• Journal of the Mineralogical Society of Korea
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• v.19 no.3 s.49
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• pp.153-162
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• 2006

Fluid inclusions in amethyst from the Samcheonpo amethyst deposit of the Waryongsan area, Kyongnam generally grouped into four different types: Type I (liquid-rich and $10{\sim}23wt%$ NaCl, $Th=289{\sim}359^{\circ}C$), Type II (vapor-rich and $2{\sim}10wt%$ NaCl, $Th=304{\sim}365^{\circ}C;$), Type III (halite-bearing, $31{\sim}54wt%$ NaCl, $Th=259{\sim}510^{\circ}C;$), and Type IV ($CO_{2}-bearing\;9{\sim}13wt%\;NaCl,\;126{\sim}277^{\circ}$). Type I, II, and III inclusions are confined in the lower part of the amethyst and Type IV in the upper, which indicates significant hydrothermal activity during the earliest stage of the amethyst growth or the solidus condition of granitic rocks. The earliest fluid exsolved from the crystallizing granitic magma formed Type IIIa which is spatially associated with silicate melt inclusions. The homogenization behavior of Type IIIa inclusions by dissolution of the halite crystal after the bubble disappearance indicates that Type IIIa inclusions were trapped at some relatively elevated pressure. Exsolution of Type IIIb, I, II forming fluids with gradual decrease in their salinity was followed. The last fluid was $CO_{2}-bearing$ fluid (Type IV), which is assumed to be derived by decarbonization reactions with the surrounding sedimentary rocks. It suggests that the fine-grained granitic rocks containing the Samcheonpo amethyst crystallized at the sub-solvus condition saturated with water and exsolved abundant water.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.37-52
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• 1998

The granites in the Jeomchon area can be divided into hornblende biotite granite (Hbgr), deformed biotite granite (Dbgr), deformed pinkish biotite granite(Dpbgr), biotite granite (Btgr), and granite porphyry(Gp). These granites show metaluminous, 1-type and calc-alkaine characteristics from their whole-rock chemistry. Hbgr and Dbgr belong to ilmenite-series granitoids, but Gp to magnetite-series. Dpbgr and Btgr show the intermediate nature between ilmenite- and magnetite-series. Tectonic discriminations indicate that Hbgr and Dbgr were formed in active continental margin environment, whereas Dpbgr, Btgr, and Gp in post-orogenic and/or anorogenic rift-related environment. From the Harker diagrams major oxide contents of Hbgr and Dbgr show a continuous variation with $SiO_2$, indicating that they are genetically correlated with each other. On the other hand, any correlation of major oxides variation cannot be recognized among Dpbgr, Btgr and Gp. It seems like that Hbgr and Dbgr were derived from a same parent granitic magma, judging from their occurrence of outcrop, mineral composition as well as whole-rock chemistry. Variation trends of major oxide contents between Hbgr and Baegnok granodiorite are very similar and continuous. If the two granites were derived from a cogenetic magma, there exists a possibility that the granitic bodies had been separated by Btgr and Gp of Cretaceous age. Three stages of the granitic intrusions are understood in the Jeomchon area. After the intrusion of Hbgr and Dbgr during middle to late Paleozoic time, Dpbgr emplaced into the area next, and finally Btgr and Gp intruded during Cretaceous time. Tectonic movement accompanying shear and/or thrust deformation seems likely to have occurred bewteen the intrusions of Dpbgr and Btgr.

