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The distribution and behaviour of gold in soils in the vicinity of gold mineralization, Nickel Plate… Sibbick, Steven John Norman 1990

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THE DISTRIBUTION AND BEHAVIOUR OF GOLD IN SOILS IN THE VICINITY OF GOLD MINERALIZATION, NICKEL PLATE MINE, HEDLEY, SOUTHERN BRITISH COLUMBIA by STEVEN JOHN NORMAN SIBBICK B.Sc. (Hons) The University of Western Ontario, 1986 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1990 (c) Steven John Norman Sibbick, 1990 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 The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT Sampling of s o i l s and t i l l are conventional methods of gold exploration i n glaciated regions. However, the exact nature of the residence s i t e s and behaviour of gold within s o i l and t i l l are poorly known. A gold dispersion t r a i n extending from the Nickel Plate mine, Hedley, southwest B r i t i s h Columbia, was investigated i n order to determine the d i s t r i b u t i o n and behaviour of gold within s o i l s developed from t i l l . Three hundred and twelve s o i l , t i l l and humus samples (representing LFH, A, B and C horizons) were c o l l e c t e d from fifty-two s o i l p i t s and t h i r t y - f o u r roadcut locations within the dispersion t r a i n . S o i l and t i l l samples were sieved into four s i z e f r a c t i o n s ; the resultant -212 micron (-70 mesh) f r a c t i o n of each sample was analysed for Au by FA-AAS. Humus samples were ground to -100 micron powder and analysed for Au by INAA. Based on the a n a l y t i c a l r e s u l t s , each LFH, A, B and C horizon was subdivided into anomalous and background populations. Detailed s i z e and density f r a c t i o n analysis was ca r r i e d out on s o i l p r o f i l e s r e f l e c t i n g anomalous and background populations, and a mixed group of samples representing the overlap between both populations. Samples were sieved to six siz e f r a c t i o n s ; three of the si z e fractions (-420+212, -212+106, -106+53 microns) were separated into two density fr a c t i o n s using methylene iodide and analysed for Au by FA-AAS. The Au content of the -53 micron f r a c t i o n was analysed by FA-AAS and cyanide extraction - AAS. Results indicate that the Au content of s o i l p r o f i l e s increase with depth while decreasing with distance from the minesite. Heavy mineral concentrates and the l i g h t mineral f r a c t i o n Au abundances reveal that d i l u t i o n by a factor of 3.5 occurs within the t i l l over a distance of 800 metres. However, free gold within the heavy mineral f r a c t i o n i s both d i l u t e d and comminuted with distance. Recombination of size and density fractions indicate that the Au contents of each siz e f r a c t i o n are equivalent; v a r i a t i o n i n Au abundance i s not observed with a change i n grain s i z e . Seventy percent of the Au i n the -53 micron f r a c t i o n occurs as free gold. Chemical a c t i v i t y has not altered the composition of gold grains within the s o i l p r o f i l e s . Compositional and morphological differences between gold grains are not i n d i c a t i v e of g l a c i a l transport distance or location within the s o i l p r o f i l e . Relative abundances of gold grains between sample locations can be used as an indicator of proximity to the minesite. The sampling medium with the best sample repre s e n t i v i t y and contrast between anomalous and background populations i s the -53 micron (-270 mesh) f r a c t i o n of the C horizon. Geochemical s o i l sampling programs i n the v i c i n i t y of the Nickel Plate mine should c o l l e c t a minimum mass of 370 grams of -2000 micron (-2 mm) s o i l f r a c t i o n i n order to obtain 30 grams of the -53 micron f r a c t i o n . V TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES x ACKNOWLEDGEMENTS xiv Chapter One - INTRODUCTION 1.1 Introduction 2 1.2 Properties of gold 2 1.3 S t a t i s t i c a l d i s t r i b u t i o n of rare grains 3 1.4 Statement of problem 8 Chapter Two - GEOCHEMICAL DISPERSION IN TILLS 2.1 Origin of t i l l 2.1.1 Introduction 12 2.1.2 T i l l formation 13 2.1.2.1 Erosion 13 2.1.2.2 Transport 16 2.1.2.3 Deposition 19 2.2 Geochemical dispersion i n t i l l 2.2.1 Introduction 22 2.2.2 Mechanical dispersion 23 2.2.3 Modification by s o i l forming processes 31 2.2.4 Summary of factors which e f f e c t the dispersion of gold within s o i l and t i l l 39 Chapter Three - DESCRIPTION OF STUDY AREA 3.1 Location and access 42 3.2 History 4 2 3.3 Regional geology 4 5 3.4 Deposit geology 47 3.5 Ore deposits and mineralogy 51 3.6 G l a c i a l history 56 3.7 S u r f i c i a l geology 58 3.8 Physiography, climate, vegetation and s o i l s 65 Chapter Four - SAMPLING METHODS 4.1 S i t e s e l e c t i o n 69 4.2 F i e l d sampling methods 69 4.3 Labratory preparation and analysis 4.3.1 Humus 72 4.3.2 S o i l s 4.3.2.1 Minus 212 micron f r a c t i o n 7 3 v i 4.3.3.2 Size f r a c t i o n , density f r a c t i o n and cyanide extraction samples 77 4.3.3 Scanning electron microscope and electron microprobe sample preparation and analysis 78 Chapter Five - RESULTS 5.1 Minus 212 micron f r a c t i o n r e s u l t s 5.1.1 R e l i a b i l i t y and a n a l y t i c a l p r e c i s i o n 5.1.1.1 Introduction 83 5.1.1.2 Scatterplots / correlations 83 5.1.1.3 Systematic bias 85 5.1.1.4 Analysis of variance 88 5.1.1.5 Thompson and Howarth pr e c i s i o n method...88 5.1.2 Grain si z e d i s t r i b u t i o n of the -2000 micron fra c t i o n s 93 5.1.3 S o i l p i t re s u l t s 93 5.1.4 Roadcut samples 9 5 5.1.5 Population d i s t r i b u t i o n s of the -212 micron re s u l t s 106 5.2 Size / density f r a c t i o n r e s u l t s 5.2.1 Introduction 115 5.2.2 R e l i a b i l i t y and a n a l y t i c a l p r e c i s i o n 115 5.2.3 Grain size d i s t r i b u t i o n of the -2000 micron f r a c t i o n 116 5.2.4 Size and density f r a c t i o n analysis 123 5.2.5 Heavy mineral f r a c t i o n r e s u l t s 12 3 5.2.6 Light mineral f r a c t i o n r e s u l t s 127 5.2.7 Minus 53 micron f r a c t i o n r e s u l t s 127 5.2.8 Total Au concentration by siz e f r a c t i o n 12 8 5.2.9 Proportion of t o t a l Au contributed from each siz e / density f r a c t i o n 128 5.2.10 Comparison of l i g h t and heavy density fractions of each size f r a c t i o n 133 5.2.11 Number of gold p a r t i c l e s i n each si z e f r a c t i o n 136 5.3 Cyanide extraction r e s u l t s 138 5.4 Grain morphology 14 2 5.5 Electron microprobe re s u l t s 150 Chapter Six - DISCUSSION 6.1 Gold grain shape and composition 159 6.2 Residence s i t e s of Au i n s o i l and t i l l 161 v i i 6.3 Var i a t i o n of Au concentration with depth 163 6.4 Var i a t i o n of Au concentration with distance 167 6.5 Origin of the dispersion t r a i n 172 6.6 Recommendations for Mineral Exploration 17 3 6.6.1 Determination of a representative f i e l d sample siz e 173 6.6.2 Analysis of heavy mineral concentrates versus the -53 micron f r a c t i o n 176 6.6.3 Analysis by f i r e assay - atomic absorption versus cyanide extraction 177 6.6.4 Optimum method for indi c a t i n g source location of the geochemical anomaly 178 6.6.5 Optimum f i e l d sample 178 Chapter Seven - CONCLUSIONS AND RECOMMENDATIONS 7.1 Conclusions and recommendations 181 REFERENCES 183 APPENDIX 194 v i i i LIST OF TABLES Table 3-1. Pebble count r e s u l t s on f i v e selected C horizon samples 63 Table 3-2. pH values of selected s o i l p r o f i l e s 67 Table 5-1. Analysis of variance re s u l t s for primary and duplicate -212 micron Au analyses 89 Table 5-2. Mean (antilog) Au content of each s o i l horizon by traverse l i n e 103 Table 5-3. Summary table for (antilog) Roadcut C horizon ( t i l l ) sample Au analyses 105 Table 5-4. Calculated (antilog) means and thresholds for the anomalous and background populations of each s o i l horizon 114 Table 5-5. Analysis of variance r e s u l t s for duplicate l i g h t and heavy mineral concentrate and -53 micron Au analyses 12 0 Table 5-6a. Grain si z e d i s t r i b u t i o n of the -2000 micron f r a c t i o n 121 Table 5-6b. Grain si z e d i s t r i b u t i o n of the l i g h t and heavy fractions of the -420 micron f r a c t i o n 122 Table 5-7. Au concentrations of heavy mineral concentrates 12 5 Table 5-8. Au concentrations of l i g h t mineral concentrates 12 6 Table 5-9. Au concentration of the -53 micron f r a c t i o n . 129 Table 5-10. Calculated Au concentration by siz e f r a c t i o n 13 0 Table 5-11. Paired t - t e s t r e s u l t s on comparisons of t o t a l Au contents of d i f f e r e n t s i z e fractions 131 Table 5-12. Calculated mass (micrograms) of Au i n each si z e and / or density f r a c t i o n 132 i x Table 5-13. Percentage of Au i n each si z e and / or density f r a c t i o n of the -420 micron f r a c t i o n 134 Table 5-14. D i s t r i b u t i o n of Au between the l i g h t and heavy fractions of each size f r a c t i o n 135 Table 5-15a. Calculated number of gold grains i n each heavy mineral si z e f r a c t i o n and the -53 micron f r a c t i o n per weight of analyzed sample (30 gram maximum) 139 Table 5-15b. Calculated number of gold grains i n each heavy mineral s i z e f r a c t i o n and the -53 micron f r a c t i o n per 3 0 gram sample weight...14 0 Table 5-16. Cyanide extractable Au and residual Au contents of the -53 micron f r a c t i o n 141 Table 5-17. Shape factor data, proximal p i t grains 147 Table 5-18. Analysis of variance re s u l t s on shape factors, by horizon 148 Table 5-19. Analysis of variance r e s u l t s on shape factor values for proximal versus d i s t a l grain shapes 149 Table 5-20. C l a s s i f i c a t i o n of shapes and surface textures of gold grains 151 Table 5-21. Results of gold grains c l a s s i f i e d using the A v e r i l l (1988) and DiLabio (1989) system for q u a l i t a t i v e grain evaluation 152 Table 5-22. Results of electron microprobe analyses on the cores and edges of 41 gold grains.... 153 Table 6-1. Contrast r a t i o s for a va r i e t y of sample media 169 Table 6-2. Estimates of the mass of sample required to contain one grain of gold 175 X L I S T OF F I G U R E S F i g u r e 1 . 1 . P o i s s o n p r o b a b i l i t y o f d e t e c t i n g N g o l d g r a i n s i n a 30 g r a m s u b s a m p l e 5 F i g u r e 1 . 2 . P o i s s o n p r o b a b i l i t y o f d e t e c t i n g no g o l d g r a i n s a s a f u n c t i o n o f g r a i n s i z e a n d s u b s a m p l e w e i g h t 7 F i g u r e 1 . 3 . R e l a t i o n s h i p b e t w e e n p a r t i c l e s i z e a n d t h e s i z e o f s a m p l e r e q u i r e d t o c o n t a i n t w e n t y p a r t i c l e s o f g o l d 9 F i g u r e 2 . 1 . S c h e m a t i c d i a g r a m o f l a r g e s c a l e b l o c k i n c l u s i o n s 15 F i g u r e 2 . 2 . S c h e m a t i c d i a g r a m o f t r a n s p o r t l o c a t i o n s o f d e b r i s w i t h i n g l a c i e r s 17 F i g u r e 2 . 3 . C l a s s i f i c a t i o n o f t i l l s a n d t h e i r r e l a t i o n s h i p t o t r a n s p o r t 2 0 F i g u r e 2 . 4 . A c t u a l a n d i d e a l i z e d d i s p e r s a l c u r v e s 24 F i g u r e 2 . 5 . R i b b o n s h a p e d d i s p e r s i o n t r a i n o f a m p h i b o l i t e b o u l d e r s 2 6 F i g u r e 2 . 6 . R e g i o n a l s i z e d , f a n s h a p e d d i s p e r s i o n t r a i n s 27 F i g u r e 2 . 7 . I d e a l i z e d m o d e l o f g l a c i a l d i s p e r s a l 29 F i g u r e 2 . 8 . P l o t o f d e p t h v e r s u s c o n c e n t r a t i o n f o r t u n g s t e n g o l d a n d a r s e n i c i n t i l l 34 F i g u r e 3 . 1 . Map o f t h e H e d l e y r e g i o n , s o u t h w e s t e r n B r i t i s h C o l u m b i a 43 F i g u r e 3 . 2 . R e g i o n a l g e o l o g y a n d l o c a t i o n o f g o l d b e a r i n g p r o p e r t i e s , H e d l e y r e g i o n 44 F i g u r e 3 . 3 . S t r a t i g r a p h y o f t h e H e d l e y r e g i o n 48 F i g u r e 3 . 4 . G e n e r a l d e p o s i t g e o l o g y , N i c k e l P l a t e m i n e 50 F i g u r e 3 . 5 . G a r n e t c o m p o s i t i o n , e x o s k a r n 52 F i g u r e 3 . 6 . P y r o x e n e c o m p o s i t i o n , e x o s k a r n 53 F i g u r e 3 . 7 . G e o l o g y o f t h e t h e s i s a r e a 54 x i Figure 3.8. S u r f i c i a l Geology, 1:12 000 map back pocket Figure 3.9. G l a c i a l s t r i a e and chattermarks on granodiorite outcrop, east of Nickel Plate mine 61 Figure 4.1. Gold dispersion t r a i n s d e l i n i a t e d by Placer Development, Inc 70 Figure 4.2. Location of sample traverse l i n e s . r e l a t i v e to the minesite 71 Figure 4.3. Schematic diagram of sample preparation 74 Figure 4.4. Wet sieving system 75 Figure 5.1. Scatterplot of duplicate Au analyses, -212 micron f r a c t i o n 84 Figure 5.2. Scatterplot of duplicate Au analyses, -212 micron f r a c t i o n . Large o u t l i e r (6350 ppb) and corresponding duplicate analysis removed 86 Figure 5.3. Thompson and Howarth error plot , -212 micron f r a c t i o n duplicate data 92 Figure 5.4. Mean grain s i z e d i s t r i b u t i o n of the -2000 micron f r a c t i o n for the A, B and C horizons of each traverse l i n e 94 Figure 5.5. Arithmetic histogram of a l l A, B and C horizon -212 micron f r a c t i o n Au analyses 96 Figure 5.6. Logarithmic histogram of a l l A, B and C horizon -212 micron f r a c t i o n Au analyses 97 Figure 5.7a. Au content of the LFH, A, B and C horizons,-212 micron f r a c t i o n , traverse l i n e 1 98 Figure 5.7b. Au content of the LFH, A, B and C horizons,-212 micron f r a c t i o n , traverse l i n e 2 99 Figure 5.7c. Au content of the LFH, A, B and C horizons,-212 micron f r a c t i o n , traverse l i n e 3 100 x i i Figure 5.7d. Au content of the LFH, A, B and C horizons,-212 micron f r a c t i o n , traverse l i n e 4 101 Figure 5.7e. Au content of the LFH, A, B and C horizons, -212 micron f r a c t i o n , traverse l i n e 5 102 Figure 5.8. Plot of the mean logarithmic Au content of the LFH, A, B and C horizons as a function of distance 104 Figure 5.9. Plot of the -212 micron f r a c t i o n Au content of the Roadcut t i l l samples with increasing distance from the minesite 107 Figure 5.10a. Probabil i t y p l o t with thresholds, LFH horizon Au content 109 Figure 5.10b. Probabil i t y p l o t with thresholds, A horizon -212 micron f r a c t i o n Au content 110 Figure 5.10c. Probabil i t y p l o t with thresholds, B horizon -212 micron f r a c t i o n Au content I l l Figure 5.10d. Probabil i t y p l o t with thresholds, C horizon -212 micron f r a c t i o n Au content 112 Figure 5.10e. Probabil i t y p l o t with thresholds, Roadcut C horizon samples, -212 micron f r a c t i o n Au content 113 Figure 5.11. Light mineral f r a c t i o n duplicate analyses 117 Figure 5.12. Minus 53 micron f r a c t i o n duplicate analyses 118 Figure 5.13. Heavy mineral f r a c t i o n duplicate analyses 119 Figure 5.14. Variation of heavy mineral content of the -420 micron f r a c t i o n with increasing distance from the minesite 124 Figure 5.15. Proportion of Au within the heavy mineral f r a c t i o n of each si z e f r a c t i o n . Points calculated using data from the B and C horizons of the Proximal, Intermediate and D i s t a l p i t s 137 x i i i Figure 5.16. Cyanide extractable Au versus Total Au (FA-AAS) , -53 micron f r a c t i o n 143 Figure 5.17. P r o b a b i l i i t y p l o t of shape factor values...145 Figure 5.18. Plot of core Au vs core Ag analyses, Proximal and D i s t a l p i t s 155 Figure 5.19. Plot of edge Au vs edge Au analyses of the A, B and C horizons, Proximal pit...156 Figure 5.20. Plot of core Au vs core Ag analyses of the A, B and C horizons, Proximal pit...157 xiv ACKNOWLEDGEMENTS Many people have assisted me during the course of my thes i s research. I would l i k e to thank industry geochemists and geologists I. Thompson, L.W. Saleken, J. Bellamy and R. Simpson f o r t h e i r help and suggestions. W.K. Fletcher provided support, guidance and h e l p f u l c r i t i c i s m . A.J. S i n c l a i r and K.W. Savigny c a r e f u l l y reviewed the manuscript. F i e l d assistance was provided by Henry Yuen. Dominic Bordin and Bruce Downing of Corona Corporation were e s p e c i a l l y h e l p f u l during the 1987 f i e l d season, providing both advice i n the f i e l d and guided tours through the n i g h t l i f e of Penticton. Laboratory processing of samples was c a r r i e d out by Joni Borges and Neesha Brar. The assistance of Joni Borges allowed t h i s thesis to be completed. Yvonne Douma did a superb job sectioning gold grains. Many enlightening conversations on geochemistry and gold were held with Steve Cook and John Knight. Geological i n s p i r a t i o n was provided by Colin Godwin. Cookies and pizza were furnished by Michelle Lamberson and Regan Palsgrove. Susan Taite c a r e f u l l y emboldened my th e s i s . Hockey i n s p i r a t i o n was provided by Bryon Cranston, K e l l y Russell and e s p e c i a l l y the Womens Geology Hockey Team. Amigos Bob Lane and Doug Reddy (and I) proved that claim staking i s n ' t a v i a b l e source of income for grad students. Fun and f r i v o l i t i e s were supplied by Myra Keep. J e f f F i l l i p o n e scared me away from a Ph.D. Marc Gilberg and Pat Shanahan helped when I needed i t . My l i f e was provided by my parents, to whom I am eternally grateful 1 Chapter One Introduction 2 1.1 Introduction Extensive portions of the Northern Hemisphere, including most of Canada, have undergone periodic g l a c i a t i o n during the past two m i l l i o n years. The e f f e c t of these g l a c i a t i o n s has been to obscure large regions of bedrock with material derived from the g l a c i a l erosion of l o c a l or distant materials. As ore deposits found i n regions of t h i n overburden have become depleted, emphasis has s h i f t e d to exploration i n areas covered by g l a c i a l sediment. T i l l , the most common g l a c i a l sediment, has received the most attention. Exploration i n t i l l covered areas i s further complicated by the development of s o i l , which can modify any geochemical signatures found i n the t i l l . 1.2 Properties of gold Gold belongs to Group IB of the periodic table, along with copper (Cu) and s i l v e r (Ag). The density of gold i s high (density of pure gold = 19.3 g/cm3), though s o l i d s o l u t i o n with elements such as s i l v e r , copper, mercury and iron w i l l decrease i t s density. Gold and s i l v e r e x i s t i n complete s o l i d solution, with most native gold containing 5 to 15 percent Ag (Boyle, 1979). Native gold containing more than 20 percent s i l v e r i s referred to as electrum. V i s u a l l y , 3 electrum i s distinguished from native gold by being pale yellow and becoming increasingly paler with increased s i l v e r content. At approximately 65 percent Ag, the colour of electrum becomes indistinguishable from pure s i l v e r (Boyle, 1979). 1.3 S t a t i s t i c a l d i s t r i b u t i o n of rare grains The d i s t r i b u t i o n of rare grains within a granular material i s described by the Poisson d i s t r i b u t i o n (Ingamells, 1981; Koch and Link, 1970): P(n) = e~ u u n/n! (1-1) where u i s the mean number of grains within a sample and P(n) i s the pr o b a b i l i t y of n grains being found within the sample. Confidence intervals for the mean (u) at a sig n i f i c a n c e l e v e l (a) can be estimated using the X 2 ( c h i -squared) d i s t r i b u t i o n (Zar, 1984): (X 2(l-a/2),2N)/2 < u < (X 2(a/2),2(N+l))/2 where N i s an estimate of u The e f f e c t of rare grains upon s o i l sampling can be i l l u s t r a t e d by a simple example. A gold dispersion t r a i n 4 derived from an auriferous quartz vein r e s u l t s i n the homogeneous d i s t r i b u t i o n of 100 micron diameter gold grains throughout the s o i l p r o f i l e giving a bulk composition of 100 ppb (100 micrograms Au per gram). The host s o i l i s composed of grains close to 100 microns i n diameter and possesses an i n s i g n i f i c a n t Au content. During a geochemical s o i l survey, a 3 00 gram B horizon s o i l sample i s taken from the dispersion t r a i n . From t h i s , a representative t h i r t y gram subsample i s taken and analysed for Au by FA-AAS. Assuming pure gold (density = 19.3 g/cm ) spheres of 100 microns diameter, the weight of each gold grain i s 10.09 micrograms. The weight of gold within the sample i s 3 0 micrograms (100 ppb X 3 00 grams), r e s u l t i n g i n the expected number of p a r t i c l e s (u) to be 2.972. The expected number of gold p a r t i c l e s i n the representative t h i r t y gram subsample w i l l be 0.297. Using the Poisson d i s t r i b u t i o n (equation 1-1) the p r o b a b i l i t y that the subsample w i l l contain no p a r t i c l e of gold (P(0), n=0) i s 0.74 (Figure 1.1). Therefore, the chance of not detecting the anomaly i s 74%. Only a 2 6% chance ex i s t s that one or more gold grains w i l l be found within the sample. Detection of a single gold grain would r e s u l t i n a reported Au concentration of 337 ppb, three times higher than the true Au concentration of 100 ppb. This feature has led to the use of the term "nugget e f f e c t " to describe high Au analyses generated by the random inclu s i o n of a sin g l e Poisson probability of detecting (N) gold grains in a 30 gram sample Probability IIP ^^^^^^^^^^ \//////////A , 0 1 2 3 Number of grains Figure 1.1 - Poisson p r o b a b i l i t y of d e t e c t i n g N g o l d g r a i n s i n a 30 gram subsample. tn 6 (or a very few) gold p a r t i c l e s within a small sample (Ingamells, 1981). Var i a t i o n i n the size f r a c t i o n and sample s i z e used for analysis w i l l have a dramatic e f f e c t upon the perceived Au concentration. In a modification of the previous example, the auriferous s o i l i s now composed of s i x equally proportioned grain sizes (300, 150, 75, 50, 10 and 2 microns), each with a gold content of 100 ppb. A l l gold within the s o i l exists as free grains. A 1800 gram sample taken i n the f i e l d provides 3 00 grams of each grain s i z e for analysis. Representative ten and t h i r t y gram s p l i t s are taken of each size f r a c t i o n and analysed by FA-AAS fo r Au. The p r o b a b i l i t y , using the Poisson d i s t r i b u t i o n , of these samples (300, 30 and 10 gram) containing no gold grains (P(0), n=0) i s shown i n Figure (1.2). Chances of encountering a gold grain within a sample are strongly dependent upon the grain size and weight of sample analysed. There i s a very high probability of not detecting Au within the coarse s i z e fractions, while there i s no chance of t h i s occurring i n the fi n e size fractions. Undersized f i e l d sample weights for the coarse s i z e fractions r e s u l t s i n a bias towards the f i n e r size fractions; Au concentrations would be perceived to increase with decreasing grain s i z e . V a r i a t i o n of a n a l y t i c a l precision with the number of gold p a r t i c l e s i n a sample was quantified by C l i f t o n et a l . Poisson probability of detecting no grains Probability 1 0.8 -0.6 0.4 ©.. - A 300 gram --S-30 gram — A — 10 gram G Sample size 250 - Q A 200 150 100 Size Fraction (microns) 0 Figure 1.2 - Poisson probab i l i t y of detect ing no gold gra ins as a function of gra in s ize and subsample weight. 8 (1969). Their work showed that the precision of an analysis i s determined so l e l y by the number of gold grains present i n the sample as long as the following conditions are met: 1) Gold p a r t i c l e mass i s uniform. 2) Gold p a r t i c l e s make up less than 0.1% of a l l p a r t i c l e s . 3) The sample contains at least 1000 p a r t i c l e s . 4) A n a l y t i c a l errors are absent. 5) The gold p a r t i c l e s are randomly d i s t r i b u t e d through the material being sampled. Based on these conditions, to achieve a p r e c i s i o n of 50%, a minimum of 20 p a r t i c l e s of gold i s required ( C l i f t o n et a l . , 1969). The r e l a t i o n between p a r t i c l e size and the s i z e of sample required to contain 2 0 p a r t i c l e s of gold i s shown i n Figure (1.3). 