Study On The Characteristics Of Magmatites And Mineralization In The Dashui Gold Deposit, Gansu Province

The Dashui gold deposit is a extra large deposit which was found in the in the south of West Qinling Mountains between Qinling and SongpanGanzi orogenic zone in the 1990s. It belongs to Xiqing Mountains metallogenic belt in the south of Xiqing Mountains uplift. The magmas which formed rock mass, apophysis and dike were strongly active in this area. Among this magmatic rocks, the rockmasses of Zhonggezhala, Zhongqu and Geerkuohe are the largest scale. Based on the works of predecessors and geological investigation in the mineralization area, Through the research of petrology, mineralogy, lithogeochemistry, rock-forming and ore-forming ages, stable isotope geochemistry et al, the author gets a large of significance geological data which provide the basis for discussing the diagenetic environment, material source, gold mineralization and the relationship between magmatic activity and mineralization. The results are as follows:1,The rockmasses of Zhonggezhala, Zhongqu and Geerkuohe in this area belong to high-K aluminous calc-alkaline-peraluminous alkaline series granites. Their zircons U-Pb ages are respectively 220.6±3.9 Ma,210.43±0.9 Ma and 215.9±1.7Ma.2,Sr, Nd isotopic compositions show that the source of magma in this area is High-K basaltic rocks in crust.3,The geodynamic settings of diagenesis and mineralization in the area are continental collision. The formation and emplacement process of magma accompanied the formation of ore-forming hydrothermal solution. The radial tensile fractures which are formed by lateral expansion and extrusion in the process of diagenesis offer the space for magmatic evolution of the dykes and ore-forming hydrothermal.4,The Rock masses, dikes and gold orebodies not only in space are closely associated, but also in time have certain coincidence; Meanwhile the ore type, material components, fluid composition and isotopic composition are also shown that mineralization and magmatic activities closely related. The magma and metallogenic event is a single undivided whole.5,The ore types of the Dashui gold deposit are complicated, which have large secondary leaching fracture-vuggy and epithermal hydrothermal vents mimics type ore, in addition to have many concealed explosive breccia and dike rock type ore This deposit presents a characteristic of multiple causes, which reverse the viewpoint of single cause. Maybe we can think that this is a special type of gold deposits.