Metallogenesis Of Gold Deposits In Tugurige Of Urad Zhongqi, Inner Mongolia

Xing’an-Mongolia Orogenic Belt(XMOB),which located in Mid-Eaetern Central Asia Orogenic Belt(CAOB), belongs to an important part of the Central Asia Metallogenic Zone,meanwhile.The Tugurige area forms the western part of XMOB and is located in the northern margin of the North China Plate, belongs to Chagancilao-Bayinhanggai gold metallogenic belt. Opinions vary and each sticks to his argument for the tectonic evolution of the northern margin of the North China Plate during Paleozoic, which restrict the research on mineralization in XMOB to a certain extent. In addition, the study on metallogenesis of gold deposits in this area is only concentration of a certain metallogenic essential factor or the survey to certain gold deposit and there were few comparative studies on same types of gold deposits in this region or typical gold deposit in other area. This paper emphatically researches on petrography,geochronology and geochemistry of Paleozoic magmatic rocks in study area in order to reduce the tectonic evolution of western and central Inner mongolia during the Paleozoic. Meanwhile,comparative study on Tugurige gold-deposit and Zhungashun god-deposit were discussed in this paper, which deepening cognition to gold metallogenic background,geological features of ore deposit,ore genesis and metallogenic model. It lay a foundation of further study on late Paleozoic metallogenesis of gold deposits in western and central Inner mongolia.In Early Paleozoic,western and central Inner mongolia is in subduction-accretionary stage of Paleo-Asian Ocean. The Late Cambrian(513Ma) amphibolite in Hadahushu area, the Early Silurian(433Ma) granodiorite in Zhungashun area and the Middle Silurian(426Ma) albite granite in Huhechulu area represent the island arc magmatism related with ocean suduction in study area during this period.The bimodal intrusive rocks which composed of 300~297Ma monzogranite,286 Ma porphyritic granite and 286 Ma gabbroic diorite record a transitional period from collisional compression to post-collisional extension. Among them, the monzogranite and porphyritic granite have characteristics of adakitic rocks and were generated during the partial melting of juvenile crustal material. The 275~266Ma ultrabasic-basic-medium acid complex in study area generated in a tectonic setting of post-collisional extension. The generation of the complex is closely related to crustal-mantle magma mixing and the fractional crystallization of the mafic mineral such as hornblende played an important role in magma evolution.Study on the fluid inclusions of Tugurige and Zhungashun gold-deposit shows that the ore-forming fluid has characteristics of low salinity and low density, it is a NaCl-H2O-CO2 system and fluid immiscibility occurred during the ore forming process. The metallogenic environment display characteristics of middle temperature and middle pressure, the metallogenic depth is middle depth.The δ34S value of pyrite from Tugurige and Zhungashun gold-deposit can be divided into two groups which range of-0.5‰ to-2.9‰ and-5.4‰ to-9.0‰, indicating that the metallogenic material mainly derived from mantle and Baoyintu Group. Pb isotope composition of pyrite has characteristic of crust-mantle mixed Pb and maybe derived from the mixture of mantle-derived lead and subduction zone lead. Studies on H-O isotopes and fluid inclusion indicate ore-forming fluids are mainly mantle fluids and magmatic water, with some meteoric water joining in the later stage.With metallogenic epoch of Triassic,Tugurige and Zhungashun gold deposits formed in the dynamics environment of post-collisional extension. They have many similar features with orogenic gold deposit which include ore-hosting rock,mineral assembly,ore-controlling structure and regional metallogenic background etc. So,they can be classified as the typical orogenic gold deposit defined by Groves in 1998.Middle Permian mafic and ulramafic rocks formed in the area of the Tugurige gold deposit. They formed in a post collision extension setting. The ultramafics are rich in chalcopyrite nickel pyrite and other metal minerals, and have certain ore potential for cobalt and nickel.