Geophysical Investigations and Structural Framework of Geothermal Systems in West and Southcentral Idaho; Camas Prairie to Mountain Home

Abstract

A recent study of the geothermal potential of the Snake River Plain (SRP) region, which adapts play fairway methodology to assess geothermal resources (Shervais et al., 2016), identified several areas in southcentral Idaho, including a broad swath from Mountain Home to the Camas Prairie in the western SRP, as regions with elevated resource potential. The present work was undertaken to better characterize these resources through detailed geophysical exploration. We focus on three areas from the western SRP that range from high to low-temperature systems, span magmatic (basaltic sill), amagmatic (Basin-and-Range), and basement related play types, and have resource potential favorable for development of direct use, conventional, and EGS resources. We performed geophysical studies of three areas (Mountain Home, Bostic, Camas Prairie), collecting high-resolution gravity and ground magnetic data, magnetotelluric data, and seismic reflection data to (1) characterize intra-basin and basin-bounding faults, (2) constrain basin geometry, (3) study fault interactions, (4) identify areas favorable to hydrothermal flow, and ultimately (5) guide exploration of the area’s geothermal system. As part of this work, we collected 1659 gravity stations, over 725 line-km of ground magnetic data, more than 50 km of seismic reflection data, and 102 MT stations. Additionally, we integrated ground water well logs into our analyses, and collected hundreds of rock-property measurements on outcrops and samples (including susceptibility, density, and magnetic remanence) to constrain potential field modeling. Assessment of surficial geology and structure has encompassed detailed review of existing geologic mapping, new structure mapping based on aerial imagery, and new boots-on-the-ground structure mapping. These data resolve key structural features that appear to be responsible for promoting permeability and facilitating hydrothermal flow. The structural and conceptual framework developed from this study provide important information relevant to future development of these geothermal resources in the western SRP.