Geological geochemical and genesis examination of Kırkbas and Sağırkoy Yalvaç (Isparta) bauxites

The bauxite deposits located in the Kırkbaş and Sağırköy regions, situated along the northern boundary of Isparta, represent significant mineral resources linked to the area's geological features. However, there has been no previous academic study conducted on these localities. Within the scope of this thesis, the study aimed to investigate and interpret the geochemical, genetic, and geological characteristics of the bauxites in the region, including their formation, modes of occurrence, and the controlling factors that influenced their development. Bauxite is a rock composed primarily of the minerals gibbsite (hydrargillite) [Al(OH)3], böhmite [AlO(OH)], and diyaspore (Al2O3·H2O), typically accompanied by silica, TiO2, and iron oxides. In general terms, bauxite is defined as a mixture of aluminum oxides and hydroxides. With a density ranging between 2.5–3.5 g/cm³ and hardness varying between 1–3, bauxite is used in various industrial applications depending on its chemical composition. As the principal raw material in aluminum metal production, bauxite holds substantial commercial value both globally and within Turkey. Mineralogical investigations were carried out on samples collected from the Kırkbaş and Sağırköy bauxite deposits located in the Yalvaç (Isparta) region. In addition to regional geological surveys, field data were evaluated to interpret the depositional environment and genesis of the bauxite occurrences. Detailed laboratory analyses, including XRD, XRF, FT-IR, ICP-MS, and SEM, were conducted on samples from bauxites and associated host rocks. Statistical data were obtained by evaluating the results of XRF analyses. The investigated bauxite occurrences were found to be situated within Jurassic-Cretaceous aged limestone units belonging to the Hacıalabaz Formation and observed approximately 250 meters southwest of the contact zone between slope deposits and clastic-carbonate sequences of the Upper Cambrian–Lower Ordovician-aged Seydişehir Formation, consisting of sandstone, mudstone, and limestone alternations. According to XRF analyses and statistical evaluations, the average Al2O3 content of the bauxite samples is approximately 48.37%, with some samples exceeding 70%, indicating values above the economic grade threshold. The Fe2O3 content averaged around 8.88%, reaching up to 21% in certain samples. This variation suggests that iron oxides developed as secondary enrichment products during the bauxitization process, reflecting the influence of regional weathering conditions. Additionally, the SiO2 content, averaging 33%, exceeded 50% in some samples, indicating the presence of silica-enriched, kaolinitic bauxite types. These findings confirm that the studied deposits represent economically valuable karst-hosted bauxite bodies with high alumina content. Geochemical data indicate that the bauxites formed not only through single-phase lateritic weathering but also through multi-phase alteration and transportation processes. It is inferred that weathering of feldspar-rich parent rocks (likely gneissic) generated aluminum- and silica-bearing materials, which were transported and deposited into cavities within karstic limestone. During this transportation process, aluminum- and silica-rich minerals were co-precipitated, forming a transported, karstic bauxite type enriched in both alumina and silica. Within the limestone levels of the Hacıalabaz formation, intercalations of basalt or dike/sill intrusions are present, which subsequently became exposed at the surface and subjected to weathering. The genesis of the bauxites has been attributed to mafic basalts containing feldspars and mafic minerals that are capable of hosting high Al2O3 contents. In conclusion, the Sağırköy–Kırkbaş bauxite deposits are characterized by high Al2O3, variable Fe2O3, and locally high SiO2 contents, and they represent the product of a complex, multi-stage geological evolution within karstic environments. These deposits formed through the combined effects of lateritic weathering, regional metamorphism, alteration, transportation, and redeposition processes, resulting in mineralogically enriched and geologically complex bauxite bodies.