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Lateritic weathering of trachyte, and bauxite formation in West Cameroon : Morphological and geochemical evolution

  • Momo, Mathieu
  • BEAUVAIS, Anicet
  • Tematio, Paul
  • Ambrosi, Jean-Paul
  • Yemefack, Martin
  • Yerima, Bernard Palmer Kfuban
  • Yongue-Fouateu, Rose
Publication Date
Jul 01, 2019
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Bauxites and Fe laterites were formed on Neogene volcanics from Fongo-Tongo region in the highlands ofwestern Cameroon, and are distributed on plateaus, slopes and downslope surfaces. Bauxitic profiles result fromintense in-situ weathering of trachytes that implied depletion of silica and labile elements from the saprolite,while alumina relatively accumulated from parent minerals pseudomorphosis by primary gibbsite formation.During ongoing lateritization and bauxite maturation, important leaching and illuviation processes resulted insecondary gibbsite crystallizations. Late incision and dissection of upper bauxitic plateau resulted in degradationand dismantling of bauxitic duricrusts with Fe-depletion and increasing silica. Compared to trachyte, bauxiticduricrusts are relatively enriched in Nb, Zr, Ga, Ni, Cu, Co, V, Cr, As, Pb, Th, Hf, U and Ta, while Y, Sr, Rb, Ba andZn are depleted. Trace elements contents depend on relative proportions of gibbsite, kaolinite, iron oxides andanatase and their affinity with these minerals across the weathering sequence. The overall REE composition andC1-Chondrite normalized REE patterns highlight significant fractionations with enrichment in the upslopeprofile and labile behavior in other profiles of the sequence. REE behavior and Eu/Ce anomalies are controlledby intensity of weathering and lateritic processes during the evolution of profiles. Our results document twomajor bauxitic phases in the Fongo-Tongo area, i.e., mid-Miocene primary in situ bauxitic weathering of trachyteand late Miocene secondary bauxitization of previously formed bauxitic profiles that led to alumina enrichmentup to 53.50 wt%. Combined together, the morphological distribution and geochemical composition of the studiedbauxitic profiles constitute guides for bauxite exploration, and more generally document the dynamics andmorphogenetic evolution of lateritic landforms in West Cameroon.

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