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白银矿田是我国著名的海相火山岩块状硫化物矿床,通常认为该火山岩是大陆裂谷环境的双峰式组合.新的地球化学数据表明,玄武岩属钙碱性系列,富集Th和轻稀土元素(LREE),亏损Ti和高场强元素(HFSE),Th/Nb比值高(0.9～1.3),εNd(T)值低(-1.2～+3.4),源于弱亏损的地幔源区,推测形成在成熟岛弧或具较薄陆壳基底的活动陆缘环境.流纹岩也为钙碱性,贫Ti,Nb,Sr和Yb;Th/Nb比值高(0.8～1.6);εNd(T)值高(>4);形成在洋内岛弧环境.玄武岩和流纹岩具有不同的地球化学性质、形成环境和时代,因此,不具备双峰式组合特征.
The silver ore field is a well-known marine volcanic massive sulphide deposit in China, and is generally considered to be a bimodal assemblage of continental rift environments.The new geochemical data show that basalts are calc-alkaline series enriched in Th and light (LREE), depleted Ti and high field strength elements (HFSE), high Th / Nb ratio (0.9-1.3) and low εNd (T) values of -1.2 ~ + 3.4. , Which is presumed to be formed in a mature island arc or a moving continental margin with a relatively thin crust basement. Rhyolite is also calc-alkaline poorly depleted in Ti, Nb, Sr and Yb; the Th / Nb ratio is high (0.8-1.6); εNd (T) is high (> 4), and formed in an intra-island arc environment.The basalts and rhyolites have different geochemical characteristics, forming the environment and the times, therefore, they do not possess the bimodal assemblage characteristics.