Longqiao iron deposit locates at the northern edge of Lujiang-Zongyang ore concentrated area in Middle -Lower Reaches of Yangtze River, the orebodies mainly hosted in argillaceous siltstone and carbonate between volcanic rocks of lower Cretaceous Longmenyuan formation and quartz syenite, monzonite;According to the biotite Ar-Ar dating associated with pyrite orebodies and calcites,Lz370-1 sample, and altered trachyandesites of country rocks,Lz370-2 sample, in 370 middle section in the deposit, We obtained the biotite 40Ar-39Ar plateau age and isochron age of the two samples, they were 133.4±1.5Ma(2σ),133.1±4.8Ma(MSWD=0.32) and 135.4±1.5Ma(2σ), 135.5±1.8Ma(MSWD=1.3), respectively. They represented the age of hydrothermal alteration and mineralization in Longqiao iron deposit. The regional magmatism ages and metallogenic epochs of typical deposits showed that it has universality on hydrothermal activity and mineralization in Middle-Lower Reaches of Yangtze River during early Cretaceous, further identified that the metallogenic epoch of Longqiao iron deposit was early Cretaceous.