*i*-V CONTROL CARD NO. 1 ** INMSDC **** INMSCC **** INMSDC **** INMSDC **** INMSDC **** INMSDC **** INMSDC ** CONTROL CARD NOo 1 FORMAT CARDS ; - (30X,6 <1X,F1.0 ),1X,3(1X,F1.C>,5X,7(lXtFl.O) 1 C Q R R E L L A T I C N M A T R I X Q U A R T Z 1 .60C6 Q U A R T Z K - S P A R B I C T I T S E R I C T C H L Q R T C L A Y E P I D O C A R B S G Y P S U M P Y R I T F H T P A T T C H A L P Y B O R N I T PAGNTT F C L Y K - S P A R B I O T I T S E R I C T CHLCRT C L A Y -O.0872 -0.0825 0.1139 - ;lo 1'519" -0.0660 -0.0422 1 . 0 0 0 0 0 . 4 3 1 6 - 0 ^ 3 0 6 - 0 . 0 0 8 0 - 0 . 0 6 5 1 0 . 0 3 6 6 1 . 0 0 0 0 - 0 . 3 0 0 2 n.O<fl - 0 . 1 1 0 8 0 . 0 2 8 7 1 . 0 0 0 0 - 0 . 0 3 3 3 0 . 3 3 1 5 -0.087 2 1 . 0 0 0 0 0 . 0 2 8 8 - 0 . 0 0 3 4 l.COOO - 0 . 0 1 3 4 E P I D O T 1 . 0 0 0 0 CARBS -0.0416 0 .0691 3 6 4 6 - 0 . 0 0 7 8 - 0 . 0 6 1 1 - 0 . 2 2 1 5 - 0 . 0 6 0 0 0 . 0 5 9 2 - 0 . 0 1 4 4 0 . 1 2 8 1 - 0 . 0 9 7 5 0 . 0 6 4 8 - 0 . 1 2 4 5 - 0 . 0 3 1 7 - 0 . 0 6 1 4 - C . 1 5 0 6 - 0 . 0 1 0 5 - 0 . 0 1 6 2 0 . 0 9 2 0 - 0 . 0 1 6 2 0 . 0 5 3 3 - 0 . 0 3 7 2 - 0 . 1 7 7 8 - 0 . 0 2 2 0 ST* - 0 . 0 2 0 4 « H f K -0.1260 0.1970 -0.0127 Q . 1 2 2 Q . - 0 . 1 9 6 6 0 . 0 2 8 8 0 - 0 3 6 4 - 0 . 0 1 6 E - 0 . 0 1 3 3 -0.6510 0 . C 1 4 8 0 . 0 1 6 2 - 0 . 0 1 6 5 0 . 0 1 2 5 - 0 . 0 0 5 2 1 . 0 0 0 0 - 0 . 3 3 8 9 - 0 . 2 5 9 4 - 1 6 . 1 4 5 3 0.1117 0.010 5 - 0 . 2 6 3 4 0 . 1 5 7 7 0 - 1 3 7 6 • 0 . 0 0 6 3 0 . 1 1 3 4 - Q . 2 1 8 2 - 0 . 0 4 2 9 0 . C 1 2 7 - 0 . 0 3 3 9 - 0 . C 3 6 4 0 . 0 4 0 7 - 0 . 0 1 2 9 0 . 0 7 5 0 0 . 1 7 4 0 0 .0550 G Y P S U M P Y R I T E HEMATT 1.OOOO Op 3 0 9 5 1 . 0 0 0 0 -U. 14Hb -0.0981 -0. 0852 -0-1517 - 0 . C 8 1 6 - 0 . 0 8 6 7 1 . 0 0 0 0 -p. 3 0 0 8 0 . 0 2 8 0 -0. C 5 4 S 0 . 0 0 8 6 -p. 2 7 5 3 0 . 0 8 5 9 -o. 1271. - 0 . 1 0 8 7 C O R R E L A T I O N M A T R I X C H A L P Y B O R N I T M A G N T T H O L Y I C H A L P Y 1 . 0 0 0 0 0 . 0 1 3 9 C". 2 4 7 4 . B C R N I T 1.0000 -0.0119 -0.078S MAGNTT M C L Y 1.0000 -0,1264 1 . 0 0 0 0 N A M E M E A N S T A N D A R D D E V I A T I O N Q U A R T Z I 4 . 4 0 0 5 4 2 . 0 9 4 4 6 K - S P A R B I O T I T S E R I C T C H L O R T C L A Y E P I D O T C A R B S G Y P S U M P Y R I T E H E M A T T C H A L P Y B C R N I T M A G N T T M C L Y 1 . 6 2 1 1 1 0 . 7 0 3 6 5 4 4 . 7 0 9 0 7 2 . 3 9 5 2 0 1 . 6 6 5 0 8 1 . 9 8 9 2 8 0.224763E 0.338295 0.270636E - 0 1 C . 3 4 7 7 0 0 C . 9 3 2 2 7 7 0 2 C . 7 3 5 7 1 2 E - 0 1 1 . 7 6 0 4 9 1 . 1 3 2 6 1 3 . 0 9 2 0 2 1 . 7 4 1 6 5 1 . 8 9 7 4 4 1 . 9 7 2 6 3 0 . 4 8 9 8 5 1 1 . 4 5 4 6 7 0 . 2 4 3 5 7 2 E - 0 1 1 . 0 9 6 1 1 1 . 6 0 5 0 5 G . 1 7 0 9 2 8 0 . 5 1 0 1 4 9 1 . 0 2 8 4 2 1 . 4 5 8 8 6 1 . 4 5 8 7 4 7 3 9 O B S E R V A T I O N S T O T A L 7 3 9 O B S E R V A T I O N S A R E C O M P L E T E 7 3 8 D E G R E E S C F F R E E D G E 123 F i g u r e 5.1: A p o s i t i v e c o r r e l a t i o n " c l u s t e r " , b a s e d on a l t e r - a t i o n f a c i e s b e t w e e n m i n e r a l s w h i c h a r e s i g n i f i c a n t l y c o r r e l a t e d . D i v i s i o n s b e t w e e n p o t a s s i c , p h y l l i c , a n d a r g i l l i c f a c i e s a r e shown. 124 (1970). F i g u r e 5.1 i s a C o r r e l a t i o n ' C l u s t e r * diagram showing mineral c o r r e l a t i o n s grouped a c c o r d i n g t o a l t e r a t i o n f a c i e s . One s i g n i f i c a n t c o r r e l a t i o n which was not i d e n t i f i e d i n the f i e l d i s carbonate - p y r i t e . A c o r r e l a t i o n which was expected to be s i g n i f i c a n t , but cannot be shown here t o be so, i s s e r i c i t e - p y r i t e . The s i g n i f i c a n t negative c o r r e l a t i o n (- 0.1284) between molybdenite and magnetite i s anomalous, s i n c e both are p o s i t i v e l y c o r r e l a t e d with K - f e l d s p a r (Table 5.2), and both occur w i t h i n the p o t a s s i c a l t e r a t i o n zone. However, molybdenite i s l a r g e l y r e s t r i c t e d to guartz v e i n s , and q u a r t z i s n e g a t i v e l y c o r r e l a t e d with magnetite. T h e r e f o r e , the r e l a t i o n s h i p between molybdenite and magnetite, may be due to the absence of magnetite near quartz v e i n s , r a t h e r than i t s true s p a t i a l r e l a t i o n s h i p to j u s t molybdenite alone. The most u s e f u l c o r r e l a t i o n f o r the economic e v a l u a t i o n of the d e p o s i t are those t h a t not only d e f i n e a l t e r a t i o n f a c i e s , but a l s o e s t a b l i s h which minerals are the most u s e f u l i n p r e d i c t i n g the occurrence and abundance of c h a l c o p y r i t e and molybdenite. C h a l c o p y r i t e i s c o r r e l a t e d p o s i t i v e l y with p o t a s s i c a l t e r a t i o n minerals, and n e g a t i v e l y with p h y l l i c a l t e r a t i o n minerals (Table 5.2). Molybdenite, l e s s w e l l d e f i n e d i n terms of f a c i e s r e l a t i o n s h i p s , i s c o r r e l a t e d p o s i t i v e l y with the p o t a s s i c a l t e r a t i o n f a c i e s minerals K - f e l d s p a r and b i o t i t e , and with q u a r t z i n the p h y l l i c a l t e r a t i o n f a c i e s . I t i s 125 TABLE 5.3 C o r r e l a t i o n s B e t w e e n M i n e r a l s B a s e d on A l t e r a t i o n F a c i e s 1 F A C I E S MINERAL +CORRELATION -CORRELATION P o t a s s i c K - f e l d s p a r b i o t i t e b i o t i t e c h a l c o p y r i t e m a g n e t i t e m o l y b d e n i t e c h a l c o p y r i t e m o l y b d e n i t e K - f e l d s p a r s e r i c i t e p y r i t e h e m a t i t e s e r i c i t e c l a y h e m a t i t e m a g n e t i t e P h y l l i c s e r i c i t e c a r b o n a t e c h a l c o p y r i t e K - f e l d s p a r q u a r t z c l a y . c a r b o n a t e h e m a t i t e q u a r t z s e r i c i t e gypsum p y r i t e m o l y b d e n i t e c h a l c o p y r i t e m a g n e t i t e K - f e l d s p a r b i o t i t e gypsum q u a r t z p y r i t e p y r i t e s e r i c i t e m o l y b d e n i t e gypsum q u a r t z h e m a t i t e m a g n e t i t e K - f e l d s p a r m a g n e t i t e c h a l c o p y r i t e m o l y b d e n i t e c l a y c a r b o n a t e A r g i i l i c c l a y s e r i c i t e gypsum b i o t i t e p y r i t e c a r b o n a t e h e m a t i t e c h a l c o p y r i t e m a g n e t i t e s e r i c i t e gypsum p y r i t e T h i s t a b l e i s a summary o f a n a l y t i c a l r e s u l t s shown i n T a b l e 5.2 126 c o r r e l a t e d n e g a t i v e l y with p y r i t e and hematite i n the p h y l l i c a l t e r a t i o n f a c i e s , and with magnetite i n the p o t a s s i c a l t e r a t i o n f a c i e s , 5,2.2 One-way C o r r e l a t i o n Matrix One-rway c o r r e l a t i o n i s c a l c u l a t e d using Equation (5. 