西藏邦铺钼多金属矿床矽卡岩地球化学特征及其地质意义

Geochemical characteristics of Skarns in Bangpu Mo Polymetallic Deposit,Tibet and its geological significance

邦铺钼多金属矿床位于冈底斯成矿带东段,由斑岩钼铜矿体和矽卡岩铅锌矿体组成。文章对矽卡岩、大理岩及二长花岗斑岩主量、稀土和微量元素组成进行了研究。主量元素研究结果显示,矽卡岩形成过程中二长花岗斑岩体与大理岩发生了显著的Si、Ca、Al等元素的交换;稀土元素组成中,除矿化矽卡岩略微富集重稀土外,其余多数矽卡岩与大理岩、二长花岗斑岩均富集轻稀土元素;微量元素蛛网图显示,矽卡岩及大理岩具有近似的组成型式,指示二者具有成因联系。以上研究结果表明,邦铺矿床矽卡岩系二长花岗斑岩交代碳酸盐岩地层形成,斑岩成矿与矽卡岩矿化密不可分。矽卡岩稀土元素组成特征值δEu和δCe研究结果表明,矽卡岩成岩环境为高温氧化环境,之后随着成矿作用的发生,逐渐转变为还原环境。

The Bangpu Mo polymetallic deposit lying in the eastern section of the Gangdese metallogenic belt are composed of porphyry Mo-Cu ore body and skarn Pb-Zn ore body. Compositions of major element, trace element and rare earth element of skarns, marble and monzonitic granite porphyry are studied in this paper. The study of major elements indicates that Si, Ca, A1 and other elements are exchanged between the marble and the monzonitic granite porphyry during skarns formation process. In the rare earth elements, the mineralized skarn is enriched in the heavy rare earth elements, and the other skarns, the marble and monzonitic porphyry are enriched in the light rare earth elements. On the aspect of trace elements compositions, skarns and the marble had the similar patterns in the spider diagram of trace elements and this feature point out that the skarns and the marble have the genetic rela- tion. All the results above show that the skarns in the Bangpu Mo polymetallic deposit are formed from the carbonate formation metamorphosed by the monzonitic granite porphyry and the porphyry mineralization and the skarn mineralization are inseparable. Values of the δEu and the δCe of skarns indicate that the skarns diagenesis environment is high temperature and oxidation environment and following the mineralization the environment turns into the reducing environment gradually.