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This paper investigates the hyper-enrichments of molybdenum (Mo), uranium (U), and vanadium (V) in the lower Paleozoic, Alum Shale of Denmark, Sweden, Norway, and Estonia. Molybdenum and U are mainly associated with organic matter and the highest contents are found in the Furongian part of the Alum Shale. This Furongian hyper-enrichment of Mo and U commenced with the Steptoean Positive Carbon Isotope Excursion (SPICE) event. The temporal distribution of V content increases moderately from the Miaolingian to the Furongian, followed by a significant increase in the Early Ordovician. In addition, the vanadium content generally increases towards the offshore, distal part of the Alum Shale basin. The geochemical affinity of V seems to change from organic matter in the Cambrian to minerals in the Early Ordovician. The hyper-enrichment of V in the Lower Ordovician succession appears to result from upwelling of deep oceanic water. The spatial distribution of V in the Alum Shale indicates that the highest concentrations are located in Scania, southernmost Sweden. • Molybdenum and U are mainly associated with organic matter. Hyper-enrichment of Mo and U commenced with the SPICE event. • The geochemical affinity of V changes from organic matter in the Cambrian to minerals in the Ordovician. • Potential areas for V mining are located in southern Sweden and northern Estonia. [ABSTRACT FROM AUTHOR]

Measuring the degree of organic matter (OM) alteration caused by uranium (U) irradiation is important in the effective evaluation of the hydrocarbon potential and thermal maturity of U-rich source rocks. This study investigates OM alteration in the Baltoscandian U-rich, lower Paleozoic Alum shale obtained from three research wells in the thermally immature parts of eastern Sweden and western Estonia. The results show a marked increase in the proportion of refractory, non-generative organic carbon (NGOC) in the U-rich shale. Fluorescence spectrometry of unicellular alginites and lamalginites show a reduction of up to 95.6% in fluorescence relative intensity (RI) with increase in U content from 29 to 401 ppm. Fluorescence spectra of the liptinites exhibit a marked "red shift" as expressed by increase in red(R)/green(G) quotients. This change in fluorescence properties of the liptinites is associated with up to 77.6% decrease in hydrogen index (HI) and hence loss of hydrocarbon generation potential. Furthermore, organic molecules show significant loss of aromatic moieties as well as aliphatic constituents resulting in a more condensed macromolecular structure. The measured random reflectance of solid bitumen (BR o) appears to be significantly elevated in micro scale proximity to the U-containing minerals. The heterogeneous distribution of U-containing minerals and the contact with solid bitumen attributes to the wider range of BR o values and lead to the overall increase in mean BR o in samples with high U contents. In contrast, R o values of zooclast macerals (GR o , e.g., graptolite, chitinozoans and vitrinite-like fragments) appear to be less influenced by U irradiation and hence are a more reliable maturity indicator in U- rich lower Paleozoic shales. • Uranium (U) irradiation is responsible for alteration of organic matter, manifested by red shift in fluorescence spectra of liptinites (Red/Green quotient) and increase in solid bitumen (thucholite) reflectance (BR o). • U irradiation attribute to hydrogen index (HI) decrease, relative non-generative organic carbon (NGOC) increase and parent macromolecule condensation. • Zooclast fragments (GR o , Graptolite, Chitinzoan and vitrinite-like particles) are more reliable maturity indicators in U-rich rocks. [ABSTRACT FROM AUTHOR]