Inactive Hydrothermal Hypogenic Karst in SW Sardinia (Italy)

In Sardinia, no active hypogenic caves have yet been discovered or described. Although there are a few thermal springs, mostly correlated to Quaternary volcanic activity, none of these thermal waters have interacted with carbonate rocks. Nevertheless, in the SW of the Island many metal ore deposits hosted in Cambrian limestones have been exploited over the last two centuries, allowing the discovery of so-called mine caves, some of which are clearly of hypogenic origin. These caves formed by thermal waters in a phreatic setting and are now located far above the water table and are no longer active, apart from some recent dripstone formation. The mine tunnels in Mount San Giovanni, near Iglesias and Gonnesa towns, have cut most of these caves: among them the well-known Santa Barbara cave, covered with barite crystals, Santa Barbara 2 cave, with its unique oxidation vents, and Crovassa Ricchi in Argento. Other hypogenic caves have been discovered in the mines of Campo Pisano and Monteponi (Iglesias), Mount Onixeddu (Gonnesa), and especially Masua (Iglesias). A very special case of hypogenic cave is the Corona ’e Sa Craba quartzite system, known for its barite crystals and rich in many mineral species. This chapter summarizes these known inactive hydrothermal and sulfuric acid caves.