MAPPING OF MIOCENE HYDROTHERMAL SYSTEMS IN THE MARYSVALE VOLCANIC FIELD, WEST-CENTRAL UTAH, USING AVIRIS SPECTROSCOPIC REMOTE SENSING DATA

New remote sensing and laboratory techniques are being used to study alteration-mineral zoning associated with acid-sulfate hydrothermal systems. Surface mineralogy and vegetation were mapped to understand the mineralization process and possible environmental effects due to acid leaching and trace metal dispersion. Data from the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) sensor were analyzed using the USGS Tetracorder expert system to construct maps of surface materials. X-ray diffraction and field studies corroborated the results. These data support an interpretation that the intrusion of monzonite stocks set into motion a series of convective hydrothermal cells around the periphery of the stocks. Several cells are characterized by a well-defined, horizontal, bulls-eye zonation pattern of acid-sulfate alteration minerals which grades outwards from a core of K-rich alunite to concentric halos of alunite-kaolinite, kaolinite and quartz-dickite. The argillic and advanced argillic alteration zones were formed in the lower parts of hot spring systems and are surrounded by propylitically-altered lava flows. Alunite grades upward to hypogene jarosite, hematite, and massive replacement, sub-sinter silica that is cut by hydrothermal breccia pipes. The Sevier River has cut down through one of the fossil hydrothermal cells at Big Rock Candy Mountain. Exposed beneath the horizontal replacement alunite layer is a propylitic mineral assemblage that includes pyrite, illite, kaolinite, and relict feldspars. Futher away from the core, montmorillonite, chlorite, epidote and calcite become more prevalent. The propylitic assemblages were formed in reducing environments beneath the paleo-groundwater table. The buff color of Big Rock Candy Mountain is due to supergene oxidation and alteration of pyrite to natrojarosite, along with gypsum and smectite.