Geological and mineralogical evolution of Lower Paleozoic (Late Cambrian) Corundum-Rich Metabauxite in the Southeast Sirjan, Sanandaj-Sirjan Zone

Bauxite deposits in Iran are dominantly hosted by Late Triassic-Early Jurassic sequences in the Alborz zone and Late Cretaceous in the Zagros zone (e.g., Zarasvandi et al., 2008). Metamorphosed bauxite deposits in Iran are very rare, such as Heidarabad corundum-rich deposit (Emamali-pour, and Mirmohammadi, 2011). The Qale-Kham ore deposit is the first report of bauxite mineralization in the Early Paleozoic sequences of Sanandaj- Sirjan zone. In southeastern Sirjan (Qale-Kham area), karstic pockets of Late-Cambrian metabauxites embedded in carbonate rocks. The corundum-rich metabauxites are very rare in the world. Bauxite deposits can be classified into three main groups: lateritic, sedimentary and karstic-types. The karstic bauxite deposits have formed on the paleokarstic surface of carbonates (Bárdossy, 1982; Bárdossy and Aleva, 1990; Bogatyrev et al., 2009). The aim of this paper is to discuss genesis of the Qale-Kham bauxite deposit based on geological, petrographic, mineralogical and geochemical evidences. A number of 95 samples were collected from the bauxite lenses in the Qale-Kham ore deposit. Optical microscopic investigations were conducted on 40 thin sections, 35 thin-polished sections and 20 polished sections of the samples using a Zeiss optical microscope equipped at the Shahrood University of Technology. Mineralogical analyses were done by X-ray diffractometer equipped with a CuKα tube and monochrometer (XRD Philips PW 1800) at the Kansaran Binaloud Company. The concentration of the major elements in the samples was determined using a wavelength X-ray fluorescence spectrometer (XRF Philips PW 1480) at the Kansaran Binaloud Company. In the Qale-Kham area, the rock units consist of amphibolite, mica schist, chlorite schist, epidotic schist and marble. The ores are mainly massive; however, pisolitic texture was observed in the deposit. Detailed mineralogical analyses of the Qale-Kham metabauxite deposit have been performed by optical microscopy and X-ray diffraction (XRD) studies. XRD results show that ore at the metabauxite deposits is composed of corundum, diaspore, chloritoid, opaque minerals (magnetite, hematite, ilmenite, and rutile), white mica (margarite, muscovite), goethite and limonite. Mineralogy of ores (such as corundum) and textures are representative of the impact of a metamorphic event on bauxite ores. This metamorphism and deformation has created structures, textures and formation of new minerals such as corundum and magnetite in the Qale- Kham ore deposit. The ores are mainly composed of Al2O3 (25–58%), SiO2 (3–15%), Fe2O3 (15– 34%) and TiO2 (2–5%). Alkalis and alkali earth elements show low values, probably because these elements are highly mobile and have usually leached out during chemical weathering (Gu et al., 2013). The triangular variation diagrams of Al2O3–SiO2– Fe2O3 are commonly used to show the degree of lateritization, mineral control and bauxite classification. Based on the mineralogical classification of Aleva (1994), most of the bauxite samples in the studied areas fall within the bauxite and ferritic bauxite fields. The chemical composition of corundum-rich metabauxites in Qale-Kham is nearly similar to those of other karst bauxite and karstic metabauxite such as corundum-rich metabauxites of the Menderes Massif (e.g., Özlü, 1983). They show generally strong enrichment in Al2O3, Fe2O3 and strong depletion in K2O, Na2O contents. Overal, the studied corundum-rich metabauxites at Qale- Kham can be classified as karstbauxites based upon their geological, mineralogical and geochemical characteristics. Corundum-rich metabauxite of Qale-Kham in the best outcrop is located at the SE Sirjan town. The metabauxite formed in the Paleozoic metamporphosed carbonate sequences of the South Sanandaj-Sirjan zone as karst-type deposits. Based on petrological and X-ray studies, the Qale- Kham ores consist of corundum, diaspore, chloritoid, opaque minerals (magnetite, hematite, ilmenite and rutile), white mica (margarite and muscovite), goethite and limonite. These studies suggest that the Qale-Kham ore deposit has been formed under suitable climatic conditions in the late Cambrian. This deposit has been metamorphesd and deformed due to the effect of early Cimmerian orogenic movements.