Chemical, Isotopic, and Dissolved Gas Compositions of the Hydrothermal System in Twin Falls and Jerome Counties, Idaho

Abstract

The chemical , isotopic, and gas compositions of the hydrothermal system in Twin Falls and Jerome counties, Idaho, change systematically as the water moves northward from the Idaho Nevada boundary toward the Snake River. Sodium, chloride, fluoride, alkalinity, dissolved helium and carbon 13 increase as calcium and carbon 14 decrease. Water rock reactions may result in dissolution of plagioclase or volcanic glass and calcite, followed by precipitation of zeolites and clays. On the basis of carbon 14 age dating, apparent water ages range from 2,000 to more than 26,000 years; most apparent ages range from about 4,000 to 10,000 year. The older waters, north of the Snake River, are isotopically depleted in deuterium and are enriched in chloride relative to waters in to the south. Thermal waters flowing northward beneath the Snake River may join a westward flow of older thermal water slightly north of the river. The direction of flow in the hydrothermal system seems to parallel the surface drainage.