• Economic and Environmental Geology
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• v.19 no.2
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• pp.97-107
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• 1986

The Cretaceous Imog granite is a calc·alkaline, subsolvus monzogranite and shows characteristics of "I-type" and "magnetite·series" granite by mineralogy and chemical composition. Many of the major and trace element characteristic of the Imog granite are consistent with a relationship by fractional crystallization of a basic magma. The primary magma of the granite derived from the subduction of oceanic crust at the destructive plate margin. The granite shows light REE enrichment with (Ce/Yb)N ratios of 7.77~12.55. All the REE patterns show Eu negative anomalies ($Eu/Eu^*=0.69$) in the pluton. The Imog granite at the southwestern part of the Hambaeg basin may be intruded along the tectonic intersections of the E-W and N-S lines such as deep faults and fractures. Radiometric age determination on the granite reveals as $96.7{\pm}2.0Ma$ by K-Ar dating on biotite.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.337-348
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• 2009

Clear and homogeneous glass inclusions are well preserved at the rim of the quartz phenocrysts of tuff from Sunshin epithermal Au deposit, Haenam, although the host rocks experienced extensive silicification and argillic alteration. Glass inclusion vary in size from $5\;{\mu}m$ to larger than $200\;{\mu}m$ consisting of glass(60~80 vol%) + vapor bubble(15~30 vol%) $\pm$ daughter crystals(<10 vol%). Most of glass inclusions are cubic to rectangular in shape, indicating that the host quartz grew in the stability field of $\beta$-quartz. All the glass inclusions appear to be primary. Glass inclusions are composed of highly evolved high-K calc-alkaline rhyolites, which can represent the final liquidus phase of the magma system. The $Au_2O_3$ concentration (<0.30 wt%) is trivial in the glass, indicating there was no enrichment in the final residual melt. Textural characteristics suggest that magma was water-saturated shortly before or during the eruption. $H_2O$ content of the glass (ca. 2-4 wt%) suggests a water saturation pressure($P_{H2O}$) of about 300-900 bars. This pressure implies a minimum depth of 0.8-2.5 km for the magma chamber.

• Journal of the Korean earth science society
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• v.18 no.6
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• pp.480-492
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• 1997

In order to understand the processes involved in the petrogenesis and the differentiation of the primary magma spectrum, a petrological and geochemical properties were investigated for the Chonju and the Sunchang foliated granites, which are located in the southwestern part of the Okchon zone and extends up to the northwestern boundary of the Ryongnam massif as two subparallel batholiths. Major element analyses show that the Chonju and Sunchang foliated granites are classified petrologically into a weakly to strongly peraluminous or calc-alkaline, but do not fit neatly into either of the I/S-type or magnetite/ilmenite-series classification schemes for granites, although the I-type and magnetite-series characteristics seem to be predominant based on the major element chemistry. In normative compositions, the Chonju granite is petrographically evolved from granodiorite to granite, whereas the Sunchang granite is from granodiorite to quartz monzodiorite. It seems to suggest a difference of the magmatic evolution processes such as crustal assimilation and/or fractional crystallization in magma. The REE patterns of both batholiths show high similarity and strongly fractionated REE distributions which show high $(Ce/Yb)_N$ ratios and little or no Eu anomalies. These REE patterns correspond broadly to those seen in the pre-Cretaceous granitoids of Korea. Apparently, the evidences obtained from the bulk compositions strongly suggest that the two foliated granitoids were formed by partial meltings of a relatively restricted and similar, may be common, source material which contains a continental crust component having an igneous composition, and have undergone a similar magmatic differentiation processes.

• Journal of the Mineralogical Society of Korea
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• v.26 no.4
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• pp.299-312
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• 2013

Magnetite, a major constituent mineral of the Hongcheon carbonatite-phoscorite complex, was produced over three stages in each rock type and decreased in quantity toward the late stage. Electron microprobe analyses for magnetite revealed that Ti and V were detected in traces, but showed increasing tendency from early to late stage. On the contrary, Mg and Mn decreased distinctly, and it is the general differentiation trend of carbonatitic magma. Al also showed decreasing tendency in carbonatite and phoscorite, and Cr was mostly below detection limit except late phoscorite. In early stage, $Fe^{2+}$ was largely replaced by $Mg{2+}$ and $Mn^{2+}$, and $Fe^{3+}$ by $Al^{3+}$ in magnetite, but it has nearly pure composition in late stage. Tendency of increase in V and decrease in Mn toward late stage represents that magma differentiation progressed under the condition of decreasing oxygen fugacity. Low concentrations of Mg, Al, Cr and Ti, as well as the absence of olivine and phlogopite, suggest that the Hongcheon carbonatite-phoscorite complex was generated from depleted magma. Especially, lower concentrations of Mg in magnetite compared to other typical carbonatite-phoscorite complex, and abundant occurrence of Fe-carbonate minerals and quartz in late stage, suggest that magma differentiation of the Hongcheon carbonatite-phoscorite proceeded to the latest stage.

