• Economic and Environmental Geology
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• v.23 no.3
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• pp.329-342
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• 1990

The purpose of this study is to clarify the nature of the differentiation and petrogenesis of igneous rocks in comparison with experimental results based on petrological and geochemical criteria. Study area is composed of the Precambrian granitic gneiss complex, Triassic meladiorite and biotite granodiorite, Jurassic biotite granite, and Cretaceous quartz porphyry. According to the data of EPMA, the clinopyroxene and orthopyroxene of meladiorite come under salite and hypersthene, respectively. Such results suggests that meladiorite is incipient differentiated products of basic magma under slow cooling condition. The petrochemical data of variation diagram of major element oxides vs. silica and of trace element oxide vs. silica, AMF triangle diagram and trace elements suggests that igneous rocks of study area are plutonic rocks belong to calc alkali rock series of the source of comagma intruded-emplaced in the order of meladiorite, biotite granodiorite and biotite granite by fractional crystallization of magma.

• Economic and Environmental Geology
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• v.26 no.4
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• pp.473-487
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• 1993

The Janggun mine area is occupied by the Proterzoic and the Paleozoic meta-pelites, which are intruded by the Jurassic Chunyang granite. The metamorphic terrain is divided into four zones of progressive metamorphism on the basis of mineral assemblages. The zones are chlorite zone, staurolite zone, andalusite zone, sillimanite zone ascending order. Boundary lines between the zones resemble outline of the Chunyang granite mass. Isograd reactions are chlorite+chloritoid+muscovite=staurolite+biotite+quartz+water, staurolite+chlorite+muscovite+quartz=andalusite+biotite+water, and staurolite+muscovite+quartz=andalusite+biotite+garnet+water between the chlorite zone and the staurolite zone, the staurolite zone and the andalusite zone, and the andalusite zone and the sillimanite zone, repectively. They are univariant reactions in KFMASH component system. Metamorphic conditions estimated from garnet-biotite geothermometers and phase equlibria are $530^{\circ}C$ and lower than 4 kb.

• Economic and Environmental Geology
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• v.31 no.1
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• pp.31-43
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• 1998

A total of 469 granitic samples were collected from 44 sites in the Ulsan fault area, southeast Korea. According to the previous petrographic studies, the granitic rocks have been divided into four groups (Hornblende biotite granodiorite, Hornblende granite, Biotite granite and Alkali-feldspar granite). NRM intensities, values of low field magnetic susceptibility, and magnetic behaviors during stepwise demagnetization experiments suggest rather a three-fold classification: In this scheme, Hornblende granite and Biotite granite are grouped together, as they did not show any significant differences in magnetic characteristics. Based on the Ishihara (1979)'s criterion, Alkali-feldspar granite is classified as ilmenite-series granite, whereas others are classified as magnetite-series granite. In the eastern part of the study area including the Tertiary basin area, declinations of site-mean characteristic remanent magnetizations (ChRMs) show clockwise deflection of more than 30 from the reference direction of east Asia. Both along and in the adjacent region of the Ulsan fault-line, however, no deflection of remanent direction was observed. A boundary line between the deflected and undeflected site-mean ChRMs is defined in this study, which runs roughly parallel to the Ulsan fault-line at the distance of about 6km eastward from the fault-line. We suggest that this newly found boundary line, which we call Yonil tectonic line, released dextral simple shear stress acted in the southeastern part of the Korean peninsula during the opening stage of the East Sea in the Early Cenozoic.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2000.05a
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• pp.24-24
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• 2000

