Scientific publications
Arlette Pulcherie Djoukouo Soh
Other affiliations: Chinese Academy of Sciences · Institute of Geology and Geophysics
* (Corresponding author)
Landry Soh Tamehe
Other affiliations: Central South University
Lianchang Zhang
Other affiliations: Institute of Geology and Geophysics
Changle Wang
Other affiliations: Institute of Geology and Geophysics
Zidong Peng
Other affiliations: Institute of Geology and Geophysics
Xiaoxue Tong
Other affiliations: Institute of Geology and Geophysics
Jean Paul Nzenti
Other affiliations: Institute of Geology and Geophysics
Geological Magazine
Abstract The newly discovered Bibole banded iron formations are located within the Nyong Group at the northwest of the Congo Craton in Cameroon. The Bibole banded iron formations comprise oxide (quartz-magnetite) and mixed oxide-silicate (chlorite-magnetite) facies banded iron formations, which are interbedded with felsic gneiss, phyllite and quartz-chlorite schist. Geochemical studies of the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations reveal that they are composed of >95 wt % Fe 2 O 3 plus SiO 2 and have low concentrations of Al 2 O 3 , TiO 2 and high field strength elements. This indicates that the Bibole banded iron formations were not significantly contaminated by detrital materials. Post-Archaean Australian Shale–normalized rare earth element and yttrium patterns are characterized by positive La and Y anomalies, a relative depletion of light rare earth elements compared to heavy rare earth elements and positive Eu anomalies (average of 1.86 and 1.15 for the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations, respectively), suggesting the influence of low-temperature hydrothermal fluids and seawater. The quartz-magnetite banded iron formations display true negative Ce anomalies, while the chlorite-magnetite banded iron formations lack Ce anomalies. Combined with their distinct Eu anomalies consistent with Algoma- and Superior-type banded iron formations, we suggest that the Bibole banded iron formations were deposited under oxic to suboxic conditions in an extensional basin. SIMS U–Pb data indicate that the Bibole banded iron formations were deposited at 2466 Ma and experienced metamorphism and metasomatism at 2078 Ma during the Eburnean/Trans-Amazonian orogeny. Overall, these findings suggest that the studied banded iron formations probably marked the onset of the rise of atmospheric oxygen, also known as the Great Oxidation Event in the Congo Craton.
