Part I - Geology and Geochemistry of the Roosevelt Hot Springs - A Summary. Part II - Geophysics of the Roosevelt Hot Springs Thermal Area, Utah. Part III - Roosevelt Hot Springs Area Field Trip

The Roosevelt Hot Springs Thermal Area is a newly discovered geothermal power prospect. Seven production wells have been drilled with a maximum flow capability averaging 4.5 x 10{sup 5} kg of combined vapor and liquid per hour at a bottom hole temperature of 260 C. The thermal area is located on the western-margin of the Mineral Mountains, which consist dominantly of a Tertiary granitic pluton 32 km long by 8 km wide. Rhyolitic tuffs, flows, and domes cover about 25 km{sup 2} of the crest and west side of the Mineral Mountains within 5 km of the thermal area. The rhyolitic volcanism occurred between 0.8 and 0.5 m.y. ago and constitutes a major Pleistocene thermal event believed to be significant to the evaluation of the Roosevelt Thermal area. Thermal waters of the dry spring, a seep, and the deep reservoir are dilute (ionic strength 0.1 to 0.2) sodium chloride brines. Spring deposits consist of siliceous sinter and manor sulfur. Alluvium is cemented by sinter and altered in varying degrees by hot, acid-sulfate water to opal and alunite at the surface, grading successively to alunite-kaolinite, alunite-kaolinite-montmorillonite, and muscovite-pyrite within 60 m of the surface. Observed alteration and water chemistry are consistent with a model in which hot aqueous solutions containing H{sub 2}S and sulfate convectively rise along major fractures. Hydrogen sulfide oxides to sulfate near the surface decreasing the pH and causes alunite to form. Opal precipitates as the solutions cool. Kaolinite, muscovite, and K-feldspar are formed in sequence, as the thermal water percolated downward and hydrogen ion and sulfate are consumed