关键词: 热液锆石, 锆石U-Pb定年, 地球化学, 冰湖沟金矿床, 夹皮沟矿集区, 中国东北

Abstract:  The Jiapigou mining district (JMD) is famous in the world for its numerous quartz vein- and altered rock-type gold deposits. The gold deposits in the JMD belong to mesothermal gold deposits and are characterized by fluids with moderate temperature and low salinity, Middle Jurassic mineralization, and genesis related to synchronic magmatism. In order to depict the process of synchronic magmatism-hydrothermalism, and tace the process of Au mineralization in this region, we present the deposit geology, petrology, and mineralogy, geochronology, and geochemistry of zircon from the Binghugou gold deposit in the JMD. The results show that: 1) Gold mainly occurs in cements of the shattered breccia; 2) Based on the morphology, internal structure, trace element composition, and U-Pb age, the zircons in the cements of the hydrothermal breccia and breccia-type ore can be divided into the captured (Group Ⅰ: 195-185 Ma), inherited (Group Ⅱ: 175-172 Ma) and hydrothermal zircons (Group Ⅲ: 176-173 Ma), and the U-Pb age of the hydrothermal zircons (Group Ⅲ) at 176-173 Ma indicating that Au mineralization occurred in the Middle Jurassic; 3) The zircons in the Groups Ⅱ-Ⅲ have low w(Y) values and high Y/Ho ratios, indicating that the late stage granitic melts coexist with the P- and Ti-rich hydrothermal fluids, and have systematic trends between w(Hf)-Th/U and w(Hf)-Yb/Gd, indicating that magma experienced gradual cooling and differentiation, and finally formed hydrothermal fluid; 4) The Ce/Ce* and Eu/Eu* ratios of the Group Ⅱ zircons are obviously higher than those of the Group Ⅲ zircons, indicating that the magma has high oxygen fugacity, and the hydrothermal fluid has low oxygen fugacity, while the values of the incompatible elements (P, Y, LREE, Nb, Th, and Pb*) gradual increase with the increase of the values of w(Hf) of the zircons (from the Group Ⅱ to Ⅲ), indicated that incompatible elements gradually entered the hydrothermal fluid phase and enriched during magmatic differentiation and magmatic-hydrothermal transition. Combined the geological observations, the magma is characterized by high temperature, high oxygen fugacity and volatile-rich components, which hindered the crystallization of sulfides in the early stage of its evolution, and promoted the enrichment of Au, S, Fe and incompatible elements in the late stage of its evolution/ hydrothermal fluid, resulting in the formation of the initial ore-bearing fluids. In the process of upward migration, abundant gold and sulfides precipitated from the ore-bearing fluids due to its unstable state caused by the intense fluid-rock interaction and decrease of pressure, temperature and oxygen fugacity, resulting in the formation of gold deposit. Combined with the regional metallogenic setting, ore geology, element geochemistry, ore-bearing fluid, and chronology of magmatism and mineralization, the above geological process is likely to have resulted in the giant gold mineralization observed in the JMD.

Key words:  , hydrothermal zircon, zircon U-Pb dating, geochemistry, Binghugou gold deposit, Jiapigou mining district, Northeast China