Die Vererzungen des Niederbergischen Landes am Nordwestrand des Rechtsrheinischen Schiefergebirges: Beitrage zu Bildungsbedingungen und Genese anhand Sphalerit-Chemie, Fluideinschluss-untersuchungen und Schwefel-Isotopengeochemie

摘要

Microprobe analyses of sphalerites from the Niederberg area resulted for the majority of samples in Fe-contents of 0.1 wt.-percent to 0.5 wt.-percent (A. V.) and Cd-contents of 0.2 wt.-percent to 0.6 wt.-percent (A. V.). Collomorph sphalerites show bright and dark layers differing significantly in Fe-content up to 0.4 wt.-percent for bright layers and > 1 wt.-percent for dark layers. The analyses are similar to postvariscan sphalerites of the Linksrheinische Schiefergebirge. Fluid Inclusion investigations reveal homogenization temperatures for quartz between 160 deg C down to 90 deg C and for sphalerite between 130 deg C and 60 deg C. The fluids are highly saline (about 22 wt.-percent CaCl_2-equiv.) and belong to the Ca-Na-Cl-type, very similar to postvariscan fluids. Simple cooling of the fluids is probably the cause of sul-fide precipitation. Sulfur isotope investigations show for the majority of base metal sulfides from the Niederberg area a narrow delta~(34)S range between 0 per thousand and +12 per thousand. In contrast, marcasite samples show delta~(34)S values between +16 per thousand and +21 per thousand. This pattern suggests two different sulfur sources for the sulfide mineralizations. For the base metal sulfides reduced sulfate of Zechstein origin and for the marcasite reduced cretaceous seawater sulfate are considered to be the most plausible sources. The investigations suggest a post Permian age of the sulfide mineralization of the Niederberg area. Sphalerite galena isotope pair thermometers correspond fairly well with homogenization temperatures of sphalerite. Thus a formation pressure of 370 bar could be estimated. All results are pointing to postvariscan mineralization events in the Niederberg area.