SEDIMENT-HOSTED MINERALIZATION IN THE NORTH GERMAN BASIN - A TARGET FOR FUTURE MINING?

Fluids in sedimentary basins play a fundamental role as media for the transport and/or redistribution of mass and heat. Rapid channelized fluid flow along fractures and faults in response to tectonic events leads to a decrease in temperature and pressure of the fluids and may induce significant mineralization. Prominent examples of mineralization in sedimentary basins are represented by world-class carbonate-hosted Pb-Zn-(F) deposits of the “Mississippi Valley-type” and the Kupferschiefer deposits in the Southern Permian Basin (SPB) in Central Europe. In the German part of the SPB mining for metals focused on some stratiform base metal deposits hosted in Zechstein carbonates, Kupferschiefer base metal deposits, or Mesozoic sedimentary iron ores.

Drilling activities for gas exploration in the North German Basin locally banked considerable mineralization to the surface. In the Salzwedel-Peckensen area in eastern Germany which hosts the giant Rotliegend Altmark gas reservoir, numerous F-Ba vein-type mineralization of considerable thickness have been drilled. The mineral association calcite-fluorite texturally and geochemically resembles those of economic calcite-fluorite veins that have been mined in the Lower Harz Mts. In both areas, F-Ba mineralization occurs on NW-SE trending faults that intersect N-S striking lineament zones. Thus it seems likely that the Ba-F mineralization in the Altmark area and the Harz Mts. are genetically linked. In the Altmark area F-Ba mineralization deposited from high-salinity basinal brines which most probably were derived from Rotliegend reservoirs as indicated by the similar chemical and isotopic composition of fluid inclusions and present day formation waters. Thus, present day formation waters from the Altmark gas reservoir are likely an analogue to hydrothermal fluids that deposited vein mineralization in the Altmark in Mesozoic times. Due to geochemical similarities and tectonic settings it cannot be excluded that fluorite vein mineralization in the Harz Mountains deposited from descending Rotliegend formation waters rather than from ascending basement brines as it was proposed in several studies before. Thus shallow buried Rotliegend units may become a target for exploration of F-Ba deposits in Germany in future.