Natural sources of CO2 and radon at Topolšica geothermal area (Šalek Valley, Slovenia)

Abstract

Carbon dioxide, radon and methane gases were measured in the Topolšica area in water wells and in diffuse emissions in order to model the mechanisms of gas transport to the surface through a faulted geothermal area. As expected, the largest gas emissions were found near the main fault planes or in areas were minor shallow crustal fractures occur, thus pointing to the fundamental role of faults in driving the rise of deep hot fluids to the surface. The source of CO2 was likely deep, whereas radon is probably shallower (hydrothermal) and was carried to the surface by the high CO2 flux. Occurrence of high concentrations of free gases in the water wells can be explained with mixing of deep hydrothermal fluids with shallow cold groundwaters and with different dissolution of gases into the latter. The results have shown the existence of an important geothermal potential in the area and the need for a better monitoring of radon accumulation into buildings to prevent health problems.