Depositional Environment and Genesis of the Nabeba Banded Iron Formation (BIF) in the Ivindo Basement Complex, Republic of the Congo: Perspective from Whole-Rock and Magnetite Geochemistry

Chesther Gatsé Ebotehouna (1) , Yuling Xie (1) , Kofi Adomako-Ansah (2) , Blandine Gourcerol (3) , Yunwei Qu (1)

1 SIE - School of Information Engineering [USTB]
2 University of Mines and Technology Tarkwa
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

The Nabeba high-grade iron deposit (Republic of the Congo) is hosted by banded iron formation (BIF) in the Ivindo Basement Complex, which lies in the northwestern part of the Congo Craton. The Nabeba BIF is intercalated with chlorite-sericite-quartz schist and comprises two facies (oxide and a carbonate-oxide). In this study, whole-rock and LA-ICP-MS magnetite geochemistry of the BIF was reported. Magnetite samples from both BIF facies had fairly similar trace element compositions except for the rare earth element plus yttrium (REE + Y) distribution patterns. The high V, Ni, Cr, and Mg contents of the magnetite in the Nabeba BIF could be ascribed to the involvement of external medium-high temperature hydrothermal fluids during their deposition in relatively reduced environment. The Post-Archean Australian Shale (PAAS)-normalized REY patterns of the Nabeba BIF magnetite were characterized by LREE depletion coupled with varying La and positive Eu anomalies. Processing of the information gathered from the geochemical signatures of magnetite and the whole-rock BIF suggested that the Nabeba BIF was formed by the mixing of predominantly anoxic seawater (99.9%) with 0.1% of high-temperature (>250 °C) hydrothermal vent fluids, similar to the formation mechanism of many Archean Algoma-type BIFs reported elsewhere in the world.

Mots clés: magnetite chemistry; banded iron formation (BIF); Nabeba deposit; Ivindo basement complex; Republic of the Congo

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

Chesther Gatsé Ebotehouna, Yuling Xie, Kofi Adomako-Ansah, Blandine Gourcerol, Yunwei Qu. Depositional Environment and Genesis of the Nabeba Banded Iron Formation (BIF) in the Ivindo Basement Complex, Republic of the Congo: Perspective from Whole-Rock and Magnetite Geochemistry. Minerals, 2021, 11 (6), pp.579. ⟨10.3390/min11060579⟩. ⟨hal-03538671⟩