Abstract: ~(40)Ar/~(39)Ar Dating Method and Ar Isotopic Mass Spectrometry Analysis of QuartzShang Haiqing; Wang Songshan;Hu Shiting; Qiu Ji (Institute of Geology, Chinese Academy of Sciences, Beijing 100029, China)Received 1993-08-09Abstract:The potassium content in the quartz is very low and contains inclusion composition which usually occurs interference of the excess Ar and Cl for 40Ar/39Ar dating. There are two chlorine isotopes (35Cl and 37Cl) in the quartz minerals. When they are irradiated in a reactor, producing the reaction 35Cl(n. γ)36Cl and 37Cl(n.γ)38Cl, followed by β-decay to 36Cl Ar and 38Ar, respectively. The half life of 36Cl is very long (3. 1 × 105 years) and 38Cl is very short (37. 3min). Therefore, by the time of Ar analysis in a typical irradiation experiment a small amout of 36Ar is produced, while all the 38Cl has decayed to 38Ar.In the 40Ar/39Ar isotopic dating technique for quartz or other minerals, the Cl and excess Ar can be corrected by samples separation, 36Cl is adsorpted at low temperature (-80～-120℃) in the experiment process. Some formulas are used to calculate 'eAr and Fvalue, and thus to obtain precise 40Ar/39Ar age of the quartz which represents the forming time of gold deposits. All the isotopes of argon are analysed using a new RGA-10 gas-source mass spectrometer (VSS Company, U. K. ) operating in the static mode.Its sensitivity is 1. 12 × 10-4A/torr(1. 42 × 10-14 mol/mV). The data are calculated with a Stone-386 computer.Keywords: quartz,~( 40(Ar/~(39)Ar age, mass spectrometry analysis