Petrographie Des Volcanites Et Plutonites De La Partie Sud Du Sillon Volcano-Sedimentaire De Toumodi-Fetekro (Cote D’ivoire)

The southern part of Toumodi-Fètêkro greenstone belt is located in the Center - Southeast of Ivory Coast. Petrographic study of volcanic and plutonic rocks shows three units. The first unit is composed of basaltic to rhyolitic lavas which imply effusive character. Then we have volcanosedimentary unit composed of pyroclastic formations (lapilli tuff, breccia, ash deposit and ignimbrites) and the pillow-lavas. Indeed, the presence of this last shows clearly that an explosive volcanism and a submarine effusive volcanism have occurred during during the setting of Toumodi-Fètêkro belt. Plutonic unit is constituted of gabbroic to granitic rocks. Sericite, chlorite, epidote observed in these rocks are consistent with the impacts of greenschist facies metamorphism. The rocks of the southern part of the Toumodi-Fètêkro greenstone belt are formed in a subduction context rather than in oceanic plateaus context because of the old inheritance, sometimes of Archean age, found somewhere in theBirimiandomain. The lithologies of the southern part of Toumodi-Fètêkro meet elsewhere in the other Birimian greenstone belts. Also, these lithologies are affected by a hydrothermal alteration due to the abundant veins of quartz, carbonates, sericite, chlorite, epidote, sulphides and oxides. However, volcanic show in some places amphibolit facies metamorphism

Petrographic and Geochemical Characteristics of the Metabasites of the SASCA Domain (Yonaké, Mani- Béréby and Dehié Sectors), South-West Côte d'Ivoire

The petrographic and geochemical study of six (6) metabasites located in the Archean-Paleoproterozoic transition domain (SASCA domain, South- West Côte d'Ivoire) identified dolerites and gabbros. The thin sections revealed two textures: the doleritic texture (dolerite) and the granoblastic texture (gabbro). The dolerites are composed of plagioclase wands, pyroxene, and olivine. Gabbros have a composition of pyroxene (clinopyroxene), green hornblende, plagioclase, biotite, and rare quartz. Geochemical analysis, especially the major elements, corroborated the gabbroic character of the metabasites. Trace elements and rare earth helped to constrain the origin of the metabasites by showing: (i) their belonging to a tholeiitic series, (ii) a mantle source contaminated by the continental crust, and (iii) their emplacement in the field of intraplate or volcanic arc basalts

Contexte geologique de la mineralisation aurifere du prospect de Bobosso (region de Dabakala, centre-nord de la Cote d’Ivoire)

La lithologie du prospect de Bobosso (région de Dabakala, centre-nord de la Côte d’Ivoire) est constituée d’une roche hypovolcanique (microdiorite quartzique) et de roches volcaniques (basalte et/ou laves andésitique). Ces roches ont été affectées par une importante activité hydrothermale marquée par des filons et filonnets de quartz, calcite, ± tourmaline, ± sulfures.La minéralisation aurifère de Bobosso a été observée localement dans toutes les formations de la zone et ne présente donc pas de contrôle lithologique. Par contre, cette minéralisation apparait principalement liée aux filons de quartz et présente donc un contrôle structural. Ainsi, la minéralisation est principalement d’affiliation hydrothermale. La paragenèse métallifère est essentiellement constituée de pyrite (sulfure principal), de chalcopyrite et d’arsénopyrite. On note souvent la présence de magnétite et d’hématite. L'or n’est pas visible à l’oeil nu même dans les sections de forage présentant les plus fortes teneurs.Mots clés: Birimien, microdiorite, or, hydrothermal, DabakalaEnglish Title: Geological context of the gold mineralization of Bobosso prospect (Dabakala region, north-central of Ivory Coast)English AbstractThe rocks of the Bobosso gold prospect (Dabakala region, north-central of Ivory Coast) consists of subvolcanic rocks (quartz microdiorite) and volcanic rocks (basalt and/or andesitic lava). These rocks have been affected by a significant hydrothermal activity characterized by veins and veinlets filled by quartz, calcite, ± tourmaline, ± sulphides.The gold mineralization of Bobosso was observed locally all of the rocks of the area and therefore does not present a lithological control. On the contrary, this mineralization appears mainly related to quartz veins and thus presents a structural control. Thus, the mineralization is of hydrothermal affiliation. The ore paragenesis consists mainly of pyrite (main sulphide), chalcopyrite and arsenopyrite ± magnetite and ± hematite. Native gold has not been observed even in the drill sections with the highest gold contents.Keywords: Birimian, Microdiorite, Gold, Hydrothermal, Dabakal

