甘肃石青硐矿区稀土元素地球化学特征及意义

REE geochemical characteristics of Shiqingdong mining area in Gansu province and the significance

石青硐矿区处于北祁连褶皱带东段,与著名的白银大型矿田组成白银-石青硐铜多金属成矿亚带。文章对石青硐矿床不同类型的含矿围岩及矿石进行了稀土元素特征的对比研究,分析认为:(1)区内含矿围岩的稀土配分模式与白银厂相似,基性岩由板块俯冲环境下地幔楔部分熔融产生,并有地壳混染,酸性岩则为基性岩浆分异并混染了地壳物质的产物,成矿与成岩物质具有一定的继承性和同源性;(2)δEu和δCe特征表明,石英脉型多金属矿石的成矿流体和物质主要来源于高温还原性质的岩浆热液,而浸染型矿石的形成可能与海底热液对流循环成矿作用相关;(3)无矿石英脉与基性岩关系密切,其可能来源于氧化条件下基性岩中的硅质淋滤和再沉淀;(4)无矿石英脉与多金属矿化石英脉的Eu异常明显不同,前者为负Eu异常而后者为正Eu异常,即Eu异常可以作为石英脉含矿性评价的地球化学标志。

Shiqingdong mining area is located in the eastern section of North Qilian fold belt.The mining area and the well known large Baiyin ore field comprise the sub-Baiyin-Shiqingdong copper-polymetallic metallogenic belt.In this paper REE characteristics of different wall rocks and ores in Shiqingdong mining area are comparatively studied.The result shows that（1）REE patterns of wall rocks in this area are similar to those of the Baiyinchang mining area.Basic rocks are generated by partial melting of mantle wedge in the process of plate subduction with some contamination of crustal materials,acid rocks from differentiation of the basic magma with also crustal materials.The rock and ore are cognate and inheritable;（2）Features ofδEu andδCe show that the ore-forming fluid and material of quartz vein type polymetallic ore are mainly derived from high temperature and reductive magmatic hydrothermal fluid,but the disseminated type ore may be related to submarine hydrothermal fluid convective circulation metallogenesis;（3）The barren quartz vein has a close relationship with basic rock,probably from leaching of the siliceousmaterials from the basic rocks and re-precipitation under oxidation condition;（4）The Eu anomalies of barren quartz vein is obviously different from that of the polymetallic ore quartz vein,the former is negative while the latter positive so theδEu value could be used to evaluate the ore quartz vein and barren quartz vein.