DISCOVERY AND ANALYSIS OF A BLIND GEOTHERMAL SYSTEM IN SOUTHEASTERN GABBS VALLEY, WESTERN NEVADA

This study assessed the potential for high-temperature (≥130°C) blind geothermal systems in southeastern Gabbs Valley, Nevada, an area with no previously known geothermal activity or geothermal exploration, by integration of geologic, geophysical, and geochemical datasets. Gabbs Valley is a complex, tectonically active basin within the Great Basin on the boundary between the transtensional central Walker Lane domain and extensional Basin and Range province. The termination of the Petrified Springs fault, a major dextral fault of the central Walker Lane, into an array of normal faults indicates that the area occupies a displacement transfer zone, which is a favorable structural setting for geothermal activity. A substantial northwest-trending gravity high within the south-central part of the basin is produced from offsets along concealed northwest-striking dextral-normal faults that intersect strands of north-northeast-striking normal faults. Multiple lines of direct and indirect evidence suggest the presence of a blind geothermal system in this area, including collocated intersecting gravity gradients, magnetic-low, low-resistivity, and 2-m temperature anomaly. Potentially related, warm (32°C) water samples from agricultural wells 7 km northwest of the 2-m temperature anomaly yield geothermometers indicating subsurface fluid temperatures of 130-140°C. Six temperature-gradient holes were drilled to target the extent of the shallow-temperature and geophysical anomalies. Two wells contained high temperatures exceeding boiling with bottom-hole temperatures of 114.5°C and 124.9°C, and the remaining wells displayed elevated to background temperatures ranging from 79.2°C to 28.7°C. The observed temperature gradients for the two hottest drill holes necessitate intercepts of hydrothermal fluids and establish the discovery of a blind geothermal system that may be capable of supporting a power plant.