Geochemical Insights and Mineral Resource Potential of Rare Earth Elements (REE) in the Croatian Karst Bauxites

Karst bauxites are valuable terrestrial records of paleoclimate and tectonic evolution formed under tropical to subtropical conditions during the subaerial exposure of carbonate platforms. This study explores Croatian bauxite deposits within the Adriatic-Dinaric Carbonate Platform (ADCP), with a focus on the distribution and enrichment of rare earth elements (REE) across eight bauxite horizons from the Triassic to Neogene periods. The research applies statistical analyses of geochemical data, as well as developed models, to assess the factors influencing REE distribution and fractionation. The study found that variations in parent material, along with changes in paleogeographical and paleotectonic settings, significantly affected the REE content. The median REE concentrations in the analyzed bauxite horizons range from approximately 250 to 570 mg/kg. Notable REE enrichment was observed in the Late Paleogene, particularly in the Middle and Upper Eocene horizons. The analysis highlights the importance of physicochemical conditions, such as Eh and pH, during the weathering processes that lead to bauxite formation. The results suggest that the presence of REE-bearing minerals, rather than clay minerals, could possibly contribute to elevated concentrations of heavy REE (HREE). These findings indicate that Croatian bauxites, enriched in REE and associated trace elements, are significant not only as geological markers of past climatic and tectonic events but also as potential sources of critical raw materials. This study underscores the potential for the economic exploitation of these deposits in the context of modern technological demands.