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

Abstract

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 CO2-rich gases which cause an increase of the water acidity promoting basalt weathering with an enrichment in certain chemical species (i.e., Na+, Ca 2+, SO42-) and a high total carbon content. The δ14S values of dissolved sulfate ranging from +4‰ to +8.6‰ can be explained by leaching of volcanites. Higher δ34S values (from 9.6‰ to 10.4‰) detected in a few water springs can be ascribed either to the interaction with the pyroclastic layer rich in feldspathoids, such as haiiyna, that have sulfur isotopic compositions up to +10.6‰ or animal manure contamination inducing localized bacterial sulfate reduction with an increase in the δ14S of sulfate. Taking into account that Upper Triassic evaporite deposits have higher δ34S values (from +13.5‰ to +17.4‰,) than those measured in all water samples the dissolution of these deposits could be excluded. Copyright © 2010 by The Geochemical Society of Japan.