Talc is associated with the Mount Sydney Williams ultramafic massif in the area between Trembleur Lake and Baptiste Creek, southwest of Mount Sydney Williams. The area is 85 kilometres northwest of Fort St. James.

The Mount Sydney Williams peridotite-dunite-harzburgite batholith is part of the Permian to Triassic Trembleur Intrusions which intrude Paleozoic cherts and argillites. The dunite and harzburgite are 60 per cent serpentinized.

Carbonate, quartz and mariposite occur in zones of hydrothermal alteration along faults, shears and fractures. However, soapstone bodies with talc and carbonate are massive and do not appear to be structurally controlled.

Two large masses of soapstone occur in the southern part of the stock. The surrounding rock is red, green and orange weathered and contains elongate euhedral olivine crystals in a talc matrix; all the serpentine and pyroxene are completely replaced.

The borders of the ultramafic bodies, especially along serpentine and siliceous sediment contacts, are altered to talc, chlorite-actinolite and tremolite. The talc and carbonate zones are greenish to buff with a greasy luster. Average compositions run 60 per cent talc, 40 per cent ankerite with accessory magnetite, chromite and pyrite.

On the southeast face of Mount Sydney Williams, a 15 to 30 metre wide talc-carbonate zone with minor actinolite crystals, marks the contact between serpentine and peridotite, and siliceous sediments. The characteristic succession for steatitization is observed here; hornblende to actinolite/tremolite to chlorite to talc to carbonate (Armstrong, 1949).