Located in the northern margin of North China craton, the Liubagou gold deposit of Inner Mongolia is a large ore deposit characterized by widespread K- feldsparthization. The authors apply the ⁴⁰Ar-³⁹Ar isotopic dating of K-feldspar to define the mineralization age, and give a detailed study on the Pb isotopes of ore. The result indicates that the Liubagou gold deposit formed in the Early Indosinian. The latest magmatic activity of Indosinian (about 220 Ma) induced the magmatic hydrothermal mineralization directly. The age of source region is 2.5 Ga by calculation of Pb isotopic data, indicating that the ore-forming materials primarily came from the strata of the Archean Wulashan Group.