1.4 Statement of problem At the Nickel Plate mine, Hedley, southwest B r i t i s h Columbia, a gold dispersion t r a i n extends downice and downslope from the minesite. The dispersion t r a i n i s found i n an oxidized basal t i l l which has been altered by the formation of a poorly d i f f e r e n t i a t e d s o i l layer i n the upper one metre of t i l l . Conventional methods of geochemical s o i l sampling r e l y upon analysis of the -80 mesh f r a c t i o n of the B horizon. However, the exact nature of the residence s i t e s and 9 Figure 1.3 - Relationship between p a r t i c l e s i z e and the s i z e of sample required to contain twenty p a r t i c l e s of gold. From C l i f t o n et a l . (1969) 10 dispersion c h a r a c t e r i s t i c s of gold within s o i l are not well known. Improved techniques for detection of gold s o i l anomalies w i l l r e s u l t from a more detailed knowledge of the behaviour and c h a r a c t e r i s t i c s of gold within the s o i l p r o f i l e . I t i s the goal of t h i s thesis to examine the following: 1) Alpine g l a c i a l dispersion of gold away from gold mineralization. 2) The d i s t r i b u t i o n and residence s i t e s of gold within s o i l p r o f i l e s . 3) The morphology and composition of g l a c i a l l y transported gold grains within s o i l s . Results of t h i s examination should provide data which can be u t i l i z e d to recommend: 1) Optimum sample si z e . 2) Optimum s o i l horizon for sampling. 3) Optimum size and / or density f r a c t i o n for analysis. 4) Optimum a n a l y t i c a l technique. 11 Chapter Two Geochemical D i s p e r s i o n i n T i l l s 12 2.1 O r i g i n of t i l l 2.1.1 Introduction T i l l i s a form of g l a c i a l d r i f t , a generic term which also includes g l a c i o f l u v i a l , g lacioeolian and g l a c i o l a c u s t r i n e sediments. These materials d i f f e r from t i l l by being sorted and reworked sediments, many of which exhib i t the c h a r a c t e r i s t i c s of reworking / redeposition by water (Goldthwait, 1971). Dreimanis, (1976) defined t i l l as a compact material which has a d i r e c t g l a c i a l o r i g i n , a variety of rock and mineral fragments of various sizes, poor sorting and a lack of s t r a t i f i c a t i o n . Where t h i s type of material composes more than f i f t y percent of a g l a c i a l d r i f t exposure or stratum, then the entire unit may be referred to as t i l l (Goldthwait, 1971) . 13 2.1.2 T i l l formation Three events contribute to the formation of t i l l : 1) Erosion 2) Transport 3) Deposition 2.1.2.1 Erosion Two forms of erosion are possible (Dreimanis, 1976): (1) e x t r a g l a c i a l debris, the passive c o l l e c t i o n of material due to rocks (sand, gravel, etc.) f a l l i n g and c o l l e c t i n g upon the g l a c i e r surface, and (2) active erosion, occurring at the base of the g l a c i e r where material i s abraded and removed from the ground surface underlying the g l a c i e r . Active erosion takes place by 1) plucking / quarrying, where c l a s t s or blocks of rock are removed from the bedrock and c a r r i e d either within the g l a c i e r or along the bedrock-g l a c i e r interface ( F l i n t , 1971); 2) abrasion, i n which entrained material at the base of the g l a c i e r acts to scrape and p o l i s h the bedrock i n a manner similar to a piece of sandpaper moving across a block of wood ( F l i n t , 1971), and l a s t l y 3) large scale block inclusions, wherein very large (up to kilometers i n size) blocks of bedrock are u p l i f t e d 14 and moved within or at the base of a g l a c i e r (Figure 2.1) (Moran, 1971). Of these three methods of active erosion, quarrying / plucking appears to be the most important ( F l i n t , 1971). The rate of erosion of material beneath a g l a c i e r depends upon the following factors ( F l i n t , 1971): 1) g l a c i e r thickness, 2) rate of movement, 3) abundance, shape and hardness of rock fragments carr i e d i n the base of the g l a c i e r , 4) e r o d i b i l i t y of ground beneath g l a c i e r . 5) state of flow (extending vs compressive) 6) hydrostatic flow S u s c e p t i b i l i t y of the ground beneath a g l a c i e r to erosion w i l l vary with depth. Weathered bedrock w i l l erode much more rapidl y than the underlying unweathered bedrock ( F l i n t , 1971). Calculations carried out on two large g l a c i e r s i n Iceland by Okko (1955) (see F l i n t , 1971) gave erosion rates of 6.4 cm / 100 years and 55 cm / 100 years. 15 F i g u r e 2 . 1 - Schematic diagram of large scale block i n c l u s i o n s . From Moran (1971). 16 2.1.2.2 Transport D r i f t may be transported by a g l a c i e r i n three general ways: 1) Basal transport 2) Englacial transport 3) Superglacial transport Basal transport Basal transport occurs i n the bottom 1 to 3 metres of a g l a c i e r (Figure 2.2). Most of the rock debris c a r r i e d by a g l a c i e r are ca r r i e d within t h i s zone, usually as t h i n bands of material within the ice (Boulton, 1970). This i s the main zone of crushing and comminution due to the high proportion of rock debris (Boulton, 1970). Less than 0.1% of a l l c l a s t s survive more than 35 km of basal transport, most are comminuted to t h e i r constituent minerals p r i o r to reaching t h i s distance (Goldthwait, 1971). Studies by Drake (1971) showed that the breakdown of c l a s t s i s dependent upon l i t h o l o g y . Also, c l a s t rounding increased greatly within the f i r s t mile of transport (Drake, 1971). Crushing (breakage) appears to be the most s i g n i f i c a n t method of s i z e reduction within the basal zone (Goldthwait, 1971). The terminal size of material crushed within the basal 17 O L D P L E I S T O C E N E SEDIMENTS AND B E D R O C K Figure 2 .2 - Schematic diagrams of transport locations of debris within g l a c i e r s . From Dremanis (1976). A) Radial section of i ce sheet i n i t s terminal zone. B) Cross section of a v a l l e y g l a c i e r . zone of a g l a c i e r was shown by Dreimanis and Vagners (1971) to be f i n e sand for g r a n i t i c and metamorphic rocks, s i l t s i z e for carbonate rocks, and clay size for shales. Upon reaching a c o n s t r i c t i o n or obstruction beneath or within a g l a c i e r , basal debris may move upwards to be emplaced within the englacial zone (Goldthwait, 1971). Englacial transport Debris i s usually more diffused within the e n g l a c i a l zone (Figure 2.2) and therefore does not s u f f e r the same degree of crushing and comminution as basal debris (Dreimanis, 1976). Soft, unresistant minerals, i f r a p i d l y u p l i f t e d out of the basal zone, may be preserved within the e n g l a c i a l zone (Dreimanis, 1976). Englacial material may survive hundreds of kilometers of transport before being comminuted (Dreimanis, 1976). Superglacial transport Material transported on the g l a c i e r surface may be derived from e x t r a g l a c i a l sources, such as debris f a l l i n g onto the g l a c i a l surface and from englacial debris u p l i f t e d to the surface near the g l a c i a l terminus (Figure 2.2) (Dreimanis, 1976). Transport of t h i s material may be by g l a c i a l movement, mechanical movement downslope, or l o c a l i z e d transport i n supraglacial meltwater streams (Sharp, 1949). 2.1.2.3 Deposition The mode of transport of g l a c i a l debris determines i t s deposition (Figure 2.3). En g l a c i a l l y and s u p e r g l a c i a l l y transported debris are deposited by downmelting of g l a c i a l ice to form ablation t i l l . Material transported within the basal zone and deposited beneath an active g l a c i e r i s referred to as basal or lodgement t i l l . Ablation t i l l S h i l t s (1973, 1976) noted that ablation t i l l generally contains more material transported from a distant source that does basal t i l l , due to the greater distance of transport of englacial-superglacial debris. Ablation t i l l i s characterized by a lack of fine sediments ( r e l a t i v e to basal t i l l s ) , angular c l a s t s , and loose compaction (Goldthwait, 1971). Ablation t i l l has been defined by Boulton (1968, 1970) to be composed of two forms, flow t i l l and melt-out t i l l (Figure 2.3). 20 GLACIAL DRIFT IN TRANSPORT GLACIAL DRIFT DEPOSITEC •V GLACIERS A 0 R O U N D ) AS TILL UNDERNEATH ICE SHELVES SUPERGLACIAL P E B R I S , •"ABLATION ^ T , L ^ASL. I iELT-OUT"nLL WATER-LAID TILL GLACIAL ICE ENGLACIAL D E B R I S / ^ ^ ^ - ' BASAL DEBRIS ~ GLACIAL ICE * ^ASALMELT-OUTTILL X LODGMENT TILL ^ T ' L L —DEFORMATION TIU DEFORMED BEDROCK, OR SEDIMENTS RELATED TO GLACIATION SLA CI ALLY ERODED SURFACE OF ROCKS OR SEDIMENTS Figure 2.3 - C l a s s i f i c a t i o n of t i l l s and t h e i r r e l a t i o n s h i p to mode of transport (Bolviken and Gleeson, 1979 a f t e r Dremanis, 1969). 21 Flow t i l l i s produced during the melting out of superglacial debris. The high proportion of g l a c i a l meltwater mixed with the debris creates a highly f l u i d t i l l which can flow downslope (Boulton, 1971). Flow t i l l s may show a greater s i m i l a r i t y to g l a c i o f l u v i a l material than t i l l and thus straddle the border between t i l l and s t r a t i f i e d d r i f t (Boulton, 1971). Melt-out t i l l forms at the surface of a g l a c i e r by i n s i t u melting under a cover of overburden, generally flow t i l l (Boulton, 1971). Basal t i l l Basal t i l l , or lodgement t i l l , i s deposited s u b g l a c i a l l y by the "plastering" of material under a c t i v e l y moving g l a c i e r s and i s characterized by moderate to high compactness (due to the compaction of rock f l o u r into void spaces) and s t r i a t e d , abraded c l a s t s ( F l i n t , 1971). V a r i e t i e s of basal t i l l are basal melt out t i l l , which forms by the melting out of basal debris i n a stagnant g l a c i e r (Goldthwait, 1971) and deformation t i l l , which i s lodgement t i l l and / or bedrock characterized by dynamic structures such as folds, shear planes and breccias (Figure 2.3) (Dreimanis, 1976). Three possible origins have been suggested by Boulton 22 (1971) for the o r i g i n of lodgement t i l l : 1) Lodgement of g l a c i a l debris: f r i c t i o n between g l a c i e r and underlying bedrock cause t i l l to melt out by pressure melting. 2) Lodgement of sheets of basal i c e : a portion of the g l a c i e r becomes attached to the bedrock while the remainder of the g l a c i e r continues movement. The t i l l i s then deposited through basal melting of the ice block or expulsion of the ice by pressure melting. 3) Basal Melting / regelation: i c e at the bottom of a moving g l a c i e r melts to form a rock / water s l u r r y which i s p r e f e r e n t i a l l y deposited on the lee side of rock knobs and large c l a s t s . 2.2 Geochemical dispersion i n t i l l 2.2.1 Introduction Within a t i l l sheet, the dispersion of gold can be separated into two d i f f e r e n t classes; mechanical dispersion during g l a c i a t i o n and p o s t - g l a c i a l dispersion due to 23 weathering. The l a t t e r can occur through both mechanical transport and chemical translocation (Bolviken and Gleeson, 1979). The factors which make t i l l useful as a geochemical sampling medium are (S h i l t s , 1975; Bolviken and Gleeson, 1979) : 1) t i l l i s the most widespread form of g l a c i a l d r i f t , 2) t i l l sheets are e a s i l y related to ice movement directions, 3) unweathered t i l l i s a d i r e c t , representative derivative of i t s source bedrock, 4) t i l l i s e a s i l y i d e n t i f i e d , and 5) dispersal t r a i n s of t i l l are larger than t h e i r source. 2.2.2 Mechanical dispersion Glaciers tend to disperse material i n the form of a negative exponential curve (Figure 2.4) ( S h i l t s , 1976). The highest concentrations appear near the source with a rapid exponential decrease i n concentration downice. The exact shape of t h i s exponential curve i s determined by the type of transport (subglacial, englacial, etc.) and the physical c h a r a c t e r i s t i c s of the material i n question ( S h i l t s , 1976). Figure 2 . 4 - Actual (A) and i d e a l i z e d (B) g l a c i a l d i s p e r s a l curves showing negative exponential decrease. From S h i l t s (1976). 25 Debris c a r r i e d e n g l a c i a l l y w i l l be dispersed further than material transported along the glacier-bedrock interface. Studies of g l a c i a l transport distances by Strobel and Faure (1987) of g r a n i t i c and metamorphic c l a s t s derived from the Canadian Shield indicated that some e n g l a c i a l l y c a r r i e d c l a s t s t r a v e l l e d over 800 kilometers before f i n a l deposition. Material dispersed by a g l a c i e r from a single source generally has a ribbon or fan shaped form (Figure 2.5 and 2.6) (Bolviken and Gleeson, 1979). Fan shaped dispersion t r a i n s may be caused by r a d i a l spreading of g l a c i e r s within lowlands, near an ice front or changing d i r e c t i o n s of i c e flow with time ( F l i n t , 1971). Irr e g u l a r l y shaped dispersion t r a i n s may be due to rough subglacial topography ( S h i l t s , 1976). Most dispersion t r a i n s of economic minerals, however, generally have a ribbon shape (Sh i l t s , 1976). The area of a dispersion t r a i n i s roughly proportional to the source area exposed to g l a c i a l erosion and i t s orientation to the d i r e c t i o n of g l a c i a t i o n (Holmes, 1952). Studies of geochemical dispersion i n alpine t e r r a i n by Evenson et a l . (1979) and Hicock (1986) indicate that v a l l e y topography and movement of individual ice lobes determines the pattern of geochemical dispersion. Dispersion t r a i n s are three dimensional features; they may reach the surface near t h e i r source or may not appear at Figure 2.5 - Ribbon shaped t r a i n of amphibolite boulders. From S h i l t s (1976). Figure 2.6 - Regional sized, fan shaped dispersion t r a i n s . From F l i n t (1971). 28 surface for several hundreds of metres downice (Bolviken and Gleeson, 1979; Drake, 1983). M i l l e r (1984) described Pb dispersion t r a i n s i n t i l l at Bathurst Norsemines N.W.T. and Lough Derg, Ireland i n which anomalous lead values were displaced 500 to 1000 metres downice from lead mineralized outcrop. Detailed sampling i n three dimensions at both s i t e s indicated t h i n (1-3 metre thick) ribbon anomalies which rose on shallow angles towards the surface (Figure 2.7). In addition, steep angle, d i a p i r i c anomalies were also delineated within the t i l l sheets. M i l l e r (1984) proposed that these anomaly patterns were due to dispersion t r a i n s r i s i n g through the t i l l at angles of 2-3 degrees along thrust or smear planes. D i a p i r i c type anomalies were regarded as being the r e s u l t of steeper thrusting angles, perhaps due to bedrock i r r e g u l a r i t i e s , which would act to d e f l e c t the dispersion t r a i n s towards the surface ( M i l l e r , 1984). Drake (1983), likened dispersion t r a i n s to plumes of smoke r i s i n g downwind from a chimney, or a l t e r n a t i v e l y , to stacks of t i l l slabs aligned s t a i r - s t e p fashion i n a downice d i r e c t i o n . Generally, i n t i l l less than one metre i n thickness, an anomaly w i l l be found d i r e c t l y above i t s source, with very l i t t l e downice movement evident (Govett, 1973). In t i l l up to 5 metres thick, the anomaly i s usually detectable at surface above i t s source, but may be displaced several tens of metres downice (Rose, Hawkes and Webb, 1979). Downice Au 29 Figure 2.7 - Idealized model of g l a c i a l d i s p e r s a l . From Coker and DiLabio (1987), modified from M i l l e r (1984). 30 dispersion of 25 to 100 metres was observed i n t h i n t i l l s overlying the Shasta Au-Ag deposit, B r i t i s h Columbia (Downing and Hoffman, 1987). As noted by M i l l e r (1984), displaced anomalies appear to be more prevalent i n t i l l greater than 6 meters i n thickness. At the QR gold deposit, B r i t i s h Columbia, Au anomalies i n t i l l are displaced up to 200 metres from t h e i r source and extend up to 3 kilometres downice (Fox et a l . , 1987). In areas where multiple sheets of t i l l are present, anomalies may not be expressed at surface or may be o f f s e t due to d i f f e r e n t g l a c i a l episodes (Rose, Hawkes and Webb, 1979). S t r a t i f i e d d r i f t or d i s t a n t l y transported t i l l may cover and block syngenetic anomalies within underlying t i l l (Klassen, 1987; Bradshaw, 1975). The morphology of free gold within unoxidized t i l l appears to change with distance of transport. Sauerbrei et a l . (1987) studied a g l a c i a l dispersion t r a i n emanating from the Golden Pond Zone, Casa Berardi area. Gold grains found within the basal t i l l l y i n g d i r e c t l y above the auriferous zone were composed of very delicate grains which showed few signs of abrasion. Gold grains found 100 metres downice from the source were s t i l l d elicate i n form; those found 400 metres downice from the mineralized zone were i r r e g u l a r i n form and abraded, indicating transport over greater distances. 31 The comminution and crushing to the terminal s i z e of gold grains i s poorly understood. Dreimanis and Vagners (1971) determined the terminal size for heavy minerals i n basal t i l l to be 250 to 30 microns. However, i t i s doubtful that the r e s i s t a t e nature of the majority of the p a r t i c l e s (garnets) within these samples i s representative of the behavior of gold. Sauerbrei et al.(1987) reported abundant gold grains i n the 50 to 150 micron range. Analysis of unoxidized basal t i l l s by Shelp and Nichol (1987) revealed that the majority (75%) of gold within the t i l l was concentrated i n the -12 5 micron f r a c t i o n . These may, however, r e f l e c t the fine grain size of the source gold and not a mechanical si z e reduction. 2.2.3 Modification by s o i l forming; processes The c o n t r o l l i n g factor i n the post depositional dispersion of gold i n t i l l i s weathering; the most important feature of the weathering of t i l l i s the development of a s o i l p r o f i l e . T h i s results i n the transformation of the upper part of the t i l l into a series of layers which have d i f f e r e n t properties and compositions (Bolviken and Gleeson, 1978) . S o i l formation i s governed by the factors: 32 1) parent material, 2) r e l i e f , 3) climate 4) b i o l o g i c a l a c t i v i t y , and 5) time In alpine glaciated areas, time for s o i l development has been limited (approx. 10 Ka). Therefore, s o i l development i s usually poor, r e s u l t i n g i n s o i l p r o f i l e s with s i m i l a r c h a r a c t e r i s t i c s to t h e i r parent t i l l (Bolviken and Gleeson, 1978). Gold may be transported mechanically or chemically (hydromorphic transport) within the s o i l p r o f i l e . Mechanical transport may be by mass movement, compaction due to s o i l development, or s o i l creep (Bolviken and Gleeson, 1978) . Pedoturbation, by various mechanisms, may also p h y s i c a l l y move material within s o i l . Chemical transport (pedotranslocation) i s largely due to the movement of water within the s o i l p r o f i l e (St. Arnaud, 1976). Gold i n unoxidized t i l l i s most common i n s i z e f r a c t i o n s which represent the o r i g i n a l grain s i z e s of the source deposit or of the g l a c i a l l y comminuted p a r t i c l e s . I t i s found as native gold or as a component of an o r i g i n a l oxide or sulphide host mineral (DiLabio, 1985; 1988). In oxidized t i l l and s o i l s DiLabio (1988) found Au mainly within f i n e r s i z e fractions, commonly of s i l t s i z e (-63 microns) or f i n e r . However, i t i s possible that sampling 33 bias, i n the form of inadequate sample sizes for the coarse fr a c t i o n s , may have influenced these r e s u l t s (section 1.2). Study of a t i l l p r o f i l e downice from a gold-scheelite occurrence at Waverly, Nova Scotia, led DiLabio (1982b, 1985) to speculate that native gold and gold l i b e r a t e d from sulphides during oxidation were absorbed onto iron and manganese oxides, hydroxides and clay minerals. An apparent enrichment of Au within the upper layer of the weathered t i l l / s o i l was interpreted as a r e s u l t of hydromorphic transport of Au towards the surface (Figure 2.8) (DiLabio, 1985). Coker et al.(1988) found gold dispersed from the Beaver Dam gold deposit, Nova Scotia, to be most abundant i n the coarser fractions of the oxidized and unoxidized t i l l , a r e f l e c t i o n of the o r i g i n a l grain size of gold within the deposit. MacEachern (1983) noted compositional differences between gold from t i l l and gold from a bedrock source at the F i f t e e n Mile Stream area, Nova Scotia and interpreted t h i s as being caused by hydromorphic r e d i s t r i b u t i o n of Au within the t i l l (MacEachern and Stea, 1985). Analysis of gold d i s p e r s a l within t i l l at the Forest H i l l D i s t r i c t , Nova Scotia by (MacEachern and Stea, 1985) revealed enrichment of Au, Cu, Pb, Zn and As within the fine (-63 micron) f r a c t i o n of a Fe-Mn cemented unit. No enrichment was found within the coarser (sand) sized f r a c t i o n . This has been interpreted as a secondary emplacement, indicating a hydromorphic o r i g i n Figure 2.8 - Plot of depth versus concentration f o r W, Au and As i n t i l l . The change i n sympathetic behavior between Au / As and W i s interpreted as being due to a hydromorphic enrichment of Au and As i n the upper section of the t i l l . From DiLabio, (1985). 