Preliminary geochemical study on the concentration of major and trace elements in the geothermal aquifer of Pantelleria Island, Italy

摘要

Major, minor and trace element concentrations were determined in 18 samples of thermal waters from Pantelleria Island (maximum estimated temperature of 260°C), a quiescent volcano located in the Sicily Channel. Waters are chloride-sulphate alkaline in composition, based on the Langelier-Ludwig classification, with Na as the most abundant cation. There are three major components inferred from the chemical composition of the samples: meteoric water, seawater, and geothermal fluids. Mixing of meteoric and sea water is the most evident geochemical process indicated, in particular, by the correlation of Br and Na with Cl. Geothermal fluids are characterised by high P_(CO_2), depletion in Mg and enrichment in F, Br, Na and K relative to their respective ratios with Cl in seawater. This indicates significant gas-water-rock interaction. Dissolved CO_2 gas, of likely mantle origin, interacts strongly with the aquifer. The general behaviour of other minor and trace elements in solution confirms the above processes, in agreement with data from other quiescent volcanic areas in Italy. Redox conditions as well as the stability of mineral phases that may act as sinks for trace metals also affect the concentration of most trace elements in solution.