• Journal of the Korean earth science society
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• v.43 no.6
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• pp.737-748
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• 2022

In this study, the composition of feldspar phenocrysts observed in the Ulleungdo Albong trachyandesite lava dome was identified by performing point and X-ray element mapping surface analysis (EPMA). Plagioclase, which appears as a phenocryst in the Albong trachyandesite, corresponds to bytownite and labradorite, and andesine, and lath in the microphenocrysts and the matrix corresponds to andesine to oligoclase. Alkali feldspar mantled around plagioclase phenocrysts and microphenocrysts correspond to anorthoclase and sanidine. Plagioclase phenocrysts with a distinct zonal structure represent a normal structure in which the An content of the zoning decreases from bytownite to labradorite or andesine as it moves from the center of the phenocrysts to the edge. The edge of the phenocryst is surrounded by alkali feldspar, showing an antirapakivi texture. X-ray mapping of feldspar phenocrysts showed a typical antirapakivi texture. Normal zoning with distinct zoning showing a difference in component composition was clearly shown. The edges were mantled with alkali feldspar, and antirapakivi represents the texture. The antirapakivi texture of feldspar in the Albong trachyandesite may have been formed in the mixing system when alkali feldspar crystallized and mantled around plagioclase phenocrysts and microphenocrysts. This is because plagioclase phenocrysts and microphenocrysts in magma that had already crystallized are more mafic than trachyandesite magma.

• Journal of the Korean earth science society
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• v.22 no.5
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• pp.405-414
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• 2001

Jecheon granite can be divided into two types; porphyritic granite (K-feldspar megacryst bearing) and medium-grained biotite granite. Porphyritic granite, host body of feldspar deposits, is 8${\sim}$11 km in diameter and about 80 $km^{2}$ in area. It mainly contains K-feldspar, plagioclase, biotite and quartz, and magnetite, zircon, sphene and apatite are accessary minerals. Enclosed minerals in K-feldspar megacryst with 3${\sim}$10 cm in diameter are hornblende, plagioclase, quartz, magnetite, apatite, sphene and zircon. Mafic enclaves mainly consisting of hornblende, plagioclase and quartz are frequently observed in porphrytic granite. Medium-grained biotite granite consists of K-feldspar, plagioclase, biotite and hornblende as main, and hematite, muscovite, apatite and zircon as accessary minerals. Core and rim An contents of plagioclase from porphyritic granite, medium biotite granite, K-feldspar megacryst, and mafic enclave are 36 and 21, 40 and 32, 37 and 32, and 43 and 36, respectively. $X_{Fe}$ values of hornblende are 0.57 at biotite granite, 0.51 at K-feldspar mehacryst and 0.45 at mafic enclave. $X_{Fe}$ values of biotite and hornblende are homogeneous without chemical zonation. K-feldspar megacryst shows end member of pure composition with exsolved thin lamellar pure albites. Characteristics of mineral compositions and petrography indicate porphyritic granite is igneous origin and medium-grained biotite granite comes from the same source of magma; biotite granite is initiated to solidly and from residual melt porphyritic granite can be formed. Possibly K-feldspar megacrysts are formde under H$_{2}$O undersaturation condition and near K-feldspar solidus curve temperature; growth rate is faster than nucleation rate. Mafic enclaves are thought to be mingled mafic magma in felsic magma, which is formed from compositional stratigraphy. Estimated equilibrium temperature and pressure for medium-grained biotite granite are about $800^{\circ}C$ and 4.83${\sim}$5.27 Kb, respectively.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.35-51
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• 1996

