The Washan iron deposit is one of the most important porphyrite deposits in the Nanjing-Wuhu Basin. In order to further confine the mineralization age and analyze the geodynamic settings of the Washan iron deposit, this paper analyzed the REE geochemistry of the rocks related to ore-bearing pyroxene dioritic porphyrites and magnetites in this deposit, and the age of the ore-bearing pyroxene dioritic porphyrites was obtained through LA-ICP-MS precise determination of the zircon U-Pb age. The dating result indicated that the ore-forming rocks of the Washan iron deposit yielded an age of 127.64-4.4Ma, belonging to early Cretaceous and representing the mineralization age of the Washan iron deposit. It is considered that the ore-forming magmas were originated from the mantle or lower crust basalt. The lithospheric thinning could be induced by the ore-forming materials of the mantle coming to the crust, the ore-forming age were the peak of the lithospheric thinning.