柴北缘东段茶卡北山伟晶岩稀土元素地球化学特征及物源分析

REE Geochemical Characteristics and Provenance Analysis of Chaka North Mountain Pegmatite in the Eastern Part of the Northern Margin of Qaidam Basin,Qinghai Province

茶卡北山地区地处柴北缘东段,位于西秦岭成矿带西段宗务隆成矿亚带;伟晶岩脉具有成群、成带产出特征,岩脉大小不等,已发现伟晶岩脉600余条;稀有金属矿物主要为锂云母、锂辉石、绿柱石、锂电气石等,具有中深伟晶岩特征;伟晶岩类∑REE平均为1.26×10^(-6),LREE/HREE平均为13.13,轻重稀土分馏显著,具轻稀土富集特征;(La/Yb)_(N)平均为27.67,δEu多数大于1.0,平均为2.74,Eu正异常明显;由伟晶岩源区及环境判别图解显示,矿区伟晶岩可能来源于上地壳源区。由此,茶卡北山地区伟晶岩脉可能来源于上地壳源区,形成于同碰撞构造环境。

Chaka north mountain area is located in the eastern part of the northern margin of Qaidam,which is located in the Zongwulong metallogenic sub-belt of the western Qinling metallogenic belt.The pegmatite veins in Chaka north mountain area are characterized by the occurrences of clustering and zonation,and have different sizes.More than 600 pegmatite veins have been found in this area.The rare metal minerals in the pegmatite veins are mainly lepidolite,spodumene,beryl and elbaite.The veins have the characteristics of medium and deep pegmatite.The average of∑REE and LREE/HREE of pegmatite is 1.26×10^(-6)and 13.13 respectively,with significant fractionation of LREE and HREE,and enrichment of LREE.The average of(La/Yb)_(N)in pegmatite veins is 27.67.Most ofδEu are greater than 1.0,with an average of 2.74,and the positive anomaly of Eu is obvious.According to the diagram of pegmatite source area and environmental discrimination,the pegmatite in Chaka north mountain area may come from the upper part source area of the earth crust.Therefore,we believe that the pegmatite veins in the North Chaka mountain area may originate from the source area of the upper crust,and the pegmatite veins formed in the syn-collisional tectonic environment.