The Cathodoluminescence, Composition And Fluid Inclusions Of Quartz,Gaogangshan Molybdenum Deposit In Heilongjiang

The Gaogangshan molybdenum deposit is located in the Xiaoxing'anling-Zhangguangcailing polymetallic metallogenic belt and is the first discovered Early Triassic porphyry molybdenum deposit in this area.In this paper,the cathodoluminescence,composition and fluid inclusions of quartz in different ore stagesare studied to define the physical-chemical conditions of the deposit,and to discuss the characteristics and evolution process of the ore-forming fluid.According to the intercalation relationship of quartz veins and mineral assemblage,the metallogenic period is divided into five stages:UST quartz stage,quartz-potassium feldspar stage?A vein?,quartz-pyrite-molybdenite stage?B?vein,quartz-pyrite or molybdenite±chalcopyrite±pyrrhotite stage?D vein?and quartz-calcite±fluorite stage?E vein?.Cathodoluminescence?CL?and LA-ICP-MS analysis of quartz showed that UST veins's CL had the strongest intensity,and the mosaic structure was obvious.A small amount of late veins?interpolation of D veins and/or E veins?were observed.Tianium content in UST veins is 40¹00ppm.The strength of A vein's CL decreased,but is still strong,most of the quartz showed a mosaic structure,a small number of late veins interspersed or appeared as a spots.And the content of Ti decreased,at 20⁵0ppm.The intensity of B veins's CL decreased and a small amount of mosaic structure is observed.The Ti content is 10³5ppm.The brightness of D veins's CL continues to decrease.The quartz growth zone is visible,and the Ti content is 2³5ppm.The E veins have the lowest intensity and is basically invisible of internal features.The fluid inclusion petrography and microscopic temperature show that the inclusions are mainly gas-liquid-water two-phase inclusions.And the fluids are medium-high temperature,medium-high-medium-low salinity fluids.Boiling of the fluid causes precipitation of metal sulfides such as molybdenum and pyrite.The inclusion components are mainly H₂O,with a small amount of CO₂ and CH₄.The intersection of the P-T isoline of Ti in quartz and the isochore line of the gas-liquid-water two-phase fluid inclusions indicates that the hydrothermal system of the Gaogangshan molybdenum deposit evolved from near-magma pressure?the existence of UST also confirms this?.The pressure and temperature of the UST veins are about 2.49kbars and 745?,respectively;the pressure and temperature of the A veins are about 1.63kbars and 587?,respectively;the pressure and temperature of the B veins are 1.50 kbars and 525?,respectively;the pressure of the D veins are about 0.63 kbars and 390?,respectively.The rutile was absent in the E vein.Considering the spatial distribution characteristics between the veins,the formation conditions of the E veins were estimated to be0.50 kbars and 300?.