Uranium potential of the Big John Caldera, Beaver County, Utah

The Big John caldera is a small subsidence structure in the Marysvale volcanic field, high along the western flank of the Tushar Mountains in west-central Utah (fig. 1). This caldera formed 22 m.y. ago in response to ash-flow eruptions of the Delano Peak Tuff Member of the Bullion Canyon Volcanics. Little, if any, mineralization took place during or shortly after caldera subsidence, but subsequent geologic events produced several environments that seem favorable for the occurrence of uranium deposits. This brief report outlines the geologic framework of these environments and is intended to serve as a guide for more detailed investigations and possible exploration of the more favorable areas.