Origin Of Ore-Forming Granite Porphyry And Metallogenic Mechanism Of The Machangqing Deposit,Northwest Yunnan,China

Machangqing ore deposit is the most significant in the middle of Jinshajiang-ailaoshan alkali-rich porphyry metallogenic belt, which is the best place to study Cu-Au-Pb-Zn-rich area Cenozoic metallogeny in China. Samples from the representative ore deposits Machangqing Cu-Mo-Au deposit and systemically investigated for the magmatic and ore-forming processes from the field scale to the geochemical lab scale, which is determination the mineralization types, find out the cause of rocks and discusses the metallogenic model. There is the following results:(1) Field and petrography observation show that the Machangqing Cu-Mo-Au porphyry deposit widespread the MME(Mafic Microgranular Enclaves), the enclaves has the characteristics of plastic flow, which has the varieties of contact relationship with the host rock that the transition distribution from the completely to the gradient;(2) The combined whole rock geochemistry and Sr-Nd-Pb isotopes analyses reveal that the enclaves and host porphyry granite have different sources, and both of them experienced a similar magma evolution process;(3) Microprobe analyses on the rock-forming minerals suggest that magma mixing and mingling played an important role during the formation the Machangjing alkali-rich porphyry, which is suggesting that associated with basic magma intrusion;(4) LA-ICP-MS of zircons extracted from the MME is 35.13±0.23 Ma and the porphyritic granite from the Machangqing ore field yielded age of 35±0.2 Ma, which is exclued out deep solid rock melting residues and xenolith of surrounding rock and provides important evidence of the origin of magma mixing. The samples from Machangqing ore field show similar geochemical and isotopic features, indicating lower crustal source with a mantle input. Combined the S and Sr-Nd-Pb isotopes analyses reveal that the mixing source is also indicated by the MME occurred in the porphyry body. The intensity magma mixing in near surface will make the bottom of basaltic magma invasion and mingling, which makes the mantle of copper, molybdenum and other ore-forming materials into the shallow crust, and eventually form the Machangqing ore deposit;(5) Based on the study of the geology of the mineral deposits, the associated controlling factors, the evolution of fluid and ore-forming processes, we presented a metallogenic model for Machangqing Cu-Mo-Au ore deposit.