The Structural Setting of the Pumpernickel Valley Geothermal System

Abstract

The Pumpernickel Valley geothermal area is located near the eastern edge of the Sonoma Range and within the structurally complex Winnemucca fold-and-thrust belt of northcentral Nevada. A series of the Basin and Range faults is superimposed on the earlier structures. Two of these faults, the Pumpernickel Valley fault and Edna Mountain fault, are range-bounding, dominated by extensional features, and display various numerous characteristics typical of divergent wrench fault systems. These characteristics combined with the recent resistivity, magnetic, and gravity data, indicate the presence of a complex pull-apart-like basin, with several subsidence centers and numerous horst blocks. The basin is located within the bend of the Pumpernickel Valley – Edna Mountain fault system. Within the project area, the Pumpernickel Valley fault displays the most striking evidence of geothermal activity manifested by three areas with active and fossil hot springs, seepages, and wet ground/vegetation anomalies. These features are located next to the fault and indicate that it focuses the geothermal fluid up-flow. The temperature data from the newly drilled and old holes suggest that geothermal gradients (>100°C/ km) typical for the Pumpernickel Valley fault zone comprise an area of a minimum 8 km2. A substantial body of evidence exists, in the form of available geothermal, geological and geophysical information, to suggest that the property hosts an extensive, structurally controlled, relatively high temperature geothermal reservoir suitable for electric power production.