Chemical and mineralogical characterization and ceramic suitability of raw feldspathic materials from Dschang (Cameroon)

The chemical and mineralogical characterization of raw feldspathic materials from Dschang (Cameroon) was realized by means of X-ray diffraction, differential thermal analyses, optical and scanning electron microscopies, and analytical techniques. It was found that these materials consist of albite (43 ± 3 wt.%), microcline (41 and 26 wt.%), quartz (14.5 ± 1.5 wt.%), plagioclase (oligoclase type) (6 and 12 wt.%) and a minor content of biotite. The amount of fluxing oxides is about 12 wt.% and those of pigments are quasi-null. The ceramic suitability of these materials was assessed in the light of the obtained chemical data and physical characteristics (fusibility, viscosity, colour). The results showed that these raw materials are convenient, as fluxing compounds, for manufacturing white ceramic.KEY WORDS: Raw feldspathic materials, Mineralogy, Chemical composition, Ceramic suitability, Cameroon   Bull. Chem. Soc. Ethiop. 2010, 24(1), 39-46

Petrology, geochemistry, Ar-Ar isotopes of an arc related calk-alkaline pluton from Mamb (Pan-African Yaounde group, Cameroon): A testimony to the subduction of a hot oceanic crust

These are mineral and whole rocks analyses of metagabbros and related rocks from Mamb, Pan-African Yaounde group Cameroon

Geochemical analyses of whole-rock samples of the Bape granitoids massif , Adamawa-Yade block, Cameroon

Data description of the manuscript entitled ‘Petrology, geochemistry and geodynamics of the Pan-African high-K calc-alkaline to shoshonitic-adakitic Bape granitoids (Adamawa-Yade block, Cameroon): hot oceanic crust subduction’ by Jacqueline Numbem Tchakountea, Fuh Calystus Gentrya, Aurélie Ngamy Kamwaa, Victor Metanga, Aurélien Eglingerb, Joseph Mvondo Ondoaa, Charles Nkoumboua*The Pan-African orogeny in Cameroon yielded two belts or domains: (i) the northern domain known as Poly-Kebbi group and (ii) the southern domain or Yaoundé group have sandwiched the central Adamawa-Yade Archaean block. North-south and south-north facing subductions have yielded many Pan-African calk-alkaline and High-K calk-alkaline intrusions in this Adamawa-Yade block. This study presents the petrography and geochemistry of the longest intrusive Bape massif (60 km-long) of the Adamawa-Yade block. The peculiar feature of the Bape granitoids is the occurrence of adakitic rocks in addition to classical High-K calc-akaline to shoshonitic series. These new results and the available data allow a conclusion that this intrusion and neighbouring ones are linked to a south-north facing subduction of a hot Yaoundé oceanic crust under the Archaean Adamawa-Yade block. The geochemical data, whole-rock analyses including major elements expressed in wt.% of oxides and trace elements expressed in terms of parts per million (ppm).THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Data for: Four Pan-African plutonic sets of the Colomines gold district (East-Cameroon): Petrogenesis, K-Ar dating and geodynamic significance

Table captionsTable 1. Microprobe analyses of amphibole, biotite, plagioclase and alkali feldspar.Table 2. Chemical analyses of intrusive rock types of Colomines area.Table 3. K-Ar data obtained on biotite separates and whole-rocks of Colomines area.Table 4. Temperatures and pressures of the crystallisation of amphibole, biotite and Zr saturation of granitoids and related rocks of Colomines area.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Data for: Petrology, geochemistry, Ar-Ar isotopes of an arc related calk-alkaline pluton from Mamb (Pan-African Yaounde group, Cameroon): A testimony to the subduction of a hot oceanic crust

Data descriptionThe table I all mineral and whole rock analyses shows the microprobe analyses of amphibole, biotite, muscovite, plagioclase, epidote, garnet and rutile from metagabbros and meta-hornblendites of Mamb, Pan-African Yaounde group (Cameroon). Then table II shows the chemical compositions of the metagabbros, meta-hornblendites, biotitites (restite) and granites (leucosomes).THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Donnees nouvelles sur les laves felsiques de ngaoundere (Adamaoua, ligne du Cameroun): chronologie K-Ar et petrologie

