湘西-黔东铅锌成矿带成矿作用及其动力学背景

The Mississippi Valley-type (MVT) Pb-Zn deposit is one of the most important types of Pb-Zn deposits in the world. As a representative metallogenic province of MVT Pb-Zn deposits in China, the Pb-Zn metallogenic belt in the western Hunan and eastern Guizhou province have the potential exploration prospect to becoming a world class Pb-Zn resource base. Being lack of geological and geochemical research for those Pb-Zn deposits in the area, and the Pb-Zn mineralization formed at lower temperature, it is difficult to understanding the regional Pb-Zn mineralization by the traditional research, and the development of metallogenic theory and the geological exploration for regional mineral resources have been restricted seriously. In the project, the typical Pb-Zn deposits, including Longshan, Baojing, Huayuan, Songtao-Tongren and Niujiaotang, will be researched. Using new advanced in situ analytical technique in the world, such as LA-ICPMS and ion microprobe, non-traditional isotope (Cd), ore-forming fluid, and isotopic dating, the geological geochemical characteristics, the regional metallogenic regularity and the key indicator of prospecting will be concluded in the area. Meanwhile, the nature, source and its evolvement of Pb-Zn ore-forming fluid and oil-field brine will be understood, a reasonable metallogenic model and geodynamic setting, including the relationship between Pb-Zn mineralization and regional geological evolution and paleo-oil reservoir will be suggested. The MVT-type Pb-Zn mineralization characteristics in the western Hunan and eastern Guizhou province will be identified. Moreover, our research will provide new theoretical and practical evidence to guide the geological exploration in the area, and it will also promote the development of MVT-type Pb-Zn metallogenic theory in China.

MVT型铅锌矿床是世界上铅锌资源最重要矿床类型之一。作为我国MVT型矿床代表性矿集区的湘西-黔东铅锌成矿带，具有成为世界级铅锌资源基地的潜力，但相关基础地质及地球化学研究薄弱，成矿作用以低温为主，常规方法已不适用于该类型矿床成矿作用研究的深入，严重制约了区域铅锌成矿理论的认识和资源勘探。本项目拟通过对该区域代表性矿床的地质剖析，借助LA-ICPMS和离子探针等原位分析国际先进测试技术，结合非传统同位素（Cd）、成矿流体和同位素精确定年等地质地球化学对比研究，总结该类型矿床地质地球化学特征和区域成矿规律，提炼出关键找矿标志，甄别已有成因观点，以揭示区域成矿流体系统的性质、来源及其演化，建立合理成矿模式，认识铅锌成矿作用与区域地质及古油气藏演化历史响应的动力学背景，突出湘西-黔东地区铅锌成矿作用特色，从而丰富我国MVT型铅锌矿床成矿理论与研究内容，为拓宽研究区铅锌地质勘探思路做出实际贡献。

湘西-黔东地区是我国重要的铅锌成矿带，通过其中李梅、渔塘、牛角塘和大硐喇等代表性铅锌矿床地质地球化学研究，总结出后生成矿特征明显、矿物组成简单、围岩蚀变弱、矿石品位低（以Zn为主）、矿体产状与围岩一致等是成矿带内铅锌矿化的共同地质特征，提供了精确硫化物原位S、Pb同位素和闪锌矿微量元素等地球化学数据，识别出研究区铅锌等成矿物质为新元古代板溪群变质基底岩石和寒武系下统清虚洞组下伏地层的多端元混合来源，不同矿床中还原硫来源可能存在显微差异，但寒武系地层中海相硫酸盐热化学还原作用是这些矿床主要硫源，流体混合是其中铅锌等金属元素富集沉淀主要机制，其成矿流体属于中低温中高盐度卤水，但在成矿过程中物质来源的供给和物理化学条件是不稳定的。通过与典型MVT型铅锌矿床等的地质地球化学特征对比，结合地球化学研究成果，认为湘西-黔东成矿带内铅锌矿床属于MVT型矿床，其形成与加里东期的陆内造山事件有关，不同于川滇黔矿集区铅锌成矿形成于印支期造山运动，提出加里东期铅锌成矿作用可能延伸到黔中五指山地区，多期次的造山运动可能致使扬子地台周缘发生了多期次的铅锌成矿事件，并建立了合理矿床成矿模式，成矿带内区域深大断裂是铅锌成矿流体主要通道，地层岩性界面、层间破碎带、背斜轴部等是铅锌富集成矿有利空间。在此基础上，总结出MVT型矿床闪锌矿微量元素组成复杂，以相对富集Cd、Ge、Hg等低温元素，贫In、Sn、Mn和Co等高温元素为特征，与岩浆热液夕卡岩型和喷硫沉积型矿床闪锌矿成因明显，从而丰富了不同类型铅锌矿床硫化物微量元素组成数据。除Pb、 Sb和Tl外，类质同象是上述微量元素在闪锌矿中主要赋存形式，这些元素在闪锌矿中替代方式不是固定的，不同矿床存在显著差异。此外，该类矿床中控制不同颜色环带闪锌矿微量元素具有多样性，胶状闪锌矿形成主要受控于非平衡的自组织过程。