Oxidative alteration of the Kupferschiefer in Poland: oxide-sulphide parageneses and implications for ore-forming models

Abstract

The Kupferschiefer ore series, between the Lower Permian (Rotliegendes) terrestrial redbeds/volcanics and the Upper Permian (Zechstein) marine sequence, is developed as dark grey organic matter rich and metal sulphide containing deposits (reduced areas) and as red-stained organic matter depleted and iron oxide-bearing sediments (oxidized areas = Rote F¬ule). A distinctive feature of the Kupferschiefer mineralization is the presence of a transition zone from oxidized to reduced rocks, both vertically and horizontally. This zone is characterized by sparse, disseminated copper sulphides within hematite-bearing sediments, oxide pseudomorphs after framboidal pyrite, and replacements of copper sulphides by iron oxides and covellite. These textural features and copper sulphide replacement of pyrite in reduced sediments imply that the main oxide/sulphide mineralization postdated formation of an early-diagenetic pyrite. The Kupferschiefer mineralization resulted from upward and laterally flowing fluids which oxidized originally pyrite containing organic matter rich sediments to form hematitic Rote F¬ule areas, and which emplaced base metals into reduced sediments. It is argued that long-lasting and large-scale lateral fluid flow caused the crosscutting relationships, expansion of the hematitic alteration front, the vertical and regional horizontal mineral zoning patterns, and the location of copper orebodies directly above and around oxidized areas.