Raman and Xrd Field Characterisation of Sulfate Efflorescences at Rio Tinto

Introduction: The Río Tinto mining district can be considered as the largest volcanogenic massive sulphide district worldwide and probably one of the oldest in the human history being in continuous operation from the Bronze Age to the XX. An important characteristic of the Rio Tinto system is derived from the interaction between the river waters and the iron-rich sulphide minerals. This interaction is mediated by a significant acidophilic biogenic activity leading to an acidic aqueous media (pH is about 2.3 along its 100 km long course) from which a large amount of oxides hydroxides and sulphates are precipitate as the mineral products. The occurrence of sulfates on Mars, expected since the Viking Landers found sulphur in the Martian soil in 1976 and detected more precisely with the Miniaturised Mössbauer spectrometer located at the robotic arm of the MER rovers and OMEGA instrument onboard Mars Express proved that these minerals are an important part of the Martian surface mineralogy. The possible relation between the formation processes of sulphates on Mars and in Rio Tinto has attracted the attention of the scientific community in the last years [1-2]. An important part of these studies is the precise identification of the mineral phases related with the bio-mineralization processes. Raman spectroscopy is a powerful tool for this task [3]. Raman is also a technique included as part of the “Pasteur” instruments payload inside the rover for “ExoMars” mission. This mission now scheduled for launch in 2016 is the first flagship mission the “Aurora” program developed by the European Space Agency (ESA). In-situ analysis of samples at the Rio Tinto area using micro-Raman spectroscopy is an important step in the development of the Raman operation mode which is part of the instrument development. Nevertheless the use of a complementary technique for mineral identification as XRD can give unique information on the mineral phase identification.