1) ; i f a p r i n c i p l e v a r i a b l e X , i s z e r o f o r a p a r t i c u l a r o b s e r v a t i o n , i , t h a t o b s e r v a t i o n i s excluded from the r e g r e s s i o n ; the secondary v a r i a b l e , Y , i s c o n s i d e r e d r e g a r d l e s s of i t s value f o r a p a r t i c u l a r o b s e r v a t i o n . The purpose of such a c a l c u l a t i o n i s to d i s t i n g u i s h those c o r r e l a t i o n s which occur between v a r i a b l e s because both, though u n r e l a t e d , maintain mutual values of zero i n a number of o b s e r v a t i o n s , and are consequently assigned a c o r r e l a t i o n c o e f f i c i e n t t h a t may not i n d i c a t e t h e i r t r u e s p a t i a l r e l a t i o n s h i p . The one-way c o r r e l a t i o n matrix (Table 5.4) i s nonsymmetrical, i n d i c a t i n g t h a t two v a r i a b l e s have d i f f e r e n t c o r r e l a t i o n c o e f f i c i e n t s , depending on which i s chosen as the p r i n c i p l e v a r i a b l e , X . This shows that the inter-dependence of the two minerals i s unequal ( i . e. .the occurrence of mineral A i s a more dependent on the occurrence of mineral B, than v i c e v e r s a ) . For example, Tahle 5.4 shows t h a t although c h a l c o p y r i t e does not c o r r e l a t e s i g n i f i c a n t l y with occurrence o f the p r i n c i p l e v a r i a b l e K - f e l d s p a r ; K - f e l d s p a r does s i g n i f i c a n t l y c o r r e l a t e with the occurrence of the p r i n c i p l e v a r i a b l e c h a l c o p y r i t e . TABLE 5.4 One-way Correlation Matrix of Alteration and Economic Minerals Quartz K-feldspar Biotite Sericite Chlorite Clay Epidote Carbonate Gypsum Pyrite Hematite Chalcopyrite Bornite Magnetite Molybdenite N 3 b r99.0 Quartz 1.0 -.146 -.1297 1.567 . 0387 - .092 -• 057 -.106 .1017 • 3897 -.054 -.095 .010 -.1932 .0769 692 0.098 K-feldspar .0459 1.0 • 3439 -.045 -.085 - .055 -• 005 -.058 -.143 -.008 -.099 -.029 -.064 0.063 +.109 286 0.151 Biotite -.137 .2082 1.0 -.1949 • 2625 0.1212 .-• 0985 -.0498 .3327 .2055 -.078 .0511 -.0519 -.2073 .1069 133 0.223 Sericite .114 -.3104 -.2745 2.0 .0745 •1111 0. 0 • 1191 -.0832 .0701 • 1162 -.2054 .0244 -.2437 -.0438 727 0.095 Chlorite 0.0 -.0848 .967 -.4698 +.106 - .1446 0. 0 -.536 • 9670 .6926 -.1501 -.6954 0.0 -.2583 0.0 12 0.695 Clay .0474 .0040 .1826 .4113 -.0602 1 .0 0. 0 -.0534 -.0379 -.1189 -.1083 .1083 -.1116 -.0951 -.0156 112 0.2iZ Epidote 1.0 1.0 1.0 1.0 1.0 1 .0 I . 0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1 1.000 Carbonate .0331 -.0699 -.0744 • 1982 0.0332 .0448 0. 0 1.0 -.2372 -.1016 .0886 .0686 .0421 .1433 .0079 484 0.115 Gypsum -.0520 -.0818 .0806 .0299 • 2272 - .0446 0. 0 -.2492 1.0 • 2947 .1360 -.0059 0.0 -.1398 .0363 230 0.170 Pyrite • 3156 -.2555 -.0723 .0735 .0154 - • ir,27 -. 0357 -.1894 .2912 1.0 .0672 -.2241 -.226 -.1882 -.2017 646 0.101 Hematite -.0411 -.1401 0.1052 .0646 .0473 - .1533 0. 0 .1445 0.1456 .0325 1.0 -.0936 .0039 -.0029 .0062 184 0.188 Chalcopyrite .0610 : .1279 .1027 -.2535 -.0769 - • 1627 -. 0156 -.0902 .2018 -.0584 • 1288 1.0 -.0276 .2263 .1170 439 0.122 Bornite -.1471 .3388 -.1677 -.2275 0.0 .2190 0. 0 -.3962 0.0 .3797 -.1862 -.4467 1.0 -.1299 -.1690 16 0.623 Magnetite -.1475 -.0113 0.1114 -.4473 -.1036 • 3072 0. 0 .0623 -.0354 -.1289 -.1196 .1688 .0028 1.0 -.1069 109 0.256 Molybdenite • 1704 .0116 .0097 -.0046 .0358 .0144 0700 -.0376 -.0466 .0549 .0153 • 2841 -.0858 -.0479 1.0 312 0.145 Underlined correlation coefficient are s t a t i s t i c a l l y significant. a) N • number of observations of a particular variable in Equation (5.1). Equal to the number of non-zero observations b) r ^ j - minimum correlation coefficient, for the number of observations, N, at the 99.0 percent confidence level. Calculated from 0 Lxon and Massey (1969) 128 R e s u l t s from the one-way c o r r e l a t i o n matrix (Table 5.4) i n ge n e r a l c o r r a b o r a t e r e s u l t s on the mineralogy of a l t e r a t i o n f a c i e s presented i n Sect i o n s 4.3, and 4.4. Quartz and s e r i c i t e c o r r e l a t e p o s i t i v e l y with each other, and n e g a t i v e l y with p o t a s s i c a l t e r a t i o n f a c i e s m i n e r a l s and c h a l c o p y r i t e . C h a l c o p y r i t e c o r r e l a t e s s i g n i f i c a n t l y with K - f e l d s p a r , gypsum, hematite, and magnetite and n e g a t i v e l y with s e r i c i t e and c h l o r i t e . Molybdenite i s p o s i t i v e l y c o r r e l a t e d with qu a r t z , and c h a l c o p y r i t e . I n c o n s i s t e n c i e s between r e s u l t s from one-way (Table 5.4) and two-way (Table 5.2) c o r r e l a t i o n matrices i n c l u d e the l a c k of a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between K- f e l d s p a r and b i o t i t e , and between these minerals and c h a l c o p y r i t e and molybdenite i n the one way c o r r e l a t i o n matrix. The lack of a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between p y r i t e and s e r i c i t e i s a l s o apparent i n Table 5.4. 5.3 M u l t i v a r i a n t A n a l y s i s 5.3.1 General Statement U n i v a r i a n t l i n e a r a n a l y s i s ( l i n e a r c o r r e l a t i o n between one dependent and one independent v a r i a b l e ) i s u s e f u l i n e v a l u a t i n g what e f f e c t , i f any, one v a r i a b l e has on another. C o r r e l a t i o n c o e f f i c i e n t s presented i n S e c t i o n 5.2 are measures of t h i s dependence between twc v a r i a b l e s . However, t h i s approach i s r e s t r i c t e d s i n c e most g e o l o g i c v a r i a b l e s are the r e s u l t o f i n t e r a c t i o n s between numerous other v a r i a b l e s (Davis, 1973). M u l t i v a r i a n t a n a l y s i s allows one to c o n s i d e r changes i n s e v e r a l p r o p e r t i e s of a system s i m u l t a n e o u s l y , i n order t o s o r t out the 129 major f a c t o r s determining the r e l a t i v e worth of v a r i a b l e s . (5.2) I = A,X(1) • A2 X (2) + . . . . . • A MX(N) • K where: Y = dependent v a r i a b l e A; = c o e f f i c i e n t of the i + K independent v a r i a b l e Xf = i f k independent v a r i a b l e K = a constant t h a t i s egual to the Y - i n t e r c e p t cn the r e g r e s s i o n hyperplane The m u l t i v a r i a n t r e g r e s s i o n s were performed using the subroutine STREG from the TRP s t a t i s t i c a l computer package (Le and T e n i s c i , 1S78). Both frontwards and backwards stepwise r e g r e s s i o n techniques were employed, with equal r e s u l t s (Equation 5.3 and 5.4). In backwards stepwise r e g r e s s i o n a l l independent v a r i a b l e s are i n c l u d e d i n the equation (5.2) at the f i r s t step; a m u l t i v a r i a n t equation i s c a l c u l a t e d with a minimum va r i a n c e i n Y f o r those v a r i a b l e s . Each v a r i a b l e i s then t e s t e d f o r s i g n i f i c a n c e by computing the p r o b a b i l i t y of o b t a i n i n g an absolute value of the c o e f f i c i e n t 'A' g r e a t e r than the one c a l c u l a t e d , i f the v a r i a b l e X made no s i g n i f i c a n t c o n t r i b u t i o n . The g r e a t e r t h i s p r o b a b i l i t y , the l e s s s i g n i f i c a n t X i s to the 130 equ a t i o n . I f t h i s p r o b a b i l i t y i s g r e a t e r than 0.05 ( f i v e percent) the v a r i a b l e i s e l i m i n a t e d from the equation. The l e a s t s i g n i f i c a n t v a r i a b l e i s dropped from the equation at each step and a new eguation i s c a l c u l a t e d by minimizing the v a r i a n c e between the remaining v a r i a b l e s . T h i s r o u t i n e i s c a r r i e d out u n t i l each independent v a r i a b l e l e f t i n the equation has an a s s o c i a t e d p r o b a b i l i t y of l e s s than 0.05. 5.3.2 M u l t i v a r i a n t Equations f o r C h a l c o p y r i t e and Molybdenite M u l t i v a r i a n t equations (5.3 and 5.4) are presented f o r the dependent v a r i a b l e s c h a l c o p y r i t e or molybdenite versus the independent v a r i a b l e s guartz, K - f e l d s p a r , gypsum, p y r i t e , and magnetite. Molybdenite was an independent v a r i a b l e i n the c h a l c o p y r i t e e quation (5.3), and c h a l c o p y r i t e was an independent i n the molybdenite equation (5.4). (5.3) C h a l c o p r y i t e = 0.78 quartz +1.5 b i o t i t e * 0.24 magnetite + 0.25 molybdenite - 0.07 s e r i c i t e - 0.20 p y r i t e + 1.59 r2 = 0.229 S.E. = 1.415 E . I . (5.4) Molybdenite = 0.12 quartz + 0.05 K - f e l d s p a r • 0.23 c h a l c o p y r i t e - 0.11 p y r i t e -0.20 magnetite + 0.52 r 2 = 0.149 S.E. = 1. 