陕西凤太铅锌-金多金属矿田热水沉积遗迹-改造成矿作用机理研究

The Research on Hydrothermal Sedimentation Relics and Reformation Metallogenic Mechanism of the Fengtai Pb-Zn-Au Polymetallic Ore Field in Shaanxi

野外调研表明,凤太矿田铅锌矿床中发育有大量的硅质岩、硅质灰岩、硅质铁白云岩等热水沉积岩,根据其地质特征划分出热水沉积岩、热水沉积-交代岩、热水同生沉积岩及受后期改造热水岩4种微相。主量元素分析结果表明,具有热水成因的沉积岩其A1/(Al+Fe+Mn)值均小于0.4,该值随陆源碎屑物质的加入而增大;纯生物成因沉积岩该值最大接近于0.6。MnO/TiO_2>0.5,(Fe+Mn)/Ti>20,高含量的Ba、As、Sb、B、Ag、Hg、U元素及较低含量的Zr元素反映出沉积物具有海相热水沉积的特点,局部受到陆源碎屑物质的影响。C-O同位素数据说明热水活动发育于浅海体制下相对滞留的裂陷槽中,H-O同位素数据表明沉积物沉积的主体为地层水,在后期的热循环过程中与灰岩发生了O同位素交换而发生了漂移。铅锌矿床的形成经历了喷流-沉积期、构造热液期和表生期3个时期。

Field survey indicated that the Pb-Zn deposits in Fengtai ore field developed a lot of hydrothermal sedimentary rocks,such as siliceous rocks,siliceous and ferruginous dolomite,siliceous and dolomitic limestone.According to the geological features,4 kinds of microfacies have been marked off,that is hydrothermal sedimentary rocks,hydrothermal sedimentary and metasomatic rocks,hydrothermal syngenetic sedimentary rocks and the post-reformation of hydrothermal sedimentary rocks.The analysis results of main elements indicated that,the ratios of Al/（Al＋ Fe＋Mn） of hydrothermal sedimentary rocks are less than 0.4,and these ratios are increasing with the addition of terrigenous detrital material.The largest ratio of pure biogenic sedimentary rocks is close to 0.6.MnO/TiO2〉 0.5,（Fe＋Mn） /Ti〉20,and the high content of Ba,As,Sb,B,Ag,Hg and U elements,as well as the low content of Zr element indicated that,these sediments have the characteristics of the hydrothermal sedimentation,and some of them were affected by terrigenousclastic substance.The C-O isotopic data show that hydrothermal activity was developed intaphrogenic trough which lied in the shallow sea The H-0 isotope data declare that the formation water was the main body of sediments,and Oisotope had exchanged between formation water and limestone in the process of thermal cycling,leading to the excursion.The formation of Pb-Zn deposits had experienced exhalative-sedimentary period,tectonic hydrothermal stage and supergene stage.