Fluid Inclusions Characteristics of Quartz Vein in Granite and Helium Accumulation in Guanzhong Basin, Shaanxi Province

The Guanzhong basin is an important structural position, which is located in the middle zone between the Qinling Orogenic belt and the Ordos Basin. Based on the analysis of petroleum wells and geothermal wells, it can be inferred that rich-helium gas resource and water soluble helium gas resource were developed in the Guanzhong Basin. The helium gas is mainly sourced from the shell source gas, with uranium rich granite served as its main source rock. In this paper, the samples are collected from the quartz veins in the granite of the southern Guanzhong basin, and the fluid inclusion of cracks in quartz has been tested by using Ramnour-u1000 laser spectrometry. The study show that the majority of fluid inclusions are consisted of vapor-liquor (two phase) and CO₂-bearing three phase inclusions. The vapor-liquor two phase fluid inclusions reveal the main components of H₂O and CO₂, with minor components of CH₄, H₂, and H₂S. According to genetic difference, the fluid inclusions of the quartz vein can be divided into approximating primary inclusion, the early-secondary inclusion and the late-secondary inclusion. The results of micro-thermal analysis show that the homogenization temperature of approximation primary inclusion are more than 430℃,the ones of early-secondary inclusion vary from 330℃ to 370℃, and the ones of late-secondary inclusion range from 170℃ to 230℃. By integrating the fluid inclusions compositions, the homogenization temperatures, and combining with the thermal evolution of the Guanzhong Basin, it is believed that the fluid inclusions of quartz vein had formed as two charging orders. It is suggested that the critical is in the Miocene Epoch-Pliocene Epoch.