Discussion of ultramafic and mafic rocks and platinum-group element analyses from the Lost Basin mining district, northwestern Arizona

Abstract

Proterozoic amphibolite that crops out in the Lost Basin Range, Mohave County, Arizona is derived from both sedimentary and igneous protoliths. Those amphibolites derived from igneous protoliths are characterized by high Ni and Cr contents, high MgO contents, low Si02 contents and the presence of palladium and platinum. Compositions, textures and stratigraphic considerations suggest that the protoliths varied from ultramafic komatiite to basaltic komatiite to tholeiite. If these represent the actual protoliths, then this Precambrian terrane could be of interest in terms of Cu-Ni sulf ide mineralization associated with komatiites.

Evaluation of metallic mineral resources and their geologic controls in the East Mojave National Scenic Area, San Bernardino County, California

“…Small exposures of ultramafic rock are reported in Early Proterozoic rocks in the McCullough Mountains and New York Mountains and elsewhere in Nevada and Arizona, and some of these exposures are associated with somewhat elevated abundances of platinum-group elements. Ultramafic rocks are known in nearby Early Proterozoic sequences in the Gold Butte area of southern Nevada (Volborth, 1962;Dexter and others, 1983), Lost Basin, northwestern Arizona (Page and others, 1986;Theodore andothers, 1987a), andnear Bagdad, Arizona (Floyd Gray, oral commun., 1988;C.M. Conway, unpub.…”