Johnston, Kendra

Recent mineral discoveries made by soil geochemical sampling along ridges and spurs prompted an increase in exploration in the unglaciated Klondike Plateau of west-central Yukon. Extensive and detailed soil sampling campaigns were extended across hillsides and into valleys, where eolian deposits, periglacial processes, and mass movements complicate the collection and interpretation of geochemical data. In support of exploration efforts, property-scale (1:20 000) surficial geology mapping was completed for several exploration projects to provide more detailed insight than is available in regional-scale (1:50 000) mapping. The culmination of this mapping work is the identification of 12 ‘landform-soil types’ (LSTs) that exhibit recognizable and repetitive patterns in the field and in aerial photographs. The suitability of each LST for different soil geochemical sampling methods and interpretation strategies depends on its soil depth, permafrost depth, surface organic thickness, loess thickness, transport distance, and type of geochemical anomaly. Conventional hand auger sampling is well suited to LSTs with residual or colluvial soils with deep or no permafrost (i.e., LSTs 1, 2, 10, 11, and 12). Power auger sampling is best suited to loess-rich colluvial soils with shallow permafrost (i.e., LSTs 3, 4, and 5), although resulting geochemical signatures may be affected by unmineralized rock fragments pulverized during augering. Reverse circulation or rotary air blast drilling, or deep- penetrating geochemical methods, may be necessary in areas of thick organics or transported cover (i.e., LSTs 6, 7, 8 and 9). The LST classification is applied retrospectively to the Coffee Gold Project to explain soil anomalies that represent geochemical dilution by loess, colluvial dispersion, and halos overlying bedrock mineralization. Application of the LST classification to the Snowcap Project reveals similarities and differences in geochemical data derived from samples collected with a mattock, hand auger, and power auger, in relationship to different LSTs.