We studied about petrological characteristics of the Bangeujin granite belongs to porphyritic biotite granite, petrogenesis of the enclaves in the granite and contact metamorphism of the sedimentary rock around the granite. The enclaves in the granite are concentrated in the eastern part of the Mipo fault but in the western part, these are rare. The enclaves can be divided into three types according to the petrographical characteristics. These three types are: (1) enclaves having few phenocrysts and fine grained igneous texture and ellipsoid is predominant; (2) enclaves similar In petrographical characteristics and having many phenocrysts considered as being originated from the granitic host rock; and (3) enclaves corresponding to granite in mode composition, having large phenocrysts and of which the matrix is corresponding to fine granular. First two types are correspond to mafic micro granular enclaves and the third is corresponds to felsic microgranular enclaves. In addition, the felsic microgranular enclaves capture the mafic microgranular enclaves. The fact that the compositions of biotite and plagioclase in the enclaves are nearly identical with those of biotite and plagioclase in the granitic host rock is considered as the results of supporting magma mingling. The major elements show well the linear variations as the SiOz$.$ content increases. The rare earth elements content decrease with increasing SiOz content, interpreted as the results of magma mingling. Therefore, we can conclude that the Bangeujin granite captured the felsic microgranular enclaves formed by collapse of early chilled margin during the crystallization and there was magma mingling by the injection of the mafic magma after that time. In addition, these aspects are predominant in the eastern part of the Mipo fault is considered as related to the fault movement.vement.

• The Journal of the Petrological Society of Korea
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• v.26 no.1
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• pp.1-11
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• 2017

We have dated the K-Ar, Ar-Ar and U-Pb ages of the Masan hornblende-biotite granite in the southern Cretaceous Gyeongsang basin to constrain its emplacement age. The ~108 Ma hornblende K-Ar age obtained in the study is similar to the previously reported Rb-Sr age. However, the single grain total fusion $^{40}Ar/^{39}Ar$ dating on hornblende failed to yield statistically meaningful ages because the isotopic system was open during its alteration. Thus the hornblende K-Ar age in the study is also unlikely to be reliable. The single grain total fusion $^{40}Ar/^{39}Ar$ dating on biotite yielded an average age of $75.8{\pm}3.0Ma$. Apart from scattered data in the range of ~45-75 Ma, the average age increased to ~80 Ma. The SHRIMP and LA-MC-ICPMS U-Pb isotopic compositions of zircon from the Masan hornblende-biotite granite yielded its emplacement age as $87.6{\pm}2.7Ma$ and $86.8{\pm}0.4Ma$, respectively. It is thus likely that the ~80 Ma $^{40}Ar/^{39}Ar$ age of biotite might reflect the cooling age of Masan hornblende-biotite granite or the thermal influences from later intense igneous activities in the Gyeongsang basin.

• The Journal of the Petrological Society of Korea
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• v.13 no.2
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• pp.81-102
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• 2004

The plutonic rocks in Seonsan area are divided into dioritic-syenitic rock, gneissose granite, biotite granite and fine grained biotite granite. These rocks intruded into the Pre-cambrian metamorphic complex and are all covered by the Cretaceous Nakdong formation. According to modal minerals, dioritic-syenitic rock corresponds to quartz monzonite, granodiorite, tonalite fields, whereas all the other plutonic rocks fall in granite field. Petrochemically the dioritic-syenitic rock is lower in SiO$_2$ content, differentiation index and Larsen index than all the other plutonic rocks. About the zircon morphology, dioritic-syenitic rock shows (100) dominant type but other granitic rocks exhibit mixed types between (100) and (110) type. The dioritic-syenitic rock could be crystallized in higher temperature than the other plutonic rocks. The plutonic rocks correspond to calc-alkaline rock series, and belong to I-type granite and mostly magnetite-series in magmatic origin. In plutonic processes, the dioritic-syenitic rock with 5kb vapor pressure could intrude into the metamorphic batement at 17km deep below the surface. Later the gneissose granite with lower 3kb vapor pressure could intrude at 10km deep. Sequentially the biotite granite with 0.7kb could intrude at 2km deep. Finally the fine grained biotite granite with 3kb vapor pressure could intrude at 10km deep.

