A Geological and Geophysical Investigation into the Evolution and Potential Exploitation of a Geothermal Resource at the Dixie Valley Training Range, Naval Air Station Fallon

This study examines the geological and geophysical controls on geothermal fluid migration in two discrete geothermal systems in the highly-extended region of the central Great Basin. Active right-lateral oblique slip of the Fairview Peak-Louderback Mountain fault zone is transferred to similarly active normal dip-slip movement in the Dixie Valley-La Plata-Sand Springs fault zone across a buried accommodation structure in southern Dixie Valley and northern Fairview Valley, central Nevada. This accommodation zone coincides with the potentially exploitable geothermal systems known as Pirouette Mountain and Elevenmile Canyon. Similar to many other Great Basin geothermal systems the translation of geothermal fluids near to the surface is related to a structural configuration that promotes fluid flow through fracture permeability. An interpretation of this relationship as it applies to these geothermal systems was completed through a combination of detailed geologic mapping, Ar-geochronology, interpretation of geophysical data (aeromagnetics, gravity, and 2D-seismic), and structural analysis. The geophysical data was critical in understanding the geometry of structures not expressed at the surface. The structural analysis included an examination of available fault kinematic data that was resolved into paleostress orientations applied to an analysis of slip and dilation tendency for all mapped structures in the study area, including 3D planes generated from the 2D-sesimic interpretation. The results indicate that the Pirouette Mountain geothermal system is associated with a concealed oblique anticlinal accommodation zone that is bound by structures that are poorly oriented for slip and dilation and act as fluid barrier to southward fluid migration in basement stratigraphy. Fault intersections with the steeply dipping, dilation prone, northern continuation of the Louderback Mountains fault appear to be critical to geothermal fluid migration in the system. The results also characterize the Elevenmile Canyon geothermal system as a discrete upwelling of geothermal fluids along faults well oriented for slip and dilation that terminate into the Elevenmile Canyon caldera margin within a broader structural setting that can be characterized as a major stepover from the Sand Springs Range frontal fault system to the Stillwater Range frontal fault system. The results of this study are meant to inspire renewed interest in further exploration and delineation of geothermal systems in Southern Dixie Valley in addition to generating new discussion on the application of these methods and others in the best practice of identifying, exploring, and exploiting additional geothermal systems in the Great Basin and beyond.