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Lead and strontium isotope study of five volcanic and intrusive rock suites and related mineral deposits,… Andrew, Anne 1987

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LEAD AND STRONTIUM ISOTOPE STUDY OF FIVE VOLCANIC AND INTRUSIVE ROCK SUITES AND RELATED MINERAL DEPOSITS, VANCOUVER ISLAND, BRITISH COLUMBIA by ANNE ANDREW B.Sc, The U n i v e r s i t y of E d i n b u r g h , 1980 M.Sc, The U n i v e r s i t y of B r i t i s h Columbia, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department of G e o l o g i c a l S c i e n c e s We a c c e p t t h i s as co n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA March 1987 © Anne Andrew 1987 32 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of ^eoloo^cxcxi Sciences' The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) ABSTRACT Lead i s o t o p e c o m p o s i t i o n s have been o b t a i n e d from f i v e major v o l c a n i c and i n t r u s i v e r o c k s u i t e s and s e v e r a l ore d e p o s i t s on Vancouver I s l a n d . Lead, uranium and t h o r i u m c o n c e n t r a t i o n s and s t r o n t i u m i s o t o p e r a t i o s have been o b t a i n e d f o r a s u b s e t of t h e s samples. The r o c k s u i t e s examined are the P a l e o z o i c S i c k e r Group, T r i a s s i c Karmutsen F o r m a t i o n , J u r a s s i c I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s , and the Eocene C a t f a c e i n t r u s i o n s . I s o t o p e g e o c h e m i s t r y of the S i c k e r Group i s c o n s i s t e n t w i t h the i n t e r p r e t a t i o n t h a t i t formed as an i s l a n d a r c . R e l a t i v e l y h i g h 207pb/204pb r a t i o s i n d i c a t e sediment i n v o l v e m e n t i n the s u b d u c t i o n p r o c e s s , which suggests t h a t the S i c k e r Group formed c l o s e t o a c o n t i n e n t . B u t t l e Lake ore d e p o s i t s d i s p l a y d e c r e a s i n g l y r a d i o g e n i c l e a d i s o t o p e r a t i o s w i t h t i m e , s u g g e s t i n g t h a t the a s s o c i a t e d magmas become i n c r e a s i n g l y p r i m i t i v e . T h i s s u p p o r t s the h y p o t h e s i s t h a t t h e s e d e p o s i t s formed d u r i n g the e s t a b l i s h m e n t of r i f t i n g i n a b a c k - a r c environment. Karmutsen F o r m a t i o n f l o o d b a s a l t s d i s p l a y i s o t o p i c m i x i n g between an ocean i s l a n d - t y p e mantle source and average c r u s t . I s o t o p i c e v i d e n c e i s used t o s u p p o r t a N o r t h e r n Hemisphere o r i g i n f o r t h e s e b a s a l t s . M i x i n g i s a p parent i n the l e a d and s t r o n t i u m i s o t o p e s i g n a t u r e s of the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s , between d e p l e t e d mantle and c r u s t a l ( p o s s i b l y t r e n c h s ediments) components. T h i s i s c o n s i s t e n t w i t h f o r m a t i o n of these r o c k s i n an i s l a n d a r c environment. Eocene C a t f a c e i n t r u s i o n s have r e l a t i v e l y h i g h 207pb/204pb i n d i c a t i n g t h a t c r u s t a l m a t e r i a l was i n v o l v e d i n t h e i r f o r m a t i o n . There are two groups of p l u t o n s c o r r e s p o n d i n g t o an e a s t b e l t and west b e l t c l a s s i f i c a t i o n . Galena from the Z e b a l l o s m i n i n g camp r e l a t e d t o the Eocene Z e b a l l o s p l u t o n i n d i c a t e s t h a t the m i n e r a l i z a t i o n was d e r i v e d from the p l u t o n . Galena l e a d i s o t o p e d a t a from Vancouver I s l a n d may be i n t e r p r e t e d i n a g e n e r a l way by comparison w i t h d a t a from d e p o s i t s e l s e w h e r e of known age and o r i g i n . No s i n g l e growth c u r v e model can be a p p l i e d . Lead i s o t o p e c h a r a c t e r i s t i c s of Vancouver I s l a n d a r e c l e a r l y d i f f e r e n t from those of the N o r t h American c r a t o n , r e f l e c t i n g the o c e a n i c a f f i n i t i e s of t h i s t e r r a n e . A new t e c h n i q u e has been dev e l o p e d t o compare 207pb/204pb r a t i o s between samples w i t h d i f f e r i n g 206pb/204pb r a t i o s . The i v p r o cedure p r o j e c t s 207pb/204pb r a t i o s a l o n g s u i t a b l e i s o c h r o n s u n t i l t h ey i n t e r s e c t a r e f e r e n c e v a l u e of 206pb/204pb. T h i s t e c h n i q u e can be used f o r i n t e r p r e t i n g l e a d i s o t o p e d a t a from o l d t e r r a n e s , i n which l e a d and uranium may have undergone l o s s o r g a i n , and i f l e a d and uranium abundances have not been measured. V T a b l e of Co n t e n t s A b s t r a c t i i Table of c o n t e n t s v L i s t of T a b l e s i x L i s t of F i g u r e s x i i Acknowledgment x v i CHAPTER 1 . INTRODUCTION 1 1 .1 SCOPE OF THESIS 1 1.2 GENERALIZED GEOLOGY OF VANCOUVER ISLAND 2 1 .3 SAMPLE SUITE 7 1.4 USE OF LEAD AND STRONTIUM ISOTOPES AS GEOCHEMICAL TRACERS 9 1.4.1 Mid-ocean r i d g e s 11 1.4.2 Ocean i s l a n d s 12 1.4.3 I s l a n d a r c s 13 1.4.4 Use of l e a d and s t r o n t i u m i s o t o p e s as t r a c e r s of a n c i e n t g e o l o g i c a l environments 14 1.5 ANALYTICAL TECHNIQUES 16 1.5.1 Galena l e a d i s o t o p e c o m p o s i t i o n s 16 1.5.2 Whole ro c k l e a d i s o t o p e c o m p o s i t i o n s 17 1.5.3 Lead c o n c e n t r a t i o n by i s o t o p e d i l u t i o n 18 1.5.4 Uranium c o n c e n t r a t i o n by' i s o t o p e d i l u t i o n ....19 1.5.5 Thorium by i s o t o p e d i l u t i o n 20 1.5.6 Uranium by d e l a y e d n e u t r o n c o u n t i n g 21 1.5.7 Thorium by n e u t r o n a c t i v a t i o n a n a l y s i s 21 1.5.8 Uranium and t h o r i u m by gamma r a y s p e c t r o s c o p y 22 1.5.9 Rubidium and s t r o n t i u m d e t e r m i n a t i o n s 23 CHAPTER 2. ISOTOPE GEOCHEMISTRY OF THE SICKER GROUP, VANCOUVER ISLAND 24 SYNOPSIS 24 2.1 INTRODUCTION 25 2.2 BUTTLE LAKE CAMP 30 2.2.1 I n t r o d u c t i o n ......30 2.2.2 Sample s u i t e 35 2.2.3 R e s u l t s 35 2.2.4 Comparison of Myra whole r o c k i n i t i a l r a t i o s and g a l e n a . 44 2.2.5 Comparison of S i c k e r Group r o c k s and o r e s w i t h t h o s e of the West Shasta D i s t r i c t of C a l i f o r n i a 46 2 . 3 MAPLE BAY 48 2.3.1 Geology 48 2.3.2 Sample s u i t e 48 2.3.3 R e s u l t s 48 2.4 MOUNT SICKER - LENORA AND TYEE MINE AREA 53 2.4.1 Geology and sample s u i t e 53 v i 2.4.2 R e s u l t s 55 2.5 DISCUSSION OF THE SICKER GROUP AS A WHOLE 56 2.5.1 Augmented sample s u i t e 56 2.5.2 P l a t e t e c t o n i c s e t t i n g of the S i c k e r Group ...57 2.5.3 Age c o n s i d e r a t i o n s 58 2.6 CONCLUSIONS 63 CHAPTER 3. ISOTOPE GEOCHEMISTRY OF THE KARMUTSEN VOLCANICS ..65 SYNOPSIS 65 3.1 INTRODUCTION 65 3.2 ISOTOPIC DATA 72 3.2.1 Lead i s o t o p e c o m p o s i t i o n s f o r r o c k s and ores .72 3.2.2 Comparison of Karmutsen F o r m a t i o n l e a d i s o t o p e d a t a w i t h those of w e l l known b a s a l t s 76 3.2.3 Lead, uranium and t h o r i u m c o n c e n t r a t i o n s 81 3.2.4 S t r o n t i u m d a t a 88 3.2.5 Evidence f o r i s o t o p i c m i x i n g 88 3.3 DISCUSSION 98 3.3.1 C r u s t a l contaminant 99 3.3.2 Mantle s o u r c e 99 3.3.3 M i x i n g mechanisms 100 3.5 CONCLUSIONS 101 CHAPTER 4. ISOTOPE GEOCHEMISTRY OF THE BONANZA GROUP VOLCANIC ROCKS AND ISLAND INTRUSIONS 104 SYNOPSIS 104 4.1 INTRODUCTION 105 4.2 RESULTS 112 4.3 DISCUSSION 125 4.3.1 An ocean i s l a n d ? 125 4.3.2 An i s l a n d a r c ? 128 4.3.3 G e o l o g i c a l c o n s i d e r a t i o n s 133 4.3.4 A model 134 4.4 CONCLUSIONS 135 CHAPTER 5. ISOTOPE GEOCHEMISTRY OF THE CATFACE TERTIARY INTRUSIONS 137 SYNOPSIS 137 5.1 INTRODUCTION 138 5.2 RESULTS 143 5.3 DISCUSSION 151 5.3.1 O r i g i n of t h e C a t f a c e i n t r u s i o n s 151 5.3.2 Galena l e a d i s o t o p e d a t a .157 5.4 CONCLUSIONS 159 CHAPTER 6. PLUMBOTECTONICS OF VANCOUVER ISLAND 161 SYNOPSIS 161 6.1 INTRODUCTION 162 6.2 ISOTOPIC COMPARISONS BETWEEN SAMPLE SUITES 163 6.3 VANCOUVER ISLAND AND THE DUPAL ANOMALY 165 6.4 INTERPRETATION OF GALENA LEAD ISOTOPE DATA ...168 v i i 6.5 VANCOUVER ISLAND LEAD COMPARED TO NORTH AMERICAN LEAD 17 3 6.5.1 N o r t h American l e a d 173 6.5.2 Vancouver I s l a n d l e a d 173 6.6 SUGGESTIONS FOR FURTHER WORK 174 CHAPTER 7. CONCLUSIONS 176 REFERENCES 180 APPENDIX A. GALENA LEAD ISOTOPE METHODOLOGY ...194 A.1 GALENA LEAD SAMPLE PREPARATION 194 A.2 PREPARATION AND LOADING OF FILAMENTS 194 A. 3 REAGENT PREPARATION 199 A.3.1 H y d r o c h l o r i c a c i d 199 A.3.2 N i t r i c a c i d 199 A. 3.3 S i l i c a g e l - p h o s p h o r i c a c i d 199 A.3.4 Q u a r t z - d i s t i l l e d water (Q-water) 199 A.3.5 T w o - b o t t l e water 199 A.3.6 Rhenium r i b b o n 199 A. 3.7 Fumed S i l i c a 199 APPENDIX B. LAB PROCEDURES FOR ROCK LEAD, URANIUM AND THORIUM ISOTOPE ANALYSIS '. 200 B. 1 SAMPLE PREPARATION 200 B.2 SAMPLE DISSOLUTION 200 B.3 ANION EXCHANGE COLUMN PROCEDURES 200 B.4 URANIUM AND THORIUM COLUMN PROCEDURES 201 B.5 PREPARATION AND LOADING OF FILAMENTS 201 B. 5.1 Lead 201 B.5.2 Uranium 201 B.5. 3 Thorium 202 B.6 MASS SPECTROMETRIC PROCEDURES 202 B.6.1 Lead I s o t o p e C o m p o s i t i o n 202 B.6.2 Lead I s o t o p e D i l u t i o n 203 B.6.3 Uranium I s o t o p e D i l u t i o n ....207 B.6.4 Thorium I s o t o p e D i l u t i o n 207 B.7 REAGENT PREPARATION 210 B.7.1 Q u a r t z - d i s t i l l e d Water 210 B.7.2 T w o - b o t t l e water 210 B.7. 3 H y d r o c h l o r i c a c i d 210 B.7.4 N i t r i c a c i d ...210 B.7.5 Hydrobromic a c i d ...210 B.7.6 H y d r o f l u o r i c a c i d ....210 B.7.7 S i l i c a g e l - p h o s p h o r i c a c i d 210 B.7. 8 C o l l o i d a l g r a p h i t e 211 B.8 MEASUREMENT OF BLANKS 211 B.9 DATA QUALITY 215 B.9.1 Lead I s o t o p e C o m p o s i t i o n 215 B.9.2 Lead C o n c e n t r a t i o n ..215 v i i i B.9.3 Uranium C o n c e n t r a t i o n 222 B. 9.4 Thorium C o n c e n t r a t i o n 222 APPENDIX C. SPIKE CALIBRATIONS 224 C.1 CALIBRATION OF STOCK (300 PPM) 207pB SPIKE 224 C. 1.1 I s o t o p i c c o m p o s i t i o n 224 C.1.2 I s o t o p e d i l u t i o n 22 4 C.2 PREPARATION OF 84-3 MIXED 207PB AND 235u SPIKE 22 5 C.3 CALIBRATION OF 84-3 MIXED SPIKE 226 C.3.1 I s o t o p e c o m p o s i t i o n of l e a d i n s p i k e 84-3 226 C.3.2 I s o t o p e d i l u t i o n c a l c u l a t i o n s f o r l e a d i n s p i k e 84-3 226 C.3.3 I s o t o p e c o m p o s i t i o n of uranium i n s p i k e 84-3 .227 C.3.4 I s o t o p e d i l u t i o n c a l c u l a t i o n s f o r uranium i n s p i k e 84-3 227 C.4 PREPARATION OF 230TH SPIKE 84-1 228 C.5 PREPARATION OF 84-2 DILUTE 230TH SPIKE 229 C. 6 CALIBRATION OF 84-2 DILUTE 230TH SPIKE ...22 9 C.6.1 I s o t o p e c o m p o s i t i o n of s p i k e 84-2 .....229 C . 6 . 2 I s o t o p e d i l u t i o n d e t e r m i n a t i o n s f o r s p i k e 84-2 229 APPENDIX D. COMPUTER PROGRAMS USED IN DATA PROCESSING 231 D. 1 WRPBIC 233 D.2 WRPBID 235 D.3 WRUCLC 238 D.4 WRTHCLC 240 D.5 T1CORR 24 2 D.6 BLANKSUB 244 D.7 CONCORD 24 6 D.8 MUCALC 247 APPENDIX E. PROJECTION TECHNIQUE FOR COMPARISON OF 207pB/206pB RATIOS WHICH HAVE VARIABLE 206PB/204PB RATIOS 248 i x L i s t of T a b l e s T a b l e Page 2.1 L o c a t i o n s and B r i e f D e s c r i p t i o n s of Samples of S i c k e r Group r o c k s from Vancouver I s l a n d , B.C 31 2.2 Lead, uranium and t h o r i u m d a t a from the S i c k e r Group v o l c a n i c r o c k s , Vancouver I s l a n d , B.C 32 2.3 G a l e n a - l e a d i s o t o p e a n a l y s e s from B u t t l e Lake, L e n o r a , Tyee, and P o r t A l b e r n i v o l c a n o g e n i c o re d e p o s i t s , Vancouver I s l a n d , B.C 34 2.4 I n i t i a l r a t i o s f o r the S i c k e r Group, Vancouver I s l a n d , B.C 45 2.5 E q u a t i o n s used i n c a l c u l a t i n g i s o c h r o n ages u s i n g common l e a d i s o t o p e a n a l y s e s . 54 2.6 Data f o r the c o n c o r d i a p l o t ( F i g . 2.8) 59 2.7 Rubidium and s t r o n t i u m i s o t o p e d a t a f o r the S i c k e r Group, Vancouver I s l a n d , B.C. 62 3.1 Whole r o c k and g a l e n a sample l o c a t i o n s (see F i g . 3.1) and b r i e f d e s c r i p t i o n s . .- 69 3.2 Lead, uranium and t h o r i u m d a t a from Karmutsen v o l c a n i c r o c k s and r e l a t e d g a l e n a l e a d i s o t o p e a n a l y s e s , Vancouver I s l a n d , B.C 70 3.3 I n i t i a l l e a d i s o t o p e r a t i o s a t 220 Ma f o r the Karmutsen F o r m a t i o n v o l c a n i c r o c k s , Vancouver I s l a n d , B.C 75 3.4 T y p i c a l l e a d , uranium and t h o r i u m c o n c e n t r a t i o n s , w i t h maximum ranges f o r v a r i o u s o c e a n i c and c o n t i n e n t a l b a s a l t s 86 3.5 Rubidium and s t r o n t i u m i s o t o p e d a t a f o r the "Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C 89 4.1 Summary of age d e t e r m i n a t i o n s f o r the Bonanza Group and I s l a n d I n t r u s i o n s 108 4.2 L o c a t i o n s and b r i e f d e s c r i p t i o n s of samples from the Bonanza Group and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C 109 4.3 Lead, uranium and t h o r i u m d a t a from the Bonanza X Group v o l c a n i c r o c k s , and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C 110 4.4 I n i t i a l l e a d i s o t o p e r a t i o s f o r the Bonanza Group and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C 117 4.5 Rubidium and s t r o n t i u m i s o t o p e d a t a f o r t h e I s l a n d I n t r u s i o n s and Bonanza Group, Vancouver I s l a n d , B.C 124 4.6 C a l c u l a t i o n s f o r secondary i s o c h r o n model, I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C 129 5.1 L o c a t i o n s ( F i g . 5.1) and b r i e f d e s c r i p t i o n s of whole r o c k samples from the C a t f a c e T e r t i a r y i n t r u s i o n s and g a l e n a from r e l a t e d m i n e r a l i z a t i o n 140 5.2 Summary of K-Ar ages o b t a i n e d f o r C a t f a c e T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C 141 5.3 Lead, uranium and t h o r i u m d a t a f o r the C a t f a c e T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C ....144 5.4 Galena l e a d i s o t o p e d a t a from Vancouver I s l a n d , B.C., f o r q u a r t z - g o l d v e i n s r e l a t e d t o the Eocene Z e b a l l o s p l u t o n and m i s c e l l a n e o u s g a l e n a samples from v e i n s of p r o b a b l e T e r t i a r y age 145 5.5 Rubidium and s t r o n t i u m i s o t o p e d a t a f o r the C a t f a c e i n t r u s i o n s , Vancouver I s l a n d , B.C 149 5.6 I n i t i a l l e a d i s o t o p e r a t i o s f o r the C a t f a c e I n t r u s i o n s , Vancouver I s l a n d , B.C 150 A.1 Broken H i l l s t a n d a r d measurements f o r the p e r i o d J a n u a r y t o March, 1983. 196 A. 2 C a l c u l a t i o n of mass f r a c t i o n a t i o n f a c t o r s u s i n g f i v e p u b l i s h e d v a l u e s of t h e Broken H i l l s t a n d a r d #1 :-1 983 197 B. 1 Broken H i l l s t a n d a r d measurements f o r the p e r i o d December 1983 t o F e b r u a r y 1985. 204 B.2 Mass f r a c t i o n a t i o n f a c t o r s c a l c u l a t e d f o r each of f i v e p u b l i s h e d Broken H i l l s t a n d a r d v a l u e s : - 1983 t o 1985 205 x i B.3 Mass f r a c t i o n a t i o n f a c t o r f o r uranium de t e r m i n e d by a n a l y s e s of the U500 NBS s t a n d a r d ( z i r c o n l a b o r a t o r y , UBC ) 208 B.4 T o t a l p r o c e d u r a l b l a n k s f o r 1 983 t o 1 985 21 2 B.5 Reagent b l a n k s f o r 1983 t o 1985 ..21 3 B.6 Summation of b l a n k s measured from 1983 t o 1985 21 4 B.7 U n c e r t a i n t y i n 206pb/204pb r a t i o s .216 B.8 U n c e r t a i n t y i n 207p'b/204pb r a t i o s 217 B.9 U n c e r t a i n t y i n 208pb/204pb r a t i o s 218 B.10 E s t i m a t e d s a m p l i n g e r r o r ....219 B.11 A c c u r a c y assessment u s i n g BCR-1 s t a n d a r d 220 B.12 R e p r o d u c i b i l i t y i n l e a d c o n c e n t r a t i o n s measured i n whole ro c k samples 221 B. 13 B i a s i n uranium c o n c e n t r a t i o n s measured by d i f f e r e n t methods 223 C. 1 I s o t o p i c c o m p o s i t i o n of s p i k e 84-2 224 C.2 I s o t o p e d i l u t i o n runs f o r s p i k e 84-2 225 C.3 C o m p o s i t i o n of l e a d i n s p i k e 84-3; 1 984 226 C.4 I s o t o p e d i l u t i o n c o n d i t i o n s and r e s u l t s f o r l e a d i n s p i k e 84-3 227 C.5 I s o t o p e d i l u t i o n r e s u l t s f o r uranium i n s p i k e 84-3 228 C. 6 D e t e r m i n a t i o n of the c o n c e n t r a t i o n of t h o r i u m i n s p i k e 84-2 230 D. 1 Summary of da t a r e d u c t i o n programs. ...... 232 E. 1 207pb/204pb r a t i o s p r o j e c t e d t o a v a l u e of 206pb/204pb of 19.0, u s i n g the 220 Ma i s o c h r o n ( F i g . E.2; t e x t ) 253 x i i L i s t o f F i g u r e s F i g u r e Page 1.1 G e o l o g i c a l s k e t c h map of Vancouver I s l a n d . 4 1.2 207pb/204pb v e r s u s 206pb/264pb diagram f o r a b y s s a l b a s a l t s (MORBs) and r o c k s from ocean i s l a n d s ( O I B s ) . ..11 2.1 D i s t r i b u t i o n of t h r e e major u p l i f t s of S i c k e r Group r o c k s , Vancouver I s l a n d , B.C., showing sample l o c a t i o n s d e t a i l e d i n T a b l e 2.1 26 2.2 Map showing the l o c a t i o n s of the B u t t l e Lake ore d e p o s i t s named i n the t e x t and p r o j e c t e d l o c a t i o n s of whole r o c k and g a l e n a samples a n a l y s e d ( T a b l e s 2.2 and 2.3) .36 2.3 207pb/204pb v e r s u s 206pb/204pb p l o t of g a l e n a ( s o l i d c i r c l e s ; T a b l e 2.3) and whole r o c k p r e s e n t ( s o l i d t r i a n g l e s ; T a b l e 2.2) and i n i t i a l r a t i o s a t 370 Ma (open t r i a n g l e s ; T a b l e 2.4) from B u t t l e Lake U p l i f t . ..39 2.4 208pb/204pb v e r s u s 206pb/204pb p l o t of B u t t l e Lake g a l e n a and whole r o c k d a t a 41 2.5 D e t a i l e d geology of Maple. Bay a r e a (from M u l l e r 1980) showing whole r o c k sample l o c a t i o n s ( T a b l e 2.1)..49 2.6 207pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k and g a l e n a d a t a from the S i c k e r Group, Vancouver I s l a n d , B.C , 51 2.7 208pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k and g a l e n a d a t a ( T a b l e s 2.2, 2.3 and 2.4) from the S i c k e r Group, Vancouver I s l a n d , B.C 52 2.8 Whole r o c k c o n c o r d i a p l o t f o r samples from the S i c k e r Group, Vancouver I s l a n d , B.C 60 3.1 D i s t r i b u t i o n of Karmutsen F o r m a t i o n r o c k s ( p a t t e r n e d ) on Vancouver I s l a n d , B.C., w i t h whole r o c k ( c i r c l e s ) and g a l e n a ( s q u a r e s ) sample l o c a t i o n s 68 3.2 a) 207pb/204pb v e r s u s 206pb/204pb and b) 208pb/204 Pb v e r s u s 206pb/204pb p l o t of whole r o c k l e a d i s o t o p e d a t a ( T a b l e s 3.2 and 3.3) from the Karmutsen Fo r m a t i o n and r e l a t e d g a l e n a samples ( T a b l e 3.2) ..74 3.3 Comparison of Karmutsen F o r m a t i o n whole r o c k i n i t i a l r a t i o s a t 220 Ma (open t r i a n g l e s ) and Karmutsen ga l e n a x i i i (open squares) w i t h 207pb/204p D and 206pb/204pb f i e l d s a d j u s t e d t o 220 Ma ( u s i n g S t a c e y and Kramers 1975 growth curve) of ocean i s l a n d b a s a l t s (Sun 1975, 1980; Tatsumoto 1978; Weis 1983); i s l a n d a r c s (Oversby and Ewart 1972; M e i j e r 1976; Kay e t a l . 1978; Church 1975); mid ocean r i d g e b a s a l t s ( E n g e l and E n g e l 1966; Church and Tatsumoto 1975; B r e v a r t e t a l . 1981; Hamelin e t a l . 1984); Ocean sediments (Chow and P a t t e r s o n 1962; Church 1976; Sun 1980; V i d a l and C l a u e r 1981 ) 78 3.4 Comparison of Karmutsen i n i t i a l r a t i o s a t 220 Ma ( t r i a n g l e s ) w i t h 208pb/204pb and 206pb/204pb f i e l d s , a d j u s t e d t o 220 Ma ( u s i n g S t a c e y and Kramers 1975 growth c u r v e ) , of mid-ocean r i d g e s , i s l a n d a r c s , ocean i s l a n d b a s a l t s and ocean sediments 79 3.5 207pb/204pb v e r s u s 206pb/204pb diagram showing g e n e r a l i z e d f i e l d s of i s o t o p e d a t a from c o n t i n e n t a l f l o o d b a s a l t s ( a d j u s t e d t o 220 Ma u s i n g S t a c e y and Kramers 1975 growth c u r v e ) , and Karmutsen F o r m a t i o n i n i t i a l r a t i o s a t 220 Ma (open t r i a n g l e s ; T a ble 3.3) and g a l e n a (open s q u a r e s ; Table 3.2) 83 3.6 208pb/204pb v e r s u s 206pb/204pb diagram showing g e n e r a l i z e d f i e l d s f o r c o n t i n e n t a l f l o o d b a s a l t s ( a d j u s t e d t o 220 Ma u s i n g S t a c e y and Kramers 1975 growth curve) and Karmutsen F o r m a t i o n whole r o c k i n i t i a l r a t i o s 85 3.7 Average l e a d , uranium and t h o r i u m c o n c e n t r a t i o n s f o r v a r i o u s b a s a l t t y p e s 87 3.8 U-Pb and Th-Pb i s o c h r o n p l o t s f o r the Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C 90 3.9 a) I n i t i a l 208pb/204pb v e r s u s 1/Pb (ppm), b) i n i t i a l 207pb/204pb v e r s u s 1/Pb (ppm) and c) i n i t i a l 206pb/204pb v e r s u s 1/Pb (ppm) p l o t f o r Karmutsen F o r m a t i o n s r o c k s , Vancouver I s l a n d , B.C 92 3.10 238u/204pb v e r s u s 1/Pb (ppm) f o r the Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C 96 3.11 87sr / 8 6 s r v e r s u s 206pb/204pb diagram f o r the Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C. 97 4.1 D i s t r i b u t i o n of Bonanza Group v o l c a n i c r o c k s ( d o t t e d ) and I s l a n d I n t r u s i o n s (shaded) on Vancouver I s l a n d , B.C 106 x i v 4.2 207pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k samples ( T a b l e 4.3) from t h e I s l a n d I n t r u s i o n s ( c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), Vancouver I s l a n d , B.C 114 4.3 208pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k samples ( T a b l e 4.3) from t h e I s l a n d I n t r u s i o n s ( c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), Vancouver I s l a n d , B.C 116 4.4 207pb/204pb v e r s u s 206pb/204pb p l o t of i n i t i a l r a t i o s ( T a b l e 4.4) f o r whole r o c k d a t a from the I s l a n d I n t r u s i o n s (open c i r c l e s ) , Bonanza Group v o l c a n i c r o c k s (diamonds) and g a l e n a from I s l a n d Copper p o r p h y r y d e p o s i t (open square) 121 4.5 208pb/204pb v e r s u s 206pb/204pb p l o t of i n i t i a l r a t i o s ( T a b l e 4.4) f o r whole r o c k data from the I s l a n d I n t r u s i o n s (open c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), and g a l e n a d a t a from I s l a n d Copper p o r p h y r y d e p o s i t (open square) 123 4.6 I n i t i a l 87sr/86sr v e r s u s i n i t i a l 207pb/204pb p l o t f o r the I s l a n d I n t r u s i o n s ( c i r c l e s ) , and Bonanza Group v o l c a n i c r o c k s (diamond), Vancouver I s l a n d , B.C 127 5.1 D i s t r i b u t i o n of Eocene C a t f a c e i n t r u s i o n s (shaded a r e a s ) , Vancouver I s l a n d , B.C 139 5.2 207pb/204pb v e r s u s 206pb/204pb and 208pb/204pb v e r s u s 206pb/204pb p l o t s of whole r o c k and g a l e n a l e a d i s o t o p e d a t a from T e r t i a r y i n t r u s i o n s and r e l a t e d o r e d e p o s i t s , Vancouver, B.C. 147 5.3 207pb/204pb v e r s u s 206pb/204pb p l o t showing p r e s e n t day ( s o l i d s q u a r e s ; T a b l e 5.3) and i n i t i a l (open s q u a r e s ; T a b l e 5.6) whole r o c k l e a d i s o t o p e c o m p o s i t i o n s f o r the T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C ....154 5.4 208pb/204pb v e r s u s 206pb/204pb p l o t showing p r e s e n t day ( s o l i d s q u a r e s ; T a b l e 5.3) and i n i t i a l (open s q u a r e s ; T a b l e 5.6) whole r o c k l e a d i s o t o p e c o m p o s i t i o n s f o r the T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C 156 6.1 207pb/204pb v e r s u s 206pb/204pb p l o t showing the N o r t h e r n Hemisphere r e f e r e n c e l i n e (NHRL; Ha r t 1984), e s t i m a t e d mantle v a l u e f o r the Karmutsen F o r m a t i o n (K; X V F i g u r e 3.9), and approximate c o m p o s i t i o n of anomalous mantle (Dupal anomaly; Ha r t 1 984) 167 6.2 Vancouver I s l a n d g a l e n a l e a d i s o t o p e data shown w i t h r e f e r e n c e growth c u r v e s r e p r e s e n t i n g "North American" l e a d . 170 A. 1 G r a p h i c a l r e p r e s e n t a t i o n of the d e t e r m i n a t i o n of mass dependent f r a c t i o n a t i o n f a c t o r s u s i n g York (1969) l e a s t squares l i n e a r r e g r e s s i o n 198 B. 1 G r a p h i c a l r e p r e s e n t a t i o n of the d e t e r m i n a t i o n of mass dependent f r a c t i o n a t i o n f a c t o r s u s i n g York (1969) l e a s t squares l i n e a r r e g r e s s i o n 206 E.1 G r a p h i c a l r e p r e s e n t a t i o n of p r o j e c t e d 207pfc>/204pb v a l u e s f o r a r o c k s u i t e w i t h an age of 220 Ma ....250 E.2 P r e s e n t 207pb/204pb ( c r o s s e s ) and p r o j e c t e d 207pb/204pb (open t r i a n g l e s ) v e r s u s 1/Pb (ppm) f o r Karmutsen F o r m a t i o n r o c k samples ( c f Chapter 3) 252 xv i Acknowledgement My t h e s i s s u p e r v i s o r C o l i n Godwin and committee members, Dr.s Armstrong, R u s s e l l , S i n c l a i r and Slawson r e a d and s u b s t a n t i a l l y improved the m a n u s c r i p t . They p r o v i d e d u s e f u l i d e a s , and c o n s t r u c t i v e c r i t i c i s m s t h r o u g h o u t t h i s s t u d y . Dr. J.E. M u l l e r p r o v i d e d the r o c k samples f o r the C a t f a c e i n t r u s i o n s and s e v e r a l o t h e r r o c k powders. H i s time spent l o c a t i n g t h e s e samples and p r o v i d i n g i n f o r m a t i o n i s g r e a t l y a p p r e c i a t e d . Samples were a l s o p r o v i d e d by C.I. Godwin, B. Marten, P. Conroy, R. Walker and D. L e f e b u r e . The development of a l e a d i s o t o p e l a b o r a t o r y was a i d e d by the h e l p f u l a d v i c e of D. K r s t i c , G. Cumming, M. B e v i e r , J . Mortensen, G.R. T i l t o n , R.L. Armstrong and J . Hooley. K. S c o t t showed me the Rb-Sr l a b o r a t o r y t e c h n i q u e s . B. Coussens g e n e r o u s l y p r o v i d e d a sample of the c o v e t e d Columbia R i v e r B a s a l t s t a n d a r d B C R - 1 . The f i n a n c i a l s u p p o r t of an N.S.E.R.C. s c h o l a r s h i p , a u n i v e r s i t y g raduate s t u d e n t f e l l o w s h i p , the Aaro Aho award, and a r e s e a r c h a s s i s s t a n t s h i p a re g r a t e f u l l y acknowledged. Many u s e f u l d i s c u s s i o n s were h e l d w i t h S. J u r a s and J . Mortensen. Thank you E r i c , Mum, J e a n , and D a n i e l f o r your h e l p , encouragement, and p a t i e n c e . 1 CHAPTER 1 INTRODUCTION 1 .1 SCOPE OF THESIS T h i s t h e s i s uses l e a d and s t r o n t i u m i s o t o p e systems as geochemical t r a c e r s t o : 1) i s o t o p i c a l l y c h a r a c t e r i z e each of f i v e major p l u t o n i c and v o l c a n i c r o c k s u i t e s from Vancouver I s l a n d , 2) d e l i n e a t e some of the r e l a t i o n s h i p s t h a t e x i s t between them, 3) i n t e r p r e t the p l a t e t e c t o n i c s e t t i n g s of the s e r o c k u n i t s by comparison w i t h the i s o t o p e c h a r a c t e r i s t i c s of modern a n a l o g u e s , and 4) p r o v i d e a framework w i t h i n which t o i n t e r p r e t g a l e n a l e a d i s o t o p e d a t a from ore d e p o s i t s i n Vancouver I s l a n d . T h i s i s the f i r s t combined l e a d and s t r o n t i u m i s o t o p e study of r o c k s on Vancouver I s l a n d , but s i m i l a r s t u d i e s have been done u s i n g neodymium, s t r o n t i u m and l e a d i s o t o p e systems f o r r o c k s f u r t h e r t o the e a s t i n the Canadian C o r d i l l e r a (Ghosh 1986; Smith 1986). Vancouver I s l a n d was chosen f o r i t s apparent g e o l o g i c a l s i m p l i c i t y w i t h c l e a r l y d e f i n e d d i s c r e t e r o c k packages t h a t form the i s l a n d . I t has an i n t e r e s t i n g p r e s e n t - d a y g e o l o g i c a l 2 s e t t i n g - - a d j a c e n t t o a s u b d u c t i o n zone. Vancouver I s l a n d was a l s o i n v e s t i g a t e d by the 1984-1985 LITHOPROBE g e o t r a v e r s e (Clowes 1984) which sought t o combine g e o l o g i c a l mapping, p e t r o c h e m i s t r y , g e o c h r o n o l o g y , r a d i o g e n i c and s t a b l e i s o t o p e s t u d i e s w i t h deep s e i s m i c , g r a v i t y , m a g n e t o t e l l u r i c , and geomagnetic s u r v e y s i n an e f f o r t t o u n d e r s t a n d a modern, a c t i v e c o n t i n e n t a l m a r g in. P r e l i m i n a r y r e s u l t s from LITHOPROBE have augmented t h i s r e s e a r c h . A number of the geochronology samples and oxygen i s o t o p e samples t h a t were a n a l y s e d by LITHOPROBE p a r t i c i p a n t s were from t h i s t h e s i s . The s e c t i o n of t h i s t h e s i s d e a l i n g w i t h the B u t t l e Lake camp v o l c a n o g e n i c massive s u l p h i d e ore d e p o s i t s forms p a r t of a c o l l a b o r a t i v e study w i t h S. J u r a s 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 study emphasizes the s i g n i f i c a n c e of l e a d i s o t o p e s and c h e m i c a l p e t r o l o g y of the S i c k e r Group i n the mine sequence, w h i l e J u r a s ' study f o c u s e d on a d e t a i l e d s t r a t i g r a p h y and p e t r o c h e m i s t r y of the v o l c a n i c r o c k s . 1.2 GENERALIZED GEOLOGY OF VANCOUVER ISLAND Syntheses of the geology of Vancouver I s l a n d have been made by M u l l e r (1977), M u l l e r e t a l . (1974) and S u t h e r l a n d Brown and Y o r a t h (1985). V a r i o u s a s p e c t s have been r e p o r t e d by 3 F y l e s (1955), Y o l e (1969), M u l l e r and Carson (1969), N o r t h c o t e and M u l l e r (1972), Carson (1973), M u l l e r (1971, 1980), Y o r a t h e t  a l . (1985a, 198 5b) and i n numerous t h e s e s of s t u d e n t s and g e o l o g i c a l r e p o r t s f o r m i n i n g companies. The magmatic h i s t o r y of Vancouver I s l a n d can be s i m p l i f i e d i n t o f o u r major e p i s o d e s : 1) P a l e o z o i c v o l c a n i c a r c f o r m a t i o n ( S i c k e r Group r o c k s ) , 2) e x t r u s i o n of T r i a s s i c t h o l e i i t i c f l o o d b a s a l t (Karmutsen F o r m a t i o n b a s a l t s ) , 3) Mesozoic v o l c a n i c a r c f o r m a t i o n (Bonanza Group and I s l a n d I n t r u s i o n s ) , and.4) T e r t i a r y t e c t o n i c and p l u t o n i c a c t i v i t y . Each e p i s o d e i s s e p a r a t e d from the next by sediment d e p o s i t i o n or l i m e s t o n e f o r m a t i o n . S i c k e r Group v o l c a n i c and v o l c a n i c l a s t i c r o c k s and greywackes ( F i g . 1.1) r e p r e s e n t the P a l e o z o i c a r c . The top of the S i c k e r Group i s d e l i m i t e d by the B u t t l e Lake l i m e s t o n e , which c o n t a i n s M i d d l e P e n n s y l v a n i a n f u s u l i n i d s (Sada and Danner 1974) t o E a r l y Permian conodont assemblages (Brandon e t a l . 1986). M a s s i v e o u t p o u r i n g of t h o l e i i t i c b a s a l t s of the Karmutsen F o r m a t i o n ( F i g . 1.1) o c c u r r e d i n t h e L a t e T r i a s s i c . These b a s a l t s unconformably o v e r l i e the S i c k e r Group, f o r m i n g a t h i c k (up t o 6 km) sequence of m a s s i v e , p i l l o w e d and b r e c c i a t e d b a s a l t s and s i l l s . L o c a l l y t h e r e a r e r h y o d a c i t e f l o w s a t the t o p of the Karmutsen F o r m a t i o n ; t h e s e may r e p r e s e n t a change i n I E C E N | 1, Tertiary sediaents E • • j~ tertiary Intrusions Middle Tertiary HetchosLn volcanic racks Late Mesozoic sediments P "] Leech River Gceplex Island Intrusions Bcnanza Group m OuBtsino, Parson Bay Farnations Karautsen Formation Sicker Group Late Jurassic to Cretaceous Jurassic . Cretaceous? Early Jurassic Iferly Jurassic Late Trlassie Triaaaic Paleozoic Metamorphic coiplex Jurassic or older 8 J F San Juan Fault L R F Leech River Fault 0 U kilometers 29 90 • 1 79 F i g u r e 1.1 G e o l o g i c a l s k e t c h map of Vancouver I s l a n d . Taken from M u l l e r e t a l . (1974). 5 t e c t o n i c regime (Marten 1984). The Karmutsen F o r m a t i o n i s o v e r l a i n c o n f o r m a b l y by the L a t e T r i a s s i c Q u a t s i n o and Parsons Bay F o r m a t i o n s , d o m i n a n t l y of l i m e s t o n e and s h a l e r e s p e c t i v e l y . An E a r l y t o m i d - J u r a s s i c i s l a n d a r c assemblage i s made up of v o l c a n i c and v o l c a n i c l a s t i c r o c k s known as the Bonanza Group ( F i g . 1.1). C o e v a l w i t h Bonanza v o l c a n i s m was the i n t r u s i o n of major q u a r t z d i o r i t e t o g r a n o d i o r i t e b a t h o l i t h s , known as the I s l a n d I n t r u s i o n s ( F i g . 1.1). C r e t a c e o u s sedimentary r o c k s of the Nanaimo and Queen C h a r l o t t e Groups are i n marked a n g u l a r u n c o n f o r m i t y a g a i n s t a l l p r e c e d i n g u n i t s . The most r e c e n t i n the s e r i e s of t e c t o n i c events i n v o l v e d the t r u n c a t i o n of Vancouver I s l a n d t o the west and s o u t h , and the a c c r e t i o n of s e v e r a l s m a l l t e r r a n e s . The P a c i f i c Rim complex, a Mesozoic s u b d u c t i o n complex analogous t o the F r a n s i s c a n of C a l i f o r n i a , was a c c r e t e d a l o n g the western margin of Vancouver I s l a n d d u r i n g the Paleocene (65 Ma t o 55 Ma--Brandon and Massey 1985). Rusmore and Cowan (1985) have i d e n t i f i e d a s m a l l t e r r a n e known as the Pandora Peak u n i t , t h a t was emplaced s o u t h of the San Juan f a u l t ( F i g . 1.1) d u r i n g the L a t e C r e t a c e o u s o r e a r l y T e r t i a r y (83 Ma t o 40 Ma). The Leech R i v e r complex ( F i g . 1.1) was a c c r e t e d t o the south of the San Juan f a u l t i n the L a t e Eocene o r E a r l y O l i g o c e n e (40 Ma t o 30 Ma--Rusmore and Cowan 1985). The paleogeography of s o u t h e r n 6 Vancouver I s l a n d was f u r t h e r m o d i f i e d by t h e a c c r e t i o n of the Eocene M e t c h o s i n v o l c a n i c r o c k s ( F i g . 1.1) south of the Leech R i v e r f a u l t ( p o s t 40 Ma). R e l a t i o n s h i p s between the s e t e c t o n i c e v e n t s , and the i n t r u s i o n i n the Eocene ( a p p r o x i m a t e l y 40 Ma, Table 5.1) of s e v e r a l s m a l l q u a r t z d i o r i t e p l u t o n s ( C a t f a c e i n t r u s i o n s ) throughout Vancouver I s l a n d , a r e e n i g m a t i c . Ewing (1981), S u t h e r l a n d Brown and Y o r a t h (1985), I s a c h s e n (1984), and Armstrong e t a_l. ( i n p r e s s ) r e l a t e the o c c u r r e n c e of these i n t r u s i o n s t o C e n o z o i c s u b d u c t i o n . They o c c u r i n the a r c - t r e n c h gap between the s u b d u c t i n g p l a t e and c o e v a l Kamloops Group v o l c a n i s m (Ewing 1981). They a r e a l s o c o e v a l w i t h a m p h i b o l i t e grade metamorphism i n the Leech R i v e r complex (Rusmore and Cowan 1985), and w i t h a major r e o r g a n i z a t i o n of p l a t e motions i n the P a c i f i c (Ewing 1981; Brandon and Massey 1985). P a l e o z o i c and Mesozoic r o c k packages of Vancouver I s l a n d comprise a l a r g e a l l o c h t h o n o u s t e r r a n e known as W r a n g e l l i a (Jones e t a l . 1977). C h a r a c t e r i s t i c of W r a n g e l l i a n s t r a t i g r a p h y i s the t h i c k sequence of T r i a s s i c t h o l e i i t i c f l o w s and p i l l o w l a v a s , which o v e r l i e a P a l e o z o i c a r c , and which a r e o v e r l a i n by p l a t f o r m c a r b o n a t e s (Jones e t a l . 1977). W r a n g e l l i a extends northwards through the Queen C h a r l o t t e I s l a n d s i n t o the W r a n g e l l Mountains of s o u t h - c e n t r a l A l a s k a . T r i a s s i c r o c k s exposed i n the 7 H e l l ' s Canyon r e g i o n of E a s t e r n Oregon (45.3o N, 116.8o w) are r e g a r d e d by some (Jones e t a l . 1977; Coney e t a l . 1980; H i l l h o u s e e t a l . 1982) t o be a p o s s i b l e s o u t h e a s t e r n e x t e n s i o n of W r a n g e l l i a . T h i s , however, i s d i s p u t e d by o t h e r s ( S c h e f f l e r 1983). The West Shasta d i s t r i c t of C a l i f o r n i a i n the E a s t e r n Klamath Mountains c o n s i s t s of a Devonian a r c sequence which s i t s on a m i d - S i l u r i a n o p h i o l i t e complex. Comparisons have been made between the major v o l c a n o g e n i c ore b o d i e s of the West Shasta D i s t r i c t and the B u t t l e Lake ore d e p o s i t s on Vancouver I s l a n d . M u l l e r (1~980) t e n t a t i v e l y c o r r e l a t e s the Myra Fomation. of the S i c k e r Group w i t h the B a l a k l a l a R h y o l i t e (West Shasta D i s t r i c t ) , and the N i t i n a t F o r m a t i o n w i t h the Copley Greenstone (West Sh a s t a D i s t r i c t ) . Lead i s o t o p e s t u d i e s of the West Shasta ore b o d i e s , the B a l a k l a l a R h y o l i t e , and the Copley Greenstone have been made by Slawson (1983) and Doe e t a l . (1985), a l l o w i n g d i r e c t comparison of the i s o t o p i c c h a r a c t e r i s t i c s of these two P a l e o z o i c a r c sequences i n we s t e r n N o r t h America. R e s u l t s i n Chapter 2 do not s u p p o r t the t e n t a t i v e c o r r e l a t i o n by M u l l e r . 1.3 SAMPLE SUITE F i v e i m p o r t a n t r o c k u n i t s from each of f o u r major magmatic 8 e p i s o d e s were sampled i n t h i s s t u d y . These a r e : the S i c k e r Group, Karmutsen F o r m a t i o n , Bonanza Group, I s l a n d I n t r u s i o n s , and C a t f a c e i n t r u s i o n s . Where p o s s i b l e , s t r o n t i u m i s o t o p e d a t a and l e a d - i s o t o p e d a t a were o b t a i n e d f o r the same samples. Lead, uranium and t h o r i u m c o n c e n t r a t i o n a n a l y s e s were done f o r a s u b s e t of samples by i s o t o p e d i l u t i o n , n e u t r o n a c t i v a t i o n a n a l y s i s , d e l a y e d n e u t r o n c o u n t i n g , or gamma ra y s p e c t r o s c o p y . The t h o r i u m i s o t o p e d i l u t i o n t e c h n i q u e attempted here was found t o be u n r e l i a b l e due t o i n t e r f e r i n g i o n s , and has o n l y been used i n one c a s e . Galena from a number of mines and showings on Vancouver I s l a n d was o b t a i n e d and a n a l y s e d . S e v e r a l samples are from t h e Kuroko-type massive s u l p h i d e ore b o d i e s a t B u t t l e Lake, and a t Mount S i c k e r . Q u a r t z - g o l d v e i n s r e l a t e d t o the T e r t i a r y C a t f a c e i n t r u s i o n s and two showings w i t h i n the Karmutsen Fo r m a t i o n were a l s o sampled. The I s l a n d Copper p o r p h y r y d e p o s i t i n Bonanza Group h y p a b y s s a l i n t r u s i v e r o c k s y i e l d e d some g a l e n a from l a t e v e i n s which p r o v i d e d a sampling of l e a d from the J u r a s s i c a r c e p i s o d e . 9 1.4 USE OF LEAD AND STRONTIUM ISOTOPES AS GEOCHEMICAL TRACERS R e c o g n i t i o n t h a t igneous r o c k s a s s o c i a t e d w i t h d i f f e r e n t t e c t o n i c environments have d i f f e r e n t g e o c h e m i s t r y was c l o s e l y f o l l o w e d by the u n d e r s t a n d i n g t h a t l e a d and s t r o n t i u m i s o t o p e s c o u l d be used as t r a c e r s of geoc h e m i c a l environment (Slawson and A u s t i n 1962; Gast e t a l . 1964). I s o t o p e s have an advantage over t r a c e elements because the degree of p a r t i a l m e l t i n g and magmatic f r a c t i o n a t i o n a re not known t o s i g n i f i c a n t l y a l t e r the i s o t o p e r a t i o s of the r e s u l t i n g magmas. Thus, f o r example, the i s o t o p e r a t i o s of m a n t l e - d e r i v e d magmas r e f l e c t the i s o t o p e r a t i o s of the mantle. The study of l e a d i s o t o p e r a t i o s of r o c k s and ore s w i t h i n the p l a t e t e c t o n i c framework has come t o be known as p l u m b o t e c t o n i c s (Doe and Zartman 1979) a f t e r t h e i r i m p o r t a n t attempt t o d e s c r i b e l e a d e v o l u t i o n i n t h r e e d i f f e r e n t r e s e r v o i r s : the upper c r u s t , lower c r u s t , and mantle, and a f o u r t h 'mixed' environment c a l l e d the orogene. T h i s study f o l l o w s t h i s approach, r e c o g n i z i n g the c o n t r i b u t i o n of l e a d and s t r o n t i u m from d i f f e r e n t r e s e r v o i r s t o v o l c a n i c and p l u t o n i c r o c k s and o r e s i n a v a r i e t y of p l a t e t e c t o n i c e nvironments. More r e c e n t l y neodymium i s o t o p e s have been s t u d i e d ( R i c h a r d e t a l . 1976) and the combined Nd-Sr-Pb i s o t o p e systems are now 10 b e i n g used t o f u r t h e r e x p l o r e g e o c h e m i c a l v a r i a t i o n s between v o l c a n i c r o c k s e r u p t e d i n d i f f e r e n t p l a t e t e c t o n i c s e t t i n g s ( e . g . Cohen e t a l . 1980; Dupre and A l l e g r e 1980; A l l e g r e e t a l . 1982; Cohen and O'Nions 1982; C a r l s o n 1984; Zartman 1984). 1.4.1 Mid-ocean r i d g e s Mid-ocean r i d g e b a s a l t s (MORBs) have been e x t e n s i v e l y a n a l y z e d f o r t h e i r l e a d and s t r o n t i u m i s o t o p e c o m p o s i t i o n s and t r a c e element p a t t e r n s s i n c e t h e mid-1960's. MORBs a r e d e p l e t e d i n l a r g e i o n l i t h o p h i l e elements ( L I L E s ) and a r e b e l i e v e d t o r e p r e s e n t m e l t s from a mantle so u r c e which has become ' d e p l e t e d ' due t o r e p e a t e d e x t r a c t i o n of m e l t s . 8 7 s r / 8 6 s r v a l u e s f o r MORBs a r e i n the range 0.702-0.703 ( B a s a l t i c V o l c a n i s m Study P r o j e c t 1981). However, the Rb/Sr r a t i o f o r t y p i c a l MORB i s 0.01, which i s not h i g h enough t o support the obs e r v e d 8 7 s r / 8 6 s r r a t i o s u n l e s s t h e r e has been some d e p l e t i o n of Rb r e l a t i v e t o Sr i n the s o u r c e . A p o s i t i v e c o r r e l a t i o n has been found between 8 7 s r / 8 6 s r and 206pb/204pb f o r A t l a n t i c MORBs (Cohen e t a l . 1980; Dupre and A l l e g r e 1980). The g e n e r a l f i e l d of MORB a n a l y s e s i s shown i n F i g u r e 1.2. The l i n e a r t r e n d s i n both 207pb/204pb v e r s u s 206pb/204pb, and 208pb/204pb v e r s u s 206pb/204pb diagrams c o r r e s p o n d t o apparent ages of between 1 and 2 Ga. I n g e n e r a l , 206pb/204pb i s l e s s than 11 F i g u r e 1.2 207pb/204pb v e r s u s 206pb/204pb diagram f o r a b y s s a l b a s a l t s (MORBs) and r o c k s from ocean i s l a n d s (OIBs). Taken from Tatsumoto 1978. 12 18.7 and 207pt>/204pb i s l e s s than 15.5. MORBs have low 207pb/204pb and 208pb/204pb r a t i o s r e l a t i v e t o average c r u s t a l growth c u r v e s such as t h a t of S t a c e y and Kramers (1975). They p l o t t o the r i g h t of the Geochron i n d i c a t i n g enrichment i n U/Pb r e l a t i v e t o a s i n g l e s t a g e s o u r c e , which i s i n c o n t r a d i c t i o n t o both Sr and Nd i s o t o p e systems. 