【作者】 钱烨；

【导师】 孙丰月；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2014， 博士

【摘要】 沱沱河地区位于青藏高原腹地的羌塘地体内，该地体自古生代以来经历了漫长而复杂的演化过程，这一过程可分为二个明显不同的阶段：其一，古特提斯演化阶段和印度-欧亚大陆碰撞与青藏高原形成阶段。金沙江构造岩浆岩带完整的记录了古特提斯洋从初始扩展到俯冲消减的全过程，因此沱沱河地区晚古生代-早中生代的构造岩浆演化与金沙江缝合带密切相关；其二，开始于65Ma左右的印度-欧亚板块对接碰撞、新特提洋的关闭，大陆俯冲碰撞阶段。这两次大的构造体制的转变造就了区内主要构造岩浆活动，也导致了研究区铅锌的成矿。本次工作对研究区与成矿有关的岩浆岩进行了岩石学、地球化学、锆石U-Pb年代学和锆石Hf同位素的研究。获得的晚古生代-早中生代岩浆岩有：巴斯湖北闪长岩（281±1Ma）、查曲怕查流纹质晶屑熔结凝灰岩（258±1Ma）、纳保扎陇流纹质晶屑玻屑熔结凝灰岩（244±1Ma）、八十八道班辉长岩（216±1Ma)。岩石地球化学和锆石Hf同位素的研究表明，巴斯湖北闪长岩和八十八道班辉长岩为岛弧火山岩，其原始岩浆应起源于受俯冲板片脱水熔融交代的亏损地幔楔；结合前人的研究成果，认为西金乌兰-玉树大洋俯冲消减早于早二叠世，碰撞后伸展发生在晚三叠世，表明早二叠世至晚三叠世期间，金沙江缝合带西段与金沙江缝合带东段的地球动力学背景是一致的。获得新生代岩浆岩有：那日利亚粗面安山岩-粗面岩（39.6Ma）、那日利亚正长斑岩（37.6Ma）、扎拉夏格涌晶屑凝灰岩（34.9Ma）、扎木曲正长斑岩（32Ma），岩浆活动跨越始新世和渐新世；这些岩石的地球化学分析结果显示其形成于高压的环境，结合研究区新生代时期的构造背景，认为它们的形成与加厚下地壳密切相关，那日利亚粗面安山岩-粗面岩为拆沉下地壳熔融遭受地幔物质交代的产物、那日利亚正长斑岩、扎拉夏格涌晶屑凝灰岩和扎木曲正长斑岩是软流圈上涌加热下地壳导致部分熔融的结果。下地壳源岩富K是造成这些岩石富碱的主要原因。这些数据表明沱沱河地区所处的高原北部大陆在40~32Ma一直处于持续增厚的状态，且主要的岩浆活动为下地壳物质再循环。在野外工作和室内研究的基础上，对研究区内典型矿床的成矿地质特征和成因类型进行了研究。确定了多才玛、孔介、楚多曲、雀莫错、那保扎陇铅锌矿为新生代中低温热液脉型铅锌矿。这些矿床的铅锌矿化受穿层、陡倾的断裂构造控制，而非前人认为的受层间构造控制；同位素的研究结果表明：成矿的铅来源于新生代加厚下地壳起源的火成岩，而与地层的铅同位素组成有较大的差别；硫以及氢、氧均主要来源于岩浆，显示出强烈的岩浆和深源属性；成矿流体为中低温、中低盐度和低密度的流体，晚期有大气水的加入；矿床受陡倾穿层断裂（张性断裂）、热穹窿（富碱岩浆流体）和岩性（碳酸盐岩）“三位一体”的控制；综合研究认为成因类型为的中低温热液脉型矿床，而非前人认为的MVT铅锌矿。根据成矿流体的中高温、低盐度、低密度特征，以及面型蚀变和细脉浸染型矿化特征，确定那日尼亚、扎拉夏格涌铅锌矿为新生代斑岩型铅锌矿，新生代加厚下地壳起源的富碱火山岩和斑岩提供了成矿物质和成矿热源；他们和中低温热液脉型铅锌矿是相同物质来源、相同热源、不同围岩条件和不同深度的成矿产物。本次工作还新发现一类产于闪长岩顶部的细网脉型铅锌矿-巴斯湖北铅锌矿，该矿床具有高温、低盐度的流体特征，矿化类型类似于斑岩型矿床，与后者相比成矿岩体为深成岩、成矿深度更大；成矿时代即闪长岩成岩时代（281Ma）或稍晚，是区内晚古生代成矿作用的代表。八十八道班、郭仓乐玛-宗陇巴铅锌矿位沱沱河河谷阶地之中，赋矿围岩为晚更新世砂砾，方铅矿在这类矿床中有两种沉积形式：一是晶形完好的方铅矿和砂砾石一起沉积，显示近源快速沉积的特征；二是以复杂的形态‘镶嵌’在砂砾的接触缝隙之间，显示其搬运距离稍远的特征。综合分析认为其为砂矿型铅矿，为高原快速差异抬升和干旱环境下风化剥蚀独有的产物，成矿物质可能来源于沱沱河北岸脉状铅锌矿体。在成矿地质背景分析和典型矿床研究的基础上，总结了沱沱河地区铅锌成矿地质特征：研究区的碳酸盐地层为热液脉型铅锌矿的形成提供了良好的在成矿环境和赋矿空间；火山岩地层为斑岩型矿床的孕育创造了条件；区域性断裂对整个沱沱河地区成矿控制作用明显，这些断裂是导矿构造，同时也是容矿构造；晚古生代-早中生代和晚始新世-早渐新世两期岩浆活动为区内铅锌形成提供了物质来源和成矿热源以及成矿流体。总结了区域铅锌矿成矿的时间规律、空间分布规律，并对保存条件和剥蚀深度进行了分析总结；依据矿床类型、成矿特征及空间分布特征，将研究区由北向南依次划分为沱沱河北侧扎木曲－扎拉夏格涌斑岩型铜铅锌多金属矿带、郭仓勒玛-八十八道班砂矿型铅矿带、那保扎陇-孔介斑岩型-热液脉型铅锌银矿带和楚多曲－日陇玛铅锌银钨锡铁矿带，提出了进一步的找矿方向。更多还原

【Abstract】 The Tuotuohe region is located in the Qiangtang massif, in the hinterland of the Qinghai–Tibet Plateau.The Qiangtang massif, an integral part of the Tethys structural domain, underwent a prolonged andcomplicated course of development, especially in terms of its history of ocean–continent conversion. Thereare two distinct phases in its development: the first involves the evolution of Tethys, and the second thecollision between the Indian and Asian continents, which caused the formation of the Qinghai–TibetPlateau.In this paper, we present new zircon U–Pb ages, whole-rock major and trace element analyses, andzircon Hf isotopic data for the Early Permian–Late Triassic and Cenozoic magmatic rocks in the Tuotuoheregion of the western segment of the Jinshajiang suture.Zircons from the Early Permian–Late Triassic magmatic rocks of the Tuotuohe region areeuhedral–subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios (0.4–4.6),indicating a magmatic origin. The zircon U–Pb ages obtained using LA–ICP–MS are281±1Ma,258±1Ma,244±1Ma, and216±1Ma, which indicate magmatism in the Early Permian–Late Triassic. A dioritefrom Bashihubei (BSHN）has SiO2=57.18–59.97wt%, Al2O3=15.70–16.53wt%, and total alkalis (Na2O+K2O）=4.46–6.34wt%, showing the rock belongs chemically to the calc-alkaline and metaluminousseries. A gabbro from Bashibadaoban (BSBDB）belongs to the alkaline series, and is poor in SiO2(45.46–54.03wt%）but rich inAl2O3(16.19–17.39wt%）and total alkalis (Na2O+K2O=5.48–6.26wt%).The BSHN diorite and the BSBDB gabbro–diorite both display an enrichment in LREEs and LILEs anddepletion in HFSEs, and they have no obvious Eu anomaly; they have relatively low MgO contents(2.54–4.93wt%), Mg#values of43to52, and low Cr and Ni contents (8.07–33.6ppm and4.41–14.2ppm,respectively), indicating they differentiated from primitive mantle magmas. They have low Nb/U, Ta/U,and Ce/Pb ratios (1.3–9.6,0.2–0.8, and0.1–18.1, respectively), and their initial Hf isotopic ratios rangefrom+9.6to+16.9(BSHN diorite）and+6.5to+12.6(BSBDB gabbro–diorite), suggesting their primarymagmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized bysubduction fluids. Taking all the new data together, we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian–LateTriassic: oceanic crust subduction before the Early Permian, continental collision during the Early–MiddleTriassic, and post-collisional extension from the Late Triassic.Zircons from the Cenozoic magmatic rocks of the Tuotuohe region, with high Th/U ratios, have agesobtained using LA–ICP–MS of39.6Ma,37.6Ma,34.9Ma, and32Ma, which indicate magmatism in theEocene–Oligocene. Rock geochemical analysis results show that they formed under high pressureenvironment. Combined Cenozoic tectonic setting of the study area, we believe that they are closely relatedto the lower crustal thickening. The Nariliya (NRNY）Trachyandesite-trachyte was a product of thedelaminated lower crustal melting and suffered by mantle. Asthenosphere upwelling and lithospheredelamination were the main causes of the NRNY orthophyre, Zhalaxiageyong (ZLXGY）crumbs tuff, andZhamuqu orthophyre magma activity. K-rich source rocks of the lower crust are the main cause of thesealkali-rich rocks. These data indicate that the Tuotuohe region has been in continuous thickening of thestate in40~32Ma and the main magmatic activity was lower crust recycling.Based on the field work and laboratory study, we are approaching a new understanding of the genesistypes and characteristics of deposits in studying the area:(1）The Duocaima, Kongjie, Chuduoqu, Quemocuo and Labaozhalong lead and zinc deposits wereepithermal vein-type. These lead-zinc deposits were controlled by steeply dipping faults instead layerstructure controlled by the previous. The results of Pb isotopes indicated that major metallogenetic matterscame from the Cenozoic igneous, and not from the formations. Sulfur, hydrogen and oxygen mainly camefrom magma, showing a strong and deep magma source property. The ore-forming fluid is low temperature,low salinity and low density, and atmospheric water added in later. Steeply dipping fracture, thermal dome(alkali-rich magmatic）and lithology (carbonates）were the main ore-control factors. Comprehensive studiessuggest that the type of the deposits was epithermal vein-type deposits, rather than MVT lead-zinc.(2）According to the high temperature,low salinity, low density characteristics of ore-formingfluid,and the planar alteration and veinlet disseminated mineralization characteristics,we determined thatthe NRNY and ZLXGY Pb-Zn deposits were Cenozoic porphyry type Pb-Zn deposits. Cenozoic Alkali richporphyry and volcanic rock, which originated from thickened lower crust, provided ore-forming materialand heat source. Origin of Cenozoic Alkali rich porphyry rock and volcano provided ore-forming materialand low temperature heat source; heat them and hydrothermal vein type lead zinc ore is the product of thesame material, the same source of metallogenic heat source, different rock conditions and depth. Theporphyry and hydrothermal vein type lead zinc deposits have the same metallogenetic matters and heatsource, and different rock conditions and metallogenic depth.