35 for the Au (MacEachern and Stea, 1985). Hydromorphic movement of Au within the s u r f i c i a l environment involves the dissolution and transport of Au followed by i t s p r e c i p i t a t i o n due to a change i n physiochemical conditions. Complexing of elemental Au with an anion i s necessary to achieve d i s s o l u t i o n and transport (Webster and Mann, 1984). A number of gold complexes have been c i t e d as possible transporting agents of Au i n solution (Krauskopf, 1951; Shacklette et a l . , 1970; Lakin et a l . , 1974; Boyle et a l . , 1975; Mann, 1984; Stoffregen, 1986): Gold Halides AuCl 4 , AuBr 4 2 , Aul 2 Gold Thiosulphate Au(S 20 3)2~ 3 Gold Thiocyanate Au(CNS) - 4 Gold Cyanide Au(CN) - 2 The increasing ease of oxidation of gold by the various anions of the gold complexes i s : CI < Br" < CNS" < S 2 0 3 ~ 2 < I < CN" Formation of gold chloride i s r e s t r i c t e d to highly a c i d i c , chloride ion r i c h areas which contain a strong o x i d i z i n g 36 agent such as Mn02, 0 2, F e + 3 , or C u + 2 (Krauskopf, 1951). Such regimes exi s t only within oxidizing sulphide deposits (Krauskopf, 1951; Lakin et a l . , 1974) and are not expected i n t i l l sheets or s o i l p r o f i l e s . Gold bromide and gold iodide both have a greater s t a b i l i t y than gold chloride, but are exceptionally rare within the natural environment, due to the low natural concentrations of Br and I (Lakin et a l . , 1974) . Thiosulphate ions occur in sulphur-rich environments, but usually i n low concentrations. Lakin et a l . (1974) suggested that the oxidation of p y r i t e i n an a l k a l i n e environment may produce s u f f i c i e n t S 2 0 3 ~ 2 or HS~ to dissolve gold. Such a solution may be a s i g n i f i c a n t complexing agent for gold around and within sulphide orebodies, but i s probably not of much consequence within t i l l and s o i l . The thiocyanate ion re a d i l y dissolves gold to form gold thiocyanate, which i s stable across a wide range of pH (Lakin et a l . , 1974). Unfortunately, thiocyanate does not appear to be useful as a large scale complexer of gold, as i t appears to be r e l a t i v e l y rare i n nature (Lakin et a l . , 1974) . The gold cyanide complex may be best suited to transport gold i n s o i l s (Lakin et a l . , 1974; G i r l i n g and Peterson, 1978). Hydrogen cyanide can be produced from plant material by the hydrolysis of cyanoglycosides, which have 37 been found i n approximately 1000 species of plants (Lakin et a l . , 1974). However, no d i r e c t proof of gold transport by complexing with cyanide i s available. Evidence such as thermodynamic data (Groen, 1987) or the singular observation of close s p a t i a l association of gold c r y s t a l s with cyanogenic plants (Warren, 1982) i s used as the argument for t h i s hypothesis. In weakly a c i d i c to basic environments, free gold can bind with a variety of compounds to form c o l l o i d a l gold. C o l l o i d a l gold i s formed when fine (<0.05 micron) gold acquires a coating of organic material, iron-manganese hydroxides, or s i l i c a (Boyle, 1979). The negative charge inherent to these c o l l o i d s increases t h e i r movement through the s o i l p r o f i l e u n t i l interaction with free cations causes t h e i r p r e c i p i t a t i o n (Boyle, 1979). Organic compounds, such as humic and f u l v i c acids, have also been suggested as complexing agents for gold (Freise, 1931; Baker, 1973; Roslyakov, 1984). Baker (1978) proved experimentally that gold could be dissolved, complexed and transported by humic acid. The reaction of A u C l - 4 with humic acid was found to produce c o l l o i d a l gold, with the humic acid forming a protective c o l l o i d for the gold (Ong and Swanson, 1969). Roslyakov (1984) found f u l v i c acids to possess a greater capacity for forming gold complexes than humic acids. Gold humic complexes do not appear to be 38 susceptible to the problems of s t a b i l i t y and s o l u b i l i t y which i o n i c and c o l l o i d a l gold complexes are subject to (Baker, 1978). Mineyev (1976) found that various microorganisms i n a l k a l i n e solutions can dissolve and uptake gold i n the s o i l p r o f i l e . Doxtader (in Lakin et a l . , 1974) analysed the a b i l i t y of bacteria to uptake gold; a wide var i e t y of s o l u b i l i z a t i o n a b i l i t i e s were revealed. Many bacteria are able to s o l u b i l i z e gold (Boyle, 1979), although no d i r e c t information i s available on t h e i r behaviour i n the s o i l . Lakin et al.(1974) observed that gold values i n a group of s o i l p r o f i l e s i n the western United States were highest i n the s u r f i c i a l (humus) and basal horizons. High concentrations of gold within the bottom horizons of the s o i l p r o f i l e s were explained by Lakin et a l . (1974) as being due to the i n s i t u breakdown of gold bearing rock fragments and the downward migration of gold p a r t i c l e s as a r e s u l t of the churning action of s o i l during downslope creep. Enrichment of Au within the humus layer i s a r e s u l t of the uptake of Au by vegetation (Lakin et a l . , 1974). G i r l i n g and Peterson (1978) determined that Au absorbed through the root systems of plants was either concentrated within the leaf t i p s / ridges or was flushed from the leaves. Au i n gold complexes washed from the plant onto the surface would 39 be concentrated within the humus layer, due to the reducing nature of the decaying plant material. Gold complexes retained within the plant would encounter the same fate upon the death of the host plant. 2.2.4 Summary of factors which e f f e c t the dispersion of  gold within s o i l and t i l l A number of relevant observations and conclusions can be derived from the l i t e r a t u r e c i t e d : 1) Mode of transport within a g l a c i e r (basal, englacial, superglacial) w i l l determine the type of t i l l formed. 2) Dispersion t r a i n s i n t i l l are three dimensional features which are ribbon or fan shaped i n plan view. 3) Experience with other minerals indicates that gold values generally decrease exponentially away from source. 4) Dispersion t r a i n s increase the anomaly s i z e of an orebody. 40 5) The comminution effects on gold grains and terminal size of the comminuted grains i s not well known, although gold grains appear to be abraded during g l a c i a l transport. 6) The ultimate appearance of a gold dispersion t r a i n i s determined by the varying e f f e c t s of transport and weathering processes upon the host t i l l sheet. 7) Any chemical or physical movement of gold i n deposited t i l l i s controlled by weathering and the development of a s o i l p r o f i l e . 8) Gold i n unweathered t i l l i s usually found as i t s o r i g i n a l grain size or as grains representative of the degree of g l a c i a l comminution. 9) Gold i n the weathering environment has a much more complex d i s t r i b u t i o n which r e f l e c t s o r i g i n a l grain size, comminuted grain si z e , grain s i z e of gold released from weathered sulphides and precipitated or adsorbed gold. 41 Chapter Three Description of Study Area 42 3.1 Location and access The Nickel Plate mine l i e s within the Hedley gold camp, approximately 40 kilometers east-southeast of Princeton, B.C. (Figure 3.1). Access to the mine i s provided by the Hedley Road, which connects the mine to nearby Hedley and to Penticton, to the east. Several other mines with s i g n i f i c a n t gold mineralization are found i n the Hedley Camp, namely the Canty, French, Good Hope, Banbury, Peggy and Gold H i l l properties (Figure 3.2). 3.2 History Attention was f i r s t directed to the Hedley area i n the 1860's by prospectors t r a v e l l i n g from C a l i f o r n i a to the newly discovered gold placer deposits of the Cariboo D i s t r i c t (Camsell, 1910). Economic concentrations of placer gold i n the v i c i n i t y of Twenty Mile Creek were discovered and worked for several years before being exhausted (Camsell, 1910). Afterwards, the region was overlooked u n t i l 1894, when several claims were staked near the peak of Nickel Plate Mountain (Camsell, 1910). Permanent work began on the claims i n 1899 with the f i r s t m i l l i n g of ore beginning i n 1904 (Camsell, 1910). Production ceased i n 1963, due to depleted reserves and r i s i n g mining costs (Ray Figure 3.1 - Map of the Hedley region, southwest B r i t i s h Columbia. Scale: 1 cm =3.5 km. LEGEND TERTIARY I u I tatfUcltom EROSONAL UNCONFORMITY EARLY CRETACEOUS | 11 | VERDE CR££K INTRUSION - granite and mcrogranite I 10 I RHYOUTE INTRUSION - quart! porphyry ~~i 1 SPENCES BRIDGE GROUP - andesltic to dacroc pyroclastics end ' I o n witt minor sedimenti CONTACT UNCERTAIN EARLY JURASSIC [ | ' » - ) | BROMLEY BATHOUTH AND CAHILL CREEK PLUTON - granodiorile to ouartz monzodKxlte ^le*\ HEDLEY INTRUSION - Quartz dorita. tiiorita. and gabbro INTRUSIVE CONTACT NICOLA GROUP LATE TRIASSIC I 6t> I WHISTLE CREEK FORMATION - bedded to massire ash and 1 1 lapiti tufl, mkHx tonecaovs syritons 6 i [ CoppmMd Conglomerate - limestone boulder conglomerate 1 1 STEMWINDER MOUNTAIN FORMATION (WESTERN FACIES) -' t^bmios* argute and llmetkxye I 4 I HEDLEY FORMATION (CENTRAL FACIES) - titnly bedded siltstone, 1 «ot*n»«lor>»l»ell and minor kitts r~3 I FRENCH MINE FORMATION (EASTERN FACIES) - limestone. knaetombnccleandc+bc^congkimerata PEACHLAND CREEK FORMATION - basaltic ash lulls and Hows with minor tnnlona and chert-pebble conglomerate CONTACT OCCUPIED BY CAHILL CREEK PLUTON PALEOZOIC I i I APEX MOUNTAIN COMPLEX - ophioUta sequence ot cherts, 1 ' greenstones, sltstones, svgftites and minor Imes tones Figure 3.2 - Regional geology and location of gold bearing properties, Hedley region. From E t t l i n g e r and Ray (1989) and Ray et a l (1987). A: Nickel Plate Mine; B: French Mine; C: Canty Mine; D: Goodhope Mine; E: Banbury Gold Mine; F: Peggy Mine. 45 et a l . , 1987). During t h i s period, 2.9 Mt of ore was mined, producing 41.6 m i l l i o n grams of Au and 4.1 m i l l i o n grams of Ag (Ray et a l . , 1986). In 1971 , Mascot Gold Mines (now part of Corona Corporation) acquired the Nickel Plate property. In August, 1987, the mine was o f f i c i a l l y reopened, as a bulk tonnage, open p i t operation. Minable reserves as of January 1, 1989 stood at 5.1 m i l l i o n tonnes grading 2.98 grams Au per tonne (Corona Corporation Annual Report for 1988) . 3.3 Regional geology The Hedley region has been mapped by a number of geologists since the early 1900's (Camsell, 1910; Bostock, 1930, 1940a, 1940b; Ray and Dawson, 1988, 1990). The Nickel Plate mine l i e s within predominantly sedimentary rocks of the Nicola Group. Flanking t h i s section of the Nicola Group to the east are rocks of the Cache Creek Group represented by the Apex Mountain complex. Granodioritic to quartz monzonitic Similkameen intrusions, are found on both the eastern contact ( C a h i l l Creek pluton) and north-northwestern edge (Bromley batholith) of t h i s Nicola Group pendant. The Apex Mountain complex consists of a sequence of highly deformed a r g i l l i t e s , cherts, t u f f s and minor limestones that Milford (1984) has interpreted to be a highly deformed o p h i o l i t e sequence formed above a subduction 46 zone dipping towards the east. F o s s i l s from rocks i n t h i s group range i n age from Upper Devonian to Late T r i a s s i c (Ray et a l . 1987). Based on the work of Ray and Dawson (1988; 1990) the overlying Nicola Group begins with basalt t u f f s , a r g i l l i t e , chert pebble conglomerate and limestone olistostrome (Peachland Creek Formation), succeeded by limestone and limestone conglomerate of the French Mine Formation; s i l t s t o n e and limestone of the Hedley Formation; and f i n a l l y a r g i l l i t e and limestone of the Stemwinder Mountain Formation. The Whistle Creek Formation, consisting of andesite ash and l a p i l l i t u f f , with minor s i l s t o n e , marks the top of the group. Lying between the Stemwinder Mountain and Whistle Creek Formations i s the Copperfield conglomerate, a 1-200 meter thick limestone-boulder conglomerate. Rocks of the Hedley and Whistle Creek sequences are cut by the quartz d i o r i t e s and gabbros of the Hedley Intrusions with K-Ar ages of 170-190 Ma (Roddick et a l . 1972) . Recently, a U-Pb zircon age date of 199 Ma has been determined by Ray and Dawson (1990) for a quartz d i o r i t e of the nearby Banbury Stock. These rocks appear as stocks with diameters up to 1500 meters and as dense swarms of s i l l s and dykes up to 200 meters thick (Camsell, 1910; Ray et a l . , 1987) . Camsell (1910) noted that gabbro dykes cut the quartz d i o r i t e - d i o r i t e s i l l s and appear to be c l o s e l y r e l a t e d 47 temporally, as the gabbro dykes seem to have cut the d i o r i t e s while they were s t i l l p l a s t i c and deformable (Camsell, 1910). Camsell (1910), B i l l i n g s l e y and Hume (1941), Dolmage and Brown (1945), Lee (1951) and Ray et a l . (1987) a l l associate the intrusion of the d i o r i t e s with the gold mineralization at the Nickel Plate Mine. The Similkameen intrusions consist of granites and granodiorites with a K-Ar age of 150 Ma (Roddick et a l . , 1972) . Zircon dates of 168 Ma and 206-210 Ma have been established for the C a h i l l Creek pluton and Bromley batholth respectively (Ray and Dawson, 1990). Hornfels and minor skarn are associated with the plutons, but with the possible exception of the French Mine, there seems to be no rela t e d Au mineralization (Ray et a l . , 1987). 3.4 Deposit geology The Nickel Plate mine i s located within the upper units of the Hedley Formation (Figure 3.3) (Ray et a l . , 1987). Ore i s stratabound and generally follows the bedding planes of the tuffaceous-calcareous s i l t s t o n e s and limestones (Camsell, 1910; B i l l i n g s l e y and Hume, 1941). The beds generally dip to the west at 20-30 degrees (Camsell, 1910). Quartz d i o r i t e to d i o r i t e s i l l s are interlayered with the sedimentary rocks and are cut by gabbro or d i o r i t e dykes Figure 3 .3 a l (1987). - Strat igraphy of the Hedley reg ion . From Ray et 49 (Camsell, 1910; B i l l i n g s l e y and Hume, 1941). Dominating the l o c a l geology i s a large mass of d i o r i t e known as the 'Toronto Stock', an oblong body approximately 1200m x 2100m i n s i z e (Rice, 1947). However, contacts of the 'stock' with the rocks of the Hedley sequence are generally conformable and not crosscutting (Lee, 1951). The 'Toronto Stock' i s i n fac t a large, i r r e g u l a r s i l l or l o p o l i t h (Lee, 1951). Swarms of smaller s i l l s and dykes, from centimetres to metres i n thickness, emanate eastwards from the Toronto Stock into the surrounding sediments (Figure 3.4) (Camsell, 1910). Skarn a l t e r a t i o n occurs i n both the calcareous sediments (exoskarn) and within the diorites/gabbros (endoskarn) and extends up to 1850 metres from the Toronto Stock (Camsell, 1910; Dolmage and Brown, 1945). I t ends abruptly along a boundary known as the Marble Line (Figure 3.4) ( B i l l i n g s l e y and Hume, 1941), a zone ranging up to t h i r t y metres i n width (Dolmage and Brown, 1945). Scapolite i s common within the boundary of the Marble Line (Dolmage and Brown, 1945). Minor non-calcareous sediments within the zone of skarn a l t e r a t i o n have been altered to quartzites (Dolmage and Brown, 1945). Garnet-rich and pyroxene-rich assemblages are the predominant v a r i e t i e s of skarn a l t e r a t i o n found i n the area (Ray et a l . 1987). I n i t i a l hornfels a l t e r a t i o n has been overprinted, f i r s t by pyroxene-r i c h skarn which was i n turn overprinted by garnet-rich skarn a l t e r a t i o n which forms the core of the a l t e r a t i o n North pit Nickel Plate ' Glory hole Central pit N I SunnyskJe 4 ' Glory hole Sunnyside 3 ^Glory hole Sunnyside 2 Glory hole ^ South pit 150 metres Early Jurassic Hedley intrusions; sills and dykes Late Triassic IV; >"•>[ Copperfield conglomerate Hedley Formation siltstone and limestone Fault • Old Glory hole workings <v _ j Approximate open pit limit — Dip and strike of bedding Figure 3 .4 - General deposit geology of the Nickel Plate mine. From E t t l i n g e r and Ray (1989). 51 envelopes (Ray et a l . , 1987). Composition of garnets found within the exoskarn (Figure 3.5) range between 25 and 80 mole percent andradite, whereas pyroxenes (Figure 3.6) generally are between 40 and 75 mole percent hedenbergerite ( E t t l i n g e r and Ray, 1989). Within the thesis area, a few outcrops of Hedley Formation s i l t s t o n e and ba s a l t i c t u f f s of Peachland Creek Formation are exposed along the Hedley Road (Figure 3.7). Hedley formation i s confined to the western half of the thesis area, while Peachland Creek occupies the eastern and southern regions. A 1 to 2 metre wide outcrop of granodiorite i s found along the Hedley Road, near the contact between the Peachland and Hedley formations (Figure 3.7) . 3.5 Ore deposits and mineralogy Ore deposits of the Nickel Plate Mine are stratabound, l e n t i c u l a r bodies that p r e f e r e n t i a l l y follow the bedding planes of the sediments (Camsell, 1910; B i l l i n g s l e y and Hume, 1941). The majority of the mineralized zones are found within the apices of f o l d structures, within fractures p a r a l l e l to the s i l l s , or at the interse c t i o n of s i l l s and dykes ( B i l l i n g s l e y and Hume, 1941; Ray et a l . , 1987). A l l the mineralized zones are located within the exoskarn, 52 Pyralspite Grossularite Andradite Figure 3.5 - Garnet composition of the exoskarn, N i c k e l P late mine. From E t t l i n g e r and Ray (1989). 53 Figure 3.6 - P y r o x e n e c o m p o s i t i o n o f t h e e x o s k a r n , N i c k e l P l a t e m i n e . F r o m E t t l i n g e r a n d R a y (1989) . Legend Granodiorite Diorite Hedley Formation Peachland Creek Formation Faults Scale 200 m Thesis area Marble Line o Figure 3.7 - Geology of the t h e s i s area. M o d i f i e d from Ray and Dawson (1988). 55 approximately 75-100 metres inside the Marble Line (Camsell, 1910; B i l l i n g s l e y and Hume, 1941; Dolmage and Brown, 1945). Some i r r e g u l a r pods of gold bearing massive sulphide, containing chalcopyrite, pyrite, pyrrhotite and arsenopyrite, are found i n the mine area (Ray et a l . , 1987). Of the three v a r i e t i e s of skarn lithology found i n the area (garnet-rich, pyroxene-rich and cherty q u a r t z i t e ) , gold mineralization appears to occur i n the pyroxene-rich exoskarn l i t h o l o g y and not i n the b r i t t l e quartzites (Dolmage and Brown, 1945). Gold i s found primarily within arsenopyrite as minute grains generally less than 7 microns i n size (Warren and Cummings, 1936). Occasional grains of gold are also found within pyrrhotite; more than 75% of the grains are less than 45 microns i n diameter (Warren and Cummings, 1936) . Minor gold i s also found within late stage, crosscutting c a l c i t e veins (Bostock, 1930; Dolmage and Brown, 1945) . Warren and Cummings (1936) concluded that the deposition of the gold and arsenopyrite were contemporaneous. After reviewing the work of Warren and Cummings (193 6), and t h e i r own work, B i l l i n g s l e y and Hume (1941) suggested that the gold-arsenopyrite was deposited closely a f t e r the development of skarn a l t e r a t i o n . Based on grain boundary r e l a t i o n s h i p s , Simpson (in E t t l i n g e r and Ray, 1989) concluded that three stages of sulphide deposition occurred: (1) p y r i t e ; (2) arsenopyrite and ger s d o r f f i t e (NiAsS); and (3) pyrrhotite, 56 chalcopyrite and sphalerite. Gold mineralization was associated with the f i n a l two sulphide stages. V i s i b l e gold was panned by early prospectors from gossans marking the surface projections of the orebodies (Camsell, 1910; J. Bellamy, personal communication, 1989). Free gold was observed by Camsell (1910) to be associated with arsenopyrite or tetradymite. Where the sulphide host had oxidized, ragged, sharp pointed gold grains with a d u l l rusty appearence were observed. When freshly cut, these grains had a bright lust r e . Very fine gold grains were found i n d r i f t derived from the gossans and could be traced f o r a very short distance downslope (Camsell, 1910). 3.6 G l a c i a l history In south-central B r i t i s h Columbia, there have been two major g l a c i a l periods and two non-glacial periods over the past 51,000 years (Fulton and Smith, 1978). The f i r s t of these events, the Okanagan Center Glaciation, ended no l a t e r than 43,800 years BP and was follwed by the Olympia I n t e r g l a c i a l period with a duration of approximately 20,000 years (Fulton and Smith, 1978) . Radiocarbon dating of organic samples by Fulton and Smith (1978) and Clague et al.(1980) indicates a readvance 57 of g l a c i e r s (Fraser Glaciation) into the major v a l l e y s of southern B r i t i s h Columbia 22,000 years BP and a complete ice cover sometime afte r 19,000 years BP. Advance to the maximum extent of the Fraser Glaciation began approximately 18,000 years BP (Clague et a l . , 1980) and ended 15,000 years BP (Mullineaux et a l . 1965). At t h i s point, the C o r d i l l e r a n Ice Sheet extended southwards into the northern United States as fa r as the forty-seventh p a r a l l e l (Mullineaux et a l . , 1965). G l a c i a l s t r i a e mapped by Rice (1960) i n south-central B r i t i s h Columbia indicate a regional ice flow i n a northwest - southeast d i r e c t i o n . Retreat of the Cordilleran sheet began almost immediately aft e r i t s maximum extension (Mullineaux et a l . , 19 65). In south-central B r i t i s h Columbia, deglaciation was well underway 11,000 years ago (Fulton and Smith, 1978), and had retreated to i t s modern day confines by 9,500 years BP (Ryder, 1978). Work by Mathews (1944) indicated that i n the Princeton area the ice lobe f i l l i n g the Similkameen Valley retreated towards the northwest. A sample of charcoal taken near Keremeos from a s o i l p i t i n the alpine zone (2480 metres elevation) gives a radiocarbon date of 9120+/-540 years, i n d i c a t i n g that t h i s area was deglaciated and forested by that time (Lowdon et a l . , 1971), and warmer than present day (Clague, 1980). A l l e y (1976) showed that climate within the nearby Okanagan Valley was warmer and d r i e r than present conditions between 8400 and 6600 years ago. 58 S u r f i c i a l mapping indicates that the g l a c i e r r e s i d i n g i n the C a h i l l Creek valley and the Nickel Plate Lake area downwasted during deglaciation. The region surrounding Nickel Plate Lake became ice-free f i r s t , depositing a veneer of g l a c i o f l u v i a l outwash upon the bedrock. Coincident to t h i s , the ice lobe f i l l i n g the C a h i l l Creek v a l l e y forced meltwaters to flow southwards through Winters Creek. At some l a t e r time, the meltwaters sh i f t e d t h e i r flow back to C a h i l l Creek, cutting a channel through the g l a c i o f l u v i a l deposits accumulated through downwasting of the i c e . During deglaciation, water saturated ground on the east and south facing slopes of a small drainage entering C a h i l l Creek underwent s o l i f l u c t i o n . 3.7 S u r f i c i a l geology The s u r f i c i a l geology of the Nickel Plate mine area can be divided into two d i s t i n c t areas (Figure 3.8, back pocket). West of the mine, along the v a l l e y slopes of Hedley Creek, topography i s steep and overburden i s t h i n or non-existent. Bedrock, th i n colluvium, and minor amounts of colluvium modified t i l l comprise the surface materials. Talus slopes occur i n the lower reaches of the steep v a l l e y s which dissect the area. F l u v i a l deposits of sand and gravel are found i n the drainages of Hedley Creek and the 59 Similkameen River. East of the mine, including the thesis area, the overburden i s generally thicker and the upland topography i s rounded and r o l l i n g . T i l l i s the dominant s u r f i c i a l material and rock outcrop i s very minor, t o t a l l i n g no more than f i v e percent. In general, the thickness of t i l l increases towards the center of the C a h i l l Creek v a l l e y f l o o r . Thus, t i l l i n the v i c i n i t y of the Nickel Plate mine i s from less than one to three meters thick, whereas near the west bank of C a h i l l Creek, i t i s on the order of sixty metres. This blanket of t i l l acts to cover and subdue the surface expression of the underlying bedrock topography. Several moraines are found within the v a l l e y of C a h i l l Creek. The largest of these i s located immediately south of the t a i l i n g s dam and stretches across the v a l l e y . I t has been modified by erosion and i s cut i n several places by g l a c i a l and p o s t g l a c i a l streams, including C a h i l l Creek. The presence of granodiorite outcrop within t h i s moraine suggests that a ridge of bedrock underlies t h i s feature. A second, smaller moraine i s located downstream from the confluence of Sunset and C a h i l l Creeks. This moraine may also be due to the presence of an underlying bedrock ridge, as outcrop i s found where t h i s ridge i s truncated by C a h i l l Creek. On the eastern slope of C a h i l l Creek, three low, southwesterly trending ridges, each approximately four 60 hundred meters long are interpreted to be l a t e r a l moraines. A small kame deposit occurs on the northwest corner of the thesis area, adjacent to the minesite. Based on v i s u a l inspection, t h i s material i s similar i n composition to the basal t i l l , but has a coarser o v e r a l l grain s i z e . Minor g l a c i o f l u v i a l and kame deposits occur within the C a h i l l Creek v a l l e y . These deposits are associated with present day creeks but appear to be the r e s u l t of modification by meltwater during deglaciation. In the v i c i n i t y of Nickel Plate Lake, an extensive blanket of sandy outwash, ablation t i l l and minor lacustrine s i l t s and clays cover the bedrock. S o l i f l u c t i o n lobes are observed on the east and south facing slopes of a small creek valley east of Lookout Mountain. Two outcrops displaying g l a c i a l s t r i a e were found within the confines of C a h i l l Creek. One location on the east slope of the creek gave eight s t r i a e measurements between 030 and 045 degrees with a mean of 039 degrees. A second location on the west slope gave f i v e s t r i a e measurements ranging from 03 5 to 040 degrees with a mean of 038 degrees. Chattermarks observed at the f i r s t l o c a tion indicate ice movement from northeast to southwest (Figure 3.9), p a r a l l e l i n g the axis of the lower reach of C a h i l l Creek and the creek valleys of adjoining Hedley and Winters Creeks. F i g u r e 3 .9 - G l a c i a l s t r i a e and chattermarks on granodiorite outcrop, 2 . 