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SCIEI北大核心CSCD

三叠纪是华北克拉通重要的成矿期,三叠纪金矿主要分布在华北克拉通北缘,构成一条近东西向延伸、长约1500km的金成矿带,其中包括乌拉山-大青山、张家口、冀东-辽西、青城子及夹皮沟等多个金矿集中区。华北克拉通北缘三叠纪金矿带的赋矿围岩主要为新太古代-中元古代变质岩系和中生代花岗岩类,金矿床以石英脉型矿化为主,伴随蚀变岩型矿化;中、西段金矿集中区矿化组合表现为金或金钼矿化,东段则以金多金属矿化为主。同位素年代学资料表明,该带金矿主要形成于晚三叠世(240~220Ma);流体包裹体特征表明,成矿流体具中温、低盐度、低密度特征,属于H_(2)O-NaCl-CO_(2)±CH_(4)体系,相分离作用可能是石英脉型金矿金沉淀的主要机制;氢-氧同位素组成进一步表明,成矿流体早期为岩浆水或变质水,后期混入了大气降水。矿石碳、硫、铅、氦-氩同位素及金矿集中区内成矿相关岩体的钕、铪同位素组成表明,华北克拉通北缘三叠纪金矿床的成矿流体和成矿物质均与壳-幔混合作用有关,其中,幔源物质及流体的贡献与区域三叠纪岩浆活动有关,壳源组分的贡献主要来自前寒武纪变质围岩。金矿床形成的构造背景整体上与中亚造山带造山后伸展作用有关:晚三叠世,华北北缘受中亚造山带碰撞后伸展作用的影响,发生岩石圈首次减薄事件,同时发育多条深大断裂及碱性花岗岩-碱性岩的侵入活动,为大规模区域金矿的形成提供了优越条件。金矿带的东段可能同时受扬子克拉通与华北板块碰撞作用的影响,是造成其与中、西段金矿集中区成矿特征有一定差异的主因。

Geological characteristics, sources and controlling factors of the Triassic gold deposits in the northern margin of the North China Craton

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 H₂O-NaCl-CO₂±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. The 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 magmatism, 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.