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Multispectral images of an area near Marysvale, Utah, were collected by using the airborne U.S. National Aeronautics and Space Administration (NASA) 24-channel Bendix multispectral scanner; they were analyzed to define areas of hydrothermally altered, potentially mineralized rocks. Hydrothermally altered rocks, particularly volcanic rocks affected by solutions rich in sulfuric acid, are commonly characterized by concentrations of argillic minerals such as alunite and kaolinite. These minerals are important for identifying hydrothermally altered rocks in multispectral images because they have an intense absorption band centered near a wavelength of 2.2 um. Unaltered volcanic rocks commonly lack these minerals and hence do not have the absorption band. Limonitic minerals, such as goethite, hematite, jarosite, and lepidocrocite also are commonly associated with these deposits as a result of primary and secondary processes. However, limonite also is widespread on unaltered rocks and is not abundant on some altered rocks in the study area. Of the minerals mentioned above, alunite is the only mineral in the area studied that is a unique product of hydrothermal processes.


United States Geological Survey Open-File Report 82-675. SuDocs call # I 19.76:82-675.