• Economic and Environmental Geology
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• v.34 no.4
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• pp.319-328
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• 2001

The Fe-REE deposit of the Hongcheon-Jaeun district occurs in Precambrian gneiss, and is classified into two ore bodies: the Jaeun ore body (northern ore body) and the Hongcheon ore body (southern ore body). Ecomonically important minerals consist of magnetite, monazite, strontianite and barite. Based on mineral assemblages and textures, the mineralization can be classified into two stages (Na-carbonatite stage and Fe-carbonatite stage). Main REE minerals were precipitated during the Fe-carbonatite stage. Some evidences of the carbonatite origin include: 1) strontianite-monazite exolution texture, 2) strontianite-barite exolution texture, 3) the occurrence of acmite of igneous origin at the area with abundant rare earth minerals, 4) the occurrence of the mineral assemblage consisting of carbonate minerals + magnetite + REE minerals. Therefore, we suggest that Fe-REE mineralization in the study area was related to carbonatite of igneous origin.

• Journal of the Mineralogical Society of Korea
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• v.12 no.2
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• pp.55-65
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• 1999

Spotted cordierite occurs as the result of intrusion of Wolaksan Granite of Cretaceous age in the northern part of the Ogcheon Metamorphic Belt, forming a contact metamorphic zoning in accordance with the distance from the granite body: a cordierite-muscovite-biotite-quartz assemblage and the higher-temperature cordierite-biotite-quartz-(cummingtonite). These quartz-ubiquitous mineral assemblages identified in the cordierite spot seem to reflect Al-deficient condition of the protolith. TEM observations of textural relations between the cordierite and mica within the cordierite spot clearly reflect that cordierite was formed at the expense of micaceous matrix. A structure refinement of the poikiloblastic cordierite was performed by the Rietveld refinement method. Unit cell of the cordierite was determined to be as follows : lower-temperature type: a=17.1480(9)${\AA}$, b=9.7743(6)${\AA}$, c=9.3184(5)${\AA}$, V=1561.9(4)${\AA}$3, higher-temperature type: a=17.136(2)${\AA}$, b=9.751(1)${\AA}$, c=9.322(1)${\AA}$, V=1557.7(4)${\AA}$3. They show a remarkable difference in the unit cell dimension. The refinement results indicate that structural sites of lower-temperature cordierite are wholly occupied by appropriating ions. Compared to this, tetrahedral sites of the higher-temperature type exhibit an order/disorder ranging about 5-8% as the result of substitution between Si4+ and Al3+, except for T26 site occupied wholly by Al3+. These structural differences seem to be related to the formation temperatures of both cordierite types.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.531-541
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• 1997

Unconsolidated sediments of Youngjong Island were investigated to consider the vertical distribution of clay minerals and their origin. At least three sedimentation units can be recognized by color, magnetic susceptibility, and pH. X-ray diffraction analysis of clay size fraction reveals that illite is the most abundant phase (52.06%), and chlorite (27.16%), kaolinite (16.92%), smectite (3.86%) occur next to it. Detailed XRD study suggests that illitic materials contain fairly large amount of ordinary muscovite derived from the mica schist in Youngjong Island and adjacent area. The relative amount of kaolinite and chlorite is less than those of samples from estuary mouth of several rivers that flow to Yellow Sea and South Sea. Especially smectite content of the present sample is much higher than those of estuary sediments. These indicate that the unconsolidated sediments of tidal-flat deposit in Youngjong Island are largely affected by marine influence and partly affected by sediment in influx from China. However, some degree of source of this unconsolidated sediments is inland origin from adjacent estuary sediment and in situ or nearby weathered materials.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.339-351
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• 1999

Petrographic and palaeomagnetic studies have been conducted to understand the origin of dark-colored enclaves occurring in the hornblende biotite granite within the Wondong caldera. The enclaves are commonly elongted and rounded in shape. They are finer-grained and darker-colored than enclosing granite, but they have simliar mineral assemblage to that of granite. Under the microscope the enclaves show microstructures reflecting an igneius origin. The microstructures of igneous origin include elongate grain shapes of plagioclase, hornblende, apatite, poikilitic anhedral quartz and zoning of plagiclase. All above features indicate that the enclaves belong to the 'microgranitoid enclaves' of Vernon (1984). a total of 91 orirnted samples were drilled from 4 sites, and their AMS (anisotropy of magnetic susceptibility) axis directions and remance components were analyzed. The result shows thar both enclave and host granite have same AMS priniciple axis direction and same remanence magnetic direction in each site. The result of this study suggests that the anclaves were derived from the globules of magma, which were formed by pillowing of synpltonic dike of magma that is more mafic than the host granite magma.

