Hydrogeothermal characteristics of groundwater from Ribarska Banja spa, central Serbia

Abstract

Ribarska Banja spa is one of the most popular balneotherapy and recreation centers in Serbia. It features several thermal groundwater sources whose temperatures range from 26 to 54°C. The mineral content of these waters is low and their composition is of the SO₄-Na or HCO₃-Na type. Thermal water exploration has been conducted in the general area for many years, to assess the hydrogeothermal potential in order to extract larger amounts of thermal water for multiple uses. The hydrogeothermal system of Ribarska Banja spa was defined based on a synthesis of the results of comprehensive structural geology, geophysical, hydrogeological, hydrochemical and geothermal research. The primary groundwater reservoir of the hydrogeothermal system is comprised of tectonic zones (systems of faults and fractures) within Cretaceous-Paleogene metamorphosed and non-metamorphosed rocks. The overlying hydrogeological and temperature barrier is made up of a series of low metamorphosed rocks (chlorite, chlorite-sericite schists, gabbros, etc.), highly metamorphosed rocks (gneisses) and Neogene clay and sand sediments. The system is recharged by infiltration of atmospheric precipitation and surface water at the highest elevations of Mt. Jastrebac. Investigations have also shown that the system’s heat source is younger granitoide intrusion spreading northwest of Ribarska Banja spa. Based on the quartz geothermometers, expected reservoir temperatures are in the range of 85-97°C that can be expected at a depth of 1.87 km. Total energy usage at Ribarska Banja spa is 31 TJ/y with thermal capacity of 1.65 MWt and utilization factor of 0.58. Geothermal gradient is 0,051°C/m, while heat flow density is 163.5 mW/m².