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The distribution and behaviour of platinum in soils of the Tulameen ultramafic complex, southern British… Cook, Stephen John 1991

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THE DISTRIBUTION AND BEHAVIOUR OF PLATINUM IN SOILS OF THE TULAMEEN ULTRAMAFIC COMPLEX, SOUTHERN BRITISH COLUMBIA: APPLICATIONS TO GEOCHEMICAL EXPLORATION FOR CHROMITITE-ASSOCIATED PLATINUM DEPOSITS by STEPHEN JOHN COOK B.Sc. (Hons) C a r l e t o n U n i v e r s i t y , 1984 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of G e o l o g i c a l Sciences We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1991 (c) Stephen John Cook, 1991 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 <^s=> (E_o[oOJ \~ca-J ^ C - \ e ^ C g ^ f The University of British Columbia Vancouver, Canada Date Z3_. Mi DE-6 (2/88) ABSTRACT E x p l o r a t i o n f o r c h r o m i t i t e - a s s o c i a t e d Pt d e p o s i t s i s hampered by a poor understanding of the d i s t r i b u t i o n and behaviour of Pt i n the s u r f i c i a l environment. T h i s study i n v e s t i g a t e s Pt content, r e s i d e n c e s i t e s and PGE mineralogy of s o i l s developed on t i l l and c o l l u v i u m above the Tulameen u l t r a m a f i c complex i n southern B r i t i s h Columbia. S e v e n t y - s i x s o i l p r o f i l e s , as w e l l as sediments, bogs and waters were sampled above the d u n i t e core of the Tulameen complex, w i t h i n which Pt occcurrences c o n s i s t of m a s s i v e - t o - d i s c o n t i n u o u s segregations of p l a t i n i c c h r o m i t i t e . Pt content of the -212 um f r a c t i o n of s o i l s and sediments was determined by f i r e a s s a y - i n d u c t i v e l y coupled plasma spectroscopy. Samples from f o u r t e e n s e l e c t e d p r o f i l e s were then examined i n d e t a i l t o determine Pt mineralogy and i t s d i s t r i b u t i o n between d i f f e r e n t s i z e , d e n s i t y and magnetic f r a c t i o n s . Pt c o n c e n t r a t i o n s i n the -212 um f r a c t i o n of C h o r i z o n s o i l s range from 2 t o 885 ppb and are c l o s e l y r e l a t e d t o s o i l d u n i t e content, as estimated from MgO content and v e r i f i e d by XRD mineralogy. Dunite c o l l u v i u m (mean: 24.2% MgO), l o c a l l y - d e r i v e d d u n i t i c t i l l (mean: 16.5% MgO) and e x o t i c n o n - d u n i t i c t i l l (mean: 5.7% MgO) have median Pt c o n c e n t r a t i o n s of 88 ppb, 36 ppb and 8 ppb, r e s p e c t i v e l y . i i i T h i s t r e n d i s e v i d e n t i n a l l s i z e and d e n s i t y f r a c t i o n s . Pt content of heavy m i n e r a l (SG > 3.3) f r a c t i o n s i s 10-2Ox g r e a t e r than i n l i g h t m i n e r a l f r a c t i o n s . Pt i s most abundant i n the heavy magnetic f r a c t i o n from n o n - d u n i t i c t i l l s and d u n i t i c t i l l s remote from known m i n e r a l i z a t i o n , but the p r o p o r t i o n of Pt i n the heavy non-magnetic f r a c t i o n i n c r e a s e s w i t h i n c r e a s i n g p r o x i m i t y t o m i n e r a l i z a t i o n . SEM and microprobe s t u d i e s of heavy f r a c t i o n s from C h o r i z o n s i d e n t i f i e d Pt-Fe-Cu a l l o y s as f r e e g r a i n s , and as i n c l u s i o n s i n M g - s i l i c a t e s and chromites. Chromite o c c u r s as Mg-Cr-rich anhedral fragments and as F e - r i c h e u h e d r a l t o subhedral c r y s t a l s . The l a t t e r , r e l a t i v e l y more important i n the magnetic f r a c t i o n , are i n t e r p r e t e d as Pt-poor g r a i n s d i s s e m i n a t e d throughout the d u n i t e whereas fragments are r e l a t i v e l y more important i n the non-magnetic f r a c t i o n and are i n t e r p r e t e d as remnants of P t - b e a r i n g massive c h r o m i t i t e s e g r e g a t i o n s . The abundance of chromite fragments i n s o i l s near c h r o m i t i t e s e g r e g a t i o n s accounts f o r the h i g h Pt content of the non-magnetic heavy f r a c t i o n s of these s o i l s . The -270 mesh f r a c t i o n or the magnetic heavy f r a c t i o n of C h o r i z o n s o i l s would be the most s u i t a b l e sample media f o r r e c o n n a i s s a n c e geochemical sampling. However, the g r e a t e r c o n t r a s t , more l i m i t e d d i s p e r s i o n and M g - C r - r i c h chromite a s s o c i a t i o n of the non-magnetic heavy f r a c t i o n make i t a more s u i t a b l e media f o r d e t a i l e d geochemical sampling. i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES x i ACKNOWLEDGEMENTS x v i i i Chapter One: INTRODUCTION 1.1 I n t r o d u c t i o n 2 1.2 P r o p e r t i e s of the Platinum-Group Elements 3 1.3 Platinum-Group Element Mineralogy 4 1.4 Platinum-Group Element Deposits 4 1.4.1 C l a s s i f i c a t i o n 4 1.4.2 Platinum-Group Element Occurrences i n B r i t i s h Columbia 6 1.5 Problems and O b j e c t i v e s 7 Chapter Two: DESCRIPTION OF THE STUDY AREA ' 2.1 L o c a t i o n and Access 11 2.2 E x p l o r a t i o n H i s t o r y 13 2.2.1 Tulameen D i s t r i c t 13 2.2.2 Grasshopper Mountain 15 2.3 Bedrock Geology 16 2.3.1 General Geology and Regional S e t t i n g 16 2.3.2 Geology of the Dunite Core 19 2.3.3 Platinum-Group Element Occurrences 23 2.3.4 Platinum-Group Mineralogy 25 2.4 Topography and Physiography 29 2.4.1 R e g i o n a l Physiography 29 2.4.2 P h y s i o g r a p h i c Zones of Grasshopper Mountain 30 2.5 Quaternary and S u r f i c i a l Geology 30 2.5.1 Quaternary H i s t o r y of the Southern I n t e r i o r 30 2.5.2 S u r f i c i a l Geology 35 2.6 C l i m a t e 40 2.7 S o i l Development 41 2.8 V e g e t a t i o n 48 Chapter Three: FIELD AND LABORATORY PROCEDURES 3.1 S e l e c t i o n of the F i e l d Area 51 3.2 Sample C o l l e c t i o n Methods 51 3.2.1 I n t r o d u c t i o n 51 3.2.2 S o i l s 54 3.2.3 Stream Sediment, Moss mat and Bank samples...56 3.2.4 Bogs 58 3.2.5 Waters 58 V 3.3 Sample P r e p a r a t i o n Methods 61 3.3.1 Overview S o i l Samples 61 3.3.2 LFH Samples 66 3.3.3 Stream Sediment, Moss mat and Bank samples...67 3.3.4 Bog samples 68 3.3.5 D e t a i l e d S o i l P r o f i l e s 68 3.3.5.1 S i z e F r a c t i o n s 70 3.3.5.2 Densit y and Magnetic F r a c t i o n s 71 3.4 A n a l y t i c a l Techniques 74 3.4.1 Overview S o i l s , Sediments, Banks and Bogs....74 3.4.2 LFH and Ashed Bog Samples 7 6 3.4.3 Waters... 78 3.4.4 D e t a i l e d S o i l P r o f i l e Samples 78 3.4.5 Subsample S i z e Experiment 79 3.5 E v a l u a t i o n of A n a l y t i c a l P r e c i s i o n 84 3.5.1 Overview C Horizons 84 3.5.2 LFH Horizons 88 3.5.3 D e t a i l e d S o i l P r o f i l e s 90 3.6 M o n i t o r i n g of A n a l y t i c a l Accuracy and D r i f t 95 3.6.1 C o n t r o l Reference Standards and D r i f t Monitors 96 3.6.2 S i l i c a Blanks 101 3.7 Scanning E l e c t r o n Microscopy and E l e c t r o n Microprobe A n a l y s i s of Heavy M i n e r a l Concentrates...103 3.7.1 Sample S e l e c t i o n and P r e p a r a t i o n 103 3.7.2 Scanning E l e c t r o n Microscopy Techniques 105 3.7.3 E l e c t r o n Microprobe Techniques 107 3.8 X-Ray D i f f r a c t i o n A n a l y s i s of S e l e c t e d S o i l H o r i z ons 109 Chapter Four: RESULTS 4.1 I n t r o d u c t i o n I l l 4.2 P a r t A: Overview R e s u l t s . . . . 112 4.2.1 S o i l s 112 4.2.1.1 G r a i n S i z e D i s t r i b u t i o n 112 4.2.1.2 R e s u l t s : Platinum and Other Elements 114 4.2.1.3 X-Ray D i f f r a c t i o n Mineralogy R e s u l t s . . . 147 4.2.2 LFH Horizons 151 4.2.3 Stream Sediments, Moss mats and Banks 163 4.2.4 Bogs 170 4.2.5 Waters 173 4.3 P a r t B: D e t a i l e d S o i l P r o f i l e R e s u l t s 178 4.3.1 G r a i n S i z e D i s t r i b u t i o n 178 v i 4.3.1.1 S i z e F r a c t i o n s 178 4.3.1.2 Density and Magnetic F r a c t i o n s 180 4.3.2 R e s u l t s : Platinum 184 4.3.2.1 S i z e F r a c t i o n s 185 4.3.2.2 Density and Magnetic F r a c t i o n s 193 4.3.2.3 T o t a l Pt Content of S e l e c t e d S o i l s . . . 2 0 7 4.4 P a r t C: Scanning E l e c t r o n Microscopy and Microprobe R e s u l t s 211 4.4.1 I n t r o d u c t i o n 211 4.4.2 Platinum-Group M i n e r a l s 211 4.4.2.1 D i s c r e t e Free PGM 214 4.4.2.2 PGM I n c l u s i o n s i n M g - s i l i c a t e s 217 4.4.2.3 PGM I n c l u s i o n s i n Chromite 221 4.4.3 Magnetite 226 4.4.4 Chromite 228 4.4.4.1 Scanning E l e c t r o n Microscopy R e s u l t s , 228 4.4.4.2 E l e c t r o n Microprobe R e s u l t s 2 34 4.4.5 I l m e n i t e 245 4.4.6 Other M i n e r a l s 246 Chapter F i v e : DISCUSSION 5.1 I n t r o d u c t i o n 249 5.2 D e t r i t a l Chromites 249 5.2.1 O r i g i n of D e t r i t a l Chromites 249 5.2.1.1 Fragments 250 5.2.1.2 C r y s t a l s 252 5.2.2 Chromite Chemistry: R e l a t i o n Between Compositional V a r i a t i o n s and Magnetic P r o p e r t i e s 254 5.2.3 O r i g i n of Compositional V a r i a t i o n s i n D e t r i t a l Chromite 258 5.3 S o i l s 263 5.3.1 I n t r o d u c t i o n 263 5.3.2 Overview S o i l s 265 5.3.3 V a r i a t i o n s i n S o i l Pt D i s t r i b u t i o n w i t h Depth 270 5.3.3.1 Primary C l a s t i c D i s p e r s i o n 271 5.3.3.2 P o s t - g l a c i a l Processes 277 5.3.4 Platinum Residence S i t e s i n M i n e r a l Horizons 280 5.3.4.1 Residence S i t e s 280 5.3.4.2 Pedogenic R e d i s t r i b u t i o n of Pt Wit h i n Horizons 287 5.3.5 Pt Residence S i t e s i n LFH Horizons 288 5.4 Hydromorphic Transport of PGE: Evidence From Seepage Bogs and Waters 293 5.4.1 C o n s t r a i n t s on PGE M o b i l i t y 295 v i i 5.4.2 Bogs 301 5.4.3 Waters 303 5.5 Recommendations For Geochemical E x p l o r a t i o n For C h r o m i t i t e - A s s o c i a t e d Platinum D e p o s i t s 306 5.5.1 Sampling of S o i l s 308 5.5.1.1 Choice of S o i l Horizon 308 5.5.1.2 Choice of S i z e F r a c t i o n 311 5.5.1.3 Sampling Densi t y 315 5.5.2 Sampling of Other Media 316 5.5.2.1 Sediments 316 5.5.2.2 Waters and Bogs 318 5.5.3 Sample P r e p a r a t i o n Methodology 319 5.5.3.1 Co n c e n t r a t i o n Techniques 319 5.5.3.2 P u l v e r i z i n g and Subsampling Methodology 324 5.5.4 Q u a l i t y C o n t r o l M o n i t o r i n g 325 5.5.5 A p p l i c a t i o n of E l e c t r o n Microprobe Techniques t o PGE E x p l o r a t i o n 326 5.5.6 Summary of Recommendations f o r E x p l o r a t i o n f o r C h r o m i t i t e - A s s o c i a t e d Pt D eposits 327 Chapter S i x : CONCLUSIONS 330 REFERENCES 333 APPENDICES 354 v i i i LIST OF TABLES Ta b l e 2-1. Tabl e 3-1. Tabl e 3-2 Tabl e 3-3, Tabl e 3-4 Tabl e 3-5. Ta b l e 3-6, Tabl e 3-7 Tabl e 4-1, Ta b l e 4-2. Ta b l e 4-3. Tabl e 4-4, Platinum-group mineralogy of Tulameen c h r o m i t i t e s and p l a c e r s 28 D i s t r i b u t i o n of sample media a c c o r d i n g t o study area 53 D i s t r i b u t i o n of s o i l p r o f i l e s a c c o r d i n g t o study area and parent m a t e r i a l 53 Sample s u i t e summary f o r Pt-Pd-Au a n a l y s e s of overview m i n e r a l s o i l s , sediments, banks and bogs; d e t a i l e d s o i l p r o f i l e s ; LFH and ashed bog samples; and waters 75 Subsample s i z e experiment: mean, median and range of Pt c o n c e n t r a t i o n s of 10 g v e r s u s 30 g subsamples of d r i f t monitors RK-05 and PT-5 81 Mean, median and range of Pt c o n c e n t r a t i o n s of c e r t i f i e d r e f e r e n c e standard PTA-1 subsamples determined by two commercial l a b o r a t o r i e s 83 Mean, median and range of Pt, Pd, and Au c o n c e n t r a t i o n s f o r d r i f t monitors RK-05 and PT-5, and f o r c o n t r o l standard PTA-1 98 Mean and median Pt c o n c e n t r a t i o n s o f d r i f t monitors RK-05 and PT-5, and of c o n t r o l standard PTA-1, i n each of f o u r a n a l y t i c a l batches 100 Mean, median and range of g r a i n s i z e d i s t r i b u t i o n i n t i l l and c o l l u v i u m as weight percent of the -10 mesh s o i l component 113 Mean, median and range of g r a i n s i z e d i s t r i b u t i o n i n t i l l and c o l l u v i u m as weight percent of the t o t a l dry weight of the th r e e f r a c t i o n s 113 Mean, median and range of major elements, s u b d i v i d e d by parent m a t e r i a l grouping, i n the -70 mesh f r a c t i o n of C h o r i z o n s o i l s . . . . 1 1 9 Mean, median and range of PGE and o t h e r s e l e c t e d c o n s t i t u e n t s of the -70 mesh f r a c t i o n of C h o r i z o n s o i l s i n v a r i o u s parent m a t e r i a l s 124 i x T a b l e 4-5. S i g n i f i c a n t c o r r e l a t i o n s i n t i l l 127 Tabl e 4-6. S i g n i f i c a n t c o r r e l a t i o n s i n c o l l u v i u m 128 Tabl e 4-7. Mean, median, minimum va l u e and maximum va l u e of Pt, Pd, Au, weight p e r c e n t ash, LFH/C h o r i z o n Pt r a t i o , Fe and p e r c e n t i n s o l u b l e r e s i d u e i n LFH h o r i z o n samples.... 153 Tabl e 4-8. Weight percent -70 mesh f r a c t i o n and Pt content of stream sediments and moss mats, Grasshopper Creek 166 Ta b l e 4-9. Mean and range of Pt content and pH of v a r i o u s types of f i l t e r e d and a c i d i f i e d Grasshopper Mountain s u r f a c e waters 176 Tabl e 4-10. Mean and range of g r a i n s i z e d i s t r i b u t i o n of s o i l s developed on d i f f e r e n t parent m a t e r i a l s 179 Tabl e 4-11. Weight percent heavy m i n e r a l s i n -70+140 and -140+270 mesh f r a c t i o n s of d e t a i l e d s o i l p r o f i l e s , and the p r o p o r t i o n s of magnetic and non-magnetic heavy m i n e r a l s i n each heavy f r a c t i o n 183 Ta b l e 4-12. Median and range of Pt c o n c e n t r a t i o n s among s i z e f r a c t i o n s of s o i l s developed on d i f f e r e n t parent m a t e r i a l s 186 Ta b l e 4-13. Median and range of Pt c o n c e n t r a t i o n s between l i g h t and heavy m i n e r a l f r a c t i o n s of s o i l s on d i f f e r e n t parent m a t e r i a l s 195 Ta b l e 4-14. Median and range of Pt c o n c e n t r a t i o n s i n magnetic and non-magnetic heavy m i n e r a l f r a c t i o n s i n s o i l s on d i f f e r e n t p a r e n t m a t e r i a l s 198 Ta b l e 4-15. Summary m i n e r a l o g i c a l r e s u l t s of SEM i n v e s t i g a t i o n of heavy m i n e r a l c o n c e n t r a t e s - P a r t A: c o l l u v i u m and secondary study area d u n i t i c t i l l and ru b b l e 212 Tabl e 4-16. Summary m i n e r a l o g i c a l r e s u l t s of SEM i n v e s t i g a t i o n of heavy m i n e r a l c o n c e n t r a t e s - P a r t B: d u n i t i c and n o n - d u n i t i c t i l l s 213 Ta b l e 4-17. Mean e l e c t r o n microprobe data f o r c o r e s of d e t r i t a l chromite c r y s t a l s and fragments from v a r i o u s C h o r i z o n s o i l s 236 X Ta b l e 4-18. Mean e l e c t r o n microprobe data f o r edges of d e t r i t a l chromite c r y s t a l s and fragments from v a r i o u s C h o r i z o n s o i l s 237 Tabl e 4-19. Anova t a b l e s showing one-way a n a l y s i s of v a r i a n c e r e s u l t s f o r Cr203 a n a l y s e s of chromite c r y s t a l s and fragments 240 Tabl e 4-20. Anova t a b l e s showing one-way a n a l y s i s o f v a r i a n c e r e s u l t s f o r MgO analyses of chromite c r y s t a l s and fragments 241 Tabl e 5-1. Composition of d e t r i t a l s o i l chromite fragments from two s i t e s a djacent t o known PGE-chromite occurrences, w i t h t h a t of c h r o m i t i t e s e g r e g a t i o n s 251 Tabl e 5-2. Recommendations f o r geochemical e x p l o r a t i o n f o r c h r o m i t i t e - a s s o c i a t e d Pt d e p o s i t s i n Alaskan-type u l t r a m a f i c complexes 328 LIST OF FIGURES F i g u r e 2-1. L o c a t i o n and g e n e r a l i z e d geology of the study areas w i t h i n the d u n i t e core of the Tulameen u l t r a m a f i c complex 12 F i g u r e 2-2. View from the summit of Grasshopper Mountain, l o o k i n g southwest up the Tulameen R i v e r v a l l e y 14 F i g u r e 2-3. S e r p e n t i n i z a t i o n w i t h i n the d u n i t e core of the Tulameen u l t r a m a f i c complex 20 F i g u r e 2-4. Discontinuous and massive c h r o m i t i t e s e g r e g a t i o n s i n d u n i t e 22 F i g u r e 2-5. T h i n d i s c o n t i n u o u s c h r o m i t i t e s e g r e g a t i o n s i n d u n i t e 22 F i g u r e 2-6. C l i f f Zone PGE occurrence i n d u n i t e on the southeast f a c e of Grasshopper Mountain 24 F i g u r e 2-7. Massive c h r o m i t i t e s e g r e g a t i o n i n d u n i t e a t the C l i f f Zone PGE occurrence 24 F i g u r e 2-8. D i f f e r e n t p h y s i o g r a p h i c zones on Grasshopper Mountain 31 F i g u r e 2-9. D i f f e r e n t p h y s i o g r a p h i c zones on Grasshopper Mountain 32 F i g u r e 2-10. Composite s o i l p r o f i l e s 38 F i g u r e 2-11. Unhorizonated o r t h i c r e g o s o l s o i l p r o f i l e s i n a c t i v e c o l l u v i u m 43 F i g u r e 2-12. Unhorizonated o r t h i c r e g o s o l s o i l p r o f i l e s i n a c t i v e c o l l u v i u m 44 F i g u r e 2-13. E u t r i c b r u n i s o l s o i l p r o f i l e s developed on d u n i t i c t i l l 45 F i g u r e 2-14. S o i l p r o f i l e s adjacent t o A-Zone PGE occurrence, secondary study area 46 F i g u r e 2-15. S o i l p r o f i l e s developed on n o n - d u n i t i c t i l l 47 F i g u r e 3-1. Sample l o c a t i o n map 52 F i g u r e 3-2. P o r t a b l e pressure apparatus f o r f i e l d f i l t r a t i o n of water samples 60 x i i F i g u r e 3-3. Flowchart f o r s o i l sample p r e p a r a t i o n and a n a l y s i s 63 F i g u r e 3-4. Wet s i e v i n g apparatus f o r overview sample p r e p a r a t i o n 64 F i g u r e 3-5. L o c a t i o n map of d e t a i l e d s o i l p r o f i l e s stream sediment s i t e 69 F i g u r e 3-6. Boxplots showing v a r i a t i o n i n Pt c o n c e n t r a t i o n s of c o n t r o l standards RK-05 and PT-5 with i n c r e a s i n g s i z e of the a n a l y t i c a l subsample 82 F i g u r e 3-7. S c a t t e r p l o t s of d u p l i c a t e a n a l y s e s o f -70 mesh overview samples f o r Pt and As 86 F i g u r e 3-8. P r e c i s i o n c o n t r o l graph of -70 mesh overview d u p l i c a t e Pt analyses 87 F i g u r e 3-9. S c a t t e r p l o t and p r e c i s i o n c o n t r o l graph of d u p l i c a t e LFH Pt analyses 89 F i g u r e 3-10. S c a t t e r p l o t s of d u p l i c a t e Pt a n a l y s e s o f d e t a i l e d s o i l p r o f i l e s i z e , d e n s i t y and magnetic f r a c t i o n s 92 F i g u r e 3-11. P r e c i s i o n c o n t r o l graph of Pt a n a l y s e s f o r d u p l i c a t e samples from d e t a i l e d s o i l p r o f i l e s 93 F i g u r e 3-12. S p l i t t e r d u p l i c a t e s : s c a t t e r p l o t and p r e c i s i o n c o n t r o l graph of d u p l i c a t e Pt analyses 94 F i g u r e 3-13. Standard c o n t r o l graphs f o r Pt standards RK-05, PT-5 and PTA-1 99 F i g u r e 3-14. V a r i a t i o n i n Pt content of s i l i c a blanks with a n a l y t i c a l batch 102 F i g u r e 4-1. MgO content of overview -70 mesh C h o r i z o n s o i l s i n the secondary study area and i n main study area t i l l 115 F i g u r e 4-2. D i s t r i b u t i o n of MgO i n C h o r i z o n c o l l u v i u m , main study area 116 F i g u r e 4-3. A r i t h m e t i c frequency d i s t r i b u t i o n s of MgO content of overview C h o r i z o n s o i l s i n t i l l and c o l l u v i u m 117 x i i i F i g u r e 4-4. P r o b a b i l i t y p l o t of MgO i n t i l l , main study area 118 F i g u r e 4-5. Pt content of overview -70 mesh C h o r i z o n s o i l s i n t i l l and c o l l u v i u m 121 F i g u r e 4-6. Log transformed c o r r e l a t i o n m a t r i c e s f o r t i l l and c o l l u v i u m 126 F i g u r e 4-7. S c a t t e r p l o t s of -70 mesh overview Pt c o n c e n t r a t i o n s with MgO and Cr203 129 F i g u r e 4-8. S c a t t e r p l o t s of -70 mesh overview s o i l Pt data with As, Sb, Au and Pd 130 F i g u r e 4-9. S c a t t e r p l o t s of -70 mesh overview s o i l Pt data with Fe203, MnO, LOI and Ba 131 F i g u r e 4-10. A r i t h m e t i c and l o g frequency d i s t r i b u t i o n s of Pt content of overview C h o r i z o n s o i l s i n t i l l and c o l l u v i u m 133 F i g u r e 4-11. P r o b a b i l i t y p l o t of Pt i n n o n - d u n i t i c t i l l , main study area 134 F i g u r e 4-12. A n t i l o g frequency d i s t r i b u t i o n s o f Cr203 and Pd content of overview C h o r i z o n s o i l s i n t i l l and c o l l u v i u m 135 F i g u r e 4-13. Pt content of overview -70 mesh C h o r i z o n s o i l s i n the secondary study area and i n main study area t i l l 137 F i g u r e 4-14. Cr203 content of overview -70 mesh C h o r i z o n s o i l s i n the secondary study area and i n main study area t i l l 138 F i g u r e 4-15. Pd content of overview -70 mesh C h o r i z o n s o i l s i n the secondary study area and i n main study area t i l l 139 F i g u r e 4-16. D i s t r i b u t i o n of Pt and Cr203 i n C h o r i z o n c o l l u v i u m , main study area 143 F i g u r e 4-17. D i s t r i b u t i o n of Pd i n C h o r i z o n c o l l u v i u m , main study area 144 F i g u r e 4-18. Concen t r a t i o n s of s e l e c t e d elements i n background t i l l samples on the northern margin and t o the west of the du n i t e core of the Tulameen complex 146 x i v F i g u r e 4-19. Schematic diagram i l l u s t r a t i n g the g e n e r a l r e l a t i o n of MgO content t o s o i l mineralogy i n s u r f i c i a l m a t e r i a l s 150 F i g u r e 4-20. A r i t h m e t i c frequency d i s t r i b u t i o n s of Pt and Fe i n LFH h o r i z o n ash 152 F i g u r e 4-21. R e l a t i o n of Pt t o weight pe r c e n t ash i n LFH h o r i z o n s above v a r i o u s s o i l p a r e n t m a t e r i a l s 154 F i g u r e 4-22. Pt d i s t r i b u t i o n i n LFH h o r i z o n s . . . . 155 F i g u r e 4-23. LFH c o r r e l a t i o n m a t r i c e s 158 F i g u r e 4-24. S c a t t e r p l o t s of Pt versus Fe and Pd i n ashed LFH h o r i z o n s above v a r i o u s parent m a t e r i a l s 159 F i g u r e 4-25. S c a t t e r p l o t of Pt c o n c e n t r a t i o n s of C h o r i z o n s o i l s from v a r i o u s parent m a t e r i a l s versus ash from c o r r e s p o n d i n g LFH h o r i z o n s 160 F i g u r e 4-26. Frequency d i s t r i b u t i o n s of LFH/C h o r i z o n Pt r a t i o s f o r n o n - d u n i t i c t i l l , d u n i t i c t i l l , and A-Zone d u n i t i c t i l l , r u b b l e and c o l l u v i u m 160 F i g u r e 4-27. D i s t r i b u t i o n of LFH horizon/C h o r i z o n Pt r a t i o s on Grasshopper Mountain 161 F i g u r e 4-28. S c a t t e r p l o t s of weight percent i n s o l u b l e r e s i d u e versus Pt and Fe i n ashed LFH h o r i z o n s above v a r i o u s parent m a t e r i a l s 162 F i g u r e 4-29. Pt, Pd and Au contents of stream sediments and moss mats at e i g h t sampling s i t e s along Grasshopper Creek 164 F i g u r e 4-30. Pt d i s t r i b u t i o n i n f i v e s i z e f r a c t i o n s and i n l i g h t , heavy, heavy magnetic and heavy non-magnetic f r a c t i o n s a t stream sediment s i t e 2 167 F i g u r e 4-31. Pt and Cr203 contents of sediments and moss mats at e i g h t s i t e s on Grasshopper Creek 168 F i g u r e 4-32. Pt contents of p u l v e r i z e d and ashed o r g a n i c bog s o i l s i n t h r e e Grasshopper Mountain bogs 172 X V F i g u r e 4-33. Pt content of f i l t e r e d stream, bog and seepage waters 174 F i g u r e 4-34. R e l a t i o n between Pt content, sample type and water c o l o u r f o r f i l t e r e d Grasshopper Mountain s u r f a c e waters 177 F i g u r e 4-35. S c a t t e r p l o t of Pt content versus pH f o r f i l t e r e d Grasshopper Mountain s u r f a c e waters 177 F i g u r e 4-36. Weight percent heavy m i n e r a l s i n -70+140 and -140+270 mesh f r a c t i o n s of h o r i z o n s from d e t a i l e d s o i l p r o f i l e s 182 F i g u r e 4-37. Pt content of the -10+40 and -40+70 mesh f r a c t i o n s of i n d i v i d u a l h o r i z o n s i n s o i l s on v a r i o u s parent m a t e r i a l s 187 F i g u r e 4-38. Pt content of the -70+140 and -140+270 mesh f r a c t i o n s of i n d i v i d u a l h o r i z o n s i n s o i l s on v a r i o u s parent m a t e r i a l s 188 F i g u r e 4-39. Pt content of the -270 mesh f r a c t i o n of i n d i v i d u a l h o r i z o n s i n s o i l s on v a r i o u s parent m a t e r i a l s 189 F i g u r e 4-40. Pt d i s t r i b u t i o n i n s i z e f r a c t i o n s of some Grasshopper Mountain s o i l s 191 F i g u r e 4-41. Pt d i s t r i b u t i o n i n s i z e f r a c t i o n s o f some c o l l u v i a l Grasshopper Mountain s o i l s 192 F i g u r e 4-42. Pt d i s t r i b u t i o n i n heavy and l i g h t m i n e r a l f r a c t i o n s of -70+140 and -140+270 mesh s i z e f r a c t i o n s 196 F i g u r e 4-43. Pt d i s t r i b u t i o n i n magnetic and non-magnetic heavy m i n e r a l f r a c t i o n s of -70+140 and -140+270 mesh s i z e f r a c t i o n s 199 F i g u r e 4-44. Pt content of -70+140 and -140+270 mesh magnetic heavy m i n e r a l f r a c t i o n s of i n d i v i d u a l h o r i z o n s of s o i l s on v a r i o u s parent m a t e r i a l s 201 F i g u r e 4-45. Pt content of -70+140 and -140+270 mesh non-magnetic heavy m i n e r a l f r a c t i o n s of i n d i v i d u a l h o r i z o n s of s o i l s on v a r i o u s parent m a t e r i a l s 202 x v i F i g u r e 4-46. Pt d i s t r i b u t i o n i n humo-ferric podzol on n o n - d u n i t i c t i l l 203 F i g u r e 4-47. Pt d i s t r i b u t i o n i n e u t r i c b r u n i s o l on d u n i t i c t i l l near A-Zone PGE oc c u r r e n c e . . . . 204 F i g u r e 4-48. Pt d i s t r i b u t i o n i n o r t h i c r e g o s o l on d u n i t i c r u b b l e immediately above A-Zone PGE occurrence 205 F i g u r e 4-49. Pt d i s t r i b u t i o n i n composite s o i l p r o f i l e of d u n i t i c c o l l u v i u m o v e r l y i n g d u n i t i c t i l l 206 F i g u r e 4-50. Percent c o n t r i b u t i o n of i n d i v i d u a l s i z e f r a c t i o n s t o t o t a l Pt content o f some s o i l h o r i z o n s i n d u n i t i c and n o n - d u n i t i c t i l l 208 F i g u r e 4-51. Percent c o n t r i b u t i o n of i n d i v i d u a l s i z e f r a c t i o n s t o t o t a l Pt content o f some s o i l h o r i z o n s i n d u n i t i c t i l l , r u b b l e and c o l l u v i u m 209 F i g u r e 4-52. D i s c r e t e f r e e PGM 216 F i g u r e 4-53. PGM i n c l u s i o n s i n M g - s i l i c a t e s 220 F i g u r e 4-54. PGM i n c l u s i o n s i n a chromite c r y s t a l 223 F i g u r e 4-55. PGM i n c l u s i o n s i n chromite fragments 225 F i g u r e 4-56. Morphology of chromite c r y s t a l s 231 F i g u r e 4-57. Morphology of chromite fragments 233 F i g u r e 4-58. Fe-C r - A l s p i n e l composition p l o t o f d e t r i t a l chromite c r y s t a l s and fragments from v a r i o u s C h o r i z o n s o i l s and from major rock types of the Tulameen complex 243 F i g u r e 4-59. P l o t of F e 2 + / ( F e 2 + + M g 2 + ) versus Cr/(Cr+Al) f o r d e t r i t a l chromite c r y s t a l s and fragments from v a r i o u s C h o r i z o n s o i l s and from major rock types of the Tulameen complex 244 F i g u r e 5-1. R e l a t i o n between volume per c e n t cumulus chromite and Mg/(Mg+Fe 2 +) of the chromite 260 x v i i F i g u r e 5-2 I d e a l i z e d model f o r m e c h a n i c a l d i s p e r s i o n o f P t on Grasshopper Mountain 273 F i g u r e 5-3 P t d i s t r i b u t i o n i n magnetic and non-magnetic heavy f r a c t i o n s o f s e l e c t e d s o i l p r o f i l e s , and i t s r e l a t i o n t o i d e a l i z e d P t o c c u r r e n c e s and l a n d s c a p e elements on Grasshopper Mountain 284 F i g u r e 5-4 Eh-pH diagram f o r P t a t 25 C and 1 b a r , w i t h superimposed s t a b i l i t y f i e l d s o f some i n o r g a n i c complexes. 298 ACKNOWLEDGEMENTS The a u t h o r i s g r a t e f u l f o r t h e a s s i s t a n c e o f numerous i n d i v i d u a l s d u r i n g t h e s i s r e s e a r c h and p r e p a r a t i o n . The a u t h o r would l i k e t o thank Pasakorn Paopongsawan f o r h i s a b l e a s s i s t a n c e i n t h e f i e l d , and J o n i Borges and Deb F e d u i k f o r t h e i r h e l p w i t h sample p r e p a r a t i o n . S e v e r a l i n d i v i d u a l s p r o v i d e d h e l p f u l s u p p o r t , d i s c u s s i o n and a d v i c e , e s p e c i a l l y D r s . P.W. F r i s k e , C E . Dunn, G.T. N i x o n , J.K. R u s s e l l , A . J . Macdonald and W.B. Coker, and S.B. B a l l a n t y n e , J . J . L y n c h , C. Bulmer and J . K n i g h t . Drs. A . J . S i n c l a i r and K.W. Sa v i g n y r e a d and commented upon t h e m a n u s c r i p t . I n a d d i t i o n , G.E.M. H a l l o f t h e G e o l o g i c a l Survey o f Canada and P.F. Matysek o f t h e B r i t i s h Columbia G e o l o g i c a l Survey B r a n c h a r e thanke d f o r p r o v i d i n g v a r i o u s c h e m i c a l a n a l y s e s . The a u t h o r i s i n d e b t e d t o Stanya Horsky f o r e l e c t r o n m i c r o p r o b e and x - r a y d i f f r a c t i o n d e t e r m i n a t i o n s , J o n i Borges f o r h e r s k i l l f u l a n a l y t i c a l work, and Yvonne Douma f o r h e r c a r e f u l p r e p a r a t i o n o f p o l i s h e d g r a i n mounts. S t e v e S i b b i c k , P a s a k o r n Paopongsawan, and T r a c y Delaney o f f e r e d i n s p i r a t i o n a l d i s c u s s i o n s on e x p l o r a t i o n g e o c h e m i s t r y . The a u t h o r a l s o w i s h e s t o thank Dr. W.K. F l e t c h e r o f t h e U n i v e r s i t y o f B r i t i s h Columbia f o r g u i d i n g t h e p r o g r e s s o f t h e p r o j e c t . The a u t h o r i s g r a t e f u l t o Newmont E x p l o r a t i o n o f Canada f o r p r o v i d i n g v a l u a b l e i n f o r m a t i o n , and t o I r e n e and K a r l Strom o f Tulameen f o r t h e i r n e i g h b o u r l y a s s i s t a n c e d u r i n g t h e summers o f 1988 and 1989. The s t u d y was s u p p o r t e d by f u n d i n g from t h e S c i e n c e and Technology Development Fund o f t h e P r o v i n c e o f B r i t i s h C olumbia t h r o u g h t h e S c i e n c e C o u n c i l o f B r i t i s h C o l u m b i a ; t h e B r i t i s h Columbia M i n i s t r y o f Energy, Mines and P e t r o l e u m R e s o u r c e s ; t h e G e o l o g i c a l Survey o f Canada; and P l a c e r Dome I n c . 1 Chapter One INTRODUCTION 2 CHAPTER ONE. INTRODUCTION 1.1 I n t r o d u c t i o n Platinum i s v a l u a b l e both as a p r e c i o u s metal and f o r i t s i n d u s t r i a l usage i n a v a r i e t y of h i g h - t e c h n o l o g y a p p l i c a t i o n s . P r o d u c t i o n of platinum i s dominated by South A f r i c a and the S o v i e t Union, which i n 1989 produced 77% and 16%, r e s p e c t i v e l y , of the 3,375,000 ounces s u p p l i e d t o the western world (Coombes, 1990). R i s i n g p l atinum p r i c e s d u r i n g 1986, f u e l e d by both concern f o r the long-term s t a b i l i t y o f c u r r e n t producers, and r a p i d l y - i n c r e a s i n g demand i n the automotive, investment and j e w e l r y markets, l e d t o a worldwide rush t o e x p l o r e and develop new d e p o s i t s . The presence of t r a n s p o r t e d overburden i n the Canadian C o r d i l l e r a has t r a d i t i o n a l l y been viewed as an o b s t a c l e t o m i n e r a l e x p l o r a t i o n . Platinum t a r g e t s may be obscured by P l e i s t o c e n e t i l l , f l u v i o g l a c i a l and g l a c i o l a c u s t r i n e d e p o s i t s . The landscape may be f u r t h e r m o d i f i e d by Recent c o l l u v i a l and pedogenic processes. Platinum e x p l o r a t i o n i s a l s o hampered by t h r e e a d d i t i o n a l f a c t o r s : the p a r t i c l e s p a r c i t y e f f e c t a r i s i n g from the low abundance and e r r a t i c d i s t r i b u t i o n of many platinum-group m i n e r a l s (PGM), a poor knowledge of t h e i r d i s t r i b u t i o n and behaviour i n the s u r f i c i a l environment, and the consequent l a c k of any e f f e c t i v e geochemical e x p l o r a t i o n techniques and g u i d e l i n e s a p p r o p r i a t e f o r the e f f i c i e n t and r e l i a b l e d e t e c t i o n of 3 platinum-group element m i n e r a l i z a t i o n . 1.2 P r o p e r t i e s of the Platinum-Group Elements Platinum i s a s o f t , m a l l e a b l e and d u c t i l e metal w i t h a w h i t i s h s t e e l - g r e y c o l o u r . I t occurs i n Group V I I I of the p e r i o d i c t a b l e t ogether with the other f i v e platinum-group elements (PGE) i r i d i u m , osmium, ruthenium, rhodium and p a l l a d i u m . The PGE comprise two subgroups based on atomic weight. The former t h r e e , i n c l u d i n g Pt, comprise the heavy platinum-group elements whereas the l a t t e r t h r e e comprise the l i g h t platinum-group elements (Wright and F l e i s c h e r , 1965). The PGE are c a t a l y s t s , have h i g h m e l t i n g temperatures and are r e l a t i v e l y u n r e a c t i v e over a wide temperature range (Westland, 1981; C a b r i , 1982). They are a l s o s i d e r o p h i l i c and c h a l c o p h i l i c , forming s o l i d s o l u t i o n a l l o y s w i t h each other and with Fe, Cu and N i as a r e s u l t of t h e i r s i m i l a r atomic r a d i i . Pt d e n s i t y of 21.45 i s reduced by a l l o y i n g , as pure end member PGE are not found i n n a t u r e . "Native p l a t i n u m " i s an a l l o y of Pt and Fe c o n t a i n i n g > 80 a t . % p l a t i n u m ( C a b r i , 1981). 4 1.3 Platinum-Group Element Mineralogy PGE form m e t a l l i c a l l o y s and a l s o combine w i t h Fe, Cu, S, Se, Te, As, Sb, B i , Sn, Pb and Hg t o form d i s c r e t e platinum-group m i n e r a l s (PGM). E i g h t y - f o u r PGM are c u r r e n t l y r e c o g n i z e d (Hulbert e t a l , 1988), the m a j o r i t y of which are P d - r i c h . PGE a l s o occur i n v a r i a b l e amounts w i t h i n s u l f i d e s , rock-forming s i l i c a t e s and hydrous i r o n o xides (Wright and F l e i s c h e r , 1965; Razin, 1965, 1971; Makovicky e t a l , 1986; Paktunc e t a l , 1990). Pt i t s e l f forms 22 m i n e r a l s ( C a b r i , 1981) comprising the n a t i v e metal, Fe and Cu a l l o y s , and v a r i o u s a r s e n i d e s , antimonides, s u l f i d e s , t e l l u r i d e s , bismides and s t a n n i d e s . Pt a l s o s u b s t i t u t e s w i t h i n other PGM. 1.4 Platinum-Group Element Deposits 1.4.1 C l a s s i f i c a t i o n S e v e r a l c l a s s i f i c a t i o n schemes have been proposed f o r PGE d e p o s i t s and occurrences (Mertie, 1969; N a l d r e t t , 1981; Macdonald, 1987; H u l b e r t e t a l , 1988), but they can be d i v i d e d r o u g h l y i n t o t h r e e g e n e t i c v a r i e t i e s : magmatic, hydrothermal, and s u r f i c i a l . 5 Magmatic d e p o s i t s comprise stratabound, d i s c o r d a n t , m a r g i n a l and u n c l a s s i f i e d v a r i e t i e s (Hulbert e t a l , 1988). Stratabound d e p o s i t s , o c c u r r i n g i n s t r a t i f o r m u l t r a m a f i c complexes formed i n c r a t o n i c environments ( N a l d r e t t and C a b r i , 1986), are by f a r the most important sources of PGE. They i n c l u d e d e p o s i t s of the Bushveld Complex, South A f r i c a , the Great Dyke, Zimbabwe, and the S t i l l w a t e r Complex, U.S.A. (Macdonald, 1987; H u l b e r t e t a l , 1988). The o t h e r v a r i e t i e s of magmatic PGE d e p o s i t s (Hulbert e t a l , 1988) comprise d i s c o r d a n t d u n i t e p i p e s of the Bushveld Complex, Cu-Ni-PGE s u l f i d e d e p o s i t s i n marginal zones of m a f i c / u l t r a m a f i c i n t r u s i o n s such as a t Sudbury and N o r i l ' s k , and u n c l a s s i f i e d d e p o s i t s i n p r i m a r i l y c o n c e n t r i c Alaskan-type m a f i c / u l t r a m a f i c i n t r u s i o n s emplaced i n the l a t t e r stages of o r o g e n e s i s ( N a l d r e t t and C a b r i , 1976) such as those of B r i t i s h Columbia and the S o v i e t U r a l s . Hydrothermal PGE d e p o s i t s have been r e c o g n i z e d as a d e p o s i t type s i n c e the 1920's (Wagner, 1929; M i h a l i k e t a l , 1974; Stumpfl, 1974, 1986; Stumpfl and T a r k i a n , 1976). Examples i n c l u d e the Pt-Pd-Cu New Rambler d e p o s i t , Wyoming; occur r e n c e s a t Messina and i n the Waterberg d i s t r i c t , South A f r i c a ; and the N i c h o l s o n Bay U-Au-Pt-Pd occurrence i n Saskatchewan (Hulbert e t a l , 1988). PGE enrichment i n P o l i s h K u p f e r s c h i e f e r black s h a l e s has been a t t r i b u t e d t o d i a g n e t i c f l u i d s (Kucha, 1982). 6 S u r f i c i a l , or p l a c e r , PGE d e p o s i t s were the o n l y world source o f platinum p r i o r t o 1919, when p r o d u c t i o n began from the Sudbury Ni-Cu d e p o s i t s (Mertie, 1969). Platinum p l a c e r s are predominantly of a l l u v i a l o r i g i n , although e l u v i a l , beach, marine, p a l e o p l a c e r and other v a r i e t i e s a re a l s o known (Mertie, 1969; Owen, 1978; Macdonald, 1987; H u l b e r t e t a l , 1988). A l l u v i a l p l a c e r s , which c o n s t i t u t e o n l y a s m a l l p r o p o r t i o n of c u r r e n t PGE pr o d u c t i o n , are formed by h y d r a u l i c c o n c e n t r a t i o n of m e c h a n i c a l l y - l i b e r a t e d PGM, although t h e r e i s evidence s u p p o r t i n g a chemical o r i g i n f o r some a l l u v i a l PGE (Cousins and K i n l o c h , 1976; Bowles, 1986, 1988; Burgath, 1988). Larger d e p o s i t s , such as those o f the S o v i e t U r a l s , A l a s k a , Columbia, E t h i o p i a and B r i t i s h Columbia are a s s o c i a t e d with Alaskan-type i n t r u s i o n s . Chromite-PGE occurrences are a l s o known i n A l p i n e - t y p e u l t r a m a f i c bodies contained w i t h i n o p h i o l i t e complexes. 1.4.2 Platinum-Group Element Occurrences i n B r i t i s h Columbia Lode and p l a c e r PGE occurrences i n B r i t i s h Columbia and the C o r d i l l e r a have been reviewed by O ' N e i l l and Gunning (1934), Boyle (1982) and Rublee (1986), and f a v o u r a b l e h o s t r o c k s by Evenchick e t a l (1987). No primary lode p l a t i n u m p r o d u c t i o n has been recorded. PGE occur p r i m a r i l y i n 7 Alaskan-type and A l p i n e - t y p e complexes and i n t h e i r a s s o c i a t e d p l a c e r s , with minor occurrences i n a l k a l i n e i n t r u s i o n s and other m a f i c - u l t r a m a f i c bodies (Rublee, 1986; Evenchick e t a l , 1987). Alaskan-type complexes, s e v e r a l of which occur i n the a c c r e t e d Quesnel and S t i k i n e t e r r a n e s , o f f e r good t a r g e t s f o r c h r o m i t i t e - a s s o c i a t e d PGE d e p o s i t s (Nixon, 1990). P l a c e r s a s s o c i a t e d w i t h the most important, the Tulameen u l t r a m a f i c complex, produced 20,000 ounces of PGE between 1887 and 1936 (Rice, 1947; M e r t i e , 1969). PGE are a l s o a s s o c i a t e d with c h r o m i t i t e i n A l p i n e - t y p e bodies w i t h i n o c e a n i c t e r r a n e s , p a r t i c u l a r l y the Cache Creek t e r r a n e (Whittaker and Watkinson, 1985; Rublee, 1986). 1.5 Problems and O b j e c t i v e s S e v e r a l f a c t o r s i n f l u e n c i n g the d e s i g n and i n t e r p r e t a t i o n of geochemical surveys f o r p l a t i n u m i n the C o r d i l l e r a are p o o r l y understood. These problems i n c l u d e : 1) i r r e g u l a r geographic d i s t r i b u t i o n and v a r y i n g background platinum contents of v a r i o u s C o r d i l l e r a n s u r f i c i a l d e p o s i t s . 2) v e r t i c a l d i s t r i b u t i o n and r e s i d e n c e s i t e s of p l a t i n u m w i t h i n s u r f i c i a l d e p o s i t s . 8 3) p h y s i c a l and chemical behaviour of p l a t i n u m and i t s h o s t g r a i n s w i t h i n s u r f i c i a l d e p o s i t s d u r i n g pedogenesis and o t h e r p r o c e s s e s . 4) mineralogy and morphology of the PGM and t h e i r h o s t g r a i n s w i t h i n the s o i l p r o f i l e O b j e c t i v e s of t h i s study are t w o f o l d . The f i r s t i s t o determine the d i s t r i b u t i o n and behaviour of p l a t i n u m i n the s u r f i c i a l environment i n the v i c i n i t y of a known occurrence, the Tulameen u l t r a m a f i c complex of southwestern B r i t i s h Columbia. Distribution r e l a t e s t o the d e t e r m i n a t i o n of the background and anomalous platinum contents of u l t r a m a f i c d i s p e r s i o n t r a i n s and other s u r f i c i a l d e p o s i t s , the v e r t i c a l d i s t r i b u t i o n and r e s i d e n c e s i t e s of platinum w i t h i n the s o i l p r o f i l e , and the mineralogy and morphology of the s o i l PGM. Behaviour r e l a t e s t o the p h y s i c a l and chemical d i s p e r s i o n of p l a t i n u m i n the s u r f i c i a l environment i n response t o p o s t -g l a c i a l and pedogenic processes. The second o b j e c t i v e i s t o apply an understanding of p l a t i n u m d i s p e r s i o n t o development of p r a c t i c a l g u i d e l i n e s f o r geochemical e x p l o r a t i o n i n the C o r d i l l e r a . T h i s study p r o v i d e s data and recommendations f o r the f o l l o w i n g c r i t e r i a : 9 1) Background and anomalous platinum contents of a v a r i e t y of types of C o r d i l l e r a n s u r f i c i a l d e p o s i t s . 2) A s s o c i a t e d p a t h f i n d e r elements. 3) Optimum s o i l h o r i z o n . 4) Optimum s i z e f r a c t i o n . 5) Optimum d e n s i t y and magnetic f r a c t i o n s . 10 Chapter Two DESCRIPTION OF THE STUDY AREA CHAPTER TWO. DESCRIPTION OF THE STUDY AREA 2.1 L o c a t i o n and Access The f i e l d area i s l o c a t e d w i t h i n NTS map area 92 H/10 on Grasshopper Mountain on the n o r t h s i d e of the Tulameen R i v e r , approximately 25 km west of P r i n c e t o n i n southwestern B r i t i s h Columbia. I t comprises the main study area on the southern s l o p e of the mountain, and a second, s m a l l e r area near the summit (Figure 2-1). The lower p a r t of the study area i s approximately 152 m (500') i n e l e v a t i o n above the Tulameen R i v e r road, and i s a c c e s s i b l e by an o l d pack t r a i l o r i g i n a t i n g on the n o r t h s i d e of the road approximately 12 km west of Tulameen. V e h i c l e access i n t o the study area i s v i a two l o g g i n g roads on the n o r t h and west s i d e s of Grasshopper Mountain; these connect w i t h s e v e r a l k i l o m e t r e s of r e c e n t l y - c o n s t r u c t e d d r i l l roads on the mountain i t s e l f . The d r i l l roads are not p a s s a b l e i n a l l areas however, p a r t i c u l a r l y i n the e a r l y p a r t of the summer. The l o g g i n g roads connect w i t h the Lawless Creek f o r e s t r y road and p r o v i d e v e h i c l e access from both Tulameen and the nearby C o q u i h a l l a Highway. Figure 2-1. Location and generalized geology of the study areas within the dunite core of the Tulameen ultramafic complex in southwestern British Columbia (modified after Nixon and Rublee, 1988) 2.2 E x p l o r a t i o n H i s t o r y 2.2.1 Tulameen D i s t r i c t The Tulameen d i s t r i c t was a prominent producer of p l a c e r g o l d and platinum i n the l a t e n i n e t e e n t h c e n t u r y . P l a c e r g o l d was f i r s t d i s c o v e r e d near the mouth of the Tulameen R i v e r i n 1860, but the area was bypassed by p r o s p e c t o r s t r a v e l l i n g t o the Cariboo d i s t r i c t . A p r o s p e c t i n g r u s h d i d not begin u n t i l the d i s c o v e r y of co a r s e g o l d i n G r a n i t e Creek, a Tulameen R i v e r t r i b u t a r y , i n 1885 (Camsell, 1913). Platinum recovered w i t h the g o l d was i n i t i a l l y d i s c a r d e d by the miners d u r i n g the f i r s t few y e a r s (Kemp, 1902), but by 1891 the d i s t r i c t had become the l a r g e s t p l a t i n u m producer i n North America (Camsell, 1913). The Tulameen R i v e r (Figure 2-2) and i t s t r i b u t a r i e s u l t i m a t e l y y i e l d e d approximately 20,000 ounces of p l a t i n u m between 1887 and 1936 (Rice, 1947; M e r t i e , 1969). P r o d u c t i o n d e c l i n e d a t about the t u r n of the c e n t u r y (Rice, 1947), but i n t e r m i t t e n t p l a c e r e x p l o i t a t i o n has c o n t i n u e d on a s m a l l s c a l e up t o the present day. Figure 2 - 2 . View from the summit of Grasshopper Mountain, looking southwest up the Tulameen River v a l l e y into the Hozameen Range of the Cascade Mountains. 2.2.2 Grasshopper Mountain E x p l o r a t i o n f o r the primary sources of the g o l d and p l a t i n u m commenced about 1898 (Camsell, 1913). U l t r a m a f i c r o c k s , p a r t i c u l a r y d u n i t e exposed on Grasshopper and O l i v i n e Mountains on the upper Tulameen R i v e r , were soon determined t o be the primary source of the platinum p l a c e r s (Kemp, 1902; MacAulay, 1919). These were noted t o be g e o l o g i c a l l y s i m i l a r t o those a s s o c i a t e d with r i c h p l a tinum p l a c e r s i n the U r a l Mountains of Russia ( P o i t e v i n , 1923). Lode p l a t i n u m e x p l o r a t i o n has been s p o r a d i c , and economic lode d e p o s i t s have not been d i s c o v e r e d . P l a t i n i c chromite occurrences on the southern s l o p e s of Grasshopper Mountain were staked d u r i n g the l a t e 1930*s and e a r l y 1940's as the G i r l c l a i m s . Assays as h i g h as 40% chromium and 0.35 o z / t p l a t i n u m were r e p o r t e d a t the time (Rice, 1947; Canmindex, 1986). The more rec e n t e x p l o r a t i o n h i s t o r y of the Grasshopper Mountain area i s g i v e n by Bohme (1987, 1988) . Most of the f i e l d area of t h i s study l i e s w i t h i n the westernmost 12 u n i t s of the Grasshopper 1 and 2. c l a i m s . These were optioned t o Monica Resources and subsequently t o Newmont E x p l o r a t i o n of Canada L i m i t e d , which undertook a p r o s p e c t i n g , c h i p sampling, and t r e n c h i n g program d u r i n g 1986 and 1987. The c l a i m s were then optioned t o Longreach Resources which i n 1988 b u i l t roads and undertook a program of mainly p e r c u s s i o n d r i l l i n g b efore c e a s i n g o p e r a t i o n s . The e x t e n t of p l a c e r mining on Grasshopper Mountain i s not known. However, the pack t r a i l from the Tulameen R i v e r Road l e a d s t o the remains of two abandoned c a b i n s on upper Grasshopper Creek, and appears on the map of Camsell (1913). More r e c e n t e x c a v a t i o n s were observed i n perched bogs and drainage channels on the p l a t e a u of the mountain. 2.3 Bedrock Geology 2.3.1 General Geology and Regional S e t t i n g Grasshopper Mountain comprises the n o r t h e r n end of the Tulameen u l t r a m a f i c complex, a zoned Alaskan-type u l t r a m a f i c - g a b b r o i c i n t r u s i o n w i t h i n metasedimentary and m e t a v o l c a n i c rocks of the Upper T r i a s s i c N i c o l a Group. The 20 km-long s o u t h e a s t - t r e n d i n g complex covers an area of 60 square k i l o m e t r e s i n the marginal r e g i o n of the Q u e s n e l l i a t e c t o n o s t r a t i g r a p h i c t e r r a n e , and i s the l a r g e s t and most s o u t h e r l y of s e v e r a l Alaskan-type complexes w i t h i n the Intermontane B e l t (Nixon and Rublee, 1988; Nixon, 1990). Recent U-Pb z i r c o n d a t i n g (204-212 Ma) suggests a L a t e T r i a s s i c t o E a r l y J u r a s s i c age of emplacement (Rublee and P a r r i s h , 1990). The geology of the complex was f i r s t d e s c r i b e d by Camsell (1913) and R i c e (1947), and more r e c e n t l y by F i n d l a y (1963, 1969) and Nixon and Rublee (1988). I t comprises a d u n i t e c o r e surrounded by c r u d e l y - c o n c e n t r i c s h e l l s of o l i v i n e c l i n o p y r o x e n i t e , hornblende c l i n o p y r o x e n i t e and ga b b r o i c r o c k s (Figure 2-1). Metasedimentary and in t e r m e d i a t e t o f e l s i c metavolcanic country r o c k s of the N i c o l a Group near Tulameen have been r e g i o n a l l y metamorphosed t o g r e e n s c h i s t grade and comprise p r i m a r i l y a r g i l l i t e , t u f f a c e o u s s i l t s t o n e and l a p i l l i t u f f , pyroxene a n d e s i t e and hornblende d a c i t e flows. Subordinate l i t h o l o g i e s i n c l u d e r h y o l i t e , c h e r t , c h e r t b r e c c i a and limes t o n e (Nixon and Rublee, 1988). The Eagle p l u t o n i c complex, comprising g r a n o d i o r i t e and g r a n i t e , o c c u r s t o the west of the Tulameen complex. The Tulameen complex i s unconformably o v e r l a i n by t e r r i g i n o u s sedimentary and v o l c a n i c r o c k s of the Eocene P r i n c e t o n Group (Nixon and Rublee, 1988). Maf.ic-ultramaf i c complexes are d i v i d e d i n t o t h r e e c l a s s e s : s t r a t i f o r m , a l p i n e , and c o n c e n t r i c complexes (Jackson and Thayer, 1972). C o n c e n t r i c complexes, a l s o known as zoned, Alaskan-type or U r a l i a n - t y p e i n t r u s i o n s , are most common i n southeastern A l a s k a and i n the U r a l Mountains of the U.S.S.R. They are c h a r a c t e r i z e d by a c o n c e n t r i c arrangement of mafic and u l t r a m a f i c rock u n i t s , the absence of orthopyroxene and p l a g i o c l a s e , s i l i c a u n d e r s a t u r a t i o n , 18 i r o n - r i c h chromite and abundant magnetite ( F i n d l a y , 1969; N a l d r e t t and C a b r i , 1976; Nixon and Rublee, 1988). The Tulameen complex d i f f e r s , however, i n t h a t the g a b b r o i c r o c k s are a l k a l i c r a t h e r than t h o l e i i t i c . A laskan-type complexes are thought t o be emplaced i n l a t e r - s t a g e o r o g e n i c s e t t i n g s ( N a l d r e t t and C a b r i , 1976). N i c o l a Group rocks r e p r e s e n t a v o l c a n i c a r c formed by l a t e T r i a s s i c subduction t o the west (Mortimer, 1987). The Tulameen complex i s one of t h r e e a l k a l i n e p l u t o n s which i n t r u d e the N i c o l a Group, and which have been i n t e r p r e t e d as b e i n g comagmatic with the N i c o l a v o l c a n i c s ( F i n d l a y , 1969; Mortimer, 1987). F i n d l a y (1969) suggested t h a t the g a b b r o i c and u l t r a m a f i c rocks of the Tulameen complex r e p r e s e n t s e p a r a t e but g e n e t i c a l l y - r e l a t e d i n t r u s i o n s . The i n t r u s i o n of a l k a l i n e g a b b r o i c rocks, and t h e i r subsequent i n t r u s i o n by l a t e r p a r t i a l l y - c o n s o l i d a t e d u l t r a m a f i c r o c k s , was contemporaneous with r e g i o n a l deformation of the N i c o l a r o c k s . The u l t r a m a f i c rocks r e f l e c t an o r i g i n a l f r a c t i o n a l c r y s t a l l i z a t i o n of an u l t r a m a f i c magma, forming a s i l l - l i k e s t r a t i f o r m body i n the order d u n i t e , o l i v i n e c l i n o p y r o x e n i t e and hornblende c l i n o p y r o x e n i t e ( F i n d l a y , 1969). Emplacement of d u n i t e as e i t h e r a c r y s t a l mush ( F i n d l a y , 1969) or as p o s s i b l y s o l i d s t a t e t h r u s t i n g (Nixon and Rublee, 1988) i n t o p y r o x e n i t e deformed the o v e r l y i n g g abbroic r o c k s and c r e a t e d the p r e s e n t c o n c e n t r i c d i s t r i b u t i o n of rock u n i t s . 