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Study of a possible geothermal system near Deeth, Elko County, Nevada, included geologic mapping, hydrogeochemical analyses, and geophysical interpretation. Geologic and geophysical methods emphasized structure, particularly Paleozoic thrust faults overprinted by Miocene listric normal faulting. Hydrogeochemical analyses showed geothermal fluids to be sodium-bicarbonate water, probably of meteoric origin. The geothermal model is convection cells caused by deep circulation along the Marys River fault zone. The reservoir is fractured rock along the fault zone. Silica geothermometry predicts a reservoir temperature of 165°C (329°F).
A Paleozoic sedimentary range block is separated by the Marys River fault zone from a Tertiary basin-fill sequence to the east. Allochthonous western facies rocks at Twin Buttes were emplaced along the Roberts Mountains thrust. Eastward-thrusted upper Paleozoic units are exposed in the Peko Hills. A thick, bimodal, Oligocene-Pliocene volcanic sequence covers the area's northwest corner. The Miocene Humboldt Formation is a tuffaceous, fluviatile lacustrine basin-fill unit that onlaps the range block and thickens basinward. Quaternary hot-spring deposits are localized along the Marys River fault zone.
The Miocene-Pliocene Marys River fault zone is a north-trending, down-to-the-east, normal fault system. A shear zone may be present where the fault zone undergoes right separation. Hydrogeochemical, thermal water, and heat-flow anomalies are localized along the fault zone.
The proposed model calls for deep circulation of meteoric water along the Marys River fault zone. Surface water from the Marys River percolates down the fault and is heated to approximately 165°C (329°F). Thermal water migrates laterally, then rises back up the fault. Upwelling thermal water creates the three observed thermal anomalies. Leakage of geothermal fluid into discontinuous sand and gravel channels of the Humboldt Formation gives rise to broad, low-temperature anomalies. The high-temperature reservoir is fractured rock along the Marys River fault zone.
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