湘西北早寒武世黑色岩系微量元素地球化学特征

TRACE ELEMENT GEOCHEMICAL CHARACTERISTICS OF THE LOWER CAMBRIAN BLACK ROCK SERIES IN NORTHWESTERN HUNAN,SOUTH CHINA

对湘西北杆子坪剖面牛蹄塘组黑色岩系进行了系统的微量元素地球化学研究,结果表明:牛蹄塘组底部黑色岩系Ni、Mo、V、U、Cu、Pb、Zn、Cd、Tl、Ba等亲硫元素与过渡元素高度富集,U/Th大于1,稀土元素具有明显的正Eu异常与正Y异常,是海底热水沉积作用的结果。牛蹄塘组上部碳质页岩与泥质页岩亲硫元素与过渡元素明显降低,而Nb、Ta、Zr、Hf、Rb等高场强与大离子元素明显增高,表明陆源碎屑来源越来越多。

Samples of black rock series collected from the Lower Cambrian Niutitang Formation, northwestern Hunan Province, China, were analyzed for trace elements. The trace element geochemical characteristics of the ore layer (high enrichments in Ni, Mo, V, U, Cu, Pb, Zn, Cd, Tl and Ba; high U/Th ratios and LREE-enriched patterns with positive Eu anomalies and positive Y anomalies) support the assumption that the Ni-Mo polymetallic layer is of submarine hydrothermal origin. High field strength elements (HFSE) and lithophile elements such as Nb, Ta, Zr, Hf, Li, Be, Rb, Cs, Th and Sc are remarkably higher in the upper unit than in the lower unit of the Niutitang Formation. These features may reflect that hydrothermal contributions were diminished, terrigenous constituents increased in the sediments of the upper unit of the Niutitang Formation.