The red-bed-type precious metal deposit in the Sieroszowice-Polkowice copper mining district, SW Poland

Since 50 years copper-silver ores have been extracted from the Lubin-Sieroszowice deposit located on the border between the Lower and Upper Permian sediments. It is a world class stratoidal type deposit. In the whole world the Kupferschiefer unit is recognized as a black, clayey organic-rich shale. The Cu-Ag deposit is a part of the Fore-Sudetic Monocline, and is located on the border of the Lower and Upper Permian strata The monocline includes three rock complexes. The first is the basement, which comprises Proterozoic crystalline rocks and Carboniferous sediments. It is overlain by monoclinally dipping Permian and Triassic sedimentary rocks. In this work, study on ore mineralisation of the red variety of the Kupferschiefer are presented. Oxidation of the Kupferschiefer as an epigenetic phenomena.The oxidized zones reveal low concentrations of simple copper sulphides with the dominating chalcopyrite accompanied by bornite, pyrite, covellite, galena, clausthalite, chalcocite, digenite, spioncopite, geerite, native Au, electrum, tetraauricupride, naumannite, native Pb, Pd-arsenides and minerals of mixed composition: Au-Ag-Pb-Bi-Se-Te, Au-Ag-Pb-Te, Bi-Cu, Bi-Pd and Pd-As-O. Most important are natural alloys of precious metals, Pd-arsenides and oxidized phases (mostly Pd ones), which strongly influence the effectiveness of froth flotation. Precious metals form several parageneses: i - clausthalite - native Pb - electrum - AuPb2, ii - Pt-native Au - native Pd - sobolevskite - native Pb, iii - native Au - haematite - bornite - minerals of covellite-chalcocite group, iiii - electrum - tetraauricupride - chalcocite, iiiii - electrum - Pd-arsenides - tellurides - selenides - BiPd and CuBi natural alloys - Pd-oxides. The red Kupferschiefer variety is distinctly lower in carbonates and resembles rather a marl. Average Fe2O3 content is about 5 times higher than that in the grey Kupferschiefer. The average TOC content in the red Kupferschiefer is about 10 times lower than that in the black Kupferschiefer and about 5 times lower than that in the grey Kupferschiefer. Average Cu content is 1,070 ppm at variability coefficient 81% . The grey Kupferschiefer contains 3 times higher contents of Cu and its variability coefficient is 2 times higher, which points out to quantitative changes during the leaching of copper when secondary oxidation of deposit proceeded. Thus, low Cu and TOC values can be indicative for oxidizing environment and, consequently, can be good exploration guides to zones enriched in precious metals. Average Au content in the red Kupferschiefer is high 15.419 ppm, is much higher than that for the grey Kupferschiefer. Comparison of metal contents in samples from the oxidized zones reveal high variability of Au values in the red, which may change from a few ppm to over 100 ppm. Negative Cu-Au correlation supports the hypothesis on the introduction of gold into the red Kupferschiefer during the leaching of copper. Au horizon is continuous and located close to the bottom contour of Cu deposit. It includes the top part of the sandstone and extends down, even beneath 1 m from the top of the sandstone. The average thickness of the high-Au zones is 0.2 m, and various from 0 up to 1.4 meters. The Au and PGE deposit described in this paper fit well in the world criteria for economic-grade accumulations.