350 E.I 131 W h e r e : r 2 = m u l t i p l e c o r r e l a t i o n c o e f f i c i e n t ; e q u a l t o t h e p r o p o r t i o n o f t h e v a r i a n c e o f t h e d e p e n d e n t v a r i a b l e , Y , a c c o u n t e d f o r b y t h e r e g r e s s i o n l i n e . S . E . = s t a n d a r d e r r o r ; t h e e s t i m a t e o f t h e v a r i a n c e o f t h e d e p e n d e n t v a r i a b l e Y , a b o u t t h e r e g r e s s i o n h y p e r p l a n e ( L e a n d T e n i s c i , 1978) . U n i t s o f s t a n d a r d e r r o r a r e t h e " r a n k e d a b u n d a n c e " u s e d i n l o g g i n g d r i l l c o r e ( A p p e n d i x B ) • E . I . M e a n s B a n k e d I n t e n s i t y . ( s e e S e c t i o n 5.3.2.1.) E q u a t i o n (5.3) i n d i c a t e s t h a t t h e e m p i r i c a l r e l a t i o n s h i p b e t w e e n c h a l c o p y r i t e a n d t h e p o t a s s i c a n d p h y l l i c a l t e r a t i o n f a c i e s i s s u b s t a n t i a t e d when t h e e f f e c t s o f t h e o t h e r v a r i a b l e s a r e t a k e n i n t o a c c o u n t . T h e n o t a b l e e x c l u s i o n o f K - f e l d s p a r f r o m t h e e q u a t i o n i s b e c a u s e i t s a s s o c i a t e d p r o b a b i l i t y w a s g r e a t e r t h a n f i v e p e r c e n t . E v e n t h o u g h K - f e l d s p a r a n d c h a l c o p y r i t e a r e c o r r e l a t e d p o s i t i v e l y a t t h e 99 p e r c e n t c o n f i d e n c e l e v e l ( S e c i o n s 5.2.1 a n d 5.2.2) K - f e l d s p a r i s i n t e r d e p e n d e n t o n t h e v a r i a b l e s i n t h e e q u a t i o n a n d f o r m s a l i n e a r c o m b i n a t i o n o f t h e o t h e r i n d e p e n d e n t v a r i a b l e s ( L e a n d T e n i s c i , 1978). T h e r e f o r e K - f e l d s p a r d o e s n o t c o n t r i b u t e s i g n i f i c a n t l y t o r e d u c i n g t h e v a r i a n c e o f t h e d e p e n d e n t v a r i a b l e ( c h a l c o p y r i t e ) . 132 The m u l t i v a r i a n t equation f o r molybdenite. (Equation 5.4) i s a l s o c o n s i s t e n t with previous o b s e r v a t i o n s ( S e c t i o n s 4.4,and 5.2.1) t h a t molybdenite i s a s s o c i a t e d with the p o t a s s i c a l t e r a t i o n f a c i e s , and n e g a t i v e l y r e l a t e d t o p y r i t e of the p h y l l i c a l t e r a t i o n f a c i e s . The absence of b i o t i t e from the equation (Equation 5,. 4) i s s u r p r i s i n g s i n c e t h e r e i s a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n between molybdenite and b i o t i t e (Table 5.2). fl s i m i l a r STPREG programme was run i n which b i o t i t e was f o r c e d i n t o the e q u a t i o n , with the r e s u l t t h a t K- f e l d s p a r was f o r c e d out; s i g n i f y i n g the strong interdependnce between K - f e l d s p a r and b i o t i t e . As with K - f e l d s p a r i n the c h a l c o p y r i t e equation (Equation 5.3), t h i s does not n e c e s s a r i l y mean t h a t b i o t i t e i s a poor " i n d i c a t o r " of molybdenite, but o n l y t h a t the i n c l u s i o n o f b i o t i t e i n t o the e q u a t i o n does not account f o r any more va r i a n c e of molybdenite than K - f e l d s p a r does s i n g u l a r l y . 5. 3. 3 E s t i m a t i o n of,, E r r o r i n M u l t i v a r i a n t Equations The standard e r r o r of the m u l t i v a r i a n t equations i n (5.3) and (5.4) i s given i n u n i t s of Ranked I n t e n s i t y . Ranked i n t e n s i t y of a l t e r a t i o n and ore minerals i s d i s c u s s e d i n S e c t i o n s 3.2, and 4.1, and Appendix B. The reason f o r using t h i s r a n k i n g was to normalize a l l m i n e r a l o g i c v a r i a b l e s so as to r e t a i n r e s o l u t i o n between s m a l l absolute changes i n s u l f i d e , and oxide m i n e r a l abundance, and to compare these with l a r g e r a b s o l u t e changes i n the abundance of s i l i c a t e , 133 carbonate, and s u l f a t e m i n e r a l s . Although t h i s r a n k i n g n o r m a l i z e s the changes i n d i f f e r e n t m i n e r a l s , i t i s d i f f i c u l t to understand the a c t u a l numerical value of the e r r o r . F i g u r e 5.2 shows the ab s o l u t e values of e r r o r a s s o c i a t e d with the standard e r r o s f o r c h a l c o p y r i t e and molybdenite. The ranking s c a l e used f o r e s t i m a t i n g abundances of c h a l c o p y r i t e and molybdenite i n the f i e l d i s geometric (Appendix 6, Table B,.6, and t h e r e f o r e i t should be noted t h a t the a b s o u l t e value c f the e r r o r i n c r e a s e s with the value of c h a l c o p y r i t e and molybdenite i n eguations (5.3) and (5.4)., 5.4 Summary o f G e o s t a t i s t i c s A simple two-way c o r r e l a t i o n matix of 15 hydrothermal minerals from the Poplar porphyry demonstrates t h a t s t a t i s t i c a l analyses supports e m p i r i c a l o b s e r v a t i o n s made i n the f i e l d r e g a r d i n g a l t e r a t i o n zoning and f a c i e s , and h e l p s d e f i n e r e l a t i o n s h i p s which were not r e a d i l y apparent. A one-way c o r r e l a t i o n technique was used t o help show (1) which m i n e r a l o g i c a l v a r i a b l e was more the dependent one i n a given c o r r e l a t i o n , and (2) to h e l p remove c o r r e l a t i o n s t h a t were s i g n i f i c a n t only because two minerals were both absent i n a number of gi v e n o b s e r v a t i o n . F i n a l l y , a stepwise m u l t i v a r i a n t r e g r e s s i o n technique was used t o determine which v a r i a b l e s were the most important f o r F i g u r e 5.2: A g r a p h o f r a n k e d i n t e n s i t y o f c h a l c o p y r i t e (as r e - c o r d e d on P o p l a r l o g and u s e d i n t h e m u l t i v a r i a n t r e g r e s s i o n e q u a t i o n ) v e r s u s t h e v a l u e o f t h e m i d p o i n t o f e a c h r a n k i n l o g p e r c e n t c h a l c o p y r i t e . The e r r o r l i m i t s a s s o c i a t e d w i t h a s t a n - d a r d e r r o r o f 1.4 2 r a n k e d i n t e n s i t y u n i t s a r e shown as d a s h e d l i n e s . 135 e s t i m a t i n g the ranked i n t e n s i t y of c h a l c o p y r i t e and molybdenite when a l l the other v a r i a b l e s were c o n s i d e r e d together. The e r r o r a s s o c i a t e d with such e s t i m a t i o n s are f a i r l y l a r g e . However, the equations serve t o q u a l i f y the o b s e r v a t i o n t h a t c e r t a i n a l t e r a t i o n minerals can be used as a t o o l i n e s t i m a t i n g p o t e n t i a l ore grade. 