Iron‐sulfur mineralogy of Mars: Magmatic evolution and chemical weathering products

Models for the evolution of sulfide minerals on Mars and reaction pathways to their oxidative weathering products in Martian regolith have been proposed based on petrogenetic associations between komatiitic rock types, Viking geochemical data, SNC meteorites, and terrestrial Fe‐Ni sulfide deposits. To test the weathering model, komatiitic pyrrhotites and olivines were exposed to sulfuric acid solutions, with and without dissolved ferric iron added to simulate deep‐weathering processes, and the reaction products were identified by Mossbauer spectroscopy. Secondary FeS 2 (pyrite or marcasite), FeOOH (goethite), and possibly jarosite were formed from pyrrhotite, while olivine was oxidized to nanophase goethite. These results suggest that on Mars, acidic groundwater induced pyrrhotite → FeS 2 → FeOOH (+ jarosite) oxidative weathering reactions, particularly in the presence of dissolved Fe 3+ . Such gossaniferous materials occurring in Martian regolith were derived mainly from Fe‐Ni sulfides associated with komatiitic basalts and not from sulfides occurring in calc‐alkaline porphyry copper deposits, granitic hydrothermal veins, sediment‐hosted PbS‐ZnS ores, etc., which presumably did not evolve on Mars due to the virtual lack of plate tectonic activity there.