Research on fluid inclusions of the Baiyun gold deposit, Liaoning Province: implications for fluid evolution and metallogenic mechanism

The Baiyun gold deposit in Liaoning province is situated at the northeastern edge of the North China Craton and is one of the significant large-scale gold deposits in the Jiaodong-Liaodong-Jinan metallogenic belt.Based on its geological features, this study thoroughly examined the fluid inclusion characteristics of the deposit, analyzed the fluid properties, evolution, and gold movement and precipitation mechanisms.According to the interlacing of veins, mineral assemblage, and metasomatism, the metallogenic process of the Baiyun gold deposit can be divided into three stages: quartz-pyrite(early stage), quartz-polymetallic sulfide(main stage)and quartz-carbonate(late stage).Petrographic observation reveals that the fluid inclusions developed in the Baiyun gold deposit are primarily H₂O two-phase inclusions(W type), CO₂-H₂O three-phase inclusions(C type)and pure CO₂ inclusions(PC type).Microthermometry results show that the homogenization temperature of fluid inclusions during the main ore-forming stage is between 240℃ and 280℃, and their salinity varies between 6 and 8% NaCl eq.The corresponding fluid density is calculated to be 0.74~0.91 g/cm³.These exhibit medium-temperature, medium-low salinity and medium-density ore-forming fluid the characteristics.H-O isotopic results suggest that the ore-forming fluid was originally magmatic hydrothermal, and atmospheric water was gradually mixed in during the ore-forming process.W type, C type and PC type inclusions coexist in the same field of view, and while the homogenization temperatures of these inclusions are comparable, their modes of homogenization are distinct, indicating the presence of fluid immiscibility.The existence of water-rock interaction is suggested by silicification and sericite alteration, which are closely connected with mineralization in the surrounding rock alteration, as well as the pyrite-sericite-quartz mineral assemblage features.Therefore, the main mechanisms of gold mineral precipitation in the Baiyun gold deposit are fluid immiscibility and water-rock interaction.On this basis, it is estimated that the metallogenic pressure is 43.4~87.5 MPa, and the corresponding metallogenic depth is 1.6~3.3 km. Combined with the previous estimation of regional denudation depth, it is inferred that the Baiyun gold deposit still has great resource potential in the deep.