Yudongzi complex, the significant occurrence horizon of iron mine , is the most important Archean basement and the oldest geological mass in the Qinling area. It is mainly composed of metamorphic strata (Yudongzi group) and granitic metamorphic intrusions with unequal size, most of which contact with structural foliation. Based on CL image features of zircon, combined with genetic analysis of zircon and microdomains U-Pb isotope LA-ICP-MS (laser ablation ICP-MS) determination, we obtained an upper intercept age of 2645±25Ma（MSWD=1.2）and an weighted mean 207Pb/206Pb age of 2645±24Ma for the magnetite-quartzite magmatic zircons in Xiaogoushan mine area. The consistent data represents the protolith formation age of quartzite , the original rock of which is intermediate-acid volcanic rocks. The upper intercept age 2555±24Ma（MSWD=1.4）for the metamorphic zircons we have also got, is consistent with the weighted mean 207Pb/206Pb age of 2527±27Ma within the error range, and indicates the metamorphic age of quartzite from volcanic. From above we can say that the age reflects an important regional metamorphism event in Archean.