[en] The Franceville Basin hosts one of the world' s largest Mn deposits, accounting for 16% of global reserves. Chemical weathering transformed a low-grade Paleoproterozoic carbonate-hosted ore into a high-grade supergene ore along several plateau levels. This study investigates regolith formation using cryptomelane 40 Ar/ 39 Ar dating and compare the mineralogy and geochemistry of different weathering profiles to assess their potential for critical metals. The results show that the Okouma-Bagombé plateaus in the NW are higher grade ores than elsewhere. This is related to longer exposure time (<14 Ma) to chemical agents, higher topography level (>550 m asl.) and consequently higher degree of hydrolysis, which led to important silica release. The lowlying Franceville-Biniomi profiles (<440 m asl.) to the SE are younger (<6Ma) and display medium ore grades. We also report important critical metal (Co, Ni, Zn, Cu, Li) accumulation at the base of the Mn ore in the Franceville area due to lithiophorite formation.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Dekoninck, Augustin; Département Géosciences, Environnement et Société, Université libre de Bruxelles, Laboratoire G-Time, Bruxelles
Ndongo, Alexis; Université des Sciences et Techniques de Masuku (USTM), Franceville
Ligna, Cédric; Université des Sciences et Techniques de Masuku (USTM), Franceville
Nazarov, Konstantin; Department of Earth Sciences, University of Oxford, London, UK
Ruffet, Gilles; Université de Rennes, Géosciences Rennes, Rennes
De Putter, Thierry
Pourkhorsandi, Hamed; Department of Earth Sciences, Royal Museum for Central Africa, Geodynamic and Mineral Resources, Tervuren ; French National Research Institute for Sustainable Development, Géosciences Environnement Toulouse, Toulouse, F R
Mattielli, Nadine ; Université de Liège - ULiège > Département de géologie > Argiles, géochimie et environnements sédimentaires ; Département Géosciences, Environnement et Société, Université libre de Bruxelles, Laboratoire G-Time, Bruxelles
Kirsimäe, Kalle; Department of Geology, University of Tartu, Tartu
Prave, Anthony; School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
Depret, Martin ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Hatert, Frédéric ; Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Mathieu, Moussavou; Université des Sciences et Techniques de Masuku (USTM), Franceville
