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Gold distrubution in glacial sediments and soils at Spyder Lake, Hope Bay greenstone belt, NWT and the… Laurus, Kathryn Anne 1995

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GOLD DISTRIBUTION IN GLACIAL SEDIMENTS AND SOILS AT SPYDER LAKE, HOPE BAY GREENSTONE BELT, NWT; AND THE EFFECTS OF A PERMAFROST ENVIRONMENT by Kathryn Anne Laurus B.Sc. Hon. Carleton University, 1991 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1995 © Kathryn Anne Laurus In presenting this thesis in partial fulfilment of the requirements f o r an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available f o r reference and study. I further agree that permission for extensive copying of this thesis f o r scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia Vancouver, Canada DE-6 (2/88) 11 ABSTRACT There is a high potential for economic gold deposits in the Slave Structural Province, NWT. Gold exploration, however, is hampered by a complex cover of Quaternary sediments and limited bedrock outcrops. Furthermore, there is a lack of information on the glacial dispersion of gold and the effects, if any, of postglacial redistribution of gold under prevailing periglacial conditions. Therefore, the partitioning of gold among size and density fractions was determined for the various surficial materials in the vicinity of, and down-ice from, known gold mineralization in the southeastern portion of the Hope Bay Greenstone Belt, 650 km northeast of Yellowknife, NWT. Terrain mapping by Ryder (1992) identified several types of surficial materials consisting of weathered rock, till, marine sediments and mixtures of the different types. Soil and humus samples were collected from thirty-seven pits along five lines on the Wally Grid. The lowermost horizons from each pit, and A and B horizons from selected soil pits, were wet sieved into four size fractions between 2000 um and 212 um; the resulting -212 um fraction was analyzed for gold by fire assay-atomic absorption spectroscopy (FA-AAS). Samples from one grid line were further sieved to obtain the -53 um fraction which was analyzed for gold by FA-AAS. LFH horizons and bog samples were milled to -1000 um and organic-rich soils (Ah and O lenses) were dry sieved to -70 um, and were analyzed for gold by neutron activation analysis. Regional till samples down-ice from known mineralization were wet sieved into six size fractions. The -53 um fraction and light and heavy mineral separates of the -212+106 um and -106+53 um fractions were analyzed for gold by FA-AAS. The -53 um fraction was analyzed for gold by aqua regia column-inductively coupled plasma spectrometry (AR column-ICP). Two distinct types of geochemical anomalies were identified in the study area: (i) an older gold anomaly in regional till, and (ii) a younger gold anomaly in locally-derived materials. Gold results of heavy mineral concentrates (HMC) of the -106+53 um fraction and the silt-clay (-53 um) fraction of regional till identified an anomalous gold zone that is detected for at least 2 km down-ice. Although the contrast and gold concentrations in the silt-clay are lower, the -53 um fraction of regional till contains over 60% of the gold with most of the balance residing in the -106+53 um HMC fraction. iii For the younger anomaly, gold concentrations in soil profiles decrease from the upper A and B horizons to lower C horizons. Exceptions occur, however, for horizons directly overlying mineralized bedrock; in these cases, gold values increase with depth. In cross section, anomalous gold zones have a 'mushroom-shaped' vertical distribution pattern in which the anomalous zone defined by the near-surface horizons is 10 to 50 m broader than the anomaly in the underlying horizons. Gold values from weathered rock are typically 10x to 100x greater than from other surficial materials as they contain a high proportion of weathered, local bedrock fragments. Results show there is no systematic variation of gold values across the surface of individual frost boils developed in these weathered rock materials. For reconnaissance scale exploration, a 500 g sample of -2 mm field material should be collected from the central portion of regional till frost boils. A 50 g subsample of the -53 um fraction should be analyzed for gold by a reliable analytical method having a low detection limit for gold. Considering the width and length of the gold dispersal train, a rectangular sampling grid should be utilized whereby grid lines oriented perpendicular to ice flow direction are spaced 500 m apart and samples collected every 40 m. As a complement to gold results from the -53 um fraction, a large, 2 to 5 kg field sample could be used to analyze the -106+53 um HMC fraction for gold. Costs would increase but would be worthwhile to provide an extra degree of assurance in identifying gold anomalies. For property scale exploration, a representative 30 g subsample of the -53 urn fraction could be analyzed by FA-AAS. However, although the -53 um fraction contains over 75% of the gold for the local materials, sample representativity is only slightly reduced if a 30 g subsample of the -212 um fraction is analyzed for gold. In most cases, a 500 g field sample of -2 mm material should initially be collected at 10 to 20 m spacings along grid lines 100 m apart. Infill sampling lines should be spaced at 50 m. It appears that marine sediments blanket geochemical anomalies but additional research is needed to address this problem, and to suggest a possible geochemical method that could be used in these areas. IV TABLE OF CONTENTS ABSTRACT » TABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES viii LIST OF PLATES x ACKNOWLEDGEMENTS xi Chapter One - INTRODUCTION 1 1.1 Research objectives and approach 2 1.2 Permafrost and the periglacial environment 3 1.3 Geochemical dispersion of gold 8 1.3.1 Introduction 8 1.3.2 Geochemical dispersion by glacial processes 8 1.3.3 Modifications within secondary environments 10 1.4 Problems associated with geochemical sampling of rare grains 13 1.5 Conclusion 18 Chapter Two - DESCRIPTION OF STUDY AREA 19 2.1 Introduction 20 2.2 Location and access 20 2.3 Regional geology '. 20 2.6 Physiography, climate and vegetation 28 2.8.2 Distribution and thickness of surficial materials 33 2.8.3 Patterned ground ...36 Chapter Three - SAMPLING AND ANALYTICAL METHODS 58 3.1 Site selection 59 3.2 Sample collection 62 3.2.1 Soil pits 62 3.2.2 Regional till frost boils ,•• 65 3.2.3 Water samples 65 3.3 Laboratory preparation methods 67 3.3.1 Soil pits 67 3.3.1.1 Minus 212 um fraction of C horizons 68 3.3.1.2 Minus 212 um fraction of A, B and C horizons 70 3.3.1.3 Minus 53 Lim fraction of A, B and C horizons 70 3.3.1.4 Vegetation and organic horizons 71 3.3.1.5 Minus 53 um fraction of local stony frost boils 74 3.3.2 Regional till frost boils 74 3.3.2.1 Size and density fractions for gold analysis 74 3.3.2.2 Size and density fractions for particulate gold grain study 77 3.3.2.2.1 Particulate gold grain recovery 78 3.3.3 Water samples 79 3.4 Analytical Methods 79 3.4.1 Analysis of soils 79 3.4.1.1 Fire assay-atomic adsorption spectroscopy (FA-AAS) 79 3.4.1.2 Aqua regia column-inductively coupled plasma spectrometry (AR column-ICP) 80 V 3.4.1.3 Neutron activation analysis (NAA) 80 3.4.2 Analysis of waters 81 3.4.2.1 Graphite furnace atomic adsorption spectrometry (GFAAS) 81 3.4.2.2 Chloride and sulphate 81 3.5 Analytical accuracy and precision 82 3.5.1 Monitoring of analytical accu racy 82 3.5.1.1 Recovery of gold by AR column-ICP 85 3.5.2 Monitoring of analytical precision 87 Chapter Four - RESULTS 92 4.1 Introduction 93 4.2 Soil texture and heavy mineral content 93 4.3 Gold distribution in mineral soils 96 4.3.1 1991 and 1992 Wally Grid data 96 4.3.2 Lowermost B and C soil horizons: -212 um fraction 110 4.3.3 A, B and C soil horizons: -212 um fraction 116 4.3.4 A, B and C soil horizons: -53 um fraction 120 4.3.5 Surface horizons of local stony frost boils: -53 Lim fraction 125 4.3.6 Regional till frost boils 130 Chapter Five - DISCUSSION 155 5.1 Introduction 156 5.2 Mode of occurrence of gold 156 5.2.1 Summary of the mode of occurrence of gold ..167 5.3 Origin of gold anomalies • 167 5.3.1 The older gold anomaly in regional till 168 5.3.2 The younger gold anomaly in locally-derived materials 179 5.4 Recommendations for mineral exploration 183 5.4.1 Sample representativity 183 5.4.2 Reconnaissance scale 184 5.4.2.1 Summary of recommendations for reconnaissance scale sampling 189 5.4.3 Property scale 190 5.4.3.1 Summary of recommendations for property scale exploration 195 Chapter Six - CONCLUSIONS AND RECOMMENDATIONS 197 REFERENCES 201 APPENDIX : 206 VI LIST OF TABLES Table 2.1. Soil description of a pit through a local stony frost boil 46 Table 2.2. Soil description of a pit through a regional till frost boil 49 Table 2.3. Soil description of a pit through a mixed till frost boil 51 Table 2.4. Soil description of a pit through an earth hummock 54 Table 3.1. Sample distribution in various media from the Boston 1 claim and areas around Spyder Lake 62 Table 3.2. Soil pit distribution in relation to gold concentration (ppb) and surficial materials 63 Table 3.3. Gold concentration (ppb) of reference standards analyzed with original soil samples, measured by FA-AAS 82 Table 3.4. Gold concentration (ppb) of reference standards analyzed with original soil samples, measured by AR column-ICP : 83 Table 3.5. Population statistics and hypothesis test results of gold concentrations in the -53 um fraction of regional till frost boils by FA-AAS and AR column-ICP 87 Table 4.1. Average weight percent (%) distribution of the -2000 um size fractions of Ah, B and C horizons from the different surficial materials and soil pits 94 Table 4.2. Average weight percent (%) distribution of light mineral fractions (LMF) and heavy mineral concentrates (HMC) from the -212+106 um and -106+53 um size fractions of regional till frost boils and one local C horizon 97 Table 4.3. Statistics and hypothesis test results of gold concentrations of an internal standard analyzed with the 1991 and 1992 soil grid samples, by AR-AA 100 Table 4.4. Probability plot populations with associated means, threshold (± 2 standard deviations) and population percentage for the combined and subdivided 1991 and 1992 Wally Grid soil gold data (ppb) 101 Table 4.5. Distribution of gold concentration (ppb) in the -70 um fraction of B horizon grid samples, in relation to surficial material type (Ryder, 1992) 103 Table 4.6. Gold concentration (ppb) of the -212 um size fractions of the lowermost B and C soil pit horizons, measured by FA-AAS 112 Table 4.7. Gold distribution (ppb) of the -212 um size fractions of the lowermost B and C soil pit horizons, in relation to surficial material type (Ryder, 1992) 114 Table 4.8. Comparison of gold concentration (ppb) of the -212 um fraction of B and C horizons from local stony frost boil soil pits, and associated soil horizon colour (Munsell, 1971) 121 Table 4.9. Gold concentration (ppb) of the -212 um and -53 um size fractions of the Ah, B and C horizons from mixed till and local stony frost boil soil pits, along Line 124+00 N , measured by FA-AAS 122 Table 4.10. Population statistics and hypothesis test results of gold concentrations of the -212 um and -53 um size fractions of Ah, B and C horizons 126 Table 4.11. Gold concentration (ppb) of the -53 um fraction of surface B horizons from local stony frost boils, measured by FA-AAS, and associated soil horizon colour 127 Table 4.12. Analysis of variance (ANOVA) results for gold concentrations of-53 um fraction of surface B horizons of local stony frost boils 129 Table 4.13. Gold concentration (ppb) of the -212+106 um and -106+53 urn density fractions of regional till frost boils and one local C horizon, measured by FA-AAS, and -53 um fraction measured by FA-AAS and AR column-ICP 131 Table 4.14. Gold concentrations (ppb) of the milled, -1000 um fraction of LFH horizons, measured by NAA, with associated gold concentrations (ppb) of the -212 um fraction of Ah horizons, measured by FA-AAS, ash amount (LOI) and ash colour 137 Table 4.15. Gold concentrations (ppb) of the milled -1000 um fraction of surface bog (O) horizons, measured by NAA 138 Vll Table 4.16. Morphology classification of particulate gold grains recovered from the -106+53 um HMC fraction of a regional till sample and from the -212+106 um and -106+53 um HMC fractions of a local C horizon 143 Table 4.17. Electron microprobe results of gold and silver analyses (wt.%) of sectioned gold grains selected from the -106+53 um HMC of a regional till sample and from the -212+106 um and -106+53 urn HMCs of a local C horizon 154 Table 5.1. Proportion (%) of gold in the -212 um size fractions of horizons from mixed till and local stony frost boil pits along LI24+00 N 158 Table 5.2. Estimated number of gold particles in the -212+53 um and -53 um fractions of horizons from soil pits along L124+00 N 160 Table 5.3. Proportion (%) of gold in the size and density fractions of regional till frost boils and one C horizon from an anomalous soil pit 163 Table 5.4. Estimated number of gold particles in the size and density fractions of regional till frost boils and one C horizon from an anomalous soil pit 165 Table 5.5. Multi-element geochemistry of the 1991 and 1992 Wally Grid samples and concentration ranges for elements related to local volcanic bedrock and secondary-mineralization : 171 Table 5.6. Hypothetical model illustrating how the gold values of HMCs from one till are reduced by the progressive dilution by barren HMCs of a second till containing far-travelled mateial 175 Table 5.7. Subsample weight (g) required to obtain 1 and 20 particles of gold in the size and density fractions of the regional till frost boils and one C horizon sample 186 Table 5.8. Field sample weight (g) of -2000 um material required to obtain 1 and 20 particles of gold in the size and density fractions of regional till frost boils and one C horizon sample ...187 Table 5.9. Subsample weight (g) required to obtain 1 and 20 particles of gold in the -212+53 um and -53 um fractions of pit horizons along L124+00N 192 Table 5.10. Field sample weight (g) of -2000 um material to obtain 1 and 20 particles of gold in the -212+53 um and -53 um fractions of pit horizons along L124+00N 193 Table 5.11. Estimated number of 50 um gold particles in a 30 g subsample of the the -212 um fraction of pit horizons along L124+00N, with the associated subsample weight and field sample weight required to obtain 1 and 20 gold particles 196 VIU LIST OF FIGURES Figure 1.1. Diagram illustrating the characteristic distribution of permafrost at three localities in the Northwest Territories 4 Figure 1.2. Diagram showing range of temperature (summer maxima and winter maxima) as a function of depth, and the resulting mean annual ground temperature of the ground 5 Figure 1.3. Schematic representation of permafrost configuration beneath water bodies 7 Figure 1.4. Poisson probability that an original 500 g sample with a gold concentration of 350 ppb, will have a 30 g subsample containing 0, 1, 2 and 3 gold particles, assuming the gold is present as spheres 200 urn in diameter and have a density of 19.3 g/cm . 15 Figure 1.5. Poisson probability of detecting zero gold grains, P(0), as a function of grain size and subsample size 16 Figure 2.1. Location map of the Boston Claims on the southeastern portion of the Hope Bay Greenstone Belt (HBGB), Slave Structural Province, N.W.T 21 Figure 2.2. Regional geology of the Hope Bay Greenstone Belt, Slave Structural Province, N.W.T 22 Figure 2.3. Local geology of the Boston Claims area at Spyder Lake, southeastern HBGB, N.W.T 25 Figure 2.4. Schematic representation of the alteration mineral zonation and gold mineralization seen within the altered (carbonatized) zone of the Boston Shear 27 Figure 2.5. Vegetation species characteristic of the different surficial materials on the upper plateau. ...29 Figure 2.6. Simplified terrain map of the Wally Grid 32 Figure 2.7. View of the western slope with a till veneer (< 1 m thick) and small earth hummocks 34 Figure 2.8. View looking North along the base of the western slope and lower plain area 36 Figure 2.9. View looking northwest along the peninsula at the northern end of the Wally Grid 37 Figure 2.10. Typical local stony frost boils with varying pebble types and surface colours 39 Figure 2.11. Typical regional till and mixed regional till frost boils on the Wally Grid 41 Figure 2.12. Typical mixed till frost boils on the upper portion of the western slope 43 Figure 2.13. Intermixed mud and earth hummocks in marine sediment areas of the upper plateau 44 Figure 2.14. Soil profile through a local stony frost boil: (A) typical profile (site L124+00 N / 12+20 E); (B) schematic representation of profile 47 Figure 2.15. Soil profile through a regional till frost boil: (A) typical profile (site L124+00 N / 13+00 E); (B) schematic representation of profile 50 Figure 2.16. Soil profile through a local stony frost boil: (A) typical profile (site LI24+00 N / 12+20 E); (B) schematic representation of profile '. 52 Figure 2.17. Soil profile through an earth hummock: (A) typical profile (site L122+00 N / 13+40 E); (B) schematic representation of mud and earth hummock profiles 55 Figure 3.1. Sample location sites for areas around the Wally Grid and Spyder Lake 59 Figure 3.2. Location of soil pits, local stony frost boil, regional till frost boil, water and bog sample sites on the Wally Grid 60 Figure 3.3. Sampling the central portion of an active regional till frost boil 65 Figure 3.4. Flow chart of sample preparation and method of gold analysis for A, B and C horizons from selected soil pits along Lines 120+00 N, 122+00 N and 124+00 N 68 Figure 3.5. Flow chart for sample preparation and analytical methods for surface humus (LFH horizon) and bog samples; and buried organic-rich lenses in soil pits 71 Figure 3.6. Flow chart of sample preparation of size and density fractions of regional till frost boils for (a) gold analysis, and (b) gold grain recovery 74 Figure 3.7. Comparison of gold concentrations (ppb) by FA-AAS versus AR column-ICP for the -53 um size fraction of surface B horizons collected from regional till frost boils 85 Figure 3.8. Comparison of duplicate analyses of (a) Ah, B and C horizons from soil pits, (b) regional till frost boils, and (c) local stony frost boils by FA-AAS 88 Figure 3.9. Comparison of duplicate analyses by AR column-ICP of the -53 um fraction of regional till frost boils 89 IX Figure 3.10. Comparison of duplicate analyses for the 1st and 2nd batches of the milled -1000 um LFH horizons and Ah and O lenses by NAA 90 Figure 4.1. Average weight percent (%) distribution of the -2000 um size fraction of Ah, B and C horizons from the different surficial material types and soil pit profiles. 95 Figure 4.2. A comparison of gold concentration (ppb) results through time for an internal standard analyzed with the 1991 and 1992 soil grid samples 99 Figure 4.3. Probability plot with thresholds for the combined 1991-1992 gold data, Wally Grid 102 Figure 4.4. Contour plot of the combined 1991-1992 gold data for the Wally Grid 105 Figure 4.5. Probability plot with thresholds for the subdivided 1991-1992 gold data for local frost boils 107 Figure 4.6. Contour plot of the subdivided 1991-1992 gold data for local frost boils 108 Figure 4.7. Probability plot with threshold for the subdivided 1991-1992 gold data for local and regional till 109 Figure 4.8. Contour plot for the subdivided 1991-1992 gold data for local and regional till 111 Figure 4.9. Plan view distribution of gold concentrations (ppb) in the -212 um fraction of the lowermost B and C soil pit horizons, measured by FA-AAS 115 Figure 4.10. Cross section view along Line 120+00 N showing surface humus and soil pit horizons with associated depths, gold concentrations (ppb) and surficial soil classification 117 Figure 4.11. Cross section view along Line 122+00 N showing surface humus and soil pit horizons with associated depths, gold concentrations (ppb) and surficial soil classification 118 Figure 4.12. Cross section view along Line 124+00 N showing surface humus and soil pit horizons with associated depths, gold concentrations (ppb) and surficial soil classification 119 Figure 4.13. Comparison of gold concentrations (ppb) in the -212 um versus -53 um size fraction of Ah, B and C soil pit horizons along Line 124+00 N , measured by FA-AAS 123 Figure 4.14. Gold concentration (ppb) of the -212 um and -53 um size fractions of the horizons from mixed till and local stony frost boil pits along LI24+00 N , measured by FA-AAS 124 Figure 4.15. Plan view distribution of gold concentration (ppb) in the -53 um fraction of surface B horizons from local stony frost boils along L120+00 N and L124+00 N , measured by FA-AAS. Associated soil horizon colour (Munsell, 1971) is also noted 128 Figure 4.16. Gold concentrations (ppb) of the -53 um size fraction of regional till frost boils, measured by FA-AAS 132 Figure 4.17. Gold concentrations (ppb) of the -53 urn size fraction of regional till frost boils, measured by AR column-ICP 134 Figure 4.18. Gold concentrations (ppb) of the -106+53 um fraction heavy mineral concentrates (HMCs) of the regional till frost boils, measured by FA-AAS 135 Figure 4.1.9. Gold concentrations (ppb) of the milled -1000 um fraction of surface humus samples collected from soil pit sites along Lines 122+00 N and 124+00 N, and bog samples from surrounding areas, measured by NAA 139 Figure 4.20. Comparison of gold concentrations (ppb) in the milled -1000 um fraction of LFH horizons, measured by NAA, versus (A) LOI ash (weight %) and (B) gold concentrations (ppb) in -212 um fraction of underlying Ah horizons, measured by FA-AAS 141 Figure 5.1. Proportion (%) of gold in the -212+53 um and -53 um size fractions of soil horizons from mixed till and local stony frost boil pits along Line 124+00 N 159 Figure 5.2. Effect of dilution by far-travelled materials on the gold concentrations in heavy minerals and total size fraction 176 Figure 5.3. Normalized gold values (ppb) in the -106+53 um HMC fraction of regional till frost boils . 178 X LIST OF PLATES Plate 4.1. Backscatter SEM photomicrographs of two modified gold grains of one regional till frost boil recovered from the -106+53 um size fraction, heavy-batea HMC 145 Plate 4.2. Backscatter SEM photomicrographs of pristine gold grains recovered from the -106+53 um HMC fraction of a local C horizon 147 Plate 4.3. Backscatter SEM photomicrographs of slightly modified gold grains recovered from the -106+53 um (A and B) and -212+106 um (C and D) HMC fractions of a local C horizon 149 Plate 4.4. Backscatter SEM photomicrographs of strongly modified gold particles recovered from the -106+53 urn fraction HMCs of a local C horizon 151 / ACKNOWLEDGEMENTS This project was funded by BHP Minerals Canada, Ltd. and the Natural Science and Engineering Research Council. I would like to thank several representatives of BHP Minerals for providing field support and assistance in the office and in the field: Neil leNobel, Paul Cowley, Dave Clarke, Randy Cullen and Jeremy Howe. Many thanks go to W.K. Fletcher for his support, helpful guidance and advice; and to A.J. Sinclair and J.M. Ryder for their careful review of the thesis and their suggestions. I am grateful to a number of the 1992 Boston Camp field crew for their able assistance: Jeff Kelner, Rob Carpenter, Gina Almeida and Marion McGill; and to Jeremy Howe for assisting with sampling of the two islands. Samples were prepared by Tainwei Sun and partly by Krista Nelson. Thanks also go to Yvonne Douma for her preparation of polished grain mounts; and to Mati Raudsepp for his advice on gold grain mounting, a tutorial on the wonderful scanning electron microscope, and for his time and assistance with the SEM and the electron microprobe. Tracy Delaney and Hou Zhihui provided many discussions and helpful comments on gold grain sampling and geochemistry...among other topics. Thanks also go to: the 'Grouse Mountain night-skiing crew' and others for great skiing and fun; to Theresa Fraser (my roomie!) and Fiona Childe for their friendship and enjoyed company in town and in Chile; to James for relaxing conversations over coffee or dinner; and to Hou and Tainwei for those wonderful meals. I would also like to thank my GSB co-workers for their support while I was trying to finish my famous 'last chapter': Barb Jennings and Dave Huntley for great eats and fun times; Steve Sibbick, Stephen Cook and Peter Bobrowsky for their helpful discussions, and also to Paul Matysek for use of the GSB office. Finally, I would like to thank my family and Cathy Freed for their unending support...it was much appreciated and needed at times. Special thanks go to my sister Linda for a great weekend at Whistler! / Chapter One - INTRODUCTION 2 1.1 Research objectives and approach Archean supracrustal rocks of the Slave Structural Province, NWT, have a high potential for economic gold deposits. However, the effectiveness of geochemical exploration is hampered by a number of factors including limited bedrock outcrops, a cover of various types of Quaternary sediments of varying thicknesses, and post-glacial modification of surficial materials by periglacial processes. Furthermore, no recommendations have been developed for the design and interpretation of geochemical exploration surveys for gold deposits in the Slave Province and areas of similar periglacial conditions. The objectives of this research are therefore, to: i) determine the spatial extent of dispersion of anomalous gold concentrations in soils and glacial sediments, ii) evaluate post-glacial redistribution of gold under periglacial conditions, iii) determine physical and chemical characteristics of individual gold particles in relation to distance from source, iv) make recommendations as to the optimum sample medium and size and/or density fractions to be analyzed for geochemical exploration studies in similar environments. Variations in gold concentrations were determined among surface humus (LFFf) horizons, mineral soil (A, B and C) horizons and organic-rich (0) lenses from soil pits. Residence sites and the partitioning of gold among size and density fractions were also determined for selected soil horizons and till. These 3 results were applied to understand the relations among periglacial modifications, till thickness, subcropping gold mineralization, and the geochemical dispersion of gold. 1.2 Permafrost and the periglacial environment Prior to discussing the geochemical dispersion of gold, it is useful to briefly discuss permafrost and the periglacial environment. Permafrost is defined as ground that remains at a temperature below 0°C for at least one year (Williams and Smith, 1989) and usually occurs at high latitudes and altitudes (the latter situation sometimes termed 'alpine permafrost'; Pewe, 1983). Permafrost varies in thickness from the arctic to subarctic regions and depending upon its continuity, is classified as either continuous or discontinuous permafrost (Figure 1.1). In the continuous zone, permafrost exists everywhere with thickness varying from 45 m at the southern boundary to over 1000 m in the extreme north (Williams and Smith, 1989). In the subarctic regions, discontinuous permafrost is present where areas of unfrozen ground or taliks are present. Taliks may also occur in the continuous permafrost zone beneath rivers or large lakes (discussed below). Permafrost is present where the mean annual ground temperature is below 0°C at depths .where the seasonal temperature variations are insufficient to raise the temperature above the freezing point (Figure 1.2). The existence of permafrost depends upon a combination of atmospheric climate and ground surface conditions, the nature of ground surface cover (snow and/or vegetation) and the thermal properties of soil materials (Williams and Smith, 1989). The zone above permafrost that annually freezes and thaws is termed the active layer. The active layer is relatively thick (1 to 2 m) in the discontinuous zone and decreases to 1 m or less in the continuous zone. Changes in the microclimate will affect the near-surface temperature regime which influences active layer thickness (Williams and Smith, 1989). For example, under the same climatic conditions, soils a. Resolute, NWT (74° N) b. Norman Wells, NWT (65° N) c. Hay River, NWT (61° N) Figure 1.1. Diagram illustrating the characteristic distribution of permafrost at three localities in the Northwest Territories: (a) very cold (mean ground temperatures many degrees below 0°C); (b) fairly cold (mean ground temperatures usually below 0°C, often by several degrees); (c) mean ground temperatures around 0°C (after Williams and Smith, 1989). TEMPERATURE + -< Maximum depth of annual variation Figure 1.2. Diagram showing range of temperature (winter minimum and summer maximum) as a function of depth. The dashed line shows the mean annual temperature of the ground (after Williams and Smith, 1989). 6 of different compositions (eg. fine sand versus silt-clay) and moisture contents will thaw to different depths where the coarse grained material has the thickest active layer. On the other hand, the same soil under different climatic conditions also thaws to a different depth. This results in lateral variations in active layer thickness. Spatial variations in ground temperatures also result from the presence of insulating materials and bodies of water. They commonly affect thickness of permafrost and active layer. For example, snow cover is an insulator and prevents the loss of heat from the ground to the air in winter. This results in relatively warm ground temperatures and thinner permafrost. Vegetation cover is also an insulator; it reduces the effectiveness of solar heating in summer leading to lower ground temperatures and relatively thin active layer. The existence of permafrost in some areas near the southern margins of the permafrost zone is associated with the presence of peat (Williams and Smith, 1989). Large and deep bodies of water (rivers and lakes) that do not freeze to the bottom in winter have a marked effect on ground temperature and the local configuration of permafrost (Figure 1.3). These bodies of water are a heat source and, depending upon their size and temperature, taliks are present beneath them. Thus, the permafrost table will occur at greater depths beneath lakes, or be absent under large, deep lakes and rivers. In the periglacial environment, mechanical processes related to the freezing and thawing of the active layer commonly result in the development of patterned ground and solifluction (discussed below). The severity of arctic climates and the presence of permafrost imposes restrictions on geochemical dispersion. Permafrost was once considered to be impermeable but recent studies have shown that water and ion movement within permafrost can result by diffusion . However, hydromorphic and mechanical dispersion are generally restricted to the active layer because the permafrost table acts as a solid boundary. Ocean Permafrost Small deep lake Shallow lake Large deep lake Figure 1.3. Schematic representation of permafrost configuration beneath water bodies (after Williams and Smith, 1989). 8 1.3 Geochemical dispersion of gold 1.3.1 Introduction In glaciated terrains, the geochemical dispersion of gold results primarily from mechanical processes during glacial transport. However, gold dispersions in glacial sediments can be disturbed and modified by post-glacial mechanical and chemical processes including soil development, plant uptake, secondary weathering and periglacial frost action. 1.3.2 Geochemical dispersion by glacial processes Over the past few decades, numerous studies have dealt with various glacial processes and their effect on the dispersion of gold and other elements. Abrasion and crushing of entrained material during glacial transport result in a decrease in grain size of the material. The degree of comminution, or terminal grade (Dreimanus and Vagner, 1971) is determined by the lithology of the entrained material and its mode of transportation: either subglacial, englacial or supraglacial (Shilts, 1985). Abrasion and comminution are greatest within the basal few metres to tens of metres of ice due to the high proportion of rock debris, and decrease in the englacial levels of the ice as the proportion of particulate material decreases (Rose et al, 1979). Lodgement till is commonly compact and contains abundant abraded debris of local origin and a moderate to high amount of silt and clay. Ablation till usually contains less abraded material and less fines than lodgement till, although materials are transported greater distances than lodgement till. Ablation till consists mainly of englacial and supraglacial material that has been "let down" onto the underlying basal material as the glacier melted and it is therefore, less compact than basal till (Shilts, 1976; 1978). 