Geothermal investigations in Idaho. Part 5. Geochemistry and geologic setting of the thermal waters of the northern Cache Valley area, Franklin County, Idaho

摘要

The thermal waters of the north-south trending graben structure known as northern Cache Valley in southeastern Idaho were sampled during the summer and fall of 1973. Geologic and gravity data for the area indicate fault control for nearly all thermal water occurrences. Thermal-water discharges are generally restricted to the course of the Bear River with few known in areas away from the river. Spring deposits in the form of travertine may not be indications of low temperature thermal waters because abundant limestone and dolomite make up the geologic framework. Much gas, believed to consist mostly of carbon dioxide, is being evolved from many of the springs. The hottest water is found near Battle Creek and Squaw hot springs approximately 4 kilometers northwest of the town of Preston. Metoric waters descend along fault planes, fractures, and fissures to depths at which they are heated by increasing rock temperatures (geothermal gradient of 5/sup 0/C per 100 meters). Due to decreased density, the heated waters rise along the same or adjacent fault planes to the surface. The quartz equilibrium geochemical thermometer applied to the thermal water discharges indicates temperatures approaching 150/sup 0/C may be encountered by deep drilling. Mixing models, based on quartz solubility, indicate higher aquifer temperatures than the quartz equilibrium thermometer, but chloride concentration vs. temperature plots are not linear. The sodium-potassium-calcium geochemical thermometer indicates higher temperatures than quartz equilibrium and mixing models. The thermal waters are higher in total dissolved solids (12,000 to 13,000 milligrams per liter) than are known elsewhere in Idaho and represent potential pollution hazards should large scale withdrawal be attempted.