Fluid inclusion studies of the Pangushan quartz-vein type tungsten deposit in southern Jiangxi Province

The Pangushan tungsten deposit is an important large-size quartz-vein type W-polymetallic deposit in southern Jiangxi Province.Based on detailed petrographic observations and using the means of Fluid Inclusion Assemblage (FIA),the authors carried out microthermometric and Raman microspectroscopic studies of fluid inclusions in early bismuthinite-wolframite-quartz veins and late (bismuthinite)-wolframite-quartz veins of the main ore-forming stage of the Pangushan tungsten deposit.The fluid inclusions are mainly of H2O-NaCl type and H2O-NaCl-CO2 type together with minor pure CO2 type.The existence of abundant CO2-rich inclusions is a typical feature of the Pangushan Tungsten deposit.Experimental results show that the main homogenization temperature range of the two-phase H2O-NaCl type fluid inclusions is comparable to that of the H2O-NaCl-CO2 type inclusions,while the salinity of the two-phase H2O-NaCl type is higher than that of the H2O-NaCl-CO2 type.In addition,the H2O-NaCl type fluid inclusions show evident decrease in homogenization temperature from the early veins to the late veins at constant salinity.Moreover,less H2O-NaCl-CO2 type inclusions occur in the (bismuthinite)-wolframite-quartz veins while relatively abundant CO2 type inclusions are existent.Raman microspectroscopic studies of various types of inclusions show that,besides water and CO2,the fluid inclusions also contain small amounts of CH4 and N2.The characteristics of fluid inclusions in the Pangushan Tungsten deposit indicate that the fluid immiscibility caused by CO2 escaping possibly led to tungsten precipitation.