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Banded Iron Formations in Congo: A Review

  • Yarse Brodivier Mavoungou (Mineral Exploration Program, Pan African University Life and Earth Sciences Institute (including Health and Agriculture)) ;
  • Anthony Temidayo Bolarinwa (Mineral Exploration Program, Pan African University Life and Earth Sciences Institute (including Health and Agriculture)) ;
  • Noel Watha-Ndoudy (Department of Geology, Faculty of Sciences and Techniques, Marien NGOUABI University) ;
  • Georges Muhindo Kasay (Mineral Exploration Program, Pan African University Life and Earth Sciences Institute (including Health and Agriculture))
  • Received : 2023.07.04
  • Accepted : 2023.12.10
  • Published : 2023.12.29
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Abstract

In the Republic of Congo, Banded iron formations (BIFs) occur in two areas: the Chaillu Massif and the Ivindo Basement Complex, which are segments of the Archean Congo craton outcropping in the northwestern and southwestern parts of the country. They show interesting potential with significant mineral resources reaching 2 Bt and grades up to 60% Fe. BIFs consist mostly of oxide-rich facies (hematite/magnetite), but carbonate-rich facies are also highlighted. They are found across the country within the similar geological sequences composed of amphibolites, gneisses and greenschists. The Post-Archean Australian Shale (PAAS)-normalized patterns of BIFs show enrichment in elements such as SiO2, Fe2O3, CaO, P2O5, Cr, Cu, Zn, Nb, Hf, U and depletion in TiO2, Al2O3, MgO, Na2O, K2O, Sc, Th, Ba, Zr, Rb, Ni, V. REE diagrams show slight light REEs (rare earth elements; LREEs) compared to heavy REEs (HREEs), and positive La and Eu anomalies. The lithological associations, as well as the very high (Eu/Eu*)SN ratios> 1.8 shown by the BIFs, suggest that they are related to Algoma-type BIFs. The positive correlations between Zr and TiO2, Al2O3, Hf suggest that the contamination comes mainly from felsic rocks, while the absence of correlations between MgO and Cr, Ni argues for negligeable contributions from mafic sources. Pr/Pr* vs. Ce/Ce* diagram indicates that the Congolese BIFs were formed in basins with redox heterogeneity, which varies from suboxic to anoxic and from oxic to anoxic conditions. They were formed through hydrothermal vents in the seawater, with relatively low proportions of detrital inputs derived from igneous sources through continental weathering. Some Congolese BIFs show high contents in Cr, Ni and Cu, which suggest that iron (Fe) and silicon (Si) have been leached through hydrothermal processes associated with submarine volcanism. We discussed their tectonic setting and depositional environment and proposed that they were deposited in extensional back-arc basins, which also recorded hydrothermal vent fluids.

Keywords

Acknowledgement

The authors express their gratitude to Mr. Urbain Fiacre OPO, the Acting Director-General of Mines, for providing valuable reports that were used in preparing this manuscript. The first author would also like to extend his gratitude to Dr. Vicky Bouenitela and Dr. Chesther Gatse whose precious comments helped us improve the manuscript. Furthermore, we also thank the anonymous reviewers and the editor for their thorough reviews and insightful comments, which greatly enhanced the quality of the manuscript. This paper is part of the first author's PhD thesis at the Pan African University Institute of Life and Earth Sciences (including Health and Agriculture).

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