Geochemistry of germanium in thermal waters of the Jelenia Góra geothermal system (Sudetes, Poland): solute relationships and aquifer mineralogy

Abstract

A long-term (2004–2021) study of the chemical composition of thermal waters in the Jelenia Góra geothermal system provided information on a wide set of components. The subject of the present study is the geochemistry of germanium (Ge), which occurs in concentrations ranging from 2.7 to 6.3 μg/L in the waters studied. Interpretation of a set of 46 chemical analyses identified relationships between germanium and other elements in thermal waters from individual intakes. In the old thermal waters of Cieplice and Karpniki of deep circulation, germanium is derived from silicates and its concentration is controlled by the solubility of Ge-bearing quartz with an average Ge content of 1.5 μg/g. The source of germanium in the deep old thermal water at Staniszów is mainly sulphides, most likely arsenopyrite, but the secondary contribution of Ge from silicates (biotites, amphiboles) should not be ignored. The mineral phase, responsible for controlling Ge activity in this water, cannot yet be identified. The shallow thermal waters at Cieplice, which are a mixture of old thermal waters and modern waters, differ from the deep waters. Germanium in shallow waters probably is derived from silicates, but owing to mixing, there are no chemical equilibrium conditions; the concentration of Ge is determined by the dynamic equilibrium of the mixed water components. The modern water of intake no. 2 (Cieplice) differs from other shallow waters and also shows similarities to the Staniszów water. The germanium in the no. 2 water probably comes mainly from ferromagnesian minerals (biotite, amphiboles), although the influence of sulphides cannot be excluded. The relationships of germanium to other elements, including the Ge/Si ratio, appear to be effective indicators of hydrogeochemical conditions. Thermal waters from the different locations show both similarities and differences in chemical composition, especially of minor and trace components. At the present, still weak stage of recognition, the Jelenia Góra geothermal system can be treated as an area of occurrence of local systems responsible for the quantity and quality of thermal waters in individual intakes.