Geochronology, fluid inclusions and isotopic characteristics of the Chaganbulagen Pb–Zn–Ag deposit, Inner Mongolia, China

• The dating data indicate that the Chaganbulagen deposit formed approximately 138 Ma ago.
• The ore-forming fluids of the deposit are moderate-temperature and low-salinity fluids.
• The ore-forming fluids of the deposit consist dominantly of meteoric water.
• The ore-forming materials of the deposit mainly came from the Mesozoic magma.
• The Chaganbulagen deposit is a low-sulfidation epithermal deposit.

The large Chaganbulagen Pb–Zn–Ag deposit is located in the Derbugan metallogenic belt of the northern Great Xing'an Range. The vein-style orebodies of the deposit occur in the NWW-trending fault zones. The ore-forming process at the deposit can be divided into three stages: an early quartz–pyrite–arsenopyrite–pyrrhotite–sphalerite–galena–chalcopyrite stage, a middle quartz–carbonate–pyrite–sphalerite–galena–silver-bearing minerals stage, and a late quartz–carbonate–pyrite stage. The sericite sample yielded a 40Ar −39Ar plateau age of 138 ± 1 Ma and an isochron age of 137 ± 3 Ma, and the zircon LA-ICP-MS U–Pb age of monzogranite porphyry was 143 ± 2 Ma, indicating that the ages of mineralization and monzogranite porphyry in the Chaganbulagen deposit should be the Early Cretaceous, and that the mineralization should be slightly later than the intrusion of monzogranite porphyry. There are only liquid inclusions in quartz veins of the Chaganbulagen deposit. Homogenization temperatures, densities, and salinities of the fluid inclusions from the early stage are 261–340 °C, 0.65–0.81 g/cm3, and 0.7–6.3 wt.% NaCl eqv., respectively. Fluid inclusions of the middle stage have homogenization temperatures, densities, and salinities of 209–265 °C, 0.75–0.86 g/cm3, and 0.5–5.7 wt.% NaCl eqv., respectively. For fluid inclusions of the late stage, their homogenization temperatures, densities, and salinities are 173–219 °C, 0.85–0.91 g/cm3, and 0.4–2.7 wt.% NaCl eqv., respectively. The ore-forming fluids of the deposit are generally characterized by moderate temperature and low salinity and density, and belong to an H2O–NaCl ± CO2 ± CH4 system. The δ18Owater values calculated for ore-bearing quartz vary from − 17.9‰ to − 10.8‰, and the δDV-SMOW values from bulk extraction of fluid inclusion waters vary from − 166‰ to − 127‰, suggesting that the ore-forming fluids consist dominantly of meteoric water. The δ34SV-CDT values range from 1.4‰ to 4.1‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ore minerals are in the ranges of 18.302–19.037, 15.473–15.593, and 38.110–38.945, respectively. The data for the S and Pb isotopic systems indicate that the ore-forming metals and sulfur came from Mesozoic magma. The Chaganbulagen deposit is a low-sulfidation epithermal Pb–Zn–Ag deposit, and the temperature decrease is the dominant mechanism for the deposition of ore-forming materials.

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