Stable Isotope Studies of the Dae Hwa Tungsten-Molybdenum Mine, Republic of Korea: Evidence of Progressive Meteoric Water Interaction

The Dae Hwa W-Mo mine is located approximately 100 km southeast of Seoul within the Precambrian metamorphic belt of the southern Korean peninsula. The major ore minerals, wolframite, scheelite, and molybdenite, together with minor cassiterite, chalcopyrite, and bismuthinite, occur within fissure-filling quartz veins contained within Precambrian granitic gneiss adjacent o a granitic stock of Cretaceous age. K-Ar dates of 88 __ _ 2 m.y. for vein muscovite suggest a Late Cretaceous age for W-Mo mineralization. The ore mineral paragenesis can be divided into three distinct stages: a molybdenite-wol-framitc stage (400ø315ø), an iron sulfide-scheelite stage (315ø230ø), and a late carbonate stage (230ø150ø). The •so values of vein minerals are: quartz, 10.6 to 11.4 per mil; muscovite, 8.2 per mil; cassiterite, 2.9 per mil; wolframite, 4.0 to 4.3 per mil; color-zoned scheelite,-7.3 to 2.2 per mil (cores =-0.8-+2.2%0, edges =-7.3--2.7%o); siderite, 11.8 per mil; dolomite, 7.7 to 10.0 per mil; calcite, 5.7 to 9.3 per mil. There is a nearly monotonic decrease in calculated $•So values of hydrothermal waters with decreasing temperature in the Dae Hwa hydrothermal system, from values of •6 per mil for quartz-muscovite-molyb