Magmatic evolution and mineralization potential of the Husite complex pluton in the Kekesala ore district, Chinese Western Tianshan: Insights from zircon and apatite geochemistry

• Zircon and apatite serve as evaluate indicators for magma fertility. • Magma mixing plays a critical role in the formation of causative magma. • Oxygen fugacity, water and S contents jointly control Fe-Cu mineralization. The Husite complex pluton (HCP), a famous pluton along the northern margin of the Yili Block in the Chinese Western Tianshan, is composed of various magmatic units and hosts numerous skarn-type Fe-Cu polymetallic deposits. The unclear relationship between magmatic evolution and mineralization hinders further exploration around the HCP and in the region. Five magmatic units in the Kekesala ore district were identified, including the dioritic porphyrite, granodiorite, monzogranite, K-feldspar granite, and granitic aplite with LA-ICP-MS zircon U-Pb ages of 370.3 ± 3.6 Ma, 369.9 ± 3.5 Ma, 367.0 ± 3.4 Ma, 364.2 ± 3.2 Ma, and 364.3 ± 3.5 Ma, respectively. The zircon Hf ( ε Hf (t) = −1.5 to +3.6) and apatite Nd isotopic compositions ( ε Nd (t) = −4.3 to −1.4) of the different magmatic units in the Kekesala ore district indicate that its magmas were derived from partial melting of ancient mafic lower crust mixed with the mantle-derived mafic magmas. These mantle-derived mafic magmas originated from mantle wedge metasomatized by subduction-zone fluids and sediment melts. The decoupling between zircon ε Hf (t) and apatite ε Nd (t) values, coupled with the presence of abundant mafic microgranular enclaves, acicular apatite and disequilibrium feldspar xenocrysts in the granodiorite, collectively indicates that magma mixing occurred during the HCP magmatic evolution. The Fe-Cu mineralized granodiorite of HCP has higher oxygen fugacity (average ΔFMQ = 0.83; Ce 4+ /Ce 3+ = 55.0–468), water content, Cl content (apatite Cl = 1.87–2.97 wt%), and weak degree of differentiation. Although dioritic porphyrite resembles granodiorite in key properties, its mineralization potential is negligible due to limited volume. In contrast, the barren monzogranite, K-feldspar granite and granitic aplite show relatively low oxygen fugacity (ΔFMQ = 0.38–0.72), water/sulfur contents, and strong degree of differentiation. The differences between the various units of intrusions demonstrate that further exploration of Fe-Cu polymetallic mineralization in the HCP and Chinese Western Tianshan should focus on the intrusions with similar fertility indicators mentioned above.