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High Lake Gossan deposit: An Arctic analogue for ancient Martian surficial processes?

Gossan samples collected during two expeditions to High Lake in Nunavut, Canada, were analyzed to determine their mineral components in order to define parameters for the geochemical environment in which they formed. The gossans represent a natural acid drainage site in an arctic environment that serves as an analogue to the conditions under which sulfate and Fe-oxide formed on Mars. Rock and soil samples were taken from three different outcrops and analyzed using XRD, SEM/EDS, and, in collaboration with R.V. Morris of Johnson Space Center, Mössbauer. Two main mineral assemblages were observed. The first assemblage, which was found primarily in samples from the first outcrop, contained chlorite, phosphate, Fe-oxide, talc and quartz. The second assemblage, which was found at the second and third outcrops, was primarily quartz, mica and jarosite. One sample (G41), which contained Fe-oxide, jarosite and the only observed appearance of gypsum, appears to be transitional between an Fe-oxide dominant assemblage to a jarosite dominant assemblage. Thermodynamic equilibrium with water from seasonal snow melt predicts that the gossan pore water should range from highly acidic and sulfate-rich (pH 0.5-3; SO₄ > 3000mg/l) for the second mineral assemblage to mildly acidic, less sulfate-rich (pH 3-6; SO₄ < 1000mg/l) for the first assemblage. The High Lake gossan differs from acid mine drainage sites located in temperate regions by its lack of diverse sulfate species and smaller crystal sizes. The smaller crystal size may reflect the slower reaction rates at colder temperatures and the seasonal water saturation. These initial results indicate that the High Lake gossan deposit does record mechanisms for which minerals like hematite, goethite, gypsum and jarosite, which are found on Mars, can form in an environment that involves seasonal water occurrence in a cold climate. A manuscript describing these results has been submitted to Planetary and Space Science.

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