The Robyn occurrence area is underlain by Weaver Lake Member rocks of the Lower-Middle Jurassic Harrison Lake Formation which are comprised of a series of basaltic to rhyolitic flows, breccias and tuffs with minor interbedded black chert. The southwest corner of the claim group is dominated by a large pyritic rhyolite dome with abundant quartz veining hosted by a sequence of andesite flows and flow breccias. Draping the dome are shallow dipping, strongly pyritic, sericitic rhyolite lapilli tuff breccia. This pyroclastic is overlain by a light grey, fine grained, pyritic felsic tuff. The pyroclastics are cut by minor andesitic dikes and several north and northwest trending normal faults.

Associated with the faulting are small, 1 to 10 centimetre wide, high angle pyrite veins with minor sphalerite +/- chalcopyrite +/- galena +/- barite.