Oxygen Isotope Geochemistry as a Tool in the Exploration for BIF-hosted Iron Ore Occurrences within the Precambrian Mineral Belt of Southern Cameroon, Northwestern Margin of the Congo Craton: A Review

Abstract

As a method for discovering the footprint of concealed iron ore enrichments, oxygen isotopes have revealed hydrothermal fluid sources and processes in Banded Iron Formation (BIF)-hosted iron ore provinces worldwide. This paper reviews the role oxygen isotopes play in exploring BIF-hosted iron ore bodies and discusses their application in southern Cameroon’s Precambrian mineral belt as an auxiliary exploration technique. Oxygen isotope analysis of iron ore species (e.g., BIFs, itabirites, and jaspilites) showed that the least altered BIFs had higher δ18O values than enriched ores. In the Nyong complex BIF sequence of southern Cameroon, δ18Omag values range from –3 to –1.8, while δ18Oqtz values range from 6.8 to 10.6, indicating a discernible shift between the δ18Omag-qtz values. Much higher δ18Omag values (2.89 to 9.30‰) have been observed for magnetite gneisses suggesting an evolved magmatic-hydrothermal fluid source. Quartz veins associated with early-stage hematite ores in the adjacent Ivindo basement complex display higher δ18O values (4.7 to 8.1%) than those associated with late-stage magnetite ores (–2.3 to –1.5%). It is evident from these values that there is an isotopic shift between early-stage and late-stage iron ores, supporting the relevance of oxygen isotope to understanding iron ore signatures within the NW margin of the Congo craton. However, since the Congo Basin is characterised by inaccessible equatorial vegetation cover and lacks superficial exposures, high-precision oxygen isotopes (δ18O and δ17O) in conjunction with other isotopic techniques (e.g., δ56Fe) and lithogeochemistry, will be more useful in constraining the isotopic signature of the BIF mineralisation.