EVALUATING MODEL-DRIVEN HYPOTHESES WITH FIELD MAPPING, FISH LAKE VALLEY, NEVADA

Faults and fractures are critical components in geothermal fields and in epithermal mineral deposits: fault interactions, fault orientations, and the distribution and magnitude of fault slip and dilation all contribute to complex permeable pathways in the subsurface and make for challenging drilling targets. Prior geologic mapping efforts in northern Fish Lake Valley, Nevada, include several decades of research by public and private interests at a variety of scales using a variety of approaches. Although there is good agreement among these groups regarding the basic geologic framework, different fault interpretations complicated early geothermal development efforts. Differences in these interpretations include fault locations, orientations, and slip vectors. Most investigations show dip-slip displacement on SSW to NNW-striking faults. More recent models include sinistral displacement on buried ENE-trending faults, similar to that observed further north in the Minas Deflection of Walker Lane.

We conducted regional fault and lithology mapping from satellite imagery and USGS 3DEP LiDAR as well as focused field investigations aided by high-resolution imagery and topography from drone-based photogrammetry. Results from this work reveal a lower-order ENE-trending fabric of faults, scarps, and veins in the field area that was not emphasized in prior efforts. We did not find strong evidence for recent strike-slip faulting in outcrop. Rather, kinematic analysis of fault slicks and veins suggests NW-SE extension, consistent with ENE orientations of meter-thick silicified fault cores and decimeter-thick sparry calcite veins observed across the map area. The significance of ENE-trending faults and fractures is supported by independent analysis of borehole televiewer data from geothermal wells in the middle of the field area. Based on these observations, we present a generalized fault map emphasizing possible ENE-trending faults and orthogonal fault intersections beneath Quaternary cover as geothermal targets of interest.