9 Glacially transported material from a point source is commonly distributed in fan shaped (Flint, 1971) or ribbon shaped dispersion trains (Shilts, 1976, 1978; DiLabio, 1982; Coker and DiLabio, 1989) that have been described as three dimensional features by Drake (1983) and Miller (1979, 1984). The dispersion trains generally extend in the down-ice direction from the bedrock source, with the dispersion distance being dependent upon the thickness of the basal till (Govett, 1973; Rose et al., 1979; Miller, 1984) and the mode of transport (ie. basal, englacial or supraglacial) by the glacier (Shilts, 1978). In general, anomaly concentrations in till are greatest near the source and decrease exponentially with increased distance as a result of the comminution of minerals with distance (Shilts, 1976) and dilution resulting from the addition of geochemically barren material during glacial transport to the fine fractions (Dreimanus and Vagner, 1971; DiLabio, 1985; Whiting and Faure, 1991). Ease of recognition of dispersion trains is influenced by many factors, such as till thickness, multiple till sheets, ice flow directions and the presence of materials overlying till. Anomalies in till less than 1 m thick are generally detectable in the A and B soil horizons directly over the bedrock source, with very little down-ice displacement (Govett, 1973). Similar surface anomalies are detectable in single till units up to 5 m thick, but may be offset several metres down-ice. The highest metal contents are typically in the basal portion of the till unit directly overlying the orebody (Govett, 1973; Rose et al., 1979; Miller, 1984). If multiple till sheets are present or multiple ice flow directions occurred within a single area, surface anomalies tend to be weak or lacking or show complex (patchy) patterns, respectively, that are offset from the source (Shilts, 1978; Rose et al, 1979). In addition, anomaly recognition is commonly complicated by the presence of other surficial materials including glaciofluvial sand and gravel and glaciolacustrine sediments overlying till, colluvium, and the reworking of till (Rose et al., 1979; Klassen, 1987; Campbell and Schreiner, 1989). For example, anomalous bedrock and till are essentially buried and 'sealed ofF by the overlying, geochemically barren deposits resulting in subsurface anomalies being 10 partially to totally obscured (Campbell and Schreiner, 1989). In these cases, anomaly recognition may be improved by sampling the till below glaciofluvial or glaciolacustrine deposits. Glacial transport also affects the morphology of gold grains. Binocular microscope and scanning electron microscope (SEM) studies have identified numerous shapes and textures of particulate gold from glaciated terrain. A classification of gold grain morphology (either pristine, modified or reshaped grains) was devised based on the degree of rounding, polishing and bending of the grains (Averill and Zimmerman, 1988; DiLabio, 1990). In general, gold grains transported short distances from the bedrock source tend to have a pristine morphology, and become increasingly modified and reshaped with greater transport distances (DiLabio, 1990). Comminution of gold-bearing primary materials during glacial transport generally promotes the liberation of free gold, thereby influencing the residence sites of gold in glacial till (DiLabio, 1985; Coker and DiLabio, 1989; Sibbick and Fletcher, 1993). Transport of free gold grains generally results in modifications of grain shapes as noted above rather than comminution of gold. Gold in oxidized till is commonly associated with the silt and clay (< 63 um) fractions (Shelp and Nichol, 1987; DiLabio, 1985) but may reflect a number of factors including: the original grain size of the gold, the grain size of gold released by comminution or weathering of gold-bearing primary materials, and the secondary adsorption of gold on to the fines (DiLabio, 1985; Shilts, 1991). However, i f the original grain size of the gold in the source rock is fine, comminution is not necessarily an influencing factor in contributing to the fine gold in glacial till. 1.3.3 Modifications within secondary environments Within the post-glacial or secondary weathering environment, gold dispersion in till may be modified by mechanical and chemical processes such as soil development, plant uptake and secondary weathering (Rose et al, 1989). In periglacial environments, gold dispersion in the active layer of soil 11 profiles and glacial sediments may also occur due to frost action. Arctic areas have limited soil development because of cold conditions and the presence of permafrost which restricts the vertical movement of water through soils (Rose et al, 1979). In tundra zones with adequate precipitation, a surface layer of organic material builds up to produce a LFH horizon since plant decay is slow in arctic climates. In well-drained soils, an underlying Ah horizon is produced by colloidal organic material being transported downwards from the humifying LFH horizon (Rose et al., 1979). Gold enrichment in these horizons may result from the adsorption of gold onto organic material and by the biogeochemical cycling of gold by plants (Rose et al, 1979; Boyle, 1979). Anomalous B and C horizons may result from the downward mixing of gold particles within the soil profile by cryoturbation. Numerous studies have identified that chemical or hydromorphic dispersion is a strong contributing factor in the secondary dissolution and movement of elements in soils (Cameron, 1977; Miller, 1984) and enrichment of gold in lateritic soils of Australia (Mann, 1984) under specific conditions. Gold is known to form complexes with cyanide, chloride, thiosulfate, bisulphide and other gold complexing agents under specific conditions of temperature, pH and Eh (redox potential), but this is more common in the laboratory than in a natural environment. There are few studies documenting the existence of these anions in sufficient quantities in soils and till of temperate and arctic climates to explain the mobility of gold (Coel, 1990). However, gold enrichment may occur in soils and perhaps tills with large amounts of decomposing organic material and weathering products (Fe- and Mn-oxides) because they have a moderate to high cation exchange capacity (CEC) and thus a moderate attraction for gold and other metals. Soils and till overlying an oxidizing sulphide orebody may exhibit an electrochemical dispersion (Smee, 1983; Kauranne et al, 1992). The generation of an electrical field around an oxidizing orebody may drive cations upwards to where they can be adsorbed by the soil or precipitated by organic compounds (Govett and Chork, 1977; Rose et al, 1979). Electrical voltages have been noted across the ice-liquid phase boundary and may 12 contribute to the dissolution and adsorption/precipitation of gold onto clay and organic materials excluded from the ice as water freezes (Watterson, 1985). In arctic environments, gold dispersion in soils and till may be disrupted or modified by a number of periglacial processes resulting in downslope movement of materials and patterned ground. Processes primarily responsible for downslope movement of materials in cold regions include frost creep or solifluction, the downslope flow resulting from frost heave and settling processes (French, 1988; Bennett and French, 1991). Resulting features include: solifluction sheets having a smooth surface and bench-like or lobate lower margins; solifluction benches that have a pronounced terrace form with the longest dimension parallel to slope contour; and solifluction lobes that are tongue-like in appearance with the longest dimension perpendicular to the slope contour (Washburn, 1979). Solifluction lobes tend to occur on steeper slopes (10° to 20°) whereas sheets and benches occur on gentle to moderate slopes (5° to 15°) (Washburn, 1979). Profiles through these downslope features commonly show a crude stratification of soil and organic horizons resulting from the progressive overriding and burial of the tundra vegetation cover (Washburn, 1979; Rieger, 1983; Williams and Smith, 1989). Arrangement of fabric commonly results from the orientation of the long axes of stone fragments in the direction of movement (Washburn, 1979; French, 1988). Patterned ground refers to the "systematic, patterned arrangement of microrelief, variously described as polygons, nets, circles and hummocks" (Williams and Smith, 1989). Such features result from cracking caused by thermal contraction and from the lateral and vertical displacement of soil associated with daily and seasonal freezing and thawing (French, 1988). Over the past several decades, numerous hypotheses have been proposed to explain the formation of patterned ground including load casting, convection or cryoturbation, cryostatic pressure, differential frost heave and differential swelling 13 (Washburn, 1979; Shilts, 1978; Mackay, 1980, 1981; French, 1988; Schunke and Zoltai, 1988; Van Vliet-Lanoe, 1991) with many processes leading to converging patterns. 1.4 Problems associated with geochemical sampling of rare grains Geochemical exploration surveys often yield erratic and irreproducible gold concentrations resulting from the nature of gold within samples, ie. the grain size and abundance of particulate gold. The distribution of these often discrete, equant grains within a granular sample can be estimated by the Poisson distribution (Ingamells, 1981): P(n) = e-u-un/n! (1-1) where p. is the mean number of equant grains within the sample and P(n) is the probability that n grains will be found within the sample. The Poisson distribution has the unique characteristic that the mean (u) is equal to the variance. Therefore, the relative error (RE) can be approximated as RE = 1/Vu. The effect of a rare grain of gold upon initial soil sampling or subsampling can be illustrated by an example. An original 500 g sample, having a bulk composition of 350 ppb gold, was taken from glacial till down ice from an auriferous quartz vein showing. The host soil was homogeneously composed of grains 200 um in diameter and contained trace amounts of gold. A representative 30 g subsample was taken from the original sample. Assuming the gold is present as spheres 200 um in diameter and is pure gold (density = 19.3 g/cnP), each gold grain will weigh 80.84 ug. The weight of gold within the original 500 g sample is 175 ug (500g x 350 ppb) representing, on average, 2.165 particles of gold. A 30 g subsample will therefore, contain 0.1299 particles of gold. Using the Poisson distribution (Equation 1-1), the probability 14 that a 30 g subsample will contain zero particles of gold is P(0) = 0.8782 (Figure 1.4). Therefore, 87.8% of these subsamples will not contain any gold resulting in the true gold concentration being undetected. A mere 11.4% probability exists that one particle of gold will exist in the subsample resulting in a gold concentration of 2694 ppb, which is about eight times greater than the true concentration. Ingamells (1981) has termed this phenomenon of elevated gold analyses produced by the random inclusion of a single gold particle within a subsample the "nugget effect". Gold results are influenced by variations in both the size fraction and the sample size being analyzed since representativity of the subsamples is highly dependent upon the number of gold particles present in the original sample and the size in which they occur. Nichol et al. (1987) suggest that when gold is present as coarse particles, the size of the samples must be increased in order for them to be representative. For example, an original 900 g sample is wet sieved into three size fractions (300 um, 150 um and 50 um) each weighing 300 g and having a gold concentration of 1000 ppb gold . The mass of gold in each size fraction is thus 300 u.g (300 g x 1000 ppb). Assuming the gold particles are present as spheres of pure gold (density = 19.3 g/cm^) with a diameter equal to the grain size of each fraction, the weight of one gold particle is 272.85 ug, 34.11 ug, and 1.263 ug for each fraction, respectively. This represents, on average, 1.100, 8.796 and 237.530 particles of gold in the respective size fractions. The effect of grain size and subsample size on sample representativity is illustrated in Figure 1.5. If ten 30 g or six 50 g subsamples were to be taken from each size fraction, using the Poisson equation (1-1), the probability of detecting zero gold grains in the subsamples decreases with decreasing grain size and increasing subsample size. For example, the 300 um size fraction contains just over one particle of gold (1.100). Therefore, only one in ten 30 g subsamples would contain any gold, resulting in a gold concentration nearly nine times greater than the true value in that sample. In contrast, since the number of gold particles increases in the fractions, the probability of containing zero gold particles in a 30 g subsample from the 150 (im fraction decreases to 41.5% and further decreases to 23.1% for 50 g subsamples. If the 150 um fraction contained Figure 1.4. Poisson probability that an original 500 g sample with a gold concentration of 350 ppb, willhave a 30 g subsample containing 0,1, 2 and 3 gold particles, assuming the gold is present as spheres 200 um in diameter with a density of 19.3 g/cm3. 16 100 80 • * 100 80 60 60 -Q CO £ 40 ©-. 40 20 20 0 300 um 150 um Grain size 30 g 50 g 300 g e~-Subsample size 50 um 0 Figure 1.5. Poisson probability of detecting zero gold grains, P(0), as a function of grain size and subsample size. Each size fraction has a gold concentration of 1000 ppb and the gold particles are assumed to be spheres of pure gold (density = 19:3 g/cm3) with a diameter equal to the grain size of each fraction. 17 1, 2 or 3 particles of gold in the 50 g subsamples, resulting gold concentrations would more closely resemble the original (1000 ppb) gold value than if the same occurred with 30 g subsamples. For each subsample size, the finest (50 um) fraction has a 0% probability of containing no gold particles and would yield the most representative gold results in its subsamples. Clifton et al. (1969) illustrated how analytical precision and the number of gold particles present in a sample are dependent for materials with a binomial gold distribution, assuming the following criteria: (1) gold particle size is uniform, (2) gold particles represent less than 0.1% of all particles, (3) the sample contains at least 1000 grains, (4) analytical errors are absent, and (5) the gold particles are randomly distributed through the material being sampled. However, the binomial gold distribution was found to approach the Poisson distribution as the number of gold particles decreased in the sample. Based on these conditions, in order to achieve a precision of ± 50% at the 95% confidence level a minimum of 20 particles of gold is required in the sample (Clifton et al., 1969). Stanley and Smee (1989) argue that a precision of ±50% is only required if an anomaly is to be defined by a single sample collected from anomalous material. However, if the sample density is increased and thus several samples are collected from anomalous material, the level of precision necessary for each sample may be poorer than that recommended by Clifton et al. (1969). In general, "increasing the sample size increases the probability of detecting gold at a specific anomalous site; increasing sample density 18 increases the probability of detecting gold at at least one of several anomalous sites" (Stanley and Smee, 1989). In both cases, the anomalous zone is detectable. 1.5 Conclusion In glaciated, permafrost terrain, the geochemical dispersion of gold results primarily from mechanical processes during glacial transport but can be modified or disturbed by a number of post-glacial mechanical and chemical processes including soil development, plant uptake, secondary weathering and periglacial frost action in the active layer. Thus, an understanding of these factors may improve the effectiveness of geochemical exploration surveys in identifying economic gold deposits in the Slave Province, NWT. Therefore, this thesis will go on to determine the distribution and characteristics of gold in soils and till in the vicinity of a mineralized source and to developed guidelines for the design and interpretation of exploration geochemical surveys for gold, as set out in the objectives. Chapter Two - DESCRIPTION OF STUDY AREA 20 2.1 Introduction Mineral and organic soil samples were collected from areas of known gold mineralization in the Hope Bay Greenstone Belt, Northwest Territories. Water samples also were collected from seepage zones and from streams and lakes in and surrounding the study area. A brief description of the study area and Quaternary history follows. 2.2 Location and access The Wally Grid lies within the Boston Claim group approximately 650 km northeast of Yellowknife and 170 km southwest of Cambridge Bay. It lies in the southeastern portion of the Hope Bay Greenstone Belt (HBGB) to the east of Bathurst Inlet in the Slave Structural Province, N.W.T. (Figure 2.1). The property, owned by BHP Minerals Canada Ltd., is located within the area of the NTS 76 0/9 map sheet on the southeastern shores of Spyder Lake. The property is easily accessible by aircraft that can be chartered from Yellowknife or Cambridge Bay. Helicopter support facilitates access to the southern claims and surrounding areas. 2.3 Regional geology The Hope Bay Greenstone Belt (HBGB) is approximately 20 to 40 km wide and 100 km long, lying within the fault-bounded Bathurst Block of the Slave Structural Province (Figure 2.2). The FD3GB trends north-south for most of its length, but curves to a northwest-southeast trend in the south. Archean supracrustal rocks of the HBGB are comparable to the Yellowknife Supergroup, with most of the belt consisting of mafic to felsic volcanic units with associated volcaniclastic and metasedimentary assemblages 21 Archean Volcanic Rocks Fault Lode Gold Volcanogenic Cu-Zn ± Pb 116° 112° 10S-Arctic Circle 64° — Rae Province 116° 112° 108° Arctic Circle 64° h- 60° Figure 2.1. Location map of the Boston Claims on the southeastern portion of the Hope B ay Greenstone Belt (HBGB), lying within the fault-bounded Bathurst Block of the Slave Structural Province, N.W.T. (modified from Gebert and Irving, 1991). 22 Figure 2.2. Regional geology of the Hope Bay Greenstone Belt (HBGB), Slave Structural Province, N.W.T. (after Gebert, 1990; Clarke and St. Pierre, 1993). 23 (Gebert, 1990; Leclair, 1991). Ultramafic sills and lamprophyre dykes are associated with the mafic volcanic rocks of the northern HBGB (Leclair and Jebrak, 1990). To the northeast and west, the belt is bounded by Late Archean granites and granodiorites and by a heterogeneous gneissic terrane to the southeast (Leclair and Jebrak, 1990; Gebert, 1990). Granitoid intrusives near Ida Point in the north, have been classified as tonalites by Leclair and Jebrak (1990) and are non-to-weakly foliated. Similar tonalitic intrusions have been recognized east of the Boston Claims (Clarke and St. Pierre, 1993). Regional metamorphism has altered the volcanic rocks of the belt to greenschist facies, and along the belt margins, a metamorphic aureole marks a transition zone where metamorphism has altered the volcanic rocks to lower amphibolite facies (Gebert, 1990). Mafic volcanic rocks have been identified as pillowed flows interlayered with massive flows and gabbro sills which, in the northern and central portions of the HBGB, have been intruded by Proterozoic diabase dykes (Leclair, 1991; Gebert, 1990). Feldspar and quartz-feldspar porphyry dykes cut the mafic units in the southern portion of the belt (Clarke and St. Pierre, 1993). Whole rock analyses by Leclair (1991) and Clarke and St. Pierre (1993) have classified the mafic volcanic rocks in the Ida Point and Spyder Lake areas as tholeiitic basalts. Felsic volcanic and volcaniclastic units of the HBGB are dacitic to rhyolitic ash, lapilli and crystal tuffs with minor flows (Gebert, 1990). U-Pb geochronology places the Hope Bay felsic volcanism at 2685 +47-3 Ma to 2677 +2/-1 Ma whereas, felsic plutonism postdates volcanism at 2672 ± 3 Ma (Bevier and Gebert, 1991). An undeformed granitic pluton to the west of the belt was dated at 2607 ± 5 Ma and, since it contains foliated mafic xenoliths, this date can provide a lower age limit for the metamorphism and deformation in the HBGB (Bevier and Gebert, 1991). Metasedimentary rocks of the HBGB occur as narrow bands interbedded with mafic and felsic volcanic units. In the northern part of the belt, interbedded greywackes, siltstones and mudstones represent 24 The HBGB has undergone a number of structural events. Several reversals in pillow topping directions indicate north to northwest trending isoclinal folds that are expressed as prominent ridges and plateaus throughout the length of the belt. Regional foliation and the eastern and western belt contacts are parallel to these fold trends (LeClair, 1991). A north trending, anticlinal fold axis is present in the medial portions of the central and southern HBGB, defined by younging directions observed from pillow tops and dip directions of mafic flows (LeClair, 1991; Gebert, 1990). Three vertical shearing events and foliations have overprinted the volcanic rocks (LeClair and Jebrak, 1991). The first event is responsible for the north-northwest stretching direction observed in the pillows. The second sinistral shear event is coincident with the anticlinal fold axis. This well-developed shear runs discontinuously in a north-south direction along most of the belt but flexes to the southeast near the southern tip. Milky-white quartz veins occur vvithin the shear zone, with gold mineralization concentrated in arsenopyrite rich bands along vein selvages (Leclair and Jebrak, 1991). Associated faults are suspected to underlie overburden-filled, north-south valleys (Clarke and St. Pierre, 1993). The final shear event trends northeast and contains smoky and white quartz veins with visible gold mineralization. A prominent hydrothermal (carbonate) alteration is associated with this shear zone and is responsible for overprinting the regional and contact metamorphic mineral assemblages. Northeast trending faults associated with this event offset the volcanic rocks and belt margins (Gebert, 1990; Clarke and St. Pierre, 1993). 2.4 Local geology The Boston Claims property is situated on north to northwest trending mafic and felsic volcanic units bounded by Archean granitic intrusives to the east and south-southwest (Figure 2.3). Within the Boston 1 Claim, sheared metabasalts define two north trending ridges separated by a broad valley. The Figure 2.3. Local geology of the Boston Claims area at Spyder Lake, southeastern Hope Bay Greenstone Belt (HBGB), N.W.T. (after Gebert, 1990; Clarke and St. Pierre, 1993). 26 Wally Grid is centred over the western ridge that hosts the Boston Shear, the southern extension of the Hope Bay axial-planar shear system. Mafic volcanic and volcaniclastic rock units within the shear have undergone intense carbonatization, resulting in alteration mineral zones around quartz and quartz-carbonate veins, as discussed below (Clarke and St. Pierre, 1993). The volcanic rocks of the Wally Grid have been intruded by two north trending, grey feldspar porphyry dykes. These fine-to medium-grained dykes dip subvertically and can be traced for about 300 m within shallow depressions (Clarke and St. Pierre, 1993). Northeast trending faults lying within overburden-filled, recessive valleys offset the Boston Shear. East of the Wally Grid, the broad valley is occupied by a lens of metasedimentary rocks consisting of siltstones and/or mudstones with graphite-rich bands (Clarke and St. Pierre, 1993). Similar metasediment lenses occur along the Spyder River valley. Archean granitic (tonalite) intrusions bound the volcanic rocks of the eastern and southern Boston Claims (Clarke and St. Pierre, 1993). Quartz and quartz-carbonate veins associated with the Boston Shear, and other areas of the belt, are symmetrically encased in alteration zones displaying varying degrees of carbonatization (Clarke and St. Pierre, 1993). This shear structure contains alteration mineral assemblages and gold mineralization similar to the mesothermal gold deposits of Yellowknife, N.W.T. and Timmins, Ontario, hosted within Archean Greenstone Belts (Guilbert and Park, 1986; Clarke and St. Pierre, 1993). Alteration mineral zonations reflects the migration of hydrothermal fluids outwards from the central shear zone to the surrounding rocks (Figure 2.4). Within the Boston Claims area, the central portion of the shear zone is the most strongly carbonatized and consists of ankerite (Fe-dolomite)-sericite schists up to 100 m in width. Abundant quartz-carbonate-gold veins occur within this central zone (Clarke and St. Pierre, 1993). An outer envelope of less altered, chlorite-sericite schists varies in width from 50 to 100 m and contains quartz and quartz-carbonate veins along the contact with the central carbonate-rich zone. Chlorite schists occur in the margins of the shear zone that grade outwards into unaltered greenstone volcanic rocks. Within the Boston Claims, the alteration mineral zonations are not evenly distributed: unaltered zones of mafic volcanics are found to occur within intensely carbonatized zones (Clarke and St. Pierre, 1993). carbonate (ankerite)-sericite schist carbonate-chlorite-sericite schist 50 to 100 m chlorite schist greenstone volcanics Figure 2.4. Schematic representation of the alteration mineral zonation and gold mineralization seen within the altered (carbonatized) zone of the Boston Shear, the southeastern extension of the Hope Bay axial-planar shear system (after Guilbert and Park, 1989). 28 2.5 Character of gold mineralization Along the length of the HBGB, gold mineralization is mainly associated with the most recent axial-planar shear zone event. Within the Wally Grid, visible gold mineralization usually occurs within the strongly iron-carbonatized veins consisting of Fe-dolomite (ankerite) and smoky and white quartz. A second type of gold mineralization is associated with quartz-carbonate veins having pyrite ± chalcopyrite ± arsenopyrite accumulations along vein selvages (Clarke and St. Pierre, 1993). 2.6 Physiography, climate and vegetation Situated within the barren lands of the Canadian Shield, the Boston property lies about 150 km north of the Arctic Circle. The property is located in the Back Lowland physiographic region (Dyke and Dredge, 1989) where broad north to northwest trending valleys are developed along zones of structural weakness (Bird and Bird, 1961). These valleys are commonly occupied by streams and lakes separated by undulating terrain. Spyder Lake occupies one of these valleys, flanked on either side by prominent north-south trending ridges rising 10 m to 50 m above lake level (Ryder, 1992). A similar valley is also found to the east of the Wally Grid (Figure 2.3). Snow cover generally lasts from late September until mid-to-late June. However, snow drifts on the lee side of large ridges and ice on Spyder Lake remain until mid-to-late July. Ryder (1992) has identified several types of tundra vegetation on the Wally Grid; certain species tend to be characteristic of the different surficial materials (discussed below) and the transition between them is often distinct (Figure 2.5a). Acid-loving plants such as "heathers", Labrador tea and Vaccinium (blueberry and cranberry) are common to till areas on the ridge or plateau. In contrast, poorly drained areas with marine sediments host grassy vegetation with dwarf birch or willow occurring in depressions between grass mounds (Figure 2.5a) Figure 2.5. Certain vegetation species tend to be characteristic of the different surficial materials: (A) Till areas (foreground) on the plateau commonly host acid-loving plants such as "heathers" and Labrador tea whereas marine sediment areas (centre) are mainly grass covered with dwarf birch and willow. Note the distinct transition between surficial materials. (B) Till veneer (< 1 m thick) areas on the western slope host grassy vegetation with dwarf birch. Note the exotic (regional till) boulders on the surface. 30 Areas around weathered rock are mainly grass covered and support flowering plants characteristic of calcareous substrate. The western slope is till covered and hosts grassy vegetation and dwarf birch (Figure 2.5b). 2.7 Quaternary history The Boston property and surrounding Bathurst Inlet area was overridden by Keewatin Ice, the northwest part of the Laurentide Ice Sheet, during each of several glaciations in the Pleistocene Epoch (Dyke and Dredge, 1989). However, evidence of only the most recent Late Wisconsinan Glaciation is preserved in the present-day landscape of the Spyder Lake area (Ryder, 1992). Smoothed outcrops, roches moutonnees, glacial striae and grooves, eskers, erratics and till are all evidence of this last glaciation. The orientations of striations and grooves around Spyder Lake identify a general north-northwest ice flow direction, with striae measurements varying from northwest to north (Ryder, 1992). Keewatin Ice retreated from the area in a southeast direction between 10 ka and 8.4 ka (Dyke and Dredge, 1989). Immediately upon retreat, the area was inundated by the sea. The marine limit in the Bathurst Inlet area lies between 200 and 225 m above present-day sea level (Dyke and Dredge, 1989). This submergence resulted in the accumulation of marine sediments on top of till (Blake, 1963; Dyke and Dredge, 1989; Ryder, 1992) with the southern limit of submergence being about 75 km south of the Arctic Coast. Rapid isostatic rebound of the Bathurst Inlet area during 1 to 2 ka after deglaciation is estimated at approximately 10 m per century, based on the averaged emergence rates (Dyke and Dredge, 1989). As the land emerged, wave action modified the landscape. Surficial materials including till, marine sediments and glaciofluvial sediments were reworked and redistributed by waves and currents (Ryder, 1992). Frost action and solifluction have since modified the Quaternary sediments, resulting in the present-day landscape (Ryder, 1992). 31 2.8 Surficial geology and terrain 2.8.1 Surficial materials Terrain mapping of the Wally Grid by Ryder (1992) identified several types of surficial materials: weathered rock, till, marine sediments and mixtures of the different types (Figure 2.6; Ryder, 1992). The following descriptions of surficial materials are based generally on the descriptions of Ryder (1992). Weathered rock refers to materials derived from local bedrock. They typically consist of angular to subangular fragments surrounded by a silt-clay matrix. Lithologies are primarily weathered sericite schist, vein quartz and quartz-carbonate material but till pebbles (discussed below) may comprise less than 10% of the clasts. Several different types of till are found in the study area. Regional till consists of a poorly-sorted silty-sand matrix and a low proportion (generally less than 25%) of pebbles, cobbles and boulders. Matrix texture varies from moderately-well-sorted fine sand to poorly-sorted silty fine-to-medium sand, partly a result of the washing and local reworking of till by waves during isostatic rebound. Clasts include a high proportion of exotic lithologies from the south and southeast, including granitoids, green and black volcanics and minor metasediments, and a minor proportion of angular local lithologies, mainly sericite schist and quartz-carbonate vein material. Exotic clasts are subrounded to rounded as a result of abrasion during glacial transport. Washed or sorted till consists of moderately-well-sorted sand with few clasts and buried boulders. These materials may represent ancient beaches that developed when some till was washed as the land emerged from beneath the sea (Ryder, 1992). Mixed or local till may have also resulted from this reworking of materials. Mixed till generally consists of moderately-sorted silty fine-to-medium sand with few pebbles and cobbles and may represent intermixed regional till and marine sediments (described below). 32 33 Marine sediments were deposited on top of till when the area was inundated by a postglacial sea. They consist primarily of far-travelled silt-clay material derived from sources to the south and southeast, and are stone-free. 2.8.2 Distribution and thickness of surficial materials The Wally Grid can be divided into an upper, plateau region, rising 10 to 50 m above Spyder Lake, and a western slope - lower plain region by an escarpment related to the north trending volcanic ridge (Figure 2.6). To the east of the escarpment, the Boston Shear Zone is exposed on the plateau as subvertical, ankerite-sericite schist subcrops and weathered rock. A till veneer (< 1 m thick) covers the remainder of the shear zone and plateau area, and boulders are scattered at the surface. Small pockets of marine sediments overlying till and infilling shallow depressions are also found in this area (Figure 2.5a). Towards the Baseline, the plateau gently slopes down to the east where the till becomes thicker (> 1.5 m). Marine sediments overlie the till near the Baseline and further to the east. Marine sediment thicknesses are not known for certain because the active layer is thin (< 0.7 m) in these areas, but they are thought to be < 1 m thick near the Baseline and 1 to 2 m thick downslope towards the eastern valley (Ryder, 1992). In the southern and central portions of the grid, the western slope is steep (> 35°) and moderately steep (10 to 35°), becoming more gentle (2 to 10°) towards the north. Subvertical, sericite schist subcrop and weathered rock are found along the top portion of the western slope, with the weathered rock commonly moving downslope due to solifluction (Figure 2.7a). The remainder of the western slope is covered by a till veneer (< 1 m thick) with subrounded boulders present at the surface (Figure 2.5b). In addition, two quartz-carbonate boulder trains are found on the western slope in the southern and central portion of the grid (Figure 2.7b). These boulders contain weathering ankerite-chlorite schist fragments and visible gold is present within a honeycomb texture in the quartz-carbonate matrix that has been retained from weathered-out 2 to 5 mm pyrite cubes (Clarke and St. Pierre, 1993). 34 A Figure 2.7. The western slope is mainly covered by a till veneer (< 1 m thick) with small hummocks. (A) Subcrops o f subvertical sericite schist arc present on the upper portion of the western slope, with rock fragments moving downslope due to solifluction. (B) Several gold-bearing quartz-carbonate boulder trains occur near the base o f the slope. 35 Minor sericite-schist subcrops are also found along the base of the slope and on the plain area. The plain consists mainly of undulating till veneer overlain by marine sediments (< 1 m thick) closer to the shores of Spyder Lake. Frost boils of local bedrock fragments (discussed below) also occur on the plain (Figure 2.8). Shoreline areas are modified by wave action and by the seasonal fluctuations in the water level of Spyder Lake, resulting in the reworking of till to produce sandy beaches. In the southern portion of the plain, an organic veneer (usually 20 to 40 cm thick) overlies the till. In several poorly-drained areas near the base of slope, till is overlain by organic-covered marine sediment. In the northern portion of the Wally Grid, between Lines 124+00 N and 126+00 N , a northeast trending valley is filled with till up to 7 m in depth (Clarke and St. Pierre, 1993). North of Line 127+00 N , the volcanic ridge is no longer exposed and the plateau region gently slopes 2° to 10° northwards to the shores of Spyder Lake (Figure 2.9). The majority of this northern area is covered by an undulating till plain with small pockets of thin (< 1 m thick) marine sediments infilling shallow depressions (Ryder, 1992). 2.8.3 Patterned ground Periglacial processes have resulted in the microtopography, or patterned ground, that is observed in the Boston Property area. Such features include unsorted circles or frost boils (Williams and Smith, 1989), mud hummocks (have mud exposed at the surface), earth hummocks (vegetation-covered) (French, 1988), organic mounds, turf hummocks (Ryder, 1992), stone polygons and frost-heaved blocks of bedrock. It was observed that certain types of patterned ground are characteristic of the different surficial materials. For example, mud and earth hummocks commonly occur in marine sediments. The following are descriptions of the different types of patterned ground observed and, in most cases, sampled within the Wally Grid. 36 Figure 2.8. View north along the base of the western slope and plain area. Due to the seasonal and daily fluctuations in the water level of Spyder Lake, shoreline areas are periodically submerged and modified by wave action. Areas of weathered rock (comprised of local bedrock fragments) are generally elongated downslope towards the lake due to solifluction. 3 7 38 Several types of frost boils are found in the Wally Grid and are distinguished according to the type of surficial material in which they have developed. Frost boils developed in weathered rock (hereafter referred to as local stony frost boils) are unsorted circles that typically have local bedrock fragments (sericite schist and quartz-carbonate) comprising greater than 80% of the surface pebbles in a silt-clay matrix (Figure 2.10a and b). These flat-topped frost boils are round to elongate in shape and vary from 1 to 2 m in width and 1 to 4 m in length. In a number of cases, subrounded till pebbles and cobbles (granitoids and green and black volcanics) comprise about 10% of the surface fragments (Figure 2.10c). Local frost boils are generally present on the plateau, where they are developed in thin (< 1 m thick) overburden, surrounding and immediately downslope from local subcrop, and on the lowland near Spyder Lake. Colours of the (moist) matrix vary greatly from reddish brown (5YR4/3 to 4/4), dark reddish brown (5YR3/2 to 3/4), medium brown (7.5YR4/4 and 10YR4/3), brown-strong brown (7.5YR5/4 to 5/6), yellowish brown (10YR5/4 to 5/8) to dark yellowish brown (10YR4/4 to 4/6). Frost boils developed in regional till (hereafter referred to as regional till frost boils) are unsorted circles that contain only subrounded till pebbles and cobbles on the surface (Figure 2.1 la). These frost boils are flat-topped, generally 15 to 50 cm in diameter and are raised 5 to 10 cm above the surrounding vegetation, that occurs in shallow depressions between frost boils (Ryder, 1992). They are developed in gentle to moderately sloping till plains (till > 1 m thick). Pebble lithologies include granitoids, green and black volcanics and minor black metasediments. Till matrix is silty sand and varies in colour from medium brown (7.5YR4/4), to brown (10YR5/3) and yellowish brown (10YR5/4). Subrounded erratic boulders are generally scattered at the surface. Mixed regional till frost boils (Figure 2.1 lb) are similar to regional till frost boils described above but about 10% of the surface pebbles and cobbles are of local lithologies. 39 Figure 2.10. (A and B) Typical frost boils developed in weathered rock that have subangular, local bedrock fragments (sericite schist and quartz-carbonate vein material) comprising > 80% of the pebbles in a silt-clay matrix. Note the active portion of the frost boil in A. (C) Several of these local frost boils also contain about 10% subrounded, regional till pebbles (granitoids and volcanics) on the surface. Note also the varying surface colours among local frost boils: (A) medium brown (10YR 4/3), (B) reddish brown (7.5YR 4/4) and (C) dark yellowish brown (10YR 4/4). Trowel is 25 cm long. Figure 2.10 continued. 