Geochemistry of the early Jurassic Soleiman Kandi karst bauxite deposit, Irano–Himalayan belt, NW Iran: Constraints on bauxite genesis and the distribution of critical raw materials

In the Irano–Himalayan karst bauxite belt, in northwestern Iran, karst bauxite orebodies are widespread. Although several of these orebodies have been characterized, no comprehensive data are available for the early Jurassic karst bauxite ores. The early Jurassic Soleiman Kandi karst bauxite deposit consists of a mineral assemblage of diaspore, hematite, kaolinite, and rutile, with lesser amounts of illite, pyrophyllite, chlorite, siderite, amesite, and quartz. The ores are characterized by similar Eu/Eu*, Sm/Nd, and Nb/Ta ratios, suggesting that they share the provenance from a mafic protolith. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor accounting for an inverse relationship between the clay minerals–diaspore–rutile–resistant minerals (e.g., zircon and monazite) pool and hematite, driven by redox fluctuations related to an upward decrease in Eh under dry climate. The other two factors are related to the capability of clay minerals in controlling the distribution of bivalent large ion lithophile elements Ba and Sr, and also to the control exerted by authigenic fluorocarbonates on rare earth elements (REE: La-Lu) + Y distribution. The Soleiman Kandi karst bauxite ores are enriched in critical raw materials, including V, Co, Ga, and Ta, with respect to the average Upper Continental Crust. Among these elements, Ta is particularly abundant, probably as a consequence of the occurrence of a Ta-rich variety of rutile, representing a peculiar feature of the Soleiman Kandi bauxite deposit.