Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon.Here,we present new field dat...Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon.Here,we present new field data,petrography,and first comprehensible wholerock geochemistry data and discuss the protolith and tectonic significance of these serpentinites in the region.The studied rock samples are characterized by pseudomorphic textures,including mesh microstructure formed by serpentine intergrowths with cores of olivine,bastites after pyroxene.Antigorite constitutes almost the whole bulk of the rocks and is associated(to the less amount)with tremolite,talc,spinel,and magnetite.Whole-rock chemistry of the Eseka serpentinites led to the distinction of two types.Type 1 has high MgO(>40 wt%)content and high Mg#values(88.80)whereas Type 2 serpentinite samples display relatively low MgO concentration and Mg#values(<40 and 82.88 wt%,respectively).Both types have low Al/Si and high Mg/Si ratios than the primitive mantle,reflecting a refractory abyssal mantle peridotite protolith.Partial melting modeling indicates that these rocks were derived from melting of spinel peridotite before serpentinization.Bulk rock high-Ti content is similar to the values of subducted serpentinites(>50 ppm).This similarity,associated with the high Cr contents,spinel-peridotite protolith compositions and Mg/Si and Al/Si ratios imply that the studied serpentinites were formed in a subductionrelated environment.The U-shaped chondrite normalizedREE patterns of serpentinized peridotites,coupled with similar enrichments in LREE and HFSE,suggest the refertilized nature due to melt/rock interaction prior to serpentinization.Based on the results,we suggest that the Eseka serpentinized peridotites are mantle residues that suffered a high degree of partial melting in a subductionrelated environment,especially in Supra Subduction Zone setting.These new findings suggest that the Nyong series in Cameroon represents an uncontested Paleoproterozoic suture zone between the Congo craton and the Sao Francisco craton in Brazil.展开更多
The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this region....The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this region.In this contribution,we firstly report detailed study of geochemistry,isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond drillcores.The Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe_(2)O_(3)+SiO_(2)contents and variable contents of CaO,MgO and SO_(3),consistent with the presence of amphibole,chlorite,epidote and pyrite,formed during amphibolite facies metamorphism and overprinted hydrothermal event.The amphibole–pyrite BIFs are typically enriched in trace and rare earth elements(REE)compared to the amphibole BIFs,suggesting the influence of detrital materials as well as secondary hydrothermal alteration.The Post Archean Australian Shale(PAAS)-normalized REE–Y profiles of the Gouap BIFs display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.We present here the first isotopic data of BIFs within the Ntem Complex.Theδ^(30)Si_(NBS28)values of the quartz from the Gouap BIFs vary from-1.5‰to-0.3‰and from-0.8‰to-0.9‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.The quartz hasδ^(18)OV-SMOW values of 6.8‰–9.5‰(amphibole BIFs)and 9.2‰–10.6‰(amphibole–pyrite BIFs).The magnetite from the Gouap BIFs showsδ^(18)O values ranging from-3.5‰to-1.8‰and from-3‰to-1.7‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.Moreover,the pyrite grains in the amphibole–pyrite BIFs displayδ34S values of 1.1‰–1.8‰.All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity.According to their geochemical and isotopic characteristics,we propose that the Gouap BIFs belong to the Superior type.In situ U–Pb zircon dating of BIFs was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section.The Gouap BIFs were probably deposited at 2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the Caue Formation of the Minas Supergroup,Brazil.The studied BIFs have experienced regional hydrothermal activity and metamorphism at 2089±8.3 Ma during the Eburnean–Transamazonian orogeny.These findings suggest a physical continuity between the protocratonic masses of both Sao Francisco and Congo continents in the Rhyacian Period.展开更多
The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon.This iron district contains numerous iron mineralization hosted...The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon.This iron district contains numerous iron mineralization hosted by the Mewongo,Bibole,Kouambo,and Zambi banded iron formations(BIFs).These BIFs contain magnetite as the main iron ore mineral associated with pyrite,and gangue minerals are quartz with minor chlorite and amphibole.The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry.The studied BIF ore samples have a narrow range of TFe between 30.90 wt.%and 43.20 wt.%,indicating a low-grade ore.The geochemical signatures of magnetite such as low contents of base metals(e.g.,Cu,Co,V,and Zn)and low Co/Zn ratios<0.85 indicate a hydrothermal origin.Combined with the geochemical features of these BIFs,e.g.,high Fe/Ti and Fe/Al ratios(mean>600 and>75,respectively),we suggest that magnetite was derived from a mixture of seawater and~0.1%low-temperature hydrothermal fluids in an oxidizing environment.Collectively,low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore.展开更多
