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Potassium-argon age determinations on biotites and amphiboles, Bethlehem Copper Property, B.C. Dirom, Gavin Ewan 1965

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POTASSIUM-ARGON AGE DETERMINATIONS ON. BIQTITES AND AMPHIBOLES, j BETHLEHEM COPPER PROPERTY, B. C. by GAVIN EWAN DIROM B.A.Sc. U n i v e r s i t y of B r i t i s h Columbia, 1962  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of GEOPHYSICS  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 June, 1965  In p r e s e n t i n g t h i s  fulfilment  of  the requirements f o r an advanced degree at the U n i v e r s i t y  of  British  Columbia,  available  for  thesis  in p a r t i a l  I agree that the L i b r a r y s h a l l  r e f e r e n c e and s t u d y .  make i t  I f u r t h e r agree that  m i s s i o n f o r e x t e n s i v e copying o f t h i s  thesis  for  freely per-  scholarly  purposes may be granted by the Head o f my Department o r by his  representatives,,  cation of t h i s  thesis  without my w r i t t e n  It  i s understood that copying o r p u b l i -  for financial  permission.  Department The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada Date  Columbia  gain s h a l l  not be allowed  ii  ABSTRACT Potassium-argon apparent ages obtained  on b i o t i t e and  amphibole from v a r i o u s phases of the Guichon Creek b a t h o l i t h present  on the Bethlehem Copper p r o p e r t y are r e p o r t e d and t h e i r  g e o l o g i c a l s i g n i f i c a n c e s are d i s c u s s e d i n t h i s t h e s i s . the i n d i v i d u a l phases were found to be e s s e n t i a l l y  Although  indistinguish-  able i n terms of t h e i r potassium-argon apparent ages, the r e s u l t s obtained  i n d i c a t e d with c o n s i d e r a b l e c e r t a i n t y t h a t these phases  were emplaced d u r i n g an i n t e r v a l not g r e a t e r than 10 m.y. around 200 m.y. occurred  centered  ago and t h a t no major metamorphic event has  i n t h i s area  s i n c e t h i s time.  I t i s also b e l i e v e d that  t h i s average apparent age of 200 m.y. may r e p r e s e n t  a better  approximation to the maximum age of the T r i a s s i c - J u r a s s i c boundary than t h a t p r e v i o u s l y r e p o r t e d i n the l i t e r a t u r e . The  potassium and argon a n a l y t i c a l techniques  are d e s c r i b e d b r i e f l y , obtained and  are d i s c u s s e d .  samples analyzed  employed  and the a n a l y t i c a l p r e c i s i o n and  accuracy  D e s c r i p t i o n s of the samples c o l l e c t e d  are g i v e n as an appendix.  iii  TABLE OP CONTENTS  ABSTRACT  i i  T A B L E OP CONTENTS  i i i  LIST OF FIGURES  v  LIST OF TABLES  VI  ACKNOWLEDGEMENTS  vii  INTRODUCTION  1  GENERAL GEOLOGY OF THE BETHLEHEM C O P P E R  CHAPTER I  PROPERTY  5  1.0  Introduction  5  1.1  Guichon Creek B a t h o l i t h  5.  1.2  Phase R e l a t i o n s on the Bethlehem property  1.2.1. ... 1 . 2 . 2 .  Copper  8  Guichon Quartz D i o r i t e  8  Bethlehem G r a n i t e  8  1.2.3.  Bethlehem Quartz D i o r i t e  10  1.2.4.  Porphyry I n t r u s i o n s  11  1.2.5.  Breccia  12  1.3  Rock A l t e r a t i o n on the Bethlehem Property  CHAPTER I I  Copper  SAMPLE COLLECTION AND PREPARATION  13 14  2.0  Sample C o l l e c t i o n  14  2.1  Mineral Separation  14  CHAPTER I I I ANALYTICAL TECHNIQUES 3.0  17  Introduction  17  3.1 P o t a s s i u m A n a l y s i s  18  iv i  3.1.1.  Equipment  18  3.1.2.  Contamination  18  3.1.3-  Chemical Procedures  19  (a)  Preparation Solutions  and A n a l y s i s of B i o t i t e  (b)  Preparation Solutions  and A n a l y s i s o f Amphibole  19 19  3.1.4.  I n v e s t i g a t i o n of I n t e r f e r e n c e E f f e c t s  20  3.1.5.  P r e c i s i o n and Accuracy  22  3.2  Argon A n a l y s i s  23  3.2.1.  Introduction  23  3.2.2.  Fusion  23  3.2.3.  Purification  26  3.2.4.  Measurement o f I s o t o p i c R a t i o s  27  3.2.5.  P r e c i s i o n and Accuracy  28  CHAPTER IV CHAPTER V  RESULTS DISCUSSION  2$ 35  CONCLUSION  40  BIBLIOGRAPHY  42  APPENDIX  44  LIST OP FIGURES  F i g u r e 1.1  Northern P o r t i o n of the Guichon Creek Batholith  F i g u r e 1.2  G e n e r a l i z e d G e o l o g i c a l Map Bethlehem Copper P r o p e r t y  F i g u r e 3.1  B l o c k Diagram of the Argon A n a l y t i c a l System  of the  vi  LIST OP TABLES  Table 4.1  K-Ar A n a l y t i c a l R e s u l t s Copper P r o p e r t y  Bethlehem  Table 4.2  Interlaboratory Results  Table 4.3  R e l a t i v e Ages of the V a r i o u s Phases on the Bethlehem Copper P r o p e r t y  vii  ACKNOWLEDGEMENTS Many persons have c o n t r i b u t e d t o the completion of t h i s thesis. of  The author i s e s p e c i a l l y indebted t o Dr. G.P. E r i c k s o n ,  the Department of Geophysics, who s u p e r v i s e d the r e s e a r c h , and  whose guidance and enthusiasm have c o n t r i b u t e d immeasurably t o t h i s study.  The author i s a l s o g r a t e f u l t o Dr. W.H. White, of  t h e Department of Mining and G e o l o g i c a l E n g i n e e r i n g , and Mr. J . E . Harakal, r e s e a r c h a s s i s t a n t , Department of Geophysics, f o r t h e i r a s s i s t a n c e and many h e l p f u l s u g g e s t i o n s .  P a r t i c u l a r thanks are  due Mr. K.E. Northcote, graduate student i n the Department of Geology,  who generously donated  s e v e r a l samples f o r the present  r e s e a r c h and c o n t r i b u t e d to many a s p e c t s of t h i s study.  The  f a c i l i t i e s of both the Department of Geology and the Department of Mining and M e t a l l u r g y are g r a t e f u l l y acknowledged. i s a l s o extended  Appreciation  to the o f f i c i a l s of the Bethlehem Copper  C o r p o r a t i o n L t d . , f o r t h e i r p e r m i s s i o n t o use samples c o l l e c t e d from t h e i r p r o p e r t y .  Thanks are due to Miss S. Newman who typed  t h e f i n a l d r a f t of t h i s t h e s i s .  T h i s work was supported mainly  by g r a n t s from the N a t i o n a l Research C o u n c i l and a l s o from Canadian E x p l o r a t i o n , L i m i t e d .  1  INTRODUCTION The potassium-argon r e s u l t s g i v e n i n t h i s t h e s i s are among the f i r s t  o b t a i n e d i n the potassium-argon l a b o r a t o r y a t  the U n i v e r s i t y of B r i t i s h Columbia.  T h i s l a b o r a t o r y was s e t  up i n order t o f u r t h e r i n v e s t i g a t e the g e o l o g i c a l h i s t o r y of B r i t i s h Columbia as w e l l as the t h e o r e t i c a l a s p e c t s of the potassium-argon t e c h n i q u e s .  C o n s t r u c t i o n of the l a b o r a t o r y  began i n e a r l y 1963 under the s u p e r v i s i o n of D r s . G.P. E r i c k s o n and W.H. White.  Dr. E r i c k s o n was r e s p o n s i b l e f o r the d e s i g n  and a p p l i c a t i o n of the a n a l y t i c a l equipment  i n the l a b o r a t o r y .  The w r i t e r j o i n e d the l a b o r a t o r y i n September 1963 and a s s i s t e d with the assemblage,  development,  and t e s t i n g of the equipment.  F u l l d e t a i l s r e g a r d i n g the d e s i g n and c o n s t r u c t i o n of the apparatus w i l l be g i v e n elsewhere and w i l l not be d e s c r i b e d here.  The  a p p l i c a t i o n of these f a c i l i t i e s to the problem of d a t i n g m i n e r a l s low i n potassium i s one of the purposes of the present study. Most of the u s e f u l potassium-argon age d e t e r m i n a t i o n s have, u n t i l r e c e n t l y , been o b t a i n e d on micas.  With the a v a i l a b l e  potassium-argon techniques, however, i t i s p o s s i b l e t o determine the ages of m i n e r a l s i n which potassium occurs as a minor  element.  T h i s a b i l i t y has made i t p o s s i b l e t o apply potassium-argon age d e t e r m i n a t i o n techniques t o a much wider range of g e o l o g i c a l problems.  I t i s now p o s s i b l e to date a c i d , i n t e r m e d i a t e , and  even b a s i c igneous r o c k s u s i n g potassium-argon methods on micas  2  and amphiboles, and, to a l i m i t e d extent, on f e l d s p a r s , and o t h e r m i n e r a l s (Hart, i 9 6 0 ; E r i c k s o n and Kulp, 1 9 6 1 ) .  pyroxenes,  I96I; A l d r i c h e t a l , i 9 6 0 ;  Potassium-argon apparent ages have  a l s o been o b t a i n e d from whole rock  samples.  L a b o r a t o r y d i f f u s i o n s t u d i e s of the r e t e n t i v i t y of argon by v a r i o u s m i n e r a l s and the i n v e s t i g a t i o n s of apparent m i n e r a l ages a c r o s s c o n t a c t metamorphic zones have shown that some m i n e r a l s low i n potassium, such as pyroxenes and amphiboles, more r e s i s t a n t t o argon l o s s than micas Hart, i 9 6 0 ;  1961).  are o f t e n  ( A l d r i c h e t a l , I960;  Damon and Kulp ( 1 9 5 8 ) , however, had p r e v i o u s l y  suggested t h a t amphiboles might c o n t a i n excess r a d i o g e n i c  argon  that had been occluded by the m i n e r a l a t the time of i t s f o r m a t i o n . T h i s h y p o t h e s i s has been c o n s i d e r e d by Hart  (I960; I 9 6 I ) ,  compared the apparent ages of a s s o c i a t e d b i o t i t e , a c t i n o l i t e , f e l d s p a r , and z i r c o n u s i n g K-Ar,  who  hornblende,  Sr-Rb,  and U-Th  techniques and found no evidence of excess argon i n amphiboles. S t u d i e s made by Evernden and R i c h a r d s (1962) e s s e n t i a l l y confirmed Hart's c o n c l u s i o n s .  A l l evidence t o date, t h e r e f o r e ,  indicate  that r e l i a b l e potassium-argon ages may be o b t a i n e d on amphiboles. The d i f f e r e n t behaviour of b i o t i t e and amphibole  under  thermal i n f l u e n c e s may be used to e v a l u a t e the r e l a t i v e m e r i t s of the apparent ages o b t a i n e d from these m i n e r a l s when they coexist.  G r e a t e r c o n f i d e n c e may be a t t a c h e d t o concordant  apparent ages o b t a i n e d on c o e x i s t i n g b i o t i t e and amphibole  than  to an apparent age o b t a i n e d on e i t h e r of these m i n e r a l s alone. When the b i o t i t e apparent age i s l e s s than the hornblende  3  apparent age, and t h i s i s b e l i e v e d to be due to r e h e a t i n g , the l a t t e r age would be c l o s e r to, although not n e c e s s a r i l y equal to, the t r u e age. In order to f u r t h e r i n v e s t i g a t e the value of potassiumargon age d e t e r m i n a t i o n s on m i n e r a l s other than micas,  i t was  decided that a study should be made on amphiboles  and  from a g e o l o g i c a l l y complex area where s u f f i c i e n t  geological  i n f o r m a t i o n was  available.  The Bethlehem Copper p r o p e r t y i n  the Highland V a l l e y area of s o u t h - c e n t r a l B r i t i s h met  these requirements and was  C a r r , 1959;  Columbia  s e l e c t e d f o r the study.  p r o p e r t y has been mapped i n c o n s i d e r a b l e d e t a i l  1957;  micas  This  (White et a l ,  I960) and c o n t a i n s a number o f - t h e i n t r u s i v e  phases which comprise the Guichon Creek b a t h o l i t h .  The  purpose  of t h i s t h e s i s i s to d i s c u s s the g e o l o g i c a l s i g n i f i c a n c e of the potassium-argon and amphibole  age r e s u l t s o b t a i n e d by the w r i t e r on b i o t i t e  present i n these phases with the aim of r e s o l v i n g  the g e o l o g i c a l h i s t o r y of the b a t h o l i t h more d e f i n i t e l y may  be done by potassium-argon  alone.  