陕西紫阳下寒武统黑色岩系地球化学特征及成因研究

通过野外研究发现陕西紫阳下寒武统黑色岩系富含多种矿产且成因复杂，主要由硅质岩、灰岩、碳质硅质灰岩、碳硅质页岩四类组成。据此进行了系统的元素地球化学分析，结果显示研究区黑色岩系富含V、Mo、As、Ba等元素，不同岩性稀土模式曲线总体特征相似指示成因联系密切。四类岩性样品各自的MnO/TiO₂均值接近或小于0.5、V/（V+Ni）均值大于0.57、V/Cr均值大于4.2等特征表明该套黑色岩系形成于浅海—半深海相缺氧还原环境。另外，As和Sb的富集、Zn?Co?Ni图解中投点大部分位于热液矿床区域、Sr/Ba小于1、La/Ce均值接近2.8、北美页岩标准化配分图解的Eu负异常—弱正异常均指示了热液参与下的正常海水沉积环境。研究区地层夹含的硅质岩和重晶石等热水沉积岩反映了同沉积时的热液活动。据此推断沉积环境是海水、热液和生物的共同作用下形成的浅海—半深海相缺氧的还原环境。

Geochemistry of the Lower Cambrian Black Rock Series in Ziyang,Shaanxi Province: Geochemical characteristics and petrogenesis

Field investigation found that the Lower Cambrian black rock series in Ziyang， Shaanxi province， is rich in various minerals and has complex genesis. It consists of siliceous rock， limestone， carbonaceous siliceous limestone and carbon?siliceous shale. The following conclusions were reached. （1） The black rock series in the research area is rich in elements such as V， Mo， As and Ba. （2） The similarity of the rare earth model curves indicates that their genesis is closely related. （3） The black rock series is usually of the LREE?enriched type. （4） The average ratios of MnO/TiO₂ of the four types of lithological samples was close to or less than 0.5； the ratios of V/（V+Ni） （>0.57） and of V/Cr （>4.2） indicate that the rock was formed during a shallow sea?semi?deep sea phase. In addition， the siliceous rocks and carbonaceous siliceous limestones are rich in Sb； most of the points in the Zn?Co?Ni diagram are located in the hydrothermal deposit area； Sr/Ba<1； La/Ce<2.8 on average； and the Eu negative?to?weakly positive anomaly for the North American Shale normalized REE patterns indicates a normal seawater depositional environment in conjunction with a seabed hydrothermal fluid. The Lower Cambrian strata in the research area contains hydrothermal sedimentary rocks such as siliceous rocks and barite， which reflects the presence of hydrothermal activity from a submarine volcano during deposition. It is suggested that the formation of the Ziyang black rock series was jointly influenced by seawater， hydrothermal fluid and living organisms to form a shallow?sea?semi?deep?sea phase oxygen?deficient reducing environment.