中、下扬子地区下寒武统黑色页岩微量元素富集特征

中国南方扬子地区下寒武统黑色页岩分布广泛，主要由黑色页岩、黑色白云质页岩，黑色粉砂质页岩和黑色硅质页岩等组成；并伴生有较厚的磷块岩矿床、钒矿床和镍、钼多元素硫化物矿床。对黑色页岩岩石学特征、元素地球化学特征进行系统研究，并详细分析微量元素的富集成因，结果表明：黑色页岩主要形成于静水还原的浅海-半深海缓坡环境，层状元素富集带为沉积成因，海底热流体提供了丰富物质来源。总体上，Co、Be、Mn、Ga等元素含量较低；Cu、V、Ni、Mo等元素的含量较高，多数超过北美页岩平均值；以Ni、Mo为主的多元素富集层通常位于磷块岩之上，以黑色页岩、黑色白云质页岩中的硫化物和硫酸盐矿物为主要载体，其中有机碳（TOC）含量可达12.2%以上，远高于其他元素富集层，随着页岩内硅质成分增加，Ni、Mo、Fe、Co等元素含量明显降低；以V为主的多元素主要赋存于黑色硅质页岩中的水云母，与页岩内硅质成分具有较好的正相关关系；黑色页岩中稀土元素含量为(76.22~290.67)×10-6，轻重稀土比值LREE/HREE介于1.21~4.22，说明轻稀土更为富集，Sr/Ba值为0.04~0.34，δEu正异常，且北美页岩标准化配分曲线呈现平缓左倾，为沉积过程中存在海底热水流体提供了进一步证据。

Trace element characteristics of the Lower Cambrian black shales in middle and lower Yangtze area,China

Lower Cambrian black shales deposited widely in South China，which are mainly composed of the black shales, black dolomitic shales, black arenaceous shales and black siliceous shales. There are thick mineral deposits of phosphorus, vanadium deposit, molybdenum and nickel in the black shales. Petrologic characteristics and elemental geochemical characteristics of black shales were studied systematically, and the causes of enrichment of trace elements were analyzed in detail. The results show that the black shales were formed in reductive environment of gentle slope in shallow to bathyal milieu. The layered element enrichment belts were of sedimentary origin, and abundant substances were mainly from oceanic hydrothermal fluid. In general, the contents of Co, Be, Mn and Ga are relatively low. Cu, V, Ni and Mo have high content, and most of them are higher than North American Shale Composite (NASC). Element layers of Ni and Mo are usually located above the phosphorites and the sulfide and sulfate minerals in black shales and black dolomitic shales are the main carriers. The content of TOC is as high as 12.2%, which is much higher than any other element layers. With the increase of siliceous component in shales, the contents of Ni, Mo, Fe and Co decrease significantly. Many elements, such as V, mainly occur in hydromicas in the black siliceous shales. The content of V has a positive relationship with the content of siliceous components in shale. REE in black shales varies from 76.22×10-6 to 290.67×10-6 and LREE/HREE changes in the range of 1.21 to 4.22, which indicate that light rare earth element has high enrichment. The value of Sr/Ba ranges from 0.04 to 0.34, δEu is positively anomalous and the distribution patterns of REE normalized by North American shales are gentle leaning to LREE. These evidences indicate the existence of oceanic hydrothermal fluid during the deposition process.