Geochemical investigations on Permo-Triassic bauxite horizon at Kanisheeteh, east of Bukan, West-Azarbaidjan, Iran

Abstract

The studied bauxite horizons of Kanisheeteh located ∼ 19 km east of Bukan (NW of Iran), are part of the Irano-Himalayan karst bauxite belt lying conformably between Permian carbonates and shales and Triassic limestones. They extend laterally over ∼ 8 km and are variable in thickness (8–28 m). Petrographically, the rocks within the horizon show nodular, panidiomorphic-granular, ooidic, pseudo-breccia and pseudo-porphyry textures along with pressure shadow features. These textural features may suggest that the bauxite has an authigenic origin but suffered tectonic deformation. Diaspore, hematite, and clay minerals are the principal constituents accompanied by some minor accessory minerals such as muscovite, plagioclase, quartz, magnesio-sidero-riebeckite, calcite and zircon. Based upon type and quantities of constituent minerals, three distinct mineralogical types can be differentiated within the horizon, namely (1) bauxitic clayey iron ore, (2) clayey bauxite, and (3) bauxitic clay. Based upon field evidence, calculation of accumulation coefficients of trace elements, concentration of elements such as Cr, Ni, Zr and Ga and the ratios of immobile elements, the diabasic rocks which occur in the study area are the most plausible and probable source rock for the bauxite deposits of Kanisheeteh. The mass changes of elements were calculated on the basis of Ti (as immobile element). These calculations demonstrate that elements such as Mg, Na, Ca, Si, Fe, Y, Rb, Ba, P, K and Mn were leached out of the weathered system whereas elements such as Nb, Hf, Cr, Ce, V, Zr, Al, La, Co, Th, U and Ni became concentrated in the residual system. The variability in obtained data is explained by factors such as stability of host minerals, fixation of elements in neomorphic phases, preferential sorption, and the chemistry of solutions involved in weathering (e.g. pH of percolating waters).