Report on dc soundings over a geothermal prospect in the Bruneau-Grand View area, Idaho

Technical Report · Tue Jan 01 04:00:00 EST 1974

DOI:https://doi.org/10.2172/7348118· OSTI ID:7348118

Jackson, D B

The d-c sounding survey confirms the presence of a large conductive section of sedimentary and volcanic rocks underlying the low-resistivity AMT anomaly defined by Hoover. Within the conductive section, resistivity boundaries between sedimentary rocks of the Idaho Group, the Banbury Basalt, and Idavada Volcanics appear to be entirely obscured, at least where well data are available. True resistivities near these contacts range from about 3 to 5.5 ohm-m, about 3 to 10 times less than would be expected for similar volcanic rock types saturated with fresh water. Because water samples from wells in the Bruneau-Grand View area are relatively fresh, the greatly decreased resistivities are probably related to a combination of thermal waters and alteration within the volcanic rocks and perhaps also within part of the sedimentary section. The d-c soundings trace the low resistivity zone beyond the limits of the AMT survey to the east as far as the town of Hammett, where a zone of 4.4 ohm-m material 640 m thick is present. To the west the conductive section terminates about 5 km east of Oreana, where truncation of the conductive section appears to be related to decreasing lateral porosity. The 1 to 7 ohm-m conductive section can still be recognized beneath the Snake River Plain between Bruneau and Mountain Home, although the top of the conductor is deeper and the thickness is less than at any other sounding location. The presence of a high-resistivity basement suggests that thermal fluids probably emanate from greater depths than this survey can resolve, rise along fault zones, of which there appear to be many, and then spread laterally through lithologic units that have sufficient porosity. Stratigraphic maps are included.

• Research Organization: Geological Survey, Reston, Va. (USA)
• OSTI ID: 7348118
• Report Number(s): USGS-OFR-74-240
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys
CURRENTS
DIRECT CURRENT
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
ELECTRICAL SURVEYS
ELECTRODES
EXPLORATION
GEOPHYSICAL SURVEYS
GEOTHERMAL EXPLORATION
Geothermal Legacy
IDAHO
MAPS
NORTH AMERICA
PACIFIC NORTHWEST REGION
PHYSICAL PROPERTIES
USA