Origin, migration pathways, and prediction of high carbon dioxide accumulations in the Lower Saxony Basin (northwestern Germany): Part I

Metal budget and origin of aqueous brines depositing deep-seated Zn-Pb mineralization linked to hydrocarbon reservoirs, North German Basin

“…Overall in the context of noble gas data, prevalent radiogenic and atmospheric contributions imply that the Zn-Pb ore-forming fluids in the LSB represent heated brines, modified to variable degrees by interactions with stored formational brines as well as crustal rocks, including crystalline basement and a coal-bearing sedimentary sequence. The range of 3 He/ 4 He ratios of sphalerite-hosted brine inclusions in the LSB (0.02-0.1R A ) is similar to that of fluid inclusions hosted in fracture-filling minerals (quartz, fluorite, calcite) from: Zechstein Ca2 reservoirs, Carboniferous blocks in the Bramsche area, and deep Devonian strata in the LSB (Lüders et al 2021). The noble gas isotope signature from fluid inclusions hosted in hydrothermal sphalerite from the Lautenthal deposit in the Harz Mountains (SE of the LSB), is similar to data from Zn-Pb ores in the LSB, suggesting a crustal contribution and a low probability of additional input from mantle degassing (Fig.…”

“…10a, Table 2), which are at the lower limit of data from the Bramsche area (Fig. 1) that is known for the presence of overmature organic matter in the Paleozoic strata (Lüders et al 2021). The most radiogenic compositions ( 3 He/ 4 He = 0.02 R A ), in fluid inclusions from deep wells in the western LSB, fall within the crustal He field, i.e., they agree with the crustal production ratio of 0.01-0.05 R A (Fig.…”

“…The ore zones and fracture-fill mineralization are well characterized and consist of sphalerite, galena, pyrite, fluorite and barite (Duschl et al 2016;Nadoll et al 2018Nadoll et al , 2019Sośnicka and Lüders 2019;Knorsch et al 2020). The mineralization in this area coincides with the presence of hydrocarbon and locally prominent CO 2 -rich gas reservoirs (e.g., Lüders et al, 2021;Sośnicka and Lüders, 2021).…”

“…Quartz and carbonate fracture-fillings in Upper Carboniferous rocks commonly host CH 4 -CO 2 ±N 2 type II inclusions. In contrast, type II inclusions in calcite, fluorite or anhydrite mineralization in Zechstein Ca2 carbonate predominantly contain CH 4 -CO 2 -H 2 S±N 2 gas mixtures Lüders 2020, 2019;Lüders et al 2021). Previously studied type I fluid inclusions, hosted in early quartz I and younger quartz II from the Piesberg quarry (Upper Carboniferous strata) differ from each other not only in terms of salinity and temperature, but also in gas composition.…”

“…Calcium enrichment of Upper Carboniferous formation waters has been ascribed to dissolution of anorthite and calcite cementing sandstones, whereas Mg depletion to dolomitization and precipitation of Mg-chlorites during diagenesis (Lüders et al 2010). Depletion of Mg in the fluid, caused by precipitation of diagenetic Mgchlorite, in fracture-fillings in the Upper Carboniferous strata in both the central (Lüders et al 2021) and the southern (Wüstefeld et al 2017) parts of the LSB is a more localized process, therefore widespread dolomitization is likely the major cause. With regard to the trends of Ca and Mg concentrations relative to seawater, the element data, presented here, are consistent with compositions of formation waters (Fig.…”