5 kilometres east of the Nickel Plate mine. cr, 62 Granodiorite e r r a t i c s are ubiquitous throughout the C a h i l l Creek vall e y . Their most l i k e l y source i s the Bromley ba t h o l i t h to the north of the mine area, and apophyses of the C a h i l l Creek pluton. The abundance of granodiorite as e r r a t i c s i s l i k e l y due to the greater outcrop area of the granodiorite within the region and the tendency of granodiorite to weather along preexisting fractures or planes of weakness into large blocks. These granodiorite blocks would have been read i l y plucked from t h e i r source outcrop by an overriding g l a c i e r . Faces of the granodiorite e r r a t i c s r e s t i n g on the surface are commonly f l a t and s t r i a t e d . Within the thesis area, overburden i s composed mainly of a hard packed t i l l consisting of a subangular c o l l e c t i o n of rock fragments i n an oxidized, red-brown s i l t y - c l a y matrix. In the south end of the area, the t i l l i s saturated by water from a seepage / stream, i s less indurated and greenish-grey i n colour. Rock fragments i n the t i l l are generally of l o c a l o r i g i n , with d i o r i t e and skarn a l t e r e d rock being the most prevalent. Cobbles of weathered, f r i a b l e granodiorite were also found i n the t i l l and the overlying s o i l horizons. Pebble counts carried out on f i v e C horizon samples (Table 3-1) indicate that l o c a l rock types ( d i o r i t e , s i l t s t o n e , limestone and skarn) dominate the c l a s t # of D i o r i t e Grano- S i l t - Quartz Skarn Limestone Other # Clasts sample d i o r i t e stone 12 21.7 0.0 58 28.6 0.0 105 28.6 0.0 135 28.8 1.7 202 63.6 0.0 24.4 0.0 30.8 25.4 0.0 22.2 33.9 0.0 21.4 20.3 1.7 37.3 9.1 0.0 22.7 20.5 2.6 78 23.8 0.0 63 10.7 5.4 56 6.8 3.4 59 4.5 0.0 22 Table 3-1 - Pebble count (+2000 micron fraction) r e s u l t s on f i v e selected C horizon samples. A l l values i n percent. Skarn catagory includes c l a s t s containing pyroxenes and / or garnet. Other catagory includes lamprophrye, a p l i t e , limestone / hornblende or feldspar / quartz c l a s t s . 64 assemblage. No changes i n o v e r a l l c l a s t (grains > 10 mm diameter) shape or composition were observed with depth i n the p i t p r o f i l e . The bimodal grain size d i s t r i b u t i o n of the t i l l i ndicates two d i s t i n c t sources for the t i l l components. Subangular rock and mineral fragments within the t i l l are presumably of l o c a l o r i g i n , having experienced l i t t l e g l a c i a l comminution. The s i l t y - c l a y matrix, however, either represents material which has originated from the incorporation of lacustrine sediments into the t i l l , or represents the f i n a l product of the comminution of less r e s i s t a t e rock types, such as fine grained sedimentary (shale, s i l t s t o n e , carbonate) rocks. The l a t t e r case i s the most l i k e l y , as tuffaceous s i l t s t o n e and t u f f units of the Whistle Creek Formation are found upice from the th e s i s area. Carbonate p r e c i p i t a t e was noted i n 45 of 52 sample p i t s as coatings on roots and rock fragments, and as i n f i l l i n g s within s h a l e - l i k e partings of the matrix. The carbonate p r e c i p i t a t e does not appear to have acted as a matrix cement, as both the calcareous and non-calcareous t i l l s were noted to have the same degree of compaction during excavation of the sample p i t s . 3.8 Physiography, climate, vegetation and s o i l s 65 The Nickel Plate mine l i e s within the Okanagan Range of the Intermontane Belt of the Western Canadian C o r d i l l e r a . The topography i s generally strongly sloping and moderately r o l l i n g , with elevations rarely exceeding 1800 meters. South of the mine, the Similkameen River flows east-west through a steep v a l l e y ; the slopes of which are precipitous and over 1200 meters high. The Similkameen River also serves to divide the r o l l i n g topography of the Okanagan Range from the higher, more rugged t e r r a i n of the Cascade Range to the south. The climate of the Nickel Plate area i s characterised by hot, dry summers and cold dry, winters. Recorded temperatures for the years 1904-17 and 1939-55 range from a maximum of 33°C i n the summer and to a minimun of -39.2°C during the winter with a mean annual temperature of 1.7°C. P r e c i p i t a t i o n for these years averaged 597 mm, with 62% of the p r e c i p i t a t i o n occurring as snowfall during the winter. On average, the Nickel Plate mine area experiences a 32-day f r o s t free period (Mackie, 1961). Tree cover i s generally sparse; northern slopes are mostly heavily wooded. Common trees are Douglas F i r (Pseudotsuga menziesii), Englemann spruce (Picea englemanni) and lodgepole pine (Pinus contorta). Grasses include bunch 66 grass (Agropyron spicatum) and pine grass (Koeleria cristata). In open meadows, sagebrush (Artemista tridentata) i s common. S o i l s developed on the t i l l s of the thesis area are r e s t r i c t e d to Eutric Brunisols and Gray Luvisols. The Eu t r i c Brunisol s o i l s generally display t h i n to nonexistent Ah horizons gradational to Bm horizons underlain by a C or Ck horizon. Also present are p r o f i l e s possessing only Bml, Bm2 and C or Ck horizons. Gray Luvisols have moderately well defined Ae and Bt horizons overlying a C or Ck horizon. S o i l s developed within a seepage zone i n the south of the study area are probably best classed as Gleyed E u t r i c Brunisols. They are water saturated, contain mottles and display weak p a r t i t i o n i n g between Ahk and Bmk horizons or possess only a Bmk horizon above the Ck layer. S o i l pH for the p r o f i l e s ranges from 5.5 to 8.2 (average pH = 7.09), and consistently increases with depth (Table 3-2). Sample Horizon pH ( i n H 20) 14 A 5.9 15 B 6.0 16 C 7.5 41 A 6.2 42 B 6.4 43 CI 6.6 44 C2 7.1 122 A 6.9 123 B 7.1 124 CI 7.6 125 C2 7.8 127 A 7.3 128 B 7.7 129 CI 8.0 130 C2 8.1 162 A 6.9 163 B 8.0 164 C 8.2 186 A 7.2 187 B 7.3 188 CI 7.4 189 C2 8.0 Table 3-2 - pH v a l u e s of s e l e c t e d s o i l p r o f i l e s . Chapter Four Sampling Methods 69 4.1 S i t e s e l e c t i o n Selection of the Nickel Plate mine s i t e was based on the r e s u l t s of a geochemical s o i l survey by Placer Development Ltd. during the 1984 f i e l d season (Young, 1984) and an orientation survey carried out by W.K. Fletcher during the 1986 f i e l d season. Data from the Placer Development Ltd. survey indicated a gold dispersion t r a i n p a r a l l e l to the l o c a l ice d i r e c t i o n and extending downice from the Nickel Plate mine for a distance of approximately one kilometre (Figure 4.1). Orientation surveys c a r r i e d out on the anomaly by W.K. Fletcher consisted of p r o f i l e sampling several exposures of the anomaly to determine r e l a t i v e gold contents of the various s o i l horizons. 4.2 F i e l d sampling methods Sampling p i t s were located f i f t e e n metres apart on a serie s of f i v e p a r a l l e l lines which traversed the dispersion t r a i n (Figure 4.2). In t o t a l , 52 p i t s were excavated, i n most cases to a minimum depth of one metre. A l l p i t s were located i n areas of undisturbed, forested ground. T i l l samples were taken every 50 metres from roadcut exposures at 33 s i t e s along the Hedley Road. Au contours 400 ppb 200 ppb 100 ppb 10 ppb . . . -N ! / / \ ! I / ! / / / - — / f i v. . / /7 / / / y / / i •A JS Figure 4 . 1 - Gold dispersion t r a i n s delineated by Placer Development, Ltd.. Thesis area defined by stippled box o Figure 4 . 2 - L o c a t i o n of sampling p i t t r a v e r s e l i n e s r e l a t i v e t o the m i n e s i t e . 72 Before digging each p i t , the overlying layer of humus was removed and sampled using a gardening trowel taking care to avoid contamination by the mineral s o i l . The p i t was then excavated and the s o i l p r o f i l e was subdivided on the basis of compaction, colour and root density of the s o i l . The presence of secondary carbonate was determined with d i l u t e HCI. S o i l horizons greater than ten centimetres thick were sampled (from the bottom up i n order to avoid contamination from overlying horizons) using a geologists' hammer (pick end) and a ten l i t r e p l a s t i c bucket. Two f i v e l i t r e samples were obtained from each horizon: a f i r s t duplicate ('A') sample and a second duplicate ('B') sample. Rocks, greater than three centimetres i n diameter, were removed from each sample by hand. 4.3 Laboratory preparation and analysis 4.3.1 Humus One half of each dried humus sample was ground to a fi n e (100 micron) powder i n a Wiley m i l l . Between each sample, the m i l l was cleaned with both a brush and a j e t of compressed a i r . Once reduced to a powder, ten gram s p l i t s of each sample were taken using a Jones r i f f l e s p l i t t e r . The 73 ten gram subsamples were then packaged i n p l a s t i c v i a l s and sent to Chemex Labs, Ltd. (Vancouver, B.C.) for neutron a c t i v a t i o n analysis. 4.3.2 S o i l s 4.3.2.1 Minus 212 micron sample preparation Labratory preparation of the s o i l s i s represented schematically i n Figure 4.3. A one-quarter s p l i t of each s o i l horizon sample was taken by c a r e f u l l y mixing the ent i r e sample on a large, clean nylon sheet. The sample was then s p l i t i n ha l f , with one half being returned to the bag. The procedure was then repeated to produce a one-quarter s p l i t of the sample for wet sieving. A small (ten gram) portion of the remaining sample was retained for determination of s o i l pH. The one-quarter s p l i t s were then wet sieved through 2000, 420, and 212 micron sieves using a r e c i r c u l a t i n g water system (Figure 4.4). Except for the -212 micron s l u r r y , the r e s u l t i n g s i z e fractions (+2000, -2000+420, -420+212 micron) were placed i n an oven and dried at 70° - 80° C u n t i l a l l excess water had been evaporated. After the samples were dry, the +2000, -2000+420, and -420+212 micron s i z e f r a c t i o n s were weighed and stored for reference. 74 Store balance of sample SAMPLE Store weighed +212 micron fractions Wet sieve to +2000, -2000+420 -420+212, -212 size fractions Dewater -212 micron traction Oven dry at 70"- 80 t Weigh fraction Disaggregate Split sample Ring mill to -100 microns FA-AAS on 30 g split 1/4 split Store unused 3/4 split Figure 4 . 3 - S c h e m a t i c d iagram of sample p r e p a r a t i o n . Recirculated water 2000 micron 420 micron 212 micron 00 CD > CD CO water & -212 sediment -212 sediment Figure 4.4 - Wet sieving system. 76 The -212 micron s l u r r y was dewatered i n a large pressure f i l t e r . This consisted of a two centimetre thick, t h i r t y centimetre diameter p l a s t i c cylinder with removable aluminium plates at either end. A sheet of wetted white paper, wider than the cylinder, was placed between the bottom baseplate and the cylinder. The s l u r r y was poured into the f i l t e r and the upper plate was bolted down. Compressed a i r was then introduced into the cylind e r u n t i l the i n t e r i o r pressure had increased to approximately 500 kPa. This pressure was maintained u n t i l dry a i r was observed to emanate from the drain hole i n the baseplate. The dewatered -212 micron f r a c t i o n was dried i n an oven at 70° -80° C, separated from the paper f i l t e r , and disaggregated. Each sample was weighed before taking a t h i r t y gram s p l i t using a Jones r i f f l e s p l i t t e r . These s p l i t s were ground to less than 100 microns i n a rin g m i l l , then sent to Chemex Labs, Ltd. (Vancouver, B.C.) for gold analysis by f i r e assay - atomic absorption. F i f t y - s i x duplicate s p l i t s were also prepared and sent for analysis. The remainder of the sample material was retained for any further work. 77 4.3.2.2 Size f r a c t i o n , density f r a c t i o n and  cyanide extraction samples Samples were sieved using 2000, 420, 212, 106 and 53 micron sieves and a r e c i r c u l a t i n g water system as shown i n Figure 4.4. Once sieved, the +2000 and -2000+420 micron si z e f r a c t i o n s were dried and stored. The -420+212, -212+106 and -106+53 micron size fractions were dried and set aside for heavy mineral separation. The -53 micron s l u r r y was dewatered i n the pressure f i l t e r ; the r e s u l t i n g cake was then dried i n a low temperature oven and pulverized i n a r i n g m i l l . Two t h i r t y gram s p l i t s were taken from each sample, plus additional t h i r t y gram s p l i t s for duplicate analyses. Twenty-two of the t h i r t y gram -53 micron subsamples was submitted to Chemex Labs, Ltd. for FA-AAS while another set of twenty-two subsamples were submitted for Au determination by cyanide extraction, solvent extraction into MIBK and atomic absorption spectrophotometry. Four duplicate samples were submitted for each of the a n a l y t i c a l techniques. Sample residues were then analysed for Au by FA-AAS. Heavy and l i g h t mineral concentrates of the -420+212, -212+106, and -106+53 micron size fractions were separated using methylene iodide (CH 2I 2; S.G.= 3.3). Methylene iodide 78 was recovered from the samples by repeated washings with acetone. After the samples were dry, they were placed within p l a s t i c bags or v i a l s (depending on sample size) and weighed. Heavy and l i g h t mineral f r a c t i o n samples weighing more than 30 grams were ground in a r i n g m i l l (to -100 micron grain size) and s p l i t to a subsample s i z e of 3 0 grams. Any remaining material was stored for further use. Samples weighing less than 30 grams were not ground, but sent d i r e c t l y for analysis. One hundred and thirty-two heavy and l i g h t mineral s i z e f r a c t i o n subsamples were sent to Chemex Labs, Ltd. for FA-AAS. Six duplicate subsamples were also submitted f o r FA-AAS. 4.3.3 Scanning electron microscope and electron  microprobe sample preparation and analyses Seven 'B' (second duplicate series) samples were sieved through 212 and 53 micron sieves. The +212 and -53 micron f r a c t i o n s were discarded, while the resultant -212+53 micron s i z e f r a c t i o n was subjected to heavy mineral separation using methylene iodide. A hand magnet was then used to remove any magnetics from the heavy mineral f r a c t i o n s . 79 I s o l a t i o n of free gold grains i n each sample was achieved by repeatedly passing the samples through a Franz isomagnetic separator. An i n i t i a l current l e v e l of 0.1 amps was raised i n 0.2 amp increments af t e r each pass to a maximum of 1.1 amps. The resultant concentrate consisted of a r e s t r i c t e d number of mineral types, of which zircon appeared to be the most prevalent. This concentrate was then examined for free gold under a binocular microscope by sp r i n k l i n g a small portion of the grains on a black cardboard tray. Gold grains were removed from each sample by using a few strands on a modified f i n e haired brush to pick up the grains. The grains were then placed i n 7 dram glass v i a l s (one v i a l per sample) for further use. Gold grains were mounted on S.E.M. stubs coated with a t h i n layer of n a i l p o l i s h (J. Knight, personal commmunication, 1988). The gold grains were placed on the p o l i s h and immersed i n acetone vapour. Once the grains were observed to begin s e t t l i n g into the poli s h , the acetone vapour was removed, allowing the p a r t i a l l y embedded gold grains to set within the rehardened p o l i s h . Mounted gold grains were studied using a SEMCO NANOLAB 7 scanning electron microscope operating at 15 kV. Qual i t a t i v e energy dispersive spectrometry (EDS) was c a r r i e d out using a Kevex Unispec System 7000. A x i a l measurements of 80 each grain were determined from photographs and SEM imagery. EDS and backscatter secondary electron imaging was used to ascertain the surface composition of each grain. A cross-section of each gold grain was prepared using a method developed by J. Knight and Y. Douma at U.B.C. Eight grains were not sectioned, while one grain was l o s t during the process. Once the sectioning was complete, the plugs were coated with carbon for electron microprobe analysis. Electron microprobe analyses of the sectioned grains was c a r r i e d out on a Cameca SX-50 electron microprobe, using operating conditions modified from Knight and McTaggart (1986): a specimen current of 100 nA on aluminium and an accelerating potential of 20 kV. Counting time for peaks was 3 0 seconds and 15 seconds for each side of background. Data were reduced with Cameca PAP program u t i l i z i n g the phi-rho-x i data reduction method (J. Knight, personal communication, 1989). The elements Au, Ag, Cu and Hg, were assumed to be present i n s u f f i c i e n t concentrations to be analysed for (Knight and McTaggart, 1986). Detection l i m i t s for Au and Ag are 0.05% (Knight and McTaggart, 1986), whereas Cu had a detection l i m i t of 0.025% and Hg a l i m i t of 0.65% (J. Knight, personal communication, 1989). Where possible, each grain was analysed i n two places ; one analysis i n the centre of the grain, and a second analysis within the outer im of the grain. Chapter Five Results 83 5.1 Minus 212 micron f r a c t i o n r esults 5.1.1 R e l i a b i l i t y and a n a l y t i c a l p r e c i s i o n 5.1.1.1 Introduction R e l i a b i l i t y and a n a l y t i c a l precision were estimated using 56 duplicate pairs of Au analyses. Duplicates were prepared by taking two representative 30 gram s p l i t s of the -212 micron (ASTM -70 mesh) fr a c t i o n . An i n i t i a l group of thirty-two randomly selected duplicates were renumbered and analysed along with 171 primary samples. A second set of twenty four duplicates were submitted f i v e months l a t e r as an independent batch, without accompanying primary samples. Estimation of the r e l i a b i l i t y and a n a l y t i c a l p r e c i s i o n of the data was c a r r i e d out using scatterplots, a bias t e s t , a one-way analysis of variance (ANOVA) t e s t and the Thompson and Howarth (1973, 1976, 1978) method of estimating p r e c i s i o n . 5.1.1.2 Scatterplots / correlations A scatterplot of primary versus duplicate Au analyses i s shown i n Figure 5.1. The Pearson c o r r e l a t i o n c o e f f i c i e n t (r) for a l l f i f t y - s i x pairs i s 0.133. Inspection of the s c a t t e r p l o t reveals an o u t l i e r (6350 ppb, 130 ppb) which 0 1300 2600 3900 5200 6500 Au (ppb) Figure 5.1 - S c a t t e r p l o t of d u p l i c a t e Au a n a l y s e s , -212 micron f r a c t i o n . CO 85 strongly skews the regression l i n e towards the o u t l i e r . Removal of t h i s o u t l i e r r e s u l t s i n a regression l i n e which better f i t s the entire data set (Figure 5.2) and gives a c o r r e l a t i o n c o e f f i c i e n t of 0.806. 5.1.1.3 Systematic bias Error i n measurement due to non-random, systematic errors was estimated by the use of a bias t e s t . Use of t h i s t e s t for determining systematic error on geological samples i s d e t a i l e d i n Matysek and S i n c l a i r (1984) and Matysek (1985). In t h i s test, the number of p o s i t i v e differences between duplicate pairs i s determined; i f no bias i s present, then the number of po s i t i v e values (m) should be close to one-half the t o t a l number of p a i r s . A normal d i s t r i b u t i o n i s assumed for the data, where n i s the t o t a l number of data points, n/2 i s the mean and n - 1 / 2 i s the standard deviation. To determine the p r o b a b i l i t y of obtaining a s p e c i f i c deviation from the mean, the number of p o s i t i v e differences (m) i s f i r s t converted to the standard normal form (Z) through the formula: Z = [m -(n/2)]/(n 1/ 2) (5-1) Au (ppb) Figure 5.2 - S c a t t e r p l o t of d u p l i c a t e Au a n a l y s e s , -212 micron f r a c t i o n . Large o u t l i e r (6350 ppb) and c o r r e s p o n d i n g d u p l i c a t e a n a l y s i s removed. CO 87 Pro b a b i l i t y i s then calculated using the formula: p = X - Z(s) (5-2) where p i s the pr o b a b i l i t y of obtaining a p a r t i c u l a r deviation, X i s the cumulative p r o b a b i l i t y (0.50) of the standard normalized d i s t r i b u t i o n where the deviation equals zero, Z i s the r e s u l t of equation (5-1), and s i s the standard deviation (0.6826) of the standard normalized d i s t r i b u t i o n . Using values of n = 56 and m = 28, the calculated p r o b a b i l i t y (p) of obtaining t h i s p a r t i c u l a r deviation i s 0.50. Under id e a l situations where no systematic bias i s present ( i e . , Z = 0), the maximum obtainable p r o b a b i l i t y (p) i s 0.50. From t h i s , i t i s determined that systematic bias has not influenced the r e s u l t s . Inspection of Figure 5.1 confirms t h i s , as 28 scatterplot points (Anall vs. Anal2) are found on or above the Anall = Anal2 l i n e , whereas 28 are found on or below t h i s l i n e . 88 5.1.1.4 Analysis of variance One way analysis of variance can be u t i l i z e d to determine whether v a r i a b i l i t y between both sets of duplicate analyses ( i e . primary analyses and duplicate analyses) i s greater than the v a r i a b i l i t y within each set. I f the n u l l hypothesis (u Q = u-^  =....= u n) i s accepted, then a n a l y t i c a l v a r i a b i l i t y between sets i s indistinguishable from a n a l y t i c a l v a r i a b i l i t y within each set. Analysis of variance (calculated at the 95% confidence level) r e s u l t s i n a calculated F r a t i o (0.865) less than the F r a t i o (1.53) required for a s i g n i f i c a n t difference. Thus the primary analyses cannot be distinguished from the duplicate analyses (Table 5-1) . 5.1.1.5 Thompson and Howarth pr e c i s i o n method Precision of geochemical data i s an estimate of the r e l a t i v e v a r i a t i o n due to sampling and a n a l y t i c a l error. This i s s p e c i f i e d as the percent r e l a t i v e v a r i a t i o n at the two standard deviation (95%) confidence l e v e l , or: 89 Group Mean N 1 298.214 56 2 190.893 56 Grand mean 244.554 112 Source of Sum of Degrees of Mean Variation Squares Freedom Square Between groups 322500.9 1 322500.9 Within groups 41029376.8 110 372994.3 Total 41351877.7 111 F c a l c = °' 8 6 5'' F(60,60,0.05) = 1 ' 5 3 Null hypothesis accepted Table 5-1 duplicate - Analysis of variance r e s u l t s for primary and -212 micron Au analyses. 90 P c = 200SC/C (5-3) where P c i s the precision (in percent) at concentration c, and S c i s an estimate of the standard deviation at concentration c. In order to determine precision using geochemical samples, Thompson and Howarth (1973,1976,1978) devised a rapid method using a minimum of 50 randomly selected duplicate p a i r s . B r i e f l y , t h i s method i s as follows (Thompson and Howarth, 1978): 1) From the duplicate analyses obtain a l i s t of the means (X 1+X 2)/2 and the corresponding absolute differences |X1-X2|• 2) Sort the l i s t i n increasing order of concentration means. 3) Select the f i r s t 11 r e s u l t s and c a l c u l a t e the mean of the concentration means and determine the median value of the absolute differences. 