Abstract: There are welldeveloped alkalirich porphyry polymetallic deposits in the eastern Jinshajiang-Ailaoshan fault, western Yunnan. The alkalirich porphyries in the region have been discovered containing deep xenoliths.The studies on the geochronology for deep xenoliths, their host alkalic porphyries and mineralizing quartz viens show that the diagenetic age of the deep xenoliths are older than that of their host alkalic porphyry, and the alkalic porphyry’s diagenesis and associated mineralization are almost same in age. Combined with the studies of Pb-Si-Sr-Nd isotopic geochemistry， it is indicated that during the period of alkalic magma diagenisis the alkalic porphyry and its country rocks were suffered metasomatic alteration by the siliconrich mineralizing fluids which were contaminated with crustal rocks, meanwhile, the ore deposits were formed. The mineralizing process of the siliconrich fluids is essentially a continuation of the mantle fluid metasomatism during mineralizing processes in the crust. The mineral crystalline age (116.0 Ma) of the mantle fluid metasomatism and the age (51.2 Ma) of the siliconrich mineralizing fluid suggest that the mantle fluid had been active through the whole processe of the alkalic magma diagenism and associated mineralization. The mantle fluid resulted in the concentrations of Si, Al, Na, K, Siincompatible elements and ore elements, and the transition of Sr-Nd isotopic geochemistry from depleted mantle to enriched mantle,and the high temperature mineralization in the porphyry and the low temperature mineralization in the country rocks. The action of the mantle fluid is not only an internal constraint to wide spread Cenozoic mineralization but also an important geochemical background for the formation of large and superlarge deposits in the western Yunnan, China.

Key words: mantle fluid process, alkalic porphyry, geochronology, isotope geochemistry, mineralization