【作者】 张洪瑞；

【导师】 侯增谦； 杨天南；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2010， 博士

【摘要】 作为一种新的矿床类型,碰撞环境下沉积岩容矿铅锌矿床的矿体就位和构造控制尚不清楚。三江北段位于大陆碰撞造山带的后陆区,大型走滑运动叠加影响较小,是研究碰撞环境下沉积岩容矿铅锌矿床的理想场所。本文通过矿区填图、显微观察和综合分析对东莫扎抓、莫海拉亨、查曲帕查三个大型矿床进行了详细解剖,填制了矿区1：1万地质图；识别出三江北段印支期的两期变形；对矿区控矿构造提出了全新观点；确定了三江北段沉积岩容矿铅锌矿床的三阶段成矿模型；建立了大陆碰撞环境下沉积岩容矿铅锌矿床的控矿模型；同时研究了浅表条件下构造变形与盆地流体成矿的联系。构造—岩相填图结果表明,三江北段印支期存在两期构造叠加,早期为波长较大的倒转线状褶皱,伴生不对称寄生褶皱；晚期为波长较短的短轴褶皱。两期褶轴以大角度相交,形成钩状—弯月状叠加干涉式样。地层不整合界限指示两期变形分别发生在二叠纪末、三叠纪末。新生代三江北段发育两大推覆系统,即唐古拉山推覆构造和风火山—囊谦逆冲褶皱带。查曲帕查矿区处于两套逆断裂系统的末梢部位,东莫扎抓和莫海拉亨矿区位于风火山—囊谦逆冲褶皱带内。详细填图表明,三个矿区逆断层总体几何学和运动学特点相类似：延伸多东西向或北西—南东向,沿走向有波状弯曲,断面都显示为北倾,断层带附近断层角砾发育,上、下盘岩石挤压变形明显。但不同矿区逆断层伴生的次级构造具有不同表现。查曲帕查矿区逆断层附近岩层产状变陡。东莫扎抓矿区逆断层上盘形成叠瓦状构造岩片；下盘发育走滑断层,同时伴生陡倾构造角砾岩带和喇叭状小型逆冲断层。莫海拉亨矿区逆断层伴生有雁列脉体和角砾破碎带,断层角砾和脉体结构指示断裂为幕式活动,类似最近发生玉树地震的甘孜—玉树断裂的活动特征。另外,查曲帕查矿区还发育伸展有关的正断层,产状陡倾。在九十道班组灰岩内呈锯齿状,在九十道班组和五道梁组接触带上代替不整合面显示为同沉积生长断层。结合区域资料,将莫海拉亨矿区逆断层活动厘定为始新世、东莫扎抓矿区逆断层发生在渐新世末,查曲帕查矿区正断层则是在中新世初。控矿因素分析表明,三江北段铅锌矿体围岩都是碳酸盐岩,但控矿构造各有不同。查曲帕查矿区矿化露头尺度上出现在锯齿状正断层附近,钻孔资料揭示主矿体出现在地下20m的角砾带内,角砾特征说明为溶洞坍塌成因,总体显示成矿在伸展构造环境中。东莫扎抓和莫海拉亨两矿区控矿构造主要为逆冲断层上盘的破碎带和次级断面、构造角砾岩带、构造透镜体带和“之”字形追踪张节理,反映成矿发生在总体挤压环境的局部张性裂隙中。显微镜观察发现三江北段铅锌矿床矿石结构都为开放空间充填,但被充填的空间性质有差异。查曲帕查矿区为网脉状、晶簇状,常在灰岩角砾间隙内与泥质、方解石一起层状生长,是边沉积边成矿的过程；而东莫扎抓和莫海拉亨两矿区主要为细脉状、浸染状,含矿热液是挤压同期或稍晚就位沉淀,其中莫海拉亨矿石还显示有明显后期破碎。控矿机制主要有碎裂作用、交代—充填作用和压溶作用。结合脆性断裂新生代演化过程,认为成矿分别发生在始新世末、渐新世末和中新世初。三江北段沉积岩容矿铅锌矿床成矿三阶段分别对应早期挤压、晚期挤压、后期伸展的背景,成矿过程中流体温度逐渐降低,而流体内压则有明显升高。从渐新世到中新世整个青藏高原发生构造体制大转换,从挤压变为伸展,赋矿部位也从挤压有关的裂隙变为张性构造空间,矿石结构由脉状、浸染状变为网脉状、晶簇状。三江北段铅锌矿床的特殊性在于成矿过程与高原隆升密切相关,另外,逆冲推覆形成的断面波状起伏、成矿晚期高压流体造成岩石破裂,这些因素造成岩石渗透性增大,有利于含矿流体向上运移；矿质可以以胶结角砾的形式出现在角砾间,也可以出现在角砾内部,具体与当时岩石渗透性有关。更多还原