136 CHAPTER VI CONCLUSIONS Th i s study was undertaken to d e f i n e and map p e t r o l o g i c u n i t s , and 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 zones at the Poplar porphyry copper-molybdenum porphyry d e p o s i t . Due t o sparse outcrop i n the study area most of the f i e l d p o r t i o n of the study i n v o l v e d the l o g g i n g of diamond d r i l l c o r e . A computer- compatible l o g g i n g format was used t o expedite t h i s work. The f o l l o w i n g aspects o f t h i s study have been presented: (1) the d e p o s i t i s g e n t i c a l l y and s p a t i a l l y r e l a t e d to a zoned c a l c - a l k a l i n e stock which ranges from hornblende q u a r t z monzodiorite t o b i o t i t e quartz monzonite i n composition. The stock i n t r u d e d the Lower Cretaceous Skeena Group, and the Upper Cretaceous Kasalka Group. These u n i t s c o n s i s t of v o l c a n i c l a s t i c and e p i v o l c a n i c l a s t i c , and c l a s t i c sedimentary r o c k s , r e s p e c t i v e l y . (2) Four K-Ar model ages have been determined and i n d i c a t e t h a t 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 were g e o l o g i c a l l y synchronous with i n t r u s i o n * The term paramagmatic i s used to d e s c r i b e t h i s r e l a t i o n s h i p . These ages range from 72.2 Ma t o 76.9 Ma, p l a c i n g 137 the event i n l a t e Upper Cretaceous time. (3) Two m i n e r a l i z e d zones and f o u r a l t e r a t i o n zones are d e f i n e d . C h a l c o p y r i t e and molybdenite are the two most abundant economic minerals; minor amounts of other s u l f i d e ore m i n e r a l s are l o c a l l y p r e s e n t . P o t a s s i c , p h y l l i c , a r g i i l i c , and p r o p y l i t i c a l t e r a t i o n f a c i e s are d e f i n e d based on the occurrence of the d i a g n o s t i c minerals K - f e l d s p a r and/or b i o t i t e , s e r i c i t e , c l a y , and epidote r e s p e c t i v e l y . C h a l c o p y r i t e and molybdenite are most c l o s e l y a s s o c i a t e d with the p o t a s s i c a l t e r a t i o n f a c i e s . C h a l c o p y r i t e occurs i n an annular r i n g with p o t a s s i c a l t e r a t i o n which surrounds a core of a r g i i l i c a l t e r a t i o n and i s bordered to the o u t s i d e by an area of high- t o l o w - i n t e n s i t y p h y l l i c a l t e r a t i o n . (4) A r g i i l i c a l t e r a t i o n o c c u r s i n two areas; at the c e n t e r of the d e p o s i t , and i n a mere r e s t r i c t e d area i n a p o r t i o n of d r i l l core which i s i n t e n s e l y f r a c t u r e d . Both areas occur w i t h i n the l a r g e r p o t a s s i c a l t e r a t i o n zone. The c e n t r a l a r g i i l i c zone occurs i n rock t h a t i s s p a r s e l y m i n e r a l i z e d , and i s due t o secondary a l t e r a t i o n of a c e n t r a l "low grade c o r e " because of l o c a l i n t e n s e f r a c t u r i n g and consequent i n c r e a s e d p e r m e a b i l i t y . (5) Based on the type of m i n e r a l i z a t i o n c o n t a i n e d at the 138 P o p l a r porphyry, i t s age and i t s geographic l o c a t i o n , i t i s considered here t o belong to the B u l k l e y i n t r u s i v e epoch, a f t e r C a r t e r (1974,and 1976). (6) S t a t i s t i c a l a n a l y s i s of m i n e r a l o g i c a l f e a t u r e s from 12 d r i l l h o les logged i n d e t a i l , show that most hypotheses made i n the f i e l d , d e a l i n g with 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 a s s o c i a t i o n s , were s u b s t a n t i a t e d by s t a t i s t i c a l c o r r e l a t i o n s . T h i s was e s p e c i a l l y u s e f u l i n d e f i n i n g a l t e r a t i o n f a c i e s , and t h e i r r e l a t i o n s h i p with molybdenite and c h a l c o p y r i t e . M u l t i v a r i a n t r e g r e s s i o n analyses are used t o show which minerals have the g r e a t e s t e f f e c t on the observed values of c h a l c o p y r i t e and molybdenite. However, c e r t a i n i n c o n s i s t e n c i e s i n r e g r e s s i o n a n a l y s i s i n d i c a t e t h a t s t a t i s t i c a l t e s t i n g must be viewed i n context of r e a l f i e l d o b s e r v a t i o n s , or e l s e m i s l e a d i n g e x p l o r a t i o n parameters may be developed. The r e s o l u t i o n of i n c o m p a t i b i l i t i e s between f i e l d o b s e r v a t i o n and s t a t i s t i c a l a n a l y s i s can l e a d t o a b e t t e r understanding of t h e a c t u a l r e l a t i o n s h i p s between mineral v a r i a b l e s . 139 BIBLIOGRAPHY Beane, R.E. ,1974. 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Geology of the Urad and Henderson Molybdenite D e p o s i t s , C l e a r Creek County, Colorado, with a S e c t i o n on a Comparison of these d e p o s i t s with those a t Climax, C o l o r a d o : Econ. G e o l . , v. 73, pp. 325-368. . White, W.H., 1959. C o r d i l l e r a n T e c t o n i c s i n North America: Amer. Assoc. Pet. Geol., B u l l . , v. 43, pp. . 60- 100. White, W.H., Harakal, J.E., and C a r t e r , N.C., 1968. Potassium- Argon Ages of Some Ore Deposits i n B r i t i s h Columbia: Can. I n s t . Min. Met. B u l l . , v. 61, pp. 1326-1334. 151 W i l t o n , D.H.C, 1978. A g e n e t i c Model f o r the Sustut Copper Dep o s i t , N o r t h - C e n t r a l B r i t i s h Columbia: Univ. B r i t . C o l . M.Sc. T h e s i s , unpubl., 215 p. W i t h e r l y , K.E., 1975. 1974 G e o p h y s i c a l Report on the Poplar Lake Property: B r i t . C o l . M i n i s t r y Min. Pet. Res. assessment Report no. 5361. Woodsworth, G.J., 1979. Geology of W h i t e s a i l Lake Map Area, B r i t i s h Columbia:in Current Research, Part A, Geol. Surv. Can., Paper 79-1A, pp. 25-29. APPENDIX A A n a l y t i c a l Da TABLE A . l POTASSIUM-ARGON ANALYTICAL. DATA 3 FROM THE POPLAR PORPHYRY DEPOSIT, D.C. Sample No. Location Rock unit;' 3 M i n e r a l 4 0 A r * d ' 40„ *d Ar Apparent 6 or Name Lat, (N) ; Long. (W) rock name da ted %K1S° 4 0 A r total (10 _5cm3STP/g) age (Ma) Time G76TR22 54°01'126°50' 3b: bi o t i t e quartz b i o t i te 7. 14±0.07 0. 878 2.080 73.7±2.5 Late Cretaceous monzonite POPLAR LAKE 54<,01'126°50 3b: b i o t i t e quartz b i o t i t e 7. 00i0.04 0. 915 2.139 76.912.3 Late Cretaceous monzonite PC-36 54 o01 ,126°50' 4a: porphyritic b i o t i t e 5. 97510.29 0. 846 1. 683 72.213.0 Late Cretaceous dacite PT-115 54°01'126 o50 1 3a: hornblende hornblende 5. 87510.05 0. 794 1.780 76.212.7 Late Cretaceous quartz monzodiorite a A l l analyses in the Geochronology Laboratory, Department of Geological Sciences, The University of B r i t i s h Columbia bRock units correspond to Map A C"S" i s one standard deviation of q u a d r u p l i c a t e analyses Ar " indicates radiogenic argon eDecay constants used: X r- 0.501 x 1 0 ~ 1 0 y r _ 1 f Xfl = 4.90 x 10~ 1 0yr'" 1, 4°K/K ° 1.167 x 10~4 fTime designed after Obradovich and Cobban, 1975 to TABLE A-2 CHEMICAL ANALYSIS .(% OXIDE WEIGHT PERCENT) AND C.I.P.W. NORMS OF IGNEOUS ROCKS FROM THE POPLAR PORPHYRY Sample: Rock unit PT51: 8 PT60: 5 Oxide S i 0 2 64. ,76 61. ,60 M 2 ° 3 15. ,38 15. ,16 F e 2 ° 3 * 8. ,89 4. ,91 MnO 0. ,09 0. ,09 MgO 1. ,33 2. ,09 CaO 2. 43 3. .84 K 20 2. ,67 2. ,92 P2°5 0. ,27 0. ,414 Na 20 4. ,89 3. ,93 T i 0 2 0.37 0. ,54 L.O.I + 2. ,94 4. ,103 TOTAL 98. 