【作者】 胡朋；

【导师】 聂凤军；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2007， 博士

【摘要】 北山南带迄今为止已发现中型金矿床四处,小型金矿床（点）数十处,是我国西北地区最为重要的金矿集中区之一。该区地处塔里木板块和哈萨克斯坦板块的结合部位,区内前长城系地层出露广泛,深大断裂和韧性剪切带发育,岩浆活动频繁,具有良好的成矿地质条件。本文从总结区域成矿地质背景着手,选择北山南带拾金坡、新老金厂、小西弓三个典型金矿床开展重点解剖研究,通过野外地质调查和室内研究相结合,查明典型金矿床区域成矿地质背景、矿床地质特征、成矿流体来源与演化、成矿物质来源以及成矿时代,阐明矿床形成机制。在典型金矿床解剖研究并与区内其它金矿床对比的基础上,划分北山南带金矿床类型,分析成矿规律和控矿因素,探讨区域构造岩浆演化与金成矿作用的关系,指明找矿方向。拾金坡金矿床赋存在拾金坡复式花岗岩体的边缘部位,金矿体以含金石英脉的方式产出。复式岩体的主侵入体斑状花岗岩中锆石的SHRIMP测年表明,拾金坡岩体是早泥盆世花牛山地体增生过程的产物。地球化学研究表明,斑状花岗岩和其中的二长质暗色包体是壳幔过渡带幔源基性岩浆及其诱发的壳源长英质岩浆混合作用的产物,岩体定位于俯冲造山过程中应力局部松弛地段。拾金坡金矿床成矿流体属于中低温（90～342℃）、低盐度（多小于10%NaCleq）的H₂O-CO₂-NaCl-CH₄体系,成矿流体中含有异常高的CO₂含量和少量的CH4,成矿过程中发生了显著的流体不混溶过程。氢氧同位素示踪表明,成矿流体来自岩浆演化热液和加热的大气降水,两者混合导致金的沉淀。矿石和围岩的硫铅同位素研究表明,成矿物质具有深源特征,应直接来自拾金坡花岗岩体。新老金厂金矿床赋存在下二叠统哲斯群火山岩和火山碎屑岩中。地球化学特征研究表明,哲斯群火山岩来自快速拉张环境中残留有石榴石的亏损地幔源区的部分熔融,在上升过程中没有陆壳物质的混染。区域构造演化分析表明,哲斯群火山岩是洋壳俯冲形成的活动大陆边缘内部或弧后盆地快速拉张阶段的产物。新老金厂矿床成矿流体属低温（100～300℃）、低盐度（小于10%NaCleq）的CO₂-H₂O-NaCl±CH₄或CO₂-H₂O-NaSO₄±CH₄体系,流体混合是引起金属沉淀的主要机制。氢氧同位素示踪表明,新金厂矿床成矿流体以岩浆水为主,而老金厂矿床混入了较多的大气降水。矿石和围岩的硫铅同位素研究表明,成矿物质具有幔源特征,应直接来自火山-沉积岩地层。根据地质特征分析,新老金厂金的成矿应紧随哲斯群火山岩-次火山岩喷发之后,成矿时代为早二叠世晚期。小西弓金矿床是与韧性剪切带有关的金矿床,矿体赋存在韧性剪切带持续演化过程中的韧脆性剪切变形带和脆性破碎带中。流体包裹体研究表明,小西弓金矿床成矿流体属中低温（133～400℃）、中低盐度（4%～20%NaCleq）的CO₂-H₂O-CH₄-NaCl体系,成矿流体中含有较高的CO2,成矿过程中发生了显著的流体不混溶过程。氢氧同位素研究表明,多种来源的成因水参与了成矿过程,包括岩浆水、变质水和大气降水。硫铅同位素示踪表明,成矿物质来源于赋矿的西尖山群上亚群变质岩和海西期变质重熔型中酸性花岗岩。小西弓金矿床成矿时代为267～284Ma。总结小西弓金矿床的成矿机制认为,海西期变质重熔型中酸性岩浆在金矿床形成过程中发挥了重要作用。以容矿围岩为基础,将北山南带金矿床划分为三类:（1）深成侵入岩型金矿床;（2）火山岩型金矿床;（3）变质岩型金矿床。研究表明,长城系、前长城系中高级变质火山-沉积岩和晚古生代海相火山-沉积岩是该区金矿床的重要矿源层。金矿床和矿体的展布受不同级别的构造控制。晚古生代以来北山南带有限洋盆双向俯冲引发的构造-岩浆热事件是金矿床形成的重要地质条件。根据北山南带金矿床的区域成矿条件、成矿规律和控矿因素,圈定出4个有利的找矿远景区:（1）小西弓外围找矿远景区;（2）白墩子-石板墩找矿远景区;（3）拾金坡-花牛山找矿远景区;（4）老金厂-古堡泉成矿远景区。更多还原

