Abstract: China;4.Qinhuangdao Mineral Resources，Hydrogeological and Engineering Geological Party，Hebei Bureau of Geology and Mineral Exploration and Development，Qinhuangdao 066000，China Geochronology of Rhyolite porphyry discovered firstly in northeastern Fanjing Mountain area of northeastern Guizhou Province was studied by using LA-ICP-MS zircon U-Pb method.The research results showed that the rhyolite porphyry is developed during the early cretaceous 98.9±1.3 Ma，and it is the product of Yanshanian magmatism activity.Besides that，there maybe exist plenty of intermediate-acid granitic batholiths in this deep area in Indosinian-Yanshanian era，and these concealed minerals have close relationship with low-medium temperature hydrothermal deposits.The discovery of rhyolite porphyry and the determination of its era are significant to discuss the tectonic-magmatic evolution characteristics of southwestern section of Jiangnan orogenic belt，especially to guide ore prospecting of magmatic hydrothermal polymetallic gold deposits.

Key words: Rhyolite porphyry, LA-ICP-MS, U-Pb Zircon Date, Yanshanian, Fanjing mountain area of northeastern