华北克拉通北缘三叠纪金矿床地质特征、物质来源与控制因素

The Triassic is an important metallogenic period of the North China Craton (NCC). Triassic gold deposits are widely distributed on the northern margin of the NCC, forming an EW-striking gold metallogenic belt with a length of ~ 1500km, including Wulashan-Daqingshan, Zhangjiakou, Jidong-Liaoxi, Qingchengzi and Jiapigou gold districts. This gold belt is mainly hosted by the Neoarchean-Mesoproterozoic metamorphic rocks and Mesozoic granites. The gold deposits are dominated by quartz-vein mineralization, accompanied by altered-rock type mineralization; the mineralization of the western and central sections of the gold belt are characterized by gold or gold-molybdenum mineralization, whereas the eastern section is dominated by gold polymetallic mineralization. Geochronology data show that the Triassic gold deposits in the northern margin of the NCC were mainly formed in the Late Triassic (240 ~ 220Ma) ; the characteristics of fluid inclusions indicate that the ore-forming fluids have characteristics of medium temperature, low salinity, and low density. It belongs to the H20-NaCl-C02 ± CH4 system, and the phase-separation may be the main mechanism of gold precipitation in quartz-vein type gold deposits; the hydrogen and oxygen isotopic composition shows that the ore-forming fluid was magmatic water or metamorphic water in the early stage and was mixed with atmospheric water in the later stage. 'Hie carbon, sulfur, lead, helium and argon isotopes of the ores and the neodymium and hafnium isotopic compositions of the mineralization-related rocks indicate that the ore-forming fluids, materials, and the mineralization-related rocks are all related to crust-mantle mixing. The contribution of mantle-derived materials and fluids is caused by regional Triassic rnagmatism, moreover, the crust-derived components mainly come from host rocks. The formation of the Triassic gold deposits in the northern margin of the NCC generally respond to the post-orogenic extension of the Central Asian Orogenic Belt. Northern margin of NCC was affected by the post-collision extension of the Central Asian Orogenic Belt in the Late Triassic, causing the initial lithospheric thinning occurred along the northern margin. Series deep-large faults, alkaline, and alkaline granites which simultaneously formed provided superior conditions for the regional gold mineralization. Furthermore, the eastern part of the northern marginal gold belt may also be affected by the collision between the Yangtze Craton and the NCC, which is the main reason for the difference in the mineralization characteristics of the central and western gold districts.