Gold distribution in glacial sediments and soils at Boston Property, Nunavut, Canada

Abstract

Geochemical exploration for gold in the Slave Structural Province, Nunavut, Canada is hampered by a complex cover of Quaternary sediments and a lack of information on the effects of glacial dispersion and periglacial conditions on gold distribution. This study investigates distribution of gold in surficial materials on the Boston Property in the southeastern portion of the Hope Bay Greenstone Belt, 650 km northeast of Yellowknife, N.W.T. The principal surficial materials are till with a discontinuous veneer of post-glacial marine sediments. In areas of shallow overburden, frost boils mix weathered bedrock with drift and bring bedrock fragments to the surface. Samples were collected from till and from soil profiles on lines across the mineralized zone. The −212 and −53 μm fractions were separated by wet sieving and heavy mineral concentrates (HMCs) prepared. Gold was determined by fire assay–atomic absorption spectroscopy (FA–AAS) or by a more sensitive aqua regia-column preconcentration–ICP procedure. There are two types of gold anomalies: (1) anomalies in the regional till, and (2) anomalies developed by ongoing frost boil action and colluvial processes. Anomalies are absent in marine sediments. Gold values in the regional till range from 15 to 1030 ppb in −106+53 μm HMCs and from 10 to 65 ppb in the −53 μm fraction, which contains ~60% of the total gold content. Anomalous values extend at least 2 km down-ice from the gold mineralization. In profile, the most recent gold anomaly is mushroom-shaped, up to ∼100 m wide at the surface, and drapes over a ridge of mineralized bedrock. The anomaly in near-surface horizons is 10–50 m broader than the anomaly in the underlying horizons. Maximum gold values (>5000 ppb) are found in areas of weathered bedrock and where frost boils include abundant fragments of mineralized bedrock. For reconnaissance-scale exploration, frost boils in the regional till should be sampled on a 500×40 m grid with lines perpendicular to ice-flow direction. The −53 μm fraction should be analyzed for gold with a detection limit of 1 ppb or lower. At the property scale, with anticipated higher gold values, it is feasible to analyze the coarser −212 μm fraction from near-surface samples collected at a 10–20 m spacing along grid lines 100 m apart.