Hydrogeochemistry and geothermometry of thermal water from north-eastern Algeria

The thermal waters from the study area are depleted in 18O and D and plot on the global meteoric water line (GMWL), their deep-circulating meteoric origin shows that most thermal waters plot on or near the meteoric water line, with some exceptions due to Mediterranean precipitation, probable water-rock isotope exchange or mixing takes place between the ascending geothermal water and shallow colder groundwater. The subsurface reservoir temperatures were calculated using different solute geothermometers and computation of saturation indices for different solid phases. The highest estimated reservoir temperatures are indicated by the cation composition geothermometer (CCG) and the Na-K-Ca geothermometer, while slightly lower estimates are obtained using silica geothermometers, with local geothermal gradients ranging from 25 to 45 °C/km.