Depositional Setting of Archean BIFs from Congo: New Insight into Under-Investigated Occurrences

Blandine Gourcerol (1) , Olivier Blein (1) , Matthieu Chevillard (1) , Yannick y Callec (1) , Florent Boudzoumou (2) , Louis-Marie Joachim Djama (2)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 umng - University Marien Ngouabi of Brazzaville

Archean banded iron formations (BIF) represent a major contributor to better constraining and assessing the paleogeography and evolution of Archean cratons. In this context, we conducted an exhaustive sampling and analysis campaign of BIF units in the Congo Craton, covering several greenstone belts within the Ivindo, Kelle-Mbomo, and Chaillu blocks. The REE + Y patterns suggest: (1) Interaction of seawater with Fe-oxyhydroxides, as illustrated by strong REE enrichment coupled with La and Y enrichment; (2) contributions from high-temperature (>250 °C) hydrothermal fluids, illustrated by positive Eu anomalies; and (3) detrital input as suggested by relatively consistent REE concentrations and a chondritic Y/Ho ratio. These observations suggest a typical environment of Algoma-type BIF deposition. Moreover, assessment of the Ce anomalies in a combination of HREE enrichment indicates that some basins in the Chaillu and Ivindo blocks may have known potential oxygen-rich episodes in the early Archean during the deposition of these BIFs.

Mots clés: BIF; Republic of the Congo; hydrothermal fluids; seawater; depositional settings; Chaillu; Ivindo; Kelle-Mbomo blocks; Congo Craton

Domaines: Planète et Univers [physics]; Sciences de la Terre; Géochimie; Minéralogie

Blandine Gourcerol, Olivier Blein, Matthieu Chevillard, Yannick y Callec, Florent Boudzoumou, et al.. Depositional Setting of Archean BIFs from Congo: New Insight into Under-Investigated Occurrences. Minerals, 2022, 12 (2), pp.114. ⟨10.3390/min12020114⟩. ⟨hal-03537204⟩