4) Repeat t h i s procedure for each successive group of eleven r e s u l t s and obtain corresponding l i s t s of means and medians. Reject any group with less than eleven r e s u l t s . 5) Calculate the intercept and slope of the regression l i n e f i t t i n g a plot of median absolute differences versus concentration means. Multiply the intercept and 91 slope by 1.048 to obtain S Q (standard deviation at zero concentration) and k (slope), r e s p e c t f u l l y . Use of t h i s method i s r e s t r i c t e d to data which follows a normal d i s t r i b u t i o n ; data drawn from non-normal populations w i l l l i k e l y r e s u l t i n erroneous conclusions (Thompson and Howarth, 1976). Five sets of eleven analyses were u t i l i z e d to determine pr e c i s i o n . Figure 5.3 graphically represents the d i s t r i b u t i o n of duplicate analyses (dots), the mean absolute difference versus median value for each group of eleven duplicates (squares) and the f i t t e d regression l i n e . The calculated intercept for the regression l i n e i s -0.822, with a corresponding slope of 0.3 09 and a c o r r e l a t i o n c o e f f i c i e n t of 0.967. The presence of a negative intercept implies that at some concentration the standard deviation (S c) i s equal to zero, a r e s u l t which i s neither r e a l i s t i c or possible to achieve. Evidently, the duplicate dataset follows a non-normal d i s t r i b u t i o n , l i k e l y a re s u l t of the nugget e f f e c t . The Thompson and Howarth (1973, 1976 and 1978) p r e c i s i o n method i s i n v a l i d for t h i s dataset. 0 100 200 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 (X1+X2J/2 Figure 5 . 3 - Thompson and Howarth e r r o r p l o t , -212 micron f r a c t i o n d u p l i c a t e data. 93 5.1.2 Grain size d i s t r i b u t i o n of the -2000 micron  fractions Grain s i z e d i s t r i b u t i o n within the -2000 micron (ASTM -10 mesh) f r a c t i o n was determined from labratory sieving of each sample into three subfractions (-2000+420 microns, -420+212 microns, and -212 microns). Results of t h i s s ieving (Figure 5.4) indicates that the majority of the mass of each s o i l horizon resides i n the -212 micron f r a c t i o n . The proportion of -212 micron material i s observed to increase with depth. 5.1.3 S o i l p i t results For s t a t i s t i c a l evaluation of r e s u l t s , the c l a s s i f i c a t i o n of the s o i l p r o f i l e s was s i m p l i f i e d into four d i s c r e t e horizons: LFH, A, B and C. The uppermost mineral horizon of each p r o f i l e was designated as the A horizon, whereas the underlying s o i l layer was denoted the B horizon. C horizon was used to specify the lowest unit(s) exposed within each s o i l p i t which exhibited the c h a r a c t e r i s t i c s of weathered parent material. In cases where two or more C horizons were encountered within a p r o f i l e , the values were combined and a mean value taken. LFH samples were not affected by t h i s regrouping. / \ A horizon O B horizon • C horizon Line 1 Line 2 Line 3 Line 4 a i 0 Line 5 A A O A O • • O' a 0 A • • -a a 0 • O A • a • i • 6 • 2 • • 8 8 7 8 + 8 7 SIZE FRACTION (microns) 8 7 Figure 5.4 - Mean grain size d i s t r i b u t i o n of the - 2 0 0 0 micron f r a c t i o n f o r the A , B and C horizons of each traverse l i n e . 95 Results of FA-AAS on t h i r t y gram s p l i t s of the -212 micron f r a c t i o n for each s o i l horizon are shown i n the Appendix. A strongly skewed arithmetic histogram of these Au analyses (Figure 5.5) indicates the presence of a s i n g l e o u t l i e r (6350 ppb). Examination of a logarithmic histogram (Figure 5.6) indicates a s l i g h t l y skewed, normal d i s t r i b u t i o n of Au values with isolated o u t l i e r s . Plots of the data by traverse l i n e (Figures 5.7a-e) shows the Au content of each horizon. Results are generally e r r a t i c , no noticable patterns of Au d i s t r i b u t i o n are observed along each traverse l i n e . As shown i n Table 5-2, the (logarithmic) mean Au content of each horizon increases with depth. Mean (antilog) Au concentrations for each horizon range from a low of 8.2 ppb (Line 5, LFH horizon) to a high of 413 ppb (Line 1, C horizon). Comparison of corresponding logarithmic horizon means from each traverse l i n e indicates that with increasing distance from the mine, the Au concentration within each horizon decreases (Figure 5.8) . 5.1.4 Roadcut samples FA-AAS re s u l t s for forty-four C horizon t i l l samples taken along the Hedley Road are l i s t e d i n the Appendix. A summary table of these re s u l t s i s shown in Table 5-3. The 2 0 0 n = 189 mean = 196.8 a = 489.2 o so^oo^ftoo^ooo^oo^oo^oo^oo^oo^ooo^oo^oo^oo Au (ppb) Figure 5 . 5 - A r i t h m e t i c histogram of a l l A, B and C h o r i z o n - 212 micron f r a c t i o n Au a n a l y s e s . 40 .00 0J0 M M M M 1.0 1.2 iA 1.8 1.6 2.0 2.2 2A 2.6 24 3.0 S J 3.4 34 3.8 44 l o g A u (ppb) Figure 5 . 6 - Logarithmic histogram of a l l A, B and C h o r i z o n -212 micron f r a c t i o n Au a n a l y s e s . 1,000 g;100 3 < 10 LFH Legend U \A — A . A •1o-Q B • c -A-.A — - e -0 \ A " • .-A .-O • 1 - H 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Sample Pit Figure 5 . 7 a - Au content of the LFH, A, B and C horizons, - 2 1 2 micron f r a c t i o n , traverse l i n e l . 100 n CL CL < 10 A -•A-G --A--0 • "I i LFH A B C - - - 4 - - - - - - G B — A - - -Legend 16 17 18 19 20 21 Sample Pit Figure 5.7b - Au content of the LFH, A, B and C horizons, -212 micron f r a c t i traverse l i n e 2. vo VO 100 a. CL < 10 A-o -e--0--A LFH Legend s A - G -• - A • B n c - A -1 - H 1 1 1 1 H 1 1 h~ 22 23 24 25 2 6 2 7 28 2 9 3 0 Sample Pit Figure 5 . 7 c - Au content of the LFH, A, B and C horizons, -212 micron f r a c t i o n , traverse l i n e 3. -O. L i A e> -• A -A / \ • L l - - - '"0-. Li r \, •0" .0 A -• / 0 ~3F 0-\-<::>" • •* - - . • LFH Legend A -0-B • C - - - A - -31 32 33 34 35 36 37 38 Sample Pit 39 40 41 42 Figure 5.7d - Au content of the LFH, A, B and C horizons, - 2 1 2 micron f r a c t i o n , traverse l i n e 4 . -A 0 100 0-10+13 • B-, A --0 ---A B LFH Legend SA 0. .--0' \ _ - A -_. . . . * - . O A •••0-B • - A c A 43 44 45 46 47 48 49 50 51 52 Sample Pit Figure 5.7e - Au content of the LFH, A, B and C horizons, -212 micron f r a c t traverse l i n e 5. 1 0 3 Horizon LFH A 13 C Line 1 2 3 . 4 1 6 2 2 5 7 4 1 7 2 1 4 . 8 1 0 0 9 9 2 0 9 3 1 2 . 9 6 6 9 8 1 2 3 4 1 4 . 1 3 5 5 8 5 9 5 8 . 1 2 8 ,. 3 2 7 4 Table 5-2 - Mean (antilog) Au content of each s o i l horizon by traverse l i n e . A l l values i n ppb. 1000 100 n a. 3 3 < 10 t + A n A A () A • 4> o O LFH horizon A A horizon • B horizon — C horizon () 1 Traverse line F i g u r e 5 . 8 - P l o t of the mean l o g a r i t h m i c Au content of the L F H , A , B and C h o r i z o n s as a f u n c t i o n of d i s t a n c e . E r r o r bars i n d i c a t e one standard d e v i a t i o n . R e s u l t s are staggered t o e l i m i n a t e o v e r l a p of p o i n t s . 105 Number of Standard Samples Mean Minimum Maximum Deviation 44 210 10 5070 (-) 59 (+) 748 Table 5-3 - Summary table for (antilog) Roadcut C horizon ( t i l l ) sample Au analyses. A n a l y t i c a l values i n ppb. 106 same general trend i s observed with the roadcut samples as with the s o i l p i t samples: i e . a decrease i n Au values with increasing distance from the mine (Figure 5.9). 5.1.5 Population d i s t r i b u t i o n s of the minus 212 micron  r e s u l t s Separation of the Au data into anomalous and background populations was achieved using logarithmic p r o b a b i l i t y p l o t s generated by the PROBPLOT program (Stanley, 1987). Logarithmic p r o b a b i l i t y plots were selected as the data approximates a normal logarithmic d i s t r i b u t i o n (see Figure 5.6). Data were f i r s t separated into subsets by horizon (LFH, A, B, and C), and C horizon samples taken along the Hedley Road (Roadcut samples) were treated as a separate set of data. A bimodal population d i s t r i b u t i o n (anomalous and background populations) was assumed for each subset. Attempts to subdivide the data into a greater number of populations was considered unreliable due to the small number of samples analysed (n = 51, maximum). Data which could not be placed confidently within either the anomalous or background populations were categorized as belonging to mixtures of the populations. Thresholds used by the PROBPLOT program were based upon the method described by S i n c l a i r (1976) and were defined as the mean +/- two standard deviations for each partitioned (anomalous and background) Roadcut Till 10,000 Linel Line 2 Line 3 Line 4 Line 5 Relative distance Figure 5 . 9 - P l o t of the -212 micron f r a c t i o n Au content of the Roadcut t i l l samples wit h i n c r e a s i n g d i s t a n c e from the m i n e s i t e . o 108 population (Stanley, 1987). Mixed samples were defined as those values which f e l l above the cumulative 98.5 p e r c e n t i l e of the background population and below the cumulative 2.5 p e r c e n t i l e of the anomalous population. Results of logarithmic p r o b a b i l i t y plots generated for each horizon and the Roadcut C horizon samples are shown i n Figures 5.10a-e. Visual inspection of the p r o b a b i l i t y plots and calculated threshold values indicates that the bimodal population model best f i t s data from the C horizon and the Roadcut C horizon samples. P a r t i t i o n of the LFH, A and B horizons into anomalous and background populations, although pl a u s i b l e , i s not as d i s t i n c t . The lower f i v e to eight percent of each dataset (excluding the LFH horizon) poorly f i t s a bimodal curve and appears to represent a t h i r d population. However, only two to four samples are represented by f i v e to eight percent of the data. I t i s possible that these data are spurious and are due to f i e l d sampling problems or a n a l y t i c a l d i f f i c u l t i e s for Au. Conversely, a t h i r d population may ex i s t within the dataset, but i s not s u f f i c i e n t l y represented to be conclusive. Calculated threshold values for each horizon and the resultant ranges for the corresponding anomalous, mixed and background populations are l i s t e d i n Table 5-4. Contrast values generated for the A, B and C horizons (where contrast equals the mean of the anomalous population divided by the PERCENT PftRftHE ICR ESTItlfiTES Figure 5.10a - P r o b a b i l i t y p l o t w i t h t h r e s h o l d s , LFH h o r i z o n Au content. Figure 5.10b - P r o b a b i l i t y p lot with thresholds , A horizon -212 micron f r a c t i o n Au content. _j—j j 1—\—i i j — i — i — i — i i i— i— i j i—i— 3i S3 35 SS 70 SO 10 15 S 1 1 RAM DATA HL PERCENT PARAHE TER ESTIMATES Figure 5.10c -c o n t e n t . P r o b a b i l i t y p l o t w i t h t h r e s h o l d s , B h o r i z o n -212 micron f r a c t i o n Au Figure 5.10d - P r o b a b i l i t y p l o t w i t h t h r e s h o l d s , C h o r i z o n -212 m i c r o n f r a c t i o n Au c o n t e n t . 21 :39 :20 N i c k e l P l a t e '87 R o a d c u t C H o r i z o n S a H p l e s L O G A R I T H M I C V A L U E S f f DE ni I t I I , F L O 1 P E R C E N T P A R A M E T E R E S T I M A T E S Figure S.lOe - P r o b a b i l i t y p l o t w i t h t h r e s h o l d s , Roadcut C h o r i z o n samples, -212 micron f r a c t i o n Au content. t-* H 114 Horizon Mean or Threshold LFH A B C Road C Anomalous (mean) 15.4 111 114 265 392 Anomalous (X + 2s) 43.6 414 589 847 1489 Anomalous (X - 2s) 5.4 30 22 83 103 Background (mean) 5.0 28 27 57 60 Background (X + 2s) 7.2 103 59 104 175 Background (X - 2s) 3.5 8 12 31 20 Contrast r a t i o 2.1 1.1 1.9 2.6 2.2 % population anomalous 93.0 59.7 86.0 59.8 67.0 % population background 7.0 40.3 14.0 40.2 33.0 T a b l e 5-4 - Calculated (antilog) means and thresholds for the anomalous and background populations of each s o i l horizon. (Contrast r a t i o = mean anomalous population divided by mean plus two standard deviations background population). Also included are the percentages of anomalous and background populations. 115 mean plus two standard deviations of the background population) reveals that contrast between anomalous and background populations increases down the s o i l p r o f i l e (Table 5-4). 5.2 Size / density f r a c t i o n r e s u l t s 5.2.1 Introduction Six p i t p r o f i l e s were chosen for d e t a i l e d s i z e and density f r a c t i o n analysis. P i t selection was based upon separation of the -212 micron C horizon Au data into anomalous and background populations. Two p r o f i l e s were chosen from the anomalous C horizon population (referred to as the Proximal pits) and two from the background population ( D i s t a l p i t s ) ; the remaining two p i t s were picked to represent the mixed group of samples (Intermediate p i t s ) . A l l p r o f i l e s were selected to represent the observed increase i n Au content with depth. A distance of 78 0 metres separates the Proximal and D i s t a l p i t s . 5.2.2 R e l i a b i l i t y and a n a l y t i c a l p r e c i s i o n R e l i a b i l i t y of the size / density f r a c t i o n analyses was 116 estimated using a t o t a l of eighteen duplicate samples. Duplicate s p l i t s of the l i g h t mineral and -53 micron f r a c t i o n s indicate good r e p r o d u c i b i l i t y (Figures 5.11, 5.12). Poor r e p r o d u c i b i l i t y (r = 0.61, r c r i t ( 0 . 0 5 ) = °* 7 4) i s displayed for duplicate pairs of the heavy mineral f r a c t i o n (Figure 5.13), and i s presumably a r e s u l t of the nugget e f f e c t . Analysis of variance carried out on the three duplicate subsets (LMC, HMC and -53 micron) i s shown i n Table 5-5. In a l l cases, the n u l l hypothesis i s accepted: i e . there i s no evidence to suggest that the primary and duplicate analyses have originated from separate populations. 5.2.3 Grain size d i s t r i b u t i o n of the -2000 micron  f r a c t i o n Grain s i z e d i s t r i b u t i o n within the -2000 micron f r a c t i o n (in weight percent) of the detailed samples i s represented i n Table 5-6a. A l l samples have a nearly i d e n t i c a l bimodal grain size d i s t r i b u t i o n , with most of the sample weight being concentrated i n the -2000+420 micron and -53 micron si z e fractions. D i s t r i b u t i o n of l i g h t and heavy mineral f r a c t i o n s within the -420 micron f r a c t i o n i s l i s t e d i n Table 5-6b. The 140 • , y 120 Light mineral duplicate analyses _ J 0 0 n LL. Q. 80 < 60 • / > ^ r = 0.967 40 ^y * • critical r = 0.666 20 ** 0 * 0 20 40 60 80 100 120 140 A U ( p p b ) Figure 5.11 - Light mineral f r a c t i o n duplicate analyses. Figure 5.12 - Minus 53 micron f r a c t i o n duplicate analyses. 00 6,000 x x x x X X X X X 5,000 X X Heavy mineral duplicate analyses . - ' X X X Q . 4,000 Q _ X X X X X • X X X < 3,000 r = 0.614 H -' critical r = 0.811 X X X X 2,000 X X X X O * X 1,000 X r = 0.614 .<5 5~~ ' •—- — ^ ~ X 0 C I 1,000 2,000 3,000 4,000 5,000 6,000 AU (ppb) Figure 5.13 - Heavy mineral f r a c t i o n duplicate analyses. 120 Light mineral concentrates Source of Variation Between groups Within groups Total Sum of Squares 12.5 24194.4 24206.9 Degrees of Freedom 1 16 17 F c a l c = 0.00027; F ( 1 6 f l f 0 > ( ) 5 ) = 4.49 Null hypothesis accepted Mean Square 12.5008 1512.2 Heavy mineral concentrates Source of Sum of Degrees of Mean Variation Squares Freedom Square Between groups 3461502 1 3461502 Within groups 27809670 10 2780967 Total 31271172 11 F c a l c = i - 2 4 5 / ' F(10,11,0.05) = 2 * 8 5 Null hypothesis accepted -53 micron f r a c t i o n Source of Variation Between groups Within groups Total Sum of Squares 1350 180300 181650 Degrees of Freedom 1 4 5 Mean Square 1350 45075 ca l c = 0.03; F ( 4 ^ 0 > 0 5 ) = 5.19 Null hypothesis accepted T a b l e 5-5 - Analysis of variance r e s u l t s for duplicate l i g h t and heavy mineral concentrate and -53 micron Au analyses. Size Fraction Sample S o i l -2000 -420 -212 -106 -53 Horizon +420 +212 +106 +53 14 A 22.6 8.8 11.3 8.6 48.5 15 B 24.7 11.2 11.1 7 . 6 45.4 16 C 29.1 13.9 11.5 7.9 37.7 41 A 28.6 9.8 10.6 7.4 43 . 6 42 B 29.0 10.3 8.7 5.3 46.7 43 CI 31.5 12.2 7.8 8.3 40.2 44 C2 36.0 14.1 11.1 7.3 31.5 122 A 21.8 8.8 10.4 7.9 51.1 123 B 24.2 10.4 10.1 7.2 48.0 124 CI 29.2 12.0 10.0 6.6 42.1 125 C2 28.0 10.3 10.0 7.0 44.7 127 A 19.7 9.4 10.0 6.9 54.1 128 B 20.7 9.1 9.7 6.1 54.4 129 CI 22.4 10.8 9.2 7.4 50. 2 130 C2 26.3 11.9 9.4 6.2 46.3 162 A 19.2 7.3 9.4 5.9 58.2 163 B 27.2 11.5 9.8 6.5 45.0 164 C 31.2 10.5 9.8 8.3 40.2 186 A 15.3 6.1 9.7 6.7 62.3 187 B 15.3 5.7 9.1 7.2 62.8 188 CI 15.5 6.0 7.8 7.3 63 . 3 189 C2 19.4 7.7 7.7 6.7 58.3 Proximal average 30.1 12.3 10.0 7.3 40.3 D i s t a l average 24.8 8.3 8.8 7.2 53.9 Contrast r a t i o 1.2 1.5 1.1 1.0 0.7 Table 5 - 6 a - Grain size d i s t r i b u t i o n of the -2000 micron f r a c t i o n . Values i n weight percent. Proximal and d i s t a l averages calculated by averaging the B and C horizons of the proximal and d i s t a l p i t s . Contrast r a t i o equals the proximal average divided by the d i s t a l average. 122 Size Fraction Sample S o i l -420+212 -212+106 106+53 -53 Horizon L H' L H L H 14 A 2.5 8.9 3.0 11.6 2.4 8.7 62.8 15 B 3.6 11.4 4.0 10.8 2.8 7.3 60.2 16 C 4.9 14.8 4.9 11.2 3.5 7.6 53.1 41 A 2.9 10.8 3.3 11.6 2.3 8.0 61.1 42 B 3.2 11.4 2.9 9.4 1.8 5.6 65.8 43 CI 3.9 13.9 3.0 8.3 2.9 9.3 58.6 44 C2 5.2 16.9 4.8 12.6 3.1 8.3 49.1 122 A 1.3 9.9 1.6 11.8 1.1 8.9 65.4 123 B 2.1 11. 6 2.2 11.0 1.5 8.1 63.4 124 CI 2.1 14.9 2.1 12.1 1.3 8 . 0 59.5 125 C2 1.9 12.4 2.2 11.8 1.4 8.2 62.1 127 A 1.3 10.4 1.4 11.0 1.1 7.5 67.3 128 B 1.2 10.3 1.5 10.8 1.0 6.8 68.6 129 CI 1.7 12.2 1.8 10.0 1.6 8.0 64.8 130 C2 2.1 14.1 2.0 10.6 0.7 7.7 63.0 162 A 0.9 8.1 1.1 10.5 0.6 6.7 72.0 163 B 1.1 14.7 1.2 12.2 0.6 8.4 61.8 164 C 0.2 15.1 0.3 14.0 0.2 11. 8 58.5 186 A 0.8 6.3 1.2 10.2 0.9 6.9 73.6 187 B 0.9 5.8 1.3 9.4 1.1 7.3 74.2 188 CI 1.2 6.0 1.3 7.9 1.0 7.6 75.0 189 C2 2.2 7.4 1.7 7.9 1.0 7.3 72.5 Proximal ave 13.7 D i s t a l ave 9.8 Contrast r a t i o 1.4 4.2 10.5 4.0 • 1.1 10.3 1.2 3.8 1.0 3.3 7.6 2.8 57.4 8.5 0.8 68.4 0.9 3.5 0.8 Table 5 -6b - Grain size d i s t r i b u t i o n of the l i g h t and heavy fr a c t i o n s of the -420+212, -212+106, -106+53 micron s i z e f r a c t i o n s and the -53 micron f r a c t i o n . Unlike Table 5-6a, a l l values i n Table 5-6b are expressed as a weight percent of the t o t a l mass of the -420 micron f r a c t i o n . 123 proportion of heavy mineral concentrate within each s i z e f r a c t i o n decreases with distance (Figure 5.14). Percent contribution of the -2000+420 micron f r a c t i o n and the -420+212 micron l i g h t mineral f r a c t i o n also decrease with distance, whereas the -212+106 and -106+53 micron l i g h t mineral fract i o n s and the -53 micron f r a c t i o n increase. 5.2.4 Size and density f r a c t i o n analysis FA-AAS analysis for Au was carr i e d out on s i z e and density frac t i o n s of selected samples (see section 4.3). Detection l i m i t s for Au determination, which are dependent upon the mass of sample analysed, varied from 5 (30 gram sample) to 30 ppb (3.55 gram sample). A l l heavy mineral analyses, save one, have Au concentrations above the detection l i m i t . In every case, l i g h t mineral analyses were also above detection l i m i t s . Heavy mineral concentrates generally returned higher Au values than t h e i r l i g h t mineral counterparts (Tables 5-7 and 5-8) . 5.2.5 Heavy mineral f r a c t i o n r e s u l t s Au concentrations within the heavy mineral f r a c t i o n s decrease by a factors ranging from 2.2 to 12.5 between l i n e 5 Ice direction Proximal - o Intermediate Distal Relative Distance Figure 5.14 - V a r i a t i o n of heavy m i n e r a l content of the -420 micron f r a c t i o n w i t h i n c r e a s e i n d i s t a n c e from the m i n e s i t e . Sample Horizon -420+212 -212+106 -106+53 14 A 110 805 1060 15 B 2200 100 875 16 C 175 505 2210 41 A 130 1115 975 42 B 180 935 1360 43 CI 895 1585 725 44 C2 125 1650 1685 122 A 50 45 330 123 B 6250 385 725 124 CI 40 305 735 125 C2 60 1180 785 127 A 60 420 560 128 B 45 165 1070 129 CI 35 45 585 130 C2 40 365 2120 162 A 20 1720 140 163 B 40 615 1360 164 C 25 70 <30 186 A 25 385 420 187 B 155 465 760 188 CI 20 40 620 189 C2 45 45 335 Proximal average (ppb) 511 682 979 D i s t a l average (ppb) 41 176 441 Contrast r a t i o 12.5 3.9 2.2 Table 5 - 7 - Au concentrations (ppb)in heavy mineral concentrates. Proximal and d i s t a l averages calcu l a t e d by averaging the Au contents of the respective B and C horizons. Contrast r a t i o s calculated by d i v i d i n g the proximal average by the d i s t a l average. Sample Horizon -420+212 -212+106 -106+53 14 15 16 A B C 85 130 150 70 90 125 40 80 125 41 42 43 44 A B CI C2 120 110 90 105 65 65 105 175 45 50 80 120 122 123 124 125 A B CI C2 30 55 80 65 40 55 60 80 20 45 40 55 127 128 129 130 A B CI C2 45 50 40 70 20 35 50 60 20 40 30 30 162 163 164 A B C 20 10 10 20 20 10 25 10 10 186 187 188 189 A B CI C2 35 50 55 40 35 40 50 40 20 30 40 30 Proximal average (ppb) 84 80 65 D i s t a l average (ppb) 24 23 17 Contrast r a t i o 3.5 3.5 3.8 Table 5 - 8 - Au concentrations (ppb)in l i g h t mineral concentrates. Proximal and d i s t a l averages calculated by averaging the Au contents of the respective B and C horizons. Contrast r a t i o s calculated by d i v i d i n g the proximal average by the d i s t a l average. 127 1 (proximal to mine) and l i n e 4 ( d i s t a l to mine) (Table 5-7). Trends i n Au content are not observed within the sample p i t s ; values appear to be e r r a t i c and unrelated to s o i l horizons. Overall, the coarse (-420+212 micron) f r a c t i o n s contain less Au than the f i n e r (-212+106 micron, -106+53 micron) f r a c t i o n s . 5.2.6 Light mineral f r a c t i o n r e s u l t s The l i g h t mineral size fractions contain Au values ranging from 10 to 150 ppb (Table 5-8). Au contents are lowest within the -106+53 micron f r a c t i o n i n 15 of 22 samples, while Au contents of the -420+212 micron f r a c t i o n are highest i n 11 of 22 samples. In contrast to the heavy mineral samples, the Au concentrations of the l i g h t mineral f r a c t i o n s appear i n many cases to be related to depth within the s o i l p r o f i l e . Increasing Au values are observed with increasing depth within the s o i l p r o f i l e i n th i r t e e n of eighteen cases (Table 5-8). Contrast r a t i o s (the r a t i o of averaged proximal B and C horizons to averaged d i s t a l B and C horizons) for the l i g h t fractions are very s i m i l a r . 5.2.7 Minus 53 micron f r a c t i o n r e s u l t s Results of FA-AAS on the -53 micron f r a c t i o n are 128 presented i n Table (5-9). Au concentrations range from 595 (C horizon sample 87-SS-44, proximal to mine) to 30 ppb (A horizon sample 87-SS-162, d i s t a l to mine). A decline i n Au content by a factor of six i s observed with increasing distance from the mine. Also noticeable i s the increase of Au concentrations with depth i n i n d i v i d u a l s o i l p r o f i l e s . 5.2.8 Total Au concentration by s i z e f r a c t i o n Au content of the l i g h t and heavy mineral f r a c t i o n s were combined to estimate the concentration of Au within each si z e f r a c t i o n . Calculated Au contents of the -420+212, -212+106, -106+53 micron size fractions are given i n Table 5-10; also l i s t e d are the -53 micron Au r e s u l t s . A l l four s i z e f r a c t i o n s have similar Au concentrations. Paired t -t e s t s c a r r i e d out between size fractions indicate that the n u l l hypothesis can be accepted i n a l l cases (Table 5-11). 