Volcanic Rocks Around The Dong'an Gold Mine, Xiaoxing'anling And The Relationship To The Gold Deposit

Xiaoxing'anling locates at northeast China with special and complex tectonic structures. This region is rich in gold, silver, zinc, tungsten and molybdenum mines as well as perlite, and other mineral resources, especially because of the discovery of the Dong'an large gold deposit in recent years, it starts to attract the attention of both Chinese and foreign geologists. Based on geological field investigation, through the study of the following three aspects: (1) petrology and geochemistry of Mesozoic volcanic rock; (2) fluid inclusion features and geochemistry; the chronology of volcanic rock and the gold mineralization, we figured out the initially volcanic genesis, forming age and the gold ore material origin, the fluid origin and the mineralization epoch of the Dong'an gold deposit in Xiaoxing'anling area, and then gave a reasonable explanation on its genesis and geodynamics background of ore forming.The intermediate-acid volcanic rock of the Ningyuancun Formation within study area is a peraluminous K-rich calc-alkaline and calc-alkaline series, which forms from the metasomatosis between differential enriched-mantle magma and continental crust. The intermediate-basic volcanic rock from the Ganhe Formation is a metaluminous K-rich calc-alkaline and calc-alkaline series, which forms fom the differentiation of the enriched-mantle magma. The intermediate-acidic volcanic rock of the Fuminhe Formation is a metaluminous-peraluminous K-rich calc-alkaline and calc-alkaline series, which forms from mix of the enriched-mantle differential magma and the delaminated mid-lower part of continental lithosphere.In the Dong'an gold mine, the measurement yields the range of major mineralization temperature 200-250℃, salinity 0.53%—5.84%, mineralization pressure 60.5-71.8 MPa. The mineralization fluid presents the mix of magmatic water and meteoric water. The Dong'an gold deposit is a typical adularia-sericite epithermal gold deposit. Its forming mechanism is that the post-magmatic hydrothermal enriched in metal elements(Au, Ag, etc.) along the faults rise up, and due to rapidly changing of physical and chemical conditions (temperature, pressure, salinity, concentration and pH), the chemical balance is destroyed, the solution redox-potential is changed, and massive gold precipitate, and meanwhile forms the quartz and adularia. After then because of the meteor water's addition, the remained gold precipitates, chalcedony and low-temperature fluorite occurs.The formation of the Dong'an gold deposit correlates to the regional geodynamic background. From early Jurassic (190 Ma) to early Cretaceous (108Ma), owning to diving function of the Pacific Ocean plate, the tectonic evolution in the area suffers a process of extrusion—extrusion-stretching alternation—extension, meanwhile the continental crust has experienced a process of lithospheric from thicking to thinning. At the early Cretaceous (130Ma-108Ma) , the thinned continent lithosphere causes secondary compresso-shear folds within the Kuerbin crust fold with equidistance distribution, which is the predominate ore-controlling tectonic structure. In the late Yanshanian (107Ma), the Dong'an gold deposit has formed along the fault zone.