The Gabon geology offered favorable and natural environments for the formation of various types of mineralization. The Etéké gold district, aim of this study, is located in the Ngounié province (souther...The Gabon geology offered favorable and natural environments for the formation of various types of mineralization. The Etéké gold district, aim of this study, is located in the Ngounié province (southern Gabon) on the western edge of the Chaillu massif. Geologically, the gold mineralization is associated with the Eburnean orogeny and hosted in the Archean greenstone belts. Also, this deposit is covered by a significant vegetation cover and a very extensive lateritic weathering profile, which hinders the most accurate study. Through this paper, we aim to propose a genesis pattern of this mineralization via a multidisciplinary approach. To do this, a petrographic, metallogenic, and geochemical characterization has been established in the different sectors of the Etéké deposit. The studied deposits display varied facies which are encased in granitoid. They are essentially formed of abundant granitoid, and amphibolite compared to the volcano-sedimentary formations. These rocks display magmatic textures, affected by metamorphism, and not sufficiently preserved. Based on our multidisciplinary approach, the studied samples collected from the core’s boreholes allowed us to decipher a volcanogenic and metamorphosed origin of the gold genesis.展开更多
The tectonic structures of the Mako area in the Kédougou-Kéniéba inlier (KKI) were mapped with tele-analytical investigation which is validated by field data. This study is based on different images pro...The tectonic structures of the Mako area in the Kédougou-Kéniéba inlier (KKI) were mapped with tele-analytical investigation which is validated by field data. This study is based on different images processing in particular: </span><span style="font-family:Verdana;">1</span><span style="font-family:""><span style="font-family:Verdana;">) the colored combinations (1 to 5) and panchromatic (8) thematic mapping bands of the Landsat-8 (ETM</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;">) satellite;</span></span><span style="font-family:Verdana;">2</span><span style="font-family:Verdana;">) Digital Elevation Model (DEM) image of Space Shuttle Radar Topography Mission (SRTM);</span><span style="font-family:Verdana;">3</span><span style="font-family:""><span style="font-family:Verdana;">) airborne geophysics (aeromagnetic and radiometric) images. In these images, four major directions of lineaments NS, NNE-SSW, NW-SE and EW would be related to the tectonic structures, have been identified and mapped. Field data confirm these four structural directions and show that most of these lineaments are related to faults, shear and/or thrust zones, or even basic rock dykes. N-S to NE-SW oriented lineaments are more frequent followed by those NW-SE oriented. These two directions of lineaments are generally in correlation with trajectories of major sinistral shear zones in the Mako area. They would be associated with the S</span><sub><span style="font-family:Verdana;">2a</span></sub><span style="font-family:Verdana;"> and S</span><sub><span style="font-family:Verdana;">2b</span></sub><span style="font-family:Verdana;"> schistosities relative to the D</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> Eburnean major deformation. They often intersect the E-W oriented lineaments which are less frequent and sometimes folded and crenulated. This E-W oriented linea</span><span><span style="font-family:Verdana;">ment would be prior and are associated with the S</span><sub><span style="font-family:Verdana;">1</span></sub><span style="font-family:Verdana;"> schistosity of the D</span><sub><span style="font-family:Verdana;">1</span></sub><span style="font-family:Verdana;"> Eburnean thrust phase of deformation. At the scale of the studied area, these major linear structures (shear zones) are conjugated and create a partitioning of deformation through an anastomosed network of mylonitic shear zones which surround weakly deformed rock bodies. All these structures would be related to the Eburnean or post-Eburnean orogenic events in this Mako area.展开更多
Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic...Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.展开更多
The West Congo Belt (WCB) is one of many Proterozoic orogens considered to be mobile belts adjacent to the margins of Archean cratons. This orogen underlies the western margin of the Congo craton in central Africa and...The West Congo Belt (WCB) is one of many Proterozoic orogens considered to be mobile belts adjacent to the margins of Archean cratons. This orogen underlies the western margin of the Congo craton in central Africa and outcrops from south-west Gabon to north-west Angola. In the Republic of Congo, the Mayombe Chain in south-west has preserved a geological record of Proterozoic to early Paleozoic rocks that have been investigated to understand the evolution of the West Congo Belt within the regional tectonic context. Investigation into lithostratigraphy and structural architecture of the Mayombe Chain has been done by earlier workers since the 19th century. However, the lack of consistent and diverse geochronological data induced several interpretations of its geodynamic setting. The chain was previously thought to be the result of more than two orogenic cycles, and subsequently to be the result of a single orogenic cycle. Recent petrographic, geochronological, geochemical data and paleogeographic reconstructions allow redefining the tectonic context and the main lithostratigraphic subdivisions of the Mayombe Chain. It is currently recognized that the Mayombe Chain consists of three major tectonostratigraphic domains: Western, Central and Eastern, which are prolongated by the Niari-Nyanga foreland basin. These lithounits seem to have been formed through a complex history that included: (i) Late Paleoproterozoic sedimentation, magmatism and metamorphism between 2110 and 1970 Ma related to the Eburnean tectono-thermal event;(ii) Neoproterozoic rifting magmatism and sedimentation;and (iii) Pan-African tectono-thermal event between 620 and 496 Ma leading to the amalgamation of western Gondwana. In this contribution, we review existing literature on this part of the West Congo Belt and summarize the current knowledge of its geologic setting with a focus on structure, lithostratigraphy and metamorphism. We aim to show how current research, with multidisciplinary approaches, changed the interpretation of the Mayombe with consideration to the Araçuaí-West Congo Orogenic system.展开更多
文摘The Gabon geology offered favorable and natural environments for the formation of various types of mineralization. The Etéké gold district, aim of this study, is located in the Ngounié province (southern Gabon) on the western edge of the Chaillu massif. Geologically, the gold mineralization is associated with the Eburnean orogeny and hosted in the Archean greenstone belts. Also, this deposit is covered by a significant vegetation cover and a very extensive lateritic weathering profile, which hinders the most accurate study. Through this paper, we aim to propose a genesis pattern of this mineralization via a multidisciplinary approach. To do this, a petrographic, metallogenic, and geochemical characterization has been established in the different sectors of the Etéké deposit. The studied deposits display varied facies which are encased in granitoid. They are essentially formed of abundant granitoid, and amphibolite compared to the volcano-sedimentary formations. These rocks display magmatic textures, affected by metamorphism, and not sufficiently preserved. Based on our multidisciplinary approach, the studied samples collected from the core’s boreholes allowed us to decipher a volcanogenic and metamorphosed origin of the gold genesis.
