• Economic and Environmental Geology
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• v.28 no.2
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• pp.123-137
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• 1995

The Mesozoic Geumsan granitic rocks of various composition are distributed in the Geumsan district, the central part of the Ogcheon Fold Belt. About 40 ore deposits of $CaF_2{\pm}Au{\pm}Ag{\pm}Cu{\pm}Pb{\pm}Zn$ are widely distributed in this district and are believed to be genetically related to the granitic rocks. Based on their petrography and geochemistry, the granitic rocks in this district can be classified into two groups ; the Group I( equigranular leucocratic granite, porphyritic biotite granite, porphyritic pink-feldspar granite, seriate leucocratic granite) and the Group II(seriate pinkfeldspar granite, equigranular alkali-feldspar granite, equigranular pink-feldspar granite, miarolitic pink-feldspar granite, equigranular biotite granite). Interpreted from their isotopic dating data and geochemical characteristics, the Group I and the Group II are inferred to be emplaced during the Jurassic(~184Ma), and the Cretaceous to the early Tertiary period(~59Ma), respectively. Both Group I and Group II generally belong to magnetite-series granitoids. The Cretaceous granitic rocks of Group II are more highly evolved than those of the Jurassic Group I. The Rb-Sr variation diagram suggests that the granitic rocks of the Jurassic Group I and of the Cretaceous Group II be evolved mainly during the processes of fractional crystallization and partial melting, respectively.

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.214-223
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• 2004

Oxygen and hydrogen isotopic compositions of the Jurassic peraluminous Hwacheon granite were measured, and compared with those of other Jurassic peraluminous Daebo granite in Korea. $\delta$$\^$18/O values for quartz and feldspar of the Hwacheon granite range from 8.2 to 10.6 and 5.8 to 9.0$\textperthousand$, respectively. Whole rock $\delta$$\^$18/O values for banded biotite gneiss country rocks surrounding the Hwacheon granites range from 8.1 to 9.4$\textperthousand$. Whole rock and biotite $\delta$D Values for Hwacheon granite range from -84 to -113 and -107 to -113$\textperthousand$, respectively. Whole rock $\delta$D values for banded biotite gneiss country rocks range from -76 to -100$\textperthousand$. Both $\delta$$\^$18/O and $\delta$D values of the Hwacheon granite are characterized by low values compared to the 'normal' values for the fresh peraluminous granitic rocks. Low $\delta$$\^$18/O values of the Hwacheon granite resulted from fluid-rock interaction for a long period. Isotopic modelling result renders that a relatively low-$\delta$$\^$18/O fluid below -1$\textperthousand$ was involved in subsolidus isotopic exchange under a relatively high fluid/rock ratio (<-6). The fluid of meteoric origin has experienced a modification of oxygen isotopic composition as a result of fluid-rock interaction with the Hwacheon granite and surrounding metapelitic country rocks.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.325-337
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• 2020

The Jurassic granitic rocks in the area of Gwangdeoksan located along the boundary between Hwacheon and Cherwon in northern Gyeonggi Massif consist of two-mica granite, garnet-bearing two-mica granite, mica-granite, and porphyritic biotite granite. These granitic rocks are calc-alkaline series and plotted in peraluminious domain in A/CNK vs. A/NK diagram. Petrographical and geochemical data indicate that the porphyritic biotite granite which intruded at the last period originated from distinct parental magma from two-mica granite, garnet-bearing two-mica granite, and mica-granite. On the basis of Rb/Sr vs. Rb/Ba diagram and Al2O3/TiO2 vs. CaO/Na2O, it is inferred the porphyritic biotite granite originated from protolith with less pelitic composition than 3 other granitic rocks. The enriched values of lithophile elements of Cs, Rb, and Ba and negative trough of Nb, P, Ti on spider diagram suggest that the peraluminous Jurassic granitic rocks in Gwangdeoksan area formed in subduction tectonic environment. Whole-rock zircon saturation thermometer indicates that the granitic rocks in the study area were melted at 692-795℃.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.1-9
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• 1996

