Geochimica delle acque nelle grotte di miniera del Monte San Giovanni, Iglesias

In the framework of a National Project PRIN 2001-2003 “Morphological and Genetic study of Speleothems of particular karst environments of Italy and of Central-South America” some water samples have been taken in Mount San Giovanni (Iglesias-Gonnesa) in the homonymous lead-zinc mine, presently abandoned, that contains one of the most interesting and beautiful mine caves known in the world, Santa Barbara cave, open to public thanks to the work and the dedication of IGEA S.p.A. of Iglesias. The main objective of this research was to supply some preliminary data on the chemical composition of the drip waters, and put these in relation with the chemical deposits actually forming and the ones formed in the past. Aside the basic chemistry and the main chemical-physical parameters also the content in many minor and trace elements has been analysed, with special interest for base metals (e.g. Pb, Zn) contained in the mineralization and those elements (e.g. Mg, Sr, Ba) that can influence the type of chemical deposit in formation. The determination of the thermodynamic state of the waters, by means of speciation and saturation calculations performed using the software PHREEQC, has allowed to model the processes of present water-rock interaction, and to simulate the geochemical conditions of the past that have brought to the formation of peculiar cave minerals such as Hydrozincite