41 Figure 2.11. (A) Typical frost boil developed in regional till containing only exotic pebbles and cobbles (granitoids, green and black volcanics, minor metasediments) in a silty-sand matrix. Pen is 15 cm long. (B) Typical frost boil in mixed regional till containing about 10% local bedrock fragments (sericite schist and quartz-carbonate vein material) intermixed with the till pebbles. Trowel is 25 cm long. 42 Frost boils developed in mixed till (hereafter called mixed till frost boils) are small (10 to 30 cm wide) hummocks covered by a thin layer (1 to 5 cm) of organic vegetation and separated by vegetated, shallow depressions (Figure 2.12). These frost boils are mainly found on the western slope but are also developed on the upper plateau in areas of intermixed till and marine sediments and sorted till. This matrix varies from silty-sand to fine-to-medium sand and varies in colour from reddish brown (5YR4/3 to 4/4), dark reddish brown (5YR3/3 to 3/4), medium brown (7.5YR4/2 and 10YR4/3) to brown-yellowish brown (10YR5/3 to 5/6). Mud hummocks are flat-topped, sorted circles developed in marine sediment that have stone free silt-clay exposed on the surface (Figure 2.13). These well-developed hummocks are generally 20 to 60 cm in diameter, rise about 15 to 20 cm and are separated by deep troughs hosting grass, dwarf birch and semi-decomposing vegetation. Cracks in these troughs can expose the underlying frozen ground. Surface matrix colours vary from light brownish grey (10YR6/2), light yellowish brown (10YR6/4), medium brown (10YR4/3) to dark yellowish brown (10YR4/4). Mud hummocks are very firm and thus easy to walk on, like stepping stones. Earth hummocks are similar to mud hummocks in size and dimension but are flat-topped mounds covered with vegetation that is 2 to 5 cm thick (Figure 2.13). Organic mounds are soft, compressible mounds consisting of living and semi-decomposed vegetation and are generally developed in poorly drained areas. Turf hummocks are small (10 to 15 cm wide) mounds of grass that rise 10 to 20 cm above the surrounding vegetation. These hummocks are very soft, compressible and often topple over when walked upon. They generally develop in poorly drained areas but are also found intermixed with organic mounds and earth hummocks (Figure 2.13b). 43 Figure 2.12. (A) Typical frost boils developed in mixed till on the upper portion of the western slope that are small hummocks covered with a thin layer o f vegetation and separated by shallow depressions. Note the till boulders on the surface and local subcrop in the background. (B) Close-up view o f a mixed till frost boil . Trowel is 25 cm long 44 Figure 2.13. (A) Typical mud hummock developed in marine sediment areas of the plateau that has silt-clay matrix exposed at the surface that is stone free. Earth hummocks are vegetation-covered and are commonly developed among mud hummocks; both rise about 15 to 20 cm above the surrounding vegetation and are separated by deep troughs hosting grass, dwarf birch and willow. (B) Turf hummocks are generally found in poorly-drained, marine sediment areas and also develop among mud and earth hummocks Trowel is 25 cm long. 2.9 Soils 45 Soils within the Wally Grid reflect the different surficial materials, and in most cases they have been formed by pedological processes and modified by periglacial processes including frost heave, cryoturbation and solifluction. Soils in the study area are Cryosolic soils, however, they are generally not well developed. Horizons were distinguished on the basis of soil texture and colour. Most of the frost boil soils have weak Ah horizons, B horizons defining the frost boil and have permafrost at depth. Soils were examined in hand-dug pits along five grid lines (see Section 3.1 and 3.2.1). Pit depths ranged from 45 to 118 cm primarily due to the varying thicknesses of overburden, underlying bedrock topography and thickness of unfrozen groun. On the western and central portion of the plateau and the western slope, soil pits were dug down to bedrock, which was encountered at depths ranging from 54 to 96 cm. On the eastern and northern flanks of the plateau, thick till allowed pits to reach depths up to 118 cm. In contrast, marine sediment on the eastern plateau had thin thawed zones; soil pits in these materials were less than 61 cm in depth. Descriptions of the different soil profiles encountered in the various types of patterned ground follow. / ' Soil pits in local stony frost boils were 54 to 96 cm deep and generally reached bedrock (Table 2.1; Figure 2.14A and B). Ah horizons are found only in depressions to the sides in the individual frost boils. B horizons are distinguished based on texture and colour differences. The B l and B2 horizons commonly define the frost boil, with the B2 horizon comprising the outer rim. Frost boil B horizons typically have a bowl-shaped lower boundary due to periglacial processes that produce patterned ground (see Discussion). A B3 horizon occurs beneath and on either side of the bowl-shape. BC horizons are transitional horizons, from B3 to C horizon, and contain abundant weathered fragments of local bedrock. C horizons, when Table 2.1. Soil description of a pit through a local stony frost boil. Horizon Depth Texture %of Shape of Clast Colour of matrix* (cm) clasts clasts lithology notation name LFH 10-0 0 n/a n/a 7.5YR2.5/0 black B l 0-26 sandy-silt 45 sub-ang sch, mfcs 7.5YR5.5/6 reddish yellow-strong brown B2 26 - 40 silt-sand 35-40 sub-ang sch, mfcs 7.5YR5/5 strong brown BC 40 - 59 silt-sand 75 ang to sub-ang sch, mfcs 7.5 YR4/4 dark brown R 59 + Note: % = percentage; * = Munsell notation (Munsell, 1971); ang = angular; sch = schist; mfc = mafic volcanics; n/a = not applicable. 47 A bedrock or permafrost Figure 2.14. Soil profile through a local stony frost boil. (A) Typical profile (site L124+OON / 12+20 E). Marker is 20 cm long; (B) Schematic representation of profile. 48 exposed, vary in thickness and material type depending upon the surrounding surficial materials thus, may be intermixed marine sediment and till or washed till. Soil pits through frost boils developed in regional till and mixed regional till ranged from 64 to 118 cm in depth (Table 2.2; Figure 2.15). Ah horizons are developed only in the shallow depressions between individual frost boils and may be up to 5 cm thick. In a few cases where moss occurs on the surface of the frost boil, an Ae horizon has developed but is often too thin (< 1.5 cm thick) for bulk sampling. A B l horizon defines the shallow frost boil which is generally outlined by a thin (< 1 cm thick) organic-stained layer. Coarse fragments within this B1 horizon are concentrated near the surface of the frost boil primarily due to uplifting of stones during frost boil development (see Discussion). Soil pits in mixed till frost boils on the plateau and western slope generally reach bedrock and range from 45 to 75 cm in depth (Table 2.3; Figure 2.16). Thin Ah horizons (up to 5 cm) generally cover the mounds but are thicker (up to 10 cm) in the depressions between frost boils. Oh the plateau (Figure 2.16A and C), a B l horizon comprises the shallow mound. Underlying B horizons are thin with a BC horizon directly overlying local, sheared bedrock. On the western slope, overburden materials have been modified by cryoturbation and solifluction, resulting in alternating B horizons and buried Ah and O lenses (Figure 2.16B and D). In most of the pits in mixed till, lenses of humic material occur below buried Ah lenses or below B horizons and vary in thickness from 2 to 10 cm. Material immediately surrounding these buried lenses are commonly organic-stained. Soil pits through mud and earth hummocks in marine sediments are typically shallow (46 to 61 cm depth) and bottom in frozen ground (Table 2.4; Figure 2.17A). Ah horizons (0 to 20 cm thick) are developed in the depressions on either side of the hummocks but also occurs as a thin (0 to 2 cm) horizon on the surface of earth hummocks. A B l horizon constitutes the hummock and is usually firm and stone 49 Table 2.2. Soil description of a pit through a regional till frost boil. Horizon Depth Texture %of Shape of Clast Colour of matrix* (cm) clasts clasts lithology notation name LFH 5-0 silty 0 n/a n/a 7.5YR2.5/0 black Ah (0-3) silt-sand 20 sub-ang, sub-rnd sch, grnt, vie 7.5YR2.5/2 brown Ae 0-1 sandy 0 n/a n/a 7.5YR6/2 pinkish grey B l 1-28 silt-sand 10 sub-rnd sch, vie 10YR4/6 dark yellowish brown 0 28-29 sand 0 n/a n/a B2 29-50 fine sand 20-30 sub-rnd, sub-ang gmt, vie, sch 10YR5/2 brown BC 50-80 silt-sand 30 sub-rnd, sub-ang gmt, vie, mfc 7.5YR5/2.5 greyish brown-brown CI 80 -100+ silt-sand 30-45 sub-rnd, rnd grnt, vie, mfc 7.5YR5/2 greyish brown Note: % = percentage; * = Munsell notation (Munsell, 1971); n/a = not applicable; ang = angular; rnd = rounded; sch = sericite schists; gmt = granitoids; vie = green volcancs; mfc = mafic volcanics 50 S3 organic stained Figure 2.15. Soil profile through a regional till frost boil. (A) Typical profile (site L124+00N / 13+00 E). Marker is 20 cm long; (B) Schematic representation of profile. 51 Table 2.3. Soil description of a pit through a mixed till frost boil. Horizon Depth Texture % of Shape of Clast Colour of matrix* (cm) clasts clasts lithology notation name LFH 5 -0 silty 0 n/a n/a 7.5YR2.5/0 black Ah 0 -2 sandy 20 sub-ang, sub-rnd sch, grnt, vie 7.5YR3/2 dark brown B l 2- 12 silt-sand 10 sub-ang, sub-rnd sch, vie 10YR4/4 dark yellowish brown BC 12 - 18 silt-sand 75 sub-ang, sub-rnd grnt, vie, sch 5YR3/2 dark reddish brown R 18- 44+ ang sch Note: % = percentage; * = Munsell notation (Munsell, 1971); n/a = not applicatble; ang = angular; rnd = rounded; sch = sericite schists; grnt = granitoids; vie = green volcancs 52 o Table 2.4. So i l description of a pit dirough an earth hummock. Hor izon Depth Texture % o f Shape of Clast Co lou r of mat r ix* (cm) clasts clasts l i thology notation name LFH 11-0 silty 0 n/a n/a 7.5YR2.5/0 black Ah 0-2 silty 0 n/a n/a 5YR2/2 dark red brown B l 2-8 silt-sand 0 n/a n/a 10YR6/2 light brownish grey B2 8-22 silt-sand 0 n/a n/a 10YR5.5/4 yellowish brown Ah2 22-27 silty 0 n/a n/a 7.5YR3/1 very dark grey CI 27 - 52+ silt-clay 0 n/a n/a 10YR4/2 dark greyish brown Note: % = percentage; * = Munsell notation (Munsell, 1971). n/a = not applicable 5 5 A permafrost continuous horizons discontinuous lenses Figure 2.17. Soil profile through an earth hummock. (A) Typical profile (site L122+OON / 13+40 E). Marker is 20 cm long; (B) Schematic representation of profile. 56 free. B2 horizons occur beneath the active hummock and rise upwards slightly on either side. These horizons are moist because of their proximity to the water table and plastic primarily due to their silt-clay texture . In most soil pits, lenses of semidecomposed organic material occur beneath the B2 horizon. Frozen ground is commonlly seen at these levels. It was observed by the author that the local relief or size of the frost boils and hummocks is related to the depth of the base of the underlying bowl-shaped profile. Frost boils developed in silty-sand regional till are relatively flat-topped, 10 to 40 cm in diameter and have a bowl-shaped profile up to 30 cm depth. In contrast, local stony frost boils are round to elongate in shape with dimensions varying from 1 to 2 m in width for round forms and up to 5 m in length for elongate forms. The bowl-shaped profiles of these frost boils can be up to 0.9 m in depth. Mud and earth hummocks are flat-topped but rise 10 to 20 cm above the surrounding vegetation. From the surface of these hummocks, the bowl-shaped profile can reach depths up to 50 cm, roughly equal to twice the height of the hummock. Generally, the development of patterned ground appears to be related to soil texture, whereby frost boils are better developed in coarser soils. Chapter Three - SAMPLING AND ANALYTICAL METHODS 58 3.1 Site selection Five grid lines were chosen for soil sampling based on the soil geochemical data provided by BHP Minerals Canada Ltd. from their 1991 field season. Soil pit sites along these lines were selected to provide a transect across the mineralized zone and to represent the different overburden types based on surficial material mapping by Ryder (1992) (Figure 3.1 and 3.2). Soil pit sites were located in soils having both anomalous and background gold concentrations. Sites were 10 to 40 m apart and located within 5 m of 1991 soil geochemistry sites. Local stony frost boils were randomly selected for surface sampling in areas with gold concentrations greater than 100 ppb. Three bog sample sites were chosen from seepage zones located within 50 m of soil pits. Regional till samples were selected at roughly equal intervals along a series of four traverse lines extending in a northwest direction, down-ice from the known gold mineralization (Figure 3.1 and 3.2). To determine the extent of down-ice gold dispersion, samples sites were chosen along the peninsula at the northern end of the Wally grid and the first two offshore islands in Spyder Lake, northwest of the grid. Only well-developed frost boils with exotic (regional till) pebbles on the surface were sampled. Water samples were collected from lakes and streams, bogs and soil pits. Sample sites from Spyder Lake were selected at input areas from streams and lakes, one lake outlet and the centre of the lake (Figure 3.1). Several lakes south and southeast of the main study area were randomly sampled during helicopter reconnaissance. Bog water samples were collected from three seepage zones located within 50 m of soil pits (Figure 3.2). Water collected in the bottom of a number of soil pits (up to 20 cm depth) mainly due to the thaw of frozen ground but water from nearby drilling was also noted to infill pits situated downslope from the drilling. Three of these pits were chosen for water sampling: one sample of water from thawing ground and two water samples from pits infilled with drill water. Figure 3.1. Sample location sites for areas around Spyder Lake and the Wally Grid. Refer to Figure 3.2 for sample sites within the Wally Grid. 61 V 3.2 Sample collection A total of 351 samples were collected from the Boston 1 Claim and areas around Spyder Lake. The sample distribution in the various media is shown in Table 3.1. 3.2.1 Soil pits A total of thirty-five pits were dug in soils having anomalous and background gold concentrations (Table 3.2), with most pits being less than 1 m in depth. In all, 216 mineral soil, 35 surface humus (LFH horizons) and three bog samples were collected. Prior to pit excavation, a description of each site was made, including location, topography, slope, drainage, parent material type and location of nearby outcrops. One to two kilograms of the surface humus was collected from within a 50 cm radius around soil pits. Surface organic material was carefully removed using a trowel, taking care to avoid contamination from underlying mineral soil, rock fragments and pebbles, and transferred into large paper bags. The top 15 to 20 cm of organic material from three bog areas was collected into plastic bags using a shovel. Excavation of the soil pits occurred in two phases. The pits were first dug down to frozen ground, the depth measured, and the pits covered with plastic. The frozen ground was left to thaw for one to two weeks, after which the pits were revisited and further excavated down to frozen ground, bedrock or C horizon (parent material). Prior to soil pit descriptions, all pit faces were cleaned off with a trowel. Soil horizons were identified based on colour and texture, marked on one pit face and measured. Data for each soil horizon was recorded in a profile table and included depth, colour, texture, percentage of coarse fragments, shape of coarse fragments and their lithology. Bulk, 10 to 15 kg, samples were collected from the main soil horizons using a trowel, with horizons greater than 20 cm thick being sampled in 15 to 20 cm increments. Smaller, 2 to 5 kg, samples were collected from the minor horizons. All samples were Table 3.1. Sample distribution in various media from the Boston 1 claim and areas around Spyder Lake. Sample Soil pits Bog Local stony Regional till Water type Humus Soil frost boils frost boils Number of samples 35 216 3 52 27 18 63 Table 3.2: Soil pit distribution in relation to gold concentration and surficial material type (Ryder, 1992). Range of Au mineralization > 1000 ppb 100 - 500 ppb 25 - 60 ppb < 8 ppb Overburden type Wv Wv Tp Wv M-Tv M Tp Number of soil pit sites 8 1 5 3 3 5 13 Note: 'Wv' refers to local stony frost boils developed in a thin (< 1 m thick) veneer ; Tp' refers to till plain (> 1 m thick) areas of the ridge, 'M-Tv' refers to areas having a mixed veneer of marine sediments and till; and 'M' refers to marine sediment areas. 64 collected into plastic bags. For each pit, horizons were sampled from the bottom of the pit upwards in order to prevent contamination from the overlying horizons. During sampling, coarse fragments greater than 3 to 5 cm were removed by hand and discarded. Prior to sampling the surfaces of local stony frost boils, site descriptions similar to those for soil pits, were recorded and sketches including dimensions, sample location sites and surface features were drawn. The number of surface samples collected from each frost boil was dependent on its size, but usually four or five samples were collected. One to three kilograms of material from the top 15 cm of the frost boil was collected into plastic bags using a trowel. Rock fragments and pebbles greater than 3 to 5 cm were removed by hand during sampling. 3.2.2 Regional till frost boils Twenty-seven regional till frost boils were sampled: twenty-three from the north end of the Wally Grid and four from the first two offshore islands in Spyder Lake. After pebbles and organic material were removed from the surface of the active frost boil using a trowel (Figure 3.3 A and B), 10 to 15 kg bulk samples were collected from the centre of each frost boil using a shovel, and transferred into plastic bags (Figure 3.3C). During sampling, large pebbles were removed by hand. Sample site descriptions included location, topography, and sample depth. 3.2.3 Water samples A total of eighteen water samples was collected from the study area: twelve from lakes and streams; three from bogs occurring on the Wally Grid and three from the bottoms of soil pits. The polypropylene water bottles used for collection were first cleaned in the laboratory by rinsing the bottles with distilled water and soaking in 50% hydrochloric (HC1) acid solution for approximately one week. 65 Figure 3.3. Sampling of a regional till frost boil: (A) surface features prior to sampling; note only the exotic, regional till pebbles and cobbles on the surface; (B) after the surface stones and moss are removed; (C) after the sample has been taken from the central portion of the active frost boil to a depth of 15 to 20 cm. Hand trowel is 25 cm long. 66 The HC1 acid solution was then decanted and the bottles rinsed thoroughly with distilled water three times. During transport to the field, the bottles were carefully sealed in garbage bags to prevent dust and/or soil contamination prior to sampling. At each sample site, a 125 mL and a 1000 mL bottle were first rinsed several times with the water to be sampled. Samples were collected from lakes and streams 20 to 30 cm below the water surface and 3 to 10 cm below the surface in bogs and soil pits to avoid sampling surface film and debris. Water pH was determined using a portable pH meter at only one site as the meter malfunctioned. A liquid pH indicator (B.D.H. Universal Indicator) was used at subsequent sites, with the resulting colour noted. Within a few hours of collection, the 1000 mL water samples were filtered using a portable compressed nitrogen gas (N2) apparatus. Samples were pressure-filtered through 0.45 um Millipore filters into clean 1000 mL sample bottles. Filters were changed as often as needed, 3 to 5 times per sample, usually when the filtering process was slowing down. In all, the procedure took 20 to 60 minutes per sample to complete, depending upon the amount of suspended material. Acid was not added to the waters for preservation as acid is used in the analytical method to wash the bottles prior to analysis. 3.3 Laboratory preparation methods 3.3.1 Soil pits Soil pit samples were prepared in six phases: 1) preparation of the -212 um fraction (-70 mesh, ASTM) of C horizons; 2) preparation of the -212 urn fraction of A, B and C horizons; 3) detailed preparation of the -53 um fraction (-270 mesh, ASTM) of A, B and C horizons; 4) vegetation and organic horizons and 5) preparation of the -53 pm fraction of surface samples from local stony frost boils. For 67 those soil pits that did not have C horizons, due to encountering either frozen ground or bedrock, the lowermost B horizon was prepared along with the other C horizons. All samples were processed together, with utensils being thoroughly cleaned between samples to prevent contamination. 3.3.1.1 Minus 212 um fraction of C horizons Samples of the lowermost B or C horizons from thirty-three soil pits were prepared using the procedure outlined in Figure 3.4. Each 10 to 15 kg sample was spread out on a clean 6' x 6' plastic tarpaulin, broken up using a trowel and/or rubber mallet, and thoroughly mixed by rolling the sample in on itself from corner to corner. The sample was then coned and quartered with the trowel and two diagonally opposite quarters, representing one half of the sample, were placed in new plastic bags and stored. The remaining half was transferred back to the original sample bag and used for wet sieving. The tarpaulin was washed clean with water and a sponge between each sample. Each split sample was wet sieved into four size fractions: +2000 um, -2000+425 urn, -425+ 212 um and -212 um using an apparatus consisting of stainless steel ASTM sieves stacked on top of a 5 gallon plastic bucket with a modified lid, and hooked up to a recirculating water pump with plastic hoses. Samples were sieved using the recirculated water to prevent loss of fine material that was collected in the 5 gallon plastic buckets during sieving. In the later stages, the sieves were washed with fresh tap water to ensure complete sieving of each size fraction. Sediment from each size fraction was then transferred into glass Pyrex pans lined with clean brown paper and the sieves washed clean with fresh tap water to ensure all material was removed. A dilute (10 mL/L) flocculant solution (Catfloc, cat. no. 61-110) was added to the -212 um slurry and allowed to settle in the plastic buckets for several weeks. At this time, excess water was decanted using the pump. The settled -212 um material was transferred into a paper-lined pyrex pan and the bucket was rinsed out with clean tap water to remove all material. Size fractions were oven dried at 70 to 80°C, transferred to plastic bags using a stainless steel spatula, weighed and stored. 68 o » ? 2 -5-.E CM _ J •<-O) T3 o co co z w o • • § . ? 7 3 CD CD O o CD + W O CM CO T -CL E CO </) "(6 c en o O-<B « c: o o in " O i o in CO m c co <S ._ To O * i <D o 5 p Q . -CO CO <£ o *}• CO FA 5 CO cu 5 CM T— CM JS ._ 3 <1) O 5 5= CO -o Q •a < J - CO I §> £ o> CD co £..«> Q-C0 CO -g-55 a: 5 E 3 -co in + " CM Q> TJ C CO £> Q o CO CO "$ o CO < LL e H u. in CM CM V-f CM + + o m S CM 8 "T o o o CM + CO TJ C CO £• Q o "5 CO C I * ' 5 o •8? ^§ 5.1 OQ 3 < IP o CO • — O co I g §§ .2 + a —1 a , d CL, O § ? CO CN t M CN O —' r* cs to fa M a g 69 The -212 um size fraction was disaggregated with a stainless steel rolling pin and dry sieved through a 212 urn stainless steel sieve: +212 um material was disaggregated further until the entire sample passed through the sieve. The samples were then split using a stainless steel Jones riffle splitter to obtain 30 g subsamples and duplicate subsamples. The rolling pin, splitter, and splitting pans were carefully cleaned with compressed air between samples. Each subsample was analyzed for gold by fire assay-atomic absorption spectrometry (FA-AAS). 3.3.1.2 Minus 212 um fraction of A, B and C horizons Soil pits along three grid lines (120+00 N , 122+00 N , and 124+00 N) were chosen for detailed study based on the evaluation of gold results obtained from the C horizons. For each of these pits, all soil horizons were wet sieved into four size fractions (+2000 um, -2000+425 um, -425+212 um and -212um) and prepared using the same procedure outlined in Section 3.3.1.1 and Figure 3.4. Main soil horizons, 10 to 15 kg, were split into roughly equal portions and one half was transferred into clean plastic bags and stored, while the second half was placed back into the original sample bag for wet sieving. Samples of the minor horizons were generally 2 to 5 kg in size and, therefore, the entire sample was used for wet sieving. Size fractions were oven dried, weighed and stored. The -212 um size fraction was disaggregated with a stainless steel rolling pin, and split into 30 g subsamples, along with duplicate subsamples, and analyzed for gold by FA-AAS. 3.3.1.3 Minus 53 um fraction of A, B and C horizons Five soil pits along Line 124+00 N were chosen for a comparison of gold concentrations between the previously analyzed -212 um size fraction and the -53 um size fraction. The remaining -212 um material from the soil horizons was re-weighed and further sieved into two size fractions (-212+53 um and 70 -53 um) following the procedure outlined in Section 3.3.1.1. These two fractions were oven dried, stored in plastic bags and weighed. After disaggregation of the -53 um fraction was completed using a stainless steel rolling pin, 30 g splits were submitted, with duplicates, for gold determination by FA-AAS. 3.3.1.4 Vegetation and organic horizons LFH samples were partially air dried in the field and further oven dried, at approximately 70° to 80°C, in the laboratory and stored in large paper bags. Samples collected from soil pit sites along Lines 122+00 N and 124+00 N were chosen for preparation, along with several buried, organic-rich lenses and three bog samples (O horizons). LFH horizons and bog samples were prepared using the procedure outlined in Figure 3.5a. LFH samples were placed on clean brown paper and disaggregated mainly by hand, removing any pebbles and rock fragments. Very hard materials were carefully crushed on the paper with a porcelain pestle. Samples were thoroughly mixed by folding the material in on itself from the corners of the paper before being coned and split into roughly equal portions by hand. The two halves were transferred into paper bags; one half was stored while the second half was milled in a Wiley mill at the Department of Soil Science, U.B.C., using a No. 2 screen (approximately 1.0 mm size fraction). Compressed air was used to thoroughly clean the mill between samples. Milled samples were then split in half using a Jones riffle splitter, placed in plastic bags and weighed. One half of the milled samples was stored while the second half was submitted for gold determination by neutron activation analysis (NAA) in pellet form. For a number of samples, the milled second half was also submitted to obtain duplicate analyses. Buried, organic-rich lenses were prepared using the procedure outlined in Figure 3.5b. Samples, usually less than 1 kg, were spread out on clean brown paper and broken up by hand. One large (2 to 5 kg) sample was broken up on clean paper with a trowel and thoroughly mixed by rolling the material in on 71 < CD E o J - T J . ° c L L CO 0> O -E (0 10 CO o TJ & CO CN CO i— CD CN CO TJ - c §5 O >> cz X O LL </) _l C i_ O O T J C CO </> c o N • c o U- O 3 CO CN S> CN CO CO 2 CO '(/) £> TJ O CN 5 CO O IN -A CN O U J v E O + 5 CO U) § r O in 11 O >> O CO V 5 O 2> IN CO • 5 O IN 2 O TO CO M O T 3 a o N •c 0 J3 b CO 1 .§ O O =3 "3 . Sa co E e 3 S "c3 o T 3 O 3 q O U l — ' CS a , " S • a . ju. • a , t* C<J O o E v i cn" u I s o T3 "C 3 X > -o co C o N •c O J3 72 itself. For this sample, material was coned and quartered and two diagonally opposite 1/8 splits transferred onto new paper for further preparation. The remaining material was transferred into a clean plastic bag and stored. All samples were oven dried at 70° to 80°C, carefully disaggregated on clean paper by hand and/or by using a porcelain pestle and stainless steel rolling pin, and dry sieved through a 70 um stainless steel sieve to remove rock fragments. Both size fractions (+70 um and -70 um) were transferred into plastic bags and weighed. For the majority of the samples, the -70 um fraction material weighed less than 50 g and thus, the whole fraction was sent for analysis. Two samples having the -70 urn material > 50 g were split using a Jones riffle splitter to obtain 50 g subsamples and duplicate subsamples. Each subsample was analyzed for gold by NAA in pellet form. Three bog samples (O horizons), 3 to 5 kg in size, were spread out on clean brown paper and broken up using a trowel and by pulling material apart by hand. Each sample was transferred into two paper-lined glass Pyrex pans and oven dried at 70 to 80°C. Dried samples were further disaggregated on clean paper using a porcelain pestle and stainless steel rolling pin and thoroughly mixed by folding the material in on itself. Material was coned and quartered with a trowel, and two diagonally-opposite quarters, representing one half of the samples, were combined in paper bags and set aside. Remaining material was transferred into paper bags and stored. The first half was milled in a Wiley mill using a No. 2 screen, placed in paper bags and weighed. Milled samples were then split into 50 g subsamples, along with duplicate samples, and analyzed for gold by NAA in pellet form. Loss on ignition (LOI) was determined for the LFH horizons by accurately weighing 2 to 3 g of the previously milled material into a crucible. For each batch of samples, six crucibles were placed in a muffle furnace and ashed at 750°C for 12 to 13 hours. The crucibles plus ash were weighed after being left to cool in the muffle furnace. Ash colour (Munsell, 1971) was also determined. 73 3.3.1.5 Minus 53 pm fraction of local stony frost boils Four local stony frost boils located along Lines 120+00 N and 124+00 N were chosen to examine the variability of anomalous gold concentrations across the surface of individual frost boils. Surface (B horizon) samples were wet sieved into five size fractions (+2000 um, -2000+425 um, -425 +212 um, -212+53 umand-53 um) using the procedure outlined in Section 3.3.1.1. Since the sample weights varied from 1 to 3 kg, the entire sample was wet sieved to obtain sufficient -53 um material. Size fractions were oven dried, placed in plastic bags and weighed. After the -53 u.m size fraction was disaggregated with a stainless steel rolling pin, 30 g splits were taken with a Jones riffle splitter and submitted, with duplicates, for gold analysis by FA-AAS. 3.3.2 Regional till frost boils Sample preparation of the regional till frost boil samples involved two major stages. First, size and density fractions of all twenty-seven samples were prepared for gold analysis; then further preparation of size and density fractions of eleven frost boils for a study of particulate gold grains. 3.3.2.1 Size and density fractions for gold analysis Twenty-seven regional till frost boil samples and one anomalous (8410 ppb) C horizon sample, from a soil pit located at Line 124+00 N/11+80 E, were wet sieved into six size fractions: +2000 um, -2000+425 um, -425+212 um, -212+106 um, -106+53 um and -53 um (Figure 3.6a). The regional till samples were placed on a clean plastic tarpaulin, broken up using a trowel and rubber mallet, and thoroughly mixed by folding the material in on itself from the corners. For the first four samples, the material was quartered with a trowel and a 1/8 split was transferred into a plastic bag and stored. The remaining 7/8 of the sample was placed back in the original sample bag and wet sieved as previously 74 CD CO CO to CO cn co m TJ a o o CO CO 2 CO o. E CO (/) _ fo c CL CD "> c o O U ) " O " o in CO in ZJ 0) o -a o 5 q= CO •o Q TJ < O CO I s -JO CO o m + <o" CN o ™ v 2> co 5 T J . co £> T J J L CO o o o I I . 1 0 CM O ^ s i s cs T CN + m o S CO CO CD h— CO . CO CO Q. CO E o o o in ° — < cz o CO Q. CO 1 n\ o co ". (0 CD 1 1 -CO 5 I'g CO r-00 e co CO CD X D) 'co TJ • C CO cn.Q E co <1> Q 5/o cn CO o <jj CO E a> < co "3 o co TJ c CO Gol grai cov grai 2> CO CO CO Q_ o <° i - MO ^ A"? .1= O m CO o CO . V CD c CO TJ c co £< TJ o co CO CO cn<f o < CO I— CO T3 GO CO "3 O 60 .9 2 & "o 0 C 1 60 * 2 —, o rzs 60 n « .11 tw c2 o ^ CO C/l O C £ j co S s CO _ ~ l M ^ CO O U I § O.T3 co o- 2 a. o E cn e c3 B O '5b 1 75 described. Wet sieving of these large samples was a very lengthy process and took an experienced person roughly 3 to 4 working days per sample. For this reason, and since there were a great number of samples to be processed, the remaining mixed samples were quartered with a trowel and two diagonally-opposite quarters, representing one half of the original sample, was combined into plastic bags and wet sieved. The remaining original material from the anomalous C horizon sample was wet sieved upon completion of the regional till samples to avoid contamination. Size fractions were oven dried, placed in plastic bags and weighed. The -53 pm size fraction of the regional till samples and C soil horizon was disaggregated with a rolling pin, and 30 g splits, taken with a Jones riffle splitter, analyzed for gold by FA-AAS. A 50 g split of the -53 um size fraction of regional till was also taken and analyzed for extractable gold by the aqua regia column-inductively coupled plasma (AR column-ICP) method. All twenty-seven -106+53 um fractions and eleven -212+106 um fractions of the regional till frost boils were separated into light and heavy mineral separates using methylene iodide (MEI; S.G. = 3.3) and a 1000 mL separatory funnel. Four samples having weights greater than 1100 g, were split in half using a Jones riffle splitter; each half was treated as a separate sample in order to provide internal sample preparation duplicates. All light mineral fractions (LMFs) and heavy mineral concentrates (FIMCs) were washed thoroughly with acetone, left to air dry in the fume hood for a few days, transferred into preweighed-plastic bags and plastic vials, respectively, and weighed. A 30 g split of the LMFs from the regional till and C horizon, along with duplicates, were taken using a Jones riffle splitter and analyzed for gold by FA-AAS. The HMCs obtained from the regional till samples varied from 13 to 32 g and therefore, the entire sample was analyzed for gold by FA-AAS. HMCs of the C horizon from a soil pit weighed 43 g and 65 g for the two size fractions and thus, were split in two using a Jones riffle splitter: one portion was ananlyzed for gold by FA-AAS, the second portion was set aside for particulate gold grain recovery. 76 3.3.2.2 Size and density fractions for particulate gold grain study Eleven regional till frost boils were chosen to study the size and morphology of particulate gold grains in the regional till. For comparison, the C horizon from a soil pit was chosen to study the size and morphology of particulate gold grains of local origin as a result of a highly anomalous gold value (8410 ppb) from the -212 um fraction material. Regional till samples were selected on the basis of gold results obtained from (i) the -53 um size fraction and (ii) the light and heavy mineral separates from the -106+53 um size fraction. Since the previously prepared regional till FfMCs were destroyed during gold analysis, the remaining original material was wet sieved into six size fractions: +2000 um, -2000+ 425 urn, -425+212 urn, -212+106 urn, -106+53 um and -53 um using the procedure outlined in Section 3.3.1.1 and Figure 3.6b. Size fractions were oven dried, transferred into plastic bags, and weighed. Light and heavy mineral separations were then performed on the new -212+106 um and -106+53 um size fractions, using MEI. The air dried LMFs were transferred into pre-weighed plastic bags, weighed and stored. The HMCs were placed into pre-weighed plastic vials, weighed, and set aside for gold grain recovery. Prior to searching HMCs for particulate gold grains, the number of free gold particles in the -212+106 um and -106+53 pm fraction HMCs were estimated based on the weight and gold content of the HMC and the assumption that the gold particles are spheres of pure gold (S.G. = 19.3 pg/g) with a diameter equal to the logarithmic mean of the size fraction (see Discussion). Only seven regional till samples having estimated numbers of free gold particles greater than 1.0 were chosen for gold grain recovery. Both size fraction HMCs from the C horizon were chosen for recovery because of their high estimated number of free gold grains. HMCs from these selected samples were further separated into magnetic and non-magnetic fractions using a hand magnet. The magnetic fractions were placed into new plastic vials and weighed, while the non-magnetic HMCs were returned to the original plastic vials and set aside for gold grain recovery. 