The Spider Peak area is underlain by a pyritic sequence of volcanic greenstone assigned to the Early Triassic Spider Peak Formation, which separates Lower and Middle Jurassic Ladner Group sediments to the east from ultramafic rocks of the Coquihalla serpentine belt and the Hozameen fault to the west.
West of Spider Peak, a narrow slice of serpentinite and quartz(-carbonate)-veined listwanite occurs within the Hozameen fault system, immediately east of a large feldspar-quartz porphyry sill. This sill has intruded chert assigned to the Hozameen Complex west of the fault. The serpentinite is dark green to black in colour and has been sheared. Weathered exposures of massive to weakly foliated, medium to coarse-grained, dark yellow-brown listwanite occur locally in association with the serpentinite. Quartz(-carbonate) veins and veinlets varying from a few millimetres to one metre wide occur throughout the listwanite and finely disseminated pyrite, magnetite (or possibly chromite) and minor chalcopyrite have been observed locally. Talc is widely developed along shear planes in the quartz-carbonate rocks and minor fuchsite occurs as sparse disseminations and rare, thin veinlets. Widespread silicification and/or carbonatization of the rocks in this area is apparent.
Precious metal values in samples of listwanite have been generally low. Higher assays have been obtained from quartz veining hosted by listwanite. A six-centimetre vein assayed 0.54 grams per tonne gold (Assessment Report 11453).