Origin of gases from the geothermal reservoir Groß Schönebeck (North German Basin)

The observed 3He/4He ratios of ≤0.0642 ± 0.0026 Ra demonstrate a crustal origin of He. The N2/40Ar ratio (1648 ± 480) indicates a crustal origin and practically without any influence of the air. 21Ne/22Ne is distinguished from the air and more enriched in nucleogenic 21Ne, relative to 22Ne, when compared to the average crustal Ne composition. The calculated residence time of fluids by means of in situ produced nuclides varies for 40Ar from 72 to 80 Ma and for 4He from 365 to 401 Ma. The apparent age discrepancy gives a hint for He migration from older stratigraphic layers or stratas enriched in parent nuclides (U, Th).