Petrography and geochemistry of major, minor, and trace elements of bauxitic facies: A case study from Gazanjeh deposit, southeast of Mahabad, NW Iran

Important known bauxite deposits in Iran, which occur in the so called Irano-Himalayan belt, are spatially distributed in four regions, namely (1) the northwest of Iran (e.g. Bukan, Shahindezh), (2) the Zagros heights, (3) the Alborz Mountain Range and (4) the central plateau of Iran. They are restricted to Permian, Permo-Triassic, Triassic, Triassic-Jurassic, and Middle Cretaceous (Cenomanian–Turonian) in ages (Abedini & Calagari, 2014).

The Gazanjeh area is located about 25 km southeast of Bukan city, south of West-Azarbaidjan Province, NW Iran. The stratigraphical gap emerged during the Late Permian is manifested by the development of a bauxite horizon in this area. The propose of the present study is to indentify the texture, mineralogical types, controlling factors of distribution and mobilization of major, minor, and trace elements in residual facies, paleo-geographical conditions, sedimentary environment of formation and development of the bauxite deposit in the Gazanjeh area.


In this study, a profle perpendicular to the strike of bauxitic layers was selected and 16 systematic and

representative samples with varying intervals (80-150 cm) were collected. Laboratory works began with preparation of thin and /or polished sections from all 16 samples and their examination under microscope. For the identification of mineralogical phases in the bauxites, 8 samples from a selective section were chosen for X-ray diffraction (XRD) analyses.  XRD analyses were carried out using diffractometer model D-5000 SIEMENS in Geological Survey of Iran (Tehran). The chemical compositions of the bauxites (#16) were determined at the Kansaran Binaloud Company, Tehran, Iran. The values of major and minor elements were determined by X-ray fluorescence (XRF). Rare Trace element contents were determined by inductively coupled plasma mass spectrometry (ICP-MS). Loss on ignition (LOI) was determined by weight loss of 1 g sample after heating at 1000 °C for 60 min.

Since the rocks are fine-grained, identifcation of minerals in the bauxite ores under a microscope was not possible.Terefore, petrographic examinations were principally focused on textural features of the ores. Considering the mode of distribution of texture-forming components and matrix, various kinds of textures such as pelitomorphic, microgranular, ooidic, pisoidic, macro-pisodic, spastoidic, colloform, nodular, pseudo-breccia, breccia, and clastic identified within the ores. These textures show allogenic origin for deposit (Bardossy, 1982). The pelitomorphic and colloformic textures imply an indirect bauxitization and weak draining processes during the evolution of this deposit. The development of hematitic nodules in the ores can be attributed to factors such as variation in water activity in pedogenic environments and/or climatic fluctuations (Mongelli, 2002). The XRD analyses show that the minerals including diaspore, hematite, pyrophyllite, chlorite, chamosite, rutile, anatase, and muscovite-illite are the main mineral phase of the phreatic.Trivariate plot of SiO2-(Al2O3+TiO2)-Fe2O3 (Balsubramaniam et al., 1984) denotes that three distinct mineralogical types can be differentiated within the horizon, namely (1) laterite, (2) ferruginous laterite, and (3) siliceous bauxite. Also, plotting the Kanigorgeh data on trivariate diagram SiO2-Al2O3-Fe2O3 (Schellmann, 1982) attests to the formation of the above ores under moderate to intense lateritization conditions. Trivariate plot of SiO2-Al2O3-Fe2O3 (Meshram & Randive, 2011) reveal that deferritization-ferritization mechanisms and destruction of kaolinite were the most important processes involving during development of ores in this deposit. Comparison of the range of stability fields of major constituent minerals of the bauxite ores with the pH and Eh variations of natural environments (Temur & Kansun, 2006) show that this deposit formed two facies, (1) oxidant-basic and (2) reduction-acidic. Geochemical investigations indicate that the degree of concentration of elements such as V, Zr, Co, Cu, Ga, Hf, Mo, Sc, U, and Zn in oxidant-basic facies and concentration of elements such as Ba, Cr, Ni, Pb, Rb, Sr, and Th in reduction-acidic facies is great. Difference in concentration of elements in these two facies can be associated with occurrence of processes such as adsoption by clays, scavening by hematite and manganese oxides, lateritization intensity, function of carbonates bedrock as geochemical barrier, and chemistry of meteoritic waters (Braun et al., 1990; Mordberg, 1996; Schwertmann & Pfab, 1996; Marques et al., 2004; Fernandez-Caliani & Cantano, 2010; Ndjigui et al., 2013; Abedini & Calagari, 2014).