f The Ischia Island hydrothermal system: hydrogeochemical conceptual model

Ischia island is located in the north-western part of the Gulf of Naples and is part of the<br>Phlegrean Fields Volcanic District. Ischia is marked to be an example of resurgent caldera<br>and is characterized by a high heat flux comprised between 200 and 400 mWm-2.<br>Hydrothermal activity is well know on the island since Roman Age and more than 200 hotels<br>and SPA resources, located all over the island, use thermal waters (T ranges from 30°C to<br>99°C) for balneo-therapeutic medical cures. The deep wells, drilled by SAFEN in 1950's and<br>subsequent investigations (De Gennaro et al., 1984; Panichi et al., 1992; Inguaggiato et al.,<br>2000), also revealed the occurrence of high temperature fluids (up to ~220°C) in the subsoil<br>of the island, hosted within a possible geothermal reservoir. The aim of this work is to<br>characterize the main geochemical processes that explain the water geochemistry of the<br>thermal fluids of Ischia Island, to classify the water composition data into genetic groups and<br>to delineate a conceptual model to explain the composition of the discharges.