Geomicrobiology of Río Tinto (Iberian Pyrite Belt): A Geological and Mineralogical Mars Analogue

Río Tinto (SW Spain) with its 92 km of extreme acidic waters and high concentration of heavy metals is the metabolic product of chemolithototrophic microorganisms sustained by the high concentration of metal sulfides existing in the Iberian Pyrite Belt (IPB). Río Tinto corresponds to the only known natural extreme environment generated by biological activity and not to planetary geophysical constrains like temperature, radiation, or pressure. The iron and sulfur cycles are the most important biogeochemical cycles operating along the river, both elements being the product of pyrite bioleaching, the most abundant metal sulfide of the IPB. The detection on Mars of iron minerals which in the Tinto basin are produced by geomicrobiological activities has given Río Tinto the status of one of the best geochemical and mineralogical Mars terrestrial analogue. For many years, Río Tinto was considered a contaminated river, the consequence of 5000 years of mining activities in the area. The recent demonstration that the origin of the extreme conditions detected in the river result from the metabolic activity of microorganisms operating in the deep subsurface of the IPB has opened an interesting perspective into the so-called dark biosphere.