The Cretaceous Horsethief Batholith intrudes sediments of the Middle Proterozoic Mount Nelson Formation, Purcell Supergroup. The intrusion is zoned from fine-grained to medium-grained granodiorite to coarse-grained quartz monzonite. In the area of the Alder showing, the Horsethief batholith is predominantly quartz monzonite.

Canadian Johns-Manville Co. Limited initiated a biogeochemistry survey along Horsethief Creek in the winter of 1970-71. They followed up with a major biogeochemical survey in late 1971 after the staking of the Alder and Talus claims. An induced polarization survey was carried out and 4 diamond drill holes were drilled.

Traces of molybdenite were found in drill core from diamond drilling done on the Alder 72 claim. The host rock is a medium to coarse-grained granite showing the pink colouration of potassium feldspar alteration. Molybdenite occurs as a sheared film along fractures and tiny flakes disseminated in rock contiguous to the fracture. A 1.5-metre drill interval assayed 0.008 per cent molybdenum and a grab sample assayed 0.24 per cent molybdenum (Assessment Report 3755, page 17).