Geology and Mineral Deposits of the Cargo Muchacho Mountains, Imperial County, California

Abstract

The study of the Cargo Muchacho Mountains presents the first account of the geology of southeasternmost California. In these mountains pre-Mesozoic kyanite schist and arkosite are intruded by a series of granitoid rocks probably Mesozoic in age. The two youngest rocks of this series were formed by granitization of arkosite. Andesite dikes of minor importance intruded the area probably in Tertiary time. Remnants of a once extensive flow of olivine basalt cover a few outlying hills. Alluvial deposits of three distinct ages occur in the area. Two of these, which are prebasalt in age, offer evidence that the Colorado River formerly flowed through the region. The Cargo Muchacho Mountains constitute an important goldmining district. The occurrence of the ore is shown to have been controlled by the regional structure. The ore deposits are mesothermal and are locally characterized by extreme alteration of the wall rock. Kyanite and sericite are also mined in the district. The record of mining activity and production of the district is brought up to date.