The Separation of Authigenic Illite from Detrital Illite in Sedimentary Rock for Ar Isotope Dating

The dating of sedimentary rock has in part been hampered by the problem of complete separation of authigenic illite from detrital illite. Taking the clay minerals of Changxing area in Zhejiang Province as an example, this paper describes the separation procedure of authigenic illite from detrital illite, with all the grain size fractions analyzed by X-ray diffraction (XRD). The result shows that impurities such as quartz, potassium feldspar, albite, calcite and dolomite decrease gradually with the reduction of grain size, and there are no detectable impurities in the 0.2 μm fraction. It is especially striking that the content of mixing I/S in the samples 5-4,6-3 and 6-4 is 100%, which shows that the separation is relatively successful.