5.2.9 Proportion of t o t a l Au contributed from each  size-density f r a c t i o n A n a l y t i c a l values and sample weights were used to c a l c u l a t e the mass of Au present i n each size-density f r a c t i o n . Table (5-12) l i s t s the mass of Au found within each f r a c t i o n . Expressed as a percentage of the t o t a l , the Sample Horizon Au (ppb) 14 A 305 15 B 390 16 C 425 41 A 200 42 B 225 43 CI 390 44 C2 595 122 A 70 123 B 120 124 CI 150 125 C2 155 127 A 55 128 B 90 129 CI 130 130 C2 120 162 A 30 163 B 55 164 C 40 186 A 45 187 B 70 188 CI 90 189 C2 95 Proximal average (ppb) 4 05 D i s t a l average (ppb) 70 Contrast r a t i o 5.78 Table 5-9- Au concentration of the -53 micron f r a c t i o n . Proximal and d i s t a l averages calculated by averaging the Au contents of the respective B and C horizons. Contrast r a t i o s c a l c u l a t e d by dividing the proximal average by the d i s t a l average. 130 Size Fraction Sample Horizon -420+212 -212+106 -106+53 -53 14 A 90.55 222.05 260.85 305 15 B 622.39 92.71 300.14 390 16 C 156.19 241.01 787.57 425 41 A 122.14 296.93 249.93 200 42 B 125.51 271.04 374.55 225 43 CI 268.52 506.26 232.61 390 44 C2 109.71 582.58 547.02 595 122 A 32.39 40.59 53.94 70 123 B 1015.58 110.57 148.38 120 124 CI 75.10 96.28 135.69 150 125 C2 64.33 , 250.76 160.79 155 127 A 46.64 65.71 87.86 55 128 B 49.49 51.10 167.22 90 129 CI 39.40 49.23 121.29 130 130 C2 66.18 107.75 205.03 120 162 A 20.00 186.86 33.86 30 163 B 12.15 74.09 95.33 55 164 C 10.22 11.09 10.90 40 186 A 33.83 70.41 66.87 45 187 B 64.60 90.24 129.32 70 188 CI 49.32 48.57 107.20 90 189 C2 41.15 40.88 68.77 95 Proximal average (ppb) 257.3 338.7 448.4 405 D i s t a l average (ppb) 35.4 52.9 82.2 70 Contrast r a t i o 7.26 6.40 5.45 5.78 Table 5-10 - Calculated Au concentration (ppb) by siz e f r a c t i o n . Proximal and d i s t a l averages calculated by averaging the Au contents of the respective B and C horizons. Contrast r a t i o s calculated by d i v i d i n g the proximal average by the d i s t a l average. 131 -420+212 -212+106 -106+53 -53 -420+212 - - --212+106 -.310 - --106+53 -.962 -1.194 --53 -.637 -.736 1.077 t ( 2 1 ,0.05) = 1 , 7 2 Table 5 -11 - Paired t - t e s t results on comparisons of t o t a l Au contents of d i f f e r e n t size fractions. Size Fraction Sample S o i l -420+212 -212+106 -106+53 -53 Total Horizon L H L H L H 14 A 15 .9 5 .9 17 . 1 51 .4 7 .3 53 .8 403 .8 555 .3 15 B 31 .9 168 .4 20 .9 8 .7 12 .5 52 .5 506 .5 801 .4 16 C 47 .1 18 .1 29 .8 52 .9 20 . 1 165 .4 478 .7 812 .2 41 A 23 .4 6 .9 13 .6 66 .3 6 .5 40 . 1 220 .8 377 .7 42 B 26 .7 12 .4 13 .0 58 .0 5 .9 53 . 1 315 .8 484 .8 43 CI 29 .8 84 .4 20 .8 116 .9 17 .8 49 .9 546 .4 866 .0 44 C2 38 .9 14 .3 48 .6 174 .9 21 .9 115 .5 641 .8 1055 .0 122 A 3 .8 0 .9 6 . 1 0 .9 2 .3 4 .7 59 . 0 77 .7 123 B 15 .7 328 .3 14 .9 21 .1 8 .9 25 .8 186 . 5 601 .3 124 CI 22 .0 1 .5 13 .4 11 .9 5 .9 17 .4 165 .2 237 .3 125 C2 26 .8 3 .9 31 .2 84 .5 8 .0 36 .4 318 .2 509 .4 127 A 9 .2 1 .5 4 .3 11 .6 2 .9 11 .7 72 . 3 113 .5 128 B 8 .8 0 .9 6 .4 4 .3 4 .6 17 . 3 105 . 0 147 .3 129 CI 7 .3 0 .9 7 .4 1 .2 3 .5 13 .6 124 .8 158 .6 130 C2 14 .0 1 .2 9 .0 10 .1 3 .3 21 . 1 107 . 1 165 .6 162 A 2 .4 0 .3 3 .2 29 . 6 2 .5 1 .2 32 .5 71 .7 163 B 1 .9 0 .6 3 .1 9 .6 1 .1 9 .8 43 . 4 69 .5 164 C 2 .5 0 . 1 2 .3 0 .3 2 .0 0 . 1 39 . 0 46 .3 186 A 3 . 4 0 . 3 5 . 6 6 .9 2 .2 6 . 0 51 .6 76 .0 187 B 4 . 9 2 . 4 6 .3 9 .9 3 . 6 14 . 6 87 . 0 128 .6 188 CI 4 . 0 0 . 3 4 .8 0 . 6 3 .7 7 .5 81 .2 101 .9 189 C2 4 .8 1 .6 5 . 1 1 .2 3 .5 5 . 7 111 . 0 132 .9 Table 5-12 - Calculated mass (micrograms) of Au i n each si z e and / or density f r a c t i o n . 133 proportion of Au i n each f r a c t i o n i s l i s t e d i n Table (5-13). The majority of the Au i s found i n the -53 micron f r a c t i o n , ranging from 31% to 84.3%. Au content of the l i g h t mineral f r a c t i o n s amount to only 1% to 9% of the whole. Conversely, heavy mineral Au contents display a wide range of Au content, from 0.1% to 55%. No consistent changes occur i n the p a r t i t i o n i n g of Au between the l i g h t and heavy mineral f r a c t i o n s with depth. Examination of contrast r a t i o s (Table 5-13) indicates that with increasing distance from the minesite, the percentage of Au within the heavy mineral f r a c t i o n s decrease. The percentage of Au i n the f i n e r l i g h t mineral f r a c t i o n s (-212+106 and -106+53 micron) and the -53 micron f r a c t i o n increases with distance, whereas the proportion of Au within the -420+212 micron l i g h t mineral f r a c t i o n decreases with distance. 5.2.10 Comparison of l i g h t and heavy density f r a c t i o n s  of each size f r a c t i o n The proportion of Au i n the l i g h t and heavy density f r a c t i o n s of the -420+212, -212+106 and -106+53 micron s i z e f r a c t i o n s are shown i n Table (5-14). Comparison of the l i g h t and heavy mineral fractions shows that differences i n Au content between the two fractions increase with decreasing grain s i z e . Au i n the -420+212 micron f r a c t i o n i s concentrated i n the l i g h t mineral f r a c t i o n , which contains 134 Size Fraction Sample S o i l -420+212 -212+106 -106+53 -53 Horizon L H L H L H 14 A 2.9 1.1 3.1 9.3 1.3 9.7 72.7 15 B 4.0 21.0 2.6 1.1 1.6 6.5 63.2 16 C 5.8 2.2 3.7 6.5 2.5 20.4 58.9 41 A 6.2 1.8 3.6 17.6 1.7 10.6 58.5 42 B 5.5 2.6 2.7 12.0 1.2 10.9 65. 1 43 CI 3.4 9.8 2.4 13.5 2 .1 5.8 63. 1 44 C2 3.7 1.4 4.6 16. 6 2.1 10.9 60.8 122 A 4.9 1.1 7.8 1.2 3.0 6.0 76.0 123 B 2.6 54.6 2 . 5 3.5 1.5 4 . 3 31.0 124 CI 9.3 0.6 5.7 5.0 2.5 7.3 69.6 125 C2 5.3 0.8 6.1 16. 6 1.6 7.1 62. 6 127 A 8.1 1.3 3.8 10.2 2.6 10.3 63 .7 128 B 6.0 0.6 4.3 2.9 3.1 11.8 71.3 129 CI 4.6 0.6 4.7 0.8 2.2 8.6 78.7 130 C2 8.4 0.7 5.4 6.1 2 . 0 12.7 64.7 162 A 3.4 0.4 4.4 41.3 3.5 1.7 45.4 163 B 2.7 0.8 4.5 13.8 1.5 14.1 62.5 164 C 5.4 0.2 5.0 0.7 4.2 0.1 84 . 3 186 A 4.5 0.4 7.3 9.1 2.8 7.9 67.9 187 B 3.8 1.9 4.9 7.7 2.8 11.3 67. 6 188 CI 3.9 0.3 4.7 0.6 3.6 7.3 79.6 189 C2 3.6 1.2 3.8 0.9 2.6 4.3 83 .5 Proximal ave. 4.5 7.4 3.2 9.9 1.9 10.9 62.2 D i s t a l ave. 3.9 0.9 4.6 4.7 2.9 7.4 75.5 Contrast r a t i o 1.2 8.4 0.7 2.1 0.7 1.5 0.8 Table 5-13 - Percentage of Au i n each size and / or density f r a c t i o n of the -420 micron f r a c t i o n . Size F r a c t i o n Sample S o i l -420+212 -212+106 -106+53 Horizon L H L II L H 14 A 73. .0 27. ,0 25. ,0 75. .0 12. ,0 88. .0 15 B 15. ,9 84. ,1 70. ,7 29. ,3 19. ,3 80. ,7 16 C 72. ,3 27. ,7 36. ,0 64. ,0 10. .8 89. ,2 41 A 77. .3 22. ,7 17. ,1 82. ,9 14. .0 86. ,0 42 B 68. .2 31. ,8 18. ,3 81. ,7 10. .0 90. ,0 43 CI 26. .1 73. ,9 15. , 1 84. ,9 26. .3 73. .7 44 C2 73. .2 26. ,8 21. ,7 78. .3 16. .0 84. .0 122 A 81. .6 18. ,4 87. ,0 13. ,0 33. .0 67. .0 123 B 4. .6 95. ,4 41. ,4 58. .6 25. .7 74. .3 124 CI 93. .5 6. .5 53. .1 46. .9 25. .4 74. .6 125 C2 87. .4 12. .6 27. .0 73. .0 19, .9 80. .1 127 A 85. .9 14. , 1 27. ,0 73. ,0 18. .0 82. .0 128 B 90. .8 9. .2 60. .0 40. .0 21. .0 79. .0 129 CI 89. .3 10. .7 86. .0 14. .0 20. .7 79. . 3 130 C2 92. .3 7. .7 47. .0 53. .0 13. ,4 86. .6 162 A 89. . 6 10. .4 9. .7 90. .3 68. , 1 31. .9 163 B 76. .4 23. ,6 24. .5 75. .5 9. ,8 90. ,2 164 C 96. .4 3. .6 88. .5 11. .5 97. ,4 2. .6 186 A 91. .4 8. .6 44. .7 55. .3 26. .4 73. .6 187 B 66, .6 33. .4 39. .1 60. .9 20. .0 80. .0 188 CI 93. .4 6. ,6 88. .3 11. ,7 33. ,0 67. ,0 189 C2 74. .8 25. .2 80. ,7 19. .3 38. , 1 61. ,9 Proximal average 51, .1 48. .9 32. .4 67. .6 16. .5 83. .5 D i s t a l average 81. .5 18. .5 64. ,2 35. ,8 39. ,7 60. ,3 Contrast r a t i o 0. .6 2. .7 0. .5 1. .9 0. .4 1. ,4 Table 5-14 - D i s t r i b u t i o n of Au between the l i g h t and heavy f r a c t i o n s of each s ize f r a c t i o n . A l l values i n percent. 136 (on average) 74% of the Au. Nineteen of twenty-two -420+212 micron samples contain more Au i n the l i g h t f r a c t i o n than i n the heavy f r a c t i o n . Heavy mineral proportions of Au i n three -420+212 micron samples (15, 43, 123) are higher than the remaining samples by a factor of two, but due to the coarse grain s i z e , t h i s i s l i k e l y a r e s u l t of nugget e f f e c t . Eight of twenty-two -212+106 micron samples contain a greater proportion of Au i n the l i g h t s than i n the heavies, whereas only two of the -106+53 micron samples display the same tendency. Thus, the largest proportion of Au within the three s i z e fractions s h i f t s from the l i g h t f r a c t i o n (-420+212 micron) to the heavy f r a c t i o n (-106+53 micron) with decreasing grain size (Figure 5.15). With increasing distance of transport, the proportion of Au s h i f t s from the heavy to l i g h t mineral f r a c t i o n f or each si z e f r a c t i o n (Figure 5.15). No consistent changes with depth i n the proportional d i s t r i b u t i o n of Au between l i g h t and heavy density fractions of ind i v i d u a l s i z e f r a c t i o n s are present. 5.2.11 Number of gold p a r t i c l e s i n each s i z e f r a c t i o n Estimates of the number (N) of gold p a r t i c l e s present i n each sample siz e f r a c t i o n were made by assuming that each si z e f r a c t i o n contained spherical gold grains with a 100 -420+212 -212+106 -106+ 53 Size fraction (microns) Figure 5.15 - P r o p o r t i o n of Au w i t h i n the heavy m i n e r a l f r a c t i o n o f each s i z e f r a c t i o n . P o i n t s c a l c u l a t e d u s i n g data from the B and C h o r i z o n s o f the Proximal, Intermediate and D i s t a l p i t s . 138 diameter equal to the geometric mean of the bounding sieve diameters. Averaged measurements of gold grain shapes extracted from the -212+53 micron f r a c t i o n of selected samples indicated a nearly spherical grain shape (see section 5.4). Based upon the res u l t s of electron microprobe analysis of grain cores (section 5.5), a density of 15.45 g/cm3 was assumed, corresponding to a fineness of 700. Table 5-15a and Table 5-15b l i s t the calculated number of gold grains (per analysed sample weight and per 3 0 gram subsample, respectively) i n the -420+212, -212+106, -106+53 micron heavy mineral fractions. Also l i s t e d are the calculated number of gold grains found within the -53 micron f r a c t i o n , assuming that a l l Au within t h i s f r a c t i o n occurs as free gold grains 50 microns i n diameter. The number of gold grains i n each heavy mineral sample increases with decreasing grain s i z e . In a l l fractions, proximal samples (14, 15, 16, 41, 42, 43, 44) contain more grains than the intermediate or d i s t a l samples. None of the samples contain more than the minimum number of gold grains (2 0) required to insure a precision of 50% ( C l i f t o n , et a l . , 1969). 5.3 Cyanide extraction results Analyses of cyanide extracted Au c a r r i e d out on s p l i t s of the -53 micron f r a c t i o n are shown i n Table 5-16. Au Sample Horizon -420+212 -212+106 -106+53 -53 14 A 0.0 15 B 0.3 16 C 0.0 41 A 0.0 42 B 0.0 43 CI 0.1 44 C2 0.0 122 A 0.0 123 B 0.9 124 CI 0.0 125 C2 0.0 127 A 0.0 128 B 0.0 129 CI 0.0 130 C2 0.0 162 A 0.0 163 B 0.0 164 C 0.0 186 A 0.0 187 B 0.0 188 CI 0.0 189 C2 0.0 0.9 9.4 9.1 0.1 7.7 11.6 0.6 19.5 2.6 1.2 8.6 5.9 1.0 12.0 6.7 1.7 6.4 11.6 1.8 14.9 17.7 0.0 0.4 0.0 0.4 6.4 3.6 0.3 5.1 4.5 1.3 6.9 4.6 0.4 3.5 1.6 0.2 5.1 2.7 0.0 4.0 3.9 0.4 6.2 3.6 1.1 0.4 0.9 0.4 2.9 1.6 0.0 0.0 1.2 0.3 1.8 1.4 0.4 4.3 2.1 0.0 2.2 2.7 0.0 1.7 2.8 Proximal average 0.0 1.0 12.1 10.0 D i s t a l average 0.0 0.2 2.2 2.1 Contrast r a t i o 0.0 5.0 5.5 4.8 Table 5-15a- Calculated number of gold grains i n each heavy mineral s i z e f r a c t i o n and the -53 micron f r a c t i o n per weight of analyzed sample (30 gram maximum). Anomalous and background averages calculated by averaging the Au contents of the respective B and C horizons. Grain sizes for the heavy mineral concentrates are assumed to be equivalent to the geometric mean of the bounding sieve diameters. Grain siz e of the -53 micron f r a c t i o n i s conservatively estimated to be 50 microns, approximately the upper grain s i z e l i m i t . 140 Sample Horizon -420+212 -212+106 -106+53 -53 14 A 0.0 15 B 0.3 16 C 0.0 41 A 0.0 42 B 0.0 43 CI 0.1 44 C2 0.0 122 A 0.0 123 B 0.9 124 CI 0.0 125 C2 0.0 127 A 0.0 128 B 0.0 129 CI 0.0 130 C2 0.0 162 A 0.0 163 B 0.0 164 C 0.0 186 A 0.0 187 B 0.0 188 CI 0.0 189 C2 0.0 .9 9.4 9.1 0.1 7.7 11.6 0.6 19.5 12.6 1.2 8.6 5.9 1.0 12.0 6.7 1.7 6.4 11.6 1.8 14.9 17.7 0.0 2.9 2.1 0.4 6.4 3.6 0.3 6.5 4.5 1.3 6.9 4.6 0.5 4.9 1.6 0.2 9.4 2.7 0.0 5.2 3.9 0.4 18.7 3.6 1.9 1.2 0.9 0.7 12 1.6 0.0 0.0 1.2 0.4 3.7 1.3 0.5 6.7 2.1 0.0 5.5 2.7 0.0 3.0 2.8 Proximal average 0.0 1.0 12.1 12.0 D i s t a l average 0.0 0.3 5.4 2.1 Contrast r a t i o 0.0 3.3 2.2 5.7 Table 5-15b - Calculated number of gold grains i n each heavy mineral s i z e f r a c t i o n and the -53 micron f r a c t i o n per 30 gram sample weight. Proximal and d i s t a l averages calculated by averaging the Au contents of the respective B and C horizons. Grain sizes for the heavy mineral concentrates are assumed to be equivalent to the geometric mean of the bounding sieve diameters. Grain size of the -53 micron f r a c t i o n i s conservatively estimated to be 50 microns, approximately the upper grain size l i m i t . Cyanide Sample Horizon Extracted Residual % Au Au (ppb) Au (ppb) Extracted 14 15 16 A B C 90 450 350 45 145 105 66.7 75.6 76.9 41 42 43 44 A B CI C2 95 130 370 510 145 115 115 145 39.6 53.1 76.3 77.9 122 123 124 125 A B CI C2 <15 (7.5) 145 145 145 20 35 35 35 27.3 80.6 80.6 80.6 127 128 129 130 A B CI C2 145 80 175 110 35 15 45 65 80.6 84.2 79.5 62.9 162 163 164 186 187 188 189 A B C A B CI C2 <15 (7.5) 65 <15 (7.5) 30 110 80 130 20 15 5 5 40 15 25 27.3 81.25 60.0 85.7 73.3 84.2 83.9 Proximal average (ppb) 362 125 72.0 D i s t a l average (ppb) 80 20 76.5 Contrast r a t i o 4.6 6.3 0.9 Table 5-16 - Cyanide extractable Au and re s i d u a l Au contents of the -53 micron f r a c t i o n . ( % Au Extracted = cyanide extractable Au/(cyanide extractable + residual Au)). For c a l c u l a t i o n s , one-half the detection l i m i t was used f o r r e s u l t s below detection l i m i t . 142 values range from <15 to 510 ppb for cyanide extractable Au whereas the sample residues (material remaining a f t e r cyanide leaching) contain 5 to 145 ppb Au. Comparison of the r e s u l t s with " t o t a l Au" FA-AAS analyses of representative -53 micron sample s p l i t s (see section 5.2.6) reveals several i n t e r e s t i n g patterns. Except for three low analyses (<15 ppb), cyanide extracted Au results have a comparable d i s t r i b u t i o n of values to those analysed for t o t a l Au by FA-AAS (Figure 5.16), including a high c o r r e l a t i o n c o e f f i c i e n t of r = 0.902. On average, cyanide leaching extracted 70% of the gold within the -53 micron samples. The mean extraction e f f i c i e n c y of A horizon s o i l s i s 54%, while B and C horizon s o i l s have a higher mean e f f i c i e n c y of 7 6%. With the exception of three A horizon samples (41, 122 and 162) and one C horizon sample (164), the Au contents of the sample residues are less than the cyanide extracted Au concentrations. 5.4 Grain morphology Scanning electron microscopy was used to study the morphological c h a r a c t e r i s t i c s of free gold grains extracted from s e l e c t samples. Samples were chosen to represent the complete s o i l p r o f i l e s of two p i t s : one proximal (Pit #6) and one d i s t a l (Pit #38) to the minesite. A x i a l dimensions of each gold grain were measured from photographs and 600 500 n a. ^400 < © CO t3 300 CO CD CD ?200 re 100 Cyanide extractable Au versus Total Au In the -53 micron fraction 4 ^ ' O o r ^y ^ 0 ~ o o , 100 200 300 Total Au (ppb) 400 500 600 F i g u r e 5.16 - Cyanide extractable Au versus Total Au (FA-AAS), -53 micron f r a c t i o n . CO 144 d i r e c t l y from SEM imagery. Axial measurements of each grain are l i s t e d i n the Appendix. Grain shape was determined using two methods; quantitatively, using an a r b i t r a r y shape factor, and q u a l i t a t i v e l y , using a system of grain c l a s s i f i c a t i o n developed by A v e r i l l and Zimmerman (1984) and modified by DiLabio (1989). Calculation of a shape factor for each grain was ca r r i e d out using a formula similar to the Cory shape factor (Cory, 1949) but modified to allow for the i d e n t i f i c a t i o n of long, c y l i n d r i c a l p a r t i c l e s (Day, 1988). The r a t i o used i s : SF = (dS*dL) - 1/ 2/dX (5-4) where dS, dX and dL are the smallest, intermediate and longest diameters respectively (Day, 1988). An SF value of 1 w i l l represent a sphere, SF>1 represents long c y l i n d r i c a l p a r t i c l e s ("needles"), and SF<1 represents f l a t c y l i n d r i c a l p a r t i c l e s ("flakes"). Modelling of the population d i s t r i b u t i o n with a p r o b a b i l i t y p l o t (Figure 5.17) indicates that three separate populations of grain shapes can be defined. Population 1 has a mean SF = 0.678 (standard deviation = 0.161) and comprises 49.4% of the grains. This corresponds to a di s c shaped grain Figure 5.17 - P r o b a b i l i i t y p l o t of shape factor values. 146 with a diameter to thickness (largest to smallest diameters) r a t i o of 2.18. Grains found within the Population 2 group have a mean SF = 1.080 (standard deviation = 0.104) and compose 36.3% of the grains. The mean grain shape for t h i s group i s spherical, with a mean r a t i o of largest to smallest diameters of 1.16. Population 3 grains make up 14.3% of the grains and have a mean SF = 1.62 8 (standard deviation = 0.140). For a l l p a r t i c l e s (n = 62), the mean SF i s 0.950 (standard deviation = 0.365), which i s equivalent to a nearly spherical p a r t i c l e . Shape factor data by horizon for the proximal p i t i s shown i n Table 5-17. Shape factors generated for the d i s t a l p i t grains are not considered due to the low number of grains recovered from each horizon (eight grains t o t a l ) . Means and standard deviations of each horizon are very s i m i l a r to the mean and standard deviation of the en t i r e sample set. Analysis of variance ca r r i e d out on the data (horizon vs. horizon) indicates that at the 95% confidence l e v e l , the n u l l hypothesis i s accepted i n a l l cases (Table 5-18). Comparison of shape factors between the proximal and d i s t a l p i t s was also performed using analysis of variance. In t h i s instance, a comparison was made between a l l proximal p i t grains (54) and a l l d i s t a l p i t grains (8). Results of the analysis of variance (Table 5-19) reveals that the n u l l hypothesis i s v a l i d at the 95% confidence l e v e l . 147 Shape Number of Factor Standard Grains Mean Deviation Horizon A 19 .933 .372 B 19 .979. .375 C 15 .931 .417 Totals 53 .949 .379 Table 5-17 - Shape factor data, proximal p i t grains. 148 Group Mean N 1 .933 19 2 .979 19 3 .931 15 Grand mean .949 53 Source of Sum of Degrees of Mean V a r i a t i o n Squares Freedom Square Between groups .026 2 .013 W i t h i n groups 7.466 50 .149 T o t a l 7.492 52 F c a l c _ 0.088; F( 2,60,0.05) - 3 • 1 5 N u l l hypothesis accepted Table 5-18 - A n a l y s i s of v a r i a n c e r e s u l t s on shape f a c t o r s , by h o r i z o n . 149 Group Mean N 1 .963 56 2 .854 7 Grand mean .951 63 Source of Sum of Degrees o f Mean V a r i a t i o n Squares Freedom Square Between groups .074 1 .074 W i t h i n groups 8.065 61 .132 T o t a l 8.139 62 F c a l c = °- 5 6'' F(l,60,0.05) = 4 ' 0 0 N u l l h y p othesis accepted Table 5-19 - A n a l y s i s of v a r i a n c e r e s u l t s on shape f a c t o r v a l u e s f o r proximal versus d i s t a l g r a i n shapes. 150 Qu a l i t a t i v e assessment of grain shape was conducted using a three-tiered categorical system developed by S.A. A v e r i l l ( A v e r i l l and Zimmerman, 1986; A v e r i l l , 1988; Sopuck, e t . a l . , 1986) and modified by DiLabio (1989). Table (5-20) l i s t s the three shape classes and t h e i r accompanying shape and t e x t u r a l c h a r a c t e r i s t i c s . Using SEM photographs, the sixty-two grains from both p i t s were c l a s s i f i e d as being eith e r p r i s t i n e , modified or reshaped. The Appendix l i s t s the r e s u l t s of t h i s evaluation. Tests of s i g n i f i c a n c e c a r r i e d out using the Chi-squared d i s t r i b u t i o n (Table 5-21) indicate that no difference i n shape exists between horizons or between the proximal and d i s t a l p i t s . 5.5 Electron microprobe data Results of electron microprobe Au, Ag analyses of the cores of 41 sectioned gold grains are presented i n Table (5-22). Also l i s t e d are the corresponding Au and Ag analyses for twenty-three grain edges. A l l grains were analysed for Au, Ag, Cu and Hg. Cu and Hg analyses generally are less than t h e i r respective detection l i m i t s (Cu: 0.025%; Hg: 0.65%) and therefore cannot be considered r e l i a b l e . Wide ranges i n gold composition are present within the analysed grains. Fineness (the r a t i o of Au/(Au+Ag) X 1000) ranges from 999.7 (pure gold) to 379.5 (Ag-rich electrum). Mean fineness for the 41 grain cores i s 698.6 (standard deviation 151 Type Shapes Surface Textures P r i s t i n e b l o c k rod wire l e a f c r y s t a l s t a r g l o b u l e -smooth s u r f a c e s - g r a i n molds c l e a r l y v i s i b l e - t h i n edges not c u r l e d -some s t r i a e M o d i f i e d a l l shapes, -primary shapes v i s i b l e damaged - l e a f edges and w i r e s bent -b l u n t e d and t h i c k e n e d edges - g r a i n molds p r e s e r v e d where p r o t e c t e d -some s t r i a e - f e l t y t e x t u r e when damaged Reshaped f o l d e d rod, -primary shapes v i s i b l e wire, f l a k e - w e l l rounded g r a i n o u t l i n e rounded b l o c k s -some s t r i a e t y p i c a l d i s c o i d -porous, s c a l y , f e l t y , o r p l a c e r f l a k e spongy Table 5-20 - C l a s s i f i c a t i o n of shapes and s u r f a c e t e x t u r e s of g o l d g r a i n s . Reproduced from D i L a b i o (1989). Proximal P i t P r i s t i n e Modified Reshaped Totals Horizon A 6 8 5 19 B 4 11 4 19 C 3 5 8 16 Totals 13 24 17 54 X2 = 4.69 X2,A n ftK,= 9.48 (4,0.05) No s i g n i f i c a n t difference D i s t a l vs Proximal P i t s P r i s t i n e Modified Reshaped Totals P i t D i s t a l 1 3 4 8 Proximal 13 24 17 54 Totals 14 27 21 62 X2 = 1.19 * 2(2,0.05) = 5 - 9 9 No s i g n i f i c a n t difference Table 5-21 - Results of gold grains c l a s s i f i e d using the A v e r i l l (1988) and DiLabio (1989) system for q u a l i t a t i v e grain evaluation. Included are Chi-squared tests of s i g n i f i c a n c e at the 95% confidence l e v e l . 153 Grain Core Core Edge Edge Number Au Aa Au Aa 23-02 74.74 24.88 70.74 28.93 23-04 57.57 41.86 59.36 40.37 23-05 61.86 37.57 66.98 33.04 23-09 63.03 36.40 62.75 36.53 23-11 60.10 39.40 - -23-12 55.99 43.09 - -23-13 93.17 6.44 -23-14 90.77 7.30 92.54 7.335 23-15 45.10 54.47 45.32 54.27 23-17 73.26 26.42 - -24-02 58.95 40.56 57.05 42.43 24-11 37.54 61.38 - -24-13 91.29 8.27 - -24-16 78.49 21.11 78.04 21.37 24-18 73.12 26.51 - -24-19 64.49 35.03 63.00 36.83 24-01 92.63 6.77 - -24-04 89.83 9.61 - -24-06 41.80 57.64. - -24-14 89.97 9.44 89.77 9.40 24-17 79.51 20.07 - -25-01 93.85 5.82 - -25-02 75.34 24.09 - -25-03 80.68 18.73 81.17 19.21 25-05 38.56 60.87 37.87 61.40 25-06 62.27 36.98 61.43 37.76 25-07 46.70 52.57 43.01 55.82 25-09 91. 50 8.29 - -25-10 99.21 0. 03 98.39 0. 08 25-11 86. 38 13.07 86.41 12.95 25-12 38.91 60.50 - -25-13 49.11 50.21 48 . 05 50.78 25-14 61.20 38.46 61.11 38.28 25-16 68.12 31.37 68.18 31.44 25-17 77.08 22.80 76.91 22.52 181-01 41.86 57.58 - -181-03 44.60 53.66 44.48 54.07 182-02 99.66 0.06 - -183-02 86.23 36. 51 - -183-03 184-0 11.26 88. 05 11. 68 184-02 68.70 30.43 69.59 29.83 Table 5-22 - Results of electron microprobe analyses on the cores and edges of 41 gold grains. 