Petrogenesis and U–Pb zircon dating of amphibolite in the Mewengo iron deposit, Nyong series, Cameroon: fingerprints of iron depositional geotectonic setting

The Mewengo iron deposit belongs to the Nyong series greenstone belt, which is located at the northwestern border of the Congo Craton in Cameroon. The amphibolites of Mewengo are associated to poorly documented banded iron formations (BIF) as layers and discontinuous pods; they are ortho-amphibolites having a basaltic protolith. They display granoblastic heterogranular texture, made up of garnet, amphibole, plagioclase, K-feldspar, and clinopyroxene, with accessory minerals such as zircon and iron oxides. Their major element contents are relatively low but they are enriched in alkalis and transition metals, (Na 2 O + K 2 O) comprised between 2.1 and 2.42 wt%, MgO (7.11–7.39 wt%), CaO (10.55–11.06 wt%), Fe 2 O 3 (13.54–14.79 wt%), SiO 2 (48.7–49.64%), Zr (45.3–55.5 ppm), V (320–340 ppm), Cu (126.5–179.3 ppm), Ni (85–109 ppm), Co (50.7–60.6 ppm). Their Mg# vary from 49.70 to 50.98 and the average value of Nb/Ta ratios is 19.4 characteristic of basaltic rocks from mantle; they are reminiscent of MORB from tholeiites series, generated by partial melting of upper mantle at the shallow depth in spinel-peridotite stability field, where slight metasomatism by subduction-derived fluids occur. Eu/Eu* (0.89–1.00) and Ce/Ce* (0.71–1.03) suggest a deep-sea environment with less input from pelagic sediments inferring the iron deposit setting. The U–Pb zircon dating yielded age of 2050 Ma for metamorphism within the Mewongo iron deposit. The results of this study compared with the previous data of metavolcanic rock-related BIFs in Nyong series suggest a deep-seated subduction setting related to an amphibolitic/granulitic metamorphism during the Transamozian/Eburnean (ca. 2050 Ma) orogeny.