2.3.2 Geology of the Dunite Core The d u n i t e core crops out over about 6 square k i l o m e t r e s on O l i v i n e and Grasshopper Mountains a t the no r t h e r n end of the Tulameen complex ( F i g u r e 2-1). The d u n i t e i s t y p i c a l l y f i n e - g r a i n e d , green t o b l a c k , and weathers b u f f brown on exposed s u r f a c e s . The primary mineralogy comprises f o r s t e r i t i c o l i v i n e ( F o g 8 ~ F o 9 i ) , w i t h a c c e s s o r y chromite and r a r e a u g i t e . Secondary a l t e r a t i o n m i n e r a l s i n c l u d e s e r p e n t i n e , carbonate, magnetite, t a l c , c h l o r i t e and a n t i g o r i t e (Nixon and Rublee, 1988; Bohme, 1988)). Serpe n t i n e i s the most common a l t e r a t i o n m i n e r a l . Primary cumulate t e x t u r e s are not preserved. S e r p e n t i n i z a t i o n of primary o l i v i n e i s widespread and v a r i a b l e , and i s s t r u c t u r a l l y c o n t r o l l e d by c o n t a c t s and f a u l t s ( F i n d l a y , 1969); l a r g e zones of s e r p e n t i n i z a t i o n were mapped by Bohme (1987, 1988) as i n f e r r e d f a u l t or shear zones. These areas of almost t o t a l s e r p e n t i n i t e a re f i n e -g r a i n e d , l i g h t green t o white, and c o n t a i n f i n e magnetite (Bohme, 1988). They weather t o a d i s t i n c t i v e r u s t y orange on exposed s u r f a c e s . The zonation of s e r p e n t i n i z a t i o n w i t h i n the d u n i t e core i s shown i n F i g u r e 2-3. The d u n i t e on Grasshopper Mountain i s more e x t e n s i v e l y s e r p e n t i n i z e d than on O l i v i n e Mountain ( F i n d l a y , 1969), but decreases westward from 80% s e r p e n t i n e i n the e a s t t o 20% s e r p e n t i n e on Mount B r i t t o n i n the west. I s o l a t e d o c c u r r e n c e s of f r e s h o l i v i n e d u n i t e are r e s t r i c t e d t o the western margin of the 20 GRASSHOPPER \ MTN. \ — ' / v r / „ % ° o O \ A f\ o \ \ . \v\ A \ ° ° \ Brtfton t-49'3/'4t LEGEND Outline of dunite Percent Serpentine •. less than 20 o o o o \ 20 - 40 40 - 60 60 - BO more than 80 \QX"V?"\ OLIVINE \ " " v V \ V V N V 1000 M M H M h\ Metres F i g u r e 2-3. S e r p e n t i n i z a t i o n w i t h i n the du n i t e core of the Tulameen u l t r a m a f i c complex (White, 1987 a f t e r F i n d l a y , 1963). cor e (White, 1987) and are not observed w i t h i n the study area. Chromite occurs as randomly d i s t r i b u t e d massive t o d i s c o n t i n u o u s pods, seg r e g a t i o n s , s c h l i e r e n and d i s s e m i n a t e d g r a i n s ( F i g u r e s 2-4 and 2-5). S c h l i e r e n t y p i c a l l y range from 5 t o 25 cm i n l e n g t h and 1 t o 4 cm i n width, w i t h maximum l e n g t h s of about 4 m. They are randomly d i s t r i b u t e d throughout the d u n i t e , are concordant w i t h the r e g i o n a l f o l i a t i o n , and may e x h i b i t f r a c t u r i n g , boudinaging and i s o c l i n a l f o l d i n g (Nixon and Rublee, 1988). C i r c u l a r r i n g s t r u c t u r e s , or condom f o l d s , of chromite o c c u r r i n g a t one of the o c c u r r e n c e s have been i n t e r p r e t e d as e r o s i o n a l e x p r e s s i o n s of domical f o l d s (Nixon and Rublee, 1988). Nixon e t a l (1990) s t a t e d t h a t c h r o m i t i t e s e g r e g a t i o n s are bordered by 1-2 mm chromite c r y s t a l s which grade s h a r p l y i n t o much s m a l l e r disseminated g r a i n s (<2 0 um) w i t h i n the s u r r o u n d i n g d u n i t e . O l i v i n e i n c l u s i o n s w i t h i n c h r o m i t i t e s are more f o r s t e r i t i c ( F 0 9 2 - F 0 9 5 ) than those i n d u n i t e (Nixon e t a l , 1990). The s e g r e g a t i o n s are thought t o r e p r e s e n t remnants of former cumulate l a y e r s which were d e p o s i t e d , d i s r u p t e d by slumping and r e d e p o s i t e d i n a c r y s t a l mush p r i o r t o magmatic c o n s o l i d a t i o n (Rice, 1947; Nixon and Rublee, 1988; Nixon e t a l , 1990). Chromite s e g r e g a t i o n s are u s u a l l y a s s o c i a t e d with a p a l e green a l t e r a t i o n h a l o o f p r i m a r i l y s e r p e n t i n e , with subordinate carbonate and c h l o r i t e (Bohme, 1988). The ha l o weathers t o a p a l e r c o l o u r 22 Figure 2-4. Discontinuous and massive c h r o m i t i t e segregations i n dunite showing as s o c i a t e d serpentine a l t e r a t i o n . Sample i s from a c t i v e c o l l u v i u m i n the main study area. Figure 2-5. Thin discontinuous c h r o m i t i t e segregations i n dunite from the A-Zone PGE occurrence, secondary study area. than the surrounding d u n i t e , and i s p a r t i c u l a r l y w e l l -developed around d i s c o n t i n u o u s chromite s e g r e g a t i o n s ( F i g u r e 2-4). Tulameen chromite has an u n u s u a l l y h i g h F e 3 + c o n t e n t , c o n t a i n i n g 15-25% Fe2C>3, and i s moderately t o s t r o n g l y magnetic ( F i n d l a y , 1969). 2.3.3 Platinum-Group Element Occurrences Platinum-group element (PGE) m i n e r a l i z a t i o n i s p r e f e r e n t i a l l y a s s o c i a t e d with massive c h r o m i t i t e s e g r e g a t i o n s i n Tulameen d u n i t e , as opposed t o d i s s e m i n a t e d chromite g r a i n s i n du n i t e or with other l i t h o l o g i e s ( F i n d l a y , 1965; St. L o u i s e t a l , 1986). Mean Pt content of u n m i n e r a l i z e d d u n i t e and s e r p e n t i n i z e d d u n i t e i s i n the range 60-85 ppb ( F i n d l a y , 1965; St. L o u i s , 1984). Massive c h r o m i t i t e s e g r e g a t i o n s , however, have maximum Pt c o n t e n t s of between 8000 and 16000 ppb ( F i n d l a y , 1965; Bohme, 1987; Nixon e t a l , 1990). C h r o m i t i t e s e g r e g a t i o n s a re most common on southern Grasshopper Mountain i n the c e n t r a l r e g i o n of the d u n i t e c o r e ; PGE are somewhat e r r a t i c a l l y d i s t r i b u t e d w i t h i n them. F i v e zones of c h r o m i t i t e - a s s o c i a t e d PGE m i n e r a l i z a t i o n were i d e n t i f i e d i n t h i s r e g i o n by Bohme (1987, 1988) w i t h i n a well-exposed 800 m x 300 m are a ( F i g u r e 2-1). The s u b v e r t i c a l C l i f f Zone area ( F i g u r e 2-6) measures about 250m x 150m and c o n t a i n s two zones (C and D) about 6m x 6m each c o n t a i n i n g 2915 ppb and 2 340 ppb of Pt, 24 F i g u r e 2-6. The C l i f f Zone PGE occurrence i n d u n i t e on the southeast f a c e of Grasshopper Mountain. F i g u r e 2-7. Massive c h r o m i t i t e s e g r e g a t i o n i n d u n i t e a t the C l i f f Zone PGE occurrence. r e s p e c t i v e l y (Bohme, 1987, 1988). One of the l a r g e s t known chromite s e g r e g a t i o n s , lm i n l e n g t h , occurs i n t h i s a r e a ( F i g u r e 2-7). The A-Zone area, near the summit of Grasshopper Mountain, c o n t a i n s more wispy and d i s s e m i n a t e d chromite than does the C l i f f Zone, wi t h a much more un i f o r m Pt c o n t e n t of 0.025 oz/ton over 26m (Bohme, 1987, 1988). Bohme (1988) noted t h a t chromite i s r a r e l y found w i t h i n 200 m of the d u n i t e - p y r o x e n i t e c o n t a c t . Exposures, however, are l e s s common i n t h i s area. 2.3.4 Platinum-Group Mineralogy PGE mineralogy of Grasshopper Mountain c h r o m i t i t e has been s t u d i e d by St. L o u i s e t a l (1986) and Nixon e t a l (1989, 1990), and i s summarized i n Table 2-1 along w i t h t h a t of a s s o c i a t e d p l a c e r s . Nixon e t a l (1989, 1990) observed t e n platinum-group m i n e r a l s (PGM), the most common of which are the t h r e e Pt-Fe a l l o y s t e t r a f e r r o p l a t i n u m (Pt2Fe2), i s o f e r r o p l a t i n u m (Pt 3Fe) and tulameenite (Pt2FeCu). G e v e r s i t e (PtSb2), h o l l i n g w o r t h i t e - i r a r s i t e [ R h - I r ( A s S ) ] , s p e r r y l i t e (PtAs2), p l a t i n i a n copper (Cu, P t ) , p l a t i n u m oxide ( P t , 0 ) ? , e r l i c h m a n i t e ( O S S 2 ) and l a u r i t e ( R U S 2 ) , i n d e c r e a s i n g o r d e r of abundance, were a l s o observed (Nixon e t a l , 1989, 1990). St. L o u i s e t a l (1986) r e p o r t e d e i g h t d i s c r e t e PGM, but d i d not d i s t i n g u i s h between the Pt-Fe a l l o y s . However, s t u m p f l i t e (PtSb) and g e n k i n i t e [ ( P t , P d ) 4 S D 3 ] were a l s o observed. Pt-Fe a l l o y s , s p e r r y l i t e and i r a r s i t e were co n s i d e r e d the most abundant PGM. PGM occur as both d i s c r e t e m i n e r a l s and as complex p o l y m e t a l l i c g r a i n s (Nixon e t a l , 1990). St. L o u i s e t a l (1986) r e c o g n i z e d two types of PGM. Type 1 PGM occur as d i s c r e t e euhedral t o subhedral i n c l u s i o n s w i t h i n chromite g r a i n s , w h i l e Type 2 PGM occur as anhedral g r a i n s i n t e r s t i t i a l t o chromite g r a i n s . Type 1 g r a i n s are dominantly Pt-Fe a l l o y s , g e v e r s i t e , s t u m p f l i t e and i r a r s i t e , and have been i n t e r p r e t e d as being of primary magmatic o r i g i n . S p e r r y l i t e (PtAs 2) i s the most common Type 2 g r a i n ; i t , w i t h the h o l l i n g w o r t h i t e - i r a r s i t e s e r i e s and p l a t i n i a n copper, r e p l a c e s the rims of Pt-Fe a l l o y s i n f r a c t u r e d chromite g r a i n s (St. L o u i s e t a l , 1986; Nixon e t a l , 1990). St. L o u i s e t a l (1986) r e p o r t e d t h a t these g r a i n s a r e r a r e l y i n d i r e c t c o n t a c t with chromite, however, and are u s u a l l y a s s o c i a t e d w i t h s e r p e n t i n e and base metal s u l f i d e s . They were i n t e r p r e t e d as having been r e m o b i l i z e d h y d r o t h e r m a l l y from p l a t i n u m o r i g i n a l l y present i n s u l f i d e s . Some a d d i t i o n a l PGM a s s o c i a t i o n s were r e p o r t e d by Newmont M e t a l l u r g i c a l S e r v i c e s (Bohme, 1988). P l a t i n u m was observed as f i n e Pt-Fe a l l o y i n c l u s i o n s i n o l i v i n e as w e l l as, more commonly, i n chromite. I t was a l s o observed as submicroscopic d i s s e m i n a t i o n s i n sparse s u l f i d e phases. Base metal s u l f i d e s , n a t i v e metals and o x i d e s , and base metal a r s e n i d e s and antimonides are a minor i n t e r s t i t i a l t o and f r a c t u r e - f i l l i n g c o n s t i t u e n t of c h r o m i t i t e s e g r e g a t i o n s (St. L o u i s e t a l , 1986; Nixon e t a l , 1990). The most common s u l f i d e m i n e r a l s i n c h r o m i t i t e are disseminated p y r i t e (Nixon e t a l , 1990) and p e n t l a n d i t e (St. L o u i s e t a l , 1986). Other n i c k e l and n i c k e l - c o b a l t - i r o n s u l f i d e s i n c l u d e v i o l a r i t e and b r a v o i t e (St. L o u i s e t a l , 1986) and m i l l e r i t e / h e a z l e w o o d i t e (Nixon e t a l ; 1989, 1990). Other f r a c t u r e - f i l l i n g m i n e r a l s i n c l u d e s e r p e n t i n e , c h l o r i t e , magnetite, carbonate, n i c k e l antimonides, n i c k e l a r s e n i d e s , n a t i v e copper, n a t i v e s i l v e r , and copper and n i c k e l o x i d e s (Nixon e t a l ; 1989, 1990). D i s c r e t e PGM u s u a l l y range i n s i z e from l e s s than 2 um t o about 30 um, although a platinum oxide g r a i n o f 150 um was r e p o r t e d by Nixon e t a l (1990). Large f r e e PGM g r a i n s of up t o 115 um are a l s o r e p o r t e d i n t h i s study, but o b s e r v a t i o n s of macroscopic primary PGM are l i m i t e d t o those of e a r l y workers. "...Small g r a i n s of p l a t i n u m . . . " were observed i n Grasshopper Mountain c h r o m i t i t e (Rice, 1947), and " . . . s e v e r a l p a r t i c l e s of n a t i v e p l a t i n u m . . . " were r e p o r t e d from O l i v i n e Mountain d u n i t e (Johnston, 1911), but no data i s a v a i l a b l e on t h e i r exact composition or s i z e . 28 Mineral Ideal Formula Minor Constituents Chromitites1 Placers' cooperite PtS Pd,Ni - X Cu-Pt alloy (Cu,Pt) Pd,Rh,Fe,Ni,Sb XX X erlichmamte OsS2 Pt,Pd,Rh,Ir X X genkinite (Pt,Pd)4Sb3 Rh,S X X geversite PtSbj Rh,Ir,Fe,Cu,Ni,As XX X nollingworthite- Rh-Ir(AsS) Pt,Pd,Rh,Os,Ru,Sb,Cu,Ni,Co XX X irarsite series iridium Ir Pd,Rh,Os,Ru,Fe,Cu,Ni - X iridosmine (Os,Ir) Pt,Pd,Rh,Ru,Fe,Cu,Ni - XX isoferroplatinum kotulskite* PtjFe Pd,Rh,Ir.Os,Cu,Ni,Sb (xxx) XXX PdTe Pt,Sb,Bi - X laurite RuSj Rh,Ir,Os x X osmiridium (Ir.Os) Pd,Rh,Ru,Fe,Cu,Ni - X osmium Os Pt,Pd,Rh,Ir,Ru,Fe,Cu,Ni - XX platiniridium (lr.Pt) Os,Ru,Fe,Cu,Ni - X platinum, ferroan (Pt,Fe)>20at.%Fe Ir.Cu.Ni - XXX platinum, native (Pt,Fe)>80at.%Pt Pd,Ir,Fe,Cu.Ni x XXX platinum oxide (Pt.O)? Rh,Ir,Fe,Cu,Ni,Sb x -Pt-Fe-Cu-Ni alloys <Pt,Fe,Cu,Ni) Pd,Rh,Ir,Sb xxx X rutheniridosmine (Ru,Os,Ir) Pt,Pd,Rh,Fe,Cu,Ni - X sperrylite PtAs2 Pd,Ni,Ru,Fe,Sb,S XX X stumpflite PtSb Pd,Ru X -tetraferroplatinum PtFe Pd,Rh,Ir,Cu,Ni,Sb (xxx) X tolovkite" IrSbS Rh,As - X tulameenite Pt2FeCu Pd,Rh,Ir,Os,Ni,Sb XX XX unnamed RhSbS RhSbS Pt,Ir,As - X ' only found as inclusions in one grain of gold; not derived from the Tulameen ultramafic complex. ** Originally reported as unnamed IrSbS 1 Frequency: xxx >= most common; xx = common; x = infrequent to rare; (xxx) = probably present in Pt-Fe-Cu-Ni alloys but not confirmed by XRD. Table 2-1. Platinum-group mineralogy of Tulameen c h r o m i t i t e s and p l a c e r s (modified a f t e r Nixon e t a l , 1990) . 2.4 Topography and Physiography 2.4.1 Regional Physiography Grasshopper Mountain l i e s on the western margin of the Thompson P l a t e a u i n a t r a n s i t i o n a l zone with the Hozameen Range of the Cascade Mountains (Holland, 1976). T h i s r e g i o n of the the I n t e r i o r P l a t e a u i s c h a r a c t e r i z e d by a r o l l i n g upland topography of b r o a d l y rounded summits and low r e l i e f l y i n g between 1220 and 1525 m (4000 and 5000 f e e t ) above sea l e v e l (Holland, 1976). Grasshopper Mountain i s v e r y near the Cascade-Thompson boundary (Figure 2-2); p l a t e a u f e a t u r e s are not completely developed and the topography assumes a more rugged appearance (Camsell, 1913). The summit r e g i o n of Grasshopper Mountain e x h i b i t s a r o l l i n g p l a t e a u - l i k e topography with a maximum e l e v a t i o n of 1507 m (4940 1). The s l o p e steepens below about 1400 m (4600*) beneath the p l a t e a u r e g i o n , and prominent c l i f f s and s c r e e s l o p e s are exposed on the steep southeast f a c e of the mountain ( F i g u r e 2-8). R e l a t i v e l y f l a t - l y i n g ledge and bench areas a t about 1220 m (4000•) and 1068 m (3500') p r o v i d e i s o l a t e d topographic breaks i n steep plunges t o the Tulameen R i v e r and B r i t t o n Creek on the southeast and southwest f a c e s of the mountain. The Tulameen R i v e r o c c u p i e s a narrow channel between Grasshopper and O l i v i n e Mountains a t an e l e v a t i o n of 885 t o 900 m (2900' t o 2950'). 30 2.4.2 P h y s i o g r a p h i c Zones of Grasshopper Mountain Four major p h y s i o g r a p h i c zones occur w i t h i n the study area on Grasshopper Mountain (Figures 2-1 and 3-1), each e x h i b i t i n g c h a r a c t e r i s t i c r e l i e f , f o r e s t cover, and s o i l development. The zones are: the c l i f f s and c o l l u v i a l s l o p e s , the r o l l i n g p l a t e a u and western f o r e s t e d s l o p e s , the southern f o r e s t e d s l o p e s , and the f l a t l y i n g bench a r e a . The c l i f f s and c o l l u v i a l s l o p e s ( F i g u r e 2-8A and 2-9) are c h a r a c t e r i z e d by steep d u n i t e c l i f f s and e x t e n s i v e accumulations of t a l u s and c o l l u v i u m . The r o l l i n g p l a t e a u ( F i g u r e 2-8B) and western f o r e s t e d s l o p e s e x h i b i t t h i n t i l l c o ver and d i s c o n t i n u o u s outcrop. The steep southern f o r e s t e d s l o p e s are c h a r a c t e r i z e d by the presence of s t a b i l i z e d c o l l u v i u m i n the western p o r t i o n , and i t s absence i n the e a s t . F i n a l l y , the bench area ( F i g u r e 2-9B) i s c h a r a c t e r i z e d by low r e l i e f , the presence of bogs and seepage zones, and the occurrence of a prominent n o r t h e a s t -southwest-trending c l a y - r i c h k n o l l . 2.5 Quaternary and S u r f i c i a l Geology 2.5.1 Quaternary H i s t o r y of the Southern I n t e r i o r Evidence of a t l e a s t f o u r Quaternary g l a c i a t i o n s and 31 F i g u r e 2-8. D i f f e r e n t p h y s i o g r a p h i c zones on Grasshopper Mountain; A. Recent c o l l u v i u m beneath steep c l i f f s on southeast f a c e of Grasshopper Mountain. C l i f f Zone PGE occurrence i s a t f a r r i g h t ; B. R o l l i n g p l a t e a u area adjacent t o s o i l s i t e 73 showing t h i n t i l l cover and d i s c o n t i n u o u s outcrop. Figure 2-9. D i f f e r e n t p h y s i o g r a p h i c zones on Grasshopper Mountain; A. Talus cone extending i n t o the f o r e s t a t the base of a c t i v e c o l l u v i u m beneath the C l i f f Zone PGE occurrence; B. f l a t -l y i n g seepage zone area below a c t i v e c o l l u v i u m . Tulameen R i v e r v a l l e y and O l i v i n e Mountain i n background. two main n o n g l a c i a l p e r i o d s has been uncovered i n the Canadian C o r d i l l e r a ( F u l t o n , 1984). The Late W i s c o n s i n F r a s e r G l a c i a t i o n was the l a s t of the C o r d i l l e r a n I c e Sheets ( B l a i s e e t a l , 1990) t o occupy southern B r i t i s h Columbia. A l l of the southern C o r d i l l e r a , i n c l u d i n g the Tulameen area (Rice, 1947) was completely i c e - c o v e r e d . Cold c o n d i t i o n s l e a d i n g t o i c e - s h e e t development began about 25,000 y e a r s ago and g l a c i a t i o n commenced about 19,000 y e a r s ago ( F u l t o n , 1975). The Tulameen v a l l e y would probably have been the l o c a l channel f o r the eastward advance of a l p i n e g l a c i e r s o r i g i n a t i n g i n the high e r Cascade mountains t o the west (Camsell, 1913). Coalescence of v a l l e y g l a c i e r s r e s u l t e d i n the southern i n t e r i o r being covered by a c o n t i n e n t a l i c e sheet by about 17,240 years ago (F u l t o n , 1984). One of the Quaternary i c e sheets was s u f f i c i e n t l y t h i c k t o erode mountaintops of 2623 m (8600') e l e v a t i o n (Rice, 1947). S t r i a e r e p o r t e d by Ric e (1947) i n d i c a t e t h a t the c o n t i n e n t a l i c e - s h e e t moved i n a roughly s o u t h e r l y d i r e c t i o n n o r t h o f the Tulameen d i s t r i c t , but began t o move i n a more sou t h w e s t e r l y d i r e c t i o n i n the area n o r t h of Grasshopper Mountain. S t r i a e mapped by Camsell (1913) on nearby Rabbit, B r i t t o n , and O l i v i n e Mountains range from 205° t o 240°, whereas those r e p o r t e d by F i n d l a y (1963) from Lodestone Mountain average 220° t o 230°. Rare s t r i a e near the summit of Grasshopper Mountain i t s e l f a l s o i n d i c a t e a s o u t h -s o u t h w e s t e r l y d i r e c t i o n of i c e movement. The F r a s e r i c e - s h e e t reached i t s maximum e x t e n t i n n o r t h e r n Washington about 15000 t o 14500 years ago p r i o r t o r e t r e a t i n g through the southern I n t e r i o r about 10500 y e a r s ago ( F u l t o n , 1975; B l a i s e e t a l , 1990). The Tulameen v a l l e y was p r o b a b l y occupied by v a l l e y g l a c i e r s r e t r e a t i n g westward (Camsell, 1913) a t t h i s time. Mathews (1944) and H i l l s (1962) have d e s c r i b e d the d e g l a c i a t i o n h i s t o r y o f the Princeton-Tulameen area. Mathews (1944) s t a t e d t h a t i c e damming c r e a t e d g l a c i a l l akes near P r i n c e t o n i n the Upper Similkameen v a l l e y w h i l e the g l a c i e r s r e t r e a t e d n o r t h or northwestward. H i l l s (1962) extended t h i s t o the Tulameen R i v e r drainage and suggested t h a t g l a c i a l l a k e s e x i s t e d i n the Whipsaw Creek and G r a n i t e Creek v a l l e y s and a t the headwaters of the Tulameen R i v e r near Jim K e l l y Creek. During i n i t i a l i c e r e t r e a t , water d r a i n e d southwards through the S k a i s t R i v e r and then s u c c e s s i v e l y westward through Snass Creek, the Podunk V a l l e y , and Vuich Creek a t a s e r i e s of e l e v a t i o n s ranging from 1510 t o 1388 m (4950 t o 4550 f e e t ) . E x i s t e n c e of the g l a c i a l l a k e s i s marked by s t r a n d l i n e s on the e a s t s l o p e of the Tulameen R i v e r o p p o s i t e Jim K e l l y Creek a t about 1280 m (4200'), and by t e r r a c e s on the Tulameen R i v e r a t 1205 m (3950'). The Tulameen R i v e r subsequently d r a i n e d north and east along the r e t r e a t i n g i c e f r o n t ( H i l l s , 1962). The two Murphy Lakes, l o c a t e d j u s t n o r t h of Grasshopper Mountain, are the o n l y remaining g l a c i a l l a k e s i n the v i c i n i t y of the study area. They are dammed by morainal m a t e r i a l i n a v a l l e y i n t e r p r e t e d by Camsell (1913) as a p o s s i b l e former drainage channel of the Tulameen R i v e r . F u l t o n (1984) suggested t h a t most of the southern i n t e r i o r was i c e - f r e e by 9510 years ago, and t h a t the p r e v a i l i n g c l i m a t e was warmer and d r i e r than p r e s e n t . 2.5.2 S u r f i c i a l Geology T i l l , f l u v i o g l a c i a l and g l a c i o l a c u s t r i n e sediments d e p o s i t e d by the Wisconsin F r a s e r g l a c i a t i o n comprise the Kamloops Lake D r i f t ( F u l t o n , 1984). I t c o n s i s t s of ( F u l t o n , 1975): a) a lower s t r a t i f i e d u n i t of s i l t and f i n e sand which cannot be d i s t i n g u i s h e d from o l d e r u n c o n s o l i d a t e d u n i t s b) n o n s t r a t i f i e d morainal d e p o s i t s , predominantly b a s a l t i l l c) an upper s t r a t i f i e d d r i f t d e p o s i t e d by water d u r i n g the r e t r e a t of the F r a s e r i c e - s h e e t The s u r f i c i a l geology of Grasshopper Mountain and the s u r r o u n d i n g area i s a composite of the products of the F r a s e r g l a c i a t i o n , p a r t i c u l a r l y the Kamloops Lake D r i f t , and the subsequent m o d i f i c a t i o n of these d e p o s i t s and c r e a t i o n of new ones by p o s t - g l a c i a l processes. C o l l u v i a l , a l l u v i a l , bog and minor v o l c a n i c ash d e p o s i t s have accumulated on Grasshopper Mountain s i n c e the d e p o s i t i o n of the Kamloops Lake D r i f t and g l a c i a l r e t r e a t . B a s a l t i l l of u n i t b of the Kamloops Lake D r i f t i s the s u r f a c e cover over much of s o u t h - c e n t r a l B r i t i s h Columbia ( F u l t o n and Smith, 1978). Grasshopper Mountain i s mantled w i t h a b a s a l t i l l of v a r i a b l e t h i c k n e s s . I t i s yellow-brown t o brown and c o n s i s t s of subrounded t o subangular l i t h i c fragments i n an o x i d i z e d s i l t - c l a y matrix. C l a s t s do not u s u a l l y exceed c o b b l e - s i z e , and l a r g e b o u l d e r - s i z e d examples are r a r e . T i l l cover i n the p l a t e a u r e g i o n of the mountain i s t h i n and d i s c o n t i n u o u s , however, p a r t i c u l a r l y near the summit where t i l l and d i s i n t e g r a t i n g bedrock l o c a l l y form a r u b b l y r e s i d u a l - l i k e s o i l . The c o n t r i b u t i o n of t i l l t o the pare n t m a t e r i a l seems t o be minimal i n some r i d g e and p l a t e a u areas. A t h i c k p o s t - g l a c i a l apron of a c t i v e c o l l u v i u m b l a n k e t s the t i l l beneath steep c l i f f s on the southeast f a c e of the mountain. Boulder accumulations, l o c a l l y s t a b i l i z e d by v e g e t a t i o n , form the lower margin of the c o l l u v i u m i n some p a r t s of the western f o r e s t e d area, but a re absent from the e a s t e r n p a r t . A prominent t a l u s cone, s t a b i l i z e d a t lower l e v e l s , occurs on the margin of the boulder f i e l d and extends from the c o l l u v i u m i n t o the f o r e s t ( F i g u r e 2-9B). M u l t i p l e parent m a t e r i a l s a re common, and g e n e r a l l y take the form of t i l l o v e r r i d e n by s t a b i l i z e d d u n i t i c c o l l u v i u m (Figure 2-10). T h i s i s p a r t i c u l a r l y widespread i n the western p a r t of the main study area, but a l s o o c c u r s on f l a n k s of the summit i n the secondary study a r e a . F l u v i o g l a c i a l sediments s i m i l a r t o u n i t c of the Kamloops Lake D r i f t dominate lower l e v e l s of the area, p a r t i c u l a r l y the v a l l e y s of the Tulameen R i v e r , i t s t r i b u t a r i e s and former drainage channels n o r t h of Grasshopper Mountain. Only minor b u r i e d channel or g l a c i o l a c u s t r i n e d e p o s i t s occur w i t h i n the study area however. These were observed i n r e c e n t roadcuts a t two h i g h - e l e v a t i o n l o c a l i t i e s a t 1159 m (3800') and 1281 m (4200'). N e i t h e r was i d e n t i f i a b l e from the s u r f a c e . Three pa r e n t m a t e r i a l s were observed a t the h i g h e r s i t e ( F i g u r e 2-10B) - t i l l , a fining-upward sequence of w e l l - s o r t e d sandy sediments, and a f i n a l b lanket of c o l l u v i u m . The l a t e r a l e x t e n t of these or other b u r i e d paleochannels on the s l o p e s of Grasshopper Mountain i s not known. A c t i v e a l l u v i a l d e p o s i t s are r e s t r i c t e d t o a s m a l l i n t e r m i t t e n t stream, Grasshopper Creek. On the p l a t e a u i t comprises a s e r i e s of i n t e r c o n n e c t e d bogs which occupy bedrock d e p r e s s i o n s . The creek d i s a p p e a r s d u r i n g the plunge down a steep s l o p e , and reappears t o flow through the lower J Figure 2-10. Composite s o i l p r o f i l e s ; A. s t a b i l i z e d colluvium (C) above non-dunitic t i l l (BC, IIC) at s o i l s i t e 31 on g e n t l e s l o p e ; B. s t a b i l i z e d c olluvium (C) and outwash (IIC) above w d u n i t i c t i l l (BC, IIIC) a t s o i l s i t e 71 on steep slope. co l e v e l s of the study area p r i o r t o e n t e r i n g the Tulameen R i v e r as a hanging v a l l e y . A second, s m a l l e r , i n t e r m i t t e n t stream s e r v e s as the e a s t e r n boundary of the study a r e a . Both d r a i n through the f l a t bench a t 1068 m (3500 1). T h i s area appears t o c o l l e c t much subsurface drainage; s m a l l seepage-zone bogs and g l e y s o l i c s o i l s occur i n t h i s area, and groundwater remains c l o s e t o the s u r f a c e w e l l i n t o June when the remainder of the mountain i s dry. A s m a l l area of the bench a t the base of the main study area i s u n d e r l a i n by c l a y c o n t a i n i n g r e l a t i v e l y few co a r s e fragments. Most, but not a l l , of t h i s area i s oc c u p i e d by a prominent k n o l l which r i s e s s e v e r a l metres above the bench. I t may be some form of g l a c i o l a c u s t r i n e d e p o s i t . A t h i n l a y e r of v o l c a n i c ash was encountered i n the top 30 cm of a perched bog near the summit of Grasshopper Mountain. Organic s o i l s of the Coley s e r i e s , which occur as s m a l l i s o l a t e d u n i t s w i t h i n the Tulameen d i s t r i c t , commonly c o n t a i n a t h i n l a y e r of v o l c a n i c ash 30 t o 45 cm (12 t o 18 inches) below the s u r f a c e (Lord and Green, 1974) . The occurrence and sources of ash l a y e r s i n southern B r i t i s h Columbia has been d i s c u s s e d by Nasmith e t a l (1967). Although the Mazama ash (6,600 y e a r s ) , o r i g i n a t i n g i n Oregon, i s the most widespread i n s o u t h - c e n t r a l B r i t i s h Columbia (Nasmith e t a l , 1967), the Grasshopper Mountain area a l s o l i e s w i t h i n the plume of the St. Helens Y ash (3,200 y e a r s ) . I t i s not known which a s h f a l l i s r e p r e s e n t e d i n t he bog. S o i l s a re developed i n what appears t o be reworked t i l l o v e r l y i n g lodgement t i l l on the east s i d e of the s p a r s e l y -f o r e s t e d r i d g e f a c i n g B r i t t o n Creek (Figure 2-1). The p r o f i l e i s unique among those s t u d i e d i n t h a t the two uppermost h o r i z o n s are p o o r l y c o n s o l i d a t e d , c o n t a i n few coa r s e fragments, and have a remarkably uniform g r a i n s i z e d i s t r i b u t i o n among f i v e f r a c t i o n s of the <2 mm component (Appendix 11.1). P r o p o r t i o n s of both the c o a r s e s t and f i n e s t f r a c t i o n s are much lower r e l a t i v e t o those o f most t i l l s , s u g g e s t i n g l o c a l reworking and s o r t i n g by water. XRD r e s u l t s (Appendix 6) show t h a t the two upper and t h e two lower h o r i z o n s are m i n e r a l o g i c a l l y d i s t i n c t ( s e c t i o n 4.6), although the boundary between the two groups i n the s o i l p r o f i l e i s g r a d a t i o n a l . 2.6 C l i m a t e The c l i m a t e i s t r a n s i t i o n a l between t h a t of the d r y southern i n t e r i o r and the much moister Cascade and Coast Mountains t o the west. Summers are hot and dry, and w i n t e r s are c o l d w i t h heavy s n o w f a l l a t hig h e l e v a t i o n s . Temperatures a t P r i n c e t o n a i r p o r t ( e l e v . 696 m/2283 1) ranged from a summer h i g h o f 41.7°C t o a wint e r low of -42.8°C d u r i n g the years 1941-1970 (Atmospheric Environment S e r v i c e , 1974). Temperatures a t A l l i s o n Pass ( e l e v . 1342 m/4400'), l o c a t e d i n the Cascades southwest of Grasshopper Mountain, ranged from 31.7°C t o -42.8°C d u r i n g the same p e r i o d . T o t a l annual p r e c i p i t a t i o n over t h i s p e r i o d averaged 1452mm a t A l l i s o n Pass ( s n o w f a l l : 9652mm), but only 359mm a t P r i n c e t o n ( s n o w f a l l : 1570mm). Patches of snow may remain on the p l a t e a u o f Grasshopper Mountain u n t i l l a t e May. The mountain i s w e l l d r a i n e d however, and d r i e s r a p i d l y d u r i n g the summer. 2.7 S o i l Development S o i l development, l i m i t e d by h i g h r e l i e f and a c t i v e c o l l u v i a l p r o c e s s e s , i s g e n e r a l l y j u v e n i l e . The t h i c k n e s s e s of s u r f i c i a l LFH h o r i z o n s seldom exceed a few c e n t i m e t r e s and a re p a r t i c u l a r l y t h i n on steep s l o p e s . The f o u r p h y s i o g r a p h i c zones of Grasshopper Mountain correspond r o u g h l y t o d i f f e r e n t types and stages of s o i l development. A c t i v e c o l l u v i u m i s c h a r a c t e r i z e d by o r t h i c r e g o s o l s ( F i g u r e s 2-11 and 2-12). Genetic h o r i z o n s are absent, although s i t e s i n the western p a r t of the c o l l u v i a l s l o p e e x h i b i t a d i s t i n c t i v e orange-brown s u r f a c e c o l o u r a t i o n and an i n c r e a s i n g f i n e s content with depth. These appear t o correspond t o upslope s e r p e n t i n i t e outcrop. LFH h o r i z o n s are g e n e r a l l y absent on a c t i v e c o l l u v i u m , and those t h a t do e x i s t u s u a l l y have a hig h content of u p s l o p e - d e r i v e d rock fragments. E u t r i c b r u n i s o l s (Figures 2-13 and 2-14A) are the dominant s o i l on the r o l l i n g p l a t e a u area of Grasshopper Mountain, and on r i d g e s and the g e n t l e western s l o p e where c o l l u v i a l a c t i v i t y i s absent or minimal. S u r f i c i a l Bm h o r i z o n s are w e l l developed, and may be g r a d a t i o n a l t o u n d e r l y i n g C h o r i z o n s . The s o i l s are almost r e s i d u a l i n o r i g i n on h i g h p l a t e a u areas of t h i n d i s c o n t i n u o u s t i l l c over over the d u n i t e bedrock, such as d i r e c t l y above the t r e n c h a t the A-Zone PGE occurrence (Figure 2-14B) The steep f o r e s t e d southern s l o p e s of Grasshopper Mountain e x h i b i t the most d i v e r s e range of s o i l t y p e s . Humo f e r r i c p o d z o l s (Figure 2-15A) and minor o r t h i c r e g o s o l s c h a r a c t e r i z e the e a s t e r n p o r t i o n , whereas the western p o r t i o n has e u t r i c b r u n i s o l s i n p l a c e s covered and m o d i f i e d by l a t e r c o l l u v i u m . The e a s t e r n p o r t i o n of the study area has more mature s o i l development than the western p o r t i o n , where s i t e s are marked by a g r e a t e r degree of c o l l u v i a l s o i l d i s r u p t i o n and are devoid of g e n e t i c h o r i z o n s . Younger stands of douglas f i r and l a r g e boulders of d u n i t e s c a t t e r e d through the lower reaches of the e a s t e r n p o r t i o n a l s o a t t e s t t o t h i s . F i g u r e 2-11. U n h o r i z o n a t e d o r t h i c r e g o s o l s o i l p r o f i l e s i n a c t i v e c o l l u v i u m ; A. s o i l s i t e 9 the margin of a s t e e p c o l l u v i a l g u l l y beneath C l i f f Zone PGE occurrences; B. s o i l s i t e 3 7 i n r e l a t i v e l y f i n e - g r a i n e d c o l l u v i u m w i t h i n a t a l u s f i e l d near the base of slope. F i g u r e 2-12. Unhorizonated o r t h i c r e g o s o l s o i l p r o f i l e ( s o i l s i t e 16) i n a c t i v e c o l l u v i u m immediately beneath one of the C l i f f Zone PGE occurrences (D Zone) ; A. gen e r a l view o f s i t e ; B. close-up o f p i t f a c e showing absence o f h o r i z o n development. Free PGM g r a i n s were o b s e r v e d i n heavy m i n e r a l c o n c e n t r a t e s from t h i s s i t e (Figure 4-52). F i g u r e 2-13. E u t r i c b r u n i s o l s o i l p r o f i l e s developed on d u n i t i c t i l l , showing Bm, BC and C m i n e r a l h o r i z o n s ; A. p r o f i l e on g e n t l e south slope ( s o i l s i t e 66); B. p r o f i l e on f l a t , s p a r s e l y - v e g e t a t e d r i d g e t o p ( s o i l s i t e 65). The l a t t e r i s a t y p i c a l due t o the absence of an LFH h o r i z o n . F i g u r e 2-14. S o i l p r o f i l e s above and adjacent t o A-Zone PGE occurrence, secondary study area; A. Unhorizonated o r t h i c r e g o s o l ( s o i l s i t e 56) i n d u n i t i c r u b b l e above t r e n c h e d occurrence; B. e u t r i c b r u n i s o l ( s o i l s i t e 57), w i t h t h i n c o l l u v i a l Bm above BC and C h o r i z o n s , i n d u n i t i c t i l l . F i g u r e 2-15. S o i l p r o f i l e s developed on n o n - d u n i t i c t i l l ; A. h u m o - f e r r i c p o d z o l (LFH, Aej , Bf, C) a t s o i l s i t e 19 on steep f o r e s t e d southeast s l o p e of Grasshopper Mountain; B. g l e y e d melanic ^ b r u n i s o l (LFH, Ah, Cg) a t s o i l s i t e 6 i n f l a t seepage area. S o i l development on the f l a t - l y i n g bench area i s dominated by seepage zones, a r e l a t i v e l y h i g h degree of o r g a n i c p r o d u c t i o n , and the l o c a l occurrence of a c l a y p a rent m a t e r i a l . The area i s c h a r a c t e r i z e d by r e l a t i v e l y t h i c k LFH h o r i z o n s , o r g a n i c - r i c h mull Ah h o r i z o n s , and both g l e y e d Cg t i l l and c l a y parent m a t e r i a l s ( F i g u r e 2-15B) a t the lower l e v e l s , and by an upslope g r a d a t i o n t o d r i e r and more j u v e n i l e r e g o s o l s a t the base of the steep f o r e s t e d s l o p e . 2.8 V e g e t a t i o n Tree cover on Grasshopper Mountain i s d i v e r s e i n both s p e c i e s and i n t e n s i t y , and r e l a t e d t o the p h y s i o g r a p h i c zones of the mountain. Flanks and s l o p e s are moderately t o well-wooded, wi t h s p a r s e l y - f o r e s t e d areas common i n t h e p l a t e a u and summit areas, and open v e g e t a t i o n dominating a c t i v e c o l l u v i u m . The p l a t e a u and western f l a n k r e g i o n of the mountain are c h a r a c t e r i z e d by mature stands of Douglas f i r , t he l a r g e s t of which are f i r e - s c a r r e d and exceed two f e e t i n diameter. The secondary study area near the summit has a more ragged assortment of t r e e s dominated by s u b - a l p i n e f i r , w i t h minor Douglas f i r , lodgepole pine and whitebark p i n e . The southern f o r e s t e d s l o p e of the mountain i s t h i c k l y -f o r e s t e d and dominated with much younger Douglas f i r . The f l a t f o r e s t e d bench area i s populated p r i m a r i l y by mature Douglas f i r , w i t h subordinate cedar, s u b - a l p i n e f i r and englemann spruce. The k n o l l i s occupied by young l o d g e p o l e p i n e . The dry and w e l l - d r a i n e d c o l l u v i a l s l o p e and c l i f f s a r e open and populated by s c a t t e r e d Douglas f i r , Ponderosa p i n e , and j u n i p e r . Trees commonly e x h i b i t curved t r u n k s i n d i c a t i v e of c o l l u v i a l creep, as w e l l as upslope s c a r s r e s u l t i n g from being s t r u c k by boulders bouncing d o w n h i l l . Ponderosa p i n e i s r e l a t i v e l y more common a t h i g h e r e l e v a t i o n s on the c l i f f , and has a much more g n a r l e d appearance than those growing a t lower e l e v a t i o n s i n the Tulameen R i v e r v a l l e y . The u n d e r s t o r y over much of the mountain comprises o n l y t h i n g r a s s e s and groundflowers. The unde r s t o r y i s much more 11 d i v e r s e i n the f o r e s t e d bench area, probably because of the g r e a t e r moisture content of the s o i l and the presence o f a more n u t r i e n t - r i c h e x o t i c t i l l . Grasses are sparse on a c t i v e c o l l u v i u m . The u l t r a m a f i c p l a n t Eriogonum heracliodes was i d e n t i f i e d i n t h i s area (R. Sc a g e l , p e r s o n a l communication, 1988). 50 Chapter Three FIELD AND LABORATORY PROCEDURES 51 CHAPTER THREE. FIELD AND LABORATORY PROCEDURES 3.1 S e l e c t i o n of the F i e l d Area S e l e c t i o n of the Tulameen u l t r a m a f i c complex as a s i t e t o i n v e s t i g a t e the s u r f i c i a l d i s p e r s i o n of p l a t i n u m was based on o r i e n t a t i o n surveys d u r i n g 1987 ( F l e t c h e r , 1989) and on f i e l d w o r k by Newmont E x p l o r a t i o n of Canada d u r i n g 1986 and 1987 (Bohme; 1987, 1988). Grasshopper Mountain was s e l e c t e d as the study area because i t hosts the most e x t e n s i v e known occurrences of chromite-hosted PGM i n the Tulameen complex. 3.2 Sample C o l l e c t i o n Methods 3.2.1 I n t r o d u c t i o n S o i l s , stream sediments and a s s o c i a t e d banks, bogs, and waters were sampled (Figure 3-1). S o i l s c o n s t i t u t e t h e main focus of the study. D i s t r i b u t i o n of samples i s shown i n T a b l e 3-1. 52 Figure 3-1. Sample location map showing soil, stream, bank and bog sample sites within the dunite core of the Tulameen ultramafic complex, Grasshopper Mountain, B.C. Site numbers are shown in Appendix 1 (basemap adapted from Bohme, 1987). Main Secondary Study Area Study Area T o t a l M i n e r a l h o r i z o n s 149 31 180 LFH h o r i z o n s 40 7 47 Stream sediments 8 - 8 Moss mats 5 - 5 Bank samples 10 - 10 Bog samples 4 2 6 Water samples 16 1 17 Background s o i l s - - 5 Ta b l e 3-1. D i s t r i b u t i o n of sample media a c c o r d i n g t o study area, Grasshopper Mountain, B.C. See F i g u r e 3-1 f o r l o c a t i o n s . Main Secondary Study Area Study Area T o t a l T i l l 38 11 49 C o l l u v i u m 25 2 27 T o t a l S o i l P r o f i l e s 63 13 76 Ta b l e 3-2. D i s t r i b u t i o n of s o i l p r o f i l e s a c c o r d i n g t o study area and parent m a t e r i a l , Grasshopper Mountain, B.C. 3.2.2 S o i l s S o i l s were p r o f i l e d and sampled i n 76 p i t s i n two study areas ( F i g u r e 3-1) d u r i n g 1988 and 1989. A t o t a l of 227 h o r i z o n s were sampled: 180 m i n e r a l s o i l s and 47 s u r f i c i a l LFH samples (Tables 3-1 and 3-2). S i t e l o c a t i o n s and numbers are g i v e n i n Appendix 1. Sampling w i t h i n the main study area was c a r r i e d out a l o n g l i n e s c r o s s i n g both t i l l and c o l l u v i u m i n order t o d e t e c t both downslope and downice d i s p e r s i o n of the C l i f f Zone Pt occurrences and from the p l a t e a u area of the mountain. The l i n e s comprise two t o twelve s i t e s each, w i t h the l o n g e s t t r a n s e c t i n g a l l major landscape environments of the study area. S t r i c t g r i d s pacing was avoided; i n d i v i d u a l sample s i t e s were s e l e c t e d t o r e f l e c t l o c a l v a r i a t i o n s i n the landscape. Sample s i t e s i n the e a s t e r n p a r t of the main study area are approximately 50 m apart, w h i l e a much wider s p a c i n g was allowed i n the western p a r t of the main study area ( F i g u r e 3-1). S e v e r a l c l o s e l y - s p a c e d p i t s were s i t u a t e d above and below the C l i f f Zone occurrences t o a l l o w both the d i s t a n c e and the manner of downslope PGE d i s p e r s i o n i n c o l l u v i u m t o be determined. The secondary study area was s i t u a t e d around the A-Zone occurrence t o assess the e f f e c t of r e p o r t e d l y more widespread disseminated chromite (Bohme, 1987, 1988) on the p l a t i n u m content of o v e r l y i n g s o i l h o r i z o n s . P i t s were dug above and downslope of the showing, and along t h r e e l i n e s r a d i a t i n g from i t a t 180 t o 210 degrees. Organic LFH h o r i z o n s were c o l l e c t e d , where p o s s i b l e , p r i o r t o the d i g g i n g of the p i t t o prevent c o n t a m i n a t i o n of the sample w i t h m i n e r a l matter. The t u r f was t u r n e d over w i t h a s h o v e l or mattock and the LFH m a t e r i a l c a r e f u l l y s e p a r a t e d from the u n d e r l y i n g m i n e r a l matter and t r a n s f e r r e d t o a l a r g e paper grocery bag. LFH h o r i z o n s were sampled a t a l l but one of the main study area t i l l s i t e s and a t 7 of the 13 secondary study area s i t e s . Only 3 were c o l l e c t e d on a c t i v e c o l l u v i u m . Most s o i l s i t e s were l o c a t e d on u n d i s t u r b e d ground. S e v e r a l s i t e s were excavated from roadcut exposures however, and one was l o c a t e d d i r e c t l y above the t r e n c h e d showing a t the secondary study area. S o i l p i t s were g e n e r a l l y dug t o a depth of s l i g h t l y l e s s than 1 m. In t i l l , p i t s bottomed out i n C h o r i z o n t i l l r e p r e s e n t i n g o x i d i z e d parent m a t e r i a l . The depth of p i t s on steep c o l l u v i a l s l o p e s was l i m i t e d by c o n s t a n t c o l l a p s e of the p i t f a c e . I n d i v i d u a l g e n e t i c h o r i z o n s were i d e n t i f i e d on the b a s i s of c o l o u r , compaction and r o o t p e n e t r a t i o n , measured, and sampled wi t h a t r o w e l from the bottom up. D u p l i c a t e samples, A and B, of 10-15 kg g e n e r a l l y were c o l l e c t e d from m i n e r a l h o r i z o n s . Samples from upper h o r i z o n s were g e n e r a l l y s m a l l e r than those from C 56 h o r i z o n s because of t h e i r t h i n n e r s i z e . Cobbles g r e a t e r than 10 cm were avoided d u r i n g sampling. S o i l pedons were c l a s s i f i e d a c c o r d i n g t o the Canadian System of S o i l C l a s s i f i c a t i o n . ( A g r i c u l t u r e Canada Expert Committee on S o i l Survey, 1987). Colour, presence or absence of m o t t l e s , percentage of coarse fragments, fragment shape and s o i l t e x t u r e were recorded f o r each h o r i z o n . Among the s i t e parameters r e c o r d e d were topography, drainage, p a r e n t m a t e r i a l , p r o x i m i t y t o bedrock, i n t e n s i t y and type of v e g e t a t i o n , and p o s s i b l e sources of contamination. Samples were removed from the f i e l d area both on f o o t and on horseback. In o r d e r t o assess the d i r e c t i o n of g l a c i a l d i s p e r s i o n , background C h o r i z o n t i l l samples were a l s o c o l l e c t e d from 5 s i t e s on the northern margin and t o the west of the d u n i t e c o r e on Grasshopper Mountain and Mount B r i t t o n ( F i g u r e 4-18) . 3.2.3 Stream Sediment, Moss mat and Bank samples Stream sediments were c o l l e c t e d from seven s i t e s a l o n g Grasshopper Creek a t approximately 100 m i n t e r v a l s , and from an a d d i t i o n a l s i t e w i t h i n a drainage trough i n the summit area of the mountain (Figure 3-1). Moss mat samples were a l s o c o l l e c t e d , i f present, and bank samples were taken a t f i v e of the s i t e s . Stream sediments were g e n e r a l l y c o l l e c t e d from s m a l l g r a v e l - f i l l e d p o o l s i n the a c t i v e stream channel. I n d i v i d u a l samples were composites of sediment from s e v e r a l such p o o l s , which r a r e l y exceeded 1 m i n width or 1-2 dm i n depth over a d i s t a n c e of s e v e r a l metres. Three samples were wet-sieved w i t h a p l a s t i c 10-mesh s i e v e and o n l y the -10 mesh f r a c t i o n c o l l e c t e d ; t h e r e was i n s u f f i c i e n t stream water a v a i l a b l e t o wet-sieve a t other s i t e s . The creek was completely dry a t s i t e s 6 and 7. Moss mat samples were c o l l e c t e d a t f i v e of the stream sediment s i t e s t o compare the Pt contents of the two a l l u v i a l media. They were mostly c o l l e c t e d from above the water l e v e l on rocks and l o g s over a d i s t a n c e of s e v e r a l metres. Bank samples were c o l l e c t e d from both banks a d j a c e n t t o f i v e of the stream sediment s i t e s . The banks were r e l a t i v e l y low with the ex c e p t i o n of those a t s i t e s 3-5, where the creek i s deeply i n c i s e d . Those a t s i t e 1 are a l l u v i a l , w h i l e the remainder are t i l l . 