The gold-deposit of shearzone-type(GST)resulting predominantly from shearing is controlled by ductile shearzones,and its general characteristics are discussed in this paper.GST can be classified differently according ...The gold-deposit of shearzone-type(GST)resulting predominantly from shearing is controlled by ductile shearzones,and its general characteristics are discussed in this paper.GST can be classified differently according to its characteristics,and the the authors offer three ways,namely the classification based on the characterisics and genesis of ore-deposits,on the occurrence of shear zones,and on the formation conditions of shear zones.展开更多
The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed f...The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed for the kinematic evolution of the sinistral and dextral shear phases in the Tikar Plain, thus in the FBSZ;early dextral and late sinistral shear phases for some authors and early sinistral and late dextral shear for others. Moreover, the NMSZ kinematic evolution implication on the mylonitization P-T-t path in the area seem to be problematic and the present paper aim is to clear enough those problems;since this shear zone is the main mylonitic corridor that registered the left and right lateral movement in this area. The NMSZ comprises amphibolites, protomylonites, strict sensus mylonites(garnet-kyanite-sillimanite mylonite and garnet-pyroxene mylonite), ultramylonites kyanite-sillimanite and garnet-kyanite-sillimanite gneiss. Field structures testify that the investigated area recorded three deformation phases:(i) the D1deformation phase which is marked by NW-SE to N-S trending S1metamorphic foliation with low to moderate dips(15°–45°) that was transposed during the D2phase, is responsible for a regional metamorphism whose mineral paragenesis is garnet-kyanite-sillimanite;(ii) the early sinistral NNE-SSW to NE-SW shear phase D2marked by S2metamorphic and mylonitic foliations;responsible for, L2stretching mineral lineation, F2fold axes and B2boudins structures;(iii) the late dextral NE-SW shear phase D3, characterized by F3folds, B3boudins and ductile dextral C3shear planes. Mineral paragenesis garnet + kyanite + sillimanite and microstructures within gneiss testify that this rock underwent high grade regional metamorphism whose peak conditions are estimated at 11.5–13.5 kbar/850–900 ℃. After the peak of metamorphism gneiss was overprinted by high grade pressure mylonitization during the early sinistral and late dextral shear deformations. Microstructural data here indicate a high-grade mylonitization whose P-T conditions are estimated at least at around 10 kbar/750 ℃ attained during the D2. Shear markers, indicates that the studied area underwent an intense mylonitization at deep crustal deformation level, probably at the ductile-brittle boundary structural level during a major dextral shear deformation.展开更多
文摘The gold-deposit of shearzone-type(GST)resulting predominantly from shearing is controlled by ductile shearzones,and its general characteristics are discussed in this paper.GST can be classified differently according to its characteristics,and the the authors offer three ways,namely the classification based on the characterisics and genesis of ore-deposits,on the occurrence of shear zones,and on the formation conditions of shear zones.
文摘The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed for the kinematic evolution of the sinistral and dextral shear phases in the Tikar Plain, thus in the FBSZ;early dextral and late sinistral shear phases for some authors and early sinistral and late dextral shear for others. Moreover, the NMSZ kinematic evolution implication on the mylonitization P-T-t path in the area seem to be problematic and the present paper aim is to clear enough those problems;since this shear zone is the main mylonitic corridor that registered the left and right lateral movement in this area. The NMSZ comprises amphibolites, protomylonites, strict sensus mylonites(garnet-kyanite-sillimanite mylonite and garnet-pyroxene mylonite), ultramylonites kyanite-sillimanite and garnet-kyanite-sillimanite gneiss. Field structures testify that the investigated area recorded three deformation phases:(i) the D1deformation phase which is marked by NW-SE to N-S trending S1metamorphic foliation with low to moderate dips(15°–45°) that was transposed during the D2phase, is responsible for a regional metamorphism whose mineral paragenesis is garnet-kyanite-sillimanite;(ii) the early sinistral NNE-SSW to NE-SW shear phase D2marked by S2metamorphic and mylonitic foliations;responsible for, L2stretching mineral lineation, F2fold axes and B2boudins structures;(iii) the late dextral NE-SW shear phase D3, characterized by F3folds, B3boudins and ductile dextral C3shear planes. Mineral paragenesis garnet + kyanite + sillimanite and microstructures within gneiss testify that this rock underwent high grade regional metamorphism whose peak conditions are estimated at 11.5–13.5 kbar/850–900 ℃. After the peak of metamorphism gneiss was overprinted by high grade pressure mylonitization during the early sinistral and late dextral shear deformations. Microstructural data here indicate a high-grade mylonitization whose P-T conditions are estimated at least at around 10 kbar/750 ℃ attained during the D2. Shear markers, indicates that the studied area underwent an intense mylonitization at deep crustal deformation level, probably at the ductile-brittle boundary structural level during a major dextral shear deformation.