than  age d e t e r m i n a t i o n s on b i o t i t e  A d e s c r i p t i o n of the potassium and argon a n a l y t i c a l t e c h -  niques employed i s a l s o presented. Chapter I of t h i s t h e s i s reviews b r i e f l y the g e n e r a l geology of the Bethlehem Copper p r o p e r t y .  Chapter I I d e s c r i b e s  the c r i t e r i a used In s e l e c t i n g the samples and the procedures used i n s e l e c t i n g mineral; concentrates, s u i t a b l e f o r a n a l y s i s . Chapter III g i v e s a review of the potassium and argon  analytical  4  techniques used and d i s c u s s e s the p r e c i s i o n and accuracy the potassium  and argon r e s u l t s .  Analytical results  of  and  c a l c u l a t e d ages f o r the v a r i o u s samples s t u d i e d are g i v e n i n Chapter IV and are d i s c u s s e d i n Chapter V.  Petrographic  d e s c r i p t i o n s of the samples c o l l e c t e d f o r t h i s study given as an appendix.  are  5 CHAPTER I GENERAL GEOLOGY OF THE 1.0  BETHLEHEM COPPER PROPERTY  Introduction The  Bethlehem Copper p r o p e r t y  area of s o u t h - c e n t r a l  In the Highland V a l l e y  B r i t i s h Columbia Is l o c a t e d  30 m i l e s southeast of the town of A s h c r o f t . The  approximately  r e g i o n a l geology of the Highland V a l l e y area has  mapped on a s c a l e of 4 m i l e s to the i n c h and Memoirs of the G e o l o g i c a l (1948),  and  geology and described  mineral deposits  McTaggart  by White, Thompson, and  i z a t i o n i n Highland V a l l e y was  two  Cockfield  (1952).  McTaggart ( 1 9 5 7 ) , breccias,  published  and  The  and  copper  by C a r r  d i s s e r t a t i o n on the geology and  the v a r i o u s  by  in  of the Highland V a l l e y were  paper d i s c u s s i n g the p o r p h y r i e s ,  doctorate  been  described  Survey of Canada, one  the other by D u f f e l l and  1.1.)  (See F i g u r e  a mineral-  (i960).  b i o t i t e K-Ar  A  ages of  phases of the Guichon Creek b a t h o l i t h , which  u n d e r l i e s the Highland V a l l e y , i s c u r r e n t l y b e i n g prepared at the U n i v e r s i t y of B r i t i s h Columbia by K.E.  Northcote.  of the g e o l o g i c a l m a t e r i a l used i n t h i s present study been obtained from the works of these authors and published 1.1  from  Much has un-  r e p o r t s by company g e o l o g i s t s .  Guichon Creek B a t h o l i t h The  i n t r u s i v e rocks u n d e r l y i n g  the Highland V a l l e y  are  p a r t of the Guichon Creek b a t h o l i t h , a n o r t h e r l y t r e n d i n g mass  LEGEND |  f Tertiary Dykes and Flows J u r a s s i c Morine  Sediments  Undivided G u i c h o n c r e e k  Batholith  r-""-J B e t h s a i d a P h a s e Skeena - Bethlehem  Yy\  Upper T r i a s s i c  Nicola  | | | | Permian c a c h e  c F i g . 1.1=  Northern (After  Portion of the G u i c h o n  c o o k f i e l d , I948t  Northcote. personal  •  Scale'  Creek  D u f f e l l and  communication.)  Group  creak Group  0  2  Phase  4 I Miles  Batholith.  McTaggart,  1862;  6  7 some 40 m i l e s l o n g and 16 m i l e s wide.  Rock types comprising  the Guichon Creek batholi.th are d e s c r i b e d i n the e a r l y  literature  simply as q u a r t z d i o r i t e , and g r a n o d i o r i t e w i t h l o c a l gabbroic phases  (Cockfield, 1948).  i s a complex  I t i s now e v i d e n t that the b a t h o l i t h  body c o n s i s t i n g of a number of i n d i v i d u a l  phases  ranging from g r a n i t i c to gabbroic i n c o m p o s i t i o n that may be d i s t i n g u i s h e d p e t r o g r a p h i c a l l y and separated i n the f i e l d on the b a s i s of t e x t u r a l , m i n e r a l o g i c a l , and s t r u c t u r a l s h i p s (White e t a l , 1957; Northcote, p e r s o n a l  relation-  communication).  The emplacement age of the b a t h o l i t h i s known w i t h i n c l o s e l i m i t s because of i t s c o n t a c t r e l a t i o n s h i p s with other rocks.  I t i n t r u d e s Upper T r i a s s i c v o l c a n i c r o c k s of the N i c o l a  group and l o c a l l y i s unconformably o v e r l a i n by Middle and Upper J u r a s s i c f o s s i l i f e r o u s marine sediments of the A s h c r o f t group  ( D u f f e l l and McTaggart,  Jurassic  1952).  S e v e r a l K-Ar age d e t e r m i n a t i o n s have been made on specimens from the Guichon Creek b a t h o l i t h by the G e o l o g i c a l Survey of Canada (Leech e t a l , 1963; Wanless e t a l , 1 9 6 5 ) .  The apparent  b i o t i t e K-Ar ages that they r e p o r t e d range from 224 t o 265 m.y. An average K-Ar apparent age of l 8 l m.y., based on the r e s u l t s obtained on three samples of b i o t i t e from the Guichon Creek b a t h o l i t h , was r e p o r t e d by F o l i n s b e e e t a l ( i 9 6 0 ) .  T h i s date  was used as a c o n t r o l p o i n t by Kulp (1961) t o e s t a b l i s h the base of the J u r a s s i c on h i s g e o l o g i c a l  timescale.  8  1.2  Phase R e l a t i o n s on the Bethlehem Copper Property On the Bethlehem Copper p r o p e r t y ,  the dominant  country rock, g e n e r a l l y r e f e r r e d t o as Guichon quartz  diorite,  i s i n t r u d e d by an i r r e g u l a r s a l i e n t composed o f g r a n i t e lehem g r a n i t e ) , a younger quartz d i o r i t e diorite),  (Bethlehem quartz  and s e v e r a l v a r i e t i e s of porphyry.  a l s o occur o u t s i d e of the s a l i e n t .  (Beth-  Porphyry dykes  The porphyry i n t r u s i o n s  on the Bethlehem Copper p r o p e r t y are of p a r t i c u l a r  interest  s i n c e i t i s b e l i e v e d t h a t they are r e s p o n s i b l e f o r the e x p l o s i o n b r e c c i a zones which are f a v o u r a b l e h o s t s f o r copper m i n e r a l i z a t i o n (White et a l , 1957; C a r r , I 9 6 0 ; Coveney, 1 9 6 2 ) . of  The d i s t r i b u t i o n  rock phases d e s c r i b e d i s shown i n F i g u r e 1 . 2 . F i g u r e 1.2 i s  a g e n e r a l i z e d g e o l o g i c a l map of the Bethlehem Copper p r o p e r t y which was t r a c e d , with some m o d i f i c a t i o n , from a p r e l i m i n a r y g e o l o g i c a l map prepared 1.2.1  by C a r r  (1959).  Guichon Quartz D i o r i t e The  Guichon quartz d i o r i t e i s the o l d e s t igneous phase  present on the Bethlehem p r o p e r t y It  (White et a l , 1957;  i s a massive, c o a r s e - t e x t u r e d , mesocratic  Carr,  1959).  rock composed of  b i o t i t e , hornblende, grey p l a g i o c l a s e , quartz, and p i n k f e l d s p a r and  i s c h a r a c t e r i z e d by evenly d i s t r i b u t e d mafic  poikilitic  biotite,  and i n t e r s t i t i a l  minerals,  quartz e x h i b i t i n g a wedge-  shaped h a b i t . 1.2.2  Bethlehem G r a n i t e There i s some disagreement r e g a r d i n g the r e l a t i v e age of  10  the Bethlehem g r a n i t e .  White e t a l (1957)  c o n s i d e r the B e t h l e -  hem g r a n i t e to be younger than the Guichon quartz d i o r i t e but o l d e r than the Bethlehem quartz d i o r i t e .  C a r r ( 1 9 5 9 ) , however,  b e l i e v e s that the Bethlehem g r a n i t e i s "probably g r a d a t i o n a l to Bethlehem quartz d i o r i t e but a l s o s e g r e g a t i o n a l and l o c a l l y i n t r u s i v e i n t o l a t t e r rock." to medium-grained,  The Bethlehem g r a n i t e i s a f i n e -  r e d d i s h rock composed of p i n k i s h - r e d  quartz, white p l a g i o c l a s e , and minor b i o t i t e .  orthoclase,  With i n c r e a s i n g  p l a g i o c l a s e , the rock grades i n t o a quartz monzonite. 1.2.3  Bethlehem Quartz D i o r i t e Carr  ( i 9 6 0 ) and Northcote ( p e r s o n a l communication) b e l i e v e  that the Bethlehem quartz d i o r i t e may be p a r t of a l a r g e r body of quartz d i o r i t e ,  r e f e r r e d t o by Northcote as the Skeena-Beth-  lehem phase, which crops out on the south side of the Highland Valley.  (See F i g u r e 1.1.)  s h i p s , White e t a l (1957)  On the b a s i s of s t r u c t u r a l  relation-  and C a r r (1959; I960) have concluded  that the Skeena-Bethlehem phase i s younger than the Guichon quartz d i o r i t e and o l d e r than the porphyry dykes, which i n t r u d e the Bethlehem quartz d i o r i t e on the Bethlehem Copper p r o p e r t y . The Bethlehem quartz d i o r i t e i s a l i g h t grey, g r a n i t i c t o porphyritic  rock composed of hornblende, b i o t i t e ,  and potassium f e l d s p a r .  quartz,  plagioclase,  The p o r p h y r i t i c v a r i e t i e s are charac-  t e r i z e d by l a r g e , well-shaped, p o i k i l i t i c  hornblende phenocrysts.  The g r a n i t i c v a r i e t i e s are d i s t i n g u i s h e d from Guichon quartz d i o r i t e by t h e i r lower mafic content and uneven d i s t r i b u t i o n of mafic m i n e r a l s .  11  1 . 2 . 4 P o r p h y r y Intrusions The v a r i o u s porphyry  i n t r u s i o n s on the Bethlehem Copper  p r o p e r t y are p a r t of a much l a r g e r porphyry dyke swarm t h a t embraces a l l the p r i n c i p l e copper d e p o s i t s of Highland V a l l e y (Carr, i 9 6 0 ) . ages,  Although the porphyry i n t r u s i o n s are of d i f f e r e n t  they are a l l younger than the Bethlehem quartz d i o r i t e .  White et a l (1957)  r e c o g n i z e d two types of porphyry on the Beth-  lehem Copper p r o p e r t y . porphyry,  type, r e f e r r e d t o as a d a c i t e  c o n s i s t s of phenocrysts of plagioclase,,  hornblende,  poikilitic  and quartz s e t i n an abundant f i n e - g r a i n e d , o f t e n  greenish matrix. porphyry  The f i r s t  The other, r e f e r r e d to as a quartz d i o r i t e  i s s i m i l a r i n composition but d i f f e r s i n t h a t i t  c o n t a i n s phenocrysts of c o n s i d e r a b l y l a r g e r s i z e which make up more than 80 per cent of the rock.  Other c h a r a c t e r i s t i c f e a t u r e s  of t h i s l a t t e r rock are w e l l developed, and the replacement  of hornblende  rounded quartz phenocrysts  by r a d i a l aggregates of e p i d o t e .  C a r r (1959) has s u b d i v i d e d the d a c i t e porphyry  i n t o two  main c a t e g o r i e s based on the presence or absence of quartz phenocrysts.  Those with few or no quartz phenocrysts are c a l l e d the  quartz-poor porphyry,  which may be f u r t h e r s u b d i v i d e d i n t o the  P-,1 and P-2 p o r p h y r i e s on the b a s i s of t e x t u r a l d i f f e r e n c e s , while those w i t h abundant kidney or round  shaped quartz phenocrysts  are c a l l e d e i t h e r the p - 3 porphyry or a p l i t i c Aplitic  quartz  porphyry.  quartz porphyry i s a p h a n e r i t i c v a r i e t y of the P-3 porphyry  and i s e a s i l y confused w i t h p o r p h y r i t i c Bethlehem quartz d i o r i t e .  12  A p o r p h y r i t i c d y k e - l i k e body, r e f e r r e d t o as the Spud Lake porphyry, salient.  crops out a short d i s t a n c e east of the Bethlehem  White e t a l (1957) suggest t h a t the Spud Lake  porphyry  i s an o f f s h o o t of the B e t h s a i d a g r a n o d i o r l t e , the main body of which i n t r u d e s the Skeena-Bethlehem phase on the south side of Highland V a l l e y .  The B e t h s a i d a g r a n o d i o r i t e i s a c o a r s e - g r a i n e d  rock composed of euhedral books of b i o t i t e ,  sub-rounded quartz  g r a i n s , grey p l a g i o c l a s e , and r a r e hornblende.  The Spud Lake  porphyry d i f f e r s somewhat from the main B e t h s a i d a body i n t h a t i t c o n t a i n s l a r g e , w e l l a l t e r e d , phenocrysts of hornblende  as  w e l l as phenocrysts of the other c o n s t i t u e n t s s e t i n a somewhat a p h a n i t i c groundmass. 