The Tinto River, an extreme acidic environment under control of iron, as an analog of the Terra Meridiani hematite site of Mars

One remarkable discovery in Mars geology is the extensive Meridiani iron formation. Although thermal oxidation mechanisms have been proposed for its origin, geomorphology and IR spectroscopy studies support an aqueous scenario as the most feasible environment to host its secondary iron-enriched mineralogy. Terrestrial hydrothermal systems or the iron-rich Precambrian oceans have been proposed as analogs to understand these interesting Martian environments. However, the available TES spectra show hematite as a mineral phase of Mars’ iron rocks, but not the cherty silica that frequently appears in hydrothermal systems or BIFs. The Tinto River Basin, an extreme acidic environment driven by iron biogeochemistry, has water rich in both ferric iron and sulfate. These acidic waters produce ferric iron-enriched sediments dominated by sulfate and oxyhydroxide associations, in which silicates are absent. Moreover, ancient iron formations, pre-Holocene relicts of similar acidic water environments found in the Tinto River Basin, suggest that the primary iron-rich associations changed with time to goethite–hematite associations through dehydration and desulfatation. These features make the Tinto River Basin a reasonable analog for the Mars hematite site if an aqueous origin for these oxides is considered.