Geology of Roosevelt Hot Springs KGRA, Beaver County, Utah

Abstract

The Roosevelt Hot Springs KGRA is located on the western margin on the Mineral Mountains in Beaver County, Utah. The bedrock geology of the area is presented. It is dominated by metamorphic and plutonic rocks of Precambrian age as well as felsic plutonic phases of the Tertiary Mineral Mountains Pluton. Rhyolite flows, domes, and pyroclastics reflect igneous activity between 0.8 and 0.5 million years ago. All lithologies present in the map area are described in detail with an emphasis on characteristics which will allow them to be distinguished in drill cuttings. The geothermal system at Roosevelt Hot Springs KGRA is structurally controlled with reservoir rocks demonstrating little primary permeability. North to north-northeast trending faults are the youngest structures in the area, and they control present fumarolic activity and recent hot spring activity which has deposited opaline and chalcedonic sinters. It is proposed here that the geothermal reservoirs are controlled primarily by intersections of the principal zones of faulting. Logs from Thermal Power Utah State 72-16, Getty Oil Utah State 52-21, and six shallow thermal gradient holes drilled by the University of Utah are presented in this report and have been utilized in the construction of geologic cross sections of themore » geothermal field.« less