1.2.5  Breccia B r e c c i a bodies on the Bethlehem Copper p r o p e r t y form  i n c l i n e d t a b u l a r bodies c l o s e l y a s s o c i a t e d with the porphyry i n t r u s i o n s (Carr, i 9 6 0 ) . voids.  The b r e c c i a i s a dense rock without  I t c o n t a i n s a v a r i e d assemblage of rock-fragments  r e p r e s e n t i n g the f o l l o w i n g types:  Guichon  Bethlehem quartz d i o r i t e , P - l porphyry,  quartz d i o r i t e ,  P-2 porphyry,  and f i n e -  grained or a p h a n i t i c v a r i e t i e s of the P-3 porphyry and, t h e r e f o r e , must be younger than a l l of these (Carr, 1959; no fragments  i960).  To date,  of the quartz d i o r i t e porphyry have been recognized  i n the b r e c c i a i n d i c a t i n g t h a t t h i s porphyry i s probably postb r e c c i a i n age.  The matrix of the b r e c c i a c o n t a i n s broken g r a i n s  of f e l d s p a r and quartz, and small rock fragments.  This cata-  c l a s t i c matrix i s p a r t l y r e p l a c e d by new m i n e r a l s i n c l u d i n g  1 3  b i o t i t e and tourmaline as the  r e s u l t of r e c r y s t a l l i z a t i o n and  accompanying metasomatism (White e t a l , suggests that b r e c c i a t i o n took p l a c e  ( 1 9 5 9 )  immediately f o l l o w i n g the  p a r t i a l c h i l l i n g of the P - 3 porphyry as the release  Carr  1 9 5 7 ) .  r e s u l t o f the  of v o l a t i l e s c o n t a i n e d i n the porphyry.  White e t a l  ( 1 9 5 7 )  suggest that the o r i g i n of the b r e c c i a i n v o l v e s  i n the  lower p a r t o f a v o l c a n i c  structure  as the  explosion  r e s u l t of the  v o l a t i l e pressure i n a cupola exceeding the c o n f i n i n g 1.3  explosive  pressure.  Rock A l t e r a t i o n on the Bethlehem Copper P r o p e r t y A l t e r a t i o n i s widespread on the Bethlehem Copper p r o p e r t y .  White e t a l  ( 1 9 5 7 )  suggest that there are two types o f a l t e r a t i o n  that are probably r e l a t e d i n time and o r i g i n . obviously  related to mineralization,  The f i r s t , not  produced widespread  weak p r o p y l i t i c a l t e r a t i o n and i s probably d e u t e r i c The  second, r e l a t e d t o m i n e r a l i z a t i o n ,  i n nature.  produced l o c a l l y  a l t e r a t i o n e f f e c t s including tourmalization,  but  intense  silicification,  c h l o r i t i z a t i o n , f e l d s p a t h i z a t i o n , and development of b i o t i t e , calcite,  and c l a y m i n e r a l s .  14  CHAPTER I I  SAMPLE COLLECTION AND 2.0  PREPARATION  Sample C o l l e c t i o n The degree of a l t e r a t i o n i n the v i c i n i t y of the Bethlehem  Copper p r o p e r t y made i t e x c e e d i n g l y d i f f i c u l t mens s u i t a b l e f o r t h i s study. collect  to o b t a i n  speci-  An e f f o r t , however; was made t o  samples r e p r e s e n t a t i v e of each phase present on the pro-r  p e r t y which showed the l e a s t evidence of a l t e r a t i o n and surface j  weathering.  Two, 60 pound samples of each phase were c o l l e c t e d from outcrops a t d i f f e r e n t  s i t e s on the p r o p e r t y .  These s i t e s were  chosen on the b a s i s of c o n t a c t r e l a t i o n s h i p s , a l t e r a t i o n , and accessibility.  The l o c a t i o n s of the samples c o l l e c t e d by the  w r i t e r and those c o l l e c t e d by K.E. Northcote are shown on F i g u r e s 1.1 and 1.2. The samples s e l e c t e d f o r a c t u a l K-Ar a n a l y s i s were chosen on the b a s i s of t h i n s e c t i o n s t u d i e s of specimens t y p i c a l of each collected  sample.  S e v e r a l of the samples c o l l e c t e d were found  to c o n t a i n no useable hornblende or b i o t i t e and, t h e r e f o r e , not be used i n t h i s study.  could  D e s c r i p t i o n s of samples c o l l e c t e d  and samples analyzed are g i v e n as an appendix. 2.1  Mineral Separations A f t e r the removal of a l l weathered s u r f a c e s , an amount of  15  e a c h sample n e c e s s a r y biotite in  or amphibole c o n c e n t r a t e  t u r n , a jaw  The  crusher,  was  through  four  fractions  size  fraction  than  100°C t o f a c i l i t a t e  mineral  Rough b i o t i t e and  amphibole  washed i n w a t e r and  t h e f o l l o w i n g means. contained an  both  electrostatic  2LAB)  s e t up  then passed  set  up  remaining  the  b i o t i t e concentrate,  the heavy l i q u i d s  size  fraction  less  was  first  The  passed  Separator  through  Co.,  electrostatic  isodynamic  by  o f a sample, i f  magnetic  t o remove a m p h i b o l e  separator,  approximately  was  90  model reject  separator, and  percent  further purified  t e t r a b r o m o e t h a n e and  other  The  purified  b i o t i t e concentrate  was  i n the b i o t i t e c o n c e n t r a t e s  2 per  by  volume.  t h e b i o t i t e K-Ar  The  size  a n a l y s i s was  a hand  washed s e v e r a l analysis.  were g e n e r a l l y l e s s  f r a c t i o n most commonly -48  t o +100  f:  Strongly  with  t o remove t h e h e a v y l i q u i d s b e f o r e  Impurities  pure,  by means o f  diiodomethane.  magnet.  in  Each  by h e a t i n g t o  g r a i n s were removed f r o m t h e c o n c e n t r a t e  cent  sieved  mesh.  magnetic  i n acetone  crusher.  minerals.  electrostatic  times  using,  c o n c e n t r a t e s were o b t a i n e d  biotite.  a Frantz  a cone  t o +100  (Dings Magnetic  vertical position,  mafic  The  through  size  g r i n d e r and  dried  amphibole,  to concentrate  was  i n the  separator  t o pea  pure  separation.  E a c h washed  b i o t i t e and  grams o f  and  a disc  r a n g i n g f r o m -28  into  was  crushed  a gyratory crusher,  s a m p l e s were t h e n p a s s e d size  50  to give approximately  mesh.  than  employed  16  Amphibole was separated from the rough mafic by means of heavy l i q u i d s ,  the i n c l i n e d isodynamic  concentrate magnetic  separator, f u r t h e r c r u s h i n g and s c r e e n i n g , and a charged sheet.  The f i n a l  amphibole c o n c e n t r a t e s were g e n e r a l l y b e t t e r  than 95 per cent pure. proved  plastic  The common i m p u r i t y was e p i d o t e which  to be very d i f f i c u l t  t o separate from amphibole due to  i t s similar physical properties.  The presence  of a small amount  of  e p i d o t e i n the amphibole c o n c e n t r a t e s , however, was shown not  to  a f f e c t the a n a l y s e s . . The amphibole c o n c e n t r a t e s  contained  both hornblende and a c t i n o l i t e as i t was not p r a c t i c a l t o make a c l e a n s e p a r a t i o n of these two m i n e r a l s when they  occurred  together.  The amphibole c o n c e n t r a t e s were washed s e v e r a l times  i n acetone  before a n a l y s i s .  The s i z e f r a c t i o n most commonly  employed i n the amphibole K-Ar a n a l y s i s was -80 t o +100 mesh.  17  CHAPTER I I I  ANALYTICAL TECHNIQUES 3.0  Introduction Potassium-argon  d a t i n g of m i n e r a l s r e q u i r e s both h i g h  p r e c i s i o n and a b s o l u t e accuracy f o r the potassium and argon determinations.  Pinson (1961) has a p t l y p o i n t e d out that i t  i s g e n e r a l l y p o s s i b l e t o analyze f o r argon, which o c c u r s i n t r a c e amounts i n a m i n e r a l sample, t o a much g r e a t e r accuracy and with more confidence than i t i s p o s s i b l e t o analyze for/ one of  i t s major c o n s t i t u e n t s ,  potassium.  The aim of t h i s p o r t i o n of the present w r i t e r ' s r e s e a r c h programme was t o develop a s u i t a b l e procedure,  with the equipment  a v a i l a b l e i n t h i s l a b o r a t o r y , f o r d e t e r m i n i n g the potassium and argon c o n t e n t s of amphibole with s u f f i c i e n t accuracy that the r e s u l t s may be used i n potassium-argon A l l potassium-argon  age i n v e s t i g a t i o n s .  apparent m i n e r a l ages i n t h i s  study  were obtained by d e t e r m i n i n g the r a d i o g e n i c argon content of a m i n e r a l by Isotope d i l u t i o n techniques u s i n g a gas source, c a l l y operated mass-spectrometer flame photometric sidered i n turn.  techniques.  stati-  and i t s potassium content by The techniques used w i l l be con-  18  3.1 3.1.1  Potassium A n a l y s i s Equipment The potassium content of the amphibole  and b i o t i t e  t r a t e s were determined on a B a i r d Atomic, model KY-1, flame photometer  u s i n g propane  concen-  clinical  as f u e l and l i t h i u m as an i n t e r n a l  standard.  R e s u l t s were recorded on a two  millivolt,  zero c e n t e r Weston r e c o r d e r connected: i n s e r i e s with  the photometer  meter.  second response,  10  The i n s t a l l a t i o n of h i g h q u a l i t y pressure  r e g u l a t i n g v a l v e s i n the a i r and f u e l l i n e s , along with the i n s t a l l a t i o n of an e x t e r n a l v o l t a g e r e g u l a t o r on the supply l i n e ,  e f f e c t i v e l y reduced instrument i n s t a b i l i t i e s .  f o r the above m o d i f i c a t i o n s , the instrument was operated a c c o r d i n g to the manufacturer's 3.1.2  photometer  set up  Except  and  instructions.  Contamination S p e c i a l care was  taken to Insure a g a i n s t contamination  of sample and standard s o l u t i o n s . i n hot HNO^, intervals.  A l l glassware used was washed  r i n s e d i n pure water, and s i l i c l a d at f r e q u e n t Sample d i g e s t i o n s were made i n t e f l o n d i s h e s which  w e r e soaked i n hot HNO^  between useage.  The water used f o r  r i n s i n g glassware and f o r d i l u t i n g standard and m i n e r a l s o l u t i o n s was  f i r s t d i s t i l l e d and then p u r i f i e d i n an Ion exchange column.  Both sample and standard s o l u t i o n s were s t o r e d i n t i g h t l y stoppered p o l y e t h y l e n e b o t t l e s .  The a n a l y t i c a l r e s u l t s of t o t a l  procedure b l a n k s i n d i c a t e d t h a t the l e v e l of potassium contamin a t i o n was n e g l i g i b l e f o r the a n a l y s e s of t h i s work.  19  3.1.3  Chemical .(a)  Procedures  P r e p a r a t i o n and A n a l y s i s of B i o t i t e S o l u t i o n s Biotite  s o l u t i o n s were prepared and analyzed by the Samples of between 0 . 5  f o l l o w i n g procedures.  decomposed at a temperature of 3 ml. c o n c e n t r a t e d H S 0 4 , 2  and 1.0  gram were  g e n e r a l l y l e s s than 200°C i n a t o t a l 35 ml. 49$ HF,  and  2 ml. concentra-  ted HNO3 and f i n a l l y h e l d i n s o l u t i o n i n approximately 3 ml. of concentrated HgSO^. e x a c t l y 1000  The  r e s i d u a l s o l u t i o n s were brought- up to  ml. with pure water and 100 ml. stock s o l u t i o n  c o n t a i n i n g 2000 ppm  l i t h i u m and 5000 ppm  reagent grade L i C l and N a S 0 4 . 2  biotite  sodium prepared  from  The potassium contents, of the  sample s o l u t i o n s were determined  by comparing the unknown  s o l u t i o n s with standard s o l u t i o n s c o n t a i n i n g 200 ppm  lithium,  ppm  These s t a n -  sodium, and an a p p r o p r i a t e amount of potassium.  500  dard s o l u t i o n s were prepared by d i s s o l v i n g weighed q u a n t i t i e s of d e s i c c a t e d , reagent grade KgSO^ i n pure water and 100 ml. of the same l i t h i u m and sodium stock s o l u t i o n used to prepare the b i o t i t e sample s o l u t i o n s and d i l u t i n g with pure water to a f i n a l volume of 1000  ml.  (b)  P r e p a r a t i o n and A n a l y s i s of Amphibole S o l u t i o n s Amphibole s o l u t i o n s were prepared by decomposing  to 2.5 biotite  1.5  gram samples i n the same reagents used f o r p r e p a r i n g the s o l u t i o n s although i n some cases p e r c h l o r i c a c i d  used i n s t e a d of n i t r i c  acid.  to 250 ml. with pure water and  was  The decomposed samples were d i l u t e d 25 ml. of the same l i t h i u m  sodium stock s o l u t i o n used f o r the b i o t i t e  solutions.  The  and  20  amphibole  s o l u t i o n s were compared w i t h standards t h a t c o n t a i n e d  the same q u a n t i t y of s u l p h u r i c a c i d as the s o l u t i o n s themselves f o r the reasons e x p l a i n e d i n the next s e c t i o n .  These standards  were about 0.4N H2SO4 and c o n t a i n e d 200 ppm l i t h i u m , 500 ppm sodium, 3.1.4  and an a p p r o p r i a t e amount of potassium. I n v e s t i g a t i o n of I n t e r f e r e n c e E f f e c t s  M i n e r a l samples used i n potassium-argon age d e t e r m i n a t i o n s c o n t a i n some or a l l of the f o l l o w i n g c a t i o n s as major ents:  S i , A l , Pe, Ca, Mg, Na, and K.  D u r i n g s u l p h u r i c and  h y d r o f l u o r i c a c i d d i g e s t i o n of a sample,  S i i s v o l a t i l i z e d as  f l u o r i d e , and the remaining elements are l e f t residual sulphuric acid solution.  as s u l p h a t e s i n a  Numerous r e f e r e n c e s , (eg.  B u r r i e l - M a r t i and Ramirez-Munoz, 1957; Dean, i 9 6 0 ; I 9 6 0 ; Cooper,  constitu-  Abbey and Maxwell,  1963) many of them c o n t r a d i c t o r y , may be found con-  c e r n i n g the I n t e r f e r e n c e e f f e c t s i n flame photometry  caused by  v a r i a t i o n s i n a c i d i t y or mutual r e p r e s s i o n or enhancement between c a t i o n s and a n i o n s .  While some ignore these e f f e c t s and analyze  the sample s o l u t i o n s d i r e c t l y a g a i n s t pure a l k a l i  standards, o t h e r s  attempt to overcome them by u s i n g c o r r e c t i o n curves, by b u f f e r i n g with the troublesome Ions, o r by the removal of a l l or some of the i n t e r f e r i n g i o n s .  Since i t was e v i d e n t t h a t some of these  e f f e c t s may r e l a t e to the flame c h a r a c t e r i s t i c s and the o p t i c a l r e s o l u t i o n of the p a r t i c u l a r flame photometer use, i t was cons i d e r e d d e s i r a b l e to e v a l u a t e them independently f o r the instrument used In t h i s work.  21  Experiments were, t h e r e f o r e , c a r r i e d out to determine e f f e c t s of the v a r i o u s c a t i o n s the  sample s o l u t i o n s and  was  introduced  ference analyses  may  ( A l , Fe,  Ca,  the e f f e c t of the  and Mg)  The  in  cation inter-  s i g n i f i c a n c e f o r amphibole potassium  than f o r mica since the c a t i o n / p o t a s s i u m  amphibole i s c o n s i d e r a b l y e f f e c t of sodium was  present  s u l p h u r i c a c i d which  d u r i n g the d i g e s t i o n procedure.  be of g r e a t e r  the  ratio  l a r g e r than t h a t of mica.  of  The  possible  e l i m i n a t e d by b u f f e r i n g both standard  and  sample s o l u t i o n s with an overwhelming q u a n t i t y of t h a t i o n . The one  problem of d e t e r m i n i n g the mutual i n t e r f e r e n c e between  element and  another i s d i f f i c u l t because the  potassium content of a s o l u t i o n may and  enhanced by another.  The  apparent  be depressed by one  procedure used i n t h i s  element  study  i n v o l v e d the a n a l y s i s of d i f f e r e n t a l i q u o t s of an amphibole s o l u t i o n d i l u t e d to d i f f e r e n t volumes with a standard potassium c o n t e n t . the c a t i o n / p o t a s s i u m p l a c e i t should  The  e f f e c t of t h i s procedure i s to reduce  r a t i o so t h a t i f i n t e r f e r e n c e i s t a k i n g  be evident  i n the r e s u l t s .  i n d i c a t e d t h a t the i n t e r f e r e n c e e f f e c t s due other  of known  The  r e s u l t s obtained  to the presence of  c a t i o n s i n the amphibole s o l u t i o n s were n e g l i g i b l e . The o n l y s i g n i f i c a n t i n t e r f e r e n c e e f f e c t was  due to s u l p h u r i c a c i d .  I t was  of potassium i n s o l u t i o n was t i o n of s u l p h u r i c a c i d . proved u n s u c c e s s f u l r e s u l t s due  found to  be  observed that the apparent amount  n o n - l i n e a r l y r e l a t e d to the  concentra-  An attempt to o b t a i n c o r r e c t i o n curves  since i t was  impossible  to the v a r i a b i l i t y of the  to o b t a i n  consistent  i n t e r f e r e n c e e f f e c t s with  22  c e r t a i n non-reproducible  instrument  adjustments.  The  observa-  t i o n s were c o n s i s t e n t with the i n t e r p r e t a t i o n t h a t the s u l p h u r i c a c i d was  somehow r e d u c i n g the l i t h i u m emmission and, t h e r e f o r e ,  a f f e c t i n g the apparent  potassium  concentration since t h i s i s  always measured r e l a t i v e to t h a t of the l i t h i u m i n t e r n a l A m o d i f i e d form of the b u f f e r technique was, and was  found to y i e l d  satisfactory results.  therefore, u t i l i z e d T h i s i n v o l v e d the  a d d i t i o n of the same amount of s u l p h u r i c a c i d ' t o the s o l u t i o n as was acidic  standard  present i n the unknown sample s o l u t i o n s .  These  standards were o n l y used f o r amphibole a n a l y s i s because  t e s t s had  shown t h a t the i n t e r f e r e n c e e f f e c t of s u l p h u r i c a c i d  i n the l e s s a c i d i c b i o t i t e The potassium i t was  standard.  s o l u t i o n s was  negligible.  content of e p i d o t e was  i n v e s t i g a t e d because  a common contaminant of the amphibole c o n c e n t r a t e s .  A n a l y s i s of an e p i d o t e s o l u t i o n , t r e a t e d i n a manner s i m i l a r to the procedure  used i n the amphibole analyses, i n d i c a t e d t h a t the  epidote c o n t a i n e d l e s s than 0 . 0 3 $ potassium.  Since most of the  amphibole c o n c e n t r a t e s c o n t a i n e d l e s s than 5 per cent e p i d o t e , the c o n t r i b u t i o n of potassium 3.1.5  P r e c i s i o n and The  IV.  from t h i s source c o u l d be n e g l e c t e d .  Accuracy  r e s u l t s of the potassium  a n a l y s e s are g i v e n i n Chapter  Twelve r e p l i c a t e r e s u l t s o b t a i n e d on s e p a r a t e l y weighed  p o r t i o n s of the i n t e r l a b o r a t o r y b i o t i t e  standard, GE  2060,  i n d i c a t e a p r e c i s i o n of 1 per cent f o r the b i o t i t e flame meter potassium  analyses.  The  accuracy of the mica  photo-  potassium  23  a n a l y s i s i s a l s o b e l i e v e d to be approximately  1 per cent s i n c e  the r e s u l t s obtained at t h i s l a b o r a t o r y on GE 2060 and the U.S.G.S. muscovite  standard, P-207, agree w i t h i n 1 per cent with  those  quoted by other l a b o r a t o r i e s .  (See Table 4 . 2 . )  t r i p l i c a t e amphibole potassium  a n a l y s e s i n d i c a t e a p r e c i s i o n of  approximately  1 per c e n t .  The  r e s u l t s of  No i n t e r l a b o r a t o r y standard  a v a i l a b l e with which to determine  the accuracy of the amphibole  a n a l y s i s , however, i t I s b e l i e v e d , on the b a s i s of the of s e v e r a l experiments  was  results  with standard s o l u t i o n s and a c a r e f u l  a c c o u n t i n g of i n t e r f e r e n c e and contamination e f f e c t s , t h a t the a b s o l u t e e r r o r of the amphibole potassium  a n a l y s i s i s l e s s than  2 per cent. 3.2 3.2.1  Argon A n a l y s i s Introduction The argon content of the amphibole and b i o t i t e  were determined Erickson.  on an a n a l y t i c a l system designed by Dr.  (See F i g u r e 3-1.)  G.P.  F u l l d e t a i l s of the: system and  a n a l y t i c a l procedures used w i l l be g i v e n elsewhere w i l l not be d e s c r i b e d i n d e t a i l here. i s o t o p e d i l u t i o n was used employing  and, t h e r e f o r e ,  B a s i c a l l y , the method of  a known q u a n t i t y of A r ^  t r a c e r or spike and c o r r e c t i o n f o r atmospheric based on the Ar36 c o n c e n t r a t i o n i n the gas 3.2.2  concentrates  argon  contamination  sample.  Fusion The  sample to be analyzed, approximately  0.7  as  to 1,0  gram  24  Air Reservoir  A.  Calibration D i f f u s i o n and Rotary Pumps  -<j>-  Section  V  10  V  9  Spike M e t e r i n g S e c t i o n  MassSpectrometer Section  Ion Pump  7  Second irif icati Section  r*£<£-  v  6  ^  V  4  D i f f u s i o n and Rotary Pumps  F u s i o n and First Purification  Section  Vl D i f f u s i o n and Rotary Pumps  F i g u r e 3.1: B l o c k Diagram of the Argon A n a l y t i c a l System.  25 b i o t i t e and 9 to 11 grams amphibole was p l a c e d i n an alundum .enclosed molybdenum c r u c i b l e and mounted on a molybdenum wire stand i n a w a t e r - j a c k e t e d pyrex f u s i o n j a r . was  This fusion j a r  connected to the argon l i n e by means of a copper-gasketed  flange coupling.  A l e a k t e s t of the argon l i n e was  c a r r i e d out  before each a n a l y s i s by opening each s e c t i o n i n t u r n to the massspectrometer and o b s e r v i n g the b u i l d - u p of the mass-40 and mass-28 signals,  i t was found t h a t the f u s i o n s e c t i o n and  sample  n o r m a l l y d i d not r e q u i r e o u t g a s s i n g , by baking, i f pumped on f o r p e r i o d s i n excess of 1 2 hours. The molybdenum c r u c i b l e was heated t o the f u s i o n of the sample by means of a 6 KW, i n d u c t i o n c o i l which was jar.  r a d i o frequency g e n e r a t o r and  c o n s t r u c t e d to f i t  The temperature of the sample  prevent d e c r e p i t a t i o n of the sample. sample  temperature  was  around the f u s i o n  g r a d u a l l y r a i s e d so as to  When the temperature of the  reached approximately 1 0 0 0 ° C , the A r ^  spike was  i n t o the f u s i o n s e c t i o n by means of the metal v a l v e s  metered and V-^Q.  A f i n a l temperature of about 1 5 0 0 ° C , maintained f o r a t l e a s t minutes, was  found to be s u f f i c i e n t to c o m p l e t e l y f u s e the  and r e l e a s e a l l the argon.  The p r e s s u r e of the f u s i o n  was monitored by means of a p i r a n i gauge and was  10  sample  section  c o n t r o l l e d by  e i t h e r v a r y i n g the temperature of a hot t i t a n i u m metal sponge i n the f u s i o n s e c t i o n or p l a c i n g l i q u i d n i t r o g e n on a c h a r c o a l trap.  A c o l d f i n g e r t r a p was kept at the temperature of dry i c e  throughout the f u s i o n i n o r d e r to remove  H 0. ?  26  3.2.3  Purification The  of the  r e l e a s e d gases, s t i l l  i s o l a t e d i n the f u s i o n s e c t i o n  system, were p u r i f i e d by a l l o w i n g them to r e a c t  with  the hot t i t a n i u m sponge as i t cooled to room temperature from 700°C.  Argon and most other remaining gases were then adsorbed  i n a c h a r c o a l t r a p kept at the temperature of l i q u i d  nitrogen.  Once e q u i l i b r i u m had been reached, the metal v a l v e , V^, the f u s i o n s e c t i o n to the pumps was c h i e f l y hydrogen, was the gas was to the  pumped out.  opened and  second p u r i f i c a t i o n s e c t i o n by adsorbing  charcoal trap.  