97 99. ,58 PT115: 3 30/132: 4 36/375: 5 62.33 66.10 • 59.75 16.59 16.55 15.62 5.55 5.41 4.98 0.12 0.05 0.12 2.60 1.69 1.91 3.75 3.38 5.40 2.70 2.31 2.87 0.30 0.31 0.40 3.94 4.29 2.32 0.624 0.515 0.525 1.94 1.64 7.29 100.29 102.26 101.18 quartz 19.47 15.18 13.70 15.99 16.63 orthoclase 16.36 17.74 15.83 13.02 17.22 a l b i t e 42.7 34.73 34.05 36.97 21.13 anorthite 10.84 15.32 16.52 14.07 23.51 magnetite 2.73 ' 2.97 3.07 2.88 2.95 illmenite 0.73 1.05 1.18 0.93 1.01 apatite 0.59 0.99 0.69 0.69 0.95 corundum 0.70 0.0 0.88 1.06 0.0 * A l l Fe as F e ^ ^L.O.I. = Loss On Ignition 155 APPENDIX B POPLARLOG The Computer Compatible D r i l l c o r e Logging Format Used In This Study. B.1 I n t r o d u c t i o n The development cf P o p l a r l o g , as a computer compatible coding format f o r the lo g g i n g of d r i l l c o r e , came about as a n e c e s s i t y t o assure t h a t g e o l o g i c i n f o r m a t i o n be recorded i n a st a n d a r d i z e d manner, and th a t each i n t e r v a l of core be examined f o r the same g e o l o g i c parameters. P o p l a r l o g was developed on the knowledge that the Poplar porphyry had an ex t e n s i v e a l t e r a t i o n halo (Schmidt, 1978, pers. comm.; Bowen, 1976; and C a r t e r , 1978, pers. comm.), and t h a t outcrop made up l e s s than one percent of the s u r f a c e area on the property. Hany ideas and suggestions on the format of P o p l a r l o g were o f f e r r e d by c o l l e a g u e s who has p r e v i o u s l y used other computer compatible l o g g i n g systems (Wilton, 1978, and pers. comm., 1978 and Mortensen, pers. comm., 1978). The major p a r t of P o p l a r l o g was formulated along the l i n e s of a p r e v i o u s l y developed coding format f o r porphyry ccpper d e p o s i t designed by Blanchet and Godwin (1972), and C. I . Godwin (pers. comm. , 1 978> and 1 976). Most o f the codes used dur i n g t h i s study and d e s c r i b e d i n Se c t i o n B.3 and B.4 are taken d i r e c t l y from Blanchet and Godwin (1S72) . 156 B. 2 D e s c r i p t i o n , and Coding A clank P o p l a r l o g d r i l l c o r e l o g g i n g form i s shown i n F i g u r e B.1. The c h a r a c t e r i s t i c s and headings of the form w i l l be d e s c r i b d from l e f t t o r i g h t . (1) V i s u a l Log; This space was used t o p l o t the a t t i t u d e s with r e s p e c t t o d r i l l core of v e i n s , f a u l t s , f r a c t u r e s , rock u n i t c o n t a c t s , bedding, f o l i a t i o n , and any other planar or l i n e a r f e a t u r e . Paragenetic r e l a t i o n s h i p s between veins was a l s o recorded. The a p p r o p r i a t e symbol was p l o t t e d adjacent t o the p o r t i o n of a p a r t i c u l a r depth i n t e r v a l being d e s c r i b e d . (2) Comments, Column 1: Column one was used t o r e c o r d one l e t t e r codes denoting d i s c o n t i n u o u s g e o l o g i c f e a t u r e s , or as a one l e t t e r " f l a g " , used to denote l i n e s which were used f o r c r i t e r i a other than formatted g e o l o g i c i n f o r m a t i o n . The comment codes used i n Column one on P o p l a r l o g are shown i n Table B.I. HOLE NUMBER II V A G L Depth to Bot tom of I n te rva 7 M i n j z n Z o n e 14—H T M y a p t Ie r R O C K T Y P E 1M1TMTTH o u 15116 Oualr. Descr. 17 na |i9i?oizr OPLARLOG II Figure B.l PAGE OF h If a. T E X T U R E DO Pol TAR I T X ft I I 0Z H I A l TF R A T I O N K F H I B I H I M U H I C L H I C Y H I M I N E R A L S E P H I C B H I A L T 1 H I A L T 2 H I S U M A L T H I P Y P H T H M H P T C P ,H P T M I N E R A L I Z A T I O N B N H P T C C H. P T M O H P T M H H P T M N H P T M N H P T S U M O R E H P T Z N 158 TABLE B.1 One Letter Comment Codes Used with Poplarlog (Column One) 1 Letter Code Meaning Bottom of hole-recorded with hole number and date; used as a fl a g i n determining the end of a hole. Comment - to denote l i n e s used for comments about the d r i l l core i n addition to, and sublimenting, normal coding; usually used to describe a par t i c u l a r geologic feature i n more d e t a i l . Dykes - used to denote the bottom of an i n t e r v a l consisting of a dyke uni,t. . Contact - used to denote contacts between rock units, superseded by D (=dyke) where appropriate. Sample - sample taken at a particular depth (which was recorded i n column 76-80). Zone of f a u l t i n g , fracture, or a shear zone. Top of hole - recorded with hole number and date; used as a f l a g i n denoting the top of a hole. (3) Depth to the bottom of the i n t e r v a l described on that .line; Columns 2-5: usually i n 10 foot (3 m) i n t e r v a l s , or les s i f geologic features changed ( i . e. contact between rock units) (4) Ore Zone; Columns 6-8: used to define which ore zone 159 t h a t p a r t i c u l a r i n t e r v a l was i n ( i . e. hypogene (HYP), supergene s u l f i d e (SOS), or supergene oxide (SUX)). (5) Type M o d i f i e r and Bock Name; Columns 9-14: used i n c o n j u n c t i o n with each other t o name the rock u n i t being d e s c r i b e d (Coumns 11-14) using f o u r l e t t e r code names which were developed as new u n i t s were i n t e r s e c t e d i n d r i l l core. Column 9 was used t o r e c o r d a one l e t t e r " f l a g " , unique t o each rock u n i t , to f a c i l i t a t e the r a p i d v i s u a l i d e n t i f i c a t i o n of the rock type i n each i n t e r v a l (Table B.2). Column 10 was used t o q u a l i t a t i v e l y d e s c r i b e with a one l e t t e r code the " c o n d i t i o n " of the core with r e s p e c t to the s t a b i l i t y of b i o t i t e ( determined to be a d i a g n o s t i c m i n e r a l , s e n s i t i v e t o v a r i o u s types of a l t e r a t i o n (Table B.3). (6) Colour; Column 15-16: a g u a l i t a t i v e estimate o f the Colour Index. DK-dark, >50% mafics; MD-medium, 25-30% mafics and; L T - l i g h t , <25% mafic m i n e r a l s . I n c l u d e s both primary and secondary m i n e r a l s . (7) M a f i c s ; Columns 17-18: c o n s i s t s of a two l e t t e r (or l e t t e r and symbol) code f o r t h e type of mafic minerals present, and t h e i r r e l a t i v e abundance. HB-hornblende o n l y ; B<-hornblend g r e a t e r than b i o t i t e ; B > - b i o t i t e g r e a t e r than hornblende and; B l - b i o t i t e only. B i o t i t e and hornblende were the only mafic minerals observed at the Popl a r porphyry. Table B.2 F i r s t Type M o d i f i e r s and Coded Names Used With Poplarlog (Columns 9, and 11-14) Rock Uni t ' Skeena(1) Quartz Monzodiorite(3a) Quartz Monzonite(3b) I n t r u s i v e Breccia(3b) Quartz L a t i t e - A n d e s i t e ( 4 a ) F e l s i t e Dykes(4b) P o r p h y r i t i c Rhyolite(5) Andesite F i e l d Name Hornfels Hornblende D i o r i t e B i o t i t e Porphyry B r e c c i a Feldspar Porphyry F e l s i t e R h y o l i t e Tracyte Type Modifier II B F F Q T 4 L e t t e r Code HORN DIOR PPBF BRXX PPFL FELS PPFQ TRAC Comments used for any country rock observed in d r i l l core - not ne c e s s a r i l y h o r n f e l s meta- morphosed . PP=Poplar porphyry BF= b i o t i t e - f e l d s p a r porphyry Sub-unit of quartz monzonite FL-feldspar porphyry Sub-unit of quartz l a t i t e andesite FQ=Feldspar-quartz porphyry T=Tracyte; o r i g i n a l l y named tr a c y t e i n f i e l d , l a t e r changed to andesite, but code kept to maintain consistency 161 (8) Q u a l i f y i n g D e s c r i p t o r ; Columns 19-21: a " c a t c h a l l " heading used t o denote unusual f e a t u r e s i n the c o r e , or changes i n the nature of the core which were too minor to d e s c r i b e under a new i n t e r v a l . Examples i n c l u d e ; CNA-a change i n a l t e r a t i o n type; XEN-xenoliths; and PAT-patches.. 162 TABLE B.3 Second Type M o d i f i e r Used With P o p l a r l o g (Column 10) Type M o d i f i e r D Dark - Secondary b i o t i t e i s observed i n the i n t e r v a l d e s c r i b e d . N Normal - B i o t i t e books are present, and thought t o be o r i g i n a l phenocrysts. rock i s f r e s h or has undergone minor a l t e r a t i o n . L L i g h t - O r i g i n a l b i o t i t e books have been a l t e r e d t o pseudomorphis of c h l o r i t e or s e r i c i t e . 