Source and mobility of minor and trace elements in a volcanic aquifer system: Mt. Vulture (southern Italy) S. Parisi a , M. Paternoster b, d, ⁎, F. Perri c , G. Mongelli b a University of Basilicata, Department of Geological Sciences, Campus Macchia Romana, 85100 Potenza, Italy b University of Basilicata, Department of Chemistry, Campus Macchia Romana, 85100 Potenza, Italy c University of Calabria, Department of Earth Sciences, Via Pietro Bucci 87036 Rende, Italy d Istituto Nazionale di Geofisica e Vulcanologia, Sez. Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy abstract article info Article history: Received 10 December 2010 Accepted 27 June 2011 Available online 8 July 2011 Keywords: Mt. Vulture Minor and trace elements Groundwaters Metal relative mobility In this paper we provide a geochemical investigation on 34 groundwater samples in the Mt. Vulture volcanic aquifer representing one of the most important groundwater resources of the southern Italy pumped for drinking and irrigation supply. The present study includes the first data on the abundance and mobility of minor and trace elements and the thermodynamic considerations on water–rock interaction processes in order to evaluate the conditions of alkali basalt weathering by waters enriched in magma-derived CO 2 . The results highlight the occurrence of two hydrofacies: bicarbonate alkaline-earth and alkaline waters deriving from low-temperature leaching of volcanic rocks of Mt. Vulture, and bicarbonate-sulfate-alkaline waters (high-salinity waters) related to prolonged water circulation in alkali and feldspathoids-rich pyroclastic layers interbedded with clay deposits. The Al-normalized relative mobility (RM) of metals in Vulture's aquifer varies over a wide range (10 −1 b RMb 10 4 ), confirming that the basalt weathering is not a congruent and isochemical process. Chemical equilibrium studies show that the bicarbonate alkaline-earth and alkaline waters, having a short interaction with silicate minerals, plot very close to the kaolinite–smectite stability boundary, whereas the high-salinity waters fall in the stability field of smectite and muscovite because of prolonged interaction with alkali and feldspathoids-rich pyroclastic layers. Overall, for the bicarbonate alkaline-earth and alkaline waters, the release of toxic metals in solutions is related to the spatial variation of host-rock geochemistry, the high-salinity waters, collected near urban areas, show values higher than legal limits for Ni and As, likely as a consequence of anthropogenic contribution. © 2011 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 2. Geology and hydrology of the Mt. Vulture volcanic aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 3. Water sampling and analytical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 4. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 4.1. Hydrogeochemical features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 4.2. Relative mobility of metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 4.3. Thermodynamic considerations for the water–rock interaction process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 1. Introduction Trace elements are highly sensitive indices of human impact from local to global scale. Pollution impact studies require knowledge of the natural background concentrations and knowledge of pollutant behavior. Water quality investigations have clearly been a stimulus for measurement of toxic trace elements in order to understand their Journal of Geochemical Exploration 110 (2011) 233–244 ⁎ Corresponding author at: University of Basilicata, Department of Chemistry, Campus Macchia Romana, 85100 Potenza, Italy. Tel.: +39 971 205832; fax: +39 971 206069. E-mail address: michele.paternoster@unibas.it (M. Paternoster). 0375-6742/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2011.06.010 Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp