ABSTRACT: Drift prospecting and case study highlights from the Northern Cordillera, Yukon Territory.

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Abstract

Recent regional till sampling programs in Yukon have been completed in the Anvil District, and the Finlayson Lake and Glenlyon map areas of central and southeastern Yukon. Drift prospecting methodologies applied in these studies were adopted from methods used in central and southern BC by the GSC and BCGS. The overall remoteness of the northern Cordillera and the absence of roads related to a blanket industry, such as forestry, has made regional till sampling surveys a strenuous undertaking. Most of the till sampling had to be completed by helicopter supported foot traverses; occasionally boats and all terrain vehicles were used to access sampling areas. Extreme variations in surficial cover and thickness, in addition to the presence of numerous Pleistocene glacial limits, provide complexities in the northern Cordillera. Discontinuous permafrost and locally thick loess deposits are further hindrances to till sampling. Despite these challenges, drift exploration in the northern Cordillera can be undertaken successfully. Three case studies describe the application of the technique to base and precious metal exploration in central and southeastern Yukon. In the Anvil District a total of 140 till samples covering a 12 km2 grid were collected down-ice of the former Faro deposit, one of five Zn-Pb-Ag ore deposits in the area. Results of this 1998 survey were compared to a 1964 industry soil geochemistry survey to highlight the similarities and differences between methodologies. A strong, yet morphologically different, base metal dispersal train, in addition to a possible palimpsest component, was found in both datasets. A drift exploration case study was completed at the Kudz Ze Kayah (KZK) massive sulphide deposit, located in the Finlayson Lake district. Results indicate a strong enrichment of lead, zinc, silver and gold down-ice of the deposit, despite widespread melt-out till in the valley bottom. A physical partitioning study reveals that lead, zinc, silver, and gold are strongly enriched in the clay-sized fraction of till compared to coarser size fractions. The high Au content of the clay-sized fraction relates to the fine grain nature of gold in the KZK mineralization. An orientation survey at the Clear Lake sedimentary-exhalative deposit in central Yukon recognized a down ice dispersal train enriched in lead and mercury. However, zinc, lead and other elements are depleted in till immediately over the deposit. This depletion is probably a consequence of leaching by acids generated by oxidation of sulphides. A direct link between limestone clasts and increased zinc values in till at Clear Lake suggests that carbonate is an important buffering agent.

Bibliography of Canadian Geomorphology