The occurrences of the rare earth elements and the platinum group elementsin relation to base metal zoning in the vicinity of Rote Faule in the Kupferschiefer of Poland

The concentrations of the lanthanide rare earth elements (REE) and Pt group elements (PGE) were measured in the Kupferschiefer from the Polish Zechste in Basin at, and in proximity to, the Rote Faule near the Lubin Mining Dist rict. The Rote Faule is a zone of post-depositional oxidation characterized by the presence of extensive amounts of Fe(III) oxides replacing syn-sedim entary framboidal pyrite. Outward from the Rote Faule, the remainder of the Kupferschiefer is composed of Cu- and Pb/Zn-mineralized shale surrounding the Rote Faule and a non-mineralized pyritic black shale in the central bas in. The leading hypothesis explaining the high concentrations of PGE, and REE i n the Kupferschiefer states that PGE, REE and the associated base metals we re mobilized by oxidizing Cl- brines which migrated outward from the Rote F aule into the reduced Kupferschiefer. According to available thermodynamic data, PGE were in all likelihood present as chloro-complexes in these oxidi zing brines, as geologically realistic concentrations of Pt, Pd and Au coul d be transported as chloro-complexes. The Ph of these brines decreased as t hey migrated further from the Rote Faule and into the Kupferschiefer. Base metals and PGE were precipitated in the order of their decreased solubility in these brines. As a result, the concentrations of least soluble PGE (Pt) are highest in the Rote Faule and in the transition zone adjacent to the R ote Faule (e.g, [Pt]=202-537 ppb) while the concentrations of the more solu ble metals in these brines (Ag, Cu, Pb, and Re) are highest in the reduced- mineralized Kupferschiefer. The sources of the PGE and REE are enigmatic. I t is likely that the metals were derived either from the underlying Rotlieg endes sandstones and volcanics, the Variscan basement rocks, or the Kupfers chiefer shale whose metals were mobilized by saline, oxidizing fluids relea sed during intra-continental rifting in the Triassic period. (C) 2000 Elsev ier Science Ltd. All rights reserved.