(3)We found a new type of lead-zinc deposit in this work–Bashihubei (BSHN）lead-zinc deposit,called ‘veinlet type located at the top of diorite’. The fluid characteristics of the ore deposit arecharacterized by high temperature, low salinity. And the mineralization type is similar to the porphyrydeposits, but metallogenetic rock is plutonic rocks and mineralization metallogenic greater depth. Themetallogenic epoch of BSHN lead-zinc deposit was281Ma or slightly later, which is metallogenicrepresentative during Late Paleozoic within the study area. (4）Eighty-eight station (BSBDB）and Guocanglema-Zonglongba (GCLM）lead-zinc deposits arelocated in Tuotuohe valley terrace, and the host rock is late Pleistocene gravel. The galena has two kinds ofdeposition form in this kind of deposit: one have the complete crystal form, which was product ofsynsedimentary together with sand and gravel, which is featured by proximity of its origin and rapiddeposition. And the others have complicated form of ’mosaic’ between the contact gap of gravel, which isfeatured by the slightly further distance. Based on a synthetical analysis of metallogenic characteristics, thedeposits are placer lead as the product of plateau fast differential uplift and denudation in the aridenvironment of weathering. The metallogenic materials of which may be derived from the upper orebody ofporphyry Pb-Zn deposits in the north of Tuotuohe River.With a basic analysis on the metallogenic geologic settings, the genetic types and geological featuresof each type of Pb-Zn deposits in Tuotuohe region are studied. The Carbonate formations in the study areaprovide a good environment and ore in space for the formation of hydrothermal vein-type lead-zincmineralization, and the volcanic strata bred to create the conditions for porphyry lead-zinc deposits. Theregional fracture obviously controlled the mineralization of Tuotuohe region, and these faults are not onlythe guided mine construction, but also the host structures. Late Paleozoic-Mesozoic and early late Eocene-Early Oligocene magmatic activities in the region provided the material source, ore-forming fluids andheat for forming the lead and zinc mineralization.This paper summarized the law of the regional lead-zinc mineralization distribution in time and spatial,and the storage conditions and erosion depth were analyzed and summarized; and analyzed the preservationconditions of the Pb-Zn deposits in Tuotuohe region. According to the deposit types, mineralizationcharacteristics and spatial distribution, We divided into four mineralization zones in Tuotuohe region fromnorth to south: Zhamuqu-Zhalaxiageyong Porphyry Cu-Pb-Zn polymetallic ore belt in the north shore ofthe Tuotuohe river, Guochanglema-Bashibadaoban placer Pb ore belt, Nabaozhalong-Kongjie Porphyry andhydrothermal vein type Pb-Zn-Ag polymetallic ore belt with and Chuduoqu-Rilongma Pb-Zn–Ag-W-Snpolymetallic ore belt. Finally, the paper presents further prospecting direction of the study area.更多还原