Primary copper sulphides from the Kupferschiefer, Poland

Abstract

Finely dispersed, primary, copper sulphide mineralization from the zones of Cu-S paragenesis in the Zechstein copper-bearing shale from the Fore-Sudetic Monocline, Poland, was studied. It is represented mostly by small spherules and framboids (5 to 10 μm in size) and framboidal clusters of digenite, chalcocite and minor covellite, dispersed throughout the whole shale but especially abundant in the organic-rich laminae. Detailed microscopic and chemical (microprobe) descriptions of this mineralization are given and a comparison with pyrite framboids is presented. Digenite usually dominates over chalcocite among dispersed mineralization, in contrast to that observed in larger diagenetic grains. The rarity of copper sulphide framboids, in comparison with spherules, can probably be explained by the fast process of their homogenization. The textures, chemistry and some different features from pyrite framboids suggest that the copper sulphides in Fe-poor zones of the Kupferschiefer are primary precipitates. The results of the study suggest that the beginning and probably the main stage of the ore mineralization process took place during the sedimentation and/or early diagenesis of the Kupferschiefer.