Mineral Paragenesis and Fluid Inclusions of the Dongbo Tungsten-Molybdenum Deposits

동보(東寶) 중석(重石)-모리브덴 광상(鑛床)의 광물공생(鑛物共生)과 유체포유물(流體包有物)

The Dongbo tungsten-molybdenum deposits are fissure-filling veins emplaced in granites of late Cretaceous age. Integrated field, mineralogic and fluid inclusion studies were undertaken to illuminate the characters and origin of the ore deposits. Mineral paragenesis is complicated by repeated fracturing, but four distinct depositional stages can be recognized; (I) tungsten-molybdenum minerals-quartz-chlorite stage, (II) iron-oxide and sulfides-quartz stage, (III) iron -oxide-base metal sulfides-sulfosalts-quartz-carbonates stage, (IV) barren rhodochrosite-zeolite stage. Fluid inclusion studies were carried out for stage I quartz and stage III quartz, sphalerite and calcite. Fluid inclusion studies reveals highly systematic trends of homogenization temperature and salinity throughout the mineralization. Ore fluids during stage I were complex, NaCl rich brine and salinity reached values as high as 34.4 weight percent equivalent NaCl, but the later ore fluids were more dilute and reached to 9.7 weight percent equivalent NaCl during stage III. Intermittent boiling of ore fluid during stage I is indicated by the fluid inclusions in stage I quartz. Depositional temperatures and pressures during stage I range from $520^{\circ}C$ to $265^{\circ}C$and from 600 to 400 bars. Homogenization temperatures of the stage III quartz, sphalerite and calcite range from $305^{\circ}C$ to $190^{\circ}C$. Fluid inclusion data from the Dongbo mine are nearly similar to those from other hydrothermal tungsten deposits in the Kyeongsang basin. Depositional temperature and salinity of ore fluids during precipitation of tungsten-molybdenum minerals in Dongbo mine were much higher, but $CO_2$ contents were much lower than those from hydrothermal tungsten-molybdenum deposits of late Cretaceous plutonic association in central parts of Korean peninsula.