Geology of the carbonate-hosted Omar copper prospect, Baird Mountains, Alaska

Abstract

Copper and iron sulfides occur in discordant veinlets, blebs, and stringers, and are strata bound within a Devonian dolostone. This commonly brecciated dolostone is part ofa Paleozoic sequence of folded and faulted carbonate rocks in the western Baird Mountains quadrangle. Sulfides, sparry dolomite, and less commonly calcite and quartz locally form the matrix surrounding the angular clasts. Bornite and chalcopyrite are the dominant copper sulfides, and chalcopyrite forms coherent exsolution lamellae and noncoherent blebs and dots within bornite or tetrahedrite. Sulfides surround euhedral dolomite rhombs in veinlets and small cavities, indicating that sulfide precipitation postdated euhedral dolomite growth. Dissolution of the host dolostone created the open spaces, which were filled in turn by dolomite, sulfide, and quartz prior to metamorphism and deformation associated with the Middle Jurassic to Cretaceous Brooks Range orogeny. Mineralization at Omar was similar in mineralogy and style to the carbonate-hosted Ruby Creek copper deposit 180 km to the east in the Ambler River quadrangle.