Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran

Abstract

The Amir-Abad karst-type bauxite deposit is located in the Irano–Himalayan bauxite belt, 8 km of south of Maragheh city in northwestern Iran. The bauxite ores occur as layers and lens-shaped pockets in the contact of the Triassic dolomitic limestone of the Elika Formation and the Lower Jurassic sandstone, siltstone, shale, and coal of the Shemshak Formation. Based on the PXRD and SEM-EDS analyses, the bauxite ores mainly consist of diaspore, hematite, and kaolinite group minerals (e.g., kaolinite and montmorillonite), with lesser amounts of goethite, anatase/rutile, and zircon. Nickel, Cr, Co, and V show a pattern similar to Fe; they were leached from the uppermost parts of the profile by acidic percolating solutions, and concentrated toward the carbonate bedrock under alkaline conditions. Aluminum, Nb, Ga, Ta, Th, Hf, and Zr can be regarded as less mobile elements. Variations of the La/Y, (ΣLREE/ΣHREE)N, and (La/Yb)N ratios across the weathering profile, together with leaching of alkali and alkaline earth metals indicate an acidic environment in the uppermost parts, and a basic environment in the basal parts of the profile. Mineral control and physico-chemical conditions (e.g., Eh and pH) probably had effective roles in the behavior of elements during weathering. Based on the concentration of trace elements, such as Zr, Cr, and Ga, and the conservative elemental indices (e.g., Sm/Nd, Ti/Zr, and Nb/Ta), the basaltic rocks were a plausible source rock for the Amir-Abad karst-type bauxite deposit.