The City of Spokane vein is part of the "North belt" zone of discontinuous veins of the Rossland mining camp. On a regional scale the veins appear continuous but in detail they are lenticular and offset by northerly trending faults. The Spokane vein strikes east-west and dips 80 degrees north.

The vein is hosted by the Rossland monzonite, an east-trending biotite-hornblende-augite monzonite stock. The intrusive is medium- grained, grey to green in color and hosts magnetite, apatite, some sphene with chlorite, epidote, pyrite and pyrrhotite. The stock intrudes siltstone, volcanics and augite porphyry (Rossland sill) of the Lower Jurassic Elise Formation, Rossland Group. A Tertiary lamprophyre dyke crosscuts the monzonite and appears to control the gold-copper mineralization. In 1983, the dyke was dated at 6.30 plus or minus 0.04 million years using biotite in potassium-argon dating. The dyke contains 20 per cent serpentine.

Mineralization in the City of Spokane vein consists of massive pyrrhotite and pyrite carrying low gold and copper values. The heavy sulphide deposit follows the footwall side of the lamprophyre dyke. Other mineralized veins, such as the Mabel (082FSW129), were exposed in open pits in the monzonite host rock further to the north.

Refer to the Le Roi deposit (082FSW093) for a summary of the Rossland mining camp.