Hydrogeochemistry and strontium isotopes of spring and mineral waters from Monte Vulture Volcano, Italy

This paper describes the results of a study that was conducted to determine the relationship between hydrogeochemica composition and 87Sr/86Sr isotope ratios of the Mt. Vulture spring waters. Forty samples of spring waters were collected from local outcrops of Quaternary volcanites. Physico-chemical parameters were measured in the field and analyses completed for major and minor elements and 87Sr/86Sr isotopic ratios. A range of water types was distinguished varying from alkaline-earth bicarbonate waters, re.ecting less intense water­rock interaction processes to alkali icarbonate waters, probably representing interaction with volcanic rocks of Mt. Vulture and marine evaporites. The average 87Sr/86Sr isotope ratios suggest at least 3 di.erent sources. However, some samples have average Sr isotope ratios (0.70704­0.70778) well above those of the volcanites. These ratios imply interaction with other rocks having higher 87Sr/86Sr ratios, probably Triassic evaporites, which is substantiated by their higher content of Na, SO4 and Cl. The Sr isotope ratios for some samples (e.g. Toka and Tra.cante) are intermediate between the value for the Vulture volcanites and that for the local Mesozoic rocks. The salt content of these samples also lies between the value for waters interacting solely with the volcanites and the value measured in the more saline samples. These waters are thus assumed to result from the mixing of waters circulating in volcanic rocks with waters presumably interacting with the sedimentary bedrock (marine evaporites).