AN ORE GENETIC MODEL FOR THE LUBIN-SIEROSZOWICE MINING DISTRICT, POLAND

The Lubin-Sieroszowice mining district is a world-class copper-silver, stratabound ore deposit that lies near the Lower-Upper Permian bounda ry. It transgresses the Werra dolomite, the Kupferschiefer organic ric h shale and the Weissliegendes sandstone, which overlie barren Rotlieg endes sandstone. On the basis of underground and microscope observatio ns and light stable isotope data, and thermodynamic calculations, a ne w ore genesis model is proposed whereby ore minerals were deposited in the following stages: Stage 0 was synsedimentary or earliest diagenet ic and contains 100s ppm of base metals trapped by clay minerals, and minor sulphides. Stage I was early diagenetic and contains 1000s ppm b ase metals. It is characterized by bornite and overlying chalcopyrite + pyrite that lie a short distance above the Rotliegendes/Weissliegend es contact. The sulphides were deposited near the interface between an overlying, buffered, reducing fluid (1), largely derived from the Kup ferschiefer, and an oxidizing fluid (2) in the Rotliegendes. Stage II is the main ore-forming stage. This stage is late diagenetic, peneconc ordant, lies near the Kupferschiefer/Weissliegendes contact, and conta ins several percent base metals. It is associated with the hematite-be aring Rote Faule facies and is characterized by vertical zonation. A c entral chalcocite zone is flanked above and below by bornite and chalc opyrite. Silver occurs with all the above sulphides. Galena and sphale rite occur mainly just above copper zone, whereas pyrite is usually pr esent in the upper part of the copper zone and together with galena an d sphalerite. Metals were transported in a copper-rich oxidizing fluid (3), which probably originated deep in the Permian basin, reacted wit h organic matter in the Kupferschiefer, and mixed with reducing fluid (1) in the Weissliegendes, resulting in the observed mineral zonation. Stage III is late diagenetic, discordant and is represented by massiv e and dispersed chalcocite ore present on the peripheries and below an hydrite-cemented Weissliegendes sandstone. It resulted from redistribu tion of earlier copper and silver minerals by descending, reduced, sul phur-rich fluids (4), Stage IV consists of rare polymetallic veins of no economic importance that cut the stratigraphy and are probably rela ted to Alpine tectonism. The richest and thickest ore is in the Weissl iegendes, 10-15 km east of the Rote Faule facies (Fig. 1). It probably occupies structures that trapped fluid (1) which was the main precipi tant of metals in the sandstone.