Serpentinization, iron oxidation, and aqueous conditions in an ophiolite: Implications for hydrogen production and habitability on Mars

a b s t r a c t Molecular hydrogen produced through iron oxidation during formation of serpentine and magnetite can sustain terrestrial subsurface ecosystems. The Fe 3+ in serpentine partitions into octahedral and tetrahedral sites differently as serpentinization proceeds, and tetrahedral Fe 3+ is present toward the end of serpentinization. We map Fe oxidation states in a serpentinite to determine the degree to which serpentinization progressed and where hydrogen production has been maximized to assess habitability at an abandoned chrysotile mine in Norbestos, Quebec, in association with the Canadian Space Agency's Mars Methane Analogue Mission. We also analyzed stable isotopes of carbon and oxygen in carbonates to constrain the conditions of water-rock interaction during serpentinization. Iron oxidation and coordination was determined through field imaging of rock walls with a visible hyperspectral imager (420-720 nm), and samples collected from imaged rocks and elsewhere in the mine were imaged in the laboratory (420-1100 nm). Sample chemistry, mineralogy, and oxidation state were determined with laboratory measurements of visible through mid-infrared reflectance spectra, major element chemistry, mineralogy, and Mossbauer spectroscopy. Mapping with hyperspectral imaging of outcrops and hand samples shows that tetrahedral Fe 3+ is common in serpentinites at this site, and results are confirmed through other measurements. Major element chemistry and mineralogy are consistent with serpentine plus minor carbonate. Carbonate samples show an exceptional range in δ 13