3.2.4 Bogs Centre and margin samples were c o l l e c t e d from t h r e e bogs w i t h i n the study areas. Two of the bogs are on u n c o n s o l i d a t e d m a t e r i a l i n the seepage zone area, whereas the t h i r d i s a perched bog o c c u r r i n g i n bedrock near the A-Zone occurrence. Samples comprised the uppermost 20-35 cm of o r g a n i c m a t e r i a l , e x c l u d i n g only the top few c e n t i m e t r e s . U n d e r l y i n g c l a y m i n e r a l matter was c o l l e c t e d from the s m a l l e s t of the t h r e e bogs. 3.2.5 Waters Water samples were c o l l e c t e d from 17 s i t e s d u r i n g the p e r i o d May 17-2 0, 1989 f o l l o w i n g the s p r i n g snowmelt when o n l y s c a t t e r e d patches of snow remained on the p l a t e a u a r e a of Grasshopper Mountain. The p e r i o d a v a i l a b l e f o r water c o l l e c t i o n i s very s h o r t because e a r l y c o l l e c t i o n may d i l u t e samples w i t h t r a n s i e n t snowmelt, but bogs and c r e e k s on Grasshopper Mountain dry up by mid-June. Samples were c o l l e c t e d i n t h r e e g e n e r a l a r e a s : Grasshopper Creek, the seepage zone i n the main study area, and the mountain p l a t e a u . Stream waters were c o l l e c t e d a t sediment l o c a t i o n s along Grasshopper Creek. A sample was a l s o c o l l e c t e d from the i n t e r m i t t e n t stream on the e a s t e r n boundary of the study area. Seepage zone samples were c o l l e c t e d from bogs and from s o i l p i t s t h a t t e m p o r a r i l y f i l l e d w i t h water. P l a t e a u samples were c o l l e c t e d from i n t e r c o n n e c t e d perched bogs and ponds i n a drainage t r o u g h and from the bog adjacent t o A-Zone m i n e r a l i z a t i o n . One l i t r e p o l y propylene b o t t l e s used f o r c o l l e c t i n g water samples were p r e - t r e a t e d i n the l a b o r a t o r y u s i n g the method o u t l i n e d by F l e t c h e r (1981). Each b o t t l e was r i n s e d w i t h d i s t i l l e d water, f i l l e d w ith 6N h y d r o c h l o r i c a c i d , and allowed t o soak f o r 24 hours. Each b o t t l e was then r i n s e d t h r e e times and r e f i l l e d w ith d i s t i l l e d water u n t i l the f i e l d sample was taken. Water b o t t l e s were kept t i g h t l y s e a l e d i n p l a s t i c sample bags d u r i n g t r a n s p o r t t o and from the f i e l d t o prevent p o t e n t i a l contamination from d i r t and dust. Samples were c o l l e c t e d from s e v e r a l c e n t i m e t r e s beneath the water s u r f a c e t o a v o i d s u r f a c e scum and d e b r i s . Water pH was measured a t the s i t e with a DSPH-3 p o r t a b l e pH meter, and water c o l o u r c a t e g o r i z e d as e i t h e r c o l o u r l e s s , l i g h t brown, or brown. P r e p a r a t i o n procedures f o r water samples were performed i n the f i e l d immediately f o l l o w i n g sample c o l l e c t i o n . Waters were f i l t e r e d t o < 0.45 um w i t h a p o r t a b l e compressed n i t r o g e n p r e s s u r e f i l t r a t i o n a p aratus ( F i g u r e 3-2) and m i l l i p o r e f i l t e r s t o remove suspended o r g a n i c and i n o r g a n i c p a r t i c l e s . One l i t r e samples were 60 F i g u r e 3-2. P o r t a b l e pressure apparatus f o r f i e l d f i l t r a t i o n o f water samples. a c i d i f i e d w i t h 20 ml of 6N h y d r o c h l o r i c a c i d w i t h i n a few hours of c o l l e c t i o n t o keep elements i n s o l u t i o n and prevent t h e i r a d s o r p t i o n onto the w a l l s of the b o t t l e (Chao e t a l , 1968). H a l l (1988) has s t a t e d t h a t 10 ml of c o n c e n t r a t e d (12N) HCL per l i t r e i s the minimum r e q u i r e d t o m a i n t a i n 50 ppt Pt and Pd i n s o l u t i o n f o r a t l e a s t two months. Three d u p l i c a t e water samples were c o l l e c t e d i n the f i e l d , i n c l u d i n g a p a i r i n which one sample was f i l t e r e d and a c i d i f i e d i n the u s u a l manner but the second was not. 3.3 Sample P r e p a r a t i o n Methods 3.3.1 Overview S o i l Samples A r e p r e s e n t a t i v e s p l i t of each C h o r i z o n s o i l , stream sediment, moss mat and bank sample was wet-sieved t o o b t a i n a -70 mesh (<212 microns) f r a c t i o n . The p r e p a r a t i o n procedure, d e s c r i b e d below, i s summarized i n F i g u r e 3-3. One of the two d u p l i c a t e C h o r i z o n s o i l samples from each s i t e was weighed, spread on a c l e a n 6'x6' p l a s t i c t a r p a u l i n and r o l l e d from end t o end s e v e r a l times t o homogenize i t . The sample was then q u a r t e r e d w i t h a t r o w e l , and two 1/8 s l i c e s from d i a g o n a l l y - o p p o s i t e q u a r t e r s removed. The 1/4 s p l i t was p l a c e d i n a p a i l , reweighed, and rehomogenized on the t a r p a u l i n . The s p l i t was a g a i n q u a r t e r e d , and two d i a g o n a l l y - o p p o s i t e q u a r t e r s , each r e p r e s e n t i n g 1/8 of the o r i g i n a l sample, were removed. One s p l i t was kept i n r e s e r v e f o r d e t e r m i n a t i o n of m i s c e l l a n e o u s s o i l p r o p e r t i e s . The second 1/8 s p l i t was weighed and s i e v e d . The t a r p a u l i n was cleaned w i t h a sponge b e f o r e and a f t e r each use. Each sample s p l i t was wet-sieved t o o b t a i n a -70 mesh (<212 microns) f r a c t i o n . The s i e v i n g apparatus, c o n s i s t i n g of two s t a i n l e s s s t e e l ASTM s i e v e s (10-mesh, 70-mesh), a l a r g e p l a s t i c bucket, a m o d i f i e d bucket l i d and a r e c i r c u l a t i n g pump i s shown i n F i g u r e 3-4. A p o r t i o n of the sample was p l a c e d i n t o the upper 10-mesh s i e v e and washed through the s i e v e s with a combination of f i n g e r a c t i o n and water r e c i r c u l a t e d from the bucket. Care must be taken t h a t the lower s i e v e does not c l o g up w i t h f i n e m a t e r i a l . F r e s h tap water was used i n the l a t t e r p a r t of each s i e v i n g c y c l e t o ensure t h a t the f r a c t i o n s were p r o p e r l y washed. The two c o a r s e f r a c t i o n s (+10 mesh, -10+70 mesh) were emptied onto k r a f t paper, a i r - d r i e d , weighed and s t o r e d . R e c i r c u l a t i n g pump hoses were r i n s e d out between samples, and s i e v e s and buckets c l e a n e d w i t h soap and water. A t o o t h b r u s h was used t o c l e a n the s i e v e s once they had d r i e d . Soil Horizon Soil Sample Bag "A" (10-15 kg) | Soil Sample Bag "B" (10-15 kg) Rolling and Quartering 1/8 split store 1/8 split weigh wet sieve air dry I weigh i store +10 mesh -10+70 -70 mesh dewater oven dry at 60C i weigh I disaggregate and homogenize I split to 300 g ring mill I split I 10g Pt-Pd-Au by Pb fire assay/ ICP-MS/AES As-Sb Major element oxides 6/8 split weigh wet sieve I +10 mesh air dry weigh store I dewater -270 mesh I oven dry at 60C i weigh disaggregate and homogenize -10+40 -40+70 -70+140 -140+270 -270 air dry I weigh Preparation of heavy mineral concentrates of -70+140/-140+270 fractions with methylene iodide (SG=3.3) Light Mineral fraction Heavy Mineral fraction dry r weigh I dry weigh Magnetic Separation split to 300 g I ring mill I split Magnetic Nonmagnetic fraction fraction weigh weigh ball mill I split i wet sieve entire sample +10 mesh -10+40 -40+70 -70+140 -140+270 -270 X |-140+2701 air dry, weigh j and store airdry other fractions I weigh Preparation of heavy mineral concentrates with methylene iodide (SG=3.3) Light Mineral fraction 1 Heavy Mineral fraction store dry i weigh Magnetic separation Magnetic fraction Paramagnetic fraction Nonmagnetic fraction weigh SEM mount 'preparation grain stub mounts polished section mounts 10g Pl-Pd-Au by Pbfireassay/ICP-AES SEM examination SEM examination I microprobe analysis Figure 3-3. Flowchart for soil sample preparation and analysis. Recirculated water Water level Fresh water -70 mesh slurry Sieves (ASTM) -70 mesh sediment Figure 3-4. Wet sieving apparatus for overview sample preparation. The -70 mesh s l u r r y was allowed t o s e t t l e i n the bucket f o r a few weeks. That p o r t i o n a l r e a d y s e t t l e d on the bucket bottom was scooped d i r e c t l y i n t o d r y i n g t r a y s and o v e n - d r i e d at 60°C. The remainder was dewatered w i t h a p r e s s u r e f i l t r a t i o n apparatus c o n s t r u c t e d i n the Department of G e o l o g i c a l S c i e n c e s a t U.B.C. The apparatus c o n s i s t s of an aluminum base w i t h a s p i g o t , a l a r g e p l a s t i c c y l i n d e r , and an aluminium cover l i n k e d t o compressed a i r l i n e . Heavy white paper was p l a c e d on the base t o serve as a f i l t e r t o t r a p the sediment. The -70 mesh s l u r r y was poured i n t o the apparatus. A b l a c k heavy m i n e r a l s e g r e g a t i o n which commonly c o l l e c t e d a t the bottom of each bucket was, however, washed w i t h a wash b o t t l e i n t o the d r y i n g t r a y r a t h e r than i n t o the f i l t r a t i o n apparatus t o prevent p o s s i b l e entrappment and l o s s of f i n e heavy minerals i n the f i l t e r paper. The top of the f i l t r a t i o n apparatus was b o l t e d on, and a i r p r e s s u r e i n c r e a s e d t o 25-50 p s i u n t i l a l l water was d i s c h a r g e d . The sediment-laden f i l t e r was then removed and o v e n - d r i e d . F i n a l l y , the sample was scraped from both the f i l t e r and d r y i n g t r a y with a p l a s t i c s c r a p e r , weighed, and p l a c e d i n a s m a l l p a s t i c p a i l t o be hand-mixed and -ground w i t h a p o r c e l e i n p e s t l e . T h i s step i s neccessary both t o homogenize sediment which may have been d e n s i t y - s t r a t i f i e d w i t h i n the d r y i n g t r a y , and t o reduce the s i z e of the d r y aggregates so they w i l l pass a r i f f l e s p l i t t e r . 66 S p l i t s of 200-300 g were taken w i t h a s t a i n l e s s s t e e l Jones r i f f l e s p l i t t e r and p u l v e r i z e d f o r t h r e e minutes i n a tungsten c a r b i d e r i n g m i l l t o approximately -200 mesh. S e v e r a l charges of about 50 g each were r e q u i r e d f o r each sample. A t u n g s t e n - c a r b i d e r i n g m i l l , r a t h e r than chrome s t e e l , was used t o prevent p o s s i b l e chromium and i r o n c o n t a m i n a t i o n of the sample (Hickson and J u r a s , 198 6). S p l i t t e r and s p l i t t i n g pans were cleaned w i t h compressed a i r between samples, and the r i n g m i l l sponge-cleaned w i t h soap and water. The f i n a l stage of overview sample p r e p a r a t i o n i n v o l v e d the f u r t h e r s p l i t t i n g of the 200-300 g s p l i t s down t o 10 g subsamples f o r a n a l y s i s . A number of d u p l i c a t e samples (Table 3-3) were a l s o prepared a t t h i s stage. 3.3.2 LFH Samples LFH samples were a i r - d r i e d , mixed w i t h i n the bag, and weighed. One-half of the sample, or more i f the weight was l e s s than 100 g, was ground i n a Wiley m i l l a t the Department of S o i l Science, U.B.C. The m i l l was c l e a n e d w i t h compressed a i r between samples. Samples were t r a n s f e r r e d t o numbered Coors c r u c i b l e s , weighed, and i g n i t e d i n a m u f f l e furnace a t 700°C u n t i l a white ash was o b t a i n e d . T h i s t y p i c a l l y r e q u i r e d about 12 hours. The r e l a t i v e l y h i g h ashing temperature i s d e s i r e a b l e t o a c h i e v e a complete r e c o v e r y of Pd (Dunn e t a l , 1989). A f t e r c o o l i n g 67 f o r a f u r t h e r 12 hours, the ash was t r a n s f e r r e d t o a p r e -weighed v i a l or bag and weighed. Ten grams of ash was o b t a i n e d i n most i n s t a n c e s ; samples l a r g e r than 20 g were f u r t h e r s p l i t i n a s t a i n l e s s s t e e l s p l i t t e r and the s p l i t s used as d u p l i c a t e s . 3.3.3 Stream Sediment, Moss mat and Bank Samples Minus 70 mesh f r a c t i o n s of stream sediment and bank samples were prepared u s i n g the same procedures as overview s o i l s ( F i g u r e 3-3). Stream sediments were d r i e d and weighed p r i o r t o w e t - s i e v i n g , however, and because of t h e i r c o a r s e r g r a i n s i z e both d u p l i c a t e bags were combined, homogenized and s p l i t . Moss mats were prepared d i f f e r e n t l y because of t h e i r h i g h p r o p o r t i o n of o r g a n i c m a t e r i a l , the s m a l l p r o p o r t i o n of c o a r s e c l a s t s , and t h e i r r e l a t i v e l y s m a l l s i z e . Samples were weighed, oven-dried, and disaggregated i n t h e i r p l a s t i c bags by g e n t l y pounding with a rubber m a l l e t ( G r a v e l and Matysek, 1989). They were then reweighed and homogenized on the p l a s t i c t a r p a u l i n . The homogenized sample was q u a r t e r e d w i t h a t r o w e l and two d i a g o n a l l y - o p p o s i t e q u a r t e r s removed. T h i s s p l i t , r e p r e s e n t i n g one-half of the o r i g i n a l sample, was then wet-sieved i n the standard manner t o o b t a i n a -7 0 mesh f r a c t i o n . 3.3.4 Bog Samples Bog samples were d r i e d , weighed, and d i s a g g r e g a t e d by pounding w i t h a rubber m a l l e t . As t h i s d i d not s u f f i c i e n t l y reduce the hard dry substance i n s i z e , samples were then t r a n s f e r r e d t o a s m a l l bucket and f u r t h e r p u l v e r i z e d w i t h a p o r c e l e i n p e s t l e . The sample was then s p l i t i n t o d u p l i c a t e 150-250 g p o r t i o n s with a Jones r i f f l e s p l i t t e r . One d u p l i c a t e was p u l v e r i z e d i n a tungsten c a r b i d e r i n g m i l l f o r 1-2 minutes. The second was hand-ground wi t h a p o r c e l e i n mortar and p e s t l e t o f u r t h e r reduce the s i z e of the aggregates and then ashed i n a m u f f l e furnace a t 700°C. 3.3.5 D e t a i l e d S o i l P r o f i l e s The second major sample p r e p a r a t i o n stage i n v o l v e d wet-s i e v i n g h o r i z o n s from each of f o u r t e e n s e l e c t e d s o i l p r o f i l e s and one stream sediment i n t o s i x ASTM s i z e f r a c t i o n s . The s i t e s (Figure 3-5) were chosen as b e i n g r e p r e s e n t a t i v e of the wide v a r i e t y of s u r f i c i a l m a t e r i a l and s o i l t y p e s , landscapes,, and Pt contents o c c u r r i n g on Grasshopper Mountain. Two s i z e f r a c t i o n s (-70+140 and -140+270 mesh) were then separated i n t o l i g h t and heavy m i n e r a l f r a c t i o n s and the l a t t e r f u r t h e r separated i n t o magnetic and nonmagnetic f r a c t i o n s . F i v e s i z e f r a c t i o n s (-10+40, -40+70, -70+140 L i g h t s , -140+270 L i g h t s , -270) and Figure 3-5. Location map of detailed soil profiles (n=14) and stream sediment site (n=1), showing surficial material type and soil site number, Grasshopper Mountain, B.C. f o u r density/magnetic f r a c t i o n s (-70+140 Magnetic Heavies, -70+140 Non-magnetic Heavies, -140+270 Magnetic Heavies, -140+270 Non-magnetic Heavies) were produced from each of 34 horizons/sediments f o r a t o t a l of 306 samples. 3.3.5.1 S i z e F r a c t i o n s Samples from p r e v i o u s l y - p r o c e s s e d C-horizons were r e t r i e v e d and s i e v e d i n t h e i r e n t i r e t y . P r e v i o u s l y unprocessed samples from A and B h o r i z o n s were f i r s t homogenized on the p l a s t i c t a r p a u l i n , q u a r t e r e d , and a 1/8 s p l i t removed f o r d e t e r m i n a t i o n of m i s c e l l a n e o u s s o i l p r o p e r t i e s . The remaining 7/8 of the sample was w e t - s i e v e d as p r e v i o u s l y d e s c r i b e d , but u s i n g a d d i t i o n a l s i e v e s t o produce s i x s i z e f r a c t i o n s (+10, -10+40, -40+70, -70+140, -140+270, and -270). Wet-sieving of s o i l i n t o m u l t i p l e s i z e f r a c t i o n s i s a lengthy and l a b o u r - i n t e n s i v e p r o c e s s . An e x p e r i e n c e d person t y p i c a l l y r e q u i r e s 2-3 working days t o s i e v e a 10 kg t i l l sample; an i n e x p e r i e n c e d person r e q u i r e s c o n s i d e r a b l y longer. The advantage of w e t - s i e v i n g over d r y -s i e v i n g i s the much g r e a t e r amount of f i n e m a t e r i a l r e c o v e r e d . Day (1988) r e p o r t e d 76% t o 676% i n c r e a s e s i n the r e c o v e r y of -270 mesh stream sediment when d r y - s i e v i n g was f o l l o w e d by w e t - s i e v i n g . S i z e f r a c t i o n s were a i r - d r i e d and weighed. The c o a r s e +10 mesh f r a c t i o n was s t o r e d , while the -270 mesh f r a c t i o n was allowed t o s e t t l e f o r s e v e r a l weeks b e f o r e r e c o v e r y from the water-sediment s l u r r y as p r e v i o u s l y - d e s c r i b e d . S e v e r a l buckets were t y p i c a l l y r e q u i r e d t o c o n t a i n the -270 mesh s l u r r y because of the l a r g e sample s i z e . The d r y i n g p r o c e s s , u s i n g both g l a s s t r a y s and the p r e s s u r e f i l t r a t i o n apparatus, o f t e n r e q u i r e d s e v e r a l days per sample. The d r y sample was then ha n d - p u l v e r i z e d and homogenized. A f t e r s e p a r a t i o n of a heavy m i n e r a l f r a c t i o n f o r the -70+140 and -140+270 mesh f r a c t i o n s ( s e c t i o n 3.3.5.2), two l i g h t (S.G.<3.3) and t h r e e whole s i z e f r a c t i o n s were s p l i t t o 200-300 g and p u l v e r i z e d t o -200 mesh i n a t u n g s t e n -c a r b i d e r i n g m i l l . A f i n e powder of a t l e a s t -150 t o -2 00 mesh i s necessary t o ensure a proper f u s i o n d u r i n g the Pb f i r e assay (Beamish and Van Loon, 1977). G r i n d i n g times v a r i e d from 1.5 t o 3.5 minutes per charge depending on the g r a i n s i z e of the f r a c t i o n . P u l v e r i z e d s p l i t s were f u r t h e r s p l i t t o 10 g subsamples i n the Jones r i f f l e s p l i t t e r . 3.3.5.2 Densit y and Magnetic F r a c t i o n s Heavy m i n e r a l s e p a r a t i o n s of the -70+140 and -140+270 mesh f r a c t i o n s were performed with the heavy l i q u i d methylene i o d i d e (S.G.=3.3). S i x t y - n i n e s e p a r a t i o n s were performed on samples from 34 h o r i z o n s and sediments. The e n t i r e u n s p l i t f r a c t i o n was used i n n e a r l y a l l cases. Because these were l a r g e , t y p i c a l l y i n the 200-400 g range, a 1000 ml s e p a r a t o r y f u n n e l was u s u a l l y used. S e p a r a t i o n s i n v o l v e d manual s t i r r i n g f o r s e v e r a l hours w i t h a g l a s s s t i r r i n g r o d . The abundance of s p i n e l - b e a r i n g M g - s i l i c a t e g r a i n s w i t h a s p e c i f i c g r a v i t y o n l y s l i g h t l y above t h a t of the heavy l i q u i d r e s u l t e d i n extremely slow s e p a r a t i o n s r e q u i r i n g 12-15 hours t o complete. Whatman 1 f i l t e r s were used t o r e c o v e r the heavy concentrates, which mostly weighed l e s s than 50 g. Methylene i o d i d e was removed from the samples by vigourous washing with acetone. The r e s u l t i n g acetone-methylene i o d i d e mixture was then mixed w i t h b u b b l i n g water i n a separatory tube t o separate and r e c o v e r the methylene i o d i d e , the s p e c i f i c g r a v i t y of which was checked w i t h a standard (S.G.= 3.27) each morning p r i o r t o b e g i n n i n g a new sample. Heavy and l i g h t m i n e r a l c o n c e n t r a t e s were l e f t t o dry o v e r n i g h t i n the fumehood; they were then t r a n s f e r r e d t o bags and v i a l s i n a s e p a r a t e fumehood and allowed t o dry f o r s e v e r a l more days b e f o r e weighing. Dry heavy m i n e r a l concentrates were weighed and then f u r t h e r separated i n t o magnetic and non-magnetic f r a c t i o n s by the repeated p a s s i n g of a hand magnet over the sample. The f a c e of the magnet was covered w i t h a p i e c e of paper t o prevent magnetic g r a i n s from becoming a t t a c h e d t o i t . Both f r a c t i o n s were weighed. Magnetic and non-magnetic heavy m i n e r a l c o n c e n t r a t e s were p u l v e r i z e d i n a Spex ceramic b a l l m i l l . The e n t i r e sample was p u l v e r i z e d t o minimize the nugget e f f e c t r e s u l t i n g from the s p l i t t i n g of such a heterogeneous medium (Coker and D i L a b i o , 1989). Samples weighing l e s s than 15 g were p u l v e r i z e d w i t h 3 b a l l s , as recommended by Lavergne (1988), f o r approximately 12 minutes. Those weighing g r e a t e r than 15 g were ground with 4 ceramic b a l l s f o r up t o 2 0 minutes. Longer g r i n d i n g times r e s u l t e d i n the sample being smeared onto the i n s i d e of the b a l l m i l l . Samples l a r g e r than about 20 g were p u l v e r i z e d i n two charges. The m i l l and b a l l s were cleaned betweem samples w i t h one, and o f t e n two, charges of quartz because of the smearing i n the m i l l . A few, p a r t i c u l a r l y the non-magnetic, f r a c t i o n s were v e r y s m a l l and 10 g of sample was not obtained. The whole of these samples was submitted f o r a n a l y s i s . The remainder were s p l i t t o the r e q u i r e d weight i n a s t a i n l e s s s t e e l m i c r o s p l i t t e r . T h i s has been shown by Otto (1933) t o be the most s a t i s f a c t o r y method of o b t a i n i n g a r e p r e s e n t a t i v e s p l i t of heavy m i n e r a l c o n c e n t r a t e s . I t s use was c o n f i n e d t o the s p l i t t i n g o f p u l v e r i z e d r a t h e r than u n p u l v e r i z e d samples. 3.4 A n a l y t i c a l Techniques A summary of the t o t a l number of samples of each type analyzed, i n c l u d i n g d u p l i c a t e s , standards and q u a r t z b l a n k s , i s shown i n Table 3-3. 3.4.1 Overview M i n e r a l S o i l s , Sediments, Banks and Bogs Overview s o i l s , stream sediments, moss mats, bank samples and bogs were analyzed f o r t h r e e groups of elements and major element oxides a t Acme A n a l y t i c a l L a b o r a t o r i e s , Vancouver. Samples were submitted i n two s e p a r a t e batches c o n t a i n i n g d u p l i c a t e s and r e f e r e n c e standards: (1) Pt-Pd-Au-Rh were determined u s i n g l e a d - f i r e assay on a 10.0 g subsample, f o l l o w i n g the procedure of Bugbee (1933) (C. Leong, p e r s o n a l communication, 1990). An i n d u c t i v e l y c oupled plasma-mass spectrometry (ICP-MS) f i n i s h i n 1988 and an i n d u c t i v e l y coupled plasma-atomic emission s p e c t r o s c o p y (ICP-AES) f i n i s h i n 1989 were used f o r a l l but Rh, which was determined by g r a p h i t e furnace-atomic a b s o r p t i o n spectrophotometry (GF-AAS). S t a t e d d e t e c t i o n l i m i t s are 1 ppb f o r Pt and Au, and 2 ppb f o r Pd and Rh. Sample Routine D u p l i c a t e Standards Quartz Other T o t a l Type Samples Samples Blanks Overview 81 8 8 2 - 99 S u i t e I Overview 32 4 6 1 - 43 S u i t e I I D e t a i l e d 216 27 22 3 2 270 S u i t e I D e t a i l e d 106 20 14 3 9 152 S u i t e I I T o t a l 435 59 50 9 11 564 LFH I 34 8 2 - - 44 LFH I I 20 2 2 - - 24 T o t a l 54 10 4 - - 68 Waters 17 3 - - - 20 A l l 506 72 54 9 11 652 T a b l e 3-3. Sample s u i t e summary f o r Pt-Pd-Au a n a l y s e s of overview m i n e r a l s o i l s , sediments, banks and bogs; d e t a i l e d s o i l p r o f i l e s ; LFH and ashed bog samples; and waters. Waters were ana l y z e d f o r Pt o n l y . 76 (2) As-Sb-Bi-Ge-Se-Te by h y d r i d e g e n e r a t i o n . A 0.5 g subsample was d i g e s t e d w i t h 3 ml o f 3:1:2 HC1-HN0 3-H 20 a t 95°C f o r one hour and d i l u t e d t o 10 ml w i t h w a t e r . H y d r i d e s a r e t h e n d e t e r m i n e d by ICP-AES. S t a t e d d e t e c t i o n l i m i t s f o r As, Sb and B i a r e 0.1 ppm. D e t e c t i o n l i m i t s f o r Ge and Se, and f o r Te, a r e 0.2 ppm and 0.3 ppm, r e s p e c t i v e l y , i n 1988 and 0.1 ppm f o r a l l i n 1989. E i g h t samples, i n c l u d i n g two s t a n d a r d s , were s u b s e q u e n t l y r e - a n a l y z e d f o r As by h y d r i d e g e n e r a t i o n a t t h e B r i t i s h Columbia G e o l o g i c a l Survey B r a n c h l a b o r a t o r y , V i c t o r i a . Samples underwent a t o t a l HF d i g e s t i o n and h y d r i d e s were d e t e r m i n e d by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (R. L e t t , p e r s o n a l communication, 1990). (3) M a j o r Element O x i d e s . A 0.2 g subsample was f u s e d w i t h L i B 0 2 , d i s s o l v e d i n 100 ml n i t r i c a c i d , and a n a l y z e d f o r S i , A l , Fe, Mg, Ca, Na, K, Mn, T i , P, Cr and Ba by ICP-AES. L o s s on i g n i t i o n was a l s o determined. 3.4.2 LFH and Ashed Bog Samples Ashed LFH and bog samples were s u b m i t t e d i n two a d d i t i o n a l b a t c h e s and a n a l y z e d f o r Pt-Pd-Au by ICP-AES and f o r Rh by GF-AAS f o l l o w i n g l e a d - f i r e a s s a y . Ashed subsamples from t h i r t y - e i g h t LFH h o r i z o n s were s u b s e q u e n t l y a n a l y z e d f o r Fe by fl a m e - a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (F-AAS) i n t h e Department o f G e o l o g i c a l S c i e n c e s i n o r d e r t o determine whether or not they had been s u b j e c t t o l i t h i c c o n t a m i n a t i o n by u n d e r l y i n g d u n i t e . Analyses were performed on a Tec h t r o n AA4 atomic a b s o r p t i o n spectrophotometer w i t h a Canlab Fe hollow cathode lamp f o l l o w i n g a hot a c i d d i g e s t i o n of the ash. D i g e s t i o n s , performed i n f o u r d a i l y batches, i n c l u d e d both blanks and d u p l i c a t e samples. Standard s o l u t i o n s of 10, 20 and 50 ppm Fe were prepared from s t o c k s o l u t i o n s , and Fe c o n c e n t r a t i o n s c a l c u l a t e d (Weberling and Cosgrove, 1965) from a standard s o l u t i o n c a l i b r a t i o n graph. A b r i e f d e s c r i p t i o n of the d i g e s t i o n procedure i s g i v e n below: 1) Ten drops of d i s t i l l e d water were added t o a t e f l o n d i s h . 2) A 0.50 g subsample of well-mixed ash was added t o the water i n the d i s h and thoroughly moistened. 3) 6 ml of 4:1 n i t r i c : p e r c h l o r i c a c i d and 2 ml of h y d r o f l u o r i c a c i d were added t o the d i s h , i n a fumehood, and tho r o u g h l y mixed. 4) The d i s h was p l a c e d on a h o t p l a t e , allowed t o evaporate t o dryness or u n t i l fuming ceased, and removed from the h o t p l a t e t o c o o l . 5) 5 ml of 6M h y d r o c h l o r i c a c i d was added t o the r e s i d u e . The d i s h was r e t u r n e d t o a warm h o t p l a t e f o r approximately f i v e minutes. 6) The l i q u i d was t r a n s f e r e d t o a 25 ml v o l u m e t r i c f l a s k , made up t o volume wi t h d i s t i l l e d water, and then f u r t h e r d i l u t e d e i t h e r lOx or lOOx with d i s t i l l e d water p r i o r t o a n a l y s i s I n s o l u b l e r e s i d u e remaining a f t e r each d i g e s t i o n was r e t r i e v e d , d r i e d , weighed and v i s u a l l y examined. 3.4.3 Waters Pt content of water samples was determined a t the G e o l o g i c a l Survey of Canada, Ottawa, O n t a r i o . The method has been d e s c r i b e d by H a l l (1988) and H a l l and Bonham-Carter (1988) . Pt and Pd i n the a c i d i f i e d and f i l t e r e d o n e - l i t r e sample i s absorbed onto 300 mg of a c t i v a t e d c h a r c o a l . The c h a r c o a l i s f i l t e r e d o f f , ashed a t 650°C, and the a n a l y t e s s o l u b i l i z e d i n 1.5 ml of aqua r e g i a ( H a l l , 1988). The sample i s evaporated, cooled, and i n c r e a s e d i n volume t o 5 ml p r i o r t o a n a l y s i s by ICP-MS. 3.4.4 D e t a i l e d S o i l P r o f i l e Samples D e t a i l e d s o i l p r o f i l e samples were submitted t o Acme A n a l y t i c a l L a b o r a t o r i e s , Vancouver, i n two se p a r a t e batches and a n a l y z e d f o r Pt-Pd-Au by l e a d - f i r e assay on a 10.0 g subsample w i t h an ICP-AES f i n i s h . S t a t e d d e t e c t i o n l i m i t s are 1 ppb f o r Pt and Au, and 2 ppb f o r Pd. 3.4.5 Subsample S i z e Experiment Incomplete d i s s o l u t i o n of chromite d u r i n g f i r e assay i s a common problem i n Pt analyses ( s e c t i o n 3.6). V a r i o u s pretreatment methods, (G r i m a l d i and Schnepfe, 1969; Moloughney, 1986; Buchanan, 1988; H a l l and Bonham-Carter, 1988), commonly i n v o l v e modifying the composition and q u a n t i t y of the f l u x and d e c r e a s i n g the subsample weight i n o r d e r t o d i s s o l v e the chromite. Use of the l a t t e r t o f a c i l i t a t e d i s s o l u t i o n negates, however, the advantage of a l a r g e r and more r e p r e s e n t a t i v e subsample s i z e i n m i n i m i z i n g the nugget e f f e c t . L a b o r a t o r i e s may f u r t h e r reduce the s i z e of 10 g c h r o m i t e - r i c h heavy m i n e r a l c o n c e n t r a t e s , most l i k e l y i n an a r b i t r a r y manner than with a r i f f l e s p l i t t e r , u n l e s s s p e c i f i c a l l y d i r e c t e d otherwise. A n a l y s i s of subsamples l a r g e r than 10 g i s c o n s i d e r e d s u p e r i o r i n a c h i e v i n g a more r e p r e s e n t a t i v e number of r a r e p a r t i c l e s i n g o l d e x p l o r a t i o n ( H a r r i s , 1982). However, concerns about complete chromite d i s s o l u t i o n and subsample s i z e r e d u c t i o n , p a r t i c u l a r l y when heavy m i n e r a l c o n c e n t r a t e s are i n v o l v e d , warranted a t e s t of Pt r e c o v e r y w i t h 10 g and 30 g subsamples. Seven 10 g and seven 30 g s p l i t s of t h e c o n t r o l monitors RK-05 and PT-5 were prepared, randomized w i t h i n t h e i r weight s u i t e , and submitted f o r a n a l y s i s . PT-5 i s c h r o m i t i f e r o u s whereas RK-05 i s not; the two are d e s c r i b e d more f u l l y i n S e c t i o n 3.6.1. 80 A n a l y t i c a l r e s u l t s (Appendix 2.1) are summarized i n Ta b l e 3-4 and F i g u r e 3-6. RK-05 shows o n l y a n e g l i g i b l e d i f f e r e n c e i n Pt content between the two s i z e ranges. The median Pt content of the 30 g subsamples (325 ppb) of c h r o m i t i f e r o u s standard PT-5, however, i s o n l y 73% t h a t of the 10 g samples (448 ppb). Furthermore, b o x p l o t s ( K u r z l , 1988) show r e p r o d u c i b i l i t y t o be poorer w i t h i n c r e a s i n g subsample s i z e ( F igure 3-6). A t - t e s t shows t h a t mean Pt c o n c e n t r a t i o n s of 10 g and 30 g subsamples are s i g n i f i c a n t l y d i f f e r e n t (p = .05). The procedure was repeated f o r PT-5 (Table 3-4). However, due t o an e r r o r by the l a b o r a t o r y , o n l y 10-20 g of the 30 g subsamples were used. Both median Pt c o n c e n t r a t i o n s are higher than those of the f i r s t group but a t - t e s t shows t h a t mean Pt content of the l a r g e r subsamples remains s i g n i f i c a n t l y d i f f e r e n t (p = .05) than t h a t of the 10 g subsamples. Ten gram subsamples of C e r t i f i e d Reference Standard PTA-1 were a l s o a n a l y z e d (Table 3-5) . A d d i t i o n a l 10 g s p l i t s of PT-5 and PTA-1 were a n a l y z e d by Chemex Labs u s i n g an ICP-AFS r a t h e r than an ICP-AES f i n i s h . The mean Pt content of PT-5 i s g r e a t e r than t h a t r e p o r t e d by Acme (Table 3-4), whereas Acme's v a l u e s a re h i g h e r f o r PTA-1 (Table 3-5; Appendix 2.2). The cause of these d i f f e r e n c e s i s not known although i n the case of PTA-1, which i s r e l a t i v e l y c o a r s e - g r a i n e d , i t may r e s u l t from a nugget e f f e c t . Standard Batch 10 g 30g RK-05 32.7 + 1.7" 33 2 (31 - 3 5 ) 3 31.7 + 0.5 32 (31 - 32) PT-5 442.1 + 23.4 448 (396 - 465) 352.3 ± 58.1 325 (274 - 438) PT-5 511.9 + 29.4 501 (488 - 567) 450.6 + 42.8* 447 (385 - 522) PT-5 B 635.7 ± 24.4 650 (600 - 650) Mean ± Is"1-Median 2 Range (Minimum t o Maximum) Ta b l e 3-4. Subsample s i z e experiment: mean + I s , median and range of Pt (ppb) c o n c e n t r a t i o n s of 10 g v e r s u s 30 g subsamples of c o n t r o l r e f e r e n c e standards RK-05 and PT-5. N=7 f o r each grouping. Samples marked w i t h an a s t e r i x (*) i n d i c a t e t h a t subsample s i z e s of 10-20 g, r a t h e r than 30 g, were used by the l a b . A = Acme Labs; B = Chemex Labs. 82 Pt (PPb) 500 475 450 425 400 375 350 325 300 275 250 t 50 45 40 35 30 25 20 15 10 5 0 Maximum M Minimum PT-5 RK-05 10g 30 g Figure 3-6. Boxplots showing variation in Pt concentrations (ppb) of control standards RK-05 and PT-5 with increasing size of the analytical subsample. N=7 for each grouping. Boxplots show median (M), minimum and maximum concentrations for each grouping; fifty percent of the data for each grouping lies within the box between the first quartile (Q,) and the third quartile (Qg). Standard Lab Batch n 10 g PTA-1 A 2 7 4367.3 3657 2 (2618 + 1635.3 1 PTA-1 B 3 7 3485.7 3400 (2100 + 839.5 4700) C e r t i f i e d 3050 + 140 Value Mean ± Is Median 2 Range (Minimum t o Maximum) Ta b l e 3-5. Mean + I s , median and range of Pt (ppb) c o n c e n t r a t i o n s of c e r t i f i e d r e f e r e n c e standard PTA-1 subsamples determined by two commercial l a b o r a t o r i e s . C e r t i f i e d v a l u e of PTA-1 from Steger (1986). A = Acme Labs; B = Chemex Labs. The r e d u c t i o n i n Pt recovery and a n a l y t i c a l p r e c i s i o n as subsample s i z e of c h r o m i t i f e r o u s samples i n c r e a s e s ( F i g u r e 3-6) has important e x p l o r a t i o n i m p l i c a t i o n s i n s o f a r as i t negates the advantage of u s i n g 30 g a n a l y t i c a l subsamples. Use of 10 g subsamples i s recommended on t h i s b a s i s . 3.5 E v a l u a t i o n of A n a l y t i c a l P r e c i s i o n 3.5.1 Overview C Horizons P r e c i s i o n i s a measure of data r e p r o d u c i b i l i t y , and was es t i m a t e d f o r the overview Pt r e s u l t s w i t h 12 s e t s o f d u p l i c a t e samples (Appendix 3.1) from a range of s o i l , sediment and bog s i t e s . D u p l i c a t e s were prepared d u r i n g the f i n a l s p l i t t i n g of 10 g subsamples from the p u l v e r i z e d subsample and i n s e r t e d randomly i n the two overview a n a l y t i c a l s u i t e s . E i g h t d u p l i c a t e s were i n s e r t e d i n the f i r s t s u i t e of 81 r o u t i n e samples, and a f u r t h e r f o u r i n the second s u i t e of 32 r o u t i n e samples (Table 3-3). A n a l y t i c a l r e p r o d u c i b i l i t y was assessed w i t h s c a t t e r p l o t s and with a p r e c i s i o n c o n t r o l graph. A l o g s c a t t e r p l o t of r o u t i n e versus d u p l i c a t e Pt a n a l y s e s i s shown i n F i g u r e 3-7A. The l i n e a r c o r r e l a t i o n c o e f f i c i e n t (r) i s 0.9975. P r e c i s i o n of the Pt analyses was es t i m a t e d w i t h a Thompson and Howarth p r e c i s i o n c o n t r o l graph ( F i g u r e 3-8). T h i s method, o u t l i n e d by Thompson and Howarth (1978) and F l e t c h e r (1981), i s a p p l i c a b l e t o data s e t s c o n t a i n i n g from 10 t o 50 d u p l i c a t e p a i r s . P l o t s of the mean c o n c e n t r a t i o n of the d u p l i c a t e s versus the a b s o l u t e v a l u e of t h e i r d i f f e r e n c e are shown f o r each d u p l i c a t e p a i r , and p r e c i s i o n c o n t r o l l i n e s f o r 90th and 99th p e r c e n t i l e s of the a b s o l u t e d i f f e r e n c e are p l o t t e d f o r the a p p r o p r i a t e l e v e l s o f p r e c i s i o n . R e s u l t s i n d i c a t e an o v e r a l l p r e c i s i o n of +- 84% a t the 95% co n f i d e n c e l e v e l , with 1 out of 12 p o i n t s f a l l i n g above the 90th p e r c e n t i l e . However, i t i s apparent from the graph t h a t the worst p r e c i s i o n i s shown by d u p l i c a t e p a i r s w i t h low Pt c o n c e n t r a t i o n s near the d e t e c t i o n l i m i t (1 ppb). I f d u p l i c a t e s w i t h mean Pt c o n c e n t r a t i o n s l e s s than 13 ppb are d i s r e g a r d e d , p r e c i s i o n i s b e t t e r than +-20% a t the 95% co n f i d e n c e l e v e l . Overview samples were analyzed f o r As by Acme A n a l y t i c a l L a b o r a t o r i e s ( s e c t i o n 3.4.1); e i g h t samples were r e a n a l y z e d (Appendix 3.2) by the B.C. G e o l o g i c a l Survey as a check of the r e l a t i v e l y high As c o n c e n t r a t i o n s i n Grasshopper Mountain s o i l s . R e s u l t i n g d u p l i c a t e a n a l y s e s , ( F i g u r e 3-7B) are i n good agreement. S l i g h t l y h i g h e r As c o n c e n t r a t i o n s r e p o r t e d by the B.C. G e o l o g i c a l Survey are a t t r i b u t e d t o the t o t a l d i g e s t i o n method employed ( s e c t i o n 3.4.1). N 86 Figure 3-7. Scatterplots of duplicate analyses of -70 mesh overview samples for A. Platinum (n=12) and B. Arsenic (n=8) Figure 3-8. Precision control graph of -70 mesh overview duplicate Pt analyses. Dashed lines indicate overall precision of P= +-84% at the 95% confidence level, while solid lines indicate precision of P= +-20% atthe 95% confidence level for concentrations > 13 ppb Pt. 88 3.5.2 LFH Horizons Ten d u p l i c a t e p a i r s , comprising nine LFH and one bog sample d u p l i c a t e , were used t o monitor a n a l y t i c a l p r e c i s i o n i n t he two batches (Table 3-3) of ashed o r g a n i c samples. A n a l y t i c a l data f o r Pt, Pd and Au are g i v e n i n Appendix 3.3. In the second batch, an a d d i t i o n a l ( t h i r d ) i n s e r t i o n of one of the e a r l i e r d u p l i c a t e p a i r s was made t o monitor between-batch as w e l l as w i t h i n - b a t c h p r e c i s i o n . P r e c i s i o n of Pt an a l y s e s was eval u a t e d with a s c a t t e r p l o t of d u p l i c a t e p a i r s and a Thompson and Howarth p r e c i s i o n c o n t r o l graph ( F i g u r e 3-9) . I t i s apparent from both graphs (F i g u r e 3-9) t h a t r e p r o d u c i b i l i t y of Pt c o n c e n t r a t i o n s i s poorer i n LFH h o r i z o n ash than i n mi n e r a l C h o r i z o n s . P r e c i s i o n i s about +-60% a t the 95% confidence l e v e l . A major d i f f e r e n c e between ashed LFH and overview C-horizon samples i s t h a t C h o r i z o n samples e x h i b i t poor p r e c i s i o n o n l y near the d e t e c t i o n l i m i t , whereas ashed LFH samples e x h i b i t i t over the e n t i r e c o n c e n t r a t i o n range. The poorer p r e c i s i o n i s a t t r i b u t e d t o the much s m a l l e r f i e l d s i z e of LFH than m i n e r a l s o i l samples and t o the e r r a t i c d i s t r i b u t i o n o f p a r t i c u l a t e P t - h o s t i n g g r a i n s w i t h i n the o r g a n i c m a t r i x of the h o r i z o n ( s e c t i o n 4.2.2). Figure 3-9. Duplicate Pt (ppb) analyses (n=10). A. Scatterplot of duplicate Pt analyses of ashed LFH and bog samples; B. Precision control graph of duplicate LFH Pt analyses, showing P=+-60% at the 95% confidence level. 3.5.3 D e t a i l e d S o i l P r o f i l e s P r e c i s i o n of Pt analyses i n d e t a i l e d s o i l h o r i z o n s was e v a l u a t e d a t two l e v e l s . At one l e v e l , 47 p a i r s of st a n d a r d d u p l i c a t e samples (Appendix 3.4) from each of the n i n e d i f f e r e n t s i z e / d e n s i t y / m a g n e t i c f r a c t i o n s were prepared d u r i n g f i n a l s p l i t t i n g of 10 g subsamples from the p u l v e r i z e d subsample. Twenty-seven d u p l i c a t e s were i n s e r t e d i n t o s u i t e 3 of 216 r o u t i n e samples; the remaining 20 d u p l i c a t e s were i n s e r t e d i n t o s u i t e 4 of 106 r o u t i n e samples (Table 3-3). D u p l i c a t e s were not i n s e r t e d randomly over the e n t i r e a n a l y t i c a l s u i t e , but w i t h i n b l o c k s of 10-24 samples of the same s i z e / d e n s i t y / m a g n e t i c f r a c t i o n . At a second l e v e l , an a d d i t i o n a l s e t of " s p l i t t e r " d u p l i c a t e s were prepared from o r i g i n a l f r a c t i o n s o f t e n -10+40 mesh and s i x -40+70 mesh samples (Appendices 3.5 and 3.6) from d e t a i l e d s o i l h o r i z o n s . S p l i t t e r d u p l i c a t e s , t y p i c a l l y 250-350 g, re p r e s e n t i n i t i a l s p l i t t i n g as w e l l as a n a l y t i c a l p r e c i s i o n . Only the c o a r s e s t s i z e f r a c t i o n s were chosen as these, with r e l a t i v e l y fewer p a r t i c l e s than f i n e r f r a c t i o n s , were c o n s i d e r e d t o be most s u b s e p t i b l e t o sample s p l i t t i n g v a r i a b i l i t y . D u p l i c a t e s were processed as i n d i v i d u a l samples, f o l l o w i n g i d e n t i c a l but s e p a r a t e p u l v e r i z i n g and f i n a l s p l i t t i n g paths. A n a l y t i c a l p r e c i s i o n was eva l u a t e d w i t h s c a t t e r p l o t s and Thompson-Howarth p r e c i s i o n c o n t r o l graphs. S c a t t e r p l o t s of s t a n d a r d d u p l i c a t e s (Figure 3-10) show t h a t t h e r e are no s y s t e m a t i c v a r i a t i o n s i n r e p r o d u c i b i l i t y w i t h e i t h e r a n a l y t i c a l batch or overburden type. S c a t t e r p l o t s o f s p l i t t e r d u p l i c a t e s (Figure 3-12A) show somewhat b e t t e r r e p r o d u c i b i l i t y f o r -10+40 mesh as opposed t o -40+70 mesh samples. O v e r a l l p r e c i s i o n of standard d u p l i c a t e a n a l y s e s as est i m a t e d from the Thompson-Howarth c o n t r o l graph ( F i g u r e 3-11) i s +-60% a t the 95% confidence l e v e l . The p o o r e s t p r e c i s i o n i s obtained near the d e t e c t i o n l i m i t (1 ppb), as w i t h the overview Pt analyses ( s e c t i o n 3.5.1), and a t the h i g h e s t mean c o n c e n t r a t i o n ( S i t e 16: 3730.5 ppb). There i s l i t t l e v a r i a t i o n i n p r e c i s i o n along the e n t i r e c o n c e n t r a t i o n range, however, and e x c l u s i o n of the t h r e e lowest and one h i g h e s t - c o n c e n t r a t i o n samples improves i t t o +-40% a t the 95% c o n f i d e n c e l e v e l i n the range 4-1800 ppb. I t i s apparent from F i g u r e 3-11 t h a t a n a l y t i c a l p r e c i s i o n i s as good w i t h heavy m i n e r a l concentrates as i t i s w i t h s t a n d a r d s i z e f r a c t i o n s . As might be expected from the s p l i t t i n g of samples co m p r i s i n g coarse p a r t i c l e s , p r e c i s i o n of s p l i t t e r d u p l i c a t e s ( F i g u r e 3-12B) i s much poorer. P r e c i s i o n o f the e n t i r e data s e t (n=16) i s worse than +-95% a t the 95% c o n f i d e n c e l e v e l , with 3 or 4 out of 16 p o i n t s p l o t t i n g 92 Platinum -1 (ppb) 1 3 10 30 100 300 1,000 3,000 Platinum -1 (ppb) Figure 3-10. Duplicate Pt analyses of detailed soil profile size, density, and magnetic fractions: A. Subdivided by analytical batch; and B. Subdivided by type of surficial material. I I j I I I I I I , 1 I I I (j) I I I I I I I I i1 1 I I I I I 1 3 10 30 100 300 1,000 3,000 10,000 (Pt-1 + Pt-2)/2 (ppb) Figure 3-11. Precision control graph of Pt analyses for duplicate samples from detailed soil profiles. Dashed lines indicate overall precision of P=+-60% at the 95% confidence level, while solid lines indicate precision of P=+-40% at the 95% confidence level for both standard size fractions and heavy mineral concentrates in the range 4-1800 ppb Pt. DUPLICATE PT A N A L Y S E S O F -10+40 A N D -40+70 1 3 10 30 100 300 1,000 Platinum -1 (ppb) B Q. OJ 2L 1,000 300 100 30 10 PRECISION C O N T R O L G R A P H O F SPLITTER D U P L I C A T E S V 3 1 0.3 0.1 * 1 -10+40 Fraction _ o " -40+70 Fraction • (n=10) (n=6) P=+95% (overall) o P=+80% (-10+40 mesh fraction only) o -/ 0 r • • ° o o 1 1 1 F 1 1 1 I 1 1 t I I I 1 1 1 1 1 1 I- . 1 10 30 100 300 1,000 3,000 10,000 (Pt-1 + Pt-2)/2 (ppb) Figure 3-12. Splitter duplicates: A. Scatterplot of duplicate Pt analyses (ppb) of -10+40 and -40+70 mesh fractions; B. precision control graph. Dashed lines indicate overall precision of P=+-95% at the 95% confidence level, while solid lines indicate precision of P=+-80% at the 95% confidence level for -10+40 mesh fraction duplicates only. above the 90th p e r c e n t i l e . P r e c i s i o n f o r the -10+40 f r a c t i o n o n l y (n=10) i s m a r g i n a l l y b e t t e r , measuring +-80% a t the 95% c o n f i d e n c e l e v e l ; only 1 of 10 p o i n t s p l o t s above the 90th p e r c e n t i l e . S p l i t t e r d u p l i c a t e s were not always a n a l y z e d i n the same batch (Appendices 3.5 and 3.6), but t h i s seems t o have had l i t t l e e f f e c t on r e p r o d u c i b i l i t y . I t must be s t r e s s e d t h a t the two coarse s i z e f r a c t i o n s used r e p r e s e n t a "worst case" s c e n a r i o . S p l i t t e r d u p l i c a t e s from f i n e r f r a c t i o n s with a r e l a t i v e l y g r e a t e r number of p a r t i c l e s would be expected t o e x h i b i t much b e t t e r p r e c i s i o n . 3.6 M o n i t o r i n g of A n a l y t i c a l Accuracy and D r i f t S ystematic a n a l y t i c a l e r r o r s may r e s u l t from contamination, d r i f t , and p h y s i c a l and chemical i n t e r f e r e n c e s ( F l e t c h e r , 1981), g i v i n g r i s e t o i n a c c u r a t e r e s u l t s . C o n t r o l r e f e r e n c e standards, d r i f t monitors, and s i l i c a b l a nks were t h e r e f o r e i n c l u d e d i n a l l f o u r sample s u i t e s t o monitor a n a l y t i c a l accuracy, as r e l i a b l e Pt f i r e -assay a n a l y s e s are d i f f i c u l t t o o b t a i n , p a r t i c u l a r l y from samples w i t h a s i g n i f i c a n t chromite content (Bugbee, 1933; Borthwick and N a l d r e t t , 1984; Bloom, 1986; Moloughney, 1986; H a l l and Bonham-Carter, 1988). The incomplete d i s s o l u t i o n of r e f r a c t o r y chromite g r a i n s d u r i n g the f i r e - a s s a y f l u x , and the heterogeneous d i s t r i b u t i o n of p a r t i c u l a t e chromite g r a i n s w i t h i n the sample are among the f a c t o r s r e s p o n s i b l e . The former r e s u l t s i n both incomplete Pt r e c o v e r y and p h y s i c a l a n a l y t i c a l i n t e r f e r e n c e s , as PGE remain as i n c l u s i o n s and i n s o l i d s o l u t i o n w i t h i n u n d i s s o l v e d chromite r a t h e r than e n t e r i n g the f l u x (Borthwick and N a l d r e t t , 1984) , w h i l e the l a t t e r causes poor a n a l y t i c a l p r e c i s i o n ( s e c t i o n 3.5). 3.6.1 C o n t r o l Reference Standards and D r i f t M o n itors One c o n t r o l r e f e r e n c e standard (PTA-1) and two d r i f t m onitors (RK-05, PT-5) were used t o monitor f o r s y s t e m a t i c e r r o r s i n m i n e r a l s o i l s u i t e s , each c o r r e s p o n d i n g t o a d i f f e r i n g o r d e r of magnitude of Pt c o n c e n t r a t i o n and v a r y i n g chromite content. P l a t i n i f e r o u s Black Sand PTA-1 i s the o n l y c e r t i f i e d r e f e r e n c e m a t e r i a l of the t h r e e . I t has a Pt cont e n t of 3050 + 140 ppb a t the 95% co n f i d e n c e i n t e r v a l (Steger, 1986). D r i f t monitors PT-5 and RK-05 are secondary standards c o n t a i n i n g approximately 500 ppb and 30 ppb Pt, r e s p e c t i v e l y . C e r t i f i e d r e f e r e n c e standards c o n t a i n i n g s i m i l a r low t o m i d - l e v e l Pt c o n c e n t r a t i o n s a p p r o p r i a t e f o r geochemical e x p l o r a t i o n are not a v a i l a b l e ( H a l l and Bonham-C a r t e r , 1988). RK-05 was prepared by the G e o l o g i c a l Survey of Canada from p y r o x e n i t e from Pyroxene Mountain, Yukon T e r r i t o r y (B. B a l l a n t y n e , p e r s o n a l communication, 1988). PT-5 was prepared by W.K. F l e t c h e r of the U n i v e r s i t y of B r i t i s h Columbia from d u n i t e from Grasshopper Mountain, B.C., and i s the onl y c h r o m i t i f e r o u s standard of the t h r e e . F o r t y - e i g h t standards i n s e r t i o n s were made i n t o the f o u r m i n e r a l s o i l s u i t e s (Table 3-3). PTA-1 was used o n l y i n t he f i n a l two s u i t e s which contained heavy m i n e r a l c o n c e n t r a t e s expected t o have s i g n i f i c a n t Pt c o n c e n t r a t i o n s . Mean, median and ranges of Pt, Pd and Au a n a l y s e s f o r each of t he t h r e e standards are shown i n Table 3-6. A n a l y t i c a l d ata f o r each of the standards and d r i f t monitors are shown i n Appendices 4.1 t o 4.3 and i n d i v i d u a l Pt c o n c e n t r a t i o n s f o r each are p l o t t e d on a c o n t r o l graph ( F i g u r e 3-13). Mean and median Pt c o n c e n t r a t i o n s were c a l c u l a t e d f o r standards and d r i f t monitors i n each of the f o u r batches (Table 3-7). A v e g e t a t i o n standard, composite ash V-3, was used t o e v a l u a t e the accuracy of the LFH ana l y s e s . V-3 was prepared by the G e o l o g i c a l Survey of Canada from v e g e t a t i o n from the Rottenstone PGE d e p o s i t i n Saskatchewan ( H a l l e t a l , 1990). Three i n s e r t i o n s were made over two batches. Pt r e s u l t s (Appendix 4.4) range from 72-75 ppb and are r e l a t i v e l y c o n s t a n t w i t h v a r y i n g subsample weights from 2.86 t o 10 g, although H a l l e t a l (1990) r e p o r t e d poor r e p r o d u c i b i l i t y (155 + 109 ppb) with 2 g subsamples. Pt (ppb) Pd (PPb) Au (PPb) RK-05 (n=20) 30.8 ± 3.3" 30 2 (25 - 3 7 ) 3 3.4 + 1.9 2.5 (2 - 9) 1.6 + 0.9 1 (1 - 4) PT-5 (n=21) 529.0 ± 73.7 505 (435 - 746) 4.0 ± 1.9 3 (2 - 8) 2.6 + 1.8 2 (1 - 7) PTA-1 2981.0 + 1116.9 2959 (n=7) (1626 - 4941) 29.7 + 5.8 29 (21 - 37) 61.7 + 19.6 59 (38 - 89) Mean + Is Median 2 Range (Minimum t o Maximum) Tab l e 3-6. Mean + I s , median, and range of Pt, Pd, and Au c o n c e n t r a t i o n s (ppb) f o r d r i f t monitors RK-05 and PT-5, and f o r c o n t r o l standard PTA-1. C e r t i f i e d v a l u e f o r PTA-1 i s 3050 + 140 ppb (Steger, 1986). XI Q. 30 a. E 3 C 13 20 CL • A , A RK-05 + 1s / v -* A X - 30.8 + 3.3 , V Batch 1 i i i i Batch 2 I I Batch 3 i i i i Batch 4 i i i i i XI CL CL E 600 3 C jo Q. • PT-5 / \ + 1s - X = 529.0 + 73.7 f\ -• )7 - i s Batch 1 i i i i Batch 2 i I Batch 3 Batch 4 I i i i I I i i i I i I i i i i B 5,000 4,500 4,000 XI S 3,500 E •£ 3,000 CL 2,500 2,000 1,500 PTA-1 Batch 3 Certified Value: 3050 ± 140 + 1s X = 2981.0 + 1116.9 Batch 4 _ 1 s J I L Figure 3-13. Standard control graphs for Pt standards A. RK-05; B. PT-5; and C. PTA-1, showing values in relation to 1s about the mean. All values in ppb. RK-05 PT-5 PTA-1 Batch 1 32.8 ± 3.3 1 656.8 +59.9 32.5 2 630 ( n x = 4 ) 3 (m = 4) Batch 2 3 5 . 0 + 2 . 8 504.5 +58.7 35 504.5 ( n 2 = 2) ( n 2 = 2) Batch 3 30.0 + 2.1 486.6 + 27.0 3346.8 + 1360.2 30 495 3410 ( n 3 = 9) ( n 3 = 9) ( n 3 = 4) Batch 4 29.0 + 3.9 515.7 + 30.8 2493.3 + 585.5 28 510 2685 ( n 4 = 5) ( n 4 = 6) ( n 4 = 3) Mean + I s Median 2 I n s e r t i o n s per batch T a b l e 3-7. Mean + Is and median Pt c o n c e n t r a t i o n s (ppb) of d r i f t monitors RK-05 and PT-5, and of c o n t r o l s t a n d a r d PTA-1, i n each of f o u r a n a l y t i c a l batches. C e r t i f i e d v a l u e f o r PTA-1 i s 3050 ± 140 ppb (Steger, 1986). 