Petrography and Geochemistry of the Jajarm Bauxite ore Deposit, Northeast Iran: Implications for Source Rock Material and Ore Genesis

Authors : DARIUSH ESMAEILY, HOSEIN RAHIMPOURBONAB, AMIR ESNAASHARI ALI KANANIAN, ALI KANANIAN

Pages : 267-284

View : 17 | Download : 7

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :The Jajarm bauxite deposit, northeast Iran, is the largest such deposit in Iran. The deposit is sandwiched between the Triassic Elika formation and the Jurassic Shemshak formation, housed within karstic features developed within the former unit. The deposit generally shows an internal layering defined by the following four distinct horizons insert ignore into journalissuearticles values(from bottom to top);: insert ignore into journalissuearticles values(a); a lower argillaceous horizon, approximately 50-80 cm thick, is mainly composed of clay minerals that directly overlies the carbonate footwall insert ignore into journalissuearticles values(Elika formation);; insert ignore into journalissuearticles values(b); a bauxitic clay layer approximately 2-3 m thick that consists mainly of hematite, kaolinite, anatase, and diaspore; insert ignore into journalissuearticles values(c); a red bauxite layer insert ignore into journalissuearticles values(the main high-grade ore);, about 5 m thick and composed of diaspore, kaolinite, anatase, and hematite; and insert ignore into journalissuearticles values(d); an upper kaolinitic layer that is 20-50 cm thick, composed mainly of kaolinite, and overlain by the Shemshak formation. Detailed petrographic studies reveal diagenetic alteration of the bauxitic protolith. The main observed bauxite textures are microgranular, oolitic, pisolitic, fluidal-collomorphic, and microclastic. Microgranular and microclastic textures associated with the residual fractured and corroded quartz grains, as well as feldspar grains are almost completely replaced by platy diaspore. Geochemical analyses of the red bauxite reveal enrichment of less mobile elements insert ignore into journalissuearticles values(Nb, Th, Zr, Mo, Ga, and Cr); and depletion of mobile elements insert ignore into journalissuearticles values(Rb, K, Na, Sr, La, Mg, and Pb);; the opposite result is obtained for the bauxitic clay. Chondrite-normalized REE insert ignore into journalissuearticles values(Rare Earth Element); patterns for the upper kaolinite layer are similar to those for the underlying red bauxite, and the patterns obtained for the lower argillaceous layer are similar to those for the overlying argillaceous bauxite horizon. Ce shows a positive anomaly in the red bauxite and a negative anomaly in the bauxitic clay. The correlation coefficients calculated between REE and other elements demonstrate that the likely REE-bearing minerals are oxides of Ti and Nb, clay minerals, and zircon. In contrast to the present diasporic mineralogical composition of the Jajarm bauxite, the geochemical and mineralogical data indicate an original gibbsitic composition. Finally, the observed mineralogical and textural evidence, combined with the evidence provided by variation diagrams and REE patterns, indicates a mixed origin for the Jajarm bauxite from both basic igneous and sedimentary rocks. In fact, bauxitization was initiated on basic source rocks and continued during reworking and replacement within the karstic features.
Keywords : Iran, karst bauxite, geochemistry, diaspore, ore deposit