【摘要】 文章通过野外地质调查和系统的岩石学、岩石化学、稀土及微量元素地球化学研究,探讨了藏北美多锑矿床容矿硅质岩的成因和大地构造环境。研究结果表明,美多锑矿容矿硅质岩以致密块状硅质岩为主;主元素化学组成表明,其形成时有大量陆源火山碎屑物质的介入;稀土元素组成及配分模式与热水硅质岩不同,显示其形成于大陆边缘环境;硅质岩和凝灰岩均呈Ba、Sr、P、Ti明显亏损和Nb弱亏损的特点,类似于成熟大陆弧花岗岩更多还原

【Abstract】 Based on detailed field geological survey and comprehensive petrological, petrochemical and geochemical studies, the authors have discussed in this paper the origin and tectonic environment of the ore_hosted siliceous rocks in the Meiduo antimony deposit, northern Tibet. Several conclusions might be drawn from the study:siliceous rocks can be divided into four types:massive, laminated, porous and brecciated;high contents of SiO 2,Al 2O 3,K 2O,Na 2O and TiO 2, together with high correlation coefficients between Al 2O 3 and K 2O,Na 2O,TiO 2, show that there existed prominent entry of volcanic and /or terrigenous constituents during the formation of the siliceous rocks;the Al/(Al+Fe+Mn)ratios, which are higher than the average value of the shales in the world, fall into the non_hydrothermal sedimentation area in the Al_Fe_Mn triangular diagram;the rare earth element distribution patterns characterized by slight enrichment of LREE, flat HREE curves, δEu 0.36～0.68 and δCe 0.51 ～1.19 are different from those of hydrothermal siliceous rocks;the Ce/Ce * (0.81 on average) and La N/Yb N (1.14 on average) values suggest that the siliceous rocks might have been formed in the continental margin environment;the Thompson spidergrams of the siliceous rocks and tuffs which show prominent depletion of Ba, Sr, P, Ti and slight depletion of Nb are similar to those of granites developed in the mature continental margin. These geological and geochemical features of siliceous rocks strongly suggest that, instead of being hydrothermal chert like those widely existent in the ocean floor, they were formed in a mature continental margin environment and genetically related to the volcanism during the orogenic activity.更多还原