Petrogenesis of the Pujue Porphyries, Southern Lhasa Terrane, China: Implications for the Porphyry Cu Mineralization Potential

ABSTRACT The Gangdese porphyry Cu metallogenic belt (GPCB) is an important metallogenic belt, in which most porphyry Cu deposits are related to high‐Sr/Y porphyries and are located east of 87° E. Although numerous coeval high‐Sr/Y porphyries have been identified in the western part of the belt, few porphyry Cu deposits have been discovered there. Key factors controlling this difference remain controversial. The newly discovered Pujue Cu deposit in the western GPCB contains three suites of porphyries, which may help address this issue. The granite porphyries have two stages (49.1 and 16.4 Ma), whereas the monzogranite porphyry formed at 24.1–23.9 Ma. The Eocene granite porphyry was generated by melting of juvenile lower crust, whereas the Oligocene monzogranite and Miocene granite porphyries were sourced from partial melting of thickened ancient lower crust. The monzogranite and Miocene granite porphyries have f O 2 and H 2 O content comparable to those of porphyries induced in the GPCMB. However, their lack of juvenile components reduces their potential to form large Cu deposits. The Eocene granite also has suitable f O 2 to form porphyry Cu deposits, but its low H 2 O content hindered its mineralization potential. The insufficient juvenile component and relatively low magma H 2 O content are the key factors limiting the mineralization potential of porphyries in the western GPCMB.