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Figure1. Geological map of the pre-drift Gondwana showing the Congo craton in Cameroon and the northern part of São Francisco craton of Brazil (modified after Ebah Abeng et al., 2012).
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Meta-ultramafic rocks from the Paleoproterozoic Nyong Series (SE Cameroon) were investigated in this study. The aim was to study trace and rare earth elements (REEs) patterns in these rocks. A layered sequence exposed on a cliff face was mapped. Samples from the various horizons were collected and subsequently analysed in the laboratory for their p...
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Citations
... Contrary to the Caico gneisses, which have higher Yb N , Rb/Sr, K 2 O/Na 2 O, and lower A/CNK, (La/Yb) N and Zr/Sc ( Table 2), gneisses of the Ako'ozam-Njabilobe area have lower Yb N , Rb/Sr, K 2 O/Na 2 O and higher A/CNK, (La/Yb) N and Zr/Sc, akin to late Archean calc-alkaline granites [43]. The Nb/Th < 1 and Th/Yb >1 of the studied gneisses indicate that the magma that sourced their protolith is mantle-derived with some degree of crustal contamination [45]. ...
... (8,28,30) The low concentrations of High Field Strength Elements (HFSE); Zr and Sr implied that the parent magma is depleted in these incompatible elements. (31) The ratios Nb/Th and Th/Yb ranges from 0.7-2.4 and 0.8-28.6 respectively and these values greater than 1 are indicative of crustal contamination of mantle derived magma. ...
... These variations could have resulted from leaching of some of the mobile and immobile elements (Compatible and Incompatible elements) during alteration(metamorphism and weathering processes) of the parent rocks. (28,33) The spidergram also revealed derivation of parent magma from a depleted mantle (34) with evidence of metasomatism as seen from the enrichment of La, Pr, Sm and Cs (31) as well as contamination of the mantle materials with crustal materials. The concentration of some trace elements in the talcose rocks also compared well with talcose rocks from other places. ...
... The REE patterns shown by the rocks indicated crustal contamination and plagioclase fractionation with more LREE fractionation compared to the HREE. (28,31) Variations in the more mobile incompatible Large Ion Lithophile Elements (LILE) observed in Figure 7A and near flat signature of the relatively immobile High Field Strength Elements (HFS) support evidences for metasomatism/hydrothermal alterations during the prevalent Pan African orogeny. (36,37) Therefore, the trends observed for the LILE, HFSE and REE suggest possible contamination or mixing of crustal and mantle materials during the formation of parent rock. ...
Background/Objectives: Talcose rocks within Precambrian Basement Complex serve as relics of Archean greenstones. alterations associated with polycyclic-orogenies that affected this complex is studied to understand miner-alogical and geochemical alterations. Methods: Five fresh samples of talcose rocks were collected during field mapping. These samples were cut into thin sections to reveal modal mineralogy, altered minerals and degree of alteration of such minerals. Mineral phase identification of the talcose rocks was conducted using X-ray Broker D8 ADVANCE diffractometer while whole rock analysis was carried out using Inductively Coupled Plasma Mass Spectrometry. Findings: Lithological relationship revealed from field evidence showed that the talc bodies occurred in close association with micaceous schist. The mineral assemblage of talc, tremolite, actinolite, chlorite and calcite suggest low grade green-schist metamorphic facies from possible hydrothermal alteration. Geochemi-cal results revealed the following range of concentrations; SiO 2 42.19-59.03%; Al 2 O 3 1.1-11.8%; Fe 2 O 3 7.64-9.56%; MgO 24.47-26.639%; Ni 594-1207ppm; Co 43.2-113.9ppm; Sn 6-41ppm; V 32-75ppm and Zr 1.3-58.7ppm, and these are typical of talcose rocks. Petrogenetic studies suggest a komatiitic origin with a peridotitic komatiite precursor for the talc-chlorite-tremolite schist. Enrichment in LREE, depletion in HREE and a negative Eu anomaly suggest alteration of the parent magma for the talcose rock and plagioclase fractionation. The trends observed for the LILE, HFSE and REE suggest possible contamination or mixing of crustal and mantle materials during the formation of the protolith. https://www.indjst.org/ 4244 Omotunde et al. / Indian Journal of Science and Technology 2020;13(40):4244-4261 Ni and Co concentrations are higher than average crustal values with implication for ultrabasic to basic magma composition for the komatiitic progenitor and also suggestive of possible mineralisation. Conclusion: Mineralogical examination has revealed a talc-chlorite-tremolite composition for the talcose rocks with peridotitic komatiite precursory while geochemical composition supported ultrabasic magmatism similar to those with the Ilesha schist belt.
