Characteristics of Ore-Forming Fluids of Gold Deposits in Daqingshan District,Inner Mongolia, China

Located in the mid-west of Inner Mongolia, Daqingshan district has many gold deposits occurring along a east-west striking ductile shear zone within a greenstone belt, which is mainly composed of the Archean Wulashan group. The hydrothermal mineralization can be divided into four stages: (1) pyrite-quartz, (2) quartz-pyrite, (3) polymetallic sulfides and (4) carbonates-quartz. The major metallic minerals in the ore of gold-bearing veins are native gold, electrum, pyrite, chalcopyrite and galena, but the gangue minerals are mainly quartz, secondarily sericite, ankerite and calcite. Principal alteration patterns in the gold deposits are sericitization, silicification, pyritization, carbonatization and chloritization. An investigation on fluid inclusions shows that the ore-forming fluids were low in salinities and high in CO₂ content. Measured δD of fluid inclusions in quartz from the ore veins ranges from -65 ‰ to -104 ‰, but δ¹⁸O_quartz from 10.0‰ to 12.8‰. These data show that the water in hydrothermal fluid precipitating the ore bodies could have been mainly magmatic water and metamorphic water, but local meteoric water might take part in the late mineralization. δ¹³C from fluid inclusions in the ore varys from -3.3‰ to -6.2‰, indicating that carbon was derived from magmatic or anatectic source. δ³⁴s from sulfide samples in gold deposits ranges from -4.1‰ to +4.0 ‰, which are identical with that from Shi, et al. It is concluded that the gold deposits in Daqingshan district are similar to those in Xiaoqinling area, in aspects of geological characteristics, mineral association and stable isotope composition.