Lithostratigraphy of the Bonikro gold deposit; contribution to the setting of the Birimian units in the Fettèkro greenstone belt, Côte d’Ivoire

Résumé

Located in the southern part of the Fettèkro greenstone belt in Côte d’Ivoire, the Bonikro gold deposit offers the opportunity to set the lithostratigraphic column and to put in light its Birimian units. This can help to understand the chronology between the Birimian units in the Fettèkro greenstone belt.

The geology of the deposit is made of three rock groups; mafic, felsic and sediments. The felsic group contains the ore through the granodiorite and aplo-pegmatite dykes and occupies the central part of the deposit.

Two major lithological units are noted: first, the basaltic complex occupying the east of the deposit and second the volcano-sedimentary rocks associated with sediments in the western side. These two units present an interface which is occupied in the south by the north-south to north-east trending Bonikro shear zone (BSZ) whereas in the centre and the NE, the interface is occupied by the BSZ and the granodiorite.

In consequence, the lithostratigraphic column realized in the south reveals that the basaltic unit and the pyroclastic unit were in contact before the setting of the BSZ. The Bonikro western side is where the petrographic diversity is well expressed. This side is likely where the lithological correlation is consistent and worthy. It appears that there is a contemporaneousness between the basaltic and the pyroclastics and sedimentary units.