Description:The Utah Geological Survey, in cooperation with University of Utah and the University of Utah Research Institute, conducted geological, geophysical, and geochemical studies over the concealed, moderate- temperature, Newcastle geothermal system located in southwestern Utah. Temperature depth measurements from 25 thermal gradient drill holes and three geothermal production wells define a thermal anomaly, centered near the surface trace of the range bounding Antelope Range fault, and an elongate thermal plume extending northward and westward within a shallow aquifer. The thermal aquifer generally occurs at depths from 65 to 95 meters (210 to 310ft). A temperature of 130C, measured in the out-flow plume of the system, is the highest temperature recorded to date. Higher temperatures, however, are expected in the fluid upflow zone. The new heat-flow data yielded a computed, anomalous heat loss of 12.4 megawatts (thermal). Chemical analyses of water samples indicate that thermal fluid, produced from wells penetrating the outflow plume, is a mixture of meteoric water likely derived from recharge areas in the Pine Valley Mountains and cold, shallow ground water. Detailed self-potential (SP) and resistivity surveys define the geometry of the probable up-flow zone indicating that the thermal fluid issues from a short segment of the Antelope Range fault and discharges laterally into a shallow aquifer beneath the Escalante Desert. Self-potential data show a high-amplitude, elliptical SP minimum coincident with the center of the thermal anomaly and with the subsurface intersection of the Antelope Range fault with older faults. We postulate that this SP minimum marks the primary upflow conduit of the hydrothermal system where most of the thermal fluid discharges from transmissive structures. Additional leakage of thermal fluid, as shown by resistivity data, occurs over a minimum distance of 1.5 kilometers (l mi) along the trace of the Antelope Range fault.
Publication Date: Jan 01, 1992