Chemical, isotopic and geotectonic relations of the warm and cold waters of the Galatro and Antonimina thermal areas, southern Calabria, Italy

A multidisciplinary approach adopting new geological, hydro-geochemical and isotopic data has been used to assess the genesis of hot and cold waters of the Galatro and Antonimina thermal areas. In these systems, waters come from two different hydrogeological circuits, which are chiefly hosted in the Palaeozoic crystalline-methamorphic rocks of the Aspromonte Unit and the overlying Oligocene-Pleistocene sedimentary sequences. In particular, the Galatro thermal water shows Na–SO4 composition, pH value of 7.85 ± 0.13, outlet temperature of 36.4 ± 1.8 °C, variable Eh (−266 to −42 mV) and total dissolved solids of 1067 ± 149 mg L−1. Conversely, the Antonimina thermal water shows Na-SO4(Cl) composition, total dissolved solid of 10,369 ± 1613 mg L−1, pH value of 7.62 ± 0.17, outlet temperature of 35 ± 0.12 °C and Eh from 25.4 to 49.2 mV. Geological and hydrogeochemical data suggest that the meteoric waters infiltrating along the Aspromonte Chain at different elevations (650 and 230 m a.s.l. for Galatro and Antonimina respectively), recharge the aquifers acquiring heat from rocks through conductive transfer reaching reservoir temperatures between 69 ± 15 °C and 101 °C for Galatro and 60 ± 19 °C for Antonimina reservoirs, as indicated by the solubility of chalcedony and quartz and Na/K geothermometers. Subsequently, the waters leaving the deep reservoirs discharge at the surface at 36.4 ± 1.8 °C and 35 ± 0.12 °C after a relatively fast upflow and limited cooling. Assuming a normal geothermal gradient (33 °C km−1), results allowed to locate the warm deeper reservoirs of Galatro and Antonimina at depths between 1.5 and 2.5 km and 1.5 km respectively.