Chemical and Isotopic Composition of Gas in Salt Beds of a Potash Mine

In eastern Hesse and western Thuringia, Germany hosts significant potassium-bearing salt deposits industrially excavated in the Werra-Fulda mining district. The salt belongs to the upper Permian (Zechstein) and was deposited around 258 to 252.5 Ma ago. In the Werra-Fulda mining district, the halite rocks (Werra-Rocksalt, z1NA) contain two minable potash seams, potash Seam Thüringen (z1KTh) and potash Seam Hessen (z1KHe), with an average thickness between 2 m and 3 m (Figure 1). To investigate the chemical and isotopic composition of the gas phase of Seam Hessen, gaseous samples were collected from five, 2-meter deep, horizontal boreholes drilled in the potash horizon which is mined at a depth of 540 m. About 4 weeks in advance of the gas sampling, the packer-closed boreholes were evacuated to about 3kPa and the pressure gradient inside the holes was continuously monitored in the boreholes D1 to D5. Selected gas samples were analyzed for their noble gas isotopic composition and the δ13C values of CO2 and CH4. The noble gas isotopic compositions were determined using a VG 5400 noble gas mass spectrometer after purification in a preparation line. The carbon isotope compositions were analysed with a GC-IRMS, comprising a GC 6890N connected to a GC-C/TC III combustion device and coupled to a MAT 253 mass spectrometer. The standard deviation of the δ13C values (in ‰ vs. VPDB) is ± 0.5 ‰. The data are provided as one, Excel file with three spreadsheets as well as three individual, tab-delimited text files.