The Sulphurets-Mitchell Creek area is underlain by rock of the Lower Jurassic Unuk River Formation, Hazelton Group. These rocks in- clude green to grey volcanic epiclastics and a sequence of dominantly fine-grained marine sediments. A third sequence of massive red and green volcanic sandstones and conglomerates form the highest peaks capping the stratigraphic sections.

The mineral occurrence is reported to lie entirely within a "tectonic shear zone". This zone contains all of the significant gold anomalies. The zone covers an elongated northern trending area, 800 to 900 metres wide and 2 kilometres long. The zone is flanked by comparitively unaltered or weakly altered, fine-grained, brownish green clastic sediments and submarine volcanic rocks on the east, and by a thick unit of basaltic andesite on the west. This tectonic zone is typically composed of moderately to strongly altered and sheared rocks, interpreted to be of volcanic, subvolcanic or plutonic origin. Most of the altered zone can be described as a sericite schist. How- ever andesitic tuffs and flows, and feldspar porphyry dykes and possible flows, can be recognized in the less altered zone. A later formed "swarm" of fine-grained, weakly altered andesite dykes cuts across the schistosity. Both the altered zone and dykes have been cut by faults. Minor sections of silty shale and siltstone occur on the western and eastern margin of the altered zone.

The Pyramid zone outcrops as a prominent, gossanous knoll in the large cirque basin on the north side of the Kerr Ridge. It lies within the same fault-bounded block of ground as the B zone and is probably the northern continuation of the B zone. The western bounding fault is the Number 3 Fault, the eastern bounding fault is the B zone Fault.

Like the B zone, the Pyramid zone consists of massive, wholly silicified country rock that has been subsequently crushed to a crackle breccia texture. The hairline fractures of the crackle breccia are lined with fine black sooty chalcocite, with lesser chalcopyrite and pyrite. The alteration assemblage also includes chlorite, sericite and pyrite. The P zone was tested by trenching and a single diamond-drill hole in 1988. No assay results are available.