Petrographic, Geochemical and Metallogenical Context of the Geological Formations of the Goumere Region (North-East of Cote D’Ivoire): Implication to the Knowledge of Gold Mineralization

The Gouméré region is located in the North-East of Côte d’Ivoire and is located in the South-West of the Bui furrow. In order to highlight the geology of the area studied, 14 samples were taken for studies using petrographic, geochemical and metallogenic methods. The study of macroscopic and microscopic petrography made it possible to highlight two major lithological units: 1) a volcano-plutonic unit, formed of gabbros, basalt, volcaniclastics and rhyodacite;2) a sedimentary unit (microconglomerate). From a geochemical point of view, the results obtained indicate that the plutonites are gabbro and gabbro diorite while the volcanics have compositions of basaltic andesites, rhyolite and dacites. The sediments have a litharenitic to sublitharenitic character. The metallogenic study made it possible to highlight hydrothermal alterations and metalliferous paragenesis on the formations studied. Hydrothermal alteration is characterized by the presence of carbonation, silicification, sericitization, sulfidation and to a lesser degree chloritization. Metalliferous paragenesis consists of pyrite, chalcopyrite, hematite and magnetite.

The Geological Formations of Koun Fao (East of Côte d’Ivoire): Petrographic Characterization and Associated Deformations

This study aims to contribute to improve knowledge on geological formations of Comoé basin. The petrographic study of the geological formations of Koun Fao has highlighted two major lithological families: magmatic rocks consisting of monzonites, monzogranites, diorites, biotite granodiorites, syenites, porphyritic micromonzonites and porphyritic dacite and metamorphic rocks from sedimentary origin (quartz schists, meta-greywackes, schists, andalusite chloritoschist and paragneiss). These formations are affected by amphibolite to greenschist facies metamorphism and hydrothermal alteration (pervasive and vein) marked by the presence of quartz, epidotes, chlorites and sericite. Minerals such as andalusite, muscovite and chlorite characterize a local low pressure contact metamorphism in the andalusite chloritoschist. Remote sensing data (Landsat 8 image) coupled with field data allowed the production of a geological map of the area. The study of the structures and microstructures highlighted two deformation mechanisms. These are flattening and simple shear (ductile and brittle). The study area is affected by four deformation phases: D1 marked by a N-S to NNE-SSW elongation, D2 marked by a NW-SE to NNW-SSE compression phase, D3 which is a NE-SW to NNE-SSW transpression phase and D4, responsible for late structures, marked by a NW-SE to NNW-SSE transpression phase.

Petrogenetic Characterization of the Geological Formations of the Localities of Goumere-Iguela in the South West of the Bui Belt (North-East of Cote d’Ivoire)

Located in the north-east of Côte d’Ivoire, the Gouméré-Iguéla sectors were the subject of a geological mapping. These geological formations are located southwest of the Bui trench. In order to improve the petrogenetic knowledge of the study area, a multidisciplinary methodology integrating microscopic observations and geochemical analyses of major and trace elements was carried out on 15 samples considered as representative of the studied outcrops. The macroscopic and microscopic petrographic study allowed to highlight three major lithological units: 1) a volcano-plutonic unit, formed by gabbros and amphibole-pyroxenite, basalt and rhyodacite;2) a volcano-sedimentary unit containing pyroclastites (of basaltic and andesitic composition);3) a sedimentary unit (meta-sedimentary). These rocks are affected by a general metamorphism of green schist facies and a hydrothermal alteration with pervasive and vein alteration marked by the presence of quartz, calcite, epidote, chlorite and sericite. From a geochemical point of view, the results obtained indicate that the plutonites are gabbros while the volcanites and volcanosedimentary rocks have compositions of basalts, basaltic andesites, rhyolites and dacites. They have mainly a tholeitic character related to subduction zones with crustal contamination. The metasediments are arenites emplaced in an active continental margin environment.

