Untitled

Abstract

Black shales of the late Neoproterozoic Gwna Group (570-580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O 2 concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record, important to understand, and suggests that new resources may be sought based on black shale protoliths from this period. 1 | INTRODUCTION Increasing market demand for previously low-demand 'critical metals' necessitates improved understanding of their enrichment processes, ensuring a reliable supply of raw material in the future. Demand for the elements Te and Se has been driven by their potential use in large-scale environmental technologies, particularly solar cells (Chelvanathan, Hossain, & Amin, 2010; Morales-Acevedo, 2006). Demand for cobalt has also increased due to its use in high-capacity batteries (Leite et al., 2017). A reliable supply of these elements is vital to allow growth of new technology, although these elements have restricted supplies from current sources (Nassar, Graedel, & Harper, 2015; Vesborg & Jaramillo, 2012). Deep marine ferromanganese crusts are considered key targets for seafloor mining due to their abundance in a range of trace elements,