Karstbase Bibliography Database

Since many years cavers from different caving teams are carrying out a systematic study on the caves of Sulcis-Iglesiente, including geomorphological studies. Over thirty natural caves have been explored, surveyed and registered in the past few years, and over half of these have been made accessible by mine galleries. Among these are worth to be mentioned the “Tre Sorelle” of Domusnovas: these are three mine caves intercepted by the San Paolo mine tunnel. This tunnel, whose collapsed entrance has been reopened after a long digging campaign, has been explored and surveyed for around 700 meters. A total of 10 natural caves, mostly developed along fractures, have been explored and mapped, with developments ranging between 10 and 250 meters and depths from 15 to over 160 meters. Only two of these caves were previously known in the Regional Cave Register. In most of the caves, speleothems consist mainly of flowstones, some of which are clear or usually white, others are dark-brown or tending to black. Some samples of the first and the second flowstone types were collected respectively from the “Sesta Sorella” and “Seconda Sorella” Caves. The powders of these samples were analysed by an X-ray diffractometer. The first type consists of thicker layers of white and fibrous aragonite, which sometimes alternate with thinner layers of grey columnar calcite. In some samples, however, calcite interlayers were absent and just aragonite was found. The second type is composed of alternating layers of darkbrown hemimorphite. Some additional analyses were performed on these samples by Laser Ablation ICP-MS to determine the concentration of minor and trace elements in the different layers and mineralogical phases. The most abundant minor elements in calcite layers are Mg and Zn. Magnesium is about constant (~ 2000 ppm) on different spots and remains under the average Mg content of the cave calcite in this region, whereas Zn ranges from 103 to 104 ppm and is well above the Zn average in calcite of caves in the world. Barium concentration is about 80 ppm and more abundant than Pb (20 ppm) and Sr (10 ppm). Barium is also the main minor element in aragonite, where it can reach almost 2000 ppm. The Zn concentration is very high even in aragonite and is comparable to that of Sr (400-500 ppm), overcoming considerably the Pb concentration (20 ppm). In hemimorphite, the most abundant minor elements are Al and Fe (about 104 ppm). However, it was not quantified how much of these are in the hemimorphite lattice or come from some impurities. Actually, we notice that concentration of Fe and Al in the black layers of hemimorphite is an order of magnitude greater than in the brown ones. In addition, the black layers show an abrupt increase of Mn concentration, which overcomes Fe and Al. The evolution of these flowstones is most probably related to the circulation of fluids connected to the oxidation of sulphides, specially sphalerite.