... (8,28,30) The low concentrations of High Field Strength Elements (HFSE); Zr and Sr implied that the parent magma is depleted in these incompatible elements. (31) The ratios Nb/Th and Th/Yb ranges from 0.7-2.4 and 0.8-28.6 respectively and these values greater than 1 are indicative of crustal contamination of mantle derived magma. ...
... These variations could have resulted from leaching of some of the mobile and immobile elements (Compatible and Incompatible elements) during alteration(metamorphism and weathering processes) of the parent rocks. (28,33) The spidergram also revealed derivation of parent magma from a depleted mantle (34) with evidence of metasomatism as seen from the enrichment of La, Pr, Sm and Cs (31) as well as contamination of the mantle materials with crustal materials. The concentration of some trace elements in the talcose rocks also compared well with talcose rocks from other places. ...
... The REE patterns shown by the rocks indicated crustal contamination and plagioclase fractionation with more LREE fractionation compared to the HREE. (28,31) Variations in the more mobile incompatible Large Ion Lithophile Elements (LILE) observed in Figure 7A and near flat signature of the relatively immobile High Field Strength Elements (HFS) support evidences for metasomatism/hydrothermal alterations during the prevalent Pan African orogeny. (36,37) Therefore, the trends observed for the LILE, HFSE and REE suggest possible contamination or mixing of crustal and mantle materials during the formation of parent rock. ...
Background/Objectives: Talcose rocks within Precambrian Basement Complex serve as relics of Archean greenstones. alterations associated with polycyclic-orogenies that affected this complex is studied to understand mineralogical and geochemical alterations. Methods: Five fresh samples of talcose rocks were collected during field mapping. These samples were cut into thin sections to reveal modal mineralogy, altered minerals and degree of alteration of such minerals. Mineral phase identification of the talcose rocks was conducted using X-ray Broker D8 ADVANCE diffractometer while whole rock analysis was carried out using Inductively Coupled Plasma Mass Spectrometry. Findings: Lithological relationship revealed from field evidence showed that the talc bodies occurred in close association with micaceous schist. The mineral assemblage of talc, tremolite, actinolite, chlorite and calcite suggest low grade greenschist metamorphic facies from possible hydrothermal alteration. Geochemical results revealed the following range of concentrations; SiO2 42.19-59.03%; Al2O3 1.1 - 11.8%; Fe2O3 7.64-9.56%; MgO 24.47-26.639%; Ni 594-1207ppm; Co 43.2-113.9ppm; Sn 6-41ppm; V 32-75ppm and Zr 1.3-58.7ppm, and these are typical of talcose rocks. Petrogenetic studies suggest a komatiitic origin with a peridotitic komatiite precursor for the talc-chlorite-tremolite schist. Enrichment in LREE, depletion in HREE and a negative Eu anomaly suggest alteration of the parent magma for the talcose rock and plagioclase fractionation. The trends observed for the LILE, HFSE and REE suggest possible contamination or mixing of crustal and mantle materials during the formation of the protolith. Ni and Co concentrations are higher than average crustal values with implication for ultrabasic to basic magma composition for the komatiitic progenitor and also suggestive of possible mineralisation. Conclusion: Mineralogical examination has revealed a talc-chlorite-tremolite composition for the talcose rocks with peridotitic komatiite precursory while geochemical composition supported ultrabasic magmatism similar to those with the Ilesha schist belt.
