ALBERT

Description: 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 ‰.

Description: This data set contains the results from a 2023 GFZ Innovative Research Expedition project to explore for natural hydrogen gas (H2) occurrences in the NW Pyrenean foreland, near the town of Biarritz in France. The data represent in-situ measurements of soil and spring water gas, as well as in-situ spring water property measurements, complemented with laboratory analysis results of gas contents and noble gas isotopic compositions of gas and spring water samples collected during the expedition. This GFZ Innovative Research Expedition was inspired by previous exploration efforts in the region by Lefeuvre et al. (2021, 2022). These authors detected elevated concentrations of natural H2 gas in the soil and interpreted this natural H2 to be derived from serpentinizing mantle rocks below the Pyrenees. The main aims of this expedition were the following: (1) in-situ measuring soil gas contents and taking soil gas samples for laboratory analysis at a site near the town of Peyrehorade in the NW of the general study area of Lefeuvre et al. (2021), thus improving the soil gas data coverage along the NW end of the North Pyrenean Frontal Thrust (NPFT); (2) taking gas samples from degassing springs (or water samples from non-degassing springs to be degassed in the lab) in the general Lefeuvre et al. (2021) study area for additional laboratory analysis of gas contents and noble gas isotopic compositions, which may be indicative of (deep) gas origins; and (3) performing a detailed soil gas analysis by means of a portable mass spectrometer at Sauveterre-de-Béarn, a site along the NPFT where Lefeuvre et al. (2022) measured elevated concentrations of natural H2 in the soil. Furthermore, we also measured the properties of the visited springs (temperature, pH, conductivity) while on site, and performed additional in-situ soil gas measurements from manual drillholes. Details on the measurement and sampling methods, on the laboratory analyses, as well as the results of these measurements and analyses are provided in the data description file The expedition involved six field days in July 2023, during which a total of 26 sites were visited. These sites were selected for their vicinity near a major geological contact or fault zone that could have facilitated upward circulation of gas or (thermal) water from the (deep) subsurface (i.e., potentially from the mantle).