SHRIMP U-Pb Zircon Age and Its Implications of Quartz Syenite in Hadamengou, Inner Mongolia *

Based on dating zircon TIMS and SHRIMP U-Pb ages for the ore-controlling quartz syenite of Hadamengou large gold deposit, Inner Mongolia, the authors confirmed that the quartz syenite intruded upon during the early of Pa- leoproterozoic. Its zircon SHRIMP U-Pb concordant point age was (2483 ± 10) Ma(1σ) and the upper intersection age gived (2508 ± 41) Ma(1σ) on the disaccording line respectively. The quartz syenite in Hadamengou was proved the oldest Paleoproterozoic alkali-rich intrusive rock in China till now. Its old age and its distribution of the alkali-rich in- trusive rock had important tectonic significance. It revealed that after the amalgamation at the end period of Archean, the crust of North China Craton had reached some thickness and had transformed into a kind of extensional tectonic settings since the intrusion of the alkali-rich intrusive rock in Hadamengou.