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Magnetic Characterization of Amphibolites from the Fomopéa Pluton(West Cameroon):Their Implication in the Pan-African Deformation of the Central African Fold Belt

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Acta Geologica Sinica(English Edition) 2012年第1期86卷 73-84页

作者： NJANKO Théophile fozing eric martial KWéKAM Maurice YAKEU SANDJO Angéline Flore NJONFANG Emmanuel Laboratory of Environmental Geology Department of Earth SciencesDschang University Laboratory of Geology ENS Yaounde I University

The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement. These gneissic and amphibolitic basement rocks are represented in the pluton＇s body as sub-rounded, elongated or stretched xenoliths. Amphibolitic xenoliths display testimonies of two main tectonic events namely：（i） El flattening deformation event characterized by a NW-SE to E-W foliation with a best pole at 246/57 and a mineral stretched lineation with a best line at 293/47; and （ii） E2 compressive event typified by （1） N-S to NNE-SSW steeply dipping foliation; （2） S-type flexion-fold indicating a sinistral shear movement. These amphibolite rocks indicate a magnetic susceptibility magnitude （Km） range from 418 ~SI to 90092 IISI for 87% of the stations showing a ferromagnetic behavior. K-T curves reveal the presence of Ti-poor magnetite as susceptibility mineral carrier. Magnetic foliation and lineation suggest that the N-S strike direction observed in the Bamendou amphibolite is, as pointed out elsewhere in the Central African Fold Belt, of paramount importance in the tectonic evaluation of the Fomopea area, since it has most likely acted as major deformation phase in the second tectonic event in the belt.

关键词： amphibolite anisotropy of magnetic susceptibility (AMS) Pan-African fold belt Cameroon

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Characteristics of Gold Mineralization at the Baguiomo Gold Panning Site, Koudougou Region, Burkina Faso, West Africa

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Open Journal of Geology 2024年第1期14卷 1-18页

作者： Pascal Ouiya Aziz Fayçal Tarnagda martial eric fozing Ecole Normale Supérieure (ENS) Institut Sciences et Technologie (IST) Ouagadougou Burkina Faso Laboratoire Géosciences et Environnement (LaGE) Earth Sciences Department Ouagadougou Burkina Faso Department of Geology University of Dschang Dschang Cameroon

The Birimian Baguiomo formations are located in the northern part of the Boromo greenstone belt. In this belt, the volcanic rocks (tholeiitic basalt, calcalkaline basalt, andesite) hosting the gold mineralization are located in the Kwademen-Baguiomo shear zone. This mineralization, located only a few kilometers from the Kwademen gold deposit, is uncharacterized and, together with the latter, could constitute a gold potential capable of being economically exploitable. It is in this sense that this work is carried out with a view to characterizing the gold mineralization of the Baguiomo gold panning site. To carry out this work, we have made direct field measurements, combined with microstructures, and combined all this with data from geochemical rock analysis of the basalts that are the main host formations. Geochemical data show that tholeitic basalts formed from a mantle plume that was emplaced in an oceanic plateau context. Calc-alkaline basalts and andesites are comparable to Paleoproterozoic tholeitic basalts (PTH3), which are slightly enriched in light rare earths. Fertility tests show that these basalts concentrate between 3 and 6 ppb of gold at the time of accretion, which is sufficient for remobilization of this primary gold during the Eburnian orogeny to yield a deposit of around 4 - 5 Moz. Gold mineralization is associated with pyrite crystals when the latter are disseminated in the rock mass, whereas it is associated with hematite in quartz veins concordant with S1 shear deformation. It is mainly the pyrite crystals in the pressure shadows that contain the gold grains, whose development would be synchronous with micro-shear zone reactivation during the first phase of D1B deformation. The second phase of D2B deformation, which is a crenulation or fracture schistosity, does not significantly affect the shear deformation that controls mineralization.

关键词： Kwademen-Baguiomo Shear Zone Gold Panning Site Gold Mineralization Eburnian Orogeny

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Kinematic Evolution of the Nyakong-Manyi Shear Zone(Adamawa,Cameroon): Constraints from Field Observations and Microstructures,and Implication for Metamorphic P-T-t Estimation

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地球科学学刊:英文版 2023年第5期34卷 1465-1487页

作者： Belmien Robinson Sobze Yemdji Jules Tcheumenak Kouémo eric martial fozing Ludovic Achu Megnemo Julios Efon Awoum Agnes Blandine Kamgang Tchuifong Brice Rostant Tepi Yemele Maurice Kwékam Department of Earth Science University of DschangDschang 67Cameroon Department of Earth Science Faculty of ScienceUniversity of DoualaDouala 24157Cameroon

The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed for the kinematic evolution of the sinistral and dextral shear phases in the Tikar Plain, thus in the FBSZ;early dextral and late sinistral shear phases for some authors and early sinistral and late dextral shear for others. Moreover, the NMSZ kinematic evolution implication on the mylonitization P-T-t path in the area seem to be problematic and the present paper aim is to clear enough those problems;since this shear zone is the main mylonitic corridor that registered the left and right lateral movement in this area. The NMSZ comprises amphibolites, protomylonites, strict sensus mylonites(garnet-kyanite-sillimanite mylonite and garnet-pyroxene mylonite), ultramylonites kyanite-sillimanite and garnet-kyanite-sillimanite gneiss. Field structures testify that the investigated area recorded three deformation phases:(i) the D1deformation phase which is marked by NW-SE to N-S trending S1metamorphic foliation with low to moderate dips(15°–45°) that was transposed during the D2phase, is responsible for a regional metamorphism whose mineral paragenesis is garnet-kyanite-sillimanite;(ii) the early sinistral NNE-SSW to NE-SW shear phase D2marked by S2metamorphic and mylonitic foliations;responsible for, L2stretching mineral lineation, F2fold axes and B2boudins structures;(iii) the late dextral NE-SW shear phase D3, characterized by F3folds, B3boudins and ductile dextral C3shear planes. Mineral paragenesis garnet + kyanite + sillimanite and microstructures within gneiss testify that this rock underwent high grade regional metamorphism whose peak conditions are estimated at 11.5–13.5 kbar/850–900 ℃. After the peak of metamorphism gneiss was overprinted by high grade pressure mylonitization during the early sinistral and late dextral shear deformations. Microstructura

关键词： structural and microstructural features pressure-temperature estimation Nyakong-Manyi Shear Zone Foumban-Bankim Shear Zone Central Cameroon ShearZone tectonics petrology

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