Abstract: The Sanandaj-Sirjan Zone and Zagros Fold-Thrust Belt in Iran host numerous Mediterranean-type karst bauxite deposits; however, their formation mechanisms and critical raw materials potential remain ambiguous. This study combines mineralogical and geochemical analyses to explore: (1) the formation of authigenic minerals, (2) the role of microbial-organic processes in Fe cycling, and (3) the assessment of their critical raw materials potential. Mineralogical analyses of the Late Cretaceous Daresard and Mid-dle-Late Permian Yakshawa bauxites reveal distinct horizons reflecting their genetic con-ditions: Yakshawa exhibits a vertical weathering sequence (clay-rich base → ferruginous oolites → nodular massive bauxite → bleached cap), while Daresard shows karst-controlled profiles (breccia → oolitic-pisolitic ore → deferrified boehmite). Authigen-ic illite forms via isochemical reactions involving kaolinite and K-feldspar dissolution. Scanning electron microscopy evidence demonstrates illite replacing kaolinite, with burial depth enhancing crystallinity. Diaspore forms through both gibbsite transformation and direct precipitation from aluminum-rich solutions under surface conditions in reducing, microbial karst environments, typically associated with pyrite, anatase, and fluorocar-bonates under neutral-weakly alkaline conditions. Redox-controlled Fe-Al fractionation governs bauxite horizon development: (1) microbial sulfate reduction facilitates Fe³⁺ → Fe²⁺ reduction under anoxic conditions, forming Fe-rich horizons; while (2) oxidative weath-ering (↑Eh, ↓moisture) promotes Al-hydroxide/clay enrichment in upper profiles, evi-denced by progressive total organic carbon depletion (0.57 → 0.08%). This biotic-abiotic coupling ultimately generates stratified, high-grade bauxite. Finally, both the Yakshawa and Daresard karst bauxite ores are enriched in critical raw materials. It is worth noting that the overall enrichment appears to be mostly driven by the processes that led to the formation of the ores and not by the chemical features of the parent rocks. Divergent baux-itization pathways and early diagenetic processes—controlled by paleoclimatic fluctua-tions, redox shifts, and organic matter decay—govern critical raw material distributions, unlike typical Mediterranean-type deposits where parent-rock composition dominates critical raw material partitioning.