1.4.2 Ocean i s l a n d s Ocean i s l a n d b a s a l t s (OIBs) have been i n t e r p r e t e d as p r o d u c t s of a mantle s o u r c e , which i s tapped by hot sp o t s or mantle plumes ( W i l s o n 1963; Morgan 1971; S c h i l l i n g 1973). T h i s mantle s o u r c e has d i f f e r e n t i s o t o p i c c h a r a c t e r i s t i c s than MORB-type mantle and has l a r g e r c o n c e n t r a t i o n s of L I L E s . I t i s r e l a t i v e l y e n r i c h e d i n the l i g h t r a r e e a r t h e l ements. S p e c u l a t i o n s on the n a t u r e . a n d l o c a t i o n of t h i s t y pe of mantle v a r y from ' p r i m i t i v e ' mantle (DePaulo 1979) t o r e c y c l e d ocean c r u s t (Chase 1981; Hofmann and White 1982), from s h a l l o w e r than MORB-type mantle ( A l l e g r e and B o t t i n g a 1977; Hedge 1978; Tatsumoto 1978; Anderson 1982) t o deeper ( S c h i l l i n g 1973; DePaulo and Wasserburg 1977; Hofmann and Ha r t 1978; Hamelin e t  a l . 1984a), and t o a d j a c e n t t o MORB-type mantle ( G i l l 1 984 ). Lead i s o t o p e a n a l y s e s have been made f o r numerous ocean i s l a n d s ( e . g . Oversby and Gast 1970; Oversby 1972a, 1972b; Sun 1980; Weis 1983). Each ocean i s l a n d has a range of l e a d i s o t o p e 13 v a l u e s , but v a r i a t i o n i n i s o t o p e r a t i o s i s much g r e a t e r between i s l a n d s t h a n w i t h i n a s i n g l e i s l a n d . Most i s l a n d s show a l i n e a r t r e n d i n t h e d a t a i n both of t h e c o n v e n t i o n a l l e a d i s o t o p e p l o t s . They te n d t o have more r a d i o g e n i c v a l u e s than MORBs (206pb/204pb > 18.5, and 207pb/204pb > 15.5), but f a l l on a p p r o x i m a t e l y the same t r e n d . P u b l i s h e d f i e l d s f o r s e v e r a l OIBs are shown i n F i g u r e 1.2. The v e r y v a r i a b l e l e a d s i g n a t u r e s d i s p l a y e d by OIBs show t h a t the mantle i s heterogeneous and t h a t h e t e r o g e n e i t i e s are p r e s e r v e d f o r l o n g p e r i o d s of ti m e . The OIB f i e l d has been g e n e r a l i z e d i n f o l l o w i n g i l l u s t r a t i o n s . S t r o n t i u m i s a l s o more v a r i a b l e and g e n e r a l l y more r a d i o g e n i c i n OIBs than i n MORBs ( B a s a l t i c V o l c a n i s m Study P r o j e c t 1981). Rb/Sr r a t i o s a r e t y p i c a l l y 0.03 i n O I B s - - l a r g e enough t o s u p p o r t the range of 8 7 s r / 8 6 s r v a l u e s , assuming c l o s e d system i s o t o p i c e v o l u t i o n of a c h o n d r i t i c i n i t i a l r a t i o s i n c e the time of f o r m a t i o n of the e a r t h . 1.4.3 I s l a n d a r c s I s l a n d a r c s form above s u b d u c t i n g p l a t e s . I t has been suggested t h a t sediment on the downgoing p l a t e i s r e c y c l e d i n t o the mantle and i s i n v o l v e d i n p r o d u c t i o n of i s l a n d a r c magmas (Tatsumoto 1969; Armstrong and Cooper 1971; Kay e t a l . 1978; Nohda and Wasserburg 1981). Lead i s o t o p e s p r o v i d e a u s e f u l way of t r a c i n g t h i s t y pe of c o n t a m i n a t i o n . C o n t i n e n t a l l y - d e r i v e d 1 4 sediments c o n t a i n h i g h c o n c e n t r a t i o n s of l e a d r e l a t i v e t o the c o n c e n t r a t i o n of l e a d i n ocean c r u s t and the mantle. They a l s o have h i g h e r 207pb/204p D r a t i o s than MORBs and OIBs. C o n s e q u e n t l y , even a s m a l l q u a n t i t y of l e a d d e r i v e d from sediments can be d e t e c t e d i n the l e a d s i g n a t u r e s of i s l a n d a r c magmas. The i s l a n d a r c f i e l d o c c u p i e s an i n t e r m e d i a t e p o s i t i o n between those of ocean sediments and MORBs (see F i g . 2.3). S e v e r a l s t u d i e s of i s l a n d a r c s demonstrate t h i s r e l a t i o n s h i p w e l l (Armstrong and Cooper 1971; Oversby and Ewart 1972; M e i j e r 1976; Kay e t a l . 1978). S t r o n t i u m i s o t o p e r a t i o s f o r i s l a n d a r c magmas a r e a l s o more r a d i o g e n i c r e f l e c t i n g sediment i n v o l v e m e n t i n s u b d u c t i o n . M e i j e r (1976) and Kay e t a l . (1978) noted a p o s i t i v e c o r r e l a t i o n between l e a d and s t r o n t i u m i s o t o p e c o m p o s i t i o n s and c o n c e n t r a t i o n s . T h i s p r o v i d e s s t r o n g s u p p o r t f o r the sediment p l u s mantle (and/or s l a b ) m i x i n g h y p o t h e s i s . 1.4.4 Use of l e a d and s t r o n t i u m i s o t o p e s as t r a c e r s of a n c i e n t  g e o l o g i c a l environments A l t h o u g h t h e r e i s l i t t l e o r no d i f f e r e n c e i n the l e a d and s t r o n t i u m d a u g h t e r : r e f e r e n c e i s o t o p e r a t i o s between the source and magma, t h e r e i s a s i g n i f i c a n t change i n the pa r e n t : d a u g h t e r r a t i o s . Thus i t i s n e c e s s a r y t o c o r r e c t f o r i n s i t u i s o t o p e e v o l u t i o n i n r o c k s o l d e r than a p p r o x i m a t e l y 20 Ma. 1 5 T h i s study examines the l e a d and s t r o n t i u m i s o t o p e c h a r a c t e r i s t i c s of i s l a n d a r c , ocean i s l a n d , and p o s s i b l y back a r c environments t h a t range i n age from o l d e r than 300 Ma t o a p p r o x i m a t e l y 40 Ma. I n i t i a l r a t i o s a r e c a l c u l a t e d u s i n g measured 238rj/204pb (p) , 232Th/238u ( k ) , and 87Rb/86sr v a l u e s , and independent i s o t o p i c or f o s s i l age e s t i m a t e s . M o b i l i t y of l e a d , uranium, t h o r i u m , r u b i d i u m and s t r o n t i u m i n r o c k s due t o s u r f a c e w e a t h e r i n g , seawater a l t e r a t i o n or metamorphism may make these i n i t i a l v a l u e s u n r e l i a b l e . Galena from s y n g e n e t i c s u l p h i d e ore d e p o s i t s has been a n a l y s e d t o p r o v i d e independent e s t i m a t e s of the l e a d i s o t o p e i n i t i a l v a l u e s f o r each r o c k s u i t e . Where comparisons are made between l e a d i s o t o p e i n i t i a l v a l u e s f o r Vancouver I s l a n d r o c k s u i t e s and a n a l y s e s of modern p l a t e t e c t o n i c e n v i r o n m e n t s , the modern f i e l d s have been p r o j e c t e d back u s i n g S t a c e y and Kramers' growth curve ( S t a c e y and Kramers 1975). T h i s i s o n l y an a p p r o x i m a t i o n , s i n c e i t i s un r e a s o n a b l e t o assume t h a t a l l of the f i e l d s e v o l v e d a t the same r a t e . F u r t h e r m o r e , s i n c e these a d j u s t m e n t s are g r e a t e r f o r the 206pb/204pb and 208pb/204pb r a t i o s than f o r the 207pb/204pb r a t i o , the 207pb/204pb r a t i o i s the most u s e f u l t r a c e r i n o l d a l l o c h t h o n o u s t e r r a n e s and o p h i o l i t e s (Hamelin e t a l . 1984b). I t i s f o r t h i s r e a s o n t h a t t h e 207pb/204pb r a t i o has been s i n g l e d out f o r p l o t t i n g a g a i n s t l e a d c o n c e n t r a t i o n and a g a i n s t 1 6 87sr/86sr i n i t i a l r a t i o s t o r e v e a l m i x i n g p a t t e r n s , 1.5 ANALYTICAL TECHNIQUES A n a l y t i c a l t e c h n i q u e s a r e d e s c r i b e d f o r a l l of the d a t a r e p o r t e d i n t h i s t h e s i s . I n many i n s t a n c e s computer programs a r e used i n o r d e r t o c a l c u l a t e the r e p o r t e d d a t a from the raw d a t a . These programs a r e r e f e r r e d t o by name ( c a p i t a l l e t t e r s i n q u o t a t i o n marks) throughout t h i s s e c t i o n . A l l of the programs are l i s t e d i n Appendix D u n l e s s o t h e r w i s e s t a t e d . T able D.1 (Appendix D) summarizes the i n p u t s and o u t p u t s of the s e programs. 1.5.1 Galena l e a d i s o t o p e r a t i o s Most g a l e n a samples were p r e p a r e d and a n a l y z e d by the a u t h o r f o l l o w i n g p r o cedures o u t l i n e d i n Appendix A* A n a l y s e s of samples conducted over the same p e r i o d of time as the whole r o c k l e a d samples were a n a l y z e d u s i n g the "UBCZPB" mass s p e c t r o m e t e r measuring program (Appendix B ) ; raw d a t a were c o r r e c t e d f o r mass f r a c t i o n a t i o n u s i n g the same f a c t o r s as f o r the whole r o c k samples (Appendix B, Ta b l e B.2). S e v e r a l samples ( Z e b a l l o s g o l d v e i n s , and o t h e r s ) were a n a l y z e d over a two month p e r i o d i n 1983, u s i n g e i t h e r the "MSCOPB" or "UBCZPB" measuring programs (Appendix B ) . Raw d a t a f o r the s e a n a l y s e s were 17 c o r r e c t e d u s i n g mass f r a c t i o n a t i o n f a c t o r s d e t e r m i n e d by r e p e a t e d a n a l y s e s of Broken H i l l S t a n d a r d #1 measured over the same time span (see Appendix A ) . A one sigma e s t i m a t e of the e r r o r a s s o c i a t e d w i t h a s i n g l e a n a l y s i s was o b t a i n e d by adding w i t h i n - r u n p r e c i s i o n a t one s t a n d a r d d e v i a t i o n t o the f r a c t i o n a t i o n v a r i a t i o n between runs and the u n c e r t a i n t y i n the mass f r a c t i o n a t i o n f a c t o r s . T h i s was done by a d d i n g the squares of each of the u n c e r t a i n t i e s and t a k i n g the r o o t . U n c e r t a i n t i e s i n mass f r a c t i o n a t i o n f a c t o r s and i n mass f r a c t i o n a t i o n v a r i a t i o n between runs a r e e s t i m a t e d i n Appendices A and B. Samples from the Myra d e p o s i t a t B u t t l e Lake and from Lenora and Tyee d e p o s i t s a t Mount S i c k e r a r e r e p o r t e d i n Chapter 2. These were a n a l y z e d by B. Ryan f o l l o w i n g p r o c e d u r e s o u t l i n e d by Andrew (1982: Appendix A ) , u s i n g the mass spectometer i n the Department of Geophysics and Astronomy, the U n i v e r s i t y of B r i t i s h C olumbia. 1.5.2 Whole r o c k l e a d i s o t o p e r a t i o s Whole r o c k samples were a n a l y z e d f o l l o w i n g t h e procedures o u t l i n e d i n Appendix B. Raw d a t a were c o r r e c t e d u s i n g mass f r a c t i o n a t i o n f a c t o r s d e t e r m i n e d from 25 runs of the Broken H i l l S t a n d a r d #1 (Appendix B: T a b l e B.1). The one sigma e r r o r s quoted 18 i n b r a c k e t s a f t e r each of the r e p o r t e d i s o t o p e r a t i o s are the sums of w i t h i n - r u n p r e c i s i o n , f r a c t i o n a t i o n v a r i a t i o n between r u n s , and u n c e r t a i n t y i n mass f r a c t i o n a t i o n f a c t o r s . They are c a l c u l a t e d u s i n g the program "WRPBIC" (Appendix D). These v a l u e s a r e g e n e r a l l y l e s s than 0.1%. U n c e r t a i n t i e s i n the v a l u e s of a s i n g l e sample were a l s o e s t i m a t e d by the method of sum of squares of the r e s i d u a l s of s e v e r a l d u p l i c a t e a n a l y s e s (Appendix B: T a b l e s B.7, B.8 and B.9). These show t h a t the u n c e r t a i n t y a s s o c i a t e d w i t h a s i n g l e a n a l y s i s i s of the o r d e r of 0.1%. G e o l o g i c a l v a r i a t i o n was e s t i m a t e d u s i n g d i f f e r e n t samples of the same roc k u n i t s , and was found t o be 0.2% (Appendix B: T a b l e B.10) f o r homogeneous r o c k t y p e s u s i n g samples t h a t were, s e p a r a t e d by more than 100 m. A c c u r a c y was t e s t e d by a n a l y s i n g the BCR-1 s t a n d a r d . The i s o t o p i c c o m p o s i t i o n measured agreed w i t h the p u b l i s h e d v a l u e s (Tatsumoto et. a l . 1 972) t o w i t h i n 0.15% (Appendix B: T a b l e B.11 ) . 1.5.3 Lead c o n c e n t r a t i o n by i s o t o p e d i l u t i o n Lead c o n c e n t r a t i o n s were d e t e r m i n e d f o r s e v e r a l samples u s i n g the p r o c e d u r e s o u t l i n e d i n Appendix B. Mixed s p i k e 84-3 (Appendix C) was added t o the samples. U n c e r t a i n t i e s i n the c o n c e n t r a t i o n were d e t e r m i n e d by e r r o r p r o p a g a t i o n (Rees 1984), u s i n g a program c a l l e d "WRPBID" ( l i s t e d i n Appendix D). The 19 u n c e r t a i n t i e s c a l c u l a t e d i n t h i s way a r e 0.01 t o 0.03 ppm. U n c e r t a i n t y i n the measured l e a d c o n c e n t r a t i o n s was a l s o e s t i m a t e d u s i n g d u p l i c a t e a n a l y s e s (Appendix B: Table B.12). The u n c e r t a i n t y measured i n t h i s way i s 0.1 ppm, much l a r g e r than t h a t e s t i m a t e d by e r r o r p r o p a g a t i o n . T h i s s u g g e s t s t h a t t h e r e are u n c e r t a i n t i e s not b e i n g c o n s i d e r e d i n the e r r o r p r o p a g a t i o n c a l c u l a t i o n s . The u n c e r t a i n t y c a l c u l a t e d by d u p l i c a t e a n a l y s e s i s more r e p r e s e n t a t i v e of a n a l y t i c a l c o n d i t i o n s . The d i s c r e p a n c y might be due t o sample h e t e r o g e n e i t i e s , o r i n c o m p l e t e d i s s o l u t i o n . Such e r r o r s can be reduced by the use of h i g h p r e s s u r e bombs i n the d i s s o l u t i o n p r o c e s s , or by s p i k i n g the sample a f t e r d i s s o l u t i o n . The d a t a a re ^ i n t e r p r e t e d w i t h t h e s e e r r o r s i n mind. A c c u r a c y was t e s t e d by a n a l y z i n g the Columbia R i v e r B a s a l t s t a n d a r d (BCR-1). The l e a d c o n c e n t r a t i o n s measured f o r the s t a n d a r d (Appendix B: Table B.11) agree w e l l w i t h the p u b l i s h e d v a l u e of Tatsumoto e t a l . (1972). 1.5.4. Uranium c o n c e n t r a t i o n by i s o t o p e d i l u t i o n Uranium c o n c e n t r a t i o n s were d e t e r m i n e d f o l l o w i n g procedures o u t l i n e d i n Appendix B. E r r o r p r o p a g a t i o n (Rees 1984) was used t o d e t e r m i n e the u n c e r t a i n t y a s s o c i a t e d w i t h each a n a l y s i s ( u s i n g the same p r i n c i p l e s as f o r l e a d c o n c e n t r a t i o n s : s e c t i o n 20 1.5.3). I t was found t h a t the r e s u l t s of uranium d e t e r m i n a t i o n by i s o t o p e d i l u t i o n were c o n s i s t e n t l y l e s s than by ne u t r o n a c t i v a t i o n a n a l y s i s or gamma r a y s p e c t r o s c o p y (Appendix B: Ta b l e B.13). A s i m i l a r d i s c r e p a n c y was r e p o r t e d by T i l t o n (1973). T i l t o n (1973) chose t o use the n e u t r o n a c t i v a t i o n numbers r a t h e r than t h o s e by i s o t o p e d i l u t i o n . I n t h i s s t u d y , I have chosen t o ac c e p t the i s o t o p e d i l u t i o n numbers and have reduced the n e u t r o n a c t i v a t i o n a n a l y s i s and gamma r a y a n a l y s i s numbers by a f a c t o r of 1.09 35 ( d e t e r m i n e d by comparison of s e v e r a l samples w i t h two methods of d e t e r m i n a t i o n , Appendix B: Ta b l e B.13) f o r the purposes of c a l c u l a t i n g an i n t e r n a l l y c o n s i s t e n t s e t of u v a l u e s . T h i s approach i s s u p p o r t e d by c l o s e agreement of uranium v a l u e s by i s o t o p e d i l u t i o n w i t h r e c e n t a n a l y s e s by L. Erdman u s i n g n e u t r o n a c t i v a t i o n a n a l y s i s a t the TRIUMF r e a c t o r i n Vancouver ( T a b l e s 2.2 and 3.2). U n c e r t a i n t i e s were c a l c u l a t e d u s i n g the e r r o r p r o p a g a t i o n program "UCALC", l i s t e d i n Appendix D. These were g e n e r a l l y b e t t e r than 1%, i n agreement w i t h one p a i r of d u p l i c a t e a n a l y s e s f o r sample 683421 (Chapter 4 ) . D i s s o l u t i o n problems might make a c t u a l u n c e r t a i n t i e s somewhat l a r g e r . 1.5.5. Thorium by i s o t o p e d i l u t i o n Thorium was de t e r m i n e d f o l l o w i n g t he proced u r e Appendix B. I n t e r f e r i n g i o n s caused i n s t a b i l i t y i n o u t l i n e d the mass i n 21 s p e c t r o m e t r y . I n o n l y one case i s the th o r i u m v a l u e r e p o r t e d by t h i s method. E r r o r p r o p a g a t i o n c a l c u l a t i o n s were made u s i n g the program "THCALC" (Appendix D). The t h o r i u m c o n c e n t r a t i o n d e t e r m i n e d by i s o t o p e d i l u t i o n i s a p p r o x i m a t e l y 15% lower than t h a t o b t a i n e d by gamma r a y s p e c t r o s c o p y . T h i s may be due t o in c o m p l e t e d i s s o l u t i o n of the sample, or t o the same e f f e c t noted f o r uranium a n a l y s e s ( s e c t i o n 1.5.4). 1.5.6. Uranium by d e l a y e d n e u t r o n c o u n t i n g Ten samples were s u b m i t t e d f o r uranium a n a l y s i s t o Neutron A c t i v a t i o n S e r v i c e s L t d . (N.A.S.), O n t a r i o . F i v e gram samples were i r r a d i a t e d f o r 60 seconds u s i n g an e n r i c h e d uranium r e a c t o r . A n e u t r o n d e t e c t o r was used t o count samples f o r 60 seconds. The d e t e c t i o n l i m i t i s 0.01 ppm. C o u n t i n g s t a t i s t i c s were not a v a i l a b l e from the l a b o r a t o r y , however, t y p i c a l u n c e r t a i n t i e s f o r t h i s method a re 10%. 1.5.7. Thorium by n e u t r o n a c t i v a t i o n a n a l y s i s Ten samples were s u b m i t t e d t o Neutron A c t i v a t i o n S e r v i c e s L t d . f o r t h o r i u m a n a l y s i s a t a d e t e c t i o n l i m i t of 0.05 ppm. One gram samples were i r r a d i a t e d f o r 60 minutes then c o o l e d f o r 7 t o 10 days. C o u n t i n g was done f o r 1,000 seconds on the p r o t o a c t i n i u m peak u s i n g a gamma r a y c o u n t e r . The peak i s a t 311 keV. Counter r e s o l u t i o n i s 1.8 keV i n the 1,332 keV range. C o r r e c t i o n s were made f o r i n t e r f e r e n c e . T y p i c a l u n c e r t a i n t i e s 22 f o r t h i s method a re 12% (Erdman 1985). 1.5.8. Uranium and t h o r i u m by gamma r a y s p e c t r o s c o p y A l l samples of the I s l a n d I n t r u s i o n s were a n a l y z e d f o r uranium and t h o r i u m c o n c e n t r a t i o n s by gamma r a y s p e c t r o s c o p y by T.J. Lewis i n 1976 a t the G e o l o g i c a l Survey o f Canada E a r t h P h y s i c s Branch l a b o r a t o r y i n Ottawa. T h i s method, o r i g i n a l l y d e s c r i b e d by Lewis (1974), i s updated i n Lewis e t a l . (1983). Gamma r a y s p e c t r a were a c q u i r e d from powdered rock samples (330 t o 800 g ) , u s i n g s o l i d s t a t e , G e ( L i ) d e t e c t o r s . The equipment used c o n s i s t s of two d e t e c t o r s w i t h e f f i c i e n c i e s of 13 t o 16% and r e s o l u t i o n s a t 1.33 meV of 1.8 t o 1.9 keV (peak w i d t h a t h a l f h e i g h t ) , an EGG-Ortec model 1710 m u l t i - c h a n n e l a n a l y z e r system, and a DEC PDP 11/23 computer system. R e s o l u t i o n c h e c k s were run a t l e a s t once each month and s t a n d a r d s were re-measured f o u r t i m e s a y e a r . O r i g i n a l s t a n d a r d s were o b t a i n e d from the New Bru n s w i c k L a b o r a t o r i e s of the US Atomic Energy Commission, and comparison of r e s u l t s from s t a n d a r d samples have been p u b l i s h e d by Lewis (1974). A c c u r a c y i s e s t i m a t e d t o be a p p r o x i m a t e l y 10% a t 1 ppm U and Th. Most samples were measured f o r a few hou r s . T h i s i s u s u a l l y l o n g e r than n e c e s s a r y t o a c h i e v e a 10% p r e c i s i o n from the c o u n t i n g s t a t i s t i c s . 23 1.5.9. Rubidium and s t r o n t i u m d e t e r m i n a t i o n s S t r o n t i u m i s o t o p i c r a t i o s were de t e r m i n e d a t the U n i v e r s i t y of B r i t i s h C olumbia. Some measurements were made by K. S c o t t or P. Holbek u s i n g a N a t i o n a l Bureau of S t a n d a r d s - t y p e , 30 cm r a d i u s , 60o s e c t o r s o l i d source mass s p e c t r o m e t e r c o n s t r u c t e d by Henry F a u l (PhD) of the U n i v e r s i t y of P e n n s y l v a n i a and automated w i t h a D a t a - G e n e r a l Nova 1210 minicomputor. L a t e r measurements were made by A. Andrew or S. J u r a s u s i n g a Vacuum-Generators Isomass 54R s o l i d source mass s p e c t r o m e t e r automated w i t h a H e w l e t t - P a c k a r d HP-85 computor. Measured r a t i o s have been n o r m a l i z e d t o a 86sr/88sr r a t i o of 0.1194, and c o r r e c t e d f o r i n t e r l a b o r a t o r y b i a s by a d j u s t i n g the 87sr/86sr r a t i o so t h a t the N a t i o n a l Bureau of S t a n d a r d s s t a n d a r d SrC03 (SRM 987) g i v e s a r a t i o of 0.71020 + 0.00002, and the Eimer and Amend Sr s t a n d a r d a r a t i o of 0.70800 +_ 0.00002. The p r e c i s i o n of a s i n g l e 87sr/86sr i s 0.0001 (one s i g m a ) . Rubidium and s t r o n t i u m c o n c e n t r a t i o n s were a l s o d e t e r m i n e d by K. S c o t t , P. Holbek, S. J u r a s or A. Andrew a t the U n i v e r s i t y of B r i t i s h Columbia by X-ray f l u o r e s c e n c e (XRF) u s i n g a P h i l i p s PW 1410 s p e c t r o m e t e r w i t h a Mo X-ray tube and a 3kW g e n e r a t o r . R e p l i c a t e a n a l y s e s were c a r r i e d out on whole-rock powder p e l l e t s u s i n g i n t e r n a t i o n a l s t a n d a r d s f o r c a l i b r a t i o n . Rb/Sr r a t i o s have a p r e c i s i o n of 2% (one sigma) where Rb c o n c e n t r a t i o n s exceed 50 ppm, 3% a t 33 ppm, and 10% a t 10 ppm. 24 CHAPTER 2 ISOTOPE GEOCHEMISTRY OF THE SICKER GROUP, VANCOUVER ISLAND SYNOPSIS Whole r o c k l e a d i s o t o p e a n a l y s e s have been o b t a i n e d f o r a v a r i e t y of l i t h o l o g i e s from the S i c k e r Group i n the Cowichan -Home Lake and B u t t l e Lake U p l i f t s . S i c k e r Group l e a d i s o t o p e r a t i o s a r e c o n s i s t e n t w i t h the h y p o t h e s i s t h a t i t formed as an i s l a n d a r c . R e l a t i v e l y h i g h v a l u e s of 207pb/204pb and 208pb/204pb suggest t h a t l a r g e q u a n t i t i e s of c r u s t a l l e a d must have been i n v o l v e d i n the f o r m a t i o n of the S i c k e r v o l c a n i c s . Thus i t i s proposed t h a t the t r e n c h r e l a t e d t o the P a l e o z o i c i s l a n d a r c had a s u b s t a n t i a l i n p u t of c o n t i n e n t a l d e t r i t u s and may have l a i n near a c o n t i n e n t . S p e c u l a t i v e models i n v o l v i n g anomalously r a d i o g e n i c mantle may a l s o be i n v o k e d t o e x p l a i n the d a t a . Galena l e a d i s o t o p e s i g n a t u r e s from the v o l c a n o g e n i c o r e d e p o s i t s a t the B u t t l e Lake m i n i n g camp are u n i f o r m w i t h i n each of the major ore b o d i e s . S l i g h t d i f f e r e n c e s i n c o m p o s i t i o n a r e , however, o b s e r v a b l e between the d i f f e r e n t o re b o d i e s , which 25 suggest t h a t the i n i t i a l r a t i o s f o r the S i c k e r Group become d e c r e a s i n g l y r a d i o g e n i c w i t h t i m e . T h i s has major s i g n i f i c a n c e i n terms of ore g e n e s i s f o r the s e i m p o r t a n t d e p o s i t s . There a r e s i g n i f i c a n t d i f f e r e n c e s i n i s o t o p i c c o m p o s i t i o n between the S i c k e r Group and Devonian i s l a n d a r c type r o c k s i n the S h a s t a D i s t r i c t , C a l i f o r n i a . T h i s r u l e s out the p o s s i b i l i t y t h a t t h e r e a r e d i r e c t c o r r e l a t i o n s between the r o c k u n i t s of these two a r e a s . 2.1 INTRODUCTION The S i c k e r Group was f i r s t mapped by Cl a p p (1912) and i s named a f t e r Mount S i c k e r ( F i g . 2.1) where i t i s exposed. I t i s the name g i v e n t o the o l d e s t r o c k s on Vancouver I s l a n d , which are exposed i n t h r e e main area s ( F i g . 2.1): the Cowichan - Home Lake, B u t t l e Lake, and Nanoose U p l i f t s . The group i s made up of v o l c a n i c , v o l c a n i c l a s t i c and se d i m e n t a r y r o c k s , which have been metamorphosed t o g r e e n s c h i s t f a c i e s . The o l d e s t f o r m a t i o n i n the S i c k e r Group has been i d e n t i f i e d by M u l l e r (1980) as the N i t i n a t , which i s made up of m a f i c a g g l o m e r a t i c and t u f f a c e o u s v o l c a n i c r o c k s , b a s a l t i c p i l l o w l a v a s and b r e c c i a t e d p i l l o w s w i t h some c h e r t y h o r i z o n s . B a s a l t s 26 F i g u r e 2.1 D i s t r i b u t i o n of t h r e e major u p l i f t s of S i c k e r Group r o c k s , Vancouver I s l a n d , B.C., showing sample l o c a t i o n s d e t a i l e d i n T a b l e 2.1 27 c o n t a i n i n g d i s t i n c t i v e u r a l i t i z e d pyroxene p h e n o c r y s t s a re exposed i n t h e Maple Bay a r e a i n the Cowichan Lake - Home Lake U p l i f t , and have been sampled i n t h i s s t u d y . A K-Ar age of 421 +_ 36 Ma was o b t a i n e d f o r a sample of N i t i n a t t u f f , but i t had a low K c o n t e n t and may t h e r e f o r e be anomalous (Brandon e t a l . 1986). Other K-Ar d a t a f o r N i t i n a t r o c k s g i v e r e s e t Permian ages (Brandon e t a l . 1986). S a l t s p r i n g I n t r u s i o n s , i n t r u s i v e i n t o the N i t i n a t F o r m a t i o n , a r e q u a r t z f e l d s p a r p o r p h y r y and g r a n o d i o r i t e b o d i e s , t h a t p r e v i o u s l y have been c a l l e d the Tyee q u a r t z - f e l d s p a r p o r p h y r y and, more g e n e r a l l y , the Tyee i n t r u s i o n s . They o c c u r on S a l t s p r i n g I s l a n d and e a s t of Cowichan Lake. Z i r c o n a n a l y s e s from t h e s e i n t r u s i o n s a r e h i g h l y d i s c o r d a n t , but g i v e a b e s t e s t i m a t e of 393 +25/-10 Ma (Brandon e t a l . 1986). I n t h i s s t u d y , these i n t r u s i o n s have been sampled a t Maple Bay. K-Ar d a t i n g of s e r i c i t e from a s e r i c i t i c q u a r t z p o r p h y r y of the S a l t s p r i n g I n t r u s i o n s ( M u l l e r 1980) gave a metamorphic age of 180 + 8 Ma, t h e time of i n t r u s i o n of major b a t h o l i t h s known as the I s l a n d I n t r u s i o n s . Deep s e i s m i c p r o f i l e s o b t a i n e d as p a r t of t h e LITHOPROBE p r o j e c t have been i n t e r p r e t e d by Y o r a t h e t a l . (1985b) as showing t h a t the S i c k e r Group s i t s w i t h i n t h e s e b a t h o l i t h s as r o o f pendants; so i t i s l i k e l y t h a t the i s o t o p e systems were a t l e a s t p a r t i a l l y r e s e t i n the J u r a s s i c . 28 O v e r l y i n g the N i t i n a t i n the B u t t l e Lake U p l i f t i s the Myra F o r m a t i o n . I t i s the Myra F o r m a t i o n t h a t i s h o s t t o the major Kuroko-type massive s u l p h i d e o r e d e p o s i t s near the south end of B u t t l e Lake. I t c o n t a i n s b a s a l t i c and a n d e s i t i c f l o w s , r h y o l i t e domes, r h y o l i t i c and d a c i t i c v o l c a n i c l a s t i c l a y e r s , b l a c k a r g i l l i t e s , s i l t s t o n e s and greywackes (Walker 1980). A p r e l i m i n a r y z i r c o n Pb-Pb age of g r e a t e r than 370 Ma age f o r the H-W q u a r t z f e l d s p a r p o r p h y r y member of the Myra Formation (Brandon e t a l . 1 986), has r e c e n t l y been r e v i s e d t o 365 _+ 3 Ma (R. P a r r i s h i n p r e s s ) . T h i s age i s i n good agreement w i t h a second z i r c o n age from the top of the Myra a t B u t t l e Lake which i s 370 +18/-6 (S. J u r a s i n p r e p . ) . S e v e r a l l i t h o l o g i c a l t y p e s have been sampled from the Myra F o r m a t i o n t o g e t h e r w i t h g a l e n a from the a s s o c i a t e d o re d e p o s i t s . A c h e r t h o r i z o n c o n t a i n i n g E a r l y M i s s i s s i p p i a n m i c r o f o s s i l s , d i s c o n f o r m a b l y o v e r l i e s the N i t i n a t Fomation i n the Cowichan Lake a r e a (Brandon e t a l . 1986). These are the o l d e s t f o s s i l s y e t found i n the S i c k e r Group. The o v e r l y i n g v o l c a n i c s t r a t a have p r e v i o u s l y been c o r r e l a t e d w i t h the Myra F o r m a t i o n , but a r e now c o n s i d e r e d t o be younger (Brandon e t a l . 1986). T h i s i n t e r p r e t a t i o n r e q u i r e s t h a t the ore d e p o s i t s a t Mount S i c k e r a r e younger t h a n t h o s e a t B u t t l e Lake. 29 The top of the S i c k e r Group i s marked by the B u t t l e Lake F o r m a t i o n , a f o s s i l i f e r o u s l i m e s t o n e u n i t . Conodant assemblages i n d i c a t e t h a t the B u t t l e Lake F o r m a t i o n spans the i n t e r v a l between E a r l y Permian and M i d d l e P e n n s y l v a n i a n (Brandon e t a l . 1986). Because the o l d e s t f o s s i l s i n the B u t t l e Lake U p l i f t a re E a r l y Permian ( Y o l e 1969), the u n d e r l y i n g v o l c a n i c s t r a t a cannot be younger than 280 Ma, u s i n g the DNAG (Decade of N o r t h American Geology) t i m e s c a l e (Palmer 1983). L i t h o l o g i e s and the c a l c - a l k a l i n e n a t u r e of the S i c k e r v o l c a n i c s a r e s u g g e s t i v e of an i s l a n d a r c environment, and i t has been c o n s i d e r e d t o be a P a l e o z o i c i s l a n d a r c s i n c e the f i r s t major p l a t e t e c t o n i c s y n t h e s i s f o r the Western C o r d i l l e r a (Monger e t a l . 1972). S i m i l a r i t i e s between the P a l e o z o i c S i c k e r Group and o t h e r P a l e o z o i c a r c - t y p e r o c k s such as those a t S h a s t a , C a l i f o r n i a , have been c o n s i d e r e d by M u l l e r (1980). T h i s i s d i s c u s s e d f u r t h e r here by comparing d a t a on t h e l e a d i s o t o p e c o m p o s i t i o n s of r o c k s and ore d e p o s i t s of the S h a s t a D i s t r i c t (Slawson 1983; Doe e t a l . 1985) t o d a t a from S i c k e r Group r o c k s and o r e s . Whole r o c k l e a d i s o t o p e a n a l y s e s have been o b t a i n e d f o r a v a r i e t y of S i c k e r Group r o c k s from the Maple Bay, B u t t l e Lake mine, Mount S i c k e r , and Mount B r e n t o n a r e a s ( F i g . 2.1, Tables 30 2.1 and 2.2). Uranium, t h o r i u m and l e a d c o n c e n t r a t i o n s were o b t a i n e d f o r a subset of samples by i s o t o p e d i l u t i o n , n e u t r o n a c t i v a t i o n a n a l y s i s , or slow n e u t r o n c o u n t i n g . T h i s s t u d y f o c u s e s on the i n t e r p r e t a t i o n of whole r o c k and g a l e n a a n a l y s e s ( T a b l e s 2.2 and 2.3). The whole r o c k a n a l y s e s are compared w i t h those of the Shasta P a l e o z o i c i s l a n d a r c , C a l i f o r n i a , and w i t h those of modern i s l a n d a r c s . A d e s c r i p t i o n of the i s o t o p i c d a t a i s p r e s e n t e d f o r B u t t l e Lake, Maple Bay, and Lenora and Tyee r o c k s and o r e s , f o l l o w e d by a d i s c u s s i o n of the S i c k e r Group as a whole. 2.2 BUTTLE LAKE CAMP 2.2.1 I n t r o d u c t i o n Westmin Resources L t d . , Vancouver, mines s e v e r a l v o l c a n o g e n i c p o l y m e t a l l i c ore d e p o s i t s i n the B u t t l e Lake camp a t the s o u t h e r n end of B u t t l e Lake i n S t r a t h c o n a P r o v i n c i a l P a r k , c e n t r a l Vancouver I s l a n d ( F i g . 2.1). Ore d e p o s i t s o c c u r a t more than one s t r a t i g r a p h i c l e v e l and are a s s o c i a t e d w i t h massive or b r e c c i a t e d f e l s i c h o r i z o n s (Walker 1980). There i s g e n e r a l agreement amongst g e o l o g i s t s t h a t the B u t t l e Lake o r e d e p o s i t s a r e Kuroko-type v o l c a n o g e n i c d e p o s i t s ( C a r v a l h o 31 TABLE 2.1 Locations and b r i e f descriptions of analyzed samples of Sicker Group rocks from Vancouver Island, B.C. General location i s on Figure 2.1. SAMPLE LAT. LONG. DESCRIPTION NAME DECIMAL DEGREES Maple Bay - collected by A. Andrew and C.I. Godwin MB1 48 .85 123.68 U r a l i t e porphyry MB2 48 .85 123.68 Quartz eye porphyry (Tyee) MB3 48 .85 123.68 Quartz eye porphyry (Tyee) MB3A 48 .85 123.68 Quartz porphyry with epidote and hornblende MB3B 48 .85 123.68 Quartz porphyry near u r a l i t e contact MB3D 48 .85 123.68 Pink-banded chert i n mafic unit MB3E 48 .85 123.68 Fragmental u r a l i t e Buttle Lake • - collected by A. Andrew and R. Walker GRHY 49 .58 125.61 Upper Lynx p i t - s i l i c i f i e d andesite or G rh y o l i t e R78 49 .57 125.58 HW massive black r h y o l i t e . W143 2357' R90 49 .57 125.58 HW massive black r h y o l i t e . W143 1631 ' R91 49 .57 125.58 HW massive black r h y o l i t e . W143 1773' R128 49 .57 125.58 Quartz feldspar porphyry (QFP) dome i n HW r h y o l i t e . P13-306 1188' R1 29 49 .57 125.58 QFP dome i n HW r h y o l i t e . P13-306 1323' R130 49 .57 125.58 QFP dome i n HW r h y o l i t e . P13-306 1411' R131 49 .57 125.58 QFP dome i n HW r h y o l i t e . P13-306 1428' W149 49 .58 125.61 Rhyolite unit at top of mine sequence; G hanging wall r h y o l i t e . W149 270'. Lenora/tyee mine area - collected by A. Andrew, D. Lefebure and C.I . Godwin LT1 48 .87 123.78 Dio r i t e sheet, possibly not Sicker LT2 48 .87 123.78 Quartz porphyry (Tyee) LT3 48 .87 123.78 Chert horizon LT4 48 .87 123.78 Di o r i t e sheet, possibly not Sicker LT5 48 .87 123.78 Intermediate t u f f LT6 48 .87 123.78 F e l s i c t u f f Mount Brenton area - Holbek (1980) suite H10A 48 .89 123.82 Meta-andesite (Appendix I i n Holbek 1980) H16 48 .89 123.82 L i t h i c t u f f (Appendix I i n Holbek 1980) H58B 48 .89 123.82 Tyee quartz feldspar porphyry Sicker General - Armstrong suite S1QE 48 .89 123.71 Quartz eye s e r i c i t e s c hist S3 48 .86 123.72 Hornblene porphyry TABLE 2.2. Lead, uranium and thorium data from the Sicker Group volc a n i c rocks, Vancouver Island, B.C. S A M P L E NAME 206pB/204pu1 207 pn/20 4 |>nl 208|>B/204pu1 pu P P M U PPM U P P M TH P P M p6 k7 (I.D.)2,3 (I.D.)2,'4 ( N . A . A . ) 5 <D.N.)5 MAPLE BAY MU1 18, .596(0. .013) 15. .583(0, .012) 38. .105(0. .037 ) 5.17 0.90(0.01) 0.97 2.5 11.1 2.7 MB2 25, .754(0, .01 6 ( 15. .973(0. .009) 44 . ,569(0. .032 ) 1 .04 nd 2.44 6.6 161 .6 2.8 MB3 22, .801(0, .009) 15. .820(0. .009) 42 . ,190(0. .031 ) 1 .90 nd nd nd nd nd MB J A 21 . 588(0, .01 8 ) 1 5 , .742(0, .0151 19. ,809(0. .041 I nd nd nd nd nd nd MB 3B 21 . 113(0, .008) 15, .715(0. .009) 39 . ,686(0. .0 30 ) nd nd nd nd nd nd MB3U 20 , .553(0, .012) 15 .705(0. .011) 39 . 115(0. .033 ) nd nd nd nd nd nd MB3E 19, .730(0. .007 ) 15. .666(0. .008) 39 . , 139(0. 028 ) nd rid nd nd nd nd WESTMIN GHMY GR11Y-AVG 19. 19. 19. .351(0, .412(0, .382(0, .01 5) .00 7 ) .012) 15 15 15 .630(0 .624(0 .627(0 .01 4 ) .008) .011) 38 38 38 .627(0. .633(0. .630(0, .039) .026) .033) 5 .08 1.42(0.05) nd nd nd nd nd nd nd nd 18.0 nd nd nd R78 R78-AVG 19. 19. 19. .561(0. .519(0, .540(0, .016) .007 ) .01 2 ) 15 15 is .596(0 .644(0, .620(0 .01 5) .008) .012) 38 38 38. .934(0, .970(0. .952(0. .040) .028 ) .035 ) 3. .85 nd nd nd nd nd R90 19. .512(0. .011) 15 .641(0 .010) 39. .047(0. .032 ) 5, 5. . 1 1 . 36 nd 2.03 5.5 23.0 2.8 R91 R91-AVG (N=2) 19. 19. 19. .430(0. .444(0. .437(0. .010) .007) .009) 15 15 1 5 .602(0 .620(0 .611(0 .009) .0081 .009 ) 38 38 38. .865(0. .900(0. .888(0. .030) .028) .029) 2. .66 nd nd nd nd nd R1 28 R128-AVG (N=2) 1 9 . 1 9 . 19. .613(0, .525(0. .569(0. .029 ) .013) .022 ) 15 1 5 1 5 .657(0. .601(0. .629(0. .023 ) .012) .018) 39. 39. J9. .267(0. .070(0. .169(0. .061 ) .035 ) .050) 4 . 47 nd nd nd nd nd Rl 29 R129-AVG (N=2) 19. 19. 19. .530(0. .603(0. .567(0. .019) ,007 ) .01 4 ) 15, 1 5 , 1 5 , .630(0. .635(0. .632(0. .017) .008 ) .013 ) 39, 39. 39. .067(0. .101(0. .084(0. .097 ) .028 ) ,071 ) 6 , .77 1.311.19) nd nd 12.6 nd Rl 30 19. ,155(0. .008) 15. .607(0. .009 ) 38. .898(0. .028) 4 , .61 1 .22(.04 ) nd 4.3 17.1 3.6 HI 31 R131-AVG (N=4) 19. 19. 19. 19. 19. ,868(0. 817(0. 991(0. 981(0. .917(0. .029) .01 3 ) .008) .01 1 ) .04 3 ) 15, 15. 15. 15. 15. .621(0. .642(0. .667(0. .643(0. .643(0 .023 ) .012) .009 ) .009) .009) 39 , 39 , 39. 39. 39. . 362(0. . !40(0. .544(0. .467(0. .428(0. ,062 ) ,036 ) .029 ) ,034 ) ,04 8 ) 2. ,84 1 .16(0.02) 1 .63 4.5 26 . 9 2.9 t o T A B L E 2.2 continued S A M P L E NAME 206pu/204p[jl 207pn/204pu 1 2()H|>u/204pn.\ pp PPM u P P M U P P M Til P P M Ji6 k7 ( I . U . ) 2 , 3 (I.U.)2 , 4 ( N . A . A . ) 5 ( D . N . ) 5 WESTMIN (CONT.) W1 49 1 h ,756(0. '.:•) ' ) 15 , .571(0, . 008 ) 311. .245(0, .028 I 18. ,748(0. .008) 15. .566(0, .009 ) Jb , .229(0. .029) W149-AVG <N = 2) 18. .752(0, .008) 15, .569(0 .009 ) 38 .237(0, .029) 6.7) nd nd nd I.F.NORA AND TYEE L/T1 18. .958(0, . 00 7 ) 15, .597(0 .008 ) 38 .559(0, .029 ) nd nd nd nd nd nd I./T2 19, .977(0, .01 3 ) 15, .673(0, .01 1 ) 39 , .248(0, .034 ) nd nd nd nd nd nd 1./T3 20 , .506(0, .007 ) 15, .680(0, .008 ) 38 , .522(0, .028 ) nd rid nd nd nd nd L/T4 18. .902(0, .008) 15, .619(0, .008 ) 38 , .501(0. .030) nd nd nd nd nd nd L/T5 20 , .255(0, .008) 15, .688(0, .008 ) 38 . 323(0. .028) nd nd nd nd nd nd I./T6 21 . 204(0. .00 7 ) 15. .750(0. .008 ) 40 , .06 1(0. .028) nd nd nd nd nd nd HOLBEK SUITE I11 OA 19. .626(0. .01 2 ) 1 5 . .644(0. .010) 38 . 933(0. ,015) 19. .639(0. .007 ) 1 5 . .643(0. .008 ) 38 . 937(0. ,028) H10A-AVG (N = 2) 19 , .632(0, .01 1 ) 15. .644(0. .009) 38 , .935(0. .032 ) 10.97 2.35(0, 2 . 4» 5.7* 13.9 2.5 H16 18. .945(0, .007 ) 15 . 642(0. .01 1 ) 38 , .582(0. .031 ) 5.35 nd 0.49 0.9 5.4 2.0 H58B 20. .535(0. .015) 15. .677(0. .01 3 ) 39 . 156(0. 039) 2.57 nd 2.01 3.5 47.1 1 . 8 ARMSTRONG SUITE S1QE 19. .381(0. .007 ) 15. ,637(0. ,008 ) 38 . 684(0. ,030 ) 5.22 nd nd nd nd nd S3 18. ,560(0. .009) 1 5 . .594(0. .009) 38 . 055(0. .030) 5.37 0.54(0. .01 ( 0.6* 0.9» 6.3 1 .6 : - - - : = = = = = !=== = =! - - - - z :====- - - - - - - - - - -1. Figures given in brackets are the one si>ima uneeria i nt iesbased on the ad d i t i o n of in-run p r e c i s i o n and mass f r a c t i o n a t i o n u n certainties. For average values (n>2) the figures in brackets are the one standard error of the mean value. 2 . I.D. i s isotope d i l u t i o n analysis (Appendix H). nd = not determined. 3. Uncertainties based on duplicate analyses are estimated to be 0.1 ppm (Appendix B ; Table B.12). 4. Figures given in brackets are the one sigma uncertainties calculated by error propagation using "WRUCLC" (Appendix D). 5. N.A.A. stands for Neutron A c t i v a t i o n Analysis. D.N. is delayed neutron counting. D e t a i l s of techniques used and uncertainties are given in Chapter 1. An asterix marks samples analysed at TRIUMF by L. Erdman, a l l others were done by Neutron A c t i v a t i o n Services Ltd., Hamilton, Ontario. 6. u values (238u/204pb) are calculated using UII.D.) valueswhere possible or U(N.A.S.) values which have been reduced by a factor of 1.0935 (Appendix B ) . na = not applicable. 7. k values (232Th/238u) are calculated using UIN.A.S.) and Th(N.A.S.), values, na = not a p p l i c a b l e . TABLE 2.3 Galena-Lead Isotope Analyses from B u t t l e Lake, Lenora, Tyee and Port A l b e r n i Volcanoqenic Ore Deposits, Vancouver Island, B.C. Sample Anal- Map I.at. Long. Lead Isotope R a t i o s (one sigma u n c e r t a i n t y ) Number2 y S t 1 Deposit Name Name North West 206/204 207/204 208/204 G-llanging w a l l sulphide UG-101 1 W162 319-342 f t UG1 49 58 1 25 61 18 539 .003) 1 5 566 (.004) 38. 1 38 (.011 ) UG-102 1 W164 355-377 f t UG2 49 58 125 61 18 61 4 .012) 15 585 (.011) 38. 494 (.027) G and S-Zone sulphides GZ-107 1 G Zone from Lynx P i t GZ7 49 58 125 61 1 8 544 .008) 15 563 (.006) 38. 1 54 (.027) GZ-107r 1 G Zone from Lynx p i t GZ7r 49 58 1 25 61 1 8 544 .008) 15 576 (.006) 38. 132 (.019) GZ-110 1 G Zone from Lynx p i t GZ10 49 58 1 25 61 18 551 .008) 15 554 (.006) 38. 1 29 (.020) GZ-IIOr 1 G Zone from Lynx p i t GZlOr 49 58 1 25 61 18 563 .004 ) 1 5 571 (.004 ) 38. 173 (.012) SZ-111 1 S Zone from Lynx p i t SI 1 49 58 125 61 1 8 554 . 004 ) 15 561 (.00 4) 38. 1 47 (.014) GS-AVG (n = 5) 49 58 125 61 18 549 .008) 15 565 (.009) 38. 1 47 (.018) HW ore HW-103 1 HW 20 l e v e l 049 hole 1698' HW3 49 57 125 57 18 548 .008) 1 5 574 (.006) 38. 177 (.020) HW-104 1 HW 20 l e v e l 049 hole 1679' HW4 49 57 125 57 18 573 .010) 1 5 573 (.009) 38. 186 ( .023) HW-108 1 HW 20 l e v e l 04 9 hole 108 m IIW8 49 57 125 57 1 8 559 .005) 15 580 (.005) 38. 186 (.014) HW-108r 1 HW 20 l e v e l 049 hole 108 m HW8r 49 57 125 57 18 546 .004 ) 1 5 580 (.004) 38. 200 (.009) HW-AVG (n=4) 49 57 125 57 18 557 .01 2) 15 577 ( .004) 38. 187 (.010) Myra ore MY-001 1 Myra M01 49 58 125 60 1 8 480 .006) 15 555 1.005) 38. 069 (.016) G79WM-001 2 Myra WM1 49 58 125 60 18 506 .011 ) 15 579 (.006) 38. 186 (.027) G79WM-002 2 Myra WM2 49 58 1 25 60 18 488 .011 ) 15 554 (.014) 38. 089 ( .015) G79WM-003 2 Myra WM3 49 58 1 25 60 18 493 .01 1 ) 1 5 561 (.011) . 18. 1 30 (.011 ) MY-AVG <n = 4) 49 58 1 25 60 18 492 .011) 1 5 562 (.012) 38. 1 1 9 (.052) Lenora and Tyee ores G79LN-AVG 2 Lenora LN 48 87 123 78 18 548 .01 1 ) 1 5 555 ( .01 2) 38. 223 (.023) G79TY 2 Tyee TY 48 87 123 78 . 1 8 558 .015) 1 5 577 (.017) 38. 123 (.042) Showing 12 km southeast of Port A l b e r n i 30457-001 1 Showing S457 49 125 1 8 350 .005) 1 5 572 (.004) 38. 003 (.014) 1 . 1 = analyses, by A.Andrew were done in the Geochronology Laboratory, The U n i v e r s i t y of B r i t i s h Columbia; 2 = analyses by B. Ryan, reported in Andrew (1982) were done in the Geophysics Laboratory, The U n i v e r s i t y of B r i t i s h Columbia. U) 35 1979; Walker 1980; Seraphim 1980). There a r e many s i m i l a r i t i e s between these and the w e l l d e c r i b e d Kuroko d e p o s i t s of Japan. Both are a s s o c i a t e d w i t h submarine, c a l c - a l k a l i n e f e l s i c v o l c a n i c s i n the waning s t a g e s of a m a f i c t o f e l s i c v o l c a n i c c y c l e . The y e l l o w o r e , b l a c k o r e , h e m a t i t i c c h e r t , s i l i c e o u s and s t r i n g e r o r e t y p e s t h a t c h a r a c t e r i z e the Japanese d e p o s i t s are a l l found i n the B u t t l e Lake d e p o s i t s . 2.2.2 Sample s u i t e Galena samples were c o l l e c t e d from the H-W d e p o s i t ( s t r u c t u r a l l y and s t r a t i g r a p h i c a l l y the l o w e s t ) , from the G hanging w a l l , G, and S zones of the Lynx d e p o s i t , and from the Myra d e p o s i t . Whole r o c k samples were c o l l e c t e d from the massive H-W r h y o l i t e (samples R78, R90 and R91), and from a f r a g m e n t a l q u a r t z f e l d s p a r p o r p h y r y u n i t w i t h i n t h i s r h y o l i t e (samples R128, R129, R130 and R131). A sample of s i l i c e o u s r o c k was t a k e n from the Lynx p i t , d i r e c t l y beneath the G zone ore (sample GRHY). Sample W149 was t a k e n a t the top of the mine sequence from the uppermost q u a r t z f e l d s p a r p o r p h y r y , the G hanging w a l l r h y o l i t e . T h i s sample c o n t a i n e d some s u l p h i d e m i n e r a l i z a t i o n . F i g u r e 2.2 shows l o c a t i o n s of the ore b o d i e s named h e r e , and of t h e samples a n a l y z e d . 2.2.3' R e s u l t s Galena and whole r o c k l e a d i s o t o p e d a t a ( T a b l e s 2.2 and 2.3) 36 F i g u r e 2.2 Map showing the l o c a t i o n s of the B u t t l e Lake ore d e p o s i t s named i n the t e x t and p r o j e c t e d l o c a t i o n s of whole r o c k and g a l e n a samples a n a l y s e d ( T a b l e s 2.2 and 2.3). 