Genesis of the Aobaotu Pb–Zn deposit in the southern Great Xing'an Range, NE China: Constraints from geochronology and C–H–O–S–Pb isotopic and fluid inclusion studies

Abstract

The Aobaotu Pb–Zn deposit (470,700 t; 1.51% Pb, 2.30% Zn) in the southern Great Xing'an Range, northeastern China, is hosted by the Late Jurassic volcanic tuff and structurally controlled by a near‐east–west‐trending fault. Three stages of mineralization were identified, namely, stage I of quartz ± pyrite veins, stage II of quartz–polymetallic sulphide veins, and stage III of late quartz–calcite veins. The quartz and calcite that formed in the three stages were selected for fluid inclusion and C–H–O isotope analyses. The results show that the ore‐forming fluid of the deposit belongs to the H2O–CO2–NaCl system at a medium temperature (concentrated at 220–300°C) and in low salinity (0.7–12.1 wt% NaCl equiv). The δ13C values of the calcite and ankerite are in the range of −8.4 to −4.8‰, indicating that as a source of deep magma. The δDV‐SMOW and values of quartz range from −108 to −88‰ and 4.55 to 5.85‰, respectively, indicating that the initial fluid of the Aobaotu deposit was a mixture of residual magmatic and meteoric water. Sulphur isotope analysis of the sulphide minerals, that is, sphalerite, galena, pyrite, and chalcopyrite, yield δ34S value in a range of 1.44–4.94‰, indicating that sulphur is mainly derived from magma. In addition, the Pb isotopic composition of the sulphides indicates that the ore‐forming material has a mixed crust–mantle source. Zircon U–Pb dating suggests that the formation of the Aobaotu deposit is genetically related to the granodiorite porphyry (130.3 ± 0.9 Ma). The combined geochronology and isotopic evidence suggest that the Aobaotu deposit is a magmatic‐hydrothermal vein‐type Pb–Zn deposit, opposite to a volcanic Pb–Zn deposit as suggested before. The Aobaotu deposit formed in an extensional tectonic setting caused by the rollback of the Palaeo‐Pacific Plate.