Mineralogy, geochemistry and origin of the Qarkhotlou bauxite deposit, southwest of Zanjan

The Qarkhotlou bauxite deposit occurs as a semi-continuous horizon situated along the parallel unconformity surfaces between Ruteh and Shemshak Formations. Based on color, facies and textural features, three distinct bauxitic facies are distinguished in the Qarkhotlou deposit, which is, from bottom to top include: (1) lower red-brown pisolitic bauxite, (2) middle red bauxite and (3) upper brick-yellow bauxite. Hematite, goethite, boehmite, diaspore, kaolinite, and pyrophillite are the major mineral components in the Qarkhotlou bauxite ores; muscovite-illite, anatase, rutile, and chlorite are minor minerals. Petrographic observations indicate that panidiomorphic, microgranular, pelitomorphic, pisolitic, and oolitic are the main texture-forming components in the Qarkhotlou ores. These ore textures suggest that the bauxite material has an authigenic origin. However, the existence of clastic assemblages in the pelitomorphic matrix, as well as flow and breccia textures of the ore indicate that the bauxite at Qarkhotlou was locally experienced transportation and re-deposition. Geochemical data indicate that the Qarkhotlou bauxite deposit has bauxite and bauxitic clay compositions, and suggests that trachy andesibasalt lavas are the main component of their parent material. This data reveals that the bauxite horizon at Qarkhotlou formed in pH of 4 to 7 and Eh of 0.4 to 0.6 and experienced a moderate degree of lateritization. The bauxite samples and trachy andesibasalt lava show similar chondrite-normalized REE patterns indicating that they are genetically related. The petrographical, textural and geochemical studies of the Qarkhotlou deposit indicate that this deposit can be classified as Mediterranean karst bauxite.