• The Journal of the Petrological Society of Korea
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• v.12 no.1
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• pp.16-31
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• 2003

The granites in the southern Gimcheon area can be divided into two parts, marginal hornblende biotite granodiorite (Mgd) and central biotite granodiorite to granite (Cgd). Mgd and Cgd are gray in color and display gradational contact relations and are mainly composed of coarse-grained and medium-grained rocks, respectively. Mgd has more frequent and larger mafic enclaves than Cgd, and the two granites partly show parallel foliation at thire contact with gneisses. From representative samples of the granites, K-Ar biotite ages of 197∼207 Ma were obtained. Considering the blocking temperature of biotite, it is suggested that the emplacement age of the granitic magma was probably late Triassic. The anorthite contents of plagioclases in Mgd display less variation than those of Cgd, indicating that Mgd crystallized within a narrow range of temperatures. In the Al$\_$total/-Mg diagram, the biotites from the granites plot within the subalkaline field, and the smooth slope indicates differentiation from a single magma. All amphiboles from the granites belong to magnesio-hornblende. The linear trends of major oxides, AFM and Ba-Sr-Rb indicate that Mgd and Cgd were fractionally differentiated from a single granitic magma body crystallizing from the margin inwards. The relations of modal (Qz+Af) vs. Op, K$_2$O vs. Na$_2$O, Fe$_2$ $O_3$ vs. FeO, Fe$\^$+3/(Fe$\^$+3/+Fe$\^$+2/) and K/Rb vs. Rb/Sr show that they belong to I-type and magnetite-series granitic rocks developed by the progressive melting products of fixed sources. REE data, normalized to chondrite value, have trends of enriched LREE and depleted HREE together with weakly negative Eu anomalies.

• Journal of Conservation Science
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• v.17 s.17
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• pp.39-56
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• 2005

The Gwangtonggyo(bridge) on the Cheonggyecheon(river) is mainly composed of biotite granite with coarse grain. The rock consists mainly of quartz, plagioclase, microcline, orthoclase and biotite with lesser amount of muscovite, sericite and chlorite. Muscovite and sericite may be formed from feldspars and chlorite from biotite by alteration(including weathering). These rocks are relatively deteriorated by weathering, polluted water running the river and heavy traffic. The main phenomena of damages are surface exfoliation, grain separation, deceleration, pollution of organic and heavy chemical elements, cracks and breakage. These phenomena have been analyzed by polarized microscope, XRD and SEM/EDX. The analyzed results show organic pollution and secondarily formed gypsum and apatite on the rock surface and micro-pores. NaCl and $CaCO_3$ as rock salt and calcite probably may be formed secondarily in some points. Also heavy chemical elements such as Cr, Pb, Pd, W, La, Zn and Nd are polluted in some samples. The contacts between rocks are generally breakdown in small scale or cracks are developed due to mainly load and vibration shock of heavy traffic.

• Proceedings of the Petrological Society of Korea Conference
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• 1998.09a
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• pp.19-19
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• 1998

• Tunnel and Underground Space
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• v.27 no.5
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• pp.263-270
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• 2017

Hydraulic rock splitting is a technique which leads to failure of rockmass by means of water injection with a pressure higher than the tensile strength of rockmass, using straddle packer installed in boreholes drilled from free surface. Field tests were conducted in this study for several slopes of biotite granite according to various designs for borehole layout and water injection. Test results showed that new cracks were generated to connect to adjacent holes or that pre-existed cracks were propagated by injection, finally leading to failure. In particular, this study suggests the possibility of controlling the direction of generated cracks with guide slot, since new cracks were generated parallel to the guide slots carved on a borehole wall before injection. Various types of borehole layout and injection methods should be further developed for the practical uses, considering the factors influencing on crack generation.

• 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.51 no.5
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• pp.439-453
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• 2018

The Eocene Gyeongju granitoids in SE Korea are alkali feldspar granite (AGR), biotite granite (BTGR), and hornblende biotite granodiorite (HBGD) along Yangsan fault and Ulsan fault. According to their geochemical characteristics, these granitoids are classified as A-type (AGR) and I-type (BTGR and HBGD) granitoids, and regarded that were derived from same parental magma in upper mantle. The hornblende and biotite of AGR as an interstitial phase indicate that influx of F-rich fluid during the crystallization of AGR magma. AGR is enriched LILE (except Sr and Ba) and LREE that indicate the influences for subduction released fluids. The highest HFSE contents and zircon saturation temperature of AGR among the Eocene Gyeongju granitoids may indicate that it was affected by partial melting rather than magma fractionation. These characteristics may represent that the high F contents of AGR was affected by F-rich fluid derived from the subducted slab and partial melting. It corresponds with the results of the REE modeling and the dehydrated fluid component (Ba/Th) modeling showing that AGR (A-type) was formed by the partial melting of BTGR (I-type) with the continual influx of F-rich fluid derived from the subducted slab.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.3
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• pp.377-386
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• 2022