77 3.3.2.2.1 Particulate gold grain recovery The non-magnetic fractions of the -106+53 um HMCs from the C horizon and one regional till frost boil were searched for particulate gold using the following procedure. A small portion of the non-magnetic HMC was transferred to a plastic petri dish and submerged with ethanol to counteract static electricity. The heavy minerals were evenly spread out with a gentle swirling action and then examined on a black background under a binocular microscope. Minerals were manouvered with a few hairs of a modified, fine-haired (000) paint brush. When gold particles were encountered in the C horizon HMC, they were suctioned into a glass pipette by a syringe (connected to the pipette by plastic tubing) and carefully transferred into 5 mL glass vials; these gold grains were set aside for scanning electron microscope (SEM) examination. Recovery of free gold was time consuming and unsuccessful for the regional till frost boil sample. Therefore, the remaining non-magnetic HMCs were further concentrated by panning using a South American batea (processed by Consorminex Inc., Gatineau, Quebec). The non-magnetic HMCs were separated into light and heavy batea fractions, transferred into pre-weighed plastic vials, weighed and set aside for future use. Particulate gold grains were further recovered from the heavy batea fractions using the above procedure but were transferred into small petri dishes using the modified paint brush rather than the syringe apparatus. Recovered gold grains, and a few sulphide grains, were mounted on SEM stubs with double-sided, conductive tape. Mounted grains were studied in secondary and backscatter imagery using a Philips XL30 scanning electron microscope operating at 15 kV. Qualitative and semi-quantitative energy dispersive spectrometry (EDS) was determined using a Princeton Gamma-Tech system. Axial measurements of each grain was determined directly from monitor images using the SEM measurement analysis tool. 78 3.3.3 Water samples Eighteen non-filtered 125 mL water samples were analyzed for their chloride (CI") and sulphate (SO4 2 ") contents. Seventeen filtered 1000 mL samples were analyzed for gold by graphite furnace atomic absorption spectrometry (GFAAS). 3.4 Analytical Methods Gold analyses of soils by FA-AAS and AR column-ICP and of organic samples by NAA were conducted by Chemex Labs Ltd., North Vancouver, B.C. Chloride and sulphate determinations on the 125 mL water samples were performed at the Department of Civil Engineering, U.B.C., whereas gold concentrations of the 1000 mL water samples was determined by G.E.M. Hall using GFAAS at the Geological Survey of Canada, Ottawa, Ontario. 3.4.1 Analysis of soils 3.4.1.1 Fire assay-atomic adsorption spectroscopy (FA-AAS) Thirty gram subsamples of soils and standards were prepared using the classical lead-fire assay procedure (Pb-FA). After fusion of the sample with a flux, the lead button undergoes a low temperature (960°C) cupellation in an oxidative atmosphere. The resulting gold-silver prill is then digested in an aqua regia solution (3:1, HC1: HNO3) and analyzed by atomic absorption spectroscopy (AAS). With this procedure, a lower detection limit of 5 ppb gold is achieved. 79 3.4.1.2 Aqua regia column-inductively coupled plasma spectrometry (AR column-ICP) Thirty to fifty gram subsamples of soils and standards are ashed at 600°C for one hour to destroy organic material. Ashed samples are digested with aqua regia solution for eight hours to solubilize the gold as the AUCI4" ion. The resulting solution is passed through an 80 to 100 mesh (177 to 149 urn) sized, gold selective absorbent resin (100 mg Amberlite XAD-8) that is packed in a lmL syringe. Gold is collected onto the column while matrix elements are not retained on the resin. The column is then eluted with a small volume of ethanol (0.5M HC1 ethanol) and ready for analysis. Analysis of the extracted solution is conducted with a multiple grating diode array spectrometer. The unique optical configuration of the spectrometer allows simultaneous acquisition of background and analytical signals. A gold selective wavelength mask selects only the gold emission lines from the inductively coupled plasma. Both the 242.795 nm line and the 267.595 nm line are observed. The results from both wavelengths are compared to ensure there are no interferences. A detection limit of 0.1 ppb gold is obtained. 3.4.1.3 Neutron activation analysis (NAA) Surface humus (LFH horizon) samples and duplicates comprised the first batch of samples analyzed by neutron activation analysis (NAA). The second batch of analyses consisted of O horizons (bog) and organic-rich lenses along with duplicates and one standard. Prior to analysis, subsamples were air dried at 60°C and milled to approximately 20 mesh (841 um) in a Wiley Mill . Thirty to fifty grams of the milled material were formed into pellets using a hydraulic press and shrink wrapped. These shrink wrapped pellets were then irradiated together with internationally recognized standards, as well as "in 80 house" standards. Samples were then cooled for five days and the gamma activity of the resulting radioactive isotope (411.8 keV) determined by computer aided interactive gamma spectroscopy. The normalized isotope activity was directly compared to activities of the standards irradiated under identical flux conditions. A detection limit of 1 ppb gold is achieved. 3.4.2 Analysis of waters 3.4.2.1 Graphite furnace atomic adsorption spectrometry (GFAAS) The 1000 mL water samples were analyzed for gold using the procedure described by Hall et al. (1986). In summary, dissolved gold in the filtered waters is adsorbed on to activated charcoal that is added to the sample. The charcoal is then filtered off, ashed at 650°C and dissolved with hydrochloric acid (HC1) and this solution diluted by 4 M HC1. Dissolved gold from the samples is then extracted through anion-exchange into methyl-isobutyl-ketone (MIBK) and washed with 0.1 M HC1 to remove any Fe present in solution. These MIBK solutions are then analyzed for gold by GFAAS. A detection limit of 0.5 ppt gold is achieved. 3.4.2.2 Chloride and sulphate Chloride (CI") and sulphate (SO4 2 ") in the 125 mL water samples was determined using the mercuric nitrate method and the turbidimetric method, respectively, as described in the Standard Methods for the Examination of Water and Wastewater, 17th Edition (Clesceri et al., 1989). 81 3.5 Analytical accuracy and precision 3.5.1 Monitoring of analytical accuracy Analytical accuracy and drift were monitored using several reference control standards. For each batch of samples analyzed, 30 or 50 g splits of one or two reference standards were submitted along with the primary samples. Seven analyses of Canadian Certified Reference Materials Project (CCRMP) standard GTS-1 by FA-AAS resulted in a mean of 334 ±11 ppb gold, 3.5% lower than the recommended gold value of 346 ppb (Table 3.3). Three Nevada Bureau of Mines (NBM) standards were analyzed by FA-AAS. Standard NBM-lb yielded a mean gold value of 1478 ±221 ppb. Two gold results for standard NBM-2a were either at or below the detection limit of 5 ppb compared to the recommended value of 9.6 ppb gold (standard deviation not given). This variability can almost certainly be attributed to analytical error. In contrast, standard NBM-2b was analyzed once by FA-AAS resulting in a concentration of 8020 ppb gold , 2.6% greater than the recommended gold value of 7818 ppb. / Results of AR column-ICP analysis of standard GTS-1 and two N B M standards were generally much lower than those obtained by FA-AAS (Table 3.4). For example, two analyses for the GTS-1 standard were, on average, 46.5% lower than the recommended gold value (346 ppb) compared to results 3.5% lower by FA-AAS. Standards NBM-lb and NBM-2a had single analyses that were 34% and 86% lower than their recommended values, respectively. However, since aqua regia is only a partial extraction for gold, results for standard materials are expected to be lower than their recommended values based on "total" extraction techniques. Standard NBM-2a is composed of material from a carbonaceous, limestone-Table 3.3. Gold concentration (ppb) of reference standards analyzed with original soil samples, measured by FA-AAS. Standard GTS-1 NBM-lb NBM-2a NBM-2b Reference 346±16* 1540±103** 9.6±?** 7810±343** value 315 1150 <5 8020 345 1620 5 340 1540 330 1600 325 335 345 Mean 334 1478 5 8020 Standard deviation 11_ 221 ins. ins. ins. = insufficient data for statistical calculations. * Recommended value (Steger, 1986). ** Recommended value (NBM, 1991). Table 3.4. Gold concentration (ppb) of reference standards analyzed with original soil samles, measured by AR column-ICP. Standard GTS-1 NBM-lb NBM-2a Reference value 346±16* 1540±103** 9.6±?** 190 180 1015 0.7 Mean 185 ins. ins. Standard deviation 7 ins. ins. ins. = insufficient data for statistical calculations. * Recommended value (Steger, 1986). ** Recommended value (NBM, 1991). 84 hosted gold deposit at the Jerritt Canyon Mine, Nevada. Gold is commonly absorbed to carbonaceous materials and thus may be responsible for the very low gold recovery from this standard. Standard NBM-2a was submitted with the second batch of organic samples analyzed by NAA. A single analysis gave a gold value of 8 ppb, wthin ± 20% of the recommended value of 9.6 ppb gold. 3.5.1.1 Recovery of gold by AR column-ICP A comparison of the gold analyses obtained for the -53 um fraction of the regional till frost boils by FA-AAS versus AR column-ICP (Figure 3.7) show that the gold results are scattered with the majority of the results by AR column-ICP being lower than those obtained by FA-AAS. The simple linear correlation coefficient (r) for the two sets of analyses is 0.548. Compared to the critical r value of 0.381 (d.f. = 25) for the 0.05 significance level, the comparison between the methods is fairly significant despite the lower AR column-ICP results. Only ten of the twenty-seven samples yielded gold results by the two analytical methods within the ± 50% limits. Since aqua regia digestion is considered to be a partial extraction technique for gold, results by AR column-ICP are expected to be lower than the "total "gold values by FA-AAS. Additional errors that may occur in the AR column method (ie. incomplete adsorption and/or desorption of gold onto and off of the column resin, respectively) may also contribute to the lower gold concentrations. Nevertheless, gold values were successfully obtained for those samples that were below the detection limit of 5 ppb gold for FA-AAS, due to the much lower detection limit of 0.1 ppb gold for AR column-ICP. However, a number of these results were greater than the FA-AAS gold concentrations and lie outside the ± 50% limits. This variability is most likely attributed to the inclusion of particulate gold in the subsamples producing the "nugget effect". 0.1 0.2 0.5 1 2 5 10 20 50 100 Au (ppb) - FA-AAS Figure 3.7. Comparison of gold concentrations (ppb) by FA-AAS versus AR column-ICP for the -53 um size fraction of surface B horizons collected from the centres of regional till frost boils. Samples having gold values below the detection limit of 5 ppb for FA-AAS were plotted as 3 ppb gold. Solid line represents the x = y line; vertical dashed lines represent the ± 50% limits; horizontal dashed line represents FA-AAS detection limit. 86 Statistical hypothesis tests (F- and t-tests) were estimated to determine whether gold results by the two analytical methods are significantly different from one another (Table 3.5). However, due to the scattered nature of the gold results and the low number of sample pairs, linear regression analysis was not conducted. In addition, there were too few pairs of analyses to determine a nonlinear regression equation that would realistically provide an estimate of the standard error (Thompson and Howarth, 1978). 3.5.2 Monitoring of analytical precision Analytical precision was estimated using 46 pairs of duplicate analyses, representing approximately 12% of the samples. Duplicates of the soils and vegetation were prepared by taking representative 30 g splits for FA-AAS and 50 g splits for AR column-ICP and NAA analyses, that were relabelled and analyzed along with the primary samples. An exception was made with the regional till frost boil heavy mineral concentrates (HMCs) due to lack of material to provide duplicate samples. However, four samples were split in two prior to heavy mineral separations in order to provide sample preparation and analytical duplicates. Analyses of duplicate Ah, B and C horizons by FA-AAS were generally precise to within ± 20% for gold concentrations greater than approximately 30 ppb and decreases for lower concentrations (Figure 3.8a). The majority of duplicate gold results from the local stony frost boil and regional till frost boil samples are also precise to within ± 20% (Figure 3.8b and c, respectively). Duplicate gold results of the regional till frost boils by AR column-ICP are generally precise to within ± 50% (Figure 3.9). The duplicates analyzed with the first batch of samples are rather imprecise, having precision greater than ± 50%. In contrast, the second batch of analyses have three of four duplicate analyses within ± 50% analytical precision. 87 Table 3.5. Population statistics and hypothesis test results of gold concentrations in the -53 um fraction of regional till frost boils by FA-AAS and AR column-ICP. If the null hypothesis, HO, is accepted at the 0.05% confidence level, the analyses are indistinguishable. F and t are the calculated F and t statistics, respectively. F* and t* are the critical values at the 0.05% confidence level for n samples. Gold values of < 5 ppb were taken as 3 ppb in the calculations. F-test t-test HO: F < F* HO: -t* > t < +t* Statistics F-test t-test FA-AAS AR column-ICP F F* HO t t* HO n mean 27 27 12.2 6.2 5.58 1.93 rejected 2.27 2.05 rejected st. dev. 16.0 6.8 min. 3 0.2 max. 65 30.8 n = number of samples; st. dev. = standard deviation; min. = minimum value; max. = maximum value -212 pm 1 10 100 1.000 10.000 10 100 1,000 10,000 Au (ppb) - Original Figure 3.8. Comparison of duplicate analyses of (a) Ah, B and C soil pit horizons, (b) regional till frost boils, and (c) local stony frost boils by FA-AAS. Solid line represents the x = y line; dashed lines represent ± 20% and ± 50% analytical precision around the diagonal. Gold values below the detection limit for FA-AAS (5 ppb) were plotted as 3 ppb gold. Figure 3.9. Comparison of duplicate analyses by AR column-ICP of the -53 um fraction of regional till frost boils. Solid line represents the x = y line; dashed lines represent ± 50% analytical precision. 90 Duplicate gold results for the two batches of organic samples analyzed by NAA are illustrated in Figure 3.10. The first batch of analyzed LFH horizon samples were submitted with three duplicate samples that have gold values generally precise to within ± 20%. The second batch of analyses by N A A were submitted with duplicate samples taken from two bog samples and one O horizon. Resulting gold concentrations have a precision to within ± 50%. Three of the previously analyzed LFH horizon samples were resubmitted for gold analysis with the second batch of samples to compare results from the two sets of analyses by NAA. Resulting gold concentrations for the second batch were greater than the previous results, having a precision greater than ± 50%. 5 10 20 50 100 200 500 1,000 Au (ppb) - Original Figure 3.10 . Comparison of duplicate analyses for the 1st and 2nd batches of the milled -1000 pm LFH horizons and Ah and O lenses by NAA. Solid line represents the x = y line; dashed lines represent ± 20% and ± 50% analytical precision limits. Chapter Four - RESULTS 93 4.1 Introduction Soil samples collected from the different types of patterned ground developed in the Quaternary sediments were separated into size and density fractions and analyzed by FA-AAS, to determine the distribution and partitioning of the gold. Later, gold particles retrieved from select density fractions were examined under the scanning electron microscope (SEM) to determine the nature of particulate gold in the till deposits and the relations to subcropping gold mineralization. 4.2 Soil texture and heavy mineral content Surficial materials identified on the Wally Grid have different soil textures (Table 4.1; Figure 4.1). Compared to regional till and locally-derived materials, marine sediments contain the greatest amount of -212 um fraction material. For example, a C horizon of marine sediment below a mud hummock contains 82% of its -2000 um material in the silt-clay (-53 um) fraction. For the regional till, B horizons collected from the central, surface (15 to 20 cm depth) portion of active frost boils, and a C horizon sampled below 50 cm depth, contain roughly equal proportions of material in the fine sand (-212+53 um) and silt-clay fractions: an average of 32% for B horizons and 37% for C horizons. In contrast, 50% of the surface B horizons of locally-derived materials (or local stony frost boils) reside in the silt-clay fraction. Size fraction results from pits in local stony frost boils show that the Ah, B and C horizons contain a higher amount of silt-clay than -212 urn sand; this difference and the amount of silt decreases with depth. For example, surface horizons of local stony frost boils contain, on average, 47% silt-clay material that decreases to 36% in the underlying C horizons. Profiles in mixed till also show a steady decrease in -53 um material with depth. B and C horizons of mixed till have the greatest amount of material in the fine sand fraction; this is similar to results of surface B horizons of regional till frost boils. Table 4.1. Average weight percent (%) distribution of the -2000 pm size fractions of Ah, B and C horizons from the different surficial materials and soil pit profiles. Overburden type Number of samples Horizon Size fraction (um) -2000+425 -425+212 -212+53 -53 Mud hummock 1 B *0.1 5.0 77.9 17.1 Marine sediment 2 C 1.0 1.2 16.3 81.5 **0.35 0.4 4.9 5.6 Regional till 27 B 19.8 15.4 33.4 31.4 frost boils (tops) 4.2 3.2 3.5 5.9 Regional till 1 C 12.7 12.7 37.6 37.0 Local stony 20 B 27.1 7.8 16.3 48.8 frost boils (tops) 6.0 1.4 4.8 8.2 Local stony 3 (Ah) 22.2 12.6 20.1 45.1 frost boil pits 6.1 1.8 4.3 9.5 8 B 21.3 10.0 20.6 48.1 6.4 1.6 4.9 6.9 2 C 16.6 12.4 34.6 36.4 6.3 2.3 8.5 7.2 Mixed till 5 Ah 19.5 13.8 24.3 42.4 frost boil pits 6.7 3.0 8.9 14.0 5 B 16.6 13.9 38.5 31.0 1.7 2.7 8.1 10.2 7 C 15.2 15.4 44.0 25.4 7.8 2.1 9.3 8.3 * = mean; ** = standard deviation; (tops) refers to samples collected from the surface (10 to 15 cm depth) horizons of frost boils; (Ah) refers to samples collected to the sides of local stony frost boils. Sample type Soil horizon 100 80 60 40 20 0 Mud hummock Marine sediment Regional till frost boils (tops) Regional till Local stony frost boils (tops) Local stony frost boil soil pits Mixed till frost boil soil pits Weight percent (%) distribution ii -2000+425 um • -425+212 Ljm II II -212+53 Ljm B -53 Mm Figure 4.1. Average weight percent (%) distribution of the -2000 pm size fraction of Ah, B and C horizons from the different surficial material types and soil pit profiles. 96 Heavy minerals of the -212+106 um and -106+53 pm fractions of eleven regional till frost boils (B horizons) comprise, on average, 2.4% and 3.3% of the material, respectively (Table 4.2). In contrast, a highly anomalous C horizon sample (see Section 4.3.2 below) directly overlying bedrock contains on average, 4.2% and 6.5% heavy minerals in the two size fractions, roughly twice the amount found in the regional till samples. This greater abundance of heavy minerals can most likely be accounted for by its close proximity to weathering, mineralized bedrock. 4.3 Gold distribution in mineral soils 4.3.1 1991 and 1992 Wally Grid data During the 1991 and 1992 field seasons, BHP Minerals Canada Ltd. collected B horizon samples (10 to 15 cm depth) from the Wally Grid, a soil grid 300 to 400 m wide and 1050 m long. In 1991, samples were collected every 10 m along grid lines 100 m apart, whereas in 1992, line spacing was decreased to 50 m and samples collected at 20 m intervals (Clarke and St. Pierre, 1993). A total of 364 samples was collected from the three main surficial material types, classified as till, marine sediments and weathered rock (or local stony frost boils) by Ryder (1992). Samples were sieved to -200 mesh (-70 pm) and analyzed for a 30-element suite by aqua regia inductively coupled plasma (AR-ICP) and for gold by aqua regia atomic absorption (AR-AA). Soil grid geochemical data (see Appendix) were statistically evaluated to determine the associations of anomalous gold values with surficial material type and to identify anomalous zones on the Wally Grid. Logarithmic probability plots were generated for both the 1991 and 1992 gold data using the PROBPLOT program (Stanley, 1987). For each data set, the form of the probability curves are similar and both plots are partitioned into five populations. Threshold gold values that were calculated by PROBPLOT based Table 4.2. Average weight percent distribution of the light mineral fractions (LMF) and heavy mineral concentrates (HMC) of the -212+106 pm and -106+53 pm size fractions of regional till frost boils and one local C horizon. Sample Size / density fraction type -212+106 um -106+53 um LMF HMC LMF HMC Regional till frost *97.6 2.4 96.7 3.3 boils (n= 11) **0.4 0.4 0.7 0.7 local C horizon 95.9 4.2 93.5 6.5 (n=D * = mean; ** = standard deviation. 98 on the mean ± 2 standard deviations for each of the partitioned populations (Stanley, 1987), were also similar. Based on these similarities, the 1991 and 1992 gold data were combined into one data set for further evaluations. Statistical tests were conducted to determine whether this was a valid assumption. To determine the analytical drift within and between the two sets of analyses, gold values of an "in house" standard analyzed several times with the 1991 and 1992 samples were examined. A comparison of the standard's gold concentrations through time (Figure 4.2) shows that the gold values obtained for the two years' data are very similar. Five 1991 analyses resulted in a mean of 48.7 ± 2.3 ppb gold and six 1992 gold analyses resulted in a mean of 48.7 ± 2.1 ppb compared to the standard value of 50 ppb gold (C. Leong, personal communication, 1994). Hypotheses tests were also estimated for the standard gold values to determine whether the means (t-test) and variances (F-test) are significantly different from one another (Table 4.3). The null hypothesis, HO, was accepted for both tests indicating there is no statistical difference between the two sets of data. Therefore, the combined dataset was used in further evaluations. A logarithmic probability plot was then generated for the combined 1991-1992 dataset and was partitioned into five populations (Table 4.4; Figure 4.3). The two lower populations contain slightly greater than 50% of the data (9% and 44%, respectively) having gold values either at or near the lower detection limit; gold values range (± 2 standard deviation threshold limits) from 0.2 to 1.7 ppb and 1.4 to 18.9 ppb, respectively. The middle population (30%) contains weakly to moderately anomalous gold values ranging from 13 to 158 ppb. The upper two populations, comprising 9% and 8% of the data respectively, consist of the moderately anomalous (131 to 1082 ppb) to strongly anomalous (740 to 18454 ppb) gold values. Comparing results of terrain mapping to the distribution of gold in the soil grid samples (Table 4.5), it is apparent that the majority of the moderately to strongly anomalous gold values (ie. values in the 100's to 1000's ppb gold) are essentially associated with materials classified as weathered rock (ie. local stony frost boils) and till- and marine sediment-with weathered rock by Ryder (1992); materials having a high proportion of weathered, mineralized local bedrock. Low gold values are also associated 60 55 + 10% GL 2; 50 < 45 10% 40 Time 1991 J992 Values Values • • Figure 4.2. A comparison of gold concentration (ppb) results through time for an internal standard analyzed with the 1991 and 1992 soil grid samples. Solid line represents the standard gold value (Leong, personal communication, 1994); dashed lines represents ± 10% limits. 100 Table 4.3. Statistics and hypothesis test results of gold concentrations of an internal standard analyzed with the 1991 and 1992 soil grid samples, by AR-AA. The gold values are indistinguishable at the 0.05% confidence level if the null hypothesis, HO, is accepted for both tests. F and t are the calculated F- and t-test statistics, respectively. F* and t* are the critical values at the 0.05% confidence level for n samples. F-test t-test HO: F < F* HO: -t* > t < +t* Statistical Statistics F-test t-test parameters -212 um -53 um F F* HO t t* HO n 5 6 mean 48.7 48.7 st. dev. 2.3 2.1 min 46.0 46.0 max 52.4 51.0 1.28 4.39 accepted 0.08 2.13 accepted n = number of samples; st. dev. = standard deviation; min = minimum value; max = maximum value Table 4.4. Probability plot populations with associated means (in bold), thresholds (± 2 standard deviations) and population percentage for the combined and subdivided 1991 and 1992 Wally Grid soil gold data (ppb). Population Dataset type 1991-1992 Combined 1991-1992 Local 1991-1992 Till (n = 364) (n=119) (n=190) x ± 2 s % x ± 2 s % x ± 2 s % 1 0.2 9.0 4.4 7.0 0.2 12.0 0.6 9.0 0.5 1.7 18.3 1.1 2 1.4 44.0 18.7 35.0 1.0 16.0 5.1 45.9 1.6 18.9 112.7. 2.5 3 12.8 30.0 101.3 28.0 2.3 48.0 45.1 243.5 7.0 158.0 585.3 21.6 4 130.6 9.0 593.6 19.0 20.1 17.5 375.9 1561.3 37.4 1081.7 4106.8 69.6 5 740.1 8.0 2831.4 11.0 57.8 6.5 3695.7 7447.3 110.2 18454.4 19588.4 209.9 "Combined" = all samples together; "Local" = subdivided local stony frost boil samples; "Till" = subdivided local and regional till samples; "x ± 2s" = mean ± 2 standard deviations (thresholds); "%" = population percentage. 103 Table 4.5. Distribution of gold concentration (ppb) in the -70 um fraction of B horizon grid samples, in relation to surficial materials (Ryder, 1992). Surficial materials Weathered rock Till and weathered Marine sediment Till veneer; till plain Marine veneer rock veneer and weathered rock (Tv.Tp) sediment plain (Wv) (T-Wv) (M-Wv) (Mp) 3 120 2 38 15 0 2 6 25 1 6 4 122 2 40 114 0 2 6 27 1 6 4 170 2 48 150 0 2 7 27 1 6 5 192 2 48 2220 0 2 7 27 2 6 5 200 3 50 0 2 7 32 2 7 7 210 3 56 1 2 8 33 2 7 8 240 4 59 1 2 8 35 2 7 8 250 4 61 1 3 8 35 2 8 10 350 5 71 1 3 8 37 2 8 12 360 5 71 1 3 8 38 3 8 13 420 5 84 1 3 8 39 3 9 14 520 6 93 1 3 8 39 3 9 16 740 7 99 1 3 8 44 3 10 21 980 8 105 1 3 9 48 4 11 21 1040 9 113 1 3 9 49 4 14 23 1080 10 120 1 3 9 50 4 16 25 1260 10 156 1 3 9 50 4 23 27 1300 11 160 1 4 9 50 4 24 28 1510 11 172 1 4 9 51 4 27 28 1580 12 220 1 4 10 52 4 32 29 1660 13 230 1 4 10 55 4 52 33 2100 16 240 1 4 10 57 5 61 33 2120 18 260 1 4 11 61 5 61 35 2650 19 310 1 5 11 64 5 80 48 3040 19 340 1 5 12 66 5 780 48 4020 21 340 1 5 12 69 49 4080 21 400 1 5 13 79 56 5670 22 420 2 5 13 84 59 5960 22 490 2 5 14 92 59 6240 24 540 2 5 14 92 61 7230 26 640 2 5 15 110 63 8680 • 30 700 2 5 15 130 73 8850 31 2320 2 5 16 153 99 8960 34 3190 2 5 16 220 110 10550 34 3420 2 5 19 250 11400 34 3560 2 5 19 380 31400 36 3840 8220 2 2 6 6 20 20 670 820 "Weathered rock" = areas with abundant weathered bedrock fragments and local stony frost boils; "till" = local and regional till; "till-" and "marine sediments-and weathered rock" = these materials intermixed with local stony frost boils; "veneer" = materials < 1 m thick; "plain" = materials > 1 m thick. 104 with these materials but may be caused by the misclassification of samples. In contrast, the till and marine sediment materials generally have gold values < 100 ppb but are typically < 25 ppb. The high gold values in these categories are most likely a result of misclassification. Therefore, the two upper probability populations consist of gold values associated with local stony frost boil samples whereas the three lower populations consist primarily of the till (local and regional) and marine sediment gold values; however, a small fraction of local stony frost boil gold values may also be included in the middle population. Contour plots for the soil grid gold data were generated using the P-RES program (Bentzen and Sinclair, 1993). Because of the minimal overlap between thresholds of the partitioned populations, the mean threshold gold values were used for the respective contour intervals except for the highest interval, in which the upper population mean gold value was used. The contour plot for the combined 1991-1992 gold data (Figure 4.4) identifies several linear, north to northwest trending anomalous zones (> 144 ppb) on the western portion of the upper plateau, that are essentially restricted to local stony frost boils and subcropping regolith classified as weathered rock and till with weathered rock by Ryder (1992). A 50 to 200 m break in the extension of the anomalous zone, between Lines 124+00 N and 126+00 N , suggests a lack of mineralization in that area but was later identified during the 1992 drilling program, as a buried valley filled with till 3 to 9 m thick (Clarke and St. Pierre, 1993). Gold concentrations in this and other local and regional till areas are weakly anomalous (1.5 to 15.8 ppb) compared to the local stony frost boil gold values. Nevertheless, if the lower gold contour interval of 15.8 ppb is used to define the anomalous zone, it is 10 to 100 m broader than the zone defined by the 144 ppb interval and outlines the weakly anomalous areas on the western slope and eastern plateau. These local and regional till anomalous zones were not identified when the higher gold values (>144 ppb) were used as the basis of identifying anomalous zones. The 1991-1992 gold data was further subdivided into three subdatasets based on the type of surficial material sampled (ie. local stony frost boils, local and regional till, and marine sediments). 105 co £ lA + + fll ui 0 0 UJ i. m 0 & a «• co CM fl 3 • • • <r co CO f 0 CM Q (0 it n II ii II II z> £ L c » "0 z • H X 19 c 0 c L n u ID 01 • P4 CO z It z Z Z ZCD II II X > 01 It u o CO 0 L 0 + 01 £ Ul CM *> CJ o c II II L • 01 CO • • in . • 3 Q c *. C X 0 II \ M Ul 0 0 o o • .• 03 H * If) a» H H a < * + £ 01 £ U 0 * 01 - o a • T5 H O H CM O a oi * • c * CO o H 1 - £ * (13 0 3 0 CM VI £ I3> 01 +> (fl »* >m H Q I. £ 19 •5 ID m % H CM H en -- i a •5 « ° E 2 "8 « 2 13 ° .1 u o >-<S « x T3 Ul 22 o o '5 3 Os g. Os O —< o. g i / O "o C u. S & S^ s <D O o g h o 3 « rt C o >.2 — « i> .SP b £ tu :5 3 106 Probability and contour plots were not examined for the subdivided marine sediment data because they are essentially restricted to the eastern portion of the grid and commonly have low to non-detectable gold values (Section 4.3.2). The probability plot of gold data for local stony frost boils was interpreted to contain five populations (Table 4.4; Figure 4.5). The two lower populations, representing 7% and 35% of the data respectively, may include missubdivided till samples resulting from the lack of 1992 sample type information. The middle population (28%) consists of gold values ranging from 101 to 585 ppb. Thirty percent of the data (36 samples) comprising the upper two populations have strongly to extremely anomalous gold values (594 to 4107 ppb; 2831 to 19588 ppb, respectively). The contour plot of gold values for local stony frost boils (Figure 4.6) identifies a number of north and north-northwest trending anomalous zones (> 589 ppb) that vary from 10 m to 120 m wide and continue intermittently along the length of the grid, similar to those areas identified in Figure 4.4. The main anomalous zones occur on the western portion of the upper plateau (11+50 E to 12+20 E) and continue down-slope 10 to 40 m, roughly outlining those areas having a thin veneer (<1 m thick) of local stony frost boils and weathered subcrop. A break in the extension of the gold anomaly once again occurs between Lines 124+00 N and 126+00 N , coincident with the valley-filled, regional till plain area. Several spot anomalies occur near the Baseline to the east of the main zones (one outlined by the 107 ppb contour interval), as well as on the lower plain to the west, near the shores of Spyder Lake. Areas of the lower plain are commonly underwater from early spring to mid-July and exposed to wave action while the lake level recedes. The latter anomalous zone was also identified as an area having weathered rock material from local stony frost boils moving downslope into Spyder Lake (Figure 2.8). The probability plot of gold data for local and regional till can be interpreted to contain five populations (Table 4.4; Figure 4.7). The lower two populations represent local and regional till values near the detection limit. The middle population consists of 48% of the data having weakly anomalous gold values ranging from 1.0 to 21.6 ppb; a portion of these gold values correspond to the weakly anomalous o o o o o N: • is Ul <7i T4 o o U i o -rl CM IS (V| •M Ui U i u> <n VI • n •H o IS U> •M III I I o o d- O o Ui I I (V| 111 I I IS Z> ' U i o O o o li T4 <N ah rr~ ZJ iH <M *> ' LCI •Ti <71 •wH -w-i _ J li _ l oz =3 VI x: »-i _ l I I «4 V i I I a • T4 CM <M a li <n I I ~ZL I I 3 : li z> I I O I I TJ • o o o O O V i li li VI Ul • i I I I I I I I I 11 •1 II 1— I I I I 4> • V i • 111 OL O o « U i o z» V i •V »—4 3= X IflELE t—* i — i U a: _ i =1 n I I I I o CM o <M u i * Iii (*i o <M zc I I I I •SI =f-U> <M IS •M Ui o o (Vl IS IS •M U i zi-C£ Ul IT I I IflELE zz\ 2Z a. a I I I I C • tr i Ui cn •jj u> o> Ci Tl is 00 O rt <M •SI ffl 111 V i Ul JZ a: <c I I I I ££ a. I I c • 33 • o •N ZJ, •3Z £t£ I I z> OC I I tL. _j I I , CL • t i i CL i <S| U i O 1 O i tL. • o_ i 108 £ io d 10 (A 5 L 10 c •m CD a a * ai II £ £ 01 +> £ -10 L Z (0 o o o « co co + + + Ul Ul o Ul N o If) H H • • • • H o co II ii II II II c X 10 c O (0 01 • H Z z z z p* 01 10 CJ o CO co c q L 0 + 01 £ Ul Ul 0 0 If) a CM CJ in (S • • 10 MJ If) c r- • L a • so II II L • • 00 0 00 3 IA H • 01 co If) H 0 N 00 • • Ul 1 . "0 • 3 1 ! c - II II It. a c j 1 ! 0 L c X 0 II * 1 ! 0 O X > M Ul 0 0 • <J * + 3> *-« Ul - 0 (0 L 3 u. CM 3> (Tt C <n o H 10 en o H j £ <~ * J § 5 c o O J3 to P § rt E t o 3 ^ co "O o "7=; O » x> •£ O . 8 c o c o CO B O o o O N 3 2 O • a . O N IS C3 :§"§ > 5. 2 | 3 -t3 c o <4_, <u o 1<2^ Q."*-! CO ts o 3 3 i g co "g rt 3 O »3 — © S oi u tt. -5 3 109 GO. or => i_i »—« z: x or a O o o L n Ln N • CN *4 v> CO fx v> o o» o LA ah-a» a - *•-* <M <M u- o *- CO V i O-O o ft o o V ) II U l o z> > *• o U i U i o o II o o *4 CM cn 0*1 41 • I N  C i _ l II or —* vi i O • CM a II —1 z: Z 1 X II or *-* • i TJ ' O o O o o V i II =i •— II II II II *-* i *> • U l II V i V i *— i V i • II o o <M a- ^ »-i U l LU z »—. or i X II a> U i CO CM CM z> _ l <_> _ i i O o 00 i— II o U i O U> C£ CO z =i I o U i <M <M v> o ro f»i I X V I U l <c z: o_ i C • CM o rx :t- OC l-l • i a > m CM CO U l o o o o ^4 U l U l CC a. i v < • V I z: <r n i o O o CM =J or => C£ or a . *4 <N *• U i o. ! CM m a- U i o a. e ZS. o I o •3 o 4 u o CM C i 01 0*1 Ul a. U © I— to CO o o C N ON ON O N ON "8 - a ••e 3 co <D M3 2 w -=! "S, ^ c3 I ^ 3 S 2.8 p o * l 110 zone (15.8 to 144 ppb) identified in Figure 4.4. The upper two populations represent 17.5% and 6.5% of the data, respectively, and include the moderately anomalous (20 to 70 ppb) to strongly anomalous (58 to 210 ppb) gold values. The gold contour plot for the local and regional till data (Figure 4.8) identifies two anomalous zones (> 20.9 ppb) along the central portion of the upper plateau, trending north to northwest, coincident with the last glacial direction. These irregularly-shaped gold anomalies vary from 20 to 240 m wide and 150 to 400 m long, and appear to be 10 to 100 m broader than the above mentioned local stony frost boil anomalies (Figure 4.6). An even broader zone is identified if the lower 2.4 ppb contour is used to define the extent of the anomalous zone. This is especially the case for the zone at the northern end of the grid that continues from the Baseline westward onto the western slope and further north near the shores of Spyder Lake. Additional anomalous zones occur on the southern portion of the western slope-lower plain that were not apparent in the local stony frost boil diagram, perhaps mainly due to the lack of frost boil samples in those areas. However, this latter anomalous zone was identified in the combined 1991-1992 gold contour plot but only when the lower 15.8 ppb contour was used to determine the extent of the anomaly (Figure 4.4). Therefore, broader anomalous zones are apparent if the lower local and regional till gold values are used as contour intervals. / 4.3.2 Lowermost B and C soil horizons: -212 pm fraction Gold concentrations of the lowermost B and C horizons from thirty-three soil pits were measured to identify the spatial distribution of anomalous gold values along three sampling lines on the Wally Grid. Gold results vary considerably between and within overburden types. The -212 pm size fraction of the lowermost B and C horizons has gold values ranging from < 5 to 8410 ppb (Table 4.6). Comparing I l l o o X. 10 L ft Q -L ID C CD o o ID » 09 o N +* a O o • N • (A 3 •H (Ti SO 00 • N <X +1 •H N H o CO 01 ID II £ II II II II II 3 01 £ c TJ c •H X ID c Q L ID ID 0) *» n Z ID z Z z z Ql ID U O •H c o L 0 • ai £ O a IM U • r» 01 o c Ul ID 00 in c o • • o L a n II L n o • • 3 01 H s0 N 0 N • • Ul . 