The granitic rocks in the vicinity of the Mt. Sorak, the northeastern part of the NE-SW elongated Mesozoic granitic batholith in the Kyeonggi massif, consist of granodiorite, biotite granite, two-mica granite and alkali feldspar granite. Variations In major and most trace elemental abundances show a typical differentiation trend in a granitic magma. Granitic rocks all display a calc-alkaline trend in the AFM diagram. Also, In the ACF diagram discriminating between I- and S-type granitic rocks, granodiorite and most biotite granite in the southeastern area represent I-type and magnetite-series characteristics, while most biotire granite and two-mica granite in the northwestern area exhibit S-type and ilmenite-series ones.According to recent studies of the granitle rocks In the Inje-Hongcheon district. all ihe granitic rocks distributed in the northeastern part of the Kyeonggi massif have been classified as late Triassic to early Jurassic Daebo granite. With reference of the formerly published ages, an age oi $125.6{\pm}4.4$ Ma calculated by the slope in the plot of $^{87}Rb/^{86}Sr-^{87}Sr/^{86}Sr$ for the biotite granite samples from the southeastern area is inferred as an emplacement age for the granitic rocks in the vicinity of the Mt. Sorak. On the basis of elemental variations and Sr isotope compositions, an possible evolutional process for the granitic magmas in this area is suggested. The primary magma of I-type and magnetite-series generated about 125 Ma by partial melting of igneous originated crustal materials, might be emplaced and evolved through fractional crystallization, convection and assimilation of the surrounding Precambrian metasediments to become S-type and ilmenlte-serles in the outer area, and then solidified to granodiorite, biotite granite and two-mica granite.At the latest stage, the evolved hydrothermal solution altered the formerly solidified biotite granite to alkali feldspar granite and probably later local igneous activities affected the alkali feldspar granite again.

• Economic and Environmental Geology
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• v.28 no.1
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• pp.25-31
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• 1995

In Dongnam area, Cretaceous igneous rocks, such as diorite, porphyritic granite, and quartz porphyry intruded Paleozoic sedimentary rocks, such as Myobong slate and Pungchon limestone. The Dongnam Fe-Mo skarn deposits were imposed on the diorite(endoskarn) and the Myobong slate(exoskarn). The ore deposits consist mainly of magnetite and molybdenite with small amounts of sulfides, such as galena, sphalerite, pyrite, chalcopyrite, and pyrrhotite. The igneous rocks show nearly constant $^{206}Pb/^{204}Pb(18.80{\sim}19.06)$ and $^{207}Pb/^{204}Pb(15.71{\sim}15.72)$ ratios. Their $^{207}Pb/^{204}Pb$ ratios higher than the typical ratios of orogene suggest that the igeneous rocks were formed from lower crust(or mantle) - derived magma excessively contaminated by upper crustal materials such as high radiogenic Precambrian basement rocks. The lead isotopic compositions of the igneous rocks, the Pungchon limestone, and the ore minerals show a well defined linear in $^{206}Pb/^{204}Pb$ - $^{207}Pb/^{204}Pb$ plot. The lead isotopic compositions of the igneous rocks are similar to those of magnetite and galena, which were formed at early skarn stage and significantly lower than those of altered quartz porphyry, molybdenites, and pyrite, which were formed at late epithermal alteration stage. Considering the systematic variation of the lead isotopic compositions in the ore minerals according to hydrothermal stages, the variation may be due to a relative variation in surrounding rock(Pungchon limestone) involvement in hydrothermal ore solution leaching the surrounding rock. Therefore, the variation of the lead isotopic compositions in ore minerals can be modeled in terms of the mixing of the leads derived from the igneous rocks as low radiogenic source and the surrounding rock(Pungchon limestone) as high radiogenic source.