Abstract

Two separate depositional facies of the Lower Permian and upper Carboniferous clastic and volcanoclastic sediments of the Stockheim basin show distinctive controls of the deposition of selected chemical elements. An older stage represents a caldera-playa environment in which there are signs of incipient rifting, lava extrusion, deposition of pyroclastic and epiclastic fans shed into a subsiding basin, and moat-fill deposition. U was syngenetically (diagenetically) concentrated in the distal fan facies in which organic matter was abundant. U, Sb, Au, Ag, and Se derived from initial volcanism occur in the lowermost gray beds. Mn-bearing carbonates occur in moat-fill deposits and show a pronounced zoning relative to feeder channels of hydrothermal fluids (T < 54 degrees C). These carbonates were then replaced by stockwork barite.A younger stage of deposition represents an estuarine-lagoonal environment and includes the Kupferschiefer. These rest unconformably on the rocks of the older stage. The estuarine sediments contain no mineralization except for abnormal abundance of Co. Early and late diagenetic Cu-Pb-Zn enrichment occurred in the Kupferschiefer lagoon. The protore of the Kupferschiefer mineral deposits is believed to be the underlying rocks, which are unconformably beneath the upper to middle "Rotliegende" boundary.Fracture-hosted ore mineralization is strikingly controlled by certain reference planes. U, Cu, Pb, Zn, and Fe were preconcentrated in coal seams (rank: high volatile A bituminous) in the lowermost gray facies and were redeposited at temperatures of less than 200 degrees C. Redeposition produced a mineral assemblage in fracture zones identical to that of their strata-bound precursors. These deposits occur only near the immediate surroundings of the area of preconcentrations. Additionally, unconformity-related vein-type Pb, Zn, and barite deposits are governed by a first-order geohydraulic plane, the Late Variscan unconformity, an ancient peneplain. Persisting Permo-Triassic heat flow in the basin, different degrees of permeability, and tilting of sedimentary beds encouraged fluids to migrate updip toward the edge of the basin where the metals were trapped in brittle host rocks. S and Sr isotope analyses corroborate this model of fluids movement.

First Page Preview

First page PDF preview
You do not currently have access to this article.