Metallogenetic and geodynamic evolution in the central European Variscides — A pre-well site study for the German continental deep drilling programme

Abstract

In the central European Variscides (Czechoslovakia, F.R. of Germany, German Democratic Republic) numerous ore deposits of different size and origin are located in the Saxothuringian-Moldanubian border zone. These ore deposits may be categorised into four different types: type I: stratabound; type II: thrustbound; type III: granite-bound; and type IV: unconformity-related. Plate tectonic concepts have only recently been applied to the geodynamic evolution of this part of the Variscides. In the Thuringian and Bavarian Facies, stratabound deposits—type I—(“massive sulfides”, carbonate-hosted PbZn deposits) evolved during the Cambrian and Early Ordovician in a continuously expanding rift basin. At its maximum extension a dismembered, immature “ophiolite sequence” with NiCrCu dissemination in meta-ultrabasic igneous rocks formed in the central European Variscides. Afterwards, an “extensional arc environment” with CuFeZn sulfides came into existence along the central Saxonian lineament. This B-subduction during the Middle to Late Ordovician reflects the change from a divergent to a convergent marginal basin. During the Devonian with the beginning of the A-subduction, stratabound and thrust-bound deposits formed by the pervasive shearing of Silurian metalliferous black shales (graptolite shale facies). As a result of distension deep-seated fault zones in Upper Devonian, relict basins were responsible for the exhalative hematite ores bound to basaltic rocks. Subsequently, thrust-bound (type II) Sb, Au, and As ore mineralisation formed along axial plane thrust faults during the Early Carboniferous. Granite-related Sn, W, and U mineralisation (type III) followed when Lower Carboniferous granites were intruded into that terrain, as a result of final plate collision. BaF and PbZn vein-type deposits occur throughout the Lower Permian to Liassic (type IV). They are related to the Late Variscan unconformity resulting from peneplanation of the uplifted basement block.