Area Specific Investigations of Three Low- to Moderate-Temperature Geothermal Resource Areas in Nevada

Abstract

The Nevada Bureau of Mines and Geology has completed three area specific investigations of geothermal resources in Nevada. The investigations included geological, geophysical, and geochemical surveys of low to moderate temperature geothermal resources that are economically attract for direct use applications. Gravity surveys helped to identify several large faults in the subsurface; portions of these faults act as conduits for rising thermal fluids. Shallow depth temperature probe surveys and existing water temperature data from residential wells were used to delineate a linear configuration of isotherms in the vicinity of thermal fluids. This lineation was almost always parallel to nearby range bounding faults, which are easily identified on aerial photographs illuminated by a low angle sun. Soil samples, analyzed for mercury, had anomalously high values near faulted areas, especially those that also contained thermal waters. Koenig and others (1980) have shown that thermal fluids form the Cason-Eagle and Big Smoky Valleys originate as meteoric waters that have been heated be deep circulation. The combined data indicated that the process may be enhanced or initiated by natural conduits formed din the subsurface at the intersection of large faults of different ages. Younger faults, which intersect both the ground surface and older faults in the deep subsurface, continue to transmit rising thermal fluids which reach the surface and form a pattern of linear isotherms.