Galenit-mineralchemie und blei-isotopengeochemie der postvariszischen gangvererzungen des Niederbergischen landes, Deutschland

Investigations of galena of post-Variscan origin from the Niederberg area reveal mainly Ag contents from 59 to 262 ppm and Sb contents from 730 to 3408 ppm. Comparative ore microscopy investigations of galena samples from the Niederberg area and some reference samples from the Rhenish Massif/Variscan Foreland revealed that no inclusions of silver and antimony carriers, especially of fahlore and bournonite, which are typical for Variscan galena, could be observed within galena of post-Variscan origin (including the Niederberg area). Silver contents of galena are apparently not suitable to discriminate between galena of Variscan and post-Variscan genesis. Lead isotope investigations of galena of post-Variscan origin from the Niederberg area reveal three distinct successive clusters with increasing ²⁰⁶Pb/ ²⁰⁴Pb ratios (Cluster I: 18.214-18.248; Cluster II: 18.273-18.322; Cluster III: 18.332-18.361). The results point to a large scale hydrothermal/reservoir fl uid system mixing lead derived from different rocks in deeper crustal levels of the Variscan orogen. This large scale reservoir system was tapped three times as suggested by the three clusters. Lead isotope patterns between the Niederberg area und the Ruhr area reveal a close genetic link between the mineralisations of these two areas. There is no isotopic similarity between post-Variscan galenas of the Niederberg area and other galenas of post-Variscan origin from the Rhenohercynian Zone and the Variscan Foreland of Central Europe. According to the similarity of the lead isotope patterns of post-Variscan galenas of the Niederberg area and galenas of preorogenic and Variscan origin in the Rhenohercynian Zone/Variscan Foreland of Central Europe, Pb isotope data alone are not suffi cient for an easy distinction between ore deposits of preorogenic, Variscan and post-Variscan origin. A comparison with the supposed range of formation ages in the Niederberg area in conjunction with direct age determinations (e.g. by Rb-Sr method) in the Rhenohercynian Zone of Central Europe implies that Pb-Pb model ages of the ores in the Niederberg area have no geologic relevance.