Distribution and behaviour of rare earth elements in stream sediments from southeast Spain: lithological and supergene controls

This study investigates the geochemical distribution and behaviour of rare earth elements (REEs) in stream sediments from Southeast Spain, where REE enrichment is generally scarce except for the El Hoyazo garnet placer deposit. Using data from the Geochemical Atlas of Spain, 337 stream sediment samples were analysed to assess REE concentrations, spatial patterns, and elemental associations through geochemical mapping and multivariate statistics. Median REE concentrations are comparable to national averages but lower than those reported in other regions, as Hercynian domains. Normalised REE patterns show an overall depletion relative to NASC, with a marked enrichment of heavy REE (HREE) along the coastal sector. Factor analysis differentiates lithological, mineralisation, and supergene controls, identifying a specific HREE fractionation statistically associated with Fe-Mn. In contrast, no significant statistical relationships were observed between REE and carbonate-related elements, suggesting that carbonate complexation is unlikely to represent a primary control on REE behaviour. Partial correlation analysis indicates that Fe shows the strongest association with HREE behaviour, suggesting a key role of Fe-bearing phases in supergene HREE enrichment under predominantly neutral to alkaline conditions. Mn also shows significant, although generally weaker, associations with HREE. In the Cabo de Gata volcanic domain, HREE enrichment appears to be primarily controlled by lithological and mineralogical factors. The influence of Fe–Mn phases is most clearly expressed in Neogene sediments, where secondary processes may partially overprint primary signatures. This study highlights the combined influence of lithology and post-depositional Fe–Mn phases on REE mobility and fractionation in a semi-arid Mediterranean environment.