37 are shown i n F i g u r e s 2.3 and 2.4. A n a l y s e s of t h r e e r o c k s from the H-W massive b l a c k r h y o l i t e group t o g e t h e r , whereas the r e s u l t s from r o c k s of the f r a g m e n t a l q u a r t z f e l d s p a r porphyry u n i t s p r e a d a l o n g a l i n e , which may be an i s o c h r o n ; however, the l i n e i s not l o n g enough t o g i v e a m e a n i n g f u l age e s t i m a t e f o r these r o c k s ( c a l c u l a t e d age i s 180 +_ 250 Ma). The H-W g a l e n a p l o t s a t the l e a s t r a d i o g e n i c end of the l i n e i n both F i g u r e s 2.3 and 2.4. V a r i a t i o n i n r a t i o s f o r the H-W g a l e n a (0.06%) i s w i t h i n the a n a l y t i c a l e r r o r . Galena from the Myra ore d e p o s i t a t B u t t l e Lake has i s o t o p i c r a t i o s t h a t are s l i g h t l y d i f f e r e n t than the H-W ore d e p o s i t . U s i n g a t w o - t a i l e d s t u d e n t s t s t a t i s t i c a l t e s t the 206pb/204pb and 208pb/204pb r a t i o s of the Myra and H-W o r e s are d i f f e r e n t a t the 0.05 l e v e l of s i g n i f i c a n c e . I t seems r e a s o n a b l e t o assume t h a t t h e r e i s a l s o a r e a l d i f f e r e n c e i n 207pb/204pb between these ore b o d i e s , as suggested i n F i g u r e s 2.3 and 2.4. Galena can t h e r e f o r e be used t o d i s t i n g u i s h between d i f f e r e n t o re b o d i e s i n t h i s camp, and t o a i d s t r a t i g r a p h i c c o r r e l a t i o n of ore h o r i z o n s . T h i s i s p a r t i c u l a r l y u s e f u l i n t h i s type of d e p o s i t where ore h o r i z o n s a r e s e p a r a t e d by f a u l t s and f o l d s . The H-W o r e i s the most r a d i o g e n i c ( w i t h the e x c e p t i o n of one sample of G hanging w a l l s u l p h i d e ) d e s p i t e i t s p o s i t i o n a t the base of the mine sequence. F u r t h e r up the sequence the o r e s 38 F i g u r e 2.3 207pb/204pb v e r s u s 206pb/204pb p l o t of g a l e n a ( s o l i d c i r c l e s ; T a b l e 2.3) and whole r o c k p r e s e n t ( s o l i d t r i a n g l e s ; T a ble 2.2) and i n i t i a l r a t i o s a t 370 Ma (open t r i a n g l e s ; T a b l e 2.4) from B u t t l e Lake U p l i f t . Three g a l e n a samples from the Cowichan - Home Lake U p l i f t (S457, LN, TY) are a l s o shown/ Galena (open c i r c l e s ) and whole r o c k ( i n v e r t e d t r i a n g l e s ) a n a l y s e s from the P a l e o z o i c v o l c a n o g e n i c ore d e p o s i t s of S h a s t a , C a l i f o r n i a a re t a k e n from Slawson (1983) and Doe e t a l . (1985). A s o l i d diamond marks the e s t i m a t e d c o m p o s i t i o n of Devonian mantle (Doe e t a l . 1985). Major f i e l d s of whole r o c k s from modern mid-ocean r i d g e b a s a l t s , ocean i s l a n d s and ocean sediments are t a k e n from the l i t e r a t u r e as f o l l o w s : mid-ocean r i d g e b a s a l t s (Church and Tatsumoto 1975, B r e v a r t e t a l . 1981, V i d a l and C l a u e r 1981); ocean i s l a n d s (Sun and Jahn 1975, Sun 1980, Tatsumoto 1978, Weis 1983); i s l a n d a r c s (Oversby and Ewart 1972, Church 1975, M e i j e r 1976, Kay e t a l . 1978); P a c i f i c sediments (Church 1976, Sun 1980, and V i d a l and C l a u e r 1981). These f i e l d s have been a d j u s t e d f o r 370 Ma l e a d e v o l u t i o n u s i n g the growth c u r v e of S t a c e y and Kramers (1975). 40 F i g u r e 2.4 208pb/204pb v e r s u s 206pb/204pb p l o t of B u t t l e Lake g a l e n a and whole r o c k d a t a . See F i g u r e 2.3 f o r e x p l a n a t i o n of symbols and sou r c e of d a t a . I s o t o p i c f i e l d s f o r MORB, i s l a n d a r c s , ocean i s l a n d s and P a c i f i c sediments have been a d j u s t e d f o r 370 Ma l e a d e v o l u t i o n u s i n g S t a c e y and Kramers (1975) growth c u r v e . 42 become l e s s e n r i c h e d i n 207pb/204pb. Whole r o c k sample W149, t a k e n from the top of the mine sequence, has the lo w e s t 207pb/204pb v a l u e of a l l r o c k s sampled. C o r r e s p o n d i n g l y , g a l e n a from the s t r a t i g r a p h i c a l l y h i g h Myra d e p o s i t has the l e a s t r a d i o g e n i c r a t i o s of the B u t t l e Lake or e s sampled ( F i g s . 2.3 and 2.4). D i f f e r e n c e s i n i s o t o p i c c o m p o s i t i o n of g a l e n a between the Myra ore and the H-W d e p o s i t s a re not s i m p l y due t o an age d i f f e r e n c e between the d e p o s i t s , because the o l d e s t of the d e p o s i t s has the most r a d i o g e n i c r a t i o s , and because the i s o t o p i c d i f f e r e n c e s a re not i n the d i r e c t i o n of a s u i t a b l e i s o c h r o n . Rather d i f f e r e n c e s must be a t t r i b u t e d t o v a r i a t i o n s i n t he i s o t o p i c c o m p o s i t i o n s of the sour c e magmas. I n an i s l a n d a r c s e t t i n g , m i x i n g of c r u s t a l l e a d w i t h m a n t l e - d e r i v e d magmas i s t o be e x p e c t e d ( M e i j e r 1976; Kay e t a l . 1982). Involvement of g r e a t e r q u a n t i t i e s of c r u s t a l l e a d i n the p r o d u c t i o n of the H-W r o c k s and o r e s , than f o r the Myra o r e , can e x p l a i n the h i g h e r 207pb/204pb r a t i o s of the former. Decrease of 207pb/204pb w i t h time i n the Myra F o r m a t i o n r o c k s and o r e s i s s i g n i f i c a n t and s u p p o r t s a new model f o r the f o r m a t i o n of the B u t t l e Lake o r e s b e i n g proposed by S. J u r a s ( i n p r e p a r a t i o n ) . Based on a d e t a i l e d s t r a t i g r a p h y of the mine sequence, he suggests t h a t the o r e s form i n a b a c k - a r c r i f t i n g 43 e nvironment. A c c o r d i n g t o t h i s h y p o t h e s i s the b a c k - a r c magmas become i n c r e a s i n g l y p r i m i t i v e as r i f t i n g p r o g r e s s e s . E a r l y magmas i n the b a c k - a r c a r e r e l a t i v e l y e n r i c h e d i n 207pb/204pb due t o the i n v o l v e m e n t of a r c c r u s t a l m a t e r i a l . As the a r c s p l i t s , the c r u s t i n the b a c k - a r c t h i n s and the magmas show l e s s c r u s t a l i n v o l v e m e n t , and c o n c o m i t t a n t l y lower 207pb/204pb v a l u e s . A s i m i l a r model, based on neodymium and s t r o n t i u m s t u d i e s , has been proposed f o r the f o r m a t i o n of the Kuroko ore d e p o s i t s i n Japan (Nohda and Wasserburg 1986). There are many i m p l i c a t i o n s of t h i s new model f o r ore g e n e s i s f o r Kuroko-type v o l c a n o g e n i c massive s u l p h i d e s i n terms of e x p l o r a t i o n s t r a t e g y . A s p e c i f i c t e c t o n i c s e t t i n g i s r e q u i r e d , namely the i n i t i a l s t a g e s of b a c k - a r c r i f t i n g i n a mature i s l a n d a r c . Thus, an i n c r e a s i n g l y p r i m i t i v e v o l c a n i c p i l e can be an e x p l o r a t i o n t a r g e t . At B u t t l e Lake, the l a r g e s t ore d e p o s i t i s a t the base of the mine sequence and has the most r a d i o g e n i c l e a d , whereas the h i g h e s t grade o re i s h i g h e r up i n the sequence and has l e s s r a d i o g e n i c l e a d c h a r a c t e r i s t i c s . V a r i a t i o n i n i n i t i a l r a t i o s f o r d i f f e r e n t s t r a t i g r a p h i c l e v e l s of the Myra F o r m a t i o n , marked by g a l e n a l e a d i s o t o p e a n a l y s e s , i l l u s t r a t e s one fundamental problem i n u s i n g whole r o c k common l e a d age d e t e r m i n a t i o n s . I s o c h r o n age c a l c u l a t i o n s r e l y on the assumption t h a t the i n i t i a l r a t i o s of the r o c k s were 44 homogeneous. I f t h i s a s sumption i s not t r u e , the s l o p e of the l i n e a r a r r a y of e v o l v e d r a t i o s i s not o n l y due t o the age of the a r r a y , but i s p a r t l y c o n t r o l l e d by i n i t i a l i n h o m o g e n e i t i e s . 2.2.4 Comparison of Myra F o r m a t i o n whole r o c k i n i t i a l r a t i o s and  g a l e n a Whole r o c k i n i t i a l r a t i o s f o r the B u t t l e Lake U p l i f t , c a l c u l a t e d u s i n g an assumed age of 370 Ma ( T a b l e 2.4), are p l o t t e d w i t h g a l e n a a n a l y s e s i n F i g u r e s 2.3 and 2.4. The g a l e n a samples have more r a d i o g e n i c r a t i o s than the whole rock i n i t i a l r a t i o s . There are t h r e e p o s s i b l e e x p l a n a t i o n s f o r t h i s : 1) The whole r o c k i n i t i a l r a t i o s were never the same as the g a l e n a r a t i o s . The assumption t h a t v o l c a n i c r o c k s and s y n g e n e t i c o r e d e p o s i t s have the same i n i t i a l r a t i o s has been shown t o be r e a s o n a b l e ( B r e v a r t e t a l . 1981). However, s m a l l d i f f e r e n c e s between whole r o c k i n i t i a l r a t i o s and ore l e a d r a t i o s were found i n the Kuroko d e p o s i t s of Japan (Fehn e t a l . 1983). Church e t a l . (1986 ) a l s o note t h a t o r e s from Cascade porp h y r y d e p o s i t s have g r e a t e r 206pb/204pb v a l u e s than the v o l c a n i c r o c k s w i t h which they a r e a s s o c i a t e d . The d i s c r e p a n c y here i s l a r g e r than i s r e a s o n a b l y e x p l a i n e d i n t h i s way. 2) The assumed age f o r the r o c k s i s t o o o l d so t h a t the i n i t i a l r a t i o s a r e u n d e r e s t i m a t e d . T h i s i s u n l i k e l y s i n c e the age of the Myra F o r m a t i o n i s based on two z i r c o n age e s t i m a t e s which show good agreement (S. J u r a s p e r s . comm. 1986). An age of TABLE 2.4 I n i t i a l r a t i o s for the Sicker Group, Vancouver Island, B.C. Age corrections are for assumed age of 370 Ma. u and k values used i n the calculations are l i s t e d i n Table 2.2. SAMPLE 206pb/204pb1 207pb/204pb1 208pb/204pb1 MB1 17.94 (0.02) 15.55 (0.01) 37.55 (0.08) MB2 16.21 (1.04) 15.46 (0.06) 36.21 (1.34) GRHY 18.32 (0.04) 15.57 (0.01) not applicable R90 18.16 (0.15) 15.57 (0.01) 37.86 (0.19) R129 18.82 (0.12) 15.59 (0.02) not applicable R130 18.17 (0.37) 15.55 (0.01) 37.76 (0.11) R131 18.33 (0.09) 15.56 (0.02) 37.99 (0.24) H10A 18.81 (0.09) 15.60 (0.01) 38.29 (0.10) H16 18.63 (0.04) 15.62 (0.01) 38.38 (0.05) H58B 17.75 (0.31) 15.54 (0.01) 37.59 (0.29) S3 18.16 (0.04) 15.57 (0.01) 37.87 (0.04) Average 370 Ma = 18.05 (0.73) 15.56 (0.05) 37.67 (0.64) 1. Figures i n brackets are the one sigma estimates of uncertainty calculated using the error propagation program "T1CORR" (Appendix D). 46 a p p r o x i m a t e l y 300 Ma i s r e q u i r e d t o a l l o w b e t t e r agreement between g a l e n a and whole r o c k i n i t i a l r a t i o s . T h i s seems to be t o o young based on o t h e r age e s t i m a t e s . 3) Recent uranium g a i n or l e a d l o s s has o c c u r r e d i n the Myra F o r m a t i o n r o c k s , c a u s i n g the measured )i v a l u e s t o be t o o h i g h . T h i s i s the most l i k e l y p o s s i b i l i t y s i n c e i t i s u n l i k e l y t h a t the S i c k e r Group r o c k s have behaved as a c l o s e d system s i n c e t h e i r t ime of f o r m a t i o n — p a r t i c u l a r l y s i n c e they have been s u b j e c t e d t o metamorphism a t l e a s t once i n t h e M e s o z o i c . The v a r i a t i o n i n i n i t i a l r a t i o s i s s u p p o r t f o r t h i s p o s s i b i l i t y . I f the r o c k s had remained c l o s e d systems, the i n i t i a l r a t i o s would p r o b a b l y d e f i n e a more c o h e s i v e f i e l d . 2.2.5 Comparison of S i c k e r Group r o c k s and o r e s w i t h those of t h e  West Sh a s t a D i s t r i c t of C a l i f o r n i a . An E a r l y Devonian v o l c a n i c sequence i s exposed i n the E a s t e r n Klamath Mountains. Here, Kuroko-type massive s u l p h i d e s o c c u r i n the B a l a k l a l a R h y o l i t e ( K i n k e l e t a l . 1956), which i s made up of s i l i c e o u s m e t a v o l c a n i c r o c k s o v e r l y i n g a low K, t h o l e i i t i c b a s a l t t o a n d e s i t e s e r i e s known as the C o p l e y Greenstone. M u l l e r (1980) t e n t a t i v e l y c o r r e l a t e d the C o p l e y Greenstone w i t h the N i t i n a t F o r m a t i o n , and the B a l a k l a l a R h y o l i t e w i t h the Myra F o r m a t i o n . The ore d e p o s i t s of the West Shasta d i s t r i c t a r e o v e r l a i n by b l a c k s h a l e s of the K e n n e t t F o r m a t i o n , which i n t u r n a r e o v e r l a i n by a Permian l i m e s t o n e u n i t a p p a r e n t l y c o r r e l a t i v e w i t h the B u t t l e 47 Lake F o r m a t i o n ( M u l l e r 1980). D e t a i l e d t r a c e element and r a r e e a r t h element a n a l y s e s of the Cople y Greenstone and the B a l a k l a l a R h y o l i t e i n d i c a t e t h a t t h i s v o l c a n i c sequence r e p r e s e n t s an immature i s l a n d a r c r e l a t e d t o a b a c k - a r c b a s i n , s i m i l a r t o the p r e s e n t day Mariana i s l a n d a r c ( L a p i e r r e e t a l . 1985). Lead i s o t o p e s t u d i e s of the Shasta d i s t r i c t (Slawson 1983; Doe e t a l . 1985), p r o v i d e d a t a f o r comparison w i t h the S i c k e r Group v o l c a n i c r o c k s and o r e s . Data from Slawson (1 983) and Doe et. a l . (1 985) have been p l o t t e d w i t h S i c k e r Group o r e s and r o c k s from B u t t l e Lake camp i n F i g u r e s 2.3 and 2.4. I t i s apparent t h a t the m a j o r i t y of ore samples from West Shasta are i s o t o p i c a l l y d i s t i n c t from t h o s e from the B u t t l e Lake camp. Lead i s o t o p e s i g n a t u r e s a l s o show t h a t the Cople y Greenstone i s not the same u n i t as the N i t i n a t F o r m a t i o n , and t h a t the B a l a k l a l a R h y o l i t e i s not the same as the Myra F o r m a t i o n . The S i c k e r Group r o c k s have h i g h e r 207pb/204pb r a t i o s than the West Sha s t a r o c k s , i n d i c a t i n g a g r e a t e r c r u s t a l component i n the former. T h i s e v i d e n c e makes i t u n l i k e l y t h a t t h e s e two areas were p a r t of the same P a l e o z o i c v o l c a n i c b e l t . There are a few o u t l i e r s i n the Sh a s t a d a t a of Slawson (1983) which p l o t c l o s e r t o the v a l u e s of t h e S i c k e r o re d e p o s i t s . There i s , however, some doubt about the c o r r e c t n e s s of 48 t h e s e o u t l i e r s (as e x p r e s s e d by Doe e t a l . 1985 because of t h e i r i n a b i l i t y t o r e p r o d u c e the o u t l y i n g v a l u e s f o r t h e B a l a k l a l a A and B ore d e p o s i t s ) . 2.3 MAPLE BAY 2.3.1 Geology P i l l o w e d b a s a l t i c u n i t s and t u f f a c e o u s r o c k s of the N i t i n a t F o r m a t i o n are exposed a t Maple Bay ( M u l l e r 1980). They are c o m p l e x l y f o l d e d w i t h a q u a r t z f e l d s p a r p o r p h y r y . M u l l e r (1980) c o r r e l a t e s the p o r p h y r y w i t h the Myra F o r m a t i o n , but Brandon e t a l . (1986) i n t e r p r e t i t as b e i n g one of the S a l t s p r i n g I n t r u s i o n s . The r o c k s i n t h i s a rea have been metamorphosed t o upper g r e e n s c h i s t f a c i e s (Brandon e t a l . 1986). 2.3.2 Sample s u i t e Samples were t a k e n from the m a f i c u n i t , the q u a r t z f e l d s p a r p o r p h y r y , and from a c h e r t h o r i z o n w i t h i n the m a f i c u n i t (Table 2.1, F i g . 2.5) . 2.3.3 R e s u l t s Lead i s o t o p e c o m p o s i t i o n s f o r the Maple Bay samples are l i s t e d i n T a b l e 2.2, and shown i n c o n v e n t i o n a l l e a d - l e a d p l o t s i n F i g u r e s 2.6 and 2.7. The s p r e a d i n 206pb/204p D and 207pb/204pb r a t i o s 49 F i g u r e 2.5 D e t a i l e d geology of Maple Bay a r e a (from M u l l e r 1980, f i g u r e 15) showing whole r o c k sample l o c a t i o n s ( T able 2.1). 50 F i g u r e 2.6 207pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k and g a l e n a d a t a from the S i c k e r Group, Vancouver I s l a n d , B.C. Squares are samples from the Cowichan - Home Lake U p l i f t . T r i a n g l e s are f o r samples from the B u t t l e Lake U p l i f t . Open symbols mark i n i t i a l r a t i o s ( T a ble 2.4) c a l c u l a t e d a t 370 Ma. S o l i d symbols are f o r p r e s e n t r a t i o s ( T a ble 2.2). S o l i d c i r c l e s a r e f o r g a l e n a samples (Table 2.3). The b e s t f i t l i n e t o the whole r o c k d a t a , e x c l u d i n g samples LT1 , LT4, H16, H58B, H10A, SQE, S3, u s i n g York (1969) l e a s t squares r e g r e s s i o n has the parameters: s l o p e = 0.057120, i n t e r c e p t = 14.516. T h i s c o r r e s p o n d s t o an age of 496 Ma +_ 76 Ma. The growth c u r v e , marked "S & K", i s t h a t of S t a c e y and Kramers (1975). F i g u r e 2.7 208pb/204pb v e r s u s 206pb/204pb p l o t ( T a b l e s 2.2, 2.3 and 2.4) from the S i c k e r Group, e x p l a n a t i o n of symbols see F i g u r e 2.6. of whole ro c k and g a l e n a d a t a Vancouver I s l a n d , B.C. For 53 between samples and the l i n e a r i t y of t h e p l o t s suggest t h a t an i s o c h r o n age can be c a l c u l a t e d f o r the s e r o c k s ( u s i n g e q u a t i o n #1 , Table 2.5). . T a k i n g a l l of t h e Maple Bay samples ( t 2 = 0 ) , the e s t i m a t e d age ( t i ) i s 320.+75/-80 Ma ( l e a s t squares r e g r e s s i o n a f t e r York 1969) and k ( e q u a t i o n #2, Ta b l e 2.5) i s 3.0 +0.2/-0.3. C a l c u l a t e d s e p a r a t e l y , the f e l s i c u n i t g i v e s an age of 424 +97/-103 Ma, and the m a f i c N i t i n a t t u f f g i v e s 700 +275/-335Ma; k v a l u e s a re 3.4 +0.4/-0.5 and 2.9 +0.3/-0.4, r e s p e c t i v e l y . The l a r g e u n c e r t a i n t i e s a s s o c i a t e d w i t h each age c a l c u l a t i o n i n d i c a t e s t h a t common l e a d age d e t e r m i n a t i o n i s not a s u i t a b l e method f o r the s e r o c k s . Common l e a d i s o t o p e i s o c h r o n s can o n l y be used w i t h c o n f i d e n c e i f the age of the r o c k s i s s u f f i c i e n t t o n u l l i f y the e f f e c t s of inhomogeneous i n i t i a l r a t i o s , and t o produce a wide s p r e a d i n v a l u e s due t o i r i s i t u a d d i t i o n of r a d i o g e n i c l e a d . 2.4 MOUNT SICKER - LENORA AND TYEE MINE AREA 2.4.1. Geology and sample s u i t e . Lenora and Tyee massive s u l p h i d e o re d e p o s i t s o c c u r on the f l a n k s of Mount S i c k e r ( F i g . 2.1). These mines, which are s i m i l a r t o those of the B u t t l e Lake U p l i f t , were p r o d u c t i v e from 54 TABLE 2.5 E q u a t i o n s used i n c a l c u l a t i n g i s o c h r o n ages u s i n g common l e a d i s o t o p e a n a l y s e s . E q u a t i o n # 1 : I s o c h r o n s l o p e i n 207pb/204pb v e r s u s 206pb/204pb = m207-206 m207-206 = 1 e>2t1 - e"X2t2 1 37.88 e x 1 t l - e > l t 2 E q u a t i o n #2 :. I s o c h r o n s l o p e i n 208pb/204pb v e r s u s 206pb/204pb = m208-206 m.208-206 = k e>"3t1 - e*3t2 e*-1t1 - e^1t2 ~X1 = 0.1 551 25 x 1 0-9 J a f f e y e t a l ^ 1971 X 2 = 0.98485 x 10-9 J a f f e y e t a l . 1971 *3 = 0 .049475 x 1 0-9 LeRoux and G l e n d e n i n 1963 1 37 .88 = p r e s e n t r a t i o 238u/235rj 55 1898 t o 1964. The ore i s h o s t e d by t u f f a c e o u s r o c k s of the S i c k e r Group, thought by M u l l e r (1980) t o bel o n g t o the Myra F o r m a t i o n . Samples were c o l l e c t e d from a c o m p o s i t i o n a l v a r i e t y c o n s i s t i n g o f : t u f f a c e o u s r o c k s , a c h e r t h o r i z o n , and a d i o r i t e s h e e t , which may be e i t h e r contemporaneous or a l a t e r i n t r u s i v e u n r e l a t e d t o the S i c k e r Group. A l l of t h e s e r o c k s were e x t r e m e l y a l t e r e d . No l e a d , uranium or t h o r i u m d e t e r m i n a t i o n s were made on t h i s sample s u i t e ; o n l y l e a d i s o t o p e c o m p o s i t i o n s were measured. Galena l e a d i s o t o p e a n a l y s e s f o r a few samples of the ore are r e p o r t e d i n Andrew e t a l . (1982). 2.4.2 R e s u l t s . Lead i s o t o p e c o m p o s i t i o n s of samples LT1 t o LT6 (Table 2.2) a r e p l o t t e d on F i g u r e s 2.6 and 2.7. The d a t a a r e not s u f f i c i e n t l y s p r e a d t o a l l o w the c a l c u l a t i o n of a m e a n i n g f u l i s o c h r o n age. The d i o r i t e sheet has a u n i f o r m i s o t o p i c c o m p o s i t i o n i n d i c a t e d by the s i m i l a r i t y i n r a t i o s from a sample t a k e n from the top of the sheet (sample LT1) and another from the bottom (sample L T 4 ) . I t i s not p o s s i b l e , however, t o t e l l c o n c l u s i v e l y from the d a t a whether or not the sheet belongs t o the S i c k e r Group or t o T e r t i a r y i n t r u s i v e s (Chapter 5 ) , because t h e r e i s an o v e r l a p i n t h e i r i s o t o p i c c o m p o s i t i o n s . The marked s i m i l a r i t y i n the i s o t o p i c c o m p o s i t i o n of the g a l e n a from the Lenora and Tyee ore d e p o s i t s t o those of the 56 Westmin ore d e p o s i t s a t B u t t l e Lake, suggests t h a t both camps ar e of the same age and o r i g i n (Andrew 1982). Brandon e t a l . (1986) r e c e n t l y c o n c l u d e d t h a t the Myra F o r m a t i o n does not o c c u r i n the Cowichan Lake U p l i f t , and t h a t t h e r e must be a minimum age d i f f e r e n c e of 20 Ma y e a r s between the Myra F o r m a t i o n i n the B u t t l e Lake U p l i f t (minimum age 370 Ma) and the r o c k s o v e r l y i n g the N i t i n a t t u f f i n the Cowichan Lake U p l i f t (maximum age 350 Ma). G i v e n t h e i r e s t i m a t e of a minimum age d i f f e r e n c e of 20 Ma between the two ore f o r m i n g e v e n t s , the g a l e n a l e a d i s o t o p e r a t i o s f o r the Lenora and Tyee o r e d e p o s i t s s h o u l d be more r a d i o g e n i c than those of the B u t t l e Lake ore d e p o s i t s . They are n o t . T h e r e f o r e , c o n t r a r y t o Brandon et. a l . ( i b i d ) , g a l e n a l e a d d a t a s u p p o r t the e x i s t e n c e of Myra F o r m a t i o n c o r r e l a t i v e s i n the Cowichan Lake U p l i f t . 2.5. DISCUSSION OF THE SICKER GROUP AS A WHOLE 2.5.1 Augmented sample s u i t e S e v e r a l whole r o c k a n a l y s e s of r o c k s from p r e - e x i s t i n g c o l l e c t i o n s are i n c l u d e d i n t h i s d i s c u s s i o n . These i n c l u d e two r o c k s from R.L. Armstrong, one sample of the Tyee q u a r t z p o r p h y r y , and a sample of u r a l i t e p o r p h y r y (samples S1QE, and S 3 ) . Three r o c k s from the B.Sc t h e s i s c o l l e c t i o n of P. Holbek (1980) were a l s o a n a l y z e d . These were a l l from the Mount B r e n t o n 57 a r e a of the Cowichan - Home Lake U p l i f t (samples H10A, H16 and H58B). A l l of the s e samples had been c r u s h e d and a n a l y s e d f o r r u b i d i u m and s t r o n t i u m . T h e i r l e a d i s o t o p e c o m p o s i t i o n s a re t h e r e f o r e r e g a r d e d w i t h s u s p i c i o n f o r reasons o u t l i n e d i n Chapter 1. A g a l e n a a n a l y s i s from near P o r t A l b e r n i , p r o v i d e d by Westmin Resources L t d . , i s a l s o d i s c u s s e d below. 2.5.2 P l a t e t e c t o n i c s e t t i n g of the S i c k e r Group F i g u r e s 2.2 and 2.3 show t y p i c a l l e a d i s o t o p e r a t i o s f o r modern p l a t e t e c t o n i c e n v i r o n m e n t s , which have been p r o j e c t e d back by 370 Ma u s i n g ah average c r u s t a l growth c u r v e (Stacey and Kramers 1975). The S i c k e r Group ( r e p r e s e n t e d i n t h i s f i g u r e by g a l e n a samples and whole r o c k samples from B u t t l e Lake U p l i f t ) has h i g h e r 207pb/204pb r a t i o s than f o r MORBs, and resembles o t h e r i s l a n d a r c type e n v i r o n m e n t s — a l t h o u g h d i r e c t comparison i s d i f f i c u l t t o make because of the age d i f f e r e n c e . A l s o shown i s t h e v a l u e f o r the Devonian mantle proposed by Doe e t a l . (1985) based on a n a l y s e s from the West Shasta d i s t r i c t of the e a s t e r n Klamath mountains. S i c k e r Group r o c k s must have i n c o r p o r a t e d r e l a t i v e l y l a r g e amounts of l e a d from s e d i m e n t a r y r o c k s i n o r d e r t o produce the ob s e r v e d r a t i o s . T h i s i m p l i e s t h a t the s u b d u c t i o n zone, which produced the S i c k e r a r c , must have been s e d i m e n t - r i c h , and t h e r e f o r e was p r o b a b l y near t o a s u p p l y of c o n t i n e n t a l d e t r i t u s . 58 A l t e r n a t i v e l y , c o n t r i b u t i o n t o the a r c of mantle which i s anomalously r a d i o g e n i c , r e l a t i v e t o the e s t i m a t e d Devonian mantle v a l u e (Doe e t a l . 1985), i s r e q u i r e d t o e x p l a i n the d a t a . 2.5.3. Age c o n s i d e r a t i o n s A n a l y s e s of a l l of the S i c k e r Group r o c k s sampled i n t h i s study (Table 2.2) a r e p l o t t e d i n F i g u r e s 2.6 and 2.7. These f i g u r e s show the g e n e r a l c o l i n e a r i t y of t h e whole r o c k d a t a . The b e s t f i t l i n e through a l l of the d a t a i n F i g u r e 2.6, u s i n g the l e a s t squares r e g r e s s i o n method of York (1969), g i v e s an i s o c h r o n age of 496 Ma + 76 Ma. The l a r g e e r r o r i n t h i s age e s t i m a t e r e f l e c t s the v a r i a t i o n i n i n i t i a l r a t i o s f o r S i c k e r Group r o c k s shown by the B u t t l e Lake g a l e n a d a t a . Whole r o c k m o d i f i e d C o n c o r d i a method ( R u s s e l l e t a l . 1967; U l r y c h 1969) u s i n g the p r i m o r d i a l l e a d c o m p o s i t i o n of Tatsumoto e t a l . (1 973) g i v e s an age of 416 ± 90 Ma f o r the lower i n t e r c e p t , and an upper i n t e r c e p t age of 4379 + 17 Ma (Table 2.6, F i g . 2.8). T h i s method r e l i e s upon the assumptions t h a t i n i t i a l r a t i o s were homogeneous and t h a t l e a d e v o l u t i o n o c c u r r e d i n a c l o s e d system. N e i t h e r assumption can be shown t o be a p p r o p r i a t e f o r the S i c k e r Group, hence the l a r g e u n c e r t a i n t i e s a s s o c i a t e d w i t h the age d e t e r m i n a t i o n . Rubidium and s t r o n t i u m i s o t o p e d a t a f o r the S i c k e r Group TABLE 2.6. Data for the Concordia p l o t (Fig. 2.8). Primordial lead composition i s from Tatsumoto et a l . (1973) as follows: 206pD/204pb = 9.307, 207pb/204pb = 10.294, 208pb/204pb = 29.476. Figures given i n brackets are one sigma uncertainties, based on propagation of errors associated with the lead isotope data and the ju values, from the program "CONCORD" (Appendix D). SAMPLE NAME 238rj/204pb1 206pb/238u 207pb/235tJ MB1 11 .08 (0.27) 0 .838 (0.020) 65.817 (1 .573) MB2 161 .58(17.38) 0 .102 (0.010) 4.846 (0 .471 ) GRHY 17 .98 (0.60) 0 .560 (0.018) 40.896 (1 .323) R90 22 .96 (2.47) 0 .444 (0.043) 32.110 (3 .119) R129 12 .59 (1.84) 0 .815 (0.104) 58.459. (7 .456) R130 17 .07 (0.57) 0 .577 (0.019) 42.915 (1 .389) R131 26 .90 (0.50) 0 .394 (0.008) 27.417 (0 .509) H10A 13 .93 (0.12) 0 .741 (0.006) 52.955 (0 .461 ) H16 5 .37 (0.59) 1 .795 (0.178) 137.315(13 .596) H58B 47 .12 (5.28) 0 .238 (0.024) 15.751 (1 .587) S3 6 .32 (0.05) 1 .464 (0.012) 115.627 (0 .929) 1. ju values and t h e i r uncertainties are calculated using the program "WRUCLC" (Appendix D) for U ppm determined by isotope d i l u t i o n (Table 2.2), and using "MUCALC" for U ppm determined by neutron ac t i v a t i o n analysis. *°rpbi2Mu Figure 2.8. Whole rock Concordia p l o t f o r samples from the S i c k e r Group, Vancouver I s l a n d , B.C. Data are i n Table 2.6. Open squares represent samples from Cowichan - Home Lake U p l i f t ; open t r i a n g l e s r e p r e s e n t samples from B u t t l Lake U p l i f t . 61 (Table 2.7) do not p r o v i d e age i n f o r m a t i o n , because of the s c a t t e r e d n a t u r e of t h e a n a l y s e s . T h i s i s p r o b a b l y due t o the f a c t t h a t many of the r o c k s have been metamorphosed s i n c e t h e i r time of f o r m a t i o n so the i s o t o p e system has been a t l e a s t p a r t i a l l y r e s e t . I t i s a l s o p o s s i b l e t h a t the S i c k e r Group does not have a s i n g l e i n i t i a l 8 7 s r / 8 6 s r , but t h a t t h e r e i s a range of a p p r o p r i a t e v a l u e s . T h i s i s t r u e f o r many i s l a n d a r c s . One a n a l y s i s of g a l e n a from the A l b e r n i a r e a (sample S457, Table 2.3, F i g s . 2.2 and 2.3) has a l e s s r a d i o g e n i c l e a d i s o t o p e s i g n a t u r e than do the s y n g e n e t i c massive s u l p h i d e o re d e p o s i t s of both the B u t t l e Lake mine and the Mount S i c k e r o r e s . T h i s may mean one of two t h i n g s , e i t h e r the A l b e r n i sample i s from an o l d e r m i n e r a l i z a t i o n e v e n t , or the i n i t i a l r a t i o s w i t h i n the S i c k e r Group a r e more v a r i a b l e than s uggested by the galena l e a d i s o t o p e r a t i o s of the B u t t l e Lake, and Lenora and Tyee ore d e p o s i t s . The time d i f f e r e n c e r e p r e s e n t e d i n the 206pb/204pb d i f f e r e n c e between sample S457 and the H-W o r e i s 100 t o 150 Ma ( u s i n g LI v a l u e s of between 8 and 12) . I f the H-W o r e i s c o r r e c t l y d a t e d a t 365 Ma, an o l d e r m i n e r a l i z a t i o n event i n the S i c k e r a t 465-515 Ma i s r e q u i r e d t o e x p l a i n the g a l e n a S457. T h i s seems h i g h l y u n l i k e l y s i n c e r o c k s of t h i s age have not y e t been i d e n t i f i e d i n the S i c k e r Group. U n f o r t u n a t e l y the geology TABLE 2.7. Rubidium and strontium isotope data for the Sicker Group, Vancouver I s l a n d , B.C. I n i t i a l r a t i o s are c a l c u l a t e d at 370 Ma, using decay constants recommended by Stei g e r and Jager (1977). SAMPLE NUMBER Sr ppm Rb ppm Rb/Sr 87Rb/86sr B7s r/86sr INITIAL REFERENCE (ALTERNATIVE) - 87sr/R6Sr MB1 (MB001) 295 1.0 0.003 0.010 0 . 7 0 5 0 0 . 7 0 4 9 MB2 (MB002) 143 21.5 0.150 0.434 0.7068 0.7045 R78 (SJR78) 50 14.1 0.283 0.81R 0.7086 0.7043 S. Juras ( i n progress) R90 (SJ90) 105 47.1 0.448 1.297 0.7094 0.7026 S. Juras ( i n progress) R1 31 307 54.8 0.179 0.517 0.7067 0.7040 III OA (79H-10A) 374 18.0 0.048 0. 1 39 0.7056 0.7049 Holbek (1980) 1116 (7911-16) 364 14.2 0.039 0.113 0.7058 0.7052 Holbek (1980) H58B (79H-58B) 22.2 54.3 2.450 7.101 0.7272 0.6898 Holbek (1980) S1QE (SickerlQE) 223 4.5 0.020 0.058 0.7039 0.7036 Armstrong et a J L . , 1986 S3 (Sicker 3) 39.6 ' 1.2 0.003 0.009 0.7055 0.7055 Armstrong et a_l. , 1986 CM 63 of the r o c k s a s s o c i a t e d w i t h the anomalous sample has not been d i s c l o s e d (Walker p e r s . comm. 1985). F u r t h e r work i s r e q u i r e d t o e s t a b l i s h the n a t u r e of the d i f f e r e n c e i n i s o t o p i c c o m p o s i t i o n between the anomalous sample (S457) and the p r o d u c t i v e massive s u l p h i d e s i n the S i c k e r Group. 2.6. CONCLUSIONS The S i c k e r Group v o l c a n i c r o c k s have been i s o t o p i c a l l y c h a r a c t e r i z e d by whole r o c k and g a l e n a l e a d i s o t o p e a n a l y s e s . Common l e a d age d e t e r m i n a t i o n methods a r e t o o i m p r e c i s e t o c o n t r i b u t e t o an u n d e r s t a n d i n g of the a b s o l u t e age of the S i c k e r Group. However, a number of c o n c l u s i o n s can be drawn from the i s o t o p i c d a t a : 1) S i c k e r Group l e a d i s o t o p e r a t i o s a r e t y p i c a l of those of an i s l a n d a r c . 2) High 207pb/204pb r a t i o s r e l a t i v e t o an e s t i m a t e d Devonian mantle v a l u e i n d i c a t e s c r u s t a l i n v o l v e m e n t i n the f o r m a t i o n of the S i c k e r Group v o l c a n i c r o c k s . T h i s s u g g e s t s t h a t c o n t i n e n t a l d e t r i t u s was a v a i l a b l e t o the t r e n c h r e l a t e d t o s u b d u c t i o n and a r c - f o r m a t i o n , and t h a t the a r c formed c l o s e t o a c o n t i n e n t a l l a n d mass. A l t e r n a t i v e l y , an anomalous mantle so u r c e i s r e q u i r e d . 3) A decrease i n the 207pb/204pb r a t i o of both o r e s and r o c k s 64 w i t h time i n the Myra F o r m a t i o n a t B u t t l e Lake s u p p o r t s the h y p o t h e s i s t h a t the magmas p r o d u c i n g t h e s e o r e s became more p r i m i t i v e w i t h t i m e , and f a v o u r s a b a c k - a r c o r i g i n f o r Kuroko-type v o l c a n o g e n i c massive s u l p h i d e s . 4) The S i c k e r Group r o c k s a r e not d i r e c t e q u i v a l e n t s of the West Shasta v o l c a n i c r o c k s . There are s i g n i f i c a n t i s o t o p i c d i f f e r e n c e s between the two a r e a s . 5) Galena l e a d i s o t o p e r a t i o s f o r the Lenora and Tyee ore d e p o s i t s i n the Cowichan Lake U p l i f t a r e so s i m i l a r t o those of the B u t t l e Lake ore d e p o s i t s t h a t i t seems u n l i k e l y t h a t t h e r e i s an age d i f f e r e n c e of 20 Ma or more between them, as r e q u i r e d by the i n t e r p r e t a t i o n of Brandon e t a l . (1986). The g a l e n a l e a d i s o t o p e i n f o r m a t i o n , h e r e , s h o u l d be r e c o n c i l e d i n any age e s t i m a t i o n s f o r the S i c k e r Group. 65 CHAPTER 3 ISOTOPE GEOCHEMISTRY OF THE KARMUTSEN VOLCANICS SYNOPSIS Lead i s o t o p e r a t i o s of the T r i a s s i c f l o o d b a s a l t s of the Karmutsen F o r m a t i o n a r e heterogeneous. E v i d e n c e f o r i s o t o p i c m i x i n g suggests t h a t one end-member has a low l e a d c o n t e n t , low 207pb/204pb and 8 7 s r / 8 6 s r , but h i g h 206pb/204pb and 208pb/204pb r e l a t i v e t o a second l e a d - r i c h end-member. The da t a can be e x p l a i n e d i n terms of c r u s t a l c o n t a m i n a t i o n of a t h o r i u m e n r i c h e d mantle s o u r c e . 3.1 INTRODUCTION The Karmutsen F o r m a t i o n i s a L a t e T r i a s s i c sequence of subaqueous t o s u b a e r i a l t h o l e i i t i c v o l c a n i c r o c k s of p r e d o m i n a n t l y b a s a l t i c c o m p o s i t i o n , r e a c h i n g a t h i c k n e s s of 6,000 m ( M u l l e r 1977). I t o v e r l i e s the P a l e o z o i c S i c k e r Group and i s o v e r l a i n by L a t e T r i a s s i c ( L a t e K a r n i a n t o E a r l y N o r i a n ) c a r b o n a t e s ( C a r l i s l e and S u z u k i 1974; M u l l e r e t a l . 1974; 66 J e l e t s k y 1970). I t forms a major p a r t of the o u t c r o p of Vancouver I s l a n d and i s a dominant and c h a r a c t e r i s t i c f e a t u r e of W r a n g e l l i a (Jones e t a_l. 1977). Concordant z i r c o n d a t e s of 217 t o 222 Ma have been o b t a i n e d f o r a K a r m u t s e n - r e l a t e d i n t r u s i v e r o c k ( I s a c h s e n e t a l . 1985). T h i s sample (S1AM) p r o v i d e s an i s o t o p i c e s t i m a t e of the age of these r o c k s which agrees w e l l w i t h the f o s s i l age of between 228 and 232 Ma u s i n g the DNAG t i m e s c a l e of Palmer (1983). Sample S1AM was a n a l y s e d f o r i t s common l e a d i s o t o p i c c o m p o s i t i o n i n t h i s s tudy (see T a b l e 3.2). Karmutsen F o r m a t i o n r o c k s a re g e n e r a l l y a c c e p t e d as the e q u i v a l e n t s of the N i k o l a i Greenstone of A l a s k a ( M u l l e r 1977). C h i l k a t b a s a l t s from the Taku t e r r a n e , A l a s k a , a r e a l s o thought t o b e l o n g t o the same group of b a s a l t s ( D a v i s and P l a f k e r 1985). Major element geo c h e m i c a l a n a l y s e s f a i l t o d i s c r i m i n a t e a d e q u a t e l y between p l a t e t e c t o n i c s e t t i n g s f o r these v o l c a n i c r o c k s ( B a r k e r e t a_l. 1985). On v a r i o u s d i s c r i m i n a n t diagrams they p l o t as mid-ocean r i d g e b a s a l t s (MORB), b a c k - a r c , w i t h i n p l a t e o r i s l a n d a r c t h o l e i i t e s . The purpose of t h i s study i s t o i s o t o p i c a l l y f i n g e r p r i n t t he Karmutsen F o r m a t i o n and t o use i s o t o p i c c o m p o s i t i o n and the c o n c e n t r a t i o n s of l e a d , uranium and t h o r i u m t o f u r t h e r d i s c r i m i n a t e between p l a t e t e c t o n i c s e t t i n g s 67 f o r t h i s type of b a s a l t . Samples were o b t a i n e d from s e v e r a l l o c a t i o n s on Vancouver I s l a n d ( F i g . 3.1 and T a b l e 3.1). The B u t t l e Lake mine ro a d , c e n t r a l Vancouver I s l a n d , p r o v i d e d a s u i t a b l e t r a n s e c t a l o n g which t o c o l l e c t samples from d i f f e r e n t s t r a t i g r a p h i c l e v e l s ( F i g . 3.1 and Table 3.1: samples KAR1, KAR2, KAR7 and KAS10, and K008). B a s a l t samples were a l s o o b t a i n e d from P i p e r ' s Lagoon on the e a s t c o a s t of Vancouver I s l a n d , about 10 km n o r t h of Nanaimo ( F i g . 3.1 and T a b l e 3.1: samples K005 and K007). Whole rock samples K609, K610, K612, K613 and S1AM were o b t a i n e d , i n powdered form, from the c o l l e c t i o n s of J . M u l l e r and R.L. Armstrong. One sample of r h y o d a c i t e from t h e Malksope R i v e r a r e a ( F i g . 3.1 and Table 3.1: sample K101) was a n a l y z e d . Two g a l e n a samples ( F i g . 3 . 1 and T a b l e 3.1) were a v a i l a b l e from d e p o s i t s of p r o b a b l e v e i n type w i t h i n the Karmutsen F o r m a t i o n . Lead m i n e r a l i z a t i o n i s v e r y r a r e i n t h e s e v o l c a n i c s p r o b a b l y r e f l e c t i n g the low c o n c e n t r a t i o n s of l e a d i n the r o c k s ( T a b l e 3.2). VICTORIA F i g u r e 3.1 D i s t r i b u t i o n of Karmutsen F o r m a t i o n r o c k s ( p a t t e r n e d ) on Vancouver I s l a n d , B.C., w i t h whole r o c k ( c i r c l e s ) and g a l e n a ( s q u a r e s ) sample l o c a t i o n s (Table 3.1). TABLE 3.1 Whole rock and galena sample locations (see F i g . 3.1) and b r i e f descriptions. NAME"! LAT. LONG. DESCRIPTION K005 49 .23 123 .95 Basalt. Piper's Lagoon K007 49 .23 123 .95 Basalt. Piper's Lagoon K008 49 .79 125 .60 Pi l l o w basalt. Buttle Lake Road K101 50 .17 127 .35 Rhyodacite. Malksope River K609 49 .94 124 .62 Basalt. Upper Campbell Lake, East side, 7 km south southeast of dam, Buttle Lake Road. K610 49 .31 124 .74 Basalt, somewhat altered. Between Marshy and Lucy lakes. K612 49 .37 124 .69 S p i l i t i c basalt. North of Home Lake. K613 49 .25 124 .87 Basalt. Sproat Lake road, east of S t i r l i n g Arm. K616 49 .23 124 .94 Basalt. South of S t i r l i n g Arm, Sproat lake. KAR1 49 .67 125 .53 S i l l - l i k e massive basalt. Buttle Lake Road. KAR2 49 .69 125 .55 Massive basalt. Buttle Lake Road KAR7 49 .85 125 .62 Amygdaloidal, scoriaceous basalt. Buttle Lake Road KAR10 49 .94 125 .61 Massive basalt near Dolly Varden Point, Buttle Lake Road. KAR11 49 .99 125 .41 Massive, fine-grained basalt, Echo Lake, Buttle Lake Road. S1AM 48 .87 123 .71 Hornblende gabbro dyke intrus i v e into Sicker Group rocks - 2.9 km south of Chemainus River bridge, Highway 1 K314 49 .06 124 .71 Galena - S t a r l i g h t prospect K335 49 .75 124 .59 Galena - Nutcracker prospect (Texada Island) 1. A l l rock samples were collected by C.I. Godwin, except S1AM which i s from the c o l l e c t i o n of R.L. Armstrong. Galena samples are from the Economic c o l l e c t i o n at the University of B r i t i s h Columbia. TABLE 3.2 Lead, uranium and thorium data from Karmutsen v o l c a n i c rocks and r e l a t e d galena lead isotope analyses, Vancouver Island, B.C. Data s i t e s are located i n Figure 3.1 and Table 3.1. SAMPLE NAME 206PB/204pol 2O7PB/204PB1 208pu/204 p[i 1 PB PPM U PPM U PPM TH PPM yf, k7 ( T . D. ) 2 , 3 ( i . D. ) 2 , 4 ( N . A . A . ) 5 ( D. N . ) 5 Whole rock samples K005 19. .18 3(0. ,01 2) 15. .605(0. ,01 1 ) 38. ,814(0. .033 ) 1 . . 36 19. .224(0. .009) 15. .618(0, .009) 38 .881(0 .030) 1 . . 42 K005-AVG ln = 2) 19 .204(0. .01 1 ) 15, .612(0, .010) 38. .848(0 . 03 2 ) 1 , . 39 0. .31(0, .01 ) 0.34 0.95 14.2 2.9 K007 19 .741(0, .01 3) 1 5 , .629(0, .010) 39 .238(0 .031 ) 19 .658(0, .023) 15. .584(0, .017) 39. .370(0, .049) 19 .733(0. .026) 15. .602(0. .020 ) 39, .202(0 .056 ) K007-AVG (n=3) 19 .711(0. .02 2 ) 15. .605(0, .01 3 ) 39, .270(0, .051 ) 0 .91 0 . 32(0. .01 ) 0.36 0.97 22.1 2.8 K008 19 .696(0, .037) 15. .590(0, .029) 39. .364(0, .078) 19 .672(0. .01 3 ) 15. ,599(0, .008) 39, .345(0, .029) 19. .660(0. .034 ) 15. .553(0. .029 ) 39 , .263( 0, .071 ) K008-AVG (n = 3) 19 .676(0. .01 1 ) 15. .581(0, .014 ) 39, .324(0, .031 ) 0, .54 0. .23(0. .01 ) nd nd 27.1 na K101 #1 21 . SO 6 ( 0 , .008) 15. .772(0. .008) 40. .151(0. .030) 1, .52 nd nd nd na na K101 #2 20. .262(0, .008) 1 5 , .675(0, .008) 39, .509(0. .028) 1. .52 nd nd nd na na K609 IB .575(0, .031 ) 1 5 . .407(0, .025) 38, .298(0. .069) nd nd nd nd na na K61 0 18 .449(0, .029) IS , .427(0, .025) 37 , .852(0, .063) 18 .361(0, .021 ) 1 5 , .428(0, .019) 37, .760(0, .050) K610-AVG (n = 2) 18. .405(0. .025) 1 5 . .428(0. .022) 37 , .806(0. .057 ) nd nd nd nd na na K61 2 19. .306(0. .061 ) 1 5 . .627(0, .050) 38, .747(0, .125) nd nd nd nd na na K61 3 1 7 , .946(0. .010) 1 5 , .379(0. .010) 37 . 679(0, .031 ) nd nd nd nd na na KAR1 19. .361(0. .01 3 ) 15 , .601(0, .012) 38. .860(0, .037 ) 1, .86 nd nd nd na na o TABLE 3.2 (continued) SAMPLE NAME 2 0 6 P B / 2 0 4 P B ' 2 0 7 P B / 2 0 4 P B 1 2 0 8 P B / 2 0 4 P B 1 P B P P M U T P M ( I . D . ) 2 , 3 < 1 . D. ) 2 , 4 U P P M Til P P M (N.A.A.)5 (D.N.)5 k7 Whole rock samples (continued) KAR2 19 .000(0, .01 3) 1 5 .599(0 .012) 38. .568(0 .036) 18, .998(0, .009) 15 .598(0 .009) 38, . 569(0 .030) KAR2-AVG (n=2) 18, .999(0, .009) 15, .598(0 .011) 38 , .569(0, .033 ) nd ' nd nd nd na na KAR7 19, .397(0, .01 5) 15 .592(0, .01 4 ) 38, .951(0 .039) 19, .416(0. .01 1 ) 15, .587(0, .010 ) 38 , .975(0 .033) KAR7-AVG (n = 2) 19, .407(0. .01 3) 15, .590(0, .01 2) 38 . 963(0, .036) nd nd nd nd na na KAR1 0 18, .71 5(0. .01 1 ) 15, .551(0, .010) 38. .144(0 .031 ) 18. .728(0. .01 0) 1 5 , .563(0. .008 ) 38 . 176(0, .030) KAR10-AVG (n = 2) 18. .722(0. ,01 1 ) 15, .557(0. .009 ) 38. .160(0. .031 ) 3.91 nd nd nd na na KAR1 1 18. .999(0. .007) 15, .583(0. .008 ) 38. .325( 0. .028) 18. .928(0. ,01 2) 15. .588(0. .01 1 ) 38 . 313(0. .033 ) KAR11-AVG <n = 2) 18, .963(0. .010) 15. .586(0. .010) 38. .319(0. .031 ) 1 .23 0.44(0.01) nd nd 22.9 na S1 AM 18. .748(0. .008) 15. .614(0. .009) 38. .469(0. .029) 5. 37 nd 0.7* 1 .4* 8.31 2.1 Galena Samples K31 4 18, .661(0. ,003) 15. .569(0. .004 ) 38. .233(0. .01 5) K335 18, .707(0. ,007) 15, .574(0. .009 ) 38 . 268(0. .020) 1. Figures given in brackets are one sigma u n c e r t a i n t i e s based on the a d d i t i o n of in-run p r e c i s i o n and mass f r a c t i o n a t i o n u n c e r t a i n t i e s , except where given for average values. Figure given in brackets f o l l o w i n g averaged values is one standard e r r o r of the mean value for n > 2. If n=2 the pooled standard d e v i a t i o n i s g i v e n . 2. I.D. i s isotope d i l u t i o n a n a l y s i s (Appendix B ) . nd = not determined. 3. U n c e r t a i n t i e s are estimated to be 0.1 ppm based on d u p l i c a t e analyses (Appendix B : Table B.12). 4. Figures given in brackets are u n c e r t a i n t i e s based on er r o r propagation c a l c u l a t i o n s , using program "WRUCLC" (Appendix D). 5. N.A.A. stands for Neutron A c t i v a t i o n A n a l y s i s . D.N. i s delayed neutron counting. D e t a i l s of techniques used and u n c e r t a i n t i e s are in Chapter 1. Analyses marked with an a s t e r i x were analyzed at TRIUMF by L. Erdman. A l l others were done by Neutron A c t i v a t i o n S e r v i c e s Ltd., Hamilton, Ontario. 6. p Values (238u/204pt>) are c a l c u l a t e d using U (I.D.) ppm. na = not a p p l i c a b l e . 7. k values (232Th/238u) are c a l c u l a t e d using U (N.A.A.) and Th (D.N.) values, na = not a p p l i c a b l e . 