Petrology of Precambrian metagranites and heavy mineral chemistry of the Olounou area within the Cameroon mineral belt (Ntem complex, South Cameroon): relationships with the Fe mineralization

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 cross-cut the above rocks: hematite ± magnetite quartzites with primary hematite enclosing magnetite relicts contain high average Fe 2 O 3 (69.05 wt%) and TiO 2 (0.73 wt%); banded magnetite-rich quartzites with magnetite partially replaced by hematite are characterized by Fe 2 O 3 (52.15 wt%), TiO 2 (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 ΣREE (9.76 to 12.07). Iron and SiO 2 were derived from weathering of Archean biotite and amphibole metagranites, deposited in existing Post-Archean intracratonic basins under greenschist facies and impacted by submarine 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 : Table S1 is available at https://doi.org/10.6084/m9.figshare.c.5426547