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Sampling stream sediments for gold in mineral exploration, southern British Columbia Day, Stephen John 1988

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SAMPLING STREAM SEDIMENTS FOR GOLD IN  MINERAL EXPLORATION,  SOUTHERN  BRITISH  COLUMBIA  By STEPHEN JOHN DAY B.Sc,  The U n i v e r s i t y  of B r i t i s h  C o l u m b i a , 1985  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in  THE  FACULTY OF GRADUATE STUDIES  Department  We a c c e p t to  THE  of G e o l o g i c a l  this  Sciences  t h e s i s as conforming  the r e q u i r e d  standard  UNIVERSITY OF BRITISH  COLUMBIA  March 1988 ©Copyright  S t e p h e n J o h n Day, 1988  In  presenting  degree  this  at the  thesis  in  partial  fulfilment  University of  British  Columbia,  freely available for reference and study. copying  of  department publication  this or of  thesis by  this  for  his thesis  or  scholarly her  I agree  purposes  may  representatives.  It  be is  requirements  for  an  CjCrOt-OG-tc/tlL SC(6(0OES  MMCH t. l9M  advanced  that the Library shall make it that permission granted  for extensive  by the head  understood  that  for financial gain shall not be allowed without  The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  the  I further agree  permission.  Department of  of  of  my  copying  or  my written  ABSTRACT The  problems  encountered  by  when s a m p l i n g s t r e a m s e d i m e n t s by  considering  their in  Fourteen from  ( 420  20-kg samples  The to  52 Um)  activation  density  fractions  concentrations gold  particles  was  used -1 mm  methods,  particles  and  locations  and  were  collected  geochemical environments i n  occurrences i n southern  were s i e v e d gold  analysis using  and  the  t o show t h a t screened  However,  to s i x  content following  size was  British  fractions  determined  preparation  methylene  Poisson  of  iodide.  probability  much l a r g e r  field  s e d i m e n t ) would due  to  nugget  i n a comparison  the lowest p r o b a b i l i t y  stream  sediment  sampling  method d e s c r i b e d  Small-scale  sediment  gold  placer  anomaly in this  be r e q u i r e d to  is  free  to  obtained  (>100  kg  to reduce acceptable  of c o n v e n t i o n a l of f a i l i n g  two  distribution  samples  effects  by  Gold  were c o n v e r t e d t o e s t i m a t e d number o f  random v a r i a b i l i t y levels.  gold  investigated  placers at certain  and  gold  samples  neutron  of  of f r e e  of -5-mm  energy  streams d r a i n i n g  Jim  were  bed.  contrasting  Columbia.  for gold  sparsity  tendency t o form s m a l l  the stream  five  the  mineral explorationists  sampling detect  using  a the  study.  formation  was  investigated  by  —i i i —  collecting  t w e n t y 60-kg samples  locations along  five  Okanagan r e g i o n , e a s t analysed  as  concentrates Gold  was  t o be  decreasing  as  enrichment  varies  slope  anomaly  dilution in  gold  sand  on  size the  a  is  for  two  size  are  sample  in  the  The  effect  level to  since  presented  in  the  transport  however  in fine  is slope  framework  model.  represent  the  processes very  high  sediment  effects. a  not  gold  channel  from  Gold  sand d e p o s i t s but  as  nugget  of  changing  gravels  q u a n t i t i e s of  alternative.  sandy-gravel  conditions.  f r o m g r a v e l s may  collected  in  i n response  sample s i n c e p l a c e r - f o r m i n g  small  fractions.  with  deposits  These r e s u l t s  heavy-mineral  decreased.  apparent  in  Creek  though  hydraulic  concentrations,  satisfactory  Harris  stream  local  lead to unacceptable  case,  sediment  deposits,  deposited  the  of  above  E i n s t e i n ' s sediment  streams, may  and  to  Sediment c o l l e c t e d  high  of V e r n o n . Samples were p r e p a r e d  sandy-gravel  geochemical  -2-mm  considerably enriched  and  preferentially  of H.A.  the  sediment  channel  decreases.  in  were o n l y p r e p a r e d  compared  apparent  ten  described  found  deposits  from  kilometres  of  sand  In  best  produce energy  in gravels the  deposit  latter is  a  -ivTABLE OF CONTENTS ABSTRACT L I S T OF TABLES L I S T OF FIGURES ACKNOWLEDGEMENTS Chapter  i i viii X xiv  1: INTRODUCTION  1.0 I n t r o d u c t i o n 2 1.1 P r o p e r t i e s o f g o l d 3 1.2 S a m p l i n g p r o b l e m s 5 1.2.1 S t a t i s t i c a l s a m p l i n g d i s t r i b u t i o n s 7 1.3 H y d r a u l i c e f f e c t s 12 1.3.1 F o r m a t i o n o f h i g h c o n c e n t r a t i o n s o f h i g h - d e n s i t y minerals 15 1.3.1.1 S e t t l i n g o r s u s p e n s i o n s o r t i n g .''21 1.3.1.2 E n t r a i n m e n t s o r t i n g 22 1.3.1.3 D i s p e r s i v e s o r t i n g 26 1.3.1.4 I n t e r s t i c e t r a p p i n g 28 1.3.2 Summary o f mechanisms l i k e l y t o p r o d u c e h i g h density mineral concentrations 29 1.4 F i e l d s a m p l i n g p r o b l e m s 30 1.4.1 F i e l d sample c o l l e c t i o n t e c h n i q u e s 30 1.4.2 S e l e c t i o n o f s a m p l i n g l o c a t i o n 33 1.5 C o n c l u s i o n s 34 Chapter  2: ORIENTATION  SAMPLING  2.0 I n t r o d u c t i o n 2.1 D e s c r i p t i o n o f s t r e a m s 2.1.1 Tsowwin R i v e r 2.1.2 ' S a l m o n b e r r y C r e e k ' 2.1.3 F r a n k l i n R i v e r 2.1.4 H a r r i s C r e e k 2.1.5 Watson B a r C r e e k 2.2 F i e l d s a m p l i n g 2.3 L a b o r a t o r y p r o c e s s i n g 2.3.1 S i e v i n g 2.3.2 Heavy m i n e r a l s e p a r a t i o n 2.3.3 P r e - c o n c e n t r a t i o n o f -270-mesh f r a c t i o n 2.3.4 C h e m i c a l a n a l y s i s 2.3.5 V i s u a l e x a m i n a t i o n o f h e a v y - m i n e r a l concentrates 2.3.6 S c a n n i n g e l e c t r o n m i c r o s c o p y 2.4 R e s u l t s 2.4.1 D i s t r i b u t i o n o f s e d i m e n t s i z e s i n -5 mm sediment  37 37 37 ....39 41 ...41 42 42 44 44 47 47 48 50 50 51 51  -v2.4.2 W e i g h t s o f h e a v y - m i n e r a l c o n c e n t r a t e s 2.4.3 R e l i a b i l i t y o f INAA 2.4.4 D i s c u s s i o n of stream gold data 2.4.5 R e d u c i n g s a m p l i n g e r r o r s 2.4.5.1 C o m b i n i n g f r a c t i o n s 2.4.5.2 C o l l e c t i o n o f l a r g e r s a m p l e s 2.4.4 Comparison of r e s u l t s with other sampling methods 2.5 C o n c l u s i o n s Chapter  73 75  3: DETAILED SAMPLING OF HARRIS CREEK SEDIMENTS  3.0 I n t r o d u c t i o n 3.1 L o c a t i o n and a c c e s s 3.2 H i s t o r y and l a n d use 3.3 C l i m a t e , v e g e t a t i o n and s o i l s 3.4 Summary o f b a s i n m o r p h o l o g y 3.5 B a s i n g e o l o g y 3.5.1 Q u a t e r n a r y g e o l o g y 3.5.2 Source o f g o l d 3.6 H a r r i s C r e e k s e a s o n a l d i s c h a r g e v a r i a t i o n 3.7 F i e l d s a m p l i n g 3.7.1 F i e l d s a m p l i n g t o d e t e r m i n e s e d i m e n t t e x t u r e : problems 3.7.2 Sampling 3.7.3 Sample l o c a t i o n d e s c r i p t i o n s 3.8 L a b o r a t o r y p r o c e s s i n g 3.8.1 S i e v i n g 3.8.2 R e l i a b i l i t y o f s e d i m e n t a n a l y s e s 3.8.3 Heavy m i n e r a l s e p a r a t i o n 3.8.4 M a g n e t i c m i n e r a l s e p a r a t i o n 3.8.5 Minus 270-mesh m a g n e t i c m i n e r a l s e p a r a t i o n 3.8.6 F r a c t i o n a l a n a l y s i s o f -270-mesh s e d i m e n t 3.9 C h e m i c a l a n a l y s e s 3.9.1 R e l i a b i l i t y o f INAA f o r Au 3.9.2 G o l d a n a l y s e s o f s u b t r a c t i o n s o f a -270-mesh sample 3.9.3 R e l i a b i l i t y o f INAA f o r Hf 3.10 Summary Chapter  51 51 .56 67 67 71  4:  79 79 79 82 83 83 85 85 86 86 86 87 93 98 98 102 104 104 105 106 106 107 110 112 112  DESCRIPTIVE GEOMORPHOLOGY AND SEDIMENTOLOGY OF THE HARRIS CREEK STUDY REACH  4.0 G e o m o r p h o l o g y o f t h e s t u d y r e a c h 4.1 T e x t u r a l a n a l y s e s o f s e d i m e n t s a m p l e s 4.1.1 T e x t u r a l f e a t u r e s o f s a n d y - g r a v e l s a m p l e s 4.1.2 T e x t u r a l f e a t u r e s o f sand s a m p l e s 4.1.3 Downstream t r e n d s i n s e d i m e n t t e x t u r e s 4.2 M a g n e t i t e ( m a g n e t i c m i n e r a l ) t e x t u r a l a n a l y s e s  116 118 120 125 129 129  -vi4.2.1  Comparison of magnetite c o n c e n t r a t i o n s s a n d y - g r a v e l and sand s a m p l e s 4.3 H e a v y - m i n e r a l c o n c e n t r a t e a n a l y s e s 4 . 4 Summary '. Chapter  in 134 135 135  5: GEOCHEMICAL DATA: RESULTS AND DISCUSSION  5.0 I n t r o d u c t i o n 138 5.1 G o l d d a t a 140 5.1.1 E v a l u a t i o n o f h y d r a u l i c and r a r e g r a i n effects..140 5.1.2 Downstream t r e n d s i n Au c o n c e n t r a t i o n 144 5.1.3 Q u a l i t a t i v e c o m p a r i s o n o f w i t h i n - s i t e and between-site v a r i a b i l i t y 147 5.1.3.1 G e o m e t r i c mean c o n c e n t r a t i o n r a t i o s (GMCR)...148 5.1.3.2 One way a n a l y s i s o f v a r i a n c e 151 5.1.3.3 C o e f f i c i e n t s o f v a r i a t i o n 151 5.1.4 Summary o f g o l d r e s u l t s 155 5.2 C o m p a r i s o n o f t h e b e h a v i o u r o f g o l d , m a g n e t i t e and z i r c o n 156 5.2.1 Trends i n magnetite c o n c e n t r a t i o n s 156 5.2.2 T r e n d s i n h a f n i u m c o n c e n t r a t i o n s 160 5.2.3 G e o m e t r i c mean c o n c e n t r a t i o n r a t i o s and concentration ratios 163 5.3 Removal o f h y d r a u l i c v a r i a b i l i t y : e m p i r i c a l d a t a transforms 166 5.3.1 Transform * i 168 5.3.2 T r a n s f o r m * 170 5.3.3 Transform * 172 5.3.4 O t h e r t r a n s f o r m s 172 5.3.5 Ratios: implications f o r exploration 173 5.4 C o n c l u s i o n s 173 2  3  Chapter  6: SEDIMENT TRANSPORT AND SMALL-SCALE PLACER FORMATION, HARRIS CREEK.  6.0 I n t r o d u c t i o n 178 6.1 D a t a b a s e 178 6.2 A s e d i m e n t t r a n s p o r t model 178 6.2.1 D e r i v a t i o n o f E i n s t e i n ' s (1950) bed m a t e r i a l load function 180 6.2.1.1 L i m i t a t i o n s o f E i n s t e i n ' s (1950) bed l o a d formula 183 6.2.2 Computer s o l u t i o n o f t h e model 183 6.2.2.1 A p p l i c a t i o n o f t h e f o r m u l a 183 6.2.2.2 N u m e r i c a l v a l u e s f o r h y d r a u l i c p a r a m e t e r s . . . . 1 8 4 6.3 W i t h i n - s i t e p r o c e s s e s 186 6.3.1 S e d i m e n t m o t i o n d u r i n g a f l o o d 186 6.3.2 D e n s i t y s o r t i n g and f o r m a t i o n o f s u r f a c e pavement 190  -vi i 6.3.3 6.3.4  Sand d e p o s i t s a t b a r t a i l s D i f f e r e n c e s between h e a v y m i n e r a l c o n c e n t r a t i o n s i n s a n d s and s a n d y g r a v e l s 6.3.5 Sediment s o r t i n g a f t e r a f l o o d 6.4 Between s i t e p r o c e s s e s 6.4.1 Heavy m i n e r a l t r e n d s 6.5 Summary and c o n c l u s i o n s Chapter  7:  APPLICATIONS FOR  7.0 I n t r o d u c t i o n 7.1 F i r s t p r i n c i p l e s 7.1.1 Mode o f o c c u r r e n c e 7.1.2 Purpose of study 7.2 R e g i o n a l s u r v e y s 7.2.1 Purpose 7.2.2 S a m p l i n g media 7.2.3 Sediment f r a c t i o n 7.3 F o l l o w - u p s u r v e y s 7.3.1 Sample s i z e 7.3.2 S a m p l i n g media 7.4 Sample p r e p a r a t i o n 7.5 C h e m i c a l a n a l y s i s 7.6 D a t a a n a l y s i s 7.6.1 Nugget e f f e c t s 7.6.2 Hydraulic effects  196 196 197 201 201 203  MINERAL EXPLORATIONISTS  of g o l d  209 209 209 209 209 209 210 210 211 211 211 211 212 212 212 212  BIBLIOGRAPHY  214  APPENDIX  223  -viiiL I S T OF TABLES Table Table  1-1. 2-1.  Examples of locations of extreme density mineral concentrations  2-2.  Table  2-3A. G o l d c o n c e n t r a t i o n s concentrates  (ppb) o f h e a v y  2-3B. G o l d c o n c e n t r a t i o n s concentrates  (ppb) o f l i g h t  Table Table  Table Table  2-4. 2-5.  2-6. 3-1.  17  Summary o f c o n d i t i o n s u s e d i n i n s t r u m e n t a l neutron activation analysis, McMaster University reactor (X-Ray Assay Laboratories)  Table  Table  high-  D u p l i c a t e INAA a n a l y s e s f o r As mineral separates ( a l l values  49  in light i n ppm)...55 mineral 59 mineral 60  C a l c u l a t e d number of gold heavy m i n e r a l c o n c e n t r a t e s  particles  in 66  Weights o f -16-mesh f i e l d sample and s u b sample c o n t a i n i n g 20 p a r t i c l e s o f g o l d i n h i g h and low e n e r g y e n v i r o n m e n t s  72  Predicted methods  76  results  Water d i s c h a r g e Creek,  of  rates  different (m /s) 3  sampling  for  Harris  i n June 1986  94  Table  3-2.  Summarised  Table  3-3.  Table  3-4.  Summary of physical and sampling c h a r a c t e r i s t i c s o f sample s i t e s 99 Change i n t h e w e i g h t o f -270-mesh f r a c t i o n following wet s i e v i n g o f a p r e v i o u s l y d r y s i e v e d sample 101  Table  3-5.  Table  3-6.  June 1986 s i t e  R e s u l t s of t e x t u r a l B2 and 86-SD-R2  descriptions  re-analysis  of  96  86-SD103  E f f e c t on Au c o n c e n t r a t i o n o f a d d i n g one spherical gold particle (density = 18 g/cm ) t o a 25 g sample of -270-mesh sediment 109 3  -ixTable  3-7.  Gold analyses mesh s e d i m e n t  for subfractions (85-SD-10)  of  -270I l l  Table  4-1.  Summarised  Table  4-2.  C h a r a c t e r i s t i c s of framework and matrix components of sandy gravels, the p r o p o r t i o n o f framework and discriminant diameter  total  weights,  D»©  Table  4-3.  C o m p a r i s o n of weights of c o n c e n t r a t i o n of magnetite  Table  5-1.  Summary statistics for c o n c e n t r a t i o n s i n sediment  Table  5-2.  Table  5-4.  Correlation ratios  Table  5-5.  Empirical text  Table  6-2.  6-3.  126  magnetite and i n two s a m p l e s . . 1 3 2 heavy  mineral 139  152  Analysis  Table  121  150  5-3.  6-1.  D  GMCRs for three high-density mineral fractions and significance tested by Duncans m u l t i p l e r a n g e t e s t  Table  Table  and  of v a r i a n c e r e s u l t s  data  matrix  of  for gold concentration  164 transforms  discussed  i n the 167  Major sedimentological features  and  geochemical  Parameters to which n u m e r i c a l v a l u e s be assigned (Einstein's (1950) material function) Sediment textures c o m p u t a t i o n s of bed  at site C used m a t e r i a l load  179 must bed 185 in 187  -xL I S T OF FIGURES Fig. Fig.  Fig.  Fig.  Fig.  Fig.  1-1. 1-2.  1-3.  1-4.  1-5.  1-6.  Example of a t y p i c a l s u r v e y f o r Au  regional  geochemical 6  Poisson frequency distributions U=0.49 and (B) u=0.12  for  (A) 9  Size o f sample r e q u i r e d t o c o n t a i n t w e n t y spherical particles of pure gold as a function o f s i z e o f p a r t i c l e s and g r a d e o f p o p u l a t i o n m a t e r i a l (rock, sediment, e t c . ) ( C l i f t o n e t a l . , 1969)  11  Stream selected minerals  14  sediment fractions  dispersion trains for o f some high-density  (A) S h i e l d s (1936) d i a g r a m o f t h e c r i t i c a l s h e a r R e y n o l d s number v e r s u s dimensionless critical shear stress with some e x p e r i m e n t a l p o i n t s and (B) c r i t i c a l shear stress of entrainment for a number of s p h e r i c a l h i g h - d e n s i t y m i n e r a l s i n water a t 20<>C d e r i v e d f r o m S h i e l d s c u r v e  23  R e l a t i o n s h i p between c r i t i c a l d i m e n s i o n l e s s s h e a r s t r e s s f o r m o t i o n and the r a t i o of particle size t o t h e median p a r t i c l e s i z e of t h e bed (Andrews, 1983)  27  Fig.  2-1.  L o c a t i o n s o f s t r e a m s sampled  38  Fig.  2-2.  Sampling  40  Fig.  2-3.  Wet-sieving  Fig.  2-4.  Cumulative sediment sediment f i n e r than  Fig.  2-5.  stations  on s t r e a m s  apparatus size 4 mm  Gold analyses (INAA) concentrate s p l i t s  45 distributions  for 52  of  heavy  mineral 54  Fig.  2-6.  C o m p a r i s o n o f Au analyses determined INAA on two d i f f e r e n t o c c a s i o n s  by ....57  Fig.  2-7.  Comparison o f Au c o n c e n t r a t i o n s d e t e r m i n e d by f i r e a s s a y / a t o m i c a b s o r p t i o n and INAA  58  -xiFig.  Fig.  Fig.  Fig.  Fig.  2-8.  2-9.  Probability showing populations  plot of inferred  shape factors (SF) component normal 63  Gold content and c o n f i d e n c e i n t e r v a l s f o r -200+270-mesh fraction of heavy mineral concentrates versus mean grain size of f i e l d sample  2-10. Number o f e f f e c t i v e p a r t i c l e s (N ) geometric midpoint of coarsest f r a c t i o n included e  3-1.  3-2.  of  Harris  Creek  upstream of the study reach  locations  3-3.  Sample  Fig.  3-4.  Typical the  head  drainage  on H a r r i s  sandy g r a v e l of a point  area  sampling  Typical  sand s a m p l i n g  Fig.  3-6.  Fig.  3-7.  Wooden p o l e w i t h n o t c h b u i l t f o r c a r r y i n g samples Gold analyses for splits sediment Hafnium a n a l y s e s f o r s p l i t s sediment  84 88  location  near  bar  3-5.  81  of  Creek  Fig.  3-8.  70  Topography  Fig.  Fig.  versus size  Geology of the drainage basin of Harris C r e e k and l o c a t i o n o f t h e s t u d y r e a c h entire  68  90  location  91  up  at  centre 95  of  -270-mesh 108  of  -270-mesh 113  Fig.  4-1.  Channel long p r o f i l e , showing average s l o p e and c h a n n e l f o r m between open c i r c l e s . The whole s e c t i o n i s 5050 m l o n g 117  Fig.  4-2.  Typical  braided  Fig.  4-3.  Typical  meandering channel s e c t i o n  Fig.  4-4.  Some examples o f p r o b a b i l i t y p l o t s f o r s i z e frequency distributions of sandy gravel samples 122  Fig.  4-5.  Probability plot for size d i s t r i b u t i o n of 86-SD-D2 s h o w i n g c h a r a c t e r i s t i c f e a t u r e s o f sandy g r a v e l d e p o s i t s 124  channel s e c t i o n  119 119  -xiiFig. Fig. Fig.  Fig.  Fig.  Fig.  4-6. 4-7. 4-8.  4-9.  5-1.  5-2.  Some e x a m p l e s o f p r o b a b i l i t y p l o t s f o r s i z e f r e q u e n c y d i s t r i b u t i o n s of sand samples  127  Downstream sediment  130  trends  diameter  of  130  Some examples of probability magnetite s i z e d i s t r i b u t i o n s  133  plots  of  Poisson confidence limits for gold c o n c e n t r a t i o n s c a l c u l a t e d as described in the text for (A) -140+200-mesh and (B) -200 + 270-mesh  142  Magnetite concentration (-70+100-mesh) versus Au concentration (-140+200mesh )  143 145  5-3.  Downstream t r e n d s  Fig.  5-4.  Coefficients concentrations fraction  5-5.  mean  Downstream t r e n d s o f w e i g h t p e r c e n t -8+4-mm sediment. Filled in circles are sandy gravel deposits, open and half filled c i r c l e s are sand d e p o s i t s  Fig.  Fig.  in  Downstream  i n Au  concentration  of variation for by s e d i m e n t d e p o s i t t y p e  Au and 154  profiles  of  magnetite  concentrations  157  Fig.  5-6.  Downstream p r o f i l e s o f Hf  Fig.  5-7.  Fig.  5-8.  Geometric mean concentration ratios c a l c u l a t e d for four d e n s i t y f r a c t i o n s C o e f f i c i e n t s of v a r i a t i o n f o r transform * (Table 5-5, case x=y only) by s e d i m e n t d e p o s i t t y p e and f r a c t i o n  169  Downstream p r o f i l e f o r * z ( c a s e mesh, y=-200 + 270-mesh) . . .  170  Fig.  5-9.  concentrations....161 162  x  Fig.  5-10.  Downstream p r o f i l e f o r t r a n s f o r m  Fig.  6-1.  Effect of increasing bed sediment transport rates d i f f e r e n t diameters  x=-140+200*-»  roughness f o r sediment  174 on of 189  -xiiiFig.  6-2.  R e l a t i o n s h i p s between (A) l o g o f framework sorting and magnetite (-40+70-mesh) c o n c e n t r a t i o n and (B) l o g o f mean diameter of matrix and m a g n e t i t e (-40+70-mesh) concentration 191  Fig.  6-3.  R e l a t i o n s h i p between l o g o f m a t r i x and l o g o f mean framework d i a m e t e r  sorting 192  Fig.  6-4.  Examples from a b a r on L y n n C r e e k o f (A) sub-surface gravel voids incompletely filled by sand and (B) g r a v e l voids c o m p l e t e l y f i l l e d by sand 194  Fig.  6-5.  Comparison of transport ratios (low density/high density) with g r a i n s i z e , bed r o u g h n e s s and d e n s i t y 198  Fig.  6-6.  High d e n s i t y mineral enrichment sample C l due t o w i n n o w i n g  Fig. Fig.  6-7. 6-8.  Effect ratios  of  slope  on  magnetite  Diagrammatic summary of involved in deposition H a r r i s Creek  of  sand 200  transport 204  the processes of sediment i n 206  - x i vACKNOWLEDGEMENTS I am g r a t e f u l t o i n d u s t r y g e o l o g i s t s and g e o c h e m i s t s D. B r a b e c , A. B u r t o n , D r . S . J . Hoffman, B. Smee, F.M. Smith, Dr. A. S o r e g o r o l i , D r . I . Thomson, A. T r o u p e and R. Walker who assisted in selecting suitable sampling locations. At t h e U n i v e r s i t y of B r i t i s h Columbia, l a b o r a t o r y and f i e l d a s s i s t a n c e was p r o v i d e d at various stages by B. S c h r o e d e r , H. Yuen, H. E i j g e l , G. H a r r o p and J . Densmore. CR. Stanley and J . K n i g h t p r o v i d e d l i v e l y d i s c u s s i o n s . Dr. W.K. F l e t c h e r p r o v i d e d guidance and encouragement a s w e l l a s c r i t i c a l comments on i d e a s and c o n c e p t s . D r s . W. Barnes and A.J. Sinclair carefully reviewed the manuscr i p t . I n t h e f i n a l s t a g e s , D r . W. M c M i l l a n gave p e r m i s s i o n t o use f a c i l i t i e s a t t h e B r i t i s h C o l u m b i a Geological Survey Branch. B r a n c h g e o c h e m i s t s P.F. M a t y s e k and J . L . Gravel helped formulate ideas through d i s c u s s i o n . Ngoc p r o v i d e d t e a and i n s p i r a t i o n a t e v e r y s t a g e .  -1-  CHAPTER 1 INTRODUCTION  -2-  1.0  Introduction Mineral  explorationists  concentrations  of  use t h e p r e s e n c e  an e c o n o m i c a l l y i n t e r e s t i n g  stream sediments  to indicate  mineral  of the sampling  are  upstream  many c o m p l i c a t i o n s t h a t  of  geochemical  modelling and  Ag  1976).  been  These  trace  data  elements  constituents  oxides  (Rose,  density s i l i c a t e s of  elements  component Zn  in  same  a s Cu, Zn, Pb Hawkes,  i n sediments  as  1)  or  (3)  as t r a c e  of  and  Mn  components o f low  p r e d o m i n a n t l y as a  in  Fe  The b e h a v i o u r  trace  or  major  m i n e r a l s ( f o r example, Au i n g o l d ,  Sn i n  e t c . ) i s not understood  to the  i s very p o o r l y understood  due t o  W in scheelite  sulphides,  degree.  The its  Cu  there  sediments,  (e.g.  on t h e s u r f a c e  of h i g h - d e n s i t y r e s i s t a n t  cassiterite,  stream  ( e . g . Pb i n K - f e l d s p a r ) .  magnetite,  the  s e c o n d a r y c l a y s and o x i d e s and 2)  absorbed  occurring  of  to misinterpretation  successful occur  mineral i n  Although  of such elements  generally  in  1975)  from  anomalous  occurrence  location.  can lead  remarkably  constituents  trace  a bedrock  obtained  of the d i s p e r s i o n has  of  behaviour  of g o l d *  h i g h d e n s i t y and  study  addresses  the  rarity effects  in  stream  of  these  sediments. problems  This i n two  '•"'Gold" r e f e r s t o the m i n e r a l w h i c h i s a n a l l o y o f Au w i t h minor Ag, Cu, Hg, Fe e t c . "Au" r e f e r s t o t h e e l e m e n t o n l y .  -3staqes: 1) D e t e r m i n a t i o n stream  of  typical  sediments,  sampling  to  techniques  meaningful  sample  2) D e t e r m i n a t i o n variables  enable  a better  of  gold  in  understanding of  required to obtain a  statistically  f o rdetermination of gold.  of  on  concentrations  the  the  effect  of other  distribution  of  (non-sampling)  gold  in  stream  sediments.  1.1 P r o p e r t i e s o f g o l d The  p r o p e r t i e s of gold are c o n s i d e r a b l y d i f f e r e n t  those  of  resistant  extremely  dense  (pure g o l d  though t h e s p e c i f i c solution and  of s i l v e r  mercury  to  flotation  effects these  with other  19.3 g/cm ) 3  and o t h e r e l e m e n t s  such  as copper,  gold  1977).  density Pure g o l d  hence, attachment  of small p a r t i c l e s ,  to a lesser  1983). extent  =  15  3  to a  of a i r bubbles  very  may  to  lead  high-density  Natural gold w i l l due  iron  t o 19 g/cm ,  i s wetted  overcoming  solid  show  solid  solution  metals,  gold i s  metals.  common  with  m a l l e a b l e and d u c t i l e natural  =  increased  (Wang and P o l i n g ,  effects  In  (Au), d e n s i t y  Gold i s  with  (natural  extent;  and o x i d e m i n e r a l s .  g r a v i t y decreases  H u r l b u t and K l e i n , limited  silicate  from  shapes  in  most which stream  other leads  native to  sediments.  a  wide  range  Although  of  i t is  -4commonly d e s c r i b e d many  regular  for gold  Knight,  pers.  rounded  as  comm.).  but  transported  gold  and  flattening  the  sieve diameter are  diameters  of  the  has  chemical  (Boyle,  gold  as  fold  and  during it  is  over  and  Smith,  1984). with  the  particles:  coarse  gold  the  and  least 1 mm  a very  are  and  fine  particles  flattened  limited  gold  solubility  1979), c o n s i d e r a b l e  m o b i l i t y of Au  in cool,  s o l u t i o n s . With r e s p e c t  with  to  the  been  used  in  work has  been  approximately  to p l a c e r  as  most  gold,  evidence  for  1979):  nuggets t y p i c a l l y  Single  3) Many  become  removed  up,  J.  systematically  (Boyle,  show i n t e r n a l  been  curl  1981;  minerals  are  are  appears to vary  approximately  surficial  mobility  2)  can  f o l l o w i n g f e a t u r e s ' have  Gold  (Tischenko,  ( f o r example, G i u s t i  of  flatness  become more f l a t t e n e d  flattened  waters  neutral,  1)  of  great  extent.  natural  the  grains  edges  affect  Although gold  done on  of  may  the  snap o f f  particles  degrees  (discs) a  Other r e s i s t a n t  points  The  greatest  irregular  flakes  i n stream sediments  the  transport,  o c c u r r i n g as  and  observed  eventually  as  zoning  have a m a m m i l l a r y h a b i t  suggesting  c r y s t a l s and  chemical  crystal  faces  on  and  may  accretion. nuggets  have  observed. gold  nuggets  (fineness  =  have  a  rind  of  lOOOAu/(Au+Ag+Cu+...)).  high  fineness  -5In  this  study  negligible  the c h e m i c a l  compared  mobility  to mechanical  transport  sediments  studied  significant  c h e m i c a l d e p o s i t i o n o f new  The  high d e n s i t y  particle  shape and  difficulty stream  are  Sampling  or  extremely  extreme  stream  at  a  rare i n stream  is  of  leads  of g o l d  complication  are  evident  sediment  high  surveys  samples  sampling  on a n a l y s i s  2  to  in active that  gold  sediments,  hence  understood.  in  attributed  to  The  gold contents  t h e Au of t h e  density  high  Typically, a  property  (e.g. that  1  Fig.  f o r example, B o y l e and 1986a).  to  a l l but  concentrations that  5  one may  of u b i q u i t o u s m i n e r a l s .  non-reproducible  Maurice,  from  mineral  few anomalous s a m p l e s a r e  extremely  1975;  and  content  most  for gold.  i t i s found  have b a c k g r o u n d Au  be  Hilchey,  variation  problems  s a m p l e s / k m ) , and  1-1,  precluding  between p a r t i c l e s  thoroughly  the  gold.  number o f s m a l l samples a r e t a k e n  region  or two  and  assumed  because  annually,  the b e h a v i o u r  A further  problems  exploration large  gold  t e c h n i q u e s must be  Sampling  a  of  composition  sediments.  sampling  reworked  in determining  particles  1•2  are  o f g o l d was  (greater than  Gleeson,  1972;  mostly 1  Brown  ppm, and  Fig. 1-1. Example of sample d i s t r i b u t i o n f o r a t y p i c a l r e g i o n a l geochemical survey f o r Au. Samples are field panned c o n c e n t r a t e s . A l a r g e number o f s a m p l e s a r e b e l o w d e t e c t i o n l i m i t (open c i r c l e s ) whereas a few a r e i n e x c e s s o f 2 ppm ( f i l l e d c i r c l e s ) ( B o y l e and G l e e s o n ( 1 9 7 2 ) , Keno H i l l A r e a , Yukon T e r r i t o r y ) .  -71.2.1  S t a t i s t i c a l sampling  The gold,  sampling  is  distribution The  distribution  diamonds,  sediments  distributions  cassiterite) typically  (Koch  and  Link,  P(n)  sample  and  particles  expected P(n)  in  significance estimated  is  the level  from the  the  is defined  of  probability  Confidence  of U.  a  obtaining  n  limits  (Zar,  (at can  be  1984):  confidence  N - 2^N  i U  < N + 2vN  of  relationships surveys  as  the  limits (l-2b)  at  a  given  discrete  sediment  location Gold  particles  to y i e l d a bulk  gold content  (1-1)  for gold are  i s very well-sorted.  homogeneously  ten  1981).  f o l l o w i n g example.  mineralisation  p. becomes g r e a t e r t h a n  95%  sampling  sediment  As  of the  (Fletcher,  The  in  p o p u l a t i o n mean (H)  chi-squared d i s t r i b u t i o n  i n the  Au.  (1-1)  the  sediment  ppb  as  particles  stream  throughout  Poisson  (mean) number o f  sample.  estimate  implications  Stream  the  = U"e-*Vn!  <x) f o r t h e  simpler estimate  The  by  stream  2  i s an  i s adequate  s o i l s and  (e.g.  1970).  2 where N  particles  in rocks,  described  Poisson d i s t r i b u t i o n  where U i s t h e  of v e r y r a r e  of t h e  and  (1-2)  illustrated  downstream of is  distributed  (diameter=0.2 composition  sediment  to  not  of  mm) 200  attributable  -8to  mineralisation  contained  in  negligible.  (that  the  i s ,  lattices  A sample w e i g h i n g  gold  solids  and a n a l y s e d  expected  weight  The  (assuming  Au  expected  pure number  Using  contain  That  without assay.  of  spheres)  1-1,  is  analysis  gold  or very  (Ingamells, The from  gold  because  in  resulting  and  3  the  on t h e p o p u l a t i o n of  gold  therefore the  that  t h e sample  i f t h e sample ( F i g . 1-2B).  This  latter  the  of gold  result  has l e d high  chance presence a  one  then the  surprisingly  in  be  weighed If  (P(l)=ll%)  to describe from  1-2A).  t h e anomaly w i l l  t h e sample  few p a r t i c l e s  small  of a  sample  1981).  extreme r a r i t y  strong  P(0)=87%  "nugget e f f e c t "  analyses  single  present  volume o f  particle  i s a 61% c h a n c e t h a t  would be 1700 ppb Au.  to the term  i s 76 c m  the  and l o s s  ( P ( 0 ) , n=0) i s 6 1 % ( F i g .  u=0.12  was  from  splitting  probability  50  particle  taken  is  (p.) i s 0.49.  the  and  gold  minerals)  80.8 Jig,  I n a more extreme c a s e ,  then  of  The t o t a l  each  undetected. g,  is  i s 40 p.q b a s e d  weight  no f r e e g o l d  i s , there  other  3  of p a r t i c l e s  equation  amounts  = 2.65 g/cm )  of gold  concentration.  will  by f i r e  (assuming d e n s i t y  of 200 g  sediment, s u i t a b l y concentrated of  small  of coarse  occurrences  probability the  true  in  particulate  stream  sediments  t h a t an anomaly w i l l concentration  gold  remain  o f t h e sample  derived  leads  to a  undetected i s grossly  -9-  n F i g . 1-2. Poisson and (B) u=0.12.  frequency d i s t r i b u t i o n s  for (A) u=0.49  -10underestimated. samples  in  content might  I n t h e example,  t h e extreme case  over  1 ppm Au.  a t t h e same l o c a t i o n  out of  ten  would r e t u r n a b a c k g r o u n d  whereas a r a r e b u t n o n e t h e l e s s contain  taken  roughly nine  significant  However,  would  probably  used  to  Au  sample  a repeat  sample  (87% chance) not  contain detectable gold. Equation  1-1  may  be  sample  that  number  of gold p a r t i c l e s  acceptable  i s required to reach such  probability  Relationships  of  determine  an  error  being detected  gold  c o n c e n t r a t i o n s of s e v e r a l samples  particles  (for  will  example,  distance  with  of sampling  vary  considerably  s p a c i n g o f sample  from  the  t o be  with  relationships  a  relative  20  particles  ( l - 2 a ) produces asymmetric  54%  the  (Clifton  relationship  lower  relative  error  (from t a b l e s of Pearson Some examples  allow  number  situation  error  et. a l . , error  of  and H a r t l e y  of  1969). of  50%  gold,  though  confidence  limits  o f 37% and an upper  o f sample s i z e s  reduce  locations with respect to  to  a  roughly  the  statistically  The n e c e s s a r y  corresponds  with  that w i l l  m i n e r a l i s a t i o n ) though a r e l a t i v e  ± 5 0 % m i g h t be c o n s i d e r e d a d e q u a t e Using  estimate  contain to  to a l e v e l  95% c o n f i d e n c e .  