0* O b l i t e r a t e d - B i o t i t e books are not observed and the t e x t u r e i s o b l i t e r a t e d by a l t e r a t i o n ( g e n e r a l l y p h y l l i c ) . I d e n t i f i c a t i o n of rock type i s d i f f i c u l t and q u e s t i o n a b l e . , X* Extremely o b l i t e r a t e d - The o r i g i n a l t e x t u r e has been destroyed by a l t e r a t i o n . Bock type i n doubt. •For both d e s i g n a t i o n s the o r i g i n a l rock type c o u l d be a s c e r t a i n e d by c o r r e l a t i o n by g r a d a t i o n a l changes t o f r e s h e i t h e r up or down the d r i l l c o r e . rock 163 (9) Texture; Columns 22-30: a gen e r a l heading which i s su b d i v i d e d i n t o seven subheadings. O r i g i n a l l y i n t e n d ed f o r r e c o r d i n g c r i t e r i a to be used i n c o r r e l a t i n g sedimentary rocks from d r i l l c o r e . These c r i t e r i a i n c l u d e ; (a) g r a i n s i z e mode, (b) maximum g r a i n s i z e , (c) open or c l o s e d packing of g r a i n s , (d) degree of s o r t i n g , and (e) and (f) p a r t i c u l a r t e x t u r a l f e a t u r e s which were determined i n the f i e l d t o be important c r i t e r i a f o r c o r r e l a t i o n . Most of these headings were never used because of the high i n t e n s i t y t o which most of the Skeena rocks were a l t e r e d , and the t e x t u r a l nature of the u n i t i t s e l f , made such o b s e r v a t i o n s d i f f i c u l t , and too i n f r e q u e n t to be of any use. However, the subheadings Texture I , and Texture I I were used t o denote unusual or d i s t i n g u i s h i n g t e x t u r e s encountered i n the d r i l l core such as FL f o r flow l i n e a t i o n o r p i l o t a x i t i c t e x t u r e , cr AG f o r amygdaloidal texture,. (10) A l t e r a t i o n M i n e r a l s ; Columns 31-54: t h i s heading c o n s i s t s of the 16 subheadings l i s t e d i n Table B.4. Each of 10 mineral subheadings c o n s i s t of two columns (except f o r c l a y , and SUM ALT which are di s c u s s e d below); the f i r s t of which (H) i s used f o r a one numeral code d e s c r i b i n g "how" the mineral o c c u r s , i . e. i t s r e l a t i v e d i s p e r s i o n (Table B.5, taken from Blanchet and Godwin); 1S72). The second column (I) i s used f o r a one l e t t e r code d e s c r i b i n g the " i n t e n s i t y " , or percentage by volume, of the mineral (Table B. 6 ) . 164 The l a s t subheading under A l t e r a t i o n M i n e r a l s on P o p l a r l o g , SUM ALT, columns 52-54, was used t o "summarize a l t e r a t i o n " f o r t h a t i n t e r v a l and to place t h a t i n t e r v a l of core i n one of 10 a l t e r a t i o n zones i n the Lowell and G u i l b e r t Model of porphyry d e p o s i t s , modified by Blanchet and Godwin (1972).. Columns 52 and 53 (H and I) were used to summarize both how the a l t e r a t i o n occurred ( i t s degree of d i s p e r s i o n ) , and i t s i n t e n s i t y (volume p e r c e n t ) . Column 54 was used t o p l a c e the i n t e r v a l d e s c r i b e d i n one of the 10 a l t e r a t i o n f a c i e s of L o w e l l and G u i l b e r t (1970) based on c r i t e r i a found i n Table B.7 (taken from Blanchet and Godwin, 1972), which i s a " c h e c k l i s t " of r e l a t i v e i n t e n s i t i e s of s i l i c a t e , and carbonate a l t e r a t i o n minerals versus the 10 a l t e r a t i o n f a c i e s . F i g u r e B.1 i s a c r o s s - s e c t i o n through a t y p i c a l porphyry d e p o s i t showing the s p a t i a l r e l a t i o n s h i p of 10 a l t e r a t i o n f a c i e s (taken from Blanchet and Godwin 1972). (11) M i n e r a l i z a t i o n ; Columns 55-75: s i m i l a r to the method f o r d e s c r i b i n g the degree of d i s p e r s i o n and i n t e n s i t y of s i l i c a t e , carbonate, and s u l f a t e a l t e r a t i o n m i n e r a l s ; the mode of occurrence and i n t e n s i t y of 7 s u l f i d e and oxide minerals i n each i n t e r v a l of c o r e was recorded i n a p p r o p r i a t e columns (Table B.8). However, because the degree of i n t e n s i t y to which oxide and s u l f i d e minerals occur i s g e n e r a l l y a great d e a l l e s s than t h a t of a l t e r a t i o n m i n e r a l s , a geometric s c a l e of abundances was used. T h e r e f o r e the n o t a t i o n "PT" was used i n the columns to d e s c r i b e i n t e n s i t y of m i n e r a l i z a t i o n , and d i s t i n g u i s h i t from the s c a l e used to r e c o r d i n t e n s i t i e s of a l t e r a t i o n (Table B.6). 165 The method used to r e c o r d degree of d i s p e r s i o n of s u l f i d e and oxide .minerals i s e x a c t l y the same as f o r a l t e r a t i o n m i n e r als as shown i n Table B.5. The subheading SUM ORE i s e x a c t l y analogous to the summary columns f o r a l t e r a t i o n m i n e r a l s , p r e v i o u s l y d e s c r i b e d i n the previous s u b - s e c t i o n (9),. The c h e c k l i s t of r e l a t i v e mineral abundance versus m i n e r a l i z a t i o n f a c i e s taken from Blanchet and Godwin (1972) i s shown i n Table B.9. A corresponding c r o s s - s e c t i o n through a t y p i c a l porphyry d e p o s i t showing the s p a t i a l r e l a t i o n s h i p between these f a c i e s i s shown i n F i g u r e B.2. (12) Sample Depth; Columns 76-80: These columns were used to r e c o r d the depth at which samples were taken(c. f. .'S' i n column 1; Table B. 1). 166 TABLE B.4 S i l i c a t e , Carbonate and Sulphate A l t e r a t i o n M inerals (Columns 31-51) P o p l a r l o g A b b r e v i a t i o n QZ KF Bl MO CH CY EP CB ALT 1 {finer a l Quartz Potassium F e l d s p a r b i o t i t e muscovite c h l o r i t e c l a y Comments ALT 2 epidote carbonate Anhydrate-Gypsum miscellaneous a l t e r a t i o n seldom used Column 43 was i n - tended to d i s t i n - guish k a o l i n i t e from m o n t m o r i l l o n i t e . i t was never used. seldom used i n c l u d e s c a l c i t e s i d e r i t e , and dolomite. Was used f o r these minerals a f t e r f i e l d w o r k i n d i c a t e d t h e i r importance used f o r seldomly observed m i nerals. 1 6 7 TABLE B. 5 Mode And Degree Of 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 . V,E,D,P Refer To Modes Of Occurrence: Veins, Envelopes, D i s s e m i n a t i o n s , And P e r v a s i v e , R e s p e c t i v e l y (from B l a n c h e t And Godwin, 1 9 7 2 ) . Mode of Oc Mine ra l i za t ion rurrence Degree of Dispersion Mode of Occurrence Alterat ion Assemblages Veins and macro - veins including stockwork and gouge V V 1 2 J 4 5 6 7 8 ' 9 V or v j V veins V e i n s , veinle ts , fracture f i l l ings Sc minor disseminations D « * V E< V or P « V veins and moderate envelopes or minor pervasive Veinleta and some disseminations t> < V E * V or P<V envelopes and veins equal or veins and moderate pervasive Veinlets with moderate disseminations r s v E > V or P S V v p + i v envelopes with some veins or pervasive with moderate veins Veinlets and disseminations more or less equal 0 • V E or P « V • i p + ^ v 8 8 envelopes or pervasive equal to veins Disseminations and moderate veinlets 0 2 V P < E or P>V — P + — E ! - ^ P + — V 8 8 * 8 8 pervasive with some envelopes or moderate veins Disseminations with some veinlets f - ° - . + f v 0 > V P* E or P>V i p + i f i ± P + J 2 - V 8 T 8 j 8 r * 6 pervasive and envelopes or w;th some veins Mos t ly dissemination with minor veinlets or mic ro -ve in - D ao V 1 6 , P>E or P » v I— p+ i r ; 8 8 pervasive with some envelopes or minor veins Disseminations 0 D l P I P 1 i P pervasive 168 TABLE B.6 One L e t t e r Codes f o r Estimated Volume Percent of S i l i c a t e , Carbonate and S u l f a t e A l t e r a t i o n M i n e r a l s , and f o r S u l f i d e and Oxide M i n e r a l i z a t i o n , from P o p l a r l o g " A l t e r a t i o n " Onec L e t t e r " M i n e r a l i z a t i o n " M i n e r a l Abundances Code M i n e r a l Abundances >60% X-extremely high >16% 50-60% V-very high 8-1655 40-50% H-high 4-8% 30-40% A-above medium 2-4% 20-30% M-medium 1-2% 15-20% B-below medium 0-5-1% 10-15% f - f a i r 0.25-0-5% 5-10% L-low <0.25% 2-5% E-extremely low « 0 . 