Chemical and Isotopic Characteristics of Thermal Waters in the Carpathian Region, South Poland: Implication to the Origin and Resources

The Polish part of the Carpathians is the region in which thermal water potential is still under investigation and exploration, mainly due to complex geological structure and variable hydrogeological settings. Excluding the quite well recognized area of the Podhale artesian basin, the huge area of the so-called Outer Carpathians is poorly recognized with respect to thermal water occurrence, resources and possibilities of their utilization. In the current study, to shed some light on the occurrence and origin of potential resources of thermal waters in different parts of the Carpathian Geothermal Province, five exemplary thermal waters have been taken into consideration. Their chemical and isotopic compositions have been shown in the light of the hydrogeological and thermal conditions of their occurrence. The Podhale basin, located within the Inner Carpathian Geothermal Region, is the best recognized with respect to thermal water occurrence. The main horizons of thermal waters occur at a depth of 1,000–3,500 m and are linked to Eocene carbonates and Middle Triassic limestones and dolomites. The meteoric origin of thermal waters, vicinity of the recharge area, low mineralization of waters (≤2.6 g/dm³) and favorable thermal conditions (outflow temperature of waters in the lower part of the hydrogeothermal systems reaches 86 °C) make this region the most perspective and the most developed with respect to thermal waters utilization. The Outer Carpathians Geothermal Province is composed entirely of flysch-type sedimentary rocks from Late Jurassic (western part) and Early Cretaceous (eastern part) to Oligocene. The characteristic feature of the Outer Carpathians is a complex, folded and thrusted structure. The distinction of individual hydrogeothermal systems is hardly possible. The thermal waters are usually brackish, saline and brine; in the eastern part they are associated with oil and gas deposits. The outflow temperatures usually do not exceed 45–50 °C and well discharges are low. The recharge areas for thermal waters are still not known; their origin is poligenetic and their resources might be limited. Also the thermal conditions in the area of flysch Carpathians seem to still be poorly recognized, reveal variable character but locally might be very promising.