3.6.2 S i l i c a Blanks Nine s i l i c a blanks were i n s e r t e d i n the f o u r sample s u i t e s t o assess l a b o r a t o r y c a r r y o v e r contamination. Pt, Pd and Au a n a l y s e s of each of the blanks are shown i n Appendix 4.5. Two v a r i e t i e s of s i l i c a were used. BDH F i n e L a b o r a t o r y Sand (about -40+100 mesh) was used i n the two blanks of the f i r s t batch. One was p u l v e r i z e d t o approximately -2 00 mesh t o e v a l u a t e c a r r y o v e r c o n t a m i n a t i o n a t the g r i n d i n g stage while the second was i n s e r t e d u n p u l v e r i z e d . F i s h e r S c i e n t i f i c Si02 f l o a t e d powder (about -240 mesh) was used f o r the remaining seven blanks and was i n s e r t e d without any a d d i t i o n a l g r i n d i n g . Blanks were not randomly p l a c e d but were i n s e r t e d e i t h e r a t the t a i l ends of the batch or immediately a f t e r c e r t i f i e d r e f e r e n c e standard PTA-1 (3050 ppb). Pt content of blanks i n the f i r s t t h r e e of the f o u r batches ( F i g u r e 3-14) i s v e r y low, i n d i c a t i n g t h a t a n a l y t i c a l c a r r y o v e r contamination and, i n the case of the f i r s t batch c a r r y o v e r from g r i n d i n g , i s n e g l i g i b l e . Blanks i n batch f o u r , however, r e t u r n e d c o n s i d e r a b l y h i g h e r Pt c o n c e n t r a t i o n s (range: 19-24 ppb). As a l l t h r e e blanks i n t h i s b atch were p l a c e d immediately a f t e r c e r t i f i e d r e f e r e n c e s t a n d a r d PTA-1, t h e i r h i g h Pt content i s most probably the r e s u l t of s y s t e m a t i c a n a l y t i c a l c a r r y o v e r contamination, e i t h e r d u r i n g f i r e assay p r e p a r a t i o n or from i n s t r u m e n t a t i o n memory. Mean 102 Figure 3-14. Variation in Pt content (ppb) of silica blanks with analytical batch. Blanks in batch 4 were placed immediately after certified reference standard PTA-1 (3050 ppb Pt) only. Pt content of the t h r e e p e r t i n e n t PTA-1 subsamples (Appendix 4.3) i s 2493 ppb and t h a t of the t h r e e c o r r e s p o n d i n g blanks (Appendix 4.5) i s 22 ppb. Assuming a 10 g subsample s i z e and a s i l i c a Pt c o n c e n t r a t i o n of 1 ppb, 0.085 g (85 mg) of PTA-1 remaining on a p o o r l y - c l e a n e d s p a t u l a would cause a c o n c e n t r a t i o n of 22 ppb Pt i n the blank. I t i s apparent t h a t extremely s m a l l q u a n t i t i e s of high-Pt m a t e r i a l can cause these Pt c o n c e n t r a t i o n v a r i a t i o n s i f i n t r o d u c e d by s l o p p y subsampling p r i o r t o f i r e assay. 3.7 Scanning E l e c t r o n Microscopy and E l e c t r o n Microprobe A n a l y s i s of Heavy M i n e r a l Concentrates 3.7.1 Sample S e l e c t i o n and P r e p a r a t i o n C h o r i z o n samples from e i g h t s o i l p r o f i l e s r e p r e s e n t a t i v e of n o n - d u n i t i c t i l l , d u n i t i c t i l l , d u n i t i c t i l l near A-Zone Pt m i n e r a l i z a t i o n , and both s e r p e n t i n i t i c and C l i f f Zone c o l l u v i u m (Tables 4-15 and 4-16) were s e l e c t e d from the d e t a i l e d sample s u i t e f o r m i n e r a l o g i c a l study u s i n g scanning e l e c t r o n microscopy (SEM). These span a range of s o i l types and development, and cover a spectrum of P t c o n t e n t s . P r o f i l e l o c a t i o n s are among those shown i n F i g u r e 3-5. As the e n t i r e heavy concentrate of each d e t a i l e d sample was p u l v e r i z e d i n the i n t e r e s t s of r e p r o d u c i b i l i t y p r i o r t o Pt a n a l y s i s , i t was necessary t o prepare a new s u i t e of heavy c o n c e n t r a t e s (Figure 3-3). The d u p l i c a t e C h o r i z o n sample from each of the e i g h t s e l e c t e d s i t e s was wet-sieved t o s i x s i z e f r a c t i o n s as p r e v i o u s l y d e s c r i b e d (see s e c t i o n 3.3.5.1) and new heavy m i n e r a l concentrates of the -140+270 mesh (106 t o 53 um) f r a c t i o n prepared. T h i s f r a c t i o n was chosen f o r m i n e r a l o g i c a l study because the heavy c o n c e n t r a t e s g e n e r a l l y c o n t a i n more Pt (Table 4-14) than those from the -70+140 mesh (212 t o 106 um) f r a c t i o n . The c o n c e n t r a t e s were then separated i n t o magnetic, non-magnetic and paramagnetic f r a c t i o n s u s i n g a hand magnet. The paramagnetic g r a i n s were i n c o r p o r a t e d i n t o the magnetic f r a c t i o n d u r i n g the i n i t i a l s e p a r a t i o n f o r Pt a n a l y s i s , but were separated f o r these samples i n case any weakly-magnetic Pt-Fe a l l o y m i n e r a l s might be p r e f e r e n t i a l l y a s s o c i a t e d w i t h i t . Twenty-three s o i l c o ncentrates were prepared, as w e l l as two each of stream sediment 503 and paleochannel sediment 207. Two types of sample were prepared f o r SEM examination: g r a i n mount stubs and p o l i s h e d g r a i n mounts. To prepare g r a i n mounts the concentrate was emptied onto a p i e c e of g l o s s y paper, and r o l l e d and tumbled back and f o r t h t o homogenize the sample p r i o r t o subsampling. Adhesive was f i x e d t o a standard c i r c u l a r SEM stub which was then dipped i n t o the sample t o p i c k up a t h i n l a y e r of g r a i n s . 105 P o l i s h e d g r a i n mounts were prepared u s i n g a method d e s c r i b e d by Douma and Knight ( i n p r e p a r a t i o n ) . Samples were r o l l e d and tumbled p r i o r t o subsampling and i n s e r t i o n i n t o a t r a n s o p t i c powder (methacrylate) mount. The mount was then p l a c e d i n a mounting press with a d d i t i o n a l m e t h a c r y l a t e and encapsulated. Hand g r i n d i n g and p o l i s h i n g on a p o l i s h e r with carbimet paper d i s c s produced a c r o s s -s e c t i o n through the c o l l e c t i o n of g r a i n s . P l u c k i n g of f i n e PGM from the sample, as d i s c u s s e d by Laflamme (1990), i s minimized by the use of methacrylate r a t h e r than epoxy as a mounting medium (Y. Douma, p e r s o n a l communication, 1990). Both stub and p o l i s h e d g r a i n mounts were carbon c o a t e d i n a Denton Vacuum DV-515 p r i o r t o SEM o b s e r v a t i o n . 3.7.2 Scanning E l e c t r o n Microscopy Techniques Samples were examined i n the Department of G e o l o g i c a l S c i e n c e s a t U.B.C. u s i n g a SEMCO Nanolab 7 scanning e l e c t r o n microscope (SEM), o p e r a t i n g a t 3 0 kV, wi t h energy d i s p e r s i v e spectrometry (EDS) q u a l i t a t i v e a n a l y t i c a l c a p a b i l i t i e s . The SEM i s capable of m a g n i f i c a t i o n s of up t o 100,000x. Photographic r e c o r d s were made with an a t t a c h e d P o l a r o i d camera. Twenty-seven g r a i n mount stubs were examined i n i t i a l l y under the b i n o c u l a r microscope and the SEM. B a c k s c a t t e r 106 e l e c t r o n imaging, i n which h i g h e r atomic number g r a i n s appear b r i g h t e r than lower atomic number g r a i n s , was used t o determine the presence of PGM and t o d i s c e r n between heavy and l i g h t m i n e r a l s . G e n e r a l l y , h i g h atomic number g r a i n s were d e f i n e d as those i n which dominant elements have atomic numbers of a t l e a s t 22 ( T i ) . EDS p r o v i d e d q u a l i t a t i v e analyses of the s u r f a c e s of PGM and o t h e r heavy m i n e r a l s ; m i n e r a l i d e n t i f i c a t i o n s i n T a b l e s 4-15 and 4-16 are based on r e l a t i v e i n t e n s i t i e s of c h a r a c t e r i s t i c peaks. Secondary e l e c t r o n imaging was used t o i n v e s t i g a t e the e x t e r n a l morphology of the heavy m i n e r a l s . Primary a t t e n t i o n was p a i d t o m e t a l l i c o x i de and s u l f i d e phases thought l i k e l y t o host PGE; s i l i c a t e phases were not i n v e s t i g a t e d . Twenty-three p o l i s h e d s e c t i o n mounts were s i m i l a r l y examined under the r e f l e c t i n g microscope and SEM i n an attempt t o d i s c o v e r PGM g r a i n s and t o o b t a i n q u a l i t a t i v e EDS a n a l y s i s from the i n t e r i o r s of chromite g r a i n s . B i n o c u l a r and r e f l e c t e d l i g h t microscopes proved t o be of l i t t l e use i n l o c a t i n g PGM g r a i n s due t o the v e r y s m a l l s i z e of both the PGM and the s i e v e d f r a c t i o n as a whole. The procedure f o r l o c a t i n g PGM g r a i n s under the SEM i n v o l v e d f i r s t scanning the e n t i r e mount at low power (50x) t o l o c a t e any l a r g e f r e e PGM or other obvious f e a t u r e s , and then m e t h o d i c a l l y s e a r c h i n g the mount on an almost g r a i n - b y - g r a i n b a s i s a t a much high e r power (500-1000x) t o l o c a t e s m a l l PGM i n c l u s i o n s w i t h i n chromite. PGM, d i s c e r n i b l e o n l y by b a c k s c a t t e r imaging b r i g h t n e s s c o n t r a s t , g e n e r a l l y appeared as o n l y t i n y p o i n t s even at h i g h power. 3.7.3 E l e c t r o n Microprobe Techniques E l e c t r o n microprobe analyses of 120 chromite g r a i n s i n s e l e c t e d p o l i s h e d g r a i n mounts were performed on a Cameca SX-50 e l e c t r o n microprobe i n the Department of G e o l o g i c a l S c i e n c e s . The o b j e c t i v e s i n c l u d e d : a) t o measure the major-element chemistry of chromite g r a i n s , and t o determine i f any s y s t e m a t i c c o m p o s i t i o n a l d i f f e r e n c e s e x i s t between s p i n e l s a s s o c i a t e d w i t h h i g h -p l a t i n u m versus low-platinum samples b) t o determine i f t h e r e are s y s t e m a t i c c o m p o s i t i o n a l d i f f e r e n c e s between edges and cores of chromite g r a i n s E l e c t r o n microprobe analyses were performed on 63 e u h e d r a l - s u b h e d r a l chromite c r y s t a l s and 57 anhedral chromite fragments from t e n p o l i s h e d g r a i n mounts. These, comp r i s i n g the magnetic and non-magnetic s e c t i o n s from f i v e C h o r i z o n s o i l s , cover a wide spectrum of s o i l t y p e s and p l a t i n u m contents, and i n c l u d e c o l l u v i u m and d u n i t i c t i l l s i t e s a d j a c e n t t o known PGE m i n e r a l i z a t i o n as w e l l as both d u n i t i c and n o n - d u n i t i c t i l l s i t e s d i s t a l from known m i n e r a l i z a t i o n . Chromites were analyzed f o r seven elements u s i n g an o p e r a t i n g p o t e n t i a l of 15 kV, a beam c u r r e n t of 30 nA, and a beam s i z e of 1-2 um. The f o l l o w i n g x-ray l i n e s and standards were used: S i K<< ( f a y a l i t e S-104) , A l K°<-(garnet S-007), T i K=< ( r u t i l e S-013), Cr (chromite S-222), Fe Koc ( f a y a l i t e S-104), Mn K<* (pyroxmangite S-245) , and Mg K<* ( f o r s t e r i t e S-022) . A n a l y t i c a l procedure c o n s i s t e d of a n a l y z i n g both the co r e s and edges of up t o 15 randomly-selected chromite g r a i n s : c r y s t a l s i n the magnetic f r a c t i o n s and fragments i n the non-magnetic and paramagnetic f r a c t i o n s . The paramagnetic f r a c t i o n was used i n p l a c e of the non-magnetic f r a c t i o n i n t h r e e cases (samples 19, 200, 156) because t h e s e c o n t a i n e d r e l a t i v e l y few chromite g r a i n s . Chromites were i d e n t i f i e d on the b a s i s of t h e i r c h a r a c t e r i s t i c s c r a t c h e d smooth p o l i s h e d s u r f a c e and t h e i r C r - r i c h EDS s i g n a t u r e ; c r y s t a l s were d i s c e r n e d from fragments by t h e i r shape. A sk e t c h was made of the shape of each analyzed g r a i n f o r subsequent r e f e r e n c e . Oxide weight percent analyses were converted t o m i n e r a l formula u n i t s on the b a s i s of a s p i n e l u n i t c e l l of 24 c a t i o n s and 32 oxygens. Fe was d i s t r i b u t e d as F e 2 + and F e 3 + u s i n g FORMULA ( E r c i t , 1987), a program f o r formula and v a l e n c e c a l c u l a t i o n . Compositions are p l o t t e d on the s p i n e l p r i s m (Stevens, 1944; I r v i n e , 1965) i n F i g u r e s 4-58 and 4-59. 3.8 X-Ray D i f f r a c t i o n A n a l y s i s of S e l e c t e d S o i l H o r i z o n s The mineralogy of i n d i v i d u a l h o r i z o n s from d e t a i l e d s o i l p r o f i l e s was determined with a f u l l y - a u t o m a t e d Siemens D-5000 X-Ray d i f f r a c t i o n system i n order t o see i f any s y s t e m a t i c r e l a t i o n e x i s t e d between s o i l mineralogy, major element composition, and platinum content. F o r t y - e i g h t samples were i n v e s t i g a t e d , comprising two d i s p a r a t e s i z e f r a c t i o n s (-10+40 and -270 mesh) from e l e v e n d e t a i l e d s o i l p r o f i l e s . The l o c a t i o n s of the p r o f i l e s are among those shown i n F i g u r e 3-5. P u l v e r i z e d sample, prepared e a r l i e r f o r Pt a n a l y s i s , was a p p l i e d t o a g l a s s s l i d e i n water suspension and a l l o w e d t o d r y . O p e r a t i n g c o n d i t i o n s were 40 kV and 3 0 mA u s i n g Cu K<< r a d i a t i o n . The angle of scan was 5° t o 60° a t the r a t e of 100 seconds per degree. Peak i d e n t i f i c a t i o n was made w i t h DIFFRAC/AT software. Chapter Four RESULTS CHAPTER FOUR: RESULTS 4.1 I n t r o d u c t i o n R e s u l t s are presented f o r : A) Overview s t u d i e s of -70 mesh s o i l s throughout the study area, as w e l l as those of a s s o c i a t e d LFH samples, banks, stream sediments, moss mats and waters, and X-ray d i f f r a c t i o n mineralogy of s e l e c t e d p r o f i l e s B) Downprofile s i z e / d e n s i t y / m a g n e t i c f r a c t i o n r e s u l t s f o r s e l e c t e d s o i l p r o f i l e s C) Scanning e l e c t r o n microscopy and e l e c t r o n microprobe s t u d i e s of PGM and t h e i r host m i n e r a l g r a i n s 112 4.2 P a r t A - Overview R e s u l t s 4.2.1 S o i l s A n a l y t i c a l r e s u l t s f o r -70 mesh C h o r i z o n s o i l s on v a r i o u s parent m a t e r i a l types are summarized i n Appendices 5.1 and 5.2. Data were evaluated i n the manner d e s c r i b e d by S i n c l a i r (1986): s u b d i v i s i o n i n t o t i l l and c o l l u v i u m p a r e n t m a t e r i a l s , f o l l o w e d by c a l c u l a t i o n of b a s i c s t a t i s t i c s , c o r r e l a t i o n a n a l y s i s and p a r t i t i o n i n g of p o p u l a t i o n s w i t h p r o b a b i l i t y graphs ( S i n c l a i r , 1976) c o n s t r u c t e d w i t h the program PROBPLOT (Stanley, 1987). S o i l mineralogy of r e p r e s e n t a t i v e p r o f i l e s of each parent m a t e r i a l i s shown i n s e c t i o n 4.2.1.3. 4.2.1.1 G r a i n S i z e D i s t r i b u t i o n . , . Overview samples were wet-sieved t o +10, -10+70, and -70 mesh s i z e f r a c t i o n s (see s e c t i o n 3.3.1). Sample weight data f o r t i l l and c o l l u v i u m are shown i n Appendices 5.3 and 5.4; weight percent data i n Appendices 5.7 and 5.8. Summary data of mean, median and range of the g r a i n s i z e d i s t r i b u t i o n i n v a r i o u s parent m a t e r i a l s f o r the -10 113 F r a c t i o n T i l l C o l l u v i u m C l a y (n=49) (n=27) (n=2) -10+70 mesh x: 37. 42 ± 8. ,24 49. 04 ± 8. .63 16. 98 ± 1. .27 M: 36. 39 46. 53 16. 98 R: (22 .75-54. .80) (31 .98-67. .93) (16 .08-17. .87) -70 mesh 62. 58 + 8. .24 50. 96 + 8, .63 83. 03 + 1. .27 63. 60 53. 47 83. 03 (45 .20-77. .25) (32 .07-68. .01) (82 .13-83. ,92) Ta b l e 4-1. Mean ± Is (x), median (M) and range (R) of g r a i n s i z e d i s t r i b u t i o n i n t i l l ( i n c l u d i n g background samples) and c o l l u v i u m as weight p e r c e n t of the -10 mesh (< 2 mm) s o i l component. F r a c t i o n T i l l C o l l u v i u m C l a y (n=49) (n=27) (n=2) +10 mesh x: M: R: 45.85 ± 11.24 46.03 (25.07-70.68) 71.65 ± 9.82 73.51 (53.39-93.94) 17.66 ± 22.43 17.66 (1.80-33.52) -10+70 mesh 19.98 ± 5.06 19.78 (9.37-33.03) 13.71 + 5.34 12.79 (3.84-31.66) 14.12 ± 4.85 14.12 (10.69-17.55) -70 mesh 34.17 ± 9.51 34.22 (16.21-54.72) 14.63 ± 6.12 12.90 (2.22-31.05) 68.22 ± 17.58 68.22 (55.79-80.65) T a b l e 4-2. Mean + Is (x), median (M) and range (R) of g r a i n s i z e d i s t r i b u t i o n i n t i l l ( i n c l u d i n g background samples) and c o l l u v i u m as weight p e r c e n t of the t o t a l dry weight of the t h r e e f r a c t i o n s (dry f i e l d w eight). 114 mesh component (Table 4-1) shows t h a t C h o r i z o n t i l l s are predominantly composed of -70 mesh (<212 um) p a r t i c l e s , whereas c o l l u v i a l s o i l s are c o a r s e r and c o n t a i n subequal p r o p o r t i o n s of both -70 mesh (<212 um) and -10+70 mesh (2 mm-212 um) m a t e r i a l . In c o n t r a s t , samples from c l a y p a r e n t m a t e r i a l c o n s i s t almost e n t i r e l y of -70 mesh p a r t i c l e s . With r e g a r d t o the e n t i r e sample (Table 4-2), c o l l u v i u m i s predominantly composed of +10 mesh fragments, and c o n t a i n s a much lower p r o p o r t i o n of -70 mesh p a r t i c l e s than e i t h e r t i l l o r c l a y . The absence of any upper s i z e l i m i t f o r the +10 mesh f r a c t i o n i n t r o d u c e s a sampling b i a s , as the absence or presence of l a r g e cobbles w i l l skew the r e s u l t s . The +10 mesh data cannot be used t o c h a r a c t e r i z e the overburden i t s e l f , as l a r g e cobbles were avoided d u r i n g sampling. I t does, however, h i g h l i g h t r e l a t i v e d i f f e r e n c e s between the t h r e e parent m a t e r i a l s . 4.2.1.2 R e s u l t s : Platinum and Other Elements a) Major Element T i l l Composition and Grouping of Surficial Materials Mean, median, and range of major elements, s u b d i v i d e d on the b a s i s of parent m a t e r i a l groupings, are shown i n Ta b l e 4-3. D i s t r i b u t i o n of MgO, which appears t o be most d i a g n o s t i c of d i f f e r e n t parent m a t e r i a l grouping, i n t i l l 115 o ^colluvium o-v A-Zone A PGE occurrence • 0.01 -10.00% O 10.01 - 20.00 % • 20.01 - 30.00 % • 30.01 - 40.00 % m 0 100 4877 A N 0.01 -10.00% O 10.01 -20.00% # 20.01 - 30.00 % A 30.01 - 40.00 % Figure 4-1. MgO content (%) of overview -70 mesh C horizon soils In A. dunitic till, rubble and colluvium adjacent to PGE mineralization In the secondary study area; and B. in dunitic and non-dunitic till in the main study area; Grasshopper Mountain, B.C. Dashed line at lower centre represents the boundary between dunitic and non-dunitic tills (basemap adapted from Bohme, 1987). 116 Figure 4-2. Distribution of MgO in C horizon colluvium, main study area (n=25), Grasshopper Mountain, B.C. (basemap adapted from Bohme, 1987). 117 O CD 4 C CD Non-dunitic Till ARITHMETIC FREQUENCY DISTRIBUTION OF MGO IN TILL (N=44) Dunitic Till 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 MgO (%) B 10 ARITHMETIC FREQUENCY DISTRIBUTION OF MGO IN COLLUVIUM (N=27) c CD CD 4 -LL 2 -2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 MgO (%) Figure 4-3. Arithmetic frequency distributions of MgO content (%) of overview C horizon soils in A. Till and B. Colluvium. FF.DEliE ILITV PLOT Pop . 1 2 Pop . 1 2 MgO UARIfiBLE = UNIT = s N = 36 N CI = If POPULATIONS flean Std.Deu. 0.7562 QAM li .0 1.20*6 O.lfjJ! *E .0 THRESHOLD! 0.5310 0.98H7 0. 951H 1. *2»H PERCENT USERS VISUAL PARAMETER E S TI MR f E S Figure 4-4. Log p r o b a b i l i t y p lo t of MgO in t i l l , main study area. MgO Cr203 Fe203 Si02 A1203 CaO Na20 K20 Ti02 P205 MnO Ba LOI (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (ppm) (%) CLAY X 5. 01 0, ,04 9. 50 53. 14 16. 00 4. .02 2. 54 1. 39 1. 00 0. 20 0. 19 587 6. 9 Main Study Area M 5. 01 0. ,04 9. 50 53. 14 16. 00 4. .02 2. 54 1. 39 1. 00 0. 20 0. 19 587 6. .9 (n=2) Min 4. 22 0. .04 9. 11 51. 87 15. 41 3. ,75 2. 52 1. 33 0. 98 0. 16 0. 12 555 6. .5 Max 5. 80 0. ,04 9. 89 54. 41 16. 58 4. ,29 2. 56 1. 45 1. 02 0. 24 0. 26 619 7. .3 NON-DUNITIC TILL X 5 . 66 0. . 07 9. 86 54. 00 14. 62 4 . 73 2. 65 1. 34 0. 95 0. 13 0. 16 474 5. .7 Main Study Area M 5 .44 0, ,06 9. 87 53. 74 14. 53 4. .79 2. 60 1. 34 0. 95 0. 13 0. 15 473 5. .6 (n=19) Min 3 .86 0. , 03 8. 38 51. 40 12. 84 3. .13 2. 34 1. 09 0. 87 0. 06 0. 12 376 4. . 1 Max 8 .23 0. .16 11. 75 56. 95 15. 83 5, .51 3. 20 1. 64 1. 05 0. 21 0. 22 554 8. .0 DUNITIC TILL X 16 . 51 0. .20 10. 87 46. 67 9. 07 3 . ,71 1. 27 0. 83 0. 63 0. 12 0. 18 248 9. .9 Main Study Area M 16 .25 0. .19 10. 82 46. 52 8. 89 3. .61 1. 13 0. 83 0. 60 0. 11 0. 18 242 9. ,9 (n=17) Min 10 .45 0. .12 8. 82 44. 23 6. 90 1. .88 0. 85 0. 57 0. 41 0. 08 0. 13 195 3. .3 Max 28 .73 0. ,29 13 . 12 50. 64 12. 44 5. .58 2. 08 1. 07 0. 90 0. 19 0. 22 352 16. .4 DUNITIC TILL X 13 . 84 0. .28 11. 78 48. 15 10. 15 3, .28 1. 72 0. 66 0. 64 0. 08 0. 18 270 9. . 3 Secondary Study M 13 .21 0, .26 11. 09 50. 00 10. 27 3, .46 1. 83 0. 73 0. 69 0. 08 0. 15 264.5 8. .5 Area (n=8) Min 10 .64 0. .12 9. 53 42. 96 7. 86 1. .24 1. 06 0. 35 0. 37 0. 06 0. 12 182 7. .2 Max 19 .06 0. ,51 14. 96 51. 01 12. 08 4. .48 2 . 29 0. 79 0. 79 0. 15 0. 29 334 14. .4 COLLUVIUM X 24 . 16 0. .33 11. 89 40. 67 5. 51 1. .73 0. 83 0. 30 0. 35 0. 12 0. 27 125 13 . 8 Main Study Area M 23 .29 0. ,32 12. 10 40. 65 5. 57 1. .90 0. 85 0. 22 0. 37 0. 11 0. 25 112 12. .7 (n=25) Min 14 .29 0. .20 9. 37 34. 60 1. 21 0. .35 0. 08 0. 05 0. 08 0. 07 0. 15 38 9. .4 Max 32 .78 0. .50 13. 72 46. 38 9. 73 3 . 29 1. 44 0. 82 0. 62 0. 22 0. 57 226 22 . 8 x=mean M=median Min=minimum value Max=maximum value Table 4-3. Mean, median and range of major elements, subdivided by parent material grouping, in the -70 mesh fraction of C horizon s o i l s . 120 and c o l l u v i u m i s shown i n F i g u r e s 4-1 and 4-2, r e s p e c t i v e l y . Frequency d i s t r i b u t i o n s (Figure 4-3) and a p r o b a b i l i t y p l o t ( F i g u r e 4-4) show t h a t two d i s t i n c t non-overlapping lognormal MgO p o p u l a t i o n s occur i n t i l l from the main study a r e a . The S-SW t r e n d i n g boundary between the two i s shown i n F i g u r e 4-1. The f i r s t p o p u l a t i o n (range: 10.45-28.73% MgO) o c c u r s i n the western h a l f of the area, has a mean MgO content of 16.51% (9.96% Mg) and i s a s s o c i a t e d w i t h g e n e r a l l y h i g h e r v a l u e s of Pt and 0 ^ 0 3 . The second (range: 3.86-8.23% MgO) occurs i n the e a s t e r n h a l f of the a r e a , has a mean MgO content of 5.66% (3.41% Mg) and i s a s s o c i a t e d w i t h lower Pt and Cr203 v a l u e s . A t - t e s t shows mean MgO c o n t e n t s of the two t i l l s t o be s i g n i f i c a n t l y d i f f e r e n t (p = .05). These are c o n s i d e r e d t o be d u n i t i c d e r i v e d and n o n d u n i t i c t i l l s , r e s p e c t i v e l y . D u n i t i c c o l l u v i u m (range: 14.29-32.78% MgO) possesses an even g r e a t e r mean MgO c o n t e n t of 24.16% (14.57% Mg). MgO content of main study a r e a c l a y i s v e r y s i m i l a r t o t h a t of n o n - d u n i t i c t i l l . b) Overall Distribution of Platinum D i s t r i b u t i o n of Pt i n C h o r i z o n s o i l s on Grasshopper Mountain i s shown i n F i g u r e 4-5. Contour i n t e r v a l s f o r P t were determined w i t h l o g p r o b a b i l i t y p l o t s and histograms t o s e p a r a t e i n d i v i d u a l Pt p o p u l a t i o n s f o r s o i l s developed on t i l l (n=44). Lower and upper p o p u l a t i o n s correspond i n a g e n e r a l way t o s o i l s developed on n o n - d u n i t i c and d u n i t i c 121 Figure 4-5. Pt content (ppb) of overiew -70 mesh C horizon soils in till (n=44) and colluvium (n=27) above the dunite core of the Tulameen ultramafic complex, Grasshopper Mountain, B.C. (basemap adapted from Bohme, 1987). 122 t i l l s , r e f l e c t e d by the i n c r e a s e i n s o i l Pt content from e a s t t o west a c r o s s the main study area, and t o a c o n c e n t r a t i o n of e i g h t t i l l / r u b b l e (mean: 158.1 ppb Pt) and two c o l l u v i a l Pt v a l u e s c l u s t e r e d around known PGE m i n e r a l i z a t i o n a t the secondary study area c o n t a i n i n g 0.024-0.039 oz/ton Pt (Bohme, 1988). Pt v a l u e s i n excess of 200 ppb occur i n t h r e e t i l l / r u b b l e (maximum: 4 55 ppb Pt) and one s t a b i l i z e d c o l l u v i u m s i t e i n t h i s area ( F i g u r e 2-14B). Pt content of c o l l u v i u m (n=27) i s approximately l o g n o r m a l l y d i s t r i b u t e d , and contour i n t e r v a l v a l u e s of F i g u r e 4-5 were made t o correspond t o t i l l i n t e r v a l s f o r ease of comparison. The g r e a t e s t Pt c o n c e n t r a t i o n of a l l C h o r i z o n s o i l s (855 ppb) occurred i n a c t i v e c o l l u v i u m ( s o i l s i t e 16) beneath one of the C l i f f Zone PGE o c c u r r e n c e s . c) Parent Material Groupings i ) B a s i c S t a t i s t i c s f o r Pt and Other Elements Mean, median and range of c o n c e n t r a t i o n s f o r Pt and o t h e r s e l e c t e d elements i n each c a t e g o r i c a l g rouping are shown i n T a b l e 4-4. O r i g i n a l a n a l y t i c a l data i s i n Appendix 5. Mean Pt content of o v e r a l l c o l l u v i u m (125.1 ppb) i s c o n s i d e r a b l y g r e a t e r than t h a t of o v e r a l l t i l l (53.3 ppb). However, f u r t h e r s u b d i v i s i o n of t i l l Pt data on the b a s i s of major element geochemistry p r o v i d e s a more meaningful grouping. When c l a s s i f i e d by MgO content and pa r e n t m a t e r i a l , the mean Pt content of main study area c o l l u v i u m (120 ppb) i s more than double t h a t of main study area d u n i t i c t i l l (52.8 ppb), while n o n - d u n i t i c t i l l e x h i b i t s the lowest mean Pt content (9.5 ppb) (Table 4-4). Median Pt v a l u e s , u n a f f e c t e d by hig h o u t l i e r s , g i v e a b e t t e r approximation of background Pt l e v e l s i n s u r f i c i a l m a t e r i a l s : 8 ppb i n n o n - d u n i t i c t i l l , 36 ppb i n d u n i t i c t i l l , and 88 ppb i n c o l l u v i u m . D i s t r i b u t i o n of ( ^ 0 3 i s g e n e r a l l y s i m i l a r t o t h a t of Pt. C o l l u v i u m has the g r e a t e s t mean Cr 203 content (0.33%; 2257 ppm C r ) , whereas s o i l s on d u n i t i c t i l l and n o n d u n i t i c t i l l w i t h i n the main study area have mean Cr 203 c o n t e n t s of 0.20% (1368 ppm Cr) and 0.07% (479 ppm C r ) , r e s p e c t i v e l y . L o c a l l y - d e r i v e d d u n i t i c t i l l i n the secondary study area has a mean 0 ^ 0 3 content of 0.28% (1915 ppb Cr) . The maximum Cr203 v a l u e of 0.51% (3,488 ppm Cr) o c c u r r e d i n t h i s a r e a . The Pd content of the s o i l s i s very low i n r e l a t i o n t o Pt. Median v a l u e s are 3 ppb i n n o n - d u n i t i c t i l l , 6.5 ppb i n d u n i t i c t i l l , and 2 ppb i n d u n i t i c c o l l u v i u m . The Au content of main study area c o l l u v i u m (mean: 21.0 ppb) i s 3-4x g r e a t e r than i n t i l l . The secondary study area c o n t a i n s the l e a s t Au (5.1 ppb), while d u n i t i c and non-Pt Pd Rh Au As Sb (PPb) (PPb) (PPb) (PPb) (ppm) (ppm) CLAY X 5.5 2.5 2 5 11.9 0.9 Main Study Area M 5 .5 2 . 5 2 5 1 1 . 9 0 . 9 (n=2) Min 4 2 2 5 9.4 0.5 Max 7 3 2 5 14.3 1.2 NON-DUNITIC TILL X 9.5 4.1 2 8.2 15.5 1.0 Main Study Area M 8 3 2 7 1 4 . 7 0 . 9 (n=19) Min 2 2 2 2 8.1 0.5 Max 20 15 2 34 23.2 1.8 DUNITIC TILL X 52.8 8.9 2.1 8.4 15.8 0.3 Main Study Area M 36 6 . 5 2 8 1 3 . 1 0 . 2 <n=17) Min 16 2 2 2 5.3 0.1 Max 311 48 3 21 52.5 0.8 DUNITIC TILL X 158.1 7.0 2.5 5.1 18.5 0.4 Secondary Study M 89 2 . 5 2 4 1 5 . 6 0 . 4 Area (n=8) Min 42 2 2 1 7.4 0.1 Max 455 36 6 10 30.5 0.8 COLLUVIUM X 120.0 2.6 2 21.0 21.3 0.6 Main Study Area M 88 2 2 18 .5 1 5 . 8 0 . 5 (n=25) Min 24 2 2 2 7.5 0.2 Max 885 5 3 56 56.3 1.2 x=mean M=median Min=minimuirt v a l u e Max=maximum v a l u e T a b l e 4-4. Mean, median and range of PGE and o t h e r s e l e c t e d c o n s t i t u e n t s of the -70 mesh f r a c t i o n of C h o r i z o n s o i l s i n v a r i o u s p arent m a t e r i a l s , Grasshopper Mountain, B.C. 125 d u n i t i c t i l l have mean Au contents of 8.4 ppb and 8.2 ppb r e s p e c t i v e l y . Rather h i g h As v a l u e s , r a n g i n g from 5.3 -52.5 ppm i n t i l l and from 7.5 - 56.3 ppm i n c o l l u v i u m , occur throughout the study area, with 90% of the s o i l s c o n t a i n i n g > 10 ppm As. Median As contents are r e l a t i v e l y s i m i l a r i n a l l p a r ent m a t e r i a l s (Table 4-4). i i ) C o r r e l a t i o n A n a l y s i s C o r r e l a t i o n m a t r i c e s f o r the two g e n e t i c c a t e g o r i c a l groups, t i l l and c o l l u v i u m , are shown i n F i g u r e 4-6. The data were log-transformed p r i o r t o c a l c u l a t i o n because of t h e lognormal nature of the Pt d i s t r i b u t i o n . Those l i n e a r c o r r e l a t i o n c o e f f i c i e n t s exceeding the c r i t i c a l v a l u e above which they are s i g n i f i c a n t l y d i f f e r e n t from zero a t the 95% c o n f i d e n c e l e v e l are l i s t e d , i n order of d e c r e a s i n g s t r e n g t h , i n Tables 4-5 and 4-6. Induced c o r r e l a t i o n s between both major element oxides and Loss On I g n i t i o n (LOI) are omitted, as these sum t o 100% and thus form p r o p o r t i o n s of a c l o s e d data s e t (Davis, 1986). Forty-one s i g n i f i c a n t c o r r e l a t i o n s occur i n the t i l l group, whereas on l y s i x t e e n occur i n the c o l l u v i u m group. The most important r e l a t i o n among the t i l l c o r r e l a t i o n s i s the p a r t i o n i n g of Pt with those elements forming m a f i c , as opposed t o f e l s i c , m i n e r a l s . Pt e x h i b i t s p o s i t i v e A. T i l l AU PT PD RH AS SB Bl SI02 AL203 FE203 MGO CAO NA20 K20 TI02 P205 AU I. .00000 PT -, .06938 1. .00000 PD .41112 .26826 1. .00000 RH .18898 .24411 .05493 1. .00000 AS .10194 -, .00502 -, .02390 .18252 1 ,00000 SB .11583 -, .58420 - , .28875 - .00023 .08572 1 .00000 Bl .01535 -, .26191 -, .15338 -. .20680 - ,03682 .11547 1 .00000 SI02 -, .00253 .74773 -, .32105 -, .04905 - .04091 .53376 .23610 1 .00000 AU03 -, .00202 .70938 -, .23219 -, .14232 .06397 .56426 .10924 .87784 1 .00000 PK203 .03699 .59846 .25734 .05461 .07701 - .37288 -. .31865 - .48531 - .51479 1. .00000 MGO .02611 .74898 .27328 .15690 -, .08263 - .61432 -, .14578 - .91110 - .96240 .46643 1 .00000 CAO .25976 -. ,55139 .11320 .00594 .07887 .32185 -, .06302 .65088 .55428 -, .11628 _ .58810 1.00000 NA30 -, .11116 -, .66354 -. ,28799 .06729 -, ,02445 .54661 .12254 .90776 .95621 -, .44248 - .92687 .53253 1.00000 K20 .10718 -. .81899 -. .05814 -, ,19954 ,09326 .55980 .28820 .77222 .85055 -, .64277 - .83336 .53402 .77496 1.00000 TI02 .11045 -. ,71046 -. .07870 -. .09530 .04130 .50482 .02652 .88419 .89298 -, .28852 -, .90714 .81354 .86501 .79571 1.00000 P205 .29571 -. .37210 .10843 -. .20836 ,06301 .27257 .13588 .03990 .21684 -, .48978 -, .21193 .03282 .06704 .42268 .11177 1.00000 MNO .08916 .40512 ,36663 -. 04449 ,04032 .11346 -. .12327 .59974 -. .40684 .32653 .41174 -.38998 -.45226 -.30180 -.44217 • 33110 CR203 -. ,23720 .83972 13273 .10911 -, ,09824 .57893 -. .27839 -. .79908 -. .83457 ,60605 .87566 -.56393 -.75432 -.85589 -.80603 -.44174 BA -. .02210 .74263 .29401 16941 -, .05885 .62121 .17359 .87233 .96229 -. .54219 - .94200 .45361 .93958 .86396 .B3169 .22611 LOI .06162 .62027 .30021 .01208 .27716 .36613 -• .23669 -• .79260 -• .55127 .20696 .61747 -.52275 -.66629 -.53361 -.64335 .08875 1.00000 .28999 -.40354 .44175 1.00000 -.81275 .55669 1.00000 -.62690 1.DO000 CRITICAL VALUE (1-TAIL, CRITICAL VALUE (2-tail, .05) - + Or .05) = +/ .25143 .29694 B. C o l l u v i u m AU PT PD RH AS SB Bl SI02 AL203 FE203 MSO CAO NA20 K20 TI02 P205 mo AU 1. .00000 PT -, .16428 1. .00000 PD -, .12471 .02622 1. .00000 RH .30014 .64792 -, .15617 1. .00000 AS .35451 .32746 -, .19666 .30149 1 .00000 SB .11945 .10484 .22438 .02347 ,47652 1. .00000 Bl .21649 .07873 .19984 .07935 .37718 .34467 1. .00000 SI02 ,08093 -. .29453 .02671 .16256 -, ,28751 .03958 -. .38109 1 .00000 AL203 .21247 -.26623 .16495 - .10824 - .34747 - .02670 .13881 .55803 1, .00000 FE203 .21836 .34678 .01068 .10278 .16307 . 18189 .16665 - .07994 .23019 1.00000 MGO .37223 .22693 - .25769 .18312 .24425 -, .10592 .00168 - .49770 -, .86549 -.28977 1. .00000 CAO -, .10348 - .08915 .25483 -, .11180 - .19792 -, .00548 .11108 .28444 .79665 .43016 - .67613 1.00000 NA20 -, .24885 - .21632 .14998 -, .06705 - .42616 - .08317 .21618 .51458 .97723 .19238 - .79310 .79936 1.00000 K20 -, .17707 - .28751 .21379 -, .29113 - .09048 .05743 ,11477 .37640 .72809 .13173 - .74760 .58645 .71150 1.00000 TI02 -, .17448 - .25160 .13552 -, .11904 - .33725 - .02029 .14008 .53302 .98580 .31302 - .85415 .84528 .96402 .70662 1.00000 P205 .05633 .09879 .14094 .05984 .29180 .13281 .49063 - .62713 - .01064 .15393 - .11971 .15646 -.04477 .06880 .01880 1. 00000 MNO .01449 .27552 .06744 .09821 .50183 .17445 ,45141 - .66624 - .16823 .41352 - .00210 -.01846 -.20963 .05042 -.14649 .79980 0000 CR203 -, .16175 .57683 .14640 .21907 .10344 .15229 .10619 - .50541 - .52433 .05144 .52028 -.33853 -.42012 -.49493 -.52667 .06798 9950 BA -, .39982 - .21105 .23063 -, .07831 - .19081 .08158 .14141 .26706 .76249 .15397 - .82128 .60702 .74343 .83723 .74813 .16843 8978 LOI -, .12015 .23464 .16486 .06062 .15721 - .02648 ,35994 - .88532 - .35218 .01179 .16133 -.16945 -.32813 -.12040 -.35125 .75157 0040 .00000 .02022 CRITICAL VALUE (1-TAIL, .05) CRITICAL VALUE (2-tail, .05) + Or - .32375 +/- .38009 F i g u r e 4-6. Log t r a n s f o r m e d c o r r e l a t i o n m a t r i c e s f o r A. t i l l and B. c o l l u v i u m . ro Pt + C r 2 0 3 , MgO, LOI, F e 2 0 3 , MnO K 20, S i 0 2 , Ba, T i 0 2 , A 1 2 0 3 , Na 20, Sb, CaO, P 2 0 5 Pd + Au, MnO, LOI S i 0 2 Sb + Ba, A 1 2 0 3 , K 20, Na 20, S i 0 2 , T i 0 2 , CaO MgO, Pt, C r 2 0 3 , F e 2 0 3 , LOI B i Fe->0 2 U3 Ba + A 1 2 0 3 , Na 20, S i 0 2 , K 20, T i 0 2 , Sb, CaO MgO, C r 2 0 3 , Pt, LOI, F e 2 0 3 , MnO LOI + Pt, Pd Ba, Sb Ta b l e 4-5. S i g n i f i c a n t c o r r e l a t i o n s (r > .29694) i n t i l l (n=44). L i s t e d from s t r o n g e s t t o weakest. 128 Pt + Rh, C r 2 0 3 As + MnO, Sb Na 20 B i + P2°5/ M n 0 S i 0 2 Ba + K 20, A 1 2 0 3 , T i 0 2 , Na 20, CaO MgO, C r 2 0 3 , Au T a b l e 4-6. S i g n i f i c a n t c o r r e l a t i o n s (r > .38009) i n c o l l u v i u m (n=27). L i s t e d from s t r o n g e s t t o weakest. 3,000 1,000 300 100 Non-dunitic Till O Dunitic Till • Dunitic Colluvium 30 10 O o o o o o o o/ /o o \ o o o / o / o Pt vs MgO 9 9 _i L 10 20 MgO (%) 30 50 B 3,000 1,000 300 100 30 10 Non-dunitic Till O Dunitic Till • Dunitic Colluvium Pt vs Cr203 • 6 ceo :o o co 8 o o 0.1 0.2 0.3 Cr203 (% 0.4 0.5 0.6 Figure 4-7. Scatterplots of -70 mesh overview Pt concentrations (ppb) with A. MgO and B. Cr203 from C horizon soils on various parent materials. 3,000 _h 100 a. Si 30 • • # o • ° o n o°o o o o oo Pt vs A s 20 30 40 As (ppm) Non-dunitic Till O Dunitic Till • Dunitic Colluvium B 3,000 1,000 300 h • 3" ioo Q. a! M s • • • ::# o 8 o o o o ° § o o o P t v s Sb Sb (ppm) Non-dunitic Till O Dunitic Till • Dunitic Colluvium O O 1.5 3,000 1,000 \r 300 S" 100 St 30 o*^ o "o o o ° o o o o o 10 20 30 40 Au (ppb) Pt vs A u Non-dunitic Till O Dunitic Till • Dunitic Colluvium SO 60 3,000 1,000 300 S" 100 Q. a. SI 30 co° 8 o •o o o P t v s Pd 20 30 40 Pd (ppb) Non-dunitic Till O Dunitic Till • Dunitic Colluvium 50 60 Figure 4-8. Scatterplots of -70 mesh overview soil Pt data (ppb) with selected elements: A. As; B. Sb; C. Au; and D. Pd. CO o B 3,000 1,000 300 J 100 ZL L 30 Non-dunitic Till O Dunitic Till • Dunitic Colluvium Pt vs Fe203 • • O ^ ° o ° Cbo o o o o oo 00 3,000 1,000 300 £" too CL Q. a. 30 10 12 Fe203 (%) 14 16 1,000 3 100 3. L 30 Non-dunitic Till O Dunitic Till • Dunitic Colluvium Pt vs Loss on Ignition o o' 0 ° SB O SB 10 15 Loss on Ignition (%) 20 25 3 h Non-dunitic Till O Dunitic Till • Dunitic Colluvium D 1,000 300 S" 1 0 0 CL Q. Si 30 10 fc-Pt vs M n O • • " • CO ° o , CO o o o oo 0.1 0.2 0.3 0.4 MnO (%) 0.5 0.6 Pt vs B a Non-dunitic Till O Dunitic Till • Dunitic Colluvium P.* °o °o °o O o o ° o o o I I i_ 100 200 300 400 Ba (ppm) 500 600 Figure 4-9. Scatterplots of -70 mesh overview soil Pt data (ppb) with selected elements/determinations: A. Fe203; B. MnO; C. LOI; D. Ba. c o r r e l a t i o n s w i t h 0x203, MgO and, t o a l e s s e r e x t e n t , LOI, Fe20 3 and MnO. I t e x h i b i t s n e gative c o r r e l a t i o n s w i t h K2O, S i 0 2 , Ba, T i 0 2 , A l 2 0 3 and o t h e r s . In c o l l u v i u m Pt c o r r e l a t e s w i t h 0x203, but not with MgO. S c a t t e r p l o t s of Pt w i t h MgO and C r 2 0 3 are shown i n F i g u r e 4-7 and w i t h o t h e r s e l e c t e d elements i n F i g u r e s 4-8 and 4-9. i i i ) S p a t i a l D i s t r i b u t i o n of Pt and Other S e l e c t e d Elements on Grasshopper Mountain P a r t i t i o n i n g of Pt, Cr 203 and Pd data i n t o s e p a r a t e p o p u l a t i o n s w i t h i n n o n - d u n i t i c t i l l , d u n i t i c t i l l and c o l l u v i u m c a t e g o r i c a l groupings was performed w i t h frequency d i s t r i b u t i o n s , ranked data, and p r o b a b i l i t y p l o t s . A r i t h m e t i c and l o g frequency d i s t r i b u t i o n s f o r t i l l and c o l l u v i u m are shown i n F i g u r e 4-10. Two s e p a r a t e l o g n o r m a l l y - d i s t r i b u t e d Pt p o p u l a t i o n s occur i n n o n - d u n i t i c t i l l ( F i g u r e 4-11), but Pt d i s t r i b u t i o n s i n both d u n i t i c t i l l and c o l l u v i u m approximate s i n g l e lognormal p o p u l a t i o n s . Log frequency d i s t r i b u t i o n s of Cr 203 and Pd i n both t i l l and c o l l u v i u m are shown i n F i g u r e 4-12. CX2O3, u n l i k e MgO, shows a s l i g h t o v e r l a p between d u n i t i c and n o n - d u n i t i c t i l l p o p u l a t i o n s ( F i g u r e 4-7). 0^03 i n d u n i t i c t i l l , l i k e Pt, i s l o g n o r m a l l y d i s t r i b u t e d , w h i l e two separate CX2O3 p o p u l a t i o n s occur i n n o n - d u n i t i c t i l l . C r 203 i n c o l l u v i u m 25 20-£ 1 5 -C <D OJ 10-ARITHMETIC FREQUENCY DISTRIBUTION OF PLATINUM IN TILL (N=44) Esil FM Wm\ ma 0 25 SO 75 100 125 150 175 200 225 250 Z75 300 325 350 375 400 425 450 475 500 Platinum (ppb) 14 12-10-O 8-c a> 2-0 ARITHMETIC FREQUENCY DISTRIBUTION OF PLATINUM IN COLLUVIUM (N=27) 0 5 O l C O 150 2 0 0 2 5 O 3 0 0 3 S 0 4 0 0 4 6 0 5 0 0 5 6 O 6 0 0 6 6 0 7 0 0 7 5 0 8 0 0 a 6 O 9 0 0 Platinum (ppb) 12 10 © 8 >. o <D 6 c r a> i t 4 10 >. 6 o c CD cr , . <D 4 -2 -LOG FREQUENCY DISTRIBUTION OF PLATINUM IN TILL (N=44) Antilog Platinum (ppb) D LOG FREQUENCY DISTRIBUTION OF PLATINUM IN COLLUVIUM (N=27) Antilog Platinum (ppb) Figure 4-10. Arithmetic and log frequency distributions of Pt content (ppb) of overview C horizon soils in: A. and B. Till; and C. and D. Colluvium. PERCENT PARAMETER ESTIMATES F i g u r e 4-11. Log p r o b a b i l i t y p l o t of Pt i n n o n - d u n i t i c t i l l , main study area. Frequency (f) Frequency (f) 3 CO c 3 o co c 3 a 3 (A 3 a CD o 8 8 I 3 > i o CO O O CO i i o a n 3D m O O Q z 2 f 1 if = S i o ro O u 01 3 a O 3 a. p a 8 3 73 T3 a O o 8 5" | c £. c 3 Frequency (f) Frequency (f) eg I Co Q . c" •D cr i s a l s o l o g n o r m a l l y d i s t r i b u t e d (Figure 4-12B). Only i n the case of normal or l o g n o r m a l l y d i s t r i b u t e d p o p u l a t i o n s were upper p o p u l a t i o n s p a r t i t i o n e d on the b a s i s of t he top 2.5 p e r c e n t i l e s ( S i n c l a i r , 1976; Rose e t a l , 1979) ; sometimes on l y a s i n g l e very h i g h v a l u e o c c u r s i n an otherwise lognormal p o p u l a t i o n . The l i m i t e d number of samples i n the secondary study area (8 t i l l , 2 c o l l u v i u m ) , and i t s b i a s e d c l o s e l y - s p a c e d sampling i n r e l a t i o n t o the main study area, p r e c l u d e d the use of p r o b a b i l i t y p l o t s t o d e f i n e p o p u l a t i o n s i n t h i s area. T h r e s h o l d v a l u e s i n t h i s a rea were t h e r e f o r e assigned on the b a s i s of frequency d i s t r i b u t i o n s and ranked data, and were s e l e c t e d t o f a c i l i t a t e comparisons with t i l l data from the main study area. Three upper-population Pt s i n g l e v a l u e s or zones occur i n t he main study area (Figures 4-13 and 4-16A), one w i t h i n each grouping. Three 01:203 ( F i g u r e s 4-14 and 4-16B) and Pd ( F i g u r e s 4-15 ands 4-17) upper-population v a l u e s or zones a l s o occur i n the main study area; the former are g e n e r a l l y c o i n c i d e n t w i t h those d e f i n e d f o r Pt, w h i l e the l a t t e r are not. 137 A-Zone PGE occurrence i • 40 - 60 ppb o 60 - 80 ppb • 8 0 - 1 0 0 p p b • 200 - 500 ppb m 0 100 4877 A t N DUNITIC TILL 1 6 - 3 0 ppb 31 - 40 ppb 41 - 55 ppb > 55 ppb 2 - 9 ppb 1 0 - 1 5 p p b 1 6 - 2 0 p p b Figure 4-13. Pt content (ppb) of overview -70 mesh C horizon soils in A. dunitic till, rubble and colluvium adjacent to PGE mineralization in the secondary study area; and B. in dunitic and non-dunitic till in the main study area; Grasshopper Mountain, B.C. Dashed line at lower centre represents the boundary between dunitic and non-dunitic tills. 138 A-Zone PGE occurrence • 0.10-0.20% o 0.21 - 0.30 % • 0.31 - 0.40 % • > 0.50 % m 0 100 Figure 4-14. Cr203 content (%) of overview -70 mesh C horizon soils In: A. dunitic till, rubble and colluvium adjacent to PGE mineralization at the secondary study area; and B. in dunitic and non-dunitic till in the main study area, Grasshopper Mountain, B.C. Dashed line at lower centre represents the boundary between dunitic and non-dunitic tills. 139 colluvium v A-Zone ~A~ PGE occurrence • 2-4 ppb o' 5-8 ppb • 9-13 ppb • 14-69 ppb m 0 100 4877 A • 2-4 ppb o 5-8 ppb • 9-13 ppb • 14-69 ppb • 2-3 ppb o 4-7 ppb • 8-23 ppb Figure 4-15. Pd content (ppb) of overview -70 mesh C horizon soils in A. dunitic till, rubble and colluvium adjacent to PGE mineralization in the secondary study area; and B. In dunitic and non-dunitic till In the main study area; Grasshopper Mountain, B.C. Dashed line at lower centre represents the boundary between dunitic and non-dunitic tills. 140 I. D u n i t i c t i l l The u p p e r - p o p u l a t i o n Pt s i t e i n d u n i t i c t i l l (311 ppb; F i g u r e 4-13) occurs w i t h i n a W-SW t r e n d of enhanced background Pt v a l u e s which i s g e n e r a l l y c o n f i n e d t o the upper p l a t e a u area. T h i s area has a t h i n t i l l c over which, though more continuous than i n the secondary study area, i s t h i n n e r and c l o s e r t o bedrock than t h a t of many downslope s i t e s w i t h lower Pt c o n c e n t r a t i o n s . There are d i f f e r e n c e s however, i n the s p a t i a l d i s t r i b u t i o n of Pt and Cr2C>3 on a more d e t a i l e d s c a l e . A zone of hig h e r C r 2 0 3 background v a l u e s i n d u n i t i c t i l l i s not c o i n c i d e n t w i t h the zone of h i g h e r P t v a l u e s (Figure 4-14B), but i s i n s t e a d l o c a t e d f a r t h e r downslope t o the southeast. A zone of enhanced d u n i t i c t i l l Pd c o n c e n t r a t i o n s (Figure 4-15), c o m p r i s i n g s e v e r a l c l o s e l y - s p a c e d s i t e s c o n t a i n i n g 10-11 ppb Pd downice from the h i g h e s t C-horizon Pd value (48 ppb), occ u r s approximately midway between the enhanced Pt and C r 2 0 3 zones. The upper-population Pd value i n t h i s area i s one of the few s i t e s where Pt i s subordinate t o Pd. Upper-population Cr 203 val u e s i n t i l l a t the secondary study area ( F i g u r e 4-14) seem t o be much more l o c a l l i z e d than u p p e r - p o p u l a t i o n Pt valu e s (Figure 4-13). T h i s may be r e l a t e d t o the more disseminated nature of A-Zone chromite (Bohme, 1987, 1988) and t o the occurrence of PGM i n Mg-s i l i c a t e s as w e l l as chromite. Upper-population Pd ( F i g u r e 4-15) i s even more l o c a l i z e d ; a s i n g l e v a l u e (36 ppb) occurs w i t h a s i m i l a r Pt value a t the secondary study area, but i s f a r removed from the A-Zone PGE occurrence. Three of the f o u r h i g h e s t t i l l As v a l u e s occur i n the secondary study area. I I . N o n - d u n i t i c t i l l An u p p e r - p o p u l a t i o n Pt zone occurs i n the e a s t s i d e of the n o n - d u n i t i c t i l l , and comprises s u b t l e anomalies which would otherwise be swamped by h i g h e r background v a l u e s f a r t h e r t o the west. Higher Pt v a l u e s c l u s t e r i n g a l o n g the t i l l c o m p o s i t i o n a l boundary probably i n d i c a t e g r a d a t i o n a l mixing w i t h the d u n i t i c t i l l ( Figure 4-13), and are not c o n s i d e r e d anomalous. The same mixing e f f e c t i s a l s o observed w i t h Cr203; an upper-population Cr2C>3 zone on the e a s t s i d e of the n o n - d u n i t i c t i l l i s p a r t i a l l y c o i n c i d e n t w i t h the c o r r e s p o n d i n g Pt zone. With a mean Cr c o n t e n t of 479 ppm, the n o n - d u n i t i c t i l l a p p a r e n t l y c o n t a i n s a t l e a s t a minor d u n i t e component. The t h i r d - h i g h e s t Pd value (15 ppb) occurs i n non-d u n i t i c t i l l , j u s t upslope from two stream bank s i t e s c o n t a i n i n g 65 and 14 ppb Pd. Two bands, i n c l u d i n g one i n the seepage zone area, of i n t e r m e d i a t e - l e v e l Pd c o n c e n t r a t i o n s (open c i r c l e s on F i g u r e 4-15) e n c l o s e an area of b a c k g r o u n d - l e v e l Pd c o n c e n t r a t i o n s i n t h i s a r e a . The 142 h i g h e s t n o n - c o l l u v i a l Au value (34 ppb) a l s o occurs w i t h i n a seepage zone g l e y s o l i c s o i l a t one of these s i t e s ( s o i l s i t e 6). S i g n i f i c a n t l y , the seepage zone area a l s o e x h i b i t s anomalous Sb v a l u e s i n the range 1.2 - 1.8 ppm, 3-6x h i g h e r than the mean Sb contents of other areas upslope (Table 4-4) • I I I . C o l l u v i u m A s i n g l e upper-population c o l l u v i a l sample (885 ppb) p i n p o i n t s the C l i f f Zone PGE occurrence ( F i g u r e 4-16A), although the remainder of the c o l l u v i a l samples do not exceed 185 ppb Pt. I t i s c o i n c i d e n t w i t h an upper-p o p u l a t i o n C r 2 0 3 v a l u e below the C l i f f Zone ( F i g u r e 4-16B); oth e r h i g h - p o p u l a t i o n C r 2 0 3 v a l u e s i n c o l l u v i u m are not r e l a t e d t o any known anomalous bedrock Pt v a l u e s . The C l i f f Zone C r 2 0 3 anomaly, however, extends c o n s i d e r a b l y f u r t h e r downslope than does the more l o c a l i z e d Pt anomaly. The uppermost Pd p o p u l a t i o n i n c o l l u v i u m i s v e r y s u b t l e (4-5 ppb), and i s l o c a t e d both above and below C l i f f Zone PGE m i n e r a l i z a t i o n (Figure 4-17). High Au v a l u e s o f up t o 54 ppb are found i n s e r p e n t i n i z e d c o l l u v i u m , although the h i g h e s t (56 ppb) occurs beneath C l i f f Zone Pt m i n e r a l i z a t i o n . Some of the h i g h e s t As v a l u e s a l s o occur i n c o l l u v i a l s o i l s immediately beneath the C l i f f Zone Pt A Figure 4-16. Distribution of A. Pt (ppb); and B. Cr203 (%) in C horizon colluvium, main study area (n=25), Grasshopper Mountain, B.C. (basemap adapted from Bohme, 1987). Figure 4-17. Distribution of Pd (ppb) in C horizon colluvium, main study area (n=25), Grasshopper Mountain, B.C. (basemap adapted from Bohme, 1987). •9 o c c u r r e n c e s , w h i l e some of the lowest c o l l u v i a l As v a l u e s are a s s o c i a t e d w i t h Pt-poor areas. d) Regional Dispersion of Platinum Background C h o r i z o n t i l l samples were c o l l e c t e d from 5 s i t e s on the n o r t h e r n margin and t o the west of the d u n i t e c o r e of the Tulameen complex t o assess g l a c i a l t r a n s p o r t and r e g i o n a l d i s p e r s i o n of Pt ( s e c t i o n 3.2.2). S i t e l o c a t i o n s on Grasshopper Mountain and Mount B r i t t o n are shown i n F i g u r e 4-18 along with Pt, Pd, MgO and Cr 203 c o n c e n t r a t i o n s of C h o r i z o n s o i l s . Only one s i t e , 402, i s a c t u a l l y s i t u a t e d above the d u n i t e c o r e . Regarding the others, i t i s apparent t h a t c o n c e n t r a t i o n s of these elements i n C h o r i z o n s o i l s a t s i t e s 403 and 404 are g e n e r a l l y s i m i l a r t o those d e f i n e d f o r non-d u n i t i c t i l l w i t h i n the main study area. R e l a t i v e l y h i g h MgO c o n t e n t s i n t e r m e d i a t e between those of the two t i l l t y p e s (Table 4-3) suggest some degree of t i l l mixing, however. Conversely, Pt, MgO and C r 2 0 3 c o n c e n t r a t i o n s a t s i t e s 405 and 406 are s i m i l a r t o those d e f i n e d f o r main study area d u n i t i c t i l l . Pt c o n c e n t r a t i o n s are s i m i l a r t o those on the p l a t e a u of Grasshopper Mountain ( F i g u r e 4-13). S i m i l a r l y , Cr 203 c o n c e n t r a t i o n s equal or exceed those a t most main study area s i t e s on Grasshopper Mountain ( F i g u r e 146 402 Pt 20 Pd 12 MgO 10.19 C r2°3 .15 7 Eagle granodiorite 5 Hornblende clinopyroxenite 2 Syenogabbro 6 Mylonitic rocks 4 Olivine clinopyroxenite 1 Nicola Group 3 Dunite 0 1 km ' Figure 4-18. Concentrations of selected elements in background till samples on the northern margin and to the west of the dunite core of the Tulameen ultramafic complex. Solid lines indicate distribution of dunitic till. Pt and Pd concentrations in ppb; MgO and Cr203 concentrations in % (modified after Nixon and Rublee, 1988). 