Carboniferous magmatism and mineralization in the area of the Fuxing Cu deposit, Eastern Tianshan, China: Evidence from zircon U–Pb ages, petrogeochemistry, and Sr–Nd–Hf–O isotopic compositions

Abstract

The newly discovered Fuxing porphyry Cu deposit is located in the Dananhu–Tousuquan arc, adjacent to the Tuwu–Yandong Cu deposits of Eastern Tianshan, in the southern Central Asian Orogenic Belt. The Fuxing deposit is hosted by volcanic rocks (basalt and dacite) in the Early Carboniferous Qi'eshan Group and Carboniferous felsic intrusions (plagiogranite porphyry, monzogranite, and quartz diorite). New SIMS zircon U–Pb dating indicates that the plagiogranite porphyry and monzogranite emplaced at 332.1±2.2Ma and 328.4±3.4Ma, respectively. The basalts are characterized by low SiO2 contents (47.47–54.90wt.%), a lack of Eu anomalies, strong depletion of Na, Ta, and Ti elements but positive Sr, U, and Pb anomalies, high Y (20.8–28.2ppm) and HREE concentrations (Yb=2.23–3.06ppm), and relatively low (La/Yb)N (2.20–3.92) values; the dacite samples have high SiO2 contents (66.13–76.93wt.%), clearly negative Eu anomalies, high Mg# values (36–51), and high Y (41.8–54.9ppm) and Yb (5.76–8.98ppm) concentrations. The basalts and dacites exhibit similar signatures as normal arc rocks, and were considered to be derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. In contrast, the plagiogranite porphyry, monzogranite, and quartz diorite show the same geochemical affinity with modern adakites, which are characterized by high SiO2 contents (67.55–79.00wt.%), minor negative to positive Eu anomalies, strong depletion of heavy rare earth elements (Yb=0.17–1.19ppm) and Y (1.86–10.1ppm), positive K, Rb, Sr, and Ba but negative Nb, Ta, Th, and Ti anomalies, and high (La/Yb)N ratios and Mg# values. Moreover, these adakitic felsic intrusions display relatively high positive zircon εHf(t) values (+11.4 to +18.3), low 87Sr/86Sr (0.706080–0.711239), high 143Nd/144Nd (0.512692–0.512922) ratios, and consistent zircon δ18O values (4.41‰–5.48‰), suggesting that their parental magma were most likely derived from partial melting of the subducted oceanic crust followed by mantle peridotite interaction. Based on the whole-rock geochemical and Sr–Nd–Hf–O isotopic data, as well as detailed petrographic analyses, we further suggest that the Fuxing igneous rocks and associated porphyry Cu mineralization were generated by the northward subduction of the paleo-Tianshan oceanic plate beneath the Dananhu–Tousuquan island arc during the Early Carboniferous.