华南下寒武统黑色岩系钒的赋存状态及富集机制

The vanadium ore deposit of the Lower Cambrian black shales, South China, which deposited during the Precambrian-Cambrian transition, has gradually become the other important source of vanadium resource besides the vanadium titanium magnetite ore deposit. Integrated with previous studies, the vanadium enrichment is widely occurred in the Lower Cambrian black shales besides the medium or large scale vanadium ore deposits in northeast of Guizhou province and northwest of Hu’nan province, South China. However, the mode of occurrence and enrichment mechanism (e.g., bio-organic matter and redox condition of seawater) of the vanadium enrichment/ore deposit were still not well-constrained. In this project, we will mainly focus on the important vanadium ore deposits and the typical sections of the Lower Cambrian black shales in South China, by using micro-beam analysis techniques (HRTEM, μ-XRD and FESEM), organic geochemical analysis (TOC, kerogen and biomarker) and the geochemical proxies of redox condition (redox sensitive elements and Fe speciation), to find out the enrichment regularity and the mode of occurrence of vanadium, to reveal the relationship among the vanadium enrichment, bio-organic matter and redox conditions of seawater, to explore the geochemical cycle of vanadium in the early Cambrian seawater, and finally to summarize the enrichment mechanism of the vanadium in the Lower Cambrian black shales, South China.

华南广泛分布的下寒武统黑色岩系钒矿形成于前寒武纪-寒武纪的转折时期，已逐渐成为我国除钒钛磁铁矿外钒资源的另一重要来源。除黔东北和湘西北等地的大中型钒矿外，综合前人的研究发现，华南下寒武统黑色岩系中钒的富集更是普遍存在。然而，该区黑色岩系中钒的赋存状态及富集机制（生物有机质、海水氧化还原条件等因素）却尚未得到很好地约束。本项目将以华南黔东北、湘西北的大中型钒矿和下寒武统黑色岩系典型剖面为研究对象，采用微束分析技术（高分辨率透射电镜、微区X射线衍射仪和场发射扫描电镜）、有机地球化学分析（总有机碳、干酪根和生物标志化合物）以及示踪海水氧化还原条件参数（氧化还原敏感元素和铁组分化学）等研究手段，以期明确华南下寒武统黑色岩系中钒的富集规律及赋存状态，揭示钒的富集与生物有机质、海水氧化还原条件之间的内在联系，探讨华南早寒武世海洋中钒的地球化学循环，归纳总结华南下寒武统黑色岩系中钒的富集机制。

华南广泛分布的下寒武统黑色岩系钒矿形成于前寒武纪-寒武纪的转折时期，已成为世界上除钒钛磁铁矿外钒资源的另一重要来源。研究发现，华南下寒武统黑色岩系底部钒的富集普遍存在，而非局部富集（如黔东北和湘西北钒矿）。本项目在岩相学和地球化学相结合的基础上，获得了早寒武世钒矿形成时海水的氧化还原条件从铁锰还原带，到缺氧/间歇性硫化条件，再到氧化水体出现的动态演化，指出钒的富集主要赋存于下寒武统黑色岩系的底部，并非所有的黑色页岩都富集钒。详细的微米-纳米尺度下的显微结构观察，查明了粘土-有机纳米复合体的形成和演化是钒在富有机质页岩中富集的主要途径：如，沉积阶段，钒与可溶有机质络合共同吸附或插层于蒙脱石层间，形成富钒的蒙脱石-有机纳米复合体；成岩阶段，伴随着蒙脱石的伊利石化和有机质的降解，钒从有机质中释放并进入伊利石结构中，形成富钒的伊利石-有机纳米复合体。华南下寒武统黑色岩系中，2M1型碎屑伊利石不含钒，而纳米级的1M/1Md型自生伊利石颗粒和集合体中有大量钒的检出（0.7到4.8 wt.%），石英、长石和黄铁矿等不含钒。本项目的实施，不但明确了钒在海洋中的地球化学循环过程，而且为钒作为氧化还原代理和钒的选冶提供了机理依据。