Timing of the formation of the Changba–Lijiagou Pb–Zn ore deposit, Gansu Province, China: Evidence from Rb–Sr isotopic dating of sulfides

•The mineralization in the deposit took place at ∼222 Ma, the Late Triassic.•The ore metals of the deposit derived mainly from the continental crust.•The granite-related polymetallic mineralization and the Pb–Zn mineralization constitute one metallogenic system.•The deposit is a product of regional epigenetic hydrothermal mineralization processes.

The giant Changba–Lijiagou Pb–Zn deposit is located in the north of the Xihe–Chengxian (abbreviated as “Xicheng”) ore cluster in Gansu Province, China. The orebodies in the deposit are mainly hosted in the marble, dolomitic marble, and biotite–calcite–quartz schist of the Middle Devonian Anjiacha Formation. The genesis of the deposit has previously been argued to be of SEDEX type (sedimentary exhalative type) or of epigenetic hydrothermal type. This paper reports results of Rb–Sr isotopic dating on sphalerite and pyrite taken from the main orebody, which yield an isochron age of 222.3 ± 2.2 Ma for eight sphalerite samples, and 222.0 ± 3.0 Ma for the eight sphalerite samples combined with four pyrite samples, indicating that the deposit formed during the Late Triassic. The (87Sr/86Sri) value of the sphalerite is 0.71370 ± 0.00013, and that of the sphalerite and pyrite is 0.71371 ± 0.00014, which are identical within experimental error, suggesting that the ore metals are derived mainly from the continental crust. By integrating the present results with the regional geology, we propose that the Changba–Lijiagou Pb–Zn deposit is a product of regional hydrothermal mineralization processes, forced by tectono-magmatic activities, which took place in the Xicheng ore cluster during Triassic orogenic processes.