Further  the remaining  T h i s valve was  t r a n s f e r r e d through the connecting  connecting gas,  then c l o s e d  metal v a l v e ,  and V2,  i t on another  cleanup of the gas c o u l d be achieved  in  t h i s p o r t i o n of the system by a l l o w i n g the gas t o r e a c t with a second t i t a n i u m sponge which c o u l d be i s o l a t e d by a metal v a l v e . When necessary, any number of p u r i f i c a t i o n c y c l e s c o u l d be c a r r i e d out by simply  a l t e r n a t i n g the gas back and f o r t h between these  p u r i f i c a t i o n sections. would, of course,  Between each c y c l e , the t i t a n i u m sponge  be outgassed by h e a t i n g to a temperature  g r e a t e r than 950°C.  The  gas r e l e a s e d d u r i n g fehe f u s i o n of  amphibole samples g e n e r a l l y r e q u i r e d at l e a s t 2 such before  i t was  s u i t a b l e f o r i s o t o p i c a n a l y s i s while  r e l e a s e d d u r i n g the f u s i o n of b i o t i t e r e q u i r e d 1 cleanup. sponge, the gas was  the  always adsorbed on c h a r c o a l at any  gas  samples n o r m a l l y only  A f t e r the f i n a l r e a c t i o n on the  n i t r o g e n temperature and  steps  titanium  liquid  remaining gas pumped away.  27 3-2.4  Measurement of I s o t o p i c R a t i o s After purification,  s u f f i c i e n t gas was  through the leak v a l v e , Vg,  allowed  to pass  i n t o the mass-spectrometer s e c t i o n  of the system to give c o n v e n i e n t l y measurable i s o t o p i c s i g n a l s , the mass-40 s i g n a l being g e n e r a l l y between 5 and i s o t o p i c composition  of the gas was  10 v o l t s .  measured s t a t i c a l l y  The  (Vg  and  Vj c l o s e d ) u s i n g a l80° d e f l e c t i o n , 2 i n c h r a d i u s , mass-spectrometer ( A s s o c i a t e d E l e c t r i c a l I n d u s t r i e s , type MS10) reed e l e c t r o m e t e r lO^  1  ohm  a m p l i f i e r (Applied P h y s i c s , model 31)  input r e s i s t o r .  s c a l e , potentiometer-type  an e l e v e n i n c h wide s t r i p c h a r t  Minneapolis-Honeywell Regulator The was  average of 10  taken to represent  using a  R e s u l t s were d i s p l a y e d on a 1/4  response, 10 m i l l i v o l t f u l l having  and a v i b r a t i n g  second  recorder,  (Brown Instrument D i v i s i o n ,  Co.).  scans f o r both the 40/36 and  40/38 r a t i o s  the argon i s o t o p i c r a t i o s s i n c e the  d e v i a t i o n of the average was  always l e s s than 1/4  standard  per cent.  The  40/36 r a t i o was  used to determine the c o r r e c t i o n to apply to the  40/38 r a t i o due  to the presence of atmospheric argon i n the  sample.  Systematic  changes i n observed r a t i o s d u r i n g  were n e g l i g i b l y small so t h a t i t was the r a t i o s to the time of admission For each a n a l y s i s , a check was  not necessary  gas  analyses  to e x t r a p o l a t e  to the mass-spectrometer.  made to determine the f r a c t i o n of  the t o t a l q u a n t i t y of gas a c t u a l l y admitted  to the mass-spectro-  meter so t h a t f r a c t i o n a t i o n e f f e c t s at the l e a k valve c o u l d  be  evaluated.  per  The  small volume, V , c  which i s approximately  cent of the volume of the second p u r i f i c a t i o n system, was  10  used  28  f o r t h i s purpose.  The measured 40/36 and 40/38 r a t i o s were  c o r r e c t e d f o r f r a c t i o n a t i o n at the valve and d i s c r i m i n a t i o n i n the mass-spectrometer 3.2.5  P r e c i s i o n and  b e f o r e being used i n the age  calculations.  Accuracy  The r e s u l t s of the argon a n a l y s e s are g i v e n i n Chapter IV. The r e s u l t s of q u a d r u p l i c a t e argon a n a l y s e s of standard GE i n d i c a t e a p r e c i s i o n of approximately 1 per cent f o r the analyses.  argon  Absolute methods. I n v o l v i n g a c c u r a t e l y measured  q u a n t i t i e s of atmospheric argon-38  2060  argon, were used to c a l i b r a t e the  s p i k e s with which the argon c o n c e n t r a t i o n s of the  v a r i o u s samples were determined.  However, a n a l y s e s of standards  based upon such c a l i b r a t i o n s were found to be  systematically  low, by a few per cent, from those r e p o r t e d by other l a b o r a t o r i e s . (See Table 4 . 2 )  F o r t h i s reason, the argon a n a l y s e s performed i n  t h i s l a b o r a t o r y are c o n s i d e r e d to be a c c u r a t e to w i t h i n a p p r o x i mately 3 per cent f o r those a n a l y s e s having l e s s than 50 per cent atmospheric  argon contamination.  than 50 per cent atmospheric  For those a n a l y s e s having more  argon contamination, the formula  g i v e n by L i p s o n ( 1 9 5 8 ) i s used to determine argon-40 r a d i o g e n i c c o n c e n t r a t i o n .  the e r r o r i n the  29  CHAPTER IV  RESULTS  The  a n a l y t i c a l data determined  d u r i n g the course of t h i s  study on specimens from the Bethlehem Copper p r o p e r t y are presented i n Table 4 . 1 . i n F i g u r e s 1.1  and  Sample numbers correspond 1.2.  Table 4 . 2  on the i n t e r l a b o r a t o r y b i o t i t e muscovite 4.3  to those  given  compares the r e s u l t s obtained  standards, GE 2060 and B-3203,  standard, P-207, with those obtained elsewhere.  compares the potassium-argon  apparent  and  Table  ages of the v a r i o u s  phases of the Guichon Creek b a t h o l i t h with t h e i r r e l a t i v e ages deduced on the b a s i s of s t r u c t u r a l The flame photometric  evidence.  potassium  a n a l y s e s were c a r r i e d  at l e a s t i n d u p l i c a t e f o r each sample. content was apparent  The average  out  potassium  c a l c u l a t e d f o r each sample and was used i n the  age c a l c u l a t i o n s .  The potassium  b i o t i t e and amphibole apparent be accurate w i t h i n 1 and  values used  i n the  age c a l c u l a t i o n s are b e l i e v e d to  2 per cent, r e s p e c t i v e l y and have a  p r e c i s i o n of approximately  1 per cent as d i s c u s s e d i n s e c t i o n  3.1.5. Normally, sample.  o n l y a s i n g l e argon a n a l y s i s was made on each  The argon v a l u e s used i n the apparent  age  calculations  are b e l i e v e d to be accurate w i t h i n a few percent and have a p r e c i s i o n of approximately  1 per cent as d i s c u s s e d i n s e c t i o n  TABLE 4.1 K-Ar A n a l y t i c a l R e s u l t s Bethlehem Copper P r o p e r t y \? = 0.58 x 1 0 - l O y r - ; 1  = 4.72 x l Q - ^ y r " ;  K / K = O.OlJ8lg  1  _M*P* Total A r  4 0  40?! ^ o ( i n 10-5 ~~#40 cc STP/g)  5  Sample Number Rock Name  Mineral  GD-2  Amphibole  0.1406 O.1386 0.1402 Av.0.l40  0.24 0.39  0.09845 0.09879  0.01041 0.01044  170±12 171*10  GD-4 Guichon Quartz D i o r i t e  Amphibole  0.1708 0.1684 0.16Q1 Av.O.169  0.60  0.1474  O.OI285  208±8  GD-5 Quartz-poor Porphyry  Biotite  5.586 5.529 Av.5.56  0.50  4.717  0.01253  203*8  GD-10 P-3  Amphibole  O.2899 0.2941 Av.0.292  0.53  0.2432  0.01230  199*8.  GD-lla Bethlehem Quartz D i o r i t e ?  Amphibole  0.1617 0.1614 Av.0.162  0.44  0.1305  0.01193  194±10  P-3  Potassium  Ar  4 0  Apparent Age (my), Estimated Analytical Error  TABLE 4.1  (Cont.)  40 Ar T o t a l Ar 40 3  Sample Number Rock Name  Mineral  GD-12 Guichon Quartz D i o r i t e  Biotite  5-544 5.577 Av.5.56  O.83  4.663  0.01239  201±8  Hornblende  0.4204 0.4282 Av.0.424  0.60  O.3629  0.01264  205*8  Biotitexs  5.98 5.84 5.91 5.87 Av.5.90  0.90  4.307  0.01196  195+8  Hornblende  O.3805 O.39.36 Av.O.387  0.39  0.3121  0.01192  194*10  K63--222 Bethlehem Granite  Biotite  7.154 7.1J5 Av.7.16  O.87  5.903  0.01218  198*8  K63-240 Breccia  Biotitesss  5.60 5.61 5.59 ^•61 Av.5•60  0.84  4.643  0.01225  199^8  K63-H5 SkeenaBethlehem  s s$  Potassium  :  Ar _ ( i n 10-5 cc STP/g) 4 0  Jj&Q 40  K  Apparent Age (my), Estimated Analytical Error  Radiogenic Concentrate prepared and analyzed by K.E. Northcote Concentrate prepared and analyzed by Dr. W.H. White •Amphibole i n d i c a t e s those samples c o n t a i n i n g both a c t i n o l i t e and hornblende 1  32  TABLE 4.2  Interlaboratory Results  Standard . Number Mineral  Laboratory Analyst  GE 2 0 6 0 Biotite  Columbia E r i c k s o n , G.P.  6.92 I 6.91 I  McDowell, P.  6.89 P  Yale  6.81 P 6.82, P  Armstrong, D.  U.B.C. Northcote, K.E. Harakal, J . E . Dirom, G.E.  P-207 Muscovite  B-3203 Biotite  6.854.O6 P«s  Ar "* Total A r 4  4of (in 1 0 - 5 cc STP/g) A r  4 0  0.97 0.90  5.57< 5.62?  0.95 0.63 O.83 0.48  5.438 5.423 5.394  5.484  Summary of 8.58±.12 Results (Lanphere and Dalrymple, 1 9 6 5 )  2.840 ± . 0 6 3  U.B.C. 8.65 Northcote, K.E. 8 . 6 3 Dirom, G.E. 8.56 Harakal, J . E . 8 . 5 9  2.742 2.666 2.722.  0.77 0.90 0.66  Summary of Results (Hurley e t a l , 1 9 6 2 ) U.B.C. Harakal, J . E .  P I 3E  Potassium  38.77±.l4  0.72  Flame photometric a n a l y s e s Isotope d i l u t i o n a n a l y s e s Radiogenic Average and standard d e v i a t i o n of 1 2 potassium  38.37  analyses  33 TABLE 4 . 3  R e l a t i v e Ages of the V a r i o u s Phases on the Bethlehem Copper Property-  Sample Number  Phase Name  Guichon Quartz Diorite  Skeena-Be.thlehem Quartz D i o r i t e  R e l a t i v e Age on Mineral S t r u c t u r a l Evidence  GD-4  GD-12 GD-12 GD-lla  K63-H5  2 or  3  or  3  K63-115  Bethlehem  Granite  K63-222  2  K-Ar App Age (my)  Amphibole Hornblende Biotite  208 205 201  Amphibole Hornblende Biotite**  194 194 195  Biotite  198  Biotite  203  Quartz-poor Porphyry  GD-5  P-3 Porphyry  GD-2 GD-10  Amphibole Amphibole  170 199  Breccia  K63-240  BiotitesaE*  199  Quartz D i o r i t e Porphyry  NB;  Spud Lake Porphyry  ND  4  7  Post Skeena-Bethlehem  ND  ND  XX Concentrate prepared and analyzed by K.E. Northcote xa?*Coneentrate prepared and analyzed by Dr. W.H. White 'Amphibole i n d i c a t e d those samples c o n t a i n i n g both a c t i n o l i t e and hornblende 1  34  The  apparent  age of each sample analyzed was  on the b a s i s of the data presented i n Table 4 . 1 . apparent limits,  calculated The  age a l s o shows the estimated e r r o r l i m i t s . ranging from 4 to 6 per cent  calculated These  of the a s s o c i a t e d apparent  age, were estimated both on the b a s i s of the r e s u l t s obtained the i n t e r l a b o r a t o r y standards and a mathematical  evaluation,  s i m i l a r to t h a t o u t l i n e d by Wanless e t a l ( 1 9 6 5 ) , v i d u a l sources of e r r o r .  The apparent  of the  ages of those  having l e s s than 50 per cent atmospheric  argon  on  indi-  samples  contamination,  however, are b e l i e v e d to be i n t e r n a l l y accurate to w i t h i n 2 per cent.  T h i s r e l a t i v e accuracy may  be used to determine  whether  there are any r e a l age d i f f e r e n c e s between the v a r i o u s i n t r u s i v e phases s t u d i e d .  35  CHAPTER V  DISCUSSION  The b i o t i t e and amphibole potassium-argon apparent ages obtained d u r i n g the course of t h i s study on the v a r i o u s phases of the Guichon Creek b a t h o l i t h p r e s e n t on the Bethlehem  Copper  p r o p e r t y are of value as c l u e s t o the g e o l o g i c a l h i s t o r y of t h i s b a t h o l i t h and to the age of the T r i a s s i c - J u r a s s i c Although the i n d i v i d u a l phases are e s s e n t i a l l y  boundary.  indistinguishable  by means of t h e i r potassium-argon apparent ages (see F i g u r e 4.3), the  r e s u l t s obtained i n d i c a t e with considerable c e r t a i n t y  that  these phases were emplaced d u r i n g an I n t e r v a l of not more than 10 m.y.  c e n t e r e d around 200 m.y.  ago.  