• Journal of the Mineralogical Society of Korea
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• v.9 no.1
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• pp.43-53
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• 1996

The detailed crystal chemistry of ilmenite from the Hadong massif was studied by the EPMA, M ssbauer spectroscopy, and Rietveld structural refinement using X-ray powder diffraction data. The ilmenite-bearing anorthosite shows complicated mineral assemblage which consists of plagioclase, clinopyroxene, hornblende, biotite, chlorite, apatite, allanite, and zircon. Anorthite is andesine in composition (Ab 28-57), and clinopyroxene drops in ferro-hypersthene (Fs 62-70). Ilmenite is trigonal symmetry with R space group, whose structure shows the alternation of Fe2+ (M1 site) octahedral layer and Ti (M2 site) layer along c axis. M ssbauer spectroscopy indicates that there are three doubles which assigned to couple of Fe2+($\delta$=0.812, 0.890mm/sec) and one Fe3+($\delta$=0.303mm/sec) in octahedral sites. Their Fe3+/$\Sigma$Fe is 0.065 and chemical formula is established as Fe2+0.94Fe3+0.07Ti0.97O3 using both EPMA and M ssbauer analysis. Rietveld structural refinement reveals that site occupancies of Fe in M1 and Ti in M2 are 91.2% and 89.4%, respectively. This implies that Ti and Fe2+ are alternatively occupy M1 and M2 sites. In addition, smaller M2 site is more preferable to Fe3+ occupancy over M1.

• Journal of the korean society of oceanography
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• v.31 no.2
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• pp.43-54
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• 1996

Jinhae Bay, one of the largest tidal bays on the southern coast of Korea, is an area with thick accumulations of recent, fine-grained sediments, mainly supplied from the Nakdong River. The preponderance of silt and clay particles reflects the large quantity of sediments transported in suspension. Although the clay mineral assemblage is similar to that derived from the nearby Nakdong River, relatively high concentration (3-9%) of smectite suggests some local input of fine particles from several streams around the bay or some contribution from the offshore water that may be influenced by the Tsushima Current. The content of organic matters in sediments is as high as 12%, and their C/N ratios imply that they are comprised of mixtures derived from marine plankton and terrestrial plants. $^{210}Pb$ excess activity profiles of sediment cores yield an average sedimentation rate (a 100-year time scale) of about 2-5 mm/yr, which coincides well with the long-term sedimentation rate (a 1000-year time scale) estimated from the sediment isopach map. On the basis of sediment bulk density and sedimentation rate, an annual sink of mud in the bay is estimated approximately 1.0 ${\times}$ $10^{6}$ tons per year.

• Journal of the Korean earth science society
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• v.23 no.7
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• pp.575-586
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• 2002

Authigenic minerals found in sandstones and mudrocks of the Lower Hayang Group (Cretaceous) in the central part of the Kyungsang Basin are carbonate minerals (calcite, dolomite), clay minerals (illite, chlorite, C/S, I/S and kaolinite), albite, quartz and hematite. Characteristic diagenetic mineral assemblages are as follows: albite-chlorite (including C/S)-hematite in the Chilgog Formation, albite-illite-calcite in the Silla Conglomerate, illite-chlorite-hematite in the Haman Formation and albite-chlorite-dolomite in the Panyawol Formation, respectively. Among clay minerals reflecting the physical and chemical change of the diagenetic process, illite, the dominant clay mineral, occurs in every formation in the study area. Chlorite occurs mainly in green or gray sandstones and mudrocks, or in sandstones and mudrocks of the Chilogok Formation which contains a high content of volcanic materials. Based on the mineral assemblage, diagenetic minerals are strongly related with source rocks. Judging from the illite crystallinity, diagenesis of sandstones and mudrocks in the study area reached the late diagenetic stage or low grade metamorphisim. The diagenetic process was much influenced by intrusion of the Bulguksa granite, content of organic materials, grain size, and depositional environment rather than burial depth.

