Shear-hosted gold mineralization in the Oumé-Fettèkro greenstone belt, Côte d'Ivoire: the Bonikro deposit

International audience ; The Bonikro deposit is the first in Côte d’Ivoire where gold is found within a sheared granodiorite and also in its veins that are associating gold with scheelite and molybdenite. The purpose of this paper is to highlight the characters of the shearing and the mineralized veins and to reveal the timing of their gold deposition in Bonikro. The investigation in the deposit and the analyses of the drill cores have recorded the main role played by the shear zone and its three principal mineralized veins: sheeted veins, planar veins and transversal veins.The deposit is dominated by a major structure: the Bonikro Shear Zone (BSZ) striking North-South. The BSZ has affected the granitoid and as a consequence, it has produced two local shears striking NW and NE. The sheeted veins are earlier: thickness (1cm) and sub-parallel sets of quartzo-feldspathic veins composed of: milky quartz (70 to 80 %), albite (5-10 %) scheelite (up to 15%) and pyrite (up to 5%). They are the main host of the scheelite and also most of the deposit visible gold.The planar veins support the powellite and pyrite minerals. The transversal veins are late and composed of: milky quartz (40 %), calcite (30 %), albite (10 %), biotite (15 %), and sulfides (molybdenite up to 5 %). The molybdenite is the principal sulfide. Each vein has its minerals and resumes a generation of setting. These veins are bordered in the granodiorite by a corridor of a strong hydrothermal activity indicated by the sericitisation, the silicification, the chloritisation and the albitisation. The introduction of the auriferous mineralization at Bonikro postdates the magmatism and appears to be syn- to post-tectonic.