1 . t) —> • 3 1 c •H II n «*. Q c 0 c X 0 II 1 ! 0 a X > M u o 0 • * + * o N -Oi <0 (Ti 0 H 0 J H — o» •* 5, «J ~ o <= 2 o 73 ^ 2 ^ 75 ^ S «J g i- i s § * <3-«3 1.1 73 _g - H> 3 IS — o a -s 60^ P a , 2 8 § XI u 73 co o c o o • o\ -g 2 5. _ o. £ >> T 3 IS •? £ ^ o. U Q . ^ 1 CO t_ « 3 3 ~» co o J2 — • -g J? c S > .2 U 2 tS 75-| CO 1) P a , 1 Table 4.6. Gold concentration (ppb) of the -212 um size fraction of the lowermost B and C soil pit horizons, measured by FA-AAS. Location: Overburden Sample Soil Au Northing/Easting material number horizon (ppb) L120+00 N 11+30 Tv-Wv 092 B 45 11+45 Tv-Wv 087 C 955 11+70 Wv 081 C 5160 11+90 M-Wv 146 Bm <5 12+10 Wv 140 B2 <5 12+30 Tp 130 C 15 12+50 Tp 135 B2 <5 12+80 Tp 098 C <5 13+00 Tp 107 C2 <5 13+20 Tp 125 C3 <5 L 122+00 N 11+10 Tv-Wv 199 C2 <5 11+30 Tv-Wv 188 CI <5 11+50 Tv 170 C3 <5 11+80 Wv 307 C 65 12+10 Wv 154 B2 55 12+30 Wv 300 C2 15 12+60 Mp 160 B2 <5 13+00 Mp 113 C <5 13+40 Mp 116 B2 <5 L 124+00 N 10+85 M-Wv 282 - - B4 <5 11+10 M-Wv 275 . C 35 11+20 T-Wv 227 C2 1860 11+40 T-Wv 183 C2 <5 11+70 Wv 218 CI 10 11+80 Wv 203 B3 8410 12+00 Tv 177 C2 <5 12+20 Wv 210 B3 35 13+05 Tp 270 C <5 L 125+00 N 11+40 Tp 285 C <5 11+60 Tp 321 C2 <5 11+90 Tp 314 C2 <5 L 126+00 N 11+40 Tp 328 C2 <5 11+60 Tp 293 C2 <5 Wv = weathered rock veneer or local stony frost boils; Tv-Wv = till veneer (<1 m thick) with weathered rock; M-Wv = marine sediments with weathered rock; Tp = till plain (>1 m thick); Mp = marine sediment plain. 113 results of terrain mapping (Ryder, 1992) to the distribution of gold in the lowermost horizons, it is apparent that the moderately anomalous (35 to 65 ppb) to strongly anomalous (955 to 8410 ppb) gold values are essentially restricted to materials having a large component of local bedrock or occurring immediately adjacent to mineralized subcrop or bedrock (Table 4.7). In contrast to the strongly anomalous gold values associated with weathered rock, C horizon gold values from till and marine sediments range from <5 to 35 ppb but are typically <5 ppb. Gold concentrations of the lowermost soil horizons are shown in plan view in Figure 4.9 and in cross section view in Figures 4.10 to 4.12 (see Section 4.3.3). On Line 120+00 N , a 40 m wide gold anomalous zone is apparent from the base of the western slope up to the western portion of the upper plateau with gold values of 45, 955 and 5160 ppb. As mentioned above, the strongly anomalous gold values are associated with horizons having a large proportion of local bedrock (eg. local stony frost boils; 5160 ppb in this case), and with horizons directly overlying mineralized bedrock (eg. 955 ppb). Along Line 122+00 N , a 50 m wide anomalous gold zone is apparent on the plateau and has moderately anomalous gold values ranging from 15 to 65 ppb. This zone is coincident with areas classified as weathered rock by Ryder (1992) (Table 4.7; Figure 4.11). Two anomalous zones are apparent along Line 124+00 N that are about 30 m apart. A 10 m wide zone at the base of the western slope has gold values of 35 and 1860 ppb and correspond to horizons directly overlying sheared, mineralized bedrock. A second 50 m wide anomalous zone is associated with gold values of 10, 35 and 8410 ppb that occur on the upper plateau areas classified as weathered rock by Ryder (1992). A strongly anomalous (8410 ppb) gold value belongs to a sample collected from the bottom of a local stony frost boil, directly overlying bedrock. The remaining lowermost horizons from local and regional till and marine sediments have gold concentrations of <5 ppb. 114 Table 4.7. Gold distribution (ppb) of the -212 um size fraction of the lowermost B and C horizons from soil pits, in relation to surficial materials (Ryder, 1992). Surficial materials Weathered Till and Marine sediment Till veneer; Marine rock veneer weathered rock and weathered till plain sediment (Wv) (T-Wv) rock (M-Wv) (Tv, Tp) plain (Mp) <5 <5 <5 <5 <5 10 <5 <5 <5 <5 15 <5 <5 <5 35 45 <5 55 955 <5 65 1860 <5 5160 <5 8410 <5 <5 <5 <5 <5 15 35 "Weathered rock" refers to areas with local stony stony frost boils; "till-" and "marine sediments and weathered rock" refers to these areas intermixed with local stony frost boils; "till veneer; till plain" refers to local and regional till areas. / 115 116 4.3.3 A, B and C soil horizons: -212 um fraction A, B and C horizons from fourteen selected soil pits were analyzed to determine the vertical distribution of gold among soil horizons from frost boils developed in the different Quaternary sediments. Gold results of the -212 pm fraction of pit horizons along Lines 120+00 N , 122+00 N and 124+00 N , measured by FA-AAS, are shown in a cross section view with the surface humus (LFH horizon) gold values, measured by NAA, in Figures 4.10, 4.11 and 4.12, respectively. As noted in the previous section, gold concentrations are generally greatest for soil profiles in local stony frost boils and for soil horizons directly overlying mineralized bedrock. For the majority of the pit profiles, gold concentrations decrease from the A and B horizons to the lower C horizons. This is especially the case with mixed till frost boils and earth and mud hummocks that occur directly over buried regional till and marine sediments, respectively; these materials typically have gold values below or near the 5 ppb detection limit for FA-AAS. Therefore, anomalous gold zones are broader in the near-surface A and B horizons than the lowermost B and C horizons. For example, along Grid line 120+00 N , near-surface soil horizons show a 50 m wide gold anomaly that is 10 m wider than the zone defined by the gold values of the underlying horizon . Similarly, the upper A and B horizons along Lines 122+00 N and 124+00 N define an anomalous zone 110 m and 80 m wide, respectively, compared to 50 m and 70 m wide anomalous zones defined by the gold content of underlying C horizons. Exceptions occur, however, where the lowermost soil horizon directly overlies mineralized bedrock and thus gold concentrations increase with depth. Numerous soil pits along the three sampling lines have buried organic-rich (Ah or O) lenses that in most cases, have gold values greater than the underlying and/or overlying soil horizons. This is especially the case for organic lenses within or overlying mixed (local) till and marine sediments. For example, along Line 120+00 N (Figure 4.10), the soil pit on the western slope (11+30 E) has two organic lenses having gold values of 212 and 180 ppb compared to 45 ppb gold for the lower B horizon. Similarly, the soil pit at 117 P co CO l i II CM >— 8 O 00 -? CN « T— o to CO to c-r~ CM CN CO - C _ . C - C < O < < co a: o o o £= O O O L O O CD T- CO -<f CO S Ol I D to r -CN CO CN LO ^ O CO CM CO CO r - » - CO CO 10 CN r CN r . < m m < U 8 8 LO CO <5 LO LO O CO LO CN OS cn LO o r-co co r oi c« fc . . < m m m O U 3 < (qdd) o co o co o LO CN LO LO O) SZ (cm) *~ Dept (cm) o LO LO CN Horizon Ah ffl B2 o Horizon 3 O -E CO CD "1 CO O .tj ° - § O CO o LO V _tg CD CD C §2 o 2 CD SI CD CD CD c u o a: o o L_ T J CD XI XI CD =y CO 1 CD c U l 8 + LU 8 + CN "S a> CL E 8 u "c CO o s Q . cu •g "co cu o TJ c 2 CL CO Q CD o z H I ^ a: LU co 1 - ? 8 8 ^ - a 3 CO <u co CL C D •S * +-» O 8 J CO -fi 'I § co OQ •!*! o o CO 9<S 3 CD a CO C co C e =*• 3 C N •S3 J 3 c co .a •§ "o r=j ? O o 0 - 0 ;^ S! 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C N CN CD c 1 3 co cS CD E CO C O N •c O JZ M 2 a C O r=: O wT 3 (~o >i 3 — Pi J3 o 3 CO O l -• E d * 60 c > c o *•*-» o CD co s O CD c o - eg " s L - O CJeg • 3 C N co i "I -o -d E ^ p S" E co a o o o o 120 11+40 E along the western slope of Line 124+00 N (Figure 4.12) has a buried organic lense with a gold value of 60 ppb compared to the overlying B horizon and underlying C horizons that have gold values either at or below the 5 ppb detection limit. A comparison of the B horizon colour (Munsell, 1971) and associated gold concentrations (ppb) of the local stony frost boil soil pit horizons are shown in Table 4.8. It is apparent that the weakly anomalous gold values (15 to 95 ppb) are mainly associated with the medium to yellowish brown (10YR 4/3 to 4/4) horizon colours, but several are also associated with a strong brown (7.5YR 4/4 to 5/6) colour. A similar trend occurs with the moderately anomalous (100 to 775 ppb) and strongly anomalous (> 1320 ppb) gold values but are generally associated with the medium to strong brown (7.5YR 4/4 to 5/6) and reddish brown (5YR 3/4 to 4/4) soil horizon colours. 4.3.4 A, B and C soil horizons: -53 um fraction Five soil pit profiles along Line 124+00 N were selected to determine the partitioning of gold between the -212 um and -53 um size fractions. Results for the A, B and C soil pit horizons show that the -53 urn fraction consistently contains greater gold values than the -212 um fraction (Table 4.9; Figures 4.13 and 4.14). Most notably, the lowermost B and C horizons from mixed till frost boil soil pits that had gold values for the -212 pm fraction at or below the detection limit for FA-AAS (5 ppb) often yielded low but detectable gold values for the -53 pm fraction (Figure 4.13). A comparison of the gold values for both size fractions down profile (Figure 4.14) also illustrates that the -53 pm fraction gold values are greater than those for the -212 pm fraction. As noted in the previous section, gold values generally decrease with depth, from the near-surface A and B horizons to the lowermost C horizons. It is also apparent that the local stony frost boil B horizons have gold values generally 10 to 100 times greater than the mixed till B horizons. Table 4.8. Comparison of gold concentration (ppb) of the -212 um fraction of B and C horizons from local stony frost boil soil pits, and associated soil horizon colour (Munsell, 1971). Location/ Sample number Soil horizon Au(ppb)_ -212 um Munsell colour notation name L120+00N 11+70E 085 084 081 Bl B2 C 3910 2660 5160 7.5YR 5/6 7.5YR4/4 5YR4/4 strong brown medium brown reddish brown L122+00N 11+80E 311 310 309 308 Bl Bl B2 BC 495 115 250 50 10YR4/4 7.5YR 5/5 7.5YR 5/6 10YR4/2 dark yellowish brown brown strong brown dark greyish brown 12+10E 152 153 154 Bl Bl B2 35 150 55 10YR4/3 10YR4/3 10YR 3/2 medium brown medium brown dark greyish brown 12+30 E 302 305 301 B2 B3 CI 415 450 95 10YR 5/6 10YR4/3 10YR4/3 yellowish brown medium brown dark greyish brown L124+00N 11+70E 219 220 221 Bl B2 B3 1510 3570 1320 7.5YR 5/4 7.5YR4/4 7.5YR 5/4 brown medium brown brown 11+80E 202 204 203 Bl B2 B3 4620 5YR 4/3 dark reddish brown 6690 5YR 4/4 reddish brown 8410 5YR4/4 reddish brown 12+20 E 208 209 210 Bl B2 B3 45 30 35 7.5YR 5/6 7.5YR 5/5 7.5YR4/4 strong brown strong brown medium brown Table 4.9 Gold concentration (ppb) of the -212 u.m and -53 um size fractions of the Ah, B and C horizons from mixed till and local stony frost boil soil pits, along Line 124+00 N, measured by FA-AAS. Location/ sample number Soil pit type Soil horizon Size fraction (um) -212 -53 11+40E 178 179 181 182 183 Mixed till frost boil Ah B CI CI C2 75 <5 <5 5 <5 105 20 30 55 20 11+70 E 213 214 216 217 218 219 220 221 Mixed till frost boil Local stony frost boil Ah B l BC CI CI B l B2 B3 325 345 160 10 10 1510 3570 1320 395 535 295 30 55 2160 4670 2180 11+80E 200 204 202 203 205 201 Local stony frost boil Ah B2 Bl B3 O CI 775 6690 4620 8410 580 60 1040 8280 5580 10280 1010 140 12+00E 171 172 173 174 175 176 177 Mixed till frost boil Ae Ah Bl B2 BC CI C2 25 130 30 20 <5 <5 <5 30 195 ins. ins. 10 20 5 12+20E 208 209 210 211 212 Local stony frost boil Mixed till frost boil Bl B2 B3 Ah BC 45 30 35 70 5 70 45 50 80 30 ins. = insufficient material for analysis. 1 10 100- 1,000 10,000 100,000 Au (ppb) of-212 |jm size fraction Mixed till frost boils Local stony frost boils A & B horizons C horizons A & B horizons C horizons o • O Figure 4.13. Comparison of gold concentrations (ppb) in the -212 um versus -53 um size fraction of Ah, B and C soil pit horizons along Line 124+00 N, measured by FA-AAS. Gold values for the -212 um size fraction below the FA-AAS detection limit (5 ppb gold) are plotted as having values of 3 ppb. i i i i i i i i i i i i i i i i u i i i i i i i i i i i i i i i i i i i i T i i i i i i i i i i i l l i i ^ ^ ^ ^ ^ H ^ ^ ^ ^ ^ H MMimTmiunnmmiH^ irrniiiiTiimmm^ ^ i m R i m u i m u M M M m i M ^ InmiuTiuiiiiTiriiTi^  Ah Mixed till frost boils Ah Local stony frost boils IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIIIIIII l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l B IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIHHIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIillllllllllll IIIIIIIIIIIIIIIIIII1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1IIIIIIIIIIIHIIIIIIII l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l I l l l l l l l l l l l l l l l I l l l l l l l l l l l l l I I l l l l l l l l l l l l l l l l I l l l l i IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l I l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l IIIIIIIIIIIIIIMIIIIIIIIIII!!!!!!!! I l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l i l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l in i l l l l o c ) l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l<l l l l" l>l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l I I I I I I I I I I I I I I I I I I I I I I I I I I I I I | _ L ' I ' l l _l ' 10 100 1,000 Au (ppb) 10,000 100,000 -212 |jm m -53 Mm Figure 4.14. Gold concentration (ppb) of the -212 um and -53 um size fractions of the A, B, O and C horizons from mixed till and local stony frost boil soil pits along Line 124+00 N , measured by FA-AAS. 125 Hypothesis tests were conducted for the -212 um and -53 um size fraction gold concentrations to determine whether the variances (F-test) and means (t-test) of the results are significantly different from one another (Table 4.10). The null hypothesis, HO, was accepted for the F-test whereas, HO rejected for the t-test, indicating the means are different at the 0.05% confidence level. However, a Pearson correlation coefficient of 0.99 is highly significant since the critical r value at the .05% confidence level is 0.413 (df= 21). This suggests that there is a strong linear relation between gold values from the two size fractions. 4.3.5 Surface horizons of local stony frost boils: -53 um fraction Surface (10 to 15 cm depth) B horizons from the active portion of selected local stony frost boils along Lines 120+00 N and 124+00 N were chosen to examine the variability of gold values across the surface of individual frost boils, and to determine the effects, if any, of frost boil development on gold distribution. Gold results of the -53 um fraction vary greatly among the four frost boils sampled, with values ranging considerably from 5 to 9190 ppb gold (Table 4.11; Figure 4.15A and B, respectively). However, gold values from the surface of individual frost boils are not as widely varied. For example, two of the four frost boils have weakly to moderately anomalous gold values (5 to 15 ppb and 80 to 125 ppb, respectively), while the two remaining frost boils have strongly anomalous gold values (1290 to 2630 ppb; 6490 to 9190 ppb). In addition, there appears to be no systematic variation in gold concentrations across the surface of each frost boil, ie. between the centres and edges (Figure 4.15A and B). Analysis of variance (ANOVA) test was performed on the gold results to determine if the variability of gold concentrations between frost boils is greater than the variation within each frost boil (Table 4.12). The null hypothesis is rejected indicating that the gold values between local stony frost boils are greater than the differences within an individual frost boil. 126 Table 4.10. Population statistics and hypothesis test results of gold concentrations of the -212 pm and -53 pm size fractions of Ah, B, and C horizons. F and t are the calculated F- and t-test statistics, respectively; F* and t* are the critical values at the 0.05% confidence level for n samples. Gold values of < 5 ppb for the -212 pm fraction were taken as 3 ppb in the calculations. F-test t-test HO: F < F* HO: -t* > t < +t* Statistics F-test t-test -212 pm -53 um F p* HO t t* HO n mean 29 993.9 29 1290.2 1.51 1.85 accepted -3.167 1.701 rejected st. dev. 2122.8 2612.2 min. 3 5 max. 8410 10280 n = number of samples; st. dev. = standard deviation; min. = minimum value; max. = maximum value Table 4.11. Gold concentration (ppb) of the -53 pm fraction of surface local stony frost boil B horizons, measured by FA-AAS, and associated soil horizon colour (Munsell, 1971). Location/ sample number Au (ppb) Surface horizon colour notation name L120+00N/ 11+70 E 253 254 255 256 11+90E 246 247 248 249 250 251 252 L124+00N/ 11+70 E 356 357 358 359 360 1670 1290 2630 1430 *1755 **604 15 15 10 5 5 15 5 10 5 125 80 95 120 120 108 20 5YR4/3 reddish brown 7;5YR4/4to 7.5YR4/6 (medium) brown strong brown 10YR 3/3 to T0YR 4/5 dark brown dark yellowish brown 11+85 E 344 345 346 347 6490 9190 7030 9110 7955 1210 5YR4/4 reddish brown * = mean; ** = standard deviation A) Line 120+00N • Surface sample site 120 Au value (ppb) 5YR 4/4 Munsell soil colour / m ( 5 5YR4/4 ^ 7.5YR4/4 / /"^• ^Ssv^ / ( 2630 « \ I ' / 1290] \ • y 15 • 10 \ • \ 1670 / \ 1430 / / • • 15 •5 ^ • ) 5 J (1.6 mX 1.1 m) (5.1 mX1.9m) 11+70E 11+90 E B) Line 124+00N 11+70 E 11+85 E Figure 4.15. Plan view distribution of gold concentration (ppb) in the -53 um fraction of surface B horizons from local stony frost boils along: (A) Line 120+00 N and (B) Line 124+00 N, measured by FA-AAS. Associated soil horizon colour (Munsell, 1971) is also noted. 129 Table 4.12. Analysis of variance (ANOVA) results for gold values of -53 pm fraction of B horizons from surfaces of local stony frost boils. F is the calculated F statistic for ANOVA. F* is the critical value at the 0.05% confidence level for n samples. Null hypothesis HO = F < F* Dependent variable Multiple R Squared multiple R -53 um fraction Au (ppb) 0.982 0.964 Analysis of variance Source of variation Sum of squares Degress of freedom Mean square F F* HO Between groups Within groups 1.88E+08 6957480 3 16 6.26E+07 143.878 434842.5 2.24 rejected Total 19 130 A relation between soil horizon colour and associated gold values is apparent for these local stony frost boils (Table 4.11), similar to results identified in section 4.3.3 (Table 4.8). The weakly and moderately anomalous (5 to 15 ppb; 80 to 125 ppb) gold values have a medium brown (7.5YR 4/4 to 4/6) and dark yellowish brown (10YR 3/3 to 4/4) surface colour, respectively. These local stony frost boils are developed in a (local) till veneer (< 1 m thick) on the upper plateau. In contrast, the two remaining frost boils have strongly anomalous (1290 to 9190 ppb) gold values associated with a reddish brown (5YR 4/3 to 4/4) surface colour and are developed in pockets of marine sediment that overlie a till veneer. 4.3.6 Regional till frost boils Gold concentrations were determined for size and density fractions of twenty-seven regional till frost boils from the peninsula at the northern end of the Wally Grid and the first two offshore islands. Gold concentrations in the -53 pm size fraction, determined by FA-AAS, have values ranging from < 5 to 65 ppb (Table 4.13). The distribution of these values is shown in a plan view, bubble plot diagram (Figure 4.16). The smallest bubble size corresponds to gold values less than the FA-AAS detection limit (5 ppb) and remaining intervals are based on the mean ± 0.5, +1.0, +1.5 and >1.5 standard deviations. The eleven sites with gold values greater than the 5 ppb detection limit (Figure 4.16) appear to define a weak anomalous gold zone in the regional till. It is detectable for about 1500 m in a northwest direction along the central portion of the northern peninsula and offshore islands, a direction coincident with the ice flow during the last glaciation. It should be noted that the apparent orientation and width of this gold anomaly may be partly due to constraints of the sample sites being oriented in a northwest direction along a narrow zone. Thus, the exact dimensions of the anomaly cannot be known for certain without further sampling in Spyder Lake. Nevertheless, as gold was detected in the distal samples along the peninsula and the two offshore islands, this suggests that a down-ice gold anomaly does extend in that general direction. The same -53 pm fraction samples were analyzed by the AR column-ICP method, having a detection limit of 0.1 ppb gold, in an attempt to better define the distribution of gold. Gold concentrations were detectable for all samples, Table 4.13. Gold concentration (ppb) of the -212+106 pm and -106+53 pm density fractions of regional till frost boils and one C soil pit horizon, measured by FA-AAS, and -53 pm fraction measured by FA-AAS and AR column-ICP. Sample Size fraction (um) number -212+106 -106+53 -53 -53* LMF HMC LMF HMC 049 <5 <5 <5 1.6 053 <5 <5 <5 1.5 054 <5 <5 10 6.2 055 <5 <5 <5 360 <5 5.8 056 <5 15 <5 <5 <5 3.3 057 <5 35 <5 1.7 058 <5 <5 <5 120 <5 9.7 059 <5 <5 ,<5 <5 15 1.6 060 <5 <5 <5 1.7 061 <5 <5 <5 <5 45 2.1 062 <5 <5 <5 1030 <5 3.5 063 <5 150 10 15.5 070 <5 65 <5 370 20 11.9 071 <5 110 10 3.8 72A <5 55 <5 6.2 72B <5 <5 <5 — 073 <5 <5 <5 25 <5 3.7 074 <5 <5 <5 40 65 30.8 075 <5 <5 <5 0.8 076 <=5 250 35 13.3 077 <5 105 20 8.7 78A <5 5 <5 0.6 78B <5 <5 <5 ~ 79A <5 15 <5 0.2 79B <5 <5 <5 — 80A <5 60 <5 6.0 80B <5 120 <5 6.0 257 <5 <5 <5 <5 40 2.0 258 <5 25 10 5.8 259 <5 <5 <5 45 <5 3.0 260 <5 315 <5 17.4 203** 330 49 302 335 27 977 10 280 -* = analyzed by AR coiumn-ICP; ** = C horizon soil pit sample; -- - material not available for analysis. 132 E 8 I CO co \ Si CL CL 5 < o 00 CD CM CN CN CO • i l CD in 1 CO T— CD CO V LO CM CN A •' • • • • • CL e o x> n CO CD CL O CO «•— o CO cu CD n o CD — o CO -r3 o o O =5 HI 8 LU 8 LU 8 UJ 8 LU 8 + o CO CO 2 "o •=> a -Si £ i •S3 c8 ° c "8 C CO 3 J2 •Si +-> c 13 !§ O C '5b 5 V—i O CO CO _N 'co S co i cu •5 o C 0 1 CD T3 X> &•« c S e -5 § 1 8 1 . "o V© GO c o cu T3 T3 Ut CO S CO A 5 a A E a a 133 with values ranging from 0.2 to 30.8 ppb gold (Table 4.13). However, most of the above mentioned eleven samples with detectable gold values by FA-AAS have lower gold values by AR column-ICP. Considering that the AR column-ICP method is a partial extraction technique for gold, concentrations are unlikely to be greater than those obtained by FA-AAS, which is considered to yield total gold values. In addition, a number of errors may occur with the AR column-ICP method (ie. incomplete dissolution of gold or incomplete adsorption or desorption of gold onto, or off of, the column resin, respectively) and may account for the lower gold values. For seven samples, however, gold concentrations are greater than the FA-AAS results and can most likely be accounted for by the nugget effect, whereby the inclusion of a particulate gold grain in the subsample may produce a gold concentration greater than the true value. The plan view bubble plot of the AR column-ICP gold values is shown in Figure 4.17. Due to the much lower detection limit than FA-AAS (0.1 ppb compared to 5 ppb), the smallest bubble size consists of gold values <0.75 standard deviation rather than less than the detection limit. Remaining intervals are similar to the FA-AAS intervals (±0.5, +1.0, +1.5 and >1.5 standard deviations about the mean). It is quite apparent from the bubble plot of the AR column-ICP gold results that a gold dispersion is present down-ice despite the low gold concentrations (Figure 4.17). The anomalous zone appears 50 to 250 m wide due to the width of sample sites and is detectable for a distance up to 2150 m north-northwest of subcropping mineralization. Gold distributions among density fractions of eleven -212+106 pm and twenty-seven -106+53 pm size fraction regional till samples were determined by FA-AAS (Table 4.13). All the light mineral fractions (LMFs) from both size fractions have gold concentrations of < 5 ppb. Results of the heavy mineral concentrates (HMCs) from the -106+53 pm size fraction have gold values ranging from < 5 to 1030 ppb. The plan view distribution of the -106+53 pm HMC gold results is shown in Figure 4.18. Bubble size intervals are the same as previously defined for the -53 pm fraction FA-AAS diagram (Figure 4.16). The nineteen sites with gold values greater than the 5 ppb detection limit define a weakly anomalous (15 to 60 ppb) to moderately anomalous (105 to 1030 ppb) gold zone that extends at least 1950 m down-ice. For this and the previous two bubble plot gold diagrams, the majority of the highest gold values are clustered in 134 _ ? J CO I CO 3 CO C L 5 T: 0 ) CM. C D CO C N C N i CO I O ) 1 o CO C N o C O V C O C D O ) A • • • • • 2 O _Q =J CO CO C L o o co CD 5 o cu — o CO -J3 o o (!) S 111 8 8 L U 8 U J 8 4 ' i l ; OON * <M 1 V NOO 124+ ; , \ ; * U J U J Q Q L U O L U Q o o £ A o + CO o 8 135 136 the area between Lines 128+00 N and 130+00 N and most values decrease further down ice. Only two of eleven HMCs from the -212+106 um size fraction have gold values greater than the 5 ppb detection limit. For a comparison to gold values from the regional till frost boil LMFs and HMCs, similar size and density fractions of a C horizon directly overlying mineralized bedrock (site LI24+00 N/11+80 E) were also analyzed for gold by FA-AAS (Table 4.13). HMC gold values from both size fractions are extremely anomalous, having values of 49302 ppb and 27977 ppb, respectively. In contrast to the regional till density fractions, the fine sand (-212+106 um) fraction HMC for the C horizon has a higher gold concentration than the very fine sand (-106+53 pm) fraction HMC. Furthermore, gold values were detectable in the C horizon LMFs (330 ppb and 335 ppb, respectively) whereas all the regional till frost boil LMFs have gold values of < 5 ppb. 4.4 Gold distribution in organic soils Surface humus (LFH horizon) samples from eighteen soil pit sites along Lines 122+00 N and 124+00 N have gold concentrations ranging from 9 to 652 ppb (Table 4.14). Gold in three bog (O horizon) samples from surrounding areas were also determined by NAA and have values of 10 to 37 ppb (Table 4.15). The plan view distribution of these values is shown in Figure 4.19, with the LFH horizon values also in cross-section view in Figures 4.11 and 4.12 (Section 4.3.3). The smallest bubble size contains gold values <0.5 standard deviation from the mean and remaining intervals are based on the mean ± 0.25, +1.0 and >1.0 standard deviations, similar to intervals used in the lowermost B and C horizon diagram (Figure 4.9, Section 4.3.2). LFH horizon results detect anomalous gold zones similar to those identified by the lowermost B and C horizons. Along Line 122+00 N , a 50 m wide, moderately anomalous (83 to 120 ppb) gold zone is defined on the upper plateau area (Figure 4.19) which coincides with the Table 4.14. Gold concentrations (ppb) of the milled, -1000 pm fraction of LFH horizons, measured by NAA, with associated gold concentrations (ppb) of the -212 pm fraction of Ah horizons, measured by FA-AAS, ash amount (LOI) and ash colour (Munsell, 1971). Northing/ easting Sample number Au (ppb) Ash LFH -1000 um Ah -212 um LOI (%) Munsell colour notation name L122+00 N 11+10E 011 10 — 40.4 7.5YR6/5 ltbrn-redd. yellow 11+30E 012 48 — 35.2 7.5YR6/6 reddish yellow 11+50E 013 16 85 35.5 7.5YR 5/4 brown 11+80E 014 83 200 25.3 7.5YR 5/4 light brown-pink 12+10 E 015 120 100 19.7 7.5YR 5.5/2 brown-pinkish grey 12+30 E 016 97 1370 35.8 7.5YR 5.5/4 brown-light brown 12+60E 017 14 20 19.5 7.5YR 5/4 brown 13+00E 018 9 — 23.1 7.5 YR 6/4 light brown 13+40 E 019 9 — 14.3 7.5 YR 6/5 light brown L124+00 N 10+90 E 020 14 — 50.2 7.5YR 5/4 brown 11+10E 021 156 — 39.4 5YR 5.5/3 light reddish brown 11+20E . 022 610 — 30.0 7.5YR 5/4 brown 11+40E 023 134 75 47.3 7.5YR 5/2 brown 11+70E 024 174 325 46.0 7.5YR 5/2 brown 11+80E 025 652 775 62.8 5YR4/4 reddish brown 12+00E 026 30 130 47.6 7.5YR 5/6 strong brown 12+20E 027 41 70 32.6 7.5YR 5.5/2 brown-pinkish brown 13+00E 030 13 31.3 7.5YR 5/4 brown — = material not available for analysis. 138 Table 4.15. Gold concentrations (ppb) of the milled -1000 pm fractionsurface bog (O) horizons, measured by NAA. Location: Sample Horizon Au northing / easting number Oppb) LI19+55 N 11+10 E 229 O 37 L120+50 N 13+80 E 207 O 10 L122+00 N 13+55 E 120 O 12 139 8 8 8 8 8 LU o O o O + + CO O) z 8 140 surficial materials classified as weathered rock by Ryder (1992). A spot anomaly (48 ppb) also occurs on this Line mid-way down the western slope (11+30 E) that was not previously identified by the lowermost B and C horizons. A broad anomalous zone is apparent along Line 124+00 N and corresponds to strongly anomalous values ranging from 134 to 652 ppb gold. This zone continues from the base of the western slope up to the western portion of the upper plateau, coincident with anomalous zones identified by the Ah and lowermost C horizons in Figure 4.12. The upper plateau portion of the anomalous zone corresponds to surficial materials classified as weathered rock and till with weathered rock, whereas the western slope portion coincides with surficial materials classified as till by Ryder (1992). Loss on ignition (LOI) amounts of the surface L F H horizons range from 14.3 to 62.8% of the samples by weight (Table 4.14). A comparison of LFH gold concentration versus LOI ash (Figure 4.20A) shows that there is no systematic relationship between the two. An estimated correlation coefficient of 0.391 is not significant since the critical r value for the 0.05 confidence level (n=18) is 0.468. There appears to be a slight relation between gold values of L F H horizons and underlying Ah horizons (Figure 4.20B). However, the estimated correlation coefficient of 0.426 is also insignificant compared to the critical r value of 0.632 (0.05 confidence level, n=10). LOI ash colours range considerably from light brown-reddish yellow (7.5YR 6/5), brown (7.5YR 5/4), pale brown (10YR 6/3), pinkish-grey (5YR 6/2) to reddish brown (5YR 4/4 to 5/3). The weakly to moderately anomalous gold values (10 to 48 ppb) along Line 122+00 N are associated with the light brown-reddish yellow ash colours. The moderately to strongly anomalous (120 to 652 ppb) gold values are associated with the brown and reddish brown colours, similar to the associations observed between B horizon colours and gold values (Sections 4.3.3 and 4.3.5). 3,000 A) 10 30 100 300 1,000 3,000 Au (ppb) - LFH horizons Figure 4.20. Comparison of gold concentrations (ppb) in the milled -1000 um fraction of L F H horizons, measured by N A A , versus A) LOI ash (weight %) and B) gold conentrations (ppb) in -212 um fraction of underlying Ah horizons, measured by FA-AAS. 4.5 Particulate gold grain morphology 142 The scaruiing electron microscope (SEM) was used to study the morphological characteristics of particulate gold grains recovered from regional till frost boils and for a comparison of these to grain morphologies of local origin. Gold grains from an anomalous (8410 ppb, -212 um fraction) C horizon overlying mineralized bedrock were also examined. Numbers of free gold particles were estimated based on the gold values from the previously analyzed HMCs, the HMC weights and assuming spheres of pure gold (S.G. = 19.3 g/cm3); samples having greater than 1.0 estimated gold particles were chosen for recovery. Four of the -106+53 um (non-magnetic) HMCs of regional till samples were selected for gold grain recovery along with both density fractions of the local C horizon. After nearly 50 hours of searching the non-magnetic HMCs using the binocular microscope, no free gold was identified in two regional till frost boil samples, whereas 16 grains were recovered from the C horizon -106+53 um HMC. Further grain recovery was improved by searching the heavy-batea (panned) fraction of the non-magnetic HMCs. After roughly 30 hours of searching these density fractions, a total of 6 gold grains were recovered from the -212+106 um fraction of the C horizon and 100 grains were selected from the -106+53 um HMC fraction. Numerous gold grains remain in the latter C horizon density fraction. In contrast, only two gold grains were identified in one regional till sample. For each of the selected gold grains, axial dimensions were measured directly from the screen image using the SEM measuring tool. From the detailed examination of each of the mounted grains, it was evident that there are many different sizes, shapes and surface textures of the gold grains. For example, gold particles from the -106+53 um fraction of the C horizon range in size from 60 pm to 248 um across and vary in shape from rods, to globules and discs. Grains were classified according to the observed morphological characteristics based on the classification scheme developed by Averill and Zimmerman (1988) and modified by DiLabio (1990); results are shown in Table 4.16. Within the different size Table 4.16. Results of classification of particulate gold grains recovered from the -106+53 pm fraction HMC of a regional till sample and from the -212+106 pm and -106+53 pm fraction HMCs of a local C horizon. Sample type/ Size Grain morphology classification Total number fraction pristine modified reshaped Regional till -106+53 2 2 062 Local C horizon -212+106 2 4 6 203 -106+53 14 42 2 58 144 fractions of both regional till and C horizon samples, one to three morphological types of gold grains are present, these being pristine, modified, and reshaped grains. Both of the regional till gold particles are modified grains. The primary shape of the smaller, 50 pm-sized gold grain (Plate 4.1 A) is still evident, but the edges have been smeared. Two indentations are also evident on the surface. In contrast, the larger gold grain from the regional till HMC appears to have been more extensively modified (Plate 4. IB and C). For example, the edges of the grain are smeared, curled and folded onto itself. Striations and gouges are also apparent on the surface of the grain (Plate 4.1C). However, a primary grain mold appears to have been preserved in a cavity (arrow). Gold particles from the C horizon HMCs have a wide variety of morphological characteristics and thus, pristine, modified and reshaped grains occur within each size fraction. Pristine gold grains are characterized as having irregular, globular or rod shapes, jagged edges and minor striations on the surface (Plate 4.2A to D). Primary surface textures are preserved, including grain molds and crystal faces that were most likely once in contact with primary sulphide or gangue minerals. A number of grains are still attached to or have inclusions of these primary minerals (Plate 4.2B and C). The majority of the C horizon gold particles are classified as modified grains. It was observed that the degree of modification varies among the grains (ie. slightly to strongly modified). Plate 4.3A to D are examples of slightly modified gold grains and show how the primary shapes and surface textures are still evident but the edges have been curled and/or folded slightly. The more strongly modified gold grains are characterized as maintaining their original grain shape but most of the edges have been damaged and the surfaces are striated and smeared (Plate 4.4A to C). For a number of particles (eg. Plate 4.4D), grain surfaces commonly have a "felty" or porous texture, and the grains appear to have been folded several times. In a number of cases, the edges have been folded over Fe-oxide and Fe-rich aluminosilicate coatings that appear on the surfaces. However, these coatings were not observed on all grains. 