Fluid Inclusions, C–H–O–S Isotope and Geochronology of the Bujinhei Pb–Zn Deposit in the Southern Great Xing'an Range of Northeast China: Implication for Ore Genesis
Authors: Zhang Xuebing , Wang Keyong , Fu Lijuan , Zhang Miao , Konare Yassa , Peng Dawei , Cai Wenyan 
Published: March 2017

The Bujinhei Pb–Zn deposit is located in the southern Great Xing'an Range metallogenic belt. It is a representative medium‐ to high‐temperature hydrothermal vein type deposit controlled by fractures, and orebodies hosted in the Permian Shoushangou Formation. The hydrothermal mineralization is classified into three stages: pyrite ± arsenopyrite–quartz (Stage 1), polymetallic sulfide–quartz (Stage 2), and polymetallic sulfide–calcite (Stage 3). Fluid inclusion petrography, laser Raman analyses and microthermometry indicate that the liquid‐rich aqueous inclusions (L) and vapor‐rich CO2 ± CH4–H2O inclusions (C) occur in the Stage 1 and as medium‐ to high‐ temperature and low‐ to medium‐salinity NaCl–H2O–CO2–CH4 hydrothermal fluids. The liquid‐rich (L) and rare vapor‐rich CO2 ± CH4–H2O inclusions (C) occur in the Stage 2 with medium‐temperature and low‐salinity NaCl–H2O ± CO2 ± CH4 hydrothermal fluids. The exclusively liquid‐rich (L) fluid inclusions are observed in the Stage 3, and the hydrothermal fluid belongs to medium‐temperature and low‐salinity NaCl–H2O hydrothermal fluids. The results of hydrogen and oxygen isotope analyses indicate that ore‐forming fluids were initially derived from the magmatic water and mixed with local meteoric water in the late stage (δ18OH2O‐SMOW = 6.0 to 2.2‰, δDSMOW = −103 to −134‰). The carbon isotope compositions (−18.4‰ to −26.5‰) indicate that the carbon in the fluid was derived from the surrounding strata. The sulfur isotope compositions (5.7 to 15.2‰) indicate that the ore sulfur was also primarily derived from the strata. The ore vein No. 1 occurs in fractures and approximately parallel to the rhyolite porphyry; orebodies have a close spatial and temporal relationship with the rhyolite porphyry. The rhyolite porphyry yielded a crystallization age of 122.9  ± 2.4 Ma, indicating that the Bujinhei deposit may be related to the Early Cretaceous magmatic event. Geochemical analyses reveal that the Bujinhei rhyolite porphyry is high in K2O and peraluminous, and derived from an acidic liquid as a result of strong interaction with hydrothermal fluid during the late magmatic stage; it is similar to A2‐type granites, and formed in a backarc extensional environment. These results indicate that the Bujinhei Pb–Zn deposit was a vein type system that formed in Early Cretaceous and influenced by the Paleo‐Pacific tectonic system.

Bujinhei deposit is a representative hydrothermal vein type deposit on the genetic types, and occurs on the western slope of the southern Great Xing'an Range. The ore‐forming fluids were medium‐ to high‐temperature and low‐to medium‐salinity NaCl–H2O–CO2–CH4 hydrothermal fluids, which became medium‐temperature and low‐salinity NaCl–H2O hydrothermal fluids in later stages, and came from magmatic water and mixed with meteoric water, whereas the ore‐forming materials were mainly derived from the surrounding strata. The LA–ICP–MS zircon U–Pb dating indicates that the Bujinhei deposit formed at the period of late Early Cretaceous, potentially in a backarc extensional environment influenced by the Paleo‐Pacific tectonic system.