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. Foliated hornblende diorite of Juro-Triassic age intrudes 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.

The Permian strata consists of a 760 metre succession of limestone and dolomitic limestone, with local chert, shale and sandstone. The pre-Upper Triassic rocks consist of fine-grained crystal tuff to lapilli tuff with intercalated phyllite and greenstone, and minor chert, jasper greywacke and limestone. These are considered to be part of the Stikinia Terrane.

A major north to northwest trend 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- fuchsite(?) (listwanites) and quartz-dolomite alteration zones. The listwanites occur in the tuffs.

The Bear Main (see 104K 079), the Fleece Bowl (see 104K 087) and the Totem Silica zones, occur along the major north trending structure.

The Totem Silica zone is a 200 by 1100 metre area of intense silicification within well-bedded, locally intensely folded limestones and dolomite. The rocks occupy the fault-bounded core of a north-trending anticline and have local, stratabound breccia zones. Late-stage northeast trending cross-fracturing is prominent and quartz-boudinage is well developed in the limestone. Pyrite occurs as disseminations in the silicified limestone and as rims around the breccia fragments. Quartz stockworks, mineralized with tetrahedrite, occur in silicified dolomite.

On the west side of the zone, a north trending, east dipping fault, separates the silicified limestone with interbedded fuchsite- bearing(?) tuff and carbonaceous siltstone. The hangingwall section consists of foliated hornblende tuff, chloritic tuff and fine-grained greenstone with hematitic fractures. Intruding the rocks on the east, is a foliated hornblende diorite, which are cut by hornblende- feldspar porphyry dykes. These dykes have been altered to epidote, chlorite and clay minerals.

Age dating of sericite from sericitic tuff, which gave an apparent age of 204 plus or minus 7 million years (Schroeter, 1987), suggests the period of mineralization occurred in Early Jurassic.

The mineralization is primarily epigenetic, although supergene enrichment occurs locally. The deposits are characteristic of a low to medium temperature, low salinity, mesothermal system. Likely, mineralized solutions ascended the fault zone to an area of extensive tectonic brecciation and alteration. Intrusive activity, alteration and mineralization along the major regional fault is postulated to have occurred over a 50 million year period, from 156 to 206 million years (Jurassic Age). (Schroeter, 1987).