Hydrothermal waters from karst aquifer: Case study of the Trozza basin (Central Tunisia)

Tunisia is rich in geothermal resources from ancient civilizations. Hydrothermal activity in Tunisia has been related to three main stages: magmatic and tectonic activities, eustatisme (Atlantic and Mediterranean coupling) and climate change. The principal factor and the responsable of this phenomenon is the meteoric water by piston flow processes. It constitue the catalyst of volcanism. The Trozza basin, well known since the Roman period for the importance of its thermo-mineral waters, is characterized by a large occurrence of thermal fluid discharges whose main thermal aquifer. Hydrochemical pattern is mainly controlled by the dissolution of evaporitic sediments (halite, gypsum and/or anhydrite) as well as by the incongruent dissolution of carbonate minerals. This reservoir represents the only vapor hydrothermal system in Tunisia. It is constitute the deepest formation cropping out in the study area. The Triassic deposits and the filonic of Pb-Zn/S caused the contamination of the Continental Intercalaire thermal water in this reservoir. The upwelling of the deep groundwater to the shallow level and discharging also in karst caves of the carbonates minerals. This carbonate reservoir of thermal water (≈ 50 °C), consist of emissions of hot air and vapors and represent a unique case gas hydrothermal karst in Tunisia. It plays a role in the attraction for local population and tourists. But the use of geothermal energy is still in its juvenile stage. Presently, the thermal waters are a resort for wellness, fitness and therapeutic purposes. Kairouan basin, in particular, has numerous thermo-mineral springs, the majority of which are used for public baths, swimming pools, and for medical treatments provided by thermal establishments. Previous studies have shown that location and chemical composition of these thermal manifestations are strongly influenced by the regional geology, the tectonic and the climate impact.