Abstract
Shale and granite are the most potential helium source rocks; however, the distinctions in geochemical characteristics and the origin of residual gas remain unclear, which restricts the exploration and development of helium resources. A total of 11 rock samples (six shales and five granites) were collected from the Yangtze region for the analysis of the chemical composition, noble gas component, and isotope ratio of rock residual gas, as well as the mineral composition, major and trace elements of rock samples. The total absolute content of residual gas in shale is much higher than that in granite. The residual gas is mainly composed of N(2), CH(4), and CO(2) in shale and granite. The noble gas constitution of the residual gas within shale and granite is (40)Ar > (4)He > (20)Ne. The helium present in the residual gas of shale and granite is predominantly of crustal and radiogenic origin. The discrepancy between the measured neon isotope ratio and the corresponding air value is likely to be primarily attributed to mass fractionation and the addition of radioactive (21)Ne. The (40)Ar/(36)Ar ratio significantly diverges from the corresponding ratio of the atmosphere, with the superfluous (40)Ar stemming from the radioactive disintegration of K. (4)He and (20)Ne are concurrently displaced and accumulated in conjunction with groundwater within the formation. (4)He and (40)Ar* are generated in greater quantities; however, a relatively smaller proportion is currently retained in rocks. The retention coefficients P-((4)He) and P-((40)Ar*) of shale are both lower than those of granite, which may mainly be related to the fact that the porosity of granite is lower than that of shale. The P-((40)Ar*) in shale and granite is higher than P-((4)He), which also proves that the sealing temperature of Ar is higher than that of He. The emission of helium and argon is primarily dictated by temperature.