Petrogenesis of Middle Devonian diorite at the Xierqu Fe–Cu deposit in the Kalatag district, eastern Tianshan, NW China

Xierqu is a skarn Fe–Cu deposit associated with porphyritic diorite, in the Kalatag district of eastern Tianshan, China. The diorite yields a sensitive high‐resolution ion microprobe U–Pb zircon date of 391 ± 3 Ma interpreted as its age of emplacement. Major element geochemistry shows that the diorite is a calc‐alkaline assaying 16.7–19 wt.% of Al2O3, with Mg# values of 56.8–67.1, and Al2O3/(CaO + Na2O + K2O) (A/CNK) values of 0.55–0.94. Trace element characteristics of the diorite show that it is enriched in Ba, K, and Sr and depleted in Nb, Ta, and Ti, with a positive Eu (1.18–1.44) anomaly and high Sr/Y and La/Yb ratios. Sr–Nd isotopic analyses yielded positive εNd(t) values ranging from 7.1 to 9.8 with low initial 87Sr/86Sr ratios of 0.703806 to 0.703856. These geochemical and isotopic characteristics indicate that the diorite is adakite‐like emplaced in an island‐arc setting and resulted from partial melting of subducted oceanic crust in a mantle wedge during the Devonian.