Integrated geophysical exploration of a known geothermal resource: Neal Hot Springs

We present integrated geophysical data to characterize a geothermal system at Neal Hot Springs in eastern Oregon. This system is currently being developed for geothermal energy production. The hot springs are in a region of complex and intersecting fault trends associated with two major extensional events, the Oregon-Idaho Graben and the Western Snake River Plain. The intersection of these two fault systems, coupled with high geothermal gradients from thin continental crust produces pathways for surface water and deep geothermal water interactions at Neal Hot Springs. New geologic mapping, geochemistry and several boreholes in the area suggest a steeply dipping 60⁰ normal fault dips to the southwest to form a half-graben basin. This basin-bounding fault serves as the primary conduit for deep water circulation. Potential field, electrical, and seismic data characterize this major fault along with other smaller scale structures in the area. A self-potential survey indicates that water is upwelling in the fault plane, and suggests that the fault does provide the means for heated water to migrate to the surface. Electrical and magnetic surveys offer methods to locate hydrothermal waters near the surface by identifying areas affected by hydrothermal waters.