Eonyang amethyst deposits are thought to be spatially and temporally associated with the biotite granite of the Kyeongsang Basin. The examined euhedral quartz crystals in cavities in the aplite intruded biotite granite are colored-zoned from white at the base to amethystine at the tops. Three types of primary Inclusions were observed and three is representing each types are constructed to constrain the trapping conditions and fluid evolution involved during the formation of the amethyst. The intersection of the isochore representing the early fluid inclusions with solidus temperature of the host granite indicates initial quartz formation at about $600^{\circ}C$ and 1.0-1.5 kbars . Intermediate quartz formation, associated with the high-salinity inclusions, occurred at somewhat lower temperatures ($400^{circ}c$) and pressures of about 1 kbar. The amethystine quartz formed from $H_2O$-$CO_2$-NaCl fluids at temperatures between 280-$400^{circ}c$ and pressures of about 1 kbar. Early quartz is interpreted to have formed from fluids that either exsolved from or were in equilibrium with the granite at near solidus conditions, whereas the amethystine quartz apparently grew from fluids of at least partial sedimentary origin.

• Economic and Environmental Geology
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• v.27 no.4
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• pp.387-396
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• 1994

Mineralogical and geochemical studies on gold-bearing quartz veins and wallrock from the Mugeug mine were carried out in order to investigate the variation of mineralogical composition and the geochemical behavior of elements with distance from the gold-bearing quartz veins. Gold-bearing quartz veins occur in early Cretaceous medium- to coarse-grained biotite granite. The unaltered wallrock is composed mainly of quartz, plagioclase, orthoclase, microcline, biotite and hornblende with accessory minerals of sphene and apatite. Mineralogical changes in altered wallrock around the gold-bearing quartz veins were observed as follows; 1) biotite and hornblende altered into chlorite, and next to sericite, 2) plagioclase, orthoclase and microcline altered into sericite, and 3) calcite and quartz introduced into wallrock. Contents of $K_2O$, Rb, Cs, Au, As and Sb in altered wallrock increase, whereas those of $Na_2O$, CaO, Ba, and Sr decrease with proximity to the gold-bearing quartz veins. The loss on ignition also increases with the increase of alteration mineral. The width of primary dispersion increases in order $Au=SiO_2<As=Cs=Rb<K_2O=Sb$ and $MnO<Na_2O=CaO=Ba<Sr$. The sericitization index, $K_2O/(K_2O+Na_2O)$, is an important indicator to interpret the degree of alteration at the Mugeug mine, which is more than 0.8 in strongly and moderately altered granite, 0.5~0.8 in wea altered granite, and less than 0.5 in unaltered granite. Alteration indices for major and trace elements, and the ratio of Rb/Sr are also useful to discriminate alteration zones.

• The Journal of the Petrological Society of Korea
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• v.28 no.2
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• pp.129-141
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• 2019

The Eoraesan area, Chungju, which is located in the northwestern part of Ogcheon Metamorphic Zone, Korea, mainly consists of the Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks which intruded it. The metaacidic rocks (MAR) of the Gyemyeongsan Formation show a maximum radioactive value, and the Early Jurassic biotite granite is regionally distributed in this area. In this paper is researched the microstructure related to the growth of rare-earth mineral of allanite in the MAR, and is considered the source and occurrence time of rare-earth element (REE) mineralization. The MAR is mainly composed of alkalic feldspar (mainly microcline), quartz, iron-oxidizing mineral, biotite, muscovite, plagioclase, hornblende, allanite, zircon, epidote, fluorite, apatite, garnet, (clino)zoisite etc. The radioactive elements contained in the allanite cause a dark brown hale in the surrounding biotite, and the allinte also occurs as aggregate along the regional foliation. The deflection of regional foliation and the strain shadows, which are common to the pre-tectonic porphyroblast grown before the formation of regional foliation, can't be observed around most allanites (aggregates). The grain size and orientation of ironoxidizing mineral included in the allanite aggregate are the same as those in the matrix. It is recognized the hydrothermal conversion of hornblende to biotite due to the intrusion of igneous rock, and the secondary biotite occurs and contacts with allanite, zircon, epidote etc. These microstructures indicate that the rare-earth mineral of allanite (aggregate) grew by the hydrothermal alteration due to the intrusion of igneous rock after the formation of regional foliation. It is considered that the REE mineralization is closely related to the intrusion of Early Jurassic biotite granite which is regionally distributed in this area.

