Characterization of thermal waters of the whole South Sétif. East Algerian
The south setifian mountains, situated in the north-east of Algeria, are the seat of aquifers with thermal waters where the temperature varies between 25°C in the east and 43°C at the centre. In order to evaluate the thermal water potential of this whole region, we have employed a multidisciplinary approach involving geology, geophysics, hydrogeology and hydrogeochemistry. The results from this approach indicate that the whole region is characterized by the presence of a series of horsts formed by thick carbonated and karstified layers dating from the Lias to the Miocene, and grabens have allowed for the establishment of a closed endorheic system occupied by chotts and sebkhas, filled with salt water. These massive carbonate outcroppings occur in the middle of the plain filled by Mio-Plio-Quaternary alluvial materials. This hydrogeological analysis indicates that these formations from the cretaceous era can offer considerable aquifer possibilities. The hydrochemical analysis showed that the waters of the region show three different chemical facies: the first, Cl-Na in the east; the second, SO4-Ca in the centre; and the third, SO4-Na to Ca, in the west. This hydrochemical analysis also allowed us to attribute the sodium, chloride and sulfate to an evaporative origin. The salinity that characterizes these thermal waters is mainly due to water circulation at great depths in the carbonate formations and to the alteration of the evaporate minerals during their ascent. The molar ratio Sr2+/Ca2+ confirmed this hypothesis. Different geo-thermometers, mainly that of silica, have shown that these thermal waters have a temperature of 80°C and come from a depth that varies between 1400 and 2200 m, through a fault system that affects the base. The decrease of the temperature to 40°C is likely due in part to mixing with surface water, as shown by the technique of Giggenbach.