摘要
秦岭造山带是世界第二大卡林—类卡林型金矿省,其地质背景与美国西部卡林—类卡林型金矿省明显不同,位于大陆内部的碰撞造山带,而非活动大陆边缘的盆岭省。秦岭卡林—类卡林型金矿主要赋存于板块缝合带及其前陆冲断带的海西—印支构造层中,以泥盆系和三叠系为主,主要岩性为潟湖—浅海相的含碳细碎屑岩—碳酸盐岩建造,即碳硅泥岩系;成矿元素为 Au—As—Sb—Hg—Ag,缺乏 Tl,共生矿种为 Sb,Hg,Ag,U和重晶石等;成矿温度为160~300℃,流体盐度为4%~10%(NaCl_(eq)),压力为5~50 MPa,深度约0.5~5 km,属于中低温中浅成热液矿床,与内华达卡林—类卡林型金矿一致。成矿流体具有建造水特点,C_2H_6 含量较高,显示了有机流体参与成矿。成矿同位素年龄介于 220~100 Ma之间,以170 Ma 为高峰,地球动力学背景属碰撞造山过程挤压—伸展转变期的减压增温体制,成矿构造模式为碰撞造山成岩成矿和流体作用模式。陆陆碰撞过程中,沿龙门山、阿坝—黑水—平青、若尔盖—文县、玛曲—勉县—略阳、白龙江、双河—公馆、凤县—镇安、安康等大型断裂带的陆内俯冲作用不仅导致了西秦岭地壳缩短增厚隆升,而且使俯冲板片变质脱水、熔融,派生成矿流体和相关熔体,流体和熔体的上升到仰冲板片次级构造带,形成了卡林—类卡林型和造山型?
The Western Qinling Mountains is the largest but one metallogenic province of Carlin and Carlin-like gold deposits in the world. Inboard a continental collision orogen, the Western Qinling Carlin and Carlin-like gold province has different geological setting from Nevada and adjacent areas in western United States, the first largest worldwide Carlin and Carlin-like gold province, which is developed in a basin-range province behind an active marginal orogen. The Carlin and Carlin-like gold deposits in the Western Qinling Mountains are mainly hosted in Hercynian-Indosinian (from Devonian to Triassic) tectonostratigraphic unit developed in a foreland fold-thrust belt south of the Shangzhou-Danfeng Early Paleozoic geosuture. The country rocks are major of carbonaceous fine clastic-chemical sediments, including calcareous sandstones, silty carbonates, shales and cherts, deposited in lagoon-shallow sea environments, although a part of the country rocks was previously suggested as turbidite. Geochemical signature of Au-As-Sb-Hg-Ag((Ba, Te, Pb-Zn), poor in Tl, characterizes most individual deposits. Sb, Hg, Ag, Pb-Zn and barite, and occasionally uranium, can be recovered as by-products. With metallogenic temperature of 160-300 ℃ , fluid salinity mainly of 4%-10% (NaCleq) , pressure of 5-50 MPa and depth of 0. 5-5 km, the gold deposits in Western Qinling Mountains are medium- or low-temperature mesozonal to epizonal deposits, consisting with those in Nevada. Ore-fluids are major of metamorphic and meteoric, despite magmatic fluid cannot be ruled out. High content of C2H6 shows that organic fluids contributed to gold metallogenesis. Histogram of isotope ages shows that metallogeny occurred in the period of 220-100 Ma, with a peak around 170 Ma. Metallogenic geodynamic setting was the transition from collisional compression to extension; and the CMF (collisional orogeny, metallogeny and fluid flow) model can be used to interpret the Carlin and Carlin-like gold mineralization in Western Qinling Mountains. During the collision between the South and North China continents, imbricate north-dipping underthrusting or intracontinental subduction occurred along regional faults such as Longmenshan fault, Ruo'ergai-Wenxian fault, Maqu-Mianxian-Lueyang fault, Bailongjiang fault, and Fengxian-Zhen'an fault. This caused intense crustal shortening, thickening and uplifting, as well as the followed slab delamination in Western Qinling Mountains. Metamorphic devolatilization and partial melting of the underthrusted slabs led to the generation of ore-fluids and related melts. Upward migration of ore-fluids and related melts into favorable structural loci must result in formation of the Carlin and Carlin-like gold systems as well as the orogenic-type gold lodes. Additionally, a huge orogenic-type gold province is stipulated to be beneath the Carlin and Carlin-like gold province in Western Qinling Mountains.
出处
《地质论评》
CAS
CSCD
北大核心
2004年第2期134-152,共19页
Geological Review
基金
中国科学院百人计划
教育部跨世纪人才培养计划
国家攀登预研(编号95-Pre-39-04)
国家自然科学基金(编号49972035)
关键词
卡林-类卡林型金矿床
西秦岭造山带
挤压向伸展转变期
成矿时代
成矿模式
Carlin and Carlin-like gold deposits
transition from compression to extension
metallogenic time
metallogenic model
Western Qinling Mountains