On the Adamawa plateau (Cameroon volcanic line), alkali basalt lava flows are dated at 6.5 ± 0.2 Ma by K-Ar method. Associated phonolitic and trachytic plugs were put in place 6.8 to 6.2 ± 0.2 Ma ago. The most recent volcanic episode aged 0.91 ± 0.06 Ma yielded maars and scoria cones with associated basaltic lava flows. The microlitic groundmass of miaskitic phonolites comprise of euhedral phenocrysts nepheline, anorthoclase, hastingsite, salite-ferrosalite, sphene and apatite. In the agpaïtic phonolites, interstitial anhedral crystals of aegirine-augite, aenigmatite and lavenite mould euhedral phenocrysts of anorthoclase, nepheline, sodalite and noseane. Through the felsic lava series, pyroxene defines an evolutionary trend from salite to aegirine augite with gradual acmite enrichment. Amphibole trend shows a limited range (kaersutite in trachytic lavas and hastingsite in miaskitic phonolites). Genetically, phonolites are linked to trachytes by crystal fractionation mechanism but this mechanism alone cannot account for the overall Na2O and MnO enrichments in lavenite-bearing agpaitic phonolites. At this stage, a migration of dissolved volatilemetal complexes may have accompanied crystal fractionation to produce lavenite: (Na, Ca)2(Mn, Fe2+)(Zr, Nb, Ti)Si2O7(OH, F).Keywords: agpa ïtic phonolites, migration of volatile-metal complexes, laveniteRésuméDans la rgion de Ngaoundr, (plateau de l'Adamaoua, Ligne volcanique du Cameroun), des coules de basaltes alcalins dats 6,5 ± 0,2 Ma sont accompagnes de necks et pitons trachytiques et phonolitiques, phonolites dates 6,8 et 6,2 ± 0,2 Ma par la mthode K-Ar. L'pisode ultime des cnes stromboliens, maars et coules basaltiques remonte 0,91 ± 0,06 Ma. L'ensemble des laves appartient une srie alcaline sodique. La msostase des phonolites miaskitiques englobe des phnocristaux automorphes d'anorthose, nphline, sodalite, nosane, hastingsite, salite-ferrosalite, sphne et apatite. Dans les phonolites agpaïtiques, les cristaux interstitiels xnomorphes de pyroxnes agyriniques, anigmatite et lavnite moulent les cristaux automorphes d'anorthose, sanidine, nphline, sodalite et nosane. Dans l'ensemble des laves felsiques, le pyroxne volue des salite et ferrosalite dans les trachytes et phonolites miaskitiques aux augite agyrinique et agyrine dans les phonolites agpaïtiques. La variation des compositions des amphiboles est limite (kaersutite dans les trachytes hastingsite dans les phonolites). Sur le plan ptrogntique, les phonolites drivent des trachytes par un mcanisme de cristallisation fractionne. A la fin de la diffrenciation, ce mcanisme a t coupl la migration des complexes mtaux-volatiles dissous dans les fluides magmatiques pour former des phonolites hyperalcalines agpatiques lavnite, subnsosilicate complexe de Ti et Zr de formule (Na, Ca)2(Mn, Fe2+)(Zr, Nb, Ti)Si2O7(OH, F). Mots cls: phonolites agpaïtiques, migration des complexes mtaux-volatiles, lavnite African Journal of Science and Technology Vol. 5(2) 2004: 113-12

Pre-collisional geodynamic context of the southern margin of the Pan-African fold belt in Cameroon

International audienceWe reassess the geodynamic context close to the Congo craton during the pre-collisional period of the Pan-African orogeny from whole-rock major and trace element compositions and isotopic data obtained in the westward extension of the Yaounde series (Boumnyebel area, Cameroon). The series consists of metasediments (micaschists, minor calc-silicate rocks and marbles) and meta-igneous rocks (hornblende gneisses, amphibolites, metagabbros, pyroxenites and talcschists) recrystallized under high-pressure conditions.Chemically, the micaschists correspond to shales and greywackes similar to the Yaounde high-grade gneisses. 87Sr/86Sr initial ratios (0.7084–0.7134), moderately negative εNd(620 Ma) values (−5.75 to −7.81), Nd model ages (1.66 < TDM < 1.74 Ga) and radiometric ages point to the conclusion that the Yaounde basin was filled with siliciclastic sediments derived from both reworked older continental crust (Palaeoproterozoic to Archaean in age) and Neoproterozoic juvenile volcanogenic material. This occurred in the same time span (625–1100 Ma) as the deposition of the Lower Dja, Yokadouma, Nola and Mintom series (Tonian–Cryogenian). Dolomitic marble associated with mafic/ultramafic rocks and characterized by high Cr (854–1371 ppm) and Ni (517–875 ppm) contents, are considered to result from chemical precipitation in relation with submarine magmatic activity.Talcschists (orthopyroxenitic to harzburgitic in composition) show primitive-mantle-normalized multi-element patterns with significant negative Nb–Ta anomalies, and slopes similar to that of average metasomatically altered lithospheric mantle. These rocks could be mantle slices involved in the collision tectonics. Amphibolites show the compositions of island-arc basalts with systematic negative Nb–Ta anomalies, 87Sr/86Sr initial ratios mostly <0.7047 and positive εNd(620 Ma) values (+1.41 to +6.58). They are considered to be the expression of incipient oceanisation to the north of the Congo craton during the early Neoproterozoic. Hornblende gneisses show andesitic compositions, with high 87Sr/86Sr initial ratios (0.7105 and 0.7125) and low εNd(620) values (−14.0 and −20.7) suggesting that their genesis involved juvenile and recycled older crustal materials. Syn-metamorphic metagabbro (Mamb) and metadiorite (Yaounde) intrusions show negative Nb–Ta negative anomalies but enrichment in light rare-earth and large-ion lithophile elements, suggesting a metasomatized mantle source. Overall, meta-igneous rocks seem to be representative of distinct magmatic events that accompanied the evolution of the Yaounde sedimentary basin, from opening and oceanisation to convergence and closure in relation with the collisional process.These data suggest that the Yaounde basin should not be considered as a back-arc basin, but more likely represents the expression of extensional processes to the north of the Congo craton, which led to rifting, fragmentation and limited oceanisation. In this view, the Adamawa-Yade block may represent a micro-continent detached from the Congo craton during the early Neoproterozoic

