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Afossil hydrothermal system on Barton Peninsula, King George Island, Antarctica, formed a series of lead-zinc-and pyrite t native sulphur-bearing epithermal quartz ? calcite veins, filling fault-related fractures in hydrothermally altered volcanic rocks of Eocene age. The lead-zinc veins occur within argillic hydrothermal alteration zones, whereas the pyrite t native sulphur veins are found within advanced argillic alteration zones. Fluid inclusion data indicate that the vein formation occurred at temperatures between about 125" and 370°C (sphalerite deposition formed at 123-211°C) from fluids with salinities of 0.5-4.6 wt. % eq. NaC1. Equilibrium thermodynamic interpretation of mineral assemblages indicates that the deposition of native sulphur in the upper and central portions of the hydrothermal system was a result of the mixing of condensates of ascending magmatic gases and meteoric water giving rise to fluids which had lower pH (<3.5) and higher fugacities cf oxygen and sulphur than the lead-zinc-depositing fluids at depth. The 634S values of sulphide minerals fiom the lead-zinc veins (634S = -4.6 to 0.7°/00> are much higher than the values of pyrite and native sulphur from the pyrite + native sulphur veins (634S = -12.9 to -20.1°/w). This indicates that the fluids depositing native sulphur had higher sulphate/H,S ratios under higher fo, conditions. Sulphur isotope compositions indicate an igneous source of sulphur with a 634S,s value near Oo/w, probably the Noel Hill Granodiorite. Measured and calculated 6l80 and 6D values of the epithermal fluids (6180water = -6.0 to 2.7°/w, 6Dwat,, = -87 to -75°/00) indicate that local meteoric water played an important role for formation of lead-zinc and native sulphur-bearing quartz veins.

High-grade Zr–Nb–Y–rare earth element (REE) mineralization occurs as zircon–allanite–magnetite bands in layered Paleozoic alkali rocks which intruded the Gyemyeongsan Formation of the Chungju unit, South Korea. The mineralization period and genesis have been controversial. We investigated the petrological and mineralogical properties of the newly discovered zircon–allanite–magnetite bands and the geochronological properties of zircon within the bands in the alkali granite. We analyzed the zircon with laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The repeated quartz–feldspar-rich layers in the alkali granite show grain-sized grading textures and equilibrium igneous textures. Magnetite and allanite grains in these layers varied in size and exhibited isolated, aggregated, and coalesced textures. In addition, the settling texture of zircon grains onto the other minerals was observed. These observations could reasonably be explained by the process of gravitational accumulation during the solidification of magma. The 206Pb/238U ages obtained from zircon from the zircon–allanite–magnetite-rich layer and the alkali aplite were 331.1 ± 1.5 Ma and 334.5 ± 8.9 Ma, respectively. Therefore, we suggest that the Zr–Y–Nb–REE mineralization developed in the alkali rocks and the Gyemyeongsan Formation in the Chungju unit were formed by fractional crystallization of alkali magma and hydrothermal fluids which evolved from alkali magma fractional crystallization, respectively. The correlation between alkaline granite and REE mineralization found in this study could be used as a tool for REE exploration in other regions where the permeable geological unit is intruded by the alkali granite.

The Sambo Pb-Zn mine is located approximately 45 km south of Seoul within the Precambrian metamorphic belt of the southern Korean Peninsula. The Sambo Pb-Zn deposits are composed of fissure-filling quartz-barite veins within Proterozoic biotite schist which has been intruded by granite ahd granodiorite stocks. K-Ar dates of biotite and muscovite from the intrusions are 177 _ 4 and 164 _ 3 m.y., suggesting a Jurassic age for Pb-Zn-Ba mineralization. This age is in agreement with data for metallogenic epochs in Korea. Ba-rich Pb-Zn deposits are related to a Jurassic-Early Cretaceous epoch, whereas Ba-poor Pb-Zn deposits are generally related to Late Cretaceous-Tertiary igneous activity.Mineralization at Sambo consists of three distinct stages of quartz-barite veins (I, II, and III) which were separated in time by tectonic fracturing and brecciation events. Ore textures of stage II suggest rhythmic deposition. Five successive mineralization cycles of stage II, each with up to seven nearly monomineralic bands, are recognized. Fluid inclusion data suggest that each stage evolved from early high temperatures (near 300øC) to later lower temperatures (less than 200øC). Although the maximum temperature of stage III is slightly lower than the maximum temperature of stages I and II, we suggest that each stage represents a separate cooling mineralizing system that was interrupted by renewed tectonism.Sulfur isotope and fluid inclusion evidence indicates that galena, sphalerite, and barite were deposited at temperatures near 160 ø to 265øC from solutions with salinities ranging from 2 to 17 equivalent weight percent NaC1. Fluid inclusion evidence of boiling suggests pressures of less than 100 bars during portions of stage II mineralization. This pressure corresponds to depths at the time of mineralization of between 500 and 1,250 m.

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