Machangqing intrusive is a typical intrusive body of the alkali rich intrusive rock belt in western Yunnan, and in which a large number of mafic microgranular enclaves have been found. While petrological, petrochemical and Sr, Nd, Pb isotopic data of mafic microgranular enclaves and their host rocks show that the Machangqing intrusive was generated from magma mixing, and formed in the tectonic background of Cenozoic continental crust thickening. These data also show that the mafic microgranular enclaves were derived from the enriched mantle magmas while their host granite porphyry were derived from felsic magmas of the continental crust. And both the mific microgranular enclaves and their host rocks were created as a result of the magma emplacement and magma mixture that evoked by the underplating of mantle derived magma and then the melting of the continental crust that above it. Mantle derived magmas play an important role in the porphyry copper—molybdenum deposit as they furnished ore forming materials and fluids to them, and also the microgranular enclaves could be an important index in porphyry copper—molybdenum deposit prospecting.