4-14). Based on these r e s u l t s and those of p a r t a) of t h i s s e c t i o n , s o l i d dark l i n e s i n F i g u r e 4-18 show the p o s s i b l e d i s t r i b u t i o n l i m i t s of d u n i t i c t i l l i n the Grasshopper Mountain-Mount B r i t t o n area. L a t e r f l u v i o g l a c i a l outwash i n the B r i t t o n Creek v a l l e y and p o s t - g l a c i a l c o l l u v i u m on Grasshopper Mountain are not shown. 4.2.1.3 X-Ray D i f f r a c t i o n Mineralogy R e s u l t s The mineralogy of 48 s o i l f r a c t i o n s , c o m p r i s i n g both c o a r s e -10+40 mesh (2mm-425um) and f i n e -270 mesh (<53um) f r a c t i o n s from 24 h o r i z o n s i n 11 p r o f i l e s , was determined by X-ray d i f f r a c t i o n ( s e c t i o n 3.8). R e s u l t s are summarized i n F i g u r e 4-19, and shown i n Appendices 6.1 t o 6.3 on the b a s i s of s o i l parent m a t e r i a l . Twenty-three m i n e r a l s were i d e n t i f i e d , i n c l u d i n g two s e r p e n t i n e m i n e r a l s , t h r e e c h l o r i t e s , two micas, two c l a y m i n e r a l s and t h r e e amphiboles. a) Non-Dunitic T i l l Horizons i n both n o n - d u n i t i c t i l l p r o f i l e s (Appendix 6.1) c o n t a i n q u a r t z , p l a g i o c l a s e , f e r r o hornblende and c l i n o c h l o r e . Serpentine group or other m i n e r a l s i n d i c a t i v e of an u l t r a m a f i c o r i g i n are absent a t s i t e 20, alth o u g h 148 c h r y s o t i l e o ccurs a t s i t e 6. There are no major m i n e r a l o g i c a l v a r i a t i o n s with e i t h e r p a r t i c l e s i z e or h o r i z o n . b) Dunitic T i l l Serpentine-group m i n e r a l s , p a r t i c u l a r l y c h r y s o t i l e , are u b i q u i t u o u s i n s o i l h o r i z o n s of s i x d u n i t i c t i l l p r o f i l e s (Appendices 6.1 and 6.2). T a l c and v e r m i c u l i t e are l o c a l l y important, but f o r s t e r i t i c o l i v i n e i s r e l a t i v e l y uncommon. Quartz and p l a g i o c l a s e occur a t most s i t e s . L i z a r d i t e r a t h e r than c h r y s o t i l e i s the dominant s e r p e n t i n e m i n e r a l i n the deepest sample d i r e c t l y above A-Zone Pt m i n e r a l i z a t i o n , although the two are d i f f i c u l t t o d i s t i n g u i s h . T a l c and v e r m i c u l i t e are l o c a l l y more dominant than c r y s o t i l e i n f i n e f r a c t i o n s , p a r t i c u l a r l y a t depth. T a l c - b e a r i n g s o i l s ( s i t e s 33, 73, 57) occur i n both main and secondary study areas, but v e r m i c u l i t e - b e a r i n g s o i l s are r e s t r i c t e d t o the p l a t e a u s i t e s (69, 73). C h r y s o t i l e i s a more common c o n s t i t u e n t of coarse f r a c t i o n s a t these s i t e s . M i n eralogy a t s i t e 43 ( s e c t i o n 2.5.2) d i f f e r s d r a m a t i c a l l y between the upper two (reworked t i l l ) and lower two (lodgement t i l l ) h o r i z o n s . Near-surface h o r i z o n s c o n t a i n f o r s t e r i t e , c h r y s o t i l e , quartz and p l a g i o c l a s e i n a l l f r a c t i o n s . The two lower h o r i z o n s , however, c o n s i s t of 149 q u a r t z w i t h l e s s e r p l a g i o c l a s e , s a p o n i t e (Mg-smectite) and g o n y e r i t e (Mn-Mg c h l o r i t e ) . D e t e c t a b l e chromite o c c u r s a t s i t e s 69, 56 and 57. Coo p e r i t e (PtS) was i d e n t i f i e d a t s i t e 73 i n the coarse f r a c t i o n of the Bm h o r i z o n . T h i s , t h e o n l y PGM d e t e c t e d by XRD, was confirmed i n a second e v a l u a t i o n . The C h o r i z o n a t t h i s s i t e c o n tained 311 ppb Pt, one of the h i g h e s t ( F i g u r e 4-13B) of the overview a n a l y s e s . c) Dunite Colluvium C o l l u v i a l s o i l p r o f i l e s beneath d u n i t e c l i f f s a r e c h a r a c t e r i z e d by a l i m i t e d mineralogy of s e r p e n t i n e group m i n e r a l s and t a l c , and the absence of o l i v i n e , q u a r t z , p l a g i o c l a s e and amphiboles (Appendix 6.3). There are important m i n e r a l o g i c a l d i f f e r e n c e s between " d u n i t i c c o l l u v i u m " ( s i t e 16) and "s e r p e n t i n e c o l l u v i u m " ( s i t e s 27 and 42), c h a r a c t e r i z e d by orange-coloured s o i l . L i z a r d i t e i s t he dominant m i n e r a l and s o l e s e r p e n t i n e group c o n s t i t u e n t of d u n i t i c c o l l u v i u m . L i z a r d i t e i s a l s o the dominant m i n e r a l , p a r t i c u l a r l y i n co a r s e f r a c t i o n s , of the th r e e samples from s e r p e n t i n e c o l l u v i u m a t s i t e 27. T a l c , however, i s an important c o n s t i t u e n t of the f i n e f r a c t i o n s . S i t e 42 e x h i b i t s the most i n t e n s e orange c o l o u r a t i o n of c o l l u v i u m p r o f i l e s . C r y s o t i l e and t a l c are the dominant m i n e r a l s and l i z a r d i t e 150 Figure 4-19. Schematic diagram illustrating the general relation of MgO content to soil mineralogy in surficial materials on Grasshopper Mountain (11 profiles). i s absent. F i n e f r a c t i o n s of s o i l s a t both s i t e s are dominated by t a l c . 4.2.2 LFH Horizons LFH h o r i z o n s were analyzed f o r Pt-Pd-Au-Rh by Pb f i r e assay w i t h an ICP-AES f i n i s h , and subsequently f o r Fe by F-AAS (see s e c t i o n 3.4). Pt and Fe content of LFH h o r i z o n s ( F i g u r e 4-20; Appendix 7) are summarized by parent m a t e r i a l type i n T a b l e 4-7. R e s u l t s are summarized as f o l l o w s : Weight % ash (remnant a f t e r ashing) content of almost a l l LFH samples l i e s i n the range 5-24 %. I t e x h i b i t s no obvious t r e n d s a c r o s s the study areas ( F i g u r e 4-21). LFH h o r i z o n s on a c t i v e c o l l u v i u m , however, have a c o n s i d e r a b l y g r e a t e r ash content (21.96%) than those on t i l l . Pt c o n tent g e n e r a l l y i n c r e a s e s g r a d u a l l y from s o u t h e a s t t o northwest a c r o s s the study area (Figure 4-22) i n much the same manner as C-horizon s o i l s . C o n c e n t r a t i o n s are low and e r r a t i c however, and are g e n e r a l l y l e s s than 20 ppb on t i l l s i n t he main study area. Median Pt c o n c e n t r a t i o n s over c l a y , n o n - d u n i t i c t i l l and d u n i t i c t i l l C-horizons i n the main study area are 4 ppb, 7 ppb and 12.5 ppb, r e s p e c t i v e l y . The g r e a t e s t Pt v a l u e s i n LFH h o r i z o n s on n o n - d u n i t i c t i l l occur i n the southeast p a r t of the study area near the base of the 25 20 &15 CZ CD 110 ARITHMETIC F R E Q U E N C Y DISTRIBUTION OF PLATINUM (PPB) IN A S H E D L F H H O R I Z O N S (N=47) 0 5 15 25 35 45 55 65 75 85 95 105 115 125 135 145 155 165 170 Platinum (ppb) B ARITHMETIC F R E Q U E N C Y DISTRIBUTION O F IRON (%) IN A S H E D L F H H O R I Z O N S (N=38) .50 1.00 1.50 2.00 2.50 3.00 Iron (%) 3.50 4.00 4.50 5.00 Figure 4-20. Arithmetic frequency distributions of A. Pt (ppb) and B. Fe (%) in LFH horizon ash. Overburden n Pt Pd Au Weight LFH/C Fe* Insoluble (ppb) (ppb) (ppb) Ash (%) Pt (%) Residue* Ratio (%) Clay 4.0 4 1 7 4.5 4 . 5 2 7 10 10 10 10 7.94 7 . 9 4 7.71 8.16 0.63 0 . 6 3 0.25 1.00 2.70 2 . 7 0 1.62 3.78 8.0 8 . 0 6.0 10.00 Non-Dun i t i c T i l l 19 7.6 7 2 18 4.5 3 2 19 8.8 7 3 46 14.37 1 3 . 9 0 5.84 37.67 1.17 0 . 8 0 0.11 3.50 2.14 1.78 1.03 3.67 10.1 8 .0 0.0 32.0 Dun i t i c T i l l 16 14.0 1 2 . 5 6 32 2 . 0 2 2 2 3.1 2 . 5 1 9 13.54 1 1 . 4 5 7.07 21.59 0.37 0 . 3 6 0.06 0.71 1.52 1.46 0.38 3.00 4.7 4 . 0 0.0 12 . 0 Dunitic 7 T i l l / R u b b l e / Colluvium (A-Zone) 104. 122 9 167 2.7 2 2 5 6.1 6 3 9 12.33 11 .34 5.54 23.35 1.14 1.36 0.12 2.29 3.64 3 .62 2.83 4.11 15.8 1 4 . 0 7.0 36.0 Dunite Colluvium 85.0 65 49 141 11.3 13 4 17 22.62 2 1 . 9 6 8.87 37.03 0.72 0 . 7 6 0.56 0.83 4.58 4 . 5 8 4.33 4.83 18.0 1 8 . 0 18.0 18.0 Table 4-7. Mean, median, minimum value and maximum value of Pt, Pd, Au, weight percent ash, LFH/C horizon Pt r a t i o , Fe, and percent insoluble residue i n LFH horizon samples. N=47 f o r a l l v a r i a b l e s except those marked with an *, i n d i c a t i n g sample si z e s (n=38) of clay, n=2; non-dunitic t i l l , n=14; d u n i t i c t i l l , n=15; A-Zone, n=5; dunite colluvium, n=2. Co LFH HORIZONS: Platinum (ppb) and Weight Percent Ash Above Various Soil Parent Materials Figure 4-21. Relation of Pt (ppb) to weight percent ash in LFH horizons above various soil parent materials on Grasshopper Mountain. Figure 4-22. Pt distribution (ppb) In LFH horizons (n=47) of A. the secondary study area and B. the main study area on Grasshopper Mountain. 156 southern f o r e s t e d s l o p e (Figure 4-22), whereas the g r e a t e s t Pt v a l u e s i n LFH h o r i z o n s on d u n i t i c t i l l occur on the p l a t e a u . S e v e r a l LFH h o r i z o n s i n the d u n i t i c t i l l a r e a are developed d i r e c t l y above s t a b i l i z e d d u n i t e c o l l u v i u m . Pt content of LFH h o r i z o n s i n c r e a s e s d r a m a t i c a l l y above c o l l u v i u m and i n the secondary study area ( F i g u r e 4-22). LFH h o r i z o n s on d u n i t i c t i l l , r u b b l e and s t a b i l i z e d c o l l u v i u m adjacent t o the A-Zone occurrence i n the secondary study area have a median Pt c o n c e n t r a t i o n of 122 ppb, almost lOx g r e a t e r than those developed on d u n i t i c t i l l i n the main study area. High Pt c o n c e n t r a t i o n s of up t o 167 ppb appear to r e f l e c t u n d e r l y i n g PGE m i n e r a l i z a t i o n , but are a p p a r e n t l y v e r y l o c a l i z e d ; a s i n g l e s i t e 125 m downice from the t r e n c h e d A-Zone occurrence has an LFH Pt content of o n l y 9 ppb ( F i g u r e 4-22). Fe content of LFH h o r i z o n ash, determined t o e v a l u a t e l i t h i c contamination by u n d e r l y i n g d u n i t e or t i l l , ranges from 0.38 t o 4.83%. I t i s bimodally d i s t r i b u t e d i n t o h o r i z o n s c o n t a i n i n g < 2.4% Fe and those c o n t a i n i n g 3-5% Fe ( F i g u r e 4-20B). LFH h o r i z o n s above d u n i t e c o l l u v i u m and ad j a c e n t t o A-Zone Pt m i n e r a l i z a t i o n have much h i g h e r median Fe c o n t e n t s than do those on e i t h e r d u n i t i c or n o n - d u n i t i c t i l l (Table 4-7). LFH c o r r e l a t i o n m a t rices (Figure 4-23) show t h a t 157 s i g n i f i c a n t c o r r e l a t i o n s e x i s t , among o t h e r s , between Pt and Fe, between Pt content of the LFH h o r i z o n and t h a t of the u n d e r l y i n g C h o r i z o n s o i l , and between Pt and i n s o l u b l e r e s i d u e . C o r r e l a t i o n s between Pt and Fe are p a r t i c u l a r l y e v i d e n t i n those LFH h o r i z o n s developed on d u n i t i c t i l l , A-Zone t i l l / r u b b l e , and c o l l u v i u m ( F i g u r e 4-24A). S i g n i f i c a n t c o r r e l a t i o n s between Pd and Au, c o n c e n t r a t i o n s of both of which are sub o r d i n a t e t o Pt i n most LFH h o r i z o n s (Table 4-7), a re l a r g e l y due t o a few h i g h - c o n c e n t r a t i o n samples. LFH Pt and Pd do not e x h i b i t sympathetic r e l a t i o n s above any type of u n d e r l y i n g s u r f i c i a l m a t e r i a l w i t h the p o s s i b l e e x c e p t i o n of n o n - d u n i t i c t i l l ( F i g ure 4-24B). The sympathetic i n c r e a s e i n LFH Pt content w i t h t h a t of the u n d e r l y i n g C h o r i z o n i s shown i n F i g u r e 4-25. Pt content of the LFH h o r i z o n i s g e n e r a l l y l e s s than t h a t of the C h o r i z o n . Frequency d i s t r i b u t i o n s of the LFH/C Pt r a t i o s are shown i n F i g u r e 4-26. D u n i t i c t i l l r a t i o s c o n s i s t e n t l y p l o t below 1, i n d i c a t i v e of low LFH Pt co n t e n t r e l a t i v e t o the C h o r i z o n . E r r a t i c r a t i o s both g r e a t e r and l e s s than l are present, however, a t s i t e s on n o n - d u n i t i c t i l l and on A-Zone t i l l , r u b b l e and c o l l u v i u m . The s p a t i a l d i s t r i b u t i o n of LFH/C h o r i z o n P t r a t i o s on Grasshopper Mountain i s shown i n F i g u r e 4-27. S i t e s w i t h r a t i o s > 1 are g e n e r a l l y l o c a t e d on or near breaks i n s l o p e . Main study area h i g h - r a t i o s i t e s are c l u s t e r e d i n the 158 PT PD AU P T - C WT%ASH PT 1 . 0 0 0 0 0 PD - . 0 7 2 9 3 1 . 0 0 0 0 0 AU . 0 5 6 5 3 . 7 4 8 0 7 1 . 0 0 0 0 0 P T - C . 6 3 7 9 0 - . 0 8 7 0 9 - . 0 5 8 3 7 1 . 0 0 0 0 0 WT%ASH . 1 8 8 2 7 - . 0 7 3 5 0 - . 1 4 2 3 5 . 0 3 5 5 5 1 . 0 0 0 0 0 C R I T I C A L V A L U E ( 1 - T A I L , . 0 5 ) = + Or - . 2 4 3 0 6 C R I T I C A L V A L U E ( 2 - t a i l , . 0 5 ) = + / - . 2 8 7 2 3 N = 47 Figure 4 - 2 3 A . LFH c o r r e l a t i o n matrix for Pt, Pd, Au, Pt (C horizon) and weight percent ash (n=47) PT PD AU P T - C WT%ASH FE %R PT 1 . 0 0 0 0 0 - . 0 3 7 9 4 . 0 6 7 4 0 . 5 7 7 1 4 . 2 4 3 1 7 . 6 4 1 2 6 . 4 4 6 7 2 PD . 0 0 0 0 0 , 7 7 6 5 1 . 0 5 0 1 7 . 0 9 8 6 5 . 12714 . 1 5 0 0 2 AU , 0 0 0 0 0 , 0 5 1 5 5 , 1 1 6 6 7 , 1 0 7 4 1 , 1 0 4 3 1 P T - C . 00000 .09079 ,39766 .11577 WT%ASH . . 0 0 0 0 0 . 2 7 1 9 9 . 3 2 4 4 9 FE %R 1 . 0 0 0 0 0 . 6 3 9 8 7 1 . 0 0 0 0 0 C R I T I C A L V A L U E ( 1 - T A I L , . 0 5 ) = + Or - . 2 7 1 1 4 C R I T I C A L V A L U E ( 2 - t a i l , . 0 5 ) = + / - . 3 1 9 7 5 N = 38 Figure 4 - 2 3 B . LFH c o r r e l a t i o n matrix for Pt, Pd, Au, Pt (C horizon), weight percent ash, Fe and percent insoluble residue (n=38) . B E .2 10 H •o CO [] PLATINUM (PPB) VERSUS PALLADIUM (PPB) IN ASHED LFH HORIZONS (N=47) O o o •o o o o o o oo o o • mt Underlying Surficial Material Clay • Non-dunitic Till O Dunitic Till • A-Zone T^ ll/Rubble Colluvium r=-0.0729 10 20 50 Platinum (ppb) 100 200 500 Figure 4-24. Scatterplots of Pt (ppb) versus A. Fe (%) and B. Pd (ppb) in ashed LFH horizons above various parent materials. 160 1 2 5 10 20 50 100 200 500 Pt in C horizon soil (ppb) Figure 4-25. Scatterplot of Pt concentrations (ppb) of C horizon soils from various parent materials versus ash from corresponding LFH horizons. Points plotting above the unity line have LFH/C horizon Pt ratios of > 1. 10 8 u. 4 0 LFH/C > 1 Non-Dunitic Till LFH/C < 1 Dunitic Till A-Zone Dunitic Till, / \ Rubble and Colluvium .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 LFH/C Horizon Pt Ratio Figure 4-26. Frequency distributions of LFH/C horizon Pt ratios for non-dunitic till (n=19), dunitic till (n=16), and A-Zone dunitic till, rubble and colluvium (n=7). 161 Figure 4-27. Distribution of LFH horizon/C horizon Pt ratios on Grasshopper Mountain. Solid dashed line at lower centre represents the boundary between dunitic and non-dunitic tills. The majority of the high-ratio soil sites are located in or near the seepage zone area in non-dunitic till. WEIGHT P E R C E N T I N S O L U B L E RESIDUE (0.50 G S A M P L E ) V E R S U S PLATINUM (PPB) IN A S H E D L F H H O R I Z O N S (N=38) o o o o o o o r=0.4467 Underlying Parent Materials Clay • Non-dunitic Till O Dunitic Till • A-Zone T l^l/Rubble Colluvium O -6, 1 , 1 r-10 20 30 Insoluble Residue (Weight %) 40 WEIGHT P E R C E N T I N S O L U B L E RESIDUE V E R S U S IRON IN A S H E D L F H H O R I Z O N S (N=38) • O : § § 8 • O o o r=0.6399 O Underlying Parent Materials Clay D Non-dunitic Till O Dunitic Till • A-Zone T l^l/Rubble Colluvium 10 20 30 40 Insoluble Residue (Weight %) Figure 4-28. Scatterplots of weight percent insoluble residue versus A. Pt (ppb) and B. Fe (%); in ashed LFH horizons above various parent materials. 163 seepage zone/southern f o r e s t e d s l o p e area above n o n - d u n i t i c t i l l , w h i l e the h i g h e s t r a t i o i n the secondary study area i s immediately downslope of the A-Zone PGE o c c u r r e n c e . Most LFH h o r i z o n ashes c o n t a i n about 2-18% i n s o l u b l e r e s i d u e (Table 4-7; Appendix 7), comprising carbon or m i n e r a l matter, f o l l o w i n g a c i d d i g e s t i o n (see s e c t i o n 3.3.2). Median p r o p o r t i o n s of i n s o l u b l e r e s i d u e (Table 4-7) i n LFH ash from a c t i v e c o l l u v i u m and the secondary study area are c o n s i d e r a b l y h i g h e r than those from t i l l s i t e s i n the main study area. S i g n i f i c a n t c o r r e l a t i o n s e x i s t between weight % i n s o l u b l e r e s i d u e and weight % ash, Pt c o n t e n t ( F i g u r e 4-28A), and Fe content (Figure 4-28B), i n d i c a t i n g t h a t the Pt content of the LFH i s c l o s e l y a s s o c i a t e d w i t h p a r t i c u l a t e m i n e r a l matter. 4.2.3 Stream Sediments, Moss mats and Banks Stream sediment, moss mat and bank samples were c o l l e c t e d along Grasshopper Creek ( s e c t i o n 3.2.3) and a n a l y z e d f o r the overview s u i t e of elements. The d i s t r i b u t i o n of Pt, Pd and Au i n both stream sediments and moss mats (Appendix 8.1) i s shown i n F i g u r e 4-29. Pt c o n t e n t s of d i f f e r e n t s i z e / d e n s i t y / m a g n e t i c f r a c t i o n s ( s e c t i o n 3.3.5) of sediment from s i t e 2 are shown i n F i g u r e 4-30. 8 Pt Pd Au Moss mat 23 24 1 Sediment 32 5 6 Pt Pd Au Moss mat - - -Sediment 91 2 5 6 Pt Pd Au Moss mat - -Sediment 20 7 6 m 300 Moss mat Sediment Pt Pd Au 11 4 19 8 3 2 Moss mat Sediment Pt Pd Au - - -11 2 3 Sediment N Pt Pd Au 8 2 29 78 2 239 Pt Pd Au 17 3 15 18 2 2 Figure 4-29. Pt, Pd, and Au contents (ppb) of stream sediments and moss mats at eight sampling sites along Grasshopper Creek on Grasshopper Mountain, B.C. Pt content (ppb) of bank samples at sites 1 -4 are shown adjacent to the site marker. Stream sites are the same as those shown for water samples in Figure 4-33. Grasshopper Creek i s s i t u a t e d e n t i r e l y on the d u n i t e core of the Tulameen complex (Figure 2-1), but a t lower e l e v a t i o n s flows o n l y through u n c o n s o l i d a t e d overburden, mostly t i l l , of mixed d u n i t i c and n o n - d u n i t i c o r i g i n . Sample weight data f o r sediments and moss mats i s shown i n Appendix 8.2. The p r o p o r t i o n of f i n e -70 mesh (<212 um) sediment, as weight % of the -10 mesh (<2mm) f r a c t i o n , i s c o n s i s t e n t l y g r e a t e r , by up t o 4x a t some s i t e s , i n moss mats (Table 4-8). The s i z e f r a c t i o n d i s t r i b u t i o n o f P t a t s i t e 2 has Pt content i n c r e a s i n g w i t h d e c r e a s i n g p a r t i c l e s i z e ( F i g u r e 4-30A). Pt c o n c e n t r a t i o n s i n sediments and moss mats are g e n e r a l l y s i m i l a r t o , or s l i g h t l y g r e a t e r than, those i n ad j a c e n t C h o r i z o n s o i l s and appear t o p a r t l y r e f l e c t l o c a l v a r i a t i o n s i n stream g r a d i e n t . Data i s l i m i t e d , but lower Pt c o n c e n t r a t i o n s occur where the g r a d i e n t i s g e n t l e o r steep, w h i l e h i g h e r c o n c e n t r a t i o n s occur a t break of s l o p e areas ( F i g u r e 4-31). Sediments g e n e r a l l y have h i g h e r Pt co n t e n t s (range: 8-91 ppb) than do moss mats (range: 8-47 ppb). The d i f f e r e n c e s a t most s i t e s are u s u a l l y s m a l l (Table 4-8), but Pt i n sediment (78 ppb) i s 4-10 x g r e a t e r than i n moss mats (8/17 ppb) a t the most s i g n i f i c a n t break of s l o p e on the creek ( s i t e 2). Pt i s most abundant i n the -70+140 mesh heavy magnetic f r a c t i o n (361 ppb), w i t h the p r o p o r t i o n of non-magnetic a s s o c i a t e d Pt i n c r e a s i n g w i t h d e c r e a s i n g g r a i n s i z e ( F igure 4-30B). Pt i n Pt i n -70# -70# Stream S i t e Sediment Moss-mat Sediment Moss-mat Topography (ppb) (ppb) (%) (%) 1 18 17 10.7 40.7 L 2 78 8 (17) 9.5 3 6.3 B 3 11 (12) - 25.2 - M 4 8 11 20.2 25.5 M 5 53 47 18.1 41.8 G 6 20 - 26.7 - G 7 91 - 33.6 - B 8 32 23 51.6 75.6 B L=Level t o g e n t l e S i t e 8 i s f a r t h e s t upstream B=Break of s l o p e G=Gentle s l o p e -70#(mesh) as Wt.% of -10 mesh M=Moderate s l o p e T a b l e 4-8. Weight percent -70 mesh f r a c t i o n and P t con t e n t of stream sediments and moss mats, Grasshopper Creek, Grasshopper Mountain, B.C. 167 88-SC-503 L w c o o CD CD N CO 10 15 Platinum (ppb) Size Fractions | -10 + 40 • -40+70 jll -70 + 140 [15 -140+270 E l "270 20 25 -70+140 -140+270 100 200 Platinum (ppb) • -70+140 L • -70+140 H B Mag HMC Wi NonMagHMC • -140+270L El -140+270H • Mag HMC 13 NonMagHMC 300 400 Figure 4-30. Pt distribution (ppb) in A. five size fractions and B. light, heavy, heavy magnetic and heavy non-magnetic mineral fractions of the -70+140 and -140+270 mesh size fractions, stream sediment site 2, Grasshopper Creek. Figure 4-31. Pt (ppb) and Cr203 (%) content of sediments and moss mats at eight sites on Grasshopper Creek. 169 Cr2C>3 content of sediments ranges from 0.10-0.35%; MgO cont e n t from 6.25-13.04%. MgO c o n c e n t r a t i o n s i n both sediments and moss mats g e n e r a l l y i n c r e a s e upstream i n t o areas of d u n i t i c t i l l . 0 ^ 0 3 t r e n d s vary w i t h the medium; c o n c e n t r a t i o n s i n sediments i n c r e a s e downstream, w h i l e those i n moss mats are r e l a t i v e l y constant ( F i g u r e 4-31). 0 ^ 0 3 and MgO c o n c e n t r a t i o n s are g r e a t e r i n sediments than i n moss mats a t f o u r out of f i v e s i t e s , w i t h the d i f f e r e n c e s b e i n g p r o p o r t i o n a l l y g r e a t e s t f o r ( ^ 2 0 3 . Pt c ontent of bank samples a t f i v e s i t e s ( F i g u r e 4-29; Appendix 8.3) v a r i e s from 7-33 ppb. A l l f i v e s i t e s a re s i t u a t e d w i t h i n n o n - d u n i t i c t i l l ( F i g u r e s 4-1 and 4-13) and t h e r e i s a g e n e r a l , i f somewhat e r r a t i c , tendency f o r the Pt cont e n t t o i n c r e a s e upstream toward the area of d u n i t i c t i l l . Low MgO and Cr203 contents of the banks are c o n s i s t e n t w i t h t h i s i n t e r p r e t a t i o n . Pd and Au contents of sediments and moss mats are low r e l a t i v e t o Pt (Appendix 8.1) but vary c o n s i d e r a b l y w i t h the medium. Pd content of sediments (maximum: 7 ppb) i s v e r y low w h i l e t h a t of moss mats (maximum: 41 ppb) a t two s i t e s i n the upper d u n i t i c t i l l p a r t of the creek are 5-2Ox g r e a t e r than i n corresponding sediments ( F i g u r e 4-29). There are no obvious d i f f e r e n c e s i n the Au co n t e n t of moss mats versus sediments on the upper h a l f of the creek where water flow i s the l e a s t . However, i n the lower h a l f of the creek Au i s e n r i c h e d 7-9x i n moss mats r e l a t i v e t o sediments a t two s i t e s on l e v e l / g e n t l e and moderately steep s l o p e s ( F i g u r e 4-29). Conversely, Au i s 8x more abundant i n sediments (239 ppb) than moss mats a t the h i g h - P t base of s l o p e s i t e . Au, l i k e Pt, content of t h i s sediment i n c r e a s e s w i t h d e c r e a s i n g p a r t i c l e s i z e , and very h i g h Au c o n c e n t r a t i o n s (1659 ppb) occur i n the -140+270 mesh heavy non-magnetic f r a c t i o n . 4.2.4 Bogs Separate s p l i t s of c e n t r e and margin o r g a n i c sediments from t h r e e bogs (Figure 3-1) were e i t h e r p u l v e r i z e d or ashed ( s e c t i o n 3.3.4), p r i o r t o Pb-FA/ICP-AES a n a l y s i s . Pt c o n c e n t r a t i o n s are shown i n F i g u r e 4-32; Pt, Pd, Rh and Au c o n c e n t r a t i o n s i n Appendix 9. Sample weight and ashing data (Appendix 9) show t h a t the Loss On I g n i t i o n (LOI) content of u n p u l v e r i z e d bog s p l i t s ashed a t UBC are almost i d e n t i c a l t o those determined on p u l v e r i z e d bog s p l i t s a t Acme Labs. However, perched bog 3 i n the secondary study area has lower LOI v a l u e s (65.9-67.4%) than the l a r g e seepage area bog 1 (84.1-93.1%). 171 Perched bog 3 a l s o e x h i b i t s almost i d e n t i c a l LOI v a l u e s a t bog c e n t r e and margin s i t e s , whereas LOI v a l u e s a t seepage zone bog 1 decrease from the c e n t r e t o the upslope margin where the p r o p o r t i o n of mi n e r a l matter i s g r e a t e s t . Weight % ash content of o r g a n i c bog s o i l s are g e n e r a l l y s i m i l a r t o those o f LFH h o r i z o n s (Table 4-7), p a r t i c u l a r l y i n the l a r g e seepage zone bog. The perched bog c o n t a i n s a somewhat g r e a t e r p r o p o r t i o n of po s t - a s h i n g m i n e r a l matter, however, than do nearby LFH h o r i z o n s . High Pt c o n c e n t r a t i o n s i n ashed samples (maximum: 67 ppb) are 2-17x g r e a t e r than i n corresponding p u l v e r i z e d samples (maximum: 21 ppb), r e f l e c t i n g the c o n c e n t r a t i o n of Pt d u r i n g the ashing process. Reconstructed dry weight P t c o n c e n t r a t i o n s f o r ashed samples, obtained by m u l t i p l y i n g t h e P t v a l u e by the weight % ash content, are i n v a r i a b l y w i t h i n 1-2.5 ppb of t h a t of the p u l v e r i z e d s p l i t and i n d i c a t e t h a t Pt i s not l o s t d u r i n g ashing. Two bogs i n the lower seepage-zone p a r t of the main study area c o n t a i n up t o 9 ppb Pt i n p u l v e r i z e d s p l i t s , c o n c e n t r a t i o n s s i m i l a r t o those on nearby s o i l s on n o n - d u n i t i c t i l l . Perched bog 3 on d u n i t e bedrock and t h i n d i s c o n t i n u o u s t i l l i n the secondary study area c o n t a i n s up t o 21 ppb Pt i n the p u l v e r i z e d s p l i t and 55 ppb i n the ashed s p l i t . An i n t e r e s t i n g r e l a t i o n i s the a s s o c i a t i o n o f h i g h e r Pt c o n c e n t r a t i o n s w i t h samples from bog margins as opposed t o 172 PLATINUM C O N T E N T (PPB) O F O R G A N I C B O G SOILS: Pulverized versus A s h e d Subsamples | j Centre: Pulverized Centre: Ashed [71 Margin: Pulverized fvv] Margin: Ashed Bog 1 Large seepage zone bog in non-dunitic till Bog 2 Small seepage zone bog in non-dunitic till Bog 3 Perched bog in dunite bedrock near A-Zone PGE occurrence Figure 4-32. Pt contents (ppb) of pulverized and ashed organic bog soils in three Grasshopper Mountain bogs. bog c e n t r e s . T h i s i s p a r t i c u l a r l y t r u e f o r the p u l v e r i z e d s p l i t s from bog margins, which c o n t a i n 2-3x as much Pt as do c o r r e s p o n d i n g bog c e n t r e s . The r e l a t i o n a l s o h o l d s f o r ashed s p l i t s of perched bog 3, but not f o r seepage zone bog 1, where Pt contents of margin and c e n t r e ashed samples are almost i d e n t i c a l . P u l v e r i z e d bog samples a l s o c o n t a i n up t o 4.1 ppm Sb (Appendix 9), wi t h the h i g h e s t v a l u e s o c c c u r r i n g i n seepage zone samples. These are more than 6x h i g h e r than the median Sb c o n t e n t of s o i l s developed on t i l l and c o l l u v i u m , and are more than 2x g r e a t e r than the h i g h e s t Sb c o n c e n t r a t i o n i n seepage zone s o i l s . 4.2.5 Waters The Pt content of Grasshopper Mountain water samples a f t e r f i e l d f i l t r a t i o n t o < 0.45 um i s very low, but i n c r e a s e s i n the order (Table 4-9): stream waters — > seepage zone waters — > p l a t e a u bog waters Stream waters were c o l l e c t e d from the same s i t e s as the sediments ( F i g u r e s 4-29 and 4-33). They almost always c o n t a i n l e s s than 1 ppt Pt (Appendix 10) w i t h a mean Pt content of o n l y 0.81 ppt (Table 4-9). Waters from seepage 174 Figure 4-33. Pt content (parts per trillion) of filtered (<0.45 microns) stream, bog, and seepage waters (n=17), Grasshopper Mountain, B.C. zones i n bogs and s o i l p i t s i n the lower p a r t of the main study area average 1.05 ppt Pt. However, bog and pond waters from the p l a t e a u r e g i o n of the mountain ( F i g u r e 4-3 3) c o n t a i n 1.3 - 3.5 ppt Pt. T h e i r mean Pt content (2.45 ppt) i s 3x g r e a t e r than t h a t of stream waters. The t r e n d t o h i g h e r Pt v a l u e s i s a s s o c i a t e d with i n c r e a s i n g i n t e n s i t y of water c o l o u r , from c o l o u r l e s s t o l i g h t brown or brown ( F i g u r e 4-34). Not a l l brown or l i g h t brown samples have h i g h Pt conte n t s , but a l l samples w i t h h i g h Pt c o n t e n t s have t h i s c o l o u r a t i o n . Water pH does not show any r e l a t i o n t o Pt co n t e n t ( F i g u r e 4-35) or c a t e g o r i c a l group (Table 4-9). Grasshopper Creek does, however, e x h i b i t a g e n e r a l downstream i n c r e a s e i n pH from 7.11 t o 8.16 (Appendix 10). High-Pt p l a t e a u waters have a much narrower range of pH v a l u e s (7.24-7.59) than stream and seepage zone waters (Figure 4-35). A few other i n t e r e s t i n g r e l a t i o n s occur i n the water d a t a . One i s the r e l a t i v e l y h i g h (2.2/1.7 ppt) Pt c o n t e n t of water from the p i t of s o i l s i t e 46, which i s s i t u a t e d on a c l a y p a rent m a t e r i a l i n an area of no currently-known P t m i n e r a l i z a t i o n . Secondly, an u n f i l t e r e d and u n a c i d i f i e d d u p l i c a t e of the 3.5 ppt sample c o n t a i n e d o n l y h a l f as much Pt (1.8 ppt) as the o r i g i n a l . Sample Type n Pt (PPt) pH Stream waters 7 0.81+0.15 7.79+0.40 (0.5 - 0.9) (7.11 - 8.16) Seepage zone bogs and s o i l p i t s on 6 1.05 + 0.58 7.04 ± 0.57 n o n - d u n i t i c t i l l (0.6 - 2.2) (6.30 - 7.99) and c l a y P l a t e a u bogs and 4 2.45+1.07 7.38 ± 0.16 ponds on (1.3 - 3.5) (7.24 - 7.59) d u n i t i c t i l l T a b l e 4-9. Mean + 1 s and range of Pt content ( p a r t s per t r i l l i o n ) and pH of v a r i o u s types of f i l t e r e d (<0.45 microns) and a c i d i f i e d Grasshopper Mountain s u r f a c e waters (n=17). Pt analyses c o u r t e s y of G.E.M. H a l l , G e o l o g i c a l Survey of Canada, Ottawa, O n t a r i o 177 4 3.5 3 •9 2.5 CL a. E 2 C — 1 5 1 0.5 0 Water Colour • Brown • • Light Brown • o Colourless - • - o o - o o o • o o s. • -o • Stream waters Seepage zone waters Plateau waters Figure 4-34. Relation between Pt content (ppt), sample type, and water colour for filtered Grasshopper Mountain surface waters. X Q . 6.5 •, o Water Type Stream waters • Seepage zone waters O Plateau waters • 0.5 1.5 2.5 Platinum (ppt) 3.5 Figure 4-35. Scatterplot of Pt content (ppt) versus pH for filtered Grasshopper Mountain surface waters. 4.3 P a r t B - D e t a i l e d S o i l P r o f i l e R e s u l t s 4.3.1 G r a i n S i z e D i s t r i b u t i o n 4.3.1.1 S i z e F r a c t i o n s The g r a i n s i z e d i s t r i b u t i o n among f i v e s i z e f r a c t i o n s of each h o r i z o n (Appendix 11.1), expressed as weight p e r c e n t of t he -10 mesh (< 2 mm) s o i l f r a c t i o n , i s shown i n Appendix 11.2 and summarized by parent m a t e r i a l type and h o r i z o n i n Ta b l e 4-10. A l l p arent m a t e r i a l and h o r i z o n types e x h i b i t a bimodal g r a i n s i z e d i s t r i b u t i o n (Table 4-10) with h i g h e r p r o p o r t i o n s i n t he coarse -10+40 mesh (2 mm - 425 um: coarse t o v e r y c o a r s e sand) and f i n e -270 mesh (< 53 um: coarse s i l t t o c l a y ) f r a c t i o n s than i n the t h r e e i n t e r m e d i a t e f r a c t i o n s . The h i g h e s t p r o p o r t i o n of sample i n t i l l p a r ent m a t e r i a l s o c c u r s i n the -270 mesh f r a c t i o n ; the lowest mean p r o p o r t i o n of -270 mesh sample occurs i n c o l l u v i u m s i t e s . The l a t t e r a l s o c o n t a i n the h i g h e s t mean p r o p o r t i o n of -10+40 mesh p a r t i c l e s . There are no s t r o n g trends i n the v e r t i c a l d i s t r i b u t i o n of g r a i n s i z e s (Appendix 11.2) w i t h i n s o i l p r o f i l e s . C o l l u v i u m e x h i b i t s r e l a t i v e l y constant g r a i n s i z e d i s t r i b u t i o n s a t a l l l e v e l s sampled. However, t i l l C 179 S i z e F r a c t i o n (ASTM) Parent M a t e r i a l and/or H o r i z o n -10+40 (%) -40+70 (%) -70+140 (%) -140+270 (%) -270 q(%) NonDunitic T i l l : N ear-Surface H o r i z o n s (3) 2 2 . 5 7 1 16.52 2 26.50 3 8.67 8.57 8.86 10.44 9.08 12.29 8.58 8.41 8.72 49.73 46.35 53.60 NonDunitic T i l l : C H o r i z o n (2) 22.79 21.30 24.27 9.42 8.82 10.01 10.27 8. 62 11.91 8.99 7.83 10.15 48.54 43. 66 53 .42 D u n i t i c T i l l : N ear-Surface Horizons (5) 18.90 16.93 22.82 14.58 6.30 23.02 18.88 9.95 26.85 11.62 9.01 13.13 36.02 20.07 56.23 D u n i t i c T i l l : C H o r i z o n (6) 29.10 22.69 37.59 13.07 9.96 20.59 12.12 9.04 21.27 8.34 7.28 10. 99 37.38 19.21 48.59 D u n i t i c T i l l (A-Zone): Near-Surface H o r i z o n s (5) 24.35 21.17 27.41 6.74 4.88 9.27 11.74 9.15 13.56 9.96 8.44 11.18 47.21 45.74 49.98 D u n i t i c T i l l (A-Zone): C H o r i z o n (3) 29.24 25.11 37.35 8.84 8.38 9.59 8.71 8.16 9.51 6.92 5.46 8.18 46.28 40. 48 50.91 Co l l u v i u m : (9) 38.81 21.11 51.03 10.05 6.56 11.68 10.89 7.70 14.95 7.81 5. 68 10.19 32.43 21.20 47.19 Mean Minimum Value Maximum Value T a b l e 4-10. Mean and range of g r a i n s i z e d i s t r i b u t i o n of s o i l s developed on d i f f e r e n t parent m a t e r i a l s . A l l v a l u e s i n weight p e r c e n t of the -10 mesh f r a c t i o n . Numbers i n parentheses ( ) a t f a r l e f t i n d i c a t e the number of h o r i z o n s i n each grouping. 180 h o r i z o n s u s u a l l y c o n t a i n a s l i g h t l y g r e a t e r p r o p o r t i o n o f -10+40 m a t e r i a l than do n e a r - s u r f a c e h o r i z o n s (Appendix 11.2). There i s l i t t l e change between n e a r - s u r f a c e and C h o r i z o n s of the mean p r o p o r t i o n of -270 mesh p a r t i c l e s , a l t h o u g h t h e r e are v a r i a t i o n s i n i n d i v i d u a l p r o f i l e s . For example, n e a r - s u r f a c e h o r i z o n s of s o i l s i t e 43 c o n t a i n a d i s p r o p o r t i o n a l l y l a r g e amount of -40+70 and -70+140 mesh m a t e r i a l and a s m a l l amount of -270 mesh m a t e r i a l . 4.3.1.2 Densit y and Magnetic F r a c t i o n s Heavy m i n e r a l content (SG>3.3) content of the -70+140 and -140+270 mesh f r a c t i o n s (Appendices 11.3 and 11.4) ranges from 2.40-22.32 weight percent of the o r i g i n a l f r a c t i o n , w i t h most samples i n the range 5-15 weight p e r c e n t ( F i g u r e 4-36). Pt content has no sympathetic r e l a t i o n w i t h weight p e r c e n t heavy m i n e r a l s . R e l a t i o n s e x h i b i t e d by heavy m i n e r a l weight p e r c e n t d a t a are so v a r i e d as t o render a c a t e g o r i c a l t a b l e s i m i l a r t o T a b l e 4-10 meaningless, and data f o r each i n d i v i d u a l p r o f i l e and h o r i z o n are i n s t e a d shown i n Tab l e 4-11. The -70+140 mesh heavy concentrates comprise a s l i g h t l y l a r g e r p r o p o r t i o n of the o r i g i n a l s i z e f r a c t i o n than do the -140+270 mesh con c e n t r a t e s (Figure 4-36 and Tab l e 4-11), p r o b a b l y a t l e a s t p a r t l y a f u n c t i o n of the l e s s e f f i c i e n t heavy l i q u i d s e p a r a t i o n of the s m a l l e r p a r t i c l e s . The l i n e s c o n n e c t i n g s a m e - p r o f i l e h o r i z o n s i n F i g u r e 4-36 i n d i c a t e the d o w n p r o f i l e t r e n d of the heavy m i n e r a l content of each f r a c t i o n . V a r i a t i o n s i n the heavy m i n e r a l content w i t h depth seem dependent on both parent m a t e r i a l and pedogenic p r o c e s s e s . Weight pe r c e n t heavy m i n e r a l content i n the -70+140 f r a c t i o n decreases (or remains constant) with depth i n n o n - d u n i t i c t i l l , but i n c r e a s e s (or remains constant) w i t h depth on d u n i t i c t i l l and r u b b l e d i s t a l and proximal t o A-Zone PGE m i n e r a l i z a t i o n . The p r o p o r t i o n i s r e l a t i v e l y c o n s t a n t w i t h depth i n s e r p e n t i n e c o l l u v i u m . Weight p e r c e n t heavy m i n e r a l s i n the f i n e r -140+270 f r a c t i o n i s g e n e r a l l y s i m i l a r t o t h a t of the c o a r s e r f r a c t i o n (Table 4-11), but some p r o f i l e s show very d i f f e r e n t t r e n d s w i t h depth ( F i g u r e 4-36). Regarding pedogenic d i f f e r e n c e s , the p o d z o l i c Bf h o r i z o n i n s o i l s i t e 20 i s almost devoid of heavy m i n e r a l s r e l a t i v e t o Aej and C h o r i z o n s (Table 4-11). Weight p e r c e n t heavy m i n e r a l s i n stream sediment s i t e 2 (88-SC-503) i s s i m i l a r t o t h a t i n s o i l s (Table 4-11). R e l a t i v e p r o p o r t i o n s of magnetic and non-magnetic heavy m i n e r a l s i n the heavy concentrates of each of the two f r a c t i o n s are shown i n Table 4-11. S o i l s on n o n - d u n i t i c t i l l , and the stream sediment, have subequal p r o p o r t i o n s of magnetic and non-magnetic c o n c e n t r a t e s . The l a t t e r i s u s u a l l y predominant, although the p o d z o l i c Bf h o r i z o n of 25 HEAVY MINERAL CONCENTRATES: WEIGHT PERCENT OF ORIGINAL FRACTION WEIGHT 20 15 10 Soil Horizons Figure 4-36. Weight percent heavy minerals (S.G.>3.3) in -70+140 and -140+270 mesh fractions of individual horizons from detailed soil profiles. Numbers are the C horizon sample numbers. Solid lines (-70+140 mesh fraction) and dashed lines (-140+270 mesh fraction) connect horizons of the same profile, and show changes in relative heavy mineral content with increasing depth in the profile. co ro 183 Soil Site Sample Number Horizon IVt.% Heavy Mineral (-70+140) Nl% Heavy Minerals (-140+270) Wt% Mag Heavies! (-70+140) Vt.% Nonmag Heavies (-70+140) WL% Mag Heavies! (-140+270) Nt% Nonmag Heavies (-140+270) Non-dunitic Till 6 18 Ah 3.57 4.72 58.90 41.10 64.23 35.77 Non-dunitic Till 6 19 eg 2.29 3.62 39.26 60.74 30.39 69.61 Non-dunitic Till 20 38 Ae] 12.16 6.83 15.88 84.12 31.62 68.38 Non-dunitic Till 20 39 Bf 2.83 3.55 59.89 40.11 60.88 39.12 Non-dunitic Till 20 40 C 10.00 3.84 23.95 76.05 44.43 55.57 Dunitic Till 33 78 Bm 8.65 9.25 70.61 29.39 64.43 35.56 Dunitic Till 33 79 C 13.17 9.88 62.30 37.70 62.19 37.81 Dunitic Till 34 81 IC 8.87 10.71 80.05 19.95 81.80 18.20 Dunitic Till 34 82 IIC 15.37 16.50 58.65 41.35 53.89 46.11 Dunitic Till 43 110 Bm 5.40 4.85 32.33 67.67 45.34 54.66 Dunitic Till 43 111 Bm 13.97 3.45 11.56 88.44 47.40 52.60 Dunitic Till 43 112 BC/C 17.95 6.86 9.59 90.41 28.59 71.41 Dunitic Till 43 113 C 5.75 3.77 26.27 73.73 50.19 49.81 Dunitic Till 69 199 Bm 9.37 8.87 63.60 36.40 66.11 33.88 Dunitic Till 69 200 C 10.91 5.56 40.07 59.93 61.96 38.04 Dunitic Till 73 215 Bm 18.73 12.79 19.51 . 80.49 31.79 68.20 Dunitic Till 73 216 C 22.32 11.20 35.48 64.52 56.80 43.20 Dunitic Till/Rubble (A-Zone) 51 133 Bm 10.93 11.03 89.06 10.94 83.40 16.60 Dunitic Till/Rubble (A-Zone) 51 134 BC 10.43 9.28 80.22 19.78 77.32 22.68 Dunitic Till/Rubble (A-Zone) 51 135 C 12.25 4.79 72.51 27.49 67.42 32.58 Dunitic Till/Rubble (A-Zone) 57 154 Bm/IC 6.00 8.73 90.15 9.85 71.20 28.80 Dunitic Till/Rubble (A-Zone) 57 155 BC 7.99 5.92 79.44 20.55 69.65 30.34 Dunitic Till/Rubble (A-Zone) 57 156 IIC 12.49 12.06 66.49 33.51 54.73 45.26 Dunitic Till/Rubble (A-Zone) 56 152 C (upper) 6.91 8.34 87.01 12.99 77.29 22.71 Dunitic Till/Rubble (A-Zone) 56 153 C (lower) 8.28 6.34 93.27 6.73 87.07 12.93 Colluvium 27 59 C (upper) 9.73 2.40 76.08 23.92 87.97 12.03 Colluvium 27 60 C (middle) 8.66 4.20 83.11 16.89 87.36 12.64 Colluvium 27 61 C (lower) 8.41 2.75 81.53 18.47 89.74 10.26 Colluvium 42 104 C (upper) 8.67 3.99 83.72 16.28 76.65 23.35 Colluvium 42 105 C (lower) 7.46 6.49 80.85 19.15 80.36 19.64 Colluvium 9 24 C (upper) 7.48 5.67 82.53 17.46 82.65 17.35 Colluvium 9 23 C (lower) 15.67 4.92 45.44 54.56 80.24 19.76 Colluvium 16 31 C 8.41 6.37 83.67 16.33 83.22 16.77 2 503 Sediment 9.65 7.98 53.05 46.95 52.82 47.18 Table 4-11. Weight percent heavy minerals (S.G.>3.3) in -70+140 and -140+270 mesh fractions of individual horizons of detailed soil profiles, and the proportions of magnetic and non-magnetic heavy minerals in each heavy fraction. 184 s i t e 20 has a l a r g e p r o p o r t i o n of magnetic m i n e r a l s r e l a t i v e t o o t h e r h o r i z o n s i n the p r o f i l e . On d u n i t i c t i l l and c o l l u v i u m , the magnetic component overwhelmingly dominates heavy c o n c e n t r a t e s of most s o i l s . Thus, e x c e p t i n g s o i l s i t e 43 which has a hig h p r o p o r t i o n of non-magnetic heavy m i n e r a l s , mean magnetic f r a c t i o n weight p e r c e n t of heavy c o n c e n t r a t e s from d u n i t i c t i l l and c o l l u v i u m are 68.03% and 77.12% (-70+140 mesh), and 66.69% and 83.52% (-140+270 mesh), r e s p e c t i v e l y . P r o p o r t i o n s of magnetic and non-magnetic c o n c e n t r a t e s v a r y e r r a t i c a l l y w i t h depth i n n o n - d u n i t i c t i l l but are r e l a t i v e l y c onstant i n s e r p e n t i n e c o l l u v i u m . However, the p r o p o r t i o n of magnetic concentrates g e n e r a l l y decreases d o w n p r o f i l e i n d u n i t i c t i l l (Table 4-11). D u n i t i c r u b b l e above the A-Zone occurrence p r e s e n t s one of the few ex c e p t i o n s t o t h i s r e l a t i o n . 4.3.2 R e s u l t s : Platinum A number of important trends are apparent. They r e l a t e t o t he g e n e r a l magnitude of s o i l Pt c o n c e n t r a t i o n s , i t s v e r t i c a l d i s t r i b u t i o n i n s o i l p r o f i l e s , and i t s r e s i d e n c y i n i n d i v i d u a l s i z e / d e n s i t y / m a g n e t i c f r a c t i o n s . Pt d i s t r i b u t i o n i n s i z e / d e n s i t y / m a g n e t i c f r a c t i o n s of a l l 14 d e t a i l e d p r o f i l e s are i l l u s t r a t e d i n Appendix 12. 4.3.2.1 S i z e F r a c t i o n s The Pt content of f i v e s i z e f r a c t i o n s from each h o r i z o n i n 14 s e l e c t e d p r o f i l e s was determined (Appendix 11.5). Median Pt contents of the v a r i o u s s o i l groupings are summarized i n Table 4-12. R e s u l t s f o r n e a r - s u r f a c e , i n t e r m e d i a t e and C h o r i z o n s i n each of the 5 s i z e f r a c t i o n s are shown i n F i g u r e s 4-37 t o 4-39. The diagrams are arranged t o show, from l e f t t o r i g h t , i n c r e a s i n g p r o x i m i t y of t i l l s i t e s t o known A-Zone PGE m i n e r a l i z a t i o n . Colluvium, i n c l u d i n g d u n i t i c c o l l u v i u m below the C l i f f Zone PGE occurrences, i s shown on the f a r r i g h t . Pt c o n c e n t r a t i o n s i n each of the f i v e f r a c t i o n s g e n e r a l l y i n c r e a s e a c c o r d i n g t o parent m a t e r i a l , i n c r e a s i n g i n t h e o r d e r n o n - d u n i t i c t i l l — > d u n i t i c t i l l — > colluvium/A-Zone t i l l and r u b b l e (Table 4-12). Pt c o n c e n t r a t i o n s among the f i v e s i z e f r a c t i o n s g e n e r a l l y i n c r e a s e , or are constant, w i t h depth ( F i g u r e s 4-37 t o 4-39). S p e c i f i c a l l y , Pt c o n c e n t r a t i o n s i n c r e a s e w i t h depth i n s o i l s developed on n o n - d u n i t i c t i l l , u s u a l l y i n c r e a s e or are r e l a t i v e l y constant w i t h depth i n s o i l s developed on d u n i t i c t i l l and r u b b l e , and are u s u a l l y c o n s t a n t w i t h depth i n unhorizonated c o l l u v i u m . The h i g h e s t s i n g l e Pt c o n c e n t r a t i o n (722 ppb) o c c u r r e d i n the -10+40 (2mm-425 um) f r a c t i o n of near-bedrock d u n i t i c r u b b l e above the A-Zone occurrence. 186 Parent S i z e F r a c t i o n (ASTM) m a t e r i a l and/or h o r i z o n -10 -40 -70 -140 -270 +40 +70 +140 +270 A) Non-Dunitic T i l l : N ear-Surface Horizons (n=3) 7 5 4 2 7 (3-13) (3-11) (4-8) (2-9) (7-10) Non-Dunitic T i l l : C H o r i z o n (n=2) 43 15 15 14 12 (9-77) (8-21) (6-23) (5-23) (9-14) B) D u n i t i c T i l l : N ear-Surface Horizons (n=5) 49 19 20 35 36 (6-81) (1-113) (3-104) (6-172) (16-104) D u n i t i c T i l l : C H o r i z o n (n=6) 34 26 24 29 23 (1-101) (1-76) (2-167) (7-50) (2-41) C) D u n i t i c T i l l / R u b b l e (A-Zone): Near-Surface Horizons (n=5) 92 128 83 53 76 (74-355) (103-402) (74-149) (38-90) (53-131) D u n i t i c T i l l / R u b b l e (A-Zone): C H o r i z o n (n=3) 119 588 157 164 150 (96-722) (152-632) (155-278) (141-257) (89-260) D) Colluvium: (n=9) 106 128 74 90 89 (16-248) (53-388) (42-277) (41-167) (53-147) T a b l e 4-12. Median and range of platinum c o n c e n t r a t i o n s (ppb) among s i z e f r a c t i o n s of s o i l s developed on d i f f e r e n t p a rent m a t e r i a l s . 187 Figure 4-37. Pt content (ppb) of the A. -10+40 mesh fraction and the B. -40+70 mesh fraction of surficial, intermediate and C horizons in soils on various parent materials. Note that site 34 has a colluvium surficial horizon. Figure 4-38. Pt content (ppb) of the A. -70+140 mesh fraction and the B. -140+270 mesh fraction of surficial, intermediate and C horizons in soils on various parent materials. Note that site 34 has a colluvium surficial horizon. -270 F R A C T I O N Figure 4-39. Pt content (ppb) of the -270 mesh fraction of surficial, intermediate and C horizons in soils on various parent materials. Note that site 34 has a colluvium surficial horizon. 190 Pt r e s i d e n c e among the f i v e s i z e f r a c t i o n s v a r i e s s l i g h t l y w i t h parent m a t e r i a l type ( F i g u r e s 4-40 and 4-41). Low-level Pt c o n c e n t r a t i o n s i n both s u r f i c i a l and C-horizons of n o n - d u n i t i c t i l l s i t e s , although sometimes e r r a t i c , a re r e l a t i v e l y c onstant between s i z e f r a c t i o n s . Most d u n i t i c t i l l h o r i z o n s , i n c l u d i n g those immediately a d j a c e n t t o the A-Zone occurrence, e x h i b i t s i m i l a r l y - c o n s t a n t Pt c o n c e n t r a t i o n s among s i z e f r a c t i o n s , although t h e r e a re e x c e p t i o n s . For example, d u n i t i c r u b b l e a t s i t e 56, d i r e c t l y above the occurrence, c o n t a i n s h i g h e r Pt c o n c e n t r a t i o n s i n the c o a r s e r s i z e f r a c t i o n s . T h i s i s a l s o observed i n one c o l l u v i a l s i t e ( s i t e 9) beneath the C l i f f Zone PGE occurrences, but not i n the second ( s i t e 16), where Pt c o n c e n t r a t i o n s are remarkably constant between s i z e f r a c t i o n s . Pt c o n c e n t r a t i o n s are a l s o r e l a t i v e l y c o n s t a n t between s i z e f r a c t i o n s i n s e r p e n t i n e c o l l u v i u m ( F i g u r e 4-41) . 191 Figure 4-40. Pt distribution in size fractions of some Grasshopper Mountain soils from A. nondunitic till; B. dunitic till; C. dunitic till near the A-Zone PGE occurrence; and D. dunite rubble immediately above the A-Zone PGE occurrence Figure 4-41. Pt distribution in size fractions of some colluvial Grasshopper Mountain soils: A. dunite colluvium beneath Cliff Zone PGE occurrences; B. serpentine colluvium. 4.3.2.2 Densit y and Magnetic F r a c t i o n s (-70+140; -140+270) a) D e n s i t y F r a c t i o n s Pt c o n c e n t r a t i o n s i n l i g h t and heavy m i n e r a l c o n c e n t r a t e s f o r the -70+140 and -140+270 mesh f r a c t i o n s from each h o r i z o n (Appendix 11.6) are summarized i n T a b l e 4-13 and F i g u r e 4-42, where l i n e s connect h o r i z o n s of i n d i v i d u a l p r o f i l e s . Light Mineral Fractions Pt c o n c e n t r a t i o n s i n l i g h t m i n e r a l f r a c t i o n s (S.G. < 3.3) g e n e r a l l y i n c r e a s e downprofile a t t i l l s i t e s ( F i g u r e 4-42) and range from 1 ppb up t o 160 ppb and 137 ppb i n t h e -70+140 and -140+270 f r a c t i o n s , r e s p e c t i v e l y . Trends i n Pt c o n c e n t r a t i o n s f o l l o w , but are much lower than, those i n the heavy m i n e r a l f r a c t i o n s . Maximum va l u e s are from a s i t e d i r e c t l y over A-Zone PGE m i n e r a l i z a t i o n ( F i g u r e s 4-42 and 4-48) . Heavy Mineral Fractions C o n c e n t r a t i o n s of Pt i n the heavy m i n e r a l f r a c t i o n (S.G. > 3.3) were obtained by c a l c u l a t i o n from a n a l y t i c a l r e s u l t s f o r the magnetic and non-magnetic heavy m i n e r a l c o n c e n t r a t e s . Pt c o n c e n t r a t i o n s i n the heavy m i n e r a l f r a c t i o n s are t y p i c a l l y 10 - 2Ox g r e a t e r than i n the c o r r e s p o n d i n g l i g h t f r a c t i o n (Appendix 11.6). They range from 11 ppb t o 2538 ppb i n the -70+140 s i z e f r a c t i o n , and from 22 ppb t o 2027 ppb i n the f i n e r -140+270 s i z e f r a c t i o n . The h i g h e s t v a l u e i n the coarse f r a c t i o n i s from C l i f f Zone c o l l u v i u m , w h i l e the h i g h e s t i n the f i n e f r a c t i o n i s from r u b b l e d i r e c t l y over A-Zone m i n e r a l i z a t i o n . Pt content of the heavy mi n e r a l f r a c t i o n i n c r e a s e s ( l e f t t o r i g h t i n F i g u r e 4-42) i n the order n o n d u n i t i c t i l l — > d u n i t i c t i l l — > A - Z o n e d u n i t i c t i l l and r u b b l e / c o l l u v i u m . However, c o n c e n t r a t i o n s are h i g h l y v a r i a b l e . They i n c r e a s e d o w n p r o f i l e i n n o n - d u n i t i c t i l l , but decrease d o w n p r o f i l e a t some d i s t a l d u n i t i c t i l l s i t e s . C o n c e n t r a t i o n s i n c r e a s e or remain r e l a t i v e l y constant with depth i n d u n i t i c t i l l and r u b b l e a d j a c e n t t o m i n e r a l i z a t i o n , and are r e l a t i v e l y c o n s t a n t w i t h depth i n c o l l u v i u m . Parent m a t e r i a l S i z e F r a c t i o n (ASTM) and/or h o r i z o n L i g h t Heavy -70 -140 -70 -140 +140 +270 +140 +270 A) Non-Dunitic T i l l : N ear-Surface Horizons (n=3) 3 1 22 30 (2-6) (1-6) (18-61) (22-46) Non-Dunitic T i l l : C H o r i z o n (n=2) 8 9 105 154 (5-10) (3-14) (67-142) (66-242) B) D u n i t i c T i l l : N ear-Surface Horizons (n=5) 9 4 142 338 (1-36) (3-50) (18-767) (78-1429) D u n i t i c T i l l : C H o r i z o n (n=6) 13 12 90 219 (1-31) (1-20) (11-669) (98-329) C) D u n i t i c T i l l / R u b b l e (A-Zone): Near-Surface Horizons (n=5) 30 24 744 340 (21-50) (18-57) (526-1292) (193-607) D u n i t i c T i l l / R u b b l e (A-Zone): C H o r i z o n (n=3) 70 110 787 817 (69-160) (74-137) (754-1590) (756-2027) D) Co l l u v i u m : (n=9) 40 70 388 503 (4-69) (2-128) (261-2538) (154-1000) T a b l e 4-13. Median and range of platinum c o n c e n t r a t i o n s (ppb) between l i g h t (S.G. < 3.3) and heavy (S.G. > 3.3) m i n e r a l f r a c t i o n s of s o i l s on d i f f e r e n t parent m a t e r i a l s . 