Sulfate-water isotope geothermometry and lead isotope data for the regional geothermal system in the Twin Falls area, south-central Idaho

Sulfate-water isotope geothermometry for the geothermal system at Twin Falls, Idaho indicates aquifer-temperatures of 90?? to 106 ??C; most sites are between 90?? and 93 ??C. 206Pb/204pb and 280Pb/204Pb of individual thermal waters are principally a function of how much lead has been dissolved from the carbonate and silicate fractions of the Paleozoic limestone collected west of Grand View Peak. Although most thermal waters are recovered from Tertiary rhyolite, very little of the dissolved lead is from the rhyolite. Recharge to this system occurs in northern Nevada and the fluid moves northward in the Paleozoic limestones. The occurrence of thermal fluid in the Idavada Volcanics near and south of Twin Falls, Idaho is the result of upward movement of this fluid from the Paleozoic limestone.