Properties And Mineralizing Significance Of CO₂-rich Fluid Inhaigou Gold Deposit, Jilin Province

Haigou gold deposit in Jilin Province is one of typical orogenic gold deposits in China, and also belongs to mesothermal hydrothermal vein deposit. The deposit locates in the junction of east of the northern edge of North China Craton and Xing’an Mongolian orogenic belt. There are many faults in this deposit. The magmatic rocks exposed in this deposit are mainly late Archaean tonalite, Hercynian biotite granite, Yanshanian monzonite-monzonitic granite, Yanshanian pyroxene diorite and so on. The stratum exposed in this deposit is primarily mesoproterozoic epimetamorphic rock of Seluohe group.The ore minerals of Haigou gold deposit are mainly natural gold, pyrite, chalcopyrite, galena, molybdenite, sphalerite and so on. The structures of ores contain vein-like structure, mesh-vein structure, massive structure, disseminated structure, and also contain brecciated structure and miarolitic structure in part of the deposit. Furthermore, the textures of ores consist primarily of crystalline texture, metasomatic texture, exsolution texture and pressure texture.The results of the research on the types, characteristics and properties of ore-forming fluid in Haigou gold deposit through the techniques of microscopic temperature testing and laser Raman testing on fluid inclusions show that the fluid inclusions of Haigou gold deposit should be divided into three types: CO2-H2O-NaCl inclusions, pure-CO2 inclusions and NaCl-H2 O inclusions. Furthermore, the properties of ore-forming fluids are low-medium salinity and low density. By the research on fluid inclusions using the testing methods of gas-liquid components analysis, the data show that there are abundant carbonaceous materials, especially high content of CO2. Results of positive and negative ions testing prove further the characteristics of low-medium salinity, and show that the fluid in Haigou deposit is a system of Cl--rich and F--poor H2O-NaCl-CO2+CH4.Through the methods of stable isotope geochemistry, the research on ore-forming fluid(C, H, O isotopes) and pyrite(S isotope) of Haigou gold deposit concludes that the δ34S figures vary from-9.5‰ to-8.3‰. Combining with the Pb isotope testing by previous researchers, the ore-forming materials are mainly derived from mantle or lower crust, following with the exchange with wall rocks, which leads some components of wall rocks to be added. As for the sources of ore-forming fluids, the δ13CCO2 figures range from-22.2‰ to-14.4‰; the δD figures vary from-106.9‰ to-52.7‰; the δ18OSMOW figures range from 12.1‰ to 13.2‰, together with the data from the previous research, showing that the early magmatic water is dominant source of ore-forming fluids, following with the mixture of atmospheric precipitation.Comparing the content of CO2 in ore-forming fluid with the content of gold in certain samples, the results suggest that there is a positive correlation between the content of gold and that of CO2, which illustrates that the higher the content of CO2 is, the higher the grade of CO2 is. The main reason of this fact could be explained that high-temperature CO2 acts as a kind of solvent in the process of moving of gold. While gold precipitates, CO2 emits and conserves as fluid inclusions. This positive correlation will provide significant clue to ore exploration in deep earth in Haigou gold deposit, and even all the gold deposits with the same origin.