Variable alteration of organic matter in relation to metal zoning at the Rote Faule front (Lubin-Sieroszowice mining district, SW Poland)

Drill core samples of the Lower Zechstein strata in the Lubin-Sieroszowice Cu-mining district (SW Poland) were collected at different distances to the oxidized zone (Rote Faule), developed around tile Zary Pericline. The samp led intervals include Kupferschiefer, underlying Weissliegendes sandstone a nd overlying Zechstein Limestone from Rote Faule zones, adjacent Cu-mineral ized strata, and drill cores from the Pb/Zn-mineralized zone more distant t o the Rote Faule front. The Kupferschiefer samples show differences in base metal and noble metal contents, accompanied by variations in the molecular composition of hydrocarbons. Organic matter is characterized by the solubl e organic matter (SOM) yields, and relative proportions of saturated and ar omatic hydrocarbons of the SOM. Our results provide evidence For an oxidati ve alteration of organic matter in Kupferschiefer samples within and adjace nt to the Rote Faule zones. The extent of this alteration is reflected by d ifferences in the composition of the saturated and aromatic hydrocarbon fra ctions of the soluble organic matter. In contrast to Kupferschiefer from Pb /Zn-mineralized areas, short-chain n-alkanes dominate the saturated hydroca rbons of oxidized samples. With decreasing distance to the Rote Faule zone, compositional changes of the aromatic hydrocarbon fractions are characteri zed by the increase in concentration of polycyclic aromatic hydrocarbons an d elevated ratios of phenanthrene to methylphenanthrenes, resulting in a de crease of the methylphenanthrene index (MPI 1). In highly oxidized samples, the increase in the ratio of phenanthrene to methylphanthrenes concentrati ons due to demethylation reactions appears to be reversed, probably caused by degradation of phenanthrene as well as the methylphenanthrenes. Organic matter of noble metal-bearing Kupferschiefer from the Rote Faule front is c haracterized by high abundances of polycyclic aromatic hydrocarbons (PAHs) and sulfur- and oxygen-bearing PAHs. This result might argue for a concomit ant transport of the PAHs and the noble metals in ascending oxidizing solut ions, and a contribution of metal-organic complexes in mobilisation and tra nsport of gold. The regional base metal zonation in the Kupferschiefer insi de the mines, is explained by redox controlled metal precipitation from oxi dizing brines through decreasing Eh-conditions during its infiltration into the reduced Kupferschiefer. Short-scale zonation in An and Pt/Pd-contents at the oxidized-reduced interface is consistent with th;it model of ore for mation. Organic geochemical maturation parameters argue for maximum tempera tures during Kupferschiefer diagenesis between 100 and 120 degreesC. Compar able temperatures are assumed for the ore fluids responsible for Cu mineral ization near Rote Faule. (C) 2001 Elsevier Science Ltd. All rights reserved .