GEOTHERMAL PLAY FAIRWAY ANALYSIS OF THE SOU HILLS, CENTRAL NEVADA

The Great Basin region of the western USA contains >400 known geothermal systems and produces ~670 MW from ~25 geothermal powerplants. Approximately 40% of these resources are blind and lack surface manifestations (e.g. hot springs or fumaroles). To facilitate discovery and development of blind geothermal systems capable of increasing electricity generation, a play fairway approach was developed to assess and integrate multiple geologic parameters for permeability and heat. Phase 1 of the project produced a geothermal potential map of a broad swath of Nevada (96,000 km²). This analysis yielded 24 highly favorable locations with particularly high fairway scores, from which five of the most promising sites were down-selected for detailed studies. One of those five, the Sou Hills, resides at the north end of Dixie Valley as a series of low ridges that form an interbasinal high between Dixie Valley on the south and Pleasant Valley on the north.

Our analysis of the Sou Hills utilized: 1) detailed geologic mapping of ~60 km², 2) reconnaissance mapping of >200 km², 3) analysis of Quaternary faults, 4) detailed logging of 4 wells (~2,000 m) and integration of ~5,500 m of existing logs from 9 other wells, 5) a new gravity survey (355 stations), 6) LiDAR acquisition for 290 km², 7) a shallow temperature survey (82 stations), 8) interpretation of 7 seismic reflection profiles, 9) slip & dilation tendency analyses, and 10) geochemical analyses of 23 water samples. Integration of these data sets shows that the structural framework comprises a major accommodation zone between oppositely-dipping Quaternary fault systems in the central Nevada seismic belt. As such, the area is characterized by multiple, closely-spaced, W- and E-dipping normal faults. Seismic reflection and gravity data show an extensional anticline in northernmost Dixie Valley directly south of the Sou Hills. The anticline marks a zone of multiple intersecting, oppositely dipping normal faults. Many Quaternary faults in the area have ruptured in the past 15 to 130 ka and have slip rates ranging from 0.01 to 0.3 mm/yr. Together, these data suggest several discrete, favorable structural targets for geothermal resources in the Sou Hills area, including fault step overs, the extensional anticline, and fault intersections.