藏南曲松-错古-折木郎剪切带韧性变形和碰撞造山型金矿成矿机制

The wellknown orogenic gold deposit model was proposed mainly based on extensive studies on shear zone hosted gold deposits in Precambrian metamorphic terrains. Most of previous researchers thought that orogenic gold deposits mainly occur in accreted terrains, and collisional orogenic belts are not in favor of gold mineralization. But in recent years, a lot of Cenozoic orogenic gold deposits were discovered in two sides of Brahmaputra suture zone. The Qusong-Cuogu-Zhemulang shear zone which is located in the south part of east section of Brahmaputra suture zone, is an important gold belt, also a significant channels for the crust-mantle interaction, and a large amount of Cenozoic mafic dykes intruded in it. But before present, systematic studies on ductile deformational characteristics, process and subsequent water/rock interactions and gold mineralization is still absent. In this study, samples from typical shear zone profiles and shear zone hosted gold deposits, such as Bangbu, Zhemulang and Juqu, in the Qusong-Cuogu-Zhemulang gold belt will be detailed investigated based on field directional sampling and by using some modern analytical methods such as HRTEM, SIMS and Ar-Ar dating, in order to understand fully ductile deformational process and the subsequent nanoscale fluid/mineral interface reaction and gold mineralization mechanism of the gold belt, and establish a new orogenic gold deposit model under continental collisional environment. Results of this study will be helpful not only for our understand of nanoscale fluid migration and ore-forming materials precipitation during mylonitization, but also for exploration for new gold deposits in the Qinghai-Tibet Plateau.

国际上流行的造山型金矿理论主要是在前寒武地体剪切带型金矿基础上发展起来的,一般认为造山型金矿主要发育在增生造山带，而碰撞造山带不利于成矿。但在青藏高原雅江缝合带两侧，就有造山型Au矿的发育。位于雅江缝合带东段南侧的曲松-错古-折木朗大型剪切带是重要的金矿带，也是壳幔物质交换的重要通道，大量基性岩脉穿插其中.但目前, 关于该剪切带的构造变形特征及金矿化尚未有系统的研究.本项目拟选择曲松-错古-折木朗剪切带典型剖面和其中邦布、折木郎和举曲等造山型金矿，在详细的野外定向采样基础上，采用HRTEM、SIMS和Ar-Ar同位素定年等先进测试方法，研究该剪切带的韧性变形特征和过程及其在纳米尺度上的流体/矿物界面反应和金成矿机制，建立陆陆碰撞条件下造山型金矿成矿模式。本研究不仅具有重要理论意义，可从纳米尺度了解矿物糜棱岩化过程中的流体活动和矿质沉质沉淀过程, 且对青藏高原寻找新的原生金矿也有指导意义

前人一般认为造山型金矿主要发育在增生造山带，而碰撞造山带不利于成矿。但在青藏高原雅江缝合带两侧，就有造山型Au矿的发育。位于雅江缝合带东段南侧的曲松-错古-折木朗大型剪切带是重要的金矿带，也是壳幔物质交换的重要通道，大量基性岩脉穿插其中. 但目前, 关于该剪切带的构造变形特征及金矿化尚未有系统的研究..本项目选择藏南目前已发现的邦布金矿、折木郎金矿、举曲金矿、故穷金银矿、念扎金矿、沙拉岗锑金矿、布主金锑矿、乌拉堆金矿和明赛金矿等开展研究，并考察了林芝地区南迦巴瓦构造结上出露的下地壳麻粒岩和角闪岩等，同时为对比研究，还考察了云南北衙金矿等与碰撞造山有关的金矿，在系统的野外调研和室内地球化学分析基础上，发现：1.邦布金矿受大型脆—韧性剪切带的次级断裂控制，是目前西藏境内发现的大型原生金矿；壳幔相互作用导致的幔源流体的加入，是邦布金矿重要的成矿条件；举曲和折木郎金矿具有相似的成矿地质特征，它们均属于典型的陆陆碰撞造山型金矿；2.故穷金银多金属矿成矿流体主要为经过氧同位素漂移的大气降水，而其中富含的CO2可能源于变质成因有机碳的脱气作用。Ar-Ar定年显示其主要矿化期为42-43Ma, 说明故穷金银矿主要形成于印度－欧亚板块主碰撞期，为典型的造山型金银多金属矿；3.利用磷灰石U-Pb定年对藏南造山型金矿成矿时代进行了制约。研究显示藏南金矿带中的念扎金矿存在岩浆型和热液型两种不同磷灰石，前者U-Pb年龄为80.7±2.9 Ma，与该区赋矿闪长岩年代相似，而后者U-Pb年龄为44.78±1.56 Ma，可以代表金矿成矿年龄。研究显示该矿岩浆热液事件和金成矿不具有成因联系，控矿因素主要为区域剪切及断层活动；4.对藏南下地壳岩石中黄铁矿等硫化物进行了原位LA-ICP-MS微量元素测定，发现其中Au含量最高可达27.5 ppm，因此可以作为该区金矿的成矿物质来源之一。.本项目共发表论文5篇，其中SCI 收录期刊上发表论文4篇，有关成果获得2017 年国土资源科技一等奖（排名第六），取得专利1项。先后培养了1名博士后和5名博士生。