Mineralogy and origin of Permian bauxite deposits in north of Saqqez, Kordestan Province

Permian bauxite deposits in north of Saqqez occurred as stratiform lenses of carbonate within Ruteh Formation. Field evidence show that these deposits formed in swampy environment in which the water table was relatively high during their evolution. According to petrographic considerations, these deposits contain ooidic, pisoidic, spastoidic, nodular, skeletal, and spongy textures and have an authigenic origin. Based on mineralogical studies, these deposits are composed of minerals of diaspore, boehmite, corundum, hematite, goethite, magnetite, rutile, anatase, montmorillonite, quartz, illite, pyrophyllite, talc, nacrite, dickite, k-feldspar, muscovite, chlorite, chloritoid, plagioclase, pyroxene, amphibole, chamosite, gypsum, calcite, and fluorite. The presence of high quantities of silicate minerals indicates immaturity and poor draining system of these deposits. Comparison of the range of stability fields of major constituent minerals of the bauxite ores with the pH and Eh variations of natural environments show that the surface waters with oxidizing-acidic nature and underground waters with reducing-basic nature played crucial roles in developing of these deposits. Combination of mineralogical and geochemical data of immobile elements indicate that Saqqez bauxite deposits were developed from alteration and weathering of basaltic-andesitic rocks.