GEOCHEMICAL CHARACTERISTICS OF LATERITES: THE AILIBALTALU DEPOSIT, IRAN

Alibaltalu laterite deposit is located ~20 km northeast of Shahindezh, south of West-Azarbaidjan province (NW of Iran). This deposit is developed as stratiform lenses along the boundary of Elika dolomites (Triassic) and Shemshak sandstones (Jurassic). The distribution fashion of minerals such as boehmite, diaspore, kaolinite, muscovite-illite, rutile, anatase, hematite and goethite in this deposit was accompanied by the development of four types of ore facies: (1) ferrite; (2) laterite; (3) bauxitic kaolinite; and (4) kaolinitic bauxite. Petrographically, the ores show conglomeratic, rounded-granular, veinlet, colloform, pelitomorphic, pseudo-porphyritic, nodular, and spongy textures. Comparison of distribution pattern of elements along a selective profile across the deposit reveals that ferrugenization-deferrugenization mechanism played a prominent role in distribution of Al, Si, Ti, HFSE, LREEs, HREEs, U, and Th during weathering processes. Distribution pattern of REEs normalized to chondrite indicates a poor differentiation of LREEs from HREEs and generation of poor negative Eu anomaly during the evolution of this deposit. These aspects along with ratios of Al2O3ITiO2 and intense differentiation of Al from Fe in the course of weathering processes may indicate a mafic protolith for the deposit. Geochemical consideration of low-mobile elements demonstrates that this deposit is likely resulted from alteration and weathering of basaltic to andesitic rocks. By regarding to the distribution mode of elements such as Ni, Cr, Zr, and Ga within the ores, it can be deduced that this deposit was initially formed authigenically and then later was contaminated by other rock materials during erosion and transportation from its original place to the present site.