2 5 % <1% T-tra c e Trace NIL hlank-none NIL 169 TABLE B. 7 C h e c k l i s t o f R e l a t i v e A l t e r a t i o n M i n e r a l s Abundances Versus A l t e r a t i o n F a c i a s i n Porphyry Deposits (taken frcm Blanchet and Godwin 1972) Alteration Facie* Fresh Rock Propylitic Montmorillonitic Intermediate Argii l ic KF - Stable Sericitic < = Phyllic) Advanced Argii l ic Potaaaic 'Chlori-Potaeeic' S ilicic (Quartt Flooding) Quartz QZ I / i \ / A \ \ K-spar K F Biotite Bl Orig.KFJ stable Mus- covite Sericite MU.MS Orig.BI ' A Mg- rich! Clays CY Kaolin KA I I /1 \ \ \ \ / • / I I I '.'</ I /! i i i IMontmor- illonite MM s Chlorite C L Epidote E P Carbon' ates CB Other and/or and/pr and/or and/or / / / / AB Remark* Also Adularia, / ' ^ S p r i t e Z £ / . ' P P AB=Albite Z E = Zeolite(s) TO TO= tourmaline PP - pyrophyilite AH= anhydrite I diagnostic t abundant a / / / j commonly present k moderate • / / infrequently present L minor = y 1 7 0 FIGDEE B.2 Model of A l t e r a t i o n F a c i e s in porphyry D e p o s i t s a f t e r L o w e l l and S u i l b e r t (1970), (taken from Blanchet and Godwin, 1972). \ I / // ,2,-3/4/5/6/ 1 ' 1 !// /' 1/ ' 1/ ' v \ \ \ M \ l MM \\\\ F r e s h Roch P r o p y litie M oiMmonl lonit ic Inter me dio 11 Artji l l ic K F - S t o o l t Sc rici1>C ( Phf l . i c ) Advortced Arg i l l i c Ii \ A! \ K V \ I A / \ I \ / \ e—V- W A 1 - C h l o r i - P o l o « * i c - S ktorn 171 TABLE B . 8 P o p l a r l o g A b b r e v i a t i o n S u l f i d e and Oxide M i n e r a l s (Columns 55-72) M i n e r a l Comments PY P y r i t e HM hematite CP c h a l c o p y r i t e BN b o r n i t e CC c h a l c o c i t e MO molybdenite magnetite added i n the f i e l d MN2 c o v e l l i t e , t e t r a h e d r i t e only r a r e l y used MN3 galena, e t c . Only r a r e l y used 172 TABLE B.9 C h e c k l i s t of R e l a t i v e S u l f i d e and Dxide M i n e r a l Abundances Versus M i n e r a l i z a t i o n F a c i e s i n Porphyry D e p o s i t s [taken from B l a n c e t and Godwin, 1972). Mineralization Zones Pyrite PY Chalco- pyrite CP Molyb- denite Wolframite Covellite Digenite WF, CV.DG Chalcocite CC Hematite Magnetite Galena- Sphalerite GX (Gold-Silver occurrence) Pyrrhotite PR Native Copper Shx oud Peripheral Shell Low Pyrite Shell Deep Ring Pyrite Shell Ore Shell L-o-*'-Grade Core Deep Core / / / / J J J A / / / / ' J /i i i / / / / 'A i i /i i /// / / i / JI A / 1/ dia-gnostic & abundant frequently present U substantial = / / / / usually present h. moderate a / / / sometimes present k minor s. / / infrequently present h. trace to minor -S 173 FIGO.EE B. 3 Model of S u l f i d e , Oxide M i n e r a l F a c i e s i n Porphyry D e p o s i t s a f t e r Lowell and G u i l b e r t (1970) (taken from Blanchet and Godwin, 1972). Compare with T a b l e B. 9, and F i g u r e 3.1. / I Sh roud , "~ —^2 r- Peripherol Shell / , ^ , — 3 ̂ — -V Low Pyrite Shell ' ' N \ \ / / ^ v i - - ^ V v ^ 5 - \ * r Pjr i le Shell / I ^ ^ \ \ \ / / / ^ ' ^ ^ S - V - ^ ^ Or, She,, 1 * | -f : I \ H Lo - Grc ie C i A ! i I /; / / \ \I A / \ ' M / , M tf p Core Deep R .ng / APPENDIX C C o m p u t e r P r o g r a m s U s e d i n t h e S t u d y C A PROGRAM 10 P L O T C H A L C O P Y R I T E ON CROSS-SECTION A-A C FORMATING I S CCMPATA6LE WITH POPLARLOG C CPYI IS CHALCOPYRITE INTENSITY - CPYri IS I T S MODE OF OCCURENCE; BOTH ARE ON R A N K E D S C A L E S C ALL ELSE IS FO U N D I N "11.B.C. PLOT" INTEGER SYM,CPYI,CPYH LOGICAL*! CO 1, COMMI 5) LOGICAL** EQCMP CALL PLCTRLI'METRIC 1,0.0) CALL SY<waHl3 .30 ,.75 ,0.25,'C<OSS-SECriiJSAL PLOT OF C H A L C O P Y R I T E A L O N G LINE A-A ',0.0,511 CALL SY130LI9. 5,0.25,0.25,'WITH SUPPERIMPOSEO ZONES OF M O L Y S O E N I T E . K - F E L O S P A R , B I O T I T E , P H Y L L I C AND A R G I L L I C A L T E R A T I O N 1 . 0 . 0 , 9 0 ) 5 READI5, l0,E. -n=-?99IC0M,C?YH,CPYI ,CASTG,DEPTH 10 FORMAT!Al,57X.2II.22X,F8.3,2X,F8.J) IFI E 5CMPII,•3•, COM)) GO TO 100 UP = 11 00.00-OEP TH UP=IUP/52tf.0)»12.0*.<.-l.*.39* ESTG = (F. ASTG/528.01*12.0*0.',*2.12 IFI CPYI .EQ.O) SYM=15 1FICPYI.E0.1ISY"*16 IFICPYI.E0.2)SYM=17 IFICPYI.EQ.3)SYM=18 lF(CPVl.E'J.<tlSY J»19 IF (CPYI .t'0.51 SYM=20 1FICPYI.EC.6ISYM=22 IFICPYI.E3.7)SYM=23 IFICPYI .EQ.B)SY.M = 26 IFICPYI.EJ.9)SYM=27 CALL SYMrtOLIESTG.UP.O.19.SYM.O.O.-l1 ii GO II) 5 100 RFA0(5,110,END = 9991 ICOMMI J l ,J»l,5l .EL.RGT 110 FOH MAT I5A I »3<,F5.2,F7.21 EL= 1100.0-EL EL=(EL/529.01*12.0*0.*-l.0*0.39% RGT=(RGT/528.0)»12.0*0.%*2.12 CALL SYMHOLUGT,EL,0.20,COMM,0.0,5) GO TO 5 999 CALL PLCTRLI'METRIC', 11 CALL AxCTRLI ' X CR I & ' ,0.0) CALL AXCTRLI'YORIG',0.0) CALL AXPLOTI'EASTING ALONG X-SECTION A-A I ME T CR S) ; ' , 0.0 ,9 3 . 726, 11 203. 0 , 1 3. 2) CALL AXPLOTI'ELEVATION ABOVE SEA LEVAL (METERS);',90.0,2%.1%,616.35,13.2) CALL PLOTNO STOP END cn COMPUTER- PROGRAM "SMLRK1- PLOTS THE GEOLOGY ALONG CROSS-SECTION A-A FORMATING IS COPA 7 IHL E WITH POPLARLOG INFORMATION OF ROCK NAMES ARE GIVEN IN APPENDIX B ALL OTHCR INFORMATION IS IN " U . 8 . C. PLOT" I NTESER SYM L O G I C A L » l C O M M I 5 ) , C O M ( 1 ) , R K U 2 ) LOG ICAL* * EQCMP ,RK2 CALL PLC T R L ( ' M E T R I C . 0 ) CALL S Y M r t Q L ( 1 3 . 3 . 9 . 5 , 0 . 2 5 , ' C R O S S - S E C T I O N A L PLOT OF GEOLOGY ALONG L INE A - 5 READl5. lO,EN: )=9 99 ICOM,RK l ,RK2,EASTG,OEPTH 10 n j R M A T U l , / X , 2 A l , A < , , 6 9 X , F 8 . 3 , 2 X , F 8 . 3 ) I F I E Q C M P I I , ' J > , C O M ( 1 ) ) I G O TO 103 0P=1100.0 -OEPTH UP= (UP/52 3.0) * 1 2 . 0 * 0 . V - l . 0 * 0 . 3 94 E STG=( EASTG/52 9 . 0 ) * 1 2 . a * 0 . < V » 2 . 12 SYM=30 IFIE<JC 'PPBF ' ,RK.2)>SYM = 3 IF! E3CM»( <,, 'PP XX' ,RK2) | SYM. U I F (FOCMP I * . , , PPFQ , ,RK2 ) ) SYM=1 I F i r . - J C M P I ^ . ' P P F L ' .RK2) )SYM=2 I F I E 3 C M P I * , ' d X I N ' , R K 2 M S Y M = 1 7 IF l E3CMPI M O R N ' tRK2) ) SYM = <,3 IF(ETCMO(<v,<FELS , .RK21,SYM=37 IF I E3CMP! • T R A C ,RK2 ) )SY,M=5 CALL SY.M30L ( ESTG. UP , C. 07 t SYM, 0 . 0 , - 1 ) IF !SYM.NE.301 GO TO 5 W R I T E ( 6 , l O I C J M , R K l , R K 2 , £ A S T G , D E P T H GO TO 5 100 R E A 0 ( 5 , U 0 . E N 3 = 999) (COMMIJ) , J » 1 . 5 ) , E L . R G T 110 F O R M A T ! 5 A I , 5 X , F 5 . 2 , F 7 . 2 ) E L = 1 1 0 0 . 0 - E L i\ EL = ( E L / 5 2 3 . 0 ) * 1 2 . 0 * 0 . 4 - 1 . 0 * . 3 9 * RGT = I R G T / 5 2 f ) . J ) * 1 2 . 0 » 0 . 4 * 2 . t 2 CALL SYMBOL I R G T , E L , 0 . 2 0 ,COMM.0.0 ,5J GO TO 5 999 CALL PI C I RL I * M E T R I C , 1 1 CALL AXCTRLI ' XOR IG ' ,0 .01 CALL A X C T R L I • Y C R I G ' , 0 . 0 J CALL AXPLOTI ' EAST ING ALONG X-SECTIUN A-A (METRES) ; ' , 0 . 0 , 9 3 . 7 2 6 , 1 1 2 0 3 . 0 , 1 3 CALL AXPLOTI ' ELEVAT ION ABOVE SEA LEVEL (METRES) ; * , 9 0 . 0 , 2 * . l < > » 6 1 6 . 3 5 , 1 3 . 2 ) CALL PLOTNO STOP END C » PROGRAM TO CHANGE FORTRN CHARACTERS TO FORTRAN REAL NUMBERS C THIS REQUIRES USE OF CCMMAND • E T J A C ' C FORMATTING IS COMPARABLE TO POPLARLOG LOGICAL ECJC L O G I C A L * l COM(1) DIMENSION ALT I (50) , XMINU 50 >, L TI 1 50) .MINI I 501 10 KE \ 0 ( 5 , 2 0 , ENO = 9 9 9 ) C O M , ( L T I ( I 1,1 = 1 , 1 0 ) , ( M I N I ( J 1 , J » 1 , 9 ) 20 FORMAT ( I A l ,29X ,61 1 I I, IX) , IX ,4(1 11 ,1 X) , 3X.9I II 1, IX) ) IF ( E O U C I 1 T 1 , C O M ) ) GO TO 10 IF (EOUC( 1 8 • , C O M 1) GU TO 10 C 00 100 1=1.10 I F ( L T I (I ) .E 3 .01ALT1[ I 1=0.0 IF I LT11 I 1 . E J . 