The late Yanshanian magmatite in the Youjiang Fold Belt of West China is represented by basic-ultrabasic dyke swarms and ultra-acid rock veins. The new data support that the Yanshanian magmatic activity concentrated on 80~100 Ma in the Youjiang Fold Belt and the surrounding area, indicating large scale extension and lithospheric thinning in western oft-com:office:smarttags" />China during the late Cretaceous. Since the granitic magmatic activity of late Cretaceous was related to a large scale Sn-(Cu-Pb-Zn) mineralization in western China, it is worth considering the prospecting potential for Sn-(Cu-Pb-Zn) in the area where quartz porphyry occurs within the Youjiang Fold Belt.