Remote Sensing Image Analysis at Leviathan Mine, Ca: a Sedimentary Sulfate Mars Analog Site

Introduction: The identification of various iron and magnesium sulfates in data from the Mars Exploration Rovers (MER), OMEGA on Mars Express, and CRISM on MRO [e.g. 1-5] provides the impetus to explore analog environments that produce these minerals on Earth. A number of mechanisms have been proposed as models of Martian surface conditions and given the diversity of surface locations on Mars where sulfates have so far been identified, a number of geochemical environments may be involved. It should also be noted that terrestrial analogs may address the geochemical and mineralogical constituents without necessarily mimicking the geologic and morphologic environment or alternately, that geomorphologic similarity to Mars does not usually incorporate similar geochemistry [6]. One of the most common areas where mineralogy similar to the acidic deposition environment inferred for the Meridiani Planum MER landing site occurs is in metal ore or other hydrothermal deposits that have been subject to alteration through exposure to air, water and microbial processes. The Leviathan Mine site was selected as an alternate to well–studied sites such as Rio Tinto, Spain [7,8], and saline lakes in Australia [9,10] due to the difference in elevation, source rock, and type of alteration setting, yet expected presence of primary and sedimentary sulfates that could be mapped in-situ and remotely for comparison with a broad range of Martian data sets and geochemical pathways. Geologic Setting: The site is located in Tertiary volcanic rocks of the Eastern Sierra Nevada, and was used economically for an elemental sulfur vein, 1-2 feet thick, first mined underground and eventually converted to an open pit operation in the 1950’s [11]. Wachter [12] mapped alteration minerals in the Monitor Pass region and note extensive outcrops of jarosite throughout the quadrangle as well as other surface exposures of small sulfur seams. While the origin of the elemental sulfur at Leviathan is unclear, it has been speculated, due to the large overburden of siliceous cap rock, that the system may represent a relic volcanic vent, sulfur condensing under impermeable cap rocks or sulfur precipitation sealing overlying tuff. The open pit area, while creating water quality problems for Leviathan creek, provides an excellent exposure for comparison of various remote sensing technologies of different wavelength and spatial resolutions. Run-off from the area is channeled into retaining ponds that are allowed to evaporate creating a man-made environment similar to the transient wet-dry cycles suggested for Meridiani sediments [5].