Stable Isotope and Geochemical Markers of Uranium Variation in Alum Shale from Southern Sweden

Sammanfattning

In the near future, uranium may once again become a target for extraction in Sweden. The ScandinavianAlum Shale hosts large quantities of low-grade uranium, estimated at 2.5 million tonnes, that couldbecome economically viable to mine with the advancement of extraction technologies. Understandingthe geochemical and depositional factors controlling uranium enrichment is essential for identifyingprospective areas.This study applies redox-sensitive trace element ratios, stable isotope analysis (δ¹³C, δ¹⁵N, δ³⁴S), and major/trace element geochemistry to reconstruct the paleoenvironmental conditions during depositionof alum shale in southern Sweden. The aim is to determine the environmental settings most favourablefor uranium accumulation and to identify co-enriched trace elements and rare earth elements (REEs)with potential economic relevance.The results show that oxygen-depleted (anoxic to euxinic) conditions, coupled with high organicmatter content, are optimal for uranium enrichment. These settings are reflected by elevated V/Cr, U/Th,and Mo concentrations, as well as high total organic carbon (TOC). Additionally, the trace elements V,Mo, Ni, Pb, and Th, along with the rare earth element Ce, show a correlation with U, indicating theirpotential for co-extraction.