In the Tatsamenie Lake area, intensely folded and regionally metamorphosed Permian, Triassic and older strata are separated from less folded and less metamorphosed Mesozoic sedimentary and volcanic rocks by a pre-Upper Triassic unconformity. Hornblende diorite and quartz-monzonite of Juro-Triassic age intrude the pre-Upper Triassic rocks. These are commonly altered to chlorite, hematite and epidote. The Mesozoic strata are overlain unconformably by flat-lying Upper Tertiary and Pleistocene plateau basalts of the Level Mountain Group.
A major north to northwest trending fault, known as the Ophir Break Zone, extends through the area for over 10 kilometres, and is defined by areas of intense fracturing with abundant slickensiding; areas of carbonaceous and siliceous black siltstone and gouge; and linear quartz-iron carbonate-pyrite and quartz-dolomite alteration zones.
The pre-Upper Triassic rocks consist of fine-grained crystal to lapilli tuff, phyllite, limestone, siltstone and intraformational breccia. These are considered to be part of the Stikinia Terrane.
Minor gold mineralization, associated with pyrite, occurs within tuff near the West Wall fault. A sample assayed over 10.0 grams per tonne gold (Assessment Report 11408).