Ore-bearing Propertites Of Intrusions In The Machangqing Porphyry Copper-molybdenum Deposit,West Yunnan China:Evidences From Composition Of Zircon And Apatite

The Machangqing copper-molybdenum deposit is mainly composed of granite porphyry,monzonite porphyry,syenite porphyry and porphyry granite.Its magmatic activity is about 36 Ma.The main ore-bearing rock body is granite porphyry.Other lithologies are not mineralized or lean.Baoxingchang ore section is the largest one,which is much larger than the Luandongshan and Shuangmacao ore sections.Porphyry copper-molybdenum ore bodies are developed in both sections.The stable properties of zircon and apatite and the indication of trace elements to magmatic oxidation and fluid activity are of great significance to the study of lithology of various rocks in Machangqing.Based on the analysis of trace elements in apatite in the study area,it is found that the distribution curve of rare earth elements in apatite of Machangqing rock mass is relatively enriched with light rare earth elements and relatively deficient with heavy rare earth elements.Compared with non-ore-forming rock mass,the distribution of light rare earth elements in ore-forming rock mass is more intensive,the aggregation degree is higher,the distribution of heavy rare earth elements is looser,the Ce anomaly is more obvious,with low Sr,Pb,Th,high Y,U,?REE,and the ratio of trace elements is higher.The values of Ce/Pb,?Eu and Th/U are higher than those of?Ce,Sr/Ce,Sr/Eu and Th/U.Therefore,apatite in ore-forming rock mass has higher oxidation,stronger fluid activity and magmatic differentiation than that in non-ore-forming rock mass.The Ce⁴⁺/Ce³⁺ratio of zircons in ore-forming bodies ranges from 156.9 to 397.2,with an average value of 225.1.The Ce⁴⁺/Ce³⁺ratio of non-ore-forming bodies is mainly concentrated between 10 and 200,with an average value of 72.10.On the whole,the Ce⁴⁺/Ce³⁺ratio of ore-forming bodies is generally higher than that of non-ore-forming porphyries.The average oxygen fugacity of ore-forming bodies is?35?FMQ=+9.8,and the average oxygen fugacity of non-ore-forming porphyries is?35?FMQ=+0.6.This is the case.The Y/Ho ratio of Machangqing ore-forming body ranges from 34.2 to 59.4 with an average of 43.2,while that of non-ore-forming porphyry ranges from 31.2 to 35.9 with an average of 33.6.The Zr/Hf value of zircon in metallogenic rocks is higher than that in non-metallogenic rocks.The distribution curve of rare earth elements in zircon shows relative deficit of light rare earth elements,relative enrichment of heavy rare earth elements,positive Ce anomaly and slight negative Eu anomaly,and?REE ore-forming body>non-ore-forming body,zircon Ti thermometer and oxygen fugacity study show that the Machangqing ore-forming rock was formed under subduction environment of high temperature and high oxygen fugacity,so the Machangqing porphyry ore-forming body is in the ring of high temperature and high oxygen fugacity.Based on previous studies,the formation time of the main metal minerals in Machangqing coincides with that of the rock mass,and it is concluded that the mineralization can take place under the environment of high temperature and high oxygen fugacity.Through the study of three different scale ore sections,it is found that the stronger the oxidization of magma,the higher the fluid activity,and the more obvious the magma differentiation,the larger the ore-forming scale.