145 Plate 4.1. Backscatter SEM photomicrographs of two modified gold grains of regional till recovered from the -106+53 um size fraction, heavy-batea HMC. A. The primary grain shape is still evident but the edges are smeared and the surface appears 'dented' and striated. B. A more extensively modified gold grain. The edges are smeared and curled and striations and gouges are evident of the surface. A primary grain mold has been preserved in a cavity (arrow). C. A close-up view of the surface of a modified gold grain. The edges have been smeared and striations are evident on the surface. 146 147 Plate 4.2. Backscatter SEM photomicrographs of pristine gold grains recovered from the -106+53 pm HMC fraction of a local C horizon soil. Pristine grains are characterized as being either irregular shaped (A and B), globular shaped (C) or rod shaped (D). Primary surface textures including grain molds and crystal feces are preserved. A number of pristine grains are still attached to or have inclusions of these primary minerals (C and D, respectively). \ 148 149 Plate 4.3. Backscatter SEM photomicrographs of slightly modified gold grains recovered from the -106+53 pm HMC (A and B) and the -212+106 pm HMC (C and D) of a local C horizon soil. Modified grains are characterized as retaining their primary shapes and surface textures. The edges are no longer jagged and have been curled and/or folded slightly. Striations are apparent on the surface of the grains. A. Slightly modified gold grain retaining its original globule shape and crystal faces. The edges have been smeared slightly and striations are apparent on the surface. B. Modified gold grain that has retained its original shape and surface texture. The edges along the bottom have been folded slightly whereas the "arm" in the middle appears to have been completely folded over onto itself. C. Modified gold particle that has its primary shape, retained (eg. hole in centre is most likely from a since weathered-out primary mineral). Grain edges have been smeared and folded slightly. A small amount of Fe-rich aluminosilicate coating is present on the surface (slightly dark area near centre) and an Fe-sulphide grain in embedded in the grain (bottom right). D. A slightly modified gold grain that has retained its original irregular shape, grain molds (left protrusion) and surface texture. Edges have been slightly smeared and minor striations are present on the surface (top centre). An Fe-rich aluminosilicate coating is scattered on the surface. 150 151 Plate 4.4. Backscatter SEM photomicrographs of strongly modified gold particles recovered from the -106+53 pm HMC fraction of a local C horizon soil. These strongly modified grains retain their original grain outline or shape, however, most of the edges are blunted and folded several times. Grain surfaces are commonly very smeared and gouged (A and B) and also have a "felty" or porous texture (C and D). Primary grain molds and surface textures are retained in protected cavities. A. Strongly modified gold particle with smeared and folded edges. Primary surface textures are retained in cavities (bottom) but most of the surface is very smeared and gouged. B. Close-up view of grain A, showing the smeared surface and edges (centre) as well as the preserved primary surface texture (bottom left). C. Modified gold particle that has retained its original shape but the once-jagged edges are now blunted and folded. The edges on the right appear to have been folded over an Fe-rich alumiosilicate coating. Darker "grain" in the centre is an Fe-oxide. D. Modified gold particle showing a felty and.somewhat porous surface texture. Grain edges are smeared and have been folded several times. 153 4.6 Electron microprobe analyses Gold particles from the regional till sample and selected gold particles from the C horizon were sectioned and analyzed for gold, silver, mercury and copper with the electron microprobe. During the sectioning procedure however, the 50 um-sized gold grain from the regional till sample was lost. Thus, results of gold and silver analyses of cores and rims of one regional till gold grain and twenty C horizon gold grains (four from the -212+106 pm fraction and sixteen from the -106+53 pm fraction) are listed in detail in the Appendix but the mean analyses are listed in Table 4.17. Mercury was not detected in the majority of analyses and copper results have a mean of 0.01 wt%, well below the detection limit of 0.1 wt%, and are therefore not considered. The core of the regional till gold grain has a mean gold value of 86.94 wt% compared to a rim value of 89.40 wt% gold, corresponding to a mean fineness (Au / (Au + Ag) x 1000) of 886.2. Silver results between the core and rim are 11.68 and 9.67 wt%, respectively. Thus, there is a slight increase in gold content in the rims versus the core. However, no gold ruriming was evident in the sectioned gold grains when observed with backscatter electron imaging. Gold and silver results of the cores and rims of C horizon gold grains are very similar for both size fractions indicating there is no difference in gold content between the two. For gold grains from both size fractions, values range from 69.30 to 84.80 wt% gold and 13.44 to 27.81 wt% silver, corresponding to a fineness of 718.7 to 848.2. 154 Table 4.17. Electron microprobe results of gold and silver analyses (wt%) of sectioned gold grains selected from the -106+53 pm HMC regional till sample and from the -212+106 p and -106+53 pm HMC of a local C horizon. Sample type/ number Size Au (wt%) Ag(wt%) Fineness Au (wt%) Ag (wt%) Fineness fraction core core rim rim Regional till -106+53 *86.94 11.68 881.55 89.4 9.67 902.49 062 **0.79 0.11 1.19 2.64 3.24 32.09 Local C horizon -212+106 81.44 17.89 819.88 79.92 19.33 805.14 203 2.62 2.6 26.16 3.13 2.8 28.81 -106+53 77.63 20.96 787.61 76.76 21.57 780.84 2.69 2.68 25.37 2.16 2.18 20.3 * = mean; ** = standard deviation Chapter Five - DISCUSSION 156 5.1 Introduction In order to understand the relations of subcropping gold mineralization, glacial processes and periglacial modifications to the geochemical dispersion of gold, it is necessary to determine the mode of occurrence of gold in the different types of surficial materials. Comparisons of the distribution of gold among soil horizons and patterned ground developed in the glacial sediments enables the identification of the spatial and vertical extent of the anomalous gold zones as well as which surficial materials yield better geochemical dispersion trains and anomaly contrast. Terrain mapping of the Wally Grid by Ryder (1992) identified surficial materials that were classified as till, marine sediments and weathered rock (or local materials) and mixtures of the different types (Figure 2.6). Section 4.3.1 and 4.3.2 showed that each of these surficial materials are different with respect to their gold concentrations (Table 4.6 and 4.7) which in turn governs the differences in gold concentrations among soil horizons developed in them. For example, regional till and marine sediments have lower gold concentrations (-212 pm fraction) than sediments having a large component of local bedrock. Therefore, the concentrations or populations of gold for each of these surficial materials is different and should be considered separately. 5.2 Mode of occurrence of gold B and C horizons from pits in mixed till have, on average, approximately 40% of their -2000 pm material in the fine sand (-212+53 pm) fraction (Section 4.2). In order to determine the proportion of gold contributed by each size fraction, the weight of gold (pg) was calculated by multiplying the gold concentration (as pg/g; Table 4.9) by the weight (g) of the respective fractions (Appendix). Samples 157 having gold values below the detection limit of 5 ppb gold were ignored. For each pit horizon, the weight of gold in the -212 pm fraction was assumed to represent the total gold. Thus, the weight of gold in the -212+53 pm fraction could then be estimated from the difference between the values calculated for the -212 pm and -53 pm fractions. Based on these results, the proportion of gold contributed by each size fraction could then be obtained (Table 5.1). Samples having an estimated weight of gold for the -53 pm fraction greater than for the total gold (ie. giving a negative value for the -212+53 pm fraction) were omitted from these tabulations. This greatly reduces the number of samples available for the estimates. For the B and C horizons of mixed till on the Wally Grid, it appears that within the -212 pm fraction more than 90% of the gold resides within the silt-clay (-53 pm) fraction (Table 5.1, Figure 5.1). The number of ideal gold particles within the -212+53 pm and -53 pm fractions were then estimated based on gold concentrations (Table 4.9) and a subsample weight of 30 grams, in order to assess the number of gold particles in an assay ton analytical sample. Gold particles were assumed to have a density of 18.15 g/cm3 based on electron microprobe results (Appendix) and for the -212+53 pm fraction, a spherical grain diameter of 75 pm was used in the calculations. Bearing in mind the possibility of a wide range of grain diameters and shapes within any size fraction range, gold grain estimates could vary by roughly a half order of magnitude. In order to estimate a very conservative or minimum number of gold particles in the -53 pm fraction, gold grains were assumed to have a large spherical diameter of 50 pm. However, it is unlikely that the gold particles in this fraction occur as 50 pm spheres and it is probably more realistic to consider a smaller grain diameter of 20 pm in the estimates. Results of this model show that the two mixed till samples contain insufficient gold in the -212+53 pm fraction to form one 75 pm gold grain (Table 5.2). This indicates that free particles of gold coarser than 75 pm must essentially be absent from the mixed till. For the -53 pm fraction, mixed till samples could contain 7 or more discrete gold particles 50 pm in diameter. However, i f a grain diameter of 20 pm is used, estimates of the number of gold particles are Table 5.1. Proportion (%) of gold contributed by the -212 pm size fractions of horizons from mixed till and local stony frost boil pits along LI24+00 N. Based on gold concentrations (Table 4.9) and size fraction weights (Appendix). Location/ sample number Soil pit type SoU horizon Au (ppb) Proportion (%) of Au -212 um -53 um -212+53 um -53 um 11+70 E 214 Mixed till B l 345 535 7.63 92.37 216 BC 160 295 7.67 92.34 219 Local stony B l 1510 2160 4.86 95.14 220 frost boil B2 3570 4670 8.20 91.80 11+80 E 202 Local stony B l 4620 5580 6.09 93.91 204 frost boil B2 6690 8280 1.32 98.68 203 c 8410 10280 23.23 76.77 12+20 E 208 Local stony B l 45 70 3.61 96.39 210 frost boil B3 35 50 0.58 99.42 159 100 Mixed till frost boil Local stony frost boil 11+70 E Local stony frost boil 11+80 E Local stony frost boil 12+20 E -212+53 pm • -53 pm Size fraction Figure 5.1. Proportion (%) of gold in the -212+53 pm and -53 pm size fractions of soil horizons from mixed till and local stony frost boil pits along LI 24+00 N. 160 Table 5.2. Estimated number of gold particles in the -212+53 um and -53 um fractions of horizons from soil pits along LI24+00 N. Calculations based on 30 g subsample weights and gold grain diameters of 75 pm for the -212+53 um fraction and 50 and 20 um for the -53 um size fraction. Location/ sample number Soil pit type Soil Au (ppb) Size fractions horizon -212 urn -53 um -212+53 urn 75 um -53 um 50 um 20 um 11+70 E 214 Mixed till B l 345 535 0.49 13.51 211.1 216 BC 160 295 0.18 7.45 116.4 219 Local stony B l 1510 2160 1.64 54.55 852.3 220 frost boil B2 3570 4670 7.35 117.94 1842.8 11+80 E 202 Local stony B l 4620 5580 9.46 140.92 2201.9 204 frost boil B2 6690 8280 3.27 209.11 3267.3 203 C 8410 10280 39.30 259.61 4056.5 12+20 E 208 Local stony B l 45 70 0.03 7.77 27.6 210 frost boil B3 35 50 0.00 1.26 19.7 161 roughly 16 times greater and both samples contain sufficient gold to form over 110 particles of gold. Based on these results, it appears that most of the gold in the mixed till horizons probably occurs as either fine particles of free gold in the silt-clay fraction or as fine inclusions in this fraction. The weight and proportions of gold contributed by the -212 pm fractions of pit horizons in locally-derived materials (or local stony frost boils) were also calculated. Results show that over 75% of the gold in the -212 pm fraction (average of 93%) is associated with the silt-clay fraction (Table 5.1, Figure 5.1). Nevertheless, estimates of the number of gold particles in the -212+53 pm fraction (Table 5.2) show that 5 of 7 samples could contain sufficient gold to form one or more gold particles 75 pm in diameter. This suggests that free particles of gold coarser than 75 pm could possibly occur in these strongly anomalous local materials whereas the weakly anomalous frost boils (eg. 12+20 E) do not contain free gold. For the silt-clay fraction, all local samples could contain one or more discrete particles of gold 50 pm or 20 pm in diameter. For example, the strongly anomalous horizons from local frost boils at 11+70 E and 11+80 E could contain well over 50 gold particles 50 pm in diameter or greater than 850 gold grains with a 20 pm diameter. Thus, it appears likely that most of the gold in these local materials occurs as free particles (and/or inclusions) in the silt-clay fraction with only a minor proportion of the gold in the fine sand fraction. This is supported by the recovery of free gold grains (Section 4.5; Table 4.16) from a 20 g heavy mineral concentrate from sample 203, a C horizon directly overlying mineralized bedrock. Gold particles in the -106+53 pm density fraction were so numerous that 100 gold grains were randomly recovered from the HMC. However, only 6 particles of gold were identified in the -212+106 pm HMC fraction. For each of the local HMC fractions, gold grains were classified as having pristine, modified and reshaped morphologies (Section 4.5). About 25% of the grain shapes were pristine rods and globules (Plate 4.2) with the remainder of the gold grains having modified and reshaped forms (Plates 4.3 and 4.4). The existence of pristine gold grains within this sample is consistent with the grains being of a local origin. 162 These locally-derived materials generally contain a high proportion of mineralized bedrock fragments that are broken down by periglacial processes (discussed below), releasing free gold particles and heavy minerals with inclusions of gold. However, since the light mineral fractions are also anomalous (ie. 330 and 335 ppb), gold also occurs as inclusions in its light mineral host, perhaps quartz-carbonate material. Therefore, gold in the locally-derived materials occurs in a variety of shapes and sizes, for example, as free gold in the silt-clay fraction and the heavy mineral concentrates of the fine sand fraction, and as inclusions in the light and heavy mineral fractions. As described in Section 4.2, frost boils in regional till contain roughly equal proportions of the -2000 pm material (average of 35%) in the fine sand and silt-clay fractions. The proportion of gold in the size and density fractions of these regional till samples were difficult to estimate because about 70% of the gold values by FA-AAS were less than the detection limit of 5 ppb (see Table 4.13). Thus, no calculations were made for samples having gold values of < 5 ppb; this included all the LMFs coarser than 53 pm. The weight and proportion of gold contributed by each size and density fraction were calculated using the individual fraction weights as recovered from the field sample (Appendix). Calculations were based primarily on.the gold values by FA-AAS except for the -53 pm fraction; for samples with gold results of < 5 ppb, the AR column-ICP gold values (detection limit of 0.1 ppb) were used. Results of this model show that all but two of the regional till samples have over 60% of the gold associated with silt-clay fraction (Table 5.3) with the remainder of the gold occurring in the heavy minerals of the very fine sand (-106+53 pm) fraction. For a number of samples, no gold was detected in the HMCs and thus, about 100% of the gold occurs in the silt-clay fraction. Gold was detected in only 2 of 11 HMCs of the -212+106 pm fraction (samples 056 and 072) and represents about 5% of the gold in these samples. The number of ideal gold particles in the regional till samples was estimated assuming gold grain diameters equal to the logarithmic mean of the size range. As mentioned above, these estimates could vary Table 5.3. Proportion (%) of gold in the size and density fractions of regional till frost boils and one C horizon from an anomalous soil pit. Calculations based on size and density fraction weights as obtained from the field sample (Appendix). Sample Size fraction lumber -106+53 um HMC -53 um -53 urn* 049 100.0 053 - — 100.0 054 - 100.0 055 40.0 60.0 056 - ~ 93.2 057 27.5 — 72.5 058 25.7 — 74.3 059 — 100.0 060 — 100.0 061 — 100.0 062 71.9 — 28.1 063 17.0 83.0 070 15.9 80.9 071 11.8 88.2 072 10.9 89.1 073 9.7 90.3 074 1.9 98.1 075 - ~ 100.0 076 11.1 88.9 077 6.3 93,7 078 11.5 88.5 079 54.5 45.5 080 25.5 74.5 257 ~ 100.0 258 2.4 97.6 259 13.7 - 86.3 260 18.8 — 81.2 203** 4.1 89.6 n/a Note: * = analysis by AR column-ICP; ** = C horizon sample; — = gold values were < 5 ppb; n/a = material not available for analysis; (100.0) indicates that no gold was detected in the HMCs and approximately 100% of the gold occurs in the -53 pm fraction. 164 by about a half order of magnitude because of the possibility of a wide range of grain diameters and shapes within any size range. For the -53 pm fraction, gold grain diameters of 50 pm and 20 pm were used in the calculations. Results indicate that 6 of 18 samples contain sufficient gold in the heavy minerals of the -106+53 pm fraction to form one or more particles of gold 75 pm in diameter (Table 5.4). Taking into account the errors associated with these estimates, another 2 or 3 HMCs could contain one particle of gold. However, results of the recovery of gold grains (Section 4.5) do not support these estimations that 6 to 8 HMCs could contain discrete particles of gold; only two gold grains were recovered from the -106+53 pm HMC fraction from 1 of 11 regional till samples (062). Both gold grains were classified as having modified morphologies (Plate 4.1) which is consistent with their having been transported. However, with so few gold particles it is unrealistic to relate grain morphologies to transport distance. Gold was detected in only 2 of 11 HMCs from the -212+106 pm fraction and each were estimated to contain less than one gold grain. Using a 50 pm grain diameter and gold values by FA-AAS for the -53 pm fraction, only 4 of 11 samples could contain sufficient gold to form one discrete gold particle. Keeping in mind however that the number of gold particles may have been underestimated by a factor of 10 or more if a smaller grain diameter is considered, all of the regional till samples could contain free gold smaller than 20 pm. Thus, it appears that most of the gold in the regional till is present as fine gold particles, either free or as inclusions, in the silt-clay fraction with only a minor amount present as free gold or inclusions within the heavy minerals of the very fine sand fraction. Proportions of gold contributed by the size and density fractions of a gold-rich C horizon directly overlying mineralized bedrock were estimated along with the regional till samples (Table 5.3). Calculations were based on the FA-AAS gold values and weights of the size and density fractions as recovered from the field sample (Appendix). Gold in this local C horizon is strongly associated with the silt-clay fraction and has a weak association with the heavy minerals of the fine sand (-212+106 pm) and very fine sand (-106+53 pm) fractions. Each of the HMCs comprise about 4% of the gold. In contrast to the regional till, Table 5.4. Estimated number of gold particles in the size and density fractions of regional till frost boils and one C horizon from an anomalous soil pit. Based on gold concentrations (Table 4.16), H M C weights as obtained from die field sample (Appendix) and 30 g and 50 g subsamples of the -53 um fraction for F A - A A S and A R column-ICP analyses, respectively. Sample Size fraction number -106+53 um H M C -53 um -53 um * Grain diameter 75 pm 50 um 20 pm 50 um 20 um 049 0.07 1.05 053 - - - 0.06 0.99 054 - 0.25 3.95 * 0.26 4.08 055 1.99 - - 0.24 3i81 056 - - — 0.14 2.17 057 0.19 ~ 0.07 1.12 058 0.77 - ~ 0.41 6.38 059 ~ 0.38 5.92 0.07 1.05 060 - - ~ 0.07 1.12 061 - 1.14 17.76 0.09 1.35 062 3.26 - - 0.15 2.30 063 1.03 0.25 3.95 0.65 10.19 070 1.64 0.51 7.89 0.50 7.83 071 0.51 0.25 3.95 0.16 2.50 072 0.55 - - 0.26 4.08 073 0.14 - - 0.16 2.43 074 0.15 1.64 25.65 1.30 20.26 075 - - 0.03 0.53 076 1.93 0.88 13.81 0.56 8.75 077 0.70 0.51 7.89 0.37 5.72 078 0.06 • - - ~ 0.25 3.95 079 0.15 - ~ 0.01 0.13 080 0.64 - - 0.25 3.95 257 - 1.01 15.78 0.08 1.32 258 0.15 0.25 3.95 0.24 3.81 259 0.25 - - 0.13 1.97 260 1.76 - 0.73 11.44 203** 231.68 259.61 4056.48 n/a n/a Note: * = analysis by A R column-ICP; ** = C horizon sample; ~ = gold values were < 5 ppb; n/a = material not available for analysis. 166 the LMFs contain moderate amounts of gold (330 and 335 ppb) although this represents less than 1% of the total gold content for each fraction. Estimates of the number of gold particles for this local sample were based on the model used for the regional till samples. Results show that each of the size and density fractions (except for the LMF of the -212+106 pm fraction) contain sufficient gold to form more than one free particle of gold (Table 5.4). The HMC of the -212+106 pm fraction could contain 32 discrete gold grains 150 pm in diameter whereas the same density fraction for two regional till samples were estimated to contain no free gold (< 1.0 particles). Based on this model, the number of 75 pm gold particles (231) in the -106+53 pm HMC fraction recovered from a 8300 g field sample is roughly comparable to the number of 50 pm gold particles (260) in a 30 g subsample of the -53 pm fraction. However, since the latter estimates represent only a minimum number of gold particles that can exist in the -53 pm fraction, a greater number of gold particles is probably present. No gold was detected in the -212 pm fraction of the lowermost (B and C) horizons developed in marine sediments. For this reason, the proportion of gold and estimates of the number of gold grains were not calculated for these materials. Terrain mapping of the Wally Grid by Ryder (1992) identified marine sediments, infilling depressions on the upper plateau and overlying till in areas on the lower plain and east of the Baseline (Figure 2.6), that consist primarily of silt-clay material derived from sources to the south and southeast. On the upper plateau, gold anomalies in the near-surface horizons become undetected when marine sediments are encountered (Figures 4.17 and 4.18). This may be caused either by these sediments blanketing an underlying gold anomaly or that the gold anomalies are not present in these areas. However, it is highly probable that the marine sediments , because of their origin (discussed below), blanket the underlying materials and any gold anomalies associated with them. Thus, marine sediments seem to have no gold geochemical response that can be related to the gold anomalies in till or the known gold mineralization. 167 5.2.1 Summary of the mode of occurrence of gold The previous section has revealed that the till and locally-derived materials differ with respect to their gold concentrations and mode of occurrence of gold. The distribution of gold among size fractions, and estimates of the number of ideal gold particles for the mixed till indicate that about 90% of the gold exists as particles less than 50 pm in diameter. Similarly, regional till samples have a large portion (60 to 100%) of the gold in the silt-clay fraction and a weak association of gold with the heavy minerals of the very fine sand (-106+53 um) fraction. Gold in this density fraction apparently occurs primarily as inclusions in the heavy minerals. Although the locally-derived materials have greater than 75% of the gold as free particles less than 50 pm, the heavy minerals of the fine sand fractions also contain moderate amounts of free gold particles. Thus, there appears to be a progression from a significant number of discrete gold grains in the sand sized heavy minerals and silt-clay of the local materials to essentially all of the gold as free particles less than 50 pm in diameter in the mixed and regional till. Finally, no detectable gold is associated with the marine sediments. 5.3 Origin of gold anomalies It is evident that the gold anomalies in the regional till and local materials differ in both magnitude and in their mode of occurrence and, therefore, can be treated as separate anomalies with respect to the processes leading to their present distribution. Differences in the anomaly signatures result primarily from the glacial processes that have affected the area as well as the ongoing periglacial processes. The anomalies also can be distinguished based on their probable relative age of formation: (i) an older weak anomaly in the regional till resulting from glacial dispersion, and (ii) a relatively young anomaly in frost 168 boils of local materials resulting from on-going periglacial modifications of local bedrock and surficial materials. 5.3.1 The older gold anomaly in regional till This anomalous zone is defined by the gold values of regional till frost boils along the peninsula to the northwest of the Wally Grid. Gold results of the size and density fractions of regional till (Table 4.13) define a dispersal train that appears to extend in a north-northwest direction for less than 2 km. A weak anomalous zone is detected in gold results of the -53 pm size fraction (10 to 65 ppb) that extends for about 1500 metres (Figure 4.16). A stronger anomaly is apparent in gold values of the -106+53 pm HMC fraction (Figure 4.18) that define a weakly anomalous (15 to 60 ppb) to moderately anomalous (105 to 1030 ppb) gold zone that continues for at least 1950 m down-ice from known mineralization. This apparent directional trend and width of the gold dispersion may be due to constraints of the orientation of sample sites being in a northwest direction along a narrow zone. If sample sites had been broadened along the peninsula and even extended to the northern part of the grid and into Spyder Lake, this may have helped to determine the exact width of the gold anomaly and whether its orientation is an actual north to northwest direction. However, considering that gold was detected in most of the distal samples (eg. on the islands) this implies that the gold anomaly does extend in a northwest direction. Down-ice dispersal trains result from mechanical processes that occur during glacial transport of bedrock material from a mineralized source. Dispersion trains have been identified as three-dimensional features that extend in a down-ice direction and rise gently away from the source in till up to 5 m thick (Drake, 1983; Miller, 1984). In the Bathurst Norsemines area, NWT, Miller (1979) identified one such dispersion train as a strongly anomalous Pb zone surrounded by a weakly anomalous envelope. These materials plunged at a gentle (2°) angle towards the mineralized source. However, not all dispersion trains 169 conform to this three-dimensional model. For example, Sibbick (1990) identified a gold dispersion train down-ice from the Nickel Plate mine area, BC, in which gold concentrations in soils consistently increased with depth. This anomaly showed no tendency to rise to the surface with increased distance from the source. In the present study area, only the surface (15 to 20 cm depth) of the regional till was sampled from frost boils and probably represents a mixture of till, not the original surface part of the till. Thus, it is impossible to determine the original three-dimensional form of the gold anomaly. However, pit profiles of regional till frost boils on the Wally Grid offer a three-dimensional view of the regional till in an area around the gold mineralization. For each of these profiles in thick till, that were about 100 cm deep, gold concentrations consistently decrease with depth. The lack of vertical variation of gold values among adjacent profiles suggests that the auriferous materials do not rise gently up profile away from the source. However, it is not known for certain if an auriferous till layer is, or is not, present directly overlying bedrock because the pits were not excavated to these depths. Thus, more work would be required to determine whether a buried anomalous till layer occurs in the regional till areas around, and down-ice from, the known mineralized bedrock. The weak gold anomaly detected in the regional till may be explained primarily as a result of dilution. During the Late Wisconsinan Glaciation, the northern part of the Laurentide Ice Sheet flowed in a northwest to north direction (approximately 275° to 345°; Ryder, 1992) in the Hope Bay area having travelled over granitic and gneissic terrain to the southeast of the study area. Large amounts of this barren or gold-poor material became entrained within the glacier. In the Wally Grid area, the mineralized shear zone is hosted in volcanics that form a prominent ridge trending in a north-south direction. The ice sheet would have flowed obliquely over the main ridge incorporating local mineralized bedrock into the glacier debris. Results of pebble counts on the 5.6 to 8.0 mm fraction of regional till down-ice from the mineralization shows that, on average, greater than 90% of the pebbles are exotic lithologies (granitoids, 170 mafic volcanics and minor metasediments). This suggests that only a relatively minor amount of the local material was actually incorporated in the regional till. Results of a study on the multi-element geochemistry of the -70 pm fraction of the 1991 and 1992 Wally Grid samples (Laurus, 1992) suggest that the incorporation of the fine fractions of local materials has only a minor influence on the geochemistry of the mixed and regional till. The geochemical data were separated into groups based on the type of surficial material sampled (ie. local frost boils, and mixed and regional till). Local frost boil samples are enriched in elements associated with local bedrock (Fe, Mn, Zn, Mg, Cr, Al and V) and mineralization (Au, Ag, As, Ca, Cu, Co). Results of probability plots indicate that the mixed and regional till samples have low concentrations for most of these elements (Table 5.5). These results suggest that only a minor amount of the local -70 pm material has been dispersed down-ice from the mineralization. This substantiates the pebble count results of the regional till samples. Several factors may be responsible for only a minor amount of local material being incorporated in the regional till. In general, the size and shape of a dispersal train are controlled by the orientation of the source relative to ice flow, by the size and erodibility of the source, and by the influence of topography on ice flow (DiLabio, 1990). Erodibility of materials is further controlled by a number of factors including the lithology of the material, and the basal thermal conditions of the glacier. For cold-based glaciers, the ground beneath the glacier is frozen and bedrock is not effectively scoured or plucked by the overriding ice (Sugden and John, 1976). The Bathurst Inlet area may have been affected by both cold-based and warm-based thermal ice conditions. During the on-set of glaciation, Keewatin ice extended outwards (Dyke and Prest, 1987) and the Bathurst Inlet area would have been overridden by the cold-based margins of the ice sheet as the ice advanced. These cold-based conditions arise due to the cold, arctic climate and the relatively thin ice at its margins. When the Laurentide Ice Sheet was at its maximum, the Bathurst Inlet area was roughly coincident with the Trans Laurentide Ice Divide (Dyke and Prest, 1987). This may have Table 5.5. Multi-element geochemistry of the 1991 and 1992 Wally Grid samples, subdivided based on the surficial material that was sampled. Elements concentration ranges refer to the minimum and maximum values related to the local local volcanic bedrock, and secondary alteration and mineralization. Rock types / Element concentration range of different materials related elements Local stony frost boils Mixed and regional till Local volcanic bedrock Fe(%) 2.1-18.0 .0.7-4.8 Mg(%) 0.3-2.5 0.8-1.0 Mn (ppm) 179 - 3200 21 - 600 Cr (ppm) 19 - 200 10 - 55 Zn (ppm) 16 - 235 9 - 88 Secondary alteration and mineralization Au (ppb) 20 - 31,400 0.2 - 260 Ag(ppm) 0.1-6.0 0.1-0.9 As (ppm) 2 - 13,000 2 - 300 Cu(ppm) 30- 1414 4 - 167 Ca (%) 0.4 - 6.6 0.2 - 3.4 Ni(ppm) 30-621 4 -60 Co (ppm) 7-291 3.-30 172 resulted in warm-based ice conditions as basal temperatures increase with increasing ice thicknesses (Eyles and Menzies, 1983) due to the effects of geothermal heat from the earth. At an ice divide, ice flow is generally very slow and thus, erosion is not extensive even though warm-based conditions may exist. During deglaciation, the study area may have once again been affected by the cold-based ice margins as the glacier thinned. Thus, the Bathurst Inlet area may have been affected by a progression of basal thermal ice conditions and it is difficult to determine how these conditions influenced the degree of bedrock erosion. The influence of topography on ice flow in the source and dispersal areas is also important because dispersal trains can become trapped in valleys and be truncated (Coker and DiLabio, 1987; DiLabio, 1990). The presence of stagnant ice in the lee side of the ridge could possibly explain why this area is not influenced by the eroded anomalous material. Stagnant ice acts like a protective blanket because the ice sheet essentially overrides the stagnant ice. The area on the lee side of the hill is thereby protected since the eroded material essentially overrides this area and moves further down-ice before being deposited. The effect of till thickness on the identification of dispersion trains may also explain the low gold signature of the regional till in the present study area. Rose et al. (1979) state that in basal till less than about 1 m thick, a geochemical anomaly is generally found in the soil directly over the source. In/till up to about 5 m thick, the anomaly is still detected in the surface horizons but offset some distance down-ice. In general, the magnitude of geochemical anomalies at the surface decrease with thickness of till and distance of down-ice transport (DiLabio, 1990). Northwest of the bedrock ridge, overburden (till) thicknesses were estimated from drill logs to be 2 to 7 m thick. Towards the Baseline to the east the till is up to 14 m thick (Clarke and St. Pierre, 1993). These areas of thick till correspond to areas having a weak gold signature. In the northern part of the grid, a weak gold anomaly is apparent in the till but becomes undetected in a valley between Lines 124+00 N and 126+00 N (Figure 4.9) that is filled with regional till up to 7 m in depth (Clarke and St. Pierre, 1993). 