196 A. -70+140 mesh fraction Heavy Fraction Light Fraction O 6 20 Dunitic Till 153 135 156 _ 61 * • • Dunitic Till and Rubble adjacent to A-Zone PGE occurrence Colluvium 31 105 o Serpentine Dunitic 33 34 43 69 73 51 57 56 Soil Profiles 27 42 9 16 B. -140+270 mesh fraction 3,000 1,000 Dunitic Till 153. Dunitic Till and Rubble adjacent to A-Zone ' PGE occurrence Colluvium 23 O Serpentine Dunitic 6 20 33 34 43 69 73 51 57 56 27 42 9 16 Soil Profiles Figure 4-42. Pt distribution (ppb) in heavy and light mineral fractions of A. -70+140 mesh and B. -140+270 mesh size fractions from soil horizons in various parent materials. Solid lines connect individual horizons within soil profiles, and show changes in Pt concentration with increasing depth (left to right; numbers are C horizon sample numbers) in the profile. b) Magnetic and Non-magnetic F r a c t i o n s Pt c o n t e n t s of -70+140 and -140+270 mesh magnetic and non-magnetic heavy f r a c t i o n s (Appendix 11.7) are summarized i n T a b l e 4-14. Maximum Pt c o n c e n t r a t i o n s are 4950 ppb i n non-magnetic f r a c t i o n s and 2782 ppb i n magnetic f r a c t i o n s . Bar graphs showing Pt contents of these and a l l o t h e r f r a c t i o n s of the 14 p r o f i l e s are presented i n Appendix 12. Pt c o n tent of both magnetic and non-magnetic f r a c t i o n s i n c r e a s e s i n the g e n e r a l order n o n - d u n i t i c t i l l — > d u n i t i c t i l l — > A-Zone d u n i t i c t i l l and r u b b l e / c o l l u v i u m (Table 4-14; F i g u r e 4-43). Pt i s u s u a l l y most abundant i n the magnetic heavy m i n e r a l f r a c t i o n i n both n o n - d u n i t i c t i l l and d u n i t i c t i l l d i s t a l from known PGE m i n e r a l i z a t i o n . C o n c e n t r a t i o n s are t y p i c a l l y 10 - 2Ox times g r e a t e r than i n the c o r r e s p o n d i n g non-magnetic f r a c t i o n , w i t h the d i f f e r e n c e b e i n g g r e a t e s t i n the -70+140 f r a c t i o n . However, a t d u n i t i c t i l l / r u b b l e and c o l l u v i u m s i t e s immediately a d j a c e n t t o both o c c u r r e n c e s , Pt c o n c e n t r a t i o n s i n non-magnetic f r a c t i o n s approach, equal or exceed those of the magnetic f r a c t i o n s . T h i s a l s o occurs i n s e r p e n t i n e c o l l u v i u m where i t i s most pronounced i n the f i n e r -140+270 f r a c t i o n ( F i g u r e 4-43). Pt c o n c e n t r a t i o n s i n n o n - d u n i t i c t i l l g e n e r a l l y i n c r e a s e d o w n p r o f i l e (Figures 4-44 and 4-45; Appendices 12.1 and 12.2). For example, the m a g n e t i c - a s s o c i a t e d Pt content Non-magnetic Magnetic Parent m a t e r i a l and/or h o r i z o n -70 -140 -70 -140 +140 +270 +140 +270 A) Non-Dunitic T i l l : N ear-Surface Horizons (n=3) 95 47 5 9 (34-96) (30-97) (4-8) (4-23) Non-Dunitic T i l l : C H o r i z o n (n=2) 356 330 12 28 (148-563) (143-517) (9-15) (22-33) B) D u n i t i c T i l l : N ear-Surface Horizons (n=5) 179 338 30 95 (51-1142) (95-1549) (10-112) (51-1195) D u n i t i c T i l l : C H o r i z o n (n=6) 87 261 10 105 (58-1732) (59-525) (5-183) (5-539) C) D u n i t i c T i l l (A-Zone): Near-Surface Horizons (n=5) 759 358 57 261 (653-962) (185-413) (8-3225) (193-1053) D u n i t i c T i l l (A-Zone): C H o r i z o n (n=3) 1075 987 466 1371 (695-1671) (359-1857) (28-870) (278-3172) D) Dunite Colluvium: (n=4) 1561 234 361 673 (331-2782) (168-855) (43-1601) (86-1128) S e r p e n t i n e Colluvium: (n=5) 317 284 530 2730 (253-393) (85-738) (257-587) (1655-4950) T a b l e 4-14. Median and range of platinum c o n c e n t r a t i o n s (ppb) i n magnetic and non-magnetic heavy m i n e r a l f r a c t i o n s i n s o i l s on d i f f e r e n t parent m a t e r i a l s . A. -70+140 mesh fraction 10,000 | 1 6 20 33 34 43 69 73 51 57 56 27 42 9 16 Soil Profiles B. -140+270 mesh fraction 10,000 | 1 Figure 4-43. Pt distribution (ppb) in magnetic and non-magnetic heavy mineral fractions of A. -70+140 mesh and B. -140+270 mesh size fractions from soil horizons in various parent materials and a stream sediment. Solid lines connect individual horizons within soil profiles, and show changes in Pt concentration with increasing depth (left to right; numbers are C horizon sample numbers) in the profile. 200 of the C h o r i z o n i n s o i l s i t e 20 (Figure 4-46) i s more than 5x g r e a t e r than t h a t of the s u r f i c i a l Aej h o r i z o n i n both s i z e f r a c t i o n s . The v e r t i c a l Pt d i s t r i b u t i o n i s more complex i n s i t e s on d u n i t i c t i l l , which g e n e r a l l y have much g r e a t e r Pt c o n c e n t r a t i o n s than n o n - d u n i t i c t i l l s i t e s ( F i g u r e s 4-44 and 4-45; Appendices 12.3 t o 12.10). P t c o n c e n t r a t i o n s are q u i t e v a r i a b l e w i t h depth a t s i t e s d i s t a l t o m i n e r a l i z a t i o n , but i n c r e a s e or remain c o n s t a n t w i t h depth a t s i t e s adjacent t o m i n e r a l i z a t i o n . The d o w n p r o f i l e i n c r e a s e i n Pt content with depth i n d u n i t i c t i l l and r u b b l e a d j a c e n t t o and above the A-Zone PGE occurrence i s i l l u s t r a t e d i n F i g u r e s 4-47 and 4-48, r e s p e c t i v e l y . The v e r t i c a l d i s t r i b u t i o n of magnetic and non-magnetic a s s o c i a t e d Pt i n s e r p e n t i n e c o l l u v i u m p r o f i l e s i s r e l a t i v e l y c o n s t a n t w i t h depth i n the -70+140 f r a c t i o n , but somewhat more e r r a t i c i n the -140+270 f r a c t i o n . Pt i n d u n i t e c o l l u v i u m i s e r r a t i c a l l y d i s t r i b u t e d a t the s i n g l e s i t e where more than one sample was c o l l e c t e d w i t h depth ( F i g u r e s 4-44 and 4-45; Appendices 12.11 t o 12.14). In a composite p r o f i l e , where s t a b i l i z e d c o l l u v i u m o v e r l i e s d u n i t i c t i l l ( Figure 4-49), the n e a r - s u r f a c e c o l l u v i a l h o r i z o n c o n t a i n s 3-40x more Pt than c o r r e s p o n d i n g f r a c t i o n s i n the u n d e r l y i n g t i l l . -70+140 MAGNETIC HEAVY MINERALS 3,000 2,500 2,000 S" Q. a. | 1,500 c CL 1,000 500 _ Surficial horizon Q - Intermediate horizon • Intermediate horizon A Dunitic Till and Rubble adjacent to A-Zone PGE occurrence / - C horizon — • — / Colluvium / Non-dunitic - Till Dunitic Till Q / / • • • \ / Dunitic I I I Serpentine I I I I 20 33 34 43 69 73 51 57 56 27 42 9 Soil Profiles 16 2,000 B -140+270 MAGNETIC HEAVY MINERALS 1,500 n CL a. I 1,000 c CL 500 - 9 Dunitic Till ; \ Dunitic Till and f Rubble adjacentfl to A-Zone PGE / \ occurrence / \ Surficial horizon — -G— -Intermediate horizon • Intermediate horizon A C horizon — • — Non-dunitic Till / 0 l Colluvium \P. / - A A; / \ / •A i i i \. b. / Dunitic T I I l l • Serpentine I i i I 20 33 34 43 69 73 51 57 56 27 42 Soil Profiles 16 Figure 4-44. Pt content (ppb) of the A. -70+140 mesh and; B. -140+270 mesh magnetic heavy mineral fractions of surficial, intermediate and C horizons of soils on various parent materials. Note that site 34 has a colluvium surficial horizon. 202 -70+140 N O N - M A G N E T I C H E A V Y M I N E R A L S 3,500 3,000 2,500 S" g 2,000 If | 1,500 Q. 1,000 500 - Surficial horizon Q • — Intermediate horizon • - Intermediate horizon A C horizon — • — Colluvium Non-dunltlc - Till Dunitic Till Dunitic Till and Rubble adjacent to A-Zone PGE occurrence -P. / \ P " Serpentine / ^\~-<j Dunitic l l T§ i B 20 33 34 43 69 73 51 57 56 27 42 9 16 Soil Profiles -140+270 N O N - M A G N E T I C H E A V Y M I N E R A L S 6,000 5,000 4,000 3" CL a I 3,000 c 1 0. 2,000 1,000 -Surficial horizon Q Intermediate horizon • Intermediate horizon A Dunitic Till and Rubble adjacent to A-Zone PGE occurrence • Colluvium C horizon — • — \ -Dunitic Till / \ \ Non-dunitic Till - O / • \ / • - J / Serpentine \ Dunitic r i > » - g ^ f fc-^ , ? l l CD l 6 20 33 34 43 69 73 51 57 Soil Profiles 56 27 42 Figure 4-45. Pt content (ppb) of the A. -70+140 mesh and; B. -140+270 mesh non-magnetic heavy mineral fractions of surficial, intermediate and C horizons of soils on various parent materials. Note that site 34 has a colluvium surficial horizon. 203 Aej 88-SC-38 (0-6/10 cm) Bf 88-SC-39 (6/10-36 cm) 88-SC-40 (36 - 82 cm) 40 60 Platinum (ppb) 100 B Bf Light and Heavy Fractions • -70+140 L • -70+140 H • -70+140 Iv* 1 -70+140 N agnatic onmagnetic • -140+270 • -140+270 H -140+270 1 -140+270 L H Magnetic Nonmagnetic 100 200 300 Platinum (ppb) 400 500 Figure 4-46. Pt distribution (ppb) in humo-ferric podzol (soil site 20) on non-dunitic till, showing A. Pt content of five size fractions and B. Pt content of light, heavy, heavy magnetic and heavy non-magnetic mineral fractions of the -70+140 (bars 1-4) and -140+270 (bars 5-8) mesh size fractions. 204 Bm 88-SC-133 (0-10/12 cm) BC 88-SC-134 (10/12-40 cm) c 88-SC-135 (40 - 70 cm) 300 400 Platinum (ppb) Size Fractions (ASTM) • -10+40 a -40+70 m -70+140 m -140+270 • -270 700 B Bm C 1 ...... 1 Light and Hes vy Fractions r U -70+140 L 3 -70+140 H • -70+140 Me 1 -70+140 Nc ignetic nmagnetic n • -140+270 L • -140+270 H • -140+270 rv 1 -140+270 N lagnetic onmagnetic :-:-:-x-:-:-:-:-:-:-:-:-:-:-l i m i •:•:•:•:•:•:•:•:•:•:•:•:•] i 0 200 400 600 800 1,000 1,200 Platinum (ppb) Figure 4-47. Pt distribution (ppb) in eutric brunisol (soil site 51) on dunitic till near A-Zone PGE occurrence, secondary study area, showing A. Pt content of five size fractions and B. Pt content of light, heavy, heavy magnetic and heavy non-magnetic mineral fractions of the -70+140 (bars 1-4) and -140+270 (bars 5-8) mesh size fractions. 205 C (upper) 88-SC-152 (0 - 20 cm) Size Fractions (ASTM) m -10+40 a -40+70 m -70+140 m -140+270 • -270 C (lower) 88-SC-153 (20 - 50 cm) 200 400 Platinum (ppb) 600 800 B C (upper) C (lower) Light and Heavy Fractions • -70+140 L • -70+140 H • -70+140 Magnetic • -70+140 Nonmag netic • -140+270 L • -140+270 H • -140+270 Magnet B -140+270 Nonma c gnetic 500 1,000 1,500 2,000 Platinum (ppb) 2,500 3,000 3,500 Figure 4-48. Pt distribution (ppb) in orthic regosol (soil site 56) on dunitic rubble immediately above A-Zone PGE occurrence, secondary study area, showing A. Pt content of five size fractions and B. Pt content of light, heavy, heavy magnetic and heavy non-magnetic mineral fractions of the -70+140 (bars 1 -4) and -140+270 (bars 5-8) mesh size fractions. 206 IC 88-SC-81 (0 - 23 cm) IIC 88-SC-82 (23 - 60 cm) Size Fractions 10 20 30 Platinum (ppb) 40 (ASTM) • -10+40 E3 -40+70 C -70 + 140 E -140+270 • -270 50 60 B e 1C 11C fe Light and Heavy Fractions • -70+140 L • -70+140 H • -70+140 Magr m -70+140 Nonn etic lagnetic • -140+270 L • -140+270 H • -140+270 Mac M -140+270 Non netic magnetic 100 200 300 400 Platinum (ppb) 500 600 700 Figure 4-49. Pt distribution (ppb) in composite soil profile (soil site 34) of dunitic colluvium (IC) overlying dunitic till (IIC), showing A. Pt content of five size fractions and B. Pt content of light, heavy, heavy magnetic and heavy non-magnetic mineral fractions of the -70+140 (bars 1-4) and -140+270 (bars 5-8) mesh size fractions. 207 4.3.2.3 T o t a l Pt Content of S e l e c t e d S o i l s C a l c u l a t e d t o t a l Pt contents of h o r i z o n s from f i v e s e l e c t e d p r o f i l e s are giv e n i n F i g u r e s 4-50 and 4-51 a l o n g w i t h s t a c k e d bar graphs showing the percent c o n t r i b u t i o n of each of the f i v e s i z e f r a c t i o n s t o the t o t a l P t con t e n t of the <2mm s o i l . Downprofile i n c r e a s e s i n t o t a l Pt con t e n t (ppb) a t 3 out of 4 t i l l and r u b b l e s i t e s a re c o n s i s t e n t w i t h p r e v i o u s l y - n o t e d downprofile i n c r e a s e s i n Pt c o n c e n t r a t i o n s ( s e c t i o n 4.3.2.1). However, one d u n i t i c t i l l p r o f i l e ( s o i l s i t e 69; F i g u r e 4-51A) e x h i b i t s a much h i g h e r Pt content i n the Bm r e l a t i v e t o the u n d e r l y i n g C h o r i z o n . The most s t r i k i n g r e l a t i o n i n F i g u r e s 4-50 and 4-51 i s t h a t , i n t i l l , the -270 mesh f r a c t i o n c o n t a i n s the g r e a t e s t p r o p o r t i o n of Pt and accounts f o r approximately o n e - h a l f of t o t a l s o i l Pt content. In c o n t r a s t , the -10+40 mesh f r a c t i o n c o n t a i n s about one-half of the t o t a l Pt con t e n t of s o i l s on c o l l u v i u m and rubble parent m a t e r i a l s . There are a l s o trends i n the v e r t i c a l d i s t r i b u t i o n of Pt. The p r o p o r t i o n of t o t a l Pt co n t a i n e d w i t h i n f i n e r -g r a i n e d , p a r t i c u l a r l y the -270 mesh, f r a c t i o n s i n c r e a s e s toward the s u r f a c e i n th r e e of the f o u r t i l l and r u b b l e p r o f i l e s ( F i g u r e s 4-50 and 4-51). There i s a coresponding decrease i n the p r o p o r t i o n of Pt i n the c o a r s e r -10+40 mesh f r a c t i o n of n e a r - s u r f a c e h o r i z o n s . The o n l y s i t e ( s o i l s i t e 208 SOIL SITE 20 Non-dunitic till 6 ppb a ppb 1.86 0.19 2.05 5 . 8 3 , 5.27 1.87 2J6 0.86 20 40 60 80 100 •10+40 • -40+70 H -70+140 [3 -140+270 • -270 0.09 1.62 1.01 9 13.46 0.68 0.06 0.47 13.47 8.81 -70+140 mesh -140 + 270 mesh Q Light Minerals | Heavy Magnetics ^ Heavy Non-magnetics SOIL SITE 57 Dunitic till near A-Zone PGE occurrence mmv.-y 85 PPb 118 ppb r wmm±-y B 21.01 49.3 51.76 1 8 - 4 6 46.08 53.64 51.94 16.97 11.04 18.85 144 ppb 61.28 65.1 57.59 23.63 36.33 74.62 20 40 60 80 1 00 -10+40 • -40+70 H -70+140 [3 -140+270 • -270 -70+140 mesh •140+270 mesh Figure 4-50. Percent contribution of individual size fractions to total Pt content (ppb; right side of each bar) of soil horizons developed in A. non-dunitic till and B. in dunitic till adjacent to the A-Zone PGE occurrence. Percent contributions of light, heavy magnetic and heavy non-magnetic mineral fractions to the -70+140 and -140+270 mesh fractions are shown in pie charts to the right of each horizon bar. Numbers indicate the Pt content (ppb) of each. 209 SOIL SITE 69 Dunitic Till 103 ppb 40 ppb 20 40 80 80 100 -10+40 H -40+70 UJ -70+140 • -140+ 270 • -270 SOIL SITE 56 Dunitic Rubble above A-Zone PGE occurrence C upper C lower 183 ppb 462 ppb 31.66 B 20 40 60 80 100 -70+140 mesh -140+270 mesh -10+40 H -40+70 H -70+140 • -140+270 • -270 SOIL SITE 16 Dunite colluvium below Cliff Zone PGE occurrences J88 ppb 20 -10+40 40 80 80 100 -40+70 M -70+140 EZJ -140+270 • -270 63.2 109.56 21.93 191.01 -70+140 mesh 12.03 45.26 -140+270 mesh Q Light Minerals • Heavy Magnetics £3 Heavy Non-magnetics Figure 4-51. Percent contribution of individual size fractions to total Pt content (ppb; right side of each bar) of soil horizons developed in A. dunitic till; B. dunitic rubble above the A-Zone PGE occurrence; and C. dunite colluvium beneath the Cliff Zone PGE occurrences. Percent contributions of light, heavy magnetic, and heavy non-magnetic mineral fractions to the -70+140 and -140+270 mesh fractions are shown in pie charts to the right of each horizon bar. Numbers indicate the Pt content (ppb) of each. 57) a t which the Pt content of the c o a r s e r f r a c t i o n i n c r e a s e s near the s u r f a c e has c o l l u v i u m , r a t h e r than a g e n e t i c Bm h o r i z o n , o v e r l y i n g t i l l . I t i s a l s o apparent t h a t a l a r g e p r o p o r t i o n - about o n e - t h i r d t o one-half - of the t o t a l Pt content o f the -70+140 and -140+270 mesh s i z e f r a c t i o n s i s c o n t a i n e d w i t h i n the l i g h t m i n e r a l component, shown i n p i e graphs al o n g w i t h r e l a t i v e p r o p o r t i o n s of magnetic and non-magnetic heavy m i n e r a l f r a c t i o n s ( F i g u r e s 4-50 and 4-51). T h i s i s d e s p i t e the extremely h i g h Pt c o n c e n t r a t i o n s i n some heavy magnetic and non-magnetic concentrates (Table 4-14). Most Pt i n the heavy m i n e r a l component occurs i n the magnetic f r a c t i o n , a lthough the p r o p o r t i o n of Pt i n the non-magnetic f r a c t i o n g e n e r a l l y i n c r e a s e s with d e c r e a s i n g g r a i n s i z e . Among the f i v e p r o f i l e s , l a r g e p r o p o r t i o n s of non-magnetic f r a c t i o n Pt occur a t o n l y s i t e 57 near the A-Zone PGE occurrence ( F i g u r e 4-50B). 4.4 P a r t C - Scanning E l e c t r o n Microscopy and Microprobe R e s u l t s 4.4.1 I n t r o d u c t i o n P o l i s h e d s e c t i o n s and g r a i n mounts from e i g h t s o i l s i t e s were s t u d i e d under the scanning e l e c t r o n microscope. Chromite g r a i n s from f i v e magnetic f r a c t i o n and f i v e norl-and paramagnetic f r a c t i o n p o l i s h e d s e c t i o n s were subsequently analyzed with the e l e c t r o n microprobe ( s e c t i o n 3.7). M i n e r a l o g i c a l r e s u l t s f o r i n d i v i d u a l f r a c t i o n s of each of the e i g h t s o i l heavy m i n e r a l c o n c e n t r a t e s are summarized i n Tables 4-15 and 4-16. 4.4.2 Platinum-Group M i n e r a l s Seven PGM g r a i n s were l o c a t e d i n a search through 46 g r a i n s t ub mounts and p o l i s h e d s e c t i o n s of magnetic, paramagnetic and nonmagnetic heavy m i n e r a l c o n c e n t r a t e s of -140+270 mesh s o i l f r a c t i o n s (see s e c t i o n 3.5). F i v e of the PGM were found i n p o l i s h e d s e c t i o n s , and the o t h e r two i n g r a i n stub mounts. T e n t a t i v e PGM i d e n t i f i c a t i o n s were made on the b a s i s o f EDS co m p o s i t i o n a l s i g n a t u r e s . S o i l PGM occur as Pt-Fe-Ni-Cu a l l o y s forming d i s c r e t e f r e e g r a i n s and i n c l u s i o n s w i t h i n both chromite and M g - s i l i c a t e s . They were i d e n t i f i e d o n l y i n the C l i f f Zone and A-Zone areas i n s o i l p r o f i l e s p roximal t o known m i n e r a l i z a t i o n ; none were found Site X X X X X M X ~ X X X X \ X X •DOMINA \ ^ ^ ^ < X M a g n e t i t e \ Chromite \ \ % - \ \ ^ \ \ $ \ HtahAtomicNo. ® Commo \ ? < ^ ' V \ " % k \ ' V \ \ \ \ V 5 ^ \ \ % \ V % \ G r a i n s • Subordi VAV^A \<£\4£\ \ C^d\^^X X <£>\ N^K\ X Trace( X ^ ^ ^ ^ ^ ^ ^ ^ C ^ ^ ^ ^ ^ V Q^XX ChromteEDS sample N jV\%\^N^X> ^ Analysis Summary nt (>50%) n (10-50%) nate(1-10%) <1%) Comments SITE 42 J Serpentine \ Colluvium MAGNETIC PARAMAGNETIC NONMAGNETIC 68.64 5.28 95-100 0-5 • • • ® ® X 1! » Cr>Fe 12.03 053 85-90 10-15 X X • • • ® X Cr>Fe 19.33 1.49 30 70 • • ® ® • • x F e" N i sulphide 1749 Cr>Fe chromite crystals more abundant -than fragments SfTE 16 Dunitic 2 "| Colluvium MAGNETIC PARAMAGNETIC NONMAGNETIC 66.67 1.71 95-100 0-5 • X • ® ® X X X 8S >5 Cr>Fe; Cr>Fe 13.84 0.35 50 50 • • • ® ® ® X 2 discrete X Tulameenile grains I Cr>Fe chromite crystals more abundant than fragments 19.49 0.50 15 85 • X • ® • • Pt-Fe alloy X En chromite fragment 1128 Cr>Fe SITE 56 Dunitic A r n Rubble 1 O O (A-Zone) MAGNETIC PARAMAGNETIC NONMAGNETIC 52.16 0.93 95-100 0-5 • X • ® ® • Pt-Fe alloy X in chromite crystal 18 57 Fe=Cr 10.49 0.19 90 10 • ® • • • Cr>Fe (crystals) Cr>Fe (fragments) primarily chromite 37.35 0.67 5-10 90-95 • • X • X Pt-Fe alloy ^ in chromite fragment 3172 Cr>Fe SITE 57 Dunitic 1 5 6 Till<A-Zone> MAGNETIC PARAMAGNETIC NONMAGNETIC 67.15 5.59 95-100 0-5 • • • ® ® • Pt-Fe alloy X bi Mg-silicate 3! 59 Fe>Cr 3.50 029 50 50 • • ® • ® X Cr>Fe 29.35 2.44 10 90 • • X • • 1371 Cr>Fe only 4 chromites Table 4-15. Summary mineralogical results of SEM investigation of heavy mineral concentrates - Part A: colluvium and secondary study area dunitic till and rubble. Site \ ^ S ^ \ S \ M a g n e t ' t e \ C h r a m i t e \ ^ \ \ ^ \ SomtoNo. ® C o m m o 9 % > \ ° « ^ \ \ S & \ \ \ \ <<i\ \ \ G r a i n s • Subordi V ^ ^ < ^ < \ ^ < i ^ % N & X Chromite EDS sample X V ^ \ \ \ \ \ ^ ^ ^ \ 4 \ Analysis Summary nt (>50%) n (10-50%) nate(1-10%) c1%) Comments SITE 69 2 0 0 °™ c MAGNETIC PARAMAGNETIC NONMAGNETIC 58.87 3.25 95-100 0-5 • • • • • 273 | Fe>Cr chromrtes are primarily crystals 3.99 052 40 60 ® • ® ® ® ® ® X I Cr>Fe chromite fragment more abundanl than crystals 37.14 2.05 10-15 85-90 X • X 179 No Chromite SITE 73 « . _ Dunitic 2 1 6 m MAGNETIC NONMAGNETIC 56.80 6.35 80 20 • • ® ® X 474 Fe>Cr concentrates split from original; no duplicate 43.20 4.83 0-5 95-100 ® ® • • X ® X 139 Cr>Fe concentrates split from original; no duplicate srrE 20 A f\ Non-dunitic Till MAGNETIC PARAMAGNETIC NONMAGNETIC 41.58 254 95-100 0-5 • ® ® ® ® X • 517 Fe=Cr 2.39 0.13 50 50 ® ® • • • • ® Cr>Fe 56.03 3.02 20 80 X X X • X REE mineral X in apatite 22 Cr>Fe 1 chromite only SITE 6 H O Non-dunitic |y Till MAGNETIC PARAMAGNETIC NONMAGNETIC 21.03 0.88 95-100 0-5 • ® ® • • X X 143 1 Cr>Fe 4.81 050 60 40 ® X ® ® ® ® ® ® X U-Nb-Y-K X mineral in ilmenite i Cr>Fe; Cr>Fe similar proportions of crystals and fragments 74.17 3.10 10 90 • • • • • • ® Discrete X HEE minerals 33 Cr>Fe 10 chromites only Table 4-16. Summary mineralogical results of SEM investigation of heavy mineral concentrates - Part B: dunitic and non-dunitic tills. M i n b a c k g r o u n d - l e v e l d u n i t i c or n o n - d u n i t i c t i l l p r o f i l e s . No P t - a r s e n i d e s , antimonides or other non-Pt-Fe a l l o y PGM phases p r e v i o u s l y i d e n t i f i e d i n Tulameen c h r o m i t i t e s o r p l a c e r nuggets (Aubut, 1978; St. L o u i s e t a l , 1986; Nixon e t a l , 1990) were found i n the s o i l s . With one e x c e p t i o n , PGM were l o c a t e d e x c l u s i v e l y i n those heavy m i n e r a l f r a c t i o n s w i t h a Pt c o n c e n t r a t i o n of a t l e a s t 1000 ppb (1 ppm). 4.4.2.1 Discrete Free PGM Two d i s c r e t e f r e e PGM g r a i n s were observed, both w i t h i n the paramagnetic heavy f r a c t i o n of C h o r i z o n c o l l u v i u m ( s o i l s i t e 16; sample 88-SC-031) immediately beneath the C l i f f Zone PGE occurr e n c e s . One g r a i n (31PM-1) was observed i n the g r a i n stub mount, w h i l e the second (31PM-2) was observed i n p o l i s h e d s e c t i o n ( F igure 4-52). Both were by f a r the l a r g e s t PGM g r a i n s encountered i n the study. G r a i n 31PM-1 i s about 115 um x 103 um, with an equant h a b i t . G r a i n 31PM-2 i s approximately 85 um x 53 um with an el o n g a t e p r i s m a t i c shape and weakly c r y s t a l l i n e o u t l i n e i n s e c t i o n . G r a i n 31PM-1 was p a r t i a l l y obscured by ot h e r g r a i n s i n the stub mount. I t i s t e n t a t i v e l y i d e n t i f i e d as tulameenite (Pt 2FeCu) on the b a s i s of a Pt-Fe-Cu EDS a n a l y s i s . The s e c t i o n of g r a i n 31PM-2 i s more i n f o r m a t i v e . I t a l s o e x h i b i t s a Pt-Fe-Cu (tulameenite) s u r f a c e / r i m composition, 215 F i g u r e 4-52 D i s c r e t e Free PGM A. B a c k s c a t t e r SEM photomicrograph of f r e e PGM g r a i n (31PM-2) from paramagnetic heavy f r a c t i o n of C h o r i z o n c o l l u v i u m beneath C l i f f Zone PGE occurrence. B. B a c k s c a t t e r SEM photomicrograph showing c l o s e - u p of 31PM-2. Pt-Fe-Cu a l l o y r i m surrounds r e l i c t c o r e of Pt-Fe a l l o y . 216 but c o n t a i n s a r e l i c t i n t e r n a l Pt-Fe a l l o y c o r e t e n t a t i v e l y i d e n t i f i e d as isoferroplatinum on the b a s i s of r e l a t i v e peak h e i g h t s . T h i s , comprising about a t h i r d of the g r a i n , i s d i s t i n g u i s h e d from the surrounding t u l a m e e n i t e i n b a c k s c a t t e r e l e c t r o n imaging (Figure 4-52) as a s l i g h t l y b r i g h t e r area i n d i c a t i v e of a h i g h e r Pt content. Cu i s v i r t u a l l y absent i n the core compared t o the s u r r o u n d i n g t u l a m e e n i t e ; the p r o p o r t i o n of Fe, as estimated from peak h e i g h t s , i s approximately the same. The g e n e r a l l y c o r r o d e d appearance of the core and i t s t r a n s e c t i o n by t u l a m e e n i t e suggests a replacement t e x t u r e of Pt-Fe a l l o y by t u l a m e e n i t e . The corroded outer rim of the g r a i n i s s u g g e s t i v e of s u r f a c e weathering. 4.4.2.2 PGM Inclusions in Mg-silicates A s i n g l e PGM i n c l u s i o n (156M-1) was found i n a Mg-s i l i c a t e g r a i n from the magnetic f r a c t i o n of C h o r i z o n s o i l (sample 88-SC-156; s o i l s i t e 57) i n a d u n i t i c t i l l p r o f i l e about 70 m SSW of known PGE m i n e r a l i z a t i o n a t the A-Zone. The M g - s i l i c a t e g r a i n i s t e n t a t i v e l y i d e n t i f i e d as t a l c ( M g 3 S i 4 O 1 0 [ ° H 3 2 ) o n t n e b a s i s of r e l a t i v e Mg and S i peak h e i g h t s from EDS analyses, and from the x-ray d i f f r a c t i o n d e t e r m i n a t i o n of t a l c as the dominant M g - s i l i c a t e c o n s t i t u e n t of the -270 mesh f r a c t i o n of t h i s h o r i z o n (Appendix 6.2). The t a l c g r a i n ( F i g u r e s 4-53A and B) i s approximately 100 x 65 um and a l s o c o n t a i n s d i s s e m i n a t e d magnetite and p o s s i b l y chromite. The PGM i n c l u s i o n i s t r i a n g u l a r or heart-shaped, and i s approximately 9 um x 9 um (Figure 4-53C). The lower t h i r d of the g r a i n i s p a r t i a l l y obscured by c o v e r i n g t a l c ; p a r t of the upper t w o - t h i r d s e x h i b i t s the remnant of a p a r t i a l l y -s h a t t e r e d hexagonal c r y s t a l h a b i t . B a c k s c a t t e r e l e c t r o n imaging ( F i g u r e 4-53D) and EDS analyses show i t t o be a P t -Fe a l l o y w i t h v e r y l i t t l e Cu or N i , but c o n s i d e r a b l e d i f f e r e n c e s i n the r e l a t i v e p r o p o r t i o n s of Pt and Fe as est i m a t e d by peak h e i g h t s . Three darker areas e x h i b i t a r e l a t i v e l y h i g h Fe composition r e l a t i v e t o Pt, s u g g e s t i v e of a tetraferroplatinum (Pt2Fe 2) composition. The p r o p o r t i o n of Pt v a r i e s even w i t h i n t h i s grouping. The lower p o r t i o n of the c r y s t a l e x h i b i t s a much darker b a c k s c a t t e r image than the upper p o r t i o n , and c o n t a i n s a much h i g h e r p r o p o r t i o n o f Fe t o Pt. I t may be a more Pt-poor v a r i e t y of t e t r a f e r r o p l a t i n u m . The top l e f t corner of the PGM e x h i b i t s the r e v e r s e , a much high e r p r o p o r t i o n of Pt t o Fe s i m i l a r t o t h a t observed i n f r e e PGM g r a i n 31PM-2. T h i s p o r t i o n of the PGM i s t e n t a t i v e l y i d e n t i f i e d as isoferroplatinum (Pt3Fe). 219 F i g u r e 4-53 PGM I n c l u s i o n s i n M g - s i l i c a t e s A. SEM photomicrograph of Pt-Fe a l l o y i n c l u s i o n (156M-1) i n M g - s i l i c a t e ( t a l c ? ) g r a i n w i t h minor magnetite from magnetic heavy f r a c t i o n of C h o r i z o n t i l l ( s i t e 57) near the A-Zone PGE occurrence. B. SEM photomicrograph showing close-up of Pt-Fe a l l o y i n c l u s i o n 156M-1 i n M g - s i l i c a t e ( s i l ) . C. SEM photomicrograph of Pt-Fe a l l o y i n c l u s i o n 156M-1. D. B a c k s c a t t e r SEM photomicrograph of Pt-Fe a l l o y i n c l u s i o n 156M-1. B r i g h t e r areas i n d i c a t e l o c a t i o n s of h i g h e r Pt content i n the g r a i n . 4.4.2.3 PGM Inclusions in Chromite Four PGM i n c l u s i o n s (Figures 4-54 and 4-55) were found w i t h i n t h r e e s o i l chromite g r a i n s , a l l from near known PGE m i n e r a l i z a t i o n . Three PGM, i n c l u d i n g two w i t h i n the same hos t g r a i n , were found w i t h i n chromite from both the magnetic (153M-1, 153M-2) and non-magnetic (153NM-1) heavy f r a c t i o n s from C h o r i z o n d u n i t i c r u b b l e ( s o i l s i t e 56) d i r e c t l y above the A-Zone PGE occurrence. The f o u r t h (31NM-1) was found i n chromite of the non-magnetic heavy f r a c t i o n from C h o r i z o n c o l l u v i u m ( s o i l s i t e 16) beneath the C l i f f Zone PGE occurrences. The two PGM i n the magnetic f r a c t i o n occur w i t h i n a s i n g l e chromite c r y s t a l (Figure 4-54), w h i l e the two PGM i n non-magnetic f r a c t i o n s occur as i n c l u s i o n s w i t h i n chromite fragments ( F i g u r e 4-55). EDS analyses of the PGM-bearing fragments i n d i c a t e a Cr>Fe composition s i m i l a r t o those of o t h e r fragments from these s i t e s . EDS a n a l y s i s of the PGM-b e a r i n g chromite c r y s t a l i n d i c a t e a subequal Cr>Fe composition a l s o s i m i l a r t o other c r y s t a l s a t t h a t s i t e ( s e c t i o n 4.4.4). C h a r a c t e r i s t i c of each of the PGM i s t h e i r l o c a t i o n near the edge of the host g r a i n s ; none are found a t the c e n t r e of a chromite. The f o u r PGM i n c l u s i o n s e x h i b i t s i m i l a r e u h e d r a l t o subhedral h a b i t s . The l a r g e s t PGM (153M-1) i s p r i s m a t i c and F i g u r e 4-54 PGM I n c l u s i o n s i n a Chromite C r y s t a l B a c k s c a t t e r SEM photomicrograph of PGM-hosting d e t r i t a l chromite c r y s t a l (cmt) from magnetic heavy f r a c t i o n o f C h o r i z o n r u b b l e ( s i t e 56) immediately above t h e A-Zone PGE occurrence. B a c k s c a t t e r SEM photomicrograph showing l o c a t i o n o f two Pt-Fe a l l o y i n c l u s i o n s (153M-1, lower; and 153M-2, upper) i n the same chromite c r y s t a l (cmt) as i n A. above. B a c k s c a t t e r SEM photomicrograph showing c l o s e - u p of Pt-Fe a l l o y i n c l u s i o n 153M-1 i n d e t r i t a l chromite c r y s t a l (cmt). Note absence of c o m p o s i t i o n a l zoning. B a c k s c a t t e r SEM photomicrograph showing c l o s e - u p o f Pt-Fe a l l o y i n c l u s i o n 153M-2 i n d e t r i t a l chromite c r y s t a l (cmt). Pt-Fe. cmt F i g u r e 4-55 PGM I n c l u s i o n s i n Chromite Fragments B a c k s c a t t e r SEM photomicrograph of PGM-hosting d e t r i t a l chromite fragment (cmt) from non-magnetic heavy f r a c t i o n of C h o r i z o n r u b b l e ( s i t e 56) immediately above the A-Zone PGE occurrence. B a c k s c a t t e r SEM photomicrograph showing c l o s e - u p of Pt-Fe a l l o y i n c l u s i o n from A. (153NM-1) i n d e t r i t a l chromite fragment (cmt). B a c k s c a t t e r SEM photomicrograph of PGM-hosting d e t r i t a l chromite fragment (cmt) from non-magnetic heavy f r a c t i o n of C h o r i z o n c o l l u v i u m ( s i t e 16) beneath C l i f f Zone PGE occurrence. B a c k s c a t t e r SEM photomicrograph showing c l o s e - u p of Pt-Fe a l l o y i n c l u s i o n from C. (31NM-1) i n d e t r i t a l chromite fragment (cmt). measures approximately 3 um x 1 um ( F i g u r e 4-54C). I t s c o n t a c t w i t h chromite i s p l a n a r on one s i d e and s l i g h t l y rounded on the other t h r e e , although the o r i g i n a l g r a i n o r i e n t a t i o n i s unknown. The remaining t h r e e PGM are much s m a l l e r , l e s s than 2 um i n diameter, and are r e l a t i v e l ] y 5 ^ e q u i g r a n u l a r . T h e i r dimensions are approximately 0.4 um x 0.4 um (153M-2; F i g u r e 4-54D); 1.4 um x 1.2 um (153NM-1; F i g u r e 4-55B), 1.4 um x 1 um (31NM-1; F i g u r e 4-55D). The PGM i n c l u s i o n s are c o m p o s i t i o n a l l y s i m i l a r P t - F e -Ni-Cu a l l o y s as determined from EDS a n a l y s e s , t e n t a t i v e l y ^ •-""''Si i d e n t i f i e d as isoferroplatinum (Pt3Fe). N i i s p r e s e n t i n ' s m a l l amounts; i t i s a more important PGM c o n s t i t u e n t than Cu, and i s p a r t i c u l a r l y abundant i n 31NM-1. Backscat t e r ' ' imaging of the l a r g e s t PGM (153M-1; F i g u r e 4-54C) shows i t t o be c o m p o s i t i o n a l l y uniform and devoid of the zoning observed i n f r e e PGM g r a i n s and those i n s i l i c a t e s . 4.4.3 Magnetite Magnetite i s the dominant mi n e r a l i n magnetic heavy c o n c e n t r a t e s , u s u a l l y comprising 70-90% of the m e t a l l i c heavy g r a i n s (Tables 4-15 and 4-16). I t most commonly occu r s as i r r e g u l a r - s h a p e d , rough-surfaced anhedral aggregate g r a i n s of magnetite and s i l i c a t e , and as smoother more angular fragments. S i l i c a t e s i n other heavy f r a c t i o n s may c o n t a i n a s m a l l p r o p o r t i o n of magnetite i n c l u s i o n s . C r y s t a l s a re a second, but l e s s common, type of magnetite. They do not occur a t a l l s i t e s but are most abundant i n magnetic c o n c e n t r a t e s from n o n - d u n i t i c t i l l (88-SC-19; -40), where they are a common c o n s t i t u e n t of the m e t a l l i c g r a i n s . C r y s t a l s are g e n e r a l l y o c t a h e d r a l but are r a r e l y w e l l -formed; those i n n o n - d u n i t i c t i l l s i t e s are g e n e r a l l y s u b h e d r a l - a n h e d r a l . Euhedral magnetite c r y s t a l s a re most common i n s e r p e n t i n e c o l l u v i u m (88-SC-105), where they e x h i b i t p r i s m a t i c c a s t marks more commonly observed on i l m e n i t e g r a i n s . The p h y s i c a l s i m i l a r i t y of magnetite and chromite c r y s t a l s i n magnetic f r a c t i o n s n e c c e s s i t a t e d c o n s t a n t EDS a n a l y s i s , from which magnetite was i d e n t i f i e d by the presence of c h a r a c t e r i s t i c Fe peaks. Magnetite was u s u a l l y e a s i l y d i s t i n g u i s h a b l e from chromite i n p o l i s h e d s e c t i o n by both i t s a s s o c i a t i o n with s i l i c a t e s and by the much more cra c k e d and furrowed appearance of the s u r f a c e . F i n e magnetite, sometimes a l t e r e d t o hematite or l i m o n i t e , f r e q u e n t l y o c c u r r e d together with M g - s i l i c a t e as a t h i n c o a t i n g on chromite c r y s t a l s (Figure 4-56). Magnetite c r y s t a l s a re sometimes t i t a n i f e r o u s , but t h e i r c ompositions and d i s t r i b u t i o n were not f u r t h e r i n v e s t i g a t e d . No magnetite g r a i n s of any type were found d i r e c t l y a s s o c i a t e d w i t h PGM g r a i n s . 228 4.4.4 Chromite 4.4.4.1 Scanning Electron Microscopy Results Chromite i s most abundant i n the magnetic f r a c t i o n , where i t i s a common t o subordinate c o n s t i t u e n t (Tables 4-15 and 4-16). Magnetic f r a c t i o n s from s i t e s a d j a c e n t t o A-Zone PGE m i n e r a l i z a t i o n c o n t a i n the g r e a t e s t p r o p o r t i o n o f chromite (30-40%), w h i l e those from some background d u n i t i c and n o n - d u n i t i c t i l l s i t e s c o n t a i n the l e a s t (5-10%). I t i s a r e l a t i v e l y much more important c o n s t i t u e n t (up t o 90%), however, of the heavy m e t a l l i c component of many paramagnetic and non-magnetic f r a c t i o n s . Chromites, p a r t i c u l a r l y fragments, are the onl y heavy m e t a l l i c d e t r i t a l g r a i n s found i n d i r e c t a s s o c i a t i o n w i t h PGM ( s e c t i o n 4.4.2.3). Chromite occurs as d i s c r e t e g r a i n s c o m p r i s i n g both eu h e d r a l - s u b h e d r a l c r y s t a l s and anhedral fragments. C r y s t a l s ( F i g u r e 4-56) are t y p i c a l l y o c t a h e d r a l t o subrounded, f r e q u e n t l y have a p a r t i a l c o a t i n g o f f i n e magnetite and M g - s i l i c a t e , and may e x h i b i t minor weathering or e r o s i o n a l f e a t u r e s such as s c a l i n g or pockmarked f a c e s and chipped c o r n e r s . Fragments (Figure 4-57) are e l o n g a t e -t o - b l o c k y , o f t e n wedge or s l i v e r - s h a p e d , g r a i n s w i t h sharp c o r n e r s and an apparent c o n c h o i d a l f r a c t u r e . Chromite fragments u s u a l l y have extremely smooth and u n a l t e r e d 229 s u r f a c e s compared t o those of c r y s t a l s . Chromites are g r o s s l y p a r t i t i o n e d between heavy f r a c t i o n s on the b a s i s of g r a i n morphology (Tables 4-15 and 4-16). C r y s t a l s are common c o n s t i t u e n t s of most magnetic f r a c t i o n s , c o n s i s t i n g predominantly of magnetite, and are r e l a t i v e l y more abundant than fragments which t y p i c a l l y occur i n o n l y t r a c e t o subordinate amounts. Conversely, fragments are r e l a t i v e l y more abundant than c r y s t a l s i n most (6 out of 8) non-magnetic f r a c t i o n s , which c o n t a i n l e s s chromite o v e r a l l and c o n s i s t predominantly of s i l i c a t e s . I t shou l d be s t r e s s e d t h a t w hile fragments are relatively more important than c r y s t a l s i n non-magnetic f r a c t i o n s , fragments are n e v e r t h e l e s s more numerically abundant i n the magnetic f r a c t i o n s than i n the non-magnetic f r a c t i o n s . The r e l a t i v e p r o p o r t i o n of fragments i n the non-magnetic f r a c t i o n i s h i g h l y v a r i a b l e . They are dominant c o n s t i t u e n t s (65-90%) of the heavy m e t a l l i c component a t s i t e s a d j a c e n t t o both A-Zone and C l i f f Zone PGE occ u r r e n c e s , but are common t o t r a c e c o n s t i t u e n t s o f most o t h e r non-magnetic f r a c t i o n s . However, chromite fragments were absent from non-magnetic f r a c t i o n s a t two s i t e s i n non-d u n i t i c t i l l (88-SC-40) and background d u n i t i c t i l l (88-SC-200). The paramagnetic f r a c t i o n , which c o n t a i n s both c r y s t a l s and fragments, u s u a l l y c o n t a i n s a r e l a t i v e l y h i g h e r p r o p o r t i o n of fragments than the non-magnetic f r a c t i o n a t 230 F i g u r e 4-56 Morphology of Chromite C r y s t a l s A. SEM photomicrograph of euhedral chromite c r y s t a l (cmt), w i t h adhering M g - s i l i c a t e , beside an i l m e n i t e (ilm) g r a i n . D u n i t i c c o l l u v i u m ( s i t e 16), 88-SC-31, paramagnetic f r a c t i o n . B. SEM photomicrograph of euhedral chromite c r y s t a l (cmt), w i t h adhering m a g n e t i t e - s i l i c a t e , b e s i d e a magnetite-s i l i c a t e (mag) aggregate g r a i n . N o n - d u n i t i c t i l l ( s i t e 20), 88-SC-40, paramagnetic f r a c t i o n . C. SEM photomicrograph of subhedral chromite c r y s t a l (cmt). Non-dunitic t i l l ( s i t e 20), 88-SC-40, magnetic f r a c t i o n . D. SEM photomicrograph of subhedral chromite c r y s t a l (cmt) enveloped i n M g - s i l i c a t e ( s i l ) . N o n - d u n i t i c t i l l ( s i t e 6), 88-SC-19, paramagnetic f r a c t i o n . 231 F i g u r e 4-57 Morphology of Chromite Fragments SEM photomicrograph of anhedral chromite fragment (cmt). D u n i t i c t i l l ( s i t e 69), 89-SC-200, paramagneti f r a c t i o n . SEM photomicrograph of anhedral chromite fragment (cmt). N o n - d u n i t i c t i l l ( s i t e 6), 88-SC-19, paramagnetic f r a c t i o n . SEM photomicrograph of anhedral chromite fragment (cmt) from immediately above the A-Zone PGE o c c u r r e n c e D u n i t i c r u b b l e ( s i t e 56), 88-SC-153, non-magnetic f r a c t i o n . SEM photomicrograph of anhedral chromite fragment (cmt) from immediately above the A-Zone PGE o c c u r r e n c e D u n i t i c r u b b l e ( s i t e 56), 88-SC-153, paramagnetic f r a c t i o n . 233 234 s i t e s which are not immediately adjacent t o known PGE m i n e r a l i z a t i o n . The p a r t i t i o n i n g of chromite among heavy f r a c t i o n s i s r e l a t e d t o g r a i n composition as w e l l as morphology. C h a r a c t e r i s t i c Cr and Fe peak h e i g h t s observed d u r i n g EDS a n a l y s e s of chromites v a r i e d a c c o r d i n g t o heavy f r a c t i o n and g r a i n morphology, i n d i c a t i n g a s y s t e m a t i c r e l a t i o n between the two. A summary of chromite EDS Cr:Fe s i g n a t u r e s f o r each f r a c t i o n of the e i g h t samples i s shown i n T a b l e s 4-15 and 4-16. Chromite c r y s t a l s , r e l a t i v e l y more abundant i n the magnetic f r a c t i o n , are g e n e r a l l y more F e - r i c h ; chromite fragments, r e l a t i v e l y more abundant i n the non-magnetic f r a c t i o n , are g e n e r a l l y more C r - r i c h . Fragments have g r e a t e r p r o p o r t i o n s of Cr r e l a t i v e t o Fe i n a l l types of parent m a t e r i a l a t a l l s i t e s , but c r y s t a l compositions are more v a r i a b l e . C r y s t a l s from s e r p e n t i n e c o l l u v i u m , c o l l u v i u m and t i l l / r u b b l e adjacent t o known PGE m i n e r a l i z a t i o n , and n o n - d u n i t i c t i l l s i t e s g e n e r a l l y c o n t a i n about subequal p r o p o r t i o n s of Cr and Fe i n the o r d e r Cr=Fe or Cr>Fe. Those showing a Fe>Cr t r e n d are o n l y found a t d u n i t i c t i l l s i t e s (88-SC-156; -200; -216) . 4.4.4.2 Electron Microprobe Results Mean e l e c t r o n microprobe (EMP) compositions o f chromite 235 c r y s t a l s and fragments from each of f i v e s o i l C h o r i z o n s ( s e c t i o n 3.7.3) are shown i n Tables 4-17 and 4-18. A n a l y s i s of v a r i a n c e r e s u l t s f o r Cr20 3 and MgO c o n c e n t r a t i o n s of g r a i n c o r e s are g i v e n i n Tables 4-19 and 4-20. I n d i v i d u a l c o r e a n a l y s e s and mean valu e s are p l o t t e d i n F i g u r e s 4-58 and 4-59. Ne a r l y a l l chromites p l o t i n the f e r r i a n chromite f i e l d on the Fe - C r - A l t e r n a r y diagram ( F i g u r e 4-58) of the s p i n e l p r i s m (Stevens, 1944). The onl y e x c e p t i o n s are two fragments and f i v e c r y s t a l s which p l o t as a l u m i n i a n chromite and chromiah magnetite r e s p e c t i v e l y . EMP r e s u l t s from g r a i n c o r e s (Table 4-17) i n d i c a t e t h a t c o n s i d e r a b l e c o m p o s i t i o n a l d i f f e r e n c e s may e x i s t between c r y s t a l s and fragments. In g e n e r a l , chromites have low A l (mean: 5.88-7.20 wt% A I 2 O 3 ) , minor T i (mean: 0.57-1.02 wt% Ti02) and minor Mn (mean: 0.23-0.71 wt% MnO) contents. A l and T i are s i m i l a r among both c r y s t a l s and fragments. Cr, Fe,Mg and Mn c o n t e n t s , however, are v a r i a b l e and r e l a t e d t o g r a i n morphology and, t o a l e s s e r extent, p r o x i m i t y t o known PGE m i n e r a l i z a t i o n . Chromite fragments have g r e a t e r Cr, l e s s e r Fe, and may have g r e a t e r Mg and Mn contents than c r y s t a l s from the same s i t e . C r / T o t a l Fe r a t i o s of cores (Table 4-17) range from 0.68-0.87 i n F e - r i c h c r y s t a l s , but from 0.94-1.32 i n Fe-poor fragments. Compositional d i f f e r e n c e s between c r y s t a l s and fragments are v e r i f i e d by a s e r i e s of t - t e s t s on s e l e c t e d elements a t each of the f i v e s o i l s i t e s . Mean Cr203 A) CRYSTALS: CORES 19 200 (n=9) (n=9) S i 0 2 0. 00 0. 00 A 1 2 0 3 6.70 5.99 T i 0 2 0.71 1. 02 C r 2 0 3 36.60 35.23 F e 2 0 3 24.65 26.25 FeO 24.86 25.82 MnO 0.65 0.71 MgO 4.53 4.47 T o t a l 98.70 99.49 Cr/Fe 0.74 0. 68 B) FRAGMENTS: CORES 156 153 31 (n=15) (n=15) (n=15) 0.07 0.01 0.01 5.88 6.14 6.96 0.73 0.65 0.67 36.17 36.59 39.54 25.44 25.04 21.63 26.26 24.73 23.80 0.49 0.44 0.45 4.15 5.00 5.78 99.19 98.60 98.84 0.70 0.74 0.87 19 200 156 153 31 (n=9) (n=9) (n=9) (n=15) (n=15) S i 0 2 0.00 0.00 A 1 2 0 3 7.10 7.20 T i 0 2 0.66 0.57 C r 2 0 3 41.07 43.81 F e 2 0 3 19.92 17.92 FeO 23.49 21.65 MnO 0.52 0.51 MgO 5.92 7.12 0.01 0.01 0.01 5.98 6.57 6.93 0.60 0.64 0.61 42.10 42.86 45.83 20.48 20.20 17.54 24.11 18.75 17.17 0.36 0.24 0.23 5.59 9.07 10.19 T o t a l 98.68 98.78 99.23 98.34 98.51 Cr/Fe 0.95 1.11 0.94 1.10 1.32 Ta b l e 4-17. Mean e l e c t r o n microprobe data (weight percent) f o r c o r e s of d e t r i t a l chromite c r y s t a l s (magnetic heavy f r a c t i o n ) and fragments ( p a r t l y magnetic and non-magnetic heavy f r a c t i o n s ) from v a r i o u s C h o r i z o n s : 1 9-non-dunitic t i l l ; 2 0 0 - d u n i t i c t i l l ; 1 5 6 - d u n i t i c t i l l near A-Zone PGE m i n e r a l i z a t i o n ; 1 5 3 - d u n i t i c t i l l / r u b b l e above A-Zone; 31-c o l l u v i u m beneath C l i f f Zone PGE m i n e r a l i z a t i o n . A) CRYSTALS: EDGES 19 200 156 153 31 (n=9) (n=9) (n=15) (n=15) (n=14) s i o 2 0. 00 0. 00 0.07 0.00 0. 01 A 1 2 0 3 6.49 5.77 5.83 6.02 6.72 TiC-2 0.70 0.92 0.70 0. 67 0. 67 C r 2 0 3 36.15 34.45 35.74 35.80 39 .12 F e 2 0 3 24.29 27.19 25.74 25.63 22.18 FeO 25.55 25.54 26.86 25.05 24.00 MnO 0.83 0.77 0.59 0. 60 0.57 MgO 4.18 4.44 3 . 67 4.63 5.54 T o t a l 98.19 99.08 99.20 98.40 98.81 Cr/Fe 0.73 0.65 0.68 0.71 0.85 B) FRAGMENTS: EDGES 19 200 156 153 31 (n=9) (n=9) (n=9) (n=15) (n=15 s i o 2 0. 00 0.00 A 1 2 0 3 6.94 7.25 T i 0 2 0.71 0.58 C r 2 0 3 40.24 43.66 F e 2 0 3 20. 35 18.16 FeO 23.78 21.57 MnO 0.58 0.51 MgO 5.59 7.22 0.01 0.01 0.00 5.97 6.63 6.93 0.60 0.61 0.61 41.05 42.83 45.54 20.72 19.87 17.51 25.81 18.64 17.21 0.36 0.26 0.23 4.42 9.02 10.07 T o t a l 98.19 98.95 98.94 97.87 98.10 Cr/Fe 0.91 1.10 0.88 1.11 1.31 T a b l e 4-18. Mean e l e c t r o n microprobe data (weight percent) f o r edges of d e t r i t a l chromite c r y s t a l s (magnetic heavy f r a c t i o n ) and fragments ( p a r t l y magnetic and non-magnetic heavy f r a c t i o n s ) from v a r i o u s C h o r i z o n s : 1 9 - n o n - d u n i t i c t i l l ; 2 0 0 - d u n i t i c t i l l ; 1 5 6 - d u n i t i c t i l l near A-Zone PGE m i n e r a l i z a t i o n ; 1 5 3 - d u n i t i c t i l l / r u b b l e above A-Zone; 31-c o l l u v i u m beneath C l i f f Zone PGE m i n e r a l i z a t i o n . 