In addition to anthropogenic origins, fluorine (F) is naturally enriched in rocks due to geological events, such as magma dissemination, hydrothermal alteration, mineralization, and fault activities. Generally, it has been well known that F is chiefly enriched in the region of igneous and metamorphic rocks, and biotite granite was mostly distributed in the study area. The F enrichment mechanism was not sufficiently elucidated in the previous studies, and the study on a fault zone was conducted to reveal it more precisely. The mineral composition of the fault zone was identical to that of the Eulwangsan biotite granite (EBG), but they were quantitatively different between the two areas. Compared with the EBG, the fault zone showed relatively higher contents of quartz and F-bearing minerals (fluorite, sericite) but lower contents of plagioclase and alkali feldspar. This difference was likely due to hydrothermal mineral alterations. The results of microscopic observations supported this, and the generation of F-bearing minerals by hydrothermal alterations was recognized in most samples. Accordingly, it might be interpreted that the mineralogical and petrological differences observed in the same-age biotite granite widely distributed in the Yongyudo was caused by the hydrothermal alterations due to small-scale geological events.

• The Journal of Engineering Geology
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• v.21 no.2
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• pp.163-178
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• 2011

A test borehole was drilled in the Cheongwon area to investigate the relationship between geochemical environment and the natural occurrence of radioactive materials (uranium and Rn-222) in borehole groundwater. The borehole encountered mainly biotite schist and biotite granite, with minor porphyritic granite and basic dykes. Six groundwater samples were collected at different depths in the borehole using the double-packed system. The groundwater pH ranges from 5.66 to 8.34, and the chemical type of the groundwater is Ca-$HCO_3$. The contents of uranium and Rn-222 in the groundwater are 0.03-683 ppb and 1,290-7,600 pCi/L, respectively. The contents of uranium and thorium in the rocks within the borehole are 0.51-23.4 ppm and 0.89-62.6 ppm, respectively. Microscope observations of the rock core and analyses by electron probe microanalyzer (EPMA) show that most of the radioactive elements occur in the biotite schist, within accessory minerals such as monazite and limenite in biotite, and in feldspar and quartz. The high uranium content of groundwater at depths of -50 to -70 m is due to groundwater chemistry (weakly alkaline pH, an oxidizing environment, and high concentrations of bicarbonate). The origin of Rn-222 could be determined by analyzing noble gas isotopes (e.g., $^3He/^4He$ and $^4He/^{20}Ne$).

• The Journal of the Petrological Society of Korea
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• v.11 no.1
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• pp.1-16
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• 2002

The study area is mostly composed of Precambrian Gyeonggi gneiss complex, Jurassic Daebo granites, Cretaceous tonalite and dykes, and so on. On the basis of field survey and mineral assemblage, the granites can be divided into three types; biotite granite (Gb), garnet biotite granite (Ggb) and two mica granite (Gtm). They predominantly belong to monzo-granites from the modes. Field relationship and K-Ar mica age data in the surrounding area suggest that intrusive sequences are older in order of Gtm, Ggb and Gb. Gb and Ggb, major study targets, occur as medium-coarse grained rocks, and show light grey and light grey-light pink colors, respectively. Mineral constituents are almost similar except for opaque in Gb and garmet in Ggb. Gb and Ggb have felsic, peraluminous, subalkaline and calc alkaline natures. In Harker diagram, both rocks show moderately negative trends of $TiO_2$, MgO, CaO, $Al_2O_3$, $Fe_2O_3$(t), $K_2O$ and $P_2O_5$ as $SiO_2$ contents increase. Among them, $TiO_2$, MgO and CaO show two linear trends. From the trends and the linear patterns in AFM, Sr-Ba and Rb-Ba-Sr relations, it is likely that they were originated from the same granitic magma and Ggb was differentiated later than Gb. REE concentrations normalized to chondrite value have trends of parallel LREE enrichment and HREE depletion. One data of Ggb showing a gradually enriched HREE trend may be caused by garnet accompaniment. Ggb have more negative Eu anomalies than Gb, suggesting that plagioclase fractionation in Ggb have occurred much stronger than that in Gb. In modal (Qz+Af) vs. Op, Gb and Ggb belong to magnetite-series and ilmenite-series, respectively. From the EPMA results, opaques of Gb are magnetite and ilmenite, and those of Ggb are magnetite-free ilmenite or not observed. Bimodal distribution of magnetic susceptibility reveals two different granites of Gb (332.6 ${mu}SI$) and Ggb (2.3 ${mu}SI$). Based on the paleomagnetic analysis as well as modal analysis, the main susceptibilities of Gb and Ggb reside in magnetite and mafic minerals, respectively. They belong to S-type granite of non-magnetic granite by susceptibility value. In addition, $SiO_2$ contents, $K_2O/Na_2O$, A/CNK molar ratio and ACF diagram support that they all belong to S-type granites.

• 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%.