The petrogeochemical analysis of the granitoids of Mount Fouimba and Mount Goma in the Seguela region (central-western Côte d'Ivoire) is the subject of this study. This analysis combines remote sensing, geophysics, petrography and geochemistry, in order to determine the major characteristics of the granitoids in the study area, and above all to participate in the detailed mapping of all the Ivorian terrains. The granitoids encountered in this region are essentially two-mica granites, granodiorites and porphyry basalts. Chemical analysis indicates that these granitoids are of the ferrous and magnesian type with peraluminous to weakly metaluminous characteristics. They originate from the mantle and were emplaced in an active continental margin context.
Located in the south-west part of the Fettekro greenstone belt, Agbaou gold deposit is marked by three major lithological units: (i) a volcano-plutonic unit composed of basaltic to andesitic lavas, amphibolites, chlorite-schists and sills of microdiorite and microgabbro; (ii) a volcano-sedimentary unit containing pyroclastic lavas (basaltic and dacitic) and sediments (shale and grauwacke); (iii) the late felsic dikes (rhyolite and rhyodacite) probably contemporary with the formation of granitoids form the third unit. These host rocks are mostly intensely deformed and altered. Alteration phenomena were revealed by the high values in fire loss, the decreasing of silica contents, the sometimes high values of alkaline for rocks also basic, the constant depletion in LREE and LILE. The Eu and Nb negative anomalies reveal a crustal contamination of magmatic series. Basaltic lavas are volcanic arc tholeiites nearing N-MORB type; they are associated to a magmatogenesis of ocean floor. Their magmatic source would probably be spinel lherzolitic type. Andesites have a calc-alkaline composition and seem far link to active subduction margin. Geodynamics context would be that of an area where transcurrent faults of lithospheric extension generate heat corridors able of generating by fusion the andesitic calc-alkaline magma. This context would probably be the one that prevailed during the establishment of the gold mineralization. Pyroclastic rocks of dacitic composition as acid lavas (rhyolite and rhyodacite) have also evolved in this same geotectonic context. Plutonic rocks are located in arc-volcanic granites field, while metasediment are linked to active continental margin field.
Les granitoïdes de la partie Sud du batholite de Ferkessédougou s’étendent ou couvrent la région d’Issia où ils sont représentés par une série de roches allant des granites à deux micas à biotite dominante aux granites à deux micas à muscovite dominante. Cette étude rapporte de nouveaux résultats pétrographiques et géochimiques des granites de la région d’Issia. Sur le plan pétrographique, ils se répartissent en trois séries granitiques à savoir les granites G1, G2 et G3. Les granites G1 sont caractérisés par une abondance de la biotite par rapport à la muscovite et ont subi une migmatisation. Les granites G2 sont marqués par une abondance de minéraux de feldspaths potassiques présents sous forme de porphyres. Les granites G3 quant à eux se distinguent par une dominance de la muscovite, suivie de la tourmaline et sont pourvus de filons de pegmatites d’épaisseurs centimétriques à métriques. Sur le plan de la chimie, les granites G1 sont faiblement peralumineux (1˂A/CNK˂1,16), les granites G2 sont moyennement peralumineux (1,14˂A/CNK˂1,18) et les G3 fortement peralumineux (A/CNK˃1,19). Les caractères pétrographiques et géochimiques rattachent les granites G1 au type I et les granites G2 et G3 au type S.
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