Characterization of clays from Mezafe and Mengono (Ne-Libreville, Gabon) for potential uses in fired products

International audienceClay materials may contribute to promote the sustainable development of population accommodations in a developing country as Gabon. They are low cost versatile raw materials for the building industry. A mineral survey led to the discovery of clay occurrences along the highway Libreville-Cocoa-beach from Mezafe to Mengono (NE Libreville). These clays were characterized by chemical analyses, grain size distribution (sieving, sedimentometry and Fraunhofer laser light scattering), plasticity, X-ray diffraction on crude powder and oriented fine fractions (natural, glycolated or heated at 550 degrees C), Fourier transform infrared spectroscopy, adsorption-desorption of nitrogen, cation exchange capacity, and scanning electron microscopy. Samples were fired from 900 to 1150 degrees C and a few properties such as water absorption, linear shrinkage and bending strength were determined. Mineralogically, raw clay samples are made up mainly of quartz, kaolinite, illite and chlorite. Accessories are orthoclase, anatase, ilmenite, magnetite, goethite, lepidocrocite, Fe-Al sulfate, La-Ce rich crandallite or a mineral likely related to Ce-belovite, pyrite, Cu-Fe rich silicate, carbonates, bitumen and other organic matters. The decrease of SiO2 contents and the increase of Al2O3 contents of fractions under 125 mu m suggest the presence of large size quartz grains and fine kaolinite particles. The sum kaolinite + illite + chlorite increases from 25-42% in crude samples to 37-48% in clay fractions (135 mu m) with an increment rate of 15-40% at Mezafe and above 50% at Mengono. Thus, screening only can yield clay-rich raw materials similar to some European commercial kaolins. Results of firing from 900 to 1150 degrees C show that water absorption, linear shrinkage and bending strength values are in the norm of tiles and fired earth. Only one sample's properties need to be enhanced for terra-cotta production

Geochemical and Mineralogical Characteristics of the Mayouom Kaolin Deposit, West Cameroon

International audienceGeological, mineralogical and geochemical studies were carried out on clay materials of the same pit from Mayouom kaolin deposit located within a mylonitic shear zone about 30 km north of Foumban town (western Cameroon), in order to define their characteristics, the ore genesis and its economic interest. Seven samples were studied using different techniques: description of the pit, optical microscopy, microprobe analysis, and bulk chemical analyses. Two different facies (sandy kaolin and sand-poor kaolin) were observed in the field. Microscopical observations show that the mylonitic schistosity is well conserved in sandy clays, while sand-poor clays reveal the transformation of muscovite/illite into kaolinite. Quantitative and qualitative mineralogical investigations reveal kaolinite as predominant mineral, associated to quartz + illite/muscovite + anatase ± hematite ± Ba, Sr-hydroxyapatite. Kaolinite (54% and 81–84% respectively) mineral presents homogeneous shape and a good crystallinity. REE pattern show a Ce negative anomaly marking a reductive milieu of alteration. All these results point out a hydrothermal alteration of feldspars and mica-rich rocks as petrogenetic origin of kaolins. Sandy kaolin comes from mylonites basement while sand-poor kaolin is related to the alteration of magmatic intrusive shape veins. Due to its high kaolinite content (up to 85%) and the low iron mineral content (less than 1.5%), Mayouom kaolin is a suitable raw material for white burning industrial clays