Geochemical characteristics and REE potential of red soils in the Seydişehir–Akseki region (Türkiye)

The karst-type bauxite deposits located in southwestern Türkiye represent the most significant bauxite resources in the country. Surrounding these bauxite deposits are widespread red soil deposits of varying sizes, developed over lithologically diverse rocks. This study aims to investigate the origin of these red soils, which were examined in two distinct groups based on their spatial relationship to the underlying geology. The first group of red soils is found on or within the fractures of karstic limestones, while the second group is primarily located in proximity to ophiolitic rocks. The investigation focused on the physical properties, as well as the mineralogical and chemical compositions, of these soils. Although both groups display partially similar mineralogical compositions and major element contents, notable differences were observed in their trace element, and especially rare earth element (REE), concentrations. The total REE contents range from 206 to 433 ppm in the first group and 853 to 4487 ppm in the second group. No significant correlations were identified between REE concentrations and either trace or major element oxides. The Ce anomalies is slightly positive (mean 1.0, std=0.18) in the most first group samples, with one second group sample at 1.07, while remaining samples exhibited a strong negative anomaly (mean 0.40, std=0.40). A positive Eu anomaly was observed in the first group (1.11), while no anomaly was found in the second group (0.99). These variations, including the wide range in REE contents and the absence of correlation with other geochemical parameters, suggest that the red soils may have different origins. The PASS-normalized REE and immobile element trends of the first group are partially aligned with the trends observed in schists, whereas the second group displays a markedly different pattern—largely parallel to that of ophiolitic rocks, and showing greater enrichment than all rock types examined in the study area.