• The Journal of the Petrological Society of Korea
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• v.8 no.1
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• pp.14-23
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• 1999

The northeastern part of the Gyeongsang Basin is widely covered by the Cretaceous Hayang Group (Aptian to Albian). The Hayang Group consists of the IIjig. Hupyeongdong, Jeomgog, and Sagog formations. Heavy mineral analysis was carried out to define the possible source rocks of the Haynag Group snadstones. Heavy minerals separated from IIjig, Hupyeongdong, and Jeomgog sandstones are hematite, ilmenite, leucoxene, magnetite, pyrite, actinolite, andalusite, apatite, biotite, chlorite, epidote, garnet, hornblende, kyanite, monazite, muscovite, rutile, sphene, spinel, staurolite, tourmaline, and zircon. Based on their close association and sensitiveness, the heavy mineral assemblages can be classified into 6 syutes: 1)apatite-green tourmaline-sphene-colorless/yellowish zircon; 2) colorless garnet-epidote-rutile-brown tourmaline; 3) rounded purple zircon-rounded tourmaline-rounded rutile; 4) augite-hornblende-color- less zircon; 5) epidote-garnet-sphene; and 6) blue tourmaline. The possible source rocks corresponding to each assemblage are 1) granitic rocks; 2) metamorphic rocks (schist and gneiss) ; 3) older sedimentary rocks; 4) andesitic rocks; 5) metamorphosed impure limestone; and 6) pegmatite, respectively. Previous paleocurrent data suggest that the sediments of the study area were mainly derived from the northeastern to southeastern directions. Thus, the most possible source areas would be the east extension part of the sobaegsan metamorphic complex to the northeast and the Cheongsong Ridge to the southeast.

• Journal of the Mineralogical Society of Korea
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• v.22 no.2
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• pp.163-176
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• 2009

The pyrophyllite deposits located in Jinhae area have been studied through field observations and laboratory works including the X-ray diffraction (XRD), X-ray fluorescence (XRF), Electron probe microanalyzer (EPMA) and Inductively Coupled Plasma (ICP). The pyrophyllite deposits consist of mainly illite, dickite, pyrophyllite, diaspore, chlorite, pyrite and copiapite. According to the mineral assemblages, geological occurrences and alteration modes, the altered rocks can be classified into four types: Type A; quartz with silicifictaion, Type B; quartz + illite with illitization, Type C; quartz + dickite + illite with kaolin alteration, Type D; pyrophyllite + illite + dickite + diaspore with pyrophyllite alteraion. Rocks in Type A, which is generated by silicifictaion, have high $SiO_2$ contents more than 90 wt% and distinctive equigranular textures with microcrtstalline quartz. The pyrophyllites from the study area belong to 2M polytype. The host rocks of the pyrophyllite ore in this mine are rhyolitic rock, andecitic tuff and volcanic breccia. The alteration products seem to be controlled by the different lithology of the host rocks. The hydrothermal solution formed the deposits would be inferred to the acidic and have relatively high ionic activity of hydrogen and silica judging from alteration mineral assemblage. Pyrophyllite alteraion zone is generated by highest temperature condition of all alteration zone.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.103-120
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• 2002

In the Baekdong-Hongseong area, the southwestern part of the Gyeonggi Massif in Korea, ultramafic rocks occur as lenses within Precambrian granitic gneiss. At Baekdong area, ultramafic lens contains metabasite boudin which had undergone at least three stages of metamorphisms. The mineral assemblage on the first stage, Garnet+Sodic Augite+Hornblende+Plagioclase+Titanite, is recognized from the inclusions in garnet. The second stage is represented by the assemblage in matrix, Garnet+ Augite+Hornblende+Plagioclase, while the third stage is identified by the Hornblende+Plagjoclase $\pm$ Garnet assemblage in the symplectite formed around garnet. The P-T conditions of the first and the third stages are $690-780^{\circ}C$, 11.8-15.9 kb and $490-610^{\circ}C$, 4.0-6.3 kb, respectively. These data indicate that metabasite in Baekdong area had experienced a retrouade P-T path from the eclogite(EG) - high-pressure granulite (HG)-amphibolite (AM) transitional facies to the AM through HG-AM transitional facies. The core and rim of garnet in country granitic gneiss give $605-815^{\circ}C$, 10.7-16.0 kb and $575-680^{\circ}C$, 5.4-7.0 kb, respectively, indicating that the retrograde P-T path of granitic gneiss is similar to that of metabasite. Trace element data reveals that the tectonic setting of metabasite is island uc. The general geology, the metamorphic evolution, the mineral chemistry and the tectonic setting of Baekdong area indicate that the Baekdong-Hongseong area in Korea is a possible extension of the Sulu collision Belt in China. On the other hand, the Sm-Nd whole rock-garnet isochron ages of metabasites are 268.7-297.9 Ma which are older than the ages of UHP metamorphism (208-245 Ma) in the Dabie-Sulu Collision Belt. The older metamorphic ages suggest that collision between Sino-Korea and Yangtz plates may have occurred earlier in Korean Peninsula than China.