Abstract:The Ngovayang massifs belong to the Paleoproterozoic Nyong unit complex located in the north western edge of the Congo Craton of southern Cameroon. It consists of granitoids and a banded series. The banded series presents the petrographic and geochemical characteristics of greenstone belts similar to those of Sao Francisco Craton in Brazil. Pervious works in this area involved geochemical (% Fe), mineralogical (hematite/magnetite) and geophysical characterization of the formation ores. The sedimentary and tectonic events related to the ore emplacement are poorly understood and has an effect on the exploitation of these ores in Cameroon. The objective of this work is to generate new petrographic and geochemical data of the Ngovayang massifs, and to determine the origin and emplacement process that favored the accumulation of these ironbearing ferruginous quartzites in the study area. Polished thin sections were produced and observed using a scanning electron microscope at the Centre for Microscopy and Microanalysis, University of Western Australia CMM-UWA. Geochemical analysis of major and trace elements were carried out using XRF and ICP/MS in OMAC laboratory of Ireland. The results showed that the iron formation of the Ngovayang area composed of ferruginous and banded ferruginous quartzites series. Quartz, hematite and aluminosilicates occur as the main minerals associated with the ferruginous quartzite series. Geochemically, these ferruginous facies are very rich in Fe and Si but poor in other elements. Platy and massive type of mineralization were common with the hematites and are indicative of either metasomatic (or hydrothermal) origin and lateritic through meteoric water circulation. Three phase mineralization were identified from microscopic study: early Syn-sedimentary phase linked to the sedimentation of BIFs, a secondary tectonics phase and a tertiary phase related to weathering. The Ngovayang iron formations are characteristic of the lake superior-type.

The Ngovayang trondhjemitic gneisses belong to the Nyong Complex at the Northwest boundary of the Ntem Complex. A combined study of whole-rock major, trace elements and isotopic data, Sm-Nd and Rb-Sr indicate that trondhjemitic gneisses are peraluminous and range from weakly I-type to S-type with nearly constant A/CNK values between 1.04 and 1.24. Their I-and S-type characters suggest that juvenile materials have been partially remobilized or recycled. These trondhjemitic gneisses have slightly to moderate MgO, Cr and Ni contents, ISr (0.703677 -0.741911) and low εNd(t) (from -16.48 to -10.6) values. Such geochemical features suggest a small mantle-source contribution, coupled with assimilation of some upper and lower crustal materials and indicate the implication of old crust probably with both Archean and Early eburnean origin (2597 -2318 Ma). They also exhibit geochemical features typical of calc-alkaline, crustal contaminated calcalkaline rocks, volcanic arc and trondhjemitic nature. These results show that old crust has recycled and trondhjemitic gneisses are linked to convergent geodynamic system. The petrogenetic diagrams of AFM vs CFM, MgO vs SiO 2 and Rb/Ba vs Rb/Sr and lower K 2 O/Na 2 O ratio values (0.38-0.51), indicate that the magmatic source materials are mainly composed of plagioclase-rich sources such as metagreywackes -metabasic mixtures, metagreywackes and metabasics and basalt or igneous rocks. These sources materials occurring in the melt originated from both slab melting and assimilation of upper and lower crust at ca. 732.4 -928.7°C and at 2597 -2318 Ma. This study shows that Archean crust may have a North-West extension beyond the actual boundary with Nyong Complex.

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The Eséka Greenstone Belt (CRVE) is located in the Nyong Paleoproterozoic unit, Northern edge of the Congo craton, Cameroon. The petrographic, geochemical, and isotopic geochemistry (Sm-Nd) approach of this Nyong complex amphibolites, allowed to highlight three petrographic facies (plagioclastic amphibolites, melanocratic amphibolites and garnet amphibolites), with mineralogical assemblies more or less similar to Hornblende and plagioclase. Fifteen amphibolites samples distributed throughout the CRVE were collected and differentiated into three main facies (garnet, plagioclastic and melanocratic amphibolites). The thin sections were made at the Langfang Rock Detection Technology Services Ltd laboratory in China. The major elements were analysed by X-ray fluorescence (XRF) in South Africa. Isotope geochemical analyses were achieved at the University of Rennes in France. The analyses were carried out following the isotopic dilution method using a multicollector mass spectrometer by thermos-ionization of the Finnigam MAT 262 type to decipher the isotopic composition of samples. Garnet amphibolites are on average richer in silica (47.40 -52.58%) compared to plagioclastic and melanocratic amphibolites. The alkali content is low in melanocratic amphibolites, in particular for K2O (0.13 -0.14%). These metabasites have several common geochemical features such as: the relatively high contents of Y (22.03 -39 ppm), Zr (63.78 -481.99 ppm), Th (0.55 -12.37 ppm), the low content of Ta ( 0.33 -1.20 ppm); a high concentration of compatible elements (5.60%