Late paleozoic gold and copper mineralization and tectonic evolution in northwestern Xinjiang, China

Upper Paleozoic gold and copper mineralization in the northwestern Xinjiang is of great economic interest. About 300 gold and copper deposits and spots have been discovered in northwestern Xinjiang. According to their host rocks and geneses, these gold and copper mineralizations can be classified into four major types:(1)volcanic-hydrothennal massive sulfides(VMS)type;(2)ductile-shear-zone type ;(3)volcanogenic hydrothermal type ; (4)porphyry type. They form several important metallogenic belts that include the Altay polymetallic metallogenic heft, Irtysh gold metallogenic belt, Sawur gold-copper metallogenic belt, Hatu gold metallogenic belt and Baogutu gold-copper metallogenic belt. Tectonically, the gold and copper mineralization was closely associated with the subduction, collision and postcollision of the Paleoasian Ocean intervened between the Siberian block and the Junggar block. An important bimodal volcanic epoch was occurred in the back-arc basin during the Early Devonian in the southern margin of the Siberian block, during which the Ashele deposit formed. In the Middle Devomian-Early Carboniferous,S-dipping subduction of Zaisan Ocean led to formation of the Sawur arc, which triggered talc-alkaline volcanic activity, leading to formation of the volcanogene hydrothermal gold deposits. In the meantime,N-dipping subduction of Junggar Ocean led to formation of the Baogutu arc and Hatu back-arc basin,which triggered tholeiite volcanic activity and the emplacement of granitic and dioritic porphyries,leading to formation of the volcanogene hydrothermal gold deposits and porphyry Cu-Au deposits. In the Late Carboniferous to Early Permian,during the closure of the ancient ocean,land-arc collisional and extensional events in the southern margin of the Altay result in the formation of ductile-shear-zone gold deposits. The gold and copper mineralization occurred in the northwestern Xinjiang could run through the whole Late Paleozoic, which the gold and copper deposits formed in early stage of the Late Paleozoic could be superimposed by the tectonism and magmatism occurred in later land-arc collisional and postcollisional events,showing the multi-period and complexity"the gold and copper mineralization in the northwestern Xinjiang.