Metallogenesis and hydrothermal evolution of the Saibo copper deposit in the western Tianshan: evidence from fluid inclusions, H−O−S isotopes, and Re−Os geochronology

The Saibo copper polymetallic deposit, located in the West Tianshan Sailimu-Sitaihaiquan copper lead and zinc ore belt, is a new breakthrough in medium-large copper mine. Through the thin section authentication and the thermometric analysis of fluid inclusion, it is concluded that skarnization was developed in this deposit, the mineralization stage can be divided into retrograde skarn stage (S 1 ), quartz-sulfide stage (S 2 ) and quartz-carbonate stage (S 3 ). Fluid inclusions (FIs) were distinguished as liquid-rich aqueous FIs (LV-type), vapor-rich aqueous FIs (VL-type), and NaCl daughter mineral-bearing three phase FIs (S-type). The mineralization fluids indicate that the initial stage (S 1 stage) is of high temperature and high salinity, with a handful of metallic matters. During the main metallogenic stage (S 2 stage), the meteoric water is mixed, the temperature and salinity gradually decrease, the fluid is distinctly boiling, and a large amount of metallic matters are precipitated, and then to the S 3 stage, when the temperature and salinity decrease along with the carbonation. Chalcopyrite Re−Os dating yielded a mineralization age of 379.2 ± 7.7 Ma, which corresponds well with the zircon U−Pb age (385.9 ± 1.3 Ma) of the granite porphyry. The C−H−O isotopes indicate that the ore-forming fluid was dominated by initial mixed magmatic water in the early stage and by meteoric water in the late stage, and C is derived from limestone strata metasomatized by magmatic fluids. The S and Pb isotopes indicate that the ore-forming materials are derived from the mixed crust-mantle source, of which S is almost entirely derived from the mantle, while Pb is mainly derived from the crustal material of the orogenic belt. On the whole, the Saibo copper deposit is a typical calcium skarn type deposit, which formed in the shallower setting at active continental margin in the Late Devonian period.