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

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-O 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.