东秦岭二郎坪群热水沉积硅质岩的地球化学特征

东秦岭二郎坪群中广泛发育一套与铜铅锌成矿作用关系密切的硅质岩。区内硅质岩总体属于低硅质硅质岩,SiO2与Al2O3呈负相关,Fe2O3/FeO比值一般小于1,与热水沉积硅质岩的特征一致;南阳盆地以西的硅质岩MnO/TiO2比值小于0.5、Al/(Al Fe)比值接近北太平洋比值,而盆地以东的硅质岩MnO/TiO2比值大于0.5、Al/(Al Fe)比值与日本中部大陆边缘的三叠纪层纹状硅质岩比值类似;硅质岩稀土元素总量较低,重稀土元素有富集的趋势,Ce亏损较明显,Eu显示正异常,表明本区硅质岩主要是热水沉积作用的产物;硅质岩的V、Ni、Cu等微量元素含量具有洋中脊(或远洋盆地)和大陆边缘硅质岩的双重特征。

Geochemical characteristics of hydrothermal sedimentary cherts in the Erlangping Group, East Qinling Range, China

A suite of cherts closely related to Cu-Pb-Zn mineralization is widespread in the Erlangping Group in the East Qinling Range.The silica content of the cherts is generally low.SiO2 is negatively correlated with Al2O3 and Fe2O3/FeO is less than 1.Their characteristics are similar to those of hydrothermal sedimentary cherts.MnO/TiO2 of cherts west of the Nanyang basin is lower than 0.5 and Al/(Al Fe)is close to that of the Northern Pacific,whereas MnO/TiO2 east of the basin is higher than 0.5 and Al/(Al Fe)is similar to that of Triassic laminated cherts on continental margins of central Japan.In the cherts,the total REE is low,the heavy REE tends to be enriched,Ce is obviously depleted,and Eu shows positive anomalies,which shows that the cherts in this area is the product of hydrothermal sedimentation.The trace elements such as V,Ni and Cu have the double characteristics of mid-oceanic ridge(or pelagic basin)cherts and continental-margin cherts.