Groundwaters of Mt. Vulture volcano, southern Italy: Chemistry and sulfur isotope composition of dissolved sulfate

We report the chemical composition of groundwaters including the first data on the sulfur isotopic composition of dissolved sulfate from the volcanic aquifers of Mt. Vulture, one of the most important hydrological basins of southern Italy. A total of 27 water samples taken at different altitudes among drilled wells and springs were collected. The majority of groundwaters have a bicarbonate alkaline and bicarbonate alkaline-earth composition. High-salinity waters are sulfatebicarbonate alkaline in composition. The water-rock interaction process is mainly affected from uprising of CO7-rich gases which cause an increase of the water acidity promoting basalt weathering with an enrichment in certain chemical species (i.e., Nat, Ca2+, SO42-) and a high total carbon content. The delta S-34 values of dissolved sulfate ranging from +4%0 to can be explained by leaching of volcanites. Higher delta S-34 values (from 9.6 parts per thousand to 10.4 parts per thousand) detected in a few water springs can be ascribed either to the interaction with the pyroclastic layer rich in feldspathoids, such as hanyna, that have sulfur isotopic compositions up to +10.6%0 or animal manure contamination inducing localized bacterial sulfate reduction with an increase in the (delta S-34 of sulfate. Taking into account that Upper Triassic evaporite deposits have higher (delta S-34 values (from +13.5 parts per thousand to +17.4 parts per thousand,) than those measured in all water samples the dissolution of these deposits could be excluded.