This study focuses on the metabasite rocks of the Nemba Complex of the Mayombe belt, an African segment of Araçuaï-West Congo Orogen (A-WCO) extending from the southwest of Gabon to the northwest of ...This study focuses on the metabasite rocks of the Nemba Complex of the Mayombe belt, an African segment of Araçuaï-West Congo Orogen (A-WCO) extending from the southwest of Gabon to the northwest of Angola. These metabasite rocks outcrops are in southwestern Congo along the Loukounga river. The Nemba complex is of Neoproterozoic age and represents the lower part of the west congolian Supergroup. The objective of this study is to constrain the geodynamic context of the Nemba complex from the petrology and geochemistry of the metabasites sampled in the Loukounga River. The observed rocks are composed of amphibolites, metagabbros, epidotites and greenschists and are affected by folding accompanied by flux schistosity and crenulation schistosity. Geochemical analyzes show that the rocks have a basic to ultrabasic chemical composition with SiO<sub>2</sub> contents between 41.85% and 58.23%. The geochemical composition of the major and traces elements shows that the rocks are basalts, basaltic andesites and andesites. The magma shows enrichment in LREE, LILE and depletion in HREE and HFSE. The multielement spectra show negative anomalies in Nb-Ta, Ti and a relatively low Nb/La ratio which characterize a lithospheric source contaminated by continental crust. Traces elements discrimination plots show that Loukounga metabasites are emplaced in intraplate geodynamic context like that associated with the basalts of the trap-types continental shelves and are possibly derived from mantle plumes contemporaneous with or slightly prior to magmatism.展开更多
The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential...The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential of the Ina batholith syenite as a feldspar minerals resource for industrial use through petrographic and geochemical characterization. Most of the rocks are grey coloured and consist of shimmering feldspar phenocrysts in a fine-grained ferromagnesian matrix. Petrography reveals the presence of two major syenite facies: a widely distributed porphyritic syenite and a less-abundant massive syenite. These facies are dominated by phenocrysts of sub-automorphic perthitic orthoclase. Its malgachite face is due to the presence of numerous inclusions of opaque minerals observed by scanning electron microscopy (ESEM-EDX). Plagioclase phenocrysts have a zonal texture characterised microscopically by an oscillatory compositional zonation. Biotite, hornblende and augite, identified by X-ray powder diffraction, are finely disseminated in the feldspar matrix. Quartz appears as small automorphic crystals with maximum abundance of about 4 wt%. The XRF chemical composition reveals, alongside silica (59.29 wt% to 63.27 wt%), significant proportion of alumina (15.82 wt% to 19.80 wt%), potassium and sodium oxides considered as fluxing elements (K<sub>2</sub>O + Na<sub>2</sub>O ≥ 10 wt%). The K<sub>2</sub>O/Na<sub>2</sub>O ratio varies between 1.65 and 5.51 (average 2.58). Iron and titanium oxides (1 ≥ wt% Fe<sub>2</sub>O<sub>3</sub> + TiO<sub>2</sub> ≥ 5), harmful in ceramic industry, are high as in most other feldspathic sources. The characteristics of the Ina syenite are close to most of the syenite ores used worldwide for ceramics and glass raw materials and necessitates purification and beneficiation treatments. Others rock types have been identified at the study site (granite, monzonite, granodiorite) and are considered as inappropriate as a source of industrial feldspars.展开更多
文摘This study focuses on the metabasite rocks of the Nemba Complex of the Mayombe belt, an African segment of Araçuaï-West Congo Orogen (A-WCO) extending from the southwest of Gabon to the northwest of Angola. These metabasite rocks outcrops are in southwestern Congo along the Loukounga river. The Nemba complex is of Neoproterozoic age and represents the lower part of the west congolian Supergroup. The objective of this study is to constrain the geodynamic context of the Nemba complex from the petrology and geochemistry of the metabasites sampled in the Loukounga River. The observed rocks are composed of amphibolites, metagabbros, epidotites and greenschists and are affected by folding accompanied by flux schistosity and crenulation schistosity. Geochemical analyzes show that the rocks have a basic to ultrabasic chemical composition with SiO<sub>2</sub> contents between 41.85% and 58.23%. The geochemical composition of the major and traces elements shows that the rocks are basalts, basaltic andesites and andesites. The magma shows enrichment in LREE, LILE and depletion in HREE and HFSE. The multielement spectra show negative anomalies in Nb-Ta, Ti and a relatively low Nb/La ratio which characterize a lithospheric source contaminated by continental crust. Traces elements discrimination plots show that Loukounga metabasites are emplaced in intraplate geodynamic context like that associated with the basalts of the trap-types continental shelves and are possibly derived from mantle plumes contemporaneous with or slightly prior to magmatism.
文摘The syenite from Ina (Central region of Cameroon) constitutes a 1000 km<sup>2</sup> syntectonic batholith intruded in the Paleoproterozoic granitic basement. The aim of this work is to assess the potential of the Ina batholith syenite as a feldspar minerals resource for industrial use through petrographic and geochemical characterization. Most of the rocks are grey coloured and consist of shimmering feldspar phenocrysts in a fine-grained ferromagnesian matrix. Petrography reveals the presence of two major syenite facies: a widely distributed porphyritic syenite and a less-abundant massive syenite. These facies are dominated by phenocrysts of sub-automorphic perthitic orthoclase. Its malgachite face is due to the presence of numerous inclusions of opaque minerals observed by scanning electron microscopy (ESEM-EDX). Plagioclase phenocrysts have a zonal texture characterised microscopically by an oscillatory compositional zonation. Biotite, hornblende and augite, identified by X-ray powder diffraction, are finely disseminated in the feldspar matrix. Quartz appears as small automorphic crystals with maximum abundance of about 4 wt%. The XRF chemical composition reveals, alongside silica (59.29 wt% to 63.27 wt%), significant proportion of alumina (15.82 wt% to 19.80 wt%), potassium and sodium oxides considered as fluxing elements (K<sub>2</sub>O + Na<sub>2</sub>O ≥ 10 wt%). The K<sub>2</sub>O/Na<sub>2</sub>O ratio varies between 1.65 and 5.51 (average 2.58). Iron and titanium oxides (1 ≥ wt% Fe<sub>2</sub>O<sub>3</sub> + TiO<sub>2</sub> ≥ 5), harmful in ceramic industry, are high as in most other feldspathic sources. The characteristics of the Ina syenite are close to most of the syenite ores used worldwide for ceramics and glass raw materials and necessitates purification and beneficiation treatments. Others rock types have been identified at the study site (granite, monzonite, granodiorite) and are considered as inappropriate as a source of industrial feldspars.