The s t r a t i g r a p h i c age of the Guichon Creek b a t h o l i t h i s c o n s i d e r e d to be known w i t h i n  close  l i m i t s since  to i n t r u d e e a r l y Upper T r i a s s i c v o l c a n i c  i t i s believed  rocks of the N i c o l a  group and to be unconformably o v e r l a i n by f o s s i l i f e r o u s e a r l y Middle J u r a s s i c marine sediments ( D u f f e l l and McTaggart,  1952).  The unconformity between the Guichon Creek b a t h o l i t h and the Middle J u r a s s i c marine sediments f a v o u r s p l a c i n g the emplacement age of the b a t h o l i t h near the top of the T r i a s s i c .  The age of  t h i s b a t h o l i t h may,  therefore,  i n d i c a t e the age of the T r i a s s i c -  J u r a s s i c boundary.  The average of a l l the potassium-argon  apparent ages o b t a i n e d i n t h i s study on both b i o t i t e and except GD-2  i s 200 m.y.  w i t h a standard d e v i a t i o n  amphibole  of the mean of  36  l e s s than 2 per c e n t .  T h i s average apparent age of 200 m.y. i s ,  t h e r e f o r e , b e l i e v e d to r e p r e s e n t a b e t t e r approximation to the maximum age of the T r i a s s i c - J u r a s s i c boundary than the l 8 l  m.y.  age suggested by F o l i n s b e e et a l ;(1960), which was based on the potassium-argon  r e s u l t s o b t a i n e d on b i o t i t e from samples c o l -  l e c t e d elsewhere  i n this batholith.  Leech et a l (1963) and Wanless et a l (1965) of the Geol o g i c a l Survey of Canada, r e p o r t e d b i o t i t e apparent ages r a n g i n g from 224 m.y.  potassium-argon  to 265 m.y.  on rocks r e p r e -  s e n t i n g v a r i o u s phases of the Guichon Creek b a t h o l i t h Guichon quartz d i o r i t e , Bethlehem quartz d i o r i t e , granodiorite. al  including  and B e t h s a i d a  These Middle Permian r e s u l t s have l e d Wanless et  (1965) t o suggest that the N i c o l a group  c o n t a c t with, or r e s t unconformably  s t r a t a are i n f a u l t  on the Guichon Creek  batholith,  or that the c o n t a c t rocks are not p a r t of the N i c o l a group but are o l d e r . The r e s u l t s o b t a i n e d i n the p r e s e n t study are i n c o m p a t i b l e w i t h those r e p o r t e d by Leech et a l (1963) and Wanless e t a l (1965) u n l e s s a l l the samples used i n t h i s study s u f f e r e d metamorphism approximately 200 m.y.. improbable f o r s e v e r a l reasons.  ago.  T h i s h y p o t h e s i s seems  First,  the concordant  ages o b t a i n e d on the c o e x i s t i n g hornblende K 6 3 - H 5 and GD-12  apparent  and b i o t i t e i n samples  i n d i c a t e that no major metamorphic event  has  occured s i n c e the i n i t i a l c r y s t a l l i z a t i o n of these rocks u n l e s s both the b i o t i t e and hornblende  ' c l o c k s ' i n these samples were  completely r e s e t as the r e s u l t of such metamorphism.  Second,  37  these two samples were c o l l e c t e d s i x m i l e s a p a r t g e o g r a p h i c a l l y i n d i c a t i n g t h a t , i f the ' c l o c k s ' i n these samples were completely r e s e t , the metamorphic event r e q u i r e d would probably have been s u f f i c i e n t l y widespread t o have a f f e c t e d the b a t h o l i t h as a whole. T h i r d , no p e t r o g r a p h i c evidence was found i n the t h i n s e c t i o n s s t u d i e d to i n d i c a t e the occurrence of a metamorphic event f i c i e n t l y i n t e n s e t o completely reset, the amphibole  suf-  'clocks'.  Fourth, the e s s e n t i a l l y i d e n t i c a l apparent ages obtained on two d i f f e r e n t GD-12, which  samples of the Guichon quartz d i o r i t e , GD-4 and show d i f f e r e n t degrees of a l t e r a t i o n of hornblende  to a c t i n o l i t e ,  i n d i c a t e t h a t t h i s a l t e r a t i o n was d e u t e r i c i n  nature, that i s , i t took p l a c e d u r i n g the f i n a l stages of the c r y s t a l l i z a t i o n p r o c e s s r a t h e r than as the r e s u l t of a l a t e r metamorphic event.  And f i n a l l y ,  i f , as g e n e r a l l y accepted, the  Guichon Creek b a t h o l i t h i n t r u d e s e a r l y Upper T r i a s s i c rocks, the date of the Middle-Upper  Nicola  T r i a s s i c boundary suggested  by Kulp (1961) t o be 200±10 m.y. can be used t o p l a c e a rough Kulp (1961) based  upper l i m i t on the age of t h i s b a t h o l i t h . date on the b i o t i t e potassium-argon  this  apparent age of 195*5 m.y.  obtained by E r i c k s o n and Kulp (1961) on the P a l i s a d e Diabase of the Newark s e r i e s which i s b e l i e v e d t o be Upper T r i a s s i c . The concordant b i o t i t e and amphibole  apparent ages obtained  i n t h i s study a l s o serve to i n d i c a t e that these amphiboles do not c o n t a i n a p p r e c i a b l e excess r a d i o g e n i c argon. e s s e n t i a l l y i n agreement w i t h the c o n c l u s i o n , A l d r i c h e t a l ( i 9 6 0 ) and Hart (I960; 1 9 6 1 ) ,  This i s  suggested by  t h a t amphiboles do  38  not n o r m a l l y c o n t a i n excess r a d i o g e n i c argon as had been c o n s i d e r e d p o s s i b l e by Damon and Kulp The one p o s s i b l y anomalous apparent GD-2,  earlier  (1958).  age obtained, that  on  i s d i f f i c u l t to r e s o l v e i n l i g h t of the other r e s u l t s  obtained d u r i n g t h i s study. checked  The a n a l y t i c a l data was  and are c o n s i d e r e d r e l i a b l e and a c c u r a t e w i t h i n the  assigned.  limits  S t r u c t u r a l l y , t h i s sample should be o l d e r than the  b r e c c i a and younger than the quartz-poor porphyry; apparent  independently  age of 170 m.y.  The  obtained  i s , t h e r e f o r e , approximately 30  m.y.  younger than one would expect on s t r u c t u r a l evidence alone.. i s p o s s i b l e that t h i s sample i s not r e p r e s e n t a t i v e of the  It  P-3  porphyry but r a t h e r a l a t e r phase, although there i s : no present p e t r o g r a p h i c evidence to support t h i s s u g g e s t i o n . does c o n t a i n a g r e a t e r percentage  Sample  GD-2  of a c t i n o l i t e than any other  sample analyzed, however, the r e s u l t s obtained by Hart  (1961)  j.  on a c t i n o l i t e i n d i c a t e t h a t t h i s m i n e r a l should r e t a i n e q u a l l y as w e l l as hornblende.  The apparent  t h i s present study on two d i f f e r e n t quartz d i o r i t e ,  GD-4  r e t a i n s argon  samples of the  actino-  well.  d i s l o c a t i o n or, l e s s l i k e l y ,  was  a f f e c t e d by  c o n t a c t or r e g i o n a l metamorphism.  T h i s p o s s i b i l i t y seems improbable  would then s t i l l  Guichon  to a c t i n o l i t e , also confirm that  Another p o s s i b i l i t y i s t h a t sample GD-2  sample K 6 3 - 2 2 2 ,  ages o b t a i n e d i n  and GD-12, which show d i f f e r e n t degrees of  a l t e r a t i o n of hornblende lite  argon  since i t i s u n l i k e l y  a b i o t i t e , c o l l e c t e d w i t h i n 2 0 0 f e e t of  that GD-2  give an apparent age i n good agreement with i t s  39  structural position.  A l d r i c h et a l ( i 9 6 0 ) have c o n s i d e r e d the  v a r i a t i o n of potassium-argon apparent ages of minerals; as a f u n c t i o n of d i s t a n c e from an i n t r u s i v e c o n t a c t .  They found t h a t ,  while hornblende r e t a i n e d e s s e n t i a l l y a l l i t s argon w i t h i n  100  f e e t of such a c o n t a c t , b i o t i t e l o s t e s s e n t i a l l y a l l i t s argon w i t h i n 300 f e e t of the c o n t a c t and as much as 50 per cent of i t s argon w i t h i n 5000 f e e t . s t r o n g l y dependent  Such v a l u e s would.be expected t o be  on the s i z e of the heat source, the depth of  b u r i a l , and other f a c t o r s .  However, they do serve to i n d i c a t e  the i m p r o b a b i l i t y t h a t b i o t i t e w i l l r e t a i n argon w i t h i n a few hundred f e e t of amphibole which has a p p a r e n t l y l o s t 15 per cent of i t s r a d i o g e n i c argon u n l e s s the thermal event was l o c a l nature.  of a very  40  CONCLUSIONS  I t i s e v i d e n t from the amphibole and b i o t i t e  apparent  ages obtained d u r i n g the course of t h i s study, t h a t the v a r i o u s phases of the Guichon Creek b a t h o l i t h present on the Bethlehem Copper p r o p e r t y were emplaced d u r i n g a p r o b a b l y short i n t e r v a l , not longer than 10 m.y., centered around 200 m.y. ago and t h a t no major metamorphic event has taken p l a c e i n t h i s area s i n c e t h i s date.  I t i s a l s o e v i d e n t , t h a t one cannot  differentiate  between the v a r i o u s phases of the Guichon Creek b a t h o l i t h on the b a s i s of t h e i r potassium-argon i n the apparent  apparent  ages s i n c e the v a r i a t i o n s  ages obtained were w i t h i n the a n a l y t i c a l  of u n c e r t a i n t y of the technique used.  The one amphibole  limits apparent  age which i s s i g n i f i c a n t l y younger than the o t h e r s o b t a i n e d i n t h i s work may i n d i c a t e an event  i n the f o r m a t i o n of t h i s b a t h o l i t h  which f o l l o w e d the major I n t r u s i v e event by approximately The average  apparent  30 m.y.  age of 200 m.y. obtained on both  b i o t i t e and amphibole from the v a r i o u s phases of the Guichon Creek b a t h o l i t h present on the Bethlehem Copper p r o p e r t y may r e p r e s e n t a b e t t e r approximation  t o the maximum age of the  T r i a s s i c - J u r a s s i c boundary than that p r e v i o u s l y r e p o r t e d i n the l i t e r a t u r e , however, t h i s c o n c l u s i o n Should be confirmed by f u r t h e r study of the s t r a t i g r a p h i c age of t h i s b a t h o l i t h and by further isotopic  s t u d i e s , p r e f e r a b l y u s i n g methods other than  potassium-argon. The  r e s u l t s obtained on the two samples c o n t a i n i n g c o e x i s t i n g  41  amphibole  and b i o t i t e i n d i c a t e t h a t amphiboles- g i v e potassium-  argon ages of q u a l i t y at l e a s t comparable  to those on b i o t i t e  and t h a t these samples do not c o n t a i n s i g n i f i c a n t excess r a d i o genic argon.  The one perhaps anomalous- amphibole  r e s u l t obtained,  although of unambiguous i n t e r p r e t a t i o n , does not d e t r a c t from the o v e r a l l value of potassium-argon d a t i n g of amphiboles or from the value of the other amphibole  apparent ages o b t a i n e d .  42  BIBLIOGRAPHY  Abbey, S., and Maxwell, J„A„, D e t e r m i n a t i o n of Potassium i n Mica, Chemistry i n Canada, V o l , 1 2 , No. 9,  pp. 3 7 - 4 1 ,  i960.  A l d r l c h , L.T., Hart, S.R., W e t h e r i l l , G.W.. Davis, G.L., T i l t o n , G.R., and Doe, B., R a d i o a c t i v e Ages of Rocks, Carnegie I n s t . Wash. Year Book, 6 0 , pp. 2 5 0 - 2 5 6 , 1960/61. B u r r i e l - M a r t i , F., and Ramirez-Munoz, J . , Flame E l s e v i e r P u b l i s h i n g Co., Amsterdam, 1 9 5 7 .  Photometry,  Carr, J.M., P r e l i m i n a r y Notes of some Rock Types O c c u r i n g on the Bethlehem Property, u n p u b l i s h e d paper, B.C. Dept. Mines, 1 9 5 9 . C a r r , J.M., P o r p h y r i e s , B r e c c i a s and Copper M i n e r a l i z a t i o n i n the H i g h l a n d V a l l e y , B.C., Canadian M i n i n g J o u r n a l , V o l . 8 1 , pp. 7 1 - 7 3 , I960. C o c k f i e l d , W.E., Geology and M i n e r a l D e p o s i t s of the N i c o l a Map-Area, B r i t i s h Columbia, G e o l . Surv. Can., Mem. 2 4 9 , 1948. Cooper, J.M., The Flame Photometric D e t e r m i n a t i o n of Potassium i n G e o l o g i c a l M a t e r i a l s used f o r Potassium Argon D a t i n g , Geochim. et Cosmochim. Acta, V o l . 