Geochemistry and metallogenesis of Lower Carboniferous black shale-hosted ore deposits, NE Rhenish Massif, FR Germany

Abstract

A number of usually small-scaled base metal, noble metal and barite deposits occur in the Lower Carboniferous black shale series of the northeastern Rhenish Massif, which were mined in the past. Field observations combined with mineralogical and geochemical analyses reveal similarities between an ore-bearing location of the Lower Carboniferous black shale series in the Marsberg area and a barren location of the same geological sequence in the Kellerwald area. Similarities exist in lithology, mineralogy and major element geochemistry of the investigated rock sequences. However, in contrast to minable base metal concentrations in the Marsberg area, the Lower Carboniferous black shale series in the Kellerwald area is characterized by base metal contents which are even lower than those of average black shales. It can be concluded, that the minable metal concentrations in the Lower Carboniferous black shale series result from longterm, multi-phase processes. Controlling conditions and factors for ore-forming processes, like sedimentary environment, favourable paleogeographical and structural position and finally the presence of redox fronts as documented in the ore-bearing Marsberg area were not realized in the barren Kellerwald area. Finally, a comparison between the Marsberg copper deposit and other black shale-hosted ore deposits, such as the uranium ore deposit of Ronneburg and the Kupferschiefer, is presented.