| Abstract |
A close spatial relationship exists between Quaternary borate deposits and moderate to high temperature (?150°C) geothermal systems in the western portion of the Great Basin, USA. Similarly, a strong correlation exists between high concentrations of boron in groundwater and geothermal activity in the Great Basin. These relationships have special significance for geothermal exploration because in a number of cases, Quaternary surface borates occur without associated springs, and thus the borates can, and are, serving as a guide to locating otherwise blind geothermal systems. Borate deposits typically form by the evaporative concentration of boron-enriched thermal spring waters in a closed basin whose topography prevents significant influx of relatively boron-poor clastic sediments and chemical constituents from outside the basin. The relatively high boron concentrations of geothermal waters may ultimately be due to the greater opportunity of hot waters, which have relatively deep circulation paths, to interact with and leach boron-bearing host rocks. Deep-seated magmas may also be a significant source of boron. In southern California and western Nevada, the highest concentrations of boron are sometimes found in warm springs instead of hot springs. In some cases, this could be caused by remobilization of boron from older borate deposits by shallowly circulating groundwater, but in other cases, geothermometry data suggests such springs may actually consist of geothermal waters that have cooled significantly below their peak temperatures before reaching the surface. Using borates as an exploration guide, and with key assistance from remote sensing techniques, three new geothermal targets have been identified in west-central Nevada at Rhodes, Teels, and Columbus Salt Marshes (playas). In each of these playas, geothermometry data from springs and wells suggest the possible presence of geothermal reservoirs at depth. |