have a n  qualitatively.  to  a sample s h o u l d  relative  distinguishable  expected  t h a t an anomaly w i l l  the  of  acceptable  l - 2 a and l - 2 b c a n be u s e d  number o f g o l d p a r t i c l e s  the s i z e of  limit  of  (1966)).  required  to  obtain  20  -11-  100 kg  1 kg S i z e of  10 g  100 mg  Sample  Fig. 1-3. S i z e of sample required to contain twenty spherical p a r t i c l e s o f p u r e g o l d as a f u n c t i o n o f s i z e o f particles and grade of population material (rock, sediment, e t c . ) ( C l i f t o n e t a l . , 1969). F o r example, i f g o l d p a r t i c l e s a r e 100 Mm i n d i a m e t e r and s e d i m e n t grades 100 ppb g o l d t h e n t h e sample r e q u i r e d weighs 2.02 k g .  -12particles al.,  of gold  1969).  fractions field  samples reports  Where  or  and/or  fine  are  sample s i z e  the  sediments The  distribution  (e.g.,  occur  few  coarse  s a m p l i n g and large  indications  f o r gold  t h e Au  in  extremely  that  distribution  in  attention  of g o l d ,  or  concentration  of  described  1976).  by  grinding.  of a second Poisson  the  ifa This  distribution  (Ingamells,  Poisson  sample  is  leads  to  onto  1981;  the  Sutherland  1984).  effects (1971)  m a t h e m a t i c a l model Me ,  Me  m  mineralisation,  exposed  A  and  and  Hawkes  (Me A m  Me»  m  are  proposed  (Me^-Meo) the  metal  +  a  AmMe , B  content  of  r e s p e c t i v e l y and A*, and A* a r e t h e a r e a s  mineralisation  respectively)  =  (1976)  anomalous s e d i m e n t s a m p l e s and b a c k g r o u n d  sediment samples,  stream  during  and K r e n d e l o v ,  and  ( C l i f t o n §_t  only  i n the l a b o r a t o r y  crushing  Polikarpochin  in  Kulikov  sampling d i s t r i b u t i o n  1.3 H y d r a u l i c  of  are  given  problems  also  superposition  where  There  required,  after  simple  i s lost  e i t h e r t o the s i z e  sampling  Dale,  1-3  present  of stream sediment surveys  the  and  is  sediment  required.  been p a i d  field  gold  ln Fig.  laboratory pre-concentration,  has  split  a r e summarised  to  and  e x p l a i n the d i l u t i o n  sediments  downstream  of  drainage  basin,  of metal  anomalies  an  occurrence  of  -13mineralisation. limitations  arising  1) c o n s t a n t  rate  following in  the  sampling,  5) o n l y  one  Despite  observed  analytical  o f Cu  such elements  as W,  Sn,  not  Ba and  do  (1976) ( e . g . , F i g . 1-4B  not  c a n be 1986,  of not  Ba,  important,  e x p l a i n e d by  resulting  to  (downstream elements  because  of  are  mostly  of  Hawkes  model  Fletcher, Fletcher,  the v a r i a b i l i t y  the v a r i a b i l i t y the  The  in high-density  hosted  S l e a t h and  effects,  1979).  to  Au  Saxby and  these authors a t t r i b u t e to hydraulic  compares w e l l  application  f o l l o w the W,  o f t h e model t o  preclude  these  t o D,  et. a l . , 1987;  F i g . 1-4A)  no  errors;  et. a l . . ,  m i n e r a l s a r e s u f f i c i e n t l y abundant t h a t are  example,  i n the b a s i n .  However,  trends  e x t r e m e l y e r r a t i c and  elements  (for  sediments  p a t t e r n s (Rose  minerals.  mineralisation)  Although  solids  interest;  application  i n stream  o f t h e model do  Fletcher  of  or c o n t a m i n a t i o n  limitations,  anomaly decay  resistate  pedogeochemical  barriers);  these  assumptions  basin;  o u t c r o p of m i n e r a l i s a t i o n  dispersion  important  assumptions:  and  exchange between water and  4) no  several  v a l u e s f o r the e l e m e n t s  precipitation  Sn,  has  lithogeochemical  background  the  model  from the  erosion  2) c o n s t a n t  3) no  The  particles rare  1986; 1982).  of  these  of  the  grain  effects  i n most g o l d  surveys  nugget  effect  from  inadequate  (e.g., sample  Taisaev, size.  -14-  0.1  t  i  1  r  1  0  1  2  3  4  r  5  D i s t a n c e (km)  (B)  i  i  0  2  1— 4  D i s t a n c e (km) Fig. 1-4. Stream sediment d i s p e r s i o n t r a i n s f o r s e l e c t e d f r a c t i o n s o f some h i g h - d e n s i t y m i n e r a l s . (A) G o l d (-5 mm) ( T a i s a e v , 1986), (B) b a r i t e (-80+270-mesh) ( S l e a t h , 1 9 8 0 ) , (C) scheelite (-80+120-mesh) (Saxby, 1985), (D) c a s s i t e r i t e (-35 + 48-mesh) ( F l e t c h e r e t a l . , 1987 ). Source of h e a v y m i n e r a l i n d i c a t e d by X.  Hawkes'  model  fails  because  components o f t h e s e d i m e n t  travel  locations  Hence/  there  i n the stream.  are  no  concentrate interest. will  or  tend  a t equal  dilute  particles  travel  at  that a l l  rates  that the  of h i g h - d e n s i t y mineral ( f o r example,  according  to  Hawkes'  rates  densities leading  model,  may m o d i f y t h e s i z e  different  degrees a t any p o t e n t i a l  1.3.1 F o r m a t i o n minerals  of high  Many d i f f e r e n t  be  local  geomorphic  sampling  of h i g h - d e n s i t y  (e.g. slope, (stream  proximity  width r a t i o ,  c r o s s - s e c t i o n a l a r e a ) v a r i a b l e s may  of magnitude v a r i a b i l i t y  (Slingerland, locations mineral  hydraulic  will  1984),  a  and  produce  abundances.  density mineral  in  hence a  wide  Locations  concentrations  velocity,  to  depth to lead  of c o n c e n t r a t i o n s  short  to  location.  and  minerals  diluted  hydraulic  tributaries)  density  reach  and d e n s i t y d i s t r i b u t i o n s  concentrations  to  (over  to a given  a point bar) should  processes  of  Thus, a l t h o u g h t h e  particles  (1976)  to  component  of d i f f e r e n t  different  that  tend  h i g h l y v a r i a b l e e n r i c h m e n t and d i l u t i o n  a stream  orders  at a l l  t h e model r e q u i r e s  processes  excessively  to  assumes  p r e d i c t e d by t h e d i l u t i o n m o d e l ) .  supply of  stream  Intuitively,  localised, that  local  i t  to  of h i g h -  reach  of  a  sampling  at  different  range  of  of extremely (placers)  high-density  elevated in  stream  high-  present-day  -16stream  beds  (Anderson, (McKay, 1984)  are  we11-documented  1887;  Basque,  1921;  (Table  Boyle,  density mineral  Rubey  (1933).  i d e a s on  The  that  concept  behave  regime are  E a r l y use  of t h e  derived  at  the  formation  concentrations  hydraulic  referred  have  said  concept  to s e t t l i n g  predict  t o be (Rubey,  1933;  agree  i n the  Witwatersrand  elsewhere.  However,  can  density  small  great to  equivalence.  lead  to  the  minerals,  equivalent.  (e.g.  be  it  for  the  deposits  satisfying  deposits size  accounted  Thus, a l t h o u g h  is  the  particles  the  of  formation settling  of  settle  This  law  qualitative occur  in  (Pretorius,  d i f f e r e n c e s are for  settling  to  1968)  Stokes  will  by  simple  equivalence  layers enriched  necessary  given  Theoretically  equations  gold  formation  mechanisms not  two  Tourtelot,  with  conglomerates  settling  any  l a r g e l e s s dense p a r t i c l e s .  superficially  f a r too  by  under a  equivalence.  velocity  the  proposed —  hydraulically  that  generally  way  high  around  that small high-density p a r t i c l e s  to  and  localised  simple  same  observation  1981)  of  centred  is  the  velocity  same r a t e as  appears  literature  Slingerland,  originally  itself  in  terminal s e t t l i n g  the  scientific  M i l n e r , 1983;  of h y d r a u l i c e q u i v a l e n c e ,  particles  Law)  1979;  and  handbooks  1-1).  Development of  concept  1979)  i n prospectors  in high-  consider  placers  equivalence.  to  other explain  -17-  T a b l e 1-1. E x a m p l e s o f l o c a t i o n s mineral concentrations. 1) 2) 3) 4) 5)  of  extreme  high-density  In r i f f l e d bedrock depressions. Downstream o f l a r g e b o u l d e r s and i s l a n d s . Any zone of f l o w s e p a r a t i o n ( B e s t and B r a y s h a w , 1 9 8 5 ) . Downstream of c o n f l u e n c e s i n s u c t i o n e d d i e s . Bar t o bank f l o w c o n v e r g e n c e z o n e s ( S m i t h and B e u k e s , 1983). 6) Heads o f p o i n t and channel bars. 7) R a p i d change of channel curvature ( c f . , Peterson e_t a l . , 1986, c o a s t a l b e a c h c u r v a t u r e ) . 8) D e c r e a s e of channel gradient. 9) Emergence o f s t r e a m s f r o m c a n y o n s ( a b r u p t v a l l e y widening). 10) A t t h e c o n t a c t between a l l u v i a l s e d i m e n t s and b e d r o c k . 11) At " f a l s e b o t t o m s " (above c l a y l a y e r s and p a n s ) . 12) In o r g a n i c mats o f l i c h e n s e t c . ( M i l n e r , 1 9 8 3 ) .  -18Two a p p r o a c h e s equivalence: sediment Wang  1)  worked w i t h  common  sands.  In  this  must  a  fractions of  the  ratios  size  based  density  mineral  departure  i t  Komar  then  for  beach  and  assumed  that  particles  are  is  deposits (e.g.  one  process  i s determined  the  different  fractions.  velocity  t o that of a low-density  from s e t t l i n g e q u i v a l e n c e .  that  w e l l - s o r t e d and f i n e - g r a i n e d , the  high-density  truncated  by  fractions.  However,  restricted comparison meaningless.  to of  a  mineral  shortage  mean  of  mineral  sizes  terminal  of the  (Barrie, settling  hight o show  T h i s method  supply of  (1984) a  will  sediments  guaranteeing  distribution  i f particles  certain  diameter  of  virtually  and  mineral  Slingerland  work s a t i s f a c t o r i l y f o r b e a c h s a n d s b e c a u s e t h e are  has  and m o d i f i c a t i o n o f a l l  on t h e mean s e d i m e n t  settling  and  (1981) have  in  several  distribution  velocity  i s obtained various  i f  deposition  t h e mean t e r m i n a l  density the  the  settling  or  2) s t r e a m  1984),  minerals  approach,  hydraulic  and  (1984) and B a r r i e  sampled  The s e d i m e n t  mean  studies  i n which the sediment  be  in  studying  (1977,  high-density  equivalent  predominated layers.  sediment  and Hand  s a m p l e s c a n be t a k e n  lamellae)  for  Slingerland  Trask  hydraulically  emerged  beach  studies.  (1984),  estuary  have  is  the  not  coarser  minerals  are  1980),  then  velocities  is  -19When w o r k i n g w i t h is  needed  because  high-density samples.  the  i t  mineral  A  minerals  stream sediments a d i f f e r e n t  mean  c a n n o t be assumed t h a t a c o m p l e t e  distribution settling  would be u n d e r e s t i m a t e d  diameter) high-density mineral  too  fine  for settling gold  Rittenhouse attempted looking  supply  of  (1943) and  variation  density  and  (1987)  used  to  of w i t h i n  variance  using  minerals  in  cassiterite (<50  Hm)  1 mm  are r a r e l y a v a i l a b l e  are not e a s i l y v a l i d a t e d  et  site  ratios one  of  same way a s t h e same  (1943) used  versus  (1986)  e_t a l .  to  assess  sampling of  Results  low-density samples  show t h a t  behave  site  low-density  concentrations  particles  collected  e q u i v a l e n t low-  (ANOVA)  between  with  coefficients  Fletcher  concentrations  fraction.  size  high-density  i s assumed t o be u n a f f e c t e d  fraction  i n another  have  i n s t r e a m s e d i m e n t s by  variance  of  unavailable.  a l . (1987)  fractions.  high-density mineral  Fletcher  (greater than  determine h y d r a u l i c a l l y  analysis  reduction  for  i n which the  Rittenhouse  high-density  high-density  i n a conglomerate are  Fletcher  fractions  in a l l  expected  were p r o b a b l y  i n a l l samples  problems.  for  large  to determine equivalence  suite  present  that  clasts  equivalence  particles  at individual  mineral  and  from  arguments t h a t g o l d p a r t i c l e s  because coarse  by  is  velocity  h y d r a u l i c regime because v e r y  Thus,  approach  of small  i n much t h e  particles.  Saxby  f r o m h i g h and low  -20energy stream micro-environments a t the and  showed,  that  high-density mineral  fractions  are  Differences the  using  very  similar  approaches above  exploration contained  and  of  sample  very  fine  in  Furthermore,  the  work  trains  However, t h e (1)  fine  for  the  not  or  (3)  comminuted  The  (e.g., beach  explorationist completely  (<60  local of the  The y.m)  for  (1985)  finest  fractions  till)  eliminate  data  free  processes.  may  r a t i o may  rare  fine  that  shows  high-density mineral by  elements  work s u g g e s t s  produces  are  for  appropriate  to best  Saxby  dilution  studies)  individual  placer-forming  high-density minerals (2)  river  The  anomaly t o b a c k g r o u n d  mineralisation,  deposits  pronounced  d e p e n d e n t on  technique  data.  sediment to  if:  finest  environments.  i n f o r m a t i o n about the  the  due  long.  the  implications  minerals.  processing  effects  dispersion  two  most  different  high-density  effects  analysing  the  stream sediment surveys in  hydraulic  for  in  (beach s t u d i e s v s .  have  f r a c t i o n approach y i e l d s sampling  concentrations  ratios,  sediment.  two  discussed  station  mean c o n c e n t r a t i o n  between e n v i r o n m e n t s a r e  coarsest The  geometric  sampling  i n the  that be be  very low  source  particles  are  sediment-rich  occurs.  studies  to  the  b e c a u s e most m o u n t a i n s t r e a m s e d i m e n t s  are  different  are  in maturity  not  as  useful  from beach sand  deposits.  -21However, t h e s e about  the  mineral  s t u d i e s do  processes  Slingerland  have p r o p o s e d  four  p l a c e r s might  form,  entrainment,  two  appropriate Suspension  major  in  particles  (Einstein,  suggests  that suspension  shear  separation settling  zones  and  sized  and  settle  transported  beach  Frostick  (1985)  by  (2)  trapping.  1950).  shaped at  to  might  similar  particles  the  same  in  occur  settling  (1984)  also  downstream  turbulence flow  large  in  different  terminal  low  the  suspension into  of  rate.  is essentially  Slingerland  sorting  implies that  and  of low  velocities scale  i n w h i c h s e d i m e n t would most l i k e l y  equivalence.  which  or s u s p e n s i o n ,  separate  according  are  of  equivalence  Deep p o o l s w i t h v e r y  downstream o f p o i n t b a r s  result  interstice  s e p a r a t i o n zone of h i g h  velocity.  high-density  sorting  flow w i l l  flow  information  mechanisms  ( S l i n g e r l a n d , 1984)  open c h a n n e l  i n the  a  (4)  contrast  velocity  dunes  as Reid  settling  or s i m i l a r l y  w i t h i n the  produce  v i z . , (1) s e t t l i n g  density  that  to  sorting  or s u s p e n s i o n  sorting  turbulent levels  (1984) and  discussed e a r l i e r ,  differently  same  Mainly  (3) d i s p e r s i o n and  1.3.1.1 S e t t l i n g  considerable  operating  concentrations.  studies,  As  provide  flow show  -221.3.1.2 E n t r a i n m e n t Entrainment the  bed i n t o  the  i s the p r o c e s s of removing  t h e f l o w by o v e r c o m i n g  particle  ability  of  sorting  in  concentrations  for  number  entrainment  used  (uniform stage  shape,  all  of s o r t i n g  difficult the any  but  of  the c r i t i c a l shear  stress  conditions.  It  is,  the p o i n t  and g r a i n  size.  Yalin  beds two  sorted  motion  difficult  to  other e f f e c t s  though  cause  define  such  some  of  as  grains  the sediment  is  c u r v e s c a n be p l o t t e d f o r  resulting  and mean  has  which  orientations  Similar  been  and 2) t h e c r i t i c a l  at  is  sediments  has s i n c e  using perfectly  sediments  begins)  from v a r i o u s d i f f e r e n t  sediment  (1972)  diameter  notes  the curve based  grain  shear  of stream  on  bed. I t i s important t o understand concept  Shields  the s t a b i l i t y  natural  to predict  of  define  bed g e o m e t r i e s  experiments,  studies  mineral  The d i a g r a m  moving b e f o r e o t h e r s even  t h e same s i e v e  degrees  flume  of the  1-5A).  In n a t u r a l  roundness  different  high-density  1) i t was e s t a b l i s h e d  particles  start  Early studies  relating  hydraulic  o f a bed ( t h a t  objectively.  to  to  diameter)  sediment  the  a diagram  (Fig.  different  shortcomings:  produce  from  t e n d i n g t o keep  to a dimensionless c r i t i c a l  extensively  under  to  followed  (1936) who p r o d u c e d Reynolds  forces  p l a c e i n the bed.  entrainment  particles  hydraulic  that the  based i t  on  i s very  geometry  of  t h e bedforms b e f o r e  equivalence  can  be  - 2 3 -  0.01  4  0.01  ,  ,  0.1  1  10  d (mm)  Fig. 1 - 5 . (A) S h i e l d s ( 1 9 3 6 ) diagram of the c r i t i c a l shear R e y n o l d s number v e r s u s d i m e n s i o n l e s s c r i t i c a l s h e a r s t r e s s w i t h some experimental points and (B) c r i t i c a l shear stress of entrainment for a number o f s p h e r i c a l h i g h density materials i n water a t 2 0 ° C d e r i v e d f r o m S h i e l d s c u r v e ( m o d i f i e d f r o m G r i g g and R a t h b u n ( 1 9 6 9 ) ) .  -24formulated  (Steidtmann,  G r i g g and R a t h b u n obtain size  critical  shear  particle result  size of  R e y n o l d s numbers Recently, modelling  mixtures  stress  but fixed  the  45°  Frostick  (1985)  is  is  implying  that  roughness,  kinematic  that  Fletcher  this  being a a t low  as  and  theoretical  have  shown  easily  size,  not  beach  the flow  (R  B  U* i s f r i c t i o n  whether A  is  the  large  into  S  a  velocity, of  where  are very  or not a  = K U*/V, K  regardless  as  distributions  minerals  density  i s entrained  defined  deposits  the s i z e  1982).  that  (1984) and R e i d a n d  and l o w - d e n s i t y  t h a t determines  viscosity)  (Slingerland,  in  has o c c u r r e d ,  b o u n d a r y R e y n o l d s numbers bed  not  (Steidtmann,  into  the  i s independent of  1984)  Komar and Wang  high-density minerals  protruding  size  of the S h i e l d s curve  1977,  showed  sorting  entrained  of d i f f e r e n t  ( F i g . 1-5B) shows  observations  equivalence  factor  to  ( F i g . 1-5A).  equivalence.  important  diagram  diagram  of s m a l l p a r t i c l e  portion  settling  similar  forparticles  f o r a given density,  (SIingerland,  entrainment  Shields  f o r entrainment  natural  entrainment  of  stress  the  The r e s u l t i n g  f o r uniform  critical  (1969) used  shear  and d e n s i t y .  that  1982).  most  particle particle  t h e f l o w a t low i s a measure o f and  v  i s the  its  density  1977).  (pers.  comm.) and S l i n g e r l a n d (1984)  used  a  -25bedload  transport  differential minerals  saltation  on  modes,  model p r e d i c t s t h a t of  irrespective  the  particles  fine  sediment  The  bedload  originally sand.  for rivers  typically  density minerals in  this  of  the  flood. beds  densities  Consequently,  rivers  close  between  be  entrainment. the  similar rates contrasts  will  however, p r o d u c e  the very  seldom  elevated  intermediate  m o d e r a t e and  Einstein  for  r a t e s are  concentrations  for  median  sizes  dissimilar  for  comm.).  (1950)  was  tested is  application  to the  of  takes place  (1983) showed and  probably  predominant bedload  i s extremely  0.3  and  greatest  transport  when  limited.  4.2  during that  times the  wide s p e c t r u m  sampling The  s t u d y have p r e d o m i n a n t l y g r a v e l  Andrews  rolling  i n which the  encountered  movement  the  rate  (Fletcher, pers.  of  As  to at  d e n s i t y are  concentrations r a t e s are  rates.  to  Transport  mineral  formula  due  model  high-density  can  transported  sorting will,  mineral  mineral  material  absolute  to  r o u g h n e s s and results  density.  s i z e s but  which t r a n s p o r t  different  bed  different  Entrainment  high-density  the  are  thus h i g h - d e n s i t y  form.  for  of  bed  and  transport  particles  bed  of t h e i r  for  low,  the  to s o r t i n g of  1950)  low-density  differential  transport  diameter  (Einstein,  of  i n t o account  correlated The  entrainment  based  model t a k e s  formula  beds  the  for - high-  rivers  sampled  i n w h i c h most  spring  particles  meltwater in  median d i a m e t e r  gravel (Doo)  -26are  entrained  is  achieved  a t n e a r l y the only during  result  is contrary  to  larger  particles  are  stages. mineral  Andrews'  same d i s c h a r g e  extreme  an  floods  hypothesis  entrained  (1983) model  concentrations  cannot  and  that  this  (Fig.  1-6).  This  that  at  i n c r e a s i n g l y higher  implies  that  form d u r i n g  because a l l t r a n s p o r t r a t e s are  the  progressively  high-density  the  spring  flood  same.  1.3.1.3 D i s p e r s i v e s o r t i n g Dispersive  or s h e a r  s o r t i n g was  proposed  (1979) a s  a mechanism f o r p r o d u c i n g  density  minerals  concentrated layer  granular  of a s t r e a m  result  fall  (Middleton, (large  is  at  that  the  for will  the be  particles.  concentrations  arises  of  the  first  i n the  twice  horizon  a  grains grading  Sallenger pressure  mechanism l a r g e  Slingerland  are  inverse  dispersive  bed  smaller  larger  deposit).  same  to develop  as  a  pressures  s i e v i n g i n w h i c h the  s p a c e s between t h e  top  possible for horizons  mineral  high  within  dispersive  a r e l a t i o n s h i p from the  density particles low-density  It  1 9 7 0 ) . B o t h mechanisms p r o d u c e  particles  shows  1984).  producing  or k i n e t i c  through the  (1979) d e r i v e d which  horizons  of  d i s p e r s i o n , f o r example a moving  (Slingerland,  1979)  Sallenger  concentrations  different  of g r a i n c o l l i s i o n s  (Sallenger, grains  at  by  as  highsmall  (1984) shows t h a t i t i n which  the  mean  high-density concentration.  -27-  Fig. 1-6. Relationship between critical dimensionless shear s t r e s s f o r m o t i o n and t h e r a t i o o f p a r t i c l e s i z e t o t h e median p a r t i c l e s i z e o f t h e bed (Andrews, 1 9 8 3 ) .  -28Kinetic  sieving  particles  falling  Although sorting  a l l the  Sallenger  may  account  o f b e a c h e s , no a  results  in  small  high-density  way  to the  base of t h e  (1979)  recognizes  for p r o f i l e s  s e e n on  w o r k e r s have p r o p o s e d  of a g r a v e l d e p o s i t bottom  (Basque,  repeated  scouring  entrained  and  dispersive the  bed  1979).  mineral  move  after  a flood  hydraulic Frostick  respect  trapping  the  event,  occur  by  during  way  It is  to the  base  or a  false  attributed failing  to  to be  bedrock.  However,  any  provided  flood  mobilised.  hence t h e with  the  the  that  high-density  fine  particles  between c o a r s e fine  coarse  matrix  particles  is  framework.  not  in  Reid  and  are  not  mechanism t h o u g h t h e y  high-density  the  to e x p l a i n  interstices  low-density  because  been gold  assuming  minerals  minerals.  coarsening-upwards deposits deposits  placers.  i s bedrock  reaching  attempts  (1985) p r o p o s e d how  with  faces  trapping  equivalence  to  has  i s completely  into  about  This  eventually  concentrations  will  base  swash  d i s p e r s i v e s o r t i n g as  work t h e i r  the  of d e p o s i t s  Interstice  Interstice  clear  whether  s o r t i n g should  layer  1.3.1.4  particles  deposit.  that dispersive  the  mechanism t o e x p l a i n a u r i f e r o u s f l u v i a l  well-known t h a t g o l d  mineral  are  pores at  behave  with  suggest  that  u n l i k e l y to produce  placer  the  They  will  surface  become  clogged;  -29however,  fining-upwards  particles  to  pores.  move  Currently,  interstice-trapping gold  t e n d s t o be  1.3.2  sequences  downward the  through  only  will  produce  more a b u n d a n t  with  all  natural  for  i n the  finer  it  result.  Although entrainment because  density minerals Frostick an  particles protrude deposit explains and  are  point  fine  the  out  forced  the  to  f l o w and  be  high-density  Keefer  sorting  topset  sorting  on  the  avalanche lamellae  trough  explains  Similar  processes  observed received  deposits beaches,  and  Large  surface  entrained. minerals. of  (1969)  high-density  the  density mineral  on  likely  that  natural the  most  of  high-  Reid  and  t h a t d i s p e r s i v e s o r t i n g may  flume o b s e r v a t i o n s  explains  on  process.  M c Q u i v e y and  Entrainment  lag  ancillary  i n t o the of  explains  commonly o b s e r v e d  (1985)  important  it  s o r t i n g has  i s that  high-density  is  mechanisms combine t o p r o d u c e t h e  that  sizes.  to produce  processes,  fine  assuming  placer deposits  several  attention,  allow  increasingly larger  basis  Summary of mechanisms l i k e l y mineral concentrations  As  would  using  c r e s t s of mineral face  This  Slingerland  scales  a  to lag  (1984)  Jobson  (1973)  three  processes.  ripples  and  explains  bottom s e t h i g h - d e n s i t y  them  leaves  lamellae;  suspension  a c t i n g at a l l  low-density  allowing  B r a d y and  be  dispersive  foreset  sorting mineral can  dunes  be  high-  in  the  lamellae. used  to  -30explain  many  experimental together  types and  qualitatively, of p l a c e r s  applying  experience.  past  Field The  sampling  aim  of  exploration gold  a  is  still  largely  to  sediment  provide  be  a  brought  matter  sampling  either:  i n a large  of  anomalous  by  taking  probability  in  catchment b a s i n  an a d e q u a t e l y  of not d e t e c t i n g  gold  mineralisation  mineral  to  warrant  large  processes.  Field  is  sampling  Hence, t h e f o l l o w i n g  due  can  to  be a waste  section will  be  sample so t h a t t h e i s t o l e r a b l y low.  by c h e c k i n g  methods  to  i n the  that  i s the r e s u l t of p r o x i m i t y  not  p r o b l e m s or t h e s u r v e y w i l l  gold  problem  the anomaly  concentration and  of  The f i r s t  s e c o n d p r o b l e m may be a p p r o a c h e d  elevated  of  (1) an i n d i c a t i o n o f  concentrations  sediments of a s i n g l e stream.  The  can  i n v e s t i g a t i o n o r (2) an i n d i c a t i o n o f p r o x i m i t y  source  solved  results  Although  problems  mineralisation  further  deposit.  p r e d i c t i o n o f t h e o c c u r r e n c e and  effective  is  placer  theoretical  concentration  1.4  of  local  must d e a l  to  hydraulic with  o f t i m e and  discuss  an  these money.  methods o f f i e l d  sampling.  1.4.1  Field  Emmons  sample c o l l e c t i o n  (1937) recommended  techniques that  prospectors  should  pan  -31stream gold be  sediments  to determine  i n the sediment. located  dispersion  by train  t h e o r y but  the g o l d  of  gold  the  of " c o l o u r s "  (small  The  i n the stream  particles  finer  t h e t e c h n i q u e and Despite  its  exploration sampling  tool  problem  quantity  method  of  prone  sediments  Poling  decreases  gold  determining  i s extremely  successfully.  presence  Many b e d r o c k  panned c o n c e n t r a t e s ) . in  the  (1985)  or a b s e n c e  occurrences  upstream  100  particles  skill  of the  can  the be  especially i f  i s too  t o be  fine that  the in  panned recovery  size  for on  panner. panning  right  can  rapid  to f a i l u r e ,  overcome  sediment  in  i s e x t r e m e l y dependent  shortcomings, in  of a  of g o l d  i s obviously quite  indicated  Jim and  can  terminus  d r a m a t i c a l l y with decrease than  of  be  is  a  hands.  The  because  a  processed  powerful statistical very  to y i e l d  large a small  h i g h - d e n s i t y m i n e r a l c o n c e n t r a t e . However, i t i s i m p o r t a n t that  the s i z e  of  gold  distribution  in  reconnaissance Gleeson from  the  the expected  sediment  are  survey beforehand  (1972) t o o k  a large  show t y p i c a l  streams  returning  extremely  (1979) s u g g e s t e d  h i g h Au that  investigated  ( B o y l e , 1979).  in  Boyle  a r e a , Yukon T e r r i t o r y .  nugget e f f e c t s  background  concentration a and  number o f panned c o n c e n t r a t e s  t h e m i n e r a l i s e d Keno H i l l  results  with  and  Au  w i t h samples  c o n t e n t and  concentration (Fig.  the w e i g h t  The  f r o m many  rare 1-1).  samples Boyle  of the c o n c e n t r a t e s h o u l d  -32be  recorded,  assessment  w h i c h may  of r e l i a b i l i t y  Zantop  and  -80-mesh  (e.g.  et.  Rose  The  anomalies  Sn  for  reproducibility w o l f r a m i t e and be  analysed noted  that  field  density  was  In  the  turnaround The  simple Mercier dredge  is  a  poor  Smith  (1986),  sluice  permitting  of  large  (1983)  show  have  They  sediments sampling  meaningful.  lower  field  riffled  were  results.  lower  much  (1986)  Poling  to  were more  Giusti  i s extremely mm.  that  and  Wang and  spot  concentrates  popular  contrast  processing  panned  for c a s s i t e r i t e ,  i t i s e x t r e m e l y p o r t a b l e and  However,  0.1  but  cost  i s t h e most  and  than  prone  than sampling  the r e s u l t s  overall  sampling  sluice  Panned  t a k e s more t i m e  pan  and  of  Even known m i n e r a l i s a t i o n c o u l d  i s shorter.  (1986)  was  of  techniques  produced  producing very r e l i a b l e  In  later  results  that  to the nugget e f f e c t  time  t o use.  the  method  and  concentration  because  in  geochemical  with  reliably.  the  gold  device  W  needed and  end  p\m)  1979)  scheelite.  panning  without  (<177  and  visually  step  values.  geochemical  due  detected  important  (1979) compared  §_1.,  concentrates.  an o f Au  Nespereira  traditional  not  be  and  concentration theoretically Maurice used  a  volumes o f  rapid  sediment.  the  i n e f f i c i e n t for c o l l e c t i n g  and  suction  extremely  that  the  riffled  gold  finer  -33Geochemical inevitably  contain  differing solved to a  skills  by  a commercial  This  the  a  of  be  large  samples  screened  t o between <1  the  The  preparation  samples can  mm  be  i s some e v i d e n c e  that  though  Fipke should  yield  procedure  there  p r o c e s s the  to  all  that  (1986),  <2  of  is  sediment  or  to  liquids.  disadvantage  industry, to  be  screened  high-density the  to  samples  i s becoming s t a n d a r d  that mm  samples  and  There  Daughtry  (1986) recommend  due  problem can  sending  using  large.  exploration  cost.  This  sieving  laboratories willing  reasonable  Smith  and  fashion.  must  sluicing  variability  advantage t h a t  i n a standard  of  mm)  concentrates the  p a n n i n g and  stream sediment  for  mineral  shortage  bulk  laboratory  samples  field  samplers.  (<2  method has  collection in  the  size  mineral  processed the  of  coarse  from  considerable  collecting  fairly  heavy  results  an  is  a  samples  at  (1986)  and  be 8 to  field10  kg  sample.  