Ore-forming Fluids Evolution Of The Hongshan Skarn-type Copper Deposit In Zhongdian, Western Yunnan China

The Hongshan copper deposit is the largest porphyry-skarn-type deposit proved in the southern part of Yidun arc, however, so far the understanding of genesis are vague, to a certain extent, these constraints the understanding of the deposit causes and mineralization enrichment laws.For this reason, this article base on the geological, advance the systematic petrographic observation and study of copper deposits, determine the ore-forming stages, petrographic, microscopic fluid inclusions analysis of temperature and C-H-O isotopic studies, discussion the origins and evolution of oreforming fluids and the genesis mechanism.1. Proved main ore body is skarn-type, divided the mineralization process into skarn period and quartz-sulfide period, before include early skarn stage, late skarn stage, late include early sulfide stage and late sulfide stage.2. The fluid inclusions can be divided into four types: liquid-rich fluid inclusions(LV), vapor-rich inclusions(VL), multiphase fluid inclusion containing halite(LS), multiphase fluid inclusion containing CO2(LC). The inclusions in early skarn stage are VL, LV, SL, LC, most are LV; The inclusions in late skarn stage are VL; The inclusions in early sulfide stage are VL, LV, SL, LC; The inclusions in late sulfide stage are VL.3. The range of the ore-forming fluid homogenization temperature, respectively, are located in early skarn stage in 402.1~529.9℃, late skarn stage in 187.1~450.1℃, the early sulfide stage in 201.4~451.2℃, the late sulfide stage in 163.5~293.5℃.In the quartz-sulfide period, there are coexistence of different types of inclusions, the range of the inclusions in liquid-gas ratio is very large, homogenization temperatures is similar, which means fluid boiling in the stage.4. The ore-forming fluid showed by the C-H-O isotopes: depend on the study of the porphyroblast quartz, the ore-forming fluid are mainly magmatic hydrothermal, in the early skarn stage and the late skarn stage, there are water-rock interaction between magmatic hydrothermal and marble; while meteoric water is added with the magmatic hydrothermal in the quarte-sulfide period.5. The ore-forming fluid evolved from high temperature and high salinity conditions to low temperature and low salinity conditions, and occur coincident in the adjacent stage which shows the continuity of fluid evolution.The formation and evolution process of the ore-forming fluids in the Hongshan copper deposit may be experienced decompression and boiling, the filling or metasomatism between magmatic hydrotherm-volatile and carbonate wall rocks, fluid mixing.Fluid boiling is suggested to be the main mechanism for matal precipitations in the Hongshan copper deposit.