Structural Control of Auriferous Mineralization in the Birimian: Case of the Agbahou Deposit in the Region of Divo, Côte d’Ivoire

Located in the southwestern of the Oume-Fettekro greenstone belt, the Agbahou gold deposit is controlled by structural factors. Geophysics, teledetection and core data suggest the presence of NE and NW faults. However, the NE-faults define two major shear zones (ATZ: Agbahou Tectonic Zone and WTZ: West Tectonic Zone) that control the Agbahou gold mineralization. These first order structures are subparallel to the regional tectonic grain mostly north-east oriented. They seem to respectively develop on the both arms (eastern and western) of an anticline moderately plunging ~25° towards northeast. Each shear-zone contains several second-order shear-zones or lenses of variable direction and of 50° - 80° dip. NW-faults however correspond to strike-slip faults and their development should be related to transcurrent tectonics. They acted as control channels on the distribution of gold mineralizations. The ductile-brittle character of shear-zones favored the ascent of hydrothermal fluids and the formation of multiple auriferous quartz veins: veins Type IIa and veins Type IIb relating respectively to the shear-veins and extensional veins. However, Agbahou also shows the existence of a disseminated sulphides-bearing mineralization within host-rocks. At Agbahou, the precipitation of gold probably occurred in a post to late ductile-brittle deformation period.

Geochemistry of Mafic Rocks from the Birimian Basement of Doropo (Northeast of Côte d’Ivoire): Petrogenetic and Geodynamic Implications

The northeastern region of Côte d’Ivoire is characterised by a granitic basement mainly composed of biotite granite rocks. According to mapping work in the Gbabédjou and Doropo areas, these Birimian granitoids are cut by gabbro dykes and amphibolite enclaves, which are the subject of this study. In order to better understand the role and the implication of mafic rocks in the Doropo basement emplacement, a multidisciplinary methodology integrating microscopic observations and geochemical analyses of major and trace elements was carried out on 4 samples considered representative of the outcrops studied. Green hornblende, clinopyroxene, and accessory sphene minerals are found in mafic mineral phases, according to petrographic research. Whole-rock analyses reveal that mafic samples with TiO2 contents 1.1 ratios giving them an orogenic granite nature (I-type). Their REE patterns are moderately fractionated (La/Sm)N = 2.66 - 6.13 and (La/Yb)N = 11.17 - 43.70) with a very negative Eu anomaly (Eu/Eu* = 0.75 - 0.97). The multi-element diagrams are characterized by negative Nb-Ta anomalies and geotectonic studies have identified them as volcanic arc formations. All these characteristics allowed us to distinguish the Doropo mafic rocks as formations originating from the juvenile continental crust, emplaced under the Archean tectonics model with significant crustal contamination in the source. Magma driven by mantle diapir has been injected at the base of the continental crust and the heat induces the partial melting of the overlying crust giving rise to mixed liquids. This magma now enriched in LILE was immediately drained to the upper crust to form the mafic rocks from the studied area.

Petro-Structural Study of Paragneiss in the SASCA Domain(GbowéSector at Grand-Bereby),Southwestern Cote d’Ivoire

The petrographic and structural study of Gbowé (Grand-Béréby) formations located in the SASCA domain (South-West of C&#244te d’Ivoire) revealed migmatitic paragneisses. For an in-depth understanding of the petrographic, structural and metamorphic characteristics, six (6) thin sections were made from these paragneisses. These gneisses are characterized by paleosomes and neosomes (leucosome and melanosome), consisting of quartz, garnet, plagioclase, biotite, cordierite, sillimanite, myrmekite and microcline. The mineralogical assemblage thus described indicates a retrograde metamorphism (transition from granulitic facies to amphibolitic facies). The structural and microstructural study identified two types of deformation (ductile and brittle). The ductile deformation is characterized by phases D1 (NE-SW flattening) and D2 (NW-SE flattening), materialized by foliations (N140&#730, N050&#730), folds (asymmetrical folds, similar folds, concentric folds, ptymatic folds) and boudins. Fracture schistosity and fold fracture schistosity are characteristic of the brittle deformation (phase D3). The microstructural study coupled with the metamorphic study shows that the deformations had an impact on the texture of the minerals (recrystallization and mineral reactions). It also allowed giving the paragenesis of phases D1 and D2. The D1 phase is characterized by garnet1, biotite1, quartz1, sillimanite1 and cordierite1 and the D2 phase is characterized by garnet1, quartz2, sillimanite2, biotite2, garnet2 and orthose2. These parageneses thus highlighted bear witness to a polydeformation and polymorphism that affects the study area.