Numerous hot springs occur in a variety of geologic provinces in central and western Alaska. Granitic plutons are common to all the provinces and the hot springs are spatially associated with the contacts of these plutons. Of 23 hot springs whose bedrock geology is known, all occur within 3 miles of a granitic pluton. The occurrence of hot springs, however, appears to be independent of the age, composition, or magmatic history of the pluton.
Preliminary chemical and isotopic analyses suggest the hot springs waters belong to two groups. Most of the analyzed hot springs appear to have chemical and isotopic compositions indicating they were derived from deeply circulating meteoric water. About 25 percent of the analyzed hot springs show a distinct saline character with high concentrations of chloride, sodium, potassium, and calcium indicating either much more complex water-rock reactions than occurred in the other hot springs or the addition of another type of water. The present chemical and isotopic data are insufficient to determine the source of the constituents of the saline hot springs.
Chemical geothermometers suggest subsurface temperatures in the general range of 100?C to 160?C. If the hot spring waters have derived their heat solely from deep circulation, the waters must have reached depths of 9,000 to 15,000 feet, assuming geothermal gradients of 30?C to 50?C/km. If hot magmatic water has Seen added to the geothermal systems or if dilution or mixing has occurred, temperatures of 100?C to 160?C may be reached at shallower depths.
The geologic and chemical data are too preliminary to make an estimate of the potential of the hot springs as a geothermal resource. The data suggest, however, that most of the hot springs of central and western Alaska have relatively low subsurface temperatures and limited reservoir capacities in comparison with geothermal areas presently being utilized for electrical power generation.
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Geologic setting and chemical characteristics of hot springs in central and western Alaska