2 7 , pp. 525-546, 1963. Coveny, C.J., The Bethlehem Copper Property, Western Miner and O i l Review, V o l . 3 5 , No. 2 , pp. 4 1 - 4 3 , 1 9 6 2 . Damon, P.E., and Kulp, J.L., Excess Helium and: Argon i n B e r y l and o t h e r M i n e r a l s , American M i n e r a l o g i s t , V o l . 4 3 , PP. 4 3 3 - 4 5 9 , 1 9 5 8 . Dean, J.A., Flame Photometry, McGraw-Hill, New  York,  i960.  D u f f e l l , S., and McTaggart, K.C., A she r of t Map-Area, B r i t i s h Columbia, G e o l . Surv. Can., Mem. 2 6 2 , 1 9 5 2 . E r i c k s o n , G.P., and Kulp, J.L., Potassium-Argon Dates on B a s a l t i c Rocks, Ann. N.Y. Acad. S c i . , V o l . 91, A r t . 2 , pp. 3 2 1 - 3 2 3 ^ 1 9 6 1 . Evernden, J.F., and Richards, J.R., Potassium-Argon Ages i n E a s t e r n A u s t r a l i a , J . G e o l . Soc. Aust., V o l . 9, pp. 1 - 5 0 , 1962. F o l i n s b e e , R.E., Baadsgaard, H., and L i p s o n , J . , PotassiumArgon Time S c a l e , Rep. XXI, I n t . G e o l . Congr., Norden, Pt. I l l , pp. 7 - 1 7 , I960.  43  Hart, S.R., E x t r a c t s from the T h e s i s I n v e s t i g a t i o n s of S.R. Hart, N.Y.O. 3 9 4 1 , E i g h t h Ann. Prog, Rept. f o r i 9 6 0 , Dept. Geol. Geophys., Mass. I n s t . Technol., pp. 87-I69,  I960.  Hart, S.R., The Use of Hornblendes and Pyroxenes f o r K-Ar Dating, J . Geophys. Res,, V o l . 166, No. 9, pp. 2 2 9 5 -  3001,  1961.  Hurley, P.M., e t a l . , Standard B i o t i t e B - 3 2 0 3 , N.Y.O. 3943, Tenth Ann. Prog. Rept. f o r 1962, Dept. Geol. Geophys,, Mass. I n s t . Technol., p. 151, 1962. Kulp, J.L., G e o l o g i c a l Time S c a l e , Science, V o l . 133, pp. 1105-1114, 1961.  No.  3459,  Lanphere, M.A., and Dalrymple, G.B., Summary of A n a l y t i c a l Data, U.S. Geol. Survey Standard Muscovite P-207, i n press, 1965. Leech, G.B., Lowdon, J.A., S t o c k w e l l , G.H., and Wanless, R.K., Age Determinations and G e o l o g i c a l S t u d i e s , Geol. Surv. Can., paper 6 3 - 1 7 , 1963.. L i p s o n , J . , Potassium-Argon D a t i n g of Sedimentary Rocks, B u l l . Geol. Soc. Amer., V o l . 69, pp. 137-150, 1958. Pinson, W.H., J r . , The Potassium-Argon Method: The Problem of Potassium A n a l y s i s , Ann. N.Y. Acad. Science, V o l . 91,  A r t . 2, pp. 221-225,  1961.  Wanless, R.K., Stevens, R.D., Lachance, G.R., and Rlmsaite, R.Y.H., Age Determinations and G e o l o g i c a l S t u d i e s , Geol. Surv. Can., Paper 6 4 - 1 7 (Part 1), 1965. White, W.H., Thompson, R.M., and McTaggart, K.C.,.The Geology and M i n e r a l D e p o s i t s of the Highland V a l l e y , B.C., C.I.M. Trans., V o l . 60, pp. 273-289, 1957-  44  APPENDIX  DESCRIPTIONS AND LOCALITIES OP SAMPLES COLLECTED i  GD-1  Mine C o o r d i n a t e s : 9350N-7430E  Quartz D i o r i t e Porphyry  T h i s sample, c o l l e c t e d from the c e n t e r p o r t i o n of a 200'  wide dyke where i t i n t r u d e s P-3 porphyry, i s an  a l t e r e d , l e u c o c r a t i e quartz d i o r i t e porphyry composed of coarse, euhedral phenocrysts of a l t e r e d  hornblende  up t o 1 cm. i n l e n g t h and grey-white p l a g i o c l a s e , with g l a s s y eyes of quartz s e t i n an a p h a n i t i c , c h l o r i t i c groundmass.  Aggregates of e p i d o t e appear t o  r e p l a c e both hornblende comprise  grey-green,  and p l a g i o c l a s e .  Phenocrysts  approximately 60$ of the rock by volume.  In t h i n - s e c t i o n , t h i s sample i s seen t o be made up l a r g e l y of s t r o n g l y s a u s s u r i t i z e d andesine set i n a very f i n e - g r a i n e d ,  phenocrysts  allotriomorphic-granular  matrix composed of p l a g i o c l a s e , quartz, and o r t h o c l a s e . Quartz phenocrysts occur as l a r g e c l e a r eyes which are sometimes l a r g e r than the p l a g i o c l a s e g r a i n s .  Horn-  blende phenocrysts have been almost completely a l t e r e d to a c t i n o l i t e , c h l o r i t e , o r e p i d o t e and, f o r t h i s reason, were not analyzed„ apatite,  Accessory m i n e r a l s i n c l u d e  sphene, and magnetite.  The estimated mode i s  70$ p l a g i o c l a s e , 20$ quartz, 4$ a l t e r e d hornblende, 2$ o r t h o c l a s e , 4$ magnetite  and other a c c e s s o r y m i n e r a l s .  45  GD-2  P-3 Porphyry  Mine C o o r d i n a t e s :  9310N - 6880E  T h i s sample, c o l l e c t e d from the c e n t e r p o r t i o n o f a 30'  wide dyke where i t i n t r u d e s Bethlehem quartz  diorite,  i s a l e u c o c r a t i c quartz d i o r i t e  porphyry  composed of l a r g e , well-formed but a l t e r e d of hornblende  phenocrysts  up to 1 cm. i n l e n g t h , subhedral pheno-  c r y s t s of f l e s h y - w h i t e p l a g i o c l a s e , and subrounded t o kidney-shaped  phenocrysts of quartz s e t I n a l i g h t  c o l o u r e d groundmass which i s r e s o l v a b l e under the handlens. In t h i n - s e c t i o n , t h i s sample i s seen to be made up l a r g e l y of zoned, m i l d l y s a u s s u r i t i z e d ,  subhedral  andesine phenocrysts s e t i n a medium-grained groundmass, composed of q u a r t z , p l a g i o c l a s e , and o r t h o c l a s e , t h a t shows a crude graphic t e x t u r e . are rounded o r kidney-shaped by the m a t r i x .  Quartz  phenocrysts  and are p a r t i a l l y embayed  Hornblende occurs as l a r g e ,  poikilitic  phenocrysts that have been p a r t i a l l y a l t e r e d to e p i d o t e , c h l o r i t e , and p a l e green a c t i n o l i t e . minerals include apatite,  sphene, and magnetite.  estimated mode i s 65$ p l a g i o c l a s e , a l t e r e d hornblende,  Accessory The  25$ q u a r t z , 5$  3$ o r t h o c l a s e , and 2$ magnetite  and other a c c e s s o r y m i n e r a l s . Approximately  40 grams of -48 t o +100 mesh amphibole  concentrate was obtained from t h i s sample.  A grain  46  10$  count i n d i c a t e d the f o l l o w i n g composition: green-black hornblende, 85$ 5$  a c t i n o l i t e , and impurity was GD-3 K63-222  light,  impurities.  olive-green  E p i d o t e was  the  although some c h l o r i t e , a p a t i t e , and  chief  sphene  noted.  Bethlehem G r a n i t e  9220N - 6 8 2 0 E  Mine C o o r d i n a t e s :  Both samples c o l l e c t e d from same outcrop. brown, medium- to f i n e - g r a i n e d , of p i n k i s h - r e d and  dark,  orthoclase,  This  g r a n i t i c rock  quartz, white  reddish  consists  plagioclase,  a small amount of dark b i o t i t e which occurs as  flakes generally  l e s s than 2 mm.  In t h i n - s e c t i o n ,  t h i s g r a n i t i c rock i s found to  made up  of p e r t h i t i c o r t h o c l a s e  oligoclase plagioclase  i n diameter.  (50$),  (15$), and  quartz(30$),  b i o t i t e (3$), with  a c c e s s o r y a p a t i t e , magnetite, sphene, and The  be  zircon  (2$).  subhedral f l a k e s of b i o t i t e e x h i b i t a wavey  e x t i n c t i o n and  are very s l i g h t l y c h l o r i t i z e d .  p e r t h i t i c orthoclase sericitic  and  and  argillic  Approximately 40 concentrate was  The  o l i g o c l a s e show s l i g h t  alteration.  grams of - 4 8 to +100  mesh b i o t i t e  obtained from sample K 6 3 - 2 2 2 .  A  g r a i n count i n d i c a t e d the f o l l o w i n g composition: reddish-brown b i o t i t e and  1$ impurities.  include- a p a t i t e ,  sphene, magnetite, and  and  b i o t i t e g r a i n s are very  quartz.  chloritic.  The  The minor  99$  impurities feldspar  slightly  4  GD-4  Guichon Quartz D i o r i t e  7  Mine C o o r d i n a t e s : 96OON -  9750E This  sample, c o l l e c t e d approximately 6 0 0 ' south of the  Snowstorm a d i t , i s a medium- t o c o a r s e - g r a i n e d , m e s o c r a t i c , moderately of f e l d s p a r ,  q u a r t z , a l t e r e d b i o t i t e , and a l t e r e d  l a t h s of hornblende length.  a l t e r e d quartz d i o r i t e composed  generally  l e s s than 5 mm. i n  The mafic m i n e r a l s are d i s t r i b u t e d u n i f o r m l y  throughout  the rock.  In t h i n - s e c t i o n ,  t h i s h y p i d i o m o r p h i c - g r a n u l a r rock i s  seen t o be made up of s a u s s u r i t i z e d andesine clase  (58$),  altered,  (10$),  orthoclase  a l t e r e d hornblende apatite,  plagio-  slightly perthitic, interstitial  interstitial,  quartz ( 1 5 $ ) , and  and b i o t i t e (15$), w i t h a c c e s s o r y •  sphene, z i r c o n , and magnetite  (2$).  Biotite  has been almost completely a l t e r e d t o c h l o r i t e while hornblende  has been l a r g e l y a l t e r e d t o e p i d o t e and .  l i g h t green a c t i n o l i t e . Approximately  40 grams of - 4 8 t o +100 mesh amphibole  concentrate was obtained from t h i s sample.  A grain  count i n d i c a t e d  34$ dark  the f o l l o w i n g  green-black hornblende, and 2$ i m p u r i t i e s . noted.  composition:  64$ olive-green a c t i n o l i t e ,  E p i d o t e was the c h i e f i m p u r i t y  48  GD-5  Quartz-poor  Porphyry  Mine C o o r d i n a t e s :  938ON - 8840E  T h i s grey, p o r p h y r i t i c rock, c o l l e c t e d from the c e n t e r of a 20' wide dyke where i t i n t r u d e s Guichon d i o r i t e , c o n t a i n s phenocrysts of b i o t i t e ,  quartz  hornblende,  and p l a g i o c l a s e s e t i n a l i g h t c o l o u r e d , a p h a n i t i c groundmass.  A few s m a l l phenocrysts of quartz are  also v i s i b l e  s u g g e s t i n g that t h i s specimen may be  e q u i v a l e n t t o the P - l porphyry as d e s c r i b e d by C a r r (1959).  Phenocrysts comprise  approximately 40$ of  the rock by volume„ In t h i n - s e c t i o n , t h i s rock i s seen t o be made up l a r g e l y of weakly s a u s s u r i t i z e d phenocrysts o f zoned, subhedral andesine p l a g i o c l a s e s e t i n a f i n e - g r a i n e d groundmass, composed of p l a g i o c l a s e , q u a r t z , and o r t h o c l a s e , that e x h i b i t s a crude g r a p h i c t e x t u r e . Small rounded phenocrysts of quartz and p a r t i a l l y chlorltized,  subhedral t o e u h e d r a l f l a k e s of b i o t i t e  ranging up t o 4 mm. throughout  i n diameter are a l s o  the s e c t i o n .  distributed  One l a r g e , p o i k i l i t i c  pheno-  c r y s t of a c t i n o l i t e - h o r n b i e n d e was r e c o g n i z e d i n the section. magnetite,  The a c c e s s o r y m i n e r a l s i n c l u d e a p a t i t e , and sphene.  The estimated mode of t h i s  s e c t i o n i s 68$ andesine p l a g i o c l a s e , 3$ o r t h o c l a s e , 2$ b i o t i t e , other a c c e s s o r y m i n e r a l s .  25$ q u a r t z ,  and 2$ magnetite and  49  Approximately 40 grams of -35 c o n c e n t r a t e was  to +100  mesh b i o t i t e  obtained from t h i s sample.  A  98$  count i n d i c a t e d the f o l l o w i n g composition: slightly chloritized biotite, Impurities  2$  and  grain  impurities.  i n c l u d e hornblende, quartz,  apatite,  and  feldspar. GD-6  Quartz-poor Porphyry  Mine C o o r d i n a t e s :  10860N-8300E  T h i s grey-green, p o r p h y r i t i c rock, c o l l e c t e d from c e n t e r of a 5 0  !  wide dyke where i t i n t r u d e s  quartz d i o r i t e , c o n s i s t s of small, of white f e l d s p a r and aphanitic  groundmass.  mately 40$  Carr  Guichon  a l t e r e d phenocrysts  dark hornblende set i n a Phenocrysts comprise  of the rock by volume.  possibly equivalent  to the  P-2  the  This  totally  approxi-  specimen i s  porphyry d e s c r i b e d  by  (1959).  In t h i n - s e c t i o n , t h i s rock i s seen to be made up  of s t r o n g l y  largely  s a u s s u r i t i z e d phenocrysts of  zoned andesine p l a g i o c l a s e  set i n a  i n t e r g r o w t h of quartz and  feldspar.  