The Iago Mountain area is underlain by granitic rocks assigned to the Eocene Needle Peak pluton. In the immediate area of the Dominion occurrence, coarse-grained quartz diorite predominates. These rocks have been intruded by numerous, variably mineralized dykes and stocks ranging in composition from rhyolite to granite. Narrow, mineralized quartz veins which strike northwest and dip steeply to the northeast also cut the diorite.

Mineralization observed near the summit of Iago Mountain consists of molybdenite, chalcopyrite, bismuthinite, pyrite and pyrrhotite occurring as disseminations in the intrusives and as cavity-fillings and on slip planes in the quartz veins. Early reports describe a quartz lens 46 centimetres wide carrying "flakes or lumps" of molybdenite as cavity-fillings. The quartz lens, being so intimately and irregularly intergrown with the diorite, is though to represent a pegmatitic phase of the intrusive, introduced during the latter stages of consolidation of the pluton.

Assays up to 1.59 per cent MoS2 have been obtained from chip samples of mineralized veining, and a 40-centimetre wide vein with molybdenite rosettes assayed 1.09 per cent MoS2 (Assessment Report 7391).