1.4.2  S e l e c t i o n of  This  aspect  described data  i n the  of  be  several  location  sampling  literature  i n t e r p r e t a t i o n with  many s m a l l can  sampling  despite  respect  streams c o l l e c t i o n  achieved  only  locations within  by  is  or  to  the  of a  a composite  distance  very  poorly  implications  hydraulic  panning  taking  a short  usually  of  effects. large  In  sample  sample each  to  from  other.  -34Smith  (1986) c o l l e c t s  finer  than  importance wherever  found  has  accumulated,  samples  from  where  sand  recognizing  similar  the  environments  possible. (1986b)  locations  that  cleavage  silt in  particles, were  2 mm  of t a k i n g  Maurice sampling  bulk samples a t l o c a t i o n s  investigated on  and  the  types  the Assemetquagan R i v e r , sand  collected  river  however;  different  bed  from  yielded  of  Quebec  between  and  slaty  h i g h numbers o f  gold  the h i g h - d e n s i t y m i n e r a l c o n c e n t r a t e s  considerably  larger  than  can  be  analysed  commercially.  1.5  Conclusions The  c u r r e n t problems  i n stream  sediment  surveys  arise  because: 1) s a m p l i n g  techniques  extreme r a r i t y 2)  traditional for be  3) t h e  of g o l d  sampling  r e c o v e r y of the best size  determined 4) v e r y l i t t l e geomorphic gravel-bed  do  fine  fraction  to  take  i n stream tools  to  account  the  sediments.  (gold  pan)  are  inefficient  particles  which  may  sample. and  shape  of  gold  is  not  sampling.  i s known q u a n t i t a t i v e l y processes c o n t r o l l i n g rivers,  into  sand-size gold  distribution prior  not  about  hydraulic  dispersion  hence Au d a t a c a n n o t  be  of g o l d  and in  corrected  -35reliably  to  remove  local  hydraulic  effects.  -36-  CHAPTER  2:  ORIENTATION  SAMPLING  - 3 7 -  2.0  Introduction Data  on  sediments in  1.2.1).  stream  streams  statistical  problems  Therefore,  sediment  draining  Columbia.  gold  Each  permitting  fraction  and  phase  was s p l i t  in  into  of the study from  southern  component  o f t h e number o f g o l d errors  fractions thereby  particles  due  to  five  British  o f Au i n t h e s a m p l e s  sampling  stream  (see d i s c u s s i o n  were c o l l e c t e d  occurrences  sample  estimation  in this  samples  to determine the d i s t r i b u t i o n  each  of sampling  f o r Au a r e n o t r e a d i l y a v a i l a b l e  section  large  the  in  t h e nugget  effect.  2.1  Description 1985,  In June sampling  of streams  based  five on  streams  the  were s e l e c t e d  known  occurrence  sediment  Au a n o m a l y or  example,  pedo- o r 1 i t h o g e o c h e m i c a l ) .  are  shown  2.1.1  From and  Tsowwin R i v e r ,  Tahsis  River Inlet  near  well-defined  a  stream  anomaly ( f o r  Locations  of streams  Tahsis  (49°48'N on t h e west  i t s headwaters falls  of  sediment  in Fig. 2-1.  Tsowwin into  other  for  through  126Q34'W,  coast  of  NTS  92E/15)  Vancouver  to the i n l e t  the stream  6 0 0 m.  small  A  drains Island.  i s 8 km  long  electrum-quartz  -38L  Fig. 2-1. L o c a t i o n s of streams sampled. 2='Salmonberry' Creek, 3=Franklin River, 5=Watson Bar C r e e k .  l=Tsowwin 4=Harris  River, Creek,  -39carbonate (Muller (B.  vein  e_t a l . ,  Smee,  1976)  pers.  flowing  over  braided  towards  The  i n a s h e a r zone  comm).  The  in  Tahsis  mineralisation  coarse  to fine  200  tributary  mineralisation  ( F i g . 2-2A).  NTS  Creek',  Creek'  92F/03,04) d r a i n s  mineralisation Volcanics,  (4 km),  flows  over t i l l  Kennedy  Lake  SD-04 and Kennedy  hosted  Island  short  of  where  boulder-choked  the  near  fast-  of  85-SD-02),  in  km  name,  a  steep  above  the  49<>01'N  125°30'W,  a r e a o f Au-Sb-As-Ag q u a r t z Island  rocks.  a larger  taken  on  stream  Group The  and  deposits,  mineralised was  small  from  (Bonanza  creek  narrow  stream.  a  fan  i s very  (<7 m)  eventually  and  reaching  Samples  85-  deposit  above  emerges f r o m t h e  hills.  on t h e b a r s were sampled  tributary  of  Ucluelet  (slope=0.4)  the  outcrop  downstream  0.5  i n Vancouver  joining  the  taken  about  fluvial  Small gravel deposits downstream  was  Intrusives)  after  inlet  r e a c h e s b u t becomes  85-SD-01,  a complex  steep and  from the  youthful,  below  (unofficial  85-SD-05 were Lake  m  (samples  (slope=0.34)  %  is  Volcanics  Inlet.  85-SD-03  2.1.2 Salmonberry  5 km  upper  gravels accumulating  Sample  'Salmonberry  stream  its  sampled,  known  rapids.  c r o p s out about  bedrock  s t r e a m was  h o s t e d by Bonanza  area.  sampled  A a  about  small short  4  km  l o g and distance  -40-  F i g . 2-2. S a m p l i n g s t a t i o n s on s t r e a m s , (A) Tsowwin R i v e r , (B) ' S a l m o n b e r r y C r e e k ' , (C) F r a n k l i n R i v e r , (D) Harris Creek, (E) Watson Bar C r e e k . D e t a i l s a r e f r o m 1:50,000 NTS maps. C o n t o u r s a r e i n m e t r e s f o r (B) and (C) and f e e t f o r ( A ) , (D) and ( E ) . P o s s i b l e s o u r c e s of g o l d i n the s t r e a m s e d i m e n t s a r e shown by s t a r s .  -f upstream bar  -41-  of  the  m i n e r a l i s a t i o n on  a small  sand and  gravel  ( F i g 2-2B).  2.1.3  Franklin River,  Franklin  west of P o r t  (49O07'N  River  meandering stream with regional  Au-Cu s o i l  formation Walker,  in  the  pers.  It  is  slope  8 km of  0.026.  considered  source  As  no  1 km  boulder from  of  the  east  of  log-jam  stream at  least  40  Creek glacial  in  Lumby.  drift  It drains  deposits.which  veins  an  (R. have  Mine). average  could  be  85-SD-09 were a small  (Fig.  sand  2-2C).  Vernon  (50O12'N 118055'W, NTS to  has  a n o m a l y on  Creek  long  and  drainage  Harris  km  Island  (Thistle  85-SD-08 and  around a  draining a  sulphide-iron  quartz  stream  downstream of t h e  H a r r i s Creek,  bed  of Vancouver  of t h e  samples  92F/02) i s a  a  Gold-bearing  part  gravel accumulation  2.1.4  Group  NTS  t o a major c o n f l u e n c e  background,  taken about and  long  and  anomaly d e r i v e d Sicker  the  124039'W,  a cobble  comm. 1 9 8 5 ) .  been mined near  Alberni  82L/02) i s a  i t s confluence a rolling overlie  with  upland  gneiss,  mature Duteau  blanketed  by  granodiorite  Q  intrusions sediments  and has  mineralisation roughly  30  km  plateau been is  basalts.  A gold  anomaly  defined  though  the  unknown.  from the  Sampling  headwaters  in  was the  Au  i n stream type  of  carried  out  dispersion  -42train  (A.  Samples sandy small  Burton, pers.  b e a c h and  point  train  25 km  Bar  long  Fraser  carbonate located taken  9 km  distance  Creek  Stirrup  Field  hosted i n of  sediment)  NTS  clastic  the c o n f l u e n c e .  fluvial  carried (H.  the  with  out upstream pers.  the  quartz  sediments Samples i n the  is were  stream  from a c h a n n e l bar a  deposits.  Warren,  920/01) i s  short  (85-SD-15) ( F i g . the stream  flows  Recently,  of the  placer  mineralisation  comm.).  Sampling  downstream  (coarse  of  Au-Ag-Sb-As  of t h e m i n e r a l i s a t i o n  each stream,  taken  taken from a  to i t s confluence  85-SD-14) and  and  at  On  122°15'W,  Downstream o f t h e m i n e r a l i s a t i o n  been  small  Lilooet  downstream of the m i n e r a l i s a t i o n  till  a  beginning  of w e l l - d e f i n e d  upstream  m i n i n g has  2.2  of the  (51<>05'N  An a r e a  upstream  through  from  85-SD-12 was  of  from the headwaters  (85-SD-13 and  2-2E).  north  mineralisation  4 km  sample  taken  sediments.  ( F i g . 2-2D).  Creek  River.  background  were  bar u p s t r e a m  Watson Bar C r e e k ,  Watson  bed  and  gravel  dispersion  2.1.5  85-SD-ll  85-SD-10 and bar  comm.) and  three of  sediment) locations  samples  the  and  low  within  were  taken:  mineralisation  two  i n high  energy  (relatively  one  two  or  metres  were energy finer  of each  -43other, of  and  the  i f possible  mineralisation  background  locations  availability  of  dug  a  t h r o u g h a 5 mm  until  the  pail  sufficient  also  sediment lost of  tipped  into  rinsed  fraction  to  pail  was  to  carry  on  the  became f u l l  of t h e  the s h o v e l  lithological  (black  discarded. of  sand)  t o be  was  sediment.  hence  very  sediment the  very  was  jigging  of sediment  was  carefully  retained.  locations  were s e l e c t e d  easy removal  o f t h e samples  were  upstream  contamination  pail  i s an o b s e r v a b l e t e n d e n c y  At e a c h sample  sample  wet  site and  The  +5  mm  photographs textural  and  o b s e r v a t i o n s were r e c o r d e d .  Sample l o c a t i o n s  taken  during  b l a d e was  cm  and o v e r f l o w e d  Fine  each s h o v e l f u l  t h e s i e v e as t h e r e  was  plastic  -5 mm  lost.  30  T h i s volume  o f water  sieve  the s i e v e  taken  20 t o  made t o c a t c h t h e o v e r f l o w ,  After  was  litre  of  visually  sediment  full.  20 kg  i n s u s p e n s i o n was  heavy-minerals  were  three-quarters  of  and  The  s c r e e n i n t o a 23  sieving.  into  volume J  a t the s i d e s  action  for  was  the  no a t t e m p t  fine  upstream  based  Usually a p i t 1 m  equivalent  Inevitably, but  taken  expected  selected  t o p r o v i d e the sample.  sieved  roughly  was  sediments  were  homogeneous s e d i m e n t . was  in  sample  Au c o n t e n t s .  Sample  deep  a third  by r o a d  of  close  to roads to  to a v e h i c l e ; nearby  materials.  road  however, bridges  allow samples  to avoid  -44-  2.3  Laboratory  2.3.1  processing  Sieving  Samples were wet Fig  2-3.  the  field  five  fractions  -270-mesh  was  23  on  s p e c i a l l y cut  the  a  hole  litre  i n the  to f i t t i g h t l y  finest  fraction  pail  pail  with  water a t t h e  of  stack  overflow  and  losses  of  30  0.5  *  i n the  stack.  filtration fine  p l a c i n g the  stack  on  allowed  A hose p r o v i d e d  a simple  from the  Collection  t h r o u g h a 1 Um were  a  the  s e d i m e n t , however t h e  and  sediment  hole  stack  possible contamination  removed.  overflow  sieve  of 270-  fresh  faucet-mounted  pail,  preventing  of a p o r t i o n of filter  showed  about  0.7  tipped  into  the that  mg/s  or  g/sample. About  of t h e the  the  removed t h e  backup  fractions  spanning  The  l i d . The  coarse be  top  by  to prevent  easily  water  each  sediment.  mesh s i e v e c o u l d  aspirator  two  in  -70+100-mesh, -100+140-mesh, -140+200-mesh,  -200+270-mesh) and mounted  shown  2 4> (-4+16-mesh (ASTM) , -16+50-mesh, 4-mesh sieve),  (-50+70-mesh,  stack  apparatus  Seven s i e v e s were used t o p r o v i d e  each spanning is  s i e v e d u s i n g the  300  g of  stack  and  s e d i m e n t was  through the sieve.  -4-mesh s e d i m e n t was washed and visibly  screen.  Water  tended  mixed w i t h  fingers  flow  out  repeated of the  for  joints  top  until  f r e e of m a t e r i a l t h a t would  T h i s s e q u e n c e was to  the  the  pass each  i n the  -45-  Fresh water  16 50 cfl  o >  CO  CO <  70 100  fresh water  I  140 200 270  1  overflow water & fine sediment water & fine sediment  (plastic pail  -270-mesh sediment  F i g . 2 - 3 . Wet-sieving  apparatus.  -4 sieve  stack  channeled of  the  due  to clogging  away  from the  l i d (Fig.  -270-mesh  2-3),  fraction  f r a c t i o n s was  before  dealing  without  were  weighed.  for  at  off  and  least  stage  The 24  when t h e to  extreme c a r e heavy  hours,  original After  than  The and  30  was Vim)  completion  were t h o r o u g h l y  the  washing  The  stored.  dried  which the  had  at to  by  was  not tend  during  hand-lens to d e t e c t  *  80°C  settle  washed  into At  from with  any one  water,  portion  of  (diameter of  the  washing.  using  followed screen  *  decanted  bottom  o f s i e v i n g of e a c h sample  cleaned  cleaner  i n the  0.5  to  weighed.  washing  2  weighed  dried at  water was then  hose  five  These p a r t i c l e s  to remain  the  wet  bags,  transferred  repeated  lost.  and  allowed  80<>C and be  bowing of  two  The  was  was  Contamination  in plastic  sediment  upward  hands  fraction.  and  but  contamination  taken to ensure t h a t a s m a l l  container  ultrasonic  by  new  after  sample  was  by  i n t o g l a s s b e a k e r s and  another  minerals  greater  a  sieves  material.  -270-mesh f r a c t i o n  beakers  container  joint  coarser  sealed,  discarded.  several  finer  immediately placed  were washed  and  lower  avoided  with  drying,  fractions  of t h e  thus a v o i d i n g  by  between  fractions  6-  by  a p a i n t brush, visual  breakages.  the  sieves  airbrush  examination using  and a  -472.3.2  Heavy-mineral  i n t h e 0.5 <t> f r a c t i o n s  Gold mineral liquid  separation  fractions  using  a  g r a v i t y o f 3.3.  from  acetone.  The  was t h e n  washed  acetone. liquid  the  resulting  liquid  by  Methylene  repeated  acetone-methylene  Washing p r o c e e d e d  reached  Concentrates  3.3 g/cm . a  manual  i o d i d e was with  iodide solution t o remove t h e  until  the d e n s i t y of the heavy  Before  use, r e - c y c l e d methylene  u s i n g Whatman  probably  were  washing  f o r s e v e r a l h o u r s w i t h water  i o d i d e was f i l t e r e d the  samples  rod.  heavy  a heavy  separatory funnel with repeated  a g i t a t i o n with a glass s t i r r i n g recovered  into  iodide (CHzIa)  u s i n g methylene  with a s p e c i f i c  prepared  was c o n c e n t r a t e d  2  filters;  remained contaminated  therefore,  with very  fine  sediment.  2.3.3  P r e - c o n c e n t r a t i o n o f -270-mesh  Several attempts heavy-mineral  were  made  concentrate  using  produce  a  methylene  i o d i d e and a  However,  the  t o g e t h e r a n d t h e wide r a n g e o f p a r t i c l e  in the leads  fraction to  coarsest  and  production  heavy m i n e r a l s  i n the f r a c t i o n  -270-mesh  centrifuge. sample  clay  to  fraction  corresponding of  a  tends  settling  concentrate  i n the f r a c t i o n .  to  bind sizes  velocities  of only the very  -482.3.4  Chemical  analysis  Heavy-mineral  concentrates,  light-mineral  -270-mesh s e d i m e n t were weighed determination  by  into  non-destructive  plastic  analysis  (Na,  Se, C r , F e , Co, N i , Zn, A s , Se, Mo,  L a , L u , Hf, T a , W, parameters  summarised  or  25 g  Creek  of  i n Table light  minerals  riffle  U).  (X-Ray A s s a y  are  light  Th,  21  Laboratories, 2-1.  minerals  Only  other  elements  Ag, Sb, Ba, analytical  Don M i l l s ,  60 g o f  Ontario)  heavy-minerals  c o u l d be a n a l y s e d ,  Heavy-mineral  concentrates to  also  large  enough  fractions),  both  splits  being  Several duplicate s p l i t s  be  therefore  mineral  using  a  from H a r r i s  split  submitted  of l i g h t  for  neutron  and -270-mesh s e d i m e n t were s p l i t  splitter.  analysed  and  Neutron a c t i v a t i o n  were  also  vials  instrumental  activation Ca,  (INAA) o f Au  s e p a r a t e s and  (coarser  for analysis. separates  s o t h a t 5% o f a l l t h e s a m p l e s were  were  analysed  as d u p l i c a t e s . After period  t h e s a m p l e s were r e t u r n e d to  acceptable for  allow radiation  analysis  Laboratories, fire finish  assay  decay levels,  by  a  North with  atomic  vials  were  also  cooling  using  spectroscopy  of samples  re-submitted  (Chemex  Columbia)  absorption  to  resubmitted  laboratory  British  A suite  the  isotopes  38 s a m p l e s were  Vancouver,  flame  radioactive  different  on t h e e l e c t r u m b e a d .  original  of  following  to  in  their  the  first  -49-  T a b l e 2-1. Summary of conditions used in instrumental neutron activation analysis, McMaster U n i v e r s i t y r e a c t o r (X-Ray A s s a y L a b o r a t o r i e s ) Parameter  Type o r  R e a c t o r power Irradiation flux I r r a d i a t i o n time P r e - a n a l y s i s decay time A c t i v i t y i n t e g r a t i o n time Au i s o t o p e Detector Au S t a n d a r d P o s t - a n a l y s i s decay time  2 Megawatts 2xl0 neutrons/cm /s 1 hour 5 t o 7 days 200 s 198 Ge(Li) In-house and MA2 At l e a s t t h r e e months 1 3  Value  2  -50l a b o r a t o r y t o check  2.3.5 V i s u a l Fine  examination  sand-size  samples  were  microscope  after  was  heavy-mineral  on a b l a c k p a p e r  against  radioactive  isotopes.  using  were  a  from a l l binocular  A 5 cm t h i c k  around t h e microscope  Gold  and  also  from  tray.  longer-lived  dimensions  concentrates  concentrates  visually  constructed  particles  concentrates  r e m o v i n g m a g n e t i c m i n e r a l s and s p r i n k l i n g  protection  relative  of heavy-mineral  examined  the c o n c e n t r a t e shield  for reproducibility.  removed  Harris  were e x t r a c t e d a n d  were  recorded.  from  Creek  to provide  ^-particle-emitting  particles  shape  lead  the  for  Gold  -140+200-mesh  detailed  shape  analys i s .  2.3.6  Scanning  Gold stubs and  e l e c t r o n microscopy  particles  by f i r s t permitting  comm.).  from  particles  the  dimensions  polish  were  by acetone to settle  examination,  H a r r i s Creek were mounted on S.E.M.  coating the stubs with cosmetic  Particles  surrounded  (S.E.M.)  stubs  were t h e n  to  then  placed  vapour  into  polish  ( J . Knight,  pers.  on  in a petri  the  were  dry  nail  polish. coated  estimated  from  the  stubs  and  dish  to allow the  Before  microscopic  with S.E.M.  carbon.  Axial  photographs.  -512.4  Results  2.4.1 D i s t r i b u t i o n Because recorded  weight  the t o t a l  However, known  the  of sediment  the  sizes  o f t h e +5 mm  weight  of  distributions  the c o a r s e r  Comparison  of  of  fractions  latter  (except  sediment  reject  sample  the  is  finer  fractions  shows t h a t  E).  As  weights.  taken  from  the weights of  a r e more t h a n t w i c e t h e w e i g h t s o f  f o r Watson Bar C r e e k  unknown.  to  have t h e g r e a t e s t  medium s a n d and f i n e r  was n o t  fractions are  ( F i g . 2-4A  h i g h and low e n e r g y e n v i r o n m e n t s the  field  each  from l a b o r a t o r y p r o c e s s i n g  expected,  i n -5 mm  the  where e n v i r o n m e n t s  former  were  quite  fraction  are  similar).  2.4.2 W e i g h t s  of heavy-mineral c o n c e n t r a t e s  Weights  of  heavy  summarised  in  the  found  appendix.  i n the c o a r s e s t  highest  minerals  fraction  concentrations  occur  in  each  The  greatest  (-50+70-mesh) in  either  weights a r e though  the  -70+100-mesh o r  -100+140-mesh.  o f INAA  2.4.3 R e l i a b i l i t y Non-destructive avoids  sample  destructive  INAA  for  preparation  techniques  (e.g.,  Au  was  selected  problems gold  a s 1) i t  encountered  in  l o s s due t o s m e a r i n g  d u r i n g m i l l i n g ) a n d , 2) i t p r e s e r v e s t h e sample  for future  -52-  0-25  0.125  0.0625  0.25  0.125  0.0625  Diameter (mm)  3 A  0.25  ,  1 «->  0.125 0.0625 Di ameter (mm)  Fig. 2 - 4 . Cumulative sediment size distributions for sediment finer than 4 mm: (A) Tsowwin R i v e r , (B) 'Salmonberry Creek', (C) F r a n k l i n R i v e r , (D) H a r r i s Creek, ( E ) Watson Bar Creek. Sample numbers are shown next to each d i s t r i b u t i o n .  -53re-analysis analyses  or e x a m i n a t i o n .  and  systematic  s h i e l d i n g ) must be Analyses provide (Fig.  an 2-5)  particles between  of  heavy-mineral  indication because  splits  Ten  give  95%  the  mineral  batch  Self-shielding  g r a i n s are  s h i e l d e d from  that  of  as  the  coarser  than  i n the  the  used  to  discrete  partitioned  splitter  is  used.  of elements not o c c u r r i n g (e.g.  (ANOVA,  95%  about  with  no  As,  case  Table  confidence). four  months  (±10%  observable  with  biases  being c l o s e to  determination  INAA i f t h e irradiating  Bloom  and  flux  gold  mm.  of  a  test  by  heavy  the  of t h e  Brooker  o n l y o c c u r s when As  of  c e n t r e s of l a r g e  underestimation  sample.  0.1  rare  unevenly  the worst  g o l d , by  overall  self-shielding  be  particles  analyses  occurs  such  content  self-  ( F i g . 2-6).  elements,  an  of  reproducibility  very  analysis  fraction,  the d e t e c t i o n l i m i t  margins g i v i n g  for  as  be  show good r e p r o d u c i b i l i t y  of Au  particular  to  cannot  adequate  determinations  confidence)  i n any  an  reproducible results  first  due  instrumental  t o be  if  samples r e s u b m i t t e d  after  (e.g.,  splits  occurs  likely  even  split  of  Au  as v e r y r a r e d i s c r e t e 2-2)  errors  reproducibility  considered.  which are  Conversely,  However,  grain  true  Au  (1986) c l a i m  particles possible  are  under-  -54-  Au (ppb)  Fig. 2-5. concentrate  Gold splits.  analyses  (INAA)  of  heavy  mineral  -55-  Table 2-2. Duplicate INAA analyses for mineral separates ( a l l values i n ppm). i n s t r u m e n t a l d e t e c t i o n l i m i t i s 1 ppm. Sample # Number 01 03 04 05 06 07 07 13 14 Analysis Null  Analys i s  Fraction  First  Second  20 8 6 4 23 7 12 81 9  22 6 7 8 20 11 16 85 13  -50+70 -100+140 -50+70 -70+100 -70+100 -70+100 -100+140 -200+270 -140+200  o f v a r i a n c e on l o g a r i t h m i c  hypothesis  :  Mi  As in light The reported  =  M =• =  ...  =  data  M-s  Source of Variability  Sum o f Squares  Between  2.1419  8  0.2677  0.0981  9  0.0109  Pairs  Degrees of Freedom  Mean Squares  F  24.56 Within  Pairs  F O R X X I C A L ( 8 , 9 , 0 .05) F  >  F c R X T l C A L ,  null  = 3. 23 hypothesis  rejected  -56-  e s t i m a t i o n o f Au analysed  by  Results are but  become  the  scatter  fraction,  content  fire  assay  scattered  fire  important  is  Bloom and on  the  INAA.  for  2-3A  2-3A)  light  detection  represent inevitable  coarser  of  that  Au  self-  fractions  as  reproducibility  and  INAA a p p e a r s t o be  («15  separates  analyses limit.  inadequate problem with  m a j o r i t y of  have c o n c e n t r a t i o n s  of  o n l y two  r e t u r n i n g higher  an  data  The  average d e t e c t i o n l i m i t mineral  However,  -70+100-mesh  f o r a l l samples are  2-3B.  the  limit:  the  2-7)  technique.  and  (Table  (Fig.  indicate  non-destructive  concentration data  Tables  the  finish.  (1986).  D i s c u s s i o n of s t r e a m Au  concentrates  the  typically  foregoing tests  adequate a n a l y t i c a l  in  atomic a b s o r p t i o n  T h i s may  Brooker  from b i a s ,  Gold  s a m p l e s were r e -  lower c o n c e n t r a t i o n s .  assay  shielding  2.4.4  thirty  i s p r i m a r i l y a s s o c i a t e d with  than  freedom  with  at  concentrations  Based  INAA,  comparable a t h i g h c o n c e n t r a t i o n s  with  suggested  by  are  are  These  ppb) a t or  the  finer  i n excess  below the  anomalous  heavy-mineral  heavy-mineral  whereas t h e  significantly  presented  majority detection  greater  samples  The  than  probably  separation,  fractions.  of  an  majority  -57-  F i g . 2-6. C o m p a r i s o n of Au two d i f f e r e n t o c c a s i o n s .  analyses  determined  by  INAA  on  -58-  Fig. fire  2-7. C o m p a r i s o n o f Au c o n c e n t r a t i o n s assay/atomic a b s o r p t i o n and INAA.  determined  -59-  T a b l e 2-3A. G o l d concentrates.  concentrations  (ppb)  Fraction Sample » L/H/B  Tsowwin  of  heavy  mineral  (mesh)  -50+70 -70+100 -100+140 -140+200 -200+270  1  River 4000 35 11  6200 5300 13  53 23000 6000  6000 140 2100  16 3400 350  31 3700 190  3400 35 8400  27 480 19000  3300 2800 2300  870 280  4100 540  12000 520  6900 22000  10000 500  H a r r i s Creek 10 L 11 H 12 B  455 750 730  1130 1480 590  890 720 3000  3250 1200 7400  3100 1600 3600  Watson B a r C r e e k 13 Ii 14 H 15 B  160 nd 11  3000 200 250  13000 nd 1000  940 2900 23  7800 6000 130  01 02 03  3200 nd nd  L H B  "Salmonberry 04 L 05 H B 06 Franklin 07 L 08 H  :  Creek"  River  (Continued) L=Low energy, H=High e n e r g y , B=Background s a m p l e . * nd=not detected. Detection limits are variable but a v e r a g e 15 ppb. 1  -60-  Table 2-3B. concentrates.  Gold  concentrations  Fraction Sample ft L/H/B  1  (ppb) o f l i g h t  mineral  (mesh)  -50+70 -70+100 -100+140 -140+200 -200+270 -270  Tsowwin R i v e r 01 L 02 H 03 B  nd nd nd  nd 15 nd  nd 15 20  20 nd 19  nd 34 nd  nd nd nd  10 nd nd  18 nd nd  5 nd nd  15 15 34  nd 39  13 nd  14 nd  nd 26  31 20  110 59  nd nd nd  nd nd nd  nd nd nd  11 13 nd  210 nd 1100  320 89 nd  Watson Bar C r e e k 13 L nd 14 H 10 15 B nd  nd nd nd  30 nd 140  nd nd nd  nd nd nd  27 50 21  "Salmonberrv 04 L 05 H 06 B Franklin 07 L 08 H  nd nd nd  2  Creek" nd nd nd  River  H a r r i s Creek 10 L 11 H 12 B  * L=Low energy, H =High e n e r g y , B=Background sample. nd=not detected. Detection limits are variable a v e r a g e 15 ppb.  a  but  -61-  of  low  minute  analyses  indicate  inclusions  detectable  level.  indication  of  fractions:  in  discrete  particles  Creek).  For  and  c o n t a i n two will  that  Au  Based  and  by  on  each  geometric  because However,  of the  visual  Au  the  is  midpoint  the s i e v e s t h e shape  from  which  the a n a l y s i s This  particles  used  no  show as  Harris  by  chance  of the  latter  observation which  in fine  was  showed  sand  size  as  free  streams.  assumption  sieve  with  occurring  e x a m i n a t i o n of samples  that  size of are  Au  occurs  sample  weight can  number o f g o l d  g i v e n assumptions The  size  contains s i x p a r t i c l e s  former.  free  good  concentrates  f o r the samples  e s t i m a t e the average  and d e n s i t y . the  that  particles,  any  six  erratic  as  fraction.  t h e Au c o n c e n t r a t i o n and  fraction  the  e q u a l weight sub-samples  four  to  provide a  in  are  i f a sample  from a l l f i v e  particles, to  implying  i s o c c u r r i n g as  fractions  used  into  not  of h e a v y - m i n e r a l  (at l e a s t  be t w i c e t h a t  confirmed  particular  example,  is split  minerals  distribution  i n any  differences  i s not o c c u r r i n g  do  concentrations  Analyses of s p l i t s large  Au  density  analyses  Au  gold  o b s e r v a b l e peaks  low  The  the  that  about  particle  of p a r t i c l e s the in  sieve  geometric  assumption r e q u i r e d  size,  c a n be  bounding a  particles  actual  be in  shape  taken  as  openings sequence.  measurement  -62of  gold p a r t i c l e s .  Creek  Gold  heavy-mineral  shape d i s t r i b u t i o n (SF)  so  that  long  cylindrical  cylindrical  by c r e a t i n g  SF=1  D ,  particles  and  z  smallest  diameters  similar  to  the  Ds/v(D Dt-)) for  identifying The  normal  2-8)  (standard  deviation  mean shape  factor  deviation  = 0.46)  0.13)  particle  with these  assumed all  that  streams  the is  used  is  shape  flakes  factor  (Corey,  plot  and  can  1949,  no  i n the  for be  of  mesh).  SFs  same  as  =  65%  is  i s 0.63  times  to  The  (standard disc  with  a  of  a  the  volume  of  that  calculations,  that  with  35%.  volume  (i.e.  would  it  of g o l d p a r t i c l e s for  29  SF=1.30  0.75  The  diameter  of  (standard  mean  ratio  1.8.  For  CSF  modelled  with  particles  ratio  is  threshold  w i t h mean SF=0.45  cylinders  a l l  and  flakes.  shape d i s t r i b u t i o n the  flat  intermediate  This  and  dimensions  same  represents  (2-1)  factor  equivalent sieve the  ratio  a  factor  represents  corresponding to a c i r c u l a r  to t h i c k n e s s  through  shape  f o r a l l shapes with  = 0.27)  for  to determine  SF>1  largest,  i s bimodal  and  diameter  pass  The  probability  of  =  of  the  shape  and  populations  sphere  are  s  long c y l i n d e r s  (Fig.  SF<1  Harris  W D B D L . ) :  =  Corey  deviation  a  and  respectively.  histogram  particles  D  from  arbitrary  ("flakes").  though CSFSl  x  an  represents a sphere,  particles  Du,  extracted  c o n c e n t r a t e s were used  SF  where  particles  Harris  was in  Creek  -63-  o o  CO  O-H 99  1  1  1  1  1  1  1  95  85  70  50  30  15  5  r 1  Cumulative Percent  Fig. 2-8. P r o b a b i l i t y p l o t o f shape f a c t o r s (SF) s h o w i n g i n f e r r e d component n o r m a l p o p u l a t i o n s . For population 1 (19 p a r t i c l e s ) , mean=0.450, s t a n d a r d d e v i a t i o n = 0 . 1 3 0 . F o r population 2 (10 particles) mean=1.30, standard deviation=0.270. Twenty-nine p a r t i c l e s are included i n the plot which was generated using Stanley's (1987) p r o g r a m w i t h t h e method o f S i n c l a i r ( 1 9 7 6 ) .  -64sedintents. The the of  d e n s i t y o f g o l d must a l s o  number o f g o l d p a r t i c l e s the fineness  calculation  of  this  15 g/cm  a  density,  reconnaissance  the  the  number  is  diameter  stage  fraction  however f o r t h e  purposes  t h e d e n s i t y was e s t i m a t e d  of p a r t i c l e s  t h a t of a sphere  of gold  i n each  c a n be e s t i m a t e d  as l i b e r a t e d  bounding s i e v e openings,  as  by  assuming  gold p a r t i c l e s ,  i s the geometric 3) t h e a v e r a g e  heavy-  2) t h e  midpoint volume  of  i s 0.63  and 4) t h e d e n s i t y o f t h e p a r t i c l e s  15 g/cm . a  The  calculated  requires  a  diameter In  fewer t h a n  assumption  background  of s i z e  0.1, for  that  c a n be  s i n c e no s m a l l e r  accounted  few g o l d p a r t i c l e s  Au  -270-mesh  average  .  Au c o n t e n t  are present  for  A r b i t r a r i l y , an  i n t h e two c o a r s e s t f r a c t i o n s  particles than  particles  i s available.  one o r v e r y  particular,  less  of  o f 20 Hm was s e l e c t e d  many s a m p l e s ,  single  number  different  bounding s i e v e s i z e  as  Measurement  p o s s i b l e u s i n g an e l e c t r o n  of p a r t i c l e s  1) a l l Au o c c u r s  times  samples.  ( F i n e n e s s = 620, e l e c t r u m ) .  mineral concentrate  sieve  is  on p o l i s h e d s e c t i o n s ,  Thus,  that  i n the  to estimate  ( F i n e n e s s = AulOOO/(Au+Ag+Cu+...)) a n d , by  the  microprobe  be d e t e r m i n e d  (Table  the concentrate  probably  minerals  by  2-4).  In  i t appears  o r , where t h e number content  for  that  i s given  represents  o r Au p r e s e n t a s  -65small  inclusions.  Even  i n the f i n e r  fractions,  only  from H a r r i s Creek c o n t a i n s u f f i c i e n t 20)  to  yield  a relative  -270-mesh m a t e r i a l  contains  quite  corresponding analytical  precision  samples  mineralisation background  to  restricted  particles  gold  ( S e c t i o n 1.2.1). potentially  particles  reliability  with  but  a  lower  are close  2-3A). taken  upstream  a comparison  Table  (i.e.,  2-3A  known  o f a n o m a l o u s and  shows  mineralisation  of  that is  based  probably  on not  t o t h e zones d e l i n e a t e d .  meaningless  gold  (Table  provide  data,  Comparison  example,  sampling  were  sediments,  concentration  of  fractions  b e c a u s e Au c o n c e n t r a t i o n s  to the d e t e c t i o n l i m i t Although  sand  from a l l streams  numbers  greater  gold  e r r o r of ±50%.  However,  high  fine  of  low  when  and  high  sampling  energy  errors  are  samples  considered.  low e n e r g y h e a v y - m i n e r a l c o n c e n t r a t e s  contents  concentrates  than  corresponding  high  f o r t h e -200+270-mesh relationship  energy  fraction  have  For  higher  heavy-mineral though  almost  the  opposite  95%  confidence  limits  are  considered  ( F i g . 2-9) t h e d i f f e r e n c e s i n c o n c e n t r a t i o n  insignificant.  