The Trillicum showing occurs near the contact of the Eocene Penticton Group, Marron Formation, on the east, and a stock of the Middle Eocene Coryell Intrusions, on the west. The Marron Formation rocks consists of andesitic flows, lapilli tuffs, tuffaceous sandstone and tuffaceous conglomerate. The intrusions are generally coarse grained and range in composition from syenite to monzonite and granite.

In 1990, some old workings consisting of a 20 metre vertical shaft, two caved adits and several pits were discovered. Exposed in the shaft is a silicified and altered structure up to 2 metres wide, striking 010 degrees and dipping 80 degrees east. On the dump near the shaft specimens of massive magnetite and pyrite were found, as were specimens containing up to 5 per cent galena with traces of sphalerite and malachite.