ORE-FORMING FLUIDS AND GENESIS OF QIYIMUCHANG LEAD-ZINC DEPOSIT IN ERGUNA AREA, INNER MONGOLIA

The Qiyimuchang lead-zinc deposit, newly discovered in the Erguna metallogenic belt, Inner Mongolia, has the ore-forming potential of middle-large scale. The petrographic observation, microthermometry and Laser Raman spectrum analysis of fluid inclusions in quartz formed in the major metallogenic stage are carried out to determine the characteristics of ore-forming fluids and the genesis of deposit. The results indicate that three main types of fluid inclusions are developed in quartz, including two-phase (liquid-rich and vapor-rich), CO₂-bearing three-phase, and a few daughter mineral-bearing three-phase inclusions, with the homogenization temperatures ranging from 132 to 342℃, generally concentrated in 130-200℃ and 240-320℃, and the salinities of three types being 0.5%-9.9%, 3.0%-11.9%, 42.4% and 44.2%, respectively. The Laser Raman spectrum analysis shows that the gaseous compositions are mainly H₂O and CO₂. The fluid boiling plays an important role in the deposition of mineral materials. The deposit, hosted in the Mesozoic volcanic rocks, belongs to the epi-mesothermal vein-type related to hypabyssal-ultra hypabyssal magmatism.