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,Blandine Gourcerol,Yuling Xie,Kofi Adomako-Ansah,Yunwei Qu

doi:10.3390/min11060579

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.

Highlights

Algoma-type banded iron formations (BIFs) are increasingly explored and studied due to their rich endowments of ironand gold
This study focuses on the BIF that hosts the Nabeba iron deposit—the deposit with the highest iron ore potential amongst the other BIFs in the Invido Basement Complex (IBC) of the Republic of Congo (Figure 1)—but its host BIF depositional environment and genesis are not well-studied
The BIF consisted of magnetite, hematite, and quartz, together with minor siderite and magnesite

Summary

Introduction

Gold (e.g., the Meliadine, Canada; [2]) In addition to their economic significance, BIFs have immense scientific value in understanding the Precambrian hydrosphere, biosphere, and atmosphere [3,4,5,6,7]. BIFs are chemical sedimentary rocks by definition and comprise alternating chert- and iron-rich (≥15% Fe) layers [8,9,10]. The BIFs in Central Africa and the Congo are much less studied than those in Cameroon.

Results

Discussion

Conclusion