An Isotopic Study of the Coso, California, Geothermal Area

Abstract

Thirty nine water samples were collected from the Coso geothermal system and vicinity and were analyzed of major chemical constituents and D and 180. Non thermal ground waters from the Coso Range were found to be isotopically heavier that on thermal ground waters from the Sierra Nevada to the west. The D value for deep thermal water at Coso is similar to that of the Sierra water, suggesting that the major recharge for the hydrothermal system comes from the Sierra Nevada rather than from local precipitation of the Coso Range. the 180 values of the thermal water are about to°/00 heavier than those of the Sierra water. This shift in 180 is the result of water rock reaction at high temperatures, and the magnitude of the shift indicates that the ratio of rock to total water has been large of the system up to its present stage of development. The isotopic data are compatible with the geochemical model previously proposed by Fournier, et e. (1980).