• Economic and Environmental Geology
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• v.18 no.3
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• pp.263-276
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• 1985

Building stones can be divided into two groups: raw stone and stone product. In Korea, they consist of granite, diorite, gabbro, andesite, tuff, slate and marble, of which granite is main product. The disribution area is approximately $31,753km^2$. The enterprises of building stone are about 1,500 at present. The granites for building stone are biotite granite, hornblende granite. granodiorite and porphyritic granite, of different colors (white, pink, grey, green and black). The compressive strength of granite ranges from 813 to $1,338kg/cm^2$, hardness from 78 to 101 and water absorption ratio from 0.09 to 0.40%. The weight reduction ratio of granite for 14 hours in aqua regia+$KMnO_4$solution is 0.3~4.5wt.%. There are eighty granite quarries in Korea. Marbles can also be extensively used for building but only a few mines are operated at present.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.375-383
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• 2014

Precambrian granitic gneisses and Cambrian meta-sedimentary rocks are prevalently distributed in the eastern part of the Taebaegsan region, and biotite granitic batholith of the Jurassic period (?) is found in the southern part of Uljin-si. But small scale leucocratic granitic stocks which commonly found here and there have been rather neglected in the previous studies. The presence of leucocratic granites could be differentiated from the older granitic rocks and biotite granite through the outcrop characteristics, mineral species and geochemical compositions. For the effective comparison between the older granitic rocks and leucocratic ones, pale gray to gray coloured Hongjesa granitic gneiss with granular texture was selectively chosen. The Hongjesa granitic gneiss and biotite granite usually have rather plenty of coloured minerals such as biotite and chlorites. But the leucocratic granites often show sericitic alteration due to the albitization and greisenisation during the post-magmatic alteration, and shows rather bright appearance because of poor amount of coloured minerals. Since all of granitic rocks passed rather high degrees of magmatic differentiation, they belong to calc-alkalic and peraluminous in their characters. Among the alkali elements of the leucocratic rocks $K_2O$ shows higher increase than those of the other granitic rocks, and $Na_2O$ only represents slight decrease than those of the Hongjesa granitic gneiss and Uljin granite. On the other hand, CaO and total Fe content are clearly decreased than those of the Hongjesa granitic gneiss and Uljin granite.

• 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.51 no.6
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• pp.521-529
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• 2018

This study was conducted to investigate the natural origin of fluorine contained in the rocks within the Eulwangsan area via petrological and mineralogical analyses. The main geology of the Yongyudo Eulwangsan area is Triassic biotite granite. Biotite granite and mylonite are the major rock types containing fluorine at high levels (up to 1,700 and 2,400 mg/kg for biotite granite and mylonite, respectively). In the case of the biotite granite, a high concentration of fluorine can be contributed to fluorite, and the results of microscopic analyses show that the fluorite was observed as small veinlets filling cleavages and micro-fractures within alkali-feldspars and plagioclases, or observed together with quartz in ore veins, indicating the secondary formation of fluorite by hydrothermal fluids. In mylonite, on the other hand, a high fluorine concentration is attributable to sericite. Microscopic analyses revealed that the boundary between sericite and surrounding quartz was not clear, the sericite occurred filling the micro-fractures of quartz and encapsulating small quartz cataclasts. These results indicate that the sericite was also formed as a result of hydrothermal alteration. Consequently, it is speculated that the high fluorine level in the rocks of the Eulwangsan area of Yongyudo is of natural origin due to hydrothermal processes.