• Journal of the Mineralogical Society of Korea
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• v.15 no.3
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• pp.183-194
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• 2002

Biotite and its weathering Products in the weathering Profile of Andong granite were examined using X-ray diffraction, chemical analysis, and electron microscopy. Major weathering product of biotite was oxidized biotite, which is decomposed into kaolinite in the upper part. Discrete vermiculite or hydrobiotite was not detected although minor vermiculite (5%) was randomly interstratified with oxidized biotite. Excess positive charge induced by iron oxidation was balanced by release of Fe (16%) and Mg (12%) from octahedral site and K (13%) from interlayer site. After slight chemical and structural modification induced by iron oxidation, oxidized biotite persists through the weathering profiles with partial decomposition in the upper part of the profile. Formation environments and dissolution experiments of oxidized biotite highly resistant to weathering are required to understand the elemental behavior in the surface environments on the biotite-bearing bedrocks.

• The Journal of Engineering Geology
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• v.18 no.1
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• pp.103-115
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• 2008

The purposes of this study are to understand characteristic water-rock interaction mechanisms of groundwater in the granite area of Geochang and Hapcheon areas, Gyeongnam-do and to clarify the origin of fluoride. The possible water-rock interaction process and the source of fluorine were studied using water chemistry, rock chemistry, mineralogy by XRD, and microtexture analysis by backscattered electron image of the electron microprobe. No clear relationships between F and hardness was found. But the fluorine content increases to some extent with pH and well depth. Preferential alteration due to water-rock interaction took place along edges or cleavage, or margins of biotite. Because biotite is highly subject to alteration in granite aquifer, fluorine in groundwater is originated from the leaching of biotite.

• The Journal of the Petrological Society of Korea
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• v.3 no.2
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• pp.109-127
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• 1994

We report field relationship, petrography and major and trace element chemistry for the central part of the Seoul granitic bathlith of Jurassic age occurring in the Kyonggi massif. The batholith consists mainly of biotite granite (BG) and garnet biotite granite (GBG) with minor tonalite-quartz diorite and biotite granodiorite with or without hornblende. The mode data, along with the those reported by Hong (1984) for the biotite granite (south-BG) in the southern part of the batholith, indicate that the many of BGs and majority of GBG and south-BG are leucocratic. Major element data indicate that these predominant rocks of the batholith are peraluminous. Variation trends in Harker diagrams for the major and trace elements suggest that the BG and GBG are not related by a simple crystal fractionation process. The same is true between the central (BG and GBG) and the southern (south-BG) parts of the batholith, suggesting that the central and southern parts of the Seoul batholith may consist of three separate intrusions. Tectonic discriminations using major and trace element data and the age of emplacement suggest that the batholith represents Jurassic plutonism related to an orogeny, perhaps to a subduction-related continental magmatic arc.

• The Journal of Engineering Geology
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• v.28 no.4
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• pp.631-643
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• 2018

Uranium and radon concentrations in groundwater from 80 wells from Daejeon area were measured to determine the range of concentrations according to the geology. The median uranium content of groundwater was $11.14{\mu}g/L$ for the two-mica granite, $0.90{\mu}g/L$ for the biotite granite, and $0.47{\mu}g/L$ for the Ogcheon group. The median radon content of groundwates was 114.3 Bq/L for the two-mica granite, 61.6 Bq/L for the biotite granite, and 42.2 Bq/L for the Ogchon group, respectively. The uranium content of two-mica granite is 3.78 mg/ kg, which is slightly higher than that of biotite granite 3.20 mg/kg. However, the uranium content in groundwatewr of two-mica granite groundwater is much higher than that of biotite granite. This can be explained by the fact that the two-mica granite is vulnerable to weathering than biotite granite, so uranium in mineral is easily leached into groundwater. The exceeding rate of samples having uranium content above $30{\mu}g/L$ in granite area was 23.8%, which is higher than that of 6.7% in Jurassic granite in Korea. On the other hand, the exceeding rate of samples having radon content above 148 Bq/L in granite rate area was 31.0% which is similar to that of Jurassic granite area of 31.7%.