The Ulsan FeW mine is located within the Cretaceous Gyeongsang volcano-sedimentary basin at the southeastern edge of the Korean Peninsula. Distinct hydrothermal events resulted in calcic skarn and vein deposits in recrystallized limestone near a Tertiary epizonal granite stock. The deposits of the Ulsan mine present a unique opportunity to document geochemically the complex evolution of a skarn-vein system that is related genetically to a low-sulfidation system. Isochemical contact metamorphism of an early skarn stage (stage I) is displayed by the presence of anhydrous Ca-Al-Mg skarn minerals at the contact between granite and recrystallized limestone. Following magnetite deposition in the main prograde skarn (stage II), the first deposition of arsenopyrite occurs intergrown with rammelsbergite-niccolite-gersdorffite-löllingite-native bismuth-bismuthinitehexagonal pyrrhotite. These common sulfide assemblages are characterized by an overall low-sulfidation state during the main skarn stage. Retrograde skarn (stage III) is characterized by minor impregnations of scheelite in calcite and quartz, with actinolite and chlorite. During the latest part of stage III, Cu-Zn and polymetallic sulfide mineralization was introduced. The latest episode in the hydrothermal system (stage IV) is characterized by Zn-Pb-Ag mineralization in siderite-quartz veins. Decreasing As contents in arsenopyrite from stages II to IV indicate a decrease in temperature or sulfur fugacity (or both) with time. The various skarn-forming events and ore minerals from various stages are interpreted to have resulted from an evolutionary trend from hypersaline magmatic fluids during prograde skarn formation associated with Fe-As(-Ni) mineralization to low-salinity and lowtemperature fluids during the retrograde skarn formation, associated with W-Cu-Zn mineralization. As the influence of magmaderived fluids waned, surficial fluids descended to deeper levels along fractures, resulting in siderite-quartz deposition associated with Zn-Pb-Ag mineralization. These results demonstrate that the Ulsan deposit is likely a skarn deposit that is genetically related to a low-sulfidation porphyry system.

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Gold mineralization of the Daerae mine represents the first recognized example of the Jurassic gold mineralization in the Sangju area, Korea. It occurs as a single stage of quartz veins that fill fault fractures in Precambrian gneiss of the centralnorthern Sobaegsan Massif. The mineralogical characteristics of quartz veins, such as the simple mineralogy and relatively gold-rich (65-72 atomic % Au) nature of electrum, as well as the CO 2 -rich and low salinity nature of fluid inclusions, are consistent with the 'mesothermal-type' gold deposits previously recognized in the Youngdong area (about 50 km southwest of the Sangju area). Ore fluids were evolved mainly through CO 2 immiscibility at temperatures between about 250 and 325 °C. Vein sulfides characteristically have negative sulfur isotopic values (-1.9 to +0.2 ‰), which have been very rarely reported in South Korea, and possibly indicate the derivation of sulfur from an ilmenite-series granite melt. The calculated O and H isotopic compositions of hydrothermal fluids at Daerae (δ 18 O water = +5.2 to +5.9 ‰; δD water = -59 to -67 ‰) are very similar to those from the Youngdong area, and indicate the important role of magmatic water in gold mineralization.The 40 Ar-39 Ar age dating of a pure alteration sericite sample yields a high-temperature plateau age of 188.3 ± 0.1 Ma, indicating an early Jurassic age for the gold mineralization at Daerae. The lower temperature Ar-Ar plateau defines an age of 158.4 ± 2.0 Ma (middle Jurassic), interpreted as reset by a subsequent thermal effect after quartz vein formation. The younger plateau age is the same as the previously reported K-Ar ages (145-171 Ma) for the other 'mesothermal-type' gold deposits in the Youngdong and Jungwon areas, Korea, which are too young in view of the new Jurassic Ar-Ar plateau age (around 188 Ma).