Brady Hot Springs Geothermal Area

The Brady’s geothermal field, in the hot spring mountains of northwestern Nevada, has a reservoir temperature of 180-193°C at 1- 2 km depth and supports a combined dual flash and binary geothermal power plant with a total installed capacity of 26 MWe. The Brady’s area is dominated by NNE-trending gently to moderately tilted fault blocks bounded by moderately to steeply dipping normal faults. Faults in the area dip both WNW and ESE and have respectively accommodated both E- and W-tilting of fault blocks. West-tilted fault blocks predominate suggesting that ESE-dipping faults have accommodated the bulk of extension in the area. No major transverse or cross faults have been observed at the surface. In terms of hydrothermal activity, the most significant fault in the area is the Brady’s fault zone, which consists of a complex system of en echelon, primarily WNW-dipping faults. The surface expression of the Brady’s geothermal system is a 4-km-long, NNE-trending zone of extensive sinter, warm ground, fumaroles, and mud pots along the Brady’s fault system. The main hot springs at Brady’s have been the site of a resort and spa for many years (1930s to 1950s). The main production wells at Brady’s appear to penetrate the down-plunge projection of a small left step in a major splay of the Brady’s fault zone. The NNE-striking Brady’s fault zone is orthogonal to the regional WNW-trending extension direction and is thus favorably oriented for fluid flow. We suggest that multiple fault intersections at depth between the WNW-dipping Brady’s fault zone and presumably older ESE-dipping faults, as well as multiple fault strands in the step-over, produce a zone of high fracture density that enhances fluid flow and facilitates the rise of a deep-seated thermal plume.^[1]