238 c o n c e n t r a t i o n s of c r y s t a l s and fragments are s i g n i f i c a n t l y d i f f e r e n t (p = .05) a t a l l f i v e s i t e s . Furthermore, mean MgO c o n c e n t r a t i o n s of the two groups are s i g n i f i c a n t l y d i f f e r e n t (p = .05) a t f o u r of f i v e s i t e s ; o n l y i n sample 19 from n o n - d u n i t i c t i l l are MgO contents of c y s t a l s and fragments s i m i l a r . Mean Cr content of c r y s t a l s (range: 20.06-45.43 wt% Cr203) i s remarkably s i m i l a r (range of means: 35.23-39.54 wt% Cr203) a t a l l f i v e s o i l s i t e s (Table 4-17) and i s more uni f o r m than suggested by EDS analyses. Mean Cr co n t e n t of fragments (range: 37.66-50.25 wt% C r 2 0 3 ) , although g r e a t e r , i s a l s o s i m i l a r between a l l s o i l s i t e s (range of means: 41.07-45.83 wt% C r 2 0 3 ) . Sample 31 ( c o l l u v i u m beneath C l i f f Zone PGE occurrences) has the h i g h e s t Cr203 content of both c r y s t a l s and fragments. E q u i v i l e n c y of mean core Cr203 c o n c e n t r a t i o n s was t e s t e d w i t h one-way a n a l y s i s of v a r i a n c e (p = .05) t o determine i f between-site v a r i a b i l i t y i s s i g n i f i c a n t l y g r e a t e r than w i t h i n - s i t e v a r i a b i l i t y . The n u l l h y p o t h e s i s (HQ) f o r each of c r y s t a l s and fragments i s : u x = u 2 = u 3 = u 4 = u 5 Acceptance of HQ i n d i c a t e s t h a t the f i v e p o p u l a t i o n means are i d e n t i c a l ; r e j e c t i o n i n favour of the a l t e r n a t e h y p o t h e s i s ( H ^ ) i n d i c a t e s t h a t between-site v a r i a b l i t y i s so l a r g e t h a t a t l e a s t one p o p u l a t i o n mean i s s i g n i f i c a n t l y d i f f e r e n t from the o t h e r s . R e s u l t s (Table 4-19) show t h a t mean Cr 203 c o n c e n t r a t i o n s are indeed homogenous i n c r y s t a l s a t a l l f i v e s i t e s . However, t h i s i s not the case f o r a t l e a s t one of the fragment means (p = .05); t h e i r C X 2 O 3 c o n t e n t s are s i g n i f i c a n t l y d i f f e r e n t between s i t e s . FeO and Fe 203 contents are r e c a l c u l a t e d from t o t a l Fe 203 on the b a s i s of the s p i n e l s t r u c t u r a l formula. Fe , showing a t r e n d g e n e r a l l y o p p o s i t e t o t h a t of Cr, ranges from 15.79-45.98 wt% Fe 203 i n c r y s t a l s (range of means: 21.63-26.25 wt% F e 2 0 3 ) and from 12.89-23.18 wt% F e 2 0 3 i n Fe-poor fragments (range of means: 17.54-20.48 wt% F e 2 0 3 ) . C r y s t a l s i n sample 200 (background d u n i t i c t i l l ) have the h i g h e s t mean Fe 203 content. Mean F e 2 + content, which i s l e s s v a r i a b l e than F e 3 + , ranges from 23.80-26.26 wt% FeO i n c r y s t a l s and from 21.65-24.11 wt% FeO i n fragments a t the t h r e e s i t e s i n which the paramagnetic f r a c t i o n was used. However, FeO co n t e n t of c r y s t a l s a t the two s i t e s which non-magnetic f r a c t i o n s were used i s c o n s i d e r a b l y lower (range of means: 17.17-18.75 wt% FeO). Both s i t e s (16 and 56) are adjacent t o known PGE oc c u r r e n c e s . T h i s i s p a r a l l e d by a s i m i l a r decrease i n Mn, and corresponds t o a Mg content (range of means: 9.07-10.19 wt% MgO) about 2x g r e a t e r t h a t of c r y s t a l s (range of means: 4.15-5.78 wt% MgO) and fragments (range of means: 5.59-7.12 wt% MgO) from the other t h r e e s i t e s . E q u i v i l e n c y of core 240 A. Cr20j (%) in chromite crystals (N=63) Sample Mean ± Is n 1) 19 36.60 ± 3.41 9 2) 200 35.23 ± 8.83 9 3) 156 36.17 ± 3.37 15 4) 153 36.59 ± 2.30 15 5) 31 39.54 ± 3.45 15 Source of V a r i a t i o n Between groups W i t h i n groups T o t a l Sum of Squares 139.26 1116.5 1255.76 Degrees of Freedom 4 58 62 Mean Squares 34.82 19 .25 F = 1.81; Fcj-JLticai = 2.53 (0.05 s i g n i f i c a n c e l e v e l ) F < ^ c r i t i c a l N u l l h y p o t h e s i s accepted; p o p u l a t i o n s are not d i f f e r e n t B. Cr202 (%) in chromite fragments (N=57) Sample Mean ± Is n 1) 19 41.07 + 1.54 9 2) 200 43.81 ± 3.81 9 3) 156 42.10 ± 1.82 9 4) 153 42.86 + 1.12 15 5) 31 45.83 ± 2.07 15 Source of Sum of Degrees of Mean V a r i a t i o n Squares Freedom Squares Between groups 158.51 4 39.63 W i t h i n groups 239.02 52 4.60 T o t a l 397.53 56 F = 8.62; F c r i t i c a l =2.53 (0.05 s i g n i f i c a n c e l e v e l ) F > ^ c r i t i c a l N u l l h y p o t h e s i s r e j e c t e d ; p o p u l a t i o n s are d i f f e r e n t T a b l e 4-19. Anova t a b l e s showing one-way a n a l y s i s o f v a r i a n c e r e s u l t s f o r Cr 203 analyses of f i v e groups of A. chromite c r y s t a l s and B. chromite fragments. A. MgO (%) in chromite crystals (N=63) Sample Mean + Is n 1) 19 4.53 + 1.55 9 2) 200 4.47 + 1.74 9 3) 156 4.15 ± 1.07 15 4) 153 5.00 ± 0.90 15 5) 31 5.78 ± 1.00 15 Source of V a r i a t i o n Between groups W i t h i n groups T o t a l Sum of Squares 22.85 84.74 107.57 Degrees of Freedom 4 58 62 Mean Squares 5.71 1.46 F = 3.91; F c r i t i c a i = 2.53 (0.05 s i g n i f i c a n c e l e v e l ) F > F c r i t i c a l N u l l h y p o t h e s i s r e j e c t e d ; p o p u l a t i o n s are d i f f e r e n t B. MgO (%) in chromite fragments (N=57) Sample Mean ± Is n 1) 19 5.92 ± 2.09 9 2) 200 7.12 ± 1.91 9 3) 156 5.59 ± 1.58 9 4) 153 9.07 ± 0.45 15 5) 31 10.19 ± 1.30 15 Source of Sum of Degrees of Mean V a r i a t i o n Squares Freedom Squares Between groups 187.28 4 46.82 W i t h i n groups 110.62 52 2.13 T o t a l 297.90 56 F = 21.98; F c j - i t i c a i = 2.53 (0.05 s i g n i f i c a n c e l e v e l ) F > F c r i t i c a l N u l l h y p o t h e s i s r e j e c t e d ; p o p u l a t i o n s are d i f f e r e n t T a b l e 4-20. Anova t a b l e s showing one-way a n a l y s i s o f v a r i a n c e r e s u l t s f o r MgO analyses (%) of f i v e groups of A. chromite c r y s t a l s and B. chromite fragments. MgO c o n c e n t r a t i o n s i n the f i v e s i t e s was a l s o t e s t e d w i t h one-way a n a l y s i s of v a r i a n c e . R e s u l t s (Table 4-20) i n d i c a t e MgO inhomogeneity between s i t e s f o r both c r y s t a l s and fragments. The c o m p o s i t i o n a l f i e l d s of some major rock types of Tulameen complex (Nixon e t a l , 1990) are shown on two f a c e s of the s p i n e l prism i n r e l a t i o n t o the compositions of i n d i v i d u a l d e t r i t a l chromites ( F i g u r e s 4-58 and 4-59). C r y s t a l s g e n e r a l l y f a l l w i t h i n the f i e l d of d u n i t e and c h r o m i t i f e r o u s d u n i t e and, t o a l e s s e r extent, o l i v i n e c l i n o p y r o x e n i t e . Fragments almost always p l o t w i t h i n the c h r o m i t i t e f i e l d . More s i g n i f i c a n t l y , fragments from r u b b l e and c o l l u v i u m (153 and 31) adjacent t o known PGE o c c u r r e n c e s p l o t w i t h i n or near the magnesiochromite f i e l d ( F i g u r e 4-59). They a l s o p l o t w i t h i n the t i g h t e s t c o m p o s i t i o n a l range, w h i l e those from d u n i t i c t i l l samples 2 00 and 156 p l o t w i t h i n the widest. D u n i t i c t i l l sample 200 a l s o p l o t s w i t h i n the widest c o m p o s i t i o n a l range among c r y s t a l s . Mean a n a l y t i c a l data of chromite cores and edges (Tables 4-17 and 4-18) i n d i c a t e n e g l i g i b l e c o m p o s i t i o n a l d i f f e r e n c e s . I t should be s t r e s s e d t h a t d e t r i t a l g r a i n s were not a c i d p u r i f i e d or u l t r a s o n i c a l l y c l e a n e d p r i o r t o mounting. Edge compositions may be a f f e c t e d by a d h e r i n g m i n e r a l s , although i t i s not r e a d i l y apparent i n the d a t a . T h i s would be expected t o a f f e c t c r y s t a l s more than Figure 4-58. Fe-Cr-AI spinel composition plot of detrital chromite crystals (n=63) and fragments (n=57) from various C Horizon soils and from some major rock types of the Tulameen complex (adapted from Nixon et al, 1990; Stevens, 1944). 100 100 100 100 100 100 80 < ± 60 I-o o o o 40 20 0 n=18 Non-Dunitic Till Soil Site 6 88-SC-019 Dunitic Till Soil Site 69 89-SC-200 . n=18 Dunitic Till Adjacent to A-Zone PGE Occurrence Soil Site 57 88-SC-156 Dunitic Rubble Above A-Zone PGE Occurrence Soil Site 56 88-SC-153 Colluvium Beneath Cliff Zone PGE Occurrences Soil Site 16 88-SC-031 Magnesiochromite Chromite crystals Chromite fragments Chromitite Dunite and Chromitiferous Dunite Olivine Clinopyroxenite Hornblende Clinopyroxenite FGrrochrornito Mean Values 19 • 0 200 < 156 * O 153 • o 31 • o n=24 n=30 n=30 20 40 60 100Fe7(Fe2++Mg) 80 100 Figure 4-59. Plot of Fe2+/(Fe2+ + Mg2+) versus Cr/(Cr+AI) for detrital chromite crystals (n=63) and fragments (n=57) from various C horizon soils and major rock types of the Tulameen complex (adapted from Nixon et al, 1990). fragments. R e l a t i v e t o cores, edges are s l i g h t l y d e p l e t e d i n Cr2C>3, u s u a l l y s l i g h t l y e n r i c h e d i n Fe20 3, and r e l a t i v e l y c o n s t a n t i n Ti02 i n both c r y s t a l s and fragments. Behaviour of o t h e r elements d i f f e r between c r y s t a l s and fragments. C r y s t a l edges are s l i g h t l y d e p l e t e d i n AI2O3 and MgO, and s l i g h t l y e n r i c h e d i n FeO and MnO. Fragment edges, however, are c o n s t a n t i n AI2O3, constant t o s l i g h t l y d e p l e t e d i n MgO, and r e l a t i v e l y constant i n FeO and MnO. Among conserved elements i n fragments, those of sample 19 seem the l e a s t c o n s t a n t . 4.4.5 I l m e n i t e I l m e n i t e was i d e n t i f i e d on the b a s i s of c h a r a c t e r i s t i c Fe and T i EDS peaks. I t occurs as subhedral c r y s t a l s e x h i b i t i n g c a s t marks of attached p r i s m a t i c s i l i c a t e s and as poorly-formed subhedral-anhedral g r a i n s w i t h c h a r a c t e r i s t i c C a - s i l i c a t e i n c l u s i o n s or t h e i r c a s t s . I l m e n i t e i s a common t o subordinate c o n s t i t u e n t o f paramagnetic and, i n some cases, nonmagnetic heavy c o n c e n t r a t e s (Tables 4-15 and 4-16). I t i s most common i n paramagnetic f r a c t i o n s from c o l l u v i u m where i t comprises 45% of the m e t a l l i c g r a i n s i n s e r p e n t i n e c o l l u v i u m (88-SC-105), and 35% of t h a t f r a c t i o n i n c o l l u v i u m beneath C l i f f Zone PGE occu r r e n c e s (88-SC-31). Il m e n i t e i s , however, r e l a t i v e l y uncommon adj a c e n t t o A-Zone PGE m i n e r a l i z a t i o n and has no apparent a s s o c i a t i o n with PGM g r a i n s . 4.4.6 Other M i n e r a l s Other m i n e r a l s , a s i d e from common s i l i c a t e s , observed d u r i n g SEM examination of heavy co n c e n t r a t e s i n c l u d e Fe oxide s and o x i d i z e d s u l f i d e s , z i r c o n , r a r e e a r t h element (REE) m i n e r a l s and a U-Nb-Y-K m i n e r a l . A v a r i e t y o f m e t a l l i c contaminants are a l s o present. Fe oxides and o x i d i z e d s u l f i d e s are most abundant i n nonmagnetic c o n c e n t r a t e s . They are dominant c o n s t i t u e n t s of t h i s f r a c t i o n a t n o n - d u n i t i c and some d u n i t i c t i l l s i t e s , where they comprise n e a r l y a l l of the heavy m e t a l l i c g r a i n s (Tables 4-15 and 4-16), but are only a su b o r d i n a t e c o n s t i t u e n t of c o l l u v i u m and d u n i t i c t i l l / r u b b l e near known PGE m i n e r a l i z a t i o n . They occur as anhedral g r a i n s and masses of Fe oxide and as o x i d i z e d anhedral-euhedral p y r i t e pseudomorphs. These o f t e n c o n t a i n i r r e g u l a r - s h a p e d c o r e s of r e l i c t p y r i t e , v i s i b l e i n p o l i s h e d s e c t i o n , and are p a r t i c u l a r l y common a t background d u n i t i c t i l l s i t e s (88-SC-200;-216) and a t a n o n - d u n i t i c t i l l s i t e (88-SC-40). P y r i t e pseudomorphs may show s u r f a c e s t r i i a t i o n s or e t c h p i t s . A s i n g l e i r r e g u l a r - s h a p e d g r a i n of Fe-Ni s u l p h i d e , p o s s i b l y p e n t l a n d i t e , was observed i n p o l i s h e d s e c t i o n of a 247 nonmagnetic c o n c e n t r a t e from s e r p e n t i n e c o l l u v i u m (88-SC-105). Subequal EDS peak h e i g h t s decreased i n the o r d e r : S > Fe > N i . Z i r c o n s occur as t r a c e - t o - s u b o r d i n a t e c o n s t i t u e n t s of non-magnetic co n c e n t r a t e s of a l l types. They are most abundant i n a n o n - d u n i t i c t i l l s i t e (88-SC-19). Most are c r y s t a l l i n e but a s i n g l e well-rounded g r a i n was observed i n A-Zone d u n i t i c t i l l (88-SC-156) from the summit of Grasshopper Mountain. A v a r i e t y of r a r e minerals were found i n p o l i s h e d s e c t i o n s of c o n c e n t r a t e s from n o n - d u n i t i c t i l l . An approximately 8 um x 4 um i n c l u s i o n of an u n i d e n t i f i e d U-Nb-Y-K m i n e r a l was found i n an i l m e n i t e g r a i n w i t h i n a paramagnetic co n c e n t r a t e (88-SC-19). Two d i s c r e t e Ce-b e a r i n g REE m i n e r a l s were found w i t h i n the nonmagnetic f r a c t i o n of the same sample. One, measuring approximately 60 um x 35 um, was an u n i d e n t i f i e d Ce-Th-La-P m i n e r a l ; the second, approximately 80 um x 25 um, was an u n i d e n t i f i e d Fe-Ca-Ce-La s i l i c a t e . A t h i r d REE m i n e r a l was found i n the nonmagnetic c o n c e n t r a t e of the other n o n - d u n i t i c t i l l sample (88-SC-40). I t o c c u r r e d as s e v e r a l s m a l l i n c l u s i o n s , approximately 1-6 um i n diameter, of an u n i d e n t i f i e d Ce-La m i n e r a l w i t h i n an a p a t i t e (Ca-P) g r a i n . Chapter F i v e DISCUSSION CHAPTER FIVE: DISCUSSION 5.1 I n t r o d u c t i o n R e s u l t s of the d i s t r i b u t i o n s of Pt and o t h e r s e l e c t e d elements w i t h i n v a r i o u s s u r f i c i a l m a t e r i a l s on Grasshopper Mountain were presented i n the p r e v i o u s chapter. In t h i s c hapter, they are used t o present a model f o r mechanical and, t o a l e s s e r l e s s e r degree, hydromorphic d i s p e r s i o n of Pt a t t h i s l o c a l i t y . Compositional v a r i a t i o n s of p l a t i n i c chromite are shown t o be t h e o r e t i c a l l y p r e d i c t a b l e , and recommendations f o r geochemical e x p l o r a t i o n f o r c h r o m i t i t e -a s s o c i a t e d Pt d e p o s i t s are o u t l i n e d . I t should be s t r e s s e d t h a t such recommendations are d i r e c t l y a p p l i c a b l e o n l y t o s i m i l a r d e p o s i t s i n temperate g l a c i a t e d environments. 5.2 D e t r i t a l Chromites 5.2.1 O r i g i n of D e t r i t a l Chromites Chromite occurs i n Tulameen d u n i t e as both massive c h r o m i t i t e s e g r e g a t i o n s and as accessory d i s s e m i n a t e d s u b h e d r a l - e u h e d r a l c r y s t a l s ( F i n d l a y , 1963; Nixon e t a l , 1990). Compositional and morphological evidence suggest t h a t anhedral chromite fragments i n s o i l s r e p r e s e n t the / 250 fragmented remnants of c h r o m i t i t e s e g r e g a t i o n s t h a t may c o n t a i n e l e v a t e d Pt c o n c e n t r a t i o n s (St. L o u i s e t a l , 1986). Conversely, d e t r i t a l chromite c r y s t a l s r e p r e s e n t r e l a t i v e l y Pt-poor c r y s t a l s l i b e r a t e d from d u n i t e and, perhaps t o a l e s s e r extent, o l i v i n e c l i n o p y r o x e n i t e ( F i g u r e s 4-58 and 4-59) . 5.2.1.1 Fragments Compositional s i m i l a r i t i e s of the d e t r i t a l fragments t o the composition of massive c h r o m i t i t e (Table 5-1) r e p o r t e d by I r v i n e (1967) and Nixon e t a l (1990), and c o m p o s i t i o n a l d i f f e r e n c e s between these and d e t r i t a l c r y s t a l s , s t r o n g l y suggest t h a t d e t r i t a l fragments d e r i v e from c h r o m i t i t e s e g r e g a t i o n s . Higher C r 2 0 3 , l e s s e r F e 2 0 3 and FeO, and h i g h e r MgO contents (Tables 4-17 and 5-1, F i g u r e s 4-58 and 4-59) c h a r a c t e r i z e both fragments and massive c h r o m i t i t e s . A s t r i k i n g f e a t u r e i s the c o m p o s i t i o n a l u n i f o r m i t y of chromite fragments from s o i l s i t e s spanning such a wide v a r i e t y of parent m a t e r i a l types and compositions (Table 4-17). Mean C r 2 0 3 and F e 2 0 3 c o n t e n t s are almost i d e n t i c a l a t a l l f i v e s i t e s , w h i l e o n l y MgO and FeO contents vary s i g n i f i c a n t l y . The narrow range of fragment compositions from s i t e s a d jacent t o PGE occ u r r e n c e s ( F i g u r e s 4-58 and 4-59) i l l u s t r a t e s t he r e l a t i v e l y r e s t r i c t e d source areas of s o i l s developed on Soil chromite fragments Chromitite segregations 88-SC-153 88-SC-031 i 147 i 148 1 50 2 FJT60-55A FJT60-540 (n=15) (n=15) (n=16) (n=12) (n=8) Si0 2 0.01 0.01 0.27 0.19 0.19 0.61 0.02 A i p 3 6.57 6.93 6.31 7.28 7.45 6.90 8.10 Ti0 2 0.64 0.61 0.78 0.42 0.51 0.58 0.86 2 3 42.86 45.83 37.03 43.65 49.01 43.90 37.70 Fe o0 Q 2 3 20.20 17.54 26.70 20.88 15.36 20.80 25.10 FeO 18.75 17.17 20.71 18.40 17.20 18.50 19.50 MnO 0.24 0.23 0.47 0.45 0.35 0.40 0.39 MgO 9.07 10.19 7.96 9.57 10.49 8.80 8.50 CaO - - - - - <0.05 <0.05 v p 3 - - - - -0.06 0.12 NiO - - - - - 0.06 0.08 Total 98.34 98.51 100.23 100.84 100.56 100.10 100.40 Table 5-1. Composition of detrital soil chromite fragments (non-magnetic fraction) from two sites adjacent to known PGE-chromite occurrences, with that of chromitite segregations. Tulameen chromitite data from 1: Nixon et al (1990) and 2: Irvine (1967). d u n i t i c c o l l u v i u m and r u b b l e , whereas the wider c o m p o s i t i o n a l v a r i a t i o n i n fragments from t i l l s i t e s i s p r o b a b l y i n d i c a t i v e of a l a r g e r source area. S i m i l a r l y , the t i g h t c o m p o s i t i o n a l grouping of chromite fragments i n non-d u n i t i c t i l l (88-SC-19) probably i n d i c a t e s a r e l a t i v e l y u n i form source. M o r p h o l o g i c a l l y , the absence of any r e c o g n i z a b l e c r y s t a l h a b i t i s the most obvious f e a t u r e l i n k i n g s o i l fragments t o massive c h r o m i t i t e . Other f e a t u r e s observed i n d e t r i t a l fragments, such as c o n c e n t r i c l i n e s and an apparent c o n c h o i d a l f r a c t u r i n g on smooth s u r f a c e s , have been p r e v i o u s l y r e p o r t e d from l a y e r e d chromite of o p h i o l i t i c p odiform d e p o s i t s (Leblanc, 1980). Smooth c o n c h o i d a l s u r f a c e s r e p r e s e n t the s u r f a c e s of t h r e e l a r g e - s c a l e o r t h o g o n a l cleavage planes along which the massive chromite s p l i t s , w h i l e the c o n c e n t r i c l i n e s were i n t e r p r e t e d as groups of l a y e r s w i t h c o n c e n t r i c edges (Leblanc, 1980). 5.2.1.2 Crystals Compositional s i m i l a r i t y of d e t r i t a l chromite c r y s t a l s w i t h those from d u n i t e and p o s s i b l y c l i n o p y r o x e n i t e ( F i g u r e s 4-58 and 4-59) suggest t h a t they o r i g i n a t e d as d i s s e m i n a t e d g r a i n s i n d u n i t e . Data are l a c k i n g f o r a d i r e c t comparison of the compositions of disseminated chromite g r a i n s (Nixon e t a l , 1990) w i t h C h o r i z o n c r y s t a l s , but compositions of chromite c o n c e n t r a t e s from d u n i t e r e p o r t e d by F i n d l a y (1963) are g e n e r a l l y s i m i l a r t o those of t h i s study. F i n d l a y ' s (1963) magnetic c o n c e n t r a t e s have lower Cr2C>3 and MgO c o n t e n t s , and h i g h e r Fe 203 and FeO contents, than do c o r r e s p o n d i n g non-magnetic c o n c e n t r a t e s . There i s i n s u f f i c i e n t i n f o r m a t i o n about the m o r p h o l o g i c a l nature of F i n d l a y ' s (1963) chromite t o d i r e c t l y compare t h e i r compositions w i t h those of the magnetic d e t r i t a l c r y s t a l s . The s t r i k i n g l y s i m i l a r mean compositions of magnetic-f r a c t i o n chromite c r y s t a l s i n a l l f i v e s o i l s (Table 4-17) suggests a r e l a t i v e l y homogenous c r y s t a l c omposition throughout the d u n i t e core. N e v e r t h e l e s s , c o m p o s i t i o n a l ranges v a r y from s i t e t o s i t e . The narrow c o m p o s i t i o n a l range of c r y s t a l s from the two s i t e s i n d u n i t i c r u b b l e and c o l l u v i u m adjacent t o PGE occurrences ( F i g u r e s 4-58 and 4-59) i s i n d i c a t i v e of the very l i m i t e d provenance of t h e s e two s o i l s . Conversely, c r y s t a l s i n d u n i t i c and n o n - d u n i t i c t i l l s i t e s e x h i b i t much wider c o m p o s i t i o n a l ranges i n d i c a t i v e of a l a r g e r source area. The two m o r p h o l o g i c a l types of chromite c r y s t a l s -e uhedral and subhedral/anhderal ( s e c t i o n 4.5.4) - may r e p r e s e n t q u i t e d i f f e r e n t c o o l i n g h i s t o r i e s i n s p i t e of t h e i r r e l a t i v e l y homogenous core compositions. Disseminated euhedral c r y s t a l s r e p r e s e n t the magmatic c r y s t a l l i z a t i o n h a b i t of chromite, but subrounded m u l t i f a c e t e d s u b h e d r a l c r y s t a l s w i t h i n podiform chromite occurrences i n o p h i o l i t e s have been i n t e r p r e t e d as a product of hydrothermal d i s s o l u t i o n p rocesses (Leblanc, 1980). Such c r y s t a l s a re most abundant on Grasshopper Mountain i n c o l l u v i u m (88-SC-105) d e r i v e d from i n t e n s e l y s e r p e n t i n i z e d d u n i t e . Although they s u p e r f i c i a l l y appear t o have been rounded by a b r a s i o n , the presence of envel o p i n g s i l i c a t e s around some subrounded chromites ( F i g u r e 4-56D) i n d i c a t e s t h a t they were rounded, perhaps v i a d i s s o l u t i o n by s e r p e n t i n i z i n g f l u i d s , p r i o r t o bei n g l i b e r a t e d from the rock. No microprobe a n a l y s e s were performed on c r y s t a l s from t h i s s i t e t o determine the presence or absence of f e r r i t c h r o m i t e rims (Ramdohr, 1969; K i m b a l l , 1990). 5.2.2 Chromite Chemistry: R e l a t i o n Between Compositional V a r i a t i o n s and Magnetic P r o p e r t i e s Chromite (AB2O4) i s a member of the chromite s e r i e s o f the s p i n e l group. The s p i n e l u n i t c e l l c o n t a i n s 24 c a t i o n s and has the g e n e r a l formula: A 8 2 + B 1 6 3 + 0 3 2 S p i n e l c l a s s i f i c a t i o n i s d i c t a t e d by the dominant B 3 + and A 2 + c a t i o n s i n s o l i d s o l u t i o n (Deer e t a l , 1966; Stowe, 1987). F e z , Mg z and t r a c e Mn z occupy the t e t r a h e d r a l c o o r d i n a t i o n (A) s i t e s , w h i le v a r i a b l e p r o p o r t i o n s of C r 3 + , F e 3 + , A l 3 + and l e s s e r T i 4 + occupy o c t a h e d r a l c o o r d i n a t i o n (B) s i t e s . C o n s i d e r a b l e c o m p o s i t i o n a l v a r i a t i o n o c c u r s even w i t h i n the same d e p o s i t (Hawkes, 1951; Peoples and Eaton, 1952) . Chromite i s u s u a l l y non-magnetic or weakly magnetic, and i s r a r e l y s t r o n g l y magnetic. I t s magnetic p r o p e r t i e s v a r y w i t h v a r i a t i o n s i n chemical composition due t o i o n i c s u b s t i t u t i o n (Stevens, 1944; Hawkes, 1951; Svoboda, 1987). Hawkes (1951), n o t i n g t h a t one of th r e e t r i v a l e n t endmembers ( F i g u r e 4-58) of the s p i n e l prism (magnetite) i s magnetic whereas the other two (chromite and s p i n e l ) are not, suggested t h a t i n c r e a s i n g magnetic s u s c e p t i b i l i t y of chromite i s r e l a t e d t o an i n c r e a s i n g p r o p o r t i o n of endmember magnetite (FeO*Fe203). I n c r e a s i n g magnetic s u s c e p t i b i l i t y w i t h i n c r e a s i n g i r o n content has been supported by s t u d i e s from I n d i a n occurrences (Rao, 1978; Radhakrishna Murthy and G o p a l a k r i s h a , 1982), the S t i l l w a t e r Complex (Peoples and Eaton, 1952), and other l o c a l i t i e s (Stevens, 1944; Owada and Harada, 1985). I t i s u n c l e a r whether i n c r e a s e d F e 2 + (Peoples and Eaton, 1952; Owada and Harada, 1985), F e 3 + (Rao, 1978), or both as FeO'Fe20 3 i s u l t i m a t e l y r e s p o n s i b l e f o r chromite magnetism. Peoples and Eaton (1952), f o r example, r e p o r t e d a l i n e a r r e l a t i o n s h i p between magnetic s u s c e p t i b i l i t y and the Fe/Fe+Mg (mol) r a t i o , but not w i t h weight p e r c e n t t o t a l Fe. Schwerer and Gundaker (1975) r e p o r t e d t h a t g r e a t e r m a g n e t i z a t i o n of chromite was induced by mechanical c r u s h i n g to f i n e r p a r t i c l e s i z e s , a phenomenom a t t r i b u t e d t o d e f e c t s t r u c t u r e s on g r a i n s u r f a c e s . T h i s has i n t r i g u i n g i m p l i c a t i o n s f o r the magnetic behaviour of g l a c i a l l y - c r u s h e d chromite g r a i n s i n t i l l r e l a t i v e t o those i n r u b b l e or c o l l u v i u m . Chromite fragments are a r e l a t i v e l y more important component of paramagnetic than non-magnetic f r a c t i o n s a t a l l t i l l s i t e s , i n c l u d i n g one near A-Zone PGE m i n e r a l i z a t i o n (Tables 4-15 and 4-16), but t h e r e i s i n s u f f i c i e n t evidence t o suggest t h a t c r u s h i n g - i n d u c e d m a g n e t i z a t i o n s i g n i f i c a n t l y a f f e c t s the primary magnetic p r o p e r t i e s of Tulameen c h r o m i t i t e . D i s c u s s i o n of the magnetic p r o p e r t i e s of chromite assumes a homogenous g r a i n composition. Occurrence of f r a c t u r e - f i l l i n g magnetite v e i n l e t s (Jenness, 1959), the f o r m a t i o n of magnetite or f e r r i t c h r o m i t e rims by e i t h e r hydrothermal a l t e r a t i o n (Beeson and Jackson, 1969; Ramdohr, 1969; K i m b a l l , 1990) or l a t e r i t i c weathering ( M i c h a i l i d i s , 1990), and the occurrence of f i n e c o a t i n g s of magnetite or o t h e r i r o n oxides on d e t r i t a l g r a i n s a l l serve t o i n c r e a s e magnetic s u s c e p t i b i l i t y . Chromites i n the p r e s e n t study were not s u b j e c t t o any pretreatment t o remove a d h e r i n g p a r t i c l e s , i n c l u d i n g magnetite, from g r a i n edges p r i o r t o 257 microprobe a n a l y s i s . However, g r a i n cores are smooth and t e x t u r a l l y homogenous; c o m p o s i t i o n a l s i m i l a r i t y between edges and c o r e s (Tables 4-17 and 4-18) suggests t h a t c o n t a m i n a t i o n i s not a major concern. Tulameen chromite i s g e n e r a l l y magnetic and c h a r a c t e r i z e d by a h i g h F e 3 + content ( F i n d l a y , 1963, 1969). T h i s i s t y p i c a l of Alaskan-type u l t r a m a f i c complexes ( I r v i n e , 1967). Using mean compositions of c o l l u v i a l c hromite g r a i n s (88-SC-031) from beneath C l i f f Zone PGE o c c u r r e n c e s , the s t r u c t u r a l formula of chromite c r y s t a l s (magnetic f r a c t i o n ) i s : ( F e 2 + 5 . 6 1 M g 2 . 4 3 M n 0 . l l ) ( C r 8 . 8 2 F e 3 + 4 . 5 9 A 1 2 . 3 1 ^ 0 . 1 4 ) ° 3 2 . 0 0 and t h a t of fragments (non-magnetic f r a c t i o n ) i s : ( M g 4 . 1 5 F e 2 + 3 . 9 3 M n 0 . 0 5 ) ( C r 9 . 9 1 F e 3 + 3 . 6 1 A 1 2 . 2 3 T i 0 . 1 3 ) ° 3 2 . 0 0 I t i s apparent t h a t d e t r i t a l c r y s t a l s are of chromite, or f e r r o c h r o m i t e , (FeCr20 4) composition, w h i l e d e t r i t a l fragments are not chromite but r a t h e r the Mg-rich chromite s e r i e s end-member magnesiochromite (MgCr20 4), a l s o known as p i c r o c h r o m i t e . T h i s i s best i l l u s t r a t e d i n F i g u r e 4-59, where a F e 2 + / ( F e 2 + +Mg 2 +) c a t i o n r a t i o of 0.5 i n the A s i t e s e p a r a t e s the two endmembers. Chromite c a t i o n data shows t h a t 12 out of 15 c o l l u v i a l nonmagnetic chromite fragments from the C l i f f Zone PGE o c c u r r e n c e s (88-SC-031) are magnesiochromite, w h i l e none of the magnetic f r a c t i o n chromite c r y s t a l s are. Although s e v e r a l fragments are extremely c l o s e , n e i t h e r the fragments nor c r y s t a l s from d u n i t i c rubble (88-SC-153) above the A-Zone PGE occurrence f a l l i n the magnesiochromite f i e l d . T h i s i s not s i g n i f i c a n t i n i t s e l f , as the primary c h r o m i t i t e f i e l d (Nixon e t a l , 1990) spans both magnesiochromite and chromite compositions. Mean c a t i o n data of the same authors show one of t h r e e c h r o m i t i t e s t o be magnesiochromite, w i t h a second q u i t e c l o s e t o the boundary. I t may be s i g n i f i c a n t t h a t the MgO-rich C l i f f Zone c h r o m i t i t e h o r i z o n s c o n t a i n massive t o semi-massive s e g r e g a t i o n s , whereas the A-Zone i s the most widespread occurrence of wispy chromite l e n s e s and c o a r s e l y d i s s e m i n a t e d g r a i n s (Bohme, 1987, 1988) which are s l i g h t l y l e s s magnesian. D e t r i t a l fragments from s i t e s u n r e l a t e d t o known m i n e r a l i z a t i o n have s i m i l a r C r 2 0 3 c o n t e n t s (Table 4-17) but are even l e s s Mg-rich. There i s o n l y a s i n g l e fragment i n background n o n - d u n i t i c t i l l (88-SC-200) of magnesiochromite composition ( F i g u r e 4-59). 5.2.3 O r i g i n of Compositional V a r i a t i o n s i n D e t r i t a l Chromite Compositional and morphological evidence suggest a c o r r e l a t i o n of nonmagnetic Cr-Mg-rich d e t r i t a l fragments w i t h massive c h r o m i t i t e , and of magnetic d e t r i t a l c r y s t a l s w i t h d i s s e m i n a t e d g r a i n s . The o r i g i n of these observed v a r i a t i o n s among d i f f e r e n t l i t h o l o g i e s i s t h e o r e t i c a l l y p r e d i c t a b l e , and i s most adequately e x p l a i n e d as s y s t e m a t i c Mg/Mg+Fe and Cr/Fe v a r i a t i o n s due t o magmatic d i f f e r e n t i a t i o n t r e n d s . Chromite composition i s i n d i c a t i v e of chemical and thermal c o n d i t i o n s of magma c r y s t a l l i z a t i o n , and v a r i e s between d e p o s i t types ( I r v i n e , 1965, 1967; Duke, 1983) . C r - r i c h chromite occurs i n f e l d s p a r - f r e e p e r i d o t i t e s , F e - r i c h chromite i n p y r o x e n e - r i c h s t r a t i f o r m complexes, and A l - r i c h chromites i n a l p i n e - t y p e p e r i d o t i t e s (Thayer, 1946; I r v i n e , 1967). The p r e f e r e n t i a l a s s o c i a t i o n of magnesian chromite w i t h massive s e g r e g a t i o n s r e l a t i v e t o disseminated g r a i n s has been e x t e n s i v e l y documented. Nixon e t a l (1990) showed t h a t Tulameen c h r o m i t i t e s have a lower F e 2 + / ( F e 2 + + M g 2 + ) r a t i o ( h igher r e l a t i v e Mg 2 +; F i g u r e 4-59), as w e l l as a lower F e 3 + / ( F e 3 + + A l + C r ) r a t i o (higher r e l a t i v e C r 3 + ) , than d i s s e m i n a t e d chromite w i t h i n d u n i t e . The l a t t e r r a t i o can a l s o be i n t e r p r e t e d as a higher Cr/Fe r a t i o i n c h r o m i t i t e , as A l i s r e l a t i v e l y constant (Table 4-17; F i g u r e 4-59). S i m i l a r Mg/Fe c o m p o s i t i o n a l v a r i a t i o n s have been r e p o r t e d from the Turnagain Alaskan-type complex i n northwestern B.C. (C l a r k , 1978) and from s t r a t i f o r m complexes ( F i g u r e 5-1). For example, the c a t i o n f r a c t i o n of M g 2 + r e l a t i v e t o F e 2 + Cr/Fe Mg/Fe F i g u r e 5-1. R e l a t i o n between volume percent cumulus chromite and Mg/(Mg+Fe 2 +) of t h e chromite, i n A. UG2 seam sequences of the western Bushveld Complex (Eale s , 1987); B. G and H c h r o m i t i t e zones of the S t i l l w a t e r Complex (Jackson, 1969); and i n C. r e l a t i o n between volume percent chromite and Cr/Fe and Mg/Fe r a t i o s i n the S t e e l p o o r t seam, e a s t e r n Bushveld Complex (Cameron and Desborough, 1969). 261 ( Mg 2 +/Mg 2 ++Fe 2 + r a t i o ) i n c r e a s e s with i n c r e a s i n g modal chromite content i n c h r o m i t i t e zones of both the S t i l l w a t e r Complex (Jackson, 1969) and the Bushveld Complex (Van der Walt, 1941; Ulmer, 1969; Cameron and Desborough, 1969; Cameron, 1977; E a l e s , 1987). The maximum M g 2 + c o n t e n t o c c u r s i n massive c h r o m i t i t e c o n t a i n i n g no o l i v i n e (Jackson, 1987) . Compositional v a r i a t i o n s i n s t r a t i f o r m complexes are not r e s t r i c t e d t o i n d i v i d u a l c h r o m i t i t e s e g r e g a t i o n s , but occur s y s t e m a t i c a l l y through the sequence (Duke, 1983). Cameron (1977) r e p o r t e d massive Bushveld Complex c h r o m i t i t e t o have h i g h e r Mg/Mg+Fe and Cr/Fe r a t i o s than d i s s e m i n a t e d (<5%) chromites i n s i l i c a t e - r i c h r o c k s . These r a t i o s a l s o decreased upward through the sequence of c h r o m i t i t e h o r i z o n s . S i m i l a r upwardly-decreasing MgO and Cr 2 0 3 c o n t e n t s o f chromite h o r i z o n s were a l s o r e p o r t e d from the Great Dyke by Worst (1958), who observed c o a r s e - g r a i n e d chromite t o be more Mg-rich than f i n e - g r a i n e d chromite. V a r i a t i o n s of Mg/Mg+Fe and Cr/Fe r a t i o s w i t h i n c r e a s i n g modal p r o p o r t i o n of chromite have been a t t r i b u t e d t o f r a c t i o n a l c r y s t a l l i z a t i o n d u r i n g magma c o o l i n g under e q u i l i b r i u m c o n d i t i o n s (Cameron, 1975; E a l e s , 1987; Stowe, 1987) . Cameron (1975) noted t h r e e main stages i n chromite d e p o s i t i o n i n the e a s t e r n Bushveld Complex: a cumulus, o r i n i t i a l , stage of formation by s e t t l i n g c r y s t a l s ; a p o s t -262 cumulus stage of c r y s t a l l i z a t i o n from intercumulus l i q u i d ; and a s u b s o l i d u s stage i n v o l v i n g r e e q u i l i b r a t i o n a f t e r t he disappearance of the l i q u i d phase. Secondary s u b s o l i d u s e q u i l i b r a t i o n d u r i n g slow c o o l i n g has been invoked as a mechanism f o r the i n c r e a s i n g M g 2 + content of o l i v i n e and Fe of chromite w i t h i n c r e a s i n g modal p r o p o r t i o n of chromite ( I r v i n e , 1967; Cameron, 1975; C l a r k , 1978; Nixon e t a l , 1989, 1990). However, f r a c t i o n a l c r y s t a l l i z a t i o n e x e r t s the primary c o n t r o l on chromite c o m p o s i t i o n a l v a r i a t i o n s (Cameron, 1975, 1977; C l a r k , 1978). Cumulate chromites of s t r a t i f o r m complexes are e a r l y , l o c a l l y - n u c l e a t i n g high-temperature p r e c i p i t a t e s i n i t i a l l y e n r i c h e d i n M g 2 + when s i l i c a t e s are i n low abundance. The F e 2 + c o n t e n t of the magma i n c r e a s e s p r o p o r t i o n a l l y as l a r g e amounts of Mg are p r e f e r e n t i a l l y p a r t i t i o n e d i n t o s i l i c a t e s . L a t e r chromite d i f f e r e n t i a t e s become more Fe-r i c h as the Mg/Mg+Fe r a t i o decreases i n oxides and i n c r e a s e s i n s i m u l t a n e o u s l y - c r y s t a l l i z i n g ferromagnesian s i l i c a t e s (Van der Walt, 1941; Haggerty, 1976; Cameron, 1977). C l a r k (1978) s t a t e d t h a t e a r l y Turnagain magmas were r i c h i n Cr, and t h a t the t r e n d i n s p i n e l compositions was from chromite t o magnetite, w i t h s l i g h t r im enrichments of Fe due t o e v o l v i n g magma composition. Postcumulus r e a c t i o n s may be important however, and have been invoked t o account f o r the more heterogeneous compositions of acce s s o r y chromites of the Bushveld Complex r e l a t i v e t o c h r o m i t e - r i c h r o c k s (Cameron, 1980). I n t e r e s t i n g l y , s i m i l a r c o m p o s i t i o n a l r e l a t i o n s occur between d e t r i t a l chromite c r y s t a l s and fragments i n t h i s study (Figure 4-59). Tulameen cumulate chromite and a s s o c i a t e d PGM are prod u c t s of e a r l y high-temperature c o p r e c i p i t a t i o n from a p r i m i t i v e magma (Nixon e t a l , 1990). E a r l y c h r o m i t i t e i s t h e r e f o r e more Mg and C r - r i c h than l a t e r d i s s e m i n a t e d chromites. Nixon e t a l (1990) have shown t h a t chromite i n c l u s i o n s i n some Tulameen p l a c e r PGM nuggets a r e among the most Mg and C r - r i c h of a l l . Consequently, primary PGM can be expected t o be p r e f e r e n t i a l l y a s s o c i a t e d w i t h Mg and Cr-r i c h c h r o m i t i t e s e g r e g a t i o n s , and PGE-hosting d e t r i t a l chromite fragments i n s u r f i c i a l m a t e r i a l s are l i k e l y t o be p a r t i t i o n e d i n t o the non-magnetic f r a c t i o n of heavy m i n e r a l c o n c e n t r a t e s . 5.3 S o i l s 5.3.1 I n t r o d u c t i o n Most s t u d i e s of PGE geochemistry have f o c u s s e d on t h e i r primary d i s t r i b u t i o n and behaviour, and few data are a v a i l a b l e on t h e i r subsequent m o b i l i t y i n the s u r f i c i a l environment. T h i s has been p a r t l y due t o a n a l y t i c a l l i m i t a t i o n s (Borthwick and N a l d r e t t , 1984; Bloom, 1986) which u n t i l r e c e n t l y hindered the a v a i l a b i l i t y o f the ppb-l e v e l a n a l y s e s necessary f o r s y s t e m a t i c geochemical i n v e s t i g a t i o n s of s o i l s and other s u r f i c i a l media. The most comprehensive study t o date i s t h a t of Fuchs (1972) and Fuchs and Rose (1974), who s t u d i e d d i s t r i b u t i o n and behaviour of Pt and Pd i n s o i l s developed from m a f i c and u l t r a m a f i c r o c k s of the S t i l l w a t e r Complex, Montana. Pd was found t o be r e l a t i v e l y mobile i n the weathering environment, having been d e p l e t e d from s u r f i c i a l A h o r i z o n s and c o n c e n t r a t e d i n u n d e r l y i n g B and C h o r i z o n s i n s o i l s developed on both t i l l and c o l l u v i u m . Pt was found t o be more u n i f o r m l y d i s t r i b u t e d i n the s o i l p r o f i l e . The r e l a t i v e i m m o b i l i t y of Pt was a t t r i b u t e d t o the o c c u r r e n c e of 70% of the element as e i t h e r i n c l u s i o n s or i n s o l i d s o l u t i o n w i t h i n chromite (Grimaldi and Schnepfe, 1969). Fuchs (1972) and Fuchs and Rose (1974) a l s o s t u d i e d the PGE s p e c i a t i o n amongst the v a r i o u s s o i l components. Pd was most abundant w i t h i n the magnetic, c l a y , and o r g a n i c component f r a c t i o n s , whereas Pt was much more v a r i a b l e and occured p r i m a r i l y i n the magnetic, s i l t , and Fe-oxide f r a c t i o n s . Other s t u d i e s of PGE i n s o i l s have c e n t r e d on podiform chromite occurrences i n the Unst o p h i o l i t e , S h e t l a n d I s l a n d s (Leake and Gunn, 1985; Gunn, 1989), the Howland Reef of the S t i l l w a t e r Complex (Riese and Arp, 1986), Cu-Ni-PGE oc c u r r e n c e s i n Quebec (Wood and V l a s s o p o u l o s , 1990) and the 265 Northwest T e r r i t o r i e s (DiLabio, 1988; Coker e t a l , 1989), and a v a r i e t y of chromite-PGE occurrences i n southern B r i t i s h Columbia ( F l e t c h e r , 1989). 5.3.2 Overview S o i l s The Pt content of -70 mesh Grasshopper Mountain s o i l s i s s t r o n g l y dependent on the amount of c o n t a i n e d d u n i t e as est i m a t e d by MgO content. The mean MgO content o f d u n i t e c o l l u v i u m (24.16%) i s t y p i c a l l y 2-4 times t h a t of t i l l , but l e s s than than the mean MgO content of Grasshopper Mountain d u n i t e (42.85%) from analyses of St. L o u i s e t a l (1986). S e r p e n t i n e and t a l c are the p r i n c i p a l s o i l m i n e r a l s (Appendix 6.3). Grasshopper Mountain c o l l u v i u m c l e a r l y r e p r e s e n t s a s o i l which i s almost e n t i r e l y d e r i v e d from mechanical weathering and mass wasting of the d u n i t e c l i f f s . Pedogenic m o d i f i c a t i o n i s the probable cause of the d i f f e r i n g MgO contents of C h o r i z o n c o l l u v i u m and the d u n i t e bedrock. Removal of Mg from s u r f a c e h o r i z o n s d u r i n g weathering (Robinson e t a l , 1935; Walker, 1954; Rabenhorst e t a l , 1982) i s much more l i k e l y t o a f f e c t the MgO c o n t e n t of c o l l u v i a l s o i l s than those on t i l l . Cr203 has a very s i m i l a r d i s t r i b u t i o n t o MgO because of the a s s o c i a t i o n of disseminated chromite and massive c h r o m i t i t e s e g r e g a t i o n s with the d u n i t e ( F i n d l a y , 1963; St. L o u i s e t a l , 1986; Nixon e t a l , 1990). The mean Cr con t e n t of Grasshopper Mountain d u n i t e and s e r p e n t i n i z e d d u n i t e i s 2902 ppm, based on analyses by St. L o u i s e t a l (1986). The mean Cr content of Grasshopper Mountain c o l l u v i u m (2257 ppm) and d u n i t i c t i l l (13 68 ppm) i s w i t h i n the range of 1000 -5000 ppm Cr found i n s o i l s developed on u l t r a m a f i c r o c k s (Kabata-Pendias and Pendias, 1984; Brooks, 1987). The Pt content of a c t i v e c o l l u v i u m (88 ppb) more c l o s e l y r e f l e c t s the mean Pt content (48-180 ppb) of Tulameen d u n i t e , s e r p e n t i n i t e and s e r p e n t i n i z e d d u n i t e (St. L o u i s e t a l , 1986) than does t i l l , which has been s u b j e c t t o v a r y i n g degrees of mixing and d i l u t i o n . The r e l a t i v e l y h i g h MgO content of t i l l from the western p a r t of the main study area (16.51%) and from the secondary study area (13.84%) suggest t h a t i t i s a r e l a t i v e l y l o c a l l y - d e r i v e d d u n i t i c t i l l . C onversely, the much lower MgO content (5.66% MgO), i t s g e o g r a p h i c a l l y - s e p a r a t e r e l a t i o n w i t h d u n i t i c t i l l ( F i g u r e s 4-1 and 4-3), and the south-southwesterly d i r e c t i o n of g l a c i a l t r a n s p o r t i n d i c a t e s a l e s s e r d u n i t e i n f l u e n c e on t i l l c o m position i n the e a s t e r n p a r t of the main study area. N o n - d u n i t i c t i l l i s probably d e r i v e d l a r g e l y from rock u n i t s n o r t h o r n o r t h e a s t of the du n i t e core ( F i g u r e 2-1). The lower background Pt contents of d u n i t i c t i l l (36 ppb) and n o n - d u n i t i c t i l l (8 ppb) r e l a t i v e t o c o l l u v i u m are a d i r e c t r e s u l t of t h e i r lower content of d u n i t e . However, the terms " d u n i t i c " and " n o n - d u n i t i c " are not a b s o l u t e and the range of major element composition suggests a degree of t i l l mixing. Thus hi g h CaO and Na 20 contents i n d u n i t i c t i l l compared t o those of c o l l u v i u m suggest t h a t d u n i t i c t i l l must c o n t a i n some e x o t i c component. S i m i l a r l y , the mean C r 2 0 3 content of n o n - d u n i t i c t i l l (0.07%; 479 ppm Cr) i n d i c a t e s a t l e a s t a minor d u n i t e component as the Cr content of n o n - d u n i t i c s o i l s i s u s u a l l y l e s s than 100 ppm (Brooks, 1987). Major element a n a l y s i s of the s o i l , p a r t i c u l a r l y f o r MgO and C r 2 0 3 , i s a u s e f u l mapping t o o l t o d e l i n e a t e the d i s p e r s i o n of d u n i t i c t i l l . XRD r e s u l t s ( s e c t i o n 4.2.1.3) c o n f i r m g e n e t i c i n t e r p r e t a t i o n s based on t i l l geochemistry. N o n - d u n i t i c t i l l has,a mineralogy c h a r a c t e r i z e d by q u a r t z , p l a g i o c l a s e , hornblende and c h l o r i t e , whereas d u n i t i c t i l l has a mineralogy c h a r a c t e r i z e d by u l t r a m a f i c - r e l a t e d m i n e r a l s such as s e r p e n t i n e , t a l c , v e r m i c u l i t e and chromite (Appendices 6.1 t o 6.3). L o c a l l y - d e r i v e d d u n i t e c o l l u v i u m might be expected t o be e f f e c t e d by windlblown d i l u t i o n , but XRD r e s u l t s (Appendix 6.3) show i t t o be de v o i d of d e t e c t a b l e q u a n t i t i e s of s i l i c e o u s m i n e r a l s such as q u a r t z and p l a g i o c l a s e . These do, however, occur i n d u n i t i c t i l l , i n d i c a t i n g a t l e a s t a minor component of t i l l m ixing. Pt c ontents of s o i l s on t i l l and c o l l u v i u m cannot, t h e r e f o r e , be d i r e c t l y compared. They must i n s t e a d be c a t e g o r i z e d on the b a s i s of parent m a t e r i a l and MgO c o n t e n t i n o r d e r t o d e l i n e a t e background and anomalous p o p u l a t i o n s w i t h i n each group. Anomalous C h o r i z o n s o i l Pt c o n c e n t r a t i o n s are d e r i v e d from the d i s p e r s i o n of massive c h r o m i t i t e and c h r o m i t i c d u n i t e (>10% chromite) w i t h mean Pt c o n t e n t s of 3410 ppb (St. L o u i s e t a l , 1986). Anomalous c o n c e n t r a t i o n s , as d e f i n e d by p r o b a b i l i t y p l o t s and frequency d i s t r i b u t i o n s , are very s u b t l e (>16 ppb) i n areas of n o n - d u n i t i c t i l l . However, they are g r e a t e r than 55 ppb i n d u n i t i c t i l l and g r e a t e r than 200 ppb i n d u n i t i c c o l l u v i u m on Grasshopper Mountain. A c c u r a t e r e c o g n i t i o n of parent m a t e r i a l i s a l s o a p r e r e q u i s i t e f o r t r a c i n g the mechanical d i s p e r s i o n of P t . T i l l r e f l e c t s u p i c e sources whereas c o l l u v i u m r e f l e c t s upslope sources. The presence on Grasshopper Mountain of complex composite s o i l p r o f i l e s where c o l l u v i u m o v e r l i e s t i l l ( F i g u r e 4-49) suggests t h a t r o u t i n e n e a r - s u r f a c e sampling of the B h o r i z o n may l e a d t o erroneous i n t e r p r e t a t i o n s of both anomaly c o n t r a s t and source u n l e s s the o r i g i n of the m a t e r i a l i s c o r r e c t l y i d e n t i f i e d . The r e l a t i o n between Pt and other t r a c e elements i s v a r i a b l e . R e l a t i v e l y h i g h Sb v a l u e s i n base of s l o p e and bog samples may be r e l a t e d t o hydromorphic d i s p e r s i o n of t h i s element from the Pt antimonides St. L o u i s e t a l (1984) r e p o r t e d i n c h r o m i t i t e . High As l e v e l s are more 269 p r o b l e m a t i c . Those i n c o l l u v i u m may be p a r t l y a t t r i b u t e d t o the l o c a l mechanical d i s p e r s i o n of s p e r r y l i t e , but h i g h As c o n c e n t r a t i o n s i n s o i l s occur with a l l parent m a t e r i a l s . N i c o l a Group rocks g e n e r a l l y c o n t a i n l e s s than 4 ppm As, but d u n i t e and c h r o m i t i t e have very e r r a t i c As c o n t e n t s r a n g i n g from 1 - 2 6 ppm (G. Nixon, p e r s o n a l communication, 1989) . The As content of standard PT-5 (Appendix 4.2), prepared from Grasshopper Mountain d u n i t e , i s a l s o s i m i l a r t o s o i l As l e v e l s . High Au c o n c e n t r a t i o n s probably o r i g i n a t e from two sour c e s . R e l a t i v e l y h i g h Au c o n c e n t r a t i o n s i n s e r p e n t i n e c o l l u v i u m and beneath PGE-chromitite occurrences are c o n s i s t e n t with, but g r e a t e r than, l i t h o g e o c h e m i c a l r e s u l t s (4.1 ppb and 8.2 ppb) f o r s e r p e n t i n i t e and c h r o m i t i t e , r e s p e c t i v e l y (St. Lo u i s e t a l , 1986). High Au v a l u e s i n the -70 mesh f r a c t i o n (34 ppb) and -70+140 mesh non-magnetic heavy f r a c t i o n (718 ppb) from a n o n d u n i t i c t i l l s i t e ( s o i l s i t e 6) may have been mec h a n i c a l l y t r a n s p o r t e d from Au occ u r r e n c e s i n the N i c o l a Group (Rice, 1947) on n o r t h e a s t e r n Grasshopper Mountain. In summary, s o i l Pt content i s r e l a t e d t o the d u n i t e c o n t e n t o f the parent m a t e r i a l and i s u l t i m a t e l y i n h e r i t e d from the primary d u n i t e of the Tulameen complex. Pt con t e n t i s g r e a t e s t i n d u n i t e c o l l u v i u m , but decreases i n t i l l w i t h the d i l u t i o n of l o c a l l y - d e r i v e d t i l l by more e x o t i c m a t e r i a l . Determination of MgO content i s a u s e f u l method of e s t i m a t i n g the degree of mixing and d i l u t i o n and, by e x t e n s i o n , the background Pt contents of t i l l s i n the v i c i n i t y of d u n i t e bedrock. 5.3.3 V a r i a t i o n s i n S o i l Pt D i s t r i b u t i o n With Depth S e v e r a l Pt c o n c e n t r a t i o n t r e n d s with depth occur on d i f f e r e n t s u r f i c i a l m a t e r i a l s and landscapes of Grasshopper Mountain. R e l a t i v e l y constant, though l o c a l l y e r r a t i c , Pt c o n c e n t r a t i o n s w i t h i n c r e a s i n g depth i n a c t i v e c o l l u v i u m are c o n s i s t e n t w i t h the unhorizonated and c o n s t a n t l y - e v o l v i n g nature of the m a t e r i a l . Pt c o n c e n t r a t i o n s i n n o n - d u n i t i c and d i s t a l d u n i t i c t i l l s i n c r e a s e with depth, whereas those of h i g h e r - c o n c e n t r a t i o n d u n i t i c t i l l / r u b b l e a d j a c e n t t o known m i n e r a l i z a t i o n e i t h e r i n c r e a s e or remain c o n s t a n t w i t h depth ( s e c t i o n 4.3.2). T o t a l Pt contents a l s o i n c r e a s e d o w n p r o f i l e a t most s i t e s ( s e c t i o n 4.3.2.3). R e l a t i v e i n c r e a s e s i n Pt c o n c e n t r a t i o n s i n C h o r i z o n s are g e n e r a l l y more apparent i n d e n s i t y / m a g n e t i t i c f r a c t i o n s than i n i n d i v i d u a l s i z e f r a c t i o n s and are most pronounced i n the n o n - d u n i t i c t i l l p r o f i l e s . V e r t i c a l Pt v a r i a t i o n s w i t h i n the s o i l p r o f i l e may be a primary c l a s t i c d i s p e r s i o n f e a t u r e w i t h i n b a s a l and/or a b l a t i o n t i l l , a r e s u l t of more r e c e n t c o l l u v i a l p r o cesses, or a product of secondary pedogenic p r o c e s s e s . C l a s t i c d i s p e r s i o n of b a s a l t i l l , however, i s 271 p r o b a b l y the main c o n t r o l on Pt v a r i a t i o n s over most of the study area on Grasshopper Mountain. 