Abstract: According to the isotopic ages measured by different methods （including the U-Th-Pb, Rb-Sr and K-Ar methods）, combined with relevant geological data, it is proposed that, except the "Weitou" gneissic plagioclase granite whose isotopic age is 140 Ma, all the other rock masses have isotopic ages of 100-110Ma, belonging to late Yanshanian intrusive rocks resulting from separate intrusions. The Rb and Sr contents and characteristics of the changes of the initial Sr isotopic values of various rocks masses indicate that the intrusive rocks of separate intrusions might be derived from the same deep-source magma. During the ascent of the magma the crustal sialic material was introduced and accordingly the magma carried more Rb, thus changing the radiogenic Sr in the original Sr isotopic composition.