Geothermal investigations in Idaho. Part 7. Geochemistry and geologic setting of the thermal waters of the Camas Prairie area, Blaine and Camas Counties, Idaho

Abstract

The thermal waters of the east-west trending intermontane basin making up the Camas Prairie area were sampled during the fall of 1973. Average ground water temperature is 15/sup 0/C (10/sup 0/C above mean annual temperature). The thermal waters, chemically similar to thermal waters discharging from granitic rocks elsewhere in Idaho, have high pH, high Na/K and Na/Ca ratios, and high fluoride content. They are low in total dissolved solids (less than 365 mg/l), low in chloride, and exhibit relatively constant chloride/fluoride ratios and silica concentrations. Geochemical thermometers are interpreted to indicate that maximum aquifer temperatures in the Camas Prairie Basin are only about 100/sup 0/C, although higher temperatures were predicted by the quartz equilibrium geochemical thermometer and mixing models. The Magic Hot Springs well, located near the north shore of the Magic Reservoir at Hot Springs Landing, is an exception to these general conclusions. These waters may be circulating to depths approaching 1,800 to 2,500 m along faults or fissures; or may be due to leakage from an aquifer or reservoir heated by a shallow heat source, related perhaps to the Holocene basalt flows south of Magic Reservoir. These waters are nearly neutral in pH, are much higher in dissolved solids, exhibit higher chloride/fluoride, chloride/carbonate plus bicarbonate, and chloride/sulfate ratios, and are, in general, chemically dissimilar to thermal waters elsewhere in the area. Temperatures predicted by geochemical thermometers are thought to indicate that Magic Hot Springs well waters are ascending from an aquifer or reservoir with temperatures from 140/sup 0/ to 200/sup 0/C. Temperatures in this range would be sufficient for application in many industrial processes, including power generation, should sufficient water be available.