Significance and Inherited Zircon U-Pb Age of Diabase-porphyrite in Qunjisayi Copper Deposit, Western Awulale Mountain, Xinjiang

As an important part of the ancient Yili rift, the western Awulale Mountain possesses many diabase dykes including the Qunjisayi diabase-porphyrite which is controlled by volcanic crypto explosive breccia pipes. The diabase-porphyrite dyke contains many inherited metamorphogenic zircons which yield weighted average ²⁰⁷Pb/²⁰⁶Pb ages of (1798.9±6.1) Ma. This age is consistent with the age of Precambrian Basement in Western Tianshan Mountain. The diabase-porphyrite dyke is characterized with higher FeO, TiO₂ and Na₂O content, little K content, lower incompatible elements content and weak negative δEu anomaly. The rocks are enriched with HFSE such as Th, U, Ta, Nb, Zr and Hf, depleted of LILE such as Rb, Ba, K, Sr and Cs. The petrogenesis of Qunjisayi diabase-porphyrite dyke indicates that the magma is derived from weak depleted mantle mingled with a little crust rocks. All the research results indicate that the Qunjisayi diabase-porphyrite dyke is generated from continental rift setting which is relevant with the underplating of the upper-mantle basaltic magma. With the basaltic magma ascending, it captures a great deal of metamorphogenic zircons from Precambrian basement rocks, which indirectly testifies the existence of early-medium Proterozoic crystalline basement in Yili microplate.