The superposition of Cretaceous mineralization events leading to the formation of the large Baiyinnuoer Pb–Zn deposit in NE China

Abstract

The Baiyinnuoer Pb–Zn deposit, estimated at 26.57 million metric tonnes (Mt) with grades of 1.77% Pb and 5.21% Zn, is situated in the southern Great Xing'an Range (SGXR) of northeast China. The deposit comprises southern and northern ore belts. The southern belt primarily contains skarn ore bodies (32% of reserves) associated with Triassic granodiorite, while the northern belt is dominated by skarn ore bodies (30% of reserves) related to Triassic diorite porphyry. In addition to Triassic skarn‐type mineralization, the deposit also exhibits Early Cretaceous mineralization. This includes vein‐type occurrences (36% of reserves) within volcanic tuff and syenite porphyry, alongside a small amount of skarn ore bodies (2% of reserves) related to syenite porphyry. LA‐ICP‐MS U–Pb dating of intrusive rocks and garnets was conducted to investigate the timing and genesis of these mineralization events, revealing two distinct stages of skarn‐type mineralization. The first stage, associated with Early Triassic granitoids, dates to 254.6 ± 1.4–241.7 ± 2.7 Ma, while the second stage is closely associated with Early Cretaceous syenite porphyry, constrained to 135.4 ± 1.1–135.2 ± 1.6 Ma. Garnet U–Pb dating in the syenite porphyry‐related skarn yielded an age of 134.9 ± 4.7 Ma; however, due to low U content, reliable dating of garnets associated with Early Triassic granitoid‐related skarn was not feasible. Micro‐thermometry and Laser Raman analyses of fluid inclusions within vein‐type ore bodies highlighted distinct differences between vein‐type mineralization and Early Triassic skarn‐type mineralization. Additionally, in situ sulfur isotope analyses of sphalerite from both Early Triassic and Early Cretaceous ore bodies indicate a magmatic origin for sulfur in both stages. Through comprehensive geological, geochronological, in situ sulfur isotope and fluid inclusion studies, the Baiyinnuoer Pb–Zn deposit is conclusively identified as a large deposit characterized by two distinct periods of mineralization (Early Triassic and Early Cretaceous), akin to several other significant polymetallic deposits in NE China.