Raman Analisys of Sulfate Sequence of Precipitation from Iron-rich Waters of Rio Tinto River

Introduction: Rio Tinto area is considered a referent as an extremophilic scenery of iron rich and acidic water conditions for life [1]. Physic-chemical equilibriums taking place along of its watercourse during a year produce a repertory of mineral species related with the main chemical species in solution (sulphates and iron). Raman spectroscopy is a powerful technique that allows studying these species with great accuracy and without any perturbation [2]. A detailed investigation of the process of precipitation needs both the insitu analysis of natural samples at the field [3] and experimental simulation at the laboratory. This last subject is considered of great importance to monitor the different mineral species produced by a definite chemical composition of the acidic aqueous solutions and their sequence of precipitation. Raman spectroscopy is regarded as a powerful characterization technique for the characterization of sulfate systems due to its intrinsic features: it requires little or no sample preparation prior to spectra collection, and allows real-time identification of species in acidic waters and associated precipitates and very rapid quantification of their abundance, among others [3]. Furthermore, recent advances in optics, lasers and detector systems allow for the development of compact field Raman instruments for in-situ analyses. This fact, together with the capabilities of the Raman spectroscopy for the unambiguous characterization of mineral phases make the Raman technique an outstanding tool for the exploration of sulfate-rich areas. A compact Raman/LIBS instrument is regarded as the highest priority instrument for mineral analysis within the ExoMars mission roadmap.