number  of  frequently  Table  particles  greater  f o r -140+200-mesh.  (calculated using  become  gold  i s seen  becomes  than  equation  If  (l-2a))  2-4 shows t h a t t h e e s t i m a t e d for  the  low  energy  corresponding  samples high  is  energy  -66-  Table 2-4. C a l c u l a t e d mineral concentrates.  Sample # L/H/B  1  i n heavy  F r a c t i o n (mesh) — — -50+70 -70+100 -100+140 -140+200 -200+270  Tsowwin R i v e r 01 L 1.0 02 H 0.0 03 B 0.0 "Salmonberry 04 L 05 H 06 B Franklin 07 L 08 H  number o f g o l d p a r t i c l e s  -270  2.2 0.0 0.0  4.6 0.6 0.0  0.1 2.4 1.9  11.3 0.0 1.5  2.9 24.7 1.9  Creek" 0.0 0.0 0.8 1.0 0.0 0.0  1.9 0.0 1.5  0.0 0.2 4.0  1.7 1.0 1.0  5.4 11.6 23.3  River 0.3 0.0  1.8 0.0  8.2 0.0  6.6 1.8  6.0 0.0  77.9 22.6  H a r r i s Creek 10 L 0.4 11 H 0.8 12 B 0.8  1.8 2.9 1.7  6.7 4.3 25.8  29.9 4.8 37.4  120.4 5.7 23.1  214.4 37.1 4.4  Watson Bar 13 L 14 H 15 B  1.4 0.1 0.0  9.3 0.0 0.4  0.8 1.4 0.0  14.6 4.8 0.0  16.6 43.5 10.3  1  L=Low  0.0 0.0 0.0  energy,  H=High e n e r g y ,  B=Background  sample.  -67environments, narrower.  hence c o n f i d e n c e l i m i t s  Fig.  2-4  generally contain  much  samples, sites  less  1.2) i n t h e sample  probability  of  e n e r g y sample the  particular usually  sediment  energy  samples  t h a n low  energy  i s higher than  (fine)  size than  et a l . ,  2.4.5  Reducing  sampling  2.4.5.1 C o m b i n i n g A greater  the  sample  sufficiently  conveniently.  of heavy  even  minerals i n a  from h i g h energy s i t e s  low e n e r g y s i t e s  particles  would  concentrates small  (e.g.  is  Saxby,  (<60 g)  be o b t a i n e d by  provided that  that the  i t  be  mathematically with  N = ( E (Mj/MJd^ ) " ; 1 3  where de = e f f e c t i v e  can  U s i n g t h e Au c o n c e n t r a t i o n d a t a , N  c a n be combined  e  samples  fractions  heavy-mineral  fractions,  Thus,  errors  number o f g o l d  d  low.  1987).  combining  fractions  very  f o r low e n e r g y  fraction for  Fletcher  analysed  is  expected concentration  1985,  is  energy  u n d e r - e s t i m a t i n g t h e Au c o n t e n t o f a h i g h  higher  gold  fine  high  are  s m a l l and t h e e x p e c t e d number o f p a r t i c l e s ( j i ,  see s e c t i o n  of  that  hence h e a v y - m i n e r a l c o n c e n t r a t e s f r o m h i g h  are  though  shows  f o r t h e former  diameter  Mj = mass o f g o l d in a l l N fractions  1  (2-2)  5 3  of gold  particles  in fraction  in  a l l N  j , M = t o t a l mass  and d j = s e d i m e n t  diameter of  -68-  100 -  08 02  07  01  10 -  04 05  E a a  11  0.1 2.0  1— 1.0 D (mm)  10  4  I  0.5  Fig. 2-9. G o l d content and c o n f i d e n c e intervals for -200+270-mesh fraction of heavy mineral concentrates v e r s u s mean g r a i n s i z e o f f i e l d sample. Error bars are 95% c o n f i d e n c e i n t e r v a l s around the r e p o r t e d g o l d c o n t e n t and t i e - l i n e s j o i n h i g h - and low-energy pairs from the same l o c a t i o n . Sample numbers a r e shown n e x t t o b a r s .  -69fraction (N )  j .  can  e  Hence t h e e f f e c t i v e  be  calculated  effective  number  for  in  N  calculating  mean  Generally,  equation  close  the  gold  t o the diameter  fraction  (Clifton  of p a r t i c l e s  population  contains  analysed  yields  number  the  the  most  particles.  concentrate  i s 'added*  additional  gold  particles.  Several curves  or a r o u n d have  very  is  the  flatten  -140-mesh and -100-mesh  though  done  -80-mesh to  'silt*  indicate finer  the than  Results  suggest  of  heavy-mineral  a  as i t  As e a c h c o a r s e r curves  this  t h r o u g h one mesh i s  fall  o r have but  numbers o f g o l d  that  provides  heavy-mineral  steeply  added b u t i s c o n t a i n e d  low e f f e c t i v e  since  in a l l material  preparation  very  particle.  passing  2-10).  the  l-2b).  of g o l d even  i s t h e most s u i t a b l e f r a c t i o n  gold  about  diameters  fraction  exploration  (Fig.  The value  (Equation  i n o n l y one  of p a r t i c l e s  (without  concentrate)  limits  the g r e a t e s t weight  each of the f r a c t i o n s -270-mesh  the a p p r o p r i a t e  of the c o a r s e s t  a l l material  particles  a i . , 1969).  effective  hence c a l c u l a t i o n s were  effective  §_t  confidence  2-2  ( f o r example,  sample),  gives  of g o l d  concentration  g o l d may be c o n t a i n e d Typically,  number  because  i n one or two  local  steepen  maxima a t again  particles  to  a t -50-  mesh. The  c a l c u l a t i o n s indicate that there  combining  coarse  and  fine  fractions  is little since  point i n  the  coarse  -70-  62.5  20  88  125 177  250  Diameter (p) Fig. 2-10. Number o f e f f e c t i v e particles (N ) versus geometric midpoint of c o a r s e s t size fraction included, e.g., f o r sample 6, N a t 20 Hm i s a p p r o x i m a t e l y 10 f o r the -270-mesh f r a c t i o n (assumed d i a m e t e r 20 Jim) b u t f a l l s to about 1 i f -270-mesh and -200+270-mesh (midpoint d i a m e t e r 62.5 Hm) f r a c t i o n s a r e c o m b i n e d . E  E  -71fractions greater  merely  add  one  random s a m p l i n g  contains detectable data  because  high  reducing  of  particles  and  calculated  number  a simple  gold  sampling  Collection  is  particles  under-estimated required of  will  samples the  finer was  that  exploration,  others sieve In  particles  have  is  gold  Given  the  i n the samples,  20 p a r t i c l e s if  more  of  of g o l d .  than  the c o n c e n t r a t i o n  of  gold  is  because,  and  the  i t is logistically sieving.  P.  t h a t about  purpose  necessary  Matysek 16-mesh  grossly  the  in  The w e i g h t  weights sediment fractions  o f -16-mesh of  to reduce  (pers.  a few  o f sample  -16-mesh  material  2-5).  for  size  Therefore,  concentrate  (Table  the  that  However,  less  consequently,  i t is  sample  is  140-mesh  found  errors.  the s i z e  be o v e r - e s t i m a t e d .  w e i g h t by f i e l d  useful  fraction  there  and,  selected  the  would p r o v i d e  have been c a l c u l a t e d f o r  than  in  sampling  to determine  heavy-mineral  required  i t yields  of l a r g e r samples  of g o l d  present  fraction  errors.  reduce  recognized  leading to  I f t h e -270-mesh  of p a r t i c l e s  would be r e q u i r e d t o y i e l d it  particles  concentrations,  large  procedure  two  error.  t h e number  2.4.5.2 C o l l e c t i o n  or  mineral sample  comm.)  and  is a practical  field  (»120 kg) -16-mesh  sample  size. many c a s e s ,  a very  large  -72-  T a b l e 2-5. W e i g h t s o f -16-mesh field sample and s u b sample containing 20 particles o f g o l d i n h i g h and l o w energy environments. Based on d a t a i n T a b l e s 2-3 and 2-4 and F i g . 2-4 f o r s a m p l e s e s t i m a t e d t o c o n t a i n more t h a n one p a r t i c l e o f g o l d . Fraction Sample #  L/H  (mesh)  -140+200  1  HMC (g)  *  01 02  L H  4.7  04 05  L H  * *  07 08  L H  10 11  L H  13 14  L H  -16# (kg)  * 45  -200+270 HMC (g)  -16» (kg)  6.4 (6.4)  27 (18)  -270 -270 (g)  *  -16# (kg)  *  37.2  2  * *  * *  *' *  82.6 83.8  11 14  15.5 (15.5)  76 (91)  3.8 (3.8)  82 (70)  11.4 21.3  1 2  33.5 89 .6  10 140  12.4 23.6  8 120  3.9 14.1  0.3 2  35 89  46.3 31.2  2 1  * *  * *  4.9 6.3  H=high e n e r g y , L=low e n e r g y . ()=Fewer than one p a r t i c l e o f g o l d b u t w e i g h t s e s t i m a t e d assuming h i g h energy sample has same gold content as associated low energy site (on b a s i s of confidence intervals in Fig. 2-9) and calculating size of field sample n e c e s s a r y t o g i v e same amount o f c o n c e n t r a t e . *=Fewer t h a n 1 g o l d p a r t i c l e ( T a b l e 2-4) i n b o t h h i g h and low energy samples and therefore no estimated weight possible. x  -73is  r e q u i r e d to obtain s u f f i c i e n t  heavy-mineral levels  (1 t o 2 kg)  shows t h e  2.4.4  concentrates  lowest  Comparison  Other  but  t o more  coarsest reasonable  Harris  Creek  r e q u i r e d sample s i z e s  in a l l fractions.  of r e s u l t s  sampling  chapter  1.  assessed  u s i n g the  particles  two  sediment.  with  other  methods f o r e s t i m a t i n g t h e  The  probability  i n the  falls  f o r -270-mesh  sediments during mineral  examples  gold  results  t h a t the  (P(0),  on  of  of t h i s  sample  based  gold content  exploration  effectiveness  the  were  these study  will  methods  not  of  stream  discussed  in  methods c a n  be  by e s t i m a t i n g t h e contain  any  gold  Poisson d i s t r i b u t i o n ) .  of e x p l o r a t i o n s t r e a m  sediment  Two  sample-types  were  selected: 1)  Field  concentrate  obtained  by p a n n i n g  material.  For  finer  than  100-mesh would be  than  50-mesh.  analysed  calculations  Ten  f o r Au  by  i t was  grams  fire  lost of  assay  20  kg  assumed and  atomic  -4-mesh  that  a l l gold  concentrate with  of  gold  is finer would  be  absorption  finish. 2) Minus 70-mesh s e d i m e n t sediment  in  the  equivalent  to  sample  which  would  of be  field.  the  analysed  obtained  10 for  collecting  T h i s sample  conventional a  by  by  approximately  exploration  g p o r t i o n of Au  is  sandy  "silt"  -70-mesh s e d i m e n t  fire  assay-atomic  -74absorption. O n l y samples considered  taken  because  f r o m low  energy  sampling  environments  is usually carried  were  out  with  c o n t a i n any  gold  time c o n s t r a i n t s . The is  probability  controlled  number of g o l d  by  particles  analysed  was  fraction (Table  in this  the  were  2-6)  compared  least  a  detected. that  case,  46%  processed  be  (20  chance  as  the  to  number  sub-sample  estimate  the  any  gold  is  the  small  obtained  f o r -200+270-  -270-mesh  sediment  been used  there  are  since  (2-3)  study.  results  a n o m a l y would probably  not  is  at  not  be  the  best  volume o f m a t e r i a l t o  though  a n o m a l y would be  certainly  the  in this  Au  detecting  In t h e  in  contain  and  the  Considerable  sediment  expected  not  those  exploration. the  The  used  described  that  expected kg)  with  i f p a n n i n g had  However,  could  greatest  = e-".  concentrates  determined  In e v e r y  the  size:  mesh h e a v y - m i n e r a l (Table  2-4).  will  P(0) Results  containing  and  sample  not  fraction  calculated  that  ( P ( 0 ) ) of t h i s  the  particles  of g o l d  probability  t h a t a sample w i l l  typical  improvements expected  in  i n the i f 100  kg  be  mineral chance of  -4  of mm  i s panned. case be  of  -70-mesh  detected  in  samples, two  of  the  the  anomaly  s t r e a m s due  would to  the  -75inclusion  of  -270-mesh  sediment.  c o n c e n t r a t i o n s are  likely  concentration  approximately  of  obtained  with  further  improvement  a n o m a l y can  be  concentrates Finally, better  a 50  Hm  in  chances  sufficient  obtained  from a s m a l l  and  f o r example  a  would  be  Au  gold p a r t i c l e . of  detecting  -200+270-mesh  heavy  f o r -270-mesh a r e  concentrates.  field  sample and  sample,  thereby  preparation are  commercially-available poor  with  -270-mesh s e d i m e n t  the  concentrations  to  the  obtained  surveys,  collection  ppb  spherical  -200+270-mesh  pre-concentrate  100  low,  Au  A the  mineral  2-6).  results  than  fairly  diameter  obtained  (Table  t o be  However,  analytical  likely  In  be  there  to  analytical  i s no  reducing  be  orientation  f o r a n a l y s i s may  stages. to  marginally  costs at  However, close  to  detection limits  reliability  and  need  low  the Au  typical leading  geochemical  contrast.  2.5  Conclusions Large  sediment  1) Twenty  kilograms  adequate an  anomaly  should 2) L a r g e  samples  be  for  of  from f i v e -4-mesh  most s t r e a m s  is required.  s t r e a m s show t h a t : sediment  is  i f qualitative  Sediment  finer  probably  evidence  than  for  200-mesh  analysed.  -16-mesh s e d i m e n t s a m p l e s  are  required  (up  to  -76-  T a b l e 2-6. P r e d i c t e d r e s u l t s o f d i f f e r e n t s a m p l i n g methods. A l l r e s u l t s a r e based on t h e f i e l d sample collected in t h i s study. F u l l e x p l a n a t i o n o f t h e method o f c a l c u l a t i o n is given i n the text. Sample Number  Sample t y p e 1  Panned HMC  2  -70-mesh  3  P(0)*» (%)  P(0) (%)  -200+270 HMC  -270  P(0) (%)  P(0) (%)  01  46  82  0.7  100  04  *100  41  45  15  07  55  0.0  6.7  0.0  10  73  0.0  0.0  0.0  13  53  11  0.2  0.1  A l l s a m p l e s a r e from low e n e r g y locations. Panned c o n c e n t r a t e = s e d i m e n t sized t o -50+100-mesh. HMC = h e a v y - m i n e r a l c o n c e n t r a t e . •* P ( 0 ) = e s t i m a t e d probability o f o b t a i n i n g no gold p a r t i c l e s i n the sample. 1  2  3  -77120  kg)  i f a relative  and  single  coarse  3) Lower sample s i z e s is  to  be  sampling  fractions are  analysed  of g o l d  first.  Concentrations  low,  commonly  lower  field ±50%  fractions  are  the  and  samples are  This stream  sediment  limit  a in is  the  hence is  heavy-mineral  i n Au,  hence  error  of  finer  sediment  most  suitable  o f g o l d d i s p e r s i o n as  easily accessible.  be  most  contrast  relative the  can  of  techniques,  with  or  determined  fraction  v e r y anomalous  concentrations  mature and  be  geochemical  required for  study  the  detection  fractions.  low.  -270-mesh  in  of c o a r s e r  a detailed  large,  Au  is desired  analysed.  should  obtained  sample s i z e s Au  fraction of  ±50%  d e t e c t a b l e presence  be  Creek  on  for  can  if  analytical  reliability  concentrates 4) H a r r i s  i n the  available  than  t o be  required  approaching  analytical  are  though the  absence  very  e r r o r of  i t is  fairly  CHAPTER  3:  DETAILED SAMPLING OF HARRIS CREEK  -79-  3.0  Introduction H a r r i s C r e e k was  distribution  of  gold  results  presented  study  was  affected Hence,  by  size  and  sampling  82L/02),  due  rises  Provincial  flows  through  the this  that  were  not  severely effects.  indication  of  respect to other  low-density  in  is  the  the  mineral  minerals  the  town of Lumby  the  Columbia  accessible  g r a v e l l o g g i n g roads i s the  Okanagan  F o r e s t ) of B r i t i s h  eventually into  reach studied  reach  and  on  of  to rare g r a i n  p r o v i d e an  of g o l d w i t h  aim  samples  location  errors  based  the  and  access  Creek  V e r n o n ) and  and  primary  of  fractions.  (Spallumcheen  This  The  d e n s i t y ( f o r example,  Harris  paved  2.  study  stream  sediment  collected  L o c a t i o n and  The  single  of the sampling  behavior  magnetite)  3.1  a  collect  the d a t a  hydraulic  in  for a detailed  i n chapter  to  representative  selected  only e a s i l y  from  by  Columbia (20 km  (NTS  east  of  River. well-maintained,  Lumby  accessible  Highlands  (about  section  10  km).  of  the  stream.  3.2  H i s t o r y and Harris  Creek  land  use  i s one  of a number of s t r e a m s  i n the  north  -80Okanagan  region  nineteenth  that  and e a r l y t w e n t i e t h  from  a  placer  Creek  (Fig.  productive  deposit  placer  colours  The g o l d  (Barlee,  dredge the  and  portable  dispersion train  Bessette  sluice ended  Bessette  1969) .though  a  as c o a r s e  nuggets.  box.  less  and A . B u r t o n  train  using  a  (pers. suction  H i s work s u g g e s t e d  that  t h a n 4 km u p s t r e a m o f t h e  The o r i e n t a t i o n phase o f t h i s  the d i s p e r s i o n  train  extends  at  least  km u p s t r e a m o f t h e c o n f l u e n c e . Very l i t t l e  the  exploration  catchment  quartz the  dispersion  Creek c o n f l u e n c e .  s t u d y showed t h a t 4.5  a gold  with  mined  from t h e s t r e a m bed a t l e a s t  3 km u p s t r e a m o f t h e main m i n i n g a r e a comm.) d e l i n e a t e d  was  s t r e a m y i e l d e d t h e most  occurred  c a n be panned  i n the late  Gold  near t h e c o n f l u e n c e  15 m above t h e p r e s e n t gravels.  gold  centuries.  3-1) i n t h e 1930s  bench about  Gold  produced  basin  has been documented.  v e i n was i n v e s t i g a t e d  time of t h e p l a c e r  exact (pers. study  t o l o c a t e a lode  by p r o s p e c t o r s  mining  l o c a t i o n o f t h e showing comm.) n o t e d reach  on  activity  t r e n c h e s near  below Miocene  plateau  basalts  ( F i g . 3-1) were t h e f o c a l  systematic  attempts  late  gold-  probably  about  (Fig.  t h e s o u t h bank o f H a r r i s  the  A small  3 - 1 ) . The  Creek.  ( C h u r c h and  1970s.  t o determine  Smith  t h e u p s t r e a m end o f t h e  located  in  source i n  i s unknown t h o u g h M.  gravels  exploration  gold  Seusser, point  However, the gold  Channel 1983)  of uranium  there  content  were no of the  -81-  Fig. 3-1. Geology of the d r a i n a g e b a s i n of H a r r i s Creek and l o c a t i o n o f t h e s t u d y r e a c h . U n i t s : l=Monashee g n e i s s ; 14,15=andesite,argillite; 18=granodiorite; 20=plateau b a s a l t ( J o n e s 1 9 5 9 ) . * = m i n e r a l o c c u r r e n c e and commodity.  -82gravels  during  auriferous Creek,  the  which  s t r e a m bed as  itself  is typical  basin  slopes  presence  of  Edward  i s being logged.  and  for cattle  has  the  1986).  catchment  a r e used  despite  plateau b a s a l t s at King  (Day,  i s on t h e v a l l e y  bottoms  trees  beneath  Coldstream  of  logging  the  gravels  near  Much  exploration  not  not  in  grazing.  been  the  Most valley  Consequently,  disturbed  by  of o t h e r a r e a s of l o g g i n g  fallen  in British  Columbia.  3.3  C l i m a t e , v e g e t a t i o n and For  are  three to f i v e  a t or b e l o w 0°C  January  p e r i o d s are  fairly  the  (180C)  precipitation  i s 547  weather  average  common  temperatures  (approximately  months o f t h e y e a r mean at  temperatures  soils  -6°C,  mm  in  60 mm/month)  however  July.  larch  occurring Canada,  forest  Forest  regosolic  Service,  reflecting where  Spilsbury,  the  1949).  daily  monthly  readings  in  January  and  1982).  Soils  i n the  valley,  land  (British  are  the s t e e p s l o p e s though is  cold  annual  predominate  1972).  topography  Lumby.  Average  t h e r e a r e s m a l l a r e a s of open r a n g e  Columbia  observed  f i r and  in  Maximum a v e r a g e  w i t h the g r e a t e s t  F e b r u a r y as snow ( E n v i r o n m e n t Douglas  station  however e x t r e m e l y  (<-20°C).  occur  temperatures  subdued  typically podzols are  (Kelley  and  -83-  3.4 Summary o f b a s i n m o r p h o l o g y The  asymmetrically-shaped  approximately over  212 km*  a large area,  poorly  drained  till  are  greater  1500.m.  Harris  Creek  considered  at a scale  the b a s i n i s about M w i t h an average  3.5 B a s i n In  felsic this  upper  (Church  tuff  deposit.  Opposite contrasting  1700 m,  of  To t h e n o r t h ,  elevations  of  no  on t h e s t u d y r e a c h when  o f 1:50,000.  The l o n g e s t c h a n n e l i n  is  on t h e n o r t h h a l f  to  of H a r r i s  regional  of a s t r i k e  Monashee  site  Creek  fault  gravel  forms  that  (Jones,  with r e c e s s i v e a r g i l l i t e s , on t h e n o r t h bank  a  1959). 3-1) have limestones  (Jones,  i s u n d e r l a i n by c l i f f - f o r m i n g  strong  i s thought t o  of the reach s t u d i e d ( F i g .  volcanics  and  p l a t e a u b a s a l t s cap  lineament  slip  Gneiss  o f t h e b a s i n by a n  1983) a l l u v i a l  Miocene o l i v i n e  The v a l l e y  geology  bank  bedrock  and S e u s s e r ,  banks  andesitic south  at  i t extends  order  reaches,  complex.  mark t h e t r a c e  The  basement.  rising  fourth  around  of  s l o p e o f 0.14.  northwest-trending  and  of  area  28 km f r o m t h e s o u t h w a t e r s h e d  1959) c a p p e d  Oligocene  an  geology  the  (Jones,  on g n e i s s i c  shorter,  is  has  ( F i g . 3 - 2 ) . To t h e s o u t h ,  at elevations  tributaries than  basin  1959).  granite  and  -84-  F i g . 3-2. Topography of the drainage area of H a r r i s Creek upstream of the study reach (lowest sampling location shown by M i n northwest c o r n e r ) . The contour i n t e r v a l i s 500 f e e t .  -85granodiorite. along  the  There  study reach  the  v a l l e y occurs  and  M the  3.5.1  north  Outcrops  the  deposits  attempt  was  No the  i n the  by  changes  trend  between s i t e s  Monashee  of A  Gneiss.  i n the  of  catchment b a s i n  glacial  drift.  however n e a r  the  lacustrine deposit the  the  north  drift  bank.  of  Mostly,  upper end  of  with  associated  No  systematic  geology.  gold lode  though there  gold are  site  source  has  been  located  numerous d e s c r i p t i o n s o f  occurrences  showing near  basin  a  occupies  of  uneconomic v e i n the  rare  to a mantle  single large basin  is underlain  made t o map  Source  lithological  downstream end:  bedrock are  section  fluvial  3.5.2  the  c o n s i s t s of t i l l ,  study  major  geology  C r e e k due  drift  the  of  no  though a sharp t u r n  near  bank  Quaternary  Harris  are  i n the  J described  of H a r r i s Creek g o l d  has  region  (for  been  small  example,  i n s e c t i o n 3.2).  probably  in  In  the  concentrated  i n t o a number o f  fluvial  deposits:  1)  Oligocene  underlying  plateau  basalts,  2)  Quaternary g l a c i o -  the  fluvial  deposits,  modern  stream  high  and  concentration  attributed  to  3)  recent 4)  the  of g o l d  repeated  benches a s s o c i a t e d bed  of  the  with  the  modern s t r e a m .  The  i n H a r r i s Creek c a n  re-working  of  gravels  perhaps  be  increasingly richer  -86fluvial  3.6  deposits.  Harris The  seasonal discharge variation  study reach freezes  March. a  Creek  Break-up  spring  Lumby.  i s followed  flood  records,  peak  The  peak,  typically  week.  Summer and  Sampling  m /s)  Field  this  sediment  a  and  led  e a r l y June  gauging  out  in  at in  3  than  one  a  from day.  June  exceptional  i n some s e c t i o n s  (16  m /s  resulting  f o r about  carried to  by  station  value i n less  last  in  r e a c h e s 18 rtvVs  discharges  s t u d y was  up  maximum o f 29.2  this  and  3  flooding  sampling t o o b t a i n sediment  is  involved  discard  1986  discharges  of the  stream.  sediment  i n the  gravels  textural and  sample  hence  analysis collection for  texture:  of g o l d  investigated,  fraction  problems  with respect field  to  sampling  i n the f i e l d  of  a  of a s c r e e n e d sand  chemical  and  textural  laboratory.  Sedimentologists sampling  had  m /s  weather  texture  finer  analysis  disused  s t u d y , the d i s t r i b u t i o n  necessarily coarse  typically  to half  4.5  May  breaks  sampling  Field  In  in late  autumn peak  for this  and  3  3.7.1  and  decays  unusual  (>30  3.7  which  storms average  when  that  1965-1983) a t t h e  1977,  rain  i n November and  have  approached  to determine sediment  the texture  problem  of  i n a number  -87of  ways  (Kellerhalls  complicated  and  Bray,  of a g r a v e l  has  range  4) t h e p r e s e n c e  fractions.  sampling  not  to c o l l e c t  incorporating a variety  A  in  sampling  i n November  total  Sampling because  would was  area  mm)  leads to  errors  for gold  f o r the  a very  amount o f l o c a l  large  (vertical  F o r example, i t  a sample  of t h e armour  (several  square  of h y d r a u l i c  1985. be  p r o g r a m was I t was  layer  metres)  and  environments.  of  initiated  intended that  taken at ten s i t e s  aborted after  the  temperature  has  sampling  detailed  reach  pavement  typically  (>64  heterogeneity is inevitable.  possible  Field  or  and  sampling  sediments  so a c e r t a i n  without covering a large  3.7.2  i s bimodal  distribution  stream  is required,  is  armour  of v e r y coarse sediment  coarser  lateral)  i n the t e x t u r e  o f 10 <t>.  binomial  and  surface  distribution  severe  sample  variations  developed.  3) t h e t e x t u r a l  When  technique is'  deposit.  2) t y p i c a l l y a v e r y c o a r s e  a size  The  because:  1) t h e r e a r e o b s e r v a b l e l a t e r a l  layer  1971).  three s i t e s  stream  began  to  -15°C.  A second  on t h e 20  along the had  freeze successful  been  due  to  sampling  study  samples stream. sampled an  air  survey  -88-  Fig. 3-3. Sample locations on Harris Creek. Flow d i r e c t i o n i s from r i g h t to l e f t . C o p i e d f r o m 1:20,000 map of the B r i t i s h Columbia F o r e s t S e r v i c e (1972).  -89was c a r r i e d locations due  to  o u t i n June 198S  (Fig.  o f t h e p r e v i o u s November high  water  levels  3-3) t h o u g h could  following  t h e sample  n o t be  re-sampled  the s p r i n g  meltwater  flood. At each five  each s i t e ,  h i g h and low e n e r g y s a m p l e s  consisting  of  gallon  samples at  (23 l i t r e )  the  2 mm)  with  e n e r g y samples rippled  and  field  very  phase.  so  (10-mesh,  over  the  of  fine was  that  i n t h e t u b was  topped  up w i t h  retrieve  the  sediment  method  energy  that  i s locations layer  greater  3-4).  The l o w  placed  in  of  i s made o f a  23  galvanised  sediment  could  pail  some  i n the tub  settle  a t t h e end o f  nylon  litre  eliminates  experienced a  sandy  ( F i g . 3-5).  This  sediment  the f i n e  water  field  high  (diameter  2 mm)  top  sediment.  occurs a t t h i s  during out from  sieving.  (e.g.  the sediment.  chemical  Inevitably,  stage,  b u t no  flocculents)  of  first,  c a r e f u l l y d e c a n t e d and t h e two extra  full  The  (Fig.  sand d e p o s i t s  o v e r f l o w and be c o l l e c t e d  very fine  of g r a v e l  30 cm d i a m e t e r ) .  The p a i l  sieving  (two  and t h e s u r f a c e  l i t t l e sand  used  snugly  losses  taken,  were t a k e n f r o m s h a l l o w p o o l s w i t h a  sieve  (approximately  the  primarily  bed o r e x p o s e d  fits  the  pails).  bed i s p o o r l y s o r t e d  (pavement) c o n s i s t s  The  plastic  sediment  were t a k e n f r o m g r a v e l d e p o s i t s ,  which  than  60 kg o f -10-mesh  were  The pails  l o s s of  practical  exists  to  -90-  F i g . 3-4. T y p i c a l sandy g r a v e l sampling l o c a t i o n near the head of a p o i n t bar. On the diagram, fine stipple represents sand, coarse s t i p p l e r e p r e s e n t s sandy g r a v e l , v e r t i c a l r u l i n g i n d i c a t e s a l l u v i a l banks and arrows show approximate d i r e c t i o n and magnitude of water flow. Orange marks on the rod are 20 cm long.  F i g . 3-5. T y p i c a l sand sampling l o c a t i o n . See F i g . 3-4 f o r explanation of symbols and s c a l e rod.  -92A r o c k e r s i e v e and were  used  to  distribution large a  volume o f  field At  plan  up  split  determine t o 256 +2  was  channel  mm  the  mm.  In  typically prepared  textures,  location  determined  using model  photographs  and  data  of  a  surface, though  used  the  -2  of  type  mm  surface layer  site  local  of t h e  useful  stream  depth  bed  stream  velocities  depth,  depth  and  in  sample.  These  data  along  sheet  type  or s u b s u r f a c e )  l a r g e sample s i z e .  water c o l o u r  terms  organic The  of  profile.  dimensions  estimated  (General  locations  competence,  flow  of  sediment  d r i v e n meter  on a s t a n d a r d  to record p o s s i b l e sources  The  or p o i n t b a r , a  most s a m p l e s were a c o m b i n a t i o n  potentially  chain  stage  c o l o u r and  as a r e s u l t  a  case  samples,  stream  bedform  of  samples  i n which  channels),  2030) p l a c e d a t h a l f  turbidity,  content  fraction  gravelly  a channel  on bank m a t e r i a l s and  locations,  mm)  produced,  a small propeller  and  conditions,  (+2  templates  showing approximate dimensions  o b s e r v a t i o n s were r e c o r d e d with  most  m a t e r i a l was  f e a t u r e s ( b a r s and  Oceanics,  coarse  and  sieved.  each s i t e , s k e t c h was  a s e t of 1 * s c r e e n s  was  of  bankfull  a t the  sample  (undecomposed) of sample ( i . e . also  recorded  of a l l t h r e e  types  A comments a r e a  of c o n t a m i n a t i o n  and  was  other  data. profile  was  determined  s t r e t c h e d a c r o s s the s t r e a m  and  using a  a steel  survey  rod with  an  -93attached  tape  inevitably water  not  depth  profiles  measure.  very accurate and  large  therefore give  cross-sectional allowing  area,  (Table  are  due  incomplete of the  due  carrying  stick  the  centre  carried  3.7.3  3-2.  s t r e a m bed.  The  discharge  (from  velocity  Many of t h e  profiles  measured  extremely the  strong  current  in  the  flood.  samples  enabling  and  of  to  the  road  weight of by  proved  the  pails.  A  b u i l d i n g up  a slot  in  samples to  be  conveniently  3-6).  location descriptions  location  Although  sub-divisions  shallow  topography  constructed  (Fig.  the  of  3-1).  was  relatively  were  bed  t o awkward shape and  up-hill  Sample  of  perimeter  t o the  of a p o l e  Sample  to the  wetted  removal of  difficult  due  profiles  s e m i - q u a n t i t a t i v e measurements  stream during  Ultimately,  depth  relief  determination  measurements)  centre  These  two  d e s c r i p t i o n s are types  sediment  1)  Sandy g r a v e l d e p o s i t s .  2)  Sand d e p o s i t s  3)  Sand  without  deposits  in  of e n v i r o n m e n t were s a m p l e d ,  of sand d e p o s i t s can  three d i s t i n c t i v e  summarised  recognized,  to  two yield  types:  visible  with  be  Table  magnetite  abundant  accumulations.  visible  magnetite  accumulations. Physical  and  sampling  characteristics  of  these  -94-  T a b l e 3-1. Water d i s c h a r g e r a t e s i n June 1986. Site M A C K D B F E G J - = channel depth e s t imated  (irrVs) f o r H a r r i s  Date  Discharge  12/06/86 10/06/86 05/06/86 11/06/86 04/06/86 09/06/86 06/06/86 08/06/86 03/06/86 07/06/86 profile  Creek,  could  5.8 6.2 10.1 5.9 6.3 10.2 6.3 -  — not  be  measured  or  -95-  F i g . 3-6. Wooden pole with notch b u i l t up at centre c a r r y i n g samples.  for  -96-  Table  3-2. Sununarised June 1986 s i t e d e s c r i p t i o n s .  Site  Sample *  M  A  C  K  D  Description  Ml  Sand deposit below a l o g jam a t t h e downstream end o f a point bar. Ripples p r e s e n t w i t h h e a v y m i n e r a l s on c r e s t s . Heavy minerals also visible i n small scours.  M2  Gravel same  Al  Sand d e p o s i t a t t h e downstream end o f a s m a l l p o i n t b a r , i n a back eddy p o o l .  A2  Gravel sample from the n e w l y emerged p o i n t b a r .  CI  C o a r s e s a n d d e p o s i t on t h e downstream newly emerged channel bar. No bedforms.  C2  G r a v e l sample f r o m u p s t r e a m end o f t h e same channel b a r , under a few c e n t i m e t r e s of water.  KI  Back eddy p o o l s u r r o u n d e d by l o g s u p s t r e a m o f a gravel riffle (submerged point bar). R i p p l e s p r e s e n t b u t v e r y low v e l o c i t y . Minor heavy mineral concentrations visible.  K2  G r a v e l sample of K I .  DI  Sand d e p o s i t on t h e downstream end o f a s m a l l p o i n t b a r , c u r r e n t l y a s m a l l beach. Visible b l a c k sand a c c u m u l a t i o n s  D2  Gravel deposit same b a r .  