Direct Re–Os dating of pyrite from the Jianchaling Au deposit, West Qinling, China

The West Qingling Orogen is endowed with more than 1100t gold resources and with 50 gold deposits, ranking it the third-largest gold province in China. The Jianchaling giant gold deposit with 52 t gold reserve is a typical orogenic gold deposit in West Qinling Orogen. The deposit lacks accurate and direct metallogenic age. Five pyrite samples collected from the quartz-polymetallic veins yielded Re–Os isochron age of 206.3 ± 2.7 Ma and an initial 187 Os/ 188 Os ratio of 0.1154 ± 0.0016 (MSWD = 0.54). The pyrites were analyzed by the electron microprobe (EMPA), and the results show that the iron content ranges from 45.1 to 47.8 wt.%, the sulfur content ranges from 52.0 to 53.5 wt.%, and the gold content varies from 0.022 to 0.035%. The higher gold content means that gold is closely related to pyrite, which is a gold-bearing mineral. Moreover, the age is very close to the previous fuchsite 40 Ar/ 39 Ar isotopic ages of 199–194 Ma, which indicates that the gold mineralization at Jianchaling has begun in the Late Triassic (206 Ma), and continued into the Early Jurassic. Through summary and comparison, it is found that the gold metallogenic age of the southern ore belt of the Mian-Lue Suture belt in the West Qinling is younger than that of the northern ore belt, suggesting that the gold deposits in the southern ore belt such as Jianchaling were formed in the transitional period from oceanic subduction to continental collision.