The present study focuses on the geochemistry and occurrence of REY (rare earth elements and yttrium)-bearing minerals in the Late Cretaceous karst bauxite deposits in the central part of the Zagros Simply Fold Belt (ZSFB), SW Iran. The ore bodies comprise a series of individual pods and/or contiguous lenses that occur as infills of deep karst cavities, depressions, and fractures within the upper neritic carbonates of the Cenomanian–Turonian Sarvak Formation. In the ZSFB bauxites, the most frequent authigenic REE-bearing minerals are light REE (LREE) fluorocarbonates of the bastnaesite group that forms a solid solution series between end members parisite [CaCe2(CO3)3F2] and bastnasite ¨ (CeCO3F). The mode of occurrence of bastn¨ asite-Ce and parisite-Ce suggests that cerium as fluoride and/or carbonate–fluoride complexes were readily leached by acidic downward solutions and finally precipitated on the geochemical barrier of the carbonate bedrock under alkaline and reducing conditions. Rhabdophane [(Ce, La) PO4⋅H2O] as an LREE phosphate mineral appears in two generations with different chemical compositions, an early one as irregular and/or acicular particles within the cavities and a later one along the margin of a goethite microvein that cuts the pelitomorphic matrix. Cerianite (CeO2) occurs mainly as sub-micrometer to micrometer grains in the porous aggregates of the aphanitic matrix and as microdomains or microveins that coexist with Al-oxyhydroxide and goethite. Cerianite precipitation may occur due to the predominance of acidic/oxidizing conditions and the dissolution of Ce-rich fluorocarbonates in the bauxitic profile, respectively. The only heavy REE (HREE) phosphate mineral within the ZFSB bauxite deposits is churchite[Y(PO4)⋅2(H2O)] that forms as single euhedral crystals at the core of the sub-spheroidal structures under an acidic condition. R-mode factor analysis revealed several significant interelemental relationships including: (i) significant and positive weightings for TiO2, Al2O3, Cr2O3, Ni, Zr, Nb, Hf, Ta, W, and Th, and a significant, negative weighting for SiO2 represent a later bauxitization stage involving silica depletion under drier conditions, promoting formation and stability of a range of minerals including detrital minerals and Al and Ti oxyhydroxides which also control, through scavenging, cations of firstrow transition metals such as Ni2+ and Cr6+; (ii) Supergene conditions, mainly acidic pH, probably played an efficient role in the formation of secondary REE-rich phosphates and Ga-hydroxide; (iii) similar and meaningful weightings for U and V suggest that the redox environment would be most important in controlling the U and V mineral phases; and (iv) the scandium co-variance with Fe2O3 represents the control exerted by iron oxyhydroxides on the critical metal Sc.
