Abstract:Xiajinbao granite-porphyry body is located in Yong’an-Xiayingfang-Maojinggou tectono -magmatite zone, which is closely related to Au, Ag and Cu polymetallic metallogenic. Zircon U-Pb geochronology and trance element geochemistry of the ore-bearing granite porphyry in the Xiaojinbao was studied first time. The weighted average of ²⁰⁶Pb/²³⁸U age of (158.0±2.5) Ma (1σ, MSWD is 0.76, n=16), the result shows that Xiajinbao granite-porphyry body forms in early Yanshanian. Using zircon Ti thermometer, the forming temperature of zircon was calculated and all of them more than 700 ℃ except one point, it shows that zircon crystallized in deep and high temperature magma. The ε_Hf(t) values of zircon ranging from -10.9130 to -7.5828, and all of them are less than 0. The characteristics of Hf isotope show that Xiajinbao granite-porphyry body originates from the partial melting of lower crust, and the formation environment is conversion environment from compression to extension. The geodynamic mechanisms of Xiajinbao granite-porphyry body formation were proposed based on the zircon U-Pb geochronology and trace element. The lower crust remelted under the magma under plating of the North China block in early Yanshanian, at the same time, involving in part of mantle material. Primary magma increases along the deep fault based on the deep pressure, showing a crystallization differentiation. The exsolution fluid from magma forms the water-rich magmatic hydrothermal. The ore-bearing granite porphyry is a product form by condensation of magmatic hydrothermal under the lower temperature and pressure of near-surface.

Key words: zircon U-Pb geochronology; zircon Hf isotope; diagenesis; diagenetic geodynamic; Xiajinbao rock body