Mineralogical and geochemical investigations of the Mombi bauxite deposit,Zagros Mountains,Iran |
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| Institution: | 1. Department of Sciences, University of Basilicata, viale dell''Ateneo Lucano 10, 85100 Potenza, Italy;2. CNR — Istituto di Metodologie per l''Analisi Ambientale, c/da S. Loya, 85050, Tito Scalo, Italy;3. CNR — Istituto di Geoscienze e Georisorse, via Ferrara 1, 27100 Pavia, Italy;1. Federal University of Pará, Belém-PA, Brazil, Rua Augusto Correa, 1, IG-UFPA, 66075-110 Belém, Pará, Brazil;2. HDgeologia, Av. Conselheiro Furtado, 2391, 66040-100 Belém, PA, Brazil;3. Halle-Wittenberg University, Halle, Germany, Von Seckendorf-Platz 3, Halle D-06120, Germany;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), Wuhan 430074, China;2. General Academy of Geological Survey of Guangxi, Nanning 530023, China;1. Center for Electron Nanoscopy, Technical University of Denmark, 2800 Kongens Lyngby, Denmark;2. Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Zografou Campus, 15784 Athens, Greece;3. Department of Geology & Mineral Engineering, Norwegian University of Science & Technology, 7491 Trondheim, Norway;4. Department of Physics, University of Ioannina, 45110 Ioannina, Greece;5. ANKA Synchrotron Radiation Facility, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;6. Karlsruhe Institute of Technology, Institute for Chemical Technology and Polymer Chemistry, Kaiserstrasse 12, 76131 Karlsruhe, Germany;7. KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, 3001 Leuven, Belgium;8. Department of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences-Wuhan, Wuhan 430074, China;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences-Wuhan, Wuhan 430074, China;3. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;4. General Academy of Geological Survey of Guangxi, Nanning 530023, China |
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| Abstract: | The Mombi bauxite deposit is located in 165 km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE = 162.8–755.28 ppm, ave. ～399.36 ppm) relative to argillic limestone (ΣREE = 76.26–84.03 ppm, ave. ～80.145 ppm) and Sarvak Formation (ΣREE = 40.15 ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation. |
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| Keywords: | Karst bauxite Geochemistry REEs fractionation Ce-anomaly Zagros mountain belt Iran |
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