5.3.3.1 Primary Clastic Dispersion The v e r t i c a l d i s t r i b u t i o n of Pt i n s o i l s on t i l l s on Grasshopper Mountain i s most c o n s i s t e n t with c l a s t i c d i s p e r s i o n plumes (Drake, 1983; M i l l e r , 1984) of d u n i t i c m a t e r i a l . Mechanical d i s p e r s i o n fans i n t i l l s g i v e n e g a t i v e e x p o n e n t i a l d i l u t i o n of the element of i n t e r e s t downice from a m i n e r a l d e p o s i t ( S h i l t s , 1976; Rose e t a l , 1979). D i s p e r s i o n plumes, however, are t h r e e - d i m e n s i o n a l f e a t u r e s i n which d u n i t i c and/or c h r o m i t i t i c m a t e r i a l , e n t r a i n e d a t the g l a c i e r base as lodgement t i l l , would be mixed and d i l u t e d w i t h e x o t i c m a t e r i a l as i t g r a d u a l l y r i s e s from the bedrock t o the t i l l s u r f a c e (Drake, 1983). Plumes may be d i v e r t e d or d i s p l a c e d i n a l p i n e areas such as the C o r d i l l e r a , however, where r i d g e s and v a l l e y s o b s t r u c t and d i v e r t g l a c i a l flow d i r e c t i o n s ( S h i l t s , 1976, 1982; Drake, 1983). Debris i s t r a n s p o r t e d f o r g r e a t e r d i s t a n c e s through v a l l e y s than ac r o s s upland areas ( C l a r k , 1987). Under such circumstances, g l a c i a l flow l i n e s p a r a l l e l the topography and d e b r i s r i s e s from the g l a c i e r base i n the l e e of the o b s t r u c t i o n (Boulton, 1978; C l a r k , 1987). The s u b p a r a l l e l r e l a t i o n of the d u n i t i c t i l l / n o n -d u n i t i c t i l l boundary with the topographic c u r v a t u r e of s o u t h e a s t e r n Grasshopper Mountain (F i g u r e s 4-1, 4-5 and 4-18) may be an example of t h i s . There i s thus a gap between the subcrop of a g e o c h e m i c a l l y d i s t i n c t u n i t and the appearance of a r e l a t e d geochemical anomaly at the s u r f a c e . In the p r e s e n t study, t h i s i s the d i s t a n c e between the margin of the d u n i t e core and i t s geochemical appearance i n n e a r - s u r f a c e t i l l . The gap may be n e g l i g i b l e , p i n p o i n t i n g the source i n t h i n t i l l as, f o r example, at the A-Zone, or i t may i n c r e a s e w i t h i n c r e a s i n g t i l l t h i c k n e s s (Drake, 1983). There are two s c a l e s of Pt d i s p e r s i o n plumes on Grasshopper Mountain: a r e g i o n a l s c a l e plume, s i m i l a r t o o t h e r l a r g e u l t r a m a f i c d i s p e r s i o n fans ( S h i l t s , 1976; Maurice, 1988) i n which hig h e r Pt v a l u e s are r e l a t e d t o h i g h Pt c o n t e n t of c o n t a i n e d d u n i t e , and much s m a l l e r plumes c o n t a i n i n g c o n s i d e r a b l y higher Pt c o n c e n t r a t i o n s d e r i v e d from c h r o m i t i t e s e g r e g a t i o n s w i t h i n the d u n i t e . These are shown i n an i d e a l i z e d model of landscape elements and mechanical Pt d i s p e r s i o n i n F i g u r e 5-2. On a r e g i o n a l s c a l e , d u n i t i c m a t e r i a l i s mixed w i t h e x o t i c m a t e r i a l from o u t s i d e the d u n i t i c c o r e . S e r p e n t i n i z e d d u n i t e , being a r e l a t i v e l y s o f t rock, p r o b a b l y p r o v i d e d a r e l a t i v e l y l a r g e amount of m a t e r i a l t o the Direction of glacial movement Very localized dispersion of chromitite in thin and discontinuous till and residual \ rubble above dunite bedrock; mechanical mixing of chromite into LFH horizons Post-glacial colluvium (high MgO, Pt) Tulameen Ultramafic Complex -Figure 5-2. Idealized model for mechanical dispersion of Pt on Grasshopper Mountain. d i s p e r s i o n plume ( S h i l t s , 1982). The s u r f a c e geochemical e x p r e s s i o n of the predominately d u n i t i c t i l l i s not encountered u n t i l the d u n i t i c / n o n - d u n i t i c t i l l boundary ( F i g u r e 4-13). Background sampling around the western edges of the d u n i t e core (Figure 4-18) i n d i c a t e s , on the b a s i s o f MgO, Cr 203 and Pt contents, t h a t the r e g i o n a l d i s p e r s i o n plume p e r s i s t s downice beyond the western margin o f the co r e . Evenson e t a l (1979) showed t h a t g l a c i a l f low d i r e c t i o n s c o u l d be determined by a n a l y s i s of heavy m i n e r a l s u i t e s . The g l a c i a l t r a n s p o r t path i n the Grasshopper Mountain area, and maximum extent of the r e g i o n a l plume southwest of the du n i t e core, c o u l d probably be o u t l i n e d i n a s i m i l a r manner by t r a c k i n g c h a r a c t e r i s t i c - c o m p o s i t i o n chromite g r a i n s from heavy mi n e r a l s i n t i l l . I t s h o u l d be noted t h a t d i s p e r s i o n p a t t e r n s of both d u n i t i c and non-d u n i t i c t i l l may be obscured by t h e i r i n c o r p o r a t i o n , a t lower e l e v a t i o n s , of p r e - g l a c i a l c o l l u v i u m l y i n g i n the path of the g l a c i e r . For example, S i b b i c k (1990) a t t r i b u t e d the l o c a t i o n o f a g o l d d i s p e r s i o n t r a i n i n southern B.C. t o the i n c o r p o r a t i o n of m i n e r a l i z e d c o l l u v i u m i n t o t i l l . There i s no evidence of t h i s on Grasshopper Mountain, but e a r t h f l o w s i n s o u t h - c e n t r a l B.C. are n e v e r t h e l e s s more common on s e r p e n t i n i z e d r o c k s than on u n a l t e r e d d u n i t e or p e r i d o t i t e , p o s s i b l y because the p l a t y h a b i t of s e r p e n t i n e m i n e r a l s a c t as e a r t h f l o w boundary shear zones (Jones, 1988). On a more d e t a i l e d s c a l e w i t h i n the d u n i t e plume, the 275 l o c a l occurrence of h i g h Pt c o n c e n t r a t i o n s i n t i l l i s dependent upon two f a c t o r s : ( i ) source rock l i t h o l o g y ; i n p a r t i c u l a r , whether the t i l l i s d e r i v e d from comminution of d u n i t e c o n t a i n i n g o n l y u b i q u i t o u s disseminated chromites, or c o n t a i n s an a d d i t i o n a l component from e r o s i o n of P t - r i c h c h r o m i t i t e s ; and ( i i ) t i l l t h i c k n e s s . F i g u r e s 4-50B and 4-51B show t h a t t o t a l s o i l Pt contents are g r e a t e s t j u s t above bedrock, r e l a t i v e t o h i g h e r p a r t s of the p r o f i l e , even i n r e l a t i v e l y t h i n t i l l and r e s i d u a l r u b b l e . Abrupt d o w n p r o f i l e i n c r e a s e s i n Pt c o n c e n t r a t i o n a t n o n - d u n i t i c t i l l s i t e s p robably i n d i c a t e the subsurface top of t h e d i s p e r s i o n plume a t those l o c a t i o n s . T h i s i n t e r p r e t a t i o n i s supported, a t s o i l s i t e 20 (Figure 4-46), by n e a r - i d e n t i c a l low Pt c o n c e n t r a t i o n s i n most Aej and Bf h o r i z o n magnetic c o n c e n t r a t e s and c o n s i d e r a b l y g r e a t e r Pt c o n c e n t r a t i o n s i n the C h o r i z o n magnetic co n c e n t r a t e s . S i t e 6 i n n o n - d u n i t i c t i l l shows a s i m i l a r r e l a t i o n . I t i s d i f f i c u l t t o e n v i s i o n t h e s e d i f f e r e n c e s a r i s i n g from any type of p o s t - g l a c i a l pedogenic p r o c e s s e s . D i s p e r s i o n of r e l a t i v e l y t h i n c h r o m i t i t e s e g r e g a t i o n s w i t h i n a s o f t e r d u n i t e envelope i s l i k e l y t o be q u i t e l i m i t e d p r i o r t o d i l u t i o n by barren d u n i t e c o n t a i n i n g o n l y background Pt c o n c e n t r a t i o n s . Consequently, d i s p l a c e d fragments of crushed PGE-rich s e g r e g a t i o n s are u n l i k e l y t o p e r s i s t f a r from source, and h i g h c o n c e n t r a t i o n s may o n l y reach the t i l l s u r f a c e i n areas of t h i n overburden ( F i g u r e 276 5-2). Even w i t h i n i n d i v i d u a l p r o f i l e s , weight p e r c e n t d i s t r i b u t i o n s of non-magnetic r e l a t i v e t o magnetic heavy m i n e r a l s i n c r e a s e with depth a t most d u n i t i c t i l l s i t e s (Table 4-11). Thus, p r o x i m i t y t o u n d e r l y i n g bedrock e x e r t s a major c o n t r o l on the v e r t i c a l Pt d i s t r i b u t i o n w i t h i n the d u n i t i c t i l l - d o m i n a t e d p a r t of the plume. There are two a l t e r n a t i v e mechanisms f o r the v e r t i c a l Pt d i s t r i b u t i o n , but n e i t h e r i s as p l a u s i b l e as the d i s p e r s i o n plume model. The abrupt 5x enrichment of magnetic heavy m i n e r a l - a s s o c i a t e d Pt i n C h o r i z o n s o i l s a t n o n - d u n i t i c t i l l s i t e s (Figure 4-46) i n r e l a t i v e l y t h i c k t i l l suggests t h a t PGM or PGE-hosting chromite g r a i n s may have been c o n c e n t r a t e d a t depth by d e n s i t y s e g r e g a t i o n ( L a k i n e t a l , 1974). However, fragmentation and downward movement of heavy p a r t i c l e s d u r i n g s o i l creep cannot e x p l a i n the s u b t l e d o w n p r o f i l e i n c r e a s e i n the Pt content of the l i g h t m i n e r a l f r a c t i o n . The upper h o r i z o n s may a l t e r n a t e l y r e p r e s e n t a poorly-compacted a b l a t i o n t i l l d e p o s i t e d above an e a r l i e r , more l o c a l l y - d e r i v e d , P t - b e a r i n g lodgement t i l l d u r i n g g l a c i a l melt out ( F l i n t , 1971). However, a b l a t i o n t i l l s t y p i c a l l y have a lower f i n e s content than lodgement t i l l s ( F l i n t , 1971). T h i s i s i n c o n s i s t e n t w i t h the g r a i n s i z e d i s t r i b u t i o n of the -270 mesh f r a c t i o n i n i n d i v i d u a l p r o f i l e s (Table 4-10, Appendix 11.2). 277 5.3.3.2 Post-glacial Processes P o s t - g l a c i a l c o l l u v i a l and pedogenic p r o c e s s e s a l s o i n f l u e n c e the v e r t i c a l d i s t r i b u t i o n of Pt. Pt c o n c e n t r a t i o n s i n a c t i v e c o l l u v i u m ( F i g u r e 5-2) are h i g h e r than i n t i l l , but v a r i a t i o n s with depth are minimal. The e x t e n t of Pt v a r i a t i o n s caused by t h i n c o l l u v i u m o v e r l y i n g t i l l are dependent on the r e l a t i v e magnitude of Pt c o n c e n t r a t i o n s i n the two parent m a t e r i a l s . For example, the c o v e r i n g of t i l l by c o l l u v i u m a t s o i l s i t e 34 ( F i g u r e 4-49) p r i o r t o v e g e t a t i o n of the area has r e s u l t e d i n near-s u r f a c e Pt c o n c e n t r a t i o n s t h a t are 2-6x t h a t of the u n d e r l y i n g t i l l . The same r e l a t i o n i s not, however, observed a t A-Zone s o i l s i t e 57 (Figure 2-14B; Appendix 12.9) because h i g h Pt c o n c e n t r a t i o n s i n the c o l l u v i a l s u r f a c e h o r i z o n are s i m i l a r t o those of the u n d e r l y i n g t i l l . Secondary pedogenic processes may a l s o modify the primary Pt d i s t r i b u t i o n by r e d i s t r i b u t i n g i t v e r t i c a l l y i n the p r o f i l e d u r i n g weathering. Here these p r o c e s s e s appear minor compared t o g l a c i a l d i s p e r s i o n and c o l l u v i a l mass wasting. The more-widespread e f f e c t of weathering on Pt d i s t r i b u t i o n s w i t h i n i n d i v i d u a l h o r i z o n s w i l l be d i s c u s s e d i n a l a t e r s e c t i o n . However, p r i o r development of composite p r o f i l e s by c o l l u v i u m ( s i t e 34), water reworking of t i l l ( s i t e 43), or d i s r u p t i o n by c o l l u v i a l b o u l d e r s ( s i t e 33) may have p r e c l u d e d pedogenic Pt enrichment or d e p l e t i o n a t some s i t e s . S i m i l a r l y , t h e r e are no apparent pedogenic m o d i f i c a t i o n s of Pt c o n c e n t r a t i o n s i n a c t i v e c o l l u v i u m , as these h o r i z o n s are j u v e n i l e and and c o n s t a n t l y e v o l v i n g . One p o s s i b l e pedogenic m o d i f i c a t i o n of the s o i l Pt d i s t r i b u t i o n occurs i n the Bf h o r i z o n of a h u m o - f e r r i c p o d z o l ( s i t e 20) i n n o n - d u n i t i c t i l l ( F i g u r e 4-46). M a t e l s k i and Turk (1947) r e p o r t e d t h a t the g r e a t e s t decomposition of both heavy opaque and ferromagnesian s i l i c a t e m i n e r a l s of some Michigan podzols o c c u r r e d i n the B h o r i z o n . They a t t r i b u t e d t h i s t o the presence of o r g a n i c c o a t i n g s on m i n e r a l p a r t i c l e s . Lower Pt c o n c e n t r a t i o n s i n both -140+270 heavy f r a c t i o n s , lower weight p e r c e n t heavy m i n e r a l s and much g r e a t e r p r o p o r t i o n s of magnetic heavy m i n e r a l s r e l a t i v e t o other h o r i z o n s (Table 4-11) suggest a s i m i l a r decomposition of non-magnetic PGE-bearing chromite or, more l i k e l y , s i l i c a t e s i n t h i s Bf h o r i z o n . A second example of p o s s i b l e pedogenic r e d i s t r i b u t i o n of Pt i n v o l v e s i t s enrichment i n the n e a r - s u r f a c e Bm h o r i z o n of a d i s t a l p r o f i l e ( s i t e 69) on the p l a t e a u o f Grasshopper Mountain. In a r e v e r s a l of more common Pt c o n c e n t r a t i o n t r e n d s , Pt a s s o c i a t e d with the magnetic and non-magnetic heavy f r a c t i o n s are g e n e r a l l y e n r i c h e d 2-6x i n the near-s u r f a c e Bm h o r i z o n r e l a t i v e t o the C h o r i z o n . Pt c o n c e n t r a t i o n s i n the Bm h o r i z o n g e n e r a l l y i n c r e a s e w i t h d e c r e a s i n g g r a i n s i z e and the g r e a t e s t d i f f e r e n c e between Pt c o n c e n t r a t i o n s of the two h o r i z o n s i s i n the f i n e r s i z e ranges ( F i g u r e 4-40B; Appendix 12.6). T o t a l Pt con t e n t o f the Bm h o r i z o n (103 ppb) i s a l s o much g r e a t e r than the C h o r i z o n (40 ppb), as shown i n F i g u r e 4-51A. XRD r e s u l t s of the -270 mesh f r a c t i o n r e v e a l i n t e r e s t i n g m i n e r a l o g i c a l d i f f e r e n c e s between Bm and C h o r i z o n s a t t h i s s i t e (Appendix 6.2). Quartz and v e r m i c u l i t e are the most important m i n e r a l s i n the two r e s p e c t i v e h o r i z o n s . The Bm h o r i z o n has more qua r t z and chromite, s i m i l a r c r y s o t i l e , and much l e s s v e r m i c u l i t e than the u n d e r l y i n g C h o r i z o n . The quartz may be i n d i c a t i v e of windblown d i l u t i o n of the Bm h o r i z o n by e x o t i c m a t e r i a l , w h i l e v e r m i c u l i t e i s probably the r e s u l t of pedogenesis i n the C h o r i z o n (Rabenhorst e t a l , 1982). C h r o m i t i c d u n i t e was a l s o observed i n Bm h o r i z o n fragments i n the f i e l d , and the h i g h Pt content of the Bm h o r i z o n r e l a t i v e t o the C h o r i z o n i s probably r e l a t e d t o i t s h i g h e r chromite c o n t e n t . However, the o r i g i n of t h i s i s somewhat of an enigma. I t seems u n l i k e l y t h a t a l a t e r a b l a t i o n t i l l would c o n t a i n more Pt than a l o c a l l y - d e r i v e d b a s a l t i l l , and e l u v i a l c o n c e n t r a t i o n of chromites (Laznicka, 1985) i s not a p l a u s i b l e e x p l a n a t i o n i n t h i s weathering environment. In summary, v e r t i c a l d i s t r i b u t i o n of Pt i n Grasshopper Mountain s o i l s i s p r i m a r i l y a c l a s t i c d i s p e r s i o n f e a t u r e . In t i l l , i t occurs on both r e g i o n a l and l o c a l s c a l e s , and i s 280 c o n t r o l l e d by source rock l i t h o l o g y and p r o x i m i t y t o bedrock. Downprofile v a r i a t i o n s are minimal i n a c t i v e c o l l u v i u m , and r e l a t i v e l y constant Pt c o n c e n t r a t i o n s a re c o n t r o l l e d by source l i t h o l o g y . Pedogenic m o d i f i c a t i o n of s o i l Pt d i s t r i b u t i o n s i s r e l a t i v e l y i n s i g n i f i c a n t , and cannot be c o n f i d e n t l y invoked t o e x p l a i n f e a t u r e s o f more than a s i n g l e p r o f i l e . 5.3.4 Pt Residence S i t e s i n M i n e r a l H o rizons Pt r e s i d e n c e s i t e s among s i z e , d e n s i t y and magnetic f r a c t i o n s of Grasshopper Mountain s o i l s depend on overburden type, source mineralogy and p r o x i m i t y t o bedrock. 5.3.4.1 Residence Sites S i m i l a r Pt c o n c e n t r a t i o n s i n a l l 5 s i z e f r a c t i o n s ( F i g u r e 4-40) of h o r i z o n s a t n o n - d u n i t i c t i l l and many d u n i t i c t i l l s i t e s i n d i c a t e t h a t Pt i s not p r e f e r e n t i a l l y p a r t i t i o n e d i n t o any s i n g l e s i z e range of the -10 mesh (<2 mm) component. Non-dunitic t i l l s i t e s are a l l , however, l o c a t e d i n r e l a t i v e l y t h i c k t i l l compared t o many d u n i t i c t i l l s i t e s . Consequently, Pt d i s t r i b u t i o n among s i z e f r a c t i o n s i n d u n i t i c t i l l , r u b b l e and c o l l u v i u m i s much more i n f l u e n c e d by p r o x i m i t y t o bedrock. There i s a tendency f o r h i g h e r Pt c o n c e n t r a t i o n s t o occur i n the c o a r s e r s i z e f r a c t i o n s of these m a t e r i a l s (Figures 4-40 and 4-41), although t h i s i s not the case f o r every p r o f i l e . These r e s u l t s do not agree with p r e v i o u s work. D i L a b i o (1988) r e p o r t e d extremely e r r a t i c Pt c o n c e n t r a t i o n s i n s e v e r a l s i z e f r a c t i o n s of gossanous m a t e r i a l from the Ferguson Lake Ni-Cu s u l f i d e occurrence, N.W.T., w i t h maximum c o n c e n t r a t i o n s g e n e r a l l y o c c u r r i n g i n the <63 um f r a c t i o n . V a r i a t i o n s from <10 ppb t o 100-1000 ppb Pt i n a d j a c e n t f r a c t i o n s were a t t r i b u t e d t o the presence of e r r a t i c a l l y -d i s t r i b u t e d micronuggets, but as no sample weight d a t a was g i v e n , t h i s cannot be evaluated. S i z e f r a c t i o n a t i o n of Pt i n d u n i t e c o l l u v i u m beneath the C l i f f Zone seems, on the b a s i s of very l i m i t e d evidence, t o be p a r t l y dependent on s l o p e morphology. S o i l s i t e 16 i s s i t u a t e d w i t h i n a uniform mass of c o l l u v i u m ( F i g u r e 2-12) immediately beneath the D-Zone and e x h i b i t s remarkably un i f o r m Pt c o n c e n t r a t i o n s among s i z e f r a c t i o n s . S o i l s i t e 9, f u r t h e r d o w n h i l l from the C-Zone, i s l o c a t e d on the edge of a narrow g u l l y which has been p a r t i a l l y s t a b i l i z e d by v e g e t a t i o n ( F i g u r e 2-11A). I t e x h i b i t s a much more e r r a t i c P t d i s t r i b u t i o n . At both s i t e s the r e l a t i v e l y c o a r s e -g r a i n e d -70+140 mesh f r a c t i o n c o n t a i n s the h i g h e s t Pt c o n c e n t r a t i o n s i n 2 out of 3 samples. 282 Pt i s p r e f e r e n t i a l l y p a r t i t i o n e d i n t o the heavy m i n e r a l f r a c t i o n by a f a c t o r of 10-20x r e l a t i v e t o the l i g h t m i n e r a l f r a c t i o n . N e v e r t h e l e s s , o n e - t h i r d t o one-half of the t o t a l Pt content of i n d i v i d u a l h o r i z o n s i s i n the l i g h t m i n e r a l component ( F i g u r e s 4-50 and 4-51). T h i s , and the sympathetic i n c r e a s e i n the Pt content of the l i g h t f r a c t i o n s w i t h t h a t of the heavy f r a c t i o n s , suggests t h a t a c o n s i d e r a b l e amount of s o i l PGM occur as e i t h e r f i n e PGM g r a i n s or as i n c l u s i o n s w i t h i n very f i n e chromite i n c l u s i o n s i n l a r g e r o l i v i n e , s e r p e n t i n e and t a l c p a r t i c l e s . PGM or o x i d e s are e v i d e n t l y not abundant enough t o cause the s i l i c a t e g r a i n s t o s i n k d u r i n g heavy l i q u i d s e p a r a t i o n . There i s abundant evidence t o support t h i s . PGM i n c l u s i o n s i n Tulameen o l i v i n e have been r e p o r t e d by Bohme (1988) and occur i n s o i l s i l i c a t e s ( t a l c ? ) examined i n t h i s study. S i l i c a t e - a s s o c i a t e d PGE have been r e p o r t e d t o c o n s t i t u t e about a t h i r d of the t o t a l PGE i n some U r a l i a n d u n i t e s (Razin e t a l , 1965; Razin, 1971). Most occur i n f o r s t e r i t i c o l i v i n e , with some adsorbed onto hydrous Fe-o x i d e s a s s o c i a t e d w i t h s e r p e n t i n e ; t h i s i n t e r p r e t a t i o n has, however, been questioned by Crocket (1974). I n t e r s t i t i a l s i l i c a t e s c o n t a i n i n g d i s c r e t e PGM have a l s o been r e p o r t e d from S t i l l w a t e r c h r o m i t i t e s (Page and Jackson, 1967). Chromite i s texture-independent i n t i l l d i s p e r s i o n f a n s from igneous sources ( S h i l t s , 1973, 1976). Consequently, PGM i n c l u s i o n s such as those i n chromites i n the -140+270 mesh 283 f r a c t i o n ( F i g u r e s 4-54 and 4-55) would a l s o be expected t o occur i n much s m a l l e r chromite g r a i n s w i t h i n s i l i c a t e s . P a r t i t i o n i n g of Pt i n t o magnetic and non-magnetic heavy m i n e r a l f r a c t i o n s appears t o be r e l a t e d t o d i s t a n c e from supposed source and, t o a l e s s e r extent, source rock mineralogy and g r a i n s i z e . The r e l a t i o n of the former t o P t - c h r o m i t i t e occurrences and landscape elements i s d e p i c t e d s c h e m a t i c a l l y i n F i g u r e 5-3 u s i n g data from s e v e r a l d e t a i l e d p r o f i l e s . S i t e s on both d u n i t i c and n o n - d u n i t i c t i l l t h a t are d i s t a l from known m i n e r a l i z a t i o n c o n t a i n 10-20x more Pt i n t he magnetic than the non-magnetic heavy f r a c t i o n . These r e s u l t s a re c o n s i s t e n t with those r e p o r t e d by F l e t c h e r (1989) f o r Grasshopper Mountain s o i l s . However, t i l l , r u b b l e and c o l l u v i u m s i t e s adjacent t o known oc c u r r e n c e s t y p i c a l l y c o n t a i n a much higher p r o p o r t i o n of Pt i n the non-magnetic f r a c t i o n , i n some cases exceeding t h a t of the magnetic f r a c t i o n s . T h i s r e l a t i o n has important i m p l i c a t i o n s f o r geochemical e x p l o r a t i o n f o r c h r o m i t i t e -a s s o c i a t e d PGM. The h i g h e s t p r o p o r t i o n s of Pt i n the non-magnetic heavy f r a c t i o n s occur i n s e r p e n t i n e c o l l u v i u m . Although SEM examination of the -140+270 mesh heavy f r a c t i o n s of one sample (88-SC-105) r e v e a l e d no d i s c r e t e PGM, the v e r y h i g h Pt c o n c e n t r a t i o n s i n the f i n e non-magnetic f r a c t i o n (Appendix 11.7) probably r e f l e c t the o r i g i n a l platinum-group 3) Soil site 51: Dunitic till 2) Soil site 57 1) Soil site 56 Figure 5-3. Pt distribution in magnetic (black bars) and non-magnetic (stippled bars) heavy fractions of selected soil profiles, and its relation to idealized Pt occurrences and landscape elements on Grasshopper Mountain. Symbols and surficial materials as in Figure 5-2. Pt distributions as in Appendix 12; for each horizon, upper two bars represent -70+140 mesh fraction and lower two bars represent -140+270 mesh fraction. mineralogy of the s e r p e n t i n e source r o c k s . Whereas even the most minute PGM w i l l p a r t i t i o n i n t o c o a r s e r f r a c t i o n s i f enc a p s u l a t e d w i t h i n a chromite host, those i n t e r s t i t i a l t o chromite g r a i n s (St. L o u i s e t a l , 1986) would be l i b e r a t e d d u r i n g e r o s i o n and fragmentation of the rock, and p r o b a b l y p a r t i t i o n i n t o the -270 mesh f r a c t i o n . I t was not, however, p o s s i b l e t o make heavy m i n e r a l s e p a r a t i o n s of the -270 mesh f r a c t i o n t o v e r i f y t h i s . In c o n t r a s t , p a r t i t i o n i n g of m a g n e t i c - f r a c t i o n Pt from d u n i t i c c o l l u v i u m i n t o the c o a r s e r -70+140 s i z e range (Figure 5-3) probably r e f l e c t s both platinum-group mineralogy and an i n i t i a l s t a t e of d u n i t e and chromite weathering. Large magnetic f r e e PGM g r a i n s i n d u n i t i c c o l l u v i u m beneath the C l i f f Zone may exceed 100 um i n diameter ( s e c t i o n 4.4.2.1), and these s i t e s have a much lower p r o p o r t i o n of f i n e - g r a i n e d f r a c t i o n m a t e r i a l than t i l l ( Table 4-10; Appendix 11.2). Heavy non-magnetic s o i l f r a c t i o n s (-140+270 mesh) g e n e r a l l y c o n t a i n about 80-90% s i l i c a t e m i n e r a l s , p r i m a r i l y M g - s i l i c a t e s , w i t h the remainder comprising chromite, i l m e n i t e , i r o n oxides, and o x i d i z e d s u l f i d e s (Tables 4-15 and 4-16). PGM were observed w i t h i n chromite, but i t i s not p o s s i b l e t o f u r t h e r s p e c i a t e the Pt content of o t h e r m e t a l l i c phases as no monomineralic separates were made or a d d i t i o n a l microprobe analyses performed. In s p i t e of the well-known s u l f i d e - P G E a s s o c i a t i o n i n many d e p o s i t s (Paktunc e t a l , 1990), t h e r e i s no evidence t h a t Pt i s a s s o c i a t e d with Fe s u l f i d e s , o x i d i z e d s u l f i d e s or Fe-oxides i n the non-magnetic heavy f r a c t i o n of Grasshopper Mountain s o i l s . No d i s c r e t e PGM were observed i n any o x i d i z e d s u l f i d e g r a i n s . S u l f i d e s are much l e s s abundant than chromite i n C h o r i z o n s a t 3 of the 4 h i g h e s t - P t s i t e s , i n c l u d i n g those adjacent t o known m i n e r a l i z a t i o n (Tables 4-15 and 4-16). Three a d d i t i o n a l t i l l s i t e s i n which o x i d i z e d s u l f i d e s and i r o n oxides are a dominant c o n s t i t u e n t of the non-magnetic heavy f r a c t i o n have very low Pt c o n t e n t s (22-179 ppb), although a f o u r t h t i l l c o n t a i n s 1371 ppb. Experimental evidence (Makovicky e t a l , 1986; Paktunc e t a l , 1990) i n d i c a t e s t h a t p e n t l a n d i t e i s the o n l y s u l f i d e i n which some of the PGE can occur i n s o l i d s o l u t i o n , and t h a t Pt i s not among these. In summary, morphological and a n a l y t i c a l evidence show t h a t h i g h e r Pt c o n c e n t r a t i o n s a s s o c i a t e d w i t h non-magnetic heavy f r a c t i o n s of c o l l u v i u m and d u n i t i c t i l l / r u b b l e a d j a c e n t t o known occurrences are r e l a t e d t o the e r o s i o n and l i m i t e d d i s p e r s i o n of nearby c h r o m i t i t e s e g r e g a t i o n s ( s e c t i o n 5.2). I t would be s i m p l i s t i c t o imply t h a t a l l Pt i s p a r t i t i o n e d i n t o non-magnetic f r a c t i o n s as t h a t i s o b v i o u s l y not the case a t most s i t e s . The occurrence o f more F e - r i c h chromite s e g r e g a t i o n s , or n e a r - s e g r e g a t i o n , Fe-r i c h , PGE-bearing chromite c r y s t a l s which may be more b r o a d l y d i s p e r s e d than the fragments themselves, are p o s s i b l e e x p l a n a t i o n s f o r the Pt content of the magnetic f r a c t i o n s . T h i s i s c o n s i s t e n t with SEM o b s e r v a t i o n of many magnetic and paramagnetic chromite fragments, the d i s c o v e r y of PGM i n c l u s i o n s w i t h i n a magnetic f r a c t i o n chromite c r y s t a l a t the A-Zone occurrence, and the v e r y h i g h (563 ppb) Pt content of a magnetic f r a c t i o n from n o n - d u n i t i c t i l l ( s i t e 20) c o n t a i n i n g no chromite fragments (Table 4-16). 5.3.4.2 Pedogenic Redistribution of Pt within Horizons C o n t r i b u t i o n s of d i f f e r e n t s i z e f r a c t i o n s t o the t o t a l Pt c o n t e n t s of i n d i v i d u a l h o r i z o n s ( F i g u r e s 4-50 and 4-51) p r o v i d e evidence f o r the pedogenic r e d i s t r i b u t i o n of Pt d u r i n g weathering. The t o t a l amount of Pt c o n t a i n e d i n i n d i v i d u a l f r a c t i o n s i s p r i m a r i l y a f u n c t i o n of p a r e n t m a t e r i a l comminution. Approximately one-half the Pt w i t h i n g l a c i a l l y - c r u s h e d t i l l occurs i n the -270 mesh f r a c t i o n , whereas about one-half t h a t i n more j u v e n i l e c o l l u v i u m and r u b b l e occurs i n the coarse -10+40 mesh f r a c t i o n . W i t h i n t h e s e major bounds, however, t h e r e i s c o n s i d e r a b l e r e d i s t r i b u t i o n of the Pt w i t h i n i n d i v i d u a l h o r i z o n s . I n c r e a s e s i n the p r o p o r t i o n of Pt i n f i n e f r a c t i o n s towards the s u r f a c e i n most t i l l and r u b b l e p r o f i l e s i s c l e a r l y a r e s u l t of g r a i n s i z e r e d u c t i o n d u r i n g weathering. Although Bm h o r i z o n heavy concentrates were not observed 288 w i t h the SEM, n e a r - s u r f a c e weathering and d i s s a g g r e g a t i o n of s i l i c a t e fragments would r e l e a s e both minute PGM and PGM-b e a r i n g s i l i c a t e and chromite g r a i n s t o f i n e r s i z e f r a c t i o n s . 5.3.5 Pt Residence S i t e s i n LFH Horizons Very l i t t l e data i s a v a i l a b l e on e i t h e r the con t e n t or behaviour of PGE i n LFH h o r i z o n s . Humus or f o r e s t l i t t e r commonly c o n t a i n s a wide range of p l a n t s p e c i e s and organs i n v a r i o u s stages of decay (Dunn, 1986). Elemental p a r t i t i o n i n g between organs has been r e p o r t e d t o be p a r t i c u l a r l y w e l l developed i n c o n i f e r s (Coker e t a l , 1989), and t h e r e a re numerous r e p o r t e d North American examples of a p p r e c i a b l e Pt i n ashed organs of v a s c u l a r p l a n t s . These i n c l u d e t r e e s such as Black spruce (Picea mariana), Jack p i n e (Pinus banksiana) (Dunn, 1986; Dunn e t a l , 1989), Douglas f i r (Pseudotsuga menziesii) (Riese and Arp, 1986) and G l a n d u l a r b i r c h (Betula glandulosa) (Coker e t a l , 1989), as w e l l as unde r s t o r y shrubs such as Labrador t e a (Ledum groenlandicum) (Dunn, 1986) and fl o w e r s such as Eritrichium chamissonis (Rudolf and Moore, 1972). Pd (Coker e t a l , 1989) and Au ( C u r t i n and King, 1983) are e n r i c h e d i n s u r f i c i a l humus by being m o b i l i z e d i n s o l u t i o n , taken up i n t o v e g e t a t i o n through the r o o t system, 289 c o n c e n t r a t e d i n p l a n t organs, and u l t i m a t e l y r e t u r n e d t o the s u r f a c e . Humus Pd c o n c e n t r a t i o n s of up t o 340 ppb have been r e p o r t e d above Pd-Pt m i n e r a l i z a t i o n a s s o c i a t e d w i t h Ni-Cu s u l f i d e s a t Lac des l i e s i n northwestern O n t a r i o (Fortesque e t a l , 1988). The dominance and s u l f i d e a s s o c i a t i o n of more-hydromorphically mobile Pd a t t h i s l o c a l i t y i s , however, probably of l i t t l e r e l e v a n c e t o chromite-a s s o c i a t e d , Pd-poor Pt d e p o s i t s such as those of Grasshopper Mountain. I t i s u n l i k e l y t h a t the Pt content of Grasshopper Mountain LFH h o r i z o n s , which are lOx g r e a t e r near known m i n e r a l i z a t i o n than i n background areas ( s e c t i o n 4.3.2.2), can be a t t r i b u t e d t o s i m i l a r biogeochemical c y c l i n g . Biogeochemical methods have had o n l y l i m i t e d s uccess on Grasshopper Mountain (Dunn, 1990). Ashed twigs and bark of Douglas f i r , Lodgepole pine and Whitebark p i n e sampled d i r e c t l y above and adjacent t o the A-Zone at the secondary study area have u n i f o r m l y low Pt c o n c e n t r a t i o n s , r a r e l y g r e a t e r than 10 ppb (C. Dunn, p e r s o n a l communication, 1990) even a t s i t e s where LFH h o r i z o n ash c o n t a i n s 100-150 ppb P t . Chromium i s most s t a b l e as Cr i n r e l a t i v e l y i n e r t and i n s o l u b l e chromite and r e l a t e d s p i n e l s t r u c t u r e s . C r 3 + i s mobile o n l y under a c i d i c and h i g h l y o x i d i z i n g c o n d i t i o n s ( B a r t l e t t and Kimble, 1976; Cary e t a l , 1977) u n l i k e l y t o occur i n Grasshopper Mountain s o i l s . P l a n t r o o t s are capable of d i s s o l v i n g and absorbing t r a c e elements from the 3 + s o i l , but cannot reduce Cr i n s o i l chromite t o s o l u b l e C r z (Kabata-Pendias and Pendias, 1984). Consequently, Cr i s not r e a d i l y a v a i l a b l e t o p l a n t s (Gough e t a l , 1979; Kabata-Pendias and Pendias, 1984). Thus, the o c c u r r e n c e of Pt as i n c l u s i o n s encapsulated w i t h i n r e s i s t a n t chromite ( F i g u r e s 4-54 and 4-55) i s the most probable cause of the poor biogeochemical response, i n h i b i t i n g i t s m o b i l i z a t i o n i n s o i l s o l u t i o n s and subsequent uptake i n t o v e g e t a t i o n . S e v e r a l f a c t o r s suggest t h a t the Pt content of LFH h o r i z o n s , p a r t i c u l a r l y those near 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 presence of p a r t i c u l a t e d u n i t e or chromite fragments w i t h i n the LFH m a t e r i a l . Foremost i s the almost u n i v e r s a l presence of a s m a l l p r o p o r t i o n of i n s o l u b l e r e s i d u e of carbon and/or m i n e r a l p a r t i c l e s , u s u a l l y 2-18 weight p e r c e n t remaining a f t e r a c i d d i g e s t i o n of the ash. Most s i l i c a t e m i n e r a l s , i n c l u d i n g o l i v i n e , t a l c , magnetite and hornblende ( s e c t i o n 4.5), are decomposed i n p e r c h l o r i c - h y d r o f l u o r i c a c i d s o l u t i o n s (Langmyhr and Sveen, 1965). However, s p i n e l s and the s u l f i d e s p y r r h o t i t e , p y r i t e and c h a l c o p y r i t e are not r e a d i l y decomposed by t h i s a c i d mixture ( R i l e y , 1958; Langmyhr and Sveen, 1965), and probably comprise the b u l k of the r e s i d u e . Higher p r o p o r t i o n s of i n s o l u b l e r e s i d u e are g e n e r a l l y g r e a t e r a t , although not r e s t r i c t e d t o , the secondary study area and t o c o l l u v i a l s i t e s where the LFH h o r i z o n i s c o n t i n u a l l y inundated with downslope-moving rock fragments (Table 4-7). M i n e r a l p a r t i c l e s are a common c o n s t i t u e n t of LFH h o r i z o n s (Dunn, 1986), p a r t i c u l a r l y i n the lowermost H h o r i z o n near the c o n t a c t with m i n e r a l s o i l ( A g r i c u l t u r e Canada Expert Committee on S o i l Survey, 1987). Pt c o n t e n t of d i i n i t e and chromite p a r t i c l e s i n dunite-dominated areas appears t o i n f l u e n c e the Pt content of the LFH h o r i z o n i n much the same manner t h a t the p r o p o r t i o n of d u n i t e i n f l u e n c e s the background Pt content of m i n e r a l s o i l s ( s e c t i o n 5.2.2). S i m i l a r l y , the presence of b a r r e n r a t h e r than P t - b e a r i n g p a r t i c l e s i n n o n - d u n i t i c s o i l s would not c o n t r i b u t e any Pt t o the LFH h o r i z o n . L i t h i c and m i n e r a l p a r t i c l e s may be n a t u r a l l y i n c o r p o r a t e d i n t o LFH h o r i z o n s i n s e v e r a l ways. Downslope movement of d u n i t i c fragments i s c l e a r l y the cause of h i g h Pt c o n c e n t r a t i o n s i n LFH h o r i z o n s on a c t i v e c o l l u v i u m . The i n t r o d u c t i o n of m i n e r a l p a r t i c l e s i n t o LFH h o r i z o n s a t f o r e s t e d t i l l s i t e s however, may be the r e s u l t of wind a c t i o n , b i o t u r b a t i o n , t r e e u p r o o t i n g or the i n c o r p o r a t i o n of p a r t i c l e - l a d e n f o r e s t l i t t e r i n t o the humus. LFH Fe c o n c e n t r a t i o n s r e p r e s e n t p a r t i a l e x t r a c t i o n s e x c l u s i v e of s p i n e l s or s u l f i d e s . R e l a t i v e l y h i g h Fe c o n t e n t s of 3-5%, a s s o c i a t e d w i t h both h i g h LFH Pt contents a t the A-Zone and on a c t i v e c o l l u v i u m , as w e l l as with low LFH Pt c o n t e n t s a t s e v e r a l n o n - d u n i t i c t i l l and c l a y s i t e s , suggest t h a t Fe-r i c h m i n e r a l g r a i n s are n a t u r a l components of LFH h o r i z o n s . The p o s i t i v e c o r r e l a t i o n between LFH Pt and C h o r i z o n Pt ( F i g u r e 4-25) supports the mixing model of Pt i n t r o d u c t i o n i n t o the LFH h o r i z o n . The o r i g i n of h i g h (>1) LFH/C h o r i z o n Pt r a t i o s ( F igure 4-26) i s not always c l e a r , however. High r a t i o s i n some A-Zone s i t e s , a lthough e r r a t i c a l l y d i s t r i b u t e d , are c l e a r l y the r e s u l t o f mixing of near-bedrock, h i g h - P t m i n e r a l s o i l i n t o t h i n LFH h o r i z o n s . The narrow normal d i s t r i b u t i o n of low r a t i o s a t background-l e v e l d u n i t i c t i l l s i t e s seems t o be a d i s t i n c t i v e f e a t u r e of these t i l l s . Furthermore, the f i v e s i t e s w i t h the lowest r a t i o s occur on r e l a t i v e l y g e n t l e topography where c o l l u v i a l a c t i o n and t r e e u p r o o t i n g are uncommon. The o r i g i n o f some h i g h e r r a t i o s (>1) on n o n - d u n i t i c t i l l i s more p r o b l e m a t i c . Some may be an a r t i f a c t of reduced a n a l y t i c a l p r e c i s i o n a t low C h o r i z o n Pt c o n c e n t r a t i o n s (Figure 3-8), but the c l u s t e r i n g of h i g h - r a t i o s i t e s on the r e l a t i v e l y t h i c k non-d u n i t i c t i l l of the seepage zone and southern f o r e s t e d s l o p e area suggests t h a t b i o g e n i c accumulation of l o w - l e v e l P t i n LFH h o r i z o n s may be comparatively more a c t i v e i n t h i s a r e a . The secondary study area was the s i t e of s u r f a c e b l a s t i n g and t r e n c h i n g d u r i n g e x p l o r a t i o n of the A-Zone (Bohme, 1987, 1988). The p o s s i b i l i t y t h e r e f o r e e x i s t s t h a t the h i g h P t c o n c e n t r a t i o n s i n some LFH r e l a t i v e t o C h o r i z o n s ( F i g u r e 4-26) might r e f l e c t a r t i f i c i a l c o n tamination from a i r b o r n e d u n i t e fragments and dust r a t h e r than n a t u r a l p r o c e s s e s . S e v e r a l f a c t o r s however, suggest 293 t h i s t o be u n l i k e l y . A i r b o r n e contamination would p r o b a b l y r e s u l t i n these samples c o n t a i n i n g a h i g h e r p r o p o r t i o n of l i t h i c fragments than are found a t other s i t e s . However, t h e r e i s no a p p r e c i a b l e d i f f e r e n c e i n the median weight p e r c e n t ash (Table 4-9) of the A-Zone s i t e s (11.34%) and t h a t of s i t e s on d u n i t i c and n o n - d u n i t i c t i l l (11.45% and 13.90%, r e s p e c t i v e l y ) , w h ile t h a t of inundated c o l l u v i u m (21.96%) i s much h i g h e r . S i m i l a r l y , the p r o p o r t i o n of i n s o l u b l e r e s i d u e a t most A-Zone s i t e s i s not v e r y d i f f e r e n t from t h a t found elsewhere, and s p a t i a l d i s t r i b u t i o n of i n s o l u b l e r e s i d u e v a l u e s are not c o n s i s t e n t w i t h a r t i f i c i a l c o n t a m i n a t i o n from b l a s t i n g . Furthermore, the h i g h e s t LFH Fe v a l u e above d u n i t i c t i l l (3.00%) c o i n c i d e s w i t h the h i g h e s t -70 mesh overview Pt value (311 ppb) i n the main study area ( s i t e 73; F i g u r e 2-8B). T h i s s i t e was not d i s t u r b e d by e x p l o r a t i o n a c t i v i t y , i n d i c a t i n g t h a t h i g h e r LFH Fe v a l u e s here and, by extension, a t the A-Zone can r e s u l t from n a t u r a l l y - o c c u r r i n g m i n e r a l s i n the u n d e r l y i n g s o i l r a t h e r than from a i r b o r n e dust. 5.4 Hydromorphic Transport of PGE: Evidence from Seepage Bogs and Waters The PGE have h i s t o r i c a l l y been c o n s i d e r e d i n e r t and i n s o l u b l e , w i t h a n e g l i g i b l e aqueous geochemistry (Plimer and W i l l i a m s , 1988). Renewed i n t e r e s t i n hydrothermal Pt d e p o s i t s has r a i s e d q u e s t i o n s concerning the r o l e t h a t c hemical, or hydromorphic, t r a n s p o r t mechanisms p l a y i n m o b i l i z i n g PGE i n the s u r f i c i a l environment. S e v e r a l s t u d i e s have p r o v i d e d evidence f o r hydromorphic r e d i s t r i b u t i o n of PGE i n d i f f e r e n t weathering environments. These i n c l u d e s o i l p r o f i l e s over the S t i l l w a t e r Complex, Montana (Fuchs, 1972; Fuchs and Rose, 1974), n i c k e l s u l f i d e gossans i n Western A u s t r a l i a ( T r a v i s e t a l , 1976; M c G o l d r i c k and Keays, 1981), oxide zones of the Bushveld Complex (Wagner and Reinecke, 1930; Cousins and K i n l o c h , 1976), l a t e r i t i c weathering p r o f i l e s i n B r a z i l (Taufen and Marchetto, 1989), E t h i o p i a (Otteman and A u g u s t i t h i s , 1967) and S i e r r a Leone (Bowles, 1986, 1988), p o l l u t e d sediments i n Germany (Dissanayake e t a l , 1984), and a l l u v i a l PGM p l a c e r s from a v a r i e t y of l o c a l i t i e s (Cousins, 1973; Cousins and K i n l o c h , 1976; Stumpfl and T a r k i a n , 1976; Burgath, 1988) . Hydromorphic r e d i s t r i b u t i o n of PGE i n the Canadian C o r d i l l e r a i s l i m i t e d by the temperate c l i m a t e , young age of the g l a c i a l l y - t r a n s p o r t e d overburden, and immature s o i l development r e l a t i v e t o t h a t of t r o p i c a l or o l d e r landscapes. With the ex c e p t i o n of zoned Os-Ir p l a c e r PGM from A t l i n and D i s c o v e r y (Cousins and K i n l o c h , 1976), hydromorphic m o b i l i z a t i o n and/or secondary growth of s u r f i c i a l PGM i n the C o r d i l l e r a has not been proposed. C l a s t i c g l a c i a l d i s p e r s i o n and p o s t - g l a c i a l mass wasting have been shown as the dominant processes i n f l u e n c i n g Pt d i s t r i b u t i o n i n Grasshopper Mountain s o i l s . However, the d i s t r i b u t i o n of PGE and other elements i n seepage zone bogs and s u r f a c e waters, together w i t h the presence of s o i l PGM g r a i n s r e l e a s e d from, or not encapsulated i n , chromite ( F i g u r e s 4-52 and 4-53) suggests the p o s s i b i l i t y of a minor hydromorphic m o d i f i c a t i o n of the c l a s t i c d i s p e r s i o n plume i n t o a downslope area dominated by n o n - d u n i t i c t i l l . T h i s s e c t i o n t h e r e f o r e examines the hydromorphic t r a n s p o r t of Pt i n groundwater, and i t s p o s s i b l e a b s o r p t i o n onto o r g a n i c matter i n l o c a l l y - r e d u c i n g break of s l o p e seepage zones and bogs. I t i s not the i n t e n t i o n of the author t o p r o v i d e a q u a n t i t a t i v e e s t i m a t i o n of PGE t r a n s p o r t i n s u r f i c i a l waters, but r a t h e r t o review t h e o r e t i c a l and f i e l d e vidence f o r and a g a i n s t i t s occurrence on Grasshopper Mountain. 5.4.1 C o n s t r a i n t s on PGE M o b i l i t y I n i t i a l l i b e r a t i o n of Pt from d u n i t e and u n c o n s o l i d a t e d sediments p r i o r t o hydromorphic t r a n s p o r t i s l a r g e l y dependent on p a r t i c l e s i z e and host mineralogy. Weathering proceeds more r a p i d l y i n t i l l than bedrock because of t h e g r e a t e r abundance of f i n e - g r a i n e d p a r t i c l e s ( F i t z P a t r i c k , 1980). F o r s t e r i t i c o l i v i n e i s a major c o n s t i t u e n t of s e r p e n t i n i z e d d u n i t e although only a minor c o n s t i t u e n t of Grasshopper Mountain s o i l s . I t i s the l e a s t r e s i s t a n t of the common s i l i c a t e s t o s u r f i c i a l weathering ( G o l d i c h , 296 1938) . O l i v i n e d i s s o l u t i o n occurs by h y d r o l y s i s ; e t c h p i t s a re formed along cleavage planes and l a t t i c e d i s l o c a t i o n s , 2 + s u r f a c e area i n c r e a s e s , and Mg i n the s t r u c t u r e i s r e p l a c e d by H + from the s o i l s o l u t i o n . Subsequent removal of Fe^ completes the breakdown of the m i n e r a l s u r f a c e ( G r a n d s t a f f , 1978; F i t z P a t r i c k , 1980; Huang, 1989), c a u s i n g m o r e - r e s i s t a n t chromite and d i s c r e t e PGM g r a i n s t o be r e l e a s e d t o the weathering environment. S e r p e n t i n e i s s i m i l a r l y weathered t o smectite (Rabenhorst e t a l , 1982). Although the weathering behaviour of f i n e magnetite ( F i t z P a t r i c k , 1980) suggests t h a t very f i n e - g r a i n e d chromite may be somewhat more s u b c e p t i b l e t o decomposition than c o a r s e r g r a i n s , PGM encapsulated w i t h i n r e s i s t a n t chromite g e n e r a l l y remain i s o l a t e d (Fuchs and Rose, 1974) from the weathering c y c l e . PGE o c c u r r i n g i n s o l i d s o l u t i o n , as f r e e g r a i n s ( F i g u r e 4-52) or as i n c l u s i o n s i n M g - s i l i c a t e s ( F i g u r e 4-53) are, however, exposed and a v a i l a b l e t o the weathering c y c l e . T h e o r e t i c a l s t u d i e s on the t r a n s p o r t of Pt and Pd i n aqueous s o l u t i o n s have been p r o v i d e d by Fuchs and Rose (1974), Mountain and Wood (1988a,b), P l i m e r and W i l l i a m s (1988) and Wood e t a l (1989). Pt and Pd may occur as e i t h e r 2+ or 4+ simple i o n s , p a r t i c u l a r l y the former. P d 2 + i s m a r g i n a l l y more s o l u b l e than P t 2 + but both are immobile a t 25°C under a l l but the most a c i d i c and o x i d i z i n g c o n d i t i o n s . They have a p r e f e r e n c e f o r c o v a l e n t bonding, however, and form s o l u b l e s t a b l e i n o r g a n i c complexes w i t h c h l o r i n e ( C l ~ ) , bromine ( B r ~ ) , i o d i n e ( I ~ ) , cyanide (CN~), t h i o c y a n a t e (SCN~), s u l f i t e ( S 0 3 " 2 ) , t h i o s u l f a t e ( S 2 0 3 " 2 ) , n i t r i t e (NO2"") / h y d r o x y l (0H~), ammonia (NH 3) and b i s u l f i d e (HS~) . The r e l a t i v e s c a r c i t y of many of these l i g a n d s i n s u r f i c i a l water, however, l i m i t s d i s c u s s i o n of PGE t r a n s p o r t t o c h l o r i d e , t h i o s u l f a t e , and b i s u l f i d e complexes, and t o p o o r l y - u n d e r s t o o d o r g a n o m e t a l l i c complexes with s o i l o r g a n i c matter such as humic or f u l v i c a c i d s (Wood, 1990). The r e l a t i v e importance of these complexing agents i s p a r t l y dependent on t h e i r s o l u b i l i t y under s u r f i c i a l c o n d i t i o n s . An Eh-pH diagram of the system Pt-O-H-S a t 25°C and 1 bar (Brookins, 1988) i s shown i n F i g u r e 5-4, a l o n g w i t h superimposed s t a b i l i t y f i e l d s of some aqueous P t -c h l o r i d e and t h i o s u l f a t e complexes and Eh-pH ranges of s o i l s , peat bogs, shallow ground waters and B r i t i s h Columbia bog waters. N a t i v e Pt i s the dominant Pt s p e c i e s w i t h i n the Eh-pH bounds of n a t u r a l waters (Brookins, 1988; F i g u r e 5-4). I t i s apparent, however, t h a t aqueous c h l o r i d e and t h i o s u l f a t e complexes may be l o c a l l y important. Pd d e p l e t i o n from s u r f a c e h o r i z o n s a t the S t i l l w a t e r Complex was a t t r i b u t e d t o c h l o r i d e complexing (Fuchs and Rose, 1974). C h l o r i d e complexes, as PtCl^ are, however, capable of m o b i l i z i n g Pt o n l y i n h i g h l y a c i d i c and o x i d i z i n g environments (Mountain 298 Eh(v) 0 2 4 6 8 10 12 14 PH Figure 5-4. Eh-pH diagram for Pt at 25C and 1 bar, with superimposed stability fields of some chloride and thiosulfate complexes. Eh-pH ranges of iron-rich and calcareous soils, peat bogs, shallow ground water and British Columbia central bog waters are also shown. Eh-pH diagram after Brookins (1988). Chemical data after Fuchs and Rose (1974), Westland (1981), and Mountain and Wood (1988a). Environmental fields after Baas Becking et al (1960) and Lett (1978). and Wood, 1988a,b; Wood and Mucci, 1988) such as those o f l a t e r i t i c s o i l s (Bowles, 1986, 1988). C h l o r i d e c o n c e n t r a t i o n i s a c r i t i c a l f a c t o r i n deter m i n i n g PGE s o l u t i o n i n s o i l s (Bowles, 1986). Eh of P t C l 4 2 ~ f o r m a t i o n i s lower, hence s u r f i c i a l m o b i l i t y g r e a t e r , w i t h i n c r e a s i n g c h l o r i d e c o n c e n t r a t i o n . C l ~ c o n c e n t r a t i o n s i n Grasshopper Mountain s o i l s o r groundwaters were not determined. However, a C l ~ v a l u e of 2 32 ppm has been r e p o r t e d f o r some Tulameen s e r p e n t i n i t e (10-75% serp e n t i n e ) by Stueber e t a l (1968). Other workers ( E a r l e y , 1958; Rucklidge, 1972) have a l s o documented the ve r y h i g h C l ~ content of s e r p e n t i n i z e d d u n i t e s . The i m p l i c a t i o n s f o r hydromorphic PGE t r a n s p o r t s h o u l d not be overlooked. C l ~ occurs i n s o l i d s o l u t i o n w i t h i n s e r p e n t i n e v e i n l e t s , where i t may have been i n t r o d u c e d d u r i n g s e r p e n t i n i z a t i o n , and a t t a i n s maximum c o n c e n t r a t i o n s of 0.8% (Rucklidge, 1972). I t i s wa t e r - s o l u b l e (Stumpfl, 1974) and e a s i l y l i b e r a t e d d u r i n g weathering (Goldschmidt, 1954). Although s p e c u l a t i v e , i t would seem t h a t the g r e a t e r the C l ~ c o n c e n t r a t i o n of the d u n i t i c s o i l s o l u t i o n , the more l i k e l y i t might complex wi t h a v a i l a b l e bedrock or s o i l PGM. Among other i n o r g a n i c l i g a n d s , t h i o s u l f a t e complexes have been t h e o r i z e d t o m o b i l i z e PGE over a n e a r - n e u t r a l t o s l i g h t l y b a s i c pH range of 5-9 d u r i n g s u l f i d e o x i d a t i o n (Mountain and Wood, 1988a; Plimer and W i l l i a m s , 1988). The 300 s t a b i l i t y f i e l d of one t h i o s u l f a t e complex, Pt(S2C>3)4 6~, o v e r l a p s the Eh-pH range of shallow groundwater ( F i g u r e 5-4) under more reasonable s u r f i c i a l c o n d i t i o n s than those r e q u i r e d f o r Pt c h l o r i d e complexes t o form. However, the importance of t h i o s u l f a t e complexing may be minimal on Grasshopper Mountain because s u l f i d e s are not abundant ( s e c t i o n 2.3). Low s u l f i d e content may a l s o l i m i t Pt t r a n s p o r t as b i s u l f i d e complexes. S o l u b i l i t y of these, although l i m i t e d by the low a c t i v i t y of Pt* under r e d u c i n g c o n d i t i o n s where HS~ i s dominant (Mountain and Wood, 1988), i n c r e a s e s w i t h i n c r e a s i n g S content a t b a s i c pH (Wood and Mucci, 1988). Fuchs and Rose (1974) s t a t e d t h a t PGE m o b i l i t y would be expanded by the e x i s t a n c e of o r g a n i c , as w e l l as i n o r g a n i c , complexes. Knowledge of the i n t e r a c t i o n of humic substances w i t h the PGE i s l i m i t e d . F u l v i c and s y n t h e t i c p h t h a l i c a c i d s are a b l e t o t r a n s p o r t ppm-levels of Pt over a wide pH range, probably by s t a b i l i z a t i o n of c o l l o i d a l suspensions r a t h e r than by formation of s o l u b l e o r g a n o m e t a l l i c complexes (Wood, 1990). Dissanayake e t a l (1984) however, showed t h a t Au, Pt and Pd are f i x e d as o r g a n o m e t a l l i c complexes i n humic a c i d - r i c h o r g a n i c sediments of the Rhine R i v e r . PGE were suggested t o have been l o c a l l y c o n c e n t r a t e d by b e i n g reduced through complexing with humic a c i d s , i n response t o l o c a l changes i n sediment redox c o n d i t i o n s , and p r e c i p i t a t e d onto c l a y m i n e r a l s i n the sediment. C o n c e n t r a t i o n of p r e c i o u s metals, up t o 1000 ppm Pd and 370 ppm Pt, near the base of the K u p f e r s c h i e f e r b l a c k s h a l e i n the Z e c h s t e i n copper d e p o s i t s of Poland have a l s o been a t t r i b u t e d t o redox p r o c e s s e s (Kucha, 1982). 5.4.2 Bogs Numerous examples e x i s t f o r the scavenging of Cu, among ot h e r metals, i n C o r d i l l e r a n bogs (Bradshaw, 1975; L e t t and F l e t c h e r , 1979). Bog i n t e r p r e t a t i o n s are based on v e r y l i m i t e d data but suggest t h a t low c o n c e n t r a t i o n s of h y d r o m o r p h i c a l l y mobile PGE may be s i m i l a r l y scavenged i n a r e d u c i n g environment. Evidence f a l l s i n t o two g e n e r a l a r e a s : the r e l a t i o n of P