Quantitative mineralogy of bauxite profiles in se Guinea Bissau |
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| Institution: | 1. School of Mining & Metallurgical Engineering, National Technical University of Athens, Greece;2. Department of Mining and Geological Engineering, Botswana International University of Science & Technology, Botswana;3. Department of Mining Engineering, University of Kentucky, Lexington, Kentucky, USA;4. School of Mineral Resources Engineering, Technical University of Crete, Greece;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 |
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| Abstract: | In the South-Eastern part of Guinea Bissau extensive, highly weathered ferrallitic mantles occur within different geomorphological levels. These weathered layers are usually capped by petroplinthite. Frequently, they are of economic interest due to their enrichment in alumina. They represent the remnants of a Mezo-Cainozoic “African Planation Surface”. One hundred auger drill samples from one geomorphological structure—Bowal, were submitted to a specially developed method of quantification of the mineral phases previously detected in the representative specimens of the batch. The method consisted of computing the mineralogical composition from the principal chemical component analyses (Al2O3, SiO2, Fe2O3, TiO2, H2O) combined with DTA/TG studies and thermodifferential X-ray diffraction studies. In addition, the samples from available core drillings, which reached the parent rocks, were investigated by means of XRD and optical microscopy. Two groups of bauxites developed on dolerite and shale yield the same mineral paragenese. The differences of mean Al2O3 and Fe2O3 content in both groups are expressed entirely by differences of concentration of gibbsite and goethite, which reflect mobility of aluminium and iron in solutions circulating through the system of open large pores. Boehmite and hematite would tend to crystallize from oversaturated solutions in confined environment of fine pores. |
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