The area of the Randeb 1 showing is underlain by mainly quartz-sericite-biotite gneiss and associated lenses of metavolcanic and ultramafic rocks. A lens of serpentinized peridotite is the primary hostrock of the showing. These rocks are part of the Custer Gniess, a metamorphic package probably derived from lower Mesozoic and possibly Paleozoic and Precambrian rocks and metamorphosed in the Late Cretaceous and early Tertiary. Intrusions of feldspar porphyry granodiorite and quartz diorite occur nearby.

Pyrrhotite and chalcopyrite occur in the peridotite. Pentlandite, cubanite and magnetite were also reported from this location. A sample of the peridotite yielded 1.8 grams per tonne gold, 2.7 grams per tonne silver, 0.06 per cent copper and greater than 0.05 per cent nickel (Assessment Report 10997). A sample of the nearby gneiss yielded 1.8 grams per tonne gold, 0.6 gram per tonne silver and negligible copper and nickel. In 1987, the zone was determined to have a maximum north-south extent of 130 metres.