Gibson Island is underlain by a north-northwest trending, steep to vertical dipping section of Permian (?) or older metasediments consisting of lenses of crystalline limestone interbedded with quartz-feldspar-biotite schist, chlorite schist, and hornblende- muscovite-garnet schist. Tight and locally intense folding and granitic dykes are common in the area.

A 100 by 20 metre discontinuous mineralized zone, along a schist- limestone contact, consists of disseminated and massive chalcopyrite, pyrite, sphalerite, galena, and sparse molybdenite in a siliceous gangue of garnet, epidote, chlorite, calcite, actinolite, and diopside. Thirty trench samples, from 1 to 4 metres wide, gave an unweighted average of 1.47 per cent copper, 1.03 per cent lead, 1.45 per cent zinc, and 25.7 grams per tonne silver (Assessment Report 9997).