Mark Higgins

Bedrock gold sources for rich placer gold deposits in West Central Yukon have been elusive since the 1898 Klondike gold rush. Poor bedrock exposure in an area that escaped Cenozoic glaciation has hindered the effectiveness of traditional exploration techniques. This study applies morphological and geochemical analysis to determine the provenance of gold grains at six placer gold operations in the Black Hills Creek (BHC) watershed, a south-flowing tributary of the Stewart River, to help identify local gold sources. The flatness index = [(a + b)/2c] of gold particles was determined using a binocular microscope and imaging software in which the long (a), intermediate (b), and short (c) axes were measured. Bulk-gold fineness is defined by the ratio of [Au/(Ag + Au)*1000] and provides information about source-rock. Fineness values were measured using microprobe analysis. Flatness has been shown to increase with downstream transport, e.g. high measured flatness values (>7.0) would suggest reworking of grain shape during transport. Contributing areas for each placer site were determined by ArcGIS watershed analysis.

Grains from the four northern placers (Sites 1 to 4) have similarly low flatness indices with averages of 5.0, 4.8, 5.4, and 4.3, suggesting short to moderate transport distances (less than 10 km). Local bedrock sources are implied and fineness values, generally less than 800 are similar to published data from the Eureka Dome. In contrast, grains from the southern two placer deposits show a broad range of flatness indices from 3.9 to 24.0, and a range of fineness values (650 to 900) which indicate provenance from multiple sources. Proximal sources were found to contribute significant portions of grains to the southern sites, and the geochemical signature of these short travelled grains has helped to better understand the mineralization style of bedrock exploration targets unique to the catchment areas of sites 5 and 6.

Keywords: Yukon Tanana Terrane, Tintina Gold Province, Particle flatness, electron microprobe, gold fineness, geochemical fingerprinting

Pages: 102
Supervisor: Michael Young