72 3.2 ISOTOPIC DATA 3.2.1 Lead i s o t o p e c o m p o s i t i o n s f o r r o c k s and o r e s Whole r o c k l e a d i s o t o p e c o m p o s i t i o n s f o r the Karmutsen F o r m a t i o n ( T a b l e 3.2) a r e p l o t t e d i n F i g u r e 3.2. S e v e r a l i n i t i a l v a l u e s (Table 3.3) a r e a l s o shown. These have been c a l c u l a t e d u s i n g measured ja and k v a l u e s ( T a b l e 3.2) and an assumed age of 220 Ma. The g a l e n a a n a l y s e s (Table 3.2) p l o t w i t h the whole r o c k i n i t i a l v a l u e s . T h i s c o n d i t i o n i s t o be e x p e c t e d i f the l e a d i n the g a l e n a has the same age and source as the l e a d i n the r o c k s . Three of the samples (K609, K610 and K613) have low 207pb/204pb v a l u e s , which were not d u p l i c a t e d by any of the f r e s h l y c r u s h e d r o c k s , d e s p i t e the f a c t t h a t KAR10 was o b t a i n e d from a s i m i l a r l o c a t i o n as K609. S e v e r a l p o s s i b i l i t i e s e x i s t t o e x p l a i n t h i s apparent d i s c r e p a n c y : 1) There a r e r e a l , major h e t e r o g e n e i t i e s i n the Karmutsen l e a d d a t a . S i m i l a r l a r g e ranges i n 207pb/204pb v a l u e s e x i s t i n the d a t a from the Deccan f l o o d b a s a l t s ( A l l e g r e e t a l . 1982). 2) The o l d r o c k powders a r e c o n t a m i n a t e d . T h i s may have o c c u r e d d u r i n g s t o r a g e or d u r i n g t h e c r u s h i n g s t a g e , which was not done s p e c i f i c a l l y f o r l e a d i s o t o p e a n a l y s e s . O l d sample powders from the Bonanza Group r o c k s u i t e a l s o have low 207pb/204pb s i g n a t u r e s which were not d u p l i c a t e d by the f r e s h r o c k s . T h i s , t h e r e f o r e , seems the most p r o b a b l e r e a s o n . 73 F i g u r e 3.2 a) 207pb/204pb v e r s u s 206pb/204 Pb and b) 208pb/204pb v e r s u s 206pb/204pb p l o t of whole ro c k l e a d i s o t o p e d a t a ( T a b l e s 3.2 and 3.3) from the Karmutsen F o r m a t i o n and r e l a t e d galena samples (Table 3.2). V e c t o r s j o i n p r e s e n t v a l u e s t o i n i t i a l v a l u e s of the same r o c k , based on a 220 Ma age and measured p v a l u e s . D u p l i c a t e d or t r i p l i c a t e d a n a l y s e s a r e e n c l o s e d w i t h i n dashed l i n e s . The growth c u r v e , marked "S & K", i s t h a t of Stacey and Kramers (1975). A s o l i d l i n e e n c l o s e s whole rock i n i t i a l r a t i o s and g a l e n a a n a l y s e s . Open c i r c l e s mark e s t i m a t e d c o m p o s i t i o n s of two p o s s i b l e end-members t h a t may c o n t r i b u t e l e a d t o the r o c k s (see t e x t f o r d e t a i l s ) . 74 75 TABLE 3.3 I n i t i a l l e a d i s o t o p e r a t i o s a t 220 Ma f o r the Karmutsen F o r m a t i o n v o l c a n i c r o c k s , Vancouver I s l a n d , B.C. I n i t i a l r a t i o s , c a l c u l a t e d from d a t a i n T a b l e 3.2, are p l o t t e d i n F i g u r e s 3.2 and 3.3. NAME 206pB/204pBl 207PB/204PB1 208PB/204PB1 K005 1 8 .71 (0 .01 ) 15. 59 (0 .01 ) 38.40 (0.07) K007 1 8 .94 (0 .04 ) 15. 57 (0 .03 ) 38.60 (0.14) K008 1 8 .74 (0 .06) 15. 53 (0 .01 ) not a p p l i c a b l e KAR1 1 1 8 .17 (0 .01 ) 15. 55 (0 .01 ) not a p p l i c a b l e S1 AM 1 8 .46 (0 .03 ) 15. 60 (0 .01 ) 38.28 (0.04) MEAN (1S) 18 .61 (0 .30 ) 15. 57 (0 .03 ) 38.43 (0.16) 1. F i g u r e s i n b r a c k e t s a r e the one sigma u n c e r t a i n t i e s c a l c u l a t e d u s i n g the e r r o r p r o p a g a t i o n program "T1CORR" (Appendix D). These r e p r e s e n t a n a l y t i c a l u n c e r t a i n t i e s , but g e o l o g i c a l u n c e r t a i n t y , a r i s i n g from th e unknown h i s t o r y of uranium and t h o r i u m s i n c e time of f o r m a t i o n , i s not i n c l u d e d . 76 3) The f r e s h r o c k s a r e c o n t a m i n a t e d . T h i s i s u n l i k e l y because of the s p e c i a l c a r e t a k e n d u r i n g c r u s h i n g . C o n t a m i n a t i o n d u r i n g a n a l y s i s by a d d i t i o n of l a b b l a n k i s not a p o s s i b l e e x p l a n a t i o n because of good agreement between d u p l i c a t e a n a l y s e s done at d i f f e r e n t t i m e s . A l s o , the g a l e n a samples have l e a d s i g n a t u r e s which agree w i t h the h i g h e r 207pb/204pb v a l u e s of the f r e s h r o c k s . Poor d u p l i c a t i o n of sample K101 ( F i g . 3.2) i s p r o b a b l y due t o sample inhomogeneity. 3.2.2 Comparison of Karmutsen F o r m a t i o n l e a d i s o t o p i c d a t a w i t h  t h o s e of w e l l known b a s a l t s R e p r e s e n t a t i v e f i e l d s f o r b a s a l t s from s e v e r a l d i f f e r e n t p l a t e t e c t o n i c environments are shown w i t h t h e Karmutsen F o r m a t i o n l e a d i s o t o p e d a t a i n F i g u r e s 3.3 and 3.4. A l l f i e l d s have been a d j u s t e d t o 220 Ma u s i n g the l e a d e v o l u t i o n model of S t a c e y and Kramers (1975). T h i s a p p r o x i m a t i o n f a c i l i t a t e s comparison of the Karmutsen whole r o c k i n i t i a l r a t i o s w i t h r a t i o s f o r younger b a s a l t s . Karmutsen F o r m a t i o n i n i t i a l r a t i o s p a r t i a l l y o v e r l a p most of the f i e l d s shown ( F i g s . 3.3 and 3.4). H i g h e r 207p D/204pb and 208pb/204pb r a t i o s than MORBs f o r most of the samples r u l e out an o r i g i n of Karmutsen F o r m a t i o n b a s a l t s a t a mid-ocean r i d g e . There a r e s i m i l a r i t i e s i n the i s o t o p i c f i e l d s of the Karmutsen F o r m a t i o n w i t h i s l a n d a r c t h o l e i i t e s and ocean i s l a n d b a s a l t s 77 F i g u r e 3.3 Comparison of Karmutsen F o r m a t i o n whole r o c k i n i t i a l r a t i o s a t 220 Ma (open t r i a n g l e s ) and Karmutsen g a l e n a (open squares) w i t h 207pb/204pb and 206pb/204pb f i e l d s a d j u s t e d t o 220 Ma ( u s i n g S t a c e y and Kramers 1975 growth c u r v e , "S & K") of ocean i s l a n d b a s a l t s (Sun and Jahn 1975; Sun 1980; Tatsumoto 1978; Weis 1983); i s l a n d a r c s (Oversby and Ewart 1972; M e i j e r 1976; Kay e t a l . 1978; Church 1976); mid ocean r i d g e b a s a l t s (Church and Tatsumoto 1975; B r e v a r t e t a l . 1981; V i d a l and C l a u e r 1981); P a c i f i c sediments (Church 1976; Sun 1980; V i d a l and C l a u e r 1981). —I co 79 F i g u r e 3.4 Comparison of Karmutsen i n i t i a l r a t i o s a t 220 Ma (open t r i a n g l e s ) and Karmutsen g a l e n a (open squares) w i t h 208pb/204pb and 206pb/204pb f i e l d s , a d j u s t e d ~ t o 220 Ma ( u s i n g S t a c e y and Kramers 1975 growth c u r v e , "S & K " ) , of mid-ocean r i d g e s , i s l a n d a r c s , ocean i s l a n d b a s a l t s and P a c i f i c s e d iments. For r e f e r e n c e s t o source of d a t a see F i g u r e 3.3. co o 81 ( F i g s . 3.3 and 3.4), and w i t h v a r i o u s c o n t i n e n t a l f l o o d b a s a l t s ( F i g s . 3.5 and 3.6). F i g u r e 3.5 shows c o n s i d e r a b l e o v e r l a p between the i s o t o p i c r a t i o s of the Karmutsen F o r m a t i o n , and C h i l c o t i n b a s a l t s , some ty p e s of Columbia R i v e r f l o o d b a s a l t s (Imnaha and P i c t u r e Gorge b a s a l t s ) , and Deccan Trap b a s a l t s . The f i e l d s f o r s e v e r a l c o n t i n e n t a l f l o o d b a s a l t s a r e s e p a r a t e d i n F i g u r e 3.6 due t o h i g h l y , v a r i a b l e 208pb/204pb r a t i o s . The Karmutsen F o r m a t i o n i n i t i a l r a t i o s p l o t w i t h some of the Columbia R i v e r b a s a l t s , but are i n t e r m e d i a t e between the C h i l c o t i n and Deccan f l o o d b a s a l t s . 3.2.3 Lead, uranium and t h o r i u m c o n c e n t r a t i o n s Lead, uranium and t h o r i u m c o n c e n t r a t i o n s a r e r e p o r t e d f o r MORBs, OIBs, i s l a n d a r c t h o l e i i t e s and C h i l c o t i n f l o o d b a s a l t s ( T a b l e 3.4). There a r e d i f f e r e n c e s i n the a b s o l u t e abundances of these elements i n each t e c t o n i c environment. Comparison of l e a d , uranium and t h o r i u m c o n c e n t r a t i o n s of the Karmutsen b a s a l t s w i t h o t h e r b a s a l t s ( T a b l e 3.4; F i g . 3.7) shows t h a t t h e y a r e r i c h e r i n l e a d than MORBs, y e t p o o r e r i n l e a d than t y p i c a l i s l a n d a r c s . There i s a c l o s e s i m i l a r i t y i n the l e a d , uranium and t h o r i u m c o n t e n t of Karmutsen b a s a l t s w i t h the C h i l c o t i n b a s a l t s and w i t h ocean i s l a n d b a s a l t s . T h i s comparison does, however, assume t h a t the l e a d , uranium and t h o r i u m c o n c e n t r a t i o n s have remained r e l a t i v e l y unchanged s i n c e t h e time of f o r m a t i o n of b a s a l t s of 82 F i g u r e 3.5 207pb/204pb v e r s u s 206pb/204pb diagram showing g e n e r a l i z e d f i e l d s of i s o t o p e d a t a from c o n t i n e n t a l f l o o d b a s a l t s ( a d j u s t e d t o 220 Ma u s i n g S t a c e y and Kramers 1975 growth c u r v e , "S & K " ) , and Karmutsen F o r m a t i o n i n i t i a l r a t i o s a t 220 Ma (open t r i a n g l e s : T able 3.3) and g a l e n a (open s q u a r e s : Table 3.2). Data are from Leeman and Manton (1972), A l l e g r e e t a l . (1982), B e v i e r (1982), C a r l s o n (1984), and Church (1985). The Columbia R i v e r B a s a l t s f i e l d has been d i v i d e d i n t o two. F i e l d #1 c o n t a i n s a n a l y s e s from the Imnaha, Grande Ronde, P i c t u r e Gorge, and Wanapum f o r m a t i o n s . F i e l d #2 c o n t a i n s a n a l y s e s of the Saddle Mountains b a s a l t s . co 84 F i g u r e 3.6 208pb/204pb v e r s u s 206pb/204pb diagram showing g e n e r a l i z e d f i e l d s f o r c o n t i n e n t a l f l o o d b a s a l t s ( a d j u s t e d t o 220 Ma u s i n g S t a c e y and Kramers 1975 growth c u r v e , ~"S & K") and Karmutsen F o r m a t i o n whole r o c k i n i t i a l r a t i o s a t 220 Ma. See F i g u r e 3.5 f o r e x p l a n a t i o n of symbols and s o u r c e of d a t a . TABLE 3.4 T y p i c a l l e a d , u r a n i u m and t h o r i u m c o n c e n t r a t i o n s , w i t h maximum r a n g e s f o r v a r i o u s o c e a n i c and c o n t i n e n t a l b a s a l t s . BASALT TYPE REFERENCE PB PPM U PPM TH PPM C o n t i n e n t a l F l o o d B a s a l t s C h i l c o t i n B e v i e r (1982) 1 , .5(1 . 1 -2 .1 ) 0 .4(0. . 2 - 1 , .0) 1 .0(0 .6 -3, .5) C o l u m b i a R i v e r C a r l s o n (1984) 4 .0(0, .8 -8 .4) Mid-Ocean R i d g e B a s a l t s Leg 37 A t l . Cumming (1980) 0. .5(0 .4 -0, .7) 0, .2(0. . 1 -0 , .3) 0, .6(0. .4 -0, .9) J u a n de Fuca C h u r c h and T a t s u m o t o (1975) 0. .5(0, .2 -1 , .0) 0, .2(0. . 1 -0. .5) 0, .3(0. . 1 -0. .9) R e y k j anes Sun & J a h n (1975) 0. .5(0, .4 -0 , .7) 0, .1(0. . 1 -0. .2) 0, .4(0. .4 -0. .5) I s l a n d A r c M a r i a n a M e i j e r (1976) 1. .9(0, .6 -3. .0) 0 , .2(0. .2 -0. .3) 0, .7(0. .4 -1 , .1 ) A l e u t i a n s Kay e t al. ( 1978) 5. ,0( 3. .8 -8. .2) 1 . .0(0. .5 -1. .7) 2. .0(0 . .9 -4, .0) J a p a n T a t s u m o t o (1969) 3. ,7(1. , 7 -7 . , 1 ) 0 . 2(0. 1 -0. .4) 0. .2(0. , 1 -0 . 4) Tonga-Kermadec O v e r s b y and Ewart (1972) 2. .2(0. . 3 -4 . 2) 0. .2(0. , 1 -0. .4) Ocean I s l a n d s I c e l a n d Sun and J a h n (1975 ) 1 . .4(1. .0 -1 . 6) 0. .4(0. , 3 -0 . 6) 1 . 3(0. .9 -1 . 3) H a w a i i K i l a u e a Sun (1980) 1 . .7(1. . 3 -2. .0) 0 . 5(0. 4 -0 . 6) 1 . 4( 1 . ,0 -2. .0) Mauna Kea Sun (1980) 1 . 2 0 . 3 1 . 3 Mauna Loa Sun (1980) 0 . 8 0 . 2 0. .6 87 6 r K A R M U T S E N PPM 6 r 4h PPM O C E A N I S L A N D S Pb U Th 6 r M O R B PPM Pb U Th 6 r ISLAND A R C S 4 PPM 2 r 6 r C H I L C O T I N B A S A L T S PPM F i g u r e 3.7 Average l e a d , uranium and t h o r i u m c o n c e n t r a t i o n s f o r v a r i o u s b a s a l t t y p e s . See Ta b l e 3.4 f o r source of d a t a . 88 the Karmutsen F o r m a t i o n . 3.2.4 S t r o n t i u m d a t a I n i t i a l s t r o n t i u m r a t i o s v a r y from 0.703-0.704 (Table 3.5; Armstrong e t a l . i n p r e s s ) . T h i s i s h i g h e r than f o r MORBs and f o r the C h i l c o t i n b a s a l t s ( B e v i e r 1982), and lower t h a n f o r c o n t i n e n t a l c r u s t , but o t h e r w i s e not u s e f u l i n d i s c r i m i n a t i n g between t e c t o n i c e n v i r o n m e n t s . S t r o n t i u m and r u b i d i u m d a t a f o r the samples s t u d i e d i n t h i s t h e s i s a r e i n Table 3.4. Other d a t a f o r the Karmutsen F o r m a t i o n i s i n Armstrong e t a l . ( i n p r e s s ) . 3.2.5 E v i d e n c e f o r i s o t o p i c m i x i n g U-Pb and Th-Pb i s o c h r o n p l o t s a r e shown i n F i g u r e 3.8 w i t h the 220 Ma i s o c h r o n f o r r e f e r e n c e . The 207pb/204pb v e r s u s 235u/204pb p l o t ( F i g . 3.8b) c l e a r l y shows t h a t t h e Karmutsen v o l c a n i c s are not s i m p l y d e r i v e d from a s i n g l e s o u r c e , which had a homogeneous i n i t i a l r a t i o t h a t remained a c l o s e d system u n t i l the p r e s e n t . R a t h e r , m i x i n g must be i n v o k e d t o e x p l a i n the a p p a r e n t l y n e g a t i v e s l o p e . M i x i n g i s a l s o e v i d e n t i n F i g u r e 3.9, which shows the i n i t i a l l e a d r a t i o s p l o t t e d a g a i n s t the r e c i p r o c a l of l e a d c o n c e n t r a t i o n . U s i n g l e a s t squares r e g r e s s i o n , i t i s p o s s i b l e t o determine the b e s t f i t l i n e s t o the d a t a f o r each of the r a t i o s ( F i g . 3.10) and hence t o e s t i m a t e the end-member c o m p o s i t i o n s . TABLE 3.5 Rubidium and strontium isotope data for the Karmutsen Formation, Vancouver I s l a n d , D.C. I n i t i a l r a t i o s are c a l c u l a t e d f or an age of 220 Ma, using decay c o n s t a n t s recommended by S t e i g e r and Jager ( 1 977 ). A l l data have been r e p o r t e d i n Armstrong et a 1. ( i n p r e s s ) . SAMPLE NUMBER Sr PPM Rb PPM 87 Rb/86 Sr 8 7 S r / 8 6 S r AGE INITIAL (ALTERNATIVE) (ASSUMED) 8 7 S r / 8 6 S r K005 (G84VI005) 241 10. 8 0.129 0 . 7040 220 Ma 0.7036 K007 (G84VI007) 223 1 7 . 8 0.231 0.7040 220 Ma 0.7033 K609 (IGC5A2) 368 13. 8 0.107 0.7044 220 Ma 0.7041 K610 (63-12N) 182 8. 2 0.130 0.7043 220 Ma 0.7039 K612 (63-78A) 270 32 . 0 0.341 0.7055 220 Ma 0.7044 Leached 170 1 9 . 6 0.336 0.7048 220 Ma 0.7037 K613 (63-87D) 263 5. 8 0.064 0 .7041 220 Ma 0.7039 K616 (67-20C) 288 3. 6 0.036 0.7040 220 Ma 0.7039 KAR1 1 473 1 1 . 6 0.071 0 .7040 220 Ma 0.7038 K101 (BP-SELCO) 29.9 70. 9 6 .870 0.7235 220 Ma1 0.70201 S1AM 223 5. 5 0.058 0.7039 220 Ma 0.7037 1. Using a two p o i n t isochron with one poi n t at K101 and the other at the average value f o r the b a s a l t samples with 87sr/86sr = 0.7040 + 0.0001 and 87Rb/86sr = 0.122 + 0.079, the age i s 203 t 5 Ha. Co to 90 k005 T k007 SI A M o 10 ao so «o F i g u r e 3.8. U-Pb and Th-Pb i s o c h r o n p l o t s f o r the Karmutsen Formation, Vancouver I s l a n d , B.C. Data i s i n Table 3.2. The 220 Ma r e f e r e n c e i s o c h r o n i s drawn, i n each case, through the mean i n i t i a l v a lue (Table 3.3). E r r o r bars mark the one sigma a n a l y t i c a l u n c e r t a i n t i e s i n the le a d r a t i o s (Table 3.2), and one sigma u n c e r t a i n t i e s i n U/Pb and Th/Pb r a t i o s of 10% and 14% r e s p e c t i v e l y . 91 F i g u r e 3.9 a) I n i t i a l 208pb/204pb v e r s u s 1/Pb (ppm), b) i n i t i a l 207pb/204p'b v e r s u s 1/Pb (ppm) and c) i n i t i a l 206pb/204pb v e r s u s 1/Pb (ppm) p l o t f o r Karmutsen F o r m a t i o n s r o c k s , Vancouver I s l a n d , B.C. Data are i n T a b l e s 3.2 and 3.3. E r r o r b ars mark the one sigma u n c e r t a i n t i e s i n the i n i t i a l r a t i o s and l e a d c o n c e n t r a t i o n s c a l c u l a t e d by e r r o r p r o p a g a t i o n (Table 3.3). Best f i t l i n e s by l e a s t squares r e g r e s s i o n and c o r r e l a t i o n c o e f f i c i e n t s ( r ) are shown f o r each p l o t . E s t i m a t e d end-member i s o t o p i c c o m p o s i t i o n s ( c i r c l e s ) a re shown f o r 1/Pb = 0.1 (10 ppm) and 1/Pb = 2.0 (0.5 ppm). to to 93 F i g u r e 3.9b shows a c o r r e l a t i o n ( c o r r e l a t i o n c o e f f i c i e n t r=-0.87) between 207pb/204pb and 1/Pb. T a k i n g a v a l u e of 10 ppm f o r the l e a d - r i c h end-member, which i s a s u i t a b l e v a l u e f o r ocean se d i m e n t s , the c o r r e s p o n d i n g 207pb/204pb r a t i o i s 15.602 ( F i g . 3.9b). C h o i c e of a d i f f e r e n t l e a d c o n t e n t f o r t h i s end-member would not s i g n i f i c a n t l y change t h e i s o t o p e r a t i o . A le a d - p o o r end-member w i t h a l e a d c o n t e n t of 0.5 ppm, which i s a s u i t a b l e mantle v a l u e , has a c o r r e s p o n d i n g 207pb/204pb v a l u e of 15.523. Lower 207pb/204pb v a l u e s can be a c h i e v e d by c h o o s i n g a lower l e a d c o n t e n t f o r t h i s end-member. The i n i t i a l 208?b/204pb v e r s u s 1/Pb diagram ( F i g . 3.9a) shows t h a t the l e a d - r i c h end-member has a lower 208pb/204pb r a t i o than the l e a d - p o o r end-member. The c o r r e l a t i o n c o e f f i c i e n t ( r ) f o r t h i s r e l a t i o n s h i p i s 0.97, but i s based on o n l y t h r e e samples. U s i n g the b e s t - f i t l i n e ( F i g . 3.9a), the 208pb/204pb c o m p o s i t i o n s a r e 38.231 and 38.884 f o r the l e a d - r i c h and l e a d - p o o r end-members r e s p e c t i v e l y . C o r r e l a t i o n between i n i t i a l 206pb/204pb and 1/Pb i n F i g u r e 3.9c i s p o o r e r t h a n f o r the o t h e r r a t i o s (r=0.44). T h i s i s p r o b a b l y because the p o s t - f o r m a t i o n i n s i t u a d d i t i o n of r a d i o g e n i c l e a d i s g r e a t e s t f o r t h i s r a t i o . Any uranium or l e a d l o s s or g a i n s i n c e the time of f o r m a t i o n w i l l t e n d t o obscure 94 the o r i g i n a l r e l a t i o n s h i p by making i t i m p o s s i b l e t o c a l c u l a t e the c o r r e c t i n i t i a l r a t i o s . There i s , however, a s u g g e s t i o n t h a t the l e a d - r i c h end-member has a lower 206pb/204pb r a t i o than the lea d - p o o r one. U s i n g the same c r i t e r i o n as above the 206pb/204pb r a t i o s a r e 18.425 and 18.833 f o r the l e a d - r i c h and lea d - p o o r s o u r c e s r e p e c t i v e l y . / The e s t i m a t e d end-member l e a d i s o t o p e c o m p o s i t i o n s a re shown i n F i g u r e 3.2. The l e a d - r i c h end-member p l o t s c l o s e t o the 220 Ma p o i n t on the average c r u s t a l l e a d growth c u r v e of Stacey and Kramers (1975) i n both f i g u r e s . P a c i f i c ocean sediments a l s o have a s i m i l a r i s o t o p i c c o m p o s i t i o n . The l e a d - p o o r end-member p l o t s c l o s e t o the mantle (MORB) t r e n d i n F i g u r e 3.2a, a t h i g h e r 206pb/204pb v a l u e s than f o r MORB. I t t h e r e f o r e resembles an OIB-type mantle s o u r c e . I t does not p l o t a t the end of the a r r a y of i n i t i a l d a ta i n F i g u r e 3.2b, and has h i g h e r 208pb/204pb v a l u e s t h a n OIB-type mantle. T h i s i s p o s s i b l y because t h e 208pb/204pb end-members were chosen on the b a s i s of o n l y t h r e e samples. I f the 206pb/204pb r a t i o s were d e t e r m i n e d u s i n g t h e same t h r e e samples, the 206pb/204pb r a t i o r e q u i r e d f o r the lea d - p o o r end-member would be h i g h e r , p r o d u c i n g a more s u i t a b l e end-member c o m p o s i t i o n , but s t i l l w i t h h i g h e r 208pb/204pb than t y p i c a l OIB-type m a n t l e . A l t e r n a t i v e l y , i f i n i t i a l 208pb/204pb data were a v a i l a b l e f o r more samples, the 208pb/204pb e s t i m a t e f o r the le a d - p o o r end-member might be lo w e r . 95 F i g u r e 3.10 shows a p o s i t i v e c o r r e l a t i o n (r=0.90) of 238u/204pb w i t h 1/Pb. Thus t h e l e a d - r i c h end-member has a lower ju v a l u e (10 a t 10ppm) than the l e a d - p o o r end-member (31 a t 0.5 ppm). These v a l u e s a r e a p p r o p r i a t e f o r ocean sediments and e n r i c h e d mantle r e s p e c t i v e l y . The r e l a t i o n s h i p between i n i t i a l s t r o n t i u m and 206pb/204pb r a t i o s i s i l l u s t r a t e d i n F i g u r e 3.11. The h i g h e r i n i t i a l s t r o n t i u m v a l u e s , which presumably r e p r e s e n t t h e c r u s t a l end-member, have lower 206pb/204pb v a l u e s . T h i s c o n f i r m s t h a t the l e a d - r i c h (presumably c r u s t a l ) end-member has a lower 206pb/204pb v a l u e than the l e a d - p o o r (presumably mantle) end-member. Samples K609, K610 and K613 must have i n i t i a l r a t i o s t h a t are lower than t h e i r p r e s e n t v a l u e s . They do not f i t the c o r r e l a t i o n diagrams, because low 207pb/204pb v a l u e s a re a s s o c i a t e d w i t h low 206pb/204pb and 208pb/204pb v a l u e s . They r e q u i r e the i n v o l v e m e n t of a t h i r d component, perhaps s i m i l a r t o d e p l e t e d m a n t l e , u n l e s s they a r e u n r e l i a b l e samples as suggested i n s e c t i o n 3.2.1. I n the absence of r e q u i r e d t o c a l c u l a t e the l e a d and uranium c o n c e t r a t i o n i n i t i a l r a t i o s , i t would s t i l l be data p o s s i b l e 40 S1AM I : 1 1 r-0.5 1.0 1.5 2.0 1 /Pb ppm F i g u r e 3.10 238u/204pb ve r s u s 1/Pb (ppm) f o r the Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C. A b e s t f i t l i n e by l e a s t squares r e g r e s s i o n i s shown, w i t h e s t i m a t e d end-member i s o t o p i c c o m p o s i t i o n s f o r 1/Pb (ppm) = 0.1 (10 ppm) and 1/Pb = 2.0 (0 . 5 ppm). E r r o r bars mark one sigma u n c e r t a i n t i e s i n the 238u/204pb of the g r e a t e r of 10% or e r r o r p r o p a g a t i o n u s i n g "MUCALC", and one sigma u n c e r t a i n t y i n 1/Pb (ppm) of the g r e a t e r of 3% or e r r o r p r o p a g a t i o n u s i n g "WRPBID". 0.706 -• k612 18.0 19.0 20.0 P b / 2 0 4 P b F i g u r e 3.11 87sr/86sr v e r s u s 206pb/204pb diagram f o r the Karmutsen F o r m a t i o n , Vancouver I s l a n d , B.C. Pres e n t r a t i o s ( f i l l e d t r i a n g l e s ) a r e connected t o i n i t i a l r a t i o s (open t r i a n g l e s ) a t 220 Ma by c o r r e c t i o n v e c t o r s . The MORB c o r r e l a t i o n l i n e i s t h a t of Hamelin e t a l . (1984a). A c o r r e l a t i o n l i n e a d j u s t e d t o 220 Ma u s i n g a Rb/Sr v a l u e of 0.01 and mu v a l u e of 10 i s a l s o shown. Data are i n T a b l e s 3.2, 3.3 and 3.5. 98 t o o b s e r v e the m i x i n g r e l a t i o n s h i p by u s i n g a s i m p l e t e c h n i q u e t o a d j u s t 207pb/204pb r a t i o s . T h i s t e c h n i q u e i s d e s c r i b e d i n Appendix E. 3.3 DISCUSSION Any p e t r o g e n e t i c model f o r the Karmutsen F o r m a t i o n has to e x p l a i n the f o l l o w i n g g e n e r a l o b s e r v a t i o n s : 1) Most of the data d i s p l a y m i x i n g between two end-members. The lead-p o o r s o u r c e has lower 207pb/204pb, and i n i t i a l 87sr/86sr, but h i g h e r 206pb/204pb, 208pb/204pb, and 238u/204pb than the l e a d - r i c h s o u r c e . 2) The l e a d - r i c h s o u r c e has the c h a r a c t e r i s t i c s of average c r u s t , by comparison w i t h S t a c e y and Kramers (1975) growth c u r v e . 3) The l e a d - p o o r source has h i g h e r 206pb/204pb and 208pb/204pb than MORB. C r u s t a l c o n t a m i n a t i o n of a m a n t l e - d e r i v e d magma can e x p l a i n t h e s e o b s e r v a t i o n s . Oxygen i s o t o p e d a t a f o r the Karmutsen F o r m a t i o n a re i n the range £18o=7.6 t o 14 . 9 per m i l (Muhlenbachs, w r i t t e n communication, 1986); c o n s i s t e n t w i t h the c r u s t a l c o n t a m i n a t i o n h y p o t h e s i s . There a re s e v e r a l p o s s i b l e types of c r u s t a l c o n t a m i n a n t s , mantle s o u r c e s and c o n t a m i n a t i o n 99 mechanisms, each of which are d i s c u s s e d below. 3.3.1 C r u s t a l contaminant The l e a d - r i c h end-member has an i s o t o p i c composition that p l o t s c l o s e to the 220 Ma p o i n t on Stacey and Kramers (1975) c r u s t a l l e a d growth curve ( F i g . 3.2). P a c i f i c sediments at 220 Ma are of a s u i t a b l e i s o t o p i c composition ( F i g s . 3.3 and 3.4). The l a b o r a t o r y blank l e a d i s o t o p i c composition a l s o has s i m i l a r values (Appendix B), which r a i s e s the q u e s t i o n of contamination d u r i n g a n a l y s i s . D u p l i c a t e analyses are good i n ge n e r a l f o r the Karmutsen samples r u l i n g out the p o s s i b i l i t y of v a r i a b l e blank contamination d u r i n g a n a l y s i s . Contamination p r i o r to a n a l y s i s i s u n l i k e l y because of the care taken d u r i n g the c r u s h i n g and subsequent stages. The samples with the l e a s t l e a d would be expected to be the most contaminated, whereas i t i s the samples with the h i g h e s t l e a d contents which show the g r e a t e s t degree of contamination with the ' c r u s t a l ' l e a d component. I t i s extremely u n l i k e l y , t h e r e f o r e , t h a t the contamination d i d occur d u r i n g a n a l y s i s . 3.3.2 Mantle source The i s o t o p i c composition of the lead-poor source has a low 207pb/204pb r a t i o , and p l o t s with t y p i c a l oceanic mantle ( F i g . 3.2a). The 20'6pb/204pb and 208pb/204pb r a t i o s are, however, 100 h i g h e r than t y p i c a l MORB, so the mantle source more c l o s e l y resembles an OIB-type s o u r c e . A mantle source e n r i c h e d i n t h o r i u m i s r e q u i r e d t o e x p l a i n the h i g h e r 208pb/204pb v a l u e s than t y p i c a l OIB m a ntle. The l o w e s t 207pb/204pb samples (K609, K610, and K613), a l s o have low 206pb/204pb r a t i o s , and may t h e r e f o r e r e p r e s e n t a second mantle s o u r c e , which resembles d e p l e t e d mantle ( F i g s . 3.3 and 3.4). Nd a n a l y s e s of the same r o c k s would h e l p t o determine the n a t u r e of the mantle source or s o u r c e s . 3.3.3 M i x i n g mechanisms There a r e s e v e r a l p o s s i b l e ways f o r i s o t o p i c m i x i n g t o have t a k e n p l a c e . Three of t h e s e a r e : 1) A s s i m i l a t i o n of c r u s t a l m a t e r i a l by m a n t l e - d e r i v e d magmas. 2) S h a l l o w r e c y c l i n g of subducted sediments i n t o a b a c k - a r c environment 3) Deep r e c y c l i n g of subducted s e d i m e n t s . Rocks from the Devonian i s l a n d a r c assemblage do not have a s u i t a b l e i s o t o p i c c o m p o s i t i o n t o be the c r u s t a l contaminant. A s s i m i l a t i o n of S i c k e r Group m a t e r i a l i s n o t , t h e r e f o r e , a p o s s i b l e e x p l a n a t i o n f o r the i s o t o p i c m i x i n g o b s e r v e d i n the Karmutsen F o r m a t i o n b a s a l t s . P e l a g i c sediments i n t e r b e d d e d w i t h the Karmutsen l a v a f l o w s may have had a s u i t a b l e i s o t o p i c 1 01 c o m p o s i t i o n , but i t i s u n l i k e l y t h a t l e a d from t h e s e sediments c o u l d have become i n c o r p o r a t e d i n t o the v o l c a n i c r o c k s i n the subaqueous environment. R e c y c l i n g of subducted c r u s t a l m a t e r i a l i n t o t h e mantle i s a more l i k e l y p o s s i b i l i t y . Church (1984) e x p l a i n s 'mixed' i s o t o p i c c h a r a c t e r i s t i c s of the Columbia R i v e r B a s a l t s of Washington and Oregon, by i n v o k i n g s h a l l o w r e c y c l i n g of sediments i n t r o d u c e d i n t o the back a r c environment by s u b d u c t i o n . Deep r e c y c l i n g of s e d i m e n t a r y m a t e r i a l i s proposed t o e x p l a i n neodymium, l e a d and s t r o n t i u m c h a r a c t e r i s t i c s of b a c k - a r c b a s a l t g l a s s e s i n the South Sandwich I s l a n d s (Cohen and O'Nions 1982). The i s o t o p i c d a t a a v a i l a b l e so f a r can not a d e q u a t e l y d i s t i n g u i s h between these p o s s i b i l i t i e s . 3.3 CONCLUSIONS Lead i s o t o p e d a t a has been o b t a i n e d from s e v e r a l whole r o c k and g a l e n a samples from the Karmutsen F o r m a t i o n v o l c a n i c r o c k s of Vancouver I s l a n d . These, combined w i t h s t r o n t i u m i s o t o p e a n a l y s e s of some of the same r o c k s , l e a d t o t h e f o l l o w i n g g e n e r a l c o n c l u s i o n s : 1) The Karmutsen F o r m a t i o n d i d not o r i g i n a t e a t a mid-ocean r i d g e . 207pb/204pb, 208pb/204pb and i n i t i a l 8 7 s r / 8 6 s r r a t i o s 102 are t oo h i g h . 2) Lead, uranium and t h o r i u m c o n c e n t r a t i o n s a r e g r e a t e r i n Karmutsen b a s a l t s than i n MORBs, but l e s s t h a n i s l a n d a re t h o l e i i t e s . They a r e s i m i l a r t o those of ocean i s l a n d s and c o n t i n e n t a l f l o o d b a s a l t s . 3) Whole r o c k i n i t i a l r a t i o s ( e x c e p t f o r t h r e e low 207pb/204pb samples) p l o t w i t h two g a l e n a samples i n both 207pb/204pb and 208pb/204pb v e r s u s 206pb/204pb diagrams. 4) A l l but t h r e e samples can be d e s c r i b e d i n terms of i s o t o p i c m i x i n g between two end-members. 5) A l e a d - p o o r end-member has lower 207pb/204pb and i n i t i a l 8 7 s r / 8 6 s r , but h i g h e r 206pb/204pb, 208pb/204pb and 238u/204pb th a n a l e a d - r i c h end-member. I t resembles ocean i s l a n d mantle. 6) The l e a d - r i c h end-member has average c r u s t a l i s o t o p i c c h a r a c t e r i s t i c s . 7) A t h i r d end-member, p o s s i b l y s i m i l a r t o d e p l e t e d mantle, i s r e q u i r e d t o e x p l a i n t h r e e , low 207pb/204pb samples, but these samples may be c o n t a m i n a t e d . 8) I s o t o p i c d a t a f o r t h e Karmutsen F o r m a t i o n can be e x p l a i n e d i n terms of the c r u s t a l c o n t a m i n a t i o n of magma from t h o r i u m - e n r i c h e d m a n t l e , but the c o n t a m i n a t i o n mechanisms cannot be u n i q u e l y i d e n t i f i e d . 9) I s o t o p i c d a t a a r e c o n s i s t e n t w i t h the o r i g i n of the Karmutsen F o r m a t i o n b a s a l t s i n a s i m i l a r manner t o those of o t h e r f l o o d b a s a l t s , such as the Columbia R i v e r B a s a l t s and the C h i l c o t i n b a s a l t s , i n a b a c k - a r c r i f t i n g environment. 104 CHAPTER 4 ISOTOPE GEOCHEMISTRY OF THE BONANZA GROUP AND ISLAND INTRUSIONS SYNOPSIS Lead i s o t o p e a n a l y s e s of f i v e p l u t o n i c r o c k s from the I s l a n d I n t r u s i o n s and s i x v o l c a n i c r o c k s from the Bonanza Group s u p p o r t a comagmatic o r i g i n f o r the two J u r a s s i c r o c k s u i t e s . Lead and s t r o n t i u m i s o t o p e systems cannot a d e q u a t e l y d i s t i n g u i s h between an i s l a n d a r c or an o c e a n i c i s l a n d o r i g i n f o r these r o c k s . C a l c u l a t e d i n i t i a l l e a d i s o t o p e r a t i o s f a l l on a l i n e a r t r e n d i n both 207pb/204pb v e r s u s 206pb/204pb, and 208pb/204pb v e r s u s 206pb/204pb p l o t s . I f i n t e r p r e t e d as a m i x i n g l i n e , the more r a d i o g e n i c end-member has a c o m p o s i t i o n which i s lower i n 207pb/204pb and h i g h e r i n 206pb/204pb than t y p i c a l upper c o n t i n e n t a l c r u s t . A s s i m i l a t i o n of S i c k e r Group m a t e r i a l d u r i n g emplacement of the i n t r u s i o n s may e x p l a i n the m i x i n g t r e n d . Galena l e a d i s o t o p e s from a v e i n w i t h i n the I s l a n d Copper p o r p h y r y d e p o s i t p l o t w i t h the i n i t i a l r a t i o s f o r Bonanza Group v o l c a n i c s and I s l a n d I n t r u s i o n s , c o n f i r m i n g the h y p o t h e s i s t h a t t h i s m i n e r a l i z a t i o n i s r e l a t e d t o the J u r a s s i c i s l a n d a r c 105 v o l c a n i c e vent. 4.1 INTRODUCTION The Bonanza Group, named by Gunning (1932), i s a sequence of c a l c - a l k a l i n e p y r o c l a s t i c , e x t r u s i v e and h y p a b y s s a l v o l c a n i c r o c k s w i t h minor i n t e r c a l a t e d s ediments. The sediments c o n t a i n E a r l y J u r a s s i c f o s s i l s ( M u l l e r e t a l . 1974), which g i v e an age range of 204 t o 187 Ma u s i n g the DNAG t i m e s c a l e (Palmer 1983). The v o l c a n i c r o c k s range i n c o m p o s i t i o n from b a s a l t i c a n d e s i t e and d a c i t e a t the base, t o r h y o l i t i c and r h y o d a c i t i c r o c k s t h a t a r e i n t e r b e d d e d w i t h b a s a l t i c a n d e s i t e and a n d e s i t e h i g h e r i n the sequence ( N o r t h c o t e and M u l l e r 1972). They o v e r l i e b a s a l t s of the T r i a s s i c Karmutsen F o r m a t i o n and l i m e s t o n e and s h a l e of the T r i a s s i c Q u a t s i n o and Parson Bay F o r m a t i o n s . The I s l a n d I n t r u s i o n s , thought t o be the p l u t o n i c e q u i v a l e n t s of the l a t e r s t a g e s of Bonanza v o l c a n i s m ( N o r t h c o t e and M u l l e r 1972), a r e m a i n l y g r a n o d i o r i t i c , and u n d e r l i e 30% of Vancouver I s l a n d ( F i g . 4.1). Chemical v a r i a t i o n diagrams show t h a t both i n t r u s i v e and v o l c a n i c s u i t e s f o l l o w t h e same d i f f e r e n t i a t i o n t r e n d s ( N o r t h c o t e and M u l l e r 1972). Age e s t i m a t e s f o r both Bonanza Group v o l c a n i c r o c k s and I s l a n d I n t r u s i o n s a re summarized i n Ta b l e 4.1. K-Ar ages o b t a i n e d f o r 106 F i g u r e 4.1 D i s t r i b u t i o n of Bonanza Group v o l c a n i c r o c k s ( d o t t e d ) and I s l a n d I n t r u s i o n s (igneous p a t t e r n ) on Vancouver I s l a n d , B.C. Whole ro c k sample l o c a t i o n s f o r Bonanza Group r o c k s are marked w i t h s q u a r e s , and I s l a n d I n t r u s i o n s are marked w i t h c i r c l e s . The I s l a n d Copper porp h y r y d e p o s i t i s marked w i t h a c r o s s . Sample d e t a i l s are i n T a b l e 4.2. 107 both s u i t e s show c o n s i d e r a b l e o v e r l a p , w i t h Bonanza v o l c a n i c ages r a n g i n g from 138 Ma t o 164 Ma ( N o r t h c o t e and M u l l e r 1972), and I s l a n d I n t r u s i o n s from 145 Ma t o 184 Ma ( M u l l e r 1977). More r e c e n t z i r c o n a n a l y s e s by I s a c h s e n (1984), and Rb-Sr i s o c h r o n s (Armstrong e t a l . i n p r e s s ) , suggest t h a t 190 Ma i s a b e t t e r e s t i m a t e of the age of t h e s e r o c k s , the p r e v i o u s ages b e i n g minimum e s t i m a t e s . N o r t h c o t e and M u l l e r (1972) and Souther (1977) proposed t h a t the Bonanza Group v o l c a n i c r o c k s and I s l a n d I n t r u s i o n s are comagmatic and r e p r e s e n t an i s l a n d a r c v o l c a n i c assemblage. I n t h i s s tudy l e a d and s t r o n t i u m i s o t o p e s a r e used as t r a c e r s t o t e s t t h i s h y p o t h e s i s , t o f i n g e r p r i n t t h e s e two r o c k s u i t e s i s o t o p i c a l l y , and t o compare t h e i r i s o t o p i c c h a r a c t e r i s t i c s w i t h those of modern p l a t e t e c t o n i c s e t t i n g s . F i v e samples from the I s l a n d I n t r u s i o n s , and s i x from the v o l c a n i c r o c k s of the Bonanza Group have been a n a l y z e d f o r l e a d and/or s t r o n t i u m i s o t o p i c c o m p o s i t i o n s . Sample l o c a t i o n s are i n F i g u r e 4.1. T a b l e 4.2 l o c a t e s the c o o r d i n a t e s of t h e samples t o g e t h e r w i t h b r i e f sample d e s c r i p t i o n s . A n a l y s e s are i n Table 4.3. A l l samples of the I s l a n d I n t r u s i o n s have uranium and t h o r i u m c o n c e n t r a t i o n s measured by gamma ra y s p e c t r o s c o p y , and l e a d c o n c e n t r a t i o n s o b t a i n e d by i s o t o p e d i l u t i o n . D e t a i l s of e x p e r i m e n t a l p r o c e d u r e s f o r l e a d i s o t o p e c o m p o s i t i o n s and 108 TABLE 4.1 Summary of age d e t e r m i n a t i o n s f o r the Bonanza Group and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C. METHOD AGE (MA)1 REFERENCE I s l a n d I n t r u s i o n s Z i r c o n Pb/Pb 1 8 7 + 6 U-Pb 126 t o 175 Armstrong e t a l . i n p r e s s Armstrong e t a l . i n p r e s s K-Ar - 145 t o 184 M u l l e r 1977, Carson 1972, N o r t h c o t e and Robinson 1972 Rb-Sr 1 83 +_ 7 Armstrong e t a l . i n p r e s s Bonanza Group K-Ar 138 t o 164 N o r t h c o t e and M u l l e r 1972 Rb-Sr 179 + 5 Armstrong e t a l . i n p r e s s 1. Ages p u b l i s h e d p r i o r t o decay c o n s t a n t s of S t e i g e r 1 977 and have been a d j u s t e d t o the new J a g e r (1977). 109 TABLE 4 .2 L o c a t i o n s and b r i e f d e s c r i p t i o n s of samples from the Bonanza Group and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C. A n a l y s e s a re r e p o r t e d i n T a b l e 4.3. SAMPLE LAT. LONG DESCRIPTION NORTH WEST Bonanza Group MT59 50.71 127. 97 A l t e r e d a n d e s i t e . MT360 50 .65 1 27 . 83 A l t e r e d a n d e s i t e . B61 9 50.46 128. 06 A n d e s i t e . 1.5 t o 3.5 km northwe s t of Cape P a r k i n s . B620 50 .47 1 28. 06 B a s a l t . L o c a t i o n i s same as B619. B621 50 .47 128. 06 B a s a l t . L o c a t i o n i s same as B619. B625 50 .1 1 1 27 . 1 4 R h y o l i t e . N o r t h shore of T a h s i s h I n l e t . I s l a n d I n t r u s i o n s 681381 50 .24 126. 46 Quartz monzonite. Nimpkish b a t h o l i t h 5 km n o r t h e a s t of Hoomak Lake. 682122 50 .1 9 126. 37 Quartz d i o r i t e . N i m pkish b a t h o l i t h 10 km E, 1 km South of Hoomak Lake 683171 50 .03 1 27 . 09 Quartz monzonite. Amai I n l e t p l u t o n . 683421 50 .31 125. 58 G r a n o d i o r i t e . Pye Lake p l u t o n on r o a d t o Rock Bay. 692131 50 .31 126. 06 G r a n o d i o r i t e . Adam R i v e r p l u t o n , n o r t h e a s t of Mount J u l i e t . I s l a n d Copper g a l e n a ISCU 50.61 1 27 . 48 Galena from v e i n s i n I s l a n d Copper p o r p h y r y copper-molybdenum mine. TABLE 4.3 L e a d , u r a n i u m and t h o r i u m d a t a from t h e Bonanza Group v o l c a n i c r o c k s , and I s l a n d I n t r u s i o n s , V a n c o u v e r I s l a n d , B.C. L o c a t i o n s of samples a r e i n T a b l e 4.2. SAMPLE NAME 206PB/204PB1 207pB/204po1 208PB/204PB1 PB PPM ( 1 . D . ) 2 , U r 3 (I PPM . D . ) 2 , 4 U PPM (G.R.)5 TU PPM (G.R.)5 TH PPM ( I . D . ) 2 k7 Bonanza G roup v o l c a n i c r o c k s MT59 18. .535(0, .007 ) 1 5 , .548(0. .008) 38, .070(0.028) 4.06 3.91 0. 21 (0,01 ) nd nd nd 3.3 na MT360 MT360-AVG 18. 18. 18, .835(0, .825(0, .830(0, .008) .031 ) .022 ) 15, 15 , 15, .556(0. .557(0. .557(0, .008) .025) .019) 38. 38, 38, .170(0.029) .151(0.067) .161(0.052) 5.24 5.35 5. 30 1 . 4 7 ( 0 . 1 5 ) nd nd nd 17.7 na B61 98 18, .332(0, .007) 15, .505(0, .008) 37 , .729(0.028) nd nd nd nd nd na na B6208 17, ,657(0. .009) 15, .456(0. .01 0 ) 37. .279(0^031) nd nd nd nd nd na na B6218 18. .225(0. .010) 15, .453(0. .010) 37, .627(0.032) nd nd nd nd nd na na B6258 19. .680(0. .01 0) 15. .560(0. .010) 38. .854(0.032) 2.16 nd nd nd nd na na I s l a n d C o pper G a l e n a 18. 5 2 7 ( 0 . .011) 15. .555(0. , 009 ) 38 . 088(.024) T A B L E 4.3 ( c o n t i n u e d ) SAMPLE NAME 206PB/204PB1 207pB/204pRl 208pp./204PB 1 PB PPM U PPM U PPM TH PPM TH PPM u6 k7 ( I . D . ) 2 , 3 ( I . D . ) 2 , 4 (C..R.)5 (G.R.)5 ( I . D . ) 2 I s l a n d I n t r u s i o n s 681381 19.480(0.007) 15.594(0.008) 38.879(0.028) 4.12 1.47(0.02) 1.68 5.02 nd 2.3.1 3.1 682122 19.049(0.007) 15.578(0.008) 38.511(0.029) 2.73 nd 0.82 2.10 nd 16.6 2.7 683171 19.721(0.020) 15.645(0.017) 38.985(0.049) IC D u p l i c a t e 1 9 . 747(0.007) 15.621(0.008) 38.937(0.027) 683171-AVG 19.734(0.015) 15.633(0.013) 38.961(0.040) 5.60 nd 2 .71 7 .41 nd 27.1 2.8 683421 1 9 . 1 0 9 ( 0 . 0 0 7 ) 15.587(0.008) 38.744(0.028) 5.11 1.04(0.01) ID d u p l i c a t e 5.02 1.03(0.01) 1.13 5.71 nd 13.1 5.2 692131 1 8 . 9 7 6 ( 0 . 0 0 7 ) 15.566(0.008) 38.311(0.027) 6.28 2.12(0.02) 2.29 5.16 4.91 21 .6 2.3 1. F i g u r e s g i v e n i n b r a c k e t s a r e t h e one sigma u n c e r t a i n t i e s based on t h e a d d i t i o n o f i n - r u n p r e c i s i o n and mass f r a c t i o n a t i o n u n c e r t a i n t i e s . 2. I.D. i s i s o t o p e d i l u t i o n a n a l y s i s ( A p p e n d i x R ) . nd = n o t d e t e r m i n e d . 3. U n c e r t a i n t y i n t h i s v a l u e i s e s t i m a t e d a t 0.1 ppm ( A p p e n d i x B; T a b l e B . 1 2 ) . 4. F i g u r e s g i v e n i n b r a c k e t s a r e u n c e r t a i n t i e s b a s e d on e r r o r p r o p a g a t i o n c a l c u l a t i o n s u s i n g t h e p r o g r a m "WRUCALC" (A ppe nd i x D) . 5. G.R. s t a n d s f o r gamma r a y s p e c t r o s c o p y . D e t a i l s of t e c h n i g u e s u s e d and u n c e r t a i n t i e s a r e i n C h a p t e r 1 . nd = n o t d e t e r m i n e d . 6. ji v a l u e s (23Bu/204pb) a r e c a l c u l a t e d u s i n g U ( I . D . ) ppm, o r U (G.R.) ppm w h i c h has been r e d u c e d by a f a c t o r o f 1.0935 ( A p p e n d i x B; T a b l e B . 1 3 ) . na = n o t a p p l i c a b l e . 7. k v a l u e s (232Th/238u) a r e c a l c u l a t e d u s i n g U (G.R.) and Th (G.R.) v a l u e s , na = n o t a p p l i c a b l e . 8. Samples B619, B620, B621 and B625 were p r e v i o u s l y c r u s h e d f o r Rb-Sr a n a l y s e s . These u n u s u a l l y low 207pb/204pb s i g n a t u r e s c o u l d n o t be d u p l i c a t e d by newl y c r u s h e d r o c k s , so the powders a r e p r o b a b l y c o n t a m i n a t e d . 112 i s o t o p e d i l u t i o n t e c h n i q u e s are i n Appendices A and B. Other methods are o u t l i n e d i n Chapter 1. The two Bonanza samples, MT59 and MT360, have uranium and l e a d c o n c e n t r a t i o n d a t a by i s o t o p e d i l u t i o n , but they were not a n a l y z e d f o r s t r o n t i u m . S e v e r a l Bonanza samples from s i m i l a r l o c a t i o n s have p r e v i o u s l y been a n a l y z e d f o r s t r o n t i u m (Armstrong e t a l . i n p r e s s ) . The l e a d i s o t o p e d a t a a q u i r e d from f o u r of these samples a re r e p o r t e d , but the l e a d s i g n a t u r e s c o u l d not be d u p l i c a t e d by f r e s h l y c r u s h e d samples, t h e r e f o r e i t i s l i k e l y t h a t the r e s u l t s are u n r e l i a b l e . 4.2 RESULTS Lead i s o t o p e r a t i o s of the Bonanza Group v o l c a n i c r o c k s and I s l a n d I n t r u s i o n s ( T a b l e 4.3) are p l o t t e d i n F i g u r e s 4.2 and 4.3. I n i t i a l l e a d r a t i o s ( T a ble 4.4) a r e shown f o r a 190 Ma time c o r r e c t i o n , u s i n g u v a l u e s o b t a i n e d by i s o t o p e d i l u t i o n methods where p o s s i b l e . Some of the I s l a n d I n t r u s i o n samples a r e c o r r e c t e d u s i n g u v a l u e s f o r which the uranium c o n c e n t r a t i o n s were d e t e r m i n e d by gamma r a y s p e c t r o s c o p y . A l l of t h e s e JJ. v a l u e s have been reduced by a f a c t o r of 1.0935 t o be c o n s i s t e n t w i t h p v a l u e s f o r which the uranium was de t e r m i n e d by i s o t o p e d i l u t i o n (see Chapter 1 ) . 113 F i g u r e 4 . 2 . 