d e p o s i t a t t h e downstream end o f t h e bar but upstream o f t h e l o g jam.  taken  on  upstream  from a r i f f l e  the  end o f a end o f visible  downstream  u p s t r e a m end o f t h e  (Continued  on n e x t  page)  -97-  Table  3-2.  Site  Samplel  B  F  E  G  J  (Continued) Description  Bl  Sand d e p o s i t a t t h e downstream end of a narrow stream cutting round t h e back o f a p o i n t b a r . A few r i p p l e s w i t h b a r e l y v i s i b l e heavy mineral concentrations.  B2  Downstream o f B l i n a s h a l l o w a submerged b a r .  Fl  F i n e sand d e p o s i t i n a back eddy p o o l on t h e downstream side of a channel bar. S l i g h t r i p p l i n g present.  F2  C o a r s e g r a v e l d e p o s i t downstream o f F l , b u t on t h e u p s t r e a m end o f a s m a l l c h a n n e l b a r .  El  Coarse sand around the present.  E2  G r a v e l d e p o s i t on t h e downstream r e c e n t l y emerged p o i n t b a r .  Gl  Sand deposit in a pool i n the middle of a braided channel bar. Ripples present with barely v i s i b l e heavy m i n e r a l c o n c e n t r a t i o n s .  G2  A very short distance small gravel r i f f l e .  Jl  Sand deposit a t t h e u p s t r e a m end o f a p o i n t bar, formed b e h i n d a s i n g l e l o g jam. Small scours and ripples with heavy mineral concentrations.  J2  Sand and g r a v e l d e p o s i t jam, u p s t r e a m o f J l .  deposit in back of, a  riffle,  a channel point bar.  upstream  behind  flowing Ripples  end  from G l  the  A number 1 i n d i c a t e s a "low e n e r g y " s i t e , i n d i c a t e s a "high energy" s i t e .  1  on t o p  same  of  on  a  a  log  a number 2  -98-  environments  3.8  in Table  S ievinq  In  the  be  extremely  large dry  first  and  because carried so  are  it out  of  sieving  was  since  has  well  commonly  the advantage and  relatively  the  f o r samples t h a t time size  i s an  fractions.  sieved  be  important  o f 10 m i n u t e s ,  s a m p l e s be  can  Dry  but  f o r no  t h i s study,  them t o be  split  Consequently, sieving  as  a l o n e and  both,  evaluated.  dry  the  large  and  dry  an  size  Compared  40  of  sediments  in  is one  to  suggests  30 m i n u t e s  to d r y s i e v i n g  by  a  either  the  require batches.  d r y or  the  wet  i t was  and  g.  several  t o combine  followed  batch,  (1963) recommends  t o 50  in  usually  in determining  o f s a m p l e s would  alternative  sieving  dry  (1965)  than  sieved  i n an a t t e m p t  Conversely,  parameter  less  fine are  sieving  Mizutani  the  to  particles  sieved  McManus  compared that  analysis  rapid.  found  t h e s a m p l e s were v e r y  sized  in  b u t was  However,  amount o f sample s h o u l d n o t e x c e e d In  used  i f bound t o g e t h e r by c l a y .  is  minimum t i m e that  technique very  i s used  sieving  purity  wet  time-consuming  the  disaggregated sieving  phase,  were p r o c e s s e d m a n u a l l y .  sieving,  fractions  of  3-3.  Laboratory processing  3.8.1  to  a r e summarised  wet  advantages sieving  found  that  was the  -99-  Table 3-3. characteristics Sediment  Summary o f sample  type  of physical sites.  and  sampling  Characteristics  Moderately to poorly-sorted sands ( s i x samples) (E1,F1,B1 K1,C1,A1)  R i p p l e d s a n d d e p o s i t s i n deep e d d y p o o l s a t t h e t a i l end o f bars. A v e r a g e t o t a l sample w e i g h t : 60 k g . Time t a k e n t o s a m p l e : 30 t o 45 minutes.  Moderately to poorly-sorted magnetite-r ich sands ( f o u r samples) (J1,G1,D1,M1)  S u b - a e r i a l sand d e p o s i t s a t bar t a i l s . V i s i b l e magnetite a c c u m u l a t i o n s where waves l a p o n t o s m a l l b e a c h f a c e s and back b a r s t r e a m l e t s wash a c r o s s t h e s a n d . A v e r a g e t o t a l sample w e i g h t : 60 kg Time t a k e n t o s a m p l e : 30 t o 45 minutes.  #  Very p o o r l y s o r t e d Sediment c o m p r i s i n g most o f b a r s . bimodal sandy c o b b l e C h a r a c t e r i s e d by a c o a r s e s a n d g r a v e l s ( t e n s a m p l e s ) d e f i c i e n t s u r f a c e pavement and f i n e r t e x t u r e d s u b s u r f a c e . No visible layering. A v e r a g e t o t a l sample w e i g h t : 250 kg Time t a k e n t o s a m p l e : 2 t o 3 h o u r s  -100weights  of  the  significantly fraction,  (up  Table fine  therefore  adopted  was  siever.  seven  undersized fraction sieves  screens  did  not  Dry  sieved  then cleaned the  apparatus  circulated fine  the  sediment.  proportion water  up  sieving,  allow  an  containing  time  the  top  -10-mesh  fractions, by  wet  in Fig.  bags.  water  i n the  However, and  the  organic  until  was  of  the  Rotap -10-mesh  and  sieved  for  for  most o f  the  sieve. any  The  The  full  lower  process  frequent  the  a  bottom  was  cleaning two  sieves  whole sample had  hours  were  of  been  needed t o  dry  sample. starting  with  the  coarsest  were  modification  of  whereby a p e r i s t a l t i c  pump r e -  pail  of  to prevent  samples  c l a y had  finer  g  16-mesh  s i e v i n g through a 2-3  using  s i e v e and  Usually  six  procedure  800  sieve  into p l a s t i c  emptied  of s i l t  because  i n samples  about  to  a brush.  kg,  of top  Approximately 60  -270-mesh  whole sample w i t h  need t o be  one  the  sieved  the  the  changed  phase.  dry  pass  for  following  second  to on  the  with  processed. sieve  minutes  were e m p t i e d  the  The  first  material  for  particularly  to  recovered  increase  Batches  retained  repeated  670%  f o r the  s e d i m e n t were added roughly  fractions  sediment.  sample  automatic  to 3-4),  abundant  Each  fine  containing  t o be  screens  flocculating  loss  a very  high  with  clean  became c l o g g e d .  After  agent  sieved  very  (Catfloc,  Calgon  -101-  T a b l e 3-4. Change i n t h e w e i g h t o f -270-mesh f o l l o w i n g wet s i e v i n g o f a p r e v i o u s l y d r y s i e v e d Sample  Weight Dry  Ml M2 Al A2 Cl C2 KI K2 Dl D2 Bl B2 Fl F2 El E2 Gl G2 Jl J2 - = data  fraction sample.  o f -270-mesh (g)  sieve  Wet  -  811 259 1110 628 547 339 1790 322 872 799 1200 495 1380 830 1630 983 358 241 1260 558  304 298 265 169  -  218 524 277 161 455 265 210 489 125 124 694 317 not recorded  Sieve  after  dry sieving.  Change  -  -  + 265 + 110 + 106 +100  -  + 300 + 110 + 334 + 207 + 203 + 213 + 676 + 101 + 186 + 94 + 82 + 76  -102Laboratories) two  days,  was added  t h e water  t o t h e -270-mesh w a s h i n g s .  was a l m o s t c l e a r  and  was  using  t h e pump and a l l o w e d t o d r y a t a m b i e n t  Only  fractions  dried  (at 80°C),  without d r y i n g  the  The  was  as  lost  resulted  86-SD-R2.  added  (Table  3-5)  fractions  a spill  small  become s m a l l e r  (89%,  -100+140-mesh).  second sediment  of  was  of i n i t i a l  1%)  the  during  of  the  and  total  coarser  transfer  The s p i l l e d  fractions  o f t h e sample sediment  was  weight  each  fraction  error  (<1 t o 3 % ) .  However, as a b s o l u t e  As  the  errors  analysis,  fractions,  i n the coarser  become  size  more e f f i c i e n t  from t h e c o a r s e r  of  the r e l a t i v e  relative  i n the second  sieving  recombined  to avoid contamination.  shows t h a t  i s quite  the  r e c o m b i n a t i o n and r e - a n a l y s i s .  o f t h e change o f  values  increases  Comparison  to another.  t o t h e sample  Comparison  stored  analyses,  (86-SD-B2) was  700 g ( a b o u t  during  from  f r o m one c o n t a i n e r not  being  of sediment  o f one sample  l o s s e s show as low w e i g h t s  and  fractions  oven  bags.  of r e p r o d u c i b i l i t y  w e i g h t s shows t h a t  sediment  temperatures.  of sediment a n a l y s e s  re-analysed  final  remaining  in plastic  laboratory portion and  drawn o f f  -140+200-mesh and -200+270-mesh were  3.8.2 R e l i a b i l i t y As a t e s t  After  of  i t  these  appears  a t removing reflecting  pronounced fractions that  the  the f i n e r some  of  -103-  T a b l e 3-5. R e s u l t s o f t e x t u r a l r e - a n a l y s i s o f 86-SD-B2 a n d 86-SD-R2 Fraction (mesh) -10+16 -16+40 -40+70 -70+100 -100+140 -140+200 -200+270  86-SD-B2 (g) 10300 39200 12400 1340 274 123 69  86-SD-R2 (g) 10000 39100 11600 919 519 159 83  Difference  (%)  -2.9 -0.3 -6.5 -31.4 + 89.4 + 29.2 + 20.3  -104the  errors occurring in rapid  re-combination  of the  have o c c u r r e d ,  interpretation  In  conclusion,  reliable,  sample t o a " n a t u r a l "  weights  t h o u g h not  f r a c t i o n s were n o t  minor  contamination of  the  -270-mesh) a r e significantly  not  of t h e  analysed  finer  fractions  not  limited. are  quite  removed.  important.  textural  The  (-140+200,  reproducible, the  may  is  is  Because  for gold content,  not  affect  mix  fractions  sediment  "is  as  results  for coarse  a l l fine  these  proportions  sample p r o c e s s i n g .  but  As this  weight -200+270,  they  do  characteristics  not  of  the  sample.  3.8.3  Heavy m i n e r a l  Heavy m i n e r a l  separation  concentrates  +270-mesh d r y  fractions  The  used  technique  was  phase  (section  3.8.4  Magnetic mineral  concentrates  p i s t o n magnet. three  other  mesh) w i t h an gauss  model  u s i n g methylene identical  for  iodide  t o t h a t used  the  two  (S.G.=3.3). i n the  first  two  heavy  2.3.2).  Magnetic minerals mineral  were p r o d u c e d  separation  were s e p a r a t e d  from  by  of a p r o s p e c t o r s  hand  were a l s o s e p a r a t e d  from  repeated  Magnetic minerals dry  fractions  induced MS-1265).  (-40+70,  magnetic The  use  -70+100 and  separator  separate  the  -100+140  (Carpco  produced  high  contains  -105particles cleaned  that are up  using  produced without strictly  in  can  the  a p i s t o n magnet.  prior  equivalent  fraction, that  w e a k l y m a g n e t i c and  because be  t o the the  extracted  mineralic  greenish-brown  mineral  is  separate  composite  especially  which  that  colour  magnetic  a hand magnet but  This  contains  the  of  to  is  the  not  magnetic particles  will true  has  be  fraction  not  sink  for  the  sufficient  separate  instead  has  separation  former c o n t a i n s  separate  particles  The  heavy m i n e r a l  with  heavy l i q u i d .  -40+70-mesh  heavy  hence  a  poly-  speckled  usual  magnetite  black.  3.8.5  Minus 270-mesh m a g n e t i c m i n e r a l  Magnetic minerals fraction water (of  by  type  manually minute  used  At  concentrate  was  washed  filter an  into  paper).  infra-red  (dry)  and  the  end  the  -270-mesh  p o r t i o n with  sufficient  stirrers)  f o r 45 m i n u t e s and washed so  into  that  of t h e  removed  from the  the  filter  separate  was  magnet stirred  beaker. suspension  beaker  Finally,  bar  removed a t  separation,  filtration  the  a  the  a Buchner  lamp,  from  A p l a s t i c coated  magnetic  required  maintained.  and  in  slurry  intervals was  g  a suspension.  i n the  stirring  separated  m i x i n g a 100  to c r e a t e  the  were  separation  the  using  funnel paper was  five  Manual could  be  magnetic the  magnet  (Whatman  #1  d r i e d under  disaggregated  using  a  -106s p a t u l a and t h e n  transferred  t o a weighing  using the  p i s t o n magnet.  Each of  these  final  consists  o n l y of magnetic m i n e r a l s  separate  contamination separate  was t h e n  portion  appreciable the  dried  gold  a  The  -270-mesh  (85-SD-10, fractions  different  olive  recorded 5Y/6/4.  clay  from  sample  known  to contain  using nylon screens: Jim and -10 Jim. separated  Each  from  into  -53 + 44 Jim, fraction  a l l samples  for  samples a r e p a l e y e l l o w , soil  colours).  the Munsell  sensitive  fine  3.9 C h e m i c a l  o f t h e -270-mesh  a l l -270-mesh f r a c t i o n s  However,  would g i v e  contents  fractions  the c o l o u r of the non-magnetic  (Munsell  sufficiently  sediment  to  soil  give  separate, pale  Munsell vary  colour  from chart  olive  colours 5Y/4/2 t o is  a range of i n d i c e s  not that  content.  analyses  Two n o n - m a g n e t i c h e a v y - m i n e r a l from  non-magnetic  -10 Jim.  example c l a y r i c h  and  without  320 ppb) was wet s i e v e d  and m a g n e t i c m i n e r a l s  are apparent for  the  o f -270-mesh  -44 + 30 Jim, -30 + 20 Jim, -20 + 10  except  The  that  a t 80°C.  analysis  of  following  was d r i e d  ensures  by n o n - m a g n e t i c m i n e r a l s .  3.8.6 F r a c t i o n a l A  stages  paper  e a c h sample  (-140+200,  concentrates  fractions  -200+270-mesh), -270-mesh non-  -107magnetic  sediment,  fractionation mineral  same s u i t e as  o f 85-SD-10  separates  instrumental  phase  3.9.1 R e l i a b i l i t y  caused  can a l s o  account gold)  splits  of  poor  of  f o r the conditions  gold  (Fig.  The  but  also  effect  effect  of  c a n be s e e n (d=53 Um)  These albeit  of  one  selected to  3  Harris  on a 25 g sample  in analyses.  of -  3-7).  g/cm ,  fineness  particle  splits  analysis  t o t h e nugget  INAA sample)  undersize gold  for  (Density=18  sizes  reproducibility  Duplicate  particles.  high  (-70+100-mesh)  poor  reproducibility  particle  (a t y p i c a l  coarse  effect".  be a t t r i b u t e d  different  50 ppb d i f f e r e n c e  (INAA)  by  2.3.4).  extremely  fo the observed  sediment A just  gold  magnetic  non-destructively  analysis  were s u b m i t t e d  by v e r y s m a l l  spherical  of  from  o f l a b o r a t o r y a n a l y s e s was d i s c u s s e d i n  f r o m t h e "nugget  extremely  results  analysed  (see s e c t i o n  showed  270-mesh s e d i m e n t  selection  w i t h t h e same a n a l y t i c a l  Duplicate  concentrates  show  a  fractions  o f INAA f o r Au  Reproducibility  resulting  were  of elements  2.  and  neutron a c t i v a t i o n  i n the f i r s t  chapter  non-magnetic  Creek  o f -270-mesh i n Table  can  3-6.  produce  a  -108-  Au  Fig.  3-7.  Gold  analyses  for s p l i t s  of  (ppb)  -270-mesh  sediment.  -109-  T a b l e 3-6. Effect on Au concentration of adding one spherical gold particle (density = 18 g/cm ) t o a 25 g sample o f -270-mesh s e d i m e n t . 3  P a r t i c l e Diameter (Um) 50 40 30 20 10  Au  Concentration (ppb) 42 22 9.2 2.7 0.34  -110-  The  effect  decreases  significantly it  is  one  40  3.9.2  pronounced  c l e a r how Um  gold  particle  mesh  Because  the  sediment  size  sample  of  than  20  Um  fractions  to have  samples  probably  low  two  effects  analysis  of  sampling  errors will be  -10  much or  Um  lower  the  split.  of  =  20  silt  Other  -270-  compositions  would  of  are  expected.  Based  a l l p a r t i c u l a t e as  appears overall  implied  by  is  medium  particles  lowest  gold  fraction  gold  it  grain  Conversion  spherical  particles. bulk  as  Sediment  content.  the  ppb)  detection  Um.  coarsest  3-7.  320  above  than  -270-  -270-mesh  concentrations  particles,  sediment, be  are  whereas the  if  i n Table  analysis  Au  ppb  -270-mesh  number o f  numbers of g o l d  one  nugget  Au  coarser  26  first  is  table,  <9  anomalous  Au  to expected  with  contain  therefore  not  most  increased  contain  and  sub-fractions  sub-fractions  shows  ppb  of a  but  this  summarised  (bulk  indicates that  calculated  may  the  f o r sediment  concentration  particles  mesh  i n the  are  24  i n the  five  indicate decreasing  decreases  Au  is  encountered  and  finer  of t h e  size  Using  return  i s present  (85-SD-10)  concentrations limit  could  of s u b f r a c t i o n s  of a n a l y s e s  sediment  particle  f o r d=30 Um.  splits  Gold a n a l y s e s sample  Results  with  that  this on  size this  relative  t h o u g h the  gold  the c a l c u l a t i o n .  - I l l -  T a b l e 3-7. Gold a n a l y s e s f o r s e d i m e n t (85 -SD-10). Fraction (um) -53+44 -44+30 -30+20 -20+10 -10 1  Wt o f Sediment (g)  Au (ppb)  39.6 12.6 9.2 10.1 15.1  630 100 57 42 57  S.G.=18 d i a m e t e r = g e o m e t r i c f o r -10 um f r a c t i o n ) /  subtractions  of  -270-mesh  Gold (spheres)  midpoint of f r a c t i o n s  1  25.8 2.9 4.2 17.7 >110 (lOum  -112-  3.9.3 R e l i a b i l i t y In t h i s with  study,  respect  - zircons  o f INAA f o r Hf  in  the behaviour  to gold the  concentration  Zircons doubly  in  and  is  s i n c e other  the  minerals  levels  density  to  the  Hf  i n t h e s e d i m e n t s do n o t  of hafnium occur  (Deer e t a l . , 1 9 6 6 ) . as t e t r a g o n a l  by t e t r a g o n a l p y r a m i d s .  (height:diameter  fractions  The c o n c e n t r a t i o n o f  proportional  concentrates  terminated  prolate  i s considered.  samples  contain appreciable  of other  prisms  The g r a i n s  are  » 5) and a r e u s u a l l y t r a n s p a r e n t  c o l o u r l e s s t h o u g h a few a r e r e d d y - b r o w n and e q u a n t . Reproducibility  consideration zircons  in  of  the  samples  errors  However,  analytical  reproducibility  are  limit  concentrations  based  than  on  the  errors  can The  to  be e s t i m a t e d  large  very  even  number  low  Poisson  apparently  3-8)  (500 ppm) times  and  though  poor  reported analytical at  higher  for  several  absolute  errors  determined maximum  of  predicted  lead to very  Reproducibility was  by  distribution.  not c l o s e t o the suggested  (1 ppm).  samples a t d i f f e r e n t less  leads  (Fig.  concentrations  were  analyses  o f -270-mesh s p l i t s .  relative  detection  Hf  10 ppm.  3.10 Summary Twenty-s i x  -10-mesh  sediment  samples  each  weighing  -113-  Hf (ppm)  Fig. 3-8. sediment.  Hafnium  analyses  for  splits  of  -270-mesh  -114roughly samples were  60 kg  were  collected  were c o l l e c t e d  collected  in  data A  were  combination  magnetic analysis.  Creek:  1985 and t w e n t y In  o u t i n June  of  of  sieving  rapid  e a c h sample  providing  1986.  Harris  the  field  and p e r t i n e n t  six  samples textural  hydrologic  collected.  comparison  allowed  i n November  June  a n a l y s e s were c a r r i e d  from  textural  techniques  dry sieving  followed  t o be p r o c e s s e d information  m i n e r a l s and t h r e e  in  showed by wet  about  two  that  a  sieving days,  f o r t h e b u l k s e d i m e n t and  fractions  Samples were a n a l y s e d by  f o r gold  INAA.  and  hafnium  -115-  CHAPTER 4: DESCRIPTIVE GEOMORPHOLOGY AND SEDIMENTOLOGY THE HARRIS CREEK STUDY REACH.  -116-  4.0  Geomorphology of the s t u d y r e a c h Examination  August  1982  shows  that  sections  the  based  (1945)  At  Creek site  with  low  (main  and  channel at  from the south  G a substantial  to  S=Channel  site  J a small  o r d e r based  on  a  o f 1:50,000)  joins  scale  sinuosity  stream  volume o f s i l t  and  0.025 ( F i g . 4 - 1 ) . Harris  Creek  site  clay.  clay  an a v e r a g e  Downstream of s i t e  (S =0.042),  sinuosity  lacustrine  G  to  of v e r y  low  slope  (S ) E  F B e e t l e Creek  Here,  t h e main  of  joins  channel  E  braided (Fig.  4-2)  (S=1.12),  f o r about  (to just  1 km  break  site  channel  channel  size  material  Downstream o f  f r o m t h e s o u t h bank.  becomes s t e e p e r higher  B o u l d e r s of t h i s  occupies a single  (S«1.01) and  a  bank.  3.5.1).  the  first  i s fourth  (Section  E  4-1).  (S*1.10,  deposit  site  several  meandering  from the p r e v i o u s l y d e s c r i b e d  and  204)  is a  i s added  to s i l t  82030  (Fig.  sediment  down r a p i d l y  taken i n  into  slope  J the stream  Close  analysis  #BC  be d i v i d e d  sinuosity  distance).  tributary  Harris  form  of s i t e  photograph  Columbia,  r e a c h can  channel  upstream  channel  Horton  1:50,000 a e r i a l  study  on  length/Valley order  a  ( P r o v i n c e of B r i t i s h  Immediately single  of  and  has  a  above  B).  Downstream o f s i t e a single  meandering  B to s i t e  M the stream  channel with gravel  point  i s reduced bars  and  to a  -117-  F i g . 4-1. C h a n n e l l o n g p r o f i l e , s h o w i n g a v e r a g e s l o p e and c h a n n e l f o r m between open c i r c l e s . The whole s e c t i o n i s 5050 m l o n g .  -118few  stable  channel  s t e a d i l y decreases 0.022.  At  islands over  high  alternating  (Fig.  this  section  flows,  sequence  of  the pools  (Andrews, 1 9 8 3 ) . On t h e s o u t h granite low  whereas  alluvium  and  contrast  in  bank  intermediate (Knighton, gneiss  between  1981).  bedrock  alternating-bar on  4.1  low s i n u o s i t y  the  laboratory  sieving  coarser  complete  As  typical  visible  north a  side  result  channel  and  M,  at  incise of  the  pattern  confined  is  meandering bends  incise  bank.  the channel  into  Lumby  channel-form  continues  valley  (Knighton  where  t o meander  i t adopts  1981)  an  superimposed  meandering.  Textural analysis Data o b t a i n e d  M,  a  (shallows)  are  upstream of s i t e  on t h e n o r t h  i t emerges  the  the  regular  is  of  t h e meanders c u t i n t o  deposits.  Just  Downstream o f s i t e until  on  average  riffles  islands  materials,  an  channel  side,  meanders  overbank  for  and  c l i f f s and s m a l l b e d r o c k  flows  4 - 3 ) . Channel g r a d i e n t  of sediment  samples  f r o m d r y and wet s i e v i n g c a n be combined fractions  textural  analysis  range of a p p r o x i m a t e l y  12 *.  summarised  as  histograms,  the c e n t r a l  in  with data the  from  field 256 mm  of sediments obtained to  tendency  plots measures  by wet  provide  a  t o 0.052 mm,  a  Size-frequency data  phi-probabi1ity  in  can  (Fig. mean  be  4-4),  (D)  and  -119-  Fig.  4 - 3 . T y p i c a l meandering channel  section  -120(D  median  )  a o  and  ( a t ) .  sorting  statistics  are  the  only  statistics  o f use h e r e b e c a u s e  traditional  these  For this  reason  multi-  skewness  k u r t o s i s were n o t c a l c u l a t e d .  4.1.2  Textural  features  Sandy g r a v e l indicated  pebble g r a v e l  of sandy g r a v e l  samples  samples a r e t e x t u r a l l y  by t o t a l  a v e r a g e sample  weight,  i s a very (Folk,  D,  highly  varied  and Do© ( T a b l e  poorly  sorted  probably  two  or  characteristic (Kellerhalls common  to  ( ? i =2.47 *)  three  and B r a y ,  sediment  size  t y p e o f sample 1965; G r a f ,  probability  form o f curve s u g g e s t s e i t h e r c l a y and s i l t  the  sample  curves should that normal  is  the  or  (2)  is  (1) t h a t  that data  populations  represent  that  rivers  the  curve  ( F i g . 4-4).  there  is  in this  a  a mixture  ( c f . Sinclair,  s e d i m e n t extreme  portion  a logarithmic  p e r c e n t a g e s and h i s t o g r a m s show t h a t mode a t t h e f i n e  as i s  This  poorly  c o n s t i t u t i n g l e s s t h a n 1%  n o t be p l o t t e d w i t h data  gravel  are  1971). A c h a r a c t e r i s t i c  plots  population  there  populations  from  s t e e p e n s r a p i d l y i n t h e 3 4> t o 5 < / > range  defined  sandy  1974).  of t h i s  many  as  4 - 1 ) . The  H i s t o g r a m s and p r o b a b i l i t y p l o t s show t h a t  of  latter  sedimentological  non-Gaussian normal  modal d i s t r i b u t i o n s a r e common. and  However,  implying  ordinate,  o f l o g n o r m a l and  1976). there  of the  Raw  weight  i s a small  size  that  isa  there  -121-  Table 4-1. Summarised t o t a l Sample Number Sand Ml Al Cl KI Dl Bl Fl El Gl Jl  T o t a l Weight (g)  weights, D s o and D. Dso (mm)  D (mm)  Samples 69900 60900 59900 67400 106000 61700 61700 70200 65100 57800  1.11 0.47 0.30 0.40 0.76 1.33 1.33 0.30 1.11 0.41  0.49 0.27 0.42 0.35 1.44 0.38 0.45 0.45 0.61 0.33  Sandy g r a v e l samples M2 147000 A2 239000 C2 320000 K2 236000 D2 222000 B2 160000 F2 709000 E2 223000 G2 199000 J2 332000  4.13 6.42 40.63 8.28 41.09 3.03 84.69 163.29 18.12 71.10  2.92 4.81 11.31 5.10 10.12 3.12 27.59 19.65 6.37 21.14  -122-  Fig. 4-4. Some examples of probability plots for size frequency d i s t r i b u t i o n s of sandy gravel samples. Note p r o m i n e n t i n f l e x i o n near m i d p o i n t and i n c r e a s e o f s l o p e a t the f i n e s e d i m e n t e x t r e m e .  -123-  distinctive On  and c l a y  histograms  range on  silt  a  prominent  -3 <t> t o -1 4> w h i c h  probability  plots  occurs  close  sample  processing  inefficient However,  for  the  and  populations. the silt  inflexion  the the  that  there  Using  components  could  slight  (less  diameter than  material. i n many  Bray,  o f sample  1971;  processing size  are well-defined  framework  and  plot  sand,  method o f  (1987) t h e c h a r a c t e r i s t i c s o f  modelled which  I t was assumed as is  ideal  by  the  ( F i g . 4-5).  o f a d i a m e t e r w h i c h c a n be  (threshold) tail  data  that  phi-normal  justified  to the r e a l  selection  of t h e low diameter  the high  and  the p r o b a b i l i t y  f i t o f model c u r v e s allows  sieving i s  a r e two d i s t i n c t i v e  gravel  an assumption  used a s a d i s c r i m i n a n t Overlap  be  field  common f e a t u r e  B e c a u s e t h e two p o p u l a t i o n s represent  point  and l a b o r a t o r y  granule-size  two components c a n be e s t i m a t e d .  method  field  (Kellerhalls  (1976) and S t a n l e y  excellent  and  of  point  inflexion  that  1979) r e g a r d l e s s  and c l a y m a t r i x .  populations,  The  imply  i s a very  reports  modes p r o b a b l y  Sinclair  might  separation  implies  i n the  i s a p p a r e n t a s an i n f l e x i o n  ( F i g . 4 - 4 ) . This  B e s c h t a and J a c k s o n , and  minimum i s p r e s e n t  t o t h e c u t - o f f between  sedimentological  method  population.  f o r t h e two components.  of the coarse  head o f t h e f i n e  population  population  i s very  2% o f e a c h d i s t r i b u t i o n ) i n a l l b u t  two  -124-  Fr ame work component Q \  72%  \  « E CO  Matrix component  5  28%  4-  5  i  1  r  30 50 70 95 Cumulative % coarser  99  1  1  F i g . 4-5. P r o b a b i l i t y p l o t f o r s i z e d i s t r i b u t i o n o f 86-SDD2 showing characteristic features of sandy gravel deposits. Mean d i a m e t e r and s o r t i n g ( s t a n d a r d d e v i a t i o n ) f o r framework and m a t r i x components c a n be r e a d from the graph.  -125cases.  Thus,  mean s i z e  the estimated  and s o r t i n g o f  easily-estimated,  the  potentially  characteristics  (see  average  material  matrix  section is  whereas framework m a t e r i a l Finally, material  gravel  the  for  and  6.3.2)  weight  4-2) w h i c h  features  probability  0.46 mm  of  at  o f sand  plots  poorly  sorted  (typically defined silt is  (coarse  least  sand  and  i s very  the  sediment  limit,  gravel.  of  close  matrix  to  that  (Fig.  a  Sand s a m p l e s a r e  an a v e r a g e  In  that  diameter  the presence  a moderately t o median  poorly  4-6) and a  The g r a v e l  commonly  implying  low  a very  by extreme s t e e p e n i n g limit.  distributions  p l o t s suggest  component w i t h  curves  size  sediment sub-groups:  t o 0.25 mm),  towards the coarse samples,  pebble  sand,  samples  histograms.  Four  c l a y component.  represented  coarse  On  framework-supported  4  p e b b l e component  and  4-2).  proportion  (cr =1.24 #) w i t h  sand).  three  0.5  (Table  1982).  mostly poorly-sorted of  are  sedimentological  poorly-sorted  Samples show an extreme v a r i e t y o f on  framework  important  rhombohedrally-packed  (Leeder,  4.1.3 T e x t u r a l  matrix  d i a m e t e r and t h e  i s poorly-sorted  average  i s 30% ( T a b l e  expected  discriminant  diameter  sorted  poorly  poorly-defined  component  typically  of p r o b a b i l i t y curves  common  with  steepen there  sandy  toward is  a  gravel the f i n e  distinctive  -126-  Table 4-2. Characteristics components of sandy g r a v e l s , and d i s c r i m i n a n t d i a m e t e r Sample  Matr i x D  M2 A2 C2 K2 D2 B2 F2 E2 G2 J2  (mm) 1.1 0.6 1.0 1.0 0.6 0.8 0.5 1. 0 1.0 1. 3  of framework the p r o p o r t i o n  Framework D  (mm)  10.2 12.6 12.5 16.5 40.0 10.0 43.1 166.0 32.1 63 .1  and matrix o f framework  Discriminant Diameter (mm) 2.6 1.9 5.0 4.0* 4.5 2.2 2.8 25.1 7.9 8.9 1  Framework Proportion (%) 55 75 78 60 73 60 96 70 58 76  Samples K2 and B2 have poor d i s c r i m i n a n t d i a m e t e r s , t h a t is, t h e r e i s s i g n i f i c a n t o v e r l a p o f framework and matrix s i z e frequency distributions. 1  -127-  0.01  1  1  1  10  1  1  1  30 50 70  1  90  -I  99  99.99  Cumulative % coarser Fig. 4-6. Some examples of p r o b a b i l i t y p l o t s f o r s i z e frequency d i s t r i b u t i o n s o f sand samples. Note extreme steepening o f C l t o w a r d s t h e c o a r s e l i m i t and p r e s e n c e o f three i n f l e x i o n p o i n t s i n the curve f o r D l .  -128-  medium t o f i n e  silt  and c l a y component  The  gravel  component  from  a  field  sampling  occur  as a v e r y t h i n  deposited deposits  gravels.  the  Contamination (samples size a  Cl, F l ,  eliminated  this  of the s i z e  be  modelled  contaminant constant  with sort  as  sand  Dl  deposit For  (5=1.443 mm) (Table 4-1).  coarse  phi-normal  t o be  material  was  by assuming would  samples  probability  the plots  can  coarse had  a  limit.  i s anomalous  reason  that the  be t h e same a s  distributions,  until  notes  appears  As t h e l a t t e r  i n that  b u t has a wide r a n g e this  sediment.  with the trimodal  the  analysis  the  i t i s easy t o  sample w e i g h t s do n o t v a r y much  which  previously between  As t h e g r a v e l  samples.  was removed  locally  was r e c o r d e d i n f i e l d  distribution  slope a t the coarse  Total  over  case  very  results  deposits  contact  horizon,.  from the t e x t u r a l  end  the  i n which  observed.  sedimentary  non-contaminated  4-6).  Sand  E l , J l ) and c o i n c i d e s  the  sand  problem.  4-6).  coarser)  (0 t o 15 cm) v e n e e r  sample  of  different  except  and  However,  distributions  coarse  (granule  i s generally diffuse,  contaminate  (Fig.  i t was t a k e n f r o m a  of sediment  D l has t h e h i g h e s t  whereas t h e r e m a i n d e r  f r o m 60 k g ,  vary  sizes ( F i g . mean d i a m e t e r  around  D=0.5 mm  -1294.1.4 Downstream t r e n d s i n s e d i m e n t Downstream for is  sandy  t r e n d s i n t h e two c e n t r a l  gravel  samples  a s l i g h t tendency  (Fig.  4-7).  obvious  D  for  increasing  appears  to  departures  f o r s i t e s recognized  enrichment  ( s i t e s J , D and M).  sandy  of weight  gravel  correlation percents size  of  weight  samples  percents increase  4.2 M a g n e t i t e  D  In  a o  .  the  -16+8 mm  downstream  (Fig.  f r a c t i o n s of to  particular,  decrease  a r e not as  of magnetite-  positive  sediment  weight  ( c o b b l e s ) and t h e mean downstream, and -8+4 mm  whereas (pebbles)  4-8).  (magnetic m i n e r a l ) t e x t u r a l a n a l y s e s 1  formed  by  combination of data f o r h i g h - d e n s i t y magnetic m i n e r a l s  ( d e n s i t y > 3 . 3 g/cm , 3  -140+200,  -200+270 mesh)  * A l t h o u g h m a g n e t i t e was n o t s e p a r a t e d f r o m the  negative  the  Magnetic m i n e r a l analyses f o r s i x f r a c t i o n s the  There  downstream w i t h  as l o c a t i o n s  from  clasts of  measures  downstream  samples  decrease  vary  -128+64 mm  framework  fractions  fineness  percentages of i n d i v i d u a l  w i t h D and  of  tendency  are p o s i t i v e l y correlated.  Downstream t r e n d s f o r s a n d  though  Trends  textures  weight  proportional  of  magnetic  t o the weight  particles  of magnetite.  