Abstract

The petrology of Achaean biotite- and amphibole-rich metagranites, the geochemistry of Fe-occurrences and heavy mineral concentrations in stream sediments from Olounou (Ntem complex) help to constrain their inter-relationships. These metagranites display granoblastic textures outlined by microcline, biotite, amphibole and oxides. Ilmenite (60 to 80%), zircon (15 to 20%) and rutile (1 to 2%) are the mineral fractions in pan concentrates. Two types of Fe-mineralization as silicified veins crosscut the above rocks: hematite± magnetite quartzites with primary hematite enclosing magnetite relicts contain high average Fe2O3 (69.05 wt %) and TiO2 (0.73wt %); banded magnetite-rich quartzites with magnetite partially replaced by hematite are characterized byFe2O3 (52.15 wt %), TiO2 (0.27 wt %), relatively high W (286 ppm) and Ni (108 ppm). Both types have Zn, Cu, Ga contents below 10 ppm, positive Eu anomalies, HREE enrichment over LREEs and low ∑REE (9.76 to 12.07). Iron and SiO2 were derived from weathering of Archean biotite and amphibole metagranites, deposited in existing Post-Archean intra-cratonic basins under greenschist facies and impacted by sub-marine hydrothermal solutions. These results are genetically comparable to other Precambrian BIFs and underline the iron potential of Olounou. They equally contribute to iron ore exploration in Cameroon and worldwide.

Supplementary material:https://doi.org/10.6084/m9.figshare.c.5426547

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