207pb/204pb v e r s u s 206pb/204pb p l o t of whole rock samples ( T a b l e 4.3) from the I s l a n d I n t r u s i o n s ( c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), Vancouver I s l a n d , B.C. One g a l e n a a n a l y s i s from I s l a n d Copper p o r p h y r y i s a l s o p l o t t e d (open s q u a r e ) . A n a l y s e s marked by an "x" a r e u n r e l i a b l e (see t e x t ) . I n i t i a l v a l u e s (open symbols) c a l c u l a t e d f o r an age of 190 Ma ( T a b l e 4.4) are connected t o the p r e s e n t v a l u e s ( s o l i d symbols) by c o r r e c t i o n v e c t o r s . The growth c u r v e shown, marked "S & K", i s t h a t of S t a c e y and Kramers (1975). F i e l d b o u n d a ries d e f i n e p r e s e n t and i n i t i a l r a t i o s of the I s l a n d I n t r u s i o n s . i s .es — i — 18.0 — I — 18.8 — I — 10.0 — I — 19.8 20.0 2 0 6 p b / 2 0 4 p b 1 1 5 F i g u r e 4.3 208pb/204pb v e r s u s 206pb/204pb p l o t of whole r o c k samples ( T a b l e 4.3) from the I s l a n d I n t r u s i o n s ( c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), Vancouver I s l a n d , B.C. One g a l e n a a n a l y s i s from I s l a n d Copper p o r p h y r y i s a l s o p l o t t e d , (open s q u a r e ) . A n a l y s e s marked by an "x" are u n r e l i a b l e (see t e x t ) . I n i t i a l v a l u e s (open symbols) c a l c u l a t e d f o r an age of 190 Ma (Table 4.4) a r e connected t o the p r e s e n t v a l u e s ( s o l i d symbols) by c o r r e c t i o n v e c t o r s . The growth c u r v e shown, marked "S & K", i s t h a t of St a c e y and Kramers (1975). F i e l d b o u n d a ries d e f i n e p r e s e n t and i n i t i a l r a t i o s of the I s l a n d I n t r u s i o n s . 11 TABLE 4.4 I n i t i a l l e a d i s o t o p e r a t i o s f o r the Bonanza Group and I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C. R a t i o s have been c o r r e c t e d f o r an assumed E a r l y J u r a s s i c age of 190 Ma. Decay c o n s t a n t s used a r e tho s e recommended by S t e i g e r and Jag e r (1977). u and k v a l u e s a r e i n T a b l e 4.3. NAME 206pb/204pb 207pb/204pb 208pb/204pb (+_ E r r o r l ) (+ E r r o r l ) (+ Error"! ) 18.44 (0.02) 18.30 (0.06) not a p p l i c a b l e not a p p l i c a b l e MT59 MT360 681381 682122 683171 683421 692131 1 8.79 18.55 18.92 18.72 18.33 (0.01 ) (0.05) (0.09) ( 0.01 ) (0.01 ) 15.54 1 5.53 15.56 1 5.55 1 5.59 15.57 1 5.53 (0.01) (0.02) (0.01 ) (0.01) (0.01) (0.01) (0.01 ) 38.20 38.09 38.24 38.10 37 .84 (0.09) (0.08) (0.14) (0.09) (0.07) 1. Numbers i n b r a c k e t s a r e e s t i m a t e d e r r o r s based on the p r o p a g a t i o n of u n c e r t a i n t i e s i n measured i s o t o p i c c o m p o s i t i o n s , and i n JJ and k v a l u e s . The program "T1CORR" (Appendix D) was used t o c a l c u l a t e these v a l u e s . 11 8 A l l of the data p l o t below S t a c e y and Kramer's (1975) curve f o r average c r u s t a l l e a d e v o l u t i o n , but w i t h h i g h e r 207pb/204pb v a l u e s than f o r the o c e a n i c t r e n d of Church and Tatsumoto (1975) ( F i g s . 4.2 and 4.3). The i n i t i a l r a t i o s f o r t h e I s l a n d I n t r u s i o n s have a l i n e a r t r e n d i n both the 207pb/204pb v e r s u s 206pb/204pb, and 208pb/204pb v e r s u s 206pb/204pb p l o t s ( F i g s . 4.2 and 4.3). T h i s l i n e a r r e l a t i o n s h i p can be shown t o be more s i g n i f i c a n t f o r the i n i t i a l r a t i o s than f o r the u n c o r r e c t e d d a t a by comparing c o r r e l a t i o n c o e f f i c i e n t s . The c o r r e l a t i o n c o e f f i c i e n t s f o r the u n c o r r e c t e d d a t a ( e x c l u d i n g I s l a n d Copper g a l e n a ) are 0.94 and 0.89 f o r F i g u r e s 4.2 and 4.3 r e s p e c t i v e l y . I n i t i a l l e a d r a t i o s d i s p l a y improved c o r r e l a t i o n c o e f f i c i e n t s of 0.95 and 0.96 d e s p i t e the o v e r a l l s h o r t e n i n g of the l e n g t h of the l i n e s ( F i g s . 4.2 and 4.3). A d d i t i o n of r a d i o g e n i c l e a d t o the r o c k s from 190 Ma t o 0 Ma has tended t o obscure the o r i g i n a l l i n e a r i t y . I n i t i a l l e a d i s o t o p e r a t i o s f o r two of the Bonanza Group v o l c a n i c r o c k s are c o l i n e a r w i t h t h o s e of the I s l a n d I n t r u s i o n s i n both 208pb/204pb v e r s u s 206pb/204pb, and 207pb/204pb v e r s u s 206pb/204pb p l o t s , s u p p o r t i n g a comagmatic o r i g i n f o r th e s e two r o c k u n i t s . Bonanza Group v o l c a n i c r o c k s have lower 207pb/204pb, 206pb/204pb and 208pb/204pb r a t i o s than those from p l u t o n i c r o c k s of the I s l a n d I n t r u s i o n s . 11 9 I s o t o p i c r a t i o s of g a l e n a from the I s l a n d Copper porphyry d e p o s i t near P o r t Hardy i s c o l i n e a r w i t h the i n i t i a l r a t i o s of b o t h Bonanza Group v o l c a n i c s and I s l a n d I n t r u s i o n s , i n d i c a t i n g a comagmatic o r i g i n f o r the m i n e r a l i z a t i o n . T h i s s u p p o r t s the J u r a s s i c age f o r the d e p o s i t d e t e r m i n e d by Rb-Sr age d e t e r m i n a t i o n , and by K-Ar on b i o t i t e from the Rupert I n l e t s t o c k ( N o r t h c o t e and Robinson 1972). G e n e r a l i z e d p l o t s of d a t a from v a r i o u s t e c t o n i c e nvironments a r e shown i n F i g u r e s 4.4 and 4.5 w i t h the l e a d d a t a f o r the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c s . D i r e c t comparison cannot be made between the l e a d i s o t o p e i n i t i a l r a t i o s and modern t e c t o n i c e n v i r o n m e n t s , so the modern l e a d i s o t o p e f i e l d s have been p r o j e c t e d back 190 Ma u s i n g Stacey and Kramers (1975) growth c u r v e . I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c l e a d d a t a o v e r l a p w i t h the f i e l d s f o r both ocean i s l a n d s and i s l a n d a r c s . S t r o n t i u m i s o t o p e d a t a a r e i n T a b l e 4.5. I n i t i a l s t r o n t i u m r a t i o s are i n the range 0.7033-0.7042, which i s w i t h i n the t y p i c a l ranges ( B a s a l t i c Study P r o j e c t 1981) of b oth ocean i s l a n d s (>0.703) and i s l a n d a r c s (0.7027-0.7062). Those Bonanza Group v o l c a n i c r o c k s , which have l e a d r a t i o s r e s e m b l i n g d e p l e t e d mantle v a l u e s ( F i g s . 4.4 and 4.5), do not have c o r r e s p o n d i n g l y 1 20 F i g u r e 4.4 207pb/204pb v e r s u s 206pb/204pb p l o t of i n i t i a l r a t i o s ( T a ble 4.4) f o r whole r o c k d a t a from the I s l a n d I n t r u s i o n s (open c i r c l e s ) , Bonanza Group v o l c a n i c r o c k s (diamonds) and g a l e n a from I s l a n d Copper p o r p h y r y d e p o s i t (open s q u a r e ) , Vancouver I s l a n d , B.C. T y p i c a l f i e l d s f o r modern mid-ocean r i d g e b a s a l t s (Church and Tatsumoto 1975; B r e v a r t e t a l . 1981; V i d a l and C l a u e r 1981), i s l a n d a r c s (Oversby and Ewart 1972; M e i j e r 1976; Kay e t a l . 1978), ocean i s l a n d s (Sun and Jann 1975; Sun 1980; Tatsumoto 1978; Weis 1983) and P a c i f i c sediments (Church 1 976; Sun 1 980; V i d a l and C l a u e r 19.81) are a l s o shown. A l l f i e l d s have been a d j u s t e d t o 190 Ma u s i n g S t a c e y and Kramers' (1975) growth c u r v e , marked "S & K". Whole r o c k l e a d i s o t o p e v a l u e s f o r S i c k e r Group v o l c a n i c r o c k s , c o r r e c t e d back t o 190 Ma u s i n g measured p v a l u e s (Table 2.3), are p l o t t e d as i n v e r t e d t r i a n g l e s . 122 F i g u r e 4.5 208pb/204pb v e r s u s 206pb/204pb p l o t of i n i t i a l r a t i o s (Table 4.4) f o r whole r o c k d a t a from the I s l a n d I n t r u s i o n s (open c i r c l e s ) and Bonanza Group v o l c a n i c r o c k s (diamonds), and g a l e n a d a t a from I s l a n d Copper p o r p h y r y d e p o s i t (open s q u a r e ) , Vancouver I s l a n d , B.C. The t y p i c a l f i e l d s f o r mid-ocean r i d g e b a s a l t s , i s l a n d a r c v o l c a n i c r o c k s , ocean i s l a n d s and P a c i f i c sediments (see F i g . 4.4 f o r r e f e r e n c e s ) are a l s o shown. Whole r o c k l e a d i s o t o p e v a l u e s f o r the S i c k e r Group v o l c a n i c r o c k s , c o r r e c t e d back t o 190 Ma u s i n g measured ju and k v a l u e s (Table 2.3), a r e p l o t t e d as i n v e r t e d t r i a n g l e s . Bonanza v o l c a n i c i n i t i a l r a t i o s (open diamonds) have been d e t e r m i n e d u s i n g measured u v a l u e s ( T a b l e 4.3) and an assumed k v a l u e of 3. These are shown connected t o the p r e s e n t r a t i o s ( s o l i d diamonds) w i t h c o r r e c t i o n v e c t o r s . 39.0 20.0 NJ TABLE 4.5 R u b i d i u m and s t r o n t i u m i s o t o p e d a t a f o r t h e I s l a n d I n t r u s i o n s and Bonanza G r o u p v o l c a n i c r o c k s , V a n c o u v e r I s l a n d , B.C. I n i t i a l r a t i o s a r e c a l c u l a t e d f o r an age of 190 Mn, u s i n g d e c a y c o n s t a n t s recommended by S t e i g e r and J a g e r ( 1 9 7 7 ) . Sample l o c a t i o n s a r e i n T a b l e 4.2. SAMPLE NUMBER (ALTERNATIVE) SR PPM RB PPM 87p,n/86sR 87SR/BC>SR AGIO I N I T I A L (ASSUMED) B7SR/R6.SR REFERENCE I s l a n d I n t r u s i o n s 681 381 (681 3811) 252 74.5 0.856 0.7056 190 Ma 0 . 7033 A r m s t r o n g e t a l . (1986) 682122 (682120) 373 683171 (683170) 179 31 .9 103 0.249 1 .670 0.7044 0 . 704 3 0.7084 1 90 Ma 190 Ma 190 Ma 0.7037 0 . 7036 0.7039 A r m s t r o n g e t a l . (1986) A r m s t r o n g e t a l . (1986) 683421 (683420) 253 47.4 0.541 0.7050 190 Ma 0.7035 A r m s t r o n g e t a l • (1986) 692131 (68213K) 330 68.8 0.603 0 . 7050 190 Ma 0.7034 A r m s t r o n g e t a l • (1986) Bonanza Group B619 (69S119L) 460.1 37.7 B620 (69S125A) 291.7 5.4 0.237 0.052 0 . 7048 0.7037 190 Ma 190 Ma 0.7042 0.7036 A r m s t r o n g e t a l . (1985) A r m s t r o n g e t a l . (1985) B621 (69S126A) 367.8 10.5 B625 (6822C) 46.1 65.8 0.081 4.134 0.7038 0.7145 190 Ma 190 Ma 0 . 7036 0.7033 A r m s t r o n g e t a l . (1985) A r m s t r o n g e t aU. (1985) 1. Age assumed f o r t h e I s l a n d I n t r u s i o n s i s b a s e d on z i r c o n a n a l y s e s of the I s l a n d I n t r u s i o n s ( s e e t e x t ) . 125 low i n i t i a l s t r o n t i u m v a l u e s . A l l the Bonanza Group samples were a l t e r e d t o some e x t e n t so t h a t t h e s t r o n t i u m r a t i o s measured may not be r e l i a b l e . There i s a . p o s i t i v e c o r r e l a t i o n between i n i t i a l 207pb/204pb and i n i t i a l 8 7 s r / 8 6 s r f o r d a t a from the I s l a n d I n t r u s i o n s ( F i g . 4.6). 4.3 DISCUSSION Lead and s t r o n t i u m i s o t o p e r a t i o s are c o n s i t e n t w i t h the o r i g i n of the Bonanza Group v o l c a n i c r o c k s and the I s l a n d I n t r u s i o n s e i t h e r i n an o c e a n i c i s l a n d or an i s l a n d a r c t e c t o n i c s e t t i n g . Both p o s s i b i l i t i e s are e x p l o r e d f u r t h e r i n the f o l l o w i n g s e c t i o n s . 4.3.1 An ocean I s l a n d ? Lead i s o t o p e data from modern ocean i s l a n d s t e n d t o d i s p l a y l i n e a r a r r a y s i n Pb-Pb p l o t s , which may be secondary i s o c h r o n s (Oversby and Gast 1970; R u s s e l l 1972; Tatsumoto 1978; Chase 1981) or m i x i n g l i n e s (Anderson 1982). Chase (1981) d i s c o v e r e d a s y s t e m a t i c r e l a t i o n s h i p between the d a t a a r r a y s f o r seven d i f f e r e n t o c e a n i c i s l a n d s . He found t h a t each i s l a n d i s c o n s i s t e n t w i t h secondary enrichment i n U/Pb of a s i n g l e p r i m a r y r e s e r v o i r , w i t h a p v a l u e of 7.91 +_ 0.04, a t a s p e c i f i c time between 2.5 Ga and 1 Ga ago. A p p l y i n g the secondary i s o c h r o n 126 F i g u r e 4.6 I n i t i a l 87sr/86sr v e r s u s i n i t i a l 207pb/204p D p l o t f o r the I s l a n d I n t r u s i o n s ( c i r c l e s ) , and Bonanza Group v o l c a n i c r o c k s (diamond), Vancouver I s l a n d , B.C. Two m i x i n g c u r v e s are shown f o r m i x i n g between a mid-ocean r i d g e type mantle source and two d i f f e r e n t c r u s t a l s o u r c e s . The MORB end-member has: 207pb/204pb = 15.43, 87sr/86sr = 0.7022, Sr = 100 ppm, Pb = 0.5 ppm. Average S i c k e r Group m a t e r i a l a t 190 Ma ( s o l i d square) has: 207pb/204pb = 15.60, 87sr/86sr = 0.7056, Sr = 200 ppm, and Pb = 5 ppm. T y p i c a l upper c o n t i n e n t a l c r u s t ( r i n g e d c i r c l e ) has: 207pb/204pb = 15.70, 87sr/86sr = 0.7070, Sr = 400 ppm, and Pb = 20 ppm. 0.710 H 0.709 H 0.708 A 0.707 0.706 0.705 0.704 0.703 0.712 A / MIOGEO-.••*: SYNCLINE 15.5 15.6 15.7 2 0 7 P b / 2 0 4 P b (initial) 128 model t o the I s l a n d I n t r u s i o n s , the c a l c u l a t e d ja v a l u e f o r the p r i m a r y r e s e r v o i r i s 7.97 and the time a t which secondary enrichment of U/Pb o c c u r s i s 1.37 Ga (Table 4.6). Good agreement of t h e s e v a l u e s w i t h t h o s e of o t h e r o c e a n i c i s l a n d s i s s u p p o r t f o r the o r i g i n of the I s l a n d I n t r u s i o n s i n an o c e a n i c i s l a n d s e t t i n g . The apparent c o r r e l a t i o n beween i n i t i a l 207pb/204pb and i n i t i a l 8 7 s r / 8 6 s r d i s p l a y e d by the I s l a n d I n t r u s i o n s n e i t h e r c o n f i r m s nor d e n i e s the o r i g i n of the I s l a n d I n t r u s i o n s i n an o c e a n i c i s l a n d . The model of Chase (1981) does not r e q u i r e t h a t t h e s e v a l u e s be c o r r e l a t e d , however, a model proposed by Anderson (1982) does r e q u i r e c o r r e l a t e d i n i t i a l l e a d and s t r o n t i u m r a t i o s i n ocean i s l a n d r o c k s . Anderson (1982) suggested t h a t the l e a d , s t r o n t i u m and neodymium i s o t o p e d a t a from mid-ocean r i d g e b a s a l t s and ocean i s l a n d b a s a l t s can be r e s o l v e d i n terms of m i x i n g of d e p l e t e d and e n r i c h e d mantle s o u r c e s . 4.3.2 An I s l a n d A r c ? Lead i s o t o p e data from i s l a n d a r c s o f t e n d i s p l a y l i n e a r a r r a y s on Pb-Pb p l o t s , and a c o r r e l a t i o n of i n i t i a l l e a d and s t r o n t i u m r a t i o s (Tatsumoto and K n i g h t 1969; Armstrong and Cooper 1971; Church and T i l t o n 1973; M e i j e r 1976; Kay e t a l . 1978; Tsunakawa 1981). I n most cases the l i n e a r t r e n d s have a 129 Table 4.6 C a l c u l a t i o n s f o r secondary i s o c h r o n model, I s l a n d I n t r u s i o n s , Vancouver I s l a n d , B.C. Slope of b e s t f i t l i n e t o i n i t i a l l e a d d a t a 0.92787 Age g i v e n by s l o p e , assuming 190 Ma f o r i n t r u s i o n ....1.37 Ga Slop e of p r i m a r y i s o c h r o n assuming the age of the e a r t h i s 4.57 Ga, and t2 i s 1.37 Ga 0.78636 I n t e r s e c t i o n of p r i m a r y and secondary i s o c h r o n s 206pb/204pb 15.648 207pb/204pb 15.280 yi v a l u e f o r f i r s t s t a g e , assuming E a r t h had the c o m p o s i t i o n of t r o i l i t e l e a d (Tatsumoto e t a l . 1 973) a t 4.57 Ga 7.97 130 s t e e p e r s l o p e ( a p p r o x i m a t e l y 0.3) than t h o s e of ocean i s l a n d s ( a p p r o x i m a t e l y 0.1) on Pb-Pb p l o t s (Kay e t a l . 1978). They a r e i n t e r p r e t e d as m i x i n g l i n e s between l e a d - r i c h , h i g h 207pb/204pb subducted or a s s i m i l a t e d c r u s t a l l e a d , and l e a d - p o o r , low 207pb/204pb o c e a n i c mantle (Church 1973 and 1 976,; Kay e t a l . 1978; M e i j e r 1976 ) . I f the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s a r e t o be i n t e r p r e t e d as an i s l a n d a r c assemblage, the low s l o p e of the m i x i n g l i n e ( a p p r o x i m a t e l y 0.1) must be e x p l a i n e d i n terms of the c o m p o s i t i o n s of the two end-members. T h i s p l a c e s i m p o r t a n t c o n s t r a i n t s on the l e a d - r i c h and s t r o n t i u m - r i c h ' c r u s t a l ' end-member. I t i s p o s s i b l e t o determine the n a t u r e of the end-members by c o n s t r u c t i n g m i x i n g h y p e r b o l i i n the i n i t i a l 207pb/204pb v e r s u s i n i t i a l 8 7 s r / 8 6 s r p l o t ( F i g . 4.6). The end-members s e l e c t e d were: a t y p i c a l MORB ( a t 190 Ma) w i t h 207pb/204pb = 15.43, 8 7 s r / 8 6 s r = 0.7022, Pb = 0.5 ppm, Sr = 100 ppm (Tsunakawa 1981), and two e s t i m a t e s of a c r u s t a l component. These were c u r v e 1, average S i c k e r Group r o c k s a t 190 Ma, w i t h 207pb/204pb = 15.60, 8 7 s r / 8 6 s r = 0.7056, Pb = 5 ppm, and Sr = 200 ppm, and c u r v e 2, average upper N o r t h American c o n t i n e n t a l c r u s t , w i t h 207pb/204pb = 15.7 (from the Shale Curve l e a d growth curve model of Godwin and S i n c l a i r 1982 a t 190 Ma), 8 7 s r / 8 6 s r = 0.707, Pb = 131 20 ppm ( t y p i c a l upper c o n t i n e n t a l c r u s t a l l e a d c o n c e n t r a t i o n e s t i m a t e d by Doe and Zartman 1979), Sr = 400 ppm (O'Nions e t a l . 1979; Weaver and Tarney 1980). The r e s u l t i n g h y p e r b o l i , c a l c u l a t e d u s i n g the g e n e r a l e q u a t i o n of Langmuir et. a l . (1978 ), are shown i n F i g u r e 4.6. I t can be seen t h a t the h i g h 207pb/204pb s i g n a t u r e of upper c o n t i n e n t a l c r u s t p r e c l u d e s i t s i n v o l v e m e n t i n the f o r m a t i o n of the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c s . R a t h e r , a s u i t a b l e c a n d i d a t e f o r the c r u s t a l end-member i s d e t r i t u s from the p r e - e x i s t i n g P a l e o z o i c S i c k e r Group a r c v o l c a n i c r o c k s , which have lower l e a d c o n c e n t r a t i o n s (Table 2.2) and 207pb/204pb r a t i o s than the s p e c i f i c upper c o n t i n e n t a l c r u s t a l type used i n the c a l c u l a t i o n . The e n v e l o p e s t o the demonstrated h y p e r b o l i ( F i g . 4.6) i n d i c a t e the v a r i a t i o n i n m i x i n g t h a t i s p o s s i b l e g i v e n the v a r i a t i o n i n end-member c o m p o s i t i o n s . Thus S i c k e r Group m a t e r i a l cannot u n i q u e l y be i d e n t i f i e d as t h e c r u s t a l end-member because many o t h e r c o n t i n e n t a l c r u s t a l and ocean sediment c o m p o s i t i o n s would be s u i t a b l e c a n d i d a t e s . I t i s , however, p o s s i b l e t o r u l e out c o n t a m i n a t i o n by sediments t h a t were d e r i v e d from the m i o g e o s y n c l i n a l p a r t of the Canadian C o r d i l l e r a , which are c h a r a c t e r i z e d by h i g h 207pb/204pb v a l u e s (Godwin and S i n c l a i r 1982; Andrew e t a l . 1984). 132 S u i t a b i l i t y of S i c k e r Group r o c k s f o r c o n t r i b u t i n g l e a d t o the m a n t l e - d e r i v e d Bonanza Group and I s l a n d I n t r u s i o n s magmas i s f u r t h e r i l l u s t r a t e d i n F i g u r e s 4.4 and 4 . 5 . I n both f i g u r e s the S i c k e r Group l e a d d a t a ( a d j u s t e d t o 190 Ma u s i n g measured ju and k v a l u e s ) p l o t a t the r a d i o g e n i c ends of the m i x i n g l i n e s . I s l a n d I n t r u s i o n s show a g r e a t e r degree of c o n t a m i n a t i o n than do the Bonanza Group v o l c a n i c r o c k s . I t i s t h e r e f o r e p o s s i b l e t h a t p a r t (or a l l ) of the m i x i n g t r e n d i s due t o a s s i m i l a t i o n of S i c k e r m a t e r i a l by the i n t r u s i o n s . The C r e t a c e o u s S i e r r a Nevada b a t h o l i t h , which i s a g r a n o d i o r i t i c body a t the r o o t of a magmatic a r c , i s a s u i t a b l e analogue t o the I s l a n d I n t r u s i o n s . Lead i s o t o p e d a t a from the S i e r r a Nevada b a t h o l i t h have a l i n e a r p a t t e r n on c o n v e n t i o n a l l e a d i s o t o p e p l o t s (Doe and Delevaux 1 9 7 3 ) , which i s s t e e p e r than t h a t of the I s l a n d I n t r u s i o n s ( a p p a r e n t secondary i s o c h r o n age i s 2900 Ma). T h i s r e f l e c t s the n a t u r e of the c r u s t a l end-member f o r the S i e r r a Nevada b a t h o l i t h which i s more c o n t i n e n t a l i n c h a r a c t e r than t h a t f o r t h e I s l a n d I n t r u s i o n s . C o r r e l a t i o n between l e a d and s t r o n t i u m i s o t o p e d ata which i s apparent f o r the I s l a n d I n t r u s i o n s i s a l s o apparent f o r the S i e r r a Nevada b a t h o l i t h (Doe and Delevaux 1 9 7 3 ) . De Pa u l o ( 1 9 8 1 ) found t h a t i n the S i e r r a Nevada, the i n t r u s i o n s are c o n s i s t e n t l y more r a d i o g e n i c than the v o l c a n i c r o c k s . Neodymium, s t r o n t i u m , 133 oxygen and l e a d i s o t o p e d a t a combine t o i n d i c a t e t h a t m a n t l e - d e r i v e d magmas have a s s i m i l a t e d o l d c o n t i n e n t a l c r u s t d u r i n g the f o r m a t i o n of the S i e r r a Nevada magmatic a r c (De P a u l o 1981). The c o n c l u s i o n t h a t a s s i m i l a t i o n of o l d c r u s t i s an i m p o r t a n t p r o c e s s i n t h e f o r m a t i o n of magmatic a r c s (De P a u l o 1981) i s s u p p o r t e d by the l e a d and s t r o n t i u m data o b t a i n e d here f o r the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s . 4.3.3 G e o l o g i c a l c o n s i d e r a t i o n s Most ocean i s l a n d s are p r e d o m i n a n t l y b a s a l t i c w i t h minor amounts of d i f f e r e n t i a t e d s i l i c i c r o c k s . The Bonanza Group v o l c a n i c r o c k s and the I s l a n d I n t r u s i o n s are more t y p i c a l of r o c k s a s s o c i a t e d w i t h i s l a n d a r c s because of t h e i r c a l c - a l k a l i n e c h e m i s t r y and f e l s i c n a t u r e . The i n t e r p r e t a t i o n t h a t t h e s e J u r a s s i c r o c k s formed an i s l a n d a r c assemblage t h e r e f o r e seems t o be most r e a s o n a b l e . I t i s p o s s i b l e t h a t neodymium i s o t o p e a n a l y s e s of the same r o c k s a n a l y z e d i n t h i s study would h e l p t o d i s t i n g u i s h between i s l a n d a r c and ocean i s l a n d o r i g i n s f o r t h e s e J u r a s s i c igneous r o c k s . I s l a n d a r c d a t a a r e u s u a l l y d i s p l a c e d away from the mantle a r r a y (DePaulo and Wasserburg 1977) t o h i g h e r , more p o s i t i v e , v a l u e s of £Sr ( t h e d e v i a t i o n i n p a r t s i n 104 of a r o c k ' s i n i t i a l 8 7 s r / 8 6 s r r a t i o from the r a t i o i n a model r e s e r v o i r thought t o be r e p r e s e n t a t i v e of the t o t a l e a r t h ) i n 134 the Nd-Sr c o r r e l a t i o n diagram ( B a s a l t i c V o l c a n i s m Study P r o j e c t 1981). T h i s d i s p l a c e m e n t has been o b s e r v e d f o r i s l a n d a r c s which show c o n t a m i n a t i o n by normal upper c o n t i n e n t a l c r u s t a l s e d i m e n t s , so i t i s p o s s i b l e t h a t the s p e c i f i c c r u s t a l type r e q u i r e d t o e x p l a i n the l e a d i s o t o p e d a t a may not s i g n i f i c a n t l y d i s p l a c e the data away from the mantle a r r a y . Neodymium a n a l y s e s would, however, h e l p t o f u r t h e r d e s c r i b e and i d e n t i f y the c r u s t a l c o n t a m i n a n t . 4.3.4 A model One p o s s i b l e e x p l a n a t i o n f o r the i s o t o p i c c h a r a c t e r i s t i c s of the Bonanza Group v o l c a n i c s and I s l a n d I n t r u s i o n s i s as f o l l o w s : 1) S u b d u c t i o n of an o c e a n i c p l a t e beneath another p l a t e c a r r y i n g the P a l e o z o i c S i c k e r Group and T r i a s s i c Karmutsen F o r m a t i o n o c c u r s away from a s u p p l y of c o n t i n e n t a l d e t r i t u s so t h a t the t r e n c h i s s t a r v e d . 2) P a r t i a l m e l t i n g o c c u r s i n the upper p a r t of the downgoing s l a b and/or i n the mantle wedge above the s u b d u c t i n g p l a t e . The i s o t o p e s i g n a t u r e of the melt i s a p p r o x i m a t e l y the same as f o r d e p l e t e d m a n t l e. 3) Magmas r i s e i n t o the upper p l a t e . E x p l o s i v e Bonanza v o l c a n i s m p r e c l u d e s the c o n t a m i n a t i o n of Bonanza magmas by c r u s t a l m a t e r i a l s , e x cept f o r o c e a n i c sediments i n t r o d u c e d i n t o the magma by s u b d u c t i o n . 4) Magmas r e s i d i n g i n the upper p l a t e a s s i m i l a t e S i c k e r Group 135 and o t h e r m a t e r i a l w h i l e c o o l i n g s l o w l y ; t h i s produces a heterogeneous, mixed l e a d i s o t o p e s i g n a t u r e i n t h e I s l a n d I n t r u s i o n s w i t h more r a d i o g e n i c i s o t o p e v a l u e s than f o r the Bonanza Group v o l c a n i c s . 5) I n s i t u a d d i t i o n of r a d i o g e n i c l e a d between 190 Ma and the p r e s e n t causes the o r i g i n a l l i n e a r m i x i n g t r e n d t o be p a r t i a l l y o b s c u r e d . 4.4 CONCLUSIONS Lead i s o t o p e data have been o b t a i n e d f o r r o c k s from the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s . S e v e r a l g e n e r a l c o n c l u s i o n s can be drawn from t h e s e , and from s t r o n t i u m i s o t o p e a n a l y s e s of the same r o c k s : 1) Lead i s o t o p e d a t a s u p p o r t a comagmatic o r i g i n f o r the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s . 2) The I s l a n d I n t r u s i o n s c o n t a i n l e a d which i s more r a d i o g e n i c t h a n i n the Bonanza Group v o l c a n i c r o c k s . 3) Lead and s t r o n t i u m i s o t o p e d a t a a l o n e cannot d i s t i n g u i s h between i s l a n d a r c and ocean i s l a n d t e c t o n i c s e t t i n g s f o r these r o c k s . L i t h o l o g i e s a r e more t y p i c a l l y t h o s e of an i s l a n d a r c . 4) The i n i t i a l l e a d d a t a form a l i n e a r a r r a y i n the Pb-Pb p l o t s . I f i n t e r p r e t e d as a m i x i n g l i n e , t he r a d i o g e n i c end-member has t o have a lower than t y p i c a l c r u s t a l v a l u e of 207pb/204pb. 1 The S i c k e r Group P a l e o z o i c r o c k s i n t o which the I s l a n d I n t r u s i o n s are emplaced are of a s u i t a b l e l e a d and s t r o n t i u m c o m p o s i t i o n . 5) Galena from the I s l a n d Copper p o r p h y r y d e p o s i t s u p p o r t s J u r a s s i c age f o r the d e p o s i t . 137 CHAPTER 5 ISOTOPE GEOCHEMISTRY OF THE CATFACE TERTIARY INTRUSIONS SYNOPSIS Lead and s t r o n t i u m i s o t o p e r a t i o s from the C a t f a c e T e r t i a r y i n t r u s i o n s i n Vancouver I s l a n d occupy a narrow range of v a l u e s , i n d i c a t i n g a homogeneous or w e l l mixed s o u r c e . W i t h i n t h i s range, the l e a d i s o t o p e d a t a f a l l i n t o two d i s t i n c t c l u s t e r s , c o r r e s p o n d i n g t o an e a s t e r n and a w e s t e r n b e l t g e o g r a p h i c a l l y . I n i t i a l s t r o n t i u m r a t i o s f o r t h e s e i n t r u s i o n s show l i t t l e v a r i a t i o n about a mean v a l u e of 0.7039 +_ 0.0002. The s o u r c e of the s e i n t r u s i o n s can not be i d e n t i f i e d u n i q u e l y u s i n g l e a d and s t r o n t i u m i s o t o p e d a t a a l o n e , but two p o s s i b i l i t i e s can be r u l e d o u t . 207pb/204pb, 208pb/204pb and i n i t i a l s t r o n t i u m r a t i o s a r e a l l t o o h i g h t o be from s o l e l y m a n t l e - d e r i v e d magmas. I n i t i a l s t r o n t i u m r a t i o s a r e too low and the 208pb/204pb and 232Th / 2 3 8 u r a t i o s t o o h i g h f o r the C a t f a c e i n t r u s i o n s t o be the p r o d u c t s of m e l t i n g of p r e - e x i s t i n g S i c k e r Group r o c k s . 138 Galena from q u a r t z - g o l d v e i n s r e l a t e d t o the Z e b a l l o s p l u t o n has a l e a d i s o t o p i c c o m p o s i t i o n s i m i l a r t o t h a t of the Z e b a l l o s p l u t o n . C o n s e q u e n t l y , i f l e a d and g o l d have the same o r i g i n , the s o u r c e of the g o l d i s the i n t r u s i o n , r a t h e r t h a n the h o s t r o c k s . 5.1 INTRODUCTION The C a t f a c e T e r t i a r y i n t r u s i o n s of Vancouver I s l a n d are s m a l l q u a r t z d i o r i t e p l u t o n s , which i n t r u d e a v a r i e t y of r o c k u n i t s . They have come t o be known as the C a t f a c e i n t r u s i o n s a f t e r the type p l u t o n near T o f i n o . Carson (1973) d i v i d e d the i n t r u s i o n s i n t o an e a s t e r n and a w e s t e r n b e l t based on g e o g r a p h i c d i s t r i b u t i o n . West b e l t i n t r u s i o n s tend t o have a f o l i a t i o n which i s absent i n E a s t b e l t p l u t o n s . P l u t o n s from b o t h b e l t s were sampled ( F i g . 5.1, T a b l e 5.1). A c o n c o r d a n t Eocene age of 41 + 1 Ma has been o b t a i n e d on z i r c o n s from the C a t f a c e i n t r u s i o n ( I s a c h s e n 1984). K-Ar ages ( c i r c a 45 Ma) have been d e t e r m i n e d ( T a b l e 5.2) f o r each of the samples here a n a l y z e d f o r l e a d . Two age g r o u p i n g s e x i s t , one a t 50-55 Ma and another a t 38-42 Ma. The u n c e r t a i n t y i n the age f o r the Z e b a l l o s p l u t o n i s such t h a t i t c o u l d b e l o n g t o e i t h e r of the two groups. However, i t seems l i k e l y t h a t the e a s t b e l t p l u t o n s are g e n e r a l l y younger than the west b e l t p l u t o n s . Sample 1 39 75 kilometers F i g u r e 5.1 D i s t r i b u t i o n of Eocene C a t f a c e i n t r u s i o n s (shaded a r e a s ) , Vancouver I s l a n d , B.C. Dots w i t h a b b r e v i a t e d sample names mark, whole r o c k sample l o c a t i o n s (Table 5.1). Galena sample l o c a t i o n s (Table 5.1) are shown as c r o s s e s , except f o r s i x samples from the Z e b a l l o s m ining camp marked ZB. P r e s e n t l o c a t i o n s of p l a t e b o u n d a r i e s are i n d i c a t e d . Diamond symbols mark named P a l e o z o i c o re d e p o s i t s . Squares l o c a t e towns. 140 TABLE 5.1 L o c a t i o n s ( F i g . 5.1) and b r i e f d e s c r i p t i o n s of whole r o c k samples from the C a t f a c e T e r i a r y i n t r u s i o n s , and ga l e n a from r e l a t e d m i n e r a l i z a t i o n . Sample symbols are used i n F i g u r e s 5.1 and 5.2. SAMPLE NAME (SYMBOL) LAT. LONG. DECIMAL DEGREES DESCRIPTION Whole r o c k samples C a t f a c e (CT) 49.24 125.95 F a i t h Lake (FL) 49.65 125.41 Mt. Washington (MW) 49.77 125.29 Stubbs I s l a n d (SI) 49.16 125.93 Z e b a l l o s (ZB) 50.04 126.78 Z e b a l l o s g o l d - q u a r t z v e i n s Q uartz d i o r i t e , west b e l t Q u artz d i o r i t e , e a s t b e l t Q u artz d i o r i t e , e a s t b e l t Q u artz d i o r i t e , west b e l t Q u artz d i o r i t e , west b e l t 3031 7 (LS) 50 .02 1 26 .79 Gal e n a , Lone St a r / R e y Oro 3031 8 (WS) 50 .03 1 26 .81 Gal e n a , White S t a r 30320 (PR) 50 .04 126 .84 Gal e n a , P e e r l e s s 30349 (PV) 50 .03 1 26 .81 Gal e n a , P r i v a t e e r 30484 (CZ) 50 .04 1 26 .78 Gal e n a , C e n t r a l Z e b a l l o s 30487 (BP) 50 .04 1 26 .78 Gal e n a , Bragg p r o p e r t y M i s c e l l a n e o u s v e i n d e p o s i t s 3031 9 (WW) 49 .03 1 24 .70 Ga l e n a , WWW showing JS (JS) 48 .94 123 .76 Ga l e n a , J and S showing 30483 (BJ) 49 .47 126 .42 Ga l e n a , Brown Jug c l a i m 30486 (LC)1 G a l e n a , L i v i n g s t o n c l a i m s 1. Cowichan Lake D i s t r i c t . E x a c t l o c a t i o n unknown. 141 TABLE 5.2 Summary of K-Ar ages o b t a i n e d f o r C a t f a c e T e r t i a r y -i n t r u s i o n s , Vancouver I s l a n d , B.C., f o r t h e samples t h a t were a n a l y z e d f o r l e a d i n t h i s s t u d y . O r i g i n a l ages have been c o r r e c t e d t o modern c o n s t a n t s of S t e i g e r and J a g e r (1977). Other K-Ar ages f o r T e r t i a r y i n t r u s i o n s on Vancouver I s l a n d a r e i n Carson (1973). NAME AGE (Ma) REFERENCE C a t f a c e 49 + 12 Wanless e t a l . (1967), p.15 F a i t h Lake 40 + 7 Wanless e t a l . (1968), p.29 Mt. Washington 36 +_ 6 Wanless e t a l . (1968), p.29-30 Stubbs I s l a n d 51 + 5 Wanless e t a l . (1968), p.30-31 Z e b a l l o s 39 + 14 Wanless e t a l . (1967), p.16 142 l o c a t i o n s and d e s c r i p t i o n s a r e i n T a b l e 5.1 and F i g u r e 5.1. Quartz v e i n s r e l a t e d t o the Z e b a l l o s p l u t o n a r e of economic i n t e r e s t s i n c e they c o n t a i n i m p o r t a n t v a l u e s i n g o l d . S e v e r a l mines were p r o d u c t i v e i n the 1930's i n the Z e b a l l o s a r e a . Comparison of l e a d i s o t o p e r a t i o s from g a l e n a i n the v e i n s t o whole r o c k l e a d r a t i o s from the p l u t o n p r o v i d e s a method f o r d e t e r m i n i n g the source of the l e a d i n the v e i n s . Galena l e a d i s o t o p e a n a l y s e s (Table 5.1, F i g . 5.1) were o b t a i n e d f o r e i g h t v e i n d e p o s i t s . P l a t e t e c t o n i c r e c o n s t r u c t i o n s of w e s t e r n N o r t h America d u r i n g the T e r t i a r y suggest t h a t v o l c a n i c and p l u t o n i c a c t i v i t y a t t h i s time was l a r g e l y r e l a t e d t o a g e n e r a l regime of e a s t e r l y s u b d u c t i o n of o c e a n i c p l a t e s beneath N o r t h America (Atwater 1970, Byrne 1979, Ewing 1981). A magmatic a r c e x i s t e d i n the Coast Mountains d u r i n g the Eocene, between a p p r o x i m a t e l y 53 and 42 Ma (Ewing 1981, Souther 1977). V o l c a n i c r o c k s e r u p t e d a t t h i s t i me i n c l u d e the S l o k o v o l c a n i c s i n n o r t h e r n B.C., Ootsa Lake Group v o l c a n i c r o c k s i n c e n t r a l B.C., and Marron F o r m a t i o n v o l c a n i c s , Kamloops Group v o l c a n i c r o c k s and C o r y e l l p r o v i n c e v o l c a n i c s i n s o u t h e r n B.C. The C a t f a c e i n t r u s i o n s o c c u r seaward of t h e s e v o l c a n i c b e l t s i n a f o r e - a r c s e t t i n g . A t a p p r o x i m a t e l y 42 Ma, which i s s i m i l a r t o the age of some 143 of the C a t f a c e i n r u s i o n s , a change i n p l a t e motions o c c u r r e d (Byrne 1979; Ewing 1981). South of 50o N, Cascade v o l c a n i s m was i n i t i a t e d i n response t o t h e e a s t e r l y s u b d u c t i o n of the F a r a l l o n (now Juan de Fuca) p l a t e (Ewing 1981; Brandon and Massey 1985). N o r t h of 50o N the P a c i f i c p l a t e motion was t a k e n up a l o n g the Queen C h a r l o t t e t r a n s f o r m f a u l t (Ewing 1981). T h i s o v e r a l l p l a t e c o n f i g u r a t i o n ( F i g . 5.1) has c o n t i n u e d t o the p r e s e n t day (Atwater 1970; R i d d i h o u g h 1977; Byrne 1979). The G a r i b a l d i v o l c a n i c b e l t r e p r e s e n t s the p r e s e n t magmatic a r c a s s o c i a t e d w i t h s u b d u c t i o n of the Juan de Fuca p l a t e (Ewing 1981); i t o c c u r s about 250 km i n l a n d from the t r e n c h . The Eocene was a l s o the time of a c c r e t i o n of t h e M e t c h o s i n v o l c a n i c r o c k s t o s o u t h e r n Vancouver I s l a n d , s o uth of the Leech R i v e r f a u l t (Rusmore and Cowan 1985). I t i s t h e r e f o r e d i f f i c u l t t o a t t r i b u t e , a s p e c i f i c p l a t e t e c t o n i c s e t t i n g t o the C a t f a c e i n t r u s i o n s g i v e n the complex t e c t o n i c h i s t o r y of the area a t the time they were i n t r u d e d . 5.2 RESULTS Lead i s o t o p e c o m p o s i t i o n s f o r the whole r o c k and g a l e n a samples ( T a b l e s 5.3 and 5.4) a r e p l o t t e d i n F i g u r e 5.2. They occupy a narrow range of v a l u e s d e s p i t e the s m a l l s i z e of the TABLE 5.3 Lead, uranium and thorium data for the Catface i n t r u s i o n s , Vancouver Is l a n d , B.C. Sample s i t e s are located in Figure 5.1 and Table 5.1. 1 S A M P L E N A M E 206pB/204pBi 207PB/204 P B 1 2 0 8 P B / 2O 4 P B I P B P P M U 1 ' PM U P P M T H P P M J J6 k? ( S Y M B O L ) ( I . D . ) 2 , 3 <I.D.)2,4 ( N . A . A . 1 5 ( D . N . ) 5 Whole rock data Catface (CT) 18. .997(0. .032 ) 15. .622(0. .026 ) 38. .657(0. .066 ) nd nd nd nd na na F a i t h Lake (FL) 18. .753(0. .009) 15 .583(0. .007 ) 38 . 400(0, .021 ) 1 . 28 0.25(0, .03 ) 0. 39 1 .5 12.4 4.0 Mount Washington 18, .734(0, .010) 15 .588(0, .008) 38 . 379(0, .021 ) 1 . 93 0.21(0, .16) nd nd 7.0 na (MW) 1 .89 Stubbs Island (SI) 19. .093(0. .004) 15. .608(0. .004 ) 38. .694(0. ,013) nd nd nd nd na na Zeballos (Z) 19, .055(0. .004 ) 15. .602(0. .004 ) 38 . 608(0. .013) 3.71 1.10(0. .16) 1 .29 4.2 19.0 3.4 1. Figures given in brackets are the one sigma u n c e r t a i n t i e s based on the a d d i t i o n of in-run p r e c i s i o n and mass f r a c t i o n a t i o n u n c e r t a i n t i e s , c a l c u l a t e d using program "WRPBIC" (Appendix D). 2. I.D. i s isotope d i l u t i o n a n a l y s i s (Appendix B); nd = not determined 3. Estimated uncertainty for t h i s value i s 0.1 ppm (Appendix B; Table B.12). 4. Figures given in brackets are u n c e r t a i n t i e s based on error propagation c a l c u l a t i o n s , using the program "WRUCLC" (Appendix D). 5. N.A.A. stands for neutron a c t i v a t i o n a n a l y s i s , D.N. i s delayed neutron counting. These samples were analyzed by Neutron A c t i v a t i o n Services Ltd., Hamilton, Ontario. U n c e r t a i n t i e s are estimated at 10%. 5. yt values (238u/204pb) are c a l c u l a t e d using U ppm (I.D.); na = not a p p l i c a b l e . 6. k values (232Th/238u) are c a l c u l a t e d using U (N.A.A.) and Th (D.N.) values; na = not a p p l i c a b l e . U n c e r t a i n t i e s are assumed to be 14% based on 10% u n c e r t a i n t i e s in each of II and Th c o n c e n t r a t i o n s . 1 45 TABLE 5.4 Galena l e a d i s o t o p e d a t a from Vancouver I s l a n d , B.C., f o r q u a r t z - g o l d v e i n s r e l a t e d t o the Eocene Z e b a l l o s p l u t o n and m i s c e l l a n e o u s g a l e n a samples from v e i n s of p r o b a b l e T e r t i a r y age. Samples a r e l o c a t e d i n T a b l e 5.1 and F i g u r e 5.1. Numbers i n b r a c k e t s a re e s t i m a t e d one sigma e r r o r s , based on the sum of e r r o r s of i n - r u n p r e c i s i o n and u n c e r t a i n t i e s i n the mass f r a c t i o n a t i o n f a c t o r s . Data are p l o t t e d i n F i g u r e 5.2. SAMPLE LABEL 206pB/204pB 207pB/204pB 208pB/204pB Galena from q u a r t z - g o l d v e i n s r e l a t e d t o t h e Z e b a l l o s p l u t o n 3031 7 LS 1 8 .979(0. 003 ) 1 5 .601(0 .004) 38 .551(0 .01 6) 3031 8 WS 1 8 .985(0. 002 ) 15 .605(0 .004 ) 38 .584(0 .01 5) 30320 PR 19 .00 3(0. 003) 1 5 .583(0 .00 5,) 38 .534(0 .01 4) 30349 PV 1 8 .983(0. 004) 1 5 .601(0 .007 ) 38 .560(0 .024) 30484 CZ 1 8 .980(0. 004 ) 15 .606(0 .004) 38 .568(0 .01 4) 30487 BP 1 9 .005(0. 002) 1 5 .611(0 .005) 38 .588(0 .01 5) Galena from m i s c e l l a n e o u s v e i n d e p o s i t s of p r o b a b l e T e r t i a r y 30319-1 WW 1 8 .993(0. 003) 1 5 .577(0 .005 ) 38 .533(0 .01 4) 30319-2 WW 1 9 .009(0. 002) 15 .604(0 .004) 38 .636(0 .01 4) JS JS 18 .725(0. 00 4) 15 .584(0 .004) 38 .283(0 .01 2) 30483 BJ 1 8 .957(0. 003) 15 .614(0 .004) 38 .551 (0 .016) 30486 LC 1 8 .967(0. 004) 15 .598(0 .006) 38 .556(0 .01 6) 1 46 F i g u r e 5.2 207pb/204pb v e r s u s 206pb/204pb, and 208pb/204pb v e r s u s 206pb/204pb p l o t s of whole r o c k and g a l e n a l e a d i s o t o p e d a t a from T e r t i a r y i n t r u s i o n s and r e l a t e d o re d e p o s i t s , Vancouver I s l a n d , B.C. S o l i d squares mark p r e s e n t whole r o c k r a t i o s ( T a ble 5.2); open squares are i n i t i a l v a l u e s ( T a b l e 5.6). P r e s e n t and i n i t i a l r a t i o s a re l i n k e d by c o r r e c t i o n v e c t o r s . T r i a n g l e s mark g a l e n a a n a l y s e s . A b b r e v i a t e d l a b e l s a r e d e f i n e d i n T a ble 5.2. XI Q. t •— -Q 0. h-O CM E A S T B E L T M W 15.55 C T W E S T B E L T B J * ? s . PV i " m • W W m a s s f r a c t i o n a t i o n 2 0 4 P b e r r o r ± 0.1% 1 _ 1 8 . 6 1 8 . 8 1 9 . 0 206Pb/204Pb i _ 1 9 . 2 1 48 p l u t o n s and t h e i r wide g e o g r a p h i c s e p a r a t i o n . I n d e t a i l the l e a d d a t a p l o t i n two c l u s t e r s i n F i g u r e 5.2, which c o r r e s p o n d t o the e a s t and west b e l t c l a s s i f i c a t i o n of Carson (1972). W i t h i n each c l u s t e r the i s o t o p i c d a t a a r e i d e n t i c a l w i t h i n a n a l y t i c a l p r e c i s i o n . The e a s t b e l t p l u t o n s ( F a i t h Lake and Mount Washington) are l e s s r a d i o g e n i c t h a n t h e o t h e r s , d e s p i t e t h e i r younger age. Both c l u s t e r s p l o t w e l l above the o c e a n i c t r e n d d e f i n e d by mid-ocean r i d g e b a s a l t s and o c e a n i c i s l a n d s (Church and Tatsumoto 1975; F i g u r e 5.2). I n i t i a l s t r o n t i u m r a t i o s (Table 5.5) average 0.7039 +_ 0.0002. Taken s e p a r a t e l y , the e a s t b e l t p l u t o n s have an i n i t i a l r a t i o of 0.7041 + 0.0001 which i s s l i g h t l y h i g h e r than f o r the west b e l t p l u t o n s (0.7038 +_ 0.0001). There i s , t h e r e f o r e , an i n v e r s e r e l a t i o n s h i p between 206pb/204pb and i n i t i a l s t r o n t i u m r a t i o s . Galena samples from the v e i n d e p o s i t s i n the Z e b a l l o s area (Table 5.4) have r e m a r k a b l y homogeneous l e a d r a t i o s . They form a t i g h t c l u s t e r c l o s e t o the Z e b a l l o s p l u t o n i n i t i a l r a t i o s (Table 5.6), which were c a l c u l a t e d u s i n g the measured u v a l u e and an assumed age f o r the p l u t o n of 40 Ma. J TABLE 5.5 Rubidium and strontium isotope data for the Catface I n t r u s i o n s , Vancouver Island, B.C. I n i t i a l 87sr/86sr r a t i o s are c a l c u l a t e d using an assumed age of 40 Ma. Samples are located in Figure 5.1 and Table 5.1. SAMPLE NAME Sr PPM Rb PPM 87 Rb/86sr 87 Sr/86sr INITIAL REFERENCE 8 7 S r / 8 6 S r Cat face 1 41 4 23. .5 0.164 0.7038 0.7037 Isachsen (1984) F a i t h Lake 548 20. .9 0.110 0.7043 0. 7042 Armstrong et a l . ( i n press) Mount Washington 595 16. .9 0.082 0.7041 0 . 7040 Armstrong et a l • ( i n press) Zeballos 381 39. .3 0.299 0 . 7040 0.7038 Armstrong et a l . ( i n press) 1. Catface sample i s not the same sample analyzed in t h i s study for lead. D e t a i l s of t h i s sample are i n Isachsen (1984) 150 TABLE 5.6 I n i t i a l r a t i o s f o r the C a t f a c e I n t r u s i o n s , Vancouver I s l a n d , B.C. Age c o r r e c t i o n s a r e f o r an assumed age of 40 Ma. One sigma u n c e r t a i n t i e s g i v e n i n b r a c k e t s are based on e r r o r p r o p a g a t i o n u s i n g the program "T1CORR" (Appendix D). JJ and k v a l u e s used i n the c a l c u l a t i o n s a re i n T a b l e 5.3. Data are p l o t t e d i n F i g u r e 5.2. SAMPLE NAME 206pb/204pb 207pb/204pb 208pb/204pb F a i t h Lake 18.68 (.01) Mt. Washington 18.69 (.01) Z e b a l l o s 18.94. ( . 