154 = 189.3), whereas the mean fineness of the 23 edges i s 677.8 (standard deviation = 171.7). Examination of the 41 grain sections using backscatter electron imaging revealed the presence of minor, patchy rimming along the edges of seven grains. An eighth grain (25-5) displayed a complete Ag-poor rim. Comparison of core and edge compositions shows excellent correlations for core Au / rim Au (0.994) and core Ag / rim Ag (0.996). No changes are observed i n core composition between the proximal and d i s t a l p i t s . Figure (5.18) shows the s c a t t e r p l o t d i s t r i b u t i o n of Au, Ag grain core values for both the proximal and d i s t a l p i t s : the d i s t a l p i t values (six t o t a l ) p l o t evenly along the li n e a r trend with no apparent bias towards a p a r t i c u l a r composition. S i m i l a r i l y , no v a r i a t i o n i n grain edge or grain core Au-Ag composition i s observed with change i n s o i l p r o f i l e depth (Figures 5.19 and 5.20). 10 20 30 40 Ag (percent) 50 Figure 5.18 - P l o t of core Au vs core Ag a n a l y s e s , Proximal and D i s t a l p i t s . A horizon • B horizon A C horizon o C D 10 20 30 40 50 60 70 Ag (percent) Figure 5.19 - P l o t of edge Au vs edge Ag a n a l y s e s of the A , B and C h o r i z o n s , Proximal p i t . 100 qr 20 bo 80 60 a < 40 A horizon • B horizon A C horizon 10 20 30 40 Ag (percent) 50 60 70 F i g u r e 5.20 - P l o t of core Au vs core Ag a n a l y s e s o f the A, B and C h o r i z o n s , Proximal p i t . Chapter Six Discussion 159 6.1 Gold grain shape and composition The e f f e c t of s o i l formation on the morphology and composition of gold grains i n temperate environments i s poorly understood. Work by Freyssinet e t . a l . (1989), Mann (1984), Webster and Mann (1984), and Wilson (1984) has dealt with gold i n l a t e r i t i c or s a p r o l i t i c t r o p i c a l environments. Investigations of gold shape i n temperate environments have been r e s t r i c t e d to studies of gold grains i n t i l l with an emphasis on the effects of g l a c i a l transport ( A v e r i l l and Zimmerman, 1984; Sauerbrei et a l . , 1987; Thorleifson and Kristjansson, 1988). MacEachern and Stea (1985) c a r r i e d out deta i l e d work on the shape and composition of gold grains extracted from t i l l s downice from gold mineralization, but did not investigate the overlying s o i l layers. Comparison with these data sets i s therefore d i f f i c u l t . At the Nickel Plate mine, the s i m i l a r i t y i n composition of the gold grain cores and rims between s o i l p r o f i l e s i s i n contrast to the res u l t s found within t r o p i c a l l a t e r i t i c s o i l p r o f i l e s . Within l a t e r i t i c s o i l s , d i s s o l u t i o n , upwards transport and r e p r e c i p i t a t i o n of Au re s u l t s i n the formation of pure Au c r y s t a l s , grains or nuggets. The chemically intense nature of l a t e r i t e formation over long (several Ma) periods versus the short (10 Ka) duration of chemical a c t i v i t y associated with s o i l formation at the Nickel Plate 160 mine obviously i s a major factor i n gold grain behaviour. Ag depleted rims, seen i n l a t e r i t i c p r o f i l e s and a common feature of placer gold, are not prevalent. Only one grain displayed a complete rim, whereas f i v e other grains showed minor rimming. It i s l i k e l y that the s c a r c i t y of rimming i s a r e s u l t of the non-chemical (ie. mechanical) transport of the grains, and t h e i r limited residence time within the t i l l . However, i t i s also possible that abrasion of the grains during transport has removed any developed rims. Use of gold grain shape to estimate transport distance i s d i f f i c u l t due to the low number of grains removed from the two s o i l p r o f i l e s (Proximal p i t , 54 grains; D i s t a l p i t , 8 g r a i ns). However, the abundance of the grains between the two p i t s i s a r e l a t i v e indicator of proximity to the minesite. The d i f f e r e n t distances of transport between the two p i t s cannot be determined through the use of a quantitative shape factor (equation 5-4), possibly because of the low number of grains i n the d i s t a l p i t , and l i k e l y because no difference exists. Application of a simple, q u a l i t a t i v e method of grain shape c l a s s i f i c a t i o n (Dilabio, 1989; Sauerbrei, e t . a l , 1987) also indicates that no difference exists i n grain shape with either increased transport distance or location within the s o i l p r o f i l e . However, the small population size for the A, B and C horizons (n= 19, 19, 16 grains, respectively) may influence these r e s u l t s . 161 6.2 Residence s i t e s of Au i n s o i l and t i l l Size f r a c t i o n analysis of twenty-two samples indicates that t o t a l Au content remains constant with decreasing grain s i z e (Table 5-10). Analysis of l i g h t and heavy mineral f r a c t i o n s for the -420+212, -212+106 and -106+53 micron si z e f r a c t i o n s indicates that a s i g n i f i c a n t proportion of the Au (10 to 175 ppb) i s concentrated within the l i g h t f r a c t i o n , as inclusions of fin e gold grains (Table 5-8). Increase i n the Au content of the heavy mineral s i z e f r a c t i o n with diminishing grain size i s a function of the abundance of free gold grains within the heavy mineral f r a c t i o n . Au concentrations of the -420+212 micron l i g h t and heavy mineral fractions are equivalent (Tables 5-7 and 5-8), in d i c a t i n g that no free gold exists within the heavy mineral f r a c t i o n (Table 5-15). Concentration of Au within the -212+106 and -106+53 micron heavy mineral f r a c t i o n s increase with decreasing grain s i z e . This i s a r e f l e c t i o n of the d i s t r i b u t i o n of gold grain sizes within the deposit, the ef f e c t s of g l a c i a l abrasion upon the orebodies during g l a c i a t i o n and the ef f e c t of comminution on the entrained c l a s t s during g l a c i a l transport. Results of cyanide extraction on the -53 micron samples reveal that approximately 70% of the Au exi s t s as free gold grains or as gold weakly bound to clays / secondary iron 162 oxides. A lower average extraction e f f i c i e n c y of 54% f o r Au from the A horizon samples i s l i k e l y due to the higher organic content of these samples r e l a t i v e to the B and C horizons. Organic (carbonaceous) material i s known to impede the e f f i c i e n c y of the cyanide extraction process fo r Au (Avraamides, 1982). Paired t - t e s t s carried out on the Au content of each s i z e f r a c t i o n ( l i g h t and heavy fractions combined) indicate that a l l s i z e fractions have a s i m i l a r Au concentration. These r e s u l t s are i n disagreement with the work of DiLabio (1982a, 1982b, 1985 and 1988) who studied 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 of Au within several t i l l dispersion t r a i n s associated with gold mineralization. Au analysis was c a r r i e d out on ten to f i f t e e n gram subsamples of s i z e f r a c t i o n s sieved from a f i e l d sample of unspecified weight. Size f r a c t i o n s greater than 63 microns in diameter were ground to -63 microns p r i o r to analysis (DiLabio, 1988). No attempt was made to separate and analyse the heavy mineral f r a c t i o n of each si z e f r a c t i o n . From t h i s , DiLabio (1982a, 1982b, 1985 and 1988) concluded that Au concentrations were enriched i n the f i n e r fractions of the t i l l s , possibly through hydromorphic r e d i s t r i b u t i o n . However, as shown i n section 1.3, use of undersized coarse sample f r a c t i o n s w i l l impart a strong bias on the a n a l y t i c a l r e s u l t s . Coarse grained fract i o n s which are not representative w i l l c o n s istently return Au contents lower than t h e i r true 163 concentrations, due to the low pr o b a b i l i t y of encountering a gold grain (or grains) within the sample. Finer f r a c t i o n s , having a more representative d i s t r i b u t i o n of gold grains, w i l l return Au values more c h a r a c t e r i s t i c of the true concentration of the size f r a c t i o n . The end r e s u l t w i l l be the perception of an increase i n Au content with decreasing grain s i z e . Use of heavy mineral concentration techniques on large samples can a l l e v i a t e t h i s problem by concentrating a l l free gold grains within a single a n a l y t i c a l subsample. Analysis of the heavy mineral concentrate, combined with an analysis of the l i g h t mineral f r a c t i o n , w i l l give a r e s u l t with a s i g n i f i c a n t l y higher degree of rep r e s e n t i v i t y . 6.3 Va r i a t i o n of Au concentration with depth Within s o i l p r o f i l e s , Au concentrations of the -212 micron f r a c t i o n increase with depth. Increases i n Au content with depth are also noted for the -53 micron f r a c t i o n , the -212+106 micron l i g h t mineral f r a c t i o n and the -106+53 micron l i g h t mineral f r a c t i o n . No comparable patterns are observed with the -420+212 micron l i g h t mineral f r a c t i o n or the heavy mineral si z e f r a c t i o n s . Except for the samples of p i t 10 (sample #'s: 41, 42, 43, 44), re s u l t s obtained from cyanide extraction do not display a consistent pattern of Au increase with depth. 164 Several possible mechanisms exis t to explain the increase down p r o f i l e of Au within s o i l s . These mechanisms can be separated into two categories: i) primary agents (those occurring during the deposition or immediately a f t e r the deposition of the t i l l ) and i i ) secondary agents (modification of the Au content of the t i l l by s o i l forming processes which occur aft e r deposition). i) Primary Agents ( G l a c i a l / P e r i g l a c i a l ) Features of t h i s category involve processes which take place during the actual physical transport and deposition of the t i l l beneath the g l a c i e r sole, or immediately a f t e r exposure of the t i l l to the atmosphere, but before the onset of s i g n i f i c a n t s o i l forming processes. An example of t h i s would be the deposition of a non-auriferous, exotic ablation t i l l on a basal t i l l of l o c a l derivation. Similar r e s u l t s would be expected i f an auriferous basal t i l l were to be ov e r l a i n by either a second, nonauriferous basal t i l l or Au poor colluvium derived from unmineralized bedrock. F i e l d observations of the s o i l p r o f i l e s , do not however support t h i s interpretation. No s i g n i f i c a n t changes were observed i n gross physical c h a r a c t e r i s t i c s of the s o i l p r o f i l e s with depth; no paleosols, erosion layers, or changes i n o v e r a l l c l a s t (grains >1 cm diameter) shape or composition were observed. Observed changes i n compaction 165 and s o i l colour with depth are attributed to s o i l forming processes. No information i s available on the influence p e r i g l a c i a l e f f e c t s , such as sheetwash and cryoturbation, could have upon the d i s t r i b u t i o n of gold grains within modern-day s o i l p r o f i l e s . However, p e r i g l a c i a l a c t i v i t y does not appear to have altered the s o i l p r o f i l e s of the t h e s i s area. P e r i g l a c i a l a c t i v i t y i s generally r e s t r i c t e d to a r c t i c or alpine environments where permafrost e x i s t s . As deglaciation i n the region occurred r a p i d l y (Ryder, 1978) and was quickly followed by temperatures warmer than the present day (Lowdon e t . a l , 1971), the amount of time av a i l a b l e for p e r i g l a c i a l processes to operate was l i m i t e d . Cryoturbation features were not observed within the thesis area, although s o l i f l u c t i o n lobes were noted nearby (approximately one kilometre distant) within a small creek v a l l e y . The most probable cause of the observed Au d i s t r i b u t i o n i s also the simplest; the downward increase i n Au content i s a primary feature related to the dispersion of Au during g l a c i a l transport. Gold grains from the Nickel Plate mine entrained within the g l a c i e r sole would p r e f e r e n t i a l l y remain near the base of the t i l l u n t i l s u f f i c i e n t new material was incorporated to disperse the grains. A small component of v e r t i c a l mixing of the auriferous t i l l during 166 transport would r e s u l t i n upwards dispersion of the gold grains through the t i l l unit r e s u l t i n g i n the observed d i s t r i b u t i o n of Au values. Such models of g l a c i a l d i s p e r s a l are common within the l i t e r a t u r e (Rose, Hawkes and Webb, 1979) . P r o b a b i l i t y plots of the d i s t r i b u t i o n of Au values for each horizon (section 5.1.5) indicate that contrast between anomalous and background populations decreases upwards through the s o i l p r o f i l e . These differences are probably a r e s u l t of v e r t i c a l mixing of the t i l l during g l a c i a l transport. i i ) Secondary Agents Assuming that the i n i t i a l concentration of Au within the basal t i l l was uniform, then several processes e x i s t which would account for the observed variat i o n s i n Au content. Addition of organic material to the upper layers of the s o i l p r o f i l e during s o i l formation would r e s u l t i n the d i l u t i o n of the primary g l a c i a l material ( t i l l ) and a commensurate decrease i n the Au content. However, d i l u t i o n of the upper s o i l horizons cannot account for the observed va r i a t i o n s i n Au content with depth. For the de t a i l e d samples, the decrease of the weight proportion with depth of -53 micron material ranges from approximately 5 to 2 0%. A si m i l a r range of decreasing weight proportions (8 to 30%) i s observed for the -212 micron f r a c t i o n . Decrease i n Au concentrations within the s o i l p r o f i l e s range from 26.1 to 58.5%, too great a range to be explained simply by d i l u t i o n . 167 Lakin et al.(1974) suggested downward movement of gold grains within the s o i l p r o f i l e during s o i l creep as a possible device for increasing Au concentrations with depth. Gradual downslope movement and the accompanying churning motion of the s o i l s might progressively lower dense minerals, such as gold, through the s o i l p r o f i l e by density sorting. Less dense, more readily dislodged minerals adjacent to the gold grains would be moved a greater distance during downslope movement of the s o i l . Repetition of t h i s process would lead to the p a r t i a l segregation of dense grains within the lower horizons of the s o i l p r o f i l e . This process, however, cannot explain the increase i n Au content of the l i g h t mineral f r a c t i o n with depth nor does i t explain the e r r a t i c behavior of Au i n the heavy mineral f r a c t i o n . S o i l creep does not appear to be a cause for increased Au content with depth. 6.4 Va r i a t i o n of Au concentration with distance A l l sample media display the same c h a r a c t e r i s t i c pattern of Au d i s t r i b u t i o n : a decrease i n concentration with increasing distance from the mine. No downice displacement of elevated Au values i s observed. Displacement of the anomaly may have occurred, but as the study area begins approximately 200 meters downice of the minesite, 168 displacement i s impossible to determine with the availa b l e data. The observed dispersal curves for the A, B, C horizon p i t samples and the roadcut C horizon samples approximate negative exponential curves. These are analogous to data obtained by S h i l t s (1976) on the regional g l a c i a l dispersion of n i c k e l i n t i l l from the Thetford Mines area, and Bird and Coker (1987) on the l o c a l g l a c i a l dispersion of gold i n t i l l from the Owl Creek mine, Timmins, Ontario. Behaviour of the Au d i s t r i b u t i o n of the t i l l with increasing distance of transport can be infer r e d through the use of contrast r a t i o s . Contrast r a t i o s (the r a t i o of proximal to d i s t a l Au values) for various s i z e and density f r a c t i o n s are shown i n Table 6-1. The percent heavy mineral content contrast r a t i o s are similar for a l l three s i z e f r a c t i o n s (-420+212, -212+106, -106+53 microns); a decrease by a factor of approximately 3.5. Assuming that the source of heavy minerals ( i . e . garnet, diopside) i s r e s t r i c t e d to zones of a l t e r a t i o n within the Marble Line (see sections 3.4 and 3.5), then the decrease of the percentage of heavy minerals i s a r e s u l t of d i l u t i o n . The s i m i l a r i t y of the contrast r a t i o s of the size fractions indicates that comminution has not s i g n i f i c a n t l y influenced the heavy mineral grains. Had comminution played a s i g n i f i c a n t r o l e during g l a c i a l transport, then contrast r a t i o s would decrease with a decrease i n size f r a c t i o n , r e f l e c t i n g the p r e f e r e n t i a l comminution of coarse grains into f i n e r grains. 169 Sample Media -420+212 -212+106 -106+53 -53 Percent heavy minerals 3.8 3.3 3.5 Percent v l i g h t minerals 1.4 1.0 0.9 0.8 Au content HMF 12.5 3.9 2.2 Au content LMF 3.5 3.5 3.8 Percent Au heavy mineral f r a c t i o n 8.4 2.0 1.5 Percent Au l i g h t mineral f r a c t i o n 1.2 0.7 0.7 0.8 Table 6-1 - Contrast r a t i o s for a variety of sample media. Ratios are taken from Tables 5-6b, 5-7, 5-8 and 5-13. Minus 53 micron r a t i o s are l i s t e d as a l i g h t mineral f r a c t i o n , but are assumed to contain a s i g n i f i c a n t heavy mineral component. 170 Contrast r a t i o s for the Au content of the heavy mineral f r a c t i o n and the proportion of Au i n the heavy mineral f r a c t i o n are a l l greater than one, ind i c a t i n g a decrease with distance. Gold grains from the Nickel Plate mine were dispersed within the t i l l as they were transported downice. However, contrary to the l i g h t mineral f r a c t i o n Au concentrations or the percentage of heavy minerals, the contrast values of the heavy mineral f r a c t i o n Au contents also lessen with a decrease i n size f r a c t i o n . This decrease i n contrast values i s a re s u l t of the comminution of sulphide and / or limonite grains within the heavy mineral f r a c t i o n s , r e f l e c t i n g the tendency for comminution to grind down coarse grained material at a faster rate than f i n e grained material. During g l a c i a l transport, these r e l a t i v e l y s o f t , coarse grained sulphides or l i m o n i t i c materials were reduced i n size , l i b e r a t i n g f i n e r gold contained within t h e i r matrix, thereby increasing the proportion of gold within the f i n e r f r a c t i o n s . Nearly i d e n t i c a l contrast r a t i o s for the Au content of the l i g h t mineral size fractions are a r e s u l t of the nearly i d e n t i c a l Au concentrations of a l l three s i z e f r a c t i o n s . This s i m i l a r i t y of the Au content i s a manifestation of the f i n e grained (<10 micron) gold, t y p i c a l of the Nickel Plate orebodies, encapsulated within grains of the l i g h t mineral f r a c t i o n . Assuming an even d i s t r i b u t i o n of t h i s f i n e grained gold throughout the grains, v a r i a t i o n of the s i z e f r a c t i o n 171 analysed should not a l t e r the r e s u l t s . Comminution of coarse grains to smaller grain diameters also should not a l t e r the contrast r a t i o s . Only u n t i l the size f r a c t i o n analysed i s near to or less than the diameter of gold grains being analysed w i l l s i g n i f i c a n t changes i n the r e p r e s e n t i v i t y of an analysis occur. Since the contrast r a t i o s are independent of grain s i z e or comminution ef f e c t s , then the decrease i n Au content with distance i s a r e s u l t of d i l u t i o n . The s i m i l a r i t y of these contrast r a t i o s to the percent heavy mineral content contrast r a t i o s suggests that d i l u t i o n i s a more s i g n i f i c a n t e f f e c t than comminution. A three dimensional dispersion t r a i n , l i k e those described by Drake (1983) or M i l l e r (1984) i s not present within the depth of t i l l sampled. High Au values are not observed to ascend towards the surface with increasing distance from the mine. Rather, they consistently increase i n value with depth (see section 5.1.3). Lack of a r i s i n g dispersion t r a i n may be due to several factors: 1) the t i l l i s t h i n (1 to 5 meters) and the underlying bedrock s u f f i c i e n t l y uneven to prevent or disrupt a r i s i n g dispersion t r a i n ; 2) post g l a c i a l processes have destroyed the presence of a t r a i n ; or, 3) the material composing the t i l l d id not originate d i r e c t l y from the mineralized bedrock of the mine, but i s reworked colluvium or t i l l from pre Fraser g l a c i a t i o n times. I t i s l i k e l y that 1) and 3) are the 172 factors which prevented the formation of a r i s i n g dispersion t r a i n . 6.5 O r i g i n of the dispersion t r a i n Relationships between the shape of the dispersion t r a i n , the r e s t r i c t i o n of mineralization within the Marble Line and the l o c a l ice movement d i r e c t i o n indicate that the dispersion t r a i n did not originate d i r e c t l y from the Nickel Plate mine area (see Figure 4.1). Rather, the dispersion t r a i n i s o f f s e t from a d i r e c t downice path from the mine by several hundred metres. The ice which deposited the dispersion t r a i n did not flow d i r e c t l y over the deposit, but flowed over mineralized colluvium which originated from the mine area. A moraine located across the C a h i l l Creek v a l l e y , downslope from the mine, indicates that the g l a c i e r r e s i d i n g within the v a l l e y was stationary for a period s u f f i c i e n t for supraglacial t i l l to develop. During g l a c i a l retreat, t h i s overlying blanket of t i l l was deposited upon the previously deposited basal t i l l . 173 6.6 Recommendations for Mineral Exploration 6.6.1 Determination of a representative f i e l d sample  size As discussed i n section 1.3, the size of sample required to give a minimum precision of 50% at the 95% confidence l e v e l i s one which contains 2 0 p a r t i c l e s of gold ( C l i f t o n et a l . , 1969). Precision of an analysis varies with the number of gold grains i n the sample; a decrease i n the number of grains r e s u l t s i n a reduction of the p r e c i s i o n . Based on the work of C l i f t o n et a l . (1969), Nichol et a l . (1989) demonstrated how the r e l a t i v e standard deviation ( c o e f f i c i e n t of variation) of a set of (50) duplicate analyses could be u t i l i z e d to determine the number of gold grains within a p a r t i c u l a r sample weight, and therefore the s i z e of sample required to contain 20 p a r t i c l e s of gold. However, the primary goal of a geochemical s o i l survey i s not to obtain reproducible Au analyses for each i n d i v i d u a l sample, but to r e l i a b l y i d e n t i f y a pattern of anomalous values which r e f l e c t s bedrock mineralization. Stanley and Smee (1988, 1989) demonstrated that samples containing 1 grain of gold, on average, could be used to define a geochemical s o i l anomaly. A s i m i l a r approach was taken here, such that the amount of -53 micron f r a c t i o n s o i l containing 1 grain of gold was 174 calculated for each of the twenty-two detailed samples. The -53 micron f r a c t i o n was selected as i t contains approximately s i x t y to seventy percent (by mass) of the Au within the -420 micron f r a c t i o n . Of t h i s proportion, an average of seventy percent exists as free gold (see section 5.3). Therefore, the greatest chance of encountering a single free grain of gold w i l l occur within the -53 micron f r a c t i o n . Table (6-2) l i s t s the calculated sample s i z e s containing a minimum of 1 grain of gold for the -53 micron s i z e f r a c t i o n . Also l i s t e d i s the mass of -2000 micron (-2 mm) f r a c t i o n containing the required amount of -53 micron material. The number of grains i n the -53 micron s i z e f r a c t i o n was calculated under the very conservative assumption that a l l gold exists as free grains 50 microns i n diameter. Only one sample (#162) requires more than 3 0 grams of -53 micron material to obtain, on average, 1 grain of gold. In general, less than 30 grams of -2000 micron material i s required to obtain a single gold grain i n the -53 micron f r a c t i o n . The maximum calculated -2000 micron sample s i z e (63 grams) i s a reasonable minimum f i e l d sample s i z e l i m i t ; a l l samples are then guaranteed to contain at lea s t 1 grain of gold, on average. The wet sieving technique used to p a r t i t i o n the various s i z e f r a c t i o n s i s up to seven times more e f f i c i e n t at 175 # g r a i n s mass f o r mass f o r of g o l d 1 g r a i n 1 g r a i n i n -53 i n -53 i n -2000 Sample Horizon micron micron micron f r a c t i o n f r a c t i o n f r a c t i o n 14 A 9.1 3.3 6.8 15 B 11.6 2.6 5.7 16 C 12.6 2.4 6.3 41 A 5.9 5.1 11.6 42 B 6.7 4.5 9.6 43 CI 11.6 2.6 6.4 44 C2 17.7 1.7 5.4 122 A 2.1 14.4 28.2 123 B 3.6 8.4 17.5 124 CI 4.5 6.7 16.0 125 C2 4.6 6.5 14.6 127 A 1.6 18.4 33.9 128 B 2.7 11.2 20.6 129 CI 3.9 7.8 15.5 130 C2 3.6 8.4 18.2 162 A 0.9 33.7 57.8 163 B 1.6 18.4 40.8 164 C 1.2 25. 