Contrasting fluids and implications for ore genesis in the Jiawula-Chaganbulagen Porphyry Mo-epithermal PbZn metallogenetic system: Evidence from fluid inclusions and H-O-He-Ar isotopes

Abstract

The Jiawula-Chaganbulagen (Jia-Cha) ore field is located in the part of the southern Erguna Block of Northeast China and has significant mineralization potential. It comprises three deposits: The Chaganbulagen hydrothermal vein-type PbZn (Ag) deposit in the southeast, the Jiawula hydrothermal vein-type PbZn (Ag) deposit in the northwest, and the blind porphyry Mo mineralization in between. Previous geochronological dates, including molybdenite ReOs, zircon UPb, sulfide RbSr, and sericite ArAr, indicate that the formation of hydrothermal molybdenite and the PbZn mineralization were coeval and that they originated from a porphyry-epithermal metallogenetic system that was related to Early Cretaceous magmatism. However, our comprehensive analysis of fluid inclusions and H-O-He-Ar isotopes reveals dissimilarities in the features and sources of the fluids that form three different deposits. Both the Jiawula deposit and porphyry Mo mineralization have three distinct types of fluid inclusions, which comprise liquid-rich two-phase aqueous inclusions (L-type), vapor-rich two-phase inclusions (V-type), and daughter mineral-bearing three-phase inclusions (S-type). The HeAr (³He/⁴He = 1.32–1.51 Ra; ⁴⁰Ar/³⁶Ar = 300 to 324) and HO (δ¹⁸O_{H2O =} − 13.4 ‰ to 4.1 ‰; δD₌ − 155.1 ‰ to −129.9 ‰) isotope analysis results suggest that the trap fluids originated from an H₂O-NaCl magmatic fluid system, which experienced Mo mineralization with high-temperature transformed into medium-temperature fluids that were primarily of meteoric water in the late-stage (Jiawula PbZn (Ag) deposit). The Chaganbulagen PbZn (Ag) deposit features L-type and V-type inclusions, along with aqueous‑carbonic inclusions (C-type). The results of Laser Raman analysis reveal that the gas phases of the fluid inclusions present in Chaganbulagen contain three different compositions: H₂O, CO_2, and CH₄. The HO isotope compositions (δ¹⁸O_H2O = −18.8 ‰ to −11.6 ‰; δD = −166 ‰ to −131 ‰) and HeAr (³He/⁴He = 0.034–0.041 Ra; ⁴⁰Ar/³⁶Ar = 296–298) in quartz of the Chaganbulagen PbZn (Ag) deposit indicate that the crustal fluids (MASW) were the main source of the ore-forming fluids, and belonged to a H₂O-NaCl-CO₂-CH₄ system, which had low-temperature and low-salinity characteristics. By combining previously published geochronological dates, we proposed a model to explain the difference in the evolution of the fluids.