The Larder Lake district lies along a narrow band of Timiskaming sediments which extends from Kenogami, Ontario, to beyond the Bell River in Quebec. On the Omega property, lavas and tuffs of the underlying Keewatin outcrop in the middle of this band in a sharply folded anticline overturned to the north. This anticline is broken by a thrust fault that follows the strike of the fold and along which the volcanics and sediments of the south limb have been up-thrown.Later dikes and larger masses of granite, syenite, porphyry and lamprophyre intrude the older rocks. The Omega ore is, in part, an intrusive pegmatite of granitic composition that came in along the thrust fault on the hanging wall or south side, and, in part, an irregular replacement of the country rock (generally a green dacite) both adjacent to the intrusive and in a flow or flows on the northern limb of the structure. End stage igneous activity involved the introduction of large volumes of carbonates that completely or partially altered zones of the country rock to calcium, magnesium and iron carbonates.