3 62.8 186 A 1.3 22.4 36.0 187 B 2.7 14.4 23.0 188 CI 2.7 11.2 17.7 189 C2 2.8 10.6 18.2 Table 6-2 - Estimates of the number of g o l d g r a i n s i n the minus 53 micron f r a c t i o n (assuming a g r a i n diameter of 50 mic r o n s ) , the mass of -53 micron sample r e q u i r e d t o c o n t a i n 1 g r a i n of g o l d , and the mass of -2000 micron m a t e r i a l n e c e s s a r y t o p r o v i d e the r e q u i r e d mass of -53 micron sample. Mass of each sample i s r e p o r t e d i n grams. 176 extracting the -53 micron f r a c t i o n than conventional dry si e v i n g (Day, 1988). Sampling programs which u t i l i z e standard commercial labratory dry sieving techniques instead of wet sieving should increase i n the amount of -2000 micron material sampled i n the f i e l d to approximately 400 grams. 6.6.2 Analysis of heavy mineral concentrates versus the  -53 micron f r a c t i o n Use of heavy mineral concentrates i n gold exploration i s a r e l a t i v e l y common practice. Analysis of a ten or t h i r t y gram heavy mineral concentrate derived from a bulk sample (hundreds to thousands of grams) e f f e c t i v e l y represents the analysis of the entire bulk sample, provided a l l the Au e x i s t s as free gold. Au retained within the l i g h t mineral f r a c t i o n w i l l not be detected through t h i s technique. Results of heavy mineral concentrate analyses were e r r a t i c with poor d e f i n i t i o n between anomalous and background populations, undoubtedly a r e s u l t of the nugget e f f e c t . Use of the -53 micron (-270 mesh) f r a c t i o n , however, was more r e l i a b l e and provided better d e f i n i t i o n of anomalous and background populations. The -53 micron f r a c t i o n i s superior to heavy mineral concentrates (or any other sampling media) since i t s fine grain s i z e reduces the nugget e f f e c t and yet s t i l l provides good contrast between 177 sampling s i t e s located at proximal and d i s t a l locations from the minesite. 6.6.3 Analysis by f i r e assay - atomic absorption versus  cyanide extraction Cyanide extraction offers comparable r e s u l t s to those obtained through conventional FA-AAS performed on -53 micron samples. Unlike FA-AAS, cyanide extraction i s incapable of analyzing for Au held within s i l i c a t e s ; micron or submicron sized gold grains trapped within a s i l i c a t e grain would not be detected. However, since seventy percent of the Au within the -53 micron f r a c t i o n exists as free grains and i s detectable by the cyanide extraction technique, the adverse e f f e c t s of the encapsulated gold i s n e g l i g i b l e . Cyanide extraction would be more advantageous than FA-AAS on bulk samples greater than t h i r t y grams i n weight. Nugget e f f e c t s would be minimized i f 100 to 1000 gram samples could be analysed by cyanide extraction. However, care should be taken to exclude A horizon s o i l s , as the higher organic content of these horizons impedes the a b i l i t y of cyanide to dissolve gold. 178 6.6.4 Optimum method for indicating source l o c a t i o n of  the geochemical anomaly Attempts to use gold grain shapes to determine transport distance and therefore, source location ( A v e r i l l and Zimmerman, 1986; DiLabio, 1989), were not successful. Comparison of the geochemical response of the various s i z e and density fractions indicates that the strongest geochemical gradient (contrast ratio) would be found by analysis of the -53 micron C horizon f r a c t i o n . The C horizon i s the u n i t most representative of the o r i g i n a l , unweathered t i l l . Both the A and B horizons have undergone s u f f i c i e n t modifications by s o i l forming processes to disrupt t h e i r o r i g i n a l Au d i s t r i b u t i o n , thereby decreasing t h e i r anomalous to background contrast. Use of the -53 micron f r a c t i o n would enhance contrast by increasing the r e p r e s e n t i v i t y of each sample and attenuating the chance of nugget e f f e c t . 6.6.5 Optimum f i e l d sample Based on the above res u l t s , a f i e l d sampling program at the Nickel Plate mine should attempt to recover samples which w i l l provide a minimum of 30 grams of -53 micron (ASTM -270 mesh) material from the C horizon. In order to obtain 3 0 grams of -53 micron material through wet sieving, a minimum of 63 grams of -2000 micron (ASTM -10 mesh) material 179 should be sampled i n the f i e l d . If dry sieving techniques are to be used, then an approximate sample weight of 400 grams of -2000 micron material should be f i e l d sampled. This s o i l sampling technique w i l l provide the best contrast and sample representivity of a l l the size and density f r a c t i o n s considered. Chapter Seven Conclusions and Recommendations 181 7.1 Conclusions and Recommendations 1) At the Nickel Plate mine, a gold dispersion t r a i n i s hosted within a t h i n (<1 to 5 metre thick) unit of oxidized basal t i l l . This dispersion t r a i n extends approximately one kilometre from the minesite and p a r a l l e l s the d i r e c t i o n of l o c a l i c e movement. 2) Au concentrations of the s o i l p r o f i l e s increase with depth, while the Au content of each horizon decrease with distance. Both are primary features related to the mechanical dispersion of t i l l during g l a c i a l transport. Post g l a c i a l s o i l development does not appear to have influenced the d i s t r i b u t i o n of Au within the t i l l . 3) Heavy mineral concentrates and l i g h t mineral f r a c t i o n Au abundances indicate that d i l u t i o n by a factor of 3.5 occurs within the t i l l over a distance of approximately 800 metres. This i s a r e s u l t of the entrainment of new material into the t i l l during g l a c i a l transport. However, Au contents of the heavy mineral s i z e fractions indicate that gold grains are both d i l u t e d and comminuted during transport. 4) Au content of the t o t a l size fractions are equivalent; no changes i n Au abundance are observed with a change i n grain s i z e . 182 5) Cyanide extraction - atomic absorption spectometry indicates that approximately 70% of the Au i n the -53 micron f r a c t i o n e x i s t s as free gold or gold weakly bound to clays and / or secondary iron oxides. Lower extraction e f f i c i e n c i e s for A horizon samples are l i k e l y a r e s u l t of higher l e v e l s of organic material within the A horizon. 6) Chemical a c t i v i t y has not altered the composition of gold grains found within the s o i l p r o f i l e s . Au enriched edges (rims) are generally absent; grain core compositions are i d e n t i c a l to grain edge Au-Ag values. 7) Compositional and / or morphological differences i n gold grains are not ind i c a t i v e of distance of transport or loc a t i o n within the s o i l p r o f i l e . However, the r e l a t i v e abundance of grains between locations can be used as an indi c a t o r of proximity to the minesite. 8) In order to obtain the best sample re p r e s e n t i v i t y and contrast between anomalous and background Au populations i n the v i c i n i t y of the Nickel Plate mine, FA-AAS analysis for Au should be car r i e d out on 3 0 grams of -53 micron C horizon material. I f conventiomal dry sieving techniques are used, the optimum f i e l d sample should have a minimum mass of 370 grams of -2000 micron (-2 mm) material. 183 References 184 References A l l e n , J . and Strobel, G. (1966) The assimmilation of HC^N by a variety of fungi. Can. J. 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Appendix A n a l y t i c a l Data and Sample Weights 195 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH +2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 2 2 1 30 3 3 1 55 4 4 1 110 6 2 2 20 7 3 2 70 8 4 2 100 10 2 3 13 11 3 3 67 12 4 3 100 14 2 4 25 15 3 4 72 16 4 4 110 18 2 5 18 19 3 5 55 20 4 5 93 21 4 5 100 23 2 6 20 24 3 6 57 25 4 6 100 27 2 7 42 28 3 7 63 29 4 7 110 31 2 8 25 32 3 8 58 33 4 8 110 34 4 8 120 36 2 9 24 37 3 9 58 38 4 9 90 39 4 9 105 41 2 10 13 42 3 10 47 43 4 10 80 44 4 10 130 46 2 11 23 47 3 11 52 48 4 11 115 49 4 11 130 51 2 12 19 52 3 12 58 53 4 12 140 55 2 13 13 56 3 13 60 7.10 619.36 284.18 7.10 883.46 259.41 7.20 781.14 317.93 7.10 479.25 132.55 7.40 978.15 254.21 7.40 826.07 244.54 6.60 579.14 181.02 6.90 648.89 231.20 7.20 629.82 281.77 7.45 699.81 245.35 7.15 936.27 259.08 7.75 832.93 327.22 7.00 697.19 242.72 7.20 481.43 247.74 7.00 725.62 265.98 7.15 554.69 294.96 6.50 695.43 186.72 7.40 667.65 235.88 7.15 842.33 273.17 6.65 663.04 282.55 7.00 748.88 277.26 7.30 1132.68 439.98 6.05 839.71 312.29 7.00 670.99 306.17 7.05 867.35 329.42 7.20 771.69 271.38 6.60 836.58 278.89 6.95 1015.65 341.48 7.00 836.12 534.39 7.20 1346.22 365.30 6.65 967.97 338.03 6.80 872.69 296.69 6.90 1050.20 365.04 7.20 1399.98 457.93 6.90 871.40 263.38 7.00 964.25 339.28 7.00 773.39 346.11 7.10 655.61 346.85 6.65 864.81 218.34 6.70 1023.22 326.21 7.15 1067.45 376.89 7.10 1156.36 341.23 6.85 1350.86 450.50 115.93 789.92 275 99.46 567.47 380 83.61 413.12 325 42.20 320.63 6350 97.80 518.01 495 81.10 701.72 280 78.90 556.54 200 102.83 661.43 250 135.63 565.88 15 100.94 696.02 410 117.13 660.87 115 174.21 558.59 225 99.02 522.93 95 108.77 370.76 270 106.43 410.14 520 145.69 623.86 285 76.98 475.29 225 100.61 667.64 200 122.08 642.21 305 134.69 869.84 1580 133.92 582.18 285 239.53 897.40 435 134.36 786.24 135 139.18 683.47 310 109.91 547.62 485 108.62 647.46 260 110.56 649.29 425 147.54 698.00 240 165.15 510.36 535 215.02 884.30 485 120.11 683.13 155 112.12 573.29 150 140.73 665.06 360 195.86 660.74 400 83.47 496.73 185 140.80 661.55 -10 152.30 482.00 465 145.03 707.20 675 102.18 592.63 210 118.15 653.56 195 162.67 835.00 810 104.66 574.75 80 137.08 784.70 480 196 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH 4-2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 57 4 13 104 58 4 13 115 60 2 14 18 61 3 14 50 62 4 14 115 64 2 15 8 65 3 15 55 66 4 15 90 67 4 15 125 70 2 16 18 72 4 16 115 73 4 16 130 75 2 17 14 99 4 17 60 100 4 17 80 101 4 17 115 79 2 18 30 80 3 18 69 81 4 18 108 82 4 18 132 83 4 18 140 85 2 19 8 86 3 19 55 87 4 19 106 88 4 19 110 90 2 20 8 92 4 20 115 93 4 20 125 95 2 21 44 96 3 21 75 97 4 21 100 98 4 21 130 103 2 22 22 104 3 22 55 105 4 22 95 106 4 22 130 108 2 23 35 109 3 23 60 110 4 23 85 111 4 23 115 113 2 24 22 114 3 24 50 115 4 24 70 6.90 970.70 403.74 6.90 1433.23 481.31 6.75 1282.51 280.89 7.00 1270.35 452.80 7.40 1338.44 325.54 6.90 858.67 203.23 6.70 1068.00 372.93 6.90 1183.49 565.21 7.15 1170.81 510.34 6.85 757.77 207.54 6.90 1741.49 448.97 7.10 712.69 266.36 7.00 634.23 194.40 6.70 1126.68 272.07 6.90 1227.74 419.32 6.60 1226.68 343.83 6.75 825.37 280.99 6.90 782.15 326.92 6.85 837.89 378.34 7.15 508.51 252.53 7.20 732.49 342.15 6.80 931.57 207.61 6.90 761.83 244.50 6.90 926.14 415.02 6.70 907.49 443.14 7.15 615.65 247.55 7.20 1513.90 688.86 6.90 922.32 368.90 7.00 840.24 298.35 7.00 1018.04 394.65 7.05 1186.51 637.23 7.00 756.83 386.03 6.90 704.33 224.34 7.00 942.48 387.43 7.60 1570.89 630.64 7.60 682.52 284.09 6.70 970.30 224.89 7.20 633.65 146.52 7.50 692.82 286.60 7.20 894.63 297.17 7.00 551.56 183.94 7.15 560.09 194.74 6.80 1090.53 373.42 158.48 469 .55 485 208.74 707 .66 1025 78.84 436.25 100 150.37 661.09 135 128.51 463 .64 295 61.49 345.47 155 121.32 588 .95 210 184.77 672 .39 445 217.49 610 .48 285 69.47 448 .33 60 143.13 524 .32 145 90.22 421 .11 150 69.00 427 .40 75 110.20 417.00 150 166.71 473.36 225 132.70 665 .37 220 80.80 549 .75 60 122.97 658 .78 130 158.25 0.00 0 104.44 619 .75 265 141.24 805 .69 255 62.49 0.00 0 80.84 385 .26 65 178.09 577 .05 145 164.94 451 .67 320 84.58 416 .12 90 285.69 622 .35 275 155.72 421 .98 155 112.48 497 .87 410 140.93 480 .98 165 244.37 574 .55 185 186.77 511 .02 225 84.13 653 .09 110 162.62 968 .13 105 239.45 897 .13 195 112.72 677 .18 110 82.01 699 .33 50 63.06 418 .47 145 119.28 606 .92 115 79.98 239 .90 190 71.89 583 .96 35 83.08 673 .36 85 148.62 874 .60 155 197 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH +2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 116 4 24 115 118 2 25 21 119 3 25 42 120 4 25 85 122 2 26 20 123 3 26 45 124 4 26 90 125 4 26 135 127 2 27 18 128 3 27 42 129 4 27 65 130 4 27 95 132 2 28 35 133 3 28 57 134 4 28 85 135 4 28 115 137 2 29 38 138 3 29 65 139 4 29 90 140 4 29 115 142 2 30 25 143 3 30 49 144 4 30 82 145 4 30 115 147 2 31 15 148 3 31 49 149 4 31 79 150 4 31 115 152 2 32 25 153 3 32 50 154 4 32 75 155 4 32 100 157 2 33 26 158 3 33 48 159 4 33 75 160 4 33 115 162 2 34 35 163 3 34 55 163 3 34 55 164 4 34 100 166 2 35 30 167 3 35 50 169 4 35 100 7.30 433.16 185.47 7.15 482.75 163.68 7.20 544.30 192.19 7.15 595.84 258.55 6.80 649.14 163.13 7.00 974.76 293.78 7.10 1034.08 323.28 6.90 1792.59 608.29 6.85 549.42 187.47 7.20 533.03 180.87 7.20 737.14 247.49 6.75 824.97 269.61 6.90 453.55 178.36 7.30 368.72 187.58 7.00 764.11 324.23 7.20 1447.06 560.59 7.10 747.66 188.62 7.10 747.74 258.70 7.15 550.02 243.99 7.25 877.50 285.42 6.90 474.97 166.04 7.10 536.53 209.27 7.15 579.48 154.34 7.15 1234.21 483.01 7.00 400.85 137.81 7.25 902.80 243.70 7.15 1068.38 346.12 7.60 786.46 313.76 7.35 388.24 127.61 7.50 387.25 185.32 7.50 555.60 206.51 7.85 1085.51 412.74 7.30 534.08 156.26 7.50 687.07 127.65 7.50 860.31 286.90 7.50 760.17 386.27 7.65 477.34 160.17 7.60 828.91 185.44 7.50 828.91 185.44 7.70 928.46 287.80 7.60 555.36 127.03 7.60 503.91 172.17 7.95 617.25 212.57 76.09 580.78 60 65.43 554.02 45 84.67 585.45 250 100.68 788.54 175 50.98 523.76 35 116.33 788.75 90 120.77 701.89 105 172.03 115.92 85 72.51 686.04 65 66.91 515.66 60 88.41 660.01 105 86.97 569.66 90 69.73 589.05 55 74.15 512.13 95 136.55 488.45 285 187.75 507.65 250 80.34 614.07 100 105.30 614.72 175 86.40 529.07 65 110.38 574.84 830 57.41 450.50 155 79.77 605.23 30 62.71 417.28 130 165.12 926.20 70 41.45 424.06 65 84.84 843.01 35 127.68 958.92 75 115.29 716.70 45 46.05 437 .36 85 66.90 589.05 60 85.20 717.12 65 151.39 878.74 50 54.47 523.34 40 48.26 352.07 100 114.32 758.91 55 134.13 787.13 75 52.94 584.00 40 72.92 519.21 65 72.92 519.21 65 87 .77 566.18 35 45.17 557.67 20 68.13 752.91 25 86.46 725.76 35 198 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH +2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 171 2 36 28 172 3 36 48 173 4 36 70 174 4 36 110 176 2 37 11 177 3 37 45 178 4 37 80 179 4 37 125 181 2 38 34 182 3 38 55 183 4 38 80 184 4 38 110 186 2 39 30 187 3 39 50 188 4 39 72 189 4 39 105 191 2 40 35 192 3 40 53 193 4 40 80 194 4 40 110 196 2 41 30 197 3 41 60 198 4 41 90 200 2 42 28 201 3 42 52 202 4 42 77 203 4 42 105 206 3 43 45 207 4 43 75 208 4 43 100 211 2 44 27 212 3 44 38 213 4 44 50 214 4 44 70 216 2 45 15 217 3 45 35 218 4 45 65 219 4 45 100 221 2 46 30 222 4 46 65 223 4 46 100 225 2 47 12 227 9 47 42 7.00 416.25 119.61 7.50 488.80 126.07 7.45 303.88 137.18 7.60 436.52 174.82 7.20 769.57 171.87 7.00 414.08 184.71 7.60 571.76 226.13 7.50 1496.97 285.62 7.30 427.61 141.20 7.35 485.78 185.04 7.70 1025.85 174.81 7.85 579.82 165.54 7.18 376.18 117.92 7.30 323.20 ,136.92 7.50 399.10 85.25 7.80 677.19 189.49 7.15 364.23 182.95 7.45 567.76 184.50 7.45 974.22 256.05 7.80 786.86 296.05 7.70 670.79 185.45 7.65 301.37 106.13 7.90 306.93 110.82 7.15 457.79 185.32 7.25 484.44 176.48 7.00 283.92 146.90 7.75 215.15 92.90 7.70 12.51 26.33 7.30 636.95 170.05 7.40 681.34 142.08 7.60 1.55 4.25 7.70 6.28 13.20 7.25 5.27 16.25 7.50 797.82 180.88 7.60 47.32 21.05 7.70 51.32 17.15 7.80 539.57 157.35 7.35 428.13 161.66 7.80 35.00 25.78 7.70 784.58 385.28 7.70 752.41 231.43 7.65 45.87 22.27 7.70 4.58 9.68 37.41 511.31 15 44.73 531.55 25 56.01 384.32 245 72.08 375.63 45 55.35 623.21 10 66.84 648.97 40 86.58 563.44 65 152.12 746.99 35 42.24 435.47 15 72.70 590.00 40 61.88 507.93 45 59.57 519.65 20 43.23 583.85 30 49.41 695.34 45 28.30 418.13 55 71.32 684.28 95 73.54 845.29 65 70.88 610.20 115 86.64 502.57 310 124.50 588.16 70 68.89 658.96 70 43.98 498.55 35 53.76 788.42 30 67.35 674.26 70 68.89 460.68 95 71.70 638.22 70 53.82 531.83 55 14.30 584.37 10 59.19 280.72 85 45.10 259.56 55 4.19 233.17 45 3.23 223.70 -15 7.31 170.91 105 71.43 328.88 60 13.86 569.89 20 8.34 639.84 20 69.43 394.88 40 75.25 446.74 45 14.61 283.91 20 174.34 637.49 55 85.95 346.76 75 14.07 466.18 35 8.60 455.56 140 1 9 9 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH +2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 228 4 47 63 229 4 47 100 231 2 48 10 233 4 48 85 235 2 49 10 236 3 49 25 237 4 49 55 240 2 50 40 244 2 51 26 245 4 51 63 246 4 51 100 250 4 52 62 258 2 53 100 259 3 53 45 260 4 53 80 261 4 53 115 262 4 54 180 264 4 55 130 266 4 56 150 267 4 56 200 268 4 57 185 269 4 57 230 272 4 59 145 273 4 59 185 275 4 60 240 277 4 61 250 278 4 62 200 279 4 63 200 280 4 64 150 283 4 66 140 284 4 66 260 287 4 68 200 289 4 70 200 290 4 72 80 292 4 73 160 293 4 74 130 294 2 76 15 295 3 76 45 296 4 76 120 297 2 77 30 299 4 77 105 300 4 78 53 301 4 78 140 7.60 334.64 64.30 7.80 346.04 177.60 7.85 18.90 13.79 7.85 611.95 167.27 7.50 47.28 23.02 7.20 181.16 74.89 7.40 896.13 158.93 7.60 523.91 58.36 7.50 118.77 33.11 7.70 814.99 353.12 7.60 445.76 202.63 8.00 389.96 207.20 6.80 322.97 123.28 6.90 473.28 155.52 7.20 1128.38 365.53 7.40 957.34 255.40 7.90 682.22 393.36 7.75 825.62 396.36 7.60 830.33 429.38 7.70 1129.37 433.15 7.40 1069.40 312.48 7.50 1253.23 302.22 6.90 807.34 325.34 7.40 520.75 258.15 7.25 342.11 99.23 7.40 1096.85 443.93 7.30 1036.37 589.08 7.50 875.25 377.17 7.65 1059.59 468.60 7.50 1004.85 449.17 7.50 544.90 243.89 8.00 1042.08 211.23 7.50 598.03 279.06 7.15 452.27 126.54 7.70 749.83 309.58 7.60 1261.28 323.55 7.30 322.97 154.88 7.75 422.63 136.54 7.50 381.32 241.14 7.45 325.33 88.45 7.50 555.22 197.54 7.50 349.59 176.54 7.90 561.77 188.44 17.98 259.77 50 65.57 564.98 75 11.03 183.44 15 63.18 397.22 300 20.00 322.35 20 26.55 591.36 60 58.12 360.62 200 104.68 546.19 170 19.15 466.48 10 149.51 480.19 80 86.15 682.71 40 85.78 576.26 70 42.52 269.98 320 52.63 283.83 140 108.14 380.47 860 67 .57 247.05 470 137.28 239.98 720 134.05 418.70 1060 126.74 244.37 1030 77.16 101.31 5070 123.99 323.59 470 103.75 226.94 590 115.13 464.69 400 84.31 210.96 400 35.09 543.15 1280 204.18 689.77 610 140.82 635.21 770 140.79 763.68 290 196.68 954.47 290 131.57 419.50 345 76.18 520.98 80 47.09 128.85 60 380.91 540.29 370 63.57 421.98 20 46.95 154.53 40 122.14 502.86 160 70.03 681.84 90 58.55 502.72 100 99.90 896.42 185 35.44 449.75 60 65.48 653.25 50 76.11 608.31 130 73.94 654.88 80 200 Nickel Plate 1987 Sample data Size F r a c t i o n Samp Horzn P i t Depth pH +2000 -2000 -420 -212 Au # (cm) (grams) +420 +212 (grams) (ppb) (grams) (grams) 302 2 80 30 304 4 81 110 305 2 82 50 306 3 82 70 308 2 83 30 310 4 83 125 311 2 84 35 312 4 84 170 313 4 84 240 315 4 85 210 316 2 86 40 317 3 86 60 318 4 86 130 320 4 87 0 7.25 255.09 74.84 7.05 516.37 141.88 7.55 364.19 167.09 7.65 502.36 204.80 7.40 353.90 137.09 7.80 943.22 401.87 7.60 711.88 154.34 7.90 432.43 144.60 7.80 465.53 228.44 7.60 381.55 188.59 7.60 548.45 163.86 7.50 839.65 320.81 7.55 1185.48 313.41 8.10 283.34 114.56 29.17 327.57 20 60.15 364.11 40 63.24 582.26 80 77.80 476.27 170 52.32 471.41 30 84.52 378.75 60 49.42 339.73 120 49.05 608.02 60 98.07 791.65 160 67 .10 541.24 100 50.90 397.16 100 93.79 262.53 270 93.46 429.93 230 53.65 377.62 10 2 0 1 Nickel Plate 1987 Size F r a c t i o n weight data Detailed Samples Samp P i t Horzn -2000 -420 -212 -106 -53 T o t a l # +420 +212 +106 +53 (grams) (grams) (grams) (grams) (grams) (grams) 14 4 2 617.75 241.05 309.34 235.33 1324.02 2727.49 15 4 3 706.00 321.31 318.22 216.93 1298.82 2861.28 16 4 4 869.64 417.24 342.84 235.56 1126.47 2991.75 41 10 2 723.98 248.00 269.37 187.38 1104.15 2532.88 42 10 3 870.61 310.56 261.60 157.91 1403.52 3004.20 43 10 4 1097.57 424.63 272.18 289.88 1400.92 3485.18 44 10 4 1235.72 482.34 382.05 250.26 1078.65 3429.02 122 26 2 359.58 145.05 171.67 129.95 842.92 1649.17 123 26 3 784.52 337.09 325.19 234.07 1554.42 3235.29 124 26 4 763.95 313.67 262.37 172.26 1101.19 2613.44 125 26 4 1287.22 475.98 461.19 321.06 2056.42 4601.87 127 27 2 477.43 228.03 243.09 167.19 1313.92 2429.66 128 27 3 443.67 195.33 208.97 131.70 1167.01 2146.68 129 27 4 427.84 206.60 175.42 142.32 959.68 1911.86 130 27 4 507.82 229.15 181.02 119.08 892.54 1929.61 162 34 2 357.45 136.22 175.76 110.70 1084.65 1864.78 163 34 3 477.36 201.60 172.07 114.90 789.54 1755.47 164 34 4 757.88 255.12 237.73 200.95 975.70 2427.38 186 39 2 281.79 111.75 177.67 123.49 1146.37 1841.07 187 39 3 301.78 113.02 179.54 141.50 1242.22 1978.06 188 39 4 221.43 86.26 111.63 104.66 901.90 1425.88 189 39 4 389.59 155.19 154.96 134.99 1168.88 2003.61 <5 Nickel Plate 1987 Size and Density f r a c t i o n weight data Samp -420 -420 -212 -212 -106 -106 # +212 +212 +106 +106 +53 +53 l i g h t heavy l i g h t heavy l i g h t heavy 14 187 .37 53.48 244.95 63.89 183 .53 50.72 15 245 .30 76 .56 232.37 86.51 156 .63 59.98 16 314 .31 103 .46 238.38 104.76 160 .69 74.85 41 194 .99 53.00 209.77 59.47 145 .38 41.09 42 242.42 68 .98 199.76 61.99 118 .48 39.02 43 331.06 94 .34 198.32 73.77 221 .91 68.78 44 370 .58 114 .10 277.61 106.00 182 .60 68.52 122 127 .72 17 .33 151.72 20.11 115.32 14.18 123 285 .16 52 .53 270.86 54.85 198 .39 35.57 124 275 .52 38 .51 223.65 38.88 148 .12 23.65 125 412 .21 64 .25 389.68 71.61 273 .30 46.32 127 203 .55 24 .96 214.53 27.68 145 .55 20.92 128 175.40 19 .80 182.92 25.85 114.89 16.19 129 181 .42 24.96 147.97 26.82 117 .95 23.22 130 199 .53 29 .12 149.49 27.75 108 .64 9.93 162 121 .80 14.10 158.13 17.21 101 .56 8.48 163 187 .20 14 .48 156.21 15.62 106.86 7.21 164 251 .15 3 .73 232.90 4.32 196 .66 3.55 186 98 .34 13 .01 159.04 17.90 108.11 14.35 187 97 .03 15 .67 158.08 21.19 121 .60 19.15 188 71 .86 13 .92 95.24 15.85 91 .95 12.05 189 119 .10 35 .65 127.39 27.06 117 .08 17.05 203 N i c k e l Plate 1987 Size and Density f r a c t i o n Au analyses Samp -420 -420 -212 -212 -106 -106 -53 # +212 +212 +106 +106 +53 +53 l i g h t heavy l i g h t heavy l i g h t heavy 14 85 110 70 805 40 1060 305 15 130 2200 90 100 80 875 390 16 150 175 125 505 125 2210 425 41 120 130 65 1115 45 975 200 42 110 180 65 935 50 1360 225 43 90 895 105 1585 80 725 390 44 105 125 175 1650 120 1685 595 122 30 50 40 45 20 330 70 123 55 6250 55 385 45 725 120 124 80 40 60 305 40 735 150 125 65 60 80 1180 55 785 155 127 45 60 20 420 20 560 55 128 50 45 35 165 40 1070 90 129 40 35 50 45 30 585 130 130 70 40 60 365 30 2120 120 162 20 20 20 1720 25 140 30 163 10 40 20 615 10 1360 55 164 10 25 10 70 10 -30 40 186 35 25 35 385 20 420 45 187 50 155 40 465 30 760 70 188 55 20 50 40 40 620 90 189 40 45 40 45 30 335 95 204 Nickel Plate 1987 Cyanide extraction - AAS r e s u l t s Sample Horzn Cyanide Residual Extractable Au (ppb) Au (ppb) 14 A 90 45 15 B 450 145 16 C 350 105 41 A 95 145 42 B 130 115 43 CI 370 115 44 C2 510 145 122 A -15 20 123 B 145 35 124 CI 145 35 125 C2 145 35 127 A 145 35 128 B 80 15 129 CI 175 45 130 C2 110 65 162 A -15 20 163 B 65 15 164 C -15 5 186 A 30 5 187 B 110 40 188 CI 80 15 189 C2 130 25 

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