Geothermal Potential of the Pyramid Lake Paiute Reservation, Nevada, USA: Evidence of Previously Unrecognized Moderate-Temperature (150-70 deg C) Geothermal Systems

摘要

At least two and possibly three previously unrecognizedmoderate-temperature (150-165 deg C) geothermal areas have been identified during a geothermal exploration program on the Pyramid Lake Paiute Reservation (PLPR) in west-central Nevada, USA. At each of these new areas --Pyramid Rock, the southwestern Smoke Creek Desert (SWSMD), and east Astor Pass, -- as well as at the known Needle Rocks geothermal area, hot springs and/or near-surface upwellings of hot water are associated with calcium carbonate (tufa) towers forming today in Pyramid Lake or formed in late Pleistocene Lake Lahontan. The structural controls on geothermal fluid flow are still being investigated, but the intersection of Quaternary faults appears to have localized the shallow upwelling of thermal fluids. Near-surface thermal waters, where identified, have temperatures ranging up to 49-97 deg C, whereas quartz and Na-K-Ca-Mg geothermometers suggest reservoir temperatures on the order of approx150 to 165 deg C. Exploration work began with compilation of existing data into a geothermal geographic information system (GIS), and acquisition of an airborne hyperspectral remote-sensing survey of the entire reservation. These efforts were followed by a reconnaissance field survey that prioritized the investigation of anomalies identified in the initial GIS and hyperspectral work. The field survey, which included temperature measurements of springs and existing wells; reconnaissance structural and geological assessments; and geochemical analyses of selected spring and well waters, identified the current areas of interest. Two promising areas have been investigated in detail with magnetic and gravity surveys; shallow temperature measurements from 2-meter-deep auger holes; detailed geologic mapping; and temperature-gradient drilling. Temperature-gradient drilling is in progress, and early results include the intersection of near-boiling waters within 60 m (200 ft) of the surface just east of Astor Pass, approx6 km northwest of Needle Rocks in an area with no springs.