The Logoualé Band: A large Archean crustal block in the Kenema-Man domain (Man-Leo rise, West African Craton) remobilized during Eburnean orogeny (2.05 Ga)

International audienceThe Archean domain of the Man Rise was strongly remobilized during Eburnean coincidentally with the genesis of the Baoulé-Mossi domain (Birimian). This remobilization has allowed the recycling of Leonian and Liberian formations to generate a large gneissic crust, represented by the Logoualé Band. Zircons dates by laser ablation (LA-ICP-MS) of two samples of biotite-bearing pink gneisses of the Logoualé Band yielded ages of 2709 ± 15 and 2804 ± 11 Ma, confirming the Archean age of the Logoualé Band formations. The Eburnean tectono-metamorphic event in the Logoualé Band has totally reset both U-Th-Pb chronometer with an average age at 2050 ± 16 Ma in recrystallized zones of monazites, and Sm-Nd chronometer of garnets with an age at 2053 ± 15 Ma. Non-recrystallized zones of monazites give an average age at 2712 ± 16 Ma. We propose that the Logoualé Band rocks were originally sediments deposited in some protocratonic rift-type basins. During Eburnean, these sediments were buried, underwent high-grade metamorphism and exhumed in a tectonic context dominated by transcurrent motion. The structural setting of banded iron formations (iron deposits), which are abundant in the Logoualé Band, would date back to the Eburnean

Chromite, mg-ilmenite and priderite as indicators minerals of diamondiferous cretaceous kimberlites and lamproites from Côte d'Ivoire (West Africa)

Seguela kimberlites are characterized by xenocrysts chromites with elevated contents of TiO2 (0.6-5%) due to reaction with the host rock and Magmatic. Chromites associated with diamonds have high levels of Cr 2O3 (usually > 55% wt), MgO (9-12%wt) and Al 2O3 (12% wt). The Cr content in xenocryst chromites is pressure dependent and thus indicative of diamond potential. Two groups characterized Seguela kimberlites chromites analyses. The first group is characterized by high contents of MgO (> 8.7 wt%) and Cr2O 3 (>57.8 wt.%). They contain more than 0.8 wt% TiO2. The Cr-Ti chromites are phenocrysts crystallized from TiO2-rich kimberlitic magmas derived from lithospheric mantle source. The second group present elevated contents of TiO2 (1-5%wt) intermediate Cr 2O3 (30%wt) and relatively low Al2O3 (<3%). The first group kimberlitic chromites are useful in diamond exploration. Chromites are associated with Mg-rich-ilmenite (Fe3+/Fe 2+ < 0.6), in kimberlite which is an important mineral indicator in diamond research. Priderite (TiO2 > 75%wt) with high K/(K+Ba > 0.8) ratio and jeppeyite with elevate BaO content (> 16%wt) and badeleyite (ZrO2> 75% wt) are characteristics minerals of Seguela olivine lamproite. These signatures allow to supose the geotectonic hypothesis of within plate continental Stratiform or Alpin (MORB) complex suggest by chromites Cr-spinels and spinels studies. Kimberlites contain diamonds with a large range in size, varying from microdiamonds (< 1 mm) weighting on average about 1 mg (0.005 carats) up to large diamonds 27 carats.29 page(s