the  and  total  sediment,  i s approximately  -130-  Fig. 4-7. Downstream t r e n d s i n mean d i a m e t e r o f s e d i m e n t . F i l l e d i n c i r c l e s a r e s a n d y g r a v e l d e p o s i t s , open and h a l f f i l l e d c i r c l e s a r e sand d e p o s i t s . 20n  1  1—i  1—i  1  1  1  1  Fig. 4-8. Downstream t r e n d s o f weight percent -8+4 mm sediment. Filled in circles are sandy g r a v e l d e p o s i t s , open and h a l f f i l l e d c i r c l e s a r e sand d e p o s i t s .  -131-  magnetic  minerals ( i . e . ,  including  ( d e n s i t y < 3 . 3 g/cm ) m a g n e t i c  particles,  3  -100+140,  -270  mesh) c a n  be  concentration  of magnetite  of  in  magnetite  comparison to  equivalent  Frostick,  concentrations are  magnetite  magnetite fraction the total  particle  weight  or  (2) w e i g h t  latter  allows  distributions (e.g.  of and  (1)  Reid  magnetite  sand  samples  B o t h sample t y p e s show a However, size  the  weight  of  d e c r e a s e s ; thus the (-40+70 mesh)  o f m a g n e t i t e due  to the  has high  plots  with sediment diameter  expressed  in  f o r c u m u l a t i v e p e r c e n t m a g n e t i t e w e i g h t s were used i n  an a t t e m p t  to determine  percentage separation magnetic  of  the  of magnetic separations  the  amount  not  determined  a t the c o a r s e  (0.5 mm).  Truncation  extremes  a normal  curvature  truncation  particles)  becomes a s y m p t o t i c  and  of  distribution  where t h e p l o t  The  -70+100,  weight.  Probability phi  4-3.  density  either  velocities  lowest c o n c e n t r a t i o n  absolute  fraction  The  sandy g r a v e l  concentration.  with the  fraction  Comparison  Table  d e c r e a s e s as  greatest  settling  for typical in  as  low-density mineral  1985).  summarised  peak  i n each  low  -40+70,  summarised  fraction.  o f h i g h - and  determine  and  each  composite,  to  distribution  o f t h e c u r v e c a n be  is  horizontal model  used  to  limit  (the by of  indicated at  the  i s appropriate. estimate  the  -132-  Table 4-3. concentration  Comparison of weights of o f m a g n e t i t e i n two s a m p l e s Sand  Fraction (mesh) Cone. -40+70 -70+100 -100+140 -140+200 -200+270 -270  (%)  0.6 2.4 4. 5 5.2 2. 7 0.8  (Ml) Wt.  magnetite  and  Sandy g r a v e l (C2) (g)  94 48 68 20 12 6 .5  Cone. 2.5 6.8 6.2 4.4 3.3 1.6  (%)  Wt. (g) 218 103 22 9.4 2.2 5.4  -133-  Fig. 4 - 9 . Some examples of s ize d i s t r i b u t i o n s .  probability  plots  of  magnetite  -134-  percent  truncation  frequency  1976).  flattening  at  suggesting  that  4-9).  gravel  of  The  the  coarse  because  trimodal.  that  the magnetite  In  end  of  cannot  samples plot  the  applied  little  distribution, i s minimal  is  i s no  about  plots  indication  trimodal.  Due  to  magnetite  o f R e i d and  others to  probability  there  the approach  (1977) and be  show v e r y  i s c o m p l i c a t e d f o r sandy  uncertainties  Slingerland  magnetite  a t t h e c o a r s e end  probability  frequency d i s t r i b u t i o n s ,  model o f t h e  of  plots  the bulk sediment  these  fundamental  sediments  weights  probability  truncation  are  (1985),  the  However, t h e p r o b l e m  samples  these  s u b s e q u e n t l y a normal  distribution  (Sinclair,  (Fig.  and  applied  very  size  Frostick to  coarse  beach fluvial  sediments. Most  curves  distribution present in  a r e s t e e p a t the f i n e  implying  i n the t o t a l  the magnetite  4.2.1  Comparison g r a v e l and  that  (Table peak  samples 4-3)  and  clay  sediment d i s t r i b u t i o n  end  of the  population  i s also present  distribution.  of magnetite c o n c e n t r a t i o n s s a n d samples  Magnetite concentrations gravel  the s i l t  sediment  rise  i n b o t h sand  smoothly to  f o r most s a m p l e s .  concentration  occurs  is  maxima The  samples in  fraction  finer  i n sandy  for  one  and  sandy  fraction  i n which sand  the  samples  -135(-140+200-mesh samples in  (-70+100-mesh).  gravel  lowest sand  o r -200+270-mesh) compared  c o n c e n t r a t i o n s occur  occurs  4.3  while  in  than  in  concentrations  i n sand  samples.  The  -40+70-mesh  samples  for  sandy g r a v e l samples  t h e minimum  i n -270-mesh.  Heavy m i n e r a l Weights  mineral  and  concentrate  analyses  concentrations  concentrates  magnetite.  of  show  non-magnetic  very  similar  O v e r a l l weights of non-magnetic  concentrates  are  corresponding  magnetite  4.4  O v e r a l l magnetite  samples a r e g r e a t e r  samples  t o sandy g r a v e l  slightly  (1.05 t i m e s )  heavy  trends  to  heavy-mineral  greater  than the  weights.  Summary The  based  reach  on c h a n n e l  channel the  sampled  slope  middle  channel  c a n be d i v i d e d i n t o  pattern  (braided  (0.02 t o 0.04).  of  the  slope  reach  section  and  A steep  produces and  a  an  lower  three sections  meandering)  and  braided section i n upper  increasing  decreasing  slope  section. Sediment t e x t u r a l bars bar  i s very tail  poorly  pools sorted  analyses  show t h a t most  p o o r l y s o r t e d sandy c o b b l e there sand.  i s a s m a l l amount In  both  types  sediment  in  g r a v e l whereas a t of  moderately  o f sample t h e r e  to is a  -136minor  (<1%  by  component. size  weight)  Gravel  modes.  samples  Since  there  discriminates  between  properties  be  can  Magnetite single  hydraulic (1977)  particles  show  is the  a  typical threshold  two  determined  in  one  others  i n the  due  coarser  silt  and  s a n d and diameter  components t h e i r  clay gravel that  textural  separately.  fraction.  of m a g n e t i t e  equivalence  and  distinctive  c o n c e n t r a t i o n s show c o h e r e n t  peaks  distributions  but  However,  c a n n o t be  using to  the  used  to  rising the  to  size  investigate  methods o f S l i n g e r l a n d  absence  fractions.  trends  of  pure  magnetite  -137-  CHAPTER 5 GEOCHEMICAL DATA: RESULTS AND DISCUSSION  -138-  5.0  Introduction Complete  in  t a b l e s of h i g h d e n s i t y m i n e r a l  the Appendix,  are  provided  however  in  Table  concentrates  magnetite, in  the data  t h e whole  data  5-1.  were  Gold  (HMCs)  to  were c o n v e r t e d  =  same t r a n s f o r m was  TOTAL.  fraction  to  which b i a s  concentrations.  i s very  (see  Samples  correct  reported  l i m i t s were c o d e d a t h a l f  average.  splits  were  A l l Hf and Au  data  favour below  skewed of  high  analytical  the l i m i t .  i n non-magnetic  were a n a l y s e d  the  The  as  minus  of  2-3B).  in  using  samples  gold i n  positively  s e d i m e n t were t r a n s f o r m e d 270-mesh  little  Table  for  statistics  H a f n i u m and Au c o n c e n t r a t i o n s  analyses  concentration  (5-1)  a p p l i e d t o Hf d a t a .  logtransformed  detection  be c o n s i s t e n t w i t h  to gold  on t h e a s s u m p t i o n t h a t t h e r e  distributions  heavy  A U M M C . Wturtc  low d e n s i t y m i n e r a l  were  i n the non-magnetic but  Wt  the  concentrations  fraction: AUTOTAL  based  are given  summary s t a t i s t i c s f o r t h e  d e t e r m i n e d as p a r t s per b i l l i o n mineral  data  equation  As  a l l  in duplicate,  the  combined  (5-1).  -270-mesh  in  a  weighted  -139-  T a b l e 5-1. Summary s t a t i s t i c s c o n c e n t r a t i o n s i n sediment. Fraction (mesh)  Au  (ppb)  -40+70 -70+100 -100+140 -140+200 -200+270 -270  -  -40+70 -70+100 -100+140 -140+200 -200+270 -270 Black  -40+70 -70+100 -100+140 -140+200 -200+270 -270  sand  -  80 80 13  34 26 42  sand poor  -  3. 7 10. 2 9 .8 7. 2 3. 9 1. 5  20 23 37  -  and  Hf  Hf X (ppm)  CV (%)  (n = 10) .  -  sand-- e n r i c h e d  CV (%)  X (%)  (%)  samples  Black  magnetite  Magnetite  Sandy q r a v e l  243 150 20  f o r Au,  sand  -  -  4.0 7.8 8. 3  122 87 28  70 57 50 59 42 67  —  _  -  -  46 28 21  20 13 8  s a m p l e s (n = 4) 1. 2 4. 9 6. 7 6. 0 4. 3 1. 9  samples 0. 5 1. 6 2. 3 2. 7 2. 5 0. 9  50 40 29 24 27 67  _  46 33 19  _  10 7 2  (n= 34 21 26 22 35 48  —  ' -  -  -  -  16 16 17  10 14 13  ' G e o m e t r i c mean f o r Au and Hf, a r i t h m e t i c mean f o r magnetite. ^ C o e f f i c i e n t of v a r i a t i o n ( i . e . standard deviation/mean). - = f r a c t i o n not determined.  -1405.1  Gold  5.1.1  data  Evaluation  In  this  emphasised the  of  study,  presenting  within  of  results, has  gold  as  this  problem,  based  on  the  and  As  95%  a  i n t e r v a l s implies  extent  estimated  chi-squared  of  after  that  f o r the  Poisson (Zar,  Cl-a/2>,2IM  £ ]d £  S  estimating sample  the  specific  colour  of  the  and  first  Before  be  evaluation  be  of  analyses  calculated  problems.  there  of  a t t r i b u t e d to  for gold  can  this  is  Overlap  a  same g o l d  to of  reasonable  concentration  simply  due  confidence  distribution  to  limits  using  the  1984): X ' Q I / Z ,  2 C f>»<- 1  >  (5~2)  2  Calculation  a  limits  N i n e t y - f i v e percent  2  in  can  to  proportion  i n the  sampling  distribution Z  the  step  s a m p l e s have t h e  nugget e f f e c t . be  been  e r r o r s due  high  a p p a r e n t d i f f e r e n c e s between them a r e  the can  a  distribution  confidence  and  that  first  the  two  sampling  discrete particles.  confidence  Poisson  that  l a r g e s a m p l e s has  variability  determine  chance  of  grain effects  i t i s necessary to e s t a b l i s h that  between s i t e  effects.  rare  statistical  been met  and  hydraulic  collection  to minimize  occurrence  condition  h y d r a u l i c and  of  gold  of  gold  (N)  in  a=.95. the  phase  gravity  number o f p a r t i c l e s  number of g o l d  particles  ( S e c t i o n 2.4.3) was of  15.  particles  However, from  based the  Harris  for on  gold  strong Creek  samples with  yellow  implies  a  -141higher  fineness  corresponding Ag  present) Shape  to  density.  A  density  distribution  of  gold  determined  The  in  "average" gold  particles  the  particle  (i.e.  identical  intermediate  an  intermediate  diameter  the geometric in  of  85-SD-10  where n o t a t i o n  concentration  (-53+44 Um)  gold for  diameter  in section Au  the e f f e c t i v e limit  estimation,  very  fine  from  5-1).  fractions,  gravels  are  very  was  openings.  of  permits  a  subbetter  using (5-3)  3  2.4.5.1.  Due  to  the  the c o a r s e s t s u b - f r a c t i o n for  the  purpose  assumptions  sand  limits  described  of  fractions  confidence (reflecting  above,  have been c a l c u l a t e d (-140+200-mesh,  s a n d y g r a v e l and sand d e p o s i t s  narrow  taken  i s 47 um.  confidence  -200+270-mesh) In both  in  1 /  the  assumed t o have  t o be made  diameter,  t h e s h a p e and s i z e  two  diameter  analyses  3-7)  3  of  concentration the  sieve  of a f r a c t i o n  = (E ( M j / M ) d j ) "  i s given  t o be 0.63  As p r e v i o u s l y ,  however  (Table  of the e f f e c t i v e  confidence  3  (section  of the bounding s i e v e  o f 20 Um,  dE  Using  same  -270-mesh s e d i m e n t was i n i t i a l l y  fractions  high  phase  was f o u n d  axes).  of p a r t i c l e s  midpoint  average diameter  estimate  g/cm ,  i n H a r r i s Creek  first  t h e volume o f a s p h e r e o f t h e  Gold  18  a f i n e n e s s o f 900 ( a s s u m i n g o n l y Au and  times  as  of  was s e l e c t e d f o r c a l c u l a t i o n s .  s e d i m e n t s was 2.4.2).  and  limits their  high  for  (Fig. sandy  number o f  -142(A)  Au (ppb) 10  1  i  M  i  1000  100  i  0  i  e  A  e  C  •  e  K D B  ——  e  •  9  F 9  E  #  ©  G C  J  (B)  1  i  M A  e  C  0  K  Au (ppb) 10  |  1000  100  i  C  _  •  •== ©  D B  9  #  F E G  e  V—  J Fig. 5-1. Poisson confidence limits for gold c o n c e n t r a t i o n s c a l c u l a t e d as d e s c r i b e d i n t h e t e x t f o r (A) -140+200-mesh and (B) -200+270-mesh. Solid circles are s a n d y g r a v e l s a m p l e s , open c i r c l e s a r e m a g n e t i t e - p o o r sand samples, half-filled circles are magnetite-rich sand samples.  - 1 4 3 -  161  12 -  # o o o I  8-  <D +-  "5 c  O)  co 2  0.1  ft,  cP  o  10  1 A  u  100  -140+200 P P (  1000  b )  Fig. 5-2. Magnetite c o n c e n t r a t i o n (-70+100-mesh) versus Au c o n c e n t r a t i o n (-140+200-mesh). S o l i d c i r c l e s are sandy gravel samples, open c i r c l e s are magnetite-poor sand samples, half-filled circles are m a g n e t i t e - r i c h sand samples.  -144-  qold  p a r t i c l e s ) and  much in  wider  these  which  confidence  fractions  hydraulic similar  trends too  occurrence In t h e  to  case  of t h e  estimated  corroborated  seriously  -270-mesh  confidence  Conclusions  about  with  by  reflect the  very  (Fig.  affected  5-2)  by  the  particles.  fractions,  diameter  limits  the  Trends  to  concentrations  be  effective  cases  believed  of m a g n e t i t e as d i s c r e t e  particles,  more  is  magnetite  high  few  f o r sandy sediments.  therefore  This  in  in only a  limits  are  effects.  are  large  overlap  of  on  to  the  -270-mesh  overlap  hydraulic effects  due  in  a l l  this  gold cases.  fraction  are  limited.  5.1.2  Downstream t r e n d s  The  two  trends  very  i n Au  fine  i n Au  sand-size  concentration  mesh Au  trends  coarser  fractions,  uncertainties  (Fig.  concentrations  5-3C)  (Fig.  5-3A,  are  p e r h a p s due  discussed  fractions  show  5-3B).  dissimilar to sampling  earlier  similar  Minus  270-  the  two  to and  (sections  analytical 3.9.1  and  5.1.1). Samples  from  concentrations there  are  a slight  sandy  from  no  marked  low  point  gravel  approximately  deposits 10  ppb  t o 1000  i n c r e a s i n g or d e c r e a s i n g is detectable  i n the  show  trends  section  of  Au  ppb  and  though steep  -145-  0.1-1—I J  G  E  1—I F  1—I 1  B D K  Fig. 5-3. Downstream trends -140+200-mesh sediment, (B) (Continued next page).  1 1  C A  M  i n Au c o n c e n t r a t i o n i n (A) -200+270-mesh sediment...  -146-  1000  J  G  E  F  B D K  C A  Fig. 5-3. ( c o n t i n u e d f r o m p r e v i o u s page) (C) -270-mesh. Filled circles = sandy g r a v e l d e p o s i t s , Open c i r c l e s = magnetite-poor sand deposits, half-filled circles magnetite-enriched sand d e p o s i t s . S i t e J i s the upstream end o f t h e r e a c h which i s 5050 m i n l e n g t h .  M  -147-  channel  and  braiding.  Gold  v a r y between a p p r o x i m a t e l y  concentrations 0.1  ppb  and  i n sand  1000  ppb  samples  and  show a  d e c r e a s i n g downstream t r e n d , t h o u g h major d e p a r t u r e s for  magnetite-enriched  results and  i n a gap  between Au  sand d e p o s i t s t h a t  diverge change  more r a p i d l y from  difference deposits  deposits  are  downstream end  in this greater of t h e  f o l l o w i n g sources  be  evaluated:  1)  Gold  concentrations  greater deposits,  than but  B  gold the  diameter  decreases.  Between  site  This  sieve  very  fraction  Au  than  sand  reach  to  channel.  in different  diameter  small  appears  corresponding  meandering  to the  This  sediment  of  sediment  f o r -270-mesh  sediment.  concentrations  in gravel  deposits  toward  the  ( F i g . 5-3C).  Q u a l i t a t i v e comparison site variability  Comparison of F i g s .  2)  site to  as  DI.  c o n c e n t r a t i o n s of s a n d y g r a v e l  concentrations  becoming  However, even  5.1.3  braided  decreases  particularly  i n c r e a s e s downstream and  after  between Au  decreases,  the  samples,  occur  5-3A,  of w i t h i n - s i t e 5-3B  and  of e n v i r o n m e n t a l  5-3C  and  between  indicates that  variability  should  i n sandy g r a v e l d e p o s i t s are concentrations difference  variability  in  adjacent  decreases  appears  mostly  t o be  as  sand  sediment  smaller  than  -148within  s i t e v a r i a b i l i t y f o r any of the t h r e e  fractions  cons i d e r e d . 3) W i t h i n for  a sediment  different  deposit-type  sediment  fractions  example g o l d c o n c e n t r a t i o n from sand d e p o s i t s appear site  variations  Three  between s i t e v a r i a b i l i t y  in  -140+200-mesh  methods  variability:  1)  (Saxby,  2) a n a l y s i s o f v a r i a n c e  of  Geometric  were  mean  for  sediment  t o show more e r r a t i c  t h a n does -200+270-mesh  statistical  1985),  i s not uniform,  between-  sediment. used  to  concentration and 3)  assess ratios  coefficients  variation.  5.1.3.1 G e o m e t r i c mean c o n c e n t r a t i o n r a t i o s Geometric Fletcher, fraction  concentration  1986) p r o v i d e within  energy gold usual  mean  site  a  means  ratios of  variability.  concentration  ratio  (GMCR)  is  (Saxby  evaluating  between  The mean h i g h  determined  and  t o low  using  the  f o r m u l a f o r t h e g e o m e t r i c mean:  GMCR = a n t i l o g  n [ ( E logCRi)/n], 1  where CRi=  A U s o , I . X A U o , * , x  n = number o f s i t e s and  A u s a . i . x ,  X  from  site  A u a . i . x  i  are gold sandy  concentrations  gravel  and  sand  in fraction deposits,  - I r respectively. The sandy  g e o m e t r i c mean i s used gravel  (GMCR<1)  is  (GMCR>1). by  with  of using  hydraulic  difference  finest test are  using  size  sand  overall  enrichment i s given  ratios  can  Duncan's m u l t i p l e an i n d i c a t i o n  fractions  to  of  deposits  or enrichment  providing  o f GMCRs f o r Au  (Table  environments  (-270-mesh).  is of  magnetite-poor downstream  is  then range  of the  reduce  local  due  for site  not  the  95% c o n f i d e n c e  at  o f CRs.  (Table  coarsest  sand the  Sites  is  size 95%  f o r the  confidence fraction  mixture  sand d e p o s i t s a t which CRs,  5-2).  have s i g n i f i c a n t l y d i f f e r e n t  range  fractions  within the  of  and t h e  magnetite-rich to  less  Removal o f t h e s e  four  GMCRs b u t a d j a c e n t  level.  f o r the  the m u l t i p l e  from  y i e l d the lowest D  greatest  extreme  magnetite-rich  higher  do  the  resulting  and  s a n d s were sampled  to  the  difference  However,  different  CRs  increase  samples y i e l d s  that  GMCRs f o r t h e two f i n e  not s i g n i f i c a n t l y This  shows  5-2) and t h e l e a s t  shows t h a t  1  to  as  dilution  thus  between  variability  than  same  each other  different  fraction  level.  respect  dilution  effects.  Calculation  fraction  the  net o v e r a l l  ( O t t , 1984),  merits  with  overall  G e o m e t r i c mean c o n c e n t r a t i o n  compared  test  weighted  No  GMCR=1.  be  deposits  so t h a t  dipping  fractions  GMCRs  (Table  still 5-2) a t  -150-  T a b l e 5-2. GMCRs f o r t h r e e h i g h - d e n s i t y m i n e r a l f r a c t i o n s and s i g n i f i c a n c e t e s t e d by Duncans m u l t i p l e r a n g e t e s t . Fraction Density Fraction  (mesh)  -40+70 -70+100 -100+140 -140+200 -200+270  Au  18.1  Au  1  Magnetite  Zircon (Hf)  4. 3  3.7  2.4  -270  7.4  1.8  35.6  10.8  2.3  1.7  1.3  1.2  1.9  1.3  1.0  B a r s a r e under f r a c t i o n s whose GMCRs are d i f f e r e n t a t t h e 95% c o n f i d e n c e l e v e l . *GMCRs c a l c u l a t e d f o r s i t e s where sands poor .  insignificantly are  magnetite-  -151Thus, sediment  GMCRs a r e  significantly  implying  that  produce d i f f e r e n t i a l in  the  stream  lower  hydraulic  gold  contents  are  subdued  bed  for  the  processes  tending  at d i f f e r e n t when  finest to  locations  acting  on  fine  sed iment.  5.1.3.2 One One  way  importance of  way  gold  of w i t h i n s i t e concentrations  concluded  the  the  test  between s i t e s  hypothesis  a l l three For  that  i f gold  considered  a  type  used  are  1984).  If  the  be  is sufficiently  low  ( a t 95%  it  null  can  However, due  concentrations  to  within  sites  confidence  level)  5-3).  the  a n a l y s i s of v a r i a n c e  between s i t e s to  i s of  delineate  a  source  of  shows  importance, dispersion  of s e d i m e n t d e p o s i t sampled  significant  the  variability  then  meaningful.  (Table  to assess  between s i t e  variability  attempting  the  be  rejected  of Au  concentration  then  is  purposes,  example when  train,  versus  i s accepted  fractions  practical  can  (Sinclair  that within site  trends  null  for  for  of  extreme v a r i a b i l i t y  the  variance  a n a l y s i s of v a r i a n c e  hypothesis  that  a n a l y s i s of  must  be  environmental  variability.  5.1.3.3 C o e f f i c i e n t s Coefficients  of v a r i a t i o n  of v a r i a t i o n  (CVs)  (relative  standard d e v i a t i o n ) :  -152-  Table Null  5-3. A n a l y s i s o f v a r i a n c e hypothesis:  Fraction/ Source of variation  U  M  results  for gold.  = U<°» == U c = . . . = U  Sum o f Squares  Degrees of Freedom  4.36 15.53  9 10  Mean Sum of Squares  -140+200-mesh Between s i t e s Within s i t e s FCALC  = 2.80  F ( 1 0 , 9 , 0 . 0 5 ) = 5. 26 .  Null hypothesis  0.484 1.353 accepted  -200+270-mesh Between s i t e s Within s i t e s FCALC  = 1.64  4.46 8.10 F ( 1 0 , 9 , 0 . 0 5 ) = 5. 26 .  9 10 Null hypothesis  0.495 0.810 accepted  -270-mesh Between s i t e s Within s i t e s FCALC  = 1.32  1.40 2.05 F ( 1 0 , 9 , 0 . 0 5 ) = 5. 26 .  9 10 Null hypothesis  0.156 0.205 accepted  -153-  CV  provide Au  (%)  = standard d e v i a t i o n Mean  a means o f c o m p a r i n g  concentrations  environment.  different In  for  magnetite-poor  the d i s t i n c t i v e  In  minus  Finally,  of  highest  (Fig.  5-4,  sediment  trends  in  CVs  a  lower  The  fraction  nugget  Au  precision  close  found i n  this  decay  coefficient t h e CV  are presumably (section  of  is  less  variation.  i s lowest  for  components o f random  5.1.1)  t o t h e INAA  due  concentrations.  overwhelming  effect  are  c u r v e 1) p r i m a r i l y  sediment,  deposit.  in this  the  instrumental  errors  and  detection  poor limit  3.9.1).  Only four  samples  each f r a c t i o n ,  of m a g n e t i t e - r i c h  however CVs  s a n d s were  ( F i g . 5-4,  as downstream d e c a y o f Au c o n c e n t r a t i o n s Gold  given  g r a v e l s are completely  i n minus 270-mesh s e d i m e n t  variability  for  any  between  downstream d e c a y o f Au  yielding  type  (section  versus  sands,  200+270-mesh  pronounced  to  from  ( F i g . 5-3).  to  due  v a r i a b i l i t y for  because downstream  sands  -140+200-mesh s e d i m e n t  this  fractions  comparisons  d e p o s i t s are not u s e f u l concentrations  between s i t e  in different  However,  .10 0  concentrations  i n t h e two  s a n d y g r a v e l s show low CVs the a b s e n c e  (Fig.  analysed  c u r v e 2) a r e  low  i s not apparent.  fine  sand  fractions  5-4,  c u r v e 3)  in  reflecting  of d e c a y o f Au c o n c e n t r a t i o n s as w e l l  as  good  -154-  160H  120-  §  80-  40-  140+200  -200+270  -270  Fraction (mesh)  F i g . 5-4. C o e f f i c i e n t s of v a r i a t i o n for Au c o n c e n t r a t i o n s by sediment deposit type and f r a c t i o n . Curve 1 = magnetite-poor sand d e p o s i t s , curve 2 = magnetite-rich sand d e p o s i t s , curve 3 = sandy g r a v e l d e p o s i t s .  -155analytical very  high  p r e c i s i o n and Au  of  variation  -270-mesh s e d i m e n t a r e that  p e r h a p s be  a  Summary of g o l d  the  nugget e f f e c t  observed mesh)  in fine  detection  variance  indicate sand  t h a t Au  not  be  (environmental) (dispersion  over  and  fractions  should  to  concentrations  in  of  the  Au  concentrations  and  low  errors  fractions  the  with  between s i t e  5 km  low  can INAA  errors  due  variability  are  Gold  mixed.  In  variability  -200+270-  concentrations  rapid  decay  long study  reach.  mean  to  data  obtained  this  case  will  obscure  in  sub-  Analysis  concentrations  i n s a n d y g r a v e l d e p o s i t s and  ratios  from  sand  fine  deposits  within  site  between  site  trends.  sensitive  GMCR a p p r o a c h e s u n i t y and sampling  and  (-140+200-mesh,  show  concentration  environment  40%)  variability  M i n u s 270-mesh s e d i m e n t a p p e a r s t o o f f e r to  to  results  geometric  train)  (30  limit.  sand d e p o s i t s  levels  Au  t o random s a m p l i n g  from sandy g r a v e l d e p o s i t s .  magnetite-poor  of  sand  for  proportion  detection  C o n s i s t e n t l y high to  e r r o r s due  a l l i n a narrow range  high  attributed  problems near the  5.1.4  random s a m p l i n g  concentrations.  Coefficients  indicating  low  environment.  CVs  coarser are  However, Au  an  fractions  similar  alternative because  the  regardless  of  c o n c e n t r a t i o n are  close  -156to the  detection limit,  analytical  precision  increasing v a r i a b i l i t y and  random e r r o r s a r e  t o s m a l l - s c a l e nugget e f f e c t s . p e r h a p s be the  attributable  lacustrine  Thus,  sampling  will  detection  be  limit  low are  Trends  concentrations value. from F  In  (Fig.  sand  sediment  from  section  4.0).  as  sensitive  fractions, being  to  anomaly  below  the  and  concentrations in  (Fig.  the  coarser  downstream 4-1)  fractions  (Fig.  then  5-5)  increase  of as as  decreases.  Conversely,  sand d e p o s i t s  fluctuate  about  magnetite  concentrations  f o r Au,  sediment  deposits  magnetite-rich  sand  magnetite  diverge  the  mean  downstream  deposits  gradually increase r e l a t i v e  sediment diameter decreases.  most extreme example w i t h being  may  of  5-3).  the  s a m p l e s as  concentrations  of g o l d , magnetite  decrease  C o n s e q u e n t l y , as  concentrations  the  in  different  site  behaviour  increases  slope  due  (see  not  coarser  very  poor  high.  initially  slope  is  G  to high  fine  c h a n c e s of  concentrations  sandy g r a v e l s  channel  the  by  site  the  i n magnetite  Magnetite  channel  as and  Comparison of the zircon  5.2.1  near  fraction  environment  contrast  5.2  the  gold  to d i l u t i o n  deposit  although  Low  due  greater  than  the  the  magnetite  to sandy g r a v e l  Site  D  represents  magnetite content corresponding  of  the  gravel for  -157-  F i g . 5-5. Downstream p r o f i l e s o f m a g n e t i t e c o n c e n t r a t i o n s i n (A) -40+70-mesh s e d i m e n t , (B) -70+100-mesh s e d i m e n t . . . ( c o n t i n u e d on n e x t p a g e ) .  -158-  Pig. 5-5. sediment...  (C) -100+140-mesh s e d i m e n t , ( c o n t i n u e d on n e x t p a g e ) .  (D) -140+200-mesh  -159-  Pig. 5-5. (E) -200+270-mesh sediment, ( F ) -270-mesh sediment. Filled circles = sandy g r a v e l d e p o s i t s , Open circles = magnetite-poor sand deposits, half-filled c i r c l e s = m a g n e t i t e - e n r i c h e d sand d e p o s i t s . S i t e J i s the u p s t r e a m end o f t h e r e a c h w h i c h i s 5050 m i n l e n g t h .  -160-  fractions  finer  Magnetite at  site  This  than  70-mesh.  concentrations  G, t h e n g r a d u a l l y i n c r e a s e downstream  effect  may  be  similar  coarser  fractions  dilution  of the f r a c t i o n  from site  G.  In  increase  the  i s added  5.2.2 T r e n d s  abundant  concentrates.  show  analysed strong  concentrations  as  f o r the  may  due  be fine  as  to  sediment  location at  concentrations  magnetite-rich  fine  from the banks.  concentrations  in  the  of z i r c o n s ,  reflect  the  non-magnetic  assuming  presence  of  heavy-mineral  are proportional to that  a l l zircons  Hafnium c o n t e n t s  f o r a l l three  a r e m o s t l y between similarities  i n t h e two f i n e  Concentrations  observed  magnetite  downstream  t h e same Hf c o n t e n t .  fractions and  case,  decrease  ( F i g . 5-5F).  the sampling  Thus, Hf c o n c e n t r a t i o n s  concentration  have  near  concentrations  zircons  that  by m a g n e t i t e - b a r r e n  deposit  i n hafnium  hafnium  to  alternatively,  latter  slightly  sediment  the  or,  the l a c u s t r i n e  High  i n -270-mesh s h a r p l y  to sand  1 ppm trends  fractions  i n -270-mesh s e d i m e n t  i n d i c a t e d i n s e c t i o n 3.9.3.  and in  100  ppm  magnetite  ( F i g . 5-6).  are not meaningful  -161-  1000  E a. a 100-  J  G  E F  100  E a a.  E F F i g . 5-6. Downstream p r o f i l e s o f Hf c o n c e n t r a t i o n s i n (A) -200+270-mesh. Filled circles -140+200-mesh and (B) Open c i r c l e s = m a g n e t i t e - p o o r sand sandy g r a v e l d e p o s i t s , sand deposits, h a l f - f i l l e d c i r c l e s = magnetite-enriched deposits. Site J i s the u p s t r e a m end o f t h e r e a c h w h i c h i s 5050 m i n l e n g t h .  -162-  100H  -70+100  -140+200  Fraction (mesh)  Fig. 5-7. G e o m e t r i c mean c o n c e n t r a t i o n r a t i o s c a l c u l a t e d f o r f o u r d e n s i t y f r a c t i o n s as d e s c r i b e d i n t h e t e x t . Curve 1 = Au, c u r v e 2 = m a g n e t i t e , c u r v e 3 = Hf and c u r v e 4 = bulk sediment.  -163-  5.2.3  G e o m e t r i c mean c o n c e n t r a t i o n concentration ratios  G e o m e t r i c mean c o n c e n t r a t i o n magnetite,  zircon  equation  5-2  mineral  fraction  decrease. unity  the so  (Table  all  5-2,  overall  logarithmic  fractions  (Table  (1986),  though they  5-4)  to those  combination mineral sampled  processes  similar  correlation  bivariate  ratios  approach finer.  shows this  that is  not  (r) determined  for  Saxby relative  coefficient  f o r two  size  plots  to  weight  that  occur  for  same d e n s i t y  (r=0.902 f o r Au  for  of  by  CRs  sediment  fractions. examining  outliers.  between a d j a c e n t for  the  high-density  types  were e v a l u a t e d  correlations  same  statistically  implies  two  weight  of t h e  and/or d e n s i t y  check  Fletcher  t o the  l e a d i n g to v a r i a b l e between t h e  interesting  and  high,  highest the  the  fraction  range t e s t  than the A  coefficients  scatter  of  sediment gets  by CRs  5-2).  concentrations are  using  a given  for magnetite  noted  correlation of  as  density  shows a number o f  determined  (equation  significant  for  coefficients  -10-mesh i n a sample r a t h e r  fraction  As  fraction  for  5-2).  of c o r r e l a t i o n  similar  in a  concentration  is significant  (Table  CRs  GMCRs  and  were d e t e r m i n e d  5-7).  Duncans m u l t i p l e  features  All  Fig.  density  trend  for zircon  ratios  sediment  decreases  although  A matrix  of  all  G e o m e t r i c mean  for  However,  and  ratios  size  The  fractions  -140+200-mesh  T a b l e 5-3. C o r r e l a t i o n m a t r i x o f c o n c e n t r a t i o n r a t i o s . C a l c u l a t i o n d e s c r i b e d I n t h e t e x t . V a l u e s t h a n 0.632 a r e s i g n i f i c a n t w i t h 9 5 % c o n f i d e n c e . Ten s a m p l e s w e r e u s e d t o g e n e r a t e m a t r i x . Magnet i t e  Gold  - 140+200 Gold -140+200 -200+270 -270  1..0000 0 .9 0 2 0 0. 4517  -200+270  - 270  1. 0 0 0 0 0. 3540  1. 0000  Zircon  -40+70 -70+100 -100+140 -140+200  Magnet i t e -40+70 0..6977 0. 7358 -70+100 0 . 8613 0 . 8271 -100+140 0 .. 8983 0 .8089 , -140+200 0..7349 0..6049 -200+270 0 . 3543 0 .4151 -270 -0 .2386 -0 .1298  0 . 6509 0 . 5038 .4429 0. 0 .. 3988 0 .3457 0 .2423 .  1. 0000 0. 8864 1. 0000 ,9788 0 ..7899 0. 1. 0000 0 ..8717 0. 8965 1.0000 0 ..6385 0..7413 0..7187 0..6146 0.5656 .0309 -0 ., 1 8 8 1 - 0 . 0 7 5 2 0.. 2297 -0 .  Z i rcon -140+200 -200+270 -270  0 . 3442 0 .1274 0 .1059  0 . 5622 0..5647 0 . 6896  0 . 7953 0 . 4328 0 . 1997  n . 5968 0 . 5959 0 . 2788  0 .8327 0 .6715 0 .4867  0 . 8873 0..6033 0 . 