文摘Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon.Here,we present new field data,petrography,and first comprehensible wholerock geochemistry data and discuss the protolith and tectonic significance of these serpentinites in the region.The studied rock samples are characterized by pseudomorphic textures,including mesh microstructure formed by serpentine intergrowths with cores of olivine,bastites after pyroxene.Antigorite constitutes almost the whole bulk of the rocks and is associated(to the less amount)with tremolite,talc,spinel,and magnetite.Whole-rock chemistry of the Eseka serpentinites led to the distinction of two types.Type 1 has high MgO(>40 wt%)content and high Mg#values(88.80)whereas Type 2 serpentinite samples display relatively low MgO concentration and Mg#values(<40 and 82.88 wt%,respectively).Both types have low Al/Si and high Mg/Si ratios than the primitive mantle,reflecting a refractory abyssal mantle peridotite protolith.Partial melting modeling indicates that these rocks were derived from melting of spinel peridotite before serpentinization.Bulk rock high-Ti content is similar to the values of subducted serpentinites(>50 ppm).This similarity,associated with the high Cr contents,spinel-peridotite protolith compositions and Mg/Si and Al/Si ratios imply that the studied serpentinites were formed in a subductionrelated environment.The U-shaped chondrite normalizedREE patterns of serpentinized peridotites,coupled with similar enrichments in LREE and HFSE,suggest the refertilized nature due to melt/rock interaction prior to serpentinization.Based on the results,we suggest that the Eseka serpentinized peridotites are mantle residues that suffered a high degree of partial melting in a subductionrelated environment,especially in Supra Subduction Zone setting.These new findings suggest that the Nyong series in Cameroon represents an uncontested Paleoproterozoic suture zone between the Congo craton and the Sao Francisco craton in Brazil.
基金the“Fundamental Research Funds for the Chinese Central Universities”(Grant No.2017CXNL03)the Chinese Scholarship Council(Grant No.2015120T19).
文摘The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this region.In this contribution,we firstly report detailed study of geochemistry,isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond drillcores.The Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe_(2)O_(3)+SiO_(2)contents and variable contents of CaO,MgO and SO_(3),consistent with the presence of amphibole,chlorite,epidote and pyrite,formed during amphibolite facies metamorphism and overprinted hydrothermal event.The amphibole–pyrite BIFs are typically enriched in trace and rare earth elements(REE)compared to the amphibole BIFs,suggesting the influence of detrital materials as well as secondary hydrothermal alteration.The Post Archean Australian Shale(PAAS)-normalized REE–Y profiles of the Gouap BIFs display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.We present here the first isotopic data of BIFs within the Ntem Complex.Theδ^(30)Si_(NBS28)values of the quartz from the Gouap BIFs vary from-1.5‰to-0.3‰and from-0.8‰to-0.9‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.The quartz hasδ^(18)OV-SMOW values of 6.8‰–9.5‰(amphibole BIFs)and 9.2‰–10.6‰(amphibole–pyrite BIFs).The magnetite from the Gouap BIFs showsδ^(18)O values ranging from-3.5‰to-1.8‰and from-3‰to-1.7‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.Moreover,the pyrite grains in the amphibole–pyrite BIFs displayδ34S values of 1.1‰–1.8‰.All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity.According to their geochemical and isotopic characteristics,we propose that the Gouap BIFs belong to the Superior type.In situ U–Pb zircon dating of BIFs was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section.The Gouap BIFs were probably deposited at 2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the Caue Formation of the Minas Supergroup,Brazil.The studied BIFs have experienced regional hydrothermal activity and metamorphism at 2089±8.3 Ma during the Eburnean–Transamazonian orogeny.These findings suggest a physical continuity between the protocratonic masses of both Sao Francisco and Congo continents in the Rhyacian Period.
基金supported by the Central South University Postdoctoral Research Fund(No.22020084)。
文摘The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon.This iron district contains numerous iron mineralization hosted by the Mewongo,Bibole,Kouambo,and Zambi banded iron formations(BIFs).These BIFs contain magnetite as the main iron ore mineral associated with pyrite,and gangue minerals are quartz with minor chlorite and amphibole.The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry.The studied BIF ore samples have a narrow range of TFe between 30.90 wt.%and 43.20 wt.%,indicating a low-grade ore.The geochemical signatures of magnetite such as low contents of base metals(e.g.,Cu,Co,V,and Zn)and low Co/Zn ratios<0.85 indicate a hydrothermal origin.Combined with the geochemical features of these BIFs,e.g.,high Fe/Ti and Fe/Al ratios(mean>600 and>75,respectively),we suggest that magnetite was derived from a mixture of seawater and~0.1%low-temperature hydrothermal fluids in an oxidizing environment.Collectively,low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore.