The area of the Alsek showing is underlain by andesitic to basaltic flows and sills with about 15 per cent massive dioritic sills of the Upper Triassic Lower Tats Complex. The original showing (McDougall), near the edge of the glacier, was described as a 0.3 metre vein of massive chalcopyrite, which assayed 0.69 grams per tonne gold, 17.14 grams per tonne silver, and 25.16 per cent copper. The showing has been identified as coinciding with an area of mala- chite staining at the east edge of Tats Glacier about 2.2 kilometres northwest of the Tats occurrence (114P 003).