Magmatism and mineralization potential of the Paertagexi copper deposit, Eastern Tianshan

• The ore-bearing Paertagexi granodiorite yields a younger U–Pb age (334.9 ± 1.3 Ma) than the ore-barren intrusions. • The Paertagexi granodiorite has high oxygen fugacity and water content, which are key for porphyry Cu formation. • Early Carboniferous adakitic rocks in the mid-west Dananhu arc are promising exploration targets. Eastern Tianshan is an important copper metallogenic belt globally, within which the porphyry copper deposits primarily found in the middle and eastern segments of the region. However, the porphyry copper mineralization in the western segment is rare and remains inadequately understood. The Paertagexi copper deposit is a new discovery in the western segment of the Eastern Tianshan, which provides an opportunity to investigate the porphyry copper mineralization system in the western segment. The Paertagexi intrusion consists of granodiorite, monzonitic granites and diorite porphyry, with the granodiorites mainly hosting disseminated or veinlet copper mineralization. New zircon U-Pb ages of 352.4 ± 1.2 Ma, 348.8 ± 1.3 Ma and 334.9 ± 1.3 Ma have been obtained from diorite porphyry, monzonitic granite and granodiorite, respectively. The monzonitic granite and diorite porphyry are intruded by the granodiorite. The ore-bearing granodiorite exhibits high contents of Na 2 O (3.63–4.09 wt%) and Sr (370.30–423.80 ppm), and low ratios of Sr/Y (39.19–46.42), Y (8.35–10.73 ppm), and Yb (0.99–1.27 ppm). In addition, they show positive εNd (t) (+6.76–+7.33) and εHf (t) values (+11.92–+14.58), along with relatively low ( 87 Sr/ 86 Sr) i values (0.703235–0.703561). These geochemical characteristics are consistent with those of adakites. We suggest the granodiorite was derived from partial melting of the subducted oceanic crust, followed by interaction with mantle peridotite. The monzonitic granite and granodiorite exhibit similar Sr-Nd-Hf isotopic characteristics, with εNd (t) values ranging from + 5.25 to + 6.55 and εHf (t) values ranging from + 10.75 to + 13.82. However, their relatively low Mg# values (32.03–35.15) and whole-rock (La/Yb) N ratios (2.89–4.45) suggest that they were derived from a juvenile lower crust. In contrast to granodiorite and monzonitic granite, the diorite porphyry is characterized by low SiO 2 (53.56–58.55 wt%), high MgO (4.66–6.53 wt%), and elevated Mg# (57.00–62.11). This rock also exhibits a low Th/Ce ratio (0.04) and a high Nb/Ta ratio (343.59). It is suggested that the diorite porphyry may have originated from a depleted mantle source modified by subduction-derived fluids and melts. Zircon trace element calculations indicate that the Paertagexi granodiorite exhibits high water content and high oxygen fugacity, which are favorable for the formation of large porphyry copper deposits. Based on a comparison of porphyry copper metallogenic systems across different segments of the Eastern Tianshan, we suggest that future exploration should focus on the western and middle segments of the Dananhu arc, particularly the Early Carboniferous adakitic rocks.