173 Numerous dispersal trains resulting from the Laurentide Ice Sheet in central and eastern Canada have been described in the past decade (Coker and DiLabio, 1987; Shilts, 1987; DiLabio, 1990). Many of these dispersal trains are ribbon- or fan-shaped and have sharp lateral contacts with the surrounding barren till (DiLabio, 1990). At the Hemlo gold mine in Ontario, anomalous HMCs are restricted to the area immediately over the deposit and showed little down-ice dispersion, whereas the silt-clay fraction identified significant down-ice dispersion with anomalous materials being detected up to 500 m down-ice from mineralization (Shelp and Nichol, 1987). Thus, the fine fraction and heavy minerals can provide different information. However, at the Owl Creek gold mine in Timmins, Ontario, Shelp and Nichol (1987) showed that both the gold content of HMCs and the -63 pm (silt-clay) material clearly identified the anomalous dispersal train, although the contrast and absolute levels of gold in the silt-clay were lower. This is very similar to the gold results of the regional till in the present study area. Interestingly, the nature of gold mineralization in the Boston Shear is comparable to that of the gold deposits at Timmins, Ontario (see Section 2.4). In Saskatchewan, regional till samples in the Star Lake and Tower Lake areas, within the La Ronge Domain, successfully delineated gold dispersal trains down-ice from mineralization (Sopuck et al, 1986). Narrow (75 to 150 m wide) dispersion trains identified by gold grain counts and heavy mineral gold analyses were detected for 300 m and 600 m down-ice, respectively. Anomalies in the -80 mesh fraction were restricted to the immediate area of mineralization compared to the large, distinct anomalies detected by gold grain counts and heavy mineral analyses. Several studies have tried to correct for the dilution of anomalous HMCs by far-travelled, shield-derived heavy minerals (Sopuck et al, 1986; Shelp and Nichol, 1987; Bloom and Steele, 1989; Bernier and Webber, 1989). For most of these studies, the erratic behaviour of gold concentrations in heavy minerals relates to the changes in heavy mineral abundances across the study area. This heavy mineral variability 174 may reflect the effects of several factors, such as: the composition and distribution of bedrock types, the nature of bedrock (heavy mineral) contributions to the till, the composition and distribution of overburden types, the reworking of surficial materials by water, and the degree of oxidation of the materials. The combined effects of these factors can influence the abundance of heavy minerals and their mineralogical characteristics (Bernier and Webber, 1989). Shelp and Nichol (1987) recognized the problem of variable HMC abundances and suggested that it is more meaningful to consider the weight (pg) of gold in the heavy mineral concentrates, based on the gold values (as ng/g) and weights (g) of the HMCs. However, this correction method fails to differentiate variations in heavy mineral abundances associated with dilution of HMCs by exotic material from that associated with local bedrock. A hypothetical situation involving two distinct tills can be used to demonstrate this point. In situation A, the till contains 10% heavy minerals that have a gold concentration of 100 ppb. In contrast, the till in situation B is heavy mineral poor (1% HMCs) and no gold was detected. Gold values in HMCs of till A would decrease with increased dilution by the barren HMCs of till B (Table 5.6). For example, if the dilution ratio is 50:50, the resulting HMC would have a gold concentration of 50 ppb. Similarly, if 90% of the barren HMC is incorporated into till A, a gold value of only 10 ppb would be detected. Therefore, if these dilution ratios are not considered in recalculating the HMC gold values, the estimated weight of gold would be greater than the actual amount. Bernier and Webber (1989) found that converting gold concentrations in HMCs to gold values in the total size fraction better corrects for dilution caused by the incorporation of far-travelled material. In order to obtain this conclusion, their model estimated the effect of progressive dilution by barren, exotic material on the gold concentrations in the HMCs and total size fraction. They found that the estimated gold values in the HMC and total size fraction are inversely proportionate to the amount of barren material that is added (Figure 5.2). Results also indicate that dilution is greater in heavy minerals than in the total size 175 Table 5.6. Hypothetical model illustrating how the gold values of H from one till are reduced by the progressive dilution by barren HMC second till containing far-travelled material. Hypothetical Percent Au situation HMCs value Till A 10% 100 ppb Till B 1% 0 ppb Dilution ratio Resulting Au Estimated weight B: A % HMCs (ppb) of Au (ug) 50:50 5.5 50 275 60:40 4.6 40 184 70:30 3.7 30 111 90:10 1.9 10 19 o h-o; o CL o CC C L < o o 0.4 0.2 Au (Total HM) / Au ( Local HM) Z O N E I ; Z O N E 2 Mixing Conditions L (HMA!= 0.1 wt.% F (HMA ) = 10 wt.% 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 _ 0 8 I PROPORTION OF LOCAL HM CO c o CL E • o O < \ a; CL e o cn "5 o < Figure 5.2. Effect of dilution by far-travelled materials on the gold concentrations in heavy minerals (HM) and total size fraction (Total Sample). L = local component; F = far-travelled component; HMA = heavy iriineral abundance (after Bernier and Webber, 1989). 177 fraction and thus, gold concentrations decrease drastically in HMCs with slight dilution whereas decreasing gold values in the total size fraction are only apparent at stronger dilutions. Based on these recalculations, Bemier and Webber (1989) found that no new anomalies were identified, however, the conversion did remove some of the erratic behaviour of HMC gold concentrations. Based on these findings, this method of correcting for dilution was used in the present study area. Gold concentrations in the regional till HMCs were recalculated to gold concentrations in the normalized size fractions based on a 10 kg field sample. This conversion was based on multiplying the gold values of HMCs (pg/g) by their respective weights (g) to give the weight of gold (pg) in the HMCs, and then dividing by the normalized weight (g) of the size fraction. This gives the normalized gold values (ppb) of the total size fraction plotted in Figure 5.3. The resulting gold distribution pattern is very similar to the pattern identified by the gold values in HMCs and the -53 pm fraction (Figures 4.18 to 4.16, respectively). However, since there is not much variation in the weight percentages of HMCs obtained from the regional till samples (Appendix), this correction for dilution does not improve the definition of the anomalous zone. Marine submergence of the Bathurst Inlet area resulted in the deposition of marine sediments over till (Dyke and Dredge, 1989; Ryder, 1992). Dyke and Dredge (1989) describe these marine sediments as predominantly horizontally stratified silts, clays and fine sands that represent distal glacial marine sediments. Ryder (1992) states that during marine submergence of the area, rock flour derived from sources to the south and southeast, was carried into the ocean by meltwater streams from the glacier. This resulted in the deposition of marine sediments on top of till. These marine sediments have been identified as being geochemically barren of gold (Table 4.6) and appear to effectively blanket gold anomalies in the underlying materials. This is especially the case in areas with a thick cover of marine sediments, such as in the eastern portion of the upper plateau near the Baseline. Marine sediment thicknesses are not known for certain but are thought to be about 1 m thick near the Baseline and become thicker in a valley to the east. 178 179 A rapid decline in relative sea level occurred during isostatic rebound and as the land emerged from the sea, surficial materials at the land surface were washed by waves. This caused the marine sediments and till to be reworked (or sorted) and redistributed (Ryder, 1992). In the Wally Grid area, pockets of washed till were identified by Ryder (1992) and observed by the author in soil pits on the upper plateau and western slope. Gold concentrations in these materials are subdued compared to the local materials (Figures 4.9 to 4.12). 5.3.2 The younger gold anomaly in locally-derived materials The anomalous zone defined by gold concentrations in locally-derived materials on the plateau represents the relatively young geochemical anomaly developed in thin, less than 1 m thick, overburden. As described in Chapter 4, the cross section distribution of gold values along the three sampling lines shows that for the majority of the soil profiles, gold values decrease from the upper A and B horizons to the lower C horizons for the -212 pm fraction (Figures 4.10 to 4.12). This is especially the case for soil profiles in mixed till frost boils and mud hummocks since they directly overly regional till and marine sediments, respectively, that typically contain < 5 ppb gold. Exceptions occur, however, for pits with the lowermost horizons directly overlying mineralized bedrock. As these horizons typically contain a large proportion of local bedrock fragments and are highly auriferous, gold concentrations in these profiles increase with depth. In cross section, the anomalous gold zone has a 'mushroom-shaped' vertical distribution pattern in which the anomalous zone defined by the near-surface, A and B horizons is approximately 10 to 50 m broader than the anomaly in the underlying, C horizons. The strongly anomalous gold zone on the plateau corresponds to surficial materials classified as weathered rock by Ryder (1992) (Figure 2.6); these materials represent the local stony frost boils and soil horizons directly overlying mineralized bedrock. Very strong (100's to 1000's ppb) gold concentrations are 180 associated with these materials, defining a narrow anomalous zone around the source that is flanked on either side by weakly anomalous mixed and regional till (Figures 4.9 to 4.12). Gold concentrations of samples collected from the surface of individual local stony frost boils (Table 4.11) indicate that there is no systematic variation of gold values across the surface. These gold anomalies can be explained by a number of periglacial processes that continue to modify surficial materials within the active zone. These periglacial processes, including cryoturbation and differential frost heave, result in patterned ground (ie. frost boils) whereas, downslope movement of materials results primarily from solifluction. Due to the high proportion (> 80%) of weathered bedrock fragments in the local frost boils, it is difficult to identify whether the original materials were regional till. Nevertheless, if the original material was regional till, it is apparent that the periglacial processes have greatly modified and overprinted any weak glacial gold anomaly that may have been present. During the development of frost boils in the relatively thin (< 1 m thick) overburden on the plateau, the mechanical actions resulting from cryoturbation and differential frost heave have incorporated large amounts of weathered bedrock. Frost action and cryoturbation result in the mechanical disintegration of sand and coarse mineralized fragments to silt and very fine sand (Rieger, 1983), thereby releasing free gold and heavy minerals with inclusions of gold. The presence of fine particles was evident in soil horizons from local stony frost boils that contain, on average, 35 to 50% of the -2000 pm material in the silt-clay (-53 pm) fraction (Table 4.1). As a result of these processes, gold in the local materials is incorporated into the silt-clay and fine sand fractions. Cryoturbation and differential frost heave are thought to produce a "circulation cell" whereby materials at depth are continually brought to the surface through the centre of the frost boil, move laterally across the surface and forced back down to depth along the margins (Mackay, 1984). However, while collecting samples on the plateau area of the Wally Grid, it was observed in many cases that the upward movement of materials is not restricted to the centre of the frost boils. Considering that most of the surface material was damp, this suggests that the entire surface area of the frost boils is active. Warburton (1990) identified similar features in sorted circles (or frost boils) and termed this secondary sorting. The processes that produce patterned ground do not appear to result in the sorting of gold particles on their surface as no variations in gold concentrations were observed across the surface of individual local frost boils (Figure 4.15). Rieger (1983) and Van Vliet-Lanoe (1991) found that cryoturbation is affected by granulometry. They state that patterned ground is more developed in fine-grained than coarser grained material. Rieger (1983) also noted that the surface area of frost boils is directly related to their degree of development. These features occur in the different frost boil types in the Wally Grid area. For example, frost boils developed in the locally-derived materials that contain up to 50% silt-clay fraction, reach depths up to 1 m and vary in diameter from 1 to 3 m. Mixed till and regional till contain up to 37% silt-clay material and up to 44% fine sand (-212+53 pm) material and are thereby coarser grained than the local materials. Frost boils developed in these till materials are generally 15 to 50 cm deep and 20 to 50 cm in diameter. However, mud and earth hummocks in marine sediments do conform to this model. They contain up to 90% silt-clay material but hummocks reach depth of only 50 cm. These materials commonly have thin active layers because of the insulating effects of vegetation cover and could explain why hummocks in marine sediments do not reach great depths. On the western slope of the ridge, buried Ah horizons found in soil pits can be explained by solifluction (Williams and Smith, 1989; Warburton, 1990). On the gentle to steep (2° to 14°) western slope, solifluction sheets and benches were observed. As the maximum downslope movement is in the upper part of the soil, there is a progressive overriding and burial of vegetation which results in buried organic layers, irregular textural boundaries and tongues of intruding materials (Williams and Smith, 182 1989). This stratification of soil and organic horizons occurs in several soil pits on the upper portion of the western slope. Arrangement of stone fragments result from the orientation of their long axes in the direction of flow associated with solifluction (Warburton, 1990). Similar orientations and movement of local bedrock materials were observed on the gentle and steep areas of the western slope ass well as on the gentle slopes of the upper plateau. The down-slope migration of local anomalous materials contributes to the formation of the mushroom-shaped gold dispersion. Hydromorphic dispersion may modify the younger gold anomaly. Mobilization and leaching of elements is confined to the thin active layer because of the permafrost below. During the summer months, the active layer thaws and is mechanically modified and flushed with meltwaters. Miller (1979) found that hydromorphic dispersion resulted in soils and LFH horizons being depleted in Zn and Cu. Well-developed hydromorphic anomalies were identified for these elements but were found in lake sediments. In the Wally Grid area, water movement within the active layer is evident. Water frequently collected in the bottom of pits as a result of thawing sediment but may also be due to water movement along the top of the frozen ground. On several occasions when drilling was taking place on the plateau, drill water was observed within several hours in pits 100 to 200 m away. In one case, drill water completely filled a pit 118 cm deep. A number of seepage zones or bogs occur in low-lying areas of the grid. Gold results of waters collected from the bottom of soil pits and from bogs range from 1.6 ppt to 4.5 ppt (Appendix) suggesting that minor hydromorphic migration of gold occurs within the active layer. As there is no evidence of high fineness gold rims on cross-sectioned gold grains from the HMCs of the regional till and one C horizon sample (Section 4.6), no secondary enrichment is evident on the gold grains. However, buried organic-rich lenses in a number of soil pits have gold values greater than the overlying and/or underlying horizons (Figures 4.10 to 4.12) that may result from hydromorphic dispersion. For example, organic lenses from pits in mixed till along Line 120+00N (Figure 4.10), have gold values of 180 and 212 ppb compared to 45 ppb gold in the underlying till horizon. Gold in solution may exist as gold 183 complexes but may be reduced by the carbon in the organic materials; this results in the precipitation of gold and enrichment of these buried, organic-rich materials. As discussed in Section 4.4, gold concentrations of LFH horizons at pit sites range from 9 to 652 ppb and define anomalous zones similar to those defined by the mineral horizon samples. These LFH gold anomalies are 10 to 30 m broader than those identified in All horizons and up to 50 m broader than the anomalies in C horizons. Plant roots were not observed below about 20 cm depth. Gold anomalies of these LFH horizons appear to reflect the near-surface mineral horizons (Table 4.14) and thus, have a local control. Biogenic uptake of gold (and other metals) from solution by plants enables them to be enriched in metals (Warren, 1986; Dunn, 1985). The accumulation of material from these plants results in the LFH horizons being enriched in gold. However, the incorporation of mineral matter in LFH horizons may result in elevated gold concentrations. This mineral matter may result from the incorporation of wind-blown material from adjacent anomalous materials, and contamination during sampling from the mineral matter of underlying horizons. 5.4 Recommendations for mineral exploration / Due to the differences in gold concentrations and mode of occurrence of gold among the different surficial material types, it is necessary to divide this section into (i) reconnaissance scale, and (ii) property scale recommendations. 5.4.1 Sample representativity As discussed in Section 1.3, in order for geochemical samples to be representative and obtain a precision of at least ± 45% at the 95% confidence level, samples must contain a minimum of 20 particles of 184 gold (Clifton et al, 1969). Conversely, provided that samples are collected at a sufficient density, Stanley and Smee (1988; 1989) argued that geochemical soil anomalies could be recognized with samples that contain one particle of gold, even though this corresponds to a precision of only ± 200%. Since the main goal of an exploration survey is to identify geochemical anomalies that will lead to mineralization, the level of sample representativity should reflect the needs of the survey. On a reconnaissance scale, sample densities are generally low and anomaly recognition is based on individual samples. These samples should be more representative and, therefore, be large enough to contain 20 particles of gold. However, if samples are closely spaced, as is generally the case of a local scale survey, smaller, less representative samples may be sufficient. In this section, reference will be made to reconnaissance scale samples containing 1 grain of gold as well as the more conservative requirement of 20 particles of gold, and local scale samples containing 1 particle of gold. 5.4.2 Reconnaissance scale Based on the gold results of the size and density fractions of regional till, it is suggested that this material can be used as a sampling medium for reconnaissance scale exploration. An anomalous gold zone that extends for more than 1 km down-ice from the known mineralization was identified by the heavy minerals and the silt-clay fractions, although die contrast and concentrations of gold in the silt-clay fraction are lower. As previously mentioned, the -53 pm fraction of the regional till typically contains over 60% of the gold with most of the balance residing in the heavy minerals of the -106+53 pm fraction (Table 5.3). Very conservative (minimum) numbers of gold particles in the analytical portions of the silt-clay fraction, estimated assuming 50 pm spheres, revealed that only 3 of the samples could contain one particle of gold (Table 5.4). Therefore, larger subsamples would be required if all the samples were to be representative. Estimations of the number of gold grains based on a more realistic diameter of 20 pm indicate that each of the eleven 30 g subsamples could contain sufficient gold to form between 3 and 25 gold particles. Because 185 calculations suggest that most of the HMCs of the -106+53 um fraction contain less than 1 particle of gold, larger subsamples would also have to be analyzed to yield representative results. Silt-clay fraction Based on the above assumptions, subsample weights required to give 1 and 20 particles of gold in the size and density fractions of regional till were calculated (Table 5.7). The amount of field material required to contain these representative subsamples was also estimated (Table 5.8) based on collecting only -2000 pm material. For the -53 pm fraction, results indicate that between 18 and 119 g of silt-clay material is needed if the analytical portions are to contain 1 gold grain 50 pm in diameter (Table 5.7). Subsample weights increase to between 400 and 2400 g if 20 particles of gold are required. Most of these analytical portions are too large to be efficiently analyzed by FA-AAS and thus, another method of analysis (eg. cyanidation) would be needed if sample errors are to be reduced. In order to obtain enough field material to provide 1 or 20 particles of gold, up to 415 g and 8300 g, respectively, of -2 mm material would be required (Table 5.8). The above calculations are all based on the very conservative estimate that gold particles'bccur as 50 pm spheres. Assuming a gold grain diameter of 20 pm, only 2 to 8 g of silt-clay material is needed to contain 1 gold grain in the analytical portion, corresponding to a maximum field sample weight of 27 g. If the representative subsamples are to contain 20 gold grains, a minimum 530 g field sample would be needed. Subsamples of this size can be analyzed by FA-AAS but, as noted in Chapter 4, gold was not detected in 60% of the -53 pm subsamples mainly due to the 5 ppb detection limit. Therefore, a method of analysis having a lower detection limit for gold, such as the AR column-ICP method (0.1 ppb gold detection limit), would give the best anomaly detection for the -53 pm fraction. Very conservative calculations based on the AR column-ICP gold results (Tables 5.7 and 5.8) indicate that a 320 g subsample of -53 pm material should 186 Table 5.7. Subsample weight (g) required to obtain 1 and 20 particles of gold i n the size and density f ract ion o f the regional t i l l frost boils and one C hor izon sample. Based on estimated number of go ld part ic les (Table 5.4), 30 g subsamples for F A - A A S analyses, and 50 g subsamples for A R co lumn- ICP analyses. Sample Size fraction number -106+53 um -53 um -53 p m * H M C G r a i n diameter 75 um 50 um 20 um 50 um 20 p m N o . of particles 1 20 1 20 1 20 1 20 1 20 049 ** ** 48 960 053 — — — - - - ** ** 51 1020 054 119 2376 8 152 192 3840 12 240 055 11 222 — - - 205 4100 13 260 056 — — - - - ** ** 23 460 057 115 2290 — - - - »* ** 45 900 058 33 668 — - - - 122 2440 8 160 059 — 79 1578 5 102 ** ** 48 960 060 — — - - - ** ** 45 900 061 — 26 526 2 34 ** »* 36 720 062 4 78 — - - - ** ** 22 440 063 27 534 119 2376 8 152 77 1540 5 100 070 11 216 59 1188 4 76 100 2000 6 120 071 36 728 119 2376 8 152 313 6260 20 400 072 73 1458 — - - - 192 3840 12 240 073 *» ** — — - 321 6420 21 420 074 ** ** 18 366 1 24 39 780 2 40 075 — — — - - - . ** ** 95 1900 076 16 320 34 678 - - 2 44 89 1780 6 120 077 38 764 59 1188 4 76 137 2740 9 180 078 ** ** — — ** ** 127 2540 ** ** ** ** * * 079 * * — — — 080 67 1336 — - - - 198 3960 13 260 257 — 30 594 2 38 ** ** 38 760 258 ** ** 119 2376 8 152 205 4100 13 260 259 89 1782 — - - - ** ** 25 500 260 13 254 - - - 68 1360 4 80 203*** 0.14 2.80 0 12 2.4 0.01 0.20 n/a n/a n/a n/a Note: * = A R co lumn- ICP gold results; * * * = C horizon sample; ~ = gold values were < 5 ppb; * * = no calculations for samples wi th <=0.15 estimated number of gold particles; n/a = material not avai lable for analysis. 187 Table 5.8. Field sample weight (g) of-2000 um material required to obtain 1 and 20 particles of gold in the siz and density fractions of regional till frost boils and one local C horizon. Based on estimated subsample weights (Table 5.7), size and density fraction weights and field sample weights (Appendix). Sample Size fraction number -106+53 um -53 um -53 um* HMC Grain diameter 75 um 50 um 20 um 50 nm 20 um No. of particles 1 20 1 20 1 20 1 20 1 20 049 ** ** 153 3060 053 — — — - - - ** • * 145 2900 054 _ 415 8301 27 531 669 13380 43 860 055 93 1865 — — - - 625 12500 40 800 056 — — - -- - - ** ** 76 1520 057 770 15402 — - - - ** ** 148 2960 058 224 4470 — — - - 572 11440 37 740 059 — 228 4551 15 291 ** ** 137 2740 060 — — — ** ** 195 3900 061 __ 85 1695 5 109 ** ** 116 2320 062 46 910 — - - - ** ** 54 1080 063 199 3976 337 6735 22 431 217 4340 14 280 070 80 1591 163 3264 10 209 274 5480 18 360 071 270 5392 376 7522 24 481 990 19800 63 1260 072 914 18273 — - - - 538 10760 34 680 073 »* ** — — — - 1356 27120 87 1740 074 *• ** 148 2959 10 189 312 6240 20 400 075 — — — - ** ** 283 5660 076 105 2096 Ill 2210 - 7 141 291 5820 19 380 077 228 4566 147 2934 9 188 337 6740 22 440 078 ** ** __ _ — ** ** 396 7920 079 *» ** - - - - ** ** ** ** 080 834 16686 — - - - 623 12460 40 800 257 85 1698 5 109 ** ** 109 2180 258 1316 26314 318 6364 20 407 549 10980 35 700 259 760 15194 — - - - ** ** 73 1460 260 94 1879 - - -- 231 4620 15 300 203*** 1 24 0.25 5 0.02 0.3 n/a n/a n/a n/a Note: * = AR column-ICP gold results; *** = C horizon sample; - = gold values were < 5 ppb; ** - no calculations for samples with <=0.15 estimated number of gold particles; n/a = material not available for analysis. 188 be analyzed to obtain one 50 pm gold grain, corresponding to a field sample weight of 1350 g. Assuming a 20 pm grain diameter, 50 g analytical portions for all but two of the samples would contain 1 gold grain. For these samples, up to 4 kg of field material would be needed to provide representative subsamples containing 20 gold particles. Heavy mineral concentrates of the very fine sand fraction Heavy mineral concentrates are commonly used in gold exploration because the HMCs derived from a bulk field sample effectively contains most if not all of the free gold in the entire field sample that is sand sized. This is only true, however, if gold is present as free particles and not associated as inclusion in the light minerals. In the present study area, no gold was detected in the light minerals of the regional till coarser than 53 pm (Table 4.16) and thus, gold resides exclusively in the heavy minerals. For this reason, analysis of the heavy mineral concentrates gave the best anomaly contrast whereby the dilution caused by the incorporation of barren light minerals is removed. Estimates of the number of gold particles in the HMCs (Table 5.4), based on the assumption that free gold exists as 75 pm spheres, indicate that most of the HMCs are not representative as they contain less than 1 particle of gold. In order to obtain 1 gold grain in the subsamples, 11 to 800 g of HMCs would have to be analyzed (Table 5.7); this corresponds to field sample weights of 46 g to 9.6 kg. However, since the estimates of the number of gold particles in the HMCs suggest that the majority of the gold in the heavy minerals is present as inclusions and not free gold, these calculations become invalid. The amount of heavy minerals that were analyzed, weighing between 14 and 30 g, may actually be representative if the gold is present as finer grained inclusions within the heavy minerals. As previously mentioned, analysis of the -106+53 pm HMC fraction effectively identified a zone of elevated gold concentrations down-ice from the mineralization. However, 3 to 10 kg of field material is required to provide these HMCs. 189 Sieving techniques Results of this study are based on the weight of size and density fractions obtained by wet sieving. Although this wet sieving technique is more effecient at extracting the -53 um fraction than dry sieving (Day, 1988), it clearly requires more time and effort than does dry sieving. Similarly, obtaining this fine fraction by either sieving technique also requires more time than does sieving to a coarser (-212 um) fraction. Delaney (1992) found that generally a 30 g subsample of -212 pm material can be obtained by dry sieving a 500 g field sample for 4 minutes. As mentioned in Chapter 4, gold values in the -212 pm fraction of regional till were commonly at or near the 5 ppb detection limit by FA-AAS whereas gold was detected in the -106+53 pm HMC fraction and the -53 pm fraction. Thus, regional till samples should be sieved to obtain sufficient amounts of -53 pm material to remove the coarser barren material and provide representative samples. 5.4.2.1 Summary of recommendations for reconnaissance scale sampling Regional till on the Wally Grid and the areas to the north and south is widespread. Regional till was estimated to comprise about 50% of the Wally Grid area based on terrain mapping by Ryder (1992). Areas to the north and south have larger areas covered with t i l l , and these materials can effectively be used as a sampling medium for reconnaissance scale exploration surveys. The central portion of regional till frost boils should be sampled but not from frost boils that contain local pebble lithologies on the surface mixed with till pebbles (see Figure 2.11). Based on the gold dispersal train in the regional till being up to 2 km in length and roughly 50 to 250 m wide, rectangular sampling grids should be used whereby grid lines are spaced 500 m apart and samples taken at 40 m intervals. Based on the above calculations, 50 g subsamples of the -53 pm fraction 190 should be analyzed by AR column-ICP, or another method of analysis having a low detection limit for gold. A standard geochemical sample (500 g) of -2 mm field material would provide sufficient material for analysis. If samples are to be processed by dry sieving, a 1 kg field sample should be collected. As a complement to gold results of the -53 um fraction, a large 3 to 5 kg field sample could be used to analyze the heavy minerals of the -106+53 um fraction. Costs would increase but gold results would give an extra degree of assurance in identifying gold anomalies. Problems may arise during sampling at the reconnaissance scale if marine sediments are encountered as gold was not detectable in these sediments. Biogeochemical sampling may be used in these cases but gold results can not be guaranteed. Further study is, therefore, needed to address this problem and to determine whether there is a geochemical sampling method that can be used in these areas. 5.4.3 Property scale Based on the gold results of pit horizons on the Wally Grid, the mixed till and locally-derived materials can be sampled at the property scale. For most of the soil pits, gold values decrease from the upper A and B horizons to the lower C horizons for the -212 pm fraction. Exceptions occur, however, for horizons directly overlying mineralized bedrock and for these cases, gold concentrations increase with depth. As previously mentioned in Chapter 4, in cross section, the anomalous gold zones on the plateau have a mushroom-shaped vertical distribution pattern in which the anomalous zone defined by the near-surface horizons is 10 to 50 m broader than the anomaly in the underlying horizons. Therefore, these easily accessible A and B horizons, rather than the horizons at depth, can effectively identify the gold anomaly at the property scale. Using these near-surface horizons will also reduce the amount of time and effort required in obtaining geochemical exploration samples. Local stony frost boil samples can essentially be used as an extension of bedrock sampling because they contain moderately to strongly anomalous (100's to 1000's ppb) gold results in proximity to the mineralization. 191 Samples on the Wally Grid were modelled based on the arguement by Stanley and Smee (1988; 1989) that a geochemical anomaly can be recognized with samples containing 1 gold grain. Estimates were also made for samples containing 20 gold particles. The subsample weights required to give 1 and 20 particles of gold in the local scale samples were estimated, as well as the amount of -2 mm field material needed to provide these required subsample weights. Mixed till As previously mentioned in Section 5.1, over 90% of the gold in the two mixed till samples occurs in the silt-clay fraction (Table 5.1). Estimates of the number of gold particles for these samples (Table 5.2) indicate that gold is probably present as inclusions in the fine sand fraction but as particles less than 50 pm in diameter in the silt clay fraction. Based on these results, up to 13 (50 pm) gold grains could occur in the silt-clay fraction based on 30 g analytical portions and could effectively be used to identify gold anomalies (ie. sufficient to contain at least 1 50 pm gold grain). Subsample weights are reduced to 4 g if only one gold particle is required in the mixed till samples (Table 5.8); this corresponds to a field sample weight of only 11 g (Table 5.9). A field weight of only 220 g is needed if the samples are to contain the more representative 20 gold grains (50 pm in diameter). Estimates for the silt-clay fraction based on a/20 pm grain diameter show that a subsample and field sample weight of 5 g and 14 g, respectively, is needed to contain 20 gold grains in the samples. Therefore, at the property scale, a 5 to 30 g subsample of the -53 pm fraction can effectively be analyzed by FA-AAS to identify gold anomalies in the mixed till. A 220 g field sample of -2 mm materials should be collected to provide these subsamples. Locally-derived materials As previously described, local stony frost boils are commonly moderately to strongly anomalous because they contain a high proportion of locally-derived mineralized bedrock. Based on 30 g subsamples, 1 Table 5.9. Subsample weight (g) required to obtain 1 and 20 particles of gold in the -212+53 um and -53 pm fractions of pit horizons along L124+00N. Location/ Soil pit Soil Au (ppb) Size fraction sample number type horizon -212 um -53 um -212+53 um -53 um -53 um Particle diameter 75 um 50 Um 20 |im No. of particles 1 20 1 20 1 20 11+70 E 214 Mixed till B l 345 535 61.6 1232 2.2 44.4 0.14 2.84 216 BC 160 295 163.2 3264 4.0 80.6 0.26 5.16 219 Local stony B l 1510 2160 18.3 366 0.6 11.0 0.04 0.70 220 frost boil B2 3570 4670 4.1 82 0.3 5.0 0.02 0.32 11+80 E 202 Local stony B l 4620 5580 3.2 64 0.2 4.2 0.01 0.28 204 frost boil B2 6690 8280 9.2 184 0.1 2.8 0.01 0.18 203 C 8410 10280 0.8 16 0.1 2.4 0.01 0.14 12+20 E 208 Local stony B l 45 70 ** ** 17.0 339.4 1.1 21.7 210 frost boil B3 35 50 ** ** 23.8 475.2 1.5 30.4 ** = no calculations were made for samples with < 0.15 estimated number of gold particles. Table 5.10. Field sample weight (g) of-2000 um material required to obtain 1 and 20 particles of gold in the -212+53 um and -53 um fractions of pit horizons along L124+00N. Location/ sample number Soil pit type Soil Size fraction horizon -212+53 um -53 Um Particle diameter 75 um 50 Um 20 um No. of particles 1 20 1 20 1 20 11+70 E 214 Mixed till B l 215 4304 5.3 106 0.3 6.8 216 BC 449 8978 11.0 220 0.7 14.2 219 Local stony B l 78 1568 1.2 24 0.1 1.6 220 frost boil B2 18 350 0.5 10 0.0 0.6 11+80 E 202 Local stony B l 20 406 0.4 8 0.02 0.40 204 frost boil B2 87 1736 0.3 6 0.02 0.40 203 C 3 60 0.3 6 0.02 0.40 12+20 E 208 Local stony B l ** ** 42.1 842.0 2.7 53.8 210 frost boil B3 ** ** 60.5 1210.0 3.9 77.4 ** = no calculations were made for samples with < 0.15 estimated number of gold particles. 194 moderately anomalous local materials are estimated to contain up to 39 particles of gold (75 um diameter) in the fine sand fraction and more than 55 gold grains in the silt-clay fraction (Table 5.2). Although these subsamples are representative, the weights required to contain 1 and 20 gold grains were calculated to determine the minimum subsample weight that could be analyzed (Table 5.9). Results indicate that for the highly anomalous samples, up to 20 g of the fine sand (-212+53 pm) fraction is needed to contain one gold grain whereas 1 g or less is required for the silt-clay fraction. Comparing these results to those obtained for the mixed till samples, it is apparent that as the gold concentrations of the local materials increase, the required subsample size decreases. For both size fractions, 100 g of -2 mm field material should be collected. For the weakly anomalous (35 and 45 ppb) local frost boils, 25 g portions of the silt-clay material are necessary to obtain representative samples, corresponding to a field sample weight of 60 g. Gold in the fine sand fraction of these frost boils probably occurs as inclusions and thus, only the silt-clay fraction should be analyzed. Estimates of the number of gold particles in the size and density fractions of a local C horizon (Table 5.4) also indicate that 30 g subsamples of the -106+53 pm HMCs, and silt-clay fraction are representative as they could contain over 230 free particles of gold. Calculations determining the subsample weights to contain 1 gold grain (Table 5.7) indicate that less than 1 g of material from either of these fractions is needed. Based on these estimations, a 25 g field sample of the locally-derived material would yield one or more gold particles in the -106+53 pm HMCs and the -53 pm fraction. Analysis of the -53 fraction versus the -212 ^infraction The above recommendations are based on the gold concentrations and distribution of materials down to the silt-clay size. However, gold results in the -212 pm fraction of local materials successfully identified anomalous gold zones in the near-surface horizons of the Wally Grid (see Section 4.3.3). Thus, 195 sieving these materials to extract the -212 um fraction may give representative samples. The number of gold particles in the -212 um fraction were recalculated based a 50 um grain diameter (Table 5.11) since over 75% of the gold in these local materials occurs as free particles less dian 50 um. A comparison of these gold grain estimates to the ones previously estimated for the -53 um fraction (Table 5.2) indicate that only slightly fewer 50 um gold particles occur in the -212 um fraction than in the silt-clay fraction. Therefore, sample representativity would not be greatly reduced if the coarser (-212 um) fraction of these local materials were analyzed by FA-AAS. Up to 30 g of -212 um material would be required to yield subsamples containing 1 gold grain (Table 5.11); this corresponds to a field sample weight of 60 g. Erratic gold concentrations caused by the nugget effect may result from using this size fraction. However, this would probably be rare considering over 75% of the gold in these samples occurs as fine (< 50 pm) gold. For this reason, preparation of heavy mineral concentrates is not necessary for the local samples. 