• 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.14 no.3
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• pp.123-142
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• 1981

Granitic complex in the Woosanbong area is composed of schistose granite, two-mica granite, biotite granite, porphyritic granite and pink feldspar granite in order of intrusion. In their boundary aspects, the gradational change between porphyritic granite and pink feldspar granite is observed in field relations. All the granites of the complex are classified to quartz monzonite by the modal compositions following Bateman's classification (1961) with the exception of pink feldspar granite which belongs to granite according to the petrographical classification. The first three granites are characterized by highly development of vein and/or lens-like pegmatites in their bodies, and two others contain green hornblende uniquely. These leucocratic two-mica granite shows an unusual character in ratio of muscovite to biotite 1: 0.7 to 1:13, and contains dominantly microcline. The content of muscovite varies in places in the field. Under the polarizing microscope it is revealed that the muscovite flakes occur as the products altered from biotite partly or completely, and it usually associates with chlorite flakes nearby. These features, therefore, suggests that biotite probably has been altered to muscovite and chlorite by hydration during deuteric processes. At the same stage, sericitization of plagioclase by the hydrolytic decomposition, and transformation of orthoclase to microcline may be taken place. Accordingly, it is obviously permissible to consider the two-mica granite as a kind of 'apo-granite' by deuteric alterations during the consolidation of magma.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.451-462
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• 2017

Physical weathering caused by external forces and chemical weathering caused by the decomposition or alteration of constituent materials are the two factors that dominate the mechanical properties of rocks. In this study, a field investigation was undertaken to identify the physical and chemical weathering characteristics of the biotite granite and granitic weathered soils in Gyeongju, South Korea. Samples were collected according to their grade of weathering and subjected to modal analysis, XRD analysis, XRF analysis, physical property tests, particle size distribution tests, and slake durability tests. Modal and XRD analysis identified these rocks as biotite granite; secondary alteration minerals were not observed. Physical property tests and particle size distribution analyses indicate an average porosity of 41.28% and a sand content of > 90 wt.%. These values are somewhat higher than those of granites in general. The results of the slake durability test and XRF analyses show that the physical and chemical weathering indices of the samples vary with the degree of weathering.

• The Journal of the Petrological Society of Korea
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• v.3 no.3
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• pp.220-233
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• 1994

The granitic rocks in the Poeun - Sogrisan area are composed of the Jurassic Poeun granodiorite and the Cretaceous Sogrisan granites. The latter can be divided into three rock types : coarse-grained biotite granite, porphritic biotite granite and granite porphyry. Petrographical observations, especially focusing on the quartz-feldspar intergrowth texture, suggest that the Sogrisan granites has emplaced at shallower level and crystallized more rapidly than the Poeun granodiorite. The F, Cl contents and the Fe/(Fe+Mg) ratio of biotite and muscovite in the Sogrisan granites are higher than those in the Poeun granodiorite. The anor-thite contents of plagioclase in the Poeun granodiorite are higher then in the Sogrisan granites. Ilmenite in the Sogrisan granites is more enriched in Mn and depleted in Fe than that in the Poeun granodiorite. The whole-rock magnetic susceptibility values (in $10^{-6}$ emu/g unit) are higher in the Sogrisan granites (33~144) than the Poeun granodiorite (9~12), indicating that the former generally belongs to magnetite-series granitoid and the latter to ilmenite-series one. The Sogrisan granites has solidified under more oxidizing environment than the Poeun gra-nodiorite, judging from the whole-rock magnetic susceptibility measurements as well as the chemical compositions of biotite and ilmenite.

• Economic and Environmental Geology
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• v.25 no.4
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• pp.463-477
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• 1992

The study area consists of sedimentary and volcanic rocks of Gyeongsang Supergroup, granitoid intrusives, and hornfelses around the granitoids. Granitoid intrusives occur in small stocks in Nijeon-ri, Uggogri, and Yul-ri area. The masses in Nijeon-ri and Uggog-ri are hornblende-biotite granodiorite, biotite granodiorite respectively, and Yul-ri mass is biotite granite. Surrounding sediments of these masses were thermally metamorphosed and contact aureoles were formed. The studied granitoids are considered to be formed by sequential crystallization-differentiation from calc-alkalic granitoid magma. Metamorphic minerals occurring in contact aureole are chlorite, actinolite, epidote, and biotite. Diopside and hornblende are observed in small amount in some lithology around contact aureole. The lithology of contact aureole is predominantly silty and sandy, and characteristic metamorphic minerals were poorly developed because of low temperature metamorphism. Low temperature in contact aureole could be deduced from the facts that the intrusions were small size, shallow depth, low temperature, and rare movement of volatiles from magma.

