Compositions Of Apatites As Metallogenic Indicators Of Porphyry Deposits In The Sanjiang Tethys Metallogenic Domain,Southwest China

Apatite has important research value in the division of lithology,judging the origin of rocks,studying the origin and process of magma and indicating the redox degree of magma.The Sanjiang Tethys metallogenic region is an important part of the Tethys metallogenic belt,and there are many super large-large porphyry deposits in this area.The study about the differences between ore-bearing porphyries and barren porphyries,and the study on the metallogenic characteristics of magma in different periods in this area are preliminary.So we select apatite as the research object,and compare the geochemical characteristics of apatite in ore-bearing porphyries and barren porphyries of Beiya.We also analyze the petrogenetic and ore-forming information recorded by apatite of ore-bearing porphyries of the Beiya gold deposit,the Pulang copper deposit and the Tongchanggou molybdenum deposit,and discuss the significance of apatite for porphyry mineralization potential.Through the study of apatite in the Beiya gold deposit,it is found that the petrographic characteristics of the two are quite different.The surface of the backscattering image of apatite in barren porphyries is smooth and smooth,but the backscattering image of apatite in ore-bearing rock mass has many holes and fractures.Compared with barren porphyries,apatite in ore-bearing porphyries has a relatively higher ?Eu value(the average is 0.69 ppm)and an obviously lower ? Ce value(the average is 1.02 ppm).This indicates that the oxidation degree of the magma forming ore-bearing porphyries is higher than that of barren porphyries.Meanwhile,the higher Ce/Pb value of apatite in ore-bearing porphyries means that the magma forming them has strong fluid activity during its evolution.Apatites of porphyries of different mineral species are distributed in the area of adakite,and this indicates that these porphyries probably all originated from the adakite magma.Degree of magma oxidation of the Beiya ore-bearing porphyries are higher than that of Pulan and Tongchanggou,and this means that porphyry Au deposits are formed from magma with a higher degree of oxidation than that of porphyry Cu and Mo deposits.According to the halogen content of apatite and the distribution characteristics of F and Cl,there is a period of either directly or indirectly with the addition of a sheet source fluid,in the process of forming the copper-bearing magma of Pulang and Tongchanggou molybdenum-bearing porphyry in Banjiang area.But the gold-bearing porphyries in Beiya may have formed in an intracontinental collision environment,so there is no sheet fluid involved.