| Laowangzhai gold deposit is the largest gold deposit in Ailaoshan orogenic belt.This article is based on the systematic petrographic observation and study of golddeposits, hydrothermal ore-forming stages as determined, petrographic, microscopicfluid inclusions analysis of temperature, fluid composition and H-O isotopic studies,discusses the origins and evolution of ore-forming fluids and gold migration andenrichment mechanism.1.Hydrothermal ore-forming processes can be divided into three stage: earlystages of quartz-polymetallic sulphides veins, the main stage ofquartz-calcite-arsenopyrite-pyrite veins, late-stage calcite-stibnite-quartz-pyrite veins.2.Ore-forming fluid homogenization temperature from early to late stage,respectively, located in200to230℃,190to210℃,160to180℃, temperaturedecreasing and salinity ranges slightly larger at the primary stage, range2.89to13.66wt%NaCl, density of ore-forming fluids in the primary stage between0.946to1.013g/cm3, CO2-H2O three-phase inclusions based on isodensity lines of p-t phasediagram, Estimating metallogenic pressure54to81MPa. Main stages of coexistenceof different types of inclusions in the Quartz, inclusions in liquid-gas ratio is verylarge, and homogenization temperatures is similar and P-T phase diagram ofCO2-H2O three-phase inclusions indicate the immiscible fluid, which means minersstage fluid boiling and CO2escaping.3. Composition analysis of the fluid inclusions indicates that Ore-forming fluidion components mainly for Na+-Cl-(SO42-), Gas composition is given priority to withH2O and CO2, ore-forming fluid of wangzhai gold is H2O-NaCl-CO2-ΣS system, andReducing fluid, pursuant to predecessors research results, gold may be migrated byAu (HS)2-and [AuAsS3]2-complexes forms, think that the boiling of fluid is mainprecipitation mechanism of gold.4. Hydrogen and oxygen isotope composition showing the source of ore-formingfluid with mixed characteristics, ore-forming fluid of laowangzhai gold deposit in theearly stage and the main stage with mantle and the metamorphic fluids mixed nature,the late stage may have mixed with atmospheric precipitation. |
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