The Cretaceous Horsethief Batholith intrudes Middle Proterozoic sediments of the Purcell Supergroup. The intrusion is zoned from fine-grained/medium-grained granodiorite to coarse-grained quartz monzonite. East trending aplite dykes cut the intrusion.

Disseminated molybdenite occurs in a pink aplite dike 30 centimetres in width. Associated parallel smaller dikes (5 centimetres wide) occur. Pyrite and sericite are associated alteration minerals. A sample of the material assayed 0.111 molybdenum (Assessment Report 3223, Map 3).

Canadian Johns-Manville Company Limited staked and investigated a number of claims in the area in 1970, including the Slide, Annette and Blue. It is reported that 739 geochemical samples were taken in 1970 (Geology, Exploration and Mining in BC 1970, page 469). In 1971, Canadian Johns-Manville completed further geochemical, geological and geophysical surveys on its Slide group of claims (Geology, Exploration and Mining in BC 1971, page 426). In 1972, the company completed further surveys on its Slide group including mapping and geochemical sampling (Geology, Exploration and Mining in BC 1972, page 74). The company returned in 1973 and conducted further surveys including some detailed mapping on the Blue claims, (Geology, Exploration and Mining in BC 1973, page 92).