02 ) 15.58 (.01) 15.59 (.01 ) 15.60 ( .01 ) 38.30 (.04) not a p p l i c a b l e 38.48 (.04) 151 5.3 DISCUSSION 5.3.1 O r i g i n o f the C a t f a c e i n t r u s i o n s T e r t i a r y i n t r u s i o n s on Vancouver I s l a n d appear t o b e l o n g t o two d i f f e r e n t magmatic e v e n t s , thus the name 'C a t f a c e i n t r u s i o n s ' may be wrongly a p p l i e d t o a l l of them, masking i m p o r t a n t d i f f e r e n c e s . F a i t h Lake and Mount Washington p l u t o n s have l e s s r a d i o g e n i c l e a d than the o t h e r p l u t o n s , d e s p i t e t h e i r younger age, but s l i g h t l y h i g h e r i n i t i a l 8 7 s r / 8 6 s r r a t i o s . U n i f o r m i t y of l e a d i s o t o p e r a t i o s w i t h i n each c l u s t e r i m p l i e s a homogeneous or w e l l mixed source f o r each magmatic event. I n i t i a l s t r o n t i u m , 207pb/204pb and 208pb/204pb are a l l t o o h i g h w i t h r e s p e c t t o 206pb/204pb, f o r the i n t r u s i o n s t o have formed d i r e c t l y from o c e a n i c mantle. A component of c r u s t a l l e a d , perhaps from subducted sediments, from u n d e r p l a t e d m a t e r i a l , or from basement r o c k s , must have been i n v o l v e d i n t h e i r f o r m a t i o n . S i c k e r Group basement r o c k s are not of a s u i t a b l e i s o t o p i c c o m p o s i t i o n t o be the major c r u s t a l component i n t h e f o r m a t i o n of the C a t f a c e i n t r u s i o n s . S t r o n t i u m r a t i o s of t h e S i c k e r Group are too h i g h (as p r e v i o u s l y p o i n t e d out by I s a c h s e n 1984, and i l l u s t r a t e d by Armstrong e t a l . i n p r e s s , f i g u r e 10). Uranium and t h o r i u m d a t a a l s o s u p p o r t t h i s c o n c l u s i o n . Th/U v a l u e s are 1 52 h i g h e r i n the C a t f a c e i n t r u s i o n s (>3, Table 5.3) than i n the S i c k e r Group (<3, T a b l e 2.2). I f m e l t i n g of the S i c k e r Group were to t a k e p l a c e , the Th/U v a l u e i n the melt would tend t o be lower than i n the r e s i d u e , s i n c e uranium i s more e f f i c i e n t l y t r a n s f e r r e d i n t o the l i q u i d phase ( S e i t z 1973; Tatsumoto 1978; Anderson 1982). F i n a l l y , the 208pb/204pb r a t i o i s s l i g h t l y h i g h e r i n the T e r t i a r y i n t r u s i o n s t h a n would be e x p e c t e d i f the c r u s t a l l e a d component was S i c k e r Group m a t e r i a l . Deep s e i s m i c r e f l e c t i o n p r o f i l e s of s o u t h e r n Vancouver I s l a n d show a zone of u n d e r p l a t e d m a t e r i a l ( Y o r a t h e t a l . 1985b; Clowes e t a l . 1987), which has been i n t e r p r e t e d as b e i n g a s s o c i a t e d w i t h the most r e c e n t s u b d u c t i o n regime t h a t was i n i t i a t e d i n l a t e Eocene, a t about the same time as the i n t r u s i o n s were b e i n g emplaced. T h i s i s , t h e r e f o r e , one p o s s i b l e s o u r c e f o r t h e s e i n t r u s i o n s . The l e a d i s o t o p e c o m p o s i t i o n of P a c i f i c ocean sediments (Church 1976) i s of a s u i t a b l e c o m p o s i t i o n t o be the c r u s t a l component i n the T e r t i a r y i n t r u s i o n s ( F i g u r e 5.3). I n t r o d u c t i o n of these sediments i n t o the s i t e of magma g e n e s i s by s u b d u c t i o n , t h e r e f o r e , i s the most l i k e l y e x p l a n a t i o n f o r t h e i r o r i g i n . The C a t f a c e i n t r u s i o n s occupy the i s o t o p i c f i e l d s c h a r a c t e r i s t i c of i s l a n d a r c s i n F i g u r e s 5.3 and 5.4, s u p p o r t i n g t h i s h y p o t h e s i s . The v a r i a t i o n i n i s o t o p e r a t i o s between the E a s t b e l t and West 1 53 F i g u r e 5.3 207pb/204pb v e r s u s 206pb/204pb p l o t showing p r e s e n t day ( s o l i d s q u a r e s ; Table 5.3) and i n i t i a l (open s q u a r e s ; Table 5.6) whole r o c k l e a d i s o t o p e c o m p o s i t i o n s f o r the T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C. A l s o shown are p r e s e n t day g e n e r a l i z e d f i e l d s f o r mid-ocean r i d g e b a s a l t s (Church and Tatsumoto 1975; B r e v a r t e t a l . 1 9 8 1 ; V i d a l and C l a u e r 1981), ocean i s l a n d s (Sun and Jahn 1975; Tatsumoto 1978; Sun 1980; Weis 1983), i s l a n d a r c s (Oversby and Ewart 1972; Church 1975; M e i j e r 1976; Kay e t a l . 1978) and ocean sediments (Church 1975; V i d a l and C l a u e r 1981; Sun 1980). The growth c u r v e f o r r e f e r e n c e i s t h a t of S t a c e y and Kramers (1975). 155 F i g u r e 5.4. 208pt>/204pb v e r s u s 206pb/204pb p l o t showing p r e s e n t day ( f i l l e d s q u a r e s ; T a b l e 5.3) and i n i t i a l (open s q u a r e s ; T a b l e 5.6) whole r o c k l e a d i s o t o p e c o m p o s i t i o n s f o r the T e r t i a r y i n t r u s i o n s , Vancouver I s l a n d , B.C. A l s o shown a r e p r e s e n t day g e n e r a l i z e d f i e l d s f o r mid-ocean r i d g e b a s a l t s , ocean i s l a n d s , i s l a n d a r c s and P a c i f i c sediments (see F i g . 5.3 f o r source of d a t a ) , The growth c u r v e f o r r e f e r e n c e i s t h a t of Stacey and Kramers (1975). 157 b e l t p l u t o n s i s more p r o b l e m a t i c and may be due t o m o d i f i c a c t i o n d u r i n g emplacement i n t o d i f f e r e n t h o s t r o c k s . G e o g r a p h i c a l v a r i a t i o n s i n i s o t o p e r a t i o s a r e found i n the Andes i n Peru ( B a r r e i r o and C l a r k 1984), and i n the Cascades (Church e t a l . 1986). I n both cases v a r i a t i o n i n c r u s t a l t h i c k n e s s or type are i n v o k e d t o e x p l a i n o b s e r v e d d i f f e r e n c e s . The h y p o t h e s i s of c r u s t a l c o n t a m i n a t i o n of mantle type l e a d w i t h upper c r u s t a l l e a d c o u l d be f u r t h e r t e s t e d u s i n g Nd i s o t o p e s . D e v i a t i o n from the mantle a r r a y i n the Nd-Sr c o r r e l a t i o n diagram towards h i g h e r Sr v a l u e s would be e x p e c t e d . The c o n s i s t e n c y of the i n v e r s e r e l a t i o n s h i p between i n i t i a l s t r o n t i u m r a t i o s and 206pb/204pb c o u l d a l s o be t e s t e d . I f the E a s t b e l t p l u t o n s have h i g h e r 8 7 s r / 8 6 s r i n i t i a l r a t i o s than the West b e l t ones t h e y s h o u l d a l s o have lower 144Nd/143Nd r a t i o s . 5.3.2 Galena l e a d i s o t o p e d a t a S i m i l a r i t y i n the i n i t i a l l e a d r a t i o s of t h e Z e b a l l o s b a t h o l i t h w i t h g a l e n a from q u a r t z - g o l d v e i n s , and the u n i f o r m i t y of t h o s e r a t i o s argue s t r o n g l y f o r a p l u t o n i c s o u r c e f o r the g o l d , assuming t h a t l e a d and g o l d have a common o r i g i n . T h i s c o n t r a d i c t s a c o n c l u s i o n a r r i v e d a t by Andrew e t a l . (1982) i n the absence of whole r o c k l e a d d a t a , thus p o i n t i n g out the advantages of i n t e r p r e t i n g g a l e n a l e a d i s o t o p e d a t a w i t h data from whole rock l e a d . The i m p l i c a t i o n t h a t the h o s t r o c k t o the v e i n s i s an 158 u n i m p o r t a n t f a c t o r i n l o c a t i n g g o l d - r i c h v e i n s r e l a t e d t o T e r t i a r y i n t r u s i o n s i s s u p p o r t e d by a s t a t i s t i c a l s t udy by Hansen and S i n c l a i r (1984). Knowledge of the i s o t o p i c c o m p o s i t i o n of T e r t i a r y i n t r u s i o n s and v e i n d e p o s i t s p r o v i d e s a u s e f u l means of i d e n t i f y i n g T e r t i a r y m i n e r a l i z a t i o n on Vancouver I s l a n d . Galena from the Brown Jug c l a i m near T o f i n o can be shown t o be r e l a t e d t o the T e r t i a r y i n t r u s i o n s by s i m p l e comparison. I t t h e r e f o r e r e p r e s e n t s a p o s s i b l e g o l d p r o d u c e r . S i m i l a r l y , l e a d from the J and S p r o s p e c t might be r e l a t e d t o T e r t i a r y i n t r u s i o n s of the e a s t e r n b e l t because of i t s s i m i l a r i t y i n i s o t o p i c c o m p o s i t i o n w i t h F a i t h Lake and Mount Washington p l u t o n s . I t i s u n l i k e l y t h a t the J and S p r o s p e c t i s r e l a t e d t o a P a l e o z o i c massive s u l p h i d e d e p o s i t , because of the d i f f e r e n c e s i n c o m p o s i t i o n between i t and the P a l e o z o i c B u t t l e Lake and Lenora and Tyee ore d e p o s i t s . L i v i n g s t o n C l a i m s , a Pb-Zn ore d e p o s i t i n Cowichan l i m e s t o n e , and the WWW ore d e p o s i t near A l b e r n i , b oth have l e a d i s o t o p e r a t i o s i n d i s t i n g u i s h a b l e from those of t h e Z e b a l l o s - r e l a t e d d e p o s i t s , i m p l y i n g t h a t t h e s e a r e T e r t i a r y d e p o s i t s r e l a t e d t o the Eocene i n t r u s i v e e v e n t . A l e a d i s o t o p e study of m i n e r a l d e p o s i t s a s s o c i a t e d w i t h T e r t i a r y p l u t o n s i n the Cascade Range of Washington and Oregon by Church e t a l . (1986) shows t h a t t hey have e x t r e m e l y 159 homogeneous l e a d i s o t o p e r a t i o s i n the same range as those of Vancouver I s l a n d . A l l the d e p o s i t s were younger (20 Ma t o 6.5 Ma) and r e l a t e d t o t h e Cascade s u b d u c t i o n regime (Church e t a l . 1986). G e o g r a p h i c a l v a r i a t i o n s i n i s o t o p e r a t i o s were a l s o found and r e l a t e d t o c r u s t a l basement v a r i a t i o n s . The l e a d i s o t o p e f e a t u r e s of t h e s e p l u t o n - r e l a t e d o r e d e p o s i t s a r e the same as f o r those of Vancouver I s l a n d . The g e n e t i c i n t e r p r e t a t i o n of t h e s e d e p o s i t s as c o n t a i n i n g m e t a l s o r i g i n a t i n g i n subducted s e d i m e n t s , i s the f a v o u r e d i n t e r p r e t a t i o n f o r the l e a d i n the C a t f a c e i n t r u s i o n s and a s s o c i a t e d g o l d d e p o s i t s . The c o i n c i d e n c e of l e a d i s o t o p e r a t i o s of T e r t i a r y p l u t o n - r e l a t e d ore d e p o s i t s over a wide g e o g r a p h i c a r e a s t r e t c h i n g from Vancouver I s l a n d a l o n g the west c o a s t t o Oregon i s of major s i g n i f i c a n c e . S p e c i f i c a l l y , T e r t i a r y m i n e r a l i z a t i o n , commonly a s s o c i a t e d w i t h g o l d , can be i d e n t i f i e d e a s i l y u s i n g l e a d i s o t o p e a n a l y s e s . 5.5 CONCLUSIONS C a t f a c e T e r t i a r y i n t r u s i o n s i n c l u d e two groups of p l u t o n s , each w i t h a homogeneous l e a d i s o t o p e s i g n a t u r e . The groups c o r r e s p o n d t o a g e o g r a p h i c a l l y d i s t i n c t e a s t b e l t and west b e l t . The o r i g i n of t h e s e p l u t o n s i s not c o m p l e t e l y r e s o l v e d . 160 I n i t i a l s t r o n t i u m , 207pb/204p D and 208pb/204pb r a t i o s r u l e out o c e a n i c mantle as the o n l y s o u r c e . S t r o n t i u m , uranium and t h o r i u m d a t a p r e c l u d e the d i r e c t g e n e s i s of the p l u t o n s from S i c k e r Group basement r o c k s . Lead i s o t o p e d a t a a r e c o n s i s t e n t w i t h the o r i g i n of the i n t r u s i o n s from a w e l l mixed c o m b i n a t i o n of m a n t l e , and upper c r u s t a l sediments i n t r o d u c e d by s u b d u c t i o n . S t r o n t i u m i n i t i a l r a t i o s a r e , however, r a t h e r low. Nd i s o t o p e s may h e l p t o r e s o l v e t h i s i n c o n s i s t a n c y . Galena l e a d i s o t o p e r a t i o s from T e r t i a r y q u a r t z - g o l d v e i n s i n Vancouver I s l a n d i n d i c a t e t h a t the o r i g i n of the g o l d i s i n the p l u t o n s , and t h a t u l t i m a t e l y the m e t a l s a r e d e r i v e d from r e c y c l e d c r u s t a l m a t e r i a l r a t h e r than the m a n t l e. The homogeneity of l e a d i s o t o p e s i g n a t u r e s from p l u t o n - r e l a t e d T e r t i a r y ore d e p o s i t s i n the P a c i f i c n o r t h w e s t r e g i o n of N o r t h America s i m p l i f i e s the i d e n t i f i c a t i o n of T e r t i a r y g o l d - r e l a t e d m i n e r a l i z a t i o n by l e a d i s o t o p e a n a l y s i s t h r o u g h o u t the w e s t e r n C o r d i l l e r a . 161 CHAPTER 6 PLUMBOTECTONICS OF VANCOUVER ISLAND SYNOPSIS P a l e o z o i c r o c k s of Vancouver I s l a n d a re c h a r a c t e r i z e d by h i g h e r 207pb/204pb r a t i o s t h a n Mesozoic v o l c a n i c and p l u t o n i c r o c k s , i n d i c a t i n g g r e a t e r i n v o l v e m e n t of upper c r u s t a l m a t e r i a l i n t h e i r f o r m a t i o n . The Mesozoic v o l c a n i c r o c k s a re d e p l e t e d i n 207pb/204pb and t h e r e i s e v i d e n c e of i s o t o p i c m i x i n g i n both the T r i a s s i c and J u r a s s i c e p i s o d e s . I n the T r i a s s i c , the mantle source resembles an ocean i s l a n d b a s a l t source and the c r u s t a l contaminant has the f e a t u r e s of average c r u s t . J u r a s s i c I s l a n d I n t r u s i o n s d i s p l a y m i x i n g between a d e p l e t e d mantle source and an o c e a n i c or a r c - t y p e c r u s t a l s o u r c e , which may be S i c k e r Group m a t e r i a l . There i s a r e t u r n t o g r e a t e r c r u s t a l i n v o l v e m e n t i n the f o r m a t i o n of the T e r t i a r y C a t f a c e i n t r u s i o n s . Galena and whole r o c k l e a d i s o t o p e c o m p o s i t i o n s from Vancouver I s l a n d a r e c h a r a c t e r i z e d by h i g h e r 206pb/204pb, and lower 207pb/204pb r a t i o s than t h o s e of c r a t o n i c N o r t h America. No s i n g l e l e a d i s o t o p e growth c u r v e model can be a p p l i e d t o Vancouver I s l a n d because i t i s a mosaic of d i f f e r e n t t e c t o n i c 162 e n v i r o n m e n t s . I n t e r p r e t a t i o n of age of d e p o s i t s from ga l e n a l e a d i s o t o p e d a t a can be made by comparison w i t h d a t a from known ore d e p o s i t s . T h i s i s d i f f i c u l t , however, i n the ranges 206pb/204pb = 18.5-18.8, and 207pb/204pb = 15.55-15.60, where some T e r t i a r y , Mesozoic and P a l e o z o i c o re d e p o s i t s f a l l . Galena w i t h 206pb/204pb > 18.8 i s T e r t i a r y . 6.1 INTRODUCTION Each of the v o l c a n i c and p l u t o n i c e p i s o d e s t h a t made up the h i s t o r y of Vancouver I s l a n d has i t s own i s o t o p i c c h a r a c t e r i s t i c s . S e v e r a l d i f f e r e n t mantle s o u r c e s have been tapped d u r i n g the development of the i s l a n d , and v a r i o u s t y p e s of c r u s t a l m a t e r i a l have c o n t r i b u t e d t o the i s o t o p i c h e t e r o g e n e i t y of W r a n g e l l i a t h r o u g h changes i n provenance or volume of t r e n c h s e d i m e n t s , a s s i m i l a t i o n , and r e c y c l i n g of c o n t i n e n t a l d e t r i t u s i n t o the mantle. T h i s c h a p t e r s y n t h e s i z e s the i s o t o p i c i n f o r m a t i o n from each of t h e v o l c a n i c and p l u t o n i c e p i s o d e s t h a t have been d i s c u s s e d i n the p r e c e d i n g c h a p t e r s . Major i s o t o p i c c h a r a c t e r i s t i c s of each of these e p i s o d e s a r e summarized and compared. R e c o g n i t i o n of i s o t o p i c d i f f e r e n c e s between r o c k s u i t e s p r o v i d e s a means of i d e n t i f y i n g the m i n e r a l i z a t i o n source and age f o r ga l e n a samples 1 63 r e l a t e d t o t h e s e v o l c a n i c and p l u t o n i c e p i s o d e s . A method of d i s t i n g u i s h i n g between m i n e r a l i z a t i o n ages u s i n g g a l e n a l e a d i s o t o p e a n a l y s e s i s d e s c r i b e d . Major d i f f e r e n c e s between the i s o t o p i c c h a r a c t e r i s t i c s of Vancouver I s l a n d and those of the N o r t h American c r a t o n a r e c o n s i d e r e d . 6.2 ISOTOPIC COMPARISONS BETWEEN SAMPLE SUITES S i c k e r Group v o l c a n i c r o c k s a r e g e n e r a l l y more e n r i c h e d i n 207pb/204pb than r o c k s from the J u r a s s i c v o l c a n i c and p l u t o n i c e p i s o d e . I f both t h e s e e p i s o d e s a re r e l a t e d t o i s l a n d a r c f o r m a t i o n , then the d i f f e r e n c e i n i s o t o p i c c o m p o s i t i o n may be e x p l a i n e d by a d i f f e r e n c e i n the provenance of the sediments i n v o l v e d i n the s u b d u c t i o n p r o c e s s . H i g h e r 207pb/204pb r a t i o s i n the S i c k e r Group r o c k s suggest t h a t c o n t i n e n t a l l y - d e r i v e d , 207pb/204pb-rich m a t e r i a l was i n v o l v e d i n t h e i r f o r m a t i o n . The S i c k e r Group may have formed above a t r e n c h f i l l e d w i t h sediment from an a d j a c e n t c o n t i n e n t . U n f o r t u n a t e l y t h e r e i s l i t t l e e v i d e n c e t o suggest where W r a n g e l l i a was d u r i n g the P a l e o z o i c , but f a u n a l s i m i l a r i t i e s have been found between the E a r l y Permian f o s s i l s i n t h e S i c k e r Group, and tho s e of A u s t r a l i a , Timor and the U r a l s i n R u s s i a (Danner 1977). T y p i c a l upper c o n t i n e n t a l c r u s t a l sediments were not 164 i n v o l v e d i n the f o r m a t i o n of the I s l a n d I n t r u s i o n s and Bonanza Group magmas (Chapter 4 ) , s u g g e s t i n g t h a t the E a r l y J u r a s s i c a r c was i n t r a - o c e a n i c or c u t o f f from c o n t i n e n t a l d e t r i t u s by. a sediment t r a p . The C a t f a c e T e r t i a r y i n t r u s i o n s have l e a d i s o t o p e r a t i o s which p l o t a l o n g the S i c k e r Group t r e n d i n 207pb/204pb v e r s u s 206pb/204pb diagrams. T h i s s i m i l a r i t y i m p l i e s a s i m i l a r i t y i n the s o u r c e s of t h e s e d i f f e r e n t r o c k u n i t s . I f the T e r t i a r y i n t r u s i o n s a r e r e l a t e d t o s u b d u c t i o n , as suggested i n Chapter 5, the r e l a t i v e l y h i g h 207pb/204pb r a t i o s ( h i g h e r t h a n f or the I s l a n d I n t r u s i o n s ) may be due t o an abundance of c r a t o n - d e r i v e d t r e n c h sediments. The u p l i f t of the Rocky Mountains i n the L a t e J u r a s s i c t o E a r l y T e r t i a r y may have a l l o w e d abundant c o n t i n e n t a l d e t r i t u s t o r e a c h the t r e n c h . There i s c o n s i d e r a b l e o v e r l a p i n the i n i t i a l r a t i o s of the T r i a s s i c Karmutsen F o r m a t i o n v o l c a n i c r o c k s w i t h t h o s e of the J u r a s s i c I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s . D e s p i t e the apparent s i m i l a r i t y between these two Mesozoic e p i s o d e s , t h e r e a r e major i s o t o p i c d i f f e r e n c e s i n d e t a i l . Both d i s p l a y i s o t o p i c m i x i n g , but the end-members a r e q u i t e d i f f e r e n t . There i s a s h i f t from an e n r i c h e d mantle ( h i g h 206pb/204pb) source i n the T r i a s s i c t o a d e p l e t e d (MORB-type) -mantle i n the J u r a s s i c . The c r u s t a l component l o o k s l i k e average c r u s t i n the T r i a s s i c , but has the f e a t u r e s of i s l a n d a r c - t y p e 165 m a t e r i a l i n the J u r a s s i c I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s . There a r e s e v e r a l p o s s i b l e e x p l a n a t i o n s f o r the s e d i f f e r e n c e s . I f the c r u s t a l component i n the Karmutsen b a s a l t s was i n t r o d u c e d i n t o the mantle source by s h a l l o w r e c y c l i n g of subducted s e d i m e n t s , the same c r u s t a l m a t e r i a l may not have been a v a i l a b l e t o the t r e n c h i n the J u r a s s i c . A l l o c h t h o n o u s t e r r a n e s were a c c r e t e d t o the margin of w e s t e r n N o r t h America d u r i n g the p e r i o d between the T r i a s s i c and E a r l y J u r a s s i c . Thus i t i s p o s s i b l e t h a t i s o t o p i c d i f f e r e n c e s between T r i a s s i c and J u r a s s i c r o c k s r e f l e c t changes i n paleogeography. I f , however, the c r u s t a l component i n the Karmutsen F o r m a t i o n i s due t o deep r e c y c l i n g , d i f f e r e n c e s i n paleogeography a r e i r r e l e v e n t . D i f f e r e n c e s i n the mantle s o u r c e s of the s e two Mesozoic. e p i s o d e s t h e n would be due t o the heterogeneous n a t u r e of the ma n t l e , and/or d e r i v a t i o n of the magmas from d i f f e r e n t depths i n a l a y e r e d mantle. 6.3 VANCOUVER I S L A N D AND THE DUPAL ANOMALY The Dupal anomaly ( H a r t 1984) i s a g l o b e - e n c i r c l i n g r e g i o n from the e q u a t o r t o 60o south w i t h i n which ocean i s l a n d s and ocean r i d g e s d i s p l a y 207pb/204pb, 208pb/204pb and 87sr/86sr r a t i o s h i g h e r than t h e i r N o r t h e r n Hemisphere c o u n t e r p a r t s . Lead i s o t o p e a n a l y s e s of r o c k s from the N i n e t y - e a s t Ridge a r e c l e a r l y 166 anomalous when compared t o the N o r t h e r n Hemisphere Refe r e n c e L i n e (NHRL: H a r t 1984). These r o c k s a r e now 40o f u r t h e r n o r t h t h a n they were a t the time they formed ( a p p r o x i m a t e l y 85 Ma ag o ) . R e s t o r i n g them t o t h e i r o r i g i n a l p o s i t i o n p u t s them w i t h i n the p r e s e n t p o s i t i o n of the Dupal anomaly, i n d i c a t i n g t h a t t h e anomaly has not changed p o s i t i o n s i g n i f i c a n t l y - - a t l e a s t not i n 85 Ma. Har t (1984) proposed t h a t t h i s r e g i o n of anomalous mantle may have e x i s t e d f o r more than t h r e e b i l l i o n y e a r s , a l t h o u g h i t s l o c a t i o n , beyond 85 Ma, i s open t o q u e s t i o n . I f , however, the Dupal anomaly e x i s t e d t h r o u g h o u t the Mesozoic c l o s e t o i t s p r e s e n t p o s i t i o n i n the Southern Hemisphere, t h e r e a r e i m p o r t a n t i m p l i c a t i o n s f o r Vancouver I s l a n d . The i s o t o p i c c o m p o s i t i o n of mantle t h a t c o u l d have been i n v o l v e d i n the g e n e r a t i o n of the Karmutsen F o r m a t i o n has been e s t i m a t e d i n Chapter 3. T h i s e s t i m a t e d c o m p o s i t i o n f a l l s c l o s e t o t he NHRL i n F i g u r e 6.1. Thus, t h e r e i s no e v i d e n c e of a Dupal anomaly i n the mantle source f o r t h e s e r o c k s . P a l e o m a g n e t i c d a t a show t h a t the Karmutsen F o r m a t i o n formed a t a p p r o x i m a t e l y 17o n o r t h or south of the equat o r ( Y o l e and I r v i n g 1980; Swartz e t a l . 1980; H i l l h o u s e and Gromme 1984). I f i t formed a t the s o u t h e r l y l a t i t u d e , i t would be e x p e c t e d t o 167 15.3 I i 17 18 19 206Pb/204Pb F i g . 6.1 207pb/204pb v e r s u s 206pb/204pb p l o t showing the N o r t h e r n Hemisphere r e f e r e n c e l i n e (NHRL; Ha r t 1984), e s t i m a t e d mantle v a l u e f o r the Karmutsen F o r m a t i o n (K; F i g u r e 3.9), and approximate c o m p o s i t i o n of anomalous mantle (Dupal anomaly; Hart 1 984 ) . 168 d i s p l a y the e n r i c h e d 207pb/204pb, 87sr/86sr and 208pb/204pb r a t i o s c h a r a c t e r i s t i c of the Dupal anomaly i n S o u t h e r n Hemisphere m a n t l e . S i n c e t h i s i s not the c a s e , th e n o r t h e r l y l a t i t u d e i s f a v o u r e d here f o r the o r i g i n of the Karmutsen F o r m a t i o n . P a l e o n t o l o g i c a l e v i d e n c e based on ammonite z o n a t i o n d u r i n g the Mesozoic ( T a y l o r e t a l . 1984) a l s o f a v o u r s the n o r t h e r n l a t i t u d e . 6.4 INTERPRETATION OF GALENA LEAD ISOTOPE DATA Galena l e a d i s o t o p e a n a l y s e s from the ore d e p o s i t s , d i s c u s s e d i n e a r l i e r c h a p t e r s , a r e shown on F i g u r e 6.2, w i t h f o u r growth c u r v e s f o r r e f e r e n c e . A l s o shown are the f i e l d s of whole ro c k i n i t i a l r a t i o s of the I s l a n d I n t r u s i o n s and the T e r t i a r y i n t r u s i o n s . These f i e l d s r e p r e s e n t p o t e n t i a l g a l e n a l e a d i s o t o p e r a t i o s f o r m i n e r a l i z a t i o n r e l a t e d t o these p l u t o n i c e p i s o d e s . S i c k e r Group whole r o c k i n i t i a l r a t i o s a r e not shown because of the u n c e r t a i n t y i n v o l v e d i n c a l c u l a t i n g t h e s e v a l u e s f o r r o c k s which have undergone changes i n the r e l a t i v e abundances of uranium, t h o r i u m and l e a d s i n c e t h e i r time of f o r m a t i o n . One of the o r i g i n a l o b j e c t i v e s of t h i s s tudy was t o produce a growth c u r v e model f o r the i n t e r p r e t a t i o n of g a l e n a l e a d 169 F i g u r e 6.2 Vancouver I s l a n d g a l e n a l e a d i s o t o p e d a t a shown w i t h r e f e r e n c e growth c u r v e s r e p r e s e n t i n g "North American" l e a d . These are the " s h a l e " c u r v e (Godwin and S i n c l a i r 1982) and B l u e b e l l c u r v e (Andrew e t a l . 1984). S t a c e y and Kramers (1975) two-stage growth c u r v e which r e p r e s e n t s average c r u s t a l l e a d growth and the mantle c u r v e of Doe and Zartman (1979) are a l s o shown. F i e l d s of whole r o c k i n i t i a l v a l u e s a r e shown f o r the J u r a s s i c I s l a n d I n t r u s i o n s and the T e r t i a r y C a t f a c e i n t r u s i o n s . 1 7 0 39.0 -0. © CM 0. CO o CM 38.5 -38.0 -TERTIARY INTRUSIONS JURASSIC ISLAND INTRUSIONS 0 Ma s Mantle curve 18.0 I 1 1 1 19.0 2 0 6 P b / 2 0 4 P b 15.7 a o a 15.8 - TERTIARY INTRUSIONS 15.5 -15.4 0 Ma JURASSIC ISLAND INTRUSIONS Galena v ZabaNoa goM vain* (Eocana) • laland Coppar porphyry (Jurats*) Triassic mtnarallzatton Votcanoganlc maaaiva aulpNdas (Palaozotc) i r 18.0 —I— 19.0 2 0 < 5 P b / 2 0 4 P b 171 i s o t o p e r a t i o s from ore d e p o s i t s on Vancouver I s l a n d . The g a l e n a d a t a , however, do not d i s p l a y a systemmatic change i n r a t i o s w i t h age a l o n g a w e l l - d e f i n e d t r e n d ( F i g . 6.2), because Vancouver I s l a n d i s made up of s e v e r a l d i f f e r e n t t e c t o n i c environments — each w i t h i t s own i s o t o p i c c h a r a c t e r i s t i c s produced by d i f f e r e n t c o m b i n a t i o n s of v a r i o u s mantle and c r u s t a l l e a d t y p e s . Growth c u r v e models work w e l l where a p a r t i c u l a r environment has p e r s i s t e d f o r a l o n g t i m e , so t h a t m i n e r a l i z a t i o n events o c c u r r i n g a t d i f f e r e n t t i m e s have l e a d i s o t o p e r a t i o s which change smoothly as a f u n c t i o n of ti m e . S i n c e t h i s i s not the case f o r Vancouver I s l a n d a s i n g l e growth c u r v e model i s i n a p p r o p r i a t e . Galena l e a d i s o t o p e d a t a from ore d e p o s i t s of unknown age and o r i g i n can be i n t e r p r e t e d i n a g e n e r a l way by comparing them t o the data from known d e p o s i t s . T h i s method i s c o m p l i c a t e d by the f a c t t h a t t h e r e i s an a r e a on the 207pb/204pb v e r s u s 206pb/204pb p l o t w i t h i n which t h e r e a re s m a l l d i f f e r e n c e s i n i s o t o p i c c o m p o s i t i o n between o r e d e p o s i t s of w i d e l y d i f f e r e n t ages. T h i s a r e a o c c u p i e s t h e range 206pb/204pb = 18.5 t o 18.8 and 207pb/204pb = 15.55 t o 15.60, and c o n t a i n s ore d e p o s i t s of P a l e o z o i c , Mesozoic and T e r t i a r y age. O u t s i d e t h i s area i t i s p o s s i b l e t o i d e n t i f y T e r t i a r y m i n e r a l i z a t i o n (206pb/204pb > 18.8) from P a l e o z o i c and Mesozoic m i n e r a l i z a t i o n (206pb/204pb < 18.5). 172 J u r a s s i c p l u t o n i c a c t i v i t y i s i s o t o p i c a l l y d i s t i n c t from the T e r t i a r y p l u t o n s ( F i g . 6.2b), so i t i s p o s s i b l e t o d i s t i n g u i s h between these m i n e r a l i z a t i o n ages f o r c ases i n which the m i n e r a l i z a t i o n i s r e l a t e d t o t h e p l u t o n s . T e r t i a r y m i n e r a l i z a t i o n i s c h a r a c t e r i z e d by h i g h e r 208pb/204pb (>38.25) tha n the J u r a s s i c m i n e r a l i z a t i o n (<38.25). P a l e o z o i c m i n e r a l i z a t i o n can be i d e n t i f i e d by comparison w i t h the B u t t l e Lake, Lenora and Tyee ore d e p o s i t s and sample S457 (Chapter 2 ) . These r a t i o s (206pb/204pb < 18.6 and 207pb/204pb > 15.56) can be d i s t i n g u i s h e d from J u r a s s i c m i n e r a l i z a t i o n t h a t has a lower 207pb/204pb r a t i o , and T e r t i a r y m i n e r a l i z a t i o n t h a t has a g r e a t e r 206pb/204pb r a t i o ( F i g . 6.2). There i s no c l e a r s e p a r a t i o n between m i n e r a l i z a t i o n s y n g e n e t i c w i t h the T r i a s s i c Karmutsen F o r m a t i o n , and S i c k e r - r e l a t e d m i n e r a l i z a t i o n ; a l t h o u g h i n g e n e r a l the Karmutsen m i n e r a l i z a t i o n has lower 207pb/204pb and g r e a t e r 206pb/204pb r a t i o s . There i s c o n s i d e r a b l e o v e r l a p between the i n i t i a l r a t i o f i e l d s f o r whole r o c k samples from th e Karmutsen F o r m a t i o n (not shown i n F i g . 6.2) w i t h those of the T e r t i a r y i n t r u s i o n s , the I s l a n d I n t r u s i o n s and Bonanza Group v o l c a n i c r o c k s , and the P a l e o z o i c g a l e n a samples. T h i s means t h a t T r i a s s i c 173 m i n e r a l i z a t i o n cannot be p o s i t i v e l y i d e n t i f i e d by l e a d i s o t o p e s a l o n e . 6.5 VANCOUVER ISLAND VERSUS NORTH AMERICAN LEAD 6.5.1 N o r t h American l e a d A model f o r the e v o l u t i o n of l e a d i n the Selwyn s h a l e b a s i n was proposed by Godwin and S i n c l a i r (1982). T h i s t h r e e - s t a g e l e a d i s o t o p e growth c u r v e known as the ' s h a l e ' c u r v e was found t o be g e n e r a l l y a p p l i c a b l e t o the m i o g e o s y n c l i n a l p a r t of the Canadian C o r d i l l e r a f o r ore d e p o s i t s of upper c r u s t a l o r i g i n (Andrew et. a l . 1984). A second c u r v e known as the ' B l u e b e l l ' c u r v e was d e v e l o p e d t o d e s c r i b e the e v o l u t i o n of a second l e a d r e s e r v o i r , p o s s i b l y the lower c r u s t , which c o n t r i b u t e d l e a d t o ore d e p o s i t s i n the s o u t h w e s t e r n p a r t of the m i o g e o s y n c l i n e . Many ore d e p o s i t s i n the Canadian C o r d i l l e r a can be i n t e r p r e t e d i n terms of m i x i n g of l e a d from the upper and lower c r u s t (Andrew e t a l . 1984). Both of these N o r t h American l e a d i s o t o p e growth c u r v e s a r e shown i n F i g u r e 6.2. 6.5.2 Vancouver I s l a n d l e a d The l e a d i s o t o p e c h a r a c t e r i s t i c s of ore d e p o s i t s from Vancouver I s l a n d a r e h i g h 206pb/204pb and low 207pb/204pb r e l a t i v e t o ore d e p o s i t s o c c u r r i n g i n the upper c o n t i n e n t a l c r u s t i n c r a t o n i c N o r t h A m e r i c a . F i g u r e 6.2 shows the f i e l d of 174 Vancouver I s l a n d o r e d e p o s i t s p l o t t e d w i t h the upper c o n t i n e n t a l c r u s t a l ' s h a l e ' c u r v e (Godwin and S i n c l a i r 1982) and the ' B l u e b e l l ' or lower c r u s t a l common l e a d growth c u r v e (Andrew e t  a l . 1984). The Vancouver I s l a n d f i e l d o c c u p i e s an a r e a which i s h i g h e r i n 206pb/204pb than a c h o r d j o i n i n g t h e two growth c u r v e s a t 0 Ma. The same p a t t e r n of h i g h 206pb/204pb and low 207pb/204pb r e l a t i v e t o an o r e l e a d growth c u r v e was shown by R u s s e l l (1972) t o be t y p i c a l of o c e a n i c l e a d . The l e a d c h a r a c t e r i s t i c s of Vancouver I s l a n d a re those of o c e a n i c and a r c v o l c a n i c l e a d - - c l e a r l y d i f f e r e n t from c r a t o n i c l e a d . Three d i s t i n c t l e a d i s o t o p e p r o v i n c e s have been r e c o g n i z e d i n the Western U n i t e d S t a t e s (Zartman 1974). Vancouver I s l a n d l e a d f a l l s i n t o c a t e g o r y I I I of Zartman (1974), h a v i n g the same f e a t u r e s of e u g e o s y n c l i n a l l e a d (207pb/204pb < 15.7, 206pb/204pb > 18.7), w h i l e the 'North American' l e a d d e s c r i b e d i n the p r e v i o u s s e c t i o n f a l l s i n t o c a t e g o r i e s I and I I . Thus, the b o u n d a r i e s between i s o t o p i c p r o v i n c e s can be t r a c e d northwards i n t o Western Canada. 6.6 SUGGESTION FOR FURTHER WORK The l e a d and s t r o n t i u m i s o t o p e s i g n a t u r e s o b t a i n e d f o r f i v e 175 r o c k s u i t e s from Vancouver I s l a n d may be compared w i t h those of o t h e r v o l c a n i c and p l u t o n i c r o c k s u i t e s which a r e thought t o be r e l a t e d i n some way. For example, T i p p e r and R i c h a r d s (1976) proposed t h a t d u r i n g the M e s o z o i c , the Bonanza and H a z e l t o n v o l c a n i c b e l t s were c o n t i n o u s . I f t h i s . w a s t h e c a s e , i s o t o p i c s i m i l a r i t i e s would be e x p e c t e d between t h e s e u n i t s ; the h y p o t h e s i s can be t e s t e d by a n a l y z i n g H a z e l t o n v o l c a n i c r o c k s f o r t h e i r l e a d i s o t o p e c o m p o s i t i o n s . A n a l y s e s of b a s a l t s of known age i n a l l o c h t h o n o u s t e r r a n e s i n the Western Canadian C o r d i l l e r a may r e v e a l i s o t o p e s i g n a t u r e s t h a t do or do not d i s p l a y the Dupal anomalous mantle s i g n a t u r e . I n some i n s t a n c e s t h i s may h e l p t o d e c i d e the provenance of a l l o c h t h o n o u s t e r r a n e s . Major d i f f e r e n c e s i n i s o t o p i c c h a r a c t e r i s t i c s between r o c k s and o r e s of the a l l o c h t h o n o u s t e r r a n e s , and those w i t h i n the N o r t h American c r a t o n , show t h a t the edge of the a n c i e n t c r a t o n can be d e l i n e a t e d u s i n g i s o t o p i c c r i t e r i a . T h i s has been done u s i n g the 0.706 i n i t i a l s t r o n t i u m r a t i o (Armstrong 1979). Lead i s o t o p e d a t a a r e another e x p r e s s i o n of t h i s boundary ( c f Ghosh 1986; Zartman 1974). 176 CHAPTER 7  CONCLUSIONS F i v e s u i t e s of r o c k s from Vancouver I s l a n d have been c h a r a c t e r i z e d i s o t o p i c a l l y by u s i n g whole r o c k l e a d and s t r o n t i u m i s o t o p e systems. P a l e o z o i c S i c k e r Group r o c k s have l e a d i s o t o p e r a t i o s which cover the range 206pb/204pb = 18.5 t o 26.0, • 207pb/204pb = 15.55 t o 16.00, and 208pb/204pb = 38.0 to 45.0. I n i t i a l r a t i o s i n d i c a t e d by g a l e n a from v o l c a n o g e n i c ore d e p o s i t s a t B u t t l e Lake, Mount S i c k e r , and P o r t A l b e r n i occupy the range 206pb/204pb = 18.3 t o 18.6, 207pb/204pb = 15.55 t o 15.60, and 208pb/204pb = 38.0 t o 38.2. A s m a l l but s i g n i f i c a n t d i f f e r e n c e i n the i s o t o p i c r a t i o s of g a l e n a samples from two ore h o r i z o n s a t B u t t l e Lake i n d i c a t e a d e c r e a s e i n c r u s t a l component w i t h t i m e , s u p p o r t i n g the h y p o t h e s i s t h a t the mine sequence developed d u r i n g i n i t i a t i o n of b a c k - a r c s p r e a d i n g . Karmutsen F o r m a t i o n v o l c a n i c r o c k s have heterogeneous l e a d i s o t o p e r a t i o s . I s o t o p e m i x i n g i s apparent between two end-member c o m p o s i t i o n s which a r e e s t i m a t e d a t : 1) 206pb/204pb = 18.425, 207pb/204pb = 15.602, and 208pb/204pb = 38.231, and 2) 206pb/204pb = 18.833, 207pb/204pb = 15.523, and 208pb/204pb = 38.884. The former has the c o m p o s i t i o n of average c r u s t , whereas the l a t t e r 177 p o s s i b l y r e p r e s e n t s ocean i s l a n d b a s a l t type mantle. C o n t a m i n a t i o n of a m a n t l e - d e r i v e d magma by s e d i m e n t a r y m a t e r i a l , which may have been i n t r o d u c e d by s u b d u c t i o n , i s a p o s s i b l e e x p l a n a t i o n . The mantle source does not d i s p l a y the Dupal anomaly, s u p p o r t i n g a N o r t h e r n Hemisphere o r i g i n f o r t h e s e b a s a l t s . I n i t i a l r a t i o s f o r the Bonanza Group v o l c a n i c r o c k s and I s l a n d I n t r u s i o n s a t 190 Ma occupy the ranges 206pb/204pb = 18.3 t o 18.9, 207pb/204pb = 15.53 t o 15.59, 208pb/204pb = 37.8 t o 38.3, and 87sr/86sr = 0.703 t o 0.704. The Bonanza v o l c a n i c r o c k s a r e l e s s r a d i o g e n i c than the I s l a n d I n t r u s i o n s , but a r e c o l i n e a r on 207pb/204pb v e r s u s 206pb/204pb and 208pb/204pb v e r s u s 206pb/204pb p l o t s i n d i c a t i n g t h a t they are comagmatic. Galena from t h e J u r a s s i c I s l a n d Copper p o r p h y r y d e p o s i t p l o t s w i t h t h e whole r o c k i n i t i a l r a t i o s , showing t h a t i t formed d u r i n g the same magmatic e v e n t . I s o t o p i c m i x i n g between a mantle s o u r c e and a c r u s t a l s o u r c e i s p a r t l y a t t r i b u t e d t o a s s i m i l a t i o n of S i c k e r Group m a t e r i a l by the I s l a n d I n t r u s i o n s , but may be.due t o the s u b d u c t i o n of i s l a n d a r c - t y p e d e t r i t u s . The l i n e a r a r r a y of i n i t i a l r a t i o s c o r r e s p o n d s t o a secondary i s o c h r o n age of 1.37 Ga, which agrees w e l l w i t h t h o s e of modern ocean i s l a n d s . I t i s not p o s s i b l e t o d i s t i n g u i s h between an i s l a n d a r c and an ocean i s l a n d o r i g i n f o r t h e s e r o c k s u i t e s , based on i s o t o p i c e v i d e n c e a l o n e . C a t f a c e i n t r u s i o n s f a l l i n t o two groups i s o t o p i c a l l y , 178 c o r r e s p o n d i n g t o an e a s t and west g e o g r a p h i c a l l o c a t i o n . The E a s t b e l t p l u t o n s occupy the ranges 206pb/204pb = 18.73 t o 18.75, 207pb/204pb = 15.58 t o 15.59, and 208pb/204pb = 38.38 t o 38.40. The West b e l t p l u t o n s are more r a d i o g e n i c w i t h : 206pb/204pb = 18.99 t o 19.09, 207pb/204pb = 15.60 t o 15 . 62 , and 208pb/204pb = 38 .60 t o 38 . 66 . S t r o n t i u m i n i t i a l r a t i o s a r e i n the range 0.7038 t o 0.7042, and are s l i g h t l y more r a d i o g e n i c i n the E a s t b e l t p l u t o n s than i n the West b e l t . The apparent i n v e r s e r e l a t i o n s h i p between l e a d and s t r o n t i u m i s o t o p e d a t a i s not e a s i l y e x p l a i n e d . Galena from g o l d v e i n s i n the Z e b a l l o s m i n i n g camp has a s i m i l a r i s o t o p i c c o m p o s i t i o n t o t h a t of the p l u t o n , which s t r o n g l y s u g g e s t s t h a t the m i n e r a l i z a t i o n has i t s o r i g i n i n the p l u t o n . D i f f e r e n c e s i n the i s o t o p i c c h a r a c t e r i s t i c s of each of the ro c k packages a n a l y z e d a re due t o the changing t e c t o n i c regimes t h a t b u i l t Vancouver I s l a n d . A g r e a t e r c o n t r i b u t i o n of c r u s t a l l e a d i n the P a l e o z o i c S i c k e r Group r o c k s than i n the Mesozoic r o c k s u i t e s i s perhaps due t o the nearness of W r a n g e l l i a t o a c o n t i n e n t i n t he Devonian. T r i a s s i c and J u r a s s i c r o c k s u i t e s a l l i n d i c a t e l e s s i n v o l v e m e n t of c r u s t a l m a t e r i a l and/or l a c k of a Dupal anomaly. Higher 207pb/204pb r a t i o s i n the C a t f a c e T e r t i a r y i n t r u s i o n s i n d i c a t e a r e t u r n t o g r e a t e r c r u s t a l i n v o l v e m e n t . I t i s i n a p p r o p r i a t e t o a p p l y a s i n g l e growth curve model t o d e s c r i b e l e a d i s o t o p e e v o l u t i o n on Vancouver I s l a n d . However, age 179 d e t e r m i n a t i o n s can be made i n a g e n e r a l way by comparing ga l e n a i s o t o p e d a t a w i t h the i n i t i a l v a l u e s of the v a r i o u s r o c k s u i t e s . Some a m b i g u i t i e s i n t h i s " f i n g e r p r i n t i n g " method o c c u r because of the o v e r l a p of f i e l d s of i n i t i a l v a l u e s . T e r t i a r y m i n e r a l i z a t i o n , however, can be d i s t i n g u i s h e d c l e a r l y from J u r a s s i c and P a l e o z o i c m i n e r a l i z a t i o n . The d a t a base p r o v i d e d by t h i s s tudy can be used i n comparing major r o c k s u i t e s from Vancouver I s l a n d t o roc k s u i t e s i n o t h e r p a r t s of W r a n g e l l i a , or i n d i f f e r e n t t e r r a n e s throughout the C o r d i l l e r a and/or w o r l d . A major d i f f e r e n c e e x i s t s i n i s o t o p i c f e a t u r e s of r o c k s and ore d e p o s i t s a s s o c i a t e d w i t h the m i o g e o s y n c l i n a l p a r t of the Canadian C o r d i l l e r a , and those of Vancouver I s l a n d . T h i s d i f f e r e n c e may be g e n e r a l t o the a l l o c h t h o n o u s t e r r a n e s , a l l o w i n g a boundary t o be drawn which marks the edge of the N o r t h American c r a t o n . 180 REFERENCES A l l e g r e , C.J. and Y. B o t t i n g a , 1977. The r i s i n g deep c r u s t : an a l t e r n a t i v e t o the hot spot model. EOS, v o l . 58, p. 535. A l l e g r e , C.J., B. Dupre, P. R i c h a r d , p. 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Two t y p e s of Sr and Pb i s o t o p i c v a r i a t i o n i n a r c v o l c a n i c r o c k s . Geochemical J o u r n a l , v o l . 15, pp. 333-335. U l r y c h , T.J., 1969. A comment on t h e c o n c o r d i a method of 192 i n t e r p r e t i n g whole r o c k U/Pb r a t i o s . E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , v o l . 7, pp.116-118. V i d a l , P.H. and N. C l a u e r , 1981. Pb and Sr i s o t o p i c s y s t e m a t i c s o f some b a s a l t s and s u l p h i d e s from the E a s t P a c i f i c R i s e a t 21o N ( p r o j e c t RITA). E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , v o l . 55, pp. 237-246. Walker, R.R., 1980. Western Mines - Lynx, Myra and P r i c e d e p o s i t s : a d i s c u s s i o n . Canadian I n s t i t u t e of M i n i n g B u l l e t i n , v o l . 73, no. 824, pp. 86-89. Wanless, R.K., R.D. S t e v e n s , G.R. Lachance, and C M . Edmonds, 1967. Age d e t e r m i n a t i o n s and g e o l o g i c a l s t u d i e s . K-Ar i s o t o p i c ages, r e p o r t 7. G e o l o g i c a l Survey of Canada Paper 66-17, 120p. Wanless, R.K., R.D. S t e v e n s , G.R. Lachance, and C M . Edmonds, 1968. Age d e t e r m i n a t i o n s and g e o l o g i c a l s t u d i e s . K-Ar i s o t o p i c ages, r e p o r t 8. G e o l o g i c a l Survey of Canada Paper 67-2, P a r t A, 141p. Weaver, B.L. and J . Tarney, 1980. C o n t i n e n t a l c r u s t c o m p o s i t i o n and n a t u r e of the lower c r u s t : c o n s t r a i n t s from mantle Nd-Sr i s o t o p e c o r r e l a t i o n . N a t u r e , v o l . 286, pp. 342-346. Weis, D., 1983. Pb i s o t o p e s i n A s c e n s i o n I s l a n d r o c k s : O ceanic o r i g i n f o r the g a b b r o i c t o g r a n i t i c p l u t o n i c x e n o l i t h s . E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , v o l . 62, pp. 273-282. W i l s o n , J.T., 1963. A p o s s i b l e o r i g i n f o r the Hawa i i a n I s l a n d s . Canadian J o u r n a l of P h y s i c s , v o l . 41, pp. 863-870. Y o l e , R.W., 1969. Upper P a l e o z o i c s t r a t i g r a p h y of Vancouver I s l a n d , B r i t i s h Columbia. P r o c e e d i n g s , G e o l o g i c a l A s s o c i a t i o n of Canada, v o l . 