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

摘要

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 delta S-34 values of chalcopyrite from stages II and III are - 0.8-0.6 parts per thousand and 1.1-1.3 parts per thousand, respectively, suggesting magmatic sources for the ore-forming components of both stages. Ar-40/Ar-39 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.