Fluid inclusions, H-O, S, Pb, and noble gas isotope studies of the Baiyun gold deposit in the Qingchengzi orefield, NE China

摘要

The Baiyun gold deposit is located in the Qingchengzi orefield, NE China. The gold mineralization occurs mainly as auriferous quartz veins and auriferous altered rock. Wall-rock alteration includes silicification and potassic alteration along with minor sericitization, carbonatization, and chloritization. Three stages of mineralization are recognized: an early quartz and coarse-grained pyrite stage (Stage I), a middle quartz-gold and fine-grained pyrite-polymetallic sulfide stage (Stage II), and a late quartz-carbonate stage (Stage III). Four types of inclusions are recognized in the quartz veins: two-phase liquid-rich fluid inclusions (Type I), CO2 three-phase aqueous fluid inclusions (Type II), two-phase vapor-rich fluid inclusions (Type III), and pure liquid fluid inclusions (Type IV). The early stage quartz contains Type I-III fluid inclusions that yield low-medium homogenization temperatures (162 degrees C-350 degrees C), low salinities (1.57-10.33 wt% NaClequiv.), and belong to a NaCl-H2O-CH4-CO2 +/- H2S hydrothermal fluid system. The middle-stage quartz also contains Type I-III fluid inclusions that yield low-moderate homogenization temperatures (148 degrees C-290 degrees C), variable salinities (1.02-16.43 wt% NaClequiv.), and belong to a NaCl-H2O-CO2-H2S +/- N-2 system. The late-stage quartz contains Type I, II, and IV fluid inclusions that yield homogenization temperatures and salinities of 150 degrees C-183 degrees C and 6.30-13.29 wt% NaClequiv, respectively, and belong to a NaCl-H2O-CO2-H2S +/- N-2 system. Therefore, the ore-forming fluids of the Baiyun gold deposit are generally characterized by low-moderate homogenization temperatures and low-medium salinities, and belong to a NaCl-H2O-CO2-H2S +/- N-2 system. The coexisting Type I and II inclusions of the early and middle stages have similar Th ranges but weakly contrasting salinities, indicating that fluid boiling occurred.