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Textures and Rare Earth Elements Composition of Banded Iron Formations (BIF) at Njweng Prospect, Mbalam Iron Ore District, Southern Cameroon

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International Journal of Geosciences 2013年第1期4卷 146-165页

作者： dieudonne charles isidore ilouga Cheo Emmanuel Suh Ghogomu Richard Tanwi Department of Earth Sciences Faculty of Science University of Yaoundé I Yaoundé Cameroon Economic Geology Unit Department of Geology and Environmental Science University of Buea Buea Cameroon

The REE signature of banded iron formations (BIF) and martite-goethite mineralization of the Njweng ridge (South Cameroon) are used here to decipher the nature of the ocean during the period of BIF precipitation. The textures of typical BIF categories are also presented as the only sedimentary feature. Two types of BIF facies are present at Njweng: the oxide and silicate facies. These facies show two stages of phase transformations. The first is the transformation of the original magnetite mineral into martite by oxidation resulting in trellis texture;the second is a simultaneous transformation by hydration into goethite and dehydration into martite. The samples typically show LREE depleted patterns relative to HREE, a characteristic similar to that of modern seawater. Also the strong positive Eu anomalies from the samples indicate the involvement of hydrothermal plumes of volcanic origin such as at mid ocean ridges (MOR). Yttrium (Y) has a strong positive anomaly pointing to the transportation of REEs as aqueous complexes within these ancient seas. The BIF samples have no positive Ce anomalies, suggesting that the oceans at that time were more reducing with no Ce fractionation than in present day oceans. The martite-goethite mineralization rather shows a positive Ce anomaly that derived from the enrichment in REE during the weathering of REE-bearing minerals. These results are integrated into existing literature on REE in BIFs worldwide and provide new insights into these heretofore unstudied BIFs of the northern edge of the Congo Craton.

关键词： REE BIF Martite Magnetite Alteration Njweng Cameroon

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Petrography, Sedimentology and Geochemistry of Rocks and Sediments from Three Key Localities from the South-East Region of the YaoundéGroup (Centre Region, Cameroon): Implications for Rutile Exploration

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International Journal of Geosciences 2021年第8期12卷 714-737页

作者： Jules Mbanga Nyobe Louise Marie Ngo Bidjeck Bondje Dieudonné charles ilouga Elisé Sababa Department of Earth Sciences University of Yaoundé I Yaoundé Cameroon Higher Teachers Training College University of Yaoundé I Yaoundé Cameroon

The Otele, Matomb and Nguibassal localities correspond to the SW part of the Yaoundé Group. Field observations, rocks and stream sediments of the study area were examined using rock tin sections, granulometric, morphoscopic and X-ray fluorescence analysis to identify their distribution, the nature of the basement, provenance useful minerals and some weathering process that affect them to show the exploration significance of these outcomes. From these it appears that, three rocks types occur in the areas: gneisses, micaschists and amphibolite, respectively with the following minerals assemblage: (Fks + Bt + Qz + Ky + Pl + Msc + Grt + Op), (Bt + Qz + Msc + Fks + Op + Ky + Grt) and (Amp + Bt + Pl + Kfs + Qz + Px + Grt + Op). Sedimentological analyses reveal the dominance of unworn grains of rutile quartz and kyanite that suggest a short transport;while less abundant minor shiny dulls and sub-rounded grains suggest a long transport. Sediments collected are homometric, well sorted, well classified, with immature rutile due to their angular shapes. Silica is the most important major element ranging in concentration between 47.56 wt% SiO2 in amphibolite to 61.21 wt% SiO2

关键词： Rutile Global Fraction SW Yaoundé Group Unworn Grains Impurities

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New detrital zircon U-Pb ages from BIF-related metasediments in the Ntem Complex (Congo craton) of southern Cameroon, West Africa

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Natural Science 2013年第7期5卷 835-847页

作者： Nelson N. Chombong Emmanuel C. Suh charles D. C. ilouga Department of Earth Sciences University of Yaoundé I Yaoundé Cameroon Economic Geology Unit Department of Geology University of Buea Buea Cameroon

Banded Iron Formations (BIFs) were formed by contemporaneous events of active sediments supply and the venting of a hydrothermal fluid source at the Mid-Ocean-Ridge. BIFs within the Ntem Complex at the northern edge of the Congo Craton are intercalated with metasandstones and siltstones. SHRIMP U-Pb analysis on detrital zircons obtained from these metasediments gave variable ages from over 3000 Ma to 1000 Ma with the maximum age of deposition clustered around 1200 Ma and the peak of deposition at 1800 Ma. This age range suggested that the sub-basin was opened sometime in the Archean and remained active up till the Neoproterozoic. Zircons with Archean ages have a provenance linked to the charnockitic suite and the high-K granites within the Ntem Complex. The Paleoproterozoic ages are attributed to clastic inputs from the neigbouring Nyong Series west of the Ntem Complex. Also the peak of deposition in the Proterozoic could probably be explained by the globally recognized intense crust-forming processes in the Early Proterozoic time. The provenance of the younger Neoproterozoic ages is tied to various lithologies within the northern mobile belts of the Adamawa-Yade massifs and correlates with Neoproterozoic sedimentation ages in the Yaoundé, Lom and Poli series. The Neoproterozoic ages obtained are comparable to those obtained from metasediments of the Amazonian Craton and provide evidence of Pre-Gondwana assemblage of the Congo and the S?o Francisco Cratons.

关键词： BIFs Metasediments Ntem Complex SHRIMP U-Pb Age Detrital Zircons

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