Controls on the distribution of rare earth elements in the Kupferschiefer series of SW Poland

Abstract

This study deals with the spatial distribution and the PAAS-normalized patterns of rare earth elements (REE) studied by ICP-MS in the Kupferschiefer series of SW Poland. The most characteristic feature is a progressive enrichment in REE content (including Y and Sc) outward from the rocks with pyritic and Pb-Zn mineralisation, across the rocks with copper mineralisation, towards the oxidized (Rote Fäule) areas. The same trend can also be observed with respect to LREE, MREE and HREE. Whereas REE distribution diagrams for shales with pyrite and Pb-Zn mineralisation are almost flat, diagrams for shales with hematite and copper mineralisation are convex-upward and the strongest convexity is attributed to the transition from hematitic alteration to copper-rich rocks. REE distribution diagrams normalized to PAAS show strong MREE enrichment relative to LREE and HREE, which is typically the highest in the hematite zone, lower in shale with copper mineralisation, and the lowest in shales with Pb-Zn and pyrite mineralisation. The systematic increase in the concentration of REE towards the Rote Fäule, and the strong enrichment in MREE in the transition zone are indicative of variable intensity of leaching and formation of the REE enrichments (including MREE) by MREE>HREE>LREE fluids, as evidenced by the MREE-enriched signatures. Overprinting of secondary enrichments over the original REE pattern due to redistribution along the pathways of expanding fluids are postulated to account for the apparent differences in the distribution and concentration of REE (including the MREE-enriched trend) between the oxidized rocks, copper-bearing rocks, and reduced lithologies barren in copper