Timing of the formation of the Baiyinnuo’er skarn Zn–Pb deposit, NE China: evidence from sulfide Rb–Sr dating

The Baiyinnuo’er deposit in northern China is located in the south section of the Great Xing’an Range, and it is the largest skarn Zn–Pb deposit in the region. Skarn and Zn–Pb orebodies mainly occur between the different units of the Permian Huanggangliang Formation, or within the contact zone between the intrusive rocks and the marble. Although Baiyinnuo’er has been well investigated previously, the timing of the Zn–Pb mineralization is still controversial, largely due to the lack of appropriate ore or alteration minerals that could be directly used for isotopic dating. In this study, we report the results of Rb–Sr isotopic analysis for sphalerite and pyrite samples from the Baiyinnuo’er orebodies, which yielded two isochron ages of 137.4 ± 3.4 and 140.0 ± 7.8 Ma, respectively, constraining the Zn–Pb mineralization time of the deposit as the Early Cretaceous. The data are also consistent with the age of the granitoids in the mining area, indicating a potential genetic relationship between the Early Cretaceous magmatism and mineralization. Many other intrusion-related hydrothermal deposits (including the two typical skarns, Huanggang and Haobugao) in the southern Great Xing’an Range also share similar mineralization ages (i.e., 140–130 Ma). Together, these data suggest an Early Cretaceous mineralization event in this region, and this large-scale mineralization could be related to the regional tectonic regime transition from compression to extension as a result of the rollback of the subducted Paleo-Pacific plate. The initial 87 Sr/ 86 Sr ratios of the sphalerite and pyrite samples are 0.70569 and 0.70616, respectively, implying that the ore-forming material could have a significant contribution from the mantle components. The current study shows that sulfide Rb–Sr dating could be used in deciphering the timing of skarn deposit formation.