【Abstract】 The study area, south Beishan Mountain area, is one of the important gold clusters in northwest China. Heretofore, three middle-scale gold deposits and several tens of small-scale gold deposits have been discovered, explored and mined. Located on the intergrated part of the Tarim plate and Kazakhstan plate, there are widely exposed Precambrian and Paleozoic strata, complex deep faults and shear zones and intensive magmatic activities in south Beishan Mountain. Although some research on the metallogenesis of individual gold deposit, i.e. Xiaoxigong gold deposit, have been done in the study area, systematic and comprehensive work on the gold metallogenesis and its relationship to the regional tectonic and magmatic events have not been developed. Started from the systematic summarize of regional metallogenic geological settings, three middle-scaled gold deposits, i.e. Shijinpo, Xinlaojinchang and Xiaoxigong gold deposits have been selected for anatomizing in detail. For the three representative gold deposits, combined with detailed field geologic survey and abundant experimental analysis, comprehensive work have been done involved their geological characteristics, the nature and evolution of ore-forming fluid, the origin of ore-forming materials and the ore-forming ages. Base on the detailed research on typical gold deposits and compared with other gold deposits, these gold deposits have been divided into three types. Furthermore, the main ore-controlled factors inclued the strata, magmatic rocks and tectonic elements have been analyzed, and the relationship between tectonic-magmatic evolution and gold metallogeny has been discussed.The Shijinpo gold deposit is located in the margin of Shijinpo composite granitic batholith and occurs as Au-bearing quartz veins. SHRIMP dating of zircon seleted from the Shijinpo porphyritic granite suggested that it is formed in early Devonian. Accroding to detailed petrologic features and geochemical data, it is indicated that the host porphyritic granite and their monzonitic enclaves were generated by mixing of mantle-derived basic magma and its induced crustal felsic magma in local tensile enviroment during the accretion of Huaniushan block. The ore-forming fluid is CO₂-H₂O-NaCl-CH₄ system with low- to intermediate-temperature （90～342℃） and low-salinity （mostly <10%NaCleq） which contain elevated CO2 and small CH4. Fluid immiscibility is common. Combined with the oxygen and hydrogen isotope features, it is concluded that the ore-forming fluids derived from the magmatic fluid and meteoric water, which mixing aroused gold deposition. The sulfur and lead isotopic character of ore minerals and wall rocks suggested that the ore-forming materials would be of deep origin and derived from the Shijinpo pluton.The Xinlaojinchang gold deposit occurs in lower-Permian Zhesi group volcanics and volcanic arenite. Study of geochemistry features indicated that the Zhesi group volcanics derived from melting partly of depleted mantle with rudimental garnet in fast tensile environment and has few hybridization with crustal metarials. It is formed in inner active continental margin or back-arc basin during the early Permian subduction of south Beishan limited ocean crust. The ore-forming fluids of Xinlaojinchang gold deposit is CO2-H2O-NaCl±CH4 or CO2-H2O-NaSO4±CH4 system with low temperature （100³00 ℃） and low salinity （mostly <10%NaCleq）. The study of oxygen and hydrogen isotope indicate that the ore-forming fluid mainly come from magmatic water in Xinjinchang mineralized zone and meteoric water in Laojinchang. Fluid mixing is the main mechanism to bring in the gold precipitation. Tracing of sulfur and lead isotope suggest that the ore-forming materials come from the Zhesi group volcanics and volcanic arenite. According to the geological features, it is deduced that the gold mineralization of Xinlaojinchang district followed closely the magmatic activity which formed the Zhesi group volcanics and the ore-forming age is about in early Permian.The Xiaoxigong gold deposit is the one related to ductile shear zone, whose orebody occures in brittle-ductile transition zone and brittle crushed zone that both are continuous evolutionary parts in one identical shear zone. Study of fluid inclusions in quartz from the Xiaoxigong gold deposit indicated that the ore-forming fluids is CO₂-H₂O-CH₄-NaCl system with low- to intermediate- temperature （133⁴00℃） and low- to intermediate- salinity which contain elevated CO₂. Fluid immiscibility is obvious. The study of oxygen and hydrogen isotope indicate that the ore-forming fluids are multiple sources, which included magmatic water, metamorphic water and meteoric water. The ore-forming materials come from upper subgroup of Xijianshan group Archaean metamorphics and Hercynian metamorphic remelted granite. The ore-forming age of the Xiaoxigong deposit is 267²84Ma ago. It is reckoned that the Hercynian granitoids play an important role in the metallogenic process.Based on the host rocks and geological features, gold deposits in south Beishan area can be classified into three types: （1） pluton-related gold deposits, such as Shijinpo, Mojindong and Huaniushan; （2） hosted by volcanics gold deposits, such as Xinlaojinchang, Beijin and Jinchanggou; （3） hosted by metamophics gold deposits, such as Xiaoxigong, Jinmiaogou and Xiaowannanshan. Proterozoic and Archaean strata and late Paleozoic marine volcanic-sedimentary rocks exposed in the south Beishan Mountain compose of the source bed of gold deposits. The distribution of these gold deposits and the orebodies thereinto are controlled by degressively ranked structure. Large-scale gold metallogenesis is triggered by tectonomagmatic events during late Paleozoic bidirectional subduction of south Beishan ocean crust. Based on the regional metallogenic condition, rules and ore-controlled factors in south Beishan Mountain, four prospective targets are outlined: （1） Periphery area of Xiaoxigong gold district; （2） Baidunzi-Shibandun area; （3） Shijinpo-Huaniushan area and （4） Laojinchang-Gubaoquan area.更多还原