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

Blandine Gourcerol,Yannick Callec,Florent Boudzoumou,Matthieu Chevillard,Olivier Blein,Louis-Marie Joachim Djama

doi:10.3390/min12020114

Blandine Gourcerol, Yannick Callec + Show 4 more

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https://doi.org/10.3390/min12020114

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Abstract

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.

Highlights

Academic Editor: Santanu BanerjeeAlgoma-type banded-iron formations (BIF) are chemically formed sedimentary units consisting of alternating chert and iron-rich layers [1]
BIF units are characterized by relatively consistent REE + Y patterns:
The Youkou (Figure 5A), Kékélé (Figure 5B), Ngoyboma (Figure 5C), Obélé (Figure 5D), and Odia (Figure 5E) BIF units are characterized by relatively consistent REE + Y patterns:

Summary

Introduction

Academic Editor: Santanu BanerjeeAlgoma-type banded-iron formations (BIF) are chemically formed sedimentary units consisting of alternating chert and iron-rich layers [1]. Archean to Early-Proterozoic greenstone belts [2,3] These Fe-rich sedimentary units have long been considered a significant contributor for constraining and assessing the geochemical evolution of atmosphere and hydrosphere throughout the Precambrian [3,4,5,6]. Despite successive chemical transformations during diagenesis, or related to multiple metamorphic recrystallizations, the REE + Y abundance of BIFs reflects a geochemical signature indicative of their primary depositional environment [7,8,9].

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