The Whitehorse claims, staked in 1960-61, covered the original magnesite discovery at the south end of Topaz Lake. The occurrence is a triangular shaped mass about 425 metres by 180 metres at the widest point. Drilling indicates 15 to 30 metres thickness of coarse- grained magnesite with 2 to 12 millimetre crystals underlain by a fine-grained cherty dolomite. The magnesite occurs in the trough of a northwest plunging syncline within the Mount Nelson dolomites and consists of a light to pearly grey rock with a rough rusty brown weathered surface. Visible impurities include quartz in scattered veinlets and grains as well as talc in minute shears.

A smaller magnesite body about 60 by 60 metres forms an apparent dip slope surface layer across the end of a low hillock about 150 metres northwest of Topaz Lake. Thickness is unknown but it is underlain by a fine-grained dolomite which hosts abundant sil- iceous chips. In addition, there are a number of other small magne- site bodies in the vicinity of the main occurrence.