20, pp. 30-40. Y o l e , R.W. and E. I r v i n g , 1980. D i s p l a c e m e n t of Vancouver I s l a n d : P a l e o m a g n e t i c e v i d e n c e from the Karmutsen F o r m a t i o n . Canadian J o u r n a l of E a r t h S c i e n c e , v o l . 17, pp. 1210-1288. Y o r a t h , C.J., R.M. Clowes, A.G. Green, A. Southerland-Brown, M.T. Brandon, N.W.D. Massey, C. Spencer, E.R. Kanasewich, and R.D. Hyndman, 1985a. LITHOPROBE - Phase 1: Southern Vancouver I s l a n d : P r e l i m i n a r y a n a l y s e s of r e f l e c t i o n s e i s m i c p r o f i l e s and s u r f a c e g e o l o g i c a l s t u d i e s , i n C u r r e n t R e s e a r c h , P a r t A, G e o l o g i c a l Survey of Canada, Paper 1985-1A, pp. 543-554. Y o r a t h , C.J., A.G. Green, R.M. Clowes, A. S o u t h e r l a n d Brown, M.T. Brandon, E.R. Kanasewich, R.D. Hyndman, and C P . Spencer, 1985b. LITHOPROBE - South e r n Vancouver I s l a n d : V i b r o s e i s 193 r e f l e c t i o n sees through W r a n g e l l i a t o the s u b d u c t i n g Juan de Fuca p l a t e . Geology, v o l . 13, pp. 759-762. Y o r k , Derek, 1969. L e a s t squares f i t t i n g of a s t r a i g h t l i n e w i t h c o r r e l a t e d e r r o r s . E a r t h and P l a n e t a r y S c i e n c e L e t t e r s , v o l . 5, pp.32 0-32 4. Zartman, R.E., 1974. Lead i s o t o p i c p r o v i n c e s i n the C o r d i l l e r a of the Western U n i t e d S t a t e s and t h e i r g e o l o g i c s i g n i f i c a n c e . Economic Geology, v o l . 69, pp. 792-805. Zartman, R.E., 1984. Lead, s t r o n t i u m and neodymium c h a r a c t e r i z a t i o n of m i n e r a l d e p o s i t s r e l a t i v e t o t h e i r g e o l o g i c e n v i r o n m e n t s . P r o c e e d i n g s of the 27th i n t e r n a t i o n a l G e o l o g i c a l Congress, v o l . 12, pp. 83-106. 194 APPENDIX A LABORATORY PROCEDURES FOR GALENA LEAD ISOTOPE ANALYSIS A.1 GALENA LEAD SAMPLE PREPARATION Galena c r y s t a l s s e l e c t e d from r o c k or ore samples are s t o r e d i n p l a s t i c v i a l s . A p p r o x i m a t e l y 10 mg of g r a i n s of c l e a n g a l e n a a r e p i c k e d o u t , u s i n g a needle and a b i n o c u l a r m i c r o s c o p e , and put i n t o a d i s p o s a b l e 10 ml p o l y p r o p y l e n e b e a k e r . A c l e a n g l a s s beaker (10 ml) and the sample are both c o v e r e d i n P a r a f i l m . The sample c o n t a i n e r i s weighed, t h e n the c o n t e n t s emptied i n t o the g l a s s beaker and the c o n t a i n e r i s reweighed. The weight of the sample i n d i c a t e s t h e amount of water t h a t must be added t o the l e a d c h l o r i d e c r y s t a l s p r i o r t o l o a d i n g . A p p r o x i m a t e l y 8 ml 2N HC1 i s added t o the sample i n the g l a s s beaker, which i s then l e f t o v e r n i g h t on a h o t p l a t e i n a l a m i n a r a i r f l o w hood i n f r o n t of a fume hood. The l e a d s u l p h i d e i s c o n v e r t e d t o l e a d c h l o r i d e w i t h the p r o d u c t i o n of hydrogen s u l p h i d e . The d r y PbCl2 c r y s t a l s a r e r i n s e d i n 4N HC1 t h r e e t i m e s , u s i n g a g l a s s p i p e t t e t o decant the e x c e s s l i q u i d . Most of the i m p u r i t i e s a r e r e a d i l y d i s s o l v e d i n 4N HC1, but PbCl2 i s l e a s t s o l u b l e a t t h i s n o r m a l i t y . Cleaned l e a d c h l o r i d e c r y s t a l s a r e d r i e d by r e t u r n i n g t h e beaker t o the h o t p l a t e f o r a few mi n u t e s . A s o l u t i o n c o n t a i n i n g 1 jug Pb per 2 jul aqueous s o l u t i o n i s p r e p a r e d by a d d i n g a c a l c u l a t e d amount of q u a r t z d i s t i l l e d water a l l o w i n g f o r the l o s s of 30% of the sample due t o n o n - d i s s o l u t i o n of some of the gal e n a and l o s s of l e a d c h l o r i d e d u r i n g r i n s i n g . A.2 PREPARATION AND LOADING OF FILAMENTS P r e - c l e a n e d rhenium r i b b o n 1.5 cm l o n g i s spot-we l d e d t o s i n g l e f i l a m e n t p o s t s . The f i l a m e n t s a r e t r a n s f e r r e d t o the l a m i n a r a i r f l o w hood where they a r e mounted onto the f i l a m e n t h o l d e r s i x a t a t i m e , t h e n r i n s e d w i t h 2 - b o t t l e w a t e r , then 2 - b o t t l e a c e t o n e . A m i c r o p i p e t t e w i t h d i s p o s a b l e t i p s i s used t o l o a d 2 u l of sample onto each f i l a m e n t , u s i n g a new t i p f o r each sample. Samples are d r i e d a t 1 Amp. 4 jal of s i l i c a g e l - p h o s p h o r i c a c i d s o l u t i o n i s l o a d e d on t o p of the d r y sample. T h i s i s l e f t t o d r y a t 1.1 Amp, th e n t h e c u r r e n t i s g r a d u a l l y i n c r e a s e d u n t i l the l o a d d i s s o l v e s and r e p r e c i p i t a t e s . T h i s p r o c e s s can be obser v e d u s i n g the b i n o c u l a r m i c r o s c o p e . When r e c r y s t a l l i z a t i o n i s 195 complete, the c u r r e n t i s s l o w l y i n c r e a s e d u n t i l w h i t e smoke i s g i v e n o f f and the l o a d t u r n s w h i t e . The c u r r e n t can then be t u r n e d up t o 2 Amps or h i g h e r t o a l l o w the l o a d t o glow g e n t l y f o r a few seconds, t h e n o f f . The e n t i r e l o a d i n g procedure s h o u l d t a k e about an hour i f done p r o p e r l y . Samples a r e l o a d e d i n t o the VG isomass 54R mass s p e c t r o m e t e r , s i x a t a t i m e , and a n a l y z e d u s i n g the measuring program "UBCZPB" which i s l o a d e d i n t o the HP85 m i n i computer. E a r l y g a l e n a runs (pre-1983) were o c c a s i o n a l l y a n a l y z e d u s i n g "MSCOPB" which has a d i f f e r e n t peak measuring sequence. Both of th e s e programs a r e d e c r i b e d i n Appendix B. "UBCZPB" has been updated by J . G a b i t e s s i n c e the g a l e n a a n a l y s e s i n c l u d e d i n t h i s t h e s i s were o b t a i n e d . The new program i s c a l l e d "UBCGPB". I t has the same peak measuring sequence as "UBCZPB" but a u t o m a t i c a l l y c o n v e r t s the measured r a t i o s t o the more u s e f u l 206pb/204pb, 207pb/204pb and 208pb/204pb r a t i o s and c o r r e c t s them f o r mass f r a c t i o n a t i o n . Raw d a t a were c o r r e c t e d f o r mass f r a c t i o n a t i o n u s i n g mass f r a c t i o n a t i o n f a c t o r s d e t e r m i n e d by r e p e a t e d a n a l y s e s of Broken H i l l S t a n d a r d #1. For a n a l y s e s o b t a i n e d i n 1983, these a re g i v e n i n T a b l e s A.1 and A.2. A l l o t h e r s were a n a l y s e d over the same timespan as the whole r o c k samples, and were t h e r e f o r e c o r r e c t e d i n the same way as f o r whole r o c k i s o t o p e c o m p o s i t i o n runs (Appendix B ) . The w i t h i n - r u n p r e c i s i o n f o r each a n a l y s i s i s added t o the f r a c t i o n a t i o n v a r i a t i o n between runs and the u n c e r t a i n t y i n the mass f r a c t i o n a t i o n f a c t o r s d e t e r m i n e d from the a n a l y s e s of Broken H i l l S t a n d a r d ( T a b l e s A.1, A.2, B.1, B.2 and F i g s . A.1 and B.1), u s i n g the e q u a t i o n : s2 = x2 + y2 + z2 where: s = s t a n d a r d d e v i a t i o n of one a n a l y s i s , x = w i t h i n - r u n p r e c i s i o n , y = f r a c t i o n a t i o n u n c e r t a i n t y between r u n s , z = u n c e r t a i n t y i n mass f r a c t i o n a t i o n f a c t o r s . TABLE A.1 Broken H i l l standard measurements for the period January 1983 to March 1983. DATE TEMPOC 206pb/204pb 207pb/204pb 208pb/204pb 09/01/83 1150 15 .959(0 .003) 15.318(0 .003) 35 .431(0 .007) 17/01/83 1150 15 .967(0 .006) 15.322(0.005) 35 .471(0 .014) 23/01/83 1150 15 .961(0 .005) 15.326(0 .005) 35 .434(0 .011 ) 02/02/83 1150 15 .964(0 .003) 15.323(0 .002) 35 .434(0 .006) 03/02/83 1150 15 .964(0 .005) 15.323(0 .008) 35 .445(0 .021 ) 25/02/83 1150 15 .964(0 .002) 15.324(0 .002) 35 .448(0 .004) 25/02/83 1150 15 .962(0 .001) 15.321(0 .001 ) 35 .435(0.003) MEAN VALUES (N=7) 15 .963 15.322 35 .443 STD. DEV. (S1 ) 0 .002 0.002 0 .013 MEAN WITHIN-RUN (S2) 0 .004 0.004 0 .009 FRACTIONATION VARIATION BETWEEN RUNS (S3)1 0 .000 0.000 0 .009 WHERE S32 = S12 - S22 1. S3 can not be negative. The fractionation v a r i a t i o n between runs i s considered to be negligible for the 206pb/204pb and 207pb/204pb r a t i o s . 1 97 Table A.2. Calculation of mass fractionation factors using f i v e published values of the Broken H i l l Standard #1:- 1983. REFERENCE 206pb/204pb 207pb/204pb 208pb/204pb 1) Coopers et al.(1969)16. 003 (0, .011 ) 15 .390 (0. 013) 35 .660 (0.036) 2) Richards et a l . 16. 004 (0. .006) 15 .390 (0. 007) 35 .651 (0.017) (1981) best double-spiked 3) Richards et a l . 16. 007 (0 .012) 15 .395 (0. 010) 35 .665 (0.046) (1981) bias corrected 4) Richards and 16. 003 (0 .013) 15 .386 (0. 013) 35 .640 (0.040) Bleckley (1984) Canberra 5) Richards and 16. 005 (0 .013) 15 .387 (0. 018) 35 .651 (0.055) Blockley (1984) Edmonton (Cumming) MEAN PUBLISHED VALUE 16. 004 (0 .002) 15 .390 (0. 004) 35 .653 (0.010) MEAN MEASURED VALUE (TABLE A.1) 15. 963 (0 .002) 15 .322 (0. ,002) 35 .443 (0.013) FRACTIONATION FACTORS1 1 . 002593 1 .004412 1 .005937 STD. DEV. 0. 000093 0 .000204 0 .000242 1 . These fractionation factors and uncertainties were used i n the determination of fractionation corrected data and t h e i r uncertainties (see t e x t ) . These are not perfectly mass dependent. o o o I o I-O < Li. < o < 198 SLOPE = 13.9 ± 0.6 MASS DIFFERENCE F i g u r e A.1 mass depend squares l i n f r a c t i o n a t i f r a c t i o n a t i l i n e w e l l , p e r i o d was f r a c t i o n a t i r e d u c t i o n , Graph ent f r ear re on, t h on f ac so i t not pe on f a c r a t h e r i c a l r e p r e a c t i o n a t i o g r e s s i o n . e l i n e mus t o r s d e t e r was assume r f e c t l y ma t o r s d e t e r than the s e n t a t i o n of the d e t e r m i n a t i o n of n f a c t o r s u s i n g York (1969) l e a s t For p e r f e c t mass dependent t pass through the o r i g i n . The mined i n Table A.2 do not f i t the d t h a t f r a c t i o n a t i o n f o r t h i s time ss dependent. T h e r e f o r e , mined i n Table A.2 were used i n data 0.139% per mass u n i t determined here, 199 A.3 REAGENT PREPARATION A.3.1 H y d r o c h l o r i c a c i d H y d r o c h l o r i c a c i d i s d i l u t e d t o 6N u s i n g d i s t i l l e d water, t h e n i s once d i s t i l l e d , u s i n g a one l i t r e d i s t i l l a t i o n f l a s k . 2N, 4N, and 6N wash b o t t l e s a re made up by d i l u t i n g t o the r e q u i r e d s t r e n g t h w i t h q u a r t z d i s t i l l e d w a t e r . A.3.2. N i t r i c A c i d Reagent grade n i t r i c a c i d (18N) i s d i l u t e d t o 9N w i t h d i s t i l l e d water and used d i r e c t l y f o r c l e a n i n g g l a s s w a r e . A.3.3. S i l i c a g e l - p h o s p h o r i c a c i d A 1N s o l u t i o n of p h o s p h o r i c a c i d i s p r e p a r e d u s i n g U l t r e x u l t r a p u r e phosphorus p e n t o x i d e and 2 - b o t t l e w a t e r . Fumed s i l i c a i s added t o t h i s and the m i x t u r e shaken then l e f t i n an u l t r a s o n i c bath f o r s e v e r a l h o u r s . A f t e r l e a v i n g t o s e t t l e f o r two days the su p e r n a t e i s decanted and kept i n a c l e a n t e f l o n b o t t l e . The r e s t i s d i s c a r d e d . A.3.4. Quartz d i s t i l l e d water (Q-water) D i s t i l l e d water i s used as f e e d f o r the q u a r t z d i s t i l l a t i o n p r o c e s s . A.3.5. T w o - b o t t l e water Quartz d i s t i l l e d water i s used as f e e d f o r the t w o - b o t t l e (2B) s u b - b o i l i n g d i s t i l l a t i o n a p p a r a t u s d e s c r i b e d i n M a t t i n s o n (1971). A.3.6. Rhenium r i b b o n Zone r e f i n e d rhenium r i b b o n (0.001" x 0.030") i s o b t a i n e d from The Rembar Company, 67 Main S t r e e t , Dobb's F e r r y , New York. T h i s i s c u t i n t o s t r i p s 1.5 cm l o n g and b o i l e d i n t w o - b o t t l e 2N HC1, then r i n s e d i n t w o - b o t t l e H20 and d r i e d under an i n f r a r e d lamp i n a c l e a n a i r hood. See Appendix B f o r p r e p a r a t i o n of t w o - b o t t l e d i s t i l l e d r e a g e n t s . A.3.7. Fumed S i l i c a Fumed s i l i c a was o b t a i n e d from BDH Chemicals L t d . 200 APPENDIX B LAB PROCEDURES FOR ROCK LEAD, URANIUM AND THORIUM ISOTOPE ANALYSIS B.1 SAMPLE PREPARATION Rock samples a r e broken u s i n g a h y d r a u l i c r o c k - s p l i t t e r u n t i l they are of a s u i t a b l e s i z e f o r c r u s h i n g (7 t o 8 cm d i a m e t e r ) . As much of the o u t e r s u r f a c e as p o s s i b l e i s d i s c a r d e d a t t h i s s t a g e . The r o c k c h i p s o b t a i n e d a f t e r c r u s h i n g w i t h a j a w - c r u s h e r are c l e a n e d u s i n g d i s t i l l e d 2N HC1 i n an u l t r a s o n i c b a t h . A f t e r r i n s i n g t h r e e t i m e s w i t h q u a r t z - d i s t i l l e d w a t e r , the r o c k c h i p s a r e d r i e d under i n f r a r e d lamps i n a l a m i n a r f l o w hood. Clea n e d r o c k c h i p s are ground u s i n g a t u n g s t e n c a r b i d e r i n g m i l l (5 minutes) u n t i l the powder does not f e e l g r i t t y . The m i l l i s c l e a n e d between samples u s i n g d i s t i l l e d water and compressed a i r . The f i r s t two l o a d s of r o c k powder are d i s c a r d e d , and t h i r d and subsequent l o a d s of r o c k powder are saved f o r a n a l y s i s . B.2 SAMPLE DISSOLUTION A p p r o x i m a t e l y 0.6 g of each sample ro c k powder i s a c c u r a t e l y weighed i n t o a 15 ml S a v i l l e x beaker ( t e f l o n ) . S u i t a b l e q u a n t i t i e s of mixed s p i k e 84 -3 or t h o r i u m s p i k e 84-2 are added f o r i s o t o p e d i l u t i o n r u n s . Samples are d i g e s t e d i n 5 ml t w o - b o t t l e d i s t i l l e d (2B) HF and 1ml c o n c e n t r a t e d 2B HNO3 i n c o v e r e d b e a k e r s . The beakers a r e heated f o r a t l e a s t t h r e e days on a hot p l a t e a t 50oc, then the l i d s a r e removed and t h e l i q u i d a l l o w e d t o e v a p o r a t e . C o n c e n t r a t e d 2B HNO3 (2 ml) i s added t o d r i e d sample r e s i d u e s and samples a r e a g a i n t a k e n t o d r y n e s s . Two t o 3 ml 2N HC1 a r e added t o each beaker and e v a p o r a t e d down t o a m o i s t p a s t e (Arden and Gale 1974). The HC1 p u t s Pb and U i n t o s o l u t i o n e a s i l y , but f o r Th a n a l y s e s the r e s i d u e has t o be c o m p l e t e l y d i s s o l v e d by s e v e r a l l e a c h i n g s w i t h 6N H C 1 . E i g h t t o 10 ml 1N HBr i s then added t o the n e a r l y d r y c h l o r i d e s i n p r e p a r a t i o n f o r a n i o n exchange column s e p a r a t i o n of l e a d , uranium and t h o r i u m . B.3 ANION EXCHANGE COLUMN PROCEDURES I n i t i a l s e p a r a t i o n of l e a d , uranium and t h o r i u m i s a c h i e v e d u s i n g d i s p o s a b l e a n i o n exchange columns c o n t a i n i n g 4 ml c l e a n 201 AG1X8 100-200 mesh r e s i n (Kraus and N e l s o n 1958), and the column p r o c e d u r e d e s c r i b e d by Oversby (1975). Columns are c l e a n e d u s i n g two column volumes (CV's) of q u a r t z - d i s t i l l e d w a t e r , f o l l o w e d by two CV's of t w o - b o t t l e (2B) 6N HC1 and two CV's 2B H20. Columns a r e p r e p a r e d u s i n g two CV's 1N HBr, then the sample, i n 1N HBr, i s l o a d e d . For i s o t o p e d i l u t i o n (ID) runs the sample e l u t e , c o n t a i n i n g U and Th, i s saved. Three 2 ml a l i q u o t s then a f u r t h e r CV of 1N HBr a r e passed t h r o u g h and saved f o r f u r t h e r p u r i f i c a t i o n of U and Th (ID runs o n l y ) or d i s c a r d e d i n the case of l e a d i s o t o p i c c o m p o s i t i o n a n a l y s i s ( I C ) . Two 2 ml a l i q u o t s of 2N HC1 a r e added and d i s c a r d e d , then l e a d i s e l u t e d from the column i n one CV 6N HC1, i n t o a s m a l l (5 ml) S a v i l l e x b eaker. A f t e r e v a p o r a t i o n t o d r y n e s s the l e a d sample i s t a k e n up i n 2 ml HBr and passed through the same column proc e d u r e f o r a second time u s i n g s m a l l e r columns w i t h a 1 ml r e s i n bed. The sample, c o l l e c t e d i n 2 ml 6N HC1 i s e v a p o r a t e d t o d r y n e s s and i s then ready t o be l o a d e d onto a c l e a n rhenium f i l a m e n t . B.4 URANIUM AND THORIUM COLUMN PROCEDURE Uranium and t h o r i u m a re f u r t h e r c l e a n e d u s i n g the column pr o c e d u r e of Tatsumoto (1966). The s o l u t i o n c o n t a i n i n g U and Th i n HBr i s e v a p o r a t e d t o d r y n e s s and c o o l e d c o m p l e t e l y . C o n c e n t r a t e d 2B HNO3 i s added t o cover the bottom of the beaker and i s warmed t o d e s t r o y B r - . T h i s p r o c e s s i s r e p e a t e d t w i c e . Two t o 3 ml 7N 2B HNO3 a r e added t o d i s s o l v e the sample f o r l o a d i n g onto the column. S m a l l a n i o n exchange columns, c o n t a i n i n g 1 ml c l e a n AG1X8 100-200 mesh r e s i n , a r e c l e a n e d as b e f o r e , and then p r e c o n d i t i o n e d w i t h 2 CV's of 7N HNO3. The sample i s l o a d e d then r i n s e d w i t h two s m a l l a l i q u o t s of 7N HNO3. Uranium and t h o r i u m a r e c o l l e c t e d i n one CV of 2B H20 f o l l o w e d by one CV of 2B 6N H C l . F u r t h e r c l e a n u p i s a c h i e v e d by r e d i s s o l v i n g t h e sample i n 7N HNO3 and p a s s i n g i t t h r o u g h a c l e a n column a second time f o l l o w i n g the same p r o c e d u r e . B.5 PREPARATION AND LOADING OF FILAMENTS B.5.1 Lead Rhenium f i l a m e n t s a re p r e p a r e d and l o a d e d f o l l o w i n g the pro c e d u r e d e s c r i b e d under g a l e n a l e a d i s o t o p e a n a l y s i s . B.5.2 Uranium Rhenium f i l a m e n t s a r e p r e p a r e d , then baked out f o r 15 minutes a t 3.2 Amps i n a vacuum (2.0 x 10-5 t o r r ) . Tantalum 202 o x i d e i s used t o enhance i o n i z a t i o n of the o x i d e s . A drop of t a n t a l u m o x i d e i s l o a d e d onto each f i l a m e n t and a l l o w e d t o dry a t 1 . 0 Amp. A uranium sample i s t a k e n up i n 0.1N H N O 3 and l o a d e d on t o p of the t a n t a l u m o x i d e c o a t i n g , u s i n g a c l e a n p i p e t t e t i p f o r each sample. When d r y , a drop of 1N p h o s p h o r i c a c i d ( H 3 P O 4 ) i s l o a d e d on t o p and the f i l a m e n t g r a d u a l l y h e a t e d t o 2 . 0 amps. The f i n a l l o a d s h o u l d appear w h i t e a f t e r w h i t e fumes of H 3 P O 4 have been g i v e n o f f . B. 5.3 Thorium Thorium samples are l o a d e d onto o u t g a s s e d rhenium f i l a m e n t s u s i n g c o l l o i d a l g r a p h i t e t o enhance metal i o n i z a t i o n (Arden and Gale 1974). A drop of c o l l o i d a l g r a p h i t e i s d r i e d onto the f i l a m e n t a t 1 amp, then the t h o r i u m sample i s l o a d e d i n a drop of 1 N H N O 3 and a l l o w e d t o d r y . A drop of p h o s p h o r i c a c i d , f o l l o w e d by a second drop of c o l l o i d a l g r a p h i t e , a r e l o a d e d on t o p . The f i l a m e n t i s h e a t e d u n t i l w h i t e fumes of p h o s p h o r i c a c i d a re g i v e n o f f , but the f i l a m e n t s h o u l d not r e a c h r e d h e a t . The l o a d s h o u l d be b l a c k and matte. An a l t e r n a t i v e , s i m p l e r and e q u a l l y e f f e c t i v e l o a d i n g method i s t o t a k e up the sample i n 2 B H 2 0 or 1 N H N O 3 and d r y i t onto a baked out t a n t a l u m f i l a m e n t . Oxide peaks a r e then measured. B.6 MASS SPECTROMETRY PROCEDURES A l l of the r e p o r t e d a n a l y s e s were done i n the Geochronology L a b o r a t o r y a t the Department of G e o l o g i c a l S c i e n c e s , U.B.C., u s i n g a VG I s o t o p e s Isomass 54R mass s p e c t r o m e t e r l i n k e d t o a HP-85 microcomputer. B.6.1 Lead i s o t o p e c o m p o s i t i o n Lead samples a r e heated t o 1150o- 1250oc and r e q u i r e f r e q u e n t f o c u s i n g f o r the f i r s t few b l o c k s of d a t a . The i s o t o p i c c o m p o s i t i o n i s measured u s i n g e i t h e r "MSCOPB" OR "UBCZPB" programs. The f o r m e r , used i n i t i a l l y f o r g a l e n a a n a l y s e s , measures 208pb/204pb, 207pb/204pb and 206pb/204pb r a t i o s d i r e c t l y i n s e t s of f i v e per b l o c k . Due t o the u n c e r t a i n t y i n measuring the 204pb peak, i t was found t o be p r e f e r a b l e t o measure the 207pb/206pb, 208pb/206pb and 204pb/207pb r a t i o s u s i n g "UBCZPB". I n t h i s program the 204pb/207pb r a t i o i s measured t w i c e as o f t e n as the o t h e r two r a t i o s , i m p r o v i n g the s t a t i s t i c s on, the r a t i o . Background counts are measured a t mass 206.5 a t the b e g i n n i n g of each b l o c k t h r e e t i m e s , and b e f o r e and a f t e r the f i r s t two s e t s of f i v e r a t i o s . The background i s measured at mass 204.5 b e f o r e and a f t e r the 207pb/204pb r a t i o . 203 Raw d a t a i s c o n v e r t e d t o the 208pb/204pb, 207pb/204pb and 206pb/204pb r a t i o s , t h e n n o r m a l i z e d t o a b s o l u t e v a l u e s u s i n g c o r r e c t i o n f a c t o r s d e t e r m i n e d by r e p e a t e d a n a l y s e s of the Broken H i l l S t a n d a r d ( T a b l e s B.1 and B.2). Each a n a l y s i s i s r e p o r t e d w i t h an a s s o c i a t e d e r r o r based on a c o m b i n a t i o n of the f r a c t i o n a t i o n v a r i a t i o n between r u n s , the u n c e r t a i n t y i n mass f r a c t i o n a t i o n f a c t o r s ( T a b l e B.2; F i g . B.1), and w i t h i n - r u n p r e c i s i o n . The c o n v e r s i o n of raw d a t a , n o r m a l i z a t i o n and c o m b i n a t i o n of e r r o r s i s done u s i n g the program "WRPBIC" (Appendix D). B.6.2 Lead i s o t o p e d i l u t i o n I s o t o p e d i l u t i o n runs a re measured u s i n g "UBCOPB". T h i s program measures the 208pb/207pb and 206pb/208pb r a t i o s . Background measurements a r e made a t 206.5 b e f o r e and a f t e r each s e t of f i v e r a t i o s . The d a t a are c o r r e c t e d f o r mass f r a c t i o n a t i o n , then used t o c a l c u l a t e l e a d c o n c e n t r a t i o n s u s i n g the f o l l o w i n g e q u a t i o n : 208pbjnmoles = wt.84-3 x 207pb84-3 x A A = (1 - 208pb/204pb84-3 x 207pb/208pbi.D.) 207pb/208pbi.D. - 207pb/208pbi.c. where: 208pbumoles = jumoles 208pb i n the sample, 207pb84-3 = umoles/g 207pb i n the s p i k e 84-3, 208pb/207pb84-3 i s the r a t i o i n the s p i k e 84-3, 207pb/208pbl.D. i s the r a t i o i n the ID r u n , 207pb/208pbl.C. i s the r a t i o i n the sample, and wt.84-3 = weight of 84-3 used i n the ID r u n . T o t a l l e a d i s found by d i v i d i n g the number of moles of 208pb by the f r a c t i o n of 208pb d e t e r m i n e d from the IC run (atomic p r o p o r t i o n s and the at o m i c w e i ght of t h e sample a r e c a l c u l a t e d from the IC d a t a i n the c o n v e n t i o n a l way). The r e s u l t i s d i v i d e d by the weight of t h e sample and m u l t i p l i e d by the at o m i c weight of the sample l e a d t o g i v e the l e a d c o n c e n t r a t i o n i n ppm. T h i s can be checked u s i n g a s i m i l a r e q u a t i o n which uses the 206pb/207pb r a t i o s f o r the IC and ID runs and the 207pb/206pb r a t i o of the 84-3 s p i k e . The p r e p a r a t i o n , i s o t o p i c c o m p o s i t i o n , and l e a d c o n c e n t r a t i o n of mixed s p i k e 84-3 are g i v e n i n Appendix C. For l e a d c o n c e n t r a t i o n s l e s s than 1.3 ppm the i s o t o p i c c o m p o s i t i o n i s a d j u s t e d f o r b l a n k l e a d of measured c o m p o s i t i o n (n=2): 206pb/204pb = 18.329 + 0.010 207pb/204pb =15.619 + 0.011 204 TABLE B.1 Broken H i l l standard measurements for the period Dec. 1983 to Feb. 1985. DATE TEMPOC 206pb/204pb 207pb/204pb 208pb/204pb 18/12/83 1150 15 .961(0 .002) 15 .323(0 .002) 35 .467(0 .005) 18/12/83 1150 15 .958(0 .002) 15 .318(0 .001 ) 35 .438(0.005) 23/12/83 1200 15 .954(0 .001 ) 15 .295(0 .001 ) 35 .371(0 .004) 09/01/84 1150 15 .950(0 .002) 15 .307(0 .002) 35 .400(0 .005) 02/02/84 1100 15 .957(0 .001 ) 15 .321(0 .001 ) 35 .442(0 .003) 20/02/84 1140 15 .955(0 .003) 15 .314(0 .003) 35 .423(0 .006) 24/02/84 1150 15 .961(0 .003) 15 .320(0 .003) 35 .435(0 .006) 02/03/84 1150 15 .952(0 .034) 15 .320(0 .033) 35 .436(0 .076) 02/03/84 1150 15 .959(0 .008) 15 .323(0 .008) 35 .453(0 .018) 16/03/84 1150 15 .950(0 .002) 15 .313(0 .002) 35 .414(0 .005) 22/03/84 1150 15 .960(0 .002) 15 .314(0 .001 ) 35 .429(0.005) 29/03/84 1150 15 .972(0 .003) 15 .319(0 .001 ) 35 .447(0 .006) 02/04/84 1150 15 .970(0 .001 ) 15 .320(0 .001 ) 35 .455(0 .003) 17/04/84 1150 15 .945(0 .007) 15 .299(0 .007) 35 .367(0 .016) 30/05/84 1150 15 .950(0 .002) 15 .308(0 .002) 35 .398(0 .005) 31/05/84 1.150 15 .951(0 .001 ) 15 .311(0 .001 ) 35 .412(0 .003) 29/06/84 1150 15 .958(0 .004) 15 .321(0 .003) 35 .442(0 .009) 29/06/84 1150 15 .958(0 .002) 15 .320(0 .002) 35 .441(0 .005) 14/08/84 1150 15 .950(0 .004) 15 .313(0 .003) 35 .416(0 .009) 16/08/84 1150 15 .959(0 .004) 15 .319(0 .003) 35 .440(0 .010) 16/08/84 1150 15 .945(0 .006) 15 .304(0 .005) 35 .383(0 .019) 28/10/84 1150 15 .953(0 .004) 15 .307(0 .002) 35 .422(0 .013) 14/12/84 1150 15 .948(0 .010) 15 .310(0 .009) 35 .387(0 .019) 15/01/85 1150 15 .963(0 .005) 15 .323(0 .004) 35 .446(0 .013) 26/01/85 1150 15 .949(0 .002) 15 .310(0 .002) 35 .407(0 .006) MEAN VALUES (N=25) 15 .955 15 .314 35 .423 STD. DEV. . (S1) 0 .007 0 .008 0 .027 WEIGHTED MEAN WITHIN-RUN (S2) 0 .004 0 .004 0 .010 FRACTIONATION VARIATION BETWEEN RUNS (S3) 0 .006 0 .007 0 .025 WHERE S32 = S12 _ S22 205 TABLE B.2. Mass fractionation factors calculated for each of f i v e published Broken H i l l Standard values:- 1983 to 1985. REFERENCE 206pb/204pb 207pb/204pb 208pb/204pb 1) Coopers et al.(1969)16 .003 (0.011) 15 .390 (0 .013) 35 .660 (0.036) 2) Richards (1981) 16 .004 (0.006) 15 .390 (0 .007) 35 .651 (0.017) best double-spiked 3) Richards (1981 ) 16 .007 (0.012) 15 .395 (0 .010) 35 .665 (0.046) bias corrected 4) Richards and Blockley (1984) 16 .003 (0.013) 15 .386 (0 .013) 35 .640 (0.040) Canberra 5) Richards and 16 .005 (0.013) 15 .387 (0 .018) 35 .651 (0.055) Blockley (1984) Edmonton (Cumming) MEAN PUBLISHED VALUE 16 .004 (0.002) 15 .390 (0 .004) 35 .653 (0.010) MEAN MEASURED VALUE 15 .955 (0.007) 15 .314 (0 .008) 35 .423 (0,027) FRACTIONATION FACTORS1 1 .003096 1 .004937 1 .006503 STD. DEV. 0 .000105 0 .000229 0 .000271 1. Graphical representation of these fractionation factors (Fig. B.1) suggests that they are mass dependent. Assuming perfect mass dependence, the fractionation factor i s 0.159 +_ 0.004% per mass unit (see F i g . B.1). Fractionation factors used i n calculations were 1.0032 + 0.0002, 1.0048 + 0.0003, and 1.0064 + 0.0004 for the 206pb/2TT4pb, 207pb/204pb and 208pb/204pb r a t i o s respectively. 06 MASS DIFFERENCE F i g u r e B.1 G r a p h i c a l r e p r e s e n t a t i o n of the d e t e r m i n a t i o n of mass dependent f r a c t i o n a t i o n f a c t o r s , u s i n g York (1969) l e a s t squares l i n e a r r e g r e s s i o n . For p e r f e c t mass dependent f r a c t i o n a t i o n , the l i n e must pass through the o r i g i n . The f r a c t i o n a t i o n f a c t o r s d e t e r m i n e d i n Table B.2 f i t the l i n e wel so i t was assumed t h a t f r a c t i o n a t i o n f o r t h i s time p e r i o d was mass dependent. The 0.16% per mass u n i t f r a c t i o n a t i o n f a c t o r d e t e r m i n e d here was used i n d a t a r e d u c t i o n . 207 208pb/204pb = 38.065 + 0.011 The u n c e r t a i n t y i n the a n a l y s i s i s t h e n a d j u s t e d t o i n c l u d e the u n c e r t a i n t i e s i n the amount of l e a d s u b t r a c t e d and i n the c o m p o s i t i o n of the b l a n k l e a d , u s i n g the program "BLANKSUB" (Appendix D) . B.6.3 Uranium i s o t o p e d i l u t i o n Uranium i s measured a t 1300o- 1400oc u s i n g the program "UBCU" which measures the r a t i o of the uranium o x i d e peaks. A mass f r a c t i o n a t i o n f a c t o r of 0.006% per mass u n i t , based on re p e a t e d measurements of NBS U500 e q u a l atom uranium s t a n d a r d ( T a b l e B.3) i s a p p l i e d t o the measured r a t i o s . Uranium c o n c e n t r a t i o n s are c a l c u l a t e d u s i n g the e q u a t i o n : 238uumoles = 235uLrmoles x wt. 84-3 238U/235U84-3 - 238u/235ui.D. 238U/235UI.D. x 1/137.88 - 1 Where: 238uumoles = rxmoles 238u i n the sample, 235uumoles = umoles/g 235u i n the s p i k e (Appendix C ) , wt. 84-3 = weight i n grams of the 84-3 mixed s p i k e , 238U/235U84-3 = r a t i o i n the s p i k e (Appendix C ) , . 238u/235ui.D. = r a t i o i n the i s o t o p e d i l u t i o n r u n , and 1/137.88 = 235u/238u i n n a t u r a l samples. B.6.4 Thorium i s o t o p e d i l u t i o n Thorium i s o t o p e s are measured as met a l i o n s i n the case of c o l l o i d a l g r a p h i t e l o a d i n g , or as o x i d e s f o r t a n t a l u m f i l a m e n t s , a t 1800oc or more, u s i n g the program "UBCTH". Mass f r a c t i o n a t i o n was not d e t e r m i n e d f o r t h o r i u m because no t h o r i u m s t a n d a r d was a v a i l a b l e . However, i t can be assumed t o be q u i t e s m a l l i f s i m i l a r t o the f r a c t i o n a t i o n f a c t o r f o r uranium ( T a b l e B3). Thorium c o n c e n t r a t i o n s are then g i v e n by the e q u a t i o n : Th pmoles/g = 232Th84-2 x wt.84-2 Where: 230Th/232Th84-2 - 230rh/232Th I. D. 230Th/232Thi.D. x wt. sample 230Th/232Th84-2 =. r a t i o i n s p i k e 84-2 (Appendix C ) , 232Th84-2 = wmoles/g 232Th i n s p i k e (Appendix C ) , 230Th/232Thi.D. = r a t i o i n i s o t o p e d i l u t i o n r u n , wt.84-2 = weight of added s p i k e i n grams. In many runs of n a t u r a l r o c k samples, the r e l a t i v e s i z e s of the t h o r i u m i s o t o p e peaks changed w i t h t i m e . The 232Th peak d e c r e a s e d t o background l e v e l w i t h i n a few b l o c k s and the 230Th peak i n c r e a s e d d r a m a t i c a l l y . T h i s i n s t a b i l i t y i n d i c a t e s t h a t t h e r e are i n t e r f e r i n g i o n s , s i n c e i t i s not p o s s i b l e f o r a 208 TABLE B.3 Mass f r a c t i o n a t i o n f a c t o r f o r uranium d e t e r m i n e d by a n a l y s e s of the U500 NBS s t a n d a r d ( z i r c o n l a b o r a t o r y , UBC). The r e s u l t s were compared t o the c e r t i f i e d v a l u e s as f o l l o w s : DATE 235u/238rj 02/02/84 1 .000048 (0 .000051) 02/02/84 0 .999649 (0 .000439) 01/I 4/85 1 .000126 (0 .001 433 ) MEAN (n=3) 0 .999941 (0 .000148) CERTIFIED VALUE 0 .999698 (0 .00199) Mass f r a c t i o n a t i o n f a c t o r = 1.000243 or 0.006% per mass u n i t 209 s i n g l e element t o d i s p l a y t h i s type of b e h a v i o u r . The i o n s i n v o l v e d were not i d e n t i f i e d , but the problem may be e l i m i n a t e d by u s i n g a more r i g o r o u s column s e p a r a t i o n f o r t h o r i u m . The problem d i d not a r i s e i n measurements of the s p i k e a l o n e . 21 0 B.7 REAGENT PREPARATION B.7.1 Q u a r t z - d i s t i l l e d water D i s t i l l e d water from the g e o c h e m i s t r y l a b o r a t o r y , room 311, Department of G e o l o g i c a l S c i e n c e s , U.B.C., i s f u r t h e r d i s t i l l e d u s i n g a q u a r t z s t i l l i n the Geochronology l a b o r a t o r y , Department of G e o l o g i c a l S c i e n c e s , U.B.C. B.7.2 T w o - b o t t l e water A t w o - b o t t l e s t i l l of the type d e s c r i b e d by M a t t i n s o n (1971) i s used t o produce u l t r a p u r e water u s i n g the q u a r t z - w a t e r as f e e d . B.7.3 H y d r o c h l o r i c a c i d Reagent grade h y d r o c h l o r i c a c i d i s d i l u t e d t o 6N (1:1) w i t h d i s t i l l e d w a t e r . T h i s i s then d i s t i l l e d once u s i n g a q u a r t z s t i l l . The d i s t i l l a t e i s d i l u t e d as r e q u i r e d f o r gale n a a n a l y s e s , and used as f e e d f o r the s u b - b o i l i n g s t i l l ( M a t t i n s o n 1971) f o r whole r o c k l e a d a n a l y s i s . The t w o - b o t t l e 6N HC1 i s d i l u t e d t o 2N HC1 u s i n g t w o - b o t t l e w a t e r , f o r use i n a n i o n exchange column s e p a r a t i o n s . B.7.4 N i t r i c a c i d Reagent grade n i t r i c a c i d i s d i s t i l l e d once, a t f u l l s t r e n g t h , u s i n g a c o n v e n t i o n a l s t i l l . Once d i s t i l l e d n i t r i c a c i d i s used i n washing p r o c e d u r e s d i l u t e d 1:1 w i t h d i s t i l l e d w ater. U l t r a p u r e n i t r i c a c i d i s produced by the t w o - b o t t l e s u b - b o i l i n g d i s t i l l a t i o n of once d i s t i l l e d n i t r i c a c i d . T w o - b o t t l e 7N n i t r i c a c i d i s o b t a i n e d by d i l u t i n g t w o - b o t t l e c o n c e n t r a t e d n i t r i c a c i d w i t h t w o - b o t t l e w a t e r . B.7.5 Hydrobromic a c i d Reagent grade hydrobromic a c i d ( a p p r o x i m a t e l y 9N) i s d i s t i l l e d u s i n g the t w o - b o t t l e s u b - b o i l i n g a p p a r a t u s ( M a t t i n s o n 1971). The d i s t i l l a t e i s th e n d i l u t e d t o 1N u s i n g t w o - b o t t l e w a t e r . B.7.6 H y d r o f l u o r i c a c i d Reagent grade h y d r o f l u o r i c a c i d i s d i s t i l l e d u s i n g the t w o - b o t t l e s u b - b o i l i n g s t i l l ( M a t t i n s o n 1971). B.7.7 S i l i c a g e l - p h o s p h o r i c a c i d A 1M s o l u t i o n of p h o s p h o r i c a c i d was p r e p a r e d i n a c l e a n t e f l o n b o t t l e u s i n g u l t r e x phosphorus p e n t o x i d e , and t w o - b o t t l e w a t e r . Fumed s i l i c a (BDH Chemicals L t d . , T o r o n t o ) was added t o the s o l u t i o n and shaken f o r s e v e r a l m i n u t e s . The s o l u t i o n was f u r t h e r shaken u l t r a s o n i c a l l y f o r an hour. The m i x t u r e was l e f t t o s t a n d f o r 24 h o u r s , then the s u p e r n a t e n t c o l l o i d a l s o l u t i o n was decanted i n t o a c l e a n t e f l o n b o t t l e f o r use i n the l o a d i n g p r o c e d u r e . 21 1 B . 7 .8 C o l l o i d a l g r a p h i t e Aquadag c o l l o i d a l g r a p h i t e was p r o v i d e d by Dr. Hooley, Department of C h e m i s t r y , the U n i v e r s i t y of B r i t i s h Columbia. B .8 MEASUREMENT OF BLANKS Lead i s a p e r v a s i v e c o n t a m i n a n t , so i t i s e s s e n t i a l t o a s s e s s the c o n t r i b u t i o n of b l a n k l e a d t o the a n a l y s e s by measuring the c o n t e n t of l e a d i n each of the r e a g e n t s , the d i s s o l u t i o n p r o c e s s , the column p r o c e d u r e s and f i n a l l y i n the l o a d i n g p r o c e s s . T o t a l p r o c e d u r a l b l a n k s a r e r o u t i n e l y measured by a d d i n g a known amount of a s p i k e s o l u t i o n t o a beaker and t r e a t i n g i t i n the same way as a sample. The change i n the i s o t o p i c c o m p o s i t i o n of the s p i k e l e a d i s the n p r o p o r t i o n a l t o the amount of contaminant or b l a n k l e a d i n the p r o c e s s . T h i s can be a c c u r a t e l y measured u s i n g the i s o t o p e d i l u t i o n e q u a t i o n and the i s o t o p i c c o m p o s i t i o n of the b l a n k l e a d (see page 203). T o t a l b l a n k s a re l i s t e d i n Ta b l e B . 4 . Reagent b l a n k s were measured by add i n g s p i k e l e a d t o two d i f f e r e n t volumes of each r e a g e n t . A graph was then drawn f o r each. The s l o p e of the l i n e g i v e s the c o n c e n t r a t i o n of b l a n k l e a d per ml, and the i n t e r c e p t s h o u l d be the l o a d i n g p l u s h a n d l i n g b l a n k . U s i n g t h i s t e c h n i q u e ( P a t t e r s o n i n p r e s s ) the reag e n t b l a n k s were measured (Table B . 5 ) . An assessment of the c o n t r i b u t i o n of r e a g e n t and o t h e r b l a n k s t o the t o t a l b l a n k i s made i n Table B . 6 . I t was found t h a t the r e a g e n t s , HBr i n p a r t i c u l a r , p r o v i d e a l a r g e p r o p o r t i o n of l e a d t o the t o t a l b l a n k , so a r e d u c t i o n i n the q u a n t i t y of r e a g e n t s used would s i g n i f i c a n t l y reduce the b l a n k . B l a n k s were not de t e r m i n e d f o r uranium and t h o r i u m i s o t o p e d i l u t i o n r u n s . S e v e r a l a t t e m p t s were made t o measure the t o t a l p r o c e d u r a l uranium b l a n k , but i n each case the 238u peak was not found. T h i s i n d i c a t e s t h a t the b l a n k l e v e l s a r e i n s i g n i f i c a n t . 21 2 TABLE B.4 T o t a l p r o c e d u r a l b l a n k s f o r 1983 t o 1985 DATE BEAKER TYPE SAMPLE SIZE BLANK (ng) 28/09/83 30ml t e f l o n 1 . Og 24 .0a 11/10/83 30ml t e f l o n 1 . Og 22 .7a 03/11/83 30ml t e f l o n 1 . Og 48 .0a 27/11/83 30ml t e f l o n 1 .0g 8 .3 1 7/02/84 1 5ml s a v i l l e x 0 .6g 7 .7 19/03/84 1 5ml s a v i l l e x 0 . 6g 7 .7 17/04/84 1 5ml s a v i l l e x 0 . 6g 8 .2 24/05/84 1 5ml s a v i I l e x 0 . 6g 21 .5b 30/05/84 1 5ml s a v i l l e x 0 .6g 10 .4b 1 1/07/84 1 5ml s a v i l l e x 0 . 6g 4 . 5 11/07/84 1 5ml s a v i l l e x 0 . 6g 8 .1 10/01/85 1 5ml s a v i l l e x 0 . 6g 4 .3 Maximum and minimum b l a n k s f o r v a r i o u s p a r t p r o c e s s e s : L o a d i n g b l a n k (n=8) 0.069-0.386ng Beaker b l a n k s ( i n c l u d e s l o a d i n g , n=7) 0.127-0.350ng D i s s o l u t i o n b l a n k (n=1) 0.755ng Large column b l a n k (n=4) 7.6-9.3ng S m a l l column b l a n k (n=2) 2.8-9.8ng a. These h i g h , v a r i a b l e b l a n k s were the r e s u l t of a h o l e i n the f i l t e r of the c l e a n a i r hood. b. High b l a n k s were measured a f t e r an u n f o r t u n a t e a c c i d e n t w i t h the c l e a n a i r hood. No samples were measured a t t h i s t i m e . 213 TABLE B.5 Reagent b l a n k s f o r 1983 t o 1985 DATE REAGENT BLANK1 SLOPE2 INTERCEPT3 Nov 83 2B H2Q 0 .043 ng/ml Jan 84 2B H20 0 .045 ng/ml Jan 85 2B H20 0 .01 7 ng/ml 0 .005 ng/ml 0 .292 ng Nov 83 Q H20 0 .107 ng/ml 0 .066 ng/ml 0 .197 ng Nov 85 HF 0 .074 ng/ml Mar 84 HF 0 .085 ng/ml Jan 85 HF 0 .045 ng/ml 0 .027 ng / ml 0 .465 ng Nov 83 cone. HN03 0 .209 ng/ml Feb 84 cone. HNO3 0 .105 ng/ml 0 .065 ng/ml 0 .438 ng Jan 85 cone. HNO3 0 .147 ng/ml Nov 83 6N HC1 0 .01 9 ng/ml Mar 84 6N HC1 0 .054 ng/ml Jan 85 6N HC1 0 .037 ng/ml 0 .02 9 ng/ml 0 .178 ng Nov 83 1N HBr 0 .104 ng/ml 0 .058 ng/ml 0 .459 ng Mar 84 1N HBr 0 .1 58 ng/ml Jan 85 1N HBr 0 .100 ng/ml 0 .088 ng/ml 0 .476 ng Mar 84 2N HC1 0 .145 ng/ml 0 .077 ng/ml 0 .544 ng Jan 85 2N HC1 0 .130 ng/ml 0 .038 ng/ml 2 .291 ng 1. B l a n k i s c a l c u l a t e d by d i v i d i n g the b l a n k by the volume of r e a g e n t on which the b l a n k was d e t e r m i n e d . Where two volumes were d e t e r m i n e d , the b l a n k quoted i s f o r the l a r g e r volume. 2. T h i s column i s f o r b l a n k s which have been determined by measuring b l a n k l e v e l s i n two d i f f e r e n t volumes of r e a g e n t . The b l a n k i s then found by d i v i d i n g the d i f f e r e n c e i n b l a n k v a l u e s by the d i f f e r e n c e i n volume. 3. The b l a n k v a l u e i n t h i s column s h o u l d be a p p r o x i m a t e l y c o n s t a n t f o r d i f f e r e n t r e a g e n t s , and s h o u l d r e p r e s e n t the b l a n k due t o sample l o a d i n g and h a n d l i n g . 21 4 TABLE B.6 Summation of b l a n k s measured from 1983 t o 1985 DISSOLUTION: 1 Beaker (10 ml) 0. 1 27 ng/ml 2B HF 5 ml § .027 ng/ml 0. 1 35 ng/ml 2B cone. : HN03 3 ml @ .147 ng /ml 0. 441 ng/ml LARGE COLUMN: 2B 2N HC1 3 ml @ .130 ng/ml 0. 390 ng/ml 2B 1N HBr 25 ml @ .088 ng/ml 2. 200 ng/ml 2B 6N HC1 8 ml § .029 ng/ml 0. 232 ng/ml SMALL COLUMN: 2B 1N HBr 10 ml @ .088 ng/ml 0. 880 ng/ml 2B 2N HC1 1 ml @ .130 ng/ml 0. 1 30 ng/ml 2B 6N HC1 4 ml @ .029 ng/ml 0. 11 6 ng/ml S m a l l beaker (5 ml) 0. 1 27 ng/ml LOADING: T o t a l l o a d i n g procedure 0. 070 ng/ml Sum of b l a n k s as above = 4.721 ng T o t a l b l a n k measured = 4.3 ng ( f o r J a n . 1985 ) Most of the measured b l a n k can be acco u n t e d f o r by the r e a g e n t s . D e c r e a s i n g the q u a n t i t i e s o f r e a g e n t s used would s i g n i f i c a n t l y reduce the t o t a l b l a n k . 21 5 B.9 DATA QUALITY B.9.1 Lead i s o t o p e c o m p o s i t i o n W i t h i n - r u n mass-spectrometer p r e c i s i o n i s u s u a l l y b e t t e r t h a n 0.03%. R e p r o d u c i b i l i t y (1 sigma) of the Broken H i l l Galena S t a n d a r d (Table B.1) i s 0.025% f o r the 206pb/204pb r a t i o , 0.052% f o r the 207pb/204pb r a t i o and 0.090% f o r the 208pb/204pb r a t i o based on 2,5 a n a l y s e s of the s t a n d a r d over the p e r i o d d u r i n g which a l l of the r o c k l e a d a n a l y s e s were done. U n c e r t a i n t y i n mass f r a c t i o n a t i o n i s added t o the measured w i t h i n - r u n p r e c i s i o n f o r each a n a l y s i s by the p r o c e s s of e r r o r p r o p a g a t i o n (Rees 1984). D u p l i c a t e a n a l y s e s of sample powders f o r t e n r o c k s ( T a b l e s B.7, B.8 and B.9) i n d i c a t e t h a t the one sigma e r r o r i n each of the r a t i o s i s as f o l l o w s : 206pb/204pb = 0.14%, 207pb/204pb = 0.08%, and 208pb/204pb = 0.06%. T h i s i s comparable t o the propagated e r r o r s based on mass s p e c t r o m e t r y and mass f r a c t i o n a t i o n e r r o r s a l o n e . I t i n c l u d e s sample inhomogeneity and/or d i s s o l u t i o n d i f f e r e n c e s between samples. G e o l o g i c a l s a m p l i n g e r r o r was a s s e s s e d by comparing r e s u l t s f o r t h r e e r o c k s from d i f f e r e n t l o c a t i o n s w i t h i n the same homogeneous r h y o l i t e dome (samples R78, R90 and R91 ), and two r o c k s (L/T1 and L/T4) from the same d i o r i t e sheet (Table B.10). Approximate e r r o r l i m i t s were det e r m i n e d as f o l l o w s : 206pb/204pb = 0.22%, 207pb/204pb = 0.08%, and 208pb/204pb = 0.15%. T h i s i n c l u d e s a l l p o s s i b l e s o u r c e s of e r r o r . A c c u r a c y was a s s e s s e d by a n a l y z i n g BCR-1 r o c k s t a n d a r d and comparing the r e u l t s t o those of Tatsumoto e t a l . (1972). R e s u l t s ( T a b l e B.11) a r e 0.10% t o 0.15% h i g h e r than the s t a n d a r d v a l u e . B.9.2 Lead c o n c e n t r a t i o n Lead c o n c e n t r a t i o n s a r e p r e c i s e t o +_ 0.1 ppm or 3% based on s i x d u p l i c a t e a n a l y s e s ( T a b l e B.12). P r o p a g a t i o n of e r r o r s u s i n g "WRPBID" p r e d i c t s a p r e c i s i o n of 0.3% based on u n c e r t a i n t i e s i n s p i k e c o n c e n t r a t i o n and c o m p o s i t i o n , w e i g h i n g e r r o r s , mass s p e c t r o m e t r y and mass f r a c t i o n a t i o n . Weighing e r r o r s and the u n c e r t a i n t y i n the c o n c e n t r a t i o n of l e a d i n the s p i k e are the major c o n t r i b u t i n g f a c t o r s t o the o v e r a l l u n c e r t a i n t y i n l e a d c o n c e n t r a t i o n s . The d i f f e r e n c e i n u n c e r t a i n t i e s c a l c u l a t e d from d u p l i c a t e a n a l y s e s , and p r e d i c t e d TABLE B.7 U n c e r t a i n t y i n 206pb/204pb R a t i o s SAMPLE NO . 