Mineralogy and geochemistry of the Kupferschiefer in the Nowa Sól, Mozów and Sulmierzyce North Cu-Ag deposits, Northern Copper Belt, SW Poland

Abstract

We describe the mineralogy and geochemistry of three deep (>1500 m BGL) Kupferschiefer-type deposits of the Fore-Sudetic Monocline: Nowa Sól, Mozów and Sulmierzyce North, which have been recently documented by the Canadian Miedzi Copper Corporation. Together with other known prospective areas, they form an extensive E-W-trending belt, referred to as the Northern Copper Belt. Samples from the 22 boreholes were examined, focusing on the Kupferschiefer-ore sensu stricto, since in each deposit the richest Cu-Ag mineralization occurs in shales. The ore minerals identified include chalcocite, digenite, djurleite, covellite, bornite, chalcopyrite, minerals from the tennantite-tetrahedrite group, native silver, silver amalgams, stromeyerite, minerals from the cobaltite-gersdorffite series, galena, sphalerite, pyrite and native bismuth. In the Nowa Sól and Mozów deposits, Cu-S-type minerals dominate the Cu-mineralization, while in the Sulmierzyce North deposit, apart from the Cu-S-type minerals, the ore mineral assemblage comprises also chalcopyrite and the tennantite-tetrahedrite group minerals. In the Nowa Sól deposit, Ag-bearing and Ag-barren chalcocite have been distinguished. Chalcocite from two other deposits is Ag-barren. Two types of Ag-amalgam have been identified: Hg-rich and Hg-poor. Other Ag minerals (stromeyerite and native Ag) also contain Hg admixtures. The chemical composition of bornite (which is the second most common ore mineral in each deposit) shows no significant variation. Only in the Nowa Sól deposit were minor amounts of Ag-bearing bornite identified. Co-Ni minerals from the Nowa Sól deposit are represented by middle members of the cobaltite-gersdorffite series. The newly documented deposits of the Northern Copper Belt belong to the same Kupferschiefer-type as well-known deposits of the Lubin-Sieroszowice area. However, some differences in distribution of ore mineralization and its chemical composition have been noted between these two areas. The results obtained support the generally accepted view, that the development of the Cu-Ag deposits of the Fore-Sudetic Monocline was a long-lasting, multiphase process.