扬子陆块东南缘寒武纪早期沉积环境和钒矿成矿作用研究

The Early Cambrian was an important period for the environmental change, life evolution and super-continental cycling of the Earth. During this period, a series of vanadium-hosting black shales were deposited along the southeast margin of the Yangtze block, South China. The enrichment and mineralization of vanadium was considered to be related to biological activities, anoxic environmental state and post-depositional alterations. However, the systematic processes of vanadium-mineralization are still unclear. In this project, we choose three typical profiles to carry out a detailed study of the early Cambrian black shales. New techniques including SEM, TEM and Raman were used for detailed observation of V-hosting minerals; In-situ trace elements, S-Pb isotopic analysis and whole rock major and trace elements, Zn-V isotopic analyses will be taken to understand their provenances, formation mechanisms and environmental and geodynamic settings. We also compared the sedimentary vanadium ores with similar ages from other continents, in order to yield information about the Early Cambrian geological evolution and mineralization of the Yangtze Block.

寒武纪早期是地球表面环境、生物组成和超大陆格局发生转变的重要时期。在此期间扬子陆块东南缘沉积了一套厚层富钒黑色页岩。前人研究表明，沉积钒矿在生物富集、环境变化和后期改造的共同作用下形成。但到目前为止，关于沉积型钒矿的赋存形式、成矿过程等尚缺乏系统的研究工作。本项目拟选取扬子陆块三个典型剖面为研究对象，对这套沉积序列和钒矿的形成、演化开展综合性研究；运用扫描电镜、透射电镜、激光拉曼等分析手段对含钒矿石进行岩相学观察和矿物、有机质成分测定，通过矿物原位微量和S同位素分析手段，结合传统的全岩主、微量元素及Zn-V等同位素分析方法，深入研究钒矿中钒的来源、成矿过程、盆地演化过程及其沉积环境；综合最新的资料并与其它已知的早寒武纪地层进行对比，探讨扬子陆块在寒武纪早期的地质演化历史和钒矿的成矿意义。

本项目对扬子陆块东南缘早寒武世厚层富钒黑色页岩和印度-阿曼等地同期地层开展了系统的野外地质、矿物学、元素和同位素地球化学研究。研究表明早寒武世沉积型钒矿含钒的主要位于扬子区域早寒武世牛蹄塘组底部；钒元素主要赋存于粘土矿物中，有机物次之，富钒Fe-Ti氧化物在页岩中普遍存在；早寒武世大型沉积矿床成矿元素（包括钒、磷等）主要来自于强烈的大陆风化作用；其在扬子地区黑色页岩中的富集受到全球氧化事件、区域海底热事件以及海水混合事件的共同影响，成岩后V等金属元素在有机质的作用下发生迁移，导致二次富集；此外研究还表明发生于寒武纪早期的环境变化、物质富集和生物灭绝事件与大火成岩省的喷发有关。