1 NO. 2 1-2 (1 -2)2 H1 OA 1 9 .626 19.639 -0.013 0. 000169 W1 49 1 8 .756 18.748 0.008 0. 000064 GRHY 1 9 .351 19.412 -0.061 0. 0,03721 R78 1 9 . 561 1 9 . 51 9 0.042 0. 001764 R91 1 9 .430 19.444 -0.014 0. 000196 K005 1 9 .183 19.224 -0.041 0. 001681 KAR2 1 9 .000 18.998 0.002 0. 000004 KAR7 1 9 . 397 19.416 -0.019 0. 000361 KAR1 0 1 8 .71 5 18.728 -0.013 0. 000169 KAR11 18 .999 18.928 0.071 0. 005041 TOTAL = = 0. 013170 S2 = (0 .013170)/(2(N -1 )) S = 0.027 (0.14%) TABLE B.8 U n c e r t a i n t y i n 207pb/204pb r a t i o s SAMPLE NO . 1 NO. 2 1 -2 (1-2)2 H1 OA 1 5 .644 15.643 0.001 0 .000001 W1 49 1 5 . 571 15.566 0.005 0 .000025 GRHY 15 .630 15.635 -0.005 0 .000025 R78 1 5 .596 15.644 -0.048 0 .002304 R91 1 5 .602 15.630 -0 .018 0 .000324 K005 1 5 .605 15.618 -0.013 0 .000169 KAR2 1 5 .599 15.596 0.003 0 .000009 KAR7 1 5 .592 15.587 0.005 0 .000025 KAR1 0 1 5 .551 15.563 -0.012 0 .000144 KAR11 1 5 .583 15.588 -0.005 0 .000025 TOTAL = = 0 .003051 S2 = 0. 003051/2(N- 1 ) S = 0.013 (0.08%) TABLE B.9 : U n c e r t a i n t y i n 208p D/204pb r a t i o s SAMPLE NO . 1 NO . 2 1 -2 (1-2)2 H1 OA 38 .933 38 .937 -0. 004 0.000016 W1 49 38 .245 38 .229 0. 01 6 0.000256 GRHY 38 .627 38 .633 -0. 006 0.000036 R78 38 .934 38 .970 -0. 036 0.001296 R91 38 .865 38 .900 -0. 035 0.001225 K005 38 .81 4 38 .881 -0. 067 0.004489 KAR2 38 .568 38 .569 -0. 001 0.000001 KAR7 38 .951 38 .975 -0. 024 0.000576 KAR1 0 38 .1 44 38 .176 -0 . 032 0.001024 KAR1 1 38 .325 38 .31 3 0. 01 2 0.000144 TOTAL = 0.009063 S2 = (0.009063)/2(N-1) 'S = 0.022 (0.06%) TABLE B.10 E s t i m a t e d s a m p l i n g e r r o r SAMPLE RATIO MEAN DIFF. DIFF.2 R78 R90 R91 L/T1 L/T4 19 1 9 • 19. 18, 18, 540 512 437 958 902 19 19 19 18 18 496 496 496 930 930 0.044 0.01 6 0.059 0.028 0 .028 0, 0, 0, 0, 0, 001936 000256 003481 000784 000784 206pb/204pb S2= 0.007241 0.007241 s = 0.043 (0.22%) R78 R90 R91 L/T1 L/T4 1 5 15 1 5 1 5 , 15, 620 641 61 1 597 61 9 1 5 1 5 1 5 1 5 15 624 624 624 608 608 0. 0 o; 0, 0, 004 01 7 01 3 01 1 01 1 0, 0, 0, 0, 0. 000016 000289 000169 000121 000121 207pb/204pb s2= 0.000716 0.000716 s = 0.014 (0.08%) R78 R90 R91 L/T1 L/T4 38.952 39.047 38.888 38.559 38.501 38.962 38.962 38.962 38.530 38.530 0.01 0 0.075 0.074 0.02 9 0.029 208pb/204pb S2= 0.013496 0.000100 0.007225 0.004489 0.000841 0.000841 0.013496 s = 0.058 (0.15%) Table B.11. Accuracy assessment using BCR-1 standard Date 206pb/204 Pb 207pb/204pb 208pb/204pb Pb (ppm) March 1985 18. .81 9 (0. .006) 15, .633 (0. .008) 38. .71 5 (0. . 027 ) 13. .40 (0.03) May 1985 1 8 , .81 0 (0. .008) 15. .626 (0. .008) 38. .693 (0. .029) 13. .89 (0.05) Tatsumoto et al. 1972 1) Double spike corrected 1 8 , .794 1 5 . . 61 0 38. .660 13. .564 (0.38) 2) s i l i c a gel--0.15% mass f r a c t i o n a t i o n c o r r e c t i o n 18. .784 1 5 . .632 38. . 653 Measured i s o t o p i c compositions of BCR-1 are 0.1-0.15% greater than p u b l i s h e d values of Tatsumoto et a 1 • 1972. Measured lead concentrations are w i t h i n ttie u n c e r t a i n t i e s quoted for the standard value. TABLE B.12: R e p r o d u c i b i l i t y i n l e a d c o n c e n t r a t i o n s measured i n whole r o c k samples SAMPLE NO. 1 NO. 2 1-2 (1-2)2 683421 5.112 5.016 0.096 0.009216 K005 1.421 1.362 0.059 0.003481 R90 5.359 5.114 0.243 0.059049 MT. W. 1.887 1.932 0.045 0.002025 MT59 4.058 3.907 0.151 0.022801 MT360 5.236 5.354 0.118 0.013924 TOTAL = 0.110496 S2 = (0.1 10496)/2(N-1 ) S = 0.105 ppm ( a p p r o x i m a t e l y 3%) 222 from e r r o r p r o p a g a t i o n , may be due to inhomogeneity i n sample powders, or i n c o m p l e t e d i s s o l u t i o n . However, the a c c u r a c y of the BCR1 a n a l y s i s argues a g a i n s t the l a t t e r , a t l e a s t f o r b a s a l t s . A c c u r a c y was t e s t e d by a n a l y z i n g BCR-1 roc k s t a n d a r d . The measured v a l u e s ( T a b l e B.11) were w i t h i n one sigma of the s t a n d a r d v a l u e of Tatsumoto e t a l . (1972). B.9.3 Uranium c o n c e n t r a t i o n One d u p l i c a t e a n a l y s i s of sample 643421 i n d i c a t e s t h a t the p r e c i s i o n might be as good as _+ 0.01 ppm or 1%. E r r o r p r o p a g a t i o n by the method of Rees (1984) suggests t h a t the uranium a n a l y s e s a re p r e c i s e t o about 1% depending on w e i g h i n g e r r o r s , u n c e r t a i n t i e s i n the s p i k e c a l i b r a t i o n and mass s p e c t r o m e t r y . A c o n s i s t a n t b i a s i s d e t e c t a b l e between d a t a from n e u t r o n a c t i v a t i o n a n a l y s i s or gamma r a y s p e c t r o s c o p y and i s o t o p e d i l u t i o n d a t a . T h i s i s p r o b a b l y due t o t h e d i f f e r e n t a n a l y t i c a l t e c h n i q u e s . Neutron a c t i v a t i o n and gamma r a y s p e c t r o s c o p y numbers are u n l i k e l y t o be more p r e c i s e than 10%, t h e r e f o r e i t was thought t o be r e a s o n a b l e t o a d j u s t t h e s e numbers by a s u i t a b l e f a c t o r t o be more c o n s i s t e n t w i t h the r e s u l t s of i s o t o p e d i l u t i o n a n a l y s i s . An adjustment f a c t o r was det e r m i n e d by comparing the r e s u l t s of n i n e samples t h a t , have uranium v a l u e s d e t e r m i n e d by both i s o t o p e d i l u t i o n and n e u t r o n a c t i v a t i o n or gamma r a y a n a l y s i s (Table B.13). B.9.3. Thorium c o n c e n t r a t i o n There a re i n s u f f i c i e n t d a t a t o a s s e s s the e r r o r l i m i t s on th o r i u m a n a l y s e s , o t h e r than by e r r o r p r o p a g a t i o n , which s u g g e s t s t h a t the e r r o r i s q u i t e s m a l l , i n the o r d e r of 1%. T h i s i s the minimum e r r o r a s s o c i a t e d w i t h an a n a l y s i s , s i n c e both l e a d and uranium c o n c e n t r a t i o n s have a c t u a l u n c e r t a i n t i e s which a r e l a r g e r than those e s t i m a t e d by e r r o r p r o p a g a t i o n . 223 TABLE B.13 B i a s i n uranium c o n c e n t r a t i o n s measured by d i f f e r e n t methods. I.D. = i s o t o p e d i l u t i o n ; " o t h e r " i s gamma r a y s p e c t r o s c o p y or n e u t r o n a c t i v a t i o n a n a l y s i s . SAMPLE I.D. o t h e r o t h e r / I . D . R1 31 1.16 1.63 1 .4052 ZEBALLOS 1.10 1 .29 1 .1727 681381 1 .47 1 .68 1 .1 429 683421 1 .04 1.13 1 .0865 6921 31 2.12 2.29 1 .0802 K005 0.31 0.32 1 .0323 K007 0.32 0.34 1 .0625 MB001 0.90 0.97 1 .0778 FAITH LAKE 0.25 0.39 1 .5600 Mean v a l u e l (n=7) = = 1.0935 + 0.0196 + one s t d . e r r o r 1.Samples R131 and F a i t h Lake were e x c l u d e d from the mean because t h e i r f a c t o r s were i n exces s of 2 sigma from the mean v a l u e . 224 APPENDIX C SPIKE CALIBRATIONS C.1 CALIBRATION OF STOCK (300 PPM) 207pB SPIKE Stock 207pb s p i k e was found on the s h e l f i n the z i r c o n l e a d c h e m i s t r y l a b i n the Department of Geophysics and Astronomy, U.B.C., l a b e l l e d : .238256 g Pb(N03)2 per 500 ml (300 ppm). 50 ml of t h i s s o l u t i o n was decanted i n t o a c l e a n t e f l o n b o t t l e and r e l a b e l l e d "84-2 cone. 207pb s p i k e " . T h i s was then c a l i b r a t e d as f o l l o w s . C.1.1 I s o t o p i c C o m p o s i t i o n The i s o t o p i c c o m p o s i t i o n of t h i s s p i k e was d e t e r m i n e d as i n Table C.1. TABLE C.1 I s o t o p i c c o m p o s i t i o n of s p i k e 84-2 Date 208Pb/207Pb 206Pb/208Pb 204Pb/206Pbi 11/11/83 0.058928(0.000054) 0.389318(0.000263) 25/11/83 0.058915(0.000009) 0.389480(0.000032) 0.004464(0.000017) 0.004744(0.000210) Mean : 0.058922(0.000039) 0.389399(0.000187) 0.004464(0.000017) 1. The 204pb/206pb r a t i o for 25/11/83 was excluded from the mean value because of i t s poor in-run precision. R a t i o s were c o n v e r t e d and c o r r e c t e d f o r 0.16% per mass u n i t mass f r a c t i o n a t i o n . G i v i n g : 1. A b s o l u t e R a t i o s : 206pb/204pb = 224.731 + 0.856, 207pb/204pb = 9809.865 + 37.405, and 208pb/204pb = 576.939 + 2.206. 2. Atomic weight = 207.009001. 3. Atom p e r c e n t : 206pb = 0.021172, 207pb = 0.924192, 208pb = 0.054542, and 204pb = 0.000094. C.1.2 I s o t o p e d i l u t i o n The c o n c e n t r a t i o n of l e a d i n the s p i k e s o l u t i o n was de t e r m i n e d by i s o t o p e d i l u t i o n u s i n g a s t a n d a r d s o l u t i o n of 225 NBS981 p r e v i o u s l y c a l i b r a t e d by Pat Shore (see z i r c o n l a b book of s t a n d a r d s and s p i k e s , 1979). The c o n c e n t r a t i o n of NBS981 79-2 s t a n d a r d was t a k e n t o be 10.734877 +/- 0.004561. E r r o r s a re based on the maximum p o s s i b l e w e i g h i n g e r r o r s ( P . J . S h o r e ) . The i s o t o p i c c o m p o s i t i o n of NBS981 i s g i v e n by t h e N a t i o n a l Bureau of S t a n d a r d s . R e s u l t s of f o u r i s o t o p e d i l u t i o n runs are i n T a b l e C.2. TABLE C.2 I s o t o p e d i l u t i o n runs f o r s p i k e 84-2 Run 84-2 (g) NBS981 (g) raw 208pb/207pb T o t a l Pb (ppm) 1 0 .00339 3.6008 2.132449(0.000169) 307.568 2 0 .00320 1.5336 1 .895208(0.0021 22) 315.361 3 0 .00916 0.5750 0.849568(0.000204) 309.001 4 0 .00961 0.6888 0.918939(0.005904) 309.067 Runs 3 and 4 i n Table C.2 were c o n s i d e r e d most r e l i a b l e because they were not swamped by NBS981 l e a d . The c o n c e n t r a t i o n i s t a k e n t o be 309 ppm. C.2 PREPARATION OF 84-3 MIXED 20_7pB AND 235TJ SPIKE S p i k e 84-3 was p r e p a r e d from 79-2 235rj c o n c e n t r a t e d s t o c k s o l u t i o n w i t h a c o n c e n t r a t i o n of 1143.5 ppm ( P . J . Shore) and 84-2 207pb s p i k e w i t h a c o n c e n t r a t i o n of a p p r o x i m a t e l y 309 ppm. R e q u i r e d c o n c e n t r a t i o n s a r e : 235IJ = 2 ppm, and 207pb = 2 ppm. A 500 ml f i n a l s o l u t i o n r e q u i r e s 1000 ug 235u (0.8745 g of s p i k e 79-2) and 1000 ug 207pb (3.236 g of s p i k e 84-2). C a l c u l a t i o n s f o r mixed s p i k e 84-3 a r e : 1. weight of c l e a n t e f l o n beaker + 235TJ 79-2 s p i k e = 10 .2421 , weight of beaker = 9.3590, 2. nominal weight of 235TJ = 0.8831 x 11 43.5 = 1009.82 jag, 3. weight of c l e a n t e f l o n beaker + 207pb 84-2 s p i k e = 12.3562, weight of beaker = 9.3750, 4. nominal weight of l e a d = 2.981 2 x 309 = 921 .19 jag. A l l of the above w e i g h i n g s were done i n t h e z i r c o n l a b u s i n g a M e t t l e r b a l a n c e . The two s o l u t i o n s were t r a n s f e r r e d i n t o a weighed 500 ml screw-top v o l u m e t r i c f l a s k w i t h TFE t e l o n cap l i n e r , and d i l u t e d t o 500 ml w i t h 2N HNO3. R e l e v a n t c a l c u l a t i o n s a r e : 1. v o l u m e t r i c f l a s k + l a b e l + cap = 179.095 g (1200 g P300 b a l a n c e ) , 2. f i n a l s o l u t i o n = 713.340 ( M e t t l e r P1200 b a l a n c e ) , 226 3. weight of s o l u t i o n = 534.245, and 4. nominal c o n c e n t r a t i o n s of Pb = 1.721 ppm, and U = 1.887 ppm. C.3 CALIBRATION OF 84-3 MIXED SPIKE C.3.1 I s o t o p e c o m p o s i t i o n of l e a d i n s p i k e 84-3 The i s o t o p i c c o m p o s i t i o n of l e a d i n 84-3 was de t e r m i n e d by the r e p e a t e d a n a l y s e s i n T a b l e C.3. TABLE C.3 C o m p o s i t i o n of l e a d i n s p i k e 84-3; 1984. Date 208pb/207pb 206pb/208pb 204pb/206pb 13/2/84 0.058932 0.390159 0.004519 1/7/84 0.058934 0.389827 0.004351 2/7/84 0 .058940 0.3901 81 0.004503 1/8/84 0.058934 0.389982 0.004481 2/8/84 0.058936 0.390229 0.004597 3/T1/84 0.058922 0.390235 0.004314 16/11/84 0.058905 0.390071 0.004488 10/12/84 0.058893 0.390033 0.004425 11/12/84 0.058910 0.389845 0.004446 MEAN1: 0.058934 0.390062 0.004458 (0.000016) (0.000154) (0.000087) C o n v e r t e d r a t i o s , c o r r e c t e d f o r mass u n i t ) , a r e : 206pb/204pb = 225.034 207pb/204pb = 9804.828 208pb/204pb = 578.758 0.16% mass f r a c t i o n a t i o n (per 208pb/207pb = 0.059028 206pb/208pb = 0.388818 Atomic weight = 207.0089702 Atomic p r o p o r t i o n s are:206pb 207pb 208pb 204pb 0.021210373 0.924145068 0.054550304 0.000094254 1. The mean v a l u e and one s t a n d a r d d e v i a t i o n i s g i v e n f o r each r a t i o . C.3.2 I s o t o p e d i l u t i o n c a l c u l a t i o n s f o r l e a d i n s p i k e 84-3 Three i s o t o p e d i l u t i o n runs were done u s i n g each of two c a l i b r a t e d s o l u t i o n s ; 79-3 mixed 235TJ and 208pb s p i k e ( z i r c o n l a b o r a t o r y ) , and NBS981 s t a n d a r d s o l u t i o n 79-3 ( z i r c o n l a b o r a t o r y ) . The f o l l o w i n g s p i k e c o n s t a n t s were used f o r the 227 mixed s p i k e from c a l i b r a t i o n s by P Van der Heyden, z i r c o n l a b o r a t o r y s p i k e s and s t a n d a r d s book, 1984: 1. atomic p r o p o r t i o n s : 20 8 p D = 0.990854254, 207pb = 0.006958367, 206pb = 0.002148874, and 204pb = 0.000038505. 2. C o n c e n t r a t i o n of l e a d = 1.08596 ppm NBS c e r t i f i e d v a l u e s were used f o r the i s o t o p i c c o m p o s i t i o n of NBS981 79-3 s t a n d a r d , and the c o n c e n t r a t i o n as b e f o r e (see c a l i b r a t i o n of s p i k e 84-2). I s o t o p e d i l u t i o n c o n d i t i o n s and r e s u l t s a re i n Table C.4. TABLE C.4 I s o t o p e d i l u t i o n c o n d i t i o n s and r e s u l t s f o r l e a d i n s p i k e 84-3 RUN 79-3 (g) 84-3 (g) 208pb/207pb T o t a l Pb cone 1 0.5555 0.4113 0.939626 x 1 .001 6 1.762 2 0.4909 0.5040 0.696130 x 1.0016 1 .757 3 0.5886 0.3481 1.161474 x 1.0016 1 .760 NBS981 (g) 4 0.8149 0.9842 1 .321 01 3 x 1 .001 6 1 .758 5 0.2204 0.4335 1.038981 x 1.0016 1 .764 6 0.1852 0.3243 1.105313 x 1.0016 1 .765 Mean v a l u e (n=6) = 1.761 +/- 0.003 ppm C .3 .3 I s o t o p e c o m p o s i t i o n of uranium i n s p i k e 84-3 The i s o t o p i c c o m p o s i t i o n of 84-3 s p i k e was t a k e n t o be the same as t h a t of the s t o c k c o n c e n t r a t e d 235u s p i k e s o l u t i o n . The 235u/238u r a t i o f o r 79-2 uranium s p i k e has been found t o be 8742 (P. Van der Heyden, z i r c o n l a b o r a t o r y s p i k e s and s t a n d a r d s book 1984). C .3 .4 I s o t o p e d i l u t i o n c a l c u l a t i o n s f o r uranium i n s p i k e 84-3 S p i k e 84-3 was c a l i b r a t e d a g a i n s t 79-5 U500 e q u a l atom s t a n d a r d (NBS), which has a c o n c e n t r a t i o n of 24.9117 ppm (P. Shore, s p i k e s and s t a n d a r d s book, 1979). R e s u l t s a r e i n Table C . 5 . 228 TABLE C.5 I s o t o p e d i l u t i o n r e s u l t s f o r uranium i n s p i k e 84-3. RUN U500 (g) 84-3 (g) 235u/238u (RAW) U ppm 1 .7408 1.9560 1.422314 1 .981 2 .6713 1 .9982 1.483982 2 .01 4 3 .6649 1.9955 1.481986 1 .989 4 .8427 0 .9689 1.185258 1 .996 Mean (n=4) = = 1.995 + 0 .014 ppm Mass f r a c t i o n a t i o n c o r r e c t i o n s of 0.006% per mass u n i t were made, based on r e p e a t e d a n a l y s e s of the U500 e q u a l atom s t a n d a r d ( T a b l e B.3). C.4 PREPARATION OF 230TH SPIKE 84-1 S p i k e 84-1 was p r e p a r e d from 230Th as Th02 from Oak Ri d g e , b a t c h number RD 1542, 1968 Th230-130A as f o l l o w s : 1. weight of beaker +Th02 = 15.2008 g, w i t h Beaker = 15.1920 g, and 3. Th02 = 0.0088 g. Th02 was d i s s o l v e d u s i n g 5 ml t w o - b o t t l e (2B) HF and a few drops HCIO4. I t was l e f t c o v e r e d and heated o v e r n i g h t . The cover was then removed t o a l l o w e v a p o r a t i o n . S u b s e q u e n t l y more HCIO4 was added and hea t e d uncovered u n t i l fuming. A few drops of c o n c e n t r a t e d HNO3 were added ( t o d r i v e o f f the HCIO4) and the sample was e v a p o r a t e d t o d r y n e s s . The r e s i d u e was t a k e n up i n 2B d i s t i l l e d w a t e r , and d i l u t e d t o 100 ml i n a screw-topped f l a s k . The i s o t o p i c c o m p o s i t i o n of the s p i k e was de t e r m i n e d by f o u r runs u s i n g the program "UBCTH" which measures the 230Th/232Th r a t i o . Two l o a d i n g methods were used and found t o g i v e the same r e s u l t s . A drop of s p i k e s o l u t i o n was e v a p o r a t e d onto a baked out t a n t a l u m f i l a m e n t and the o x i d e peaks were measured a t a p p r o x i m a t e l y 1800oc. A l t e r n a t i v e l y a drop of c o l l o i d a l g r a p h i t e ( p r e p a r e d from Aquadag c o l l o i d a l g r a p h i t e ) was d r i e d onto a baked out rhenium f i l a m e n t , then a drop of the s p i k e s o l u t i o n added on t o p , and heated t o d r y n e s s . I n t h i s case the me t a l peaks were measured. The f o u r i s o t o p e c o m p o s i t i o n runs were as f o l l o w s : 1 ) 230Th/232Th = 11 .361 2) 230Th/232Th = 11 .383 3) 230Th/232Th = 11.425 MEAN (n=4) 11.406 (0.042 ) , where 4) 230Th/232Th = 11.456 0.042 i s the s t a n d a r d d e v i a t i o n . 229 Other parameters a r e : 1. Atomic p r o p o r t i o n s a r e : 230-rh = 0.91 9394, and 232-rh = 0.080606 2. Atomic weight of s p i k e = 230.1948. 3. Weight of t h o r i u m i n s p i k e = 230.1948/262.1936 x 0.0088 g = 0.007726 g 4. Weight of 100 ml s o l u t i o n H20 + Th02 = 167.39 g 5. Weight of 100 ml screw-top f l a s k = 68.10 g 6. Nominal c o n c e n t r a t i o n of Th i n s p i k e = 0.007726/99.29 = 77.812 jug Th/g s o l u t i o n = 0.033802675 umoles Th = 0.031077977 jamoles 230-rh = 71.4896 ppm 230Th = 6.3224 ppm 232Th C.5 PREPARATION OF 84-2 DILUTE 230TH SPIKE S p i k e 84-2 was p r e p a r e d from 84-1 c o n c e n t r a t e d 230Th s p i k e as f o l l o w s : 1. R e q u i r e d c o n c e n t r a t i o n = 10 ppm 2. 100 ml s o l u t i o n r e q u i r e s 1000 rig Th, a p p r o x i m a t e l y 12.85 g 84-1 3. Weight of beaker + s p i k e = 30.6349 g 4. Weight of empty beaker = 17.7337 g 5. Weight of 84-1 = 12.9012 g 6. Weight of Th i n new s p i k e = 12.9012 x 77.812 ug = 1003.8681 74 ;ug 7. S p i k e was d i l u t e d t o 100 ml w i t h t w o - b o t t l e d i s t i l l e d 2N HNO3 i n a c l e a n t e f l o n b o t t l e . 8. F i n a l weight of b o t t l e p l u s s p i k e = 151.1057 g 9. I n i t i a l weight of t e f l o n b o t t l e = 37.4733 g 10. Weight of s o l u t i o n = 113.6324 g 11. Nominal c o n c e n t r a t i o n of Th = 8.834 ppm C.6 CALIBRATION OF 84-2 DILUTE 23_0_TH SPIKE C.6.1 I s o t o p e c o m p o s i t i o n o f s p i k e 84-2 The i s o t o p e c o m p o s i t i o n of 84-2 i s assumed t o be the same as f o r 84-1. C.6.2 I s o t o p e d i l u t i o n d e t e r m i n a t i o n s f o r s p i k e 84-2 S p i k e 84-2 was c a l i b r a t e d u s i n g 84-4 232-rh s t a n d a r d which was p r e p a r e d from specpure Th02 as 23 2Th i n the same way as g i v e n f o r 84-1 . Neutron a c t i v a t i o n a n a l y s i s (by Neutron A c t i v a t i o n S e r v i c e s L t d , H a m i l t o n , O n t a r i o ) showed t h e c o n c e n t r a t i o n t o be 97 ppm. Three i s o t o p e d i l u t i o n runs were 230 measured and a r e r e p o r t e d i n T a b l e C.6. TABLE C.6 D e t e r m i n a t i o n of the c o n c e n t r a t i o n of t h o r i u m i n s p i k e 84-2. 84-2 g 84-4 g 232Th/230ThiD Th ppm 1.1077 2.8778 30.137 9.0492 1.2954 1.2461 11.276 8.9989 2.0581 1.0061 5.770 9.0044 MEAN (n=3) = 9.018 (0.028) ppm (1 s t d . dev.) The f o l l o w i n g i s o t o p e d i l u t i o n e q u a t i o n was used: 230Th84-2 = 232-rh84-4 x (230Th/232Th84-4 - 230Th/232ThiD) (232Th/230Th84-2 x 230Th/232ThiD - 1) where: 230Th84-2 i s the umoles 230Th i n s p i k e 84-2 232Th84-4 i s the ^ umoles/g 232Th i n s t a n d a r d 84-4 230Th/232Th84-4 i s the r a t i o i n the s t a n d a r d 230Th/232ThiD i s the r a t i o i n the i s o t o p e d i l u t i o n run 232Th/230Th84-2 i s the r a t i o i n s p i k e 84-2 231 APPENDIX D PRINTOUTS OF COMPUTER PROGRAMS USED IN CALCULATION OF DATA A summary of each of the l i s t e d programs i s g i v e n i n Table D.1 TABLE D.I. Summary of data reduction programs. PROGRAM INPUTl UNCERTAINTIES CONSIDERED OUTPUT1 WRPBIC WRPBID in-run p r e c i s i o n BLANKSUB WRUCLC MUCALC T1CORR WRTHCLC CONCORD Raw data with 207pb/206pb • 208pb/206pb + 204pb/207pb + 206pb/204pb • s 207pb/204pb • s 2O8pb/204pb + s spike weight + 0.0003g sample weight +_ O.OOOig raw 208pb/207pb (ID run) output from WRPBIC _f s Pb ppm •• 0.1 ppm sample weight * 0.0003g amount of blank to be subtracted Raw 235u/238u spike weight < sample weight 0.0003g t 0.0003g 204pb micromoles + uncertainty based on 0.1 ppm t o t a l u n certainty in lead content U(GR) or U(NAA) + 10% d i v i d e d by 1.0935 204pb micromoles ^ uncertainty based on 0.1 ppm t o t a l u n certainty in lead content 206pb/204pb + s 207pb/204pb t s 208pb/204pb + s 238u/204 P b +~s raw 230Th/232Th t. i spike weight *_ 0.0003g sample weight 0.0003g Age c o r r e c t i o n 238u/204pb • s 206pb/204pb • s 207pb/204pb t s Mass f r a c t i o n a t i o n f a c t o r s , f r a c t i o n a t i o n v a r i a t i o n s between runs. Spike 84-3 i s o t o p i c composition and concentration, mass f r a c t i o n a t i o n , a l l u n c e r t a i n t i e s a s s o c i a t e d with the input data. blank composition, a l l u n c e r t a i n t i e s a s s o c i a t e d with i nput data. Spike 84-3 i s o t o p i c composition and co n c e n t r a t i o n , uranium mass f r a c t i o n a t i o n , a l l u n c e r t a i n t i e s a s s o c i a t e d with the input data. U n c e r t a i n t i e s a s s o c i a t e d with input data. U n c e r t a i n t i e s a s s o c i a t e d with input data. Spike 84-1 composition and conce n t r a t i o n , mass f r a c t i o n a t i o n , input data. U n c e r t a i n t i e s a s s o c i a t e d with input data. 206pb/204pb + s 207pb/204pb •» s 208pb/204pb + s Pb (ppm) _» s un c e r t a i n t y based on e r r o r propagation 204pb (micromoles) + blank c o r r e c t e d 206pb/204 Pb + s 207pb/204pb 4 s 208pb/204pb • s U (ppm) u n c e r t a i n t y based on e r r o r propaga t ion 238u/204pb (MU) * s 238u/204pb (MU) + s i n i t i a l : 206pb/204pb • s 207pb/204pb + s 208pb/204pb + s Th (ppm) j» s 235u/207pb *_ s 238u/206pb + s 1 . i = in-run p r e c i s i o n (standard e r r o r ) . (one sigma). estimated u n c e r t a i n t y based on propagation of e r r o r s U> to 233 D.1 WRPBIC 10 REM PROGRAM WRPBIC TO CALC 6/4, 7/4 AND 8/4 RATIOS FROM 20 REM RAW DATA USING FRACTIONATION FACTORS 0.16% PMU 30 REM AND FRACTIONATION VARIATION BETWEEN RUNS 40 REM DETERMINED FROM REPEATED ANALYSES OF BHS 50 REM FRACTIONATION VARIATION ADDS .006,.007 AND .025 60 REM TO 6/4 7/4 8/4 RATIOS RESPECTIVELY. 70 PRINT "TYPE IN 7/6 RATIO, ERROR" 80 INPUT R76,ERR1 90 PRINT "TYPE IN 8/6, ERROR" 100 INPUT R86,ERR2 110 PRINT "TYPE IN 4/7, ERROR" 120 INPUT R47,ERR3 125 PRINT "TYPE SAMPLE NAME" 126 INPUT A$ 130 ERR1P=(ERR1/R76)*100 140 ERR2P=(ERR2/R86)*100 150 ERR3P=(ERR3/R47)*100 160 R74=1/R47 170 E74=(ERR3P*R74)/100 180 S=R76*R47 190 R64=1/S 200 E64=ERR1P~2+ERR3P~2 210 E64A=SQR(E64) 220 E64=(E64A*R64)/l00 230 R84=R86*R64 240 E84=ERR2P A2+E64A A2 245 E84=SQR(E84) 247 E84=(E84*R84)/100 250 REM NOW MULTIPLY RAW RATIOS BY FRACTIONATION FACTORS 260 REM AND ADD FRACTIONATION VARIATION ERRORS AND 270 REM FRACTIONATION FACTOR UNCERTAINTY TO IN-RUN ERRORS 280 R64=R64*1.0032 290 R74=R74*1.0048 300 R84=R84*1.0064 305 REM FRACTIONATION VARIATION BETWEEN RUNS (ABSOLUTE) FV1 -3 310 FV1=.006 320 FV2=.007 330 FV3=.025 335 REM UNCERTAINTY IN ABSOLUTE BHS VALUE (STD DEV) FFU1-3 340 FFU1=.002 350 FFU2=.004 360 FFU3=.01 370 E64=E64"2+FV1"2+FFU1*2 380 E64=SQR(E64) 390 E74=E74 A2+FV2"2+FFU2"2 400 E74=SQR(E74) 410 E84=E84"2+FV3"2+FFU3"2 420 E84=SQR(E84) 422 LPRINT "INPUT",A$ 423 LPRINT "207PB/206PB ="R76 "("ERR1")" 424 LPRINT "208PB/206PB ="R86 "("ERR2")" 425 LPRINT "204PB/207PB = MR47 "("ERR3")" 426 LPRINT "RESULTS" 427 LPRINT "206PB/204PB ="R64 " ( " E 6 4 " ) " 428 LPRINT "207PB/204PB ="R74 " ( " E 7 4 " ) " 429 LPRINT "208PB/204PB ="R84 " ( " E 8 4 " ) " 430 PRINT A$,R64 E64,R74 E74,R84 E84 440 PRINT "MORE DATA ? Y=1,N=2" 450 INPUT Y 460 IF Y=1 THEN 10 47 0 END 235 D.2 WRPBID 10 REM WRPBID PROGRAM CALCULATES PB PPM AND ASSOCIATED ERRORS 20 DIM X(15),Y(15),S(7,15) 50 PRINT "TYPE IN SAMPLE NAME" 60 INPUT A$ 70 PRINT "TYPE IN 6/4, ERROR" 80 INPUT X(1 ),Y(1 ) 90 PRINT "NOW 7/4, ERROR" 100 INPUT X( 2 ) , Y ( 2 ) 110 PRINT "8/4, ERROR PLEASE" 120 INPUT X ( 3 ) , Y ( 3 ) 130 PRINT "MASS FRACTIONATION IS .16%+/-.01%" 240 REM WEIGHTS OF EACH PB ISOTOPE ARE AS FOLLOWS: 250 WT4=203.973044# 260 WT6=205.974468# 270 WT7=206.975903# 280 WT8=207.97665# 290 IF Y=1 THEN 500 300 REM SPIKE CONSTANTS ARE;8/7, 6/8, 4/6 310 X(4)=.059017# 320 Y(4)=.000017# 330 X(5)=.388818# 340 Y(5)=.000166# 350 X(6)=.004444# 360 Y(6)=8.700000000000005D-05 365 REM SPIKE CONCENTRATION 370 X(7)=1.761 380 Y.(7) = .003 400 X(8)=1 .001 6 410 Y(8)=.0001 420 PRINT "ENTER WT SPIKE, WEIGHING ERROR, WT SAMPLE, ERROR" 430 INPUT X ( 9 ) , Y ( 9 ) , X ( 1 0 ) , Y ( 1 0 ) 440 PRINT "ENTER 8/7 ID, ERROR" 450 INPUT X(11),Y(11) 500 REM ZERO VARIABLES BEFORE CALCS 510 FOR 1=0 TO 3 52 0 FOR J=0 TO 11 530 S ( I , J ) = 0 540 NEXT J 550 NEXT I 560 X(0)=0 570 Y(0)=0 580 FOR J=0 TO 11 590 X ( J ) = X ( J ) + Y ( J ) 600 REM BEGIN CALCULATIONS 620 A=X(1) 630 B=X(2) 640 C=X(3) 236 650 REM NOW CALC ATOMIC WEIGHT AND ATOMIC PROPORTIONS FOR SAMPLE 660 TOT=1+A+B+C 670 AT4=1/TOT 680 AT6=A/TOT 690 AT7=B/TOT 700 AT8=C/TOT 710 AWT=AT4*WT4+AT6*WT6+AT7*WT7+AT8*WT8 715 S(1,J)=AWT 719 IF Y=1 THEN 940 720 REM CALCULATE SPIKE CONSTANTS 730 SP64=1/X(6) 740 SP84=1/(X(6)*X(5)) 750 SP74=(1/X(4))*SP84 760 RFM SPIKE .ATOMIC PROPORTIONS 770 TOTSP=1+SP64+SP84+SP74 780 AT4SP=1/TOTSP 790 AT6SP=SP64/TOTSP 800 AT7SP=SP74/TOTSP 810 AT8SP=SP84/TOTSP 820 AWTSP=AT4SP*WT4+AT7SP*WT7+AT6SP*WT6+AT8SP*WT8 830 REM CORRECT ID RATIO TO 7/8 AND MASS FRACTIONATION 840 ID78=1/(X(11)*X(8)) 850 IC78=B/C 86 0 PB8=X(9)*X(7)*AT7SP*(1-(X(4)*ID7 8 ) ) / ( I D 7 8 - I C 7 8 ) 870 PB8=PB8/AWTSP 880 TOTPB=(PB8/AT8)/X(10) 890 PB4#=TOTPB*AT4 910 T0TP3=T0TPB*AWT 920 S(2,J)=TOTPB 930 S(3,J)=PB4# 94 0 REM RESTORE VARIABLES TO FORMER VALUE 950 X ( J ) = X ( J ) - Y ( J ) 960 NEXT J 1500 REM ERROR SUMMATION 1510 PRINT "ERRORS >0.5% ; I , J " 1520 FOR 1=1 TO 3 1530 E=0 1540 FOR J=1 TO 11 1550 IF Y(J)=0 THEN 1590 1 560 IF ABS(S ( I , J - ) - S ( I , 0 ) ) < . 0 0 5 * S ( I , 0 ) THEN 1580 1570 PRINT I , J 1580 E = E + ( S ( I f J ) - S ( I f 0 ) ) A 2 1590 NEXT J 1600 S(I,1)=SQR(E) 1610 NEXT I 1620 PRINT 16 30 LPRINT 1640 PRINT "RESULTS AND ERRORS FOR "A$":" 1650 LPRINT "RESULTS AND ERRORS FOR "A$":" 1680 PRINT "ATOMIC WT OF SAMPLE:",S(1,0) S ( 1 , 1 ) 1690 LPRINT "ATOMIC WEIGHT OF SAMPLE:",S(1,0) S(1,1) 1695 IF Y=1 THEN 1740 1700 PRINT "TOTAL PB IN ROCK" S ( 2 , 0 ) " + / - " S ( 2 , 1 ) " P P M " 1710 LPRINT "TOTAL PB IN ROCK "S(2,0)"+/-"S(2,1)"PPM" 1720 PRINT "204PB IN MICROMOLES "S(3,0) S(3,1) 1730 LPRINT "204PB IN MICROMOLES "S(3,0) S(3,1) 1740 PRINT "MORE DATA ? Y=1, N=2" 17 50 INPUT N 1760 IF N=1 THEN 50 1770 END 238 D.3 WRUCLC 10 REM WRUCLC A PROGRAM TO CALC. UPPM, MU AND ASSESS THE ERROR IN EACH 20 REM THE FOLLOWING CONSTANTS ARE ASSUMED 30 U8NAT=.9928 40 UAW=238,0291503# 50 A5=235.044 60 A8=238.051 70 REM DECLARE VARIABLES 80 DIM X ( 7 ) , Y ( 7 ) , S(2,7) 90 REM CORRECTION FACTOR 100 X(1)=1.0002430 110 Y(1)=.000257# 120 PRINT "CORRECTION FACTOR IS 1.000243 +/- .000257" 130 PRINT "TYPE IN SAMPLE NAME" 140 INPUT A$ 150 PRINT "TYPE IN 5/8 U RATIO (RAW) AND ERROR " 160 INPUT X(2),Y ( 2 ) 190 REM SPIKE CONSTANTS ARE AS. FOLLOWS 200 X(3)=.00011439# 20 5 REM THAT WAS 238U ATOMIC PROPORTION 210 Y(3)=4.070000000000001D-06 270 REM SPIKE CONCENTRATION 280 X(4) = 1 .995 290 Y(4)=.014 300 PRINT "TYPE IN WT OF 84-3 USED, MAX WEIGHING ERROR" 310 INPUT X(5),Y ( 5 ) 32 0 PRINT "TYPE IN WT OF SAMPLE, WEIGHING ERROR" 330 INPUT X(6),Y ( 6 ) 340 PRINT "TYPE IN 204PB MICROMOLES, ERROR" 350 INPUT X(7),Y ( 7 ) 1000 REM BEGIN CALCULATIONS, FIRST ZERO EVERYTHING 1010 FOR 1=0 TO 2 1020 FOR J=0 TO 7 1030 S ( I , J ) = 0 10 40 NEXT J 1050 NEXT I 1060 Y(0)=0 1070 X(0)=0 1075 FOR J=0 TO 7 1080 X ( J ) = X ( J ) + Y ( J ) 1081 ID85=1/X(2) 1082 ID85=ID85*X(1) 1083 X3=1/X(3) 1084 XT=1+X3 1086 AT5SP=X3/XT 1087 AT8SP=1/XT 1088 AWTSP=AT5SP*A5+AT8SP*A8 1089 REM THAT WAS THE ATOMIC WEIGHT OF THE SPIKE 10 90 U8=((X(4)*AT5SP*X(5))/(AWTSP))*((X(3)-ID85)/(ID85* 1100 U8=U8/X(6) 1110 TOT = (U8/U8NAT)*UAW 1120 MU = U8/X(7) 11 30 S(1,J)=TOT 1140 S(2,J)=MU 1150 X( J ) =X ( J ) - Y ( J ) 1160 NEXT J 1500 REM ERROR SUMMATION 1510 PRINT "ERRORS > .5% FOR " A $ " l , J " 1515 LPRINT 1516 LPRINT "ERRORS > .5% FOR " A $ " l , J " 1520 FOR 1=1 TO 2 1530 E=0 1540 FOR J=1 TO 7 1550 IF Y(J)=0 THEN 1590 1560 IF A B S ( S ( I , J ) - S ( I , 0 ) ) < . 0 0 5 * S ( I , 0 ) THEN 1580 1570 PRINT I , J 1580 E = E + ( S ( I , J ) - S ( I f H ) ) * 2 1590 NEXT J 1600 S(I,1)=SQR(E) 1610 NEXT I 1620 PRINT "U PPM F O R "A$" = "S(1,0)"+/-"S(1,1) 1630 PRINT "MU = "S(2,0)"+/-"S(2,1) 1640 LPRINT "U PPM F O R "A$" = "S(1 ;0)"+/-"S(1,1) 1650 LPRINT "MU = "S(2,0)"+/-"S(2,1) 1660 END 240 D.4 WRTHCLC 10 REM WRTHCLC A PROGRAM TO CAL PPM, K AND ASSESS THE ERROR IN EACH 20 REM THE FOLLOWING CONSTANTS ARE ASSUMED 30 THNAT=1 40 THAW=232.038 50 A0=230.033 60 A2=232.038 70 REM DECLARE VARIABLES 80 DIM X ( 8 ) , Y ( 8 ) , S(3,8) 90 REM CORRECTION FACTOR 100 X(1)=1.00016 110 Y(1)=.00016 120 PRINT "CORRECTION FACTOR IS 1.00016 +/- .00016" 130 PRINT "TYPE IN SAMPLE NAME" 140 INPUT A$ 150 PRINT "TYPE IN 0/2 TH RATIO (RAW) AND ERROR " 160 INPUT X( 2 ) , Y ( 2 ) 190 REM SPIKE CONSTANTS ARE AS FOLLOWS 200 X(3)=11.40600000000001# 205 REM THAT WAS 232TH/230TH SPIKE ATOMIC PROPORTION 210 Y(3)=.042 270 REM SPIKE CONCENTRATION 280 X(4)=9.018 290 Y(4)=.028 300 PRINT "TYPE IN WT OF 84-2 USED, MAX WEIGHING ERROR" 310 INPUT X( 5 ) , Y ( 5 ) 32 0 PRINT "TYPE IN WT OF SAMPLE, WEIGHING ERROR" 330 INPUT X( 6 ) , Y ( 6 ) 340 PRINT "TYPE IN MU , ERROR" 350 INPUT X{7),Y(7) 360 PRINT "TYPE IN 204PB MICROMOLES, ERROR" 370 INPUT X( 8 ) , Y ( 8 ) 1000 REM BEGIN CALCULATIONS, FIRST ZERO EVERYTHING 1010 FOR 1=0 TO 2 1020 FOR J=0 TO 8 1030 S(I,J ) = 0 10 40 NEXT J . 10 50 NEXT I 1060 Y(0)=0 1070 X(0)=0 1075 FOR J=0 TO 8 1080 X ( J ) = X ( J ) + Y ( J ) 1082 ID02=X(2)*X(1 ) 1083 X3=X(3) 1084 XT=1+X3 1086 AT0SP=X3/XT 1087 AT2SP=1/XT 1088 AWTSP=AT0SP*A0+AT2SP*A2 1089 REM THAT WAS THE ATOMIC WEIGHT OF THE SPIKE 1090 TH2=((X(4)*AT2SP*X(5))/(AWTSP))*((X(3)-ID02)/(ID02)) 1100 TH2=TH2/X(6) 1110 TOT=(TH2/THNAT)*THAW 1120 W=TH2/X(8) 1123 S(2,J)=W 1125 K=(TH2/(X(8)*X(7))) 1127 S(3,J)=K 1130 S(1,J)=TOT 1150 X ( J ) = X ( J ) - Y ( J ) 1160 NEXT J 1500 REM ERROR SUMMATION 1510 PRINT "ERRORS > .5% FOR " A $ " l , J " 1515 LPRINT 1516 LPRINT "ERRORS > .5% FOR " A $ " l , J " 1520 FOR 1=1 TO 3 1530 E=0 1540 FOR J=1 TO 8 1550 IF Y(J)=0 THEN 1590 1560 IF A B S ( S ( I , J ) - S ( I , 0 ) ) < . 0 0 5 * S ( I , 0 ) THEN 1580 1570 PRINT I , J 1580 E = E + ( S ( I , J ) - S ( I , 0 ) ) * 2 1590 NEXT J 1600 S(I,1)=SQR(E) 1610 NEXT I 1620 PRINT "TH PPM FOR "A$" = "S(1,0)"+/-"S(1,1) 1630 PRINT "W = "S(2,0)"+/-"S(2,1) 1640 LPRINT "TH PPM FOR "A$" = "S(1,0)"+/-"S(1,1) 1650 LPRINT "W = "S(2,0)"+/-"S(2,1) 1660 PRINT "K =" S(3,0) "+/-"S(3,1) 1670 LPRINT " K = "S(3,0) "+/-"S(3,1) 1680 END 242 D.5 T1C0RR 10 REM THIS PROGRAM (T1CORR) CORRECTS WHOLE ROCK LEAD DATA 20 REM FOR THE MEASURED MU AND K VALUES 30 REM THE DECAY CONSTANTS USED ARE AS FOLLOWS: 40 L1=1.55125E-10 50 L2=9.8485E-10 60 L3=4.9475E-11 65 DIM X ( 7 ) , Y ( 7 ) , S ( 4 , 7 ) 70 PRINT "TYPE IN THE SAMPLE NAME, AND THE AGE OF THE ROCK,ERROR" 80 INPUT A$,X(1 ) ,Y(T) 85 LPRINT X(1 ) ,Y(1 ) 90 T2=0 100 PRINT "TYPE IN MEASURED MU,ERROR" 110 INPUT X(2), Y ( 2 ) 115 LPRINT "MU I S : " X(2)"+/-"Y(2) 120 PRINT "NOW ENTER 6/4,ERROR,7/4,ERROR" 125 INPUT X ( 3 ) , Y ( 3 ) , X ( 4 ) , Y ( 4 ) 130 PRINT "DO YOU WISH TO CORRECT FOR TH AS WELL? Y=1,N=2" 140 INPUT Y 150 IF Y=2 THEN 16 5 155 PRINT "TYPE IN K,ERROR, 8/4, ERROR" 160 INPUT X ( 5 ) , Y ( 5 ) , X ( 6 ) , Y ( 6 ) 165 REM ZERO VARIABLES 170 FOR 1=0 TO 3 180 FOR J=0 TO 6 190 S(I , J ) = 0 20 0 NEXT J 210 NEXT I 220 X(0)=0 230 Y(0)=0 240 FOR J=0 TO 6 250 X ( J ) = X ( J ) + Y ( J ) 260 T1=X(1 )*1E+06 270 A1=X(3)-X(2)*(EXP(T1*L1)-EXP(T2*L1)) 280 B1 =X(4)-(X(2)/137.88)*(EXP(T1*L2)-EXP(T2*L2)) 290 IF Y=2 THEN 320 30 0 C1=X(6)-(X(5)*X(2))*(EXP(T1*L3)-EXP(T2*L2)) 310 S(3,J)=C1 320 S(1,J)=A1 330 S(2,J)=B1 340 X ( J ) = X ( J ) - Y ( J ) 350 NEXT J 10 00 REM ERROR SUMMATION 1010 FOR 1=1 TO 3 1020 E=0 1030 FOR J=1 TO 6 1040 E = E + ( S ( I , 0 ) - S ( I , J ) ) A 2 1050 NEXT J 1060 S(I,1)=SQR(E) 1070 NEXT I 10 80 PRINT "TIME CORRECTED VALUES FOR "A$ 2 4 3 10 90 LPRINT "TIME CORRECTED VALUES FOR "A$ 1100 PRINT S(1,0),S(1,1 ) 1110 LPRINT S(1,0),S(1,1) 1120 PRINT S(2,0),S(2,1 ) 1130 LPRINT S(2,0),S(2,1) 1140 IF Y = 2 THEN 1170 1150 PRINT S(3,0),S(3,1) 1160 LPRINT S(3,0),S(3,1) 1170 LPRINT. 1180 PRINT "MORE DATA? Y=1, N=2" 1190 INPUT N 1200 IF N=1 THEN 70 1210 END 244 D.6 BLANKSUB 10 15 20 30 40 50 60 70 71 72 73 74 75 76 77 78 79 80 81 82 89 90 100 1 1 0 1 20 1 30 1 40 1 50 1 51 1 52 1 53 1 54 1 55 1 56 1 57 1 58 .159 1 60 1 70 180 1 90 200 210 220 230 270 280 290 300 REM PROGRAM BLANKSUB TO SUBTRACT BLANKS FROM IC RUNS REM ERROR CALCULATED REM THE FOLLOWING CONSTANTS ARE ASSUMED A4=203.973044# A6=205.974468# A7=206.9759030 A8=207.97665# DIM X ( 1 2 ) , Y ( 1 2 ) , S(5,12) PRINT "TYPE IN PB PPM IN SAMPLE, ERROR" X(4 ) , Y ( 4 ) "TYPE IN WT SAMPLE,ERROR" X(5 ) , Y ( 5 ) "INPUT AMT OF BLANK TO BE SUBTRACTED" X(9 ) , Y ( 9 ) 329 IN SAMPLE NAME" IN X(1 ),Y(1 ) "TYPE IN X(2) ,Y(2) "TYPE IN X(3),Y ( 3 ) 3 9 6/4, ERROR" 7/4,ERROR" 8/4, ERROR" INPUT PRINT INPUT PRINT INPUT X( 6)=18 Y(6)=.01 X(7)=15.619 Y(7)=.011 X(8)=38.065 Y(8)=.011 PRINT "TYPE INPUT A$ PRINT "TYPE INPUT PRINT INPUT PRINT INPUT FOR 1=1 TO FOR J=0 TO S(I,J)= 0 NEXT J NEXT I X(0)=0 Y(0)=0 FOR J=0 TO 9 X( J ) = X ( J ) + Y ( J ) REM THE ATOMIC PROPORTIONS OF SAMPLES ARE: SAMTOT=1+X(1)+X(2)+X(3) AP4=1/SAMTOT AP6=X(1)/SAMTOT AP7=X(2)/SAMTOT AP8=X(3)/SAMTOT AWTSAM=AP4*A4+AP6*A6+AP7*A7+AP8*A8 TOTMOL=X(5)*X(4)/AWTSAM MOL4=AP4*TOTMOL MOL6=AP6*TOTMOL MOL7=AP7*TOTMOL MOL8=AP8*TOTMOL 310 REM BLANK COMPOSITION TO BE SUBTRACTED I S : 360 BLKTOT=1+X(6)+X(7)+X(8) 37 0 BAP4=1/BLKTOT 380 BAP6=X(6)/BLKTOT 390 BAP7=X(7)/BLKTOT 400 BAP8=X(8)/BLKTOT 410 AWTBLK=BAP4*A4+BAP6*A6+BAP7*A7+BAP8*A8 420 REM AMT OF BLANK IN MOLES TO BE SUBTRACTED IS SUBBLK 430 SUBBLK=X(9)/AWTBLK 440 NEW4=MOL4-SUBBLK*BAP4 450 NEW6=MOL6-SUBBLK*BAP6 460 NEW7=MOL7-SUBBLK*BAP7 470 NEW8=MOL8-SUBBLK*BAP8 480 SAM1=NEW6/NEW4 490 SAM2=NEW7/NEW4 500 SAM3=NEW8/NEW4 510 S(1,J)=SAM1 520 S(2,J)=SAM2 530 S(3,J)=SAM3 540 X ( J ) = X ( J ) - Y ( J ) 550 NEXT J 1000 REM ERROR SUMMATION 1010 PRINT "ERRORS>.5%, I , J " 1020 FOR 1=1 TO 3 1025 E=0 1030 FOR J=1 TO 9 1040 IF Y(J)=0 THEN 1090 1060 IF A B S ( S ( I , J ) - S ( I , 0 ) ) < . 0 0 5 * S ( I , 0 ) THEN 1080 1070 PRINT I , J 1080 E = E + ( S ( I , J ) - S ( I , 0 ) ) "2 1090 NEXT J 1100 S(I,1)=SQR(E) 1110 NEXT I 1120 PRINT 1130 LPRINT 1140 PRINT "RESULTS AND ERRORS FOR"A$":" 1150 LPRINT "RESULTS AND ERRORS FOR "A$":" 1160 PRINT "BLANK CORRECTED RATIOS 6/4,7/4,8/4" S ( 1 , 0 ) , S ( 1 , 1 ) , S ( 2 , 0 ) , S ( 2 , 1 ) , S ( 3 , 0 ) , S ( 3 , 1 ) 1170 LPRINT "BLANK CORRECTED 6/4, 7/4, 8/4 RATIOS"S(1,0), S ( 1 , 1 ) , S ( 2 , 0 ) , S ( 2 , 1 ) , S ( 3 , 0 ) , S ( 3 , 1 ) 1180 PRINT "MORE DATA , INPUT Y=1, N=2" 1190 INPUT N 1200 IF N=1 THEN 71 D.7 CONCORD 10 REM PROGRAM CONCORD TO CALC ERRORS ON COORDS 20 REM USING TATSUMOTO PRIMORDIAL LEAD 30 REM 6/4=9.307, 7/4=10.294 70 DIM X ( 1 2 ) , Y ( 1 2 ) , S(5,12) 75 X(4)=9.307 76 Y(4)=.001 77 X(5)=10.294 78 Y(5)=.001 89 PRINT "TYPE IN SAMPLE NAME" 90 INPUT A$ 100 PRINT "TYPE IN 6/4, ERROR" 11 0 INPUT X(1 ),Y(1 ) 120 PRINT "TYPE IN 7/4,ERROR" 130 INPUT X(2), Y ( 2 ) 140 PRINT "TYPE IN MU, ERROR" 150 INPUT X(3), Y ( 3 ) 151 FOR 1 = 1 TO 2 152 FOR J=0 TO 5 153 S(I,J ) = 0 154 NEXT J 155 NEXT I 156 X(0)=0 157 Y(0)=0 158 FOR J=0 TO 5 159 X ( J ) = X ( J ) + Y ( J ) 160 REM COORDS ARE GIVEN AS FOLLOWS 170 P6U8=(X(1)-X(4))/X(3) 180 P7U5=((X(2)-X(5))/X(3))*137.88 190 S(1,J)=P6U8 200 S(2,J)=P7U5 540 X ( J ) = X ( J ) - Y ( J ) 550 NEXT J 10 00 REM ERROR SUMMATION 1010 PRINT "ERRORS>.5%, I , J " 1020 FOR 1=1 TO 2 1025 E=0 10 30 FOR J=1 TO 5 1040 IF Y(J)=0 THEN 1090 1060 IF A B S ( S ( I , J ) - S ( I , 0 ) ) < . 0 0 5 * S ( I , 0 ) THEN 1080 1070 PRINT I , J 1080 E = E + ( S ( I , J ) - S ( I , 0 ) ) * 2 1090 NEXT J 1100 S(I,1)=SQR(E) 1110 NEXT I 1120 PRINT 1130 LPRINT 1140 PRINT A$,S(1,0) S(1 ,1 ),S(2,0) S(2,1) 1180 PRINT "MORE DATA , INPUT Y=1, N=2" 1190 INPUT N 1200 I F N=1 THEN 75 1210 END D.8 MUCALC 10 REM PROGRAM MUCALC TO CALC MU AND ITS ERROR 20 DIM X ( 3 ) , Y ( 3 ) 30 PRINT "TYPE IN UPPM, ERROR" 40 INPUT X(1 ),Y(1 ) 50 PRINT "TYPE IN 204PB MICROMOLES, ERROR" 60 INPUT X ( 2 ) , Y ( 2 ) 70 REM BEGIN CALCULATIONS - FIRST CALC 238U MICROMOLES 80 U8=X(1)*.9928 90 U8=U8/238.0291503# 100 Y(1 ) = (Y(1 )*.9928)/238.0291 2 5030 110 ERR1P=Y(1)*100/U8 120 ERR2P=Y(2)*100/X(2) 130 MU=U8/X(2) 140 Y(3) = (ERR1P)"2 + (ERR2P)"2 150 Y(3)=SQR(Y(3)) 160 Y(3)=(MU*Y(3))/100 170 PRINT "MU IS"MU, "ERROR IS *'Y(3) 180 PRINT "AGAIN? Y=1,N=2" 190 INPUT Y 200 IF Y=1 THEN 30 210 END 248 APPENDIX E PROJECTION TECHNIQUE FOR COMPARISON OF 2_0_2PB/2_04PB RATIOS WHICH HAVE VARIABLE 206_PB/204pB RATIOS M i x i n g of c r u s t a l and mantle l e a d i n the s o u r c e s of i s l a n d a r c magmas has been documented by s e v e r a l a u t h o r s and has been found, i n t h i s t h e s i s , t o be a r e a s o n a b l e e x p l a n a t i o n f o r the i s o t o p i c s i g n a t u r e s of the Karmutsen F o r m a t i o n and the I s l a n d I n t r u s i o n s . G e n e r a l l y , m i x i n g r e l a t i o n s h i p s a r e found by d i s c o v e r i n g l i n e a r r e l a t i o n s h i p s i n the i n i t i a l l e a d i s o t o p e d a t a . O f t e n , however, uranium and l e a d d e t e r m i n a t i o n s are not made, so the i n i t i a l r a t i o s can not be d e t e r m i n e d (JJ v a l u e s are r e q u i r e d t o c a l c u l a t e i n i t i a l r a t i o s ) , or the i n i t i a l r a t i o s a re u n r e l i a b l e due t o the m o b i l i t y of uranium and l e a d . A s i m p l e t e c h n i q u e , d e s c r i b e d h e r e , p r o j e c t s 207pb/204pb r a t i o s a l o n g i s o c h r o n s t o a r e f e r e n c e v a l u e of 206pb/204pb may be used i n or d e r t o det e r m i n e r e l a t i v e e nrichment or d e p l e t i o n of 207pb/204pb i n a s u i t e of r o c k s . The degree of enrichment or d e p l e t i o n can th e n be used t o d e c i p h e r m i x i n g r e l a t i o n s h i p s i n the i s o t o p e d a t a . The 207pb/204pb r a t i o i s s i n g l e d out f o r p r o j e c t i o n because i t i s the most i n d i c a t i v e of r e l a t i v e c r u s t a l i n v o l v e m e n t i n 249 v o l c a n i c r o c k s t h a t o r i g i n a t e i n the m a n t l e . P a l e o z o i c or younger a d d i t i o n s of r a d i o g e n i c 207pb a r e s m a l l due t o t h e r e l a t i v e l y s m a l l p r o p o r t i o n of 235u r e m a i n i n g , i n comparison t o 238TJ and 232Th. Any s i g n i f i c a n t d i f f e r e n c e s i n 207pb/204b r a t i o s between r e s e r v o i r s must be due t o l o n g term d i f f e r e n c e s i n i s o t o p i c h i s t o r y . H i g h 207pb/204pb r a t i o s a r e g e n e r a t e d i n c o n t i n e n t a l r o c k s due t o l o n g term ( g r e a t e r than 2 Ga) h i g h yx e v o l u t i o n . Mantle l e a d , on the o t h e r hand has low 207pb/204pb r a t i o s because the e v o l u t i o n took p l a c e i n a low p environment and i n c r e a s e s i n ;u have o c c u r r e d r e l a t i v e l y r e c e n t l y ( l e s s than 2 Ga). I t i s , t h e r e f o r e , u s e f u l t o o r d e r a r o c k s u i t e by rank of 207pb/204pb. The p r o j e c t i o n t e c h n i q u e d e s c r i b e d here s t a n d a r d i z e s a l l 207pb/204pb r a t i o s by p r o j e c t i n g them onto a s i n g l e v a l u e of 206pb/204pb. T h i s l e s s e n s the e f f e c t s of i r i s i t u l e a d e v o l u t i o n , a l l o w i n g the o r i g i n a l 207pb/204pb o r d e r i n g t o be seen, even i f the a b s o l u t e i n i t i a l r a t i o s a re not known. I n o r d e r t o de t e r m i n e the p r o j e c t e d v a l u e , t h e age of the r o c k s must be known by i s o t o p i c or p a l a e o n t o l o g i c a l methods. The s l o p e of the i s o c h r o n a l o n g which the p r o j e c t e d (and i n i t i a l ) r a t i o must l i e , can then be c a l c u l a t e d u s i n g t h e secondary i s o c h r o n e q u a t i o n of Kanasewich (1968), e q u a t i o n 1: Sl o p e M = 1 (e^2t1 - e x 2 t 2 ) 137.88 ( e ^ 1 t l - e ^ 1 t 2 ) where: V|. = decay c o n s t a n t f o r 238U = 0.98485 x 10-9 ( j a f f e y e t Actual Data Reference Value 19.0 206Pb/204Pb F i g u r e E.1 G r a p h i c a l r e p r e s e n t a t i o n of p r o j e c t e d v a l u e s f o r a roc k s u i t e w i t h an age of 220 Ma. P r e s e n t 207pb/204p D r a t i o s (x's numbered 1 t o 5) a r e p r o j e c t e d onto a 206pb/204pb r e f e r e n c e v a l u e of 19.0. Slope of p r o j e c t i o n v e c t o r s i s u n i q u e l y c a l c u l a t e d u s i n g e q u a t i o n 1, w i t h t i = 220 Ma and t2 = 0 Ma. M on o 251 a l . 1971) = decay c o n s t a n t f o r 235U = 0.155125 x 10-9 ( j a f f e y e t a l . 1971 ) t i = age of t h e r o c k t2 = z e r o Ma (time of a n a l y s i s ) The i s o c h r o n i s p r o j e c t e d t h r o u g h the p r e s e n t 207pfc>/204pb v a l u e u n t i l i t i n t e r s e c t s a r e f e r e n c e v a l u e of 206pb/204pb. T h i s p o i n t of i n t e r s e c t i o n i s the p r o j e c t e d v a l u e . F i g u r e E.1 i l l u s t r a t e s the d e t e r m i n a t i o n of p r o j e c t e d v a l u e s f o r samples from a ro c k u n i t w i t h an age of 220 Ma, and a r e f e r e n c e 206pb/204pb v a l u e of 19.0. F i g u r e E.2 shows both p r e s e n t (Chapter 3: Table 3.2) and p r o j e c t e d ( Table E.1) 207pb/204pb r a t i o s f o r samples from the Karmutsen F o r m a t i o n p l o t t e d a g a i n s t 1/Pb. No l i n e a r r e l a t i o n s h i p i s a pparent between the p r e s e n t v a l u e s ( x ' s ) and l e a d c o n c e n t r a t i o n , but a n e g a t i v e c o r r e l a t i o n i s apparent when the p r o j e c t e d 207pb/204pb v a l u e s ( t r i a n g l e s ) a r e used. The same n e g a t i v e c o r r e l a t i o n i s i l l u s t r a t e d u s i n g the i n i t i a l 207pb/204pb v a l u e s i n Chapter 3. Only f i v e i n i t i a l r a t i o s were used i n F i g u r e 3.9b, because the s e were the o n l y samples w i t h measured uranium and l e a d c o n c e n t r a t i o n s . P r o j e c t e d 207pb/204pb v a l u e s can be de t e r m i n e d f o r a l l samples f o r which l e a d i s o t o p i c c o m p o s i t i o n s have been d e t e r m i n e d . F i g u r e E.2 shows t h a t 1 5 . 7 JD CL o CM Q_ o CM 1 5 . 6 _ S1AM 1 5 . 5 0 . 4 0 .8 1 . 2 1 . 6 1/Pb ppm F i g u r e E.2 P r e s e n t 207pb/204pb ( c r o s s e s ) and p r o j e c t e d 207pb/204pb (open t r i a n g l e s ) v e r s u s 1/Pb (ppm) f o r Karmutsen F o r m a t i o n r o c k samples ( c f Chapter 3 ) . The l i n e shown i s the b e s t f i t l i n e t o the p r o j e c t e d d a t a and has a c o r r e l a t i o n c o e f f i c i e n t of 0.70. 253 TABLE E.1 207pb/204pb r a t i o s p r o j e c t e d t o a v a l u e of 206pb/204pb of 19.000, u s i n g the 220 Ma i s o c h r o n ( F i g . E.2; t e x t ) . SAMPLE PROJECTED NAME 207pb/204pb K005 15.602 K007 15.569 K008 15.547 K101-1 15.645 K1 01-2 15.611 KAR1 15.583 KAR2 15.598 KAR7 15.569 KAR1 0 15.571 KAR1 1 15.585 S1 AM 15.627 254 p r o j e c t e d 207pt>/204pb v a l u e s a r e j u s t as u s e f u l as i n i t i a l r a t i o s i n r e v e a l i n g the l i n e a r r e l a t i o n s h i p between l e a d c o n c e n t r a t i o n and i s o t o p i c c o m p o s i t i o n . 

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