1 1ALTII I )=2.5 IF (LT 11 I I .h'3.2 1 AL TI (I ) = 7.5 I F I L TII I) . £ 3. 3 I ALII (I I = 12.5 I F I LT K I 1.E3.%1ALTI 111 = 17.5 I F I L T I I I ) . E Q . 5 ) A L T I ( I ) = 2 5 . 5 I F I L T I I I ) . E 0 . 6 ) A L T I I I 1 = 3 5.5 1 F I LT I ( I 1 - E Q . 7 1 ALTI I I )=<,5.5 i r ( L T I ( I I . E 3 . 9 ) A L T I ( I ) = 5 5 . 5 IF ILT 11 I 1 . E 0 . 9 ) A L T I I I ) * 6 5 . 5 100 CONTINUE C 00 200 J=1.9 1 FI M IN I ( J> .EJ .01XM IN l ( J l = 0 . 0 ; ! i r ( M I N | ( J l . E 7 . 1 ) X M I N J I J I = 0 . 0 1 IF I M IN I ( J I . E 3.21XMINI (J ) = .13 , i r I MINI I J ) . F 3 .31XM1NI IJ i = .37 I F ( M I N I ( J 1 . E 3 . % ) X M I N I ( J ) » . 7 5 I F I M I N K J 1 . E 3 . 5 1 XMI N I I J l = I . 5 I F ( M I N i ( J ) . E 3 . 6 1XM lN I I J )=3 .0 IF I V I Nl I J 1 . E 7IXMINI I J ) = 6.0 1 F ( M I N I ( J ) . E 3 . 8 ) X M I N I ( J I » 1 2 . 0 IFIMINI I J ) . E J . 9 1 X M I N I ( J l - 2 % . 0 200 CONTINUE C HRI TE (6,3001 ( A L T K I 1 . 1-1 ,91 ,( XMINI ( J ) , J - l .7 ) 300 F 0 R M 4 T ( 9 F 5 . 2 , 1 X , 7 F 5 . 2 ) GO TO 10 999 STOP E SO 17 8 APPENDIX D T h i n S e c t i o n D e s c r i p t i o n s Rock U n i t : Skeena Group (Unit 1); c r y s t a l t u f f . T h i n S e c t i o n No. 30; Sample No. PT-116 L o c a t i o n : 5,4 4 ON; 11.61.7.E 179 M i n e r a l Mode quartz c r y s t a l s 5% c h l o r i t e ( c l o t s ) 10% c l a y ( c l o t s ) 20% groundmass 65% D e s c r i p t i o n : Broken 0.1-1.0 mm q u a r t z c r y s t a l s , l o c a l l y sphera- l i t i c , i n a l t e r e d groundmass of c l a y , c h l o r i t e , and l i m o n i t e . Pseudomorphs o f c h l o r i t e a f t e r m afics (?) are 0.1-1.5 mm i n d i a - meter. C l a y patches, pseudomorphic a f t e r p l a g i o c l a s e , are 0.5- 1.5 mm i n diameter. Rock U n i t : hornblende quartz monzodiorite (Unit 3a) T h i n S e c t i o n No. 29; Sample No. PT-115 L o c a t i o n : 5,370N; 11,640E M i n e r a l Mode p l a g i o c l a s e phenocrysts 25% hornblende phenocrysts 10% quartz phenocrysts 2% e p i d o t e 10% magnetite 2% groundmass 51% D e s c r i p t i o n : P r o p y l i t i c a l t e r a t i o n ; hornblende phenocrysts are 1-3 mm i n l e n g t h , and are s t i l l f r e s h . P l a g i o c l a s e phenocrysts ( A n 3 1 ) range from 1-3 mm, and are a l t e r e d to carbonate, a l b i t e , and e p i d o t e . Groundmass p l a g i o c l a s e (45%) i s l e s s than 0.1 mm i n diameter. Magnetite ranges from 0.1-1 mm i n v/idth. Rock U n i t : b i o t i t e q uartz monzonite (Unit 3b) T h i n S e c t i o n No. 1; Sample No. PT-1 L o c a t i o n : 6,087N; 11,567E 180 M i n e r a l Mode p l a g i o c l a s e p h e n o c r y s t s 50% q u a r t z p h e n o c r y s t s 15% b i o t i t e p h e n o c r y s t s 5% groundmass p l a g i o c l a s e 15% K - f e l d s p a r 10% q u a r t z 5% D e s c r i p t i o n : C rowded g l o m e r o p h y r i t i c p l a g i o c l a s e p h e n o c r y s t s r a n g e f r o m 0 . 5 - 4 mm i n w i d t h - a n d a r e l o c a l l y z o n e d . Some p l a g i o - c l a s e r e p l a c e d b y s e r i c i t e a n d c a r b o n a t e . No An d e t e r m i n e d . A n - h e d r a l q u a r t z p h e n o c r y s t s r a n g e f r o m 0 . 5 - 2 mm i n d i a m e t e r . B i o - t i t e p h e n o c r y s t s a r e m o s t l y f r e s h ; some a r e a l t e r e d t o c h l o r i t e . M i n o r b i o t i t e i n g r o u n d m a s s i s i n t e r s t i t i a l t o q u a r t z a n d p l a g - i o c l a s e . Groundmass i s e q u i g r a n u l a r 0 .0 5 -0 .1 mm a n h e d r a l c r y s t - a l s o f q u a r t z , b i o t i t e , K - f e l d s p a r , and p l a g i o c l a s e . Rock U n i t : i n t r u s i v e b r e c c i a (Unit 3b) T h i n S e c t i o n No. 80 L o c a t i o n : D. D. H. 24- 567 f t . M i n e r a l Mode M a t r i x b i o t i t e 3 0 % m a g n e t i t e (?) 3% p l a g i o c l a s e 4 0 % K - f e l d s p a r 1 7% q u a r t z 1 0 % C l a s t s : p o r p h y r i t i c quartz monzonite D e s c r i p t i o n : Euhedral to anhedral 0.01-0.5 mm brown b i o t i t e i n - tergrown i n mats. P l a g i o c l a s e phenocrysts are zoned and glomero- p o r p h y r i t i c . Most are cloudy and are a l t e r e d to a l b i t e and K- f e l d s p a r ( ? ) . Groundmass p l a g i o c l a s e i s 0.025 mm i n l e n g t h , and i s cloudy. Anhedral K - f e l d s p a r and q u a r t z , 0.01-0.0 5 mm ac r o s s i n groundmass. Euhedral c u b i c magnetite (?) i s i n t e r s p e r s e d i n the groundmass wi t h b i o t i t e . Rock U n i t : p o r p h y r i t i c d a c i t e (Unit 4a) Thin S e c t i o n No. 76 L o c a t i o n : D. D. H. 36- 375 f t . 181 M i n e r a l Mode p l a g i o c l a s e phenocrysts 10% hornblende phenocrysts 2% b i o t i t e phenocrysts 3% quartz phenocrysts 10% groundmass 7 5% D e s c r i p t i o n : P o r p h y r i t i c t e x t u r e ; normal zoning i n 1-4 mm glome- r o p o r p h y r i t i c p l a g i o c l a s e , l o c a l l y r e sorbed (rounded w i t h r e a c t - i o n r i m ) , and a l b i t i z e d . Extremely h i g h carbonate a l t e r a t i o n of p l a g i o c l a s e p henocrysts, and i n groundmass. Hornblende pheno- c r y s t s a l t e r e d to c h l o r i t e and c l a y magnetite s e r i c i t e . 1-3 mm b i o t i t e phenocrysts are f r e s h . Groundmass i s too f i n e g r a i n e d to i d e n t i f y . Rock U n i t : p o r p h y r i t i c r y o l i t e (Unit 5) Thin S e c t i o n No. 56 L o c a t i o n : D. D. H. 29- 154 f t . M i n e r a l Mode p l a g i o c l a s e phenocrysts 15% b i o t i t e phenocrysts 5% quar t z phenocrysts 5% groundmass 7 5% D e s c r i p t i o n : C l o t s o f c l a y and carbonate, o.5-2 mm a c r o s s , r e - , p l a c e p l a g i o c l a s e phenocrysts. Pseudomorphs a f t e r b i o t i t e are c h l o r i t e ; replacements along cleavage i s e v i d e n t . Quartz pheno- c r y s t s are rounded and 1-5 mm i n diameter. Quartz i s l o c a l l y po- l y c r y s t a l l i n e . Groundmass c o n s i s t s o f very f i n e g r a i n e d anhedral 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 ( ? ) . Rock U n i t : a n d e s i t e (Unit 6) Thin S e c t i o n : No. 72 '•'> L o c a t i o n : D. D. H. 34- 435 f t . 18 2 M i n e r a l Mode quar t z phenocrysts 1% c h l o r i t e a f t e r hornblende 5% p l a g i o c l a s e phenocrysts 1% groundmass 93% D e s c r i p t i o n : Quartz and p l a g i o c l a s e phenocrysts are 0.5-1 mm ac r o s s . P l a g i o c l a s e i s a l t e r e d to carbonate and c l a y . C l o t s of c h l o r i t e and carbonate r e p l a c e hornblende. Groundmass c o n s i s t s of 0.1-0.2 mm p l a g i o c l a s e w i t h minor quartz and magnetite. P l a - g i o c l a s e i s a l t e r e d to carbonate and c l a y or s e r i c i t e . Rock U n i t : Ootsa Lake Group (Unit 7) Thin S e c t i o n No. 7; Sample No. PT-51 L o c a t i o n : 5,900N; 10,800E M i n e r a l Mode p l a g i o c l a s e phenocrysts 20% hornblende phenocrysts 3% groundmass p l a g i o c l a s e 50% K - f e l d s p a r 5% quar t z 20% a p a t i t e 1% opaques 1% D e s c r i p t i o n : Zoned 1 mm p l a g i o c l a s e phenocrysts (An2g) are s l i g h t l y a l t e r e d to carbonate. Some p l a g i o c l a s e phenocrysts are a l b i t i z e d and some are s t a i n e d from hematite i n c l u s i o n s . 1-2 mm hornblende is. a l t e r e d to c h l o r i t e and carbonate. Groundmass i s f r e s h , opaques i n c l u d e l i m o n i t e , hematite, and magnetite. Small carbonate v e i n c u t s t h i n s e c t i o n .

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