Abstract: The Jiawula deposit is one of the large-scale Pb-Zn-Ag deposits in Derbugan Cu(Mo)-Ag-Pb-Zn metallogenic belt in the western slope of the Great Xing'an Range,and has been still considered as an epithermal deposit related to volcanic-subvolcanic hydrothermal. Recent researches show that the mineralization has closely genetic association with the fine vein and disseminated Cu mineralization in the deep. The geochronology and geochemistry researches have been carried out on the ore-hosting granite porphyry associated with the fine vein and disseminated Cu mineralization. The experimental results show that the granite porphyry has the w(SiO₂) content ranging from 71.59% to 72.36%,w(TiO₂) from 0.46% to 0.58%,w(Al₂O₃) from 15.45% to 15.92%,w(Fe₂O₃) from 0.74% to 0.90%,w(FeO) from 1.67% to 1.96%,w(MgO) from 0.55% to 0.89%,w(Na₂O+K₂O) from 9.01% to 9.91%,w(K₂O/Na₂O) from 1.37 to 2.15,rittmann index(σ) from 2.77 to 3.43,and alkalinity index(AR) from 3.13 to 3.96. The major element composition indicate that the rock belongs to shoshonite series,high potassium,peraluminous A type alkali-rich granite granite porphyry. The total amount of rare earth elements(∑REE) changes from 350.11×10^-6 to 408.80×10^-6,the ratio of light and heavy rare earth(∑LREE/∑HREE) varies from 11.25 to 11.44,and value of δ Eu mainly ranges from 0.38 to 0.44. These granite porphyry samples also have such geochemical characteristics as stronger fractionation of light and heavy rare earth, obvious negative Eu anomaly, strong depletion of compatible elements(Ni,Co,Cr,V,Yb,Eu,etc.),enrichment in incompatible elements(Cs,Rb,Pb,U,Th,Zr,Hf,etc.),relative depletion of Li,Sr and other incompatible elements, higher ratio values of Rb/Sr(0.93 to 1.31) and Zr/Hf(29.38 to 35.61). According to data mentioned above, it can be concluded that the original magma of the granite porphyry was derived from the partial remelting of lower crustal layer metasomatized by the fluid dominated with CO₂ or H₂O,and the magmatic process were suffered from strong hybridization with carbonate,which is favorable for ore-forming fluid of Cu-Ag-Pb-Zn mineralization. Considering the facts that there are both magmatic and hydrothermal zircon grains in the granite porphyry samples, and the weighted average of magmatic zircon ²⁰⁶Pb/²³⁸U age is (146.4±1.6)Ma(MSWD=1.30,n=12) and the weighted average of hydrothermal zircon ²⁰⁶Pb/²³⁸U age is(143.1± 3.9)Ma(MSWD=0.56,n=5),such conclusions can be drawn as followings. The first is that the Jiawula deposit formed at the initial stage of Early Cretaceous,and the magmatism closely related to the mineralization occurred at the end of Later Jurassic. The second is that the Jiawula deposit belongs to the porphyry Cu-epithermal Cu-Ag-Pb-Zn metallogenic system. The third is that the geodynamic background of diagenesis and metallogenesis was either conversion from extrusion to extension related to the subduction of the Paleo Pacific plate to the Eurasian plate,or extension stage after the collision associated with the closure of the Mongolia-Okhotsk ocean.

Key words: geochronology, geochemistry, geodynamics, alkali-rich granite porphyry, Jiawula Cu-Ag-Pb-Zn deposit, western slope of the Great Xing'an Range