Multiple mineralization events of the Paleozoic Tuwu porphyry copper deposit, Eastern Tianshan: evidence from geology, fluid inclusions, sulfur isotopes, and geochronology

The Tuwu porphyry Cu deposit, located in Eastern Tianshan, NW China, is hosted by a plagiogranite porphyry and Carboniferous Qi’eshan Group volcanic rocks. Based on crosscutting relationships and mineral assemblages, hydrothermal alteration and mineralization processes at Tuwu can be divided into four stages: early propylitic alteration (stage I), porphyry mineralization (stage II), overprinting mineralization (stage III), and post-mineralization (stage IV). The porphyry mineralization stage (stage II) contributed to the majority of the Cu–Mo resource, with Cu mineralization occurring mainly as quartz-chalcopyrite veins. Stage III also produced minor Cu mineralization, characterized by chalcopyrite–anhydrite–chlorite–calcite assemblages. Fluid inclusion (FI) study reveals that stage II is characterized by a high-temperature, high-salinity, highly oxidized, and K-rich H₂O–NaCl–CaCl₂ fluid. Fluid boiling and mixing likely occurred during the porphyry mineralization stage, leading to the precipitation of chalcopyrite and pyrite. Alteration and mineralization in stage III were derived from a S-rich H₂O–NaCl–CaCl fluid, with fluid boiling leading to the precipitation of chalcopyrite. The δ³⁴S values of chalcopyrite from stages II and III are − 0.8–0.6 ‰ and 1.1–1.3 ‰, respectively, suggesting magmatic sources for the ore-forming components of both stages. ⁴⁰Ar/³⁹Ar dating indicates that stage II likely occurred at 328.1 ± 1.4 Ma, around the age emplacement of the causative plagiogranite porphyry (ca. 337.7–330.3 Ma). We suggest the overprinting mineralization event occurred at ca. 323 Ma, spatially and genetically related to the emplacement of the quartz albite porphyry at 323.6 ± 2.5 Ma.