Quantitative Analyses of Radiogenic Argon in Micas by Isotope Dilution Method

To extract radiogenic argon from micas and to purify extracted gases, an apparatus was constructed. The procedures for the extraction and the purification were described. Purified gases were analysed by a mass spectrometer and methane and helium were observed as main components of their impurities. Extracation efficiency of radiogenic argon from the muscovite(Mt. Ishikawa, 16-80 mesh)was studied and it was seen that among the total argon extracted during 20hours' heating at 1100°C, more than 99 percent was extracted in 10 hours. Quantitative analyses of radiogenic argon with two kinds of Japanese mica (Mt. Ishikawa, Fukushima-ken and Mt. Daiichi-suisho, Fukushima-ken) and M. I. T. standard biotite 3203 were carried out isotope dilution method. Quantities of radiogenic argon per one gram of these micas were 3.65×10-5cc STP, 2.84×10-5cc STP and 3.87×10-4 cc STP, respectively. K-Ar age of these two kinds of Japanese micas were estimated to be 1.3×108 years and 1.5×108 years respectively. The quantity of radiogenic argon in standard biotite 3203 obtained in this work were in good agreement with those reported by others.