The E4Geo Project aims to explore fault-bound hydrothermal systems associated with the hidden granite pluton of Eichigt-Schönbrunn in the Vogtland region of SW Saxony, Germany, for potential use as deep geothermal reservoirs. Evidence for enhanced geothermal gradients in this region has existed for several decades, but attempts at utilization for energy production and heating have thus far been limited.
We aim to constrain 1) composition of the thermal water, 2) reservoir temperature, 3) the effects of water-rock interaction, 4) fluid residence times and recharge rates, 5) contributions of radioactive decay to the local heat source, and 6) approximate heat flux. For this purpose, we present new geochemical data from time-series measurements performed on local water samples from regional thermal springs at Neumühle/Vogtland, which are contrasted with samples from the nearby Erzgebirge (Georgsquelle/Wiesenbad, Silbertherme/Warmbad) and Fichtelgebirge (Siebenquell/Weissenstadt) regions.
Geochemical time-series measurements of major cations and anions allow us to estimate reservoir temperatures via geothermometry and to characterize the chemical nature of the thermal waters, including potential scaling effects that may occur during operation of a geothermal plant. Potential hydrochemical effects of rainfall and regional swarm seismicity are likewise examined. Stable isotope analyses (δ18O and δ2H) of water samples are utilized to decipher the origin of thermal waters and to evaluate potential mixing with meteoric components. Lastly, specific activities of nuclides from the 238U and 232Th decay series are applied with 40K in preliminary heat flux estimates and identification of ground water types, while residence times are approximated from 14C and 3H.