3645  greater  0.9645 0.5085 0.2783  200+270  1 .0000 0. ,2414  - 2 7 0 -140+200  -200+270 -270  1.. 0000  0 .4651 - 0 ..1352 0..0184 0 .8429 0 .6314 0..4194  1.0000 0.4046 0.1923  1.0000 0.4032  1,. 0 0 0 0  -165and  -200+270-mesh).  difference values  between  diameter  decrease,  confidence. size  indicates  with  that  fine  size  sand  increase  minerals and  sand  for  intermediate  density  fine  drawn at  share  in  The f i n e  GMCRs  Similarly,  size  with  similar  a high  -140+200-mesh  These  results  however r - v a l u e s  and  behaviour  high-  i n sandy  gravel  CRs  correlation  indicate  that  ( m a g n e t i t e ) behave (gold).  The  in Fig.  size  which w i l l magnetic  of the gold  correlation  be  results  are  5-7:  line  minerals  fractions  in  the  a  curves  hydraulically do  not  considered.  c o e f f i c i e n t between  magnetite  coarse  similarly  t h e m a g n e t i t e and g o l d  fractions  with  finer  However,  a s c a n be s e e n  and  magnetite  behaves s i m i l a r l y t o  coarse s i l t  minerals  any  for  increases.  deposits.  sand  high  and  i s i n s u f f i c i e n t data t o  forzircon,  f o r GMCR=4 i n t e r s e c t s  similar.  95%  i n -140+200-mesh  gold  There  minerals  consistent  different  of s i m i l a r  -100+140-mesh.  logarithmic  high density  internally  the r -  the behaviour  are  size  that  show  coefficients  to  increases  the  with  as sediment s i z e  Thus GMCRs i n d i c a t e  deposits  as  significant  f o r gold  magnetite.  draw t h e same c o n c l u s i o n  density  that  magnetite  -70+100-mesh and  magnetite  that  of sediment  remain  coefficients  -200+270-mesh  medium sand  shows  i s c o m p a r a b l e a s would be e x p e c t e d .  Correlation  suggest  but  This  fractions  fractions  Magnetite  same  zircon fraction  -166-  corresponds  to  almost  identical  GMCRs  for  the  two  fractions.  5.3 Removal of h y d r a u l i c v a r i a b i l i t y : e m p i r i c a l data transforms Comparison  of  downstream p r o f i l e s  of raw d a t a ,  that at a given s i t e high c o n c e n t r a t i o n s density  fraction  are  matched  patterns  to  be  correlations  permitting become  between  comm.)  useful  though there  of  this  suggests  type  elimination anomaly  Similarly,  observed elsewhere  i s no evidence is  seen  suitable  investigation  of  hydraulic  i m p l i e s that the  in  Harris  ratios  negative  (D.  Creek  has  Brabec,  effect  sediments.  implications  equivalence  fractions  since  used are  to  a useful  behaving  in  a  fashion.  transform must be determinable only  magnetic weights  of  decay  that a d i l u t i o n  As w e l l as e l i m i n a t i n g h y d r a u l i c e f f e c t s ,  Thus,  of  that a product transform might be  of  similar  to  downstream  visible.  Determination  ratio  or  c o n c e n t r a t i o n of gold and weight of  heavy-mineral concentrate pers.  size  T h i s o b s e r v a t i o n shows  t h a t r a t i o i n g of f r a c t i o n s might lead effects  one  by high c o n c e n t r a t i o n s  another d e n s i t y and s i z e f r a c t i o n .  hydraulic  of  shows  transforms  heavy have  mineral been  from e a s i l y  involving gold, concentrate  investigated.  The  and  a  potential  collected  data.  magnetite,  non-  fine  sediment  data are s u p p l i e d  -167-  Table text.  5-5.  Empirical  *z.  3.  data  =  log  x . v-  =  log(C A«_« ,  »< , y  -  transforms  10  Wt ,^ Wt  1  A u  x  )/  d i s c u s s e d i n the  CtlAQ ,  log  y  10' W t e E D , y  where  Wt*,j Ci.. j  = =  weight of m i n e r a l i i n fraction j . c o n c e n t r a t i o n of mineral i i n fraction j .  -168oriqinally mineral ratio  as c o n c e n t r a t i o n  concentrates Table  (<frx,  downstream  5-5).  A  is  *  and  concentrations relative  and r e p r e s e n t s  profiles  concentrations  o f Au i n  show  non-magnetic  a simple,  transform since  3  but l o g i c a l  suggested  by  logarithmic  gold  non-logarithmic  similar  to low-density  trends.  minerals  magnetite  Behaviour  was  heavy-  of gold  investigated  using  transform * . 3  The  ability  effects  ratios.  profiles  The b e s t  reduction  of  5.3.1 T r a n s f o r m This  gold  ratio  original  Table  using:  and  transform  1) v i s u a l  yields  a  examination  represents  re-conversion  form r e p o r t e d  to  of  mean c o n c e n t r a t i o n  low  GMCR  (implying shows  <t>x  since  variability  eliminate hydraulic  curve.  concentration  closer  to  2) g e o m e t r i c  by t h e  5-5). I n t u i t i v e l y ,  sediment is  transform  w i t h i n s i t e v a r i a b i l i t y ) and v i s u a l l y  anomaly decay  the  a  c a n be e v a l u a t e d  downstream  an  of  of the data  laboratory  GMCRs s h o u l d  expressed  relative  due  to  of  gold  laboratory  and  to  the  and w e i g h i n g a r e n o t i n c l u d e d .  reduced  but remain high  x=y,  weight  of  concentrates  additional  processing  sieving  (case  be l o w e r t h a n f o r  the d e n s i t y of heavy-mineral that  back t o  random  errors during  However, GMCRs a r e  (GMCR*14 f o r -140+200-mesh).  -169-  ' - 1 4 0 - 2 0 0  1 - 2 0 0 - 2 7 0  1 -270  Fraction (mesh) Fig. 5-8. C o e f f i c i e n t s of v a r i a t i o n for transform (Table 5-5, case x=y o n l y ) by s e d i m e n t d e p o s i t t y p e and fraction. C u r v e 1 = m a g n e t i t e - p o o r sand d e p o s i t s , c u r v e 2 = m a g n e t i t e - r i c h sand d e p o s i t s , curve 3 = sandy gravel deposits.  -170Coefficients similar CVs  of v a r i a t i o n  diagram  ( F i g . 5-8) t o t h a t p r e s e n t e d  are reduced  (R;10%)  were  concentrates  from  8) i m p l y i n g  a  for  for  sandy g r a v e l d e p o s i t s  considerable Thus,  cases  (Table  this  advantage fraction  i t was  in ratioing other  than  5.3.2 T r a n s f o r m This which  t o the weight  magnetite  hydraulic  must  taken.  be  this  case  y  are  used  i s no a d d i t i o n a l  ratios  calculated: MTR  TR± =  thus  i n some  of  profiles  in  very similar to  the  Calculation  ratio  should  act similarly GMCRs  i s not  s i n c e a l o g a r i t h m of a l o g a r i t h m as  sediment  =  are  i f the e f f e c t s  However,  between  where  must be low.  of c o n c e n t r a t e  trends  effects  difference were  site  t o be t h e b e s t  by downstream  trends,  on a l l p a r t s o f t h e r e a c h . in  5-  analysed.  i s suggested  gold content  possible  between  and  that there  3, F i g .  2  arithmetic  eliminate  x  low CVs  4>  transform  logarithmic  in  appears  range of  5-4.  heavy-mineral  variability  found  that  Very  (Curve  reduction  fraction  where t h e f u l l  5-5),  in Fig.  -140 + 200-mesh  s t u d i e s where between s i t e For  t o produce a  by up t o 60% i n some c a s e s .  obtained  variability.  were c a l c u l a t e d  an  types  indication mean  E(TR /n); t  $ 2 , 8 A N D Y $ 2 , B A N D  S R A W E L .  of  the  transformation  -171-  F i g . 5-9. Downstream p r o f i l e f o r * a ( c a s e x=-140+200-mesh, y=-200+270-mesh). F i l l e d c i r c l e s = sandy g r a v e l d e p o s i t s , Open c i r c l e s = m a g n e t i t e - p o o r sand deposits, half-filled c i r c l e s = m a g n e t i t e - e n r i c h e d sand d e p o s i t s . S i t e J i s the u p s t r e a m end o f t h e r e a c h w h i c h i s 5050 m i n l e n g t h .  -172The very that  MTRs  f o r a l l p o s s i b l e combinations  close t o u n i t y with within  site  low s t a n d a r d  variability  is  profiles  of *  similar,  e x p l a i n i n g t h e low MTRs  there  i s a peak  followed  by  i n values  steady  of  reduced.  (Fig.  the  downstream  appears t o i n d i c a t e that the formation  deviation  show t h a t g r a v e l and sand  2  of h i g h - d e n s i t y  implying Downstream  results  are  very  5-9). In a d d i t i o n ,  transform  decay.  at  This  conditions  mineral  o f x and y a r e  Site  F  transform  leading  to the  concentrations  i n sandy  g r a v e l s and s a n d s a r e l i n k e d .  5.3.3 It  T r a n s f o r m 4>  3  is  anticipated  hydraulically and  equivalent  feldspar)  information  that  certain to  fractions  low d e n s i t y m i n e r a l  fractions.  c a n be g a i n e d  gold  However,  from c a s e s  no  are  (quartz  additional  where x / y ( T a b l e  5-5)  o v e r t h e c a s e where x=y.  5.3.4  Other  transforms  Inter-relationships deposits  s e d i m e n t s a r e shown  *t>*t- —  IJt A u  ,  -  1 4 0 + 2 0 0 ,  W t s E D , - 4 0 + 7 0 ,  The  between  resulting  by r a t i o s  S A N D Y  gravel  and  sand  such as  G R A V E L  S A N D  downstream  downstream p r o f i l e  sandy  profile  i s very  similar  to the  f o r Au i n -140+200-mesh s e d i m e n t  being  -173very  smooth,  with  sands  ( F i g . 5-10).  5.3.5 R a t i o s : Empirical  major  data  transforms  that:  1) G o l d  concentrations  lowest  2) W i t h i n  in  magnetite  trends  sediment  relative  from  t o the weight  i n t h e same f r a c t i o n  have  variability  variability log  by raw d a t a  -140+200-mesh  concentrate  between s i t e  site  dividing  3) No  suggested  g r a v e l deposits expressed  of h e a v y m i n e r a l the  for magnetite-rich  implications for exploration  indicate  sandy  departures  c a n be r e d u c e d  transformed  gold  considerably  by  concentrations  by  concentration.  additional  dispersion  obtained  by  expressing  fraction  relative  train  gold  t o the weight  information  concentration of sediment  can in  be one  i n another  fraction.  5.4 C o n c l u s i o n s 1) A t  Harris  Creek  allow a s u f f i c i e n t gold can 2) G o l d  sixty  kilograms  reduction  concentration trends be d i s c u s s e d w i t h concentrations  reproducible  due  to  o f -10-mesh s e d i m e n t  i n rare grain effects  i n two  reference  fine  sand  to hydraulic  that  fractions effects.  i n -270-mesh s e d i m e n t s a r e p o o r l y the  occurrence  of  Au  in  the  -174-  0.20  Fig. 5-10. Downstream calculation described in  profile text.  for  transform  -175fraction scarcity  a s one or two s i l t of gold  dilution  by  lacustrine 3) G o l d  silt-  deposits  decrease  Fletcher, mineral deposits  as 5)  concentration  1986)  show  combined site  decrease  fairly  concentrations  whereas  constant.  ratios  (Saxby  and  ratio  between  heavy  f o r sandy than  with  gravel  unity  and  f o r the  sand coarser  GMCRs a p p r o a c h u n i t y f o r  For a given  in  fraction,  the  -270-mesh  GMCRs  decrease  decreases.  variability  from both  or  concentrations  A n a l y s i s of v a r i a n c e  trends.  Au c o n c e n t r a t i o n s  downstream,  the  However,  mineral  fraction.  density  site  that  greater  studied.  heavy  sediment  mean  are  fractions all  remain  with  Au c o n c e n t r a t i o n s i n  rapidly  concentrations  to  from t h e  correlated  magnetite  Conversely,  magnetite c o n c e n t r a t i o n s 4) G e o m e t r i c  increase  whereas  i n c r e a s e downstream.  The  due  sediment  However,  not  downstream  probably  positively  concentrations.  distance  is  particles.  G.  are  do  gold  clay-sized  deposit at site  sandy g r a v e l s  sand  fraction  and  concentrations  magnetite in  in this  sized  Thus,  and  is  GMCRs  indicate  sufficient  Au d a t a  s a n d y g r a v e l and sand d e p o s i t s  variability  can  be  purposes. reduced  within  t o mask between  i n e x p l o r a t i o n surveys,  for interpretation  that  must  However,  site  obtained not  be  within  considerably  by  -176ratioing  log  transformed  gold  concentrations  to the  c o n c e n t r a t i o n of magnetite. The  longest detectable d i s p e r s i o n t r a i n ,  site  variability  found  f o r gold  and  greatest  concentrations  magnetic heavy m i n e r a l  lowest  between  Au c o n c e n t r a t i o n s a r e in  concentrates.  -140+200-mesh  non-  -177-  CHAPTER  6:  S E D I M E N T TRANSPORT AND S M A L L - S C A L E FORMATION, HARRIS CREEK  PLACER  -178-  6.0  Introduction Results  show  have been p r e s e n t e d  that  vary  heavy  mineral  systematically.  sediment  texture  quantitative formation  In  data  this are  features  discussed  within  site  between s i t e  (Table  6.1  chapter, used  to  i n the  in  to  Creek  of  semi-  sediment  gravel  (dispersion  a  and  bed  be  and  rivers.  divided  train)  into  features  6-1).  Database  morphological Creek  data  i n March  1987  geometry at d i f f e r e n t  A sediment Graf  sediment  Einstein transport  and  is  a  sediment p a r t i c l e  model  Knighton  stochastic movement.  was  f u r t h e r data  on  gravel  Lynn  visited  stream  bed  bars.  ( E i n s t e i n , 1950). (1974) r e c o g n i z e  model.  uniquely  stream  i n 1986,  Columbia  locations across  transport  (1950)  British  to obtain  transport  (1971)  g e o c h e m i c a l and  c o l l e c t e d a t H a r r i s Creek  i n North Vancouver,  briefly  of  at Harris  generate  model c a n  In a d d i t i o n t o s e d i m e n t o l o g i c a l ,  6.2  chapter  geochemical  for transport  placers  Major  and  previous  concentrations  h y d r a u l i c model  of s m a l l - s c a l e  i n the  However,  recognizes process For  this  due  three  the that to  the  reason,  types  model  of  sediment nature the  of  model  -179-  Table 6-1. features. A.  Within  site  Major  sedimentological  and  geochemical  features:  Sandy g r a v e l : - t r i m o d a l s i z e f r e q u e n c y d i s t r i b u t i o n s w e l l - d e f i n e d t h r e s h o l d d i a m e t e r between s a n d and g r a v e l , s u r f a c e pavement. Sand:  bimodal s i z e frequency d i s t r i b u t i o n s t h r e s h o l d d i a m e t e r between sand and s i l t .  Heavy minerals:  c o n c e n t r a t i o n i n g r a v e l g r e a t e r than c o n c e n t r a t i o n i n sand, sands a r e o c c a s i o n a l l y heavy m i n e r a l r ich. heavy m i n e r a l c o n c e n t r a t i o n s a r e p o s i t i v e l y c o r r e l a t e d , f o r a l l sediment types. GMCRs d e c r e a s e a s s e d i m e n t d i a m e t e r decreases. GMCRs f o r a g i v e n d i a m e t e r d e c r e a s e a s d e n s i t y of m i n e r a l s decrease, f i n e high d e n s i t y mineral p a r t i c l e s (gold) a p p e a r t o behave t h e same a s c o a r s e r intermediate density p a r t i c l e s .  B.  Dispersion t r a i n features - c o n c e n t r a t i o n r a t i o s i n c r e a s e downstream. - g o l d CRs i n c r e a s e a t t h e expense o f d e c r e a s i n g c o n c e n t r a t i o n s i n s a n d s whereas m a g n e t i t e CRs i n c r e a s e due t o i n c r e a s i n g concentrations i n gravels.  -180shows t h e b e s t  agreement w i t h n a t u r a l  s a n d and g r a v e l though Y a l i n  r i v e r s (Graf,  measurements i n b o t h  1971;  (1972) o f f e r s some  Parker  e t a l . , 1982)  f u n d a m e n t a l c r i t i c i s m s and  modifications. In  the  empirical a  model,  observations  bed m a t e r i a l  the  transport  contact  probability  load rates  with  and  hydraulic  f r o m f l u m e s a r e combined  function.  That  of sediment  the bed.  rate  of t r a n s p o r t  that  These r a t e s  contact  with  the  characteristics location.  of sediment  bed  In g r a v e l  drainage  at  with  6.2.1 D e r i v a t i o n function  of E i n s t e i n ' s  The  full  therefore presented evidence  here. that  relationship 1) A  the  observed  interest,  is  of  basin  the  formula  indicates  and  upstream a l l coarse  that  function  physical is  by t h e of  the  sediment  there  i s very  aspects  based  intensive  exchange  particles  move  in  long,  will  be  on e x p e r i m e n t a l  is  between t h e moving bed l o a d  2) I n d i v i d u a l  whereas  determined  between t h e bed and t h e b e d l o a d  steady  makes  (1950) bed m a t e r i a l  important  The  time  the bed.  derivation  only  some  a r e d e t e r m i n e d by t h e  bed r i v e r s a l m o s t  moves by c o n t a c t  t o produce  i n suspension but not i n  (washload)  of the  and  i s , calculations yield  g e o m e t r y o f t h e bed a t t h e l o c a t i o n o f the  theory  of  an  intimate  (Graf,  1971):  particles  is  and t h e b e d .  quick  steps  with  -181-  3)  long  rest  periods.  The  average  independent and  the  the  particles  depends  of  the  between  moving  deposited  per  on  stress  stress  particle due  a Gaussian  erosion  will  of  to  be  assumes  be  of  is  a  The  be  rate,  turbulent  particle  transport  is  I f the  small  sites  rare  to  ( S l i n g e r l a n d and  hypothesis  to  include  sediment  transport  intensity  the  erosion if  the shear  distribution  of  low  anywhere,  after  unit  i n t e r a c t i o n with  other  potential depositional  the  a dimensionless  during  is possible  Smith,  on  probability  (e.g.  rates deposition  uses t h i s  by  critical  The  of  f l u c t u a t i o n s i s modelled  Under t h e s e c o n d i t i o n s ,  the  the  number  since  the  entrained.  particles.  i n t e r m s of  change of  p r o b a b i l i t y of  exceeds  i s l e s s p r o b a b l e due  derived  a  and  the  turbulence  jump l e n g t h  Hence,  by  controlled  normal d i s t r i b u t i o n .  however a t g r e a t e r  expression.  steps  that  t r a n s p o r t ) , then d e p o s i t i o n  are  transport  achieved  two  unit area  level  shear  shear  the  appears to  layer.  of a p a r t i c l e .  the  the  sediment  time  (1950)  stress  particle  condition,  r a t e s can  Einstein  instantaneous  of  flow  by any  composition.  jump l e n g t h  using  the  average  Thus,  made  transport  thickness  unit  of  bed  4) D i f f e r e n t of  step  1986).  effect  the  average  bedload  p r o b a b i l i t y of e r o s i o n  of  Einstein relative  jump  length  equation (p).  is  -182Analytically, noting Using  that  a second  the l i f t  three  expression  empirical  boundaries,  particles  corrections:  lift  due  to  characteristic at of  (2)  shielded  a bed l o a d  for  the  different  flow  by  the  flow  (3)  on  f o r the  expressed  (Das),  small  as  a  Einstein arrives  i s expressed  i n terms  i n t e n s i t y (*») and  i n t e n s i t y (ip*) ( F i g . 6 - 1 ) .  B*W,-i/ e~*" d t = p = A*** J- B * ^ _ i / 1+A*** n o  n  where A*, B* and n  transport  and  transport  f  determined  for  acting  roughnesses  sediment  1 - 1 VK  be  lift  roughness diameter  stream  found  t o h y d r a u l i c a l l y smooth and  f u n c t i o n . The f u n c t i o n  dimensionless  (1)  by l a r g e r p a r t i c l e s  dimensionless  is  must overcome t h e e f f e c t i v e w e i g h t .  v e l o c i t y d i s t r i b u t i o n adjacent rough  for p  o  are s o - c a l l e d  CT  "universal constants"  by flume e x p e r i m e n t s .  rates  is  a  introduces  a  to  The d e t e r m i n a t i o n  long,  but  of  straightforward  calculation. Einstein function is  at  by a s s u m i n g a  height  diameter  of the  material  load  formula  since  continuum.  that  above sediment.  function sediment  suspended  bed  material  the l i m i t  o f bed l o a d  the  equal  bed  Therefore, is  not a t r u e  transport  i s not  load  transport  t o two t i m e s t h e  the  Einstein  bed  bed m a t e r i a l  load  determined  as  a  -1836.2.1.1 L i m i t a t i o n s The this  f o l l o w i n g major  study:  sand-size that The  of E i n s t e i n ' s  l i m i t a t i o n s are  sediment  though Parker  geometry of a g r a v e l  may  that be  tested  o f a sand  erroneous.  only  distributions gravel  (Chein,  diameter  selection  The  lift  (2)  different corrections  densities  i n the  1954) a n d , d e v i a t i o n s  at very  (4)  as  the  o f t h e bed i s b a s e d on sand  size  and may be t o o  sediments.  stream.  4>*-^U r e l a t i o n s h i p has been  for particle  d e n s i t i e s a r e unknown.  characteristic  (1982) i n d i c a t e  bed  bed t h u s E i n s t e i n ' s The  to  f o r non-cohesive  e_t a l ^ .  for gravel  formula  importance  bed may be c o n s i d e r a b l y  (3)  experimentally  r a n g e 1.052 t o 4.22 high  of  (1) t h e f o r m u l a was d e v e l o p e d  i t i s p r o b a b l y adequate  from  (1950) bed l o a d  same  low  Choice  for  of  a a  bimodal  objection  o f Des as t h e bed r o u g h n e s s  D  applies  sand to  and the  descriptor.  6.2.2 Computer s o l u t i o n o f t h e model 6.2.2.1 A p p l i c a t i o n o f t h e f o r m u l a Manual s o l u t i o n o f t h e requiring graphs.  iterative  for a  extremely  Fletcher  tedious empirical  (1968) and Burkham §_t a l . (1977)  programs u s i n g  the graphs.  is  s o l u t i o n s and use o f s e v e r a l  S h u l i t s and H i l l  wrote F o r t r a n  formula  line  segment  (1986) m o d i f i e d  approximations t h e program f o r  microcomputer. For  the purpose  of t h i s  s t u d y t h e p r o g r a m was  rewritten  -184in  TurboPascal to permit rapid  reduce  the time taken  program  was  example  checked  for errors  using  Einstein's  understanding  of sediment  t o the program  respect  limited  The  original  Missouri).  model o f b e h a v i o u r  with  is  and  determination.  particularly  conditions  code  load  Several modifications a better  of  f o r a bed  ( B i g Sand C r e e k ,  provide  modification  to  and  in gravel  bed  transport cannot  were a t t e m p t e d bed  streams,  geometry.  However,  mechanisms under be  used  to  these  t o improve  the  model.  6.2.2.2 N u m e r i c a l v a l u e s f o r h y d r a u l i c Parameters summarised would  to  in  which  Table  be c a l c u l a t e d  values  6-2.  sharp  bends t h e range  beds.  no  single  Therefore, to  diameter  frequency  t h e b a r was velocity used over  provide  used  and  to define the  in gravel  to  single  sediment  the  textures  bar  (site  parameters The  and  width  wetted  range  encountered  Channel  i s so  the range C)  slope  of was  sediment  («6.1  m)  perimeter,  d e p t h were e s t i m a t e d f o r v a r i o u s the d i s c h a r g e .  transport  especially at  characterise  distributions.  are  of t h e s t r e a m a t a  rivers,  channel  geometric  define  assigned  of s e d i m e n t  sample c o u l d a  selected  be  f o r t h e whole w i d t h  However,  wide t h a t  must  Normally,  given station. meander  parameters  of and  s t a g e s and was  i n the s t u d y r e a c h  varied (0.02  to  -185-  T a b l e 6-2. P a r a m e t e r s t o w h i c h n u m e r i c a l v a l u e s must a s s i g n e d ( E i n s t e i n ' s (1950) bed m a t e r i a l function).  be  E q u i l i b r ium Fluid properties Kinematic v i s c o s i t y (1x10 D e n s i t y (1000 kg/m )  s  m /s) 2  3  Flow p r o p e r t i e s D i s c h a r g e (Q) V e l o c i t y (v) Wetted p e r i m e t e r ( P ) Slope ( S ) B  E  Sediment p r o p e r t i e s Specific gravity (S ) Size d i s t r i b u t i o n (f(D)) Percentiles (Das, D optionally pre-defined) Fall velocity ( v from Y a l i n ( 1 9 7 2 ) , p.70) s  & S 5 /  Q  /  Other properties G r a v i t y (9.8 m / s ) 2  "Non-equilibrium" ( i t e r a t i v e solution) Above p a r a m e t e r s Number o f i t e r a t i o n s P e r c e n t s e d i m e n t removed e a c h i t e r a t i o n P e r c e n t i l e s ( D , D B S c o n s t a n t or v a r y i n g 3  9  a s bed m o d i f i e d )  -1860.04).  Clearly,  discharge, the  variation  kept constant  6.3  t o monitor  variable  at site  site  November  Creek.  was  At v e r y a  very  indicate of as  presents  the  of  visibly  or  a histogram  the f i n e s t  for a l l  of  Creek  was  material.  s i z e s caught  low  not  Andrews  discharges  time.  starts  t o move  These  in a small  during  Erosion  i n the subsurface,  a  flood,  the  the c r i t i c a l of  the  an e f f e c t  dislodging  during  observations  g r a v e l pavement p r e v e n t s  may e v e n t u a l l y e x c e e d  C r e e k by a r t i f i c i a l l y  t h e bed o f H a r r i s  of sediment at  discharge  s e d i m e n t a t low d i s c h a r g e s .  increases  pavement members.  stream  Lynn  coarser  a l l sediment  coarse  fine  1987,  that  interval  that very  average  s e d i m e n t move o v e r t h e g r a v e l b e d .  high discharges  discharge  sediment  Therefore,  flood  moving o v e r  i n March  indicating  short  a  during  sand-size  subsurface  stress  1985,  Similarly,  sediment t r a p amounts  parameters.  must be  processes  not  transporting (1982)  d i s t r i b u t i o n of  C were used a s t h e b a s i s  6.3.1 S e d i m e n t m o t i o n d u r i n g  sediment  (slope,  (Table 6-3).  With-in  In  radius  however c e r t a i n c h a r a c t e r i s t i c s  textures  modelling  hydraulic  v e l o c i t y ) implies that the s i z e  bed c h a n g e s ,  sediment  of  erosion However,  bed  shear  shear  s t r e s s of  pavement  exposes  reproduced  i n Lynn  cobble-size  particles.  -187-  Table 6-3. Sediment textures c o m p u t a t i o n s o f bed m a t e r i a l l o a d Sediment Diameter (mm)  128 64 32 16 8 4 2 1 0.5 0.25 0.125 0.0625 0.0312  at  Sand Low Density (% o f total) 0.0 0.0 0.0 0.0 0.0 1.1 1.6 46.8 40.1 6.7 2.4 0.8 0.5  T o t a l (%) 100 .0 Wt. (g) 60070  site  C  used  Sandy g r a v e l  High Density (% o f total)  Low Dens i t y (% o f total)  High Density (% o f total)  0.0 0.0 0.0 0.0 0.0 0.0 3.4 16 . 3 36.1 29 .1 11. 5 1.7 1.8  8.6 23 .0 21.8 14 . 5 8.5 4. 4 7 .1 8.7 2.2 0.8 0.2 0.1 0.1  0.0 0.0 0.0 0.0 0.0 0.3 3. 4 16.3 36.0 29 .0 11.5 1.7 1.8  100.0 1121  100 .0 999300  100.0 1125  in  -188In  the experiment sand-size  the  r e s u l t i n g depression,  distance  and t r a p p e d  Thus, d u r i n g be  define rates  i f the t o t a l  f o r the f i n e r  easily.  larger  particles.  sediment  This  By l o w e r i n g  of magnitude,  are  roughness  i s decreased  raised  model a l s o  shows  transported  in  rates  low.  reality  through  are  case,  are  p a r t i c l e s may  low  to  transport  ( F i g . 6-1)  t h e p a r t i c l e s c a n n o t be  the roughness diameter ( D S B ) rates  for  sand-size  ( F i g . 6-1) i n d i c a t i n g t h a t by e r o s i o n  that  f o r sediment very  finer  although finer  than  bed  than  contacting  0.1 mm  gravel  The is load  are  probably  t h e bed  increases,  0.5 mm  material  f i n e s e d i m e n t would  the i n t e n s i t y of a f l o o d  t h e bed  o f pavement c l a s t s .  sediment  the s e c t i o n without  continually  these  i s permitted  sediment  very  transport  suspension  transport In  short  i s due t o t h e s h i e l d i n g e f f e c t o f t h e  sediment  As  In t h i s  from  stones.  sediment mixture  t h e model a n t i c i p a t e s t h a t  an o r d e r  downstream a  E i n s t e i n ' s model d o e s n o t a g r e e w i t h  eroded  by  between pavement  t h e bed r o u g h n e s s .  because  transported  a f l o o d b o t h sand and g r a v e l  mobilised.  observations  p a r t i c l e s were e n t r a i n e d  very pass  (washload). particles  e r o d e d and w i l l  roll  i n t e r m i t t e n t l y down  the  s t r e a m whereas s a n d - p a r t i c l e s  will  move  and  suspension. Discharges capable  probably  last  for  of d i s l o d g i n g  large  a few d a y s a t H a r r i s  by  saltation  pavement  clasts  Creek d u r i n g t h e  -189-  3H CO  -34  0.01  1  1  0.1  1  1  3  •  10  100  1000  Sediment Diameter (mm)  Fig. 6-1. E f f e c t o f i n c r e a s i n g bed r o u g h n e s s on s e d i m e n t t r a n s p o r t r a t e s f o r sediment of d i f f e r e n t d i a m e t e r s . A l l c u r v e s were c a l c u l a t e d w i t h v=2 m/s, Q=9.32 m=Vs, S = 0 . 0 3 P =6.1 m, S =2.65. Sample C2 (sandy gravel) used to d e f i n e bed c o m p o s i t i o n . C u r v e (1) D e s = 2 mm, D a l mm, (2) E  B  /  B  =  3  Dees=4  mm,  geometry,  D »=l 3 =  mm,  (3) D  & a  =8  i . e . D = 4 0 . 6 mm, 6a  D  mm, 3=s  D3==l  =13.0  mm.  mm  (4) Bed  defined  -190spring  flood.  deposition geochemical that  of  decrease  to  move  poorly-sorted  deposits  observed and  the  at  sequence  the  deposits.  explain  and  i t i s implied same  This  heavy-mineral  cannot  of  textural  Traditionally,  ceases  chaotic,  the  determines  characteristics.  incompatible with  gravel  flows  sediment  a l l sediment  producing is  As water  the  time  concept  sorting  in  genesis  of  pavement.  6.3.2 D e n s i t y s o r t i n g Several density  and f o r m a t i o n o f s u r f a c e  features  sorting  of  concentrations  of g r a v e l sediment  of  gold  and  6-1).  magnetite  For  are  is  positively  distinction  between t h e framework and m a t r i x components o f  very  4-5). Furthermore,  linear  relationships  sorting  o f framework and mean  between m a g n e t i t e size  of  (see s e c t i o n  4.1.2 f o r d e s c r i p t i o n  these  parameters)  and  there  is  there  matrix  are  of  ( F i g . 6-  of e s t i m a t i o n of  a positive  and mean s i z e  clear  c o n c e n t r a t i o n s and  2A,B),  between m a t r i x s o r t i n g  a  example,  (Fig.  deposits (Fig.  there  s i z e and  correlated  the g r a v e l  5-2)  deposits indicate  (Table  and  pavement  correlation  framework ( F i g .  6-3). Einstein  (1968) and B e c h t a and J a c k s o n  flume  studies  into  the  to investigate  spaces  between  (1979) have  t h e movement o f f i n e gravel  clasts.  used  sediment  As t h e c o a r s e r  -191-  12  (A)  • M2  # 9o + O  I CD  c  CO CO  • F2  0  02  OA  0i6  0.8  Log Framework Sorting (mm) 12i  +• o  (B) M2  9-  5  6.-1  C CO CO 2  3-  -0.3  -0.2  -0.1  0.0  ~oi  Log Matrix Mean Diameter (mm)  Fig. 6-2. R e l a t i o n s h i p s between (A) l o g o f framework s o r t i n g and m a g n e t i t e (-40+70-mesh) c o n c e n t r a t i o n ( s a m p l e s M2 and F2 a p p e a r t o be o u t l i e r s f r o m a c u r v i l i n e a r t r e n d ) and (B) l o g o f mean diameter of m a t r i x and magnetite (-40+70-mesh) c o n c e n t r a t i o n ( o m i s s i o n o f o u t l i e r M2 y i e l d s a Pearson linear correlation coefficient (0.511) s i g n i f i c a n t l y d i f f e r e n t from zero with 86% confidence). Data f o r a l l t e n s a n d y g r a v e l sample a r e shown.  -192-  E  S CD •» CD  2.5i  E CO  5c  2.0-  co CD  2 O CD  E  1.5-  co O)  o  B2 1.0. 0.3  0.4  0.5  0.6  Log Matrix Sorting (mm) Fig. 6-3. R e l a t i o n s h i p between l o g o f m a t r i x s o r t i n g and log o f mean framework diameter. The Pearson linear c o r r e l a t i o n c o e f f i c i e n t (0.821) i s s i g n i f i c a n t l y d i f f e r e n t f r o m z e r o w i t h b e t t e r t h a n 99% c o n f i d e n c e . Data fora l l t e n s a n d y g r a v e l samples a r e shown.  -193-  sediment  c e a s e s t o move  through  which  flow  water  discharges,  represent occur.  and f i n e  the  smaller  than  between t h e g r a v e l subsurface. filling  Thus, the  the  voids  voids w i l l  Jackson,  there  average  will  composite  has  a  of c l a s t  fill  move  f r o m t h e base  The s p a c e s w i l l to  the  voids  half-voids  surface  additional  Creek  gravel deposit  location  At H a r r i s  interstices  be  size  only  of the spaces  the voids  i n the  deposit break  (Fig.  formed i n the  4-5).  upwards  (Bechta  until  when  and  will  either  the  be (a)  flow  is  sediment d e p o s i t e d i n eroded  preventing  E v i d e n c e f o r the former  near t h e head  voids contained  a depth of s e v e r a l  different  will  a c c u m u l a t i o n of sand.  was f o u n d a t L y n n  conditions  continue to f i l l  fill  s o r t i n g can  flow v e l o c i t i e s  the  that  clasts  distinctive  1979) a s i t i s h e r e t h a t  i s no s a n d  6-4B).  