宁夏西吉盆地找矿前景与绿片岩地球化学特征分析

Geochemical prospecting features and geochemical characteristics of greenschist in Xiji basin, Ningxia

西吉盆地钻孔所见绿片岩均呈灰绿色,具海底喷发岩的典型颜色—灰绿色,在稀土元素图解中,绿片岩样品点均落在基性火成岩区,在常量元素图解中,样品点几乎全部落在火成岩区,西吉盆地钻孔所见绿片岩为基性火山岩建造,为正变质岩。稀土分配曲线分布在岛弧-弧后盆地拉斑玄武岩的范围内,在Hf/3-Th-Ta图解中,5件样品落入岛弧玄武岩区,在Ti/100-Zr-Y×3图解中,5件样品落入岛弧碱性玄武岩区,5件样品的Th/Ta值大于2,显示岛弧玄武岩的特征,西吉盆地钻孔所见变质基性火山岩应形成于岛弧-弧后盆地构造环境。通过区域成矿条件分析,认为西吉盆地很可能具备形成铜、锌等多金属矿的地质背景和条件。

The green schist in the Xiji basin is greyish green with typical greyish green color, in the diagram of rare earth elements, the greenschist samples are all located in the basic igneous rock area, in the constant element diagram, the sample point is almost all tribes in igneous rock area. it can be inferred that the greenschist in Xiji Basin is a basic volcanic formation and a normal metamorphic rock. The distribution curve of REE is in the range of tholeiitic basalt in island arc back arc basin,in the Hf/3-Th-Ta diagram, 5 samples fell into the island arc basalt area, in the Ti/100-Zr-Y ＊ 3 diagram, 5 samples fell into the alkaline basalt area of the island arc,the Th/Ta value of the 5 samples is greater than 2, indicating the characteristics of island arc basalt, the metamorphic basic volcanic rocks in the Xiji basin should be formed in the tectonic environment of the island arc back arc basin. Based on the analysis of regional metallogenic conditions, it is believed that the Xiji Basin may have the geological background and conditions for the formation of copper and zinc polymetallic deposits.