【Abstract】 As a new deposit type, the sediment-hosted Pb-Zn deposit in collisional orogenic belt remains poorly understanded. The Northern segment of the Sanjiang orogenic belt (NSOB), which is located in the hinterland of Tibetan continent-continent collisional orogen, has little been influenced by late large-scale strick-slip fault systems, and thus provides an ideal place for study of the sediment-hosted Pb-Zn deposits under collision environments. Here I try to describe the deformational structures, Ore-controlling structures and Ore micro-texture of the Chaqupacha, Dongmozhazhua, and Mohailaheng deposits in the NSOB by geological field mapping, thin section observations, and synthesizing all available informations of multi-desiphilines. Accordingly we got below main progresses:1) made three geological maps with scale of 1:10000 of the Chaqupacha, Dongmozhazhua, and Mohailaheng Pb-Zn deposits, respectively; 2) two phases of Indosinian structures and their interference pattern are identified; 3) new interpretation of ore-control structures is suggested; 4) a three-phases metallogenetic model is proposed to explain the three kinds of sediment-hosted Pb-Zn deposits in the NSOB,5) establishing structure-control model for sediment-hosted Pb-Zn deposits in continent-continent collision orogen; and 6) discussed the correlation between deformation and metallogenesis of basin fluid under upper crustal environments.Detailed geological mapping reveals two stages of folding in the Late Palaeozoic to Early Mesozoic strata. The earlier one is reversal linear fold with numerous asymmetric parasitism folds. The later fold overprinted the earlier one resulting in hook- or crescent- like interference patterns. The angular disconformities suggest that the two stages folding developed in the Late Permian and Late Triassic, respectively.Previously studies have identified two Cenozoic thrust nappe systems in NSOB:the Tanggula Thrust System (TTS), and the Fenghuoshan-Nangqian Thrust System respectively. The Chaqupacha deposit is located at the tip portion of the two systems, while the Dongmozhazhua and Mohailaheng are located within the Fenghuoshan-Nangqian thrust system. The thrusts in the three deposit regions have similar geometry and kinematics; all are characterized by a northward, northwestward, or northeastward dipped plane depended on its location. Fault breccia developed very well. On the other hand, the fault-associeted small structures are quite variable among the three deposit regions. For example, imbricate slices, strike-slip faults and associated tectonic breccia developed very well in the Dongmozhazhua deposit region, which have not been identified in the Chaqupacha area, while en-echelon extensional veins occur in the lower plate of the thrusts in Mohailaheng. Microtectural observations reveal episodic brecciation suggesting episodic faulting for the thrusts, just like the fault activity of the Ganzhi-Yushu fault that caused the 4.14 Yushu earthquake. In the Chaqupacha deposit region, normal fault cut across the thrusts. These normal faults commonly have zig-zag geometry in map-view, and its fracture is locally filled by marl of the Wudaoliang Formation. Taking regional geological data into account, we suggest that the thrust in Mohailaheng developed at the Eocene; that in Dongmozhazhua at the end of Oligocene; and normal fault in Chaqupacha occurred at the Miocene.Although all the Pb-Zn deposits in NSOB are hosted in carbonatic rocks, ore-controlling structure differs from one to other. The surface mineralization of Chaqupacha Pb-Zn deposit is identified mainly along the normal fault; but drilling data reveal that main ore bodies are located at ca.20 m below the surface. Further more, the main ore-body is strictly limited in breccia belts; there is evidence that the breccias formed by dissolution and collapse of paleo-caves. In contrast, the ore-control structures in Dongmozhazhua and Mohailaheng deposits are mainly subsidiary fractures of the thrusts, including locally developed extensional breccias and minor trans-extensional fault.Micro-textural observations reveal that all Pb-Zn minerals deposited in open-space; but the filled voids have different geometrical and/then kinematic feature. The vein-like ore bodies in Chaqupacha interconnect each other to form network, whereas drustic texture is widespread in these ore veins. Among the drusy calcite and sulfides, marl is common displaying stratiform structure. Such phenomenon suggests a syn-sedimentation mineralization. On the other hand, the ore body of the Dongmozhazhua and Mohailaheng deposits presents as minor veins or porphyry ore. The tightly correlationship between the thrust and the ore veins suggests that the precipitation of sulfides in both Dongmozhazhua and Mohailaheng occurred during or slightly later than the N-S direction compression. As evidence, the ores in Mohailaheng are commonly broken up. The ore-forming processes may include cataclasis, strain-solution, dissolution to form cavies and/then filling the cavies. Because of the tight relationship between the evolution of brittle faults and the ore-bodies, we suggest here that the Dongmozhazhua, Mohailaheng and Chaqupacha deposits formed at the Late Eocene, Late Oligocene and Early Miocene, respectively.The suggested three satges of ore-forming process are tightly correlated with two compressional at eaerly and middle periods and an extensional strain at late time respectively. During the ore-forming process, the temperature of fluid gradually decreased while the inner pressure of the fluid increased very likely due to a decrease in the confining pressure. Such a variation is in consistence with the Cenozoic tectonic evolution of the North-central Tibet:A change in tectonic regime from compression to extension completed during the interval of the Oligocene to Miocene in the Tibet Plateau; in corresponding, the the ore-filling structures changed from thrust-related ones to those formed by extensional strain, which have filled by ore-bodies with different texture.Conclusively, the Pb-Zn deposits in NSOB are tightly related with the tectonic evolution of Himalayan-Tibetan Plateau. Intensive and multi-stages compressional and extensional deformations, which are likely alternative, greatly increased permeability of the carbonitic rocks in the study areas. A high permeability in host rock is very significant for fluid moving and ore-mineral precipitation.更多还原