Petrogenesis of the Precambrian basement rocks in the Bogoin area, southwestern Central African Republic

The Central African Orogenic Belt, characterized by Archean and Paleoproterozoic basement with Neoproterozoic metasedimentary units, remains underexplored despite its economic significance. This study investigates the petrogenesis and geotectonic setting of Precambrian rocks in the Bogoin area, southwestern Central African Republic. The granitic rocks belong to the calc-alkaline series and exhibit evidence of complex interplay between crustal and mantle processes in a subduction zone setting. The REE patterns suggest subduction zone granites typical of volcanic arcs, with enrichment in Cs, Rb, Ba, K, and U indicating magmatic fractionation and potential mineralization. Extreme arsenic enrichment (up to 21,809 ppm) in mica schist points to arsenopyrite and pyrite, suggesting significant gold mineralization potential particularly linked to dolerite dykes within greenschist-facies Paleoproterozoic formations. Chondrite-normalized REE patterns reveal that metadiorite, granite gneiss, and granite are not co-magmatic. Metadiorite displays REE patterns suggesting garnet fractionation and a positive Eu anomaly, indicating magma generation at depths within the garnet stability field. The composition of calc-silicate rocks suggests an origin from calcareous or dolomitic sediments interbedded with siliceous materials prior to metamorphism. Amphibolites likely formed from a mafic protolith subjected to high-grade metamorphism, while chlorite and mica schists likely originated from shale under intermediate-grade conditions. The region experienced three phases of deformation: the first phase features NW-SE foliation, aligning with a dextral shear zone in the Central African Shear Zone; the second phase reflects a sinistral shear plane in the N-S direction; and the third phase consists of NE-SW trending regional lineaments.