The study area is located in a Cu-Au metallization belt in Bainaimiao-Gunawusu, Inner Mongolia. A set of quartz-vein group is found in the Xuniwusu Formation by recent geological mapping, distributing in the Shiertai area, west of Bainaimiao Cu-Au deposit, but exhibiting a large similarity with the gold metallization veins of Bainaimiao Cu-Au deposit. The mineral assemblage of the quartz-vein group can be divided into two stages: the early pyritequartz stage （M1） and the late quartz-calcite stage （M2）. In M1 stage, homogenization temperature of the three phase inclusion bearing daughter crystal is of 256-320 ℃, and salinity of 31.4%-39.8% NaCl eqv. Homogenization temperature of the two-phase aqueous inclusion is of 210-260 ℃, and salinity of 17.1%-22.8% NaCl eqv, and CH4 enriched, less CO2, H2O , and small amount of H2S, C6H6, N2 at gas phase composition; whereas by temperature of 170-210 ℃, CO2 or H2O enriched, less CH4, and minor N2, the salinity is as much as that of the former, but with participation of low salinity end-member. The CH4 and CO2 or only CH4 is shown by the pure gas inclusion. In M2 stage, homogenization temperature of two-phase aqueous inclusions is of 90-160 ℃, salinity of 15.82%-21.1% NaCl eqv, and the two-phase aqueous inclusion has a mixture with low salinity fluid. It is proposed that fluids of quartzvein group should be regarded as aCH4-CO2-H2O-NaClsystem in the low salinity and low temperature with a small amount of H2S and N2, C6H6. In comparison with gold ore-forming fluid, fluid inclusion of Bainaimiao Cu-Au deposit, and data of chemical analysis of quartz-vein group, we suggest that the quartz-vein group would be a potential exploration target of gold metallization.
