Regional Metallogenic System In The Bikou Terrane

This Dissertation focuses on the relationship between tectonic evolution and metallogeny in the Bikou Terrane, and a series of field and experimental work have been leaded on the rock formations and regional metallogenic systems(including banded iron formation-hosted iron ore deposit, volcanic-associated massive sulphide deposits, sedimentary silicon deposits and orogenic gold deposits) in the Bikou Terrane, such as detailed geological investigation, geochemistry, U-Pb geochronology, Hf isotopes, electron probe, in-situ LA-ICP-MS. The conclusions show as follows:(1) The Neo-Archean continental nucleus was made up of Yudongzi Group and intrusive granites, which also represented the granite-greenstone belt. Yudongzi Group was metamorphic product of marine volcanic rocks and formed at 2.6 Ga, the BIF-hosted iron ore deposit also formed in this geological process. EPMA and LA-ICP-MS for magnetite from iron ore deposit show it belongs to iron deposits of metamorphic volcanic-sedimentary rock, which is also call Algoma-type.(2) The massive Neoproterozoic magmatic rocks compose the main body of the Bikou Terrane, and these rocks were mainly formed in a rifting setting or a subducted island arc. The bimodal volcanic rocks keep genetic connection with the VMS deposits in the Bikou Terrane. The basic volcanic rocks(spilite) are related to Besshi type of VMS deposits, such as Xujiagou, Yangba, Damaoping and Baizao deposits, while the intermediate-felsic volcanic rocks(ceratophyre and quartz-ceratophyre) are related to Kuroko type of VMS deposits, like Donggouba and Shanping deposits. The LA-ICP-MS analyses show higher Pb, Bi, Ag contents of chalcopyrite and Co/Ni<1 of pyrite in Kuroko type rather than Beshhi type of VMS deposit.(3) The northern margin of the Bikou Terrane was continental rift in the Late Paleozoic. According to the petrology, geochemistry, U-Pb geochronology and Hf isotopes of the detrital zircons of the Devonian chert in the Mianlue Suture Zone, we inferred that the chert forming in different geological time were formed by the deposition of deep Si-rich fluid and the debris from Neoproterozoic magmatic rocks in the South China Block(especially in the Bikou Terrane), and these cherts with different time inferred that the beginning of the rifing in the east of the northern Bikou Terrane is earlier than that in the west. The chert in the Mianlue Suture is quite pure, and commonly the content of SiO2 is higher than 95%, which lead the forming of economic silicon deposits.(4) The Bikou Terrane and the northern Mianlue Suture were involved into the intra-continental orogenic stage after the finally collision between the North and the South China Blocks. In this converted tectonic regime, it shows stress relaxation after the N-S compressive stress, which leads the sinistral shearing strike and forms the regional shearing belt. In this tectonic regime, a series of granitoids were intruded as post-collisional granites in the Bikou Terrane and in the Mianlue Suture. Meanwhile, a numerous of metamorphic fluid in the orogenic belt were formed. The fluid were transported along the shearing belt, and deposited in the suitable structural location. Finally, a series of orogenic gold deposit with different depth were formed in the Mianlue Suture Zone, like Huachanggou epizonal-mesozonal gold deposit, Yangshan epizonal orogenic gold deposit.