Geology of the Central Mineral Mountains, Beaver County, Utah

Bruce S. Sibbett, Earth Science Laboratory, University of Utah Research Institute
Dennis L. Nielson, Earth Science Laboratory, University of Utah Research Institute



The Mineral Mountains are located in Beaver and Millard Counties, southwestern Utah. The range is a horst located in the transition zone between the Basin and Range and Colorado Plateau (Stokes, 1977) geologic provinces. A multiple-phase Tertiary pluton forms most of the range, with Paleozoic rocks exposed on the north and south and Precambrian metamorphic rocks on the west in the Roosevelt Hot Springs KGRA (Known Geothermal Resource Area). Precambrian banded gneiss and Cambrian carbonate rocks have been intruded by foliated granodioritic to monzonitic rocks of uncertain age.

The Tertiary pluton consists of six major phases of quarttz monzonitic to leucocratic granitc rocks, two diorite stocks, and several more mafic units that form dikes.

During uplift of the mountain block, overlying rocks and the upper part of the pluton were partially removed by denudation faulting to the west. The interplay of these low-angle faults for the structural control of the Roosevelt Hot Springs geothermal system. The structrual complexity of the Roosevelt Hot Springs KGRA is unique within the range, although the same tectonic style continues throughout the range.

During the Quaternary, rhyolite volcanism was active in the central part of the range and basaltic volcanism occurred in the northern portion of the map area. The heat source for the geothermal system is probably related to the Quaternary rhyolite volcanic activity.

This study did not document any additional evidence of recent geothermal activity. It has, however, documented several areas of young basaltic volcanism in the northern portion of the Mineral Mountains. In addition, a structural framework has been developed which will be of use to geothermal explorationists working in the area.