Abstract: Abstract: The Meishan polymetallic iron deposit is one of the representative deposits in Ningwu Basin, with its Fe-Cu-Au-Mo mineralization related closely with the gabbro-diorite porphyry. In this paper, the authors conducted LA-MC-ICP-MS zircon U-Pb dating of the ore-bearing gabbro-diorite porphyry and the fresh gabbro-diorite porphyry under the orebody, and obtained the U?Pb ages of (137.8±1.7) Ma and (141.2±1.0) Ma, respectively, suggesting that the gabbro-diorite porphyry was formed in 138~141Ma, the accompanying Fe-Cu-Au-Mo mineralization might have taken place later, and both occurred in Early Cretaceous, constrained by a tectonic regime extension and lithospheric thinning environment. Depending on the chronology and geological facts evidence, the authors put forward a new viewpoint that the volcanic-magmatism of Ningwu Basin began from the north and lasted for 7~10 Ma at least. The U-Pb ages of the older zircons from the gabbro-diorite porphyry range from 1903 to 1898 Ma, 1163 Ma and 296 to 292 Ma, suggesting Paleoproterozoic, Neoproterozoic and Early Permian. These data imply that the basement rocks made some contribution to the magmatism and there existed the so-called double layer structure of the Paleoproterozoic crystalline basement plus the Mesoproterozoic-Neoproterozoic fold basement in the Middle-Lower Yangtze River valley metallogenic belt (YRB).