MAPPING MIOCENE HYDROTHERMAL SYSTEMS AND ASSOCIATED MINE SITES IN THE ANTELOPE RANGE, MARYSVALE VOLCANIC FIELD, UTAH, USING AVIRIS SPECTROSCOPIC REMOTE SENSING, STABLE ISOTOPES, ARGON DATING, X-RAY DIFFRACTION, AND ICP-MS

An integrated suite of analytical remote sensing and laboratory techniques was employed to study patterns of mineral zoning and hydrogeochemistry associated with Tertiary acid-sulfate hydrothermal systems formed at 21.3 Ma in the Marysvale Volcanic Field of southern Utah, USA. Imaging spectroscopy was applied to this study for the purposes of refining the existing genetic model for this type of relict epithermal hot springs system, and to more fully understand the relations between mineralization and possible environmental effects due to acid leaching and trace metal dispersion.

Data from the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) sensor were spectrally analyzed and integrated with digital terrain models to generate three-dimensional maps of surface materials. ICP-MS, X-ray diffraction, and field studies were used to verify the results of the AVIRIS-based mineral mapping. Studies of stable isotopes and 40Ar/39Ar dating were applied to trace the hypogene origin and supergene destruction of the replacement alunite deposits through time.

The intrusion of quartz monzonite stocks at ~23 Ma set into motion a series of convective, meteoric water-dominated hydrothermal cells around the periphery of the stocks. Several cells are characterized by a well-defined, horizontal zonation pattern of acid-sulfate alteration minerals that grades outwards from a core of K-rich alunite to concentric halos of alunite-kaolinite and quartz-dickite-kaolinite. Alunite grades upward to paleo-vadose zone mineral assemblages that include hypogene jarosite, hematite, and massive replacement, sub-sinter silica that is cut by hydrothermal breccia pipes.

At Big Rock Candy Mountain, erosion has exposed the propylitically altered feeder zone of the hydrothermal cell beneath a thin, sub-horizontal layer of residual alunite. The feeder zone assemblage formed in a reducing environment beneath the paleo-groundwater table and includes pyrite, illite, kaolinite, local fracture-controlled pyrophyllite, and relict feldspars. Montmorillonite, chlorite, epidote and calcite become more prevalent with increased distance from the core of the feeder zone. Natrojarosite, gypsum, and clay minerals are currently forming via supergene oxidation and weathering of both pyrite and alunite.