Blind or hidden geothermal systems have been identified as an underutilized source of renewable energy in the Great Basin region of the western USA and developing techniques and strategies to detect such resources is an active area of research. The US DOE BRIDGE project has identified several petrophysical patterns that are associated with resource-capable geothermal systems in the Great Basin region that can be detected by geophysical methods like magnetotelluric (MT), gravity and aeromagnetic surveys. These include detecting low resistivity hydrothermal smectite alteration near the water table, densification of sediments due to precipitation of silica along cooling geothermal outflows, and variation in magnetite content of sediments due to hydrothermal alteration. Although geophysical interpretations have been plausibly attributed to hydrothermal alteration and precipitation, few publications report systematic analyses of subsurface samples to validate the petrologic basis for these geophysical interpretations in the moderate temperature (~120-200°C) deep circulation systems commonly found in the Great Basin. Here we present results of petrologic analyses of core and cuttings from the Don A Campbell geothermal field to validate our interpretation of gravity and aeromagnetic data that was already available for this area and Helicopter Transient Electromagnetic (HTEM) resistivity data collected for the BRIDGE project over the site. This field currently produces from a shallow 120 to 130 °C outflow reservoir hosted in basin-fill sediments. The sample analysis methods utilized include sample inspection, infrared reflectance spectroscopy in the Short-Wave InfraRed range (SWIR), and Methylene-Blue (MeB) analysis to estimate smectite abundance. These results are integrated with supporting geologic and temperature data in the context of the natural state conceptual model for the reservoir. We found several hydrothermal alteration minerals that are relevant to the interpretation, including smectite, interlayered illite-smectite, kaolinite, silica, carbonate, hematite, and pyrite. These minerals are found with a distinct zonation with common hydrothermal alteration mineral assemblages, including a shallow smectite-bearing argillic zone, a shallow silica-carbonate-pyrite-illite-smectite zone embedded within the argillic zone, a deeper silica-carbonate-pyrite-illite-smectite with minor chlorite zone, and a shallow kaolinite-smectite-hematite zone near the water table. The relative smectite content of each of these zones can be inferred from the HTEM, with low-resistivity (between 3 and 5 ohm.m) zones correlated with the argillic zone containing between 5 and 13% smectite, and relatively high-resistivity values (between 5 and 7.5 ohm.m) correlated with the silica-carbonate-pyrite-illite-smectite zones that have smectite content less than 3%. In addition, the highest values in the first-derivative of the gravity data, inferred to be due to near-surface densification, correspond to the shallow silicified zone identified in the core and cuttings. These results are applicable to the interpretation of the regional HTEM and aeromagnetic data. Sandia is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Press the Back button in your browser, or search again.

Copyright 2025, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.