The Bonikro deposit is the first in Côte d'Ivoire where gold is found within a sheared granodiorite, in the zones of boudins and faults. Gold is associated with scheelite and molybdenite in veins. 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 the Bonikro deposit. The investigation in this deposit and the observations of the drill cores have demonstrated 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 display the more visible gold in the deposit. 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 sulfide (molybdenite up to 5 %). The molybdenite is the main sulfide.Each vein shows its typical 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.Gold is observed in both the granodiorite and in the basalt in the areas where these lithologies are sheared. It appears that the introduction of the auriferous mineralization at Bonikro postdates the magmatism and seems to be syn-to post-tectonic. This direct link between the structural features and the gold deposition has shown that the Bonikro deposit is a case of shearcontrolled gold mineralization.

La présente étude évalue les connaissances gîtologiques ainsi que les impacts environnementaux liés aux activités aurifères artisanales pour l’or de Doumbiadougou en Côte d’Ivoire. L’étude s’appuie sur des données issues de la description in situ des puits de prospection, des carrières ainsi que des méthodes de récupération de l’or. La typologie des gîtes indique deux ensembles à Doumbiadougou : d’une part les gîtes alluvionnaires dans les bas-fonds et d’autre part les gîtes filoniens sur les collines environnantes. Leur prospection s’effectue par le fonçage de puits tests de 1m3 jusqu’à 16m3 dans les bas-fonds, également sur les pentes et autour des veines de quartz sur les collines. L’exploitation des gîtes alluvionnaires se fait par l’ouverture de carrières de 5 m x 2 m x 2 m soit 20 m3 tandis que ceux filoniens se fait par l’ouverture de puits de 80 cm de diamètre et de profondeur allant jusqu’à 25 m. Le minerai alluvionnaire est traité par les lavages à la batée ou au sluice tandis que celui des filons est pulvérisé avant de subir le même traitement. La production aurifère se termine par la récupération de l’or après amalgamation au mercure. Sur le volet environnemental, ces méthodes laissent des puits béants, détruisent les cultures tout en réduisant les espaces cultivables, accélèrent le drainage minier acide, réactivent les conflits fonciers et exposent les communautés locales à l’inhalation du mercure.

The mining company Sama Nickel-CI during its exploration activities in the Bounta area (Biankouma department, western Côte d'Ivoire) identified rocks with magmatic and metamorphic characteristics of felsic to mafic compositions mineralized in sulfide but unknown in the region. Thus, the petrographic characterization of these rocks of Bounta as well as the sulfides they contain, was carried out from macroscopic to microscopic observations. Petrographic analysis of these rocks has shown that these rocks are trondhjemite, tonalite and granodiorite (TTG) suites, composed of the main minerals (quartz, plagioclase, orthopyroxene, amphibole, feldspar) and accessory minerals (biotite, garnet) with magmatic textures supplanted by metamorphic textures. They were set up by fractional crystallization and would be products of Archean crustal anatexis formed from the partial melting of basaltic protocrust during the Liberian orogeny. The Bounta's series of trondhjemite, tonalite and granodiorite (TTG) contain speckles of sulfide (pyrite and pyrrhotite) which are disseminated in places and are relatively abundant, as well as iron oxides (magnetite) which are of low proportion.

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In this study, nickeliferous soils' effects on grain legume and cereal growth as well as their potential to accumulate nickel and related micronutrients were examined. A completely randomized block design with six repetitions was set up. Samples were collected from eight points and the experiment was conducted for six weeks at the University of Man. In order to fill a plastic container, eight soil samples were used. The soil humidity was controlled with SONKIR MS02 multimeter. Common bean (Phaseolus vulgaris), soybean (Glycine max), and maize (Zea mays) were the test plants. Each soil sample was air dried and sieved with a 2 μm mesh. The X-ray fluorescence (XRF) technique was used to carry out a chemical analysis. Statistica 7.1 was used to conduct statistical analysis like the ANOVA and correlation test. At Moyango, the soil was developed on dunite. The soil had a colour varying from 7.5YR6/2 to 10YR5/6.). The dominant oxides found were Fe2O3, SiO2, and P2O5 with wt% > 7. The soil Ni was negatively correlated with K, Ca and, V. The soils had significant effect on soybean, common bean, and maize growth. However, the negative effect was more on common bean. The lowest soybean plant’s heights were observed on plant grown on soil from the mining site. The soil had a significant effect on soybean Ni, V, Mn, and Co content. Soybean plant Ni contents were 9.20 and 7.31 wt%, respectively from plants grown on soils M1 and M2. The content of Ni in soil had significant effect on plant growth, specifically it has reduced the height of grain legumes. From the results observed, maize should be the one most suitable for cultivation in the vicinity of the Ni mining region of Foungouesso-Moyango. Further investigation is needed with more test plants to prevent population health.