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

Abstract

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.

Petrology and geochemistry of metamorphosed rocks associated with iron formations of the Toko‐Nlokeng iron deposit, (Southern Cameroon): Implications for geodynamic evolution and mineralization

“…The Toko-Nlokeng iron deposit belongs to the major metallogenetic events in the Congo Craton. In particular, iron mineralization was related to the extensional stage, which is consistent with the cases of modern and ancient iron deposits that are also preferentially associated with rift environments and/or magmatic products that indicate extensional activity (e.g., Ganno et al, 2017;Gatsé et al, 2021;Gourcerol et al, 2022;Soh et al, 2021;Swiffa Fajong et al, 2022). It is known that this specific context would induce thinning of the thrust plate and the formation of numerous normal faults (e.g., synvolcanic and synsedimentary faults).…”

Banded Iron Formations in Congo: A Review

“…Mineralization found in this area consists mainly of scree or exposed hydrated platelet formations, which can be weathered or unaltered itabirites (Meloux et al, 1983). The Nabeba BIFs exhibit two distinct facies: oxide and carbonateoxide (Gatsé et al, 2021). The paragenesis of this deposit includes minerals such as magnetite, hematite, quartz, siderite and magnesite (Gatsé et al, 2021).…”

“…The Nabeba BIFs exhibit two distinct facies: oxide and carbonateoxide (Gatsé et al, 2021). The paragenesis of this deposit includes minerals such as magnetite, hematite, quartz, siderite and magnesite (Gatsé et al, 2021). In terms of rock types encountered in the Nabeba drill holes, itabirites and weathered white mica-chlorite schists have been found to be dominant (Longley et al, 2013).…”

“…The host rocks associated with the Nabeba BIFs are amphibolites and greenish actinolite-chlorite schists (Fig. 6) (Gatsé et al, 2021;Gourcerol et al, 2022).…”

Texture and iron‐oxygen isotope composition of magnetite in the Sanaga iron ore prospect, Nyong Series, southwestern Cameroon: Implications for the origin of the magnetite mineralization

“…The Sanaga iron ore prospect within the Palaeoproterozoic Nyong Series in Cameroon is a magnetite‐rich iron ore deposit hosted within gneissic rocks referred to as magnetite gneiss (Ilouga et al, 2017), with an estimated resource of 82.9 Mt @ 32.1% Fe (West African Minerals Corporation Press Release of February 2015). Previous studies based on petrography and whole‐rock geochemistry suggest that the Sanaga iron ore formed as BIFs (Bonda et al, 2017; Ndema Mbongue & Alemnji, 2020), though they lack the typical physical/chemical characteristics of BIFs such as banding, HREE enrichment relative to LREE, positive Eu, La and Y anomlaies and spatial association with sedimentary rocks or their para‐drived equivalents (Alibo & Nozaki, 1999; Bolhar et al, 2004; Planavsky et al, 2010; Thurston et al, 2012; Taylor et al, 2016; Moon et al, 2017; de Moraes et al, 2020; Djoukouo Soh et al, 2021; Gatse Ebotehouna et al, 2021). Detailed petrography using backscattered (BSE) images and stable isotope data has not been reported for the Sanaga iron ore deposit.…”