• Economic and Environmental Geology
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• v.33 no.2
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• pp.147-163
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• 2000

The Buseok pluton in the Yeongju Batholith is a comagmatic plutonic rocks which haveconcentrically compositional zoning. The lithofacies of the Buseok pluton comprise hornblende biotite tonalite in the southern part of the pluton, porphyritic and equigranular biotite granodiorite in the northern part and biotite granite in the north-central part. The compositional variations change gradually with continuity both within and between the lithofacies. The concentrically zoned pattern is relatively mafic rocks composed of high-temperature mineral assemblages in margin of the southern part, passing inward and northward gradually to more felsic rock in core of the north-central part. Changes in the textures and microstructures, as well as in the mineral content, take place between rock types of the plutons. Darker colored, generally coarse-grained, well foliated tonalite pass inward to light colored, coarse-grained, poorly foliated granodiorite, and finally give way to lighter colored, medium-grained, nearly nonfoliated granite. The foliation are best developed in the marginal part of the tonalite. Here, the regional myolitic foliation in the tonalite is steep northward and parallels to its southeastern contact with the country rock, but the magmatic foliation from disc-shaped mafic microgranitoid enclaves is subvertical and parallels the contacts with the country rock. As the tonalite approaches biotite granite in composition, the foliation is indistinct. Modal and chemical data for the pluton show quantitative compositional variation from the margin of the southern part to the core of the north-central part. Quartz and K-feldspar increase toward the core of the pluton, whereas hornblende, biotite and color index decrease. /Abundances of $SiO_2$and $K_2O$$_2$O increase toward the core according to the variation in quartz and K-feldspar, whereas those of MnO, CaO, $TiO_2$, $Fe_2O_3$, MgO and $P_2O_5$ decrease corresponding to the variation in mafic and accessaries. The compositional zonation resulted from fractional crystallization involving downward settling of earlier crystals, accompanied by upward movement of melt and volatiles, and followed by accessary marginal accretion of crystalline material in the magma to the marginal part. Although a little crustal contamination by the wall rock is recognized from the isotope data, the contamination is not only dominated over but also appropriate for forming the compositional variation in the pluton.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.87-104
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• 1990

Foliated granites between Damyang and Jinan are subdivided into Daegang foliated granite, Foliated hornblende biotite granodiorite, Sunchang foliated granodiorite, Foliated two mica granite and Samori foliated granite by mineral and texture. From EPMA data of the foliated granites following results are achieved. Composition of plagioclase are correspond to andesine, oligoclase and albite in Foliated hornblende biotite granodiorite, Sunchang foliated granodiorite and other foliated granites, respectively. And amphiboles are calcic hornblende in Foliated hornblende biotite granodiorite, and riebeckite in Daegang foliated granite. In differentiation index(D. I.) and Larsen index(L. I.), Daegang foliated granite, Foliated two mica granite and Samori foliated granite which belong to granite are 83.12-95.54 and 25.86-29.05 and Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite of diorite to granodiorite are 54.99-78.54(D. I.) and 6.48-21.01(L. I.). Harker and AMF diagrams plotted from foliated granites show that the granites are product of calc alkali rock series orignated from co-magma. Characteristic foliation of foliated granites fromed by ductile deformation at deep zone of dextral strike slip fault. Foliated granites are considered as a series of differentiated product of Triassic Igneous activity of Songrim disturbance. According to REE, (La/Lu) and Eu/Sm, Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite are correspond to granodiorite, and other foliated granites are monzo-and syeno-granite. Foliated granites having 0.20-0.01 of Em/Sm ratio are plutons emplaced by the tectonic setting in continents and continental margin.

• Economic and Environmental Geology
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• v.32 no.6
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• pp.585-597
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• 1999

Plutomic rocks of the Mabogsan, located in the southestern part of the Koheung Eup are composed of granite gneiss, diorite, biotite grantie and granophyre. On the basis of Rb-Ba-Sr diagram, the diorires are plotted from granodiorite to quartz diortie, the biotite granites from granodiortie to anomalous granite and the granophyres in normal granite filed. The plutonic rocks tend to show the I-type characteristics in terns of ACF diagram, $K_2O-Na_2O$ diagram and $Al_2O_3/Na_2O+K_2O+CaO$ diafram, while have values of ilmenite series in magnetic subseptibility. The plutons could have formed in the tectonic environment of VAG+COLG+ORG based on the silica vs. trace element diagrams. Gold contents with major and trace elements have been determined for 21 granophyres, 13 biotite granites and 4 diorites are; (1) for the diorite, the rangs is 0.508~1.73 ppb with an average of 0.5ppb;(2) for the biotite granites, the range is 0.449~13.5ppb with an average of 3 ppb;(3)for the granphyres, the range is 0.508~23.1ppb with an average of 4.5ppb. The gold content of the studied plutons tends to increase from mafic to felsic rocks. Gold contents tend to show positive correlations with those of Ag and Zn, negative correlations with those of As, Ba and Rb. The copper contents of the plutons are comparatively high. Average copper contents of diorite, biotite granite and granophyre are 710ppm, 587ppm and 484ppm, respectively. The copper contents of the plutons tend to have good correlations with those of Ag, Bi and Pb.

• The Journal of the Petrological Society of Korea
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• v.1 no.1
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• pp.34-41
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• 1992

The Precambrian granitic gneisses are widely distributed in the Danyang-Yecheon area, eastern part of Korea, where the Ryeongnam massif borders the Ogcheon fold belt. They are composed of migmatitic, biotite granitic, garnet-bearing and granoblastic granitic gneisses. The common joint sets of the granitic gneiss are NE and NS directions, which are probably related to the effects of Daebo orogeny and Bulgugsa disturbance, respectively. Mineral assemblages of the banded gneiss xenolith in the garnet-bearing granitic gneiss are quartz-plagioc1ase-biotite-mus-covite-orthoclase and quartz-plagioc1ase-biotite-garnet, belonging to the amphibolite facies. The granoblastic granitic gneiss is felsic, metaluminous, and granitic, and shows subalkaline trend. The garnet-biotite geothermometry of garnet-bearing granitic gneiss yields 640$^{\circ}$-708$^{\circ}C$ at pressure of 4 kb.

• 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.