phenocrysts of quartz and  small,  fine-grained Rare, rounded  a l t e r e d l a t h s of  hornblende occur d i s t r i b u t e d throughout the A l t e r a t i o n m i n e r a l s present i n c l u d e calcite,  a c t i n o l i t e , e p i d o t e , and  Accessory m i n e r a l s i n c l u d e magnetite.  The  section.  sericite,  albite,  possibly kaolinite.  apatite,  sphene,  and  mode of t h i s rock i s s i m i l a r to  that  50  g i v e n f o r GD-5  w i t h the e x c e p t i o n t h a t  occurs i n p l a c e of b i o t i t e .  hornblende  T h i s sample does not  c o n t a i n s u f f i c i e n t u n a l t e r e d hornblende  f o r K-Ar  analysis. GD-7  Bethlehem Quartz D i o r i t e  Mine C o o r d i n a t e s :  780ON -  9790E T h i s sample, c o l l e c t e d from a t r e n c h i n the White zone area, i s a l e u c o c r a t i c , medium-grained, g r a n i t i c rock composed of f e l d s p a r , quartz, and a l t e r e d blende and b i o t i t e . litic  In  Hornblende occurs as l a r g e p o i k i -  g r a i n s which have been almost completely  to c h l o r i t e and  i s seen to be made up of s l i g h t l y zoned, s a u s s u r i t i z e d , andesine  plagioclase  rock  moderately  (69$ ), (  interstitial  i n t e r s t i t i a l o r t h o c l a s e (10$), and  a l t e r e d hornblende magnetite,  altered  actinolite.  t h i n - s e c t i o n , t h i s hypidiomorphic-granular  quartz ( 1 5 $ ) ,  horn-  and b i o t i t e  a p a t i t e , and  (5$),  sphene (1$).  with a c c e s s o r y Chlorite  occurs  as pseudomorphs a f t e r b i o t i t e , and l e s s commonly, hornblende.  Most of the hornblende  by a c t i n o l i t e and e p i d o t e .  has been r e p l a c e d  T h i s sample does not c o n t a i n  s u f f i c i e n t u n a l t e r e d b i o t i t e or hornblende analysis.  f o r K-Ar  51  GD-8 K63-240a  Spud Lake Porphyry  Mine C o o r d i n a t e s :  6200N - 11450E  T h i s medium-grey, p o r p h y r i t i c rock c o n t a i n s l a r g e euhedral t o subhedral phenocrysts of f l e s h y - w h i t e plagioclase,  subrounded eyes of quartz, and  scattered  phenocrysts of a l t e r e d b i o t i t e and hornblende a dense, muddy brown, a p h a n i t i c groundmass. c r y s t s comprise  set i n Pheno-  50$ of the rock by volume.  In t h i n - s e c t i o n , t h i s rock i s seen to be composed of a few l a r g e c l e a r eyes of u n a l t e r e d q u a r t z , completely c h l o r i t i z e d phenocrysts of b i o t i t e and hornblende,  and  r e l i c c r y s t a l s of s a u s s u r i t i z e d p l a g i o c l a s e set i n a moderately  a l t e r e d groundmass composed of quartz and  feldspar.  Accessory m i n e r a l s i n c l u d e a p a t i t e ,  and magnetite.  sphene,  These samples were not analyzed  because they do not c o n t a i n s u f f i c i e n t u n a l t e r e d b i o t i t e or GD-9  hornblende.  Quartz D i o r i t e Porphyry  Mine C o o r d i n a t e s :  10110N -  7200E T h i s m e s o c r a t i c , p o r p h y r i t i c rock c o n t a i n s euhedral to subhedral, f l e s h y - w h i t e phenocrysts of p l a g i o c l a s e , subrounded eyes of quartz, and a l t e r e d phenocrysts of hornblende  set i n a scant m a t r i x .  R a d i a l aggregates  of e p i d o t e appear to have r e p l a c e d o r i g i n a l Phenocrysts comprise volume.  hornblende.  approximately 80$ of the rock by  52  In t h i n - s e c t i o n , t h i s rock i s seen to be made up strongly saussuritized,  subhedral phenocrysts  p l a g i o c l a s e , c l e a r rounded g r a i n s of q u a r t z , a l t e r e d phenocrysts  of and  of hornblende set i n a scant  matrix composed of quartz and f e l d s p a r .  Alteration  minerals include s e r i c i t e , a l b i t e , epidote, c h l o r i t e , and p o s s i b l y k a o l i n i t e . include apatite,  of  calcite,  Accessory  sphene, and magnetite.  minerals  The mode of  t h i s rock i s s i m i l a r to t h a t g i v e n f o r QDrl.  This  sample does not c o n t a i n s u f f i c i e n t u n a l t e r e d hornblende f o r K-Ar GD-10  P-3  analysis.  Porphyry  Mine C o o r d i n a t e s :  9920N - 7070E  P e t r o g r a p h i c a l l y , t h i s sample i s the same as  GD-2  w i t h the e x c e p t i o n t h a t i t c o n t a i n s a t r a c e amount of biotite,  along with the hornblende,  quartz, and f e l d R  spar, set i n a s l i g h t l y c o a r s e r m a t r i x .  Both samples  appear to have undergone the same degree of a l t e r a t i o n . Approximately  30 grams of - 8 0  concentrate was count  mesh amphibole  obtained from t h i s sample.  i n d i c a t e d the f o l l o w i n g composition:  a c t i n o l i t i z e d hornblende, GD-lla  to +140  5$ b i o t i t e ,  P o r p h y r i t i c Bethlehem Quartz D i o r i t e ? ordinates:  A grain 65$  and 30$ ep&flote. Mine  Co-  10180N - 5730E  T h i s sample was  c o l l e c t e d w i t h i n 10' of GD-llb i n an  53  area mapped by C a r r (1959) as Bethlehem quartz d i o r i t e . GD-llb was  c l a s s i f i e d as Bethlehem quartz d i o r i t e  s i n c e i t i s s i m i l a r to GD-7  but G D - l l a d i f f e r s  from  these samples i n t h a t i t has a p o r p h y r i t i c r a t h e r than a g r a n i t i c t e x t u r e .  No c o n t a c t , however,  e v i d e n t between G D - l l a and G D - l l b .  was  GD-lla i s a  l e u c o c r a t i c , p o r p h y r i t i c rock composed of euhedral, milky-white phenocrysts of p l a g i o c l a s e ,  anhedral  phenocrysts of q u a r t z , and well-formed but a l t e r e d phenocrysts of hornblende l i g h t green groundmass.  slightly  set i n an a p h a n i t i c ,  Phenocrysts comprise  approxi-  mately 35$ of the rock by volume. In t h i n - s e c t i o n , t h i s rock i s seen to be made up of scatterecL.phenocrysts of moderately andesine p l a g i o c l a s e hornblende (65$)  (6$)  (25$),  saussuritized  quartz (4$), and  altered  set i n a very f i n e - g r a i n e d groundmass  composed of quartz and f e l d s p a r .  The  horn-  blende phenocrysts, g e n e r a l l y l e s s than 5 mm.  In  l e n g t h , have been l a r g e l y a l t e r e d t o a c t i n o l i t e , c h l o r i t e , and e p i d o t e . a p a t i t e and  Accessory m i n e r a l s i n c l u d e  magnetite.  Approximately  40 grams of -48 to +100  concentrate was  mesh amphibole  obtained from t h i s sample.  count i n d i c a t e d the f o l l o w i n g composition: green-black hornblende, impurities.  E p i d o t e was  75$  actinolite,  and  A grain 21$  dark  4$  the c h i e f i m p u r i t y noted.  54  GD-llb  Bethlehem Quartz D i o r i t e  Mine C o o r d i n a t e s :  k01:90N - 5730E T h i s sample i s e s s e n t i a l l y the same as GD-7 with the e x c e p t i o n t h a t i t i s f i n e r g r a i n e d and darker i n colour.  T h i s sample, however, does n o t c o n t a i n  s u f f i c i e n t u n a l t e r e d hornblende  o r b i o t i t e f o r K-Ar  analysis. GD-12  Guichon Quartz D i o r i t e  Mine C o o r d i n a t e s :  12510N -  5400E T h i s sample i s a t y p i c a l example of the Guichon quartz diorite.  I t i s a medium-grained, m e s o c r a t i c ,  rock composed of p o i k i l i t i c hornblende p i n k o r t h o c l a s e , quartz, and white B i o t i t e and hornblende 5 mm.  crystals,  and b i o t i t e ,  plagioclase.  g e n e r a l l y l e s s than  i n l e n g t h , occur i n equal amounts and are  evenly d i s t r i b u t e d throughout In  granitic  the rock.  t h i n - s e c t i o n , t h i s rock i s seen t o be made up of  s l i g h t l y s a u s s u r i t i z e d andesine p l a g i o c l a s e s l i g h t l y p e r t h i t i c o r t h o c l a s e (15$),  interstitial  quartz (10$), green p o i k i l i t i c hornblende slightly chloritized biotite magnetite,  augite was noted i n the hornblende  the pyroxene.  (10$), and  ( 5 $ ) , with accessory  sphene, z i r c o n , and a p a t i t e  t h a t some of the hornblende  (58$),  (2$).  Some  grains suggesting  formed a t the expense of  55  100 grams of -65 t o +100 mesh b i o t i t e  Approximately  c o n c e n t r a t e was obtained from t h i s sample.  A grain  count i n d i c a t e d the f o l l o w i n g composition: 98$ b i o t i t e and  2$ i m p u r i t i e s .  The i m p u r i t i e s i n c l u d e  hornblende,  a p a t i t e , and minor amounts of quartz and f e l d s p a r . 50 grams of -35 t o +65 mesh  Approximately  hornblende  concentrate was obtained from t h i s sample. count  A grain  i n d i c a t e d the f o l l o w i n g composition: 98$ dark  green-black hornblende  and 2% i m p u r i t i e s .  The  i m p u r i t i e s i n c l u d e d a c t i n o l i t e , e p i d o t e , and l e s s than 12$ b i o t i t e . K63-H5  Skeena-Bethlehem Quartz D i o r i t e Long.  L a t . 50°29'20"N,  121°06»30"W  T h i s sample, c o l l e c t e d by K.E. Northcote,  i s considered  to be e q u i v a l e n t t o the Bethlehem quartz d i o r i t e .  It  i s a medium grained, l e u c o c r a t i c t o mesocratic, g r a n i t i c rock composed of white p l a g i o c l a s e ,  clear  i n t e r s t i t i a l g r a i n s of quartz, p i n k i s h c o l o u r e d o r t h o c l a s e , p o i k i l i t i c hornblende 5 mm.  i n l e n g t h , and hexagonal p l a t e s of b i o t i t e which  seldom exceed  2 mm.  i n diameter.  are evenly d i s t r i b u t e d throughout In  l a t h s ranging up t o  The mafic  minerals  the rock.  t h i n - s e c t i o n , t h i s hypidiomorphic-granular  i s seen t o be made up of zoned, weakly a l t e r e d plagioclase  (6l$),  rock andesine  s l i g h t l y p e r t h i t i c orthoclase (15$),  56  i n t e r s t i t i a l quartz (15$), p o i k i l i t i c  hornblende  c o n t a i n i n g c o r e s of a u g i t e (4$), and b i o t i t e with a c c e s s o r y a p a t i t e , magnetite, zircon  sphene, and  (2$).  Approximately  10 grams of -35  concentrate was sample.  to +100  obtained by K.E.  mesh b i o t i t e  Northcote from  this  The estimated composition of the concentrate  i s as f o l l o w s : biotite  95$  b l a c k , mottled by golden brown  and 5$ i m p u r i t i e s .  blende but some a c t i n o l i t e , quartz noted. 15$  (3$),  I m p u r i t i e s mainly  horn-  e p i d o t e , f e l d s p a r , and  The b i o t i t e appeared to be from 10 to  chloritized.  Approximately  30 grams of -48  c o n c e n t r a t e was count  to +100  mesh  hornblende  obtained from t h i s sample.  A grain  i n d i c a t e d the f o l l o w i n g composition:  p a r t i a l l y a c t i n o l i t i z e d hornblende  and 2$  98$ impurities.  I m p u r i t i e s i n c l u d e quartz, sphene, a p a t i t e , e p i d o t e , and l e s s than 0.3$ K63-222  See  GD-3  K63-240a  See  GD-8  K63-240  Breccia  Mine C o o r d i n a t e s :  C o l l e c t e d by K.E. White.  biotite.  Northcote  The b i o t i t e  885ON - 8050E and analyzed by Dr.  concentrate separated from  W.H. this  sample i s r e p o r t e d by White ( p e r s o n a l commumication)  57  to c o n t a i n a mixture of primary and secondary b i o t i t e . The apparent age o b t a i n e d on t h i s mixture, however, should r e p r e s e n t the f o r m a t i o n age of the b r e c c i a s i n c e i t i s probable t h a t the primary b i o t i t e In t h i s sample l o s t i t s o r i g i n a l r a d i o g e n i c argon a t the same time the secondary b i o t i t e formed as the  result  of hydrothermal p r o c e s s e s t a k i n g p l a c e d u r i n g brecciation. text.  See a l s o d e s c r i p t i o n of b r e c c i a i n  

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