gravel  sediment  r e d u c e d or (b) f u r t h e r  to  At high  into  sizes  framework  can flow.  these  sufficiently  The  porous  between  under  the  clasts  frequency d i s t r i b u t i o n  lowest.  a  sediment  spaces  I t i s apparent that  The  form  l o c a t i o n s a t w h i c h d e n s i t y and s i z e  sediment  by  i twill  of  a  channel  a few p a r t i c l e s  bar.  of sand  c e n t i m e t r e s ( F i g . 6-4A) whereas a t a  t h e v o i d s were c o m p l e t e l y f i l l e d ( F i g .  Creek  filled  as f l o w v e l o c i t y  i n some c a s e s  with sediment. i s reduced the  even  the  Einsteins same  pavement  model shows  sediment  load  -194-  Fig. 6-4. Examples from a bar on Lynn Creek of (A) subsurface g r a v e l voids incompletely f i l l e d by sand and (B) gravel voids completely filled by sand. Pen is approximately 15 cm l o n g .  -195can  be  transported  T h i s can with  be  achieved  by  the  bed  filling  pavement  filling  concept  of  1971),  a  of  because  the  is  large  decreased.  gravel  voids  then  protrusion  of  is  all  coupled the  sand  size  that  " v e r t i c a l winnowing" o c c u r s .  allows  fine  probability the  sediment to  fall  of r e - e r o s i o n , This  thus  Furthermore, high clast  by  probability as  it  leads  is  a  hiding  rolls  forward,  and  extreme  of  small and  they  claim  Removal o f  large  clasts  the  fine  hole  and  sediment is  erosion  hole  under  feature  t h a t the  will  of  be  leading  reduce  the  burrows  to  contrary  to  that  fine  E i n s t e i n ' s (1950) a r g u m e n t s , t h a t the  high  Parker  mentioned e a r l i e r to  under  (1973)  mechanism  o b s e r v a t i o n a t Lynn C r e e k , clasts  into  unlikely  m o b i l i t y of g r a v e l  Following Milhous  subsurface.  large  with  The  removed  pavement and  (Graf,  i n a flume.  1935).  stages  r e q u i r e d to balance  material.  sediment  subsequently  discharge  lack  traditional  i s deposited  that  large clasts  the  i s i n r e a l i t y very  (Hjulstrom,  (1982) p r o p o s e d at  fine  t h a t ' sand  conditions  observable  i n t e r m s of  demonstrated  process  c o n d i t i o n s and  Klingemann  surface  easily  requires  flow  clasts  of  favoured  it  is explained  s u r f a c e v o i d s r a t h e r than  process  discharge low  formation  winnowing  traditional,  of  roughness  sand.  Thus, of  if  the  removal  sediment. there  is  a  filled  by  to  subsurface  a  another  -196depleted  6.3.3  in fine  sediment d u r i n g  Sand d e p o s i t s a t bar  Deep p o o l s  at  bar  of g r a v e l s d u r i n g  As  levels  water  high  d r o p but  that  failed  distance around  to  the  the  to  flood  peak  (Richards  deep p o o l  Harris  6.3.4  to the  to very pools  but  This  these  on  the  some  local  of  the  i n the  pool  The  sediment  gravels  a  short  m a t e r i a l swept meander bed  in  not  affected  by  and  is  deposits  probably  observed  at  Creek.  D i f f e r e n c e s between h e a v y m i n e r a l s a n d s and s a n d y g r a v e l s  The  concentrations  m a j o r i t y of sand moving downstream  into  contact  pools  settles  near  zero  with out  t o or  contact  with  the  bed  and  under g r a v i t y .  cannot  through bed  occur.  the  will  sand c a u g h t A l l sediment  v e l o c i t y c o n d i t i o n s , thus  density minerals close  remain  become  represents  overbank  1982).  flow v e l o c i t i e s .  p r e s u m a b l y was  s t r e a m bed in  pools  the  outside  preferential  generally  include  in  mostly  sediment  sand  low  may  deposited  g e o m e t r y of t h e  similar  the  be  upstream  suspension. the  these  peak.  due  flow v e l o c i t i e s  of d e p o s i t i o n due  sediment r e a c h i n g  flood  form  enough t o t r a n s p o r t s a n d ,  sites  the  tails  tails  erosion  the  However,  gravel  not  subsurface  come  i n bar  tail  settles  enrichment sand  in  of  that comes  in high  passes into  roughness elements p e r m i t t i n g s o r t i n g  by  -197density.  Because  deposited  from  heavy  sand  minerals  passing  are  through  preferentially  the  gravel,  this  modelled  by an e q u i l i b r i u m model s u c h a s t h a t  However,  n o n - e q u i l i b r i u m process cannot  the  rates prior  ratio  of l i g h t  for  for  the rough  a given grain regime  size  are  bed.  transported  trapped i n the gravel  sediment  Comparison  ratios  of  the  (Fig.  roughness  6-5B).  and water  that  lower  6-5A).  enhancing  heavy  r a t e and  The r e m a i n i n g  low  shows t h a t  extent  than  heavy  ratios  (cf.  indicating  gold  mineral  as  (S.G.=18) i s  magnetite,  i n g e o m e t r i c mean  Furthermore,  transport  6-5B)  apparent  ratio  m i n e r a l s and may be d e p o s i t e d  densities  difference  increases  t o t h e same  6-  deposits.  t o a much g r e a t e r  decreases,  Fig.  i n sand  It i s  bed ( F i g .  pool thereby  concentrations  explains  mineral transport  at a relatively  c o n t a i n s few heavy  i n a bar t a i l  trapped  and compared  be  of E i n s t e i n .  encountered as the sediment  pass through the g r a v e l  are  and h e a v y  strictly  t o r e a c h i n g t h e bed c a n be e s t i m a t e d ( F i g .  5)  minerals  voids of the  which  concentration  sediment  diameter  do n o t change a p p r e c i a b l y a s  c u r v e s 3 and that  GMCRs w i l l  4  for  magnetite,  approach  unity at  small diameters.  6.3.2 Sediment After  sorting  after  a  pavement has d e v e l o p e d  flood fully,  gravel  beds  cannot  -198-  6 -I  0.01  0.1  1 10 Diameter (mm)  100  Diameter (mm) F i g . 6-5. C o m p a r i s o n o f t r a n s p o r t r a t i o s ( l o w d e n s i t y / h i g h density) with g r a i n s i z e , bed r o u g h n e s s and d e n s i t y . A l l c u r v e s computed w i t h v = l m/s, Q=1.83 m /s, P © = 6 . 1 m and D = 1 mm. S i n c e o n l y sand i s i n m o t i o n , sample C I d e f i n e d the transportable sediment. (A) T r a n s p o r t ratios for magnetite (S =5.2). Curve (1) D&==8.0 mm, (2) 4.0 mm (3) 2.0 mm. (B) T r a n s p o r t r a t i o s f o r g o l d (So=18, C u r v e s 1 (De» =8 mm) and 2 (D =4 mm)) and m a g n e t i t e (Curves 3 (D ==8 mm) and 4 (D ==4 mm)). 3  3 S  s  a  s  e=(  s  -199be  modified  sand  further  deposits  water  at  levels  bar  fall  channels  wash  across  channel  lap  onto  magnetite  lag  permit  iterations  of  form  the  enrichment.  most  important  were  needed  concentrations  because  assuming  size  the  that  as  result  as the  develop  observed  at  that  at  some  modelled stream  by  will  not  assumes  that  all  simulates  small  amount  of  transport  removed  slightly  thousands  of  substantial  heavy  occurs,  model  were  the  (D =, e  D  conducted  3  =  ). to  extreme  heavy  mineral  site  would  develop.  D)  sediment  high  the  mineral  parameters  which  initial  was  also  model  (such  heavy  sediment are  sorting texture  visible  model  a  to  can  at  to  it  main  time,  Fletcher  between  conditions  used  the  lead  of  was  Although  bar  the  Malaysian  model  tests  CI  a  over  Several  Sample  in  when  back  comm.)  and  sediment  concentrations  this  minerals,  As  small from  (pers.  minerals  the  the  At  However,  erosion  that  deposition,  re-calculates  investigate  of  exceptional  studied  light  flood.  waves  deposits.  by  heavy  sites  Fletcher  be  major  and  difference  that  than  mineral  sand  e q u i l i b r i u m by  The  means  faster  the  next  extent  model.  to  from  erosion.  rates  the  balanced  departure net  to  processes  Einsteins  is  become  W.K.  winnowing  erosion  tails  the  winnowing  adapting  the  deposits  concentrations. similar  until  mixture.  "channel" high  sites  slopes  heavy  (Fig.  6-6).  The (Se)  mineral These  -200-  10-  Diameter (mm) Fig. 6-6. High d e n s i t y mineral enrichment of sand sample CI due to winnowing. Enrichment f a c t o r is expressed as concentration of high d e n s i t y mineral of a given diameter a f t e r 3000 i t e r a t i o n s (5% e r o s i o n of sediment at each i t e r a t i o n ) d i v i d e d by c o n c e n t r a t i o n before e r o s i o n b e g i n s . A l l curves determined with u=0.5 m/s and Q=0.305 m . Curve (1), S =0.2, S =18; (2), S =0.2, S =5.2; (3) S = 0 . 1 , S =18; (4) Se=0.1, S = 5 . 2 . 3  E  e  a  e  a  s  E  -201slopes  are  s e v e r a l times greater  Harris  Creek showing  generation  local  of h e a v y m i n e r a l  variability deposits  is  introduced  by  concentration enrichment at  that  has  variables  enriched into  control  sands.  gold  Thus,  of the  extreme  analyses  of  sand  processes,  for  example  ratios  sites  heavy  mineral  for  occurred  has  average slope  post-flood  non-enriched  generally  t h a n the  are  sites no  are  control  less as  where  than u n i t y , high  over  as  whereas  1291.  estimation  CRs  The  sampler  of  these  var i a b l e s .  6.4  Between s i t e  6.4.1  Heavy m i n e r a l  The slope  most  Slope  sections  then  model  equilibrium  may  site  upper  reaches,  such be  increases decreases  of d i f f e r i n g  a  between  In the  which s t e a d i l y  B.  using  trends  apparent  ( F i g . 4-1).  0.025, and  processes  slope as  the  section  increasing  slope  Slope sediment  slope  averages  0.042 between s i t e s  t o 0.022.  exist,  i n v e s t i g a t e d by  variables,  decreasing  the  for  Although the  reach  considering may  be  purpose  followed  changes  considered by  a  E  three  E i n s t e i n ' s where d e p a r t u r e s  important of  to  v a r i a b l e i s channel  of from in  as  one  section  of  slope.  affects not  the  coming  g e o m e t r y of t h e into contact  with  bed. the  Therefore, bed  will  not  any be  -202affected  by  small  changes  travelling  downstream  controlled  by slope  s l o w l y decrease  in  in  channel  suspension  be  to the extent that flow v e l o c i t y  will  It  is  pools w i l l  in  only r e f l e c t  slope and w i l l  of sediment  to  Sand  only  as slope d e c r e a s e s .  will  sediment caught i n bar t a i l channel  slope.  the  reach.  Thus,  expected  not r e f l e c t changes  that  changes  i n supply  magnetite,  which  is  s u p p l i e d c o n s t a n t l y to the study reach by the g r a n o d i o r i t e on  the south bank w i l l  deposits  with d i s t a n c e downstream ( F i g .  Conversely, reach  not be d i l u t e d or e n r i c h e d i n sand  in  gold i s probably not s u p p l i e d to the  a p p r e c i a b l e q u a n t i t i e s and w i l l  d i l u t e d with d i s t a n c e downstream as decay of the gold 100 ppb  5-5).  to  anomaly  sub-detection  in  study  be c o n t i n u o u s l y  i n d i c a t e d by the  sand  levels  deposits  steep  from  over  at s i t e s A and C ( F i g .  5-3 ) . The e f f e c t deposits  is  of slope  complicated  sediment subsurface study, bed  it  is  on d e p o s i t i o n of sediment by  how  is affected  the  geometry  of  by slope changes.  the  In t h i s  is assumed that sediment motion through a g r a v e l very  similar  to  E i n s t e i n ' s model i n d i c a t e s  sediment  increase  motion  over  a bed.  that as discharge of the stream  decreases d e n s i t y t r a n s p o r t r a t i o s density)  in gravel  implying  minerals i n the subsurface voids  (low  net  density  deposition  thereby  to of  decreasing  high heavy bed  -203roughness. then  The  decrease  discharge  model  balancing  of d e c r e a s i n g  (Fig.  6-7).  heavy  minerals  of  causes  slope  result  a break  i n slope  mineral  placers  Magnetite section  i s to increase the  of  a  i s a good  concentrations  i n the coarsest  hand,  constant extreme anomaly  slopes ( c f . differing  heavy  mineral  decreasing  slope  i n gravel deposits.  the prospector's  rule  f o r formation  that  of heavy  (Table 1-1). decrease  gold  which  concentrations  into  (to s i t e  fractions  5-5) downstream o f s i t e  other  ratios  locations, a section  of  location  the  transport  ignoring  heavy m i n e r a l s  agrees with  Now,  cannot  as a t h i g h  section  would  decreasing  transport  i n decreasing  due t o i n c r e a s i n g s l o p e  rapidly  stream  Overall,  results  by  equilibrium).  to d i f f e r e n t  whereas  enrichment  latter  of  t o t h e same e x t e n t  of heavy m i n e r a l s  concentrations  Fig.  slope  F i g . 6-7).  increasing  This  the i n c r e a s e caused  At low s l o p e s  A and B,  supply  that transport ratios  (re-establishment  effect  curve  shows  F)  (-35+70,  F as s l o p e  the but  e n r i c h m e n t due t o d e c r e a s i n g  increase  -70+100-mesh,  decreases.  is continually diluted downstream  braided  of  site  slope  On t h e maintains  F  because  i s balanced  by  dilution.  6.5 Summary and c o n c l u s i o n s Although  g r a v e l d e p o s i t s commonly a r e d e s c r i b e d  as v e r y  -204-  -1-1 0.01  i 0.1  ,  r-  1  10  Diameter (mm) Fig. 6-7. E f f e c t of slope on magnetite t r a n s p o r t r a t i o s . C o n d i t i o n s used f o r a l l curves are u=l m/s, Q=1.83m /s D 3=4 mm, D = l mm. Since only sand i s t r a n s p o r t a b l e , CI was used to d e f i n e the bed. (1) S =0.02, (2) S =0.03, (3) S =0.04. 3  /  3 a  S!  E  E  E  -205poorly  sorted  correlated  have  heavy  magnetite fine  and  and  mineral  has  by  assuming  flood  fine  waters.  As  form a porous can  flow. to  entrap  heavy  deposits  because are  enriched  they are  trapped  the  residue  of  of  heavy  they This  mostly  the low  exposed  to  of  wave  r e s u l t s i n winnowing of  very  high  three  orders  channel  slopes  of m a g n i t u d e of  all  in  they  sites  gravel  gravity  minerals.  heavy m i n e r a l  enrichment,  to  represents enrichment sand  enrichment main  minerals.  required  unknown  However,  a c t i o n f r o m the  are  without  An  following  deposits.  light  minerals  suspension  i n these d e p o s i t s  gravels  become s i t e s  are  i n heavy  under  density minerals in  the  preferentially  Thus,  depleted  heavy  sediment  in  minerals.  out  of  time  sediment  clasts  will  6-8).  are  settle  of  and  be  gravel  cease motion  l o c a t i o n s where p a r t i c l e s  minerals  are  (Fig.  enrichment of  may  period  gravel  the  can  become s u s p e n d e d  that  i n heavy  and  proportion  deposits  roughness  minerals  deposits  preferential  sorting in  distinctive  gravel-size clasts  s p a c e between t h e  surface  are  Sand  the  the  to  gold,  observation  for a short  silt  well-  for  framework t h r o u g h w h i c h water  The  similar  and  density  This  that  i s mobile  sand  appearance,  concentrations  occurred.  framework component allowing  chaotic  zircon indicate that  fractions  explained  a  stream.  Generally,  p r o d u c e two thus  if  or  extremely  -206-  Coarse magnetite & fine Au trapped in gravel bed Fine magnetite, very fine Au & sand overpass bed GENTLE GRADIENT  STEEP GRADIENT  No pronounced affect on washload  Heavies transported  c 2  O  *  #  2  «  Heavies trapped  Fig. 6-8. D i a g r a m m a t i c summary o f t h e p r o c e s s e s i n v o l v e d i n d e p o s i t i o n o f s e d i m e n t i n H a r r i s C r e e k . (A) W i t h i n s i t e (at a point b a r ) and (B) between sites (as c h a n n e l gradient decreases).  -207rich  d e p o s i t s may  different  be  from those  produced present  under  i n the  conditions main  channel.  Downstream d i s p e r s i o n of heavy m i n e r a l s function (Fig. south  of b o t h  6-8). bank  supplied  heavy m i n e r a l  Magnetite of  the  stream  and  the  to  be  reach,  braided  but  with  decreasing constant Since  is  but  F.  in  slope the  presumably  is  study  reach.  channel  slope  not  are  magnetite  not  slope decreases  enriched  the  u p s t r e a m end  As  supply  therefore gold concentrations  increases  Because enrichment  resulting  sandy  light  gravels  slope  visible, in  Thus  as  downstream,  reflect  station,  the  magnetite.  concentrations  sediments  sampling  rapidly  site  distance  heavy m i n e r a l s  these any  at  6-8).  toward  become d e p l e t e d  slope Au  (Fig.  a  from  the  shows t h a t as  diminishes  become e n r i c h e d  diluted  gold  u p s t r e a m of  magnetite-enriched  section  gravels  channel  d i f f e r e n c e between t r a n s p o r t r a t e s of  heavy m i n e r a l s  tend  and  whereas  Sediment t r a n s p o r t m o d e l l i n g the  a p p e a r s t o be  is supplied continuously  from a p o i n t source  increases  supply  completely  into  of a  further gold  is  due  to  in  nearly  gravel  deposits.  sand  deposits,  in  of h e a v y m i n e r a l s concentrations remain  constant.  to  decay  -208-  CHAPTER  7:  APPLICATIONS  FOR M I N E R A L  EXPLORATIONISTS  -209-  7.0 I n t r o d u c t i o n This for  study  a sampling  occurrence  understood.  stream  sediment  mode  of  Specifically, severely  of g o l d  s t r a t e g y c a n be f o r m u l a t e d  o f Au i n t h e t a r g e t  the  study t o determine occurrence  of  the sampling  complicated  mode  m i n e r a l i s a t i o n must be  In common w i t h a l l o t h e r g e o c h e m i c a l  orientation  and  of  principles  Mode o f o c c u r r e n c e  Before  an  general guidelines  i n exploration f o r coarse, native gold deposits.  First  7.1.1  of  the f o l l o w i n g  o p t i m i s i n g the chances of success  surveys  7.1  provides  the  size  surveys,  distribution  g o l d s h o u l d be c a r r i e d o u t .  problems encountered  i f Au o c c u r s a s c o a r s e ,  will  be  native gold  particles.  7.1.2  Purpose  The p u r p o s e is,  will  locate  o f t h e s u r v e y must  be c l e a r l y  the s u r v e y d e l i n e a t e broad  a mineral  7.2 R e g i o n a l 7.2.1  of survey d e f i n e d . That  regional  trends  or  occurrence?  surveys  Purpose  Regional  surveys  generally  attempt  to  determine  -210presence  or a b s e n c e  which case,  the  Sampling  Ten by  to  field  mesh. gold  20  sediment  very  kg  is  is  the no  practical  be c o l l e c t e d  the  site  of  of  where  fine  Island),  the  energy sandy d e p o s i t s  within will  regions  gravels.  10-  enrichment  Vancouver  same t y p e  However,  sediment  variability  mask between s i t e  may  be  it  is  i s sampled due  to  gold  trends.  fraction fraction size  sought  to  analysed  in  be  and  the  the  optimised  of  sediment  s u c h as  this  difficulty  depends  distribution  materials  However,  sample  In  that  -270-mesh f r a c t i o n s a l l o w e d in  natural  from  surficial  deposits.  gravels.  f r o m low  i n c l u d i n g the  local  the  (e.g.  in gravels  mineralisation  samples s h o u l d  obtained  sediment  factors  in  otherwise  Sediment  The  gold  evaluated.  sediment  scarce  important  7.2.3  to contain  In  g r a v e l l y sediments to approximately  derived  consistently  of  bulk  than that  enrichment  must be  fails  basin.  media  occurs  information  large drainage  a sample  medium o p t i m i s e s  that  better  area  screening  This  in a  chance t h a t  in a mineralised  7.2.2  of g o l d  number  in  the  distribution  and  lacustrine  -200+270-mesh  of  gold  for several  in laboratory  several  gold  size  till  s t u d y the  on  and  particles  streams.  There  s i e v i n g of  -200-  -211mesh s e d i m e n t  from bulk  7.3  surveys  Follow-up  7.3.1  Sample  Very train be  large  samples  may  do  Sample  such  that  size  can  Screened  only  The random  be  samples  collected  reliability.  anomaly  dispersion  due  needed  t o the  dilution  must nugget  trends.  determined  f r o m sand  anomaly  decay,  dispersion  train  by  an  appear  to  in  Consequently,  s t u d y the  very rapidly.  anomaly  Furthermore  r e d u c i n g anomaly c o n t r a s t collected  concentrations  from  gravel not  in  the  p r o b a b l y be more o b v i o u s  than  a  sharp  i t i s recommended  but  and  did  however  c u r v e would  deposits  in this  Samples  m a i n t a i n e d h i g h Au  sands.  errors  though  c o n c e n t r a t i o n s were low,  show  a  o f sample  adequately  to sub-detection l e v e l s  deposits  size  if  media  show Au anomaly d i l u t i o n ,  analytical  samples.  survey.  Sampling  decayed  required  n o t mask between s i t e  orientation  Au  be  i s t o be d e l i n e a t e d .  effect  sediment  size  selected  7.3.2  field-screened  break  that  gravels  be  sampled.  7.4  Sample  preparation  Samples must  be  pre-concetrated,  for  example  using  -212methylene  i o d i d e so  reducing  the  other  nugget  minerals  Grinding  of s a m p l e s  between-sample  and  sediment  7.5  effect.  further  and  data  that a very  is  Removal  magnetite  enhances  i s not  of  Au  may  smearing  result.  weights should  be  analysed, and  concentrations.  recommended as  contamination  fraction  l a r g e sample  of  Field  gold  sample  recorded  to a i d i n  analysis  currently  interpretation.  Chemical  analysis  Instrumental allows  Au  to  concentrate  neutron be  activation  determined  in  permitting further  a  60  reduction  g  heavy of  mineral  the  nugget  e f fect.  7.6  Data a n a l y s i s  7.6.1  Nugget  Using  effects  the  weight  concentration, can  be  of  random  the  estimated. errors  w h e t h e r or n o t of  follow-up  7.6.2  number  a  sample  of g o l d  due  to  the  and  particles  This c a l c u l a t i o n  ranking  provides  nugget  of g o l d a n o m a l i e s  its  i n the an  sample  indication  effect for  gold  and  the  shows  purpose  is significant.  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Methods f o r r e c o v e r i n g fine placer gold. Can. I n s t . M i n . M e t a l . B u l l . 76:47-56. Yalin, M.S. 1972. Mechanics Pergamon P r e s s , 290 p a g e s .  of  sediment  transport.  Z a n t o p , H. and N e s p e r e i r a , J . 1979. H e a v y - m i n e r a l p a n n i n g techniques i n the exploration f o r t i n and t u n g s t e n i n northwestern Spain. Trans. 7 t h I n t . Geochem. Explor. Symp. G e o c h e m i c a l E x p l o r a t i o n 1978. pp 329-336. Zar, Inc.  J.H. 1984. 718 p a g e s .  Biostatistical  analysis.  Prentice-Hall  -223-  APPENDIX: CHEMICAL AND  SEDIMENTOLOGICAL  DATA  -224-  ORIENTATION SAMPLING WEIGHT OF SEDIMENT FRACTIONS SAMPLE NUMBER 85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD-  -4 + 16 01 02 03 04 05 06 07 08 10 11 12 13 14 15  13080 16200 15670 14400 15000 12800 9850 11910 3510 12400 14800 14400 11500 13200  -16 +50  —  (GRAMS) (CHAPTER 2)  FRACTION (ASTM MESH) -50 +70  -70 -100 +100 +140  6660 374 .0 183 .0 105 .0 2380 106 . 0 48 .3 25 .6 2140 106 .0 56 .8 35 . 3 5460 316 .0 110 .0 61 .0 3 46 0 154 .0 59 . 7 30 . 3 4760 336 . 0 145 .0 86 .4 10200 644 . 0 283 . 0 152 . 0 4100 137 .0 51 . 6 27 .3 15700 2060 .0 1080 . 0 641 . 0 13900 1000 .0 441 . 0 225 .0 10100 995 .0 550 .0 330 . 0 9090 948 . 0 479 .0. 289 .0 8310 658 . 0 327 . 0 189 .0 14000 2820 . 0 639 .0 332 .0  -140 +200  _ -200 -270 +270  55 .3 49 .0 154 .0 10 .9 42 .4 42 . 4 19 .9 19 .7 73 .0 24 .7 19 .4 44 .9 12 .7 9 . 5 22 .0 34 . 8 29 .7 82 .5 65 .3 39 . 2 172 .0 13 .8 10 . 6 49 .7 209 .0 144 .0 292 .0 75 .1 46 . 8 96 .9 122 .0 124 .0 585 .0 111 . 0 112 . 0 308 .0 86 .9 81 . 4 238 .0 193 .0 67 .8 53 .2  WEIGHT OF HEAVY MINERAL CONCENTRATES (CHAPTER 2) SAMPLE NUMBER 85-SD-01 85-SD-02 85-SD-03 85-SD-04 85-SD-05 85-SD-06 85-SD-07 85-SD-08 85-SD-10 85-SD-ll 85-SD-12 85-SD-13 85-SD-14 85-SD-15  FRACTION (ASTM MESH) ——— -50 -70 -100 -140 +70 +100 +140 +200 17 . 50 3. 02 6 .78 21. 90 13 . 20 5. 78 21. 40 4 . 38 204 . 00 117. 00 122 . 00 12. 70 7 .74 2 . 15  10 . 90 1. 54 3 .70 8. 94 5. 78 2. 83 8 .99 1. 44 252 . 00 77 . 20 115. 00 9 .22 5. 53 2 . 44  6 .03 0 . 77 2 .04 4 .08 2 .68 1 . 31 4 .99 0 .65 219 .00 41 .40 60 . 30 5 .25 3 .06 2 . 73  2. 330 0 .269 0 .797 1. 100 0 .817 0 .528 2 . 350 0. 202 67 . 300 10. 100 12 . 100 2. 220 1. 150 1. 190  -200 +270 1. 810 0 .146 0 .635 0 .449 0. 323 0 . 393 0 .532 0 .086 33 . 200 3. 090 5. 410 1. 600 0 .696 0. 209  -225-  GOLD IN HEAVY MINERAL CONCENTRATES (PPB). REPORTED DETECTION LIMIT IS 5 PPB OR GREATER DEPENDING ON THE SAMPLE (CHAPTER 2) FRACTION (ASTM MESH) — -70 -100 -140 +100 +140 +200  -200 +270  85-SD-01 3200 4000 6200 53 85-SD-02 5 35 5300 23000 85-SD-03 6 11 13 6000 85-SD-04 16 31 3400 27 85-SD-05 3400 3700 35 480 85-SD-06 350 190 8400 19000 85-SD-07 870 4100 12000 6900 85-SD-08 280 540 520 22000 85-SD-10 18/910 960/2300 380/1400 3700/2800 8 5 - S D - l l 1500/12 2100/850 720 1200 85-SD-12 940/520 190/990 3000 7400 85-SD-13 160 3000 13000 940 85-SD-14 5 200 5 2900 85-SD-15 5 250 1000 23  6000 150 21 3300 2800 2300 10000 500 3100 1600 3600 7800 6000 130  SAMPLE NUMBER  -50 +70  -226-  GOLD IN LIGHT MINERAL SEPARATES (PPB) DETECTION LIMIT IS 5 PPB (CHAPTER 2 ) . SAMPLE NUMBER 85-SD-Ol 85-SD-02 85-SD-03 85-SD-04 85-SD-05 85-SD-06 85-SD-07 85-SD-08 85-SD-10 85-SD-ll 85-SD-12 85-SD-13 85-SD-14 85-SD-15  REPORTED  FRACTION (ASTM MESH) -50 + 70  -70 + 100  5/5 5 5/5 5/5 5/5 5 5 39 5/9 5 5/5 5 10 5  5/5 5 5 8 5/5 11/16 5/18 5 5 5 5 5 5 5  -100 + 140 5 15 5/5 10 5 8 ,„ 14/21 5 5 5 5/5 30 8 140  -140 + 200  -200 + 270  •270  5 5 20 18 5 5 5 26 11 13 5/5 5 5/5 5  5 7 19 5 5 5 31 20 210 5 1100 5/5 5 5  5 34 5 15 5 34 110 59 320 89 5 27 50 21  -227-  AU (PPB) AND HF(PPM) RE-ANALYSES OF SELECTED SAMPLES BY INAA. ALL +270 FRACTIONS ARE HEAVY MINERAL CONCENTRATES. SAMPLE  85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD-  FRACTION (ASTM MESH) 02 04 05 07 08 08 11 10 14 15  -200+270 -200+270 -50+70 -70+100 -100+140 -140+200 -270 -270 -270 -50+70  AU 1ST  HF 2ND  150 180 3300 3000 3400 3900 4100 3200 520 520 22000 20000 89 80 320 380 50 57 12 25  1ST  2ND  45 210 3 1 4 6 17 43 4 10  42 200 2 1 4 5 19 55 4 8  -228-  AU (PPB) RE-ANALYSIS OF SELECTED FRACTIONS BY FIRE ASSAY/ATOMIC ABSORPTION (FA/AA) SAMPLE NUMBER 85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD85 -SD-  08 13 14 01 10 02 14 14 03 04 08 05 06 07 01 13 02 14 05 11 14 03 06 07 05 07 10 12 12 01 06 02  FRACTION (H=HMC) (L=NMS)  AU FA/AA  INAA  -50+70H -50+70H -50+70H -50+70H -70+100H -70+100H -70+100L -70+100H -70+100H -70+100H -70+100H -70+100H -70+100H -100+140H -100+140H -100+140H -140+200H -140+200H -140+200H -140+200H -140+200H -140+200H -140+200H -200+270H -200+270L -200+270L -200+270H -200+270L -200+270H -200+270H -270 -270  260 175 140 4720 50 380 40 205 350 65 20 4225 300 13320 6725 14395 20000 4650 740 1885 10 6500 22550 5580 5 35 3335 1000 3935 5950 30 40  280 160 140 3200 6 35 6 200 11 31 250 3700 190 12000 6200 13000 23000 2900 380 1200 6 6000 19000 10000 9 31 3100 1100 3600 6000 34 34  -229-  HARRIS CREEK HARRIS CREEK FIELD SIEVED FRACTION WEIGHTS (GRAMS) FRACTION (MM) SAMPLE NUMBER  +128  86 -SD -Ml 0 86 -SD--M2 0 86 -SD - A l 0 86 -SD--A2 0 86 -SD - C l 0 86 -SD--C2 0 86 -SD -KI 0 86 -SD--K2 0 86 -SD - D l 0 86 -SD -D2 0 86 -SD - B l 0 86 -SD -B2 0 86 -SD - F l 0 86 -SD -F2 81600 ,8 6-SD - E l 7300 86 -SD -E2 46200 86 -SD - G l 0 86 -SD -G2 0 86 -SD - J l 0 86 -SD -J2 112400  -128 +64  -64 +32  -32 +16  -16 +8  -8 +4  -4 +2  0 0 0 0 0 0 4200 20400 22200 18400 0 0 0 0 0 0 22200 39000 51000 39200 2000 6800 4200 2100 900 27500 73800 69800 50400 27200 0 0 0 800 1000 7400 29600 32000 31000 32800 1000 725 4625 6000 6900 35000 41500 40000 30500 15500 0 0 0 0 0 4600 3600 13800 29000 27200 4400 1100 1200 1100 2700 88500 105600 94200 67200 42600 5100 400 350 600 750 77000 6000 12800 10800 9200 0 0 500 500 1650 5800 36000 38000 29000 9000 0 1000 575 700 300 76000 58600 33800 25400 15000  0 14800 0 20000 650 14200 950 35800 6600 7000 500 19200 6400 20400 1600 7400 3175 18200 850 10800  -230-  HARRIS CREEK LAB SIEVED FRACTION WEIGHTS (GRAMS) SAMPLE NUMBER 86 -SD--Ml 86 -SD -M2 86 -SD-- A l 86 -SD -A2 86 -SD - C l 86 -SD -C2 86 -SD -KI 86 -SD -K2 86 -SD - D l 86 -SD -D2 86 -SD - B l 86 -SD -B2 86 -SD - F l 86 -SD -F2 86 -SD - E l 86 -SD -E2 86 -SD - G l 86 -SD -G2 86 -SD - J l 86 -SD -J2  FRACTION (ASTM MESH) -10 +16  -16 +40  2350 13900 228 12800 960 22600 1350 21300 7540 10600 1800 10000 11800 13000 4590 8160 6440 25100 1630 18600  46900 47200 5790 29400 28100 27800 16200 27400 29700 21400 24800 39100 20600 14300 27000 30800 29400 26500 15900 25000  -40 -70 -100 -140 -200 -270 +70 +100 +140 +200 +270 15500 3830 41500 19600 24100 8700 35300 14600 23100 14000 25000 11600 19400 9850 25400 9220 20200 9680 26200 13600  1990 835 8540 2980 4010 1520 3540 2260 3800 4610 5100 919 5310 1940 4980 3230 2360 1060 6370 2419  1510 393 256 127 3160 493 1410 395 1165 262 352 213 3620 2600 1050 267 1310 288 642 194 2400 772 519 159 2520 493 789 172 2760 406 1390 216 250 174 234 141 3620 1570 406 292  439 135 120 140 86 66 275 87 127 100 157 83 200 80 158 99 75 63 362 130  811 259 1110 628 547 339 1790 322 872 799 1200 495 1380 830 1630 983 358 241 1260 558  -231-  HARRIS CREEK NONMAGENTIC HEAVY MINERAL CONCENTRATE (NMHMC) WEIGHTS (GRAMS), AU CONCENTRATIONS (PPB) AND HF - CONCENTRATIONS (PPM). AU CONCENTRATIONS IN -270 MESH ARE GIVEN IN NON-MAGNETIC SEDIMENT (NMS). REPORTED AU DETECTION LIMIT IS 5 PPB. REPORTED HF DETECTION LIMIT IS 1 PPM. SAMPLE NUMBER  —  FRACTION (ASTM MESH) NMHMC WT  - 140 + 200 86 -SD- -Ml 86 -SD -M2 86 -SD - A l 86 -SD -A2 86 -SD -CI 86 -SD ~C2 86 -SD- -KI 86 -SD -K2 86 -SD -DI 86 -SD -D2 86 -SD -BI 86 -SD -B2 86 -SD - F I 86 -SD -F2 86 -SD - E l 86 -SD -E2 86 -SD - G l 86 -SD -G2 86 -SD - J l 86 -SD -J2  - 200 + 270  NMHMC AU NMS AU NMHMC HF NMS HF -140 + 200  -200 + 270  270 -140 -200 B + 200 + 270  A  23 .20 16 . 30 300 560 5 5 950 800 11 .73 7 .93 3300 8900 140 62 1300 1100 22 .10 5 .49 5 5 25 5 390 300 20 .40 3 .99 19000 26000 20 11 1000 880 11 .50 2 . 29 5 28 5 5 390 910 12 .72 2 .27 1500 590 5 13 540 780 37 .50 17 . 20 170 350 5 11 500 470 28 .90 3 .22 7500 350 30 51 1200 1000 22 . 20 5 . 53 7200 13000 32 42 940 830 16 . 00 7 . 17 5600 7000 31 60 620 570 52 .63 3 . 43 90 3500 13 9 400 1400 7 .28 1 .63 2600 2100 5 94 760 1200 19 .60 7 . 49 1000 4700 5 5 420 320 4 . 43 1 .14 1100 980 5 5 370 940 19 . 80 5 .19 400 3400 16 15 440 400 14 . 30 2 .34 5700 850 24 5 880 1000 7 .60 2 .89 2400 9200 55 5 770 740 5 .24 1 .06 5000 1300 5 0 1200 2300 60 .80 15 . 60 1025 3400 14 11 850 1100 17 .10 3 .99 9900 6600 41 47 1200 890  18 26 40 25 24 14 21 23 23 24 22 18 19 14 16 11 21 25 36 27  A  270 B 17 25 20 22 22 22 18 16 14 19 19 32 31 13 16 17 20 31 28  -232-  MAGNETIC MINERAL CONCENTRATIONS HARRIS CREEK SEDIMENT SAMPLE NUMBER 86-SD-Ml 86-SD-M2 86-SD-A1 86-SD-A2 86-SD-Cl 86-SD-C2 86-SD-K1 86-SD-K2 86-SD-D1 86-SD-D2 86-SD-B1 86-SD-B2 86-SD-F1 86-SD-F2 86-SD-E1 86-SD-E2 86-SD-G1 86-SD-G2 86-SD-Jl 86-SD-J2  (%) IN  -40 +70  FRACTION (ASTM MESH) — -70 -100 -140 -200 -270 +100 +140 +200 +270  0.6 9. 4 0.4 3.7 0.5 2. 5 0.8 4. 6 1.4 3. 3 0.5 1.8 0.6 0.8 0.7 2.1 0.9 2. 3 2.0 6.7  2.4 23.2 1.2 13.0 2.0 6. 8 1.3 12 . 5 6.9 6. 2 1.6 9.9 1.6 1.8 2.0 7.6 4. 3 8. 0 5.8 13 . 2  4.5 17.4 1.7 11.3 2.8 6.2 2.2 14 . 5 9.2 5.6 2.4 9.9 1.5 1.4 3.0 7.4 6.6 8. 8 8.7 15.0  5.8 14.1 2.4 5.6 3.2 4. 4 1.9 15 . 4 8.2 4. 3 2.6 5.3 2.7 2.2 3.6 7. 0 5.3 6 .1 5.4 7. 6  2.7 7.7 2.6 3.4 3.1 3.3 3.9 5.2 4. 8 3. 3 1.4 2.8 2.0 1.6 2.2 3. 4 4.2 3. 7 5.3 4. 8  GOLD (PPB) IN HARRIS CREEK MAGNETITE FRACTIONS SAMPLE NUMBER  FRACTION (ASTM MESH)  86-SD-Jl 86-SD-Jl 86-SD-Jl  -140+200 -200+270 -270  AU 5/23 5 5  0.8 1.9 1.4 1.2 1.3 1.6 0.7 0.8 1.0 2.2 0.7 0.6 0.8 0.6 0.3 0.6 1.8 2.0 4.0 3.9  -233-  GOLD (PPB) IN WET-SIEVED OF 85-SD-10 -270 MESH. FRACTION (U) -53+44 -44 + 30 -30+20 -20+10 -10  SUB-FRACTIONS  WEIGHT (G) 39 .6 12 .6 9.2 10.1 15.1  AU 630 100 57 42 57  

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