5.4.3.1 Summary of recommendations for property scale exploration For the mixed till and locally-derived materials on the Wally Grid, the near-surface (A and B) horizons should be sampled. In order to obtain the most representative gold results, 30 g of the -53 pm fraction should be analyzed by FA-AAS. It is suggested that in order to reduce the amount of time that is necessary to process the field samples, 30 g subsamples of the -212 pm fraction could be analyzed even though the sample representativity is slightly reduced. Based on the above estimations and the width of the gold anomaly that was identified by the gold results, a 400 g field sample collected at 10 to 20 m spacings should effectively identify the anomalous gold zones. If marine sediments are encountered at the local scale, these materials should be avoided during sampling as they appear to blanket out the underlying materials and any geochemical anomalies that may be associated with them. Table 5.11. Estimated number of 50 um gold particles in a 30 g subsample of the -212 pm fracti of pit horizons along L124+00 N , with the associated subsample weight (g) required to obtain 1 a 20 particles of gold, and the necessary field sample weight (g) to contain the subsample. Location/ Soil pit Soil -212 um fraction sample number type horizon Estimated no. Subsample Necessary field of particles weight (g) sample weight (g) Particle diameter 50 pm 50 um 50 pm No. of particles 1 20 1 20 11+70 E 214 Mixed till B l 8.7 3.4 68 4.9 97.2 216 BC 4.0 7.4 148 10.2 203.8 219 Local stony B l 38.1 0.8 16 1.1 22.6 220 frost boil B2 90.2 0.3 6 0.4 8.6 11+80 E 202 Local stony B l 116.7 0.3 5 0.4 7.4 204 frost boil B2 169.0 0.2 4 0.3 6.8 203 C 212.4 0.1 3 0.2 4.0 12+20 E 208 Local stony B l 1.1 26.4 528 40.5 810.0 210 frost boil B3 0.9 33.9 678 60.2 1203.8 Chapter Six - CONCLUSIONS AND RECOMMENDATIONS 198 CONCLUSIONS AND RECOMMENDATIONS Based on the results of this study, several conclusions can be made about the mode of occurrence of gold and the spatial distribution of gold concentrations in the various surficial materials: • On average, 31% of B horizon material from frost boils in regional till resides in the -53 um fraction whereas similar horizons in weathered rock contain 49% of the -53 um fraction. Marine sediments have 82% of C horizon material in the silt-clay (-53 um) fraction. Ah, B and C horizons from pits in local stony frost boils and mixed till frost boils contain a higher proportion of silt-clay than -212 pm sand although this difference and the amount of silt decreases with depth. • Heavy mineral concentrates (HMCs) of regional till comprise 2.4% and 3.3% of the -212+106 um and -106+53 um fractions, respectively. In contrast, HMCs of a local C horizon directly overlying mineralized bedrock comprise 4.2% and 6.5% of the respective size fractions. • Regional till has a large portion (60 to 100%) of the gold in the -53 pm fraction with most of the balance residing in the -106+53 um HMC fraction. Although locally-derived materials have greater than 75% of the gold less than 53 pm, heavy minerals of the fine sand fractions also contain moderate amounts of gold. • Gold concentrations are relatively weak in the mixed and regional till compared to the locally-derived materials. Local stony frost boils typically have gold values that are lOx to 100x greater than the other surficial materials as they contain a high proportion of weathering, local bedrock fragments. Results show that there is no systematic variation of gold values across the surface of individual local frost boils. Finally, gold was not detectable for the marine sediments. 199 • Based on the above results, two distinct types of gold anomalies were interpreted to occur in the study area: (i) an older gold anomaly in regional till caused by glacial dispersion, and (ii) a younger gold anomaly in locally-derived materials caused the postglacial modifications in a periglacial environment. • For the older gold anomaly, gold values of the -106+53 um HMC fraction and the -53 um fraction of regional till define a 50 to 250 m wide anomalous gold zone that extends for less than 2 km down-ice. However, the gold concentrations and anomaly contrast is lower in the silt-clay fraction. • For the younger geochemical anomaly, gold concentrations in soil profiles generally decrease with depth except for profiles where the lowermost horizons directly overly mineralized bedrock. In cross section, anomalous gold zones have a 'mushroom-shaped' vertical distribution pattern in which the gold anomaly in the near-surface, A and B horizons is 10 to 50 m broader than the anomaly in the underlying C horizons. Recommendations for gold exploration can also be made: • For reconnaissance scale exploration, a 50 g subsample of the -53 um fraction of regional till should be analyzed by a reliable analytical method that has a detection limit lower than 5 ppb gold. A standard, 500 g sample of -2 mm field material could be collected. Sampling lines should be spaced 500 m apart and oriented perpendicular to ice flow direction, with samples collected every 40 in. • As a complement to gold results of the -53 um fraction of regional till, a large 2 to 5 kg field sample could be used to analyze the heavy minerals of the -106+53 um fraction for gold. This would provide an extra degree of assurance in identifying gold anomalies at the reconnaissance scale. • At property scale exploration, a 30 g subsample of the -53 um fraction should be analyzed for gold by FA-AAS. Sample representativity, however, is only slightly reduced if a 30 g subsample of the -212 um fraction is 200 analyzed for gold. A 500 g field sample should initially be collected at 10 to 20 in spacings along grid lines 100 m apart. Infill sampling lines should be at 50 in spacings. Marine sediments appear to blanket the underlying materials and geochemical anomalies that may be associated with them. 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Evanston, II: SYSTAT, Inc. 207 APPENDIX Weight (g) of material in each size fraction of the lowermost horizons from soil pits 208 Weight (g) of material in each size fraction of A, B and C horizons from selected soil pits along L120+00N, 122+00N and 124+00N, sieved down to -212 pm fraction 209 Weight (g) of material in each size fraction of A, B and C horizons from selected soil pits along L124+00N, sieved down to -53 pm fraction 211 Weight (g) of material in each size fraction of surface B horizons from local stony frost boils 212 Weight (g) of material in each size fraction of central B horizons from regional till frost boils, and one local C horizon directly overlying mineralized bedrock 213 Normalized weight (g) of material in each size fraction of regional till frost boils and one local C horizon. Normalized to 10 kg of -2000 pm material 214 Weight (g) of light mineral fractions (LMF) and heavy mineral concentrates (HMC) of the -212+106 pm and -106+53 pm size fractions of regional till frost boils and one anomalous C horizon, for the first and second separations 215 Weight percent (%) of material in each size fraction of the lowermost horizons from soil pits 216 Weight percent (%) of material in each size fraction of A, B and C horizons from selected soil pits along L120+00N, 122+00N and 124+00N, sieved down to -212 pm fraction 217 Weight percent (%) of material in each size fraction of A, B and C horizons from selected soil pits along L124+00N, sieved down to -53 pm fraction 219 Weight percent (%) of material in each size fraction of surface B horizons from local stony frost boils 220 Weight percent (%) of material in each size fraction of central B horizons from regional till frost boils, and one local C horizon directly overlying mineralized bedrock 221 Weight percent (%) of material in each size fraction normalized to 10 kg of -2000 pm material, for regional till frost boils and one local C horizon 222 Weight percent (%) of light mineral fractions (LMF) and heavy mineral concentrates (HMC) of the -212+106 pm and -106+53 pm size fractions of regional till frost boils and one anomalous C horizon, for the first and second separations 223 Electron microprobe analyses of the cores and rims of gold grains recovered from the -106+53 pm HMC fraction of one regional till frost boil sample, and from the -212+106 pm and -106+53 pm HMC fractions of one anomalous C horizon 224 Gold (ppt), chloride (mg/L) and sulphate (mg/L) concentrations of water samples collected from lakes, bogs, seepage zones and soil pits in the Wally Grid / Spyder Lake area 226 N. Weight (g) of material in each size fraction of the lowermost horizons from soil pits. 208 Location: Soil pit Sample Soil Size fraction (pm) Total wt. Northing/ type number horizon +2000 -2000+425 -425+212 -212 -2000 pm easting (g) L120+00 N 11+30 Mixed till 092 B 11+45 Mixed till 087 C 11+70 Local fr. boil 081 C 11+90 Marine sed. 146 Bm 12+10 Load fr. boil 140 B2 12+30 Mixed till 130 C 12+50 Mixed till 135 B2 12+80 Regional till 098 C 13+00 Regional till 107 C2 13+20 Regional till 125 C3 L122+00 N 11+10 Mixed till 199 C2 11+30 Mixed till 188 Cl 11+50 Regional till 170 C3 11+80 Local fr. boil 307 C 12+10 Local fr. boil 154 B2 12+30 Local fr. boil 300 C2 12+60 Marine sed. 160 B2 13+00 Marine sed. 113 C 13+40 Marine sed. 116 B2 L124+00 N 10+85 Local fr. boil 282 B4 11+10 Mixed till 275 C 11+20 Mixed till 227 C2 11+40 Mixed till 183 C2 11+70 Local fr. boil 218 Cl 11+80 Local fr. boil 203 C 12+00 Washed till 177 C2 12+20 Local fr. boil 210 B3 13+05 Regional till 270 C L125+00 N 11+40 Regional till 285 C 11+60 Regional till 321 C2 11+90 Regional till 314 C2 L126+00 N 11+40 Regional till 328 C2 11+60 Regional till 293 C2 510.5 193.8 74.5 463.1 1241.9 495.1 201.3 66.1 410.6 1173.1 873.2 122.0 27.0 190.8 1213.0 70.2 62.6 57.9 697.4 888.1 246.5 71.3 50.8 532.7 901.3 649.0 373.2 97.6 311.7 1431.5 185.6 188.9 410.3 584.5 1369.3 719.3 231.6 80.9 135.8 1167.6 406.8 196.5 118.8 530.0 1252.1 244.7 163.4 129.6 508.5 1046.2 119.3 499.0 139.3 174.2 931.8 228.3 143.4 81.8 528.7 982.2 316.1 156.0 115.7 597.2 1185.0 536.1 101.3 40.8 250.5 928.7 59.1 62.1 65.5 784.5 971.2 261.8 54.4 34.6 520.3 871.1 4.3 8.5 10.5 669.7 693.0 0.0 6.5 7.8 866.0 880.3 0.0 0.5 46.4 887.5 934.4 243.5 145.4 63.7 392.9 845.5 319.2 113.0 79.1 433.9 945.2 326.8 173.4 88.2 315.7 904.1 82.3 49.6 130.9 657.6 920.3 244.3 68.1 80.9 578.0 . 971.3 300.9 139.2 75.7 477.2 993.0 215.3 97.2 97.6 574.2 984.3 541.8 140.0 49.5 245.0 976.3 170.1 186.9 193.7 1013.5 1564.2 346.3 100.7 79.6 439.0 965.7 260.2 125.6 100.1 488.9 974.8 337.6 105.4 83.5 465.2 991.7 242.4 101.2 81.7 568.6 993.9 219.7 133.8 99.8 535.5 988.8 Local fr. boil = local stony frost boil; Marine sed. = marine sediments. Weight (g) of material in each size fraction of A, B and C horizons from selected soil pits. Location / Sample number Soil pit type Soil horizon +2000 Size fraction (um) -2000+425 -425+212 -212 Total wt. -2000 u.m material (g) L120+00 N/11+30 E 096 Mixed till Ah 53.7 144.9 366.0 343.0 853.9 094 Ah2 65.9 237.3 752.2 191.0 1180.5 093 Ah3 45.7 167.9 430.1 389.1 987.1 L120+00 N/11+45 E 089 Mixed till Ah 286.7 171.7 117.6 326.6 615.9 088 B l 227.4 196.6 106.4 405.7 708.8 103 B2 333 1 62.6 18.9 598.8 680.2 L120+00 N/11+70 E 086 Local stony Ah 593.8 136.0 31.4 134.1 301.4 085 frost boil B l 106.4 91.5 31.4 210.4 333.3 084 B2 778.4 229.3 54.5 333.7 617.5 082 Ah2 1176.1 140.7 34.3 123.5 298.5 L120+00 N/11+90 E 144 Marine Ah 847.0 125.5 51.0 308.7 485.1 150 sediment Bgl 345.8 104.6 .57.6 390.6 552.8 145 Bg2 237.0 108.9 59.5 474.2 642.6 147 O 194.2 37.4 20.2 327.2 384.8 148 C 466.0 122.1 49.1 253.9 425.2 L122+00 N/11+50 E 163 Regional Ah 206.1 1-120.9 72.9 431.5 625.2 165 till B l 182.4 152.76 137.0 600.3 890.1 166 B2 176.2 134.0 101.7 507.4 743.1 168 CI 220.3 137.2 107.7 459.2 704.1 169 C2 220.2 136.0 94.4 417.5 647.9 L122+00 N/11+80 E 312 Local stony Ah 290.7 146.8 79.7 250.3 476.8 311 frost boil B l 444.3 139.5 50.0 297.9 487.3 310 B l 440.5 147.9 55.2 279.5 482.6 309 B2 340.9 132.9 54.3 376.7 563.9 308 BC 314.2 162.8 93.0 363.0 618.8 L122+00 N/12+10 E 151 Local stony Ah 676.4 103.6 47.5 200.7 351.8 152 frost boil B l 241.5 94.9 49.1 510.9 654.9 153 B l 244.3 71.0 48.7 525.7 645.4 L122+00 N/12+30 E 306 Local stony Ah 281.1 88.7 52.6 501.5 642.9 302 frost boil B2 299.6 103.7 39.2 443.6 586.5 305 B3 385.3 93.2 31.8 378.6 503.6 Weight (g) of each size fraction continued. Location / Soil pit Soil Size fraction (pm) Total wt. Sample number type horizon +2000 -2000+425 -425+212 -212 -2000 pm material (g) L122+00 N/12+30 E 301 Local stony C l 338.5 54.6 31.2 457.0 542.7 303 frost boil B l 419.6 106.2 32.7 341.1 480.0 304 B l 496.3 101.3 31.8 284.3 417.4 L122+00 N/12+60 E 158 Marine Ah 1.3 6.5 7.1 475.8 489.5 159 sediment B l 2.5 10.5 16.6 767.0 794.1 L124+00 N/11+40 E 178 Mixed till Ah 58.8 87.4 99.5 620.6 807.4 179 B 98.6 115.4 120.1 540.1 775.6 181 C l 291.9 94.4 100.4 442.5 637.2 182 C l 342.3 109.4 92.3 393.1 594.8 L124+00 N/11+70 E 213 Mixed till Ah 263.0 155.1 72.7 314.8 542.6 214 B l 216.9 130.7 69.3 484.5 684.5 215 O 4550.9 2272.9 602.1 1106.4 3981.4 216 BC 238.7 103.3 83.3 500.0 686.6 217 C l 188.9 79.0 100.6 550.4 730.0 219 Local stony B l 434.8 104.3 51.0 355.0 510.2 220 frost boil B2 108.9 101.6 68.0 608.9 778.5 221 B3 156.8 93.4 79.7 570.7 743.8 L124+00 N/11+80 E 200 Local stony Ah 151.5 137.6 89.7 411.0 638.3 204 frost boil B2 329.5 117.0 42.4 395.6 555.0 201 C l 157.4 154.4 113.2 491.3 758.9 205 O 348.9 289.0 255.7 380.2 924.9 202 B l 426.2 105.8 40.6 343.9 490.2 L124+00 N/12+00 E 171 Washed Ae 49.8 73.4 61.4 . 203.3 338.0 172 till Ah 101.0 152.1 112.5 428.0 692.6 173 B l 393.8 414.8 153.8 49.8 618.3 174 B2 249.2 535.7 137.9 33.1 706.7 175 BC 141.5 134.3 133.6 517.7 785.6 176 C l 239.5 201.6 134.1 371.5 707.2 L124+00 N/12+20 E 211 Local stony Ah 203.88 84.0 53.3 304.8 442.1 208 frost boil B l 206.3 162.7 86.7 465.6 715.0 209 B2 267.5 167.1 72.6 402.0 641.7 212 BC 138.5 129.9 110.4 526.9 767.2 Weight (g) of material in each size fraction of A, B and C horizons from selected soil pits along L124+00 N, sieved down to -53 pm fraction. Location/ sample numbei Soil Size fraction (um) Total wt -2000 r horizon +2000 -2000+425 -425+212 -212+53 -53 11+40E 178 Ah 58.8 87.4 99.5 206.6 448.0 841.4 179 B 98.6 115.4 120.1 308.1 228.8 772.4 181 C l 291.9 94.4 100.4 269.6 171.2 635.5 182 C l 342.3 109.4 92.3 266.4 125.6 593.7 183 C2 82.3 49.6 130.9 514.8 141.9 837.1 11+70 E 213 Ah 263.0 155.1 72.7 100.4 213.5 541.7 214 B l 216.9 130.7 69.3 195.0 288.6 683.6 215 O 4550.9 2272.9 602.1 516.9 589.5 3981.4 216 BC 238.7 103.3 83.3 247.5 250.4 684.5 217 C l 188.9 79.0 100.6 308.5 240.2 728.2 218 C2 244.3 68.1 80.9 308.6 268.2 725.9 219 B l 434.8 104.3 51.0 118.2 236.1 509.5 220 B2 108.9 101.6 68.0 173.3 427.3 770.2 221 B3 156.8 93.4 79.7 210.7 357.7 741.5 11+80 E 200 Ah 151.5 137.6 89.7 160.9 257.5 645.6 201 C l 157.4 154.4 113.2 269.7 218.8 756.1 202 Bl 426.2 105.8 40.6 76.4 267.4 490.1 203 C2 300.9 139.2 75.7 176.4 299.7 691.1 204 B2 329.5 117.0 42.4 79.9 315.4 554.7 205 O 348.9 289.0 255.7 184.6 195.6 924.9 12+00E 171 Ae 49.8 73.4 61.4 132.0 70.1 336.9 172 Ah 101.0 152.1 112.5 167.6 318.8 751.0 173 B l 393.8 414.8 153.8 ins. ins. 568.6 174 B2 249.2 535.7 137.9 ins. ins. 673.6 175 BC 141.5 134.3 133.6 398.7 117.5 784.1 176 C l 239.5 201.6 134.1 247.2 123.0 705.9 177 C2 215.3 97.2 97.6 288.8 283.8 767.4 12+20 E 208 B l 206.3 162.7 86.7 175.4 288.5 713.2 209 B2 267.5 167.1 72.6 122.6 277.7 640.1 210 B3 541.8 140.0 49.5 73.9 170.5 433.9 211 Ah 203.9 84.0 53.3 85.7 285.2 508.1 212 BC 138.5 129.9 110.4 284.1 240.9 765.3 Note: ins = insufficient material for sieving. Weight (g) of material in each size fraction of surface B horizons from local stony frost boils. Location/ Size fraction (um) . Total wt. sample number +2000 -2000+425 -425+212 -212+53 -53 -2000 um material (g) L120+00 N / 11+70 E 253 959.7 679.8 160.4 257.5 676:2 1773.9 254 1061.4 437.3 120.4 148.3 673.2 1379.2 255 960.5 544.9 129.7 188.1 703.7 1566.4 256 1022.3 525.1 123.4 178.1 624.9 1451.5 11+90 E 246 1218.9 330.4 139.6 419.0 717.9 1606.9 247 1399.1 381.4 108.7 281.4 559.2 1330.7 248 1229.4 386.7 106.6 292.0 653.2 1438.5 249 1009.4 422.6 138.6 349.9 702.2 1613.3 250 1175.4 393.2 136.5 381.1 776.7 1687.5 251 1065.0 395.5 159.0 376.2 704.3 1635.0 252 1252.1 398.8 120.2 269.9 560.1 1349.0 L124+00 N / 11+70 E 356 1223.9 351.5 97.9 134.1 634.5 1218.0 357 1355.5 341.1 90.7 152.9 320.0 904.7 358 872.6 301.6 94.1 206.5 - 687.6 1289.8 359 963.3 328.3 103,4 226.1 850.4 1508.2 360 898.9 239.2 65.6 158.1 779.0 1241.9 11+85E 344 519.2 263.4 61.6 157.3 873.9 1356.2 345 877.8 321.2 105.5 198.3 836.7 1461.7 346 974.3 310.1 85.1 178.7 747.3 1321.2 347 1036.6 276.9 70.6 124.9 631.3 1103.7 Weight (g) of material in each size fraction of regional till frost boils and one local C horizon directly overlying mineralized bedrock. Sample Size Fraction (um) _ _ Total wt. number +2000 -2000+425 -425+212 -212+106 -106+53 -53 -2000 um material (g) 049 934.2 053 1233.0 054 3068.1 055 1469.6 056 1162.9 057 815.8 058 1636.6 059 893.9 060 1407.0 061 1825.8 062 1135.1 063 2006.5 070 2110.9 071 1774.8 072 1452.4 073 1520.7 074 3380.8 075 806.1 076 1434.4 077 823.9 078 3102.5 079 1428.2 080 3041.6 257 935.7 258 1392.6 259 1347.8 260 1359.5 203* 2635.0 1251.8 1009.4 911.0 647.4 1750.0 1191.9 1372.7 1188.5 927.8 668.1 645.3 640.9 747.0 816.0 826.6 765.5 851.3 1229.6 907.6 567.6 1033.5 692.9 940.5 907.7 845.1 610.2 1071.1 685.2 1213.3 911.0 1306.6 1062.5 1373.1 850.0 928.3 755.3 1248.0 832.0 815.5 634.5 1712.5 1323.2 1481.6 1516.3 1505.0 1137.8 1160.3 849.4 1289.8 854.9 1354.6 885.0 1241.1 792.0 1545.2 878.7 1589.5 986.4 944.3 729.8 988.7 ,532.7 922.1 752.8 920.0 633.4 824.7 570.8 1180.5 644.5 1270.7 922.9 1158.0 486.4 803.3 682.3 842.7 428.2 1073.3 765.9 839.9 625.5 905.4 655.5 1825.7 1288.1 1385.3 822.0 847.8 311.7 1043.4 791.0 1041.3 884.9 749.6 859.8 1772.8 1557.1 1807.8 1149.8 1478.9 1258.9 1223.2 697.7 1262.0 822.6 1096.7 727.9 1335.0 802.6 1035.3 997.2 2171.8 7008.9 1728.7 4961.2 1789.6 6252.9 2066.8 6302.9 1366.9 4516.2 1155.7 3837.4 923.8 4311.8 2020.7 5806.4 1107.5 4832.8 1338.9 4299.7 2010.4 5007.7 2009.7 5697.1 1671.4 4592.1 1531.4 4848.6 2901.3 8139.4 1419.6 5996.0 476.7 3859.3 1778.0 5296.0 1776.6 5782.8 2081.6 5141.0 2997.6 9363.2 2451.8 8407.3 2506.7 7887.3 2114.0 6044.6 2519.4 6748.7 2142.5 6206.7 1752.5 5923.2 3844.0 8300.4 * = C horizon soil Normalized weight (g) of material in each size fraction of regional till frost boils and one local C horizon. Normalized to 10 kg of -2000 um material. Sample Size Fraction (um) umber -2000+425 ^25+212 -212+106 -106+53 -53 049 1786.0 1440.2 2267.8 1407.4 3098.6 053 1836.2 1304.9 1903.4 1471.0 3484.4 054 2798.7 1906.2 1581.2 851.9 2862.0 055 2177.9 1885.6 1463.0 1194.4 3279.1 056 2054.4 1479.3 2037.1 1402.5 3026.7 057 1681.6 1670.1 2149.1 1487.5 3011.7 058 1732.5 1892.5 2737.8 1494.7 2142.5 059 1423.6 1318.4 2188.4 1589.5 3480.1 060 1761.5 2544.3 : 2396.1 1006.5 2291.6 061 2110.8 1320.1 1868.3 1586.9 3113.9 062 2063.8 1383.7 1682.8 855.1 4014.6 063 1650.8 1593.3 1883.9 1344.4 3527.6 070 1840.3 1328.8 1829.0 1362.1 3639.7 071 2209.1 1413.2 1867.3 1351.9 3158.4 072 1490.7 1119.2 2243.0 1582.5 3564.5 073 2179.1 1772.0 2310.4 1370.9 2367.6 074 3557.9 2202.5 2196.8 807.7 1235.2 075 1752.8 1426.2 1970.2 1493.6 3357.3 076 2158.1 1438.7 1800.7 1530.2 3072.2 077 1586.3 1234.2 1458.1 1672.4 4049.0 078 1829.0 1413.2 . 1893.4 1663.0 3201.5 079 1762.3 1803.6 2150.3 1367.6 2916.3 080 1908.1 1442.6 1875.0 1596.1 3178.1 257 1919.6 1405.2 2023.6 1154.3 3497.3 258 1911.2 1266.8 1870.0 1218.9 3733.2 259 2182.5 1425.9 1767.0 1172.8 3451.9 260 2095.3 1337.1 2253.8 1355.0 2958.7 203* 1861.6 1058.6 1247.3 1201.4 4631.1 * = C horizon soil. Weight (g) of light mineral fractions (LMF) and heavy mineral concentrates (HMC) of die -212+106 pm and -106+53 urn size fractions of regional till frost boils and one local C horizon, for the (i) first and (ii) second separations. (i) First separation (ii) Second separation Sample number Size fraction Size fraction -212+106 um L M F HMC -106+53 um LMF HMC -212+106 um LMF HMC -106+53 um L M F HMC 049 953.9 31.7 053 703.3 25.9 054 508.3 24.0 055 1155.8 32.0 729.6 22.2 751.2 19.6 964.0 30.5 056 897.7 22.0 610.8 22.2 636.5 15.9 618.3 22.4 057 548.7 21.3 058 1146.6 33.7 617.9 25.8 904.4 23.4 598.1 24.6 059 1243.3 26.4 899.0 22.5 907.5 21.8 774.6 19.6 061 783.2 19.9 661.9 19.4 645.8 16.3 637.3 20.9 062 820.8 20.3 415.1 12.7 637.4 15.1 739.0 22.2 063 737.3 27.5 070 819.2 20.1 606.9 17.8 653.5 14.7 797.8 26.5 071 636.1 18.7 72A 630.0 19.2 72B 614.7 20.8 073 1355.4 29.8 799.0 22.6 889.3 17.7 688.7 20.1 074 822.5 24.6 296.6 14.8 499.1 16.9 281.5 15.0 075 767.7 22.8 076 852.7 31.0 077 832.2 26.7 78A 756.5 24.2 78B 747.6 22.6 79A 543.4 19.9 79B 561.5 19.3 80A 609.8 21.6 80B 601.8 21.4 257 1196.6 26.0 674.6 22.0 1056.8 21.4 904.5 28.6 258 797.0 24.6 259 1070.0 26.6 704.5 22.7 914.0 19.7 854.9 25.7 260 779.8 22.4 203* n/a n/a n/a n/a 992.9 43.4 932.3 64.5 Note: * = C horizon sample; A or B in the sample number refers to the sample being split in two before completing the separations; n/a = material not available for separations. Weight percent (%) of material in each size fraction of the lowermost horizons from soil pits. Location: Northing/ easting Soil pit type Sample number Soil horizon Size fraction (um) -2000+425 -425+212. -212 L120+00 N 11+30 Mixed till 092 B 15.6 6.0 37.3 11+45 Mixed till 087 C 17.2 5.6 35.0 11+70 Local fr. boil 081 C 10.1 2.2 15.7 11+90 Marine sed. 146 Bm 7.0 6.5 78.5 12+10 Load fr. boil 140 B2 7.9 5.6 59.1 12+30 Mixed till 130 C 26.1 6.8. 21.8 12+50 Mixed till 135 B2 13.8 30.0 42.7 12+80 Regional till 098 C 19.8 6.9 11.6 13+00 Regional till 107 C2 15.7 9.5 42.3 13+20 Regional till 125 C3 15.6 12.4 48.6 L122+00 N 11+10 Mixed till 199 C2 53.6 14.9 18.7 11+30 Mixed till 188 CI 14.6 8.3 53.8 11+50 Regional till 170 C3 13.2 9.8 50.4 11+80 Local fr. boil 307 C 10.9 4.4 27.0 12+10 Local fr. boil 154 B2 6.4 6.7 80.8 12+30 Local fr. boil 300 C2 6.2 4.0 59.7 12+60 Marine sed. 160 B2 1.2 1.5 96.6 13+00 Marine sed. 113 C 0.7 0.9 98.4 13+40 Marine sed. 116 B2 0.1 5.0 95.0 L124+00 N 10+85 Local fr. boil 282 B4 17.2 7.5 46.5 11 + 10 Mixed till 275 C 12.0 8.4 45.9 11+20 Mixed till 227 C2 19.2 9.8 34.9 11+40 Mixed till 183 C2 5.4 14.2 71.5 11+70 Local fr. boil 218 CI 7.0 8.3 59.5 11+80 Local fr. boil 203 C 14.0 7.6 48.1 12+00 Washed till 177 C2 9.9 9.9 58.3 12+20 Local fr. boil 210 B3 14.3 5.1 25.1 13+05 Regional till 270 C 11.9 12.4 64.8 L125+00 N 11+40 Regional till 285 C 10.4 8.2 45.5 11+60 Regional till 321 C2 12.9 10.3 50.2 11+90 Regional till 314 C2 10.6 8.4 46.9 L126+00 N 11+40 Regional till 328 C2 10.2 8.2 57.2 11+60 Regional till 293 C2 13.5 10.1 54.2 Local fr. boil = local stony frost boil; Marine sed. = marine sediments. Weight percent (%) of material in each size fraction of A, B and C horizons from soil pits. Location / Sample, number Soil pit type Soil horizon Size fraction (pm) -2000+425 -425+212 -212 L120+00 N/ll+30 E 096 094 093 Mixed till Ah Ah2 Ah3 17.0 20.1 17.0 42.9 63.7 43.6 40.2 16.2 39.4 L120+00 N/11+45 E 089 088 103 Mixed till Ah Bl B2 27.9 27.7 9.2 19.1 15.0 2.8 53.0 57.2 88.0 L120+00 N/11+70 E 086 085 084 082 Local stony frost boil Ah Bl B2 Ah2 45.1 27.5 37.1 47.1 10.4 9.4 8.8 11.5 44.5 63.1 54.0 41.4 L120+00 N/11+90 E 144 150 145 147 148 Marine sediment Ah Bgl Bg2 O C 25.9 18.9 16.9 9.7 28.7 10.5 10.4 9.3 5.2 11.5 63.6 70.7 73.8 85.0 59.7 L122+00 N/11+50 E 163 165 166 168 169 Regional till Ah Bl B2 Cl C2 19.3 17.2 18.0 19.5 21.0 11.7 15.4 13.7 15.3 14.6 69.0 67.4 68.3 65.2 64.4 L122+00 N/11+80 E 312 311 310 309 308 Local stony frost boil Ah Bl Bl B2 BC 30.8 28.6 30.6 23.6 26.3 16.7 10.3 11.4 9.6 15.0 52.5 61.1 57.9 66.8 58.7 L122+00 N/12+10 E 151 152 153 Local stony frost boil Ah Bl Bl 29.4 14.5 11.0 13.5 7.5 7.5 57.1 78.0 81.5 L122+00 N/12+30 E 306 302 305 Local stony frost boil Ah B2 B3 13.8 17.7 18.5 8.2 6.7 6.3 78.0 75.6 75.2 21© Weight percent (%) of each size fraction continued. Location / Sample number Soil pit type Soil horizon Size fraction (pm) -2000+425 -425+212 -212 L122+00 N/12+30 E 301 303 304 Local stony frost boil C l B l B l 10.1 22.1 24.3 5.7 6.8 7.6 84.2 71.1 68.1 L122+00 N/12+60 E 158 159 Marine sediment Ah B l 1.3 1.3 1.5 2.1 97.2 96.6 L124+00 N/11+40 E 178 179 181 182 Mixed till Ah B C l C l 10.8 14.9 14.8 18.4 12.3 15.5 15.7 15.5 76.9 69.6 69.4 66.1 L124+00 N/11+70 E 213 214 215 216 217 219 220 221 Mixed till Local stony frost boil Ah B l O BC C l B l B2 B3 28.6 19.1 57.1 15.0 10.8 20.4 13.0 12.6 13.4 10.1 15.1 12.1 13.8 10.0 8.7 10.7 58.0 70.8 27.8 72.8 75.4 69.6 78.2 76.7 L124+00 N/11+80 E 200 204 201 205 202 Local stony frost boil Ah B2 C l O B l 21.6 21.1 20.3 31.2 21.6 14.0 7.6 14.9 27.6 8.3 64.4 71.3 64.7 41.1 70.1 L124+00 N/12+00 E 171 172 173 174 175 176 Washed till Ae Ah B l B2 BC C l . 21.7 22.0 67.1 75.8 17.1 28.5 18.2 16.2 24.9 19.5 17.0 19.0 60.1 61.8 8.1 4.7 65.9 52.5 L124+00 N/12+20 E 211 208 209 212 Local stony frost boil Ah B l B2 BC 19.0 22.8 26.0 16.9 12.1 12.1 11.3 14.4 68.9 65.1 62.6 68.7 Weight percent (%) of material in each size fraction of A, B and C horizons from selected soil pits along LI24+00 N, sieved down to -53 urn fraction Location/ Soil Size fraction (um) sample number horizon -2000+425 -425+212 -212+53* -53* 11+40 E 178 Ah 10.4 11.8 24.6 53.2 179 B 14.9 15.6 39.9 29.6 181 CI 14.8 15.8 42.4 26.9 182 CI 18.4 15.5 44.9 21.2 183 C2 5.9 15.6 61.5 16.9 11+70E 213 Ah 28.6 13.4 18.5 39.4 214 B l 19.1 10.1 28.5 42.2 215 O 57.1 15.1 13.0 14.8 216 BC 15.1 12.2 36.2 36.6 217 CI 10.8 13.8 42.4 33.0 218 C2 9.4 11.1 42.5 37.0 219 Bl 20.5 10.0 23.2 46.3 220 B2 13.2 8.8 22.5 55.5 221 B3 12.6 10.7 28.4 48.2 11+80E 200 Ah 21.3 13.9 24.9 39.9 201 CI 20.4 15.0 35.7 28.9 202 B l 21.6 8.3 15.6 54.6 203 C2 20.1 11.0 25.5 43.4 204 B2 21.1 7.6 14.4 56.9 205 O 31.2 27.6 20.0 21.2 12+00 E 171 Ae 21.8 18.2 39.2 20.8 172 Ah 20.2 15.0 22.3 42.5 173 B l 67.1 24.9 ins. ins. 174 B2 75.8 19.5 ins. ins. 175 BC 17.1 17.0 50.8 15.0 176 CI 28.6 19.0 35.0 17.4 177 C2 12.7 12.7 37.6 37.0 12+20 E 208 Bl 22.8 12.2 24.6 40.4 209 B2 26.1 11.3 19.2 43.4 210 B3 32.3 11.4 17.0 39.3 211 Ah 16.5 10.5 16.9 56.1 212 BC 17.0 14.4 37.1 31.5 Note: * = corrected weight percents for total -212 um size fraction; ins. = insufficient material left over from previous analysis for sieving. Weight percent (%) of material in each size fraction of surface B horizons from local stony frost boils. Location/ Size fraction (um) sample number -2000+425 -425+212 -212+53 -53 L120+00 N / 11+70 E 253 38.3 9.0 14.5 38.1 254 31.7 8.7 10.8 48.8 255 34.8 8.3 12.0 44.9 256 36.2 8.5 12.3 43.1 11+90 E 246 20.6 8.7 26.1 44.7 247 28.7 8.2 21.1 42.0 248 26.9 7.4 20.3 45.4 249 26.2 8.6 21.7 43.5 250 23.3 8.1 22.6 46.0 251 24.2 9.7 23.0 43.1 252 29.6 8.9 20.0 41.5 L124+00N/ 11+70 E 356 28.9 8.0 11.0 52.1 357 37.7 10.0 16.9 35.4 358 23.4 7.3 16.0 53.3 359 21.8 6.9 15.0 56.4 360 19.3 5.3 •12.7 62.7 11+85 E 344 19.4 4.5 11.6 64.4 345 22.0 7.2 13.6 57.2 346 23.5 6.4 13.5 56.6 347 25.1 6.4 11.3 57.2 Weight percent (%) of material in each size fraction of regional till frost boils and one local C horizon. Sample Size fraction (um) umber -2000+425 +^25+212 -212+106 -106+53 -53 049 17.9 14.4 22.7 14.1 31.0 053 18.4 13.0 19.0 14.7 34.8 054 28.0 19.1 15.8 8.5 28.6 055 21.8 18.9 14.6 11.9 32.8 056 20.5 14.8 20.4 14.0 30.3 057 16.8 16.7 21.5 14.9 30.1 058 17.3 18.9 27.4 14.9 21.4 059 14.2 13.2 21.9 15.9 34.8 060 17.6 25.4 24.0 10.1 22.9 061 21.1 13.2 18.7 15.9 31.1 062 20.6 13.8 16.8 8.6 40.1 063 16.5 15.9 18.8 13.4 35.3 070 18.4 13.3 18.3 13.6 36.4 071 22.1 14.1 18.7 13.5 31.6 072 14.9 11.2 22.4 15.8 35.6 073 21.8 17.7 23.1 13.7 23.7 074 35.6 22.0 22.0 8.1 12.4 075 17.5 14.3 19.7 14.9 33.6 076 21.6 14.4 18.0 15.3 30.7 077 15.9 12.3 14.6 16.7 40.5 078 18.3 14.1 18.9 16.6 32.0 079 17.6 18.0 ... 21.5 13.7 29.2 080 19.1 14.4 18.8 16.0 31.8 257 19.2 14.1 20.2 11.5 35.0 258 19.1 12.7 18.7 12.2 37.3 259 21.8 14.3 17.7 11.7 34.5 260 21.0 13.4 22.5 13.6 29.6 203* 18.6 10.6 12.5 12.0 46.3 * = C horizon soil. Weight percent (%) of material in each size fraction normalized to 10 kg of-200 pm material, for regional till frost boils and one local C horizon. Sample Size Fraction (um) number -2000+425 -425+212 -212+106 -106+53 -53 049 17.9 14.4 22.7 14.1 31.0 053 18.4 13.0 19.0 14.7 34.8 054 28.0 19.1 15.8 8.5 28.6 055 21.8 18.9 14.6 11.9 32.8 056 20.5 14.8 20.4 14.0 30.3 057 16.8 16.7 21.5 14.9 30.1 058 17.3 18.9 27.4 14.9 21.4 059 14.2 13.2 21.9. 15.9 34.8 060 17.6 25.4 24.0 10.1 22.9 061 21.1 13.2 18.7 15.9 31.1 062 20.6 13.8 16.8 8.6 40.1 063 16.5 15.9 18.8 13.4 35.3 070 18.4 13.3 18.3 13.6 36.4 071 22.1 14.1 18.7 13.5 31.6 072 14.9 11.2 22.4 15.8 35.6 073 21.8 17.7 23.1 13.7 23.7 074 35.6 22.0 22.0 8.1 12.4 075 17.5 14.3 19.7 14.9 33.6 076 21.6 14.4 18.0 15.3 30.7 077 15.9 12.3 14.6 16.7 40.5 078 18.3 14.1 18.9 16.6 32.0 079 17.6 18.0 21.5 13.7 29.2 080 19.1 14.4 . 18.8 16.0 31.8 257 19.2 14.1 20.2 11.5 35.0 258 19.1 12.7 18.7 12.2 37.3 259 21.8 14.3 17.7 11.7 34.5 260 21.0 13.4 22.5 13.6 29.6 203* 18.6 10.6 12.5 12.0 46.3 * = C horizon soil. Weight percent (%) of light mineral fractions (LMF) and heavy mineral concentrates (HMC) of die -212+106 um and -106+53 um size fractions of regional till frost boils and one local C horizon, for the (i) first and (ii) second separations. (i) First separation (ii) Second separation Sample Size fraction Size fraction number -212+106 um -106+53 um -212+106 um -106+53 um L M F HMC LMF HMC LMF HMC LMF HMC 049 96.8 3.2 053 96.4 3.6 054 95.5 4.5 055 97.3 2.7 97.0 3.0 97.5 2.5 96.9 3.1 056 97.6 2.4 96.5 3.5 97.6 2.4 96.5 3.5 057 96.3 3.7 058 97.1 2.9 96.0 4.0 97.5 2.5 96.0 4.0 059 97.9 2.1 97.6 2.4 97.7 2.3 97.5 2.5 061 97.5 2.5 97.2 2.8 97.5 2.5 96.8 3.2 062 97.6 2.4 97.0 3.0 97.7 2.3 97.1 2.9 063 96.4 3.6 070 97.6 2.4 97.2 2.8 97.8 2.2 96.8 3.2 071 97.1 2.9 72A 97.0 3.0 72B 96.7 3.3 073 97.8 2.2 97.2 2.8 98.1 1.9 97.2 2.8 074 97.1 2.9 95.2 4.8 96.7 3.3 95.0 5.0 075 97.1 2.9 076 96.5 3.5 077 96.9 3.1" 78A 96.9 3.1 78B 97.1 2.9 79A 96.5 3.5 79B 96.7 3.3 80A 96.6 3.4 80B 96.6 3.4 257 97.9 2.1 96.8 3.2 98.0 2.0 96.9 3.1 258 97.0 3.0 259 97.6 2.4 96.9 3.1 97.9 2.1 97.1 2.9 260 97.2 2.8 203* n/a n/a n/a n/a 95.8 4.2 . 93.5 6.5 Note: * = C horizon sample; A or B in the sample number refers to the sample being split in two before completing the separations; n/a = material not available for separations. 224 Electron microprobe analyses of the cores and rims of gold grains from the non-magnetic heavy minerals of: the -106+53 um fraction of only one regional till sample (062), and from the -212+106 um and T106+53 um fractions of one local C horizon sample (203). Gold grain Au Ag Hg Cu Fineness Gold grain Au Hg Cu Fineness Regional till: -106+53 nm fraction Local C horizon: -212+106 um fraction C3C 87.16 11.57 0.00 0.02 882.84 A1C 78.08 21.33 0.00 0.02 785.42 C3C2 86.88 11.73 0.00 0.00 881.08 A1C2 78.10 20.98 0.00 0.00 788.28 C3C3 86.97 11.75 0.00 0.04 881.01 A1C3 75.12 24.19 0.00 0.01 756.43 C3C4 85.31 11.57 0.00 0.00 880.61 AIR 73.40 23.03 0.00 0.03 761.15 C3C5 87.35 11.86 0.00 0.01 880.45 A3C 77.77 21.93 0.00 0.00 780.03 C3R 91.27 7.38 0.00 0.00 925.18 A3C2 76.74 22.64 0.00 0.00 772.17 C3R2 87.54 11.96 0.00 0.01 879.80 A3R 76.93 22.78 0.00 0.00 771.52 C3C7 87.86 11.58 0.00 0.03 883.59 A3R2 71.83 21.26 0.00 0.00 771.60 C3C8 87.09 11.73 0.00 0.00 881.29 A3R3 76.24 23.02 0.00 0.00 768,12 A3R4 73.66 24.18 0.00 0.00 752.86 A4C 78.78 20.36 0.00 0.00 794.60 Local C horizon: -106+53 um fraction A4C2 78.43 20.27 0.00 0.03 794.62 B1C 84.15 15.58 0.00 0.00 843.74 A4C3 78.62 20.30 0.00 0.00 794.82 B1C2 83.82 15.12 0.00 0.01 847.16 A4C5 80.74 . 17.77 0.00 0.01 819.64 B1R 84.80 15.18 0.00 0.00 848.20 A7C 77.50 20.91 0.00 0.03 787.54 B1R2 82.25 16.97 0.00 0.00 828.99 A7C2 78.25 21.06 0.00 0.00 787.94 B2C 79.80 19.26 0.00 0.00 805.59 A7R 78.73 21.32 0.00 .0.01 786.94 B2C2 79.18 19.97 0.00 0.00 798.61 A7R2 78.86 21.58 0.00 - 0.02 785.12 B2R 79.47 20.79 0.00 0.00 792.65 A7R3 77.56 22.33 0.00 0.00 776.46 B2R2 75.32 22.87 0.00 0.00 767.11 A7R4 77.05 21.29 0.00 0.00 783.54 B4C 79.02 20.93 0.00 0.03 790.62 A8C 72.46 27.00 0.00 0.00 728.52 B4C2 78.16 20.92 0.00 0.04 788.86 ' A8C2 71.49 26.87 0.00 0.01 726.80 B4R 78.44 20.97 0.00 0.01 789.06 A8C3 71.04 27.81 0.00 0.00 718.66 B4R2 76.67 22.05 0.00 0.02 776.68 A9C 76.44 22.44 0.00 0.00 773.07 B5C 84.00 15.55 0.00 0.00 843.79 A9C2 76.29 22.39 0.00 0.00 773.10 B5C 83.41 15.81 0.00 0.04 840.63 A9R 76.10 22.51 0.00 0.00 771.75 B5R 82.13 16.59 0.00 0.01 831.92 A10C 72.87 25.93 0.00 0.01 737.52 B5R 80.25 19.26 0.00 0.02 806.50 A11C 79.36 19.69 0.00 0.00 801.19 A11C2 79.48 19.89 0.00 0.01 799.86 A13C 79.27 19.50 0.00 0.00 802.58 A13C2 80.41 19.16 0.00 0.02 807.61 A13C3 79.03 20.54 0.00 0.00 793.74 Note: In the gold grain numbers: 'C refers to analyses taken in the cores of the gold grains, and 'R' refers to analyses taken along the rims of the grains. Electron microprobe analyses continued. Gold Au Ag Hg Cu Fineness Gold Au Ag Hg Cu Fineness grain grain Local C horizon: -212+106 u.m fraction continued A14C 75.35 23.25 0.00 0.00 764.20 A19C 81.02 17.03 0.00 0.01 826 33 A14C2 76.50 22.80 0.00 0.02 770.41 A19C 78.80 19.76 . 0.04 0.00 799 51 A14R 75.02 23.51 0.00 0.01 761.38 A19C2 79.51 19.62 0.05 0.00 802 10 A14R2 77.36 22.78 0.00 0.00 772.52 A19C2 78.59 20.03 0.00 0.01 796 91 A14R3 75.01 23.74 0.00 0.00 759.63 A20C 79.31 20.35 0.00 0.03 795 80 A15C 79.29 16.97 0.00 0.00 823.71 A20C2 79.80 19.45 0.00 0.00 804 04 A15C 79.11 19.88 0.00 0.02 799.16 A20R 74.27 24.37 0.00 0.03 752 99 A15C2 69.30 13.44 0.00 0.01 837.60 A20R 75.83 22.75 0.00 0.06 769 22 A15C2 79.24 19.87 0.00 0.00 799.52 A20R2 77.91 21.64 0.01 0.00 782 66 A17C 77.12 21.93 0.00 0.01 778.63 A20R2 76.52 21.82 0.00 0.00 778 10 A17C 77.61 21.67 0.00 0.00 781.71 A23C 79.00 20.09 0.00 0.02 797 25 A17C2 77.00 21.74 0.00 0.02 779.85 A23C2 79.41 20.32 0.00 0.00 796 27 A18C 78.85 19.64 0.00 0.02 800.56 A23R 80.09 19.91 0.00 0.00 800 93 A18C 79.64 19.88 0.00 0.00 800.28 A23R 78.59 19.83 0.00 0.00 798 52 A18C2 79.91 19.75 0.00 0.01 801.81 A23R2 78.34 19.61 0.00 0.00 799 79 A18R 75.23 13.82 0.00 0.01 844.76 A18R 78.65 20.82 0.00 0.01 790.67 A18R 79.43 19.95 0.00 0.01 799.30 A18R2 79.59 19.81 0.00 0.00 800.71 / Gold (ppt), chloride (mg/L) and sulphate (mg/L) concentrations of water samples collected from lakes, bogs, seepage zones and soil pits in the Wally Grid / Spyder Lake area. Sample Location Type of Au Cl- S04= number Easting Northing water sample (ppt) (mg/L) (mg/L) 32 441400 7499150 lake 2.9. 3.3 4 37 441995 7504025 lake 2.1 14.4 5 38 442350 7504000 lake 1.4 5.2 26 46 438900 7508850 lake 1.8 5.0 9 50 13+55E L122+00N bog 2.8 8.5 6 51 13+80E L120+00N bog 1.6 5.2 2 52 11+10E L119+55N bog 2.3 2.6 2 64 449150 7489250 lake 1.8 5.0 10 65 446675 7493100 lake 1.5 3.0 15 66 444550 7494100 lake < 1.0 2.2 21 67 440900 7497250 lake < 1.0 1.9 4 68 442655 7499450 lake 1.0 23.4 10 69 442625 7502150 lake 1.0 5.5 19 101 440400 7503650 lake 1.4 3.5 6 102 439900 7503250 seepage zone 60.2 1.5 1 119 12+10E L122+00N soil pit ~ 5.2 51 156 12+50E L124+00N soil pit 2.9 6.3 8 157 12+70E L124+00N soil pit 4.5 5.2 6 

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