Geochronology and Geochemistry of Zhaibeishan Granite and Its Relationship with Copper Deposit in the Eastern Tianshan, NW China

Abstract

The Zhaibeishan copper deposit is located at the eastern part of Aqishan-Yamansu metallogenic belt in eastern Tianshan. Zircon U-Pb geochronology, major and trace element, and Sr-Nd isotopic characteristics of Zhaibeishan granite and its relationship with mineralization have been studied. SHRIMP zircon U-Pb dating indicates an Early Carboniferous intrusive time (334.5 ± 2.6 Ma) of the granite. Chemically, Zhaibeishan granites have high silica (71.50–75.06%), aluminum (A/CNK = 1.02–1.23), sodium (Na₂O/K₂O = 0.95–23.83 with 6.89 on average), and total alkalis (Na₂O + K₂O = 6.65–8.43%), and low magnesium (<1%) and titanium (<1%) contents. The Chondrite-normalized REE patterns are characterized by enrichment of LREE relative to HREE (La_N/Yb_N = 4.05–6.85) with moderate negative Eu anomalies (δEu = 0.38–0.73). The Zhaibeishan granites show enrichment of K, Rb, (Large Ion Lithophile Elements), LREE and depletion of Nb, Ta, Ti, and P (High Field Strength Elements), indicating island arc magmatic characteristics. Sr-Nd isotopic data reveal that the I_Sr values range from 0.70473 to 0.70551, while ε_Nd(T) values range from 2.3 to 3.2. We suggest that the Zhaibeishan granites formed in continental arc setting in subduction zone and were probably derived from the product of magma mixing between crust and mantle magmas and experienced subsequent fractional crystallization. Combined with the fluid inclusion and published ore-forming age and isotopic data, we suggest that porphyry mineralization and blind copper orebodies probably exist in the deep part of the Zhaibeishan copper mining area.