文摘The tectonic structures of the Mako area in the Kédougou-Kéniéba inlier (KKI) were mapped with tele-analytical investigation which is validated by field data. This study is based on different images processing in particular: </span><span style="font-family:Verdana;">1</span><span style="font-family:""><span style="font-family:Verdana;">) the colored combinations (1 to 5) and panchromatic (8) thematic mapping bands of the Landsat-8 (ETM</span><sup><span style="font-family:Verdana;">+</span></sup><span style="font-family:Verdana;">) satellite;</span></span><span style="font-family:Verdana;">2</span><span style="font-family:Verdana;">) Digital Elevation Model (DEM) image of Space Shuttle Radar Topography Mission (SRTM);</span><span style="font-family:Verdana;">3</span><span style="font-family:""><span style="font-family:Verdana;">) airborne geophysics (aeromagnetic and radiometric) images. In these images, four major directions of lineaments NS, NNE-SSW, NW-SE and EW would be related to the tectonic structures, have been identified and mapped. Field data confirm these four structural directions and show that most of these lineaments are related to faults, shear and/or thrust zones, or even basic rock dykes. N-S to NE-SW oriented lineaments are more frequent followed by those NW-SE oriented. These two directions of lineaments are generally in correlation with trajectories of major sinistral shear zones in the Mako area. They would be associated with the S</span><sub><span style="font-family:Verdana;">2a</span></sub><span style="font-family:Verdana;"> and S</span><sub><span style="font-family:Verdana;">2b</span></sub><span style="font-family:Verdana;"> schistosities relative to the D</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> Eburnean major deformation. They often intersect the E-W oriented lineaments which are less frequent and sometimes folded and crenulated. This E-W oriented linea</span><span><span style="font-family:Verdana;">ment would be prior and are associated with the S</span><sub><span style="font-family:Verdana;">1</span></sub><span style="font-family:Verdana;"> schistosity of the D</span><sub><span style="font-family:Verdana;">1</span></sub><span style="font-family:Verdana;"> Eburnean thrust phase of deformation. At the scale of the studied area, these major linear structures (shear zones) are conjugated and create a partitioning of deformation through an anastomosed network of mylonitic shear zones which surround weakly deformed rock bodies. All these structures would be related to the Eburnean or post-Eburnean orogenic events in this Mako area.
文摘Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.
文摘The West Congo Belt (WCB) is one of many Proterozoic orogens considered to be mobile belts adjacent to the margins of Archean cratons. This orogen underlies the western margin of the Congo craton in central Africa and outcrops from south-west Gabon to north-west Angola. In the Republic of Congo, the Mayombe Chain in south-west has preserved a geological record of Proterozoic to early Paleozoic rocks that have been investigated to understand the evolution of the West Congo Belt within the regional tectonic context. Investigation into lithostratigraphy and structural architecture of the Mayombe Chain has been done by earlier workers since the 19th century. However, the lack of consistent and diverse geochronological data induced several interpretations of its geodynamic setting. The chain was previously thought to be the result of more than two orogenic cycles, and subsequently to be the result of a single orogenic cycle. Recent petrographic, geochronological, geochemical data and paleogeographic reconstructions allow redefining the tectonic context and the main lithostratigraphic subdivisions of the Mayombe Chain. It is currently recognized that the Mayombe Chain consists of three major tectonostratigraphic domains: Western, Central and Eastern, which are prolongated by the Niari-Nyanga foreland basin. These lithounits seem to have been formed through a complex history that included: (i) Late Paleoproterozoic sedimentation, magmatism and metamorphism between 2110 and 1970 Ma related to the Eburnean tectono-thermal event;(ii) Neoproterozoic rifting magmatism and sedimentation;and (iii) Pan-African tectono-thermal event between 620 and 496 Ma leading to the amalgamation of western Gondwana. In this contribution, we review existing literature on this part of the West Congo Belt and summarize the current knowledge of its geologic setting with a focus on structure, lithostratigraphy and metamorphism. We aim to show how current research, with multidisciplinary approaches, changed the interpretation of the Mayombe with consideration to the Araçuaí-West Congo Orogenic system.
